Synthesis And Modification Of Layered Lithium-rich Mangnese-based Cathode For Lithium Ion Batteries

As the high-voltage,high-energy lithium-ion battery cathode material,the lithium-rich manganese-based materials have gradually attracted people’s attention.However,due to the poor rate performance,poor cycle stability and voltage drop,it is difficult to commercialize.The"micro-nano structure"lithium ion battery cathode material has attracted much attention due to its excellent electrochemical performance.Based on the summarization of lithium ion batteries,especially the lithium-rich manganese-based materials,"Micro-nano structure"method is proposed and Li_1.2Ni_0.13Co_0.13Mn_0.54O₂electrode in synthesis and modification of electrode materials for research;and a series of strategies about mitigating voltage drop,improving cycle stability and rate performance are proposed.1.Using lithium polyacrylate（LIPAA）instead of the traditional binder-Polyvinylidene Fluoride（PVDF）:the electrode materials,carbon black and current collector are bonded into a complete conductive network to form a"micro-nano structure".The lithium-rich manganese-based electrode material with special"micro-nano structure"exhibits good electrochemical performance.The first discharge specific capacity is as high as 373.4 m Ah g^-1.At 1 C,the specific capacity is still as high as 186m Ah g^-1 after 200 cycles,the average discharge medium voltage is still maintained at3.1 V,and the specific capacity retention rate is as high as 52%at 5 C current density.It is much higher than the lithium-rich manganese-based lithium battery with PVDF binder at the same condation.2.The spray-drying is a common secondary particle construction technique.In this chapter,the nanoparticles can be successfully constructed into a secondary spherical particle with a"micro-nano structure"through the spray drying technology;the uniform carbon network is constructed inside the"micro-nano structure"by the helping of sucrose.In this chapter,we focus on the ball milling speed,ball milling time and wind frequency on the secondary particles.It is found that the ball milling speed,ball milling time and wind frequency are 1000 r/min,10min and 200Hz,respectively which are satisfied with the secondary particles.It is found that lithium-rich manganese-based material coated 8wt%carbon has the most excellent electrochemical performance.The specific capacity is still maintained at about 200 m Ah g^-1 after 100 cycles,and the voltage platform is as high as 3.20 V.3.Make full use of coprecipitation method and heterogeneous nucleation technology to synthesize lithium-rich manganese-based materials coated nano-Cu O with"micro-nano structure".In the process,when the p H,the sintering temperature and time are10.0,950℃and 14 h,respectively,electrochemical performance of the Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ is the most prominent by co-precipitation method.After 100cycles,the specific capacity and the first coulombic efficiency are as high as 169.3 m Ah g^-1 and 84.13%,respectively.After the nano-Cu O modification,the lithium-rich manganese-based material has a first coulombic efficiency of 89.5%.The specific capacity is 168.3 m Ah g^-1 after 200 cycles at the current density of 1 C,which is much higher than the unmodified lithium-rich manganese-based materials.4.Making fully utilizing the characteristics that redox reaction of sodium carboxymethyl cellulose（CMC）heated in air at high temperature to form lithium-rich manganese-based materials with ultrathin spinel structure materials（Na-doped）.In this way,the heterojunctions between the spinel and layered materials are losing in which the structural advantages from the three-dimensional pores are fully utilized.The rate performance is greatly improved that the specific capacity is still as high as 105 m Ah g^-1 at the rate of 10 C.Subsequently,the specific capacities of all electrode materials are still maintained at～200 m Ah g^-1 when the test magnification rapidly changes to 0.1 C,in which showing excellent Li⁺conductivity and structural stability.The lithium-rich manganese-based materials with"micro-nano structure"are constructed by L IPAA binders,spray-drying method and co-precipitation method.At the same time,the carbon coating,heterogeneous nucleation technology and in-situ generation Na-doped spinel structure technology are used improved the cyclic performance,rate performance,the first coulombic efficiency and relieving voltage drop of the Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ achieving excellent electrochemical performance.It provides some reference for the modification of other electrode materials.