  Non-destructive determination of lithium distribution in a working battery is
key for addressing both efficiency and safety issues. Although various
techniques have been developed to map the lithium distribution in electrodes,
these methods are mostly applicable to test cells. Here we propose the use of
high-energy x-ray Compton scattering spectroscopy to measure the local lithium
concentration in closed electrochemical cells. A combination of experimental
measurements and parallel first-principles computations is used to show that
the shape parameter S of the Compton profile is linearly proportional to
lithium concentration and thus provides a viable descriptor for this important
quantity. The merits and applicability of our method are demonstrated with
illustrative examples of LixMn2O4 cathodes and a working commercial lithium
coin battery CR2032.
