Key Impact Factors on Cycling Capacity Evolution of Commercial LTO Based Pouch Cells

Lithium titanium oxide or commonly known as LTO-anode based lithium ion batteries are popular choice for electric vehicles (EV’s) and hybrid electric vehicles (HEV’s) thanks to their extended cycle life and fast charging capabilities. It also outperforms graphite as negative electrode in terms of safety and calendaric storage. This ageing study consists of extensive cycle life tests of 56 commercially available first generation EIG 5Ah pouch cells at 27 different test conditions including three DoD levels (20%, 50%, 90%), four temperatures (-15°C, 10°C, 25°C, 45°C), several C-rates or nominal capacity rates (0.5C to 5C) and with mid-State of Charge (SoC) (50%). The studied cell type has Lithium Nickel Cobalt Aluminium Oxide (NCA) as cathode material with nominal voltage of 2.2V. The capacity evolution of all the cells are compared and analyzed in this paper explaining the impact of depth-of-discharge (DoD), temperature and C-rate on cycle ageing. Results show that indeed, LTO cells have longer cycle life and the capacity retention has only reached the end-of-life (EoL) threshold (State of health/SoH < 80% of nominal capacity) at elevated temperature (45°C). At room temperature, with 90% DoD cycling, the cells have survived more than 4500 cycles so far and the tests are ongoing. Interestingly, most of the cells had negative capacity fade at investigated temperatures. These type of LTO cells are also capable of fast charging and have performed well under stressed discharge conditions.

Publication year:2018

Keywords:LTO, capacity increase, NCA, cycling ageing, capacity evolution, degredation factors