Various CuO nanostructures have been well studied as anode materials for lithium ion batteries (LIBs); however, there are few reports on the synthesis of porous CuO nanostructures used for anode materials, especially one-dimensional (1D) porous CuO. In this work, novel 1D highly porous CuO nanorods with tunable porous size were synthesized in large-quantities by a new, friendly, but very simple approach. We found that the pore size could be controlled by adjusting the sintering temperature in the calcination process. With the rising of calcination temperature, the pore size of CuO has been tuned in the range of ∼0.4 nm to 22 nm. The porous CuO materials have been applied as anode materials in LIBs and the effects of porous size on the electrochemical properties were observed. The highly porous CuO nanorods with porous size in the range of ∼6 nm to 22 nm yielded excellent high specific capacity, good cycling stability, and high rate performance, superior to that of most reported CuO nanocomposites. The CuO material delivers a high reversible capacity of 654 mA h g(-1) and 93% capacity retention over 200 cycles at a rate of 0.5 C. It also exhibits excellent high rate capacity of 410 mA h g(-1) even at 6 C. These results suggest that the facile synthetic method of producing a tunable highly porous CuO nanostructure can realize a long cycle life with high reversible capacity, which is suitable for next-generation high-performance LIBs.

In this work, nanocrystalline-assembled bundle-like CuO structures were successfully synthesized in large-quantity by a friendly, facile two-step process. The bundle-like CuO particles are produced by thermolysis of bundle-like Cu(OH) 2 precursors, which exhibit excellent high specific capacity, high stability, and especially high rate performance for anode materials in lithium-ion batteries, superior to that of most reported CuO-based anodes. The assembled structure of CuO endows it with high rate capacities of 666 mAh g À1 , 609 mAh g À1 , and 499 mAh g À1 at a current rate of 0.3 C, 1 C and 2 C after 50 cycles, respectively. Even at a high rate of 6 C, the bundle-like CuO can still deliver a capacity of 361 mAh g À1 . It is observed that the electrochemical performance of the nanocrystalline-assembled bundle-like CuO is much better than that of CuO nanoparticles obtained by destroying the assembled bundle-like CuO through grinding. XRD analysis of both the electrodes after ending the discharge/ charge proved that during the discharge/charge process, the conversion reactions occurring in the assembled structures have better reversibility, leading to the high rate capacity and cycling performances. The better reversibility originates from the better contact area for CuO/electrolyte, enhancing many sites to the access of Li + in the electrolyte Li + . In addition, the assembled bundle-like CuO architectures can also relieve the volume variations during the Li + uptake-release process, which also contributes to the excellent electrochemical performance. The high rate capacity and enhanced cycling stability of the bundle-like CuO structure make it a promising candidate as an anode material for high-performance Li-ion batteries.

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