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A persistent challenge for lithium-ion batteries (LIBs) is operation under extreme environments, where temperatures can exceed −40 and 60 °C. At the same time, a growing number of high-impact applications require batteries that demonstrate longevity and high performance during low- and high-temperature operation, such as vehicle electrification, polar expeditions, and satellites/spacecraft. The discovery of novel electrolytes is therefore critical for developing next-generation energy storage solutions to widen operational capabilities beyond current technologies. Though trade-offs exist for targeting either low- or high-temperature performance, solutions that address both operational domains simultaneously are still sparse. In this Perspective, we highlight recent advancements in electrolyte formulations that enable a wide operating temperature window beyond −20 and 60 °C. Emerging research in fluorinated electrolytes, liquefied gas electrolytes, ionic liquids, and even aqueous chemistries offers a unique approach to overcoming this trade-off between low- and high-temperature operation of LIBs. The works highlighted in this Perspective present an exciting direction in the energy storage field that provides potential electrochemical solutions where engineering solutions may become exhausted.

Novel economically-sustainable and environmentally-friendly technologies for per- and poly-fluoroalkyl substance (PFAS) destruction are becoming increasingly important as PFAS contamination has increased in drinking water throughout the globe. UV-Fenton chemistry catalyzed by nanosize magnetite (Fe3O4) particles in aqueous environments is a promising method for production of reactive oxygen species (ROS), capable of disrupting PFAS carbon-fluorine bonds. Here we demonstrate greater than 90% degradation efficiency for a wide variety of PFAS compounds by ROS generated in a UV-Fenton reaction, involving naturally-occurring Fe3O4nanoparticles. In order to demonstrate that ROS are indeed formed under our experimental conditions, we utilized a fluorescent probe to confirm the presence of ROS in the reaction solution. PFAS destruction efficiency is increased at elevated pH levels; however, by varying both the Fe3O4and hydrogen peroxide (H2O2) concentrations in solution, high efficiency can be achieved at neutral pH conditions, like those found in drinking water. PFAS destruction occurred with UV exposure times on the order of minutes. Nano Fe3O4retained its oxidation state and catalytic efficiency after multiple cycles of PFAS destruction, indicating that the material is reusable. High resolution mass spectrometry was utilized to demonstrate destruction efficiency and to identify the degradation products. ROS generation utilizing naturally-occurring Fe3O4nanoparticles has been shown to be an efficient method for PFAS destruction with potential scalability for drinking water decontamination.

Graphene oxide and carbon nanotube composites are considered to be an ideal electrode for electrochemical energy storage and conversion. Herein, we prepare electrodes via a green synthesis that yields a binderless, flexible, and free-standing electrode. To improve the performance of these electrodes comprising graphene oxide and carbon nanotubes (GO–CNT), we carry out carbothermal shock (CTS), which reduces graphene oxide in a rapid (millisecond time scale) and tunable manner (1000–2000 K). When CTS is employed, the specific capacitance of GO–CNT increases by 50%, from 30 to 45 F g–1, for reduced GO–CNT (GO–CNT_CTS). When benchmarking against activated carbon, both GO–CNT and GO–CNT_CTS outperform in terms of capacitance and rate capability. We then examine impedance spectroscopy data in the form of two-dimensional color-mapped surface plots to analyze the dependence of the real and imaginary capacitance and the phase angle as a function of both frequency and potential. This analysis provides key mechanistic insight into the electrochemical double-layer response, such as the characteristic relaxation time and charge-transfer resistance. This analysis shows that, upon CTS, the relaxation times of GO–CNT-based electrodes are 70% faster than that of activated carbon and charge-transfer resistances are reduced dramatically.

Identifying positive electrode materials capable of reversible multivalent electrochemistry in electrolytes containing divalent ions such as Mg2+, Ca2+, and Zn2+at high operating potentials remains an ongoing challenge in “beyond lithium-ion” research. Herein, we explore the Zn2+charge-storage mechanism of a vanadium-based Na+superionic conductor (NASICON), Na3V2(PO4)3. By using X-ray synchrotron techniques to unravel potential-dependent structure–property relationships, we ascribe the reversible electrochemical behavior of Na3V2(PO4)3to a quasi-two-stage intercalation process that involves both Na+and Zn2+. Initial charging of Na3V2(PO4)3leads to a Na+-extracted phase corresponding to NaV2(PO4)3, whereas subsequent discharge results predominantly in Na+intercalation followed by Zn2+intercalation. Operando X-ray diffraction of Na3V2(PO4)3was used to study the phase changes associated with the first charge/discharge process, and ex situ measurements were used to precisely link the changes in the crystal structure to a quasi-two-stage intercalation of Na+and Zn2+. The corresponding changes in the V-oxidation state, V-O coordination, and the presence of Zn2+were confirmed by X-ray absorption spectroscopy. The results of this work present a comprehensive understanding of the charge-storage properties for a well-established NASICON structure that confers both the high capacity (∼100 mA h g–1) and high potential (1.35 and 1.1 V vs Zn/Zn2+).

Conventional Li-ion cathodes store charge by reversible intercalation of Li coupled to metal cation redox. There has been increasing interest in new materials capable of accommodating more than one Li per transition-metal center, thereby yielding higher charge storage capacities. We demonstrate here that the lithium-rich layered iron sulfide Li2FeS2as well as a new structural analogue, LiNaFeS2, reversibly store ≥1.5 electrons per formula unit and support extended cycling. Ex situand operandostructural and spectroscopic data indicate that delithiation results in reversible oxidation of Fe2+concurrent with an increase in the covalency of the Fe–S interactions, followed by reversible anion redox: 2 S2–/(S2)2–. S K-edge spectroscopy unequivocally proves the contribution of the anions to the redox processes. The structural response to the oxidation processes is found to be different in Li2FeS2in contrast to that in LiNaFeS2, which we suggest is the cause for capacity fade in the early cycles of LiNaFeS2. The materials presented here have the added benefit of avoiding resource-sensitive transition metals such as Co and Ni. In contrast to Li-rich oxide materials that have been the subject of so much recent study and that suffer capacity fade and electrolyte degradation issues, the materials presented here operate within the stable potential window of the electrolyte, permitting a clearer understanding of the underlying processes.

Electrochemical energy storage arises from processes that are broadly categorized as capacitive, pseudocapacitive, or battery-like. Advanced charge-storing materials that are designed to deliver high capacity at a high rate often exhibit a multiplicity of such mechanisms, which complicates the understanding of their charge-storage behavior. Herein, we apply a “3D Bode analysis” technique to identify key descriptors for fast Li-ion storage processes, where AC impedance data, such as the real capacitance (C′) or phase angle (ϕ), are represented versus the frequency (f) and a third independent variable, the applied DC cell voltage. For double-layer processes, a near-constant C′ or ϕ is supported across the entire voltage range, and the decrease in these values shows a near-linear decrease at higher f. For pseudocapacitance, an increase in C′ is delivered, accompanied by high C′ retention at higher fcompared to double-layer processes. Interestingly, the lower ϕ values, where C′ is highest, suggest that this is a key descriptor for pseudocapacitance, where high-rate charge storage is still facilitated within a kinetically limited regime. For battery-like processes, a high C′ is only observed at the voltage at which the material stores charge, while outside that voltage, C′ is negligible. The three-dimensional (3D) Bode analysis allows charge-storage dynamics to be mapped out in great detail with more delineation between mechanisms compared to the more frequently deployed kinetic analyses derived from cyclic voltammetry.

Low-temperature operation (–20 °C and below) under high-rate conditions is a critical deficiency for lithium-ion batteries. To achieve size, weight, and power requirements tailored for demanding applications, novel materials are needed to sustain high performance. In the present study, we synthesize a series of niobate anode materials (Nb2O5, Nb2O5–x, and Nb12O29) to tailor their particle size, defect nature, and electrical/ionic conductivity to enable high performance operation at –20 °C under high-rate conditions (1.2C to 2C). When paired with lithium manganese oxide (LMO) in a full cell configuration, the Nb2O5–x-based full cells achieve high-rate capability (∼90 mAh g–1up to 2C cycling rate at –20 °C) and great long-term stability (>98% retention up to 50 cycles at –20 °C). During a simulated 30 min duty cycling test synthesized from measured data from an actual drone flight (continuous range of 1.2C to 2C cycling rates), the Nb2O5–x||LMO cell enables full discharge at –20 °C with only a 0.3 V loss in voltage when compared to duty cycling at room temperature. The work presented herein demonstrates the future possibilities of the expanding operational capabilities of lithium-ion batteries.

Abstract

Zinc-based batteries are experiencing a resurgence in interest owing to their promising energy and power metrics, and inherent safety advantages compared with lithium-ion batteries. As scientists worldwide address the remaining obstacles to realizing competitive performance across the family of zinc batteries, the enthusiasm to report new “breakthroughs” at the materials or small-device level must be tempered by a realistic understanding of how such improvements will translate to practical energy-storage devices. Framing early-stage results in such a context will advance the prospects of next-generation Zn batteries while avoiding the “hype cycle” that has plagued research and development for other energy-storage technologies. Herein, we present guidelines by which to evaluate and report data derived from new electrode formulations and cell components such that the results will directly inform which breakthroughs are technologically relevant to scale up.

We assess the effect of the pore-solid architecture of cryptomelane-type manganese oxide (MnOx) xerogels and aerogels on electrocatalysis of the oxygen-reduction reaction (ORR) using three different electrochemical test platforms. Rotating-disk electrode measurements at ink-cast films of carbon + MnOx show that both MnOx nanoarchitectures exhibit comparable intrinsic ORR activity for four-electron reduction with a low onset overpotential ([?]310 mV). The MnOx xerogel and aerogel powders were also incorporated into practical powder-composite electrodes that include carbon and polymer binder. When evaluated in an air-breathing three-electrode electroanalytical cell, the aerogel-based composite electrode exhibits an overpotential lowered by [?]50 mV compared to the xerogel-based analog. The superior performance of the aerogel-based composite is also demonstrated in zinc-air button cells, with up to 100 mV improvement in discharge voltage at moderate-to-challenging current densities (5-125 mA cm-2). We ascribe the enhanced activity of the MnOx aerogel-based composite to a more uniform dispersion of the aerogel powder within the carbon/binder matrix, as verified by focused-ion beam[?]scanning electron microscopy and elemental mapping. The results reported herein highlight the importance of assessing the translation of electrocatalytic activity from fundamental measurements to technologically relevent electrode structures.

The high theoretical energy density of alloyed lithium and germanium (Li15Ge4), 1384 mAh/g, makes germanium a promising anode material for lithium-ion batteries. However, common alloy anode architectures suffer from long-term instability upon repetitive charge–discharge cycles that arise from stress-induced degradation upon lithiation (volume expansion >300%). Here, we explore the use of the two-dimensional nanosheet structure of germanane to mitigate stress from high volume expansion and present a facile method for producing stable single-to-multisheet dispersions of pure germanane. Purity and degree of exfoliation were assessed with scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. We measured representative germanane battery electrodes to have a reversible Li-ion capacity of 1108 mAh/g when cycled between 0.1 and 2 V vsLi/Li+. These results indicate germanane anodes are capable of near-theoretical-maximum energy storage, perform well at high cycling rates, and can maintain capacity over 100 cycles.

The short charging times and high power capabilities associated with capacitive energy storage make this approach an attractive alternative to batteries. One limitation of electrochemical capacitors is their low energy density and for this reason, there is widespread interest in pseudocapacitive materials that use Faradaic reactions to store charge. One candidate pseudocapacitive material is orthorhombic MoO3(α-MoO3), a layered compound with a high theoretical capacity for lithium (279 mA h g−1or 1,005 C g−1). Here, we report on the properties of reduced α-MoO3−x(R-MoO3−x) and compare it with fully oxidized α-MoO3(F-MoO3). The introduction of oxygen vacancies leads to a larger interlayer spacing that promotes faster charge storage kinetics and enables the α-MoO3structure to be retained during the insertion and removal of Li ions. The higher specific capacity of the R-MoO3−xis attributed to the reversible formation of a significant amount of Mo4+following lithiation. This study underscores the potential importance of incorporating oxygen vacancies into transition metal oxides as a strategy for increasing the charge storage kinetics of redox-active materials.

The increasing interest in Na-ion batteries (NIBs) can be traced to sodium abundance, its low cost compared to lithium, and its intercalation chemistry being similar to that of lithium. We report that the electrochemical properties of a promising negative electrode material, Na2Ti3O7, are improved by exfoliating its layered structure and forming 2D nanoscale morphologies, nanoplatelets, and nanosheets. Exfoliation of Na2Ti3O7was carried out by controlling the amount of proton exchange for Na+and then proceeding with the intercalation of larger cations such as methylammonium and propylammonium. An optimized mixture of nanoplatelets and nanosheets exhibited the best electrochemical performance in terms of high capacities in the range of 100–150 mA h g–1at high rates with stable cycling over several hundred cycles. These properties far exceed those of the corresponding bulk material, which is characterized by slow charge-storage kinetics and poor long-term stability. The results reported in this study demonstrate that charge-storage processes directed at 2D morphologies of surfaces and few layers of sheets are an exciting direction for improving the energy and power density of electrode materials for NIBs.

We evaluate a series of nanoparticulate NaTi2(PO4)3 (NTP) powders as Na+-insertion hosts in either nonaqueous or aqueous electrolyte, correlating electrochemical properties such as capacity and electrode kinetics (in the form of powder-composite electrodes) with the degree of crystallinity in NTP. Starting with amorphous NTP powders prepared using the Pechini method, calcination from 500 to 800degC was used to induce varying degrees of crystallinity and to remove carbonaceous species. Poorly crystalline NTP powders derived by heating at 500-600degC exhibit low specific capacities and broad voltammetric features for Na+-insertion, characteristic of surface-limited processes. Heating at higher temperatures (700-800degC) yields the nanocrystalline form with the NASICON structure. Nanocrystalline NTP exhibits sharp voltammetric peaks and diffusion-limited kinetics in both aqueous and nonaqueous electrolytes. The electrochemical performance of nanocrystalline NTP is further enhanced when integrated with reduced graphene oxide (rGO) to increase local electronic conductivity; theoretical specific capacity for NTP (133 mAh g[?]1) is achieved when NTP-rGO is cycled in a nonaqueous electrolyte, and 100 mAh g[?]1 in a mild aqueous electrolyte. This nanocomposite also exhibits long-term stability (86% capacity retention after 1000 charge/discharge cycles) in a nonaqueous electrolyte.

Charge storage devices with high energy density and enhanced rate capabilities are highly sought after in today’s mobile world. Although several high-rate pseudocapacitive anode materials have been reported, cathode materials operating in a high potential range versuslithium metal are much less common. Here, we present a nanostructured version of the well-known cathode material, LiMn2O4. The reduction in lithium-ion diffusion lengths and improvement in rate capabilities is realized through a combination of nanocrystallinity and the formation of a 3-D porous framework. Materials were fabricated from nanoporous Mn3O4films made by block copolymer templating of preformed nanocrystals. The nanoporous Mn3O4was then converted viasolid-state reaction with LiOH to nanoporous LixMn2O4(1 < x< 2). The resulting films had a wall thickness of ∼15 nm, which is small enough to be impacted by inactive surface sites. As a consequence, capacity was reduced by about half compared to bulk LiMn2O4, but both charge and discharge kinetics as well as cycling stability were improved significantly. Kinetic analysis of the redox reactions was used to verify the pseudocapacitive mechanisms of charge storage and establish the feasibility of using nanoporous LixMn2O4as a cathode in lithium-ion devices based on pseudocapacitive charge storage.

Electrochemical ion insertion into transition metal oxides forms the foundation of several energy technologies. Transition metal oxides can exhibit sluggish ion transport and/or phase-transformation kinetics during ion insertion that can limit their performance at high rates (<10 min). In this study, we investigate the role of structural water in transition metal oxides during Li+insertion using staircase potentiostatic electrochemical impedance spectroscopy (SPEIS) and electrochemical quartz crystal microbalance (EQCM) analysis of WO3·H2O and WO3thin-film electrodes. Overall, the presence of structural water in WO3·H2O improves Li+insertion kinetics compared to WO3and leads to a less potential-dependent insertion process. Operandoelectrogravimetry and 3D Bode impedance analyses of nanostructured films reveal that the presence of structural water promotes charge accommodation without significant co-insertion of solvent, leading to our hypothesis that the electrochemically induced structural transitions of WO3hinder the electrode response at faster timescales (<10 min). Designing layered materials with confined fluids that exhibit less structural transitions may lead to more versatile ion-insertion hosts for next-generation electrochemical technologies.

Zinc continues to garner immense interest due to its versatility as an anode material in several configurations utilizing either alkaline or mild-pH electrolytes. Current research on using mild-pH electrolytes has improved the rechargeability aspect of Zn-based batteries since Zn2+is solely utilized for plating/stripping of Zn. Several studies have incorporated Zn metal foils, yet, dramatic improvements can be achieved by expressing Zn as a porous structure. Herein, we use a quasi-pulsed electrodeposition process to prepare a conformal Zn coating onto 3D porous copper foam. By tuning the electrodeposition parameters, we achieved an optimal Zn coating that undergoes reversible plating/stripping when tested in symmetric Zn cells, which supported a low overpotential of ?60 mV for up to 100 cycles. We further investigated changes in the surface morphology by studying the Zn surface of both foil and 3D structure using scanning electron microscopy and X-ray micro-computed tomography. Both techniques showed that the Zn foil undergoes dramatic alterations at the surface, which results in inhomogeneous deposition of Zn, whereas the 3D form exhibited minimal changes. Lastly, we paired both Zn foil and 3D Zn with vanadium oxide and demonstrated that the porous structure supports high rate capability and high specific capacity.

A straightforward hydrothermal process followed by a controlled calcination technique is proposed for the synthesis of a Ni(OH)2 modified NiO nanohybrid structure. Conversion materials such as Li-ion battery anodes, NiO in this case, suffer from capacity fade and structural/morphological instability during lithiation and delithiation. The novelty of this work is in utilizing this hybrid configuration to increase the specific capacity and enable reversible electrochemistry. In the present work, we study the lithiation/delithiation process of NiO using a suite of spectroscopy and microscopy techniques from the atomic to electrode scale. We propose a mechanism for a reversible redox couple behavior of the NiO electrode by means of a hybrid Ni(OH)2/NiO structure. The ultimate objective of this work is to guide the development of anode with rationally designed heterogeneity to create high-capacity Li-ion batteries with excellent cycling and rate performance.

We assess the effect of the pore–solid architecture of cryptomelane-type manganese oxide (MnOx) xerogels and aerogels on electrocatalysis of the oxygen-reduction reaction (ORR) using three different electrochemical test platforms. Rotating-disk electrode measurements at ink-cast films of carbon + MnOxshow that both MnOxnanoarchitectures exhibit comparable intrinsic ORR activity for four-electron reduction with a low onset overpotential (∼310 mV). The MnOxxerogel and aerogel powders were also incorporated into practical powder–composite electrodes that include carbon and polymer binder. When evaluated in an air-breathing three-electrode electroanalytical cell, the aerogel-based composite electrode exhibits an overpotential lowered by ∼50 mV compared to the xerogel-based analog. The superior performance of the aerogel-based composite is also demonstrated in zinc–air button cells, with up to 100 mV improvement in discharge voltage at moderate-to-challenging current densities (5–125 mA cm–2). We ascribe the enhanced activity of the MnOxaerogel-based composite to a more uniform dispersion of the aerogel powder within the carbon/binder matrix, as verified by focused-ion beam−scanning electron microscopy and elemental mapping. The results reported herein highlight the importance of assessing the translation of electrocatalytic activity from fundamental measurements to technologically relevent electrode structures.

We evaluate a series of nanoparticulate NaTi2(PO4)3(NTP) powders as Na+-insertion hosts in either nonaqueous or aqueous electrolyte, correlating electrochemical properties such as capacity and electrode kinetics (in the form of powder–composite electrodes) with the degree of crystallinity in NTP. Starting with amorphous NTP powders prepared using the Pechini method, calcination from 500 to 800°C was used to induce varying degrees of crystallinity and to remove carbonaceous species. Poorly crystalline NTP powders derived by heating at 500–600°C exhibit low specific capacities and broad voltammetric features for Na+-insertion, characteristic of surface-limited processes. Heating at higher temperatures (700–800°C) yields the nanocrystalline form with the NASICON structure. Nanocrystalline NTP exhibits sharp voltammetric peaks and diffusion-limited kinetics in both aqueous and nonaqueous electrolytes. The electrochemical performance of nanocrystalline NTP is further enhanced when integrated with reduced graphene oxide (rGO) to increase local electronic conductivity; theoretical specific capacity for NTP (133 mAh g−1) is achieved when NTP-rGO is cycled in a nonaqueous electrolyte, and 100 mAh g−1in a mild aqueous electrolyte. This nanocomposite also exhibits long-term stability (86% capacity retention after 1000 charge/discharge cycles) in a nonaqueous electrolyte.