Controllable Preparation And Performance Regulation Of Iron-Manganese Binary Layered Oxide Cathode Materials For Potassium Storage

Potassium has extremely high resource reserves.Besides,it has low standard electrode potential and excellent transport kinetics in electrolyte.Because of the shortage of lithium resources,the price of energy storage equipment has been raised and the market of lithium-ion battery is in short supply.Therefore,the development of high-performance potassium-ion batteries is considered to be an effective way to solve the problem.The radius of potassium ions are large,which makes it difficult for them to diffuse in the material.For this reason,structural deformations are often caused during the ion de-intercalation process,resulting in poor cycle performance of battery.Therefore,potassium-ion batteries lack cathode materials with high capacity,high redox potential,and good structural stability to meet practical needs.Some researchs show that binary iron manganese layered transition metal oxide cathode(K_xFe_0.2Mn_0.8O₂)has low manufacturing cost and high capacity,so it is considered as a valuable and potential electrode material.To increase the study of correlation between structure and performance,this work research the effect of changes in K content to the structure and electrochemical performance.This study is wished to improve the performance of material.Besides,binary iron manganese carbonate precursor is produced by coprecipitation and the reaction conditions are researched to get a better product.The final product is affected by precursor and we wish that we can improve the electrochemical performance by nanostructured design.The specific research contents are as follows:（1）A series of K_xFe_0.2Mn_0.8O₂（x=0.4,0.5,0.6,0.7）with different K contents were prepared by the simple method of ball milling assisted solid phase sintering.We regulatory component by controlling molar ratio of potassium salt to ferromanganese transition metal oxide.It was found that the increased K content not only leads to the increase of layer spacing,but also improves the absorbency and alkaline of product.Besides,the increased K content can increase the size of K_xFe_0.2Mn_0.8O₂ flake particles to a certain extent.Observed by HRTEM and EDS,the producted K_xFe_0.2Mn_0.8O₂ particles are single-phase particles with uniform composition.The electrochemical test results show that the producted K_xFe_0.2Mn_0.8O₂ exhibits the highest capacity,optimal cycling and rate performance as an electrode material for potassium-ion batteries when the content of K is 0.5.When the current densities are 20,50 and 100 m A g^-1,K_0.5Fe_0.2Mn_0.8O₂ can deliver the specific capacity of 128.4,86.4,72.6 m Ah g^-1,respectively,which is better than other products.（2）Spherical iron-manganese-based oxides was prepared by coprecipitation method,and synthesis conditions which can affect product structure,morphology and composition have been explored,including the effect of each reaction condition and ascorbic acid（VC）.The spherical iron-manganese-based binary cathode materials were successfully prepared.The results show that the product without VC addition is covered by a large number of iron oxide particles and the composition of the product is more uniform and the structure is more compact with the addition of VC.Finally,A series of spherical iron-manganese-based binary layered oxide cathode materials with poor surface potassium are produced by mixing the prepared spherical precursor and appropriate amount of potassium salt and plasma assisted solid state sintering technology.The research shows the Fe-Mn-based binary layered oxide cathode materials（named KMFO-VC and KMFO,respectively）obtained from the precursors with and without VC addition during the preparation process exhibit similar potassium storage performance.Even KMFO-VC show higher specific capacities at current density of 20 and 50 m A g^-1,KMFO presents better long cycle performance at the above current densitiesAfter analysis and comparison,the above results show that the simple method of ball milling assisted solid phase sintering is more simple and more suitable for chemical composition regulation and product manufacturing than coprecipitation method.K_0.5Fe_0.2Mn_0.8O₂ produced by ball milling assisted solid phase sintering shows higher capacity and has better rate capability and cycling stability than KMFO and KMFO-VC with mesoporous nanostructure.Finally,precise control of structure and content is the key to developing high-performance cathode potassium storage materials.