Research On Energy Storage Properties Of Vanadium-based Nanostructure As Cathode Materials For LIBs And KIBs

Nowadays,lithium ion batteries（LIBs）have developed into a type of efficient and mature energy storage unit which is widely applied in people’s life.LIBs have the advantages of long cycle life,environment-friendliness and high operating voltage.However,the large-scaled application of LIBs in the field of energy storage is greatly restricted by the shortage,uneven distribution and high cost of lithium resources.Therefore,it is necessary to explore alternative alkaline metal-ion batteries.As an emerging energy storage unit,potassium-ion batteries（KIBs）show great development potential owing to its advantages of abundant potassium reserves,low cost and low desolvation energy of K⁺.The electrode materials play a key role in the properties of alkali metal-ion batteries,especially for cathode materials.Vanadium-based materials have become a class of ideal cathode materials for LIBs and KIBs due to their specially layered and multichannel structure,favorable stability,low cost and multi-valence state.In this work,we studied the preparation and energy storage characteristics of LiV₃O₈and K_xV₂O₅as cathode materials for LIBs and KIBs,respectively.On one hand,it provides the promising cathode candidate for the development of traditional high-performance LIBs;on the other hand,it offers the necessary supplements and explorations for the future novel cathode materials of KIBs.In the aspect of LiV₃O₈cathode materials for LIBs,we employed suitable vanadium source,lithium source and structure-directing agent and dispersant as raw materials to prepare LiV₃O₈samples with different morphologies（denoted as M-LVO,N1-LVO and N2-LVO,respectively）through three different routes involving solid-phase sintering,one-pot hydrothermal and two-step synthesis methods.The formation mechanisms of LiV₃O₈samples under different conditions are discussed.The relationships between lithium storage characteristics and morphology as well as crystallinity are analyzed in detail.Among them,N1-LVO prepared by one-pot method delivers the highest specific capacity（the initial reversible capacity is 289.5m Ah/g,which remained at 199.7 m Ah/g after 100 cycles at 100 m A/g）;N2-LVO synthesized by two-step method gives an initial reversible discharge capacity of 269.3 m Ah/g,which kept at 183.4 m Ah/g for the 100^thcycle;Under the same testing conditions,the beginning capacity of M-LVO obtained by solid-phase sintering is only 204.4 m Ah/g,which maintained just at 121.2m Ah/g after 100 cycles.The better lithium storage properties of N1-LVO and N2-LVO compared to M-LVO can be attributed to their special nanostructures,which facilitate the rapid transfer of Li⁺and increase the active sites of lithium storage.In comparison with N2-LVO,N1-LVO exhibits a larger capacity for lithium storage,which is mainly due to its higher degree of nanocrystallization and special formation mechanism.With regard to K_xV₂O₅as cathode for KIBs material,a series of one-dimensional vanadium-based nanoribbons were synthesized through one-pot hydrothermal way by using V₂O₅powder,KI and KCl as raw materials,H₂O₂as solation reagent and glucose as reductant.The effects of H₂O₂and glucose on formation of K_xV₂O₅nanostructures were studied.The corresponding mechanisms were proposed.Based on systematic electrochemical tests,the influence of high temperature sintering and working voltage window on the potassium storage performance of K_xV₂O₅nanoribbons cathode were explored.Besides,we analyzed and elaborated the dependence of potassium storage performance on the morphology,degree of crystallization and testing voltage window of samples.The results indicated that the utilization of H₂O₂promotes the growth of K_xV₂O₅nanoribbons with more regular shape at hydrothermal condition;the introduction of excessive glucose will cause the decrease of vanadium valance in samples,which prevents the generation of K_xV₂O₅.In addition,a certain amount of bonding-water in K_xV₂O₅was conducive to its structural stability upon K⁺intercalation/de-intercalation;the narrow voltage window was beneficial to the cyclic stability of K_xV₂O₅.Among all samples,K_xV₂O₅-G exhibited the well combination properties,whose capacity can retain at 46.8 m Ah/g after 50 cycles（1.8-3.8 V,50 m A/g）.In this work,we investigated the preparation of two kinds of vanadium-based materials and their energy storage characteristics when used as cathodes for LIBs and KIBs accordingly.The formation mechanism and relationship between structure/property for the involved vanadium-based cathodes were elaborated.We analyzed the similarities and differences of vanadium-based materials as cathodes for LIBs and KIBs,which provides valuable reference for the subsequent application of vanadium-based cathodes in alkali metal-ion batteries with high-performance.