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Electrolyte engineering is crucial for improving battery performance, particularly for lithium metal batteries. Recent advances in electrolytes have greatly improved cyclability by enhancing electrochemical stability at the electrode interfaces, but concurrently achieving high ionic conductivity has remained challenging. Here we report an electrolyte design strategy for enhanced lithium metal batteries by increasing the molecular diversity in electrolytes, which essentially leads to high entropy electrolytes (HEEs). We find that in weakly solvating electrolytes, the entropy effect reduces ion clustering while preserving the characteristic anion-rich solvation structures, which is characterized by synchrotron-based X-ray scattering and molecular dynamics simulations. Electrolytes with smaller-sized clusters exhibit a 2-fold improvement in ionic conductivity compared to conventional weakly-solvating electrolytes, enabling stable cycling at high current densities up to 2C (6.2 mA cm-2) in anode-free LiNi0.6Mn0.2Co0.2 (NMC622) || Cu pouch cells. The efficacy of the design strategy is verified by performance improvements in three disparate weakly solvating electrolyte systems.

Improving Coulombic efficiency (CE) is key to the adoption of high energy density lithium metal batteries. Liquid electrolyte engineering has emerged as a promising strategy for improving the CE of lithium metal batteries, but its complexity renders the performance prediction and design of electrolytes challenging. Here, we develop machine learning (ML) models that assist and accelerate the design of high-performance electrolytes. Using the elemental composition of electrolytes as the features of our models, we apply linear regression, random forest, and bagging models to identify the critical features for predicting CE. Our models reveal that a reduction in the solvent oxygen content is critical for superior CE. We use the ML models to design electrolyte formulations with fluorine-free solvents that achieve a high CE of 99.70%. This work highlights the promise of data-driven approaches that can accelerate the design of high-performance electrolytes for lithium metal batteries.

Electrolyte engineering is a critical approach to improve battery performance, particularly for lithium metal batteries. In this work, we introduce the concept of high entropy electrolytes (HEEs) that achieve improved ionic conductivity while maintaining excellent electrochemical stability. We find that increasing the molecular diversity and concomitantly the mixing entropy of weakly solvating electrolytes can reduce ion clustering while retaining anion-rich solvation structure, confirmed through synchrotron-based X-ray scattering and molecular dynamics simulations. Less clustered electrolytes exhibit higher diffusivity and ionic conductivity, enabling high current density cycling up to 2C (> 6 mA cm-2) for up to ~80 cycles in anode-free NMC-Cu pouch cells. We substantiate the generality of the concept by verifying performance improvement in three disparate electrolyte systems. This work highlights a large unexplored design space of HEEs that can improve electrolyte properties for lithium metal batteries.

Direct optical polymer patterning As a platform for electronic devices, polymeric materials offer the advantages of intrinsic flexibility and stretchability relative to hard material devices. However, unlike materials such as silicon, there are few tools for large-scale patterning of monolithic devices. Zheng et al. developed an optical lithography technique for the high-throughput fabrication of transistor circuitry on stretchable substrates. In this method, ultraviolet light is used to control the local solubility of the polymer, which makes it possible to fabricate transistors on the micrometer scale. These devices can be made with high yield and excellent uniformity without compromising their electronic and mechanical characteristics. Science , abh3551, this issue p. 88

Rechargeable lithium (Li) metal batteries must have long cycle life and calendar life (retention of capacity during storage at open circuit). Particular emphasis has been placed on prolonging the cycle life of Li metal anodes, but calendar ageing is less understood. Here, we show that Li metal loses at least 2–3% of its capacity after only 24 hours of ageing, regardless of the electrolyte chemistry. These losses of capacity during calendar ageing also shorten the cycle life of Li metal batteries. Cryogenic transmission electron microscopy shows that chemical corrosion of Li and the continuous growth of the solid electrolyte interphase—a passivation film on Li—cause the loss of capacity. Electrolytes with long cycle life do not necessarily form a solid electrolyte interphase with more resistance to chemical corrosion, so functional electrolytes must simultaneously minimize the rate of solid electrolyte interphase growth and the surface area of electrodeposited Li metal. Batteries keep degrading even when they are not in operation, but their calendar life is rarely studied in advanced batteries that are still in the development stage. Here the authors quantify the calendar ageing of Li metal anodes and report its underlying mechanisms.

Advanced electrolytes were developed to improve the cyclability of lithium (Li) metal anodes, yet their working mechanisms remain unclear. Here, we study the Li cycling performance under different ...

Polymeric materials in nature regularly employ ordered, hierarchical structures in order to perform unique and precise functions. Importantly, these structures are often formed and stabilized by the cooperative summation of many weak interactions as opposed to the independent association of a few strong bonds. Here, we show that synthetic, flexible polymer chains with periodically placed and directional dynamic bonds collectively assemble into supramolecular nanofibers when the overall molecular weight is below the polymer's critical entanglement molecular weight. This causes bulk films of long polymer chains to have faster dynamics than films of shorter polymer chains of identical chemical composition. The formation of nanofibers increases the bulk film modulus by over an order of magnitude and delays the onset of terminal flow by more than 100 °C, while still remaining solution processable. Systematic investigation of different polymer chain architectures and dynamic bonding moieties along with coarse-grained molecular dynamics simulations illuminate governing structure-function relationships that determine a polymer's capacity to form supramolecular nanofibers. This report of the cooperative assembly of multivalent polymer chains into hierarchical, supramolecular structures contributes to our fundamental understanding of designing biomimetic functional materials.

Electrolyte engineering is critical for developing Li metal batteries. While recent works improved Li metal cyclability, a methodology for rational electrolyte design remains lacking. Herein, we propose a design strategy for electrolytes that enable anode-free Li metal batteries with single-solvent single-salt formations at standard concentrations. Rational incorporation of –CF2– units yields fluorinated 1,4-dimethoxylbutane as the electrolyte solvent. Paired with 1 M lithium bis(fluorosulfonyl)imide, this electrolyte possesses unique Li–F binding and high anion/solvent ratio in the solvation sheath, leading to excellent compatibility with both Li metal anodes (Coulombic efficiency ~ 99.52% and fast activation within five cycles) and high-voltage cathodes (~6 V stability). Fifty-μm-thick Li|NMC batteries retain 90% capacity after 420 cycles with an average Coulombic efficiency of 99.98%. Industrial anode-free pouch cells achieve ~325 Wh kg−1 single-cell energy density and 80% capacity retention after 100 cycles. Our design concept for electrolytes provides a promising path to high-energy, long-cycling Li metal batteries. The realization of the full potential of Li metal batteries requires high-performance electrolytes. Here Z. Bao and colleagues develop low-concentration electrolytes with a single-solvent and single-salt formulation, offering promise for high-energy and long-cycling batteries.

Conjugation breakers (CBs) with different H-bonding chemistries and linker flexibilities are designed and incorporated into a diketopyrrolopyrrole (DPP)-based conjugated polymer backbone. The effects of H-bonding interactions on polymer semiconductor morphology, mechanical properties, and electrical performance are systematically investigated. We observe that CBs with an H-bonding self-association constant >0.7 or a denser packing tendency are able to induce higher polymer chain aggregation and crystallinity in as-casted thin films, resulting in a higher modulus and crack on-set strain. Additionally, the rDoC (relative degree of crystallinity) of the stretched thin film with the highest crack on-set strain only suffers a small decrease, suggesting the main energy dissipation mechanism is the breakage of H-bonding interactions. By contrast, other less stretchable polymer films dissipate strain energy through the breakage of crystalline domains, indicated by a drastic decrease in rDoC. Furthermore, we evaluate their electrical performances under mechanical strain in fully stretchable field-effect transistors. The polymer with the highest crack on-set strain has the least degradation in mobility as a function of strain. Overall, these observations suggest that we can aptly tune the mechanical properties of a polymer semiconductor by modulating intermolecular interactions, such as H-bonding chemistry and linker flexibility. Such understanding provides molecular design guidelines for future stretchable semiconductors.

Preservation of cycling behavior Understanding the changes in interfaces between electrode and electrolyte during battery cycling, including the formation of the solid-electrolyte interphase (SEI), is key to the development of longer lasting batteries. Z. Zhang et al . adapt a thin-film vitrification method to ensure the preservation of liquid electrolyte so that the samples taken for analysis using microscopy and spectroscopy better reflect the state of the battery during operation. A key finding is that the SEI is in a swollen state, in contrast to current belief that it only contained solid inorganic species and polymers. The extent of swelling can affect transport through the SEI, which thickens with time, and thus might also decrease the amount of free electrolyte available for battery cycling. —MSL

Silicon is expected to become the ideal anode material for the next generation of high energy density lithium battery because of its high theoretical capacity (4200 mAh g

1,2-Dimethoxyethane (DME) is a common electrolyte solvent for lithium metal batteries. Various DME-based electrolyte designs have improved long-term cyclability of high-voltage full cells. However, insufficient Coulombic efficiency at the Li anode and poor high-voltage stability remain a challenge for DME electrolytes. Here, we report a molecular design principle that utilizes a steric hindrance effect to tune the solvation structures of Li+ ions. We hypothesized that by substituting the methoxy groups on DME with larger-sized ethoxy groups, the resulting 1,2-diethoxyethane (DEE) should have a weaker solvation ability and consequently more anion-rich inner solvation shells, both of which enhance interfacial stability at the cathode and anode. Experimental and computational evidence indicates such steric-effect-based design leads to an appreciable improvement in electrochemical stability of lithium bis(fluorosulfonyl)imide (LiFSI)/DEE electrolytes. Under stringent full-cell conditions of 4.8 mAh cm-2 NMC811, 50 μm thin Li, and high cutoff voltage at 4.4 V, 4 M LiFSI/DEE enabled 182 cycles until 80% capacity retention while 4 M LiFSI/DME only achieved 94 cycles. This work points out a promising path toward the molecular design of non-fluorinated ether-based electrolyte solvents for practical high-voltage Li metal batteries.

Next-generation wearable electronics require enhanced mechanical robustness and device complexity. Besides previously reported softness and stretchability, desired merits for practical use include elasticity, solvent resistance, facile patternability and high charge carrier mobility. Here, we show a molecular design concept that simultaneously achieves all these targeted properties in both polymeric semiconductors and dielectrics, without compromising electrical performance. This is enabled by covalently-embedded in-situ rubber matrix (iRUM) formation through good mixing of iRUM precursors with polymer electronic materials, and finely-controlled composite film morphology built on azide crosslinking chemistry which leverages different reactivities with C–H and C=C bonds. The high covalent crosslinking density results in both superior elasticity and solvent resistance. When applied in stretchable transistors, the iRUM-semiconductor film retained its mobility after stretching to 100% strain, and exhibited record-high mobility retention of 1 cm2 V−1 s−1 after 1000 stretching-releasing cycles at 50% strain. The cycling life was stably extended to 5000 cycles, five times longer than all reported semiconductors. Furthermore, we fabricated elastic transistors via consecutively photo-patterning of the dielectric and semiconducting layers, demonstrating the potential of solution-processed multilayer device manufacturing. The iRUM represents a molecule-level design approach towards robust skin-inspired electronics., Next-generation skin-inspired electronics require enhanced mechanical robustness and device complexity including elasticity, solvent resistance, and facile patternability. Here, the authors show a molecular design concept that simultaneously achieves all these requirements by covalently linking an in-situ formed rubber matrix with polymer electronic materials.

Next-generation light-emitting displays on skin should be soft, stretchable and bright

Designing a stable solid-electrolyte interphase on a Li anode is imperative to developing reliable Li metal batteries. Herein, we report a suspension electrolyte design that modifies the Li

Summary Implementation of lithium (Li)-metal anodes requires developments to solve the heterogeneity and instability issues of naturally formed solid-electrolyte interphase (SEI). The artificial SEI, as an alternative, enables an ideal interface by regulating critical features such as fast ion transport, conformal protection, and parasitic reaction mitigation. Herein, for the first time, we integrate all of these desired properties into a single matrix, the dynamic single-ion-conductive network (DSN), as a multifunctional artificial SEI. The DSN incorporates the tetrahedral Al(OR)4− (R = soft fluorinated linker) centers as both dynamic bonding motifs and counter anions, endowing it with flowability and Li+ single-ion conductivity. Simultaneously, the fluorinated linkers provide chain mobility and electrolyte-blocking capability. A solution-processed DSN coating was found to simultaneously hinder electrolyte penetration, mitigate side reactions between Li and electrolyte, maintain low interfacial impedance, and allow homogenous Li deposition. With this coating, long cycle life and high Coulombic efficiency are achieved for Li-metal battery in a commercial carbonate electrolyte.

The anode-free cells have emerged due to the need to maximize Li metal batteries' energy density. However, anode-free Li batteries suffer from short cycle life because of the lack of Li inventory at the anode. Freshly deposited Li metal anodes usually take hundreds of cycles to reach initial SEI stabilization optimum coulombic efficiency (CE) due to initial SEI stabilization and electrode activation. The anode-free cell design requires high Li metal CE over the whole cycling life, particularly during the initial activation cycles. A holistic approach to electrolyte design, mechanism understanding, and battery engineering is needed to fulfill these requirements. Here, we present a mechanistic study on lithium plating and stripping from next generation electrolytes. We conducted dynamic impedance spectroscopy (dEIS) to probe the formation and evolution of the SEI during Li plating and stripping on copper current collectors. dEIS superimposes a multisine waveform atop the dc stimulus signal, as shown by the lightly shaded curves in Fig 1 (top left). We applied a sliding window FFT protocol that takes the complex ratio of the measured potential and current signals obtained from Fig 1 (top right) and transforms it into complex impedance. We will discuss two Li platting systems, Lipon (an amorphous ceramic) and a liquid electrolyte with stabilizing additives. We observed drastic changes in the cells' impedance during plating and stripping, Figure 1 (bottom plots). We will show how the passivation layer's impedance continues to evolve during Li cycling and accounts for a significant amount of the overall cell resistance. The US Department of Energy’s Energy Efficiency and Renewable Energy Vehicles Technologies Office provided funding for this work under the US-German Cooperation on Energy Storage: Lithium-Solid-Electrolyte Interfaces program. Figure 1

Shape memory polymers are promising materials in many emerging applications due to their large extensibility and excellent shape recovery. However, practical application of these polymers is limited by their poor energy densities (up to ∼1 MJ/m3). Here, we report an approach to achieve a high energy density, one-way shape memory polymer based on the formation of strain-induced supramolecular nanostructures. As polymer chains align during strain, strong directional dynamic bonds form, creating stable supramolecular nanostructures and trapping stretched chains in a highly elongated state. Upon heating, the dynamic bonds break, and stretched chains contract to their initial disordered state. This mechanism stores large amounts of entropic energy (as high as 19.6 MJ/m3 or 17.9 J/g), almost six times higher than the best previously reported shape memory polymers while maintaining near 100% shape recovery and fixity. The reported phenomenon of strain-induced supramolecular structures offers a new approach toward achieving high energy density shape memory polymers., We report an approach to achieve a high energy density shape memory polymer based on the formation of strain-induced supramolecular nanostructures, which immobilize stretched chains to store entropic energy.

The electrolyte plays a critical role in lithium-ion batteries, as it impacts almost every facet of a battery's performance. However, our understanding of the electrolyte, especially solvation of Li+, lags behind its significance. In this work, we introduce a potentiometric technique to probe the relative solvation energy of Li+ in battery electrolytes. By measuring open circuit potential in a cell with symmetric electrodes and asymmetric electrolytes, we quantitatively characterize the effects of concentration, anions, and solvents on solvation energy across varied electrolytes. Using the technique, we establish a correlation between cell potential (Ecell) and cyclability of high-performance electrolytes for lithium metal anodes, where we find that solvents with more negative cell potentials and positive solvation energies-those weakly binding to Li+-lead to improved cycling stability. Cryogenic electron microscopy reveals that weaker solvation leads to an anion-derived solid-electrolyte interphase that stabilizes cycling. Using the potentiometric measurement for characterizing electrolytes, we establish a correlation that can guide the engineering of effective electrolytes for the lithium metal anode.

The increasing demand for next-generation energy storage systems necessitates the development of high-performance lithium batteries

Fast-charging is considered as one of the most desired features needed for lithium-ion batteries to accelerate the mainstream adoption of electric vehicles. However, current battery charging protocols mainly consist of conservative rate steps to avoid potential hazardous lithium plating and its associated parasitic reactions. A highly sensitive onboard detection method could enable battery fast-charging without reaching the lithium plating regime. Here, we demonstrate a novel differential pressure sensing method to precisely detect the lithium plating event. By measuring the real-time change of cell pressure per unit of charge (dP/dQ) and comparing it with the threshold defined by the maximum of dP/dQ during lithium-ion intercalation into the negative electrode, the onset of lithium plating before its extensive growth can be detected with high precision. In addition, we show that by integrating this differential pressure sensing into the battery management system (BMS), a dynamic self-regulated charging protocol can be realized to effectively extinguish the lithium plating triggered by low temperature (0 °C) while the conventional static charging protocol leads to catastrophic lithium plating at the same condition. We propose that differential pressure sensing could serve as an early nondestructive diagnosis method to guide the development of fast-charging battery technologies.

Increasing battery energy density is greatly desired for applications such as portable electronics and transportation. However, many next-generation batteries are limited by electrolyte selection because high ionic conductivity and poor electrochemical stability are typically observed in most electrolytes. For example, ether-based electrolytes have high ionic conductivity but are oxidatively unstable above 4 V, which prevents the use of high-voltage cathodes that promise higher energy densities. In contrast, hydrofluoroethers (HFEs) have high oxidative stability but do not dissolve lithium salt. In this work, we synthesize a new class of fluorinated ether electrolytes that combine the oxidative stability of HFEs with the ionic conductivity of ethers in a single compound. We show that conductivities of up to 2.7 × 10

Liquid electrolyte engineering plays a critical role in modern lithium-ion batteries. However, the existing electrolytes fall short when used with some trending battery chemistries such as high-voltage and high-energy-density electrodes. Fluorination of electrolyte solvents has been identified as an effective approach for improved cyclability, but few works systematically studied the effects of fluorination extent of carbonate solvents on battery performance. Here we design and synthesize a family of fluorinated ethyl methyl carbonates. Different numbers of F atoms are finely tuned to yield monofluoroethyl methyl carbonate (F1EMC), difluoroethyl methyl carbonate (F2EMC) and trifluoroethyl methyl carbonate (F3EMC). The cycling behavior of several types of lithium-ion pouch cells, including graphite (Gr)/single-crystalline LiNi0.8Mn0.1Co0.1O2 (SC-NMC811), Gr-SiOx/LiNi0.6Mn0.2Co0.2O2 (NMC622), high-voltage Gr/LiNi0.5Mn1.5O4 (LNMO), Gr/layered Li-rich Mn-based oxide (LLMO) and fast-charging Gr/NMC622, were systematically investigated to understand the impact of fluorination degree. Compared to the commercially available F3EMC, we found that the partially-fluorinated F1EMC and F2EMC in some cases showed improved cycling stability, which we attribute to their locally-polar –CH2F and –CHF2 groups and thus fast ion conduction than –CF3. This work suggests that highly or fully fluorinated solvents are not necessarily desirable; instead, fluorination degree needs to be rationally and finely tuned for optimized lithium-ion cell performance.

Highly ordered nanostructures assembled from conjugated polymers have great potential for probing fundamental structure-property relationships, as well as boosting the charge transport performance. To date, the effect of solution-state aggregation on crystallization and charge transport in conjugated polymers is still unclear and in need of precise description at the molecular level. In this work, we report a systematic study of solution-state aggregation on crystallization and charge transport in BDOPV-based conjugated polymers through side chain engineering. Detailed analysis of crystal packing structures of conjugated polymers reveals that intermolecular displacements are substantially modified in order to minimize steric hindrance caused by the alkyl side chains. Moreover, subtle differences in side chain chemical structures play a vital role in regulating solution-state aggregation, and thus crystalline domain sizes in both microwires and thin films. Farther branched side chain leads to larger polymer aggregates in solution and therefore larger crystalline domains in solid films. Subsequently, an increase in electron mobility is obtained with the highest mobility values surpassing 10 cm2 V−1 s−1. This work unravels that the modification of the side chains is an efficient strategy for fine-tuning the interchain organization of conjugated polymers from solution to solid state.

The emergence of wearable electronics puts batteries closer to the human skin, exacerbating the need for battery materials that are robust, highly ionically conductive, and stretchable. Herein, we introduce a supramolecular design as an effective strategy to overcome the canonical tradeoff between mechanical robustness and ionic conductivity in polymer electrolytes. The supramolecular lithium ion conductor utilizes orthogonally functional H-bonding domains and ion-conducting domains to create a polymer electrolyte with unprecedented toughness (29.3 MJ m−3) and high ionic conductivity (1.2 × 10−4 S cm−1 at 25 °C). Implementation of the supramolecular ion conductor as a binder material allows for the creation of stretchable lithium-ion battery electrodes with strain capability of over 900% via a conventional slurry process. The supramolecular nature of these battery components enables intimate bonding at the electrode-electrolyte interface. Combination of these stretchable components leads to a stretchable battery with a capacity of 1.1 mAh cm−2 that functions even when stretched to 70% strain. The method reported here of decoupling ionic conductivity from mechanical properties opens a promising route to create high-toughness ion transport materials for energy storage applications., Typically, ion conducting polymers exhibit a trade-off between mechanical robustness and ionic conducting performance. Here, the authors utilize supramolecular chemistry obtaining extremely tough electrolytes with high ionic conductivity and enabling stretchable lithium-ion batteries.