Key Takeaways & Executive Findings
- •• Host–guest inversion engineering creates a novel 'polymer guest-in-ceramic host' architecture (PVH-in-SiO2) that optimizes interfacial contacts and comprehensive properties. • The PVH-in-SiO2 electrolyte achieves an exceptional ionic conductivity of 1.32 × 10−3 S cm−1 at 25 °C with an ultralow residual solvent content of 2.9 wt%. • LiFePO4|PVH-in-SiO2|Li full cells demonstrate a significant capacity retention of 92.9% at an ultrahigh rate of 3C after 300 cycles at 25 °C. • The strategy is versatile, extending to Na+ and K+ based PVH-in-SiO2 CSEs, delivering excellent ionic conductivity of 10−4 S cm−1 at 25 °C, outperforming previous reports.
Abstract
Composite solid electrolytes (CSEs) are promising for solid-state Li metal batteries but suffer from inferior room-temperature ionic conductivity due to sluggish ion transport and high cost due to expensive active ceramic fillers. Here, a host–guest inversion engineering strategy is proposed to develop superionic CSEs using cost-effective SiO2 nanoparticles as passive ceramic hosts and poly(vinylidene fluoride-hexafluoropropylene) (PVH) microspheres as polymer guests, forming an unprecedented “polymer guest-in-ceramic host” (i.e., PVH-in-SiO2) architecture differing from the traditional “ceramic guest-in-polymer host”. The PVH-in-SiO2 exhibits excellent Li-salt dissociation, achieving high-concentration free Li+. Owing to the low diffusion energy barriers and high diffusion coefficient, the free Li+ is thermodynamically and kinetically favorable to migrate to and transport at the SiO2/PVH interfaces. Consequently, the PVH-in-SiO2 delivers an exceptional ionic conductivity of 1.32 × 10−3 S cm−1 at 25 °C (vs. typically 10−5–10−4 S cm−1 using high-cost active ceramics), achieved under an ultralow residual solvent content of 2.9 wt% (vs. 8–15 wt% in other CSEs). Additionally, PVH-in-SiO2 is electrochemically stable with Li anode and various cathodes. Therefore, the PVH-in-SiO2 demonstrates excellent high-rate cyclability in LiFePO4|Li full cells (92.9% capacity-retention at 3C after 300 cycles under 25 °C) and outstanding stability with high-mass-loading LiFePO4 (9.2 mg cm−1) and high-voltage NCM622 (147.1 mAh g−1). Furthermore, we verify the versatility of the host–guest inversion engineering strategy by fabricating Na-ion and K-ion-based PVH-in-SiO2 CSEs with similarly excellent promotions in ionic conductivity. Our strategy offers a simple, low-cost approach to fabricating superionic CSEs for large-scale application of solid-state Li metal batteries and beyond.
1. Introduction
The ever-growing anxieties about the battery life and safety of liquid lithium-ion batteries are boosting the flourishing development of solid-state Li metal batteries as they can simultaneously improve energy density and inhibit thermal runaway [1–3]. Solid-state electrolytes are fundamental to solid-state Li metal batteries, requiring decent interfacial contacts, high mechanical modulus, wide electrochemical window, and, in particular, high ionic conductivity (at least 10−3 S cm−1 at room temperature) to meet practical applications [4–6]. In this sense, composite solid-state electrolytes (CSEs), which are commonly comprised of active ceramics as fillers (i.e., guests) and polymers as matrices (i.e., hosts) to form traditional “ceramic guest-in-polymer host” architectures, have provoked significant interest. Because active ceramic guests are ion-conducting, CSEs can integrate the high modulus and ionic conductivity of active ceramic guests with the excellent processability and interfacial compatibility of polymer hosts [7, 8].
To date, various active ceramic guests have been introduced, including oxides (e.g., Li7La3Zr2O12) [9–13], sulfides (e.g., Li6PS5Cl) [14, 15], and phosphates (e.g., Li1.3Al0.3Ti1.7(PO4)3) [16, 17]. However, CSEs based on active ceramic guests are still far from practical applications because of their insufficient ionic conductivities (generally 10−5–10−4 S cm−1 at room temperature) [18–20]. Another critical challenge is induced by the high cost, harsh synthesis, and complex handling of active ceramic guests [21, 22]. To address these problems, passive ceramics, which are not ion conductors, have been proposed as guests to incorporate with polymer hosts, including SiO2, Al2O3, TiO2, etc. [23, 24]. Compared to active ceramics, passive ceramics possess advantages such as lower cost, simpler preparation, and better compatibility with polymers, but their incorporation often leads to reduced ionic conductivity due to dilution of ion-conducting phases. Therefore, innovative strategies are needed to fully exploit the benefits of passive ceramics while maintaining high ionic conductivity.
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Xiong Xiong Liu, Long Pan, Haotian Zhang, Pengcheng Yuan, Mufan Cao, Yaping Wang, Zeyuan Xu, Min Gao, Zheng Ming Sun (2025). Host–Guest Inversion Engineering Induced Superionic Composite Solid Electrolytes for High-Rate Solid-State Alkali Metal Batteries. Nano-Micro Letters. https://doi.org/10.1007/s40820-025-01691-7
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Frequently Asked Questions
What is host–guest inversion engineering in the context of composite solid electrolytes?
Host–guest inversion engineering is a novel strategy that inverts the traditional roles of polymer and ceramic in composite solid electrolytes. Instead of using active ceramic fillers as guests in a polymer host, it uses passive ceramic nanoparticles (e.g., SiO2) as the host and polymer microspheres (e.g., PVH) as the guest, forming a 'polymer guest-in-ceramic host' architecture. This design optimizes interfacial contacts and enhances ionic conductivity.
How does the PVH-in-SiO2 composite solid electrolyte achieve high ionic conductivity?
The PVH-in-SiO2 electrolyte achieves high ionic conductivity (1.32 × 10−3 S cm−1 at 25 °C) by promoting excellent Li-salt dissociation, leading to high concentration of free Li+ ions. The low diffusion energy barriers and high diffusion coefficient at the SiO2/PVH interfaces facilitate fast ion transport, even with an ultralow residual solvent content of 2.9 wt%.
What are the performance benefits of PVH-in-SiO2 in solid-state batteries?
PVH-in-SiO2 demonstrates excellent high-rate cyclability in LiFePO4|Li full cells, with 92.9% capacity retention at 3C after 300 cycles at 25 °C. It also shows outstanding stability with high-mass-loading LiFePO4 (9.2 mg cm−1) and high-voltage NCM622 (147.1 mAh g−1), indicating its practical applicability.
Is the host–guest inversion engineering strategy versatile?
Yes, the strategy is versatile. It has been successfully applied to fabricate Na-ion and K-ion-based PVH-in-SiO2 composite solid electrolytes, which also exhibit excellent ionic conductivity (10−4 S cm−1 at 25 °C), outperforming previous reports (10−6–10−5 S cm−1). This demonstrates its potential for various alkali metal battery systems.
What are the advantages of using passive ceramics like SiO2 over active ceramics?
Passive ceramics like SiO2 are cost-effective, simpler to prepare, and easier to handle compared to active ceramics. They also offer better compatibility with polymers. The host–guest inversion engineering leverages these advantages while overcoming the typical drawback of reduced ionic conductivity, resulting in a superionic electrolyte at lower cost.
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