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The combined effect of concentrated electrolyte and cycling protocol on the cyclic performance of the anode-free battery (AFB) is evaluated systematically. In situ deposition of Li in the AFB configuration in the presence of a concentrated electrolyte containing fluorine-donating salt and resting the deposit enables the formation of stable and uniform SEI. The SEI intercepts the undesirable side reaction between the deposit and solvent in the electrolyte and reduces electrolyte and Li consumption during cycling. The synergy between the laboratory-prepared concentrated 3 M LiFSI in the ester-based electrolyte and our resting protocol significantly enhanced cyclic performances of AFBs in comparison to the commercial carbonate-based dilute electrolyte, 1 M LiPF6. Benefitting from the combined effect, Cu∥LiFePO4 cells delivered excellent cyclic performance at 0.5 mA/cm2 with an average CE of up to 98.78%, retaining a reasonable discharge capacity after 100 cycles. Furthermore, the AFB can also be cycled at a high rate up to 1.0 mA/cm2 with a high average CE and retaining the encouraging discharge capacity after 100 cycles. The fast cycling and stable performance of these cells are attributed to the formation of robust, flexible, and tough F-rich conductive SEI on the surface of the in situ-deposited Li by benefiting from the combined effect of the resting protocol and the concentrated electrolyte. A condescending understanding of the mechanism of SEI formation and material choice could facilitate the development of AFBs as future advanced energy storage devices.

The utilization of an anode-free lithium-metal battery (AFLMB) is pivotal in meeting the high-energy-density demand for portable electronic devices and vehicles. However, the dendritic growth of lithium (Li) and continuous SEI formation on Copper (Cu) current collector limits the lifetime of a cell. Here we report the effect of milled Al 2 O 3 /polyacrylonitrile (PAN) composite layer (AOP) coated on Cu, as AOP@Cu, to encourage compact and smoother Li + deposition extracted from NMC (333) cathode. The excellent wettable nature of the AOP layer promotes uniform ionic flux and improved kinetics. The multifunctional AOP layer offers moderate mechanical support and sufficient strength to the SEI layer to suppress dendritic growth. The formation of Li−Al−O/Al 2 O 3 species at the bottom part of the layer reveals AOP's lithiophilicity to form new SEI components, besides Al−F, by regulating Li + deposition. PAN synergism is manifested by its flexible binding role and nitrogen content that has an excellent affinity to Li + . The resulting AOP@Cu||NMC and AOP@Cu||Li cells demonstrated improved cycling stability and Coulombic efficiency. An AOP@Cu||NMC cell run at 0.2 mA cm −2 exhibits a first cycle discharge capacity of 160 mAh g −1 that retains 30% after 82 cycles, whereas the Cu||NMC cell retains ∼30% after only 52 cycles.