Modeling the Interface between Lithium Metal and Its Native Oxide

Abstract

Owing to their high theoretical capacities, batteries that employ lithium (Li) metal as the negative electrode are attractive technologies for next-generation energy storage. However, the successful implementation of lithium metal batteries is limited by several factors, many of which can be traced to an incomplete understanding of surface phenomena involving the Li anode. Here, first-principles calculations are used to characterize the native oxide layer on Li, including several properties associated with the Li/lithium oxide (Li 2 O) interface. Multiple interface models are examined; the models account for differing interface (chemical) terminations and degrees of atomic ordering (i.e., crystalline vs amorphous). The interfacial energy, formation energy, and strain energies are predicted for these models. The amorphous interface yields the lowest interfacial formation energy, suggesting that it is the most probable model under equilibrium conditions. The work of adhesion is evaluated for the crystalline interfaces, and it is found that the O-terminated interface exhibits a work of adhesion more than 30 times larger than that of the Li-terminated model, implying that Li will strongly wet an oxygen-rich Li 2 O surface. The electronic structure of the interfaces is characterized using Voronoi charge analysis and shifts in the Li 1s binding energies. The width of the Li/Li 2 O interface, as determined by deviations from bulklike charges and binding energies, extends beyond the region exhibiting interfacial structural distortions. Finally, the transport of Li ions through the amorphous oxide is quantified using ab initio molecular dynamics. Facile transport of Li + through the native oxide is observed. Thus, increasing the percentage of amorphous Li 2 O in the solid electrolyte interphase may be beneficial for battery performance. In total, the phenomena quantified here will aid in the optimization of batteries that employ high-capacity Li metal anodes.

Suppressing void formation in all-solid-state batteries: the role of interfacial adhesion on alkali metal vacancy transport

“…The oxide and phosphate terminated surfaces (Li 2 O, Li 3 OCl (O-term) and Li 3 PO 4 ), have W ad values in-between the alkali halide and metallic substrates, consistent with previous reports. 26,70,71 From Table S6, the magnitude of W ad is correlated with the substrate surface energy, , as expected from Equation 4.…”

“…17,81 However, the nature of the surface termination/interfaces of secondary phases formed at the alkali metal chemical potential may also be significantly different to those under synthesis conditions, as was recent shown computationally for Li 2 O. 70 Previous DFT calculations have indicated that Li 7 La 3 Zr 2 O 12 garnet materials, which are stable against Li metal, have larger average works of adhesion, approaching or exceeding the W ad =2 ( =0°) criteria for Li metal ( =0.471 J/m 2 ). 17,25 The larger W ad values for Li 7 La 3 Zr 2 O 12 may be related to the open dshell structure of Zr, which has previously been shown to increase adhesion in other metal ceramic systems.…”

“…In the current study, only sharp alkali metal/SSE interfaces were considered from DFT calculations, whereas in real systems, significant reconstruction or amorphization of the alkali metal at the interface may occur. 47,70,77 The simple bond breaking model is still likely to be applicable for these systems, as was the case for incoherent interfaces, although care must be taken to accurately model the distribution of possible and values in systems with lower crystallinity. Due to the large cost of DFT calculations of explicit interfaces, only single, isolated alkali metal vacancies were considered in this study to understanding the fundamental relationship between interfacial adhesion and vacancy segregation.…”

Moving beyond 99.9% Coulombic efficiency for lithium anodes in liquid electrolytes

“…For example, Guo et al have found the diffusivities of phase-pure, nanocrystalline LiF or Li 2 O thin films on Li to be several orders of magnitude higher, at 1.8 × 10 −9 cm 2 s −1 (Li 2 O) and ~4.5 × 10 −10 cm 2 s −1 (LiF), than their bulk crystalline powder counterparts of ~10 −12 cm 2 s −1 (refs. [68][69][70] ), but significantly lower than that of liquid electrolytes (10 −5 to 10 −8 cm 2 s −1 ) 6 . ultimately electrolyte derived.…”

Recent Progress in Understanding Solid Electrolyte Interphase on Lithium Metal Anodes

“…In addition, according to the simulations performed by Lowe et al., the ionic conductivity of amorphous Li 2 O can also be three magnitudes higher than that of the crystalline Li 2 O. [ 39 ] Both discoveries reemphasize the importance of the structure of SEI on the conductivity. Based on the conductivity dependence of Li 2 O SEI on temperature, the activation energy for Li + transportation in Li 2 O in SEI is determined to be 0.58 eV.…”