Morphology Investigation On Ni-Co-Mn Ternary Cathode Material By Hydrothermal Method For Lithium Ion Batteries

With the advantages of high energy density,long cycle life,low price,friendly environment and no memory effect,rechargeable lithium ion batteries（LIBs）have been recognized as the most promising portable power source,dominating portable electronics market.Furthermore,they also have a great development prospect in the frontier,such as medical,military and aerospace.Recent years,the energy crisis and the global environmental pollution are becoming more and more serious.Along with the aggravating global warming and energy crisis,there has been a strong desire using LIBs to power future transportation such as pure electric vehicle（EVs）,hybrid electric vehicles（HEVs）,and plug-in HEVs.The lower energy density and shorter lifetime of cathode materials limit the application of LIBs in electrified vehicles.The ternary cathode material Li（Ni0.33Co0.33Mn0.33）O2 has a huge advantage,higher specific capacity than lithium iron phosphate,lower price and higher performance than lithium cobalt oxide.However,it also has been identified with some defects,e.g.,the cation mixing of Li⁺（0.76?）and Ni²⁺（0.69?）between the Li layers and the transition metal layers.This hinders Li⁺diffusion and leads to the deterioration of electrochemical performance under high rates and some irreversible side reactions with electrolytes under high cut-off voltages.Many researched illustrate that different preparation methods have great influence on the morphology of cathode materials,which will affect the crystallization,specific surface area,cation mixing degree and structural stability,so the morphology-control has become a hot spot in the synthesis of ternary cathode materials.In this paper,the hydrothermal method has been used to prepare the ternary precursor,with special morphology,optimizing the solvent volume ratio of water and glycol and calcination temperature after mixing with lithium source,successfully obtained the ternary cathode materials with excellent electrochemical performance.In the follow-up study,we also adjust the solvent in hydrothermal reaction and obtain many precursors with different morphology.In ethylene glycol（EG）/water solvent system,the pinecone-liked（Ni0.33Co0.33Mn0.33）CO3is obtained in V EG:V water=1:1 solvent system.The final Li（Ni0.33Co0.33Mn0.33）O2 products is synthesized after mixing with lithium source and the subsequence step calcination process in850℃。Its has a uniform particle size with a length and a width in range of 3⁴ and 1²μm,respectively,well crystallinity,lower cation mixing degree and most excellent electrochemical performance.It exhibits a high initial discharge capacity of 161.3 mAh g^–11 at 0.2 C under 4.3 V cut-off voltage,and a capacity retention of⁹5%after 80 cycles.In addition,electrochemical testing also disclosed an excellent rate capability of the pinecone-liked Li（Ni0.33Co0.33Mn0.33）O2sustaining a capacity of 161.6,154.7,149.8,142.4,和159.4 mAh g^–1 at a current density of0.2 C,0.5 C,1 C,2 C and 0.2 C,respectively.When the charge and discharge cut-off voltage is increased to 4.6 V,the discharge specific capacity is increased to 199.0 mAh g^-1 at 0.2C rate current.In addition,changing the solvent of hydrothermal process can obtain various（Ni0.33Co0.33Mn0.33）CO3 precursors with different morphology.In this work,XRD,SEM,ICP-AES,TEM,CV,EIS etc.were uesd to characterize the structure and performance of the materials,revealing the connection of morphology and performance.