Development of Zinc Ion Battery Anodes by Zinc Electrodeposition on Controllable Three-Dimensional Carbon Framework

Lithium-ion batteries (LIBs) are widely used as energy storage devices, but their low level of safety, high cost, and unstable supply of lithium metal due to increased demand are challenging. Therefore, environmentally friendly and sustainable energy devices are required. In particular, rechargeable aqueous zinc-based batteries (ZIBs) are expected to be a new electrochemical energy storage device due to their low cost, non-toxicity, and high energy density. However, short circuits due to zinc metal dendrite formation at the anode and poor cycle characteristics due to reduced reversibility have hindered their practical application. Stable and dendrite-free cycling zinc anode with zinc electrodeposition confined in 3D carbon nanotubes network structure has been reported^[1], hence zinc electrodeposition on dense 3D carbon frameworks is an effective approach. 3D printers are gaining attention among the methods for fabricating 3D carbon frameworks^{[2], [3]}. The use of 3D printers for current collector fabrication allows for flexible form factors and scale control on the order of micrometers to centimeters. Therefore, the objective of this study was to develop a high-performance zinc anode material by zinc deposition on 3D carbon modeled by an LCD (Liquid Crystal Display) 3D printer.<br/><br/>3D carbon was designed using computer aided design (CAD). To avoid asymmetric structural parameters, a unit lattice with symmetric framework diameter and vacancies was used in the design. 3D polymer samples were fabricated using an LCD 3D printer (Mars3, ELEGOO) with photo-curing resin (ABS-like resin, SK hompo). The printed samples were rinsed with 2-propanol to remove the uncured resin, dried, and then pyrolyzed in a tube furnace under vacuum at 400 °C for 4 hours and then at 1000 °C for 4 hours. The 3D carbon was subjected to activation treatment (heating under CO₂ atmosphere), and the zinc electrodeposition behavior was evaluated pristine carbon and CO₂ activated carbon. For zinc electrodeposition, 3D carbon was fixed with Au mesh, and the electrolyte was 1M ZnSO₄ aqueous solution, and the current density was 1 mA cm^–2. The zinc electrodeposited 3D carbon samples were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and Raman spectroscopy. To evaluate the electrochemical properties, galvanostatic charge-discharge tests were conducted using a Zn foil and Zn/3D carbon in symmetrical cell.<br/><br/>Pyrolysis reduced it to a quarter of its original size, and even after pyrolysis, it retained its structure at the time of modeling. From the result of SEM observation, there was almost no zinc deposition on the carbon skeleton surface of pristine 3D carbon, but plenty of zinc was deposited on the surface of the carbon skeleton after CO₂ activation treatment. The CO₂ activation treatment was found to increase the specific surface area of the 3D carbon, thereby increasing the number of zinc nucleation sites and achieving uniform zinc deposition. Zinc deposition was also observed inside the CO₂ activated carbon structure, therefore the three-dimensional zinc metal anode was fabricated. Zn/CO₂ activated carbon showed similar low overpotential and long-term cycling stability compared with zinc foil, suggested to be promising as a zinc anode material.<br/><br/>[1] Y Zhou, <i>et al. J. Mater Chem. A.</i> <b>8</b>, 11719-11727 (2020).<br/>[2] K Narita, <i>et al. Adv. Energy Mater.</i> <b>11</b>, 2002637 (2021).<br/>[3] Xiaolong Li, <i>et al. Adv. Energy Mater.</i> 2000233 (2022).