| At present,people's lives are seriously disrupted as the problems such as energy shortages and environmental pollution are becoming more and more serious.People are seeking to develop and research new energy sources to reduce environmental pollution and achieve sustainable development because of this problem.Lithium-ion battery is an efficient energy storage technology with high energy density and good cycle stability.LiTi2(PO4)3is a fast ion conductor with NASCION structure as a kind of lithium ion battery material.It has a suitable lithium deintercalation potential and a stable charging and discharging platform.When LiTi2(PO4)3is used as a negative electrode assembly combined to metal lithium,the electronic conductivity of the material is not high,which is easy to cause serious polarization of the material during charging and discharging procedure.Carbon coating and element doping can improve ion conductivity.In this paper,Li3Mn Ti(PO4)3?Li5Mn0.1Ti0.95(PO4)3?LiYbxTi2-1.5x(PO4)3and LiCexTi2-1.5x(PO4)3were prepared by combination of spray drying method and high temperature sintering method.The materials were characterized by XRD,SEM,TEM,BET,TGA,EDS,XPS,CV,et al.LAND tests were performed on the synthesized samples,and the charging and discharging platform,rate performance,cycle performance of the samples.(1)Carbon-coated Li3Mn Ti(PO4)3was prepared by using LiH2(PO4)3,Mn(CH3COO)2·4H2O as raw materials,C6H18N2O8Ti as the titanium source and glucose or citric acid as carbon sources.The influence effect of temperature on the properties of synthetic materials was studied.The results showed that the Li3Mn Ti(PO4)3material has the best morphology and the best electrochemical performance when the carbon source is citric acid and the sintering temperature is 700?.The synthesized material was assembled as the positive electrode in a lithium battery.The current-voltage(CV)curve exhibited has three sets of stable redox peaks.The specific capacity of the first discharge cycle at a high current density(500 mA/g)is 56 mAh/g.After 500 cycles,the capacity of Li3Mn Ti(PO4)3still maintain 99.2%and the capacity attenuationis is only 0.8%.The material exhibits a specific capacity of 54.4 mAh/g(500 mA/g),when a full battery is assembled with the synthesized material as the negative electrode.(2)Carbon-coated Li5Mn0.1Ti0.95(PO4)3was prepared by using CH3COOLi·H2O,LiH2(PO4)3,C6H18N2O8Ti and Mn(CH3COO)2·4H2O as raw materials and citric acid as the carbon source.The results indicated that the Li5Mn0.1Ti0.95(PO4)3material at a synthesis temperature of 700? has the best electrochemical performance in the two electrolyte systems.In a lithium battery with organic electroly system,Li5Mn0.1Ti0.95(PO4)3still possessed a specific capacity of 68.7 mAh/g after 500 cycles at a current density of 500 mA/g,and a specific capacity of 62.7 mAh/g in the first cycle and a specific capacity of 60.8 mAh/g after1000 cycles at a current density of 1000 mA/g.In a full battery with aqueous electroly system,the specific capacity of the material has always been maintained at about 59 mAh/g,and it has only decayed by 2%in the process.(3)Carbon-coated LiYbxTi2-1.5x(PO4)3/C was prepared by using LiOH as the lithium source,C6H18N2O8Ti as the titanium source,NH4H2PO4as the phosphate source,and Yb(NO3)3·5H2O as the Yb source to study the influence of the material proportion,source type and sintering temperature of doping elements on the material properties.The assembled lithium battery holds the best electrochemical performance,when the doping ratio of Yb is0.04 and the synthesis temperature is 700?.At a current density of 1000 mA/g,the initial discharge specific capacity is 143 mAh/g.After 1000 cycles,there is still a specific capacity of 133 mAh/g.The specific capacity of the pure phase of LiTi2(PO4)3is 103 mAh/g at a current density of 1000 mA/g in the first cycle.After 1000 cycles,there is a specific capacity of 102 mAh/g.Compared with carbon-coated LiTi2(PO4)3,carbon-coated LiYbxTi2-1.5x(PO4)3material has higher specific capacity and better cycle performance.(4)Carbon-coated LiCexTi2-1.5x(PO4)3was synthesized by spray drying method and high temperature sintering method using Ce(NO3)3·5H2O as Ce source.The proportion of impurities and the sintering temperature of the material affect the properties of the material.The lithium storage performance of the carbon-coated LiCexTi2-1.5x(PO4)3material was tested.The results showed that the LiCexTi2-1.5x(PO4)3/C material can still maintain 99%coulombic efficience after 1000 cycles at a current density of 1000 mA/g.Compared with the carbon-coated LiTi2(PO4)3material,the discharge specific capacity of the carbon-coated LiCexTi2-1.5x(PO4)3is 25 mAh/g higher and the capacity retention rate is 6%higher.The superior performance of the material may be attributed to the expansion of the path of lithium ion deintercalation because of the doped-Ce. |
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