Solvent-free protic liquid enabling batteries operation at an ultra-wide temperature range

Realization of Long-Life Proton Battery by Layer Intercalatable Electrolyte

Proton batteries have attracted increasing interests because of their potential for grid-scale energy storage with high safety and great low-temperature performances. However, their development is significantly retarded by electrolyte design due to free water corrosion. Herein, we report a layer intercalatable electrolyte (LIE) by introducing trimethyl phosphate (TMP) into traditional acidic electrolyte. Different from conventional role in batteries, the presence of TMP intriguingly achieves co-intercalation of solvent molecules into the interlayer of anode materials, enabling a new working mechanism for proton reactions. The electrode corrosion was also strongly retarded with expanded electrochemical stability window. The half-cell therefore showed an outstanding long-term cycling stability with 91.0 % capacity retention at 5 A g-1 after 5000 cycles. Furthermore, the assembled full batteries can even deliver an ultra-long lifetime with a capacity retention of 74.9 % for 2 months running at -20 °C. This work provides new opportunities for electrolyte design of aqueous batteries.

Emerging Two-Dimensional Materials for Proton-Based Energy Storage

The rapid diffusion kinetics and smallest ion radius make protons the ideal cations toward the ultimate energy storage technology combining the ultrafast charging capabilities of supercapacitors and the high energy densities of batteries. Despite the concept existing for centuries, the lack of satisfactory electrode materials hinders its practical development. Recently, the rapid advancement of the emerging two-dimensional (2D) materials, characterized by their ultrathin morphology, interlayer van der Waals gaps, and distinctive electrochemical properties, injects promises into future proton-based energy storage systems. In this perspective, we comprehensively summarize the current advances in proton-based energy storage based on 2D materials. We begin by providing an overview of proton-based energy storage systems, including proton batteries, pseudocapacitors and electrical double layer capacitors. We then elucidate the fundamental knowledge about proton transport characteristics, including in electrolytes, at electrolyte/electrode interfaces, and within electrode materials, particularly in 2D material systems. We comprehensively summarize specific cases of 2D materials as proton electrodes, detailing their design concepts, proton transport mechanism and electrochemical performance. Finally, we provide insights into the prospects of proton-based energy storage systems, emphasizing the importance of rational design of 2D electrode materials and matching electrolyte systems.

Symmetrical Design of Biphenazine Derivative Anode for Proton Ion Batteries with High Voltage and Long-Term Cycle Stability

Organic anodes have emerged as a promising energy storage medium in proton ion batteries (PrIBs) due to their ability to reversibly accommodate non-metallic proton ions. Nevertheless, the currently available organic electrodes often encounter dissolution issues, leading to a decrease in long-cycle stability. In addition, the inherent potential of the organic anode is generally relatively high, resulting in low cell voltage of assembled PrIBs (<1.0 V). To address these challenges, a novel long-period stable, low redox potential biphenylzine derivative, [2,2'-biphenazine]-7,7'-tetraol (BPZT) is explored, from the perspective of molecular symmetry and solubility, in conjunction with the effect of the molecular frontier orbital energy levels on its redox potential. Specifically, BPZT exhibited a low potential of 0.29 V (vs SHE) and is virtually insoluble in 2 m H2SO4 electrolyte during cycling. When paired with MnO2@GF or PbO2 cathodes, the resulting PrIBs achieve cell voltages of 1.07 V or 1.44 V, respectively, and maintain a high capacity retention of 90% over 20000 cycles. Additionally, these full batteries can operate stably at a high mass loading of 10 mgBPZT cm-2, highlighting their potential toward long-term energy storage applications.

Wafer Scale Gallium Nitride Integrated Electrode Toward Robust High Temperature Energy Storage

Gallium Nitride (GaN), as the representative of wide bandgap semiconductors, has great prospects in accomplishing rapid charge delivery under high-temperature environments thanks to excellent structural stability and electron mobility. However, there is still a gap in wafer-scale GaN single-crystal integrated electrodes applied in the energy storage field. Herein, Si-doped GaN nanochannel with gallium oxynitride (GaON) layer on a centimeter scale (denoted by GaN NC) is reported. The Si atoms modulate electronic redistribution to improve conductivity and drive nanochannel formation. Apart from that, the distinctive nanochannel configuration with a GaON layer provides adequate active sites and extraordinary structural stability. The GaN-based supercapacitors are assembled and deliver outstanding charge storage capabilities at 140 °C. Surprisingly, 90% retention is maintained after 50 000 cycles. This study opens the pathway toward wafer-scale GaN single-crystal integrated electrodes with self-powered characteristics that are compatible with various (opto)-electronic devices.

An Emerging Chemistry Revives Proton Batteries

Developing new energy techniques that simultaneously integrate the fast rate capabilities of supercapacitors and high capacities of batteries represents an ultimate goal in the field of electrochemical energy storage. A new possibility arises with an emerging battery chemistry that relies on proton-ions as the ion-charge-carrier and benefits from the fast transportation kinetics. Proton-based battery chemistry starts with the recent discoveries of materials for proton redox reactions and leads to a renaissance of proton batteries. In this article, the historical developments of proton batteries are outlined and key aspects of battery chemistry are reviewed. First, the fundamental knowledge of proton-ions and their transportation characteristics is introduced; second, Faradaic electrodes for proton storage are categorized and highlighted in detail; then, reported electrolytes and different designs of proton batteries are summarized; last, perspectives of developments for proton batteries are proposed. It is hoped that this review will provide guidance on the rational designs of proton batteries and benefit future developments.

Hydronium Intercalation Enables High Rate in Hexagonal Molybdate Single Crystals

Rapid proton transport in solid-hosts promotes a new chemistry in achieving high-rate Faradaic electrodes. Exploring the possibility of hydronium intercalation is essential for advancing proton-based charge storage. Nevertheless, this is yet to be revealed. Herein, a new host is reported of hexagonal molybdates, (A2 O)x ·MoO3 ·(H2 O)y (A = Na+ , NH4 + ), and hydronium (de)intercalation is demonstrated with experiments. Hexagonal molybdates show a battery-type initial reduction followed by intercalation pseudocapacitance. Fast rate of 200 C (40 A g-1 ) and long lifespan of 30 000 cycles are achieved in electrodes of monocrystals even over 200 µm. Solid-state nuclear magnetic resonance confirms hydronium intercalations, and operando measurements using electrochemical quartz crystal microbalance and synchrotron X-ray diffraction disclose distinct intercalation behaviours in different electrolyte concentrations. Remarkably, characterizations of the cycled electrodes show nearly identical structures and suggest equilibrium products are minimally influenced by the extent of proton solvation. These results offer new insights into proton electrochemistry and will advance correlated high-power batteries and beyond.

Water-in-Salt: Fast Dynamics, Structure, Thermodynamics, and Bulk Properties

We present concentration-dependent dynamics of highly concentrated LiBr solutions and LiCl temperature-dependent dynamics for two high concentrations and compare the results to those of prior LiCl concentration-dependent data. The dynamical data are obtained using ultrafast optical heterodyne-detected optical Kerr effect (OHD-OKE). The OHD-OKE decays are composed of two pairs of biexponentials, i.e., tetra-exponentials. The fastest decay (t1) is the same as pure water's at all concentrations within error, while the second component (t2) slows slightly with concentration. The slower components (t3 and t4), not present in pure water, slow substantially, and their contributions to the decays increase significantly with increasing concentration, similar to LiCl solutions. Simulations of LiCl solutions from the literature show that the slow components arise from large ion/water clusters, while the fast components are from ion/water structures that are not part of large clusters. Temperature-dependent studies (15-95 °C) of two high LiCl concentrations show that decreasing the temperature is equivalent to increasing the room temperature concentration. The LiBr and LiCl concentration dependences and the two LiCl concentrations' temperature dependences all have bulk viscosities that are linearly dependent on τcslow, the correlation time of the slow dynamics (weighted averages of t3 and t4). Remarkably, all four viscosity vs 1/τCslow plots fall on the same line. Application of transition state theory to the temperature-dependent data yields the activation enthalpies and entropies for the dynamics of the large ion/water clusters, which underpin the bulk viscosity.

Poly(benzimidazobenzophenanthroline)-Ladder-Type Two-Dimensional Conjugated Covalent Organic Framework for Fast Proton Storage

Electrochemical proton storage plays an essential role in designing next-generation high-rate energy storage devices, e.g., aqueous batteries. Two-dimensional conjugated covalent organic frameworks (2D c-COFs) are promising electrode materials, but their competitive proton and metal-ion insertion mechanisms remain elusive, and proton storage in COFs is rarely explored. Here, we report a perinone-based poly(benzimidazobenzophenanthroline) (BBL)-ladder-type 2D c-COF for fast proton storage in both a mild aqueous Zn-ion electrolyte and strong acid. We unveil that the discharged C-O- groups exhibit largely reduced basicity due to the considerable π-delocalization in perinone, thus affording the 2D c-COF a unique affinity for protons with fast kinetics. As a consequence, the 2D c-COF electrode presents an outstanding rate capability of up to 200 A g-1 (over 2500 C), surpassing the state-of-the-art conjugated polymers, COFs, and metal-organic frameworks. Our work reports the first example of pure proton storage among COFs and highlights the great potential of BBL-ladder-type 2D conjugated polymers in future energy devices.

Temperature Effects on Electrochemical Energy-Storage Materials: A Case Study of Yttrium Niobate Porous Microspheres

Lithium-ion batteries (LIBs) are very popular electrochemical energy-storage devices. However, their applications in extreme environments are hindered because their low- and high-temperature electrochemical performance is currently unsatisfactory. In order to build all-climate LIBs, it is highly desirable to fully understand the underlying temperature effects on electrode materials. Here, based on a novel porous-microspherical yttrium niobate (Y0.5 Nb24.5 O62 ) model material, this work demonstrates that the operation temperature plays vital roles in electrolyte decomposition on electrode-material surfaces, electrochemical kinetics, and crystal-structure evolution. When the operation temperature increases, the reaction between the electrolyte and the electrode material become more intensive, causing the formation of thicker solid electrolyte interface (SEI) films, which decreases the initial Coulombic efficiency. Meanwhile, the electrochemical kinetics becomes faster, leading to the larger reversible capacity, higher rate capability, and more suitable working potential (i.e., lower working potential for anodes and higher working potential for cathodes). Additionally, the maximum unit-cell-volume change becomes larger, resulting in poorer cyclic stability. The insight gains here can provide a universal guide for the exploration of all-climate electrode materials and their modification methods.

A fluoropolymer bifunctional solid membrane interface for improving the discharge duration in aqueous Al-air batteries

Herein, a fluoropolymer bifunctional solid membrane interface (SMI) for an aqueous Al-air battery is proposed, which inhibits anodic self-corrosion, while concurrently reducing the accumulation of undesirable by-products. A battery using the SMI exhibits a remarkable anticorrosion efficiency of 81.31% and achieves an astonishing battery lifetime improvement rate of 184.37% under the condition of 5 min intermittent discharge.

Rational Design of Electrode-Electrolyte Interphase and Electrolytes for Rechargeable Proton Batteries

Rechargeable proton batteries have been regarded as a promising technology for next-generation energy storage devices, due to the smallest size, lightest weight, ultrafast diffusion kinetics and negligible cost of proton as charge carriers. Nevertheless, a proton battery possessing both high energy and power density is yet achieved. In addition, poor cycling stability is another major challenge making the lifespan of proton batteries unsatisfactory. These issues have motivated extensive research into electrode materials. Nonetheless, the design of electrode-electrolyte interphase and electrolytes is underdeveloped for solving the challenges. In this review, we summarize the development of interphase and electrolytes for proton batteries and elaborate on their importance in enhancing the energy density, power density and battery lifespan. The fundamental understanding of interphase is reviewed with respect to the desolvation process, interfacial reaction kinetics, solvent-electrode interactions, and analysis techniques. We categorize the currently used electrolytes according to their physicochemical properties and analyze their electrochemical potential window, solvent (e.g., water) activities, ionic conductivity, thermal stability, and safety. Finally, we offer our views on the challenges and opportunities toward the future research for both interphase and electrolytes for achieving high-performance proton batteries for energy storage.