Study On Design And Sodium Storage Performance Of Carbon-coated NaTi₂?PO₄?₃ Mesoporous Microflowers

Using renewable and clean energy sources and developing new energy storage technologies play an important role in current society because of the ever-growing energy demands and fossil-fuel shortage.Throughout the various battery technologies,lithium-ion batteries?LIBs?have covered a wide range of applications from portable electronics to?plug-in?hybrid electric vehicles due to the advantages of energy density and cycle life.However,the potential increasing costs and limited resources for Li are detrimental to the future large-scale application.Na with abundant reserves,low cost,and easy availability manifests similar physicochemical properties to Li.Therefore,developing sodium-ion batteries?SIBs?with a similar working principle to LIBs for large-scale applications is a reasonable alternative.The NASICON structured compounds present an open framework containing large interstitial channels,which can provide high ionic mobility.Among these compounds,NaTi₂?PO₄?₃?NTP?with high theoretical capacity and thermal stability has been regarded as a promising electrode material for SIBs.However,the NTP inevitably faces the intrinsic problem of low electronic conductivity,which results in poor cycling ability and inferior rate performance.Therefore,adopting effective methods to improve the electrical conductivity of the NTP is the key to solve the problem of poor electrochemical performance.Herein,we first present a facile and controllable synthesis of carbon-coated hierarchical NaTi₂?PO₄?₃ mesoporous microflowers?denoted as NTP/C-F?.Advanced testing methods were utilized to characterize the phase and structure of the product.A series of electrochemical measurements were carried out to study the electrochemical performance of NTP/C-F.Besides,time-resolved in-situ X-ray diffraction study manifested the enhanced sodium storage mechanism and structural changes of the NTP/C-F during the galvanostatical discharge-charge process.The main results from experiments are listed below:?1?The NTP/C-F was prepared through hydrothermal and annealing treatment,and the phase and structure were characterized by XRD,XPS,SEM,TEM and so on,revealing the unique structural advantage.?2?The NTP/C-F exhibits outstanding rate capability and ultra-long cycling stability.It delivers an initial capacity of 95 mA h g^-11 even at an ultrahigh rate of 100C?8 s for the full discharge/charge process?.After 10,000 cycles at 20 C,the capacity retention is as high as 77.3%.?3?Time-resolvedin-situX-raydiffractionresultsrevealthat sodiation/desodiation procedure of NTP/C-F occurs via a typical two-phase electrochemical reaction with reversible structure change.Therefore,the NTP/C-F electrode materials possess enhanced electrochemical reaction kinetics.?4?The superior electrochemical performance of NTP/C-F can be attributed to the following factors:?1?the rich mesopores on the surface of nanosheets ensure not only intimate contact between liquid electrolyte and active NaTi₂?PO₄?₃ nanocrystals,but also short pathways for Na⁺and electron transport;?2?the carbon skeleton facilitates fast electron transfer and further maintains the structural stability.