How to select the most reliable lithium battery technology

In recent years, electric vehicles and new energy have become an important development direction in China, and batteries can be called the core technology in this field. At the same time, there are many battery-related news on the market. The news that "X minutes X seconds is fully charged and the battery life is 1000 kilometers" is amazed by the public. However, from a professional perspective, we need to be cautious about these novelty news.

Although battery technology has improved in recent years, its performance seems to be far from public expectations: the power battery capacity used in electric vehicles has indeed increased, but its mileage is not satisfactory; On the mobile phone side, Samsung only moderately increased its battery energy density, coupled with some management and design problems, NOTE 7 suffered from "Waterloo." Although batteries have become a hot spot in society, we must rationally realize that although there are many possibilities for battery progress, it is not easy to choose a viable path and pass it(industrialization to serve society). Because choice and research and development require a lot of effort. Therefore, for the current lithium battery industry and the general community expectations: the public's expectation of rapid operation as soon as possible is understandable, but it is not desirable in industry practice. Therefore, it is very important to select and screen lithium battery technology carefully!

It is well known that lithium-ion batteries have good comprehensive performance and are the main force in the consumer electronics, electric vehicles and even energy storage industries. In recent years, social and professional expectations for them have also been high. At present, there are a variety of lithium battery technologies in the market, which to some extent has greatly attracted the attention of investors and local governments. However, it is worth noting that these technologies are generally mixed, and there are no lack of the following situations: Some packaging is very good, but the actual advanced technology is a big question mark.

Under this background, the author introduces the basic knowledge of screening lithium-ion batteries in order to carry out popular science and knowledge propaganda to the general public.

What is a lithium-ion battery? How does it work?

A lithium ion battery is a secondary battery (a battery that can be repeatedly charged and discharged), and it mainly relies on lithium ions moving between the positive electrode and the negative electrode to work. During charge and discharge, Li+ (lithium ion) is intercalated and deintercalated between the two electrodes because lithium ions store energy in the positive and negative materials, and the energy difference is the amount of lithium battery that can be stored/released. When charging, Li+ is deintercalated from the positive electrode, embedded in the negative electrode through the electrolyte, the negative electrode is in a lithium-rich state, and the positive electrode is in a delithiated state; The following figure is a typical schematic diagram of the operation of a lithium-ion battery. The reaction system used is the most classic lithium cobaltate cathode-graphite anode.

Because of the limitations of the nature of the material body, during the positive reaction process, lithium cobalt acid can generally only remove 0.5 lithium ions, and more than that will lead to structural collapse and damage. Therefore, the theoretical capacity of lithium cobalt acid is generally limited. Only about 140mAh/g, the theoretical density of negative graphite is 360mAh/g. In addition, the average voltage of the discharge of lithium cobalt acid is 3.7 V(in fact, it gradually drops from the maximum charged voltage of 4.2 to about 3V, 3.7 is the average), and at the same time, considering the very low negative potential value of graphite, And the proportion of various other components in the battery, and finally we can get the lithium battery(eg mobile phone) with an energy density of about 160 Wh / kg.

Energy density is the most basic core parameter for various batteries and must and should be open and transparent data. However, in commonly used lithium-ion batteries, due to different materials and technical systems, the energy density can range from several tens(such as lithium titanate) to about 200 Wh / kg. Once this value is extremely high(or extremely low), it is worth focusing on: On the one hand, with the efforts of technicians, a high energy density has been made, and there may be technical breakthroughs that are worth celebrating; On the other hand, it is not ruled out that some people have exaggerated performance. If energy density data are not easily marked, consumers should think carefully before buying / investing(because careful speculation: reluctant to tag is mostly due to poor performance). The basis of the battery is electrochemical science, and for this field, there is a simple but most basic principle: any type of battery, the mechanism of storing energy needs to write a corresponding electrochemical reaction equation so that its voltage situation can be known. Determine its theoretical limit energy density, etc., and these are only the most basic information for the battery. No matter how new this battery technology is(or just what related people say), its principle must be written as a chemical equation and implemented on paper so that it can withstand the test of common sense in the academic world. I recently have friends who have been promoted a battery, but salespeople are very reticent about the principle of the most basic battery reaction, because "fear of leaks" and say some theories that violate the basic knowledge of electrochemistry, so it is still recommended to do a careful study before purchasing and adopting this technology. Be careful. In the case of batteries, the mechanism of electrochemical reactions is the most basic information, requires transparency, and this is only the first step. The real barrier to battery engineering lies in the optimization of materials, overall structure, and processes. Even if the basic principles are clear, it is still necessary to consider the difficulty of implementation. The hardships of new technology engineering are far beyond the imagination of many people. In recent decades, China's industrial achievements have benefited from the hard work of technicians, unremitting persistence and rigorous research. The battery industry in China can not achieve the current achievements without the same down-to-earth practical spirit and hard exploration in industrial engineering.

Therefore, allow me to extend it again. There have been many previous analyses of the doubts about "graphene(base)(lithium ion) batteries", "graphene enhanced(lithium ion) batteries" and "graphene assisted(lithium ion) batteries". There are no other technologies such as lead acid).

Here again, it is emphasized that graphene is used in lithium batteries and can only be used as a negative active material and conductive additive. The negative electrode material has high cost, low volume density, extremely low efficiency for the first time, and there will be structural change during use. The cost is high and it is basically impossible. As a conductive additive, it competes with other carbon materials and has no obvious advantages. It also faces a series of practical problems such as dispersion in the project. In fact, few of the various graphene battery technologies in the market today are willing to explicitly and openly write their electrochemical reaction equations, so that their peers can be tested from a scientific point of view. The reason is worth thinking about.

In addition, Advanced Materials recently published a long summary of why graphene has made little progress in batteries in recent years. The original address was: Http://onlinelibrary.wiley.com/doi/10.1002/adma.201603421/abstract. A professional is currently translating it into Chinese. If you are interested, please visit the relevant link at: Https://zhuanlan.zhihu.com/p/24844227.

In contrast, many new points, such as batteries such as aluminum and magnesium, do exist beyond the technical reliability of the reaction mechanism, so there is at least room for further discussion and analysis of this technology.

It's important to name a name-whether it's reliable or not

It's important to name -- having a catchy name is good for memory and communication. There are many "graphene batteries" in the market that spread in this way. The main advantage is that it is also easy to remember. In contrast, three lithium batteries, Silicon negative battery appears to be more common. It is important to enhance communication, but if the name is too important to hide or distort the technology that is truly core and competitive, then it is to some extent a matter of name. In fact, lithium batteries are generally named in the industry with general rules, which can be briefly introduced here:

1) Named after the most important component, because the cathode material of the lithium battery is often the most important decision link in the energy density of the lithium battery, it is the most named. For example, lithium iron phosphate batteries, ternary batteries, lithium cobalt acid batteries and so on. With the development of technology in recent years, some high-performance negative electrode materials have appeared or are on the scene, so the naming of lithium titanate batteries, including later Silicon negative electrodes(batteries), is also reasonable. Similarly, this principle is also applicable to batteries of other systems, such as nickel hydrogen, lead acid, etc.. Almost the battery name can initially summarize the core reaction. We need to emphasize here: Lithium-ion batteries with a little graphene can not be called graphene batteries, and lithium air batteries with a little graphene can not be called graphene batteries. This is like adding MSG fish meat or is only regarded as fish meat. Of course, if the addition of graphene does enhance performance, then the enhanced performance needs to prove the effect so that scientific research and industry can be convinced.

2) Named after the reaction mechanism/characteristic, the most typical is the liquid-flow battery. Liquid flow batteries are positive and negative substances that exist in liquid form. They are separated by a diaphragm in different cavities. They are transported to the diaphragm interface by a pump for electrochemical response to realize batteries that are stored or released by electric energy. From a popular perspective, it can be understood that liquid-flow batteries are several chemical tanks that pump reaction liquids to the interface to achieve current storage. Such a battery has a low energy density of only a few dozen Wh/kg, which is only suitable for industrial fixed storage and can hardly be used in automobiles. Because the vanadium system in liquid-flow batteries is relatively mature, it is sometimes referred to as a vanadium battery. A previous report said that "vanadium" batteries are used in cars, the market size is trillions of dollars, and the mileage is N kilometers. From a professional point of view, the message is false. Of course, the author does not deny the meaning of vanadium liquid-flow batteries: such batteries have a long life, so in the site of easy storage energy application scenes will have their own unique advantages.

Preliminary summary: The battery is either named after the main group element, or named after the reaction mechanism and characteristics. In short, it must be named after its most core components or its most representative characteristics. Once separated from the naming of such principles, there may be a mystery behind it: there may be a meaning of processing packaging with popular concepts, and it may be a cover for its technical essence. Therefore, the author recommends that the public, when seeing some professional and fashionable battery names, need to look like a torch, starting from the name of the root.

Third, what should you pay attention to in the publicity of good news and bad news?

Recently, many batteries have exaggerated the facts in their promotional materials, such as "charging two days at a time, energy density 1000 Wh / kg, performance improvement of 50 %, life span X years", etc.. Ordinary people may easily believe it. But after testing, many may find that such battery technology is not as magical in practice as advertised. So how do you sift through the root cells?

The simple rule: Many companies advertise themselves and promote good news. That is, only 5 of the 10 very important core properties are marked. If you don't know, the other 5 performance may not be as good as the industry average. For any engineering application technology, all aspects of the product's performance should reach the basic pass line, otherwise it can not be used in practice. Therefore, if a certain performance of the battery is really good, the company will definitely report positively, but if it is not actively marked, it is very likely that the performance can not be done well enough.

Therefore, it is recommended to study the performance of each battery in practice. If the technology provider does not disclose these performances, there is a good chance that there will be a short plate in this area. The author believes that it is particularly necessary to pay attention to the relative opposition of the performance of a battery. For example, a fast-charging battery needs to know its energy density, and an energy-type battery needs to know its power density, life, and especially volume-related density parameters. This may reduce the probability of buying a product that is not in line with the actual product, and the worst can also negotiate with it.

In general, a battery product generally has to introduce its mass energy density, volume energy density, mass power density, volume power density, life span, voltage, cost(price information may not be in the brochure), applicable environment, safety. It is important to emphasize here: 1) The volumetric energy density is very important. A battery of the same mass and energy can not be used if it is too large to completely plug into the actual service space. The mobile phone is precisely because of the small volume space, so the use of the largest volume energy density of lithium cobalt acid batteries. 2) Power density is popular, that is, the characteristics related to fast charging. Here we must emphasize that the author believes that the battery body performance is good enough, and the contribution to fast charging accounts for more than half, compared to electric control and other links are slightly smaller. For the analysis of power density and fast charging, see the previous article: "The fast charging technology that is full of words for a few minutes and no other performance is said is a rogue."

IV. Screening of Two Publicity Strategies

One: "Performance improvement XX %". This can be said to be meaningful, but it can also be said to be meaningless, because the explanation for the improvement of the reference material is in the hands of the manufacturer -- the manufacturer can make a sample with poor performance as a control sample -- and the researchers are very familiar with this process. Therefore, the key is not the relative increase of the manufacturer, but the absolute value of its performance -- such as the 35 % increase in the energy density of the XX reinforced iron phosphate battery -- can actually be verified. What are the basic/enhanced energy density values? 100 Wh / kg? 130 Wh / kg? And ...

The second: "How many kilometers to continue, standby X days." This is a scientifically less rigorous expression. It is recommended that the public not believe such data and pay more attention to the "hard indicators" of the battery body mentioned above. The reasons are as follows:

The X-kilometer can be used to maximize the endurance by stacking a large number of batteries based on the “one car battery” method, but this is completely different from the actual load of the electric vehicle in the actual service, so it is only for reference (and the new version) The electric vehicle specification has already begun to stipulate that the battery accounts for the weight ratio of the whole vehicle.

The standby X-day is also different from the normal power consumption: What are the standby test conditions? Do you need to turn on the power saving mode? Do you want to turn off the Wi-Fi function? These elements can not generally be mentioned. It is also possible to do such non-rigorous tests in the private sector. However, if it rises to local industrial investment, it involves a large amount of money and manpower investment. It uses such emotional words as policy guidelines for the development of a region, and then invests tens of millions of dollars in funds. It is reckless.

5. Which tomorrow's star technologies may be more promising?

With the unremitting efforts of scientists and engineers, many new energy storage technologies have gradually matured in recent years, and it is expected to enter our lives in the next few years and bring changes to the world. In these tomorrow's star technologies, the technical route and maturity are different, and this can be briefly introduced.

All-solid-state battery technology: addresses safety, energy density, and special features such as flexibility. At present, some technical routes are close to the conditions of industrialization. In the next few years, there should be products coming out, and advanced technology routes such as all ceramics may be more oriented towards special high-performance batteries, and mature in the next few years. hope.

Lithium-sulfur battery technology: Solving the safety of cycle and dendrite is a big problem, and its technology maturity time may be longer, and the main solution is the demand of high energy density direction.

Sodium-ion battery technology: more oriented to fixed energy storage needs, the technology is currently in the experimental research - industrial incubation stage, Enli Energy and Aquion's technology are worthy of attention, there are also manufacturers in Japan to step up the introduction of this aspect product.

Metal air secondary battery technology: This type of battery can theoretically achieve extremely high energy density, but in fact it faces problems such as large overvoltage, poor reaction kinetics, and side reaction of impurity gases in the air. Lower, the time required for industrialization may be longer.

postscript:

The new energy industry related to lithium batteries is currently developing rapidly, which embodies the ardent expectations of the Chinese government. In general, the lithium battery industry has developed rapidly, but in the past two years, there have been surprises and disappointments (such as deception). It is really good for the industry to attract people, but it is inevitable that there are people with different voices and motives. What we can do is to promote the healthy development of the industry, rationally optimize the allocation of social resources, and issue a voice based on the experience of production-study-research, so that more people outside the industry can understand the basic situation within the industry, thus promoting the health of the whole industry. Development contributes to its own meager strength.

The page contains the contents of the machine translation.