2020年7月17日星期五

Nano Tungsten Oxide Expected to Solve the Problem of Lithium-ion Battery Material Shortage

With the vigorous development of the new energy vehicle industry, the demand for power lithium-ion battery continues to heat up, causing many lithium-ion battery materials to face supply shortages. Many people in the industry said that whoever has the upstream lithium resources, nickel resources and cobalt resources will have the initiative to develop power batteries.

In view of the above situation, perhaps tungsten resources can effectively alleviate it. It is reported that in recent years, energy storage scientists have developed a lithium-ion battery using nano tungsten oxide as the electrode material, which has good physical and chemical stability, strong endurance and the advantage of civilian prices, mainly because of the oxidation tungsten powder is easy to prepare and has relatively new photoelectric properties. In addition, China is the country with the most abundant tungsten resources in the world, distributed in 23 provinces and autonomous regions, and its output ranks first in the world, that is, its reserves are four times the combined reserves of other countries in the world. Therefore, tungsten resources are considered by many people as one of the most likely mineral resources to solve the shortage of lithium-ion battery materials in the future.

tungsten trioxide nanoparticles photo

At present, China is the world's largest lithium-ion battery market, and it faces a shortage of various lithium-ion battery materials, such as lithium resources. Domestic lithium resource consumption accounts for more than 40% of the world's total. Although China's lithium resource reserves account for 20% of the world's total, mining is difficult and costly, unable to meet domestic market demand, and has a high degree of external dependence. Therefore, Zheng Mianping, an academician of the Chinese Academy of Engineering, said that lithium raw materials can be extracted by improving the adsorption and membrane technology, precipitation method, ion exchange adsorption method and other methods to improve the recovery rate of lithium metal in the battery.

lithium ion battery photo

In short, there are many ways to solve the shortage of lithium-ion battery materials. Lithium battery companies can choose the appropriate way according to their actual situation.

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Niobium Tungsten Oxide Expected to Realize Fast Charge of Lithium-ion Batteries

As the lithium-ion batteries that power most phones, laptops, and electric vehicles become increasingly fast-charging and high-performing, they also grow increasingly expensive and flammable.

In research published recently in Energy Storage Materials, a team of engineers at Rensselaer Polytechnic Institute demonstrated how they could — by using aqueous electrolytes instead of the typical organic electrolytes — assemble a substantially safer, cost-efficient battery that still performs well.

If you were to take a look inside a battery, you’d find two electrodes — an anode and a cathode. These electrodes are immersed in a liquid electrolyte that conducts ions as the battery charges and discharges.

niobium tungsten oxide photo

Aqueous electrolytes have been eyed for that role because of their non-flammable nature and because, unlike non-aqueous electrolytes, they aren’t sensitive to moisture in the manufacturing process, making them easier to work with and less expensive. The biggest challenge with this material has been maintaining performance.

“If you apply too much voltage to water it electrolyzes, meaning the water breaks up into hydrogen and oxygen,” said Nikhil Koratkar, an endowed chair professor of mechanical, aerospace, and nuclear engineering at Rensselaer. “This is a problem because then you get outgassing, and the electrolyte is consumed. So usually, this material has a very limited voltage window.”

In this research, Koratkar and his team — which included Fudong Han, an endowed chair assistant professor of mechanical, aerospace, and nuclear engineering and Aniruddha Lakhnot, a doctoral student at Rensselaer — used a special type of aqueous electrolyte known as a water-in-salt electrolyte, which is less likely to electrolyze.

niobium tungsten oxide structure photo

For the cathode, the researchers used lithium manganese oxide, and for the anode, they used niobium tungsten oxide — a complex oxide that Koratkar said had not been explored in an aqueous battery before.

“It turns out that niobium tungsten oxide is outstanding in terms of energy stored per unit of volume,” Koratkar said. “Volumetrically, this was by far the best result that we have seen in an aqueous lithium-ion battery.”

The niobium tungsten oxide, he explained, is relatively heavy and dense. That weight makes its energy storage based on mass about average, but the dense-packing of niobium tungsten oxide particles in the electrode makes its energy storage based on volume quite good. The crystal structure of this material also has well-defined channels — or tunnels — that allow lithium ions to diffuse quickly, meaning it can charge quickly.

The combination of fast-charging capability and the ability to store a large amount of charge per unit volume, Koratkar said, is rare in aqueous batteries.

Achieving that kind of performance, with a low cost and improved safety, has practical implications. For emerging applications such as portable electronics, electric vehicles, and grid storage, the ability to pack the maximum amount of energy into a limited volume becomes critical.

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Nano Tungsten Oxide in Anti-virus Application

At present, the spreading of COVID-19 is furious in the world. Several previous difficult viruses (such as HIV, HBV, PIV, etc.) have not yet been attacked, and new mutant viruses (such as SARS coronavirus, avian influenza virus, and H1N1 influenza virus, etc.) have appeared in humans, seriously affecting human health. 

Many viruses, such as influenza virus, SARS coronavirus, avian influenza virus, and human immunodeficiency virus, are difficult to control. The main reason is that these viruses are infected on the mucosal surface, the antigenicity is weak, and antigenic mutations and drug resistance mutations are prone to occur. This has led to poor clinical prevention or treatment of these viruses.
tungsten trioxide structure photo
The detection, prevention and treatment of infectious diseases are difficult problems in the medical field. At present, the control of viral infectious diseases is mainly vaccine prevention, but there is no effective treatment strategy for established viral infections. However, with the advancement of medical research, researchers have discovered that there are some antiviral materials in the world, and some have already been clinically applied.

The application research of nano tungsten oxide in biomedicine is currently less. With the development of nano-medical science, some new functions of nano tungsten oxide have been gradually discovered, especially in the field of anti-virus application, showing broad prospects. For example, tungsten oxide nanodisks with specific surface morphology can be well used for antibacterial applications; two-dimensional layered tungsten oxide nanosheets have a plasmon resonance effect, which can absorb near-infrared light, making them suitable for photoacoustic diagnosis and treatment of tumors. Photothermal removal and other biomedical applications have a wide range of applications. Tungsten trioxide nano spheres have great potential for insoluble drug loading and delivery. 2nm-sized tungsten trioxide nanoparticles can be used as biological enzyme catalysts by electron transfer achieves sulfite oxidase activity.

Nano particles such as gold, copper, zinc oxide, and titanium dioxide have antibacterial and antiviral activities. The heavy metals silver, copper, lead, mercury and other salts can react with sulfhydryl groups in proteins or replace metal ions in enzymes, inactivating most enzymes. Therefore, heavy metal ions have a broad spectrum of antibacterial and antiviral activities.

It is worth noting that although metal nanomaterials have excellent antibacterial and antiviral activity, there is still some controversy about their toxicity mechanism, and the release of metal ions will pose a potential threat to the environment and the human body.
graphine oxide structure photo
As a derivative of graphene, graphene oxide is a flake of graphite oxide. Through plaque formation test, indirect immunofluorescence and Westernblot verification, the researchers found that graphene oxide nanomaterials are prevalent to pseudorabies virus (DNA virus) and swine Diarrhea virus (RNA virus) has a good antiviral effect, and this inhibitory effect has a time and dose-dependent effect. In addition, the researchers also found that two-dimensional sheet-like nanomaterials such as molybdenum disulfide and tungsten disulfide also have good antiviral effects, but compared with graphene oxide, their inhibitory effect is reduced.

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Nano Tungsten Oxide Applied in Cobalt-free Lithium Ion Battery

As one of the most hot topics recently, cobalt-free lithium ion battery is considered as an upgraded version of the current commercial ternary lithium ion battery. Because of their higher energy density and lower production costs, they are popular among many battery manufacturers. As a typical transition metal N-type semiconductor material, how should nano tungsten oxide be used in cobalt-free lithium battery?

Nano tungsten oxide can be used as a modifier for the anode material of cobalt-free batteries, and can also be used to produce high-performance anode materials. In terms of cathode materials, the use of WO3 can not only reduce the use of cobalt metal, but also effectively improve the specific capacity and thermal stability of the product. In terms of anode materials, the use of WO3 can significantly improve the rate performance and lithium storage kinetics.

nano tungsten oxide photo

As we all know, the biggest cost of new energy vehicles lies in power batteries. As far as the ternary lithium battery that currently dominates the market, the cobalt contained in it is a very important rare metal with a small distribution area and low output, making the cobalt price center of gravity relative to other rare metals for a long time. All are in a higher position, which greatly increases the production cost of power batteries.

At present, the price range of electrolytic cobalt is between 245~255 thousand RMB/ton, the price range of cobalt powder is between 266~269 thousand RMB/ton, cobalt sulfate is 4.45-4.70 million yuan/ton, cobalt chloride is between 54-57 thousand RMB /ton, tricobalt tetrachloride is between 175,000-180 thousand RMB /ton, cobalt chloride is 174~179 thousand RMB /ton. and cobalt sulfide is between 116~119 thousand RMB /ton.

cobalt free battery photo

In the context of the gradual retreat of subsidies for new energy vehicles in 2019 and the attack of COVID-19 in 2020, the removal of cobalt and chemical conversion have become the common choice of many power battery companies. In February 2020, the concept of Tesla's cobalt-free battery was introduced, and cobalt removal was pushed to the cusp. Various cobalt-free solutions gradually appeared in power battery companies.

Tungsten trioxide nanoparticles are often used by domestic researchers to replace the cobalt element in lithium ion batteries because of their unique physical and chemical properties. This is mainly because tungsten oxide has the characteristics of large specific area, high specific gravity, and good mechanical stability, which can significantly improve the specific energy density and thermal stability of the cathode material. This means that the positive electrode material containing tungsten trioxide is less likely to undergo thermochemical reaction with the electrolyte, thereby reducing the possibility of a sudden rise in partial pressure and temperature in the battery.

In order to further improve the capacity and charge-discharge rate performance of cobalt-free batteries, some researchers have indicated that tungsten trioxide powder can also be used to prepare the anode material. However, it should be noted here that tungsten trioxide needs to be compounded with graphene (RGO), which can significantly improve the overall electrochemical lithium storage performance of the composite material.

Due to the synergistic effect between tungsten trioxide and graphene, the reversible specific capacity of WO3/RGO nanocomposites at 0.1C rate is not only far superior to WO3 and RGO monomers, but also greater than the sum of the two monomers.

In addition, WO3/RGO nanocomposites also have stable cycling performance and good rate performance. After 100 cycles at 0.1C rate, its reversible specific capacity remains at 635mA/g, and the capacity retention rate is 83.4%; at 5C rate, its reversible capacity can still maintain 460mA/g, which is lower than the graphite negative electrode used in commercial lithium batteries. The theoretical specific capacity of the material (372mA/g) is much higher, which also indicates the potential application of the prepared tungsten trioxide/graphene composite material in a new generation of lithium ion batteries.

The vigorous development of cobalt-free batteries may help to further increase the demand for tungsten trioxide.

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2020年6月24日星期三

Photocatalytic Production of Benzoic Acid with Bismuth Tungstate

Benzoic acid is a flake or needle like crystalline with a smell of benzene or formaldehyde, usually made by selective oxidation of toluene.

photocatalytic production of benzoic acid with bismuth tungstate image

Toluene is obtained by a series of oxidation processes. Benzoic acid is an important food preservative, and is also used in medicine, dye carriers, plasticizers, spices and antibacterial agents. In the traditional chemical process, the production of benzoic acid from toluene requires selective oxidation of toluene under severe conditions, such as high temperature, high pressure, and acidic solvents. Generally speaking, the process is costly and polluting.

Tungstate is a kind of photocatalyst which is widely used in industrial wastewater treatment, but some scholars have made use of the principle of petal type bismuth tungstate photocatalyst to produce benzoic acid. Because bismuth tungstate can use oxygen as oxidant to catalyze the oxidation of toluene and its derivatives, thereby simplifying the preparation of benzoic acid and reducing pollution.

In the process of studying the oxidation of benzoic acid by catalytic oxidation of toluene with bismuth tungstate, it is found that the petal like bismuth tungstate powder has the highest activity. By means of X ray diffraction, scanning electron microscopy, UV Vis absorption spectra and experimental results indicate that surface flower like bismuth tungstate powder showed the best activity for the oxidation of toluene and it is likely to be the largest surface area has a relationship. Because Bi2WO6 is excited by light, electrons are excited by light and leave holes that form electron hole pairs, these photogenerated electron hole pairs give rise to stronger oxidation and reduction signals because of their strong redox power, while electrons and holes play a corresponding role in the oxidation of toluene, thus facilitating the reduction.

In recent years, bismuth tungstate has become a new force for environmental protection because of its good photocatalytic performance, but it is rare in the application of catalysts, the reduction of benzoic acid with bismuth tungstate not only provides a new idea for the oxidation and reduction of toluene, but also provides an effective method for the green production of benzoic acid.

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Tungsten Trioxide Helps Catalyze SCR Soot Denitrification Technology

The nitrogen oxides produced by coal combustion as a pollutant will affect human health.

The most harmful is NO2, which mainly affects the respiratory system of human beings, and can cause bronchitis and emphysema.

SCR selective catalytic reduction technology has become the most widely used and most effective flue gas denitrification technology in the world. It has the advantages of low reaction temperature, high purification rate, reliable operation and small two pollution. After its catalysis, the main non-toxic and non polluting N2 and H2O are produced.

SCR soot denitrification technology image

In the SCR soot denitrification technology selective catalytic reduction system, it is generally composed of ammonia storage system, ammonia and air mixing system, ammonia injection system, reactor system and monitoring control system, the thermal power plant, SCR reactor is usually installed in the boiler economizer and air preheater, here for the high dust temperature arrangement, smoke temperature in this region for SCR denitrification reaction, ammonia injection in the appropriate position in the flue between economizer and SCR reactor, and the flue gas mixture after the reaction with NOx catalyst in the reactor. The catalyst is placed in a solid reactor. The catalyst unit is usually vertically arranged and the flue gas flows up and down.

Catalyst is one of the core of SCR technology, its cost is about 20%~40% of the total cost of SCR system, and the performance of catalyst has a direct impact on the removal efficiency of NOx. For SCR systems, the three main commercial catalysts are noble metal catalysts, metal oxide catalysts, and molecular sieve catalysts. At present, metal oxide catalysts are the most widely used in industry because they are the cheapest. In the past, vanadium titanium catalyst is the main catalyst for selective catalytic reduction system of SCR in China. But in recent years, scientists have found that titanium tungsten vanadium catalysts are more active, selective, antioxidant and anti toxic, and they are expected to be the first choice of catalysts.

Some scholars use imported V2O5 - WO3/TiO2 catalyst to test the effect of SCR, with the help of tungsten trioxide, SCR denitration ratio reached 100%, compared with the traditional vanadium and titanium powder, the effect increased by 30%, the effect is very obvious, but the cost has also increased a lot. For some enterprises, environmental protection measures are only a move, and raising environmental costs is tantamount to their lives, which is the biggest obstacle to the commercial popularization of titanium tungsten vanadium SCR catalyst.

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Single Layer Tungsten Disulfide Challenge Graphene (2)

Tungsten and carbon have many similar physical properties, such as high melting point, high hardness, and better conductivity and thermal conductivity.

So foreign scientists first took aim at tungsten. In recent years, foreign scholars through the study found that single layer tungsten disulfide also has excellent semiconductor performance, it not only has excellent characteristics of graphene, there are more excellent than the characteristics of the semiconductor, two tungsten sulfide has a considerable band gap, and it also shows new properties: As the number of atoms increases, the bandgap becomes tunable, and its electron migration rate is better than that of graphene, which is the ideal choice for transistor materials.

single layer two tungsten sulfide image

There is no doubt that the emergence of graphene and other two-dimensional materials to the world's material industry brought about tremendous changes, as China attaches great importance to the material industry, graphene manufacturing technology has achieved many achievements, the cost of graphene has greatly declined, making the use of two-dimensional materials rapidly spread. In many areas, graphene has the advantage of excellent compatibility and cost control, and is "the king of new materials". But in the field of semiconductor such as transistors, high-performance single layer two tungsten sulfide has the absolute strength beyond the performance of graphene.

China is not only a big producer of graphene, but also a major producer of tungsten. Tungsten is an important strategic resource of non renewable. The price of monolayer tungsten disulfide is one to two times higher than that of graphene, which is probably the main reason why monolayer tungsten disulfide is difficult to produce as much as graphene. However, if a single layer of tungsten disulfide and graphene made of composite material? This may be feasible. Looking forward to the future, we can exploit the advantages of raw materials to develop a microprocessor with Chinese proprietary rights. In the future of the intelligent world, we use those than the performance speed is almost a few times or even hundreds of times the computer, mobile phone, or VR equipment, and even intelligent robots, they can be a real Chinese core.

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