Li2S as a cathode additive to compensate for the irreversible capacity loss of lithium iron phosphate batteries

The formation of the solid electrolyte interface (SEI) on the surface of the anode during the formation stage of lithium-ion batteries leads to the loss of active lithium from the cathode, thereby reducing their energy density. Graphite-based lithium iron phosphate (LiFePO4) batteries show about a 10% loss of irreversible capacity. Herein, we report a composite of Li2S/super activated carbon (SAC) as a cathode prelithiation material to compensate for the initial irreversible capacity of the graphite||LiFePO4 battery. The Li2S/SAC composite prepared by a simple method of mixing Li2S and SAC shows an initial charge specific capacity of 1087 mAh·g−1, and the discharge specific capacity is only 7 mAh·g−1, indicating that it has a lithium compensation capacity of 1080 mAh·g−1. The LiFePO4 cathode sprayed with Li2S/SAC slurry has a 13.9 mAh·g−1 higher initial charge specific capacity than that pristine LiFePO4 cathode at 0.2 C. Paired with a graphite anode, a full-cell using such a LiFePO4 (Li2S) cathode demonstrates 11.7% higher discharge capacity than that using pristine LiFePO4 at 1 C, as well as excellent cycle stability.