Controllable Synthesis And Electrochemical Properties Of Layered Manganese-based Oxide CathodeMaterials For Li/Na-ion Battery

The continuous development of new energy strorage field requires low-cost lithium/sodium ion batteries with high energy density.The cathode material determines the cost and energy density of lithium/sodium ion batteries.It is important to prepare layered manganese-based oxide cathode materials with low cost and high discharge capacity.In this paper,layred Li-riched manganese-based cathode materials with different structure were prepared by lithiated or sodiated spinel Li(Mn1.35Co0.325Ni0.325)O4,and P2-phase layered manganese-based cathode materials with different composition were prepared by introducing interlayer water and Li/Ti co-doping.The electrochemical properties of the two kinds of materials in lithium/sodium ion batteries were tested in detail.The intrinsic relationship between material structure and electrochemical properties was discussed.1.Li-riched manganese-based cathode materials with cation ordered and disordered composite phases were prepared by lithiated spinel Li(Mn1.35Co0.325Ni0.325)O4 in inert atmosphere.The formation of composite phase and the mechanism of low voltage fade were studied.The formation of cation disordered phase in the composite can be explained that in cationic ordered phase,the transition metals migration induced by oxygen loss and structural rearrangement at high temperature and in inert gas.Because of the existence of transition metals between layers,which hinders the further TM migration in electrochemical process,the cation ordered and disordered composite phase prepared in 600? exhibits low voltage drop(voltage fade of 2.30 mV/cycle in 50 cycles).2.Through lithiated spinel Li(Mn1.35Co0.324Ni0.325)O4 in oxygen atmosphere,high-voltage layered Li-riched manganese-based cathode materials with low oxygen vacancy content were prepared,and the relationship between oxygen vacancy content and discharge voltage was explored.Through theoretical calculation results,it is proved that the more oxygen vacancies the layered lithium-rich manganese-based cathode materials are,the lower the discharge voltage is.A series of layered lithium-riched manganese-based cathode materials with different oxygen vacancy content were synthesized by controlling the conditions of preparing layered lithium-rich manganese-based materials from lithiated spinel Li0.4Mn0.54Co0.13Ni0.13O1.6.The average discharge voltage increased with the decrease of oxygen vacancies Therefore,in oxygen atmosphere,the layered Li-riched manganese-based cathode materials with the least oxygen vacancy content exhibit an average discharge voltage of 3.65 V(vs.Li/Li+).3.Through sodiated spinel Li(Mni.3sCo0.32sNi0.325)O4 combined with ion-exchange method,layered Li-riched manganese-based cathode materials with O2/O3 composite phase was prepared,and the composite phase formation mechanism and low voltage fade mechanism were deeply analyzed.The experimental results show that when the initial sodium content is 0.65,the as-prepared material is O2/O3 composite phase layered Li-riched manganese-based cathode material and performs the best electrochemical performance.Compared with pure O2 phase and pure O3 phase,O2/O3 composite phase materials exhibit high initial Coulomb efficiency(108.2%),high rate capability(187.1 mAh/g at 250 mA/g current density),high discharge voltage(3.57 V vs.Li/Li+),high capacity(90.5%in 120 cycles)and voltage retention rate(2.63 mV/cycle in 120 cycles).Further researchments shows that the stable voltage mainly comes from the small size effect of the broken particles formed by the asynchronous volume change of each phase to the phase transition during the cycle.4.By water rinsing,the P2-phase layered manganese-based cathode material containing interlayer water was prepared,and its structure and high rate performance mechanism were studied in depth.P2 phase layered manganese-based cathode materials with water-intercalated were prepared by washing the sodiated hydroxide precursors,and the interlayer distance was extended.The materials with water-intercalated perform the high discharge specific capacities at current densities of 30,150,300 and 750 mA/g are 124.8,111.4,106.1 and 97.2 mAh/g,respectively,and a high cycle stability(75.6%at 250 weeks).Compared with the materials for removing interlayer water at high temperature,it is found that the existence of interlayer water can effectively increase the diffusion coefficient of Na ions and decrease the material resistance.5.Layered manganese-based cathode materials with Li/Ti co-doping were prepared by chemical-precipitation-assisted solid-state method,and mechanism of stabilizing the slabs in charge and discharge process were studied deeply.The uniform distribution of Li/Ti in P2 layered manganese-based cathode was achieved by chemical precipitation-assisted solid-state reaction,using the same hydrolysis pH of TiOSO4 and precipitation pH of nickel manganese-based carbonate.Further studies show that Li and Ti occupy transition metal sites and cause changes in lattice parameters.Moreover,the strong Ti-O bond enhances the stability of the slabs,and the rapid diffusion of Li releases the stress.Thus,the Li/Ti co-doped samples exhibit high discharge voltage(3.66 V vs.Na/Na+;3.55 V vs.hard carbon),stable reverisble specific capacity and discharge voltage(74.2%and 95.9%for half-cell;80.8%and 92.7%for full cell retention rate in 100 cycles,respectively)under nearly 20%volume expansion.