Lithium metal batteries (LMBs) are considered to be a substitute for lithium-ion batteries (LIBs) and the next-generation battery with high energy density. However, the commercialization of LMBs is seriously impeded by the uncontrollable growth of dangerous lithium dendrites during long-term cycling. The generation and growth of lithium dendrites are mainly derived from the unstable solid–electrolyte interphase (SEI) layer on the metallic lithium anode. The SEI layer is a key by-product formed on the surface of the lithium metal anode during the electrochemical reactions and has been the barrier to development in this area. An ideal SEI layer should possess electrical insulating, superior mechanical modulus, high electrochemical stability, and excellent Li-ion conductivity, which could improve the structural stability of the electrode upon a long cycling time. This mini-review carefully summarizes the recent developments in the SEI layer for LMBs, and the relationship between SEI layer optimization and electrochemical property is discussed. In addition, further development direction of a stable SEI layer is proposed.

FeF 3 has been extensively studied as an alternative positive material owing to its superior specific capacity and low cost, but the low conductivity, large volume variation, and slow kinetics seriously hinder its commercialization. Here, we propose the in situ growth of ultrafine FeF 3 • 0.33H 2 O NPs on a three-dimensional reduced graphene oxide (3D RGO) aerogel with abundant pores by a facile freeze drying process followed by thermal annealing and fluorination. Within the FeF 3 •0.33H 2 O/RGO composites, the three-dimensional (3D) RGO aerogel and hierarchical porous structure ensure rapid diffusion of electrons/ions within the cathode, enabling good reversibility of FeF 3 . Benefiting from these advantages, a superior cycle behavior of 232 mAh g −1 under 0.1C over 100 cycles as well as outstanding rate performance is achieved. These results provide a promising approach for advanced cathode materials for Li-ion batteries.

Fe2O3 has been widely investigated as an anode material for its high theoretical capacity and natural abundance, but the low conductivity, large volume variation, and slow kinetics seriously hinder its commercialization. Here, we propose the in situ growth of ultra-fine Maghemite (γ-Fe2O3) NPs on the 3D rGO aerogel with abundant pores by a facile freeze-drying process followed by thermal annealing, which is confirmed by X-ray diffraction and high-resolution-tunneling electron microscopy. This novel 3D porous structure ensures fast electron and ion diffusion within the electrode, which effectively mitigates the volume expansion of Fe2O3 during cycling. Benefiting from these advantages, an excellent cycling performance of 668 mAh g-1 at 0.5 A g-1 over 100 cycles as well as outstanding rate performance are achieved. These results provide a promising approach of advanced anode materials for lithium-ion batteries.