NMC cathode
Nickel, manganese and cobalt in a layered oxide — the high-energy cathode, and a family whose whole recent history is trying to use less cobalt.
NMC is not one compound but a family, and the numbers attached to it are the recipe: NMC 111 is equal parts nickel, manganese and cobalt, NMC 622 is six parts nickel to two each of the others, NMC 811 is eight parts nickel to one each. The formula is written LiNiₓMnᵧCoᵣO₂ with the three fractions summing to one, so it is treated here as a family rather than pretending a single stoichiometry is the material.
The three metals do three jobs. Nickel supplies capacity, and more of it means more energy stored. Cobalt stabilises the layered structure and keeps the lithium and nickel from swapping places, which is what would otherwise wreck the cathode. Manganese is cheap, adds structural stability and contributes nothing electrochemically.
Everything about the last fifteen years of this material is one movement: raise the nickel, cut the cobalt, and manage the consequences. NMC 111 is a third cobalt. NMC 811 is a tenth. The energy went up, the cost went down, and the material became harder to make, more moisture-sensitive and less thermally stable at every step.
Why it behaves as it does
A layered oxide cathode is sheets of transition-metal oxide with lithium between them, and the whole engineering problem is keeping the sheets in order while the lithium leaves and returns.
Nickel and lithium ions are almost exactly the same size, which is the root of the difficulty. As nickel content rises, nickel ions increasingly sit in the lithium layer — cation mixing — and block the channels the lithium has to move through. Cobalt suppresses it, which is what cobalt is actually for, and is why removing cobalt is not a matter of leaving it out.
High-nickel material is also chemically reactive in ways low-nickel material is not. It picks up moisture and carbon dioxide from the air and forms lithium hydroxide and carbonate on the surface, which gels the electrode slurry during manufacture and gasses in the finished cell, so NMC 811 production runs in dry rooms that are a substantial part of the plant's cost.
And it is less stable when hot. The temperature at which the lattice begins releasing oxygen falls as nickel rises, which is why the industry's move up the nickel ladder has been accompanied by increasingly elaborate cell-level and pack-level thermal management — and why LFP, which does not have this problem at all, has taken the applications where energy density is not the binding constraint.
NCA — lithium nickel cobalt aluminium oxide — solves the same problem a different way, using a little aluminium instead of manganese as the structural dopant. Tesla built its early packs on it, and it behaves like a high-nickel NMC in most respects.
Uses
Long-range electric vehicles, which is the application that pays for it: where the requirement is the most kilometres for a given pack mass and volume, no phosphate cathode competes.
Power tools, e-bikes and aviation, where the same logic applies more sharply — anything that has to be carried or lifted is buying energy per kilogram.
Laptops, phones and cameras, though the smallest cells still use plain lithium cobalt oxide, which stores more per unit volume and does not have to survive a car's duty cycle.
It has been steadily displaced from standard-range vehicles and stationary storage, and that displacement is the largest single materials shift in the battery industry to date.
Economic significance
NMC is where the battery industry's raw-material exposure lives, and reducing that exposure has been its central materials programme.
Cobalt is the acute problem. Roughly seventy per cent of mine supply is Democratic Republic of the Congo, refining is overwhelmingly Chinese, a substantial artisanal share is mined in conditions including documented child labour, and the price is volatile enough to have moved car pricing. The move from NMC 111 to 811 cuts the cobalt per kilowatt-hour by roughly two thirds and is straightforwardly a response to that.
Nickel is the chronic one. Batteries need Class 1 nickel — the high-purity grade — and most of the world's nickel is not that. Indonesian laterite converted to Class 1 by high-pressure acid leaching has supplied the growth, at a real energy and tailings cost, and it is the reason nickel supply has kept up at all.
The strategic reading is that NMC buys energy density with supply risk and LFP buys supply security with mass, and which is the better trade has moved back and forth with metal prices twice in five years. It will move again.
How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.
How this connects
Where a connection has been confirmed by an outside reference, that reference is named beside it.
is used in
- Lithium-ion cell — object · in long-range vehicles and anything that has to be carried, where the requirement is energy per kilogram and no phosphate cathode competes
- Automotive manufacture — industry · in long-range vehicles, and steadily displaced from standard-range ones by LFP — the largest single materials shift the battery industry has made
is an alternative to
- Lithium iron phosphate — compound · the substitution the whole industry has been arguing about: no cobalt and no nickel, thousands of cycles instead of hundreds, very much harder to set on fire — and roughly a third less energy for the same mass, which is a range figure a buyer feels immediately
contains
- Lithium — element · the working ion
- Nickel — element · the capacity, and the fraction the family is named by — 111, 622 and 811 are the nickel-manganese-cobalt ratios
- Cobalt — element · the structural stabiliser that keeps nickel out of the lithium layer, and the element the last fifteen years of development has been trying to use less of
- Manganese — element · cheap, structurally useful and electrochemically inert — it is there to hold the lattice together and contributes no capacity
- Oxygen — element · and it is released from the lattice when the cell overheats, which is what makes thermal runaway self-sustaining
is sourced from
- Nickel — element · and it must be Class 1, the high-purity grade, which most of the world's nickel is not — Indonesian laterite leached to battery grade has supplied most of the growth
- Cobalt — element · roughly seventy per cent of it mined in the Democratic Republic of the Congo and refined overwhelmingly in China, which is the concentration the whole low-cobalt programme is a response to
is used as
- Battery electrodes — application · as the high-energy cathode — the one that buys kilometres per kilogram and pays for them in supply risk
succeeded
- Lithium cobalt oxide — compound · everywhere the pack is large: substituting nickel and manganese for two thirds of the cobalt cut the cost and the supply exposure, and gave up some volumetric density that a car has room for and a phone does not
is produced by
- Calcination — process · a mixed hydroxide precursor co-precipitated first so the three metals are evenly distributed, then fired with lithium — and the precursor step is where most of the quality is decided
Sources
- Material WorldOur own writing
- Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)