The arms race for solid-state batteries in electric vehicles began quietly.

In the past few years, the technology of power battery has developed by leaps and bounds, but safety risks and mileage anxiety are still the "curse" that it is difficult to get rid of. At the same time, solid-state battery has become the new favorite of the industry in the midst of controversy and skepticism. With the entry of various giants, the future of solid-state battery is gradually clear.

On January 9 this year, NYSE:NIO launched a high-profile 150kWh solid-state battery package with an energy density of 360Wh/kg on its NIO Day. The 360Wh/kg ET7 sedan with the battery pack will last for more than 1000km, which is eye-catching.

The popularity of Weilai has not subsided. Volkswagen Group said on its Power Day on March 15 that it would focus on solid-state battery technology in the future, while Volkswagen directly and rudely threw out its goal: solid-state batteries are expected to start using in 2025.

In April, the not-to-be-left-behind BMW Group also laid out plans for solid-state batteries: a prototype car with solid-state batteries by 2025 and mass production by 2030.

Not only car companies, but power battery giants are also laying out solid-state batteries: Ningde Times has invested 3.3 billion yuan to build a 21C innovation laboratory for the research and development of next-generation batteries such as metal lithium batteries and all-solid-state batteries; LG Chemical says it will commercialize all-solid-state batteries between 2025 and 2027; Panasonic plans to launch an electric vehicle with solid-state batteries in 2025.

For a while, solid-state batteries have become an invisible battlefield for industry giants. Why are solid-state batteries so attractive and what is the current progress of development?

Solid-state battery has become a must-compete high ground for giants.

[1] what is a solid-state battery?

Solid-state batteries sound mysterious, but it's easy to understand them with traditional liquid lithium batteries, because they work on the same principle. The traditional liquid lithium battery is also vividly called "rocking chair battery" by scientists. The two ends of the rocking chair are the positive and negative poles of the battery, and in the middle are liquid electrolytes and diaphragms, while lithium ion is like an "athlete". The athlete runs back and forth at both ends of the rocking chair, and the process of charging and discharging the battery is completed.

When it comes to the solid-state battery, the "athlete" still runs back and forth between the positive and negative poles. The difference is that the sports ground has changed from liquid electrolyte to solid electrolyte. In addition, solid-state electrolytes also play the role of separating positive and negative electrodes, that is, they act as diaphragms, so solid-state batteries no longer need diaphragms.

In terms of composition and structure, solid-state batteries are simpler.

Let's talk about the classification of solid-state batteries, solid-state batteries are divided into three routes: polymer, oxide and sulfide according to their electrolytes, which will be analyzed in detail below.

Figure 2: main types of solid electrolytes, source: Tianfeng Securities

Solid state battery VS liquid lithium battery

Compared with liquid batteries, solid-state batteries have the advantages of safety and energy density.

Let's start with the security issue of the highest concern. Nowadays, the development momentum of electric vehicles is strong, and the sales of electric vehicles have repeatedly reached new highs, but the hidden danger of battery has always been the "sword of Damocles" hanging over electric vehicles. For example, Weimar had four spontaneous combustion accidents in more than a month last year, which once raised concerns about the future of electric vehicles.

In fact, the safety risk of electric vehicles lies in the liquid lithium battery. Once the battery is squeezed and impacted, the diaphragm will break, causing a positive and negative short circuit, and a large amount of heat is generated inside the lithium battery, coupled with the flammable organic solvent in the liquid electrolyte, the result is that the battery catches fire or even explodes.

Car companies and power battery companies have been doing their best to improve battery safety performance. For example, adding flame retardants to the electrolyte, optimizing the BMS thermal management system, and using high-strength, high-temperature battery diaphragm, it is a pity to cure the symptoms rather than the root of the problem.

But solid-state batteries are expected to completely solve the safety problem. First of all, the positive and negative poles of solid-state batteries are not prone to short circuit. Secondly, the solid electrolyte is not only non-flammable, non-volatile and even resistant to high temperature, and the battery will not catch fire or explode under the same extreme circumstances.

Let's talk about the energy density of the battery, that is, mileage anxiety. Although the range of mainstream electric cars can reach more than 500km, high-end models even exceed 700km. But in practice, this range is discounted (the so-called operating mileage), and, unlike fuel-fueled cars, most electric car owners don't drive their cars until they have 10% left to recharge.

Mileage anxiety can only be solved by stacking the energy density of the battery. According to the Roadmap of Energy Saving and New Energy vehicle Technology, the energy density target for power batteries will be 400Whhand kg in 2025 and 500Wh/kg in 2030. To achieve the 2030 goal, the existing liquid lithium battery technology route may not be a big task, just 350Wh/kg energy density ceiling is difficult to break, but solid-state battery energy density can easily surpass 350Wh/kg.

It should be noted in advance that the energy density of the battery depends on the positive and negative materials. If the liquid electrolyte is simply replaced by solid electrolyte, if the existing positive and negative materials are not changed, the battery safety can only be improved, but the battery energy density can not be improved. Therefore, solid-state batteries need to be equipped with the innovation of positive and negative materials.

When it comes to cathode materials, the current power battery enterprises are developing towards high nickel. From the ternary 5 system to the ternary 8 system, the nickel content becomes higher, but the stronger the battery activity is, the more unstable the battery will be, and the safety problems mentioned above are more prominent. Although the current energy density of the ternary 8-series is high, it is not widely used, and the mainframe factory installation still uses 5-series power batteries. There is also a cost factor, which will not be discussed here.

Thanks to the high safety of solid-state batteries, the positive electrode of solid-state battery does not have to stop at 8-series materials, and can even dry up to 9-series (ultra-high nickel). The energy density of the positive link can reach 700Whhand kg, which will make a qualitative leap.

And look at the negative material. In fact, the upgrading route of negative materials has reached a consensus in the industry, that is, from the current graphite negative electrode to lithium metal negative electrode. Among the known negative electrode materials, the energy density of lithium metal negative electrode is the highest, and its gram capacity is more than 10 times that of graphite negative electrode in liquid lithium battery.

The question is, since the lithium negative electrode is so good, why don't existing power batteries use it? The crux of the problem is still in the liquid electrolyte, lithium metal negative electrode in the liquid electrolyte is basically unstable, the two will react violently, it can be said that "fire and water are incompatible". But in solid-state batteries, they can live in harmony.

In a word, it is the solid-state battery that gives room for the development of new cathode and cathode materials.

In addition, it is worth adding that liquid lithium batteries often need to package the single cell first and then in parallel and then in series, if you want to save the process in direct series, it will lead to positive and negative short circuit. Because the solid-state battery does not contain liquid and does not have the problem of short circuit, it can be assembled in series directly. In addition, liquid lithium-ion batteries need a cooling system to prevent excessive temperature during their use. For solid-state batteries, because of their high safety, the cooling system can be simplified or even eliminated. Therefore, in the actual mass production process of solid-state battery, the group cost will be lower, and the whole production process will be simpler.

The solid-state battery is not so much a "subversive" liquid lithium battery as an upgraded version of the liquid lithium battery.

[3] flaws and shortcomings coexist with each other.

Since solid-state batteries are so good, why don't car companies "upgrade" quickly, instead of using traditional liquid lithium batteries? The reason is that replacing liquid electrolyte with solid electrolyte not only solves some problems, but also brings new troubles. Before solid-state batteries are in mass production, there are several key issues that need to be overcome.

First, the ionic conductivity of solid electrolyte is on the low side. The so-called ionic conductivity refers to the smooth movement of lithium ions in the electrolyte.

The conductivity of solid-state battery is generally lower than that of liquid ion, such as polymer electrolyte, and its ionic conductivity is even several orders of magnitude lower than that of liquid ion. It is equivalent to the resistance of the "athlete" to run, and the speed is much slower than before, or even too much resistance to run.

Second, the interface impedance between the solid electrolyte and the electrode is large.

There is a solid-liquid contact between the traditional liquid electrolyte and the positive and negative electrodes, and the interface has good wettability, which can be said to be a "tight seam", and there is no great impedance between the interfaces. However, the solid electrolyte and the positive and negative electrodes are in solid-solid contact, and the contact effect is much worse, so the transmission resistance of lithium ion between the interface is greater. This is like an "athlete" who used to run on a flat track, but now it is replaced by a potholed mud road, which naturally cannot give full play to its true level.

Because of the low conductivity and high interface impedance of solid-state battery, the transfer efficiency of lithium ion in the battery is too low, which affects the fast charging capacity and cycle life of the battery, and can not release the capacity of the battery normally.

Considering the existing technology level, it is still difficult for many companies to achieve all-solid-state batteries in one step, and the second step is to take the "three-step" path from semi-solid state, quasi-solid state to all-solid state. The Weilai solid-state battery mentioned at the beginning of the article is actually a semi-solid state battery.

Third, the cost is high.

Oxides and sulphide electrolytes are porous ceramic materials, which are characterized by brittleness. It is difficult to process them into thin electrolytes, and they break off at the slightest inadvertent. Even if it can be processed, the yield of the finished product is not much better with the existing process level and equipment capacity.

And solid-state batteries are still far away from mass production, not to mention the supporting industrial chain. The reason why traditional liquid lithium batteries have been able to reduce costs in the past few years is largely due to the coordination of the industry chain. At present, the cost of solid-state batteries remains high.

All kinds of players enter the game, and mass production is still in the long term.

The technical bottleneck of solid-state battery has not been broken through, and industrialization still has to face many problems, but it does not affect the enthusiasm of all kinds of players flocking in.

For car companies, the starting point is much more complicated. First of all, it is certain that electric cars are the future of cars, and traditional car companies are eager to transform. Battery is the core of electric vehicles, car companies naturally want to be in their own hands, car companies have been "stuck" by power battery companies for a long time, how willing to be controlled by others again. Solid-state batteries are a great opportunity to regain the initiative, which is why fuel vehicle giants such as Volkswagen and Toyota deploy solid-state batteries.

For power battery enterprises, on the one hand, solid-state battery can solve its long-term problems of safety and energy density, which is very attractive. It is no exaggeration to say that whoever first mastered solid-state battery technology in the future will be able to give advice. Therefore, not only Ningde era, LG, like BYD, Guoxuan Hi-Tech and other second-line battery companies, all have the same layout of solid-state batteries. On the other hand, under the existing liquid lithium battery route, domestic second-line battery enterprises have been suppressed by Ningde era. Even BYD, which has a "blade battery" in hand, can hardly shake the position of Ningde era. On solid-state batteries, everyone has the opportunity to stand on the same starting line.

Throughout the global participants, different enterprises "believe" in different solid electrolyte routes: domestic enterprises are mainly oxide routes, European and American enterprises prefer polymer routes, while Japanese and Korean enterprises are more keen on sulphide systems.

Figure 8: global overview of key solid-state battery enterprises, source: forward-looking Industrial Research Institute

[1] Polymer faction

The polymer electrolyte route is the earliest solid-state battery route to realize application.

As early as 2011, the French Bollore company launched the solid-state battery with polymer electrolyte, but the ionic conductivity of the solid-state battery at room temperature is so low that it needs to be equipped with an extra heater, and the energy density can only reach 100Whhampkg, which basically has no commercial value.

As the problem of low conductivity of polymer electrolytes has been difficult to solve, the mainstream solid-state battery enterprises are still dominated by oxide electrolytes and sulfide electrolytes.

[2] oxide faction

The comprehensive performance of oxide faction is the best among the three solid electrolyte routes, and the more representative ones are Jiangsu Qingtao, Taiwan Huineng and foreign QuantumScape companies.

Jiangsu Qingtao is a typical start-up, founded in 2016. Compared with power battery companies, without technical baggage, progress is smooth. Qingtao has completed the country's first mass-produced solid-state lithium battery production line in November 2018, and has been formally used in special power supplies, high-end digital and other fields. Last year, a new energy prototype equipped with Qingtao solid-state power lithium battery was successfully launched at BAIC, while Qingtao's first phase of the 1GWh solid-state power battery project was officially put into production.

Compared with Qingtao, Taiwan Huineng has a clearer plan for the future of solid-state batteries. In 2013, Huineng achieved commercial mass production of solid-state lithium batteries in the consumption of lithium electricity. In 2019, Huineng partnered with Weilai to produce a customized "MAB" solid-state battery package (semi-solid). According to its plan, semi-solid lithium-ion batteries will reach the capacity of 1GWh in 2021 and all-solid-state batteries will be mass-produced in 2024.

Peripheral contestant Ganfeng Lithium Power, although it is a lithium material enterprise, has also done a lot of layout on solid-state batteries. According to the information disclosed in the 2020 report, Ganfeng Lithium Power has invested in the first and second generation of solid-state lithium battery research and development pilot production lines, but they still belong to the mixed solid-liquid electrolyte stage, and the energy density can not exceed 300Wh/kg. Ganfeng Lithium Power has been in the layout of the third generation of solid-state lithium batteries based on metal lithium negative electrodes, and the energy density will exceed that of 400Wh/kg in the future.

Finally, QuantumScape, a company focused on investment by Volkswagen Group, listed through SPAC in November last year, is the only listed company in the industry with solid-state battery as its main business.

According to the information published on its website, QuantumScape has technically broken through the bottleneck of low ionic conductivity of solid-state batteries, quickly charging even faster than traditional liquid lithium batteries, charging 80% in 15 minutes, and significantly superior to existing liquid lithium batteries in terms of energy density, cycle life and safety.

However, it only shows the test results of monomer lamination, not the effect of being loaded on a car. In the final analysis, this is still a laboratory product, and there is still a gap between mass production and mass production. According to QuantumScape's prospectus, the company will set up a 1GWh pilot production line in 2024 and carry out tests on Volkswagen to achieve commercial mass production of its solid-state batteries.

[3] sulphide factions

Sulfide electrolytes are actually derived from oxide electrolytes. considering the low conductivity of oxide electrolytes, scientists replace oxygen in oxide electrolytes with sulfur. Because the electronegativity of sulfur is smaller than that of oxygen and the binding of lithium ion is smaller, it is beneficial to get more free-moving lithium ion. To put it simply, sulphide electrolytes have higher ionic conductivity, which is close to the level of liquid lithium battery system.

However, sulphide electrolytes solve the problem of ionic conductivity, but also bring other difficulties. Because sulphide electrolytes are sensitive to air and prone to adverse reactions, the production of sulphide electrolytes is demanding on the environment. It is a big test for the equipment, and the result is that the production cost is extremely high.

The fastest progress in the sulphide route is Toyota of Japan.

At present, Toyota has more than 1000 patents in the field of solid-state batteries, ranking first in the world. In July last year, the general manager of Toyota's battery business revealed that Toyota had successfully built solid-state batteries as planned and installed them in the concept car, which is expected to be in mass production in 2025.

Finally, it is worth talking about the Ningde era in China. As early as 2016, Ningde Times announced its R & D path on sulphide solid-state batteries. However, the information about its solid-state battery has been kept secret, and there is very little public information until January this year. It was not until January this year that it took the initiative to disclose two patents related to solid-state battery, namely, "a solid-state electrolyte preparation method" and "a sulfide solid-state electrolyte sheet and its preparation method". According to the patent summary, the above patents are aimed at improving the electrical conductivity of the solid-state electrolyte and reducing the impedance of the solid-solid interface. That is, the deficiency of solid-state battery mentioned earlier.

Ningde era has not disclosed the mass production time of solid-state batteries. In the past year, Ningde era has frantically increased its power battery capacity, with the announced long-term planned total production capacity approaching 500GWH, and some of which has been scheduled for after 2025. From this point of view, Ningde's solid-state battery is also not the focus of mass production in the short term.

An unfinished ending to be continued

It is undeniable that the technology of power battery is changing with each passing day, which plays an important role in the development of electric vehicles. With the continuous improvement of the permeability of new energy vehicles, the market demand for power batteries is getting higher and higher. the traditional liquid lithium battery with obvious shortcomings has been difficult to adapt to the future rhythm.

As a recognized next-generation battery route in the industry, solid-state battery can perfectly solve the shortcomings of traditional liquid lithium battery. Enterprises at home and abroad have high hopes for it, one after another to speed up the research and development of solid-state battery, hoping to seize the market opportunity.

Nowadays, solid-state battery has made a lot of substantial progress, but technology and cost are still two mountains blocking the industrialization of solid-state battery, which can not be crossed in a short time. With reference to the planning of mainstream solid-state battery enterprises, mass production time is generally after 2025, and the industrialization of solid-state battery is estimated to be 10 years later.

Looking back at history, 10 years is actually not a long dimension. Ten years ago, China sold less than 10, 000 pure electric vehicles. By 2020, it has sold more than 1 million pure electric vehicles. Now in the industry optimistic and various enterprise layout, solid-state battery industrialization process is expected to achieve faster than expected development, while waiting for solid-state battery, we also have confidence.

For the players who end up, the problem they have to face is that the industrialization of solid-state batteries will reshape the existing lithium battery supply chain, such as diaphragms and liquid electrolyte companies, which will be "subverted" if they are not transformed and upgraded in time.