High-performance Batteries Research Articles

Flexible and Compact PVDF/PMMA-Based Gel Polymer Electrolytes for High-Performance Sodium Metal Batteries.

Sodium is gaining recognition as a promising alternative to lithium for battery applications, particularly in sodium metal batteries (SMBs), where the performance is critically influenced by the choice of electrolyte. Although conventional organic liquid electrolytes are widely used, they pose significant issues. Gel membrane (GM)-based electrolytes have demonstrated enhanced reliability and stability. Nevertheless, there remains a pressing need to improve their electrochemical and mechanical properties to fulfill the demands of next-generation batteries, which require extended lifespan, rapid charging capabilities, and excellent flexibility. To address these challenges, a compact and flexible GM is developed by gelating a cast Polyvinylidene fluoride (PVDF)/Polymethyl methacrylate (PMMA) blend film. The resulting GM possesses a suitable sodium ionic conductivity of 0.507 mS cm-1 and an impressive ion transference number of 0.47, enabling dendrite-free reversible sodium plating and stripping for up to 300 h at a current density of 0.8 mA cm-2. Furthermore, the effectiveness of sodium dendrite suppression is demonstrated in Na/GM/Na3V2(PO4)3 cells, which exhibit a high discharge capacity and excellent cycling stability. The flexible SMB retains stable voltage output and continues to function even when bent or twisted. This study introduces a novel strategy for creating gel electrolytes for high-performance flexible SMBs.

Unlocking the Ultrafast Deposition Kinetics within Bi-Tailored Core-Shell Structured Carbon Nanofibers for Highly Efficient and Ultrastable Sodium Metal Batteries.

Sodium metal anodes (SMA), featuring high energy content, low electrochemical potential and easy availability, are a compelling option for sustainable energy storage. However, notorious sodium dendrite and unstable solid-electrolyte interface (SEI) have largely retarded their widespread implantation. Herein, porous amorphous carbon fiber embedded with Bi nanoparticles in nanopores (Bi@NC) was rationally designed as a 3D host for SMA. In-situ and ex-situ characterizations, along with theoretical simulations unlock that the in-situ formed Na-Bi alloy significantly accelerates sodium metal nucleation and sodium ion diffusion kinetics, enabling uniform sodium plating within the void spaces and a stable SEI outside the carbon fiber. Particularly, the Bi@NC electrode achieved a high Coulombic efficiency of 99.99% at 3 mA cm-2 and 3 mAh cm-2 in half-cell tests, a cycle life of 1000 hours at 5 mA cm-2 and 10 mAh cm-2, and sustained performance over 600 cycles under harsh conditions under 30 mA cm-2 and 3 mAh cm-2 within symmetrical cells. The full battery assembled with a Na3V2(PO4)3@C cathode and Bi@NC anode delivered long-term cyclability over 800 cycles, demonstrating its potential for flexible application of sodium-based energy storage systems. This work highlights the Bi@NC electrode as a promising candidate for high-performance and flexible sodium metal batteries.

Metal-Organic Coordination Enhanced Metallopolymer Electrolytes for Wide-Temperature Solid-State Lithium Metal Batteries.

The practical application of polymer electrolytes is seriously hindered by the inferior Li+ ionic conductivity, low Li+ transference number (tLi+), and poor interfacial stability. Herein, a structurally novel metallopolymer is designed and synthesized by exploiting a molybdenum (Mo) paddle-wheel complex as a tetratopic linker to bridge organic and inorganic moieties at molecular level. The prepared metallopolymer possesses combined merits of outstanding mechanical and thermal stability, as well as a low glass transition temperature (Tg < -50 °C). Based on this metallopolymer, an advanced metal-organic coordination enhanced metallopolymer electrolyte (MPE) is developed for constructing high-performance solid-state lithium metal batteries (LMBs). Due to the unsaturated coordination of Mo atoms, the uniformly distributed Mo-polyoxometalates (Mo-POMs) in metallopolymer skeleton can effectively bis(fluorosulfonyl)imide anions (FSI-) and promote the dissociation of Li salts. Moreover, dynamic metal-organic coordination bonds endow the MPE with re-processability and self-healing, enabling it to accommodate electrode volume changes and maintain good interfacial contact. Consequently, the MPE achieves a competitive ionic conductivity of 0.712 mS cm-1 (25 °C), a high tLi+ (0.625), and a wide electrochemical stability window (> 5.0 V). This study presents a unique MPE design based on metal-organic coordination enhanced strategy, providing a promising solution for developing wide-temperature solid-state LMBs.

Mxene and GaIn Alloy Nanostructures Regulate Zn Surface Ion Deposition for High-Performance Zinc-Ion Battery.

Zinc is an ideal energy storage material because of its low toxicity, nonflammability, and good biocompatibility. However, the commercial application is seriously hindered due to problems such as dendrite growth, hydrogen evolution, and interface passivation caused by "dead zinc" in the process of cyclic deposition. Herein, a nanoscale deposition dispersion model is designed in order to achieve directional deposition and uniform distribution of zinc ions for the growth of interfacial dendrites. Liquid metal GaIn was combined with Mxene for this nanostructure, which provides a rapid ion transfer channel to achieve lower overpotentials, a more uniform electric field distribution, and stronger corrosion resistance in a core-shell structure to achieve interface reaction suppression. The material was coated on the surface of the zinc metal as an artificial protective layer. It has a better cycle life at 1 mA·cm-2 compared with the bare Zn metal anode, achieving a long cycle time of 1100 h and an ultralow voltage lag (28.1 mV). It maintains the stability for 1000 cycles at 1 mA·cm-2 after assembling the complete battery. This provides a way to improve the performance of zinc-ion secondary batteries and paves the way for the next generation of energy storage devices.

Construction of N-doped carbon/MnO nanoparticles/hollow carbon spheres nested structure with tunable valence state for high-performance aqueous zinc ion batteries enables 10000 cycling stability

The practical applications of manganese-based aqueous zinc ion batteries (AZIBs) have been hindered by issues such as structural collapse, dissolution of active substances, and poor conductivity. Herein, a novel N-doped carbon/MnO nanoparticles/hollow carbon spheres nested structure (HCSs@MnO@NC) is fabricated as the active cathode material for AZIBs by controlled carbothermal reduction strategy. The internal hollow structure mitigates the volume expansion of MnO and improves material stability. The Mn-O-C heterojunction structure accelerates charge transfer and enhances structural stability. By controlling the carbothermal reduction process to adjust the valence state, electrochemical determinations demonstrate that divalent manganese exhibits a higher capacitance contribution rate, which is conducive to a faster ion migration rate. In situ UV–vis is firstly employed to detect the change of Mn2+ concentration in the electrolyte, revealing a Mn2+ deposition phenomenon in addition to the ion embedding mechanism during the initial charge. Owing to these favorable structural characteristics, the prepared HCSs@MnO@NC cathode delivers a specific capacity of 320.5 mAh g−1 at 0.1 A g−1 and maintains an excellent capacity after 10,000 cycles at 3 A g−1. This work can provide a new pathway for constructing advanced AZIBs by optimizing the nanostructure of composite electrode materials.

Supramolecular macrocycle grafted Nb-MXene nanosheets constructing self-supporting framework for high-performance lithium-sulphur batteries

The advancement of lithium-sulphur (Li-S) batteries with high-energy density has been hindered by the high energy conversion barrier of sulphur and the shuttle effect of polysulfides. In this study, we successfully graft monocarboxylic pillar[5]arene (PA5-COOH) onto niobium carbide MXene (Nb2CTx) through an esterification reaction to obtain the PA5-COOH/Nb2C hybrid multi-functional separator. The incorporation of organic molecules increases the interlayer spacing, creating more active sites for capturing polysulfides. Through a combination of experimental and theoretical calculations, we find that the presence of the organic macromolecular structure can facilitate rapid polysulfide conversion, while Nb2CTx provides support sites for PA5-COOH and its larger specific surface area helps mitigate sulphur volume changes. By equipping Li-S batteries with a PA5-COOH/Nb2C separator, the Li-S battery supports an impressive reversible specific capacity of 1317mAh g−1 at 0.2C and demonstrates exceptional rate performance (303 mAh g−1 at 10C). The incorporation of the PA5-COOH/Nb2C hybrid separator expands the application potential of organic macrocyclic molecules and presents a stable self-support structure for developing high-performance lithium-sulphur batteries using macrocycle organic molecules.

Coupling 5 d metallic and conductive Network for promoting polysulfide conversion

The reaction kinetics of lithium-sulfur (Li-S) battery mainly depends on the capture and catalytic conversion efficiency of lithium polysulfide (LiPSs). The unique electron configuration of the 5d metal and the high electrical conductivity of MXene can enhance the interaction between the catalyst and LiPSs. However, the challenge of enhancing the adsorption of LiPSs by regulating the electronic structure of the catalyst with 5d metal and MXene remains unresolved and obscure. In this work, we have developed molybdenum disulfide (MoS2)-tungsten disulfide (WS2) @MXene (MoS2-WS2@MX) heterostructure catalysts for separator coatings in Li-S batteries by introducing W and MXene for the first time. Theoretical calculations demonstrate that the 5 d metallic and conductive MXene coupling effectively modulate the orbital hybridization degree between the catalyst and LiPSs, thereby reducing the energy barrier for LiPSs conversion. Electrochemical test and in situ tests verify the effectiveness of the strategy on the adsorption and conversion of LiPSs. Consequently, the MoS2-WS2@MX based batteries exhibit high initial reversible capacity of 950.3 mAh g−1 and low capacity decay of 0.066 % per cycle over 500 cycles at 2 C, which is superior to most reported catalysts. This study provides a dual regulatory strategy for enhancing catalytic activity, offering valuable insights for the advancement of high-performance Li-S batteries.

Rechargeable lithium-hydrogen gas hybrid batteries.

The global clean energy transition and carbon neutrality call for developing high-performance new batteries. Here we report a rechargeable lithium metal - catalytic hydrogen gas (Li-H) hybrid battery utilizing two of the lightest elements, Li and H. The Li-H battery operates through redox of H2/H+ on the cathode and Li/Li+ on the anode. The universal properties of the H2 cathode enable the battery to demonstrate attractive electrochemical performance, including high theoretical specific energy up to 2632 Wh kg-1, discharge voltage of 3 V, round-trip efficiency of 99.7%, reversible areal capacity of 5~20 mAh cm-2, all-climate characteristics with a wide operational temperature range of -20 ~ 80 °C, and high utilization of active materials. A rechargeable anode-free Li-H battery is further constructed by plating Li metal from cost-effective lithium salts under a low catalyst loading of < 0.1 mg cm-2. This work presents a route to design batteries based on catalytic hydrogen gas cathode for high-performance energy storage applications.

Coordination-Driven Crosslinking Electrolytes for Fast Lithium-Ion Conduction and Solid-State Battery Applications.

Rechargeable batteries paired with lithium (Li) metal anodes are considered to be promising high-energy storage systems. However, the use of highly reactive Li metal and the formation of Li dendrites during battery operation would cause safety concerns, especially with the employment of highly flammable liquid electrolytes. Herein, a general strategy by engineering coordination-driven crosslinking networks is proposed to achieve high-performance solid polymer electrolytes. Through the coordination of metal-organic polyhedra (MOPs) with cellulose-based copolymers, the Li+-conducted hypercrosslinked MOP (CHMOP-Li) polymer network is capable of enabling the rapid transport of Li+. In addition to the high Li+ conductivity (1.02×10-3 S cm-1 at 25 °C), CHMOP-Li electrolyte also exhibits a high Li+ transference number (0.75) and a wide electrochemical stability window. Benefiting from the thermally stable and mechanically strong CHMOP-Li electrolyte film, the short-circuiting of the symmetric batteries is prevented even after 3200 h of cycling and a high specific energy of 300 Wh kg-1 is achieved for the Li-metal battery. The solid-state Li-O2 batteries fabricated with CHMOP-Li electrolyte also show good cycling performance (500 cycles) and high discharge capacity (15740 mAh g-1). The proposed coordination-driven crosslinking strategies offer an alternative route to design high-performance next-generation sustainable battery chemistries.

Mechanical Characterization and Modeling of Large-Format Lithium-Ion Battery Cell Electrodes and Separators for Real Operating Scenarios

This study presents a novel application-oriented approach to the mechanical characterization and subsequent modeling of porous electrodes and separators in lithium-ion cells to gain a better understanding of their real mechanical operating behavior. An experimental study was conducted on the non-linear stiffness of LiNi0.8Co0.15Al0.05O2 and graphite electrodes as well as PE separators, harvested from large-format lithium-ion cells, using compression tests. The mechanical response of the components was determined for different operating conditions, including nominal stress levels, mechanical loading rates, and mechanical cycles. The presented work describes the test procedure, the experimental setup, and an objective evaluation method, allowing for a detailed summary of the observed mechanical behavior. A distinct nominal stress level and mechanical cycle dependency of the non-linear stiffnesses of the porous materials were found. However, no clear dependency on compression rate was observed. Based on the experimental data, a poroelastic mechanical model was utilized to predict the non-linear behavior of these porous materials under real mechanical operating scenarios with a normalized root-mean-squared error less than 5.5%. The results provide essential new insights into the mechanical behavior of porous electrodes and separators in lithium-ion cells under real operating conditions, enabling the accelerated development of high-performing and safe batteries for various applications.

A cellular automata modelling approach for grain growth topological evolution process of ternary cathode materials combined with deep neural networks

Ternary cathode materials are pivotal in high-performance battery technologies, with grain size influencing their electrochemical performance. However, the absence of real-time grain size inspection during material preparation poses challenges in maintaining the consistent quality of ternary cathode materials. To address this, this paper proposes a novel method employing cell automata to model the topological evolution of grain growth in these materials, integrated with deep neural networks (DNN). The grain growth process is divided into two stages: heating and constant temperature. In the heating stage, varying heating rates and plateau temperatures serve as DNN inputs, yielding the primary grain distribution for the cell automata model in the constant temperature stage. Based on cell automata, the grain growth model links the grain growth rate to the grain size distribution in the constant temperature stage. A surface energy constraint rule, based on local curvature and grain boundary surface tension, governs growth rates. The grain boundary growth ratio is also used to create a grain ID transition variable, dictating grain ID conversion in the model. This approach accurately simulates the dynamic evolution of polycrystalline grain size and morphology. Simulation results show that this method effectively models grain growth in ternary cathode materials, offering insights for optimising the sintering process and improving material quality.

Topological Defect-Regulated Porous Carbon Nanoribbon for High-Performance Potassium-Ion Batteries.

Potassium-ion batteries (PIBs) using carbonaceous anode materials have attracted a great deal of research interest. However, the large atomic size of potassium ions inevitably leads to huge volume expansion and the collapse of anodes during intercalation, which greatly hinders rate performance and cycling life. In this work, carbon nanotube-derived porous N-doped carbon nanoribbon (CNR) bundles are designed as an anode for PIBs. These CNR materials are in rich defects which provide fast channels for charge transport and abundant active sites for potassium ion storage. The CNR materials exhibit a maximum capacity of 441.4mAhg-1 at a current density of 0.2Ag-1 after 200 cycles as well as a highly reversible capacity of 263.6mAhg-1 at a current density of 5.0Ag-1 even after 1000 cycles. This work provides guidance for the structure design of nanoribbon materials for high-performance PIBs.

A Bifunctional Iron-Nickel Oxygen Reduction/Oxygen Evolution Catalyst for High-Performance Rechargeable Zinc-Air Batteries.

Efficient and robust electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial for fuel cells, metal-air batteries, and other energy technologies. Here, a highly stable, efficient bifunctional OER/ORR electrocatalyst (FeNi-NC@MWCNTs) is reported and demonstrated its integration and robust performance in an aqueous Zinc-air battery (ZAB). The catalyst is based on neighboring iron/nickel sites (FeNiN6) which are atomically dispersed on porous nitrogen-doped carbon particles. The particles are wrapped in electrically conductive multi-walled carbon nanotubes for enhanced electrical conductivity. Electrocatalytic analyses show high OER and ORR performance (OER/ORR voltage difference = 0.69V). Catalyst integration in a ZAB results in excellent performance metrics, including an open circuit voltage of 1.44V, a specific capacity of 782 mAh g-1 (at j = 15mA cm-2), a peak power density of 218mW cm-2 (at j = 260mA cm-2) and long-term durability over 600 charge/discharge cycles. Combined experimental and theoretical (density functional theory) analyses provide an in-depth understanding of the physical and electronic structure of the catalyst and the role of the FeNi dual atom reaction site. The study therefore provides critical insights into the structure and reactivity of high-performance bifunctional OER/ORR catalysts based on atomically dispersed non-critical metals.

Design and manufacture of structure-function integrated carbon fiber reinforced plastics for composite construction

Structure-function integrated composite can replace traditional structural components to bear loads, offering an innovative solution to reduce overall weight while storing energy in aircraft composite wings. The structural electrolyte featuring high ionic conductivity and tough mechanical properties is one of the vital components to realize high-performance multifunctional structural composite batteries. Herein, a functional ternary hydrogel electrolyte (i.e., MAP electrolyte) is elaborately engineered through the strategical incorporation of multiple hydrogen bonding among polyacrylamide (PAM) with rigid-reinforcing aramid nanofibers (ANFs) and ion-conductive Ti3C2Tx MXene nanosheets. Accordingly, the ANFs fortify the fracture toughness and self-healing properties of MAP hydrogel, and the MXene enables a doubled ionic conductivity of MAP electrolyte (32.48 mS cm−1) than that of pure PAM (16.18 mS cm−1). In addition, the capacity retention of the MAP-based full cell (81.9 %) is double of the liquid electrolyte (40.6 %) within 1000 cycles at 1 A g−1. Impressively, the MAP electrolyte remarkably enhances the flexural performance of structural batteries, with a flexural modulus (14.5 GPa) nearly three times that of structural batteries with liquid electrolytes (5.3 GPa) due to hydrogen-bonded ANFs. Simulation results and mechanical-electrochemical tests further underscore the imperative functions of MAP electrolyte as a structural component to empower the stiffness and maintain the integrity of structural batteries. Moreover, fabricating curved wing scaled components utilizing multi-point flexible forming technology demonstrates the practical feasibility of replacing structural components with complex shapes. This work will expedite the exploitation of structural battery prototypes and their real applications in EVs, UAVs, and electric-powered maritime vehicles.

Entropy Engineering-Modulated D-Band Center of Transition Metal Nitrides for Catalyzing Polysulfide Conversion in Lithium-Sulfur Batteries.

The sluggish sulfur redox kinetics and severe polysulfide shuttle effect seriously restrict the cycling stability and lower the sulfur utilization of lithium-sulfur (Li-S) batteries. Efficient catalytic conversion of polysulfides is deemed a crucial strategy to address these issues, but still suffers from an unclear electronic structure-activity relationship and a limited catalysis performance. Herein, entropy engineering-induced electronic state modulation of metal nitride nanoparticles embedded within hollow N-doped carbon (HNC) polyhedra are theoretically and experimentally constructed as a catalyst to accelerate the redox process of sulfur and suppress polysulfide migration in Li-S batteries. By introducing V, Cr, and Nb elements to engineer the entropy of TiN, the metal d-band center is optimized to approach the Fermi level, significantly facilitating the conversion of sulfur species. Accordingly, the TiVCrNbN@HNC catalyst enables Li-S batteries to achieve a high initial capacity (1299 mAh g-1 at 0.1C) and excellent cycling stability with a low capacity decay rate of 0.086% per cycle after 500 cycles. This work may provide a new insight into entropy engineering in catalyst design for high-performance Li-S batteries.

Eliminating chemo-mechanical degradation of lithium solid-state battery cathodes during >4.5 V cycling using amorphous Nb2O5 coatings.

Lithium solid-state batteries offer improved safety and energy density. However, the limited stability of solid electrolytes (SEs), as well as irreversible structural and chemical changes in the cathode active material, can result in inferior electrochemical performance, particularly during high-voltage cycling (>4.3 V vs Li/Li+). Therefore, new materials and strategies are needed to stabilize the cathode/SE interface and preserve the cathode material structure during high-voltage cycling. Here, we introduce a thin (~5 nm) conformal coating of amorphous Nb2O5 on single-crystal LiNi0.5Mn0.3Co0.2O2 cathode particles using rotary-bed atomic layer deposition (ALD). Full cells with Li4Ti5O12 anodes and Nb2O5-coated cathodes demonstrate a higher initial Coulombic efficiency of 91.6% ± 0.5% compared to 82.2% ± 0.3% for the uncoated samples, along with improved rate capability (10x higher accessible capacity at 2C rate) and remarkable capacity retention during extended cycling (99.4% after 500 cycles at 4.7 V vs Li/Li+). These improvements are associated with reduced cell polarization and interfacial impedance for the coated samples. Post-cycling electron microscopy analysis reveals that the Nb2O5 coating remains intact and prevents the formation of spinel and rock-salt phases, which eliminates intra-particle cracking of the single-crystal cathode material. These findings demonstrate a potential pathway towards stable and high-performance solid-state batteries during high-voltage operation.

Synthesis-Structure-Property of High-Entropy Layered Oxide Cathode for Li/Na/K-Ion Batteries.

Increasing demand for rechargeable batteries necessitates improvements in electrochemical performance. Traditional optimal approaches such as elemental doping and surface modification are insufficient for practical applications of the batteries. High-entropy materials (HEMs) possess stable solid-state phases and unparalleled flexibility in composition and electronic structure, which facilitate rapid advancements in battery materials. This review demonstrates the properties of HEMs both qualitatively and quantitatively, and the mechanisms of their enhancement on battery properties. It also illustrates the progress in high-entropy layered oxide cathode materials (HELOs) for lithium/sodium/potassium ion batteries (LIBs/SIBs/PIBs) in the perspectives of synthesis, characterization and application, and elucidating the synthesis-structure-property relationship. Furthermore, it outlines future directions for high-entropy strategies in battery study: precise synthesis control, understanding of reaction mechanisms through structural characterization, elucidation of structure-performance correlations, and the computational and experimental methods integration for rapid screening and analysis of HEMs. The perspective aims to inspire researchers in the development of high-performance rechargeable batteries.

Holey etching strategy of siloxene nanosheets to improve the rate performance of photo-assisted Li-O2 batteries.

Improving the rate performance is of great significance to achieve high-performance photo-assisted Li-O2 batteries for developing new optimized bifunctional photocatalysts. Herein, a holey etching strategy is developed to prepare porous siloxene nanosheets with a size of 10 nm and few layers (P-siloxene NSs) by a modified Ag+-assisted chemical etching method, and the optimized pore-forming conditions are: Ag+ ion concentration 0.01 mol dm-3, HF concentration 0.565 mol dm-3, and H2O2 concentration 0.327 mol dm-3. By using P-siloxene NSs with a bandgap of 2.77 eV as a novel bifunctional photo-assisted Li-O2 system, the rate performance of the assembled P-siloxene NSs photo-assisted Li-O2 batteries is clearly improved. At a current density of 0.1 mA cm-2, the system shows a low overpotential of 0.35 V, full discharge capacity of 3270 mA h g-1, and 69% round-trip efficiency at 100 cycles. In particular, at a current density of 0.8 mA cm-2, the P-siloxene NSs photo-assisted Li-O2 batteries still give a relatively good charge potential of 3.66 V and a discharge potential of 2.97 V. This work provides a new approach for improving the rate performance of photo-assisted Li-O2 systems and will open up opportunities for the high-efficiency utilization of solar energy in electric systems.

Surface-dominated sodium storage enabled by TiO2 nanosheets with 84 % exposure of (0 0 1) facets for high-performance Na-ion battery anodes

Anatase titanium dioxide (TiO2) has garnered enormous attention as a promising anode material for sodium-ion batteries (SIBs), owing to its non-toxicity, superior structural stability, and cost-effectiveness. Nevertheless, its intrinsic low electrical conductivity poses a substantial challenge to its practical applications. Here, the ultrathin TiO2 nanosheets were obtained. The TiO2 nanosheets with a thickness of ∼8 nm and exposed 84 % (001) facet. The exposed (001) crystal facets and ultrathin nanosheet structure provide abundant active sites for Na-ion adsorption, shortens ion diffusion pathways, enhances reaction kinetics, and significantly boosts the pseudocapacitive effect. This synergistic strategy of exposed (001) facet with nanosheets structure leads to an exceptional capacity of 177.1 mAh/g at 0.1 A/g, and 59 % capacity retention at 5 A/g. This work will contribute to the understanding of facet-dependent electrochemical behavior anode materials for high-performance SIBs.

In situ reconstruction of bimetallic heterojunctions encapsulated in N/P co-doped carbon nanotubes for long-life rechargeable zinc-air batteries

Efficient and stable bifunctional electrocatalysts are crucial for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in high-performance rechargeable zinc-air batteries (ZABs). Despite significant advancements in non-noble metal-based catalysts over the past decades, the rational tuning of various active materials for efficient ORR and OER, along with the identification of genuine active sites, remains a formidable challenge. Encouraged by the development of in-situ characterization technologies, research on bifunctional catalysts for ZABs has gradually shifted to exploring the true active sites and investigating catalyst evolution and degradation, which is vital for further breakthroughs in bifunctional catalysts. In this study, we developed a facile method to encapsulate bimetallic heterojunction CoFe/CoFeP in N/P co-doped carbon nanotubes (CNTs) as a bifunctional catalyst for ZABs. This unique heterojunction structure prevents the dissolution and erosion of transition metals, enhances continuous electron transfer and mass transport, and effectively boosts the catalyst's bifunctional activity and stability. Importantly, ex-situ and in-situ techniques were employed to track the dynamic ORR and OER catalytic processes, capture the reconstructions of bifunctional catalysts, and reveal the real active sites. The CoFe/CoFeP@NPC catalyst exhibits superior bifunctional catalytic activity and stability, especially with a half-wave potential of 0.887 V for ORR and 1.55 V at 10 mA cm−2 for OER. Impressively, the assembled rechargeable ZABs demonstrate a high-power density (550 mW cm−2), a low charge-discharge voltage difference (0.7 V), and ultralong cycling for over 1600 h.