Rapidly Grown IBAD LiPON Films with High Li-Ion Conductivity and Electrochemical Stability

Abstract

LiPON films have been produced by nitrogen ion beam assisted deposition ͑IBAD͒ of thermally evaporated Li 3 PO 4 . This process allowed us to rapidly deposit X-ray amorphous LiPON films with densities close to that of the handbook value for Li 3 PO 4 , high ionic conductivity (1.6 ϫ 10 Ϫ6 S/cm), electronic conductivity smaller than 8 ϫ 10 Ϫ13 S/cm, and an electrochemical stability window of over 6.0 V. These properties, combined with the high deposition rates that can be achieved with this process (Ͼ1.0 nm/s), make it an attractive candidate for industrial production of LiPON thin films for Li-ion batteries.Nitridation of phosphate glasses is known to increase their chemical stability. [1][2][3][4] reported on the production of lithium phosphorus oxynitride ͑LiPON͒ thin films deposited by reactive sputtering of Li 3 PO 4 in a nitrogen atmosphere. These films were both more electrochemically stable ͑5.5 V stability window vs. Li/Li ϩ ) than their non-nitrided counterparts and exhibited a 40 times higher room temperature Li-ion conductivity of 2 ϫ 10 Ϫ6 S/cm. 6 This has led to much interest in using LiPON as an electrolyte for solid-state lithium-ion thin film batteries. [7][8][9] Since the conventional means to deposit LiPON films, sputtering, is a relatively slow process, we decided to explore the use of nitrogen ion beam assisted deposition ͑IBAD͒ of thermally evaporated Li 3 PO 4 as a possible improved process. In this paper, we present a brief description of this process and a summary of our results for two representative films. We show that the process provides for significantly higher deposition rates and gives films with equivalent, if not improved, electrochemical properties. The process has the additional advantage that, at least in principle, it allows one to readily vary the amount of incorporated nitrogen by simply adjusting the ion beam gun current. The main drawback of the process to date is a residual, largely thermal ͑mostly determined by substrate temperature͒, tensile stress that the LiPON films exhibit after their depositions. Cracks arising from this stress have been identified as a major cause of electrical shorts that occasionally are found in asdeposited cells that use LiPON as their electrolyte. 10 ExperimentalThe base pressure of the vacuum chamber in which the films were deposited was 4 ϫ 10 Ϫ7 Torr. Pressed pellets of Li 3 PO 4 ͑Alfa͒ were placed in an electrically heated tungsten boat ͓purchased from Mathis, reference no. S36.010W͔ and were melted during the pump-down and chamber bakeout ͑for Ͼ48 h at approximately 150°C͒ prior to the deposition. The sample holders were part of a planetary system that allowed the substrates to revolve and rotate above the centrally located source to ensure a uniform thickness. The throw distance between the source and the samples was approximately 22 cm. During deposition the substrates were simultaneously bombarded with nitrogen ions provided by a Commonwealth Mark I ion gun, placed to one side of the chamber. The ion gun center was at the same height ...

All‐Solid‐State Lithium‐Ion Microbatteries: A Review of Various Three‐Dimensional Concepts

“…In (sputtered fi lms), [ 15 ] 1.6 ⋅ 10 − 6 S ⋅ cm − 1 (pulsed laser deposition) [ 120 ] or 1.3 ⋅ 10 − 6 S ⋅ cm − 1 (IBAD). [ 121 ] LIPON also has a low electronic conductivity of 8 ⋅ 10 − 13 S ⋅ cm − 1 (IBAD). [ 121 ] In addition, it is stable within a wide voltage range and can be used in combination with many different electrode materials, varying from pure lithium to LiCoPO 4 .…”

“…[ 121 ] LIPON also has a low electronic conductivity of 8 ⋅ 10 − 13 S ⋅ cm − 1 (IBAD). [ 121 ] In addition, it is stable within a wide voltage range and can be used in combination with many different electrode materials, varying from pure lithium to LiCoPO 4 . [ 71 ] …”

Ultra-thin LiPON films – Fundamental properties and application in solid state thin film model batteries

“…metal organic chemical vapor deposition (MOCVD) [15] or ion beam assisted sputter deposition [16]. However, specific conductivities of the resulting LiPON layers are quite similar to those deposited by magnetron sputter deposition, i.e.…”

Effects of sputtering pressure on the characteristics of lithium ion conductive lithium phosphorous oxynitride thin film

“…It is certain that a small substitution of nitrogen for oxygen in the amorphous Li 3 PO 4 material greatly enhances the Li mobility, due to either the formation of additional cross-linking between phosphate groups or a decrease of the electrostatic energy when P O is exchanged by P N bonds [6]. In spite of the advantages of Lipon as solid electrolyte for thin film batteries [7][8][9], the influence of deposition parameters on the characteristics of Lipon have not been thoroughly investigated. Therefore, there is variation in results from group to group, for this reaction is a non-equilibrium synthesis.…”