Preparation and electrochemical properties of Y-doped Li_3V_2(PO_4)_3 cathode materials for lithium batteries

Y-doped Li3V2（PO4）3 cathode materials were prepared by a carbothermal reduction（CTR） process.The properties of the Y-doped Li3V2（PO4）3 were investigated by X-ray diffraction（XRD） and electrochemical measurements.XRD studies showed that the Y-doped Li3V2（PO4）3 had the same monoclinic structure as the undoped Li3V2（PO4）3.The Y-doped Li3V2（PO4）3 samples were investigated on the Li extraction/insertion performances through charge/discharge, cyclic voltammogram（CV）, and electrochemical impedance spectra（EIS）.The optimal doping content of Y was x=0.03 in Li3V2-xYx（PO4）3 system.The Y-doped Li3V2（PO4）3 samples showed a better cyclic ability.The electrode reaction reversibility was enhanced, and the charge transfer resistance was decreased through the Y-doping.The improved electrochemical perormances of the Y-doped Li3V2（PO4）3 cathode materials were attributed to the addition of Y3＋ ion by stabilizing the monoclinic structure.

Synthesis and Electrochemical Properties of Cr-doped Li_3V_2(PO_4)_3 Cathode Materials for Lithium-ion Batteries

Cr-doped Li3V2（PO4）3 cathode materials Li3V2-xCr（PO4）3 were prepared by a carbothermal reduction（CTR） process. The properties of the Cr-doped Li3V2（PO4）3 were investigated by X-ray diffraction （XRD）, scanning electron microscopic （SEM）, and electrochemical measurements Results show that the Cr-doped Li3V2（PO4）3 has the same monoclinic structure as the undoped Li3V2（PO4）3, and the particle size of Cr-doped Li3V2（PO4）3 is smaller than that of the undoped Li3V2（PO4）3 and the smallest particle size is only about 1 1μm. The Cr-doped Li3V2（PO4）3 samples were investigated on the Li extraction/insertion performances through charge/discharge, cyclic voltammogram （CV）, and electrochemical impedance spectra（EIS）. The optimal doping content of Cr was that x=0.04 in the Li3V2-xCrx（PO4）3 samples to achieve high discharge capacity and good cyclic stability. The electrode reaction reversibility was enhanced, and the charge transfer resistance was decreased through the Cr-doping. The improved electrochemical performances of the Cr-doped Li3V2（PO4）3 cathode materials are attributed to the addition of Cr^3＋ ion by stabilizing the monoclinic structure.

Electrochemical performance of Al-substituted Li_3V_2(PO_4)_3 cathode materials synthesized by sol-gel method

The effect of Al-substitution on the electrochemical performances of Li3V2(PO4)3 cathode materials was studied.Samples with stoichiometric proportion of Li3AlxV2-x(PO4)3(x=0,0.05,0.10)were prepared by adding Al(NO3)3 in the raw materials of Li3V2(PO4)3.The XRD analysis shows that the Al-substituted Li3V2(PO4)3 has the same monoclinic structure as the un-substituted Li3V2(PO4)3.The SEM images show that Al-substituted Li3V2(PO4)3 has regular and uniform particles.The electrochemical measurements show that Al-substitution can improve the rate capability of cathode materials.The Li3Al0.05V1.95(PO4)3 sample shows the best high-rate performance.The discharge capacity at 1C rate is 119 mA·h/g with 30th capacity retention rate about 92.97%.The electrode reaction reversibility and electronic conductivity are enhanced,and the charge transfer resistance decreases through Al-substitution.The improved electrochemical performances of Al-substituted Li3V2(PO4)3 cathode materials offer some favorable properties for their commercial application.

Stabilization of high-voltage layered oxide cathode by utilizing residual lithium to form NASICON-type nanoscale functional coating

High-voltage medium-nickel low-cobalt lithium layered oxide cathode materials are becoming a popular development route for high-energy lithium-ion batteries due to their relatively high capacity,low cost,and improved safety.Unfortunately,capacity fading derived from surface lithium residue,electrode-electrolyte interfacial side reactions,and bulk structure degradation severely limits large-scale commercial utilization.In this work,an ultrathin and uniform NASICON-type Li_(3)V_(2)(PO_(4))_(3)(LVP)nanoscale functional coating is formed in situ by utilizing residual lithium to enhance the lithium storage performance of LiNi_(0.6)Co0.05Mn_(0.35)O_(2)(NCM)cathode.The GITT and ex-situ EIS and XPS demonstrate exceptional Li+diffusion and conductivity and attenuated interfacial side reactions,improving the electrode-electrolyte interface stability.The variable temperature in-situ XRD demonstrates delayed phase transition temperature to improve thermal stability.The battery in-situ XRD displays the singlephase H1-H2 reaction and weakened harmful H3 phase transition,minimizing the bulk mechanical degradation.These improvements are attributed to the removal of surface residual lithium and the formation of NASICON-type Li_(3)V_(2)(PO_(4))_(3)functional coatings with stable structure and high ionic and electronic conductivity.Consequently,the obtained NCM@LVP delivers a higher capacity retention rate(97.1%vs.79.6%)after 150 cycles and a superior rate capacity(87 mAh·g^(-1)vs.58 mAh·g^(-1))at a 5 C current density than the pristine NCM under a high cut-off voltage of 4.5 V.This work suggests a clever way to utilize residual lithium to form functional coatings in situ to improve the lithium storage performance of high-voltage medium-nickel low-cobalt cathode materials.