Coating Modification Study Based On Lithium Nickel Manganese Oxide And Sodium Vanadate Phosphate As High Energy Density Cathode Materials

Developing secondary cell with high-energy densities and low-cost is also one of the research hotspots.It is well-known,however,that the energy density of secondary cell is limitted mainly by the inherent low energy density of the available cathode materials.Meanwhile,the cost of cathode materials represents more than one third of all processing cost.Therefore,the development of cathode materials with high energy density becomes significant.The LiNi0.5Mn1.5O4(LNMO)and Na3V2(PO4)3(NVP)as a highly efficient cathode material for lithium-ion batteries(LIBs)and aqueous zinc ion batteries(AZIBs),can fully satisfy the current demands such as high energy density and low cost.However,its poor cycle performance and structural instability limited their commercialization.In this work,improving the electrochemical performance of LNMO and NVP cathode materials through surface coating was were systematically studied.The specific content is as follows:Taking the advantages of the fascinating properties of dopamine(DA)of self-polymerization,PDA@TiO2 composite was prepared through strong adhesion of polydopamine(PDA)to solid substrates.A homogeneous PDA@TiO2 coating layer on the surface of LNMO materials was formed through a simple liquid mixing and rotary evaporating approach,denoted as PDA@TiO2-LNMO.The crystal structure,fine morphology and electrochemical and electrochemical performances of PDA@TiO2-LNMO were investigated in detail.As a result,the 2 wt.%PDA@TiO2 modified LNMO cathode exhibited a high reversible capacity of 117 mAh·g-1,after 1000 cycles with a capacity retention of 90.7%at 1C,and a superior rate capability(78.5 mAh·g-1 at 5 C).The honeycomb-like porous structure NVP@C composite material was synthsized with sol-gel processing.The crystal structure,fine morphology and electrochemical performances of NVP@C were investigated in detail.The NVP@C prepared by adding 5 wt.%glucose and calcined at 700℃ had a continuous honeycomb-like porous structure with 2～3 nm of the surface carbon layer thickness.The initial discharge capacity was 113 mAh·g-1 at 0.5 C and the capacity loss could be 20%of its initial discharge capacity after 1000 cycles at 5 C.