Surface Reactions Between LiHMDS, TMA and TMP Leading to Deposition of Amorphous Lithium Phosphate

The treatment and coating of electrode/electrolyte interfaces is a promising route to increase lithiumion battery performance for next-generation energy storage. This work reports on the atomic layer deposition process combining lithium hexamethyl disilazide (LiHMDS) and trimethylphosphate (TMP), with an additional trimethylaluminum (TMA) pulse in between. Minimal traces of aluminum are observed, yet the deposited layer is amorphous instead of crystalline. The TMA-TMP interaction plays a key role in this process and is revealed by time-resolved full-range quadrupole mass spectrometry. We hypothesize that the interaction of unreacted OCH3 groups with TMA and the formation of Li4P2O7 units lead to higher growth and structural changes as compared to the phosphate process without TMA. The amorphous mix of Li4P2O7 and Li3PO4 units in the films grown with TMA benefits the conductive properties of the material: an ionic conductivity of 1.47±0:09·10−7 S/cm at 30°C, with an activation energy 0.58±0:02 eV is observed.