**3.2 Long-term cycling stability**

The lifetime of Li-ion micro-batteries is typically less than 1000 cycles, with charges retention higher than 98% after 1000 charge-discharge cycles in supercapacitors. Generally, these materials have lifetimes of over 100,000 cycles with excellent recharge rate capabilities.

#### **3.3 Power performance**

The power density is different in various active materials. For PPY, the capacity can reach 230 mF/cm2 , while for MnO2, the capacity can reach as high as 570 F/g, and asymmetric micro-SC has a maximum volumetric energy density. The supercapacitors shown high-power density with many other advantages, the low-energy density limits their applications. The future trend of supercapacitors is still to overcome this drawback and find the active materials with more energy density. For energy transform devices, the unstable voltage supplied by energy harvesting limits their applications; thus, we will not compare their performance.
