Preparation And Properties Of Prelithiation Of Tin-based Anode Materials

With the rapid development of electric vehicles,the demand for lithium ion batteries is highly increasing.The traditional lithium cobalt oxide/graphite battery system is far from meeting the demand for high range of electric vehicles.It is of great signi:ficance to develop high capacity electrode materials.Among the substitutable anode materials,tin base anode has been widely studied due to its advantages of high capacity,low voltage and abundant sources.However,similar to other alloy anode materials,tin base anode has some disadvantages.Huge volume expansion(260%)during the charge-discharge process lead to rapid capacity fading.To solve the problem,the researchers have proposed many strategies,including various nanostructures of tin,or combining it with carbon matrix.These methods improved the electrochemical performance of Sn,but brought other problems at the same time.The large specific surface area of nano-Sn lead to more formation of SEI,which causes a large number of lithium consumption.Although the irreversible lithium consumption can be compensate by the excessive loading of the positive material,which will reduce the energy density of the whole battery.Prelithiation is a common way to compensate for the consumption of lithium.There are three common prelithiation methods to realize anode with pre-stored Li.One approach is electrochemical prelithiation by directly contact the electrode with the Li foil,which requires complex process.Another method is utilize stabilized lithium metal powder(SLMP)to compensate for the irreversible lithium loss.However,it is difficult to synthesize SLMP in laboratory.Herein,we report a simple and reliable prelithiation approach that chemically synthesized LixSn based anode.Challenges of LixSn NPs is the high chemical reactivity and huge volume variation.After thermally alloying with lithium,Sn based materials is converted into LixSn alloy anode,which exhibits high chemical reactivity.A protective coating needed to stabilize the alloy anode.In this paper,we choose two coating layers:conducting polymer coating and MnO2 coating layer.1.We conformally coated a conductive polypyrrole on the Sn nanoparticle,and first time studied the protection effect of the polymer on thermal lithiation process of the Sn nanoparticles.By tuning the thickness of polypyrrole from 8 to 40 nm,we find that the optimized coating layer(20 nm)keeps intact during the thermal lithiation,and ensures LixSn nanoparticles a very high stability in dry air condition.Moreover,the flexible and conductive polypyrrole accommodates huge volume variation of LixSn nanoparticles and enhances the electronic connections of interparticles.As a result,the composite maintains 75%of its prelithiated capacity after exposure to dry air for 5 days and delivers a stable reversible capacity of 534 mAh/g for 300 cycles.When paired with traditional LiFePO4 cathode,it achieves a stable full cell cycling.2.SnO2 based materials have shown great potential in replacing commercial graphite as high energy density anode materials,But they usually suffer from low initial Coulombic efficiency and continual capacity fading.Here,we first time coated MnO2 layer on the SnO2 nanoparticles by using polyacrylic acid as surfactant,and then we studied the thermal lithiation of the composite.With fully expanded LixSn nanoparticles confined in the Li2O/MnxOy matrix,the composite exhibits stable cycling performance.It delivers a capacity of 480 mAh/g at 1C,and maintains approximately 80%capacity retention after 500 cycles.Profitting from the robust protection layer,side reaction and undesirable solid electrolyte interphase are suppressed,which ensure lower polarization and faster reaction kinetics.