Engineering core‐shell materials with rationally designed architectures and components is an effective strategy to fulfill the high‐performance requirements of supercapacitors. Herein, hierarchical candied‐haws‐like NiCo2S4@NiCo(HCO3)2 core‐shell heterostructure (NiCo2S4@HCs) is designed with NiCo(HCO3)2 polyhedrons being tightly strung by cross‐linked NiCo2S4 nanowires. This rational design not only creates more electroactive sites but also suppresses the volume expansion during the charge–discharge processes. Meanwhile, density functional theory calculations ascertain that the formation of NiCo2S4@HCs heterostructure simultaneously facilitates OH− adsorption/desorption and accelerates electron transfer within the electrode, boosting fast and efficient redox reactions. Ex situ X‐ray diffraction and Raman measurements reveal that gradual phase transformations from NiCo(HCO3)2 to NiCo(OH)2CO3 and then to highly‐active NiCoOOH take place during the cycles. Therefore, NiCo2S4@HCs demonstrates an ultrahigh capacitance of 3178.2 F g−1 at 1 A g−1 and a remarkable rate capability of 2179.3 F g−1 at 30 A g−1. In addition, the asymmetric supercapacitor NiCo2S4@HCs//AC exhibits a high energy density of 69.6 W h kg−1 at the power density of 847 W kg−1 and excellent cycling stability with 90.2% retained capacitance after 10 000 cycles. Therefore, this novel structural design has effectively manipulated the interface charge states and guaranteed the structural integrity of electrode materials to achieve superior electrochemical performances.

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Large-scale synthesis of graphene-based nanomaterials in stirred tank reactor (STR) often results in serious agglomeration because of the poor control during micromixing process. In this work, reactive impingement mixing is conducted in a two-stage impinging jet microreactor (TS-IJMR) for the controllable and scale-up synthesis of nickel-cobalt boride@borate core-shell nanostructures on RGO flakes (NCBO/RGO). Benefiting from the good process control and improved micromixing efficiency of TS-IJMR, NCBO/RGO nanosheet provides a large BET surface area, abundant of suitable mesopores (2–5 nm), fast ion diffusion, and facile electron transfer within the whole electrode. Therefore, NCBO/RGO electrode exhibits a high specific capacitance of 2383 F g−1 at 1 A g−1, and still retains 1650 F g−1 when the current density is increased to 20 A g−1, much higher than those of nickel boride@borate/RGO (NBO/RGO) and cobalt boride@borate/RGO (CBO/RGO) synthesized in TS-IJMR, as well as NCBO/RGO-S synthesized in STR. In addition, an asymmetric supercapacitor (NCBO/RGO//AC) is constructed with NCBO/RGO and activated carbon (AC), which displays a high energy density of 53.3 W h kg−1 and long cyclic lifespan with 91.8% capacitance retention after 5000 charge-discharge cycles. Finally, NCBO/RGO is used as OER electrocatalyst to possess a low overpotential of 309 mV at a current density of 10 mA cm−2 and delivers a good long-term durability for 10 h. This study opens up the potential of controllable and scale-up synthesis of NCBO/RGO nanosheets for high-performance supercapacitor electrode materials and OER catalysts.

In this study, cuboid‐like anhydrous CoC2O4 particles (CoC2O4‐HK) are synthesized through a potassium citrate‐assisted hydrothermal method, which possess well‐crystallized structure for fast Li+ transportation and efficient Li+ intercalation pseudocapacitive behaviors. When being used in lithium‐ion batteries, the as‐prepared CoC2O4‐HK delivers a high reversible capacity (≈1360 mAh g‐1 at 0.1 A g‐1), good rate capability (≈650 mAh g‐1 at 5 A g‐1) and outstanding cycling stability (835 mAh g‐1 after 1000 cycles at 1 A g‐1). Characterizations illustrate that the Li+‐intercalation pseudocapacitance dominates the charge storage of CoC2O4‐HK electrode, together with the reversible reaction of CoC2O4+2Li++2e−→Co+Li2C2O4 on discharging and charging. In addition, CoC2O4‐HK particles are also used together with carbon–sulfur composite materials as the electrocatalysts for lithium–sulfur (Li–S) battery, which displays a gratifying sulfur electrochemistry with a high reversibility of 1021.5 mAh g−1 at 2 C and a low decay rate of 0.079% per cycle after 500 cycles. The density functional theory (DFT) calculations show that CoC2O4/C can regulate the adsorption‐activation of reaction intermediates and therefore boost the catalytic conversion of polysulfides. Therefore, this work presents a new prospect of applying CoC2O4 as the high‐performance electrode materials for rechargeable Li‐ion and Li–S batteries.

Developing the high-capacity anode materials such as conversion-type metal oxides which possess both Li and Na storage activity is very practical for the high-energy LIBs/SIBs. Herein, we use NiCo2O4 anodes as a model to investigate the morphology evolution which accounts for the poor cycling performance and understand the effect of structure optimization on the electrochemical performance. Three NiCo2O4 samples with different morphologies of microspheres, nanospheres and nanosheets are synthesized. Firstly, the serious structural degradation of NiCo2O4 microspheres is observed whether it works as a LIB or SIB anode. In addition, a significant difference between the lithiation and sodiation capacity of NiCo2O4 materials reveals Na+ ions only partially intercalated in NiCo2O4 and the conversion reaction limited by the strain. Next, NiCo2O4 nanosheets on Ni foam as a binder-free anode for LIBs are investigated which suggest the positive effect of 3D nanostructures on the morphology stability. As a result, NiCo2O4 nanosheets deliver a high lithiation capacity of 1092 mAh g− 1 after 100 cycles at 0.5 A g− 1 and an excellent rate capacity of 643 mAh g− 1 at 4 A g− 1. Finally, NiCo2O4 nanospheres are evaluted as a SIB anode which indicate the smaller particle size of active materials is beneficial to the release of stress and structure stability during discharge-charge processes. A rational design of the electrode’ architecture is very important for the conversion-type 3d transition metal oxide anodes for advanced LIBs and SIBs.