Superior Cathode Research Articles

A Novelly Hierarchical LDHs−Based Cathode with Reduced Deprotonation Barrier Toward High−Performance Alkaline Energy Storage

AbstractLayered double hydroxides (LDHs) are promising electrode materials for alkaline electrochemical energy storage (EES). However, their low capacity, sluggish rate performance, and limited cycle life significantly hinder practical applications. This study unlocks the direct deprotonation reaction pathway for LDH materials through theoretical calculations. Guided by this insight, a novelly hierarchical composite (LDH−TPA) with various dimensions and components is fabricated by introducing terephthalic acid (TPA), serving as a superior cathode material for alkaline EES devices. Experimental results and theoretical investigations reveal the transformation process for metal–organic framework quantum dots (MOF−QDs) and the enhanced mechanism of reaction kinetics in the LDH−TPA electrode. Benefiting from the reduced deprotonation barrier, optimized electronic structure, and fast electrons/ions transport rates, the LDH−TPA1 electrode demonstrates a high specific capacity of 267 mAh g−1 at 1 A g−1 and retains 167 mAh g−1 even at 20 A g−1, along with excellent cycling stability. Furthermore, an alkaline nickel−zinc battery (AZB) with LDH−TPA1 cathode is assembled, achieving a lifespan exceeding 3400 cycles, and a high energy density of 341.3 Wh kg−1 at a power density of 1640.9 W kg−1. This study is expected to provide new insight into the modification of LDHs and the advancement of alkaline energy systems.

Application of isoindigo-based small molecule conjugated electrolytes at interfaces with organic solar cells

Zwitterionic small molecule materials are widely employed in the cathode interface layer of organic solar cells (OSCs). Nevertheless, the exploration of superior cathode interface materials with the objective of enhancing the performance of OSCs remains a significant challenge. Two water/alcohol soluble n-type self-doped small molecule conjugated electrolytes were synthesized using isoindigo as the acceptor unit and triphenylamine (TPA) as the donor unit. Quaternary ammonium salts or pyridine salts were used as the polar side chains. When applied to organic solar cells (OSCs) with PTB7-Th: PC71BM as the active layer, the devices showed improved performance. The power conversion efficiency (PCE) reached 8.59 % (IIDN2TPA) and 8.81 % (IIDPy2TPA), respectively. These results demonstrate the water/alcohol-soluble D-A-D-type small-molecule conjugated electrolytes offer an effective strategy in designing cathode interlayer (CIL) and preparing the high-performance OSCs.

Review on layered oxide cathodes for sodium‐ion batteries: Degradation mechanisms, modification strategies, and applications

AbstractExploiting high‐capacity cathode materials with superior reliability is vital to advancing the commercialization of sodium‐ion batteries (SIBs). Layered oxides, known for their eco‐friendliness, adaptability, commercial viability, and significant recent advancements, are prominent cathode materials. However, electrochemical cycling over an extended period can trigger capacity fade, voltage hysteresis, structural instability, and adverse interface reactions which shorten the battery life and cause safety issues. Thus, it is essential to require an in‐depth understanding of degradation mechanisms of layered oxides. In this review, the crystal and electronic structures of layered oxides are revisited first, and a renewed understanding is also presented. Three critical degradation mechanisms are highlighted and deeply discussed for layered oxides, namely Jahn–Teller effect, phase transition, and surface decomposition, which are directly responsible for the inferior electrochemical performances. Furthermore, a comprehensive overview of recently reported modification strategies related to degradation mechanisms are proposed. Additionally, this review discusses challenges in practical application, primarily from a degradation mechanism standpoint. Finally, it outlines future research directions, offering perspectives to further develop superior layered cathode materials for SIBs, driving the industrialization of SIBs.

N/O co-doped poly(γ-glutamic acid)/Ni2+/melamine/chitosan nanoparticle-based hollow graphite carbon spheres for aqueous zinc-ion hybrid supercapacitors

Hollow carbon spheres (HCSs) have attracted broad attention in aqueous zinc-ion hybrid supercapacitors (ZIHSCs) owing to their distinctive properties. However, traditional methods for fabricating HCSs face limitations, including complex multistep procedures, the use of corrosive chemicals, and stringent reaction conditions. In this work, biomass-based poly(γ-glutamic acid)/Ni2+/melamine/chitosan nanoparticles were used as the precursors to fabricate N/O co-doped hollow graphite carbon spheres (HGCSs). Thanks to the appropriate hydrophilic characteristic, specific surface area, pore size distribution, and electrical conductivity, the fabricated HGCSs cathode exhibited superior electrochemical properties. The assembled HGCSs-based ZIHSCs device showed a satisfactory specific capacitance of 133.2 mAh·g−1 at a current density of 1.0 A·g−1, high energy densities of 75.2 Wh·kg−1 at 10,000 W·kg−1 and 107.9 Wh·kg−1 at 1000 W·kg−1, respectively. Additionally, the assembled HGCSs-based ZIHSCs device displayed an exceptional cycling stability, enduring up to 10,000 cycles at 0.5 A·g−1 with a capacity retention rate of 98.1 %. This work provides a facile and novel strategy to prepare superior electrochemical performance biomass-based HGCSs cathode for ZIHSCs.

Carbonized Ganoderma Lucidum/V2O3 Composites as a Superior Cathode for High-Performance Aqueous Zinc-Ion Batteries.

In response to the suboptimal electrochemical performance of low-valence vanadium oxides, Ganoderma lucidum biomass-derived carbon@V2O3 (V2O3@CGL) composites were prepared by evaporative self-assembly technology and high-temperature calcination. In the prepared composites, V2O3 effectively encapsulates CGL, serving as a support for V2O3 and enhancing electrical conductivity and structural stability. This results in improved overall performance for the composites. They revealed satisfactory electrochemical properties when assembled in aqueous zinc-ion batteries (AZIBs). The preliminary discharge specific capacity of the V2O3@CGL-2 (VOCG-2) composite electrode reached 407.87 mAh g-1 at 0.05 A g-1. After 1000 cycles, the capacity retention is 93.69% at 3 A g-1. This research underscores the feasibility of employing V2O3 and abundantly available biomass for high-performance AZIB cathodes.

Prevention of morphological change for (Ba,Sr)(Co,Fe)O3 cathodes by incorporating (Ce,Gd)O2 for intermediate-temperature solid oxide fuel cells

Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) generally exhibits superior cathode activity compared to La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) for intermediate-temperature solid oxide fuel cells (IT-SOFCs). However, the chemical stability of BSCF is inferior to that of LSCF. When BSCF cathodes are sintered at a high temperature of 1050 °C, performance was compromised due to the formation of (Ba,Sr)ZrO3 between the scandia-stabilized zirconia (ScSZ) electrolyte and gadolinia-doped ceria (GDC) interlayer. The oxide ionic conductivity of (Ba,Sr)ZrO3 was low, decreasing the cathode performance. Furthermore, the BSCF grains enlarged, and cobalt oxide formed due to BSCF decomposition, decreasing the active specific surface area. However, by incorporating GDC into the BSCF cathode, the morphology remained unchanged and cobalt oxide formation was prevented, despite (Ba,Sr)ZrO3 still forming. The performance of the cell with the BSCF-GDC composite cathode surpassed that with the BSCF cathode due to decreased polarization resistance attributed to the oxygen surface exchange and diffusion processes in the cathode.

Highly Crystalline Multivariate Prussian Blue Analogs via Equilibrium Chelation Strategy for Stable and Fast Charging Sodium-Ion Batteries.

Prussian blue analogs (PBAs) have been widely recognized as superior cathode materials for sodium-ion batteries (SIBs) owing to numerous merits. However, originating from the rapid crystal growth, PBAs still suffer from considerable vacancy defects and interstitial water, making the preparation of long-cycle-life PBAs the greatest challenge for its practical application. Herein, a novel equilibrium chelation strategy is first proposed to synthesize a high crystallinity (94.7%) PBAs, which is realized by modulating the chelating potency of strong chelating agents via "acid effect" to achieve a moderate chelating effect, forcefully breaking through the bottleneck of poor cyclic stability for PBAs cathodes. Impressively, the as-prepared highly crystalline PBAs represent an unprecedented level of electrochemical performance including ultra-long lifespan (10000 cycles with 86.32% capacity maintenance at 6Ag-1), excellent rate capability (82.0mAhg-1 at 6Ag-1). Meanwhile, by pairing with commercial hard carbon, the as-prepared PBAs-based SIBs exhibit high energy density (350Whkg-1) and excellent capacity retention (82.4% after 1500 cycles), highlighting its promising potential for large-scale energy storage applications.

Ultra-Fast-Charging, Long-Duration, and Wide-Temperature-Range Sodium Storage Enabled by Multiwalled Carbon Nanotube-Hybridized Biphasic Polyanion-Type Phosphate Cathode Materials.

Sodium-ion batteries (SIBs) represent a promising energy storage technology with great safety. Because of their high operating potential, superior structural stability, and prominent thermal stability, polyanion-type phosphates have garnered significant interest in superior prospective cathode materials for SIBs. Nevertheless, the disadvantages of poor intrinsic electronic conductivity, sluggish kinetics, and volume variation during sodiation/desodiation remain great challenges for satisfactory rate performance and cycle stability, which severely hinder their further practical applications. In this work, by adjusting the amounts of pretreated multiwalled carbon nanotubes (CNT) added intentionally at the beginning of the preparation, biphasic polyanion-type phosphate materials (marked as NFC) are synthesized through a one-pot solid state reaction methodology, which are composed of CNT-interwoven Na3V2(PO4)2F3 (NVPF) and a small amount of Na3V2(PO4)3 (NVP). Benefiting from the improved electronic conductivity and unique composition and structure, the optimized sample (labeled as NFC-2) illustrates exceptional cycle stability and remarkable rate performance. The discharge capacities of the NFC-2 electrode are 114.8 and 78.6 mAh g-1 tested at 20 and 5000 mA g-1, respectively. Notably, such an electrode still gives out 75.7% capacity retention upon 10 000 cycles at 5000 mA g-1. In situ X-ray diffraction analysis demonstrates that the NFC-2 cathode has outstanding structural reversibility during charge/discharge cycles. More importantly, such a biphasic material has achieved impressive electrochemical performance within a wide operating temperature range of -20-50 °C. When temperature is decreased to -20 °C, the NFC-2 electrode still delivers an initial discharge capacity of 102.4 mAh g-1 and exhibits a remarkable capacity retention of 97.8% even after 500 cycles at 50 mA g-1. In addition, the sodium-ion full cell assembled by integrating NFC-2 cathode and hard carbon anode shows a satisfying energy density of 431.3 Wh kg-1 at 20 mA g-1 with a better long-term cycle performance. The synergistic effect among high energy NVPF, conductive CNT, and stable NVP may lead to the great improvement in the electrochemical sodium storage performance of the NFC-2 sample. Such biphasic polyanion-type phosphate materials will inject new ideas into the material design for SIBs with excellent electrochemical performance and further promote practical applications of this advanced energy storage technology.

Superior fast-charging Ni-rich cathode via promoted kinetic-mechanical performance

The sluggish Li-ion kinetics restrict the rapid charging capabilities and contribute to the structural deterioration of Ni-rich cathode materials. Notably, crack propagation during repeated charging cycles deteriorates the electrochemical stability, which hinders the further development of high-energy-density batteries for electric vehicles (EVs). In this paper, we proposed a simple yet effective method to enhance the Li-ion diffusion and mechanical properties of Ni-rich cathodes via straightforward Zr doping. In-situ high-rate XRD reveals that the detrimental uneven delithiation under the fast-charging process has been largely alleviated. Particularly, a robust structure with higher modulus and fracture strength is constructed owing to the higher Zr-O bond. By mitigating the kinetic hindrance and increasing the particle’s stiffness, the proposed Ni-rich cathode shows an impressive 97.6 % capacity retention under a 5 C rate current. This work provides a facile and efficient strategy for large-scale production of fast-charging Ni-rich cathode materials.

Pressure-driven molecule implantation enabling ultrahigh-rate and ultralong-life zinc ion batteries

Durable cathode materials with high specific capacity are essential for aqueous zinc ion batteries (AZIBs). However, vanadium-based materials endure irreversible structural collapse, sluggish diffusion kinetics, and low working voltage. In this study, we propose a unique pressure-driven molecule implantation (PMI) strategy to fabricate a laminar organic–inorganic hybrid cathode (PMI-VO) for AZIBs by coupling polyaniline (PANI) with vanadium oxide. The bipolar protonation of implanted electroactive PANI provides abundant active sites for ion/electron transfer and Zn2+/H+ storage in PMI-VO. Importantly, the formed C-V-O interfacial coupling bonds in the cycling process effectively relieve the intercalation stress and strengthen the redox kinetics and structural integrity of V2O5. In situ infrared spectroscopy and theoretical calculations reveal the PMI-induced multiple ions storage mechanisms in the PMI-VO cathode. Accordingly, PMI-VO cathode performs a superior specific capacity of 522 mAh∙g−1 at 0.2 A∙g−1, a high operating voltage of 0.86 V, a high energy density (387.4 Wh∙kg−1), and splendid long-life stability (over 15,000 cycles at 20 A∙g−1 with 191 mAh∙g−1). Therefore, this pressure-driven molecule implantation strategy provides a pioneering method to fabricate superior cathode materials of advanced AZIBs.

Healable and Conductive Two-Dimensional Sulfur Iodide for High-Rate Sodium Batteries.

Self-healing functional materials can repair cracks and damage inside the battery, ensuring the stability of the battery material structure. This feature minimizes performance degradation during the charging and discharging processes, improving the efficiency and stability of the battery. Here, we have developed a novel healing conductive two-dimensional sulfur iodide (SI4) composite cathode. This process integrates both sulfur and iodine compounds into carbon nanocages, forming a SI4@C core-shell structure. This cathode design improves electrical conductivity and repairability, facilitates rapid activation, and ensures structural integrity, resulting in a typical Na-SI4 battery with high capacity and an exceptionally long cycle life. At 10.0 A g-1, the capacity of the Na-SI4 battery can still reach 217.4 mAh g-1 after more than 500 cycles, and the capacity decay rate per cycle is only 0.06%. In addition, the cathode exhibits a cascade redox reaction involving S and I, contributing to its high capacity. The in situ growth of a carbon shell further enhances the conductivity and structural robustness of the entire cathode. The flexibility and bendability of SI4@C-carbon cloth make it applicable for flexible electronic devices, providing more possibilities for battery design. The strategy of engineering a two-dimensional self-healing structure to construct a superior cathode is expected to be widely applied to other electrode materials. This study provides a new pathway for designing novel binary-conversion-type sodium-ion batteries with excellent long-term cycling performance.

Understanding the Role of Imide-Based Salts and Borate-Based Additives for Safe and High-Performance Glyoxal-Based Electrolytes in Ni-Rich NMC811 Cathodes for Li-Ion Batteries.

Herein, the design of novel and safe electrolyte formulations for high-voltage Ni-rich cathodes is reported. The solvent mixture comprising 1,1,2,2-tetraethoxyethane and propylene carbonate not only displays good transport properties, but also greatly enhances the overall safety of the cell thanks to its low flammability. The influence of the conducting salts, that is, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI), and of the additives lithium bis(oxalato)borate (LiBOB) and lithium difluoro(oxalato)borate (LiDFOB) is examined. Molecular dynamics simulations are carried out to gain insights into the local structure of the different electrolytes and the lithium-ion coordination. Furthermore, special emphasis is placed on the film-forming abilities of the salts to suppress the anodic dissolution of the aluminum current collector and to create a stable cathode electrolyte interphase (CEI). In this regard, the borate-based additives significantly alleviate the intrinsic challenges associated with the use of LiTFSI and LiFSI salts. It is worth remarking that a superior cathode performance is achieved by using the LiFSI/LiDFOB electrolyte, displaying a high specific capacity of 164mAhg-1 at 6C and ca. 95% capacity retention after 100 cycles at 1C. This is attributed to the rich chemistry of the generated CEI layer, as confirmed by ex situ X-ray photoelectron spectroscopy.

Cathode|Electrolyte Interface Engineering by a Hydrogel Polymer Electrolyte for a 3D Porous High-Voltage Cathode Material in a Quasi-Solid-State Zinc Metal Battery by In Situ Polymerization.

This work highlights the development of a superior cathode|electrolyte interface for the quasi solid-state rechargeable zinc metal battery (QSS-RZMB) by a novel hydrogel polymer electrolyte using an ultraviolet (UV) light-assisted in situ polymerization strategy. By integrating the cathode with a thin layer of the hydrogel polymer electrolyte, this technique produces an integrated interface that ensures quick Zn2+ ion conduction. The coexistence of nanowires for direct electron routes and the enhanced electrolyte ion infiltration and diffusion by the 3D porous flower structure with a wide open surface of the Zn-MnO electrode complements the interface formation during the in situ polymerization process. The QSS-RZMB configured with an integrated cathode (i-Zn-MnO) and the hydrogel polymer electrolyte (PHPZ-30) as the separator yields a comparable specific energy density of 214.14Whkg-1 with that of its liquid counterpart (240.38Whkg-1, 0.5MZn(CF3SO3)2 aqueous electrolyte). Other noteworthy features of the presented QSS-RZMB system include its superior cycle life of over 1000 charge-discharge cycles and 85% capacity retention with 99% coulombic efficiency at the current density of 1.0Ag-1, compared to only 60% capacity retention over 500 charge-discharge cycles displayed by the liquid-state system under the same operating conditions.

Improving Zinc-Ion Batteries’ Performance: The Role of Nitrogen Doping in V2O3/C Cathodes

This study presents the synthesis and electrochemical evaluation of nitrogen-doped vanadium oxide (N−V2O3/C) as a cathode material for aqueous zinc-ion batteries (AZIBs), using a hydrothermal method. Compared to undoped V2O3/C, N−V2O3/C exhibits enhanced electrical conductivity, capacity, and electrochemical kinetics, attributed to the incorporation of pyridinic and pyrrolic nitrogen. The initial charge–discharge cycles indicate phase transitions to amorphous vanadium oxides, enhancing conductivity. N−V2O3/C shows a high specific capacity of 168.4 mAh g−1 at 10 A g−1 and remarkable reversibility, highlighted by the transient existence of intermediate species during cycling. Optimal electrochemical performance is achieved with a vanadium-to-nitrogen molar ratio of 2:3, indicating the significant impact of the nitrogen doping concentration on the material’s efficiency. This work underscores the potential of N−V2O3/C as a superior cathode material for AZIBs.

Polyoxovanadate Li7[V15O36(CO3)] and its derivative γ-LiV2O5 as superior performance cathode materials for aqueous zinc-ion batteries

Recently, many reports have been published about polyoxovanadates (POVs) with multiple electrons redox activity for energy storage. However, they are easily transformed into solid-state oxides after calcination. We noted that although dehydrated Li7[V15O36(CO3)] (Li7V15) exhibited a high capacity for lithium-ion batteries (LIBs), it was reported that the electrochemical behavior of the dehydrated sample same as γ-LiV2O5 (γ-LVO) which prepared by annealing the cluster and undehydrated Li7V15 was not redox-active. Interestingly, we were surprised to find that undehydrated Li7V15 and its derivative γ-LVO showed better electrochemical performance than LIBs when first proposed as the cathode to store Zn2+. Both Li7V15 and γ-LVO electrodes provided excellent rate performance and satisfied cyclability (135.0 and 214.1 mAh g−1 at 3 A g−1 after 1000 cycles, respectively). The fast kinetics of Li7V15 and γ-LVO were verified by pseudocapacitive analysis, GITT and EIS tests. Moreover, the Zn2+ storage mechanism and redox behavior of Li7V15 and γ-LVO were examined by ex-situ measurements. First-principles calculations revealed that the Zn2+ was chemisorbed on the clusters and physisorbed between the clusters. This work enriches the POVs cathode chemistry in aqueous energy storage.

CoNi hexacyanoferrate nanoparticles anchored on carbon nanotubes as superior cathode materials for rechargeable aqueous zinc-ion batteries

Prussian blue analogues (PBAs) have attracted growing interest as competitive cathode materials for aqueous zinc-ion batteries (AZIBs). However, their low conductivity and easy structural collapse often lead to poor reversible capacity and cyclability. Herein, cobalt‑nickel hexacyanoferrate (CoNiHCF), a CoNi-Prussian blue analogue, are designed as AZIBs cathode materials for the first time, in which highly uniform CoNiHCF nanocubes are in-situ decorated on carbon nanotubes (CNTs) via a simple co-precipitation method. The resulted CoNiHCF/CNTs composite displays superior zinc ion storage performance, with a great reversible capacity of 124.9 mAh g−1 at the current density of 50 mA g−1, and a high capacity retention of 81.8 % at 3000 mA g−1 for 1000 cycles, which are remarkably superior to those of CoHCF, NiHCF and CoNiHCF. The excellent Zn2+ storage properties of CoNiHCF/CNTs can be ascribed to the bimetallic synergistic effect of Co and Ni as well as the introduction of conductive CNTs skeleton. This study offers a straightforward and efficient method for promoting the application of PBAs-based cathodes in AZIBs.

Study of Zinc Diffusion Based on S, N-Codoped Honeycomb Carbon Cathodes for High-Performance Zinc-Ion Capacitors.

Capacitors with zinc ions, with excellent stabilities, low cost, and high energy density, are expected to be promising energy storage devices. However, the development of zinc-ion capacitors is quietly restricted by low specific capacity and cycling stability. Herein, to overcome these limitations, honeycomb-structured S, N-codoped carbon (SNPC) is constructed by one-pot calcination of waste corn bracts and thiourea. The honeycomb structure of SNPC is demonstrated to provide abundant active sites that can enhance the extron/ion transport, conductivity for high power export, and ion adsorption capacity in energy storage applications, leading to a higher electrochemical performance achieved. The electrolytes of zinc salt have also been studied. It reveals that the SNPC electrode presents the best electrochemical performance in a 2 M ZnSO4 and 0.5 M ZnCl2 electrolyte mixture because in the electrolyte mixture, Cl- can replace the existing bound water in the solvation structure to form an anion-type water-free solvation structure ZnCl42-. The SNPC-800 electrode with a highly improved surface area (∼909.0 m2 g-1) is proved to be more suitable as the electrode than other materials. Aqueous zinc-ion capacitors (ZICs) have been assembled by the honeycomb-structured SNPC-800 as the cathode, which can achieve a relatively wide working voltage range of 0.1-1.8 V. The SNPC-800 ZICs exhibit a superior specific capacity of 179.1 mA h g-1 at 0.1 A g-1. The energy density of SNPC-800 ZICs reaches an impressive value of 89.6 Wh kg-1 at 53.8 W kg-1, and it sustains 28.3 Wh kg-1 at 1997.6 W kg-1. In addition, there is 99.8% capacity retention in the SNPC-800 ZICs over 5000 cycles. The absorption energy in SPNC is much higher than that in undoped CPC, as confirmed by density functional theory, which reveals that introducing of heteroatoms (S, N) has a comparatively active advantage at increasing the Zn-ion storage capacity. This work proposes a practical strategy for the effective recycling of waste biomass materials into honeycomb carbon electrode materials. Moreover, the honeycomb carbon-based ZICs with excellent electrochemical performance and long-term cycling stability possess great potential to be a superior cathode in practical applications.

Nb-doping of cation-disordered rocksalt oxides with B2O3 surface modification for superior performance cathode

As the growing price and inadequate reserves of cobalt, the demand for cobalt-free materials with superior energy density to apply in Li-ion batteries has increased distinctly. Li-rich cation disordered rocksalt (DRX) material has aroused research hotspot because of high specific capacity and wide compositional space. However, irreversible oxygen loss as well as sluggish kinetic raise the problem in large polarization and inevitable capacity decay in cycling process, which have impeded the commercialization of these electrode materials. In this work, we have synthesized cobalt-free boron trioxide (B2O3)-modified Li1.2Ni0.3Ti0.3Nb0.2O2 compounds with cation disordered rocksalt structure through mechanochemical method. It is a fact that B2O3-modified cathodes possess outstanding cyclic stability as well as rate properties. Particularly, the Li1.2Ni0.3Ti0.3Nb0.2O2 electrode with 2.0 wt% B2O3 displayed a competitive capacity of 192.4 mAh/g at 10 mA g−1 and retained 134.7 mAh/g after 100 charge/discharge times. The redox mechanism is explored through ex-situ XPS measurement, verifying the reversible cationic redox of Ni2+/Ni4+ accompanying small Ti4+/Ti3+ reduction and anionic O2−/O− evolution, which results in unusual high capacity. Such an optimized surface modification combines with the Nb doping, can promote Li ion transport, reduce polarization, protect cathode from reacting with electrolyte. These findings provide important implications to improve performance of DRX cathodes.

Pre‐Intercalation of Zn Ions to Enlarge and Stabilize Hierarchical Structure of ZnxMn1‐xSe Cathode for Flexible Zn‐Ion Capacitor

AbstractZn‐ion capacitors (ZICs) assembled from cathodes with diffusion‐controlled behaviors and capacitive anodes have attracted increasing interest thanks to their satisfactory and balanced energy and power densities. However, currently, only two cathode materials of this type, MnO2 and V2O5, are applied to ZICs. MnSe is increasingly being reported to exhibit diffusion‐controlled characteristics in metal‐ion batteries and supercapacitors, yet its insufficient interlayer spacing and unstable structure lead to poor energy storage capacity. Herein, ZnxMn1‐xSe microflowers with nanosheets can be in situ pre‐intercalated with Zn ions to enlarge and stabilize the interlayer spacing of hierarchical porous structure, demonstrating to be a superior cathode for ZICs. During the charging/discharging process of Zn0.14Mn0.86Se electrode, a redox couple at ≈0.6/0.3 V on cyclic voltammetry profile, and a potential plateau appearing at ≈0.2 V on discharge curve is detected, corresponding to the insertion/extraction of Zn ions. Thus, a long discharge time realizes on the discharge curve of flexible ZIC assembled from polyacrylamide gel electrolyte and activated carbon anode, achieving a superb areal capacitance of 2,038.2 mF cm−2 at 1 mA cm−2. This work offers an exemplary effort to unlock fresh cathodes for ZICs.

Promoting Na-ion storage in P2-Na0.67Ni0.33Mn0.67O2 cathode via synergetic Ti and Zn Co-incorporation

P2-Na0.67Ni0.33Mn0.67O2 (NNMO) is regarded as a promising cathode candidate for sodium-ion batteries due to its high energy density. However, the electrochemical performance is hindered by Na+/vacancy order, irreversible P2–O2 phase transition at high voltage (>4.2 V), and harmful oxygen evolution. Herein, a synergetic Zn and Ti co-incorporation tactic is proposed for designing a Na0.67Ni0.29Zn0.04Mn0.63Ti0.04O2 (NNZMTO) cathode to overcome the above-mentioned challenges. First, the incorporated Ti heteroatom could break down Na+/vacancy order of NNMO by taking advantage of a similar ionic radius and substantially different Fermi levels with host Mn atom. Subsequently, the introduced Zn heteroatom could induce local Na–O–Zn configurations, buffer interlayer O2−–O2− electrostatic repulsion, as well as inhibit unfavorable phase transition. Moreover, the d10 band of Zn is lower than the oxygen states, and the Zn behaves like an s/p metal with oxygen, thus avoiding O2 release. Notably, in comparison with highly oxidized (Ni4+/Mn4+O6)δ− octahedron, the partial Na+ for charge neutrality in alkali metal layers could be well maintained in the as-designed (Zn2+/Ti4+O6)δ′−, which could be served as “pillars” to avoid layer gliding and structural collapse in the c-direction. As a result, an excellent electrochemical performance with high specific capacity of 90.9 mA h g−1 at 7 C could be retained for NNZMTO thanks to the synergetic effect from Ti and Zn incorporation. This study provides deep insights for designing superior layered cathode via conducting a rational cations co-incorporation strategy.