Li-ion battery safety issues&technology

　　1. The dangers of lithium-ion batteries

　　a. High chemical activity

　　Lithium is an element of main group I of the second period of the periodic table and has extremely active chemical properties.

　　b. High energy density

　　Lithium-ion batteries have a very high specific energy (≥140Wh/kg), which is several times that of nickel-cadmium, nickel-hydrogen and other secondary batteries. If a thermal runaway reaction occurs, it will release a high amount of heat and easily lead to unsafe behavior.

　　c. Use organic electrolyte system

　　Organic solvents are hydrocarbons, have low decomposition voltage, are prone to oxidation, and the solvent is flammable; if leakage occurs, it will cause the battery to catch fire, or even burn or explode.

　　d. High probability of side reactions

　　During normal use of lithium-ion batteries, under certain conditions, such as overcharging, overdischarging or overcurrent operation, it is easy to cause chemical side reactions inside the battery, which will seriously affect the performance and service life of the battery, and A large amount of gas may be generated, causing the pressure inside the battery to rapidly increase and then explode and fire, causing safety problems.

　　e. The structure of the electrode material is unstable

　　The overcharge reaction of lithium-ion batteries will change the structure of the positive electrode material and cause the solvent in the electrolyte to be strongly oxidized; and this effect is irreversible, and the heat generated by the reaction may cause thermal runaway.

　　2. Analysis of the causes of safety problems of lithium-ion battery products

　　After 30 years of industrial development, lithium-ion battery products have made considerable progress in safety technology, effectively controlling the occurrence of side reactions in the battery and ensuring the safety of the battery. However, with the increasing use of lithium-ion batteries and higher energy density, safety incidents have occurred frequently in recent years.

　　We conclude that the main reasons for the safety problems of lithium-ion battery products are as follows:

　　a. Material issues

　　When selecting materials, the manufacturer did not conduct a certain assessment of the raw materials, which caused the inherent deficiencies in the safety of the batteries.

　　b. Production process issues

　　The raw materials are not strictly tested and the production environment is poor, resulting in the mixing of impurities in the production, which not only has a great disadvantage to the capacity of the battery, but also has a great impact on the safety of the battery; in addition, if too much water is mixed in the electrolyte, Side reactions may occur and increase the internal pressure of the battery, which will affect safety.

　　c. Defects in battery cell design and reduced safety performance

　　In terms of structural design, there is no insulating tape in key parts, or insufficient margin, unreasonable design of the length of the tab, etc., all of which may bury hidden dangers to the safety of the battery.

　　d. The energy density is too high

　　At present, the market is pursuing higher-capacity battery products. In order to increase product competitiveness, manufacturers continue to increase the volumetric specific energy of lithium-ion batteries, which greatly increases the risk of batteries.

　　Three, security technology

　　Although lithium-ion batteries have many hidden dangers, the use of certain measures can effectively ensure their safety.

　　The following briefly introduces several commonly used safety technologies for lithium-ion batteries.

　　a. Choose raw materials with higher safety factor

　　b. Strengthen the overall safety design of the battery cell

　　1) Using switching elements, when the temperature in the battery rises, its resistance rises, and when the temperature is too high, it will automatically stop power supply;

　　2) Set up a safety valve (that is, the vent on the top of the battery). When the internal pressure of the battery rises to a certain value, the safety valve will automatically open to ensure the safety of the battery.

　　c. Improve process level

　　Efforts to standardize and standardize the production process of batteries, improve process methods, do a good job of process control, ensure process quality, reduce differences between products, implement standardized quality monitoring, eliminate defective parts, and eliminate defective products; maintain the production site Tidy and clean, implement 5S management and 6-sigma quality control to prevent impurities and moisture from being mixed in production, and minimize the impact of accidents in production on safety.

　　Lithium-ion battery (LIB) has become the main energy storage solution in modern social life. Among them, lithium iron phosphate batteries are a perfect substitute for lead-acid batteries, and are the first choice for grid-connected peak shaving, off-grid energy storage, photovoltaic energy storage, UPS, data center and other industries.