Influence of Battery Electrode Manufacturing Process on Electrode Characteristics and Electrochemical Performance

Abstract

The numerous battery gigafactory projects show that the Li-ion battery sector is booming. Although groundbreaking technologies such as all-solid-state batteries mobilize a lot of research effort, current Li-ion liquid technology still needs to be updated. Only a few publications are related to electrode manufacturing. However, increasing the active material content, the areal capacity, or the solid slurry content is key to improve the energy density but also the manufacturing costs.The objectives of this thesis work are to understand and improve the preparation of the slurry and the manufacturing process as a whole in order to obtain the best possible performances depending on the material used. Initially, the study is carried out in an aqueous formulation for negative graphite electrodes. Still, it will be extended after that to the positive electrode in an organic formulation. The negative electrode is very interesting from a fundamental study point of view because of its specificities that limit the fast charge operation of the cells with a risk of metallic lithium deposit. This electrode's basic composition, in weight, is 96.5% graphite (90/10 mixture of natural and artificial graphite), 1.3% Na-CMC, 1.7% latex, and 0.5% electronic conductor.Eleven significant parameters were selected thanks to preliminary results and literature outcomes. Their impact is determined by crossing experiences and varying them thanks to a rational approach based on the design of experiments (DOE) methodology. A DOE is carried out to be able to study this large number of parameters with a limited number of trials. Apart from the active material and the mixer used, the parameters are grouped into three categories:- The CMC (CarboxyMethylCellulose) polymer, with the molar mass, the substitution degree, and its content.- The electronic conductors, the content as well as the nature (nanotube, nano-sphere, and platelet)- Electrode properties such as coating speed, porosity, or loading.To determine their influences, characterizations are carried out throughout the electrode coating. The slurries are analyzed by rheology and scanning electron microscopy (SEM). The adhesion of the electrodes and their structuring are measured, with particular attention on the electronic resistivity and tortuosity. Finally, the electrodes obtained are tested by electrochemical cycling at various charging rates.Tortuosity is a particularly sensitive factor in relation to the issue of rapid charge/discharge [1]. The tortuosity is measured by electrochemical impedance in the blocking and symmetric electrode configuration and corresponds to the measurement of the distance traveled by the ions in order to cross an electrode (Figure 1). [2]The results of this wide study will be presented with parameter sensitivity on capacity retention, high charging rate capabilities, or electrode mechanical properties. Interrelations between the parameters will be pointed out. Optimal electrode formulations and designs will be presented to validate the approach.[1] D. Grießl, A. Adam, K. Huber, and A. Kwade, "Effect of the Slurry Mixing Process on the Structural Properties of the Anode and the Resulting Fast-Charging Performance of the Lithium-Ion Battery Cell," J. Electrochem. Soc., vol. 169, no. 2, p. 020531, 2022, doi: 10.1149/1945-7111/ac4cdb.[2] J. Landesfeind, J. Hattendorff, A. Ehrl, W. A. Wall, and H. A. Gasteiger, "Tortuosity Determination of Battery Electrodes and Separators by Impedance Spectroscopy," J. Electrochem. Soc., vol. 163, no. 7, pp. A1373–A1387, 2016, doi: 10.1149/2.1141607jes Figure 1