Development And Energy Storage Properties Of High Tap Density Positive Materials And Electrodes

In recent years,the global energy storage industry has developed rapidly,and the demand for high-energy and high-power lithium-ion batteries in emerging industries represented by electric vehicles continues to rise.The serious concern are causing by the limited resources of lithium,in the industry and the scientific communities,and with the price of lithium-ion batteries higher.Therefore,the development of cheap and high performance potassium（sodium）ion batteries and their application in the field of large-scale energy storage has become the only way to relieve the excessive dependence of human society on lithium ion batteries and realize the sustainable development of energy.However,both lithium ion batteries and potassium（sodium）ion batteries are facing with the same dilemma,that is,the low energy density of the battery is caused by the problems of low specific capacity,low bulk density and low load of positive electrode active material.Because of this problem,the industrial prospects of polyanion cathode materials with low bulk density,such as lithium iron phosphate,are always bleak.Although the safety performance of lithium iron phosphate is far better than that of oxide cathode,high capacity ternary transition metal oxide cathode materials with higher bulk density still occupy the majority of market share.In view of the above key scientific problems,this paper starts researching from two aspects of cathode structure and cathode material;on the one hand,the traditional electrode structure of slurry coating cathode material on aluminum foil current collector is abandoned,and the three-dimensional composite conductive network of aluminum powder and carbon nanotubes is used to prepare ultra thick electrode,which greatly improves the load of cathode active material per unit,On the other hand,the oxygen-rich plasma-enhanced sintering（ORPES）technique was introduced to solve the problem of overburning and homogenization caused by lack of oxygen during the preparation of potassium ion transition metal oxide cathode materials,and ternary transition metal oxide positive electrode potassium ion storage material with high bulk density was successfully prepared,which laid a foundation for the subsequent development of high energy density potassium ion battery.The specific research results are as follows:（1）In order to improve the energy density of lithium iron phosphate anode,aluminum powder was used to replace the traditional metal aluminum foil to construct a three-dimensional fluid collector,to minimize the proportion of non-active components in the electrode.Adding carbon nanotubes to build a three-dimensional conductive network inside the electrode can effectively improve the electronic conductivity and the transmission performance of lithium ions in the thick electrode,and reduce the internal resistance of the battery and the excessive concentration of local current.The ultra-thick lithium iron phosphate electrode with ultra-high load was prepared by mechanical pressure molding method.The key problems such as poor magnification performance and slow reaction kinetics of the super-thick electrode were solved.A small amount of polytetrafluoroethylene was introduced as an auxiliary molding agent to assist the pressure molding and improve the mechanical properties of the ultra-thick electrode.Based on the above electrode structure design and molding process control,the thickness of 400μm Li Fe PO₄ ultra-thick electrode was successfully prepared.The loading capacity of active substance can reach 66 mg·cm^-2 and shows excellent rate performance.With lithium metal as the negative electrode,the capacity of the electrode is maintained at 130 m Ah·g^-1 after 35 cycles at 0.1 C.In addition,the cell battery was assembled by a negative electrode with a load of about 38 mg·cm^-2 lithium titanate materials and a positive electrode with a load of 39 mg·cm^-2 lithium iron phosphate materials,at 0.2 C rate,the capacity of the battery could still maintain 100m Ah·g^-1 after 50 cycles.（2）In line with the original intention of developing cheap and high energy density potassium ion battery,this paper had successfully developed K_0.6Ni_0.2Co_0.3Mn_0.5O₂ layered porous microspheres with high bulk density by using the high bulk density mesoporous microspheres rich in manganese oxide developed by the project team in the early stage as the precursor.The effects of the synthesis process on the structure,morphology and potassium storage properties of the layered cathode materials were also studied.The results showed that the sintering environment and sintering temperature of the mixture of oxide precursor and potassium carbonate had significant effects on the morphology,structure and potassium-storage properties.Among them,in oxygen atmosphere,when the sintering temperature is 750℃and 800℃,the products can keep good spherical shape and high capacity,but there are still many impurity phase.By introducing plasma technology into the sintering process to enhance the sintering degree,single-phase P3 layered structure K_0.6Ni_0.2Co_0.3Mn_0.5O₂porous microspheres with high crystallinity can be obtained while reducing the sintering time and sintering temperature.and the nanostructure and morphology of the precursors are also better maintained.Finally,the layered microsphere transition metal oxide cathode material prepared by oxygen enriched plasma-enhanced sintering technology at 750℃can achieve discharge specific capacity of 108 m Ah·g^-1 at the charge and discharge current density of 10 m A·g^-1,showing a good cycle and excellent rate performance.Although the above two parts of the work need to be further optimized and improved,the combination of aluminum powder、carbon nanotubes and polytetrafluoroethylene assisted mechanical pressure molding technology to prepare high load electrode and high bulk density K_0.6Ni_0.2Co_0.3Mn_0.5O₂ positive electrode can not only better solve the problem of low energy density of potassium ion battery positive electrode,In addition,it can avoid the problem that the cathode material of potassium rich lithium-ion battery is sensitive to water in the traditional slurry coating process,which provides a relatively feasible scheme for the development of more practical low-cost high-energy density potassium ion battery in the future.