Pressure-sensitive Adhesives Applied In Both Silicon Anodes And Lithium Metal Anodes

Silicon(Si)and lithium(Li)has been regarded as the promising candidates of anode materials due to their high theoretical capacities.On the other hand,the Li dendrite growth on Li metal anode will causes many problems including the low-usage of capacities and serious security issues.Si anodes suffer form lage volume change(up to 300%)during the initial cycle,which will lead to unstable cycling performance.Pressure-sensitive adhesives(PSAs)are selected as efficient materials applied in both Si anodes and Li metal anodes in the current paper due to their controllable rheology,glass transition temperature and mechanical strength,served as polymer binder and artificial protective layer,respectively.Firstly,the obtained polymers were synthesized via the copolymerization of 2-Ethylhexyl acrylate(2-EHA)and acrylic acid(AA).Both FT-IR and 1H NMR were conducted to verify the chemical structures of the PSAs,and their rheologies,glass transition temperature and ductility were also measured.We can see that the obtained polymers with more 2-EHA contents will be more viscoelastic,have lower glass transition temperature and be more elastic.Secondly,considering the using of PSAs as polymer binders in Si anodes,their electrochemical performance is controlled by viscoelasticity and the amounts of AA segments.PSA should be proper voscoelastic to contact efficiently with Si surface,and it also should have enough AA segments to form strong hydrogen bonding with Si surface.The PSA with 20 mol% 2-EHA(PSA-20%)exhibits better binding performance,and it has a strongest adhesion force with Si O2 surface measured by atomic force microscopy compared to all other samples.Si anode using PSA-20% as binder exhibit an initial capacity of 3028 m Ah g-1 at a current density of 0.1 C(1 C=3600 m Ah g-1),and it delivers a capacity retention of 83% after 100 cycles.When the electrode tested at a higher current density of 0.5 C,it still shows a capacity retention of 1731 m Ah g-1 after 350 cycles.Finally,as the interfacial protective layer on Li metal anode,the electrochemical performance of PSAs is controlled by flowability,flexibility and mechanical strength.The polymer with increasing 2-EHA contents exhibits more flowability,higher flexibility but lower mechanical strength.The PSA with 70 mol% 2-EHA(PSA-70%)shows better electrochemical performance compared to PSA-50% and PSA-80%.In order to improve the elasticity and mechanical strength of PSA-70%,chemically crosslinked polymer(C-PSA-70%)was synthesized.The C-PSA-70% protected Li|Cu half cell delivers an average CE of 96.7% for 250 cycles with a current density of 1 m A cm-2 and a capacity of 1 m Ah cm-2.Furthermore,the C-PSA-70% modified full cell using Li Fe PO4 cathode exhibits a capacity retention of 93% after 150 cycles at a current density of 0.5 C(1 C=140 m Ah g-1).The PSAs used in the current paper can be synthesized easily,and they can be served as polymer materials in many fields,providing an insight on the next-generation batteries with high energy density.