Intrinsic Chemical Reactivity of Silicon Electrode Materials: Gas Evolution

Abstract

In this work, we explore how the chemical reactivity toward an aprotic battery electrolyte changes as a function of lithium salt and silicon surface termination chemistry. The reactions are highly correlated, where one decomposition reaction leads to a subsequent decomposition reaction. The data show that the presence of silicon hydrides (SiH x ) promotes the formation of CO gas, while surface oxides SiO x drive the formation of CO2. The extent and rate of oxidation depend on the surface basicity of the SiO2 surface species. The most acidic surfaces seem to hinder CO2 generation but not the decomposition of the salt. Indeed, the presence of F-containing salts (LiPF6 and LiTFSI) promotes the reactions between carbonate electrolyte and silicon surfaces. Surfaces with high Li content seem to be the most passivating to gassing reactions, pointing to a pathway to stabilize the interfaces during cell formation and assembly.

Recent Advances in Silicon‐Based Electrodes: From Fundamental Research toward Practical Applications

“…This gassing issue is amplified for Si‐based electrodes due to their large volume changes, which result in continuous SEI growth and hastened electrolyte decomposition. [ 125 ] While difficult to observe in laboratory‐based coin cells, the gas generation in Si‐based LIBs is so severe that it leads to the apparent swelling of pouch cells or prismatic cells during their initial charging/discharging cycles. [ 126 ] Therefore, in order to suppress gas generation, it is of great importance to develop Si‐based anodes which exhibit stable SEI formation.…”

Ending the Chase for a Perfect Binder: Role of Surface Chemistry Variation and its Influence on Silicon Anodes

“…However, as a comparison, materials with the highest Si : O surface ratio and lowest binding energy P2 (64 wt % Si, 36 wt % O [102.5 eV] – 80 % retention‐summarized in Table S1), as measured by XPS, display higher retention than the other materials (M1 65 wt % Si, 35 wt % O [103 eV] – 70 % retention) > (M2 54 wt % Si, 46 wt % O [103.7 eV] –70 % retention) >(P1 49 wt % Si, 51 wt % O [104 eV] – 40 % retention). This would indicate the capacity retention is related to the speciation of the Si on the surface, as indicated by several recent papers . At this point the correlation is difficult to confirm due to possible changes in the silicon during processing, as mentioned previously, but would be worthy of further study.…”

“…How the silicon is made will result in different surface terminations . The history of the preparatory reactors, age, and starting material (i. e., metallurgical grade Si vs semiconductor grade) will all change the defects, structure and surface chemistry.…”

Quantum Chemical Calculations of Lithium-Ion Battery Electrolyte and Interphase Species

“…While many electrolyte chemistries have been developed for use in LIBs, the most widely used formulations involve a fluorinated salt such as lithium hexafluorophosphate (LiPF 6 ), [41][42][43][44][45] lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 20,46 or lithium bis(flurosulfonyl)imide (LiFSI) 47, dissolved in a solvent blend of cyclic carbonates such as ethylene carbonate (EC), 31,41 or fluroethylene carbonate (FEC) 13,[49][50][51] and linear carbonates like dimethyl carbonate (DMC), 52,53 diethyl carbonate (DEC), 54,55 or ethyl methyl carbonate (EMC). 31,41 At the current stage, LIBE contains molecules relevant to such systems but does not consider other electrolyte components or additives.…”

“…31), lithium ethylene dicarbonate (LEDC) and related derivatives(32)(33)(34)(35), lithium butylene dicarbonate (LBDC) and related derivatives(36)(37)(38)(39)(40)(41)(42)(43), lithium ethylene monocarbonate (LEMC) and related derivatives(44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56), ethanol and related derivatives (57-58), ethylene glycol (EG) and related derivatives (59-66), 1,4-butanediol and related derivatives(67)(68)(69), other molecules related to LiEC decomposition(70)(71)(72)(73), and other molecules related to PF 6 decomposition (74-83).…”