Voltage fade

Example

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Capacity fade

The loss of charge a cell can store and deliver, for example through lithium locked into the SEI or active material that has cracked out of service.

Nominal energy

Nominal capacity times nominal voltage, in watt-hours: the headline energy figure on a datasheet. The energy actually delivered depends on the load, the temperature and how the voltage curve is weighted.

Phase transition

A change of crystal structure as lithium content varies, which fixes the potential while two phases coexist. Graphite fills in stages, LFP switches between two phases across almost its whole range, and these transitions make the peaks that aging diagnostics read.

State of energy

Remaining energy as a fraction of total energy, which differs from state of charge because the voltage falls as a cell empties. It is the quantity behind a range estimate, and is harder to estimate than SOC.

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

Further reading on this topic

These sources provide broader context; they are not presented as citations for every statement in this entry.

1. Lithium ion battery degradation: what you need to know

   Physical Chemistry Chemical Physics · 2021

   Topic background · Degradation mechanisms, modes, operational effects and their interactions.