Aqueous zinc metal batteries (AZMBs) hold significant promise due to their safety and low cost. However, their commercial viability largely depends on improving the stability of the zinc (Zn) anode under high depth of discharge (DOD). Side reactions, such as Zn dendrites, are considered the primary obstacles to further development, fundamentally attributed to non-uniform electron transport during the interface reaction. Free electrons of Zn metal are often conceptualized as a high-density free-electron gas, the collective movement of which substantially increases the likelihood of mutual interference and scattering. Especially at edge positions, the tip effect gathers abundant electrons; without a proper "bridge" to unblock conduction, this leads to local excessive deposition and dendrite evolution. Current interface optimization strategies remain limited to low areal capacity conditions, and the uncontrolled deposition behavior of the Zn anode restricts practical application, particularly under high area capacity and high DOD conditions. Without electron transport guidance, high DOD will gradually exacerbate local volume expansion and damage the interface, despite the initial application of interfacial protection.
Non-metallic compound semiconductors, with their highly tunable electron transport properties, offer a new approach to addressing interface failure in Zn anodes under high areal capacity conditions. These semiconductors form electron delocalization systems through covalent bonds with directionality and saturation or through mixed bonds, enabling electrons to distribute in specific directions and quantities among atoms. Thereby, they suppress disordered deposition caused by local electron aggregation or deficiency during high-capacity reactions. When a semiconductor forms an interface with the Zn anode, if the energy band structures exhibit good continuity and compatibility, electrons can cross the interface without significant energy barriers. This effectively prevents deposition interface collapse and active material loss due to uneven charge distribution.
Taking the ohmic heterojunction formed between an n-type semiconductor and a metal as an example, the Fermi level of the n-type semiconductor is lower than that of the metal. After intimate contact, electrons tend to transfer into the semiconductor, lifting the energy bands of the semiconductor to achieve level alignment. This electron migration smoothens the tip effect, enhances the advantage of a uniform interface, and creates an electron-rich region through the transfer of electrons from the Zn metal to the n-type semiconductor. This electron-rich region facilitates the rapid and uniform deposition of Zn 2+ via electrostatic attraction. This modification provides pre-deposited nucleation sites for Zn 2+ , alleviating concerns associated with non-uniform electron transport. Furthermore, at the nanoscale, the self-supporting porous framework formed by semiconductor nanoparticles can effectively buffer stress changes during Zn deposition and maintain the structural integrity of the interface. Although the lack of atomic bonding on the semiconductor surface may cause a Fermi pinning effect and weaken the heterojunction performance, surface functionalization (such as the introduction of hydrogen bonding) can create energy-band-tunable interfaces.
This research proposes a work-function-guided electron-bridge interface using n-type Zn-Al layered double hydroxide (AZH). When aligning with Zn, the Fermi energy of AZH is raised to the conduction band, endowing it with conductor-like properties and allowing it to accept electrons from Zn metal through the ohmic electron-bridge. This activates the pre-prepared AZH deposition sites with surface activity and conductivity, leading to simultaneous Zn deposition at both the interface and surface and enhancing the anode's adaptability to volume changes. Experiments demonstrate that the AZH-modified Zn anode achieves long-term stable cycling at ultra-high capacities of 30 to 50 mAh cm −2 , which is a considerable advance over most current research. Additionally, the corresponding full cells achieve a cycle life exceeding 5000 cycles, and large-capacity pouch cells operate effectively under high performance.
Science Bulletin
Experimental study