Coating Modification Of LiNi_0.8Co_0.1Mn_0.1O₂Cathode Materials For Li-ion Batteries

Abstact:LiNi0.8Co0.1Mn0.1O2is considered to be a promising cathode material which possesses the merit of LiCoO2、LiNiO2、LiMnO2and owns high capacity. However, a few drawbacks such as the cycling performance and storage performance in air are need to overcome, otherwise, the wide application of LiNi0.8Co0.1Mn0.1O2is limited. Therefore, we coat an electrochemical active or inactive material layer to improve the electrochemical performance of the material. We mainly discuss the effect of the Ni-poorer layred coating on LiNi0.8Co0.1Mn0.1O2.LiNi1/3Co1/3Mn1/3O2is coated on LiNi0.8Co0.1Mn0.1O2via co-precipitation method, and the formation of Li(Ni0.8Co0.1Mn0.1)1-x(Ni1/3Co1/3Mn1/3)xO2is confirmed by the EDS analysis of the cut plane of the particle. When x=0.17, the initial specific discharge capacity of the coated sample is185mAh g-1at0.1C, a slightly lower than the bare one. After100cycles at25℃, the coated LiNi0.8Co0.1Mn0.1O2preserves a capacity retention of94.5%, while the bare sample keeps a capacity retention of88.3%. At elevated temperature (55℃), the cycling behavior of the LiNi1/3Co1/3Mn1/3O2-coated LiNi0.8Co0.1Mn0.1O2is remarkably improved, showing a capacity retention of90%after100cycles, while the bare electrode shows a gradual decrease in capacity, with a capacity retention of only74%. At the same time, the coated LiNi0.8Co0.1Mn0.1O2has a lower capacity than the bare at low rates (0.1C and1C), whereas, with the rise of the discharge rate, the coated LiNi0.8Co0.1Mn0.1O2shows a higher capacity than the bare material in spite of the thick clad layer. After cycled, the electrode material prepared by two samples are both eroded to some extent, while the bare sample is more severe. We compare the two different method (mix and coating) to combine the material, and find that the initial specific discharge capacity of mixed and coated samples are close, but the cycle performance of the later sample is superior to the former.After strorage in air for a period of time, Li(Ni0.8Co0.1Mn0.1)0.83(Ni1/3Co1/3Mn1/3)0.17O2can obviously alleviate the adsorption of CO2and H2O. The initial specific capacity, cycle performance and rate capacity of the coated sample are all superior to the bare sample.CaF2is uniformly coated on the surface of LiNi0.8Co0.1Mn0.1O2in ethyl alcohol. The test of a range of coating amount of CaF2shows, the larger the coating amout, the lower the initial specific capacity. When the amount of CaF2is0.5wt.%, the initial capacity is190mAh g-1at0.1C. After100cycles at2C, the capacity retention of CaF2-coated LiNi0.8Co0.1Mn0.1O2is90.1%, which is superior to the bare LiNi0.8Co0.1Mn0.1O2.