Overcoming Chemo-Mechanical Instability at Silicon-Solid Electrolyte Interfaces in Solid-State Batteries

Abstract

Silicon is the preferred choice for lithium-ion battery anodes due to its high theoretical capacity and low lithiation potential. However, achieving high areal capacity with silicon anodes in solid-state batteries (SSBs) is challenging because of poor electronic and ionic conductivity, as well as chemo-mechanical instability at the silicon|solid electrolyte (Si|SE) interfaces. Here, we propose fabricating and testing composite anodes made of nanosized Si powder embedded in partially fluorinated graphene (Si-FG) and Li₆PS₅Cl (LPSCl) sulfide SE. X-ray photoelectron spectroscopy revealed that the in situ formation of LiF-rich SEI can protect against SE decomposition at the interface in the Si-FG-LPSCl composite anode. FIB-SEM and EIS analyses also indicate a stable structure and low interfacial resistance after one cycle for a composite anode containing FG. The incorporation of partially FG enhances both electronic (through heterojunction formation with Si) and ionic conductivities, buffers significant volume changes, and ensures chemo-mechanical stability in the composite anode. The Si-FG-LPSCl composite anode in SSBs delivered high discharge/charge capacities of 3499/2994 mAh g^-1 at a C-rate of C/20 and an ICE of 85.6% in a half cell. This work provides valuable insights for advancing high-capacity Si composite anodes to meet future energy needs.

Keywords: all-solid-state batteries; chemo-mechanics; conductive agent; in situ LiF formation; silicon anode.

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Characterization of Si-FG composite: XRD patterns of Si and Si-FG composite (a), zoom in around peak (111) (b), Raman spectrum of FG, Si, and Si-FG composite (c). Surface SEM images of Si (d), FG (e), Si-FG (f), and EDS elemental mapping of Si-FG: Si (g), O (h), C (i), and F (j).

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TEM image (a), HRTEM and inset enlarged images (b), SAED pattern (c), HAADF image (d), and corresponding EDS mapping (e, f) of Si. TEM image (g), HRTEM and inset enlarged images (h), SAED pattern (i), HAADF image (j), and corresponding EDS mapping (k–n) of Si-FG composite.

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Morphology of Si anodes evolution analysis: Cross-sectional FIB-SEM of pristine state Si (a), Si-LPSCl (b), and Si-FG-LPSCl (c); lithiated Si (d), Si-LPSCl (e), and Si-FG-LPSCl (f), delithiated Si (g), Si-LPSCl (h), and Si-FG-LPSCl (i), in half-cell configuration.

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Electrochemical stability analysis of Si-SE and Si-FG-SE composite anodes: XPS spectra of Si 2p (a), S 2p (b), and Li 1s (c) for Si-LPSCl anode, and Si 2p (d), S 2p (e), and Li 1s (f) for Si-FG-LPSCl anode, at pristine state (top) and after initial delithiation (bottom).

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CV profile of Si-FG-LPSCl anode (a), the first CV profile of Si anodes: Si, Si-LPSCl, and Si-FG-LPSCl (b). Equivalent circuit fitting diagram (c), the Nyquist plots of Si anodes after the first discharge (lithiation) (d) and after the first charge (delithiation) (e); the corresponding fitted parameters result after lithiation (f) and delithiation (g).

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Si anodes electrochemical performance in half-cell configuration in Si|SE|In–Li. Si-FG-LPSCl composite anode preparation and cell assembly illustration (a). For the charge/discharge curve: Si (b), Si-LPSCl (c), and Si-FG-LPSCl (d), the half-cell assembly procedure is the same as described in (a). The corresponding dQ/dV of Si anodes: Si (e), Si-LPSCl (f), and Si-FG-LPSCl (g).

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Electrochemical performance of Si anodes in a full-cell. The full-cell performance of SiFG-LPSCl at C/20 (a). Cycling performance comparison of Si anodes in full cell with high loading of cathode, 22.93 mg cm^–2 at C/10 (b); rate capability of the three Si anodes (c), charge–discharge profiles of the three Si anodes at different C-rates: Si (d), Si-LPSCl (e), and Si-FG-LPSCl (f).