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Li-rich Li-Si alloy as a lithium-containing negative electrode material towards high energy lithium-ion batteries.

Iwamura S, Nishihara H, Ono Y, Morito H, Yamane H, Nara H, Osaka T, Kyotani T - Sci Rep (2015)

Bottom Line: Since Li-Si is free from severe constriction/expansion upon delithiation/lithiation, it shows much better cyclability than Si.The feasibility of the Li-Si alloy is further examined by constructing a full-cell together with a lithium-free positive electrode.Though Li-Si alloy is too active to be mixed with binder polymers, the coating with carbon-black powder by physical mixing is found to prevent the undesirable reactions of Li-Si alloy with binder polymers, and thus enables the construction of a more practical electrochemical cell.

View Article: PubMed Central - PubMed

Affiliation: 1] Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan [2] Division of Chemical Process Engineering, Graduate School of Engineering, Hokkaido University, N13W8 Kita-ku, Sapporo 060-8628, Japan.

ABSTRACT
Lithium-ion batteries (LIBs) are generally constructed by lithium-including positive electrode materials, such as LiCoO2, and lithium-free negative electrode materials, such as graphite. Recently, lithium-free positive electrode materials, such as sulfur, are gathering great attention from their very high capacities, thereby significantly increasing the energy density of LIBs. Though the lithium-free materials need to be combined with lithium-containing negative electrode materials, the latter has not been well developed yet. In this work, the feasibility of Li-rich Li-Si alloy is examined as a lithium-containing negative electrode material. Li-rich Li-Si alloy is prepared by the melt-solidification of Li and Si metals with the composition of Li21Si5. By repeating delithiation/lithiation cycles, Li-Si particles turn into porous structure, whereas the original particle size remains unchanged. Since Li-Si is free from severe constriction/expansion upon delithiation/lithiation, it shows much better cyclability than Si. The feasibility of the Li-Si alloy is further examined by constructing a full-cell together with a lithium-free positive electrode. Though Li-Si alloy is too active to be mixed with binder polymers, the coating with carbon-black powder by physical mixing is found to prevent the undesirable reactions of Li-Si alloy with binder polymers, and thus enables the construction of a more practical electrochemical cell.

No MeSH data available.


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(a,d) SEM images and (b,c,e,f) elemental mappings for Si and Cu at the cross-section of Li21Si5(2–5 μm)/Cu electrodes (a–c) before charge/discharge measurements and (d–f) after 10 cycles (after delithiation). The positions of Li-Si alloy or Si are indicated by arrows. (g,h) TEM images of Li21Si5(2–5 μm) (g) before and (h) after charge/discharge measurements. Insets represent SAD patterns. (i) N2 adsorption isotherm (−196°C) of porous Si shown in (h).
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f4: (a,d) SEM images and (b,c,e,f) elemental mappings for Si and Cu at the cross-section of Li21Si5(2–5 μm)/Cu electrodes (a–c) before charge/discharge measurements and (d–f) after 10 cycles (after delithiation). The positions of Li-Si alloy or Si are indicated by arrows. (g,h) TEM images of Li21Si5(2–5 μm) (g) before and (h) after charge/discharge measurements. Insets represent SAD patterns. (i) N2 adsorption isotherm (−196°C) of porous Si shown in (h).

Mentions: Microstructures of Li-Si/Cu electrode before and after 10 charge/discharge cycling are directly observed by SEM equipped with an energy dispersive X-ray spectrometer (EDX). Fig. 4a shows a cross-sectional SEM image of the pellet electrode prepared from Li21Si5(2–5 μm) and Cu powder before the electrochemical measurements. The positions of Li-Si alloy and Cu can be identified from the elemental mappings for Si (Fig. 4b) and Cu (Fig. 4c), respectively. In Fig. 4a, Li-Si particles, which are indicated by arrows, have relatively smooth surface. The other particles with rather wrinkled appearance must be Cu, as found from Fig. 4c. Li-Si alloy and Cu particles are homogeneously mixed and they are closely packed in the pellet electrode. Fig. 4d shows a SEM image of the pellet electrode after the 10th delithiation, and the positions of Si and Cu are confirmed by Fig. 4e and f, respectively. Also in Fig. 4d, Si particles are clearly identified as indicated by arrows from the Cu matrix. It is noteworthy that the size and the shape of the Si particles (Fig. 4d) after 10 cycles are almost the same as those of the original Li-Si particles (Fig. 4a). Such similarities in morphology seem a little strange, when considering the very different densities of Li21Si5 (1.18 g cm−3) and Si (2.33 g cm−3). In order to elucidate this result, the electrodes shown in Fig. 4a and d are further observed by a transmission electron microscope (TEM) and selected area electron diffraction (SAD) equipped with EDX, as shown in Fig. 4g and h. Note that we confirmed the absence of Cu in the viewing fields of Fig. 4g and h by EDX. From the change of the SAD pattern, it is found that polycrystalline Li-Si alloy, which is assigned as Li21Si5 or Li17Si4 (Fig. 4g), is turned into amorphous Si (Fig. 4h) by the charge/discharge cycling, as we have already presumed. In addition, the original dense structure of Li-Si alloy (Fig. 4g) is changed into an aggregation of very small particles (Fig. 4h), indicating that the amorphous Si has a sponge-like porous structure and the density of the particles shown in Fig. 4d is actually much lower than that of crystalline Si (2.33 g cm−3) due to its inner porosity. N2 adsorption isotherm of the sponge-like porous Si after the delithiation (Fig. 4i) indeed shows adsorption uptake above P/P0 = 0.8, which corresponds to the presence of large mesopores/macropores in this sample. With becoming porous structure, surface decomposition of the electrolyte becomes intense, and thus, Li-Si alloy shares the same problem with a Si anode, which also increases its surface area during charge/discharge cycling39. It is therefore important to suppress/delay the evolution of porosity. The carbon-coating of Li-Si alloy and/or the restriction of upper-limit capacity may be effective, like the case of Si39. Another method is the use of effective additives of electrolyte48.


Li-rich Li-Si alloy as a lithium-containing negative electrode material towards high energy lithium-ion batteries.

Iwamura S, Nishihara H, Ono Y, Morito H, Yamane H, Nara H, Osaka T, Kyotani T - Sci Rep (2015)

(a,d) SEM images and (b,c,e,f) elemental mappings for Si and Cu at the cross-section of Li21Si5(2–5 μm)/Cu electrodes (a–c) before charge/discharge measurements and (d–f) after 10 cycles (after delithiation). The positions of Li-Si alloy or Si are indicated by arrows. (g,h) TEM images of Li21Si5(2–5 μm) (g) before and (h) after charge/discharge measurements. Insets represent SAD patterns. (i) N2 adsorption isotherm (−196°C) of porous Si shown in (h).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4308695&req=5

f4: (a,d) SEM images and (b,c,e,f) elemental mappings for Si and Cu at the cross-section of Li21Si5(2–5 μm)/Cu electrodes (a–c) before charge/discharge measurements and (d–f) after 10 cycles (after delithiation). The positions of Li-Si alloy or Si are indicated by arrows. (g,h) TEM images of Li21Si5(2–5 μm) (g) before and (h) after charge/discharge measurements. Insets represent SAD patterns. (i) N2 adsorption isotherm (−196°C) of porous Si shown in (h).
Mentions: Microstructures of Li-Si/Cu electrode before and after 10 charge/discharge cycling are directly observed by SEM equipped with an energy dispersive X-ray spectrometer (EDX). Fig. 4a shows a cross-sectional SEM image of the pellet electrode prepared from Li21Si5(2–5 μm) and Cu powder before the electrochemical measurements. The positions of Li-Si alloy and Cu can be identified from the elemental mappings for Si (Fig. 4b) and Cu (Fig. 4c), respectively. In Fig. 4a, Li-Si particles, which are indicated by arrows, have relatively smooth surface. The other particles with rather wrinkled appearance must be Cu, as found from Fig. 4c. Li-Si alloy and Cu particles are homogeneously mixed and they are closely packed in the pellet electrode. Fig. 4d shows a SEM image of the pellet electrode after the 10th delithiation, and the positions of Si and Cu are confirmed by Fig. 4e and f, respectively. Also in Fig. 4d, Si particles are clearly identified as indicated by arrows from the Cu matrix. It is noteworthy that the size and the shape of the Si particles (Fig. 4d) after 10 cycles are almost the same as those of the original Li-Si particles (Fig. 4a). Such similarities in morphology seem a little strange, when considering the very different densities of Li21Si5 (1.18 g cm−3) and Si (2.33 g cm−3). In order to elucidate this result, the electrodes shown in Fig. 4a and d are further observed by a transmission electron microscope (TEM) and selected area electron diffraction (SAD) equipped with EDX, as shown in Fig. 4g and h. Note that we confirmed the absence of Cu in the viewing fields of Fig. 4g and h by EDX. From the change of the SAD pattern, it is found that polycrystalline Li-Si alloy, which is assigned as Li21Si5 or Li17Si4 (Fig. 4g), is turned into amorphous Si (Fig. 4h) by the charge/discharge cycling, as we have already presumed. In addition, the original dense structure of Li-Si alloy (Fig. 4g) is changed into an aggregation of very small particles (Fig. 4h), indicating that the amorphous Si has a sponge-like porous structure and the density of the particles shown in Fig. 4d is actually much lower than that of crystalline Si (2.33 g cm−3) due to its inner porosity. N2 adsorption isotherm of the sponge-like porous Si after the delithiation (Fig. 4i) indeed shows adsorption uptake above P/P0 = 0.8, which corresponds to the presence of large mesopores/macropores in this sample. With becoming porous structure, surface decomposition of the electrolyte becomes intense, and thus, Li-Si alloy shares the same problem with a Si anode, which also increases its surface area during charge/discharge cycling39. It is therefore important to suppress/delay the evolution of porosity. The carbon-coating of Li-Si alloy and/or the restriction of upper-limit capacity may be effective, like the case of Si39. Another method is the use of effective additives of electrolyte48.

Bottom Line: Since Li-Si is free from severe constriction/expansion upon delithiation/lithiation, it shows much better cyclability than Si.The feasibility of the Li-Si alloy is further examined by constructing a full-cell together with a lithium-free positive electrode.Though Li-Si alloy is too active to be mixed with binder polymers, the coating with carbon-black powder by physical mixing is found to prevent the undesirable reactions of Li-Si alloy with binder polymers, and thus enables the construction of a more practical electrochemical cell.

View Article: PubMed Central - PubMed

Affiliation: 1] Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan [2] Division of Chemical Process Engineering, Graduate School of Engineering, Hokkaido University, N13W8 Kita-ku, Sapporo 060-8628, Japan.

ABSTRACT
Lithium-ion batteries (LIBs) are generally constructed by lithium-including positive electrode materials, such as LiCoO2, and lithium-free negative electrode materials, such as graphite. Recently, lithium-free positive electrode materials, such as sulfur, are gathering great attention from their very high capacities, thereby significantly increasing the energy density of LIBs. Though the lithium-free materials need to be combined with lithium-containing negative electrode materials, the latter has not been well developed yet. In this work, the feasibility of Li-rich Li-Si alloy is examined as a lithium-containing negative electrode material. Li-rich Li-Si alloy is prepared by the melt-solidification of Li and Si metals with the composition of Li21Si5. By repeating delithiation/lithiation cycles, Li-Si particles turn into porous structure, whereas the original particle size remains unchanged. Since Li-Si is free from severe constriction/expansion upon delithiation/lithiation, it shows much better cyclability than Si. The feasibility of the Li-Si alloy is further examined by constructing a full-cell together with a lithium-free positive electrode. Though Li-Si alloy is too active to be mixed with binder polymers, the coating with carbon-black powder by physical mixing is found to prevent the undesirable reactions of Li-Si alloy with binder polymers, and thus enables the construction of a more practical electrochemical cell.

No MeSH data available.


Related in: MedlinePlus