Preparation And Electrochemical Performance Of Titanium/Vanadium-based Phosphates Electrode Material

Phosphate materials have attracted increasing attention due to their excellent electrochemical performance and versatile structure,and are considered as promising energy storage electrode materials.However,its low conductivity,poor rate performance and cycle life limit its application,especially at high rates,these problems appear to be particularly prominent.For the purpose of exerting greater advantages of phosphate electrode material in energy storage and conversion applications,various strategies,such as composing with carbon,reducing the size,and doping elements,have been carried out for improving the electron transport kinetics and electrochemical performance.The main contents and research results are summarized as follows:1.Self-supporting and flexible carbon nanotube/Carbon-coated Nitrogen-doped LiTi2(PO4)3(CNT/LTP@C-N)hybrid films are manufactured via vacuum filtration.LTP@C-N is entangled into CNT networks to build a 3D conductive network.Such hybrid electrodes endow large surface area,enhance the overall conductivity of these composite electrodes,and facilitate the electrolyte infiltration;therefore,resulting in advanced electrochemical properties.Typically,the CNT/LTP@C-N electrodes afford a high initial discharge capacity of 143 mAh g-1 at 1 C,considerable rate property(85 mAh g-1 at 30 C),and good cyclability(87.3%capacity retention in 1500 cycles at 5 C)in non-aqueous electrolyte.When utilized as anodes for aqueous lithium-ion batteries(ARLBs),high energy density(67 Wh kg-1 calculated from the mass of anode and cathode active materials)and long term cycling stability(capacity retention of 70.2%over 1000 cycles at 3 C)can be achieved.2.NASICON-structured NaTi2(PO4)3(NTP)with three-dimensional open framework and appropriate negative voltage window is a significant anode material for sodium-ion batteries,whereas its intrinsic low electronic conductivity severely degrades the performance of SIBs.Herein,a fluorine-doped NTP embedded in porous N-doped carbon nanofiber(NTPF0.1-CNF)was prepared via electrospinning technique and subsequent carbonization treatment.Benefiting from favorable synergistic effect of a 3D porous carbon structure and F-doping,the resulting NTPF0.1-CNF film electrode delivered outstanding rate performance(77.8 mAh g-1 at 40 C)and specific capacity(131.3 mAh g-1 at 1 C)as well as cycle stability(95.7%of initial capacity after 10000 cycles at 10 C).Coupling with a Na3V2(PO4)3 cathode,the SIB full cell exhibit durable and practical sodium storage performance.In addition,a LiMn2O4//NTPF0.1-CNF Li/Na hybrid ion battery delivers 86.7%capacity retention after 1500 cycles at 5 C.3.Lithiated transition metal phosphates with large theoretical capacities have emerged as promising cathode materials for rechargeable lithium-ion batteries.However,the poor kinetic properties caused by their low intrinsic electronic and ionic conductivity greatly hinder their practical applications.In this work,a feasible electrospinning/annealing avenue for the construction of 1D Li3V2(PO4)3 carbon nanofibers in situ coated with carbon nanoshell(LVP-CNF)as self-standing cathode for Li-ion batteries and hybrid Li/Zn-ion batteries(HLZIBs)is reported.For Li-storage,this electrode exhibits extraordinary electrochemical performance:a high capacity(129.5 mA h g-1 at 1 C),a superior rate capability(101.3 mA h g-1 at 30 C),and ultralong cyclability(89.3%capacity retention after 2000 cycles at 5 C).Moreover,the fascinating electrochemical performance of LVP-CNF remains stable when used as the cathode material for a full cell,suggesting the fiber-shape LVP-CNF as one of the most promising applicable materials for Li-ion batteries and HLZIBs.4.Na3V2(PO4)3,a promising cathode candidate for sodium ion batteries(SIBs),is restricted by the poor intrinsic conductivity and sever volumetric shrinkage.Herein,a combined strategy of carbon coating and Cr3+ doping is proposed via a facile electrospinning method.The substitution of Cr3+ to V3+in the NVP structure significantly enhanced the structural stability of the electrode,while the uniform and thin carbon layer improved the electrical conductivity.Meanwhile,the coated carbon layers and enwrapped CNFs construct an effective conductive framework for accelerated electronic migration.The twining CNFs can inhibit the growth of the sintered grains,reducing the particle size to provide shortened pathway for the migration of Na+.Consequently,the optimized Na3V1.7Cr0.3(PO4)3-CNF(NV1.7Cr0.3PCNF)material achieved an excellent performance of 115.1 mAh.g-1 at 1 C and a highcapacity retention ratio of 91.5%even after 2000 cycles at 5 C in a half cell.Moreover,the NV1.7Cr0.3P-CNF presents competitive electrochemical property and potential applicability in Na-ion full batteries and hybrid Na/Zn-ion batteries.