Recent Advances in Metal Oxide‐based Electrode Architecture Design for Electrochemical Energy Storage

Abstract

Metal oxide nanostructures are promising electrode materials for lithium-ion batteries and supercapacitors because of their high specific capacity/capacitance, typically 2-3 times higher than that of the carbon/graphite-based materials. However, their cycling stability and rate performance still can not meet the requirements of practical applications. It is therefore urgent to improve their overall device performance, which depends on not only the development of advanced electrode materials but also in a large part "how to design superior electrode architectures". In the article, we will review recent advances in strategies for advanced metal oxide-based hybrid nanostructure design, with the focus on the binder-free film/array electrodes. These binder-free electrodes, with the integration of unique merits of each component, can provide larger electrochemically active surface area, faster electron transport and superior ion diffusion, thus leading to substantially improved cycling and rate performance. Several recently emerged concepts of using ordered nanostructure arrays, synergetic core-shell structures, nanostructured current collectors, and flexible paper/textile electrodes will be highlighted, pointing out advantages and challenges where appropriate. Some future electrode design trends and directions are also discussed.

Ultrahigh‐Power Pseudocapacitors Based on Ordered Porous Heterostructures of Electron‐Correlated Oxides

“…However, conventional pseudocapacitors made from state‐of‐the‐art electrode materials, typically transition‐metal oxides (TMOs) such as MnO 2 ,5, 15, 19, 20 TiO 2 ,6, 16 and Co 3 O 4 ,19, 21 often exhibit much lower power capability than EDLCs due to their intrinsically poor conductivity 15, 21. It thus remains a primarily challenge in realizing high‐power and high‐energy densities in pseudocapacitors, which requires pseudocapacitive electrode materials simultaneously providing large specific surface area and ultrahigh transports of ions and electrons 22, 23, 24. In this regard, controlling nanostructures and exploring novel materials have become critical processes to meet these requirements in developing TMO‐based composite electrodes,1, 6, 17, 23, 25 wherein various conductive materials, including nanostructured carbons (such as porous carbon,14, 26 carbon nanotubes,27, 28, 29, 30 and graphene 31, 32) and conducting polymers, are extensively employed to serve as electron pathways.…”

“…It thus remains a primarily challenge in realizing high‐power and high‐energy densities in pseudocapacitors, which requires pseudocapacitive electrode materials simultaneously providing large specific surface area and ultrahigh transports of ions and electrons 22, 23, 24. In this regard, controlling nanostructures and exploring novel materials have become critical processes to meet these requirements in developing TMO‐based composite electrodes,1, 6, 17, 23, 25 wherein various conductive materials, including nanostructured carbons (such as porous carbon,14, 26 carbon nanotubes,27, 28, 29, 30 and graphene 31, 32) and conducting polymers, are extensively employed to serve as electron pathways. Although the large specific surface area in these low‐dimensional composite nanostructures allows ion transports,1, 17, 23, 26, 27, 28, 29, 30, 31, 32 their assembled bulk electrodes usually exhibit high electrical resistance as a result of the short electron transport distance within these low‐dimensional conductive materials, the undesirably high contact resistances produced by the coating of electrically insulating active TMOs and polymer binders, as well as the weak and noncoherent TMO/conductor interfaces 24, 33, 34, 35.…”

“…Although the large specific surface area in these low‐dimensional composite nanostructures allows ion transports,1, 17, 23, 26, 27, 28, 29, 30, 31, 32 their assembled bulk electrodes usually exhibit high electrical resistance as a result of the short electron transport distance within these low‐dimensional conductive materials, the undesirably high contact resistances produced by the coating of electrically insulating active TMOs and polymer binders, as well as the weak and noncoherent TMO/conductor interfaces 24, 33, 34, 35. This inevitably leads to unsatisfactory improvements in rate capability, volumetric energy and power densities of pseudocapacitors 1, 17, 23. Therefore, it is imperative to explore novel and low‐cost conductive electrode materials that can make their composite electrodes deliver more volumetric energy at high rates with long‐term cycling stability by tackling all the three of abovementioned problems.…”

Reconstruction of Mini‐Hollow Polyhedron Mn2O3 Derived from MOFs as a High‐Performance Lithium Anode Material

“…Owing to their high specific theoretical capacity, low cost, and environmentally benign nature, manganese oxides (MnO x , 1 ≤ x ≤ 2) are believed to be the most promising alternative anode materials for next generation LIBs 11, 13, 16, 17. Moreover, the low operating voltages (1.3–1.5 V for lithium extraction) and small voltage hysteresis (<0.8 V) endow these materials with higher output voltage and higher energy density 14, 15, 18.…”

Recent Progress in Self‐Supported Metal Oxide Nanoarray Electrodes for Advanced Lithium‐Ion Batteries

“…In this regard, rational design and fabrication of high‐performance nanostructured electrode materials play a significant role in developing next‐generation LIBs with high energy density and power density. As a group of potential alternatives to commercialized electrodes, metal oxides have been comprehensively researched as potential high‐performance electrode materials 15, 16, 17, 18. Notably, the fabrication of self‐supported metal oxide nanoarray electrodes without the addition of binders and conductive additives (namely, binder‐free electrodes) provides unique benefits over slurry‐cast electrodes such as enhanced charge transfer efficiency and improved gravimetric capacity.…”