Co3O4 is considered as one of the most promising candidates in lithium-ion batteries (LIBs) anodes due to its lowcost, abundant availability, and high theoretical capacity. However, problems of heavy aggregation, and volume change of Co3O4 hinder its practical applicability. Based on above challenges, we successfully designed and prepared an electrode by adding carbon nanotubes (CNTs) and carbon nanofiber (CNF) via directional freezedrying. The as-prepared Co3O4/N-CNTs-CNF anode exhibits three-dimensional (3D) network structure to alleviate the volume expansion of Co3O4 and short the electron/ion transport paths. CNTs form a continuous conductive network that provides electron migration paths and prevents agglomeration of Co3O4, while CNF enhances the mechanical strength granting better flexibility. Density functional theory (DFT) calculations reveal that the N-CNTs/Co3O4 interface resulted in an electric field of the heterointerface, which facilitated charge transport. Moreover, the heterointerface possesses good electronic conductivity since more electronic states across the Fermi level. Based on these advantages, Co3O4/N-CNTs-CNF anode demonstrates an initial discharge capacity of 1176 mAh g-1 at a current density of 0.2C, high discharge specific capacity of 545 mAh g-1 at a current density of 5C, only 17.5% capacity loss over 824 cycles at 5C rate. Owing to its good electrochemical performance and flexibility, such design has great potential for applications of portable electronics.

Cobalt oxide (Co3O4) is currently suitable in energy storage applications because of its high capacity based on the conversion reaction mechanism. However, unmodified Co3O4 suffers from distinctly inferior rate capability and poor cycling stability. On the basis of the aforementioned considerations and density functional theory (DFT) simulations, the three-dimensional hierarchical porous structure (HPS) ultrasmall Co3O4 anchored into ionic liquid (IL) modified graphene oxide (GO) has been successfully prepared (ultrasmall/Co3O4-GA-IL). The ultrasmall/Co3O4-GA-IL consists of Co3O4 co-assembled with IL modified GO to generate the HPS which can facilitate ion transfer channels through reduction of the electron and ion transportation path and transmission impedance. In addition, N-doping graphene can enhance the inherent electrical conductivity of Co3O4, which is proved by the DFT calculations. By virtue of the novel superstructure, the ultrasmall/Co3O4-GA-IL electrode demonstrates a high reversible capacity of 1,304 mAh·g−1, an enhanced high-rate capability (715 mAh·g−1 at 5 C), and a capacity retention of 98.4% even after 500 cycles at 5 C rate, which corresponds to 0.0003% capacity loss per cycle. Pouch cells based on the cathode are further fabricated and demonstrate excellent mechanical and electrochemical properties under bent and folded state, highlighting the practical application of our deliberately designed electrode in wearable electronics.

Transition metal oxide Co3O4 is a candidate anode material for lithium-ion batteries (LIBs) due to its high theoretical specific capacity and easy preparation. However, unmodified Co3O4 suffers from distinctly inferior rate capability and poor cycling stability. Here, we design and fabricate a three-dimensional (3D) island bridge structure (IBS) Co3O4 anchored into IL [BMIm][N(CN)2] modified PAN (Co3O4-PAN-IL) composite. The Co3O4 is uniformly dispersed microspheres, and IL modified PAN constitute a conductive network, which together form an IBS. The structure can effectively promote electron transfer, improve the specific surface area of the material, and alleviate the volume effect of cobalt oxide. More importantly, IL modified PAN has been considered as a highly conductive N-doping matrix after annealing. By virtue of these merits, the Co3O4-PAN-IL electrode demonstrates a high reversible capacity of 1499 mA h g-1 at 0.5C. After 800 cycles, the capacity of 1239 mA h g-1 was maintained, and the attenuation rate of each cycle was 0.022%. Compared with pure Co3O4, the electrochemical performance was significantly improved. The excellent electrochemical performance was due to the synergistic effect of nitrogen doping carbon network and uniformly dispersed Co3O4 particles. Furthermore, flexible pouch cells based on the cathode are further fabricated and demonstrate excellent electrochemical properties, highlighting the practical application of our deliberately designed electrode in flexible wearable electronics.

本工作以硫酸亚铁和乙酸锰为原料,在表面活性剂双(2-乙基己基)琥珀酸酯磺酸钠气溶胶作用下,通过微乳液法合成了前体,锻烧后得到了具有多孔结构的一维棒状MnFe2O4材料.棒直径约200 nm、长度2～3 μm,含有大量孔径在13～35 nm的介孔结构.将制备的MnFe2O4作为锂离子电池负极材料,进行电化学性能测试,在100 mA/g的电流密度下200圈循环仍能保持630 mA·h/g以上的容量,同时也具有良好的倍率性能.研究显示多孔棒状MnFe2O4是一种具有应用前景的锂离子电池负极材料.