Take you to correctly know the working principle, performance and advantages of LiFePO4 batteries

Lithium iron phosphate battery is actually a kind of cathode material for lithium ion batteries, so people named it lithium iron phosphate battery after its cathode material.

• Working principle

Lithium iron phosphate battery refers to a lithium ion battery that uses lithium iron phosphate as a positive electrode material. The cathode materials of lithium-ion batteries mainly include lithium cobaltate, lithium manganate, lithium nickelate, ternary materials, lithium iron phosphate and so on. Among them, lithium cobalt oxide is currently the cathode material used in most lithium-ion batteries.

• significance

In the metal trading market, cobalt (Co) is the most expensive and has a small storage capacity. Nickel (Ni) and manganese (Mn) are cheaper, while iron (Fe) has more storage capacity. The price of the cathode material is also consistent with the price of these metals. Therefore, the lithium ion battery made of LiFePO4 cathode material should be quite cheap. Another feature of it is that it has no pollution to the environment.

As a rechargeable battery, the requirements are: high capacity, high output voltage, good charge and discharge cycle performance, stable output voltage, high current charge and discharge, electrochemical stability, safety in use (not due to overcharge, overdischarge and short circuit Burning or explosion caused by improper operation), wide operating temperature range, non-toxic or less toxic, and non-polluting to the environment. The lithium iron phosphate battery using LiFePO4 as the positive electrode has good performance requirements, especially in the high discharge rate discharge (5～10C discharge), the discharge voltage is stable, safety (non-burning, non-explosive), and life (cycle times) ) It is the best in terms of pollution-free environment, and is currently the best high-current output power battery.

• Structure and working principle

As the positive electrode of the battery, LiFePO4 is connected with the positive electrode of the battery by aluminum foil. In the middle is a polymer separator, which separates the positive electrode from the negative electrode, but lithium ion Li can pass but electron e- cannot pass. The right side is made of carbon (graphite). The negative electrode of the battery 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.

When the LiFePO4 battery is charged, the lithium ion Li in the positive electrode migrates to the negative electrode through the polymer separator; during the discharge process, the lithium ion Li in the negative electrode migrates to the positive electrode through the separator. Lithium-ion batteries are named after lithium ions move back and forth during charging and discharging.

• Main performance

The nominal voltage of the LiFePO4 battery is 3.2V, the final charging voltage is 3.6V, and the final discharge voltage is 2.0V. Due to the different quality and technology of the positive and negative materials and electrolyte materials used by various manufacturers, there will be some differences in their performance. For example, the battery capacity of the same model (standard battery in the same package) is quite different (10%-20%).

What I want to explain here is that lithium iron phosphate power batteries produced by different factories have some differences in various performance parameters; in addition, some battery performance is not listed, such as battery internal resistance, self-discharge rate, charge and discharge temperature, etc.

• Advantage

1. Improvement of safety performance

The P-O bond in the lithium iron phosphate crystal is stable and difficult to decompose. Even at high temperature or overcharge, it will not collapse and generate heat like lithium cobalt oxide or form strong oxidizing substances, so it has good safety. A report pointed out that a small number of samples were found to burn in the actual operation of acupuncture or short-circuit experiments, but no explosion occurred. In the overcharge experiment, high voltage charging that was several times higher than the self-discharge voltage was used, and it was found that there were still Explosion phenomenon. Nevertheless, its overcharge safety has been greatly improved compared with ordinary liquid electrolyte lithium cobalt oxide batteries.

2. Improved lifespan

Lithium iron phosphate battery refers to a lithium ion battery that uses lithium iron phosphate as a positive electrode material.

The cycle life of a long-life lead-acid battery is about 300 times, the highest is 500 times, while the cycle life of a lithium iron phosphate power battery is more than 2000 times, and the standard charge (5 hour rate) use can reach 2000 times. Lead-acid batteries of the same quality are "new half a year, half a year old, and half a year for maintenance", which can take up to 1 to 1.5 years. When used under the same conditions, lithium iron phosphate batteries have a theoretical life of 7 to 8 years. Comprehensive consideration, the performance-price ratio is theoretically more than 4 times that of lead-acid batteries. High-current discharge can quickly charge and discharge high-current 2C. With a dedicated charger, the battery can be fully charged within 40 minutes of 1.5C charging, and the starting current can reach 2C, but lead-acid batteries have no such performance.

3. Good high temperature performance

The peak value of lithium iron phosphate electric heating can reach 350℃-500℃, while lithium manganate and lithium cobaltate are only around 200℃. Wide operating temperature range (-20C--75C), with high temperature resistance, lithium iron phosphate electric heating peak can reach 350℃-500℃, while lithium manganate and lithium cobaltate are only around 200℃.

4. Large capacity

The capacity of the battery will quickly fall below the rated capacity value when the battery is always fully charged and not discharged. This phenomenon is called the memory effect. Like nickel-metal hydride and nickel-cadmium batteries, there is memory, but lithium iron phosphate batteries do not have this phenomenon. No matter what state the battery is in, it can be charged and used without having to discharge it first.

5. Light weight

The volume of the lithium iron phosphate battery of the same specification and capacity is 2/3 of the volume of the lead-acid battery, and the weight is 1/3 of the lead-acid battery.

6. Environmental protection

Lithium iron phosphate batteries are generally considered to be free of any heavy metals and rare metals (the nickel-hydrogen battery requires rare metals), non-toxic (SGS certified), non-polluting, in line with European RoHS regulations, and an absolute green battery certificate. Therefore, the reason why lithium batteries are favored by the industry is mainly due to environmental protection considerations. The export volume of China's electric bicycles will increase rapidly, and the electric bicycles entering Europe and the United States have been required to be equipped with pollution-free batteries.

However, some experts said that the environmental pollution caused by lead-acid batteries mainly occurred in the company's irregular production process and recycling process. In the same way, lithium batteries belong to the new energy industry, but it cannot avoid the problem of heavy metal pollution. Lead, arsenic, cadmium, mercury, chromium, etc. in the processing of metal materials may be released into dust and water. The battery itself is a chemical substance, so there may be two kinds of pollution: one is the pollution of process excrement in the production engineering; the other is the pollution of the battery after it is scrapped.