Although numerous studies have been performed with the aim of mitigating the inherent challenges associated with Li metal negative electrodes, the commercialization of Li metal-based rechargeable batteries has not yet been realized because of safety concerns and poor cycling performance. The use of a 3D carbon-based matrix as a substrate material is an effective approach to addressing cycling issues associated deposition/dissolution of Li metal. The present study demonstrates that the electrical conductivity of the carbon nanofibers is an important factor determining the Li metal deposition behavior in such 3D matrices. A 3D matrix composed of highly conductive carbon fibers was found to simply function as a pathway for electron transfer, and the deposition of metallic Li preferentially proceeded at the outer surfaces of the matrix rather than the internal pores. In contrast, in the case of a 3D matrix composed of less conductive carbon fibers, Li metal deposition/dissolution occurred in the interior of the matrix, suppressing the undesired formation of dendritic Li. These results show that the proper control of fiber electrical conductivity is crucial for the practical utilization of carbon-based 3D matrices in Li metal-based rechargeable batteries. (C) 2019 Elsevier Ltd. All rights reserved.