Application Of Functional Electrolyte In Rechargeable Lithium Metal Battery

With the rapid development of the electric vehicle and consumer electronics products markets,there is an urgent need to develop high energy density storage devices.Lithium-metal batteries（LMBs）,containing Li-S₈,Li-O₂,and high-Ni cathode recently began to gain attention for energy storage with high energy density.The stability of lithium metal anode plays a critical role in the electrochemical performances of full cells,which can directly determine the commercialization of LMBs.The unstable SEI and low Coulombic efficiency and accumulate of dead lithium are the main problems of the Lithium metal electrode.In addition,most of the reported in the literature were tested on the basis of thick lithium metal anode,which is contrary to the practical application principles of high-energy-density lithium metal batteries.In view of the above problems,it is of great scientific and practical significance to effectively control the morphology of lithium deposition,stable the SEI film and realize the high-specific-energy density of lithium metal under practical conditions.（1）As is well known that typical dendrite morphology of lithium metal in ester-based electrolyte,Two-dimensional vermiculite nanosheets（VS）were used as electrolyte additives to regulate the morphology of lithium deposition.With the abundant negative charge of VS,the laminated structure of VS leading to flake-like Li nucleation and co-deposit with Li.Furthermore,VS can serve as flat substrates for Li diffusion and deposition.The accumulation of Li⁺in VS can decreases the concentration gradient in electrolyte containing TTSP and increase the lithium ion transference number.The Li||Li symmetric cells could cycle stably for 600 h in ester-based electrolyte containing VS.The evolution of deposition morphology was recorded synchronously by in-situ microscope video.（2）Aiming at the important role of electrolyte additives in the formation SEI of lithium metal anode,the effects of different electrolyte additives on the plating/stripping efficiency of lithium were investigated.After tested of Li||Cu half-cells,the phosphorous organics tris（trimethylsilyl）phosphate（TTSP）was usually used as cathode additive also can stabilize the lithium metal anode for 400 cycles.The experiment result showed that the high content Li₃PO₄ and organic silicon in SEI film,which forming in electrolyte containing TTSP.On the one hand,the Li₃PO₄ has higher ionic conductivity can increase the Li⁺transfer and improve the Li plating/stripping kinetics process.On the other hand,organic silicon can enhance the flexibility of the SEI film and adhesion on lithium metal,which can stable SEI in long cycling testing.All above that can effectively reduce Li plating/stripping overpotential and battery impedance.（3）50μm thin lithium metal electrode was used as the research object to solve the problem of low utilization rate of lithium metal electrode.The electrochemical behaviors of the LMBs full cells were studied under the practical conditions,such as higher load cathode electrode,high-voltage,low N/P ratio and lean electrolyte.Experiments show stable solid electrolyte interphase film can simultaneously form on both Li metal anode and NCM811 cathode via the reduction and oxidation of TTSP.High-specific-energy of 373 Wh kg^-1 is achieved with the help of TTSP additive under the practical condition with N/P ratio of 2.3,areal capacity of 4.5 mAh cm^-2,high-voltage of 4.5 V and lean electrolyte of 2.8μL mAh^-1.