Preparation And Electrochemical Properties Of Phosphate Cathode Materials For Sodium-ion Batteries

Sodium ion battery is considered as the ideal choice of the next generation of energy storage devices because of its rich raw materials,low resource cost,safety and environmental protection.Polyanionic phosphate cathode material is the most promising cathode material for sodium ion battery because of its stable skeleton structure,suitable operating voltage and fast ion diffusion channel.It has great research value and application prospect.In this paper,the homogeneous hybridization of Na₃V₂（PO₄）₃ and Na₇V₄（P₂O₇）₄PO₄ synergizes to improve the rate characteristics and cycle stability of miscible materials.The application of KVP₂O₇ in sodium-ion batteries is realized through the advantages of reversible phase transformation in the process of sodium ion deinking.It provides a new direction for the modification of polyanionic phosphate materials for sodium ion batteries.First of all,the reaction components were adjusted according to the phase diagram,and Na₃V₂（PO₄）₃ and Na₇V₄（P₂O₇）₄PO₄ were homogenized to get miscible positive HNVP,which gave full play to the synergistic effect of the two phases and initiated the fast kinetics in the sodium ion battery.The dynamics of HNVP are enhanced to a large extent by the close interaction between homogeneous hybridized Na₃V₂（PO₄）₃ and Na₇V₄（P₂O₇）₄PO₄,the intermediate state of Na₇V₄（P₂O₇）₄PO₄,and the in situ formation of amorphous grain boundaries.This homogeneous hybridization gives HNVP an ultra-high rate capacity of up to 50C and a high load of 48.85mg cm^-2,achieving a commercial area capacity of 3.81m Ah cm^-2.Meanwhile,the HNVP with stable structure has a low attenuation rate of 0.0051%per cycle capacity after 2100 cycles.In addition,HNVP//Na Ti₂（PO₄）₃ full battery also showed excellent rate performance and cycle stability of over 1500 cycles.This homogeneous hybrid strategy can be further extended to various types of composite cathode to achieve the innovation of phosphate cathode materials for sodium ion batteries.In addition,the diffusion kinetics of sodium ion was enhanced by preparing the cathode material KVP₂O₇.The dynamics of KVP₂O₇ are enhanced to a large extent by the attraction of the extended lattice structure of KVP₂O₇ to sodium intercalation,the presence of P₂O₇ groups,and the reversible phase transitions of monoclinic KVP₂O₇（P2₁/C）and triclinic K_1-xVP₂O₇（P1）during sodium ion deintercalation.The application of KVP₂O₇in the sodium ion battery gives it an ultra-high rate capacity of up to 50C and a high load of 46.38mg cm^-2,achieving an area capacity of 1.80m Ah cm^-2.At 5C rate,the capacity decay rate of each cycle is 0.0093%after 3000 cycles.At 10C rate,the capacity decay rate per cycle is 0.0065%after 2000 cycles.At the same time,KVP₂O₇//Na Ti₂（PO₄）₃ full battery also shows up to 50C rate performance and relatively superior cycle stability.This method of preparing potassium phosphate cathode material and applying it to sodium ion battery can further expand the research range of sodium ion battery cathode material.In summary,this paper takes polyanionic phosphate materials in sodium ion batteries as the main research content,expands the research scope of cathode materials for sodium ion batteries,and provides beneficial exploration for the research of polyanionic phosphate cathode materials in sodium ion batteries.