Limin Zhou

Abstract Since their successful commercialization in 1990s, lithium‐ion batteries (LIBs) have been widely applied in portable digital products. The energy density and power density of LIBs are inadequate, however, to satisfy the continuous growth in demand. Considering the cost distribution in battery system, it is essential to explore cathode/anode materials with excellent rate capability and long cycle life. Nanometer‐sized electrode materials could quickly take up and store numerous Li + ions, afforded by short diffusion channels and large surface area. Unfortunately, low thermodynamic stability of nanoparticles results in electrochemical agglomeration and raises the risk of side reactions on electrolyte. Thus, micro/nano and hetero/hierarchical structures, characterized by ordered assembly of different sizes, phases, and/or pores, have been developed, which enable us to effectively improve the utilization, reaction kinetics, and structural stability of electrode materials. This review summarizes the recent efforts on electrode materials with hierarchical structures, and discusses the effects of hierarchical structures on electrochemical performance in detail. Multidimensional self‐assembled structures can achieve integration of the advantages of materials with different sizes. Core/yolk–shell structures provide synergistic effects between the shell and the core/yolk. Porous structures with macro‐, meso‐, and micropores can accommodate volume expansion and facilitate electrolyte infiltration.

Urchin‐like CoSe 2 assembled by nanorods has been synthesized via simple solvothermal route and has been first applied as an anode material for sodium‐ion batteries (SIBs) with ether‐based electrolytes. The CoSe 2 delivers excellent sodiation and desodiation properties when using 1 m NaCF 3 SO 3 in diethyleneglycol dimethylether as an electrolyte and cycling between 0.5 and 3.0 V. A high discharge capacity of 0.410 Ah g −1 is obtained at 1 A g −1 after 1800 cycles, corresponding to a capacity retention of 98.6% calculated from the 30th cycle. Even at an ultrahigh rate of 50 A g −1 , the capacity still maintains 0.097 Ah g −1 . The reaction mechanism of the as‐prepared CoSe 2 is also investigated. The results demonstrate that at discharged 1.56 V, insertion reaction occurs, while two conversion reactions take place at the second and third plateaus around 0.98 and 0.65 V. During the charge process, Co first reacts with Na 2 Se to form Na x CoSe 2 and then turns back to CoSe 2 . In addition to Na/CoSe 2 half cells, Na 3 V 2 (PO 4 ) 3 /CoSe 2 full cell with excessive amount of Na 3 V 2 (PO 4 ) 3 has been studied. The full cell exhibits a reversible capacity of 0.380 Ah g −1 . This work definitely enriches the possibilities for anode materials for SIBs with high performance.

Ether based electrolytes have surfaced as alternatives to conventional carbonates allowing for enhanced electrochemical performance of sodium-ion batteries; however, the primary source of the improvement remains poorly understood. Here we show that coupling titanium dioxide and other anode materials with diglyme does enable higher efficiency and reversible capacity than those for the combination involving ester electrolytes. Importantly, the electrolyte dependent performance is revealed to be the result of the different structural evolution induced by a varied sodiation depth. A suit of characterizations show that the energy barrier to charge transfer at the interface between electrolyte and electrode is the factor that dominates the interfacial electrochemical characteristics and therefore the energy storage properties. Our study proposes a reliable parameter to assess the intricate sodiation dynamics in sodium-ion batteries and could guide the design of aprotic electrolytes for next generation rechargeable batteries.

Building rechargeable lithium batteries for wide-temperature applications requires us to investigate the battery failure mechanism at low/high temperature, design advanced electrode/electrolyte materials, and optimize the battery management system.

By a novel in situ chemical vapor deposition, activated N-doped hollow carbon-nanotube/carbon-nanofiber composites are prepared having a superhigh specific Brunauer–Emmett–Teller (BET) surface area of 1840 m(2) g(–1) and a total pore volume of 1.21 m(3) g(–1). As an anode, this material has a reversible capacity of ~1150 mAh g(–1) at 0.1 A g(–1) (0.27 C) after 70 cycles. At 8 A g(–1) (21.5 C), a capacity of ~320 mAh g(–1) fades less than 20% after 3500 cycles, which makes it a superior anode material for a Li-ion battery.