Dilute Aqueous-Aprotic Hybrid Electrolyte Enabling a Wide Electrochemical Window through Solvation Structure Engineering

Dilute Aqueous-Aprotic Electrolyte Towards Robust Zn-Ion Hybrid Supercapacitor with High Operation Voltage and Long Lifespan

With the merits of the high energy density of batteries and power density of supercapacitors, the aqueous Zn-ion hybrid supercapacitors emerge as a promising candidate for applications where both rapid energy delivery and moderate energy storage are required. However, the narrow electrochemical window of aqueous electrolytes induces severe side reactions on the Zn metal anode and shortens its lifespan. It also limits the operation voltage and energy density of the Zn-ion hybrid supercapacitors. Using 'water in salt' electrolytes can effectively broaden their electrochemical windows, but this is at the expense of high cost, low ionic conductivity, and narrow temperature compatibility, compromising the electrochemical performance of the Zn-ion hybrid supercapacitors. Thus, designing a new electrolyte to balance these factors towards high-performance Zn-ion hybrid supercapacitors is urgent and necessary. We developed a dilute water/acetonitrile electrolyte (0.5 m Zn(CF3SO3)2 + 1 m LiTFSI-H2O/AN) for Zn-ion hybrid supercapacitors, which simultaneously exhibited expanded electrochemical window, decent ionic conductivity, and broad temperature compatibility. In this electrolyte, the hydration shells and hydrogen bonds are significantly modulated by the acetonitrile and TFSI- anions. As a result, a Zn-ion hybrid supercapacitor with such an electrolyte demonstrates a high operating voltage up to 2.2 V and long lifespan beyond 120,000 cycles.

Unlocking the Effect of Chain Length and Terminal Group on Ethylene Glycol Ether Family Toward Advanced Aqueous Electrolytes

Constructing high-performance hybrid electrolyte is important to advanced aqueous electrochemical energy storage devices. However, due to the lack of in-depth understanding of how the molecule structures of cosolvent additives influence the properties of electrolytes significantly impeded the development of hybrid electrolytes. Herein, a series of hybrid electrolytes are prepared by using ethylene glycol ether with different chain lengths and terminal groups as additives. The optimized 2 m LiTFSI-90%DDm hybrid electrolyte prepared from diethylene glycol dimethyl ether (DDm) molecule showcases excellent comprehensive performance and significantly enhances the operating voltage of supercapacitors (SCs) to 2.5 V by suppressing the activity of water. Moreover, the SC with 2 m LiTFSI-90%DDm hybrid electrolyte supplies a long-term cycling life of 50 000 cycles at 1 A g-1 with 92.3% capacitance retention as well as excellent low temperature (-40 ºC) cycling performance (10 000 times at 0.2 A g-1). Universally, Zn//polyaniline full cell with 2 m Zn(OTf)2-90%DDm electrolyte manifests outstanding cycling performance in terms of 77.9% capacity retention after 2,000 cycles and a dendrite-free Zn anode. This work inspires new thinking of developing advanced hybrid electrolytes by cosolvent molecule design toward high-performance energy storage devices.

Synergistic Ion Sieve and Solvation Regulation by Recyclable Clay-Based Electrolyte Membrane for Stable Zn-Iodine Battery

The high dissolution of polyiodides and unstable interface at the anode/electrolyte severely restrict the practical applications of rechargeable aqueous Zn-iodine batteries. Herein, we develop a zinc ion-based montmorillonite (ZMT) electrolyte membrane for synergizing ion sieve and solvation regulation to achieve highly stable Zn-iodine batteries. The rich M-O band and special cation-selective transport channel in ZMT locally tailor the solvation sheath around Zn2+ and therefore achieve high transference number (t+ = 0.72), benefiting for uniform and reversible deposition/stripping of Zn. Meanwhile, the mechanisms for three-step polyiodide generation and shuttle-induced Zn corrosion are highlighted by in situ characterization techniques. It is confirmed that the strong chemical adsorption between O atoms in ZMT and polyiodides species is the key to effectively inhibit the shuffle effect and side reactions. Consequently, the ZMT-based Zn-iodine battery delivers a high capacity of 0.45 mAh cm-2 at 1 mA cm-2 with a much improved Coulombic efficiency of 99.5% and outstanding capacity retention of 95% after 13 500 cycles at 10 mA cm-2. Moreover, owing to its high durability and chemical inertness and structural stability, ZMT-based electrolyte membranes can be recycled and applied in double-sided pouch cells, delivering a high areal capacity of 2.4 mAh cm-2 at 1 mA cm-2.

A Ti3C2Tx MXene cathode and redox-active electrolyte based flexible Zn-ion microsupercapacitor for integrated pressure sensing application

Frequently used aqueous electrolytes in MXene-based Zn-ion hybrid microsupercapacitors (MSCs) limit their cycling and rate stability. The use of metal and nonmetal additives in electrolytes for the performance improvement of Zn-ion MSCs is considered a valid method. Herein, we propose an additive assisted Zn(CF₃SO₃)₂ electrolyte as a redox-active electrolyte to prepare a flexible MXene-based Zn-ion hybrid MSC by a facile spraying method, and it consists of a conductive Ti₃C₂T_x-LiCl current collector and a Ti₃C₂T_x-DMSO cathode. In the process of the current density change (from 5 A cm^-3 to 30 A cm^-3 and then to 5 A cm^-3), the capacity retention of the as-fabricated MSC with K₃Co(CN)₆ additive is over 99.0%, which is higher than 96.7% for the MSC with CKNSe additive and 82.3% for the MSC without an additive. Moreover, the designed MSC with the redox-active K₃Co(CN)₆ electrolyte exhibits a maximal capacitance retention of 70% after 5000 cycles. Furthermore, the flexible Zn-ion MSC with the Ti₃C₂T_x MXene cathode and a redox-active electrolyte was used to power a Ti₃C₂T_x based pressure sensor; the excellent press response of the integrated system not only provides insights into the development of large capacity and long-period stable energy storage devices, but also paves a new way for the development of capacitor-sensor integrated systems.

Biaxial Stretching Array Based on High-Energy-Efficient MXene-Based Al-Ion Micro-supercapacitor Island and Editable Stretchable Bridge

Employment of multivalent charge carriers with higher charge density to replace frequently used univalent ones can effectively increase the areal capacitance of micro-supercapacitors utilizing few-layered MXene self-assembled electrodes. However, their larger charge density and ionic size usually lead to a sluggish extraction/insertion dynamic between MXene interlayers with limited free space, greatly offsetting the benefits. Herein, we show how to facilitate de-/intercalation of high-valence charge carriers (Al³⁺) by using polypyrrole-coated bacterial cellulose (BC@PPy) nanospacers to expand MXene interlayer space. Together with the longitudinal electron transport path between interlayers synchronously constructed by the conductive PPy shell, a significant 496% areal capacitance enhancement (232.79 mF cm^-2) is realized in the fabricated symmetric Al³⁺-ion micro-supercapacitors (AMSCs) with the obtained MXene/BC@PPy hybrid film electrodes employing polyacrylamide/1 M AlCl₃·6H₂O hydrogel electrolyte relative to the cell with pure MXene film electrodes (39.02 mF cm^-2). Further benefiting from a high output voltage of 1.2 V, the AMSCs acquire an areal energy density up to 45.3 μW h cm^-2. As a device demonstration, we further fabricate a biaxially stretchable AMSC array, simulate its spatial strain distribution during biaxial stretching, and characterize its electrochemical and mechanical properties up to an extreme areal strain of 300%. The proposed rational fabrication paradigm achieves a new level of combined energy density, stretch performance, and architectural simplicity, which presents a route toward a commercially viable stretchable micro energy-storage system with high energy efficiencies.

Integrated Construction Improving Electrochemical Performance of Stretchable Supercapacitors Based on Ant-Nest Amphiphilic Gel Electrolytes

Aqueous integrated stretchable supercapacitors (ISSCs) have attracted extensive attention due to the intrinsic safety in future wearable electronics. However, aqueous ISSCs usually suffer from low energy density and poor dynamic deformation stability owing to the conventional hydrogel electrolytes' narrow electrochemical stability window (ESW) and dissatisfied interface bonding. Herein, an ant-nest amphiphilic polyurethane hydro/organogel electrolyte (sAPUGE) with a wide ESW (≈2.2 V) and superb self-adhesion is prepared by electrospinning, which interacts with carbon-based stretchable electrodes for the construction of flame-retardant PU-based sAPUGE-ISSC. Benefitting from the synergistic effect of chemical bonding and mechanical meshing between the electrode and gel electrolyte interface, as-assembled sAPUGE-ISSC delivers a high energy density of 13.7 mWh cm^-3 (at a power density of 0.126 W cm^-3 ) and outstanding dynamic deformation stability (98.3% capacitance retention after 500 stretching cycles under 100% strain). This unique hydro/organogel electrolyte provides a pathway toward the next generation of wearable energy products in modern electronics.

Electrolyte Solvation Structure Design for Sodium Ion Batteries

Sodium ion batteries (SIBs) are considered the most promising battery technology in the post-lithium era due to the abundant sodium reserves. In the past two decades, exploring new electrolytes for SIBs has generally relied on the "solid electrolyte interphase (SEI)" theory to optimize the electrolyte components. However, many observed phenomena cannot be fully explained by the SEI theory. Therefore, electrolyte solvation structure and electrode-electrolyte interface behavior have recently received tremendous research interest to explain the improved performance. Considering there is currently no review paper focusing on the solvation structure of electrolytes in SIBs, a systematic survey on SIBs is provided, in which the specific solvation structure design guidelines and their consequent impact on the electrochemical performance are elucidated. The key driving force of solvation structure formation, and the recent advances in adjusting SIB solvation structures are discussed in detail. It is believed that this review can provide new insights into the electrolyte optimization strategies of high-performance SIBs and even other emerging battery systems.