In-situ Composites Of Transition Metal Oxide And Nanocarbon As Anode Materials For Lithium/Sodium-ion Batteries

At present,lithium ion battery and sodium ion battery want to be used in large-scale commercial applications,the most difficult problem to be solved is to find suitable anode materials.Transition metal oxides,possessing high theoretical specific capacities,are promising anode materials for lithium/sodium-ion batteries.However,the sluggish sodiation/desodiation kinetics and poor structural stability restrict their electrochemical performance.Generally,there are two effective strategies that can be implemented to mitigated the above-mentioned issues and improve the Li/Na storage capability of TMO-based electrodes.One strategy is engineering robust nanostructures,such as nanowires and nanosheets,and reducing particle size,which can effectively shorten Li⁺/Na⁺ion diffusion path and facilitate efficient accommodation of volume changes.Another strategy is to prepare TMO-based composites with highly conductive carbon materials,such as carbon nanotubes and graphene.Herein,the cycle stability and rate property of transition metal oxides are enhanced by in-situ composite of transition metal oxides and carbon materials.The mesoporous carbon in the composite increases the electronic conductivity of the composite,and acts as a buffer for volume change during the Li/Na uptake/removal,providing enough structural stability for the electrode and culminating in its better cycling stability.Finally,the carbon can also restrain the growth of TMO,which results in less volume change during discharge/charge process and improves the cycling performance.The sizes of the transition metal oxides are below 10 nm.In addition,it just needs one-pot to get the composite materials in our work,which simplifies the reaction steps and breaks the traditional composite process.It has certain guiding significance for improving the electrochemical properties of transition metal oxides.Our work mainly has the following two research contents:1.Rambutan-like hybrid hollow spheres of carbon confined Co₃O₄ nanoparticles are synthesized by a facile one-pot hydrothermal treatment with post annealing.The hierarchy hollow structure with ultrafine Co₃O₄ nanoparticles embedded in the continuous carbon matrix enables greatly enhanced structural stability and fast electrode kinetics.When tested in sodium-ion batteries,the hollow structured composite electrode exhibits an outstandingly high reversible specific capacity of 712 mAh g^-1 at a current density of 0.1 A g^-1,and retains a capacity of 223 mAh g^-1 even at a large current density of 5 A g^-1.Besides the superior Na storage capability,good cycle performance is demonstrated for the composite electrode with74.5%capacity retention after 500 cycles,suggesting promising application in advanced sodium-ion batteries.2.By directly pyrolyzing MOFs,as self-sacrificing template,the porous structure of in-situ composite of transition metal oxide and carbon is generated.Cr₂O₃ octahedron in-situ doped with porous carbon was prepared by direct pyrolysis of MIL-101?Cr?in Ar atmosphere.The composite exhibits better properties than puer bulk Cr₂O₃ sample.It not only shows the high lithium storage capacity of 770mAh g^-1,but also has good rate performance and excellent cycling stability.The above studies have fully demonstrated the effectiveness and universality of one-step in-situ porous carbon composite for improving the electrochemical performance of transition metal oxides,which is expected to be used in the design of other advanced anode materials for lithium/sodium ion batteries.