Degradation Mechanisms - Battery Design

A look at the degradation mechanisms in the battery electrochemistry.

Cation Mixing (Cation Disorder)

A degradation mechanism in layered cathodes where nickel and lithium ions exchange lattice sites, blocking lithium diffusion pathways.

Chemical Crosstalk

Degradation species generated at one electrode migrating through the electrolyte and reacting at the other. HF generated from LiPF₆ hydrolysis leaches transition metals from the cathode, which then migrate to poison the anode SEI; gases such as C₂H₄ generated at the anode during SEI formation can migrate back and parasitically react with the cathode surface. Not all crosstalk is harmful, some crossing species are consumed in reactions that stabilise the opposing interface rather than degrade it [1].

Gas Evolution (Gassing)

The generation of gas inside a cell from electrolyte or additive decomposition, a common cause of pouch cell swelling. The dominant chemistry shifts with when it happens: gassing during formation is mostly CO₂, C₂H₄, CO and H₂ from the initial SEI-forming reduction of carbonate solvents at the anode, and cells are normally degassed and re-sealed after this step; gassing under overcharge produces more CO₂, CO and O₂ from electrolyte oxidation and cathode oxygen release at high voltage, and is generally more severe than heating alone at the same temperature; gassing during high-temperature storage or aging instead comes from ongoing parasitic reactions and the slow thickening of the cathode-electrolyte interphase [2].

Lithium Dendrite

Filamentary metallic lithium growth that can pierce the separator and cause an internal short circuit, distinct from the more general phenomenon of lithium plating.

Micro-Cracking (High-Nickel Cathodes)

Intergranular cracking between the primary crystallites inside a secondary cathode particle, driven by anisotropic lattice strain (particularly along the c-axis) as the particle repeatedly delithiates and relithiates. Crack susceptibility rises sharply with nickel content, becoming markedly worse once nickel exceeds roughly 80% of the transition metal fraction (NMC811 and similar), because the larger phase transformations these chemistries undergo concentrate strain rather than dissipating it smoothly [3]. Once cracks form, electrolyte can penetrate into the particle interior and create fresh, unpassivated surface area for side reactions, while electrons are forced to detour around the cracks — the combination drives both capacity fade and rising impedance. See Particle Cracking for the more general, chemistry-agnostic mechanism.

Transition Metal Dissolution

A degradation mechanism where transition metal ions leach from the cathode into the electrolyte and migrate to poison the anode’s solid electrolyte interphase. Manganese dissolved from spinel or manganese-rich layered cathodes deposits on graphite, blocking Li-ion intercalation sites and disrupting the SEI, which accelerates SEI thickening and active-lithium loss even at room temperature. Nickel dissolution becomes the more significant contributor at elevated temperature, where oxygen-related structural instability in the layered cathode and faster electrolyte decomposition both promote nickel loss and the formation of an inorganic-rich SEI that hinders interfacial Li-ion transport [4].

References

Review: mechanisms and consequences of chemical cross-talk in advanced Li-ion batteries. Journal of Physics: Energy, IOPscience, 2020. iopscience.iop.org/article/10.1088/2515-7655/ab8b68
High temperature in situ gas analysis for identifying degradation mechanisms of lithium-ion batteries. Chemical Science, Royal Society of Chemistry, 2025. pubs.rsc.org/en/content/articlehtml/2025/sc/d4sc08105f
Cracking vs. surface reactivity in high-nickel cathodes for lithium-ion batteries. Joule, Cell Press, 2023. cell.com/joule/fulltext/S2542-4351(23)00396-3
Overlooked electrolyte destabilization by manganese (II) in lithium-ion batteries. PNAS (via PMC), 2019. pmc.ncbi.nlm.nih.gov/articles/PMC6668472