Principles and Design of Biphasic Self-Stratifying Batteries Toward Next-Generation Energy Storage.

Large-scale energy storage devices play pivotal roles in effectively harvesting and utilizing green renewable energies (such as solar and wind energy) with capricious nature. Biphasic self-stratifying batteries (BSBs) have emerged as a promising alternative for grid energy storage owing to their membraneless architecture and innovative battery design philosophy, which holds promise for enhancing the overall performance of the energy storage system and reducing operation and maintenance costs. This minireview aims to provide a timely review of such emerging energy storage technology, including its fundamental design principles, existing categories, and prototype architectures. The challenges and opportunities of this undergoing research topic will also be systematically highlighted and discussed to provide guidance for the subsequent R&D of superior BSBs while conducive to bridging the gap for their future practical application.

Extending Ring-Chain Coupling Empirical Law to Lithium-Mediated Electrochemical Ammonia Synthesis.

With its efficient nitrogen fixation kinetics, electrochemical lithium-mediated nitrogen reduction reaction (LMNRR) holds promise for replacing Haber-Bosch process and realizing sustainable and green ammonia production. However, the general interface problem in lithium electrochemistry seriously impedes the further enhancement of LMNRR performance. Inspired by the development history of lithium battery electrolytes, here, we extend the ring-chain solvents coupling law to LMNRR system to rationally optimize the interface during the reaction process, achieving nearly a two-fold Faradaic efficiency up to 54.78±1.60 %. Systematic theoretical simulations and experimental analysis jointly decipher that the anion-rich Li+ solvation structure derived from ring tetrahydrofuran coupling with chain ether successfully suppresses the excessive passivation of electrolyte decomposition at the reaction interface, thus promoting the mass transfer of active species and enhancing the nitrogen fixation kinetics. This work offers a progressive insight into the electrolyte design of LMNRR system.

Strong Replaces Weak: Design of H-Bond Interactions Enables Cryogenic Aqueous Zn Metal Batteries.

Despite the numerous advantages of aqueous Zn batteries, their practical application under cryogenic conditions is hindered by the freezing of the electrolyte because the abundance of hydrogen bonds (H-bonds) between H2O molecules drives the aqueous system to transform to an orderly frozen structure. Here, a design of H-bond interactions based on the guiding ideology of "strong replaces weak" is proposed. The strong H-bonds formed between introduced eutectic components and water molecules break down the weak H-bonds in the original water molecule network, which contributes to an ultralow freezing point and a high ionic conductivity of 1.7 mS cm-1 at -40 °C. Based on multiperspective theoretical simulations and tailor-made in situ cooling Raman characterizations, it has been demonstrated that substituting weak H-bonds with strong H-bonds facilitates the structural reshaping of Zn2+ solvation and remodeling of the H-bond network in the electrolyte. Endowed with this advantage, reversible and stable Zn plating/stripping behaviors could be realized at -40 °C, and the full cells display a high discharge capacity (200 mA h g-1) at -40 °C with ∼75% capacity retention after 1000 cycles. This study will expand the design philosophy of antifreezing aqueous electrolytes and provide a perspective to promote the adoption of Zn metal batteries for cryogenic environment large-scale energy storage.

Molecular Imprinting Technology Enables Proactive Capture of Nitrogen for Boosted Ammonia Synthesis under Ambient Conditions.

Electrochemical nitrogen reduction reaction (NRR) is a burgeoning field for green and sustainable ammonia production, in which numerous potential catalysts emerge endlessly. However, satisfactory performances are still not realized under practical applications due to the limited solubility and sluggish diffusion of nitrogen at the interface. Herein, molecular imprinting technology is adopted to construct an adlayer with abundant nitrogen imprints on the electrocatalyst, which is capable of selectively recognizing and proactively aggregating high-concentrated nitrogen at the interface while hindering the access of overwhelming water simultaneously. With this favorable microenvironment, nitrogen can preferentially occupy the active surface, and the NRR equilibrium can be positively shifted to facilitate the reaction kinetics. Approximately threefold improvements in both ammonia production rate (185.7 µg h-1 mg-1 ) and Faradaic efficiency (72.9%) are achieved by a metal-free catalyst compared with the bare one. It is believed that the molecular imprinting strategy should be a general method to find further applicability in numerous catalysts or even other reactions facing similar challenges.

Eliminating Concentration Polarization with Cationic Covalent Organic Polymer to Promote Effective Overpotential of Nitrogen Fixation.

Electrocatalytic nitrogen reduction reaction offers a sustainable alternative to the conventional Haber-Bosch process. However, it is currently restricted by low effective overpotential due to the concentration polarization, which arises from accumulated products, ammonium, at the reaction interface. Here, a novel covalent organic polymer with ordered periodic cationic sites is proposed to tackle this challenge. The whole network exhibits strong positive charge and effectively repels the positively charged ammonium, enabling an ultra-low interfacial product concentration, and successfully driving the reaction equilibrium to the forward direction. With the given potential unchanged, the suppressed overpotential can be much liberated, ultimately leading to a continuous high-level reaction rate. As expected, when this tailored microenvironment is coupled with a transition metal-based catalyst, a 24-fold improvement is generated in the Faradaic efficiency (73.74 %) as compared with the bare one. The proposed strategy underscores the importance of optimizing dynamic processes as a means of improving overall performance in electrochemical syntheses.

Exploiting nonaqueous self-stratified electrolyte systems toward large-scale energy storage.

Biphasic self-stratified batteries (BSBs) provide a new direction in battery philosophy for large-scale energy storage, which successfully reduces the cost and simplifies the architecture of redox flow batteries. However, current aqueous BSBs have intrinsic limits on the selection range of electrode materials and energy density due to the narrow electrochemical window of water. Thus, herein, we develop nonaqueous BSBs based on Li-S chemistry, which deliver an almost quadruple increase in energy density of 88.5 Wh L-1 as compared with the existing aqueous BSBs systems. In situ spectral characterization and molecular dynamics simulations jointly elucidate that while ensuring the mass transfer of Li+, the positive redox species are strictly confined to the bottom-phase electrolyte. This proof-of-concept of Li-S BSBs pushes the energy densities of BSBs and provides an idea to realize massive-scale energy storage with large capacitance.

Achieving Rapid Ultralow-Temperature Ion Transfer via Constructing Lithium-Anion Nanometric Aggregates to Eliminate Li+-Dipole Interactions.

Sluggish desolvation in extremely cold environments caused by strong Li+-dipole interactions is a key inducement for the capacity decline of a battery. Although the Li+-dipole interaction is reduced by increasing the electrolyte concentration, its high viscosity inevitably limits ion transfer at low temperatures. Herein, Li+-dipole interactions were eliminated to accelerate the migration rate of ions in electrolytes and at the electrode interface via designing Li+-anion nanometric aggregates (LA-nAGGs) in low-concentration electrolytes. Li+ coordinated by TFSI- and FSI- anions instead of a donor solvent promotes the formation of an inorganic-rich interfacial layer and facilitates Li+ transfer. Consequently, the LA-nAGG-type electrolyte demonstrated a high ionic conductivity (0.6 mS cm-1) at -70 °C and a low activation energy of charge transfer (38.24 kJ mol-1), enabling Li||NiFe-Prussian blue derivative cells to deliver ∼83.1% of their room-temperature capacity at -60 °C. This work provides an advanced strategy for the development of low-temperature electrolytes.

Solvent-in-Gas System for Promoted Photocatalytic Ammonia Synthesis on Porous Framework Materials.

Photocatalytic nitrogen reduction reaction (PNRR) is emerging as a sustainable ammonia synthesis approach to meet global carbon neutrality. Porous framework materials with well-designed structures have great opportunities in PNRR; however, they suffer from unsatisfactory activity in the conventional gas-in-solvent system (GIS), owing to the hindrance of nitrogen utilization and strong competing hydrogen evolution caused by overwhelming solvent. In this study, porous framework materials are combined with a novel "solvent-in-gas" system, which can bring their superiority into full play. This system enables photocatalysts to directly operate in a gas-dominated environment with a limited proton source uniformly suspended in it, achieving the accumulation of high-concentrated nitrogen within porous framework while efficiently restricting the solvent-photocatalyst contact. An over eightfold increase in ammonia production rate (1820.7 µmol g-1 h-1 ) compared with the conventional GIS and an apparent quantum efficiency as high as ≈0.5% at 400 nm are achieved. This system-level strategy further finds applicability in photocatalytic CO2 reduction, featuring it as a staple for photosynthetic methodology.

Weakening Li+ De-solvation Barrier for Cryogenic Li-S Pouch Cells.

Li-S batteries hold promise for pushing cell-level energy densities beyond 300 Wh kg-1 while operating at low temperatures (LTs, below 0 °C). However, the capacity release of existing Li-S batteries at LTs is still barely satisfactory, and there is almost no verification of the practicability of Li-S batteries at LTs in the Ah-level pouch cell. Here, antecedent molecular dynamics (MDs) combined with density functional theory analysis are used to systematically investigate Li+ solvation structure in conventional Li-S batteries at LTs, which unprecedentedly reveals the positive correlation between lithium salt concentration and Li+ de-solvation barrier, indicating dilute electrolytes can enhance the Li+ de-solvation kinetics and thus improve the capacity performance of cryogenic Li-S batteries. These insights derived from theoretical simulations invested Li-S batteries with a 67.34% capacity retention at -40 °C compared to their room temperature performance. In particular, an Ah-level Li-S pouch cell using dilute electrolytes with a high sulfur loading (5.6 mg cm-2 ) and lean electrolyte condition is fabricated, which delivers a discharge capacity of about 1000 mAh g-1 and ultra-high energy density of 350 Wh kg-1 at 0 °C, offering a promising route toward a practical high-energy cryogenic Li-S battery.

Unity of Opposites between Soluble and Insoluble Lithium Polysulfides in Lithium-Sulfur Batteries.

Rechargeable batteries based on Li-S chemistry show promise as being possible for next-generation energy storage devices because of their ultrahigh capacities and energy densities. Research over the past decade has demonstrated that the morphology of lithium polysulfides (LPSs) in electrolytes (soluble or insoluble) plays a decisive role in battery performance. Early studies have focused mainly on inhibiting the dissolution of LPSs and invested considerable effort to realize this objective. However, in recent years, a completely different view that the dissolution of LPSs during battery discharge/charge should be promoted has emerged. At this critical juncture in the large-scale application of Li-S batteries, it is time to summarize and discuss both sides of the contradiction. Herein, an overview of these two opposite views pertaining to soluble and insoluble LPSs, including their historical environment, classical strategies, advantages, and disadvantages. Finally, the future morphology of LPSs in Li-S batteries is predicted based on a multiangle review of research studies conducted thus far, and the reasoning behind this conjecture is thoroughly discussed.

Coordination Symmetry Breaking of Single-Atom Catalysts for Robust and Efficient Nitrate Electroreduction to Ammonia.

Nitrate electrocatalytic reduction (NO3 RR) for ammonia production is a promising strategy to close the N-cycle from nitration contamination, as well as an alternative to the Haber-Bosch process with less energy consumption and carbon dioxide release. However, current long-term stability of NO3 RR catalysts is usually tens of hours, far from the requirements for industrialization. Here, symmetry-broken Cusingle-atom catalysts are designed, and the catalytic activity is retained after operation for more than 2000 h, while an average ammonia production rate of 27.84 mg h-1 cm-2 at an industrial level current density of 366 mA cm-2 is achieved, obtaining a good balance between catalytic activity and long-term stability. Coordination symmetry breaking is achieved by embedding one Cu atom in graphene nanosheets with two N and two O atoms in the cis-configuration, effectively lowering the coordination symmetry, rendering the active site more polar, and accumulating more NO3 - near the electrocatalyst surface. Additionally, the cis-coordination splits the Cu 3d orbitals, which generates an orbital-symmetry-matched π-complex of the key intermediate *ONH and reduces the energy barrier, compared with the σ-complex generated with other catalysts. These results reveal the critical role of coordination symmetry in single-atom catalysts, prompting the design of more coordination-symmetry-broken electrocatalysts toward possible industrialization.

Cationic Covalent Organic Framework with Ultralow HOMO Energy Used as Scaffolds for 5.2 V Solid Polycarbonate Electrolytes.

Solid polymer electrolytes (SPEs) have become promising candidate to replace common liquid electrolyte due to highly improved security. However, the practical use of SPEs is still restricted by their decomposition and breakage at the electrode interfacial layer especially at high voltage. Herein, a new cationic covalent organic framework (COF) is designed and synthesized as a reinforced skeleton to resist the constant oxidative decomposition of solid polycarbonate electrolyte, which can stabilize cathode electrolyte interphase layer to develop long-term cycle solid lithium metal battery. The ultralow HOMO energy (-12.55 eV according to density functional theory (DFT) calculations), reflecting its oxidation resistance at positive potential, would be responsible for the high decomposition voltage of 5.2 V versus Li+ /Li of solid polycarbonate electrolyte. Furthermore, the smooth surface of interfacial layer and inhibited decomposition reaction at cathode side is confirmed in solid LiCoO2 cell, which realizes high initial capacity up to 160.3 mAh g-1 at 0.1 C and greatly improved stability in 4.5 V class solid polymer lithium metal battery with high capacity retention over 200 cycles. This new type of high-voltage resistant solid polymer electrolyte promotes the realization of high-voltage cathode materials and higher energy density lithium metal battery.

Eliminating Stubborn Insulated Deposition by Coordination Effect to Boost Zn Electrode Reversibility in Aqueous Electrolyte.

Aqueous rechargeable zinc-ion batteries (ZIBs) have recently shined in energy storage and transmission, which are due to high safety and low cost. However, the extremely stubborn by-products in the Zn anode severely inhibited the Zn2+ adsorption/desorption and exacerbated the dendrite formation. Herein, we report a facile strategy to eliminate inert Zn4(OH)6SO4·xH2O for the improvement of ZIBs according to the coordination effect by employing ethylenediaminetetraacetic acid-diamine (EDTA-2Na) as a coordination additive in traditional electrolyte. Zn2+ is coordinated with the carboxyl group of the four acetyl carboxyl groups and the N in C-N bonds, forming a new chelating structure, and thus stubborn deposition will be dissolved in the electrolyte. As a result, the discharge capacity of 102 mAh g-1 in the ZnSO4/Li2SO4 with EDTA-2Na electrolyte at a current density of 4 C and a stable cycle life with a capacity of 90.3% after 150 cycles are achieved. It has been concluded that the coordination effect strategy provides a valuable idea for solving the defects of ZIBs.

Surpassing the Redox Potential Limit of Organic Cathode Materials via Extended p-π Conjugation of Dioxin.

The key to enabling high energy density of organic energy-storage systems is the development of high-voltage organic cathodes; however, the redox voltage (<4.0 V vs Li/Li+) of state-of-the-art organic electrode materials (OEMs) remains unsatisfactory. Herein, we propose a novel dibromotetraoxapentacene (DBTOP) redox center to surpass the redox potential limit of OEMs, achieving ultrahigh discharge plateaus of approximately 4.4 V (vs Li+/Li). As theoretically analyzed, electron delocalization between dioxin active centers and benzene rings as well as electron-withdrawing bromine atoms endows the molecule with a low occupied molecular orbital level by diluting the electron density of dioxin in the whole p-π conjugated skeleton, and the strong π-π interactions among the DBTOP molecules provide a faster electrochemical kinetic pathway. This tetraoxapentacene redox center makes the working voltage of OEMS closer to the high-voltage inorganic electrodes, and its chemical and structural tunability may stimulate the further development of high-voltage organic cathodes.

New Type of Dynamically "Solid-Liquid" Interconvertible Electrolyte for High-Rate Zn Metal Battery.

The practical application of aqueous high-rate Zn metal battery (ZMB) is limited due to accelerated dendrite formation at high current densities. It is urgent to find an electrolyte, which could not only be mechanically stiff to clamp down dendrites but also not sacrifice ionic conductivity and interfacial compatibility. Herein, a new type of dynamically "solid-liquid" interconvertible electrolyte based on non-Newtonian fluid (NNFE) is proposed. Liquidity characteristic of NNFE is favorable for electrochemical kinetics and interfacial compatibility. Furthermore, in an area with high current rate NNFE would respond and mechanically stiffen to dissuade localized increase in Zn dendrite growth. Even at a current density of 50 mA cm-2, NNFE enables reversible and stable operation of a Zn symmetrical cell over 20 000 cycles. For Zn//Na5V12O32 (NVO) full cell, the NNFE also realizes lengthy cycling for 5000 periods at 5 A g-1. This research opens up new inspirations to high-rate Zn metal even other metal batteries.

Altering the rate-determining step over cobalt single clusters leading to highly efficient ammonia synthesis.

Activation of high-energy triple-bonds of N2 is the most significant bottleneck of ammonia synthesis under ambient conditions. Here, by importing cobalt single clusters as strong electron-donating promoter into the catalyst, the rate-determining step of ammonia synthesis is altered to the subsequent proton addition so that the barrier of N2 dissociation can be successfully overcome. As revealed by density functional theory calculations, the N2 dissociation becomes exothermic over the cobalt single cluster upon the strong electron backdonation from metal to the N2 antibonding orbitals. The energy barrier of the positively shifted rate-determining step is also greatly reduced. At the same time, advanced sampling molecular dynamics simulations indicate a barrier-less process of the N2 approaching the active sites that greatly facilitates the mass transfer. With suitable thermodynamic and dynamic property, a high ammonia yield rate of 76.2 µg h-1 mg[Formula: see text] and superior Faradaic efficiency of 52.9% were simultaneously achieved.

Molecular Simulations Guided Polymer Electrolyte towards Superior Low-Temperature Solid Lithium-Metal Batteries.

Low-temperature operation is a challenge for solid-lithium-metal batteries (LMBs), and insufficient ionic conductivity is the main obstacle. Herein, guided by the molecular dynamics simulations (MDS), a solid polymer electrolyte (SPE) based on poly(1,3-dioxolane) (PDOL) with sufficient ionic conductivity at low temperature is reported. In situ X-ray diffraction (XRD) and differential scanning calorimetry (DSC) tests reveal that the PDOL-based SPE could well maintain amorphous nature at low temperatures, contributing to excellent ionic transport. The MDS analysis of the Li-O coordination environment indicates that more oxygen atoms bonded with Li+ in PDOL than in poly(ethylene oxide) (PEO) at low temperatures, thus we could envision the preponderance of PDOL as a better polymer matrix of SPE for low-temperature solid LMBs. It delivers a high capacity of 103 mAh g-1 and 85% retention for 200 cycles for Li||LiFePO4 at -20 °C, showing great potential for application in low-temperature solid LMBs in cold climates.

All-Liquid-Phase Reaction Mechanism Enabling Cryogenic Li-S Batteries.

The sluggish solid-solid conversion kinetics from Li2S4 to Li2S during discharge is considered the main problem for cryogenic Li-S batteries. Herein, an all-liquid-phase reaction mechanism, where all the discharging intermediates are dissolved in the functional thioether-based electrolyte, is proposed to significantly enhance the kinetics of Li-S battery chemistry at low temperatures. A fast liquid-phase reaction pathway thus replaces the conventional slow solid-solid conversion route. Spectral investigations and molecular dynamics simulations jointly elucidate the greatly enhanced kinetics due to the highly decentralized state of solvated intermediates in the electrolyte. Overall, the battery brings an ultrahigh specific capacity of 1563 mAh g-1sulfur in the cathode at -60 °C. This work provides a strategy for developing cryogenic Li-S batteries.

Built-in Electric Field Triggered Interfacial Accumulation Effect for Efficient Nitrate Removal at Ultra-Low Concentration and Electroreduction to Ammonia.

A built-in electric field in electrocatalyst can significantly accumulate higher concentration of NO3 - ions near electrocatalyst surface region, thus facilitating mass transfer for efficient nitrate removal at ultra-low concentration and electroreduction reaction (NO3 RR). A model electrocatalyst is created by stacking CuCl (111) and rutile TiO2 (110) layers together, in which a built-in electric field induced from the electron transfer from TiO2 to CuCl (CuCl_BEF) is successfully formed . This built-in electric field effectively triggers interfacial accumulation of NO3 - ions around the electrocatalyst. The electric field also raises the energy of key reaction intermediate *NO to lower the energy barrier of the rate determining step. A NH3 product selectivity of 98.6 %, a low NO2 - production of <0.6 %, and mass-specific ammonia production rate of 64.4 h-1 is achieved, which are all the best among studies reported at 100 mg L-1 of nitrate concentration to date.

Accelerating Ion Dynamics Under Cryogenic Conditions by the Amorphization of Crystalline Cathodes.

The normal operation of lithium-ion batteries (LIBs) at ultralow temperature (<-40 °C) is significant for cold-climate applications; however, their operation is plagued by the low capacity of the conventional intercalation cathodes due to their sluggish kinetics and the slow solid diffusion of Li+ in their frameworks. Here, it is demonstrated that amorphization is an effective strategy to promote the low-temperature dynamics of cathodes by relieving the blocking effect of a dense lattice structure on ion transport under cryogenic conditions. As a result, due to the decreased charge transport impedance and enhanced Li+ diffusion rate, the obtained covalent amorphous polymer (CAP) with an abundance of pyrazine and carbonyl active sites displays a remarkably outstanding specific capacity of 141 mAh g-1 at -80 °C, which is superior to its structural analog, a covalent crystalline polymer (43.8 mAh g-1 ). Furthermore, 84.7% of the initial capacity of the CAP can be retained after 500 cycles of charge and discharge at -60 °C. Molecular dynamic simulations show that the channel-rich amorphous structure is highly conducive for lithium ions to diffuse quickly in the interstitial space of organic solids. This work provides an effective strategy regarding the amorphization of crystalline cathodes to develop low-temperature (Low-T) batteries.