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.

Accelerating Rate Calorimetry and Complementary Techniques to Characterize Battery Safety Hazards.

The hazards associated with lithium-based battery chemistries are well-documented due to their catastrophic nature. Risk is typically qualitatively assessed through an engineering risk matrix. Within the matrix, potentially hazardous events are categorized and ranked in terms of severity and probability to provide situational awareness to decision makers and stakeholders. The stochastic nature of battery failures, particularly the lithium-ion chemistry, makes the probability axis of a matrix difficult to properly assess. Fortunately, characterization tools exist, such as accelerated rate calorimetry (ARC), that characterize degrees of battery failure severity. ARC has been used extensively to characterize reactive chemicals but can provide a new application to induce battery failures under safe, controlled experimental conditions and quantify critical safety parameters. Due to the robust nature of the extended volume calorimeter, cells may be safely taken to failure due to a variety of abuses: thermal (simple heating of cell), electrochemical (overcharge), electrical (external short circuit), or physical (crush or nail penetration). This article describes the procedures to prepare and instrument a commercial lithium-ion battery cell for failure in an ARC to collect valuable safety data: onset of thermal runaway, endotherm associated with polymer separator melting, pressure release during thermal runaway, gaseous collection for analytical characterization, maximum temperature of complete reaction, and visual observation of decomposition processes using a high temperature borescope (venting and cell can breach). A thermal "heat-wait-seek" method is used to induce cell failure, in which the battery is heated incrementally to a set point, then the instrument identifies heat generation from the battery. As heat generates a temperature rise in the battery, the calorimeter temperature follows this temperature rise, maintaining an adiabatic condition. Therefore, the cell does not exchange heat with the external environment, so all heat generation from the battery under failure is captured.