Preparation And Lithium Storage Performance Of Cobalt-based Bimetallic Phosphide Anode Materials

With the excessive consumption of earth resources and the continuous deterioration of the ecological environment,it is urgent to find green,efficient,sustainable and economical energy storage technology.Among them,lithium-ion batteries（LIBs）are widely used in various energy storage systems due to their unique advantages such as high capacity,high energy density,long cycle life,and economic and environmental protection.However,the current performance parameters of LIBs have gradually been difficult to meet the growing market demand,especially in the field of portable electronic products and electric vehicles.As the core component of LIBs,anode materials play an important role in the specific capacity,energy density and cycle number of batteries.Cobalt-based bimetallic phosphides have attracted extensive attention from researchers due to their high capacity,low polarization,suitable lithium intercalation potential,long cycle life and economic safety.However,as a negative electrode of LIBs,it inevitably has problems such as large volume expansion and slow charge-discharge rate in the cycle.In this paper,cobalt-based bimetallic phosphides are taken as the research object,and the performance parameters of lithium-ion batteries are improved by rationally designing nanostructures,heteroatom doping and compounding with carbon matrix,so as to promote the development of high capacity,long life and ultra-fast charging lithium-ion batteries.The specific research contents and results are as follows.1.Preparation and lithium storage properties of Co_1.4Ni_0.6P@C HNFs materials.Based on the rational design of nanostructures and the modification scheme of carbon materials,a series of Co_2-xNi_xP@C composites are prepared by solvothermal,phosphating and carbonization methods.The Co_1.4Ni_0.6P@C hollow nanoflowers(Co_1.4Ni_0.6P@C HNFs)sample with the best performance is synthesized by controlling the ratio of nickel ions and cobalt ions in the precursor.In this design,the introduction of a small proportion of Ni atoms can not only produce the optimal electronic structure,but also accelerate the speed of charge transfer,thus accelerating the reaction kinetics;the carbon protective layer outside the Co_1.4Ni_0.6P nanosheets enhances the structural stability of the active material while improving the conductivity of the material,thereby effectively improving the conductivity;the hollow structure can well adapt to the volume change during charging and discharging,thus improving the battery capacity and cycle times;the ultrathin nanosheets are tightly anchored on the conductive carbon,which not only effectively inhibits the agglomeration of the material but also promotes the Li⁺penetration in the electrolyte,thereby prolonging the charge-discharge life of the material.Based on the above advantages,the Co_1.4Ni_0.6P@C HNFs as LIBs anodes exhibits high specific capacity and long cycle life at high rates,that is,the capacity decay rate per cycle at 5.0 A g^-1 is only 0.0015%;after 2000 cycles at10.0 A g^-1,the capacity is 240.6 m Ah g^-1;after 1000 cycles at 20.0 A g^-1,the capacity is still as high as 267.6 m Ah g^-1.2.Preparation and lithium storage properties of Ni-CoMoP@C NSs materials.Based on heteroatom doping and rational design of nanostructure modification schemes,the Ni-CoMoP@C nanosheets（Ni-CoMoP@C NSs）is prepared by solvothermal and annealing methods.In this synthesis method,Ni doping enriches the lattice defects,increases the carrier concentration and conductivity,which is conducive to the rapid electrochemical reaction at high current;porous nanosheets have abundant active sites,which accelerate the transport of ions/electrons,thereby increasing the lithium storage capacity of the material;carbon coating promotes electron transfer and inhibits volume fluctuations during charge and discharge,thereby improving the structural stability of the material.Based on the above advantages,it exhibits high capacity and long cycle life as a negative electrode for LIBs at a large rate,that is,after charging and discharging 800 times at 5.0 A g^-1,the discharge capacity is still 263.0 m Ah g^-1;it has a cycle life of 1700 cycles at 10.0 A g^-1 and a reversible capacity of 261.6 m Ah g^-1.