Rechargeable batteries: Search on for safer, faster, high energy storage devices

Teams from US, Japan, China, Canada find solutions to decades-old challenges

Scientists world over have been striving to develop safer, higher-capacity, and faster charging rechargeable batteries which can keep the volatile metallic structure in them intact. There are several challenges before these batteries can be widely used in practical applications.

The Japanese team from Tohoku University has come up with a solution by adding multivalent cations, such as calcium ions, that could fix the age-old issue of energy degradation. They were able to stabilize lithium or sodium depositions effectively by this process.

Close on the heels of this, a team of researchers led by chemists at the US Department of Energy’s (DOE) Brookhaven National Lab has learned that an electrolyte additive allows stable high-voltage cycling of nickel-rich layered cathodes, which may change the limits of energy density of lithium batteries widely used in electric vehicles.

Another team from China and Canada found a solution in lithium-sulfur (Li-S) batteries, to provide a high energy density, while being low cost and environmentally friendly.

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The team has proposed an atomic terminated concept to design the facet via single-crystal architecture for Li-S batteries where the chemical reaction significantly boosts the electrocatalyst performance.

Japanese team’s findings
Usually, in a rechargeable battery, ions pass from the cathode to the anode when charging, and in the opposite direction when generating power.

Repeated cycle in metal deforms the structures of lithium and sodium and the repeated process results in the formation of needle-like microstructures called dendrites, which are weakly bonded and peel away from the electrodes, resulting in short circuiting.

The research team led by Hongyi Li and Tetsu Ichitsubo from Tohoku University’s Institute for Materials Research added calcium ions to alter and strengthen the solvation structure of lithium or sodium ions in the electrolyte.

“Our modified structure moderates the reduction of lithium or sodium ions on the electrode surface and enables a stable diffusion and electric field,” said Dr Li.

The stabilized ions, in turn, preserve the structure of the electrodeposited metals. The team hopes to improve the metal anodes’ interfacial design further to enhance the cycle life of the batteries.

US team’s findings
The team from Brookhaven National Laboratory has learned that an electrolyte additive allows stable high-voltage cycling of nickel-rich layered cathodes in lithium batteries widely used in electric vehicles.

The findings, published on May 9 in Nature Energy, offer a remedy to notorious degradation problems in these materials, especially at high voltages.

This research was conducted as part of the DOE-sponsored Battery500 Consortium, which is led by DOE’s Pacific Northwest National Laboratory (PNNL) to significantly increase the energy density of lithium batteries for electric vehicles.

Sha Tan, a PhD candidate at Stony Brook University conducting research with the Electrochemical Energy Storage group at Brookhaven Lab, tried using the additive for high voltage cycling at room temperature and was able to push the voltage up to 4.8 volts.

“This additive really gives great protection over the cathode and the battery achieved excellent cycling performance,” Tan said.

Researchers found that introducing a small amount of additive to the electrolyte stifles energy loss and also enables a nickel-rich layered cathode to be cycled at high voltages to increase the energy density and still retain 97 percent of its initial capacity after 200 cycles.

“Practically speaking, this could be a low-cost and easy-to-adopt solution,” says Tan.

Looking ahead, the researchers want to test the additive under more challenging conditions to explore whether the cathode materials can withstand even more cycles for practical battery use.

Canadian, Chinese teams’ solution
The team of researchers in China and Canada, in their atomic terminated concept to design the facet via single-crystal architecture for Li-S batteries, altering surface matrix of one or two layered atoms.

Using the atomic high-rich Co3+-Se terminated (ACT) concept they created a high-performance matrix. They wrapped a single-crystal CoSe2 (scCS) with reduced graphene oxide using a simple hydrothermal process.

This single-crystal architecture in scCS suppressed the shuttle effect and also reduced polarization. This has effectively boosted the lithium-ion migration and lowered the barrier of polysulfides.

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Using this method, they achieved a high efficient surface-active sites concentration of more than 69 percent. They believe the new method might prove useful in areas beyond the Li-S batteries.

“This surface lattice strategy with element terminated mode is a promising approach for designing electrocatalyst effect-based energy systems, not merely for Li-S batteries,” said Xing Ou, School of Metallurgy and Environment, Central South University in China.

As today’s and tomorrow’s technologies call for effective high energy storage devices, the need for an effective solution, however, remains green as ever.

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