Novel Binder with Cross-Linking Reconfiguration Functionality for Silicon Anodes of Lithium-Ion Batteries

Polyacrylic Acid Binder Enabling High Areal Capacity V2O5·nH2O Cathode for Aqueous Zinc-Ion Batteries

Polyvinylidene difluoride (PVDF) is traditionally used as a cathode binder in aqueous zinc-ion batteries. However, its poor mechanical properties lead to cycling degradation of the electrodes. Herein, It is reported that polyacrylic acid (PAA) with hydrophilic carboxyl groups can serve as a high-performance binder for aqueous zinc-ion batteries. The structure and electrochemical properties of the V2O5·nH2O electrode is significantly improved by using the PAA binder, showing desirable mechanical properties, enhanced electrolyte wettability, and greatly improved electrochemical reaction kinetics compared to the traditional PVDF binder. The V2O5·nH2O-PAA electrode demonstrates a high-capacity retention of 84.1% after 2000 cycles at the 2 A g-1 current density. Moreover, the thick electrode with a high active material loading of 21.4 mg cm-2 retains a large areal capacity of 7.44 mAh cm-2 with stable cycling, highlighting the great potential of PAA binder in practical aqueous zinc ion batteries.

Construction of Protein-Like Helical-Entangled Structure in Lithium-Ion Silicon Anode Binders via Helical Recombination and Hofmeister Effect

In this study, a novel gelatin-xanthan gum composite binder is successfully developed with a protein-like helical-entangled network structure through thermo-responsive and Hofmeister effect to improve the cycling stability of silicon anodes in lithium-ion batteries. As the temperature changes, the molecular chains of xanthan gum and gelatin undergo de-helixing, intertwining, and co-helixing, ultimately self-assembling into a protein-like spatial structure. Furthermore, immersing in Hofmeister salt solution enhances the degree of helical entanglement, significantly improving strength and toughness. This novel helical-entangled structure absorbs and dissipates the stress and strain caused by silicon volume expansion through repeated bending, twisting, and stretching, similar to protein spatial structures, thereby maintaining the integrity of the silicon anode and enhancing its cycling stability. The silicon anode with the optimized binder exhibits high initial Coulombic efficiency, favorable rate performance, and long-term cycling stability. At a current density of 0.5 A g⁻¹, the silicon anode has a specific capacity of 1779.8 mAh g⁻¹ after 300 cycles, with a capacity retention rate of 80.65%. This study demonstrates the feasibility of natural polymers forming complex 3D network structures through self-assembly and intermolecular forces, providing a new approach for the design of silicon anode binders.

Silicon anode modification strategies in solid-state lithium-ion batteries

The development and application of solid-state electrolytes in lithium-ion batteries (LIBs) have become mainstream in the industry of LIBs. Compared with liquid electrolytes, solid-state electrolytes offer higher safety and energy density and are expected to further broaden the application fields of lithium-ion batteries. Conventional solid-state lithium-ion batteries (SSLIBs) employ lithium metal as their anode, which raises new concerns about their safety and waste management. Therefore, silicon, with high safety, high theoretical capacity, low electrochemical plateau, and low handle cost, has become the most promising new-generation anode material. However, due to the volume expansion of silicon and the low contact with solid-state electrolytes, resulting in poor conductivity, the SSLIBs' capacity has not reached the expected level and the cycle performance is also poor. Therefore, further modification of silicon anodes has become one of the key points in the development of SSLIBs. This paper comprehensively expounds on the application and optimization of silicon anodes in SSLIBs. It proposes further optimization strategies, which focus on preventing the destruction of silicon and extending its lifespan. The strategies include (1) silicon with different morphologies; (2) the formation of amorphous silicon; and (3) silicon composites.

Stable Silicon Anodes Enabled by Innovative Biobased Binder with Cross-Linking Network in Lithium-Ion Batteries

Graphite anodes, with their capacity nearing the theoretical maximum of 372 mA h g-1, are increasingly being complemented by silicon-based materials, which offer a 10-fold higher capacity. Nevertheless, extreme volume expansion (>300%) of Si during cycling poses significant challenges to its practical deployment. Previous studies on the synthesis of binders are often intricate and not conducive to large-scale implementation. In this study, an innovative binder, denoted as HM, is developed by combining the macromolecular polysaccharide sodium hyaluronate with the small organic molecule malic acid without the need for any external triggers. A cross-linked network structure is formed in situ after heat treatment with silicon under vacuum conditions. The contact interface establishes a robust network structure through multiple macromolecular hydrogen bonds and chemical interactions. Consequently, the HM binder exhibits exceptional mechanical properties and efficiently lessens the volumetric change of silicon particles, thereby benefiting the generation of a stable solid electrolyte interphase. Electrochemical characterization demonstrates that the exceptional cycling stability of Si@HM electrodes can maintain a high capacity of 1949 mA h g-1 at 0.1 C and 1426 mA h g-1 at 0.5 C after 100 cycles. Furthermore, silicon anodes employing the HM binder demonstrate superior rate performance and reduced internal resistance compared to those of conventional binders, representing a significant advancement in performance. This research provides crucial perspectives for binder design and experimental evidence for the commercial utilization of silicon anodes within lithium-ion batteries.

Dual Cross-Linked Poly(ether imide)/Poly(vinyl alcohol) Network Binder with Improved Stability for Silicon Based Anodes in Lithium-Ion Batteries

The abundance and exceptional theoretical capacity of silicon make it a leading contender for next-generation lithium-ion battery anodes. However, its practical application is significantly hindered by rapid capacity degradation arising from substantial volume fluctuations during cycling. To address this limitation, an subtly dual cross-linked binder system was developed by incorporating soft poly(vinyl alcohol) (PVA) macromolecules into a poly(ether imide) (PEI) matrix. This innovative design leverages the rigid PEI framework, fortified through chemical ester cross-linking, to effectively suppress the expansion for silicon nanoparticles. Concurrently, the reversible hydrogen bonding within PVA could dissipate the stress to inhibit the volume changes, thereby preserving the materials' mechanical stability and structural integrity. This synergistic interplay ensures a stabilized electrode interface and enhanced durability with outstanding cycling stability, that of a high specific capacity of 2126 mAh/g and 92.1% retention over 200 cycles at 0.84 A/g. Further refinement of the anode formulation enabled an impressive areal capacity of 9.3 mAh/cm2 with submicron silicon, underscoring the transformative potential of this dual cross-linked system for next-generation energy storage solutions.

Cooperation of covalent bonds and coordinative bonds stabilizing the Si-binder-Cu interfaces for extending lifespan of silicon anodes

Binders provide a straightforward and efficient strategy to mitigate the significant challenge of volume expansion in silicon anodes for lithium-ion batteries. To improve the cycle life of silicon anodes, a cross-linked binder carboxymethyl cellulose-phytic acid-pyrrole (CMC-DP) is designed and synthesized using carboxymethyl cellulose, phytic acid, and pyrrole. The numerous hydroxyl groups in phytic acid provide abundant binding sites for the formation of hydrogen and ester bonds. The formation of hydrogen bonds and covalent bonds enhances the mechanical properties of the adhesive. The amino groups in the binder form NSiO covalent bonds with silicon particles, while the hydroxyl and carboxyl groups form (COO)2Cu and (OH)2Cu coordination bonds with the copper foil, enhancing interfacial adhesion. When the CMC-DP10 (10 µL pyrrole) binder is applied to silicon nanoparticles (∼30 nm), the specific capacity of the electrode can be maintained at around 1700 mAh/g after 500, whereas the CMC binder achieves only ∼100 mAh/g under the same conditions. This work demonstrates that the CMC-DP binder exhibits strong adhesion to both silicon nanoparticles and copper foil.

Poly(Acrylic Acid)-Based Polymer Binders for High-Performance Lithium-Ion Batteries: From Structure to Properties

Poly(acrylic acid) (PAA) and its derivatives have emerged as promising candidates for enhancing the electrochemical performance of lithium-ion batteries (LIBs) as binder materials. Recent research has focused on evaluating their ability to improve adhesion with silicon (Si) particles and facilitate ion transport while maintaining electrode integrity. Various strategies, including mixing modifications and copolymerization methods, are highlighted and the structural and physicochemical properties of these binders are examined. Additionally, the interaction mechanisms between PAA-based binders and active materials and their impact on key electrochemical properties such as initial Coulombic efficiency (ICE) and cycle stability are discussed. The findings underscore the efficacy of tailored PAA-based binders in enhancing the electrochemical properties of LIBs, offering insights into the design principles and practical implications for advanced battery materials. These advancements hold promise for developing high-performance lithium batteries capable of meeting future energy storage demands.

Impact of Binder Content and Type on the Electrochemical Performance of Silicon Anode Materials

Binders are crucial for stabilizing the cycling performance of silicon (Si) materials by preventing Si particle pulverization during lithiation and delithiation. Poly(acrylic acid) (PAA) and carboxymethyl cellulose (CMC) are the two most studied binders for Si electrodes, with PAA being an elastic polymer and CMC a rigid polymer. Starting with the elastic PAA, in this work the impact of binder content on the cycling performance of Si electrodes is studied. It is found that regardless of Si particle size, there is an optimal binder content between 20 % and 25 % for the cycling stability of Si electrodes. On the other hand, the rigid CMC binder results in lower capacity and faster capacity fading for Si electrodes compared with the elastic PAA. AC-impedance analysis reveals that the lower capacity is due to higher grain boundary resistance (Rgb) in CMC-coated electrodes, leading to high charge-transfer resistance (Rct) and increased polarization. This high polarization triggers premature termination during the discharging process (i. e., the lithiation) of Li/Si cells, underutilizing the Si active material. Additionally, the rapid capacity fading of CMC-coated electrodes is attributed to the rigid binder's inferior ability to prevent Si particle pulverization.

Dramatic Enhancement Enabled by Introducing TiN into Bread-like Porous Si-Carbon Anodes for High-Performance and Safe Lithium Storage

Doping modifications and surface coatings are effective methods to slow volume dilatation and boost the conductivity in silicon (Si) anodes for lithium-ion batteries (LIBs). Herein, using low-cost ferrosilicon from industrial production as the energy storage material, a bread-like nitrogen-doped carbon shell-coated porous Si embedded with the titanium nitride (TiN) nanoparticle composite (PSi/TiN@NC) was synthesized by simple ball milling, etching, and self-assembly growth processes. Remarkably, the porous Si structure formed by etching the FeSi2 phase in ferrosilicon alloys can provide buffer space for significant volume expansion during lithiation. Highly conductive and stable TiN particles can act as stress absorption sites for Si and improve the electronic conductivity of the material. Furthermore, the nitrogen-doped porous carbon shell further helps to sustain the structural stability of the electrode material and boost the migration rate of Li-ions. Benefiting from its unique synergistic effect of components, the PSi/TiN@NC anode exhibits a reversible discharge capacity up to 1324.2 mAh g-1 with a capacity retention rate of 91.5% after 100 cycles at 0.5 A g-1 (vs fourth discharge). Simultaneously, the electrode also delivers good rate performance and a stable discharge capacity of 923.6 mAh g-1 over 300 cycles. This research can offer a potential economic strategy for the development of high-performance and inexpensive Si-based anodes for LIBs.