Kate Leslie

Thermal management of Li-ion cells within battery packs for stationary energy storage and electric vehicles is critical to ensure longevity. Cells within packs are often heated or cooled using a thermal plate underneath the pack, which could lead to non-uniform temperature in the cells. To test the effects of temperature gradients on LFP/graphite cylindrical cells, a specialized cell holder was designed to apply a constant temperature to the top of a cell and a different constant temperature to the bottom. Temperatures of 30 °C–40 °C, 25 °C–45 °C, and 15 °C–55 °C were applied to the bottom and tops of the cells, respectively, and verified using an infrared camera. Cells were cycled at a variety of rates for approximately six months, and the capacity loss was compared between the different conditions. For most conditions there was no difference in the capacity fade based on temperature gradient and performance closely matched that of cells tested at a constant temperature of 35 °C. Thermal modelling of the jelly roll suggests that the temperature gradient does not penetrate deeply into the jelly roll due to the excellent axial thermal conductivity and this can explain the independence of capacity loss on the magnitude of the applied temperature gradient.

LiMn _0.8 Fe _0.2 PO ₄ (LMFP)/graphite Li-ion cells are an emerging low-cost, Ni and Co free alternative to the existing NMC battery technology. Although cells with this chemistry are promising, various issues impact the commercialization of this material. A major failure mechanism identified in these cells is the loss of lithium inventory due to solid-electrolyte interphase breakdown when Mn dissolves from the positive electrode at high temperature and deposits on the negative electrode. Herein, we propose the use of various blends of conducting salts to minimize this failure mode in LMFP/graphite cells and extend cycle life. Using LiFSI or LiTFSI as the primary salt in combination with 20 wt% of different co-salts such as LiDFOB, LiBOB, and LiPF ₆ resulted in reduced Mn dissolution and deposition on the negative electrode and improved cycle life, especially for blends containing LiDFOB. However, Mn dissolution could not be completely prevented, and salt consumption occurred during cycling, requiring further optimization before these electrolytes can be used in applications.