All-solid-state batteries have long been promoted as one of the most promising routes toward safer, higher-energy electric vehicles. By replacing the flammable liquid electrolyte used in conventional lithium-ion cells with an inorganic solid-state electrolyte, researchers hope to create batteries that can store more energy, tolerate demanding operating conditions and reduce the risk of fire. Yet a new study suggests that even batteries built from nonflammable solid materials may quietly lose their charge while sitting unused. The cause is not necessarily a defect in the electrodes or an unwanted chemical reaction. Instead, the solid electrolyte itself may allow a small but persistent flow of electrons, creating a hidden pathway for physical self-discharge.
The finding, reported by Chang Wang, Rui Xu, Yifan Zhong and colleagues in Nature Energy, identifies electronic conductivity in solid-state electrolytes as a potentially major limitation for all-solid-state batteries, or ASSBs. In an ideal battery electrolyte, lithium ions should be able to move between the positive and negative electrodes while electrons remain confined to the external circuit. That separation is what forces electrons to travel through a motor, charger or other electrical load, allowing the battery to deliver useful energy. If the electrolyte also conducts electrons, however weakly, some of the battery’s stored electrochemical energy can bypass the external circuit and dissipate internally.
This process is distinct from the more familiar forms of self-discharge associated with parasitic chemical reactions. In a conventional battery, self-discharge can result from reactions involving electrode materials, impurities, electrolyte decomposition or internal redox processes. The mechanism highlighted in the new work is more physical: an electric field across the solid electrolyte drives a small electronic current directly through the separator between the electrodes. Over time, that current reduces the voltage difference and state of charge, even when the battery is disconnected from every external device. The battery is effectively leaking energy through the material that is supposed to keep its two sides electrically isolated.
The issue becomes especially important because solid-state electrolytes are extremely thin in practical cell designs. Many prototype and next-generation ASSBs use electrolyte layers only tens of micrometres thick, a scale comparable to or smaller than the width of a human hair. A thin electrolyte reduces the distance lithium ions must travel, lowering ionic resistance and helping the cell deliver power. It also enables a larger quantity of active electrode material to fit into a given battery volume, an essential requirement for achieving the high energy density demanded by electric vehicles. But the same reduction in thickness increases the electric field for a given voltage and shortens the path through which unwanted electronic leakage can occur.
The researchers point to a critical mismatch between the electronic properties of currently used solid electrolytes and the requirements of thin, high-energy cells. Many inorganic solid-state electrolytes exhibit electronic conductivities in the range of approximately 10⁻⁸ to 10⁻⁹ siemens per centimetre. Those values may appear extraordinarily small when compared with the conductivity of metals, which can be millions of times higher. Yet in a battery containing a large electrode area and an electrolyte layer only a few tens of micrometres thick, even such a minute conductivity can generate a meaningful leakage current over long periods. The battery may perform well during a charge-discharge test while still losing a substantial fraction of its stored energy during storage.
The distinction between ionic and electronic conductivity is central to understanding the challenge. Ionic conductivity describes how readily lithium ions migrate through the solid electrolyte, a property researchers have spent decades improving. High ionic conductivity allows rapid charging and discharging and reduces internal resistance. Electronic conductivity, by contrast, describes the movement of electrons through the same material. For an electrolyte, this value should be as close to zero as possible. In a real material, defects, impurities, crystal disorder, variable oxidation states and interfaces between different phases can create electronic pathways. These pathways may be too weak to affect short laboratory cycling tests but become significant when the battery remains charged for hours, days or weeks.
According to the study, reducing the physical self-discharge of thin ASSBs would require electronic conductivity near 10⁻¹² siemens per centimetre, far below the range commonly reported for prevalent inorganic solid electrolytes. The gap is not a minor optimization target. It represents a reduction of several orders of magnitude, highlighting how a property that has often received less attention than ionic conductivity could become a decisive factor in commercial battery design. A material can therefore be an excellent lithium-ion conductor and still be unsuitable for a practical all-solid-state cell if it permits too much electronic leakage.
The consequences could extend well beyond how long a parked electric vehicle retains its charge. Self-discharge affects the reliability of battery-powered transport, the amount of energy available after storage, the accuracy of state-of-charge estimates and the durability of cells subjected to repeated periods of inactivity. Fleet vehicles, emergency systems and cars kept at airports or in long-term parking may be particularly sensitive to the phenomenon. If a battery loses charge internally, drivers may need to recharge more frequently, while battery-management systems may struggle to distinguish physical leakage from other causes of capacity loss. In large battery packs, small leakage currents repeated across many cells could also complicate thermal, electrical and safety management.
The study does not suggest that all-solid-state batteries are doomed, but it does change the priorities for their development. Improving the bulk electrolyte will be important, yet the interfaces where the electrolyte meets the electrodes may be equally influential. Interfacial layers could be engineered to block electrons while preserving rapid lithium-ion transport. Cell architectures might also be designed to reduce leakage pathways, control electric-field concentrations and prevent electronically conductive secondary phases from connecting the two electrodes. Manufacturing quality will matter as well, because microscopic defects, contamination or local variations in composition could create disproportionately conductive regions in an otherwise insulating separator.
The results arrive as the battery industry continues to pursue solid-state technologies for electric vehicles, consumer electronics and grid storage. Companies and research groups have often focused on energy density, fast charging, mechanical stability and resistance to dendrite formation. The new findings add long-duration charge retention to that list and emphasize the importance of testing cells under realistic storage conditions. A battery that appears stable during rapid cycling may behave very differently when held at high voltage for an extended period. Future evaluations will need to measure not only capacity, power and safety, but also the electronic leakage of the electrolyte and the rate at which a complete cell loses charge while disconnected.
The central message is both simple and consequential: an electrolyte must conduct lithium ions without conducting electrons, and the required degree of electrical insulation becomes far more demanding as the material gets thinner. Existing solid electrolytes may still support impressive cell performance, but their electronic conductivity could impose a hidden ceiling on the practical benefits of all-solid-state batteries. Developing materials with electronic conductivity close to 10⁻¹² siemens per centimetre, combined with carefully engineered interfaces and full-cell structures, may be essential for turning the promise of safer, higher-energy batteries into dependable products. As the race toward next-generation electric vehicles accelerates, the smallest invisible current may prove to be one of the technology’s biggest obstacles.
Subject of Research: Electronic conductivity and physical self-discharge in all-solid-state batteries
Article Title: Electronic conductivity of solid electrolytes causes physical self-discharge in all-solid-state batteries
Article References: Wang, C., Xu, R., Zhong, Y. et al. Electronic conductivity of solid electrolytes causes physical self-discharge in all-solid-state batteries. Nature Energy (2026). https://doi.org/10.1038/s41560-026-02090-x
Image Credits: AI Generated
DOI: https://doi.org/10.1038/s41560-026-02090-x
Keywords: all-solid-state batteries, solid-state electrolytes, electronic conductivity, physical self-discharge, electric vehicles, battery energy density, lithium-ion transport, battery interfaces, energy storage, battery safety
