Study On Preparation And Properties Of Electrodes For Stretchable Lithium-ion Batteries

Lithium-ion batteries(LIBs)have been widely used in various electronic devices because of high energy density,output power and long life etc.In recent years,the stretchable electronics have emerged and developed fast,however,the conventional LIBs are not stretchable.It will be an effective way to prepare stretchable LIBs by looking for stretchable materials with good conductivities and electrochemical properties to replace the counterparts of LIBs.As the carriers of electrode materials,current collectors are the key parts when making batteries stretchable.The main challenge of making electrode stretchable is that high level of deformation loosens active materials on the conventional current collectors,impairing electrochemical performance.The conductive elastomers prepared by combining stretchable polymer and highly conductive materials may well substitute metal current collectors.Although binders only occupy a small proportion of electrodes,they play an important role in stabilizing the electrode structure.The commercial polyvinylidene fluoride(PVDF)binder is not elastic and difficult to ensure the active materials can be adhered tightly to the current collectors under large tensile deformation..Thus,the binders with good elasticity and cohesiveness are also one of the keys to prepare stretchable electrodes.In this paper,the styrene and n-butyl acrylate were used to synthesize poly(styrene)-b-poly(n-butyl acrylate)-poly(styrene)(SBAS)triblock copolymer by macromolecule reversible addition fragmentation chain transfer emulsion polymerization which can control the molecular weight of each block of copolymer.Then the SBAS latex and the aqueous dispersion of single-walled carbon nanotubes(SWCNTs)were mixed to prepare SBAS/SWCNTs composite conductive elastomers.The conductive elastomers with good conductivity,mechanical strength and stretchability were employed as the current collectors.Poly(styrene)-b-poly(methyl acrylate)-poly(styrene)(SMAS)was used as the binder.The conductivity and mechanical properties of the current collectors were evaluated,as well as the electrochemical performance of stretchable electrodes before and after being stretched.The relationships between the performance of stretchable electrodes and the structure of current collectors or the characteristics of binder were also investigated.In the study of SBAS/SWCNTs composite conductive elastomer,we obtained composites with different properties by mainly regulating the content of SWCNTs.With the increase of the SWCNTs content,the conductivity of elastomer correspondingly increases,but the elongation at break will decreases.After the first stretch,the structure of composite will be in a new stable state,so its conductivity will not sharply change with the increasing number of stretching.In the study of stretchable electrodes,the elastic SMAS can reduce the negative effect of large deformation on electrode.The positive correlation between the electrochemical performance and the conductivity of current collectors was observed.When the current collectors were highly conductive,the electrochemical performance of stretchable electrodes is similar to that of metal electrodes,and these stretchable electrodes can tolerate 50%tensile strains.Without sacrificing the electrochemical performance drastically,the bearable tensile deformation of stretchable electrodes using current collectors with lower conductivities can reach 100%.After the first stretch,the electrochemical performance of stretchable electrodes will decrease,but the structure and conductivity of current collectors will remain stable.So the electrochemical performance will remain unchanged after the electrodes being stretched many times.