<2024> Development Trends and Outlook of Anode-Free Technology for Secondary Batteries
(Focusing
on Plating-Type Anode-Free Technology)
With the growth of
the electric vehicle market, various requirements for battery technology are
emerging, and particular attention is being paid to improving the energy
density of cells, as higher energy density in EVs directly translates into
longer driving range per charge. Therefore, new research efforts aimed at
increasing energy density are gaining traction.
Existing research
includes increasing the Ni content in the active material, using solid
electrolytes, or developing lithium-metal batteries that use lithium as the
anode material to significantly reduce anode thickness.
Lithium-metal anodes
theoretically exhibit high gravimetric capacity (3862 mAh g⁻¹) and volumetric capacity (2093 mAh cm⁻³), and possess the lowest redox potential (-3.05 V vs. SHE).
Therefore, replacing graphite anodes with lithium metal provides more than ten
times the capacity of graphite at the same weight, enabling lithium-metal
batteries (LMBs) to achieve an energy density of 500 Wh kg⁻¹ (750 Wh L⁻¹).
However,
lithium-metal batteries face several issues, including dendrite formation on
the lithium-metal anode, side reactions between the electrolyte and metal,
electrolyte consumption and depletion caused by the formation of a thick SEI
layer, and low coulombic efficiency (CE) resulting from the instability of the
lithium plating/stripping process.
The concept of the
anode-free lithium-metal battery (AFLMB) emerged as a result of these issues.
Along with the recent development of all-solid-state batteries, anode-free
batteries have been receiving increasing attention. Anode-free cells use only a
current collector without any active material at the anode, offering the
advantage of achieving a dramatic improvement in energy density.
Anode-free batteries
are being highlighted as one of the promising future battery technologies due
to their theoretical gravimetric and volumetric energy density. Although they
theoretically provide higher energy density than conventional lithium-ion batteries,
their current development is limited by the absence of a Li⁺
reservoir and severe lithium loss at the anode, resulting in only a few cycles
of operation at room temperature.
Anode-free, also
referred to as anode-less, batteries are a next-generation technology expected
to overcome the limitations of lithium-ion batteries. The anode plays a
critical role in determining battery lifetime and charging rate, and in the
case of graphite anodes currently used in LIBs, technological development has
already reached a mature stage, making further performance improvement
difficult. If the amount of anode material is reduced or eliminated, the volume
and mass of the cell decrease, resulting in higher energy density.
In conventional
LIBs, charging and discharging occur as lithium ions in the cathode active
material move between the anode and cathode through the electrolyte. In other
words, lithium ions deintercalated from the cathode are inserted into the
layered structure of graphite at the anode, and conversely, lithium ions are
deintercalated from the anode and move back to the cathode repeatedly. In
contrast, in anode-free lithium secondary batteries, only the anode current
collector exists without any anode active material to store lithium ions coming
from the cathode. Copper (Cu) is typically used as the anode current collector,
and the charging process involves lithium ions being deposited on the current
collector surface in the form of lithium metal. During discharge, the deposited
lithium is stripped back into ion form and moves to the cathode, repeating this
cycle.
The cost of
anode-free lithium batteries is reduced because there are no expenses
associated with raw materials, solvents, additives, or processing for the
anode. In addition, cost issues related to the transportation, storage, and
refining of lithium metal are eliminated. Finally, since the conventional anode
structure is replaced with a metal foil, it becomes possible to achieve the
highest theoretically attainable gravimetric and volumetric energy densities.
Due to the absence of an
anode active material that can stably store lithium, the anode volume in
anode-free batteries expands during cycling, which leads to degradation of
battery life. Although they offer a significant advantage in terms of
dramatically improved energy density, they still face the inherent limitation
of performance deterioration caused by dendrite formation. Recently, as the
development of all-solid-state batteries applying solid electrolytes has
advanced considerably to enhance safety, various approaches have been explored
to suppress dendrites in anode-free batteries and improve their performance.
This report summarizes the
development status of anode-free batteries by development period, covering both
academic research and industrial efforts led by companies such as Samsung SDI,
to provide a structured understanding of anode-free battery research and
development.
Strong Points of This
Report
①
Detailed summary of the introduction, research trends, and development status
of anode-free batteries
②
Summary of recent R&D results for next-generation batteries such as
anode-free all-solid-state batteries, Li-metal batteries, Na batteries, and
Li–S batteries
③
Summary of government-supported anode-free battery development programs and
related technological achievements across major countries
④
Detailed overview of recent activities and patent analysis of companies
developing anode-free batteries
Anode-free lithium battery advantages. (A) Schematic diagram of a lithium-ion battery and an anode-free full cell.
1. Basic Understanding of Anode-Free (Anode-Less) Batteries
1.1
Improving Coulombic Efficiency of Anode-Free Lithium Metal Batteries 13
1.2.
Implementation of Practical Anode-Free Batteries 14
1.2.1.
Cell Modification 15
1.2.2.
Separator Modification 16
2.
Anode Active Materials for Anode-Free Batteries
2.1.
Requirements for Anode Active Materials 16
2.2.
Properties of Lithium Metal 16
2.3.
Use of Lithium Metal Electrodes 17
2.4.
Non-uniform Lithium Deposition 20
2.5.
Suppression of Dendrite Formation by Solid Electrolytes 26
3.
Anode-Free Lithium Batteries: Materials, Electrode, and Electrolyte Development
3.1.
Overview 27
3.2.
Optimization of Testing Methods 29
3.2.1.
Hot Formation Protocol 30
3.2.2.
Asymmetric Charge-Discharge Protocol 31
3.3.
Electrolyte Modification 32
3.3.1.
Liquid Electrolytes 32
3.3.1.1
Solvent Composition 33
3.3.1.2.
Salt and Anion Composition 36
3.3.1.3.
Electrolyte Additives 38
3.3.1.4.
Solid Electrolytes 41
3.3.1.5.
Organic Materials 45
4.
Interfacial Chemistry of Anode-Free Cells: Challenges and Strategies
4.1.
Overview 47
4.2.
Interfacial Issues 47
4.3.
Interfacial Engineering Strategies 49
4.3.1.
SEI Layer Regulation via Electrolyte Design 49
4.3.2.
Artificial SEI 51
4.3.3.
Wetting of Cu Current Collectors 53
4.3.4.
3D Current Collectors 55
4.3.5.
Interfacial Chemistry in Anode-Free All-Solid-State Batteries (AFSSBs) 57
5.
Anode-Free Lithium Pouch Cells: Dual-Salt Electrolyte Application
5.1.
Summary 57
5.2.
Research Results 58
5.2.1.
Cell Performance of Dual-Salt Electrolytes 58
5.2.2.
Effect of External Pressure on Li Morphology and Cell Performance 59
5.2.3.
Anode–Electrolyte Interface 61
5.2.4.
Electrolyte Consumption 61
6.
Strategies for Long Cycle Life in Anode-Free Lithium Metal Batteries
6.1.
Research Summary 62
6.2.
Theoretical Basis and General Characteristics 64
6.2.1.
Configuration and Basic Principle of Anode-Free Lithium Metal Batteries 64
6.2.2.
Energy Density 64
6.2.3.
Assembly Process and Cost 65
6.3.
Factors Affecting the Lifespan of Anode-Free Lithium Metal Batteries 65
6.3.1.
Formation and Characteristics of the SEI Layer 67
6.3.2.
Formation of Dead Lithium 67
6.4.
Strategies for Building Long-Life Anode-Free Lithium Metal Batteries 70
6.4.1.
Additional Li Compensation from the Cathode 70
6.4.2.
SEI Design through Electrolyte Composition Tuning 71
6.4.2.1.
Liquid Electrolytes 71
6.4.2.2.
Solid-State Electrolytes for Long-Life Anode-Free Batteries 74
6.4.2.3.
Li-Metal Deposition via Substrate Design 76
6.4.2.4.
Regeneration of Dead Li 81
6.4.2.5.
Test Protocols 83
6.4.3.
Research Outcomes 85
7.
Energy Density Comparison: Anode-Free vs. Lean Anode Batteries
7.1.
Energy Density Comparision 88
7.2.
Cycle Life Compariosn 90
7.3.
Research Summary 94
8.
Cathode Development for Anode-Free Lithium Metal Batteries
8.1.
Li-Rich Li2[Ni0.8Co0.1Mn0.1]O2 Cathode 95
8.1.1.
Research Overview 95
8.1.2.
Cathode Material Synthesis and Characterization
97
8.1.3.
Electrochemical Evaluation 99
8.1.4.
Full-Cell Evaluation 102
8.1.5.
Conclusion 103
8.2.
Development of Mn-Based Li-Rich Spinel Cathodes 103
8.2.1.
Research Overview 103
8.2.2
Coin Cell Evaluation 104
8.2.3
Cathode Structural Analysis 107
9.
Current Collectors for Anode-Free Lithium Metal Batteries
9.1.
Research Overview 109
9.2.
Porous-Defective (MV) Carbon Current Collectors 111
9.3.
Defect-Free SEI Layers at the Current Collector/Electrolyte Interface 114
9.4.
Uniform Lithium Deposition Facilitated by Porous Defects 117
9.5.
Cycling Stability of Porous-Defective Carbon Current Collectors 119
9.6.
Electrochemical Performance of Anode-Free Lithium Metal Full Cells 122
10.
Anode-Free All-Solid-State Batteries: Current Status, Issues, and Challenges
10.1.
Advantages and Disadvantages of Anode-Free Batteries 124
10.1.1.
Advantage of Anode-Free Cell (1): Enhanced Energy Density (assuming a cathode
thickness of 100 μm) 124
10.1.2.
Manufacturing and Cost 126
10.1.3.
Recyclability 126
10.2.
Anode-Free Lithium Metal Batteries (with Liquid Electrolytes) 127
10.2.1.
Current Collector Modification 127
10.2.2.
Modification of Liquid Electrolytes 129
10.2.2.1.
Dual-Salt and Multi-Salt Electrolytes 129
10.2.3.
Modification of Cycling Protocols 129
10.2.4.
Synergistic Strategies 130
10.2.5.
Strategies for the Successful Implementation of Anode-Free All-Solid-State
Batteries 130
10.3.
Anode-Free All-Solid-State Batteries 131
10.3.1.
Thin-Film Anode-Free All-Solid-State Batteries 131
10.3.2.
Composite Cathodes for Anode-Free All-Solid-State Batteries 132
10.3.3.
Key Challenges and the Most Promising Solution Strategies for Anode-Free
All-Solid-State Batteries 134
10.3.3.1.
Coulombic Efficiency and Lithium Inventory Retention 134
10.3.3.2.
Interfacial Issues 136
10.3.3.2.1.
Interfacial Stability 136
10.3.3.3.
Interfacial Effects 138
10.3.3.3.1.
Implications for Anode-Free All-Solid-State Batteries 139
10.3.3.4.
Dendrite Formation 141
10.3.3.4.1.
Mechanism of Dendrite Formation 141
10.3.3.4.2.
Implications for Anode-Free All-Solid-State Batteries 143
10.4.
Cell Design and Practical Energy Density 145
10.5.
Conclusion 147
11.
Anode-Free All-Solid-State Batteries: Recent Advances and Future Prospects
11.1.
Sulfide-based solid electrolytes 149
11.2.
Oxide, Polymer, and Composite Solid Electrolytes 151
11.3.
Future Perspectives 154
11.3.1.
General Considerations 154
11.3.2.
Anode-Free All-Solid-State Batteries: Application of Sulfide-Based Solid
Electrolytes 155
11.3.3.
Application of Oxide/Polymer/Composite Electrolytes in Anode-Free SSBs 155
12.
Fabrication of Anode-Free All-Solid-State Batteries: Application of LLZO
Electrolytes
12.1.
Research Summary 156
12.2.
Experimental 157
12.2.1.
In-Situ Plating of Lithium 157
12.2.2.
Lithium Dynamics and Nucleation at the Current Collector/LLZO Interface 160
12.2.3.
Performance of In-Situ Plated Lithium-Metal Anodes 161
12.3.
Conclusion 162
13.
Anode-Free Solid-State Batteries : Composite Applications
13.1.
Research Summary 163
13.2.
Results and Discussion 166
13.2.1.
3D Interconnected Carbon Layer 166
13.2.2.
Ion–Electron Conducting Network 166
13.2.3
Lithium Plating/Stripping Behavior 168
13.2.4.
Electrochemical Performance 169
14.
Anode-Free Liquid-Based Li–S Batteries
14.1.
Research and Experimental Overview 171
14.2.
Cycling Performance and Electrochemical Analysis 173
14.3.
Effect of Nd(OTf)₃ on the Cathode 175
14.4.
Effect of Nd(OTf)₃ on the Anode 177
15.
Anode-Free Li–S (Quasi-Solid) Batteries
15.1.
Research Summary 179
15.2.
Research Background 179
15.3.
Results 182
15.3.1.
Cell and Materials 182
15.3.2.
Fabrication and Characterization of Li₂S@MX Cathodes 183
15.3.3.
Electrochemical Properties of Li‖Li₂S@MX Cells with Non-Aqueous Liquid
Electrolytes 184
15.3.4.
Li₂S|CGPE|Cu Cell and Energy Storage Performance 185
15.3.5.
Battery Safety Evaluation 186
15.3.6.
Conclusion and Summary 187
16.
Anode-Free Sodium-Metal Batteries (AFSMBs)
16.1.
Overview of Anode-Free Sodium-Metal Batteries 188
16.2.
Advantages of the Anode-Free Configuration 189
16.3.
Limitations of Sodium Foil 190
16.4.
Energy Density 190
16.5.
Carbon Footprint and Cost 191
16.6.
Sustainability 193
16.7.
Impact on Upstream Industries 193
16.8.
Transition Metals 194
16.9.
Cathode Material: Na₂CO₃ 195
16.10.
Al foil 196
16.11.
Key Challenges and Strategies for Optimization 197
16.11.1.
Limited Sodium Source 197
16.11.2.
Na-Rich Cathode Materials 197
16.11.3.
Na-Ion Augmentation Coatings 199
16.11.4.
Super-Concentrated Electrolytes 200
16.11.5.
Irreversible Sodium-Ion Loss 201
16.11.6.
Artificial Interlayer Engineering 201
16.11.7.
Electrolyte Modification 202
16.12.
Conclusion and Summary 204
17.
Anode-Free Sodium Solid-State Batteries
17.1.
Results 207
17.1.1.
Electrochemically Stable Electrolytes 207
17.1.2.
Interfacial Contact 207
17.1.3.
Dense Solid Electrolytes 209
17.1.4.
High-Density Current Collectors 210
17.1.5.
Stack Pressure and Sodium Morphology 212
17.1.6.
Anode-Free Na All-Solid-State Full Cell 214
17.1.7.
Conclusion 215
18.
National Program on Anode-Free Li Batteries
18.1.
PNNL DOE Program: Project ID #BAT585) 216
18.1.1.
Project Approaches 216
18.1.2.
High-Performance Localized High-Concentration Electrolytes 216
18.1.3.
Polymer-Coated Cu substrates (PLCu) for Improved Li Stripping Uniformity 216
18.1.4.
Pressure Optimization in 2032 Coin Cells 217
18.1.5.
Li morphology after 200 cycles in Cu||NMC811 Cells 217
18.1.6.
Electrochemical Performance of Multilayer Cu||NMC532 pouch cells (250 mAh) 218
18.1.7.
Thermal Stability Improvement in 250 mAh Pouch Cells using E1 Electrolyte 218
18.2.
SOLVE Program: Horizon Europe Project 219
18.3.
Europe AM4BAT: Solid-State Battery Development via 3D Printing 220
18.3.1.
Development of 3D Metallic Nanostructures and Lithiophilic Current Collectors 221
18.4.
South Korea: Development of Anode-Free Lithium Batteries 223
19.
Patent Analysis on Anode-Free Batteries
19.1.
Samsung SDI 224
19.2.
Samsung Electronics 226
19.3.
Samsung Electronics 228
19.4.
LG Chem 232
19.5.
LGES 235
19.6.
Hyundai Motor 237
19.7.
Tesla 239
19.8.
Terawatt Technology 241
19.9.
Korea Electrotechnology Research Institute (KERI) 244
19.10.
Korea Advanced Institute of Science and Technology (KAIST) 247
19.11.
Korea Institue of Industrail Technology (KITECH) 248
20.
Development Trends by Company
20.1.
Samsung SDI 250
20.2.
Quantumscape 253
20.3.
ONE(Our Next Energy) 257
20.4.
ION Storage Systems 262
20.5. Jinyu New Energy 268