Effect Of Three Kinds Of Aluminum-containing Coatings On The Electrochemical Properties Of Lithium-rich Manganese-based Material

With the increasingly large-scale employment of electric vehicles,energy storage devices and 3C（Computers,Communications,Consumer Electronics）products,more and more requirements are emerging for batteries.Due to their high energy density,fast charge and discharge rate and long service life,lithium-ion batteries have been received increasing attention.However,there are only a few cathode materials for lithium-ion batteries that have been commercially available since 1991 when Sony Corporation developed the first batch of lithium-ion batteries.With the rising demands for high-performance lithium-ion batteries,it is pretty challenging to use traditional cathode materials to satisfy people’s ever-increasing needs.Therefore,lithium-rich manganese-based materials have gained a significant amount of attention from researchers because of their high capacity and energy density.Nevertheless,many improvements remain to be brought about.Herein we systematically investigated the surface coating effects on lithium-rich manganese-based material Li_1.2[Mn_0.54Co_0.13Ni_0.13]O₂by treating it with three kinds of aluminum-containing compounds to improve its electrochemical properties.Moreover,the effect of secondary sintering on material properties was also examined.The main research contents and results are summarized as follows:1.The substrate material Li_1.2[Mn_0.54Co_0.13Ni_0.13]O₂was synthesized by sol-gel method,followed by surface coated with AlPO₄ of two thicknesses（AlPO₄@LMNCO-1 and AlPO₄@LMNCO-2）by wet coating method.LMNCO-700was obtained by secondary sintering at 700℃.AlPO₄@LMNCO-2 exhibited good electrochemical performance with much higher initial coulombic efficiency,86.3%compared to 71.0%of the LMNCO.However,sintering at 700℃ had negligible impacts on the electrochemical performance of the substrate material.2.Based on substrate material LMNCO,Al₂O₃@LMNCO-1 and Al₂O₃@LMNCO-2 were obtained by coating Al₂O₃ via carbamide-assistant hydrothermal process.Then,LMNCO-500 was prepared by secondary sintering at500℃.The initial coulombic efficiencies of Al₂O₃@LMNCO-1 and Al₂O₃@LMNCO-2 were both improved,with Al₂O₃@LMNCO-1 displaying higher enhancement,reaching up to 77.7%.Although LMNCO-500 showed somewhat improved discharge specific capacity,the initial coulombic efficiency dwindled.As for capacity retention rate during cycling,Al₂O₃@LMNCO-1,Al₂O₃@LMNCO-2 and LMNCO-500 all manifested significant improvements,among which Al₂O₃@LMNCO-2 outperformed the other two,remaining 96.1%after 50 cycles,in contrast to that of LMNCO（58.9%）.Meanwhile,the capacity retention rate of LMNCO-500 was also greatly improved,reaching to 65.6%.3.On the basis of substrate material LMNCO,AlF₃@LMNCO-1 and AlF₃@LMNCO-2 were prepared by AlF₃ coating with wet coating method.And LMNCO-400 was acquired by a 400℃ secondary sintering procedure.Finally,we systemically studied the effects of three different aluminum-containing coatings on electrochemical properties.To begin with,AlF₃@LMNCO-1,AlF₃@LMNCO-2 and LMNCO-400 all exhibited improved initial coulomb efficiency and capacity retention rate.Among them,AlF₃@LMNCO-2 achieved the best performance,with initial coulomb efficiency of 81.1%and the capacity retention rate of 92.4%after 50 cycles.Additionally,LMNCO-400 showed a great enhancement in capacity retention rate,increasing to 75.9%.In terms of coating effects,the initial coulombic efficiency of AlPO₄@LMNCO-2 was boosted mostly,while Al₂O₃@LMNCO-2 was responsible for the highest capacity retention rate.In comparison,AlF₃@LMNCO-2 demonstrated the best overall electrochemical performance.