4680 refers to a cylindrical battery with a diameter of 46mm and a height of 80mm. Large cylinders are relative to small cylinders. Tesla's original power battery was a cylindrical 18650 battery (diameter 18mm, height 65mm).
The size of cylindrical batteries has grown from small to large, which does not only mean size upgrades, but also factors in terms of battery safety, cruising range, and charging capacity. Large cylindrical batteries are not limited to a certain company, but a track drawn by many car companies and battery factories. The future replaceability and subsequent iteration range of this field will gradually expand.
1. Cylindrical batteries from small to large
Sony was the first to commercialize cylindrical lithium batteries. In 1991, Sony released the 18650 cylindrical battery, which opened the commercial era of lithium batteries. Panasonic is the first to provide cylindrical batteries to car companies.
In 2008, Tesla's first luxury coupe, the Roadster, came out, using more than 7,000 18650 ternary lithium batteries made by Panasonic, which kicked off the long-term cooperation between Tesla and Panasonic. In 2017, the 21700 cylindrical battery jointly developed by Tesla and Panasonic was applied to Model 3, using the positive electrode material NCA + negative electrode silicon carbon solution, and the capacity of the single cell was about 35% higher than that of the 18650 battery.
In September 2020, Tesla launched the 4680 large cylindrical battery, marking that the power battery industry has entered the era of large cylindrical batteries. Since then, companies in the field of complete vehicles and batteries have been scrambling to deploy large cylindrical batteries, hoping to gain the initiative in the design of next-generation models and batteries.
The top 10 power battery companies in the world are actively deploying large cylindrical batteries, and some car manufacturers are also developing large cylindrical power batteries.
Professionals said that the large cylinder itself is a pressure vessel. All battery chemistries emerging in the industry can be loaded into large cylinders. Including all-solid-state battery, semi-solid battery, high nickel ternary battery, low nickel NCM622, NCM532, lifepo4 battery, lithium iron manganese phosphate battery, sodium battery for the cathode.
There is also lithium metal, graphite + silicon-pure graphite for the anode. This is also another very core advantage of large cylindrical batteries, which is better adaptability and better compatibility with different platforms. From the perspective of different materials, the average energy density of ternary batteries installed in new energy vehicles sold in 2022 is about 154Wh/kg, and the average energy density of lithium iron phosphate batteries installed is about 128Wh/kg.
Therefore, according to the order demand of car companies, the large cylindrical batteries that began to increase in volume this year are mainly suitable for mid-to-high-end models. It is estimated that the global installed capacity of large cylindrical power batteries will reach 15.6GWh in 2023, and the installed capacity of large cylindrical household storage batteries will be 0.4GWh.
2. What is the breakthrough of the 46mm of the large cylinder 4680
The diameter of the cylindrical battery has been gradually upgraded from the initial 18mm and 21mm to 26mm (2665), 32mm (3265), and 34mm (3420). Why is the diameter of the mainstream large cylindrical battery set at 46mm?
In the field of power, although the increase in the size of cylindrical batteries can reduce the number of cells used in the vehicle and reduce the difficulty of BMS management, it will bring performance and safety problems. According to research, for every 10% increase in battery capacity, its cycle life will be reduced by about 20%, the charge and discharge rate will be reduced by 30%-40%, and the battery will have a temperature rise of about 20%. If you continue to increase battery size, you run the risk of sacrificing safety.
Starting from the diameter of 46mm, the battery life of the whole vehicle began to decline, and the marginal benefit of cost reduction gradually slowed down. Therefore, from the perspective of the overall performance and cost of the battery, the diameter of 46mm is the optimal solution under the current production technology level.
From 18650 to 21700 battery, the capacity of battery cells has increased by 35%, the energy density has increased by 20%, and the price of the system has dropped by about 9%. From 21700 to 4680, according to Tesla, the energy density of its 4680 battery has increased by 5 times, the charging and discharging power has increased by 6 times, the cruising range has increased by 16%, and the system cost per KWh has decreased by about 16%.
Compared with traditional batteries, large cylindrical batteries are not only upgraded in size, but also technologically innovative at the monomer and system levels. The biggest innovation of the 4680 battery is the new non-tab technology, also known as the full-tab technology. Compared with traditional battery technology, the advantages of using non-tab are:
- It can shorten the electron movement path by 5%-20%, and reduce the internal resistance by 5-10 times;
- It can avoid the occurrence of electronic offset and overpotential phenomenon, and improve the battery life;
- The contact area between the conductive coating and the battery case reaches 100%, which disperses the heating area and effectively solves the problem of battery heating.
The non-tab design shortens the moving distance of the electronic current in the battery, solves the problem of temperature rise during high-rate charging and discharging, greatly improves the charging speed, and breaks through the bottleneck of fast charging.
Different from the aluminum wire welding used in traditional batteries, the cells and current collectors of 4680 batteries are welded by laser. It eliminates the problem of current collector failure caused by wire connection, reduces the number of parts used for electrical connection, reduces the resistance of parts, increases the energy density of the battery, and is beneficial to increase the size of the battery. At present, the energy density of dry electrodes exceeds 300Wh/kg, and it can reach 500Wh/kg in the long run.
3. The bottleneck of 4680 battery mass production
The poleless lug solution adopted by Tesla is the current mainstream technical route for large cylinders. The specific operation is to cut some small openings on the pole piece before winding the pole piece and entering the winding machine. When rolling up, guide the cut tab to a position while rolling. Finally, all guide to one position, and finally solder the tab and reflow plate together.
The 4680 battery structural parts designed by each manufacturer are different and belong to non-standard parts. Both the upper and lower surfaces of the Tesla 4680 battery are mechanically connected to the battery side case. According to LG New Energy's 4680 battery patent description, the upper surface of the battery is assembled independently, and the lower surface is integrated with the side.
From winding cell-non-tab-process to equipment, some battery companies that started earlier also have their own technical routes. Each company specializes in different fields and has its own barriers. From the perspective of the industry, the bottleneck of mass production of large cylindrical batteries at this stage mainly comes from the process level.
The innovative technology of non-tab for large cylindrical batteries adds more difficulties in the process of tab die-cutting, flattening, non-tab and collector plate laser welding, which directly affects the battery yield rate and makes mass production of batteries difficult.
Achieving large-scale mass production requires a yield rate of more than 90%, which is difficult to achieve only by battery companies developing and designing large cylindrical battery assembly sections. It is also necessary to cooperate with lithium battery equipment companies to carry out product upgrades and process innovations, so as to achieve a breakthrough in yield rate and meet the requirements of mass production.
The core of the large-scale production and application of non-tab cylindrical batteries lies in the full-area welding of current collectors, current collectors, and positive and negative electrode covers through laser welding.
The increase in the number of tabs puts forward higher requirements for the accuracy, quality and consistency of welding. It can promote the transformation of laser technology equipment from pulse laser spot welding of traditional batteries to 4680 continuous laser welding equipment, and the laser welding process is increased from 5 to 7.
The battery capacity of a single square battery is about 150-250Ah, while the battery capacity of a single 4680 battery is only 25Ah. About 960 4680 batteries are needed to produce a Tesla Model Y.
Therefore, the number of solder joints brought by 4680 battery technology is about 5 times higher than that of traditional batteries, no matter from the level of single cells or the total number of batteries required. That is, to produce 1GWh of 4680 batteries, compared with 18650 and 21700 battery production lines, it is necessary to add 5 welding equipment.
The challenges faced by large cylindrical batteries at this stage are also business opportunities. The requirements for large cylindrical batteries are more stringent in terms of technology and structure, which brings upgrade needs for equipment such as ear laser cutting, kneading, and laser welding. And the industry barriers of structural parts have been raised, and leading comapnies of structural parts with global competitiveness are expected to benefit.
In terms of battery chemical materials, chemical systems with higher energy densities such as high-nickel positive electrodes and silicon-based negative electrodes may usher in a new round of growth opportunities. At the same time, it will further promote the update of the large cylindrical battery material system, and promote single-walled carbon nanotubes and new lithium salt LiFSI to gain a larger market share.