Study On Stability Of Tin-based Microsphere Anode Electrodes Of Lithium Ion Battery

As a new generation of green energy storage devices,lithium-ion batteries?LIBs?have been widely used in daily electronic devices.With the rapid development of industries such as portable electronic devices and electric vehicles,the lithium-ion batteries with high capacity and long cycling life are demanding.Sn has been an attractive anode material of LIBs because of its relatively high gravimetriccapacity of 992 mAh·g^-1.One of the challenges of using Sn as the anode in LIBs is the huge volume change of 300%during lithiation/delithiation,which causes thepulverizationand desquamation of Sn-based structures from current collector and theloss of capacity.Condering the aforementioned issues,in the present work,hollow Sn microspheres?Sn HMs?and porous Sn@acetylene black composite microspheres?Sn@Ab PMSs?were fabricated and used as anode materials for LIBs.The voids in hollow or porous structures and acetylene blackwere utilized as a buffer to limit the structural degradation/damage induced by the volumetric change during electrochemical cycling,in order to improve the cycling performance.1.Hollow Sn microparticles?Sn HMs?were sysnthizedvia a galvanic replacement reaction using Zn microspheres template.The Sn in the synthesized Sn-HMs exhibits tetragonal crystal structure,and the size of the Sn-HMs is in a range of 3–8?m from scanning electron microscopy?SEM?,X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?.The Sn-HMs were used as anode materials for LIBs,and the electrochemical results indiacted that there are multi-step reactions involving the lithiation?alloying?and delithiation?de-alloying?of the Sn-HMs during electrochemical cycling.The charge capacity of the Sn-HMs after 100 cycles at a current density of 100 m A·g^-1 is 263.4 mAh·g^-1,which is higher than 148 mAh·g^-1 of solid Sn nanospheres,which is ascribed to that hollow structure can alleviate the volume expansion during electrochemical cycling.The stress distribution of Sn HMs during discharge/charge process was investigated.It can be found that the hoop and radial stress of hollow spheres are lower than those of the solid spheres.Also,increasing the current density,the hoop and radial stress increased.There are two modes of structural degradation/damage contributing to the capacity loss during electrochemical cycling;one is the disintegration of the Sn-HMs,and the other is the fracturing of the electrode layer.2.Porous Sn@acetylene black composite microparticles?Sn@Ab PMSs?weresynthesized by a galvanic replacement reaction of Zn microshperes with acetylene black as carbon matrix.The analytical techniques of SEM,TEM,XRD,EDS and N₂adsorption/desorption isotherm have been used to investigate the chemical composition,microstructure,crystal structure and surface property of the Sn@Ab PMSs.The Sn@Ab PMSs are porous with the diameter of 5–7?m,and consist of Sn nanocrystals and amorphous carbon,and the fraction of Sn in the Sn@AB MSs to be 87.9 wt%.The Sn@Ab PMSs were used as anode materials,and the half cells with the Sn@Ab PMSs as the working electrode deliver a charge capacity of 480.8 mAh·g^-1 at a current density of 100 mA·g^-1 after 100 cycles and a charge capacity of339.5 m Ah·g^-1at a high current density of 1600 m A·g^-1,which are higher than the corresponding charge capacities of263.4 mAh·g^-1 and 277.3 m Ah·g^-1for the half cells with Sn HMsas the working electrode,which indicates that the lithium-ion batteries with Sn@Ab PMSs as anode can possess better cycle stability and higher rate capacities than those with Sn HMs as anode.More importantly,the half cells with the Sn@AbPMSs exhibit a slight increase of the charge capacity after the 80th cycle,which is likely associated with the self-organization of Sn and AB driven by electrochemical cycling and the self-healing of cracks.3.The stability of Sn@Ab PMSs electrodes under quasi-static and contact load was investigated,and the results indicated that the stability and capacity of Sn@AbPMSs electrodes decreasedwhen the half cells with the Sn@Ab PMSs were compressed under quasi-static and contact load,andthe reversible capacity increased with load.The half cells with the Sn@Ab PMSsexhibited a larger irreversible capacity under contact load than that under quasi-static load,because the contact load can result in the occurrence of concave and fracture of the cells.4.The mechanical behavior of the current collector during discharge/charge was investigated.The results showed that there exists a Young's modulus and hardness increases for copper current collectors after cycling.Such an increase can be ascribed to the inseration of carbon in Cu current and the formation of cubic Li₂SnCu during electrochemical cycling,which exhibited the high Hardness and brittleness.