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Nb16W5O55 emerged as a high-rate anode material for Li-ion batteries in 2018 [Griffith et al., Nature2018, 559 (7715), 556−563]. This exciting discovery ignited research in Wadsley−Roth (W−R) compounds, but systematic experimental studies have not focused on how to tune material chemistry and structure to achieve desirable properties for energy storage applications. In this work, we systematically investigate how structure and composition influences capacity, Li-ion diffusivity, charge−discharge profiles, and capacity loss in a series of niobium tungsten oxide W−R compounds: (3 × 4)-Nb12WO33, (4 × 4)-Nb14W3O44, and (4 × 5)-Nb16W5O55. Potentiostatic intermittent titration (PITT) data confirmed that Li-ion diffusivity increases with block size, which can be attributed to an increasing number of tunnels for Li-ion diffusion. The small (3 × 4)-Nb12WO33 block size compound with preferential W ordering on tetrahedral sites exhibits single electron redox and, therefore, the smallest measured capacity despite having the largest theoretical capacity. This observation signals that introducing cation disorder (W occupancy at the octahedral sites in the block center) is a viable strategy to assess multi-electron redox behavior in (3 × 4) Nb12WO33. The asymmetric block size compounds [i.e., (3 × 4) and (4 × 5) blocks] exhibit the greatest capacity loss after the first cycle, possibly due to Li-ion trapping at a unique low energy pocket site along the shear plane. Finally, the slope of the charge−discharge profile increases with increasing block size, likely because the total number of energy-equivalent Li-ion binding sites also increases. This unfavorable characteristic prohibits the large block sizes from delivering constant power at a fixed C-rate more so than the smaller block sizes. Based on these findings, we discuss design principles for Li-ion insertion hosts made from W−R materials. 

Scanning probe-based microscopes (SPMs) are widely used in biology, chemistry, materials science, and physics to image and manipulate matter on the nanoscale. Unfortunately, high school and university departments lack expensive SPM tools and materials microscopy activities to educate a large number of students in this vital SPM imaging technique. As a result, students face challenges participating in and contributing value to the nanotechnology revolution driving modern scientific innovations. Here we demonstrate an affordable scanning laser-based imaging system (approximately $400, excluding the computer) to introduce students to the point-by-point image formation process underlying SPM methods. In this laboratory activity, students learn how to construct and optimize images of a working solar panel using a laser beam-induced current (LBIC) imaging system. We envision undergraduate and graduate students should be able to use this LBIC system for independent solar energy research projects as well as apply fundamental knowledge and measurement skills to understand other SPM techniques. 

Understanding how particle size and morphology influence ion insertion dynamics is critical for a wide range of electrochemical applications including energy storage and electrochromic smart windows. One strategy to reveal such structure–property relationships is to perform ex situ transmission electron microscopy (TEM) of nanoparticles that have been cycled on TEM grid electrodes. One drawback of this approach is that images of some particles are correlated with the electrochemical response of the entire TEM grid electrode. The lack of one-to-one electrochemical-to-structural information complicates interpretation of genuine structure/property relationships. Developing high-throughput ex situ single particle-level analytical techniques that effectively link electrochemical behavior with structural properties could accelerate the discovery of critical structure-property relationships. Here, using Li-ion insertion in WO 3 nanorods as a model system, we demonstrate a correlated optically-detected electrochemistry and TEM technique that measures electrochemical behavior of via many particles simultaneously without having to make electrical contacts to single particles on the TEM grid. This correlated optical-TEM approach can link particle structure with electrochemical behavior at the single particle-level. Our measurements revealed significant electrochemical activity heterogeneity among particles. Single particle activity correlated with distinct local mechanical or electrical properties of the amorphous carbon film of the TEM grid, leading to active and inactive particles. The results are significant for correlated electrochemical/TEM imaging studies that aim to reveal structure-property relationships using single particle-level imaging and ensemble-level electrochemistry.