Three Dimensional Structural Design And Interface Optimization For Stabilizing Li/Na Metal Anode

Owing to the high specific capacity(3860 mAh g-1)and the lowest electrode potential(-3.04 V vs.standard hydrogen electrode),Li metal anode can significantly improve the energy density of present lithium-ion battery system,playing a key role in anode materials for achieving the next generation lithium secondary batteries with high energy density.However,due to the low surface energy and high ion diffusion barrier of lithium anode,dendritic Li is easily formed during the deposition process.And Li is a kind of conversion-reaction negative electrode material without matrix,which shows infinite volume expansion in theory.Therefore,dendrite growth and volume expansion of Li anode can trigger many problems,including surface solid-electrolyte interphase(SEI)instability,dead lithium aggregation,increased polarization voltage,short circuit of battery.Because Na is an alkali metal element of the same group of Li and its resource is more abundant than that of Li,so the research of Na secondary batteries is also of great significance.Na metal anode presents the advantages of high specific capacity(1166 mAh g-1)and the lowest electrode potential(-2.71 V vs.standard hydrogen electrode)in Na-storage anode materials,which brings about a significant improvement of the battery energy density.The existing problems of Na are similar to those of Li,mainly focusing on dendrite growth and volume expansion.Therefore,with regarding to these problems of Li and Na anode,this paper mainly focuses on constructing three-dimensional(3D)matrixes with lithiophilic/sodiophilic properties for pre-storing Li/Na metal to play the confining effect and studying the function mechanism of inducing deposition and stabilizing SEI derived from the secondary products.In addition,we also build an artificial inorganic protection layer to stabilize the interface of Li anode for reducing side reactions,promoting the rapid transport of ions and alleviating the dendrite growth.In Chapter 1,we first briefly introduced the constitution,working principle of Li/Na metal battery and the research status of Li/Na metal anode,then analyzed the growth mechanism and model of dendrite of Li/Na metal anode,and detailly reviewed the main solutions to inhibit the dendrite growth of Li/Na metal,finally led to the research ideas of this paper.In Chapter 2,we briefly introduced the experimental materials,equipments and characterization methods employed in this paper.In Chapter 3,we constructed evenly distributed carbon nanotubes(CNTs)on carbon fiber cloth by chemical vapor deposition(CVD).And then Li composite anode was prepared through molten Li infiltration method.In the composite anode,the carbon fiber framework and CNTs can limit the volume expansion of Li and homogenize the Li ions flux,respectively,thus promoting the uniform deposition of Li.Therefore,the Li composite anode can realize a stable cycling lifespan of 500 h at 1 mA cm-2 and 1 mAh cm-2 in the symmetrical battery.And the LiFePO4-based full battery paired with Li composite anode show a capacity retention rate of 98.1%after 100 cycles at 1 C.In Chapter 4,we designed evenly distributed Co3O4 nanowires on the carbon fiber film for prestoring Li anode by hydrothermal method.The Li composite anode was fabricated by molten Li infiltration method.And we confirmed that the secondary product Co/Li2O composite structure presents higher adsorption energy for Li through density functional theory(DFT)calculation,which indicates the secondary product can promote the uniform distribution of Li ions flux and homogeneous Li deposition from the view of chemical adsorption and physical confinement.Therefore,the Li composite anode can realize a stable cycling lifespan of 500 h at 1.5 mA cm-2 and 3 mAh cm-2 in the symmetrical battery.And the LiFePO4-based full battery paired with Li composite anode show a capacity retention rate of 94.3%after 250 cycles at 1 C.In Chapter 5,we developed a low temperature gas/solid reaction method to prepare a composite Li2S/Li2Se inorganic protective layer with high ion conductivity,uniform and compact structure.DFT calculation reveals that the introduction of Li2Se can further improve the ionic conductivity of Li2S system,thus promoting the rapid migration of Li ions to avoid the growth of Li dendrites.Therefore,the Li composite anode can realize a stable cycling lifespan of 900 h at 1.5 mA cm-2 and 3 mAh cm-2 in the symmetrical battery.Moreover,the composite anode matched with LiFePO4 can stably cycle for 460 cycles at the current density of 1 C.In Chapter 6,we designed uniformly distributed Cu2Se nanosheets on porous copper framework by one-step solution selenidation method and constructed a stable 3D composite Na anode via molten Na infiltration method.By means of electrochemical kinetics analysis and atomic force microscopy,we revealed that the secondary product Na2Sc/Cu can promote the rapid migration of Na ions and stabilize the SEI interface.Therefore,the Na composite anode can realize a stable cycling lifespan of 500 h at 1 mA cm-2 and 1 mAh cm-2 in the symmetrical battery.And the composite anode matched with Na3V3(PO4)3 can stably cycle for 800 cycles at the current density of 10 C.In addition,we also show that this three-dimensional matrix has good application feasibility in potassium metal anode.In Chapter 7,we summarized the innovations and shortcomings of this paper and looked forward to the future research.Additionally,in Appendix A of this paper,we introduced the research of 3D graphene/Nb2O5 nanospheres as anode materials for sodium ion batteries,and revealed the influence on the electrochemical performance of heteroatom doping and nanostructure,finnaly realizing a stable and reversible anode material for Na storage.