The Research Of Preparation And Modification Of Li Rich Layered LiNi_0.8Co_0.15Mn_0.05O₂ For Lithium-ion Battery Cathode

Lithium-rich layered Li Ni_0.8Co_0.15Mn_0.05O₂ solid material is a promising lithium-ion battery cathode material,and its theoretical capacity is up to 280 m Ah/g.which is higher than the common cathode materals,such as lithium iron phosphate,lithium cobalt oxide and lithium manganese oxide cathode material.Moreover,the cobalt content of Li Ni_0.8Co_0.15Mn_0.05O₂ is lower than that of NCM?111?,NCM?523?and other types on the market.Therefore,the material can be applied to lithium ion batteries with advantages of high performance and low cost.At present,the Li Ni_0.8Co_0.15Mn_0.05O₂ material is gradually paid attention by many scientific institutions,and has became a research hotspot in the field of lithium ion battery cathode materials.However,the nickel content of high-nickel ternary NCM material is relatively high,and the more severe Li and Ni mixing phenomenon is likely to occur in the material layered structure,the cycle stability of the material is greatly reduced,this is also the biggest obstacle to the practical application of this material.In this paper,the method of solid-state calcination with high-temperature is employed to prepare the NCM material with high content of nickel.First of all,the research of following aspects are studied,including that all parametes of solid-state calcination with high-temperature,the electrochemical properties of modified NCM materials,the source and introduction method of lithium.Subsequently,in order to avoid disadvantages of low efficiency,poor cycle stability and poor cycle rate performance for as-obtained lithium-rich layered Li Ni_0.8Co_0.15Mn_0.05O₂,all of doping with the element of Mg,Al into NCM and making a NCM composite with LPAN are carried out respectively.The research results are as followed:?1?Through the TG thermogravimetric analysis of the as-obtained high-nickel NCM material precursor after the pretreatment,it is preliminarily confirmed that the calcination temperature ranged from 400°C to 600°C and the second calcination temperature ranged from 700°C to 950°C.The corresponding electrochemical tests show that the electrochemical performance of the as-obtained NCM materials are better than others with first calcination temperature of 550°C and the final calcination temperature is 800°C.Subsequently,the effect of different Li sources?Li OH,Li Ac?on the electrochemical performance of materials was further explored.Combined with the characterization results of XRD,the results show that the as obtained NCM material possessed high crystallinity with Li Ac as lithium source,and the corresponding cathode material could deliver good cycle performance.With the condition of Li Ac as the lithium source,the process parameters such as lithium ratio,pre-calcination and final calcining temperature were further explored.The results showed that the obtained NCM cathode materials,which prepared with the conditions of the lithium ratio of 1.05,the pre-calcination time of 6h and the final calcination time of 10 h,possessed the first discharge capacity of 176.4m Ah/g,capacity retention of 85.21% over 50 cycles.Further,the research ratio of cobalt and manganese in the composition of materials were discussed.The electrochemical performance of as-obtained NCM cathode revealed that,when the Co:Mn ratio is 1.5:0.5,the initial discharge specific capacity of the material is 179.8 m Ah/g at 0.1C,and the cycle capacity retention rate is 85.21%.In order to improve the cycling stability of the NCM material,oxalic acid with an appropriate proportion is introduced at the stage of material pretreatment.The experimental results show that when the ratio of oxalic acid is 0.5,the initial specific capacity is 155.6 m Ah/g at 0.1C,and the capacity retention rate is 90.62% after 50 cycles.?2?By introducing Mg or Al elements into the NCM material,all of the cycling stability for cathode materials were improved,respectively.The corresponding electrochemical performance tests showed that when the stoichiometric ratio of Mg doping is 0.010,the Mg-NCM material initial discharge capacity is 179.1m Ah/g.After 50 cycles,the capacity retention is 88.67%.At the same time,when the stoichiometric ratio of Al doping is 0.04,the Al-NCM material initial discharge capacity of 145 m Ah/g.After 50 cycles,the capacity retention rate is 90.79%.In addition,compared with the XRD patterns of NCM materials before and after doping the Mg or Al elements,the heterophasic peak do not appear,which indicates that the Mg or Al elements doping does not cause the crystal change of the NCM material.?3?In order to suppress the effect of Li⁺ and Ni²⁺ cation during charging and discharging for the Li Ni_0.8Co_0.15Mn_0.05O₂ material,the LPAN-NCM material was fabricated with using LPAN to modified NCM way,and modified NCM material exhibits higher specific discharge capacity and cycle stability.The experiment results show that,with the condition that the ratio of LPAN is 10% and the sintering temperature of LPAN-NCM composites is 750°C,the initial discharge specific capacity of the LPAN-NCM material is 185.3m Ah/g at 0.1C,and the corresponding coulomb efficiency is 75.39%.After 50 cycles,Compared with NCM cathode material,all of the initial discharge specific capacity,the corresponding comlombic efficiency and the cycle stability for LPAN-NCM composites increased obviously.In addition,by comparing the NCM materials obtained with three different preparation methods,it was found that the performance of NCM materials with LPAN modified and oxalic acid pretreatment were more attractive.The rate performance of NCM cathode material was test,the discharge capacity gradually decreased with increasing current density.The initial discharge specific capacity was 178.3 m Ah/g at 0.1C,and with the increasment of current to 1.0C,the discharge specific capacity was 134.8 m Ah/g.When the current density come back to 0.1C,the reversible capacity was 175.1 m Ah/g and the capacity retention was 98.21%.