Research on the safety of the lithium iron phosphate batteries

Source: 2020 - 04 - 14 little hits: the time using lithium iron phosphate material studied the safety of the lithium iron phosphate battery lithium iron phosphate is a major positive electrode material of lithium ion batteries, widely recognized around the world, the security problem is power type lithium ion batteries used for electric car care about most, many factors, including anode materials, membrane, electrolyte, and battery power supply design and management system and a series of problems. At present, the safety of the lithium ion battery, test and evaluation are through to the battery products in different sampling, the excessive use of state and under the condition of the test material and iron phosphate lithium iron phosphate the excellent safety performance of lithium-ion batteries. Lithium ion battery safety related a more important factor is that due to the internal causes material and battery, the high probability of the possibility of short circuit and short circuit. For lithium metal anode of lithium secondary battery in the process of charging and discharging due to the production of lithium dendrite can cause the security problems of internal short circuit and the membrane was abandoned. Lithium ion battery in normal use are generally considered safe, as Toyota use nickel compounds as cathode materials, nickel compounds are considered the most unsafe industries. Although the thermal stability and the stability of the structure of lithium iron phosphate material is the highest in all current positive material thermodynamics, and verified in practical safety performance test, this is probably the most unsafe internal short-circuit the possibility and probability of materials and battery. First of all, from the preparation of lithium iron phosphate material solid phase sintering is a complex multiphase reaction ( Although some liquid phase synthesis technology synthesis process, but in the end all need high temperature solid phase sintering process) , there is a solid phosphoric acid, ferric oxide and lithium salt, plus the precursor and carbon aerosols. In order to ensure that the lithium iron phosphate is bivalent iron, sintering reaction must be in reducing atmosphere, and in the process of reducing iron ferric iron bivalent iron ion in strong reducing atmosphere, can reduce iron bivalent iron ion of trace iron in one step. Elemental iron can lead to the battery short circuit, which is the most taboo in the battery material, also Japan in dynamic lithium ion battery don't use one of the main reasons for the lithium iron phosphate. In addition, a significant feature of solid phase reaction is the reaction of slow and incomplete, which exist in the lithium iron phosphate trace amounts of Fe2O3 is possible. The Argonne laboratory will be high temperature lithium iron phosphate defects due to bad circulation charge and discharge cycle and the dissolution of Fe2O3 in elemental iron deposits on the cathode. In addition, in order to improve the performance of lithium iron phosphate, the particles must be nanoscale. Nanometer material is one of the distinctive features of structural stability and low thermal stability, high chemical activity, it has increased to a certain extent the possibility of iron dissolved in the lithium iron phosphate, especially under the condition of high temperature cycle and storage. The experimental results showed that by chemical analysis and energy spectrum analysis on the cathode detected the presence of iron. From the preparation of lithium iron phosphate batteries, due to the lithium iron phosphate nanoparticles of small, high specific surface area, therefore in the process of carbon coating, gases, such as specific surface area activated carbon of high moisture in the air and has a strong adsorption, electrode processing performance is poor, binder poor adhesion of nanoparticles. Nanoparticles in preparation of the battery, and battery charge and discharge cycle easily separated from the electrode in the process of storage, lead to the battery short circuit. As far as we know, the lithium iron phosphate batteries in the battery manufacturer's manufacturing process, or in the process of the use of consumers, the short circuit rate is very high. Battery manufacturers often found the problems in the process of from the preparation of the battery, but due to the lithium iron phosphate material internal causes of short circuit problem tend not to be recognized. A123 type 18650 lithium iron phosphate batteries a few years ago in a car driving on the highway of the electric car on fire.