What is the Role of Sodium Carboxymethyl Cellulose in Lithium Ion Batteries?

What is the Role of Sodium Carboxymethyl Cellulose in Lithium Ion Batteries?

1. What is sodium carboxymethyl cellulose?

Sodium Carboxymethyl Cellulose (CMC) is an anionic linear polymer material, non-toxic, tasteless, and odorless. It is usually a white or slightly yellow powder. Its preparation process includes solvent method and water medium method. The solvent method is suitable for preparing medium and high-grade CMC, and the water medium method is suitable for preparing medium and low-grade CMC.

2. Physical and chemical properties of sodium carboxymethyl cellulose

(1) Solubility

Water is the best common solvent for sodium carboxymethyl cellulose. The dispersibility of CMC in water is related to its degree of substitution and molecular weight. When the degree of substitution is greater than 0.4, it has good water solubility. CMC is soluble in glycerol under heating and good stirring conditions, and is more soluble in the presence of a small amount of water.

(2) Hygroscopicity

Sodium carboxymethyl cellulose is a highly hydrophilic polymer material with good hygroscopicity. Its equilibrium moisture content increases with the degree of substitution of the product. At 25°C, the CMC with a substitution degree of 0.4 has a moisture absorption rate of about 20% at a relative humidity of 80%. When the degree of substitution reaches 1.2, the moisture absorption rate of sodium carboxymethyl cellulose can be as high as 35% or more.

(3) Film-forming properties

Good film-forming is another one of the sodium carboxymethyl cellulose properties. Generally, the films made of CMC with high viscosity and high molecular weight have high strength and high flexibility. It is this performance that is used in some industries. The film formed by mixing resin and CMC using some aqueous solutions can be dried and plasticized to become a water-insoluble film product.

3. Battery grade sodium carboxymethyl cellulose

Substituting carboxymethyl cellulose sodium system for polyvinylidene fluoride (PVDF) used in traditional battery production can reduce costs and reduce pollution. At the same time, because the production process does not require environmental humidity, the battery capacity can be increased and the cycle life can be extended. At the end of battery life, sodium carboxymethyl cellulose is easier to decompose than PVDF. When studying the cyclic voltammetry curves of polysulfonate (AQ) based electrodes when using different binders. Among them, the peak potential difference of the oxidation-reduction peak of sodium carboxymethyl cellulose is smaller than when PVDF is used, indicating that the reaction is less hindered, and the sodium carboxymethyl cellulose binder is more conducive to the occurrence of redox. Sodium carboxymethyl cellulose as a binder can be used in different types of electrode materials such as natural graphite, mesocarbon microspheres, lithium titanate, tin-based silicon-based anode materials and lithium iron carbonate cathode materials, which can increase battery capacity, cycle stability and cycle life are improved compared to when PVDF is used.