High Gravimetric Energy Density Research Articles

Ultrasimple air-annealed pure graphene oxide film for high-performance supercapacitors

Realizing both high gravimetric and volumetric specific capacitances (noted as CW and CV, respectively) is an essential prerequisite for the next-generation, high performance supercapacitors. However, the need of electronic/ionic transport for electrochemical reactions causes a “trade-off” between compacted density and capacitance of electrode, thereby impairing gravimetric or volumetric specific capacitances. Herein, we report a high-performance, film-based supercapacitor via a thermal reduction of graphene oxide (GO) in air. The reduced, layer-structured graphene film ensures high electrode density and high electron conductivity, while the hierarchical channels generated from reduction-induced gas releasing process offer sufficient ion transport pathways. Note that the resultant graphene film is employed directly as electrodes without using any additives (binders and conductive agents). As expected, the as-prepared electrodes perform particularly well in both CW (420F g−1) and CV (360F cm−3) at a current density of 0.5 A g−1. Even at an ultrahigh current density of 50 A g−1, CW and CV maintain in 220F g−1 and 189F cm−3, respectively. Furthermore, the corresponding symmetric two-electrode supercapacitor achieves both high gravimetric energy density of 54 W h kg−1 and high gravimetric power density of 1080 W kg−1, corresponding to volumetric energy density of 46 W h L-1 and volumetric power density of 917 W L-1.

Multi-hierarchical earbuds-ball-like silicon suboxide-carbon hybrids design for high-performance lithium storage

Silicon suboxide (SiOx) is considered a promising substitute for silicon (Si) anode materials in lithium-ion batteries due to its high specific capacity (>2200 mAh g−1) and improved cycling performance. However, its volume expansion (∼200%) and low conductivity cannot be ignored. Here, inspired by earbuds, we design and mass synthesize (240 g h−1) the earbuds-like three-dimensional SiOx nanonetworks (3D-SiOx NNs) by a radio-frequency thermal plasma (RF-plasma) system. The spray drying technology is used to further accelerate the winding of 3D-SiOx NNs to prepare micron-sized multi-hierarchical earbuds-ball-like SiOx/C (E-SiOx/C) with enhanced elasticity and high tap density. As anodes, E-SiOx/C exhibits the high gravimetric/volumetric specific capacity of 1790 m Ah g−1/1137 m Ah cm−3 and excellent rate cycling performance (1480 m Ah g−1 at 2.0 A g−1 for 700 cycles). In addition, full battery constructed with LiNi0.5Co0.2Mn0.3O2 cathode exhibit high gravimetric energy density of 530.9 Wh kg−1 and impressive cycling performance (513.9 Wh kg−1 for 100 cycles), manifesting great promise for the application of high-performance batteries.

Garnet solid electrolyte blended LiNi0.6Mn0.2Co0.2O2 as high-voltage stable cathodes for advanced lithium-ion batteries

Ni-rich LiNi1-xCox/2Mnx/2O2 layered materials have been widely adopted as cathodes for current electric vehicles (EVs) due to their high gravimetric and volumetric energy densities. However, their high-voltage instability (e.g., > 4.3 VvsLi) limited their usable capacities corresponding to about 60 – 70 % of theoretical capacities. The major problems of high-voltage operation stem from instability of Ni3+/4+ at cathode-electrolyte interphase (CEI) in contact with electrolytes. Here we propose garnet-type Li6.7La3Zr1.7Ta0.3O12 (LLZT) solid-electrolyte-blended LiNi0.6Mn0.2Co0.2O2 (NMC) as high-voltage stable cathodes. The LLZT not only passivates the CEI but scavenges protons and moisture in electrolytes. From well-balanced ionic and electronic transport properties, 5 wt% LLZT blended NMC cathodes delivered enhanced electrochemical performances in full-cells. Unlike other complicated coating processes, our proposed solid-electrolyte blending approach can be readily implementable in commercial Li-ion batteries due to its manufacturing friendliness, energy saving, and cost effectiveness.

Conjugated diketone-linked polyimide cathode material for organic lithium-ion batteries

Aromatic polyimides have been considered promising organic cathode materials for lithium-ion batteries (LIBs) due to their excellent solvent resistance, superior electrochemical capability and highly designable structure. However, the inferior intrinsic conductivity and limited redox-active sites lead to their suboptimal comprehensive electrochemical performance and restrict their applications in LIBs. Herein, a novel conjugated diketone-based polyimide (PTN) cathode material with multiple carbonyl redox sites is proposed and prepared for LIBs. The integration of electron-withdrawing π-conjugated diketone with naphthimide can effectively regulate the electronic structure and elevate the working potential of the polyimide-based cathode, and improve its comprehensive electrochemical performance. The PTN-based cathode delivers a high specific capacity of 213.4 mAh g−1, excellent cycling stability (97.3% capacity retention after 2000 cycles at 2000 mA g−1) and high rate performance (78.2% capacity retention at 2000 mA g−1 vs. 50 mA g−1), high gravimetric energy density (380 Wh kg−1) at a high power density (4417 W kg−1) simultaneously. This comprehensive electrochemical performance is among the best results of reported polyimide cathode materials and suggests that PTN has great potential in energy storage applications.

Zinc-Ion Storage Mechanism of Polyaniline for Rechargeable Aqueous Zinc-Ion Batteries.

Aqueous multivalent ion batteries, especially aqueous zinc-ion batteries (ZIBs), have promising energy storage application due to their unique merits of safety, high ionic conductivity, and high gravimetric energy density. To improve their electrochemical performance, polyaniline (PANI) is often chosen to suppress cathode dissolution. Herein, this work focuses on the zinc ion storage behavior of a PANI cathode. The energy storage mechanism of PANI is associated with four types of protonated/non-protonated amine or imine. The PANI cathode achieves a high capacity of 74 mAh g−1 at 0.3 A g−1 and maintains 48.4% of its initial discharge capacity after 1000 cycles. It also demonstrates an ultrahigh diffusion coefficient of 6.25 × 10−9~7.82 × 10−8 cm−2 s−1 during discharging and 7.69 × 10−10~1.81 × 10−7 cm−2 s−1 during charging processes, which is one or two orders of magnitude higher than other reported studies. This work sheds a light on developing PANI-composited cathodes in rechargeable aqueous ZIBs energy storage devices.

Aqueous Quaternary Polymer Binder Enabling Long-Life Lithium-Sulfur Batteries by Multifunctional Physicochemical Properties.

Lithium-sulfur batteries (LSBs) have been considered promising candidates for application in high-density energy storage systems owing to their high gravimetric and volumetric energy densities. However, LSB technology faces many barriers from the intrinsic properties of active materials that need to be solved to realize high-performance LSBs. Herein, an aqueous binder, that is, PPCP, based on polyethyleneimine (PEI), polyvinylpyrrolidone (PVP), citric acid (CA), and polyethylene oxide (PEO), was developed. The synthesized PPCP binder has incredible mechanical properties, suitable viscosity, and essential functional groups for developing an effective and reliable LSB system. This study demonstrates that CA is crucial in cross-linking PEI-PVP polymer molecules, and PEO segments significantly enhance the flexibility of the PPCP binder; thus, the binder can mechanically stabilize the cathode structure over many operating cycles. The redistribution of active materials during the charge-discharge processes and reduction of the shuttle effect originate from the excellent chemical interactions of PPCP with lithium polysulfides, which is confirmed by the density functional theory calculation, enabling an ultra-long electrochemical cycle life of 1800 cycles with a low decay rate of 0.0278% cycle-1.

S-doped graphene nano-capsules toward excellent low-temperature performance in Li-ion capacitors

The electrochemical properties of LICs are greatly decreased at a low-temperature condition due to the sluggish Li-ion storage kinetics coupled with poor structural stability. Herein, S-doped graphene nano-capsules (SGCs) with good dispersibility is rational designed and serves as both the anode and cathode in symmetric LICs. At room temperature, all the half-cells of SGCs exhibit excellent high capacity, outstanding rate performance and ultra-long cycling stability. Furthermore, the assembled SGCs//SGCs LICs shows a high gravimetric energy density of 249.9 W h kg−1 at 2116.7 W kg−1 and high volumetric energy density of 172.4 W h L−1 at 1460.5 W L−1 coupled with 95.4% capacity retention for 10000 cycles. Even at −30 °C, It still displays 179.6 W h kg−1 at 1658.2 W kg−1 and 68.8 W h kg−1 at 4755.7 W kg−1 coupled with 84.3% capacity retention for 10000 cycles. Furthermore, a fabricated density functional theory (DFT) further demonstrates that the doped S atom plays a key role in enhancing the electronic conductivity and Li+ storage capability. Our results offer a promising application reserve force for the next generation energy storage devices in LICs.

Investigation into the morphological implications on electron transfer dynamics of lithium peroxides by scanning electrochemical microscopy

AbstractLithium–air batteries are highlighted as one of promising next generation battery technology with high gravimetric energy density. To date, however, cyclability of lithium–air batteries has been low, insufficient for commercial use. Many recent research accounts focused on understanding the mechanism of the discharge reaction in attempts to improve the cyclability, and revealed that two structurally distinct lithium peroxide species form during discharge, thin films and toroids, among which toroids formation results in beneficial effects in both cyclability and overall discharge capacity. In this work, scanning electrochemical microscopy was applied to investigate electron transfer dynamics of the two lithium peroxide species, from which a much faster surface electron transfer was observed from lithium peroxide toroids compared to that of thin films. The difference is postulated to stem from the difference in the formation mechanism of the two species.

Innovative battery thermal management system based on hydrogen storage in metal hydrides for fuel cell hybrid electric vehicles

This study proposes a new approach for dealing with the thermal management of batteries in fuel cell hybrid electric vehicles, by introducing a new concept of on-board energy storage system which integrates the battery pack with a metal hydride tank. The rationale behind this solution is to use the exothermic absorption and endothermic desorption processes of hydrogen in metal hydrides for heating and cooling the battery pack, respectively, thus ensuring an optimal thermal management control. An experimental investigation is carried out on a prototype in order to proof the concept and preliminary assess its feasibility for actual implementations. The results show that the system is capable to effectively control the temperature variations within the battery pack: for 1C and 1.5C constant-current discharge tests, a desorption of 30%–40% of hydrogen, over the total amount stored into the metal hydride tank of the system, allows the final average temperature of the battery pack to be around 15 °C lower than the one reached without thermal management. Moreover, it is found that the system is potentially capable of providing a suitable thermal management for more than four hours under realistic driving conditions. The proposed energy storage system also achieves inherently high gravimetric and volumetric energy densities, with theoretical values equal to 182 Wh/kg and 530 Wh/L, respectively. These estimates represent reference values for further design improvements.

Model-Based Design of High Energy All-Solid-State Li Batteries with Hybrid Electrolytes

As the aircraft industry becomes more committed to sustainable aviation, hybrid-electric propulsion systems containing batteries with higher gravimetric energy density attract increasing attention to reduce fuel consumption. Future aircrafts could benefit from next-generation chemistries like oxide-based all-solid-state Li-battery (ASSB) technologies. However, producing and evaluating a wide range of design parameters for maximising the gravimetric energy density of ASSB experimentally is both time- and resource-intensive. Physics-based modelling promises to identify optimal designs for battery cells with respect to high gravimetric energy density more time and cost-efficient. In this regard, we applied a pseudo-two-dimensional model for the model-based evaluation of Li-ASSB with various hybrid electrolytes containing oxide and polymer electrolytes. This way we elucidate which electrolyte performs well with present technology and which has the potential to become an attractive alternative in the future. After identifying design variables to improve ASSB with the help of sensitivity analysis, a genetic algorithm is used to predict the optimal design parameters to achieve higher gravimetric energy density. The conducted study reveals that ASSB based on 12.7 vol% of garnet Li6.4La3Zr1.4Ta0.6O12 (LLZTO) is the best option based on present manufacturing constraints. Hybrid electrolytes based on 10 wt% of Li1.3Al0.3Ti1.7(PO4)3 (LATP) could be promising for future aircrafts with further improvements in ASSB manufacturing process.

Zinc-ion hybrid supercapacitors with ultrahigh areal and gravimetric energy densities and long cycling life

Zinc ion hybrid supercapacitor (ZIHSC) with promising energy and power densities is an excellent answer to the ever-growing demand for energy storage devices. The restricted lifespan due to the dendrite formation on metallic zinc (Zn) is one of the main roadblocks. Herein, we investigate the electrochemical capability of oxygen-enriched porous carbon nanofibers (A-CNF) and nitrogen, oxygen-enriched porous carbon nanofibers (N-CNF) cathode materials for structural ZIHSCs. To this end, a series of samples with different chemical compositions (N and O contents) are prepared to present deep insight into the electrochemical mechanism between N/O doping and Zn-ion storage. The as-prepared ZIHSC in the presence of N-CNF cathode and ZnCl2 electrolyte offers a battery-level gravimetric energy density of 143.2 Wh kg−1 at a power density of 367.1 W kg−1. The free-standing N-CNF electrodes in ZIHSCs enjoy delivering an outstanding areal energy density of 110.4 µWh cm−2 at 0.24 mW cm−2, excellent rate capability, and noticeable cycling stability over 10,000 cycles at 10 A g−1 with less than 7% decay. It was also concluded that active pyrrolic N dopants might deliver and facilitate more pseudocapacitance in ZIHSCs than other N configurations,resulting in higher adsorption/ desorption and insertion/extraction process of ZnCl+. Taking advantage of the beneficial properties of a free-standing continuous cathode, this novel generation of structural cathode material offers high areal and gravimetric energy densities and mechanical properties in a single zinc-ion-based package.

Multimodal Capturing of Polysulfides by Phosphorus-Doped Carbon Composites for Flexible High-Energy-Density Lithium-Sulfur Batteries.

The widespread adoption of Li-ion batteries is currently limited by their unstable electrochemical performance and high flammability under mechanical deformation conditions and a relatively low energy density. Herein, high-energy-density lithium-sulfur (Li-S) batteries are developed for applications in next-generation flexible electronics and electric vehicles with long cruising distances. Freestanding high-S-loading carbon nanotubes cathodes are assembled with a phosphorus (P)-doped carbon interlayer coated on commercial separators. Strategies for the active materials and structural design of both the electrodes and separators are highly efficient for immobilizing the lithium polysulfides via multimodal capturing effects; they significantly improve the electrochemical performance in terms of the redox kinetics and cycling stability. The foldable Li-S cells show stable specific capacities of 850 mAh g-1 over 100 cycles, achieving high gravimetric and volumetric energy densities of 387Wh kgcell -1 and 395Wh Lcell -1 , respectively. The Li-S cells show highly durable mechanical flexibilities under severe deformation conditions without short circuit or failure. Finally, the Li-S battery is explored as a light-weight and flexible energy storage device aboard airplane drones to ensure at least fivefold longer flight times than traditional Li-ion batteries. Nanocarbon-based S cathodes and P-doped carbon interlayers offer a promising solution for commercializing rechargeable Li-S batteries.

High-energy–density carbon-coated bismuth nanodots on hierarchically porous molybdenum carbide for superior lithium storage

The use of carbon-based supports, such as graphene and porous carbon, is a well-established approach to overcome the rapid capacity fading issues associated with alloy-based anode materials in lithium-ion batteries (LIBs). However, adopting carbonaceous materials that typically exhibit a low density eventually diminishes the primary purpose of alloys as high-energy–density anode materials. In this study, we introduce three-dimensional hierarchically porous molybdenum carbide (PMC) with high energy density, robust mechanical strength, and high electronic conductivity, which make it a promising alternative support for suppressing the huge volume expansion of alloying-based materials. Carbon-coated, ultrasmall Bi nanodots with an average size of 6.4 nm are uniformly embedded on the PMC surface (denoted as C-Bi/PMC) by facilitating heterogeneous nucleation. When tested as an anode in an LIB, the C-Bi/PMC electrode exhibits a high reversible capacity of 422 mAh g−1 at 50 mA g−1, high-rate capacity of 268 mAh g−1 at 1000 mA g−1, and long-term stability of 400 mAh g−1 at 250 mA g−1 over 500 cycles followed by 0.002 mAh g−1 decay per cycle at 5000 mA g−1 over subsequent 1000 cycles. When paired with LiNi0.5Co0.2Mn0.3O2 cathode as full-cell LIBs, the C-Bi/PMC anode deliver high gravimetric and volumetric energy densities of 352 Wh kg−1 and 563 Wh L–1, respectively. In-situ X-ray diffraction patterns captured during cycling reveal that the Li+-ion insertion mechanism in the voltage plateau region at 0.7–1.0 V consists of the intercalation between Bi layers followed by the formation of triclinic LiBi phase and the subsequent transition of triclinic LiBi to cubic Li3Bi phase.

Applications of Nickel‐Based Electrocatalysts for Hydrogen Evolution Reaction

The desire to exploit clean and sustainable energy sources with high gravimetric energy density has greatly inspired the exploration of hydrogen energy as an affordable alternative to fossil energy. Electrocatalytic water splitting is an efficient method for the low‐cost production of pure H2, but the use of platinum (Pt)‐like active electrocatalysts for the hydrogen evolution reaction (HER) remains necessary. In attempts to replace high‐value, scarce Pt catalysts, nickel‐based materials are being developed, as earth‐abundant HER electrocatalysts. Recently, a number of advanced nickel (Ni)‐based catalysts have been developed by rational synthesis strategies, including morphology control, structure tailoring, and interface engineering, significantly improving the HER performance. This review summarizes recent achievements in the application of Ni‐based HER electrocatalysts and demonstrates the advantages of each category in enhancing the HER performance. The current progress in the theory of water evolution and various modern techniques for characterizing catalysts are also reviewed, along with the rational design of Ni‐based nanostructure catalysts. Finally, the challenges in the practical applications of Ni‐based HER catalysts are highlighted.

Complex permittivity‐dependent plasma confinement‐assisted growth of asymmetric vertical graphene nanofiber membrane for high‐performance Li‐S full cells

AbstractVertical graphene (VG), possessing superior chemical, physical, and structural peculiarities, holds great promise as a building block for constructing a high‐energy density lithium‐sulfur (Li‐S) battery. Therefore, it is desirable to develop a new VG growth technique with a novel structure to enable wide applications. Herein, we devise a novel complex permittivity‐dependent plasma confinement‐assisted VG growth technique, via asymmetric growing a VG layer on one side of N‐doped carbon nanofibers for the first time, using a unique lab‐built high flux plasma‐enhanced chemical vapor deposition system, as a bifunctional nanofiber membrane to construct Li‐S batteries with low negative/positive (N/P) and electrolyte/sulfur (E/S) ratios. The unique nanofiber membrane could simultaneously protect the cathode and anode, enabling an excellent electrochemical performance with low N/P and E/S ratios in Li‐S batteries. Such a full cell delivers high gravimetric energy density and volumetric energy density of 340 Wh kg−1 and 547 Wh L−1, respectively, at low N/P (2:1) and E/S (4:1) ratios. Furthermore, a pouch cell achieves a high areal capacity of 7.1 mAh cm−2 at a sulfur loading of 6 mg cm−2. This work put forward a novel pathway for the design of high‐energy density Li‐S batteries.image

A “Three‐Region” Configuration for Enhanced Electrochemical Kinetics and High‐Areal Capacity Lithium–Sulfur Batteries

AbstractA main hurdle for the commercial application of lithium–sulfur (Li–S) batteries lies in inadequate loading of sulfur due to a huge volume change over charging–discharging, poor electric conductivity of sulfur and associated sulfides, and the shuttling effect of lithium polysulfides (LiPS). Herein, a universal “three‐region” configuration including: Region I (sulfur source region), Region II (LiPS electrocatalysis region), and Region III (multi‐functional shield) for high‐areal capacity Li–S batteries is proposed. Mechanism of the configuration including the competitive relationship between Region II and Region III based on the Sabatier principle is further confirmed through density functional theory theoretical simulation and a series of in situ experimental methods. Compared with a conventional mechanical mixing electrode structure, it is demonstrated that the orderly integration “three‐region” configuration is able to prevent shuttling of LiPS effectively, which delivers high gravimetric energy density at the sulfur loading of 10.7 mg cm−2. Furthermore, a pouch cell achieves a high capacity of 148.15 mAh at a sulfur loading of 108 mg, which is by far higher than that of most previous batteries and pouch Li–S cells. Impressively, with bending and even partial damage, the pouch cell can still work normally, showing considerable safety.

Assessing the Feasibility of a Cold Start Procedure for Solid State Batteries in Automotive Applications

This paper addresses the thermal management of a solid polymer electrolyte battery system, which is currently the only commercialized solid-state battery chemistry. These batteries aim to increase the range of electric vehicles by facilitating a lithium metal anode but are limited by operational temperatures above 60 °C. The feasibility of a cold start procedure is examined, which would enable a solid polymer battery to be used, without preconditioning, in a wide variety of ambient temperatures. The proposed solution involves dividing the solid-state battery into smaller sub-packs, which can be heated and brought online more quickly. Thermal modelling shows a cold start procedure is theoretically feasible when using a small liquid electrolyte lithium battery at the start. The key bottlenecks are the rate at which the solid-state batteries can be heated, and the discharge rates they can provide. After resistive heating is used for the first solid-state module, all subsequent heating can be provided by waste heat from the motor and operating battery modules. Due to the insulation required, the proposed system has lower volumetric, but higher gravimetric energy density than liquid electrolyte systems. This work suggests that with suitable system-level design, solid-state batteries could be widely adopted despite temperature constraints.

Hierarchical conformal coating enables highly stable microparticle Si anodes for advanced Li-ion batteries

Microsized silicon powders have great potential for high capacity anode materials in next-generation lithium ion batteries, because of the high gravimetric and volumetric energy densities, ease of mass production and low costs. However, large volume change and consequently rapid capacity fading upon lithiation and delithiation prevent its practical applications. Herein, we demonstrate an effective hierarchical conformal coating strategy for high-performance microsized Si anodes. The Si-based composites consist of an amorphous Li-Si-O inner coating layer and a graphene outer encapsulation layer, which are prepared by coupling reactive milling with electrostatic self-assembly. This unique hierarchical conformal coating structure not only strengthens the mechanical property (31.8 GPa for the elastic modulus) and promotes the ionic diffusion (2.03 × 10−10 cm2 s−1) of Si anode, but also effectively stabilizes the electrode/electrolyte interfaces and increases the electronic conductivity. As a result, a high reversible capacity (1450 mA⋅h g−1 at 0.1 A g−1), good cycling stability (97.7% of capacity retention from the 2nd to the 310th cycle at 0.5 A g−1), and high rate capability (703 mA⋅h g−1 at 5 A g−1) have been successfully achieved. These findings provide new insights into the improvement of electrochemical properties of microsized Si composite anodes for high-performance Li-ion batteries.

Hydrogen as a Potential Fuel for the Shipping Industry

Mobility is a socioeconomic concept, and the demand for it is only going to grow in importance in the foreseeable future. Clean, cost-effective, and ecologically acceptable modes of transportation should be used wherever possible. Hydrogen is an attractive synthetic energy source for the transportation industry because of its high gravimetric energy density and availability in combined form throughout the world. In contrast, its oxidation component somehow doesn't contribute to greenhouse emissions, enabling it a potential replacement to fossil fuels. Its economically practical electricity generated by sustainable resources, on-board collection to give a required driving range, employment of long-lasting types of energy, and the construction of infrastructures for its supply continue to be important challenges. Using hydrogen energy source presents a variety of environment related implications, which are covered in this article. Recent developments in the manufacturing, transport, administration, and transport of hydrogen also are mentioned. This study finds that nonrenewable sources now dominate hydrogen manufacturing processes; nevertheless, improvements and encouragement of the use of renewable sources for hydrogen production are required in order to make it completely sustainable.

An altered nanoemulsion assembly strategy for in-situ synthesis of Co2P/NP-C nanospheres as advanced oxygen reduction electrocatalyst for zinc-air batteries

The design of highly active and stable non-noble metal catalysts for oxygen reduction reaction (ORR) is indispensable for metal-air batteries. Herein, an altered nanoemulsion assembly approach is developed to synthesize fine Co 2 P dispersed in N, P doped carbon nanospheres (Co 2 P/NP-C) as prominent ORR electrocatalyst for zinc-air batteries (ZABs). A high half-wave potential of 0.81 V vs. RHE and a limiting current density of 4.54 mA cm −2 is exhibited for Co 2 P/NP-C, which are comparable with those of commercial Pt/C, indicating excellent ORR electrocatalytic activity. Moreover, a big peak power density of 152.4 mW cm −2 and a high gravimetric energy density of 1286.0 Wh kg Zn −1 are delivered for the assembled primary ZAB using Co 2 P/NP-C as cathode catalyst with a high open circuit voltage of 1.448 V. The excellent performance should be attributed to the in-situ formed Co 2 P nanoparticles and N, P heteroatoms in nanospherical carbon matrix with high accessible surface area, which both provide sufficient catalytic active sites and ensure efficient mass/charge transport in ORR process. • An altered nanoemulsion assembly strategy was used to prepare Co 2 P/NP-C nanospheres. • Co 2 P nanocrystallites and N, P heteroatoms were in-situ formed in carbon matrix. • High activity and stability for catalyzing oxygen reduction reaction were achieved. • The as-assembled zinc-air battery showed high power density and specific capacity.