61 binders are those based on the polymer complex known as poly(3,4ethylenedioxythiophene (PEDOT)) and polystyrene sulphonate (PSS) – collectively referred to as PDOT:PSS. The charge-carrying PDOT component is a conjugated polymer that is intrinsically conductive in its doped state. The PSS component is a watersoluble insulating polymer with two roles. In its first role, the sulphonate groups dope the PDOT chain, making it conductive, while its second role is to act as a dispersant so that the otherwise insoluble PDOT can form a stable water-based dispersion or ‘ink’. However, PDOT:PSS comes with a number of limitations that the industry is working to overcome. While this binder is electrically conductive, it is a poor conductor of ions, meaning that lithium-ion transport can be hindered, particularly in thick electrodes, limiting charge/discharge rates. The thiophene-based backbone of the PDOT component can be electrochemically unstable at cell potentials above 3.8 V. It can undergo oxidation and degrade cathode surfaces, causing capacity to grow and impedance to fade, severely limiting its use with high-voltage cathode materials such as NMC and NCA. Also, the PSS component is highly acidic and corrosive to the cathode’s aluminium current collector foil and it can also degrade active materials, necessitating the use of costly neutralisation or barrier layers. The film is also hygroscopic, and retention of water is catastrophic for cell assembly and long-term performance, so extremely thorough drying is demanded. Furthermore, its adhesion to electrode materials is often inferior to that of binders such as PAA and PVDF. Hybrid systems in which PEDOT:PSS is mixed with a stronger binder are being explored but dilute its conductivity. Lastly, its cost is orders of magnitude higher than that of traditional binders and carbon black. Research and development to mitigate these problems focuses on niche applications and material modifications. The most promising application for PEDOT:PSS is in silicon or silicon-based anodes because it can accommodate silicon’s expansion while providing both binding and electronic conductivity, and its poor voltage stability is not a problem in the anode where voltages are typically between 0.1 and 0.8 V. One area of focus for material modification is treating PEDOT:PSS with solvents such as dimethyl sulphoxide (DMSO) or ethylene glycol, for example, or with bases to increase its electronic conductivity and reduce acidity. Another is on hybrid/composite binders in which PEDOT:PSS is used with small amounts of a strong adhesive binder such as PAA, or incorporating inorganic nanoparticles to improve adhesion and stability. As with other conductive binders such as π-conjugated polymers, or hybrid ionic–electronic conductors, PEDOT:PSS can eliminate or drastically reduce the need for carbon black, thereby improving volumetric and gravimetric energy density. However, their cost is higher owing to the more complex synthesis process, leading to higher battery cost-per-cyclelife, making them about 20–40% more expensive than SBR/CMC + CB electrodes. Conductive competitors Overall, PEDOT:PSS is transformative in concept, but remains challenging for mainstream EV batteries – because of its high cost in particular – and there is significant r&d into potential competitors. For anode applications, these include intrinsically conductive polymers (ICPs), carbon-based conductive binders and multifunctional hybrid/composite binders. ICPs such as polyaniline (PANI) and polypyrrole (PPy) compete directly with PEDOT:PSS but come with their own trade-offs. PANI offers good conductivity, but its complex doping/ de-doping chemistry in the battery voltage window can be unstable and lead to side reactions. PANI is often used in composite binders. PPy polymerises relatively easily but, like PEDOT, has marginal stability during long-term cycling. Furthermore, most ICPs suffer from poor ionic conductivity and can swell/shrink with their own redox reactions, compromising their stability as binders. As a group, carbon-based conductive binders constitute important pragmatic competition for PEDOT:PSS. The most promising examples include graphene oxide (GO) / reduced graphene oxide (rGO) and carbon nanotube (CNT) ‘liquids’ or dispersions. E-Mobility Engineering | January/February 2026 Aqueous binders Licity 2680 for graphite anodes and Licity 2668 F suited for both graphite and silicon-containing anodes exhibit superior mechanical performance to reference SBR binders (Image: BASF)
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