Battery Degradation

The performance of lithium-ion batteries deteriorate over time whether they are used or not. This affects the performance and range of EV's.

Ageing based on use are called cycle ageing and ageing based on time is called calendar ageing.

The two main consequences of ageing are energy capacity reduction and power reduction.

In an EV, the energy capacity determines the range an EV can travel on a single charge, and the power determines the maximum acceleration and top speed.

Energy capacity reduction can be caused by a loss of battery charge capacity or in the rise of the impedance.

Loss of the cyclable lithium or deactivation of the active electrode material are the primary sources of capacity reduction.

The rise in impedance is caused by the chemical or physical transformation of the various materials and interfaces.

When the internal impedance increases this affect the power since the battery voltage is reduced.

Calender Ageing

Most cars are parked more than they are driven. Calender aging is degradation that happens while time passes.

The factors that affects calender aging is State of Charge and environmental temprature.

EV storage stress

Storage stress

Scientfictic articles to read to understand more about Calender aging

Cycle ageing

Cycle ageing is the reduction of energy capcaity or power caused bey charging/discharging.

Cycle aging based on SOC area

The below diagram show how the SOC area used when charging/discharging affect the degredation

Cycles

Cycle stress

Charging speed affect on cycle aging

The most important factor for cycle charging is the charging speed. High speed DC charging increase the effect called lithium plating that converts the lithium ions to lithium metal. When this happens the available ions in battery is reduced. Higher speed charging increases the amount of litium ions that are not able to reach the anode. This is again caused by limitiations on the chemistry process. If you want to learn more about lithium plating you can read this presentation from Nasa.

Scientfictic articles to read to understand more about cycle aging

How to preserve battery

  • Don’t park car with High SOC over long time
  • Don’t park car in extreme heat
  • Limit high speed charging.