We are excited to share our latest work accepted in Energy & Environmental Science: "Conformal hetero-electrolyte interface between soft oxyhalides and garnet enables low-pressure lithium-reservoir-free solid-state batteries." The paper was co-first authored by group member Vipin Singh.
Solid-state batteries can offer high energy densities and improved safety, but no solid electrolyte is simultaneously compatible with both a lithium metal anode and a high voltage uncoated cathode yet. Dual solid electrolyte (DSE) batteries are attractive because they can meet both requirements. However, the contact of different solid electrolyte layers introduces significant challenges associated with the resulting hetero-electrolyte (H-E) interface and can yield large resistances (>500 Ω cm2) at low stack pressures, significantly hindering battery performance. Here, we report that H-E interface resistances down to 150 Ω cm2 can be achieved at relatively low stack pressures (i.e., 2–3 MPa) and 25 °C, with a combination of soft oxyhalide catholytes and garnet separator as anolytes. Mechanical analysis and mesoscale modelling reveal that oxyhalides (hardness ≤0.4 GPa) are significantly softer than sulfide and halide electrolytes, resulting in a larger transfer-active contact area at the oxyhalide|garnet H-E interface compared with a sulfide|garnet interface. Moreover, the H-E interfacial activation energy (Ea) closely matches the grain-boundary Ea of the garnet once the geometric current constriction is removed. We demonstrate that the DSE design with LiNbOCl4 and Li6.5La3Zr1.5Ta0.5O12 solid electrolytes allows for the incorporation of a high voltage cathode and a Li-reservoir-free anode. The DSE batteries achieve a high Coulombic efficiency (>99.7%) at 5 MPa and 60 °C over 120 cycles. This work demonstrates the potential for Li-reservoir-free DSE batteries at low pressures.
DOI: 10.1039/D5EE07777J