Cross-Linked Poly(acrylic acid) with Polycarbodiimide as Advanced Binder for Si/Graphite Composite Negative Electrodes in Li-Ion Batteries

Abstract

Cross-linked poly(acrylic acid) (PAA) with polycarbodiimide (PCD) is utilized as a binder for the Si/graphite composite electrode. Cross-linkage of PAA can be modulated by the addition of the PCD as a cross-linker into the slurry. Compared to PAA binder, initial reversible capacity of Si/graphite composite electrodes is increased with suppressed electrolyte decomposition by the use of cross-linked PAA. The electrode adhesion strength onto current collector is increased by the cross-linking of PAA with PCD. The Si-composite electrode with optimal amount of 1 wt% PCD cross-linker delivers more than 1,000 mAh g −1 of reversible capacity with improved capacity retention.In the past two decades, the demand to increase energy density for lithium-ion batteries (LIB) is continuously growing, 1 which will certainly lead to replacing conventional carbon-based materials with the next-generation negative electrode materials having higher specific energy. Silicon has been extensively studied to satisfy the growing demand as a promising electrode for LIBs, because silicon is capable of electrochemically alloying with lithium, ∼3.75 Li per Si, resulting in the high specific capacity (ca. 3600 mAh g −1 ). 2 Utilization of Si as negative electrode materials, however, suffers from the huge volume expansion (∼3.8 times) when the full lithiation from Si to Li 3.75 Si is achieved during the electrochemical cycling. The huge volume change induces the damage to integrity of composite electrodes, leading to the insufficient capacity retention as electrode materials. To prevent the deterioration of reversible capacity for Si-based electrode materials, most research efforts have been directed toward the development and modification of pure silicon; 3 for instance, silicon nanotube, 4 nanoporous silicon, 5 Si thin platelet 6 and so on. However, the synthesis of nanoarchitectured silicon materials inevitably increases the materials' production cost.Recently, many researchers in the field of battery technology are being interested in a study on polymer binders as simple and cost-effective methods to improve the reversibility of Si-based electrode. 7-10 Instead of the conventional poly(vinylidene fluoride), polymer binders possessing carboxylic groups; such as calboxy methylcellulose (CMC) 11-17 and alginate, 18 have been proposed to be capable of improving capacity retention of the Si-based electrodes. Our group has also reported poly(acrylic acid) (PAA) and its alkaline salts 19-24 as efficient functional binders for graphite 25,26 and Si/graphite-based negative electrodes. Recently, the effectiveness of PAA-based binders for a Li-alloy system was also supported by other research group. 27,28 Since the carboxylic groups in these polymers dissolved in water are electrolytically dissociated or undissociated (to form -COO − or -COOH, respectively) depending on the neutralization degrees (pH value of aqueous solution), its polymer conformation can be also modulated in aqueous media. A PAA molecule without the neutralization has the agglomerated...

Acrylic Acid-Based Copolymers as Functional Binder for Silicon/Graphite Composite Electrode in Lithium-Ion Batteries

“…Moreover, the retention depends on the amount of added cross-linkers, which agrees with the previous result of the polycarbodiimide cross-linkage. 7 As a result, the moderate cross-linkage attains the better capacity retention, and 10CLPAH is the most optimum binder among them. Figure 3d further compares the cyclability with the NaOH-neutralized binders.…”

“…5 Furthermore, PAH binders with cross-linkage between two carboxylic groups with polycarbodiimide efficiently improved the lithiation performance of Si. 7 The cross-linkage proceeded in organic solvent during slurry process. In this study, we prepare a new water-soluble crosslinked binder, synthesized by copolymerization of acrylic acid with coexistence of crosslinker, diallyl ether, and demonstrate the battery performance of silicon-graphite electrodes with the copolymers.…”

Recent Progress on Polymeric Binders for Silicon Anodes in Lithium-Ion Batteries

“…They demonstrated that the resulting hierarchical hydrogel framework provides a continuous electrically conductive polyaniline (PANi) network, binding with the Si surface via crosslinker hydrogen bonding with phytic acid or electrostatic interaction between the positively charged PANi doped with phytic acid and the negatively charged surface oxide (-Si-O-) on the Si, with a porous space for a large volume expansion of the Si nanoparticles. The Si nanoparticle-PANi hydrogel composite is fabricated by solution-phase synthesis by mixing Si nanoparticles with phytic acid and an aniline monomer in water to produce a suspension [43]. The SiPANi composite electrode exhibited relatively stable cycling performance compared to other samples and delivered a high Li extraction capacity of ~1,200 mAh g -1 after 1,000 cycles ( Fig.…”

“…20(b)). Komaba et al reported crosslinked PAA with polycarbodiimide (PCD) as a binder for a Si/graphite composite anode [43]. They demonstrated the positive effect of PCD as a crosslinker for a PAA binder on the electrochemical performance of Si/graphite anodes.…”

“…This cross-link process also improves the mechanical stability of the composite electrode against the strain induced by the severe volume expansion of Si nanoparticles upon Li insertion. The Si/graphite anode with the crosslinked PAA-1% PCD delivered more than 1,000 mAh g -1 and showed improved cycling stability compared to PVDF and PAA binders [43]. Recently, Ryu et al synthesized polymers with carboxylic acid (COOH), carboxylate (COO-), and hydroxyl (OH) groups in a single polymer backbone to develop a new polymeric binder system for Si anodes in LIBs [44].…”