In 2023, 13.7 million passenger electric vehicles (EVs) were sold worldwide. While sales are projected to reach 16.7 million in 2024, a slowdown in annual growth is on the horizon. Driving this trend are consumer concerns over the high cost, safety, and cold weather performance of lithium-ion (Li-ion) battery systems in today’s EVs.
Most research to improve Li-ion batteries has been centered on improving the performance of the positive and negative (anodes and cathode) electrode components. Tremendous progress has been made with silicon anodes and various cathode chemistries that offer lower cost and higher energy density. The electrolyte is quickly becoming the Achilles’ heel of Li-ions. These liquid electrolytes limit energy, safety, and low-temperature performance.
Although solid-state electrolytes are currently in development and have demonstrated improved energy and safety, they typically fall short of desired performance in cold weather and are unable to charge quickly.
One electrolyte innovation that improves the energy, cost, and performance of Li-ion batteries employs liquefied gas (LiGas) electrolytes. The LiGas electrolyte was first developed by a team of engineers in Professor Shirley Meng’s lab at the University of California San Diego (UCSD). The team’s study on liquefied gas electrolytes was first published in the journal, Science, in 2017.
Liquid versus liquefied gas
The LiGas electrolyte replaces the liquid electrolyte used in the traditional Li-ion batteries with a blend of non-toxic and non-corrosive gases that liquefy when pressurized, which has been demonstrated and commercialized in San Diego.
Figure 1. Conventional liquid, solid, and new liquefied gas electrolyte for Li-ion batteries.
LiGas electrolytes create a more stable class of advanced Li-ion batteries for EVs. They have found early applications in defense, energy storage, aerospace, electric power tools, and consumer devices. The platform nature of this technology enables such a variety of applications, demonstrated to work across varying anodes (graphite, silicon), cathodes (NMA, NCA, LFP, and LNMO), and cylindrical form-factors (18650, 2170, and 46xx).
The specific benefits provided by LiGas electrolytes include:
- Improved performance in extreme temperatures
- Higher energy density
- Reduction of $ / kWh cost
- Reduced risk of thermal propagation when damaged or punctured
- Efficient EV thermal management
Let’s break this down.
Temperature and range
Traditional liquid electrolytes perform best between 0° and 45° C. Data from Recurrent Research shows that, depending on the make and model of the vehicle, the range of EVs is reduced between 16 and 46% in below-freezing temperatures.
Figure 2. Freezing temperatures reduce the range of electric vehicles.
This range loss can equate to 125 to 200 miles and leave drivers stranded in cold weather. The data, verified from onboard devices and real-time usage, were analyzed from more than 3.5 million data points.
Researchers have shown that LiGas-based 18650 cells can consistently retain high energy capacity and, consequently, minimal range degradation in below-freezing and elevated temperature environments (-60° to +60° C). For example, at freezing, LiGas cells maintained nearly their full energy, and at arctic temperatures of -40° C (-40° F), they maintained 75% of their energy.
Figure 3. Conventional liquid electrolyte versus LiGas: At 0° C energy delivery is similar; at -40° C conventional electrolyte is frozen — LiGas delivers 75% energy.
Through research conducted in conjunction with the US Department of Energy’s Advanced Research Projects Agency-Energy’s (ARPA-E) (EVs4ALL) program, 18650 cells using the LiGas electrolyte also demonstrated full compatibility with the low-cost and high voltage 4.6-volt Lithium Nickel Manganese Oxide (LNMO) cathode.
In this advanced battery chemistry, LiGas-based cells retained 96% energy at -20° C (-4° F) vs <5% for standard liquid electrolytes at the same temperature.
Improved energy density
Improvements in Li-ion battery energy density are on the path to bringing down the cost of EVs. With batteries representing between 30% and 40% of an EV’s cost, there’s a compelling case for the adoption of LiGas electrolytes inside Li-ion batteries for next-gen EVs.
Due to their lower viscosity and pressure, LGEs can penetrate electrodes more effectively and efficiently than conventional liquid electrolytes, enabling thicker and denser electrodes and higher energy density.
Cost reduction
After assembly, every lithium-ion battery undergoes a formation process where the solid electrode Interphase (SEI) is established. A proper SEI is essential to Li-ion battery life and performance. Formation equipment and time inside a Li-ion battery factory are extensive and represent 40% of these production facilities’ capital and operating expenses, according to the Volta Foundation’s 2023 Battery Report.
The LiGas electrolyte has demonstrated shorter formation: hours, not days. This allows fewer formation systems and improved cycle time, resulting in significant CapEx and OpEx savings.
LiGas’ material compatibility across anodes and cathodes also allows for easy integration into today’s Li-ion Giga factories. From electrode manufacturing to cell assembly and formation, the end-to-end cost to manufacture of LiGas-based Li-ion battery cells can be lowered by 30%.
With a 30% reduction in $/kWh cost, the LiGas electrolyte can enable the next step in EV cost reduction towards parity with internal combustion engine (ICE) vehicles.
Reduced risk of thermal propagation
National Transportation Safety Board (NTSB) statistics show that EVs are far less likely to catch fire than gas or hybrids. However, Li-ion battery fires do burn longer and more intensely. The reason is thermal propagation: one cell in a multi-thousand-cell pack burns for five to ten minutes, which allows the fire to propagate to other cells in the pack.
LiGas electrolyte-based cells have shown promising results in response to physical or electrical abuse. To demonstrate safety under the most abusive battlefield conditions, ballistics testing was conducted on the LiGas cells in 2023. After being shot with high-caliber bullets, it was demonstrated that LiGas cells had no thermal propagation compared to the full thermal runway experienced by traditional liquid electrolyte cells.
The rapid release of the LiGas electrolyte from inside the cells reduced the burn time of the Li-ion fuel from six minutes to six seconds, which is insufficient time for thermal propagation.
Figure 4. Conventional liquid electrolyte burns for about six minutes. If punctured, the electrolyte within LiGAs cells evaporates immediately.
EVs are outfitted with a sophisticated network of sensors to monitor temperature, prevent long-term damage to battery systems, and maintain charging efficiency. These sensors feed a layer of complex thermal or heating management systems to maintain battery health. These thermal management components add extra costs, weight, and bulk. The added weight and energy used in preconditioning battery packs can also reduce the vehicle’s maximum range.
Taken together, adopting the LiGas-based battery backs could render heat management systems redundant — reducing the overall weight and price of an EV.
LiGas electrolyte for Li-ion batteries is currently being validated today for tomorrow’s EVs. This solution has the potential to expand consumer adoption in cold-weather geographies, increasing the market for EVs. LiGas also promises to address driver anxiety over range, performance, safety, and costs.
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