Safe, stable, environmentally friendly and efficient BYD iron battery technology analysis

With the rapid development of the automobile industry, fossil energy is decreasing, and the pollution caused by automobile exhaust is becoming more and more serious. The world's major auto companies continue to launch their own new energy vehicles, such as natural gas, hydrogen energy, fuel cells and so on. In the current fuel cell technology, there is a new battery technology - iron battery technology.

At present, iron batteries studied at home and abroad include high-iron batteries and lithium-iron batteries. The high-iron battery is a new type of chemical battery made of synthetically stable ferrate (K2FeO4, BaFeO4, etc.) as a positive electrode material for high-iron batteries; and the lithium-iron battery is mainly a lithium iron phosphate battery, which is more common than other primary batteries (commonly known as dry batteries). The battery that can't be recharged after being discharged and restored can have a high voltage of 0.2-0.4V, and the discharge is stable, pollution-free, safe, and excellent in performance.

[ET-Power iron battery]

● What is a lithium iron phosphate battery?

The full name of lithium iron phosphate battery should be lithium iron phosphate lithium ion battery, referred to as lithium iron phosphate battery. It is lithium ion battery with lithium iron phosphate (LiFePO4) material as battery positive electrode. It is a product launched after 2002 and is lithium. A new member of the ion battery family.

【Lithium iron phosphate battery】

● What are the characteristics of lithium iron phosphate batteries?

Lithium iron phosphate battery is a rechargeable battery with high capacity, high output voltage, good charge and discharge cycle performance, electrochemical stability, safety in use, wide operating temperature range, and no environmental pollution. Good, especially in large discharge rate discharge (5 ~ 10C discharge), discharge voltage stability, safety (no combustion, no explosion), life (cycle number), no pollution to the environment, is currently * * High current output power battery. On the eve of the ninth high-tech fair, BYD announced that “the global iron battery that can be used for car charging has been born in Shenzhen”, but according to Li Liguang, deputy dean of the Automotive College of Tongji University, “BYD’s 'iron battery’ is iron phosphate. lithium battery".

The internal structure of the lithium iron phosphate battery is shown in the figure. On the left is the olivine-structured LiFePO4 as the positive electrode of the battery. The aluminum foil is connected to the positive electrode of the battery. The middle is the polymer diaphragm. It separates the positive electrode from the negative electrode, but the lithium ion Li+ can pass and the electron e- cannot pass. The right side is composed of A battery negative electrode composed of carbon (graphite) is connected to the negative electrode of the battery by a copper foil. Between the upper and lower ends of the battery is the electrolyte of the battery, and the battery is hermetically sealed by a metal casing.

[Internal structure of lithium iron phosphate battery]

When the lithium iron phosphate battery is charged, the lithium ion Li+ in the positive electrode migrates toward the negative electrode through the polymer separator; during the discharge, the lithium ion Li+ in the negative electrode migrates toward the positive electrode through the separator. Lithium-ion batteries are named after the lithium ions migrate back and forth during charging and discharging.

[Li-phosphate lithium battery charging and discharging process]

● Comparison of performance of lithium iron phosphate battery and other battery performance

Comparison of lithium iron phosphate battery performance and other battery performance
Â	General lithium ion battery	Lithium ion power battery	Lithium iron phosphate battery	NiMH batteries
Standard voltage V	3.6 or 3.7	3.6 or 3.7	3.2	1.2
Operating voltage range V	3.0-4.2	3.0-4.2	3.0-3.3	1.0-1.4
Unit mass capacity mAb/g	180	130	130	80
Unit weight energy Wb/kg	90-110	60-75	60-75	50-60
Unit volume energy Wb/l	280-300	220-240	220-240	200-220
**Charging rate C	0.2-0.5	0.5-1.0	0.5-1.5	0.2-0.5
Working discharge rate CmA	1	2	2	0.5
**Discharge rate CmA	1.5	5	10	2
Instantaneous high current pulse CmA (10s)	2	10	20	3
Cycle life (2CmA charging)	100 times	300 times	500 times	50 times
Cycle life at high current discharge (5CmA charge)	-	300 times	300 times	10 times
Safety	It is possible to burn and explode	It is possible to burn and explode	No burning, no explosion	It is possible to burn
Zero voltage storage for 30 days	Leakage, damage	Leakage, damage	no damage	Leakage, damage

　　 Note: Lithium iron phosphate battery produced by different factories will have some differences in various performance parameters; in addition, some battery performance is not included, such as battery internal resistance, self-discharge rate, charge and discharge temperature.

By comparison, the lithium iron phosphate battery can be output with high efficiency. Standard discharge is 2C, continuous high current discharge can reach 10C, instantaneous pulse discharge (10S) can reach 20C; battery does not burn, does not explode, safety **; has good cycle life, after 500 cycles, its discharge capacity Still greater than 95%; fast charging and no pollution to the environment.

[Lithium iron phosphate battery has good performance]

● What are the advantages of lithium iron phosphate batteries?

Lithium iron phosphate battery is used as a lithium ion secondary battery (also known as a rechargeable battery, which refers to a battery that can be activated by the activation of the active substance after the battery is discharged), and now the main direction is the power battery. Compared to NI-H, Ni-Cd batteries have great advantages.

Safety The safety properties of lithium iron phosphate are among the current materials. Of course, it has the same safety performance as other phosphates. It uses lithium iron phosphate as a battery, so you don't have to worry about the explosion.

[BYD e6 pure electric vehicle burned in Shenzhen 5.26 traffic accident]

High stability, including high-temperature charging, good capacity stability, and good storage performance. This is the advantage of **, and among all the materials known, it is also **.

Green and environmental protection For the pollution of dry batteries, I believe that you have already known in the textbook "Nature" in primary school. There is a large amount of lead in the lead-acid battery, and if it is improperly disposed after being discarded, it will be secondary pollution to the environment. However, lithium iron phosphate battery does not contain any heavy metals and rare metals (Ni-MH batteries require rare metals), non-toxic (SGS certification passed), no pollution, in line with European RoHS regulations, is a green battery certificate.

The price of the cathode material of the lithium ion battery on the market is mainly lithium cobalt oxide (LiCoO2), and a few lithium ion batteries using lithium manganese oxide (LiMn2O4) and lithium nickel oxide (LiNiO2) as the positive electrode material, generally the latter two A lithium ion battery of a positive electrode material is referred to as a "lithium manganese battery" and a "lithium nickel battery". Lithium-ion batteries made of LiFePO4 cathode material should be the cheapest.

Part of the metal price quotes that make up the battery cathode material
Metal name	Material	price	unit
cobalt	1#	209,000-215,000	Yuan / ton
nickel	Electrolytic nickel 1#	127,500	Yuan / ton
manganese	Electrolytic manganese	14,000	Yuan / ton
iron	Steelmaking	2,750-2,800	Yuan / ton

It can be seen from this that the lithium ion battery made of LiFePO4 cathode material should be the cheapest.

● Lithium iron phosphate battery also has its shortcomings

For example, the low temperature performance is poor, the tap density of the positive electrode material (refers to the mass per unit volume measured after the powder in the container under the specified conditions) is small, and the volume of the lithium iron phosphate battery of the same capacity is larger than that of the lithium cobalt oxide. Lithium-ion batteries are therefore not advantageous in terms of miniature batteries. When used in a power battery, a lithium iron phosphate battery, like other batteries, needs to face battery consistency problems. The life of a single lithium iron phosphate battery is currently more than 2,000 times, but the life of the battery pack will be greatly reduced, possibly 500 times. Because the battery pack is made up of a large number of single cells, the overall life of the battery pack depends on the battery with the shortest life.

Therefore, only when the battery performance is highly consistent, the life can be brought close to the level of the single battery.

Summary: As one of the first car companies in the world to realize the industrialization of lithium iron phosphate battery, BYD first put the lithium iron phosphate electric vehicle on the market, 300 e6 taxis and 200 K9 buses successfully operated for more than two years, making the battery The performance advantage is fully demonstrated. On the road of new energy vehicles, I hope that BYD will get better and better.