Ether‐Based Electrolyte Chemistry Towards High‐Voltage and Long‐Life Na‐Ion Full Batteries

Abstract

Although ether-based electrolytes have been extensively applied in anode evaluation of batteries,a nodic instability arising from solvent oxidability is always at remendous obstacle to matching with high-voltage cathodes.H erein, by rational design for solvation configuration, the fully coordinated ether-based electrolyte with strong resistance against oxidation is reported, whichr emains anodically stable with high-voltage Na 3 V 2 (PO 4 ) 2 O 2 F( NVPF) cathode under 4.5 V (versus Na + /Na) protected by an effective interphase.T he assembled graphite//NVPF full cells displays uperior rate performance and unprecedented cycling stability.Beyond that, the constructed full cells coupling the high-voltage NVPF cathode with hardc arbon anode exhibit outstanding electrochemical performances in terms of high average output voltage up to 3.72 V, long-term cycle life (such as 95 %c apacity retention after 700 cycles) and high energy density (247 Wh kg À1 ). In short, the optimizede ther-based electrolyte enriches systematic options,t he ability to maintain oxidative stability and compatibility with various anodes,e xhibiting attractive prospects for application.

Electrolyte Sieving Chemistry in Suppressing Gas Evolution of Sodium‐Metal Batteries

“…This also shows the powerful function of sieved electrolytes in inhibiting gassing and mitigating safety threat under abuse condition of over‐discharging. Ethylene carbonate (EC) is the most widely used solvent in battery technology, but it has a lower LUMO, [5a, 18b, 25] indicating that it has higher reactivity towards Na metal. Therefore, the role of this sieved electrolytes in EC‐based electrolytes is more convincing.…”

“…Ether-based electrolytes have a good compatibility with Na metal and exhibit a high average Coulombic efficiency (CE) over 99.9 % for Na plating/stripping process. [4] However, it is prone to be electrochemically oxidized and generate flammable olefins even below 4.0 V. [5] Therefore, traditional cathodes such as transition metal oxides, [6] Prussian blue analogues [7] and Na 3 V 2 (PO 4 ) 2 F 3 cathodes [8] with operating voltage over 4.0 V cannot be coupled with such electrolytes. The unfavorable oxidative degradation is well mitigated in common carbonate ester electrolytes.…”

Hard‐Carbon Anodes for Sodium‐Ion Batteries: Recent Status and Challenging Perspectives

“…For example, most ether‐based electrolytes reported are unstable and easy to be decomposed under high potential, which is inapplicable in going with full cells. [ 214 ] Meanwhile, reducing the defects, functional groups, and surface area will sacrifice lots of active sites, leading to a descended specific capacity as well as rate capability of the anode. [ 168 ] In addition, most chemical sodiation agents are sensitive to O 2 and H 2 O, while the sacrificial additives still suffer from either dead‐mass or gas evolution after Na ions release, thereby hindering their large‐scale applications.…”

Optimizing the Electrolyte Systems for Na3(VO1‐xPO4)2F1+2x (0≤x≤1) Cathode and Understanding their Interfacial Chemistries Towards High‐Rate Sodium‐Ion Batteries

“…[41] Wu and co-workers explored a modified ether-based electrolyte of NaPF 6 /diethylene glycol dimethyl ether (DEGDME) with 1,3-dioxolane (DOL) diluent, achieving an unprecedented cycle stability and rate capability in Na 3 V 2 (PO 4 ) 2 O 2 F (NVPF)/ graphite and NVPF/hard carbon full cells with oxidative stability under 4.5 V (vs. Na/Na + ). [42] However, as far as our knowledge is concerned, the impact of different electrolyte salt anions of PF 6 À and ClO 4 À in NaPF 6 and NaClO 4 , the influence of different electrolyte solvents of either diglyme or single/mixed carbonate esters (linear/cyclic carbonate solvents EC-DMC/PC), and the commonly used electrolyte additives FEC on the stability and composition of CEI layer for NVPF cathode are still unclear and require a more systematic investigation, especially the electrode/electrolyte interfacial properties of NVPF at high potential. So far, there are few studies focusing on comprehensive investigation and comparison of the commonly used or commercialized electrolyte systems on the stability and composition of CEI layer on NVPF cathode, not to mention the functionality of FEC additive.…”

“…reported an optimal electrolyte composition of EC 0.45 /PC 0.45 /DMC 0.1 for NVPF cathode and HC anode, resulting in excellent cycle stability and good rate capability upon cycling [41] . Wu and co‐workers explored a modified ether‐based electrolyte of NaPF 6 /diethylene glycol dimethyl ether (DEGDME) with 1,3‐dioxolane (DOL) diluent, achieving an unprecedented cycle stability and rate capability in Na 3 V 2 (PO 4 ) 2 O 2 F (NVPF)/graphite and NVPF/hard carbon full cells with oxidative stability under 4.5 V (vs. Na/Na + ) [42] . However, as far as our knowledge is concerned, the impact of different electrolyte salt anions of PF 6 − and ClO 4 − in NaPF 6 and NaClO 4 , the influence of different electrolyte solvents of either diglyme or single/mixed carbonate esters (linear/cyclic carbonate solvents EC‐DMC/PC), and the commonly used electrolyte additives FEC on the stability and composition of CEI layer for NVPF cathode are still unclear and require a more systematic investigation, especially the electrode/electrolyte interfacial properties of NVPF at high potential.…”