Degradation Mechanisms

Why batteries fade. Drag the cycle slider or press Play to watch four common mechanisms develop. Each is described with the degradation mode it causes: loss of lithium inventory, loss of active material, or rising resistance.

SEI growth

Loss of lithium inventory · rising resistance

The solid electrolyte interphase (SEI) forms on the anode when the electrolyte is reduced. It protects the anode, but keeps growing slowly, consuming lithium and electrolyte.

Triggered by
High temperature, high state of charge and long storage.
Effect
Cyclable lithium is lost and the interphase resistance rises: capacity fades and power drops.
Mitigation
Electrolyte additives that form a thinner, more stable SEI; moderate temperatures and states of charge.

Sources: [51] Peled et al. (1979) · [52] Vetter et al. (2005) · [53] Birkl et al. (2017)

Lithium plating and dendrites

Loss of lithium inventory · safety risk

When Li⁺ reaches graphite faster than it can slide between the layers, lithium deposits on the surface as metal. Metallic lithium can grow into branching dendrites.

Triggered by
Fast charging, low temperature and high state of charge.
Effect
Plated lithium is partly lost for good; dendrites that pierce the separator can short-circuit the cell.
Mitigation
Limit charge rate in the cold, design electrodes with spare anode capacity, and solid electrolytes that block dendrites.

Sources: [43] Lin et al. (2017) · [54] Waldmann et al. (2018)

Particle cracking

Loss of active material · rising resistance

Ni-rich layered cathodes change volume unevenly as lithium leaves and returns. Repeated strain opens microcracks between the primary grains of each particle.

Triggered by
High nickel content, deep charging to high voltage.
Effect
Electrolyte floods the cracks, fresh surfaces react and fragments lose contact: capacity fades faster for Ni-richer grades.
Mitigation
Protective coatings, single-crystal particles, avoiding the highest charge voltages.

Sources: [39] Ryu et al. (2018) · [53] Birkl et al. (2017)

Transition-metal dissolution

Loss of active material · faster SEI growth

Manganese slowly dissolves from the cathode, travels through the electrolyte as Mn²⁺ and ends up in the anode's SEI.

Triggered by
Elevated temperature; manganese-based cathodes such as LiMn₂O₄.
Effect
The cathode loses active material, and manganese in the SEI makes it grow faster, trapping more lithium.
Mitigation
Surface coatings, electrolyte additives and avoiding high temperatures.

Sources: [52] Vetter et al. (2005) · [55] Zhan et al. (2013)

Illustrations are schematic: the cycle slider shows how each mechanism progresses, not a measured rate. Real degradation speed depends strongly on chemistry, temperature, charge rate and voltage window.