Preparation And Modification Of Al³⁺ Doped LiNi_0.5Mn_1.5O₄ Cathode Material

The LiNi_0.5Mn_1.5O₄（LNMO）material has gradually become an important cathode material for lithium-ion batteries due to its internal three-dimensional tunnel that facilitates Li⁺transmission and de-embedding,as well as its low price,safety,non-toxicity,and voltage platform up to 4.7V.However,LNMO material still have problems such as poor conductivity,low theoretical rapid capacity,and capacity retention decline fast during cycling.These disadvantages have affected its wide application in the industry.Therefore,the modification of the material has become the focus of research.This article is based on the ion doping with simple process and obvious effect,combined with the optimization of the preparation process and surface coating modification,and the composite modification method to improve the cycle performance and conductivity LNMO material.1.Li_1+xAl_x Ni_0.5Mn_1.5-xO₄（LNMO）materials with different Al³⁺doping amount（x）were prepared and characterized by XRD and SEM and so on techniques.The electrochemical properties of the samples were determined by CV test and AC impedance spectroscopy.The influence of Al³⁺doping amount on the structure and properties of materials was discussed.The results showed that proper Al³⁺doping increased the structural stability,cycle and rate performance of the material.The doping of Al³⁺will gradually increase the amount of Mn³⁺in the material.Although this will improve the conductivity of the material,too much Mn³⁺will cause side reaction to generate Mn²⁺to destroy the structure of the material.When Al³⁺doping amount was 0.06,the prepared sample had the best properties,the retention rates of circulating100 times at 0.5C and 2C reached 95.2%and 90%,respectively.Moreover,the potential difference of the redox peak was small,and the cycle reversibility was the best.2.Based on Al³⁺doping and solid-state method as the basic method,the preparation process of LNMO material was formulated and optimized.By discussing the structure,morphology,and electrochemical properties of the material,the polymer-assisted high-temperature solid phase was obtained The method is most suitable for the preparation process of Al³⁺doped LNMO materials.The sample prepared by this method has high crystallinity and regular octahedron in morphology.Under the effect of these two aspects,the electrochemical performance of the material is significantly improved.The specific charge capacity of this sample after 100 cycles at 0.5C rate can still reach 129.4mAh/g,the capacity retention rate is97.1%,and the cycle performance is higher than other samples.The charging specific capacity at 2C rate can also reach 137mAh/g,and the capacity retention rate after cycling is 93%,which can be used for further modification3.LNMO material was co-modified with Al³⁺doping and Al₂O₃ coating via solid-state method and wet chemical method.Remarkably,the co-modification effect was most favorable when the coating content was 1wt%,the retention rates after 100 cycles at 0.5C and 2C reached99.1%and 91.7%respectively,which can be ascribed to the Al³⁺doping can improve the electronic conductivity of the material.Furthermore,Al₂O₃ coating can improve the ionic conductivity,LANMO-1wt%sample got the best charge transfer resistance and Li⁺diffusion coefficient.Al₂O₃ layer can hinder the side reaction between the material and the electrolyte,and reduce polarization effect,thereby improving the cycle and rate performance of the material.