Enabling Long-Cycling Life of Si-on-Graphite Composite Anodes via Fabrication of a Multifunctional Polymeric Artificial Solid–Electrolyte Interphase Protective Layer

Abstract

The energy density of lithium-ion batteries (LIBs) can be meaningfully increased by utilizing Si-on-graphite composites (Si@Gr) as anode materials, because of several advantages, including higher specific capacity and low cost. However, long cycling stability is a key challenge for commercializing these composites. In this study, to solve this issue, we have developed a multifunctional polymeric artificial solid−electrolyte interphase (A-SEI) protective layer on carbon-coated Si@Gr anode particles (making Si@Gr/C-SCS) to prolong the cycling stability in LIBs. The coating is made of sulfonated chitosan (SCS) that is crosslinked with glutaraldehyde promoting good ionic conduction together with sufficient mechanical strength of the A-SEI. The focused ion beam-scanning electron microscopy and high-resolution transmission electron microscopy images show that the SCS is uniformly coated on the composite particles with thickness in nanometer. The anodes are investigated in Li metal cells Si@Gr/C-SCS||Li metal) and lithium-ion full-cells (LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM-622)||Si@Gr/C-SCS) to understand the material/electrode intrinsic degradation as well as the impact of the polymer coating on active lithium losses because of the continuous SEI (re)formation. The anode composites exhibit a high capacity reaching over 600 mAh g −1 , and even without electrolyte optimization, the Si@Gr/C-SCS illustrates a superior long cycle life performance of up to 1000 cycles (over 67% capacity retention). The excellent long-term cycling stability of the anodes was attributed to the SCS polymer coating acting as the A-SEI. The simple polymer coating process is highly interesting in guiding the preparation of long-cycle-life electrode materials of high-energy LIB cells.

Efficient Utilization of Macropores as Artificial Solid–Electrolyte Interphase Channels for High-Capacity Silicon/Graphite Anode Materials

“…For comparison, a sample is prepared by a conventional solution coating method, which our group has already developed for solid/nonporous particles . Typically, SCS (0.03 g) and GA (0.003 g) were dissolved in DI water.…”

“…Si/Gr composite powder was provided by a local producer in Taiwan based on a proprietary process. SCS and GA were prepared as reported in our previous paper . The IWI method is also known as capillary impregnation, a well-known method for the fabrication of heterogeneous catalysts .…”

“…SCS and GA were prepared as reported in our previous paper. 18 The IWI method is also known as capillary impregnation, a well-known method for the fabrication of heterogeneous catalysts. 19 This method could be highly suitable for the polymer coating of porous materials.…”

“…The mechanical stability of the cross-linked SCS (SCS + GA) is investigated using the dynamic mechanical analysis from our previous study, and the film showed a high Young's modulus of over 1 GPa. 18 Free amine and hydroxyl groups in the SCS polymer chain can have a binding affinity with the surface of the Si anode. The as-prepared mechanically robust A-SEI induced Si/Gr composite via this unique approach exhibits a remarkable cycling performance for hundreds of charge− discharge cycles.…”

“…Moreover, SCS is cross-linked with GA to improve the mechanical strength of the polymer to sustain the massive volume expansion of Si. The mechanical stability of the cross-linked SCS (SCS + GA) is investigated using the dynamic mechanical analysis from our previous study, and the film showed a high Young’s modulus of over 1 GPa . Free amine and hydroxyl groups in the SCS polymer chain can have a binding affinity with the surface of the Si anode.…”