High-nickel ternary batteries are becoming an important way to improve battery energy density. In addition, in the field of lithium-ion batteries, giants such as Guoxuan Hi-Tech and Ningde Times are targeting research in frontier fields such as solid electrolytes and metal lithium anodes. , the competition in the battery industry is moving upstream, and disruptive key technologies are also very likely to appear in this field. Recently, a research team of Chinese scientists published the latest research on battery materials in the excellent academic journal "SCIENCE". The results show that they have made a major breakthrough in the field of cathode materials (battery cathodes), which are seriously constrained by resources in lithium-ion batteries. This breakthrough is worthwhile. Practitioners in the lithium-ion battery industry pay attention.
On October 9, 2017, a breakthrough research result was published in the journal "Nature Energy". A materials science research team led by famous Chinese material scientists Bao Zhenan and Cui Yi has successfully developed a new cathode material for sodium-ion batteries. With extremely high battery capacity and significantly increased cycle life, the material is expected to replace expensive lithium-ion batteries due to limited mineral reserves.Also read：48v lithium ion battery 200ah
Figure | Famous Chinese material scientists Stanford University professor Bao Zhenan (left), Cui Yi (middle) and the first author of this paper, Stanford University postdoctoral Minah Lee (right)
This new type of material uses a new idea to greatly improve the performance of sodium-ion batteries - its cycle battery capacity reaches 484mAh/g, and the cathode energy density is as high as 726Wh/kg.
"Our novel cathode, composed of oxygen and sodium, has an energy density comparable to that of conventional lithium cathodes, and can be used as a reliable cathode for sodium-ion batteries to replace lithium-ion batteries," said Minah Lee, the first author of the paper and a postdoctoral fellow at Stanford University.
What is even more remarkable is that due to the extremely abundant reserves of sodium on the earth, the cost of mining and production of cathode materials for sodium-ion batteries is only 1/100 of that of lithium-ion batteries, so that the overall cost of sodium-ion batteries is controlled to 80% of that of lithium-ion batteries. %about. This ground-breaking technological advance has once again taken a solid step forward on the road to large-scale energy storage.
Figure | With the increasing global demand for lithium-ion batteries, the mining supply of lithium ore is in short supply, and the price is also rising. Its price could climb further as reserves are depleted
In fact, as the most reliable battery for mobile terminals at present, lithium-ion batteries dominate most of the application scenarios of rechargeable batteries such as mobile phones, computers, and electric vehicles with higher energy density and more thorough charge and discharge depth. Moreover, with the increase in the production of lithium-ion batteries, under the use of economies of scale, its prices have maintained a downward trend for many years, further consolidating its competitive advantages relative to other battery technologies.
Some scientists even believe that until all the lithium mines on earth are mined, there will be no other batteries to replace the status of lithium-ion batteries.
However, the seemingly unrealistic scenario of "depletion of reserves" is becoming a real worry for many people in the industry. In the context of the global production of lithium-ion batteries rushing to new highs and the sharp decline in the overall price of lithium-ion batteries, the prices of some raw materials used to produce lithium-ion battery electrodes have soared. This is because the earth's mineral resources (lithium ore, cobalt ore, etc.) that can be used to produce cathode materials for lithium-ion batteries are actually not abundant at all.Also read：48v 500ah lithium ion battery
In order to meet the existing demand for lithium-ion battery production, the production of various mines around the world has been pushed to the limit, and it is very difficult to add new production. Not to mention, accelerated mining would also deplete these limited mineral resources earlier, further driving up prices. As a result, lithium-ion batteries face a challenge that most commodities will never face: As production increases, prices can not only fail to fall continuously, but may rise sharply.
To solve this problem, scientists turned their attention to another element on the periodic table that is next to lithium and has very similar properties: sodium. Compared with lithium resources, the reserves of sodium resources on the earth are so rich that it is "impossible to be exhausted": from the vast sea to the dining table of every household, there is sodium chloride - table salt everywhere. Compared with the price of lithium-ion battery materials as high as $15,000 per ton, if sodium ions are used as electrode materials, the cost per ton will be only $150, which is 100 times cheaper.
Figure | Compared with lithium, the sodium resources on the earth are too rich. In the sea, salt lakes, and salt mines, sodium occupies more than 2.7% of the mass of the earth's crust. Therefore, batteries based on sodium will be far cheaper than lithium-ion batteries.
However, although the application prospect is broad, the research of Na-ion battery has not made a decisive breakthrough.
In fact, research on sodium-ion batteries started at the same time as lithium-ion batteries. Unlike other batteries that require redox reactions, these two types of batteries are "rocking chair batteries" - ions shuttle back and forth between the cathode and anode to achieve the purpose of charging and discharging. In other words, the purpose of the cathode and anode is to collect, store, and release the ions used to generate an electrical current.
Figure | Many elements are used to make batteries. Considering a variety of properties, lithium is the best option at present. However, the lack of mineral resources reserves of electrode materials for lithium-ion batteries has laid hidden worries for its future development.
In the 1980s, the first breakthrough was made in the research of lithium ion cathode materials. The combination of cathode materials represented by lithium cobalt oxide and other materials, and anode materials usually composed of graphite, allowed lithium ion batteries to obtain the best performance. Replacing the previous nickel-metal hydride rechargeable batteries, it has entered thousands of households. However, the research on electrode materials for sodium-ion batteries is far from smooth.
In fact, if the ion battery is to operate efficiently, the following two conditions must be met. But in previous studies, cathode materials for sodium-ion batteries have either high energy density but short cycle life, or long cycle life but low energy density.
The energy density is high enough, and the battery per unit mass can supply enough electricity;
The cycle life is long, and the power will not decrease significantly with the increase of the number of charge and discharge cycles.
This time, the Stanford University team jumped out of the previous thinking frame of using transition element oxides or polyanions as cathode materials, and used a brand new organic material "inositol" combined with sodium ions.
You may not have heard of this tongue-in-cheek name, but this organic substance with a structure very similar to glucose is widely found in animals and plants. It is a growth factor for animals and microorganisms, and it is also a common nutrient in food. As an organic substance well known to the industry, inositol is mature and widely used, which is crucial for controlling the cost of sodium-ion batteries.Also read：48v 400ah lithium battery
Sodium and inositol can be combined into Na2C6O6. This compound is a very ideal cathode material. It can theoretically carry 4 sodium ions at a time, so the battery can have a very high capacity - 501mAH/g.
In fact, before Bao Zhenan's team, someone had tried to use Na2C6O6 as an electrode material to produce sodium-ion batteries. However, the theoretical maximum transport capacity of 4 sodium ions is difficult to achieve in practice, making the energy density of Na2C6O6 batteries much lower than expected.
In addition, after only one charge-discharge cycle, the energy density of the second cycle will further drop sharply, which cannot meet the needs of practical use at all. In actual use scenarios, the battery should still maintain a relatively sufficient power after hundreds or even thousands of charge and discharge cycles.
Figure | The new cathode material for sodium ion batteries used by Bao Zhenan's team. In the right picture, the yellow is sodium ions, which are embedded in the inositol marked in red and gray. A Na2C6O6 can carry up to 4 sodium ions at a time and has a very high energy density
"The biggest hurdle in this study is that this compound can only store less than two units of sodium and electrons in previous studies, which is not enough to compete with the energy density of lithium-ion battery cathodes," Minah Lee said. But here , we allow this compound to store four sodiums by understanding and addressing the kinetic limitations of phase transitions during redox reactions."
In this study, the Stanford team conducted a very in-depth exploration of the mechanism of Na2C6O6 batteries. Through a detailed analysis of the applied force at the atomic level, they successfully revealed the mystery that the actual charge of this material is lower than the ideal charge: it turns out that in the process of combining and de-intercalating sodium ions with the electrode, only when the material undergoes a reversible phase When changing, it is possible to let all four sodium ions participate in the reaction. In previous studies, the material was not specially treated and would only undergo an irreversible phase change, resulting in fewer than four sodium ions participating in the reaction, thus lower than the ideal energy density.
After figuring out the principle, they successfully converted the irreversible process into a reversible process by reducing the volume of active particles and selecting a suitable electrolyte, thereby increasing the cyclable battery capacity of the Na2C6O6 battery to 484mAH/ g. Moreover, the rate of decline of the maximum battery capacity is also significantly lower than before, and the cathode energy conversion efficiency has reached 87%.
This is the best achievement in the field of cathode materials for sodium-ion batteries so far, and it is of great breakthrough significance. They made sodium-ion batteries the first to achieve high energy density while basically achieving the goal of cycle stability. Because of the use of cheap sodium and inositol, and the energy density is significantly higher than that of lithium-ion batteries, the researchers claim that the cost of this battery is expected to be controlled at less than 80% of the same amount of lithium-ion batteries, which is a huge improvement.
Figure | Na2C6O6 nanoparticles before charging (left), which can bind a large amount of sodium ions (right) after full charging
However, this is only a preliminary research result, and there is still a certain distance from practical application.
First of all, Bao Zhenan's team has only initially solved the problem of cycle life of cathode materials. After 50 cycles, the capacity of the Na2C6O6 electrode has dropped by about 10%. Although this is a remarkable achievement compared to previous studies, it is still far from the requirement of hundreds of cycles in practical use.
Second, they have not yet conducted research on anode materials that can be industrialized. For sodium-ion batteries, the research on anode materials is also difficult. Despite the team's confidence, because sodium ions are much larger than lithium ions (about 50 percent larger in diameter), they cannot be absorbed by graphite, which is commonly used to make anode materials for lithium-ion batteries. So far, no anode material that works well enough and is inexpensive (such as graphite) has been developed. And this will also be the future research direction of the team. MinahLee introduced that this study shows that phosphorus is a good candidate material, but it is still difficult to produce in large quantities, so they are also trying to explore how to deal with this in a simpler way. materials.
Regarding the team's next steps, Minah Lee revealed: "Currently, our full cell energy density is limited by the anode (higher working potential), so we are working on making better anodes."
In short, this is a technology that has made major breakthroughs, but is still far from industrial application. However, any technology is very naive in its earliest days. It is also an innovation in the field of material science. The hard disk, which is now very popular, has a total weight of about 1 ton when it first made a technological breakthrough and realized MB-level data storage.
But it is this "monster" that has nothing to do with portability, which has laid the foundation for today's portable hard drives with a capacity of several TB (1TB=1024GB) but only pocket-sized. It is very likely that the Na2C6O6 material, which seems to be still in the primary stage, is the precursor to the foundational significance of large-scale grid-level power storage technology in the future.