Method development for the investigation of Mn 2+/3+ , Cu 2+ , Co 2+ , and Ni 2+ with capillary electrophoresis hyphenated to inductively coupled plasma-mass spectrometry.

The lifetime of lithium ion batteries (LIBs) decreases under continuous cycling due to various degradation processes, such as dissolution of transition metals (TMs) from the electrodes. Therefore, suitable methods to analyze the oxidation states of TMs are mandatory to better understand the dissolution mechanisms of TMs from positive and negative electrodes (LIBs). To investigate the dissolution of Mn 2+ and Mn 3+ in electrolytes of LIBs, a previously implemented capillary electrophoresis (CE) method with UV/Vis spectroscopy detection was further developed with the aim of higher sensitivities and additional detection of other dissolved divalent TMs such as Co 2+ , Ni 2+ , and Cu 2+ . Therefore, inductively coupled plasma-mass spectrometry was applied instead of UV/Vis for detection. This also allows the use of Ga 3+ instead of the previously used Cu 2+ as an internal standard, which solves the limitation of this method for cycled LIBs due to copper dissolution from the copper-based current collector. The CE buffer based on sodium diphosphate as complexing agent for the stabilization of Mn 3+ and cetyltrimethylammonium bromide as dynamic capillary wall modifier was optimized in terms of concentrations and pH. Finally, both manganese species and Co 2+ , Ni 2+ , and Cu 2+ could be analyzed within 15 min. With this improved method, the dissolution of TMs in LIBs for positive electrode materials such as LiNi 0.5 Mn 1.5 O 4 (LNMO) or LiNi x Co y Mn z O 2 (NCM, x + y + z = 1) can be studied in future in more detail.