Unraveling the structural transformation of Li-rich materials in lithium-batteries

Lithium-Ion Batteries (LIBs) are essentials in everyday life in mobile applications as well as in hybrid/electric mobility. The extraordinary market success of this technology is forcing hard the need of LIBs with improved energy density, environmental compatibility and safety, making necessary to push this technology beyond the current state of the art. In this framework, Co-poor Lithium Rich Layered Oxides (LRLOs) are the most strategic alternative to current Co-rich layered oxide positive electrode materials thanks to the excellent combination of large specific capacity (>250 mAhg-1), high energy density (up to 900 WhKg-1), small costs and improved environmental benignity. The excellent performance of LRLOs derives from the peculiar combination of redox processes originated from the transition metals and the oxygen anions sublattice. The practical use of LRLOs is hindered by several drawbacks, such as voltage decay, capacity fading, and an irreversible capacity lost in the first cycle. These issues are related to structural rearrangements in the lattice upon cycling.

In this work, we demonstrate a new family of LRLOs with general formula Li1.2+xMn0.54Ni0.13Cox-yAl0.03O2 (0.03 ≤ x ≤ 0.08 and 0.03 ≤ y ≤ 0.05), obtained from the replacement of cobalt with lithium and aluminum and we highlight how the balancing of the metal blend can lead to improvements of the Coulombic efficiency in the first cycle, a better capacity retention and reduced voltage decay. To shed light on the complex crystal-chemistry of this class of LRLOs we studied the Co-poorest member of this homologue material series, namely Li1.28Mn0.54Ni0.13Co0.02Al0.03O2, in order to prove the structural evolution occurring upon charge/discharge in lithium cell. To these aims, electrodes have been recovered during the first cycle, the second cycle and after ten cycles of charge/discharge by de-assembling lithium cells into an Ar-filled glove box. These post mortem materials have been sealed in borosilicate capillary tubes (see Fig. 1a) and studied ex situ by X-ray powder diffraction at the MCX beamline.

Read more on the Elettra website

Image: Fig. 1b shows the potential curves vs time for the first two cycles and highlights the points, marked with A, B, C and so on, where the charge or discharge step was stopped and the materials recovered for analysis. According to the diffraction data (Fig. 1c), structural alterations of Li1.28Mn0.54Ni0.13Co0.02Al0.03O2 start with a fast broadening and a shift of the peaks suggesting a smooth lattice modification. When the cell reaches 4.8V vs Li+, a second phase can be identified. In the discharge process opposite structural transformations occur.

Modelling electrochemical potential for better Li-batteries

To understand the electrochemical potential of lithium-ion batteries, it’s important to decipher the chemical processes at electrode interfaces occurring during device activity. Using HIPPIE beamline, a research group investigated and modelled the influence of electrochemical potential differences in operando in these batteries.

“With our experiments at HIPPIE, we had the opportunity to look at battery materials and interface reactions under operating conditions exploring the capabilities of the electrochemical setup at the end station,” said Julia Maibach, study author and professor at the Institute for Applied Materials – Energy Storage Systems at Karlsruhe Institute of Technology (KIT) in Germany. “We were among the first users testing the electrochemical set up including the glove box for inert sample transfer.”

Why study electrochemical potential difference in batteries? This phenomenon drives the transfer of charged particles to different phases in redox reactions at battery electrode-electrolyte interfaces. In simple terms, the difference enables the chemical reaction necessary for Li-ion battery function.

Read more on the MAX IV website

Image: Research group studies gold and copper model electrodes at MAX IV’s HIPPIE beamline with Ambient Pressure Photoelectron Spectroscopy (APPES) during lithiation

Credit: MAX IV Laboratory

What drives rechargeable battery decay?

How quickly a battery electrode decays depends on properties of individual particles in the battery – at first. Later on, the network of particles matters more.

Rechargeable lithium-ion batteries don’t last forever – after enough cycles of charging and recharging, they’ll eventually go kaput, so researchers are constantly looking for ways to squeeze a little more life out of their battery designs.

Now, researchers at the Department of Energy’s SLAC National Accelerator Laboratory and colleagues from Purdue University, Virginia Tech, and the European Synchrotron Radiation Facility have discovered that the factors behind battery decay actually change over time. Early on, decay seems to be driven by the properties of individual electrode particles, but after several dozen charging cycles, it’s how those particles are put together that matters more.

“The fundamental building blocks are these particles that make up the battery electrode, but when you zoom out, these particles interact with each other,” said SLAC scientist Yijin Liu, a researcher at the lab’s Stanford Synchrotron Radiation Lightsource and a senior author on the new paper. Therefore, “if you want to build a better battery, you need to look at how to put the particles together.”

Read more on the SLAC website

Image: A piece of battery cathode after 10 charging cycles. A machine-learning feature detection and quantification algorithm allowed researchers to automatically single out the most severely damaged particles of interest, which are highlighted in the image.

Credit: Courtesy Yijin Liu/SLAC National Accelerator Laboratory

X-rays capture ageing process in EV batteries

CLS researcher Toby Bond uses x-rays to help engineer powerful electric vehicle batteries with longer lifetimes. His research, published in The Journal of the Electrochemical Society, shows how the charge/discharge cycles of batteries cause physical damage eventually leading to reduced energy storage. This new work points to a link between cracks that form in the battery material and depletion of vital liquids that carry charge.

Bond uses the BMIT facility at the Canadian Light Source at the University of Saskatchewan to produce detailed CT scans of the inside of batteries. Working with Dr. Jeff Dahn at Dalhousie University, he specializes in batteries for electric vehicles, where the research imperative is to pack in as much energy as possible into a lightweight device.

“A big drawback to packing in more energy is that generally, the more energy you pack in, the faster the battery will degrade,” says Bond.

In lithium-ion batteries, this is because charging physically forces lithium ions between other atoms in the electrode material, pushing them apart. Adding more charge causes more growth in the materials, which shrink back down when the lithium ions leave. Over many cycles of this growing and shrinking, micro-cracks begin to form in the material, slowly reducing its ability to hold a charge.

Read more on the CLS website

Image: Toby Bond adjusts a battery sample on the BMIT beamline

Korean scientists test the brand-new MYSTIIC

Jongwoo and his team from Seoul are “friendly users”. This name is given to scientists who do their experiments on a pristine machine, before it goes into user operation. Back in Korea we called them to hear more about their special beamtime and what it means for their battery research.

Who are you and how did you discover BESSY II?

I am Jongwoo Lim, assistant professor at the department of chemistry at Seoul National University. My research group “Battery and Energy Research Lab” counts many talented young scientists. In 2018 a colleague from the Max Planck Society invited me to give a talk and, on this occasion, I visited BESSY II. Back in Seoul I wanted my team to discover this amazing science environment.

Getting beamtime at BESSY II, how does this work?

The competition for beamtime is very strong, many scientists want to come to BESSY II! We send in a proposal and were rejected several times. Finally, after 2 years we got the green light for some beamtime at MAXYMUS, the beamline of the Max Planck Institute for Intelligent Systems (more below). And on top of that, beamline scientist Markus asked us if we were interested to use and test MYSTIIC (Microscope for x-raY Scanning Transmission In-situ Imaging of Catalysts). This new microscope will go into operation in Spring 2022.

Read more on the HZB blog science site

Image: Jongwoo’s team from Korea at BESSY II

Preparing for the next generation of batteries

In the ongoing quest to build a better battery, researchers used the Canadian Light Source (CLS) at the University of Saskatchewan to identify the potential of using polymer composites as electrode matrices to increase the capacity of rechargeable lithium-ion (Li-ion) batteries.

“The composition of the adhesive and conductive framework for batteries hasn’t changed in years,” said Dr. Christian Kuss, assistant professor in the Department of Chemistry at the University of Manitoba and one of three researchers on the project. “But, we’re reaching the limit of how much capacity Li-Ion batteries have so this work is essentially preparing for the next generation of batteries.”

Over many cycles of charging and discharging, battery materials begin to break down, he explained. “The goal is to find new matrix materials that allow the electrode to stay intact over longer periods of time and thereby increase capacity.”

The new matrix material Kuss and his colleagues studied was based on a mixture of two polymers – one adhesive and the other conductive. The adhesive polymer is cellulose based, he said, while the conductive one “is easily synthesized and fairly cheap.” Cost is an important consideration “because you ultimately want a battery that is comparable in terms of pricing to what’s already available.”

At the CLS, the researchers used the Spectromicroscopy beamline to study the chemical structure of the polymer mixture. “With this technique, we could see the mixture and see how the polymers were distributed at a microscale.”

Read more on the CLS website

Image: Battery cyclers for running and testing batteries.