Design,Performance Optimization And Large-Scale Preparation Of Lithium-Rich And Manganese-Based Cathode Materials

In order to meet the fast-growing demand of high energy density lithium-ion battery,lithium-rich layered oxide(LRLO)cathodes have received extensive attention.They are considered to be an ideal cathode material because of its ultra high discharge specific capacity(>250 mA h g-1).However,their practical application is hindered by drawbacks of fast capacity and voltage fading as well as poor rate performance.In this work,a co-precipitation method was used to large-scale prepare LRLOs.Sodium tartrate is used as complexing agent to obtain uniform particle size and element distribution.The designed bayberry-like core-shell structure of LRLOs can enhance their comprehensive electrochemical properties effectively.(1)A microstructure engineering strategy is put forward to synthesize bayberrylike Li1.2Mn0.54Co0.13Ni0.13O2(LRLO-S)cathode material,which has a spherical core self-assembled by many nanoparticles and a shell made up of radially-oriented microrods.The special bayberry-like structure can resist electrolyte corrosion,and its more uniform lithiation-delithiation processes enabled by the fast diffusion of electron and Li+in microrod building blocks can effectively disperse strain to stabilize the structure.Therefore,the LRLO-S cathode shows outstanding long-term cyclic stability with a high reversible capacity of 219 mA h g-1 at 1 C after 500 cycles,and good rate capability with a very high capacity retention of 80.3%after cycling 1000 times at 5 C.The voltage is higher than 3.1 V with a voltage retention as high as 89.6%after 500 cycles.Furthermore,after increasing the output,we can synthesize 2 kg of bayberry-like LRLO-S at one time,and the electrochemical performance is still excellent.This simple strategy opens an applicable way for the large-scale synthesis(kilograms level)of highperformance Li-rich layered cathode materials.(2)The cobalt-free lithium-rich cathode material Li1.2Mn0.6Ni0.2O2 was prepared by the same synthesis method,and the influence of different mixing amount of lithium on the electrochemical properties of cobalt-free lithium-rich cathode materials was investigated.The experimental results show that as increasing of lithium content,the Li2MnO3 phase in Li1.2Mn0.6Ni0.2O2 can be activated at lower voltage and then contribute to a higher capacity.While the Li2MnO3 in the low lithium content sample needs to be activated at about 4.7 V.The prepared cobalt-free lithium-rich material shows excellent cycling stability,the voltage of LR-0.79 can be maintained at 3.22 V after 300 cycles at 1 C.Compared to Li1.2Mn0.54Ni0.13Co0.13O2 with same structure,although the capacity of LR-0.79 is slightly reduced,the cycing stability is still outstanding with a lower cost due to its cobalt-free feature.