Plasma-Enhanced Atomic Layer Deposition of Iron and Titanium Phosphates as Electrode Materials for 3D-Structured Lithium-Ion Microbatteries

摘要

Using novel PE-ALD processes based on exposures to trimethyl phosphate (TMP) plasma, O_2 plasma, and a metal precursor, thin films of either iron phosphate or titanium phosphate were deposited using either tert-butylferrocene as the iron precursor or titanium isopropoxide as the titanium precursor. Both processes worked optimally at substrate temperatures of 300°C, where in both cases linear and self-limiting growth was observed with unusually high growth rates of 1.1 nm/cycle (for iron phosphate) and 0.66 nm/cycle (for titanium phosphate). The as-deposited films were amorphous. They could be used as lithium-ion battery electrodes after electrochemical lithiation, showing activity around 3.1 V (iron phosphate) and 2.7 V (titanium phosphate) relative to Li/Li~+. By depositing the films on 3D-structured micropillar substrates rather than planar ones, the footprint-normalized capacity could be increased by more than a factor of 15.