Synthesis And Structure Optimization Of LiNi_1-xMg_xO₂ High Nickel Binary Cathode Material

LiNiO₂,as a promising cathode material for lithium-ion batteries,has a theoretical specific discharge capacity of 275 mAh/g.however,it is difficult to prepare accurate stoichiometric target material and serious Li-Ni mixed discharge,which makes it prone to collapse of layered structure during charging and discharging process,resulting in poor cycling and rate performance,This kind of structural collapse will also lead to security risks,so it has not entered the market-oriented process.At present,the way to solve the problem of serious cation mixing of LiNiO₂is to add transition metal elements to stabilize the structure and reduce the cation mixing,so as to improve the cycle performance.The added metal elements are Mg,Al,Mn,Co,Nb,W and so on.As a doping metal element,Mg has the advantages of simplicity and rich mineral resources.In this paper,by comparing different layered materials,the binary cathode materials doped with Mg based on nickelbased materials were selected as the main research direction,and LiNi_1-xMg_xO₂（x=0.05,0.1,0.2）cathode materials with different Ni-Mg ratios were prepared by optimized chemical coprecipitation method.By exploring the different calcination temperature,calcination time and lithium ratio of binary cathode materials,high nickel binary cathode materials with good electrochemical performance were obtained.In order to further improve the internal stress and cycle performance of the material,the gradient design of the binary Ni-Mg cathode material was carried out,and the evolution of the phase microstructure was observed from the gradient change by using the adjustable means,so as to further improve the electrochemical performance of the material.The precursors with different Ni/Mg ratios were prepared by coprecipitation method.The precursors were prepared by adding Ni and Mg sulfate as starting materials,NaOH as precipitant and ammonia as complexing agent in a coprecipitation reactor according to stoichiometric ratio.The results show that the secondary grain porosity of the precursor with different Ni-Mg ratio is different.The precursor with Ni-Mg ratio of 95:05 has the advantages of compactness,uniformity,good sphericity,high discharge capacity and good cycle retention.The first discharge capacity is 216.4 mAh/g,and the cycle retention rate is 89.6%at 1 C 100th.The results show that when the ratio of lithium to nickel is 1.06,the cathode material with95:05 ratio of nickel to magnesium is calcined at 700℃for 0.1 C,and the highest discharge capacity is 218.7 mAh/g.In the case of low Mg content,the gradient modified Ni-Mg ratio of 95:05 was synthesized by optimized coprecipitation method.The precursor of Ni_0.95Mg_0.05（OH）₂ has the characteristics of Ni rich core and Mg rich shell.This kind of element gradient distribution not only keeps high capacity,but also alleviates the structure collapse caused by internal stress during the charging and discharging process.Through the measurement of electrochemical performance and other characterization tests,the specific discharge capacity of 0.1 C is 225.6 mAh/g,and the cycle retention rate of 1 C is 95.3%.The electrochemical performance of the cathode material is better than that of the reported cathode material with the same stoichiometric ratio.