Synthesis And Properties Of LiNi_1/3Co_1/3Mn_1/3O₂ As Lithium Ion Battery Cathode Materials

As a new type of rechargeable battery,lithium-ion battery improves disadvantages of traditional rechargeable battery,such as low energy density,poor safety performance and short service time.Furthermore,it retains the advantage of high open circuit voltage which traditional rechargeable battery does not have.In the thesis,the material of LiNi_1/3Co_1/3Mn_1/3O₂ was synthesized by hydrothermal template method,and the electrochemical properties of LiNi_1/3Co_1/3Mn_1/3O₂ samples were improved by doping（Al）and surface composites（graphene）.The main results are as follows:1.The cathode material of LiNi_1/3Co_1/3Mn_1/3O₂（111）was synthesized by hydrothermal template method.The influence of hydrothermal time on the structure of MnO₂ precursor was investigated by experiments.The electrochemical properties of materials were compared which synthesized by hydrothermal template method and traditional hydrothermal.Moreover,the influence of the related properties of the synthesized materials by different transition metal salts were compared.The results show that the LiNi_1/3Co_1/3Mn_1/3O₂ which prepared by hydrothermal template method keep excellent electrochemical performance.At 0.1 C,the discharge capacity of the LiNi_1/3Co_1/3Mn_1/3O₂ reaches 175.3 m Ah g^-1,and the capacity retention rate of the sample is 90.3%after 30 cycles.2.The cathode material（Ni,Co,Mn）of Al doping was synthesized by hydrothermal template method.The effects of the electrochemical properties of the LiNi_1/3Co_1/3Mn_1/3O₂ with different contents of Al was investigated.The experimental results show that the chemical properties of the LiNi_1/3Co_1/3-xMn_1/3Al_xO₂ are excellent when the Al content is 0.05.The initial discharge specific capacity of the material reached 186.2 m Ah g^-1 at 0.1C.The outstanding capacity of the LiNi_1/3Co_1/3-0.05Mn_1/3Al_0.05O₂ was maintained at different rates,and the cyclic performance showed that the capacity retention rate of the material was 95.6%after 30cycles.In the materials of LiNi_1/3-xCo_1/3Mn_1/3Al_xO₂,when the Al doping content was0.03,the initial discharge specific capacity reached 173.1 m Ah g^-1 at 0.1C,and the capacity retention rate of the material was 92.1%after 30 cycles and the initial discharge specific capacity reached 92.1%at 0.1C.In the LiNi_1/3Co_1/3Mn_1/3-0.03Al_0.03O₂material,the initial discharge specific capacity of the LiNi_1/3Co_1/3Mn_1/3-0.03Al_0.03O₂reaches 173.3 m Ah g^-1 at 0.1C,and the capacity retention rate of the material is 92.3%after 30 cycles.It was found that LiNi_1/3Co_1/3-0.05Mn_1/3Al_0.05O₂ had excellent electrochemical properties.3.By compounding graphene on the surface of LiNi_1/3Co_1/3-0.05Mn_1/3Al_0.05O₂,the effects of different mass fractions of graphene（0 wt%,3 wt%,5 wt%,8 wt%and 10wt%）on the electrochemical properties of the material were studied.The experimental results show that when the mass fraction of graphene is 3wt%,the cathode material has the best properties.After 30 cycles,the capacity retention rate of LiNi_1/3Co_1/3-0.05Mn_1/3Al_0.05O₂/GR-3wt%was 96.1%.