Preparation Of Key Materials And Electrochemical Performance Research For Li–CO₂ Battery

Developing rechargeable batteries with high energy density,high safety,and stability remains a long-term goal in the field of electrochemical energy storage devices and new energy technologies.Among the candidates for next-generation energy storage systems,lithium–carbon dioxide（Li–CO₂）batteries,due to their ultra-high energy density and ability to convert CO₂,are considered as one of the most promising new types of rechargeable batteries.However,the development of these batteries still faces a series of scientific challenges that hinder their progress towards mass production and application.Chief among these challenges is the slow reaction kinetics at the cathode,a critical area for the CO₂ redox reaction,which results in substantial polarization during charge/discharge cycles,low energy efficiency,poor rate performance,and short life cycles.Moreover,as an open system,the use of flammable liquid electrolytes poses safety risks.This thesis addresses these challenges through a series of research initiatives aimed at optimizing and enhancing the performance and safety of Li–CO₂batteries.1.Development and design of high-performance porous cathodes through light field assisted strategies to improve battery reaction kinetics.（1）Inspired by photocatalytic CO₂ reduction,a flexible and self-supporting In2S3@CNT/SS photocathode from a structural and functional perspective was prepared.The construction of a heterojunction composite structure of In₂S₃ with CNTs facilitated the effective separation of photogenerated electrons and holes,thereby enhancing the kinetics of the CO₂ redox reaction.Photo-assisted Li–CO₂ battery assembled by In₂S₃@CNT/SS photocathode demonstrated a high discharge platform of3.14 V and a round-trip efficiency of up to 98.1%.Owing to the flexible design of the electrode,the photo-assisted Li–CO₂ battery also shows excellent bending adaptability.Furthermore,the impact of photogenerated electrons and holes on the deposition and decomposition processes of discharge products was thoroughly explored,proving the efficacy of the In₂S₃@CNT/SS photo-cathode in controlling discharge products.（2）Based on plasmonic resonance effects,the Au@Ti O₂ photocathode was designed and synthesized to study the impact of introducing light energy on battery performance from both photovoltaic and photothermal conversion aspects.This cathode effectively expanded the light absorption range,as well as facilitated the efficient separation of photogenerated electrons and holes through the construction of a Schottky heterojunction,promoting the kinetics of CO₂ redox reactions.Utilizing the Au@Ti O₂photocathode loaded on the solid electrolyte LAGP framework,an all-solid-state Li–CO₂ battery was assembled and its electrochemical performance was studied.The Au@Ti O₂/LAGP framework efficiently transmits Li⁺and heat,ensuring safe and stable operation of the all-solid-state Li–CO₂ batteries over a wide temperature range（-73 to150°C）.Under illumination,the all-solid-state Li–CO₂ batteries exhibited significant improvements in rate performance(1 m A cm^-2)and cycle life（400 h）.2.Enhancing battery safety through the design of new solid-state electrolytes for battery solidification.（1）Combining the advantages of ILs and MOFs,an IL@MOF new solid-state electrolyte was prepared using an encapsulation strategy.The micro-mesoporous structure of MIL-101 effectively encapsulates the internal ionic liquid,facilitating the dissociation and efficient transport of Li⁺.The MOF framework filled with ionic liquid not only improved mechanical strength but also reduced interfacial impedance.IL@MOF exhibits excellent conductivity(1.03 m S cm^-1)and high Li⁺transference number（0.80）.Furthermore,a CNT-IL@MOF solid-state cathode was prepared to improve ion/electron transport channels at the cathode/electrolyte interface.The IL@MOF/CNT-IL@MOF-based solid-state Li–CO₂ battery demonstrates high safety and a long cycle life of up to 441 cycles.（2）Investigating new structures led to the development of a new solid-state electrolyte based on the Keggin framework of polyoxometalate,Li₃PW₁₂O₄₀.The three-dimensional ion transport channels in the Keggin framework provide an efficient pathway for Li⁺with low activation energy.Benefiting from the good plasticity of Li₃PW₁₂O₄₀,a high-density electrolyte could be fabricated using cold press technology.Utilizing recycling strategies,the cost of Li₃PW₁₂O₄₀ is reduced to$5.68 kg^-1.Expanding the Keggin framework through ion equivalent substitution,Li₃PMo₁₂O₄₀was further fabricated as a solid-state cathode.The Li₃PW₁₂O₄₀/Li₃PMo₁₂O₄₀-based solid-state battery not only demonstrates improvements in reaction kinetics and cycle life but also exhibits high environmental adaptability,capable of operating safely at humidity levels up to 50%.In this thesis,solutions to key scientific challenges faced by Li–CO₂ batteries are proposed from the perspectives of light field assistance and battery solidification.Various testing methods were employed to study the electrochemical performance,reaction kinetics,and control over the deposition and decomposition of discharge products of the cathode and solid-state electrolyte.This dissertation providing new research directions for the development of Li–CO₂ batteries.