Methylboronic Acid Mida Ester (Adm) as an Effective Additive in Electrolyte to Improve Cathode Electrolyte Interlayer Performance of Lini0.8co0.15al0.05o2 Electrode

Abstract

We investigated the effectiveness of using methylboronic acid MIDA ester (ADM) as an additive in an electrolyte to enhance the overall electrochemical and material properties of an LNCAO (LiNi0.8Co0.15Al0.05O2) cathode. The measurement of the cyclic stability of the cathode material, carried out at 40°C (@ 0.2 C), showed an enhanced capacity of 166 mAhg-1 (@ 50 cycles), a capacity retention of 90%, and a high coulombic efficiency (99.5 %), in contrast to these same properties without the electrolyte additive (91.48 mAhg-1, ~50%, and 91%, respectively), thus confirming the effectiveness of the additive. A Fourier transform infrared spectroscopy (FTIR) analysis distinctly showed that the ADM additive suppressed the EC-Li+ ion coordination (1197 cm-1 and 728 cm-1) in the electrolyte, thereby improving the cyclic performance of the LNCAO cathode. A morphological analysis of the cathode after 100 charge/discharge cycles revealed that the ADM-containing system exhibited better surface stability (less cracking) of the grains in the LNCAO cathode, whereas distinct cracks were observed in the system without the ADM in the electrolyte. A transmission electron microscopy (TEM) analysis revealed the presence of a thin, uniform and dense CEI film on the surface of LNCAO cathode, indicating that the additive prevented the decomposition of the electrolyte. An operando synchrotron X-ray diffraction (XRD) test identified the high structural reversibility of the LNCAO cathode with a CEI layer formed by the ADM, which effectively maintained the structural stability of the layered material. The additive effectively inhibited the decomposition of LiPF6 into LiF, as confirmed by X-ray photoelectron spectroscopy (XPS) which showed that the concentration of Li salt (LixPOyFz and LixPFy) reached 47.9 % with the additive, compared to 40.1% without it.

Keywords: LNCAO cathode, ADM additive, electrochemical performance, In-operando synchrotron X-ray diffraction