Surface reactivity of ultrathin atomic layer deposited Al2O3 on Li[Ni0.8Mn0.1Co0.1]O2

Sammanfattning: The nickel-rich cathode material Li[Ni0.8Mn0.1Co0.1]O2 is a much sought after material in Li-ion batteries for the future of electric vehicles due to its high specific capacity. However, it exhibits fast degradation during its use due to the interaction between the electrolyte and the cathode surface leading to capacity loss. In this thesis, the surface interaction of pristine and alumina coated NMC811, and NiO powder with electrolyte was investigated to observe difference in surface reactivity and if hydroxide groups on the surface could be a potential culprit in degradation. Thermogravimetric analysis (TGA) and Brunauer–Emmett–Teller (BET) analysis were used to measure thermal properties, surface area and adsorptive properties respectively between pristine and coated powders but no distinct difference was found. A soaking experiment was performed to induce electrolyte degradation on the powders by soaking them in the electrolyte LP40 for a duration of two weeks at 50°C. The electrolyte and the soaked powders were thereafter investigated through various spectroscopy methods like Attenuated Total Reflection – Fourier Transform Infrared (ATR-FTIR) and Raman spectroscopy to find potential degradation products but were found insignificant or inconclusive difference. The electrochemical testing was performed on NMC811 half-cells at 3-4.2V and 3-4.4V with a 0.5C – rate. The coated heat-treated NMC811 was found to have the best cyclability at both potential ranges. In conclusion, the difference in surface reactivity of the pristine, coated, and coated heat-treated powders were found to be insignificant. However, the coated heat-treated NMC811 was found to have improved electrochemical performance at both potential ranges but it remains uncertain if hydroxide groups could be a culprit in the degradation.