Sodium-Ion Batteries E-Book
115,99 €
Mehr erfahren.
- Herausgeber: Wiley-VCH GmbH
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Sodium-Ion Batteries
Practice-oriented guide systematically summarizing and condensing the development, directions, potential, and core issues of sodium-ion batteries
Sodium-Ion Batteries begins with an introduction to sodium-ion batteries (SIBs), including their background, development, definition, mechanism, and classification/configuration, moving on to summarize cathode and anode materials, discuss electrolyte, separator, and other key technologies and devices, and review practical applications and conclusions/prospects of sodium-ion batteries.
The text promotes the idea that SIBs can be a good complement, or even a strong competitor, to more mainstream energy technologies in specific application scenarios, including but not limited to large-scale grid energy storage, distributed energy storage, and low-speed electric vehicles, by virtue of considerable advantages in cost-effectiveness compared with lithium-ion, lead-acid, and vanadium redox flow batteries. This book delves into what we have done, where we are, and how we should proceed in regards to the advancement of SIBs, in order to make the technology more applicable in real-world situations.
Specific sample topics covered in Sodium-Ion Batteries include:
- Electrochemical test techniques, including cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy
- Advanced characterization techniques and theoretical calculation, covering imaging and microscopy, and the synchrotron radiation x-ray diffraction technique
- Designing and manufacturing SIBs, covering types of cells (cylindrical, soft-pack, and psitmatic), and design requirements for cells
- Performance tests and failure analysis, covering electrochemical and safety performances test, failure phenomenon, failure analysis method, and cost estimation
- Solid-state nuclear magnetic resonance spectroscopy, covering principles of ssNMR and shift ranges for battery materials
A complete review of an exciting energy storage technology that is undergoing a crucial development stage, Sodium-Ion Batteries is an essential resource for materials scientists, inorganic and physical chemists, and all other academics, researchers, and professionals who wish to stay on the cutting edge of energy technology.
Sie lesen das E-Book in den Legimi-Apps auf:
Seitenzahl: 710
Veröffentlichungsjahr: 2023
Ähnliche
Table of Contents
Cover
Table of Contents
Title Page
Copyright
Preface
1 Introduction
1.1 Overview
1.2 The Birth and Development of Sodium‐ion Batteries
References
2 Characteristics of Sodium‐ion Batteries
2.1 Basic Features
2.2 Working Principle
2.3 Concepts and Equations
2.4 Structural Composition
References
3 Cathode Materials of SIBs
3.1 Polyanion Cathode
3.2 Oxide Cathode
3.3 Prussian Blue and their Analogues
3.4 Perovskite Transition Metal Fluorides
3.5 Organic Cathode
References
4 Anode Materials of Sodium‐ion Batteries
4.1 Carbon‐based Anode
4.2 Titanium‐based Anode
4.3 Conversion Anode
4.4 Metal/Alloy Anode
References
5 Electrolyte, Separator, Binder and Other Devices of Sodium Ion Batteries
5.1 Introduction
5.2 Organic Liquid Electrolytes
5.3 Solid State Electrolytes
5.4 Separator
5.5 Binder
5.6 Conductive Agent
5.7 Current Collector
5.8 Conclusion and Perspectives
References
6 Advanced Characterization Techniques and Theoretical Calculation
6.1 Imaging and Microscopy
6.2 Synchrotron Radiation X‐Ray Diffraction Technique
6.3 Synchrotron Radiation X‐ray Absorption Spectroscopy Technique
6.4 Solid‐state Nuclear Magnetic Resonance Spectroscopy
6.5 Electrochemical Test Techniques
6.6 Other Characterization Techniques
6.7 Theoretical Calculation
References
7 Practical Application of SIBs
7.1 Introduction
7.2 Commercial Sodium Battery
7.3 Design and Manufacture Process of SIBs
7.4 Presodiation Techniques
7.5 Performance Tests and Failure Analysis
7.6 Commercial Application and Future Perspectives
References
Index
End User License Agreement
List of Tables
Chapter 2
Table 2.1 Comparison of the properties of Li and Na.
Chapter 5
Table 5.1 Physical and chemical properties of the ester‐based solvents for S...
Table 5.2 Physical and chemical properties of the ether‐based solvents for S...
Table 5.3 Basic properties of the most commonly adopted Na salts for SIB ele...
Table 5.4 Basic properties of the additives for SIBs electrolytes.
Table 5.5 The chemical structures of cations and anions for ILs.
Table 5.6 The basic electrochemical properties of some ISEs used for SIBs.
Table 5.7 The basic electrochemical properties of polymer matrix for SIBs.
Table 5.8 The basic electrochemical properties of GPEs for SIBs.
Table 5.9 The basic electrochemical properties of CSEs using passive fillers...
Table 5.10 The basic electrochemical properties of CSEs using active fillers...
Table 5.11 A summary of basic information for current collector.
Chapter 6
Table 6.1 Comparisons of characteristics of different microscopies.
Table 6.2 Characteristics of various synchrotron X‐ray imaging techniques.
Chapter 7
Table 7.1 Common test and analysis techniques.
List of Illustrations
Chapter 1
Figure 1.1 Characteristics of sodium‐ion batteries.
Figure 1.2 The development of room‐temperature sodium‐ion batteries.
Figure 1.3 Research articles about sodium‐ion batteries between 2000 and 202...
Chapter 2
Figure 2.1 Reserve content of elements in the earth's crust.
Figure 2.2 Cost components of lithium‐ion batteries (LIBs) and sodium‐ion ba...
Figure 2.3 (a) Comparison of charge/discharge curves of Li||LiCoO
2
and Na||N...
Figure 2.4 The “rocking chair” working principle of rechargeable sodium‐ion ...
Figure 2.5 Voltage, specific capacity, and energy density of classified cath...
Figure 2.6 Average voltage (discharge) versus capacity plot of anode materia...
Chapter 3
Figure 3.1 (a) Classification and (b) comparison of cathode materials for SI...
Figure 3.2 Crystal structure and voltage profiles for (a, b) olivine‐ and (c...
Figure 3.3 (a) Typical crystal structure of NASCON‐type Na...
Figure 3.4 (a) Crystal structure, (b) voltage profiles (inset: d
Q
/d
V
curves)...
Figure 3.5 Crystal structure of monoclinic Na
2
MSiO
4
, projected from (a) [010...
Figure 3.6 (a) Structure and compositional evolution of NaF‐VPO
4
mixture (1...
Figure 3.7 (a) Initial charge/discharge profiles of Na
3
V
2
(PO
4
)
2
F
3
with opene...
Figure 3.8 Illustration of (a) structural components, (b) P2‐type structure,...
Figure 3.9 (a) Illustration the thickness of TMO
2
slab (
d
O‐M‐O
) ...
Figure 3.10 (a) Illustration of the P2‐“Z”‐O2 the phase transition process. ...
Figure 3.11 Summary of phase evolution vs. Na content upon first charge for ...
Figure 3.12 (a) Illustration of P'2 phase and a comparison with P2 phase. (b...
Figure 3.13 (a)
In situ
XRD for NaFe
0.5
Co
0.5
O
2
. (b) HR‐STEM image of Na...
Figure 3.14 (a) The schematic band structure of transition‐metal oxides and ...
Figure 3.15 Structural illustration and voltage profiles for (a) Ordered Na
1
Figure 3.16 (a) The schematic illustration of Fe migration during Na extract...
Figure 3.17 The comparison of the main redox couples in layered sodium trans...
Figure 3.18 (a) XRD and SEM, (b) initial charge/discharge profiles, and (c) ...
Figure 3.19 (a) HADDF‐STEM image of P2/O3 intergrown structure. (b) Illustra...
Figure 3.20 (a) Illustration of tunnel‐type structure, (b) First‐cycle volta...
Figure 3.21 Structural illustration of (a) An intact Na
2
M
II
[Fe
II
(CN)
6
] frame...
Figure 3.22 (a) First‐cycle voltage profiles (inset: crystal structure) and ...
Figure 3.23 (a) Voltage profile, (b)
ex situ
XRD patterns, and (c) cycling p...
Figure 3.24 (a) Charge/discharge curves, (b) rate performance, (c) cycling p...
Figure 3.25 Crystal structure of (a) FeF
3
and (b) NaFeF
3
.
Figure 3.26 (a) Crystal structure of Na
2
TiFeO
7
and (b) predicted redox poten...
Figure 3.27 (a) The classification and working mechanism of organic electrod...
Figure 3.28 (a) Chemical and crystal structures of Na
2
C
6
O
6
. (b) Voltage prof...
Chapter 4
Figure 4.1 The simple classifications of anodes.
Figure 4.2 The ion storage mechanism of carbon from the important review of ...
Figure 4.3 For 1D CNF: the forming mechanism, SEM images, and ling‐life cycl...
Figure 4.4 For Ni‐doped CoS
2
@N, P‐doped samples: SEM, TEM images and long‐te...
Figure 4.5 For ultrafine FeS
2
@CNT composites: the simple formation mechanism...
Figure 4.6 For FeP quantum dots@P‐doped carbon: the preparing mechanism, TEM...
Figure 4.7 The simple sodium‐storage mechanism of different Sb‐type about ma...
Figure 4.8 For Sb–Ni–C samples: the preparing mechanism, TEM images and cycl...
Figure 4.9 The ultrasmall Sn@carbon from aerosol spray pyrolysis: SEM and TE...
Chapter 5
Figure 5.1 The main ingredients and their specific compositions of SIBs exce...
Figure 5.2 (a) Electrostatic potential maps (EPM) of different Na
+
‐solva...
Figure 5.3 (a) X‐ray photoelectron spectroscopy (XPS) spectra of the i...
Figure 5.4 (a) Schematic diagram of the formed SEI layer in NaBOB/trimethyl ...
Figure 5.5 (a) Schematic diagram of SA, FEC, and PC with HOMO and LUMO value...
Figure 5.6 The classification of solid‐state electrolytes (SSEs) used in SIB...
Figure 5.7 Crystal structure and ideal Na
+
transfer path of (a) NVP and ...
Figure 5.8 The Na
+
ions transportation in hyperbranched β‐CD based SPE....
Figure 5.9 (a) Scanning electron microscope (SEM) photographs of CNC/CNF bas...
Figure 5.10 (a) The structures of UIO‐66 (left) MOF and UIOSNa (UIO‐66 with ...
Figure 5.11 (a) The schematic diagram illuminating Ans‐GPE structure and its...
Figure 5.12 (a) Schematic illustration of the mechanism for improving ionic ...
Figure 5.13 (a) Schematic illustration for the fabrication of carbon quantum...
Figure 5.14 SEM images of PEO‐based electrolyte (a) without NaAlO
2
and (b) w...
Figure 5.15 (a) Schematic diagram demonstrating the electrode surface and sp...
Figure 5.16 Schematic illustration of Na
+
migration in (a) THF and (b) P...
Figure 5.17 (a) Reduction potentials of various salts (stars) and solvents (...
Figure 5.18 Designed CEI and its impact on the electrochemical performance....
Figure 5.19 The requirements for ideal separator used in SIBs.
Figure 5.20 The fabrication process of poly (ether imide) (PEI)/PVP separato...
Figure 5.21 SEM images of (a) SP; (b) KB; (c) C45; (d) CNT.
Figure 5.22 Field emission scanning electron microscopy (FESEM) images of th...
Figure 5.23 (a) Schematic diagram expounding the presodiation, assembly, and...
Figure 5.24 (a) Iconography of the fabrication process for NVP@CP. (b) Low m...
Chapter 6
Figure 6.1 Schematic illustration of
in situ
TEM experimental result of the ...
Figure 6.2 Visualization of 3D microstructural evolution of Sn anodes in SIB...
Figure 6.3
In situ
STM images and the corresponding height profiles.
Figure 6.4 (a) Configuration of a typical customized coin cell and battery r...
Figure 6.5 Understanding the phase transitions of Na
1.73
Fe[Fe(CN)...
Figure 6.6 (a, b) Schematic diagrams of XAS experimental set‐up in transmiss...
Figure 6.7 Schematic illustration of
in situ/operando
XAS experiments conduc...
Figure 6.8 Evolution of
operando
Ti K‐edge XANES of TiO
2
anatase anodes for ...
Figure 6.9 The disordered nuclear spin forms a net magnetic moment under the...
Figure 6.10 The measurement is free induction decay (FID), which converts a ...
Figure 6.11
Ex situ
23
Na NMR spectra (normalized) of...
Figure 6.12 (a) Selected different states of charge and the normalized
23
Na ...
Figure 6.13 Variable‐temperature
23
Na NMR VOCS spectra and fitting curves, i...
Figure 6.14 CVs of an EC/DMC (1 : 1 in volume +1 M NaPF...
Figure 6.15 GCD profiles of the Na
2
Ni
2
TeO
6
cathode in a voltage window of 3–...
Figure 6.16 (a) EIS of battery under different initial discharge voltages, (...
Figure 6.17 X‐ray and neutron scattering lengths of some selected elements. ...
Figure 6.18 Observed (crosses), calculated (line), and difference (bottom) n...
Figure 6.19 Schematic illustration of
in situ
FTIR measurement cell.
Figure 6.20 FTIR Spectral Study of PHATN in SIBs.
Figure 6.21
In situ
Raman spectra of the MoS...
Figure 6.22 General overview of how ML‐based interatomic potentials are cons...
Figure 6.23 AIMD simulation of 4.1m NaTFSI/DMSO solution: (a) a snapshot fr...
Figure 6.24 The calculated phonon dispersion relation (solid black line) in ...
Figure 6.25 (a) The machine‐learned molecular dynamics (MLMD) calculated Na‐...
Figure 6.26 The machine‐learned molecular dynamics (MLMD) calculated self‐Va...
Chapter 7
Figure 7.1 Structure and working principle of high‐temperature Na–S battery ...
Figure 7.2 Structure of ZEBRA battery [8].
Figure 7.3 Schematic diagram of button cell assembly order.
Figure 7.4 18650 cylindrical battery outline diagrams.
Figure 7.5 SIBs production process.
Figure 7.6 Principles for bipolar electrode structure.
Figure 7.7 (a) Influence of presodiation on the initial CE of SIBs. (b) Infl...
Figure 7.8 Common battery failure phenomenon.
Figure 7.9 Failure analysis process of SIBs.
Guide
Cover
Table of Contents
Title Page
Copyright
Preface
Begin Reading
Index
End User License Agreement
Pages
iv
xiii
xiv
1
2
3
4
5
6
7
8
9
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
Sodium‐Ion Batteries
Technologies and Applications
Edited by Xiaobo Ji, Hongshuai Hou, and Guoqiang Zou
Editors
Prof. Xiaobo Ji
Central South University
College of Chemistry and Chemical Engineering
No. 932, Lushan South Road
YueLu District
410083 Changsha
China
Prof. Hongshuai Hou
Central South University
College of Chemistry and Chemical Engineering
No. 932, Lushan South Road
YueLu District
410083 Changsha
China
Prof. Guoqiang Zou
Central South University
College of Chemistry and Chemical Engineering
No. 932, Lushan South Road
YueLu District
410083 Changsha
China
Cover Image: © Ohoishi/Shutterstock
All books published by WILEY‐VCH are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.
Library of Congress Card No.: applied for
British Library Cataloguing‐in‐Publication Data A catalogue record for this book is available from the British Library.
Bibliographic information published by the Deutsche Nationalbibliothek The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at <http://dnb.d-nb.de>.
© 2024 WILEY‐VCH GmbH, Boschstraße 12, 69469 Weinheim, Germany
All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law.
Print ISBN: 978‐3‐527‐35061‐2
ePDF ISBN: 978‐3‐527‐84166‐0
ePub ISBN: 978‐3‐527‐84167‐7
oBook ISBN: 978‐3‐527‐84168‐4
Preface
Although originated from almost the same era around 1970s and held similar working principles, sodium‐ion batteries (SIBs) had grasped too less attention than lithium‐ion batteries (LIBs) before 2010s due to the inferiority of energy density, cycle life, and essentially the lack of suitable electrode materials. However, since the booming success of commercial LIBs brought with it the anxiety over lithium and cobalt sources and prices, SIBs have gained renewed and ever‐increasing focus in the past decade owing to the unlimited sodium sources and the diverse choices of transition metals, giving birth to numerous research papers and some start‐ups endeavoring to push for commercialization of SIBs. It can be foreseen that the predominance of LIBs in the market may be difficult to shake, at least in the next decade. Nonetheless, SIBs can be a good complement, or even a strong competitor, in specific application scenarios, including but not limited to large‐scale grid energy storage, distributed energy storage, and low‐speed electric vehicles, by virtue of their considerable advantages in cost‐effectiveness compared with LIBs, lead‐acid batteries, and vanadium redox flow batteries. The rapid scaling up of energy storage systems, which is critical to address the hour‐to‐hour variability of wind and solar electricity generation on the grid, is of great urgency in the global demand to develop low‐carbon energy, offering golden opportunities for the development of SIBs. One of the vital preconditions that allow us to consider the real‐world utilization of SIBs is the great breakthrough in battery materials we have achieved in the past few years. Regarding cathode materials, plenty of candidates, such as transition metal oxides/fluorides, Prussian blue analogs, and polyanionic compounds with improved specific capacity and prolonged cycle life, have been successfully discovered. On the anode side, the advent of hard/soft carbon has significantly promoted the practical application of SIBs, while the extensive explorations of non‐ferrous‐based conversion‐type materials have furnished abundant choices of anode materials to equip SIBs for different applications. Other materials have also achieved tremendous progress toward the requirements of application‐wise sceneries, while diverse characterization techniques have been successfully utilized to deepen the understanding of the fundamental working mechanisms of all these battery materials. Today, materials engineering for SIBs is still ongoing while research is updating superfast. Therefore, it is of great importance to look back from time to time at what we have done, where we are, and how we should proceed for the advancement of SIBs. In this book, we would like to present a comprehensive review of the research history and the state‐of‐the‐art progresses of SIBs, accompanied with in‐depth discussions on key issues of materials and some perspectives for the future development of SIBs based on the best of our knowledge.
This book is prepared with the support of many peer researchers who made important contributions to the final version of this book. Chapter 4 is authored by Associate Professors Peng Ge and Yue Yang, Chapter 5 is authored by Associate Professors Mingjun Jing and Tianjing Wu, and Chapter 6 is authored by Dr. Zhibin Wu. The other chapters are mainly authored by Professor Xiaobo Ji, Hongshuai Hou, and Guoqiang Zou, and they also completed the compilation and revision of this book.
Finally, the authors would like to acknowledge the financial support of National Natural Science Foundation of China (5221101846, U21A20284).
17 August 2023Changsha, China
Professor Xiaobo Ji
Professor Hongshuai Hou
Professor Guoqiang Zou
Central South University,Changsha, China
1Introduction
Jinqiang Gao, Wentao Deng, Guoqiang Zou, Hongshuai Hou, and Xiaobo Ji
Central South University, School of Chemistry and Chemical Engineering, Changsha, China
1.1 Overview
Since humans have obtained energy by drilling wood for fire, every energy revolution has been accompanied by great progress in human civilization. However, the consumption of fossil energy has caused irreversible pollution and damage to the human environment, so it is urgent to replace fossil energy with renewable energy to get mankind out of the upcoming energy crisis and environmental disaster.
In recent years, the technology of converting wind, solar, hydraulic, tidal, and other renewable energies into electric energy has rapidly developed [1]. However, the power generation is limited by natural conditions, owing to randomness, intermittent and fluctuating characteristics, leading to a great impact on the state grid if the generated electric energy were to be fed directly into the grid. The new energy power generation industries are still facing serious energy wastage problems, such as wind and light wastage. Therefore, in order to greatly improve the utilization of renewable energy and establish a green, low‐carbon, efficient, and sustainable development society, it is necessary to develop an efficient and convenient large‐scale energy storage technology and form an “energy internet” of renewable energy–energy storage system–smart grid–users.
At present, the storage of electrical energy mainly includes physical energy storage, chemical energy storage, electrochemical energy storage, and other technologies [2]. Physical energy storage includes pumped hydro storage, compressed air energy storage, flywheel energy storage, and superconducting energy storage. Chemical energy storage includes various types of fossil fuels and hydrogen energy. Electrochemical energy storage includes secondary batteries and supercapacitors. Electrochemical energy storage, such as secondary batteries, has a wide range of application prospects in the energy field, owing to the advantages of high energy density, high energy conversion efficiency, and fast response speed. At present, there are four types of secondary batteries that have realized commercial applications: lead‐acid batteries, high‐temperature sodium batteries, vanadium flow batteries, and lithium‐ion batteries. However, these batteries are limited by their disadvantages, such as lead‐acid batteries with low energy density (30–50 W h kg−1), high‐temperature sodium batteries that need to operate at higher temperatures (300–350 °C), and the low energy conversion efficiency of vanadium flow batteries (75–82%).
The secondary battery represented by the lithium‐ion battery has many advantages, such as high energy density, high energy storage efficiency and nonmemory effect, small self‐discharge, long cycle life, and wide application range. Currently, lithium‐ion batteries have been successfully used in small electronics, electric vehicles, and aerospace. At the same time, the research direction of lithium‐ion batteries is gradually toward ultrahigh energy density and ultralong cycling life. However, lithium resources are relatively concentrated in a few countries, the overall reserves are limited, and the mining conditions are relatively harsh. So, it is difficult to support the development of electric vehicles and large‐scale energy storage.
In recent years, sodium‐ion batteries (SIBs) with the same working principle and similar battery components as lithium‐ion batteries have received widespread attention, owing to the advantages of abundant sodium resources, cost‐effectiveness, and outstanding comprehensive performance. SIBs can meet the requirements of low cost, long cycling, and high‐safety performance, alleviating the limited development of energy storage batteries caused by the shortage of lithium resources, which is a promising supplement to lithium‐ion batteries and can gradually replace lead‐acid batteries. Therefore, SIBs are expected to play an important role in renewable energy storage [3].
In the early 1970s, the research on SIBs was almost simultaneously carried out with that on lithium‐ion batteries, and lithium‐ion batteries were successfully commercialized in 1991, while SIBs have not yet been commercialized. The research on SIBs can learn from the research experience of lithium‐ion batteries because the working principle, materials, and battery components of the two batteries are similar. It is worth noting that it cannot be fully copied due to differences in charge carriers (Li+ vs. Na+). Therefore, finding suitable materials for SIBs and building suitable SIB systems are the key to its practical application. In recent years, a series of advances have been made at home and abroad on the core material systems (cathode material, negative electrode, electrolyte, and separator), main auxiliary materials (binders, conductive agents, and current collectors), key battery technologies (nonaqueous, aqueous, and solid‐state batteries), and analytical characterization, material prediction, and failure mechanism, which have laid a solid foundation for the commercialization of SIBs [4, 5].
With the deeper insight into this field, more and more potential advantages of SIBs have been found, which will give SIBs more characteristics and a favorable position in the future energy storage market [6]. Some advantages of SIBs are summarized (Figure 1.1):
(1) Sodium resources are abundant, widely distributed, economical, and there are no bottlenecks for the development of SIBs.
(2) The working principles of SIBs and lithium‐ion batteries are similar, and they are compatible with the existing production equipment of lithium‐ion batteries.
(3) Alloying reactions can be avoided between sodium and aluminum, and the current collectors of the positive and negative electrodes for SIBs can use cheap aluminum foil, which can further reduce costs with no overdischarge problems.
(4) Bipolar SIBs can be constructed; that is, the positive and negative electrode materials can be coated on both sides of the same aluminum foil. The electrodes are periodically stacked under the isolation of solid electrolytes, which can achieve higher voltage, save inactive materials, and improve the energy density.
(5) The Gibbs free energy of solvation of sodium ions is lower than that of lithium ions, which is beneficial for interface desolation.
(6) The Stokes diameter of the sodium ion is lesser than that of the lithium ion, and a high ionic conductivity can be achieved with a low concentration of sodium salt electrolyte, making the low salt concentration electrolyte suitable for use in SIBs.
(7) SIBs have excellent rate performance as well as outstanding cycling performance at high and low temperatures.
(8) The SIB does not catch fire or explode in the safety test, and the safety performance is good.
Figure 1.1 Characteristics of sodium‐ion batteries.
1.2 The Birth and Development of Sodium‐ion Batteries
Since the concept of sodium batteries was proposed in the science fiction novel “Twenty Thousand Leagues Under the Sea,” the real emergence of sodium batteries has taken nearly 100 years. In 1967, Yao and Kummer [7] found the conduction of Na+ in Na‐β″‐Al2O3. In 1968, the Ford Company invented high‐temperature sodium–sulfur battery (Na‐Na‐β″‐Al2O3|S) (300–350 °C) with sodium and sulfur as the negative and positive electrodes, respectively, and Na‐β″‐Al2O3 as the solid electrolyte. In 1986, Coetzer [8] replaced sulfur with NiCl2 and invented the ZEBRA battery (Na|Na‐β″‐Al2O3|NiCl2). In 2003, NGK company realized the commercialization of high‐temperature sodium–sulfur batteries. However, both sodium–sulfur batteries and ZEBRA batteries are sodium batteries that work at high temperatures. In order to reduce the working temperature of sodium batteries to improve their safety, a lot of research work began to develop sodium batteries that work at room temperature. Taking this into consideration, the development of room‐temperature SIBs has undergone a long process (Figure 1.2).
Figure 1.2 The development of room‐temperature sodium‐ion batteries.
In 1976, Whittingham et al. [9] conducted a study of the behavior of Li+ intercalating TiS2, followed by the electrochemical reversible deintercalation of Na+ in TiS2 at room temperature [10]. France Armand [11] proposed the concept of “rocking chair batteries” at the NATO Conference on Materials for Advanced Batteries held in 1979, which opened up the research on lithium‐ion and SIBs. In 1981, French Delmas et al. [12] firstly reported the electrochemical properties of NaxCoO2‐layered oxide cathode materials and proposed a classification trend for layered oxide structures, according to the coordination environment of alkali metal ions. Layered oxides are divided into O type or P type (O refers to octahedron and P refers to triangular prisms), and numbers (such as 2 and 3.) represent the number of stacking layers of the least repeated oxygen units. During that period, a variety of sodium‐containing transition metal‐layered oxides, NaxMO2(M = Ni, Ti, Mn, Cr, Nb), were reported. When studying the behavior of Na+ in the NaTi2(PO4)3 electrode material, it was found that NASICON‐structured solid electrolyte Na3M2(PO4)3 (M = Ti, V, Cr, Fe, etc.) [4] could also be used as electrode material. However, in the late 1980s, research reports on sodium‐ion intercalating materials were very limited, and only a few papers and patents were published, mainly because [13]: (i) The research on lithium‐ion intercalating materials was just beginning in this period, and a large number of researchers focused their research on lithium‐ion batteries. (ii) Limited by the research conditions (such as the low purity of the electrolyte, the poor tightness of the glove box, and the low purity of argon.), it is difficult to use the active metal sodium as an electrode to accurately evaluate the performance of the electrode material in the half‐batteries. (iii) The graphite successfully applied in lithium‐ion batteries has almost no sodium storage capacity in carbonate electrolytes, resulting in the lack of suitable anode materials for the study of SIBs. In fact, before the successful commercialization of lithium‐ion batteries, some companies in the United States and Japan carried out research on sodium‐ion full batteries, such as P2‐NaxCoO2, which was used as positive electrode and Na–Pb alloy as negative electrode. Although the SIB can reach 300 cycles, its average discharge voltage is below 3 V, which has no advantage over C||LiCoO2 battery (3.7 V) and thus failed to attract the attention of researchers.
In 2000, the SIB got its first opportunity. Stevens and Dahn [14] prepared a hard carbon anode material for SIB via pyrolysis of glucose for the first time and demonstrated a specific capacity of 300 mAh g−1. It is worth noting that, up to now, hard carbon materials are still the most promising anode materials for SIBs. The second important finding was the reversible variability of the Fe4+/Fe3+ pair in NaFeO2 reported by Okada et al. [13], which has no electrochemical activity in LiFeO2. Except for the layered oxides, Na2FePO4F polyanionic material reported in 2007 by Nazar and coworkers [15] exhibits only 3.7% volumetric change during the deintercalating/intercalating of sodium ions, which is lower than that of olivine‐type NaFePO4 (15% volumetric change). So far, the papers published between 2000 and 2009 on SIB materials have shown a slow growth trend and are mainly concentrated in a few laboratories.
Since 2010, the research of SIBs has entered a period of revival, and the number of related articles has increased rapidly (Figure 1.3), mainly due to the following reasons [16]: (i) The research on lithium‐ion battery materials at this time mainly focuses on the application improvement and the in‐depth analysis of electrochemical processes, and the difficulty of developing new materials has significantly increased. So, many researchers turned to the exploration of SIB material systems. (ii) Concerns about lithium resources and the demand for new large‐scale energy storage applications also make researchers to develop new battery systems. On this background, SIBs developed rapidly with the research experience of the lithium‐ion battery. So far, researchers have reported a variety of SIB cathode materials, anode materials, and electrolyte systems [17]. Among them, cathode materials mainly include layered and tunneled transition metal oxides, polyanionic compounds, Prussian blue analogs, and organic materials. Anode materials mainly include carbon materials, alloys, phosphorus compounds, and organic carboxylates. Except for new material systems, the research and development of SIBs is also working in the direction of low cost and practicality. In 2011, Komaba et al. [18] firstly reported the electrochemical performances of hard carbon||NaNi0.5Mn0.5O2full‐cell. In the same year, the world's first SIB company, FARADION, was established in the United Kingdom. In 2013, Goodenough and coworkers [19] proposed a Prussian white cathode material with high voltage and excellent magnification performance. In 2017, China's first SIB company (HiNa Battery Technology Co., Ltd.) was founded, which built the first low‐speed electric vehicle powered by SIB and the first 100 kW h SIB energy storage power station in 2018 and 2019, respectively [20]. As of 2020, more than 20 companies around the world are committed to the research and development of SIBs, indicating that SIBs are moving toward practical application. At the same time, in order to develop more secure SIBs for large‐scale energy storage, the research and development of aqueous SIBs and solid‐state SIBs that replace organic electrolytes with aqueous electrolytes and solid electrolytes, respectively, are also being carried out simultaneously.
Figure 1.3 Research articles about sodium‐ion batteries between 2000 and 2021.
Nowadays, the development of SIBs has attracted the attention of many countries around the world, and China is one of the strongest competitors in the research and development of SIB technology. HiNa Battery, Natrum Energy, and CATL have accelerated the commercialization of SIBs. In the near future, SIBs are expected to be applied in commercialization in China first, providing a strong guarantee for national energy security.
References
1
Zhao, C., Wang, Q., and Hu, Y.S. (2020). Rational design of layered oxide materials for sodium‐ion batteries.
Science
370: 708–711.
2
Dunn, B., Kamath, H., and Tarascon, J.M. (2011). Electrical energy storage for the grid: a battery of choices.
Science
334: 928–935.
3
Lu, Y.X., Zhao, C.L., Rong, X.H. et al. (2022). Compositionally complex doping for zero‐strain zero‐cobalt layered cathodes.
Nature
610: 67–73.
4
Delmas, C. (2018). Sodium and sodium‐ion batteries: 50 years of research.
Advanced Energy Materials
8: 1703137.
5
Pan, H.L., Hu, Y.S., and Chen, L.Q. (2013). Room‐temperature stationary sodium‐ion batteries for large‐scale electric energy storage.
Energy & Environmental Science
6: 2338–2360.
6
Winter, M., Bamett, B., and Xu, K. (2018). Before Li ion batteries.
Chemical Reviews
118: 11433–11456.
7
Yao, Y.F.Y. and Kummer, J.T. (1967). Ion exchange properties of and rates of ionic diffusion in beta‐alumina.
Journal of Inorganic and Nuclear Chemistry
29: 2453–2475.
8
Coetzer, J. (1986). A new high‐energy density battery system.
Journal of Power Sources
18: 377–380.
9
Whittingham, M.S. (1976). Electrical energy storage and intercalation chemistry.
Science
192: 1126–1127.
10
Newman, G.H. and Klemann, L.P. (1980). Ambient temperature cycling of an Na‐TiS
2
cell.
Journal of the Electrochemical Society
127: 2097–2099.
11
Armand, M.B. (1980).
Intercalation Electrodes//Murphy DW. Materials for Advanced Batteries
, 145–161. New York: Springer.
12
Delmas, C., Braconnier, J.J., Fouassier, C. et al. (1981). Electrochemical intercalation of sodium in Na
x
CoO
2
bronzes.
Solid State Ionics
3: 165–169.
13
Okada S, Takahashi Y, Kiyabu T, et al. 210th ECS Meeting Abstracts, 2006, MA 2006‐02, 201.
14
Stevens, D. and Dahn, J.R. (2000). High capacity anode materials for rechargeable sodium‐ion batteries.
Journal of the Electrochemical Society
147: 1271–1273.
15
Ellis, B.L., Makahnouk, W.R.M., Makimura, Y. et al. (2007). A multifunctional 3.5V iron‐based phosphate cathode for rechargeable batteries.
Nature Materials
6: 749–753.
16
Kubota, K. and Komaba, S. (2015). Review—practical issues and future perspective for Na‐ion batteries.
Journal of the Electrochemical Society
162: A2538–A2550.
17
Palomares, V., Casas‐Cabanas, M., Castillo‐Martinez, E. et al. Update on Na‐based battery materials.(2013). A growing research path.
Energy & Environmental Science
6: 2312–2337.
18
Komaba, S., Murata, W., Ishikawwa, T. et al. (2011). Electrochemical Na insertion and solid electrolyte interphase for hard‐carbon electrodes and application to Na‐ion batteries.
Advanced FunctionalMaterials
21: 3859–3867.
19
Wang, L., Lu, Y., Liu, J. et al. (2013). A superior low‐cost cathode for a Na‐ion battery.
Angewandte Chemie International Edition
52: 1964–1967.
20
Lu, Y.X., Rong, X.H., Hu, Y.S. et al. (2019). Research and development of advanced battery materials in China.
Energy Storage Materials
23: 144–153.
2Characteristics of Sodium‐ion Batteries
Haoji Wang, Wentao Deng, Hongshuai Hou, Guoqiang Zou, and Xiaobo Ji
Central South University, College of Chemistry and Chemical Engineering, Changsha, China
2.1 Basic Features
Sodium‐ion batteries (SIBs) have attracted attention in large‐scale energy storage applications due to the abundance and global distribution of sodium resources in the earth's crust. The crustal abundance of sodium resources reaches 2.74%; however, it is only 0.0065% for lithium resources. And lithium resources are unevenly distributed, 70% of which are concentrated in South America and a few countries and regions. In addition, the reserves of elements commonly used in SIBs, such as iron and manganese, are relatively high in the crust, while the nickel and cobalt commonly used in lithium‐ion batteries (LIBs) are relatively poor, as shown in Figure 2.1[1]. In theory, sodium ions do not react with aluminum, so cheap aluminum foil can be used as the anode collector, substituting copper foil in SIBs. In general, compared with LIBs, the material cost of SIBs can be reduced by about 30–40%, with the largest difference in the cathode materials, as shown in Figure 2.2. At the same time, large‐scale production of SIBs is not limited by geographical factors, which is conducive to the sustainable development of large‐scale energy storage.
In the periodic table, the sodium element is located in the third period of the first main group. Its atomic mass and atomic radius are second only to lithium. Sodium has two different electron clouds (spherical and dumbbell shaped) outside the atomic nucleus, and the outermost electrons occupy 3s orbits. SIBs and LIBs have similar working principles, but the differences in physical and chemical properties between Na and Li will inevitably lead to the differences in electrochemical performances as shown in Table 2.1. The standard hydrogen potential of Na+ is −2.71 V (Na+/Na, standard hydrogen electrode, SHE), which is slightly higher than that of Li+ (−3.04 V, Li+/Li, standard hydrogen electrode, SHE). In addition, the weight and volume energy density of SIBs are not comparable to that of LIBs due to the heavier mass of Na (23 g mol−1). However, the large ion radius of Na+ makes the detrimental migration resistance and sluggish kinetic reaction in host lattice. Meanwhile, it also leads to the severe lattice stresses, complex structural evolution, and drastic interface reactions in the process of sodium de‐/intercalation. For example, NaCoO2 and LiCoO2 have the same layered crystal structure because the ion radius of Co (0.54 Å) is smaller than that of Na (1.02 Å) and Li (0.76 Å). The theoretical specific capacity of NaCoO2 cathode material in SIBs is 235 mAh g−1, which is less than LiCoO2 in LIBs (274 mAh g−1). And the working voltage of NaCoO2 is about 1.0 V lower than that of LiCoO2. After 0.5 Li+/Na+ is removed, the potential difference between NaCoO2 and LiCoO2 drops to about 0.4 V. During the charging and discharging process, there are multiple platforms in the electrochemical curve of NaCoO2 that correspond to different phase transitions. In particular, the ordered and disordered distributions of Na+ and vacancies have a great impact on the performance of electrode materials, as shown in Figure 2.3a [2].
Figure 2.1 Reserve content of elements in the earth's crust.
Source: Reproduced from Li et al. [1]/with permission of Elsevier.
Figure 2.2 Cost components of lithium‐ion batteries (LIBs) and sodium‐ion batteries (SIBs).
Table 2.1 Comparison of the properties of Li and Na.
Parameters
Li
Na
Relative atomic mass
6.94
23.00
E
Θ
(A
+
/A
aq
)(V vs. SHE)
−3.04
−2.71
E
Θ
(A
+
/A
pc
)(V vs. Li
+
/Li
pc
)
0
0.23
Shannon's Radii/Å
0.76
1.02
Theoretical mass specific capacity of ACoO
2
(mAh g
−1
)
a)
274
235
Stokes radii (H
2
O)/Å
2.38
1.84
Stokes radii (PC)/Å
4.8
4.6
Desolvation free energy (PC)/(KJ mol
−1
)
215.8
158.2
Melting point (°C)
180.5
97.8
Precursor price/($/t)
5 000
150
Geographical distribution
70% in South America
Global distribution
a) The theoretical mass specific capacity of ACoO2 (mAh g−1) based on LiCoO2 and NaCoO2.
Figure 2.3 (a) Comparison of charge/discharge curves of Li||LiCoO2 and Na||NaCoO2 half‐cells.
Source: Reproduced from Yabuuchi et al. [2]/with permission of American Chemical Society.
(b) Charge–discharge curves of graphite electrodes in (I) Li (blue), (II) Na (green), and (III, IV) K cells (black and red), respectively.
Source: Reproduced from Komaba et al. [3]/with permission of Elsevier.
As for anode materials, the Na‐ and Li‐storage behavior of graphite materials is different. As shown in Figure 2.3b, although graphite has excellent lithium storage capacity in LIBs, it has almost no sodium storage capacity [3]. The reason is that Li+ can embed in graphite electrodes and form a stable first‐order intercalation compound, LiC6, with a theoretical capacity of 372 mAh g−1, while Na+ cannot form a first‐order stable intercalation compound (NaC70) with graphite due to the large radius of Na+ and thermodynamic factors. Consequently, the sodium storage activity of graphite is low, and the theoretical capacity is only 31 mAh g−1. All these indicate that it is necessary to explore new systems different from LIBs in order to give play to the advantages of SIBs in the development of electrode materials.
Every coin has two sides. The effect of large Na+ radius is not all negative. During the process of development, some differences exist between LIBs and SIBs: (i) It is easier to separate sodium ions from transition metals to form a layered structure at high temperatures due to the large radius difference between sodium and transition metal ions. In the layered structure, lithium‐containing oxides are mainly O‐type structures, while sodium‐containing oxides have an extensive category of O‐type and P‐type materials, providing more options for developing advanced cathode materials for SIBs. For example, P2/O3 biphasic layered oxides Na0.7Ni0.2Cu0.1Fe0.2Mn0.5O2−δ show excellent electrochemical performances [4]. (ii) Many transition metal elements that are not electrochemically active in lithium‐containing layered oxides are active in sodium‐containing layered oxides within the normal charge/discharge voltage range. Only three elements, including Ni, Co, and Mn, are able to reversibly gain or lose electrons in lithium‐containing oxides, while Ni, Co, Mn, Cr, V, Fe, Cu, and Ti elements are electrochemically active with a high degree of reversibility in sodium‐containing oxides. (iii) The diffusion rate of large‐radius Na+ in electrode materials is not necessarily lower than small radius Li+, because it is related to the crystal structure of electrode materials. For example, the diffusion rate of Na+ in layered Na2/3[Ni1/3Mn2/3]O2 is higher than the diffusion rate of Li+ in spinel Li4Ti5O12[5]. (iv) The large Na+ insertion/extraction during the charge and discharge process does not necessarily result in a dramatic volume change. For example, the volume change of layered P2‐Na0.66[Li0.22Ti0.78]O2 after Na+ extraction is only 0.77%, which is much smaller than that of LiMn2O4 (V: ∼5.6%), LiCoO2 (c: ∼2.6%), and LiFePO4 (V: ∼6.8%) [6]. (v) The large Na+ radius, on the one hand, gives it a strong ability to desolvate in polar solvents, leading to a high conductivity in the electrolyte, and on the other hand, allows to use low salt concentration electrolytes to achieve the same conductivity, which further reduces the cost.
2.2 Working Principle
SIBs and LIBs have a similar principle that uses alkali metal ions to migrate back and forth between the cathode and anode electrodes, which was named as “rocking chair battery” proposed by M. Armand, as shown in Figure 2.4. It is essentially a concentration cell where the cathode and anode materials are made up of compounds with different sodium‐ion contents. During charging, Na+ is removed from the sodium‐rich cathode and inserts into the sodium‐poor anode through the electrolyte and separator, along with a valence increase of transition metal ions in the cathode (loss of electrons), and the electrons migrate from the cathode to anode via an external circuit. This process generally presents an overall voltage increase. During discharging, the whole process is reversed. Na+ is extracted from the sodium‐rich anode, passes through the electrolyte and separator, and comes back to the sodium‐poor cathode electrode with the simultaneous movement of electrons and decrease of transition metal valence in the cathode electrode (gaining electrons). Therefore, Na+ migration inside the cell accompanied by electron transfer in the external circuit maintains charge balance of the whole system.
Figure 2.4 The “rocking chair” working principle of rechargeable sodium‐ion batteries.
Source: Reproduced from Li et al. [1]/with permission of Elsevier.
Similar to the LiCoO2//graphite battery, the SIBs can be expressed as an NaxTMO2//hard carbon battery, with NaxTMO2 as the cathode electrode and hard carbon as the anode electrode. The reaction equations can be expressed as:
Ideally, the Na+ extraction/insertion between the cathode and anode materials does not destroy the crystal structure; thus, SIBs are viable rechargeable secondary batteries that can be used in a variety of applications such as large‐scale energy storage and low‐speed electric vehicles. Due to the similar structural components between SIBs and LIBs, it can highly borrow from the LIBs equipment, technology, and methods to accelerate the industrialization process of SIBs.
2.3 Concepts and Equations
When describing the electrochemical performance of SIBs, some terms are usually involved.
2.3.1 Cell Voltage
2.3.1.1 Electromotive Potential
The electrochemical charging and discharging process of cell is actually achieved through chemical reactions. The relationship between the Gibbs free energy and cell potential is as follows:
where n is the amount of transferred electrons in the electrode reaction; F is Faraday's constant, F = 96 485 C mol−1 (or F = 26.8 A h mol−1); and EΘ is standard electrode potential. The output voltage is equal to the cell potential EΘ when the discharge current tends to zero.
Equation (2.4) shows the maximum limit of the conversion of chemical energy into electrical energy, which provides a theoretical basis for improving the cell performance.
At nonstandard condition:
2.3.1.2 Theoretical Voltage EΘ
Cathode (reduction potential) + Anode (oxidation potential) = Standard cell electromotive potential. The voltage difference between the two electrodes is called the cell voltage. The theoretical voltage is the maximum limit of the cell voltage, and the theoretical cell voltage of different materials is also different.
Beyond these, cell voltages also include the following.
2.3.1.3 Open Circuit Voltage Eocv
The open circuit voltage is the voltage difference between the cathode and anode of the cell without loading. The open circuit voltage is always less than the cell electromotive potential.
2.3.1.4 Operating Voltage Ecc
The operating voltage is the voltage difference between the cathode and anode of cell with loading. It is the actual output voltage when the cell is operating, and it changes with the current and the discharge depth. The operating voltage is always lower than the open circuit voltage since the existence of the polarization resistance and ohmic resistance (Ecc = Eocv − IRi) and the cell operating voltage is influenced by the discharge regime and the ambient temperature.
2.3.1.5 Cutoff Voltage
The cutoff voltage refers to the maximum charge voltage or minimum discharge voltage specified when the cell is charged or discharged.
2.3.2 Cell Capacity and Specific Capacity
The cell capacity is the amount of electricity obtained from the cell under certain discharge conditions, expressed as ampere per hours (A h). The cell capacity also contains theoretical capacity, actual capacity, and rated capacity.
2.3.2.1 Theoretical Capacity (Co)
The theoretical capacity is the amount of capacity provided by all active materials fully participating in the electrochemical reaction. The actual capacity is only a fraction of the theoretical capacity, corresponding to the real capacity that cells can provide.
Faraday's law states that the amount of material participating in the electrochemical reaction at the electrode is directly proportional to the amount of released electricity. For example, 1 mol of active material participating in the electrochemical reaction will release the electricity of F = 96 485 C mol−1 (or F = 26.8 A h mol−1). Therefore, the theoretical capacity is calculated as follows:
where m is the mass of active materials in complete reaction; M is the molar mass of the active materials; ne is the number of electrons gained or lost during the electrode reaction; and q is the electrochemical equivalent of the active materials. For NaFeO2, the theoretical capacity is 26.8 A h mol−1.
2.3.2.2 Actual Capacity (C)
The actual capacity is the amount of electricity actually released by the cell under certain discharge conditions (e.g. 0.2 C). The actual capacity of a cell in an unspecified discharge regime is usually expressed as the nominal capacity. The nominal capacity is only an approximate representation of the actual capacity. The discharge current intensity, temperature, and cutoff voltage of the cell are called the discharge regime of the cell. Different discharge regimes result in different capacities, calculated as follows:
Constant current discharge:
Constant resistance discharge:
Approximate calculation formula:
where I is the discharge current; R is the discharge resistance; t is the time discharging to the cutoff voltage, and Vave is the average discharge voltage of the cell.
2.3.2.3 Rated Capacity (Cr)
Rated capacity is the minimum amount of electricity discharging under certain discharge conditions as the cell is designed and manufactured.
2.3.2.4 Specific Capacity (Cm or CV)
In order to compare the electrochemical performance differences of different cells, the specific capacity is introduced. The specific capacity is the capacity per unit mass or volume of cell (or active material), referred to as mass specific capacity (A h kg−1) or volume specific capacity (A h l−1), respectively.
where m is the cell mass (kg); and V is the cell volume (L).
2.3.3 Cell Energy and Specific Energy
The cell energy refers to the electrical energy output from the external work of the cell under certain discharge conditions, usually expressed as watt per hour (W h).
2.3.3.1 Theoretical Energy (Wo)
The cell output energy is the theoretical energy Wo when the discharge capacity is equal to the theoretical capacity. That is to say:
This is also the maximum external work of a reversible cell at constant temperature and pressure:
2.3.3.2 Actual Capacity (W)
The actual energy is the actual output energy as the cell discharge, which is numerically equal to the product of the actual capacity and average operating voltage of the cell. The cell operating voltage is always less than the electromotive potential, and the actual energy is always less than the theoretical energy because the active material cannot be fully utilized.
2.3.3.3 Specific Capacity (Wm or Wv)
Specific energy, also known as energy density, is the amount of energy per unit mass or volume of a cell, referred to as mass specific energy (Wm) and volume specific energy (Wv), respectively, and is often expressed as W h kg−1 or W h L−1. The specific energy also contains theoretical specific energy and actual specific energy.
2.3.4 Cell Power and Specific Power
Cell power is the output energy per unit time, expressed as watts (W) or kilowatts (kW) under a certain discharge regime, and the output power per unit mass or unit volume of the cell is the specific power, expressed as W kg−1 or W l−1. The theoretical power can be expressed as
where t is the discharge time; Co is the theoretical capacity of the cell; I is the constant current; and EΘ is the electromotive potential.
And the cell actual power can be expressed as
where I2Ri is the consumed power by the internal resistance of the cell, which is useless to the load.
2.3.5 Charge and Discharge Rate
The charge/discharge rate is generally expressed as time rate or rate. The time rate is the hours that it takes for a cell to discharge its rated capacity at a given current. And the rate is the current that is required to discharge its rated capacity within a given time. The rate is usually denoted by the letter C, and 0.2 rate is also called 0.2C. Time rate and rate are reciprocals of each other, C = 1/h.
2.3.6 Constant Current Charge and Discharge
Constant current charge and discharge is the process of charging or discharging cell at a constant current. The charge and discharge process generally completes as reaching the set cutoff voltage.
2.3.7 Constant Voltage Charge
Constant voltage charge is the process of charging cell at a constant voltage. The cutoff current is set, and the charging process ends as the current is less than this value.
2.3.8 Coulombic Efficiency
Under certain charge and discharge conditions, the percentage of the charge released from the discharge (discharge capacity) to the charge charged during charging (charge capacity) is called the coulombic efficiency, also called the charge and discharge efficiency. The coulombic efficiency is affected by many factors, such as electrolyte decomposition, passivation of electrode interface, and changes in the structure, morphology, and conductivity of electrode materials.
2.3.9 Energy Conversion Efficiency
Energy conversion efficiency refers to the ratio of cell discharge to charge energy. It is a dimensionless number ranging from 0 to 1 and is sometimes expressed as a percentage.
2.3.10 Cell Internal Resistance
The cell internal resistance consists of ohmic resistance (RΩ) and polarization resistance (R). Ohmic resistance contains the resistance of electrode material, electrolyte, separator, current collector, and contact resistance between components. Polarization resistance refers to the resistance caused by polarization during an electrochemical reaction. Polarization resistance includes the resistance induced by electrochemical polarization and concentration polarization.
In order to compare the internal resistance of different cells, the specific resistance R′ is introduced. That is, the internal resistance of cells per unit capacity:
where C is cell capacity, A h.
2.3.11 Cell Life
Cell life includes cycle life and rest life. Cycle life refers to the number of cycles that a battery can charge and discharge to a given value (e.g. 80% of the initial value) under certain conditions (e.g. a certain voltage range, charge/discharge rate, and ambient temperature). Rest life refers to the aging time for the cell without load to reach a given index in a given environment.
2.3.12 State of Charge (SOC)
State of charge (SOC) is the ratio of the remaining capacity to the initial charge state used for a period of time or aging for a period of time, usually expressed as a percentage. SOC = 100% means the fully charged state of cells.
2.3.13 Depth of Discharge (DOD)
Depth of discharge (DOD) is the degree of discharge. It reflects the percentage of the cell discharge capacity and the rated discharge capacity.
2.4 Structural Composition
SIBs mainly include the cathode material, anode material, electrolyte, separator, binder, conductive agent, and current collector.
2.4.1 Cathode Materials
The cathode material is an important part of the secondary SIBs, which not only participates in the electrochemical reaction as an electrode but also provides sodium sources. But it is not appropriate to directly replace lithium with sodium in the electrode material of LIBs. Specific energy, cyclic performance, safety, cost, and environmental impact should be considered comprehensively when designing and selecting cathode materials for SIBs. The ideal cathode material for SIBs should meet the following conditions:
(a) Large specific capacity, which requires the cathode material with a low relative molecular mass, and a large amount of Na can be inserted into the host structure;
(b) High operating voltage, which requires the largely negative Gibbs free energy of the discharge reaction;
(c) Good rate charge and discharge performance, which requires a high Na
+
diffusion rate in the electrode material and surface;
(d) Long cycle life, which requires the small structural change during the process of Na
+
extraction/insertion;
(e) Good safety, which requires the electrode materials to have high chemical stability and thermal stability;
(f) Easy manufacture, environmental friendliness, and cheapness.
The cathode materials mainly include oxides, polyanions, Prussian blue analogs, and organics. The oxides mainly include layered structure and tunnel structure oxides, and polyanions include phosphate, fluorinated phosphate, pyrophosphate, and sulfate. The operating voltages of common cathode materials are summarized in Figure 2.5[7]. Similar to LIBs, almost all cathode materials of SIBs contain variable valence transition metals, which can maintain the electrical neutrality of the host materials during the Na+ extraction/insertion. Among them, the layered oxides with periodic layered structures have attracted much attention due to the simple preparation method, high specific capacity, and voltage. In addition, the lattice oxygen redox can be used to further improve the energy density of such materials. However, most of the layered materials are sensitive to water and moist air, which affects the stability and electrochemical performance of the electrode materials. Type tunnel oxides with a unique “S”‐shaped channel are resistant to water and moist air, have excellent ability, and have the advantage of high electrochemical stability in both organic and aqueous environments. But their practical application is still restricted by the low first charging capacity. Polyanions with a solid three‐dimensional skeleton have the characteristics of high operating voltage and high‐rate charge/discharge. In general, the stronger the electronegativity of polyanions, the higher the voltage the material possesses. The combination of different polyanions can produce new hybrid polyanion units with different electronegativities, thus enhancing the electrochemical properties of the material, which is important for the design of high‐voltage and energy‐density materials. However, the electrical conductivity of these compounds is generally poor. In order to improve their electronic and ionic conductivity, carbon coating and doping methods are often employed, which will lead to the reduction in their volume energy density. Prussian blue compounds with a more open skeleton have a moderate discharge capacity and operating voltage. The interstitial sites in the crystal structure provide space for Na+ transport during the charge and discharge process, but the presence of interstitial water will also occupy the sodium storage sites, thus reducing the sodium storage capacity. It is important to investigate the mechanism of interstitial water in Prussian blue compounds to improve their electrochemical performances. Organic cathode materials generally have the characteristics of multielectron reaction, resulting in high specific capacity, but they generally suffer from the problems of easily dissolving in organic electrolytes and poor electronic conductivity.
Figure 2.5 Voltage, specific capacity, and energy density of classified cathode materials for SIBs.
Source: Reproduced from Tian et al. [7]/with permission of American Chemical Society.
2.4.2 Anode Materials
The anode material is also the main component of SIBs. The ideal negative electrode material should meet the following conditions:
(a) Low redox potential for the Na extraction/insertion reaction to cater to the high output voltage of SIBs;
(b) Small potential change of the electrode during Na
+
extraction/insertion to ensure low‐voltage fluctuations in the charge and discharge process;
(c) Good structural and chemical stability during Na
+
extraction/insertion to enable a high cycle life and safety of cell;
(d) High reversible specific capacity;
(e) Good ion and electron conductivity to obtain high‐rate charge/discharge and excellent low‐temperature charge/discharge performances;
(f) Ability to form a dense and stable solid electrolyte film (SEI) with the electrolyte to prevent continuous reduction of the electrolyte on the anodic surface and irreversible consumption of Na from the cathode electrode;
(g) Simple manufacture and low cost;
(h) Abundant resources and environmental friendliness.
The anode materials mainly include carbon‐based, organic, alloy, and other anode materials. As the sodium storage capacity of graphite is too low to be used as anode materials for SIBs, carbon‐based materials mainly refer to amorphous carbon and nanocarbon materials. Amorphous carbon‐based anode materials with large disorder have low sodium storage potential, moderate storage capacity (higher than titanium‐based materials and lower than alloy‐based materials), small volume deformation after Na+ extraction, and excellent cycling performance, as shown in Figure 2.6[8]. Nanocarbon materials mainly include graphene and carbon nanotubes (CNTs), relying on the surface adsorption to realize Na+ storage achieving rapid charge and discharge. However, low initial coulombic efficiency and poor cycling performances make it difficult to obtain practical applications. Titanium‐based materials have good stability in air and low strain after Na+ extraction but poor capacity. Organic compounds have chemical richness, low cost, environmental friendliness, multielectron reaction, and tunable electrochemical window but suffer from poor electronic conductivity and are easily soluble in electrolytes.
Figure 2.6 Average voltage (discharge) versus capacity plot of anode materials for SIBs.
Source: Reprinted with permission from Kang et al. [8]. Copyright 2015 Royal Society of Chemistry.
