Lithium iron phosphate battery refers to a lithium ion battery that uses lithium iron phosphate as a positive electrode material. There are many kinds of cathode materials for lithium-ion batteries, mainly lithium cobaltate, lithium manganate, lithium nickelate, ternary materials, lithium iron phosphate, etc. Among them, lithium cobalt oxide is the cathode material used in most lithium-ion batteries at present, while other cathode materials have not been mass-produced in the market due to various reasons. Lithium iron phosphate is also one of the lithium-ion batteries. In terms of material principle, lithium iron phosphate is also an intercalation/deintercalation process, which is exactly the same as lithium cobaltate and lithium manganate. Lithium iron phosphate batteries are used as lithium-ion secondary batteries, and now the main direction is power batteries, which have great advantages over NI-H and Ni-Cd batteries. The charge and discharge efficiency of lithium iron phosphate batteries is relatively high. Between 88%-90%. The lead-acid battery is about 80%.
The lithium iron phosphate electrode material is mainly used in various lithium-ion batteries. Since 1996, Japan's NTT first disclosed AyMPO4 (A is an alkali metal, M is a combination of CoFe and CoFe: LiFeCOPO4) after the olivine structure of the lithium battery cathode material, In 1997, the research group of Texas State University in the United States also reported the characteristics of LiFePO4 reversibly moving in and out of lithium. The United States and Japan published the olivine structure (LiMPO4) by coincidence, which made this material receive great attention. And cause extensive research and rapid development. Compared with the traditional cathode materials for lithium ion secondary batteries, LiMn2O4 with spinel structure and LiCoO2 with layered structure, LiMPO4 has a wider range of raw materials, lower prices and no environmental pollution.
Positive electrode: The positive electrode material in the lithium iron phosphate battery uses lithium iron phosphate (LiFePO4) as the main raw material;
Negative electrode: The negative electrode active material is made of a mixture of carbon materials and binders and an organic solvent to make a paste, and is coated on the copper substrate in a thin layer distribution;
Diaphragm plate: called the diaphragm or isolation diaphragm, its function plays the role of closing or blocking the channel, generally using the microporous membrane of polyethylene or polypropylene material. The so-called closing or blocking function is to block or block the pores as ion channels when the battery temperature rises abnormally, so that the battery stops the charge and discharge reaction. The diaphragm plate can effectively prevent the abnormal heating of the battery due to excessive current caused by internal and external short circuits.
PTC element: Inside the cap of the lithium iron phosphate battery, when the internal temperature rises to a certain temperature or the current increases to a certain control value, the PTC acts as a thermal fuse and an overcurrent fuse, and will automatically break or disconnect. Thereby creating an internal circuit breaker. In this way, the working reaction inside the battery stops and the temperature drops. The safe use of the battery is guaranteed (double insurance).
Safety valve: In order to ensure the safety of the lithium iron phosphate battery, a safety device that cuts off abnormal current is generally provided through the control of the external circuit or inside the lithium iron phosphate battery. Even so, there may be other reasons that cause the internal pressure of the lithium iron phosphate battery to rise abnormally during use. In this way, the safety valve releases gas to prevent the battery from bursting or bursting.
The safety valve is actually a one-time non-repairable rupture membrane. Once it enters the working state, it protects the battery and stops it from working, so it is the last means of protection for the battery.
When the battery is charged, the lithium ions in the positive electrode material come out, pass through the electrolyte, and enter the negative electrode material through the diaphragm; when the battery is discharged, the lithium ions are removed from the negative electrode again, pass through the electrolyte, and pass through the diaphragm to return to the positive electrode material. middle. (Note: Lithium-ion batteries are named after lithium ions migrate back and forth during charging and discharging, so lithium-ion batteries are also known as "rocking chair batteries" lithium iron phosphate batteries. * Advantages
Seven advantages of lithium iron phosphate power battery:
1. Ultra-long life, the cycle life of long-life lead-acid batteries is about 300 times, and the maximum is 500 times, while the lithium iron phosphate power battery produced by Shandong Haiba Energy Group Co., Ltd. has a cycle life of more than 2,000 times, standard charging (5 hours rate) use, can reach 2000 times. The lead-acid battery of the same quality is "new half year, old half year, and maintenance and maintenance for half a year", which is 1-1.5 years at most, while lithium iron phosphate battery will reach 7-8 years when used under the same conditions. Taken together, the price-performance ratio will be more than 4 times that of lead-acid batteries.
2. Safe use. Lithium iron phosphate completely solves the hidden safety problems of lithium cobaltate and lithium manganate. Lithium cobaltate and lithium manganate will explode under strong collisions, posing a threat to the life safety of consumers, while iron phosphate Lithium has undergone rigorous safety testing and will not explode even in the worst traffic accidents.
3. It can quickly charge and discharge at 2C with high current. Under the special charger, the battery can be fully charged within 40 minutes at 1.5C, and the starting current can reach 2C, but lead-acid batteries do not have this performance now.
Fourth, high temperature resistance, the peak value of lithium iron phosphate electric heating can reach 350"C--500"C, while lithium manganate and lithium cobaltate are only around 200'C. 5. Large capacity.
Has a larger capacity than ordinary batteries (lead acid, etc.). 5AH- 1000AH (single)
6. No memory effect.
Rechargeable batteries often work under the condition of being fully charged, and the capacity will quickly drop below the rated capacity. 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 used at any time without having to discharge it before charging.
Seven, green environmental protection. The battery does not contain any heavy metals and rare metals (nickel-metal hydride batteries require rare metals), non-toxic (SGS certification), non-polluting, in line with European RoHS regulations, and is an absolute green battery certificate. There is a large amount of lead in lead-acid batteries. If it is disposed of improperly, it will cause secondary pollution to the environment, and lithium iron phosphate materials are pollution-free in both production and use. Therefore, the battery has been included in the "863" national high-tech development plan during the "Tenth Five-Year Plan" period, and has become a key project supported and encouraged by the state. With China's entry into the WTO, the export volume of China's electric bicycles will increase rapidly, and now electric bicycles entering Europe and the United States have been required to be equipped with non-polluting batteries.
It can be seen that compared with traditional batteries, lithium iron phosphate batteries are only at a certain disadvantage in terms of price, and other indicators have obvious advantages. But if you consider battery life, the price of lithium iron phosphate batteries is the lowest. Except for the two indicators of tap density and gram capacity, lithium iron phosphate is slightly insufficient, and other indicators have great advantages, especially in terms of cycle performance, environmental protection, safety performance, raw material cost and application fields.
Lithium iron phosphate batteries also have their shortcomings: for example, low temperature performance is poor, the tap density of positive electrode materials is small, and the volume of lithium iron phosphate batteries of equal capacity is larger than that of lithium ion batteries such as lithium cobalt oxide, so it has no advantages in micro batteries. When used in power batteries, lithium iron phosphate batteries, like other batteries, need to face the problem of battery consistency. The following specific analysis:
1. Poor conductivity and slow diffusion of lithium ions. When charging and discharging at a high rate, the actual specific capacity is low. This problem is a difficulty that restricts the development of the lithium iron phosphate industry. The reason why lithium iron phosphate has not been widely used so late is a major problem.
2. The tap density is low. Generally, it can only reach 0.8-1.3. The low tap density can be said to be a big disadvantage of lithium iron phosphate. This determines that it has no advantages in small batteries such as mobile phone batteries, so its range of use is limited to a certain extent. Even if it has low cost, good safety performance, good stability and high cycle times, if the volume is too large, it can only replace lithium cobalt oxide in a small amount. But this - the disadvantage will not be prominent in the power battery. Therefore, lithium iron phosphate is mainly used to make power batteries.
3, -. The coherence problem is serious. The life of a single lithium iron phosphate battery is currently more than 2000 times, but the consistency of the produced battery is not good, which in turn affects the performance and overall life of the battery pack. Therefore, there are certain obstacles in the application of power vehicles. 4. The low temperature performance of lithium iron phosphate battery is poor. The inherent characteristics of lithium iron phosphate materials determine that its low-temperature performance is inferior to other cathode materials such as lithium manganate. In general, for a single cell, the capacity retention rate is about 60~70% at 0C, 40~55% at -10C, and 20~40% at -20C. Such low temperature performance obviously cannot meet the use requirements of power supply. 5. High manufacturing cost. There is no doubt that lithium iron phosphate has the advantages of safety, environmental protection and high cycle times, but the current manufacturing cost is higher than that of lead-acid batteries and lithium manganate batteries. The main reasons are:
1) The physical properties of the material are quite different from other lithium battery materials, its particle size is small, the tap density is small, the specific surface area is large, the processing performance of the material is not good, and the coating amount is low, which leads to an increase in the cost of the battery;
2) The lithium iron phosphate battery is only 3.2V, which is about 20% lower than other lithium batteries, and the single battery needs to be used 20% more, resulting in a large increase in the cost of the battery pack. .
With the development of technology, these shortcomings of lithium iron phosphate materials are gradually being solved, its cost performance is gradually improved, and its application scope is gradually expanding. We believe that lithium iron phosphate battery technology has entered a stage of rapid development, which is driving the entire The industry has entered a high-speed growth stage from the market cultivation and introduction period.
