A Li2CO3 sacrificial agent for anode-free lithium metal batteries

Abstract

Anode-free lithium metal batteries (AFLMBs), such as those composed of high-nickel cathodes and a copper current collector without any excess lithium, exhibit great advantages in energy density and safety. However, the structural transformation of high-nickel cathodes and accumulation of dead lithium continuously consume the limited lithium resource, resulting in sharp capacity degradation of AFLMBs. Herein, we introduce Li2CO3 onto the LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode and current collector as a lithium sacrificial agent to offset the irreversible lithium loss Li during cycling. The Li2CO3 effectively consumes the PF5 group produced by LiPF6 to generate abundant LiF, which inhibits the decomposition of electrolyte solvent induced by highly reactive PF5 and results in the proportions of inorganic component LiF in the solid electrolyte interface and cathode electrolyte interface increasing by 15.90 % and 13.91 %, which realizes highly uniform and reversible lithium transfer. In addition, as confirmed by ex-situ X-ray diffraction, the Li2CO3 introduction reduces the cation mixing degree and the stress accumulation of phase transformation. With the Li2CO3 sacrificial agent, the Cu@Li2CO3/NCM811@Li2CO3 battery delivers a remaining discharge capacity of 110.4 mAh/g with a capacity retention of 81.60 % after 100 cycles. Moreover, the AFLMB with the Li2CO3 modification shows a low polarization (0.15 V) and a high rate capacity (37.3 mAh/g) at 5 C. This study provides an efficient and simple design to prolong the cycle life of AFLMBs.