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 easily loses electrons to be oxidized to Li+, so 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 a material with very These characteristics of lithium determine that it is a material with high specific energy. Ternary lithium battery refers to the lithium secondary battery using nickel cobalt manganese three transition metal oxides as the cathode 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, and synthesizes the multi-element synergistic composite embedded lithium oxide such as nickel cobalt manganese by using molecular level mixing, doping, coating and surface modification. It is a kind of lithium-ion rechargeable battery which is widely researched and applied at present.
Ternary lithium battery life
The so-called lithium battery life refers to the battery after a period of time, the capacity decay to 70% of the nominal capacity (room temperature 25 ℃, standard atmospheric pressure, and 0.2C discharge battery capacity), can be considered the end of life. The industry generally calculates the cycle life by the number of cycles of lithium battery full and full discharge. In the process of use, irreversible electrochemical reactions will occur inside the lithium battery resulting in a decrease in capacity, such as decomposition of electrolyte, deactivation of active materials, collapse of the positive and negative electrode structure resulting in a reduction in the number of lithium ions embedded and de-embedded, etc. Experiments have shown that higher discharge rates lead to faster capacity decay, and if the discharge current is lower, the cell voltage will be close to the equilibrium voltage and more energy can be released.
The theoretical life of ternary lithium batteries is about 800 cycles, which is medium in the commercial rechargeable lithium batteries. 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 cells in the specification book promised greater than 500 times (standard conditions charge and discharge), but the cells in the group made into a battery pack, due to consistency issues, mainly voltage and internal resistance is not exactly the same, its cycle life of about 400 times. Manufacturers recommend the use of SOC window of 10% to 90%, it is not recommended for deep charging and discharging, otherwise it will cause irreversible damage to the positive and negative structure of the battery, if the shallow charge and shallow discharge to calculate, the cycle life of at least 1000 times. In addition, if the lithium battery is often discharged at a high rate and high temperature, the battery life will be significantly reduced to less than 200 times.
Advantages and disadvantages of ternary lithium batteries
Ternary lithium battery is a balanced battery in terms of capacity and safety, and is a battery with excellent overall performance. The main roles, advantages and disadvantages of the three metal elements are as follows.
Co3+: reduces cation mixing occupancy, stabilizes the layered structure of the material, reduces impedance value, improves conductivity, and improves cycling and multiplier performance.
Ni2+: It can increase the capacity of the material (improve the bulk energy density of the material), while due to the similar radius of Li and Ni, too much Ni will also lead to lithium-nickel mixing due to the dislocation phenomenon with Li. The larger the concentration of nickel ions in the lithium layer, the more difficult it is to de-embed lithium in the lamellar 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. However, too high Mn content will easily appear in the spinel phase and destroy the laminate structure, resulting in lower capacity and cycle decay.
High energy density is the biggest advantage of ternary lithium batteries, and the voltage platform is an important indicator of the energy density of the battery, which determines the basic efficiency and cost of the battery, the higher the voltage platform, the greater the specific capacity, so the same volume, weight, and even the same ampere-hour battery, the voltage platform is higher than the ternary lithium battery with longer range. Single ternary lithium battery discharge voltage platform up to 3.7V, lithium iron phosphate is 3.2V, while lithium titanate is only 2.3V, so from the energy density point of view, ternary lithium battery than lithium iron phosphate, lithium manganate or lithium titanate has an absolute advantage.
Poor safety and short cycle life is the main shortcomings of ternary lithium batteries, especially safety performance, is a major factor that has been limiting its large-scale grouping, and large-scale integrated applications. A large number of actual tests show that the larger capacity of ternary batteries are difficult to pass safety tests such as pinprick and overcharge, which is the reason why more manganese elements are generally introduced in large-capacity batteries, and even mixed with lithium manganate. 500 times cycle life in lithium batteries is moderately low, so the main application areas of ternary lithium batteries are 3C digital and other consumer electronics.
