A Stanford-led research team invented a new coating—a multifunctional network material—to stabilize lithium-metal anodes and finally make lightweight lithium-metal batteries safe and long lasting, which could usher in the next-generation of electric vehicles.

By integrating dynamic flowability, fast single-ion conduction, and electrolyte-blocking property into a single matrix—the dynamic single-ion-conductive network (DSN)—the researchers achieved long cycle life for a lithium-metal full battery in a commercial carbonate electrolyte.

After 160 cycles, the lithium metal cells still delivered 85% of the power that they did in their first cycle. Regular lithium metal cells deliver about 30% after that many cycles, rendering them nearly useless even if they don’t explode. A paper on the work is published in the journal Joule.

The DSN incorporates the tetrahedral Al(OR)₄^- (R = soft fluorinated linker) centers as both dynamic source and counter anions, rendering it flowability and Li⁺ single-ion conductivity; meanwhile, the fluorinated linkers provide chain mobility and electrolyte-blocking capability. A solution-processed DSN coating was found to simultaneously hinder electrolyte penetration, mitigate Li/electrolyte side reactions, maintain low interfacial impedance, and allow homogenous Li deposition. With this coating, long cycle life and high Coulombic efficiency are achieved for Li-metal battery in a commercial carbonate electrolyte.

—Yu et al.

The coating also greatly limited the formation of dendrites that pierce the separator between the anode and cathode. In addition to ruining the battery, dendrites can create a short circuit within the battery’s flammable liquid. Lithium-ion batteries occasionally have the same problem, but dendrites have been a non-starter for lithium metal rechargeable batteries to date.

Zhenan Bao, a professor of chemical engineering at Stanford, is senior author of the paper along with Yi Cui, professor of materials science and engineering and of photon science at SLAC. Bao said that dendrification has prevented lithium metal batteries from being used in what may be the next generation of electric vehicles.

The new coating prevents dendrites from forming by creating a network of molecules that deliver charged lithium ions to the electrode uniformly. It prevents unwanted chemical reactions typical for these batteries and also reduces a chemical buildup on the anode, which quickly devastates the battery’s ability to deliver power.

Our new coating design makes lithium metal batteries stable and promising for further development.

—co-lead author, Stanford PhD student Zhiao Yu

The group is now refining the coating design to increase capacity retention and testing cells over more cycles.

While use in electric vehicles may be the ultimate goal, commercialization would likely start with consumer electronics to demonstrate the battery’s safety first.

—Yi Cui

Zhenan Bao and Yi Cui are also senior fellows at Stanford’s Precourt Institute for Energy. Other Stanford researchers include Jian Qin, assistant professor of chemical engineering; postdoctoral scholars Dawei Feng, Jiheong James Kang, Minah Lee, Chibueze Amanchukwu, Xuzhou Yan, Hansen Wang and Kai Liu; students Wesley Michaels, Allen Pei, Shucheng Chen and Yuchi Tsao; and visiting scholar Qiuhong Zhang from Nanjing University.

This work was supported by the US Department of Energy Office of Energy Efficiency & Renewable Energy. The facility used at Stanford is supported by the National Science Foundation.

Resources

• Zhiao Yu, David G. Mackanic, Wesley Michaels … Jian Qin, Yi Cui, Zhenan Bao (2019) “A Dynamic, Electrolyte-Blocking, and Single-Ion-Conductive Network for Stable Lithium-Metal Anodes” Joule doi: 10.1016/j.joule.2019.07.025