Industrial Carbon-Coated Current Collectors Grades for Higher Energy and Power Density Lithium Ion Batteries

Abstract

Electric mobility and renewable energy storage became very challenging and will continue growing up in interest on the next decades. Lithium-ion batteries are one of the most acclaimed devices to treat these problematics and constant developments on this technology aim to achieve higher specific energy density and specific power in order to fit numerous applications. Since the beginning of research on lithium ion energy storage devices, a large part of studies focus on the optimization of electrolytes, active materials and also, but more recently, on the electrode formulation. Although they are effective ways to improve these systems performances, they usually put aside the current collectors influence. However, several shortened lifetime, failures, or reduced performance can be ascribed to the metallic current collector. We can take as an example the electrode delamination [1], the metallic corrosion [2] or the electrical contact resistivity between the current collector and the electrode [3]. To avoid these problems, a conductive and protective coating of the metallic current collector (fig.1) can be added to obtain a better interface between the electrode and its substrate. In the present work, various types of carbon-coated aluminum current collectors for positive electrodes will be presented and compared to bare aluminum foils. Their characteristics such as physical properties, ageing on electrolyte, electrode affinity and electrical resistivity will be presented. The electrochemical performance will be assessed in full cells with a LiFePO4 – PVdF positive electrode, graphite negative electrode and carbonate-based electrolyte with LiPF6. Results of electrochemical impedance spectroscopy, C-rate capability and cycling experiments will be discussed. By reducing the carbon content of electrode, the bare aluminum shows a raising internal resistance by more than a factor two, an optimized coated current collector allows containing a smaller value. With a low carbon content in the electrode formulation, the capacity retention is about only 40% for bare aluminum system, and 60% for a coated current collector after 500 cycles in severe cycling conditions. These results show that an improvement of energy density and power capability are possible with an adapted coated current collector. [1] S. Lee, E-S. Oh, J. Power Sources 244 (2013) 721-725. [2] I. Doberdò, N. Löffler, N. Laszczynski, et Al . ,, J. Power Sources 248 (2014), 1000-1006. [3] S. Wennig, U. Langklotz, G-M. Prinz, et Al., J. Appl. Electrochem 45 (2015), 1043-1055. Figure 1