Plasma-Enhanced Atomic Layer Deposition of Iron Phosphate as a Positive Electrode for 3D Lithium-Ion Microbatteries

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• 作者：Thomas Dobbelaere ; Felix Mattelaer ; Jolien Dendooven ; Philippe Vereecken ; Christophe Detavernier
• 刊名：Chemistry of Materials
• 出版年：2016
• 出版时间：May 24, 2016
• 年：2016
• 卷：28
• 期：10
• 页码：3435-3445
• 全文大小：801K
• 年卷期：0
• ISSN：1520-5002

文摘

A new plasma-enhanced atomic layer deposition process was developed to deposit iron phosphate by using a sequence of trimethyl phosphate (TMP, Me₃PO₄) plasma, O₂ plasma, and tert-butylferrocene (TBF, Fe(C₅H₅)(C₅H₄C(CH₃)₃)) exposures. Using in situ spectroscopic ellipsometry and ex situ X-ray reflectometry, the growth linearity, growth per cycle (GPC), and density of the resulting thin films was investigated as a function of the pulse times and the substrate temperature. At a substrate temperature of 300 °C and using saturated pulse times, an exceptionally high GPC of 1.1 nm/cycle without nucleation delay was achieved, resulting in amorphous films with an empirical stoichiometry of FeP_1.5O_4.7 with 0.9% hydrogen and no detectable carbon residue. Trigonal FePO₄ (Berlinite) was formed upon annealing in air. Remarkably, annealing in helium resulted in the formation of elemental phosphorus. The as-deposited, amorphous material became active as a Li-ion cathode after an initial irreversible electrochemical lithiation, showing insertion and extraction of Li⁺ around a potential of 3.1 V vs Li/Li⁺. By conformally depositing the same material on a 3D-microstructured substrate consisting of Pt-coated Si micropillars, the capacity could be drastically increased without sacrificing rate performance.