3, University of Connecticut, Storrs, Connecticut, United States
2, Clemson University, Clemson, South Carolina, United States
Using elemental lithium (Li) as anodes will be highly advantageous in electrochemical energy storage devices in terms of capacity and cell voltage. Li has a high theoretical capacity (3860 mAhg-1) and the lowest potential among all elements (-3.040 V versus a standard hydrogen electrode). However, the main challenge preventing this beneficial anode selection is formation of un-wanted Li-dendrites during the charge and discharge cycles of a battery. The dendrite formation can lead to performance failures such as short circuiting. The solution to this challenge is to design a solid-state electrolyte that is mechanically robust enough to block dendrite propagation while simultaneously allowing fast conduction of ions. Using super ion conductor solid state electrolytes will enable fast charge-discharging which is a crucial goal in developing the next generation of high-performance batteries. However, high-rate cycling will be hindered if the large amount of inevitable heat generated by joule heating is not accounted for in cell design. Overheating batteries can cause catastrophic safety issues such as ignition. Therefore, information on the thermal behavior of each battery component over the operating temperature range is necessary. Herein, we will present thermal conductivity measurements of Li1+x+yYxZr2−x(PO4)3 (x = 0.15, -0.3 ≤ y ≤ 0.4) over a wide temperature range from ~ 20 to 973 K. Stabilization of the rhombohedral phase is obtained by adding 15% Y3+. The charge imbalance caused by this substitution is taken into account by adding equivalent charges from excess Li+. The thermal diffusivity measurements are conducted on spark plasma sintered pellets with a diameter of 12.7 mm via a NETZSCH laser flash LFA-457 from room temperature to 973 K. The obtained results indicate that thermal discursivities of the samples range from 0.6 to 0.3 mm2 s-1 as the temperature changes from ~300 to 973 K. The density is measured by the Archimedes method. The heat capacity measurements are conducted on a NETZSCH DSC 404 C. The low temperature measurements of thermal conductivity (20 K- room temperature) are carried out on polished bars using a custom designed apparatus according to [Pope and Tritt et al., Cryogenics 41 (2001) 725–731].