Impact of Lithium Salt Blends on Capacity Retention and Mn Dissolution of LiMn 0.8 Fe 0.2 PO 4 /Graphite Li-ion Cells

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Abstract
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.

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