Preparation And Modification Of LiNi_0.8Fe_0.1Al_0.1O₂ As Rich Ni Cathode Material For Lithium Ion Batteries

In recent years,with the rapid development of electric vehicles,efficient,sustainable and economical lithium-ion batteries have become the ultimate goal of the development of the battery industry.Although the proportion of Co in cathode materials has been greatly reduced,it is still used in large quantities due to the expanding demand for batteries in the electric vehicle market.Since Co is a scarce element on Earth,the ethical and political dilemmas of mining and refining have posed significant challenges to the low-cost and sustainable goals envisioned by the battery industry,hence the urgent need to develop cathode materials with less Co content.Compared with NCM and NCA,the nickel-rich and cobalt-free cathode material LiNi_0.8Fe_0.1Al_0.1O₂（NFA）has lower cost and excellent electrochemical performance due to the elimination of cobalt,and is the best candidate for the preferred cathode material for lithium ion batteries.Therefore,this research paper takes LiNi_0.8Fe_0.1Al_0.1O₂ as the research object.Optimization of synthesis process,modification research to prepare NFA cathode material with good electrochemical performance.The morphology,structure and electrochemical performance of NFA cathode materials were characterized and analyzed,which provided basic data for the development of low-cost new nickel-rich and cobalt-free cathode materials.（1）NFA was synthesized by sol-gel method.The effects of synthesis process conditions（p H value,pre-calcination temperature,calcination temperature,calcination time,and lithium preparation amount）on the morphology,crystal structure and electrochemical performance of synthesized NFA were studied.The research results show that NFA particles are irregular secondary particles formed by the close packing of primary particles.The crystal structure of the material grows well,the distribution of elements is uniform,and the peak ratio of I_（003）/I_（104）is 1.67,which has good crystallinity.The initial discharge capacity of NFA cathode material is 159.4 m Ahg^-1 at the voltage window of 3～4.5 V,at 0.05 C,and the initial Coulomb efficiency is 79.7%.The capacity retention of NFA cathode material is 65.1%after 50 cycles at 0.1 C.（2）In order to improve the cycle life of NFA cathode material during charge and discharge,Mg²⁺doping modification was studied.The Mg²⁺radius（0.771（?））is similar to the Li⁺radius（0.773（?））,and Mg²⁺can occupy the Li⁺site of nickel-rich layered cathode material.The constant pricing state of Mg²⁺shows a very stable pillar role in the charging and discharging process.By analyzing the influence of different Mg²⁺doping amounts on the morphology,crystal structure and electrochemical performance of NFA cathode materials,the mechanism of the influence of Mg²⁺doping on the structural stability of NFA was clarified.The research results show that Mg²⁺doping increases the structural stability of NFA cathode materials during Li⁺extraction and intercalation processes,and significantly improves the cycle life.The capacity retention of the sample with 0.01 Mg²⁺doping content for 50 cycles was 74.15%at 0.1 C.（3）Under the condition of determining the optimal doping amount of Mg²⁺,the influences of different F^-doping amount on the morphology,structure and electrochemical performance of NFA cathode materials were investigated.Achieving Mg²⁺and F^-co-doping to synergistically improve the electrochemical performance of NFA cathode materials.The research results show that Mg and F are uniformly dispersed on the surface of the material,and a small amount of Mg²⁺and F^-co-doping does not change the layered structure of the material.The samples with Mg²⁺doping amount of 0.01 and F^-doping amount of 0.02exhibited the best electrochemical performance,the first discharge specific capacity and first coulombic efficiency were 170.0 m Ahg^-1 and 88.1%at 0.05 C,respectively.The specific capacity and capacity retention rate are 130.5 m Ahg-1 and 80.6%after 50 cycles at 0.1 C,respectively.Due to the maximum electronegativity of F,the bond between the transition metal and F is stronger,resulting in a highly stable structure.