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

Abstract

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 spx (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 spx-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.