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

Abstract

to an unstable solid electrolyte interphase (SEI) [4][5][6][7] and large volumetric changes that lead to particle pulverization and loss of electrical contact between the active particles and the current collector. [8][9][10][11][12] Several approaches are being pursued to address these challenges, which include the following: electrolyte additives to improve SEI integrity, [5,7] electrode binders with enhanced mechanical [13] and chemical properties, [6] morphological engineering of Si particles (nanowires, nanotubes, porous particles, nanospheres, etc.), [12,14] limited-capacity cycling to limit volume expansion of the Si particles, [8,15] and developing electrodes that contain blends of Si and Gr materials. [3,7,11] The latter approach, coupled with SEI modifying additives such as fluoroethylene carbonate (FEC), has markedly improved electrode cycling performance compared to that of pure Si electrodes. [3,7,16] The potentials and kinetics for Li insertion and extraction from Si and Gr are known to be different. During electrochemical cycling of cells with a Li metal electrode ("half cells"), Si is active in the entire voltage range of 0-1.0 V, whereas Gr is active mainly below ≈0.25 V versus Li/Li + (abbreviated as V Li ). [3,8,15] The relative lithiation/delithiation behavior of the Si and Gr components in blended electrodes is not well understood. Knowledge of Li distribution between the two active components is important as it determines the volume change of the electrode during electrochemical cycling (mainly due to Si particle expansion). One reason for the knowledge gap is the amorphization of crystalline Si that occurs during lithium insertion, which makes it difficult to track the evolution of the component by conventional techniques such as X-ray diffraction (XRD).In this study, operando energy dispersive XRD is used to quantify Li content of Gr in a 15 wt% Si-Gr composite electrode. In parallel, data obtained from operando studies on a Gr-only electrode are used to calibrate behavior of the Gr component in the blended electrode. By combining the knowledge of Gr lithiation with information on the coulometric capacity for the same cell obtained from electrochemistry, the Li content of the Si component can be inferred, and the fractional lithiation of each component is obtained. The knowledge gained from our study can be used to optimize the Si and Gr contents in the blended electrode, as well as to select cutoff capacities in limited-capacity schemes, which aim to limit electrode expansion by limiting expansion of the Si component. Additional 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 compon...

Low‐Temperature Charging and Aging Mechanisms of Si/C Composite Anodes in Li‐Ion Batteries: An Operando Neutron Scattering Study

“…During charging of the Si/C composite, the graphite particles are most likely preferentially lithiated before the Si compound (see Figure a, c–e for model). Thermodynamically, Si should be lithiated before graphite . However, charging at a high rate of 0.5 C moves the system away from the equilibrium situation.…”

“…Yao et al. recently investigated Si/C composite anodes (15 % Si) in half cells by using energy‐dispersive XRD . For coin half cells, they found that nanometer‐sized Si was alloying before the lithiation of graphite at low C‐rates …”

Recent Progress in Advanced Characterization Methods for Silicon‐Based Lithium‐Ion Batteries

“…Since the lithiation/delithiation behaviors of Si and carbon components in mixed electrodes are still unclear, in situ XRD has been applied to understand the structural changes in two components in Si‐composite anodes during charge/discharge. As shown in Figure , aided by an additional pure graphite (Gr) electrode study, Yao et al investigated the lithiation behavior of Gr in a mixed electrode. The average voltage plateaus of Gr in pure Gr electrodes were lower than those in Si–Gr electrodes (Figure A,B), indicating that the addition of Si reduced the lithiation overpotential of Gr components.…”

“…Labels G1–G6 and Si1–Si3 next to the XRD spectra designate data taken at voltages corresponding to the same labels in the electrochemical cycling plots. Reproduced with permission . Copyright 2019, Wiley‐VCH.…”

SnO2 as Advanced Anode of Alkali‐Ion Batteries: Inhibiting Sn Coarsening by Crafting Robust Physical Barriers, Void Boundaries, and Heterophase Interfaces for Superior Electrochemical Reaction Reversibility

“…Due to the lithium storage mechanism of SnO 2 which is a combination of the alloying–dealloying reaction and conversion reaction, the working voltage of SnO 2 (≈1.0 V vs Li/Li + ) is higher than alloying reaction‐type anodes (e.g., silicon (Si, ≈0.4 V vs Li/Li + ), germanium (Ge, ≈0.5 V vs Li/Li + ), and tin (Sn, ≈0.6 V vs Li/Li + )), but lower than conversion reaction‐type anodes (e.g., transition metal oxides TMOs (M = Mn, Fe, Co, Ni, Cu, etc., TC), ≈1–2 V vs Li/Li + ) . The moderate working voltage of the SnO 2 anode (i.e., ≈1.0 V) can effectively inhibit the generation of lithium dendrites to improve the safety of LIBs; additionally, it results in an appropriate output voltage of the full LIB cells and prevents the decomposition of organic electrolytes which occurs at high potentials …”