Research On Precise Regulation Of Lithium Peroxide And Mechanism In Non-aqueous Lithium Oxygen Batteries

With the rapid development of high energy density electrochemical energy storage systems,the requirements for portable electronic devices and electric vehicles to extend their service life and increase the driving range are constantly raising.Existing rechargeable secondary batteries are close to the limits of their theoretical energy density but still struggle to meet the demand for range,therefore,it is urgent to develop high specific energy secondary battery systems to meet future energy demands.Lithium-oxygen（Li–O₂）batteries with high theoretical energy density(3500 Wh kg^-1)are considered to be a promising choice.However,many key scientific issues such as seious polarization,poor rate,capacity and inferior cycle performance have severely limited its commercialization process.The sluggish cathode reaction kinetics and the irregular deposition of the insulated discharge product Li₂O₂ on the surface of cathode would block the migration of superoxide,electrons and Li⁺at the cathode,leading to large polarization and poor energy conversion efficiency.To solve the above problems,this research mainly focuses on precisely regulating the morphology,structure and deposition of Li₂O₂ to improve the round-trip efficiency and cycle life of the battery,and the following work are carried out:1.The localized surface plasmon resonance（LSPR）effect was introduced into the Li–O₂battery system to accelerate the redox reaction kinetics and effectively regulate the morphology of the discharge products.Firstly,a flexible air cathode（Ag@CC）was prepared by in-situ deposition of Ag nanoparticles with a diameter of about 20 nm on a conducting carbon fiber（CC）by chemical deposition method.The related electrochemical performance and the product selectivity have been systematacially studied in Li–O₂ batteries.Benefiting from the synergistic effect of the hot electron effect and plasmonic thermal effect,the discharge voltage is significantly increased to 3.217 V,the charging voltage is reduced to 3.249 V,and the round-trip efficiency is up to 99%.In addition,during discharge,the amount of Li₂O₂ on the surface of the cathode rapidly increased due to the amounts of nucleation sites provided by the excited hot electrons on the surface of Ag@CC cathode with LSPR.Under illumination,a film-like discharge product of0.2～0.3μm is formed on the surface of Ag@CC.Compared with the toroidal shape Li₂O₂without illumination,good electronic transmission and high electrochemical activities are displayed.2.The study of dynamic evolution of catalytic activity centers and battery reaction intermediates under working conditions is crucial to the electrochemical performance and the effective regulation of the product microstructure of Li–O₂ batteries.Based on the designed model of Co single-atom catalyst with the same chemical environment and uniform distribution,the structural dynamic evolution of near-free active centers and the complex cathode electrochemical reaction pathway are deeply studied at the atomic level for the first time by monitoring the changes of their structure and composition at multiple scales.Compared with the saturated Co-N₄ structure,the near-free Co（Co₁-N₃）active center interacts weaker with the substrate,and its 3d orbitals also show higher electron density,forming a freer O^*-Co₁-N₂active site during the discharge process.Energetically,more electrons transfer from the 3d orbital of Co to the adsorbed O^*intermediates,which is conducive to the surface adsorption and activation of key intermediates,thus achieving an efficient oxygen reduction process.In addition,due to the higher lattice matching degree of Co₁-N₃ and（100）crystal face of Li₂O₂,the preferential nucleation growth of Li₂O₂ crystals at（100）crystal plane occured to inhibit the growth of thickness direction（（101）crystal plane direction）,contributing to the generation of two-dimensional sheet-like Li₂O₂ with uniform size and orientation.Compared with the toroidal Li₂O₂,single-oriented sheet-like Li₂O₂ displays higher electron transport capacity and weaker^*LiO₂ combination,thus improving the kinetics of oxygen evolution reaction.Therefore,by regulating the matching degree between the active center and the Li₂O₂lattice,the morphology and crystal structure of the product can be controlled efficiently.The results demonstrate that the morphology and crystal structure of the product can be efficiently regulated by adjusting the matching degree between the active center and the Li₂O₂ lattice.3.The insulated discharge products deposited on the cathode of Li–O₂ batteries would hinder the diffusion of oxygen and the transfer of electrons.Adjusting the deposition process of the product in the discharge stage,and then accurately regulating the deposition position of the product would effectively improve the battery performance.Inspired by the self-assembly of biomineral tissues,we develop the ammonium bromide-modified zeolite microtube woven fabric（NH₄ZMT WF）separator by a precursor scaffold-solid phase crystallization strategy to construct Li–O₂ batteries,and its electrochemical properties and precise regulation of products were studied in depth.Since the surface of NH₄ZMT WF separator is rich in positively charged NH₄⁺,O₂^-can be trapped by the generated ion pairs with NH₄⁺（NH₄⁺-O₂^-CIP）,followed by disproportionation reaction and conversion to the final product during the discharge process.NH₄ZMT WF separator can effectively combine both the capture and conversion steps,then extend the discharge reaction region to the separator and and relieve the cathode passivation.The Li–O₂ batteries with NH₄ZMT WF separator exhibit a greater capacity than 25000 mAh g^-1 and a prolong cyclability of 4000 h.The encouraging performance offers hope for the practical application of Li–O₂ batteries.In this paper,to solve the key scientific problem of cathode passivation for Li–O₂ batteries,we propose a series of novel strategies to achieve the precise regulation on the morphology,structure and deposition of Li₂O₂.Combined with multi-dimensional monitoring methods,the reaction kinetics and the deposition/decomposition mechanism of the discharge products for Li–O₂ batteries were studied,which has provided a new idea for the in-depth research of lithium oxygen battery and lays a theoretical and experimental foundation for the development of high-performance Li–O₂ batteries.