The Preparation Of Carbon-Cobalt Phosphide Composite Material And Its Properties Of Lithium(Sodium) Storage

Due to its high energy density,no memory effect and low environmental pollution,Lithium（sodium）ion batteries are considered as important candidates for the next generation of energy storage devices.Consequently,the continuous developing of electric vehicles have been promoted the lithium（sodium）ion batteries reseach on exploring suitable electrodes with high specific capacity,high rate performance,long cycle life and low-cost.Based on these considerations,many researchers expanded their sight to phosphides due to its good thermal stabilities and abundance resource.Among those phosphides,CoP with a high theoretical capacity of 894 mAh g^-1 and relatively low charge and discharge voltage platforms（0.9 and 0.6 V,respectively）is suitable for secondary battery anodes.However,the rapidly decrease of specific capacity and cycle life from the structure change and serious volume expansion,which usually leads to the irreversible collapse and mechanical damage during charge and discharge processes.In view of the above problems,this paper focus on the construction and development of a mild synthetic route to synthesis carbon/cobalt phosphide composite materials to accommodate the volume change and thus with enhanced the electrochemical performance,the main work of this dissertation is as follows:The composite of biomass carbon and cobalt phosphide（CoP/C）was constructed by three steps consisting of impregnation recrystallization-in situ chemical transformation and low temperature phosphating.Dried hericium erinaceus were first immersed in the Co（NO₃）₂ solution containing different concertation,and made the salt recrystallized into the internal pore with the water evaluation.Up on the calcined process,the decomposition of the salt crystal will caused an in-situ activation and synchronous cobalt nanoparticles doping into the carbon matrix.The nanorod morphology were formed during the chemical reaction between Co nanoparticels and the oxalic acid.Finally,the CoP/biomass dervied carbon composites were obtained by low-temperature phosphating.By controlling the concertation of cobalt nitrate,CoP/C with different CoP loading materials were prepared and further used as the anode of Li-ion battery.Among them,when the concentration of cobalt nitrate solution is 0.15 mol L^-1,the as-prepared material（CoP/C-0.15）exhibited the best performance,a specific capacity of 292 mAh g^-1 is obtained at a current density of 1000 mA g^-1,and the specific capacity can still kept 152 mAh g^-11 at a current density of 5000 mA g^-1.As an anode for sodium ion batteries,the CoP/C-0.15 showed a 99 mAh g^-1 specific capacity after 100 cycles at a current density of 100 mA g^-1.By using zeolite imidazole framework（ZIF-67）as templates,the CoP@CNTs with a core/shell structure have been successfully fabricated via a low temperature phosphidation process.The obtained CoP@CNTs sample displays uniform polyhedral morphology with an average size of 700 nm.The CoP@CNTs composite was tested as an anode material for lithium ion batteries.The initial discharge/charge capacity is 1401/851 mAh g^-1,respectively,corresponding to an initial coulombic efficiency of 60.7%.After 100 cycles at a current density of 100 mA g^-1 and 1200 cycles at a current density of 1000 mA g^-1,specific capacity of 507 and 494 mAh g^-1 were retained for CoP@CNTs,it showed good lithium storage properties as anode materials for LIBs.In the meantime,the composite also exhibited excellent Na storage properties.After 100 cycles at a current density of 100 mAh g^-1,the capacity of the CoP@CNTs nanorods electrode remains around 251 mAh g^-1.After 1000cycles at current density of 1000 mA g^-1,the specific capacity was 155 mAh g^-1,showing a good sodium storage performance.