Neutron depth profiling technique for studying aging in Li-ion batteries

During operation of a Li-ion cell, lithium diffuses in and out of the solid phase anode and cathode. Measuring the lithium concentration within the electrodes of the cell over its operational life could provide key information for understanding the loss of active lithium and the associated aging mechanisms. Concentration profiles of lithium in a cell are difficult to measure with traditional spectroscopic techniques. Here, neutron depth profiling was used to measure lithium near-surface concentration profiles along the anode and cathode strips in off-the-shelf cylindrical Li-ion batteries as a function of the aging process. A buildup of the surface concentration of lithium was found in graphite anode as well as a general decrease in the intercalation efficiency in lithium iron phosphate cathode material with aging.

Research highlights
► The Li build up on the surface of the anode increases with C-rate.
► In anode, the Li concentration profile decays exponentially along its thickness.
► The Li concentration profile changes along the length of the anode.
► There is no buildup of the lithium near the cathode surface.
► The Li concentration in the cathode decreases with increasing C-rate.