Synthesis And Properties Of Micro-nano Structuresof Lithium-rich Manganese-based Cathode Materials

Lithium-ion batteries?LIBs?are currently the most promising high-efficiency secondary batteries and the fastest-growing chemical energy storage power supply.The lack of high-performance LIBs cathode materials has been a bottleneck restricting the development of LIBs.Lithium-manganese-rich cathode materials have become a research hotspot because of their high voltage platform,high specific capacity,low cost,and environment friendly.For its own complex structure,there are still some shortcomings such as the first coulomb inefficiency and poor cycle life.Therefore,the preparation methods and process studies of materials are particularly important.This dissertation is oriented towards industrial application,and focuses on the preparation methods and synthetic processes of lithium-manganese-based materials.Research is carried out by using high-gravity technology,chemical self-assembly reaction,microwave chemical synthesis,and soft template assisted chemical self-assembly.With new physical and chemical synthesis methods,we designed a series of lithium-manganese-based material with nano-micro structures.At the same time,we optimize experimental conditions,and study the influence of material composition,morphology,and structure on the performance of lithium-rich manganese-based cathode materials.The main research contents of this paper are as follows:?1?The metal salt aqueous solution and the precipitant solution in the reactor were evenly mixed on the molecular scale and chemical reactions were carried out by high-gravity technology.The effects of high-gravity processes,including feeding rate,rotating bed speed,heating temperature,on the micro-morphology and structure of lithium-rich manganese-based cathode materials were studied.Under the same high-gravity preparation process,the precursors prepared by different components had different nano-micro structures.It's found that the precursors with the composition of Mn_0.58Ni_0.18Co_0.04?CO₃?_0.8 possessed micro-peanut structure.After sintered with high temperature,micro-sized single crystal structure of Li_1.2Mn_0.58Ni_0.18Co_0.04O₂ was obtained.Compared with the traditional chemical co-precipitation method,high-gravity method,which had no aging process,were high efficiency,energy saving,uniform product quality,good repeatability,and easy of mass production.?2?lithium-manganese-based layered composite oxide cathode materials were successfully prepared by chemical co-precipitation method combined with microwave chemical rapid hydrothermal synthesis method.The obtained material had good crystallinity,uniform particle size distribution,regular morphology,hollow microsphere structure,good cycle and rate performance.The initial charge and discharge capacity of the sample was 275.8 mAh/g under the 0.1C test condition.Under the test condition of 1C,the sample's capacity remained 150 mAh/g.When the test current density was restored to 0.2C,the specific discharge capacity of the composite rapidly recovered to 250 mAh/g,and the specific capacity remained stable for the subsequent 50 cycles,showing good cycle stability and rate performance.Taking advantages of the combination of chemical self-assembly and microwave chemical rapid hydrothermal synthesis,lithium-rich manganese-based layered composite oxide cathode material with a hollow microsphere structure was prepared,which provided experimental basis for the preparation of high-performance energy storage devices.?3?This paper further prepared the lithium-manganese-based precursor Mn_0.58Ni_0.18Co_0.04?OH?_1.6 nanosheets by a modified chemical co-precipitation processcombined with a soft template assisted.The shape of the nanosheets of the precursor wasirregular,and the size distribution range of the nanosheets was large,ranging from several hundred nanometers to several micrometers,meanwhile the thickness was uniform,being about 10-12 nanometers.The prepared positive electrode material had uniform particle size distribution,regular topography,flower-like structure,and good crystallinity.Electrochemical tests showed that Li_1.2Mn_0.58Ni_0.18Co_0.04O₂ had good cycle performance and rate performance:the initial discharge specific capacity was 320-330mAh/g,and the specific capacity attenuation of the material after 140 charge and discharge was very small.