Ultrafine MoO2‐Carbon Microstructures Enable Ultralong‐Life Power‐Type Sodium Ion Storage by Enhanced Pseudocapacitance

The achievement of the superior rate capability and cycling stability is always the pursuit of sodium‐ion batteries (SIBs). However, it is mainly restricted by the sluggish reaction kinetics and large volume change of SIBs during the discharge/charge process. This study reports a facile and scalable strategy to fabricate hierarchical architectures where TiO₂ nanotube clusters are coated with the composites of ultrafine MoO₂ nanoparticles embedded in carbon matrix (TiO₂@MoO₂‐C), and demonstrates the superior electrochemical performance as the anode material for SIBs. The ultrafine MoO₂ nanoparticles and the unique nanorod structure of TiO₂@MoO₂‐C help to decrease the Na⁺ diffusion length and to accommodate the accompanying volume expansion. The good integration of MoO₂ nanoparticles into carbon matrix and the cable core role of TiO₂ nanotube clusters enable the rapid electron transfer during discharge/charge process. Benefiting from these structure merits, the as‐made TiO₂@MoO₂‐C can deliver an excellent cycling stability up to 10 000 cycles even at a high current density of 10 A g^?1. Additionally, it exhibits superior rate capacities of 110 and 76 mA h g^?1 at high current densities of 10 and 20 A g^?1, respectively, which is mainly attributed to the high capacitance contribution.     

Phase Boundary Derived Pseudocapacitance Enhanced Nickel‐Based Composites for Electrochemical Energy Storage Devices

Several strategies have been employed to improve the performance of energy storage devices through the development of new electrode materials. The construction of transition metal compound composite electrodes plays an important role in promoting the performance of energy storage devices. However, understandings of and insight into how to enhance the composites properties are rarely reported. Taking nickel‐based compounds as an example, Ni₃N@Ni₃S₂ hybrid nanosheets are reported as a high‐performance anode material for lithium‐ion batteries that delivers higher lithium storage properties than the pristine Ni₃N and Ni₃S₂ electrodes. This demonstrates that the phase boundaries between the Ni₃N and Ni₃S₂ may contribute additional lithium storage, which leads to a synergistic effect via the high pseudocapacitance contribution from the outstanding conductivity of Ni₃N and enhanced diffusion‐controlled capacity of Ni₃S₂. The use of composites prepared through sulfuration of hydrothermally annealed nickel hydroxide‐based precursor provides an enhancement of the energy storage properties. These results provide an important approach for increasing the electrochemical activity of composites by the combined effect of interfacial mismatch and pseudocapacitance, as well as understandings of the mechanism of the enhancement of the composite electrode properties.     

Pseudocapacitive Charge Storage in Thick Composite MoS2 Nanocrystal‐Based Electrodes

A synthesis methodology is demonstrated to produce MoS₂ nanoparticles with an expanded atomic lamellar structure that are ideal for Faradaic‐based capacitive charge storage. While much of the work on MoS₂ focuses on the high capacity conversion reaction, that process is prone to poor reversibility. The pseudocapacitive intercalation‐based charge storage reaction of MoS₂ is investigated, which is extremely fast and highly reversible. A major challenge in the field of pseudocapacitive‐based energy storage is the development of thick electrodes from nanostructured materials that can sustain the fast inherent kinetics of the active nanocrystalline material. Here a composite electrode comprised of a poly(acrylic acid) binder, carbon fibers, and carbon black additives is utilized. These electrodes deliver a specific capacity of 90 mAh g^?1 in less than 20 s and can be cycled 3000 times while retaining over 80% of the original capacity. Quantitative kinetic analysis indicates that over 80% of the charge storage in these MoS₂ nanocrystals is pseudocapacitive. Asymmetric full cell devices utilizing a MoS₂ nanocrystal‐based electrode and an activated carbon electrode achieve a maximum power density of 5.3 kW kg^?1 (with 6 Wh kg^?1 energy density) and a maximum energy density of 37 Wh kg^?1 (with 74 W kg^?1power density).