The performance of lithium-ion batteries fades over time, but the underlying causes are not fully understood. Analysis of lithium- and manganese-rich cathodes now reveals how the lattice of atoms in these materials becomes strained, which releases oxygen and leads to battery failure.
That leads to structural collapse, new surface exposure, and electrolyte decomposition. The residual lithium compounds (e.g., Li 2 CO 3 and LiOH) form an insulating passivation layer on the surface of cathode materials, increasing the charge transfer resistance.
Below this critical lithium content, exponentially growing strain and large lattice distortions occur, which may favor irreversible cracks. Since lithium loss upon cycling induces a shift towards lower lithium content in positive active material, the consequences of repeated and irreversible stress are expected to be exacerbated on the long-term.
The residual lithium compounds (e.g., Li 2 CO 3 and LiOH) form an insulating passivation layer on the surface of cathode materials, increasing the charge transfer resistance. Moreover, the residual lithium compounds bring about decomposition of electrolyte solution, leading to gas evolution and slurry gelation.
We discover that strain appears when the structure collapses, below 40% lithium in the layers. Below this critical lithium content, exponentially growing strain and large lattice distortions occur, which may favor irreversible cracks.
The accumulated lattice strain has an undeniable role in the batteries’ structural decomposition and electrochemical fade, and we expect that they are common in other cathode materials that include lithium diffusion.