Aluminum foil negative electrodes with multiphase microstructure for all-solid-state Li-ion batteries.

Metal negative electrodes that alloy with lithium have high theoretical charge storage capacity and are ideal candidates for developing high-energy rechargeable batteries. However, such electrode materials show limited reversibility in Li-ion batteries with standard non-aqueous liquid electrolyte solutions. To circumvent this issue, here we report the use of non-pre-lithiated aluminum-foil-based negative electrodes with engineered microstructures in an all-solid-state Li-ion cell configuration. When a 30-µm-thick Al94.5In5.5 negative electrode is combined with a Li6PS5Cl solid-state electrolyte and a LiNi0.6Mn0.2Co0.2O2-based positive electrode, lab-scale cells deliver hundreds of stable cycles with practically relevant areal capacities at high current densities (6.5 mA cm-2). We also demonstrate that the multiphase Al-In microstructure enables improved rate behavior and enhanced reversibility due to the distributed LiIn network within the aluminum matrix. These results demonstrate the possibility of improved all-solid-state batteries via metallurgical design of negative electrodes while simplifying manufacturing processes.

Role of Areal Capacity in Determining Short Circuiting of Sulfide-Based Solid-State Batteries.

Solid-state batteries (SSBs) with lithium metal anodes offer higher specific energy than conventional lithium-ion batteries, but they must utilize areal capacities >3 mAh cm-2 and cycle at current densities >3 mA cm-2 to achieve commercial viability. Substantial research effort has focused on increasing the rate capabilities of SSBs by mitigating detrimental processes such as lithium filament penetration and short circuiting. Less attention has been paid to understanding how areal capacity impacts lithium plating/stripping behavior in SSBs, despite the importance of areal capacity for achieving high specific energy. Here, we investigate and quantify the relationships among areal capacity, current density, and plating/stripping stability using both symmetric and full-cell configurations with a sulfide solid-state electrolyte (Li6PS5Cl). We show that unstable deposition and short circuiting readily occur at rates much lower than the measured critical current density when a sufficient areal capacity is passed. A systematic study of continuous plating under different electrochemical conditions reveals average "threshold capacity" values at different current densities, beyond which short circuiting occurs. Cycling cells below this threshold capacity significantly enhances cell lifetime, enabling stable symmetric cell cycling at 2.2 mA cm-2 without short circuiting. Finally, we show that full cells with LiNi0.8Mn0.1Co0.1O2 also exhibit threshold capacity behavior, but they tend to short circuit at lower current densities and areal capacities. Our results quantify the effects of transferred capacity and demonstrate the importance of using realistic areal capacities in experiments to develop viable solid-state batteries.

Linking void and interphase evolution to electrochemistry in solid-state batteries using operando X-ray tomography.

Despite progress in solid-state battery engineering, our understanding of the chemo-mechanical phenomena that govern electrochemical behaviour and stability at solid-solid interfaces remains limited compared to at solid-liquid interfaces. Here, we use operando synchrotron X-ray computed microtomography to investigate the evolution of lithium/solid-state electrolyte interfaces during battery cycling, revealing how the complex interplay among void formation, interphase growth and volumetric changes determines cell behaviour. Void formation during lithium stripping is directly visualized in symmetric cells, and the loss of contact that drives current constriction at the interface between lithium and the solid-state electrolyte (Li10SnP2S12) is quantified and found to be the primary cause of cell failure. The interphase is found to be redox-active upon charge, and global volume changes occur owing to partial molar volume mismatches at either electrode. These results provide insight into how chemo-mechanical phenomena can affect cell performance, thus facilitating the development of solid-state batteries.