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Anode material for safe and long-lasting batteries

The research team wants to use new materials to enable safe and durable high-performance cells. 
Photo Credit: Julia Maibach, KIT.

Researchers at the Karlsruhe Institute of Technology (KIT) and at Jilin University in Changchun / China have investigated a promising anode material for future high-performance batteries: lithium lanthanum titanate with perovskite crystal structure (LLTO). As reported by the team in Nature Communications, LLTO can improve the energy density, power density, charge rate, safety and lifespan of batteries without reducing the particle size from the micrometer to the nanometer scale. (DOI: 10.1038 / s41467-020-17233-1)

The demand for electric vehicles is increasing. At the same time, the need for intelligent power grids for a sustainable energy supply is growing. These and other mobile and stationary technologies require suitable batteries. Storing as much energy as possible in the smallest possible space with the lowest possible weight - lithium-ion batteries (LIB) still best meet this requirement. The research aims to increase the energy density, power density, safety and service life of these batteries. The electrode materials are essential. Anodes in LIB consist of a current collector and an active material applied to it, in which energy is stored in the form of chemical bonds. The active material used is predominantly graphite. However, negative electrodes made of graphite have a low charge rate. They also have security problems. Lithium titanate oxide (LTO) has already been commercialized among the alternative active materials. Negative electrodes with LTO offer a higher charge rate and are considered safer than those made with graphite. However, LIBs with LTO anodes tend to have a lower energy density.

Schematic representation of the perovskite crystal structure of lithium lanthanum titanate.
Image Credit : Fei Du / Jilin University.

The team around Professor Helmut Ehrenberg, head of the Institute for Applied Materials - Energy Storage Systems (IAM-ESS) at KIT, has now researched another promising anode material: lithium lanthanum titanate with a perovskite crystal structure (LLTO). As the study carried out jointly with scientists from Jilin University in Changchun, China, and other research institutions in China and Singapore, has shown that LLTO anodes have a lower electrode potential than commercialized LTO anodes, which results in a higher cell voltage and can achieve a higher capacity. "Ultimately, cell voltage and storage capacity determine the energy density of a battery," explains Ehrenberg. “In the future, LLTO anodes could enable particularly safe and durable high-performance cells.

In addition to energy density, power density, safety and service life, the charge rate also determines the suitability of a battery for demanding applications. Basically, the maximum discharge current and minimum charge time depend on the ion and electron transport in the solid and at the interfaces between electrode and electrolyte materials. To improve the charge rate, it is common to reduce the particle size of the electrode material from the micrometer to the nanometer scale. As the study by the researchers at KIT and their cooperation partners published in the journal Nature Communications shows, even particles of a few micrometers in perovskite-structured LLTO enable a higher power density and a better charge rate than LTO nanoparticles. The research team attributes this to so-called pseudocapacitive properties of LLTO: Not only are individual electrons attached to this anode material, but also charge-carrying ions, which are bound by weak forces and can reversibly transfer charges to the anode. "Thanks to the larger particles, LLTO enables in principle simpler and less expensive methods of electrode production," explains Ehrenberg.

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