Identification of phosphorus sites in amorphous LiPON thin film by observing internuclear proximities

Amorphous lithium phosphorus oxynitrides (LiPON), prepared by reactive magnetron sputtering, have become the electrolytes of choice for all-solid-state thin film microbatteries since its discovery in early 1990s. Nevertheless, there is still a lack of understanding of their atomic-level structure and its influence on ionic conductivity. Solid-state NMR spectroscopy represents a promising technique to determine the atomic-level structure of LiPON glasses but is challenging owing to its low sensitivity in the case of thin film materials. Recently, 31P solid-state NMR spectra of LiPON thin films were acquired under magic-angle spinning (MAS) conditions and assigned with the help of density functional theory (DFT) calculations of NMR parameters. However, the identification of the different P local environments in these materials is still a challenge owing to their amorphous structure and the lack of resolution of the 31P MAS NMR spectra. We show herein how the NMR observation of internuclear proximities helps to establish the nature of P sites in LiPON thin films. The 31P-14N proximities are probed by a transfer of population in double resonance (TRAPDOR) experiment, whereas 31P-31P proximities are observed using one-dimensional (1D) 31P double-quantum (DQ)-filtered and two-dimensional (2D) 31P homonuclear correlation spectra as well as dipolar dephasing experiments using DQ-DRENAR (DQ-based dipolar-recoupling effects nuclear alignment reduction) technique. The obtained NMR data further support the recently proposed assignment of 31P NMR signals of LiPON thin films. With the help of this assignment, the simulation of the quantitative 1D 31P NMR spectrum indicates that PO43- orthophosphate anions prevail in LiPON thin films and N atoms are mainly incorporated in [O3PNPO3]5- dimeric anions. PO3N4- isolated tetrahedra and [O3POPO3]4- anions are also present but in smaller amounts.

Dual Cation- and Anion-Based Redox Process in Lithium Titanium Oxysulfide Thin Film Cathodes for All-Solid-State Lithium-Ion Batteries

A dual redox process involving Ti³⁺/Ti⁴⁺ cation species and S^2-/(S₂)^2- anion species is highlighted in oxygenated lithium titanium sulfide thin film electrodes during lithium (de)insertion, leading to a high specific capacity. These cathodes for all-solid-state lithium-ion microbatteries are synthesized by sputtering of LiTiS₂ targets prepared by different means. The limited oxygenation of the films that is induced during the sputtering process favors the occurrence of the S^2-/(S₂)^2- redox process at the expense of the Ti³⁺/Ti⁴⁺ one during the battery operation, and influences its voltage profile. Finally, a perfect reversibility of both electrochemical processes is observed, whatever the initial film composition. All-solid-state lithium microbatteries using these amorphous lithiated titanium disulfide thin films and operated between 1.5 and 3.0 V/Li⁺/Li deliver a greater capacity (210-270 mAh g^-1) than LiCoO₂, with a perfect capacity retention (-0.0015% cycle^-1).

Thorough characterization of sputtered CuO thin films used as conversion material electrodes for lithium batteries

CuO thin films were prepared by radio frequency magnetron sputtering using a copper target in a (Ar + O2) reactive mixture. Different sputtering parameters were varied including oxygen flow rate, total pressure, target-substrate distance, substrate temperature and target orientation. As expected, the thin film chemical composition is strongly dependent on the oxygen flow rate. CuO thin films having a good electronic conductivity (9.3 × 10(-1) S·cm(-1)) were obtained with an oxygen concentration of 12%. The texture and the columnar growth are amplified when the target is tilted. Preliminary electrochemical results highlight that CuO thin film performances in lithium systems are tightly related to their morphology and structure.