Lithium metal is considered to be the most promising anode for next-generation batteries due to its high energy density of 3840 mAh g(-1). However, the extreme reactivity of the Li surface can induce parasitic reactions with solvents, contamination, and shuttled active species in the electrolyte, reducing the performance of batteries employing Li metal anodes. One promising solution to this issue is application of thin chemical protection layers to the Li metal surface. Using a custom-made ultrahigh vacuum integrated deposition and characterization system, we demonstrate atomic layer deposition (ALD) of protection layers directly on Li metal with exquisite thickness control. We demonstrate as a proof-of-concept that a 14 nm thick ALD Al2O3 layer can protect the Li surface from corrosion due to atmosphere, sulfur, and electrolyte exposure. Using Li-S battery cells as a test system, we demonstrate an improved capacity retention using ALD-protected anodes over cells assembled with bare Li metal anodes for up to 100 cycles.

Substantial efforts are underway to develop all-solid-state Li batteries (SSLiBs) toward high safety, high power density, and high energy density. Garnet-structured solid-state electrolyte exhibits great promise for SSLiBs owing to its high Li-ion conductivity, wide potential window, and sufficient thermal/chemical stability. A major challenge of garnet is that the contact between the garnet and the Li-metal anodes is poor due to the rigidity of the garnet, which leads to limited active sites and large interfacial resistance. This study proposes a new methodology for reducing the garnet/Li-metal interfacial resistance by depositing a thin germanium (Ge) (20 nm) layer on garnet. By applying this approach, the garnet/Li-metal interfacial resistance decreases from ≈900 to ≈115 Ω cm due to an alloying reaction between the Li metal and the Ge. In agreement with experiments, first-principles calculation confirms the good stability and improved wetting at the interface between the lithiated Ge layer and garnet. In this way, this unique Ge modification technique enables a stable cycling performance of a full cell of lithium metal, garnet electrolyte, and LiFePO cathode at room temperature.

Over the past three decades, batteries based on Li-ion chemistry have attracted attention because of the lowest redox potential and small ionic size of Li. 1,2 The recent rise of the cost of Li-ion batteries (LIBs) due to the shortage of lithium containing resources and their uneven distribution has spurred research efforts in battery systems using other alkali metal ions, such as Na + , K + , Mg 2+ and Al 3+ . [3][4][5][6][7] Among them, Na-ion systems have drawn considerable interest because they share a similar chemistry with Li-ion chemistry, and sodium minerals are more abundant and available than lithium resources. [8][9][10] To date, Na/S batteries operating at high temperatures (300-350 C) have been successfully commercialized and have shown promising performance for large scale energy storage. 11 However, safety issues related to the highly reactive molten Na metal and corrosive molten sulfur have limited their widespread application. As a result, room temperature Na-ion based batteries (NIBs) are beginning to garner interest in the scientific community.Recently, various cathode materials have been reported for NIBs, which exhibited comparable performance to their counterparts in LIBs. [12][13][14] Unfortunately, only a small

We demonstrate an atomic layer deposition (ALD) process for the solid electrolyte lithium phosphorousoxynitride (LiPON) using lithium tert-butoxide (LiO t Bu), H 2 O, trimethylphosphate (TMP), and plasma N 2 ( P N 2 ) as precursors. We use in-situ spectroscopic ellipsometry to determine growth rates for process optimization to design a rational, quaternary precursor ALD process where only certain substrate−precursor chemical reactions are favorable. We demonstrate via in-situ XPS tunable nitrogen incorporation into the films by variation of the P N 2 dose and find that ALD films over approximately 4.5% nitrogen are amorphous, whereas LiPON ALD films with less than 4.5% nitrogen are polycrystalline. Finally, we characterize the ionic conductivity of the ALD films as a function of nitrogen content and demonstrate their functionality on a model battery electrodea Si anode on a Cu current collector. W hile planar thin film solid-state microbatteries are in commercial production, the push for higher energy and power density necessitates development of 3D device geometries, realized by improvements in device fabrication processes. 1,2 Moving from planar layer structures to high aspect ratio 3D electrode structures holds promise for significant power enhancement without much loss of energy density, or alternatively a tunable optimization and trade-off between power and energy to fit the application.Since its discovery in the early 1990s, 3 LiPON (lithium phosphorus oxynitride) has been one of the most popular solid state electrolytes used for planar lithium ion microbatteries. LiPON thin films are commonly deposited using reactive sputtering of a Li 3 PO 4 target in an N 2 atmosphere. 4−8 Generally, sputtered LiPON films are ∼1 μm thick, but sputtering of much thinner LiPON films (12 nm) has recently been demonstrated. 9 As a physical deposition technique, sputtering is generally unable to deposit high quality films on 3D geometries. 10 Also, the low reactivity of the N 2 gas during the sputtering process makes it difficult to dope these films with >2% N.Highly tunable N doping of LiPON is possible through ebeam evaporation of Li 3 PO 4 coupled with a N 2 plasma discharge above the substrate; 11 however, this technique is also limited to planar substrates.More recently, Kim et al. developed a MOCVD process for LiPON, 12 but the high deposition temperatures reported (500°C ) are undesirable for coprocessing with many battery materials and packaging components, precluding deposition on materials such as (i) Li 2 CoO 3 cathodes without degradation during the deposition process or (ii) metallic Li metal anodes without melting them.ALD has emerged as the premier deposition process for fabrication of uniform, thin, conformal films on high aspect ratio scaffolds, 13−16 and ALD has previously been used to fabricate the solid electrolytes (Utilizing a unique integrated high-vacuum deposition, surface characterization, and battery assembly system, 22 we have developed a quaternary ALD process for the solid electrolyte LiPON. We ...

ABSTRACT:Several active areas of research in novel energy storage technologies, including threedimensional solid state batteries and passivation coatings for reactive battery electrode components, require conformal solid state electrolytes. We describe an atomic layer deposition (ALD) process for a member of the lithium phosphorus oxynitride (LiPON) family, which is employed as a thin film lithium-conducting solid electrolyte. The reaction between lithium tertbutoxide (LiO t Bu) and diethyl phosphoramidate (DEPA) produces conformal, ionically conductive thin films with a stoichiometry close to Li 2 PO 2 N between 250 and 300C. The P/N ratio of the films is always 1, indicative of a particular polymorph of LiPON which closely resembles a polyphosphazene. Films grown at 300C have an ionic conductivity of 6.51 (±0.36) × 10 −7 S/cm at 35C, and are functionally electrochemically stable in the window from 0 to 5.3V vs. Li/Li+. We demonstrate the viability of the ALD-grown electrolyte by integrating it into full solid state batteries, including thin film devices using LiCoO 2 as the cathode and Si as the anode operating at up to 1 mA/cm 2 . The high quality of the ALD growth process allows pinhole-free deposition even on rough crystalline surfaces, and we demonstrate the fabrication and operation of thin film batteries with the thinnest (<100nm) solid state electrolytes yet reported. Finally, we show an additional application of the moderate-temperature ALD process by demonstrating a flexible solid state battery fabricated on a polymer substrate.3