Lithium-sulfur batteries suffer from polysulfide shuttle (PS) and lithium metal anode instability. We developed a mixed-anion ionic liquid (IL) electrolyte combining N-trimethyl-N-propylammonium bis(fluorosulfonyl)imide (N1113FSI) with LiFSI and LiTFSI, enabling stable lithium metal passivation while suppressing polysulfide dissolution to sub-mM levels. Electrochemical testing demonstrates a specific capacity of 900 mA h g- 1 with 70% retention after 300 cycles. Electrochemical impedance spectroscopy (EIS) reveals a substantial reduction in charge-transfer resistance post-lithiation and stable impedance during extended cycling. Raman spectroscopy confirms effective polysulfide suppression. Notably, cell performance is insensitive to the electrolyte-to-sulfur ratio (10-45 µL mg- 1), in contrast to conventional ether-based electrolytes. Depth-resolved x-ray photoelectron spectroscopy (XPS) reveals that N1113FSI forms abundant LiF through efficient anion reduction, yielding a dense, inorganic-rich solid-electrolyte interphase (SEI). In contrast, P111i4FSI retains incompletely reduced anions and exhibits diminished LiF, demonstrating cation-dependent control of SEI chemistry. The N1113FSI interphase contains higher levels of LiF, Li-sulfide, oxidized sulfur, and inorganic oxygen species, which correlate with superior cycling stability. Compared to P111i4FSI, N1113FSI achieves higher discharge capacity (DC), faster Coulombic efficiency (CE) stabilization, and sustained reversibility. Tailored IL design effectively suppresses polysulfide solubility and engineers efficient SEI chemistry, mitigating shuttle effects and enabling stable Li-S operation across varying electrolyte concentrations.

Lithium-sulfur (Li-S) batteries are among the most promising next-generation energy storage technologies due to their high theoretical energy density and the abundance of sulfur. However, their practical implementation is limited by active material loss, unstable electrode interfaces, intermediate polysulfide dissolution, and low sulfur utilization. In this study, we present a hybrid binder composed of a lithium-ion-conductive poly(ionic liquid) (PIL), poly(diallyldimethylammonium) bis(trifluoromethanesulfonyl)imide (PDADMA-TFSI), and carboxymethyl cellulose (CMC) engineered to operate synergistically with ionic liquid (IL) electrolytes based on trimethylisobutylphosphonium bis(fluorosulfonyl)imide [P111i4][FSI] and N-trimethyl-N-propylammonium bis(fluorosulfonyl)imide [N1113][FSI]. This PIL-CMC binder significantly improves interfacial stability and enables efficient sulfur utilization in polysulfide-free cycling. Among all combinations tested, 50 mol% LiTFSI in [N1113][FSI] exhibited the best electrochemical performance, sustaining capacities above 1100 mA h g-1 for over 100 cycles at 50 degrees C. A reduced total binder content formulation (5 wt% PIL and 5 wt% CMC) maintained comparable performance, suggesting potential for further optimization. Electrochemical analysis revealed low voltage polarization and high Coulombic efficiency of up to 99.5 %, while UV-vis and Raman spectroscopy confirmed the absence of dissolved polysulfides. Overall, this work demonstrates a robust and scalable strategy for realizing additive-free, thermally stable Li-S cathodes, emphasizing the importance of binder-electrolyte integration in the design of high-performance Li-S batteries.

Despite the potential for a greater energy density than lithium-ion batteries, polysulphide dissolution, the polysulphide shuttle effect, and lithium metal instability impede the commercialization of lithium–sulfur (Li–S) batteries.

Organic ionic plastic crystals (OIPCs) are attractive solid electrolyte materials for advanced energy storage systems owing to their inherent advantages (e.g., high plasticity, thermal stability, and moderate ionic conductivity), which can be further improved/deteriorated by the addition of polymer or metal oxide nanoparticles. The role of the nanoparticle/OIPC combinations on the resultant interphase structure and transport properties, however, is still unclear due to the complexity within the composite structures. Herein, we demonstrate a systematic approach to specifically interrogating the interphase region by fabricating layered OIPC/polymer thin films via spin coating and correlating variation in the ionic conductivity of the OIPC with their microscopic structures. In-plane interdigitated electrodes have been employed to obtain electrochemical impedance spectroscopy (EIS) spectra on both OIPC and layered OIPC/polymer thin films. The thin-film EIS measurements were evaluated with conventional bulk EIS measurements on the OIPC pressed pellets and compared with EIS obtained from the OIPC-polymer composites. Interactions between the OIPC and polymer films as well as the morphology of the film surfaces have been characterized through multiple microscopic analysis tools, including scanning electron microscopy, energy-dispersive X-ray spectroscopy, atomic force microscopy, and optical profilometry. The combination of EIS analysis with the microscopic visualization of these unique layered OIPC/polymer thin films has confirmed the impact of the OIPC-polymer interphase region on the overall ionic conductivity of bulk OIPC-polymer composites. By changing the chemistry of the polymer substrate (i.e., PMMA, PVDF, and PVDF-HFP), the importance of compatibility between the components in the interphase region is clearly observed. The methods developed here can be used to screen and further understand the interactions among composite components for enhanced compatibility and conductivity.

Organic ionic plastic crystals (OIPCs) combine some advantages of liquid electrolytes and ion-conducting ceramic electrolytes in the form of nonvolatile, nonflammable, and mechanically stable electrolytes that improve electrolyte/electrode interfacial contact and have good thermal stability. Investigations of the interactions (e.g., between cation/anion pairs or between OIPC/second phases) and ion transport behaviors are crucial to understand the physical chemistry nature of their interactions, which benefits the development of new electrolyte systems. In this report, we first analyzed the thermal phase behavior and ion transporto: f a new OIPC, triethyl(methyl)phosphonium tetrafluoroborate [P-1222] [BF4]. We further discussed how the interactions between poly(vinylidene difluoride) (PVDF) and the OIPC, as well as the Li-doped [P-1222] [BF4], improve OIPC properties such as crystalline behavior, conductivity, ion mobility, and electrochemical behaviors. We found that less conductive secondary phases are formed after doping with LiBF4; however, the crystallization of the secondary phase is suppressed in the presence of PVDF nanoparticles. Lithium symmetric cell cycling shows that [P-1222] [BF4]-based composites show stable Li plating/stripping behaviors at a high temperature of 100 degrees C, with a current density up to 0.2 mA cm(2). This work demonstrates the potential of [P-1222] [BF4] composites as solid electrolytes in next-generation solid-state secondary batteries.

Organic ionic plastic crystals (OIPCs) are promising solid electrolytes because of their inherent advantages such as non-volatility, non-flammability, good thermal stability, favourable plasticity, and improved electrolyte/electrode interfacial contact. Incorporating nanoparticles into some OIPC matrixes has proven an effective strategy for further increasing conductivity and mechanical integrity. However, the nature of the interaction between the cations and anions of OIPCs with polymers requires further study. In this work, various OIPCs consisting of N-ethyl-N-methyl pyrrolidinium cations ([C2mpyr] ) and three different anions bis(trifluoromethanesulfonyl)imide ([TFSI] ), (bis(fluorosulfonyl)imide ([FSI] ) and tetrafluoroborate, [BF4] ) are selected. The interactions between the OIPCs and poly(vinylidene fluoride) (PVDF) are studied by incorporating different volume fractions of PVDF nanoparticles into the OIPC matrices. Differential scanning calorimetry (DSC), electrochemical impedance spectroscopy (EIS), nuclear magnetic resonance (NMR) and synchrotron X-ray diffraction (XRD) techniques confirm that the OIPCs with different anions interact differently with PVDF. Furthermore, we propose that the degree of the interaction and ionic conductivity enhancement relates to different dipole moments of the OIPC anions. This anion originated interaction induces the formation of disordered OIPC interphases which accounts for the ionic conductivity enhancement.

Sodium ion batteries are widely considered to be a feasible, cost-effective, and sustainable energy storage alternative to Lithium, especially for large-scale energy storage applications. Next generation, safer electrolytes based on ionic liquid (IL) and organic ionic plastic crystals (OIPCs) have been demonstrated as electrochemically stable systems which show superior performance in both Li and Na applications. In particular, phosphonium‐based systems outperform most studied nitrogen‐based ILs and OIPCs. In this study triisobutyl(methyl)phosphonium bis(fluorosulfonyl)imide ([P 1i444 ][FSI]) OIPC mixed with 20 mol% of NaFSI or NaTFSI were combined with an electrospun polyvinylidene fluoride (PVDF) support to create self-standing electrolyte membranes, and their thermal phase behaviour and ionic conductivity were investigated and compared with the bulk electrolytes. The ability of the solid-state composite electrolytes to support the cycling of sodium metal with good efficiency and without breakdown were examined in sodium metal symmetrical coin cells. The sodium transference number was determined to be 0.21. The electrochemical performance of Na/Na 3 V 2 (PO 4 ) 3 cells incorporating the composite electrolytes, including good cycling stability and rate capability, is also reported. Interestingly, the mixed anion systems appear to outperform the composite electrolyte containing only FSI anions, which may relate to electrolyte interactions with the PVDF fibres.

Understanding the mechanisms controlling ionic conductivity is critical for the development of the next generation of batteries and supercapacitors. This paper discusses the significant role played by ionic correlations in conductivity of concentrated ionic systems. Our studies of an organic ionic plastic crystal reveal that correlations in ions dynamics suppress conductivity by 25-100 times in comparison to the expected uncorrelated ionic conductivity estimated from the Nernst-Einstein relationship. Additional analysis also demonstrates that ionic correlations suppress conductivity in polymerized ionic liquids and gel by similar to 10 times. Thus, ionic correlations, usually neglected in many studies, play a very important role in conductivity of concentrated ionic systems. These results cannot be explained by a diffusion of ion pairs because all these systems are essentially single ion conductors. In contrast, strongly correlated motions of mobile ions with the same charge (cation-cation or anion-anion correlations) are the major mechanism suppressing the ionic conductivity in these systems. On the basis of these results, we emphasize that charge transport rather than ion diffusion is critical for electrolyte performance and suggest the potential design of plastic crystals and polymer electrolytes with enhanced ionic conductivity.

The interactions between OIPCs and polymer nanoparticles create interfacial layers that control the ion mobility of the resulting composite.