Ternary lithium-ion battery is a secondary lithium-ion battery using three nickel-cobalt-manganese transition metal oxides as the cathode material. It completely combines the good performance of lithium cobaltate cycle, the high specific capacity of lithium nickelate and the high safety and low cost of lithium manganate. It is a composite lithium intercalation oxide with multiple elements (such as cobalt and manganese) at the molecular level by mixing, doping, coating and surface modification of synthetic nickel. It is a rechargeable lithium-ion battery that has been widely studied and applied.
Ternary lithium-ion battery life
Lithium-ion battery life is defined as the battery capacity decomposed to 70% of the nominal capacity after a period of use (discharged and discharged at 25°C at room temperature, standard atmospheric pressure) at 0.2C), which can be considered as the end of service life. In industry, cycle life is usually calculated by the number of cycles when a lithium-ion battery is filled and discharged.
During use, irreversible electrochemical reactions will occur inside the Li-ion battery, which will lead to a reduction in capacity, such as electrolyte breakdown, deactivation of the active material, collapse of the positive and negative electrode structure, and a reduction in the number of internal and external Li-ions. Experiments have shown that a higher discharge rate will result in a faster capacity drop, and if the discharge current is lower, the cell voltage will approach the equilibrium voltage and release more energy.
The theoretical life of a ternary lithium-ion battery is about 800 cycles, which is the average life of a commercial rechargeable lithium-ion battery. Lithium iron phosphate lasts about 2,000 cycles, while lithium titanate reaches 10,000 cycles. Currently, conventional battery manufacturers have committed their ternary cells to specifications in excess of 500 times (charging and discharging under standard conditions), but after assembling the cells into a battery pack, the lifetime is about 400 times due to problematic resistances, where the relationship between resistance and internal resistance is not identical.
The manufacturer recommends a window of 10% to 90% for SOC use. Deep charging and discharging is not recommended as it will cause irreversible damage to the positive and negative electrode structure of the battery. If calculated by surface charge and surface discharge, the cycle life is at least 1,000 cycles. In addition, if the lithium-ion battery is frequently discharged at high speed and high temperature, the battery life will be significantly reduced to less than 200 times.
Advantages and disadvantages of ternary lithium-ion batteries
Ternary lithium-ion batteries are relatively balanced in terms of capacity and safety, and are batteries with excellent overall performance. The important functions of these three metal elements, advantages and disadvantages are as follows.
Co3+: reduces the mixed occupancy of cations, stabilizes the layered structure of the material, reduces electrical resistance, increases electrical conductivity and improves cycling performance and speed. Ni2+: can add new capacity to the material (energy density of the new material volume). Due to the similar radius of Li and Ni, too much Ni can also cause mixed Li-Ni discharge due to the dislocation with Li and the concentration of nickel ions in the lithium layer. The larger the Li, the more difficult it is to de-interlace it in the layer structure, leading to poor electrochemical performance.
Mn4+: Not only can reduce the material cost, but also can improve the safety and stability of the material. However, if the content of Mn is too much, the spinel phase will easily appear and destroy the laminate structure, thus reducing the capacity and decay of the cycle.
High energy density is the biggest advantage of ternary lithium-ion batteries, and the voltage platform is an important indicator of battery energy density, which determines the basic efficiency and cost of the battery. An-time batteries with a higher voltage plateau and ternary Li-ion batteries have a longer battery life. The discharge voltage platform of a single ternary lithium-ion battery is as high as 3.7 V, while lithium iron phosphate is 3.2 V and lithium titanate is only 2.3 V. Therefore, from the perspective of energy density, ternary lithium-ion batteries are better than lithium phosphate, and lithium manganate or lithium titanate have absolute advantages.
Poor safety and short cycle life are important drawbacks of ternary lithium-ion batteries, especially safety performance, which has become an important factor limiting their large-scale implementation and large-scale integration applications. Numerous practical tests have shown that high-capacity ternary batteries have difficulty passing safety tests such as acupuncture and overload, which is the reason why high-capacity ternary batteries usually introduce more manganese or even use manganates.
