Eliminating concentration polarization with gradient lithiophilic sites towards high performance lithium metal anodes under low N/P ratio

Three-dimensional (3D) skeletons have been extensively explored for effectively inhibiting dendrite growth and mitigating the volume change of lithium (Li). However, the ionic concentration polarization ascribing to the different ionic transmission distance in 3D skeletons inevitably induce the uneven growth of Li, leading to preferential deposition of Li in the top region rather than a spatially ordered manner from bottom-up. This uncontrollable deposition will deviate the original guidance of 3D skeleton. In this study, a gradient lithiophilic carbon fibers (CFs) is designed and constructed by regulating the distribution of ZnO nucleation sites (CFs@GZnO skeleton) to achieve a spatially ordered Li plating/stripping process. Additionally, the top lith-iophobic CFs layer acts as a buffer layer to accommodate inactive Li, avoiding the block of Li+ inward migration, the middle and bottom CFs layer decorated with different amounts of lithiophilic ZnO nucleation sites enable lithium preferentially deposits in the bottom layer and further supporting the sequential bottom-up depositing process. Benefiting from this gradient lithiophilic design, the non-uniform ionic polarization within the 3D skeleton is mitigated, effectively inducing Li plating/stripping in a controllable spatially ordered manner and suppressing the volume variation. Full cell with an ultrahigh mass loading NCM811 cathode (38 mg cm-2) and Li-CFs@GZnO (CFs@GZnO skeleton pre-plated with Li) anode under a low negative to positive N/P ratio of 2 achieved a lifespan of 100 cycles with a capacity fading of only 0.083 % per cycle and an average CE of 99.7 %. Thus, the strategy of inducing gradient lithiophilic sites into 3D skeletons may provide a new avenue to construct a dendrite-free and stable metal anode for high energy density LMBs.