A pyrene–poly(acrylic acid)–polyrotaxane supramolecular binder network for high-performance silicon negative electrodes

Although being incorporated in commercial lithium‐ion batteries for a while, the weight portion of silicon monoxide (SiOx, x ≈ 1) is only less than 10 wt% due to the insufficient cycle life. Along this line, polymeric binders that can assist in maintaining the mechanical integrity and interfacial stability of SiOx electrodes are desired to realize higher contents of SiOx. Herein, a pyrene–poly(acrylic acid) (PAA)– polyrotaxane (PR) supramolecular network is reported as a polymeric binder for SiOx with 100 wt%. The noncovalent functionalization of a carbon coating layer on the SiOx is achieved by using a hydroxylated pyrene derivative via the π–π stacking interaction, which simultaneously enables hydrogen bonding interactions with the PR– PAA network through its hydroxyl moiety. Moreover, the PR's ring sliding while being crosslinked to PAA endows a high elasticity to the entire polymer network, effectively buffering the volume expansion of SiOx and largely mitigating the electrode swelling. Based on these extraordinary physicochemical properties of the pyrene–PAA–PR supramolecular binder, the robust cycling of SiOx electrodes is demonstrated at commercial levels of areal loading in both half‐cell and full‐cell configurations

Highly elastic polyrotaxane binders for mechanically stable lithium hosts in lithium‐metal batteries

Despite their unparalleled theoretical capacity, lithium‐metal anodes suffer from well‐ known indiscriminate dendrite growth and parasitic surface reactions. Conductive scaffolds with lithium uptake capacity are recently highlighted as promising lithium hosts, and carbon nanotubes (CNTs) are an ideal candidate for this purpose because of their capability of percolating a conductive network. However, CNT networks are prone to rupture easily due to a large tensile stress generated during lithium uptake– release cycles. Herein, CNT networks integrated with a polyrotaxane‐incorporated poly(acrylic acid) (PRPAA) binder via supramolecular interactions are reported, in which the ring‐sliding motion of the polyrotaxanes endows extraordinary stretchability and elasticity to the entire binder network. In comparison to a control sample with inelastic binder (i.e., poly(vinyl alcohol)), the CNT network with PRPAA binder can endure a large stress during repeated lithium uptake–release cycles, thereby enhancing the mechanical integrity of the corresponding electrode over battery cycling. As a result, the PRPAA‐incorporated CNT network exhibits substantially improved cyclability in lithium–copper asymmetric cells and full cells paired with olivine‐LiFePO4, indicating that high elasticity enabled by mechanically interlocked molecules such as polyrotaxanes can be a useful concept in advancing lithium‐metal batteries

Zn2+-Imidazole Coordination Crosslinks for Elastic Polymeric Binders in High-Capacity Silicon Electrodes

Recent research has built a consensus that the binder plays a key role in the performance of high-capacity silicon anodes in lithium-ion batteries. These anodes necessitate the use of a binder to maintain the electrode integrity during the immense volume change of silicon during cycling. Here, Zn2+-imidazole coordination crosslinks that are formed to carboxymethyl cellulose backbones in situ during electrode fabrication are reported. The recoverable nature of Zn2+-imidazole coordination bonds and the flexibility of the poly(ethylene glycol) chains are jointly responsible for the high elasticity of the binder network. The high elasticity tightens interparticle contacts and sustains the electrode integrity, both of which are beneficial for long-term cyclability. These electrodes, with their commercial levels of areal capacities, exhibit superior cycle life in full-cells paired with LiNi0.8Co0.15Al0.05O2 cathodes. The present study underlines the importance of highly reversible metal ion-ligand coordination chemistries for binders intended for high capacity alloying-based electrodes.

Glycerol as a Binder Additive for Low-Resistance Graphite Anodes in Lithium-Ion Batteries

Lithium-ion batteries (LIBs) have matured as a technology and serve as power sources in a wide range of applications. Nonetheless, emerging applications, represented by electric vehicles, have been imposing ever-challenging criteria with regard to the key electrochemical properties. Low-resistance anodes are highly desired for high-power and supercharging capabilities of LIBs, and these properties are collectively determined by the electrolyte composition and electrode binder. Here, we report the use of glycerol as an additive to the conventional styrene-butadiene rubber/carboxymethyl cellulose (SBR/CMC) binder for graphite anodes with the aim of lowering the interfacial resistance and thus improving the operating capability at high C-rates. Glycerol, as a plasticizer, increases the interchain free volume in the binder network and also promotes the dissociation of lithium salt owing to its high dielectric constant, both of which jointly facilitate lithium ion diffusion at the anode interface. As a result, the addition of a small amount (0.18 wt% of the entire electrode) of glycerol enhances the high-rate capability (i.e., >1 C). This study highlights the usefulness of small molecules as binder additives for improving the key performance parameters of LIBs without sacrificing other critical properties. (C) 2022 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.N

Preparation of a hydrophobic cerium oxide nanoparticle coating with polymer binder via a facile solution route

In this work, cerium oxide (CeO2) nanoparticles (NPs) were synthesized using a facile, low temperature solution process and coated using spin coating and spray coating approaches, for the fabrication of a hydrophobic surface coating. Silicon wafer (Si) substrates coated with CeO2 NPs exhibited excellent hydrophobic behavior, but poor adhesion of the NPs to the substrate was observed - likely due to the low surface polarity of CeO2 NPs. Polyacrylic acid (PAA) was introduced as an adhesion promoter to improve NP surface characteristics and obtain an adherent and cohesive coating. Slight polarity tuning and binder inclusion significantly enhanced the binding capability of the NPs as determined by peel-off measurements. The superior mechanical properties of NP coatings were attributed to the incorporation of PAA in the polymeric network. It improves inter-particle and particle-substrate secondary interactions, ultimately aiding NP cohesion and adhesion when deposited onto the Si substrate. The adhesive and hydrophobic properties of CeO2 NP coatings were maintained upon exposure to high temperatures, and the coatings are transparent as well, making them suitable for various applications, such as cookware, glass coating and technology components.

Highly Elastic Binder for Improved Cyclability of Nickel-Rich Layered Cathode Materials in Lithium-Ion Batteries

Nickel-rich layered cathode materials are predominantly used for lithium-ion batteries intended for electric vehicles owing to their high specific capacities and minimal use of high-cost cobalt. The intrinsic drawbacks of nickel-rich layered cathode materials with regard to cycle life and safety have largely been addressed by doping and by applying surface coatings. Here, it is reported that a highly elastic binder, namely spandex, can overcome the problems of nickel-rich layered cathode materials and improve their electrochemical properties drastically. The high elasticity of spandex allows it to uniformly coat LiNi(0.8)Co(0.1)Mn(0.1)O(2)particles via shear force during slurry mixing to protect the particles from undesired interfacial reactions during cycling. The uniform coating of spandex, together with its hydrogen bonding interaction with LiNi0.8Co0.1Mn0.1O2, leads to enhanced particle-to-particle interaction, which has multiple advantages, such as high loading capability, superior rate and cycling performance, and low binder content. This study highlights the promise of elastic binders to meet the ever-challenging criteria with respect to nickel-rich cathode materials in cells targeting electric vehicles.