What safety issues still exist in lithium batteries?

Viewing the flatulence/high temperature/explosion of lithium batteries from a micro view. The charging and discharging of lithium batteries is a chemical reaction process. Under a calm surface, lithium ions run back and forth between the positive and negative electrodes. When a lithium battery is charged, the lithium atom of the positive electrode loses electrons and is oxidized to lithium ions. The lithium ion enters the negative electrode through the electrolyte and obtains an electron, which is reduced to lithium atoms. When discharging, the process is reversed. In addition, in order to prevent the positive and negative electrodes of the battery from directly touching and short-circuiting, the battery uses a separator with fine pores to separate the positive and negative electrodes. Lithium battery flatulence, high temperature, explosion and other problems are usually related to overcharging, overdischarging and high current, and the three will cause damage to the battery. When overcharge occurs, the number of lithium atoms remaining in the positive electrode material is too small, resulting in a permanent decrease in battery capacity. At the negative electrode end, after the lithium atoms are saturated, recharging will cause the lithium metal to accumulate on the surface of the negative electrode material, forming dendrites. Over time, lithium dendrites will pierce the diaphragm, causing short circuits between the positive and negative electrodes. When overcharged, the electrolyte and other materials will often crack and produce gas, causing the battery casing or pressure valve to swell and rupture, and the lithium atoms accumulated on the surface of the negative electrode react with oxygen and cause an explosion. Similarly, when over-discharged, it will cause damage to the material. In addition, when the current is too large, lithium ions will not have time to enter the material and will accumulate on the surface of the material. After these lithium ions gain electrons, lithium atoms will crystallize on the surface of the material. Because lithium is the most active metal on the chemical periodic table, lithium atoms It is easy to oxidize with oxygen and explode. The new high-temperature resistant separator is expected to be commercialized. The important function of the battery separator is to separate the positive and negative plates in the lithium battery and prevent the direct contact between the positive and negative plates from short-circuiting. Therefore, the performance of the separator has a greater impact on the safety of lithium batteries. Generally speaking, the parameters for investigating diaphragm performance are as follows: 1. Thickness 2. Air permeability 3. Infiltration 4. Chemical stability 5. Pore size and distribution 6. Puncture strength 7. Thermal stability 8. Closed cell temperature, Membrane breaking temperature 9. Porosity. The industry's research on diaphragms has also been improved from these aspects. At present, the large-scale application of lithium battery separators on the market is mainly polyolefin organic separators. This type of separator has low processing cost, good mechanical properties and electrochemical stability, but has low porosity and wettability to electrolyte. The thermal stability and thermal stability are both poor, which may cause a short circuit of the battery, which may cause a fire or explosion in severe cases. Not long ago, the team led by Zhu Yingjie, a researcher at the Shanghai Institute of Ceramics of the Chinese Academy of Sciences, worked with a team led by Professor Hu Xianluo of Huazhong University of Science and Technology to develop a new type of inorganic refractory paper based on the previous hydroxyapatite ultra-long nanowires. A new type of hydroxyapatite ultra-long nanowire-based high-temperature lithium battery separator has been developed. According to the battery my country website, the battery separator has high thermal stability, high temperature resistance, flame retardancy and fire resistance. It can still maintain its structural integrity at a high temperature of 700°C, and can maintain a normal working state in a high temperature environment of 150°C. Japan's Mitsubishi Paper Co., Ltd. uses non-woven fabrics as raw materials to develop a new separator, coating ceramic particles on a non-woven separator composed of polyester fibers to enhance the high temperature resistance of the battery separator, which can withstand three times High temperature (up to 470°C). In 2018, it is estimated that nearly 3 billion Japanese Yen equipment will be invested in the Takasago Plant in Japan, and the annual processing capacity will increase to 33 million square meters. It is precisely because of the critical use of the separator to solve the lithium battery explosion problem, a project team from the School of Materials Engineering and Science of Southwest Petroleum University also started from the material of the separator and developed a natural lignocellulose lithium battery separator. Compared with advanced diaphragm products in the world, natural lignocellulosic lithium battery diaphragms have the advantages of green environmental protection, high efficiency and safety, simple process and low cost. The person in charge of the project team analyzed that with this new material, the processing cost of each cell phone lithium battery diaphragm is only a dime. For newly developed diaphragm products, the Ru0026D work can achieve maximum value only when commercialized processing is achieved. The new hydroxyapatite ultra-long nanowire-based high-temperature battery separator developed by the Shanghai Institute of Ceramics, Chinese Academy of Sciences is also expected to be used in various types of high-temperature batteries and energy storage systems such as sodium ion batteries and supercapacitors. Relevant research results were published in 'Advanced Materials' and an invention patent was applied for, but there is no news about mass production yet. The non-woven fabric separator developed by Japan's Mitsubishi Paper Co., Ltd. is expected to be mass-produced in 2018. It is known that the natural lignocellulosic lithium battery separator developed by Southwest Petroleum University is also seeking commercial cooperation. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous article: What are the correct ways to use lithium battery electric vehicles?