A Fast-Charge Graphite Anode with a Li-Ion-Conductive, Electron/Solvent-Repelling Interface.

Graphite has been serving as the key anode material of rechargeable Li-ion batteries, yet is difficultly charged within a quarter hour while maintaining stable electrochemistry. In addition to a defective edge structure that prevents fast Li-ion entry, the high-rate performance of graphite could be hampered by co-intercalation and parasitic reduction of solvent molecules at anode/electrolyte interface. Conventional surface modification by pitch-derived carbon barely isolates the solvent and electrons, and usually lead to inadequate rate capability to meet practical fast-charge requirements. Here we show that, by applying a MoOx-MoNx layer onto graphite surface, the interface allows fast Li-ion diffusion yet blocks solvent access and electron leakage. By regulating interfacial mass and charge transfer, the modified graphite anode delivers a reversible capacity of 340.3 mAh g-1 after 4000 cycles at 6 C, showing promises in building 10-min-rechargeable batteries with a long operation life.

Quantification of Charge Transport and Mass Deprivation in Solid Electrolyte Interphase for Kinetically-Stable Low-Temperature Lithium-Ion Batteries.

Graphite (Gr)-based lithium-ion batteries with admirable electrochemical performance below -20 °C are desired but are hindered by sluggish interfacial charge transport and desolvation process. Li salt dissociation via Li+-solvent interaction enables mobile Li+ liberation and contributes to bulk ion transport, while is contradictory to fast interfacial desolvation. Designing kinetically-stable solid electrolyte interphase (SEI) without compromising strong Li+-solvent interaction is expected to compatibly improve interfacial charge transport and desolvation kinetics. However, the relationship between physicochemical features and temperature-dependent kinetics properties of SEI remains vague. Herein, we propose four key thermodynamics parameters of SEI potentially influencing low-temperature electrochemistry, including electron work function, Li+ transfer barrier, surface energy, and desolvation energy. Based on the above parameters, we further define a novel descriptor, separation factor of SEI (SSEI), to quantitatively depict charge (Li+/e-) transport and solvent deprivation processes at Gr/electrolyte interface. A Li3PO4-based, inorganics-enriched SEI derived by Li difluorophosphate (LiDFP) additive exhibits the highest SSEI (4.89×103) to enable efficient Li+ conduction, e- blocking and rapid desolvation, and as a result, much suppressed Li-metal precipitation, electrolyte decomposition and Gr sheets exfoliation, thus improving low-temperature battery performances. Overall, our work originally provides visualized guides to improve low-temperature reaction kinetics/thermodynamics by constructing desirable SEI chemistry.