We present a strategic approach for enhancing the ionic conductivity of block copolymer electrolytes. This was achieved by introducing mixed ionic liquids (ILs) with varying molar ratios, wherein the imidazolium cation was paired with either tetrafluoroborate (BF4) anion or bis(trifluoromethylsulfonyl)imide (TFSI) anion. Two polymer matrices, poly(4-styrenesulfonate)-b-polymethylbutylene (SSMB) and poly(4-styrenesulfonyl (trifluoromethanesulfonyl)imide)-b-polymethylbutylene (STMB), were synthesized for this purpose. All the SSMB and STMB containing mixed ILs showed hexagonal cylindrical structures, but the type of tethered acid group significantly influenced the interfacial properties. STMB electrolytes demonstrated enhanced segregation strength, which was attributed to strengthened Coulomb and hydrogen bonding interactions in the ionic domains, where the ILs were uniformly distributed. In contrast, the SSMB electrolytes exhibited increased concentration fluctuations because the BF4 anions were selectively sequestered at the block interfaces. This resulted in the effective confinement of imidazolium TFSI along the ionic domains, thereby preventing ion trapping in dead zones and facilitating rapid ion diffusion. Consequently, the SSMB electrolytes with mixed ILs demonstrated significantly improved ionic conductivities, surpassing the expected values based on the arithmetic average of the conductivities of each IL, whereas the ionic conductivity of the STMB was aligned with the expected average. The methodology explored in this study holds great promise for the development of solid-state polymer electrolytes.

Ionic liquid (IL)-containing polymers have been attracting increasing interest as nonflammable electrolytes in diverse applications such as energy storage systems,1,2 electrochromic devices,3 and electromechanical devices.4,5 These materials can be designed to exhibit flexibility6 and self-healing capabilities,7,8 making them suitable for integration into wearable electronics that are subjected to frequent movements and mechanical stress.

Ionomers, which possess ionic moieties covalently attached to their backbones, are commonly employed as matrix polymers to incorporate ILs.9–12 The hydrophobic nature of ionomer backbones and strong electrostatic interactions among the ionic moieties facilitate microphase separation, resulting in the formation of ion-rich domains embedded within the hydrophobic polymer matrix.13–15 These domains serve as conduits for ion diffusion, while the electrostatic interactions involving them play a crucial role in determining the ion relaxation, ion distribution, and morphology of ion aggregates.16,17

However, the interactions between ions and the polymer matrix often hinder ion relaxation, leading to their sluggish dynamics.18,19 Additionally, excessive ion agglomeration at high ion concentrations creates discrete ionic domains that impede efficient ion transport and pose challenges for practical applications.11,20 Consequently, researchers have pursued various strategies to achieve a delicate balance between the connectivity of ion-rich domains and rapid ion diffusion, such as the chemical control of the polymer backbone,21–23 exploration of different ILs,24–28 and modulation of local ion concentrations.29,30

An extensive body of literature is available on the widespread utilization of block copolymers comprising ionomer chains and ionophobic polymers to enhance the connectivity of ion-rich regions and facilitate ion migration along well-defined pathways.10,31 Hierarchical self-assembled structures of various lengths can be achieved by incorporating ILs into these block copolymers.32,33 Valuable insights into the arrangement of ions and polymer chains of different length scales were obtained through advanced imaging techniques34,35 and computational modeling,32,36,37 shedding light on their influence on ion-transport properties.

Tailoring of ionophilic and ionophobic blocks allows the control of mechanical and ion-transport properties of block copolymers.7,21,38,39 Additionally, the electrolyte properties, including the ion diffusion coefficients and ion solvation characteristics, can be modified by choosing appropriate cations and anions in ILs.24–26,40,41 A large number of studies have focused on investigating the relationship between the morphology and transport properties of block copolymers containing ILs for simultaneously enhancing their mechanical and ion-transport properties.42,43 However, this objective has not yet been achieved because of significant challenges, such as small grain sizes that form dead ends44,45 and the occurrence of dead zones where ions become trapped at block interfaces.46 

Hence, significant efforts have been made for modulating the ion-transport properties of block copolymer electrolytes through interfacial manipulations.26,32,44 Although block copolymer electrolytes form similar lamellar structures, their ionic conductivities can significantly vary by several orders of magnitude owing to their distinct interfacial properties. Min et al. recently proposed the concept of creating an interfacial passivation layer between the ionophobic and ionophilic domains of acid-tethered polymers using nonstoichiometric ILs.32 This approach enhances the ion-transport efficiency by reducing composition fluctuations at the interfaces and establishing a more favorable pathway for ion diffusion. Importantly, this concept has been successfully applied to homopolymers5 as well as block copolymers.32 

This study discusses a methodology to enhance the ionic conductivity of block copolymers containing ILs by combining two different ILs at varying molar ratios. Selective sequestration of one type of IL at the block interfaces was achieved by tailoring electrostatic interactions between each IL and the polymer matrix, thereby effectively reducing the interfacial energy. However, other types of ILs can predominantly exist in ionophilic domains, thereby preventing ion trapping in dead zones. The resulting ionic conductivity is greater than the expected values determined based on the simple arithmetic average of the conductivity of the block copolymer electrolyte with each IL.

Intermolecular attractions within polymer electrolytes were regulated by simultaneously controlling both the polymer matrices and physically embedded ILs. This process involved the synthesis of two types of acid-tethered block copolymers with distinct acid groups. First, a polystyrene-b-poly(methylbutylene) (PS-b-PMB) block copolymer was synthesized, followed by the sulfonation of the PS block of PS-b-PMB to produce poly(4-styrenesulfonate)-b-polymethylbutylene (SSMB) with a sulfonation level of 33 mol. %. Subsequently, the sulfonic acid groups of the SSMB were converted to sulfonyl(trifluoromethanesulfonyl) imide, affording a poly(4-styrenesulfonyl (trifluoromethanesulfonyl)imide)-b-polymethylbutylene (STMB) block copolymer (details shown in the supplementary material). Figure 1(a) shows the chemical structures of both SSMB and STMB. Note that both SSMB and STMB contain identical polymer backbones with the same degree of polymerization and molecular weight distribution, except for the presence of different acid functional groups.

FIG. 1.

Chemical structures of (a) two types of acid-tethered block copolymers (SSMB and STMB) and (b) ionic liquids ([HMIm][BF4] and [HMIm][TFSI]) comprising different anions.

FIG. 1.

Chemical structures of (a) two types of acid-tethered block copolymers (SSMB and STMB) and (b) ionic liquids ([HMIm][BF4] and [HMIm][TFSI]) comprising different anions.

Close modal

We utilized two imidazolium ILs: 1-hexyl-3-methylimidazolium tetrafluoroborate ([HMIm][BF4]) and 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([HMIm][TFSI]). Their chemical structures are presented in Fig. 1(b). [HMIm][TFSI] consists of a large TFSI anion with a delocalized charge, resulting in low binding energy between the HMIm cation and the TFSI anion (Table S1, supplementary material). This is connected to the facile dissociation of the IL within the ionophilic domains of the SSMB and STMB block copolymers. In contrast, the dissociation of [HMIm][BF4] requires a higher energy barrier owing to the relatively strong binding energy of the HMIm cation with the BF4 anion, as compared to the interaction with polymer acid groups. Given the lower viscosity and higher ionic conductivity of neat [HMIm][TFSI] than those of [HMIm][BF4] (Fig. S1, supplementary material), it is anticipated that polymer electrolytes containing [HMIm][TFSI] will exhibit higher conductivity than that of the polymers containing [HMIm][BF4].

Based on the estimated ion-dissociation behavior of each IL, we herein propose a method to control the charging behavior and distribution of ions within acid-tethered block copolymers using the mixed ILs: [HMIm][BF4] and [HMIm][TFSI]. The relative molar ratios of [HMIm][BF4]:[HMIm][TFSI] with respect to the acid groups in the polymer matrix were systematically varied as 1:0, 0.67:0.33, 0.5:0.5, 0.33:0.67, and 0:1, denoted by specific codes B1, B2T1, B1T1, B1T2, and T1, respectively (Table I). The total amount of the IL used was adjusted to be equimolar to the number of acid functional groups in the polymer. This deliberate adjustment allowed us to systematically modulate the intermolecular interactions between ionic moieties within the polymer matrices. Proton nuclear magnetic resonance (1H-NMR) spectra were employed to validate the compositions of the ionic liquids in the prepared polymer electrolytes (Fig. S2, supplementary material).

TABLE I.

Codes of mixed ionic liquids, [HMIm][BF4] and [HMIm][TFSI], introduced into the SSMB and STMB.

Molar ratiosTotal wt. %Total wt. % ofVolume fraction (f)Volume fraction (f)a
Mixed ionicof R:[HMIm][BF4]of ionicionic liquidsaof ionicof ionic
liquid code:[HMIm][TFSI] liquids in SSMBin STMB domain in SSMBdomain in STMB
B1 1.0:1.0:0 27 23 0.595 0.624 
B2T1 1.0:0.67:0.33 31 27 0.610 0.637 
B1T1 1.0:0.50:0.50 34 29 0.617 0.643 
B1T2 1.0:0.33:0.67 36 31 0.624 0.649 
T1 1.0:0:1.0 39 35 0.637 0.660 
Molar ratiosTotal wt. %Total wt. % ofVolume fraction (f)Volume fraction (f)a
Mixed ionicof R:[HMIm][BF4]of ionicionic liquidsaof ionicof ionic
liquid code:[HMIm][TFSI] liquids in SSMBin STMB domain in SSMBdomain in STMB
B1 1.0:1.0:0 27 23 0.595 0.624 
B2T1 1.0:0.67:0.33 31 27 0.610 0.637 
B1T1 1.0:0.50:0.50 34 29 0.617 0.643 
B1T2 1.0:0.33:0.67 36 31 0.624 0.649 
T1 1.0:0:1.0 39 35 0.637 0.660 
a

f = fSS(or ST) + fionic liquid.

Small-angle x-ray scattering (SAXS) experiments were conducted to investigate the morphologies of STMB- and SSMB-containing mixed ILs. The neat STMB and SSMB block copolymers, with symmetric compositions, exhibited lamellar structures with domain spacings (d10) of 12.1 and 11.4 nm, respectively (Fig. S3, supplementary material). When ILs are added, these lamellar structures transform into gyroid or hexagonal cylindrical (HEX) structures, depending on the composition of the ILs. As depicted in Fig. 2, both STMB and SSMB electrolytes displayed gyroid structures with T1, despite having significantly different domain spacings (14.6 nm for STMB and 13.1 nm for SSMB), as shown in the insets. This corresponds to 21% and 15% increments in the domain spacings for STMB and SSMB electrolytes, respectively, compared to those of their neat counterparts. The enhanced swelling behavior of STMB with T1 can be attributed to the chemical similarity between the TFSI moieties of the ILs and those of poly(4-styrenesulfonyl (trifluoromethanesulfonyl)imide) (PST) blocks. In contrast, [HMIm][TFSI] was less compatible with the poly(4-styrenesulfonate) (PSS) chains in the SSMB.

FIG. 2.

Small-angle x-ray scattering profiles and domain spacings of STMB and SSMB comprising mixed ionic liquids with various ratios. Both STMB and SSMB exhibit gyroid structures with T1, whereas samples with other ionic liquid compositions show hexagonal cylindrical structures, as indicated by Bragg peaks (inverted filled triangles).

FIG. 2.

Small-angle x-ray scattering profiles and domain spacings of STMB and SSMB comprising mixed ionic liquids with various ratios. Both STMB and SSMB exhibit gyroid structures with T1, whereas samples with other ionic liquid compositions show hexagonal cylindrical structures, as indicated by Bragg peaks (inverted filled triangles).

Close modal

HEX structures were observed in all the SSMB and STMB electrolytes containing B1T2, B1T1, B2T1, and B1. Interestingly, the presence of [HMIm][BF4] promoted the swelling of the SSMB, resulting in notably reduced differences in domain sizes between the SSMB and STMB electrolytes. Furthermore, the introduction of mixed ILs markedly enhanced the segregation strength of the STMB electrolytes compared to that of their SSMB counterparts. This increase in the Flory–Huggins interaction parameter of the STMB electrolytes can be attributed to the enhanced Coulomb and hydrogen bonding interactions between the ILs and PST chains, owing to effective charging. The relatively less-ordered HEX structures of the SSMB electrolytes indicate that the type of tethered acid groups in the polymers significantly affects the interfacial properties and concentration fluctuations of block copolymers when combined with mixed ILs. These observations highlight the potential for elaborately modulating the phase behavior of block copolymer electrolytes through effectively and strategically using mixed ILs.

The ionic conductivities of the STMB and SSMB electrolytes with different mixed ionic compositions are depicted in Figs. 3(a) and 3(b), respectively. The most significant difference was that the highest ionic conductivity was achieved when T1 was incorporated into STMB; however, when it was incorporated into SSMB, the ionic conductivity drastically decreased by several orders of magnitude. The conductivity of SSMB electrolytes with T1 was not measurable below 80 °C, despite [HMIm][TFSI] being a room-temperature IL. This phenomenon was attributed to the ineffective plasticization of the PSS chains with [HMIm][TFSI], which impeded ion/polymer relaxation at temperatures below the glass transition temperature (Tg) of the PSS chain.

FIG. 3.

Ionic conductivities of (a) STMB and (b) SSMB electrolytes. Comparative 19F NMR spectra of TFSI and BF4 anions in (c) STMB and (d) SSMB electrolytes, highlighting the distinctions between single ionic liquid and mixed ionic liquids.

FIG. 3.

Ionic conductivities of (a) STMB and (b) SSMB electrolytes. Comparative 19F NMR spectra of TFSI and BF4 anions in (c) STMB and (d) SSMB electrolytes, highlighting the distinctions between single ionic liquid and mixed ionic liquids.

Close modal

The addition of B1 significantly reduced the conductivity of the STMB electrolytes by two orders of magnitude compared to that of T1. This decrease aligns with the anticipated outcome based on two factors: (1) the lower conductivity of neat [HMIm][BF4] than that of neat [HMIm][TFSI], and (2) the strong binding between the HMIm cations and BF4 anions, which hinders ion dissociation. However, this prediction is not consistent with the conductivity trend observed for the SSMB electrolytes. Incorporating B1 into SSMB enhanced the conductivity by more than two orders of magnitude compared to that of T1. This enhancement can be partially attributed to the effective swelling of the PSS domains by B1 (Fig. 2), which transforms them into major domains and creates less tortuous ion-conducting pathways.

The ionic conductivity results obtained for the mixed ILs also showed significant differences between the STMB and SSMB electrolytes. For the STMB electrolytes, the overall ionic conductivity followed a trend that matched the arithmetic average of the [HMIm][TFSI] and [HMIm][BF4] compositions in the order of T1 > B1T2 > B1T1 > B1, as shown in Fig. 3(a). Conversely, as depicted in Fig. 3(b), the ionic conductivity of the SSMB was unexpected when mixed ILs were used and surpassed the arithmetic means of T1 and B1. Although the ionic conductivity of the SSMB electrolytes with mixed ILs showed minimal alteration with the [HMIm][BF4] and [HMIm][TFSI] compositions, the highest conductivity was obtained for the SSMB with B1T1.

19F NMR provides valuable insights into ion relaxation within the STMB and SSMB electrolytes. In STMB containing T1 (represented by the dotted red line), as shown in Fig. 3(c), a single 19F NMR peak was evident, and this peak remained relatively unchanged in the presence of coexisting BF4 anions (indicated by the dotted purple line). It is inferred that TFSI anions have effective Coulomb interactions with PST chains owing to their chemical similarity with PST chains. On the other hand, BF4 anions exist in various states when they coexist with TFSI anions, as evident from the considerable peak broadening. The observed F-electron shielding in the BF4 signal of STMB with B1T1 serves as an evidence of the close association of BF4 anions with TFSI anions for further ionization.

In SSMB, the TFSI and BF4 signals exhibited notable differences compared to STMB. As depicted in Fig. 3(d), the SSMB with T1 (solid red line) exhibited three distinct TFSI peaks (indicated by inverted red arrows). This observation suggests the existence of three different states of TFSI anions in the SSMB electrolyte: hydrogen bonding between –SO3H and TFSI (broad peak downfield), Coulomb interaction of TFSI anions with PSS chains facilitated by HMIm cations (strongest peak), and the presence of TFSI anions in the form of an IL (upfield). This phenomenon arises because of the incomplete ionization of –SO3H groups and the limited access of bulky [HMIm][TFSI] to the acid groups in SSMB. This result is in good agreement with the limited swelling behavior shown by SSMB electrolytes with T1 (Fig. 2).

Given the weak affinity of TFSI anions with PSS chains, the coexisting B1 effectively altered the ionic state of TFSI. An examination of SSMB with B1T1 showed the occurrence of a single TFSI peak, accompanied by a considerable upfield shift [indicated by the solid purple line in Fig. 3(d)]. We surmise that [HMIm][BF4] has easy access to the PSS chains at the block interfaces, leading to improved dissociation of sulfonic acid groups and, consequently, increased effective proton concentration. Hence, the efficacy of Coulomb interactions between the TFSI anions and the PSS chains enhanced because of the formation of a –SO3H+⋯TFSI⋯HMIm+ complex, resulting in the F-electron shielding of the TFSI anions. This result could be closely related to the enhanced ionic conductivity observed in the SSMB with B1T1 [Fig. 3(b)].

To validate our hypothesis and obtain a comprehensive understanding of ion distribution in SSMB electrolytes containing mixed ILs, we employed dynamic secondary ion mass spectrometry (DSIMS). To ensure the accuracy of the DSIMS analysis, we synthesized high-molecular-weight SS153MB313 (total degree of polymerization: 466) with a sulfonation level of 25 mol. %. This synthesis resulted in the formation of lamellar structures in the SSMB electrolyte, featuring a larger domain of >42 nm, which improved the resolution of the DSIMS profiles. SAXS profiles of high-molecular-weight SSMB electrolytes with B1 and T1 are provided in the supplementary material (Fig. S4).

The SSMB electrolytes with B1 and T1 were spin-coated onto Si/SiO2 substrates. Parallel alignment of the lamellae was achieved by thermal annealing. Surface morphologies of resulting SSMB films are shown in the supplementary material (Fig. S5). Based on the detection of S and F ions, we observed both sulfonic-acid-rich and IL-rich regions in the aligned lamellar structures. It should be mentioned that conducting DSIMS analysis on STMB electrolytes was a challenging task, primarily due to the complexity of interpreting the F-signal, which could originate from both PST chains and ionic liquid anions. Furthermore, the hygroscopic nature of PST chains, which absorbed significant amounts of water, led to poor-quality data due to film dewetting.

Figures 4(a) and 4(b) reveal the distinct distributions of anions in the SSMB electrolytes containing both B1 and T1. Fascinatingly, the hydrophilic [HMIm][BF4] did not exhibit selective accumulation in the ionophilic PSS domains; rather, BF4 anions predominantly resided at the interfaces between the PSS and PMB domains, consistent with our hypothesis based on the SAXS profiles and 19F NMR spectra. This is likely owing to the small size of the BF4 anions, which enables [HMIm][BF4] to form a passivation layer primarily at the block interfaces of the SSMB electrolytes to reduce the interfacial energy. In contrast, the TFSI anions from [HMIm][TFSI] tended to be preferentially positioned within the PSS domains rather than at the block interfaces.

FIG. 4.

Secondary dynamic ion mass spectroscopy profiles of SSMB electrolytes with (a) B1 and (b) T1. (c) Schemes depicting the preferential migration of [HMIm][BF4] at SSMB electrolyte interfaces, with [HMIm][TFSI] being effectively localized within PSS domains.

FIG. 4.

Secondary dynamic ion mass spectroscopy profiles of SSMB electrolytes with (a) B1 and (b) T1. (c) Schemes depicting the preferential migration of [HMIm][BF4] at SSMB electrolyte interfaces, with [HMIm][TFSI] being effectively localized within PSS domains.

Close modal

The precise assessment of the selective distribution of each anion in SSMB electrolytes containing mixed ILs is challenging because of the lower ionization ratio of TFSI anions than that of BF4 anions. However, reasonable conclusions can still be drawn. The presence of a passivation layer formed by [HMIm][BF4] at the interface facilitated the rapid diffusion of the coexisting [HMIm][TFSI] along the ionophilic domains. The preferential accumulation of [HMIm][BF4] in the PSS/PMB interface is expected to prompt a lateral expansion of the block copolymer. To substantiate this, the thickness values of the PMB and PSS domains were experimentally determined via Kratky analysis of SAXS data (Fig. S6, supplementary material). Notably, the PMB domain thickness remained unaltered when [HMIm][TFSI] was introduced into SSMB, whereas SSMB with B1 exhibited a substantial increase in PMB thickness. By considering the volumes and densities of each constituent, we projected an increase in the interfacial area per junction point from 3.68 nm2 (neat SSMB) to 3.93 nm2 (SSMB with B1).

This phenomenon allowed for more effective Coulomb interactions between [HMIm][TFSI] and the PSS chains, thereby preventing ion trapping in the dead zones. These underlying mechanisms account for the high ionic conductivities of the SSMB electrolytes with mixed ILs, surpassing the arithmetic means of the conductivity values obtained with B1 and T1 [Fig. 3(b)]. This tendency remained consistent for high-molecular-weight SSMB electrolytes, even though the resulting self-assembled structures were lamellae (unlike the HEX structures seen in small-molecular-weight samples), as shown in Fig. S7 of the supplementary material.

Considering the inherently higher ionic conductivity of neat [HMIm][TFSI] compared to neat [HMIm][BF4] (as listed in Table S1), one might anticipate that SSMB with T1 would exhibit higher conductivity when compared to SSMB with B1. However, the Tg values of SSMB with B1 and T1 were 43.2 and 86.7 °C, respectively. This indicates limited plasticization of the PSS chains by [HMIm][TFSI], resulting in the notably lower conductivity, attributed to incomplete ionization of the –SO3H groups. When B1T1 was used, the Tg of SSMB decreased to 59.3 °C (Table S2). It is evident that the enhanced conductivity of SSMB with B1T1, compared to B1, was not due to Tg considerations. Instead, it can be attributed to the enhanced charging of TFSI anions in the presence of coexisting BF4 anions played a role in improving conductivity of SSMB containing B1T1. It is important to note that this Tg trend was not observed in STMB electrolytes: the Tg values were 13.8, 18.5, and 29.3 °C with T1, B1T1, and B1, respectively, correlating with the conductivity in the order of T1, B1T1, and B1. This is owing to the high dissociation of [HMIm][TFSI] in PST domains, which remained consistent regardless of the type of ionic liquids employed.

It is important to highlight that our investigations into SSMB electrolytes containing different combinations of ionic liquids, such as [HMIm][PF6] and [HMIm][TFSI], consistently revealed higher conductivity when employing mixed ionic liquids compared to individual ones (Fig. S7, supplementary material). Additionally, DSIMS profiles again confirmed the preferential interactions of PF6 anions at PSS/PMB interfaces (Fig. S8, supplementary material). This validates our hypothesis that the efficiency of Coulomb interactions between TFSI anions and PSS chains is enhanced when smaller anions coexist. In contrast, when we conducted experiments using a combination of [HMIm][BF4] and [HMIm][PF6] with similar-sized anions, we did not observe an enhancement in conductivity when using mixed ionic liquids (Fig. S7).

The investigation of the selective migration of ions of different sizes within confined spaces has been attracting increasing research attention.48–50 These confined spaces encompass micropores, mesopores, and nanogaps between metal electrodes. Computational simulations and models yielded interesting findings. When mixed counterions of the same valence coexist, the preferential adsorption of smaller counterions onto the charged surfaces of the micropores occurs, owing to the surface energy and entropic effect.47,48

Block copolymers containing mixed ILs notably differ from these porous systems. First, the ionophilic nanodomains contain polymer chains instead of being vacant. Second, the TFSI and BF4 anions serve as co-ions for the acid functional moieties of the polymers (assuming deprotonation), thus envisioning the preferential adsorption of HMIm+ cations. The adsorption of anions occurs either to uphold charge balance or through hydrogen bonding interactions with polymer acid groups. Consequently, the formation of a passivation layer in the SSMB electrolyte interfaces involving BF4 anions becomes intricate because of ion–ion and ion–polymer interactions as well as the interfacial energies of the ionophilic and ionophobic blocks. We infer that smaller BF4 anions, owing to their strong binding, are selectively positioned at the PSS/PMB interfaces to lower the interfacial energy. Conversely, the larger TFSI ions with delocalized charges lack the entropic and enthalpic driving forces to penetrate the interfaces.

This study explored an approach to manipulate the morphology and ionic conductivity of acid-tethered block copolymers using mixed ILs. The distinctive strength of the intermolecular interactions exhibited by each IL with acidic functional groups played a significant role in influencing the phase separation behavior, interfacial properties, and concentration fluctuations in the resulting block copolymer electrolytes. Notably, the sacrificial interaction between [HMIm][BF4] and the acid functional groups at the block interfaces in the SSMB electrolytes allows for the efficient confinement of [HMIm][TFSI] within the PSS domains, leading to effective Coulomb interactions with the acid groups and resulting in rapid ion diffusion when mixed ILs are employed. These findings provide invaluable insights into enhancing the ion-transport properties of block copolymer electrolytes by precisely modulating the ion distribution through finely tuned intermolecular interactions with mixed ILs within confined nanostructures.

Refer to the supplementary material for experimental details, ionic conductivity results of neat ILs, 1H-NMR spectra of SSMB and STMB electrolytes, SAXS profiles of neat block copolymers, surface morphologies of SSMB films with T1 and B1, Kratky analysis determining the thickness values of PMB and PSS domains, SAXS profiles and ionic conductivities of high-molecular-weight SSMB electrolytes.

This work was financially supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (Grant Nos. NRF-2022R1A2C3004667, NRF-2017R1A5A1015365, and NRF-2018M3D1A1058624). Professor Park also acknowledge financial support from Korea Toray Science Foundation.

The authors have no conflicts to disclose.

M.J.P. conceived the idea and designed the project. J.M. and S.B. carried out the synthesis, morphology analyses, and conductivity measurements. D.K. and K.T. performed DSIMS experiments and analyzed data. M.J.P. and J.M. wrote the manuscript.

Jaemin Min: Data curation (lead); Formal analysis (lead); Methodology (equal); Validation (equal); Writing – original draft (supporting). Suhyun Bae: Data curation (supporting); Formal analysis (supporting). Daisuke Kawaguchi: Data curation (supporting); Formal analysis (supporting); Investigation (equal). Keiji Tanaka: Formal analysis (supporting); Investigation (supporting); Supervision (supporting). Moon Jeong Park: Conceptualization (lead); Funding acquisition (equal); Investigation (lead); Supervision (lead); Validation (equal); Writing – original draft (lead); Writing – review & editing (equal).

The data that support the findings of this study are available within the article and its supplementary material.

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Supplementary Material