Features of ternary lithium battery

Ternary lithium battery
Ternary lithium batteries generally refer to ternary polymer lithium batteries. Ternary polymer lithium batteries (ternary lithium batteries) refer to lithium batteries that use lithium nickel cobalt manganese or lithium nickel cobalt aluminate as the positive electrode material. There are many kinds of cathode materials for ion batteries, mainly lithium cobalt oxide, lithium manganate, lithium nickelate, ternary materials, lithium iron phosphate and so on. The ternary composite cathode material is made of nickel salt, cobalt salt, and manganese salt. The ratio of nickel, cobalt and manganese inside can be adjusted according to actual needs. The battery with ternary material as the cathode is safer than lithium cobalt oxide batteries, but the voltage Low, when used on a mobile phone (the cut-off voltage of a mobile phone is generally around 3.0V), there will be an obvious feeling of insufficient capacity.
Ternary lithium battery refers to a lithium ion battery that uses lithium nickel cobalt manganese (Li (NiCoMn) O2) ternary cathode material 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. The battery with ternary material as the positive electrode is safer than the lithium cobalt oxide battery. Ternary lithium batteries are suitable for power batteries or small batteries, especially batteries with relatively high capacity. At present, batteries made of ternary materials have replaced the previously widely used lithium cobalt oxide batteries and are widely used in the field of notebook batteries.
The early 18650 batteries were mostly lithium iron phosphate batteries. With the improvement of technology, the current 18650 battery uses ternary material cells. The common capacity is 2200mAh-3600mAh.
Compared with lithium cobalt oxide, the voltage of ternary lithium battery is generally lower, and the range of use is limited. With the continuous improvement of the formula and the perfect structure, the nominal voltage of the ternary lithium battery has reached 3.7V, and the capacity has reached or exceeded the level of the lithium cobalt oxide battery. The world’s five major battery cell brands SANYO, PANASONIC, SONY, LG, and SAMSUNG have launched ternary material batteries, and SANYO and SAMSUNG cylindrical batteries have completely stopped production of lithium cobalt oxide batteries and switched to ternary battery manufacturing. Most small high-rate power batteries use ternary cathode materials.
Compared with lithium iron phosphate batteries, the weight energy density of ternary lithium batteries is much higher, about 200Wh/kg, which means that ternary lithium batteries of the same weight have a longer range than lithium iron phosphate batteries. . However, its shortcomings are also obvious. When its own temperature is 250-350℃, the internal chemical components begin to decompose. Therefore, extremely high requirements are placed on the battery management system. It is necessary to install a safety device for each battery. In addition, Because of the small size of the cells, the number of battery cells required for a bicycle is very large. Taking MODEL S as an example, more than 7000 18650 ternary lithium batteries can meet the assembly consumption of a car. This is undoubtedly a further step for the battery management system. Increased the difficulty of control. Therefore, among the current models on the market, only Tesla uses ternary lithium batteries.
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 a battery pack of the same weight has a larger battery capacity, and the car can run farther and faster. But its weakness lies in its poor stability. If there is an internal short circuit or the cathode material encounters water, there will be an open flame. Therefore, generally 18650 batteries will have a layer of steel protection. Since Tesla’s battery pack is composed of about 7000 18650 batteries, although Tesla has carried out all-round 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 because it has a complete battery management system that can better manage the more active ternary lithium battery. 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.
Energy density is the core element
Energy density refers to the amount of energy stored in a certain space or mass matter. The energy density of a battery is the electric energy released by the average unit volume or mass of the battery. Battery energy density=battery capacity×discharge platform/battery thickness/battery width/battery length, the basic unit is Wh/kg (watt hour/kg). The greater the energy density of the battery, the more electricity stored per unit volume.
BYD's lithium iron phosphate battery has a single energy density of 150Wh/kg, and BYD's ternary lithium battery has an energy density of 200Wh/kg. It can be seen that the advantages of ternary lithium materials over lithium iron phosphate are still very obvious. Another battery company in Shenzhen, BAK Battery's ternary material power battery cell energy density is nearly 220Wh/kg, which is relatively high in the industry.
Here, I have to say that the national policy is also very clear in guiding the industry. On March 1, 2017, the four central ministries and commissions issued the "Action Plan to Promote the Development of the Automotive Power Battery Industry" notice, clearly stating that "increasing battery specific energy will be one of the key development goals in the future."
The following three points are important:
1. By 2020, the specific energy of lithium-ion power battery cells will be greater than 300Wh/kg; the specific energy of the system will reach 260Wh/kg; the cost will be less than 1 yuan/watt-hour; the use environment will reach -30℃ to 55℃; it has 3C charging capacity .
2. By 2025, the specific energy of the monomer will reach 500Wh/kg.
3. Strive to realize the industrialization and vehicle application of lithium-ion battery products with a single battery of 350Wh/kg and a system of 260Wh/kg.
In fact, it is precisely because of this development direction that the spring of ternary lithium batteries is truly here, because there is not much room for lithium iron phosphate to break through in the monomer energy density, and the potential of ternary lithium batteries has not been fully tapped. come out.
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
The cycle life of the lithium iron phosphate battery is more than 2000 times, and the standard charge (5 hour rate) can reach 2000 times. However, lithium iron phosphate batteries have a fatal disadvantage, that is, poor low-temperature performance, even if they are nano-sized and carbon coated, this problem has not been solved. Studies have shown that if a battery with a capacity of 3500mAh is operated in an environment of -10°C, after less than 100 charge-discharge cycles, the power will decay sharply to 500mAh and is basically scrapped. So in the north, the working conditions of this battery are really worrying.