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How Graphene Defects Affect Lithium Metal Battery Performance

Time : 2019.08.08

Lithium (Li) metal batteries (LMB) are a promising alternative to lithium-ion batteries (LIB) because the lithium metal anode-electrode "Grail" has a higher energy density. If LMB is to be commercialized on a large scale, then energy-intensive applications that require longer runtimes, such as electric vehicles and drones, will take off.
However, this commitment is influenced by the formation of a solid electrolyte mesophase (SEI) layer on the metal Li in a conventional carbonate electrolyte due to irreversible reduction and chemical decomposition of the electrolyte in contact with the anode.
 
The SEI layer is associated with the growth of Li dendrites, resulting in short cycle life and potential safety issues. To address this critical issue, several strategies have been employed, including the use of electrolyte additives and carbon-based supports (eg, graphene, graphene oxide, and nitrogen-doped graphene) to stabilize the Li metal anode.
 
It is still clear now how the structure and chemistry of carbon bodies affect lithium dendrite growth and cell performance. Recently, a group of researchers at Clarkson University (USA) and Sichuan University (China) made significant progress in battery research by explaining how graphene defects play an important role in dendritic formation.

A clear understanding of how the structure and chemistry of the carbon host affects Li dendrite growth and battery cell performance has been lacking until now. Recently, a team of researchers from Clarkson University (USA) and Sichuan University (China) has made a significant advancement in battery research by explaining how graphene defects play an important role in the formation of dendrites.
 

They compared intrinsic SEI formation on ultrapure, “defect-free” graphene (df-G), fabricated using a novel wet approach called “flow-aided sonication,” to a highly defective Hummers graphene (r-GO).

In the absence of electrolyte, the first cycle irreversible capacity loss of r-GO reached 1863 mA g−1compared to 148 mAh g−1 for df-G. When fluoroethylene carbonate (FEC) was added, df-G yields state-of-the-art electrochemical performance with a relatively smooth, dendrite-free surface morphology.

These observations uncover a critical new finding: SEI formation occurring before metal plating actually dictates dendrite formation. That is, the fate of the Li metal anode is effectively sealed once the carbon host forms an SEI at the initial charge.

In contrast, r-GO promotes rapid consumption of the FEC electrolyte, leading to extensive dendrite formation.

 

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