Current collector optimization in anode-free lithium metal batteries

Reducing greenhouse gas emissions is one of the main challenges for the energy transition. This context fosters the rise of electric vehicles, triggering the growth of the battery industry. Anodefree lithium metal batteries are an interesting alternative to Li-ion batteries, providing high energy density and simplifying the manufacturing process. Indeed, the cell is assembled without Li metal as negative electrode; instead, the electrode is generated “in situ” during the deintercalation of Li ion from the positive electrode, which is then electro-plated onto the negative electrode current collector1. Several limitations hinder the development of this technology, the first being the irreversibility of the plating/stripping process and the second being the current collector’s properties. The former is generally characterized by a low coulombic efficiency (CE). Deposited lithium metal can react with the electrolyte and be passivated, leading to the formation of mossy and dead Li, which reduces the amount of active Li, reducing the achievable specific capacity1. The latter influences the homogeneous deposition of Li onto the current collector, which mainly depends on the current collector’s surface lithiophilicity, morphology, and the pressure of the cell. In this presentation, we focused on the Cu current collector surface by implementing a pre-treatment. We have tested different strategies in order to foster Li nucleation at the negative electrode, such as depositing a lithiophilic layer (alloying-type) on Cu or applying a chemical surface treatment to clean the Cu and prevent parasitic reactions. We have characterized the two optimized Cu surfaces electrochemically in half-cells against Li metal, which gives a large reservoir of Li allowing long-term cycling analyses. We compared the electrochemical performance of both current collectors regarding their polarization, their CE, and the irreversible Li loss during cycling, and compared them to a bare Cu foil. Post-mortem analyses with SEM and XPS complement these results by revealing the difference in morphology and composition of the deposit. Finally, operando electrochemical dilatometry (OED)2 was used to monitor the thickness of plated Li and stripped Li, giving information about plating reversibility, its homogeneity, and its porosity.