Advantages and disadvantages of ternary lithium battery and lithium iron phosphate battery
According to the material, the battery core is mainly divided into lithium iron phosphate and manganese (including cobalt lithium, ternary and other materials).
The nominal voltage of iron and lithium is 3.2-3.3V, and the manganese is 3.6-3.7V. This is the most obvious difference.
Advantages of iron-lithium system: long theoretical life, excellent resistance to overcharge and over discharge
The advantages of the ternary system: high energy density, good low temperature performance, small volume, and good discharge linearity.
Disadvantages of iron lithium: large volume, heavy weight, poor discharge linearity, poor low temperature performance.
Disadvantages of the ternary system: the cycle life is slightly poor, and the life is poor under high temperature conditions.
Low temperature performance
The low-temperature performance of iron-lithium is a hard injury. In Jiangsu and Zhejiang, the performance of iron-lithium is about 75% in summer at temperatures of 0-5 degrees in winter, and even lower under high current conditions of high-power vehicles. The ternary battery is about 90% of the summer at the same temperature, but it is not obvious. In the more northerly regions, the decline will be a little more. Customers in different regions must consider this when selecting lithium materials.
Discharge linearity
The linearity of discharge is simply the relationship between the remaining charge and the voltage. Due to material properties, iron lithium has a high pressure zone, a plateau zone and a low pressure zone. In the high-voltage and low-voltage areas, the voltage drop is very fast, and in the platform area, the drop is very full. The final performance is full of iron and lithium. When you start a few hundred meters, it will lose a few V of virtual power, and then enter a platform area where the voltage drops very slowly. After releasing 80-90% of the stored power, it will enter the low voltage. Area. In terms of this discharge characteristic, the voltage in the main discharge interval is very gentle. From a bad point of view, it is difficult for the user to judge the amount of remaining power based on the voltage display data.
Overcharge and over discharge performance
One of the advantages (theory) of iron-lithium is overcharge and over-discharge. Generally speaking, iron-lithium is not dangerous when it is overcharged to 5V for a short time. If the excess power is released immediately, there is no obvious effect on the performance. However, manganese batteries have a significant overcharge reaction to 5V, which will cause serious damage to the battery cells. In the over-discharge state, the iron-lithium can return to normal at 0V (the performance will drop slightly), and the ternary system will be scrapped when it is placed at 0V. Based on the above literal understanding, iron lithium has better overcharge and over discharge performance. In fact, since the high-voltage and low-voltage region charge and discharge curves of iron and lithium are very steep, weak power causes a significant change in voltage. The performance of the facts is just the opposite of what is literally. For example, the same capacity of iron lithium and ternary system cells, under full conditions, in series to do a charge test, the voltage of iron and lithium will rise very fast, will be earlier than the manganese system scrap; over-release test is the same, if It is a single block, and the minimum lower limit of over-discharge is 0V. In the actual battery pack, over-discharge to 0V will not stop, and the battery will become negative pressure at a very fast speed and cause scrapping.
Volume
The volume of iron and lithium is a natural disadvantage. Under the same size conditions, iron lithium can be loaded with 10AH, and the ternary system can usually be installed above 15AH. This is a very big difference for the current high-power electric motorcycle. Taking the ride model as an example, the iron-loaded lithium battery is generally around 72V80AH. It is necessary to make a relatively large change to install 100AH. It is relatively simple to replace it with a ternary battery. It is not difficult to install it to 200AH. For customers who need long-distance and high-current discharge, the disadvantage of iron-lithium is very large. No matter the discharge output current or the cruising range, it is not a little bit worse.
Actual life
In the case of better quality of iron and lithium, 1 attenuation can be controlled within 5%, and the second year can be within 15%. For the ternary type, the decline is 7-10% in 1 year and 20-25% in 2 years. Of course, the specificity is also related to the use of the load and the frequency of use. This is just a rough expression.
Based on a variety of factors, the use characteristics of iron and lithium can be expressed as: relatively large size, low temperature performance, can maintain a relatively gentle decay rate during the lifetime, generally 5 years or so is acceptable; ternary system Features: small size, can accommodate larger capacity, less performance in winter, large initial capacity, obvious mileage advantage than iron and lithium, there will be a significant decline in the later life, the general life expectancy is about 3 years