Lithium titanate battery technology
The ideal negative electrode material for power batteries should have the following properties: high charge and discharge efficiency and cycle life; high structural stability, chemical stability and thermal stability; high specific capacity, good safety; abundant resources, low price, relatively simple preparation and no pollution to the environment.
The current commercial lithium-ion battery anode materials mainly focus on carbon-based materials. The potential of the carbon negative electrode after lithium insertion during the battery reaction is close to that of metallic lithium. Once the battery is overcharged, metallic lithium dendrites will easily precipitate on the surface of the carbon electrode. The produced lithium dendrites easily break down the diaphragm, cause internal short circuit of the battery, and cause thermal runaway of the battery; in addition, the carbon negative electrode will form an unstable solid electrolyte membrane (SEI membrane) at a low lithium insertion potential, which brings considerable safety risks to the power battery. In addition, the graphite-based negative electrode material has the problem of co-intercalation with the electrolyte, which is highly sensitive to the electrolyte, and the limited stability causes the cycle stability of the electrode to be affected. Although alloy anode materials have a higher specific capacity than carbon anode materials, the repeated insertion/deintercalation of lithium during charging and discharging will cause large changes in the volume of alloy anode materials, resulting in poor cycle performance. The lithium titanate anode material has inherent advantages in these aspects. Some property parameters of graphite-based and lithium titanate anode materials are shown in Figure 1.
Performance improvement of lithium titanate battery
(1) Strictly control the moisture in materials and electrolyte.
(2) Optimize the electrolyte formulation, such as increasing the concentration of lithium salt.
(3) Treatment of LTO, such as carbon modification, system doping and nanoization.
For carbon modification, inorganic carbon sources usually have higher electronic conductivity, but advanced carbon sources (carbon nanotubes or graphene, etc.) and suitable preparation methods are required to ensure uniform dispersion with lithium titanate. Otherwise, not only the high rate performance of lithium titanate cannot be effectively improved, but also the uneven current distribution on the electrode surface may be caused, which may cause more serious safety problems. Although the organic carbon source can be more uniformly coated on the surface of the lithium titanate particles, it is still necessary to make a reasonable selection of the carbon conductivity and the cost price obtained after the cracking. As shown in Figure 2, for morphology control, nano-scale lithium titanate materials undoubtedly show better rate performance. But considering the requirements of industrialized high tap density, it is considered that the multi-layered near-spherical/quasi-spherical structure of the primary crystal grain nanometer level and the secondary particle micrometer level is the best morphology. Reasonable element doping and impurity phase recombination can change the position of Li atoms in the crystal lattice and the valence state of Ti element to improve the rate performance of lithium titanate. Some doping can also increase the theoretical capacity of lithium titanate. For example, larger radius ions (Na+, K+, Gd3+, Zr4+, Ta5+, V5+, etc.) are doped in Li sites and Ti sites, which can accommodate more Li by expanding the unit cell coefficient. In addition, reducing the discharge cut-off potential of lithium titanate from 1V to 0V can also increase its theoretical capacity from 175mA·h/g to 250mA·h/g, but it will sacrifice the excellent cycle performance of lithium titanate.
In summary, the main reason for lithium titanate gas production is the decomposition of electrolyte on the surface of lithium titanate under high potential conditions;
Modifying the surface of the lithium titanate material to prevent the electrolyte from reacting on the surface of the lithium titanate material is a feasible way to suppress the gas production of the battery. For example, Zhuhai Yinlong has achieved the suppression of gas production through graphene doping and coating technology, thereby improving the applicability of the product;
The same type of technology is Tianjin Pulan Nano, which announced its successful development in early 2016 and put it into mass production.