The hottest Na ion battery, another blue ocean beh

2022-08-26
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Na ion battery: another blue ocean behind lithium ion battery

after lithium-ion batteries quickly occupied the market in the field of consumer electronics with excellent performance, in recent years, with the rapid development of new energy vehicle industry, lithium-ion batteries have been widely used in the field of power batteries, Dow and DuPont were founded in 1897 and 1802 respectively in successive years. The soaring market demand makes us have to face a very realistic problem - can the Li reserves on earth meet the needs of large-scale electric vehicle applications

after lithium-ion batteries quickly occupied the market in the field of consumer electronics with excellent performance, in recent years, with the rapid development of new energy vehicle industry, lithium-ion batteries have been widely used in the field of power batteries. The surge in market demand year after year makes us have to face a very realistic problem - can the earth's Li reserves meet the needs of large-scale electric vehicle applications

so people began to turn their attention to Na ion batteries with similar performance to Li ion batteries. In fact, it is not difficult to understand that carbon fiber composites have become the best choice for automobile lightweight. If we look carefully at the periodic table of elements, we can find that Li and Na are both alkali elements, and the similar outer electronic structure also makes the two metals have similar electrochemical characteristics. At the same time, Na element is very abundant on earth, The sea, which accounts for 70% of the earth's surface area, is a natural treasure house of Na resources, which undoubtedly makes Na ion batteries the most promising alternative to lithium-ion batteries

in fact, looking back on the history of sodium ion batteries, it is not difficult for us to find that Na ion batteries started no later than Li ion batteries, and the battery technology was not mature in the 1960s and 1970s. Therefore, the early battery research work mainly focused on how to design a stable battery system, and the specific energy and other indicators were not the priority, So at that time, the research on Na metal battery system was even more than that on Li metal system

in the late 1970s, people found that Li, Na, etc. could be reversibly embedded and removed from some metal oxides (such as LiCoO2 and NaCoO2), which was also the embryonic form of cathode materials for modern lithium-ion batteries, but this research was not the mainstream at that time. It was not until the mid-1980s that the reversible insertion and removal of alkali metals (Li, Na) in materials gradually became a research hotspot. At that time, people carried out a lot of research on Li and Na, which were equal. However, as the research enters the practical stage, specific energy and other indicators become more important, and Li element gradually attracts more attention with its better electrochemical performance. Especially after Sony launched the first commercial lithium-ion battery with graphite anode in 1991, Li ion battery has left Na ion battery far behind. We can learn from Li The number of research articles published by Na ion battery year by year shows a clue. At the beginning, the number of research articles published by Li and Na ion battery each year is relatively close, but since 1995, the number of research articles on lithium ion battery has increased rapidly, and since then, lithium ion battery has become a dust horse

however, there is no unique way. Since 2000, with the development of the electric vehicle industry, the demand for power batteries has increased exponentially. However, Li has obvious shortcomings in both price and resource reserves. Therefore, the research on Na ion batteries, which are also more abundant in resource reserves, has begun to pick up gradually. As can be seen from the figure below, from 2011, The number of research articles on Na ion batteries began to increase rapidly, and the number of articles published in 2018 alone has reached 2317, showing a trend of catching up with and surpassing lithium-ion batteries. So is it possible for Na ion battery to replace lithium ion battery? Let's talk about it today

1. Energy density

if we directly convert to Na ion battery based on the current Li ion battery material technology, we must accept that the energy density of Na ion battery will be lower than that of Li ion battery, which mainly comes from two aspects. First, the molecular weight of Na is much higher than that of Li (1mol Li weight is 7g, while 1mol Na weight must reach 23g), In addition, the working voltage of Na lithium-ion battery is also lower than that of lithium-ion battery (about 0.2V). Therefore, when lithium-ion battery embedded materials are applied in Na ion battery at present, even if they have the same capacity, the energy density of Na ion battery is lower than that of Li ion battery

2. Cost

the research on Na ion battery is mostly based on the assumption of low cost, so is the cost of Na ion really lower than that of lithium ion battery? In terms of resource reserves, the reserve of Li resources is only 1/1000 of that of Na resources, so the price of Na element is indeed relatively cheap. However, whether for Li ion batteries or Na ion batteries, the cost of Li and Na elements accounts for a very small proportion of the total cost of batteries, and the cost of other materials is the bulk

according to the calculation of Passerini et al., if Na is used to replace Li, the cost of cathode material can only be reduced by 3.6%. If considering the higher energy density of lithium-ion battery, if only relying on this advantage, the cost per wh of Na ion battery is even higher than that of lithium ion battery. The real advantage of Na lithium-ion battery is that Al foil can also be used as the negative collector. We know that in lithium-ion battery, because Al can form an alloy with Li, only Cu foil can be used as the negative electrode, while Al and Na will not form an alloy in Na ion battery. Therefore, Al foil can also be used as the negative electrode and fluid, which can not only reduce the cost by 8%, but also significantly improve the energy density of the battery (the density of Al is only 1/3 of Cu). However, since the production cost of lithium-ion battery has been greatly reduced after long-term industrialization, Na ion battery has no advantage in cost

3. Opportunities

from the above analysis, it is not difficult to see that based on the current technology, Na ion batteries do not have advantages in energy density or cost, so what are the real advantages of Na ion batteries? The answer is infinite "possibility". After more than 20 years of development, Li ion batteries have been very thorough in the study of materials and mechanisms, which are both "advantages" and "disadvantages". On the one hand, the speed of good software automatic adjustment is mature in the industrial chain, and on the other hand, lithium ion batteries have reached the stage of stagnation due to the lack of "opportunities". However, Na ion battery is not. It is still blank in a large area of research, and there are infinite "possibilities"

progress of ion batteries

4.1 cathode materials

the development of lithium-ion battery technology is mainly based on the excellent embedding and stripping performance of graphite materials. However, the performance of Na ions embedded in graphite materials is far worse than that of lithium-ion batteries. Therefore, for Na ion batteries, finding a high-performance cathode material is a very challenging work

hard carbon

hard carbon materials have larger layer spacing than graphite materials (0.372nm vs 0.344nm), so the embedding characteristics of Na ions are also better. Therefore, hard carbon materials have also become the most promising cathode materials for Na ion batteries

metal Na

like lithium-ion batteries, metal Na can also be used as the negative material of batteries. However, the reaction activity of Na metal is greater than that of metal Li, so there are more side reactions at the interface. At the same time, metal Na negative also has dendrite problems, so metal Na negative is not a good option for Na ion batteries

titanate spinel

li4ti5o12 material has won a place in the field of lithium-ion battery cathode materials with excellent electrochemical performance. However, when it is applied to Na ion batteries, due to the relatively large ion radius of na+, its performance is not ideal

4.2 cathode material

layered structure material

LiCoO2 material in lithium-ion battery can obtain a very high theoretical capacity (about 290mah/g) due to its relatively light molar weight, but in fact, only half of li+ can be removed reversibly, so the reversible capacity of LiCoO2 material is about 140mah/g. If Li is replaced with Na, the theoretical capacity of NaCoO2 will be reduced due to the increase of molar weight, However, Hwang et al. Found that even charging to na0.12coo2 will not cause structural damage, so the actual capacity of NaCoO2 can be almost the same as LCO, but it should be noted that the reaction mechanism of NaCoO2 material is more complex, and there are multiple platforms in the charge discharge curve

the success of layered mixed metal oxide

ternary material NCM in lithium-ion batteries gives researchers of Na ion batteries hope that cathode materials containing two or three metal elements, such as na2/3fe1/2mn1/2o2 and Na (fe1/3ni1/3ti1/3) O2, have been successively developed, but its capacity is difficult to exceed 100mah/g, and its performance needs to be further improved

k ionic metal oxide

because the ion radius of na+ is relatively large, more space is needed in the process of embedding. Therefore, people try to use k+ with larger ion radius to replace na+ in the material, so as to provide more space for na+ in the material. Research shows that k0.7fe0.5mn0.5o2 material has a capacity of 181mah/g at low magnification and a cycle life of more than 1000 times. It is an ideal cathode material

the success of phosphate materials

lifepo4 in lithium-ion batteries has also made phosphate widely studied in Na ion batteries. Na3v2 (PO4) 3 materials have obtained mah/g capacity in Na ion batteries, but the main problem of phosphate materials is low solid diffusion coefficient. The research of Gao et al. Shows that the electrical performance of phosphate materials has been greatly improved after they are prepared into nanostructures

Prussian blue

most of the cathode materials introduced earlier evolved from the cathode materials of lithium-ion batteries, so their electrical properties are not very ideal. Prussian blue material is a real cathode material of Na ion batteries. When used in Li ion batteries, this material has poor cycle performance, but when used in Na and K Lithium-Ion batteries, its cycle performance is very excellent, up to tens of thousands of times, But the main problem is that the capacity is relatively low and the weight is relatively heavy

4.3 electrolyte

electrolyte plays a very important role in both Na ion batteries and lithium ion batteries. At present, electrolyte can be roughly divided into several categories: 1) organic liquid electrolyte; 2) Ionic liquid electrolyte; 3) Gel polymer electrolyte; 4) Solid polymer electrolyte; 5) Solid inorganic electrolyte. Among them, organic liquid electrolyte is the most studied and mature electrolyte at present

solvents

the following table shows the physical property parameters of common organic solvents. From the table, we can notice that cyclic solvents, such as EC and PC, have high dielectric constant, but high viscosity, while linear solvents, such as DMC and Dec, have low dielectric constant, but low viscosity ratio. Therefore, in order to meet the requirements of high dielectric constant and low viscosity at the same time, In lithium-ion batteries, ring solvents and linear solvents are usually mixed. Ponrouch et al. Further showed that mixing carbonate solvents with ether solvents can obtain better conductivity and better cycle performance. Therefore, the electrolysis of Na ion batteries is usually

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