A Comprehensive Study of Hydrolyzed Polyacrylamide as a Binder for Silicon Anodes

Abstract

Silicon anodes have a high theoretical capacity for lithium storage, but current composite electrode formulations are not sufficiently stable under long-term electrochemical cycling. The choice of polymeric binder has been shown to impact stability and capacity of silicon anodes for electrochemical energy storage. While several promising polymeric binders have been identified, there is a knowledge gap in how various physicochemical propertiesincluding adhesion, mechanical integrity, and ion diffusionimpact electrochemical stability and performance. In this work, we comprehensively investigate the physical properties and performance of a molecular-weight series (3−20 × 10 6 g/ mol) of partially hydrolyzed polyacrylamide (HPAM) in silicon anodes. We quantify the mechanical strength, electrolyte uptake, adhesion to silicon, copper, and carbon, as well as electrochemical performance and stability and find that HPAM satisfies many of the properties generally believed to be favorable, including good adhesion, high strength, and electrochemical stability. HPAM does not show any electrolyte uptake regardless of any molecular weight studied, and thin films of mid-and high-molecular-weight HPAM on silicon surfaces suppress lithiation of silicon. The resulting composite electrodes exhibit an electrochemical storage capacity greater than 3000 mAh/g initially and 1639 mAh/g after 100 cycles. We attribute capacity fade to failure of mechanical properties of the binder or an excess of the solid electrolyte interphase layer being formed at the Si surface. While the highest-molecular-weight sample was expected to perform the best given its stronger adhesion and bulk mechanical properties, we found that HPAM of moderate molecular weight performed the best. We attribute this to a trade-off in mechanical strength and uniformity of the resulting electrode. This work demonstrates promising performance of a low-cost polymer as a binder for Si anodes and provides insight into the physical and chemical properties that influence binder performance.

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

“…Besides, a series of PAA‐based polymer binders have been developed for Si‐based anodes through polymerization, 85‐88 blending 89‐96 and post‐modification 64,97,98 methods. Deng et al designed a water‐soluble triblock copolymer polydopamine‐polyacrylic‐polyethylene oxide (PDA‐PAA‐PEO) binder for Si anodes via reversible addition fragmentation chain transfer (RAFT) polymerization and a coupling reaction (Figure 6A).…”

“…78,79 In addition, the binding ability of PAA can also be regulated or optimized though neutralization by NaOH or LiOH, and controlling its M w (Figure 5C). 41,42,53,[80][81][82][83][84] Besides, a series of PAA-based polymer binders have been developed for Si-based anodes through polymerization, [85][86][87][88] blending [89][90][91][92][93][94][95][96] and post-modification 64,97,98 methods. Deng et al designed a water-soluble triblock copolymer polydopamine-polyacrylicpolyethylene oxide (PDA-PAA-PEO) binder for Si anodes via reversible addition fragmentation chain transfer (RAFT) polymerization and a coupling reaction (Figure 6A).…”

Dynamically Cross-Linked Polymeric Binder-Made Durable Silicon Anode of a Wide Operating Temperature Li-Ion Battery

“…(d) Comparison of the properties of the Si@PAA-B-HPR anode prepared in the present work with those of the reported Si anodes for Li-ion batteries. Note: All the data cited from the literature were measured at room temperature. ,,,− …”

“…Polyvinylidene fluoride, the common binder for Li-ion cells, is not qualified for buffering volume changes in Si anodes due to its weak bonding (i.e., van der Waals interaction) between Si particles and the copper current collector. Accordingly, other synthetic polymers have been adopted instead, such as poly­(acrylic acid) (PAA), , styrene–butadiene rubber, and poly­(acrylamide). ,, Especially, a few water-soluble natural binders, like guar gum, polysaccharide and its derivatives, − chitosan, − and carboxymethylated cellulose were also applied in hopes of reducing the usage of toxic organic solvents for the oil-soluble polymeric binders . The abundant polar groups including carboxyl and hydroxyl of these binders favored the formation of strong interaction with the silanol groups on the Si particles, promoting stable adhesions between the active materials and the current collector …”

Key Factors for Binders to Enhance the Electrochemical Performance of Silicon Anodes through Molecular Design

“…In the study of partially hydrolyzed polyacrylamide (HPAM) with different molecular weights in the Si anode, the influence of molecular weight on the performance of the binder was further analyzed. [41] Specifically, although HPAM binder increases with MW, the viscosity, bonding force with Si and tensile strength are all increasing, middle MW HPAM shows the best cycle stability in Si anodes. It was attributed to the trade-off between mechanical properties and electrode uniformity.…”