The Research Of Construction Of Carbon-based High-capacity,high-rate,Stable Electrode

Energy shortages and environmental pollution caused by the massive consumption of fossil fuels have attracted much attention.In order to overcome these problems,the development of efficient energy storage and conversion systems,such as rechargeable batteries,supercapacitors,and fuel cells,has increasingly shown urgency and importance.The construction of new electrode materials with unique structural characteristics is the key to the preparation of high-performance electrochemical energy storage and conversion systems.Metal oxides and sulfides have high theoretical capacities,but their poor cycle stability and low initial coulombic efficiency hinder their application in lithium-ion batteries.Carbon materials have the advantages of easy preparation,low cost,abundant reserves,stability,non-toxicity,and excellent conductivity are widely used in various energy storage devices such as lithium ion batteries and aluminum ion batteries.The combination of carbon materials with metal oxides and sulfides is a feasible method to improve the cycle stability and the initial coulombic efficiency of lithium ion battery electrode materials,and the construction of a new type of carbon material is the key to improving the performance of aluminum ion batteries.This paper uses chemical vapor deposition,hydrothermal reaction and high temperature carbonization to prepare a series of new carbon-based electrode materials with high capacity,long cycle life and excellent rate performance,and apply them to lithium ion batteries,potassium ion batteries and aluminum ions.The specific content is summarized as follows:(1)Molybdenum disulfide(MoS₂)as a negative electrode for lithium ion batteries has a high theoretical capacity,but its cycle stability is poor.The 1T-MoS₂-graphene composite material with graphene-encapsulated metal phase 1T-MoS₂ was prepared by hydrothermal method.Graphene is used to confine the metal molybdenum(Mo)atoms in the graphene"nano reactor".The unique structure allows molybdenum and l ithium sulfide(Li₂S)to be fully converted into MoS₂.As a negative electrode of a lithium ion battery,when the current density is 1000 mA g^-1,the specific capacity of 1T-MoS₂reaches 1800 mA h g^-1,which is 2.6 times the value of the intercalation reac tion capacity.Different from traditional research,this work proposes a new lithium storage mechanism with high capacity and growing.Theoretical calculations and experimental results show that the combination of Mo atoms and lithium ions(Li⁺)is the main reason for the overcapacity of MoS₂ anodes.The precipitation of Mo and its sufficient contact with the Li₂S matrix cause the reversible reaction Mo?Li_xMo?Mo?1T-MoS₂ during the charging and discharging process.After a long cycle,each Mo atom can hold six lithium ions.This research will promote the development of MoS ₂lithium storage kinetics.(2)Metal oxide has a high theoretical capacity as a negative electrode m aterial for lithium-ion batteries,but its low initial coulombic efficiency and poor rate performance hinder its practical application.Partially oxidized two-dimensional porous iron composite nitrogen-doped carbon nanosheets were prepared by freeze-drying combined with high-temperature carbonization.The partially oxidized atomic thickness iron oxide provides a high specific capacity,and the two-dimensional sheet-like porous structure can effectively reduce and alleviate the stress generated during the volume change of the material and improve the cycle performance.At the same time,the porous structure increases the active site of the material and shortens the transmission distance of lithium ions.At the same time,the composite nitrogen-doped carbon further enhances the overall conductivity of the material and makes the material exhibit excellent electrochemical performance.The partially-oxidized two-dimensional porous iron of composite nitrogen-doped carbon has an initial coulombic efficiency of 77.33%,exhibits an average reversible capacity of up to 927 mA h g^-1 at a current density of 1000 mA g^-1,and the capacity is almost no attenuation after 1000 cycles.In addition,the material also has excellent rate performance,exhibiting reversible capacities of 1130,1065,982,841 and 643 mA h g^-1at current densities of 200,500,1000,2000 and 5000 mA g^-1,respectively.This work provides new ideas for the future research of metal oxides in lithium ion battery anode materials.(3)Aluminum ion batteries have attracted much attention due to their low cost,theoretically high energy density,and high safety.However,the current commercial graphite used in aluminum ion batteries has poor cycle stability.Covalent organic frameworks(COFs)are porous structures composed of non-metallic elements with large specific surface area and versatility.They are a good energy storage material,but their poor conductivity hinders their use in energy storage batteries,especially Application on aluminum ion battery.Using nitrogen-rich COF-JLU2 as a precursor,a high-temperature carbonization method was used to prepare COF-derived nitrogen-doped porous carbon for aluminum ion batteries.Porous structure as interconnected channels could promote high electrolyte permeability and larger interlayer spacing to facilitate the transfer of Al Cl ₄^-anion,thus improving the electrochemical performance.The first-principles calculations confirmed that the COF-derived nitrogen-doped porous carbon has good conductivity and optimized electron density distribution.Therefore,overcoming the problem of poor conductivity of COF and optimizing its electrochemistry performance in aluminum ion batteries.NPC cathode for aluminum ion batteries could achieve high coulo mbic efficiency(close to 100%)and almost no capacity decay at a high current density of 5000 mA g^-1for 30000 cycles.(4)The high energy consumption and complicated process of high-quality graphene synthesis process hinders the application of graphene in aluminum-based rechargeable batteries.In order to reduce the synthesis cost of graphene,especially three-dimensional graphene,a low-cost,low-temperature(600°C)chemical vapor deposition method was proposed to synthesize edge-rich three-dimensional graphene paper and apply it to aluminum ion batteries.The low-temperature production of graphene can achieve low energy consumption and low cost production,which is beneficial to the large-scale production of graphene and its application in energy storage systems.The edge-rich and interconnected structure of graphene with continuous electron-conducting matrix yields a large current transportation and increases the active site for the insertion/desertion of chloroaluminate anion.Therefore,the edge-rich and interconnection design of graphene can effectively improve its performance in aluminum ion batteries.The reversible capacity is up to128 mA h g^-1 at 2000 mA g^-1.The aluminum ion battery based on this edge-rich graphene paper cathode also shows excellent cycle stability.For example,it could achieve high Coulombic efficiency(>99.2%)and almost no capacity decay at a high current density(8000 mA g^-1),even after 20,000 cycles.The preparation method of this novel graphene provides a new method for the low-cost preparation of three-dimensional graphene,which provides the possibility of its large-scale application in aluminum ion batteries,and will promote the development of aluminum ion batteries.