The implementation of lithium metal batteries is hindered by the difficulty in controlling the Li metal plating microstructure. Ex-situ solid-electrolyte interphases (SEIs) have been shown to curtail the electrochemical instabilities of lithium, and atomic layer deposition (ALD) is useful for the synthesis of ex-situ thin-film SEIs such as Al2O3 and alucone. However, these ALD-grown SEIs become delaminated as a result of their innate resistance to the cyclic shuttling of Li ions, resulting in marginal performance benefits.
Herein, we report the use of ALD-grown TiO2 as a nucleation layer, rather than as an artificial SEI. We show that by depositing TiO2 directly on the Cu current collector, we can control the deposition morphology of Li in the widely studied ether-based electrolyte - 1M LiTFSi in an equal volume mixture of 1,3 dioxolane and 1,2 dimethoxyethane, with 1 weight percent of lithium nitrate as an additive. By optimizing the thickness of TiO2, we show that lithium nucleates into large deposits under reduced overpotential, resulting in a reduction in contact surface area with the electrolyte and an increase in cell performance. Furthermore, we report substantial improvements in cycling reversibility with an average Coulombic efficiency of 96% after 150 cycles at 1mA cm-2 in Li/Cu cells. The performance of the TiO2 film, and the origin of its effects as established by spectroscopy and microscopy techniques, will be reported and discussed.
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