Ultrathin V6O13 nanosheets assembled into 3D micro/nano structured flower-like microspheres for high-performance cathode materials of Li-ion batteries

Benefiting from its unique high theoretical capacity and energy density, V6O13 is considered an outstanding cathode candidate. Nevertheless, the lithium ions will form LixV6O13 when embedded in V6O13, resulting in volume expansion and crystal structure instability. For that reason, the construction of three-dimensional nanostructures is an awfully serviceable method to resolve the above problems. Herein, we adopt a green and convenient hydrothermal method to synthesize three-dimensional microsphere structure composed of nanoflakes, and flower-like V6O13 microspheres are synthesized by adjusting the concentration of nitric acid (HNO3). Meanwhile, the formation mechanism of flower-like V6O13 microspheres is investigated by controlling the hydrothermal reaction time and the concentration of HNO3. As a lithium-ion cathode material, flower-like V6O13 microspheres show an initial discharge specific capacity of up to 368.1 mAh/g at a current density of 0.1 A/g. There was still a discharge specific capacity of up to 313.1 mAh/g after 50 charge/discharge cycles, with a capacity retention rate of 85.1%. The flower-like V6O13 microsphere electrode also combines an excellent rate performance with a satisfactory cycling stability, which achieves a cycle retention rate of 80.2% even after 200 charge/discharge cycles, and an initial discharge specific capacity of 216.9 mA/g even at a high current density of 1 A/g. The results show that, benefitting from its large specific surface area and robust three-dimensional structure, the flower-like V6O13 microsphere electrode material exhibits excellent cycling performance, and the lithium-ion batteries which use it as the cathode material perform equally well in terms of high capacity and high rate.