<p>Rapid
charging of Li-ion batteries is limited by lithium plating on graphite anodes,
whereby Li<sup>+</sup> ions are reduced to Li metal on the graphite particle
surface instead of inserting between graphitic layers. Plated Li metal not only
poses a safety risk due to dendrite formation, but also contributes to capacity
loss due to the low reversibility of the Li plating/stripping process.
Understanding when Li plating occurs and how much Li has plated is therefore vital
to remedying these issues. We demonstrate a titration technique with a minimum
detection limit of 20 nmol (5×10<sup>-4</sup> mAh) Li which is used to quantify
inactive Li that remains on the graphite electrode after fast charging. Additionally,
the titration is extended to quantify the total amount of solid carbonate
species and lithium acetylide (Li<sub>2</sub>C<sub>2</sub>) within the solid
electrolyte interphase (SEI). Finally, electrochemical modeling is combined with
experimental data to determine the Li plating exchange current density (10 A/m<sup>2</sup>)
and stripping efficiency (65%) of plated Li metal on graphite. These techniques
provide a highly accurate measure of Li plating onset and quantitative insight
into graphite SEI evolution during fast charge.</p>
Comparing the Solid Electrolyte Interphases on Graphite Electrodes in K and Li Half Cells
