Fabrication And Properties Of Dendrite Suppression Structures For Lithium And Zinc Metal Anodes

With the rapid development of portable electronic devices,power batteries and other fields,people’s demand for high energy density energy storage devices is increasing.The widely used commercial graphite anode materials can no longer meet the needs of high energy density,and there is an urgent need to develop high-performance anodes that can replace graphite.Metal batteries using metal as anodes can provide high energy density.Among them,lithium（Li）metal anode is the most promising candidate due to the high theoretical specific capacity(3860 m Ah g^-1)and ultra-low redox potential（-3.04 V vs.SHE）.The more environmentally friendly aqueous zinc（Zn）metal anode also has a larger theoretical specific capacity(820 m Ah g^-1)than graphite,and the advantages of high safety and low cost make it one of the research hotspots.However,both Li and Zn metal anodes have the problem that the local aggregation of ions during the deposition process leads to the generation and growth of dendrites,resulting in the short circuit of batteries.In this paper,the structural fabrication of the Li/Zn metal anode has played a good role in optimizing the Li metal SEI film and mitigating the Zn metal side reaction.The current density distribution on the electrode surface is regulated to prevent the formation of dendrites caused by uneven deposition of Li/Zn metal.Commercial copper（Cu）foil was etched with alkaline solution,heated and dehydrated,and copper oxide（Cu O）nanowire arrays were prepared on the surface.The Cu O was converted into Cu and lithium oxide（Li₂O）by pre-lithiation to obtain a lithiophilic CL-matrix@Li₂O current collector.The three-dimensional（3D）structure of the current collector can reduce the local current density during Li metal deposition,thereby suppressing dendrite generation and realizing a highly reversible Li deposition/stripping process.The average Coulombic efficiency of Li deposition/stripping at 0.5 m A cm^-2for 360 cycles was97.98%.The CL-matrix@Li@Li₂O metal anode was fabricated by electrodepositing Li on the current collector,and the cycle life of the symmetrical cell can reach 1400 h at 1 m A cm^-2.The SEM images of the electrode after cycling showed that the SEI film on its surface was uniform and flat,indicating that the Li deposition was uniform.The full cell composed of CL-matrix@Li@Li₂O anode and lithium iron phosphate（LFP）cathode exhibited superior rate performance and cycle stability,the capacity retention rate of 150 cycles at 0.5 C(1 C=170m A g^-1)was 90%.The Cu foam（CF）with a 3D pore structure was used as the framework,and a uniformly wrapped MXene layer was fabricated by the self-assembly of Ti₃C₂T_x-MXene on its surface.With the help of the lithiophilic/zincophilic properties of MXene,MCF current collector with low Li/Zn nucleation barriers was obtained.The MXene layer exhibited a microscopic wrinkled structure,which reduced the local current density of Li/Zn deposition and played a role in inhibiting dendrite growth.MCF showed high metal deposition/stripping reversibility,with average Coulombic efficiencies of 94.5%and 97.7%for Li and Zn deposition/stripping at current densities of 3 m A cm^-2and 5 m A cm^-2,respectively.The Li/Zn metal anodes fabricated by electrodeposition on MCF current collectors all exhibited good cycle stability.MCF@Li was stably cycled for 1800 hours at 1 m A cm^-2;MCF@Zn was stably cycled for300 hours at 5 m A cm^-2.The MCF@Li||LFP full cell assembled with MCF@Li anode and LFP cathode exhibited a capacity retention rate of 91.7%at 10 C for 3500 cycles;the aqueous MCF@Zn||AC capacitor battery assembled with MCF@Zn anode and activated carbon（AC）cathode exhibited a capacity retention rate of 100%at 10 A g^-1for 3000 cycles.The surface meshed GZn anode was fabricated by pressing the Cu mesh in the surface of the Zn foil by a simple pressing method.COMSOL simulations of the Zn²⁺ion flux on the surface of GZn showed that it has the effect of reducing the Zn²⁺ion flux on the surface of the Zn foil to avoid the"tip effect".The symmetric cell was stably cycled for 1200 h at 0.2 m A cm^-2,and Zn was uniformly deposited on the surface of the Cu mesh during cycling.SEM test results showed that no Zn dendrites are formed on the electrode surface after cycling.GZn anodes,Mn O₂cathodes and AC cathodes were assembled into full cells and capacitor batteries,respectively.They all had improved rate capability and cycle stability.The capacity retention rates of GZn||Mn O₂full cell and GZn||AC capacitor battery after 1500 cycles and10000 cycles at 5 A g^-1were 78.1%and 92.6%,respectively.The silver（Ag）metal with lower Zn nucleation barrier was chosen to modify the Zn anode.The porous Ag layer was fabricated on the Zn surface through a rapid replacement reaction.According to the cycle performance of the symmetric cells and the electrode morphologies before and after cycling,the thickness of the Ag modification layer was optimized to 8μm（Zn@12.5Ag）.The COMSOL simulation result showed that the Zn²⁺ion flux distribution on the electrode surface was uniform,which prevented Zn dendrites caused by excessive local current density.Ag was converted into a stable Ag Zn₃alloy during cycling,which suppresses the generation of by-products.In situ optical microscopy showed that the surface of Zn@12.5Ag was less prone to dendrites and hydrogen gas during Zn deposition.The symmetric cell of Zn@12.5Ag operated stably for 80 h at an ultra-high current density of50 m A cm^-2（2000 cycles）.Zn@12.5Ag anodes and AC cathodes constituted capacitor batteries,which achieved superior rate performance and cycle stability.The capacity retention rate after 15000 cycles at 20 A g^-1was 87.4%.