Which is more suitable for electric vehicles, ternary lithium-ion battery or lithium-iron phosphate battery?

Lithium-ion phosphate is resistant to overcharge and over discharge, and can recover more than 80% in a short time. While lithium ions over-discharged to 2.6V may cause irreversible damage.

Lithium-iron phosphate does not catch fire when it overcharged to 100%. When the lithium ion exceeds 4.35V, the gassing will swell.

Lithium-iron phosphate puncture does not fire and does not explode. Lithium ions will. (Now it is safer)

Lithium-iron phosphate is resistant to high temperatures and can used after more than 200 degrees of recovery. Lithium ions are not working.

Lithium-iron phosphate can discharge at a large current, can be above 10C20C, lithium ion can only discharge 3~5C

In the above, Lithium-iron phosphate is the safest among lithium batteries.

However, the energy density of Lithium-iron phosphate is not as great as that of lithium ion batteries. The voltage is also relatively low. Due to its large discharge characteristics, it mainly uses power sources such as electric vehicles and aircraft models. The lithium ion capacity is large, and it mainly used in the field of civilian consumption. So look at the different batteries you want to use in what way.

After 30 years of development, lithium-ion batteries have greatly improved in terms of specific energy and specific power, and have successfully applied to automobiles. Limited by the specific energy of the battery, the limited range of pure electric vehicles is a bottleneck restricting development. The foreign automobile factory plans to develop hybrid vehicles in the near future. At present, the positive electrode materials used in lithium ion batteries mainly include lithium manganate, Lithium-iron phosphate, lithium cobaltate, ternary materials and the like. Currently, the positive electrode of the power battery mainly uses Lithium-iron phosphate and ternary materials.

After 30 years of development, lithium-ion batteries have greatly improved in terms of specific energy and specific power, and have successfully applied to automobiles. Limited by the specific energy of the battery, the limited range of pure electric vehicles is a bottleneck restricting development. The foreign automobile factory plans to develop hybrid vehicles in the near future. At present, the positive electrode materials used in lithium ion batteries mainly include lithium manganate, Lithium-iron phosphate, lithium cobaltate, ternary materials and the like. Currently, the positive electrode of the power battery mainly uses Lithium-iron phosphate and ternary materials.

In 2017, the subsidy policy for new energy vehicles began to decline, but it still could not stop the expansion of lithium-ion enterprises. As the power source of new energy vehicles, power batteries closely related to all uses such as battery life, safety, charging and discharging, and market.

Among the power batteries, the main applications of new energy vehicles are Lithium-iron phosphate batteries and ternary lithium batteries. The biggest difference between them is energy density and safety. The energy density related to the endurance of the car. The safety mainly reflected in the decomposition of materials at high temperatures. These two points are the most concerned issues when consumers buy new energy vehicles. They are also the most controversial places in the industry.

The energy density of Lithium-iron phosphate batteries is far less than that of ternary lithium batteries, but its safety is generally considered to better than ternary lithium. Let us talk about energy density. At present, the subsidy standard for new energy vehicles depends on the energy density of the battery system. The specific policy is that when the energy density of the battery system exceeds 120Wh/kg, you can enjoy 1.1 times subsidy, which is between 90Wh/ only one-time subsidy can enjoyed between kg and 120Wh/kg.

It understood that the current Lithium-iron phosphate battery on the market has not been difficult to achieve 90Wh / kg, but there are very few companies to achieve 120Wh / kg. BYD has been focusing on Lithium-iron phosphate battery, which is at the domestic leading level in this technology. It has rumored that BYD has developed a high-energy density Lithium-iron phosphate battery with a capacity density of 150Wh/kg, which is equivalent to ternary lithium. The battery is almost equal. Whether the rumor is true or not is not discussed at present, but as the industry leader BYD can only achieve this level, it can be seen that the use of Lithium-iron phosphate battery to get 1.1 times subsidy is not difficult, but this problem for the ternary Lithium batteries are easy to achieve.

In addition, from the capacity planning of several power batteries in 2017, it can see that the capacity expansion of ternary lithium batteries is also particularly obvious. Even BYD, a company that loves Lithium-iron phosphate batteries in the past, maintains iron phosphate in 2017. Lithium production capacity remains unchanged and the expansion of ternary lithium batteries.

Security comparison

In addition to the expansion of the ternary lithium battery at the supply end, it also amplified at the demand side. The energy density requirement just mentioned is a driving force for the demand side of the ternary lithium battery and the other from the ternary lithium battery will officially released in 2017. This is the second point of discussion on the pros and cons of ternary lithium batteries and Lithium-iron phosphate batteries - "safety."

The ternary lithium battery will decompose at about 200 degrees (Lithium-iron phosphate requires a temperature of up to 700 degrees), and it will produce a more severe chemical reaction after decomposition, so it is easier to catch fire when the car collides. This is also a ternary lithium battery. It generally considered to unsafe where it is because of this reason that the ternary lithium battery previously suspended in the passenger car.

However, the safety is actually more dependent on the entire power battery system, especially the battery management system (BMS). The qualified BMS can cut off the power in case of accidents to avoid fire, and cannot easily pyrolyzed only because of the ternary lithium material. It considered that the ternary lithium battery is not safe. As the safety of the ternary lithium battery is re-evaluated, the passenger car will lift the ternary lithium battery, which undoubtedly released a large market.

Temperature effect

China has a vast territory and a complex climate. The temperature changes from the northernmost three northeastern provinces to the southernmost Hainan islands are very rich. Taking Beijing as an example, as the main market for electric vehicles, the highest summer temperature in Beijing is around 40 °C, while in winter it is basically at around 16 °C, or even lower. Such a temperature range is obviously suitable for a ternary lithium battery having a better low temperature performance. The Lithium-iron phosphate battery, which focuses on high temperature resistance, appears to be somewhat weak in winter in Beijing. What's more, the high temperature resistance of ternary lithium batteries is not much different from that of Lithium-iron phosphate.

The results of ternary PK Lithium-iron phosphate known at a glance.

We have learned that the most common charging method currently on the market is constant current and constant voltage charging. Generally, constant current charging used at the beginning of charging, the current at this time is large, and the charging efficiency is relatively higher. After the voltage reaches a certain value, the current is reduced to constant voltage charging, which can make the battery charge more full.

It can see from the table that when the ternary lithium battery and the Lithium-iron phosphate battery charged below 10C, there is no significant difference in the constant current ratio. When charging at 10C or higher, the constant current ratio of the Lithium-iron phosphate battery rapidly decreased, and the charging efficiency rapidly lowered.

Conclusion: The dispute between Lithium-iron phosphate and ternary has not reached a clear conclusion, and battery technology is changing with each passing day. It expected that revolutionary changes will come in the near future, but the author believes that with mature technology, ternary battery will have a potential market in the new market due to its high energy density and large room for improvement, inferior safety, low temperature resistance and high charging efficiency.

The page contains the contents of the machine translation.