Microstructure and property evaluation of lithium iron phosphate thin films for application in microbatteries
The shortage of fossil fuels and the requirements to produce clean, environmental friendly, efficient, and economical energy are the principal problems in the context of energy technology for current and future generations. Therefore, advanced energy storage and conversion capabilities with higher capacity and efficiency are desired. Currently, there is an enormous interest in the development of high energy density rechargeable batteries for use in domestic applications, automotive industries and portable electronic applications. The present research focuses on the development of LiFePO4 thin films for solid-state thin-film microbatteries. The present effort was performed with a specific purpose of understanding the effect of temperature, an important thermodynamic variable, on the microstructure and electronic properties of LiFePO4 films fabricated by radio-frequency (RF) magnetron sputtering. LiFePO 4 films were grown under varying deposition temperatures in the range of 25 to 400°C. In addition, LiFePO4 films were annealed in temperature range of 400 to 800°C for 1 and 2 hours. The effect of growth temperature on the crystal structure, surface morphology, chemical quality and electronic properties is investigated in detail. Characterizations of the films were performed using X-ray diffraction (XRD), high resolution scanning electron microscopy (HRSEM), energy dispersive X-ray spectrometry (EDS), optical spectrophotometer, and electrical resistivity measurements. The grain size increased as the annealing temperature increased from 400 to 800°C. The optical properties of the LiFePO4 films indicate that, as the growth temperature is increased, the transmittance of the films increases. The band gap increases from 2.75 eV to 3.28 eV with increasing temperature from RT-400°C. When the films were annealing at 1 hour form 400-800°C the band gap increased from 3.12 eV to 3.7 eV. Annealing for 2 hours at temperatures from 400 to 800°C showed an increase in band gap 3.12 eV to 3.75 eV showing the maximum value at 600°C. The electrical capacity indicates that with an increase in substrate temperature the resistivity of the films also increases.
Mares, Jose Marcos, "Microstructure and property evaluation of lithium iron phosphate thin films for application in microbatteries" (2010). ETD Collection for University of Texas, El Paso. AAI1483873.