Brief Description of the Effect of Lithium Ion Storage on the Energy Density of Lithium Ion Batteries

Those companies that convinced at the beginning of the year how to achieve at the end of the year, whether they are shrinking or not; those enterprises that have achieved fruitful results in the "golden" craze of lithium batteries have forgotten their original dependence after repenting in the sudden changes in policy. Regardless of how turbulent this year, people who are lithium batteries have to admit that 2017 is really exciting.

In this year, the Matthew effect of the market to leading enterprises has become more prominent, and the elimination of small and medium-sized enterprises has begun. In this year, the cooperation between power companies and car companies has further deepened, and the integration of the two sides has become the consensus of the industry; Capital is more imprinted on the industry. Whether it is mergers and acquisitions or IPO, capital has become an essential option for power companies.

From a technical point of view, 2017 is hailed as a first year. Starting from the father of lithium battery John Goodnorf, major companies and research institutions have successively displayed swords in the battlefield of "solid-state batteries", 2017 into the first year of solid-state batteries; BMW, Daimler, GM, Volkswagen, Toyota, Honda Mainstream automakers such as Hyundai and others have announced the progress of fuel cell vehicles, and 2017 is the first year of fuel cells. The ternary market accounted for the overtaking of lithium iron phosphate. BYD, which adheres to lithium iron phosphate, announced that next year, pure electric vehicles will be converted 2017 into the first year of ternary battery.

There are too many things worth saying in 2017, but what I want to emphasize is that for power batteries, lithium batteries are always the mainstream technology route, and will not be replaced for at least a few decades. Among them, the short-term goal of lithium battery technology is to achieve 300wh/kg through high-nickel ternary positive electrode and silicon-carbon negative electrode; the medium-term (2025) target is based on lithium-rich manganese-based/high-capacity Si-C negative electrode to achieve monomer 400 wh/kg; The period is to develop lithium-sulfur and lithium-air batteries to achieve a monomer specific energy of 500wh/kg.

Of course, this long-term goal remains to be discussed, and the development of science is often unexpected, especially in the industry with a broad spectrum of lithium batteries, but its core problem is to solve energy density, power density and safety.

Let's take a look at some of the new technologies and events in the lithium battery industry this week.

1. New fuel cell catalysts significantly reduce hydrogen production costs

According to foreign websites, a research team at the University of California, Santa Barbara (UCSB) has explored a new method for producing hydrogen from methane, which is cheaper than previous technologies and also prevents greenhouse gases (such as carbon dioxide) generation?

The UCSB team studied the use of molten metal and molten salts as a new catalytic system. Experiments have shown that different metal combinations in molten alloys may enhance their catalytic activity, converting methane to hydrogen and solid carbon. Researchers have developed a single-step method by which methane can be converted to hydrogen, which is simpler, cheaper than conventional SMR methods, and by-products are solid carbon for convenient storage.

The researchers introduced methane gas into the bottom of a catalytically active molten metal reactor. As the bubbles rise, the catalyst on the methane molecular vessel wall contacts to form carbon and hydrogen. When the methane bubble reaches the top of the vessel, it has broken down into hydrogen and is released from the top of the reactor. Carbon solids floating on top of liquid metal can also be easily separated.

The surface of the molten metal alloy is not deactivated by the accumulation of carbon as compared with the conventional method of relying on the reaction occurring on the solid surface, and can be reused indefinitely. The reaction product is separated from the reaction system in time to promote the reaction, and the process can be operated under high pressure in principle, so that the conversion rate of methane is high.

Comments: The current fuel cell industrialization is not yet large, and the demand for hydrogen is not strong. Therefore, this steam methane reforming technology (SMR), which has been commercialized for decades, is not cold. After all, SMR not only consumes a lot of energy, It also produces carbon dioxide. However, with the upgrade of fuel cell technology, once the scale application is realized, the value of this new type of catalyst will be reflected in geometric multiples.

2. The new composite lithium battery separator can store lithium ions

Prof. Leif Nyholm and Wang Zhaohui researchers from Uppsala University in Sweden successfully synthesized Redox-active composite lithium-ion battery separators using a simple and economical paper-making method, creatively transforming the inert membrane layer into lithium ions. The storage capacity of the conductive polymer material layer effectively increases the energy density of the lithium ion battery.

The core idea is to convert the traditional thick diaphragm into a double-layer diaphragm (Redox-active Separator) consisting of a thin insulating layer and a thick active layer to increase the capacity density of the lithium-ion battery.

The thin insulating layer in the Redox-active separator is composed of nanocellulose fibers (NCFs: Nanocellulose fibers), and the thick active layer is composed of nanocellulose fibers and a conductive polymer polypyrrole (PPy: Polypyrrole) composite. In the design, the PPy layer needs to be placed against the positive electrode of the battery, because the electrochemically active PPy material can provide the battery with a capacity other than the positive electrode material through the anion deintercalation mechanism when the battery is in operation.

Comments: In theory, the storage of lithium ions through the diaphragm can indeed greatly increase the energy density. However, there are many ways to increase the energy density. It is hard to say whether the new diaphragm has the basic function of the traditional diaphragm besides storing lithium ions. Whether the existence of the diaphragm will affect the electrolyte is lack of a large number of experiments. The most important thing is whether mass production can be achieved. If not, the meaning of this diaphragm will disappear.

3. ASU researchers use ceramics instead of electrolytes to solve lithium battery safety problems

Experts at Arizona State University have solved a big problem, and the future battery will become a portable small electronic piece. Chan's team proposed replacing ceramics with flammable electrolytes. Most of the safety problems are caused by short circuits. The electrolyte is easy to catch fire and cause chain reactions such as gas emission and material degradation.

Researchers are now using more stable solid materials to replace electrolytes and maintain their high ionic conductivity. The challenge now is that many solid electrolytes are brittle, and the team is exploring the fusion of lithium-ion-conducting ceramic nano materials with polymers to achieve the desired solid electrolyte and ensure good mechanical properties and high lithium Ionic conductivity and improved safety.

Comments: Solid-state batteries are nothing new, and ceramic solid-state electrolytes are not even ranked in many technical routes of solid-state batteries. Their superior electrochemical performance limits their application scenarios. In the field of mobile phone digital and so on, of course, its application difficulty is also lower than the research direction of solid electrolytes such as sulfides and oxides. However, in general, ceramic solid-state batteries should be applied to consumers in real time.

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