A new high-concentration solid polymer electrolyte for high-voltage lithium-metal batteries

Lithium-metal batteries, which contain anodes based on metallic lithium, are promising rechargeable batteries that could help to meet the growing demands of the electronics industry. These batteries have various advantages, including high energy density and fast charging times.

Researchers have recently been trying to design new electrolytes that could further advance the performance of lithium-metal batteries. These are often either organic liquid electrolytes or inorganic solid electrolytes.

While some of these electrolytes have performed better than others, both liquid and solid alternatives have significant limitations. Organic liquid electrolytes can compromise a battery’s safety, while inorganic solid electrolytes typically exhibit a high interface resistance, resulting from poor contact between the solid electrolytes and solid electrodes.

A potential alternative to these existing liquid and solid electrolytes is the use of polymer-based electrolytes. By leveraging the advantageous properties of polymers, these electrolytes could overcome the limitations of previously introduced electrolytes.

Researchers at the University of Maryland, University of Illinois, and other institutes recently introduced a new high-concentration, solid polymer electrolyte for lithium-metal batteries. Their proposed electrolyte, outlined in a paper published in Nature Energy, could enhance the safety, stability, and energy density of lithium-metal batteries, by maintaining good mechanical strength, eliminating the interface in the polymer, and suppressing Li dendrite growth.

“Polymer electrolytes can take advantage of the low-contact resistance of liquid electrolytes and the high safety of solid electrolytes but still suffer from two issues: low ionic conductivity and Li dendrite growth at the anode and along the interface,” Weiran Zhang, a Ph.D. student in Chunsheng Wang’group at UMD and first author of the paper, told Tech Xplore.

“To overcome these challenges, we drew inspiration from the state-of-the-art high-concentration liquid electrolytes, where an elevated concentration of Li-salt promotes the Li⁺ conduction and forms a protective solid electrolyte interphase (SEI) to suppress the Li dendrite growth at the anode.”

While a high Li-salt concentration can facilitate the formation of the inorganic-rich SEI and thus suppress the growth of Li dendrites, it can also compromise the mechanical strength of polymers. Zhang and his colleagues set out to devise an approach to design high-concentration polymer blends that retain good mechanical strength.

Their approach builds on insights gathered in previous studies to add another composition to reinforce the mechanical strength. However, previous studies also found that the interface within solid electrolytes can facilitate Li dendrite growth. The researchers therefore hypothesized that polymers should be miscible with one another, which would eliminate this interface.

Based on this assumption, they then screened the composition of various polymers and ultimately designed a new promising polymer electrolyte. This electrolyte is based on blends of two miscible polymers.

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