With the rapid development of portable electronics, wearable sensors, and micro-electromechanical systems, technologies and energy supply for sustainable and maintenance-free operation of the intelligent devices are imperative. [1][2][3] At present, the mainstream power supply for electronic devices relies on rechargeable batteries, accompanying with some problems such as heavy weight, difficulty to be recycled, potential environmental pollution, and explosion risk. [4] Energy harvesting with nanogenerators (NGs) from ambient environment and regular human motions in low frequency integrated with energy storage devices may offer a safe, efficient, and environment-friendly way to power portable electronics. [5][6][7][8][9] The rapid development of personal electronics imposes a great challenge on sustainable and maintenance-free power supplies. The integration of nanogenerators (NG) and electrochromic supercapacitors (SC) offers a promising solution to efficiently convert mechanical energy to stored electrical energy in a predictable and noticeable manner. In this paper, by integrating hybrid NGs and electrochromic micro-SCs (µ-SCs) array, the authors demonstrate a smart self-charging power package capable of indicating the charging state with color change. The electrochromic µ-SC employs Ag nanowires/NiO as electrode materials, exhibiting high capacitance (3.47 mF cm −2 ) and stable cycling performance (80.7% for 10000 cycles). The hybrid NG can produce a high output voltage of 150 V and an enhanced output current of 20 µA to satisfy the self-charging requirements. The integrated electrochromic µ-SCs array is capable of self-charging to 3 V to light up a LED under human palm impact. The charging states can be estimated according to the color differences with the naked eye during the self-charging process. Moreover, it is possible to design the planar interdigitated electrodes into different shapes according to user demand. The proposed simple and cost-effective approaches for smart self-charging power package may pave the way for future intelligent, independent and continuous operation of daily electronics.

The triboelectric nanogenerator (TENG) is a promising mechanical energy harvesting technology, but its pulsed output and the instability of input energy sources make associated energy‐storage devices necessary for real applications. In this work, feasible and efficient charging of Li‐ion batteries by a rotating TENG with pulsed output current is demonstrated. In‐depth discussions are made on how to maximize the power‐storage efficiency by achieving an impedance match between the TENG and a battery with appropriate design of transformers. With a transformer coil ratio of 36.7, ≈72.4% of the power generated by the TENG at 250 rpm can be stored in an LiFePO4–Li4Ti5O12 battery. Moreover, a 1 h charging of an LiCoO2–C battery by the TENG at 600 rpm delivers a discharge capacity of 130 mAh, capable of powering many smart electronics. Considering the readily scale‐up capability of the TENG, promising applications in personal electronics can be anticipated in the near future.

Although Ni-rich layered oxides are considered a candidate of next-generation cathode materials, their inherent properties, such as surface lithium residues and structural destruction, cause detrimental electrochemical performance, especially at elevated temperatures. Here, a facile ball-milling method is proposed to remove the lithium residues and enhance the electrochemical performance of LiNi0.6Co0.2Mn0.2O2. After NH4VO3 treatment, a lithium ion-conductive Li3VO4 coating layer is found on the LiNi0.6Co0.2Mn0.2O2 surface at heat-treatment temperatures of 300 and 450 °C, with a small part of vanadium ions diffusing into the surface lattice. When the temperature surpasses 600 °C, almost all vanadium ions dope into the bulk structure. The complex relationships between the post-sintering temperature and surface structure and their impact on electrochemical properties are discussed in detail. Electrochemical tests show that 0.5 wt% NH4VO3 treated LiNi0.6Co0.2Mn0.2O2 at 450 °C exhibits much improved cycling stability (96.1% cycling retention at 0.5C after 100 cycles and 97.2% after 50 cycles at 55 °C), rate capability (117.0 mA h g-1 at 5C), and storage property (4683 ppm lithium residue amount after storing in air for 7 days). Such superior performance is ascribed to the Li3VO4 coating layer that inhibits the electrolyte decomposition and helps create a stable and thinner cathode-electrolyte interface, resulting in decreased interfacial resistance. In addition, this coating layer suppresses internal micro-stress and phase transformation from a layered to spinel and rock-salt structure, which increases the structural integrity of LiNi0.6Co0.2Mn0.2O2 during repeated charge-discharge cycling.