Reaction Kinetics And Performance Research Of Ti₂CT_x MXene And Co_0.85Se@CNT Cathode Catalysts In Li-O₂ Batteries

The power generation principle of lithium-oxygen batteries is to oxidize lithium metal at the anode to produce electrons and lithium ions.The electrons supply power to the external circuit.The lithium ions are conducted to the cathode through the electrolyte inside the battery,and oxygen molecules in the air and electrons flowing into the external circuit.The reaction is carried out to form a complete electrochemical reaction to generate electricity.The lithium-air battery uses air as the reactant,which solves the problem of fuel storage space,which makes the lithium-air battery more portable and compact.Lithium-air battery is the development direction of the future battery.In the past one or two years,the research on it has gradually increased.Its advantages mainly include the following points:(1)Ultra-high specific energy.Compared with normal cathode materials for lithium-ion batteries,the cathode active material of lithium-air batteries is air,which is inexhaustible.In the case of excessive anode,the termination of discharge is caused by the discharge product blocking the air electrode pores.In practical applications,oxygen is provided by the external environment,so the energy density after removing oxygen reaches an astonishing 11140 Wh kg-1,which is one to two orders of magnitude higher in lithium battery systems.(2)It is reversible.In 2006.P.G Bruce reported for the first time a lithium-air battery with good cycle performance.A suitable catalyst also helps to reduce the charging voltage and prolong the battery life.(3)Environmentally friendly and low price.As an environmentally friendly battery system,lithium-air batteries are clean energy sources and undoubtedly have broad application potential and are expected to be widely used in the future.The practical application of lithium-air batteries is currently still limited by several key factors,such as severe polarization,high overpotential,poor cycle stability,low energy conversion efficiency,and easy corrosion of lithium metal anodes.The development and optimization of cathode catalyst materials for lithium-oxygen batteries will help improve and enhance the electrochemical performance of the batteries,and promote the development of lithium-oxygen battery applications.Stable and efficient cathode catalyst materials can effectively promote the lagging redox reaction kinetics of lithium-oxygen batteries,reduce battery overpotential,and improve energy conversion efficiency.As an ultra-thin two-dimensional carbide or nitride material,MXene has the advantages of lower resistivity,controllable surface functional groups and adjustable interlayer spacing than graphene.The unique electronic structure,large surface area,and lattice matching with Li2O2 make MXene one of the most promising cathode materials for lithium-oxygen batteries.The microscopic morphology of the cathode catalyst material has a great impact on the performance of lithium-oxygen batteries.Transition metal selenides have been widely researched and applied in the fields of energy,catalysis,electromagnetics,etc.due to their excellent catalytic performance,diverse electronic structures,easy-to-control microscopic morphology,and rich reserves.In addition,adjusting the composition and electronic structure of the cathode catalytic material can have a huge impact on the formation and decomposition of the discharge product Li2O2 in the lithium-oxygen battery,thereby affecting its morphology and the final electrochemical performance of the battery.The main research contents of this paper are as follows:(1)In this paper,the catalytic properties and mechanism of Ti2C MXene nanosheets with heterogeneous surface groups(-O,-F)as cathode catalysts for lithium oxygen batteries are studied.Fabricated Ti2C MXene nanosheets with-O and-F functional groups on the surface,which were used in lithium-oxygen battery cathode catalysts to obtain superior electrocatalytic activity,and first-principles theoretical calculations were used to study ORR/OER under different surface conditions.The reaction path and catalytic activity.DFT calculations show that compared with Ti2CF2 surface,Ti2CO2 surface as the main catalytic site provides an efficient one-electron reaction pathway for the adsorption nucleation-decomposition process of Li2O2,while the exposed surface of Ti2C leads to catalytic ability due to the strong chemical bond combination with Li2O2 reduce.In addition,uneven surface conditions are believed to promote the polarization nucleation and growth of the discharge products,and the nano flakes accumulated perpendicular to the direction of the lamellae eventually form a porous structure of the discharge products,thereby providing an effective way for electron and ion transport.(2)This article introduces a Co0.85Se@CNT as a high-efficiency lithium-oxygen battery cathode catalyst material,and further studies its electrochemical performance and the corresponding reaction catalytic mechanism.Through the one-step hydrothermal method,cobalt selenide nanoparticles anchored on carbon nanotubes are prepared and used in the research of lithium oxygen battery catalysts.Preliminary experiments and experimental results demonstrate that Co0.85Se@CNT composite material has good catalytic performance in lithium oxygen batteries.The mechanism of promoting the growth and decomposition of lithium peroxide is explored,and the synthesis conditions are adjusted to obtain the optimal material structure.And electrochemical performance.The obtained optimal material expresses an excellent capacity of 9327.9 mAh g-1 at a current of 100 mA g-1,and has an excellent stability of more than 200 cycles under the capacity limit of 600 mA g-1.