Lithium-ion battery failure classification and failure cause analysis

The reasons for the failure of lithium-ion batteries can be divided into internal and external causes. The internal cause mainly refers to the nature of the physical and chemical changes of the failure. The research scale can be traced back to the atomic and molecular scales to study the thermodynamic and kinetic changes of the failure process. External factors include impact, acupuncture, corrosion, high-temperature combustion, man-made damage and other external factors. 1. In the capacity decay failure standard cycle life test, the discharge capacity should not be less than 90% of the initial capacity when the number of cycles reaches 500. Or the discharge capacity should not be less than 80% of the initial capacity when the number of cycles reaches 1000. If the capacity drops sharply within the standard cycle range, it is a capacity decay failure. The root cause of battery capacity decay failure is the failure of materials, and it is closely related to objective factors such as battery manufacturing process and battery use environment. From a material point of view, the main reasons for the failure are the structural failure of the positive electrode material, the transitional growth of SEI on the negative electrode surface, the decomposition and deterioration of the electrolyte, the corrosion of the current collector, and the trace impurities of the system. Structural failure of positive electrode material: The structural failure of positive electrode material includes crushing of positive electrode material particles, irreversible phase transition, material disorder, etc. During the charging and discharging process of LiMn2O4, the structure of LiMn2O4 will be distorted due to the Jahn-Teller effect, and the particles may even be broken, causing the electrical contact between the particles to fail. The LiMn1.5Ni0.5O4 material will undergo a tetragonal-cubic phase transition during the charge and discharge process. The LiCoO2 material will enter the Li layer due to the transition of Li during the charge and discharge process, causing the layered structure to become chaotic and restrict Its capacity to play. Anode material failure: The failure of graphite electrode mainly occurs on the graphite surface. The graphite surface reacts with the electrolyte to process the solid electrolyte interface phase (SEI). If overgrowth, the lithium content in the internal system of the battery will decrease, and the result will be the capacity decline. The failure of silicon anode materials is mainly due to the cycle performance problems caused by their huge volume expansion. Electrolyte failure: LiPF6 has poor stability and is easy to decompose to reduce the migrating Li+ content in the electrolyte. It also easily reacts with trace amounts of water in the electrolyte to generate HF, causing corrosion inside the battery. Poor air-tightness causes the electrolyte to deteriorate, and the viscosity and chromaticity of the electrolyte change, which ultimately leads to a sharp drop in ion transmission performance. The failure of the current collector: the current collector corrodes and the adhesion of the current collector decreases. The HF generated by the failure of the above electrolyte will corrode the current collector and generate compounds with poor conductivity, resulting in increased ohmic contact or failure of the active material. After the Cu foil is dissolved at a low potential during the charge and discharge process, it is deposited on the surface of the positive electrode, which is the so-called copper precipitation. The common form of current collector failure is that the binding force between the current collector and the active material is not enough, which causes the active material to peel off and cannot supply capacity for the battery. 2. Increase in internal resistance The increase in internal resistance of a lithium-ion battery will be accompanied by failure problems such as a decrease in energy density, a decrease in voltage and power, and battery heat generation. The important factors that lead to the increase of the internal resistance of lithium-ion batteries are divided into key battery materials and battery use environment. Key battery materials: microcracks and breakage of the positive electrode material, destruction of the negative electrode material and excessive surface SEI, electrolyte aging, active material separation from the current collector, poor contact between the active material and conductive additives (including the loss of conductive additives), Diaphragm shrinkage hole is blocked, battery tab welding is abnormal, etc. Battery use environment: the ambient temperature is too high/low, overcharge and overdischarge, high rate charging and discharging, manufacturing process and battery design structure, etc. 3. Internal short circuit Internal short circuit often causes self-discharge, capacity degradation, local thermal runaway and safety accidents of lithium-ion batteries. Short circuit between copper/aluminum current collectors: untrimmed metal foreign bodies pierce the diaphragm or electrode during battery processing or use, and the displacement of the pole pieces or tabs in the battery package causes the positive and negative current collectors to contact. Short circuit caused by diaphragm failure: diaphragm aging, diaphragm collapse, diaphragm corrosion, etc. will cause the diaphragm to fail. The failed diaphragm loses electrical insulation or the gap becomes micro-contact between the positive and negative electrodes. Then there will be severe local heating, and continued charging and discharging will spread to the surroundings. , Resulting in thermal runaway. Impurities cause short circuits: Failure to remove the transition metal impurities in the positive electrode slurry will cause piercing the separator or promote the generation of lithium ion dendrites in the negative electrode, leading to internal short circuits. Short circuit caused by lithium ion dendrites: Lithium ion dendrites will appear in places where the local charges are uneven during the long cycle, and the dendrites will penetrate the diaphragm to cause internal short circuits. In the process of battery design and manufacturing or battery pack assembly, unreasonable design or excessive local pressure can also cause internal short circuits. Internal short circuit will also occur under the induction of battery overshoot and overdischarge. 4. Gas production The gas production phenomenon that occurs when the electrolyte is consumed to form a stable SEI film during the battery formation process is normal gas production, but excessive consumption of the electrolyte releases gas or the cathode material releases oxygen and other phenomena are abnormal outgassing. It often appears in soft pack batteries, which will cause the internal pressure of the battery to be too large and deform, break the packaging aluminum film, and internal battery contact problems. Disclaimer: Some pictures and content of the articles published on this site are from the Internet. If there is any infringement, please contact to delete it. Previous post: Is the electric bicycle lithium-ion battery or lead-acid better?