Why Does Lithium Battery Capacity Degrade? The reasons are as follows: 1. Structural Changes in Cathode Materials: The cathode material is the primary source of lithium-ion batteries. When lithium ions are extracted from the cathode, to maintain the material's electrical neutrality, metal elements are inevitably oxidized to a higher oxidation state, accompanied by component transformation. This transformation can lead to phase transitions and changes in the bulk structure. Phase transitions in electrode materials can alter lattice parameters and cause lattice mismatch, inducing stress that results in grain fragmentation and crack propagation, leading to mechanical damage to the material's structure and subsequent electrochemical performance degradation. 2. Anode Material Structure: Common anode materials for lithium batteries include carbon materials and lithium titanate. The first capacity degradation occurs during the chemical stage, where the formation of the SEI (Solid Electrolyte Interphase) on the anode surface consumes some lithium ions. As the battery is used, changes in the graphite structure also contribute to capacity loss. 3. Electrolyte Oxidation Decomposition and Interface Reactions: The properties of the electrolyte significantly affect the specific capacity, lifespan, charge-discharge rate performance, operating temperature range, and safety of lithium-ion batteries. The electrolyte mainly consists of solvents, electrolytes, and additives. Decomposition of solvents and electrolytes leads to capacity loss. Electrolyte decomposition and side reactions are major factors in lithium battery capacity degradation. Regardless of the cathode or anode materials or manufacturing processes used, electrolyte decomposition and interface reactions with electrode materials during cycling cause capacity degradation. 4. Cathode Overcharge Reaction: When the ratio of cathode active material to anode active material is too low, cathode overcharging is likely to occur. Overcharging the cathode leads to capacity loss primarily due to the formation of electrochemically inert substances (e.g., Co3O4, Mn2O3), which disrupt the capacity balance between electrodes, resulting in irreversible capacity loss. 5. Electrode Instability: During charging, unstable cathode active materials can react with the electrolyte, reducing capacity. Factors affecting cathode material instability include structural defects in the cathode material, carbon black content, and charging conditions.
