Enabling Bottom-Up Li Deposition: A Smart Pore-Size/Lithiophilicity Dual-Gradient Three-Dimensional Host.

Abstract

The electrochemical performance of Li composite anodes can be enhanced by introducing a three-dimensional host structure with a gradient configuration. However, the undesirable Li dendrites and Li top-growth behavior are difficult to tackle since the conventional lithiophilicity/conductivity gradient is quickly attenuated with the cycling. Herein, a pore-size gradient is hybridized with a lithiophilic gradient by simply infiltrating molten Li-Mg alloy into the bottom of a double-layered carbon paper host consisting of a macroporous carbon fiber (CF) layer and a microporous carbon black (CB) particle layer. When the CF layer is on the upper side and the Li-Mg alloy is composited with the CB layer at the bottom, the as-formed dual-gradient electrode with the positive pore-size gradient shows the best performance compared with the nongradient, single lithiophilicity gradient, and negative pore-size dual-gradient Li composite electrodes. The symmetric cell with the positive pore-size dual-gradient electrode runs for 2200 h at 1 mA cm^-2 and 1 mAh cm^-2 in a carbonate-based electrolyte, and LiFePO₄-based full cell with an extremely low negative/positive ratio of ∼1.26 demonstrates capacity retention of ∼85.7% after 650 cycles. The synergistic effect between the positive pore-size gradient and lithiophilicity gradient ensures a bottom-up Li deposition behavior and prevents the growth of Li dendrites, leading to improved performance toward practical applications.