Most next-generation Li ion battery chemistries require a functioning lithium metal (Li) anode. However, its application in secondary batteries has been inhibited because of uncontrollable dendrite growth during cycling. Mechanical suppression of dendrite growth through solid polymer electrolytes (SPEs) or through robust separators has shown the most potential for alleviating this problem. Studies of the mechanical behavior of Li at any length scale and temperature are limited because of its extreme reactivity, which renders sample preparation, transfer, microstructure characterization, and mechanical testing extremely challenging. We conduct nanomechanical experiments in an in situ scanning electron microscope and show that micrometer-sized Li attains extremely high strengths of 105 MPa at room temperature and of 35 MPa at 90°C. We demonstrate that single-crystalline Li exhibits a power-law size effect at the micrometer and submicrometer length scales, with the strengthening exponent of −0.68 at room temperature and of −1.00 at 90°C. We also report the elastic and shear moduli as a function of crystallographic orientation gleaned from experiments and first-principles calculations, which show a high level of anisotropy up to the melting point, where the elastic and shear moduli vary by a factor of ∼4 between the stiffest and most compliant orientations. The emergence of such high strengths in small-scale Li and sensitivity of this metal's stiffness to crystallographic orientation help explain why the existing methods of dendrite suppression have been mainly unsuccessful and have significant implications for practical design of future-generation batteries.dendrite | size effect | elastic anisotropy | dislocation | elevated temperature I ncreased adoption of electric vehicles requires an improvement in the energy density of rechargeable Li ion batteries. Li metal anode is a common and necessary ingredient in commercialization pathways for next-generation Li ion batteries. In the near term, Li metal coupled with an advanced cathode could lead to a specific energy of 400 Wh/kg at the cell level, which represents 200% improvement over current state of the art (1). In the longer term, Li metal coupled with a S and O 2 cathode could lead to even higher specific energies of >500 Wh/kg. Despite over 40 y of research, overcoming the uncontrollable dendrite growth during cycling has remained an insurmountable obstacle for Li-based components (2). Among multiple attempted approaches to eliminate or even reduce the dendrite growth, mechanical suppression has emerged as one of the most promising routes. In their pioneering theoretical work, Monroe et al. (3) considered a solid polymer electrolyte (SPE) in contact with a Li metal electrode and performed a linear stability analysis of the deformation at the interface. They used linear elasticity to compute the stresses generated at the interface due to small deformations. They found that the dendrite growth decays with time if the shear modulus of the SPE is higher than about t...

We generalize the conditions for stable electrodeposition at isotropic solid-solid interfaces using a kinetic model which incorporates the effects of stresses and surface tension at the interface. We develop a stability diagram that shows two regimes of stability: a previously known pressure-driven mechanism and a new density-driven stability mechanism that is governed by the relative density of metal in the two phases. We show that inorganic solids and solid polymers generally do not lead to stable electrodeposition, and provide design guidelines for achieving stable electrodeposition.

Next generation batteries based on lithium (Li) metal anodes have been plagued by the dendritic electrodeposition of Li metal on the anode during cycling, resulting in short circuit and capacity loss. Suppression of dendritic growth through the use of solid electrolytes has emerged as one of the most promising strategies for enabling the use of Li metal anodes. We perform a computational screening of over 12 000 inorganic solids based on their ability to suppress dendrite initiation in contact with Li metal anode. Properties for mechanically isotropic and anisotropic interfaces that can be used in stability criteria for determining the propensity of dendrite initiation are usually obtained from computationally expensive first-principles methods. In order to obtain a large data set for screening, we use machine-learning models to predict the mechanical properties of several new solid electrolytes. The machine-learning models are trained on purely structural features of the material, which do not require any first-principles calculations. We train a graph convolutional neural network on the shear and bulk moduli because of the availability of a large training data set with low noise due to low uncertainty in their first-principles-calculated values. We use gradient boosting regressor and kernel ridge regression to train the elastic constants, where the choice of the model depends on the size of the training data and the noise that it can handle. The material stiffness is found to increase with an increase in mass density and ratio of Li and sublattice bond ionicity, and decrease with increase in volume per atom and sublattice electronegativity. Cross-validation/test performance suggests our models generalize well. We predict over 20 mechanically anisotropic interfaces between Li metal and four solid electrolytes which can be used to suppress dendrite growth. Our screened candidates are generally soft and highly anisotropic, and present opportunities for simultaneously obtaining dendrite suppression and high ionic conductivity in solid electrolytes.

Dendrite formation during electrodeposition while charging lithium metal batteries compromises their safety. 1-6 While high shear-modulus (G s ) solid-ion conductors (SICs)have been prioritized to resolve pressure-driven instabilities that lead to dendrite propagation and cell shorting, it is unclear whether these or alternatives are needed to guide uniform lithium electrodeposition, which is intrinsically density-driven. 7-9 Here, we show that SICs can be designed within a universal chemomechanical paradigm to access either pressure-driven dendrite-blocking or density-driven dendrite-suppressing properties, but not both. This dichotomy reflects the competing influence of the SIC's mechanical properties and partial molar volume of Li + (V Li+ ) relative to those of the lithium anode (G Li and V Li ) on plating outcomes. 9 Within this paradigm, we explore SICs in a previously unrecognized dendrite-suppressing regime that are concomitantly "soft", as is typical of polymer electrolytes, but feature atypically low V Li+ , more reminiscent of "hard" ceramics. Li plating (1 mA cm -2 ; T = 20 ˚C) mediated by these SICs is uniform, as revealed using synchrotron hard x-ray microtomography. As a result, cell cycle-life is extended (>300 cycles vs. ~100 cycles for control cells), even when assembled with thin Li anodes (~30 µm) and high-voltage NMC-622 cathodes (1.44 mAh cm -2 ), where ~20% of the Li inventory is reversibly cycled.Heterogeneous nucleation and ramified growth of lithium metal electrodeposits while charging lithium metal batteries is tied to uneven Li + transport across the anode-electrolyte interface. 7-11 Whereas the increasingly fractal character of this interface during battery cycling accelerates electrolyte degradation, rare events associated with dendrite formation, if left unchecked, can lead to device shorting and in some cases thermal runaway. 1-6 Both early-and late-stage instabilities associated with dendrite formation and propagation can be modeled using Butler-Volmer physics, 8

Rechargeable zinc–metal batteries have attracted widespread attention recently as a potential substitute for lithium-ion batteries due to their low cost, large volumetric capacity, and capability to use a safe aqueous electrolyte. However, dendrite growth during charging results in degradation of battery performance and aggravates safety concerns. In this work, we use phase-field simulations to analyze the design space for a porous polymer/aqueous ZnSO4 hybrid electrolyte. We show that dendrite growth could be suppressed, utilizing both the mechanical suppression effect from the polymer framework and the high diffusivity from the aqueous electrolyte. We identify some concrete directions to experimentally access these ranges of mechanical properties and porosity. As done in our previous work, we make all code available to spur growth of phase-field modeling for Zn-based rechargeable batteries.