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

The appeal of halide-based solid electrolytes lies in their ability to combine properties that are rarely found together. Conventional oxide electrolytes are generally chemically robust, but they are often brittle and require high-temperature sintering to create dense, low-resistance interfaces. Sulfide electrolytes can offer excellent ionic conductivity and mechanical softness, yet they are sensitive to moisture and may release toxic hydrogen sulfide when exposed to air. Polymer electrolytes are easier to process, but their lithium-ion conductivity commonly falls at room temperature. Halide materials occupy an important middle ground, offering ionic conductivities ranging from approximately 10⁻⁴ to above 10⁻³ S cm⁻¹, broad electrochemical stability windows, and comparatively improved tolerance to air.

This combination is especially important for high-voltage cathodes. In a battery, the electrolyte must transport lithium ions while preventing electrons from passing through it. At the same time, it must remain stable against the chemical potential of both electrodes. Many solid electrolytes degrade when placed next to cathode materials charged to more than 4 volts, creating resistive interphases that slow ion transport and reduce battery life. Halide-based compositions, by contrast, can be engineered for improved oxidative stability, making them promising candidates for direct contact with high-voltage layered oxides such as nickel-rich NCM811 and lithium cobalt oxide.

The review organizes halide-based solid electrolytes into five broad families according to the chemical identity and oxidation state of their central metal: divalent, trivalent, tetravalent, pentavalent, and non-metal-centered frameworks. This classification is more than a cataloging exercise. The central metal influences the crystal structure, the distribution of lithium vacancies, the polarizability of the halide anions, and the energy barriers that lithium ions must overcome as they move through the solid. By adjusting these features, researchers can manipulate the balance between structural stability and rapid ion conduction.

Some of the strongest results have emerged from trivalent compounds, including Li₃InCl₆ and Li₃ScCl₆. These materials can reach ionic conductivities of roughly 1 to 3 mS cm⁻¹, a range that begins to approach the performance required for practical solid-state cells. Their behavior is linked to disordered lithium sublattices and carefully controlled vacancies. In a crystalline solid, lithium ions do not move through an empty space as they would in a liquid; instead, they hop between energetically favorable sites. Disorder and vacancies can create additional pathways, reducing the activation energy required for movement.

The researchers also highlight high-entropy halide electrolytes, which contain several different metal species distributed across similar crystallographic positions. One reported composition, Li₂.₂In₀.₂Sc₀.₂Zr₀.₂Hf₀.₂Ta₀.₂Cl₆, achieved an ionic conductivity of 4.69 mS cm⁻¹ and an oxidation stability limit approaching 5.5 volts. High-entropy design introduces chemical complexity that can disrupt unfavorable ordering and generate a broader network of lithium-ion pathways. The same complexity may also help stabilize the material against structural transformations during repeated charging and discharging.

Another striking direction involves oxyhalides, which incorporate oxygen into halide frameworks. The compound Li₃Ta₃O₄Cl₁₀ has been reported to deliver ionic conductivity as high as 9 mS cm⁻¹ at 30°C. Such performance is significant because conductivity at or near room temperature is crucial for electric vehicles and stationary storage systems. Higher conductivity allows a thinner electrolyte layer or lower internal resistance, both of which can improve power capability and reduce energy lost as heat during fast charging and discharging.

Performance depends not only on chemical composition but also on how the electrolyte is made. The review compares mechanochemical processing, co-melting, and wet-chemical synthesis, showing how each route affects particle size, crystallinity, defects, impurities, and contact with electrode materials. Mechanochemical milling can produce intimate mixtures and enable reactions at relatively low temperatures, while wet-chemical approaches may offer better control over composition and morphology. Co-melting can promote uniformity in some systems, although it may require careful control of volatility and thermal stability. These processing choices directly influence critical current density, area-specific resistance, and long-term cycling behavior.

Interface engineering is emerging as one of the most decisive tools in the field. Even a highly conductive electrolyte can perform poorly if it forms a chemically unstable or mechanically fragile boundary with an electrode. Bilayer and dual-electrolyte designs address this challenge by assigning different materials to different sides of the battery. A halide electrolyte can serve as a catholyte, where it faces the oxidizing environment of a high-voltage cathode, while a sulfide electrolyte provides a softer, more conductive interface near the anode. Fluoride-doped halide compositions have also shown promise in improving compatibility with lithium metal, with some configurations maintaining stable lithium stripping and plating for more than 1,000 hours.

According to the review, halide-based cells paired with high-voltage NCM811 and LiCoO₂ cathodes have demonstrated capacity retention of about 70% over 1,600 cycles at a 4C rate, operation at voltages up to 5.5 volts, and projected energy densities approaching 400–500 Wh kg⁻¹. The materials are also being explored beyond conventional lithium-ion chemistry. Halide electrolytes may help stabilize sulfur cathodes in lithium–sulfur batteries, modify reactive air electrodes in lithium–oxygen systems, and support high-voltage sodium-ion solid-state batteries, where reported cells have retained about 90% of their capacity over 300 cycles. The researchers argue that continued progress will depend on scalable synthesis, standardized testing, improved mechanical contact, and a deeper understanding of interfacial reactions. If those challenges can be resolved, halide electrolytes could become a key component of batteries that combine the safety of solid-state architecture with fast charging, high voltage, and substantially greater energy density.

Subject of Research: Halide-based solid electrolytes for advanced all-solid-state batteries

Article Title: Halide-Based Solid Electrolytes for Advanced All-Solid-State Batteries: Design, Interfaces, and Electrochemical Performance

News Publication Date: 22-Jul-2026

Web References: https://doi.org/10.1007/s40820-026-02251-3

References: Nano-Micro Letters, DOI: 10.1007/s40820-026-02251-3

Image Credits: Shivaraju Guddehalli Chandrappa, Gerardo Morell, and Ram S. Katiyar

Keywords

Halide solid electrolytes, all-solid-state batteries, lithium-ion batteries, high-voltage cathodes, lithium metal batteries, sodium-ion batteries, lithium–sulfur batteries, lithium–oxygen batteries, ionic conductivity, interface engineering, high-entropy materials, electrochemistry