Dissolution Of Active Material Research Articles

Hollow Octahedral Pr6O11‐Mn2O3 Heterostructures for High‐Performance Aqueous Zn‐Ion Batteries

AbstractMn‐based oxides are broadly prospected cathode materials for aqueous Zn‐ion batteries (AZIBs) due to their rich abundance, low cost, and plentiful valence states. However, the further development of Mn‐based oxides is severely restricted by the dissolution of active materials and poor structural stability. Herein, hollow octahedral Pr6O11‐Mn2O3 (denoted as PrO‐MnO) heterostructures are developed through a facile metal–organic framework‐engaged templating approach, which realizes boosted Zn ion storage performance. Pr6O11 can not only effectively suppress the dissolution of Mn to stabilize Mn2O3 but also induce interfacial charge rearrangement and promote electron/ion transfer, contributing to the improved electrochemical activity and stability of PrO‐MnO. Moreover, the rationally designed hollow nanostructure offers sufficient active sites and facilitates the reaction kinetics. As expected, the PrO‐MnO cathode exhibits excellent rate and cycling performance with a high reversible capacity of 140.8 mAh g−1 after 2000 cycles at 1 A g−1, outperforming the Mn2O3 cathode.

Investigating Capacity Fade Mechanisms in Dual-Ion Mg-MCl x Batteries

Mg batteries are a promising alternative to Li-based chemistries due to the high abundance, low cost, and high volumetric capacity of Mg relative to Li. Mg is also less prone to dendritic plating morphologies, promising safer operation. Mg plating and stripping is highly efficient in chloride-containing electrolytes; however, chloride is incompatible with many candidate cathode materials. In this work, we capitalize on the positive effect of chloride by using transition metal chloride cathodes with a focus on low cost, Earth-abundant metals. Both soluble and sparingly soluble chlorides show capacity fade upon cycling. Active material dissolution and subsequent crossover to the Mg anode are the primary drivers of capacity fade in highly soluble metal chloride cathodes. We hypothesize that incomplete conversion and chemical reduction by the Grignard-based electrolyte are major promoters of capacity fade in sparingly soluble metal chlorides. Modifications to the electrolyte can improve capacity retention, suggesting that future work in this system may yield low cost, high retention Mg-MClx batteries.

Poly(3,4-ethylenedioxythiophene) encapsulation/intercalation boosting stability and zinc ion storage properties of vanadyl phosphates

The electrochemical properties of vanadyl phosphates as cathode materials for Zn-ion batteries have been severely hindered by their inherent poor electronic conductivity, unavoidable dissolution in aqueous solutions, and sluggish reaction kinetics. In this study, poly(3,4-ethylenedioxythiophene) (PEDOT) is introduced in vanadyl phosphates (PEDOT-VOP) through the in situ polymerization as interlayer guest species and surface coating layer, along with the generation of oxygen vacancies. The intercalated PEDOT develops strong interaction with the host layer, which can maintain its structural integrity. In addition, the PEDOT coating shell can enhance electronic conductivity together with oxygen vacancies to promote efficient electron transfer and prevent dissolution of active materials to stabilize the vanadyl phosphate core. As a result, the PEDOT-VOP electrode demonstrates a high discharge capacity of 180 mA h g−1 at 0.1 A/g with good rate performance (128 mA h g−1 at 2 A/g) and enhanced cycling stability (a capacity retention of 88.6 % after 2000 cycles at 1 A/g). The reversible Zn2+ insertion/extraction mechanism is further validated by diverse ex situ tests.

Rocking-Chair Aqueous Fluoride-Ion Batteries Enabled by Hydrogen Bonding Competition.

Aqueous fluoride ion batteries (FIBs) have garnered attention for their high theoretical energy density, yet they are challenged by sluggish fluorination kinetics, active material dissolution, and electrolyte instability. Here, we present a room temperature rocking-chair aqueous FIBs featuring KOAc-KF binary salt electrolytes, enabling concurrent fluorination and defluorination reactions at both cathode and anode electrodes. Experimental and theoretical results reveal that acetate ions in the electrolyte compete with fluoride ions in hydrogen bonding formation, weakening the excessively strong solvation between H2O and F- ions. This results in the suppression of detrimental HF formation and a reduced desolvation energy of F- ions, enhancing the electrochemical reaction kinetics. The bismuth-based cathode exhibits direct conversion in the optimized electrolyte, effectively suppressing the detrimental disproportionation reactions from Bi2+ intermediates. Additionally, zinc anode undergoes a typical fluorination process, forming solid KZnF3 as the electrode product, minimizing the risks of hydrogen evolution. The proposed aqueous FIBs with the optimized electrolyte demonstrate high discharge capacity, long-term cycling stability and excellent rate capabilities.

Rocking‐Chair Aqueous Fluoride‐Ion Batteries Enabled by Hydrogen Bonding Competition

AbstractAqueous fluoride ion batteries (FIBs) have garnered attention for their high theoretical energy density, yet they are challenged by sluggish fluorination kinetics, active material dissolution, and electrolyte instability. Here, we present a room temperature rocking‐chair aqueous FIBs featuring KOAc‐KF binary salt electrolytes, enabling concurrent fluorination and defluorination reactions at both cathode and anode electrodes. Experimental and theoretical results reveal that acetate ions in the electrolyte compete with fluoride ions in hydrogen bonding formation, weakening the excessively strong solvation between H2O and F− ions. This results in the suppression of detrimental HF formation and a reduced desolvation energy of F− ions, enhancing the electrochemical reaction kinetics. The bismuth‐based cathode exhibits direct conversion in the optimized electrolyte, effectively suppressing the detrimental disproportionation reactions from Bi2+ intermediates. Additionally, zinc anode undergoes a typical fluorination process, forming solid KZnF3 as the electrode product, minimizing the risks of hydrogen evolution. The proposed aqueous FIBs with the optimized electrolyte demonstrate high discharge capacity, long‐term cycling stability and excellent rate capabilities.

A sulfur-rich copolymer hybrid cathode for anchoring polysulfides and accelerating redox reaction in lithium sulfur batteries

In lithium-sulfur batteries (LSBs), sulfur-rich copolymers have attracted wide attention due to the reduced dissolution of active material and alleviated self-discharge problem through the efficient chemical interaction between polysulfide and carbon. Herein, we present an effective strategy to encapsulate sulfur-rich copolymer into NiCo2S4 encapsulated hierarchical porous N/O dual-doped graphitic carbon nanocages (GCNs), named S-DIB@NiCo2S4@PDA@rGO-GCNs. The host NiCo2S4@PDA@rGO-GCNs matrix can not only provide the “lithiophilic”-rich polar sites and tight anchored LiPSnon the N/O dual-doped GCNs surface, and “sulfphilic” NiCo2S4 electrocatalyst for accelerated sulfur electrochemistry, but also offer abundant hierarchical pores for accommodating sulfur and cushioning its volume expansion. Both of the experimental and theoretical analyses reveal the S-DIB@NiCo2S4@PDA@rGO-GCNs possesses the strong chemisorptions and catalytic ability with the synergetic mechanism, suppressing the self-discharge problem. As a proof-of-concept study, the assembled LSBs cells show excellent discharge capacities of 486 and 324 mA h g−1 at 5C and 10C after 1000 cycles, respectively. The corresponding capacity loss rate is as low as 0.032 % and 0.030 % per cycle, respectively. Thanks to the exceptional lithiophilic and sulfiphilic characteristic, the LSBs pouch cell also demonstrates high cycling stability. The proposed hierarchical encapsulation strategy with synergetic chemisorptions and catalytic ability shows great potential for developing advanced electrodes for next-generation high-performance rechargeable batteries.

Indolocarbazole‐Based Small Molecule Cathode‐Active Material Exhibiting Double Redox for High‐Voltage Li‐Organic Batteries

Most organic electrode materials (OEMs) for rechargeable batteries employ n‐type redox centers, whose redox potentials are intrinsically limited <3.0 V versus Li+/Li. However, p‐type materials possessing high redox potentials experience low specific capacities because they are capable of only a single redox reaction within the stable electrochemical window of typical electrolytes. Herein, we report 5,11‐diethyl‐5,11‐dihydroindolo[3,2‐b]carbazole (DEICZ) as a novel p‐type OEM, exhibiting stable plateaus at high discharge potentials of 3.44 and 4.09 V versus Li+/Li. Notably, the second redox potential of DEICZ is within the stable electrochemical window. The mechanism of the double redox reaction is investigated using both theoretical calculations and experimental measurements, including density functional theory calculations, ex situ electron spin resonance, and X‐ray photoelectron spectroscopy. Finally, hybridization with single‐walled carbon nanotubes (SWCNT) improves the cycle stability and rate performance of DEICZ owing to the π–π interactions between the SWCNT and co‐planar molecular structure of DEICZ, preventing the dissolution of active materials into the electrolyte. The DEICZ/SWCNT composite electrode maintains 70.4% of its initial specific capacity at 1‐C rate and also exhibits high‐rate capability, even performing well at 100‐C rate. Furthermore, we demonstrate its potential for flexible batteries after applying 1000 bending stresses to the composite electrode.

A polydopamine coating enabling the stable cycling of MnO2 cathode materials in aqueous zinc batteries.

MnO2 is a desired cathode candidate for aqueous zinc batteries. However, their cycling stability is seriously limited by active material dissolution, and pre-addition of Mn2+ salts in electrolytes is widely required to shift the dissolution equilibrium. Herein, we synthesize a polydopamine (PDA) coated MnO2 composite material (MnO2/PDA) to realize stable cycling in zinc cells without relying on pre-added Mn2+. The functional groups on PDA exhibit strong coordination ability with the Mn active material. It not only confines dissolved species within the cathode during discharge, but also enhances their deposition back to the cathode during charge to retrieve the active material. Thanks to this effect, the cathode achieves 81.1% capacity retention after 2000 cycles at 1 A g-1 in the 1 M ZnSO4 electrolyte, superior to 37.3% with the regular MnO2 cathode. This work presents an effective strategy to realize the stable cycling of manganese oxide cathode materials in aqueous zinc batteries.

Solvent-in-Salt Electrolytes for Fluoride Ion Batteries

The fluoride ion battery (FIB) is a promising post-lithium-ion battery chemistry owing to its high theoretical energy density and the large elemental abundance of its active materials. Nevertheless, its utilization for room-temperature cycling has been impeded by the inability to find sufficiently stable and conductive electrolytes at room temperature. In this work, we report the use of solvent-in-salt electrolytes for FIBs, exploring multiple solvents to show that aqueous cesium fluoride exhibited sufficiently high solubility to achieve an enhanced (electro)chemical stability window (3.1 V) that could enable high operating voltage electrodes, in addition to a suppression of active material dissolution that allows for an improved cycling stability. The solvation structure and transport properties of the electrolyte were also investigated using spectroscopic and computational methods.

Designing mesostructured iron (II) fluorides with a stable in situ polymer electrolyte interface for high-energy-density lithium-ion batteries

As high-energy cathode materials, conversion-type metal fluorides provide a prospective pathway for developing next-generation lithium-ion batteries. However, they suffer from severe performance decay owing to continuous structural destruction and active material dissolution upon cycling, which worsen at elevated temperatures. Here, we design a novel FeF2 cathode with in situ polymerized solid-state electrolyte systems to enhance the cycling ability of metal fluorides at 60 ​°C. Novel FeF2 with a mesoporous structure (meso-FeF2) improves Li+ diffusion and relieves the volume change that typically occurs during the alternating conversion reactions. The structural stability of the meso-FeF2 cathode is strengthened by an in situ polymerized solid-state electrolyte, which prevents the pulverization and ion dissolution that are inevitable for conventional liquid electrolytes. Under the double action of this in situ polymerized solid-state electrolyte and the meso-FeF2's mesoporous structure, the active material maintains an intact SEI layer and part of the mesoporous structure after long charge–discharge cycling, showing excellent cycling stability at high temperatures.

Stable quasi-solid-state lithium-organic battery based on composite gel polymer electrolyte and compatible organic cathode material

High-performance organic small-molecule electrode materials are troubled with their high solubility in liquid electrolytes. The construction of quasi-solid-state lithium organic batteries (LOBs) using gel polymer electrolytes with high mechanical properties, compromised ionic conductivity, high safety, and eco-friendly is an effective way to inhibit the dissolution of active materials. Herein, two hexaazatriphenylene (HATN)-based organic cathode materials (HATNA-6OCH3 and HATNA-6OH) are synthesized and then matched with polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP)-based gel polymer electrolytes to construct quasi-solid-state LOBs. Thanks to the enhanced interfacial compatibility between organic cathode material and gel polymer electrolyte, HATNA-6OH with compatible hydroxyl group shows the enhanced electrochemical properties compared with HATNA-6OCH3. Further, the electrochemical performance is improved when HATNA-6OH is combined with a gel polymer electrolyte modified with a succinonitrile (SN) plasticizer (GPE-0.4SN), including a high specific capacity of 153.3 mAh g−1 at 50 mA g−1 and a good reversible capacity of 88 mAh g−1 after 100 cycles at 200 mA g−1. In addition, the good electrochemical properties and lithium-ion storage mechanism of HATNA-6OH have been elucidated using density functional theory (DFT) and spectral characterizations.

Solvent-in-Salt Electrolytes for Fluoride Ion Batteries.

The fluoride ion battery (FIB) is a promising post-lithium ion battery chemistry owing to its high theoretical energy density and the large elemental abundance of its active materials. Nevertheless, its utilization for room-temperature cycling has been impeded by the inability to find sufficiently stable and conductive electrolytes at room temperature. In this work, we report the use of solvent-in-salt electrolytes for FIBs, exploring multiple solvents to show that aqueous cesium fluoride exhibited sufficiently high solubility to achieve an enhanced (electro)chemical stability window (3.1 V) that could enable high operating voltage electrodes, in addition to a suppression of active material dissolution that allows for an improved cycling stability. The solvation structure and transport properties of the electrolyte are also investigated using spectroscopic and computational methods.

Recent Progress and Regulation Strategies of Layered Materials as Cathode of Aqueous Zinc‐Ion Batteries

Aqueous zinc‐ion batteries (ZIBs) have shown great potential in the fields of wearable devices, consumer electronics, and electric vehicles due to their high level of safety, low cost, and multiple electron transfer. The layered cathode materials of ZIBs hold a stable structure during charge and discharge reactions owing to the ultrafast and straightforward (de)intercalation‐type storage mechanism of Zn2+ ions in their tunable interlayer spacing and their abilities to accommodate other guest ions or molecules. Nevertheless, the challenges of inadequate energy density, dissolution of active materials, uncontrollable byproducts, increased internal pressure, and a large de‐solvation penalty have been deemed an obstacle to the development of ZIBs. In this review, recent strategies on the structure regulation of layered materials for aqueous zinc‐ion energy storage devices are systematically summarized. Finally, critical science challenges and future outlooks are proposed to guide and promote the development of advanced cathode materials for ZIBs.

An Artificial MnWO4 Cathode Electrolyte Interphase Enabling Enhanced Electrochemical Performance of δ-MnO2 Cathode for Aqueous Zinc Ion Battery.

The dissolution of active material in aqueous batteries can lead to a rapid deterioration in capacity, and the presence of free water can also accelerate the dissolution and trigger some side reactions that affect the service life of aqueous batteries. In this study, a MnWO4 cathode electrolyte interphase (CEI) layer is constructed on a δ-MnO2 cathode by cyclic voltammetry, which is effective in inhibiting the dissolution of Mn and improving the reaction kinetics. As a result, the CEI layer enables the δ-MnO2 cathode to produce a better cycling performance, with the capacity maintained at 98.2% (vs. activated capacity at 500 cycles) after 2000 cycles at 10 A g-1. In comparison, the capacity retention rate is merely 33.4% for pristine samples in the same state, indicating that this MnWO4 CEI layer constructed by using a simple and general electrochemical method can promote the development of MnO2 cathodes for aqueous zinc ion batteries.

Unlocking Enhanced Capacitive Deionization of NaTi2(PO4)3/Carbon Materials by the Yolk–Shell Design

The low salt adsorption capacities (SACs) of benchmark carbon materials (usually below 20 mg g-1) are one of the most challenging issues limiting further commercial development of capacitive deionization (CDI), an energetically favorable method for sustainable water desalination. Sodium superionic conductor (NASICON)-structured NaTi2(PO4)3 (NTP) materials, especially used in combination with carbon to prepare NTP/C materials, provide emerging options for higher CDI performance but face the problems of poor cycling stability and dissolution of active materials. In this study, we report the development of the yolk-shell nanoarchitecture of NASICON-structured NTP/C materials (denoted as ys-NTP@C) using a metal-organic framework@covalent organic polymer (MOF@COP) as a sacrificial template and space-confined nanoreactor. As expected, ys-NTP@C exhibits good CDI performance, including exemplary SACs with a maximum SAC of 124.72 mg g-1 at 1.8 V in the constant-voltage mode and 202.76 mg g-1 at 100 mA g-1 in the constant-current mode, and good cycling stability without obvious performance degradation or energy consumption increase over 100 cycles. Furthermore, X-ray diffraction used to study CDI cycling clearly exhibits the good structural stability of ys-NTP@C during repeated ion intercalation/deintercalation processes, and the finite element simulation shows why yolk-shell nanostructures exhibit better performance than other materials. This study provides a new synthetic paradigm for preparing yolk-shell structured materials from MOF@COP and highlights the potential use of yolk-shell nanoarchitectures for electrochemical desalination.

Inside Front Cover: Carbon Neutralization, Volume 2, Issue 2, March 2023

Inside front cover image: Aqueous Zn-ion batteries (AZIBs) have exhibited great potential in large-scale energy storage systems. However, delivery of stable electrode-electrolyte interface (EEI) become the main challenge for the development of AZIBs. On the cathode side, dissolution of active materials, formation of byproducts, and unsatisfactory interfacial compatibility frequently occur. Meanwhile, the Zn metal anodes usually suffer from inevitable Zn dendrites and parasitic reactions. In article number 10.1002/cnl2.54, key scientific issues occurred at EEI have been comprehensively summarized. Additionally, corresponding interfacial optimization strategies including surface modification and electrolyte optimization are proposed, aiming at providing guideline for the design of high-performance AZIBs.

Electrode/electrolyte interfacial engineering for aqueous Zn‐ion batteries

AbstractAqueous Zn‐ion batteries (AZIBs) hold great promise for large‐scale energy storage applications due to their low cost, intrinsic safety, and high theoretical capacity. However, the delivery of stable electrode–electrolyte interface becomes the main challenge for developing high‐performance AZIBs with long cycle life and high capacity. On the cathode side, the dissolution of active materials, formation of byproducts, and unsatisfactory interfacial compatibility frequently occur. Meanwhile, the Zn metal anodes usually suffer from inevitable Zn dendrites and parasitic reactions. Both the electrode–electrolyte interface issues for the cathodes and anodes will finally result in poor electrochemistry reversibility and fast capacity decay. With this perspective, this review focuses on the key scientific issues occurred at the electrode interfaces, and also proposes corresponding interfacial optimization strategies, including surface modification and electrolyte optimization, aiming at providing guidelines for the design of high‐performance AZIBs based on the understanding of interface improvement and practical application considerations.

Construction of highly stable LiI/LiBr-based nanocomposite cathode via triple confinement mechanisms for lithium-halogen batteries

Lithium-halogen batteries (LHBs), including lithium iodide (Li-I2) and lithium bromide (Li-Br2) batteries, are receiving more attention for offering high energy density and excellent kinetic performance. However, LHBs commercialization is seriously hindered by the high solubility of halides, causing lower capacity and poor cyclability. This research covers the fabrication of a highly stable cathode of amorphous carbon coated CMK-3/LiI/LiBr nanocomposite for metal lithium batteries. The nanopores and coated layer can physically trap the dissolution of active materials. The amorphous carbon generated from polyacrylonitrile carries abundant nitrogen heteroatoms for the stable anchorage of halogens and halides via strong chemical adsorption. In addition, iodine can act as a complexing agent with bromine to reduce solvation energy. Consequently, the as-prepared CMK-3/LiI/LiBr/carbon (CIBP) nanocomposite cathode demonstrates an ultra-high reversible capacity of 407.4 mAh/g at the current density of 1.0 C performing up to 300 stable cycles.

Wide-voltage-window amphiphilic supramolecule excluded-volume electrolytes for ultra-durable full-cell aqueous potassium-Ion batteries

Aqueous potassium-ion batteries (AKIBs) are promising candidates for large-scale energy storage. However, the performance of AKIBs is restricted the dissolution of electrode materials and the narrow voltage window of aqueous electrolytes. Herein, we report the amphiphilic supramolecule modified aqueous K-ion electrolytes with synergistic functions of excluded-volume effect and hydrogen bond networks, which greatly reduce the activity of water molecules, inhibit the dissolution of active materials, and expand the operation voltage window (>3.4 V). Moreover, the as-assembled full-cell AKIBs exhibit an open-circuit voltage of 2.0 V, good rate capability, wide operating temperature range (−20 to 90 °C), and ultralong cycling life (with a capacity retention of 97.8 % after 10,000 cycles at 10 C). The study makes it possible for aqueous electrolytes to possess wide voltage window and temperature endurance, greatly expanding the choices of practicable electrolyte and paving the way of high-voltage aqueous batteries towards sustainable, safety and low-cost energy storage.

Voltage induced lattice contraction enabling superior cycling stability of MnO2 cathode in aqueous zinc batteries

The cycling stability of MnO2 cathodes in aqueous zinc batteries is highly relied on Mn2+ additives in electrolytes. Herein, we demonstrate a voltage induced lattice contraction mechanism for α-MnO2 to realize stable cycling in Mn2+ free electrolytes. Analysis reveals the accumulation of electrochemically inactive parts is mainly responsible for capacity decay when cycled with 1.8 V top voltage cut-off, whereas the contribution from irreversible dissolution of active material is smaller. With the extension of voltage limit to 2.2 V and a voltage hold process during the initial charge, the inactive parts are activated to undergo reversible two electron transfer reaction. Further studies suggest that high voltage induces the contraction of original lattice. It stabilizes entered structural water and enhances Mn release. Meanwhile, more oxygen vanacies are generated, which also leads to the weakening of Mn binding in the lattice. Therefore, MnO2 achieves 323 mAh g−1 capacity with 94.6% retention over 300 cycles (>1800 h) at 0.1 A g−1 in the Mn2+ free electrolyte of 3 M ZnSO4. This work provides an effective path to realize stable cycling of MnO2 cathodes in zinc batteries.