Electrochemical storage is the most efficient way to store energy produced from renewable sources. Leading the way in electrochemical energy storage is the lithium ion battery (LIB). Traditionally, electrode production for LIBs has required the use of hazardous solvents like NMP due to the fluoropolymers used to hold the active and conductive material together on the current collector. These solvent based binder systems are a driving factor in the cost and environmental friendliness of LIBs.
The Role of a Binder in Lithium Ion Battery Electrodes
Battery electrodes are composed of 3 main components; the active material, a conductive additive, and a polymeric binder. The active material provides the electrochemical reactions necessary to power the battery and the conductive material helps to facilitate the flow of electricity. Often overlooked, the polymeric binder is used to provide the mechanical integrity of the electrode during manufacturing and provide optimal dispersion and adhesion of the active material and conductive additive to the current collector. Traditionally, fluoropolymers like PVDF have been used for this purpose, but as the demand for LIBs increases there is a need to move to more environmentally friendly "green" binders.
Aqueous Binders vs. Solvent Binders
As mentioned above, solvent based binders present a number of concerns in regards to environmental impact, manufacturing, and cost of lithium ion batteries. The benefits of using an aqueous binder like TEXTURECEL™ over a solvent based polymer are outlined below.
Fluoropolymers used as electrode binders are themselves teratogenic and mutagenic. In addition, they require the use of hazardous solvents like NMP which is strictly regulated by many countries due to serious and irreversible effects it can have on human health and the environment. Alternatively, aqueous binders such as TEXTURECEL™ carboxymethyl cellulose are non-hazardous and only require the use of water for manufacturing. Additionally, the low drying temperature and shortened drying time of TEXTURECEL™ aqueous binders results in a significant decrease in carbon dioxide emissions.
Slurry preparation of solvent based electrode binders requires special ventilation systems to protect workers, and the solvent must be recovered during the drying step in order to prevent release into the environment. Preparation of water based electrode slurries only require standard PPE and there is no added step of recovering a hazardous solvent during drying. Additionally, aqueous binders dry faster than solvent based binders allowing for an increase in production output.
Aqueous binders like TEXTURECEL™ CMC are significantly less expensive than fluoropolymers like PvDF (usually 2-3X). The NMP required for fluoropolymers is also rather expensive when compared to water. While these cost savings are significant perhaps the greatest savings comes from the elimination of the solvent recovery step. This process can account for up to half of the production cost of electrodes and if eliminated can go a long way into reducing the production cost of lithium ion batteries.
TEXTURECEL™ Sodium Carboxymethyl Cellulose
The most commonly used aqueous binder used in lithium ion battery electrodes is carboxymethyl cellulose (CMC). TEXTURECEL™ CMC has an extremely high purity (>99.5%), a low moisture content, tailored degrees of substitution, and excellent quality consistency. A summary of benefits provided to LIB electrodes by TEXTURECEL™ are listed below.
Optimal dispersion of active material and conductive additive.
Mechanical integrity during manufacturing and cycling.
Strong adhesion to current collector improves capacity