Caption: A breakthrough battery technology doubles typical energy densities and survives extreme heat and puncture, promising safer, longer-range electric vehicles (EVs). Credit: Tsinghua University
An ultra-energy-dense battery incorporates an innovative fluorine-rich polymer electrolyte to achieve safer and more efficient energy storage.
The range of electric vehicles (EVs) could potentially double if the latest advance in high-performance batteries detailed by Tsinghua researchers reaches the market1.
They reported in Nature that a quasi-solid-state lithium battery developed at Tsinghua University in 2025 has achieved more than twice the energy storage capacity of a conventional lithium-ion cell, weight for weight. This means that one of these new EV batteries that weighed the same as a conventional battery, could allow cars to travel twice as far.
The new battery safely withstood extreme stress testing while fully charged, outperforming conventional batteries, adds research leader, Qiang Zhang. He says that EVs, e-bikes, electric airplanes and portable electronics could all benefit from the performance and safety gains that battery’s innovative polymer electrolyte has enabled.
Liquid luck
Electrolytes form the core of any battery, keeping the anode and cathode safely separated while balancing and facilitating rapid ion flow between them, which completes the circuit, allowing continuous electron flow and energy delivery.
Regular lithium-ion batteries typically use a liquid electrolyte, which have some drawbacks: they have a limited safe range of voltages within which a battery’s electrodes and electrolyte can function; can form unstable interfaces with the anode and cathode; and they are flammable — limiting safety, longevity and performance.
Designer polymer electrolytes could overcome many of these limitations, Zhang and his team have shown. They developed a tough, fluorine-rich polymer electrolyte, tailor-made for a high voltage experimental battery design that combines a lithium-rich manganese-based layered oxide (LRMO) cathode within an ‘anode-free’ battery design.
Caption: Fluorine-rich polymer electrolytes enable lighter, safer, high-voltage batteries, boosting energy density. Credit: Tsinghua University
An anode-free battery has no traditional anode, the conductive material that allows electrical current to leave a battery. Instead, it starts with a bare metal strip, and during charging, lithium from the cathode, where the electrical current enters, coats the metal strip to form an anode able to interact with ions safely in a lithium-ion battery. This makes the battery lighter and more energy-dense, but harder to manage.
Commercial polymer electrolytes such as polyethylene oxide (PEO) are incompatible with this promising battery technology, Zhang explains. “PEO and related electrolytes decompose at the high voltages these batteries reach,” he says.
PEO decomposition at the electrolyte-cathode interface can result in damaging, irreversible oxygen loss from the battery. “So, we tried replacing some of the polymer’s oxygen atoms with fluorine,” Zhang says.
The team designed their polymer electrolyte to balance stability with performance, explains team member. Chen-Zi Zhao. “The oxygen-based segments of the polymer that we retained facilitated rapid lithium-ion transport, while the fluoride segments that we added stabilized the high voltage interface between polymer and cathode,” she says.
Investigating the nature of this stabilizing effect, the team showed that a thin protective coating rich in lithium fluoride had formed over the LRMO cathode surface. Some fluorine also became directly incorporated into the cathode’s outer layers. “Together, these layers provided a very stable shell coating the cathode, and we observed no oxygen loss,” Zhang says.
Trial by fire
The battery’s energy density reached 604 watt hours per kilogram, more than double that of conventional lithium-ion batteries. Demonstrating its safety, the fully charged battery survived heat treatment at 120C for six hours, and having a nail driven through it, without catching fire.
The results are expected to generate broad interest, Zhao says. And energy densities of 800 watt hour per kilogram or higher could be reachable, she says, which would be ideal for demanding applications, such as electric airplanes.
Zhang’s next task is to further stabilize the electrolyte’s interface with the lithium anode, to maximize the battery’s long-term performance. “We hope to optimize our electrolyte design to get a stable interface at both the anode and cathode from a single polymer,” he says.
Caption: Professor Qiang Zhang and his team from the Department of Chemical Engineering at Tsinghua have pioneered a next-generation lithium battery using a fluorine-rich polymer electrolyte. Credit: Tsinghua University
Reference
1. Huang, X.-Y., et al. Nature 646, 343 (2025)
