Is battery technology about to change? How far away are we from the next generation of lithium metal batteries?

Hello everyone, I am the president of the Electric Vehicle Commune.

Recently, GAC Aion took the lead in releasing the world's first vehicle with a range of 1,000 kilometers, which is comparable to many hybrid and extended-range models, and really surprised many people.

No one expected that a car with a range of more than 1,000 kilometers would come so soon! And no one expected that the promise made by GAC at the beginning of the year would actually come true.

Range anxiety no longer seems to be the biggest obstacle to purchasing a new energy vehicle.

However, the key point for new energy vehicles to achieve an ultra-long range of 1,000 kilometers is energy density.

We know that lithium batteries are composed of positive electrodes, negative electrodes, electrolytes (also known as electrolytes), separators and battery casings.

Loosely speaking, the proportion of lithium ions in the battery determines the amount of stored energy.

For example, the sponge silicon negative electrode battery technology used in AION LX, starting from the silicon-carbon material of the negative electrode, increases the battery pack's group energy density by almost 20% (205Wh/kg, 144.4kWh).

The NIO ET7, which will be equipped with a 150-degree battery next year, also uses a mixed solid-liquid electrolyte on the basis of the silicon-carbon negative electrode to increase the energy density of the single cell to 360Wh/kg.

Even if the group efficiency is 70%, the density of the battery pack will be greater than 250Wh/kg. 1000 km achievement get√.

In the industry's mass-produced battery technology, these two companies are basically reaching the ceiling of lithium-ion battery energy density.

But the real ceiling is still the all-solid-state battery that uses solid electrolytes and has higher energy density.

When the moment of large-scale mass production comes, perhaps any car will have a range of 1,800 kilometers. With supercharging, there is only one word to describe it: great.

But just a few days ago, several battery startups such as SES and Enli Power suddenly emerged, claiming that they have successfully developed a new type of lithium metal battery and will soon be able to mass produce it.

This battery uses lithium metal directly at the negative electrode, and its energy density is actually close to that of the all-solid-state batteries that will be mass-produced in a few years!

This made the president curious: What is the origin of this lithium metal battery? Is it the next generation of new battery technology?

Will there be any new changes in the landscape of battery giants?

Let’s have a good chat today.

01. The past of lithium metal batteries

From the examples of GAC and NIO, it is not difficult to find that the two car companies seem to have agreed in advance that both use silicon-carbon composite materials as negative electrodes. Of course, Zhiji, which "doped silicon to supplement lithium", is also ruthless in negative electrode materials.

Compared with the graphite negative electrode batteries used in most new energy vehicles on the market, the theoretical lithium-ion capacity of silicon negative electrode materials can reach 4200Ah/kg, which is more than ten times higher than the 372Ah/kg of graphite, thus indirectly increasing the energy density.

If we follow the definition of the U.S. Department of Energy and divide lithium battery technology into three generations based on different negative electrode materials and gradually increasing energy density, the most common graphite negative electrode battery is the first generation, and the silicon-carbon negative electrode battery that is about to be rolled out belongs to the second generation.

The third generation is the battery that directly uses metallic lithium in the negative electrode.

Friends who are familiar with new energy vehicles know that in 1881, French engineer Gustave Truffaut built the world's first electric car, which was powered by lead-acid batteries and driven by DC motors, four years earlier than the first Mercedes-Benz.

The development history of lithium metal batteries also has some similarities to early electric vehicles.

As early as the 1970s, when lithium batteries were first invented, scientists tried to use metallic lithium as the negative electrode of the battery, 20 years earlier than Sony launched the first lithium-ion battery to the market.

Today's lithium-ion batteries may have to call lithium metal batteries "Dad" when they see them.

The reason why scientists value lithium metal directly as the negative electrode is also very simple.

The performance of metallic lithium is really amazing!

Its theoretical lithium-ion capacity can reach 3850 Ah/kg, which is similar to the theoretical capacity of silicon negative electrode.

At the same time, it has the lowest density (0.534g/cm³) and the most negative electrochemical potential (-3.045V) among metals, and it is very easy to attract electrons.

This means that lithium metal is better than silicon as a negative electrode material. It has a very high energy density, and the battery voltage is easier to make higher.

In real life, the lithium metal battery we are most exposed to is actually the button battery in the car key. It can be used for about 3 years at a time and can be made very small.

For example, in the CR2032 button battery, the C represents the lithium metal negative electrode. Of course, the same logic applies to 2032R and Tesla's 18650, representing a cylinder with a diameter of 20mm and a height of 3.2mm.

But it is not difficult to find out from this: no one ever asked to charge this button battery, and they just replaced it when it ran out of power.

This is a disposable battery that can be thrown away after use!

That’s right, this is also the biggest reason why lithium metal batteries have not been mass-produced: safety.

In fact, ICAO has already banned the transportation of individual lithium metal batteries UN3090 as cargo on passenger aircraft since January 2015. This ban came more than a year earlier than the ban on lithium-ion batteries UN3480, which shows how dangerous they are.

To find out why it is unsafe, please refer to the Samsung mobile phone explosion incident.

The reason why lithium metal batteries are unsafe is similar to the reason for the explosion of mobile phones. The separator between the positive and negative electrodes is pierced. The direct connection between the positive and negative electrodes causes the battery to short-circuit, overheat, catch fire and explode.

It's like a cheese sandwich, with the bread on the top and bottom piercing the cheese in the middle. But the cost of the battery "bread" being directly connected is really heavy.

The difference between lithium metal batteries and Samsung Note7 is that Note7's diaphragm was pierced due to process problems, and the solder joints on the positive and negative electrodes had burrs (the bread was hard and rough, and the cheese was pierced through).

Lithium metal batteries are caused by irreversible lithium dendrite growth. It is like a piece of bread growing out of it during the storage/eating process, which pierces the cheese. (Cheese: What did I do to offend anyone? I am angry.)

As for why lithium dendrites grow, the simple answer is that lithium ions are too playful and naughty. They get lost while running between the positive and negative electrodes, and eventually settle on the surface of the negative electrode and never move again.

Moreover, it particularly likes to hang on rough surfaces with bumps. Over time, it grows longer and longer, eventually forming lithium dendrites that look like saplings.

In fact, at the beginning, no one discovered the destructive effect of lithium dendrites, but it was learned through blood and tears.

As the world's first company to bring rechargeable lithium batteries to market, Moli Energy from Canada can be said to be at the forefront of the times.

It uses molybdenum disulfide as the positive electrode and metallic lithium as the negative electrode, and launched a battery with an energy density of more than 100Wh/kg. Once it was launched on the market, it became popular all over the world in the context of the rapid development of consumer electronics products and received a large number of orders.

But the good times didn’t last long. Just after the first generation of products sold 2 million, a safety accident occurred, causing fire and explosion. Subsequently, the company announced the recall of all products and provided financial compensation. In the end, it could only go bankrupt and auctioned off due to insolvency.

The Japanese NEC company that took over subsequently produced another 500,000 battery cells and installed them in new mobile phones.

Unfortunately, after a year and a half of "torture", almost all of these mobile phone batteries had problems, ranging from battery degradation to fire and explosion. Behind the countless funds, there was only a brilliant firework.

Fortunately, this batch of batteries was only used for testing and was not delivered to consumers.

After paying a painful price to prove the extremely low reliability of lithium metal batteries, lithium metal batteries were also sealed off by the times.

02. The present life of lithium metal batteries

Two things happened in 2008 that indirectly caused lithium metal batteries to excitedly bang their coffin lids and revive.

The first thing is the emergence of Tesla Roadster.

This small gasoline-to-electric sports car with a range of more than 300 kilometers and a 0-100 km/h acceleration of less than 4 seconds made many people see the infinite possibilities of new energy vehicles for the first time, and also saved Tesla, which was on the verge of bankruptcy for the first time.

What enabled Musk to successfully convince investors was the high energy density of the 18650 battery.

For new energy vehicles, high energy density means everything - longer battery life, faster charging speed, lighter vehicle weight...all benefits with no disadvantages.

As the joke goes, "The best part of a fuel car is the fuel tank, and the worst part is the engine; the best part of an electric car is the motor, and the worst part is the battery."