Mechanistic Insights into the Pre‐Lithiation of Silicon/Graphite Negative Electrodes in “Dry State” and After Electrolyte Addition Using Passivated Lithium Metal Powder

Abstract

Because of its high specific capacity, silicon is regarded as the most promising candidate to be incrementally added to graphite‐based negative electrodes in lithium‐ion batteries. However, silicon suffers from significant volume changes upon (de‐)lithiation leading to continuous re‐formation of the solid electrolyte interphase (SEI) and ongoing active lithium losses. One prominent approach to compensate for active lithium losses is pre‐lithiation. Here, the “contact pre‐lithiation” of silicon/graphite (Si/Gr) negative electrodes in direct contact with passivated Li metal powder (PLMP) is studied, focusing on the pre‐lithiation mechanism in “dry state” and after electrolyte addition. PLMP is pressed onto the electrode surface to precisely adjust the degree of pre‐lithiation (25%, 50%, and 75%). By in situ XRD and ex situ 7Li NMR studies, it is proven that significant lithiation of Si/Gr electrodes occurs by direct contact to Li metal, that is, without electrolyte. After electrolyte addition, de‐lithiation of silicon and graphite is confirmed, resulting in SEI formation. The amount of Li metal highly impacts the presence and durability of the LixC and LixSi phases. Finally, the challenges for homogeneous pre‐lithiation and SEI formation are identified, and the impact of electrolyte addition is assessed by analysis of the lateral and in‐depth lithium distribution within the Si/Gr electrode.

Storage of Lithium Metal: The Role of the Native Passivation Layer for the Anode Interface Resistance in Solid State Batteries

“…It is also reported that Li 2 CO 3 protects lithium from reaction with all atmospheric gases except H 2 O. 45 Consequently, this passivation layer must have been at least partly destroyed for the samples which tarnished and reacted with nitrogen forming Li 3 N. To verify this, we prepared a bunch of samples through tearing and ripping instead of controlled slicing to destroy the passivation layer on purpose. In most cases, the samples prepared in this way reacted to Li 3 N.…”

“…As lithium hydroxide and carbonate form a stable and well-covering passivation layer according to their PBRs, lithium foils covered with these compounds appear to be protected against reaction with nitrogen. It is also reported that Li 2 CO 3 protects lithium from reaction with all atmospheric gases except H 2 O . Consequently, this passivation layer must have been at least partly destroyed for the samples which tarnished and reacted with nitrogen forming Li 3 N. To verify this, we prepared a bunch of samples through tearing and ripping instead of controlled slicing to destroy the passivation layer on purpose.…”

Influence of Temperature and Electrolyte Composition on the Performance of Lithium Metal Anodes

“…Another method for investigating lithium deposition during cycling is insitu observation using special cell holders. Insitu observations in the ECC-Opto Stud, manufactured by EL-Cells GmbH (Hamburg, Germany), on battery cells were made in [26][27][28][29][30][31][32][33] using Raman spectroscopy, X-ray diffraction (XRD) and optical analytics. Observations were made using Raman spectroscopy [27,31,32] and XRD [26,28,33] to observe changes in electrodes and SEI during aging.…”

“…Insitu observations in the ECC-Opto Stud, manufactured by EL-Cells GmbH (Hamburg, Germany), on battery cells were made in [26][27][28][29][30][31][32][33] using Raman spectroscopy, X-ray diffraction (XRD) and optical analytics. Observations were made using Raman spectroscopy [27,31,32] and XRD [26,28,33] to observe changes in electrodes and SEI during aging. Merryweather et al [29] used the above-mentioned cell housing for optical interferometric scattering measurements to detect single-particle ion dynamics, and Rittweger et al [30] observed the reflectivity of cathodes during charge and discharge.…”

From solid waste to a high-performance Li3.25Si anode: towards high initial Coulombic efficiency Li–Si alloy electrodes for Li-ion batteries

“…After crack formation on the intrinsic SEI, the side reactions continue, leading to further consumption of Li and electrolyte, which results in low Coulombic efficiency (CE) and rapid capacity decay. 2,20,23,24 In previous reports, focusing on the volume variation, various strategies have been employed in anode material designs, such as nanowires, 25,26 nanofibers, 27,28 nanotubes, 29,30 and nano/ microstructured composites. [31][32][33][34][35][36] In addition, the huge volume expansion of anodes can also be accommodated through the ingenious introduction of void space in nanostructures of yolkshell, 37,38 hollow nanospheres, [39][40][41][42] and porous materials.…”