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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.


Related in: MedlinePlus

Energy density of a LIB cell versus capacity of a negative-electrode material.Three lines are calculated with assuming different positive-electrode materials considering their different operating potentials; LiCoO2 (ca. 140 mAh g−1, 3.7 V), S (1672 mAh g−1, 1.8 V), and S (2.1 V). Details about the calculation are given in the Supporting Information.
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f1: Energy density of a LIB cell versus capacity of a negative-electrode material.Three lines are calculated with assuming different positive-electrode materials considering their different operating potentials; LiCoO2 (ca. 140 mAh g−1, 3.7 V), S (1672 mAh g−1, 1.8 V), and S (2.1 V). Details about the calculation are given in the Supporting Information.

Mentions: Lithium-ion batteries (LIBs) are widely used for various mobile electronics123, but their energy density is required to be increased further especially for automobile applications such as electric vehicles. The development of new electrode materials having large capacities are of great interest in recent years4. For example, silicon (Si) has an extremely large theoretical capacity of 3572 mAh g−1 (as Li15Si4)56 as a negative-electrode material, compared to conventional graphite (theoretical capacity is 372 mAh g−1), and Si-containing negative-electrode materials with excellent performances have been intensively developed7891011121314151617181920. It should be, however, noted that the energy density of a LIB cell (Wcell) depends both on negative- and positive-electrode capacities21, i.e., a very large negative-electrode capacity does not always result in a significant increase of Wcell without the increase of a positive-electrode capacity at the same time. This could be easily understood from Fig. 1, where Wcell is plotted against a negative-electrode capacity (based on the construction of a common cylindrical 18650 cell). The present LIBs are generally constructed by graphite (372 mAh g−1) and LiCoO2 (140 mAh g−1) and this combination produces a cell voltage of 3.7 V, so that the value of Wcell can be calculated to be about 188 Wh kg−1 (See the calculation details in the Supporting Information). As long as LiCoO2 is used as a positive electrode, its Wcell levels off around 250 Wh kg−1, even if the capacity of a negative electrode is increased much more than that of graphite (Fig. 1). There are several candidates for positive electrode materials, such as lithium nickel manganese cobalt oxide, lithium iron phosphate, lithium manganese oxide, and lithium titanate, but their effective capacities are no more than ca. 220 mAh g−12223. Thus, as long as using these lithium-containing materials as a positive electrode, it is intrinsically unable to significantly improve the energy density of LIBs. Recently, lithium-free positive-electrode materials have attracted great interests from their very high capacities: for example, metal fluorides24 and sulfur (S)252627 have theoretical capacities of 600 and 1672 mAh g−1, respectively. In order to use such lithium-free positive-electrode materials, however, it is necessary for a negative-electrode material to contain lithium beforehand. At a laboratory level, it is common to use Li foil as a counter of the lithium-free positive electrode materials. However, Li foil has a problem of dendrite growth during charge/discharge, and it is difficult to adopt it to commercial LIBs, especially large batteries. Lithiated graphite (LiC6; theoretical capacity is 339 mAh g−1-LiC6) can be considered as a probable candidate, because it has been already commercialized in lithium-ion capacitors28. With the combination of LiC6 and S, the operating potential could be 2.1 V, and the energy density of LIB reaches 296 Wh kg−1 (Fig. 1). If much higher capacity material could be used, the energy density of LIB would be further increased. An ultimate candidate is Li-Si alloy29. One method to prepare Li-Si alloy is electrochemical pre-lithiation of Si like the case of the aforementioned lithiated graphite. However, the pre-lithiation requires complicated cell design and the application to Si would be very difficult because of its severe volume expansion upon the lithiation. Thus, the use of thermochemically-synthesized Li-Si alloy is more favorable. There are several Li-rich stable phases in the Li-Si binary system, such as Li21Si5 (theoretical capacity: 1967 mAh g−1-Li21Si5)30 and Li17Si4 (theoretical capacity: 1978 mAh g−1-Li17Si4)31. With combining S with either Li21Si5 or Li17Si4, very high Wcell of 814 or 816 Wh kg−1 could be achieved (Fig. 1). Thus, Li-rich Li-Si alloy has a great potential as a lithium-containing negative electrode.


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)

Energy density of a LIB cell versus capacity of a negative-electrode material.Three lines are calculated with assuming different positive-electrode materials considering their different operating potentials; LiCoO2 (ca. 140 mAh g−1, 3.7 V), S (1672 mAh g−1, 1.8 V), and S (2.1 V). Details about the calculation are given in the Supporting Information.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: Energy density of a LIB cell versus capacity of a negative-electrode material.Three lines are calculated with assuming different positive-electrode materials considering their different operating potentials; LiCoO2 (ca. 140 mAh g−1, 3.7 V), S (1672 mAh g−1, 1.8 V), and S (2.1 V). Details about the calculation are given in the Supporting Information.
Mentions: Lithium-ion batteries (LIBs) are widely used for various mobile electronics123, but their energy density is required to be increased further especially for automobile applications such as electric vehicles. The development of new electrode materials having large capacities are of great interest in recent years4. For example, silicon (Si) has an extremely large theoretical capacity of 3572 mAh g−1 (as Li15Si4)56 as a negative-electrode material, compared to conventional graphite (theoretical capacity is 372 mAh g−1), and Si-containing negative-electrode materials with excellent performances have been intensively developed7891011121314151617181920. It should be, however, noted that the energy density of a LIB cell (Wcell) depends both on negative- and positive-electrode capacities21, i.e., a very large negative-electrode capacity does not always result in a significant increase of Wcell without the increase of a positive-electrode capacity at the same time. This could be easily understood from Fig. 1, where Wcell is plotted against a negative-electrode capacity (based on the construction of a common cylindrical 18650 cell). The present LIBs are generally constructed by graphite (372 mAh g−1) and LiCoO2 (140 mAh g−1) and this combination produces a cell voltage of 3.7 V, so that the value of Wcell can be calculated to be about 188 Wh kg−1 (See the calculation details in the Supporting Information). As long as LiCoO2 is used as a positive electrode, its Wcell levels off around 250 Wh kg−1, even if the capacity of a negative electrode is increased much more than that of graphite (Fig. 1). There are several candidates for positive electrode materials, such as lithium nickel manganese cobalt oxide, lithium iron phosphate, lithium manganese oxide, and lithium titanate, but their effective capacities are no more than ca. 220 mAh g−12223. Thus, as long as using these lithium-containing materials as a positive electrode, it is intrinsically unable to significantly improve the energy density of LIBs. Recently, lithium-free positive-electrode materials have attracted great interests from their very high capacities: for example, metal fluorides24 and sulfur (S)252627 have theoretical capacities of 600 and 1672 mAh g−1, respectively. In order to use such lithium-free positive-electrode materials, however, it is necessary for a negative-electrode material to contain lithium beforehand. At a laboratory level, it is common to use Li foil as a counter of the lithium-free positive electrode materials. However, Li foil has a problem of dendrite growth during charge/discharge, and it is difficult to adopt it to commercial LIBs, especially large batteries. Lithiated graphite (LiC6; theoretical capacity is 339 mAh g−1-LiC6) can be considered as a probable candidate, because it has been already commercialized in lithium-ion capacitors28. With the combination of LiC6 and S, the operating potential could be 2.1 V, and the energy density of LIB reaches 296 Wh kg−1 (Fig. 1). If much higher capacity material could be used, the energy density of LIB would be further increased. An ultimate candidate is Li-Si alloy29. One method to prepare Li-Si alloy is electrochemical pre-lithiation of Si like the case of the aforementioned lithiated graphite. However, the pre-lithiation requires complicated cell design and the application to Si would be very difficult because of its severe volume expansion upon the lithiation. Thus, the use of thermochemically-synthesized Li-Si alloy is more favorable. There are several Li-rich stable phases in the Li-Si binary system, such as Li21Si5 (theoretical capacity: 1967 mAh g−1-Li21Si5)30 and Li17Si4 (theoretical capacity: 1978 mAh g−1-Li17Si4)31. With combining S with either Li21Si5 or Li17Si4, very high Wcell of 814 or 816 Wh kg−1 could be achieved (Fig. 1). Thus, Li-rich Li-Si alloy has a great potential as a lithium-containing negative electrode.

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