Separator key when it comes to 'stable' vs. 'safe' battery
Pore size of a battery separator makes all the difference

Date:
February 28, 2022
Source:
Washington University in St. Louis
Summary:
Researchers have discovered the key to making a stable, safe
battery.



FULL STORY ========================================================================== Research from the lab of Peng Bai, assistant professor of energy,
environmental and chemical engineering at the McKelvey School of
Engineering at Washington University in St. Louis, recently revealed
the formula for building a perfectly stable sodium electrode. The team
has now discovered the formula for a perfectly stable and safe electrode.


==========================================================================
The research was published last month in the journal Advanced Energy
Materials.

Stability in an electrode is key to a well-performing battery. Instability
is caused by irregular distribution of metal ions as they move from the
cathode to the anode. The more uniformly the ions move, the smoother the outgrowth of metal deposits. This results in a longer-lasting battery
and, importantly, a battery that is less likely to short and create a
hazardous situation.

"Does absolute stability guarantee absolute safety?" Bai asked. It
does not, especially during the fast charging. Bai and Bingyuan Ma,
a postgraduate research associate, determined why.

The short answer: A critical component that has been left out in
laboratory experiments is more important than previously thought. A
perfectly safe battery that can undergo fast recharging requires
cooperation from the separator.

When researchers observe the changes of metal anodes in real-time during battery fast charging, they do it in a lab setup that leaves out the
separator, which is a crucial part of the battery. This porous divider separates the anode side from the cathode side of a battery. It turns
out that the separator plays an outsized role in how safe a battery is,
no matter the stability of its electrode.

"We found that safety depends on the pore size of the separator,"
Bai said.

Battery separators are porous in order to hold liquid electrolytes for
metal ions to move, but some have bigger pores than others. "The lower
the pore size, the lower the chance of localized pore selection by the
growing metal deposits." That means that as the electrode moves toward
the separator, if the pore sizes are small, there are fewer places the
metal ions can penetrate. Instead of evenly spreading out, much of the
current ends up in some naturally selected spots, which can lead to a
battery short circuiting.

Bai and Ma have devised a mathematical model, called the Young-Laplace overpotential, that captures the dynamics of the physics inside an actual battery, which is now guiding Bai's lab to develop more stable and safer
anode- free metal batteries.

"We had already found a physical threshold for the ideal
cases," Bai said. "But the practical threshold is much
lower. And it depends on the microstructure of the separator
precisely following the mathematical model we developed." ========================================================================== Story Source: Materials provided by
Washington_University_in_St._Louis. Original written by Brandie
Jefferson. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Bingyuan Ma, Peng Bai. Fast Charging Limits of Ideally Stable Metal
Anodes in Liquid Electrolytes. Advanced Energy Materials, 2022;
2102967 DOI: 10.1002/aenm.202102967 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220228103827.htm

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