German research reveals keys to "perpetual youth" batteries

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With the application of lithium ion batteries in e-mobility, to support electrical grids or offgrid locations, and in solar+storage systems rapidly increasing, any increase in battery life could potentially deliver major benefits. German researchers report that they may have discovered a key to “perpetual youth for batteries” in the way in which pacifying layers are formed on graphite anodes.

The team from the TUM report that lithium ion batteries with graphite anodes can lose as much as 10% of their capacity in the initial charging cycle. This is largely due to active lithium being consumed in the formation of a pacifying layer on the anode, the team reports. The pacifying layer protects the battery electrolyte from decomposition at the anode.

The Munich researchers believe that certain additives may alter the way in which the pacifying layer is formed, therefore retaining more of the active lithium and as a result battery capacity. The team also suggests modifying the cathode surface may deliver advantageous results.

Electrochemical investigations were combined with methodologies including “X-ray diffraction, impedance measurements and prompt activation analysis” in the research. The team specifies that neutron activation analysis held the key to observing “extremely minute quantities” of transition metals on graphite electrodes.

Temperature effects were also carried out as a part of the study, with the scientists concluding that capacity loss due to active lithium consumption occurring at far greater rates at high temperatures (60C) when compared to room temperature (25C).

Higher voltages also increased lithium ion cell capacity loss, with voltages above 4.6 V increasing the conductivity of the pacifying layer and therefore the decomposition of the electrolyte.

“Using our insights, now individual processes can be improved,” said Irmgard Buchberger, PhD candidate at the Department of Electrochemistry at TU Munich. “Possibilities include additives that improve the build-up of the pacifying layer, for example, or modifications of the cathode surface.”

The TUM team’s findings were published in the Journal of the Electrochemical Society last month. The researchers came from TUM’s Department of Technical Electrochemistry and the Research Neutron Source FRM II.

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