Warum können Festkörperbatterien bisher noch nicht in Kraftfahrzeuge verbaut werden?

Solid-state batteries have high thermal stability of their electrolytes, which allows them to balance long-range driving and safety. For a long time, they have been regarded by the industry as the ultimate form of power batteries. However, due to multiple challenges such as technology, process, and cost, solid-state batteries have never been able to leave the laboratory and be widely used in vehicles.

Recently, however, some second- and third-tier power battery companies, as well as automakers like Chery, have successively announced their R & D progress on solid-state batteries, giving the industry a glimmer of hope for the mass production of solid-state batteries.

On October 23rd, Sunwoda released its solid-state battery "Xin·Bixiao" at the New Energy Battery Conference. It said that the energy density of this product can reach 400Wh/kg. In contrast, the energy density of current mainstream lithium iron phosphate batteries is about 200 - 250 Wh/kg, and that of ternary lithium batteries is 250 - 300 Wh/kg.

The operating temperature range of this solid-state battery is from -30°C to 60°C, and its cycle life is 1,200 cycles.

Meanwhile, Sunwoda also claimed that it will build a 0.2GWh pilot production line for polymer solid-state cells by the end of this year and has successfully developed and tested a laboratory sample of a lithium-metal super battery with an energy density of 520Wh/kg.

On October 18th, at the Chery Global Innovation Conference, Chery showcased its self-developed "Rhino S" all-solid-state battery module. The energy density of the cells of this product reaches 600Wh/kg, and it is expected to have a range of 1,200 - 1,300 kilometers after being installed in a vehicle. Chery plans to mass-produce the "Rhino S" battery in 2027.

The joint promotion by battery manufacturers and automakers, combined with several recent cases of new energy vehicle fires, have suddenly brought solid-state batteries into the spotlight.

However, the hype in public opinion is unlikely to change the reality that solid-state batteries cannot be mass-produced on a large scale in the short term.

As early as July this year, CATL clearly stated in an earnings conference call that solid-state batteries will only be produced in small quantities in 2027 and may be mass-produced on a large scale in 2030. Last year, Zeng Yuqun, the chairman of CATL, also pointed out that if the maturity of solid-state battery technology and manufacturing is rated on a scale of 1 to 9, the current highest level in the industry is only 4.

Sunwoda is more conservative than CATL. On the day of the release of "Xin·Bixiao", a senior executive of Sunwoda said, "Japanese and American companies once claimed that they would industrialize all-solid-state batteries in 2027, which was overconfident. The most optimistic scenario is that small-scale production may start after 2030." Recently, at the Chery Technology Day, Chery adjusted its previous claim of "installing solid-state batteries in vehicles in 2026 and mass-producing them in 2027" to "conducting the first batch of vehicle installation verification in 2027".

Then why have solid-state batteries, which the industry has been eagerly awaiting, been slow to be used in vehicles?

The Problem of Solid-Solid Interfaces in Solid-State Batteries

The poor dynamics of the electrolyte in solid-state batteries and the large impedance between solid-solid interfaces are important technical challenges that hinder the large-scale mass production of solid-state batteries.

Since the electrolyte in solid-state batteries is solid, its ion conductivity is naturally weaker than that of liquid electrolytes.

Moreover, the electrolyte in liquid batteries can fully infiltrate the positive and negative electrodes of the battery, forming a stable ion transport channel. In contrast, the contact between the solid electrolyte and the solid electrode is a hard contact, and the contact degree is not as good as that of the solid-liquid combination. In addition, during the charging and discharging process of the battery, the negative electrode will experience a breathing effect due to the intercalation and deintercalation of lithium ions, causing the negative electrode to expand and contract, which leads to the failure of the contact between the negative electrode and the solid electrolyte.

Therefore, it is crucial to find battery materials that can not only provide high energy density but also overcome the above-mentioned obstacles.

A person in the battery industry told 36Kr that the industry currently generally uses nine-series high-nickel materials as the positive electrode material for solid-state batteries, in which the ratio of nickel, cobalt, and manganese is 9:0:1.

Since high-nickel materials have been used in ternary lithium batteries, companies like CATL, which have accumulated some experience in the field of high-nickel ternary batteries, can reuse most of their previous technological capabilities in solid-state batteries.

The choice of electrolyte material is a controversial topic in the solid-state battery industry.

Zhu Xingbao, the chief scientist of Gotion High-Tech, once told 36Kr, "There are six technical routes for the electrolyte of solid-state batteries. The polymer route was the first to be proposed. It is easy to handle at the interface and can quickly recover after fragmentation. Its fatal problem is poor conductivity, except at temperatures between 60 - 80°C."

Later, the oxide route was proposed. It has high stability and conductivity, but poor mechanical processing performance, just like a glass cup that breaks easily when touched.

Today, the most mainstream electrolyte technical route is the sulfide route. Its ion conductivity is close to that of the electrolyte solution, but this material is very sensitive. Once it comes into contact with liquid, its conductivity declines rapidly, and it quickly produces hydrogen sulfide when it comes into contact with water.

There are also other types of materials such as halides, borohydrides, and thin-film solid electrolytes."

In addition, 36Kr also learned from other people in the battery industry that although sulfides have strong ion conductivity, their manufacturing process is relatively complex. Since sulfide electrolytes are sensitive to air and the hydrogen sulfide produced by their reaction with air is highly toxic, developing highly automated, corrosion-resistant, and airtight processes and equipment for mass production is quite difficult. Moreover, due to the air sensitivity of sulfides, it is also difficult to ensure the yield and consistency of the electrolyte and the battery.

"Oxides have relatively poor ion conductivity, but they have better contact with the electrode interface. Currently, sulfides are the main direction, and less attention is paid to oxides. However, no company has completely abandoned oxides."

Some people have also tried to solve the problem of interface contact in solid-state batteries through methods other than materials.

Recently, Xinhua News Agency reported that some researchers have tried to introduce iodine ions into the electrolyte, which move to the electrode interface under the action of an electric field to form an iodine-rich interface. This interface can attract lithium ions and fill the gaps and pores between the electrolyte and the electrode.

However, a preliminary analysis by a person in the industry for 36Kr shows that "iodine ions are easily reduced to iodine, which accumulates at the interface. At this time, these iodine ions may not be able to fill the gaps between the electrolyte and the electrode."

Immature Anodes, Complex Processes, and an Unviable Business Closed-Loop

Not only are the electrolyte materials immature, but the anode materials for solid-state batteries are also not well-developed.

An engineer from a battery manufacturer explained to 36Kr that the purpose of developing solid-state batteries is to pursue higher energy density. Therefore, although graphite can also be used as the anode for solid-state batteries, due to its low energy density, the industry generally uses a silicon-carbon anode, which is a mixture of graphite and silicon, in the field of solid-state batteries.

However, while the silicon-carbon anode increases the energy density of solid-state batteries, it also brings a new problem. "Since the anode material undergoes continuous lithium-ion intercalation and deintercalation processes, the current graphite anode will expand to a certain extent as the material ages. Silicon-carbon is more prone to expansion than artificial graphite because the material property of silicon is to expand easily. That is to say, the cycle life of the silicon-carbon anode is actually quite short."

The manufacturing process is another important factor that hinders the large-scale mass production of solid-state batteries.

Zhu Xingbao once quantified the changes in the production line from liquid batteries to semi-solid batteries and then to solid-state batteries for 36Kr: "When liquid batteries evolve into semi-solid batteries, there will be a 3% - 5% change in the production line. The change in the production line from liquid batteries to all-solid-state batteries is even greater."

Pan Ruijun, the chief engineer of Gotion High-Tech's solid-state battery project, gave a more detailed introduction to the difficulties at the process level of solid-state batteries: "In the solid-state battery experimental line that Gotion High-Tech has currently established, at least about 60% of the changes are made from the power system to the equipment." In his view, the biggest process obstacle in the production of solid-state batteries at Gotion High-Tech is the coating of the solid electrolyte.

"Solid-state batteries require thin coating, which has requirements for the film. In addition, the high-temperature formation process requires new equipment. Solid-state batteries do not have a separator, so the separator needs to be made by coating and then placed between the positive and negative electrodes by a certain method. It took us many years to figure out this difference."

Since solid-state batteries require significant changes to the existing production lines of liquid batteries, many companies today regard semi-solid batteries as a transitional technology. They first use the production equipment of liquid lithium batteries to mass-produce batteries with higher energy density and greater safety. At the same time, they gradually iterate on the process and equipment until they meet the mass production standards for solid-state batteries.

The significant changes in the process and equipment, combined with the higher raw material costs in the bill of materials (BOM), make the comprehensive cost of solid-state batteries high enough to discourage many players with insufficient financial strength.

Recently, Yang Hongxin, the chairman of Honeycomb Energy, publicly pointed out that the current cost of all-solid-state batteries is 5 - 10 times that of liquid batteries. Even with sufficient scale, the cost of liquid batteries already accounts for more than 30% of the total cost of a vehicle, causing many automakers under great cost-reduction pressure to complain. The 5 - 10 times higher cost of solid-state batteries is obviously difficult for both automakers and end-users to bear.

That is to say, at least for now, it is difficult to make the business logic of solid-state batteries work.

Then why has this battery, which is difficult to be widely used in vehicles in the short term from both technical and commercial perspectives, been hyped up recently?

For second- and third-tier power battery manufacturers, they hope for a complete technological route change in the battery industry to gain an opportunity to overtake CATL by changing lanes. Solid-state batteries are a completely new system that is different from liquid and semi-solid batteries.

For automakers, if the landscape of the battery industry can be reshaped, they will have more initiative in the game with CATL.

For end-users, the recent concentrated cases of new energy vehicle fires have raised their concerns about the safety of liquid batteries. These accidents have made them more eager than ever for the arrival of a safer battery with higher energy density.

As a result, many people have forgotten that solid-state batteries may not be mass-produced even in 2027.

Author's WeChat: luckg17305264638