Low Cyclability Research Articles

Rechargeable Organic Molecule-Air Battery

[Introduction] The development of environmentally friendly batteries, such as rechargeable aqueous metal-air batteries, has been required for sustainable energy supply. Aqueous zinc-air batteries, composed of zinc as the anode, O2 in the air as the cathode, and a very base aqueous solution (e.g., 6 M KOH aqueous solution) as the electrolyte, are one of the representative environmentally friendly batteries, because of their high energy density (1353 W h kg−1 excluding oxygen) compared to conventional lithium-ion batteries (limited to be <350 W h kg−1 based on the intercalation chemistry).[1] However, these batteries usually have extremely low cyclability because of dendrite formation on the anode and carbonate salt clogging (i.e., the reaction between CO2 in the air and the base) in the electrolyte during charging and discharging.To improve their cyclability, we previously reported a rechargeable organic polymer-air battery using a redox polymer with an anthraquinone derivative (which has a one-step two-electron redox capability in an acidic aqueous solution).[2] This rechargeable organic polymer-air battery exhibits a very high Coulombic efficiency of 99% because of the distorted structure of the anthraquinone derivative. However, organic redox polymers with linear polymer structures are not sufficiently robust for long-term use as an anode-active material in aqueous air batteries.On the other hand, Prof. Yu et al. have recently fabricated a rechargeable organic polymer-air battery using a networked polymer based on anthraquinone as an anode-active material and demonstrated very high cyclability of presumably 99% capacity retention even after 60,000 cycles.[3] This is presumably because the networked polymer forms a robust three-dimensional network that prevents it from decomposing or dissociating from the electrode. However, the Coulombic efficiency was lower than that of organic polymer-air batteries with organic linear polymers, and was only 95%.To achieve both the sufficiently high cyclability and high Coulombic efficiency as an aqueous air battery, the anode-active material must possess high hydrophilicity, exhibit high diffusivity of compensating ions in the material, and have a robust structure that is not decomposed or dissociated from the electrode during charging and discharging.In this work, as the anode-active material, we focused on the anthraquinone molecule itself, which has a reversible redox capacity at the very negative potential close to the potential window in aqueous electrolytes and whose redox properties can be modulated by facile organic synthesis. To improve anthraquinone’s hydrophilicity and inhibit its aggregation, we synthesized 2-propoxyethyl anthraquinone-2-carboxylate. 2-propoxyethyl anthraquinone-2-carboxylate had a reversible redox potential in an acidic aqueous solution, and we established a novel rechargeable organic molecule-air battery using2-propoxyethyl anthraquinone-2-carboxylate as the anode-active material and an acidic aqueous solution as the electrolyte. [Results & Discussions] The battery was chargeable and dischargeable, with the very high Coulombic efficiency of >99% at 15 C. The discharge capacity was almost full capacity, indicating that almost all the molecules contributed to charging and discharging. The discharge capacity remained >99% even after 100 cycles, indicating that the battery had a very high cyclability. Even at 60 C, the discharge capacity of the battery was almost the same as that at 15 C, indicating a high-rate capability. Moreover, the results confirm that this novel rechargeable organic molecule-air battery exhibits the highest cyclability and Coulombic efficiency in rechargeable organic-based aqueous air batteries. Using 2-propoxyethyl anthraquinone-2-carboxylate as an anode-active material in aqueous air batteries will potentially achieve almost the same energy density and increase power density by several times or more, compared to the polymer-air batteries demonstrated. Therefore, the energy density of the aqueous air battery using 2-propoxyethyl anthraquinone-2-carboxylatewill be almost the same as that of metal-air batteries (e.g., zinc-air batteries), and its power density is expected to be higher than that of lithium-ion batteries.We want to discuss this in more detail at the poster session. [Reference] [1] J. Zhang et al., Chem. Sci. 2019, 10, 8924-8929.[2] K. Oka et al., Macromolecules 2021, 54, 4854-4859.[3] L. Zhong et al., Angew. Chem. Int. Ed. 2021, 60, 10164-10171. Figure 1

Electrochemical Analyses of the Li-Ion Transfer Resistances at the Chloride Solid Electrolyte | Sulfide Solid Electrolyte Interfaces

Introduction The all-solid-state Li-ion battery is expected to be a next-generation battery owing to its enhanced safety and high rate-capability ascribed to sulfide solid electrolytes (SEs) having incombustibility and high ionic conductivity. However, low cyclability hinders their practical application. Since the oxidative decomposition of the sulfide SE in the positive electrode is known as one of the main degradation modes, bilayer SE cells are promising to suppress the degradation where the chloride SE having relatively high stability against oxidation is placed on the positive electrode side and the reduction-resistive sulfide SE is placed on the negative electrode side. [1]. While it is reported that the interface between the sulfide and chloride SEs is not chemically stable and interphases are formed between the SEs [1], the effect of the interphase on the Li-ion transport between the sulfide and chloride SEs has not been investigated. As a way to analyze the resistance between two SEs, we have recently established an all-solid-state electrochemical four-electrode cell using a partially reduced lithium titanate (R-LTO) reference electrode (RE) [2,3]. Experimental In this study, we apply the electrochemical four-electrode cell to the sulfide SE | chloride SE interfaces to analyze the Li-ion transport resistance. The glass-ceramic Li2S-P2S5-LiI (LPSI) was synthesized by the method reported by X. Feng et al. [4]. The chloride SEs, Li3InCl6 (LIC), Li3SrCl6 (LSC), and Li3YCl6 (LYC) were synthesized following the previous report [1]. The ionic conductivities and activation energies of the LPSI, LIC, LSC, and LYC were measured to be 2.1, 0.36, 0.5 and 0.28 mS cm–1 at 25 °C, and 29.8, 33.5, 38.5 and 38.6 kJ mol–1, respectively. The R-LTO REs were fabricated by the previously reported method [2]. All-solid-state four-electrode cells (Fig. 1(a)) were fabricated in the following way. First, the LPSI pellet incorporating the R-LTO was fabricated by hand pressing in a mold. Then, the chloride SE powder was sandwiched with the LPSI layers followed by cold pressing at ca. 290 MPa. Finally, Li-In foil synthesized with a chemical lithiation of the In foil was put on the outer sides of the stacked pellet as the counter electrodes (CEs) [2]. Electrochemical impedance spectroscopy (EIS) was conducted between 50 mHz and 7 MHz with an AC amplitude of 10 mV at OCV using an electrochemical measurement system (VSP-300, BioLogic). Results and Discussion Fig. 1(b) shows the impedance spectrum obtained by EIS using a pristine LIC | LPSI cell at 25 °C. Two semicircles P 1 and P 2 are found in higher and lower frequency regions and assigned as bulk and interfacial Li-ion transfer from the frequency response [2]. The interfacial resistance of the LPSI | LIC | LPSI cell shows a continuous increase at 25 °C, though it does not change significantly at –5 °C. This result indicates that the resistive interphase is formed by a chemical reaction. The growth ratios of the interfacial resistances of the LPSI | LIC | LPSI, LPSI | LYC | LPSI, and LPSI | LSC | LPSI cells for 50 h are 2.2,1.6 and 1.4 respectively. References 1) M. Chandrappa et al., J. Am. Chem. Soc., 144, 18009 (2022).2) K. Yoshida et al., submitted to Electrochim. Acta (2024).3) A. Ikezawa et al., Electrochem. Commun., 116, 1067433 (2020).4) X. Feng et al., Energy Storage Mater., 22, 397 (2019). Acknowledgment This work was supported by JSPS KAKENHI Grant Number JP22H04608. Figure 1

Development and Upscaling of a Waterborne Formulation for High‐Energy Density NMC811 Cathodes

AbstractThe pursuit of high‐energy lithium‐ion cells has led to an increase in the fraction of nickel in the LiNixMnyCozO2 (NMC, with x+y+z=1) layered oxide, a state‐of‐the‐art cathode material in electric vehicles. NMC is usually processed using organic solvents that are non‐sustainable. Nevertheless, increasing the Ni fraction entails a decrease in the electrode stability and the processability of this material in water. In this work, high‐nickel NMC materials have been subjected to water processing. In an initial stage, water sensitivity of the materials has been studied. Then, the formulation has been adapted to enhance the NMC fraction without penalizations in the electrochemical performance and compared to an organic solvent‐based formulation. The recipe developed, consisting of 93 % of NMC, has been successfully upscaled to a semi‐industrial coating line. The pH buffering has been observed as a critical step to mitigate lithium leaching and implement this process in an industrial environment. The obtained electrodes have been tested in single‐layer pouch cells using silicon‐based negative electrodes, also processable in water‐based slurries. The resulting cells provide limited cycling life due to the low cyclability of the negative electrode but evidence that it is industrially viable to manufacture high‐energy cells consisting only of water‐processed electrodes.

N, S Co-doped carbon anchored Co9S8 cathode: Advancing sustainable energy through efficient Li–CO2 Mars batteries

Owing to their higher capacity and ability to address global warming, Li–CO2 batteries have potential for next-generation energy storage systems on Earth and for space applications. However, the key drawbacks of high overpotential and low cyclability of Li–CO2 batteries substantially hinder their practicality. In this study, we develop uniquely designed cobalt sulfide (Co9S8) nanoparticles anchored onto the N, S dual-doped hetero atoms graphitized mesoporous carbon (NSC) as a low-cost but highly effective cathodic catalyst for Li–CO2 batteries with a large number of active sites with enhanced conductivity. The as-developed Li–CO2 batteries under simulated Martian gas atmosphere conditions (Li–CO2 Mars) display a high discharge capacity and exceptional rate performance. The Li–CO2 Mars battery offers a high discharge capacity of 15147 mAh g−1 at 500 mA g−1 current density and maintains a stable performance over 120 cycles for a limited capacity of 500 mAh g−1. Further, the first-principle calculations provide a deeper understanding of the reaction pathways during discharging and charging. These results create new avenues for designing novel catalysts for high-performance Li–CO2 Mars batteries for their use in interplanetary missions.

Organoboron-thiophene-based polymer electrodes for high-performance lithium-ion batteries.

Polymer electrodes are drawing widespread attention to the future generation of lithium-ion battery materials. However, weak electrochemical performance of organic anode materials still exists, such as low capacity, low rate performance, and low cyclability. Herein, we successfully constructed a donor-acceptor thiophene-based polymer (PBT-1) by introducing an organoboron unit. The charge delocalization and lower LUMO energy level due to the unique structure enabled good performance in electrochemical tests with a reversible capacity of 405 mA h g-1 at 0.5 A g-1 and over 10 000 cycles at 1 A g-1. Moreover, electron paramagnetic resonance (EPR) spectra revealed that the unique stable spin system in the PBT-1 backbone during cycling provides a fundamental explanation for the highly stable electrochemical performance. This work offers a reliable reference for the design of organic anode materials and expands the potential application directions of organoboron chemistry.

Nature of Li2O2 and its relationship to the mechanisms of discharge/charge reactions of lithium-oxygen batteries.

Lithium-air batteries (LABs) are considered one of the most promising energy storage devices because of their large theoretical energy density. However, low cyclability caused by battery degradation prevents its practical use. Thus, to realize practical LABs, it is essential to improve cyclability significantly by understanding how the degradation processes proceed. Here, we used online mass spectrometry for real-time monitoring of gaseous products generated during charging of lithium-oxygen batteries (LOBs), which was operated with pure oxygen not air, with 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) tetraethylene glycol dimethyl ether (TEGDME) electrolyte solution. Linear voltage sweep (LVS) and voltage step modes were employed for charge instead of constant current charge so that the energetics of the product formation during the charge process can be understood more quantitatively. The presence of two distinctly different types of Li2O2, one being decomposed in a wide range of relatively low cell voltages (2.8-4.16 V) (l-Li2O2) and the other being decomposed at higher cell voltages than ca. 4.16 V (h-Li2O2), was confirmed by both LVS and step experiments. H2O generation started when the O2 generation rate reached a first maximum and CO2 generation took place accompanied by the decomposition of h-Li2O2. Based on the above results and the effects of discharge time and the use of isotope oxygen during discharge on product distribution during charge, the generation mechanism of O2, H2O, and CO2 during charging is discussed in relation to the reactions during discharge.

Fabrication of BiOBr on carbon fiber cloth as easily recyclable visible-light-driven photocatalyst for purifying wastewater

Visible light-response bismuth bromide oxide (BiOBr) is a widely sought-after semiconductor nanomaterial due to its high photocatalytic activity, but its applications have been limited by complex synthesis methods and low cyclability. Hence, we successfully deposited BiOBr nanosheets on carbon fiber cloth (CFC) by chemical bath precipitation method to obtain efficient and easily recyclable CFC/BiOBr-x photocatalysts (4 × 4 cm2). After in-situ growth of BiOBr nanosheets on CFC, the diameter of a single fiber (CFC/BiOBr-6) was increased from 6.9 to 7.4 μm. Under visible light irradiation, CFC/BiOBr-6 exhibits excellent photocatalytic activity toward RhB (completely degrade) and LVFX (88.9 %) within 120 min, respectively. In addition, CFC/BiOBr-6 still maintained good photocatalytic activity after four cycles (97.9 %). Therefore, CFC/BiOBr-6 possesses great potential for practical photocatalytic applications.

Fluorination of (Mg,Cu,Al,Fe)-based LDHs template for conversion materials usable in all-solid state lithium metal batteries

Iron and copper fluorides are of interest as conversion cathode materials in lithium batteries but they suffer from high hysteresis and low cyclability, respectively. To overcome these limitations and take advantage of the electrochemical properties of each of the fluorides, fluoride mixtures that combine the two redox centers Fe3+ and Cu2+ are synthesized using Layered Double Hydroxides (LDH) as a 2D multi-metallic template. Hydrotalcite-type phases substituted with Cu2+ and Fe3+ ions are prepared by coprecipitation then fluorinated with fluorine gas in static mode at temperatures chosen according to their thermal evolution monitored by mass spectrometry. After each fluorination treatment, the materials are characterized by X-ray diffraction and most LDH materials are found stable up to 200 °C, treatment above leads to the formation of fluorides of each of the cations. The initial dispersion of the cations in the LDH sheets nevertheless allows, after fluorination, a composite of fluorides making them totally accessible to the phenomenon of electrochemical conversion shown here in a metallic lithium battery assembly with a Solid Polymer Electrolyte (SPE). In such All-Solid-State Battery (ASSB) configuration often limiting in terms of columbic efficiency, 76% the first discharge capacity is recovered in charge for an optimized composition (up to 560 mAh.g−1). This good reversibility positions these LDH templates very well for future investigations in the field of electrochemical storage.

Non-volatile electrically programmable integrated photonics with a 5-bit operation

Scalable programmable photonic integrated circuits (PICs) can potentially transform the current state of classical and quantum optical information processing. However, traditional means of programming, including thermo-optic, free carrier dispersion, and Pockels effect result in either large device footprints or high static energy consumptions, significantly limiting their scalability. While chalcogenide-based non-volatile phase-change materials (PCMs) could mitigate these problems thanks to their strong index modulation and zero static power consumption, they often suffer from large absorptive loss, low cyclability, and lack of multilevel operation. Here, we report a wide-bandgap PCM antimony sulfide (Sb2S3)-clad silicon photonic platform simultaneously achieving low loss (<1.0 dB), high extinction ratio (>10 dB), high cyclability (>1600 switching events), and 5-bit operation. These Sb2S3-based devices are programmed via on-chip silicon PIN diode heaters within sub-ms timescale, with a programming energy density of sim 10,{fJ}/n{m}^{3}. Remarkably, Sb2S3 is programmed into fine intermediate states by applying multiple identical pulses, providing controllable multilevel operations. Through dynamic pulse control, we achieve 5-bit (32 levels) operations, rendering 0.50 ± 0.16 dB per step. Using this multilevel behavior, we further trim random phase error in a balanced Mach-Zehnder interferometer.

Influence of graphene wrapped-cerium oxide coating on spherical LiNi0.5Mn1.5O4 particles as cathode in high-voltage lithium-ion batteries

Cobalt-free LiNi 0.5 Mn 1.5 O 4 (Lithium Nickel Manganese Oxide; LNMO) has garnered considerable interest as a cathode material due to its high working voltage, lower cost, and environmental friendliness. However, LNMO cathodes currently exhibit low cyclability and capacity deterioration, severely restricting their use on a broader scale. To this end, microwave-assisted chemical co-precipitation was used to produce spherical aggregated nanoparticles of LiNi 0.5 Mn 1.5 O 4 (LNMO) coated with CeO 2 (LNMO-Ce) and wrapped in graphene (LNMO-Ce-GO). Structural analysis demonstrates that the ceria coating along with the graphene wrapping prevents unwanted phases from forming and altering the morphology of the LNMO microspheres. LNMO-Ce-GO exhibits a discharge capacity of 132.4 mAhg −1 at the C/10 rate with a capacity retention of 95.3 % after 100 cycles, compared to LNMO-Ce and bare LNMO samples that provide a capacity retention of 91.6 % and 84.7 % respectively. DSC analysis elucidate that the ceria coating helps to suppress the adverse reactions at the electrode/electrolyte interface and reduce the Mn 3+ dissolution due to the Jahn Teller effect, increasing cell cyclability. The graphene wrapping reduces material aggregation and provides conductive pathways that significantly improve the electrochemical performance of the LNMO cathode. This innovative material design strategy can be efficiently expanded to other classes of lithium-ion battery cathode materials to enhance their electrochemical performance. • Graphene wrapped ceria coated LiNi 0.5 Mn 1.5 O 4 was synthesized utilizing microwave-assisted chemical co-precipitation technique. • SEM analysis illustrates the formation of secondary spherical microspheres with primary nanoparticles of LiNi 0.5 Mn 1.5 O 4 . • TEM analysis exhibits a 1–3 nm ceria coating and graphene wrapping over LiNi 0.5 Mn 1.5 O 4 particles. • Surface-modified disordered LNMO exhibits improved cyclability with a 98.6 % capacity retention after 100 cycles at C/10 rate. • Graphene wrapping & ceria coating reduces interfacial resistance and increases lithium-ion diffusion kinetics.

Novel Co‐Catalytic Activities of Solid and Liquid Phase Catalysts in High‐Rate Li‐Air Batteries

AbstractLi‐air batteries are considered strong candidates for the next‐generation energy storage systems designed for electrical transportation. However, low cyclability and current rates are two major drawbacks that hinder them from further realization. These issues necessitate the discovery of novel materials to significantly enhance the redox process of discharge products. In this study, a novel catalytic system comprised of tin sulfide (SnS) nanoflakes as a solid catalyst and tin iodide (SnI2) as a dual‐functional electrolyte additive is discovered. This system enables operating the battery at high current rates up to 10 000 mA g−1 (corresponding to 1 mA cm−2). The SnS catalyst shows outstanding catalytic activity for both oxygen reduction and evolution reactions compared to carbon, noble metals, and other transition metal dichalcogenides. It also exhibits good structural integrity at high rates. The computations indicate numerous possible oxygen reduction sites without oxygen dissociations on the SnS surface through solution mechanism that is likely responsible for the formation of Li2O2. The calculations also indicate that the role of the SnI2 is not only reacting with the lithium anode to provide protection but reducing the charge potential by promoting catalytic decomposition of the Li2O2. This work provides new novel additives for designing high‐rate Li‐air batteries.

Effects of Discharge/Charge Cycles on Inner Structures of Laminated Cells of Lithium Air Batteries By X-Ray CT, SEM/EDS and FIB-SEM/EDS

Lithium-air battery (LAB) is considered to be one of the most promising energy storage devices because of its large theoretical energy density. However, low cyclability caused by battery degradation prevents its practical use.Here we employed X-ray CT to monitor the structural development of laminated cell of lithium air batteries without dismantling the cells. The results are compared with those of SEM/EDS and FIB-SEM/EDS analyses, which were carried out after dismantling the cells.Figure 1 shows XCT images of cross section and slice of laminated cell of lithium air battery after several discharge/charge cycles. Each component is well resolved. Figure 2 shows XCT images of cross section of laminated cell of lithium air battery (a) as prepared, and after (b) one, and (c) ten discharge/charge cycles. It is clear lithium became porous even just after one cycle. The porous layer became much thicker after 10 cycles. For detailed understanding of the structure of the porous layer of lithium, the cells were dismantled and were subject to SEM/EDS and FIB-SEM/EDS analyses. Degradation of lithium layer was much less significant if the anode and cathode were separated by solid electrolyte (Ohara). Detailed results and advantages of XCT will discussed. Figure 1

(Digital Presentation) Mass Spectroscopic Products Analysis during Charging of Li-O2 Cell with Tegdme Based Electrolyte

Rechargeable lithium-air battery (LAB) is considered to be one of the most promising energy storage devices because of its large theoretical energy density. Despite significant efforts by many research groups, LAB is still far from practical use and many problems must be overcome [1]. The first problem is associated with the use of air as it contains many components other than oxygen including N2, water, and CO2, which interfere battery reactions. Thus, most of the fundamental studies are not on LAB but on Lithium-oxygen battery (LOB), which uses pure oxygen as an active material. Even LOB has many serious problems, including low cyclability caused by (1) high charging overpotential, which induces degradation of positive electrode (carbon) and electrolyte solution, and (2) degradation/dendrite formation of negative Li metal electrode. To improve the cyclability, it is essential to clarify the mechanism of degradation of electrodes and electrolyte.Here we employed mass spectroscopy to follow products generation during charging so that we can clarify the degradation mechanisms of electrodes and electrolyte. Porous carbon sheet (KJCNT from KJ Specialty Paper), lithium metal (Honjo Metal), 1 M LiTFSI TEGDME (both from Sigma-Aldrich) solution, PE separator (W-Scope), and stainless steel mesh (Hohsen) were used as positive electrode, negative electrode, electrolyte, separator, and gas diffusion layer, respectively. Isotope exchanged TEGDME, i.e., 13CH3-TEGDME and CD3-TEGDME, which were synthesized in our laboratory, and 18O2 (Taiyo Nippon Sanso) were used for mass spectroscopy for precise products assignments. Details of set-up for mass analysis have been reported elsewhere [2]. We carried out online QMS (Quadrupole Mass Spectrometer) measurement for mass numbers of decomposition products between 12-90 during the potential sweep from OCP to 4.8 V (0.05 mV/s).Figure 1 shows the current and mass signals of m/z = 18 (H2O), 32 (O2), and 44 (CO2) as a function of potential. It is clear that current increased immediately as potential was scanned from OCP (~2.8 V ), reached a maximum at 3.3 V, decreased gradually, reached a minimum at 4.0 V, increased again to reach a maximum at 4.4 V, decreased to reach a minimum at 4.6 V and increased again. The potential dependence of O2 signal is very similar to that of current as the main battery reaction is Li2O2 → 2Li+ + O2 + 2e-. Two clear peaks were observed at around 3.3 V and 4.4V, showing the presence of two kinds of Li2O2 [3]. The H2O signal started to increase just after the 1st current/O2 peaks where the current efficiency for O2 generation current efficiency started to decrease, suggesting the H2O formation is related to the decrease of the current efficiency. The CO2 signal started to be significant at 4.1 V where current and the O2 signals started to increase again and reached a maximum at ca. 4.5 V, which is more positive than those of current and O2 signal but equal to H2O peak. Although current increased again significantly at potentials more positive than 4.65 V, no mass signals of O2, H2O and CO2 increased. Instead signals such as m/z = 15, 29, 31, 45, and 60, which are related to organic molecules derived from TEGDME, became significant. Figure 2 shows the online QMS results at 4.65 V. We can see that various mass signals such as 15, 29, etc. were observed at this potential. By careful analysis of the results with the assistance of isotopes 18O2, 13CH3-TEGDME, and CD3-TEGDME, presence of CH3OH, HCHO and other organic molecules with high vapor pressure originated from TEGDME were confirmed. Additionally, we detected molecules with low vapor pressure such as CH3O(CH2)2OH, CH3OCH2COCH3, etc., which were derived from TEGDME by GC/MS analysis of samples collected every 1hr. Based on the products detected by online QMS and GC/MS, possible degradation mechanism of electrolyte can be deduced. I will discuss the degradation mechanism of electrolyte based on the above results.[1] Liu T., et al. Current challenges and routes forward for nonaqueous lithium–air batteries. Chemical reviews, 2020, 120(14): 6558-6625.[2] Ue, M., et al. Material balance in the O2 electrode of Li–O2 cells with a porous carbon electrode and TEGDME-based electrolytes, RSC Advances, 2020, 10(70): 42971 - 42982.[3] Nishioka K, et al. Isotopic depth profiling of discharge products identifies reactive interfaces in an aprotic Li–O2 battery with a redox mediator. Journal of the American Chemical Society, 2021, 143(19): 7394-7401. Figure 1

Silicon nanocrystals-embedded carbon nanofibers from hybrid polyacrylonitrile – TEOS precursor as high-performance lithium-ion battery anodes

The high capacity of silicon (Si) for lithium incorporation makes it a promising anode material for lithium-ion batteries; however, pulverization of Si due to huge volume changes during lithiation/delithiation leads to significant capacity loss during cycling. To address challenges in low cyclability, nanostructured Si in carbon nanocomposites offers an attractive solution. In this study, we report an efficient method for the synthesis of a nanocomposite containing Si nanoparticles homogeneously embedded in an electrically conductive carbon nanofiber (CNF) network. Electrospinning of polyacrylonitrile (PAN) solution containing hydrolyzed tetraethyoxysilane (TEOS), as a Si precursor, and subsequent carbonization of hybrid nanofibers yielded a composite of SiO2 ultrafine nano-domains in the carbon network (C-SiO2). Low temperature molten salt-assisted aluminothermic reduction of C-SiO2 nanofibers allowed us to produce a C-Si/SiOx nanocomposite without forming detrimental SiC, which is thermodynamically favorable at high temperatures in a system with a high interfacial surface area between the carbon and SiO2 phases. The nanocomposite C-Si/SiOx anodes showed a reversible capacity of 860 mAh g−1 at a current rate of 200 mA g−1, retaining a capacity of 680 mAh g−1 after 100 cycles. In addition, the nanocomposite anodes delivered a reversible capacity of 569 mAh g−1 at a current rate of 400 mA g−1 while maintaining 95% of maximum capacity after subsequent 100 cycles. This study demonstrates the capability of designing nanocomposite anodes from reaction precursors combined with low-temperature aluminothermic reduction to produce a capacity-retaining anode composite of Si nanocrystals uniformly dispersed in the carbon matrix.

Decoupling the Dynamics of Zinc Hydroxide Sulfate Precipitation/Dissolution in Aqueous Zn–MnO2 Batteries by Operando Optical Microscopy: A Missing Piece of the Mechanistic Puzzle

AbstractEnergy storage provides flexibility to an energy system and is therefore key for the incorporation of renewable energy sources such as wind and solar into the grid. Aqueous Zn–MnO2 batteries are promising candidates for grid‐scale applications due to their high theoretical capacity (616 mAh g–1) and the abundance of their components in the Earth's crust. However, they suffer from low cyclability, which is probably linked to the dramatic pH variations induced by the electrochemical conversion of MnO2. These pH variations are known to trigger the precipitation/dissolution of zinc hydroxide sulfate (Zn4(OH)6SO4 . xH2O, (ZHS)), which might have an influence on the conversion of MnO2. Herein, optical reflectometry is used to image and quantitatively monitor the MnO2 electrode's charge and discharge in situ and under operation. It emphasizes how solid‐phase ZHS rules the dynamics of both charge and discharge, providing a comprehensive picture of the mechanism at play in aqueous Zn–MnO2 batteries. If the precipitation of ZHS might impede the MnO2 electrode's discharge, it is a crucial pH buffer delaying the occurrence of the competing oxidation of water on charge.

Iongel Soft Solid Electrolytes Based on [DEME][TFSI] Ionic Liquid for Low Polarization Lithium‐O2 Batteries

AbstractLithium‐air/O2 batteries are a promising battery technology for automotive applications due to their high energy density. However, many challenges need to be solved, particularly the high reactivity of the electrolyte with oxygen superoxide radicals and its low cyclability. In this work, we present a simple and fast way to prepare polymer‐based iongel soft solid electrolytes. Thermally and mechanically stable iongels are prepared by fast UV‐photopolymerisation exhibiting a high ionic conductivity (∼1.2×10−3 S cm−1 at 25 °C). When used as solid electrolytes in lithium symmetrical cells, they can withstand a critical current density of 0.5 mA cm−2. Performance in Li−O2 cells showed capacities as large as 3.3 mAh cm−2, and cycling capability of 25 cycles, exceeding results on liquid‐counterpart cells.

Lithiation MAX derivative electrodes with low overpotential and long-term cyclability in a wide-temperature range

Rechargeable lithium metal battery (LMB), as an attractive candidate for the next-generation of high-energy-density storage system, is plagued by high overpotential and low cyclability due to uncontrolled dendrite growth and weak solid electrolyte interface (SEI). Herein, we report an accordion-like S/F co-doped carbon (SFC) prepared by etching Ti3SiC2 under SF6-containing atmosphere, and then its lithiation SFC composite electrode provides a long-term cyclability (1600 h) in combination with a low overpotential (12.1 mV), overwhelming Li-based electrodes reported so far. More attractively, long-term cyclability of 160, 350, and 500 h at 2 mA cm−2 is achieved in symmetrical cells at temperatures of -10, 25, and 50 °C, respectively. Dependent on DFT calculations and experimental tests, we confirm that SFC has large adsorption energy and strong coupling interaction with Li, which improves the lithiophilicity of the electrode, reduces the battery overpotential, and inhibits the growth of dendrites. Additionally, the formation of Li2S-LiF-enriched SEI film produced by the gradual release of S and F ions from the SFC into the electrolyte also attributed to the electrode stability. This work sheds new light on the applications of MAX derivatives for wide-temperature lithium metal batteries.

Interfacial Self-assembly of Organics/MXene Hybrid Cathodes Toward High-Rate-Performance Sodium Ion Batteries.

Conjugated quinones are promising cathode materials for sodium-ion batteries. However, the contemporary primary conjugated quinones cathodes still hold to limited capacity, poor rate performance and low cyclability, due to the poor electronic and ionic conductivity. Herein, a series of high-performance conjugated-quinones@MXene hybrid cathodes is constructed by an in situ polymerization-assembly strategy based on the hydrogen bond and S-Ti interaction. The PAQS@Ti3C2Tx MXene hybrid, as a typical example, exhibits sandwiched structure with intimate PAQS@MXene contact, resulting in efficient interfacial mass transfer. The assembled MXene is able to build interconnected conductive channels in the hybrid cathodes for continuous and fast electrons/ions transport, which is verified by both the experimental results and density functional theory (DFT) calculations. As a result, the optimal PAQS@MXene hybrid electrode delivers excellent electrochemical performances with high capacity (∼242 mA h g-1 at 100 mA g-1), superior fast-charge/discharge ability (∼148 and 121 mA h g-1 at 5 and 10 A g-1, respectively), and ultralong cycle life (capacity as high as 57 mA h g-1 after 9000 cycles at 5 A g-1), which are more superior to that of the pure PAQS electrodes. Besides, the analogous PPTS@Ti3C2Tx MXene hybrid cathode also shows better performances compared to the pure materials.

Revealing the Sulfur Redox Paths in a Li-S Battery by an In Situ Hyphenated Technique of Electrochemistry and Mass Spectrometry.

The lithium-sulfur (Li-S) battery is one of the most promising next generation energy storage systems due to its high theoretical specific energy. However, the shuttle effect of soluble lithium polysulfides formed during cell operation is a crucial reason for the low cyclability suffered by current Li-S batteries. As a result, an in-depth mechanistic understanding of the sulfur cathode redox reactions is urgently required for further advancement of Li-S batteries. Herein, the direct observation of polysulfides in a Li-S battery is reported by an in situ hyphenated technique of electrochemistry and mass spectrometry. Several short-lived lithium polysulfide intermediates during sulfur redox have been identified. Furthermore, this method is applied to a mechanistic study of an electrocatalyst that has been observed to promote the polysulfides conversion in a Li-S cell. Through the abundance distributions of various polysulfides before and after adding the electrocatalyst, compelling experimental evidences of catalytic selectivity of cobalt phthalocyanine to those long-chain polysulfide intermediates are obtained. This work can provide guidance for the design of novel cathode to overcome the shuttle effect and facilitate the sulfur redox kinetics.

Stabilization of high-voltage lithium metal batteries using a sulfone-based electrolyte with bi-electrode affinity and LiSO2F-rich interphases

High-voltage cathodes paired with lithium metal anode have aroused extensive interests owing to their application potentials for high-density energy storage. Nevertheless, conventional electrolytes fail to maintain the stability of high-voltage cathodes and Li anode, due to their rigid interfacial chemistry with low adsorption of transition metal and strong bonding with Li+ ions. These inadequate interactions exacerbate issues such as transition metal dissolution and non-uniform Li+ transference, ultimately resulting in low cyclability of high-voltage lithium metal batteries (HVLMBs). By incorporating fluoroethylene carbonate (FEC) into lithium bis(trifluoromethane sulfonyl) imide (LiTFSI)/tetramethylene sulfone (TMS) solution, we design a sulfone-based electrolyte to improve the cyclability of HVLMBs with bi-electrode affinity characteristic—the TMS solvent with outstanding anti-oxidation stability preferentially tends to the aggressive cathodes while the FEC solvent with excellent film-forming ability approaches to the Li anode, attributed to the different adsorption energy between various solvents and electrodes. In addition, the sulfone electrolyte forms ultra-thin fluorine and sulfur-rich interphases, containing LiSO2F with S=O bonds of low electron density, associated with Li+ and e− species attacking the S-C and S-N bonds of LiTFSI and the S-C bonds of TMS. As confirmed by in-situ Raman, Ab initio molecular dynamics, and phase field simulations, the LiSO2F uniformizes in-plane Li+ transfer and mitigates transition metal dissolution, owing to the smallest Li+-LiSO2F bonding value (-1.95 eV) and the largest transition metal absorption value with LiSO2F (-3.86 eV) ever reported in the interfacial components. With Coulombic efficiency of 99.3%, the electrolyte enables an 86.1% retention after 500 cycles for Li/NMC811 (4.40 V) batteries.