Scientists probe the chemistry of a single battery electrode particle both inside and out

The results show how a particle’s surface and interior influence each other, an important thing to know when developing more robust batteries.

The particles that make up lithium-ion battery electrodes are microscopic but mighty: They determine how much charge the battery can store, how fast it charges and discharges and how it holds up over time – all crucial for high performance in an electric vehicle or electronic device.

Cracks and chemical reactions on a particle’s surface can degrade performance, and the whole particle’s ability to absorb and release lithium ions also changes over time. Scientists have studied both, but until now they had never looked at both the surface and the interior of an individual particle to see how what happens in one affects the other.

Read more on the SSRL (SLAC National Accelerator Laboratory) website

Image: Images made with an X-ray microscope show particles within a nickel-rich layered oxide battery electrode (left). In a SLAC study, scientists welded a single charged particle to the tip of a tungsten needle (right) so they could probe its surface and interior with two X-ray instruments. The particle is about the size of a red blood cell. (S. Li et al., Nature Communications, 2020)

How a new electrocatalyst enables ultrafast reactions

The work provides rational guidance for the development of better electrocatalysts for applications such as hydrogen-fuel production and long-range batteries for electric vehicles.

The oxygen evolution reaction (OER) is the electrochemical mechanism at the heart of many processes relevant to energy storage and conversion, including the splitting of water to generate hydrogen fuel and the operation of proposed long-range batteries for electric vehicles. Because the OER rate is a limiting factor in such processes, highly active OER electrocatalysts with long-term stability are being sought to increase reaction rates, reduce energy losses, and improve cycling stability. Catalysts incorporating rare and expensive materials such as iridium and ruthenium exhibit good performance, but an easily prepared, efficient, and durable OER catalyst based on earth-abundant elements is still needed for large-scale applications.

Key insight: shorter O-O bonds
In an earlier study, a group led by John Goodenough (2019 Nobel laureate in chemistry) measured the OER activities of two compounds with similar structures: CaCoO3 and SrCoO3. They found that the CaCoO3 exhibited higher OER activity, which they attributed to its shorter oxygen–oxygen (O-O) bonds. Inspired by this, members of the Goodenough group have now analyzed a metallic layered oxide, Na0.67CoO2, which has an even more compact structure than CaCoO3. X-ray diffraction (XRD) experiments performed at the Advanced Photon Source (APS) confirmed that the shortest O-O separation in Na0.67CoO2 is 2.30 Å, compared to 2.64 Å for CaCoO3. The researchers then compared the OER performance of Na0.67CoO2 with IrO2, Co3O4, and Co(OH)2. They found that Na0.67CoO2 exhibited the highest current density, the lowest overpotential (a measure of thermodynamic energy loss), and the most favorable Tafel slope (sensitivity of the electric current to applied potential). The Na0.67CoO2 also showed excellent stability under typical operating conditions.

>Read more on the Advanced Light Source website

Image: (extract, full image here) A new electrocatalyst prepared for this study, Na0.67CoO2, consists of two-dimensional CoO2 layers separated by Na layers (not shown). The Co ions (blue spheres) have four different positions (Co1-Co4), and the distorted Co–O octahedra have varying oxygen–oxygen (O-O) separations (thick red lines connecting red spheres). All of the O-O bonds are shorter than 2.64 Å (the length of the corresponding bonds in a comparable material), and the shortest bonds are less than 2.40 Å. It turns out that O-O separation has a strong effect on the oxygen evolution reaction (OER) in this material.

The role of synthesis gas in tomorrow’s sustainable fuels

In a new publication in Nature Communications, a team from the Dutch company Syngaschem BV and the Dutch Institute for Fundamental Energy Research elucidates for the first time some aspects of the Fischer-Tropsch reaction, used for converting synthesis gas into synthetic fuels.

Analysis performed at HIPPIE beamline at MAX IV were instrumental to achieve these results. The adoption of sustainable and renewable energy sources to permanently move beyond the dependence from fossil fuels constitutes one of the great challenges of our time. One that is made more urgent by the effects of climate change we witness on a daily basis. Electrification, such as we see in the development of electric vehicles, seems a promising strategy, but it cannot be the solution for all applications. In many cases liquid fuels are still considered the best and most efficient option. Is there a way to produce liquid fuels in an efficient and sustainable manner, one that does not rely on fossil sources?

>Read more on the MAX IV website

Toward better motors with X-ray light

Making Switzerland’s road traffic fit for the future calls for research, first and foremost. In the large-scale research facilities of PSI, chemists and engineers are investigating how to improve the efficiency of motors and reduce their emissions.

“The overall transportation system of Switzerland in 2040 is efficient in all aspects.” The primary strategic goal of the Federal Department of the Environment, Transport, Energy and Communications (DETEC) sounds good. The subordinate Swiss Federal Office of Energy (SFOE) specifies that vehicular traffic should pollute the environment less and become more energy-efficient and climate-friendly. Switzerland has set an ambitious goal for itself: to be climate-neutral by 2050.
This is a major challenge. According to the most recent “microcensus” on mobility from 2015, every person living in Switzerland travels around 24,850 kilometres per year. A high number, which also includes trips abroad. In everyday life and within Switzerland, the average per person is nearly 37 kilometres per day – and rising.
According to the Federal Office for the Environment (FOEN), cars, trucks, and buses produce three-fourths of the greenhouse gas emissions in the transportation sector. From this it follows: Whether or not the nation achieves its goal depends heavily on the motors used in these modes of transportation. Their CO2 emissions must be radically reduced. This is precisely the starting point for researchers at PSI and other institutions.

> Read more on the Swiss Light Source (PSI) website

Image: Passenger cars powered by hydrogen fuel cells have a greater range than electric cars, but they are less efficient. PSI researchers want to change that.
Credit: Adobe Stock/Graphic: Stefan Schulze-Henrichs