The Study On The Lithium Rich Layered Oxides For Lithium Ion Battery

To meet the increasing demand for lithium-ion batteries,new cathode for li thium-ion batteries has drew more attention.Li-rich layered oxides?LLOs?Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ supplying high specific capacity and lithium manganese pho sphate?LiMnPO₄?with high voltage are both considered as promising cathode materials for next generation lithium-ion batteries.However,owing to the defec ts and difficulties in commercialization,the improvement of electrochemical pro perties of these materials are still needed.By adjusting preparation condition,type of additive and amount of suface coating within sol-gel method,synthesis of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ with better electrochemical performance is mainly introduced in this paper.Using citric aci d as the chelating agent,the LLOs with different particle sizes were prepared by sol-gel method under different calcination temperatures and aging times.The results indicate that the particle sizes grow with the increase of calcination te mperature,and first increase then decrease with the prolonging of aging time.When the calcination temperature is 850 °C and ages for 10 days,the material presents the best electrochemical performance,especially rate performance.Wh en the Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ electrode was charged /discharged at 0.1 C betw een 2.0-4.8 V,the discharge capacity is still 206.7 mA h g-1 after 60 cycles a nd the discharge capability is 125.6 mA h g-1 at 2 C.To make the aging time of sol-gel method required short,three different ty pes of surfactants were added to the sol system,resulting in different shapes a nd sizes of particles.When added ammonium dodecylbenzenesulfonate?ADBS?to the sol,the the particle size of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ material is the fine st,and has a single-layer sheet-like structure consisted by the cubic particles.As a better layered crystal structure and special appearance,this sample has th e best electrochemical performance,especially in discharge performance and cy cle stability.Within the range 2.0-4.8 V voltage charge-discharge rate of 1 C,discharge capacity is 158.3 mA h g-1 and capacity retention rate is 87.7% after50 cycle.The discharge capacities are 281.3 and 121.9 mA h g-1respectively at 0.1 C and 2 C.With the above preparation method,the lithium-rich layered oxides with s maller particle size and good electrochemical performance can be prepared.But there are still some gaps in cycling stability relative to other cathode material s.To solve this problem,a series Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ materials with differe nt YOF coating amount were prepared.It is found that when coated with an a ppropriate amount of YOF?2 wt%?,the electrochemical properties of the mater ial is improved.2 wt% YOF coated sample possesses greater discharge capacit y of 150 mA h-1at 1 C than the uncoated material and capacity retention rate is 85.6% after the 100 cycles.In addition,explores of combining lithium rich layered composite material Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ with lithium manganese phosphate LiMnPO₄,the prepar ation of LiMnPO₄ with special morphology and new phosphate cathode materia ls have also been done in this paper.