As the society attaches great importance to green and environmental protection, new electrochemical energy storage technologies are constantly updated. Lithium-ion batteries, due to their high energy density, high safety, light weight and long life, occupy a large market share in electrochemical energy storage technologies, such as new energy vehicles, mobile phones and power tools.
However, with the widespread use of lithium-ion batteries, its disadvantages are becoming more and more apparent
Due to the scarcity of lithium resources, high price and low power density, the study of new electrochemical energy storage technology to replace lithium-ion batteries has become the focus of research on chemical power sources. Potassium and lithium are in the same group of elements, but potassium reserves in the Earth’s crust are much richer than lithium, and it is widely distributed and cheap. More importantly, potassium is used in ion batteries, which has a reaction mechanism similar to that of lithium-ion batteries. So it becomes the focus of current electrochemical research.
Potassium vanadium phosphate (k3v2 (po4)3) belongs to polyanion compounds, which has the advantages of stable crystal structure, high working voltage, large diffusion channel and high safety performance. It is regarded as a positive material for potassium ion batteries with promising application prospects. However, due to the low electronic conductivity and ionic diffusion coefficient of phosphate polyanions, their multiplier properties, cycling properties and capacity are affected, resulting in poor electrochemical performance and difficult to be applied in practice. The literature on potassium vanadium phosphate is mainly based on morphology change, ion doping and nanostructure design. In order to improve the electrochemical performance of the material, however, the preparation method is complicated, the conditions are harsh, the cost is high, and the cycle is long, which is not conducive to the realization of commercial production
The following steps are included: (1) Weighing phosphorus salt compounds, vanadium source compounds, potassium source compounds, iron source compounds and complexing agents according to molar ratio p:v:k:fe:c=3:2-x:3:x:3, dissolve in a certain amount of deionized water, heat and stir complexing for 1 hour to form orange sol slurry.
(2) Spray drying the orange-yellow sol slurry in (1). The sample pump of the spray dryer will press the slurry into the nozzle and spray it to form very fine spherical droplets, which will fall in the hot air flow at a certain velocity for heat exchange
Large, so that the solvent evaporates quickly, drying and granulation process can be completed instantaneously, to obtain blue green dry porous loose, uniform without agglomeration, ultrafine precursor.
(3) The precursor dried in (2) is calcined by two-step method under inert atmosphere. It is heated to 250-400℃ at the heating rate of 1-10℃/min and kept for 4-6h. Then it was heated to 600-1000℃ at the heating rate of 1-10℃/min, held for 8-16h, and then cooled to room temperature in the furnace to obtain black cavernous porous iron-doped modified vanadium potassium phosphate/carbon composite cathode material.
The invention has the following beneficial technical effects: 1. The invention stabilizes the crystalline structure of the material through iron ion doping modification, and the doping of iron ions produces lattice defects, which is conducive to the removal and embedding of potassium ions, so as to improve the charge-discharge capacity and cyclic performance of the material.
By sol-gel method, the reactants in the solution can reach a uniform distribution at the molecular level, which is conducive to the completion of the reaction in a low temperature and a short time. By controlling ph value, reaction temperature and time, the sol slurry suitable for molecular size and viscosity can be obtained, and the production process is simple and can be effectively controlled, with high product consistency.
By spray drying, the invention has low energy consumption and high production efficiency, and can obtain porous precursor, uniform without agglomeration and ultra-fine, which is conducive to improving the electrochemical performance of the material.
The present invention forms carbon coating with high electron conductivity on the surface of the product through carbonization of the complex agent under inert atmosphere and high temperature. At the same time, the in-situ carbon coating can inhibit the particle agglomeration and crystal growth of the material, which is conducive to obtaining the product with smaller size and improving the electronic conductivity of the material.
The particle size of the porous porous Fe-doped modified vanadium potassium phosphate/carbon composite anode material prepared by the invention can be controlled within 2-5μm. It has high specific capacity and good rate performance, but also shows excellent charge-discharge cycle stability, so as to improve the electrochemical performance and energy density of potassium ion batteries, and is conducive to the application and development of ion batteries. It has good application prospect.
