Preparation And Modification Of Layered And Tunnelled Vanadate As Cathode Material For Lithium Ion Battery

Developing novel cathode material for lithium ion battery with high capacity and low cost is one of the main trend in the future,which is also the key to solve the bottleneck for high-energy lithium-ion battery development.Among numerous positive electrode materials,vanadate compound has the ability to insert and extract multiple lithium ion reversibly,which deliver higher specific capacity.Meanwhile,the V element has a rich of valence state,and the derived vanadium-based compound display more special crystal structure.The layered V₂O₅ and LiV₃O₈ is the representative of vanadate compound,which has poor electronic conductivity and poor structural stability as cathode material of lithium ion battery.Different from the layered structure,?-M_xV₂O₅?M=Li,Na?possess special 3D tunnelled crystal structure,which has high structural stability under high Li uptake,while the related study of the synthesis and the modification of ?-M_xV₂O₅ was rare.This paper focused on the synthesis and electrochemical behavior of layered LiV₃O₈ and tunnelled vanadate bronze M_x V₂O₅?M=Li,Na?material,investigated the influence of different calcination temperature on the morphology,phase structure and electrochemical properties.Meanwhile,the surface modification of tunnel type vanadate nanorods was carried out with conductive graphene and ion conductor La PO₄,the main work is listed as follows:The?-Li_xV₂O₅ cathode exhibited higher capacity retention ratio under subzero temperatures than at room temperature.The discharge capacity under-40? at current density of 30 mAg^-1upon 100 cycles maintain 109.7 mAhg^-1,with the corresponding capacity retention of 88.6%,while the capacity retention under room temperatuer was 55.0%.Based on the calculation results derived from electrochemical impedance spectroscopy tested under different charge and discharge states and under different temperature,the?-Li_xV₂O₅ electrode exhibit almost the same activation energies for charge-transfer and solid-state lithium diffusion under different charge and discharge states,suggesting that the electrochemical process dynamics of the?-Li_xV₂O₅ electrode is controlled by the sluggish charge-transfer kinetics as well as solid-state ionic diffusion.?-Na_0.33V₂O₅ nanorods were prepared via a facile soft chemistry strategy using Na⁺intercalated?NH₄?_0.5V₂O₅ nanosheets as precursor,which was transformed into?-Na_0.33V₂O₅ nanorods after calcination.Based on X-ray diffraction,Fourier transform infrared spectra and scanning electron microscope analysis,the formation mechanism of?-Na_0.33V₂O₅ nanorods was proposed,which involved cation co-intercalation,crystal structure slipas well as phase transformation process induced by cation release.The calcination temperature play significant influence on the electrochemical behavior of?-Na_0.33V₂O₅ positive electrode.Constant current charge-discharge test results show that?-Na_0.33V₂O₅ nanorods calcined at 600^oC exhibited good stable cycling behavior,which deliver an initial discharge specific capacity of 223.9 mAhg^-1at the current density of 60 mAg^-1,and the discharge specific capacity remain 182.1 mAhg^-1after 50 cycles with capacity retention as as high as 81.3%.rGO/?-Na_0.33V₂O₅ composite materials was prepared via freeze-dried method combined with low temperature calcination.Constant current charging and discharging test results show that the 10-rGO/NVO samples deliver an initial discharge capacity of 222.9 mAhg^-1at the current density of 60 mAg^-1,and the discharge specific capacity can maintain at 196.1 mAhg^-1after 100 cycles with the capacity retention as high as 88.0%,which was much higher than the unmodified?-Na_0.33V₂O₅ electrode materials?68.9%?.EIS and CV results under different scanning speeds show that the introduction of r GO significantly reduces the electrochemical reaction resistance and improve the lithium ion diffusion coefficient.rGO/LaPO₄/?-Li_xV₂O₅ composite materials was obtained by freeze drying.Electrochemical test results show that rGO/La PO₄/?-Li_xV₂O₅ exihibit significantly improved electrochemical performance compared with the?-Li_xV₂O₅ materials.rGO/La PO₄/?-Li_xV₂O₅ composites display a high capacity retention of 84.1%under the current density of 60 mAg^-1after 100 cycles,while the uncoated?-Li_xV₂O₅electrode exhibit a low capacity retention of only 37.3%.The EIS results under different Li⁺intercalated states show that electrochemical reaction resistance of rGO/La PO₄/?-Li_xV₂O₅ electrodes decreased significantly during the lithiation process when compared with the unmodified?-Li_xV₂O₅ electrode.The lithium ion diffusion coefficient of rGO/LaPO₄/?-Li_xV₂O₅ electrode materials was about two orders of magnitude higher than the unmodified?-Li_xV₂O₅ electrode under the low lithiation state.The XRD and SEM results before and after cycles show that the crystal structure and morphology were well-maintained after 100 times of charging and discharging for the surface modified electrode.LiV₃O₈ microrods were prepared by simple one-step lithification combined with calcination treatment.The calcination temperature has great influence on the morphology and electrochemical performance of LiV₃O₈ electrode.LiV₃O₈mirocrods was obtained when treated at 600?,which delivers an initial discharge capacities of 212.8 mAhg^-1at current density of 60 mAg^-1with high capacity retention of 80.5%after 100 cycles,and excellent rate capability with discharge specific capacity of 178.9 mAhg^-1and 147.8 mAhg^-1was exhibited at current density of 150 mAg^-1and 300 mAg^-1.The outstanding cycling performance of LiV₃O₈ electrode can be attributed to the balance between moderate particle size and high crystallinity as well as the excellent structural stability.?-Li_xV₂O₅/LiV₃O₈bi-phase composite microrods would obtained when increasing the addition of H₂O₂in the process of precursor preparation,and calcined at different temperatures.Calcination temperature play significant influence on the morphology,structu re and phase composition of the product.The?-Li_xV₂O₅ phase content reach 20.4%in the product when calcinated at 600?.Electrochemical test results show that Li-V-O600bi-phase electrode showed the highest initial discharge specific capacity of 244.2mAhg^-1at current density of 60 mAg^-1,while there still exists obvious capacity fading for the bi-phase electrode.The EIS results under different lithium insertion/extraction potential states show that the capacity decay is associated with larger interfacial film resistance,which would makes the lithium ion migration more difficult between the electrolyte and electrode interface,leading to the capacity attenuation.