Total reflection X-ray fluorescence in the field of lithium ion batteries – Elemental detection in Lithium containing electrolytes using nanoliter droplets

Abstract

In this work, an approach for the measurement of transition metal dissolution from the respective cathode active material LiNi1/3Co1/3Mn1/3O2 is presented. Furthermore, undiluted lithium ion battery electrolyte solutions with practical (=high) salt concentration are used. It is demonstrated, that nanoliter dispensers are capable to compensate the formation of an excessive salt crust compared to conventionally prepared total reflection X-ray fluorescence (TXRF) carriers (μL droplet application), resulting in improved recovery rates. The quantification is conducted by application of an internal standard solution placed between the sample dots composed of highly concentrated salts.The application procedures are compared to inductively coupled plasma-optical emission spectroscopy. The recovery rates of the new TXRF sample preparation vary between 98% and 105%, compared to 85% to 90% obtained with the conventional application procedure.The concentration of transition metals (TMs) in real cells does not exceed a few mg L−1. To demonstrate the applicability of the nanoliter droplet approach, components from cells aged by charge/discharge cycling were analyzed. Noteworthy, though the TMs are present in the cathode material in the same amounts, the concentration of nickel in the electrolyte was three times higher than that of manganese (1.4 mg L−1 to 0.4 mg L−1). Cobalt could not even be quantified as it did not exceed the limit of quantification (LOQ > 0.3 mg L−1). This was further confirmed by the deposition of the TMs on the other cell parts (anode and separator), where nickel showed always the highest value.