While lithium-ion batteries offer several advantages, such as high energy density and long cycle life, they are subject to degradation over time. Understanding the degradation mechanisms is crucial for improving battery performance, extending their lifespan, and ensuring safe operation.
The major 'Degradation Mechanisms':
Copper Dissolution:
- Copper from the anode may dissolve into the electrolyte over time.
- Copper ions may migrate to the cathode, inducing side reactions that degrade the cathode material and electrolyte.
- Contributes to reduced capacity and cycle life of the battery.
Pulverization & Electrical Isolation:
- Mechanical stress during charge and discharge cycles can cause the electrode particles to fracture and disintegrate.
- Leads to loss of electrical contact between active materials, increasing internal resistance and decreasing capacity.
Dendrites and SEI Growth:
- Dendrites are tiny metallic branches that form on the lanode during charging.
- They can penetrate the separator, causing internal short circuits or even thermal runaway events.
- The solid electrolyte interphase (SEI) layer can grow excessively, hindering efficient lithium ion transport and reducing capacity.
Chemical Crosstalk, Oxygen Evolution & Gassing:
- Unwanted side reactions, like electrolyte component oxidation and gas bubble generation, occur at the anode and cathode interfaces.
- Consumption of active lithium ions, electrolyte degradation, and cell swelling can compromise battery performance.
Transition Metal Dissolution:
- Cathode materials containing transition metals can dissolve into the electrolyte during cycling.
- Contaminates the cathode surface, leading to reduced capacity and accelerating degradation reactions.
Microcracking & Electrolyte Penetration:
- Repeated expansion and contraction of electrode materials cause microcracks.
- Electrolyte penetrates into the electrode particles, forming a resistive solid-electrolyte interphase (SEI), reducing capacity and performance.
Structural Disordering:
- Repetitive lithium ion insertion and extraction induce changes in active material lattice structure and morphology.
- Results in decreased electrochemical reactivity, reduced capacity, and increased resistance.
Aluminium Corrosion:
- The cathode current collector, often made of aluminium, may corrode in the presence of the electrolyte.
- Corrosion leads to the formation of resistive species, compromising conductivity and mechanical stability.
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