Traction battery: Degradation and aging

1. Basic properties and characteristics of Li-ion batteries

1.8. Degradation and aging

Natural aging - the battery loses capacity spontaneously after a few years and fails without drawing power.
Tunneling of electrons through SEI into the electrolyte.
The electrons react with the electrolyte and form additional layers SEI → SEI increases and the electrolyte is gradually consumed.
This process is significantly accelerated when the battery is used and current is drawn.
Li+ passing through the electrolyte → entrains solvent molecules → reacts with tunneling electrons → SEI layer grows → electrolyte and lithium are consumed → battery destruction.

_{Christoph R. Birkl, Matthew R. Roberts, Euan McTurk, Peter G. Bruce,
David A. Howey: Degradation diagnostics for lithium ion cells, Journal
of Power Sources 2017, Elsevier}