Zinc (Zn) metal is considered the promising anode for "post-lithium" energy storage due to its high volumetric capacity, low redox potential, abundant reserve, and low cost. However, extravagant Zn is required in present Zn batteries, featuring low Zn utilization rate and devicescale energy/power densities far below theoretical values. The limited reversibility of Zn metal is attributed to the spontaneous parasitic reactions of Zn with aqueous electrolytes, that is, corrosion with water, passive by-product formation, and dendrite growth. Here, a new ionselective polymer glue coated on Zn anode is designed, isolating the Zn anode from the electrolyte by blocking water diffusion while allowing rapid Zn 2+ ion migration and facilitating uniform electrodeposition. Hence, a record-high Zn utilization of 90% is realized for 1000 h at high current densities, in sharp contrast to much poorer cyclability (usually < 200 h) at lower Zn utilization (50-85%) reported to date. When matched with the vanadium-based cathode, the resulting Zn-ion battery exhibited an ultrahigh device-scale energy density of 228 Wh kg −1 , comparable to commercial lithium-ion batteries.

To develop wearable and implantable bioelectronics accommodating the dynamic and uneven biological tissues and reducing undesired immune responses, it is critical to adopt batteries with matched mechanical properties with tissues as power sources. However, the batteries available cannot reach the softness of tissues due to the high Young's moduli of components (e.g., metals, carbon materials, conductive polymers, or composite materials). The fabrication of tissue‐like soft batteries thus remains a challenge. Here, the first ultrasoft batteries totally based on hydrogels are reported. The ultrasoft batteries exhibit Young's moduli of 80 kPa, perfectly matching skin and organs (e.g., heart). The high specific capacities of 82 mAh g−1 in all‐hydrogel lithium‐ion batteries and 370 mAh g−1 in all‐hydrogel zinc‐ion batteries at a current density of 0.5 A g−1 are achieved. Both high stability and biocompatibility of the all‐hydrogel batteries have been demonstrated upon the applications of wearable and implantable. This work illuminates a pathway for designing power sources for wearable and implantable electronics with matched mechanical properties.

Mg-air batteries are explored as the next-generation power systems for wearable and implantable electronics as they could work stably in neutral electrolytes and are also biocompatible. However, high corrosion rate and low utilization of Mg anode largely impair the performance of Mg-air battery with low discharge voltage, poor specific capacity and low energy density. Here, to the best of our knowledge, we first report a dual-layer gel electrolyte to simultaneously solve the above two problems by preventing the corrosion of Mg anode and the production of dense passive layer, respectively. The resulting Mg-air batteries produced an average specific capacity of 2190 mAh g À1 based on the total Mg anode (99.3 % utilization rate of Mg anode) and energy density of 2282 Wh kg À1 based on the total anode and air electrode, both of which are the highest among the reported Mg-air batteries. Besides, our Mg-air batteries could be made into a fiber shape, and they were flexible to work stably under various deformations such as bending and twisting.Wearable and implantable electronic devices represent the next-generation electronics and are booming rapidly in the recent decade. [1][2][3] To stably and long-termly power these electronic devices, it is critical to make matchable and safe energy storage devices. [4][5][6][7] To this end, metal-air batteries with high energy densities have attracted increasing interests. [8,9] Among them, Mg-air batteries work stably in neutral electrolytes and are also biocompatible as Mg 2+ ions are harmless to the human body. [10][11][12] Therefore, Mg-air batteries are explored as promising candidates on the skin and inside the body.