Lithium-ion batteries are highly efficient, dissipating less than 10% of their energy as heat during operation. However, they require thermal management systems to regulate this heat, as it can negatively impact their performance and lifespan. On the other hand, their far more inefficient electrochemical distant cousin, the human body, generates enough heat to boil over 100 cups of tea daily and is literally just chillin’.
The secret? Our skin and its ability to sweat. A team of researchers from the City University of Hong Kong may have found a way to give batteries this ability, using a Skin-Inspired Adaptive Nanocomposites Cooling Membrane.
Thermal management for lithium-ion batteries has been in place as long as the batteries themselves. While highly efficient, these batteries still lose a portion of their energy as heat during the conversion between electrical and chemical energy as they charge and discharge. Without proper management, the dissipated heat can degrade the battery, impacting its lifespan over time. In severe cases, it can trigger thermal runaway, a dangerous chain reaction that may result in fire or explosion.
It is no surprise, therefore, that virtually every lithium-ion-powered system, from the device you are currently holding to electric vehicles, incorporates some form of thermal management. Over the years, engineers have developed fans, heat sinks, liquid cooling loops, phase-change materials, and other technologies to keep cell temperatures within safe operating bounds. These methods have proven effective. However, they are often complex and almost always require additional space and energy.
Taking inspiration from nature’s overlooked but highly effective cooling system, mammals’ skin, the team of researchers developed a cooling membrane that “sweats” as an alternative to conventional thermal management systems.
Dr. Sui Zengguang, City University of Hong Kong
“We noticed how sweating helps keep body temperature relatively stable even under intense exertion. It’s a simple phenomenon, but it reflects an extremely efficient thermoregulation capability shaped by evolution. We asked ourselves: can we translate this ‘sweating + evaporation’ principle into high-power device/battery thermal management in a controlled, engineering-friendly way?” says Dr. Zengguang Sui of the research team.
The membrane, which wraps around the battery like a skin, is a composite material comprising lithium chloride (LiCl), graphene oxide (GO), and active carbon fiber (ACF), all encased in a porous PTFE membrane and supported by a copper frame.
Dr. Sui Zengguang, City University of Hong Kong
Quite a mouthful, but every component plays a crucial role. Let’s unpack them one by one.
LiCl is a highly hygroscopic salt that efficiently absorbs and releases water. When the battery is cool, the salt pulls in and retains water from the atmosphere. The graphene oxide forms an efficient heat-transfer network, spreading thermal energy across the membrane as the battery heats up, while the active carbon fiber’s porous structure maximizes surface area for water evaporation. The copper frame ensures even heat distribution and prevents localized saturation. Lastly, the PTFE membrane prevents solution leakage while allowing water vapor to escape freely.
When the battery heats up, the water absorbs the heat and evaporates, transferring it away from the battery. This mechanism is known as desorption cooling. When the battery cools, the membrane spontaneously absorbs moisture from the surrounding air, restoring its water content.
So … what makes the membrane special as a thermal management system? For starters, it is highly effective. Proof-of-concept tests show that the self-adaptive cooling membrane delivers an average cooling power of 802.5 W·m⁻² and reduces temperature by a total of 34.3 °C (61.7 °F) under a 2.7 kW·m⁻² heat flux. When applied to a commercial 3.7 V/12 Ah lithium-ion battery under high-rate discharging and charging, the membrane extended battery lifetime from 118 to 233 cycles.
In English, under very high heat, similar to what high-performance batteries produce, the material managed to remove a lot of heat per unit area, achieving a temperature drop of over 30 °C (54 °F). Beyond cooling, the membrane offers excellent flame retardancy, preventing thermal runaway under conditions that would normally cause combustion. The system is also highly repeatable and long-lasting. During testing, the membrane held up its thermal management properties after 1,000 hours of rigorous use.
In addition to these factors, the system implements passive cooling. Unlike fans and liquid cooling systems, the adaptive nanocomposite cooling membrane does not require energy to function. The hygroscopic LiCl in the membrane automatically draws water from the surrounding air whenever the battery cools.
“Our goal was to develop a passive, compact, low-cost, and practical thermal management approach that can deliver high cooling capability without external power, while also addressing reliability and safety for real battery operation,” says Dr. Sui.
Lastly, the cooling membrane is a compact, non-complex system that is highly scalable. The membrane can be sized for both portable devices and large li-ion systems, such as EVs.
Now, with all its beneficial characteristics, the technology is truly a potential game-changer for lithium-ion battery thermal management. However, it is important to note that the system performs best in applications with intermittent or cyclic heat loads. Cooling in continuous-heat scenarios is limited, as the system requires time to cool down and reabsorb moisture.
Dr. Sui Zengguang, City University of Hong Kong
While it is still a relatively new technology and would require further research and development to achieve full viability, the prospects are exciting.
“We see strong potential anywhere that needs lightweight, compact, power-free thermal control with meaningful cooling performance. In particular, we believe the most compelling and near-term opportunities are Humanoid robots and Unmanned aerial vehicles (UAVs)/drones, where weight and packaging are critical,” Dr. Sui explains.
A paper detailing the research was published in the journal ACS Nano.
Source: ACS Axial