Lacunary strategy facilitates catalytic conversion of polysulfides by polyoxometalates for high-performance quasi-solid-state Li–S batteries based on LLZTO electrolyte

Abstract

Solid-state lithium–sulfur (Li–S) batteries are deemed next-generation energy storage systems based on their high theoretical energy density and enhanced safety. However, challenges such as sluggish sulfur conversion kinetics and the polysulfide shuttle effect remain critical obstacles to their practical deployment. Herein, a novel surface-modified garnet-type Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) solid-state electrolyte (SSE) is proposed, utilizing a mono-lacunary Keggin-type polyoxometalate (PW₁₁) to overcome the aforementioned limitations. The optimized PW₁₁-LLZTO composite electrolyte exhibits a uniform surface morphology and improved interfacial stability with lithium metal. Symmetric Li/PW₁₁-LLZTO/Li cells achieve a critical current density of 0.9 mA cm⁻² and stable cycling over 800 h with low polarization. When applied in quasi-solid-state Li–S batteries, the PW₁₁-LLZTO SSE significantly suppresses polysulfide shuttling, enhances sulfur redox kinetics, and delivers a superior reversible capacity of 619.4 mAh g⁻¹ after 200 cycles at 1C. Density functional theory (DFT) calculations reveal that the lacunary structure alters the electron cloud density of oxygen atoms in PW₁₁, resulting in enhanced nucleophilicity and stronger Lewis basicity, which in turn strengthens its binding interaction with Li⁺. Therefore, the mono-lacunary PW₁₁ exhibits efficient Lewis acid–base interactions between the oxygen atoms of polyoxoanions and Li moieties in polysulfides, thereby facilitating the conversion kinetics of polysulfides. This work demonstrates the great potential of the lacunary strategy of polyoxometalates in designing high-performance SSEs for advanced quasi-solid-state Li–S batteries.

---

Introduction

The widespread adoption of portable electronic devices has established lithium-ion batteries as an integral component of modern daily life, driving an increasing demand for advanced energy storage systems with higher energy density.^1–3 Lithium–sulfur (Li–S) batteries are considered as promising candidates for next-generation high-energy-density systems. However, the limited cycling stability and safety concerns associated with conventional liquid electrolytes remain major obstacles to their commercialization.^4–6 In the course of the charge and discharge processes of liquid Li–S batteries, the intermediate lithium polysulfides (LiPSs) dissolve into the liquid electrolyte.^7–10 The shuttle effect of LiPSs, along with active sulfur consumption due to their parasitic reactions, thus deteriorates the cycling performance of Li–S batteries.^11–13 Meanwhile, the use of lithium metal anodes in liquid systems raises safety concerns, as lithium dendrite formation can cause internal short circuits, thereby leading to serious safety hazards.^14,15 It is widely acknowledged that all-solid-state batteries offer exceptional intrinsic safety and a broad electrochemical stability window. Unavoidably, there is a rigid interfacial contact between the electrolyte and electrodes. The interface impedance is high and the ion transmission is difficult, which easily lead to a low utilization rate of active substances (even lower than 80% in the early stage) and poor cycling performance.¹⁶ Moreover, in all-solid-state Li–S batteries, the conversion of polysulfides proceeds via a solid–solid reaction, which suffers from sluggish kinetics and imposes extremely stringent requirements on cathode architecture design. For quasi-solid-state Li–S batteries, the incorporation of trace amounts of electrolyte enables effective wetting of both the cathode and the intermediate electrolyte layer, thereby significantly reducing the interfacial impedance while only marginally compromising safety. The polysulfide conversion mechanism resembles that of liquid-electrolyte batteries (a solid–liquid–solid conversion process), and the associated kinetic limitations are significantly alleviated.¹⁷ Meanwhile, a quasi-solid-state Li–S battery system can employ the same conventional cathodes as liquid-electrolyte batteries, enabling simple processing and facile fabrication.^18,19 However, it still faces challenges such as low utilization of the sulfur cathode, slow conversion kinetics, and the persistence of a partial shuttle effect.^20,21 Therefore, it is urgent to explore the appropriate solid-state electrolytes (SSEs) with certain functionality to address these issues.

Currently, there are three types of SSEs: inorganic, polymer, and inorganic/polymer composite electrolytes.^22,23 Polymer electrolytes and composite electrolytes exhibit good flexibility but are limited by their low ionic conductivity.^24,25 In comparison, inorganic SSEs demonstrate high room-temperature ionic conductivity.²⁶ Among them, the garnet-type Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) is a candidate electrolyte owing to its good electrochemical stability for lithium metal and wide electrochemical window.^27,28 However, relying solely on LLZTO SSEs cannot resolve the aforementioned issues of the sulfur cathode. Functional modification of LLZTO SSEs may present an effective solution. Owing to the distinctive and structurally stable properties, multiple oxidation states, and adjustable redox potentials, polyoxometalates (POMs) have garnered extensive application in fields such as photochemistry, catalysis, biochemistry, and energy storage.^29–54 In recent years, several excellent POM-based materials have been demonstrated to suppress the shuttle effect of liquid Li–S batteries and accelerate sulfur conversion kinetics, including H₃[PW₁₂O₄₀],⁵⁵ H₃[PMo₁₂O₄₀],⁵⁶ K₆P₂W₁₈O₆₂,⁵⁷ (NH₄)₆V₁₀O₂₈,⁵⁸etc. Notably, Dong et al. developed an Ag(I)-substituted Keggin-type POM, K₃[H₃AgIPW₁₁O₃₉], in which the incorporation of Ag atoms leads to a localization of the highest occupied molecular orbital (HOMO) around the oxygen atoms adjacent to the Ag sites.³¹ Therefore, the oxygen atoms around the Ag sites readily participate in Lewis acid–base interactions with polysulfides. The Ag⁺ ions act as Lewis acid sites that adsorb the basic S atoms of LiPSs, while the terminal oxygen atoms serve as Lewis base sites interacting with the acidic Li termini. Afterwards, Ni et al. constructed a POM-cyclodextrin supramolecular framework.⁵⁹ The cyclodextrin cavities physically confine polysulfides through host–guest recognition, while the oxygen atoms of two adjacent basic W₃O₁₃ triplets in the [B-β-SbW₉O₃₃]⁹⁻ structure engage in Lewis acid–base interactions with the lithium atoms of polysulfides, thereby playing a dual role in strongly anchoring polysulfides to suppress the shuttle effect and catalyzing the liquid–solid conversion kinetics. Compared to saturated POMs, lacunary POMs lack one or several coordination polyhedra.^60,61 Due to the increased anionic charge resulting from the removal of partial ligands from the saturated POM framework, the resulting lacunary anions become highly nucleophilic and readily react with electrophilic groups.⁶² Based on this characteristic, lacunary POMs may exhibit stronger Lewis acid–base interactions with polysulfides. If the lacunary POMs are applied to the LLZTO SSEs, it is expected to overcome the key challenges existing in quasi-solid-state Li–S batteries.

In this work, we propose a functional modification strategy for garnet-type LLZTO SSEs using a representative lacunary POM, tetrabutylammonium 11-tungstophosphate ([(n-C₄H₉)₄N]₄H₃PW₁₁O₃₉, denoted as PW₁₁), and systematically compare its performance with the saturated Keggin-type phosphotungstate ([(n-C₄H₉)₄N]₃PW₁₂O₄₀, denoted as PW₁₂). The primary objective is to leverage the unique structural features and high catalytic activity of lacunary POMs to enhance the interfacial stability, suppress the polysulfide shuttle, and accelerate sulfur conversion kinetics in quasi-solid-state Li–S batteries. A systematic series of characterization methodologies and electrochemical measurements are applied to investigate the morphology, structure, and electrochemical properties of POM-LLZTO SSEs. Furthermore, density functional theory (DFT) calculations are conducted to gain deeper insights into the interaction mechanisms between the lacunary POMs and LiPSs. This study aims to provide a novel and effective lacunary strategy of POMs for developing high-performance SSEs, thereby advancing the practical implementation of quasi-solid-state Li–S batteries.

Experimental section

LLZTO SSEs, PW₁₁, and PW₁₂ were synthesized according to the modified literature procedures.^63–65 Specifically, a certain amount of PW₁₁ was uniformly dissolved in 20 mL of acetonitrile. By adjusting the mass of PW₁₁, solutions of 0.5, 2.5, and 5.0 mg mL⁻¹ were prepared, respectively. Subsequently, LLZTO SSEs were immersed in the aforementioned solution and reacted at 90 °C for 3 days. After the reactor was allowed to cool, the samples were cleaned, vacuum-dried, and stored in a glove box free of water and oxygen. The final obtained samples were, respectively, labeled as PW₁₁-LLZTO-I, PW₁₁-LLZTO-II, and PW₁₁-LLZTO-III. For comparison, PW₁₂-LLZTO was prepared using the same process as described above, and the PW₁₂/acetonitrile solution was 2.5 mg mL⁻¹.

Results and discussion

For effective loading of PW₁₁ onto the LLZTO surface, a uniform distribution across this surface is essential. It can be seen from Fig. S1 that the diameter and thickness of the LLZTO pellet are 9.619 mm and 1.144 mm, respectively. Fig. S2 presents the scanning electron microscopy (SEM) image of pristine LLZTO SSE, showing a smooth surface. When PW₁₁ is introduced (as presented in Fig. 1a), the surface distribution of PW₁₁ is uneven with incomplete coverage for PW₁₁-LLZTO-I, which is not conducive to the transport of lithium ions and the conversion of polysulfides. As the PW₁₁ content increases, PW₁₁-LLZTO-II with an appropriate PW₁₁ content exhibits uniform and dense surface coverage (see Fig. 1b). However, the surface of PW₁₁-LLZTO-III shows signs of cracking due to the excessive PW₁₁ (see Fig. 1c). The elemental mapping images verify the uniform distribution of P, W, and O elements in the PW₁₁-LLZTO-II SSE (Fig. 1d), and the digital photograph is shown in Fig. S3. As observed from Fig. 1e, X-ray diffraction (XRD) is performed on three PW₁₁-LLZTO SSEs. All PW₁₁-LLZTO SSEs exhibit a standard cubic garnet phase of Li₅La₃Nb₂O₁₂ (JCPDS no. 80-0457). Note that no diffraction peaks corresponding to PW₁₁ are observed, which may be attributed to the relatively low content of PW₁₁. Fig. 1f shows the Fourier transform infrared (FTIR) spectrum of PW₁₁-LLZTO-II SSE. This spectrum presents some signals of PW₁₁, but they are still not very distinct. In order to verify whether the PW₁₁ is damaged during the process of preparing PW₁₁-LLZTO SSEs, we prepare PW₁₁-LLZTO powder using the same treatment method, except that it is not pressed into tablets. As expected, the characteristic absorption peaks of PW₁₁ are clearly visible (Fig. 1g). Specifically, the characteristic absorption peak of the P–O bond appears at 1049 cm⁻¹, and the characteristic absorption peak at 949 cm⁻¹ is caused by the vibrational stretch of W=O. The peaks at 887 cm⁻¹ and 814 cm⁻¹ are ascribed to the bridging vibrations of W–O_c–W and W–O_b–W, respectively.⁶⁴ X-ray photoelectron spectroscopy (XPS) is used to investigate the elemental composition as well as the chemical valence states of PW₁₁-LLZTO-II SSE. For the W 4f spectrum (Fig. 1h), the peaks at 37.0 eV and 34.8 eV correspond to the W 4f_5/2 and W 4f_7/2 orbitals, respectively. In Fig. 1i, the spectral peaks at 532.6 eV and 531.3 eV are assigned to the adsorbed oxygen on the PW₁₁ surface and lattice oxygen, respectively. These results further demonstrate the presence of PW₁₁ on the surface of LLZTO SSEs.

Fig. 1 The surface SEM images of (a) PW₁₁-LLZTO-I, (b) PW₁₁-LLZTO-II, and (c) PW₁₁-LLZTO-III SSEs. (d) The EDS mappings of PW₁₁-LLZTO-II SSE. (e) XRD patterns of PW₁₁-LLZTO-I, PW₁₁-LLZTO-II, and PW₁₁-LLZTO-III SSEs. (f) FTIR spectra of PW₁₁-LLZTO-II and pristine PW₁₁. (g) FTIR spectra of PW₁₁-LLZTO powder and pristine PW₁₁. (h) W 4f and (i) O 1s high-resolution XPS spectra of PW₁₁-LLZTO-II SSE.

The critical current density (CCD) is a key parameter for evaluating the stability of the lithium/SSE interface.⁶⁶ The Li/LLZTO/Li symmetric cell exhibits a short-circuit current density of merely 0.3 mA cm⁻², which can be ascribed to insufficient interfacial contact between bare LLZTO SSE and metallic lithium (Fig. 2a). In contrast, the CCD values of Li/PW₁₁-LLZTO-I/Li, Li/PW₁₁-LLZTO-II/Li, and Li/PW₁₁-LLZTO-III/Li symmetric cells are 0.5, 0.9, and 0.7 mA cm⁻², respectively (Fig. 2b–d). This phenomenon indicates that the introduction of PW₁₁ can enhance interfacial stability, especially for PW₁₁-LLZTO-II with an appropriate content of PW₁₁. Galvanostatic cycling measurements further evaluate the long-term stability of these symmetric cells (Fig. 2e). At a current density of 0.2 mA cm⁻² and an areal capacity of 0.1 mAh cm⁻², the Li/LLZTO/Li symmetric cell exhibits relatively high overpotentials. By comparison, three Li/PW₁₁-LLZTO/Li symmetric cells present enhanced cycling performance. Specifically, the overpotential of the Li/PW₁₁-LLZTO-I/Li symmetric cell is increased from 36 mV after 1 cycle to 43 mV after 400 cycles. The Li/PW₁₁-LLZTO-III/Li symmetric cell maintains at approximately 35 mV after cycling for over 800 h. Notably, the Li/PW₁₁-LLZTO-II/Li symmetric cell exhibits no short circuit or considerable voltage polarization, achieving a stable overpotential as low as 15 mV over all cycles. Subsequently, quasi-solid-state Li–S batteries are assembled using C/S composite cathodes to test the performance of PW₁₁-LLZTO SSEs. Fig. 2f compares the cyclability of Li–S batteries with different SSEs at a rate of 0.2C. The Li/LLZTO/S cell shows a rapid decay rate, with its discharge capacity fading to 501.2 mAh g⁻¹ following 200 cycles. Fortunately, three Li/PW₁₁-LLZTO/S cells exhibit enhanced reversible capacities. After 200 cycles, the discharge capacities of Li/PW₁₁-LLZTO-I/S and Li/PW₁₁-LLZTO-III/S cells remain at 601.2 mAh g⁻¹ and 750.5 mAh g⁻¹, correspondingly. Notably, the Li/PW₁₁-LLZTO-II/S cell achieves a capacity of 820.1 mAh g⁻¹ in the 200th cycle. These experimental results demonstrate that the PW₁₁-LLZTO-II SSE possesses excellent cycling stability and electrochemical compatibility. In the subsequent work, PW₁₁-LLZTO-II with the optimized PW₁₁ content is further studied. Meanwhile, PW₁₁-LLZTO-II is simplified to PW₁₁-LLZTO.

Fig. 2 Critical current density test of (a) Li/LLZTO/Li, (b) Li/PW₁₁-LLZTO-I/Li, (c) Li/PW₁₁-LLZTO-II/Li, and (d) Li/PW₁₁-LLZTO-III/Li symmetric cells. (e) Galvanostatic cycling curve of Li/LLZTO/Li, Li/PW₁₁-LLZTO-I/Li, Li/PW₁₁-LLZTO-II/Li, and Li/PW₁₁-LLZTO-III/Li symmetric cells at 0.2 mA cm⁻² and 0.1 mAh cm⁻². (f) Cycling performance of Li/LLZTO/S, Li/PW₁₁-LLZTO-I/S, Li/PW₁₁-LLZTO-II/S, and Li/PW₁₁-LLZTO-III/S cells at 0.2C.

To examine the effect of the saturated and lacunary Keggin-type phosphotungstates on SSEs, the PW₁₂-LLZTO SSE is synthesized via a similar method to that of the PW₁₁-LLZTO SSE, and the morphological features are presented in Fig. S4. To further verify whether PW₁₂ is damaged during the preparation of the PW₁₂-LLZTO SSE, we prepare PW₁₂-LLZTO powder using the same treatment method as that used for PW₁₁-LLZTO powder. FTIR spectra show that the characteristic absorption peaks of PW₁₂ are clearly visible (Fig. S5), confirming the structural integrity of PW₁₂. Moreover, Raman spectra (Fig. S6) and XPS (Fig. S7) results confirm the successful synthesis of PW₁₂-LLZTO SSE. The lithium ion migration number (t_Li⁺) represents the fraction of the total conductivity carried by Li⁺.⁶⁷Fig. 3a–c shows the potentiostatic polarization curves measured at 10 mV intervals and the corresponding electrochemical impedance spectroscopy (EIS) results. According to eqn (S1), the t_Li⁺ value of PW₁₁-LLZTO SSE is computed to be 0.40, superior to bare LLZTO SSE (t_Li⁺ = 0.29) and PW₁₂-LLZTO SSE (t_Li⁺ = 0.35). Subsequently, silver paste with a thickness of approximately 335 nm is applied to both sides of the exposed LLZTO, PW₁₁-LLZTO, and PW₁₂-LLZTO SSEs. They are then dried in a vacuum drying oven and assembled into blocking cells for the ion conductivity test. Fig. 3d shows the impedance of each blocking cells, and the ionic conductivity obtained through calculation is shown in Fig. 3e. PW₁₁-LLZTO SSE shows an excellent ionic conductivity of 5.98 × 10⁻⁴ S cm⁻¹, compared with PW₁₂-LLZTO SSE (5.23 × 10⁻⁴ S cm⁻¹) and bare LLZTO SSE (3.98 × 10⁻⁴ S cm⁻¹). The above results indicate that lacunary PW₁₁ facilitates the transmission of lithium ions, thereby facilitating the uniform deposition of lithium ions. As shown in Fig. S8, the Li/PW₁₂-LLZTO/Li symmetrical cell presents the lower CCD value (0.5 mA cm⁻²), which points to the formation of an unstable interphase between the Li anode and the PW₁₂-LLZTO SSE. Fig. 3f shows galvanostatic cycling curve of the Li/PW₁₁-LLZTO/Li and Li/PW₁₂-LLZTO/Li symmetrical cells at 0.2 mA cm⁻² and 0.1 mAh cm⁻². Specifically, the overpotential of the Li/PW₁₂-LLZTO/Li symmetric cell is increased from 24 mV after 1 cycle to 35 mV after 600 h. By contrast, the Li/PW₁₁-LLZTO/Li symmetrical cell has a smaller overall overpotential with more stable cycling. Fig. 3g compares the rate performance of symmetrical cells with PW₁₁-LLZTO and PW₁₂-LLZTO SSEs. For the Li/PW₁₂-LLZTO/Li symmetrical cell, when the current densities are 0.1, 0.2, and 0.4 mA cm⁻², the overpotentials stabilize at 27, 56, and 151 mV, respectively, which exceed that of the Li/PW₁₁-LLZTO/Li symmetric cell. This result further indicates that the PW₁₁ active site has the ability to promote rapid ion and charge transfer, enabling the realization of outstanding electrochemical performance.

Fig. 3 Critical current density under 10 mV polarization for (a) Li/LLZTO/Li, (b) Li/PW₁₁-LLZTO/Li, and (c) Li/PW₁₂-LLZTO/Li symmetric cells. (d) Blocking battery impedance and (e) ionic conductivity of LLZTO, PW₁₁-LLZTO, and PW₁₂-LLZTO SSEs. (f) Galvanostatic cycling curve of Li/PW₁₁-LLZTO/Li and Li/PW₁₂-LLZTO/Li symmetric cells at 0.2 mA cm⁻² and 0.1 mAh cm⁻². (g) Rate performance of Li/PW₁₁-LLZTO/Li and Li/PW₁₂-LLZTO/Li symmetric cells from 0.1 to 0.4 mA cm⁻² under 0.1 mAh cm⁻².

In Fig. S9, no dissolution of the PW₁₁ and PW₁₂ occurs in the electrolyte, and no characteristic peaks of the PW₁₁ and PW₁₂ are found through UV-Vis spectra analysis of the electrolyte supernatant. These results indicate that both PW₁₁ and PW₁₂ exhibit negligible solubility in the electrolyte, thereby ensuring the structural stability of the modified layer during electrochemical cycling. The polysulfide shuttle effect presents a significant drawback for quasi-solid-state Li–S full batteries, leading to substantial performance degradation.⁶⁸ Permeation experiments are demonstrated via the H-type cell configuration to directly assess the efficacy of different functional materials in impeding the diffusion of polysulfides. It is worth noting that the prepared SSEs could not be assembled in the H-type cell due to material issues. Therefore, the powders of LLZTO, PW₁₂, and PW₁₁ are, respectively, coated onto the polypropylene (PP) separator to identify their adsorption effect on polysulfides. As observed from Fig. S10, a bare 1,2-dimethoxyethane (DME) and 1,3-dioxolane (DOL) (v/v = 1 : 1) solvent (the right side) and the DME/DOL solution with 0.2 M Li₂S₆ (the left side) are injected into H-type glass cells and, respectively, separated by the LLZTO, PW₁₁, and PW₁₂ coated separators. Within a span of 6 h, polysulfides express rapid permeation through the LLZTO coated separator, evident by discernible color changes observed in the right ventricle. In contrast, PW₁₂ and PW₁₁ coated separators exhibit a weakened phenomenon of polysulfide migration, with the PW₁₁ coated separator being particularly effective in inhibiting polysulfides. Fig. 4a shows the shuttle currents of Li–S cells with PW₁₁-LLZTO, PW₁₂-LLZTO, and bare LLZTO SSEs. The cell with PW₁₁-LLZTO SSE demonstrates the smallest shuttle current of 0.028 mA cm⁻², compared to those with PW₁₂-LLZTO SSE (0.047 mA cm⁻²) and LLZTO SSE (0.071 mA cm⁻²). This confinement effectively restricts polysulfide migration, thereby improving sulfur utilization and mitigating capacity fade. The enhanced reaction kinetics and electrocatalytic activity toward polysulfides are further investigated by analyzing Tafel plots (Fig. 4b). The electrodes for symmetrical cells are fabricated by blending the constituent materials. A slurry is prepared by, respectively, mixing LLZTO/PW₁₁/PW₁₂ with Super P and polyvinylidene fluoride (PVDF) at a weight ratio of 7 : 2 : 1 in N-methyl-2-pyrrolidone (NMP). This slurry is then coated onto an aluminum foil and vacuum-dried at 60 °C for 12 h. Tafel plots are recorded at a scan rate of 0.1 mV s⁻¹. The cell with PW₁₁ exhibits the most prominent response current, which corresponds to the highest exchange current density of 7.94 × 10⁻⁴ mA cm⁻², surpassing that of PW₁₂ (4.37 × 10⁻⁴ mA cm⁻²) and LLZTO (1.48 × 10⁻⁴ mA cm⁻²). Furthermore, to investigate the catalytic oxidation of Li₂S, linear sweep voltammetry (LSV) measurements are performed on a range of active materials. Consistent with its exceptional catalytic performance, PW₁₁ shows the most favorable onset potential at −0.37 V (Fig. S11), corresponding to the minimal energy barrier for Li₂S oxidation. This conclusion is further validated by the corresponding Tafel plots (Fig. 4c). PW₁₁ shows a minimal Tafel slope of 164.17 mV dec⁻¹, as opposed to those of PW₁₂ (224.88 mV dec⁻¹) and LLZTO (269.05 mV dec⁻¹), respectively.⁶⁹ The precipitation and dissolution capabilities of Li₂S are determined through the Faraday's law (the detailed experimental methods are presented in the SI).¹⁴ As shown in Fig. 4d and e, the PW₁₁ electrode exhibits the fast response time and the high capacity (152.6 mAh g⁻¹) for Li₂S precipitation, indicating its pronounced ability to promote Li₂S nucleation. To clarify the kinetics of Li₂S deposition on different substrates, the dimensionless current–time transients are subsequently plotted. The results can be fitted using four classical electrochemical nucleation models. Fig. 4f and g clearly shows that, in contrast to PW₁₂, PW₁₁ follows a three-dimensional (3D) growth model, which is favorable for enhancing deposition capacity. The 3D Li₂S deposition behavior leads to a lower nucleation density and suppresses electrode surface passivation, thereby promoting rapid phase transformation during the liquid–liquid/solid conversion process, accelerating LiPS redox kinetics, and underpinning outstanding long-term cycling stability. The oxidation of deposited Li₂S is studied by potentiostatic charging (Fig. 4h and i). Clearly, the dissolution capacity of PW₁₁ is higher than that of PW₁₂, indicating that the PW₁₁ active site notably promotes the solid–liquid conversion from Li₂S to LiPSs. These results collectively demonstrate that PW₁₁ possesses superior catalytic activity toward both the precipitation and dissolution of Li₂S. In Fig. S12, the results of 100 consecutive cyclic voltammetry (CV) scans demonstrate that both PW₁₁ and PW₁₂ possess the enduring electrochemical stability.

Fig. 4 (a) Shuttle current tests of Li/PW₁₁-LLZTO/S, Li/PW₁₂-LLZTO/S, and Li/LLZTO/S cells. (b) Tafel plot of symmetric cells with LLZTO, PW₁₂, and PW₁₁ electrodes. (c) The corresponding Tafel plots of sulfide oxidation reactions with different electrodes. Fitting of current vs. time curve for potentiostatic discharge at 2.05 V on (d) PW₁₁ and (e) PW₁₂. Dimensionless transient profiles at 2.05 V for (f) PW₁₁ and (g) PW₁₂. Potentiostatic charge profiles at 2.35 V for (h) PW₁₁ and (i) PW₁₂.

CV tests are operated at a sweep rate of 0.1 mV s⁻¹ within the voltage window of 1.7 V–2.8 V (Fig. 5a).⁷⁰ For the Li–S cell with PW₁₁-LLZTO SSE, two peaks at 2.21 V and 1.87 V are observed, characteristic of the reduction of S₈ to Li₂S_x (4 ≤ x ≤ 8) and its subsequent conversion to Li₂S₂/Li₂S, respectively. Conversely, the oxidation peak at 2.52 V corresponds to the conversion of Li₂S₂/Li₂S to Li₂S_x and finally to S₈. The Li–S cell employing the PW₁₁-LLZTO SSE exhibits a lower oxidation potential and a higher reduction potential than that with the PW₁₂-LLZTO SSE, demonstrating that PW₁₁ effectively reduces electrochemical polarization and enhances the reversible specific capacity. Furthermore, the excellent overlap of CV curves for the Li/PW₁₁-LLZTO/S cell demonstrates its superior electrochemical reversibility and stability (Fig. S13). It can be seen from Fig. S14 that the self-discharge of the Li/PW₁₁-LLZTO/S cell is slower than that of Li/PW₁₂-LLZTO/S and Li/LLZTO/S cells during the 100 h evaluation. The open-circuit voltage of the Li/PW₁₁-LLZTO/S cell decreases to 2.51 V at 18 h and then remains nearly steady for the remaining test period. It can be seen from Fig. 5b that the Li/PW₁₁-LLZTO/S cell exhibits lower charge transfer resistance, indicating that PW₁₁ can effectively enhance the lithium-ion transmission capacity of the interface. The equivalent circuit shown in Fig. S15 is used to simulate EIS curves. Fig. 5c compares the cycling performance of Li–S cells at a rate of 0.2C. The Li/PW₁₂-LLZTO/S cell shows a rapid decay rate, with its discharge capacity fading to 670.6 mAh g⁻¹ after 200 cycles. The Li/PW₁₁-LLZTO/S cell achieves a capacity of 820.1 mAh g⁻¹ in the 200th cycle. The average Coulomb efficiency of the Li/PW₁₁-LLZTO/S cell exceeds 99.5%, which is higher than that of the Li/PW₁₂-LLZTO/S cell (99.2%). The PW₁₁-LLZTO SSE is retrieved from the cycled cell after cycling at 0.2C. In Fig. S16, the SEM image confirms that the PW₁₁-LLZTO SSE retains its structural integrity, with no observable cracks or defects, demonstrating excellent mechanical robustness and cycling durability. EDS mapping further verifies the uniform elemental distribution of the PW₁₁ component, supporting its sustained functionality during long-term electrochemical operation. To comprehensively assess the long-term interfacial stability, EIS data collected after battery cycling are presented in Fig. S17. Compared with the Li/PW₁₂-LLZTO/S cell, the Li/PW₁₁-LLZTO/S cell has the lower charge transfer resistance, indicating the stable interface compatibility during the cycling process. As evidenced by Fig. 5d, the Li/PW₁₂-LLZTO/S cell exhibits the rapid capacity degradation, decreasing to 625.9 mAh g⁻¹ after 100 cycles under 0.5C. As expected, the Li/PW₁₁-LLZTO/S cell delivers an initial discharge capacity of 965.1 mAh g⁻¹ and maintains 650.8 mAh g⁻¹ after 450 cycles, with an average coulombic efficiency of 99.1%. The charge–discharge profiles of the Li/PW₁₁-LLZTO/S and Li/PW₁₂-LLZTO/S cells at 0.5C are presented in Fig. S18. It can be seen that until the 400th cycle, there is still a distinct charge–discharge plateau for the Li/PW₁₁-LLZTO/S cell. Meanwhile, the Li/PW₁₁-LLZTO/S cell exhibits a reduced overpotential during the initial charge–discharge cycle, reflecting its improved electrode kinetics. For rate capability tests (Fig. 5e), when the current densities are 0.1, 0.2, and 0.5C, the discharge capabilities of the Li/PW₁₁-LLZTO/S cell are 981.4, 870.4, and 789.1 mAh g⁻¹, correspondingly, which are superior to other cells. Moreover, the discharge capacity returns to 859.3 mAh g⁻¹ upon returning the current density to 0.1C. Subsequently, we conduct further cycling tests on the Li–S full cell assembled with PW₁₁-LLZTO SSE at a rate of 1C. In Fig. 5f, the Li/PW₁₁-LLZTO/S cell shows a discharge capacity of 619.4 mAh g⁻¹ after 200 cycles at 1C, confirming the outstanding electrochemical performance under higher current density. Moreover, we compare the electrochemical performance of the Li/PW₁₁-LLZTO/S cell with the recently published all-solid-state Li–S batteries based on inorganic solid electrolytes and sulfide-based electrolytes (Table S1). It can be found that PW₁₁-LLZTO SSE demonstrates a significant advantage in promoting the kinetics of electrode reactions.

Fig. 5 (a) CV curves of Li/PW₁₁-LLZTO/S and Li/PW₁₂-LLZTO/S cells at a scan rate of 0.1 mV s⁻¹. (b) Nyquist curves of Li/PW₁₁-LLZTO/S and Li/PW₁₂-LLZTO/S cells. Cycling performance of Li/PW₁₁-LLZTO/S and Li/PW₁₂-LLZTO/S cells at (c) 0.2C and (d) 0.5C. (e) Rate performance of Li/PW₁₁-LLZTO/S and Li/PW₁₂-LLZTO/S cells at current densities from 0.1 to 0.5C. (f) Cycling performance of the Li/PW₁₁-LLZTO/S cell at 1C.

The intrinsic nature of PW₁₁ and PW₁₂ induced enhancement of the electrochemical performance of Li–S batteries has been investigated via DFT calculations. Fig. 6a shows the optimized adsorption configurations between various polysulfides and PW₁₁/PW₁₂. Fig. 6b shows the corresponding statistical graph of the binding energy values. Clearly, the calculated binding energies of Li₂S₈, Li₂S₆, Li₂S₄, and Li₂S₂ on the PW₁₁ are higher than that of PW₁₂. This result confirms that PW₁₁ has a strong anchoring effect on polysulfides, which inhibits shuttle effect and ensures efficient catalytic activity. We measure the lengths of Li–O bonds (the terminal oxygen atoms of PW₁₁ clusters bind to the Li moieties in polysulfides). As shown in Fig. S19, the bond lengths are comparable to those of strong hydrogen bonds. Based on the previous reports,³¹ it can be concluded that the PW₁₁ clusters have a moderate binding affinity for the LiPS molecules. The formation and dissociation of the Li–O bonds are likely reversible, and thus the interaction strength is insufficient to hinder the electrochemical oxidation–reduction reaction of LiPSs. Interestingly, the binding energies between various Li₂S_x and PW₁₁ close to the lacunary site are lower than those far from the lacunary site. The charge density distribution and frontier orbital analysis are carried out to explain this phenomenon. As shown in Fig. 6c, the charge density distribution at the oxygen sites of PW₁₁ is more concentrated compared to that of PW₁₂, and the oxygen atoms far from the lacunary site exhibit greater charge localization than the oxygen atoms close to the lacunary site within the PW₁₁ structure. According to previous reports,³¹ the Li moieties in Li₂S_x act as Lewis acid sites; the polysulfides serve as Lewis base sites. The terminal oxygen atoms of polyoxoanion clusters can act as Lewis basic sites to bind with the Li moieties in polysulfides. Therefore, the oxygen atoms in PW₁₁ that are located farther from the lacunary site preferentially interact with the lithium moieties of Li₂S_x species. Furthermore, the frontier orbital analysis of PW₁₁ and PW₁₂ is shown in Fig. 6d. The HOMO of PW₁₂ is uniformly delocalized over oxygen atoms, while the HOMO of PW₁₁ is mainly spread around the oxygen atoms far from the lacunary site. The HOMO energy level of PW₁₁ is elevated to −6.54 eV, relative to −8.50 eV for PW₁₂. These results indicate that the lacunary introduction can modify the electron cloud density of oxygen atoms in PW₁₁, thereby enhancing its nucleophilicity and strengthening its Lewis basicity. As a result, the obtained PW₁₁ facilitates the redox reaction kinetics of LiPSs and enhances the adsorption of polysulfides. In addition, the PW₁₁ active site can promote the transmission of lithium ions, thereby facilitating the uniform deposition of lithium ions. All these factors are conducive to the improvement of the performance of quasi-solid-state Li–S batteries, and the working mechanism of PW₁₁-LLZTO SSE is shown in Fig. 6e.

Fig. 6 (a) Optimized adsorption configurations of various Li₂S_x on PW₁₁: (I) close to the vacancy site and (II) far from the vacancy site; optimized adsorption configurations of various Li₂S_x on PW₁₂. Color codes: P, pink; W, blue; O, red; Li, violet; S, yellow. (b) The corresponding statistical graph of the binding energy values. (c) Charge density distribution of PW₁₁ and PW₁₂. (d) The HOMO of PW₁₁ and PW₁₂ based on frontier orbital analysis. (e) Schematic diagram of the working mechanism of PW₁₁-LLZTO SSE in quasi-solid-state Li–S batteries.

Conclusions

In summary, we have successfully developed a functionalized SSE by modifying garnet-type LLZTO with lacunary Keggin-type polyoxometalate of PW₁₁. The optimized PW₁₁-LLZTO composite electrolyte exhibits uniform surface morphology, enhanced interfacial stability with lithium metal, and superior ionic conductivity compared to both bare LLZTO and PW₁₂-LLZTO. Electrochemical evaluations confirmed that the symmetric cells with PW₁₁-LLZTO SSE achieve a high critical current density of 0.9 mA cm⁻² and stable long-term cycling over 800 h with minimal polarization. When applied in quasi-solid-state Li–S batteries, the PW₁₁-LLZTO electrolyte significantly suppresses the polysulfide shuttle effect, facilitates rapid sulfur conversion kinetics, and improves the reversible capacity and cycling stability. DFT calculations further demonstrated that the lacunary structure can modify the electron cloud density of oxygen atoms in POMs and PW₁₁ presents stronger nucleophilicity relative to saturated PW₁₂. Therefore, PW₁₁ promotes more effective Lewis acid–base interactions, thus enhancing the adsorption of polysulfides and improving the catalytic conversion kinetics of Li–S batteries. This work highlights the great potential of lacunary POMs as functional materials for SSEs, providing a feasible strategy to address the key challenges of quasi-solid-state Li–S batteries.

Author contributions

Jiaxin Zuo: writing – original draft, methodology, investigation, formal analysis, and conceptualization. Yi Feng: methodology, investigation, and funding acquisition. Yundong Cao: investigation, formal analysis, and DFT calculation. Linlin Fan: methodology, investigation, supervision, and funding acquisition. Caili Lv: investigation. Hong Liu: writing – review & editing, supervision, funding acquisition, and conceptualization. Yihai Song: formal analysis. Guanggang Gao: writing – review & editing, supervision, funding acquisition, and conceptualization.

Conflicts of interest

The authors declare no conflict of interest.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request. Supplementary information: Table S1, FTIR, XPS, SEM, and expermental details.

Supplementary information (SI) is available. See DOI: https://doi.org/10.1039/d5qi02333e.

Acknowledgements

We gratefully acknowledge the financial support from the National Natural Science Foundation of China (22201098 and 22471095), the Natural Science Foundation of Shandong Province (ZR2024QB211), the Jinan City “New University 20” Project (202228113), and the Science and Technology Program of the University of Jinan (XBS2404).

References

1. Y. Liu, S. Liu, G. Li and X. Gao, Strategy of enhancing the volumetric energy density for lithium-sulfur batteries, Adv. Mater., 2021, 8, 2003955.
2. Z. Song, Y. Cao, L. Fan, J. Song, Y. Feng, H. Liu, C. Lv and G. Gao, WSe₂/MoSe₂ with a better-matched heterointerface dominating high-performance potassium/sodium storage, Rare Met., 2025, 44, 195–208.
3. J. Song, Y. Jiang, Y. Lu, C. Zhao, Y. Cao, L. Fan, H. Liu and G. Gao, Utilizing decavanadate as an artificial solid electrolyte interface to effectively suppress dendrite formation on a lithium metal anode, Inorg. Chem. Front., 2025, 12, 2070–2080.
4. Q. Zhou, Y. Liu, H. Zhang, C. Feng, X. Jiang, G. Yang, Y. He, M. Chen, G. Diao and L. Ni, Defect spinel aluminum molybdenum sulfide: a dual-function catalyst for polysulfide conversion and aluminum intercalation in aluminum-sulfur batteries, Adv. Sci., 2025, 12, 2417061.
5. J. Zhang, X. Zhang, J. Wang, Y. Feng, L. Fan, Y. Cao, H. Liu, C. Lv and G. Gao, The explicit multi-electron catalytic mechanism of heteropolyvanadotungstate dominating ultra-durable room-temperature Na-S batteries, Adv. Funct. Mater., 2024, 34, 2400170.
6. H. Zhang, Y. Zhang, C. Cao, W. Zhao, K. Huang, Y. Zhang, Y. Shen, Z. Li and Y. Huang, Lithium-sulfur pouch cells with 99% capacity retention for 1000 cycles, Energy Environ. Sci., 2024, 17, 7047–7057.
7. T. Deng, Z. Jin, L. Jin, H. Luo, J. Wang, J. Gao, Y. Zhang, Y. Liu, J. Wang, R.V. Kumar and G. Feng, Relay catalyst for accelerating lithium polysulfide conversion kinetics and long-life lithium sulfur batteries, Nano Energy, 2025, 138, 110896.
8. Y. Song, J. Zhang, C. Zhang, L. Fan, J. Song, Y. Cao, Y. Feng, H. Liu and G. Gao, Constructing artificial interphase layer of polyoxovanadates with high oxidizability and reversibility to boost dendrite-free lithium metal anode, Chem. Eng. J., 2025, 519, 165237.
9. W. Zhang, J. Zhu, Y. Ye, J. She, X. Kong, S. Jin, Z. Peng and H. Ji, Suppressing shuttle effect via cobalt phthalocyanine mediated dissociation of lithium polysulfides for enhanced Li-S battery performance, Adv. Funct. Mater., 2024, 34, 2403888.
10. B. Wei, Y. Tu, Y. Xia, W. Theis, J. Zhang, Z. Xu, S. Chen, J. Chen, G. Yin and H. Wang, Engineering conductive and catalytic triple-phase interfaces for high efficiency polysulfides conversion in Li-S batteries, Chem. Eng. J., 2023, 43, 144887.
11. Q. Lin, J. Liang, R. Fang, C. Sun, A. Rawal, J. Huang, Q. Yang, W. Lv and D. Wang, A lewis acid-lewis base hybridized electrocatalyst for roundtrip sulfur conversion in lithium-sulfur batteries, Adv. Energy Mater., 2024, 14, 2400786.
12. X. Tao, Y. Qi, Q. Gu, Y. Cao, Z. Zhai, C. Zhang, W. Han, N. Huang, M. Lu, L. Wang and B. Zhang, Ti₃C₂QDs@CNTs with active titanium species as bidirectional catalytic cathode for facilitating lithium polysulfide conversion in Li-S batteries, Adv. Funct. Mater., 2025, 35, 2420532.
13. J. Song, Y. Jiang, Y. Lu, Y. Cao, Y. Zhang, L. Fan, H. Liu and G. Gao, A forceful “dendrite-killer” of polyoxomolybdate with reusability effectively dominating dendrite-free lithium metal anode, Small, 2023, 19, 2301740.
14. Y. Zhang, Y. Cao, L. Fan, G. Shi, T. Zheng, H. Liu, J. Song and G. Gao, Structure-defined viologen-polyoxometalate modified separator dominating endurable Li-S batteries by a synergistic adsorption-electrocatalysis mechanism, Chem. Eng. J., 2024, 482, 148991.
15. H. Hu, Q. Zhang, J. Liu, J. Li, P. Wu, C. Li, P. Du, H. Li and X. Liu, Bi-functional diaminopropane additive enables stable Li anodes and highly efficient cathodes for high-performance Li-air batteries, Adv. Sci., 2025, 12, e05539.
16. S. Zhang, F. Zhao, L. Li and X. Sun, Solid-state electrolytes expediting interface-compatible dual-conductive cathodes for all-solid-state batteries, Energy Environ. Sci., 2025, 18, 6530–6539.
17. S. Han, B. Hu, Z. Zheng, K. Huang, T. Zhu and J. Xu, Research on electrolyte structure and interface design for solid state Lithium-Sulfur batteries: Challenges, strategies and prospects, J. Power Sources, 2025, 636, 236575.
18. L. Yu, S. Pan, J. Tian, Y. Liang, H. Zhong, R. Ma and J. Gu, et al., Engineering triple-phase interfaces with hierarchical carbon nanocages for high-areal-capacity all-solid-state li-s batteries, Adv. Mater., 2024, 36, 2413325.
19. C. Pan, G. Kuo and C. Li, Solid electrolytes and dendrite dynamics in solid-state lithium-sulfur batteries, Appl. Mater. Interfaces, 2025, 17, 12136–12146.
20. M. Wang, H. Su, Y. Zhong, X. Hu, X. Wang, C. Gu and J. Tu, Localized S-Li₂S conversion with accelerated kinetics mediated by mixed conductive shell for high-performance solid-state lithium sulfur battery, Adv. Energy Mater., 2024, 14, 2302255.
21. Q. Yang, N. Deng, Y. Zhao, L. Gao, B. Cheng and W. Kang, A review on 1D materials for all-solid-state lithium-ion batteries and all-solid-state lithium-sulfur batteries, Chem. Eng. J., 2023, 451, 138532.
22. H. Wang, S. Duan, Y. Zheng, L. Qian, C. Liao and L. Dong, Solid-state electrolytes based on metal-organic frameworks for enabling high-performance lithium-metal batteries: Fundamentals, progress, and perspectives, eTransportation, 2024, 20, 100311.
23. K. Daems, P. Yadav, K. Dermenci, J. Mierlo and M. Berecibar, Advances in inorganic, polymer and composite electrolytes: mechanisms of lithium-ion transport and pathways to enhanced performance, Renewable Sustainable Energy Rev., 2024, 191, 114136.
24. Z. Wei, J. Huang, Z. Liao, A. Hu, Z. Zhang, A. Orita, N. Saito and L. Yang, Solid-state rigid polymer composite electrolytes with in situ formed nano-crystalline lithium ion pathways for lithium-metal batteries, Energy Storage Mater., 2024, 72, 103714.
25. H. Liang, L. Wang, A. Wang, Y. Song, Y. Wu, Y. Yang and X. He, Tailoring practically accessible polymer/inorganic composite electrolytes for all-solid-state lithium metal batteries: a review, Nano-Micro Lett., 2023, 15, 42.
26. J. Guo and C. Chan, Lithium dendrite propagation in Ta-doped Li₇La₃Zr₂O₁₂ (LLZTO): comparison of reactively sintered pyrochlore-to-garnet vs LLZTO by solid-state reaction and conventional sintering, ACS Appl. Mater. Interfaces, 2024, 16, 4519–4529.
27. F. Shen, W. Guo, D. Zeng, Z. Sun, J. Gao, J. Li, B. Zhao, B. He and X. Han, A simple and highly efficient method toward high-density garnet-type LLZTO solid-state electrolyte, ACS Appl. Mater. Interfaces, 2020, 12, 30313–30319.
28. Y. Lee, S. Hong, B. Pan, X. Wu, E. Dickey and J. Whitacre, Improving bulk and interfacial lithium transport in garnet-type solid electrolytes through microstructure optimization for high-performance all-solid-state batteries, ACS Appl. Mater. Interfaces, 2024, 16, 60340–60347.
29. C. Zhang, J. Wang, J. Zhan, R. Yang, G. Gao, J. Zhang, L. Fan, M. Wang and H. Liu, Highly sensitive hydrazine detection through a novel Raman scattering quenching mechanism enabled by a crystalline and noble metal–free polyoxometalate substrate, Chin. Chem. Lett., 2025, 36, 109719.
30. J. Wang, W. Zhu, J. Zhang, B. Qi, J. Wang, G. Gao, L. Fan and H. Liu, Ratiometric response to formaldehyde by 3D silver SERS substrate with polyoxometalate as internal label, Sens. Actuators, B, 2023, 381, 133450.
31. J. Ye, J. Chen, R. Yuan, D. Deng, M. Zheng, L. Cronin and F. Dong, Strategies to explore and develop reversible redox reactions of Li-S in electrode architectures using silver-polyoxometalate clusters, J. Am. Chem. Soc., 2018, 140, 3134–3138.
32. B. Zeng, G. Liu, M. Zhou, Z. Zhang, Y. Li, L. Chen and J. Zhao, Novel multi-lanthanide-substituted poly (polyoxometalate) nanocluster as electrode modified material used for the detection of persistent pollutant 2, 4-dichlorophenol, Chem. Eng. J., 2025, 509, 161375.
33. R. Sun, X. Ma, K. Chen, J. Yang, Y. Liu, X. Li, P. Cai, Z. Wen and S. Zheng, Self-assembled polyoxometalate supramolecular nanosheets for efficient and durable water oxidation, Angew. Chem., 2025, 137, e202513915.
34. B. Hu, B. Liu, Q. Pan, H. Ren, F. Yu, Q. Du, Y. Li and H. Zang, Structural effects in polyoxometalate-based supramolecular assemblies for enhanced proton conduction, Angew. Chem., Int. Ed., 2025, e17958.
35. Y. Liu, C. Zhu, X. Zhao, H. Tan, S. Cheng, D. Yang, X. Wang and Y. Li, CdWO₄ Sub-1 nm nanowires for visible-light CO₂ photoreduction, Angew. Chem., Int. Ed., 2025, 64, e202418349.
36. Z. Wang, Y. Yang, J. Chen, C. Zhong, H. Sun, G. Lu, S. Liang, Z. Liu and H. Zang, Proton superhighways enabled by hofmeister-electrostatic synergy in all-inorganic polyoxometalate hydrogels for electronics, Adv. Mater., 2025, e15892.
37. J. Shi, N. Li, Y. Liang, S. Xu, L. Dong, D. Zhang, J. Niu, R. Li, J. Liu, S. Li and Y. Lan, Charge-transport divergence in ultrastable heterometal-oxo clusters exerting significant effect on photoreactivity, Angew. Chem., 2025, 137, e202502654.
38. M. Bai, L. Qin, X. Zeng, M. Wu, L. Yao and G. Yang, Dithiocarbonate-protected Au₂₅ nanorods of a chiral D₅ configuration and NIR-II phosphorescence, J. Am. Chem. Soc., 2024, 146, 12734–12742.
39. F. Feng, M. Zhao, J. Yang, Z. Wang, P. Bai, Y. Liu, H. Lv and G. Yang, Wearing gigantic silver armor on transition-metal-containing polyoxometalates: formation of supertetrahedral intercluster compounds, Angew. Chem., Int. Ed., 2025, 64, e202505511.
40. D. Zhang, C. Wang, Z. Lin, L. Dong, C. Zhang, Z. Yao, P. Lei, J. Dong, J. Du, Y. Chi, Y. Lan and C. Hu, Fullerene-like niobovanadate cage built from {(Nb)V₅} pentagon, Angew. Chem., 2024, 136, e202320036.
41. W. Geng, D. Zhang, N. Zhen, J. Du, J. Dong, C. Liu, S. Chen, Y. Chi and C. Hu, Electroreductive C–C coupling of furfural to jet fuel precursors in neutral media via synergistic catalysis of the polyoxotungstate and Cu complex, ACS Catal., 2024, 14, 10040–10052.
42. M. Chi, J. Wei, Z. Zhao, X. Liu, W. Sun, Y. Feng, H. Lv and G. Yang, Structural isomerism of {Ag₁₄}¹⁰⁺ nanocluster encapsulated by bowl-like polyoxometalates, Angew. Chem., 2025, 137, e202424499.
43. W. Ruan, Y. Feng, Y. Gao, K. Yonesato, L. Lan, Z. Guo, P. Yin, M. Wang, K. Suzuki, H. Lv and X. Fang, Homoleptic and heteroleptic polyoxotungstate-organic cages for efficient photocatalytic hydrogen evolution, Angew. Chem., 2025, 137, e202508797.
44. P. Wang, S. Xu, S. Guo, L. Zhang, T. Lu and Z. Zhang, Polyoxometalate electron-sponge-mediated photooxidative hydroxylation of arylboronic acids, Angew. Chem., 2025, 137, e202514184.
45. J. Ren, B. Wang, H. Yin, P. Zhang, X. Wang, Y. Quan, S. Yao, T. Lu and Z. Zhang, Single dispersion of Fe(H₂O)²⁻ based polyoxometalate on polymeric carbon nitride for biomimetic CH₄ photooxidation, Adv. Mater., 2024, 36, 2403101.
46. T. Li, Y. Liu, X. Zhang, L. Zhang, Y. Wu, X. Jiang, Q. Zhou, C. Ma, L. Ni and G. Diao, Polyoxometalate/cobalt selenide functional separator for synergistic polysulfide anchoring and catalysis in lithium-sulfur batteries, Energy Chem., 2025, 104, 551–564.
47. K. Tong, Y. Wang, J. Du, C. Chen, Y. Lan and P. Yang, Splicing them together: construction of polyoxovanadate-organic polyhedral-based pyrgoscages and catenanes, Angew. Chem., Int. Ed., 2025, 64, e202504424.
48. C. Zhang, Y. Chen, L. Chen, M. Wang, J. Wei, R. Sun, Z. Yang, Y. Zhang, D. Yang, Z. Chen and J. Zhao, Electrode design as the Lego assembling: Advanced aqueous batteries based on polyoxometalate molecular engineering, Energy Storage Mater., 2025, 81, 104490.
49. N. Song, M. Lu, J. Liu, M. Lin, P. Shang, J. Wang, B. Shi and J. Zhao, A giant heterometallic polyoxometalate nanocluster for enhanced brain-targeted glioma therapy, Angew. Chem., Int. Ed., 2024, 63, e202319700.
50. M. Du, H. Xiao, R. Xu, X. Sun, X. Wang, D. Li, S. Yue, Z. Zhang, X. Huang, Y. Gao, X. Shang, X. Li and S. Zheng, A sonosensitive heterometallic polyoxometalate for highly efficient chemo-sonodynamic synergistic cancer therapy, Angew. Chem., Int. Ed., 2025, 202514859.
51. Z. Guo, Y. Yan, Y. Chen, Y. Li, X. Li, C. Sun and S. Zheng, An all-inorganic three-dimensional polyoxoniobate framework with ppb-level chemiresistive sensing for ammonia, Nat. Commun., 2025, 16, 6379.
52. Y. Liu, X. Wang, Z. Lang, Y. Li, F. Yu, H. Dong, R. Yao, S. Geng, Z. Liu, H. Tan and Y. Li, Pd 0-polyoxometalates cluster–cluster catalyst for efficient selective hydrogenation of olefins, Nano Res., 2025, 18, 94907437.
53. Y. Liu, X. Zhou, T. Qiu, R. Yao, F. Yu, T. Song, X. Lang, Q. Jiang, H. Tan, Y. Li and Y. Li, Co-assembly of polyoxometalates and porphyrins as anode for high-performance lithium-ion batteries, Adv. Mater., 2024, 36, 2407705.
54. C. Lv, Y. Cao, Y. Feng, L. Fan, J. Zhang, Y. Song, H. Liu and G. Gao, Crosslinked vinyl-capped polyoxometalates to construct a three-dimensional porous inorganic-organic catalyst to effectively suppress polysulfide shuttle in Li-S batteries, Adv. Energy Mater., 2025, e05978.
55. X. Jiang, Y. Wu, Z. Lv, G. Yang, M. Wang, Q. Zhou, Y. Shen, M. Chen, L. Ni and G. Diao, Fabrication of a multi-functional separator incorporating crown ether-polyoxometalate supramolecular compound for lithium-sulfur batteries, Chem. – Eur. J., 2024, 30, e202402706.
56. H. Zhou, Z. Ma, G. Yang, X. Jiang, S. Duan, Y. Wu, M. Wang, L. Ni, L. Feng and G. Diao, Regulating polysulfide transformation and stabilizing lithium anode using [PMo₁₂O₄₀]³⁻ cluster@carbon nanotube–modified separator for lithium–sulfur batteries, Batteries Supercaps, 2024, 7, e202300563.
57. J. Song, Y. Jiang, Y. Lu, M. Wang, Y. Cao, L. Fan, H. Liu and G. Gao, Effective polysulfide adsorption and catalysis by polyoxometalate contributing to high-performance Li-S batteries, Mater. Today Nano, 2022, 19, 100231.
58. Y. Yu, T. Li, H. Zhang, Y. Luo, H. Zhang, J. Zhang, J. Yan and X. Li, Principle of progressively and strongly immobilizing polysulfides on polyoxovanadate clusters for excellent Li-S batteries application, Nano Energy, 2020, 71, 104596.
59. L. Ni, J. Gu, X. Jiang, H. Xu, Z. Wu, Y. Wu, Y. Liu and J. Xie, Polyoxometalate-cyclodextrin-based cluster-organic supramolecular framework for polysulfide conversion and guest-host recognition in lithium-sulfur batteries, J. Am. Chem. Soc., 2023, 62, e202306528.
60. C. Li, N. Mizuno, K. Yamaguchi and K. Suzuki, Self-assembly of anionic polyoxometalate-organic architectures based on lacunary phosphomolybdates and pyridyl ligands, J. Am. Chem. Soc., 2019, 141, 7687–7692.
61. K. Xia, T. Yatabe, K. Yonesato, T. Yabe, S. Kikkawa, S. Yamazoe, A. Nakata and K. Yamaguchi, Supported anionic gold nanoparticle catalysts modified using highly negatively charged multivacant polyoxometalates, Angew. Chem., Int. Ed., 2022, 61, e202205873.
62. Y. Yang, Y. Guo, C. Hu and E. Wang, Lacunary keggin-type polyoxometalates-based macroporous composite films: preparation and photocatalytic activity, Appl. Catal., A, 2003, 252, 305–314.
63. X. Huang, J. Tang, Y. Zhou, K. Rui, X. Ao, Y. Yang and B. Tian, Preparation craft platform for solid electrolytes containing volatile components: experimental study of competition between lithium loss and densification in Li₇La₃Zr₂O₁₂, ACS Appl. Mater. Interfaces, 2022, 14, 33340–33354.
64. A. Magerat, S. Hermans and E.M. Gaigneaux, A novel versatile platform as efficient deoxydehydration (DODH) catalysts: Keggin polyoxometalates, Appl. Catal., B, 2025, 375, 125432.
65. M. Simões, C. Conceição, J. Gamelas, P. Domingues and A. Cavaleiro, Keggin-type polyoxotungstates as catalysts in the oxidation of cyclohexane by dilute aqueous hydrogen peroxide, J. Mol. Catal. A: Chem., 1999, 144, 461–468.
66. Y. Lu, C. Zhao, H. Yuan, X. Cheng, J. Huang and Q. Zhang, Critical current density in solid-state lithium metal batteries: mechanism, influences, and strategies, Adv. Funct. Mater., 2021, 31, 2009925.
67. C. Lei, T. Zhou, M. Zhang, T. Liu, C. Xu, R. Wang, X. He and X. Liang, Universal copolymerization of crosslinked polyether electrolytes for all-solid-state lithium-metal batteries, Adv. Sci., 2024, 11, 2405482.
68. L. Zhang, Y. Liu, Z. Zhao, P. Jiang, T. Zhang, M. Li, S. Pan, T. Tang, T. Wu, P. Liu, Y. Hou and H. Lu, Enhanced polysulfide regulation via porous catalytic V₂O₃/V₈C₇ heterostructures derived from metal-organic frameworks toward high-performance Li-S batteries, ACS Nano, 2020, 14, 8495–8507.
69. W. Yao, J. Xu, Y. Cao, Y. Meng, Z. Wu, L. Zhan, Y. Wang, Y. Zhang, I. Manke, N. Chen and C. Yang, Dynamic intercalation-conversion site supported ultrathin 2D mesoporous SnO₂/SnSe₂ hybrid as bifunctional polysulfide immobilizer and lithium regulator for lithium-sulfur chemistry, ACS Nano, 2022, 16, 10783–10797.
70. J. Song, Y. Jiang, Y. Lu, Y. Cao, Y. Zhang, L. Fan, H. Liu and G. Gao, Boosting the high rate and durability of lithium-sulfur batteries using a bidirectional catalyst of a polyoxometalate-cyclodextrin supramolecular compound, Inorg. Chem. Front., 2024, 11, 1710–1723.

---