Innovative discontinuous-SEI constructed in ether-based electrolyte to maximize the capacity of hard carbon anode

Compared with graphite,the lower sodiation potential and larger discharge capacity of hard carbon(HC)makes it the most promising anode material for sodium-ion battery.Utilizing ether-based electrolyte rather than conventional carbonate-based electrolyte,HC achieves superior electrochemical performance.Nevertheless,the mechanism by which ether-based electrolyte improves the properties of HC is still controversial,primarily focusing on whether it forms solid electrolyte interphase(SEI)film.In this work,according to the sodium storage mechanisms in HC at low voltage(<0.1 V),including Na^(+)-diglyme co-interaction into the carbon layer(SEI forbidden)and desolvated Na^(+)insertion in the irregular carbon holes(SEI required),the NaPF6concentration in ether-based electrolyte was regulated,so as to construct a discontinuous-SEI on the surface of the HC anode,which significantly enhances the electrochemical performances of HC.Specifically,with 0.2 M NaPF6ether-based electrolyte,HC deliverers a discharge capacity of 459.7 mA h g^(-1)at 0.1 C and stays at 357.2 mA h g^(-1)after 500 cycles at 1 C,which is substantially higher than that of higher/lower salt concentration electrolytes.

Enhanced interphasial stability of hard carbon for sodium-ion battery via film-forming electrolyte additive

Although the operating mechanism of sodium-ion battery(SIB)resembles that of lithium-ion battery,common film-forming additive for lithium-ion battery does not play its role in SIB.Therefore,it is essential to tailor new additives for SIB.Hard carbon(HC),as the most used anode material of SIB,has the disadvantage of interphasial instability,especially under the condition of long-term cycling.The incessant accumulation of electrolyte decomposition products leads to a significant increase in interphasial impedance and a sharp decline in discharge capacity.In this work,N-phenyl-bis(trifluoromethanesulfonimide)(PTFSI)was proposed as a novel film-forming electrolyte additive,which effectively enhances the long-term cycling performance for HC anode in SIB.The passivation film generated from the preferential reduction of PTFSI improves the capacity retention of HC/Na half-cell from 0%to 68%after 500 cycles.Profoundly,the enhanced interphasial stability of HC anode results in a 52%increase in capacity retention of HC/Na_(3)V_(2)(PO_(4))_(3)full-cells after 100 cycles.