Tech Insights

Purdue Researchers Improve Electrolyte Stability in Lithium-metal Batteries

April 10, 2023 by Shannon Cuthrell

A team from Purdue University has published research showing how a low-concentration, ether-based electrolyte can enhance stability and extend high-voltage capabilities for lithium-metal batteries in electric vehicles and other applications. 

Researchers from Indiana-based Purdue University recently developed a low-concentration, ether-based electrolyte offering stronger oxidation stability and thermal safety advantages over conventional materials in lithium (Li)-metal batteries for energy storage, consumer electronics, and electric vehicle applications.

 

Ether-based electrolyte offers stronger oxidation stability and thermal safety advantages over conventional materials in lithium-metal batteries. Image used courtesy of Adobe Stock

 

The study, published in Nature Communications, explored strategies to improve the long-term cycling of Li-metal anode and high-voltage cathode materials using a dilute ether-based electrolyte. As ethers have poor oxidation stability, the researchers aimed to extend their high-voltage capabilities and performance on a positive electrode. 

Purdue’s announcement mentions that the Li-metal battery (LMB) developed in the study is expected to improve energy density by 40% compared to lithium-ion batteries, the current industry standard in most EVs on the market today. Vilas Pol, a chemical engineering professor who leads Purdue’s Vilas Pol Energy Research (ViPER) Group, told EE Power in an email that this finding is based on data obtained by replacing low-capacity graphite with lithium metal. 

Pol noted that more research is needed to evaluate the electrolyte’s application on EVs. “Though the lithium-metal batteries are highly promising with [this] innovative electrolyte, it would take additional research and development efforts and safety testing before it’s use in EVs,” Pol said. 

 

New Approach to Battery Chemistry 

Using Li-metal anodes with high-voltage lithium, nickel, cobalt, and manganese (NCM) cathodes increases energy density to meet the demands for better energy storage. 

However, its volume change and dendritic decomposition mean it has low cyclability. While ether solvents yield better Li-metal anode compatibility than conventional carbonates, their oxidation instability prevents high-voltage battery operation beyond 4.3 volts. 

The researchers developed dilute lithium bis(fluorosulfonyl) imide (LiFSI)-based, non-aqueous electrolytes in nonfluorinated ether solvents, finding that the low-concentration ether-based electrolyte successfully endured long-term high-voltage operation of LMBs when using the highly non-polar dipropyl ether (DPE)-based electrolyte as the solvent. 

When the DPE-based electrolyte was tested with a Li-metal negative electrode and a nickel-rich NCM-based positive electrode at 25 degrees Celsius (77 degrees Fahrenheit) in a pouch cell configuration, the researchers returned a capacity retention of about 74% after 150 charge/discharge cycles. 

 

As shown in this image published in Nature Communications, Purdue University’s researchers tested the electrochemical performance of ether-based electrolytes under practical conditions. Image used courtesy of Creative Commons Attribution 4.0 license

 

The research received funding from the Naval Enterprise Partnership Teaming with Universities for National Excellence (NEPTUNE) program, part of the U.S. Department of the Navy’s Office of Naval Research. 

 

Other Battery Research and Patents 

The researchers hail from Purdue’s ViPER Group, a unit of the Davidson School of Chemical Engineering focusing on Li-ion, Li-sulfur, and sodium-ion batteries. 

 

Video used courtesy of Purdue University’s Engineering Graduate Program

 

The ether-based electrolyte study is the latest in an extensive archive of more than 250 publications since ViPER’s founding in 2014. The group also landed a Guinness World Record title in December 2022 for the lowest temperature to charge a Li-ion battery, at -100 °C (or -148 °F). 

Purdue’s Research Foundation Office of Technology Commercialization recently submitted a patent application for ViPER’s composite solid electrolyte, which retains stability at about 330 °C (626 °F) and through cell damage. This increases safety and prevents thermal runaway compared to standard solid polymer or liquid electrolyte materials. EE Power recently covered this concept in detail in a separate article

 

Purdue researchers’ composite electrolyte demonstrates stability when bent, cut, and punched. Image used courtesy of Purdue University
 

Pol told EE Power that the ViPER team is working to secure intellectual property rights for its composite solid-state electrolyte materials and batteries. 

“So far, we have two patents filed on solid state and two to three on electrolytes, including LMB,” Pol said.