NiMH No. 7 battery

　　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, and ρ=0.53g/cm3. Lithium is chemically active and easily loses electrons and oxidizes to Li+. Therefore, the standard electrode potential is the maximum negative value at -3.045V, and the minimum electrochemical equivalent is 0.26g/Ah. These properties of lithium determine it to be a specific high-energy material. Ternary lithium battery refers to a secondary lithium battery that uses three kinds of nickel-cobalt-manganese transition metal oxides as positive electrode materials. It completely combines the good performance of lithium cobalt oxide cycle, the high specific capacity of lithium nickel oxide, and the high safety and low cost of lithium manganate. It is synthesized by mixing, doping, coating and surface modification methods to synthesize nickel in Complex lithium intercalated oxides with multiple elements such as cobalt and manganese at the molecular level. It is a rechargeable lithium-ion battery that has been widely researched and used.

　　Ternary lithium battery life

　　The so-called lithium battery life refers to the battery capacity that decomposes to 70% of the nominal capacity after being used for a period of time (the battery capacity that has been discharged and discharged at room temperature of 25°C and standard atmospheric pressure). At 0.2C), it can be regarded as the end of service life. In industry, cycle life is usually calculated by the number of cycles when a lithium battery is fully charged and discharged. During use, irreversible electrochemical reactions will occur inside the lithium battery, which will lead to capacity reduction, such as electrolyte breakdown, active material deactivation, positive and negative electrode structure collapse, and reduction in the number of internal and external lithium ions. Experiments show that a higher discharge rate will cause the capacity to decrease faster, and if the discharge current is lower, the battery voltage will be close to the equilibrium voltage and more energy will be released.

　　The theoretical life of ternary lithium batteries is about 800 cycles, which is the average life of commercial rechargeable lithium batteries. NiMH No. 7 battery phosphate lasts about 2,000 cycles, while lithium titanate reaches 10,000 cycles. At present, traditional battery manufacturers have promised that the specifications of their ternary batteries are more than 500 times (charged and discharged under standard conditions). However, after the battery pack is assembled into a battery pack, due to the problem of resistance, resistance and internal resistance It can't be exactly the same, its lifespan is about 400 times. Manufacturers recommend a SOC usage window of 10% to 90%. It is not recommended to carry out deep charging and discharging, otherwise it will cause irreversible damage to the positive and negative electrode structures of the battery. If calculated by surface charge and surface discharge, the cycle life is at least 1,000 times. In addition, if lithium batteries are frequently discharged in high-speed and high-temperature environments, the battery life will be significantly shortened to less than 200 times.

　　The advantages and disadvantages of ternary lithium batteries

　　Ternary lithium batteries are relatively balanced in terms of capacity and safety, and are batteries with excellent overall performance. The main functions, advantages and disadvantages of these three metal elements are as follows:

　　  Co3+: Reduce the mixed occupation of cations, stabilize the layered structure of the material, reduce the resistance value, increase the conductivity and improve the cycle performance and speed. Ni2+: can increase the capacity of the material (increase the energy density of the material volume). Since the radii of Li and Ni are similar, too much Ni will 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, the more difficult it is to deinterlace it in the layered structure, resulting in poor electrochemical performance.

　　Mn4+: It can not only reduce the material cost, but also improve the safety and stability of the material. However, if the content of Mn is too high, the spinel phase will easily appear and the layered structure will be destroyed, thus reducing the cycle capacity and attenuation.

　　 High energy density is the biggest advantage of ternary lithium batteries. The voltage platform is an important indicator of battery energy density, which determines the basic efficiency and cost of the battery. An-time batteries and ternary material 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, NiMH No. 7 battery phosphate is 3.2V, and lithium titanate is only 2.3V. Therefore, from the perspective of energy density, ternary lithium batteries are better than lithium phosphate, lithium manganate or lithium titanate have absolute advantages.

　　 Poor safety and short cycle life are the main shortcomings of ternary lithium batteries, especially safety performance, which have become important factors limiting their large-scale implementation and large-scale integration applications. A large number of actual tests have shown that large-capacity ternary batteries are difficult to pass safety tests such as acupuncture and overload, which is why large-capacity ternary batteries usually introduce more manganese or even use manganate. The 500 times life cycle of lithium batteries is in the middle of lithium batteries. Therefore, the most important application field of ternary lithium batteries is consumer electronics products, such as digital 3C.

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