Preparation And Properties Of Lithium Vanadium Phosphate Cathodes

Since the transition to a low-carbon economy is underway,affordable energy storage solutions have become increasingly urgent.To address this issue,lithium-ion batteries?LIBs?have attracted tremendous attention due to their higher energy densities,energy conversion efficiencies,and longer life.Hence,LIBs are recognized as the most potential power resources of choice for modern electronic applications,especially the plug-in hybrid electric vehicles?PHEVs?and electric vehicles?EVs?.Cathode material is a key part of LIB,which determines its electrochemical performance,safety and cost.Currently,a number of advantages held by monocline Li₃V₂?PO₄?₃ makes them ideal cathode materials for LIB applications:1)high energy density;2)high theoretical capacity?197 m Ah/g?and operating voltage?up to 4.6 V?;3)relatively good Li⁺mobility;4)excellent thermal and cyclic stability;and 5)high safety performance.However,Li₃V₂?PO₄?₃ has poor intrinsic electronic conductivityapplications.Based on the previous studies,the electrochemical properties of the composites were improved by carbonthermal reduction method,hydrothermal method and sol-gel method respectively.XRD,SEM and electrochemical tests were used to analyze the structure,morphology and electrochemical properties of the composites.The research contents of this paper are as follows:1?Li₃V₂?PO₄?₃/C composites with monoclinic structure were prepared by carbon thermal reduction method with sucrose?20 wt%?.The electrochemical properties of Li₃V₂?PO₄?₃/C composites were investigated.The results show that the morphology of Li₃V₂?PO₄?₃/Cparticles are uniformly distributed and the particle size is 100-500 nm.The carbon is uniformly coated on the surface of the sample,which is helpful to shorten the diffusion path of lithium ions in Li₃V₂?PO₄?₃.In the voltage range of3.0-4.3 V,the first discharge capacity of the sample was 105.51 m Ah/g and the sample had a specific capacity of 99.55 m Ah/g,with a capacity retention of 94.35%and a coulombic efficiency retention of 98.89%after 78 cycles at 0.5 C.2?Li₃V₂?PO₄?₃/C composites prepared by hydrothermal method,PVP?10%?as carbon source and oxalic acid as carbon source and chelating agent were investigated.The results show that the morphology of prepared Li₃V₂?PO₄?₃/C is a mixture of particles and rods with a particle size of 100-500 nm,and the length of rod-like structure is 500 nm-1 um,with width of less than 10 nm.The cyclic stability and magnification performance of the sample were excellent.In the voltage range of3.0-4.3 V,the first discharge capacity of the sample was 85.32 m Ah/g at 10 C,and the discharge capacity was 85.25 m Ah/g after 10 cycles,with capacity retention of99.92%.3?Li₃V₂?PO₄?₃/C composites with monoclinic structure were prepared by sol-gel method with PVP?10 wt%?as carbon source.The electrochemical properties of Li₃V₂?PO₄?₃/C composites were investigated.The results show that the surface of Li₃V₂?PO₄?₃/C particles has a porous structure,with pore size less than 200 nm,which is favorable for the permeation of electrolyte.The sample showed excellent electrochemical performance.At 5 C,the first discharge capacity of the sample was115.39 m Ah/g in 3.0-4.8 V,the discharge capacity was 111.25 m Ah/g after 10 cycles,with the capacity retention was as high as 96.40%.4?The author expounds the conclusion of the paper,compares the three experimental methods,the shortcomings of the paper were summarized,and the future work were prospected.