What is a ternary lithium battery?
In nature, lithium element is the lightest metal with the lowest atomic mass, its atomic weight is 6.94g/mol, ρ=0.53g/cm3. Lithium has active chemical properties and is easily oxidized to Li+ by losing electrons. Therefore, the potential of the standard electrode is the most negative, which is -3.045V, and the electrochemical equivalent is the least, which is 0.26g/Ah. These characteristics of lithium determine that it is a material with very high specific energy. The ternary lithium battery refers to the lithium secondary battery which adopts three transition metal oxides of nickel, cobalt and manganese as cathode materials. It fully integrated the characteristics of good cycling performance of lithium cobaltate, high specific capacity of lithium nickelate, high safety and low cost of lithium manganate and so on, using molecular level mixing, doping, coating and surface modification and other methods to synthesize multielement synergistic composite embedded lithium oxides. It is a kind of lithium ion rechargeable battery which is widely studied and applied at present.
Ternary lithium battery life
The so-called lithium-ion battery life refers to the battery in the use of a period of time, capacity attenuation to the nominal capacity (room temperature 25℃, standard atmospheric pressure, and 0.2C discharge battery capacity) 70%, can be considered to end the life. In the industry, cycle life is generally calculated by the number of cycles of full discharge of lithium battery. In the process of use, the capacity of lithium batteries will be reduced due to irreversible electrochemical reactions, such as the decomposition of electrolyte, the deactivation of active materials, and the collapse of positive and negative structures, which leads to the reduction of the number of lithium ions embedded and deembedded, etc. Experiments show that higher discharge rate will lead to faster capacity decay, if the discharge current is lower, the battery voltage will be close to the equilibrium voltage, can release more energy.
The theoretical life of ternary lithium battery is about 800 cycles, which is in the middle of commercial rechargeable lithium battery. Lithium iron phosphate is about 2,000 cycles, while lithium titanate is said to be able to reach 10,000 cycles. At present, the mainstream battery manufacturers in their production of ternary cell specifications promise more than 500 times (charge and discharge under standard conditions), but the cell in the distribution group made of battery pack, due to the consistency problem, mainly voltage and internal resistance can not be exactly the same, its cycle life is about 400 times. The manufacturer recommends that the SOC use window is 10%~90%, and deep charge and discharge is not recommended, otherwise it will cause irreversible damage to the positive and negative structure of the battery. If it is calculated by shallow charge and shallow discharge, the cycle life will be at least 1000 times. In addition, the battery life of a lithium battery will drop to less than 200 cycles if it is constantly charged at high power rates and high temperatures.
Three lithium battery advantages and disadvantages
The ternary lithium battery is balanced in capacity and safety, which is an excellent battery with comprehensive performance. The main functions and advantages and disadvantages of the three metal elements are as follows:
CO3 + : reduces cationic mixture occupancy, stabilizes the lamellar structure of the material, reduces the impedance value, improves the electrical conductivity, and improves the cycling and scaling performance.
Ni2+ : it can improve the capacity of the material (improve the volume energy density of the material). However, due to the similar radius of Li and Ni, excessive Ni will also cause Li-Ni mixing due to the dislocation phenomenon with Li. The higher the concentration of Ni ions in the lithium layer, the more difficult it is to displace lithium in the lamellar structure, resulting in poor electrochemical performance.
Mn4+ : It can not only reduce the material cost, but also improve the safety and stability of the material. However, too high Mn content will easily appear spinel phase and destroy the lamellar structure, resulting in lower capacity and cyclic attenuation.
High energy density is the biggest advantage of ternary lithium batteries, the platform is an important indicator of the battery energy density and voltage, determines the basic performance and cost of batteries, the higher the voltage platform, the greater the specific capacity, so the same volume, weight, and even the same ampere hour battery, high voltage platform ternary material lithium battery life is longer. The discharge voltage of the monomer lithium battery is as high as 3.7V, 3.2V, and 2.3V, respectively. Therefore, from the perspective of energy density, the lithium battery has an absolute advantage over the lithium iron phosphate, lithium manganate or lithium titanate.
Poor safety and short cycle life are the main shortcoming of ternary lithium battery, especially safety performance, which has been a major factor limiting its large-scale grouping and large-scale integration applications. A large number of measurements show that the ternary battery with large capacity is difficult to pass the safety tests such as needling and overcharging, which is also the reason why more manganese elements should be introduced into the battery with large capacity, or even mixed with lithium manganese ate. The cycle life of 500 times is below the medium in lithium batteries, so the main application field of ternary lithium batteries is consumer electronics products such as 3C digital.
