Safe Lithium‐Metal Anodes for Li−O₂ Batteries: From Fundamental Chemistry to Advanced Characterization and Effective Protection

Abstract

Rechargeable LiÀ O 2 batteries play an increasing important role as energy storage devices, which have both, a high capacity anode and a cathode using an inexhaustible resource. As a key component in LiÀ O 2 batteries, the Li-metal anode suffers from major drawbacks related to Li dendrite formation and SEI layer growth, which are also major issues for Li-metal rechargeable batteries. This review presents an overview on the scientific challenges, fundamental mechanisms and modification strategies of Li-metal anodes for LiÀ O 2 batteries. Firstly, basic principles and challenges on Li-metal anodes are briefly retrospected. We further summarize and categorize the prevailing characterization techniques based on Li dendrite morphology characterization and SEI composition analysis. The up-to-date development of in-situ and operando characterization is also included. Following the obtained insights, effective protection/modification strategies towards practical application for LiÀ O 2 batteries are presented. Furthermore, we highlight the significance of advanced characterization techniques in interrogating the buried keys for solving practical hindrances for LiÀ O 2 batteries. The comprehensive characterization and analysis of Li anodes, cathodes, and electrolytes by various methods together with the development of novel techniques are expected to be indispensable to gain a thorough understanding of the battery operation and for offering guidelines for their practical development.

Lithium Metal Interface Modification for High‐Energy Batteries: Approaches and Characterization

“…Besides this, being in the air, which includes only a small amount of H 2 O, can give rise to the very fast corrosion of Li metal to form a layer containing Li carbonate (Li 2 CO 3 ), Li nitride (Li 3 N), and Li hydroxide (LiOH). [143][144][145] This corrosion brings about some critical problems, such as low reversibility, the accumulation of byproducts, an increase in overpotential, depletion of the electrolyte, the formation of unstable SEI layers, and eventually leads to the premature death of LiÀ O 2 batteries. Accordingly, besides many studies that have been carried out on the cathode side, such as structural modification, improvements in the catalyst activity, and redox mediator introduction, the development of practical and effective ways to protect Li metal is vital for commercialization of the LiÀ O 2 battery, while still very challenging.…”

Superoxide Anion Disproportionation Induced by Li+ and H+: Pathways to 1O2 Release in Li−O2 Batteries

“…The molecular orbitals at different nuclear geometries were optimized using a 2-state-averaged CASSCF (1 singlet + 1 triplet) with the ma-def2-TZVP basis set [31] within a [18,12] active space. CASSCF wavefunctions were optimized using an equal weight for the singlet and triplet state.…”

“…In all computations, the resolution of identity (RI) approximation for the evaluation of two-electron integrals was employed, which allows remarkable time savings at the price of a negligible loss of accuracy. The [18,12] active space was chosen to include all the p-type valence orbitals and electrons from the oxygens (12 orbitals, 18 electrons). The valence orbitals of the cations (1 s of H and 2 s of Li), when included in the active space in a test calculation, turned out to be substantially inactive, with occupation numbers very close to zero; therefore, we excluded them in the final calculations, leading to a 18-in-12 active space.…”

“…In order to compute also the adiabatic electronic states in the proximity of the crossing point (see again Figure 1) we have further characterized this region by performing a 5-state CASSCF [18,12] calculation in either the singlet and triplet multiplicity followed by a quasi-degenerate QD-NEVPT2. [35] In this way we obtained fully adiabatic NEVPT2 energies and ensured that the lowest-lying NEVPT2 energies computed previously were not significantly influenced by the number of states used in the CAS step.…”

“…[1][2][3][4] While aLOBs theoretical performance overcomes all other proposed battery chemistries, [5,6] their implementation in real devices requires to successfully tackle many unsolved issues, such as the reversibility of the redox reaction, [7] the parasitic release of CO 2 /CO/ H 2 , [8] the degradation of the electrolyte to Li 2 CO 3 or other organic by-products [9][10][11] and the stability of the lithium negative electrodes. [12] The chemical disproportionation of lithium superoxide R1 is a key step in the complex redox chemistry occurring in aLOBs: [13,14] 2LiO 2 Ð Li 2 O 2 þO 2 (R1)…”