Anion Insertion Research Articles

Theoretical Analysis of Anion Intercalation Process into Cathode Conductive Carbon

High-voltage Li-ion batteries have been extensively studied to increase the energy density of batteries. To achieve this goal, 5 V class cathode materials have been developed, but the long-term stable operation has not been achieved. Recently, we reported that the poor cycle stability comes not only from the oxidative degradation of the electrolyte and/or cathode active material, but also from side reactions caused by the insertion of anions into the interlayer of a cathode conductive carbon [1]. However, the detailed mechanism of anion insertion into the conductive carbon is still not well understood. In this study, we theoretically investigated the anion insertion process at the interface between a graphite and EC-based electrolyte solution (1 M LiPF6 / EC).We adopted a density functional theory (DFT) in combination with the effective screening medium and reference interaction site model (ESM-RISM) method to analyze the insertion process of a PF6 - anion into the graphite [2]. The simulation cells are composed of graphite electrode (C252(PF6)9H36) and the 1 M LiPF6 / EC electrolyte, where the entire graphite electrode are treated quantum mechanically, whereas the electrolyte components are treated classically by the RISM method. The activation energy was calculated by computing the grand potential (Ω) at each point while moving a PF6 - anion from its initial position on the electrolyte side (r = 20 Å) to the electrode interior (r = 0 Å). These calculations were performed at two different electrode potentials, the potential of zero charge (PZC) and the equilibrium potential of the anion insertion reaction, respectively. All the DFT and ESM-RISM calculations were conducted using the Quantum Espresso v.6.1 code.The figure shows the profiles of Ω along the insertion process of the PF6 – anion into the graphite layer. The activation energies were estimated to be 0.49 eV (ΩPZC, black line) and 0.37 eV (Ωeq, red line) at the PZC and the equilibrium potential, respectively, considerably smaller than that of Li+ (0.6 eV) [3]. Importantly, the coordination number of EC molecules around PF6 – (N EC, blue line) decreases from about 10 Å and Ω becomes correspondingly unstable, indicating that the desolvation of PF6 – contributes significantly to the activation barrier. Furthermore, systematic calculations of the desolvation energies for different solvent species show that the calculated values tend to increase as the dipole moment of the solvent molecule decreases. Therefore, a use of solvents with smaller dipole moments would increase the desolvation energy, thus suppressing the anion insertion.1) S. Ko et al., Joule, 5, 998 (2021).2) S. Nishihara et al., Phys. Rev. B, 96, 115429 (2017).3) J. Haruyama et al., J. Phys. Chem. C, 122, 9804 (2018). Figure 1

(Invited) Anion-Intercalated Cathode Concept for Fast and Stable Cycling of LIC and Batteries

Behavior of Graphene-like Graphite Cathode in Ionic Liquid Electrolytes Research and development of energy storage devices with higher energy densities than those of ordinary supercapacitors is underway. In the field of rechargeable batteries, a rechargeable battery that utilizes anion intercalation between graphite layers for charge compensation is being considered as one of the post-lithium ion batteries1). Anion intercalation is the insertion and desorption of anions between the layers of cathode materials during charging and discharging. The wider the interlayer of the cathode material, the greater the amount of anion insertion, leading to higher battery capacity. Generally, graphite is used as the cathode material for secondary batteries that utilize anion insertion. However, graphite has narrow interlayer spaces, making it impossible to increase intercalation capacity. Therefore, the use of graphene-like graphite (GLG), which has been reported to have wider interlayer space than graphite, is expected to provide high-speed operating performance and high capacity equivalent to that of ordinary capacitors2). In a previous study by the presenter, a two-electrode cell was constructed with GLG as the working electrode, Li metal as the counter electrode, and 1.0M LiFSI / Pyr13FSI ionic liquid electrolyte as the electrolyte, and a high discharge capacity of approximately 200mAh g-1 was demonstrated3).In this study, we attempted to examine and develop a LIC using GLG as a cathode material. Since both the cathode and anode are carbon materials, the LIC is lighter, safer, and more environmentally friendly than conventional LIBs. In addition, the operating voltage per cell is high due to the large redox potential difference. Therefore, the energy density of the LIC can be expected to be comparable to that of a conventional LIB using transition metal oxides for the cathode. However, the reversible capacity of graphite as a cathode material depends on the type of anion and is lower than that of conventional LIB cathodes with transition metal oxides4). In addition, the high redox potential may cause undesirable side reactions such as oxidative decomposition of the electrolyte, so an electrolyte with oxidation resistance is required. Therefore, we focused on GLG as a cathode material to replace graphite and ionic liquid electrolyte as an oxidation-resistant electrolyte. LICs were fabricated using GLG as the cathode, graphite as the anode, and LiFSI/Pyr13FSI ionic liquid electrolyte as the electrolyte. The results showed that the initial discharge capacity and electrolytic efficiency in the first cycle were lower than those of the GLG cathode-Li half cell. Therefore, we analyzed the structure of each electrode and conducted charge-discharge tests under various conditions to investigate the improvement of discharge capacity and initial coulombic efficiency. Development of LICs using Nitrogen-Doped Graphene Conventional dual carbon energy storage devices use graphite with narrow interlayer space as the cathode active material, and the capacity was limited by the reduced utilization of the graphene layer due to the insertion of anions5) . To solve this problem, reduced nitrogen-doped graphene (N-rGO), in which nitrogen is doped into graphene with wider interlayer space than graphite, was applied as cathode active material in LIC and dual carbon batteries. The results showed that N-rGO exhibited higher specific capacitance than graphite. In general, a plateau region originating from the step structure of graphite was observed in the charge-discharge curve of anion insertion-desorption reaction using graphite as the cathode active material6), but no plateau region originating from the step structure was observed in the charge-discharge curve using N-rGO as the cathode active material. This result suggests that the anion insertion/desorption reaction of N-rGO has different reactivity between cathode active materials. References T. Ishihara et al., J. Phys. Chem. C., 120 (2016) 22887.J. Inamoto, Y. Matsuo et al., J. Electrochem. Soc., 168(2021) 010528.M. Yoshie, M. Ishikawa et al., of the 62nd battery Symposium in Japan (2021) 3A13.J.A. Read et al., Energy Environ. Sci., 7 (2014) 617.X. Qi et al., J. Mater. Sci., 56 (2021) 10555.W. Zhou et al., ACS Omega, 5 (2020) 18289.

Development of High-Performance Lithium-Ion Capacitor Using Reduced Nitrogen-Doped Graphene as Capacitor-Type Cathode Material Exhibiting Anomaly Anion Storage Mechanism

1.IntroductionLithium-ion capacitor (LIC) is a capacitor with improved energy density by applying a battery-type active material capable of lithium storage as the anode material. However, a typical cathode of LIC applies a capacitor-type active material that adsorbs anions, limiting its specific capacity as LIC. Therefore, we synthesized and applied reduced nitrogen-doped graphene (N-rGO) as a new cathode active material to achieve high energy density in LIC. The N-rGO cathode exhibits capacitance via an anion intercalation mechanism, a faradaic reaction, and initial charge-discharge characteristics in the N-rGO/Li half-cell showed a high specific capacitance exceeding 160 mAh g-1 in a 2.0 - 4.8 V voltage range and a current density of 150 mA g-1. We also reported that N-rGO cathode exhibits high rate characteristics due to a unique anion storage mechanism in which the capacity increases proportionally to the voltage after the first charge cycle. [1, 2] This suggests that it is suitable as a new cathode material for LIC. This unconventional anion storage mechanism would be ascribed to a change in the N-rGO morphology due to anion intercalation during the initial charging, but there have been still many unresolved points. In this study, we further analyzed the anion storage mechanism in N-rGO cathode and constructed a LIC device using N-rGO, which exhibits an anomaly anion storage mechanism, and examined the possibility of achieving high capacity.2.Experimental sectionN-rGO was synthesized by a hydrothermal reaction of ball-milled graphene oxide (GO) as a N-rGO precursor with urea as a nitrogen source and distilled water as a solvent in an autoclave at 180°C in 12 hours under high pressure conditions. N-rGO and graphite electrodes were prepared by mixing each active material with acetylene black (AB), carboxymethyl cellulose (CMC), and styrene butadiene rubber (SBR) in the weight ratio of 90:5:3:2, respectively. The slurry was coated onto Al and Cu current collector, respectively. Cathode half-cells were assembled with the N-rGO cathode, Li-metal as the counter electrode, and 1.0 mol dm-3 LiPF6 / EC : DMC = 1 : 1 (by vol.) as the electrolyte to analyze the anion storage mechanism of N-rGO cathode. Full-cells were assembled with the N-rGO cathode, graphite anode, and 1.0 mol dm-3 LiPF6 / EC : DMC = 1 : 1 (by vol.) as the electrolyte, and its performance as LIC was evaluated.3.Results and discussionIn our previous report, a conventional anion intercalation mechanism undergoes expansion and shrinking of the interlayer distance of carbon as anions are inserted and removed, whereas the N-rGO cathode goes through expanding the interlayer distance of carbon due to anion insertion at the initial charging, and then the expanded interlayer distance is maintained during subsequent charge-discharge cycles. Morphology difference between these materials may have altered the anion storage mechanism. The microstructure within the interlayer was investigated using XANES. Details will be explained in this poster presentation. Constant current charge-discharge tests were conducted to investigate the performance of LIC with this N-rGO as a capacitor-type cathode. With the previous LIC, we pre-doped Li in the graphite anode and constructed a full cell. The specific capacity was almost the same as the N-rGO/Li half cell, but the capacity retention was poor and the capacity was significantly reduced after 10 cycles. We speculated that this was due to a plateau in the charge curve even after the initial charge, and that the morphological change due to sufficient anion insertion had not occurred. Therefore, in addition to pre-doping Li into the graphite anode, we pre-cycled the N-rGO cathode as a single cycle prior to constructing full cell. As a result, the plateau in the charge process almost disappeared, and the specific capacity and high capacity-retention were almost the same as those of the N-rGO/Li half-cell, and long-term cycling was achieved.Reference[1] J. Ishikawa et al., The 64th Battery Symposium Japan, 1F01 (2023).[2] M. Zhang et al., Energy Stor. Mater., 16 (2019) 65-84.

Dopant Engineering of Conductive Polymer for Developing High-Efficiency, Membrane-Free, Full-Polymer Electrochemical Deionization Systems

Electrochemical deionization (ECDI) systems represent an enticing avenue in desalination technology, offering notable desalination capacity while maintaining energy efficiency, thus presenting themselves as potential replacements for existing desalination methods. Traditionally, ECDI systems rely on electric double-layer (EDL) materials to eliminate salts via electrode-induced ion adsorption under external electric fields. However, the practical utility of this conventional approach is hindered by the limitations of the EDL mechanism, constraining desalination capability. Consequently, there has been a notable shift towards exploring pseudocapacitive-type or battery-type faradaic materials, which offer promising alternatives. This novel approach entails the capture of ions within the solution through electrode charge transfer, effectively reducing energy consumption and bolstering desalination performance. Furthermore, the unique characteristic of the "memory effect" in faradaic materials, as proposed by Hu et al., has revolutionized resource recovery and water purification, eliminating the need for membranes and further elevating the appeal of such materials within the field [1]. Among these faradaic materials, polypyrrole (PPy) is recognized for its affordability, stability, and straightforward synthesis, rendering it an excellent choice for anion insertion applications. Prior research indicates that PPy demonstrates distinct behaviors depending on dopant variations. Large-size dopants confer cation exchange capabilities to PPy, whereas small-size dopants imbue it with anion exchange characteristics. Despite these qualities, conducting polymers have predominantly served as either anion or cation-removal electrode materials in ECDI systems [2].As a result, the study aims to design a low-voltage, membrane-free, ECDI system with high salt-removal capacity and excellent cycling stability through the utilization of an identical conducting polymer (i.e., PPy) doped with anions of different sizes for the positive (4-methylbenzenesulfonic acid, p-TS) and negative (ClO4 −) electrodes. Essentially, PPy is tailored to possess either cation or anion-exchange abilities to serve as both positive and negative electrode materials in the ECDI system. According to the results of XPS and CV measurements, the schematic diagram of the salt removal/release mechanisms on the two PPy electrodes is shown in Figure 1 [3]. The positive electrode (PPy-p-TS) exhibits the cation-capturing ability due to the trapping of bulky p-TS dopants with high electronegativity from the sulfonic acid groups during the electro-polymerization. Therefore, the reduction of PPy polarons (i.e., the + symbols) results in the presence of negative charges within the PPy-p-TS matrix, electrostatically attractive to cations. On the other hand, the negative (PPy-ClO4) electrode exhibits the anion-removing ability due to the positive charges generated on the oxidized PPy, which are charge-compensated by the small anion dopants (i.e., ClO4 − during the electro-polymerization step, which is replaced with Cl− during the desalination step). Moreover, to apply the unique "memory effect" in the ECDI system, the salt-removal/salt-concentration test was conducted in a full cell and the conductivity profile is shown in Figure 2. The PPy-p-TS//PPy-ClO4 system can transfer the total amount of 342 mg g−1 of NaCl in only 5 cycles with only 0.1902 kWh/kg-NaCl. With the characteristics of dual function and membrane-free, this full-polymer ECDI system has become an attractive and competitive technology in the water purification field.Furthermore, the similar redox couples between positive and negative electrode materials result in closely aligned redox potentials for ion capturing/releasing, leading to significantly reduced cell voltages during both deionization and concentration processes. Through optimization of mass loading ratios, the positive and negative electrodes in this ECDI system operate within their respective desirable potential windows, demonstrating substantial desalination capabilities of up to 83.4 mg g−1 in a 60-minute single-pass operation. Additionally, the adjustments in the charging/discharging time ratio and mass loading of active materials yield a low energy consumption (EC) of 0.2225 kWh/kg-NaCl. Therefore, in comparison with the other ECDI systems in Figure 3, this full-polymer ECDI system lies in the ideal performance area with great SAC and SAR performance. Moreover, this system shows ultra-low EC compared to other systems and industrial RO plants. Meanwhile, this system demonstrates its great stability with a SAC retention of 88 % after 250 cycles (66.7 h). Ultimately, according to the proposed design guidelines, we successfully demonstrate a superior desalination performance, high stability, and dual-function ECDI system without membrane as a potential future desalination system.

Synthesis of 2,4-D/LHD hybrid nanocomposite using different aging times

Different aging times (1, 2, 4, and 18 h) were used to intercalate the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) into the layered double hydroxide (ZnAl-LDH) using the coprecipitation method to form the 2,4-D/LDH hybrid nanocomposite. The XRD and FTIR results demonstrated that the herbicide was introduced into the layered structure of the LDH, forming an organic-inorganic crystalline nanohybrid in very short aging times, such as one h. The herbicide molecules introduced into the LDH-ZnAl produced an increase in basal spacing, a decrease in crystallinity, and changes in the morphology and particle size of the nanohybrid. The release kinetics obeyed the pseudo-second-order model, and the herbicide release mechanism was done via ion exchange. The analysis of the nanohybrids after herbicide release confirmed the insertion of carbonate anions via ion exchange into the lamellar structure of the LDH by decreasing the basal spacing.

Evaluation of the Polypyrrole Coupling Mode for High-Performance Dual-Ion Batteries.

Due to the advantages of large interstitial sites, antisolubility, and reversible insertion and extraction of anions, polypyrrole (PPy) has become an excellent P-type electrode material for dual-ion batteries. Unfortunately, PPy electrodes inevitably suffer from low specific capacity and poor cycle stability because of structural disintegration during repeated cycling as well as poor doping ability brought on by aggregation or cross-linking within the PPy chain. In this work, PPy with different proportions of coupling mode (α-α, α-β, or β-β coupling) was derived from different preparation methods. Among them, PPy derived from the interfacial frozen polymerization method (I-PPy) is dominated by the α-α coupling mode and possesses the best anion doping ability and the highest specific capacity of 119 mAh g-1 at 100 mA g-1 compared with PPy derived from electrochemical deposition (E-PPy) and chemical oxidation method (C-PPy) (both less than 40 mAh g-1). This work verifies that increasing the proportion of the α-α coupling mode in the PPy electrode is a useful strategy to enhance the anion doping ability and capacity of dual-ion batteries.

Recycling of Spent Graphite from Lithium-Ion Batteries for Aqueous Zn Dual-Ion Batteries.

As lithium-ion batteries (LIBs) become more widespread, the number of spent LIBs gradually increases. Until now, recycling of spent LIBs has mainly concentrated on high-value cathodes, but the anode graphite has not yet attracted wide attention. In this work, spent graphite from LIBs was oxidized to graphene oxide and then thermally reduced to reduced graphene oxide (RGO), which serves as the cathode of aqueous Zn dual-ion batteries (ZDIBs). The thermal reduction process enables RGO with a large layer spacing and porous structure, which increase the anion insertion sites and transfer kinetics. As a result, the corresponding battery exhibits a high specific capacity of 96.82 mAh g-1 at 1 A g-1, superior rate capability, and a high capacity retention rate of 80% after 2000 cycles. Moreover, RGO gradually transforms into a long-range disordered structure during the cycling process, which provides more transport routes and active sites for anion insertion and thus leads to the increase of capacity. This work combines the recycling of spent graphite with aqueous ZDIBs, realizing the high-value use of spent graphite.

Porous Azatruxene Covalent Organic Frameworks for Anion Insertion in Battery Cells.

Covalent organic frameworks (COFs) containing well-defined redox-active groups have become competitive materials for next-generation batteries. Although high potentials and rate performance can be expected, only a few examples of p-type COFs have been reported for charge storage to date with even fewer examples on the use of COFs in multivalent ion batteries. Herein, we report the synthesis of a p-type highly porous and crystalline azatruxene-based COF and its application as a positive electrode material in Li- and Mg-based batteries. When this material is used in Li-based half cells as a COF/carbon nanotube (CNT) electrode, a discharge potential of 3.9 V is obtained with discharge capacities of up to 70 mAh g-1 at a 2 C rate. In Mg batteries using a tetrakis(hexafluoroisopropyloxy)borate electrolyte, cycling proceeds with an average discharge voltage of 2.9 V. Even at a fast current rate of 5 C, the capacity retention amounts to 84% over 1000 cycles.

A non-aqueous Li+/Cl− dual-ion battery with layered double hydroxide cathode

Dual-ion batteries (DIBs) have unique advantages in energy storage, such as high energy density and low cost. However, most studies on organic DIBs use anions with a large ionic radius (PF6−, TFSI−, etc.). Here, we propose a Li+/Cl− dual-ion battery (DIB) through using CoFe-Cl layered double hydroxides (LDHs) and non-aqueous LiCl electrolytes, with a mechanism involving anionic insertion into the LDHs cathode and lithium plating/stripping on the anode. Coupled X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques indicate reversible expansion/extraction of (003) crystal planes of LDHs and valence state changes of Co and Fe, enabling high Cl− storage capacities of 145 mAh/g and 137 mAh/g at 200 mA/g and 1 A/g, respectively. Furthermore, this DIB demonstrates an impressive power density of 1770 W/kg with an energy density of 240 Wh/kg. This work provides a reference for developing high performance DIBs and expands the electrochemical application field of LDHs.

Efficient fabrication of high-quality graphene via alternating-current co-intercalation and microwave-assisted expansion

To facilitate the transformation of inexpensive and abundant graphite resources into two-dimensional graphene materials with promising applications, the development of efficient, cost-effective, and scalable technologies for large-scale production of high-quality graphene is crucial. Here, we propose an effective electrochemical dual-electrode co-intercalation exfoliation strategy. During the process, precise control of the electrochemical intercalation is achieved by adjusting the working bias and alternating current (AC) cycle, while ensuring the ion insertion rate through gradual voltage escalation. Repeated insertion of cations and anions under AC accelerates the graphite exfoliation. Following complete ion inserting, suitable microwave processing was employed to achieve rapid graphite expansion. Ultimately, ultra-sonication in NMP is employed to achieve final exfoliation between graphite layers. The resulting few-layer graphene (2–3 layers) exhibited minimal defects (ID/IG = 0.0405), low oxygen content (C/O = 44.62), high yield (95.3 %), and excellent conductivity (625 S/cm), enabling its potential commercialization and large-scale application. This outcome also serves as a significant reference for the commercial production of environmentally friendly and cost-effective graphene.

One-step electrodeposited nickel-cobalt-layered double hydroxide nanosheets with anion intercalation for supercapacitor

NiCo-layered double hydroxide (LDH) is a frequently used materials for electrodes in supercapacitors to achieve high conductivity, large capacity, tunable layered structure and cheap. But its poor rate capability and the lack of active sites requires improvement to release maximum performance. Herein, an electrodeposition method is employed to grow NiCo-LDHs with a series of intercalated anions on carbon paper. It is investigated that the insertion of anions between the layers of LDH augments the quantity of available active sites. These locations enable the diffusion phenomenon and enhance specific capacity. As the current density is set at 1 A·g−1, NiCo-LDH intercalated with PO43− reaches a maximum specific capacity of 287.5 mAh·g−1 (2070 F·g−1). Moreover, the asymmetrical supercapacitor was put together with this material as cathode has a substantial energy density of 49.2 Wh·kg−1 at 375 W·kg−1, exceptional cycle stability with a 92.0 % capacity retention and 99.5 % coulombic efficiency retention after 10,000 cycles. This study offers fresh perspectives on the compositional and structural design of LDH materials for effective and good cyclic stable supercapacitors. In present research, a novel perspective on the composition and structural design of LDH-based electrode materials was provided for outstanding supercapacitors.

Building a Rechargeable Voltaic Battery via Reversible Oxide Anion Insertion in Copper Electrodes.

Voltaic pile, the very first battery built by humanity in 1800, plays a seminal role in battery development history. However, the premature design leads to the inevitable copper ion dissolution issue, which dictates its primary battery nature. To address this issue, solid-state electrolytes, ion exchange membranes, and/or sophisticated electrolytes are widely utilized, leading to high costs and complicated cell configuration. Herein, we build a rechargeable zinc-copper voltaic battery from simple and cheap electrolyte/separator materials, thus eliminating the need to use the above components. Notably, our battery leverages the Zn4SO4(OH)6·xH2O precipitation in ZnSO4 electrolytes, a common side reaction in zinc batteries, to provide a "locally alkaline" environment for copper electrodes. Consequently, oxide (O2-) anion insertion takes place and readily transforms copper to copper(I) oxide (Cu2O) without any copper ion dissolution issue. Therefore, this battery realizes a high capacity of ∼370 mA h g-1 and a long cycling of ∼500 cycles. Our work provides an innovative approach to stabilize anion insertion in metal electrodes for energy storage.

Anion electrostatic insertion boosts efficient zinc ferrocyanide cathode for aqueous dual-ion battery

Prussian blue analogs (PBAs) have been considered as a kind of promising cathode materials, but its poor cycle performance severely hinders their industrialization. Herein, by combining a zinc ferrocyanide (ZnHCF) cathode with aqueous ZnSO4/LiTFSI electrolyte and zinc metal anode, we achieved a stable anion insertion-type aqueous dual-ion battery (DIB) which displays a discharge specific capacity of 75.9 mAh g–1, an energy density of 124 Wh kg–1, and a discharge plateau of 1.8 V at 5 A g–1. Its specific capacity can still reach 57.4 mAh g–1 after 1200 cycles with a Coulombic efficiency of 97 %. A reversible anion insertion mechanism of ZnHCF cathode based on the changes of the valency of iron and the insertion of TFSI– ion on crystal surface caused by electrostatic interaction is proposed and confirmed with a series of characterizations and density functional theory calculations (DFT). This work proposes the study of anion energy storage mechanism of PBAs and brings more opportunities for their large-scale applications in the future.

Advanced cathodes for aqueous Zn batteries beyond Zn2+ intercalation.

Aqueous zinc (Zn) batteries have attracted global attention for energy storage. Despite significant progress in advancing Zn anode materials, there has been little progress in cathodes. The predominant cathodes working with Zn2+/H+ intercalation, however, exhibit drawbacks, including a high Zn2+ diffusion energy barrier, pH fluctuation(s) and limited reproducibility. Beyond Zn2+ intercalation, alternative working principles have been reported that broaden cathode options, including conversion, hybrid, anion insertion and deposition/dissolution. In this review, we report a critical assessment of non-intercalation-type cathode materials in aqueous Zn batteries, and identify strengths and weaknesses of these cathodes in small-scale batteries, together with current strategies to boost material performance. We assess the technical gap(s) in transitioning these cathodes from laboratory-scale research to industrial-scale battery applications. We conclude that S, I2 and Br2 electrodes exhibit practically promising commercial prospects, and future research is directed to optimizing cathodes. Findings will be useful for researchers and manufacturers in advancing cathodes for aqueous Zn batteries beyond Zn2+ intercalation.

Temperature Influence on the Staging Process in Carbon Materials during Anionic Intercalation

A typical set-up of a dual-carbon battery consists of a pair of carbon electrodes and an organic-based electrolyte with a broad window of electrochemical stability. When such a cell is being charged to a reasonably high voltage, two processes occur: intercalation of cations at the electrode with low potential, and intercalation of anions at the one with high potential [1-2]. Although there are significant limitations for practical application of such systems, mostly related to electrolyte decomposition and exfoliation of carbon, the concept appears to be rather inspiring for investigations, as the materials required for dual-carbon batteries would be significantly cheaper compared to those for state-of-the-art electrochemical energy storage solutions.The general idea of using carbon as a cathode material is known for many decades, however, most of the studies dedicated to it pursue the improvement of specific electrochemical characteristics through variation of the cell materials, mostly by trial and error approach [3-4]. Clearly, the results of such research are highly important, but the topic itself lacks the knowledge of electrochemical kinetics for the process of various anions being inserted into graphitic materials, which are typically used as dual-carbon battery cathodes.In our work, we attempted to overcome the limiting factor of electrolyte decomposition by selecting a relatively unusual organic sulfones as solvents. Addition of a salt reduces the melting point of the sulfone, allowing to consider the system as a classic liquid electrolyte. Such cells are known to sustain the high voltages long enough to conduct the studies on structural evolutions which occur in the graphite cathode [4]. We selected two commercial graphitic materials and subjected them to anionic intercalation in various alkali-based electrolytes. Galvanostatic cycling with intermittent titration was conducted to evaluate the diffusion coefficients of anion insertion. The best-performing system was also studied in operando X-ray diffraction cells using the synchrotron radiation facilities, so anionic diffusion was coupled to different stages of intercalation. The staging process itself appears to be completely different at evaluated temperature. Thus, the experiment with KPF6 electrolyte at 298 K showed similar results with the work [5], with subsequent formation of intercalated stages down to stage 2 (see the figure), whereas at 358 K, multiple stages are present together almost from the beginning of intercalation process.The results of the current study show a drastic influence of temperature on the structural behavior of graphite during anionic intercalation, and by electrochemical methods, the kinetics of these changes is characterized, which is necessary for further development of dual-carbon battery topic. R. T. Carlin, H. C. De Long, J. Fuller, and P. C. Trulove, J. Electrochem. Soc., 141, L73, 1994.R. Santhanam and M. Noel, J. Power Sources, 76, 147, 1998.L. Zhang, J. Li, Y. Huang, et al., Langmuir, 35(11), 3972-3979, 2019.M. Tebyetekerwa, T. T. Duignan, Z. Xu, et. Al, Adv. Energy Mater. 12, 2202450, 2022.J. A. Seel and J. R. Dahn, J. Electrochem. Soc. 147, 892, 2000. Figure 1

Reversible Insertion of [AlCl4 ]- Superhalides in Graphite.

Graphite-based dual-ion batteries are with potential higher energy density, making them a unique candidate in energy storage systems. However, anion insertion into graphite in aqueous environment remains a significant challenge. Herein, we report that the reversible insertion of Al-Cl superhalide into expanded graphite (EG) delivers an ultrahigh specific capacity of ~171 mAh g-1 from an aqueous deep eutectic solvent (DES) gel electrolyte of 50 m ChCl+5 m AlCl3 . High-resolution transmission electron microscopy (HRTEM), Raman spectra and X-ray diffraction (XRD) show that the EG generates turbostratic structure during Al-Cl superhalide (de)insertion instead of presenting typical graphite intercalation compounds (GIC), thus attributing to the high capacity during Al-Cl superhalide insertion.

Heterostructure of NiCoAl-layered double hydroxide nanosheet arrays assembled on MXene coupled with CNT as conductive bridge for enhanced capacitive deionization

Layered double hydroxide (LDH) is considered as an attractive capacitive deionization (CDI) faradic material for anion (such as Cl−) capture due to its excellent anion storage capacity, highly reversible anion (de)insertion and superior chemical stability. Nevertheless, the self-stacking property and poor conductivity of LDH lead to undesirable CDI performance. Herein, the CNT@NiCoAl-LDH@MXene heterostructure with three-dimensional (3D) interconnected network was rationally designed with MXene as the conductive substrate for the uniform and vertical growth of NiCoAl-LDH nanosheet arrays and CNT as the conductive bridge for fast electron transfer. Strong chemical bonding interactions were formed at the interface of this heterostructure, creating tighter and more stable interconnections. Moreover, the specific surface area of this unique arrays structure is 4.28 and 8.62 times that of NiCoAl-LDH and MXene, respectively, effectively suppressing the aggregation of layered materials and providing more exposed active sites. Therefore, the obtained CNT@NiCoAl-LDH@MXene electrode exhibits prominent specific capacitance (179F g−1), decreased equivalent series and transfer resistance, increased ion diffusion rate and splendid electrochemical stability (capacitance retention rate of 107.5 % after 1500 GCD cycles). Consequently, as employed for Cl− intercalation anode coupled with AC cathode for CDI, the CNT@NiCoAl-LDH@MXene//AC cell exhibited excellent Cl− removal capacity (79.5 mg g−1), higher charge efficiency (88.4 %), lower energy consumption (0.62 kWh kg−1-NaCl) and exceptional desalination capacity retention rate (96.4 % after 40 adsorption/desorption cycles). This work provides an excellent anode material selection for the enhancement of CDI performance and valuable insights for the design of 3D interconnected network heterostructure.

Reaction induced conformational change in polyindole: Polyindole/PVA film as biomimetic sensors of temperature and electrical energetic condition.

The influence of surrounding temperature and electrical energetic condition on the conformational movements (cooperative actuation) of polyindole is verified using a polyindole-coated polyvinyl alcohol (PIN/PVA) film. Chronopotentiometric studies revealsthat the consumed electrical energy during the reaction varies linearly with the change in working temperature. The influence of temperature on the reversible conformational movements of the polymer chain is related to the charge consumed during the reaction. The logarithmic dependence of reversible redox charge obtained from coulovoltammogram with inverse of temperature further proved the temperature sensing characteristics and the influence of temperature on the cooperative actuation of the PIN/PVA film. The conformational relaxation increases as the temperature increases through hosting higher number of counter anions with the solvent molecule. The extension of the redox reaction or charge consumption was found to decrease as the scan rate increases. The double logarithmic relation between the consumed redox charge and the scan rate has proved that the electrical energetic condition can influence the conformational movement or the extension of the redox reaction in a reversible manner. The results suggest that the PIN/PVA film can act as a biomimetic macro molecular sensor of working temperature and electrical energetic condition as biological muscles do.

Topochemical Anionic Subunit Insertion Reaction for Constructing Nanoparticles of Layered Oxychalcogenide Intergrowth Structures.

Intergrowth compounds contain alternating layers of chemically distinct subunits that yield composition-tunable synergistic properties. Synthesizing nanoparticles of intergrowth structures requires atomic-level intermixing of the subunits rather than segregation into stable constituent phases. Here we introduce an anionic subunit insertion reaction for nanoparticles that installs metal chalcogenide layers between metal oxide sheets. Anionic [CuS]- subunits from solution replace interlayer chloride anions from LaOCl to form LaOCuS topochemically with retention of crystal structure and morphology. Sodium acetylacetonate helps extract Cl- concomitant with the insertion of S2- and Cu+ and is generalized to other oxychalcogenides. This topochemical reaction produces nanoparticles of ordered mixed-anion intergrowth compounds and expands nanoparticle ion exchange chemistry to anionic subunits.

Insertion of AlCl3 in graphite as both cation and anion insertion host for dual-ion battery

Dual-ion batteries (DIBs) are emerging energy storage devices with the unique energy storage mechanism in which both anions and cations are involved during charge-discharge processes. Graphite is usually used as both cathode and anode in DIBs, however, the limited layer spacing and the elongated diffusion channels make the ion migration resistance larger. To break the bottleneck, a strategy is proposed by incorporating AlCl3 into the layer of graphite, which increases the layer spacing while acting as a pillar to stabilize the structure. In addition, a significant fraction of defects is inducted at the edges of the folds of graphite. This engineering accelerates the electron/ion transport on the stable graphite stacking microstructure. As a result, it could be used as both cation and anion insertion host in DIBs. Electrochemical tests showed that AlCl3-GICs-5 materials could deliver a Li+ storage capacity of 169.1 mAh g−1 at 2A g−1 when cycles consistently for over 500 cycles which is much higher than graphite (60.7 mAh g−1). Furthermore, when used as a PF6− insertion cathode in a DIB, it showed a high specific capacity of 100.8 mAh g−1at 100 mA g−1. This research is anticipated to provide inspiration to design new materials for DIBs.