In nature, lithium is the lightest, smallest atomic metal with an atomic weight of 6.94 g/mol and ρ = 0.53 g/cm3. Lithium is chemically active, and it is easy to lose electrons to be oxidized to Li+. Therefore, the standard electrode potential is the most negative, -3.045V, and the electrochemical equivalent is the smallest, 0.26g/Ah. These characteristics of lithium determine that it is very High specific energy material. The ternary lithium battery refers to a lithium secondary battery using three kinds of transition metal oxides of nickel, cobalt and manganese as a positive electrode material. It fully integrates the good cycle performance of lithium cobaltate, the high specific capacity of lithium nickelate and the high safety and low cost of lithium manganate. It synthesizes nickel by molecular level mixing, doping, coating and surface modification. A multi-element synergistic composite lithium intercalation oxide such as cobalt manganese. It is a lithium ion rechargeable battery that has been widely studied and applied.
What is a ternary lithium battery?
In nature, lithium is the lightest, smallest atomic metal with an atomic weight of 6.94 g/mol and ρ = 0.53 g/cm3. Lithium is chemically active, and it is easy to lose electrons to be oxidized to Li+. Therefore, the standard electrode potential is the most negative, -3.045V, and the electrochemical equivalent is the smallest, 0.26g/Ah. These characteristics of lithium determine that it is very High specific energy material. The ternary lithium battery refers to a lithium secondary battery using three kinds of transition metal oxides of nickel, cobalt and manganese as a positive electrode material. It fully integrates the good cycle performance of lithium cobaltate, the high specific capacity of lithium nickelate and the high safety and low cost of lithium manganate. It synthesizes nickel by molecular level mixing, doping, coating and surface modification. A multi-element synergistic composite lithium intercalation oxide such as cobalt manganese. It is a lithium ion rechargeable battery that has been widely studied and applied.
Ternary lithium battery life
The so-called lithium battery life means that after the battery has been used for a period of time, the capacity is attenuated to 70% of the nominal capacity (room temperature 25 ° C, standard atmospheric pressure, and battery capacity discharged at 0.2 C), and the end of life can be considered. In the industry, the cycle life is generally calculated by the number of cycles in which the lithium battery is fully charged. During the process of use, irreversible electrochemical reactions inside the lithium battery lead to a decrease in capacity, such as decomposition of the electrolyte, deactivation of the active material, collapse of the positive and negative structures, reduction in the number of lithium ion insertion and deintercalation, etc. . Experiments have shown that higher rate discharges result in faster attenuation of the capacity. If the discharge current is lower, the battery voltage will approach the equilibrium voltage and release more energy.
The theoretical life of a ternary lithium battery is about 800 cycles, which is medium in commercial rechargeable lithium batteries. Lithium iron phosphate is about 2000 times, and lithium titanate is said to reach 10,000 cycles. At present, the mainstream battery manufacturers promise more than 500 times in the ternary battery specifications produced by them (charge and discharge under standard conditions), but after the batteries are assembled into battery packs, due to consistency problems, mainly voltage and internal The resistance cannot be exactly the same, and its cycle life is about 400 times. The manufacturer recommends that the SOC use window be 10%~90%. It is not recommended to carry out deep charge and discharge. Otherwise, it will cause irreversible damage to the positive and negative structures of the battery. If it is calculated by shallow charge and shallow release, 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 drop to less than 200 times.
Advantages and disadvantages of ternary lithium battery
The ternary lithium battery is relatively balanced in terms of capacity and safety, and is a battery with excellent comprehensive performance. The main functions, advantages and disadvantages of the three metal elements are as follows:
Co3+: Reduces the mixing of cations, stabilizes the layered structure of the material, reduces the impedance value, improves the conductivity, and improves the cycle and rate performance.
Ni2+: can increase the capacity of the material (increasing the volumetric energy density of the material), and due to the similar radius of Li and Ni, excessive Ni will also cause lithium nickel to be mixed due to dislocations with Li, and the concentration of nickel ions in the lithium layer. The larger the lithium, the more difficult it is to deintercalate 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, an excessively high Mn content tends to occur in the spinel phase and destroy the layered structure, resulting in a decrease in capacity and cycle decay.
High energy density is the biggest advantage of ternary lithium battery, and voltage platform is an important indicator of battery energy density, which determines the basic performance and cost of the battery. The higher the voltage platform, the larger the specific capacity, so the same volume, weight, and even the same Anshi's battery, the high voltage ternary material lithium battery has a longer battery life. The discharge voltage platform of the single ternary lithium battery is up to 3.7V, the lithium iron phosphate is 3.2V, and the lithium titanate is only 2.3V. Therefore, from the perspective of energy density, the ternary lithium battery is more than lithium iron phosphate or lithium manganate. Lithium titanate has an absolute advantage.
Poor safety and short cycle life are the main shortcomings of ternary lithium batteries, especially safety performance, which is a major factor that has limited its large-scale assembly and large-scale integration applications. A large number of actual measurements show that it is difficult to pass the safety test such as needle punching and overcharging for the ternary battery with large capacity. This is also the reason why the manganese element is generally introduced in the large-capacity battery, and even mixed lithium manganate is used together. The cycle life of 500 cycles is medium to low in lithium batteries, so the most important application field of ternary lithium batteries is consumer electronic products such as 3C digital.
Post time: Apr-18-2019
