Article Highlight | 12-Dec-2025

Host–guest inversion engineering induced superionic composite solid electrolytes for high‑rate solid‑state alkali metal batteries

Shanghai Jiao Tong University Journal Center

Host–Guest Inversion Engineering Induced Superionic Composite Solid Electrolytes for High‑Rate Solid‑State Alkali Metal Batteries

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  • Host–guest inversion engineering is proposed to create poly(vinylidene fluoride-hexafluoropropylene) (PVH)-in-SiO2 composite solid electrolytes with an original “polymer guest-in-ceramic host” architecture, exhibiting optimized interfacial contacts and comprehensive properties.
  • The PVH-in-SiO2 exhibits an overwhelming ionic conductivity of 1.32 × 10−3 S cm−1 at 25 °C, with an ultralow residual solvent content of 2.9 wt%. In addition, the LiFePO4|PVH-in-SiO2|Li full cells deliver a significant capacity retention of 92.9% at an ultrahigh rate of 3C after 300 cycles at 25 °C.
  • The host–guest inversion engineering is a versatile strategy, as proved by preparing Na+ and K+-based PVH-in-SiO2 composite solid electrolytes, delivering excellent ionic conductivity of 10−4 S cm−1 at 25 °C (vs. 10−6–10−5 S cm−1 of previous reports).
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Credit: Xiong Xiong Liu, Long Pan*, Haotian Zhang, Pengcheng Yuan, Mufan Cao, Yaping Wang, Zeyuan Xu, Min Gao, Zheng Ming Sun*

Composite solid electrolytes (CSEs) promise safer, energy-dense batteries, yet room-temperature conductivities ≥1 mS cm-1 still rely on costly, moisture-sensitive active ceramics. Now, researchers at Southeast University (China), led by Prof. Long Pan and Prof. Zheng-Ming Sun, overturn the conventional “ceramic-guest-in-polymer-host” paradigm through host–guest inversion engineering, creating a “PVH-in-SiO2” architecture that delivers 1.32 × 10-3 S cm-1 at 25 °C with only 2.9 wt % residual solvent—a 10× leap over passive-ceramic CSEs and competitive with best-in-class oxides/sulfides.

Why This Electrolyte Matters

  • Superionic Highways: 158 nm SiO2 nanoparticles densely wrap interconnected PVDF-HFP micro-spheres, maximizing continuous SiO2/PVH interfaces where DFT shows Li⁺ diffusion barriers as low as 0.26 eV (vs 0.51 eV for SiO2/SiO2).
  • Solvent-Lite: 2.9 wt % residual solvent (8–15 wt % typical) suppresses Li-metal side reactions while 87 % free-TFSI⁻ (Raman) ensures high mobile-ion concentration.
  • Universal Alkali-Ion: Identical protocol yields 3.0 × 10-4 S cm-1 (Na⁺) and 2.6 × 10-4 S cm-1 (K⁺)—14× & 64× boosts versus polymer-only analogues.
  • Scalable & Flexible: 11 cm-diameter, foldable films cast from water/acetone in minutes; provisional patent filed (CN202310061247.3).

Electrochemical Performance

  • LiFePO4|PVH-in-SiO2|Li (25 °C)
    – 157 mAh g-1 @ 0.1C; 92.9 % retention after 300 cycles at 3C (capacity fade <0.025 % per cycle).
    – High-loading (9.2 mg cm-2) cathode: 136 mAh g-1, 92 % retention/100 cycles.
  • NCM622|PVH-in-SiO2|Li (4.3 V cut-off)
    – 147 mAh g-1 @ 0.2C, >100 cycles with 99.9 % CE.
  • Na & K Full-Cells
    – NVP|PVH-in-SiO2-Na|Na: 95 mAh g-1, 86 % retention/500 cycles @ 0.5C.
    – KPB|PVH-in-SiO2-K|K: 84 % retention/500 cycles; PVH-K cells fail within 5 cycles.

Mechanistic Insights

SS-NMR tracking of 6Li shows 53 % of Li⁺ resides at SiO2/PVH interfaces after cycling (vs 2 % initially). MD simulations give Li⁺ diffusion coefficient 3.3 × 10-9 cm2 s-1 in PVH-in-SiO2, 3× steeper MSD slope than SiO2-in-PVH. Finite-element modeling visualizes current density 102–103 mA cm-2 localized along interfacial highways, confirming they dominate bulk transport.

Challenges & Next Steps

Thickness reduction to ≤25 µm and ceramic volume fraction optimization (currently 41 %) are underway to push areal capacity >3 mAh cm-2 with Ni-rich cathodes. Roll-to-roll coating trials with industry partners target pilot-scale pouch cells (2 Ah) by late-2025.

This host–guest inversion strategy turns low-cost, passive SiO2 into a superionic scaffold, offering a universal, solvent-lean platform for solid-state Li, Na and K batteries without the price or moisture penalties of active ceramics.

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