Design,Preparation And Electrochemical Performance Of Ultralight Porous Copper Current Collector For Lithium Metal Anodes

The escalating consumption of traditional fossil fuels,such as coal,oil,and natural gas,not only depletes their reserves but also causes greenhouse gas emissions that lead to global environmental pollution and climate degradation.Therefore,introducing renewable and clean energy sources on a vast scale can maintain the sustainability of human ecology.Energy storage devices can integrate intermittent,low-density renewable clean energy into the smart grid,enabling large-scale and efficient utilization.Electrochemical energy storage has become the most extensively applied energy storage system due to its superior conversion efficiency,excellent cycling performance,and environmental friendliness.As a key support for the new energy industry and a pivotal unit of the future energy internet,lithium（Li）-ion batteries（LIBs）represent high-performance electrochemical energy storage technology that contributes to China’s energy transformation and green low-carbon development.However,the theoretical specific capacity of current graphite anode materials limits the energy density of LIBs(270 Wh kg^-1).Hence,the development of anode materials with higher specific capacity is essential for achieving a breakthrough in the energy density of Li batteries.Li metal possesses an extremely high specific capacity(3860 m Ah g^-1)and a low operating voltage（-3.04 V vs.Standard Hydrogen Electrode）,making it a promising solution for elevating energy density.However,Li metal batteries（LMBs）face several critical scientific challenges that need to be addressed for practical applications:（1）Li is susceptible to dendrite growth during cycling,which can puncture the diaphragm and cause short-circuiting,leading to safety hazards.（2）Additionally,the volume expansion of the Li metal anode（LMA）during deposition/dissolution is difficult to control,resulting in interface fluctuations and internal stress changes that negatively impact the stability of the electrode structure.These problems significantly compromise the cycle stability,lifetime,and safety of the battery.To address these issues,designing the electrode structure to regulate Li deposition/dissolution and stabilize the current collector at the Li/electrolyte interface is an effective and scalable solution for achieving high-performance LMBs.However,the currently reported 3D metal current collectors have low porosity to accommodate high Li loads,poor mechanical properties,and high inactive material mass ratios that do not meet modern energy storage device demands for lightweight,portability,and flexibility.Therefore,the development of new 3D lightweight and flexible porous copper（Cu）current collectors will provide new opportunities for the commercial application and mass production of LMBs.This thesis focuses on the structured design of a new lightweight and flexible porous Cu current collector,emphasizing the conformational relationship between the three-dimensional porous structure and the Li deposition/dissolution process.We aim to enhance the electrochemical performance of the Li metal anode by increasing the porosity of the current collector material,improving its mechanical properties,and optimizing the pore structure.The specific objectives are as follows:1.The integrated bifunctional gradient porous Cu nanowires（Cu NWs）current collector（MS@Cu NWs）prepared by vacuum-assisted film-forming technique,which resulted in a"large pore-small pore"pore gradient and an"electrically insulating-highly conductive"conductive gradient by combining melamine foam and Cu NWs.The Li/MS@Cu NWs current collector demonstrated stable cycling capability and long cycle life,with 3900 h cycle life under 3 m A cm^-2 and 3 m Ah cm^-2 charge/discharge conditions.The full cell assembled with Li Fe PO₄ cathode shows high cycling stability and high capacity retention at different multipliers.In addition,the assembled flexible cells can be stably cycled 400 cycles and maintain excellent mechanical stability under different folding states.This bifunctional gradient flexible MS@Cu NWs current collector significantly extends the cycle life of the battery,which is a simple and effective way to realize the scalability of high-performance Li-metal batteries.2.Ultralight porous Cu nanowires aerogel（UP-Cu）prepared by the freeze-drying method has high electrical conductivity,ultra-high porosity（93.44%）,ultra-low density(0.0759 g m L^-1),high elasticity,high mechanical stability,and excellent pore structure.The UP-Cu offers a high Li loading capacity of 77 wt%.When assembled into a composite anode which can provide 2715 m Ah g^-1.The Li/UP-Cu-50 electrode maintains a low hysteresis voltage and can cycle stably for more than 1200 h under 1 m A cm^-2,1 m Ah cm^-2 charge/discharge conditions for the assembled symmetric cell.The full cell assembled with the Li Fe PO₄ cathode maintains a discharge-specific capacity of 102.2 m Ah g^-1after 5000 cycles at 5 C.The pouch battery assembled with UP-Cu also demonstrates high capacity retention（99.11%,98.62%,and 97.91%）under different states,including an initial flat state（0～120cycles）,bending state（121～240 cycles）,and recovery flat state（241～360 cycles）.The excellent electrochemical performance of the ultralight and porous UP-Cu current collector has great potential for applications in high-energy-density batteries.