<2024 New Edition> Current Status and Future Outlook of Bipolar Battery Technology Development
A single-cell
secondary battery consisted of monopolar electrodes, where both sides of the
current collector are composed of the same electrode material, has all
electrodes immersed in the same electrolyte. Since each electrode is connected
in parallel using external connecting wires, a significant amount of inactive
material has been integrated into the battery system. As a result, it is
estimated that the volumetric energy density may experience a loss of
approximately 40%, and the gravimetric energy density approximately 20%.
The bipolar battery
features a simple cell configuration and shape as it does not utilize
electrical connectors or other accessories. The volume of the battery is close
to the product of the total stack thickness of the individual unit cells and
the substrate area of the unit cell, while the weight of the battery is
comparable to the total mass of all components. Although the capacity of the
bipolar battery is equivalent to that of a single unit cell, the output voltage
of the bipolar battery is determined by the number of unit cells connected in
series and the voltage of each cell multiplied together.
Using bipolar electrodes
in batteries significantly increases both volumetric and gravimetric energy
density. Additionally, based on application-centric design, the battery shape
can be easily adjusted to maximize the utilization of the battery storage space
in the target device. In other words, the battery volume decreases, and by
minimizing the BMS, energy density enhancement and cost savings can be
simultaneously pursued through minimized use of cell packaging materials. This
ultimately translates into the ability to install more batteries in limited
electric vehicle battery mounting spaces, potentially leading to increased
driving range. Therefore, these advantages of bipolar electrodes are highly
attractive for the design of secondary batteries used in mobile electronic
devices and electric vehicles.
Another advantage of bipolar electrodes is that
electron flow occurs vertically through the substrate, and when the substrate's
cross-sectional area is large, current density and distribution are
significantly improved. Therefore, using bipolar electrodes allows
fast-operating secondary batteries to function safely without any safety
issues.
Starting with Furukawa Electric's compact
batteries featuring bipolar electrodes, Toyota has recently commercialized
bipolar Ni-MH batteries, which were applied to the Aqua HEV. In the
announcement at June 2023, Toyota revealed a roadmap stating that they plan to
produce bipolar LFP batteries for volume-grade EVs in 2026-2027 and bipolar
Ni-based LIBs for future versions of EVs in 2027-2028. This roadmap aims to
enhance driving range and reduce costs compared to performance versions of
LIBs.
The recently released Toyota Crown Crossover
and Lexus RX feature an improved version of the traditional Ni-MH battery,
known as the bipolar Ni-MH. This marks a departure from the previous trend of
using LIBs, especially in high-end and fuel-efficient models. This shift
suggests an intention to gradually expand the use of Ni-MH batteries across the
lineup, indicating a strategic change in battery technology adoption.
In this report, we have compiled the history of
the development of bipolar electrodes, which have recently begun to be applied,
as well as the current status of research and development. We have detailed
each development to provide a comprehensive overview, making it easy to
understand the overall situation.
The
strong points of this report are as follows:
① Detailed coverage of recent
technological trends related to bipolar batteries
② Detailed coverage of the development history
and current status of bipolar battery developers
③ Concentrated coverage of the
development status of bipolar batteries at Toyota Motor Corporation
④ Analysis of bipolar battery's
key patent
(The history of bipolar electrode development and key timeline)
(Bipolar Ni-MH batteries equipped in the new model of Toyota's 2nd generation Aqua)
(Comparison between the
traditional structure and the bipolar structure of secondary batteries)
(There is a size reduction of
the battery pack when applying a bipolar solid-state battery.)
Table
of Contents
1.
Bipolar Electrodes for Secondary Batteries···························································
10
1.1.
The Necessity of Battery Structure
Optimization·········································
10
1.2.
Bipolar Electrodes··················································································
12
1.3. Development of Bipolar Electrodes···························································
14
1.3.1. History of Bipolar
Electrode Development···········································
14
1.3.2. Reduction in Weight,
Size, and Cost···················································
15
1.3.3. Improvement
in Energy Density/Power Density····································
15
1.3.4. Requirements
and Disadvantages of Bipolar Electrodes·······················
17
1.4.
Applications of Bipolar Electrodes·····························································
18
1.4.1. Bipolar Lead-Acid Batteries (LAB) ···················································· 18
1.4.2. Improvement
of Bipolar Lead-Acid Batteries·······································
18
1.4.2.1.
Surface Modification·································································
19
1.4.2.2. Corrosion Prevention·································································
19
1.4.3. Commercialization of Bipolar Lead-Acid
Batteries·······························
20
1.5.
Bipolar Alkaline Batteries·········································································
21
1.5.1. Bipolar Ni-MH·················································································
21
1.5.2. Bipolar Al and Zn Batteries·······························································
22
1.6.
Bipolar Lithium-Ion Batteries····································································
22
1.7.
Bipolar post-LiB(Li-S, Na-ion) ································································· 24
1.8.
Challenges and Outlook··········································································
25
1.8.1. Substrate Materials·········································································
26
1.8.2. Electrode Materials··········································································
26
1.8.3. Electrolyte Materials········································································
27
1.8.4. Engineering Technologies································································
27
1.8.5. Outlook of Bipolar Electrode·····························································
27
1.8.6. Hurdles to Commercialization···························································
28
1.8.7. Other Bipolar Batteries·····································································
29
1.8.8. Bipolar Solid-State Batteries·····························································
31
2.
Bipolar Solid-State Batteries: Design, Fabrication, and Electrochemistry·················· 33
2.1.
Overview·······························································································
33
2.1.1.
Advantages of Bipolar Solid-State Batteries········································
34
2.1.2.
Technical Challenges of Bipolar Batteries···········································
34
2.1.3.
Requirements for Bipolar Materials····················································
34
2.2.
Bipolar Plates·························································································
35
2.3.
Fabrication and Electrochemical Characteristics of Bipolar Solid-State
Batteries 37
2.3.1.
Free standing Lamination Bipolar Solid-State Batteries························ 37
2.3.2.
Printing Bipolar Solid-State Batteries·················································
40
2.4.
Results and Future Outlook·····································································
43
3.
Bipolar Solid-State Batteries: Design of Energy Density········································· 45
3.1.
Overview·······························································································
45
3.2. Results and Discussion···········································································
46
3.2.1.
SolidPAC demo···············································································
46
3.2.2.
Comparison of Bipolar Stacking and Conventional Stacking················· 49
3.2.3.
Sensitivity Analysis··········································································
50
3.2.4. Experimental Data Analysis······························································
51
4.
Bipolar Solid-State Batteries: Based on Quasi-Solid Electrolytes····························· 54
4.1.
Quasi-Solid Li-Glyme complex·································································
54
4.2.
Evaluation of Bipolar Solid-State LIBs·······················································
54
4.3.
SEM Analysis of Bipolar Solid-State LIBs···················································
56
4.4.
Conclusion·····························································································
57
5.
Bipolar Solid-State Batteries: Based on Sulfide Electrolytes···································· 58
5.1.
Overview·······························································································
58
5.2. Results and
Discussion···········································································
59
5.2.1. Manufacturing and
Characteristics of Cathode Layers·························
60
5.2.2. Manufacturing and
Characteristics of Anode Layers····························
61
5.2.3. Manufacturing and
Characteristics of Mono cells··································
63
5.2.4. Characteristics of Bipolar
Stacked Solid-State Batteries·······················
64
5.2.5. Comparison of Energy Densities
in Bipolar Solid-State Batteries···········
65
5.3.
Conclusion·····························································································
67
6.
Bipolar Solid-State Batteries: Based on Multistage Printing Manufacturing··············· 68
6.1.
Overview·······························································································
68
6.2. Introduction····························································································
68
6.3. Experiment····························································································
69
6.3.1. Manufacturing of SWCNT-Coated
Electrode Active Material·················
69
6.3.2. Fabrication of Printed Bipolar
LIB······················································
70
6.4. Results and Discussion···········································································
70
6.4.1. Solid Gel Composite Electrolyte(GCE)···············································
71
6.4.2. Fabrication and Characteristics
of Printed Electrodes··························
72
6.4.3. GCE and Electrode Paste Control·····················································
75
6.4.4. Mechanical Flexibility and
Thermal Stability········································
77
6.5. Conclusion·····························································································
78
7.
Bipolar Solid-State Batteries: Application of FeOx-LFBO Anode······························ 79
7.1.
Overview·······························································································
79
7.2. Introduction····························································································
79
7.3. Experiment Results·················································································
82
7.3.1. Synthesis and Characteristics of
FeOx-LFBO·····································
82
7.3.2. Electrochemical Performance of
FeOx-LFBO Anode····························
83
7.3.3. Mechanism Analysis········································································
86
7.3.4. Electrochemical Performance of
Cu-free LIB······································
88
7.4. Conclusion·····························································································
90
8.
Bipolar LFP/LTO Batteries: LIBs for Micro/Mild Hybrid············································ 92
8.1.
Overview·······························································································
92
8.2.
Introduction····························································································
92
8.3.
Experiments···························································································
93
8.4.
Results and Discussion···········································································
95
8.4.1.
LFP, LTO························································································
95
8.4.2.
15Wh Bipolar Battery·······································································
96
8.4.3.
Safety····························································································
98
8.5.
Conclusion·····························································································
99
9.
Bipolar Ni-MH Batteries····················································································
100
9.1.
Overview·····························································································
100
9.2.
Battery Design······················································································
100
9.3. Application
of Wafer Cells········································································
101
9.4. Application in HEVs················································································
102
9.5. Application in PHEVs··············································································
103
9.6. Application in Utility·················································································
106
9.6.1. High-Power Bipolar Batteries····························································
109
9.6.2. High-Energy Bipolar Batteries···························································
111
10.
Bipolar High-Voltage Na-ion Batteries·······························································
113
10.1. Overview·····························································································
113
10.2. Introduction·······················································································
113
10.2.1. Monopolar 48V Battery System··················································
114
10.2.2. Commercialization
Issues of Bipolar Batteries······························
115
10.3. Experiment and Method·········································································
116
10.4. Results································································································
116
10.4.1. Bipolar Batteries with
Liquid Electrolytes·········································
116
10.4.2. nS mP(Series-Parallel)
Bipolar Batteries·········································
118
10.4.3. Na-ion Bipolar
Batteries with Above 5V··········································
120
10.4.4. Custom Cell Voltage
Profile Design···············································
122
11.
Bipolar All Polymer Batteries···········································································
123
11.1. Characteristics of All
Polymer Batteries····················································
123
11.1.1.
Advantages of All Polymer Batteries··············································
125
11.1.2.
Disadvantages of All Polymer Batteries··········································
125
11.1.3.
Energy Density of All Polymer Batteries·········································
125
11.1.4. Manufacturers of All
Polymer Batteries···········································
126
11.1.4.1.
Kawasaki Heavy Industries················································
126
11.1.4.2.
JFE Chemical··································································
127
11.1.4.3.
Teijin···············································································
127
11.1.4.4.
Gunze/Sanyo Chemical Industries······································
127
11.2.
Manufacturing Methods of All Polymer Batteries····································
128
11.3.
Characteristics of All Polymer Batteries················································
130
11.3.1. Voltage Increase by Stacking····················································
130
11.3.2. Elimination of Drying Process···················································
130
11.3.3. Improve of Production Speed·····················································
131
11.4.
Basic Structure of All Polymer Batteries················································
132
11.5. All Polymer Batteries Stacked in Series·························································· 132
11.6.
Safety-Enhanced Bipolar All Polymer Batteries······································
133
11.7.
Core-Shell Type Electrode Materials····················································
134
11.8.
Bipolar All Polymer Batteries by APB Corporation·································· 135
11.9.
Future Outlook of All Polymer Batteries················································
137
12.
Bipolar Lead-Acid Batteries (Furukawa電工)····················································· 138
12.1.
World's First Commercialization··························································
138
12.1.1. Structure and Challenges of
Bipolar Lead-Acid Batteries·················
138
12.1.2. Overcoming Challenges with
Metal/Polymer Materials····················
139
12.2.
ESS Batteries for Long-Term Power Storage········································
140
13.
Bipolar LIBs (Fraunhofer IKTS)········································································
143
13.1.
Overview··························································································
143
13.2.
Concept of Bipolar Batteries·······························································
143
13.3.
Wet Process Electrode Manufacturing··················································
144
13.4.
Separator Coating·············································································
146
13.5.
Bipolar Cells and Stacks·····································································
147
13.6. Roll Clad Foil for Bipolar Battery (SCHLENK)
······································ 148
14.
Bipolar Ni-MH Batteries (TOYOTA)··································································
151
14.1.
Characteristics of Bipolar Batteries······················································
153
14.2.
New Battery Technologies··································································
154
14.3.
Battery Innovation by TOYOTA···························································
156
14.4.
Timeline of TOYOTA··········································································
158
14.5.
Manufacturing Process by TOYOTA·····················································
159
15.
Bipolar Battery Patents···················································································
162
15.1.
TOYOTA: Bipolar Ni-MH Batteries·······················································
162
15.2.
Hyundai Motor Company: Bipolar Solid-State Batteries·························· 168
15.3.
TOYOTA: Bipolar Solid-State Batteries·················································
175
15.4.
Samsung SDI: Bipolar Electrodes and Manufacturing···························· 180
15.5.
LG Chem: Bipolar Batteries································································
184
15.6.
LGES: Bipolar LIBs············································································
187
15.7.
KITECH: Bipolar Solid-State Batteries··················································
192
15.8. ProLogium: Horizontal Composite
Electric Supply Structure····················
197
References········································································································
201