Production Atmosphere Requirements for the Use of Direct-Contact Prelithiation within Lithium-Ion Battery Production

Direct-contact prelithiation is a promising method to increase the energy density and the cycle life of lithium-ion batteries. In this process, the anode active material is brought into direct contact with lithium metal. The additional lithium compensates for the loss of active lithium due to the solid electrolyte interphase formation during cell formation and operation. The formed intermediate product, a combination of lithium metal with anode active material or already partially lithiated anode active material show increased reactivity to moisture, nitrogen, oxygen, carbon dioxide, and other air components. Though, the requirements on the production atmosphere for these intermediate products are not known, hindering the industrialization of direct-contact prelithiation. The knowledge of the production atmosphere requirements is crucial to ensure process stability and material integrity, allowing for the industrial implementation of innovative materials, production processes, and intermediate products. However, the influence of different production atmospheres on the stability and electrochemical performance of anodes in direct contact with lithium metal for direct-contact prelithiation has not been sufficiently investigated. In this study, silicon-based anodes were prelithiated by applying lithium foil onto the anode surface. A calender integrated in an argon-filled glove box was used to form this anode-lithium composite. The anode-lithium composites were stored under specific atmospheric conditions, including argon, nitrogen, and dry room environments with various dew points. Storage durations of 8hours, 24hours, and one week were evaluated. For comparison, pristine lithium foil was stored under the same conditions. The stored anode-lithium composites were analyzed using optical microscopy and electrochemically tested in both half and full cells. The results indicate that the storage of prelithiated anodes has a negative impact on their electrochemical performance in all tested atmosphere conditions and should be minimized. The anode-lithium composites show a faster change in color than the pure lithium foil. Negligible degradation was observed at dry room conditions with a dew point smaller than -47°C and an exposure time of up to 24hours.