Tremendous efforts have been devoted to the development of electrode materials, electrolytes, and separators of energy-storage devices to address the fundamental needs of emerging technologies such as electric vehicles, artificial intelligence, and virtual reality. However, binders, as an important component of energy-storage devices, are yet to receive similar attention. Polyvinylidene fluoride (PVDF) has been the dominant binder in the battery industry for decades despite several well-recognized drawbacks, i.e., limited binding strength due to the lack of chemical bonds with electroactive materials, insufficient mechanical properties, and low electronic and lithium-ion conductivities. The limited binding function cannot meet inherent demands of emerging electrode materials with high capacities such as silicon anodes and sulfur cathodes. To address these concerns, in this review we divide the binding between active materials and binders into two major mechanisms: mechanical interlocking and interfacial binding forces. We review existing and emerging binders, binding technology used in energy-storage devices (including lithium-ion batteries, lithium-sulfur batteries, sodium-ion batteries, and supercapacitors), and state-of-the-art mechanical characterization and computational methods for binder research. Finally, we propose prospective next-generation binders for energy-storage devices from the molecular level to the macro level. Functional binders will play crucial roles in future high-performance energy-storage devices.

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Owing to the four features summarized in this review, i.e., low-cost resource, high-power performance, all-climate adaptability and full-batty recyclability, sodium ion batteries show great promise for large-scale energy storage systems used for the application of renewable energy sources and smart grids.

storage and engineering heterogeneous structure for lithium transfer are the key for improving the energy density and rate performance of LIBs. [4][5][6][7][8] Silicon (Si), a naturally abundant material with outstanding theoretical capacity (4200 mAh g −1 ), has attracted extensive attention as an alternative promising anode for high-energydensity LIBs, which is ten times larger than the conventional graphite anode (372 mAh g −1 ). [9][10][11][12] However, Si inherently has large volume change that seriously undermines electrode integrity and solid electrolyte interface (SEI) film formed on the Si surface. Repairing and growth of the SEI film leads to reduced amount of available Liions, corresponding to the capacity decline of LIBs. [13][14][15] Generally, engineering Si materials is widely adopted to relieve the influence of large volume change and enhance lithium diffusion within the electrode. [16][17][18] However, high cost is barely accepted into the industry due to complex preparation process. Furthermore, most methods are not based on the mass-loading-oriented strategy for high-energy-density LIBs. [19] Binder is the key component in the electrode to bond active material and conductive additive together on current collector and keep electrode integrity during charge/discharge processes. [20][21][22] Recently, the functions of the binders, such as N-P-LiPN) is constructed by the partially lithiated hard polyacrylic acid as a framework and partially lithiated soft Nafion as a buffer via the hydrogen binding effect. N-P-LiPN has strong adhesion and mechanical properties to accommodate huge volume change of the Si anode. In addition, lithiumions are transferred via the lithiated groups of N-P-LiPN, which significantly enhances the ionic conductivity of the Si anode. Hence, the Si@N-P-LiPN electrodes achieve the highest initial Coulombic efficiency of 93.18% and a stable cycling performance for 500 cycles at 0.2 C. Specially, Si@N-P-LiPN electrodes demonstrate an ultrahigh-areal-capacity of 49.59 mAh cm −2 . This work offers a new approach for inspiring the battery community to explore novel binders for next-generation high-energy-density storage devices. High-capacity electrode materials play a vital role for high-energy-density lithium-ion batteries. Silicon (Si) has been regarded as a promising anode material because of its outstanding theoretical capacity, but it suffers from an inherent volume expansion problem. Binders have demonstrated improvements in the electrochemical performance of Si anodes. Achieving ultrahigh-areal-capacity Si anodes with rational binder strategies remains a significant challenge. Herein, a binder-lithiated strategy is proposed for ultrahigh-areal-capacity Si anodes. A hard/soft modulated trifunctional network binder (

needs while signifi cantly reducing battery cost. For this reason, the combination of lithium and sulfur has been considered as one of the most promising battery chemistries for full electrifi cation of vehicles. [ 3 ] Despite these advantages, Li S batteries have a few critical barriers to be overcome. Besides the insulating properties of sulfur and polysulfi des, Li S batteries also suffer from dramatic (i.e., ≈76%) volume change of sulfur during cycling and shuttling effect of polysulfi des that sulfur species transport back and forth between electrodes. These lead to the destruction of sulfur cathodes and the corrosion of lithium anode resulting in short battery life.In a traditional Li S cell, a typical sulfur electrode consists of three components, i.e., the electrochemically active sulfur material, the conductive carbon additive, and the polymeric binder. [ 4 ] Through the syntheses of nanoarchitectured carbon additives, the electrochemical performance and cycle life of Li S batteries have been successfully improved. [ 5 ] Although signifi cant achievements have been made in designing nanostructured carbon/sulfur composites for cycle life improvement of Li S batteries, these processes are commonly sophisticated, high cost, and not suitable for large-scale manufacturing.The sulfur cathode in traditional lithium-sulfur batteries suffers from poor cyclability due to polysulfi de shuttling effect as well as large volume change during charge/discharge processes. Gum arabic (GA), a low cost, nontoxic, and sustainable natural polymer from Acacia senegal , is adopted as a binder for the sulfur cathode to address these issues. The excellent mechanical properties of GA endow the cathode with high binding strength and suitable ductility to buffer volume change, while the functional groups chemically and physically confi ne sulfur species within the cathode to inhibit the shuttling effect of polysulfi des. Additionally, GA shifts the electrode fabrication process from the organic solvent process to an aqueous process, eliminates the use of toxic organic solvents, and achieves uniformly distributed electrode with lower impedance. A remarkable cycling performance, i.e., 841 mAh g −1 at low current rate of C /5, is achieved throughout 500 cycles due to the bifunctions of the GA binder.

In this work, we synthesized graphene oxide (GO) using the improved Hummers' oxidation method. TiO2 nanoparticles can be anchored on the GO sheets via the abundant oxygen-containing functional groups such as epoxy, hydroxyl, carbonyl, and carboxyl groups on the GO sheets. Using the TiO2 photocatalyst, the GO was photocatalytically reduced under UV illumination, leading to the production of TiO2-reduced graphene oxide (TiO2-RGO) nanocomposite. The as-prepared TiO2, TiO2-GO, and TiO2-RGO nanocomposite were used to fabricate lithium ion batteries (LIBs) as the active anode materials and their corresponding lithium ion insertion/extraction performance was evaluated. The resultant LIBs of the TiO2-RGO nanocomposite possesses more stable cyclic performance, larger reversible capacity, and better rate capability, compared with that of the pure TiO2 and TiO2-GO samples. The electrochemical and materials characterization suggest that the graphene network provides efficient pathways for electron transfer, and the TiO2 nanoparticles prevent the restacking of the graphene nanosheets, resulting in the improvement in both electric conductivity and specific capacity, respectively. This work suggests that the TiO2 based photocatalytic method could be a simple, low-cost, and efficient approach for large-scale production of anode materials for lithium ion batteries.

Si has attracted enormous research and manufacturing attention as an anode material for lithium ion batteries (LIBs) because of its high specific capacity. The lack of a low cost and effective mechanism to prevent the pulverization of Si electrodes during the lithiation/ delithiation process has been a major barrier in the mass production of Si anodes. Naturally abundant gum arabic (GA), composed of polysaccharides and glycoproteins, is applied as a dualfunction binder to address this dilemma. Firstly, the hydroxyl groups of the polysaccharide in GA are crucial in ensuring strong binding to Si. Secondly, similar to the function of fiber in fiberreinforced concrete (FRC), the long chain glycoproteins provide further mechanical tolerance to dramatic volume expansion by Si nanoparticles. The resultant Si anodes present an outstanding capacity of ca. 2000 mAh/g at a 1 C rate and 1000 mAh/g at 2 C rate, respectively, throughout 500 cycles. Excellent long-term stability is demonstrated by the maintenance of 1000 mAh/g specific capacity at 1 C rate for over 1000 cycles. This low cost, naturally abundant and environmentally benign polymer is a promising binder for LIBs in the future.

LiNO 3 has been widely used as an effective electrolyte additive in lithium-sulfur (Li-S) batteries to suppress the polysulfide shuttle effect. To better understand the mechanism of suppressed shuttle effect by LiNO 3 , herein we report a comprehensive investigation of the influence of LiNO 3 additive on the formation process of the solid electrolyte interphase (SEI) layer on lithium anode of Li-S batteries by operando X-ray absorption spectroscopy (XAS). We observed that a compact and stable SEI layer composed of Li 2 SO 3 and Li 2 SO 4 on top of lithium anode is formed during the initial discharge process due to the synergetic effect of shuttled polysulfides and LiNO 3 , which can effectively suppress the subsequent reaction between polysulfides in electrolyte and lithium metal and thus result in the alleviation of polysulfide shuttle effect. In contrast, when using electrolyte without LiNO 3 , the shuttled polysulfides continuously react with lithium metal to form insulating Li 2 S on lithium anode, leading to the irreversible capacity loss. Our present operando XAS study provides a valuable insight into the important role of LiNO 3 for the protection of lithium anodes, which will be beneficial for the further development of new electrolyte additives for high-performance Li-S batteries.