Tailored 3D-Microstructured Electrode Substrates for Increased Performance in Zero-Excess Lithium Metal Batteries

Abstract

Meeting the growing demands on modern batteries in many diverse areas such as energy density, safety, sustainability and cost is a key challenge in research and development related to electrochemical energy storage today. While lithium metal batteries (LMBs) are often cited as a potential alternative to current lithium ion battery (LIB) technology that provides a high theoretical energy density, large-scale commercialization efforts have so far been hindered by significant challenges regarding the LMBs operational safety and large volume changes during cycling as well as continuous parasitic side reactions between the lithium metal and the electrolyte, among other issues.[1] A particularly interesting and promising approach to overcome these challenges is the use of a so-called “zero-excess” or “anode-free” cell configuration for lithium metal batteries. Such cells are very similar to both LIBs and conventional LMBs in terms of construction except for their omittance of a traditional anode material. The only component in a zero-excess LMB (ZELMB) to carry lithium upon fabrication of the cell is the cathode material. When the cell is charged, the lithium inventory is electroplated onto the anode current collector to form a temporary lithium metal anode. During the subsequent discharging of the cell, this lithium metal layer is electrodissolved again and the lithium ions are integrated back into the cathode. This way, the amount of lithium that is present in the cell is reduced to the absolute minimum amount necessary for the operation of an LMB, which provides several benefits including drastically increased safety, reduced cost, and simplicity of construction. On the other hand, the inherent scarcity of lithium in a ZELMB requires the Coulombic Efficiency (CE) during cell operation to be as high as possible to prevent quick capacity fading as a consequence of any lithium losses. Therefore, parasitic reactions between the lithium and the electrolyte as well as the formation of disconnected “dead” lithium have to be minimized.[2] One way to boost the performance of ZELMBs is by employing a modified anode current collector instead of the standard planar copper foil. Applying a suitable coating to the current collector surface can lead to a more homogeneous lithium cycling behavior yielding an increased CE and prolonged cycle life. Similar effects can also be achieved when the 2D copper foil anode substrate is replaced by a host structure with a microporous 3D morphology. The increased surface area of such 3D structures leads to a reduction of the local current density at the substrate surface which is beneficial for uniform lithium electroplating. Also, depositing lithium inside a host structure instead of onto a plain foil eliminates continuous volume changes that can induce heavy mechanical stress in the cell. This presentation covers various types of 3D microstructured copper host materials that are used as negative electrode substrates in ZELMBs to increase the performance of the cells. Ranging from the employed preparatory procedures to the electrochemical characterization of battery cells encompassing the fabricated microporous 3D anode substrates, this work aims to give an insight into the process of developing the tailored materials needed to make ZELMBs a viable alternative to both common LIBs and LMBs.[1] A. Pei, G. Zheng, F. Shi, Y. Li, Y. Cui, Nano Lett. 2017, 17, 2, 1132-1139.[2] M. Genovese, A. J. Louli, R. Weber, S. Hames, J. R. Dahn, J. Electrochem. Soc. 2018, 165, 14, A3321 – A3325.