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Jittraporn Saengkaew, Lukas Herbers, Martin Winter, [Shoichi Matsuda](https://orcid.org/0000-0002-0640-3404), [Peter Bieker](https://orcid.org/0000-0003-4378-4805)

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[Solid‐State Lithium Metal Rechargeable Batteries With High‐Mass‐Loading NMC Electrode and Multilayer Hybrid Solid Electrolyte Thin‐Film](https://mdr.nims.go.jp/datasets/d1fdc4f1-ccaa-4d03-aa6d-18f5ca91834f)

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Solid‐State Lithium Metal Rechargeable Batteries With High‐Mass‐Loading NMC Electrode and Multilayer Hybrid Solid Electrolyte Thin‐FilmSolid-State Lithium Metal Rechargeable Batteries WithHigh-Mass-Loading NMC Electrode and MultilayerHybrid Solid Electrolyte Thin-FilmJittraporn Saengkaew1 | Lukas Herbers2 | Martin Winter2,3 | Shoichi Matsuda1 | Peter Bieker31Center for Green Research on Energy and Environmental Materials, National Institute for Material Science, Ibaraki, Japan | 2MEET Battery ResearchCenter, Institute of Physical Chemistry, University of Münster, Münster, Germany | 3Helmholtz-Institute Münster (HIMS), Münster, GermanyCorrespondence: Shoichi Matsuda (MATSUDA.Shoichi@nims.go.jp) | Peter Bieker (p.bieker@fz-juelich.de)Received: 5 March 2026 | Revised: 27 April 2026 | Accepted: 1 May 2026Keywords: cathodes | high-active-mass-loading | lithium metal batteries | solid-state batteriesABSTRACTSolid-state lithium metal batteries, assumed to show improved safety and high energy density, have garnered growing interest.Nevertheless, establishing an effective ionic conduction pathway within the composite positive electrode remains challenging, espe-cially with high-active- materials mass-loading in the electrode. Herein, we develop a high-active-mass loading positive electrode forsolid-state Li metal rechargeable batteries, optimized for operation at an elevated temperature of 60°C. The electrode is based onNMC622 as active material, incorporating the ionic liquid Pyr14TFSI and LiTFSI (combined-electrolyte, cE). The positive electrodemembranes are successfully prepared by preventing undesired gelation of the slurry solution and seamlessly integrating themwith athin-film multilayer hybrid solid electrolyte. Notably, the NMC622-based electrode with 10wt% of cE achieves a specific capacityexceeding 160mAh g−1 at a high mass loading of 40mg cm−2. The methodology demonstrated in the present study highlights thepotential of incorporating a cE into cathode compositions for high energy density solid-state Li metal batteries.1 | IntroductionThe growing demand for safe, reliable, and cost-effective energystorage devices has driven extensive research and development inbattery technology over the past decade. While lithium-ion bat-teries utilizing organic liquid electrolytes are reaching their phys-icochemical limits, solid-state batteries (SSBs) have emergedas a promising next-generation energy storage solution [1–3].By eliminating more flammable liquid organic electrolytes, SSBsare reported to notably enhance safety, while the use of high-capacity anodes, such as lithium (Li) metal, offers the potentialfor increased energy density [4]. A wide range of solid electrolytes(SIEs) has been explored, including solid polymer electrolytes(SPEs) [5–7], inorganic SIEs [8, 9], and especially hybrid solidelectrolytes [10–13]. However, each system presents inherentlimitations. SPEs typically suffer from low ionic conductivitydue to restricted polymer chain mobility, whereas SIEs oftenexhibit poor interfacial contact arising from their rigid nature.To address these challenges, hybridization strategies combiningmultiple electrolyte components have been widely investigated toachieve synergistic improvements in ionic transport, mechanicalproperties, and interfacial stability. In particular, multilayer HSEarchitectures have recently attracted significant attention as aneffective strategy to address the distinct requirements at the cath-ode and anode interfaces. For example, Herbers et al. developeda thin-film multilayer HSE derived from a commercial separa-tor, integrating different functional layers for cathode stability,mechanical strength, and Li metal compatibility [10]. This sys-tem exhibited high thermal stability (>250°C), good interfacialcompatibility, and long-term cycling performance. However,the demonstrated electrochemical performance was limited to rel-atively low cathode mass loading (4mg cm−2), which remainsinsufficient for achieving practical high energy density. Achievinghigh energy density at the cell level requires optimization of keyThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, providedthe original work is properly cited.© 2026 The Author(s). Batteries & Supercaps published by Wiley-VCH GmbH.Batteries & Supercaps, 2026; 9:e70329 1 of 8https://doi.org/10.1002/batt.70329Batteries & SupercapsRESEARCH ARTICLEhttps://orcid.org/0000-0002-0640-3404https://orcid.org/0000-0003-4378-4805mailto:MATSUDA.Shoichi@nims.go.jpmailto:p.bieker@fz-juelich.dehttp://creativecommons.org/licenses/by/4.0/https://doi.org/10.1002/batt.70329https://doi.org/10.1002/batt.70329http://crossmark.crossref.org/dialog/?doi=10.1002%2Fbatt.70329&domain=pdf&date_stamp=2026-05-15technological parameters. One important approach involves uti-lizing high-mass-loading positive electrodes to achieve high arealcapacity [14–16]. However, constructing an effective ionic con-duction network in thick composite cathodes remains a majorchallenge, as increased electrode thickness leads to sluggish Li+transport, poor interfacial contact, and increased polarization.In addition, incorporating ionic liquids into composite cathodeshas been explored as a strategy to enhance ionic conductivityand interfacial wetting. Ionic liquids can facilitate Li+ transportand improve interfacial contact while maintaining thermal stabil-ity and safety. Nevertheless, their role within high-mass-loadingcathodes, particularly in combination with advanced multilayerelectrolyte architectures, has not yet been systematically clarified.In this work, we combine a thin-film multilayer HSE, previouslyreported by Herbers et al. with a high-active-mass-loading posi-tive electrode to investigate the physical properties and Li metalbattery performance at 60°C within a voltage range of 3.00–4.25 V[10]. The multilayer hybrid electrolyte is engineered to improvemechanical strength, cathode contact, oxidative stability, interfa-cial compatibility, and overall safety. Furthermore, we introducea combined-electrolyte (denoted as cE in this study), consistingof Pyr14TFSI ionic liquid and LiTFSI, into the cathode to enhanceLi+ transport and electronic conduction pathways. As a result, wesuccessfully fabricate NMC622-based positive electrodes with highactive mass loadings of 30 and 40mg cm−2, achieving improvedelectrochemical performance.2 | Results and DiscussionIn this study, we propose a well-designed NMC622-based positiveelectrode, featuring an optimized Li+ transfer and electronic con-ducting network, to achieve superior high-active-mass-loadingpositive electrodes. To evaluate the electrochemical performanceof cathode materials with variable electrolyte compositions(Pyr14TFSI ionic liquid and LiTFSI) ratios of 2 and 10 wt%, wefabricated NMC622-based electrodes with active mass loading of30 mg cm−2 and 40mg cm−2. These were compared to NMC622-based electrodes that did not contain cE in cathode slurry.In addition, this study is built upon the thin-film multilayerHSE system previously reported [10]. In the original approach,a sandwich-like multilayer electrolyte was constructed bycombining a mechanically reinforced separator with tailoredelectrode-facing layers. A cathode-facing layer based on LATPand PVDF-HFP provides oxidative stability against high-voltageNMC cathodes, while an anode-facing PEO-based layer ensuresstable contact with Li metal. These layers are interconnected bythe ionic liquid Pyr14TFSI and LiTFSI, which enhance ionic con-ductivity and interfacial contact across the multiphase electrolytesystem. Building on this established electrolyte chemistry (PVDF-HFP/Pyr14TFSI/LiTFSI), the present work introduces a key mod-ification by incorporating these electrolyte components directlyinto the cathode composite. In addition to the active material(NMC622) and conductive carbon, the cathode contains PVDF-HFP, Pyr14TFSI, and LiTFSI as a combined electrolyte (cE), form-ing a percolating ionic conduction network within the electrode.This design is particularly beneficial for high-mass-loading electro-des, where conventional solid-state configurations often suffer fromlimited ionic accessibility and increased polarization. Within thecathode, the roles of these components differ from those in the bulkelectrolyte. PVDF-HFP functions not only as a binder but also as apolymer matrix that accommodates the ionic liquid and lithiumsalt. Although PVDF-HFP lacks strong coordinating groups forLi+ transport compared to PEO, its relatively high dielectric con-stant supports partial dissociation of LiTFSI, especially in the pres-ence of fluorinated anions such as TFSI−. Meanwhile, Pyr14TFSIfacilitates phase connectivity and enhances ionic mobility; how-ever, Li+ transport is strongly influenced by the Pyr14TFSI/LiTFSI ratio due to the formation of [Li(TFSI)n](n−1)− complexes.Therefore, optimizing the composition of the combined electrolyteis essential to balance ionic conductivity and electrochemical per-formance. Table 1 presents the fabrication details and physicalproperties of the electrode membrane, including density, thickness,and calculated porosity values. Figure 1a illustrates the fabricationprocedure for high-active-mass-loading cathode membranes. Thecathode membranes were fabricated by mixing the active material,carbon powder, polymeric binder, cross-linking agent, and cE.In the coating process, a well-mixed slurry was prepared by disper-sion on the carbon-coated alumina foil by using a doctor blade.Subsequently, the cathode membranes were cross-linked via UVcuring and dried under vacuum conditions at 80°C for 48 h.The detailed membrane preparation process is described in theExperimental section. The resulting electrode membranes exhib-ited thickness ranging from 130–150 μm for 30mg cm−2 loadingand 160–170 μm for 40mg cm−2 loading. As the active mass load-ing increased, the electrode thickness also expanded. Additionally,an increase in electrolyte ratio corresponded to higher density val-ues and lower calculated porosity due to the increased electrolytecontent within the composite.To further investigate the morphology of the electrodes, a CrossSection Polisher (CSP) was used to treat the positive electrode foil,and the cross-sectional SEM images are displayed in Figure 2a–c,TABLE 1 | Physical properties of high-active-mass-loading positive electrode membranes, including density, active mass loading, thickness, andcalculated porosity.RunDensity(g cm−3)Active mass loading(mg cm−2)Thickness(μm)Calculated porosity(%)NMC622 2.45 ± 0.09 30 126.7 ± 6.8 44.15 ± 2.11NMC622 2.51 ± 0.05 40 164.0 ± 3.0 42.99 ± 1.19NMC622+ 2 wt% cE 2.56 ± 0.07 30 146.7 ± 2.6 39.55 ± 1.68NMC622+ 2 wt% cE 2.45 ± 0.05 40 171.7 ± 1.0 42.27 ± 1.13NMC622+ 10 wt% cE 2.62 ± 0.20 30 149.2 ± 3.3 27.55 ± 5.53NMC622+ 10 wt% cE 2.76 ± 0.06 40 167.7 ± 6.2 23.58 ± 1.742 of 8 Batteries & Supercaps, 2026 25666223, 2026, 5, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/batt.70329 by National Institute For, Wiley Online Library on [12/07/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons LicenseFigure S2, and Figure S3, Supporting Information. All electrodetypes predominantly consist of spherical-shaped NMC particleswith diameters ranging from 9 to 20 μm. The cross-sectional SEMconfirmed a homogeneous distribution of NMC622 particles for allelectrode types throughout the entire electrode depth (Figure 2cand Figure S2). A porous structure for the binder (representedfor the binder without cE) and binder-conductive matrix (repre-sented for the binder with cE) are detected. Furthermore, cross-sectional SEM images and corresponding EDS elemental mapsfor the electrodes are presented in Figure 2d, Figure S4, andFigure S5, Supporting Information. SEM and EDX analysesof NMC622+ 2wt% cE and NMC622+ 10 wt% cE electrodemembranes revealed a homogeneous distribution of oxygen (O),nickel (Ni), manganese (Mn), and cobalt (Co) throughout the NMCparticles. Carbon (C), fluoride (F), and sulfur (S) elements were pri-marily located around the NMC622 particles, indicating their asso-ciation with the binder–conductive electrolyte matrix. Especially,sulfur was found in the cE containing Pyr14TFSI ionic liquid andLiTFSI, with its atomic percentage (At%) increasing in correlationwith the electrolyte content, as shown in Table S1. In contrast, sul-fur was absent in the NMC622 electrode without cE additive.Figure 3a exhibits the experimental results of the peel test, whichevaluated the adhesion strength between the electrode surfaceFIGURE 1 | Schematic illustration of the fabrication procedure for (a) high-active-mass-loading cathode membrane and (b) multilayer HSE thin-film.FIGURE 2 | Cross-sectional SEM images of positive electrode membranes: (a) NMC622, (b) NMC622+ 2wt% cE, and (c) NMC622+ 10wt% cE, eachwith active mass loading of 40 mg cm−2. (d) SEM and EDS mapping analysis of the NMC622+ 10wt% cE (40 mg cm−2) positive electrode membrane,including a table of atomic percentages (%).Batteries & Supercaps, 2026 3 of 8 25666223, 2026, 5, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/batt.70329 by National Institute For, Wiley Online Library on [12/07/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licenseand adhesive tape. As a result, the average pulling force of theelectrode incorporating cE (NMC622+ 2 wt% cE and NMC622+10 wt% cE) was higher than that of NMC622 electrode withoutelectrolyte. The average pulling force of the NMC622+ 10 wt% cEexhibited the highest value. Specifically, the average pulling forceincreased with the addition of cE from 7.59 ± 1.34 N forNMC622 to 11.31 ± 2.12 N for NMC622+ 2 wt% cE and reachedits maximum at 15.98 ± 5.15 N for NMC622+ 10 wt% cE. Thisenhancement in adhesion strength is attributed to the cross-linked binder, which improves bonding properties within thebinder-conductive matrix as the cE content increases. The varia-tion of average conductivity depending on the applied force isshown in Figure 3b for positive electrode sheets. The conductivityvalues correspond to the electronic conductivity of the calen-dered electrode sheets. These values were calculated from themeasured absolute resistance, sample thickness, and electrodearea. The measurements were conducted at room temperatureusing a Zwicki universal testing machine under applied force.It can be observed a positive linear correlation between averageconductivity and applied force for all cathode membranes. Thecorrelative coefficient (r) values between conductivity andapplied force of all samples are between 0.98–1 which indicatesa strong to perfect linear correlation between parameters. Underlow applied forces, the average conductivity values of all electro-des were not significantly different. On the other hand, the aver-age conductivity of NMC622+ 10 wt% cE exhibited higher thanthat of other samples at the large applied force with 50, 100, 150,185, and 195 N. The increase in conductivity (S cm−1) withenhancing applied force (N) can be attributed to two key factors:(1) a reduction in contact resistance when materials compress,leading to better contact between the conductivity pathway fromthe binder-conductive matrix in the electrode membranes withcE additives [17, 18]; (2) an improved percolation pathway facili-tated by the binder-conductive matrix [19]. Consequently, theintegration of Pyr14TFSI ionic liquid and LiTFSI within the cath-ode composite improves conductivity while reducing interfacialresistance.To assess battery cell performance, electrochemical cells wereassembled using NMC622, NMC622+ 2 wt% cE, and NMC622+10wt% cE electrodes with active mass loading of 30mg cm−2 and40mg cm−2. To quantify evaluate the performance of the positiveelectrode, a thin-film multilayer HSE was employed, coatedonto a commercial Celgard separator, as illustrated in Figure 1b.The practical solid electrolyte was provided by coating two spe-cific different cathode and anode pastes on both sides of theCelgard2500 (≤50 μm) and a relatively thick 150 μm lithium foilas the negative electrode. This electrolyte systemwas adapted froma previous study by Herbers et al. [10]. For the multilayer hybridelectrolyte, the Cg-coated displayed a high mechanical strength toprevent short-circuits, a cathode-facing electrolyte layer (PVDF-HFP-based) provided a high oxidative stability (>4.5 V) by lithiumaluminum titanium phosphate (LATP), and an anode-facing elec-trolyte layer (PEO-based) offered to stable cycling of the Li metalbattery. Furthermore, Pyr14TFSI and LiTFSI were incorporatedacross all electrolyte layers to enhance ionic conductivity, interfa-cial contact, and safety. A schematic representation of the coin-typecell (CR2032) configuration is shown in Figure S1. We investigatedthree types of positive electrode (NMC622, NMC622+ 2 wt% cE,and NMC622+ 10wt% cE) and two different loading levels ofNMC622 material, specifically 30mg cm−2 and 40mg cm−2, at60°C with a current density of 0.1mA cm−2 and cut-off voltagesranging from 3.00 to 4.25 V. Figure 4 presents the charge/dischargeprofiles for the 1st, 5th, and 10th cycles of NMC622‖Li, NMC622+2 wt% cE‖Li, andNMC622+ 10wt% cE‖Li cells at activemass load-ing of 30mg cm−2 (Figure 4a–c) and 40mg cm−2 (Figure 4d–f ).During the first charging process, the voltage of the NMC622+10wt% cE‖Li metal cell (Figure 4a) gradually increased from3.50 to 3.83 V before reaching the cut-off voltage of 4.25 V witha capacity of 179mAh g−1. Upon switching to discharge, the volt-age initially remained around 4.2 V before gradually decreasing to3.50 V, reaching the cut-off voltage of 3.0 V with a capacity of157mAh g−1. Additionally, the voltage curves of cell chargingequipped with NMC622+ 2 wt% cE shifted to higher voltages,causing the cut-off voltage to be reached at a lower stage of chargewithin the set voltage range. Moreover, the average cell voltagedeclined, as indicated by a shift to the lower voltage of discharging.However, the capacities at the first cycle of the NMC622+ 2 wt%cE did not show a significant difference compared to NMC622+10wt% cE. On the other hand, the first cycle of cell equippedwith NMC622 exhibited a notably lower specific capacity. Forthe NMC622+ 10wt% cE‖Li metal cell (30mg cm−2), the specificcapacities remained stable from the 1st cycle to the 5th cycle, witha capacity retention of 89%. The specific capacities of the electrodesincorporating cE in composite cathodes remained high eventhrough the 10th cycle, as illustrated in Figure 4c, and Figure 4f.At a higher active mass loading of 40mg cm−2, the specific dis-charge capacities of NMC622+ 10wt% cE‖Li metal cell at theFIGURE 3 | (a) Average pulling force measured for three electrodes. (b) Relationship between average conductivity and applied force for high-active-mass-loading positive electrode membranes.4 of 8 Batteries & Supercaps, 2026 25666223, 2026, 5, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/batt.70329 by National Institute For, Wiley Online Library on [12/07/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License1st, 5th, and 10th cycles are 162, 146, and 110mAh g−1, respectively.Moreover, the specific charge capacities of NMC622+ 10wt% cEcell (40mg cm−2) at the 1st, 5th, and 10th cycles are 183, 154, and115mAh g−1, respectively. These values were slightly higher thanthose observed for the lower active mass loading, with a capacityretention of 90% at the 5th cycle and 68% at the 10th cycle. In addi-tion, the specific discharge capacities of NMC622+ 10wt% cE‖Limetal cell with 30mg cm−2 were 157, 140, and 93 mAh g−1 for the1st, 5th, and 10th cycles, respectively.Interestingly, the specific capacity of the sample with the cE sub-stantially increased compared to the active material without thecE in the cathode composite. This enhancement is attributedto improved ionic contact and favorable ionic percolation. Weinvestigated two different loading levels, ranging from 30mg cm−2to 40 mg cm−2. Figure 5a exhibits the average discharge capaci-ties at the first cycle for various loading levels, revealing thatthe specific capacity of the cell equipped with NMC622+10 wt% cE remained nearly unchanged across both active massloadings. Intriguingly, the specific capacities increased approxi-mately 42–55 times in NMC622+cE‖Li meal cell compared toNMC622 without cE at 40mg cm−2 active mass loading. The spe-cific energies resulting from the material calculation (calculatedbased on the total mass of active material, binder, conductiveadditive, and cE) are shown in Figure 5b. At 60°C, the specificenergies for NMC622, NMC622+ 2 wt% cE, and NMC622+ 10 wt%cE cells are 12, 494, and 496Wh kg−1, respectively, for the30 mg cm−2, and 9, 532, and 511Wh kg−1, respectively, for the40 mg cm−2 mass loading. The specific energies were directlyrelated to the active mass loading level, which agrees with theprevious report that an increase in mass loading from 10 to30 mg cm−2 resulted in energy densities exceeding 500Wh kg−1[14]. The cycling performance of NMC622, NMC622+ 2 wt% cE,and NMC622+ 10 wt% cE electrodes based on the 30 mg cm−2,and 40mg cm−2 active mass loading was given in Figure 5c,and Figure 5d, respectively. Cells equipped with NMC622+cEcells exhibited stable cycling performance and high specificcapacity from the 1st cycle to the 10th cycle, with a highCoulombic efficiency of over 85% compared to the NMC622 cell,particularly for NMC622+ 10 wt% cE at a current density of0.1 mA cm−2, indicating the high ionic conductivity of theNMC622 matrix electrode. Interestingly, the effect of electrodeFIGURE 4 | Charge/discharge profiles of the 1st, 5th, and 10th cycles for electrochemical cells equipped with (a–c) 30 mg cm−2 and (d–f ) 40 mg cm−2active mass loading of NMC622, NMC622+ 2 wt% cE, and NMC622+ 10 wt% cE as the positive electrode at 60°C with 0.1 mA cm−2 and cut-off voltagesfrom 3.00–4.25 V.Batteries & Supercaps, 2026 5 of 8 25666223, 2026, 5, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/batt.70329 by National Institute For, Wiley Online Library on [12/07/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensemass loading on cycling performance strongly depends on thecontent of the combined electrolyte (cE). At a mass loading of30 mg cm−2, the capacity retention shows a moderate improve-ment with increasing cE content (46% for 2 wt% cE and 60% for10 wt% cE). In contrast, at 40 mg cm−2, the impact of cE becomessignificantly more pronounced, with capacity retention increas-ing from 26% (2 wt% cE) to 68% (10 wt% cE). This trend suggeststhat the role of cE becomes increasingly important as the elec-trode thickness increases. At lower mass loading, ionic transportpathways are relatively less limiting, and the contribution of cE istherefore less significant. However, at higher mass loading,where ionic transport limitations are more severe, the incorpo-ration of cE facilitates the formation of effective Li+ conductionpathways and improves interfacial contact within the compositecathode [20–23]. As a result, the cE effectively mitigates polari-zation and enhances cycling stability under high-mass-loadingconditions. Therefore, the observed cycling behavior reflectsnot only the effect of electrode thickness but also the synergisticcontribution of cE in overcoming transport limitations in thickelectrodes. Figure 5e illustrates a schematic representation ofthe structural design of the high-active-mass-loading electrodes(NMC622+ 2 wt% cE, and NMC622+ 10 wt% cE) combined witha multilayer hybrid electrolyte. The high-active-mass-loadingelectrodes often suffer from lacking electronic conductivity;therefore, the cE additives were incorporated with the assistanceof a binder. The conductive electrolyte matrix facilitated strongparticle adhesion and excellent attachment to the current collec-tor, forming a percolation pathway for efficient charge transport.(a) (b)30 mg cm-240 mg cm-2(c) (d)Al current collectorConductive ConductiveMatrixNMC622CATHODEMULTI-LAYER HYBRID ELECTROLYTEANODELi+ diffusionLi+ migrationAl current collectorNMC622High-mass-loading electrode with combined electrolyteActive Mass Loading (mg cm-2)EnergyDensityANODEConventional NMC-basedelectrodeEnergy DensityIncreasingHigher AdhesionAbility(e)020406080100120140160180200Averagedischargecapacity(mAhg-1)Sample Types30 mg cm-240 mg cm-2NMC622 NMC622+2wt% cE NMC622+10wt% cE NMC622 NMC622+2wt% cE NMC622+10wt% cE0100200300400500600SpecificEnergy(Whkg-1)Sample Types30 mg cm-240 mg cm-20 5 10 15 20 25 30400350300250200150100500Cycle NumberNMC622NMC622+2wt% cENMC622+10wt% cEDischargecapacity(mAh/g)020406080100Coulombicefficiency(%)0 5 10 15 20 25 30400350300250200150100500Cycle NumberNMC622NMC622+2wt% cENMC622+10wt% cEDischargecapacity(mAh/g)020406080100Coulombicefficiency(%)FIGURE 5 | (a) Average discharge capacities and (b) specific energies and average energies of high-active-mass-loading electrodes at various loadinglevels at 60°C with 0.1 mA cm−2 and cut-off voltages from 3.00–4.25 V. Discharge capacity and Coulombic efficiency over cycling for high-active-mass-loading positive electrode with (c) 30 mg cm−2 and (d) 40 mg cm−2 active mass loading. (e) Schematic illustration of the structural design of high-active-mass-loading electrode with a multilayer hybrid electrolyte.6 of 8 Batteries & Supercaps, 2026 25666223, 2026, 5, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/batt.70329 by National Institute For, Wiley Online Library on [12/07/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons LicenseMoreover, the incorporation of the cE into the cathode slurryfacilitates the formation of effective ionic conduction pathwaysbetween active material particles and reduces interfacial resis-tance at the cathode–hybrid electrolyte interface. On one hand,the presence of the ionic liquid (Pyr14TFSI) and LiTFSI enhancesLi+mobility within the composite electrode by establishing a per-colating ionic conduction network. On the other hand, the cEimproves interfacial contact between active material particlesand the multilayer HSE, thereby lowering interfacial resistanceand stabilizing the electrode/electrolyte interface. As the cE isdistributed throughout the cathode matrix, bulk ionic transportand interfacial effects are intrinsically coupled. Therefore, theimproved electrochemical performance is attributed to the syn-ergistic combination of enhanced Li+ transport within the elec-trode and improved interfacial stability. As a result, NMC622+cE‖Li metal cells demonstrated a superior electrochemicalperformance compared to conventional NMC622‖Li metal cell,particularly under high mass loading levels and elevated temper-ature conditions.3 | ConclusionIn this study, we fabricated NMC622-based positive electrodesincorporating cE with a variable electrolyte composition ratioof 2 wt% (NMC622+ 2 wt% cE) and 10 wt% (NMC622+ 10 wt%cE) for application in solid-state Li metal rechargeable batteries.High-active-mass-loading electrodes (30 and 40mg cm−2) weresuccessfully prepared by suppressing undesired gelation of theslurry solution by integrating them with a thin-film multilayerHSE. The binder-conductive matrix in the cathode possessesan effective ionic percolation pathway between the electrode par-ticles and improved interfacial contact with the electrolyte layer.Notably, the NMC622+cE‖Li metal cells exhibited superior bat-tery performance in comparison to the conventional NMC622‖Limetal cell. The specific energies were directly correlated withthe active mass loading level. Under a high mass loading,NMC622+cE‖Li cells delivered a specific capacity exceeding150 mAh g−1 when operated at 60°C within cut-off voltages from3.00 V to 4.25 V. In terms of cycling stability, cell equipped withNMC622+ 10 wt% cE demonstrated better capacity retention(68% after 10 cycles) than other samples. The methodology dem-onstrated in the present study highlight the potential of incorpo-rating cE into cathode compositions for high energy densitysolid-state Li metal batteries.4 | Experimental SectionPreparation of NMC622-based high-active-mass-loading positive elec-trode: A slurry of NMC622 powder (LiNi0.6Mn0.2Co0.2O2, ShanShanTech Co.; d50= 10.22 μm, d90= 14.09 μm; 85–94 wt%), carbon black(Super C65; Imerys Graphite & Carbon; 3 wt%), polyvinylidene fluo-ride (PVDF-HFP; Sigma–Aldrich; 3 wt%) binder, Benzophenone(BP, Merck, 99%), Pyr14TFSI (Solvionic, 99.9%), and LiTFSI (TCI,>98%) dissolved in N-methyl-1,2-pyrrolidone (NMP, ThermoFisher Scientific, 99.5%, AcroSeal, over molecular sieve) was coatedonto a carbon-coated aluminum (Al) current collector (a thicknessof 20 μm). The slurry film was cross-linked by UV curing(UVACUBE 100, 100W lamp, Dr. Hönle AG) for 40min. Then,the NMP solvent was removed by heating at 80°C under reducedpressure for 48 h, and the electrode sheets were obtained. The load-ing amount of the active materials was about 30 and 40mg cm−2.Chemicals were dried at 100°C under reduced pressure≤10−3 mbarfor 48 hours. For the NMC622 sample, the mixing process was con-ducted without the cE of Pyr14TFSI and LiTFSI.Electrode characterization: Field-emission scanning electronmicroscopy (S-4800, Hitachi) was used to characterize the mor-phology of the samples. Adhesion and conductivity measurementswere conducted on the calendered electrode sheets using a Zwickiuniversal testing machine (ZwickRoell GmbH and Co. KG). Bothmeasurements were carried out at room temperature. Prior to test-ing, the electrode sheets were calendered under an applied forceof �9.8 kN to ensure uniform thickness and mechanical integrity.For conductivity measurements, the applied force was varied from10 to 195 N, and each measurement was repeated three times toensure reproducibility. For the peeling test, the electrode sheetswere affixed to the top and bottom of two splints of double-sided3M tape. The splints were initially pressed together with a force of2000N for 60 s, after which they were gradually pulled apart underincreasing traction to determine the maximum adhesion force andeach measurement was repeated three times.Preparation of the multilayer HSE thin-film: Two electrolytepastes were prepared for coating both sides of the Celgard2500(Cg2500, Celgard), as illustrated in Figure 1b. For the anodepaste, PEO (Dow Chemical, molecular weight 4,000,000) was dis-solved in ACN (Carl Roth, ≥99.9%, ROTIDRY, ≤10 ppm H2O;333mg per 15 mL) by stirring at 60°C. Pyr14TFSI, LiTFSI, andBP (5 wt% of PEO content) were then added and mixed untila homogeneous mixture was obtained. This paste was appliedto one side of the Cg using a doctor blade, with the slit sizeadjusted to achieve a 12.5 μm thick PEO-based layer after dryingfor 30 min at room temperature in a dry room. For the cathodepaste, PVDF-HFP (Sigma–Aldrich, molecular weight 400,000)was dissolved in NMP (500mg per 5 mL) at 60°C, then mixedwith Pyr14TFSI, LiTFSI, and LATP (MSE PRO SolidElectrolyte, 300 nm; 325mg). This PVDF-HFP-based paste wasapplied to the opposite side of the Cg using a doctor blade, form-ing a 12.5 μm thick layer after drying. The coated films were thendried at 60°C under reduced pressure for 48 h to remove ACNand NMP, followed by UV cross-linking for 10min.Electrochemical measurements: All CR2032 two-electrode coincells were assembled in a dry room, utilizing 12 mm diameterround electrodes and 15mm diameter electrolyte films, as illus-trated in Figure S1. The separator (Cg2500) was coated on bothsides with PEO-based and PVDH-HFP-based electrolyte pastes,following the preparation of the thin-film multilayer HSE part.A relatively thick 150 μm lithium foil was used as negative elec-trode. Electrochemical characterization was performed on aMACCOR Series 4000 battery tester (MACCOR, Inc.) at 60°C.All the cells were cycled at a constant current density of0.1 mA cm−2 within a voltage range of 3.00–4.25 V.AcknowledgmentsThe authors gratefully acknowledge support of this work by JapanScience and Technology Agency (JST), Adopting Sustainable PartnershipsBatteries & Supercaps, 2026 7 of 8 25666223, 2026, 5, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/batt.70329 by National Institute For, Wiley Online Library on [12/07/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensefor Innovative Research Ecosystem (ASPIRE), under Contract No.JPMJAP2309. This work also received support from the National Institutefor Materials Science (NIMS) Battery Research Platform.Open Access funding enabled and organized by Projekt DEAL.Conflicts of InterestThe authors declare no conflicts of interest.Data Availability StatementThe data that support the findings of this study are available from thecorresponding author upon reasonable request.References1. S. H. Jung, U.-H. Kim, J.-H. Kim, et al., “Ni-Rich Layered CathodeMaterials with Electrochemo-Mechanically Compliant Microstructuresfor All-Solid-State Li Batteries,” Advanced Energy Materials 10, no. 6(2020): 1903360, https://doi.org/10.1002/aenm.201903360.2. P. Minnmann, F. Strauss, A. 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Introduction 2. Results and Discussion 3. Conclusion 4. Experimental Section