Fabrication Of Novel Silicon Anode For Lithium Ion Batteries By Laser Remelting-Diffusion Welding-Dealloying Hybrid Method

Silicon presents very high theoretic discharge capacity of 3579 mA·h/g at room temperature for lithium,which is about ten times that of graphite,as well as the moderate voltage platform,the wide source,the cheap price and so on,making it an attractive anode material for rechargeable lithium ion batteries(LIB).At present,the silicon powder with the binder and the conductive agent are mixed and coated on the surface of the current collector to realize the structure of silicon negative electrode.However,the practical implementation of Si anode is impeded by well-known detrimental pulverization effect and conductivity fading during charge and discharge,which mainly caused by the following two-phase reactions(Si?Lix Si?Li15Si4).The inhomogeneous volume expansion(difference could reach 300%)during the above reactions induces severe stress causing Si pulverization and loss electrical contact with current collector,which results in the conductivity deteriorates continuously.In addition,the addition of binder and conductive agent reduces the loading density of silicon,limits the total capacity of silicon anode and its practical application.Here,we have fabricated a unique integrated anode metallurgically-bonded with Cu current collector without conductive and binder additives,which can be realized through laser remelting-diffusion welding-dealloying hybrid method from cheap commercial Al-Si alloy.First,the Al-Si alloy layer with fine dendrite microstructure was fabricated on the surface of cast AlSi12 alloy by a high-power laser.Then,the laser remelting Al-Si layer was metallurgically bonded with Cu substrate through diffusion welding to form Al-Si/Cu composite,which was served as the precursor.Finally,Al in precursor was selectively removed through dealloying to leaving Cu and Si.The Si anode consisted of walls perpendicular to Cu substrate surface and porous structure wrapped by the walls as well as Si microflakes.Both regions were mellurgically bonded with below Cu substrate.The size of Cu walls is about 60?m,the size of the pore wrapped by the walls is about 0.8?m~1.4?m.The structure is formed by the combination of laser and diffusion welding.This Cu network can accommodate large volume expansion,allows for increased contact area with the electrolyte.Si is wrapped in copper walls prevents pulverized Si losing electrical contact,which therefore renders superior electrical conductivity and stability upon cycling.Meanwhile,the metallurgical bonding of the Si anode with current collector can avoid the addition of conductive agent and binder,making the loading density of Si reach up to 7.8 mg/cm~2.In the first charge discharge cycle,the capacity of Si anode is up to 8.5 mA·h/cm~2.After 10 cycles,the capacity was maintained at 0.5 mA·h/cm~2,indicating that the electrode had good conductive stability.By changing the laser remelting parameters,the morphology of Si can be tuned.When the laser scanning rate is from 5 mm/s to11 mm/s,the pore size of porous Si is from 4.2?m~1.6?m,indicating that the flexibility of laser control of material structure and morphology.