What keeps lithium-ion batteries intact? This is inseparable from the role of the battery anode binder. It is like a “glue” that binds the active particles tightly together and ensures that these particles are firmly attached to the current collector (such as copper foil) inside the battery anode.
Battery binders are the backbone of the battery’s structural integrity and directly affect performance and life. When the battery undergoes charge and discharge cycles, the binder is always working at high intensity. Without a high-quality binder, the battery will lose its ability to provide stable power, which is also the direction of research on battery production materials.
The Common battery Binders
Here we explore some of the top battery anode binder material:
SBR (silica bentonite rubber)
Binders for anodes have long been one of the go-to choices, often combined with Carboxymethyl Cellulose (CMC) thickener as thickening agents. What sets SBR apart? Water solubility sets it apart as being eco-friendly over other alternatives and traditional SBR can have difficulty dispersion and swelling issues; newer variants like Targray’s PSBR-100 address these concerns by providing lower manufacturing costs and faster drying times.
Polyvinylidene Fluoride (PVDF)
For a long time, PVDF has been the go-to binder, especially for cathodes, but it’s also been used in anodes. PVDF is known for its excellent mechanical strength, chemical resistance, and electrochemical stability. It processes well too. The main downside? It typically requires a solvent called NMP (N-Methyl-2-pyrrolidone), which isn’t great for the environment or for production costs. This has driven the industry to look for greener alternatives.
Polytetrafluoroethylene (PTFE)
You’ve likely encountered this material while cooking with nonstick pans; now PTFE can also serve as battery binder! With outstanding thermal and mechanical stability, chemical inertness, resistance to high voltages and solvent-free electrode manufacturing capabilities; its use as battery binder has even been researched further. Unfortunately however, dispersion issues exist with limited lithium-ion conductivity and adhesion issues can often arise with its usage resulting in poor adhesion in solution or poor dispersion dispersion!
Polyacrylic Acid (PAA)
it is a low-cost binder with easy preparation that offers strong adhesion for silicon anodes. Packed full of -COOH groups for modification purposes, PAA’s linear structure may not always suit materials with large volume changes; nevertheless it serves as an excellent basis for developing complex cross-linked biners.
LA Binders (e.g., LA133)
Here’s an exciting development! Binders like LA133 are aqueous-based, meaning they’re water dispersions of acrylonitrile multi-copolymers. What makes them stand out? They can be used without needing a thickener like CMC or toxic organic solvents like NMP. This makes the production process simpler, safer, and much more environmentally friendly! LA binders have been shown to improve battery safety, cycle performance, and rate capability, and they cause less cell polarization. For specific applications like lithium-sulfur cathodes and silicon-based anodes, LA133 has even demonstrated lower internal resistance and faster lithium-ion diffusion rates compared to CMC/SBR binders.
the Challenges of battery Binders
Just being “glue” isn’t enough in the demanding world of lithium-ion batteries. Binders face some serious challenges:
The Volume Expansion Nightmare
Imagine a balloon inflating and deflating repeatedly. That’s what happens inside your battery, especially with cutting-edge anode materials like silicon, which can expand by over 300% during charging! This massive change can cause active material particles to detach from each other and from the current collector, leading to cracks, electrode deformation, and a swift decline in battery capacity. Traditional linear binders just can’t handle this kind of stress.
Keeping the Current Flowing
While binders hold things together, they also need to ensure that electrons and lithium ions can zip around freely. Most binders are insulators, which means they can actually impede conductivity. If active particles detach from the conductive carbon/binder network (CBD), it forces electrons to take a longer, less efficient path, impacting performance.
Environmental and Cost Headaches
As we touched on with PVDF, using toxic solvents like NMP isn’t ideal for our planet or for worker safety. Plus, in much of the current battery research, binders are used in higher proportions (10-20% by weight) than they would be in commercial batteries (typically less than 5%). While this might help with performance in a lab setting, it increases production costs and can actually raise the internal resistance of the electrode, reducing overall battery performance.
Innovation Station: New-Age Anode Binders to the Rescue!
Researchers are hard at work developing innovative anode binder technologies to address today’s challenges head on. Here’s an insight into some of their breakthroughs:
Reducing Volume Expansion for Silicon Anodes
Silicon anodes are notorious for swelling and shrinking as they charge and discharge; to combat this effect, scientists are investigating binders with cross-linked structures–think tightly woven net rather than loose threads–in order to limit volume expansion during charging and discharging cycles. Polymers such as PAA, PVA, PAM and Polyimide (PI) can now be modified into powerful three dimensional networks that absorb mechanical stress caused by volume fluctuations – creating more stable long-lasting electrodes with reduced mechanical stresses. Resonac’s polyamide-imide resin forms extremely tough films to prevent electrode deformation, even with silicon content up to 30%. BASF Licity(r) biners like 2678X F are specifically tailored to handle silicon anodes easily.
Self-Healing Binders
Now comes the really exciting part: self-healing binders. Imagine healing a cut on yourself; these self-healing binders work similarly in electrodes, keeping structural damage under control over time for improved durability and lifespan. Some promising candidates include modified PAA-TUEG formulations with zinc-imidazole coordination as well as certain CMC formulations incorporating zinc-imidazole coordination for zinc iminazole coordination; it could become the future of battery technology where electrodes regenerative power ensure better performance over longer lifespans!
Boosting Conductivity
To counteract the insulating nature of binders, scientists are designing conductive binders. These polymers are engineered with special conjugated structures or ion-conducting groups. The goal is to promote electron and ion transport so effectively that the need for additional conductive agents (like carbon black) can be reduced or even eliminated, allowing for higher active material loading and increased energy density in the battery! Some examples include PEO-b-PAN, PPC, CS-g-PANI, and PEDOT:PSS.
Embracing Eco-Friendliness and Cost-Effectiveness
The trend is strongly towards water-based binder systems, moving away from harmful organic solvents like NMP. Additionally, researchers are exploring natural polymers such as Chitosan, Sodium Alginate, and various starches. These are abundant, low-cost, water-soluble, and their rich polar groups make them excellent candidates for building innovative cross-linked binders.
The Future is Bright (and Well-Bound!)
Anode binders may only account for a minor portion of a battery’s overall performance, yet their impactful role cannot be overstated. Their growth has been incredible and driven by increasing demands for higher capacity batteries with faster charging times, enhanced safety features and sustainable production – these innovations are shaping battery technology’s future and we are getting ever closer to powerful yet eco-friendly batteries with each breakthrough! It is truly exciting watching its development!
The ideal binder of the future will be a true all-rounder:
- Strong adhesion and mechanical properties to bind active materials and current collectors efficiently, accommodating volume changes and maintaining electrode stability.
- Excellent conductivity (both ionic and electronic) to ensure swift energy flow, potentially even reducing the need for other conductive additives.
- Chemical functionality to adapt to various electrode materials and even offer additional benefits like self-healing or flame retardancy.
- Environmentally friendly and low cost, with raw materials that are readily available and processes that are suitable for large-scale production.
- Crucially, it will achieve all this while being used in small quantities (less than 5% by weight) to avoid increasing the electrode’s internal resistance.
The journey to perfect these tiny titans of battery technology continues, paving the way for the next generation of powerful and sustainable lithium-ion batteries!
