Multifunctional Manganese Ions Trapping and Hydrofluoric Acid Scavenging Separator for Lithium Ion Batteries Based on Poly(ethylene-alternate-maleic acid) Dilithium Salt

Manganese dissolution from positive electrodes seriously reduces the life of Li-ion batteries, due to its detrimental impact on the passivation of negative electrodes. A novel multifunctional separator incorporating inexpensive mass-produced polymeric materials may dramatically increases the durability of Li-ion batteries. The separator is made by embedding the poly(ethylene-alternate-maleic acid) dilithium salt polymer into a poly(vinylidene fluoride-hexafluoropropylene) copolymer matrix. LiMn2O4-graphite cells comprising a 1 m LiPF6 solution in ethylene carbonate plus dimethyl carbonate (1:1 v/v) and the functional separator retain 31% and 100% more capacity than baseline cells with plain commercial separators after 100 cycles at C/5 rate, respectively, at 30 and 55 degrees C. Analyses of cycled cells indicate greatly reduced Mn contamination of the graphite negative electrodes and almost no irreversible structural change in the LiMn2O4 positive electrodes from cells containing the functional separator. The Mn amount in the graphite electrodes from cycled cells with functional separators is approximate to 80% lower than in the graphite electrodes from cycled baseline cells. Mn ions are found in the functional separators but not in baseline (plain) separators from cycled cells. Finally, it is shown that the reported performance improvements stem from the ability of the novel separator to chelate Mn ions and to scavenge trace HF.