Sustainable Reuse of FePO4 for Charged-State Lithium Metal Battery with High Energy Density and Stable Cycle Performance

A lithium metal–free battery (LMFB, so-called anode-free batteries) offers an ideal configuration of lithium metal batteries (LMB), theoretically achieving the highest energy density by eliminating excess lithium metal on the negative electrode. However, the limited reversibility of lithium metal deposition and dissolution prevents the stable cycling of LMFBs. In contrast, the lean LMB (LLMB) concept maintains a small amount of lithium metal on the negative electrode side, offering energy density comparable to LMFB while improving cyclability. Another advantage of LMFBs is that they do not require a lithium source in the positive electrode. Building on this, the charged-state LMB (CSLMB), which combines a charged-state positive electrode with a lean lithium metal, is introduced. Herein, the charge-state positive electrode is formed by chemically delithiating LiFePO₄ using O₂ as an oxidizing agent, while the extracted lithium is recovered as lithium acetate. This lithium can then be used to resynthesize LiFePO₄, enabling a closed-loop lithium recycling process. Finally, the CSLMB, with its charged-state lean Li/FePO₄ full cell, demonstrates stable cycling performance and a gravimetric energy density comparable to conventional LMFBs.