Studies On The Construction Of Stable Solid-Liquid Interfaces For Anodes In Lithium Metal Batteries And Their Electrochemical Performance

The growing demand for energy storage has promoted the vigorous development of high energy density battery systems.Lithium metal has a very high theoretical specific capacity and the lowest electrochemical potential,making it an ideal anode material for next-generation high-energy-density batteries.However,due to its low hardness and hostless property,highly reactive Li is prone to severe interfacial side reactions and significant volume changes during cycling,resulting in the formation of unstable solid electrolyte interphases（SEIs）and uncontrolled lithium dendrite growth,causing low Coulomb efficiency（CE）and internal short circuits.These issues worsen the performance of Li metal anodes and hinder their practical application.Based on above challenges,this article focuses on the optimization of electrolyte system and the construction of a stable artificial SEI layer.Stable SEIs have been constructed through multiple strategies to improve the coulombic efficiency,cycle life,and thereby the electrochemical performance and practical prospects of lithium metal batteries.These strategies include the introduction of lithium nitrate into carbonate electrolytes,adopting an electroplating leveling agent as an electrolyte additive,constructing an artificial SEI rich in inorganic components via preplanting anions,building an artificial SEI of mixed fluorinated components and alloys,regulating electrolyte concentration to reveal the structure-activity relationship between concentration and SEI and then fabricate a stable SEI relying on the synergistic effects of low concentration and additives.The main research contents and conclusions are as follows:（1）To address the poor compatibility between carbonate electrolytes and Li metal anodes,the disordered lithium dendrite growth,and the inability to achieve rational use of Li NO₃ additives in carbonates,a solvent pyridine was proposed as a carrier solvent for Li NO₃ to achieve the successful introduction of Li NO₃ into conventional carbonate electrolytes.The plating/stripping behavior,electrochemical performance,and interfacial components of Li metal anodes in modified electrolyte after cycling were studied.It was found that Li NO₃ participated in the stable SEI construction and changed the lithium deposition kinetics,demonstrating an even morphology of the deposited Li during cycling without interference from lithium dendrites.A full battery matched with NCM cathodes can maintain a reversible capacity of 147.6 m Ah g^-1 after 200 cycles at 1 C rate.（2）To address limited protection duration due to the continuous consumption of finite Li NO₃ during cycling,the electroplating leveling agent 4,6-dimethyl-2-pyrimidinethiol（DMP）is used as an electrolyte additive to achieve uniform Li deposition and significantly improve the protection effect.Using DMP-containing electrolytes,the cycle reversibility,cycle stability,electrode deposition morphology,properties of the SEI on LMAs and electrochemical performance of full cells were improved.Further,kinetic testing and theoretical simulation revealed that DMP would update the Li⁺solvation structure and occupy the inner interface layer of Li metal anodes by adsorption effect but without excessive consumption to participate in the formation of SEI,thereby inhibiting the continuous side reactions between Li and electrolytes,as well as changing the deposition behavior of Li through spatial steric effect,inducing and promoting uniform Li deposition.Under practical test conditions of 3 m Ah cm^-2,Li metal anodes can stably cycle for over 800hours in this system.（3）To address the uneven organic/inorganic SEI caused by electrolyte modification and the formation of lithium dendrites attributed to potential interfacial layer damage and reforming,an inorganic rich artificial SEI layer（DDDF）was constructed on the surface of Li metal anode using an anion-planting strategy.According to release experiments and energy level orbital calculations,multiple anions in the interface layer preferentially undergo electrochemical reduction reactions to form more inorganic components to stabilize Li anode,and the slow-release property of anions can achieve longer protection effects.In addition,the cycling reversibility,deposition/stripping behavior,electrode micro-area morphology,interface dynamics,and structural composition of the SEI layer of DDDF@Li anodes were studied.It was found that DDDF can induce flat and smooth Li deposition and can withstand current densities up to 6 m A cm^-2.The performance evaluation of lithium iron phosphate full cell also proves that the artificial SEI can achieve long life and high-performance lithium metal batteries.The Li Fe PO₄（LFP）battery with DDDF@Li maintained a reversible capacity of 103.5 m Ah g^-1 at 2 C after 1000 cycles,as well as a stable CE at 99.8%.（4）To address the issues of rich inorganic interface layers such as more brittle structure,slightly poor affinity to lithium,and higher surface tension,a mixed phase artificial SEI containing more inorganic components and Li-Ge alloy was prepared by brush coating method.Studies on the cycling reversibility,lithium deposition/stripping behavior,electrode dynamics,and interface components of modified Li metal anodes（NGF-Li）under different test conditions have found that mixed phase artificial SEI layers exhibited better interfacial affinity and protection effects for Li metal anodes.A variety of full cell systems based on NGF-Li were constructed by matching different cathode materials.The lithium sulfur battery delivered a reversible capacity of 647.4 m Ah g^-1 after 200cycles at 0.5 C,and the LFP full battery showed a reversible capacity of145.2 m Ah g^-1 after 500 cycles at 0.5 C,with a capacity retention of 96.2%and a high Coulombic efficiency of 99.37%.（5）In view of the fact that the formation and evolution of SEI on Li metal anodes are closely related to electrolyte formulations,while the compatibility of emerging low concentration electrolytes with Li metal anodes and the structure-activity relationship of the interface layer have not yet been explored in detail.Electrochemical performance tests of cycling reversibility and deposition/stripping behavior of Li metal anodes were conducted using electrolytes of different concentrations（0.1 to 1 mol concentration,M）,and it was found that low concentration systems such as 0.1 M systems caused severe performance degradation.The interface morphology is also more disordered and rougher.By further combining a series of experimental investigations and theoretical simulations,the concentration effect on interface layer was revealed in detail,that is,concentration can affect the solvated structure of the electrolyte,and low electrolyte concentration can form an organic-rich interface layer that destabilizes Li anode,but at the same time,it exhibits advantages such as better charge transfer kinetics.Therefore,further combining a low concentration strategy and polysulfide additives to play a synergistic role has achieved high-performance lithium metal batteries in a wider operating temperature range.Even at-20℃,lithium sulfur battery based on low concentration electrolytes can maintain a high reversible capacity of 454m Ah g^-1 after 80 cycles at 0.2 C.130 figures,4 tables,and 206 references...