Influence of Initial Porosity on the Expansion Behavior of Electrodes in Lithium-Ion Batteries

Abstract

When charging or discharging a lithium-ion-battery (LIB), lithiation or delithiation of the electrodes takes place. Especially in the case of anode active materials, lithiation often leads to a significant volume increase. The latter can cause a rearrangement of the particles. Although the volumetric changes of state-of-the-art cathode materials have been found to be smaller than for anodes, they remain relevant. The combined volumetric changes of anodes and cathodes are an important factor influencing the lifetime of LIBs. An electrochemical dilatometer was used to measure the thickness change of various electrode active materials under minimal constant pressure (≈ 16 kPa): graphite, silicon-graphite (SiG) composite electrodes, and high-voltage spinel lithium-nickel-manganese-oxide (HVS-LNMO). The influencing factors investigated included the initial porosity of the electrodes, the particle shape of graphite, and the silicon content in the case of the silicon-graphite composite electrodes. Regarding all investigated electrodes, the initial electrode porosity is shown to correlate negatively with the irreversible thickness change during the initial cycles. The thickness change in each electrode was constant over the post-formation cycles, regardless of the initial porosity. Spherical particles in graphite resulted in slightly higher thickness changes than flake-type particles. The thickness change of SiGs increased linearly with silicon content.