Selective surface treatment by means of IR-laser – A new approach to enhance the rate capability of cathodes for Li-ion batteries

Abstract

To meet today’s demands on lithium-ion batteries for battery electrical vehicles in terms of energy density, electrodes with a high active mass loading as well as a low porosity are strived for. However, such high energy electrodes exhibit a poor rate capability, mainly due to limited lithium-ion diffusion. In this work, we present a laser-based surface treatment of calendered cathodes to partially overcome this conflict of objectives. NCM-based electrodes with different porosities were superficially modified by using IR-laser radiation with pulse duration in the nanosecond-regime. By detailed microscopic analysis, we show that it is possible to selectively ablate the binder/additive-compound without impairing the active material particles. Thus, it is possible to open surface pores which were closed during calendering by the binder/additive-compound. As a result, laser treated highly densified cathodes show a significantly improved rate capability at C-rates > 2C compared to untreated reference samples. The most significant improvement of >20% of the rate capability is found at 5C for electrodes with lowest porosity of 20%. The experimental findings suggest that an enhanced electrolyte access to the active mass and thus, a reduced lithium-ion transport resistance lead to the improved electrochemical characteristics. In addition to the short-term rate capability tests, preliminary investigations of the cyclic stability of electrodes modified in such a way were performed. The state-of-health after one hundred 1C charge/discharge-cycles was about 95% for both, the laser treated and the pristine electrodes.