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Research Highlights

PNNL Research Featured in Special Issue Exploring Lithium Sulfur Battery Technology

Enables "apples to apples" comparisons of the various Li-S batteries for specific research and market applications

September 2015
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Batteries work by converting chemical energy to electricity through a reaction between positive (cathode) and negative (anode) electrodes. The Li-S battery contains a lithium metal anode and a mixed carbon/sulfur cathode. During discharge, lithium ions travel from the anode to the cathode, where they react with sulfur and generate byproducts which impede the overall process.
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Lithium sulfur (Li-S) batteries are considered one of the most promising technologies for meeting the high-energy demands of transportation and large-scale energy storage applications—electric vehicles, renewable energies, and the grid—in sustainable ways. But despite advantages of higher theoretical energy, reduced cost, and environmental friendliness, the Li-S battery has yet to realize its potential. Why?

An August 2015 special issue of the journal Advanced Energy Materials explores the different facets of Li-S battery technology and points out the main concerns and problems revealed by current Li-S battery research. The collection of papers covers the breadth of the latest research to enable "apples to apples" comparisons of the various Li-S batteries for specific research and market applications.

The special issue includes three invited papers by researchers in PNNL's Energy Processes and Materials division, including Jie Xiao, who is also the guest editor. As stated in Xiao's editorial remarks, the dissolution of long-chain polysulfide species gradually diffuse out of the cathode, contaminating almost the entire battery cell and causes a series of "key-chain side reactions" in the cell.

"The end result is the loss of active sulfur material, quick degradation of storage capacity, and poor Coloumbic efficiency," Xiao states in her remarks. Coloumbic efficiency refers to the efficiency with which the charged electrons lead to an electrochemical reaction.

Xiao's paper, "High Energy Li-Sulfur Batteries: Challenges of Thick Sulfur Cathode," was supported by DOE's Office of Energy Efficiency and Renewable Energy, Office of Vehicle Technologies under the Battery Materials Research (BMR) program.

The two other PNNL papers, supported by the Joint Center for Energy Storage Research, a Department of Energy Innovation Hub, are:

PNNL's Power Grid Integrator
Jie Xiao is guest editor for the August 2015 Advanced Energy Materials Special Issue: Understanding the Lithium-Sulfur Battery System at Relevant Scales
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  • "Anode for Li-S Batteries," by Jason Zhang
  • "Understanding and Controlling the Solution Chemistry of Lithium Polysulfide to Enable Development of a High Energy Li-S Redox Flow Battery," by Jun Liu.

A Missing Link?

Most published Li-S battery research is based on the use of a sulfur cathode with thin-film configurations—a convenient platform for understanding the material properties and their interactions with other species at the nanoscale. Many innovative approaches using this configuration have been demonstrated effectively in lab tests. The question remains, however, what may be missing to effectively transfer that fundamental research into real systems.

Xiao posits that future research in the Li-S battery system will likely investigate materials, chemistry, and electrochemistry at a scale that leads to more practical materials selection, electrode modification, and cell design, ultimately moving the technology forward for successful market applications.

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