When it comes to Loofah, I believe everyone is not unfamiliar. It is a network-like object obtained by drying the loofah fruit after it has been removed from the epidermis. Many people like to use a loofah to wash dishes. The effect is not inferior to a brush made of synthetic fibers.
However, loofah not only can be used to brush bowls, but also can have more high-usage - to do the battery. What's going on here?
As we all know, portable electronic products such as laptops and mobile phones mainly rely on lithium-ion batteries to provide energy. Compared with other types of batteries, lithium-ion batteries have a higher energy density, so it is almost the only choice for portable devices that are "expensive".
However, with the wide application of portable electronic products, people hope that these devices can be more compact and light, while the battery can have more endurance, which requires a further increase in the energy density of lithium-ion batteries. At the same time, the development of new products such as electric vehicles also puts higher demands on lithium-ion batteries.
Unfortunately, the performance of current lithium-ion batteries has almost reached its limit, and it is difficult to make even greater improvements.
In the face of challenges, scientists have suggested that lithium-ion batteries must be "reborn" to make greater improvements if they want to go further.
One such solution is to replace various lithium salts currently used as cathode materials for lithium ion batteries with sulfur.
Sulfur can participate in the electrochemical reaction with metallic lithium, achieving the charge/discharge cycle of the battery. As a result, lithium-ion batteries become lithium-sulfur batteries.
Lithium-sulfur batteries are theoretically capable of providing higher energy densities than lithium-ion batteries, and sulfur is abundant on the earth and its production cost is not high. Lithium-sulfur batteries are therefore highly favored by researchers.
However, so far, the industrialization of lithium-sulfur batteries is still facing considerable difficulties. There are many technical problems that have not yet been completely overcome. One of the major problems is the so-called shuttle effect.
What does it mean? Ideally, sulfur should stay solid in the positive electrode during charge and discharge. However, actually in this process, a substance called polysulfide ion formed in the positive electrode can be dissolved in the battery. In the electrolyte, the shuttle between the positive electrode and the negative electrode travels back and forth, and the two electrodes continuously undergo a chemical reaction. As a result, the performance of the battery rapidly declines during use.
So how to suppress the shuttle effect? Some researchers think that since polysulfide ion likes to run inside the electrolyte, add a protective membrane outside the anode, so polysulfide ions can't run away.
What material should the diaphragm be made of? It must be able to conduct electricity, and it is best to loose the porous, so as to block polysulfide ions without affecting the normal operation of the battery.
Smart researchers quickly came to think that the carbon element is a very suitable choice. Soon, people can think of carbon-containing materials, such as carbon nanotubes and graphene, have been pulled for "interview", and the test results are not bad. The diaphragm made of these materials can really inhibit the shuttle effect. Improve the life of lithium-sulfur batteries.
But the problem has followed: materials such as carbon nanotubes often require artificial synthesis, are time-consuming and labor-intensive, and often have high prices.
Of course, through continuous improvement of the process, the production costs of these materials are likely to continue to be reduced. However, some researchers have also changed their thinking. They pointed out: Is there any ready-made material in nature?
Following this idea, researchers from both China and Australia turned their attention to Loofah.
Loofah itself has a highly porous structure, which is very consistent with the requirements of the diaphragm. Loofah itself is composed of cellulose and other materials, is not conductive, can not be used directly as a diaphragm, but this problem is not difficult to solve, only need to put the loofah to a few hundred degrees Celsius high temperature isolation of oxygen for processing, this is called For thermal cracking.
Usually at such a high temperature, organic matter such as loofah tends to burn off quickly. However, due to the isolation of oxygen, the loofah does not burn. Instead, both hydrogen and oxygen become gas escapes. However, the carbon element is left behind. The holes originally found in loofahs are basically exposed.
The loofah treated in this way was ground into a powder and then mixed with other materials to make a film, and the diaphragm that we needed was obtained.
Interestingly, the loofah contains a small amount of nitrogen, which is retained after high temperature treatment. However, the researchers do not think this is a disadvantage, but rather welcome the retention of nitrogen.
Because previous studies have shown that adding a small amount of nitrogen to the separator made of carbon simple substance can improve the performance of the separator. Something else that someone else wants to add is "self-contained" here. Of course it's a good thing.
What about the film made of loofah? Tests have shown that if the electrode is not protected with a separator, the specific capacity of the lithium-sulphur battery after 500 charge-discharge cycles (the amount of energy per unit mass or volume of battery or active material that can be discharged, in this case mass-specific capacity) is only The original less than 20%, and if you use the diaphragm made of loofah after 900 °C pyrolysis, after 500 cycles, the specific capacity of the battery can still maintain the original half.
This is equivalent to the protective effect provided by the diaphragms previously made using synthetic methods, but the use of Loofah as raw material undoubtedly has certain advantages in terms of raw materials and production costs.
In fact, loofah is not the only material that comes to mind from nature. A few years ago, researchers had done almost exactly the same research, except that the separator they used to protect lithium-sulfur batteries came from cassava cracking at high temperatures.
In addition, there are many raw materials from the natural world, especially waste from agricultural and pastoral production, which were once used for similar purposes. The elemental carbon obtained in this way is called biochar.
Biochar is not something new, but for a long time, people think that biochar has no value in addition to being used as a fuel or for purposes such as water purification and soil improvement. However, in recent years, people have come to realize that these easily accessible and porous materials can also be used for high-end applications such as batteries. With the deepening of research, the value of biochars will be further increased. Excavation.
Perhaps in the not-too-distant future, when you see a car loaded with loofah sailed out of the farm, don’t take it for granted that these loofahs will only go to the table or become a bowl cloth. They are likely to become the battery of your laptop. Part of it.
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