Study On The Fabrication Of Three-dimensional Porous Cu Current Collector For Lithium-ion Batteries Using Space Holder Method

As the current leader in energy storage equipment,lithium-ion batteries were widely used in transportation,communication equipment,intelligent power systems,and other fields,and they are moving towards high volume and high power density.Sn anode far exceed the current commercial graphite anodes which has superior high theoretical capacity(994m Ahg^-1),and it was considered to be a new generation of anode materials with great research and commercial value that can replace graphite.However,the intercalation/de-intercalation of Li⁺during the charge and discharge process will cause violent lattice expansion/shrinkage of Sn,which will cause great damage to the anode,making it powdery or even break.The introduction of 3D porous metal as the current collector is an effective way to alleviate the damage of the anode.Among various methods of preparing porous metals,the space holder method has advantages of simple operation,low cost,low equipment requirements,adjustable pore structure,and environmentally friendly.This study uses space holder method based on powder metallurgy to prepare three-dimensional（3D）porous Cu current collector,and changing the content and particle size of the space holder to change the porosity and pore size of the current collector,then testing its mechanical properties.Next electrolessly plate a layer of Sn to prepare the Sn anode used 3D porous current collector,carried out its structure characterization and cycle performance.Finally,the Sn anode used 3D porous current collector was improved by a heat treatment method.The contents and results are as follows:1.Anhydrous potassium carbonate（K₂CO₃）was selected as the space holder,and the 3D porous Cu current collector with a porosity of 48.2%-81.7%and a pore diameter of 213.36μm-760.75μm was successfully prepared by powder metallurgy.The increase in the content of the space holder increases the porosity of the current collector,and the decrease in the particle size of the space holder reduces the average pore diameter of the current collector.The discharge specific capacity of the Sn anode increases with the increase of porosity,and the capacity retention rate increases with the decrease of the pore size.2.Compared with the copper foil current collector,the 3D porous Cu current collector significantly improves the performance of the Sn anode of the lithium ion battery.Under the same current density,the 3D porous Cu current collector greatly improves the specific capacity and cycle stability of the Sn anode.After 100 cycles,the 3D porous Cu current collector can better maintain its structure shape.3.The mechanical properties of the current collector decrease with the increase of the content of the space holder.When the content of the space holder exceeds 70%by volume,the excessive content of the space holder leads to the deterioration of the mechanical properties of the current collector,the structure of which cannot support the stress caused by the volume change of Sn and breaks,and the cycle stability is rapidly reduced.The decrease of the particle size of the space holder improves the cycle stability of the anode,but when the particle diameter of the space holder less than 50-60 mesh,the cycle stability deteriorates sharply.The optimal content and particle size of the space holder is 70%volume fraction and 50-60 mesh.At this time,the capacity retention rate is the highest at 50.41%,and the initial discharge specific capacity can reach 906.7 m Ahg^-1.4.Heat treatment of the anode can further improve the cycle stability.When the anode was heat-treated at 150℃for 2h,the discharge specific capacity increased to952.1m Ahg^-1,and the capacity retention rate increased to 72.99%.When the anode is heat-treated at 500℃for 2h,the discharge specific capacity is reduced to 862.6m Ahg^-1,and the capacity retention rate is reduced to 57.04%,but it is still higher than the capacity retention rate of the non-heat-treated anode.The best heat treatment process is 150℃heat treatment for 2h.