There has truly been a significant breakthrough in all-solid-state batteries this time.

During the National Day holiday, there have been a series of technological breakthroughs in the field of all-solid-state batteries, which have been a hot topic in recent years.

On October 7th, the research team led by Huang Xuejie from the Chinese Academy of Sciences and others published a latest research paper on all-solid-state batteries in Nature Sustainability. The Xinhua News Agency reported on this research, and many media outlets reposted the news. The core of this research lies in overcoming the "solid-solid interface" problem of all-solid-state batteries.

According to the paper, this research can form a DAI (Dynamic Adaptive Interface) layer during the charging and discharging of solid-state batteries, ultimately maintaining stable cycling under low or even zero external pressure. When the battery is out of the laboratory environment, the capacity of the pouch battery remains above 70% after 300 cycles, and it supports a 5C charge-discharge rate.

Another piece of news is that the research team from the Institute of Metal Research of the Chinese Academy of Sciences has also made an innovation at the "molecular scale", significantly reducing the interface impedance of solid-state batteries and improving the ion transport efficiency. The relevant results were published in Advanced Materials.

Moreover, before the holiday, a research on solid-state battery electrolytes by the team led by Professor Zhang Qiang from Tsinghua University was accepted by Nature. That is to say, Chinese research teams have successively published three important technical papers, continuously announcing major breakthroughs in this field.

Of course, these three technologies are still in the paper and laboratory stages. There is still a long way to go before the actual commercialization, engineering application, and mass production of all-solid-state batteries. So, this is like the L3 and L4 levels of intelligent driving, which seem close but are actually far away. Don't get too excited yet. Let's take a closer look.

The "Stumbling Block" of the Solid-Solid Interface

"This is an important technological breakthrough." However, when I asked a battery technology expert about when the DAI technology will be put into practice, he remained silent on this question.

However, as I learned from a battery expert in a previous conversation, based on his experience, it usually takes about 5 to 8 years for relevant research papers in this field to reach the mass production stage. So, if we take the current situation as a starting point, it would be relatively fast if large-scale mass production can be achieved by 2030.

Mr. Huang Xuejie, the corresponding author of this paper, is also a doctoral supervisor at the Institute of Physics of the Chinese Academy of Sciences and currently serves as the deputy director of the Songshan Lake Materials Laboratory (one of the first four provincial laboratories in Guangdong Province).

When Huang Xuejie was interviewed by the media, he introduced that although the lithium metal anode is regarded as the "ideal anode" in lithium batteries, voids are easily formed at the interface between the lithium metal anode and the solid electrolyte and will deteriorate with cycling, resulting in interface contact failure and rapid performance degradation. This is one of the main challenges faced by all-solid-state lithium metal batteries. In other words, the problem of the solid-solid interface is still a "stumbling block".

Previously, the industry believed that solid electrolytes are safer because they do not contain flammable organic solvents, perfectly avoiding the three conditions for combustion. Therefore, all-solid-state batteries have become the ideal ultimate solution.

However, as Wang Fang, the chief scientist of the China Automotive Technology and Research Center, said at a forum not long ago, "Although the safety margin of solid-state batteries is indeed wider than that of liquid batteries, once the margin is breached, the consequences may be more serious than those of liquid batteries." At the same time, the current problem in the entire industry is that in addition to the high cost, the "solid-solid interface" problem of all-solid-state batteries cannot be solved in the short term.

Dr. Gao Xiang, the chairman and CTO of Tailan New Energy, also once told me that the impedance problem of the solid-solid interface is the most important and core problem among the three major problems of solid-state batteries. From a technical perspective, the interface problem is the most difficult to solve, followed by the manufacturing problem and the cost problem.

Therefore, although the lithium metal anode is regarded as the "ideal anode", the contact surface between the lithium metal anode and the solid electrolyte cannot be "seamless" at the micro level, which is difficult to achieve like a liquid electrolyte. As a result, voids are generated at the interface.

This can cause two types of disasters. One is an electrical disaster, that is, the ion channels are blocked, the internal resistance of the battery cell increases, the polarization increases, and further leads to non-uniform current and local hot spots.

The other is a mechanical disaster. During the stripping (discharging) and deposition (charging) processes of the lithium metal anode, there will be significant volume shrinkage and expansion, resulting in the growth of lithium dendrites. The growth of lithium dendrites can pierce the electrolyte, causing the battery to short-circuit and fail.

The solution proposed in this paper, especially the DAI, is to transform the "static film" into a "dynamic body". By introducing iodine ions into the electrolyte, they will move to the electrode interface under the action of an electric field to form an iodine-rich interface. This interface can actively attract lithium ions and automatically fill all the gaps and holes, in-situ generating a compliant and functional lithium iodide-rich layer.

Previously, the common practice in the industry was the "external pressure" mode adopted by Toyota, which uses a sulfide electrolyte. For example, Toyota's early all-solid-state battery prototypes used external pressure, with a pressure of up to 5 MPa. It is reported that under a pressure of 1 MPa, the initial impedance between the sulfide electrolyte and the lithium metal anode can be reduced by 80%. Under a pressure of 2 MPa, the growth rate of lithium dendrites during deposition can be reduced by 90%.

The Dynamic Adaptive Interface (DAI) Achieves Excellent Electrochemical Cycling Performance

However, this method will increase the volume and weight of the battery and is also difficult to commercialize. Toyota was unable to solve the technical problems of all-solid-state batteries on its own. Later, it announced that it had found a solution after collaborating with Idemitsu Kosan this year.

Another method is the "Reducing Electrophiles (REs) Strategy" proposed by the University of Maryland in the United States. Their method is to use difluorophosphoryl fluoride to in-situ generate a 20 - 30 nm ultra-thin SREI interface layer, which has lithium-phobicity, electronic insulation, and high ionic conductivity (>1 mS/cm). However, the drawback of this method is that the stability of the interface layer needs to be verified through long-term cycling, and the large-scale preparation process is complex.

Now, the method of Huang Xuejie's team is quite innovative. It is reported that this new design is not only simpler to manufacture, uses less materials, but also makes the battery more durable. According to media reports, Professor Wang Chunsheng, an expert in solid-state batteries from the University of Maryland, commented that "this research has solved the key bottleneck problem restricting the commercialization of all-solid-state batteries and taken a decisive step towards their practical application."

Change the Electrolyte and "Bake" It

In addition to solving the solid-solid interface problem, the Chinese research teams' technological breakthroughs this time also focus on the materials of solid electrolytes. On September 28th, it was reported that the team led by Professor Zhang Qiang from the Department of Chemical Engineering at Tsinghua University successfully developed a new type of fluorine-containing polyether-based polymer electrolyte (PTF-PE-SPE).

A pouch battery without an anode using this new material, combined with a high-loading LRMO cathode (high-capacity lithium-rich manganese-based oxide), a lean electrolyte design (the ratio of electrolyte to capacity is 1.2 g/Ah), and an anode-free structure (using copper foil as the anode current collector), can achieve a gravimetric energy density of up to 604 Wh/kg and a volumetric energy density of 1027 Wh/L for the solid-state battery.

In terms of data, this is almost twice the energy density of the most advanced liquid electrolyte lithium batteries today.

It is worth mentioning that LRMO is an advanced cathode material with a very high theoretical specific capacity, and its capacity usually exceeds 250 - 300 mAh/g. However, the oxidation of lattice oxygen in LRMO is prone to becoming irreversible. The research from Tsinghua University breaks the attenuation chain of LRMO by stabilizing the anionic redox process itself, especially by preventing the irreversible final step of oxygen generation.

The paper shows that the researchers used an "in-situ polymerization" technique. They injected a liquid monomer precursor solution into the battery and then initiated a polymerization reaction by heating, directly forming a solid electrolyte on the electrode surface. To put it in an inappropriate way, it's like directly heating the prepared liquid electrolyte into a solid electrolyte and "baking" it to eliminate the common pores and high interface impedance problems of traditional solid electrolytes.

This battery also has good lifespan and safety performance. In battery tests, the battery using FPE-PE-SPE still has a capacity retention rate of 72.1% after 500 cycles at a 0.5C rate. In contrast, the capacity of the battery using the traditional PE-SPE electrolyte decays to 80% after only 50 cycles. In the nail penetration test, the fully charged FPE-SPE pouch battery also shows strong tolerance to internal short circuits.

A similar "in-situ polymerization" approach was also used in the research of the team from the Institute of Metal Research of the Chinese Academy of Sciences mentioned earlier. They innovatively designed an "all-around" polymer material at the "molecular scale" to solve the interface impedance and ion transport efficiency problems of solid-state batteries.

The specific method is to install two functional modules on the main chain of the polymer electrolyte material at the same time. One part is an "ethoxy chain", and the other part is a "short sulfur chain". Then, before battery assembly, a low-viscosity precursor solution is injected into the battery cell. Finally, by "baking" it at 80 °C for a few hours, the interface fit is directly upgraded from "point contact" to "surface contact", allowing the electrode and the electrolyte to achieve "molecular-level fusion".

What's the effect? The performance of the integrated flexible battery made with this material hardly decreases after being bent 20,000 times. At the same time, the energy density of the composite cathode is directly increased by 86%.

Moreover, the significance of this research lies in providing a new concept and idea of "molecular-level interface integration" for the interface design of solid-state batteries. "The spring of solid-state batteries may be hidden in these 'small molecule' innovations."

Facing the pressure from Chinese research teams and major battery companies, Toyota, the leading Japanese company betting on solid-state batteries, keeps announcing the mass production time and aims to launch electric vehicles equipped with all-solid-state batteries between 2027 and 2028.

In November 2024, Toyota announced on its official website that its high-performance batteries and solid-state batteries had been recognized by the Japanese Ministry of Economy, Trade and Industry, and it plans to start mass production gradually in 2026. On April 15th this year, Toyota announced a historic cooperation with Idemitsu Kosan and officially claimed to have broken through the mass production technology bottleneck of all-solid-state batteries. The models equipped with Toyota's solid-state batteries are expected to be launched as early as 2027.

On April 20th, Toyota and Panasonic Holdings announced the deepening of their cooperation in the R & D of solid-state batteries. The two parties plan to invest 500 billion yen to build a battery factory with a production capacity of 10 GWh in Japan. The factory is expected to start trial production in 2026 and full-scale mass production in 2027.

The mass production time is constantly confirmed to be 2027, but can it really be achieved? As I also wrote in The Right Solution for All-Solid-State Batteries: Oxides?, from the equipment perspective, sulfide all-solid-state batteries require new equipment (such as isostatic pressing equipment). From the material perspective, during small-scale mass production, the cost of sulfides, including R & D costs, is much higher than that of oxides.

For example, the current market price of sulfide materials is about 50 million yuan per ton (domestic manufacturers have reduced the price to 12 million yuan per ton), while the price of oxides has dropped to less than 500,0