Ultra-high lithium reversibility achieved by partially pyrolyzed polymeric copper phthalocyanines for superior anode-free lithium metal batteries

Anode-free lithium metal batteries (AFLMB) can maximize the energy density by eliminating active materials, conductive agents and binders from the anode. However, intrinsic issues of lithium (Li) metal anodes, such as non-uniform Li growth, large volume changes and unstable solid electrolyte interphase (SEI), become much pronounced, rapidly degrading the cyclability of AFLMB. Herein, we present a superior three-dimensional (3D) AFLMB host, which takes advantage of partially decomposed polymeric copper phthalocyanines bridged by di-thioether linkers (CuPPc-S) as an ultra-thin surface coating layer. By intensive material characterizations alongside in-situ thermal gravimetric analyses coupled with mass spectrometer, we demonstrate that our controlled pyrolysis results in the formation of partially pyrolyzed CuPPc-S (PP-CuPPc-S), where intrinsic redox active sites of CuPPc-S and newly formed ultra-fine Cu–S inorganic compounds co-exist. The preserved redox active sites can not only improve lithiophilicity, but also facilitate the decomposition of TFSi^⁻, inducing abundant LiF in the SEI, while Cu–S compounds can serve dual roles as active Li nucleation sites and ionically conductive Li₂S inducer in the SEI. Benefiting from these components, PP-CuPPc-S coated carbon fiber (PP-CuPPc-S@CF) can form a multifunctional SEI and induce dense Li nucleation, achieving the stable operation of 1000 cycles with a LiFePO₄ cathode in AFLMB configuration.