The low-temperature chemical synthesis of Li4Ti5O12 powder for Li-ion battery anodes

Abstract

While using Li4Ti5O12 as the anode material in lithium ion batteries greatly enhances their operation safety and avoids the formation of a solid electrolyte interface, the synthesis of this material often comes at a high time and energy cost. A typical solid-state synthesis method requires the reagents to be kept at temperatures up to 900 °C for several hours. Both synthesis temperature and processing time were reduced by applying the concept of solution combustion synthesis, where a sol-gel precursor is synthesized which generates the energy needed for complete sample conversion and crystallization by itself when it is heated to a relatively low process temperature. The large amount of parameters inherent to this concept, such as fuel and oxidizer amount, heating rate and atmosphere were studied and the physical properties of both precursor gels and thermally processed powders were characterized by thermogravimetric analysis (TGA) coupled with differential scanning calorimetry (DSC), fourier transform infrared spectroscopy (FT-IR) and mass spectrometry (MS), Raman spectroscopy and X-ray diffraction (XRD). By using the concept of solution combustion synthesis, the synthesis temperature was reduced to a temperature as low as 250 °C, while the processing time required was in the order of seconds. The oxidizer amount, NH4NO3 in this case, is of great importance, since while it is necessary for a balanced combustion reaction, an excess also decomposes endothermically, thereby preventing the necessary accumulation of heat within the sample. Solution combustion synthesis can considerably lower the temperature and time required for the synthesis of ceramic materials, but careful optimization of the precursor gel is necessary, since the mechanism of thermal degradation is complex and dependent on a large amount of parameters.