Understanding Component‐Specific Contributions and Internal Dynamics in Silicon/Graphite Blended Electrodes for High‐Energy Lithium‐Ion Batteries

Abstract

Blended electrode materials containing high‐capacity silicon (Si) and robust graphite (Gr) materials are considered advanced alternatives to pure graphite electrodes used in Li‐ion batteries. Understanding the component‐specific lithiation and delithiation behavior and electrochemical interactions between the blended materials is of crucial importance for targeted optimization of composition and microstructural design, yet hardly addressed to date. Herein, a model‐like Si/Gr blended electrode and special electrochemical cell are introduced to directly capture the component specific behaviors for the first time. This includes studies of the formation cycles, the reaction distribution between Si and Gr, the component‐specific contributions to the capacity at different charge and discharge rates, and the internal dynamics during pulse loads and subsequent relaxation. The deconvolution of the components’ behavior during operation provides fundamental insights that contribute to a profound understanding and targeted optimization of Si/Gr blended electrodes. Furthermore, the application of the presented experimental approach can serve scientists to identify and study other advanced materials combinations as blended electrodes for rechargeable batteries.

Chemical Interplay of Silicon and Graphite in a Composite Electrode in SEI Formation

“…As mentioned in the Introduction, the electrochemical contributions from each component change during the operation of the cell. , This result raises not one but two logical questions: do the contributions of Gr and Si to SEI formation change with electrolyte composition, and are the relative contributions different from 1?…”

“…Their results suggest that, during lithiation at rates greater than about 0.2-C, the contribution from silicon predominates, most likely due to better reaction kinetics. 8 Further emphasizing the inhomogeneity of the lithiation process, Ruther et al used vibrational, Raman, and Fourier transform infrared (FT-IR) spectroscopy techniques to show that the distribution of silicon-and graphite-rich areas were not uniform and that lithiation of the two materials was also not uniform. They also identified several side reactions that contributed to the solid electrolyte interphase (SEI) layer.…”

“…The use of silicon-graphite composite electrodes and their electrochemical properties are the topics of many papers in the open literature. As these are very extensively reported topics, only a few papers will be cited to serve as examples. − Given the nature of the electrode, researchers are asking, quite logically: how do the two materials interact? Some reports address how graphite and silicon contribute to the overall capacity of the electrode, showing the potential ranges where each makes a significant contribution. − For example, Moon et al discuss what they termed as “Li + crosstalk” between the two materials.…”

“…An in-depth study of the above electrochemical interaction was reported by Heubner et al Using what was termed a “model-like blended electrode,” which consisted of two single-component electrodes that were short-circuited, they showed how the contributions from the graphite and silicon portions change with the silicon/graphite ratio, SOC, time and current (rate), and during lithiation and delithiation. Their results suggest that, during lithiation at rates greater than about 0.2-C, the contribution from silicon predominates, most likely due to better reaction kinetics …”

Electrochemical Patterning of Cu Current Collectors: An Enabler for Pure Silicon Anodes in High‐Energy Lithium‐Ion Batteries

“…[4] These effects typically lead to low coulombic efficiency (CE) and unsatisfactory cycling stability that makes pure Si challenging for the commercial roll out. To enable Si anodes for LIB, researchers identified several promising approaches to reduce or accommodate the effects of the volume changes by appropriate (nano) structuring [5][6][7] or by blending Si with active [8,9] and inactive [10] materials. [11] Physical vapor deposition (PVD) proved to be a versatile method for applying pure Si on a variety of current collectors (CCs).…”