Mechanical stiffness of oxide-type solid-electrolytes is a major drawback which has hindered their practical application in all-solid-state Li-ion batteries to date. Despite their enhanced structural and electrochemical stabilities, lack of deformability of fast-ion conducting oxides impedes the integration of these materials in bulk-type solid-state cells. Deformable solid-electrolytes such as sulfides, on the other hand, lack sufficient electrochemical stability in contact with conventional cathodes. This has recently triggered a search for new materials that combine high ion-conductivity, deformability and sufficient electrochemical stability. Here, we report the synthesis of a novel form of Li₄P₂O₇ that can be densified by cold-pressing and possesses an ion conductivity that is two orders of magnitude higher than conventional Li₄P₂O₇ phases. The material is synthesized by a combination of microwave synthesis and chemical lithiation and adopts a nanostructured morphology with a small amorphous component. The material is electrochemically stable at voltages >5 V vs. Li⁺/Li, which suggests safe use with high-voltage cathodes. The newly-synthesized material is therefore a bulk, deformable analogue of LiPON, with comparable ion conductivity and phase stability. This research highlights the potential of using novel low-temperature synthetic routes to control the morphology and enhance the electrochemical performance of conventional functional materials.