Synthesis Of Carbon-Based Composites And Research Of Their Potassium Storage Performance

Potassium ion batteries are one of the most promising secondary battery energy storge systems to replace lithium ion batteries because of their low cost and high energy density.However,the large radius of potassium ions?1.38??would result in the great volume expansion and possible collapse structure of the electrode materials during the cycling process of potassium ion battery,which leads to poor electrochemical performance.In view of the above problems,this paper focuses on the transition metal phosphide and transition metal chalcogenide with high theoretical specific capacity,optimizing the structure of Mo P and MoSSe through carbon material compounding and the introduction of dual anionic vacancies,which effectively improve the structural stability and facilitate the potassium ions and electrons transporting.Two novel carbon-based anode comopsites with excellent cycling stability and rate performance are constructed to provide support for the design and application of potassium ion battery.The main research contents and results of this paper were summarized as follows:?1?The Mo P nanoparticles splotched nitrogen-doped carbon sheets?Mo P@NC?were prepared via in-situ polymerization the polyacrylamide hydrogel and Mo P precursor mixture followed by carbonization process.The larger specific surface area of nitrogen-doped carbon matrix effectively increases the Mo P active sites,and the carbon-coated structure relieves large volume expansion of the electrode material during potassiation/depotassiation process.The Mo P@NC//AC potassium ion capacitor device is constructed by using Mo P@NC as an anode and commercial activated carbon as a cathode,which can well integrate the features of high energy density of batteries and long cycle life of capacitors,delivering high energy/power densities(86.5 Wh kg^-1 and 6204 W kg^-1)in a potential window of 1.0-4.0 V,as well as a long lifespan of over 5000 cycles at 1.0 A g^-1 with a high capacity retention of69.5%.?2?The dual anionic vacancy-rich MoSSe arrays in combination of carbon nanofiber membrane?v-MoSSe@CM?were prepared by using electrospun carbon nanofibers?CM?as a flexible substrate after undergoing hydrothermal,washing,and annealing processes.The vacancy-rich MoSSe arrays in v-MoSSe@CM dramatically increase the reactive sites,leading to a higher capacity of 370.6 m Ah g^-1 at 0.1 A g^-1over 60 cycles as compared with that 168.5 m Ah g^-1 of vacancy-free MoSSe@CM.Meanwhile,the density functional theory calculations demonstrate a facilitated ability for potassium ions insertion into v-MoSSe interlayers with a much more negative adsorption value of-1.74 e V than that?0.53 e V?of vacancy-free MoSSe.The thousands of carbon nanofiber-supported three-dimensional frameworks can not only inhibit the agglomeration of MoSSe nanosheets,but also remit the volume expansion and avoid possible collapse of the nanostructures during cycling,resulting into a high capacity retention of 220.5 m Ah g^-1 at 0.5 A g^-1 after 1000 cycles.In addition,the potassium storage mechanism of v-MoSSe was revealed by means of ex situ X-ray diffraction and cyclic voltammetry,combined with the capacitor contribution calculation,that is,the v-MoSSe anodes undergo a sequential conversion?MoSSe to K_xMoSSe,K₂Se and K₂S?.