Not all lithium chemistries are equal
The catch-all term "lithium battery" hides several chemistries that behave very differently. Lithium refers to the ion shuttling between the electrodes; it's the cathode composition that defines the families. Two dominate mobility and storage today: NMC (nickel-manganese-cobalt) and LFP (lithium iron phosphate, LiFePO₄).
You'll also meet NCA (nickel-cobalt-aluminium, close to NMC, used by some carmakers), LCO (cobalt, in portable electronics) and LTO (titanate, very durable but expensive and low-density). For second-life stationary use, the trade-off is essentially between NMC and LFP.
Energy density: NMC's advantage
NMC stores more energy per kilo and per litre: typically 150–250 Wh/kg versus 90–160 Wh/kg for LFP. That's decisive in mobility, where weight and bulk matter — so most scooter, e-bike and moped batteries are NMC (or NCA). In fixed stationary storage, however, a few extra kilos are irrelevant, and NMC's density edge loses all its value.
Lifespan: LFP's advantage
This is the criterion that flips the trade-off for stationary use. LFP withstands far more cycles before reaching 80% capacity:
| Criterion | NMC | LFP |
|---|---|---|
| Energy density | 150–250 Wh/kg | 90–160 Wh/kg |
| Cycles (to 80% SOH) | 1,000–2,000 | 3,000–6,000 |
| Nominal cell voltage | ~3.6–3.7 V | ~3.2 V |
| Thermal stability | Fair | Excellent |
| Cobalt | Yes | No |
At one cycle per day, 3,000 cycles is more than eight years, and a quality LFP often far exceeds that. LFP also tolerates full 100% charges better, which simplifies storage management.
Safety: LFP clearly ahead
The iron-phosphate bond in the LFP cathode is chemically very stable. Its thermal runaway triggers at a higher temperature (~270 °C versus ~150–210 °C for NMC) and releases far less oxygen, sharply reducing the risk and intensity of a fire. For a battery installed permanently in a home or a room, that safety margin is a serious argument.
LFP is also cobalt-free — cobalt being problematic for both ethics and supply — an extra environmental plus.
Why cirBATT favours LFP for second life
The logic of stationary reuse is clear: we recover cells from mobility (often NMC), test them, and assemble packs suited to fixed use. For packs meant to last on site, LFP is ideal — endurance, safety, tolerance of full charges. That's why our storage modules are built around individually selected and tested LFP cells.
The common thread across all chemistries: what determines a cell's second-life value is not its brand but its measured SOH and internal resistance. An NMC cell at 85% SOH can perfectly well end up in a stationary pack; a mistreated LFP cell may be out. Sorting is done on data, not on the label.