-What is the difference between the performance of lithium iron phosphate battery and ternary lithium ion battery

What is the difference between the performance of lithium iron phosphate battery and ternary lithium ion battery
author:enerbyte source:本站 click497 Release date: 2023-02-13 08:47:07
abstract:
The so-called lithium iron phosphate battery refers to the lithium ion battery using lithium iron phosphate as the cathode material. The characteristic of this type of battery is that it does not contain precious metal elements (such as cobalt). In practical use, lithium iron phosphate battery...

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The so-called lithium iron phosphate battery refers to the lithium ion battery using lithium iron phosphate as the cathode material. The characteristic of this type of battery is that it does not contain precious metal elements (such as cobalt). In practical use, lithium iron phosphate battery has the advantages of high temperature resistance, strong safety and stability, low price and better cycle performance.

The ternary lithium-ion battery refers to the lithium-ion battery using nickel-cobalt lithium manganate as the positive material and graphite as the negative material. Unlike lithium iron phosphate, the voltage platform of the ternary lithium ion battery is very high, which means that the specific energy and specific power of the ternary lithium ion battery are higher under the same volume or weight. In addition, ternary lithium-ion batteries also have great advantages in terms of high rate charging and low temperature resistance.

The nominal voltage of lithium iron is 3.2-3.3V, and that of manganese is 3.6-3.7V, which is the most obvious difference. Advantages of iron lithium system: long theoretical life, excellent theoretical overcharge and discharge resistance. Advantages of ternary system: high energy density, good low-temperature performance, small volume, good discharge linearity. The disadvantages of lithium iron: large volume, large weight, poor discharge linearity, and poor low-temperature performance.

Disadvantages of ternary system: slightly poor cycle life, and poor life at high temperature.

In terms of battery alone, there is no such thing as who is better and who is worse. Just applied to the actual use scenario, the ternary lithium ion battery is more suitable for the current and future domestic electric vehicles than the lithium iron phosphate battery.

Ternary battery is more suitable for passenger cars

Better low-temperature discharge performance

China has a vast territory and a complex climate. The temperature changes from the three northeastern provinces in the northernmost to the Hainan islands in the southernmost are very rich. Take Beijing as an example. As the main market of electric vehicles, the highest temperature in Beijing in summer is about 40 ℃, while in winter, it basically remains around - 16 ℃, or even lower. Such temperature range is obviously suitable for ternary lithium ion batteries with better low-temperature performance. However, lithium iron phosphate battery, which attaches importance to high temperature resistance, will be somewhat weak in winter in Beijing.

Relative 25 ℃ capacity refers to the ratio of discharge capacity at different temperatures to discharge capacity at 25 ℃. This value can accurately reflect the attenuation of battery life under different temperature conditions. The closer to 100%, the better the battery performance.

As can be seen from the above figure, with 25 ℃ as the reference room temperature, the discharge capacity of the two types of batteries at 55 ℃ and 25 ℃ is almost the same. However, at minus 20 ℃, ternary lithium ion battery has obvious advantages over lithium iron phosphate battery.

Higher energy density

According to the data provided by the leading company of the 18650 cylindrical battery in China, the energy density of its 18650 battery has reached 232Wh/kg, and will be further increased to 293Wh/kg in the future. In contrast, the current domestic mainstream lithium iron phosphate battery energy density is only about 150Wh/kg. According to the analysis of domestic battery industry experts, there is very little hope that the energy density of lithium iron phosphate battery can reach 300Wh/kg in the next few years.

Unlike the bulky electric bus, space is always the first place for the household electric vehicle. Lithium iron phosphate battery with low energy density will occupy a small amount of car space, and due to its heavier quality, its discharge duration will also be greatly affected during use. Relatively speaking, the ternary lithium-ion battery with high energy density can not only solve the weight problem, but also save space for household vehicles.

Higher charging efficiency

In addition to battery life, charging is also an important link in the actual use of electric vehicles, and the ternary lithium ion battery has a great advantage over the lithium iron phosphate battery in terms of charging efficiency.

At present, the common charging mode on the market is constant current and constant voltage charging. Generally, constant current charging is adopted at the beginning of charging. At this time, the current is larger and the charging efficiency is relatively higher. After the voltage reaches a certain value, reduce the current and change to constant voltage charging, so that the battery can be fully charged. In this process, the ratio of constant current charging capacity to total battery capacity is called constant current ratio. It is a key value to measure the charging efficiency of a group of batteries during charging. Generally, the higher the percentage is, the higher the charge in the constant-current phase is, which also proves that the charging efficiency of the battery is higher.

It can be seen from the table that there is no significant difference in the constant current ratio between the ternary lithium ion battery and the lithium iron phosphate battery when charged at a rate below 10C. When charged at a rate above 10C, the constant current ratio of the lithium iron phosphate battery decreases rapidly and the charging efficiency decreases rapidly.

Guaranteed cycle life

With regard to household vehicles, the rated cycle life of ternary materials and lithium iron phosphate power lithium batteries is far beyond the use habits of actual users, so the service life can be completely assured.

Take the current high capacity 18650 battery of Bike battery as an example. After 1000 charge-discharge cycles, the battery capacity can still maintain above 90% of the original capacity.

As the author is also the owner of the electric vehicle, only the coldest month in winter can be reached in the whole year. When the warm air is turned on frequently, it can be charged every 2 days, and the rest time is basically charged every 3-4 days. Assuming the annual average of three days of charging, it will take about six times to charge in one year, and it will take about eight years to complete the cycle life of 1000 times, which also basically exceeds the current average car change cycle of Chinese consumers.

Safe materials and processes

The most dangerous part of the traditional internal combustion engine vehicle is the fuel containing huge energy. Once the liquid fuel with low ignition point and easy to explode, such as gasoline, is leaked, it is very easy to cause great safety hazards.

The power lithium battery of new energy vehicles can be controlled most accurately through the perfect battery management system (BMS) monitoring to prevent accidents.

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