What is the impact of the lithium battery aging system on battery performance?

According to incomplete statistics, there have been more than 30 fire accidents involving new energy vehicles in China in 2018. The frequent occurrence of safety accidents has caused the entire new energy automobile industry to pay attention to the technical problems behind spontaneous combustion. Many investigations have pointed the cause of the accident to the power battery.

Some experts said that this is the result of the industry's recent unilateral pursuit of energy density. Because the battery is charging and discharging, improper operation or excessive current will cause the battery temperature to be too high. In the event of a violent collision, a short circuit will occur inside the battery, which will easily lead to spontaneous combustion of the battery. At this time, the lithium iron phosphate battery, which has a low energy density but is safe and reassuring, has once again gained attention.

At the beginning of the development of new energy vehicles in China, lithium iron phosphate batteries occupy the main technical route of power batteries. According to the data, the installed capacity of lithium iron phosphate battery and ternary lithium battery in 2015 accounted for about 7:3. In 2016, this figure became 6:4. Although the bus subsidy declined in 2017, the production and sales of electric buses decreased. The two are still basically flat. With the increasing demand for new energy vehicles in China, the ternary lithium battery with higher energy density quickly catches up with the market share of lithium iron phosphate battery. After 2018, only half a year, ternary lithium The battery is complete.

Constrained by energy density, the market demand for lithium iron phosphate battery is sluggish

In the past two years, the main increase in the new energy vehicle market has come from the passenger vehicle market. According to the new energy vehicle subsidy new policy requirements, automobile subsidies will be linked to the renewal mileage and energy density. The orientation of the subsidy policy and the high energy density requirements of the passenger car battery make the lithium iron phosphate battery market decline and the installed capacity shrinks. However, some sub-models that do not pursue high endurance will selectively use lithium iron phosphate batteries, such as passenger cars for intercity commuting.

The data shows that in the first three quarters of this year, the total installed capacity of electric passenger vehicles in China was 16.06GWh, of which ternary lithium batteries accounted for 87%, which was 13.98GWh; lithium iron phosphate batteries accounted for 12%, which was 1.92GWh.

Four months ago, ternary lithium still occupied the absolute advantage of the power battery market. The data shows that the installed capacity of power batteries in China's new energy vehicle market in July was 3.34 Gwh, a year-on-year increase of 29.01%. Among them, the installed capacity of ternary lithium battery is 2.35Gwh, accounting for 70.26%; the installed capacity of lithium iron phosphate battery is 0.93Gwh, accounting for 27.81%.

The energy density of a battery refers to the electrical energy released by the average unit volume or mass of the battery. Why is it so much concerned? There are roughly two reasons for this:

First, money; according to the requirements of subsidizing the New Deal in June this year, the subsidy threshold for the energy density of the new energy vehicle battery system is 105Wh/Kg, of which 105 (inclusive)-120Wh/kg is subsidized by 0.6 times, 120 (inclusive)-140Wh. The model of /kg is subsidized by 1 time, the model of 140 (inclusive)-160Wh/kg is subsidized by 1.1 times, and the model of 160Wh/kg and above is subsidized by 1.2 times.

The second is the renewal mileage; for electric vehicles, especially passenger cars, the amount of electricity determines the length of the vehicle's continuous mileage, and the energy density of the battery directly affects the battery pack's power, which can be said to be the continuous mileage. The direct determinant.

The common ternary lithium battery cell core is 200Wh/kg, and the battery system energy density is about 140Wh/kg; while the previous lithium iron phosphate battery cell core energy density is about 140-150Wh/kg, the battery system energy density is about It is 110-120Wh/kg. It is this gap that makes the market demand for lithium iron phosphate batteries rapidly sluggish, and the installed capacity declines, which also makes the lithium iron phosphate material capacity oversupplied and prices fall. At the beginning of this year, the mainstream price of lithium iron phosphate materials was 90,000-95,000 yuan/ton. At present, this figure is about 60,000-70,000 yuan/ton, which is about 30% lower.

Subsidy of the New Deal implementation, the proportion of lithium iron phosphate market and installed capacity increased steadily

However, the situation of "three yuan alone, iron and lithium is gradually weakening" has not been maintained for a long time. In the seven months and eight months of this year, the installed capacity of lithium iron phosphate battery has gradually increased, especially in the passenger vehicle field. According to public data, China's power battery production in August totaled 6.69GWh, of which ternary battery output was 3.78GWh, accounting for 56.51% of total output, and lithium iron phosphate battery output was 2.83GWh, accounting for 42.35% of total output, both of which occupied absolute subjects. status. Judging from the development of the battery market in the first eight months of this year, after the implementation of the subsidy new policy, the proportion of lithium iron phosphate batteries in the new energy passenger cars and special vehicles has increased.

The data change in September was more obvious. The installed capacity of China's new energy vehicle power battery was as high as 6.01GWh, a year-on-year increase of 66.32%. Among them, the ternary lithium battery accounted for 59.8%, which was 3.59GWh; the lithium iron phosphate battery accounted for 39.2%, which was 2.35GWh.

A series of signs of warming have made lithium iron phosphate regained popularity. In addition to the expansion of the technology route, the development of the energy storage market is also an important factor driving the growth of lithium iron phosphate.

In terms of technical routes, more and more extended-range electric vehicles have begun to adopt lithium iron phosphate batteries, which not only improve the safety of vehicles, but also reduce the cost of vehicle manufacturing, and help increase the number of electric vehicles in the new energy vehicle market. Share. For example, a battery with a battery capacity of 25 Ah and a voltage of 48 V, the lowest market price for a lithium iron phosphate battery and a ternary lithium battery is generally 1020 yuan and 1210 yuan.

In the energy storage market, thanks to some power battery companies began to deploy energy storage business, the market demand for lithium iron phosphate began to expand. According to the energy storage report of GTM Research, an international market research institute, the decline in the price of lithium-ion batteries in 2018 has slowed down. The application of China's grid-side energy storage projects has continued to increase the use of lithium iron phosphate batteries.

On the other hand, with the continuous improvement of technology, the energy density of some lithium iron phosphate batteries has reached the level of ternary NCM523 (the mainstream NCM523 battery energy density is 160-200Wh/kg), which has basically reached the highest subsidy requirement. Compared with the ternary lithium battery, the lithium iron phosphate battery has an advantage in stability.

Finally, the subsidy has fallen sharply. The reason why lithium iron phosphate has low risk in the supply and price of raw materials is because it does not need to use precious metals such as cobalt, which will help battery manufacturers reduce the cost pressure to some extent. .

The decisive factor for whether to recover is the "market choice"

As the signs of warming up of lithium iron phosphate have become more apparent, the industry is also controversial. One of the focuses of the debate is the issue of security. Under normal circumstances, the more energy accumulated in the unit cell space, the greater the risk of an instant burst, and the lower the safety. Therefore, the safety of the lithium iron phosphate battery having a lower energy density is slightly higher than that of the ternary lithium battery.

From a technical point of view, the way to increase the energy density of lithium iron phosphate batteries is mainly to improve the overall group efficiency of the battery. The higher the efficiency of the group, the fewer safety components in the battery.

However, according to the policy plan, the energy density of domestic lithium-ion power battery cells should reach 300Wh/kg in 2020, and strive to reach 350Wh/kg. With the increase of nickel content, higher requirements are also placed on the performance of the battery module in terms of vibration resistance, impact resistance, expansion resistance, insulation and heat insulation. Although the current energy density of lithium iron phosphate battery cells can be 180Wh/kg, it is only in the experimental stage, and the stability of the product needs further experiment and verification. There is still a long way to go before the batch is listed.

However, the automobile market is large in volume and diverse in application scenarios. Commercial vehicles, trucks, etc. will use lithium iron phosphate batteries, and passenger cars and cars will be biased toward ternary lithium batteries. The development of the future battery market will be determined by multi-dimensional market choices such as technical routes and price mechanisms.