Establishing a Resilient Conductive Binding Network for Si-Based Anodes via Molecular Engineering

Abstract

Metrics & MoreArticle Recommendations CONSPECTUS: Silicon-based anode materials have become a research hot spot as the most promising candidates for next-generation high-capacity lithium-ion batteries. However, the irreversible degradation of the conductive network in the anode and the resultant dramatic capacity loss have become two ultimate challenges that stem from inherent characteristics of the Si-based materials, including poor conductivity and massive volume changes (up to 300%) during cycling. Apart from optimization of the active materials, one effective way to stabilize high-capacity Sibased anodes is by designing polymeric binders to reinforce the conductive networks during repeated charge and discharge processes. As an inactive component in the electrode, the binder not only holds other components (e.g., active materials, conductive agents, and current collectors) together to maintain the mechanical integrity of the electrode but also serves as a thickener to facilitate the homogeneous distribution of particles. Therefore, binders play a key role in Si-based anodes by maintaining the integrity of conductive networks in the electrode.In this Account, on the basis of the extensive binder-related work on Si-based anodes since the 2000s, efforts made on maintaining the conductive network can be categorized into two main strategies: (1) stabilization of the primary conductive network (which generally refers to conductive agents) by enhancing the binding strength and resilience of the binding between electrode components (i.e., Si particles, conducting agents, and current collectors) via various interactions (e.g., dipolar interactions and covalent bonds) and (2) construction of the secondary conductive network by employing conductive binders, which serve as a molecular-level conductive layer on active materials. In this sense, functional groups in binders can be divided into two categories: mechanical structural units and conductive structural units. On the one hand, functional groups with strong polarities (e.g., −OH, −COOH, −NH 2, and −CONH−) generally serve as binding structural units because of their bonding tendencies; on the other hand, exhibiting high electronic conductivity, conjugated functional groups (e.g.

Conductive Polymer Frameworks in Silicon Anodes for Advanced Lithium-Ion Batteries

“…Moreover, the employed polymer must also provide high adhesion to tie the Si particles together and connect them electronically. Therefore, a conductive polymer framework is obligatory to demonstrate high intermolecular interaction of the polymer to facilitate mechanical bonding and the electronic pathway and high polymer–Si interaction to facilitate tight adhesion . Additionally, strong interaction between the polymer and current collector is required to prevent electric contact loss due to delamination .…”

“…Therefore, a conductive polymer framework is obligatory to demonstrate high intermolecular interaction of the polymer to facilitate mechanical bonding and the electronic pathway and high polymer−Si interaction to facilitate tight adhesion. 46 Additionally, strong interaction between the polymer and current collector is required to prevent electric contact loss due to delamination. 47 These interactions can be improved by appropriately designing the structure of conductive polymers to acquire unique features.…”

Practical evaluation of prelithiation strategies for next‐generation lithium‐ion batteries

“…With a high theoretical specific capacity of 1500–4200 mAh g −1 , Si‐based anodes are one of the most promising candidates for next‐generation batteries. Nevertheless, the relatively low ICE (60%–85%) and continuous reconstruction of the solid electrolyte interphase (SEI) film of Si‐based anodes have also markedly hindered their practical application 6 . Therefore, when these anode materials are coupled with cathode materials (e.g., LiCoO 2 and LiFePO 4 ) with limited Li + , the capacity of full‐cells shows high irreversible active Li loss during prolonged cycling due to undesirable side reactions (e.g., electrolyte decomposition), resulting in capacity decay and structural degradation.…”

Three-Dimensional Crosslinked PAA-TA Hybrid Binders for Long-Cycle-Life SiOx Anodes in Lithium-Ion Batteries

“…High-capacity electrode materials are generally recognized as the key for achieving high energy density in lithium-ion batteries (LIBs). − Among them, SiO x have been considered as ideal candidates because of their higher specific capacity relative to graphite and smaller volume change compared with pure silicon. − However, a large volume expansion (118%), poor electronic conductivity, and low initial coulomb efficiency (ICE) hinder their practical application. , Numerous design strategies have been explored to solve these inherent disadvantages, such as core–shell structures, , size refinement, and carbon coating. ,, However, the synthesis of modified silicon-based materials often involves high cost and complex fabrication processes . Binders, as essential components with a simple preparation process and low cost, offer an effective adhesive network to keep active materials and conductive agents on the current collectors, retaining the structural integrity of electrodes. − Nevertheless, conventional binders including poly­(vinylidene fluoride) (PVDF) and carboxymethylcellulose (CMC) fail to provide sufficient adhesion and mechanical properties for suppressing the severe volume expansion of silicon-based anodes due to the comparatively weak interactions. − …”

“…Therein, poly­(acrylic acid) (PAA) possesses a high density of −COOH polar groups, providing robust interfacial adhesion with hydroxyl groups on the silicon surface, which has been employed as a functional binder for silicon-based anodes. , However, the linear polymer chain structure of the PAA binder is not strong enough to withstand the structural distortion of silicon-based anodes with large volume variability. , Based on the characteristics of PAA, different binders with expected features such as self-healing ability , and soft/hard elastic-plastics have been constructed for a robust long-term cycling performance of silicon-based anodes. It is noteworthy that physical dynamic crosslinking via three-dimensional (3D) hydrogen-bonding networks has been emphasized as a validated method to improve the lithium storage performance of silicon-based electrodes. ,, Compared with polymer binders based on irreversible covalent crosslinking, H-bond-crosslinked polymeric binders with self-healing ability can guarantee intact electrical contact between the anode material and the current collector during cycling. ,− Therefore, constructing robust and reversible H-bond-crosslinked PAA-based binders through a facile method is desired to boost the electrochemical performance of SiO x electrodes.…”