Structural Design,Construction And Potassium Storage Properties Of Cobalt/Molybdenum-Based Chalcogenide/Carbon Materials

Due to low self-discharge rate and high energy density,lithium-ion batteries are widely used in power batteries and energy storage batteries.However,due to the low crustal abundance and high cost of lithium,the development of new battery systems is urgently needed.Potassium-ion batteries are considered as one of the feasible alternatives to lithium-ion batteries because of their abundant potassium resources,low cost,and redox potential（-2.93 V）similar to Li⁺/Li electrodes（-3.04 V）.However,due to the large radius of potassium ions,severe volume changes and slow reaction kinetics occur during the potassium insertion/depotassification process.Transition metal chalcogenides,used as anode materials for potassium-ion batteries,have the advantages of suitable potential,sufficient reserves,and high theoretical capacity,but their inherent low conductivity,shuttle reaction of polysulfides,and poor structural stability limit their practical applications.In this paper,cobalt selenide and molybdenum disulfide are selected as the research objects,and strategies such as structural design,carbon material composite,and heteroatom doping are used to improve the electrochemical performance.The main research contents are as follows:（1）To mitigate the volume change,a series of carbon-coated copper cobalt selenide nanoparticles（（CuCo）Se-NC@C）embedded in a nitrogen-doped carbon layer were prepared by precipitation and thermal annealing methods.Taking advantage of the tunable MOF composition,the introduction of perovskite doping improves the intrinsic conductivity of cobalt selenide and accelerates the reaction kinetics.The externally coated carbon layer can effectively adapt to the volume expansion during the charging and discharging process.Due to the synergistic effect of heteroatom doping and carbon coating,the electrode maintains a high reversible specific capacity of 592.57 mAh g^-1after 100 cycles at 0.1A g^-1.（2）To improve the degree of reversible reaction and further limit the decomposition of polysulfides,MoS₂ nanoflowers containing sulfur vacancies grown on N-doped graphene nanosheets(MoS_2-x/NG)were prepared using polyaniline（PANI）treatment of graphene oxide to adsorb anions.The formation of Mo-N bonds is beneficial to improve the kinetics of Mo/K₂S during charging and improve the degree of reversible conversion.The introduction of sulfur vacancies can adjust the adjacent atomic arrangement and electronic structure,and the extended layer spacing is beneficial to mitigate the volume change during cycling and improve the ion diffusion kinetics.As anode material of potassium-ion battery,it has good cycling performance,showing a specific capacity of 220.06 mAh g^-1 after 1000 cycles at 1.0 A g^-1,which can provide even a high rate capacity of 172.20 mAh g^-1 at current density of 10.0 A g^-1.（3）To further improve the discharge capacity of PIBs,nickel/cobalt co-doped molybdenum disulfide nanosheet/reduced graphene oxide composites（Ni Co-MoS₂/r GO）were synthesized by hydrothermal and high-temperature carbonization methods.The composite with reduced graphene oxide nanosheets constructs a three-dimensional structure,which can prevent the accumulation and agglomeration of MoS₂nanosheets,shorten the diffusion path of K⁺ions,and effectively mitigate the volume change during potassium ion storage.Double doping is more favorable than single doping to enhance electron transfer,thus improving conversion reaction reversibility and reaction kinetics.As anode material of potassium-ion battery,it exhibits a better cycle life(177.18 mAh g^-1 after 800 cycles at 1.0 A g^-1)and great rate performance(202.73 mAh g^-1 at 5.0 A g^-1).