Simple Evaluation of Viscoelastic Properties of Polymer Binder in Anode Material for Lithium-Ion Battery

Binders influence mechanical and electrochemical properties of electrodes in lithium-ion battery. In order to estimate the mechanical properties of binders in anode materials, this study proposed a simplified mechanical model of the anode materials based on their microscopic structures. A series of tensile tests and dynamic mechanical analysis were performed on the anode materials made of polyvinylidene fluoride (PVDF) and styrene-butadiene rubber (SBR) based binders at multiple mixing ratios. The mechanical model was applied on the test results to estimate the stress, strain, storage modulus, loss tangent, and dissipated strain energy of the binder in the anode materials. The results are summarized as follows. (1) The validity of the mechanical model was confirmed by the static tensile test of the PVDF-based anode material. (2) The mechanical model could be applied to the SBR-based anode material. The estimation results indicated that the higher the mixing ratio of carboxymethyl cellulose (CMC) to SBR, the higher the stiffness and strength of the binder. (3) Under a practical condition of test temperature 25℃ and load frequency of 0.1 to 20 Hz, the storage modulus and loss tangent of the anode materials were in the condition above the glass transition temperature. (4) As same as the static tensile tests, the estimated viscoelastic properties of the PVDF-based binder agree regardless of the mixing ratio of PVDF. The estimated viscoelastic properties of the SBR-based binder agree when the mixing ratio of CMC to SBR was same.