60 Fomenting aqueous revolution Driven by the perennial need for cost reduction and reduced environmental impact, a shift to aqueous binders is in prospect. Aqueous binders are already used for graphite anodes (very common in lithium-ion batteries), the standard being the combination of styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC). While SBR/CMC has high binding strength, it is also sensitive to moisture, which therefore has to be meticulously controlled during manufacture. Additionally, its temperature stability is limited, making it less than ideal for very high-power or high-temperature applications, while its elasticity is inadequate for silicon anodes. For cathode use, however, the persistent challenge of aluminium current collector corrosion during processing and long-term cycling, especially with high-voltage NMC chemistries, still stands in the way of aqueous binders in mass-produced lithium-ion batteries. Different methods have been proposed to address this, including: control of the slurry chemistry to ensure a buffer pH of around 7–8 and/or using acid (HF) scavengers; and engineering the Al surface using a primer or inorganic passivation on the foil. Promising new aqueous binders for cathodes are based predominantly on polyacrylic acid (PAA) chemistry, with materials like CMC also seeing some use. The PAA-based LA133, for example, is designed as a drop-in replacement for PVDF that eliminates the toxic NMP solvent, and provides good adhesion and stability for cathode materials such as NMC and LFP. However, while PVDF is inexpensive, PAA is priced at $20,000 to $28,000 per ton, making it a speciality material. LA133 is a trademarked product, so its exact formulation is secret. However, it is widely acknowledged to be a waterbased PAA derivative or copolymer with an acrylic-based backbone and carboxylate salt (-COO⁻Li+) functional groups. These are formed when carboxyl (-COOH) groups lose the hydrogen (a single proton) when reacted with a hydroxide ion (OH-) to yield a carboxylate salt (-COO⁻) and water (H₂O) – the hydroxide ion in question would be lithium hydroxide (LiOH) to yield -COO⁻Li+. This deprotonation/ neutralisation is a key design feature that prevents corrosion of the aluminium current collector, provides optimal slurry rheology, and – combined with a stabilised polymer backbone – ensures high-voltage electrochemical stability. The ratio of -COOH to -COO⁻ in a binder (its degree of neutralisation) is a critical, tunable parameter for battery engineers, and is a key differentiator between PAA-derived binders suited to silicon anodes on the one hand and cathodes (as above) on the other. For silicon anodes, a high -COOH content is essential to enable strong hydrogen bonding with the silicon oxide layer for realisation of the elastic adhesion essential to accommodate silicon’s massive expansion caused by its absorption of lithium ions, while aqueous cathodes require a high -COO⁻ Li⁺ content for Al corrosion protection and slurry stability. For silicon-dominated anodes, the primary goal for next-gen binders is maximising the elasticity to accommodate silicon’s large volume changes, measured by capacity retention over 500 or more cycles and coulombic efficiency greater than 99.5%. However, advanced binders in general and aqueous ones in particular affect slurry rheology (shear-thinning) and drying behaviour, requiring tighter process controls (pH, viscosity and drying ramps) to avoid defects like cracking. Furthermore, switching from PVDF/NMP to aqueous systems can reduce OPEX and CAPEX (no NMP recovery is needed, for example) but may introduce higher quality risks and lower yields. Conductive binders Both energy- and power-density in lithium-ion cells can be improved by reducing the resistance to electron and ion flow in anodes and cathodes, much of the electronic portion of which is caused by the inherently insulating nature of polymers such as PVDF. This is where conductive binders come in. These can replace carbon black to improve energy density but are 20–40% more expensive than traditional systems (SBR/CMC + CB). Key challenges include poor mechanical properties and electrochemical degradation. The most prominent conductive January/February 2026 | E-Mobility Engineering Product focus | Battery electrode binders BASF Licity is an example of an aqueous binder, meaning that it uses water as the solvent, reducing processing costs and eliminating the associated with conventional solvents such as NMP – a VOC (Image: BASF)
RkJQdWJsaXNoZXIy MjI2Mzk4