Composite Cathode Research Articles

Constructing an All Solid-state Flexible Lithium-Manganese Battery with High Performance

Due to a lack of portable flexible power supply, flexible electronic products can still not be applied in a large scale, particularly in the high energy density devices. To resolve this issue, flexible solid-state lithium batteries with a high safety, excellent mechanical property, and high energy densit，is proposed. In this paper, a flexible solid-state lithium-manganese battery is developed, which is assembled with a lithium cloth composite anode, a composite solid-state electrolyte poly (vinylidene fluoride)-hexafluoropropylene (PVDF-HFP)/Li6.4La3Zr1.4Ta0.6O12 (LLZTO), and a composite cathode (Fe ion-doped MnO2-carbon cloth). To improve the conductivity and stability of cathode, a mixture of conductive carbon black (Super P) and sodium alginate (SA) is employed. To ensure the high capacity and low price, the MnO2-based cathode is used.The obtained solid state batteries can deliver an initial capacity of 275.9 mAh g−1 at a current density of 1 C and a capacity retention of 57.9% (159.7 mAh g−1) after 1000 cycles. Also the produced flexible punch cell can light up the light-emitting diode(LED), and its capacity is 0.58 mAh cm−2 after 100 cycles at current density of 0.2 C.

In Situ Investigation of Lattice Oxygen Loss from Preferentially Faceted Electrodeposited LiCoO2 via Scanning Electrochemical Microscopy

Lattice oxygen loss from transition metal oxide cathodes in Li-ion batteries (LiBs) is a key factor responsible in their gradual capacity decline over time. Understanding and mitigating this phenomenon is crucial for the development of next-generation LiBs. The effect of various parameters on lattice oxygen loss, such as cathode chemical composition, has been studied extensively. However, there is a lack of experimental investigation into the lattice oxygen stability across different crystallographic facets within the same cathode composition. Here, we employed in situ scanning electrochemical microscopy (SECM) to investigate oxygen evolution from preferentially faceted, electrodeposited LiCoO2 cathodes. Samples predominantly exposing the (003) basal planes and the (101), (102), (110) fast Li-ion diffusing facets exhibited oxygen evolution at potentials exceeding 3.5 V vs Li+/Li. Finite element simulations helped quantify the flux of oxygen evolution on the first charge cycle to 33 ± 5 pmol cm−2s−1 for the basal plane and 37 ± 9 pmol cm−2s−1 for the faceted samples at potentials above 4 V based on single spot measurements. However, spatially resolved measurements showed that faceted samples exhibited significant heterogeneity in their oxygen evolution, reaching twofold values compared to the basal plane samples at potentials beyond 4.5 V.

Effective polysulfide control in lithium–sulfur batteries utilizing BiFeO3 nanoparticles

Lithium–sulfur batteries (LiSBs) offer high energy density, cost-effectiveness, and eco-friendliness, making them promising for future energy storage. This study explores using BiFeO3 (BFO) nanoparticles (NPs) to tackle challenges such as lithium polysulfides (LiPs) and shuttle issues in LiSBs. It employs a solid-state melt diffusion technique, encapsulates sulfur in single-walled carbon nanotubes (SCNTs), and utilizes BFO for effective polysulfide control. Herein, composite cathodes of sulfur (S)/SCNTs (abbr. SCNT) were fabricated, and cells were designed using a BFO-coated separator (SCNT-BFS). In addition, a cathode modification was performed with composite S/SCNTs/BFO (SCNT-BF), and a comparative analysis was conducted to assess the effectiveness of the BFO in the separator and the cathode. Cyclic voltammetry measurements revealed that the increased current peak intensity at lower reduction potential in SCNT-BF and SCNT-BFS indicated control of higher-order LiPs (Li2Sx, where 4 ≤ x ≤ 8), resulting in the generation of more stable lower-order products (Li2S2/Li2S). The charge/discharge analysis revealed controlled LiPs, resulting in high-capacity retention in SCNT-BF (∼75%) and SCNT-BFS (∼88%) over 200 cycles, which yielded capacities of 526 and 700 mAh/g at C/8 (1C = 1675 mA/g). These promising results suggest that incorporating BFO into the cathode and separator can advance the commercialization of durable LiSBs.

Quantifying Resistive and Diffusive Kinetic Limitations of Thiophosphate Composite Cathodes in All-Solid-State Batteries

Increasing the specific capacity and rate performance of thiophosphate composite cathodes is a major challenge in solid-state battery development. Understanding the charge transport kinetics and rate-limiting mechanisms within the cathode is key towards efficient optimization. Herein, we use quantitative analysis of chronoamperometric rate performance data to differentiate between resistive and diffusive rate limitations of NCM811—Li6PS5Cl cathodes with different morphology and composition. We substantiate our findings with separate measurements of the effective ionic conductivity and Li+ diffusion coefficients using impedance spectroscopy and GITT techniques, respectively. Increasing the active material to solid electrolyte ratio is found to increase diffusive limitations, which originate from the small contact area between the active material and solid electrolyte. The diffusive limitation is especially pronounced for single crystal NCM811 cathodes at over 84% AM. Employing fine particle catholyte significantly increases the contact area, alleviates the diffusive limitation, and increases rate performance. These results provide guidelines towards bringing the solid-state battery performance levels closer to practical targets.

Novel MOF-derived Fe/CoNHDC-400@GF cathode with improved in-situ catalytic degradation of chloroquine phosphate during heterogeneous electro-Fenton process

The preparation of stable and high-efficiency heterogeneous electro-Fenton cathodes for the treatment of pollutants is important for environmental remediation. Herein, a novel N-doped MOF-derived Fe/Co bimetallic catalyst was in-situ grown on graphite felt (GF) surface to yield a composite cathode Fe/CoNHDC-400@GF for use in electro-Fenton process. The introduction of cobalt accelerated electron transfer due to existing polyvalent metals. The synergistic effect between Co0, CoⅡ, CoШ, FeⅡ, and FeШ enabled the continuous generation of reactive oxygen species (•OH and •O2−). Under near-neutral conditions (pH=6.5), complete removal of 10 mg L−1 chloroquine phosphate (CQP) was achieved within 60 min. Additionally, efficient removal was also achievable over a wide pH range (pH=3–11). The mechanistic investigations indicated •OH as a major active oxygen species for CQP degradation. A combination of the experimental results with density functional theory calculations (DFT) clarified the degradation pathway and intermediate products of CQP. Moreover, the toxicity of degradation products significantly reduced. Overall, valuable insights on preparing composite cathodes grown in-situ for efficient removal of refractory pollutants from wastewater during the heterogeneous electro-Fenton process were provided, useful for future consideration.

High-Performance and Robust Composite Cathode via W Doping-Induced Phase Separation for Proton Ceramic Fuel Cells

High-Performance and Robust Composite Cathode via W Doping-Induced Phase Separation for Proton Ceramic Fuel Cells

Enhanced electrode reaction for La0.8Sr0.2FeO3-δ-Sm0.2Ce0.8O1.9 composite cathode by barium carbonate nanoparticles as a synergistic catalyst

Enhanced electrode reaction for La0.8Sr0.2FeO3-δ-Sm0.2Ce0.8O1.9 composite cathode by barium carbonate nanoparticles as a synergistic catalyst

High‐Performance All‐Solid‐State Lithium Metal Batteries Enabled by Ionic Covalent Organic Framework Composites

AbstractIonic covalent organic frameworks (iCOFs) are crystalline materials with stable porous structures. They hold great potential for ion transport, particularly as solid‐state electrolytes (SSEs) for all‐solid‐state lithium metal batteries (ASSLMBs). However, achieving an ionic conductivity of over 10−3 S cm−1 at room temperature using pure‐iCOF‐based SSEs, even adding additives such as lithium salts, is challenging as the voids work as strong resistances. Thus, highly conductive iCOFs typically require quasi‐solid‐state configurations with organic solvents or plasticizers. In this study, composites comprising iCOFs and poly(ionic liquid) (PIL) are prepared to make all‐solid‐state iCOFs electrolytes with an exceptional ionic conductivity up to 1.50 × 10−3 S cm−1 and a high Li+ transference number of > 0.80 at room temperature. Combined experimental and computational studies show that the co‐coordination and competitive coordination mechanism established between the PIL, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and iCOFs enabled rapid Li+ transport while restricting TFSI− movement. ASSLMB cells, made of composite SSEs and LiFePO4 composite cathode, demonstrate an initial discharge capacity of 141.5 mAh g−1 at 1C and r.t., with an impressive capacity retention of 87% up to 800 cycles. Overall, this work presents a breakthrough approach for developing advanced SSEs for next‐generation high‐energy‐density ASSLMBs.

Dual-type confinement strategy: Improving the stability of organic composite cathodes for Lithium-ion batteries with longer lifespan

Inclusive reports on organic cathodes are the key evidence of their superior performance for Lithium-ion batteries. However, it is still promising to simultaneously achieve a higher practical specific capacity and longer cycling life, owing to the crucial concern of the dissolution of active molecules in organic electrolytes. The introduction of porous carbon confinement and coating which can impart discharge capacity and cycling stability, is highly beneficial. Herein, we designed and prepared a novel composite cathode (designated as HKUST-1-C@DHAQ@TiO2) with small molecules (DHAQ) in porous carbon skeleton (HKUST-1-C) as core and TiO2 as shell. The unique dual-type confinement strategy offers short Li+/e- diffusion directions for redox reactions and superior structural stability during cycling without dissolution or decomposition of the components, resulting in excellent electrochemical performance. The HKUST-1-C@DHAQ@TiO2 cathode delivers significant specific capacity (209 mAh g−1, 0.1 A g−1), markable Coulombic efficiency (nearly 100 %), notable cycling stability (86 % retention for provided 200 cycles) and excellent rate capacity (138 mAh g−1 at 1.0 A g−1). The presented findings offer the deep understanding of redox reactions and organic cathode evolution mechanisms for the progress of smarter energy storage batteries.

Synergistic effects of Ag nanoparticles in the rGO and Co3O4 based electrode materials for asymmetric supercapacitors

A systematic investigation of the composite electrode materials is vital in fabricating supercapacitors with high specific capacitance and good stability. The present work systematically studies the synergistic effects of Ag nanoparticles (AgNPs) on the electrochemical behaviour of rGO-based supercapacitor anode and Co3O4/rGO composite cathode. The Co3O4/(Ag/rGO) composite has been fabricated by hydrothermally growing Co3O4 nanoparticles over the previously prepared Ag/rGO support in the 70:30 ratio. The electrochemical performance of fabricated electrodes was evaluated by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) in 1 M KOH electrolyte. The Ag/rGO electrode having 15 - 20 % of AgNPs displays a specific capacitance of 553.6 F/g by CV (@10 mV/s) and 449.4 F/g by GCD (@0.35 A/g), which is 2.9 – 3.1 times higher than pristine rGO, when scanned in the range of – 1.0 V - 0.0 V (Vs. Ag/AgCl). The Co3O4/(Ag-20/rGO) composite electrode (in the ratio 70:30) possesses 244.9 F/g of specific capacitance (by GCD @3.8 A/g in the range of – 0.2 V - 0.5 V (Vs. Ag/AgCl)), which is 3.2 and 2.0 times higher than Co3O4 and Co3O4/rGO respectively. The Co3O4, Co3O4/rGO and Co3O4/(Ag/rGO) samples retained 67 % (at 3.8 A/g), 91 % (@1.4 A/g), and 82 % (@1.4 A/g) of specific capacitance after 2000 cycles. The asymmetric supercapacitor device in rGO||Co3O4/Ag/rGO configuration shows an initial specific capacitance of 438.0 F/g, energy and power densities of 38.9 Whkg‒1 and 640 Wkg‒1, respectively, at 2 A/g current density. The demonstrated boost in performance arises due to the presence of Ag nanoparticles leading to enhanced conductivity, catalyzing the pseudocapacitive reactions and preventing the graphene layers from aggregation by acting as spacers, spacers, thus making Ag/rGO and Co3O4/Ag/rGO as potential electrode materials for asymmetric supercapacitors.

Facile Composition of CoNi and Graphene as a Free-Standing Cathode for a High-Performance Solid-State Zinc–Air Battery

The development of solid-state zinc–air batteries (SZABs) has stimulated significant interest. However, the practical use of SZABs still encounters difficulties due to the complicated preparation process and low-performance air cathode. In this study, we developed a free-standing CoNi/graphene composite cathode without current collectors and binders. The simplified cathode structure decreased the preparation process, and the self-assembled conductive matrix increased charge transfer, which holds promise for facile preparation and high-performance SZABs. Specifically, a free-standing CoNi/graphene film was fabricated by a simple composition method. The CoNi/graphene electrocatalyst exhibited comparable oxygen reduction reaction (ORR) catalytic activity to that of Pt/C. Furthermore, the CoNi/graphene film could be directly used as a cathode, which showed an open-circuit voltage of 1.41 V and a power density of 210 mW cm−2 in alkaline liquid ZABs, as well as an open-circuit voltage of 1.43 V and a power density of 40 mW cm−2 in alkaline SZABs. This facile preparation and excellent performance offer substantial potential for practical SZAB applications.

A dual modification strategy of highly active catalytic cathode for proton-conducting solid oxide fuel cell with Ni-doped PrBaFe1.9Mo0.1O6-δ

The cathode catalytic activity and stability in a temperature range of 550–700 °C is crucial to the development of proton-conductive solid oxide fuel cells (PCFCs). A facile dual-modification strategy is developed for the design of Ni-doped PrBaFe1.9Mo0.1O6-δ (PBFMN), composed of a major perovskite and a minor NiO phases, as a cobalt-free cathode. The composite cathode PBFMN exhibits high catalytic activity and stability. Computational simulation indicates that the perovskite phase increases the oxygen vacancies and enhances the proton transfer, while nickel oxide nanoparticles improve oxygen adsorption and dissociation. The fuel cell with as-prepared PBFMN reached a peak power density 1.23 W cm−2 at 700 °C. The improved performance of the cell is mainly due to the fast ORR kinetics. This work provides a new insight into the design of cobalt-free cathode for a PCFC.

Low‐Strain and High‐Energy KVPO4F Cathode with Multifunctional Stabilizer for Advanced Potassium‐Ion Batteries

KVPO4F with excellent structural stability and high operating voltage has been identified as a promising cathode for potassium‐ion batteries (PIBs), but limits in sluggish ion transport and severe volume change cause insufficient potassium storage capability. Here, a high‐energy and low‐strain KVPO4F composite cathode assisted by multifunctional K2C4O4 electrode stabilizer is exquisitely designed. Systematical electrochemical investigations demonstrate that this composite cathode can deliver a remarkable energy density up to 530 Wh kg−1 with 142.7 mAh g−1 of reversible capacity at 25 mA g−1, outstanding rate capability of 70.6 mAh g−1 at 1000 mA g−1, and decent cycling stability. Furthermore, slight volume change (~5%) and increased interfacial stability with thin and even cathode–electrolyte interphase can be observed through in situ and ex situ characterizations, which are attributed to the synergistic effect from in situ potassium compensation and carbon deposition through self‐sacrificing K2C4O4 additive. Moreover, potassium‐ion full cells manifest significant improvement in energy density and cycling stability. This work demonstrates a positive impact of K2C4O4 additive on the comprehensive electrochemical enhancement, especially the activation of high‐voltage plateau capacity and provides an efficient strategy to enlighten the design of other high‐voltage cathodes for advanced high‐energy batteries.

Novel Electrospun Sn-Based Composite Cathodes Exhibiting Extended Cycle Life for Hybrid Magnesium-Lithium Batteries.

In this study, we present a strategic approach for the structural design and composite modification of one-dimensional Sn-based nanocomposites to enhance the overall electrochemical performance of hybrid magnesium-lithium batteries (MLIBs), which are emerging as promising successors to lithium-ion batteries. By using electrospinning technology, we successfully synthesized NST-SnO2, NST-SnO2-NiO, Sn-CNF, and Ni3Sn2-CNF composite cathodes, as well as analyzed the synthesis mechanism of the four Sn-based cathodes. The 100-cycle testing at a current density of 500 mA·g-1 revealed that NST-SnO2 maintained a discharge specific capacity of 129.8 mA h·g-1 with a retention rate of 90.76%, while NST-SnO2-NiO achieved a higher capacity of 147.4 mA h·g-1 and an 88.05% retention rate. Notably, Sn-CNF and Ni3Sn2-CNF exhibited initial discharge capacities of 66.7 and 79.6 mA h·g-1, respectively, coupled with exceptional cycle stability, evidenced by retention rates of 104.19 and 102.38%. The remarkable cycling stability observed in these novel cathodes is attributed to their robust structural integrity, thus demonstrating the potential for an extended cycle life in MLIBs. This work provides significant advancement in the development of high-performance electrode materials for next-generation hybrid magnesium-lithium energy storage systems.

Microstructure-chemomechanics relations of polycrystalline cathodes in solid-state batteries

Lithium-nickel-manganese-cobalt-oxides (NMC) embedded in solid-electrolytes are being extensively applied as composite cathodes to match the high energy density of metallic anodes. During charge/discharge, the cathode composite often degrades through the evolution of micro-cracks within the grains, along the grain boundaries, and delamination at the particle-electrolyte interface. Experimental evidence has shown that regulating the morphology of grains and their crystallographic orientations is an effective way to relieve the volume-expansion-induced stresses and cracks, consequently stabilizing the electrochemical performance of the electrode. However, the interplay among the crystal orientation, grain morphology, and chemo-mechanical behavior has not been holistically studied. In that context, a thermodynamically consistent computational framework is developed to understand the role of microstructural modulation on the chemo-mechanical interactions of a polycrystalline NMC secondary particle embedded in a sulfide-based solid electrolyte. A phase-field fracture variable is employed to consider the initiation and propagation of cracks. A set of diffused phase-field parameters is adopted to define the transition of chemo-mechanical properties between the grains, grain boundaries, electrolyte, and particle-electrolyte interfaces. This modeling framework is implemented in the open-source finite element package MOOSE to solve three state variables: concentration, displacement, and phase-field damage parameter. A systematic parametric study is performed to explore the effects of aspect ratio, the crystal orientation of grains, and the interfacial fracture energy through the chemo-mechanical analysis of the composite electrode. The findings of this study offer predictive insights for designing solid-state batteries that provide stable performance with reduced fracture evolution.

Development and understanding of the lithiation/de-lithiation mechanism of a low cobalt and nickel-rich cathode material for lithium‐ion batteries

Nickel-rich LiNixMnyCo1−x−yO2 (NMC, with x ≥ 0.6) layered oxides are regarded as cathode candidates for high-energy density lithium-ion batteries (LIBs). However, this technology faces several challenges due to the scarcity of crucial raw materials such as cobalt precursors and the negative environmental impact of their extraction process. It is therefore, it becomes imperative to develop low cobalt content cathode compositions that offer alternative options with comparable electrochemical performance. Herein, we have used a systematic approach to modify the composition while keeping all other properties (particle size and morphology) constant to synthesise low-Co-cathode materials, namely LiNi0·8Mn0·1Co0·1O2 (NMC-10 %) and LiNi0·8Mn0·15Co0·05O2 (NMC-5%). A co-precipitation route using a continuous stirred thank reactor was used for synthesis. The physico-chemical properties, electrochemical performances, cycling stability, and rate capabilities of NMC-5% materials are comparable to those of NCM-10 % materials. NMC-10 % and NMC-5% half cells show initial specific discharge capacities of 191 mAh.g−1, and 185 mAh.g−1, respectively, in a voltage range of 2.8–4.3 V (vs. Li+/Li). The NMC-5% exhibits excellent thermal stability, characterized by a predominant exothermic peak at 432 °C and significantly lower total heat energy when compared to NMC-10 % counterpart, which displayed its main exothermic peak at 339 °C. The structural and electronic changes of both materials were evaluated through in operando synchrotron-based X-ray techniques. Regardless of the cobalt content, both materials show comparable structural and electronic evolution upon the de-intercalation/intercalation of Li+ ions. An irreversible phase transition at the first delithiation was observed as emphasized by diffraction of synchrotron radiations.

External Pressure in Polymer-Based Lithium Metal Batteries: An Often-Neglected Criterion When Evaluating Cycling Performance?

Solid-state batteries based on lithium metal anodes, solid electrolytes, and composite cathodes constitute a promising battery concept for achieving high energy density. Charge carrier transport within the cells is governed by solid-solid contacts, emphasizing the importance of well-designed interfaces. A key parameter for enhancing the interfacial contacts among electrode active materials and electrolytes comprises externally applied pressure onto the cell stack, particularly in the case of ceramic electrolytes. Reports exploring the impact of external pressure on polymer-based cells are, however, scarce due to overall better wetting behavior. In this work, the consequences of externally applied pressure in view of key performance indicators, including cell longevity, rate capability, and limiting current density in single-layer pouch-type NMC622||Li cells, are evaluated employing cross-linked poly(ethylene oxide), xPEO, and cross-linked cyclodextrin grafted poly(caprolactone), xGCD-PCL. Notably, externally applied pressure substantially changes the cell's electrochemical cycling performance, strongly depending on the mechanical properties of the considered polymers. Higher external pressure potentially enhances electrode-electrolyte interfaces, thereby boosting the rate capability of pouch-type cells, despite the fact that the cell longevity may be reduced upon plastic deformation of the polymer electrolytes when passing beyond intrinsic thresholds of compressive stress. For the softer xGCD-PCL membrane, cycling of cells is only feasible in the absence of external pressure, whereas in the case of xPEO, a trade-off between enhanced rate capability and minimal membrane deformation is achieved at cell pressures of ≤0.43 MPa, which is considerably lower and more practical compared to cells employing ceramic electrolytes with ≥5 MPa external pressure.

Novel Cu(II)-based metal–organic framework STAM-1 as a sulfur host for Li–S batteries

Due to the increasing demand for energy storage devices, the development of high-energy density batteries is very necessary. Lithium–sulfur (Li–S) batteries have gained wide interest due to their particularly high-energy density. However, even this type of battery still needs to be improved. Novel Cu(II)-based metal–organic framework STAM-1 was synthesized and applied as a composite cathode material as a sulfur host in the lithium–sulfur battery with the aim of regulating the redox kinetics of sulfur cathodes. Prepared STAM-1 was characterized by infrared spectroscopy at ambient temperature and after in-situ heating, elemental analysis, X-ray photoelectron spectroscopy and textural properties by nitrogen and carbon dioxide adsorption at − 196 and 0 °C, respectively. Results of the SEM showed that crystals of STAM-1 created a flake-like structure, the surface was uniform and porous enough for electrolyte and sulfur infiltration. Subsequently, STAM-1 was used as a sulfur carrier in the cathode construction of a Li–S battery. The charge/discharge measurements of the novel S/STAM-1/Super P/PVDF cathode demonstrated the initial discharge capacity of 452 mAh g−1 at 0.5 C and after 100 cycles of 430 mAh g−1, with Coulombic efficiency of 97% during the whole cycling procedure at 0.5 C. It was confirmed that novel Cu-based STAM-1 flakes could accelerate the conversion of sulfur species in the cathode material.

Approaching high rate All-Solid-State Lithium-Sulfur batteries via promoted sulfur conversion with nickel oxide nanoparticle electrocatalyst

All-solid-state lithium-sulfur battery (ASLSB) is deemed a promising next-generation energy storage device owing to its combination of high theoretical specific energy (2600 Wh kg−1) derived from the sulfur active material, and exceptional safety characteristics and the ability to suppress the polysulfide shuttle effect through the use of solid electrolyte (SE). However, the low electronic and ionic conductivity of sulfur, coupled with the poor solid–solid interfacial contact inherent in all-solid-state configuration, has resulted in poor electrochemical performance. Herein, NiO electrocatalyst supported on N-doped sites of super-p was synthesized and incorporated as a carbon additive in the composite cathode of the ASLSB. The direct growth of nanosized NiO electrocatalyst on the N-doped sites of super-p ensures facile electron transfer to the electrocatalyst surface, while maximizing the electrocatalyst’s surface area. As a result, the overpotential during charging and discharging of the ASLSB was significantly reduced, as assessed through galvanostatic intermittent titration technique and cyclic voltammetry, indicating enhanced redox conversion of sulfur. Furthermore, the Li6PS5Cl sulfide SE induces solid–solid conversion of sulfur, eliminating the dissolution issue of polysulfide intermediates and ensuring good cycle performance. The assembled ASLSB exhibits a high reversible capacity of 1845 mAh g−1 at 0.05C at room temperature and enhanced rate capability at high C-rates, operated at 60 °C. Even at a substantially high sulfur loading level of 6.65 mg cm−2, a maximum areal capacity of 9.48 mAh cm−2 was achieved at room temperature, highlighting the important role of electrocatalyst in realizing high performance ASLSBs.

Silver nanoparticle−decorated MnO2 for promoted Mn4+/Mn2+ redox reaction in aqueous Zn−MnO2 batteries

Rechargeable aqueous Zn−MnO2 batteries have garnered increasing attention recently due to intrinsic safety, high theoretical capacity, appealing output voltage, and low material cost. However, challenges still exist in exploring for high−performance manganese oxides capable of delivering comparable capacity to the Zn anode. Herein, a composite material made of layered MnO2 decorated with Ag nanoparticles (Ag NPs) can be prepared by a one−step hydrothermal reaction. The silver decoration strategy can provide facile electron transport of the composite cathode and induce structural vacancies via forming Ag−O−Mn bond. These features enable the AgMO cathode to exhibit smaller charge−transfer resistance (23.0 vs 41.3 Ω) and accelerated ion transport kinetics (1.25×10−10 vs 3.90×10−11 cm2 s−1). More importantly, the presence of Ag NPs is found to promote the reaction kinetics of Mn4+/Mn2+ redox. By taking these advantages, the AgMO sample exhibits a higher attainable capacity of 333 mAh g–1 at 0.3 A g–1 compared with the Ag−free counterpart (MO, 268 mAh g–1). Moreover, AgMO demonstrates better rate performance with the discharge capacity of 109 mAh g–1 at 8 A g–1 (90 mAh g–1 for MO), and a specific capacity of 93 mAh g–1 can still be achieved for AgMO after 2000 cycles at 4 A g–1 (55 mAh g–1 for MO). This work presents a holistic approach to enhance the energy storage capability of MnO2 cathode in rechargeable aqueous Zn−ion batteries.