Ternary Nickel Cobalt Molybdenum:Preparation And Study On Its Sodium Electrochemical Properties

In the family of rechargeable ion batteries（RIBs）,lithium ion batteries（LIBs）have been widely used in portable electronic devices and electric vehicles,and sodium ion batteries（SIBs）are also shown great application potential in the field of energy storage.Due to slow kinetics and metal dendrite formation,LIBs/SIBs suffer from low power density and poor cycle stability and safety.ECs are devices that rapidly store energy by physical adsorption,with reversible or quasi-reversible redox reactions at the surface of the active material.Compared with LIBs/SIBs,they present higher power density and long cycle life.However,lower energy density limits the commercial competitiveness of ECs.Lithium/Sodium-ion capacitors（LICs/SICs）have recently garnered attention for the development of ECs with high energy density and high power densitiy.Compared with LICs,SICs are rich in sodium resources,low in cost,and do not compete for sodium resources unlike that between LIBs and LICs,thus SICs are considered to be a viable replacement for LICs.However,SICs have such defects as larger Na⁺radius,higher embedding/removing potential than Li⁺,especially the low power density caused by the slow dynamic behavior,that makes the wide application of SICs more challenging.In this paper,Mo₂C is applied to the SICs system for the first time.By metals element doping and the introduction MWCNTs to modify Mo₂C,multiple composite materials are prepared.The specific screening methods and results of this composite material used as the negative electrode of SIBs and SICs are as follows:Sodium citrate-derived charcoal（SCDC）was prepared by high temperature calcination and KOH activation.The characterization shows that SCDC is composed of about 300 nm nanoplates stacked together with aboundant micro-interstitial gaps and specific surface area up to 302 m²·g^-1.The CV curve of SIBs assembled by SCDC-800 shows excellent of capacitance behavior.The capacity of 0.4 A·g^-1current density after 1600 cycles is stable at 90 mAh·g^-1,indicating that SCDC-800 is of potential value as SICs anode material.The nickel-cobalt-molybdenum carbonization and pyrolysis carbon and multi-wall carbon nanotubes composite material were prepared by hydrothermal method,and the ratio of nickel-cobalt-molybdenum were optimized.The Ni_0.44Co_0.22Mo_0.34C@Double-Carbon（NCMC@DC）composite was a flower-like structure assembled by about 20-30 nm uniform nanoplates with good crystallinity.When used as negative material for SIBs,NCMC@DC shows high specific capacity of 131 and 75 mAh·g^-1 at a current density of 0.1 and 1 A·g^-1 after300 and 150 cycles.The specific capacity at 5 A·g^-1 current density can reach 70mAh·g^-1.The button-type SICs（NCMC@DC//SCDC）exhibit a significant energy density of 112.5 Wh·kg^-1 and power density 70.1 W·kg^-1.When the current density is increased to 5 A·g^-1,SIC still retains a high power density of 8 kW·kg^-1 and energy density of 66.7 Wh·kg^-1.The outstanding electrochemical performance of the button-type SICs（NCMC@DC//SCDC）can be attributed to the following two aspects:The flower-like nanoarchitecture assembled by nanoplates can increase the contact area between the electrolyte and the active material to improve the infiltration rate,and provide more active sites,and buffer the volume change caused by the Na⁺deintercalation process;The presence of metallic Ni,Co,pyrolytic carbon and CNTs improve the electrical conductivity of composite materials,endowed with excellent rate performance and long-term cycle stability.