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Breakthrough stable long-life high-voltage solid-state conductor for sodium-ion batteries

Wed, 03/10/2021 - 13:05 -- Paul Crompton

A research team led by UC San Diego nanoengineering professor Shyue Ping Ong has designed and manufactured a new sodium-ion conductor for solid-state sodium-ion batteries that is stable when incorporated into higher-voltage oxide cathodes. 

A proof of concept battery, built with the new material, lasted more than 1,000 cycles while retaining 89.3% of its capacity. 

Researchers detailed their findings in the peer reviewed journal Nature Communications.

The work is a collaboration between researchers at UC San Diego and UC Santa Barbara, Stony Brook University, the TCG Center for Research and Education in Science and Technology in Kolkata, India, and Shell International Exploration.

Researchers ran a series of computational simulations powered by a machine learning model to screen which chemistry would have the right combination of properties for a solid state battery with an oxide cathode. 

Once a material was selected, Meng’s research group experimentally fabricated, tested, and characterised it to determine its electrochemical properties.

By rapidly iterating between computation and experiment, the UC San Diego team settled on a class of halide sodium conductors made up of sodium, yttrium, zirconium and chloride. 

The material, which they named NYZC, was both electrochemically stable and chemically compatible with the oxide cathodes used in higher voltage sodium-ion batteries. The team then worked with researchers at UC Santa Barbara to study and understand the structural properties and behaviour of this new material.

NYZC is based on Na3YCl6, a well-known material that is a very poor sodium conductor. Therefore, Ong suggested substituting zirconium for yttrium because it would create vacancies and increase the volume of the cell battery unit, two approaches that increase the conduction of sodium ions. 

Researchers also noted that, in conjunction with the increased volume, a combination of zirconium and chloride ions in this new material undergoes a rotating motion, resulting in more conduction pathways for the sodium ions.

In addition to the increase in conductivity, the halide material is much more stable than materials used in solid-state sodium batteries.

Ong said: “These findings highlight the immense potential of halide ion conductors for solid-state sodium-ion battery applications. It also highlights the transformative impact that large-scale materials data computations coupled with machine learning can have on the materials discovery process.”

Sodium-ion chemistries are of interest because sodium is low-cost and abundant. The goal is to build batteries that can be used in large-scale grid energy storage applications, especially to store power generated by renewable energy sources to mitigate peak demand.

Picture: If Zr-Cl rotation is artificially frozen, sodium diffusivity plummets to negligible results. Zr-Cl rotation thus aids sodium conductivity. Credit: University of California San Diego

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