Why Do Lithium-ion Batteries Degrade?

[DiAubrey]

Here are the reasons for the degradation of lithium-ion batteries: 1. Structural changes in cathode materials: The cathode material is a critical component of lithium-ion batteries. When lithium ions are removed from the cathode, to maintain the material's electrically neutral state, metal elements will inevitably oxidize to higher oxidation states, accompanied by changes in composition. This transformation can easily lead to phase transitions and alterations in the bulk structure. The phase change of the electrode material causes variations in lattice parameters and lattice mismatch, inducing stress that results in grain fracture and crack propagation within the material. This mechanical damage to the material structure ultimately leads to the decline in the electrochemical performance of the lithium-ion battery. 2. Structure of anode materials: Carbon materials and lithium titanate are commonly used in commercial lithium-ion batteries. Taking the typical anode graphite as an example, the capacity degradation of lithium-ion batteries first appears during the formation stage, where the SEI (Solid Electrolyte Interphase) consumes some lithium ions on the anode surface.

[DeTessa]

As a long-time enthusiast studying battery technology, I've found that lithium-ion battery degradation primarily stems from internal molecular changes: during each charge-discharge cycle, lithium ions shuttle between the positive and negative electrodes. This causes electrode materials like graphite or metal oxides to gradually fatigue and detach, accumulating on the surface to form a thickening SEI film that impedes ion flow. High-temperature environments, such as summer car interiors, accelerate this aging process. Additionally, deep discharges can create lithium metal plating that consumes battery life. After several hundred cycles, capacity naturally declines - electric vehicle batteries being a classic example. While engineers mitigate this chemical aging through improved electrode coatings, they cannot completely eliminate it. This degradation manifests as reduced range, making proper charging habits crucial.