What is a ternary lithium battery?
In nature, lithium is the lightest metal with the smallest atomic mass, its atomic weight is 6.94g/mol, ρ=0.53g/cm3. Lithium is chemically active, and it is easy to lose electrons and be oxidized to Li+. Therefore, the standard electrode potential is the most negative, which is -3.045V, and the electrochemical equivalent is the smallest, which is 0.26g/Ah. Materials with high specific energy. Ternary lithium battery refers to a lithium secondary battery using three transition metal oxides of nickel, cobalt and manganese as positive electrode materials. 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 uses molecular level mixing, doping, coating and surface modification to synthesize nickel. Cobalt manganese and other multi-element synergistic composite lithium intercalation oxides. It is a lithium-ion rechargeable battery that has been widely researched 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 decays to 70% of the nominal capacity (the capacity of the battery at room temperature 25°C, standard atmospheric pressure, and the battery capacity discharged at 0.2C), which can be considered as the end of life. In the industry, the cycle life is generally calculated by the number of cycles of full discharge of lithium batteries. In the process of use, irreversible electrochemical reactions will occur inside the lithium battery, resulting in a decrease in capacity, such as the decomposition of the electrolyte, the deactivation of active materials, and the collapse of the positive and negative structures, resulting in a reduction in the number of lithium ions intercalated and deintercalated, etc. . Experiments have shown that a higher rate of discharge will lead to faster capacity decay, and if the discharge current is lower, the battery voltage will be close to the equilibrium voltage and more energy can be released.
The theoretical life of a ternary lithium battery is about 800 cycles, which is medium among commercial rechargeable lithium batteries. Lithium iron phosphate is about 2,000 cycles, while lithium titanate is said to be capable of 10,000 cycles. At present, mainstream battery manufacturers promise more than 500 times (charge and discharge under standard conditions) in their ternary battery specifications. The resistance cannot be exactly the same, and its cycle life is about 400 times. The manufacturer recommends that the SOC use window is 10%~90%. It is not recommended to perform 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 charging and shallow discharging, 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 greatly reduced 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 and advantages and disadvantages of the three metal elements are as follows:
Co3+: Reduce cation mixed occupation, stabilize the layered structure of the material, reduce the impedance value, improve the electrical conductivity, and improve the cycle and rate performance.
Ni2+: It can improve the capacity of the material (increase the volume energy density of the material), and due to the similar radius of Li and Ni, too much Ni will also cause the dislocation phenomenon with Li to cause the mixed arrangement of lithium and nickel, and the concentration of nickel ions in the lithium layer The larger it is, the harder it is for lithium to be deintercalated in the layered structure, resulting in poor electrochemical performance.
Mn4+: Not only can reduce the material cost, but also can improve the safety and stability of the material. But too high Mn content will easily appear spinel phase and destroy the layered structure, reduce the capacity and decrease the cycle.
High energy density is the biggest advantage of ternary lithium batteries, 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 greater the specific capacity, so the same volume, weight, even the same An hour's battery has a longer battery life than a ternary material lithium battery with a higher voltage platform. The discharge voltage platform of single ternary lithium battery is as high as 3.7V, lithium iron phosphate is 3.2V, and lithium titanate is only 2.3V. Therefore, from the perspective of energy density, ternary lithium battery is better than lithium iron phosphate, lithium manganate or lithium iron phosphate. Lithium titanate has absolute advantages.
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 configuration and large-scale integrated applications. A large number of actual measurements show that it is difficult for a ternary battery with a large capacity to pass safety tests such as acupuncture and overcharge, which is why more manganese is generally introduced into large-capacity batteries, or even mixed with lithium manganate. The cycle life of 500 times belongs to the middle and lower part of the lithium battery, so the main application field of ternary lithium battery is 3C digital and other consumer electronic products.