Protective electrode/electrolyte interphases for high energy lithium-ion batteries with p-toluenesulfonyl fluoride electrolyte additive

High energy density lithium-ion batteries using Ni-rich cathode(such as LiNi0.6Co0.2Mn0.2O2) suffer from severe capacity decay.P-toluenesulfonyl fluoride(pTSF) has been investigated as a novel film-forming electrolyte additive to enhance the cycling performances of graphite/LiNi0.6Co0.2Mn0.2O2 pouch cell.In comparison with the baseline electrolyte,a small dose of pTSF can significantly improve the cyclic stability of the cell.Theoretical calculations together with experimental results indicate that pTSF would be oxidized and reduced to construct protective interphase film on the surfaces of LiNi0.6Co0.2Mn0.2O2 cathode and graphite anode,respectively.These S-containing surface films derived from pTSF effectively mitigate the decomposition of electrolyte,reduce the interphasial impedance,as well as prevent the dissolution of transition metal ions from Ni-rich cathode upon cycling at high voltage.This finding is beneficial for the practical application of high energy density graphite/LiNi0.6Co0.2Mn0.2O2 cells.

Sulfolane-Graphite Incompatibility and Its Mitigation in Li-ion Batteries

The non-flammability and high oxidation stability of sulfolane(SL)make it an excellent electrolyte candidate for lithium-ion batteries(LIBs).However,its incompatibility with graphitic anode prevents the realization of these advantages.To understand how this incompatibility arises on molecular level so that it can be suppressed,we combined theoretical calculation and experimental characterization and reveal that the primary Li^(+) solvation sheath in SL is depleted of fluorine source.Upon reduction,SL in such fluorine-poor solvation sheath generates insoluble dimer with poor electronic insulation,hence leading to slow but sustained parasitic reactions.When fluorine content in Li^(+)-SL solvation sheath is increased via salt concentration,a high stability LiF-rich interphase on graphite can be formed.This new understanding of the failure mechanism of graphite in SL-based electrolyte is of great significance in unlocking many possible electrolyte solvent candidates for the high-voltage cathode materials for next-generation LIBs.

Moisture stable and ultrahigh-rate Ni/Mn-based sodium-ion battery cathodes via K^(+)decoration

As one of the most promising cathodes for sodium-ion batteries(SIBs),the layered transition metal oxides have attracted great attentions due to their high specific capacities and facile synthesis.However,their applications are still hindered by the problems of poor moisture stability and sluggish Na^(+)diffusion caused by intrinsic structural Jahn–Teller distortion.Herein,we demonstrate a new approach to settle the above issues through introducing K^(+)into the structures of Ni/Mn-based materials.The physicochemical characterizations reveal that K^(+)induces atomic surface reorganization to form the birnessite-type K_(2)Mn_(4)O_(8).Combining with the phosphate,the mixed coating layer protects the cathodes from moisture and hinders metal dissolution into the electrolyte effectively.Simultaneously,K^(+)substitution at Na site in the bulk structure can not only widen the lattice-spacing for favoring Na^(+)diffusion,but also work as the rivet to restrain the grain crack upon cycling.The as achieved K^(+)-decorated P2-Na_(0.67)Mn_(0.75)Ni_(0.2)5O_(2)(NKMNO@KM/KP)cathodes are tested in both coin cell and pouch cell configurations using Na metal or hard carbon(HC)as anodes.Impressively,the NKMNO@KM/KP||Na half-cell demonstrates a high rate performance of 50 C and outstanding cycling performance of 90.1%capacity retention after 100 cycles at 5 C.Furthermore,the NKMNO@KM/KP||HC fullcell performed a promising energy density of 213.9 Wh·kg^(−1).This performance significantly outperforms most reported state-ofthe-art values.Additionally,by adopting this strategy on O3-NaMn_(0.5)Ni_(0.5)O_(2),we further proved the universality of this method on layered cathodes for SIBs.