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Pressure Action Can Improve The Conductivity Of Lithium Battery

- Jan 08, 2019 -

Rechargeable batteries have become one of the indispensable daily supplies in the information age. Its wide application has successfully liberated many previously immovable electrical equipment and instruments, and promoted the rapid development of many industries such as electronics, information and transportation. Although lithium-ion batteries are already being used in electric cars, the most advanced lithium-ion batteries currently have less than one-fifth the energy density of gasoline fuel. Therefore, it is urgent to develop battery materials with better performance.

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Spinel lithium titanate (Li4Ti5O12, LTO) is called "zero strain" lithium battery material. Its structure is very stable, and its crystal cell volume is almost unchanged during the lithium ion embedding and stripping process. The higher stability of crystal structure gives it excellent cycling performance and stable discharge voltage. In addition, it also has the advantages of higher electrode voltage and faster charging and discharging speed. These advantages make LTO an important lithium-ion battery material. However, the low conductivity of LTO restricts its application in high-power batteries. In order to improve its electrical conductivity, scientists have done a lot of research and exploration, but the effect is not significant.

Pressure, as an important thermodynamic parameter, can change the atomic distance of a substance and cause a series of changes in the structure and properties of the material. Many materials that are stable at room temperature and pressure will undergo pressure-induced phase transition under high pressure, resulting in one or more new compounds. Therefore, pressure provides a new dimension for the exploration of new materials. Therefore, exploring and synthesizing new materials under high pressure has become an important research direction. However, for lithium ion battery materials, pressure usually limits the migration and diffusion of lithium ions in the lattice, resulting in low lithium ion conductivity and hindering its application in lithium ion batteries.

Wang Lin high scientific research center recently, the Beijing research and institute of geochemistry, Chinese academy of sciences, Beijing institute of physics, and other units cooperation, combined with high pressure experimental research in situ and first principles calculation method, the structure of LTO at high pressure stability and conductivity properties such as looking closely related research results with Li - ion 'material under high pressure.Amorphization and enhanced conductivity ofLi4Ti5O12 issues online comment in national science in the study, the authors use diamond anvil high pressure in situ measurement technology, the structure of LTO at high pressure had been used to characterize the phase transformation and conductivity, found LTO structure under high pressure is not stable, distortion will happen;When pressure of 270000 atmospheres, due to the lattice distortion is too serious, irreversible amorphous phase change will happen in the process of unloading, found that the amorphous phase of LTO can keep to atmospheric pressure conductivity measurement in situ, found that the amorphous of LTO at high pressure and pressure have higher conductivity by using first principles calculation, the team of phase change and the change of electrical conductivity mechanism of LTO at high pressure were studied the results show that the LTO lattice under the high pressure of two kinds of unit LiO6 and TiO6 octahedral compression rate difference is very big.LiO6 compression rate is less than a quarter of the TiO6 this leads to the instability of LTO at high pressure, and as the pressure rises, the lattice distortion distortion, in about 270000 when atmospheric pressure led to the crystallization of the amorphous LTO provides more space for lithium ion migration, thus even also has high lithium ionic conductivity at room temperature the results improves our LTO structure performance under high pressure and the electric conductivity of understanding with higher ionic conductivity, amorphous LTO is likely to be a potential good lithium-ion battery materialsMore importantly, this study shows that the effect of pressure can improve the ionic conductivity of materials, thus providing a new way to develop more lithium ion battery materials with higher ionic conductivity.