Synthesis Of Transition Metal Oxides/carbon Composites And Their Electrochemical Performance As Anode Materials For Lithium-ion Batteries

Global energy shortage leads to increasing demand for advanced energy storage equipment.Lithium-ion batteries have become the most widely used in portable electronic devices such as laptops,mobile phones,medical microelectronic devices,and electric vehicles due to their many advantages including high energy density,no memory effect,environmental protection,and long cycle life.However,the demand for lithium-ion batteries is also increasing,including improving safety,extending service life,reducing size,weight,and cost.Transition metal oxides based on conversion mechanisms have the high theoretical capacity and abundant resources and are considered to be a very promising class of anode materials for lithium-ion batteries.In recent years,through continuous research on transition metal oxides,the research results show that due to the synergy between different metal cations,binary transition metal oxides have better electrochemical performance than monovalent transition metal oxides.Although transition metal oxides have high theoretical capacity when used as anode materials,they still have problems such as low conductivity and large volume changes during cycling.These defects limit the further application of transition metal oxides in lithium-ion batteries.To address these issues,transition metal oxides can be modified by methods such as nanomaterialization,modification of conductive materials,and construction of three-dimensional composite electrodes to improve their electrochemical performance.This paper selects NiCo₂O₄ and ZnMn₂O₄ as two potential transition metal oxides as research objects.Firstly,an improved experimental method was used to neologize the material and then modified by conducting materials and constructing three-dimensional composite structures.NiCo₂O₄/C nanofibers and ZnMn₂O₄ nanoparticle/carbon cloth composites were successfully prepared.The composites have excellent electrochemical performance.The experimental method used in this paper provides experimental data and theoretical basis for the practical application of transition metal oxides as lithium-ion anode materials.The main research results are as follows:?1?We used a two-step method?hydrothermal and heat treatment?,using nickel chloride hexahydrate as the source of the metal nickel,cobalt chloride hexahydrate as the source of metal cobalt,and cotton fiber as the template Carbon source,carbon-coated NiCo₂O₄ nanofibers were prepared.Subsequently,the phase characterization was performed,and the results showed that this method successfully synthesized NiCo₂O₄/C nanofibers with uniform size.The composite structure of NiCo₂O₄ and carbon has the advantages of good mechanical flexibility,large specific surface area,and fast electron transport speed.Compared with pure NiCo₂O₄,NiCo₂O₄/C nanofibers electrodes have higher discharge specific capacity.The NiCo₂O₄/C nanofibers electrode still has a reversible capacity of 732 mAh g^-1 after 100 cycles at a current density of 100 mA g^-1,the reversible capacity does not decrease significantly during the entire cycle and has good cycle stability.Under different current densities,the capacity of the NiCo₂O₄/C nanofibers electrode is higher than that of the NiCo₂O₄ electrode,which has excellent rate performance.After 200 cycles under a large current density of 1A g^-1,the composite electrode still has a reversible capacity of 416 mAh g^-1 and is still higher than commercial graphite anode materials.In addition,the use of cotton fiber as a carbon source effectively reduces costs and provides a feasible approach for the preparation of composite materials of carbon and transition metal oxide.?2?We used a one-step solvothermal method,using manganese nitrate,zinc nitrate,cetyltrimethylammonium bromide,and citric acid as raw materials,to grow ZnMn₂O₄nanoparticles in situ on the carbon cloth substrate for the first time.The ZnMn₂O₄nanoparticles/carbon cloth composite electrode can be used as without binders anode material for lithium-ion batteries.The phase characterization results proved that the method successfully synthesized ZnMn₂O₄ nanoparticles with uniform size on the carbon cloth substrate.Due to the advantages of the three-dimensional composite structure and the synergistic effect between the ultra-fine ZnMn₂O₄ nanoparticles and the conductive carbon cloth,compared with pure phase ZnMn₂O₄ and pure carbon cloth,the ZnMn₂O₄nanoparticles/carbon cloth composite electrode has higher Specific discharge capacity,it has a reversible capacity of 3.10 mAh cm^-2 and 1.48 mAh cm^-22 after 100 cycles at a current density of 0.12 mA cm^-2 and 2.4 mA cm^-2.The flexible composite electrode prepared by carbon cloth as a current collector meets the requirements of flexible electronic devices and has a wide application prospect in realizing high-performance flexible energy storage devices.