What is a ternary lithium battery(NCM)?
Lithium is the lightest metal in nature, with an atomic weight of 6.94g/mol, =0.53g/cm3. Lithium is chemically active and easily loses electrons and is oxidized to Li+. Therefore, the standard electrode potential is the most negative (-3.045V) and the electrochemical equivalent is the smallest (0.26g/Ah). These characteristics of the lithium element determine that it is a material with a high specific energy. The ternary lithium battery is a lithium secondary battery made of three transition metal oxides of nickel, cobalt, and manganese. It fully integrates the good cycling performance of lithium cobaltate, the high specific capacity of lithium nickelate, high safety and low cost of lithium manganate, and USES molecular level mixing, doping, coating, and surface modification methods to synthesize complex intercalated lithium oxide with multiple elements such as nickel cobalt manganese. It is a kind of lithium-ion rechargeable battery that has been widely researched and applied.
Ternary lithium battery life
The lithium battery life refers to the battery after a period of use, the capacity attenuation to the nominal capacity (room temperature 25℃, standard atmospheric pressure, and discharge at 0.2C battery capacity) of 70%, can be considered as the end of the life. In the industry, the cycle life is generally calculated by the cycle times of lithium battery full discharge. In the process of use, irreversible electrochemical reactions will occur inside the lithium battery, leading to the decrease of capacity, such as electrolyte decomposition, the inactivation of active materials, and the collapse of positive and negative electrode structures, leading to the reduction of the number of lithium ions embedded and de-embedded, etc. Experiments show that a higher discharge rate leads to a faster attenuation of capacity, and if the discharge current is lower, the battery voltage will approach the equilibrium voltage, releasing more energy.
The theoretical life of ternary lithium batteries is about 1,000 cycles, which is a medium among commercial rechargeable lithium batteries. Lithium iron phosphate runs about 3,000 times, while lithium titanate is said to cycle 10,000 times. The current mainstream battery manufacturers in their production of ternary cell specifications promised more than 500 times (charging and discharging under standard conditions), but the cell in the configuration of the battery pack, due to the consistency problem, mainly is the voltage and internal resistance can not be the same, its cycle life is about 400 times. The use window of SOC is recommended by the manufacturer to be 10%~90%, and deep charging and discharging is not recommended, otherwise, irreversible damage will be caused to the positive and negative structure of the battery. If calculated by shallow charging and discharging, the cycle life will be at least 1000 times. Also, lithium-ion battery life can be significantly reduced to less than 200 times if the battery is frequently charged in a high-power and high-temperature environment.
Advantages and disadvantages of ternary lithium battery
The ternary lithium battery is balanced in capacity and safety, and it is a battery with excellent comprehensive performance. The main functions, advantages, and disadvantages of the three metal elements are as follows:
Co3+: Reduces cationic mixed occupancy, stabilizes the layered structure of the material, reduces impedance, improves electrical conductivity, and improves circulation and multiplier performance.
Ni2+: The capacity of the material can be increased (the volume energy density of the material can be increased). Due to the similar radius between Li and Ni, too much Ni will dislocate with Li and lead to the mixed arrangement of lithium and nickel. The higher the concentration of nickel ion in the lithium layer, the more difficult it will be for lithium to disinsert in the layered structure, leading to the deterioration of electrochemical performance.
Mn4+: Not only can reduce the cost of materials, but also can improve the safety and stability of materials. However, too high Mn content is likely to occur spinel phase and destroy the layered structure, resulting in reduced capacity and cyclic attenuation.
High energy density is the biggest advantage of ternary lithium batteries, the platform is an important indicator of the battery energy density and voltage, determines the basic performance and cost of batteries, the higher the voltage platform, the greater the specific capacity, so the same volume, weight, and even the same ampere-hour battery, high voltage platform ternary material lithium battery life are longer. The discharge voltage platform of a single ternary lithium battery is as high as 3.7V, lithium iron phosphate is 3.2V, and lithium titanate is only 2.3V. Therefore, from the perspective of energy density, the ternary lithium battery has an absolute advantage over lithium iron phosphate, lithium manganate, or lithium titanate.
Poor safety and short cycle life are the main shortcomings of ternary lithium batteries, especially safety performance, which has been a major factor restricting their large-scale configuration and large-scale integration applications. A large number of test results show that the large-capacity ternary batteries are difficult to pass safety tests such as acupuncture and overcharging, which is also the reason why more manganese elements are generally introduced into large-capacity batteries and even mixed lithium manganese acid are used together. The cycle life of 500 times belongs to the middle and lower in lithium battery, so the main application field of three-yuan lithium battery is 3C digital and other consumer electronic products.