What is a ternary lithium battery?
In nature, lithium is the lightest and smallest metal with an atomic weight of 6.94g/mol. =0.53g/cm3. The chemical properties of lithium are active, and it is easy to lose electrons to be oxidized to Li+, so the standard electrode potential is the most negative, which is -3.045V, and the electrochemical equivalent is the smallest, which is 0.26g /Ah. These characteristics of lithium determine that it is a material with a very high specific energy. Ternary lithium battery refers to the lithium secondary battery using three transition metal oxides of nickel, cobalt and manganese as positive electrode materials. It fully synthesizes the good cycling performance of lithium cobaltate, the high specific capacity of lithium nickelate and the high safety and low cost of lithium manganate, and uses molecular level mixing, doping, coating and surface modification methods to synthesize nickel-cobalt-manganese and other multi-element synergistic compound lithium embedded 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 battery life refers to the battery after use for a period of time, the capacity decay to the nominal capacity (room temperature 25℃, standard atmospheric pressure, and 0.2C discharge battery capacity) 70%, you can consider the end of life. In the industry, the cycle life of lithium batteries is generally calculated by the number of cycles of full discharge. In the process of use, irreversible electrochemical reactions will occur inside the lithium battery leading to a decrease in capacity, such as the decomposition of the electrolyte, the inactivation of the active material, and the collapse of the positive and negative electrode structures leading to a reduction in the number of lithium ion embedment and deembedment.
The theoretical life of ternary lithium batteries is about 800 cycles, which is medium in commercial rechargeable lithium batteries. Lithium iron phosphate is about 2,000 cycles, while lithium titanate is said to reach 10,000 cycles. At present, the mainstream battery manufacturers promise more than 500 times in the ternary cell specifications they produce (charge and discharge under standard conditions), but after the cell is made into a battery pack, due to consistency problems, mainly the voltage and internal resistance can not be exactly the same, and its cycle life is about 400 times. The manufacturer recommends that the SOC use window is 10% to 90%, it is not recommended to carry out deep charge and discharge, 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 is at least 1000 times. In addition, if the lithium battery is often discharged in a high rate and high temperature environment, the battery life will be significantly reduced to less than 200 times.
Ternary lithium battery advantages and disadvantages:
Ternary lithium battery is more balanced in terms of capacity and safety, and is a battery with excellent comprehensive performance. The main functions and advantages and disadvantages of the three metallic elements are as follows:
Co3+ : Reduce cationic mixing occupy, stabilize the layered structure of the material, reduce the impedance value, improve the conductivity, improve the cycle and rate performance.
Ni2+ : can improve the capacity of the material (improve the volume energy density of the material), and due to the similar radius of Li and Ni, too much Ni will also cause the lithium nickel mixture due to the dislocation phenomenon with Li, the greater the concentration of nickel ions in the lithium layer, the more difficult the lithium in the layered structure, resulting in poor electrochemical performance.
Mn4+ : Not only can reduce the cost of materials, but also improve the safety and stability of materials. However, too high Mn content will easily appear spinel phase and destroy the layered structure, resulting in reduced capacity and cyclic attenuation.
High energy density is the biggest advantage of ternary lithium battery, and the voltage platform is an important indicator of battery energy density, which determines the basic efficiency and cost of the battery, the higher the voltage platform, the larger the specific capacity, so the same volume, weight, and even the same ampere-hour battery, the voltage platform is longer than the ternary material lithium battery. The discharge voltage platform of a single ternary lithium battery is as high as 3.7V, lithium iron phosphate is 3.2V, and lithium titanate is only 2.3V, so from the perspective of energy density, ternary lithium batteries have absolute advantages over lithium iron phosphate, lithium manganate or lithium titanate.
Poor safety and short cycle life are the main shortcomings of ternary lithium batteries, especially safety performance, which has been a major factor limiting its large-scale assembly and large-scale integration applications. A large number of measurements show that it is difficult for ternary batteries with large capacity to pass safety tests such as acupuncture and overcharge, which is also the reason why manganese is generally introduced into large-capacity batteries, and even mixed lithium manganate is used together. The cycle life of 500 times is low in the lithium battery, so the most important application field of ternary lithium battery is consumer electronics such as 3C digital.