Introduction to the Classification of New Energy Vehicle Batteries
1. Lead-acid batteries
Low cost, good low-temperature performance, and high cost-effectiveness; however, low energy density, short lifespan, large size, and poor safety. Due to its low energy density and lifespan, electric vehicles powered by it cannot achieve good speeds and long driving ranges, and are generally used in low-speed vehicles.
2. Nickel-metal hydride batteries
Low cost, mature technology, long lifespan, and durability; however, low energy density, large size, low voltage, and battery memory effect. Due to its superior durability, it has been used in Toyota's Prius hybrid model for a long time. Compared to lithium-ion batteries, the single-cell voltage of nickel-metal hydride batteries is only 1.2V, one-third that of lithium-ion batteries. Therefore, for a given voltage requirement, nickel-metal hydride batteries are significantly larger than lithium-ion batteries. Although their performance is superior to lead-acid batteries, they contain heavy metals and cause environmental pollution when disposed of.
3. Lithium-ion batteries
It is one of the most technologically advanced batteries currently available. This type of battery has high energy density, meaning it can store a lot of electricity; it also has a long cycle life, meaning it can be charged and discharged many times and lasts for a long time. Currently, the two main types of lithium-ion batteries used in electric vehicles are lithium iron phosphate batteries and ternary lithium-ion batteries. Simply put, "lithium iron phosphate" and "ternary lithium" are both positive electrode materials in power lithium batteries, playing a decisive role in the battery's energy density. Therefore, in battery naming conventions, they are mostly named after the positive electrode material; this is the origin of the names of ternary lithium-ion batteries and lithium iron phosphate batteries.
4. Lithium iron phosphate battery
Lithium iron phosphate batteries offer excellent thermal stability, safety, low cost, and long lifespan; however, they have low energy density and are susceptible to low temperatures. Their thermal stability is the best among power lithium-ion batteries. The internal chemical components only begin to decompose at temperatures of 500-600℃, and they will not burn or explode even under puncture, short circuit, or high temperatures. Therefore, they are safer and have a longer lifespan than Panasonic's lithium cobalt oxide batteries.
However, the low energy density results in heavier and larger batteries, leading to a generally shorter driving range. Its biggest drawback is low-temperature charging; when the temperature drops below -5°C, charging efficiency is low, making it unsuitable for the charging needs of northern regions during winter.
5. Ternary lithium-ion batteries
Ternary lithium-ion batteries have high energy density, long cycle life, and are resistant to low temperatures; however, they are less stable at high temperatures. They can achieve the highest energy density, but their high-temperature performance is relatively poor. For pure electric vehicles with range requirements, they are the mainstream choice and are suitable for northern climates, where the batteries are more stable at low temperatures. Tesla's Model 3 uses Panasonic's 21700 ternary cylindrical batteries.
The disadvantage is that the deoxygenation temperature of ternary materials is 200℃, and they cannot pass the needle penetration test, indicating that ternary batteries are prone to safety accidents such as combustion and explosion when there is an internal short circuit or damage to the battery casing.
What exactly are the three elements in a ternary lithium-ion battery? The "ternary" in ternary lithium-ion batteries refers to a polymer containing three metallic elements: nickel (Ni), cobalt (Co), and manganese (Mn) or aluminum (Al). These elements serve as the positive electrode in ternary lithium-ion batteries. All three are indispensable and play a crucial role within the battery.
Nickel: Its main use is to increase the volumetric energy density of batteries, which is a key breakthrough in improving driving range. However, excessive nickel content can cause nickel ions to occupy lithium ion positions (nickel-metal hydride mixing), resulting in a decrease in capacity.
Cobalt: It suppresses the mixing of cations to improve stability and extend battery life. In addition, it also determines the charging and discharging speed and efficiency (rate performance) of the battery. However, excessive cobalt content will lead to a reduction in actual capacity.
Aluminum or manganese: Cobalt is a very expensive rare metal with high cost. The purpose of manganese or aluminum is to reduce the cost of cathode materials while improving the safety and stability of the battery.
To increase the capacity of ternary lithium-ion batteries, the proportion of nickel in the cathode must be increased. Therefore, the proportion of nickel has been continuously increasing, from the early NCM111 to the NCM523 and NCM611 in the last two years, and then to the NCM811 that has been launched this year. As battery energy density increases, the use of nickel is becoming more and more extensive.
Using more nickel inevitably reduces the proportion of cobalt and manganese, which might affect battery life and stability. Theoretically, yes, but currently, the mainstay of ternary lithium-ion batteries is undoubtedly the "high-nickel" ternary lithium-ion battery. This is partly due to policy reasons: electric vehicles with longer driving ranges and higher battery energy densities receive more government subsidies. On the other hand, automakers are vying for attention, engaging in a driving range race, as if whoever has the longest range has the most advanced technology.
It's not accurate to say which is better, lithium iron phosphate (LFP) batteries or ternary lithium-ion batteries; rather, each has its strengths. LFP batteries excel in long lifespan, safety, and low cost, but their energy density and low-temperature performance are slightly inferior. Ternary lithium-ion batteries, on the other hand, boast high energy density and large capacity, but their safety and lifespan are slightly less desirable.
Compared to the traditional automotive industry, electric vehicles (EVs) use electricity as their power source, fundamentally changing the energy sources of traditional automobiles. While most traditional cars use fossil fuels, EVs primarily rely on electricity, representing a significant transformation driven by societal development. The core of EV development lies in its batteries; EV batteries represent a crucial breakthrough for the modern industry.
