Synthesis Of High-voltage Cathode Material LiNi_0.5Mn_1.5O₄ For Lithium-ion Batteries By Molten Salt Method And Its Properties

Spinel LiNi_0.5Mn_1.5O₄ material is a potential cathode material for lithium ion batteries by virtue of its high potential plateau of 4.7 V,three-dimensional lithium ion rapid diffusion channel,low price and environmental friendly advantages.Studies have shown that the order degree of Ni/Mn,the content of Mn³⁺,the presence of impurities,grain size and particle morphology of spinel LiNi_0.5Mn_1.5O₄ cathode material have a very important effect on the structure and electrochemical properties.These factors are closely related to the synthesis of materials.In order to study the relationship between these factors and meterail synthesis and their effects on the structure and properties of materials,the following studies were carried out in this paper:In this paper,molten salt method is used to study the synthesis of LiNi_0.5Mn_1.5O₄cathode materials under three different molten salt environments of neutral,oxidizing and reducing properties,and the influence of sintering temperature and Li excess on the synthesis of LiNi_0.5Mn_1.5O₄ cathode materials.It is found that the neutral molten salt environment is the most suitable condition for the synthesis of LiNi_0.5Mn_1.5O₄,and the pure phase LiNi_0.5Mn_1.5O₄ with good crystallinity can be synthesized.However,in the oxidizing molten salt environment,impurity phases such as Li₂Mn O₃,Ni O and Na₂Mn₃O₇ are easy to appear in the synthesized materials.However,in the reduced molten salt environment,impurities such as Li Mn O₂ and Ni O are easy to appear,and it is difficult to synthesize the target material.Compared with the LiNi_0.5Mn_1.5O₄ cathode materials synthesized at three sintering temperatures of 800?,850? and 900? under the condition of neutral molten salt,it is found that the sintering temperature of850? is the most favorable for the synthesis of LiNi_0.5Mn_1.5O₄ spinel with good crystallinity and electrochemical performance.Based on the synthesis research,six different Li excesses of 0%,5%,10%,15%,20%and 25%(molar ratio),particle sizes,and additives were further explored for performance of spinel LiNi_0.5Mn_1.5O₄ cathode materials.We found that with the gradual increase of Li excess from 0%,the cell parameters increased first,then decreased gradually and finally stabilized.Li excess 5%,the maximum cell parameter reaches8.1819(?),and the content of Mn³⁺in the material is the highest.After the excess of lithium reaches 15%,the impurity phase begins to appear,but the intensity of(220)peak gradually decreases.By comparison,it was found that the materials with Li excess of 20%had the least Mn³⁺content,the least cell parameters,the most impurity phase content,the least transition metal ions occupying the tetrahedral Li site,and the best electrochemical performance.The discharge specific capacity reached 126.8 m Ah g^-1.This indicates that the transition metal ions in the tetrahedral Li site have a more significant influence on the performance of LiNi_0.5Mn_1.5O_4,in the Mn³⁺content,impurities content,transition metal ions in the tetrahedral Li site and other factors.This conclusion is of great significance for the rational design and synthesis of high performance LiNi_0.5Mn_1.5O₄ cathode materials.Moreover,it is found that larger particle size is beneficial to the electrochemical properties of materials,and the introduction of additives can improve material properties to a certain extent by exploring the effects of particle size and the introduction of additives on material properties.