Acrylic acid-based copolymers are synthesized by polymerization of acrylic acid with a small portion of crosslinker, diallyl ethers. The obtained copolymers are soluble in water, and viscosity of their aqueous solution incrementally varies with increase in the amount of crosslinker and neutralization degree of -COOH groups with NaOH. The copolymers are examined as binders for silicon/graphite composite electrodes for lithium-ion batteries. Reversibility and lithiation capacity of the composite are highly improved by the selection of copolymers, which is due to better homogeneity and mechanical durability of the composite electrodes. © The Author Electrochemical lithiation has been extensively studied and discussed for application in lithium-ion batteries. Generally, active materials with higher-capacity lithiation suffers from repeated volume change during lithiation/delithiation especially in lithium silicide system. 1 Si-based electrodes demonstrate high-capacity lithiation, however, capacity fade inevitably arises from the huge volume change. The lithiation of Si-based electrodes is improved by binder selection, e.g. carboxymethylcellulose, 2 polyimide, polyacrylate, 3,4 compared to conventional fluorinated binders.Poly(acrylic acid) (PAH), commodity chemicals used in industry, improves mechanical stability of composite electrodes against the volume change. 5,6 Because poly(acrylic acid) is weak polyacid, its conformation in water is modulated by neutralization with alkali hydroxides, which is capable to adjust the slurry rheology and leads to better electrode performance. 6 The capacity retention of the Si-based composite was highly improved with 80% neutralized polyacrylate binders because of self-forming porous structure of the composite.
5Furthermore, 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.
ExperimentalCross-linked poly(acrylic acid)s were synthesized by copolymerization of acrylic acid with different amount of dially ether as a crosslinker, H 2 C=CH-CH 2 -(O-CH 2 -CH 2 ) n -O-CH 2 -CH=CH 2 (n = 1 ∼ 4) as shown in Fig. 1a.8 Acrylic acid monomers were polymerized with different amounts of the crosslinker, 0, 0.007, 0.07, 0.14, and 0.7 mol% and the obtained polymers are hereafter denoted as PAH, 1CLPAH, 10CLPAH, 20CLPAH, and 100CLPAH, respectively. The polymers were dissolved in water to prepare 1 wt% binder solution, and further neutralized by dropping 1 mol dm −3 NaOH (titration up to pH 6.7) to convert 80% of -COOH into -COONa, 6 and they are similarly denoted as PAH 0.2 Na 0.8 , 1CLPAH 0.2 Na 0.8 , 10CLPAH 0.2 Na 0.8 , 20CLPAH 0.2 Na 0.8 , and 100CLPAH 0.2 Na 0.8 . Viscosity measurement o...
