Preparation And Perporformances Investigation Of Cathode Material LiCoPO₄ As Cathode Material For Lithium-ion Batteries

Polyanion cathode LiCoPO₄ material has been received a great attentions due to its high energy density and thermostability.However,its lower conductivity and worse cycleability become "bottleneck" and impede its further research and application.Synthesis method has important effects on the crystal structure,morphology,particle size and distribution of resultant material,thus the electrochemical properties would be also affected.In this paper,the investigation of the recently research on LiCoPO₄ material has been reviewed.Based on the reviews,we have firstly investigated systematically the effects of various synthesis method,such as sol-gel method,hydrothermal method,spray drying method and polymer method,on on the crystal structure,morphology,particle size,distribution and electrochemical properties of resultant LiCoPO₄ material.The optimal synthesis conditions are investigated.The novel LiCoPO₄/Li₄Ti₅O₁₂ full cells are firstly assembled and the electrochemical properties of LiCoPO₄/Li₄Ti₅O₁₂ full cell are also investigated.Besides,the effects of different ratio between the cathode material and anode material on the LiCoPO₄/Li₄Ti₅O₁₂ full cells have been investigated.At last,the effects of charge mode and mixture ratio between LiNi0.5Mn1.5O4 and Li CoPO4 on the electrochemical performances of LiCoPO₄ cathodes have also been firstly investigated.The solid state method is used to prepare LiCoPO₄ material.After investigations of the different synthesis factors,the optimal conditions are obtained and the synthesis parameters are shown in the following: the preheating temperature and time are 500 oC and 9 h,the calcination temperature and time are 750 oC and 12 h.The resultant LiCoPO₄ has shown the average working voltage of 4.71 V?vs.Li/Li+?at the discharge rate of 0.1 C.This material delivers the initial discharge capacity of 82 mAh g-1.After 30 cycles,the discharge capacity can retain 34 m Ah g-1.The fitting of EIS results indicates that LiCoPO₄/Li has lower electrochemical reaction resistance?145.2??.The sol-gel method is used to prepare LiCoPO₄ material.After investigations of the different synthesis factors,the optimal conditions are obtained and the synthesis parameters are shown in the following: the molar ratio of chelating agent and cobalt acetate is 1:,the preheating temperature and time are 350 oC and 6 h,the calcination temperature and time are 600 oC and 12 h,the.The resultant Li1.02CoPO4 has shown the average working voltage of 4.69 V?vs.Li/Li+?at the discharge rate of 0.1 C.This material delivers the initial discharge capacity of 110 mAh g-1.After 30 cycles,the discharge capacity can retain 50 mAh g-1.The fitting of EIS results indicates that LiCoPO₄/Li has lower electrochemical reaction resistance?150.2??.The hydrothermal method is used to prepare LiCoPO₄ material.After investigations of the different synthesis factors,the optimal conditions are obtained and the synthesis parameters are shown in the following: the hydrothermal temperature and time are 180 oC and 12 h,the calcination temperature and time are 500 oC and 8 h.The resultant LiCoPO₄ has shown the average working voltage of 4.73 V?vs.Li/Li+?at the discharge rate of 0.1 C.This material delivers the initial discharge capacity of 89 mAh g-1.After 30 cycles,the discharge capacity can retain 35 mAh g-1.The fitting of EIS results indicates that LiCoPO₄/Li has lower electrochemical reaction resistance?121.2??.The spray drying method is used to prepare LiCoPO₄ material.After investigations of the different synthesis factors,the optimal conditions are obtained and the synthesis parameters are shown in the following: the calcination temperature and time are 550 oC and 6 h.The resultant Li CoPO4 has shown the average working voltage of 4.73 V?vs.Li/Li+?at the discharge rate of 0.1 C.This material delivers the initial discharge capacity of 99 mAh g-1.After 30 cycles,the discharge capacity can retain 42 mAh g-1.The fitting of EIS results indicates that LiCoPO₄/Li has lower electrochemical reaction resistance?175.8 ??.The polymer method is firstly used to prepare LiCoPO₄ material and the effects of synthesis conditions like acrylamide amount,ammonium persulfate amount,calcination duration and calcination temperature on the electrochemical properties of resultant LiCoPO₄ material are studied.After investigations of the different synthesis factors,the optimal conditions are obtained and the synthesis parameters are shown in the following: the optimized powder with the best electrochemical performance is obtained at an acrylamide and reactants mass ratio of 0.4,ammonium persulfate and monomer mass ratio of 0.02 and calcined at 550 oC for 12 h.The resultant LiCoPO₄ has shown the average working voltage of 4.76 V?vs.Li/Li+?at the discharge rate of 0.1 C.This material delivers the initial discharge capacity of 126 mAh g-1.After 30 cycles,the discharge capacity can retain 58 mAh g-1.The fitting of EIS results indicates that LiCoPO₄/Li has lower electrochemical reaction resistance?77.6 ??.LiCoPO₄ and Li₄Ti₅O₁₂ powers were successful synthesized by polymer method and solid reaction method,respectively.The Li CoPO4/Li₄Ti₅O₁₂ cell systems were firstly constructed and the electrochemical performances of the full cells have been investigated in detail.Besides,the effect of the theoretical capacity matching ratio of cathode and anode was studied in the LiCo PO4/Li₄Ti₅O₁₂ cell system on the electrochemical performances.The two pairs of voltage plateaus in the charging and discharging process in Li CoPO4/Li₄Ti₅O₁₂ cell confirm the two-step lithium extraction/ insertion process occurring in the cell.As the ratio of cathode and anode increase,the initial discharge capacity and cycle performance of LiCoPO₄/Li₄Ti₅O₁₂ cell firstly increase until the ratio is 1.4,then decrease.The initial discharge capacity of LiCoPO₄/Li₄Ti₅O₁₂ cell?ratio=1.4?at 0.1 C is 136 mAh g-1.After 10 cycles,the capacity can retain 127 mAh g-1,which keep an capacity retention of 93.7%.The LiCoPO₄/Li₄Ti₅O₁₂ cell has a lower electrochemical reaction resistance?79.2 ??.At last,the effects of charge mode and mixture ratio between LiNi0.5Mn1.5O4 and LiCoPO₄ on the electrochemical performances of LiCoPO₄ cathodes have also firstly been investigated.The results show that the LiCoPO₄ cathode material can deliver higher discharge capacity and a better cycle ability in 3.0-5.1 V at constant current charge mode.LiNi0.5Mn1.5O4 material also has been prepared via polymer method and shows a high working voltage of 4.7 V?vs.Li/Li+?at the discharge rate of 0.1 C.?1-x?Li CoPO4·x LiNi0.5Mn1.5O4 can obtain a better electrochemical performances with increasing of x.Besides,the high working voltage still retain at 4.7 V?vs.Li/Li+?.Thus,our work has an important role in research,development and industrialization of high voltage electrode materials.