Preparation And Properties Of KMnF₃ And Its Composites By Microreactor Combined With Ultrasonic Microwave

Since its discovery,supercapacitor material has been the highlight in the field of energy storage,which makes up for the shortage of traditional battery materials in the field of high-current charging and discharging,leading to possible energy storage devices with both high power density and high energy density.KMn F₃ and its composite materials have been highly expected because of its abundant storage capacity and low price;however,the synthesis route of KMn F₃ and its composites has problems such as difficult continuous synthesis and wide particle size distribution.In this work,a new process was developed for the preparation of KMn F₃ and its composites by combining a countercurrent-flow micro-channel reactor（CFMCR）with an ultrasonic microwave treatment.By comparing the physical and electrochemical properties of the prepared materials,the optimal process route was determined as precipitation and crystallization in a countercurrent flow microchannel reactor combined with ultrasonic microwave coupling（CFMCR M-U）for material aging,labelling as the CFMCR M-U method.Highly crystalline KMn F₃ materials were successfully synthesized and used as electrode materials for supercapacitors.The results showed that the combination of microwave and ultrasonic waves has a decisive influence on the crystal growth,and the KMn F₃ samples obtained by the CFMCR M-U method have a spherical morphology and excellent electrochemical properties.The KMn F₃ samples obtained by the CFMCR M-U method yield smaller KMn F₃ particle materials（～120 nm particle size）compared to previous studies（～5μm）and other literature.This method provides a longer microscopic mixing time,resulting in a more uniform size distribution and elemental distribution of the precipitates,as well as a higher specific capacitance.The optimal process conditions for the CFMCR M-U method were determined as follows:the CFCMR inlet flow rate was set to 40m L·min^-1;the KF and Mn Cl₂ solution concentrations were 10 mol·L^-1 and 50mmol·L^-1,respectively;the total volume of the two solution feeds was equal,and the aging mode was set to 120 min under combined ultrasonic microwave conditions with an aging temperature of 30°C.The ultrasonic power was set to1000 W,the ultrasonic generator operating mode was set to continuous operation,and the microwave was controlled by a temperature sensor with a power setting of 1000 W.The optimized KMn F₃ materials synthesized by the CFCMR M-U method had specific capacitances of 738.18 F·g^-1 and 601.82F·g^-1 at current densities of 1 A·g^-1 and 5 A·g^-1,respectively.It was significantly higher than previous materials prepared by CFCMR,showing a higher energy storage capacity and excellent cycling stability:the initial specific capacitance retention was 91.8%after 2500 cycles of charge and discharge.The effects of the introduction of Ni,Co elements on the synthesized KMn F₃ materials were investigated preliminarily,and better specific capacitance performance was achieved at Mn-Co and Mn-Ni molar ratios of4:6 and 2:8,respectively.The sample with Mn-Co ratio of 4:6 in the material exhibited a specific capacitance of 883 F·g^-1 and a specific capacitance retention rate of 102.7%after 1000 cycles of charge and discharge.The sample with Mn-Ni ratio of 2:8 exhibited a specific capacitance of 1186 F·g^-1 and a specific capacitance retention rate of 91.4%after 1000 cycles.This was consistent with the effect of Co and Ni in the ternary material to enhance the cyclic charge-discharge performance,respectively.