Effect of the Number of Graphene Layers in rGO-CNT Current Collectors for Anode-Free Li Metal Batteries
Authors: Yang Subi , Lee Seungho , Lee Juhyun , Han Seungmin , Jeong Woojin , Chun Jinyoung , Choi Junghyun 
Published: December 2024

Lithium (Li) ion batteries (LIBs) are the most widely used energy storage devices for the electronic devices and transportation sector due to their excellent electrochemical performances. However, since the conventional graphite anodes of the LIBs has saturated their theoretical capacity limits, it is needed to develop new battery systems to meet the increasing demands for the high-energy-density batteries. In this respect, Li metal batteries that employ the Li metal anode are considered as the most promising next-generation batteries owing to extremely high theoretical specific capacity (3860 mAh g–1) and the lowest redox potential (–3.040 V vs standard hydrogen electrodes) of the Li metal anode. Moreover, the pursuit of the higher energy density leads to the development of LMBs with anode-free configuration, so-called anode-free LMBs (AFLMBs). In these batteries, all the Li ions are extracted from the cathode materials and then form a Li metal on the anode current collector during the charge process. The absence of the Li metal anode during the cell manufacturing process leads to the simple fabrication process, low cost, and higher energy density even compared to the LMBs. However, the practical application of the AFLMBs is still hindered by several obstacles, such as poor coulombic efficiency (CE), severe volume change, and dendritic Li growth during cycling owing to their irreversible electrochemical reactions.

In order to handle these problems, various approaches have been explored such as using novel electrolyte additives, modifying separators and introducing three–dimensional (3D) current collectors. Among the strategies, 3D current collectors have been proven to be effective in stabilizing the Li plating/stripping process and preventing the severe volume expansion during cycling due to the reduced local current density. In addition, the large specific surface area of the 3D current collectors leads to the accommodation of more excess Li than the conventional Cu current collector. However, the critical problem of the Li dendrites growth accompanied with continuous electrolyte decomposition still remains, which is inevitable in Li plating/stripping process. Thus, it is needed to develop a new type of current collector that has different Li storage mechanism.

In this article, we designed two different rGOCNT current collectors to study how the intercalation behavior of the Li ions into the current collectors affects the electrochemical performances of the AFLMBs. With different number of graphene layers, each current collector showed a different extent of intercalation reaction, more in multi-layer rGOCNT current collector (MG-CC) and less in single-layer rGOCNT current collector (SG-CC). When the current collectors were evaluated in Li–metal cell tests, the MG-CC exhibited a significantly longer lifespan compared to the SG-CC. In addition, the MG-CC showed more stable cycling performances than the SG-CC in anode–free cell tests with a LiFePO4 (LFP) as a cathode. These results are attributed to the graphene-stacked structure of the MG-CC, which is more favorable for reversible intercalation/deintercalation process of Li ions, resulting in uniform Li plating and suppression of dendritic Li growth. As a result, this work demonstrates that introducing the intercalation behavior of Li ions into the current collector has a promising potential for achieving the stable cycling performances of AFLMBs.