Development of simple estimation method of creep properties of lithium-ion battery electrode (Investigation when applied to water-immersed anode and comparison with atmosphere environment)

This study has developed a novel method to estimate the creep deformation and rupture of electrode materials for lithium-ion batteries by simplified calculations using mechanical models which approximate the microscopic structure of the electrode materials. In order to verify the basic validity of the estimation method, a series of static tensile and creep tests was performed on carbon-based anode and binder materials, and the creep deformation and rupture of the anode material were estimated by the estimation method. In this verification experiment, considering applications to aqueous batteries and all-solid-state batteries, polyvinylidene fluoride (PVDF) that is a solvent-based binder with greater water resistance than aqueous binders was used for the specimens. The test results showed that both the anode and binder materials exhibited a transition creep region, in which the creep rate, that is the increase in the amount of tensile strain with respect to time, gradually decreases after reaching the holding stress, and a steady-state creep region, in which the creep rate remains constant after the transition creep region. Due to the binder material softening, the creep transition region became longer, and the creep strain was larger in water than in air. Using the mechanical properties of the binder material, the proposed method successfully estimated the creep deformation and rupture of the anode material.