New test procedure for developing quick-charging lithium-ion batteries

Jülich / Munich, 6 December 2017 - When lithium-ion batteries are charged too quickly, metallic lithium gets deposited on the anodes. This reduces battery capacity and lifespan and can even destroy the batteries. Scientists at the Forschungszentrum Jülich and the Technical University of Munich (TUM) have now presented a process that, for the first time ever, allows this so-called lithium plating process to be investigated directly. This puts new strategies for quick-charging strategies close at hand.

Lithium plating, the depositing of metallic lithium at the anodes of lithium-ion batteries, is one of the primary factors that limits charging current. The performance of batteries suffers significantly from these metallic deposits. In extreme cases this can result in short circuits and even batteries going up in flames.
When charging batteries, the positively charged lithium ions move through the liquid electrolytes and are deposited in the porous graphite anodes. However, the larger the current and the lower the temperature, the greater the probability that the lithium ions will not be deposited within the electrodes, as desired, but rather as a solid metallic layer on the outer surface.

Indirect evidence does not serve the goal
Even though this phenomenon is basically well-known, many aspects remain shrouded in mystery. Until now, it was not possible to directly observe how and under which circumstances lithium plating takes place. “Using traditional methods of microscopy, we can only observe a battery after the fact, because it needs to be cut open,” explains Dr. Josef Granwehr at the Jülich Institute of Energy and Climate Research (IEK-9). “In the process, further reactions that distort the results become inevitable.”
Even highly developed processes like neutron scattering allow for only indirect analyses. Compounding the problem is the fact that available slots for measurements at research reactors and large particle accelerators are scarce. This makes these tools more suitable for fundamental investigations than for tedious, practical test series.

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