14250 battery

　　14250 battery will be a very promising high specific capacity battery technology

　　14250 battery will be a very potential high-specific capacity battery technology - in fact, the main driving force for the rapid expansion of the battery industry in recent years comes from the demand of the power battery industry. Therefore, the development of battery technology and the practical process of technology The most important thing to consider is the needs of power batteries. At this time, the extreme polarization of lithium-air batteries even at low rates will inevitably lead to very unsatisfactory energy efficiency and rate performance. This is also its role in power batteries. An important obstacle to overcome for practical application in the field.

　　In fact, the main driving force for the rapid expansion of the battery industry in recent years comes from the demand of the power battery industry. Therefore, the most important thing to consider in the development and practicalization of battery technology is the needs of power batteries. At this time, The extreme polarization of lithium-air batteries even at low rates will inevitably lead to very unsatisfactory energy efficiency and rate performance, which is also an important obstacle to overcome for its practical use in the field of power batteries.

　　14250 battery is a very promising high-specific-capacity battery technology. It utilizes the reversible reaction of lithium metal and oxygen. Its theoretical energy density upper limit reaches 11,000Wh/kg, which is far higher than the current actual energy density of 200+Wh/kg. Therefore, It has received enthusiastic support from academia and industry and is widely regarded as a future disruptive technology in the battery field. However, there have been many doubts about the research on lithium-air batteries in the industry. Many people believe that the definition of lithium-air batteries is unclear (should be called lithium oxygen), the reaction mechanism is complex, the polarization efficiency is high, the cycle life is poor, It is not a reliable development direction for the battery industry in the future (where demand for power batteries is an important industry driver). Of course, during this process, researchers continued to work hard and produced many results, and discussions on the prospects of this direction were also in-depth.

　　Recently, American scientists have achieved a breakthrough in the research of lithium-air batteries. They published a paper in "NATURE" and successfully made a battery that can cycle more than 700 times in an air-like atmosphere. This is a good solution to the problem that many previous systems could only be combined with The problem of pure oxygen reactions and poor cycle life (often only a few dozen times) has led to significant progress at the scientific level in this field. Here, the author will briefly introduce the research progress of this article and briefly look forward to the future industrialization and practical prospects of 14250 battery technology.

　　1. Introduction to the work of American scientists 1.1 Discussion on the concept of 14250 battery technology and the importance of suppressing side reactions

　　One of the major advantages of 14250 battery technology is that its theoretical density limit of 11,000Wh/kg is almost comparable to fossil fuels. However, this data is only the most optimistic estimation method. The currently generally recognized reaction mechanism of this battery is:

　　2Li+O2? Li2O2

　　In this reaction, if the mass proportion of O2 is not calculated, it is considered to be inexhaustible from the air. Of course, the ideal value of 11500Wh/kg can be directly calculated based on the energy change value of pure lithium in this reaction (picture below) . However, this calculation is actually not rigorous: 1) The calculation of the specific energy of the reaction system should not discard the mass of the reaction gas. If the mass of O2 is included in the calculation, the energy density of the reaction system will immediately drop to 3500Wh/kg; 2) In practice Lithium metal will undergo complex irreversible reactions with almost all components in the air, which is also a major bottleneck in 14250 battery system technology.

　　Calculation of the theoretical energy density of lithium-air batteries (excluding the mass of oxygen), excerpted from Jeff Dahn's report "Electrically Rechargeable Metal-air Batteries Compared to Advanced Lithium-ion Batteries"

　　Therefore, in fact, the strict definition of 14250 battery (Li-air) is lithium oxygen battery (Li-O2), and suppressing the complex reaction between lithium metal and other components in the air is actually the most important priority of 14250 battery. basic problems to be solved.

　　1.2 Solution to this article

　　The solution proposed by the author of this article is to perform repeated electrochemical charge and discharge cycles on the lithium negative electrode in an atmosphere full of CO2 to form a Li2CO3/C composite protective layer on its surface. The researchers used SEM, EELS, and XPS to characterize the dense morphology, chemical bonding state, and elemental presence of the layer, and confirmed the formation of the layer. Then they tested the lithium electrode with a protective layer. They found that even in the stripping test (0.5mA/cm2) where all the lithium was used up in deep cycles, it could achieve a retention rate of 99.97% of lithium capacity/material in weekly cycles. , this data is much higher than other research results in the industry.

　　1.3 Full battery reaction, lifespan and optimization of protective layer preparation process

　　The author of this article used MoS2 cathode, lithium anode with this protective layer, and EMIM-BF4/DMSO (25%/75%) mixed electrolyte to make a full battery, and conducted experiments in an artificial air-like atmosphere. The reaction in the first week started at 2.92V, which is very close to the potential formed by Li2O2 at 2.96V, indicating that the main reaction progressed well and reached a specific capacity of 500mAh/g at 3.75V. The polarization voltage difference was 0.88V in the first cycle, 1.3V after 50 cycles, and 1.62V after 550 cycles. After the reaction reaches 700 cycles, the battery can still work; in contrast, the unprotected 14250 battery can only cycle about 10 times before failing. Regarding the thickness selection of the protective layer, the author of the article believes that a protective layer that is too thin will cause the electrolyte to decompose, and a thick protective layer will cause a large charge transfer potential and side reactions, so it needs to be optimized. After experiments, it was found that the thickness of the protective layer prepared by 10 cycles was the most suitable.

　　A The charge and discharge curve of the battery with a protective layer in this article from the first week to the 550th week B The protective layer sample prepared by 10 pre-cycles can achieve optimal cycle performance

　　The polarization voltage of the lithium-air and lithium-oxygen batteries prepared in this article changes with cycling

　　1.4 Various characterization methods illustrate the suppression of side reactions

　　Furthermore, the author used RAMAN to study the discharge products on the cathode surface after cycling and found that there was only Li2O2 required for the reaction and no other impurities. The Li2O2 also showed good stability in the electrolyte. The author also combined the NMR method to further prove that there are no more complex reactions caused by CO2 and H2O that are common in the air in this system. Finally, the author also combined the DFT calculation method to show that the protective layer can effectively prevent N2 and O2 from diffusing to the lithium metal anode (suppressing side reactions), but is conducive to the diffusion of lithium ions to the cathode (required reaction). ABINITIO's algorithm was also used to illustrate that the reaction between water molecules and Li2O2 is thermodynamically difficult. The reaction with CO2 requires multiple clusters of CO2, which is difficult to achieve under low CO2 concentrations in the air.

　　1.5 Summary

　　As can be seen from the above, this article provides detailed analysis and characterization methods, indicating that this method of growing a protective layer has obvious effects on suppressing side reactions and improving cycle life of lithium-air batteries. These two issues are core challenges plaguing lithium-air batteries, so the work in this article can be said to have made an important breakthrough in basic research.

　　2. 14250 battery technology outlook

　　14250 battery technology has always been a hot technology that has attracted people's attention. Its high theoretical energy density has been unanimously expected by everyone. However, there have always been many problems and challenges with this technology. Many people in the industry have pointed out that lithium-air batteries combine the shortcomings of fuel cells and lithium-ion batteries and a series of problems such as too many side reactions. Here, the author also wants to briefly look at the prospects of 14250 battery technology based on the progress of this article and the industry’s expectations for battery technology.

　　2.1 Substantial side reactions caused by lithium-oxygen batteries and various components in the air

　　As mentioned in the analysis just now, the essence of lithium-air batteries is lithium-oxygen batteries. Various other components widely present in the air, except for inert gases, will almost always have adverse chemical reactions with lithium, greatly affecting the life of lithium-air batteries. In previous studies, poor cycles (mostly dozens of times) of lithium-air batteries were basically related to this problem.

　　Of course, some studies will also suggest using external oxygen tanks to provide pure oxygen to solve this problem, but this is an extremely impractical option in practical applications: 1) The oxygen tank will greatly reduce the theoretical energy density of the system. Continuing to deduct the weight of the oxygen tank from the theoretical density of 3500Wh/kg may eventually cause the system to completely lose its only advantage of energy density; 2) Extreme danger, the oxygen tank itself will bring dangers to use, which The safety requirements for batteries are even more difficult to cross.

　　This article has indeed achieved good results in inhibiting the reaction with N2, CO2, and H2O in the air through a not too difficult surface protective layer generation process. At least in basic research, it has proven the possibility of breaking through this problem. Of course, some people in the industry pointed out that the stability of this type of protective layer is not particularly ideal, and further in-depth research and repeated verification may be needed to further implement the results of this research direction to guide the next development direction.

　　2.2 Polarization, energy conversion efficiency, and volume parameters are important parameters that restrict practical application

　　This article studies the addition of a protective layer, which actually trades stability and cycle life at the expense of increased internal resistance (increased initial polarization). Therefore, we can see that under the condition of low reaction current, the polarization voltage difference in the first cycle is large (0.88V), and as the cycle proceeds, the system performance further decays, reaching 1.3V after 50 weeks, and 550 Week after week is 1.62V. In contrast, commercial lithium-ion batteries often only have an overpotential of about 0.1V under low current conditions, which still clearly illustrates the distance between 14250 battery technology and practical use.

　　The energy conversion efficiency corresponding to such a large polarization of lithium-air batteries is actually only 60~70%, which is still a very unacceptable data for actual use, especially for power batteries. In addition, like many nanometer-related research directions, there are few reports on the volume specific energy (Wh/L) of lithium-air batteries, and this parameter is also a crucial parameter in the field of power batteries. Here again, the content of Professor JEFFDAHN's report is quoted, which points out that the theoretical volume specific energy of lithium-air batteries is 3400Wh/L (about three times that of lithium-ion batteries). Therefore, although it has advantages in this regard, it is not as good as imagined. big. And if the excess lithium required for lithium anode applications is taken into account, the advantage may be even smaller. Therefore, the practical implementation of lithium-air technology also requires the advancement of lithium metal electrode technology.

　　Volume specific energy comparison (theoretical value) of lithium air and lithium-ion batteries, excerpted from Jeff Dahn's report "Electrically Rechargeable Metal-air Batteries Compared to Advanced Lithium-ion Batteries"

　　In addition, in this article, there seems to be no mention of mass specific energy (unit Wh/kg). You must know that when making lithium air, what we are looking for is high specific energy because the other properties of lithium air are actually not ideal. Therefore, we also very much hope that the author can release further work and provide us with information and guidance in this regard. In addition, the successful use of secondary lithium-air batteries still cannot get rid of the dependence on suitable ORR/OER catalysts, and it is even more difficult to find materials that can perform both functions at the same time.

　　2.3 Demand for power batteries

　　In fact, the main driving force for the rapid expansion of the battery industry in recent years comes from the demand of the power battery industry. Therefore, the most important thing to consider in the development and practical application of battery technology is the needs of power batteries. The main ones are as follows: aspect:

　　1) High-quality specific energy is related to the cruising range of electric vehicles, which is also where the potential and hope of 14250 battery technology lie. Of course, theoretical capacity and actual capacity are one thing, and laboratory capacity and industrial mass production capacity are another thing. In this regard, lithium-air technology still has a long way to go.

　　2) High volume specific energy Electric vehicles, represented by passenger cars, have strict requirements for battery volume. At this time, the battery must not only be light, but also small, and must be able to be stuffed into the car. For many emerging battery technologies, including lithium-air batteries, their volume-related parameters are often very unsatisfactory because low-density, high-porosity material systems are often used. Therefore, if these parameters are not considered, they may essentially be more suitable for fixed energy storage situations where volume requirements are not high, but at this time the requirements for energy conversion efficiency will be more stringent, so there seems to be some dilemma.

　　3) Energy conversion efficiency & fast charging and discharging. In fact, when we use batteries, we all hope that how much energy can go in and how much energy can come out. Of course, this is impossible, but high conversion efficiency means less energy loss and fast charging. (Small internal resistance, high energy conversion efficiency, small heat waste and small waste are more conducive to the use of fast charging). At this time, the extreme polarization of lithium-air batteries even at low rates will inevitably lead to very unsatisfactory energy efficiency and rate performance, which is also an important obstacle to overcome for its practical use in the field of power batteries.

　　4) The simple and crude reaction mechanism and fine control in industrialization may be a bit too straightforward, and may even seem inconsistent. In fact, many technologies can be developed in laboratories, but only a few have been successfully industrialized. Why?

　　For a technology to become practical, it must first clarify its basic mechanism in the laboratory, then determine the technical route that can be scaled up for industrialization, and finally achieve stable mass production through pilot scale-up. If the control of a technical reaction is too complex and difficult to fully understand even at the laboratory level, then it is almost impossible to control the reaction well and scale it up in industrial reactions. Unfortunately, lithium-air batteries are still almost at the stage where they need to be clarified in the laboratory, because they have too many side reactions and are difficult to control. It can be said that there is not even a recognized technical route in the industry, let alone Needless to say, there is still a long way to go to make it practical.

　　Compared with lithium air, the reaction of ordinary lithium-ion batteries is simple, crude and easy to implement, which is also a prerequisite for industrialization. This technology should be simple, crude and easy to understand so that it can be implemented to the operators on the production line in the simplest way. standardized processes to scale up production. At the same time, these technologies also need to be able to simply improve every step of the process, so that every detail of the process can be perfectly controlled, so that the products produced on a large scale have sufficient consistency and stability, so that the technology can truly of practicality.

　　3. In summary, lithium-air batteries are a promising technology. The latest research shows that it is very promising to solve an important technical bottleneck. However, if industrial practicality is the desired goal, it still has a long way to go. Long-term development requires joint efforts from the scientific research community and industry.

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