细菌纤维素衍生的三维碳集流体用于无枝晶的锂金属负极

Bacterial Cellulose-Derived Three-Dimensional Carbon Current Collectors for Dendrite-Free Lithium Metal Anodes

锂金属是下一代高能量密度电池的关键负极,然而其实用化面临着一系列问题,主要包括循环过程中体积变化大、枝晶生长等。使用三维集流体是解决这些问题的有效方法,然而现有大多数三维集流体存在重量大、体积大、表面亲锂性差、成本高等问题。针对上述问题,本文以低成本的细菌纤维素为前驱体,通过直接碳化制备出具有连通网络的轻质三维碳集流体,其表面均匀分布的含氧官能团可以促进锂离子的均匀成核和沉积,有效抑制了枝晶生长。值得注意的是,该集流体的面密度仅为0.32 mg·cm^(−2),在3 mAh·cm^(−2)比容量的锂金属负极中质量占比仅为28.8%。电化学测试结果表明,该集流体在3 mA·cm^(−2)的高电流密度或4 mAh·cm^(−2)的高循环容量的工作条件下,稳定循环超过150次,并且在对称电池或与LiNi0.8Co0.15Al0.05匹配的全电池中也表现出良好的电化学性能。

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 LiNi0.8Co0.15Al0.05 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.