From the perspective of the automotive industry product, there are several more dimensions that determine the power battery, such as safety, energy density, nominal voltage of the unit, service life, application cost, low temperature attenuation ability, etc., in this respect, international standards are strict. Models that can be sold on the market must first meet the standards.
I believe that many friends who are concerned about electric vehicles are familiar with ternary lithium batteries. The famous Tesla uses this kind of battery. The domestic battery giant BYD has been using lithium iron phosphate batteries for a long time in the past, and announced in the second half of this year that it will also focus on the development of ternary lithium batteries. So, what exactly is a ternary lithium battery? Why has it suddenly become the darling of power batteries?
Ternary polymer lithium battery refers to a lithium battery that uses lithium nickel cobalt manganate (Li (NiCoMn) O2) as the cathode material. The precursor product of the ternary composite cathode material is nickel salt, cobalt salt, and manganese salt. As raw materials, the ratio of nickel, cobalt and manganese inside can be adjusted according to actual needs.
Safety is the top priority
The ternary lithium battery is characterized by high energy density and higher voltage, so the battery capacity of the battery pack of the same weight is larger, the distance the car can run is longer, and the speed can also be faster. But its weakness lies in its poor stability. If an internal short circuit or the positive electrode material meets water, there will be an open flame. Therefore, the 18650 battery generally has a layer of steel protection. Since Tesla’s battery pack is composed of about 7,000 18650 batteries, although Tesla has carried out a full range of protection for the battery pack, it is in the extreme In a collision accident, there are still potential fire hazards.
The reason for this is that the two materials decompose when they reach a certain temperature. The ternary lithium material will decompose at a lower 200 degrees, while the lithium iron phosphate material is about 800 degrees. And the chemical reaction of the ternary lithium material is more intense, it will release oxygen molecules, the electrolyte will burn rapidly under the action of high temperature, and a chain reaction will occur. To put it simply, ternary lithium materials are more likely to catch fire than lithium iron phosphate materials. However, it should be noted that we are talking about materials, not batteries that have become finished products.
Lithium iron phosphate batteries are much more stable. Even if the battery board is punctured or short-circuited, it will not explode and burn, and will not catch fire when exposed to a high temperature of 350°C (the ternary lithium battery cannot hold it at 180-250°C). Therefore, in terms of safety performance, lithium iron phosphate batteries are slightly better.
Because of the potential safety hazards of ternary lithium materials, manufacturers are also working hard to prevent accidents. According to the easy pyrolysis characteristics of ternary lithium materials, manufacturers will do a lot of overcharge protection (OVP), over discharge protection (UVP), over temperature protection (OTP), and over current protection (OCP). effort. The reason why Tesla is confident in safety is that it has a complete battery management system that can manage the more active ternary lithium battery better. Of course, as more and more battery companies, car companies, and professional battery management companies continue to research and develop in this field, more companies can also achieve excellent battery management, greatly improving safety.
Ternary cathode materials have advantages in battery specific energy, specific power, high-rate charging, and low-temperature performance. In terms of cycle performance, lithium iron phosphate is better, but it becomes worse in cold environments. In terms of safety, lithium iron phosphate was originally the most ideal, but under the continuous strengthening of battery management technology of ternary lithium, it has gradually improved.
Questions about battery life
The theoretical life of a ternary lithium battery is 2000 charge-discharge cycles, but in actual use, after 900 charge-discharge cycles, the battery capacity basically decays to 55%. In other words, a full charge can only run half of the original mileage. But if each battery charge and discharge is controlled to work in a cycle of 0%-50% or 25%-75%, even after 3000 charge-discharge cycles, the battery capacity can basically be maintained at about 70%. But this also requires an excellent battery management system
From this we understand that in the field of commercial vehicles, such as buses, which have large space and relatively low requirements for battery specific energy and specific power, lithium iron phosphate batteries can be selected to give play to its good cycle performance characteristics.
With limited space for cars and electric vehicles and small battery usage, it is more appropriate to use ternary material batteries with high specific energy and high specific power. From the perspective of adaptation policies, the future energy density requirements will be higher, and the potential of ternary lithium batteries will be more fully utilized.
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