Sequence‐Defined Peptoids with OH and COOH Groups As Binders to Reduce Cracks of Si Nanoparticles of Lithium‐Ion Batteries

Abstract

Silicone (Si) is one type of anode materials with intriguingly high theoretical capacity. However, the severe volume change associated with the repeated lithiation and delithiation processes hampers the mechanical/electrical integrity of Si anodes and hence reduces the battery's cycle‐life. To address this issue, sequence‐defined peptoids are designed and fabricated with two tailored functional groups, “OH” and “COOH”, as cross‐linkable polymeric binders for Si anodes of LIBs. Experimental results show that both the capacity and stability of such peptoids‐bound Si anodes can be significantly improved due to the decreased cracks of Si nanoparticles. Particularly, the 15‐mer peptoid binder in Si anode can result in a much higher reversible capacity (ca. 3110 mAh g−1) after 500 cycles at 1.0 A g−1 compared to other reported binders in literature. According to the density functional theory (DFT) calculations, it is the functional groups presented on the side chains of peptoids that facilitate the formation of Si−O binding efficiency and robustness, and then maintain the integrity of the Si anode. The sequence‐designed polymers can act as a new platform for understanding the interactions between binders and Si anode materials, and promote the realization of high‐performance batteries.

Advances of polymer binders for silicon‐based anodes in high energy density lithium‐ion batteries

“…To make better use of the advantages of –COOH and –OH, Zhang et al fabricated a sequence‐defined peptoids (P1) with programmed –COOH and –OH groups on the chain as a crosslinkable binder for SiNP anodes (Figure 7B). 106 The results showed that SiNP anodes with P1 binder showed excellent cycling performance (~3110 mA h g −1 after 500 cycles at 1.0 A g −1 ) and good rate capability (1328.2 mA h g −1 even at 7 C), compared with CMC or P2 (substituting the –OH groups in P1 by –OCH 3 groups) binders (Figure 7C). Mussel‐inspired polymer binders have attracted a lot of research interests due to the excellent adhesion by the catechol groups 107‐110 .…”

“…(A) Chemical structure of poly(vinyl alcohol) (PVA). (B) Chemical structure of peptoids (P1) 106 . Copyright 2020, Wiley‐VCH.…”

“…Copyright 2020, Wiley‐VCH. (C) Cycling and rate performances of SiNP anodes with CMC, P1, and P2 binders 106 . Copyright 2020, Wiley‐VCH.…”

“…Esterification reaction has been widely employed for constructing the covalently crosslinked polymer binders for Si‐based anodes. Due to the high availability of –COOH and –OH groups in a lot of water‐soluble polymers, thermally activated esterification reaction between these two groups has been widely used to fabricate the 3D crosslinked polymer binders for Si‐based anodes 89,90,93,106,130‐135 . Cho et al reported a 3D crosslinked PAA/CMC binder for SiNP anodes by thermally curing the electrodes at 150°C under vacuum (Figure 11A).…”

“…(B) Chemical structure of peptoids (P1). 106 Copyright 2020, Wiley-VCH. (C) Cycling and rate performances of SiNP anodes with CMC, P1, and P2 binders.…”