I would like to start with a conceptual clarification: stacked batteries versus polymer batteries versus bagged batteries
The query was regarding "laminated (polymer) lithium-ion batteries." It is important to note that laminated and polymer batteries are distinct concepts. A polymer battery contains a polymer or colloidal electrolyte, while a traditional lithium-ion battery uses a liquid electrolyte. A laminated battery is composed of stacked layers of electrode sheet and diaphragm, in contrast to the winding cell used in batteries such as the 18650. 18650 manufacture Polymer batteries often have a laminated structure, hence they may also be referred to as laminated batteries. However, not all laminated lithium-ion batteries are polymer batteries, as some use liquid electrolytes. This is evident in most power batteries for electric vehicles like the Nissan Leaf and GE Volt, which utilize liquid electrolytes. The confusion likely arises because both laminated and polymer batteries are commonly enclosed in aluminum-plastic films known as "bag-like" packaging. It is worth noting that these bags can also contain coiled battery cells.
Currently, polymer batteries aren't being used in electric vehicles, and I suspect the main reason may be that colloidal electrolytes do not conduct electricity well, so they have high internal resistance.
What is the reason for Tesla's use of 18650 batteries?
There are questions I want to ask.
How does Tesla's Battery Management System (BMS) differ from those of other electric vehicles?
This article mentions several reasons.
Continuity
The 18650 battery is the earliest, most mature and most stable lithium-ion battery, which is widely used in electronic products, with about several billion units shipped each year. Having gained a lot of experience in manufacturing 18650 batteries over the years, Japanese manufacturers are now able to produce 18650 batteries that are very consistent and safe.
In an exchange with an American battery professor, he half-jokingly said that you should test your battery charging and discharging tester at the same time if you purchase the same batch of batteries directly from a Japanese manufacturer. Different discharge curves for different channels indicate a problem with your device, not the battery.
By contrast, stacked lithium-ion batteries are still in their infancy (see
What are the reasons why enterprise-standard batteries are not promoted by the electric vehicle technology industry?
Even in terms of size, size, pole position and so on, they are not uniform, and the battery manufacturer is inexperienced, so the consistency of the battery can't reach the standard of the 18650 battery. A large number of batteries in series or parallel will be difficult to manage if the battery's consistency cannot meet the requirements.
Generally, 18650 battery cells have a small capacity (typically no more than 3 Ah), require more cells (Roadster has 6831), but have excellent consistency. It is possible to increase the capacity of stacked batteries (30 Ah or 40 Ah), and reduce the number of cells, but the consistency is poor.
While Tesla may not specialize in battery production, they lack a significant amount of accumulated battery technology. As a result, they faced challenges in devoting resources and effort towards collaborating with battery suppliers to improve the manufacturing of stacked batteries. Thus, when it came to creating their sports car and Model S, their only option was sourcing batteries from the market and developing their own battery system. From a technical standpoint, it is simpler to design a battery system that regulates over 6,000 cells with consistent performance compared to one that manages 200 cells with varying levels of consistency. Even with a larger number of individual batteries, reliable performance makes them easier to manage.
With a laminated lithium-ion battery, it differs from Nissan Leaf, another successful pure electric car. Since Nissan and NEC have been cooperating for many years and have gained a lot of battery knowledge, they should be well versed in quality control. AESC, a joint venture between Nissan and NEC, manufactures the LEAF's batteries.
Comparing automobile manufacturers in the United States, Japan, and other countries and regions at the medium level of electric vehicle development and utilization is interesting.
Costs
By using 18,650 batteries, Tesla can build on previous production lines from Japanese manufacturers like Panasonic. As the competition for 18650 batteries in consumer electronics gets tougher, I think companies like Panasonic would love to work with Tesla to upgrade their product lines and produce power batteries.
Moreover, industrial production has scale effects. A Tesla needs thousands of 18650 batteries, so the price of a single battery is quite low.
Dissipation of heat
A thin and large stacked battery absorbs and dissipates heat well, and Nissan's LEAF employs an active thermal management system (it doesn't!). Heat is carried away by natural convection.
This battery module consists of four cells in two parallel strings:
The battery pack consists of 48 battery management modules connected in series as follows:
There are no fans, cooling tubes, or other thermal management systems on this battery pack.
The 18650 battery size is relatively small, which means that during normal charging and discharging, the internal temperature difference of the single battery will not be large. Tesla has managed to keep the temperature of more than 6,000 individual batteries within the range of 5 ° C, but how did you do it? Please refer to
Compared to other electric vehicles, what are the advantages of Tesla's Battery Management System (BMS)?
Here is a picture of Tesla's cooling system,
Data pipes are the flow channels of the coolant, and the flow channel crossing is arranged like the exhaust manifold of the engine, so that the flow resistance of various pipelines can be roughly balanced to develop the enterprise.
As a result of Tesla's adoption of a small capacity 18650 battery, the thermal management system is significantly more complex. As a result, the use of low-capacity 18650 batteries does not provide the best heat dissipation.
Density of energy
It is necessary to distinguish between the energy density of a single cell and that of a battery pack when discussing energy density.
When considering the energy distribution density of a single battery, the 18650 battery surpasses the stacked lithium-ion power battery. For instance, while examining the data from Nissan LEAF's use of a 33 Ah lithium ion battery, I discovered an energy information density of 157 Wh/kg. Meanwhile, GM Volt's use of a stacked battery yields an energy density of approximately 150 Wh/kg. In comparison, Tesla's Roadster typically boasts an energy utilization density of around 211 Wh/kg when utilizing an 18650 battery. It should be noted that neither Roadster nor Volt have verified this information independently, but rather it is based on data gathered from batteries produced by the same enterprise or used by other electric car manufacturers with similar environmental capacities.
The management system of the 18650 battery is more complicated, and the extra weight will reduce the energy density of the battery pack much more than that of a single battery. A Roadster's battery pack weighs 450 kg and has an energy density of 118 Wh/u002Fkg, while a LEAF's battery pack weighs 225 kg and has a density of 107 Wh/u002Fkg. Both cars have an energy density that is comparable on a battery level.
There is no solution for analysis at present because I have not collected enough face-to-face research data, and the design company of Model S should be much better than Roadster.
The security of information
The advantages of cascaded lithium-ion batteries have been mentioned above, but there are also some disadvantages. It is difficult for vehicles to survive a collision because of the thin thickness and low mechanical strength of the aluminum-plastic film, which makes it easy for the aluminum-plastic film to break, resulting in safety accidents. Nissan added an aluminum case to the four-cell battery pack for that reason.
With the continuous improvement of the production process for 18650 batteries, safety is also improving. 18650 batteries are generally steel shelled, relatively safe;
Also, Tesla has worked hard to address potential safety issues with its 18,650 batteries. If the temperature of the individual battery is too high, or other abnormal conditions, depending on the severity of the abnormal condition, the battery or its module will be shut down to prevent the spread of the accident. In view of the small capacity of the unit, as long as it does not spread, the severity of an accident will be reduced.
As Tesla gains experience in the battery field, they should try other battery configurations. Tesla used 18650 batteries at the time, which were the best choice.