Application Of The Dual Strategy Of Three-dimensional Carbon Skeleton And Polymer In Lithium Metal Batteries

Due to their high energy density and operating voltage,as well as being environmentally friendly,lithium-ion batteries（LIBs）are widely used in electric vehicles and consumer electronics.Currently,the energy density of LIBs is approaching 300 Wh kg^-1,which is hard to break through.Lithium metal has an extremely high theoretical specific capacity(3860 m Ah g^-1)and the lowest redox potential（-3.04 V vs.standard hydrogen electrode）.It is expected that it will be used as the anode material for the next generation of high-specific energy batteries.In order to design lithium metal battery with high performance and security,a variety of strategies are used to coordinate optimization in this article.First of all,the three-dimensional（3D）carbon skeleton host was designed,and the lithiophilic site was introduced on the surface of the nanocarbon fiber to regulate the nucleation of lithium metal.Lithium metal was limited to plating/stripping in the carbon skeleton,the growth of dendrite and volume expansion in charge and discharge process were restrained effectively.A solid polymer electrolyte was introduced by in-situ polymerization to keep good interface contact and inhibit the growth of lithium dendrites.Finally,the 3D carbon-based host was used as the composite anode,and the polymer electrolyte was optimized to obtain the high-performance lithium metal battery with small volume change,high coulombic efficiency and long cycle life.The details are as follows:（1）Poly（vinylalcohol）（PVA）/magnesium gluconate（Mg-Glu）/poly（tetrafluoroethylene）（PTFE）nanofiber precursor was prepared by electrospinning method.After calcination in high temperature,Mg F₂-doped carbon fiber skeleton host with macropore/micropore was obtained（MF-PCNF）.The open multistage pore structure was designed to improve the plating/stripping kinetics of lithium,and the uniformly dispersed Mg F₂particles were used as nucleation sites to regulate the uniform deposition of lithium and construct Li F-rich SEI layer.The assembled symmetric cell can achieve a super-long cycle life of more than 3500 h under the current density of 1 m A cm^-2,and the full battery with Li Fe PO₄cathode still has a high capacity retention of 80%after 1000 cycles.（2）The precursors of poly（acrylonitrile）（PAN）/cobalt nitrate（Co（AC）₂）nanofibers were prepared by electrospinning.ZIF-67 was grown uniformly on the surface of the fibers.After calcination at high temperature,the N-Co doped carbon fiber skeleton（NC@CF）was obtained to form a composite anode with lithium metal.The ternary-salts solid polymer electrolyte（TS-SPE）was then introduced by in situ polymerization,which inhibited the growth of lithium dendrites and improved the safety of the battery.Under the dual strategy of 3D carbon host and solid polymer electrolyte,the half cells show more than 700cycles of life with the Coulombic efficiency of 99%at 3 m A cm^-2.The assembled symmetrical cell can achieve continuous lithium plating/stripping for 1400 h and has extremely low polarization voltage of 15 m V under the current density of 2 mA cm^-2.