Surface Modified Li-rich Layered Metal Oxides Cathode Materials For Advanced Li-ion Batteries

With the rapid development of portable electronics and electric vehicles,it has become a hot research topic in recent years to develop the cathode materials with high energy and high power to realize the efficient conversion and storage of clean energy.Li-rich layered metal oxides(LLMO)cathode materials attract researcher's attention due to its high specific capacity(more than 200 mAh·g-1)and high operating voltage.However,the existence of large irreversible capacity loss at the first cycle,voltage fade and poor rate performance limit its development and application.In this work,Li[Li0.2Mn0.54Co0.13Ni0.13]O2 was prepared by co-precipitation method with Mn,Co,Ni acetate as raw materials and the surface modification of alumina oxide was studied.The main contents are as follows:(1)Various surfactants were introduced into the preparation of Al2O3-modified LLMO.The roles of surfactants were systematically investigated to reveal the mechanism of Al2O3 modification.The experimental results showed that Al2O3 nanoparticles were uniformly dispersed on the surface of LLMO by using N,N,N-trimethyl–1-dodecanaminium bromide(DTAB)as the surfactant.Al2O3-modified LLMO used DTAB as surfactant delivered an initial discharge capacity of 186 mAh·g-1at the current density of 600 m A·g-1.After 500 cycles,the reversible discharge capacity was 132 mAh·g-1with a satisfactory capacity retention of 71%.Moreover,the voltage fading of LLMO was greatly suppressed after Al2O3 modification,which exhibited superior electrochemical performances.(2)Al2O3-modified LLMO was prepared by the hydrolysis of aluminium isopropoxide.The experimental results showed that the Al2O3 coating layer could improve the electrochemical performances by minimizing the direct contact of theactive material with electrolyte.The sample with 3 wt.% Al2O3 content exhibited superior electrochemical performances.A-3 LLMO delivered an initial discharge capacity of 143 mAh·g-1 at the current density of 600 m A·g-1.After 200 cycles,the reversible discharge capacity was 113 mAh·g-1 with a satisfactory capacity retention of 79%.(3)Al2O3-modified LLMO was prepared by thermal decomposition of aluminum nitrate.The results showed that as-prepared material had better electrochemical performance.Among the samples with different content of Al2O3,the sample with 3wt.% Al2O3 exhibited superior electrochemical performances.A-3 LLMO delivered the initial discharge capacity of 134 mAh·g-1 at the current density of 600 mA·g-1.After 500 cycles,the reversible discharge capacity was 95 mAh·g-1 with a satisfactory capacity retention of 71%.Meanwhile,the voltage fading was suppressed and the high rate capacity improved.