The Simple And Efficient Synthesis Methods For Electrode Materials Of Na-ion Batteries And Their Properties

Benefiting from the abundance and low price of sodium resources,Na-ion batteries?NIBs?have been widely considered as low cost and environmentally friendly energy storage and conversion devices for grid-scale energy storage systems.However,compared to the mature technologies of Li-ion batteries?LIBs?,NIBs are still in their infancy stage,which are in urgent need of further explorations of electrode,electrolyte,binder,and separator for improving the electrochemical performance before reaching a practical industrial application level.Moreover,from the perspective of industrial production,the batteries designs and manufacturing process of NIBs could be directly learned from the existing production technologies of LIBs;on the other hand,the simple and efficient synthesis methods of electrode materials with the assistance of simple technologies would save the cost effectively and generalize the applications of NIBs.Among numerous influence factors,the lack of considerable electrode materials is still the key one that restrains NIBs commercialization.In this paper,the general and convenient methods of synthesizing some promising and novel electrode materials for NIBs are presented together with the corresponding sodium ion storage abilities.The works are carried out as follow:1.Exploring new low-cost cathode material:P3-type K_0.32Fe_0.35Mn0.₆₅O₂·0.39H₂O?KFM?made from environmentally friendly and low cost elements is first synthesized through sol-gel method and demonstrated to be a novel cathode for NIBs.The KFM exhibits outstanding electrochemical performances including high specific capacity of 137.5 mAh g^-1at 10 mA g^-1,remarkable rate capability and Coulombic efficiency?ca.100%?,and long cycle stability(1000 cycles at 1000 mA g^-1).Furthermore,a highly efficient prototype NIB was first realized using this KFM cathode and a Na_x-Sb₂O₃ anode,which shows high energy density and power density(220.5 W h kg^-1;4340 W kg^-1)even with high round-trip energy efficiency?ca.100%?and excellent cycling stability(over 900 cycles at 1000 mA g^-1).2.Simplifying the synthesis method of known anode material:coaxial nanostructure composed of PPy coated amorphous Sb₂S₃ grafted on multiwalled carbon nanotubes?MWNTs?backbones is presented.The structure is obtained by bottom-up heterogeneous nucleation of amorphous Sb2S3 colloids on MWNTs through a solution-based route and subsequent surface-coating by a PPy layer through oxidative polymerization of pyrrole.The MWNTs@Sb₂S₃@PPy?MSP?nanocables deliver a considerable discharge capacity of 596mAh g^-1 at 100 mA g^-1 with capacity retention of 84%over 80 cycles.The reported green synthesis process of MSP is simple and gives a high yield without the assist of any lethal or volatile toxic chemical substances,the requirement for high temperature and special equipment is also avoided.3.Exploring new low-cost anode material:with the assistance of a pretty simple calcination method and common raw materials,the environment friendly and nontoxic N-doped C@Zn₃B₂O₆ composite is directly synthesized and proved to be potential anode material for NIBs.The composite could demonstrate high reversible charge capacity of446.2 mAh g^-1 at 20 mA g^-1,safe and suitable average voltage of 0.69 V together with application potential in full cells(300 cycles at 1000 mA g^-1).In addition,the sodium ion storage mechanism of N-doped C@Zn3B2O6 is subsequently studied through air-insulated ex-situ characterizations of XRD,XPS,FTIR and is found rather different from the previous reports on the borate anode materials for NIBs and LIBs.The reaction mechanism is deduced and proposed as:Zn₃B₂O₆+6Na⁺+6e^-?3Zn+B₂O₃·3Na₂O which indicates the generated boracic phase is electrochemical active and participates in the later discharge/charge progress.4.Exploring new bifunctional electrode material:a novel bifunctional electrode material,P3-type K_0.33Co_0.53Mn_0.47O₂·0.39H₂O?KCM?is synthesized through an easily-operated sol-gel method and delivers considerable Na ion storage abilities.As cathode,the compound displays remarkable average voltage potentials?over 3 V?and a high discharge capacity(114 mAh g^-1 at 100 mA g^-1).As anode,safe and ideal average voltage potential?0.53 V?,high discharge capacity(174 mAh g^-1 at 100 mA g^-1),and long cycle life(950 cycles at 500 mA g^-1)are also together delivered.In addition,a novel KCM-based full cell is subsequently built and it can still exhibit high energy density(91 Wh kg^-1)accompanied with long cycle performance(100 cycles at 100 mA g^-1)even without any optimization.