Atomic Layer Deposition of Lithium-Silicon-Tin Oxide Nanofilms for High Performance Thin Film Batteries Anodes

Abstract

Tin oxide is the most promising material for thin film anodes of Li-ion batteries due to its cycling performance and high theoretical capacity. It is assumed that lithium-tin oxide can demonstrate even higher performance. Lithium-silicon-tin oxide nanofilms were prepared by atomic layer deposition (ALD), using the lithium bis (trimethylsilyl) amide (LiHMDS), tetraethyltin (TET) as a metal containing reagents and ozone or water or oxygen plasma as counter-reactants. Monocrystalline silicon (100) and stainless steel (316SS) were used as supports. The thicknesses of the nanofilms were measured by spectral ellipsometry (SE) and scanning electron microscopy (SEM). It was found that oxygen plasma is the most optimal ALD counter-reactant. The composition and structure were studied by Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS), X-ray Photoelectron Spectroscopy (XPS) and X-ray diffraction (XRD). The nanofilms contain silicon as impurity, whose source is the ALD precursor (LiHMDS). The nanofilms deposited on stainless steel have shown the high Coulombic efficiency (99.1-99.8%) and cycling performance at a relatively high voltage (0.01 to 2.0V).

Atomic and Molecular Layer Deposition of Alkali Metal Based Thin Films

“…Besides aluminum, ternary Li–M–O thin films have been deposited for several other metal constituents: Ti, , Mn, , Co, , Nb, , Ta, − and Sn, by using various three-precursor processes. In particular, Li x TiO y , Li x MnO y , and Li x CoO y are all important electrode materials in LIBs.…”

“…Lithium tin oxide films have been investigated as promising candidates for a negative electrode material. These films were deposited from Li-HMDS, SnEt 4 , and different oxygen coreactants, but were found to contain significant C and Si impurities (resulting from the use of Li-HMDS), even to the point that these could be described as core constituents . Indeed, some ternary ALD processes of Li-containing material can yield quaternary products, such as LiB x C y O z and LiNi x Si y O z ; both oxygen sources investigated (O 2 -plasma and O 3 ) were found to decompose the metal precursors such that the different elements effectively incorporated into the films.…”

“…69 Also, amorphous Li−Al−S films with the measured Li/Al ratio of 2.9−3.5 have been fabricated for use as a solid-state electrolyte by combining the processes for Li 2 S (LiO t Bu + H 2 S) and Al 2 S 3 (Al(NMe 2 ) 3 + H 2 S). 94 Besides aluminum, ternary Li−M−O thin films have been deposited for several other metal constituents: Ti, 107,108 Mn, 97,99 Co, 95,96 Nb, 16,100 Ta, 103−106 and Sn, 120 by using various three-precursor processes. In particular, Li x TiO y , Li x MnO y , and Li x CoO y are all important electrode materials in LIBs.…”