Atomic Layer Deposition of Hierarchical CNTs@FePO_4 Architecture as a 3D Electrode for Lithium-Ion and Sodium-Ion Batteries

摘要

3D microbatteries hold great promise as on-board energy supply systems for microelectronic devices. The construction of 3D microbatteries relies on the development of film deposition techniques that can enable coatings of uniform electrode and electrolyte materials in high-aspect-ratio substrates. Here, a 3D FePO_4 on carbon nanotubes (CNTs@FePO_4) structure is fabricated by coating FePO_4 on CNTs/carbon paper substrate using atomic layer deposition. Compared to FePO_4 on a planar substrate, the 3D CNTs@FePO_4 electrode exhibits significantly increased areal capacity and excellent rate capability for lithium-ion and sodium-ion storage. The 3D CNTs@FePO_4 maintains areal capacities of 64 and 33 μAh cm~(?2) after 180 cycles for lithiumion batteries (LIBs) and sodium-ion batteries, which are 16 and 33 times higher than those of planar FePO_4 electrode, respectively. Moreover, hybrid 3D CNTs@FePO_4@Li_3PO_4 structure is fabricated by coating Li_3PO_4 solidstate electrolyte on 3D CNTs@FePO_4. The CNTs@FePO_4@Li_3PO_4 electrode shows stable cycling performance in LIBs. Hard X-ray photoemission spectroscopy analysis demonstrates that the Li_3PO_4 coating prevents the formation of undesirable LiF in the solid-electrolyte interphase layer, which is believed to be responsible for the performance degradation in CNTs@FePO_4. This work paves the way to building reliable 3D nanostructured electrode and electrolyte architectures for high areal capacity microbatteries.