High-rate magnesium rechargeable batteries move one step closer to
realization

Date:
August 23, 2021
Source:
Tohoku University
Summary:
Magnesium rechargeable batteries show immense promise for a
greener future because of their energy density, safety, and
cost. But the lack of high-performance cathode materials has
impeded their development. Now, a research team has developed
liquid-sulfur/sulfide composite cathodes that enable high-rate
magnesium batteries.



FULL STORY ========================================================================== Magnesium rechargeable batteries (MRBs), where high-capacity Mg metal is
used as the anode material, are promising candidates for next-generation batteries due to their energy density, safety, and cost. However, the
lack of high- performance cathode materials impedes their development.


==========================================================================
Like their lithium-ion counterparts, transition metal oxides are the
staple cathode materials in MRBs. Yet the slow diffusion of Mg ions inside
the oxides poses a serious problem. To overcome this, some researchers
have explored sulfur-based materials. But sulfur-based cathodes for
MRBs have severe limitations: low electronic conductivity, sluggish Mg diffusion in solid Mg- S compounds, and dissolubility of polysulfides into electrolytes, which results in low-rate capability and poor cyclability.

Now, a research team that included Tohoku University's Dr. Shimokawa
and Professor Ichitsubo has developed liquid-sulfur/sulfide composite
cathodes enabling high-rate magnesium batteries. Their paper has been
published in the Journal of Materials Chemistry A.

The liquid-sulfur/sulfide composite materials can be spontaneously
fabricated by electrochemically oxidizing metal sulfides, such as iron
sulfide, in an ionic liquid electrolyte at 150. The composite material
showed high performance in capacity, potential, cyclability, and rate capability.

The researchers achieved the discharge capacity of ~900 mAh/g at a high
current density of 1246 mA/g based on the mass of active sulfur. In
addition, they revealed that the discharge potential was enhanced by
utilizing non-equilibrium sulfur formed by fast charging processes.

This material allowed for a stable cathode performance at 150 for more
than 50 cycles. Such a high cyclability could be attributed to the
following points: high structural reversibility of the liquid state
active material, low solubility of polysulfides into the ionic liquid electrolyte, and high utilization ratio of sulfur due to its adhesion
to conductive sulfide particles that form a porous morphology during
the synthesis of the composite materials.

Despite the researchers' progress, several problems remain. "We need electrolytes that are compatible with both the cathode and anode materials because the ionic liquid used in this work passivates the Mg-metal
anode," said Shimokawa. "In the future, it is important to develop new electrochemically stable electrolytes to make MRBs more practical for widespread use." Although MRBs are still in the development stage,
the research team is hopeful their work provides a new way to utilize
liquid sulfur as high-rate cathode materials for MRBs. "This would boost
the improvement of sulfur-based materials for achieving high-performance next-generation batteries," added Shimokawa.

========================================================================== Story Source: Materials provided by Tohoku_University. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Kohei Shimokawa, Takuya Furuhashi, Tomoya Kawaguchi, Won-Young Park,
Takeshi Wada, Hajime Matsumoto, Hidemi Kato, Tetsu Ichitsubo.

Electrochemically synthesized liquid-sulfur/sulfide composite
materials for high-rate magnesium battery cathodes. Journal of
Materials Chemistry A, 2021; 9 (30): 16585 DOI: 10.1039/d1ta03464b ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210823125733.htm

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