Separator Modification And Three-Dimensional Structure Design For Stable Li Metal Anode

With the increasing development and practical applications of new energy vehicle market,the key technologies and components are strongly requested.As the core components of the automotive power unit in new energy vehicle,power batteries will directly the endurance of new energy vehicles.Therefore,exploring new battery technology,controlling battery cost and improving battery energy density will enhance the long-term development trend and competitive advantage in the automobile consumption market.At present,lithium-ion batteries are a better electrochemical power source and have been used commercially in new energy vehicles.However,lithium-ion batteries with the traditional graphite anode have a theoretical specific capacity of only 372 m Ah·g^-1.As technology has progressed,lithium-ion batteries have approached their theoretical energy density and are now unable to meet the ever-increasing demand for high energy density and safety storage.Lithium metal should be one of the best choices for the anode due to its extremely high theoretical specific capacity of 3860 m Ah·g^-1and lowest redox potential of-3.04V（vs.standard hydrogen electrode）.However,commercial applications of lithium metal batteries are hampered by the uncontrollable growth of lithium dendrites on the lithium metal surface and the relatively infinite volume change during repeated Li stripping/plating processes.Therefore,suitable and effective strategies to modify lithium metal anodes that can suppress lithium dendrite growth,cycle stability and safety of lithium metal batteries are sought.In this paper,two methods including separator lithiophilic modification and lithiophilic interlayer have been adopted to slow down lithium dendrite growth in order to achieve long-term cycling performance of lithium metal battery.The specific research contents are shown as follows:1.Lithiophilic fibrous Si O₂nanospheres were coated on a separator to form a composite electrode with lithium sheets.The fibrous Si O₂nanosphere has a larger specific surface area and can allow more functional groups to participate in the reaction to guide the uniform deposition of lithium ions.The porous structure can provide more space for free lithium ion deposition,thus reducing dead lithium deposition on the electrode surface.As a result,the Li||Cu half cell exhibited a high Coulombic efficiency of 97%for the first 96 cycles and maintained 95%after 200cycles at 0.5 m A·cm^-2.In addition,the Li||Li Fe PO₄cells show excellent stabilization for 200 cycles at 2.0 C with a high capacity retention of 82%.2.The lithiophilic 3D mullite（3Al₂O₃·2Si O₂）fiber sheet is produced from mullite fiber and silica sol bonded together with high sintering temperature.And the lithiophilic 3D mullite fiber sheet as interlayer is placed between the separator and Li metal anode,which can inhibit lithium dendrite growth and reduce dead Li accumulation to achieve excellent cycle stability.The deposition and growth of lithium dendrites can be efficiently regulated by adequate polar functional groups of the mullite fiber.At the same time,the 3D matrix structure can reduce the dead Li accumulation to a certain extent.According to these two aspects,the Li||Cu cell with lithiophilic 3D mullite fiber sheet delivers high Coulombic efficiency above 98%over271 cycles at the current density of 1.0 m A·cm^-2.The use of the lithiophilic 3D mullite fiber sheet as an interlayer enables efficient operation of the Li||Li Fe PO₄full cell in terms of excellent cycle stability（capacity retention>89%,after 800 cycles at 5.0 C）.3.The flexible Ag-Si O₂fibre sheet is prepared by electrospinning followed by Tollens reagent infiltration and glucose reduction.The Ag nanoparticles act as a homogeneous pre-planted seed with ultralow Li nucleation overpotential,spatially directing uniform Li nucleation and deposition in the matrix.The skeleton of the Si O₂fibres is also effectively lithiophilic,further suppressing Li dendrite formation.Furthermore,the 3D porous framework of the Ag-Si O₂fibre sheet can effectively alleviate the volume expansion and reduce the accumulation of dead Li on the Li metal anode surface.As a result,the 3D flexible Ag-Si O₂fibre sheet enables high Coulombic efficiency in Li||Cu cells and leads to long-term stability and safety of Li-symmetric battery.The Li||Li Fe PO₄full cells with the 3D flexible Ag-Si O₂fibrous sheet show excellent stability for 1000 cycles at 5.0 C with high capacity retention of92.7%.