Brief Introduction Of Lithium Iron Phosphate Battery

  1. Definition of lithium iron phosphate battery

    The lithium iron phosphate battery refers to a lithium ion battery using 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 currently used as the cathode material for the vast majority of lithium-ion batteries, while other cathode materials are currently not mass-produced on the market for various reasons. Lithium iron phosphate is also one of the lithium-ion batteries. From the principle of materials, lithium iron phosphate is also an intercalation/deintercalation process. This principle is exactly the same as lithium cobalt oxide and lithium manganate.

    Lithium iron phosphate is gradually entering the lithium ion power battery market due to the advantages of safety, cycle life advantage, and material cost.

    2. Lithium iron phosphate cathode material

    In 1997, A.K.Padhi reported for the first time that lithium iron phosphate (LiFePO4) has the function of deintercalating lithium. This material has an olivine-type phosphate-based lithium intercalation material, LiMPO4 (M: Mn, Fe, Co, Ni), and has become a very promising cathode material for lithium ion batteries. Lithium iron phosphate as a positive electrode material for lithium ion batteries has good electrochemical performance, the charging and discharging platform is very stable, and the structure is stable during the charging and discharging process. At the same time, the material is non-toxic, non-polluting, has good safety performance, can be used in a high-temperature environment, and has a wide range of raw material sources. It is currently a hot spot in the battery industry for development and research.

    This material has the crystal structure shown in the figure above.

    Operating voltage range: 2.5 ~ 3.6V, the platform is about 3.3V, which is lower than the 3.7V lithium cobalt oxide battery.

    Due to the poor conductivity of the material, it is necessary to dope the conductive carbon material or conductive metal particles into the lithium iron phosphate particles, or coat the surface of the lithium iron phosphate particles with conductive carbon material to improve the electronic conductivity of the material; or doping with metal ions to improve Conductivity. The density of the material is low, and the volume specific capacity of the battery is low, only 180Wh/L (lithium cobalt oxide can be more than 400Wh/L). In the field of small batteries, the same size battery is less than half of the existing battery capacity.

    3. Lithium iron phosphate battery and its advantages and disadvantages

    Advantages of lithium iron phosphate:

    1. Safety. The safety performance of lithium iron phosphate is the best among all materials at present. Of course, it has the same safety performance as other phosphates. If you use lithium iron phosphate as the battery, you should never worry about the problem of explosion.

    2. High stability. Including high-temperature charging, good capacity stability, good storage performance, etc. This is the biggest advantage, and it is the best among all known materials.

    3. Environmental protection. The whole production process is clean and non-toxic. All raw materials are non-toxic. Unlike cobalt is a toxic substance.

    4. The price is cheap. Phosphate uses phosphoric acid source, lithium source and iron source as materials, these materials are very cheap, no strategic resources and rare resources.

    Disadvantages of lithium iron phosphate:

    1. Poor conductivity. This issue is its most critical issue. The reason why lithium iron phosphate has not been widely used so late is a major problem. However, this problem can now be solved perfectly: it is to add C or other conductive agents. Laboratory reports can reach a specific capacity of 160mAh/g or more. The lithium iron phosphate material produced by our company has been added with a conductive agent during the production process, and does not need to be added when making the battery. In fact, the material should be: LiFePO4/C, such a composite material.

    2. The tap density is low. Generally it can only reach 1.3-1.5, and the low tap density can be said to be the biggest disadvantage of lithium iron phosphate. This shortcoming determines that it has no advantage in small batteries such as mobile phone batteries. Even though 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 small amounts. This shortcoming will not be prominent in power batteries. Therefore, lithium iron phosphate is mainly used to make power batteries.

    3. At present, research and development are not in-depth. The current industrialization of lithium iron phosphate as the cathode material is not optimistic. Because it has been developed in the last two years, research in various fields needs to be continued.

    4. Other

    In the field of power batteries, due to the safety problems and high prices of lithium cobalt oxide, it has been hovering outside the door of power batteries, and has never fully entered the field of power batteries. The current situation is that lithium cobaltate and lithium manganate are used in small batches. However, due to their inherent defects, they have not been commercialized in large quantities. The products are only in the trial production stage of small batches. Currently, large-scale commercialization There are still some insurmountable difficulties in operation. In the field of power batteries, phosphoric acid-based positive electrode materials have long cycle life, excellent safety performance, good high temperature performance, extremely low price, and low temperature performance and rate discharge can already reach the level of lithium cobalt oxide. It becomes the most promising power battery material, it may become the main substitute for nickel-cadmium batteries in the next 5 years, it will become a strong competitor of lead-acid batteries in the next 10 years, and it may be replaced in the next 20 years Lead-acid batteries have become the main starting power supply, UPS power supply and backup power supply, and become the leader of secondary batteries.

    The main problems of lithium iron phosphate are low capacity, high manufacturing cost, and difficult processing in battery production (pulp, drawing, rolling and other processes require special treatment, many companies cannot handle it well) rate discharge Unstable (requires a specific battery process coordination, which is greatly affected by the process) and the current trend of the use of electrical appliances is the compact development, so the battery also has the same requirements for high volume energy density. From the capacity point of view, lithium iron phosphate has no future. Certain battery fields have advantages, such as power batteries.

    Lithium iron phosphate has a low tap density and a large specific surface area. It is necessary to change the advanced technology of the battery, and the surface density of the battery pole piece is low, so the capacity of the same type of battery is lower.

    The electrolyte also needs to re-develop a suitable electrolyte system, and it is difficult to exert its performance with the existing mature electrolyte.

    In addition, because the operating voltage range of lithium iron phosphate batteries is 2.5 to 3.6V, and the platform is about 3.3V, there is no bulk protection circuit and charger, it is difficult to exert its characteristics on existing electronic equipment, and a whole needed is industry integration.