Tag Archives: #batteries

Researchers Developed A New Method to Recycle Batteries Using A Ground-breaking New Approach (Chemistry)

Researchers at the University of Leicester have developed a new method to recycle electric vehicle batteries using a ground-breaking new approach that many will have experienced in the dentist’s chair.

The Faraday Institution project on the recycling of lithium-ion batteries (ReLiB) led by Professor Andy Abbott at the University of Leicester used a new method, involving ultrasonic waves, to solve a critical challenge: how to separate out valuable materials from electrodes so that the materials can be fully recovered from batteries at the end of their life.

Current recycling methods for lithium-ion battery recycling typically feed end-of-life batteries into a shredder or high-temperature reactor. A complex set of physical and chemical processes are subsequently needed to produce useable materials. These recycling routes are energy intensive and inefficient.

If an alternate approach is taken and end-of-life batteries are disassembled rather than shredded, there is the potential to recover more material, in a purer state. The disassembly of lithium-ion batteries has been shown to recover a high yield (around 80% of the original material) in a purer state than was possible using shredded material.

The stumbling block – of how to remove and separate critical materials (such as lithium, nickel, manganese and cobalt) from used batteries in a fast, economical and environmentally-friendly way – can now be avoided thanks to the new approach which adapts technology currently in widespread use in the food preparation industry.

The ultrasonic delamination technique effectively blasts the active materials required from the electrodes leaving virgin aluminium or copper. The process proved highly effective in removing graphite and lithium nickel manganese cobalt oxides, commonly known as NMC.

The research has been published in Green Chemistry and the research team led by Professor Abbott have applied for a patent for the technique.

Professor Abbott said:

“This novel procedure is 100 times quicker and greener than conventional battery recycling techniques and leads to a higher purity of recovered materials.

“It essentially works in the same way as a dentist’s ultrasonic descaler, breaking down adhesive bonds between the coating layer and the substrate.

“It is likely that the initial use of this technology will feed recycled materials straight back into the battery production line. This is a real step change moment in battery recycling.”

Professor Pam Thomas, CEO, The Faraday Institution commented:

“For the full value of battery technologies to be captured for the UK, we must focus on the entire life cycle — from the mining of critical materials to battery manufacture to recycling — to create a circular economy that is both sustainable for the planet and profitable for industry.”

Faraday Institution researchers have been focused on the life cycle of the battery – from their first production to their re-use in secondary applications to their eventual recycling, to ensure that the environmental and economic benefits from Electric Vehicle batteries are fully realised.

The research team are in initial discussions with several battery manufacturers and recycling companies to place a technology demonstrator at an industrial site in 2021, with a longer-term aim to license the technology.

The research team has further tested the technology on the four most common battery types and found that it performs with the same efficiency in each case.

Featured image: Diagram showing the ultrasonic process which assists in the delamination of lithium-ion batteries. © University of Leicester

Provided by University of Leicester

Low-cost Imaging Technique Shows How Smartphone Batteries Could Charge in Minutes (Chemistry)

Researchers have developed a simple lab-based technique that allows them to look inside lithium-ion batteries and follow lithium ions moving in real time as the batteries charge and discharge, something which has not been possible until now.

Using the low-cost technique, the researchers identified the speed-limiting processes which, if addressed, could enable the batteries in most smartphones and laptops to charge in as little as five minutes.

The researchers, from the University of Cambridge, say their technique will not only help improve existing battery materials, but could accelerate the development of next-generation batteries, one of the biggest technological hurdles to be overcome in the transition to a fossil fuel-free world. The results are reported in the journal Nature.

While lithium-ion batteries have undeniable advantages, such as relatively high energy densities and long lifetimes in comparison with other batteries and means of energy storage, they can also overheat or even explode, and are relatively expensive to produce. Additionally, their energy density is nowhere near that of petrol. So far, this makes them unsuitable for widespread use in two major clean technologies: electric cars and grid-scale storage for solar power.

“A better battery is one that can store a lot more energy or one that can charge much faster – ideally both,” said co-author Dr Christoph Schnedermann, from Cambridge’s Cavendish Laboratory. “But to make better batteries out of new materials, and to improve the batteries we’re already using, we need to understand what’s going on inside them.”

To improve lithium-ion batteries and help them charge faster, researchers need to follow and understand the processes occurring in functioning materials under realistic conditions in real time. Currently, this requires sophisticated synchrotron X-ray or electron microscopy techniques, which are time-consuming and expensive.

“To really study what’s happening inside a battery, you essentially have to get the microscope to do two things at once: it needs to observe batteries charging and discharging over a period of several hours, but at the same time it needs to capture very fast processes happening inside the battery,” said first author Alice Merryweather, a PhD student at Cambridge’s Cavendish Laboratory.

The Cambridge team developed an optical microscopy technique called interferometric scattering microscopy to observe these processes at work. Using this technique, they were able to observe individual particles of lithium cobalt oxide (often referred to as LCO) charging and discharging by measuring the amount of scattered light.

They were able to see the LCO going through a series of phase transitions in the charge-discharge cycle. The phase boundaries within the LCO particles move and change as lithium ions go in and out. The researchers found that the mechanism of the moving boundary is different depending on whether the battery is charging or discharging.

“We found that there are different speed limits for lithium-ion batteries, depending on whether it’s charging or discharging,” said Dr Akshay Rao from the Cavendish Laboratory, who led the research. “When charging, the speed depends on how fast the lithium ions can pass through the particles of active material. When discharging, the speed depends on how fast the ions are inserted at the edges. If we can control these two mechanisms, it would enable lithium-ion batteries to charge much faster.”

“Given that lithium-ion batteries have been in use for decades, you’d think we know everything there is to know about them, but that’s not the case,” said Schnedermann. “This technique lets us see just how fast it might be able to go through a charge-discharge cycle. What we’re really looking forward to is using the technique to study next-generation battery materials – we can use what we learned about LCO to develop new materials.”

“The technique is a quite general way of looking at ion dynamics in solid state materials, so you can use it on almost any type of battery material,” said Professor Clare Grey, from Cambridge’s Yusuf Hamied Department of Chemistry, who co-led the research.

The high throughput nature of the methodology allows many particles to be sampled across the entire electrode and, moving forward, will enable further exploration of what happens when batteries fail and how to prevent it.

“This lab-based technique we’ve developed offers a huge change in technology speed so that we can keep up with the fast-moving inner workings of a battery,” said Schnedermann. “The fact that we can actually see these phase boundaries changing in real time was really surprising. This technique could be an important piece of the puzzle in the development of next-generation batteries.”

Reference: Merryweather, A.J., Schnedermann, C., Jacquet, Q. et al. Operando optical tracking of single-particle ion dynamics in batteries. Nature 594, 522–528 (2021). https://doi.org/10.1038/s41586-021-03584-2

Provided by University of Cambridge

Hybrid Membrane Doubles The Lifetime of Rechargeable Batteries (Material Science)

Chemists from the University of Jena prevent dendrite formation in lithium metal batteries

The energy density of traditional lithium-ion batteries is approaching a saturation point that cannot meet the demands of the future – for example in electric vehicles. Lithium metal batteries can provide double the energy per unit weight when compared to lithium-ion batteries. The biggest challenge, hindering its application, is the formation of lithium dendrites, small, needle-like structures, similar to stalagmites in a dripstone cave, over the lithium metal anode. These dendrites often continue to grow until they pierce the separator membrane, causing the battery to short-circuit and ultimately destroying it.

For many years now, experts worldwide have been searching for a solution to this problem. Scientists at Friedrich Schiller University in Jena, together with colleagues from Boston University (BU) and Wayne State University (WSU), have now succeeded in preventing dendrite formation and thus at least doubling the lifetime of a lithium metal battery. The researchers report on their method in the renowned journal “Advanced Energy Materials”.

Two-dimensional membrane prevents dendrite nucleation

During the charge transfer process, lithium ions move back and forth between the anode and the cathode. Whenever they pick up an electron, they deposit a lithium atom and these atoms accumulate on the anode. A crystalline surface is formed, which grows three-dimensionally where the atoms accumulate, creating the dendrites. The pores of the separator membrane influences the nucleation of dendrites. If ion transport is more homogeneous, dendrite nucleation can be avoided.

“That’s why we applied an extremely thin, two-dimensional membrane made of carbon to the separator, with the pores having a diameter of less than one nanometer,” explains Professor Andrey Turchanin from the University of Jena. “These tiny openings are smaller than the critical nucleus size and thus prevent the nucleation that leads to the formation of dendrites. Instead of forming dendritic structures, the lithium is deposited on the anode as a smooth film.” There is no risk of the separator membrane being damaged by this and the functionality of the battery is not affected.

“To test our method, we recharged test batteries fitted with our Hybrid Separator Membrane over and over again,” says Dr Antony George from the University of Jena. “Even after hundreds of charging and discharging cycles, we couldn’t detect any dendritic growth.”

“The key innovation here is stabilizing electrode/electrolyte interface with an ultra-thin membrane that does not alter current battery manufacturing process,” says Associate Professor Leela Mohana Reddy Arava from the WSU. “Interface stability holds key in enhancing the performance and safety of an electrochemical system.”

Applied for a patent

High energy density batteries extend the driving range of electric vehicle (EVs) for the same weight/volume of the battery that a modern EV possesses and make portable electronic devices last longer in a single charge. “The separator gets the least amount of attention when compared to the other components of the battery,” says Sathish Rajendran, a graduate student at WSU. “The extent to which a nanometer thick two-dimensional membrane on the separator could make a difference in the lifetime of a battery is fascinating.”

As a result, the research team is confident that their findings have the potential to bring about a new generation of lithium batteries. They have therefore applied for a patent for their method. The next step is to see how the application of the two-dimensional membrane can be integrated into the manufacturing process. The researchers also want to apply the idea to other types of batteries.

Die Dendritbildung (l.) wird durch die Nanomembran (r.) verhindert
a) Regular battery separators with microscale porosity cause non-uniform lithium transport during the battery charge-discharge cycles resulting in needle-like growth of metallic lithium. This leads to short circuits and premature failure of lithium metal batteries. b) By introducing a carbon nanomembrane on the regular battery separator, the growth of lithium needles can be suppressed. The sub-nanometer-sized pores in carbon nanomembranes regulate the transport of lithium ions during the battery charge-discharge cycles, resulting in the deposition of a smooth film and the battery life can be increased significantly.Image: Turchanin et al./Wiley

Featured image: Prototype lithium metal batteries with carbon nanomembrane modified separators being tested at Wayne State University . © (Photo: Sathish Rajendran/Wayne State University)

Original publication

Rajendran, Z. Tang, A. George, A. Cannon, C. Neumann, A. Sawas, E. Ryan, A. Turchanin & L. M. R. Arava: Inhibition of Lithium Dendrite Formation in Lithium Metal Batteries via Regulated Cation Transport through Ultrathin Sub-Nanometer Porous Carbon Nanomembranes, Advanced Energy Materials, 2021, DOI: 10.1002/aenm.202100666

Provided by University of Jena

Making Batteries Live Longer With Ultrathin Lithium (Chemistry)

Researchers from Korea utilized LiNO3 pre-planted lithium particles to design a stable, long-lasting lithium metal battery

Our lives today are governed by electronics in all shapes and forms. Electronics, in turn, are governed by their batteries. However, the traditional lithium-ion batteries (LIBs), that are widely used in electronic devices, are falling out of favor because researchers are beginning to view lithium metal batteries (LMBs) as a superior alternative due to their remarkably high energy density that exceeds LIBs by an order of magnitude! The key difference lies in the choice of anode material: LIBs use graphite, whereas LMBs use lithium metal.

Such a choice, however, comes with its own challenges. Among the most prominent ones is the formation of needle-like structures on the lithium anode surface during cycling called “dendrites” that tend to pierce the barrier between the anode and cathode, causing short-circuit and, consequently, safety issues. “Li dendrite formation is strongly dependent on the surface nature of lithium anodes. A crucial strategy for LMBs, therefore, is to build an efficient solid-electrolyte interface (SEI) at the lithium surface,” explains Prof. Yong Min Lee from Daegu Gyeongbuk Institute of Science and Technology (DGIST), Korea, who specializes in battery design.

Conventional lithium-ion batteries (LIBs) are quickly falling out of favor as researchers are beginning to view lithium metal batteries as a superior alternative due to their relatively longer battery life. © Unsplash

Accordingly, researchers have explored a variety of strategies, from 2D interfacial engineering to 3D lithium anode architecture. In each case, solving one problem has merely given way to another. However, a new approach based on lithium metal powder (LMP) composite electrodes promises to stand out. The appeal of LMP lies in their spherical shape, which results in higher surface area, and ease of thickness tunability, allowing for wider and thinner electrodes. However, problems with LMP use still exist, such as the morphological failure caused by the inherent nature of their uneven surface.

Now, in a new study published in Advanced Energy Materials, Dr. Lee, along with researchers from Korea, adopted a novel approach in which they pre-planted LiNO3 to the LMP itself during the electrode fabrication process, allowing them to fabricate ~150-mm-wide and 20-μm-thick electrodes, which showed a coulombic efficiency of 96%.

The addition of LiNO3 to LMP accomplished two things: it induced a uniform N-rich SEI on the LMP surface and led to its sustained stabilization over prolonged cycling as LiNO3 was steadily released into the electrolyte. In fact, LMBs with LiNO3 pre-planted LMP (LN-LMP) demonstrated an outstanding cycling performance, with 87% capacity retention over 450 cycles, outperforming even cells with LiNO3-added electrolytes.

Prof. Lee is thrilled by these findings and speaks of their practical ramifications. “We expect that pre-planting Li stabilized additives into the LMP electrode would be a stepping-stone towards the commercialization of large-scale Li-metal, Li-S, and Li-air batteries with high specific energy and long cycle life,” he says.

With respect to batteries, it looks like lithium is not going out of fashion anytime soon!

Featured image: Clockwise from left: Prof. Yong Min Lee, Prof. Hongkyung Lee, and Ph.D. student Dahee Jin from the Department of Energy Science and Engineering, DGIST, Korea, who, along with collaborators, designed a LiNO3-pre-planted lithium powder anode for their battery. © DGIST

Reference: Jin, D., Roh, Y., Jo, T., Ryou, M.-H., Lee, H., Lee, Y. M., Robust Cycling of Ultrathin Li Metal Enabled by Nitrate-Preplanted Li Powder Composite. Adv. Energy Mater. 2021, 11, 2003769. https://doi.org/10.1002/aenm.202003769

Provided by DGIST

One-step Mechanochemical Method to Improve Performance of Cathode Materials in Na-ion Batteries (Chemistry)

Na-ion batteries are promising in large-scale energy storage owing to the abundant raw material resources, low cost and high safety.

Sodium vanadium fluorophosphate (Na3(VOPO4)2F) with theoretical energy density of 480 Wh/Kg is regarded as a strong candidate among various cathode materials. However, the intrinsic low conductivity and high energy-consumption during synthesis process hinder its commercialization. 

Researchers from the Institute of Process Engineering (IPE) and Institute of Physics of the Chinese Academy of Sciences developed one-step mechanochemical method to rapidly prepare the polyanionic compound sodium vanadium fluorophosphate as the cathode materials for Na-ion batteries, which exhibited excellent rate performance and cycle stability. 

This work was published in Nature Communications on May 14. 

The prepared Na3(VOPO4)2F/KB composite delivered a high discharge capacity of 142 mAh g-1 at 0.1C. The extra capacity beyond the theoretical specific capacity (130 mAh g-1) benefited from the interfacial charge storage.

Moreover, a specific capacity of 112 mAh g-1 can be obtained even at 20 C, which means this Na-ion battery could be fully charged/discharged in three minutes.

Superior cycle stability of this composite was demonstrated by an ultrahigh cycling stability with 98% retention over 10,000 cycles.

High resolution transmission electron microscopy revealed that the nanocrystallines of Na3(VOPO4)2F about 30 nm were embedded in the carbon framework, which facilitated the rapid conduction of electrons and Na ions.

The reversible structural evolution and negligible volume change of Na3(VOPO4)2F/KB composite during charging/discharging were also demonstrated by in situ X-ray diffraction and 23Na nuclear magnetic resonance spectrum. 

“The method provides a feasible strategy to improve the rate performance and cycle performance of cathode materials. Besides, the kilogram-scale product indicates the mechanochemical method is suitable for rapid large-scale production electrode materials for Na-ion batteries,” said Prof. ZHAO Junmei, a co-corresponding author of the study.  

Featured image: The electrochemical performance of sodium vanadium fluorophosphate synthesized by mechanochemical method. (Image by IPE)

Reference: Shen, X., Zhou, Q., Han, M. et al. Rapid mechanochemical synthesis of polyanionic cathode with improved electrochemical performance for Na-ion batteries. Nat Commun 12, 2848 (2021). https://doi.org/10.1038/s41467-021-23132-w

Provided by Chinese Academy of Sciences

Skoltech Researchers Proposed an Attractive Cheap Organic Material for Batteries (Material Science)

A new report by Skoltech scientists and their colleagues describes an organic material for the new generation of energy storage devices, which structure follows an elegant molecular design principle. It has recently been published in ACS Applied Energy Materials and made the cover of the journal.

While the modern world relies on energy storage devices more and more heavily, it is becoming increasingly important to implement sustainable battery technologies that are friendlier to the environment, are easy to dispose, rely on abundant elements only, and are cheap. Organic batteries are desirable candidates for such purposes. However, organic cathode materials that store a lot of energy per mass unit can be charged quickly, are durable and can be easily produced on a large scale at the same time, remain underdeveloped.

To address this problem, researchers from Skoltech proposed a simple redox-active polyimide. It was synthesized by heating a mixture of an aromatic dianhydride and meta-phenylenediamine, both easily accessible reagents. The material showed promising features in various types of energy storage devices, such as lithium-, sodium- and potassium-based batteries. It had high specific capacities (up to ~140 mAh/g), relatively high redox potentials, as well as decent cycling stability (up to 1000 cycles), and abilities to charge quickly (<1 min).

The new material’s energy and power outputs were superior compared to its previously known isomer, which is derived from para-phenylenediamine. With the help of collaborators from the Institute of Problems of Chemical Physics of the Russian Academy of Sciences, it was shown that there were two reasons for the better performance of the new polyimide. Firstly, it had smaller particles and a much higher specific surface area, which enabled easier diffusion of the charge carriers. Secondly, the spatial arrangement of the neighbor imide units in the polymer allowed a more energetically favorable binding of metal ions, which increased the redox potentials.

“This work is interesting not just because another organic cathode material was researched”, – says Roman Kapaev, a Skoltech PhD student who designed this study, – “What we propose is a new molecular design principle for battery polyimides, which is using aromatic molecules with amino groups in meta positions as building blocks. For a long time, scientists have paid little attention to this structural motif, and used para-phenylenediamine or similar structures instead. Our results are a good hint for understanding how the battery polyimides should be designed on a molecular level, and it might lead to cathode materials with even better characteristics”.

Featured image: Cover of ACS Applied Energy Materials Volume 4 Issue 5; Credit by ACS Applied Energy Materials

Provided by Skoltech

World First Concept For Rechargeable Cement-based Batteries (Chemistry)

Imagine an entire twenty storey concrete building which can store energy like a giant battery. Thanks to unique research from Chalmers University of Technology, Sweden, such a vision could someday be a reality. Researchers from the Department of Architecture and Civil Engineering recently published an article outlining a new concept for rechargeable batteries – made of cement.

The ever-growing need for sustainable building materials poses great challenges for researchers. Doctor Emma Zhang, formerly of Chalmers University of Technology, Sweden, joined Professor Luping Tang’s research group several years ago to search for the building materials of the future. Together they have now succeeded in developing a world-first concept for a rechargeable cement-based battery. 

The concept involves first a cement-based mixture, with small amounts of short carbon fibres added to increase the conductivity and flexural toughness. Then, embedded within the mixture is a metal-coated carbon fibre mesh – iron for the anode, and nickel for the cathode. After much experimentation, this is the prototype which the researchers now present.

Results from earlier studies investigating concrete battery technology showed very low performance, so we realised we had to think out of the box, to come up with another way to produce the electrode. This particular idea that we have developed – which is also rechargeable – has never been explored before. Now we have proof of concept at lab scale,” Emma Zhang explains. 

Luping Tang and Emma Zhang’s research has produced a rechargeable cement-based battery with an average energy density of 7 Watthours per square metre (or 0.8 Watthours per litre). Energy density is used to express the capacity of the battery, and a modest estimate is that the performance of the new Chalmers battery could be more than ten times that of earlier attempts at concrete batteries. The energy density is still low in comparison to commercial batteries, but this limitation could be overcome thanks to the huge volume at which the battery could be constructed when used in buildings.     

A potential key to solving energy storage issues    

The fact that the battery is rechargeable is its most important quality, and the possibilities for utilisation if the concept is further developed and commercialised are almost staggering.Energy storage is an obvious possiblity, monitoring is another. The researchers see applications that could range from powering LEDs, providing 4G connections in remote areas, or cathodic protection against corrosion in concrete infrastructure.

It could also be coupled with solar cell panels for example, to provide electricity and become the energy source for monitoring systems in highways or bridges, where sensors operated by a concrete battery could detect cracking or corrosion,” suggests Emma Zhang.   The concept of using structures and buildings in this way could be revolutionary, because it would offer an alternative solution to the energy crisis, by providing a large volume of energy storage.

Concrete, which is formed by mixing cement with other ingredients, is the world’s most commonly used building material. From a sustainability perspective, it is far from ideal, but the potential to add functionality to it could offer a new dimension. Emma Zhang comments: 

“We have a vision that in the future this technology could allow for whole sections of multi-storey buildings made of functional concrete. Considering that any concrete surface could have a layer of this electrode embedded, we are talking about enormous volumes of functional concrete”.  

Challenges remain with service-life aspects 

 The idea is still at a very early stage. The technical questions remaining to be solved before commercialisation of the technique can be a reality include extending the service life of the battery, and the development of recycling techniques. 

Since concrete infrastructure is usually built to last fifty or even a hundred years, the batteries would need to be refined to match this, or to be easier to exchange and recycle when their service life is over. For now, this offers a major challenge from a technical point of view,” says Emma Zhang.

But the researchers are hopeful that their innovation has a lot to offer.

We are convinced this concept makes for a great contribution to allowing future building materials to have additional functions such as renewable energy sources,” concludes Luping Tang.

Read the scientific article, Rechargeable Concrete Battery in the scientific journal Buildings.  

The research project was funded by the Swedish Energy Agency (Energimyndigheten) 

Featured image: Rechargeable cement-based batteries utilised as functional concrete. Illustration: Yen Strandqvist.

Provided by Chalmers University of Technology

New Findings on NaVPO4F Helps Designing High-performance Sodium Ion Batteries (Chemistry)

With the advantages of abundant resources, low cost and high safety, sodium ion batteries (SIBs) have broad application prospects. NaVPO4F is regarded as one of the most competitive cathodes in high-performance SIBs. 

Two polymorphs with the tetragonal and monoclinic NaVPO4F have been reported. However, the accurate crystal structure, the transformation mechanism and the Na-storage dynamic of two-phase NaVPO4F have not been well studied, limiting further application of NaVPO4F in SIBs. 

Recently, a research group led by Prof. LI Xianfeng and Prof. ZHENG Qiong from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) revealed the irreversible phase transition mechanism under variable temperature and sodium storage kinetics of monoclinic and tetragonal NaVPO4F. 

This study was published in Advanced Energy Materials on April 22.

The researchers obtained tetragonal and monoclinic NaVPO4F with high crystallinity and purity by low temperature hydrothermal and high temperature calcination. 

“We first observed the accurate cell structure of the two phases in atomic scale, the cell boundary of tetragonal phase is square, while that of monoclinic phase is parallelogram,” said Prof LI. “TheNaVPO4F crystal undergoes an irreversible crystal conversion from tetragonal to monoclinic phase.” 

Moreover, they revealed the difference of binding energy caused by different V-P-V bond angles in tetragonal and monoclinic phases. Compared with tetragonal NaVPO4F, monoclinic phase exhibited better thermal stability due to its higher bond binding energy. As a result, the irreversible phase transition from tetragonal to monoclinic phase would occur when the temperature rises above 650 ℃. 

The researchers also analyzed the Na-storage mechanism and electrochemical kinetics of the two crystal structures. They confirmed that the solid solution reaction process of tetragonal phase and “monoclinic to orthorhombic” two-phase transition reaction of monoclinic phase were in the electrochemical reaction, proving better electrochemical stability of tetragonal NaVPO4F. 

In terms of kinetics, monoclinic NaVPO4F had higher intrinsic conductivity and sodium ion diffusion rate, showing higher power density, while the intrinsic Na-extraction activation energy of tetragonal NaVPO4F was higher, which was attributed to the higher working voltage and higher energy density. 

As a result, monoclinic NaVPO4F could be employed as electrode in priority for high-power-density type SIBs, and tetragonal NaVPO4F could be used as the candidate electrode for high-energy-density type SIBs. 

This study provides theoretical basis and technical support for the designing of high-performance sodium ion battery electrodes and the development of next generation sodium ion battery systems with high-energy-density and high-power-density. 

The above work was supported by the Strategic Priority Research Program of CAS, the National Natural Science Foundation of China, the DNL Cooperation Fund of CAS, and the Youth Innovation Promotion Association CAS. 

Featured image: Phase transition mechanism and Na-storage kinetics of monoclinic and tetragonal NaVPO4F (Image by LING Moxiang)

Reference: Ling, M., Jiang, Q., Li, T., Wang, C., Lv, Z., Zhang, H., Zheng, Q., Li, X., The Mystery from Tetragonal NaVPO4F to Monoclinic NaVPO4F: Crystal Presentation, Phase Conversion, and Na‐Storage Kinetics. Adv. Energy Mater. 2021, 2100627. https://doi.org/10.1002/aenm.202100627

Provided by Chinese Academy of Sciences

Single-atom Electrocatalyst Synthesized with N-doped Holey Carbon Matrix for Zinc-air Batteries (Chemistry)

In recent years, the exploration and exploitation of green energy promote the development energy transformation and storage techniques such as zinc-air batteries (ZAB). 

ZAB has been considered as a crucial technical direction of electricity conversion and storage. It possesses the advantages including using aqueous electrolyte uniquely, larger power density and less cost. However, the oxygen reduction reaction (ORR) in discharging endures sluggish kinetics requiring high over-potential and leading energy voltage loss, which become the essential issue restricting the performance of ZAB. 

In a study published in Applied Catalysis B: Environmental, the research group led by Prof. CAO Rong and Prof. CAO Minna from Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences reported a series of single-atom catalysts (M-NHC, M=Fe, Co, Ni) loaded on holey carbon matrix, in which Fe-NHC sample exhibited better catalytic ORR performance and cycle performance superior to commercial Pt/C +Ir/C catalyst when applied to ZAB. 

The M-N-C single-atom catalysts possess the isolated M-N-C configuration and maximal atom utilization, presenting high activities for various electrocatalytic reactions. For the improvement of their performance, the support is crucial in requiring exposure and stabilization of sufficient atomically dispersed M-Nx sites as well as ample electrode/electrolyte interface. N-doped holey carbon materials possessing high surface area and abundant defects are suitable candidates. 

The researchers mixed supramolecular cucurbit[6]uril (CB[6]) self-assemblies and metal salts as precursor. With pyrolysis in N2 atmosphere, the mixture was transferred to carbonaceous material. The supramolecule self-assembly with regular tunnels and carbon/nitrogen sources was transferred to holey carbon matrix possessing hierarchical micro/mesoporous structure. The formation of holey structure does not rely on templates or pre/post treatments. 

N2 adsorption-desorption analysis showed the sample displayed typical type-IV isotherms with hysteresis loops in the P/P0 range of 0-1.0, suggesting the existence of hierarchical micro/mesoporous structure. Non-local density functional theory (NLDFT) analysis also confirmed that carbon matrixes mainly included micropores and mesopores over the range of 1.0-2.0 nm and 2.5-10 nm respectively. The calculated pore distribution of CB[6]-derived M-N-C catalysts was in agreement with the holey structures owning diameter less than 10 nm distinguished in the high angle annular dark-field scanning (HAADF) transmission electron microscopy images. 

The powder X-ray diffraction (PXRD) analysis results confirmed that no detective agglomeration of metal species occurred in the pyrolysis procedure. The only two peaks around 25° and 43° were ascribed to (002) and (100) planes of graphitized carbon.  

Besides, the aberration-corrected high angle annular dark-field scanning transmission electron microscopy (ACHAADF-STEM) and Fe K-edge X-ray absorption fine structure (XAFS) spectra confirmed the isolated Fe metal sites. Numerous highly dispersed bright dots detected in ACHAADF-STEM images with size less than 0.5 nm were attributed to heavier atomic dispersed metal atoms. X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra of the sample differ from those of bulk metals and metal oxides. 

The Fe loaded N-doped holey carbon single-atom electrocatalyst (Fe-NHC) exhibited high activity with the half-wave potential (E1/2) of 0.89 V versus reversible hydrogen electrode (RHE) for ORR in alkaline condition, which was better than those of Co or Ni loaded catalyst and commercial Pt/C (E1/2 = 0.83 V). The corresponding Tafel slope calculated for Fe-NHC was the smallest one (53.7 mV/dec), which was lower than that of commercial Pt/C (74.7 mV/dec) manifesting a good kinetic process for the ORR on Fe-NHC electrocatalyst. 

For the activity test of ZAB, the maximum power density of the ZAB employing Fe-NHC catalyst was as high as 157 mW/cm2, better than that of Pt/C + Ir/C catalyst (120 mW/cm2). The galvanostatic charge-discharge test was also used to examine the rechargeable ZAB with current of 10 mA/cm2

For Fe-NHC catalyst, battery was able to work continuously over 60 h cycling without observed loss of the voltage gap for charge/discharge potentials. In contrast, the voltage gap of Pt/C + Ir/C catalyst dramatically increased after 4 h test. On the whole, Fe-NHC was a promising alternative catalyst with better activity and stability to replace precious metal-based catalysts in rechargeable ZABs. 

This study holds great promise for fabricating catalysts with high surface area from macrocycle self-assembly in enabling reversible energy storage and conversion devices. 

Featured image: CB[6]-derived M-N-C single-atom catalysts was applied to ZAB with excellent catalytic activity and durability. (Image by Prof. CAO’s group)

Reference: Suyuan Zhang, Weiguang Yang, Yulin Liang, Xue Yang, Minna Cao, Rong Cao, Template-free synthesis of non-noble metal single-atom electrocatalyst with N-doped holey carbon matrix for highly efficient oxygen reduction reaction in zinc-air batteries, Applied Catalysis B: Environmental, Volume 285, 2021, 119780, ISSN 0926-3373, https://doi.org/10.1016/j.apcatb.2020.119780. (https://www.sciencedirect.com/science/article/pii/S0926337320311978)

Provided by Chinese Academy of Sciences