In this work, a new bulk Li 3.6 PO 3.4 N 0.6 crystalline polymorph has been prepared from low-cost precursors, following a simple ball-milling procedure. The densified powder exhibits a conductivity of 5.0 × 10 −6 S cm −1 at 70 °C and an electrochemical stability allowing operation with high-voltage materials up to 5.0 V vs Li/Li + . Stripping and plating of lithium in a symmetric cell demonstrates the forthcoming bulk application of LiPON in electrochemical devices. Widening the use of lithium phosphorus oxynitride compositions to bulk solid-state batteries will have relevant implications because of its unique compatibility with both high-voltage electroactive materials and lithium metal and its low density.

Solid polymer electrolyte batteries with a Li-metal anode and high-voltage active materials hold promising prospects to increase the energy density and improve the safety of conventional Li-ion batteries. An adequate choice of the polymers used for the cathode (catholyte) and for the separator (electrolyte) to create a sufficient energy gap and improve the chemical compatibility at both the positive electrode and Li-metal anode is required. The present work highlights the advantages of the double-layer polymer electrolyte approach in cells with a LiNi x Mn y Co z O2 active material, a poly­(propylene carbonate) (PPC) catholyte, and a poly­(ethylene oxide) (PEO) electrolyte. Replacing PEO in the catholyte with PPC results in a remarkably improved cycling performance. In addition, the higher lithium transference number of electrolytes with single lithium ion conductors leads to a smooth cycling of solid-state batteries. Cells with 1 mAh cm–2 deliver 160 mAh g–1, with a capacity retention above 80% over 80 cycles and a Coulombic efficiency close to 100%.

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Aluminum oxide (Al2O3) is a well‐known electrolyte filler for stabilizing the Li‐metal (Li0) anode in all‐solid‐state Li0‐based batteries. However, its strong interactions with lithium polysulfides (PS) hinder the direct application of Al2O3‐added electrolytes in all‐solid‐state lithium‐sulfur batteries (ASSLSBs). Herein, the role of Al2O3 in ASSLSBs both as electrolyte filler and cathode additive is studied. The combination of Al2O3‐added electrolyte and Al2O3‐added S8 cathode with optimum cell configuration could deliver an unprecedented discharge capacity of 0.85 mAh cm−2 (C/10, 30 cycles) for polymer‐based ASSLSBs. These results suggest that the rational incorporation of Al2O3 can lead simultaneously to PS anchoring and Li0 anode stabilizing benefits from the ceramic filler, thus improving the electrochemical performance of ASSLSBs.