Comparison between lithium iron phosphate battery and NMC lithium battery, which one has more advantages

Lithium iron phosphate batteries and NMC lithium batteries are two different types of batteries. Their main difference lies in the different cathode materials. The positive electrode of lithium iron phosphate batteries is made of iron phosphate, while the positive electrode of NMC lithium batteries is made of NMC materials. Due to the different cathode materials, there are also significant differences in performance, cost and safety between the two batteries.

The negative electrode of NMC lithium batteries is generally made of graphite. Graphite has a multi-layer structure that can accommodate lithium atoms. The positive electrode of the NMC lithium battery is made of NMC materials (the current commercially available positive electrode materials mainly include lithium cobalt oxide, lithium manganate, and lithium iron phosphate. The negative electrode materials are basically graphite). The positive electrodes of some NMC lithium batteries are made of nickel, cobalt, and manganese, and the positive electrodes of some NMC lithium batteries are made of nickel, cobalt, and aluminum.

The energy density of NMC lithium batteries is relatively high, and the low-temperature performance of this battery is also relatively good, but the safety of this battery is not very good. NMC lithium batteries will start to burn at 200 degrees Celsius, so you can often see spontaneous combustion and explosions in pure electric vehicles in the news.

Advantages and Disadvantages of NMC Lithium Batteries

The NMC lithium battery is relatively balanced in terms of capacity and safety, and is a battery with excellent overall performance. The main functions, advantages and disadvantages of the three metal elements are as follows:

Co3+: Reduce the mixed cation occupation, stabilize the layered structure of the material, reduce the impedance value, increase the conductivity, and improve the cycle and rate performance.

Ni2+: It can increase the capacity of the material. Due to the similar radii of Li and Ni, too much Ni will also cause the mixing of lithium and nickel due to dislocations with Li. The greater the concentration of nickel ions in the lithium layer, the more lithium will form in the layered structure. The more difficult it is to deintercalate, resulting in poor electro chemical performance.

Mn4+: Not only can it reduce material costs, but it can also improve the safety and stability of materials. However, if the Mn content is too high, the spinel phase will easily appear and destroy the layered structure, resulting in reduced capacity and cycle attenuation.

High energy density is the biggest advantage of NMC lithium batteries, and voltage platform is an important indicator of battery energy density, which determines the basic performance and cost of the battery. The higher the voltage platform, the greater the specific capacity, so the same volume, weight, or even the same Amp-hour batteries have a longer battery life than NMC material lithium batteries with a higher voltage platform. The discharge voltage platform of a single NMC lithium battery is as high as 3.7V, that of lithium iron phosphate is 3.2V, and that of lithium titanate is only 2.3V. Therefore, from the perspective of energy density, the NMC lithium battery is higher than lithium iron phosphate, lithium manganate or Lithium titanate has absolute advantages.

Poor safety and short cycle life are the main shortcomings of NMC lithium batteries, especially safety performance, which has been a major factor limiting their large-scale assembly and large-scale integration applications. A large number of actual measurements have shown that it is difficult for NMC batteries with larger capacities to pass safety tests such as acupuncture and overcharge. This is why large-capacity batteries generally have to introduce more manganese elements or even mix lithium manganate for use together. The cycle life of 500 times is medium to low among lithium batteries. Therefore, the most important application field of NMC lithium batteries is currently consumer electronic products such as 3C digital products.

Advantages of lithium iron phosphate batteries:

1. Good safety: Lithium iron phosphate batteries are relatively safe in high temperature environments and have good thermal stability.

2. Low cost: Compared with NMC lithium batteries, the manufacturing cost of lithium iron phosphate batteries is lower.

3. Environmental protection: Lithium iron phosphate battery materials have low material cost and do not contain heavy metals, making them environmentally friendly batteries.

Disadvantages of lithium iron phosphate batteries:

1. Relatively low energy density: The energy density of lithium iron phosphate batteries is low, and the battery with the same capacity is also heavier.

2. Slow charging speed: Compared with NMC lithium batteries, lithium iron phosphate batteries have a slower charging speed.

Service life

Lithium iron phosphate has more advantages than NMC lithium batteries in terms of recycling rate.

Under experimental conditions, the lithium iron phosphate battery has a remaining capacity of 84% after 5,000 cycles, and the NMC lithium battery has a remaining capacity of 66% after 3,900 cycles.

In terms of cycle life, the actual life of lithium iron phosphate batteries is much longer than that of NMC lithium batteries. Under the same number of cycles, the remaining capacity of lithium iron phosphate batteries is also much greater than that of NMC lithium batteries.

3. Safety performance

Lithium iron phosphate batteries are safer than NMC lithium batteries.

Lithium iron phosphate battery has good thermal stability. In the acupuncture experiment, there was no open flame and the surface temperature was 30℃-60℃. When the ambient temperature reached 600℃, it began to dissolve.

The stability of NMC lithium batteries at high temperatures is insufficient. When NMC batteries are internally short-circuited or the battery casing is damaged, they can easily cause safety accidents such as combustion and explosion, and they have always failed to pass the acupuncture test. NMC lithium batteries begin to dissolve at around 300°C.

4. Low temperature performance

The performance of NMC lithium batteries at low temperatures is better than that of lithium iron phosphate batteries.

When the lithium iron phosphate battery is at -10℃, the battery capacity drops to about 50%, and the battery cannot operate above -20℃ at most.

The lower limit of NMC lithium is -30°C, and the attenuation degree of NMC lithium at the same temperature is smaller than that of lithium iron phosphate batteries. And the battery is more stable at low temperatures.

5. Energy Density

In terms of unit volume or weight, NMC lithium batteries can store more power, and the vehicle's cruising range will be greater.