Which two-dimensional materials are used in energy storage devices?

Two-dimensional materials such as layered transition-metal dichalcogenides, carbides, nitrides, oxides and graphene-based materials have enabled very thin active electrodes with high energy density and excellent cyclability for flexible energy-storage devices.

Why do we need flexible energy storage devices?

To achieve complete and independent wearable devices, it is vital to develop flexible energy storage devices. New-generation flexible electronic devices require flexible and reliable power sources with high energy density, long cycle life, excellent rate capability, and compatible electrolytes and separators.

What is a hybrid energy storage device?

Hybrid devices, which take advantage of both battery-type materials and capacitive materials, aim to simultaneously produce high energy density and high power density, striking a balance between both 60, 61, 62, 63, 64. Developing flexible or even stretchable energy-storage devices is particularly important for wearable devices (Fig. 2e).

Can energy storage materials shift to sustainable and flexible components?

However, most of these power sources use plastic substrates for their manufacture. Hence, this review is focused on research attempts to shift energy storage materials toward sustainable and flexible components.

What types of energy sources are available for portable and wearable devices?

The energy sources available for portable and wearable electronic devices, such as mechanical energy, thermal energy, chemical energy, and solar energy, are extensive. According to the characteristics of these forms of energy, energy harvesting systems suitable for collecting various forms of energy have gained substantial attention.

What is the mechanical reliability of flexible energy storage devices?

As usual, the mechanical reliability of flexible energy storage devices includes electrical performance retention and deformation endurance. As a flexible electrode, it should possess favorable mechanical strength and large specific capacity. And the electrodes need to preserve efficient ionic and electronic conductivity during cycling.