Study On The Construction And Performance Of Dendrite-free Lithium/sodium Metal Anode

The theoretical specific capacities of lithium（Li）and sodium（Na）metal anodes are as high as 3861 and 1165 m Ah g^-1,which are much higher than the specific capacity of graphite anodes of commercial lithium-ion batteries(372 m Ah g^-1).Therefore,Li/Na metal battery（LMB/SMB）composed of Li/Na metal anode is considered to be the most promising energy storage system for the next generation.However,Li/Na metal anode suffer from the issue of uncontrolled dendrite growth,which seriously hinder the large-scale application of LMB and SMB in the field of secondary batteries.In order to solve the above problems and obtain long-cycle stable,safety and reliable LMB/SMB,strategies including designing three-dimensional（3D）current collectors,optimizing electrolytes,constructing artificial solid electrolyte interface（SEI）,improving the wettability of the substrate,and adjusting battery test conditions,etc.have been proposed to solve the dendrite problem of LMB/SMB.Among them,the 3D current collector,due to its large surface area,can effectively reduce the local current density and make the Li/Na metal deposit uniformly,thereby inhibiting the growth of Li/Na dendrites.This paper uses 3D Cu Foam modified with platinum（Pt）and palladium（Pd）to construct a Li/Na metal negative electrode.Among them,Pt and Pd can form an alloy with Li/Na metal,which can greatly reduce the nucleation overpotential of Li/Na,promote uniform deposition of Li/Na metal,and inhibit the growth of dendrites.In addition,the higher Li/Na affinity of Pt and Pd can increase the Li⁺/Na⁺ion flux,further promote the uniform deposition of Li/Na metal and inhibit the growth of dendrites.The main research contents and results are as follows:（1）Pt-Cu Foam is used as the current collector of the Li metal anode.The Pt-Cu Foam prepared by the galvanic replacement reaction has a large surface area and high Li affinity,which can effectively reduce the local current density and Li nucleation overpotential and improve the uniformity of ion flux distribution.In addition,Pt has a certain solubility in Li metal,so Pt atoms can be lithiated,the lithiated Pt atoms can prevent the formation of large crystalline domains on the SEI film,therefore increasing the diffusion rate of Li⁺at the electrode/electrolyte interface.After the Pt atoms leave,micro-sized voids are left in the Pt-Cu alloy layer,which can provide additional accommodation for Li deposition.Moreover,the 3D skeleton of Cu Foam can also effectively alleviate the large volume change of the metal negative electrode during electroplating/stripping.Therefore,the Li@Pt-Cu Foam||Pt-Cu Foam@Li symmetrical cell is cycled for more than 900 h at a current density of 1 m A cm^-2 and an ultra-high area capacity of 20 m Ah cm^-2.（2）Pt-Cu Foam is used as the current collector of the Na metal anode.Pt-Cu Foam possesses a large surface area and high Na affinity.Although Pt atoms can be sodiated,the sodiated Pt atoms will not dissolve into the Na phase.The volume expansion caused by sodiation produces a large number of micro-sized blocks in the Pt-Cu alloy layer.The voids among the micro-sized blocks and the voids on the Cu Foam can provide more vacancies for Na deposition,and thus achieve the suppression of Na dendrites.Therefore,the Na@Pt-Cu Foam||Na@Pt-Cu Foam symmetrical cell can be cycled for more than 300 h at a current density of 1 m A cm^-2 and an ultra-high area capacity of 20 m Ah cm^-2.（3）Pd-modified Cu Foam is used as the current collector of the Li metal anode.This chapter mainly uses the prepared Pd-Cu Foam to construct a dendrite-free Li metal anode.Pd and Pt belong to the Pt series of elements.They have similar chemical properties.Pd-Cu Foam has a uniform 3D porous structure,large surface area and high Li affinity,which greatly reduces the nucleation overpotential,interface resistance and local current density,increases the Li⁺ion flux and promotes the uniform deposition of Li metal,the suppression of Li dendrites is achieved.Therefore,the Pd-Cu Foam|Li half-cell can run more than 200 cycles at a current density of 0.5m A cm^-2 and an area capacity of 1 m Ah cm^-2,and the coulomb efficiency is still as high as 97%.Moreover,the Pd-Cu Foam|Li half-cell can also run 23 cycles at an ultra-high current density of 10 m A cm^-2 and an area capacity of 10 m Ah cm^-2.