Degrading biomass to construct cation-gathered spongy layer conjugated electron-enriched carbon framework for Li metal battery

Herein, a controllable hydrothermal degradation strategy is developed for converting Pinus sylvestris into multi-gradient spongy carbon-coated three-dimensional carbon framework (HPSC) with negatively charged surface. It is confirmed that the inner carbon skeleton is highly conductive and rigid, while the sponge-like outer layer composed of coralloid carbon exhibits low conductivity and high toughness. This unique structure enables lithium metal to nucleate and grow uniformly within HPSC in carbonate electrolyte, observed by in situ optical microscopy and X-ray computed tomography (XCT). Nuclear magnetic resonance (NMR), atomic force microscopy (AFM) and COMSOL multiphysics simulations further demonstrate that the stable lithium plating/stripping is driven by: (I) the negatively charged surface for high lithium ions concentration at the electrode/electrolyte interface; (II) the tough and porous sponge layer with strong capillary force on rigid skeleton for perfect accommodation and homogenization of deposited lithium metal; (III) gradient conductive carbon framework for preferential nucleation and uniform growth on the carbon skeleton. As a result, HPSC-Li symmetric cells exhibit a long-term cycling stability over 2000 h at 0.5 mA cm⁻² with low voltage overpotential (< 30.0 mV). Importantly, the HPSC-Li//LiCoO₂ cells also show much improved performances with high LiCoO₂ mass of about 20.0 mg cm⁻².