Recent advances in heterostructured cathodic electrocatalysts for non-aqueous Li-O2 batteries

Abstract

Developing efficient energy storage and conversion applications is vital to address fossil energy depletion and global warming. Li-O₂ batteries are one of the most promising devices because of their ultra-high energy density. To overcome their practical difficulties including low specific capacities, high overpotentials, limited rate capability and poor cycle stability, an intensive search for highly efficient electrocatalysts has been performed. Recently, it has been reported that heterostructured catalysts exhibit significantly enhanced activities toward the oxygen reduction reaction and oxygen evolution reaction, and their excellent performance is not only related to the catalyst materials themselves but also the special hetero-interfaces. Herein, an overview focused on the electrocatalytic functions of heterostructured catalysts for non-aqueous Li-O₂ batteries is presented by summarizing recent research progress. Reduction mechanisms of Li-O₂ batteries are first introduced, followed by a detailed discussion on the typical performance enhancement mechanisms of the heterostructured catalysts with different phases and heterointerfaces, and the various heterostructured catalysts applied in Li-O₂ batteries are also intensively discussed. Finally, the existing problems and development perspectives on the heterostructure applications are presented.

Fig. 1. Gravimetric energy densities (W h kg⁻¹) of typical rechargeable batteries and gasoline.

Fig. 2. (a) Schematic of a nonaqueous Li–O₂ cell. (b) Reduction mechanisms of Li–O₂ batteries through different reaction routes.

Fig. 3. Summary of the typical heterostructures and their functions in Li–O₂ batteries.

Fig. 4. (a) Schematic of the biphasic N-doped cobalt@graphene multiple capsule heterostructure and the proposed reaction mechanism during the discharge process. Reproduced with permission: copyright 2017, American Chemical Society. (b) Top and (c) side views from the nanowire-axis direction. Reproduced with permission: copyright 2018, Wiley. Different formation mechanisms of Li₂O₂ aggregates on (d) P-HSC and (e) HSC cathodes. Reproduced with permission: copyright 2013, Springer Nature.

Fig. 5. (a) XPS valence band spectra and (b) band diagram of ZIS, ZIS-Vs and RuZIS-Vs. Reproduced with permission: copyright 2020, Royal Society of Chemistry. (c) Molecular orbital structure change of Pd@NiCo₂O₄ as a result of Pd impregnation. Reproduced with permission: copyright 2017, Royal Society of Chemistry. (d) Optimized structures and the corresponding binding energies of O₂ and LiO₂ on LFO and Ag@LFO. Color codes: Li (violet), O (red), Fe (golden), Ag (light gray for Ag clusters and gray for replacing lanthanum in perovskite), lanthanum (green) and oxygen atom of O₂ and LiO₂ (blue). Reproduced with permission: copyright 2019, American Chemical Society. (e) The mechanisms of electrochemical growth of the film-like and nanosheet-like Li₂O₂. Reproduced with permission: copyright 2017, American Chemical Society.

Fig. 6. (a) Views of MoO₂ (−111), Mo₂C (101) and MoO₂/Mo₂C interfaces with corresponding O₂ adsorption models (red, cyan and grey balls are O, Mo, and C atoms). Reproduced with permission: copyright 2020, Elsevier. (b) Summary of the enhanced high rate reaction mechanism with unique local electric fields from the NiCo₂S₄/NiO heterostructure. For the spheres in the models (gray, blue, yellow and red balls represent Ni, Co, S and O atoms). Reproduced with permission: copyright 2019, Wiley. (c) Specific roles of the NiO–NiCo₂O₄ heterostructure for Li–O₂ catalysis during discharge and recharge processes. Reproduced with permission: copyright 2019, Royal Society of Chemistry. (d) Schematic illustration of different discharge product morphologies on carbon paper supported MnO₂ and Co₃O₄ cathodes. Reproduced with permission: copyright 2017, Wiley.

Fig. 7. (a) Charge distribution at the interface of NiS₂ and ZnIn₂S₄ with (b) adsorption energies (ΔE_ads) of Li⁺, O₂ and LiO₂ adsorbed on NiS₂@ZnIn₂S₄ with optimized structures. Reproduced with permission: copyright 2020, American Chemical Society. (c) Nyquist plots of different cathodes with the inset showing the fitting equivalent circuits. (d) Schematic diagram of the reaction mechanisms of the Ni₃Se₂/NiSe₂@NF cathode during discharge and charge processes. Reproduced with permission: copyright 2020, Elsevier. (e) HRTEM image of CoSe₂@NiSe₂ at the interface with the disordered edges. (f) HRTEM image of CoSe₂@NiSe₂ and inset shows the corresponding FFT pattern from the distortion region. (g) Schematic illustration of the oxygen electrode reactions on the CoSe₂@ NiSe₂ cathode during cycling. Reproduced with permission: copyright 2020, Elsevier.

Fig. 8. . (a) Schematic illustration of the synthesis of Co and Fe layered double hydroxide (LDH)–RuO₂ nanosheets. Reproduced with permission: copyright 2019, Elsevier. (b) Schematic illustration of the h-BN/(111) heterostructure. (c) Free energy diagram of the ORR on the h-BN/Ni (111) surface. Reproduced with permission: copyright 2016, Elsevier. (d) The theoretical energy band diagram for the improved performance of rechargeable photoelectrochemical Li–O₂ batteries. Reproduced with permission: copyright 2018, Elsevier.

Fig. 9. Directions and perspectives for future studies on heterostructured cathode catalysts for Li–O₂ batteries.