Positive Electrode Research Articles

Lignin-Based N-Carbon Dots Anchoring NiCo2S4/Graphene Hydrogel Exhibits Excellent Performance as Anodes for Hybrid Supercapacitor.

A NiCo2S4/N-CDs/RGO ternary composite hydrogel was prepared via a one-step hydrothermal method, utilizing lignin-based nitrogen-doped carbon dots as a bridge connecting NiCo2S4 and graphene. The specific capacitance of NiCo2S4/N-CDs/RGO significantly outperforms that of the GH and NiCo2S4/RGO electrodes, achieving 1050 F g-1. The 3D mesh porous hydrogel structure mitigates NiCo2S4 nanoparticle aggregation, providing a larger specific surface area for enhanced charge storage. The abundant functional groups of N-CDs interact with Ni (II) and Co (III) cations, favoring NiCo2S4 particle synthesis. Additionally, an assembled solid-state asymmetric supercapacitor employing NiCo2S4/N-CDs/RGO as the positive electrode exhibited excellent energy density (68.4 Wh kg-1) and cycle stability (82% capacitance retention after 10,000 constant current charge-discharge cycles).

Conformational isomerism breaks the electrolyte solubility limit and stabilizes 4.9 V Ni-rich layered cathodes

By simply increasing the concentration of electrolytes, both aqueous and non-aqueous batteries deliver technical superiority in various properties such as high-voltage operation, electrode stability and safety performance. However, the development of this strategy has encountered a bottleneck due to the limitation of the intrinsic solubility, and its comprehensive performance has reached its limit. Here we demonstrate that the conformational isomerism of the solvent would significantly affect the solubility of electrolytes. By transforming the configuration of solvent from cis-cis to cis-trans upon thermal triggering, we successfully break the solubility limit, and a beyond concentrated electrolyte with the lowest solvent-to-salt molar ratio of 0.70 is constructed. Transitions between cis-cis and cis-trans conformers are observed through Nuclear Magnetic Resonance (NMR) testing. The electrolyte consists entirely of anion-mediated solvation structures and promotes the formation of robust inorganic-dominated cathode electrolyte interphase. As a result, it enables stable cycling of 4.9 V-class LiNi0.8Co0.1Mn0.1O2 positive electrodes. Moreover, a high capacity of 151.2 mAh g−1 can be maintained after 1000 cycles at cut-off voltage of 4.8 V. This work provides a chemical pathway to build new concept electrolytes working under harsh conditions.

An Alternative Polymer Material to PVDF Binder and Carbon Additive in Li-Ion Battery Positive Electrode.

Li-ion battery performance relies fundamentally on modulation at the microstructure and interface levels of the composite electrodes. Correspondingly, the binder is a crucial component for mechanical integrity of the electrode, serving to interconnect the active material and conductive additive and to firmly attach this composite to the current collector. However, the commonly used poly(vinylidenefluoride) (PVDF) binder presents several limitations, including the use of toxic solvent during processing, a low electrical conductivity which for compensation requires the addition of carbon black, and weak interactions with active materials and collectors. This study investigates Poly(3,4-ethylenedioxythiophene):poly[(4-styrenesulfonyl) (trifluoromethylsulfonyl) imide] (PEDOT:PSSTFSI) as an alternative binder and conductive additive, in replacement of both PVDF and carbon black, in Li-ion batteries with LiFe0.4Mn0.6PO4 at the positive electrode. Complex PEDOT:PSSTFSI significantly improves the electronic conductivity and lithium diffusion coefficient within the electrode, in comparison to standard PVDF binder and carbon black. This enhances significantly the electrochemical performance at high C-rates and for high active mass loading electrodes. Furthermore, an excellent long-range cyclability is achieved.

Performance study of bimetallic Mn-Zn porous flower-like nanosheets as supercapacitor positive electrode materials

As environmental and carbon emission issues become increasingly severe, electrochemical energy storage systems have gained attention. Compared to traditional supercapacitors, zinc-ion hybrid capacitors (ZIHCs) are not only environmentally friendly but also cost-effective. MnO2, with its low cost, eco-friendliness, high theoretical capacity, and stable crystal structure, is considered a promising positive electrode material. In this study, the morphology of MnO2 was optimized using electrodeposition. During cycling, zinc ions reversibly intercalate and extract from MnO2, forming a cactus-like nanoflower structure. This structure is loose and porous, providing ample reaction space for active materials. The assembled device exhibits excellent performance in both energy density (85.68 Wh kg−1) and stability (91.60 %).

Bifunctional Role of High-Entropy Selenides in Accelerating Redox Conversion and Modulating Lithium Plating towards Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries, recognized as one of the most promising next-generation energy storage systems, are still limited by the "shuttle effect" of soluble polysulfides (LiPSs) on the cathode and the uncontrolled growth of lithium dendrites on the anode. These issues are critical obstacles to their practical application. Currently, many researchers have addressed these challenges from a unilateral perspective. Herein, we propose bifunctional hosts based on high-entropy selenides (HE-Se) to simultaneously tackle the persistent problems on both the positive and negative electrodes of Li-S batteries. On the one hand, HE-Se interacts with polysulfides to promote their conversion, effectively mitigating the shuttle effect. On the other hand, HE-Se provides multiple lithophilic sites during the initial nucleation of Li+, which reduces overpotential and exhibits excellent lithophilicity and cyclic stability. As a result, Li-S batteries incorporating the HE-Se hosts demonstrate outstanding performance in terms of rate capability and cycling stability. Additionally, the porous lithophilic HE-Se structure offers sufficient nucleation sites, inhibits the growth of dendritic lithium, and accommodates volume changes during charging and discharging cycles. This study highlights the potential of sulphophilic/lithophilic high-entropy materials in designing advanced Li-S batteries and encourages further exploration in this area.

Novel Binders for Aqueous Electrode Processing of Electrochemical Capacitors.

This work studies the use of epoxy and polyurethane formulations as binders for the aqueous processing of activated carbon (AC) electrodes used as positive and negative electrodes in Electrochemical Double Layer Capacitors (EDLCs). The use of amine and carbodiimide as crosslinkers is also evaluated. The mechanical properties of those different binders have been investigated, looking towards aqueous processable and flexible electrodes. Microstructural analysis of the fabricated AC electrodes has been carried out to understand the pore-blocking effect exhibited by certain polymers. Furthermore, electrochemical characterization of all the systems has been performed by cyclic voltammetry, electrochemical impedance spectroscopy, and constant current charge/discharge measurements at different current densities. The obtained results show that polyurethane outperforms in terms of energy and power density the CMC:SBR reference system. Moreover, the studied polyurethanes maintain close to 100% of their initial capacitance after 2500 cycles under a current density of 5 A g-1 and a discharge time of 20 s.

Optimization of electrode thickness of lithium-ion batteries for maximizing energy density

AbstractThe demand for high capacity and high energy density lithium-ion batteries (LIBs) has drastically increased nowadays. One way of meeting that rising demand is to design LIBs with thicker electrodes. Increasing electrode thickness can enhance the energy density of LIBs at the cell level by reducing the ratio of inactive materials in the cell. However, after a certain value of electrode thickness, the rate of energy density increase becomes slower. On the other hand, the impact of associated limitations becomes stronger, reducing the practical applicability of LIBs with thicker electrodes. Hence, an optimum value of thickness is of utmost importance for the practicability of thicker electrode design. In this paper, both the cathode thickness and the anode thickness of an NCM LIB cell were optimized by applying response surface methodology (RSM) with a Box-Behnken design (BBD) to maximize the energy density. Moreover, the influence of electrode porosity, together with the interaction of porosity with cathode and anode thickness, was incorporated into the optimization. A full factorial design of 3-level, 3-factor was used to generate 15 simulation conditions in accordance with the design of experiment (DoE) achieved through BBD. Then, those conditions were used to achieve 15 responses by simulating a reduced-order electrochemical model. Finally, the statistical technique analysis of variance (ANOVA) was used to analyze and validate the results of RSM. The results show that the RSM-BBD optimization method, coupled with ANOVA, has successfully optimized the thicknesses of both positive and negative electrodes for maximum energy density, despite the nonlinearity of the electrochemical system. The findings suggest an optimized cathode thickness of 401.56 µm and anode thickness of 186.36 µm for a maximum energy density of 292.22 of an NCM LIB cell, while electrode porosity is preferred to be 0.2.

Synthesis and Fabrication of Metal Cation Intercalation in Multilayered Ti3C2Tx Composite CNF Electrode for Asymmetric Coin Cell Supercapacitors.

Ti3C2Tx has attracted considerable attention from researchers in energy storage due to its unique structure and beneficial surface functional group characteristics. Recent studies have focused extensively on developing Ti3C2Tx composites to create potential electrode materials for energy storage applications. Carbon nanofiber is often combined with Ti3C2Tx to produce high-performance functional nanocomposites, effectively harnessing the unique properties of Ti3C2Tx nanosheets while ensuring exceptional electrochemical behavior. This work employs an ultrasonication method to prepare a Na-Ti3C2Tx/CNF electrode. Establishing a stable interlayer structure between Ti3C2Tx nanosheets and cationic metal intercalation materials is crucial for expanding the interlayer spacing of Ti3C2Tx and creating multidirectional stable ion transport channels. Consequently, this process exposes more active sites that are accessible to ions. At a current density of 1 A g-1, the resulting Na-Ti3C2Tx/CNF demonstrates an impressive specific capacitance of 680.2 F g-1. Notably, the asymmetric supercapacitor assembled with Na-Ti3C2Tx/CNF as the positive electrode and activated carbon as the negative electrode exhibits remarkable cyclic retention of 83.1% and the Coulombic efficiency of 90.5% after 10,000 cycles at 10 A g-1, a wide voltage window of 1.5 V, a high energy density of 102.5 W h kg-1, and a power density of 2963.7 W kg-1. The fabricated coin cell ASC devices, which include glowing red light-emitting diodes, were demonstrated in practical applications. The optimization strategy for developing Na-Ti3C2Tx/CNF provides essential technical support for integrating Na-Ti3C2Tx/CNF into the next generation of portable and adaptable wearable electrochemical energy storage devices.

Tuning solvation behavior within electric double layer via halogenated MXene for reliable lithium metal batteries

Solid electrolyte interphase (SEI)/electrolyte interface is critical in determining the lithium (Li) plating/stripping behavior. The solvation structure of Li-ion is well understood in the bulk electrolyte. Still, the mechanism of how SEI components affect the Li-ion solvation structure and desolvation energy barrier at the SEI/electrolyte interface is still unclear. Herein, Ti3C2 Maxine with single halogenated terminations (−Cl, −Br, −I) are synthesized and used as a model system, because their surface terminations induce a double halide-rich SEI formation (LiF and LiCl/LiBr/LiI). We examine the influence of the interaction strength between different Li halides and Li-ion on coordination number of Li ions and distribution of Li ions within the inner Helmholtz plane (IHP). A solvation sheath with a low solvent coordination number forms near the IHP of the LiBr interphase, improving the kinetics of Li deposition. Accordingly, half-cells utilising Li-carbon fiber/Ti3C2Br2 electrodes exhibit a long lifespan of 12,000 h (1 mA cm−2, 1 mAh cm−2). A pouch cell comprising Li-carbon fiber/Ti3C2Br2 anode and LiFePO4 cathode displays a capacity retention rate of 97 % after 300 cycles even at a low negative to positive electrode capacity ratio of 2.26. Our research provides crucial principles for the design of SEI components in Li metal batteries.

A hierarchical host microstructure enables regulated inner Li deposition for stable Li metal electrodes

Dendritic lithium (Li) deposition is a critical issue hindering the development of next-generation high-energy-density Li metal batteries (LMBs). Confining Li deposition within a three-dimensional host is a general strategy to suppress the volume expansion of the Li electrode. However, precise control of continuous Li growth in the pore space of the host is rarely investigated, which is a crucial issue to enable a high utilization ratio of the hosted Li for practical LMBs. Herein, a novel hierarchical host structure possessing a multifunctional secondary porous structure to regulate the continuous Li growth with high uniformity and reversibility is proposed. The secondary porous structure consisting of carbon nanotubes, nickel and Li2O-enriched solid electrolyte interphase is in-situ generated via lithiation reaction of a modified nickel foam scaffold, exhibiting high lithiophilicity, fast Li+ transportation and charge transfer. The LMB utilizing Li metal electrodes hosted by this rational structure achieved a stable cycling over 300 cycles with a practical LiFePO4 positive electrode (~2.5 mAh cm-2) at 0.5C/0.5C in the voltage window of 2.5-4.4 V. This work provides a novel approach to designing the host microstructure for constructing more stable Li metal electrode in practical LMBs.

Optimization of the Chemical Li Predoping Process of S-Confined Microporous Activated Carbon Positive Electrodes for Li–S Batteries

Optimization of the Chemical Li Predoping Process of S-Confined Microporous Activated Carbon Positive Electrodes for Li–S Batteries

Areal capacity balance to maximize the lifetime of layered oxide/hard carbon sodium-ion batteries

Optimizing the areal capacity balance between the negative and positive electrodes is crucial for enhancing the performance of sodium-ion batteries (SIBs). This study investigates NaNi1/3Fe1/3Mn1/3O₂ || hard carbon full cells with varying N/P ratios, employing three-electrode measurements to evaluate cycling performance and identify failure mechanisms in situ. A novel full cell design principle is proposed to determine the threshold N/P ratio for sodium plating. Electrochemical tests demonstrate that an N/P ratio slightly above the threshold value, particularly around 0.9, provides the best cycling performance within 1.5–4.1 V. The cycling degradation mechanism with different N/P ratios was also elucidated. It is due to either the PE or NE exceeding its critical window, leading to active material loss on the positive side and loss of sodium inventory on the negative side. The research further emphasizes that reasonably adjusting the working voltage window can significantly extend the battery's lifetime by suppressing degradation processes. The optimized cell, with an N/P ratio of 0.9 and operating within a 1.0–4.0 V window, demonstrates an 81 % capacity retention over 500 cycles. These findings provide a practical framework for designing high-performance SIBs that balance energy density and longevity.

Nb1.60Ti0.32W0.08O5−δ as negative electrode active material for durable and fast-charging all-solid-state Li-ion batteries

Li-based all-solid-state batteries (ASSBs) are considered feasible candidates for the development of the next generation of high-energy rechargeable batteries. However, ASSBs are detrimentally affected by a limited rate capability and inadequate performance at high currents. To circumvent these issues, here we propose the use of Nb1.60Ti0.32W0.08O5-δ (NTWO) as negative electrode active material. NTWO is capable of overcoming the limitation of lithium metal as the negative electrode, offering fast-charging capabilities and cycle stability. Physicochemical and electrochemical characterizations of NTWO in combination with the Li6PS5Cl (LPSCl) solid-state electrolyte demonstrate that the formation of LiWS2 at the electrode|electrolyte interphase is the main responsible for the improved battery performance. Indeed, when an NTWO-based negative electrode and LPSCl are coupled with a LiNbO3-coated LiNi0.8Mn0.1Co0.1O2-based positive electrode, the lab-scale cell is capable of maintaining 80% of discharge capacity retention after 5000 cycles at 45 mA cm−2 at 60 °C and 60 MPa.

Conformal Li2O2 Growth and Decomposition Within 3D Lithiophilic Nanocages of Metal–Organic Frameworks for High‐Performance Li─O2 Batteries

AbstractLi─O2 batteries (LOBs) have the largest theoretical capacity among current batteries, but the irreversible growth and decomposition of Li2O2 products in positive electrodes cause dramatic degradation of their capacities over charging–discharging cycles. Herein, a metal–organic framework is reported with bipyridinic N linkers attached to graphene (bpyN‐MOF/g) as a positive electrode material to overcome the challenge. The bpyN‐MOF/g promotes conformal Li2O2 growth during discharging, while allowing Li2O2 decomposition at a low overpotential (0.487 V vs Li+/Li at 200 mA gc−1) during charging process, outperforming the Pt/C‐based electrode (0.857 V). Moreover, 3D‐tomography and density functional theory calculations consistently support the Li2O2 growth and decomposition mechanism inside bpyN‐MOF/g. Furthermore, bpyN‐MOF/g//Li LOBs achieve an exceptional discharge capacity (17 275 mAh gc−1 at 100 mA gc−1) and steady cycling for 270 cycles at 1000 mAh gc−1 under 2000 mA gc−1. Additionally, high gravimetric capacity at low mass loadings (0.27–0.44 mg cm−2) and stable cycle operation at a high areal current density (0.5 mA cm−2) open new opportunities for various practical applications.

Effect of micromechanical properties of commercial grade electrolytic copper foils on lithium-ion batteries

As the carrier and electrical conduction component of positive and negative electrode materials, current collector plays an important role in lithium-ion batteries(LIBs). With the industrial application of silicon-doped anode materials with higher gram capacity, the huge volume change of silicon-doped anode materials puts forward higher requirements for the mechanical properties of copper foils(CFs). It is of great significance to study the effect of micromechanical properties on LIBs for the application screening of CFs. In this article, the effects of micromechanical properties of conventional tensile strength(CTS), high tensile strength(HTS) and ultra-high tensile strength(UHTS) commercial grade electrolytic CFs on LIBs were studied. The tensile strength of CTS, HTS and UHTS was 316.88 MPa, 464.74 MPa and 673.43 MPa, respectively; the elongation were 6.49 %, 5.38 % and 4.47 %, respectively. The surface morphology and XRD tests show that the microstructure such as grain size and dislocation density are the key factors affecting the mechanical properties of CFs. And under the same conditions, the main factors affecting bonding strength of electrode are microstrain and residual stress of CFs rather than surface roughness. The larger the microstrain and residual stress of CFs, the worse the interface bonding strength between CFs and coating materials, and the larger the corresponding interface charge transfer impedance, which is well confirmed by DCR and EIS. The charge-discharge test results show that the mutual stress between CFs and coating materials also have a great influence. The lower elastic modulus and microscopic stress of CFs can better eliminate the expansion pressure and contraction tension of coating materials, thereby reducing the resistance and overpotential in the process of lithium-ion diffusion, and achieving higher capacity under high rate system. The retention rates of three CFs after 500 cycles at 25℃ and 45℃ were 25-CTS(92.64 %), 25-HTS(90.63 %) 25-UHTS(89.11 %), and 45-CTS(82.17 %), 45-HTS(82.14 %), 45-UHTS(80.77 %), respectively, which indicates that the difference in mechanical properties of CFs have an important influence on long-term application of LIBs. The primary cause of the variation in electrochemical performance, aside from copper foil’s conductivity, is the phase interface shift brought on by the microstress of the material; and the overpotential caused by the phase interface force cannot be ignored.

Layer-by-Layer-Assembled Polyaniline/MXene Thin Film and Device for Improved Electrochromic and Energy Storage Capabilities.

Polyaniline (PANI) is an attractive electrochromic and storage material due to its reversible and sustainable electrochemical redox processes. However, the insufficient surface area and excessive charge intercalation after long-term cycling results in limited charge capacitance and unsatisfactory cycling stability. In this work, we demonstrate an innovative method to increase PANI's electrochromic and energy storage performance by incorporating MXene, to enhance electrochemical activity and reveal more active areas of ion/electron intercalation/deintercalation and charge transfer. The hydrogen bonds formed between N-H, C-H, and C-N of PANI and -OH and -O surface functional terminations of MXene further enhance the interface interaction. With substantial optical transmittance modulation and charge capacitance, excellent coloration efficiency, and outstanding durability, the PANI/MXene thin film demonstrates exceptional color-switching and energy storage characteristics. Furthermore, the sandwich device with a PANI/MXene thin film as the positive electrode and zinc foil as the negative electrode demonstrates exceptional electrochromic and Zn2+ storage capability. This work raises possibilities for next-generation intelligent energy conversion and storage technologies and offers fresh perspectives on the design of ionic devices.

MXene Electrodes for All Strain-Free Solid-State Batteries.

All-solid-state batteries with nonflammable inorganic solid electrolytes are the key to addressing the safety issues of lithium-ion batteries with flammable organic liquid electrolytes. However, conventional electrode materials suffer from substantial volume changes during Li+ (de)intercalation, leading to mechanical failure of interfaces between electrode materials and solid electrolytes and then severe performance degradation. In this study, we report strain-free charge storage via the interfaces between transition metal carbides (MXenes) and solid electrolytes, where MXene shows negligible structural changes during Li+ (de)intercalation. Operando scanning electron transmission microscopy with electron energy-loss spectroscopy reveals the pillar effect of trapped Li+ in the interlayer spaces of MXene to achieve the strain-free features. An all strain-free solid-state battery, which consists of a strain-free Ti3C2Tx negative electrode and a strain-free disordered rocksalt Li8/7Ti2/7V4/7O2 positive electrode, demonstrates long-term stable operation while preserving the interfacial contact between electrode materials and solid electrolytes.

Promoting Interfacial Reaction via Quantifying NMC811 CEI Evolution and Li+ Desolvation Using Single‐Particle Electrochemical Methods

AbstractPromoting interfacial kinetics of high‐nickel LiNi0.8Mn0.1Co0.1O2 (NMC811) is a critical strategy for enhancing rate capability of lithium‐ion batteries (LIBs). At the solid‐liquid interface of positive electrode, charge transfer across the cathode‐electrolyte interphase (CEI) is responsible for the interfacial redox reaction, which is dominated by desolvation process of Li+ and NMC811 CEI evolution. Since these two processes are significantly impacted by the solvation effect of electrolytes, herein single‐particle Raman spectroscopy and single‐particle probes are established to quantitatively study the influences of solvation effect on CEI evolution and desolvation process of Li+, respectively. Owing to oxidation of the unstable free cyclic carbonate ester from dissociation of solvation structure, the CEI is found to grow thicker during discharge process. Due to the decreased concentration of cyclic carbonate in the solvation structure, the desolvation process of Li+ in the ethyl methyl carbonate‐ethylene carbonate electrolyte can be reduced by 11.8% compared to that in the dimethyl carbonate‐ethylene carbonate electrolyte. With the presence of ethyl methyl carbonate‐ethylene carbonate electrolyte, thinner CEI and easier desolvation process of Li+ can be simultaneously achieved on the NMC811 surface. Accordingly, its corresponding LIBs deliver the highest specific capacity ≈138.8 mAh g−1 at 5C among the LIBs with the other commonly used electrolytes.

Experimental Set‐Up for Measurement of Half‐Cell‐ and Over‐Potentials of Flow Batteries during Operation

The study of flow batteries (FBs) requires the development of tools able to evaluate their performance during operation in a reliable and simple way. In this work, we present an experimental set‐up that allows the on‐line monitoring of the half‐cells state of charge and apparent overpotentials on the positive and negative electrodes during battery operation. These measurements are feasible by using additional flow cells that include a reference electrode on each side. We used the experimental set‐up to study the performance of the vanadium system as well as a previously reported stable organic couple. The studies consisted on short cycling operation at different current densities and polarization curves at different flow rates and states of charge. By confirming previous results obtained for vanadium‐FBs and extending the analysis to further systems, we demonstrated that this approach provides a reliable deeper insight into the battery performance and the processes taking place during operation.

Comparative Analysis of Thermal Activation on Felts and Continuous Carbon Filament Electrodes for Vanadium Redox Flow Batteries

AbstractThermal treatments are commonly used to improve electrode kinetics in vanadium redox flow batteries (VRFB). The impact of the widely adopted thermal treatment—400 °C for least 24 hours—was investigated on polyacrylonitrile (PAN)‐based continuous carbon filaments (tows) and compared to PAN‐based graphite felts. Surface properties were assessed with scanning electron microscopy (SEM), Raman spectroscopy, X‐ray photoelectron spectroscopy (XPS) and wettability measurements. The electrode activity was investigated via electrochemical impedance spectroscopy (EIS). Charge‐transfer resistances and the constant phase element parameters related to the electric double layer were determined, revealing a correlation between enhanced electrode activity and increased double layer across all electrodes. An 8‐hour 400 °C thermal treatment was sufficient to improve electrode activity for tows, whereas felts required longer durations, up to 24 hours, attributed to differences in the carbonization process employed for each material, with the tows undergoing continuous processing and the felts following a batch process. Three‐electrode half‐cell EIS measurements were conducted to elucidate positive and negative electrode contributions. Activated continuous carbon filament electrodes exhibited consistent electrode activities in both the catholyte (VO2+/VO2+) and anolyte (V3+/V2+), whereas the electrochemical activity of felts was limited by the electrode deactivation in the anolyte.