Understanding the lithium-ion battery's aging mechanisms of mesophase graphite negative electrodes with/without amorphous titanium(IV) oxide nanocoatings by atomic layer deposition

Abstract

Graphite is still the mainstream anode materials among others in commercial lithium battery market. The solid electrolyte interphase (SEI) film formed by the reaction of graphite surface and electrolyte, which are significantly influenced the cell aging behaviors, which some innate aging mechanisms of graphite remained to be clarified. In this work, amorphous titanium(IV) oxide (A-TiO2) nanocoatings with different thicknesses (1–11 nm) are uniformly grown on mesophase graphite (MPG) negative electrodes by atomic layer deposition (ALD) to compare the material characteristics and electrochemical performance of the assembled cell samples. The cycling performance of the A-TiO2/MPG negative electrodes are significantly improved with the increase of the A-TiO2 nanocoating thickness that the cell capacities (capacity retention rates) are about 172 (52.2 %), 240 (72.6 %), 270 (79.4 %), 277 (82.6 %), 298 (89.7 %), 315 (92.0 %) and 321 mAhg−1 (93.6 %) for MPG electrodes with the A-TiO2 thicknesses of 0, 1, 3, 5, 7, 9 and 11 nm, respectively after the 230th cycle test. The improvement in cell cycle life is attributed to the A-TiO2 nanocoatings as protective layers that isolate the ion diffusions which are from the degraded electrolyte compounds into graphite and protect the graphite from having further reactions with electrolyte.