2024 ROCKY MOUNTAIN CHAPTER AVS SYMPOSIUM

Abstract: All solid-state batteries that replace the highly flammable liquid electrolytes that are presently used will dramatically reduce the incidence of battery fires, for which expensive on-board fire mitigation and suppression strategies are now required. Unfortunately, solid-state electrolytes (SEs) face significant technical challenges, in large part because Li dendrites readily penetrate through SEs, leading to short circuits and cell failure. This presentation will discuss a new and general paradigm via stress engineering for enabling all-solid-state batteries that use lithium or sodium (Li or Na) metal anodes. Completely different from the existing approaches, which either apply high stack pressures or add a buffer layer between Li and the SEs, this approach will suppress dendrites and cracks in SEs by putting the SE surfaces into a state of residual compressive stress via ion implantation. In addition, this talk will present the understanding of surface/grain boundary science and its impact on electrochemistry, as well the future strategies to improve electrodeposition efficiency via surface and stress engineering. Combining the results from spectroscopic and structural characterization, this invited talk will highlight the impact of stress and surface engineering on reversible electrochemistry of the Garnet solid-state electrolytes and provide insights in designing all-solid-state batteries for cycling at room temperature and low stack pressure.

Abstract: All-solid-state batteries hold the potential to transform electrochemical energy storage technologies. Replacing the flammable liquid electrolyte with a solid-state ion conductor can improve battery safety and may further increase battery energy density when paired with lithium metal anodes. The halide argyrodites Li6PS5X (X = halide, pseudohalide) are a promising family of candidate solid electrolytes, as they can achieve ionic conductivities that are nearly competitive with liquid electrolytes. In this work, we have discovered the new solid electrolyte Li6PS5CN in which the halide site is occupied by the orientationally-disordered cyanide ion. The new cyanide argyrodite exhibits lower activation barriers for Li-ion conductivity compared to the current champion argyrodite Li6PS5Br and comparable room temperature lithium-ion conductivities. Structurally, the similar sizes of cyanide and bromide ions produce nearly identical lithium conduction pathways. We further unravel the connections between static and dynamic disorder of cyanide and the subsequent impact on ion transport processes in Li6PS5CN. Through this study, we find that anion disorder plays a decisive role in dictating the extent and timescales of both lithium and cyanide dynamics in Li6PS5CN.

Global and domestic demand for electricity is increasing, and energy storage systems are needed to provide reliable power, especially as the supply shifts to intermittent renewables such as wind and solar. Beyond supply and demand imbalances, the current electric transmission and distribution system requires massive infrastructure buildout to account for changes in the location of wind/solar power sources and to accommodate two-way power flows from net metering, where homes and businesses with solar power can become both users and producers of electricity, depending on the time of day. Otoro Energy, Inc. is working to build an iron/chromium-based flow battery that will store megawatts of power. The flow battery will charge using extra energy from renewable sources and then discharge when renewable energy sources are not available. The flow battery could also be used as backup power, such as when utilities must turn off power due to fire risks. Otoro’s battery is efficient, safe, high performance, scalable, validated, and can be located anywhere. This talk will delve more deeply into Otoro’s flow battery technology and how the chemistry works.

Bifacial solar modules will be in high demand in the coming decade, but adapting the bifacial configuration to CdTe modules is hindered by high contact resistance, sheet resistance, and back surface recombination. Cracked film lithography (CFL) is a low-cost method for fabricating narrow metal gridlines that are ideal for CdTe rear contacts due to their high transparency and low sheet resistance. We demonstrate bifacial CdTe solar cells with greater power density than the monofacial baselines using a CuGaOx rear interface buffer that passivates while reducing sheet resistance and contact resistance. Inserting CuGaOx between the CdTe and Au increases mean power density from 18.0 ± 0.5 to 19.8 ± 0.4 mW cm−2 for one sun front illumination. However, coupling CuGaOx with a transparent conductive oxide leads to an electrical barrier. Instead, CuGaOx is integrated with CFL-patterned metal grids. CFL grid wires are spaced narrowly enough (≈10 µm) to alleviate semiconductor resistance while retaining enough passivation and transmittance for a bifacial power gain: bifacial CuGaOx/CFL grids generate 19.1 ± 0.6 mW cm−2 for 1 sun front + 0.08 sun rear illumination and 20.0 ± 0.6 mW cm−2 at 1 sun front + 0.52 sun rear—the highest reported power density at field albedo conditions for a scaled polycrystalline absorber.