Investigation On Synthesis And Electrochemical Performance Of Li-Rich Mn-Based Cathode Material For Lithium-ion Batteries

Lithium-rich cathode material xLi₂MnO₃·?1-x?LiMeO₂?0<x<1,Me = Ni,Co,Mn??OLO?has great potential for application in the field of vehicles and energy storage due to its high discharge specific capacity,low cost and clean environment.Moreover,the complex structure and disadvantage such as low initial coulomb efficiency and poor rate performance of OLO become one of the key factors to limit its further application.In OLO,the composition of the material composition has a great deal of plasticity because of the flexible of Li₂MnO₃ and Me.Based on component design,in this thesis,a sphericallike Lithium-rich cathode material xLi₂MnO₃·?1-x?LiNi_0.45Co-?0.2?Mn_0.35O₂ with novel composition was prepared.Besides,the effect of co-precipitation conditions,the amount of lithium,Li₂MnO₃ proportion,and graphene nanoribbons modification?GONR?were systematically studied.The morphology,particle size and tap density of precursor MCO₃?M = Ni,Co,Mn?were systematically studied by environmentally friendly carbonate coprecipitation method,and the precursor which has large particle size?D₅0 = 13.97 ?m?,high tap density(1.82 g·cm^-3)and oxidation resistance was obtained when PH = 7.7,C(M²⁺)= C(CO₃^2-)= 3.0 mol·L^-1,V₀ = 25 ml·h^-1,V₁ = 2000 rpm,t = 12 h.Deep research was taken on the structure and electrochemical performance of OLO with different amount of lithium and Li₂MnO₃.0.5Li₂MnO₃·0.5LiNi_0.45Co0.2Mn_0.35O₂?OLO-0.5?with 104 % lithium content exhibits a good initial discharge capacity of 219.9 mAh·g^-1 and an excellent cycle life with 95.5 % specific capacitance retention over 100 cycles at 25 mA·g^-1.In addition,OLO-0.5 exhibits a good rate performance with 140.2 mAh·g^-1 discharge specific capacity at 500 mA·g^-1 and an eximious structural stability with 232.8 mAh·g^-1 discharge specific capacity when restored to 25 mA·g^-1.The OLO/GONR-y?y = 1,3,5 wt%?composites were obtained by a simple solution diffusion method in C₄H₁0 O with OLO-0.5 and GONR.We found that GONR show significant inhibitory effect to the release of Li₂ O from Li₂MnO₃ when charged to high voltage for the first time,which significantly improved the initial coulomb efficiency of cathode materials and increased the specific capacity.Among them,OLO/GONR-1 wt% shows a low cation mixing and good first discharge specific capacity of 205.8 mAh·g^-1,as well as good capacity retention of 87.4 % after 100 cycles at 50 mA·g^-1.