| Silicon and sulfur have a wide range of sources and high theoretical specific capacities,which are expected to become the electrode materials for the next generation of commercial lithium secondary batteries.However,these materials have not been commercialized on a large scale due to some problems.For example,when silicon is used as a negative electrode material,a volume expansion rate higher than 300%is generated during the lithium intercalation process,causing problems such as powdering and falling off of silicon particles,and reducing the specific capacity of the electrode.When sulfur is used as a positive electrode material,the lithium polysulfide shuttle effect,lower lithium ion diffusion rate,and large volume change during the lithium deintercalation process result in lower capacity and cycle performance.Binders have a significant impact on the electrochemical performance of lithium secondary batteries,although small amount of binder is applied.A desirable binder can effectively improve the performance of batteries,especially the cycling stability.Traditional binder,polyvinylidene fluoride（PVDF）,for electrodes with high theory special capacity does not offer satisfactory electrochemical performance,owing to its week interaction with the active materials.Besides,the volatile toxic organic solvent,N-methyl-2-pyrrolidone,is applied as the solvent of PVDF.In order to overcome these issues and improve the electrochemical performance of the batteries,a series of aqueous-processable binders for lithium secondary batteries have been prepared in this paper.The main contents and results are as follows:1.A new low-cost and environmentally friendly binder（PAA/EVA）is prepared through blending of poly（acrylic acid）（PAA）and poly（ethylene-co-vinyl acetate）（EVA）latex.PAA with a large number of carboxyl groups provides high adhesion to the silicon particles.EVA with high elastic property enhances the ductility of the PAA/EVA binder.Besides,EVA colloids acting as host materials for electrolyte increase the electrolyte uptake of electrodes,resulting in high lithium ion conductivity.Therefore,the PAA/EVA binder with strong adhesion,high ductility and lithium-ion conductivity effectively inhibits the volume change,keeps the integrity of electrodes during cycling process,and improves the cycling stability.The silicon electrode with PAA/EVA binder displays a reversible capacity of 2120 mAh g?1 at current density of 500 mA g?1 after140 cycles.2.An amorphous dynamic cross-linked binder（ppSA-ppCMC）is achieved through hydrogen bonds between partially protonated sodium alginate and sodium carboxymethyl cellulose.The amorphous cross-linked structure effectively enhances the flexibility and strength of the binder,resulting in strong adhesion between the binder and other components in the silicon anodes.Furthermore,this binder tolerates the volume change,reduces the pulverization of silicon,and keeps the integrity of silicon anode during the charge/discharge process,leading to an excellent rate performance and cycling stability.3.A physical and chemical cross-linked polymer-Laponite nanocomposite binder（c-LiPAACA-Laponite）for sulfur cathode was prepared through free radical polymerization.The polymer and cross-linked structure of this binder drastically increase the uniform dispersion of active materials and adhesion property.The Laponite,a physical cross-linker,effectively enhances the lithium-ion transfer and greatly retard the shuttle effect,leading to low polarization and high capacity at high rate.Therefore,the c-LiPAACA-Laponite binder significantly improves the cycling performance and high-rate capability of the electrode.The electrode with this binder exhibits a reversible capacity of 593 mAh g?1 after 500 cycles at the current density of 0.5 C,which is much higher than that of PVDF.4.A copolymer micelles cross-linked binder（FNA）was obained through one-pot environmental friendly approach using the cross-linker of diacrylic Prunic F127micelles,the monomers of N-acryloyglycine lithium salt and 2-acrylamido-2-methylpropane lithium sulfonate.The FNA binder provides multiple lithium-ion diffusion pathways to increase the lithium-ion diffusion,which reduces the polarization of sulfur cathode during cycling process.The lithium-ion diffusion pathways of the FNA are provided by the electrolyte hosted in micelles,the polyethylene oxide and polypropylene oxide segments,and the carboxylate and sulfonate groups in the FNA.In addition,FNA possesses strong lithium polysulfides adsorption and high adhesion properties.Therefore,the electrode with the FNA binder presents the reversible capacity of 571 mAh g?1 with the capacity fade of 0.032%after 1000 cycles at a cycling rate of 0.5 C,which is much higher than those of PVDF sulfur cathode. |
