Kinetic Limits of Graphite Anode for Fast-Charging Lithium-Ion Batteries

Highlights The microstructure of graphite upon rapid Li+ intercalation is a mixture of differently staging structures in the macroscopic and microscopic scales due to the incomplete and inhomogeneous intercalation reactions hindered by the sluggish reaction kinetics. The Li+ interface diffusion dominates the reaction kinetics at high rates in thin graphite electrode, while Li+ diffusion through the electrode cannot to be neglected for thick graphite electrode

Deciphering the Role of Fluoroethylene Carbonate towards Highly Reversible Sodium Metal Anodes

Sodium metal anodes (SMAs) suffer from extremely low reversibility (95% with conventional NaPF6 salt at a regular concentration (1.0 M). The peculiar role of FEC is firstly unraveled via its involvement into the solvation structure, where a threshold FEC concentration with a coordination number>1.2 is needed in guaranteeing high Na reversibility over the long-term. Specifically, by incorporating an average number of 1.2 FEC molecules into the primary Na+ solvation sheath, lowest unoccupied molecular orbital (LUMO) levels of such Na+-FEC solvates undergo further decrease, with spin electrons residing either on the O=CO(O) moiety of FEC or sharing between Na+ and its C=O bond, which ensures a prior FEC decomposition in passivating the Na surface against other carbonate molecules. Further, by adopting cryogenic transmission electron microscopy (cryo-TEM), we found that the Na filaments grow into substantially larger diameter from ~400 nm to >1 μm with addition of FEC upon the threshold value. A highly crystalline and much thinner (~40 nm) solid-electrolyte interphase (SEI) is consequently observed to uniformly wrap the Na surface, in contrast to the severely corroded Na as retrieved from the blank electrolyte. The potence of FEC is further demonstrated in a series of “corrosive solvents” such as ethyl acetate (EA), trimethyl phosphate (TMP), and acetonitrile (AN), enabling highly reversible SMAs in the otherwise unusable solvent systems

Localized‐domains staging structure and evolution in lithiated graphite

Abstract Intercalation provides to the host materials a means for controlled variation of many physical/chemical properties and dominates the reactions in metal‐ion batteries. Of particular interest is the graphite intercalation compounds with intriguing staging structures, which however are still unclear, especially in their nanostructure and dynamic transition mechanism. Herein, the nature of the staging structure and evolution of the lithium (Li)‐intercalated graphite was revealed by cryogenic‐transmission electron microscopy and other methods at the nanoscale. The intercalated Li‐ions distribute unevenly, generating local stress and dislocations in the graphitic structure. Each staging compound is found macroscopically ordered but microscopically inhomogeneous, exhibiting a localized‐domains structural model. Our findings uncover the correlation between the long‐range ordered structure and short‐range domains, refresh the insights on the staging structure and transition of Li‐intercalated/deintercalated graphite, and provide effective ways to enhance the reaction kinetic in rechargeable batteries by defect engineering

Surface Engineering Strategy Enables 4.5 V Sulfide-Based All-Solid-State Batteries with High Cathode Loading and Long Cycle Life

Sulfide-based all-solid-state lithium batteries (ASSLBs) with LiCoO2 (LCO) operating at high voltage (≥4.5 V vs Li+/Li) hold promise in realizing high energy density while maintaining safety. Here, we propose a solid electrolyte coating strategy to stabilize the cathode electrolyte interface and demonstrate the benefit of lithium difluoro(oxalate)borate (LiDFOB) as coating layer on the surface of Li6PS5Cl (LPSCl) to improve the performance of LCO at 4.5 V. 89.3% of initial discharge capacity can be retained after 1500 cycles at 1C (1C = 150 mA g–1). ASSLBs with high cathode loading (35.7 mg cm–2) could deliver an areal capacity over 6 mAh cm–2 (167 mAh g–1) at 0.1C and keep 85% capacity retention after 200 cycles at 0.3C. The investigation of the improvement mechanism further verifies that in situ decomposition of LiDFOB would build an (electro)chemomechanically stable interface, which not only suppresses interfacial side reactions but also buffers the cathode cracking