Dendrite initiation and propagation in lithium metal solid-state batteries.

All-solid-state batteries with a Li anode and ceramic electrolyte have the potential to deliver a step change in performance compared with today's Li-ion batteries1,2. However, Li dendrites (filaments) form on charging at practical rates and penetrate the ceramic electrolyte, leading to short circuit and cell failure3,4. Previous models of dendrite penetration have generally focused on a single process for dendrite initiation and propagation, with Li driving the crack at its tip5-9. Here we show that initiation and propagation are separate processes. Initiation arises from Li deposition into subsurface pores, by means of microcracks that connect the pores to the surface. Once filled, further charging builds pressure in the pores owing to the slow extrusion of Li (viscoplastic flow) back to the surface, leading to cracking. By contrast, dendrite propagation occurs by wedge opening, with Li driving the dry crack from the rear, not the tip. Whereas initiation is determined by the local (microscopic) fracture strength at the grain boundaries, the pore size, pore population density and current density, propagation depends on the (macroscopic) fracture toughness of the ceramic, the length of the Li dendrite (filament) that partially occupies the dry crack, current density, stack pressure and the charge capacity accessed during each cycle. Lower stack pressures suppress propagation, markedly extending the number of cycles before short circuit in cells in which dendrites have initiated.

Achieving Ultrahigh-Rate Planar and Dendrite-Free Zinc Electroplating for Aqueous Zinc Battery Anodes.

Despite being one of the most promising candidates for grid-level energy storage, practical aqueous zinc batteries are limited by dendrite formation, which leads to significantly compromised safety and cycling performance. In this study, by using single-crystal Zn-metal anodes, reversible electrodeposition of planar Zn with a high capacity of 8 mAh cm-2 can be achieved at an unprecedentedly high current density of 200 mA cm-2 . This dendrite-free electrode is well maintained even after prolonged cycling (>1200 cycles at 50 mA cm- 2 ). Such excellent electrochemical performance is due to single-crystal Zn suppressing the major sources of defect generation during electroplating and heavily favoring planar deposition morphologies. As so few defect sites form, including those that would normally be found along grain boundaries or to accommodate lattice mismatch, there is little opportunity for dendritic structures to nucleate, even under extreme plating rates. This scarcity of defects is in part due to perfect atomic-stitching between merging Zn islands, ensuring no defective shallow-angle grain boundaries are formed and thus removing a significant source of non-planar Zn nucleation. It is demonstrated that an ideal high-rate Zn anode should offer perfect lattice matching as this facilitates planar epitaxial Zn growth and minimizes the formation of any defective regions.

An in Situ-Formed Mosaic Li7Sn3/LiF Interface Layer for High-Rate and Long-Life Garnet-Based Lithium Metal Batteries.

Garnet-type solid electrolytes are suitable for solid-state batteries with a lithium metal anode, but it is challenging to fabricate garnet-based lithium metal batteries with a long cycle life at high rates. This study demonstrates that a mosaic Li7Sn3/LiF interface layer formed in situ on the surface of garnet-type Li6.75La3Zr1.75Ta0.25O12 (LLZT) through the reaction between a SnF2 coating layer and a lithium metal enables stable, high-rate cycling for LLZT-based batteries. The interface layer possesses a nanomosaic structure of Li7Sn3 nanoparticles and surrounding LiF, enabling fast lithium-ion conduction. Meanwhile, ion insulating Li2CO3 on the surface of LLZT pellets is completely removed by SnF2 during the formation of the interface layer, which reduces the ion diffusion barrier from LLZT to the lithium anode. Benefiting from the advantageous interface layer, LiFePO4∥SnF2-LLZT∥Li cells show superior cycle performance over 200 cycles at 1 C (272 µA cm-2) with a capacity of 140.6 mAh g-1 (94.6% retention) at 30 °C. Even at 2 C, a capacity of 102.9 mAh g-1 remains after 200 cycles. This work provides an optimal interfacial structure to enhance lithium-ion migration between garnet electrolytes and a lithium metal and paves the way for developing high-performance solid-state batteries.