Solid-Solution or Intermetallic Compounds: Phase Dependence of the Li-Alloying Reactions for Li-Metal Batteries

Abstract

Electrochemical Li-alloying reactions with Li-rich alloy phases render a much higher theoretical capacity that is critical for high-energy batteries, and the accompanying phase transition determines the alloying/dealloying reversibility and cycling stability. However, the influence of phase-transition characteristics upon the thermodynamic properties and diffusion kinetic mechanisms among the two categories of alloys, solid-solutions and intermetallic compounds, remains incomplete. Here we investigated three representative Li-alloys: Li–Ag alloy of extended solid-solution regions; Li–Zn alloy of an intermetallic compound with a solid-solution phase of a very narrow window in Li atom concentration; and Li–Al alloy of an intermetallic compound. Solid-solution phases undertake a much lower phase-transition energy barrier than the intermetallic compounds, leading to a considerably higher Li-alloying/dealloying reversibility and cycling stability, which is due to the subtle structural change and chemical potential gradient built up inside of the solid-solution phases. These two effects enable the Li atoms to enter the bulk of the Li-Ag alloy to form a homogeneous alloy phase. The pouch cell of the Li-rich Li20Ag alloy pairs with a LiNi0.8Co0.1Mn0.1O2 cathode under an areal capacity of 3.5 mAh cm–2 can retain 87% of its initial capacity after 250 cycles with an enhanced Coulombic efficiency of 99.8 ± 0.1%. While Li-alloying reactions and the alloy phase transitions have always been tightly linked in past studies, our findings provide important guidelines for the intelligent design of components for secondary metal batteries.

Synergistic Evolution of Alloy Nanoparticles and Carbon in Solid-State Lithium Metal Anode Composites at Low Stack Pressure

“…In contrast, given the high concentration of Li in the composites (Table S2), the Si and Sn will form highly lithiated intermetallic alloys such as Li 15 Si 4 and Li 22 Sn 5 . 50,51 Since they are insoluble, these intermetallic alloys are responsible for the nonuniform distribution of the lithiated phases (Figure 5e,f). 28,50 Although the insoluble alloy particles can provide a lithiophilic environment to aid the Li growth within the rGO/M scaffolds, as shown in Figure 5e,f, these localized particles do not become uniformly redistributed each stripping half-cycle, leading to current concentrations and poor cyclability (Figure 3d).…”

“…50,51 Since they are insoluble, these intermetallic alloys are responsible for the nonuniform distribution of the lithiated phases (Figure 5e,f). 28,50 Although the insoluble alloy particles can provide a lithiophilic environment to aid the Li growth within the rGO/M scaffolds, as shown in Figure 5e,f, these localized particles do not become uniformly redistributed each stripping half-cycle, leading to current concentrations and poor cyclability (Figure 3d). This finding suggests that the morphological reversibility of Li during cycling of the composite electrodes is strongly influenced by the solid solution vs intermetallic nature of the Li alloy phases, since dissolution in a solid solution allows for more uniform spatial redistribution of the alloy component each cycle.…”

“…This behavior enhances the morphological reversibility of Li deposition by providing uniformly distributed NPs within the rGO/M scaffold from which Li can grow in the subsequent deposition step (Figure b and d). In contrast, given the high concentration of Li in the composites (Table S2), the Si and Sn will form highly lithiated intermetallic alloys such as Li 15 Si 4 and Li 22 Sn 5 . , Since they are insoluble, these intermetallic alloys are responsible for the nonuniform distribution of the lithiated phases (Figure e,f). , Although the insoluble alloy particles can provide a lithiophilic environment to aid the Li growth within the rGO/M scaffolds, as shown in Figure e,f, these localized particles do not become uniformly redistributed each stripping half-cycle, leading to current concentrations and poor cyclability (Figure d). This finding suggests that the morphological reversibility of Li during cycling of the composite electrodes is strongly influenced by the solid solution vs intermetallic nature of the Li alloy phases, since dissolution in a solid solution allows for more uniform spatial redistribution of the alloy component each cycle.…”

Nonconventional Electrochemical Reactions in Rechargeable Lithium–Sulfur Batteries

“…3 With the continuous development of advanced characterization techniques in recent years, the study of the lithium−metal anode has received increasing attention, and enormous efforts have been devoted to addressing the critical issues of dendritic metal deposition and parasitic interfacial reactions. 4 However, advancing the practical development of RLSBs still requires comprehensive multiscale research on the sulfur cathode to enhance its electrochemical performance. Sulfur has been widely known for its commonest (and the most stable) yellow-colored allotrope in an orthorhombic αform, consisting of cyclo-S 8 molecules with a typical crown structure (Figure 1a).…”

“…Since then, extensive efforts have been made on further improving the performance of RLSBs, with main focuses on design of the cathode host for effective trapping of soluble polysulfides, regulation of electrolyte compositions for inhibiting polysulfides shuttle, and development of highly efficient electrocatalysts for mediating sulfur redox kinetics . With the continuous development of advanced characterization techniques in recent years, the study of the lithium–metal anode has received increasing attention, and enormous efforts have been devoted to addressing the critical issues of dendritic metal deposition and parasitic interfacial reactions . However, advancing the practical development of RLSBs still requires comprehensive multiscale research on the sulfur cathode to enhance its electrochemical performance.…”