Under the background of increasingly depleted oil resources and environmental pollution, electric vehicles have entered a period of rapid development. However, due to the high cost of electric vehicles, short battery cycle life, and short cruising range, it also restricts the further large-scale promotion of electric vehicles.
When the motor and control technology are well-documented and mature, the most difficult situation and the biggest competition for electric vehicles come from battery technology. Major auto manufacturers have also stepped up their research efforts in new energy vehicles. Tesla is a global leader in the smart electric vehicle industry. Its products are outstanding in performance and core technology, and BYD is known as the leader of new energy vehicles. BYD, battery and generator technologies such as R&D roads have been at the forefront of the country. So in terms of batteries, is Tesla and BYD more cattle?
The Tesla Model S uses a battery pack consisting of the Panasonic 18650. A single battery is larger than the usual No. 5 battery, also known as a ternary lithium battery, while BYD specializes in a mainstream lithium battery on the market. It is called lithium iron phosphate battery.
Battery construction comparison
In terms of battery construction, Tesla chose 7000 sets of small cells. The reason for choosing a small battery is that Tesla only needs to replace a small piece after the battery is broken in the future, instead of replacing a large group of batteries collectively. The technology that Tesla is best at is the BMS (Battery Manager), which can fully coordinate the 7000 batteries. The actual situation is that the Panasonic lithium cobalt oxide battery cannot be made into a large battery because of its high energy density. Moreover, Panasonic's small battery production process and production line are relatively mature. Compared with this situation, BYD chose a large battery pack. It is because of the small energy density of the battery that the control unit is reduced for making a large battery pack. Difficulty, this is undoubtedly a good choice for electric vehicles that are not mature in technology. The battery construction is undoubtedly indifferent, each has its own merits.
Battery performance comparison
Tesla used a modified ternary lithium battery (nickel-cobalt lithium aluminate battery) on the Model S model, bringing its total battery to more than 7,000 knots. Despite this, the very limited number of cycles is still a problem for the application of such batteries in electric vehicles. The battery will be dead after about three to four years, based on the charging frequency every two days.
If the ternary lithium battery is internally short-circuited or the positive electrode material is in contact with water, an open flame will be generated. Therefore, the general 18650 battery will have a layer of steel shell protection. Since Tesla's battery pack is composed of 7000 or so 18650 batteries, Tesla provides a full range of protection for the battery pack, but in extreme In the event of a collision, there is still a fire hazard.
In contrast, the lithium iron phosphate battery used by BYD is a more widely used battery. Its advantage is that the thermal stability is very high, the structure is still relatively stable at 600 degrees, and because the ferric ions are not active, it is difficult to make chemical changes again, and the panel will not explode and burn even if it is puncture or short circuit. It has a relatively long life, theoretically can be greater than the life of the vehicle, and the cost of long-term use is lower. At the same time, the lithium iron phosphate battery has a relatively good power density, can be discharged at a large rate, and has good acceleration performance.
| Two lithium battery characteristics comparison table | ||
| Ternary lithium battery (18650) | Lithium iron phosphate battery | |
| Safety (relative to two batteries) | low | high |
| Weight energy density (Wh/kg) | 200 | 100-110 |
| Battery cell nominal voltage (V) | 3.8 | 3.2 |
| Resilience (life) | low | high |
| Application cost (country) | high | low |
| Resistance to low temperature attenuation | Strong | weak |
In terms of comprehensive performance, lithium iron phosphate batteries are still more optimistic and more pragmatic battery types. Therefore, in terms of safety performance, lithium iron phosphate battery is slightly better.
Synchronous and asynchronous, motor selection
In the process of leaving the battery and reaching the motor, the current needs to pass through the inverter to "reform" the direct current into the alternating current that is driven by the motor, and then input the motor, and the driving circuit drives the motor to rotate the output torque. In the idea of ​​motor selection, Tesla is conservative. It adopts the asynchronous motor with more mature technology and wide application fields. However, BYD has chosen a relatively difficult and difficult permanent magnet synchronous motor.
There is no essential difference between the two in terms of working principle. They rely on electromagnetic induction between the stator and the rotor to generate and output torque. Asynchronous motors establish the rotor magnetic field through the stator windings, while permanent magnet synchronous motors, as the name suggests, use permanent magnet materials in the rotor section. Choosing the right motor will also compensate for the battery drop, which will save some battery costs.
The reserve technology of asynchronous motors is relatively mature, reliable and long-lasting. Whether it is a factory high-power motor or a refrigerator or washing machine at home, it can almost be seen. This is a very rational and simple choice for expensive electric vehicles. At the same time, compared with other electrical appliances, the more meticulous pursuit of electric vehicles for electric vehicles also highlights the shortcomings of asynchronous motors. In addition to the need to consume more power, the rotors are also prone to heat, and the speed-up performance is more common.
In order to improve the disadvantages caused by asynchronous motors, Tesla first made an article in the ESC section, using IGBTs to meet high-efficiency substation control, and reorganizing the electrical connection between the motor and the gearbox to improve the motor at low Output torque at speed.
The permanent magnet synchronous motor used by BYD has not been improved in terms of efficiency and power density. The speed-up performance is faster than that of an asynchronous motor, and the structure is simple and relatively easy to maintain. However, its technical reserves and application fields have not yet matured. Moreover, the high cost of rare earth materials contained in permanent magnets has always been a chronic disease of permanent magnet synchronous motors. BYD made such a choice, on the one hand, it saved the adjustment of the drive device to the power demand, but on the other hand it also brought difficulty to the cost control. How to use the magnets to achieve their original performance with lower rare earth materials may require BYD to continue thinking.
Integration and reshaping, who is closer to the future
With the arrival of the Model S model, Tesla has repeatedly subverted its charging time, expanding the number and coverage of super-charged piles, as well as leading car-making concepts and sales models, making it the "Apple" in the automotive industry. "the company. However, in the eyes of many traditional auto companies, Tesla's emergence is not enough to have a subversive impact on the auto industry. There are still many differences in understanding the way in which new energy vehicles exist.
Among the self-owned brands, “making Tesla in minutes†became a buzzword. BYD, a new energy auto company, took the lead in releasing a rhetoric. Recently, Geely’s boss Li Shufu also expressed similar meaning. In the original, perhaps because Tesla is behind the advanced concept of building a car, it reflects its strong technical integration and integration capabilities. From the perspective of its choice of batteries and motors, Tesla intends to refine existing and more mature technologies, reduce the innovation cost of basic product technologies, and maximize the integration potential between components.
For auto companies that are simultaneously developing and matching basic technologies, Tesla is hard to be regarded as a powerful auto company. Starting from high-end models and temporarily lacking civilian models, it is also a revolution in the new energy field. "The statement is less convincing, but it complements Tesla's development history."
In fact, as the same car-making decade, BYD has not yet established its absolute advantage in the field of new energy vehicles, and even needs to constantly respond to questions and comparisons from all sides. But it is worth noting that the product ideas adopted by BYD and Tesla are not the same. Relying on the vertical integration of the industrial chain, BYD has taken the independent production of most of its components. In addition, the core technology and control unit of the dual-engine dual-mode are also derived from independent research and development. Compared with Tesla's innovation and ultimate pursuit in integration capabilities, BYD chose to find a breakthrough from the perspective of emerging technologies, which is closer to the foundation of innovation, but also poses a great challenge to the reserve of technological strength.
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