Application Of Transition Metal Sodium (Pyro-) Phosphate In Sodium-ion Battery

With the development and progress of society,the demand of energy is increasing.Lithium-ion batteries are widely used in various mobile devices and electronic products because of their high energy density and power density.However,the shortage of lithium resources and rising prices have seriously hindered the further development of lithium-ion batteries.Therefore,the development of low-cost,high-performance energy storage systems is urgent.The content of sodium in the earth's crust?2.74%?is more than that of lithium.And the standard electrode potential of sodium?-2.71 V?is very close to lithium,the operating voltage is controllable,so it has become one of the powerful substitutes for lithium-ion batteries.The cathode materials of sodium ion batteries mainly include transition metal oxides,polyanionic compounds,Prussian blue and its analogues,and organic compounds.Polyanionic compounds become ideal materials for the cathode of sodium ion batteries due to their unique open frame structure,excellent thermal stability,simple synthesis and low cost.However,the poor conductivity of polyanionic compound limits its practical application.Therefore,improving the conductivity and electrochemical performance of polyanionic materials has become a hot research topic.In addition,many researches on sodium-ion batteries are mainly focused on sodium-ion half batteries,but relatively few studies on full batteries.In order to promote the industrial production of sodium ion batteries and accelerate the pace of sodium ion batteries from laboratory to practical applications,the research of sodium ion batteries is urgent.Based on this,this paper aims to synthesize the cathode material of sodium ion battery through low cost and explore their application in sodium ion full battery.The main research contents and results are as follows:1.In this work,3D honeycomb-like carbon-coated Na₇Fe_4.5?P₂O₇?₄nanocomposites are fabricated by a simple sol-gel method and used as cathode materials for the sodium-ion batteries.The electrochemical results reveal that the 3D hierarchically porous Na₇Fe_4.5?P₂O₇?₄@C nanocomposites provide a high reversible specific capacity and a good rate performance.After even 100 cycles at 1 C,85%of the capacity retentions can be maintained in half batteries.In addition,the material still maintains excellent cycling performance and stability in full batteries.The good electrochemical performance thanks to the porous structure and carbon coating.The porous structure can be completely wetted by the electrolyte,which contributes to Na⁺de/intercalation.After coating carbon,the capacity and rate performances of Na₇Fe_4.5?P₂O₇?₄ composites were greatly improved.2.Na₃TiV?PO₄?₃@C nanoparticles are synthesized by a simple ball-milling method and studied for cathode of sodium-ion batteries.The half battery exhibits a specific capacity of about 115 mA h g^-1 and possesses good cycle stability and rate performance.In addition,the materials have been studied for the performance of symmetrical battery and full battery.In a symmetrical battery,the first circle still possesses acceptable capacity,but the stability is poor and the attenuation is fast.However,sodium-ion full battery exhibits an initial specific capacity of 200 mA h g^-1.Overall,the Na₃TiV?PO₄?₃material is coated with carbon,which improves the electrical conductivity and the electrochemical performance.But the instability of the material itself causes its attenuation to be greater than that of the same type of material.3.Na₂TiV?PO₄?₃@C is synthesized by a simple wet-milling method and possesses excellent electrochemical performance.The liquid electrolyte battery shows specific capacity of 90 mAh g^-1 at 100 mA g^-1 and possesses good cycle stability and rate performance.In contrast,the quasi-solid sodium-ion battery displays better electromance performance.And the EIS test shows the quasi-solid batteries have comparable dynamic performance to liquid electrolyte batteries.Moreover,the wide sources of raw materials and low environmental pollution are conducive to mass production of Na₂TiV?PO₄?₃@C material,and this work makes further exploration for the practical application of solid sodium-ion batteries.