Dual Ion Research Articles

High‐Performance Synaptic Devices Based on Cross‐linked Organic Electrochemical Transistors with Dual Ion Gel

AbstractOrganic electrochemical transistors (OECTs) represent a promising approach for flexible, wearable, biomedical electronics, and sensors integrated with diverse substrates. Their ability to operate at low voltages and interact effectively with biological systems makes them particularly suitable for neuromorphic applications. For neuromorphic devices, OECTs must enhance electrical performance, biocompatibility, and signal storage/erasure capabilities. While UV cross‐linking methods with various side effects on organic semiconductors are predominant in improving mobility and current retention time, thermal cross‐linking based on the solution process has not been extensively explored. Additionally, despite significant research on the modification of electrolyte property, the ionic charge compensation mechanisms between multiple electrolytes are still unclear. This study employs a cross‐linking strategy involving the chemical reaction of poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) with di‐tert‐butyl‐peroxide (DTBP) to create a cross‐linked P3HT active layer. Furthermore, a dual ion gel structure combining a conventional ion gel with a chitosan‐based ion gel is investigated for increased ionic transport to enhance OECT performance. Using the above two methods, the enhanced electrical performance showing the mobility of 25 F cm−1 V−1 s−1 and synaptic properties showing long‐term plasticity of cross‐linked OECTs with a dual ion gel structure are demonstrated, suggesting their potential application as high‐performance neuromorphic devices.

Dual Ion Co‐Insertion Induced Spontaneous and Reversible Phase Conversion Chemistry for Unprecedented Zn2+ Storage

AbstractPrussian blue analogues are highly promising electrode materials due to their versatile electrochemical activity and low cost. However, they often suffer from severe structural damage caused by the Jahn–Teller distortion and dissolution of high‐spin outer metal ions, resulting in poor cycle life. Material modification and electrolyte regulation have been the common approaches to address this issue, albeit with very limited success. We report here a novel and efficient strategy to preserve structural stability by co‐inserting Co2+ and Zn2+ ions in KCo[Fe(CN)6]. This co‐insertion induced a spontaneous and reversible phase conversion by the replacement of low‐spin inner ion (Fe3+), which efficiently relieves structural damage caused by Jahn–Teller distortion and metal‐ion dissolution, leading to an outstanding Zn2+ storage capacity and an exceptional improvement of cycle life with a capacity retention of 97.7 % over 4400 cycles at 40 C. We also demonstrated the enhancement of co‐intercalation on ion migration using a combined approach of experimental and density functional theory (DFT) calculations. This work provides an important progress to solve the cycle stability of Prussian blue analogues towards their practical application as electrode materials for aqueous batteries.

Dual Ion Co-Insertion Induced Spontaneous and Reversible Phase Conversion Chemistry for Unprecedented Zn2+ Storage.

Prussian blue analogues are highly promising electrode materials due to their versatile electrochemical activity and low cost. However, they often suffer from severe structural damage caused by the Jahn-Teller distortion and dissolution of high-spin outer metal ions, resulting in poor cycle life. Material modification and electrolyte regulation have been the common approaches to address this issue, albeit with very limited success. We report here a novel and efficient strategy to preserve structural stability by co-inserting Co2+ and Zn2+ ions in KCo[Fe(CN)6]. This co-insertion induced a spontaneous and reversible phase conversion by the replacement of low-spin inner ion (Fe3+), which efficiently relieves structural damage caused by Jahn-Teller distortion and metal-ion dissolution, leading to an outstanding Zn2+ storage capacity and an exceptional improvement of cycle life with a capacity retention of 97.7 % over 4400 cycles at 40 C. We also demonstrated the enhancement of co-intercalation on ion migration using a combined approach of experimental and density functional theory (DFT) calculations. This work provides an important progress to solve the cycle stability of Prussian blue analogues towards their practical application as electrode materials for aqueous batteries.

Tetraphenylethylene-Derived Tetracarboxylate Featuring AIE Properties for Dual Ion Sensing and Mechanochromic Self-Erasable Writing.

The integration of multiple functions within a single fluorescent molecule provides a promising platform for developing versatile, efficient, and cost-effective materials with enhanced performance across diverse applications. In this study, we introduce TPEC, an aggregation-induced emission (AIE) molecule derived from tetraphenylethylene-based tetracarboxylate, which demonstrates multifunctional capabilities, including metal ion sensing and self-erasable writing. TPEC exhibits amphiphilicity in water, self-assembling into single-layer nanosheets with robust blue fluorescence. Notably, the aqueous solution of TPEC displays a fluorescence colorimetric response to Al3+ ions and fluorescence quenching in the presence of Fe³⁺ ions. Additionally, TPEC powders undergo fluorescence colorimetric changes under mechanical stimulation, enabling self-erasable writing on prepared paper. This study presents a straightforward strategy for the development of multifunctional luminescent materials based on the self-assembly of a single-component fluorophore.

Helmholtz Plane Regulation Empowers PF6− Permselectivity Towards High Coulombic Efficiency Dual Ion Battery of 5.5 V

AbstractHigh‐voltage dual ion battery (DIB) is promising for stationary energy storage applications owing to its cost‐effectiveness, which has been a hot topic of research in rechargeable battery fields. However, it still suffers from rapid battery failure caused by the severe solvent co‐intercalation and electrolyte oxidation. To address these bottlenecks, herein a functional electrolyte additive hexafluoroglutaric anhydride (HFGA) is presented based on a Helmholtz plane regulation strategy. It is demonstrated that the HFGA can precisely enter into the Helmholtz plane and positively regulate anion solvation behaviors near the graphite electrode surface owing to its considerable H−F affinity with ethyl methyl carbonate (EMC), thus alleviating EMC‐related co‐intercalation and oxidation decomposition during DIB charging. Meanwhile, HFGA can copolymerize with the presence of PF5 at the Helmholtz plane to participate in forming a CF2‐rich CEI layer with excellent PF6− permselectivity, conducive to achieving PF6− de‐solvation and simultaneously suppressing electrolyte oxidation decomposition. By virtue of such beneficial effects, the graphite cathode enables a 5.5 V DIB with a prominent capacity retention of 92 % and a high average Coulombic efficiency exceeding 99 % within 2000 cycles at 5 C, demonstrating significantly enhanced electrochemical reversibility. The Helmholtz plane regulation strategy marks a milestone in advancing DIB technologies.

Helmholtz Plane Regulation Empowers PF6 - Permselectivity Towards High Coulombic Efficiency Dual Ion Battery of 5.5 V.

High-voltage dual ion battery (DIB) is promising for stationary energy storage applications owing to its cost-effectiveness, which has been a hot topic of research in rechargeable battery fields. However, it still suffers from rapid battery failure caused by the severe solvent co-intercalation and electrolyte oxidation. To address these bottlenecks, herein a functional electrolyte additive hexafluoroglutaric anhydride (HFGA) is presented based on a Helmholtz plane regulation strategy. It is demonstrated that the HFGA can precisely enter into the Helmholtz plane and positively regulate anion solvation behaviors near the graphite electrode surface owing to its considerable H-F affinity with ethyl methyl carbonate (EMC), thus alleviating EMC-related co-intercalation and oxidation decomposition during DIB charging. Meanwhile, HFGA can copolymerize with the presence of PF5 at the Helmholtz plane to participate in forming a CF2-rich CEI layer with excellent PF6 - permselectivity, conducive to achieving PF6 - de-solvation and simultaneously suppressing electrolyte oxidation decomposition. By virtue of such beneficial effects, the graphite cathode enables a 5.5 V DIB with a prominent capacity retention of 92 % and a high average Coulombic efficiency exceeding 99 % within 2000 cycles at 5 C, demonstrating significantly enhanced electrochemical reversibility. The Helmholtz plane regulation strategy marks a milestone in advancing DIB technologies.

Bipolar BINOL-PIM Cathode for High-Performance Aluminum Batteries.

Given the high abundance of aluminum in the Earth's crust, the development of aluminum-ion batteries can provide a cost-effective solution for large-scale energy storage. However, the key challenge in this field is to identify high-quality cathode materials that enable effective insertion/extraction of aluminum complex ions. In this regard, we present a strategy to prepare high-capacity, long-cycling aluminum-ion batteries aluminum-ion batteries (ALBs) cathode materials. High capacity was achieved by introducing multiple active sites into a 1,1'-bi-2-naphthol (BINOL) polymer of intrinsic microporosity cathode material to realize dual aluminum complex ion adsorption. The cathode had adjustable mesoporous structure that enabled its activation, wherein the pore size gradually increased during the insertion/extraction of aluminum complex ions, effectively enhancing battery capacity and cycling stability. The aluminum-ion battery cathode material achieved a high capacity of up to 110 mAh/g at a current density of 200 mA/g and could withstand over 3000 cycles at a high current density of 1 A/g. These findings provide a design approach for aluminum-battery cathode materials intended for low-cost, large-scale energy storage.

2-Nitro-4-Carboxyphenylhydrazine and 2,4-Dicarboxylphenylhydrazine as a Pair of Novel Reactive MALDI Matrices for Rapid and Accurate Profiling of N-Glycome in Dual Ion Modes.

N-glycosylation is closely linked to a wide range of biological functions in organisms. Owing to the constriction of awful crystals formed by conventional MALDI matrices and the extremely inferior ionization efficiency of N-glycans, the traditional direct detection of N-glycans by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has been gradually replaced by postderivatization detection using reactive matrices. Nevertheless, the laborious identification of complex spectral peaks remains the major difficulty in N-glycan profiling. Hence, we logically designed and synthesized two novel reactive matrices, 2-nitro-4-carboxylphenylhydrazine (NCPH) and 2,4-dicarboxylphenylhydrazine (DCPH), and separately combined them with the acidic matrix 2,5-dihydroxybenzoic acid (DHB) to constitute two composite matrices with high on-target derivatization efficiency and significant promotion of N-glycan ionization for productive MALDI analysis in dual ion modes. Using both composite matrices, we can actualize MALDI-MS and MS2 mass calibration in dual ion modes by postderivatization detection and fragmentation of dextrans and selectively enhance the ionization effect of oligosaccharides in mixed systems. Quite homogeneous cocrystals can ensure N-glycan quantification with decent linearity and reproducibility. A fixed mass difference derived from the identical N-glycan in two ion modes is available for rapid identification in complex biological samples. Ultimately, the developed strategy was triumphantly employed to identify and quantify the relative content and alteration tendency of peach N-glycans, which can be referable to the latent correlation between N-glycan expression and peach ripening.

Numerical Study of Sputter Deposited Ultra-Low Loaded Effective Platinum Electrocatalyst Utilization in Proton Exchange Membrane Fuel Cell

High Platinum loading levels in fuel cells may ensure better durability and catalytic activity but increases fuel cells’ cost, thereby hindering large-scale commercialization. The use of non-precious catalysts may seem like a lucrative solution, but they cannot substitute platinum completely. Hence, the focus should also be given to alternate fabrication methods of the catalyst layer that will achieve ultra-low platinum loadings. Some of the methods are modified thin film method, electrodeposition, sputter deposition method, dual ion beam assisted deposition, and electroless deposition. Nano carbons as catalyst support can also be given priority as they aid the catalyst with mechanical properties. Each method is compared, reflecting the inherent advantages and disadvantages. Finally, the sputter deposition method was chosen as the most promising method in the current state of technology and research. A computational fluid dynamics simulation of a fuel cell using the sputter deposition method was performed which showed high power utilization thereby validating the benefits of the method.

Highly efficient removal of trace thallium from surface water by Co@Fe Prussian blue analogue coated membrane

Super trace thallium(I) (Tl+) is still highly toxic and its removal from surface water is challenging. Here, we developed a new adsorptive membrane by immobilizing bimetal (cobalt and iron) Prussian blue analogues (Co@Fe-PBAs) on a polytetrafluoroethylene microporous membrane (Co@Fe-PBAs-M). The prepared membrane displayed precise adsorption of trace Tl+ (50 μg/L) from complex water. A variety of interfering factors, such as water pH, competitive adsorption of positive ions (Na+ and K+) and negative ions (CO32– and PO43-), natural organic matters (e.g., fulvic acid and bovine serum albumin) were evaluated during Tl removal. The composite membrane showed high removal efficiency (over 80 %) during long-term dynamic membrane separation of surface water containing super trace Tl+ (<2.0 μg/L), breaking through the adsorption limitation in ultralow concentration of Tl+. The unique bimetal electron transfer of Co@Fe-PBAs-M reinforced the adsorptive performance to Tl+ through dual ion exchange and intercalation. In the treatment of real Pearl River water containing 0.5 μg/L of Tl+, our membrane effectively reduced the Tl+ concentration to 0.04 μg/L during 6-h continuous separation, which was far below the required level for drinking water (i.e., 0.1 μg/L). This work offers a promising solution for safe drinking water by remedying ultralow Tl+ contaminated surface water.

Effect of annealing on ion-beam-sputtered hafnium oxide thin films properties

HfO2 films are high laser damage-threshold and low-absorption thin-films that can be utilized for a broad range of optoelectronic and optical applications. In this study, HfO2 thin films were prepared via dual ion beam sputtering followed by annealing in the atmosphere at temperatures ranging from 200 to 700 °C. The optical properties, microstructure, film stress, and absorption loss of the HfO2 films at various annealing temperatures were then systematically characterized. The results revealed that the properties of the films were improved after annealing at temperatures below 500 °C. Specifically, at an optimal annealing temperature of 400 °C, the residual stress of the films was minimized close to zero and the absorption loss was as low as 1 ppm. However, at annealing temperatures reaching 600 °C, the films began to crystallize, leading to the deterioration of their optical properties. Optimizing the process parameters for HfO2 thin film deposition is crucial for developing the next generation of high-performance laser optics.

Anion Storing Boron Nitride Hybrid Nanosheets for High-Performance Dual Ion and Zinc Alkaline Full Cells.

Hexagonal boron nitride (BN), a well-known member of 2D materials, has a structure similar to graphene and is often referred to as white graphene. Despite its unique physical and chemical properties for energy storage applications, there have been very few studies on how BN stores anion carriers. Herein, the hybrid architecture and anion storage mechanism of BN nanosheets for high-performance hybrid energy storage full cells based on dual-ion and Zinc (Zn) alkaline systems is demonstrated. The chemical bonding between BN and reduced graphene oxide (rGO) is attributed to the formation of the heterointerface, which facilitates the charge transfer kinetics during an OH storing process. Based on the reversible surface redox reaction of BN and rGO hybrid (BN@rGO) confirmed by computational and spectroscopic analyses, the BN@rGO electrode is applied to both Na and OH dual-ion and Zn alkaline full cells. In the dual-ion system, Ti3C2‖BN@rGO full cells extended the operating voltage range up to 1.7V, delivering a cell capacity of 49.4mAhg-1 at 1000mAg-1 and retaining 80% of its initial capacity after 40000 cycles. In the Zn alkaline system, Zn‖BN@rGO full cells achieved a cell capacity of 58.1mAhg-1 at 1000mAg-1 and retained 80% capacity over 90000 cycles.

IR and UV Spectroscopy of Gas-Phase Monohydrated Protonated Guanine.

We use UV and infrared photodissociation spectroscopy to study monohydrated protonated guanine in a dual cryogenic ion trap spectrometer. The monohydrated complexes are formed through helium-mediated collisions between bare electrosprayed protonated guanine and low-pressure water vapor in a clustering trap maintained at 180 K, before being transferred to a quadrupole ion trap at 10 K. The spectrum of the monohydrated complex exhibits sharp vibronic transitions at the band origin and becomes broader and higher in intensity further in blue, which is very similar to protonated guanine but with a notable blue shift of ∼1850 cm-1 (∼0.23 eV). The UV hole-burning experiments showed that the vibronic bands recorded in the region of the band origin belong to a single conformer under our experimental conditions. The IR photodissociation spectrum in the 3000-3600 cm-1 range, with the aid of theoretical calculations (SCS-CC2/aug-cc-pVDZ), allowed us to assign the structure to the lowest energy N7-O conformer.

LiF/ LixPOy/ LixPOyFz-based artificial interface on graphitic cathode for improving the cycle life of dual ion batteries

The emerging dual-ion batteries are a sustainable analog of conventional Lithium-ion batteries. It yields high voltage output and satisfying capacity, replacing transition metal-based cathodes with graphitic carbon. Despite the advantages, the systems suffer from inadequate cycling efficiencies and triggered electrolyte decomposition on cathode surface that cut short the cycle life. As a protective measure, the carbon cathode is coated using a LiF/LixPOy/LixPOyFz-based hybrid coating layer derived from the thermal decomposition of LiPF6 salt. The coated layer acts as an artificial interface that safeguards the surface from electrolyte attack and enhances cycling efficiencies. It forms a mechanochemically robust cathode-electrolyte interface that preserves the graphitic order and structural integrity of the electrode. As a result, the bulk of the coated material is not ruptured like in the uncoated pristine sample, thereby assisting in long-term cycling. The coated material retains 85 % capacity even after 1000 cycles with a 10 % improved coulombic efficiency and 130 mV reduced voltage hysteresis instead of losing 15 % capacity within 50 cycles with poor efficiency and elevated resistances in the pristine material. The strategy brings fruitful outcomes when applied in dual carbon cell and is believed to be equally effective in other dual-ion systems.

Achieving Stable Cycling Performance in a P2-Type Layered Oxide Cathode through a Synergic Li/Zn Doping for Sodium-Ion Batteries.

It has been suggested that sodium layered transition metal oxides could potentially serve as excellent cathodes for sodium-ion batteries (SIBs) because of their appropriate operating potentials and high capacities. However, the growing reliance on energy requirements has necessitated a higher energy density of SIBs. It has been demonstrated that activating oxygen-related activities for SIBs is a viable method to improve energy density. Herein, we suggest applying the synergy of Li and Zn codoping to activate the anionic redox reactions (ARRs) and improve their reversibility in Na0.75Ni0.3Mn0.7O2. The dual ion doping alleviates the phase transition and inhibits the Na+/vacancy arrangements, consequently improving the rate capacity and cyclic stability. The Na0.75Li0.15Ni0.1Zn0.05Mn0.7O2 delivers a discharge capacity of 134 mA h g-1 and no significant capacity loss at 100 mA g-1 between 2 and 4.5 V after 200 cycles. More importantly, the density functional theory (DFT) calculation proves that the codoping strategy triggers more ARRs compared to single-element doping, thereby providing enhanced capacity. The codoping induced oxygen redox strategies will create a new path for rational design of cathodes to enhance the energy density for SIBs.

Dual Li ion transport channels in a dynamical supramolecular solid electrolyte toward safety and high-performance Li metal batteries

The polymer based quasi-solid electrolyte (QSE), which combines the high ionic conductivity of the liquid electrolytes with the excellent mechanical flexibility of the polymer matrix, is highly desired and most promising for Li metal batteries (LMBs). However, the Li+ transfer pathways in QSE is not clear enough, and the practical applications in LMBs are also hindered by safety hazards arising from risks of mechanical damage, flammability and high voltage instability. Here, a dynamical supramolecular QSE with abundant hydrogen bonds to fabricate stable and safety LMBs, is reported. In this designed electrolyte, both thermal stability and superior interface stability with anode/cathode electrodes were achieved. Notably, the dual Li+ transport channels in QSE were investigated using in-situ FTIR technology and DFT calculations, providing insights into both the “wet” liquid phase and “dry” polymer chain channels. Benefiting from this design, the Li||NCM622 full batteries based on this QSE exhibit excellent long-term cycling stability.

Dual‐Ion Co‐Insertion Engineering for Kinetics Enhancement and Stress Regulation in Cu3VS4 Toward Durable Magnesium/Lithium Hybrid Batteries

AbstractRechargeable magnesium batteries (rMBs) have tremendous development prospects in the field of energy storage, however, the strong electrostatic interactions induced by divalent Mg2+ give rise to the sluggish diffusion kinetics. Herein, the dual ion co‐intercalation strategy is proposed to expedite ion migration in Cu3VS4, achieving elevated specific capacity, transcendent rate capability, and ultra‐stable cycling capability. Kinetic analyses combined with DFT calculations indicate that the dual‐ion co‐insertion can fast charge transfer, reduce the diffusion barrier of Mg2+and optimize the reaction kinetics. Finite element simulations quantitatively verify that dual ion co‐intercalation contributes to alleviating magnesiation/lithiation‐induced stress in the shell layer and maintains structural integrity from a mechanical standpoint. Ex situ characterizations profoundly illustrates the multistep magnesium/lithium storage mechanisms and the evolution of structure. The proposed cation co‐intercalation strategy not only holds promise in opening new insights for high‐performance, continuously stable rMBs, but also provides inspiration for multivalent battery systems.

Predicting Effective Transport Properties of Randomly Oriented Polycrystalline Li-Ion Battery Electrodes

Widely practiced Li-ion battery models, such as pseudo-two-dimensional (P2D) models [1-3], use representative spherical electrode particles with assumed isotropic transport properties. Electrode particles, such as NMC, are typically composites that are comprised of numerous randomly oriented crystallites. Each of the single-crystal primary particles that compose secondary particle can have strongly anisotropic transport properties that affect the intercalation process. The empirically approximated effective properties (e.g., diffusion coefficients) as reported in literature vary by as much as six orders of magnitude. In many cases, the effective diffusion coefficients are determined as a part of a parameter-fitting procedure to represent battery polarization measurements.The present approach develops both analytical and computational homogenization methods that derive effective properties based upon the intrinsic single-crystal properties of the crystallites. Homogenization techniques are computationally effective methods to predict macroscale behavior based on microscale properties.As illustrated in Fig. 1, the computational approach begins by assembling over 1000 randomly oriented single-crystal primary particles, with each crystallite having anisotropic properties associated with the crystal lattice. The dodecahedron-shaped primary particles are tightly assembled into a secondary particle that is approximately spherical. A three-dimensional finite-element model predicts transient Li-intercalation fractions throughout a secondary particle during charge or discharge processes. In graphite, the transverse and normal diffusion coefficients differ by approximately six orders of magnitude. Based on the cut plane in Fig. 1, and despite extreme anisotropy within the crystallites, the homogenized macroscopic behavior is nearly isotropic.The analytical approach extends a self-consistent method (SCM) for polycrystalline materials first presented by Ponte-Castañeda and Willis [4], which mathematically combines tensors describing diffusion pathways for every primary particle. The present study considers the concentration-dependent and anisotropic diffusion parameters collected by Persson et al. [5] and Zhou et al. [6] for graphite and NMC, respectively. Another homogenization method is the use of an orientation distribution function (ODF) [7], which predicts the effective diffusion parameters based on the statistical average of every possible primary particle orientation. Fig. 2 shows the predicted effective diffusion coefficients bounded by Hashin-Shtrikman bounds for anisotropic composites proposed by Willis [8] and the experimentally determined diffusion coefficients. The predicted effective diffusion coefficients are lower than the experimentally determined values in transverse direction but are significantly larger than the values in the normal direction. Additionally, the in-plane diffusion dominates the curvature of the predicted effective properties.[1] M. Doyle, T. F. Fuller, and J. Newman. Modeling of galvanostatic charge and discharge of the lithium/polymer/insertion cell. J. Electrochem. Soc., 140:1526–1533, 1993.[2] T. F. Fuller, M. Doyle, and J. Newman. Simulation and optimization of the dual lithium ion insertion cell. J. Electrochem. Soc., 141:1–10, 1994.[3] M. Doyle, J. Newman, A. S. Gozdz, C. N. Schmutz, and J.-M. Tarascon. Comparison of modeling predictions with experimental data from plastic lithium ion cells. J. Electrochem. Soc., 143:1890–1903, 1996[4] P.P.- Castañeda and J.R. Willis. The effect of spatial distribution on the effective behavior of composite materials and cracked media. J. Mech. Phys. Solids, 43:1919–1951, 1995[5] K. Persson, V. A. Sethuraman, L. J. Hardwick, Y. Hinuma, Y. S. Meng, A. van der Ven, V. Srinivasan, R. Kostecki, and G. Ceder. Lithium diffusion in graphitic carbon. J. Phys. Chem. Lett., 1:1176–1180, 2010[6] H. Zhou, F. Xin, B. Pei, and M. S. Whittingham. What limits the capacity of layered oxide cathodes in lithium batteries? ACS Energy Lett., 4:1902–1906, 2019[7] S. Nemat-Nasser, M. Hori, and J. D. Achenbach. Micromechanics: Overall properties of heterogeneous materials. In Micromechanics, volume 37. Elsevier Science I& Technology, The Netherlands, 1993[8] J.R. Willis. Bounds and self-consistent estimates for the overall properties of anisotropic composites. J. Mech. Phys. Solids, 25:185–202, 1977 Figure 1

Solid-State Lithium Batteries with in-Situ Polymerized Acrylate-Based Electrolytes Capable of Electrochemically Stable Operation at 100 ℃

In-situ polymerized acrylate-based polymers are very appealing as solid polymer electrolytes (SPEs) in lithium (Li) batteries due to the drop-in compatibility of such in-situ polymerization with conventional battery production, the ease of acrylate polymerization and their inexpensive, facile SPE chemistry. We identified, however, that such SPEs suffer from either a low cationic transference number with dual ion conducting salts (0.12-0.2) or a low ionic conductivity with single Li-ion conducting (SLIC) salts (6·10-6 S cm-1). In this project we overcame these limitations and developed significantly improved SPE with ionic conductivity of up to 2·10-4 Scm-1 and a relatively high Li-ion transference number of 0.4. With a significantly reduced fraction of mobile anions in the hybrid SPE, in-situ polymerized SPE cells with an LiFePO4 (LFP) cathode achieve a stable performance for over 100 cycles at temperatures as high as 100 °C, which is unattainable with conventional Li salts or electrolytes. Furthermore, the motional narrowing observed in the line-shapes of solid-state nuclear magnetic resonance (SS-NMR) spectra provided additional insights of the differences in Li nucleus environments and revealed a reduced activation energy for the hybrid salt SPEs due to their more open structure. This study opens the path for the fabrication of high-performance solid polymer lithium batteries capable of operating at high temperatures using commercial battery fabrication equipment. We expect that further tuning of the acrylate based SPE composition may allow further increases in its conductivity without sacrifices in its electrochemical stability or mechanical properties.

The Challenge of Polyanion Redox Process in Oxalates

Lately, polyanionic compounds have received great interest as alternative cathode materials to conventional oxides due to their different advantages in cost, safety, structural stability, as well as being environmentally friendly. However, the vast majority of polyanionic cathodes reported so far rely primarily upon the redox reaction of the transition metal for lithium/sodium transfer. The development of multielectron redox-active cathode materials is a top priority for achieving high energy density with long cycle life in the next-generation secondary battery applications. Triggering anion redox activity is considered to be a promising strategy to successfully enhance the energy density of polyanionic cathodes for Li/Na-ion batteries. In addition to transition metal redox activity, the oxalate group itself also shows redox behaviour enabling reversible charge/discharge and high capacity without gas evolution.Recently, our group reported dual ion redox in the lithium iron oxalate, in the potassium iron oxalate and in the sodium lithium iron oxalate, Li2Fe(C2O4)2, K2Fe(C2O4)2 & NaLiFe(C2O4)2 1 ,2,3 in which both the iron and the oxalate group appear to exhibit reversible redox activity. We also found this phenomenon present in the lithium-rich KLi3Fe(C2O4)3.4 Different characterisation techniques such as Raman spectroscopy or Synchrotron HAXPES and XAS analyses make it possible to show this phenomenon experimentally. First-principles calculations also help to understand the interactions between the transition metal and the oxalate group as the main factor that modulates the cationic and polyanionic redox couples in these materials.Our current results suggest that this phenomenon could be widespread among transition metal oxalates.Moreover, the oxalate anion is a particularly versatile species and may be monodentate, bidentate, tridentate, or even tetradentate, giving rise to a huge range of possible compounds and a very rich structural chemistry. It is important to establish the structural requirements that give rise to polyanion redox behaviour and a range of materials are being synthesised and characterised by our group. In addition to pure oxalates, it is possible to prepare materials with mixed polyanions e.g., oxalate/phosphate.In our work, we demonstrate that oxalate has a role as a family of cathode materials and suggests a direction for the identification and design of electrode materials with polyanionic frameworks.(1) Yao, W.; Armstrong, A. R.; Zhou, X.; Sougrati, M. T.; Kidkhunthod, P.; Tunmee, S.; Sun, C.; Sattayaporn, S.; Lightfoot, P.; Ji, B.; Jiang, C.; Wu, N.; Tang, Y.; Cheng, H. M. An Oxalate Cathode for Lithium Ion Batteries with Combined Cationic and Polyanionic Redox. Nat. Commun. 2019, 10 (1), 1–9.(2) Pramanik, A.; Manche, A. G.; Sougrati, M. T.; Chadwick, A. G.; Lightfoot, P.; Armstrong, A. R. K2Fe(C2O4)2: a New Oxalate Cathode for Li/Na ion Batteries Exhibiting a Combination of Multielectron Cation and Anion Redox. Chem.of Mat. 2023, 35, 2600–2611.(3) Manche, A. G.; Pramanik, A.; Lindgren, F.; Ericsson, T.; Häggström, L.; Armstrong, A. R. NaLiFe(C2O4)2: A New Iron-Based Polyanionic Cathode for Next-Generation Li/Na-ion Battery Exhibiting Reversible Cationic and Anionic Redox Behaviour. Energy Storage Mat. 2024, In review (4) Pramanik, A.; Manche, A. G.; Clulow, R.; Lightfoot, P.; Armstrong, A. R. Exploiting Anion and Cation Redox Chemistry in Lithium-Rich Perovskite Oxalate: A Novel next-Generation Li/Na-Ion Battery Electrode. Dalt. Trans. 2022, 51 (33), 12467–12475.