Converting Fabric to Textile Nickel Current Collector with Ag2s Decoration for Producing Dendrite-Free Lithium Metal Anode
Authors: Zhu Ruijie , Zhu Chunyu , Kitano Sho , Aoki Yoshitaka , Habazaki Hiroki 
Published: December 2020

1. Introduction

Lithium (Li) metal is regarded as the ideal anode for lithium batteries due to its ultra-high theoretical specific capacity (3860 mAh g-1), low density (0.59 g cm-3) and lowest negative electrochemical potential (-3.04 V vs. Standard Hydrogen Electrode).(1) However, caused by several remaining hurdles, including i) the thermodynamic instability of Li metal and ii) the growth of Li dendrites, the practical application of Li metal anode is still facing challenges from low Coulombic efficiency (CE), insufficient safety performance and poor cyclic stability. To overcome these problems, several strategies have been employed, including the optimization of electrolyte, utilization of solid-state electrolyte and the anode host structure design.(2) The use of hierarchically porous 3D current collector as Li metal host is an effective way to enhance the performance of Li metal anode. In this study, through a simple bio-template method, a textile-structured nickel (Ni) framework is fabricated as current collector for Li metal anode, whose unique micro-nano hierarchical structure is adequate for accommodating Li. With further decoration of uniform silver sulfide nanoparticles (Ag2S NPs), which endows lithiophilicity to the textile-structured Ni framework, a dendrite-free and highly reversible Li metal anode can be achieved after plating Li metal onto the obtained Ni current collector.

2 Experimental

Textile-structured Ni current collectors were prepared as follows. Cotton fabric was firstly soaked in aqueous ammonia solution of nickel acetate ((CH3COO)2Ni in NH3·H2O) to form the Ni source coated textile precursor. The precursor was then calcined in air to remove the cotton template and obtain the textile-structured nickel oxide (NiO). Finally, the oxide textile was reduced under hydrogen flow at elevated temperatures to prepare the textile-structured Ni current collector (Textile-Ni). Then, the Textile-Ni was soaked into a prepared silver ammonia solution to form uniformly distributed silver nanoparticles (Ag NPs). After performing a mild sulfidation reaction in a sulfur-dimethyl sulfoxide (S in DMSO) solution, the Ag NPs can be converted to Ag2S NPs without any damage of the Textile-Ni framework.
The Li plating/stripping behavior on different current collectors (including planar Cu foil, Textile-Ni, Ag2S decorated Textile-Ni) was firstly examined in a half cell configuration, in which a Li foil was used as the reference and counter electrode and a current collector was used as the working electrode. Li was repeatedly plated/striped to/from the current collectors with controlled capacity and current density. The plating/stripping voltage was monitored and the Coulombic Efficiency (CE) was calculated. Symmetric cells with two identical pre-plated Li@current collector electrodes were also assembled to observe the cycling stability. Finally, full cells consisting of Li@current collector anode and LiCoO2 cathode was also assembled and cycled at specific current densities.
The structure and morphology of the current collectors were observed by XRD, SEM and EDS.The morphology and composition of Li plated/stripped current collectors were observed by SEM and XPS.

3. Results and discussion

As shown in Fig. 1a, the Textile-Ni was successfully prepared, with the textile structure being similar to the cotton template. Moreover, after the decoration of uniformly distributed Ag2S NPs, the Ag2S decorated Textile-Ni can still maintain the textile structure (Fig. 1b).
Fig. 2 shows the dendrites-free morphology of Ag2S decorated Textile-Ni after Li plating. Benefiting from the dendrites-free nature, the Li@Textile-Ni (with Ag2S) supported a Li | LiCoO2 battery to stably cycle for 300 cycles with a high CE (>99%) and a high capacity retention (>140 mAh g-1 for the 1st cycle and maintained 90% capacity after 300 cycles, Fig. 3). As a comparison, the cell using Li foil only maintained a capacity retention of ~30% due to the severe formation of Li dendrites. The electrochemical measurements in symmetric cell and full cell also show that Textile-Ni (with Ag2S) presents superior performance of higher stability and rate capability. The large surface area of Textile-Ni network decreases the local current density and the presence of Ag2S enhance the lithophilicity of the scaffold, which results in uniform deposition of Li.
(1) W. Xu, J. Wang, F. Ding, X. Chen, E. Nasybulin, Y. Zhang, J-G. Zhang, Energy Environ. Sci. 2014, 7, 513–537.
(2) X. Cheng, R. Zhang, C. Zhao, F. Wei, J. Zhang, Q. Zhang, Adv. Sci. 2016, 3, 1500213.

Figure 1