Study On The Synthesis And Surface Modification Of Ternary Cathode Material NCA For Lithium-ion Batteries

LiNi0.8Co0.15Al0.05O2(NCA),as the cathode material of lithium ion battery,has a theoretical capacity of 279 mAh/g and an actual capacity of 199 mAh/g.It has a broad application prospect in lithium ion battery and has entered the commercialization stage at the same time.However,in practical application,it is found that the cycling stability,rate cycle performance and security of NCA are the technical bottlenecks restricting its development.In order to make NCA anode materials adapt to lithium ion secondary batteries with high energy density,good cycling life and excellent safety performance,people began to improve its performance through various modification methods to meet the growing lithium ion battery market.In this paper,surface modification of NCA anode materials was carried out.AIPO4 and Ti3(PO4)4 were coated on the surface to inhibit the generation of microcracks,oxygen loss caused by surface phase transition and the dissolution of transition metals in the cycling process.Ni0.842Co0.158(OH)2 was used as precursor to prepare NCA.Ni0.842Co0.158(OH)2 precursor was achieved with good crystallinity by coprecipitation method.LiNi0.8Co0.15Al0.05O2 cathode material was prepared by high temperature solid state method which need surface modification.During this process,the best calcining technology is calcining under 500? in 5 h and calcining under 780? for 16 h in an oxygen atmosphere.The main contents of surface modification are as follows.(1)Different contents of AIPO4 coated NCA samples were prepared by homogeneous precipitation method.In the selection of experimental materials,NaAlO2 was selected based preparation method with low cost and the characteristic of gradually releasing Al3+in solution.According to the results,the coating layers were uniformly distributed on the surface of the samples.In the electrochemical performance test of the coated samples after heat treatment,1 wt%AIPO4 coated NCA had the best performance.Compared with the bare NCA,the capacity retention after 100 cycles at 0.2 C was increased from 87.38%to 94.28%,and the specific capacity of discharge at 5 C was improved by 40-50 mAh/g.Besides,the thermal stability was also improved.(2)Different contents of Ti3(PO4)4-coated NCA cathode materials were prepared by sol-gel method.The characterization analysis confirmed that Ti3(PO4)4 layers were uniformly coated on the surface of all samples.Similarly,comparsion studies were analyzed the coated samples with the original NCA in detail.Among all coated samples,1 wt%Ti3(PO4)4 coated NCA had the best performance.The capacity retention was up to 94.90%after 100 cycles at 0.2 C and the the specific capacity of discharge at 5 C increased by 30 mAh/g.At the same time,the thermal stability was also improved.