Study of the Reaction of Lithium with Isostructural A[sub 2]B and Various Al[sub x]B Alloys

Abstract

Since the first evidence for the alloying reactions of Li with various elements in nonaqueous media, 1-3 a great deal of research has been conducted on intermetallic phases as a possible replacement for the carbon used as an anode material in lithium-ion batteries. The electrochemical capacities associated with the formation of Li alloys can produce very large capacities (Li 4.4 Si: 4200 mAh/g, Li 4.4 Ge: 1600 mAh/g, LiAl and Li 4.4 Sn: 990 mAh/g), compared to that for the insertion of lithium in carbon (372 mAh/g). However, the inhomogeneous expansion due to successive two-phase domains in the Li-A phase diagrams result in severe cracking of the particles and the loss of electrical contact that is held responsible for poor process reversibility. 1 (Here, A represents an element that forms intermetallic phases with lithium.)To solve this problem, the preparation of small particles of active materials has been proposed as an alternative. 4 Discrete Li-A intermetallic phases cannot form in small clusters of A atoms, so homogeneous expansion upon reaction of Li should result. The homogeneous expansion should prevent cracking of the particles, and enhanced electrochemical performance is observed.The use of active/inactive composites, where an inert matrix holds the reacting component, has been proposed. 5 Recently, this has been studied thoroughly by Mao et al. 6,7 for the case of nanocomposites of Sn 2 Fe/SnFe 3 C and by Beaulieu et al. 8 for the analogous system Sn 2 Mn/SnMn 3 C. In these composites, the SnM 3 C phase reacted with little Li (inactive) and the Sn 2 M phase reacted completely to form Li 4.4 Sn and M (active). In order to fully exploit the active/inactive composite approach it is important to understand why some intermetallic compounds react with Li and others do not.In this work, an attempt is made to determine the role of structure as well as chemistry on the reactivity of an alloy toward Li. First, different isostructural A 2 B compounds were prepared and studied. These were selected such that A is known to alloy with Li and form Li x A compounds (A ϭ Sb, Sn, Al, Ge) and B forms no alloys with lithium (B ϭ Ti, Mn, V, Fe, Co, Cu). Isostructural intermetallics with the -Al 2 Cu structure that crystallize in the same tetragonal system and space group (I 4 /mcm, no. 140) were selected. 9 Eight compounds were found that met these criteria: Sb 2 Ti, Sb 2 V, Sn 2 Co, Sn 2 Mn, Sn 2 Fe, Al 2 Cu, Sn 2 Ru, and Ge 2 Fe. Based on our results for the reaction of Li with these materials, we then studied the reaction of Li with other Al transition metal alloys of unrelated structure.Experimental The A 2 B samples were prepared using two methods. For Sb 2 Ti, Sb 2 V, and Sn 2 Co hardened steel vials were charged under purified Ar with elemental powder (Sb, Sn, Ti, V, Co) in stoichiometric proportions (A:B 2:1) and ballmilled in a commercial SPEX-8000D high energy ball mill. The ball-to-sample weight ratio used was 21:1. Milling of each sample proceeded until the proper structure was reached as determined by X-ray ...

Preparation and Li-storage properties of SnSb/graphene hybrid nanostructure by a facile one-step solvothermal route

“…However, the Sn anode undergoes rapid capacity fading upon cycling due to large volume changes. Although the introduction of a Li-inert element to form Sn alloys [1][2][3][4][5][6] can alleviate the volume change to some extent, it will decrease the overall capacity or even make the alloy electrochemically inert [7]. An alternative strategy is to form Sn alloys with another Li-active element.…”

Synthesis and electrochemical performance of aluminum based composites

“…2 To overcome these problems, Al-based intermetallic materials such as Al 2 Cu, Al 6 Mn, AlSb and Fe 2 Al 5 have been investigated. 3,4 However, all these materials give small reversible capacities in the first cycle and show fast capacity fading. Particulatereinforced composites or mixtures, for instance, Al-SiC and Al-Al 3 Ni, have also been exploited.…”

“…3,4 However, all these materials give small reversible capacities in the first cycle and show fast capacity fading. Particulatereinforced composites or mixtures, for instance, Al-SiC and Al-Al 3 Ni, have also been exploited. 5,6 Among these composites or mixtures, aluminum acts as an active component storing lithium, while the other component is unalloyable with lithium and serves only for the improvement of the mechanical stability.…”

Thermo‐electrochemical Activation of an In–Cu Intermetallic Electrode for the Anode in Lithium Secondary Batteries

“…[8][9][10][11][12][13][14][15][16] The previous literature complains that many binary intermetallic compounds are inactive or show a much lower capacity than the theoretical one at room temperature, even if the reactions are thermodynamically feasible; Ni x Sn, [12] Co 3 Sn 2 , [14] Cu 3 Si, [17] Ni x Si, [18] Cu 3 Sn, [19] and Al-M (M ¼ Cr, Fe, Mn, and Ni) alloys. [20,21] Simply, such a slow kinetics can be attributed to a high activation energy needed either for Li þ ion insertion (addition-type reaction) or for A-B bond cleavage (conversion reaction). [10,20,21] A more systematic study is, however, needed in order to address the kinetic barriers in these materials and to further find a way to enhance their reactivity, which is the major concern in this work.…”

“…[20,21] Simply, such a slow kinetics can be attributed to a high activation energy needed either for Li þ ion insertion (addition-type reaction) or for A-B bond cleavage (conversion reaction). [10,20,21] A more systematic study is, however, needed in order to address the kinetic barriers in these materials and to further find a way to enhance their reactivity, which is the major concern in this work. We studied the electrochemical reactivity and structural change upon lithiation of an In-containing binary intermetallic compound (Cu 7 In 3 ), which is inactive for lithiation at room temperature.…”