*3.2. Influence of C-Rate*

In Figure 4, the influence of the C-rate on the Coulombic efficiency is presented for the measurements using LiFSI with a concentration of *c* = 2 M and varying C-rates of *I*Cell{0.5, 1, 2} C at *T*Cell = 25 ◦C.

**Figure 4.** Galvanostatic cycling performance of cells with Cu/Li structure using LiFSI 2M in DME as the electrolyte. Cells are run each with an individual C-rate of *I*Cell{0.5, 1, 2} C and are shown with orange, black and blue colors, respectively. The cell temperature for all three experiments was set to *T*Cell = 25 ◦C.

Interestingly, the cycling results presented in Figure 4 show that increasing the current density of charging and discharging positively influence the cyclability of *insitu* deposited lithium electrodes. All three cells during the initial cycles have a relatively low Coulombic efficiency which increases gradually with increasing cycle number for all three cells until a Coulombic efficiency of *η*CE ≈ 0.99 is reached. This could be caused by a rapid SEI formation during the initial cycles. Interface reactions consume electrolytes and a part of the cyclable Li, which negatively influences the Coulombic efficiency during the formation cycles, as can be seen in Figure 4. The cell with the lowest C-rate (*I*Cell = 0.5 C), which is highlighted with the orange color, illustrates an instability at the early cycles (*η*CE > 1). Further, a fast drop of the Coulombic efficiency was found and already after 50 cycles the cell reached an efficiency below the set threshold value of *<sup>η</sup>*CE < 0.95. Due to this reason, the cycling of the cell was stopped after 100 cycles. The cell with the medium C-rate (*I*Cell = 1 C) presented in the black color is more stable at the first cycles and the Coulombic efficiency of the cell is very high with *η*CE ≈ 0.99 for the first 160 cycles. This leads to an increase of the maximum number of cycles by a factor of 3.2 compared to the cell cycled at *I*Cell = 0.5 C. Finally, the cell with the highest C-rate (*I*Cell = 2 C, blue) shows the most stable behavior. This is visible in the Coulombic efficiency, which drops below the set reference value of *<sup>η</sup>*CE < 0.95 not until the 220th cycle.
