What is a ternary lithium battery?
In nature, lithium is the lightest and lightest metal with the smallest atomic mass, with an atomic weight of 6.94 g/mol, ρ=0.53g/cm3。 Lithium has active chemical properties and is easily oxidized to Li+by losing electrons. Therefore, the standard electrode potential is the most negative, at -3.045V, and the electrochemical equivalent is the smallest, at 0.26g/Ah. These characteristics of lithium element determine that it is a material with high specific energy. A ternary lithium battery refers to a lithium secondary battery that uses nickel cobalt manganese transition metal oxides as positive electrode materials. It fully integrates the excellent cycling performance of lithium cobalt oxide, the high specific capacity of lithium nickel oxide, and the high safety and low cost of lithium manganese oxide. It uses molecular level mixing, doping, coating, and surface modification methods to synthesize nickel cobalt manganese and other multi-element synergistic composite lithium embedded oxides. It is currently a widely researched and applied lithium-ion rechargeable battery.
The lifespan of ternary lithium batteries
The so-called lifespan of a lithium battery refers to the fact that after a period of use, the capacity of the battery decays to 70% of its nominal capacity (at room temperature of 25 ℃, standard atmospheric pressure, and discharged at 0.2C), which is considered the end of its lifespan. The industry generally calculates the cycle life of lithium batteries based on the number of cycles they are fully charged and discharged. During use, irreversible electrochemical reactions occur inside lithium batteries, leading to a decrease in capacity, such as electrolyte decomposition, deactivation of active materials, and collapse of positive and negative electrode structures, resulting in a reduction in the number of lithium ion insertions and deintercalations. Experiments have shown that higher discharge rates lead to faster capacity decay. If the discharge current is low, the battery voltage will approach the equilibrium voltage and release more energy.
The theoretical lifespan of ternary lithium batteries is about 800 cycles, which is considered moderate among commercial rechargeable lithium batteries. Lithium iron phosphate has about 2000 cycles, while lithium titanate is said to achieve 10000 cycles. At present, mainstream battery manufacturers promise in their specifications for ternary battery cells that they will be charged and discharged more than 500 times under standard conditions. However, after the battery cells are assembled into a battery pack, due to consistency issues, the voltage and internal resistance cannot be exactly the same, and their cycle life is about 400 times. The manufacturer recommends a SOC usage window of 10%~90% and does not recommend deep charging and discharging, as it may cause irreversible damage to the positive and negative electrode structures of the battery. If calculated based on shallow charging and discharging, the cycle life is at least 1000 times. In addition, if lithium batteries are frequently discharged in high rate and high temperature environments, the battery life will significantly decrease to less than 200 cycles.
Advantages and disadvantages of ternary lithium batteries
Ternary lithium batteries have a balanced capacity and safety, making them an excellent battery with comprehensive performance. The main functions and advantages and disadvantages of the three metal elements are as follows:
Co3+: Reduce cation mixing occupancy, stabilize the layered structure of materials, lower impedance values, improve conductivity, and enhance cycling and rate performance.
Ni2+: It can increase the capacity of the material (increase the volumetric energy density of the material), but due to the similar radius of Li and Ni, excessive Ni can also cause lithium nickel mixing due to dislocation phenomena with Li. The higher the concentration of nickel ions in the lithium layer, the more difficult it is for lithium to be deintercalated in the layered structure, resulting in poorer electrochemical performance.
Mn4+: Not only can it reduce material costs, but it can also improve the safety and stability of materials. However, excessive Mn content can easily lead to spinel phase and damage the layered structure, resulting in reduced capacity and cyclic decay.
High energy density is the biggest advantage of ternary lithium batteries, 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. Therefore, for batteries of the same volume, weight, and even the same ampere hour, ternary lithium batteries with higher voltage platforms have longer battery life. The discharge voltage platform of a single ternary lithium battery is as high as 3.7V, while that of lithium iron phosphate is 3.2V, and that of lithium titanate is only 2.3V. Therefore, from the perspective of energy density, ternary lithium batteries have an absolute advantage over lithium iron phosphate, lithium manganese oxide, or lithium titanate.
Poor safety and short cycle life are the main shortcomings of ternary lithium batteries, especially in terms of safety performance, which has been a major factor limiting their large-scale assembly and integration applications. A large number of actual tests have shown that high-capacity ternary batteries are difficult to pass safety tests such as needle punching and overcharging. This is also why large capacity batteries generally introduce more manganese elements, and even mix lithium manganese oxide together for use. The 500 cycle life of ternary lithium batteries is relatively low compared to lithium-ion batteries, so the main application areas of ternary lithium batteries are consumer electronics such as 3C digital products.
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