Riemannian Surface on Carbon Anodes Enables Li-Ion Storage at -35 °C

Since sluggish Li⁺ desolvation leads to severe capacity degradation of carbon anodes at subzero temperatures, it is urgently desired to modulate electron configurations of surface carbon atoms toward high capacity for Li-ion batteries. Herein, a carbon-based anode material (O-DF) was strategically synthesized to construct the Riemannian surface with a positive curvature, which exhibits a high reversible capacity of 624 mAh g^-1 with an 85.9% capacity retention at 0.1 A g^-1 as the temperature drops to -20 °C. Even if the temperature drops to -35 °C, the reversible capacity is still effectively retained at 160 mAh g^-1 after 200 cycles. Various characterizations and theoretical calculations reveal that the Riemannian surface effectively tunes the low-temperature sluggish Li⁺ desolvation of the interfacial chemistry via locally accumulated charges of non-coplanar sp (2 < x < 3) hybridized orbitals to reduce the rate-determining step of the energy barrier for the charge-transfer process. Ex-situ measurements further confirm that the sp -hybridized orbitals of the pentagonal defect sites should denote more negative charges to solvated Li⁺ adsorbed on the Riemannian surface to form stronger Li-C coordinate bonds for Li⁺ desolvation, which not only enhances Li-adsorption on the curved surface but also results in more Li⁺ insertion in an extremely cold environment.