| Lithium ion batteries(LIBs)have been developed very quickly,becoming the most important energy storage devices in daily life during the last decade.However,the consumption of lithium resources has doubled,and their fast growing prices have become more and more Unacceptable.Meanwhile,the quite low content of lithium resources in earth crust has severely limited the further development and the extended application of LIBs.Therefore,developing inexpensive and high performance non-lithium based electrochemical energy storage devices has become an urgent research task for researchers in related field.Sodium ion batteries(SIBs),owing to their similar working mechanism with LIBs and their abundant,cheap and widespread distribution of resources,have received extensive attention.However,the radius of sodium ion is 1.06 ?,which is 39.5% larger than the lithium ion(0.76 ?),making the transmission of sodium ions much more difficult than lithium ions,and blocking the transfer of electrons at the same time.Hence,improving the ion transmission capability and the conductivity of electrons in electrode materials is the key for the development of the high performance SIBs.In this paper,the usage of Low graphitized carbon anode and carbon materials to improve the sodium storage properties in MnSe and alloyed Sb,and the controllable preparation of the carbon anode and the anode composite,have been studied to synthesize high performance SIBs anode materials.Specific research as follows:1.A flexible phosphorous doped carbon cloth(abbreviated as FPCC)with the self-supporting structure was successfully prepared using the commercialized cotton as materials.The carbon tubes in the FPCC were weaved by the porous carbon microtubules which were 500 nm thick.When the FPCC was directly used as SIBs anode without binder,it displays excellent electrochemical sodium storage properties,which delivers a reversible capacity of 242.4 mA h g-1 with a coulombic efficiency of 72 %,a great rate performance(the capacity of 123.1 mA h g-1 at 1 A g-1),and an impressive cycling stability(the capacity retention of above 88 % at 0.2 A g-1 over 600 cycles).Compared with the undoped carbon cloth(abbreviated as UCC),The electrochemical parameters above are higher,which indicates the phosphorous doping process could efficiently improve the sodium storage properties of the cotton cloth based carbon anode materials.Moreover,a comparative study of the FPCC and the UCC was conducted about the Charge transfer resistance in electrodes and the sodium ion transfer kinetic parameters,by using the galvanostatic intermittent titration technique(GITT),the electrochemical impedance spectroscopy(EIS)and the cyclic voltammetry(CV),proving that the phosphorus doping process is an optimization of the electrochemical parameters.2.We successfully synthesized the composite I-Sb/rGO,which comprised of the Sb and the reduced graphene oxide(rGO)with micro/nano-structures,via a simple in-situ preparation method,by which batch preparation can be achieved.The Sb nanoparticles embedded in rGO conductive networks of the composite uniformly,forming unique micron scale secondary particles.The composite displays higher sodium storage capacity,better rate and cycle performances(the reversible capacity of 112 mA h g-1 at 6 A g-1),compared with the E-Sb/rGO(the capacity of 20 mA h g-1 at 6 A g-1)which was prepared through ex-situ preparation method,when it was used as the SIBs anode material.The in-situ preparation method provided in this chapter,which is very simple and efficient,could be used in preparing other high performance SIBs composite anode materials.3.We successfully synthesized the Sb/C/G composite modified with double carbon,which has micro/nano-structures.Inducing graphene nano-sheets could inhibit the growth of Sb particles in heating process,moreover preventing the aggregation of Sb nanoparticles,and coating all the particles to the carbon conductive networks.As for the composite without graphene inducing,most of the Sb particles still adhered on the surface of carbon sheets,leading to an incomplete coating state.In the Sb/C/G composite,Sb nanoparticles are evenly distributed between 20 and 50 nm,where almost all Sb nanoparticles were well coated in the double carbon conductive networks.When used as the negative electrode for SIBs,the test of storage performance showed that the Sb/C/G micro/nano composites exhibit the best electrochemical performance,including the highest reversible capacity,the fastest sodium storage capacity and the best cycle stability,compared to the Sb/C and pure Sb materials.The improved sodium storage properties origins from the optimization of the double carbon conductive network structures.The concept of the double carbon modification could be used in preparing other high performance composite electrode materials.4.First,the one-dimensional α-MnO2 nanotube template material was prepared by simple hydrothermal preparation method according to the reported method.Then,through the simple liquid phase reaction,a layer of poly dopamine was uniformly coated on the surface of the α-MnO2 nanotubes,and the one-dimensional α-MnO@C nanotubes were obtained from heating treatment.Finally,MnO@C nanotubes and selenium powder were mixed under the vacuum condition,and sintered at high temperature,afterwards the α-MnO@C nanotubes were obtained,which were consisted of the hollow carbon coating stabilized α-MnSe material.When used as the negative electrode,it exhibited good electrochemical performance.In this material,the one-dimensional tubular hollow structure constructed by the carbon nanotubes can well buffer the volumetric effect during the process of electrochemical sodiation/desodiation,as well as facilitate the infiltration of the electrolyte,shorten time and the transmission distance of the sodium ions and the electrons in the electrode material,thus enhancing the cycle stability and the rate performance of the composite material.Meanwhile,the excellent conductivity of the carbon material can improve the conductivity of the composite materials,and promoting the synergistic transmission process of sodium ions. |
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