Operando Quantification of (De)Lithiation Behavior of Silicon-Graphite Blended Electrodes for Lithium-Ion Batteries

Due to the high lithium capacity of silicon, the composite (blended) electrodes containing silicon (Si) and graphite (Gr) particles are attractive alternatives to the all-Gr electrodes used in conventional lithium-ion batteries. In this Communication, the lithiation and delithiation in the Si and Gr particles in a 15 wt% Si composite electrode is quantified for each component using energy dispersive X-ray diffraction. This quantification is important as the components cycle in different potential regimes, and interpretation of cycling behavior is complicated by the potential hysteresis displayed by Si. The lithiation begins with Li alloying with Si; lithiation of Gr occurs at later stages when the potential dips below 0.2 V (all potentials are given vs Li/Li+). In the 0.2-0.01 V range, the relative lithiation of Si and Gr is approximate to 58% and 42%, respectively. During delithiation, Li+ ion extraction occurs preferentially from Gr in the 0.01-0.23 V range and from Si in the 0.23-1.0 V range; that is, the delithiation current is carried sequentially, first by Gr and then by Si. These trends can be used for rational selection of electrochemical cycling windows that limits volumetric expansion in Si particles, thereby extending cell life.