Effects of the Mixing Sequence on Making Lithium Ion Battery Electrodes

Slurry making is a critical step that can irrevocably affect the subsequent steps in battery manufacturing. Many experimental parameters, including the mixing sequence, must be considered in making the slurry. In this work, we investigated the effects of the two main industry-used mixing sequences on the rheological behavior of the slurry, and the relation of the slurry rheology to structural, mechanical, and electrochemical performance of LiNi_0.33Mn_0.33Co_0.33O₂ (NMC) electrodes. We show that: (1) mixing carbon black (CB) with polyvinylidene fluoride (PVDF) solution before adding NMC can facilitate the formation of a gel-like slurry; (2) porous clusters of CB/PVDF can form around NMC after drying the gel-like slurry, providing a high C-rate capability; (3) dry powder mixing of CB and NMC can facilitate the binding of the CB to the NMC surfaces, reducing the amount of CB in the PVDF and resulting in a liquid-like slurry; (4) after drying of the liquid-like slurry, a dense CB/PVDF layer can form on the NMC surfaces; and (5) this dense layer can provide high binding strength but may block ionic transport and weaken the electronic connection, reducing the C-rate capability. Thus, it is critically important to understand the effects of mixing sequence in electrode manufacturing.