During the discharge of a lithium-sulfur (Li-S) battery, an electronically insulating 2D layer of Li2S is electrodeposited onto the current collector. Once the current collector is enveloped, the overpotential of the cell increases, and its discharge is arrested, often before reaching the full capacity of the active material. Guided by a new computational platform known as the Electrolyte Genome, we advance and apply benzo[ghi]peryleneimide (BPI) as a redox mediator for the reduction of dissolved polysulfides to Li2S. With BPI present, we show that it is now possible to electrodeposit Li2S as porous, 3D deposits onto carbon current collectors during cell discharge. As a result, sulfur utilization improved 220% due to a 6-fold increase in Li2S formation. To understand the growth mechanism, electrodeposition of Li2S was carried out under both galvanostatic and potentiostatic control. The observed kinetics under potentiostatic control were modeled using modified Avrami phase transformation kinetics, which showed that BPI slows the impingement of insulating Li2S islands on carbon. Conceptually, the pairing of conductive carbons with BPI can be viewed as a vascular approach to the design of current collectors for energy storage devices: here, conductive carbon "arteries" dominate long-range electron transport, while BPI "capillaries" mediate short-range transport and electron transfer between the storage materials and the carbon electrode.

Intermittent energy sources, including solar and wind, require scalable, low‐cost, multi‐hour energy storage solutions in order to be effectively incorporated into the grid. All‐Organic non‐aqueous redox‐flow batteries offer a solution, but suffer from rapid capacity fade and low Coulombic efficiency due to the high permeability of redox‐active species across the battery's membrane. Here we show that active‐species crossover is arrested by scaling the membrane's pore size to molecular dimensions and in turn increasing the size of the active material above the membrane's pore‐size exclusion limit. When oligomeric redox‐active organics (RAOs) were paired with microporous polymer membranes, the rate of active‐material crossover was reduced more than 9000‐fold compared to traditional separators at minimal cost to ionic conductivity. This corresponds to an absolute rate of RAO crossover of less than 3 μmol cm−2 day−1 (for a 1.0 m concentration gradient), which exceeds performance targets recently set forth by the battery industry. This strategy was generalizable to both high and low‐potential RAOs in a variety of non‐aqueous electrolytes, highlighting the versatility of macromolecular design in implementing next‐generation redox‐flow batteries.

Redox flow batteries (RFBs) present unique opportunities for multi-hour electrochemical energy storage (EES) at low cost. Too often, the barrier for implementing them in large-scale EES is the unfettered migration of redox active species across the membrane, which shortens battery life and reduces Coulombic efficiency. To advance RFBs for reliable EES, a new paradigm for controlling membrane transport selectivity is needed. We show here that size- and ion-selective transport can be achieved using membranes fabricated from polymers of intrinsic microporosity (PIMs). As a proof-of-concept demonstration, a first-generation PIM membrane dramatically reduced polysulfide crossover (and shuttling at the anode) in lithium-sulfur batteries, even when sulfur cathodes were prepared as flowable energy-dense fluids. The design of our membrane platform was informed by molecular dynamics simulations of the solvated structures of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) vs lithiated polysulfides (Li2Sx, where x = 8, 6, and 4) in glyme-based electrolytes of different oligomer length. These simulations suggested polymer films with pore dimensions less than 1.2-1.7 nm might incur the desired ion-selectivity. Indeed, the polysulfide blocking ability of the PIM-1 membrane (∼0.8 nm pores) was improved 500-fold over mesoporous Celgard separators (∼17 nm pores). As a result, significantly improved battery performance was demonstrated, even in the absence of LiNO3 anode-protecting additives.

Cationic naked nanocrystals (NCs) are useful building units for assembling hierarchical mesostructured materials. Until now, their preparation required strongly electrophilic reagents that irreversibly sever bonds between native organic ligands and the NC surface. Colloidal instabilities can occur during ligand stripping if exposed metal cations desorb from the surface. We hypothesized that cation desorption could be avoided were we able to stabilize the surface during ligand stripping via ion pairing. We were successful in this regard by carrying out ligand stripping under equilibrium control with Lewis acid-base adducts of BF3. To better understand the microscopic processes involved, we studied the reaction pathway in detail using in situ NMR experiments and electrospray ionization mass spectrometry. As predicted, we found that cationic NC surfaces are transiently stabilized post-stripping by physisorbed anionic species that arise from the reaction of BF3 with native ligands. This stabilization allows polar dispersants to reach the NC surface before cation desorption can occur. The mechanistic insights gained in this work provide a much-needed framework for understanding the interplay between NC surface chemistry and colloidal stability. These insights enabled the preparation of stable naked NC inks of desorption-susceptible NC compositions such as PbSe, which were easily assembled into new mesostructured films and polymer-nanocrystal composites with wide-ranging technological applications.

Here we report a new redox-active perylene bisimide (PBI)polysulfide (PS) gel that overcomes electronic charge-transport bottlenecks common to lithium−sulfur (Li−S) hybrid redox flow batteries designed for long-duration grid-scale energy storage applications. PBI was identified as a supramolecular redox mediator for soluble lithium polysulfides from a library of 85 polycyclic aromatic hydrocarbons by using a high-throughput computational platform; furthermore, these theoretical predictions were validated electrochemically. Challenging conventional wisdom, we found that π-stacked PBI assemblies were stable even in their reduced state through secondary interactions between PBI nanofibers and Li 2 S n , which resulted in a redoxactive, flowable 3-D gel network. The influence of supramolecular charge-transporting PBI-PS gel networks on Li−S battery performance was investigated in depth and revealed enhanced sulfur utilization and rate performance (C/4 and C/8) at a sulfur loading of 4 mg cm −2 and energy density of 44 Wh L −1 in the absence of conductive carbon additives.

In recent years, organic electrochemical transistors (OECTs) have found applications in chemical and biological sensing and interfacing, neuromorphic computing, digital logic, and printed electronics. However, the incorporation of OECTs in practical electronic circuits is limited by the relative lack of control over their threshold voltage, which is important for controlling the power consumption and noise margin in complementary and unipolar circuits. Here, the threshold voltage of OECTs is precisely tuned over a range of more than 1 V by chemically controlling the electrochemical potential at the gate electrode. This threshold voltage tunability is exploited to prepare inverters and amplifiers with improved noise margin and gain, respectively. By coupling the gate electrode with an electrochemical oscillator, single-transistor oscillators based on OECTs with dynamic time-varying threshold voltages are prepared. This work highlights the importance of electrochemistry at the gate electrode in determining the electrical properties of OECTs, and opens a path toward the system-level design of low-power OECT-based electronics.

amplification, making them ideal candidates for miniaturized chemical and ion sensors that can be used for spatial mapping of analytes or multi-analyte sensing in space-limited applications. [9,10] However, in order to realize this, it is equally important to devise an addressing system that allows the output of each sensor to be measured while minimizing the number of signal lines leaving the sensor array. To accomplish this, we monolithically integrated indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) and ionselective OECTs (IS-OECTs) on a flexible substrate to yield an array of ion-sensors addressed by a multiplexer (Figure 1). This system enables multiple sensors to be addressed and read out by low-cost measuring equipment, which opens the door to multi-analyte sensing and spatial mapping of analytes in applications ranging from environmental monitoring to biomedical research. The device architecture and principle of operation for the IS-OECTs used in this work are depicted in Figure 2a. The conductance of the OECT channel is dependent on the channel's oxidation state, which is in turn controlled through an ionically conductive medium by the application of a gate voltage from a reference electrode. [11][12][13][14] These devices are inherently sensitive to the total ion concentration, [15] and they can be made ion-selective by depositing an ISM on top of the channel. [6,7] As shown in Figure 2a, the ISM consisted of a salt of the ion of interest and an ionophore (depicted by stars) dissolved in a hydrophobic polymer membrane. The ionophore selectively solvates the cation of interest, and the anion is hydrophobic so it is soluble in the hydrophobic membrane and insoluble in the aqueous analyte. When the membrane is exposed to an analyte, some of the cations diffuse into the analyte because they are better solvated by water than by the ionophore. However, the hydrophobic anions are trapped in the membrane, leading to a phase-boundary potential between the membrane and the electrolyte. Since the fraction of ions that partition into the analyte is a function of the ion's concentration in the analyte, the membrane potential is also a function of the analyte concentration. Furthermore, since the ionophore selectively solvates the ion of interest, other ions do not diffuse into the membrane to any great extent, making the membrane potential predominantly a Organic electrochemical transistors (OECTs) are a promising class of devices for chemical and ionic sensing in aqueous media. Compared with conventional potentiometric techniques, OECT ion-sensors exhibit low output impedance that aids their miniaturization and integration in multi-sensor systems. However, in order to implement arrays of OECT sensors for multianalyte detection or spatial mapping of analytes, it is critical that the sensors be integrated with an addressing system that minimizes the number of signal lines leaving the sensor array. In this work, an integrated system comprising miniaturized ion-selective OECTs (IS-OECTs) that are addresse...

Intermittent energy sources, including solar and wind, require scalable, low‐cost, multi‐hour energy storage solutions in order to be effectively incorporated into the grid. All‐Organic non‐aqueous redox‐flow batteries offer a solution, but suffer from rapid capacity fade and low Coulombic efficiency due to the high permeability of redox‐active species across the battery's membrane. Here we show that active‐species crossover is arrested by scaling the membrane's pore size to molecular dimensions and in turn increasing the size of the active material above the membrane's pore‐size exclusion limit. When oligomeric redox‐active organics (RAOs) were paired with microporous polymer membranes, the rate of active‐material crossover was reduced more than 9000‐fold compared to traditional separators at minimal cost to ionic conductivity. This corresponds to an absolute rate of RAO crossover of less than 3 μmol cm−2 day−1 (for a 1.0 m concentration gradient), which exceeds performance targets recently set forth by the battery industry. This strategy was generalizable to both high and low‐potential RAOs in a variety of non‐aqueous electrolytes, highlighting the versatility of macromolecular design in implementing next‐generation redox‐flow batteries.