| Nowadays,the rapid growth of the energy storage system such as consumer electronics,electric vehicles,pursue conventional lithium-ion batteries(LIBs)with higher energy density.Rechargeable LiCoO2(LCO)based lithium ion batteries with enhanced specific capacity and improved voltage outputs at high operating voltage,are promising candidates for high energy batteries.However,various challenges for the LCO at high cutoff voltage,such as instability of cathode materials,dissolution of the active materials and decomposition of the liquid electrolytes,impair the cycling performance of LCO batteriesTo solve these challenges,we propose a class of facile and cost-effective strategies via creating an artificial passivation layer on the surface of the cathode particles by both physical and chemical methods.First,we used simple blade technique to coat LCO electrode with piperidinium-based ionic liquid functionalized-colloidal silica nanoparticles(SMPP),thereby forming a stable interfacial passivation layer to protect the LCO particles from electrolytes.Cells using SMPP-LCO electrodes display stable cycling behavior at high cut-off voltage,and the capacity loss is as low as 0.148%per cycle when cycled between 3-4.6 V.Furthermore,we designed a class of ternary Li,Al,F-modified LCO(LAF-LCO)with a stable and highly conductive layer using hydrothermal-assisted hybrid surface treatment.Such surface treatment hinders direct contact between liquid electrolytes and LCO particles,which reduces the loss of active cobalt.It also forms a subsurface doping layer that consists of a Li-Al-Co-O-F solid solution,which enables the phase transition of LCO reversibly when operated at voltages>4.55 V.Modified LAF-LCO cells display excellent electrochemical performance with a high discharge capacity of 170.7 mAh g-1 and enhanced capacity retention of 81.8%after 200 cycles.In addition,we prepared graphite/LAF-LCO cells that achieves a high specific energy density of 600 Wh kg-1 at material level after 70 cycles. |
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