Mixed Magic: Crafting Super Thin Films for Energy Storage

The world of energy storage is buzzing with excitement over tiny, powerful devices. These gadgets need special materials and clever fabrication methods to work their best. One standout technique is atomic layer deposition (ALD). This method allows for the creation of incredibly thin, complex structures. This is crucial for making solid-state devices with high energy and power densities. However, there's a catch. The ionic conductivity of these thin films has been a bit of a challenge. Scientists need materials that have the right composition and crystal structure. This is where a mixed metal phosphate called LiTi2(PO4)3 (LTP) comes into play. LTP is a strong candidate for pushing the limits of ALD ionic materials. It has a fast Li+-conducting NASICON-type crystalline phase. Researchers have developed a process for creating mixed ion-electron conducting NASICON-type thin films using ALD. This process is perfect for microbatteries and pseudocapacitors. They achieved compositional tunability by alternating between lithium oxide (Li2O) and titanium phosphate (TiPO) subprocesses. By tweaking the ratio between Li2O and TiPO cycles, they could adjust the Li content in LTP between 8 and 34 atomic % Li. After depositing the LTP films, they were annealed between 650 and 850 °C. This step was crucial for achieving a NASICON-type crystalline structure. The resulting semicrystalline LTP thin film showed impressive ionic conductivity. It had a conductivity of 9. 3 × 10^-7 S/cm at room temperature and 1. 7 × 10^-5 S/cm at 80 °C. Additionally, it had an electronic conductivity of 2. 5 × 10^-7 S/cm at room temperature. The study delved into how tuning the composition of LTP affects the film's properties. This includes its structure and conductivity within the mixed metal phosphate phase space. Understanding these complexities is key to advancing energy storage technologies.