Analyses and discusses the safety of the lithium battery

Source: 2020 - 04 - 12 'hits: first lithium battery safety analysis and discussion of chemical power source technology difficulty, low production cost is low, than can, in the present production has been widely used. Chemical power supply in use process, constantly through chemical reaction, generate directional flow to provide continuous power supply, electronic production in chemical reaction heat, heat is not spread in time, will lead to thermal runaway, thermal runaway lead to cell damage occurs, such as violence discouraged, rupture, with fire, if you want to safely use the battery, must be in the limited temperature range, charge ratio, charging and discharging termination voltage, to ensure the safe operation of the battery. The core reason analysis of lithium battery, battery explosion explosion type can be summarized as external short circuit, internal short circuit and overcharge. Here refers to the external part of the outer part of the battery, including due to bad battery internal insulation design of short circuit. When external short circuit batteries, is not electronic components to cut off the circuit, inside the battery can produce a high quantity of heat, cause the electrolyte evaporation, pull the battery shell. When the battery internal temperature reaches 135 ℃, the high quality of the diaphragm paper will closed the tiny hole, electrochemical reaction, or close to terminate current plummeted, temperature and slow drop, so as to avoid the explosion. However, if the diaphragm paper pore closure rate is very low, or no closed, can make the battery to heat up, evaporate more electrolyte, eventually lead to the battery shell is broken, and even the battery temperature increase to the point of material combustion and explosion. Factors affecting the safety of lithium-ion batteries in general, lithium ion batteries in addition to meet the capacity, internal resistance, and high and low temperature cycle performance requirements, also need through a variety of safety performance test. Usually lithium ion battery overcharge, short circuit, thermal shock and mechanical shock are easy to affect the safety of the battery, but the function and role of these factors is not the same. 1. Acupuncture, short circuit, the influence of extrusion on the battery safety when the battery external short circuit or acupuncture and extrusion, often easy to cause the battery internal diaphragm rupture, lead to the battery in a very short period of time, there are a large number of electrical current, which directly lead to a sharp rise in the internal temperature of the battery, so in a very short period of time to trigger a series of violent reaction even burning, explosion and other security issues. For less safe batteries, usually within a few seconds to complete the process. Due to very high specific energy li-ion battery, such as laptop battery 2200 mah, a single energy can reach about 30 kj, in case of short circuit, the battery can achieve a high heating power, lead to the battery in a very short period of time up to very high temperature, the battery after sealing the danger of melted aluminum explosion-proof valve is usually. 2. Thermal shock effect on the battery when the battery by thermal shock, the battery of heat conduction is relatively slow, can withstand thermal shock for a short period of time. Compared with the short circuit and acupuncture extrusion, if the temperature of the thermal shock is low, the impact on the battery is not big, if the temperature of the thermal shock is higher, leading to decomposition of SEI battery cathode surface, high intercalated-li anode materials and electrolyte battery exothermic reaction in crisis now, but whether to risk depends on the speed of heat dissipation, if the cooling speed is slow, it is easy to cause the battery internal temperature rise further, diaphragm melting, internal short circuit batteries, rapid temperature rise, cause is material in reaction, the final explosion accident, this process is usually referred to as' thermal runaway. 3. Overcharge the battery safety when battery overcharge, the influence of different electrode materials because of its chemical properties of different will have different impact. In the early days of high speed charge, most of the electricity is stored through reversible chemical reaction, battery produces less heat. But in the late charge, due to the irreversible chemical reactions, electrical energy into heat energy, causing the battery temperature rise rapidly, a series of chemical reactions.