Abstract:

Lithium (Li) metal anodes are critical components for next-generation high-energy density batteries, owing to their high theoretical specific capacity (3800 mAh·g^-1) and low voltage (-3.040 V versus the standard hydrogen electrode). However, their applications are hindered by dendrite growth, which potentially induces inner short circuit and leads to safety issues. Employing three-dimensional (3D) current collectors is an effective strategy to suppress dendrite growth by decreasing the local current density. However, many of the reported 3D current collectors have a lithiophobic surface, which leads to non-uniform Li⁺ ion deposition. Thus, a complicated modification process is required to increase the lithiophilic property of the current collectors. In addition, they have a large weight or volume, which greatly lowers the energy density of the entire anode. In this work, we report a lightweight 3D carbon current collector with a lithiophilic surface by employing the direct carbonization of low-cost bacterial cellulose (BC) biomass. The current collector is composed of electrically conductive, robust, and interconnected carbon nanofiber networks, which provide sufficient void space to accommodate a large amount of Li and buffer the volume changes during Li plating and stripping. More importantly, homogeneously distributed oxygen-containing functional groups on the nanofiber surface are retained by controlling the carbonization temperature. These functional groups serve as uniform nucleation sites and help realize uniform and dendrite-free Li deposition. Notably, the areal mass density of the 3D carbon current collector was only 0.32 mg·cm^-2 and its mass ratio in the whole anode was 28.8%, with a capacity of 3 mAh·cm^-2. This 3D carbon current collector facilitates the stable working of the half cells for 150 cycles under a high current density of 3 mA·cm^-2 or a high capacity of 4 mAh·cm^-2. Symmetric cells exhibit a steady cycling life as long as 600 h under a current density of 1 mA·cm^-2 and a capacity of 1 mAh·cm^-2. Moreover, appreciable cycling performance was realized in the full cells when the anodes were paired with LiNi_0.8Co_0.15Al_0.05 cathodes. Furthermore, the low-cost raw materials and the simple preparation method promise significant potential for the future applications of the proposed 3D current collectors.

Key words: Lithium metal anode, Bacterial cellulose, Three-dimensional current collector, Lithium dendrite, Oxygen-containing functional group