Synthesis Of Layered Lithium-Rich Manganese-Based Cathode Materials With Single Crystal And Modification

Laminated lithium-rich manganese-based cathode materials are expected to be one of the most promising cathode materials for next-generation lithium batteries due to their high specific capacity,low cost and high energy density.However,layered Li Mn-rich materials have low first Coulomb efficiency,severe voltage attenuation,poor multiplicity performance and severe surface side reactions,which greatly affect their industrial application.In this paper,lithium-rich manganese-based precursors were synthesized by co-precipitation process using sulfate,and layered lithium-rich manganese-based cathode materials were obtained by high-temperature solid-phase calcination method.The key parameters such as different Ni-Mn precursor stoichiometric ratios,solid-phase sintering temperatures and lithium ratios were optimized to determine the best preparation process.Ta-Zr ion co-doping was used to modify the Li_1.32Mn_0.56Ni_0.24O₂ cathode material.ITO（In₂O₃:Sn O₂=9:1）was used to modify Li_1.32Mn_0.56Ni_0.24O₂ by encapsulation.The experiments are as follows:（1）Firstly,Mn_0.75-xNi_0.25+x（OH）₂（x=0.00,0.05,0.10,0.15 and 0.20）precursors were prepared by co-precipitation method.Next,the lithium ratio and calcination temperature were explored and optimized,and the best preparation process was obtained as follows:the precursor molecular formula was Mn_0.7Ni_0.3（OH）₂,the lithium ratio was Li:M（M=Ni+Mn）=1.65:1,the calcination temperature was 550°C for 5 h pre-sintering,and the anode material synthesized at 950°C for 14 h sintering in air atmosphere had a good lamellar structure,primary single crystal.The discharge capacity was 206.39 m Ah·g^-1 after 100 cycles,and the capacity retention rate was94.72%.（2）Li_1.32Mn_0.56Ni_0.24O₂ and Ta-Zr ions co-doped Li_1.32Mn_0.56Ni_0.24Ta_xZr_xO₂（x=0.005,0.01,0.015）composite anode materials were synthesized by co-precipitation and high-temperature solid-phase methods to investigate the effects of doping amount on the crystal structure and electrochemical properties of the materials.The results show that the Li_1.32Mn_0.56Ni_0.24Ta_xZr_xO₂（x=0.01）cathode material has a low Li⁺/Ni²⁺mixing arrangement,a good layered structure,a large lattice spacing（0.4896 nm）and the best electrochemical performance.From the electrochemical performance,it was concluded that the specific capacity of Li_1.32Mn_0.56Ni_0.24Ta_xZr_xO₂（x=0.01）discharge was 222.97 m Ah·g^-1 with 99.06%capacity retention after 100 cycles at 0.5 C multiplicity.While Li_1.32Mn_0.56Ni_0.24O₂ had a discharge specific capacity of 211.71m Ah·g^-1 after 100 cycles,with a capacity retention rate of 95.31%.（3）The ITO was coated on the surface of Li_1.32Mn_0.56Ni_0.24O₂ cathode sheet by magnetron sputtering method.The experimental results showed that the cladding treatment did not change the crystal structure of the cathode material.The cladding modification reduced the generation of side reaction oxygen and improved the stability of the material.The electrochemical results showed that the discharge specific capacity of the clad cathode sheet was 223.53 m Ah·g^-1 after 100 cycles at 0.5 C,with a cycle retention rate of 98.39%.However,the discharge specific capacity of the uncoated cathode sheet was 206.86 m Ah·g^-1 after 100 cycles at 0.5 C,with a cycle retention rate of 95.81%.Meanwhile,the cladding modification reduced the electrochemical polarization and charge transfer resistance,suppressed the transition metal dissolution rate,and greatly alleviated the Jahn-Teller（J-T）phenomenon in the lithium-rich manganese-based cathode material.