Large-scale,Controllable Synthesis And Electrochemical Performance Regulation Of Vanadium-based Electrode Materials

In this dissertation,we focus on the aim to promote the commercialization process of vanadium-based electrode materials.Taking advantages of spray-drying in synthesizing electrode materials,we obtain the vanadium-based electrode materials with high capacity,excellent rate performance and outstanding cycling performance on the basis of output guaranty.Moreover,we explore the applications of vanadium-based electrode materials in the fields of sodium-ion battery and polymer-based solid-state lithium metal battery.The research results summarized are shown in the following text:（1）A spray-drying route was adopted to prepare Na₃V₂（PO₄）₃ electrode material in the large-scale.Thinking of the two factors of electrochemical performance and production efficiency,the optimum process parameters were determined.Moreover,we designed and assembled Na₃V₂（PO₄）₃/Na Ti₂（PO₄）₃（NTP）Na-ion full battery,accompanying with the characterization of electrochemical performance.It can be sure that the NVP/NTP Na-ion full battery possesses excellent electrochemical reversibility.To promote the commercialization process of Na₃V₂（PO₄）₃（NVP）as cathode material,Furthermore,for the first time,practical NVP/Hard carbon（HC）sodium-ion pouch cells were designed and assembled,which display excellent discharging property under high and low temperature,high rate performance and excellent thermal stability.Moreover,puncturing experiment results can further prove the excellent safety performance of NVP/HC pouch cells.Therefore,the large-scale,synthesis technology of Na₃V₂（PO₄）₃ cathode material for sodium-ion battery has been nearly mature,and its development will be beneficial to the commercialization of sodium-ion battery.（2）For developing the higher energy density of sodium-ion battery,it is depending on exploring the cathode material with the high average discharge potential.We synthesized Na₃V₂（PO₄）₂F₃/C（NVPF/C）cathode material in the kilogram class by a spray-drying method.It is proved that the spherical NVPF/C electrode materials with outstanding electrochemical performance can be obtained by using the deionized water as ball-milling solvent and carrying out the pre-sintering process.Moreover,we designed and assembled NVPF/NVP all vanadium-based sodium-ion full battery,and improve the electrochemical performance by pre-sodiation in the NVP anode.It can be demonstrated that NVPF cathode combined with NVP pretreated by galvanostatic discharge to 80%of the total capacity in half cells could exhibit the optimized sodium-ion storage performance.Besides,NVPF/HC sodium-ion full batteries were designed and assembled,and we probed into the effect of the electrochemical performance of sodium-ion full batteries by using HC with the different degrees of pre-sodiation.According to the characterization of electrochemical performance,it suggests that the sodium-ion full batteries of NVPF-HC（D100,100%DOD）can provide the optimal sodium-ion storage performance,and another conclusion can be obtained that controlling the cut-off voltage（COV）of HC pretreated can affect the electrochemical performance of the corresponding HC-based full Na-ion cells.The moisture contents of different cathode materials were measured by using Karl Fischer Titrator,and it indicates that anode materials addressed by pre-sodiation can eliminate maximumly the negative effect of moisture on the electrochemical performance of vanadium-based sodium ion full battery.（3）Except the strategy of addressing anode materials by pre-sodiation,it is proved that the electrode collocations of vanadium-based cathode and graphite or hard carbon（HC）anode addressed by the 100%DOD（depth of discharge）pre-lithiation can still provide the optimized sodium-ion storage performance.Such finding gives us a new understanding that graphite can be applied in the field of sodium-ion battery.Besides,it can be found that sodium ion battery containing HC anode pre-lithiated by galvanostatic discharge to 100%of the total capacity in half cells and vanadium-based cathode possess the better cycling performance,which may be explained that the SEI film formed in lithium ion half battery is more stable than that from sodium ion half battery（4）For solving the existing safety question of liquid lithium metal battery,developing the polymer-based solid-state lithium metal battery has become a feasible option.We adopted a spray-drying route to synthesize a new composite of CNTs/Li V₃O₈/Y₂O₃.A proof by facts is that CNTs/Li V₃O₈/Y₂O₃ composites with outstanding lithium-ion storage performance can be obtained by using the deionized water as ball-milling solvent,carrying out the sintering process at 300°C and introducing 2%Y₂O₃into host material.For putting Li V₃O₈ into the practical application,we designed all-solid-state Li||PEO-Li Cl O₄||Li V₃O₈rechargeable lithium metal battery,in which CNTs/Li V₃O₈/Y₂O₃ composite could provide the excellent electrochemical performance.By conducting EIS measurement,it can be proved that the open-circuit potential（OCP）is negatively correlated with R_SPEunder different operation temperature.Moreover,it is also demonstrated that R_ct is negatively correlated with the operation temperature.Remarkably,for M-LVO-Y-2 electrode,the energy density estimated to be 779.4 W h Kg^-1 is far higher than other cathodes applied in solid-state lithium metal battery reported in the literatures.All in all,the CNTs/Li V₃O₈/Y₂O₃ composite exhibiting excellent electrochemical performance could be a successful option for practical solid-state lithium metal battery applied in harsh environment with high temperature.