Ether Electrolytes Regulation For Enhancing The Sodium/Potassium Storage Performance Of Na₃（VOPO₄）₂F Cathode Material

Ether-based electrolytes can generate thin and robust solid electrolyte interphase on the anode side and significantly improve the electrochemical performance of anode materials,but their poor oxidation stability leads to their incompatibility with high-voltage cathode materials,limiting further development of sodium/potassium ion batteries with ether-based electrolytes.As a typical polyanionic cathode material,Na₃（VOPO₄）₂F has a wide range of application prospects due to its high operating voltage,fast ion transport and stable structure.In-depth exploration of the sodium/potassium storage properties of Na₃（VOPO₄）₂F cathodes in ether electrolytes is of great significance for promoting the practical application of sodium/potassium ion batteries,but it is rarely reported.Herein,the oxidation stability of ether electrolyte was significantly enhanced by optimizing the composition,state,and concentration of the electrolyte,thereby realizing a better sodium/potassium storage capability of Na₃（VOPO₄）₂F cathode in ether electrolytes.The interface issues closely related to the performance improvement were further analyzed by combining various microscopic and spectroscopic characterizations.The specific research contents are as follows:（1）Electrochemical tests and theoretical calculations show that the combination of salt and solvent is very important,which can effectively control the highest occupied molecular orbital energy level of ether-based liquid electrolytes,thereby improving the oxidation stability of the electrolyte.The microscopic and spectroscopic characterization of the cathode/electrolyte interface revealed that the Na F-rich inorganic-organic integrated interphase derived on high-voltage cathode surface has a lower energy barrier for ion diffusion and can effectively protect the electrode.Benefiting from the enhanced oxidation stability of the electrolyte and its derived beneficial interphase,the high-voltage Na₃（VOPO₄）₂F cathode exhibits excellent rate capability（140 C）and ultra-long cycle life（over 10 000 cycles）in the optimized ether electrolyte.The ether-based Na-ion full battery based on Na₃（VOPO₄）₂F cathode,Na₂Ti₂O₅ anode and Na PF₆-DIGLYME electrolyte also possesses high energy density and high power density.（2）The ether-based liquid electrolyte was bound in the polymer network to obtain a solidified ether-based gel electrolyte,which further enhanced the oxidation stability of the electrolyte.Electrochemical tests show that the gel electrolyte still maintains a high ionic conductivity(2.33 m S cm^-1)similar to that of the liquid electrolyte,and can effectively inhibit the formation of sodium dendrites,thereby improving safety.By further designing the integrated electrode structure,the Na₃（VOPO₄）₂F cathode can still achieve high rate performance up to 40 C and longer cycle life（over 50 000 cycles）in this ether-based gel electrolyte than in the liquid electrolyte.Finally,both sodium titanate and graphite anodes show higher cycle stability in this electrolyte,and the quasi-solid-state full battery assembled with graphite as the anode also has excellent electrochemical performance.（3）Based on ether-based gel electrolyte,the reversible and stable potassium storage performance of Na₃（VOPO₄）₂F material was explored and revealed,and potassium metal battery with higher operating voltage was constructed.Studies have shown that the regulation of polymer ratio and salt concentration can effectively reduce the free solvent content in the gel electrolyte,thereby improving the oxidation stability of the electrolyte.Electrochemical impedance spectroscopy,Fourier transform infrared spectroscopy,and X-ray photoelectron spectroscopy showed that the KF-containing inorganic-organic integrated cathode/electrolyte interphase derived from high-salt gel electrolyte further improved the potassium storage stability of Na₃（VOPO₄）₂F material.