Three-Dimensional Host Design And Interfacial Regulation Of Lithium Metal Anode

Metallic lithium（Li）has low redox potential,high theoretical specific capacity and high compacted density and is considered to be the"Holy Grail"of Li battery anode materials.However,the uncontrollable growth of Li dendrites,poor interfacial stability,and unrestricted volume expansion severely limit its widespread commercial applications.Therefore,research on the modification of Li anode is the key to realizing its practical applications.In view of the key issues faced by Li metal anode,this dissertation focuses on the impact of three-dimensional lithiophilic hosts and interface regulation on the electrochemical performance and intrinsic modification mechanism of Li metal anodes.Its main innovation points and main research contents are divided into the following five parts:（1）Preparation of Ni₄N/Zn₃N₂ heterostructure nanosheet array on the surface of carbon cloth and study of its lithiophilic/sulfophilic properties.Firstly,the Ni₄N/Zn₃N₂heterostructure nanosheet array is prepared on the surface of carbon cloth through hydrothermal method combined with ammonia atmosphere sintering technology（CC@Ni₄N/Zn₃N₂）,and is used as a“dual service”host to simultaneously realize efficient Li and S loading to induce uniform Li deposition and efficient catalytic conversion of Li polysulfides（Li PSs）.Specifically,due to the different intrinsic Fermi levels of Ni₄N and Zn₃N₂,the Ni₄N/Zn₃N₂ heterostructure after bimetal nitride coupling has a large amount of vacancy defects and built-in electric fields at the heterojunction interface,which accelerate the migration of electrons and holes.Secondly,the Ni₄N/Zn₃N₂ heterostructure achieves a more reasonable transition metal d-band center and d-p orbital hybridization intensity through its tunable electronic structure interface,which enables the catalyst to balance chemical adsorption and desorption based on the Sabatier principle.As a result,when used for Li loading,CC@Ni₄N/Zn₃N₂ host provides a large number of lithiophilic sites to induce uniform Li nucleation and growth,and also derives a Li₃N-rich interphase layer with high Li⁺flux to accelerate Li⁺transport.When used for S loading,Ni₄N/Zn₃N₂heterostructure nanosheet array also provides excellent adsorption ability to anchor soluble Li PSs,and shows electrocatalytic effect on the"solid-liquid-solid"multi-step conversion reaction toward Li PSs.（2）Construction of artificial fluorinated dual-phase interphase and study of its Li deposition behavior mechanism.Firstly,a submicron polyhedral Bi F₃ precursor is prepared using a hydrothermal method,which is then dispersed in dimethyl carbonate（DMC）solvent and dropped onto the surface of Li anode,ultimately forming a fluorinated artificial dual-phase SEI composed of Li₃Bi/Li F.The artificial SEI can exhibit high Li⁺diffusion rate,high electronic resistivity,and high mechanical strength,which confines Li deposition to occur at the Li/SEI interface,ultimately improving the safety of Li metal anode.Specifically,Li₃Bi alloy,as a super Li⁺conductor,can accelerate the transport of Li⁺and stabilize the artificial interface.Meanwhile,Li F component,as an excellent electron blocker,can inhibit the tunneling of electrons from Li anode into the SEI.As a result,for the symmetric cell test,the modified Li anode provided a stable cycle life of1000 cycles even at an ultra-high current density of 20 m A cm^-2.When assembled with a Li Fe PO₄ cathode and a high surface capacity Li Ni_0.8Co_0.1Mn_0.1O₂ cathode(4.4 m Ah cm^-2),the modified Li anode enables the assembled cell to exhibit a better electrochemical performance.（3）Preparation of multifunctional artificial fluorinated soft/hard hybrid seamless interphase and study of its Li deposition behavior mechanism.An artificial PVDF-HFP（soft）/Li₃Sb-Li F（hard）hybrid seamless interphase is spontaneously formed by dropping Sb F₃/PVDF-HFP/ethylene glycol dimethyl ether（DME）solution onto the surface of Li metal anode.The designed artificial hybrid SEI synergizes the flexibility of the organic interphase and the rigidity of the inorganic interphase,showing high mechanical strength（2.7 GPa）,high Li⁺conductivity(3.1×10^-4 S cm^-1),excellent adaptability properties,and good compatibility with electrolytes（low contact angle 11.3°）.Among them,the PVDF-HFP component forms a continuous adaptive polymer interphase,which not only blocks the direct contact between Li anode and electrolyte but also eliminates the huge contact resistance between the artificial interphase and Li anode.Meantime,Li₃Sb component,as a Li⁺conductor,can accelerate the transport of Li⁺,while Li F can suppress the"electron tunneling effect"within the artificial interphase.As a result,even under lean electrolyte conditions(12μL m Ah^-1),the artificial fluorinated soft/hard hybrid SEI can enable the Li（50μm）||Li Ni_0.8Co_0.1Mn_0.1O₂(4.4 m Ah cm^-2)cell to show excellent cycling performance.（4）Preparation of nano lithium fluoride（Li F）and lithium nitrate（Li NO₃）modified ester-based electrolyte and study of its solvation structure control mechanism.Firstly,the high-concentration dissolution of Li F and Li NO₃ additives in ester-based electrolyte is successfully achieved by synthesizing nanocubic Li F and using the polar solvent carrier sulfolane（TMS）.The 1M Li PF₆ ethylene carbonate（EC）/DMC（V:V=1:1）electrolyte modified with 5wt.%nanocubic Li F and 5wt.%Li NO₃/TMS realizes an ideal SEI dominated by Li F and Li₃N inorganic components on the surface of the Li metal anode.It is found that nanocubic Li F particles exposed abundant（111）crystal faces to enhance the interaction with EC solvents,ultimately improving their solubility in ester-based electrolytes.Meanwhile,the Li NO₃/TMS additive extensively participates in the construction of the solvation shoe layer and induces the Li₃N-rich SEI.As a result,the as-designed modified electrolyte can make Li||Cu half-cells show higher cycling life and average Coulombic efficiency,and can also make Li（50μm）||Li Ni_0.8Co_0.1Mn_0.1O₂(4.4m Ah cm^-2)cells exhibit higher capacity retention and higher average Coulombic efficiency.（5）Preparation of ester-based electrolyte modified with complex ion additives and study on the mechanism of directional lithium deposition behavior.A multi-layer SEI on the surface of Li metal anode is achieved by co-introducing lithiophilic complex ionic additives（In（NO₃）₃,lithium difluoro（oxalate）borate（Li DFOB）and Li NO₃）into commercial 1M Li PF₆ EC/DMC（V:V=1:1）electrolyte.It is found that the In（NO₃）₃additive induced the inner SEI containing Li-In alloy.The（200）crystal plane of this Li-In alloy substrate has the lowest crystal plane energy,thus inducing the directional growth of subsequent Li deposition.In addition,Li DFOB additive was used to obtain Li F-rich intermediate SEI to improve the interfacial energy of SEI.Finally,the Li NO₃/TMS additive optimized the solvation structure of the Li anode surface and reduced the content of organic solvent derivatives,and also generated an Li₃N and Li N_xO_y-rich outer SEI to accelerate the transport of Li⁺within SEI layer.Different from the obvious Li dendrites growth in commercial carbonate-based electrolyte,Li deposition in modified electrolyte is dense and has a spherical morphology.Finally,the modified electrolyte enabled the Li（50μm）||Li Ni_0.8Co_0.1Mn_0.1O₂(4.4 m Ah cm^-2)cell to show higher average Coulombic efficiency and higher capacity retention.