Tailoring Three-Dimensional Cross-Linked Networks Based on Water-Soluble Polymeric Materials for Stable Silicon Anode

Abstract

For stable battery operation of silicon (Si)-based anodes, utilizing cross-linked three-dimensional (3D) network binders has emerged as an effective strategy to mitigate significant volume fluctuations of Si particles. In the design of cross-linked network binders, careful selection of appropriate cross-linking agents is crucial to maintaining a balance between the robustness and functionality of the network. Herein, we strategically design and optimize a 3D cross-linked network binder through a comprehensive analysis of cross-linking agents. The proposed network is composed of poly(vinyl alcohol) grafted poly(acrylic acid) (PVA-g-PAA, PVgA) and aromatic diamines. PVgA is chosen as the polymer backbone owing to its high flexibility and facile synthesis using an ecofriendly water solvent. Subsequently, an aromatic diamine is employed as a cross-linker to construct a robust amide network that features a resonance-stabilized high modulus and enhanced adhesion. Comparative investigations of three cross-linkers, 2,2′-bis(trifluoromethyl)benzidine, 3,3′oxidianiline, and 4,4′-oxybis [3-(trifluoromethyl)aniline] (TFODA), highlight the roles of the trifluoromethyl group (−CF 3 ) and the ether linkage. Consequently, PVgA cross-linked with TFODA (PVgA-TFODA), featuring both −CF 3 and −O−, establishes a wellbalanced 3D network characterized by heightened elasticity and improved binding forces. The optimized Si and SiO x /graphite composite electrodes with the PVgA-TFODA binder demonstrate impressive structural stability and stable cycling. This study offers a novel perspective on designing cross-linked network binders, showcasing the benefits of a multidimensional approach considering chemical and physical interactions.

Cross-Linkable Binders for Si Anodes in High-Energy-Density Lithium-Ion Batteries

“…The former is ascribed to a Li–Si alloying process, and the latter corresponds to a dealloying process. , From Figure S6b, it can be seen that Si@ c -POAH exhibits good reversibility and higher redox peak currents. The increased peak currents are indicative of faster lithium-ion transport because larger peak currents correlate with more rapid ion movement . The intensity of the redox peaks gradually increases with the cycle numbers, indicating improved electrochemical kinetics. , …”

“…The results verify that the high resilience of the c -POAH binder is very helpful for keeping the structure integrity of the Si@ c -POAH anode, and the pulverization of the Si anode has been greatly depressed. Hence, it is supposed that the newly exposed surface should be much less, and so are the side reactions with LE, which is beneficial for high-capacity retention. , …”

“…As an anode material for lithium-ion batteries (LIBs), silicon (Si) has high theoretical capacity (4200 mAh g –1 ), − significantly higher than currently used graphite (372 mAh g –1 ). Furthermore, there is a high abundance of Si in nature (second only to oxygen) .…”

“…Therefore, it has been one of the most promising anode materials for high-energy-density LIBs. However, when the Si anode is charged or discharged, the alloying and dealloying reactions of Si with lithium result in significant volume expansion and contraction (∼300%). , Severe volume change will induce high stress in Si particles, leading to the pulverization of Si particles and causing delamination among Si particles, conductive agents, and the current collector. The broken part will no longer maintain current contact with the electrode, which will become “dead” materials, leading to fast capacity decay of the anode .…”

“…However, the Si anode with PVDF binder exhibits poor performance due to the weak van der Waals interactions between Si and PVDF. , Carboxymethyl cellulose (CMC) with polar groups is reported to enhance cycle performance through hydrogen bonding with the Si anode. Nevertheless, its inadequate mechanical strength renders CMC less than ideal as a binder for Si . Other binders, such as poly­(acrylic acid), sodium alginate, guar gum, etc., have also been reported.…”