Study On Construction And Performance Of Lithium-ion Capacitors Based On Natural Ore Molybdenite

With the rapid development of the global economy,environmental pollution and energy crisis are becoming increasingly serious.The use of traditional energy such as coal and oil will cause the greenhouse effect.In order to achieve the concept of"carbon neutrality",it is very important to develop clean,efficient and low-cost energy storage systems.In addition,military drones,electromagnetic catapults,high-power detection and other weapons require fast-charge power supply equipments,among which,supercapacitors show promising applications due to their unique advantages（such as high power density,fast charge and discharge and long cycle life）.However,the low energy density limits its wide application.The ideal solution is to combine battery-type and capacitive electrode materials into one system to build a so-called lithium-ion capacitor（LIC）.As a new type of energy storage device,LICs have the double advantages of lithium-ion battery and supercapacitor,showing high energy density,high power density and good cycle stability.The key to building a high-performance LIC is to couple the anode material and the cathode material with matching capacity and dynamics.At present,most of the positive electrodes of commercial lithium ion capacitors use activated carbon with high specific surface area.However,the research and development of negative electrode materials are still difficult to match the commercial application and production.Among many anode materials,molybdenite has the advantages of environmental protection,low price,abundant reserves and high specific capacity.The main component of natural molybdenite is Mo S₂,which has the advantages of high theoretical specific capacity,large natural reserves and low cost.Among them,the layer spacing of molybdenum disulfide is conducive to the diffusion of metal ions,and is an ideal anode material for preparing high-performance lithium ion capacitors.In addition,vigorously developing the comprehensive utilization of mineral resources also matches the national sustainable development policy.This paper takes molybdenite based composite materials as the research object,and uses the unique morphological characteristics of natural molybdenite and the characteristics of cheap and easy to get,to build a high-performance,low-cost lithium ion capacitor device,which provides a new idea for the application of natural mineral materials in lithium ion capacitors.By synthesizing composite materials from molybdenite,aiming at its performance defects,design and optimize the preparation of negative electrode materials,match with high capacity positive electrode,discuss the energy storage mechanism of positive and negative electrodes,and then assemble lithium ion capacitors.It also provides theoretical basis and application guidance for the development of lithium ion capacitor systems with high power density and high energy density.The research results of the thesis are as follows:1.Study on Li⁺storage performance of molybdenite@pitch-derived carbon.A soft carbon coated molybdenite based anode material was prepared using natural molybdenite as the substrate and asphalt as the carbon source.The composite material could be used as the anode to assemble lithium ion capacitors,which could achieve excellent lithium storage performance.We choose a cheap bitumen as a carbon source.By using the asphalt burn into a soft carbon uniformly coated in natural glow molybdenum.The coating of soft carbon on the surface of molybdenite forms Mo-C bond,which effectively improves the cycle stability and electronic conductivity,and the synergy of the two effectively improves the electrochemical performance of the energy storage device.This method is simple and convenient for mass production.The Mo S₂/carbon electrodes derived from the glow molybdenum not only exhibit excellent Li⁺storage properties,including ultra-high specific capacity(1427 m Ah g^-1 after 1000times,1000 cycles)and magnification capacity(at 10 A g^-1,546 m Ah g^-1),and the vibration density is four times the commercial graphite.By using Mo S₂/carbon as an anode,activated carbon（AC）as a cathode,an assembled lithium-ion capacitor device exhibits high energy density of 114 WH kg^-1,and the performance will not have too much attenuation after undergoing cycles.2.Study on lithium storage performance of thin-layer natural molybdenite with reduced graphere oxide（r GO）.The thin layer of molybdenum disulfide was prepared from natural molybdenite by simple expansion and stripping method,and the r GO coated thin layer Mo S₂composite（TMG）was prepared by compounding it with graphene oxide.The lithium ion capacitor assembled with it as the anode can achieve excellent long cycle stability and magnification performance.r GO plays the role of packaging protection and improving conductivity.Molybdenum disulfide in the thin layer has more reactive active sites.The synergy of the two makes the device obtain excellent performance.Lithium-ion hybrid capacitors were assembled with thin-layer molybdenum disulfide&r GO composite（TMG）as anode and activated carbon（AC）as cathode.The assembled LIC devices provided high energy/high power density and long cycle life.Nanocomposites prepared by using natural molybdenite for lithium-ion capacitors have shown excellent performance,which also provides a reference for the commercial utilization of molybdenum resources in the field of energy storage.3.Lithium storage properties of C/Mo S₂ composites prepared in-situ from molybdeniteBy in-situ calcination conversion method.Molybdenite was oxidized to molybdenum oxide,and carbon coated Mo S₂ samples（RM）were successfully prepared by carbothermal reaction and subsequent sulfurization treatment.Lithium ion capacitors assembled with them as negative electrodes have high power density/energy density.The synthesized carbon coated molybdenum disulfide composite shows excellent lithium-ion storage performance,and shows a high specific capacity and long cycle stability of 913.8 m Ah g^-1 at a current of 1 A g^-1 in a lithium ion half-cell.A lithium-ion hybrid capacitor was assembled with RM as the anode and activated carbon（AC）as the cathode,achieving a high energy density of 116.8 Wh kg^-1.Molybdenum disulfide forms a unique interface with the carbon generated in the reaction,which can greatly promote the transport and diffusion of lithium ions and electrons,slow down the volume expansion of the electrode to a certain extent,and improve the cycle stability.In this work,high-performance composites prepared by a simple and low-cost way are expected to be applied to the next generation of lithium-ion capacitors on a large scale.4.Study on lithium storage properties of carbon nanofiber coated molybdenite CompositesThe natural molybdenite and polyacrylonitrile（PAN）are compounded by using the electrospinning technology that can be produced in a large scale,and the carbon nanofiber coated molybdenite composite（EM）is further calcined to prepare,which can be directly used as the cathode of lithium ion capacitors and show excellent lithium storage performance and commercial application potential.The carbon nanofibers in the composite material wrap molybdenite to form a composite interface,providing a channel for the transmission and diffusion of lithium ions and electrons in the device.The carbon fiber layer on the surface of molybdenum disulfide can effectively buffers the volume change caused by the insertion and removal of lithium ions.These structural characteristics make EM exhibit high specific capacity and long cycle stability.The direct combination of natural minerals and electrospinning has made a breakthrough in performance,which also provides a new research idea for follow-up researchers to develop low-cost and efficient hybrid ion capacitors in the field of energy storage.In this thesis,a variety of composite materials based on natural molybdenite were designed and prepared for the anode of hybrid ion capacitors.By selecting the positive electrode material of activated carbon and matching the prepared negative electrode material to assemble a lithium-ion hybrid capacitor,high energy density/power density and long cycle stability can be achieved.It provides a new research approach and method for the efficient utilization of natural mineral composite materials and the development of mixed ion capacitor anode materials with good market prospects.