Tag: coating

New protective coating can improve battery performance

New protective coating can improve battery performance

A research team at the Paul Scherrer Institute PSI has developed a new sustainable process that can be used to improve the electrochemical performance of lithium-ion batteries. Initial tests of high-voltage batteries modified in this way have been successful. This method could be used to make lithium-ion batteries, for example those for electric vehicles, significantly more efficient.

Lithium-ion batteries are considered a key technology for decarbonisation. Therefore, researchers around the world are working to continuously improve their performance, for example by increasing their energy density. “One way to achieve this is to increase the operating voltage,” says Mario El Kazzi from the Center for Energy and Environmental Sciences at Paul Scherrer Institute PSI. “If the voltage increases, the energy density also increases.”

However, there is a problem: At operating voltages above 4.3 volts, strong chemical and electrochemical degradation processes take place at the transition between the cathode, the positive pole, and the electrolyte, the conductive medium. The surface of the cathode materials gets severely damaged by the release of oxygen, dissolution of transition metals, and structural reconstruction – which in turn results in a continuous increase in cell resistance and a decrease in capacity. This is why commercial battery cells, such as those used in electric cars, have so far only run at a maximum of 4.3 volts.

To solve this problem, El Kazzi and his team have developed a new method to stabilise the surface of the cathode by coating it with a thin, uniform protective layer. The researchers report on their discovery in a study published in the scientific journal ChemSusChem (Wiley).

Read more on PSI website

Image: Mario El Kazzi and his team have developed a cathode surface coating that enables operating voltages of up to 4.8 volts.

Credit: Paul Scherrer Institute PSI/Mahir Dzambegovic

Studying Interfacial Effects in Solid-Electrolyte Batteries

Studying Interfacial Effects in Solid-Electrolyte Batteries

At the Advanced Light Source (ALS), an ambient-pressure probe of a solid electrolyte revealed how surface electrochemical mechanisms lead to poor electrolyte performance and battery failure.

The results can help scientists engineer better coatings and interfaces, which are essential for building safer and better-performing batteries, particularly for use in vehicles.

A solid prospect for better batteries

Global efforts to electrify transportation and provide grid-level energy storage have driven demand for new battery technologies with improved safety, power density, and energy density. Ceramic solid electrolytes potentially offer significant advantages compared to the traditional liquid electrolytes used in lithium-ion batteries, including lower flammability and greater compatibility with high-energy electrode materials such as lithium metal. Among solid-electrolyte contenders, tantalum-doped lithium lanthanum zirconium oxide (LLZO) has garnered significant attention as a separator material because of its high bulk ionic conductivity and minimal chemical reactivity with lithium metal.

However, LLZO performance is limited by reactions that produce surface contaminants. Understanding the mechanisms behind these reactions is crucial for improving material processing. In this work, researchers used ambient-pressure x-ray photoelectron spectroscopy (APXPS) as part of a systematic investigation of the impacts of electrochemical reactions and contamination. The results will inform the design of safer and more-efficient batteries for electric vehicles or renewable energy storage.

Facing the interfacial challenges

It is well known that, in the presence of water vapor in air, LLZO undergoes Li+/H+ exchange, where protons (H+) can take up lithium-ion (Li+) sites without modifying the cubic crystal structure. This results in the formation of surface contaminants such as LiOH and Li2CO3 that contribute to poor interfacial contact and the constriction of current.

Numerous studies have explored different aspects of the surface contamination mechanisms on LLZO along with various processing techniques aimed at improving surface properties. However, most studies have focused on critical current density (CCD) tests, which provide limited mechanistic insight, or impedance analyses, with limited rationale behind their interpretation.

In this study, the researchers utilized a variety of surface-treatment processes on LLZO pellets to selectively induce proton exchange and contamination reactions in LLZO. The resulting bulk and surface chemistry was systematically characterized and correlated to changes in electrochemical properties.

ALS studies at ambient pressure

To observe the evolution of chemical species near the LLZO surface, ambient-pressure x-ray photoelectron spectroscopy (APXPS) was performed at ALS Beamline 9.3.2. The ability to tune the gas environment and temperature during measurement was crucial, as it allowed the researchers to optimize conditions (pressure, temperature, time) for removing surface contaminants. Also, the ability to vary the probe depth via beam energy was also essential for chemical speciation.

Read more on ALS website

Image: Illustrations of some of the surface treatments applied to a solid-state battery-electrolyte material (LLZO) as part of this study: glovebox polishing (Gb:Pol), heat treatment (HT), acid treatment (AT), water treatment (WT), and water treatment + heat treatment (WT:HT). Proton concentration (the result of H+ displacing Li+) is indicated by the color gradient, from low (orange) to high (blue). Pink and purple indicate surface contaminants.