Wird die nächste Automobilrevolution ausgelöst werden? Wie weit entfernt sind wir von der Festkörperbatterie?

Since June, the new energy vehicle circle has been abuzz again because of "solid-state batteries". First, Xiaomi Auto announced that it had obtained patents related to solid-state batteries. Then, industry leader BYD was rumored to be the first to equip its new flagship models with solid-state batteries. Although most of these news are still in the stage of "rumors" or "long-term plans", the enthusiastic response of the capital market and the wide public attention are enough to prove how much expectation this technology bears.

We often hear about the disruptive claims of solid-state batteries, such as "1000-kilometer range" and "fully charged in 10 minutes". But what exactly is it? Why is it hailed as the "Holy Grail" of next-generation battery technology? To understand all this, we have to start with the most common lithium batteries in our mobile phones and electric vehicles.

The lithium batteries we currently use are like a miniature "swimming pool". There are four core players in this pool:

Positive Electrode: The "resort" for lithium ions. During charging, lithium ions have to leave here.

Negative Electrode: The "workstation" for lithium ions. During charging, lithium ions are forced to come here to store energy.

Electrolyte: The "pool water" connecting the "resort" and the "workstation". It is the only channel for lithium ions to move back and forth, and it is an organic liquid.

Separator: A special plastic film full of micropores. It physically separates the positive and negative electrodes to prevent them from directly contacting and causing a short-circuit "fight", but it also allows lithium ions to freely "swim" through.

Then the entire charging process is like driving countless lithium ions (Li⁺) out of the "resort" of the positive electrode, forcing them to swim through the electrolyte, pass through the separator, and finally embed into the "workstation" of the negative electrode for storage. When the negative electrode is filled with lithium ions, the battery is fully charged.

The discharging process (when we use our mobile phones or drive) is just the opposite. The lithium ions in the negative electrode spontaneously and eagerly swim back to the "resort" of the positive electrode. In this process, they release electrons (e⁻). The electrons flow through an external circuit, forming an electric current that drives our devices.

Scientists call this process a "rocking-chair battery" because lithium ions are like sitting on a rocking chair, swinging back and forth between the positive and negative electrodes to achieve energy storage and release.

Although this "swimming pool" model has been very successful and supported the entire era of consumer electronics and new energy vehicles, its inherent defects are becoming more and more obvious.

The biggest problem lies in the electrolyte. This organic liquid is highly flammable, just like gasoline. And the separator is just a thin layer of plastic. If the separator is damaged due to collision, puncture, or overheating of the battery, the positive and negative electrodes will directly contact, triggering a violent chemical reaction and an instant short circuit, which we call "thermal runaway". This will cause the electrolyte to burn, and the battery may catch fire or even explode. Many of the frequent spontaneous combustion incidents of new energy vehicles in recent years are largely related to this.

The amount of electricity a battery can hold depends on its "energy density". For the safety of traditional lithium batteries, the negative electrode usually uses graphite materials, and the choice of positive electrode materials is also subject to many restrictions. It's like there are limited workstations in the "workstation" and limited rooms in the "resort".

After decades of development, the energy density of traditional liquid lithium batteries has approached its theoretical ceiling, and it is difficult to make a qualitative leap. The simplest and most straightforward way to achieve a longer driving range is to add more batteries, but this will increase the vehicle weight, occupy interior space, and significantly drive up costs, which is not worth it.

Everyone wants lightning-fast charging speeds. But for liquid lithium batteries, charging too quickly is a dangerous game. If the current is too large, lithium ions don't have time to orderly embed into the "workstations" of the negative electrode and will "cluster" on the surface of the negative electrode, forming needle-like crystals called "lithium dendrites".

These sharp crystals are like daggers and will continue to grow, eventually piercing the fragile separator, also leading to internal short circuits and thermal runaway. Therefore, current fast-charging technologies are like "dancing in shackles", strictly controlling temperature and current through a complex battery management system (BMS) to sacrifice a certain charging speed in exchange for safety.

Facing the various "troubles" of liquid batteries, scientists have proposed a radical solution: If the "pool water" is the root of the problem, why don't we drain the water and replace it with something solid?

This is the core idea of the solid-state battery (Solid-State Battery).

A solid-state battery completely replaces the original liquid electrolyte and the separator with a solid electrolyte.

This solid electrolyte is the soul of the entire technology. It must be able to effectively isolate the positive and negative electrodes like a separator and allow lithium ions to shuttle efficiently like an electrolyte. Then the original "pool water" for lithium ions to swim in has now become a "molecular tunnel" or "ionic highway" composed of special crystals, and lithium ions can perform jump-like transmission in this solid lattice.

This change has brought about all-round and revolutionary improvements.

Solid-state batteries have stable properties, are resistant to high temperatures, and are not afraid of punctures. This means that they will not catch fire, burn, or explode like traditional batteries. It is both an ionic channel and a strong "firewall", completely isolating the positive and negative electrodes. It's like replacing the pool water with cement. Even in the event of the most serious collision, the battery will not leak or burn, eliminating the risk of thermal runaway at the physical level.

Due to the greatly improved safety, solid-state batteries can unlock more "aggressive" material systems. For example, the negative electrode can directly use metallic lithium, whose theoretical energy capacity is more than 10 times that of traditional graphite negative electrodes. The positive electrode can also use materials such as lithium-rich manganese-based materials with higher gram capacities.

This means that under the same size and weight, a solid-state battery can store twice or even more electricity than existing batteries. Currently, the range of high-end electric vehicles is generally between 600 - 700 kilometers. After replacing with solid-state batteries, easily exceeding 1000 kilometers will no longer be a dream, completely ending users' range anxiety.

The strong solid electrolyte can effectively inhibit the growth of lithium dendrites. Without this "Damocles' sword" hanging over their heads, the battery can withstand a larger charging current. Theoretically, the time to charge an electric vehicle from 0 to 80% can be shortened from the current 30 - 40 minutes to 10 - 15 minutes, almost approaching the refueling experience of traditional fuel vehicles.

The liquid electrolyte will have side reactions with the positive and negative electrodes during repeated charging and discharging and gradually be consumed, leading to a decline in battery capacity. The structure of the solid electrolyte is more stable, and there are fewer side reactions, so the battery has a longer cycle life. At the same time, it has better temperature tolerance and can maintain stable performance both in the cold winter and the hot summer.

The popularization of solid-state batteries will completely reshape the energy replenishment ecosystem of new energy vehicles and have a profound impact on the existing "charging pile" and "battery swapping station" models.

The ultra-fast charging ability of solid-state batteries will bring about a qualitative change in the "charging" experience. When charging for 10 minutes can increase the driving range by hundreds of kilometers, the utilization rate of public charging piles will double. The current embarrassing situation of queuing for hours to charge at highway service areas during holidays will become history. Users no longer need to deliberately plan their trips for charging and can easily complete energy replenishment during fragmented time such as shopping in the mall or dining in a restaurant.

This may even change users' charging habits. For users who do not have the conditions for home charging piles, public fast-charging stations can fully meet their daily needs, further lowering the threshold for owning an electric vehicle.

However, we still need to pour some cold water. If solid-state batteries are so perfect, why haven't they been widely used yet?

It is extremely difficult to make lithium ions "run" as smoothly in a solid as in a liquid. Currently, although scientists have found several materials with good conductivity (such as sulfides, oxides, and polymers), their comprehensive performance still needs to be improved.

A liquid can perfectly contact the electrodes, while it is difficult to achieve seamless contact between solids. The electrode materials will expand and contract during the charging and discharging process, which can easily lead to interface separation and form a large "interface resistance", seriously affecting battery performance and life. How to make the solid electrolyte and the electrodes "intimate" and "stay together for a long time" is the core technical bottleneck.

More importantly, the material cost of solid electrolytes is high, and the manufacturing process is complex. It is not compatible with the existing production lines of liquid lithium batteries and requires new equipment and processes. Before achieving large-scale mass production and reducing the cost to a level acceptable to the market, it can only be a "luxury" for a few high-end models.

For this reason, the industry generally believes that the large-scale commercialization of real "all-solid-state batteries" may still take 5 to 10 years. Some so-called "solid-state batteries" on the market are actually "semi-solid batteries" - a transitional solution in which a small amount of liquid components are still doped in the solid electrolyte to improve the interface problem. They are an important step towards the ultimate goal but not the end of the revolution.

In the cost structure of new energy vehicles, the power battery is undoubtedly the core. Its performance directly determines the vehicle's range, safety, and charging experience. It is the key to consumers' decision-making and the focus of competition among car manufacturers. It can be said that whoever masters the next-generation battery technology will master the initiative in the future automotive market.

Solid-state batteries are precisely that highly anticipated next-generation technology. It promises a future of greater safety, longer range, and faster energy replenishment, directly hitting the three major pain points of current electric vehicles. Although the road from the laboratory to large-scale mass production is still full of challenges, the global R & D competition has fully begun.

Therefore, this technological revolution centered around "solid-state" is far more than just about the battery itself. It is a reshaping of the entire automotive industry chain. Every step forward will have a profound impact on the future form of automotive products and the market pattern. The upgrading of battery technology is definitely of great significance to the entire automotive market.

This article is from the WeChat official account "Cheyun" (ID: cheyunwang), author: Cheyunjun. It is published by 36Kr with permission.