Why is Tesla changed to 2170? What are the advantages of ternary lithium battery

18650 battery was a legend of Tesla. Now, with the mass production of Model 3, the historical mission of 18650 battery is coming to an end. All Tesla models may replace the 21700 lithium battery. What is the reason behind this?

1. Composition and classification?

Lithium battery means that the electrochemical system contains lithium battery, which can be roughly divided into lithium battery and lithium battery. Due to its commercial nature of not containing metallic lithium and being rechargeable, lithium battery can be divided into cylindrical and square in appearance, and it is mainly composed of four parts: positive electrode material, negative electrode material, electrolyte and diaphragm material (this article is an original, please specify if it is reproduced).

Different anode materials and anode materials used in lithium batteries can be divided into different types of batteries. For example, the commonly used anode materials include lithium cobalate, lithium manganate, nickel, lithium iron phosphate and ternary materials. The commonly used anode materials include graphite carbon materials, tin based materials, silicon materials and titanium based materials. Among them, lithium cobalate is the majority of anode materials for lithium batteries.

2. What is the technical direction of lithium battery?

It is also called tri cobalt manganese, which means that three materials of nickel, cobalt and manganese are positive materials, graphite is positive material of the battery, and its nickel salt, cobalt salt and manganese salt are raw materials. The proportion of nickel, cobalt and manganese can be adjusted according to the actual situation. Battery companies with main technical directions, such as Japan and Korea, lithium iron phosphate battery is based on lithium ferrous phosphate as negative material, and graphite as negative material, which is BYD's main technical direction; Lithium titanate batteries can be divided into two types. One is lithium titanate as the cathode material, while lithium manganate and lithium iron phosphate are ternary materials and the cathode material of lithium batteries. This is the main direction of Zhuhai Silver at present. The other is lithium titanate as the cathode, and lithium metal or lithium alloy cathode lithium battery (this is an original product, cat car starter, please specify the transfer).

3. What are the advantages of the ternary lithium battery?

The biggest advantage of the ternary lithium battery lies in its high energy storage density, usually above 200WH/kg, and related to the 90-120Wh/kg of lithium iron phosphate, which is more suitable for the demand of the passenger car market for mileage. The decomposition temperature of ternary lithium battery materials is about 200 ℃, which will release oxygen molecules. In the case of high temperature and rapid combustion, electrolyte batteries and spontaneous combustion and explosion hazards, the management requirements for batteries are very high. (OVP) should be composed of overcharge protection, discharge protection (UVP), over temperature protection (OTP) and over-current protection (OCP). Therefore, ternary lithium batteries are used by pure electric vehicles in the Chinese market up to 76%. However, the number of electric buses is only 27.6%, while lithium iron phosphate is 64.9%.

4. Why did Tesla switch to 2170?

The battery number 18650 and 2170 used by Tesla are ternary copolymer lithium batteries. 18650 is a cylindrical battery with a diameter of 18mm and a length of 65mm, and 2170 is a cylindrical battery with a diameter of 21mm and a length of 70mm. As it is impossible to improve the energy density and reduce the battery cost through process control and raw material, the 2170 battery with larger volume becomes an inevitable choice. The model and ModelX are expected to be replaced after the first use of Model3.

Musk claims that the battery in 2170 is the highest energy density and cheapest battery in the world, with an energy density of up to 300 WH/kg, which is related to 233 WH/kg in 18650. The energy density has increased by nearly 20%, but the cost of its battery system is 155 dollars/WH, which is related to 171/18650 WH, which is a limited reduction. Although there is still a long way to go before Musk achieves the goal of $100 per watt hour, it is still a step forward. The next step should be to innovate new battery materials to reduce costs. Ternary lithium battery is a kind of lithium battery composed of lithium nickel cobalt manganese oxide (Li (NiCoMn) O2) terpolymer. The precursor product of ternary composite cathode material takes nickel salt, cobalt salt and manganese salt as raw materials, and the proportion of nickel, cobalt and manganese can be adjusted according to the actual situation.

Safety is the top priority

The characteristics of the ternary lithium battery are high energy density and high voltage, so the battery pack with the same weight has greater capacity, and the car can go farther and faster. However, its weakness lies in its poor stability. If there is an internal short circuit or the positive substance encounters water, there will be open flames. Therefore, a layer of steel shell is generally used for protection. Tesla's battery pack is composed of about 7000 18650 batteries. Although Tesla provides all-round protection for the battery pack, there is still a fire hazard in extreme collision accidents.

This is because these two materials will decompose when they reach a certain temperature. Lithium ternary is about 200 ℃ lower and lithium iron phosphate is about 800 ℃ lower. The chemical reaction of ternary lithium material is more intense, which will release oxygen molecules, and the electrolyte will burn rapidly at high temperature, leading to chain reaction. In short, lithium ternary is easier to ignite than lithium iron phosphate. It is worth noting that we are talking about materials, not ready-made batteries.

The lithium iron phosphate battery is much more stable. Even if the panel is broken down, the short circuit will not explode and burn, and the battery will not catch fire under the high temperature of 350 ℃ (three lithium batteries cannot be carried at 180-250 ℃). Therefore, in terms of safety performance, lithium iron phosphate battery is better.

As ternary lithium materials have such potential safety hazards, manufacturers are also trying to prevent accidents. According to the pyrolysis characteristics of ternary lithium materials, manufacturers will attach great importance to overcharge protection (OVP), over discharge protection (UVP), over temperature protection (OTP) and over current protection (OCP). Tesla is confident in safety because it has a battery management system that can better manage its more active lithium batteries. Of course, as more and more battery companies, automobile companies and professional battery management companies continue to develop in this field, more and more companies can also achieve excellent battery management, which will greatly improve safety.