Preparation Of Three-dimensional Porous Copper Collector And Study On Stabilizing Li Metal Anodes

The high-energy-density battery is a strategic and advanced technology in fierce competition around the world.In the National 13th Five-Year Plan,a goal of achieving a battery energy density of 350 Wh kg^-1 in 2030 is proposed.Graphite,an anode material for conventional Li-ion batteries,is difficult to meet this requirement.Owing to the high theoretical specific capacity(3860 m Ah g^-1),low potential（-0.304 V vs SHE）and low density(0.534 g cm^-3),Li metal is one of the most ideal anode materials for the next generation of batteries.However,the growth of Li dendrites during the charge and discharge processes seriously affects the stability and safety of batteries.In addition,the volume expansion during charge and discharge cannot be effectively controlled,leading to the continuous consumption of electrolytes.Therefore,the stabilization of the Li metal anode is the key point to its practical application.By replacing the conventional copper（Cu）foil planar current collector with a porous structure current collector,the growth of Li dendrites can be inhibited,because it can provide a large surface area and sufficient diffusion channels to balance the charge transport and mass transfer of Li ions.However,the reported three-dimensional（3D）Cu current collectors usually have the low pore volume and limited Li loading,which seriously restricts the performance of the Li metal anode.Therefore,it is of great theoretical value and practical significance to implement the rational design and preparation of 3D Cu current collectors for stable Li metal anodes.In this dissertation,the innovative structural design of the stabilized Li metal electrode materials by constructing several Cu-based current collectors have been proposed.Firstly,a new method for the preparation of a 3D porous Cu current collector is proposed.Secondly,a new strategy for Li metal stabilization is developed.Thirdly,a new approach to the large-scale preparation of composite anodes is provided for the Li metal anode.On this basis,the design of 3D structural current collector is proposed to establish theoretical and experimental foundations for a better understanding of the correlation between electrode structure and electrochemical performance of the Li metal batteries.In addition,with the proposed current collectors,the key issue on Li metal anode research of fabricating a high loading Li metal anode with suppressed growth of Li dendrite has been solved.Moreover,the proposed novel 3D Cu structural current collector can meet the requirement for the development of high-energy-density batteries.The main contents of this dissertation can be summarized as follows:1.A self-supporting 3D porous Cu current collector is constructed by the powder welding method.The prepared 3D porous Cu current collector has a large pore volume and can accommodate Li up to15.8 m Ah cm^-2,which solves the problem of low Li loading of the 3D Cu current collectors.In addition,this 3D porous Cu current collector maintains a high Coulombic efficiency for 500 cycles at a current density of 1 m A cm^-2.The assembled symmetrical battery can work at different current densities from 1 to 50 m A cm^-2 with a maximum overpotential of 286 m V.It exhibits excellent cycle stability and high capacity retention by assembling a full battery with lithium iron phosphate（Li Fe PO₄）cathode.The 3D Cu current collector exhibits high discharge specific capacity(122 m Ah g^-1)and long cycle life in Li Fe PO₄ soft pack batteries because of its excellent electrical conductivity and flexibility.As a result,improved safety and rechargeability of Li metal anodes are achieved based on this structural design.The ingenious structural design makes it possible for the utilization in the next generation of high-energy-density batteries.2.A dynamic intelligent 3D Cu（DICu）collector is constructed by using the particle accumulation structure of the Cu micropowder（Cu MPs）.In this structure,it connects Cu MPs to form films by physical adhesion.When Li deposits over its accumulated pore volume,Cu MPs can accommodate more Li by automatically adjusting the particle spacing,which shows the“intelligent”adaptive behavior.The current collectors with different pore volumes are achieved by changing the thickness（25-400μm）of the coating layer,which can meet the needs of different gradient Li(1.14～28.6 m Ah cm^-2)deposits.The DICu collector with a thickness of 100μm can achieve a large amount of Li deposition(12 m Ah cm^-2).The Li/DICu composite anode has a long-term deposition/dissolution efficiency up to 99%.The assembled symmetrical battery still maintains ultra-high stability over 1000h at a current density of 10 m A cm^-2.This DICu collector provides a new way to stabilize Li metal anode,especially to solve the stress problem caused by volume fluctuation.3.The stabilized Li metal powder（LP）is mixed with Cu MPs to make a slurry and then coated on the Cu foil to form a 3D structure-stabilized Li composite anode.The one-step coating method for preparing the LP/3DCP composite anode has the advantages of simple preparation method,easy scale production,and quantitative adjustment of Li loading.It effectively solves the problem that metal Li and current collector are difficult to recombine.The 3D porous structure composed of Cu MPs stabilizes metal Li and suppresses the growth of Li dendrites.The LP/3DCP exhibits high cycle efficiency in a half-cell system,and its coulombic efficiency is as high as 99.8%after 100 cycles.In a symmetrical battery system,the LP/3DCP anode can maintain a low overpotential at a current density of 20 m A cm^-2.In the full battery system,the specific capacity of LP/3DCP|Li Fe PO₄ battery is still as high as 148 m Ah g^-1 at 2 C,and the specific capacity is 116 m Ah g^-1 at 4 C.The electrochemical tests confirm the stable cycling performance and excellent capacity retention of the LP/3D Cu composite anode.4.The free-standing 3D porous Cu nanowires（Cu NWs）network current collector is prepared using the ultra-large aspect ratio Cu NWs.The 3D Cu current collector has excellent electrical conductivity,flexibility,and expandability,enabling a large loading of Li deposition(10.25 m Ah cm^-2).The free-standing Cu NWs network current collectors also have“dynamic intelligence”behavior,which can effectively alleviate the stress caused by the volume change of Li metal through volume expansion.In a symmetrical battery,it maintains a low polarization voltage after 4000 h at a current density of 5 m A cm^-2.The full battery system exhibits a high discharge specific capacity,a good rate performance,and excellent cycle stability.The Li-S soft-package battery assembled by the Cu NWs network current collector exhibits high flexibility and cycle stability.Through the optimization of the matching of the cathode and anode capacity,it is revealed that the best matching ratio of the cathode and anode in the Li|Li Fe PO4 full battery is 1:1.2;in the Li-S full battery,the optimal matching ratio is 1:4.0.This research provides an experimental basis for the development of a Li metal full battery.