Synthesis And Performance Research Of Core-shell High Nickel Cathode Materials For All-solid-state Lithium-ion Battery

Traditional lithium-ion batteries adopt liquid organic electrolyte,existing serious security risks.All Solid State lithium-ion battery?ASS-LIB?employing solid electrolyte are capable of completely solving those safety issues.However,the electrochemical performance of ASS-LIB is still not up to the requirements of current practical standard,which result from their own defects such as low ion conductivity of solid electrolyte,“interface problem”and so on.At present,sulfide electrolyte possessing high ion conductivity has been up to 2.5×10^-2S cm^-1 reaching the level of that of liquid electrolyte completely.Cathode material is one of the pivotal factors affecting the performance of ASS-LIB,the interface compatibility between cathode materials and solid electrolyte is not well so that"interface problems"are easy to form.In the area of cathode materials,there are two methods to improve performance of ASS-LIB,which include the preparation of high-performance cathode material and to the improvement of cathode/solid electrolyte interface compatibility.In the reported literature,interfacial compatibility between LiCoO₂ and sulfide electrolytes are better than other oxide cathode materials.LiNi_0.8Co_0.1Mn_0.1O₂ exhibits high capacity in lithium ion batteries adopting liquid electrolyte.According to the principle of complementary function of core-shell structure,cathode material with core-shell structure is designed.Specifically,LiNi_0.8Co_0.1Mn_0.1O₂ serves as for core material,LiCoO₂ for shell.The cathode material is employed in ASS-LIB so as to achieve high capacity and high cycle performance simultaneously.Cathode materials with different core-shell ratio are synthesized by co-precipitation and high temperature solid-phase reaction.The core-shell ratio of hydroxide precursors can be precisely controlled by co-precipitation method,which is good for controlling the morphology of the materials.Precursors mixed Li₂CO₃ are sintered under O₂ flow forming oxide cathode material with core-shell structure.After assembling the battery,the performance of cathode materials is compared.The materials with optimum core-shell ratio is Li[(Ni_0.8Co_0.1Mn_0.1)_0.9Co_0.1]O₂,which possesses high discharge specific capacity and better cycle performance.Based on the above experimental results,in order to further improve the battery performance,the positive electrode material is modified by means of coating.From cathode/solid electrolyte interface this direction,a"buffer layer"is introduced between cathode material and solid electrolyte so as to ameliorate the interfacial compatibility of cathode/solid electrolyte.Li[(Ni_0.8Co_0.1Mn_0.1)_0.9Co_0.1]O₂ selected for modification was coated with two kinds of"buffer layer"material including 3wt%of Li₄Ti₅O₁₂,LiNbO₃by using the sol-gel method on the surface of Li[(Ni_0.8Co_0.1Mn_0.1)_0.9Co_0.1]O₂.After comparing the electrochemical properties of those three materials,it was found that the properties of the coated materials are superior to those of Li[(Ni_0.8Co_0.1Mn_0.1)_0.9Co_0.1]O₂,which demonstrates that coating does be beneficial to ameliorate“interface problem”.What's more,the coating effect of LiNbO₃ is superior to that of Li₄Ti₅O₁₂ due to the high ionic conductivity of LiNb O₃.