Preparation Of Vanadi?m And Titani?m Compounds And Their Potassi?m Storage Properies

With the development of social economy,secondary battery has played an increasingly important role on the production and living of people.Lithi?m ion batteries?LIBs?have made great achievement in the portable electronics,electric vehicles?EVs?,and part of the smart grid storing energy because of its high energy density and good cycle performance.However,lithi?m is not abundant and unevenly distributed,leading to its increasing cost that has limited widespread large-scale application of LIBs.Recently,the increasingly serious environmental pollution along with the economic development make people turning to the clean energy such as solar energy,wind energy,tidal power,and geothermal energy,which put forward a new challenge for the cheap and efficient large-scale energy storage device.Sodi?m as one of the alkali metal has abundant reserves and similar physicochemical properties.Sodi?m-ion batteries?NIBs?in recent years have captured significant attention and made great success.Potassi?m as one of the alkali metal also has abundant reserves and similar physicochemical properties with lithi?m and sodi?m,and potassi?m ion batteries?KIBs?recently have caught the attention of some researchers.Remarkably,the standard electrode potentials of Na/Na+?-2.71 V vs.the SHE?is much higher than that of Li/Li+?-3.04 V vs.the SHE?and K/K+?-2.93 V vs.the SHE?.This makes KIBs more competitive than SIBs in the discharge voltage and capacity.Furthermore,KIBs may show a better rate performance in that K+ havs more superior properties of mobility than Li+ and Na+ in the electrolyte and electrode/electrolyte interface,owing to the fact that the weaker Lewis acidity of K+ could cause a smaller Stoke's radius of solvated ions in liquid electrolyte.Thus,it becomes significant to develop KIBs.Recently,cathode materials of KIBs are mainly focused om Prussian blue and its analogues,polyanionic compounds,transition metal oxide salt,etc.The materials such as graphite,hard carbon,Ti-based anodes have drawn much attention as anode materials for KIBs.However,the performance of these electrode materials are not desirable as a possible result of great ionic radius of K+.Hence,it is significant to design electrode material with outstanding performance for KIBs.Based on the experience of developing electrode materials for LIBs and NIBs,much progress has been made on vanadi?m and titani?m compounds when regarded as electrode materials in chemical energy storage.Moreover,vanadi?m and titani?m have relatively abundant reserves and low price.Therefore,we mainly choose to design some vanadi?m and titani?m based compounds with novel morphology and structure of as electrode materials for KIBs.Based on a review of the latest research progress in KIBs,we creatively prepared some novel vanadi?m and titani?m based compounds to solve the lack of electrode materials for KIBs and provide a new sight into developing electrode materials with excellent performance for KIBs;Micro/nano materials with novel morphology and structurehave been synthesized and characterized.Besides,their electrochemical performance have been tested,and analyzed combined with the influence of their structure;The electrochemical property is improved via the carbon coating,and the improved performance is researched.The main research content of this paper are as follows:1.Novel book-like K_0.23V₂O₅ crystals are prepared by solvent thermal method and explored as cathode materials for KIBs for the first time.It reavels a poor electrochemical performance as a probable result that the large ion radius of K+ hamper its insertion/extraction in the crystals during the cycle.Then we try to treat the material as cathode material for LIBs,and it reveals outstanding electrochemical performance with a specific capacity of 244 mA h g-1 at a current density of 50 mA g-1.After further study,it is found that the novel layered structure short the distance of lithi?m ion migration distance and promote the efficiency of lithi?m ion migration;Doping of the potassi?m ion in the K_0.23V₂O₅ crystals keeps the structure stable.2.Three dimensional porous K₃V₂?PO₄?₃/C nanocomposite is prepared and first treated as cathode materials for KIBs.It reveals improved electrochemical performance compared with the bulk K₃V₂?PO₄?₃,which is attributed to three-dimensional porous structure,the nano-sized K₃V₂?PO₄?₃ and in-situ carbon coating.Remarkably,three-dimensional porous structure promotes the mobility of potassi?m ions and short the distance of the mobility;Nanoscale K₃V₂?PO₄?₃ particles are more easily infiltrated by electrolyte,and more likely to participate in the reaction from the dynamic factors;In-situ carbon coating increases the conductivity of the material,and promote the formation of SEI film and keep the material structure stable.3.Titani?m based compound K₂Ti₈O₁₇ composed of nanorods is synthesized by solvent thermal method and treated as cathode materials for KIBs for the first time.Furtherly,the effect of novel morphology and structure of K₂Ti₈O₁₇ on the electrochemical performance is researched,and higher mobility of potassi?m ions is presented in the novel K₂Ti₈O₁₇ compared with the bulk K₂Ti₈O₁₇.4.Nanocubic KTi₂?PO₄?₃ is synthesized and regarded as electrode materials of KIBs for the first time.It shows poor electrochemical properties at first,and electrochemical performance is significantly improved after carbon-coating.The effect of the carbon coating on the improved performance is researched and explained by measurement of the impedance,fitting the impedance and calculation of the potassi?m ion mobility.