Preparation And Electrochemical Performance Of Potassium-ion Battery Anode Materials

Lithium-ion batteries(LIBs)are the most common energy storage systems,which have been widely applied for portable electric energy storage devices,electronic products and electric vehicles ascribed to excellent energy and power densities.However,the geographical distibution and costly price of lithium resources have greatly hamperedlarge-scale applications of LIBs.In this case,potassium-ion batteries(PIBs)have received extensive attentions owing to low-cost and abundant-reserve K resources.Moreover,K⁺/K has a similar redox potential with Li⁺/Li(-2.93 V vs.-3.04 V),enabling PIBs as promising alternative to LIBs,particularly for applications in large-scale energy-storage devices.Therefore,the development of low-cost,large-scale preparation and excellent electrochemical performance of PIBs electrode materials is the key to promote the development of PIBs.Thereinto,carbon-based materials are the extremely attractive ones due to their high electrical conductivity and chemical stability.Besides,hard carbon has large interlayer spacing,more active sites and larger capacity,which is widely concerned by researchers.However,these materials are synthesized in small-scale and complex processes,which have prevented their potential industrial applications.Thus,it is crucial to design a concise,low-cost,large-scale and environment-friendly strategy to prepare carbonaceous materials with high reversible capacity and superior cycling stability to accelerate the commercialization of PIBs.Additionally,the large size of K⁺leads to poor high-rate performance of PIBs,and the theoretical capacity of carbon-based materials is limmtted.In order to develop the PIBs with high power and high energy density,it is necessary to develop new high-performance electrode materials to further improve the rate performance and discharge capacity of PIBs.In view of this,this paper focuses on the preparation of low-cost and high-performance PIBs anode materials:(1)The N/O codoped hard carbon(NOHC)was constructed by a simple,efficient and low-cost one-step carbonization method in large-scale using piths of sorghum straw as precursor.The obtained NOHC presents large layer spacing,hierarchical micro/mesopores structures,functional groups,and abundant active sites.As an anode material for PIBs,NOHC displays a high reversible specific capacity(304.6 m Ah g^-1 at 0.1 A g^-1 after 100 cycles)and prominent cycling stability with a capacity(189.5 m Ah g^-1 at 1 A g^-1 over 5000 cycles),outperforming most carbonaceous materials.(2)In order to further enhance the rate performance and capacity of PIBs,the ball-cactus-like Bi nanospheres were embedded in three-dimensional(3D)N-riched carbon nanonetworks(Bi NSs/NCNs)by electrospinning.The Bi NSs/NCNs hybrid owns a cross-linked carbon nanonetwork structure and high nitrogen doping(14.9 at%).In addition,the Bi NSs will gradually evolve into three dimensions porous structure during the cycling process,which is convenient for ion/electron transport,abundant active sites and relieving the volume expansion appeared in cycling test.At the same time,the effects of different electrolytes on the structure and electrochemical performance of the Bi NSs/NCNs composite electrode were studied.The density functional theory calculation showed that the Bi/NCNs interface of the composite had a large adsorption energy,which was conducive to increasing the adsorption of K⁺,increasing the contribution of pseudocapacitance,and facilitating the alloying reaction between Bi and K⁺.Therefore,the composite exhibits excellent rate performance(489.3 m Ah g^-1 at 50 A g^-1)and high discharge capacity(457.8 m Ah g^-1 at 10 A g^-1 after 2000 cycles).