I recently constructed several sodium-ion full cells for my project, but the cathode and anode only deliver about one third of their achievable capacities as observed in their respective half-cells. I tried to control the cathode to anode capacity ratio in a way that the 1st cycle SEI loss can be compensated by the extra cathode material while allowing a somewhat balanced reversible capacity.
I would greatly appreciate if anyone can provide some recommendations (based on experience) or references on how to balance cell and to determine working voltage window.
Hello,
How did you operate the half cells to measure their capacities? and how are you operating the full cell?
Also, are you using the same electrical connections for the full cell as you did for the two half-cells?
Hi Avigail,
I have hard carbon anode (cycled at 1mV-2V) and NaCrO2 cathode (cycled at 2.5V-3.6V). Both electrodes were cycled against Na metal in CR2032 cells. GF separators and 1M NaClO4 in PC are used. For full cell, I just cycled the two electrodes against each other using the same CR2032 cells. All cells were cycled using Arbin cycler so the same electrical connections were used.
Hi,
Correct me if I'm wrong but usually in Li-ion you will try not to oversize the positive as it can lead to lithium plating on the negative. Most of the time it will be OK in these R&D coin-cells because of a huge SEI formation consuming Li.
The hysteresis between half and full-cell can be attributed to many things but my first think is an impedance related problem. In full cell you add a new inter-phase modelled by a semi-infinite diffusion of Na into the second active material, thus leading to a global increase of the impedance. The final result can be a modification of the cut-off voltages by polarisation.
Maybe you can check these potentials ?
Julien
Hi Julien,
Thank you for your comment. You are absolutely right about the plating issue with having larger cathode. I recently started constructing three-electrode coin cells to better monitor the cycling voltage of individual electrodes in full cell configuration. I did notice some plating on anodes (as indicated by the negative potential of the anode vs. ref) in the cases with excessive cathode. For now, I will just use cathode to anode ratio of one and work on optimizing the cycling voltage windows.
Jimmy
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