The Preparation And Lithium-ion Energy Storage Characteristic Of Pseudocapacitive Controlled Perovskite Fluorides Anode Materials

The limited reserves,low efficiency and high pollution of traditional fossil fuels have promoted the development and utilization of efficient,environmentally friendly,green and sustainable energy.Energy storage technology is crucial to the practical application of these green energy,among which,lithium-ion batteries,lithium-ion capacitors and lithium-based dual-ion batteries are three types of electrochemical energy storage devices with great application prospects.These three types of devices show their respective advantages and disadvantages in electrochemical performances such as energy density,power density,and cycle life based on the cathode materials with different energy storage mechanisms.However,battery-type anodes are commonly used for these three devices.At present,the most studied and commercialized battery-type materials are graphite anodes with lithium-ion intercalation mechanism.However,the limited active sites and the slow Li⁺diffusion of this kind of intercalation-type anodes lead to inferior specific capacity and rate capability of the three lithium-ion based devices.Therefore,to develop pseudocapacitive conversion or alloying type anode materials with fast kinetics is a novel research idea to build efficient lithium-based energy storage devices.In this paper,two types of pseudocapacitive controlled transition metal perovskite fluorides materials were synthesized and used as anodes for the above lithium-based energy storage devices.The kinetics characteristics and lithium storage mechanisms of these materials were also discussed.The main contents are as follows:?1?A series of bimetallic perovskite fluorides,KCo_xMn_1-xF₃?KCMF?with different Co/Mn mole ratios were synthesized by one-pot solvothermal method.The optimal Co/Mn?3:2?was assessed by electrochemical performance of KCMF electrodes.A typical pseudocapacitive controlled conversion mechanism for lithium-ion storage of KCMF?3:2?anode could be deduced by ex-situ XPS?TEM and SAED characterizations of pristine KCMF?3:2?powder,fully discharged-state and charged-state KCMF?3:2?electrodes as well as CV tests with different scan rates of KCMF?3:2?half cells.KCMF?3:2?/r GO composite was further synthesized through the combination of one-pot solvothermal method and ball-milling.The crystal structure and micro-morphology of KCMF?3:2?and KCMF?3:2?/r GO composite were compared by XRD,SEM,TEM,TG,Raman,etc.The robust hetero-nanostructure between the KCMF?3:2?particles and graphene sheets made the KCMF?3:2?/r GO electrode exhibiting higher capacity,more superior rate capability and cycling performance.The constructed lithium-ion battery,lithium-ion capacitor and lithium-ion capacitor/battery hybrids with KCMF?3:2?/r GO anode exhibited superior electrochemical performance.This work is of great significance to the development of conversion-type anode materials with pseudocapacitive characteristics and the design of novel lithium-based energy storage devices.?2?Low-cost metallic perovskite fluorides KZn F₃?KZF?was synthesized by one-pot solvothermal.The physicochemical properties,such as crystal structure,micro-morphology,specific surface area,pore size distribution,et al.of KZF sample were characterized by SEM,TEM,BET,et al.Novel pseudocapacitive controlled conversion/alloying hybrid mechanisms for lithium-ion storage of KZF anode could be deduced by ex-situ XPS characterization of KZF powder and the first fully discharged/charged KZF electrodes as well as CV tests of KZF half cells.The constructed lithium-ion based dual-ion battery with KZF anode and graphite?918?cathode exhibited superior electrochemical performance.This work is of great significance to the development of conversion/alloying hybrid type anode materials with pseudocapacitive characteristics.