China’s Thermal Battery Breakthrough Solves the ‘Shuttle Effect’ Problem With Atomic-Scale Precision

A New Era for High-Temperature Energy Storage

Scientists in China have achieved a significant advance in thermal battery technology that could extend the operational life and efficiency of power systems designed for extreme environments. A research team from the Institute of Process Engineering at the Chinese Academy of Sciences has developed a novel cathode material that effectively suppresses the persistent “shuttle effect,” a chemical degradation process that has limited thermal battery performance for decades. The breakthrough, published in the journal Advanced Science on January 4, 2026, demonstrates record-breaking energy density metrics while solving one of the field’s most stubborn technical challenges.

The research, led by Professors Wang Song and Zhu Yongping, centers on transition metal fluoride cathodes, specifically cobalt difluoride (CoF2), encapsulated within a specialized carbon shell derived from covalent organic frameworks (COFs). This innovative “plum pudding@shell” architecture creates selective ion channels that permit necessary lithium ion transport while blocking the larger molecular complexes responsible for capacity fade. The resulting battery cathode achieved a discharge plateau voltage exceeding 2.5 volts at 500 degrees Celsius, with a specific energy of 882 watt-hours per kilogram. These figures represent the highest reported values among high-voltage thermal battery cathodes to date, potentially opening new applications for this specialized power technology beyond its traditional military and aerospace niches.

Understanding Thermal Batteries and Their Unique Challenges

Thermal batteries represent a distinct class of electrochemical cells engineered to function in conditions that would destroy conventional lithium-ion systems. Unlike standard batteries that operate at room temperature, thermal batteries utilize molten salt electrolytes that become ionically conductive only when heated to temperatures between 350 and 550 degrees Celsius. This requirement for extreme heat makes them unsuitable for consumer electronics or typical electric vehicles, but invaluable for applications where reliability under thermal stress is non-negotiable.

Current applications for thermal batteries include military hardware such as missiles and guided munitions, aerospace systems including spacecraft and aircraft emergency power units, deep-well drilling equipment, and certain industrial processes. These devices can sit inert for years without degradation, then activate instantly when heated to operating temperature, delivering bursts of high-power energy in environments ranging from the vacuum of space to the crushing depths of boreholes. The batteries effectively function as single-use power sources that prioritize absolute reliability over rechargeability, making them essential for mission-critical systems where failure is not an option.

However, the high-temperature molten salt environment creates unique chemical challenges. Traditional cathode materials in thermal batteries suffer from dissolution and migration within the electrolyte during operation. Active material particles essentially drift away from their intended locations, reducing usable capacity and creating unwanted side reactions that drain performance. This phenomenon, known as the shuttle effect, causes active material loss and long-term structural damage that has historically limited the energy density and operational lifespan of thermal cells. Until now, engineers have struggled to prevent this dissolution while maintaining the ionic conductivity necessary for battery function.

The Shuttle Effect: A Molecular Migration Problem

To appreciate the significance of the Chinese breakthrough, one must understand the specific chemistry causing the shuttle effect in transition metal fluoride cathodes. During battery operation, CoF2 undergoes anion exchange with lithium chloride (LiCl) in the electrolyte, forming cobalt tetrachloride complexes (CoCl4 2-). These complexes are primarily responsible for the active material migration that degrades battery performance. Like bricks floating away from a construction site, these dissolved complexes migrate through the electrolyte, leading to irreversible capacity loss and reduced charge efficiency over time.

Previous attempts to address this issue included adding different types of sulfur electrodes or creating various barriers within the battery structure. While some approaches showed partial success at suppressing the dissolution, none provided a comprehensive solution that maintained high performance while ensuring long-term stability. The challenge lies in creating a barrier that is selectively permeable: it must block the larger CoCl4 2- complexes while simultaneously allowing the smaller Li+ ions to move freely between electrodes. Traditional solid barriers either blocked everything, effectively stopping battery function, or were too porous to prevent the shuttle effect.

The research team recognized that solving this puzzle required precise control at the nanometer scale. The difference in size between the beneficial lithium ions and the harmful cobalt complexes provided a potential avenue for selective blocking, but manufacturing materials with sufficiently uniform pore sizes to exploit this size difference remained difficult. The solution came from an unexpected material class: covalent organic frameworks, crystalline porous materials with well-defined structures that can be engineered with sub-nanometer precision.

The COF Shell Solution: Precision Engineering at the Atomic Scale

The breakthrough centers on constructing a specialized shell around CoF2 particles using COF-derived carbon materials. Covalent organic frameworks are crystalline, porous substances featuring highly ordered structures with uniform pore sizes. By converting a COF precursor into a carbonaceous coating through controlled thermal processing, the researchers created a shell with uniform sub-nanometer channels measuring just 0.54 nanometers across. This dimension proved critical: small enough to block the larger CoCl4 2- complexes, yet large enough to permit rapid transport of Li+ ions.

The resulting structure resembles a plum pudding, with active CoF2 particles encapsulated within the porous carbon shell. This configuration creates what the researchers term a “size-sieving confinement mechanism.” Thermodynamic analysis and experimental validation confirmed that the tailored channels effectively block diffusion of the problematic cobalt complexes while allowing lithium ions to pass, thereby suppressing the shuttle effect without compromising ionic conductivity.

Our findings provide a mechanistical foundation for designing next-generation high-energy-density thermal batteries through precise interfacial engineering.

Professor Wang Song, corresponding author of the study, emphasized that this approach offers more than just incremental improvement. The CoF2@CSC700-24 cathode (where CSC denotes the COF-derived shell carbon processed at 700 degrees Celsius for 24 hours) achieved experimental results that set new benchmarks for the field. At 100 milliamps per square centimeter and 500 degrees Celsius, the cathode maintained a discharge plateau voltage above 2.5 volts, delivered a specific capacity of 365 milliampere-hours per gram, and achieved a specific energy density of 882 watt-hours per kilogram. These metrics represent a substantial leap forward compared to existing thermal battery technologies.

Implications for Aerospace, Defense, and Beyond

The performance improvements enabled by this cathode design could expand thermal battery applications beyond traditional single-use military and aerospace systems. Current thermal batteries are essentially disposable power sources activated once for specific missions. The suppression of the shuttle effect suggests potential for longer operational lifespans and improved reliability, possibly enabling reusable thermal battery systems or applications requiring sustained power delivery in extreme environments.

Military applications remain the primary near-term market, as thermal batteries already serve as the power source of choice for guided missiles, torpedoes, and emergency systems in combat aircraft. The improved energy density could extend mission durations or reduce battery weight for equivalent power output, critical factors in aerospace engineering where every gram affects range and maneuverability. Deep-well drilling operations, where equipment encounters both high temperatures and high pressures miles beneath the Earth’s surface, represent another immediate beneficiary of more robust thermal cells.

Looking further ahead, solving the shuttle effect could theoretically enable thermal batteries for grid-scale energy storage in extreme climates, emergency power systems for industrial facilities, or specialized electric vehicle applications in Arctic or desert environments where conventional lithium-ion batteries struggle. While thermal batteries will likely never power consumer smartphones due to their high operating temperatures, the technology could play a role in next-generation energy systems requiring instantaneous high-power delivery in harsh conditions.

China’s Comprehensive Battery Research Ecosystem

This thermal battery breakthrough emerges within a broader context of intensive battery research across Chinese institutions. Parallel efforts explore multiple pathways beyond traditional lithium-ion technology, suggesting a strategic approach to dominating next-generation energy storage markets through diversified innovation.

Recent months have seen announcements of significant progress in solid-state batteries, including a self-healing interface developed by researchers at the Chinese Academy of Sciences that eliminates the need for high external pressure to maintain contact between battery layers. This technology uses iodide ions that migrate to form adaptive interphases, potentially enabling solid-state batteries with energy densities exceeding 500 watt-hours per kilogram. Meanwhile, Tianjin University has developed lithium-metal batteries with energy densities double those of current Tesla packs, and Shanghai Jiao Tong University unveiled an anode-free sodium-sulfur battery achieving 1,198 watt-hours per kilogram at estimated costs of just $5.03 per kilowatt-hour.

Other research tracks include graphene-based batteries promising five-minute charging times and fourfold lifespan improvements over lithium-ion, and sodium-ion alternatives using hard carbon anodes that charge faster than conventional lithium systems. The Chinese government has supported this research through substantial funding initiatives, including a 6-billion-yuan special project for solid-state battery development launched in 2024 and mid-term reviews conducted by the Ministry of Industry and Information Technology.

This multi-pronged approach reflects recognition that no single battery chemistry will serve all applications. Thermal batteries fill a specific niche for extreme environments, solid-state systems promise safer electric vehicles, sodium-ion offers cost-effective grid storage, and lithium-metal pushes the boundaries of energy density. By advancing simultaneously across these fronts, Chinese research institutions position themselves to supply whatever battery technologies dominate the coming decades.

From Laboratory to Real-World Applications

Despite the promising results, several challenges remain before this thermal battery technology sees widespread deployment. The research demonstrates proof-of-concept at the laboratory scale, but scaling production of the COF-derived carbon shells while maintaining precise 0.54-nanometer channel uniformity presents manufacturing obstacles. Thermal batteries themselves require specialized handling due to their molten salt electrolytes and high operating temperatures, limiting them to applications where such complexity is justified by operational requirements.

Long-term cycling stability, while improved by the shuttle effect suppression, requires further validation. The current study demonstrates the mechanism’s effectiveness, but thermal batteries for aerospace and defense applications typically require demonstrated reliability over thousands of potential activation cycles and years of shelf storage. Additional testing must confirm that the COF shell maintains its structural integrity and selective permeability under repeated thermal cycling and extended high-temperature operation.

The corrosive nature of molten salt electrolytes also poses material compatibility challenges for battery housings and seals. While the cathode breakthrough addresses one major degradation pathway, complete battery systems must integrate this advancement with equally robust anode and electrolyte management technologies. Research teams will likely focus next on optimizing the full cell architecture around the new cathode design.

The Bottom Line

• Chinese researchers have solved the “shuttle effect” in thermal batteries by developing a covalent organic framework (COF)-derived carbon shell with sub-nanometer channels that block harmful cobalt complexes while allowing lithium ions to pass.
• The novel cathode achieved record performance metrics: 2.5V discharge voltage, 365 mAh/g capacity, and 882 Wh/kg energy density at 500 degrees Celsius, representing the highest values reported for high-voltage thermal battery cathodes.
• Thermal batteries operate at 350-550 degrees Celsius using molten salt electrolytes, making them essential for military, aerospace, and deep-drilling applications where conventional batteries fail.
• The breakthrough could extend thermal battery applications beyond single-use military hardware toward longer-lasting systems for extreme environment energy storage.
• This research forms part of China’s broader battery innovation strategy, which includes parallel advances in solid-state, lithium-metal, sodium-ion, and graphene battery technologies.