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Electrochemically Controlled Pre-lithiation of Si-containing Anodes for Enhancing the Cycling Performance

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In order to meet the increased demands for energy storage that has a higher capacity and energy density, silicon has been proved as one of the most promising candidates to replace current graphite as an active material of the anode. Despite its higher theoretical capacity and abundant deposits, it has not been widely used for commercialized cells due to some lethal drawbacks such as drastic volume expansion upon lithiation/delithiation and low initial coulombic efficiency (ICE).

In this regard, some strategies to compensate for the aforementioned issues have emerged and one of them is to dope the Si electrodes with lithium ions before the assembly of a battery cell. The pre-positioned lithium enables the cell to have an increased reversible capacity even after the formation of the solid electrolyte interphase (SEI). A diversity of experiments has been tried to implement this pre-lithiation process, however, there has yet to be no game-changing technology to satisfy all essential requirements enough to be scaled up for the real industrial process such as safety, homogeneous quality of lithiation, economic feasibility, and expandability.

Since the prelithiation process by means of electrochemical way is expected as one of the most feasible techniques, it is being investigated in this work. First of all, a proper anode formulation such as Si source, content, and binder combination was delicately selected and this anode was eventually combined with an NMC622 cathode as a full cell configuration. From the half cell tests, it was possible to predict the prelithiation effect in terms of an improved ICE, a safety factor, and residual energy inside a cell with respect to the prelithiation degree. We accordingly decided to set 20 % as a maximum prelithiation degree considering the given balance between areal capacities of the anode and cathode. Two different scale prelithiation processes were carried out: one inside a coin cell and the other with a larger-sized setup. For the coin cell setup, lithium metal was used as a counter electrode during the process. The full cell with the prelithiated anode has shown a significant improvement in their cyclability and it was found irreversible reaction was suppressed at its first cycle. To boost up this effect, the process rate was tuned and a few specific additives were newly introduced. For a large-scale setup, the carbon was chosen as a counter electrode, which means lithium solely comes from the solution, because it will have more benefit considering the feasibility of application to industrial cell production. In this case, the prelithiated cells also showed a higher initial capacity and ICE while having an adverse effect on the capacity retention. This fact requires further development, therefore in-depth investigation will be conducted on this point to have a prelithiated cell better performance over its entire cycle life even without Li metal during the process.

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