Musk has been touting the "light of lithium battery" 4680 for three years. What's going on now?

In December, the delivery of Tesla Cybertruck set off a wave of Tesla technology craze. In addition to bulletproof body and acceleration performance that surpassed 911, Tesla 4680 battery technology has once again become a topic.

Currently, there are three main types of power batteries used by major manufacturers . European and Korean car companies mostly use soft-pack batteries, while most domestic car companies use prismatic batteries, and then Tesla uses cylindrical power batteries on a large scale. The 4680 battery refers to a cylindrical battery with a diameter of 46 mm and a height of 80 mm.

01

When did the 4680 battery originate?

The connection between Tesla and cylindrical batteries originated when Tesla launched its first model, the Roadster sports car. At that time, Tesla used the 18650 battery invented by Japan's Sony Corporation in 1991, which is a cylindrical battery with a diameter of 18mm and a height of 65mm. This is also the oldest lithium-ion battery in the world . Tesla assembles a large number of 18650 batteries together to make a high- endurance battery pack. The Roadster sports car has made a breakthrough, and the 18650 battery is indispensable.

After that, Tesla and Panasonic became close partners. The two parties jointly developed the second-generation circular battery, namely 2170, with a diameter and height of 21mm and 70mm respectively. This battery helped Tesla model 3 top the sales list. On the surface, Tesla and Panasonic seem to be cooperating smoothly, each getting what they need. In fact, Panasonic has been secretly poking Mr. Kama’s neck. Model 3 orders are pouring in, but battery production capacity is like squeezing out toothpaste.

As the world's top industrial strongman, how can Musk be willing to be controlled by others? The road to self-research on batteries that is bound to come is already in planning. Since 2018, Tesla has established a special project team to develop its own batteries, striving to master one of the core technologies of electric vehicles. Subsequently, in order to support the low-price electric vehicle plan and get rid of the constraints of suppliers, Tesla increased its efforts to promote battery cost reduction. Against these backgrounds, in 2020, the 4680 large cylindrical battery came into being.

I remember that at the press conference of the 4680 battery, Musk praised it extremely and used a considerable amount of space to introduce this battery: "The 4680 battery is a huge technological breakthrough. It is expected that it will only take three years for the 4680 battery to be mass-produced." , then Tesla will be able to create a very attractive new electric car with a price of only 24,000.”

Why is Musk so optimistic about the 4680 battery? From a technical perspective, it's certainly worth it. It is reported that the 4680 battery can increase the battery life of Tesla vehicles by 16%, increase the output power by 6 times, its battery capacity is 5 times that of the batteries at the time, and the cost is reduced by 16%. The successful mass production of 4680 batteries is a milestone breakthrough for Tesla.

02

Large battery core + all-pole tabs + dry process

Compared with the 18650 and 21700 cylindrical lithium batteries previously used by Tesla , the 4680 battery has great advantages in terms of battery capacity, production cost and efficiency.

The first is the big battery cell:

Compared with square batteries, when cylindrical batteries are packaged as battery packs, there will be gaps between cylinders, and the space utilization rate is relatively low. The increase in cylinder volume can reduce the gaps. Some researchers pointed out that the diameter of cylindrical batteries for vehicles should be controlled within 45-50mm can best balance battery capacity and space utilization. After multiple experiments and going through all key indicators, Tesla found that 46mm is the smallest cost battery outer diameter, with a diameter of 46mm and a height of 80mm, which is the most cost-effective battery outer diameter. Perfect cylindrical battery proportions.

The increased appearance reduces the number of single cells in the battery pack, reduces the proportion of the shell in the unit battery capacity, and significantly reduces the number of structural parts and welds. Compared with the 2170 battery, the cost is reduced by 14%. At the same time, the proportion of metal casing in the battery pack is reduced, the proportion of positive electrode, negative electrode and other materials is increased, and the energy density is improved.

In addition, the structural strength of the 4680 battery is increased, which is perfectly combined with CTC technology. The 4680 is larger in size and has higher structural strength. As a structural battery, it becomes part of the vehicle structure. It not only provides energy but also serves as a structural support, saving space and reducing weight by 10%. The cruising range is increased by 14%.

All-pole ears:

Structurally, compared with the previous generation 2710, in addition to being larger in size, the 4680 battery has a revolutionary introduction of a full-tab plus current collector structure.

(Tesla 4680 Proless Ear Rendering)

The tabs are metal conductors that lead out the positive and negative electrodes from the battery core. They are the contact points when charging and discharging the battery. During battery operation, electrons flow from the positive terminal to the negative terminal. The flow path is proportional to the battery's internal resistance, the flow width is inversely proportional to the battery's internal resistance, and the battery's internal power loss is proportional to the square of the internal resistance, so The larger the contact area between the tabs and the shorter the distance between the tabs, the higher the battery output power.

Traditional batteries have only two tabs, which are connected to the positive and negative electrodes respectively. The 4680 battery removes the protruding tab structure of the traditional battery, allowing the entire bottom and shell of the battery to serve as the tabs.

(Picture source of bipolar and all-polar ears plan view: Yifei Laser)

The benefits brought by this improvement are as follows: Since the battery current path is widened, the internal resistance is reduced, and the internal loss is reduced, thereby greatly increasing the output power, which is equivalent to 6 times of the 2170 battery; full-pole lugs improve battery safety sex, the heat transmission channel is wide, which enhances the thermal stability of the battery and makes it easier to dissipate heat; due to the full tab structure, electrons are easier to move inside the battery, and the current rate is increased, so the charging and discharging speed is faster, etc.

Dry cell technology:

Currently, there are two main battery manufacturing technologies, wet process and dry process.

For the past 30 years, battery companies have been using wet processes. The wet process includes the processes of mixing, coating, drying, NMP recovery, and rolling. During this process, toxic solvents and moisture need to be fully evaporated. The process is cumbersome and the manufacturing cost is high. The cost of equipment, labor, and factory buildings account for approximately 22.76% of the entire battery manufacturing.

In order to reduce battery production costs, Tesla spent US$219 million to buy the supercapacitor company Maxwell in 2019. It applied the dry electrode process of supercapacitors to lithium batteries without using liquid adhesives and eliminating expensive coatings. Covering the machine, skipping traditional steps such as baking, the process is simple, saving costs, and greatly improving production efficiency. Musk has disclosed that with this process alone, Tesla can reduce equipment expenditures per unit of production capacity by one-third and reduce the floor space and energy consumption of the electrode production workshop by 90%.

In addition to this, the dry process also increases battery energy density. In the presence of solvent, lithium and carbon mixed with lithium metal cannot blend well with each other, causing the problem of first cycle capacity loss. Dry battery technology will greatly improve this problem, thereby increasing battery energy density.

In addition to large cell + full-pole + dry battery technology, new materials and technologies such as silicon carbon anode used in Tesla's 4680 battery have also redefined cylindrical batteries. Its large-scale mass production and use will drive positive and negative electrode materials, Comprehensive breakthroughs in areas such as packaging technology and structural parts have driven technological innovation throughout the industry chain.

03

Dystocia 4680

The production of 4680 batteries has not been smooth sailing. The integration of multiple innovative technologies in the 4680 battery also brings difficulties in mass production. Since the release of the 4680 battery in 2020, Tesla has been in the stage of technical research and production capacity climbing. Specifically, there are three main technologies that affect the mass production progress of 4680: full tab molding, current collecting plate welding, and laser sealing.

All poles are molded. For full tab forming, there are two main solutions in the lithium battery industry - cutting and folding and flattening. The flattening process refers to mechanically flattening the end surface of the wound pole core into a dense plane. The full-lug electrolyte injection time of the cutting and folding process is shorter. Tesla aims to improve production efficiency and adopts the cutting and folding full-lug technology.

This technology requires very high precision for the battery winding machine. The surface flatness and precision deviation must be maintained within a very small range. The battery is large and the battery core is thick, which can easily lead to inconsistent contact between the tabs and uniform internal resistance. The performance is poor, the material connection after welding is unstable, and the yield is difficult to guarantee.