Synchrotron X‐ray Tomographic Study of a Silicon Electrode Before and After Discharge and the Effect of Cavities on Particle Fracturing

Abstract

Silicon (Si) has been proposed as one of the most promising anode materials for next-generation lithium ion batteries (LIBs). However, unsatisfactory discharge capacity/energy density and inevitable performance worsening prevent their commercialization. Herein, an in-depth investigation on the same Si composite electrode before and after the first discharge by employing in situ synchrotron X-ray tomography is presented. It is found that i) on the electrode level, the Si particles located in the central part of the electrode preferentially experience crack formation; ii) on the individual particle level, heterogeneous electrochemical lithiation behaviour is observed; iii) cavities are formed during the electrode preparation and battery operation. Moreover, the correlation between the electrochemical activities of Si particles and their individual electrical contact to the electron conducting network is investigated. For the first time it is quantified that Si particles will experience lithiation only under the condition that at least 40% of their surface is electrically connected. These novel insights are possible explanations for low discharge capacity/energy of Si electrode LIBs, and would open new design principles and opportunities for high-capacity electrode materials for next-generation energy storage systems.

Improving the Performance of SiOx/Carbon Materials for High Energy Density Commercial Lithium‐Ion Batteries Based on Montmorillonite

“…The peaks at 2θ=21.0°, 28.5°, 56.1° were all ascribed to that of silica. However, they still had many differences, where the peak at 2θ=47.5° indicated the presence of crystal silicon while the peaks at 2θ=26.5°, 44.5°, 50.5°, 60.1° were assigned to characteristic peaks of graphite, which suggested an amount of layered structure carbon was formed . In order to confirm the existing form of silicon, X‐ray photoelectron spectroscopy was conducted to MSBC and the results are plotted in Figure S1 and Figure S2.…”

“…Based on Figure a, statistical analyses showed that the size of the MSBC particles varied from 0.06 to 42.25 μm with an average diameter (D50) of 7.83 μm. Such size distribution is among the preferred range for electrode fabrication and is beneficial for compaction of materials and producing high density commercial LIBs . Figure b is the N 2 adsorption/desorption isotherms of the MSBC particles at 77 K, which displayed a typical IV isotherm.…”

“…The Brunauer‐Emmett‐Teller (BET) specific surface area of MSBC was calculated to be 7.91 m 2 /g. Since a large specific surface area indicates a high surface SEI, the SEI films on the smaller particles have larger challenge of overgrowth and higher irreversible lithium ions consumption . Thus, in the commercial batteries design, the parameters of particle size and specific area must meet a certain requirement, and those of the prepared composite just laid in such range.…”

“…However, they still had many differences, where the peak at 2θ = 47.5°indicated the presence of crystal silicon while the peaks at 2θ = 26.5°, 44.5°, 50.5°, 60.1°were assigned to characteristic peaks of graphite, which suggested an amount of layered structure carbon was formed. [22,[40][41] In order to confirm the existing form of silicon, X-ray photoelectron spectroscopy was conducted to MSBC and the results are plotted in Figure S1 and Figure S2. The Si 2p spectra clearly indicated that MSBC contained two forms of silicon, namely, SiO x (x < 2)(103.2 eV) and SiÀ Si (99 eV) [42] However, the amount of the latter is much less than the former, thus, silicon in the composite was mainly in the form of SiO x and the capacity of the composite was mainly from SiO x .…”

Practical Implications of Using a Solid Electrolyte in Batteries with a Sodium Anode: A Combined X‐Ray Tomography and Model‐Based Study

“…The present work focuses on monitoring the SE in contact with the Na metal anode during cycling and aims to derive practical guidelines for long‐term stable operation. First, cells with Na metal anode and liquid electrolyte are cycled and investigated with in situ synchrotron X‐ray tomography (similar method as reported elsewhere) and with ex situ surface analytic methods to assess the deleterious effects of dendrite formation as a reference case. Then, Na‐β‐alumina is introduced to protect the electrodes during cycling.…”