Operando setup enables visualization of battery aging processes during charging cycles

Lithium button cells with electrodes fabricated from nickel-manganese-cobalt oxides (NMC) are very highly effective. Sadly, their capability decreases over time. Now, for the primary time, a group has used a non-destructive technique to look at how the fundamental composition of the person layers in a button cell adjustments throughout charging cycles.

The research, published within the journal Smallconcerned groups from the Physikalisch-Technische Bundesanstalt (PTB), the College of Münster, researchers from the SyncLab analysis group at HZB and the BLiX laboratory on the Technical College of Berlin. Measurements had been carried out within the BLiX laboratory and on the BESSY II synchrotron radiation supply.

Lithium-ion batteries have change into more and more higher. The mixture of layered nickel-manganese-cobalt oxides (NMC) with a graphite electrode (anode) has been effectively established because the cathode material in button cells and has been repeatedly improved. Nonetheless, even one of the best batteries don’t final perpetually; they age and lose capability over time.

“A lot happens at the interfaces between the anode, separator and cathode while a battery is charging or discharging,” explains Ioanna Mantouvalou, physicist at HZB and first writer of the research. Usually, these adjustments are solely studied after the battery has been disassembled, i.e., ex situ and at a selected level within the biking course of.

However there may be now one other approach: in situ and operando experiments permit researchers to look contained in the battery whereas the processes are happening, utilizing X-ray fluorescence (XRF) and X-ray absorption spectroscopy (XAS) in a so-called confocal geometry. This geometry permits 3D scanning of a pattern with depth resolutions right down to 10 µm. Such experimental setups are already potential on the synchrotron radiation supply BESSY II. Nonetheless, the measurement time at BESSY II is proscribed, so batteries can’t be studied over their total lifetime.

Ioanna Mantouvalou due to this fact makes use of a confocal micro X-ray fluorescence spectrometer at BLiX, which might analyze samples absolutely robotically over lengthy durations of time.

“The confocal setup allows us to distinguish the individual layers from the NMC cathode to the back contact and to study their elemental composition. This gives us spatially resolved insights into the operation without changing the layer stack; non-destructive, quantitative, under operating conditions, i.e., operando,” says Mantouvalou.

The researchers analyzed a lithium button cell on the BLiX instrument for a number of weeks and over 10,000 cost cycles, offering knowledge on the degradation of the NMC electrode over time. As well as, the pattern was examined on the new microfocus beamline (MiFO) within the PTB laboratory at BESSY II.

The research exhibits that through the first three weeks, manganese specifically dissolves from the NMC cathode and migrates to the carbon anode. This course of takes about 200 cycles. After that, the compound more and more dissolves within the intermediate layers, which stops additional reactions and processes.

“We urgently need such quantitative results to further improve batteries,” says Mantouvalou.

The system within the BLiX laboratory will also be used for experiments on different supplies.