With the rapid iteration and update of wearable flexible devices, high-energy-density flexible lithium-ion batteries are rapidly thriving. Flexibility, energy density, and safety are all important indicators for flexible lithium-ion batteries, which can be determined jointly by material selection and structural design. Here, recent progress on high-energy-density electrode materials and flexible structure designs are discussed. Commercialized electrode materials and the next-generation high-energy-density electrode materials are analyzed in detail. The electrolytes with high safety and excellent flexibility are classified and discussed. The strategies to increase the mass loading of active materials on the electrodes by designing the current collector and electrode structure are discussed with keys of representative works. And the novel configuration structures to enhance the flexibility of batteries are displayed. In the end, it is pointed out that it is necessary to quantify the comprehensive performance of flexible lithium-ion batteries and simultaneously enhance the energy density, flexibility, and safety of batteries for the development of the next-generation high-energy-density flexible lithium-ion batteries.