Controllable long-term lithium replenishment for enhancing energy density and cycle life of lithium-ion batteries

Abstract

A persistent challenge plaguing lithium-ion batteries (LIBs) is the consumption of active lithium with the formation of SEI. This leads to an irreversible lithium loss in the initial cycle and a gradual further exhaustion of active lithium in subsequent cycles. While prelithiation has been proven effective in compensating for this loss by introducing additional active lithium into batteries, prior studies have predominantly concentrated on offsetting the initial lithium loss, often overlooking the continuous lithium consumption that occurs throughout cycling. To address this challenge, we employed a sustained in situ lithium replenishment strategy that involves the systematic release of additional lithium inventory through precise capacity control during long-term cycling. Our method utilizes a lithium replenishment separator (LRS) coated with dilithium squarate-carbon nanotube (Li₂C₄O₄–CNT) as the lithium compensation reagent. Placing Li₂C₄O₄ on the separator rather than within the cathode significantly reduces disruptions in conduction pathways and inhibits catalytic reactions with LiFePO₄, preventing the formation of carbon residues. When implemented in the LiFePO₄||graphite battery system, our approach resulted in an impressive 12.9% capacity improvement in the initial cycle and a remarkable 97.2% capacity retention over 700 cycles, surpassing the comparison group, which exhibited 80% capacity retention after 426 cycles.