Niobium Tungsten Oxides Applied to Negative Electrodes of Lithium Battery

According to some reports, Shanghai-Hangzhou intelligent expressway will adopt the most advanced unmanned intelligent transportation system during the 2022 Hangzhou Asian Games. Based on this, we can imagine the scene of future transportation with 5G technology, BeiDou Navigation Satellite System and wireless charging technology.

You are sitting in a driverless vehicle and watching the latest film which is broadcast on screen window. You do not perceive that the intelligent has already gone for more than 4 hours on the intelligent expressway at all. The intelligent car is receiving the signal of satellite navigation and changing lanes at a uniform speed according to the real-time road condition information. The smart car has reached the destination after continuous and intermittent wireless fast charging. In addition, it will remind you that you have already paid for expressway toll, charging fee and service charge of intelligent navigation information center and then pull out of expressway. The car will ask if you are willing to switch it to the daytime mode and interested in driving the car by yourself to enjoy the city scenery. Moreover, you can decide whether the next restaurant suits your taste or not. Of course, the price list and the menu have already been shown on the screen. 

There is no doubt that this will be the transportation you can choose in 2030 when you miss the high-speed train. 

Certainly, one of core technologies that this means of transportation depends on is wireless fast charging battery. In order to realize this dream, in the field of new energy, a lot of manpower and material resources have been thrown into the research of on the high-power vehicle battery, long battery life, fast charging, long battery lifespan, the security and so on. At present, people continue to expand based on current the lithium battery technology in order to gain the breakthrough of new energy vehicles and enter into the future intelligent transportation.  

Compared with traditional battery, the lithium battery has been widely applied owing to its high open circuit voltage, high energy density, good cycle performance and so on. At present, most of the negative electrodes materials which are applied to the business are graphite. Although it owns good cycle performance but its theoretical capacity is so small that cannot meet people’ need for the battery with high energy density. Therefore, the research and development of negative electrodes material with high theoretical capacity has been a hot research topic. The negative electrode materials which own the potential value include the material of alloy reaction, conversion reaction and titanium base, such as silicon, stannum, tungsten, niobium and transition metal oxides.

The negative electrode material is used as the main part of lithium storage and to achieve the insert and the ejection of lithium ions. The electric potential of graphite is 0.1V vs Li+/Li and forms a film at the interface with the electrolyte. It is easy to form lithium dendrites. However, due to the layered structure of graphite, the intercalation and deintercalation of lithium ions causes large deformation (10.3%), which results in the low ion migration rate of Li + in graphite and slow charging and discharging rate. Therefore, the scientists diligently strive for the development of other negative electrode materials with high capacity.

Recent studies have shown that the battery charging rate partly depends on the rate at which positively charged ions move toward the negative electrode. When a battery is charging, lithium ions are extracted from the positive electrode and move through the crystal structure and electrolyte to the negative electrode, where they are stored. The faster this process occurs, the faster the battery can be charged. One of the major factors that limit our ability to create fast-charging "super" batteries is the travelling speed of lithium ions in ceramic media. One possible solution is to use nanoparticles to reduce the materials. But the production of nanoparticles is costly and complicated. So, scientists have been looking for alternative materials to solve this problem.

Recently, a new type of material which can achieve the goal of fast charging rate has been discovered. It can not only increase the probability of smart phones being fully recharged within a few minutes, but also increase the application of clean technologies, such as battery electric vehicle and solar technology. Researchers at the University of Cambridge have discovered that lithium ions can move at very high speed through the niobium tungsten oxides, which means that batteries can be quickly recharged.

Certainly, niobium tungsten oxide is not the common tungsten oxide and tungstate. We don’t know the difficulty of synthesis and industrial production. Compared with high-purity tungsten, tungsten oxide, tungstate, partial tungstate, rare earth doped tungstate, and various kinds of nanometer tungsten products, we can know that the preparation of nano tungsten trioxide doped with niobium is special and difficult with reference to the patent documents at home and abroad. The process of preparation is described as follows:

At first, we should pour 4-10 samples of tungsten hexachloride solutions of which the concentration 0.2~0.3mol/L into reaction kettle of poly tetra fluoroethylene and add 12-20 samples of redistilled water. And then we can stir to make it fully dissolved and add 1-10 samples of niobium(V) chloride ethanol solution. The nano tungsten trioxide doped with niobium will be formed through a series of process, such as stirring, mixing, purification, crystallization, re- crystallization and drying. 

Although the cost is relatively high, the prospect of its development and application are worth waiting.  

On July 25th, 2018, “Niobium tungsten oxides for high-rate lithium-ion energy storage” written by Kent J. Griffith, Kamila M. Wiaderek, Giannantonio Cibin, Lauren E. Marbella and Clare P. Grey has been published by Nature. “These niobium tungsten oxides are fundamentally different,” said Griffith, the paper’s first author. “This material has been identified in 1965. The niobium tungsten oxides own a rigid, open structure, and have larger particle sizes than many other electrode materials.”

In order to measure movement of the lithium ion in the unusual media, the researchers adopt the technology which is similar to the MRI. They found that the lithium ion moves a few hundred times faster speed in these media than in the traditional ceramic electrode material. These alternative materials are cheap and suitable for the production. “These oxides are easy to produce without additional chemicals and solution,” said Griffith. “The optimization of battery can improve two major clean technologies: electric cars and grid-scale storage for solar power.”

Clare Grey said that the next step is to optimize this material’s application in the battery so that the battery can be reused within the required time and mileage of the electric vehicle. For example, people can charge the electric bus quickly at the station.

Dan Brett, a professor of electrochemical engineering at University of London, who did not participate in the research, appreciates the discovery. "The discovery is exciting, especially with regard to the performance of the battery," he said. "The superiority of this research is that it can observe a kind of measurement adopted to measure the travelling speed of lithium ions in this medium.”

“Nanoparticles can be tricky to make, which is why we’re searching for materials that

inherently have the properties we’re looking for even when they are used as comparatively large micron-sized particles. This means that you don’t have to go through a complicated process to make them, which keeps costs low,” said Professor Clare Grey, also from the Department of Chemistry and the paper's senior author. “Nanoparticles are also challenging to work with on a practical level, as they tend to be quite ‘fluffy’, so it’s difficult to pack them tightly together, which is key for a battery’s volumetric energy density.”

The niobium tungsten oxides applied in the current work own a rigid, open structure that does not trap the inserted lithium. Its particle sizes are larger than many other electrode materials. Griffith speculates that the reason why these materials have not received attention previously is related to their complex atomic arrangements. Meanwhile, he believes that the complexity of structure and the composition of mixed metals are the reason of its special transport property. “Many battery materials are based on the same two or three crystal structures, but these niobium tungsten oxides are fundamentally different,” said Griffith. The oxides are held open by ‘pillars’ of oxygen, which enables lithium ions to move through them in three dimensions. “The oxygen pillars, or shear planes, make these materials more rigid than other battery compounds, so that, plus their open structures means that more lithium ions can move through them, and far more quickly.”

Through the adoption of PFG and NMR which are not easily applied to electrode material, the researchers has measured the movement of lithium ions through the oxides and found that its speed is faster than through the typical electrode materials. At present, most negative electrode of lithium-ion batteries is made by graphite with high energy density. But during the fast charging, it will form spindly lithium metal dendrites which will lead to the short and cause the batteries to catch fire.

Griffith suggests that the structure of nanoparticles is formed through a lot of processes while we only need a little. Therefore, the extensibility is the key problem. These oxides are easy to produce without additional chemicals and solution. The technology will also be adopted to optimize these materials. We can expect that the power, energy, and service life of battery will be improved in the future.

For details, see the link.

http://news.chinatungsten.com/pdf/Niobium-tungsten-oxides-for-high-rate-lithium-ion-energy-storage-20180701.pdf

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