A Li2CO3 sacrificial agent for anode-free lithium metal batteries

• The cheap and air-stabilized Li 2 CO 3 is introduced to prolong AFLMB life. • The Li 2 CO 3 as a sacrificial agent provides an additional lithium source. • The layered structure of cycled NCM811@Li 2 CO 3 is maintained. • The Li 2 CO 3 introduction promotes the LiF-rich SEI and CEI formation. 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 Li 2 CO 3 onto the LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathode and current collector as a lithium sacrificial agent to offset the irreversible lithium loss Li during cycling. The Li 2 CO 3 effectively consumes the PF 5 group produced by LiPF 6 to generate abundant LiF, which inhibits the decomposition of electrolyte solvent induced by highly reactive PF 5 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 Li 2 CO 3 introduction reduces the cation mixing degree and the stress accumulation of phase transformation. With the Li 2 CO 3 sacrificial agent, the Cu@Li 2 CO 3 /NCM811@Li 2 CO 3 battery delivers a remaining discharge capacity of 110.4 mAh g -1 with a capacity retention of 81.60% after 100 cycles. Moreover, the AFLMB with the Li 2 CO 3 modification shows a low polarization (0.15 V) and a high rate capacity (37.3 mAh g -1 ) at 5 C. This study provides an efficient and simple design to prolong the cycle life of AFLMBs.