Exploring the Promise of Multifunctional “Zintl-Phase-Forming” Electrolytes for Si-Based Full Cells

Abstract

Li−M−Si ternary Zintl phases have gained attention recently due to their high structural stability, which can improve the cycling stability compared to a bulk Si electrode. Adding multivalent cation salts (such as Mg 2+ and Ca 2+ ) in the electrolyte was proven to be a simple way to form Li−M−Si ternary phases in situ in Si-based Li-ion cells. To explore the promise of Zintl-phaseforming electrolytes, we systematically investigated their application in pouch cells via electrochemical and multiscale postmortem analysis. The introduction of multivalent cations, such as Mg 2+ , during charging can form Li x M y Si ternary phases. They can stabilize Si anions and reduce side reactions with electrolyte, improving the bulk stability. More importantly, Mg 2+ and Ca 2+ incorporate into interfacial side reactions and generate inorganic-rich solid− electrolyte interphase, thus enhancing the interfacial stability. Therefore, the full cells with Zintl-phase-forming electrolytes achieve higher capacity retentions at the C/3 rate after 100 cycles, compared to a baseline electrolyte. Additionally, strategies for mitigating the electrode-level fractures of Si were evaluated to make the best use of Zintl-phase-forming electrolytes. This work highlights the significance of synergistic impact of multifunctional additives to stabilize both bulk and interface chemistry in high-energy Si anode materials for Li-ion batteries.

Binary Cation Matrix Electrolyte and Its Effect on Solid Electrolyte Interphase Suppression and Evolution of Si Anode

“…The role of EC in the SEI formation and its function in electrolyte are critical since initial SEI acts as a protective and stabilizing layer for Si against further interfacial side reactions during subsequent electrochemical cycling . Such a finding is further supported by the ex situ XPS analysis investigating the post-mortem SEI chemical structure, revealing a notable decrease in carbonate species with Mg 2+ additives …”

“…38 Such a finding is further supported by the ex situ XPS analysis investigating the post-mortem SEI chemical structure, revealing a notable decrease in carbonate species with Mg 2+ additives. 31 To further explore possible mechanisms that led to the reduced EC solvent decomposition, the FTIR spectra of two electrolytes, the mixed cation of the Mg 2+ +Li + ion matrix, and the solely Li + electrolyte, were compared. The interaction of the EC with the Mg 2+ center was evident from the FTIR spectra (Figure 1d coordination of EC with the Mg ions.…”

“…31,32 chemical ex situ analysis investigated SEI at the Li-M-Si Zintlphase interface suggesting that improved interphase stability and ion diffusion can be achieved through the formation of the inorganic-rich SEI with multivalent cation additives (such as Mg 2+ and Ca 2+ ). 31 However, the mechanisms of why and how the binary cation matrix benefits SEI stability are not fully understood. A significant barrier to investigating the intricate mechanisms that govern the SEI evolution during electrochemical cycling lies in the lack of in situ techniques that can capture SEI's dynamics and monitor its electronic and physical properties.…”

“…One effective and simple strategy to enhance the stability and reduce the reactivity of lithiated Si involves the in situ electrochemical formation of Li-M-Si (M = Mg, Al, Ca, Zn) ternary Zintl phases. − The simplicity of this approach presents an introduction of a multivalent cation salt as a secondary component in the conventional Li electrolyte, promising advancements in structural integrity and performance enhancement for Si anodes. , Previous postelectrochemical ex situ analysis investigated SEI at the Li-M-Si Zintl-phase interface suggesting that improved interphase stability and ion diffusion can be achieved through the formation of the inorganic-rich SEI with multivalent cation additives (such as Mg 2+ and Ca 2+ ) . However, the mechanisms of why and how the binary cation matrix benefits SEI stability are not fully understood.…”

The Synthesis and Crystal Structure of Six Quaternary Lithium-Alkaline Earth Metal Alumo-Silicides and Alumo-Germanides, A2LiAlTt2 (A = Mg, Ca, Sr, Ba; Tt = Si, Ge)

“…Zintl phases typically contain electropositive cations (alkali, alkaline earth, or rare earth metals) and electronegative early p-block metals and semimetals from groups 13 to 15, which are the (poly)anions [1]. Given that many Zintl phases are intrinsic semiconductors, they could be the bases for materials with applications in solid-state energy conversion and/or storage [2][3][4][5][6][7][8][9][10], which further sustainability.…”