The problem with solid-state lithium-ion batteries, at least to date, has been the poor conductance of the solid electrolyte. Most solids that conduct ions do so only sparingly, especially near room temperature, which is key for portable electronics. And an improvement in one property often comes at the expense of another. For example, modifying a solid to boost its ionic conductivity via chemical treatment or other means could make it more difficult to process, less stable electrochemically, or more expensive.