Mechanical Damage of Surface Films and Failure of Nano-Sized Silicon Electrodes in Lithium Ion Batteries

Abstract

This work demonstrates that the mechanical damage of surface passivation films plays an underlying role in the failure of nano-sized Si electrodes in lithium-ion batteries. The surface film derived from the standard electrolyte (1.3 M LiPF 6 dissolved in ethylene carbonate/diethyl carbonate) during the first lithiation step is damaged by the mechanical stress caused by the volume contraction of Si particles during the subsequent de-lithiation period. The electrolyte decomposes on the newly exposed Si surface and film deposition occurs, which is then mechanically damaged again owing to volume change of the Si particles. Such film deposition/damage cycles are repeated until the mechanical stress becomes insignificant as a result of capacity decay. Continued electrolyte decomposition, which prevails in the early cycling period, produces electronically insulating films located between Si particles, which cause Li trapping within the Si matrix. Li trapping is found to be responsible for the rapid decrease in capacity and Coulombic efficiency in the intermediate period of cycling. When fluoroethylene carbonate (FEC) is added to the electrolyte, a surface film that is robust against mechanical stress is produced. As a result, the FEC-derived surface film maintains its passivating ability and suppresses the irreversible reactions, resulting in a better cycling performance.

Robust Solid/Electrolyte Interphase (SEI) Formation on Si Anodes Using Glyme-Based Electrolytes

“…Given that continuous lithiation/delithiation leads to expansion/contraction of the Si, the already-formed SEI could be destroyed and the Si surface area could be increased due to Si fracture. 32,33 The increased surface area results in an overall reduced anode/ electrolyte interfacial resistance in successive cycles. It is noteworthy that the polarization for LiFSI-3DME-3TTE reaches steady state earlier than GenF, suggesting that a more protective SEI forms more rapidly, agreeing with the smaller parasitic current observed for LiFSI-3DME-3TTE compared to GenF (Figure 1A).…”

“…Such a phenomenon is likely due to the disruption of the resistive native SiO x layer on a-Si upon lithiation. , Notably, polarization decreases for both LiFSI-3DME-3TTE and GenF upon cycling, whereas other electrolytes show fluctuating lithiation potentials, indicating multiple competing mechanisms in the SEI (Figure D). Given that continuous lithiation/delithiation leads to expansion/contraction of the Si, the already-formed SEI could be destroyed and the Si surface area could be increased due to Si fracture. , The increased surface area results in an overall reduced anode/electrolyte interfacial resistance in successive cycles. It is noteworthy that the polarization for LiFSI-3DME-3TTE reaches steady state earlier than GenF, suggesting that a more protective SEI forms more rapidly, agreeing with the smaller parasitic current observed for LiFSI-3DME-3TTE compared to GenF (Figure A).…”

Interphasial Engineering via Individual Moiety Functionalized Organosilane Single-Molecule for Extreme Quick Rechargeable SiO/NCM811 Lithium-Ion Batteries

“…40 (Figure S6). Given that the shrinkage of the SiO active material during the de-lithiation mechanically degrades the SEI film on its surface, 17,41,42 the exposure of Si−C peaks from the carbon-coated SiO electrode is predicted. If that, the higher Si−C peak intensity can be regarded as the more exposure of the C-coated SiO surface.…”

An Azamacrocyclic Ligand-Functionalized Transition-Metal Scavenging Polymer for 5.0 V Class High-Energy Lithium-Ion Batteries

“…Since the material degradation of LNMO and graphite is very minor during the cycle, the degradation of SEI is suppressed with the functionalized electrode comprised cell . Furthermore, the irreversible capacity , during the cycle is suppressed with the functionalized layer (Figure S8). Thus, the additional electrolyte decomposition on the negative electrode is suppressed from functionalized coating.…”