Positive Electrode Active Material Research Articles

Lithium loss, resistance growth, electrode expansion, gas evolution, and Li plating: Analyzing performance and failure of commercial large-format NMC-Gr lithium-ion pouch cells

Analysis of the performance evolution and failure mechanisms of commercial Li-ion batteries is crucial for improving testing methods, accurately modeling battery performance, and ensuring safe battery operation. Here, we present the results of a 2-year aging study conducted on commercial large-format LiNiMnCoO2-graphite pouch cells. Loss of lithium inventory (LLI) and loss of positive electrode active material (LAMPE) are shown to dominate capacity fade, as quantified by differential voltage-capacity analysis; only a small amount of LAMPE was measured in extracted electrode material, indicating that LAMPE in full cells was due to electrode dry-out. Resistance evolution, observed by direct current pulses and electrochemical impedance spectroscopy analyzed using the distribution of relaxation times, shows complex trends. Particle cracking and electrode expansion is theorized to cause most changes to resistance. Post-mortem measurements reveal a 10% increase in electrode stack thickness and substantial gas generation, with lithium plating observed in extreme cycling conditions, causing large resistance increases. Circumstantial evidence for self-discharge via redox shuttle, which decomposes the electrolyte, is shown. Overall, electrolyte stability was determined to be the limiting factor for cell lifetime. The impacts of many degradation mechanisms on diagnostic signals substantially overlap, making it challenging to monitor cell health and safety.

Research on the separation process of positive electrode active material and aluminum foil

Separating the cathode active material and aluminum foil is an important step in the recovery of materials from used lithium-ion batteries. It is difficult to separate aluminum foil and positive active material because of the strong bonding of polyvinylidene fluoride (PVDF). During the conventional stripping technology, using corrosive acids/alkalis, toxic reagents and releasing toxic gases such as dioxins and HF, which are harmful to human health and the environment. In the study, a low-toxic, efficient and low-cost solvent consisting of “propylene glycol and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm][BF6]) ionic liquid” was used to solve these questions. The experimental results showed that the separation rate of the positive active material from the aluminum foil was more than 99 % when the anodes were stirred in propylene glycol and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm][BF6]) ionic liquid (the volume ratio of 5:1) at 140 ℃ for 30 min. This work would provide an insight into the environmentally friendly, simple and effective solution to separate of cathode material and aluminum foil in waste lithium-ion batteries.

Development of Multi-Analysis By Operando Spectroscopy / Elemental Measurement in Oxide-Type All-Solid-State Na Batteries

Introduction Oxide-type all-solid-state Na batteries (ASSBs) are attracted attention owing to their high safety, resource abundant and intrinsic chemical stability, toward electric storage system for renewable energies, such as photovoltaics and wind generations, using electrochemical devices in urban locations. Although the ASSBs shows low output performances and high internal resistances due to their low sinter density in general, the improvement of these properties have been strenuously studied by using the spark-plasma-sintering (SPS) and sintering additives of low melting point material such as B2O3. However, charge-discharge process is complex reactions extremely, which includes redox reactions of electrode, ionic transport of solid electrolyte at macro / micro-scales every component material. Therefore, to perspective understanding of charge-discharge reactions in the ASSBs, the construction of analysis technique is strongly desired by combination of evaluation methods with suitable selection for each scale. Herein, the multi-scale analysis was demonstrated by using Operando scanning electron microscopy / energy dispersive X-ray spectroscopy (SEM / EDS) (µm-scale) and Raman spectroscopy (atomic-order) for observing changes of Na concentration, bonding states during charge-discharge processes, respectively, in addition evaluation of elemental distributions through the time-of-fright secondary ion mass spectrometry (TOF-SIMS) (nm-scale). Experimental The ASSBs were fabricated by multi-step-sintering method using SPS1 from Na3V2(PO4)3 (NVP) as positive (PE) and negative electrode (NE) active materials, Na3Zr2Si2PO12 (NZSP) as solid electrolyte (SE), B2O3 as adhesive between PE/SE and SE/NE layers. The electrode composition were NVP : NZSP : carbon = 25 : 60 : 15 by weight ratio. The sintered ASSB was physically split for arbitrary size, and then obtained piece loaded into a sample holder of Ar-ion milling system in Ar atmosphere to prepare smooth surface of cross-sectional direction. After the Ar-ion milled sample was transferred to holder enabled to apply voltage, Operando SEM-EDS was performed by cyclic voltammetry (CV) with 0.2 mV s-1 of scan rate, 0.5 - 2.5 V of voltage range at room temperature, and acquired elemental mapping images every 0.5 V for 3 min of recording time. As evaluation at 2, 3 cycle, Operando Raman spectroscopy using the same sample was performed by CV with same conditions at room temperature (at 2 cycle) and 60oC (at 3 cycle), using electrochemical measurement cell having observation window of quartz glass. After 3 cycles, the TOF-SIMS mappings were acquired from all area of the cross-sectional ASSB by using plus mode. Results & Discussion From the Operando SEM / EDS, the distributions of Na element clear changed in PE and NE layers under charge-discharge processes, the 2D-dimensional profile on Na counts normalized by P, which is estimated to be not contribute electrochemical reactions, is shown Figure 1 (a). The Na concentration were confirmed decrease / increase trends at charge process, even though there were decreased / increased at discharge process in the PE and NE layers, respectively. These behaviors of concentration change mean to Na transport between the PE and NE layers with deintercalation and intercalation reactions of NVP during charge-discharge processes. On other hand, Figure 1 (b), (c) shows the Raman spectra changes for PE and NE layers at 2 cycle. Although the D- (1380 cm-1) and G- (1520 cm-1) bands related to carbon material did not change, the integrated intensities at about 780 cm-1 clear increased / decreased at PE layer in charge-discharge processes, respectively. These peaks were assigned to PO4 bonding of NVP, and suggested to reversible structural change owing to intercalation and deintercalation reactions of Na. In addition, the calculation result of Na pathway in the NVP was reported by migration between PO4 tetrahedral along the x direction with low activation energy, and should affect bonding states owing to change of backbone structure during charge-discharge processes.2 Therefore, the peak of PO4 bonding is considered as estimation index on the state-of-charge with electrode redox reactions in ASSBs. In other words, intercalation / deintercalation of Na affects not only structural change of NVP, but also concentration change in all areas of PE and NE layers and these reactions could be directly observed by combination of Operando SEM / EDS and Ram.an spectroscopy. In this presentation, we will also report the results of elemental distributions after 3 cycles by acquired from the TOF-SIMS analysis and correlationship between each evaluation technique for ASSB. D. Kutsuzawa, et al., ACS Appl. Energy Mater., 5, 4025–4028 (2022)W. Song et al., J. Mater. Chem. A, 2, 5358 (2014). Figure 1

Investigation of Interfacial Behavior of Ni-Rich NCM Cathode Particles in Sulfide-Based Solid-State Electrolyte

All-solid-state batteries (ASSBs) are currently investigated as a future battery technology with conventional layered cathode materials because they can offer benefits in the gravimetric and volumetric energy densities compared to flammable liquid electrolyte lithium-ion batteries with graphite intercalation anode. The solid electrolyte is believed to suppress dendritic growth and low Coulombic efficiency on the lithium metal anode side, which are the key issues for the use of a lithium metal electrode in conventional batteries with liquid electrolyte. Moreover, layered transition metal oxides such as LiNixCoyMnzO2 (NCM, 0 < x, y, z < 1) are one of the most promising positive electrode active material candidates being developed to increase the energy density. In particular, recent studies have shown a tendency to decrease the cobalt content and increase the nickel content to increase energy density and price competitiveness, so high-nickel NCM can be the optimal material suitable for this purpose. However, the remaining interfacial challenges of the cathode / solid electrolyte interface still need to be solved.Herein, we investigated the kinetics such as charge transfer resistance at the interface between high nickel (Ni0.94) NCM particles and argyrodite (Li6PS5Cl) solid electrolytes using the microcavity electrode with the negative and positive pulsed current measurement technique and compared with liquid electrolytes using the same manner measurement technique. The cavity-electrode system is adopted to analyze the electrochemical properties of active particles and electrolytes confined in the cavity to exclude the effects of surrounding interfaces, barriers, and side reactions caused by battery components around the electrodes and the impact of loading and current collectors of the composite electrode. Therefore, understanding the electrode-electrolyte interface between cathode active particles and solid electrolytes is crucial for theoretical studies on the interfacial phenomenon in solid electrolyte batteries.

Novel Operando Nuclear Magnetic Resonance Approach for Tracking the Electrode State of Charge in Li/Na-Ion Batteries

Lithium and sodium-ion batteries have become the focal point of interest for the energy transition due to their promising applications for electric cars and energy grid storage. Operando characterization of batteries is critical to understand the degradation processes and increasing their electrochemical performance, especially in abusive conditions like during fast charges. Knowledge of the redox state of each electrode is essential to identify the origins of capacity loss in full batteries. Among the methods used for these investigations, operando Nuclear Magnetic Resonance (NMR) methods are promising since, without destroying the battery, they enable monitoring in real-time the electrochemical processes and the formation of short-lived metastable or reactive phases [1,2].Up to now, most operando NMR studies have focused on 7Li NMR spectroscopy to follow the lithiation and degradation processes in the solid electrodes of lithium-ion batteries. However, the large shifts and broadenings of the NMR spectra, which result from the redox-active paramagnetic ions (Ni2/3+, Co4+, Mn3/4+) or from the metallicity of the electrodes [3], complicate operando NMR spectra acquisition and interpretation for full batteries.Herein, we demonstrate that the 1H operando NMR signal of the liquid electrolyte solvent can be used to spy on the positive electrode evolution while benefitting from the high sensitivity of 1H liquid-state NMR compared to 7Li NMR. So far, operando NMR using the liquid electrolyte signal was mainly exploited to follow electrolyte decomposition [4] or to image indirectly dendrite formation [5]. Contrary to the lithium or sodium atoms composing the electrodes, hydrogen atoms in the electrolyte solvent are not a direct probe of the state of charge of the electrode. We demonstrate that the 1H NMR signal of the electrolyte molecules in the battery is, however, highly sensitive to the magnetic susceptibility (and therefore the redox state) of the neighboring particles of positive electrode active material.The state-of-charge (SOC) of the positive electrodes in the charging battery can be tracked indirectly through distortion in the spectrum of the dimethyl carbonate (DMC) solvent near the positive electrode. The effect of the other battery components such as current collectors, separators, or even negative electrodes is shown to be negligible compared to the perturbations induced by the positive electrode. We define specific descriptors to track the changes in the distorted 1H NMR spectrum of the battery and we correlate these changes with the state-of-charge of the positive electrode inside the battery as it is charged and discharged. This approach will enable measuring, operando, the redox state of positive electrodes in batteries, even when their 7Li signals cannot be detected by NMR. Exact knowledge of the redox state will contribute to a better exploitation of the electrochemical curves in full batteries.[1] Bagheri, K.; Deschamps, M.; Salager, E. Nuclear Magnetic Resonance for Interfaces in Rechargeable Batteries. Current Opinion in Colloid & Interface Science 2023, 64, 101675. https://doi.org/10.1016/j.cocis.2022.101675.[2] Liu, X.; Liang, Z.; Xiang, Y.; Lin, M.; Li, Q.; Liu, Z.; Zhong, G.; Fu, R.; Yang, Y. Solid‐State NMR and MRI Spectroscopy for Li/Na Batteries: Materials, Interface, and in Situ Characterization. Advanced Materials 2021, 33 (50), 2005878. https://doi.org/10.1002/adma.202005878.[3] Grey, C. P.; Dupré, N. NMR Studies of Cathode Materials for Lithium-Ion Rechargeable Batteries. Chemical Reviews 2004, 104 (10), 4493–4512. https://doi.org/10.1021/cr020734p.[4] Wiemers-Meyer, S.; Winter, M.; Nowak, S. NMR as a Powerful Tool to Study Lithium Ion Battery Electrolytes. Annual Reports on NMR Spectroscopy 2019, 121–162. https://doi.org/10.1016/bs.arnmr.2018.12.003.[5] Ilott, A. J.; Mohammadi, M.; Chang, H. J.; Grey, C. P.; Jerschow, A. Real-Time 3D Imaging of Microstructure Growth in Battery Cells Using Indirect MRI. Proceedings of the National Academy of Sciences 2016, 113 (39), 10779–10784. https://doi.org/10.1073/pnas.1607903113.

Degradation Control of All-Solid-State Na Batteries by Inorganic Oxide Coated Positive Electrode Active Material

All-solid-state Na batteries (ASSBs) are attracted attention owing to their high safety and resource properties for next-generation batteries. Na has the advantage of abundant resources compared to Li. In addition, polymer electrolyte is expected to improve the safety of the battery by suppressing the risk of ignition with liquid leakage. In general, the degradation of batteries using polymer electrolyte mainly occurs at the positive electrode (PE)/electrolyte interface during charge process. In case of batteries using active material having layered structures such as NaCoO2 and polyether electrolyte, the degradation of CoO2 structure and decomposition of polyether during the deintercalation of Na+ in the active material. These PE / electrolyte interface degradations contribute to increasing resistance of the battery. To suppress interfacial degradation, inorganic oxides coating for active materials were reported in the Li-based battery[1]. In this study, Na3PO4 or Na3Zr2Si2PO12 (NZSP) coated PEs were applied for ASSBs to suppress degradation. The degradation behavior of ASSBs was investigated by charge / discharge test and XRD analysis using extracted PE sheet from cell. Furthermore, Raman spectroscopy was applied on the cell before and after charge / discharge test to investigate structural changes in active material and polymer electrolyte.NaTFSA as Na salt, P(EO/PO) as polyether-based macromonomer, and DMPA as photoinitiator were mixed into Ar-filled glovebox. NaTFSA was added by ratio of [Na]/[O]=0.1 per molar of oxygen units of P(EO/PO). Polymer electrolyte films were prepared by UV irradiation for obtained homogeneous solution. NaCoO2 (NCO) as active material, acetylene black (AB) as conductive additive, and P(EO/MEEGE)-NaTFSA as binder were mixed by 82:5:13 weight ratio. The Na3PO4 and NZSP as inorganic oxides were added 5 wt.% and 10 wt.% for NCO, respectively. Applied slurry (thick. 50 µm) onto Al foil was cut to Φ16 mm after vacuum dry. The PE sheet, Na metal negative electrode, and polymer electrolyte were assembled into coin-cell to fabricate ASSBs. The charge / discharge tests for more than 10 cycles were performed at 333K after heat-treated at 363K for 48h. After charge / discharge test, XRD analysis was applied to extracted PE sheet from the cell under a low dew point for structural evaluation. Moreover, PE, polymer electrolyte, and Na metal were initially cut to 9 mm × 9 mm and introduced into the Raman cell with observation window to observe the cross-section of the cell. Raman spectroscopy was performed to the cross-section of the cell before and after charge / discharge test in order to investigate the degradation behavior of PE and polymer electrolyte.Fig. 1 shows charge / discharge profiles of non-coated and 10 wt.% NZSP coated PE in the cells. The 1st discharge capacity was 36 mAhg-1 in the non-coated system, and was also the insufficient capacity of about 30% from the theoretical capacity (ca. 118 mAhg-1) of NCO. In contrast, the NZSP-coated PE improved the 1st discharge capacity to 60 mAhg-1, and clear plateau was observed owing to their crystal structure change of NCO. These results suggest that inorganic oxide served as sufficient ionic conduction path between PE and electrolyte, reducing the interfacial resistance. Fig. 2 shows the cycle number dependencies of capacity and Coulombic efficiency. ASSB with inorganic oxides coated PE showed high discharge capacity retention and Coulombic efficiency in comparison with non-coated system. These results are suggesting that inorganic oxides coating active material surface suppress increase of interfacial resistance and degradation of the PE/electrolyte by prevent the formation of side products such as Co3O4 [2]. NZSP has higher Na ionic conductivity than Na3PO4, and can cover more apparent area of NCO surface than Na3PO4 because of their smaller particle size. Therefore, from comparing Na3PO4 and NZSP coating, NZSP more contributes to suppressing degradation of the cell. Fig. 3 shows the results of XRD analysis for PEs after charge / discharge test. Peaks attributed to NCO were confirmed in the PE before degradation, however, peak intensity decreased after degradation, especially for (003) and (006) of NCO. The peak derived from Co3O4 was confirmed only after degradation. These results suggest that structural degradation of NCO occurs during charging and discharging of the cell, resulting in the formation of Co3O4. In addition, the inorganic oxide coating should be contributed to maintaining the structure of the active material. In this presentation, the analysis results of structural changes of PE and electrolyte before and after charge / discharge test by Raman spectroscopic measurement will be also reported.

Silicon Negative Electrodes—What Can Be Achieved for Commercial Cell Energy Densities

Historically, lithium cobalt oxide and graphite have been the positive and negative electrode active materials of choice for commercial lithium-ion cells. It has only been over the past ~15 years in which alternate positive electrode materials have been used. As new positive and negative active materials, such as NMC811 and silicon-based electrodes, are being developed, it is crucial to evaluate the potential of these materials at a stack or cell level to fully understand the possible increases in energy density which can be achieved. Comparisons were made between electrode stack volumetric energy densities for designs containing either LCO or NMC811 positive electrode and silicon-graphite negative electrodes, where the weight percentages of silicon were evaluated between zero and ninety percent. Positive electrode areal loadings were evaluated between 2.00 and 5.00 mAh cm−2. NMC811 at 200 mAh g−1 has the ability to increase stack energy density between 11% and 20% over LCO depending on percentage silicon and areal loading. At a stack level, the percentage of silicon added results in large increases in energy density but delivers a diminishing return, with the greatest increase observed as the percentage of silicon is increased from zero percent to approximately 25–30%.

Cell Design Considerations and Impact on Energy Density—A Practical Approach to EV Cell Design

Higher-energy-density, Wh L−1 or Wh kg−1, lithium-ion cells are one of the critical advancements required for the implementation of electric vehicles. This increase leads to a longer drive distance between recharges. Aside from material development, full lithium-ion cell design parameters have the potential to greatly influence fabricated cell energy density. The following work highlights the impact of these full-cell design parameters, investigating the effect of a negative to positive capacity ratio, positive electrode porosity, positive electrode active material content, and overall charge voltage on stack volumetric energy density. Decreasing the N:P ratio or increasing active material content results in an almost identical volumetric energy density increase: ~4%. Decreasing the positive electrode porosity from 40–30% or increasing the charge voltage from 4.2–4.35 V also results in an almost identical increase in volumetric energy density: ~5.5%. Combining all design changes has the potential to increase stack volumetric energy density by 20% compared to the baseline cell design.

Charge–discharge properties of LiMn 2 O 4 -group positive electrode active materials for lithium-ion batteries using high-throughput experimental screening and machine learning models

Charge–discharge properties of LiMn ₂ O ₄ -group positive electrode active materials for lithium-ion batteries using high-throughput experimental screening and machine learning models

Realizing long-cycling all-solid-state Li-In||TiS2 batteries using Li6+xMxAs1-xS5I (M=Si, Sn) sulfide solid electrolytes

Inorganic sulfide solid-state electrolytes, especially Li6PS5X (X = Cl, Br, I), are considered viable materials for developing all-solid-state batteries because of their high ionic conductivity and low cost. However, this class of solid-state electrolytes suffers from structural and chemical instability in humid air environments and a lack of compatibility with layered oxide positive electrode active materials. To circumvent these issues, here, we propose Li6+xMxAs1-xS5I (M=Si, Sn) as sulfide solid electrolytes. When the Li6+xSixAs1-xS5I (x = 0.8) is tested in combination with a Li-In negative electrode and Ti2S-based positive electrode at 30 °C and 30 MPa, the Li-ion lab-scale Swagelok cells demonstrate long cycle life of almost 62500 cycles at 2.44 mA cm−2, decent power performance (up to 24.45 mA cm−2) and areal capacity of 9.26 mAh cm−2 at 0.53 mA cm−2.

Bridging multiscale interfaces for developing ionically conductive high-voltage iron sulfate-containing sodium-based battery positive electrodes

Non-aqueous sodium-ion batteries (SiBs) are a viable electrochemical energy storage system for grid storage. However, the practical development of SiBs is hindered mainly by the sluggish kinetics and interfacial instability of positive-electrode active materials, such as polyanion-type iron-based sulfates, at high voltage. Here, to circumvent these issues, we proposed the multiscale interface engineering of Na2.26Fe1.87(SO4)3, where bulk heterostructure and exposed crystal plane were tuned to improve the Na-ion storage performance. Physicochemical characterizations and theoretical calculations suggested that the heterostructure of Na6Fe(SO4)4 phase facilitated ionic kinetics by densifying Na-ion migration channels and lowering energy barriers. The (11-2) plane of Na2.26Fe1.87(SO4)3 promoted the adsorption of the electrolyte solution ClO4− anions and fluoroethylene carbonate molecules, which formed an inorganic-rich Na-ion conductive interphase at the positive electrode. When tested in combination with a presodiated FeS/carbon-based negative electrode in laboratory- scale single-layer pouch cell configuration, the Na2.26Fe1.87(SO4)3-based positive electrode enables an initial discharge capacity of about 83.9 mAh g−1, an average cell discharge voltage of 2.35 V and a specific capacity retention of around 97% after 40 cycles at 24 mA g−1 and 25 °C.

Preparation of nanosphere-interspersed flower-like heterostructure of ZnS/ZnCo2S4@Ni(OH)2 and its application for asymmetric solid-state supercapacitor

Poor conductivity and easy aggregation of the two-dimensional Ni(OH)2 astrict their extensive applications in supercapacitors. In the current study, a nanosphere-interspersed flower-like heterostructure of ZnS/ZnCo2S4@Ni(OH)2 is successfully synthesized by exploiting high conductivity of ZnS/ZnCo2S4 nanosphere which are gown on the ultra-thin sheets of Ni(OH)2 via a solvothermal reaction. ZnS/ZnCo2S4@Ni(OH)2 electrode delivers a remarkable specific capacitance of 2276.9 F/g at 1 A/g, a considerable high-rate capability (1327.5 F/g at 15 A/g), and an excellent cycling stability (retention of 90.4 % at 15 A/g after 5000 cycles). The all-solid-state hybrid supercapacitor (HSC) device is constructed using ZnS/ZnCo2S4@Ni(OH)2 and active carbon as positive and negative electrode active material, respectively. Imposingly, the device manifests high operating potential of 1.6 V, large energy density of 61.4 Wh/kg at power density of 1.0 kW/kg, as well as good stability of 94.5 % retention after 10,000 cycles. This study provides insight into electro-active materials design and construction of heterostructures for high-performance supercapacitors.

Cross-linked polyaniline for production of long lifespan aqueous iron||organic batteries with electrochromic properties

Aqueous iron batteries are appealing candidates for large-scale energy storage due to their safety and low-cost aspects. However, the development of aqueous Fe batteries is hindered by their inadequate long-term cycling stability. Here, we propose the synthesis and application as positive electrode active material of cross-linked polyaniline (C-PANI). We use melamine as the crosslinker to improve the electronical conductivity and electrochemical stability of the C-PANI. Indeed, when the C-PANI is tested in combination with a Fe metal negative electrode and 1 M iron trifluoromethanesulfonate (Fe(TOF)2) electrolyte solution, the coin cell can deliver a specific capacity of about 110 mAh g−1 and an average discharge voltage of 0.55 V after 39,000 cycles at 25 A g−1 with a test temperature of 28 °C ± 1 °C. Furthermore, mechanistic studies suggest that Fe2+ ions are bonded to TOF− anions to form positively charged complexes Fe(TOF)+, which are stored with protons in the C-PANI electrode structures. Finally, we also demonstrate the use of C-PANI in combination with a polymeric hydrogel electrolyte to produce a flexible reflective electrochromic lab-scale iron battery prototype.

Dual redox electrolytes for improving the performance of asymmetric supercapacitors constructed from heteroatom-doped green carbon spheres

Although supercapacitors benefit from both long-cycle durability and extraordinary power density, unmet energy demands still remain the key challenge on the path of their practical applications. Boosting energy densities without sacrificing the remarkable power densities and long cycle life is of special significance in developing high-performance energy storage systems. Herein, the synergy between reversible redox mediator addition and heteroatom-doping of carbon-based electrode active materials represents an enhanced electrochemical performance of the fabricated energy storage devices. Green carbon spheres (CSs) were synthesized through the eco-benign hydrothermal carbonization (HTC) approach. CSs were then chemically decorated by metal nanoparticles. A carbothermic reduction, in which metallic nano particles nanoparticles played a role as a sacrificial agent, was conducted to prepare highly porous CSs (PCSs). The carbothermic reduction process was followed by heteroatom doping of the PCSs. Nitrogen- and boron-doped PCSs were then utilized as positive and negative electrode active materials, respectively. A combination of potassium iodide (KI) and sodium anthraquinone-2-sulfonic acid (AQSA) was employed as dual-redox mediators to boost the electrochemical performance of the fabricated N-PCS//B-PCS ASC devices. The assembled ASCs coupled with AQSA/KI dual redox additives rendered not only remarkable energy density (86.3 W h kg−1) at a reasonable power density of 340 W kg−1 but also exhibited outstanding cyclic stability (only 22 % decay of initial capacitance observed after 5000 charge/discharge cycle). The encouraging features parallel to the remarkable capacitive performance of the fabricated ASCs make these supercapacitors immensely promising for practical applications.

Development of rechargeable high-energy hybrid zinc-iodine aqueous batteries exploiting reversible chlorine-based redox reaction

The chlorine-based redox reaction (ClRR) could be exploited to produce secondary high-energy aqueous batteries. However, efficient and reversible ClRR is challenging, and it is affected by parasitic reactions such as Cl2 gas evolution and electrolyte decomposition. Here, to circumvent these issues, we use iodine as positive electrode active material in a battery system comprising a Zn metal negative electrode and a concentrated (e.g., 30 molal) ZnCl2 aqueous electrolyte solution. During cell discharge, the iodine at the positive electrode interacts with the chloride ions from the electrolyte to enable interhalogen coordinating chemistry and forming ICl3-. In this way, the redox-active halogen atoms allow a reversible three-electrons transfer reaction which, at the lab-scale cell level, translates into an initial specific discharge capacity of 612.5 mAh gI2−1 at 0.5 A gI2−1 and 25 °C (corresponding to a calculated specific energy of 905 Wh kgI2−1). We also report the assembly and testing of a Zn | |Cl-I pouch cell prototype demonstrating a discharge capacity retention of about 74% after 300 cycles at 200 mA and 25 °C (final discharge capacity of about 92 mAh).

Li3TiCl6 as ionic conductive and compressible positive electrode active material for all-solid-state lithium-based batteries

The development of energy-dense all-solid-state Li-based batteries requires positive electrode active materials that are ionic conductive and compressible at room temperature. Indeed, these material properties could contribute to a sensible reduction of the amount of the solid-state electrolyte in the composite electrode, thus, enabling higher mass loading of active materials. Here, we propose the synthesis and use of lithium titanium chloride (Li3TiCl6) as room-temperature ionic conductive (i.e., 1.04 mS cm−1 at 25 °C) and compressible active materials for all-solid-state Li-based batteries. When a composite positive electrode comprising 95 wt.% of Li3TiCl6 is tested in combination with a Li-In alloy negative electrode and Li6PS5Cl/Li2ZrCl6 solid-state electrolytes, an initial discharge capacity of about 90 mAh g−1 and an average cell discharge voltage of about 2.53 V are obtained. Furthermore, a capacity retention of more than 62% is attainable after 2500 cycles at 92.5 mA g−1 and 25 °C with an applied external pressure of 1.5 tons. We also report the assembly and testing of a “single Li3TiCl6” cell where this chloride material is used as the solid electrolyte, negative electrode and positive electrode.

A monofluoride ether-based electrolyte solution for fast-charging and low-temperature non-aqueous lithium metal batteries

The electrochemical stability window of the electrolyte solution limits the energy content of non-aqueous lithium metal batteries. In particular, although electrolytes comprising fluorinated solvents show good oxidation stability against high-voltage positive electrode active materials such as LiNi0.8Co0.1Mn0.1O2 (NCM811), the ionic conductivity is adversely affected and, thus, the battery cycling performance at high current rates and low temperatures. To address these issues, here we report the design and synthesis of a monofluoride ether as an electrolyte solvent with Li-F and Li-O tridentate coordination chemistries. The monofluoro substituent (-CH2F) in the solvent molecule, differently from the difluoro (-CHF2) and trifluoro (-CF3) counterparts, improves the electrolyte ionic conductivity without narrowing the oxidation stability. Indeed, the electrolyte solution with the monofluoride ether solvent demonstrates good compatibility with positive and negative electrodes in a wide range of temperatures (i.e., from −60 °C to +60 °C) and at high charge/discharge rates (e.g., at 17.5 mA cm−2). Using this electrolyte solution, we assemble and test a 320 mAh Li||NCM811 multi-layer pouch cell, which delivers a specific energy of 426 Wh kg−1 (based on the weight of the entire cell) and capacity retention of 80% after 200 cycles at 0.8/8 mA cm−2 charge/discharge rate and 30 °C.

Nanotwinned Copper Foil for “Zero Excess” Lithium–Metal Batteries

The “zero excess” lithium–metal battery cell concept, in which the pristine negative electrode consists only of the current collector, while all lithium is present only in the positive electrode active material, promises substantial improvements in energy density. However, the achievement of stable cycling for more than just a few cycles requires a careful design and adjustment of all cell components─especially the current collector at the negative electrode. Herein, we provide a comparative investigation of commercial, polycrystalline copper foil, characterized by a rather random [111], [200], and [220] orientation and a high concentration of grain boundaries, and nanotwinned copper foil, which has a solely [111]-oriented grain structure. Remarkably, the plated lithium on the foil with [111] orientation reveals a much more homogeneous morphology independent of the current density applied, while several dendritic lithium deposits are observed on the polycrystalline copper foil. This also translates into higher Coulombic efficiency and stabilized cycling performance of Cu[111]||NMC811 cells, highlighting the important impact of the crystal orientation of the current collector.

Aqueous synthesis of Li2MnAO4/C (A = Si, Ge) as positive electrode active materials for lithium-ion batteries by acid–base reaction

Li2MnAO4/C (A = Si, Ge) and their solid solutions are successfully synthesized by a simple, economical, and environmentally friendly process.

Depth of discharge characteristics and control strategy to optimize electric vehicle battery life

To comply with the global low-carbon green growth policy, the automobile industry is rapidly shifting from internal combustion engine to electric vehicles, which use high-Ni cathode active materials with high energy density, because mileage per charge is prioritized by the user. However, the high-Ni active material presents poor cycle characteristics because impurities generated by cation mixing increase the resistance and are also structurally unstable. Accordingly, the energy efficiency and safety of the battery were improved in this study by controlling the depth of discharge (DOD) in accordance with the state of health (SOH) of the battery. The charge/discharge characteristics and deterioration factors of 18,650 cylindrical batteries were investigated based on the set DOD conditions. The optimal DOD was set by analyzing the total discharge energy up to the end of life of the battery, Coulombic efficiency, internal resistance, Li plating, and the state of the positive electrode active material. Considering the optimal DOD setting conditions corresponding to the battery condition, DOD70 at 100–90 % SOH and DOD60 at 90–80 % SOH were found to be the most effective in terms of cycle characteristics and safety. The optimal DOD control method increased the total discharge energy by approximately 45 % relative to DOD60.