Lithium-rich manganese cathode

Example

Use in Lemonergy

Separate chemistry from form factor.

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Disordered rock salt

A cathode family in which lithium and transition-metal ions share the same crystal sites at random instead of forming ordered layers. With about 10–20 % excess lithium, percolating diffusion paths open, giving over 250 mAh/g from abundant manganese, titanium or iron instead of nickel and cobalt. Slow kinetics, voltage hysteresis and oxygen loss keep it in the laboratory.

First-cycle loss

The lithium consumed in forming the SEI on the first charge, which never returns to the positive electrode: about 5–10 % of capacity for graphite and far more for silicon. Pre-lithiation is the way to pay this debt in advance.

High-nickel cathode

A layered oxide with 80 % or more nickel, such as NMC811 or NCA. Nickel raises capacity and lowers cobalt content, but the material is less thermally stable, more sensitive to moisture and ages faster at high voltage.

Layered oxide

The crystal structure of LCO, NMC and NCA: close-packed oxygen layers with lithium and transition-metal ions in alternate layers of octahedral sites, so lithium moves in two-dimensional sheets. The structure offers high capacity and voltage but can distort or mix cations when deeply delithiated. Sodium versions are labelled O3 or P2 by their stacking.

NMC

A family of layered-oxide positive electrode materials, LiNiₓMnᵧCo₁₋ₓ₋ᵧO₂, used in many electric-vehicle cells. Variants are named by their metal ratio: NMC811 has eight parts nickel to one each of manganese and cobalt.

Structural degradation

Changes in the crystal structure of a positive material as it cycles: layered oxides can rearrange into spinel or rock-salt phases at the surface, with nickel ions migrating into lithium sites. The new phases block lithium transport and raise resistance.

References & further reading

Technical references

1. A reflection on lithium-ion battery cathode chemistry

   Arumugam Manthiram · Nature Communications · 2020

   Technical reference · Layered oxides, spinels and polyanion cathodes; links between composition, structure and performance.