Lifespan of ternary lithium-ion batteries
Lithium-ion battery life refers to the period after which the battery capacity degrades to 70% of its nominal capacity (at room temperature, 25°C, and standard atmospheric pressure, after being discharged and fully discharged). This can be considered the end of its service life. Industrially, cycle life is typically calculated by the number of full-charge and discharge cycles of a lithium-ion battery.
During use, irreversible electrochemical reactions occur inside lithium-ion batteries, leading to capacity reduction due to factors such as electrolyte breakdown, deactivation of active materials, collapse of the positive and negative electrode structures, and a decrease in the number of lithium ions both inside and outside the battery. Experiments show that higher discharge rates result in faster capacity loss, while lower discharge currents allow the battery voltage to approach the equilibrium voltage and release more energy.
The theoretical lifespan of ternary lithium-ion batteries is approximately 800 cycles, which is the average lifespan of commercially available rechargeable lithium-ion batteries. Lithium iron phosphate batteries last about 2,000 cycles, while lithium titanate batteries reach 10,000 cycles. Currently, traditional battery manufacturers have promised their ternary batteries specifications to be more than 500 times greater (under standard charging and discharging conditions), but after assembling the battery packs, due to issues with resistance, the relationship between resistance and internal resistance is not entirely identical, resulting in a lifespan of approximately 400 times greater.
The manufacturer recommends a SOC usage window of 10% to 90%. Deep charging and discharging are not recommended, as they will cause irreversible damage to the positive and negative electrode structures of the battery. Based on surface charge and surface discharge calculations, the cycle life is at least 1,000 cycles. However, if lithium-ion batteries are frequently discharged in high-speed and high-temperature environments, the battery life will be significantly reduced to less than 200 times.
Advantages and disadvantages of ternary lithium-ion batteries
Ternary lithium-ion batteries offer a relatively balanced performance in terms of capacity and safety, and possess excellent overall performance. The key functions, advantages, and disadvantages of these three metallic elements are as follows:
Co3+: Reduces the mixing and occupation of cations, stabilizes the layered structure of the material, lowers resistivity, increases conductivity, and improves cycle performance and speed. Ni2+: Can increase the capacity of the material (increase the energy density of the material volume). Due to the similar radii of Li and Ni, excessive Ni can also cause mixed discharge of lithium and nickel due to dislocations with Li and the concentration of nickel ions in the lithium layer. The larger the lithium content, the more difficult it is to deintertwine in the layered structure, resulting in poor electrochemical performance.
Mn4+ can not only reduce material costs but also improve the safety and stability of materials. However, if the Mn content is too high, a spinel phase is likely to form, which will destroy the layered structure and thus reduce the cycling capacity and decay.
High energy density is the biggest advantage of ternary lithium-ion batteries. Voltage plateau is a crucial indicator of battery energy density, determining its basic efficiency and cost. An-time batteries and ternary lithium-ion batteries with higher voltage plateaus have longer lifespans. The discharge voltage plateau of a single ternary lithium-ion battery is as high as 3.7V, compared to 3.2V for lithium iron phosphate and only 2.3V for lithium titanate. Therefore, from an energy density perspective, ternary lithium-ion batteries are superior to lithium phosphate, lithium manganese oxide, or lithium titanate batteries, which have a clear advantage.
Poor safety and short cycle life are significant drawbacks of ternary lithium-ion batteries, especially safety performance, which has become a major factor limiting their large-scale implementation and integrated application. Numerous practical tests have shown that high-capacity ternary batteries struggle to pass safety tests such as acupuncture and overload tests, which is why high-capacity ternary batteries typically incorporate more manganese or even use manganate salts.
