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

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The existence of passivating layers at the interfaces is a major factor enabling modern lithium-ion (Li-ion) batteries. The properties of the passivation layers determine the cycle life, performance, and safety of batteries. One critical passivation layer is the solid electrolyte interphase (SEI), a heterogeneous multicomponent film formed due to the decomposition of the electrolyte at the surface of the anode. The multicomponent nature is critical for its functioning as the interfaces between these components play a critical role in determining performance and safety. In this work, we use first-principles simulations to investigate the thermodynamic, kinetic, and electronic properties of the interface between lithium fluoride (LiF) and lithium carbonate (Li2CO3), two common SEI components present in Li-ion batteries with organic liquid electrolytes. We construct a coherent interface between these components that restricts the strain in each of them to below 3%. We find that the interfacial structure has a formation energy of the Frenkel defect higher than bulk calculations and similar to pristine Li2CO3, generating Li vacancies in LiF and Li interstitials in Li2CO3 responsible for transport. On the other hand, the Li interstitial hopping barrier is reduced from 0.3 eV in bulk Li2CO3 to 0.10 or 0.22 eV in the interfacial structure considered, demonstrating the favorable role of the interface. Controlling these two effects in a heterogeneous SEI is crucial for maintaining fast ion transport in the SEI. We further perform Car–Parrinello molecular dynamics simulations to explore Li-ion conduction in our interfacial structure, which reveal an enhanced Li-ion diffusion in the vicinity of the interface. Understanding the interfacial properties of the multiphase SEI represents an important frontier to enable next-generation batteries.

The unique electronic and mechanical properties of two-dimensional (2D) materials make them promising next-generation candidates for a variety of applications. Large-scale searches for high-performing 2D materials are limited to calculating descriptors with computationally demanding first-principles density functional theory. In this work, we alleviate this issue by extending and generalizing crystal graph convolutional neural networks to systems with planar periodicity and train an ensemble of models to predict thermodynamic, mechanical and electronic properties. We carry out a screening of nearly 45,000 structures for two separate applications: mechanical strength and photovoltaics. By collecting statistics of the screened candidates, we investigate structural and compositional design principles that impact the properties of the structures surveyed. Our approach recovers some well-accepted design rules: hybrid organic-inorganic perovskites with lead and tin tend to be good candidates for solar cell applications and titanium based MXenes usually have high stiffness coefficients. Interestingly, other members of the group 4 elements also contribute to increasing the mechanical strength of MXenes. For all-inorganic perovskites, we discover some compositions that have not been deeply studied in the field of photovoltaics and thus open up paths for further investigation. We open-source the code-base to spur further development in this space.

Lithium metal batteries are a critical piece toward electrifying aviation. For electric aircraft, high discharge power requirements necessitate stripping of lithium metal in a uniform way. Recent studies have identified the evolution of surface voids and pits as a failure mechanism. In this work, using density functional theory calculations and thermodynamic modeling, we investigate the initial step associated with void formation, that is, vacancy congregation, on lithium metal surfaces and interfaces with solid electrolyte interphase (SEI) materials. For isolated lithium slabs, the (111) surface is the least likely to exhibit pitting issues. However, once interfaces with SEI materials are considered, only the (110) lithium facet has the potential of preventing void growth, and exclusively when paired with lithium carbonate. Our work suggests that faceting control during electrodeposition could be a key pathway toward preventing voids and highlights the importance of interface design for optimal battery performance.