Multiscale Multiphase Lithiation and Delithiation Mechanisms in a Composite Electrode Unraveled by SimultaneousOperandoSmall-Angle and Wide-Angle X-Ray Scattering

Abstract

The (de)lithiation process and resulting atomic and nanoscale morphological changes of an a-Si/ c-FeSi 2 /graphite composite negative electrode are investigated within a Li-ion full cell at several current rates (Crates) and after prolonged cycling by simultaneous operando synchrotron wide-angle and small-angle X-ray scattering (WAXS and SAXS). WAXS allows the probing of the local crystalline structure. In particular, the observation of the graphite (de)lithiation process, revealed by the Li x C 6 Bragg reflections, enables access to the respective capacities of both graphite and active silicon. Simultaneously and independently, information on the silicon state of (de)lithiation and nanoscale morphology (1 to 60 nm) is obtained through SAXS. During lithiation, the SAXS intensity in the region corresponding to characteristic distances within the a-Si/c-FeSi 2 domains increases. The combination of the SAXS/WAXS measurements over the course of several charge/ discharge cycles, in pristine and aged electrodes, provides a complete picture of the C-rate-dependent sequential (de)lithiation mechanism of the a-Si/c-FeSi 2 /graphite anode. Our results indicate that, within the composite electrode, the active silicon volume does not increase linearly with lithium insertion and point toward the important role of the electrode morphology to accommodate the nanoscale silicon expansion, an effect that remains beneficial after cell aging and most probably explains the excellent performance of the composite material.

Nano‐Architectured Composite Anode Enabling Long‐Term Cycling Stability for High‐Capacity Lithium‐Ion Batteries

“…Indeed, it can be noticed that the half‐cell capacity stays close to 70% of its initial value at C /20 (black squares), whereas after 700 cycles it has decreased down to 45% and 35% at C /5 (red circles) and C (blue triangles) current rates, respectively. This high loss of capacity at high C ‐rates is a consequence of electrode polarization that is attributed to the disruption of the lithiation mechanism 50. As seen in Figure 1b, the displacement of the negative electrode potential (the greater difference between charge and discharge potential) lowers the amount of lithium that can be stored before the cell cut‐off potential (5 mV) has been attained, therefore reducing the cell performance.…”

Multi-scale quantification and modeling of aged nanostructured silicon-based composite anodes

“…In general, lithiation of the graphite phase is also important in Si/FeSi 2 -graphite composites, each active component contributing to the electrode capacity according to a potential-driven sequential lithiation mechanism 42,43 . Wide-angle X-ray scattering (WAXS) is used at this stage to confirm the state of lithiation of the graphite phase in the anode.…”

Elimination of Fluorination: The Influence of Fluorine-Free Electrolytes on the Performance of LiNi1/3Mn1/3Co1/3O2/Silicon–Graphite Li-Ion Battery Cells

“…The anode was composed of silicon alloy (L-20772, provided by 3 M), graphite (BTR 918), super-P carbon black, and lithium polyacrylate (LiPAA, 450 K) binder in a mass ratio of 25:66:2:7 and had an areal capacity of 2.4 mAh cm –2 . The composition and morphology of the silicon alloy have been recently published by Berhaut et al 42 The cathode consisted of LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC111), super-P carbon black, and poly(vinylidene difluoride) binder in a mass ratio of 94:3:3 and had an active mass loading of 13.7 mg cm –2 , equivalent to an areal capacity of 2.0 mAh cm –2 (corresponding to a nominal capacity of 146 mAh g –1 ). The ⌀13 mm electrodes were punched out and dried at 120 °C under vacuum for 12 h prior to battery assembly.…”