Louis A. Madsen

Solid-state batteries hope to offer improved safety over commonly used liquid electrolytes. Carbonate solvents offer low flashpoints and can ignite at low temperatures. Molecular ionic composites (MICs) are a class of solid polymer electrolytes (SPEs) capable of safe operation at elevated temperatures. The MIC in our study contains a structural domain that consists of charged rigid rods of Lithium Poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) (LiPBDT). Pools of free ions from Li-salts and ionic liquid support ion conduction in the MIC, while the composite structure is maintained through intermediary associated ions between the LiPBDT and free ions. We have observed that cathodes paired with MICs do not need additional ion conductors to deliver full capacities. We believe this behavior is a result of ionic liquid infiltrating the cathode structure generating a conductive network in the porous structure. Infiltration and activation of the cathode appear to happen in two steps. The initial infiltration occurs during cell assembly and likely promoted by capillary action as cathodes with lower porosities deliver the highest initial performance. Secondary activation occurs during the first few cycles. In higher porosity cathodes, we observe lower overpotential and capacity growth with cycling. Furthermore, we observe a growth in electrochemically active surface area from cathodes rested in a cell with a MIC to cathodes cycled with a MIC. Through careful control of electrode porosity and the initial cycles we aim to find conditions that promote infiltration and full activation of cathodes in solid-state batteries.

Polymer electrolytes hold great promise for safe and high-energy batteries comprising solid or semi-solid electrolytes. Multiphase polymer electrolytes, consisting of mobile and rigid phases, exhibit fast ion conduction and desired mechanical properties. However, fundamental challenges exist in understanding and regulating interactions at the electrode|electrolyte interface, especially when using high-voltage layered oxide active materials at the positive electrode. MICs consist of a charged rigid-rod ionic polymer, poly-2,2’-disulfonyl-4,4’-benzidine terephthalamide (PBDT), combined with mobile ions from ionic liquids, lithium salts, and functional additives. The associative interactions between PBDT and mobile ions create a tunable platform with exceptional mechanical strength, high ionic conductivity, and enhanced electrochemical stability over a wide temperature range. Here, we demonstrate that depletion of the mobile conductive phase at the interface contributes to battery performance degradation. Molecular ionic composite electrolytes, composed of a rigid-rod ionic polymer with nanometric mobile cations and anions, serve as a multiphase platform to investigate the evolution of ion domains at the interface. Chemical and structural characterizations enable the visualization of concentration heterogeneity and spatially resolve the interfacial chemical states over a statistically significant field of view for buried interfaces. We report that concentration and chemical heterogeneities prevail at electrode|electrolyte interfaces, leading to phase separation in polymer electrolytes. Understanding the hidden roles of interfacial chemomechanics in polymer electrolytes enables us to design an interphase tailoring strategy based on electrolyte additives to mitigate the interfacial heterogeneity and improve battery performance.

Regioselectively substituted amylose acetate-graft-polylactide (AmAc-g-PLA) graft polymers were synthesized via grafting-to “click” reaction between C6-azide functionalized AmAc and alkyne-terminated PLA. Alkyne-terminated PLA synthesized through organocatalytic ring-opening polymerization (ROP) permitted control over graft degree of polymerization (DP) and stereochemistry, while azide functionalized AmAc with tailorable C6-azide degree of substitution (DS) allowed graft density control. This describes the first synthesis of polysaccharide-based graft polymers with exclusive C6 grafting and controllable topology. Thermal analysis indicates that glass transition temperatures (Tg) of AmAc and PLA segments are affected after grafting-to coupling, with poly­(l-lactide) (PLLA) grafts maintaining crystallizability. AmAc-graft-poly­(d,l-lactide) (PDLLA) graft polymers were effective compatibilizers for immiscible blends of starch acetate (StAc) and PDLLA as evidenced by small-angle laser light scattering (SALLS) and phase contrast optical microscopy (PCOM). This method permits the determination of structure–property relationships with regard to the effect of graft polymer topology on blend compatibilization, which will be invaluable in designing compatibilized biobased polymer blends as sustainable materials.

Semiconductor quantum dots (QDs) show promise for various applications, including biological imaging and photovoltaics. QDs are typically stabilized by surface-bound ligands, which exhibit a dynamic binding equilibrium. This study combines nuclear magnetic resonance (NMR) spectroscopy and diffusometry to quantify the populations and kinetics of oleic acid (OAH) ligand binding to PbS QD surfaces. In addition to quantifying ligand population fractions in bound and free states, our analysis reveals the existence of a third ligand state, which we hypothesize to be the weak coordination of the OAH at (100) sites through the acidic headgroup (-COOH). Thus, bound ligands exist in two subpopulations: weakly bound OAH on (100) facets and strongly bound oleate (OA) on (111) facets. Through variations in temperature and concentration, we assess the changes in ligand populations in different states and determine the energetics of their exchange equilibria. Additionally, using dynamic NMR spectroscopy, we quantify rapid exchange rates (0.09-2 ms) between weakly bound and free OAH ligands as a function of OAH titration concentration and temperature. These findings highlight the complexity of ligand binding mechanisms and enable strategies for precisely tuning QD surface properties, with significant implications for the innovation of next-generation optoelectronic materials.

Polymer electrolytes are promising candidates for enabling safe, high-energy lithium batteries, particularly when paired with high-voltage layered oxide cathodes and lithium metal anodes. However, challenges at electrode|electrolyte interfaces, such as parasitic side reactions and electrolyte decomposition, have hindered the widespread adoption of polymer electrolyte-based high-voltage lithium batteries. To address these issues, this study introduces molecular ionic composites (MICs) as free-standing polymer electrolyte membranes, eliminating the need for any additional liquid electrolytes during cell assembly. MICs consist of a charged rigid-rod ionic polymer, poly-2,2″-disulfonyl-4,4'-benzidine terephthalamide (PBDT), combined with mobile ions from ionic liquids, lithium salts, and functional additives. The associative interactions between PBDT and these ions create a tunable platform with exceptional mechanical strength, moderate ionic conductivity, and enhanced electrochemical stability of polymer electrolyte over a wide temperature range. The optimized MIC electrolytes exhibit high ionic conductivity (3.21 mS cm^-1 at 60 °C), a wide electrochemical stability window (5 V vs Li|Li⁺ based on linear sweep voltammetry), and excellent mechanical properties (tensile strength of 6.3 MPa, elastic modulus of 450 MPa). Furthermore, MICs enable good cycling stability in NMC811||Li metal cells, delivering an initial specific discharge capacity of 212 mAh g^-1 and 93% capacity retention after 100 cycles at 2.8-4.4 V, C/3, and 60 °C. These results underscore the potential of MICs as a promising electrolyte platform for next-generation high-voltage lithium batteries and broader electrochemical energy storage applications.

Polymer electrolytes hold great promise for safe and high-energy batteries comprising solid or semi-solid electrolytes. Multiphase polymer electrolytes, consisting of mobile and rigid phases, exhibit fast ion conduction and desired mechanical properties. However, fundamental challenges exist in understanding and regulating interactions at the electrode|electrolyte interface, especially when using high-potential layered oxide active materials at the positive electrode. Here we demonstrate that depletion of the mobile conductive phase at the interface contributes to battery performance degradation. Molecular ionic composite electrolytes, composed of a rigid-rod ionic polymer with nanometric mobile cations and anions, serve as a multiphase platform to investigate the evolution of ion conductive domains at the interface. Chemical and structural characterizations enable the visualization of concentration heterogeneity and spatially resolve the interfacial chemical states over a statistically significant field of view for buried interfaces. We report that concentration and chemical heterogeneities prevail at electrode|electrolyte interfaces, leading to phase separation in polymer electrolytes. Understanding the hidden roles of interfacial chemomechanics in polymer electrolytes enables us to design an interphase tailoring strategy based on electrolyte additives to mitigate the interfacial heterogeneity and improve battery performance.

Polymer electrolytes hold great promise for safe and high-energy solid-state batteries. Multiphase polymer electrolytes, consisting of mobile and rigid phases, exhibit fast ion conduction and desired mechanical properties. However, fundamental challenges exist in understanding and regulating intricate chemomechanical interactions at the electrode-electrolyte interface, especially when using a high-voltage layered cathode. Here, we report that depletion of the mobile conductive phase at the interface contributes to battery performance degradation. Molecular ionic composite electrolytes, composed of a rigid-rod ionic polymer with small mobile cations and anions, serve as a multiphase platform to investigate the evolution of conductive domains at the interface. Synchrotron chemical and structural analyses enable the direct visualization of concentration polarization and spatially resolve the interfacial chemical states over a statistically significant field of view for buried interfaces. We discover that concentration and chemical heterogeneities prevail at electrode-electrolyte interfaces, leading to interfacial chemomechanical degradation. We further demonstrate an interphase tailoring strategy based on electrolyte additives to mitigate such interfacial heterogeneity and improve battery stability. While polymer electrolytes have been considered "deformable" for conformal interfaces, our work shows the hidden roles of interfacial chemomechanics in polymer electrolytes and provides an effective mitigation approach. Figure 1

Polymer electrolytes hold great promise for safe and high-energy solid-state batteries. Multiphase polymer electrolytes, consisting of mobile and rigid phases, exhibit fast ion conduction and desired mechanical properties. However, fundamental challenges exist in understanding and regulating intricate chemomechanical interactions at the electrode-electrolyte interface, especially when using a high-voltage layered cathode. Here, we report that depletion of the mobile conductive phase at the interface contributes to battery performance degradation. Molecular ionic composite electrolytes, composed of a rigid-rod ionic polymer with small mobile cations and anions, serve as a multiphase platform to investigate the evolution of conductive domains at the interface. Synchrotron chemical and structural analyses enable the direct visualization of concentration polarization and spatially resolve the interfacial chemical states over a statistically significant field of view for buried interfaces. We discover that concentration and chemical heterogeneities prevail at electrode-electrolyte interfaces, leading to interfacial chemomechanical degradation. We further demonstrate an interphase tailoring strategy based on electrolyte additives to mitigate such interfacial heterogeneity and improve battery stability. While polymer electrolytes have been considered “deformable” for conformal interfaces, our work shows the hidden roles of interfacial chemomechanics in polymer electrolytes and provides an effective mitigation approach.

Anionic macromolecules are found at sites of CaCO₃ biomineralization in diverse organisms, but their roles in crystallization are not well-understood. We prepared a series of sulfated chitosan derivatives with varied positions and degrees of sulfation, DS(SO₃ ^-), and measured calcite nucleation rate onto these materials. Fitting the classical nucleation theory model to the kinetic data reveals the interfacial free energy of the calcite-polysaccharide-solution system, γ_net, is lowest for nonsulfated controls and increases with DS(SO₃ ^-). The kinetic prefactor also increases with DS(SO₃ ^-). Simulations of Ca²⁺-H₂O-chitosan systems show greater water structuring around sulfate groups compared to uncharged substituents, independent of sulfate location. Ca²⁺-SO₃ ^- interactions are solvent-separated by distances that are inversely correlated with DS(SO₃ ^-) of the polysaccharide. The simulations also predict SO₃ ^- and NH₃ ⁺ groups affect the solvation waters and HCO₃ ^- ions associated with Ca²⁺. Integrating the experimental and computational evidence suggests sulfate groups influence nucleation by increasing the difficulty of displacing near-surface water, thereby increasing γ_net. By correlating γ_net and net charge per monosaccharide for diverse polysaccharides, we suggest the solvent-separated interactions of functional groups with Ca²⁺ influence thermodynamic and kinetic components to crystallization by similar solvent-dominated processes. The findings reiterate the importance of establishing water structure and properties at macromolecule-solution interfaces.

Polymer electrolytes have received tremendous interest in the development of solid‐state batteries, but often fall short in one or more key properties required for practical applications. Herein, a rigid gel polymer electrolyte prepared by immobilizing a liquid mixture of a lithium salt and poly(ethylene glycol) dimethyl ether with only 8 wt% poly(2,2′‐disulfonyl‐4,4′‐benzidine terephthalamide) (PBDT) is reported. The high charge density and rigid double helical structure of PBDT lead to formation of a nanofibrillar structure that endows this electrolyte with stronger mechanical properties, wider temperature window, and higher battery rate capability compared to all other poly(ethylene oxide) (PEO)‐based electrolytes. The ion transport mechanism in this rigid polymer electrolyte is systematically studied using multiple complementary techniques. Li/LiFePO₄ cells show excellent capacity retention over long‐term cycling, with thermal cycling reversibility between ambient temperature and elevated temperatures, demonstrating compelling potential for solid‐state batteries targeting fast charging at high temperatures and slower discharging at ambient temperature.