JP2003346793A - Negative electrode material for lithium ion secondary battery and its manufacturing method, lithium ion secondary battery negative electrode and lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery negative electrode and a negative electrode material used for the negative electrode which are superior in the initial charge and discharge efficiency and in which cycle deterioration due to charge and discharge is suppressed and high discharge capacity is realized, and their manufacturing method and a lithium secondary battery having the negative electrode. <P>SOLUTION: The negative electrode material contains an alloy having the composition of the formula (1) (Li)x(R)y(Sn)z(Ma)w(Mb)v and its manufacturing method comprises a process (a) for manufacturing the molten alloy having the composition of the formula (1), a process (b) for cooling and solidifying the molten alloy, and a process (c) for holding the cooled and solidified alloy for one minutes to 100 hours in the temperatures of 100-1150°C in a rare gas and/or hydrogen gas of 0.07-10 MPa. In the formula, R is a lanthanoid-series element or the like, Ma is B, C, Si or the like, and Mb is Ti, V, Cr or the like and Ma≠Mb. 0≤x≤13, 0.70≤y≤1.10, 2.20≤z≤3.50, 0≤w≤0.70, 0≤v≤0.70, and 0≤w+v≤0.70. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to Li, rare earth elements,
For a negative electrode material for a lithium ion secondary battery composed of an alloy containing Sn as a main component, a method for producing the same, a negative electrode using the negative electrode material, and a lithium ion secondary battery including the negative electrode, High efficiency, large discharge capacity,
The present invention relates to a negative electrode for a lithium ion secondary battery having excellent cycle characteristics and excellent industrial productivity, a negative electrode material as a raw material thereof, a production method thereof, and a lithium ion secondary battery.

[0002]

2. Description of the Related Art Since a lithium ion secondary battery has a remarkably high theoretical energy density as compared with other secondary batteries, not only high performance batteries used for mobile phones and electronic devices, but also
Recently, there has been strong interest in new batteries for electric vehicles. At present, a graphite-based carbon material in which lithium ions are intercalated is used as a negative electrode active material of a lithium ion secondary battery that has been put into practical use. However, graphite-based carbon material has lithium 1 for 6 carbon atoms.
The limit is to intercalate atoms, and the theoretical electrical capacity of carbon material is 372 mAh / g. Therefore, development of a new negative electrode material is desired in order to satisfy the high capacity characteristics required for a secondary battery in the future. Under these circumstances, Si (density: 2.33 g / cm ³ ) and Sn (density: 7.3 g / cm ³ )
Are very attractive materials because they can store up to 4.4 Li atoms per atom. However, Si and Sn cause a very large volume expansion of three times or more when occluding Li. As a result, pulverization occurs, detachment from the electrode or the like is caused, sufficient conduction cannot be maintained, and the capacity is reduced to 1/5 or less of the initial discharge capacity in about several cycles. Under such a background, at the present, elements with different volume expansion coefficients (difficult to alloy with Li) and Si or Sn are compounded or alloyed at the nano level to suppress fine powder and extend cycle life Attempts are being made energetically. For example, as a negative electrode active material of a lithium ion secondary battery, FeSi ₂ , N
iSi ₂ , CoSi ₂ , VSi ₂ , MnSi ₂ , or Ni ₃ Sn ₂ , Ni ₃ S for Sn-based
The possibility of using intermetallic compounds such as n, Ni ₃ Sn ₄ , FeSn ₂ , FeSn, and CoSn ₂ has been studied. However, intermetallic compounds that are alloyed with the above-mentioned elements having different volume expansion rates are also presently very important factors at the time of battery design, that is, initial charge / discharge efficiency (the ratio of initial discharge capacity to initial charge capacity).
, The discharge capacity is small, and the cycle characteristics are not good.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide an excellent initial charge / discharge efficiency, suppress cycle deterioration due to charge / discharge, and achieve a discharge capacity that greatly exceeds 372 mAh / g, which is the theoretical capacity of a graphite-based carbon material. It is an object of the present invention to provide a realized negative electrode for a lithium secondary battery, a negative electrode material used for the negative electrode, a method for producing the negative electrode, and a lithium secondary battery including the negative electrode.

[0004]

Means for Solving the Problems In order to solve the above problems, the present inventors have developed a _three- phase RSn (R =
Focusing on the rare earth element, etc., the Li remaining in the alloy by the first charge / discharge is stored in advance (charged) RSn ₃ -Lix (0 ≦
An alloy having x ≦ 13) as a basic skeleton was produced by a high-frequency melting method. As a result, a high discharge capacity and excellent cycle characteristics were achieved. Next, as a result of intensive studies on an additive element that increases the charge and discharge capacity of Li and an additive element that improves the cycle life, it was found that by adding an appropriate amount of a specific element, the discharge characteristics could be further improved, The present invention has been completed.

That is, according to the present invention, there is provided a negative electrode material for a lithium ion secondary battery including an alloy having a composition represented by the formula (1). (Li) x (R) y (Sn) z (Ma) w (Mb) v ・ ・ ・ (1) (where R is selected from the group consisting of elements from lanthanide series La to Lu including Y and Sc One or two or more, Ma is
B, C, Si, P, Al, Zn, V, Mn, Cu, Ag, In, Sb, Pb and
One or more selected from the group consisting of Bi, Mb is Ti,
V, Cr, Fe, Co, Ni, Cu, B, Mg, Zr, Hf, Nb, Ta and Mo
Ma ≠ Mb in at least one kind selected from the group consisting of
x, y, z are each a molar ratio, 0 ≦ x ≦ 13, 0.70 ≦ y ≦ 1.1
0, 2.20 ≦ z ≦ 3.50, 0 ≦ w ≦ 0.70, 0 ≦ v ≦ 0.70, 0 ≦ w + v ≦
It is 0.70. According to the present invention, according to the present invention, a step (a) of producing a molten alloy having a composition represented by the formula (1), a step (b) of cooling and solidifying the produced molten alloy, and ~ 10MPa
The method for producing a negative electrode material for a lithium ion secondary battery, comprising the step (c) of maintaining the composition in a rare gas and / or hydrogen gas at a temperature of 100 to 1150 ° C. for 1 minute to 100 hours. Further, according to the present invention, there is provided a negative electrode for a lithium ion secondary battery including the negative electrode material as an active material. Furthermore, according to the present invention, there is provided a lithium ion secondary battery including the above-described negative electrode.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The negative electrode material of the present invention, when used as a negative electrode for a lithium ion secondary battery, exhibits a discharge capacity much higher than the theoretical capacity of a conventional carbon material, an initial charge / discharge efficiency equal to or higher than that of a conventional carbon material, and The cycle characteristics can also exhibit much better cycle characteristics than conventional alloy-based negative electrode materials, and include alloys having the composition represented by the above formula (1).

In the formula (1), R is one or more selected from the group consisting of elements from the lanthanoid series La to Lu containing Y and Sc (hereinafter abbreviated as rare earth (R)). The rare earth
(R) has a large difference in electronegativity in combination with Sn, has strong polarity, and is ionically alloyed with Sn, so that an improvement in cycle life can be expected. C among rare earth (R)
e belongs to the class having the largest difference in electronegativity in combination with Sn, and makes it possible to achieve an alloy system that is very difficult to pulverize. Also, Ce has an oxidation number up to tetravalent, so that Li
Belongs to an element that has a large coordination ability and enables the production of an alloy system having the largest charge / discharge capacity among various rare earths (R). Therefore, the rare earth (R) is Ce alone or C
e and less than 90 mol%, especially less than 50 mol% of rare earths other than Ce
(R) is preferred. The rare earth (R) mainly forms an intermetallic compound with Sn, but even if the rare earth (R) itself exists, the volume expansion accompanying the occlusion and release of Li can be reduced. If the amount of the rare earth (R) is too large, the charge / discharge capacity is reduced.If the amount is too small, pulverization cannot be suppressed.
The range of y indicating the amount of the rare earth (R) in (1) is 0.70 ≦ y ≦
1.10, preferably 0.90 ≦ y ≦ 1.05.

In the formula (1), the content ratio of Li can be appropriately selected in consideration of the initial charge / discharge efficiency of a desired alloy composition. good. If the content of Li is too large, handling becomes difficult, and the charge / discharge capacity may be reduced. Therefore, the range of x indicating the amount of Li in the formula (1) is 0 ≦ x ≦ 13, preferably 4.0 ≦ x ≦ 8.0.

In the formula (1), Sn is a metal that stores Li. If the content ratio of Sn is too small, the charge / discharge capacity becomes small. If it is too large, the capacity increases, but the proportion of residual metal Sn that cannot be alloyed with other elements increases, so that pulverization is promoted and the cycle life may decrease. Therefore, the expression
In (1), the range of z indicating the amount of Sn is 2.20 ≦ z ≦ 3.50, preferably 2.70 ≦ z ≦ 3.10. The allowable proportion of residual metal Sn in the alloy having the composition represented by the formula (1) of the present invention is such that the peak intensity of the (200) plane of Sn in powder X-ray diffraction is RSn ₃ phase (R is the formula (Same as R in (1).) 30% or less of the strongest peak intensity in the peak derived from, preferably 15%
The ratio is more preferably 5% or less.

In the formula (1), the substitution element Ma is represented by B, C, Si,
One or more selected from the group consisting of P, Al, Zn, V, Mn, Cu, Ag, In, Sb, Pb and Bi. The substitution element Ma
Can increase the amount of Li occluded and released, and consequently the charge / discharge capacity can be increased. The reason is that B and C of the substitution element Ma can penetrate the interstitial,
Si, P, Al, Zn, V, Mn, Cu, Ag, In, Sb have atomic radii of Ce
Or, since it is smaller than Sn, the lattice can be strained and lattice defects can be generated.
It is presumed that Li can be occluded. Further, among the substitution elements Ma, Al, Zn, V, Cu, Ag, and In have higher conductivity than Ce or Sn, so that the conductivity of the alloy itself can be improved, and as a result, the charge / discharge capacity increases. Conceivable.
In the formula (1), the substitution element Mb is Ti, V, Cr, Fe, Co, Ni,
One or more selected from the group consisting of Cu, B, Mg, Zr, Hf, Nb, Ta and Mo, and Ma ≠ Mb.
The cycle life can be extended by using the substitution element Mb.

The substitution element (Ma, Mb) forms an intermetallic compound of the substitution element alone or the substitution element (Ma, Mb) with the rare earth (R) and / or Sn. It is presumed that it is dispersed in the alloy and reduces the volume expansion of Sn due to charging and discharging of Li. By adjusting the content ratio of these substitution elements (Ma, Mb) to an appropriate value, the balance of the discharge characteristics can be controlled. When the content of Ma is large, the amount of occluded Li increases, but the cycle life tends to decrease. Also, when the content of Mb is large, the cycle life is improved, but Li
The occlusion amount tends to decrease, and the discharge capacity also tends to decrease. Therefore, the ranges of w or v indicating the amount of Ma or Mb in the formula (1) are 0 ≦ w ≦ 0.70, 0 ≦ v ≦ 0.70, and 0 ≦ w + v ≦ 0.70, respectively.

In the present invention, the structure of the alloy represented by the formula (1) is preferably an RSn ₃ phase mainly having a Cu ₃ Au structure. The RSn ₃ phase is the phase having the largest number of Sn bonds in the R-Sn binary alloy. In other words, it is the phase having the largest discharge capacity. The structure of the alloy represented by the formula (1) may contain another phase for the purpose of improving the cycle life and obtaining an appropriate degree of activity. However, it is not preferable to include a Sn single phase because the characteristics are significantly deteriorated. The content ratio of phases other than the RSn ₃ phase is 0.5 to ₃₀ in area ratio when the structure of the alloy is observed.
%, Particularly preferably 2 to 5%. As phases other than RSn ₃ phase,
Intermetallic compound phase of Ma and rare earth (R), intermetallic compound phase of Mb and rare earth (R), intermetallic compound phase of Ma and Sn, intermetallic compound phase of Mb and Sn, rare earth (R) And an intermetallic compound phase of Sn and Sn. Further, the replacement elements Mb and Ma may exist as a single element. These intermetallic compounds or substitutional elements alone are dispersed in the alloy in a complex manner, and have an effect of alleviating the volume expansion of the alloy accompanying the occlusion and release of Li. One or more kinds of the intermetallic compound phases may be present.

The intermetallic compound phase of Mb and the rare earth (R) includes, for example, Ce ₂ Fe ₁₇ , Ce ₂ Fe ₂ , Nd ₂ Fe ₁₇ , Pr ₂ F
_{e 17, PrFe 2, Sm 2} Fe 17, SmFe 3, SmFe 2, Ce 24 Co 11, CeC
_{o 2, CeCo 3, Ce 2} Co 7, Ce 5 Co 19, Ce 2 Co 17, CeCo 5, LaC
_{o 13, LaCo 5, La 5} Co 19, α-La 2 Co 7, β-La 2 Co 7, La 2 C
_{o 3, La 2 Co 1.7,} LaCo, Nd 2 Co 17, NdCo 5, Nd 5 Co 19, Nd 2 Co
_{7, NdCo 3, NdCo 2,} α-Nd 2 Co 3, β-Nd 2 Co 3, Nd 2 Co 1.7, N
_{d 7 Co 3, Nd 3 Co} , Pr 2 Co 17, PrCo 5, Pr 5 Co 19, PrCo 3, Pr 2 C
o ₇ , PrCo ₂ , Pr ₂ Co _1.7 , Pr ₅ Co ₂ , Pr ₃ Co, α-Sm ₂ Co ₁₇ , β
_{-Sm 2 Co 17, SmCo 3,} SmCo 2, Sm 9 Co 4, Sm 3 Co, Ce 7 Ni 3, CeN
_{i, CeNi 2, CeNi 3,} Ce 2 Ni 7, CeNi 5, La 3 Ni, La 7 Ni 3, LaN
i, La ₂ Ni ₃ , La ₇ Ni ₁₆ , LaNi ₃ , α-La ₂ Ni ₇ , β-La ₂ Ni ₇ , L
_{aNi 5, Nd 3 Ni, Nd} 7 Ni 3, NdNi, NdNi 2, NdNi 3, Nd 2 Ni 7, N
_{dNi 5, Nd 2 Ni 17,} Pr 3 Ni, Pr 7 Ni 3, PrNi, PrNi 2, PrNi 3,
Pr ₂ Ni ₇ , PrNi ₅ , Sm ₃ Ni, SmNi, SmNi ₂ , SmNi ₃ , Sm ₂ Ni ₇ ,
_{Sm 5 Ni 19, SmNi 5,} Sm 2 Ni 17, CeCu 6, CeCu 4, CeCu 2, CeC
u, LaCu ₆ , LaCu, NdCu ₆ , NdCu ₅ , NdCu ₄ , Nd ₂ Cu ₇ , NdC
_{u 2, NdCu, PrCu 6,} PrCu 4, PrCu 5, PrCu 2, PrCu, SmC
_{u 6, SmCu 4, SmCu 5} , Sm 2 Cu 7, SmCu 2, SmCu, CeB 4, Ce
_{B 6, LaB 4, LaB 6} , LaB 9, Nd 2 B 5, NdB 4, NdB 6, NdB 66, Sm
_{2 B 5, SmB 4, SmB} 6, SmB 66, CeMg 12, Ce 5 Mg 4 1, CeMg 3, Ce
_{Mg 2, CeMg, CeMg 10.3,} LaMg 12, La 2 Mg 17, LaMg 3, LaM
g ₂ , LaMg and the like.

The intermetallic compound phase of Mb and Sn includes:
For example, Ti ₃ Sn, Ti ₂ Sn, Ti ₅ Sn ₃ , α-Ti ₆ Sn ₅ , β-Ti ₆ S
n ₅ , V ₃ Sn, V ₂ Sn ₃ , Fe ₅ Sn ₃ , Fe ₃ Sn ₂ , FeSn, FeSn ₂ , α-C
o ₃ Sn ₂ , β-Co ₃ Sn ₂ , CoSn, CoSn ₂ , Ni ₃ Sn, Ni ₃ Sn ₂ , Ni ₃ S
_{n 4, Cu 6 Sn 5,} Cu 3 Sn, Mg 2 Sn, Zr 4 Sn, Zr 5 Sn 3, ZrSn 3, Hf
₅ Sn ₃ , Hf ₅ Sn ₄ , HfSn, HfSn ₂ , Nb ₃ Sn, Nb ₆ Sn ₅ , NbSn ₂ , M
o ₃ Sn, MoSn _{2 and the} like.

The intermetallic compound phase of Ma and the rare earth (R)
For example, CeB_Four, CeB₆, LaB_Four, LaB₆, LaB₉, Nd_TwoB
_Five, NdB_Four, NdB₆, NdB₆₆, PrB_Four, PrB₆, Sm_TwoB_Five, SmB_Four, SmB
₆, SmB₆₆, Ce_TwoC_Three, Α-CeC_Two, Β-CeC_Two, La_TwoC_Three, Α-La
C_Two, Β-LaC_Two, Pr_TwoC_Three, Α-PrC_Two, Β-PrC_Two, Ce_FiveSi_Three, Ce_ThreeS
i_Two, Ce_FiveSi_Four, CeSi, Ce_ThreeSi_Five, CeSi_Two, Nd_FiveSi_Three, Nd_FiveSi_Four, N
dSi, Nd_ThreeSi_Four, Α-Nd_TwoSi_Three, Β-Nd_TwoSi_Three, Α-Pr_FiveSi_Three, Β-P
r_FiveSi_Three, Pr_FiveSi_Four, PrSi, Pr _ThreeSi_Four, Α-PrSi_Two, Β-PrSi_Two, S
m_FiveSi_Three, Sm_FiveSi_Four, SmSi, Sm_ThreeSi_Five, Α-SmSi_Two, Β-SmSi_Two, P
rP, PrP_Two, PrP_Five, PrP₇, Α-Al₁₁Ce_Three, Β-Al₁₁Ce_Three, Al_ThreeC
e, Al_TwoCe, AlCe, α-AlCe_Three, Β-AlCe_Three, Α-Al₁₁La_Three, Β
-Al₁₁La_Three, Al_ThreeLa, Al_TwoLa, AlLa, AlLa_Three, Α-Al₁₁Nd_Three,
β-Al₁₁Nd_Three, Al_ThreeNd, Al_TwoNd, AlNd, AlNd_Three, Α-Al₁₁P
r_Three, Β-Al₁₁Pr _Three, Al_ThreePr, Al_TwoPr, α-AlPr, β-AlPr, Al
Pr_Two, Α-AlPr_Three, Β-AlPr_Three, Al_ThreeSm, Al_TwoSm, AlSm, AlS
m_Two, CeZn, CeZn_Two, CeZn_Three, Ce_ThreeZn₁₁, Ce₁₃Zn₅₈, CeZn_Five,
Ce_ThreeZn_{twenty two}, Ce_TwoZn₁₇, CeZn₁₁, LaZn, LaZn_Two, LaZn_Four, LaZn
₈, LaZn₁₃, NdZn, NdZn_Two, NdZn_Three, Nd_ThreeZn₁₁, Nd₁₃Zn₅₈,
Nd_ThreeZn_{twenty two}, NdZn₁₁, NdZn₁₂, Nd_TwoZn₁₇, PrZn, α-PrZn_Two,
β-PrZn_Two, PrZn_Three, Pr_ThreeZn₁₁, Pr₁₃Zn₅₈, Pr_ThreeZn_{twenty two}, Α-Pr
_TwoZn₁₇, Β-Pr_TwoZn₁₇, PrZn₁₁, SmZn, α-SmZn_Two, Β-SmZn
_Two, SmZn_Three, Sm_ThreeZn₁₁, Sm₁₃Zn₅₈, Sm_ThreeZn_{twenty two}, Sm_TwoZn₁₇, Nd₆
Mn_{twenty three}, NdMn_Two, Mn_{twenty three}Pr₆, Mn_{twenty three}Sm₆, Mn_TwoSm, Cu₆Ce, Cu_FiveC
e, Cu_FourCe, Cu_TwoCe, CuCe, α-Cu₆La, β-Cu₆La, Cu_FiveLa,
Cu_FourLa, Cu_TwoLa, CuLa, Cu₆Nd, Cu_FiveNd, Cu_FourNd, Cu₇Nd_Two, C
u_TwoNd, CuNd, Cu₆Pr, Cu_FourPr, Cu_TwoPr, CuPr, Cu₆Sm, Cu_FiveS
m, Cu_FourSm, Cu₇Sm_Two, Cu_TwoSm, CuSm, Ag_FourCe, Ag₅₁Ce₁₄, Α
-Ag_TwoCe, β-Ag_TwoCe, γ-Ag_TwoCe, α-AgCe, β-AgCe, α-A
g_FiveLa, β-Ag_FiveLa, Ag₅₁La₁₄, Ag_TwoLa, AgLa, Ag₅₁Nd₁₄,
α-Ag_TwoNd, β-Ag_TwoNd, AgNd, Ag_FivePr, Ag₅₁Pr₁₄, Α-Ag_TwoP
r, β-Ag_TwoPr, AgPr, Ag₅₁Sm₁₄, Α-Ag_TwoSm, β-Ag_TwoSm, A
gSm, Ce_ThreeIn, Ce_TwoIn, Ce_ThreeIn_Five, CeIn_Two, CeIn_Three, In_ThreeLa, In
_TwoLa, In_FiveLa_Three, InLa, InLa_Two, InLa_Three, Nd_ThreeIn, Nd_TwoIn, NdI
n, Nd_ThreeIn_Five, NdIn_Three, Pr_ThreeIn, Pr_TwoIn, Pr_ThreeIn_Five, PrIn_Three, Sm_Three
In, Sm_TwoIn, SmIn, Sm_ThreeIn_Five, SmIn_Three, Ce_TwoSb, Ce_FiveSb_Three, Ce_Four
Sn_Three, CeSb, CeSn_Two, La_TwoSb, La_ThreeSn_Two, LaSb, LaSb_Two, Nd_TwoS
b, Nd_FiveSb_Three, Nd_FourSn_Three, NdSb, NdSb_Two, Pr_TwoSb, Pr_FiveSn_Three, Pr_Four
Sb_Three, Α-PrSb, β-PrSb, Sb_TwoSm, SbSm, Sb_ThreeSm_Four, Α-Sb_Three
Sm_Five, Β-Sb_ThreeSm_Five, La_FivePb_Three, La_FourPb_Three, La_FivePb_Four, Α-La_ThreeP
b_Four, Β-La_ThreePb_Four, LaPb_Two, LaPb_Three, Ce_TwoPb, CePb, CePb_Three, P
b_ThreePr, Pb_TwoPr, Pb_FourPr_Three, Pb_TenPr₁₁, Pb_FourPr_Five, Pb_ThreePr_Five, PbP
r_Three, Pb_ThreeSm, Pb_TwoSm, Pb_TenSm₁₁, Pb_FourSm_Five, Pb_ThreeSm_Five, PbS
m_Three, La_TwoBi, La_FiveBi_Three, La_FourBi_Three, LaBi, LaBi_Two, Ce_TwoBi, Ce_Five
Bi_Three, Ce_FourBi_Three, CeBi, CeBi_Two, Bi_TwoPr, BiPr, Bi_ThreePr_Five, BiP
r_Two, Nd_TwoBi, Nd_FiveBi_Three, Nd_FourBi_Three, NdBi, NdBi_TwoEtc.
You.

The intermetallic compound phase of Ma and Sn includes:
For example, Sn ₄ P ₃ , Sn ₃ P ₄ , SnP ₃ , V ₃ Sn, V ₂ Sn ₃ , Mn ₃ Sn, Mn
₂ Sn, MnSn ₂ , Cu ₆ Sn ₅ , Cu ₃ Sn, Ag ₃ Sn, Ag ₄ Sn and the like.

The rare earth (R) and Sn are intermetallic compound phases.
RSn_3-X(X = rational number, 0 <X <3)
For example, Ce_ThreeSn, α-Ce_FiveSn_Three, Β-Ce_FiveSn_Three, Ce_Five
Sn_Four, Ce₁₁Sn_Ten, Ce_ThreeSn_Five, Ce_ThreeSn₇, Ce_TwoSn_Five, Α-La_FiveSn_Three,
β-La_FiveSn_Three, La_FiveSn_Four, La₁₁Sn_Ten, LaSn, La_TwoSn_Three, La_ThreeS
n_Five, PrSn_Three, Α-Pr_FiveSn_Three, Β-Pr_FiveSn_Three, Pr_FiveSn_Four, PrSn, α-
Pr _ThreeSn_Five, Β-Pr_ThreeSn_Five, Nd_FiveSn_Three, Nd_FiveSn_Four, Nd₁₁Sn_Ten, NdS
n, Nd_ThreeSn_Five, NdSn_Two, Nd_TwoSn₇, Nd_TwoSn_Five, Sm_FiveSn_Three, Sm_FourSn_Three,
Sm₁₁Sn_Ten, Sm_FiveSn_Four, Sm_TwoSn_Three, SmSn_Two, SmSn_ThreeIs mentioned
You. The RSn_3-XPhase is RSn_ThreeLow Sn content compared to phase
Phase. In other words, it is a phase in which the amount of absorbed Sn is small,
RSn_ThreeVolume expansion due to occlusion / release of Li is smaller than that of phase
No. This phase has a higher charge / discharge capacity as its proportion in the alloy increases.
However, if present in the alloy to some extent, Li
Has the effect of alleviating the volume expansion associated with occlusion and release.

In order to use the alloy represented by the formula (1) as an active material of a negative electrode material, it can be usually used in the form of a powder. twenty five
It is preferably μm. The average particle size of the crystals contained in the powdered alloy is 15 μm to suppress cycle deterioration.
m or less, particularly preferably 10 μm or less. When the average particle size of the crystals is less than 0.1 μm, pulverization of the alloy powder is suppressed, but the surface area is increased, and the oxygen value is extremely increased, so that the charge / discharge efficiency is reduced and the charge / discharge capacity is reduced. It is not preferable.

The alloy represented by the formula (1) may contain oxygen and / or nitrogen and the like due to the manufacturing process and the like in addition to the composition of the formula (1). The oxygen is mainly a rare earth (R)
Alternatively, it is present as an oxide with Sn on the surface of the alloy particles, and forms an oxide film to reduce the volume expansion of the alloy accompanying the charging and discharging of Li. If the proportion of such oxides is too small, the cycle deterioration becomes severe, and if it is too large, Li
The diffusion of ions into the alloy is inhibited, the charge / discharge capacity is reduced, and the occluded Li is oxidized, leading to a reduction in charge / discharge efficiency. Therefore, the content of the oxygen element in the alloy is preferably 0.05 to 5% by weight, more preferably 0.10 to 3% by weight.
Is particularly preferred. Similarly, the nitrogen contained in the alloy can improve the cycle life by containing an appropriate amount.
Therefore, the content ratio of the nitrogen element contained in the alloy is 0.00
It is preferably from 05 to 2% by weight, more preferably from 0.0005 to 0.5% by weight.

The production of the above-mentioned negative electrode material of the present invention includes, for example,
Step of manufacturing a molten alloy having a composition represented by formula (1)
(a), step (b) of cooling and solidifying the molten alloy, and step (c) of subjecting the cooled and solidified alloy to heat treatment under specific conditions. Process
It can also be obtained by a method containing (a) and (b) but not containing step (c).

In the step (a), the raw material of the molten alloy may be a mixture of simple metals having the composition represented by the formula (1) or a mother alloy pre-alloyed. Known methods can be used for the production of the molten alloy, but the high-frequency melting method is preferable, and the arc melting method and the mechanical alloying method are not preferable because the residual metal Sn of the obtained alloy tends to increase. The atmosphere for producing the molten alloy is preferably an inert gas atmosphere to prevent oxidation of the molten metal. Further, in order to improve the yield of the raw materials, the individual raw materials may be melted at a different timing.

In step (b), the molten alloy can be cooled by a known cooling method such as a die casting method, an atomizing method, a roll cooling method, and a rotating electrode method. The atmosphere for cooling the molten alloy is preferably an inert gas atmosphere to prevent oxidation of the obtained alloy. It is desirable that the structure of the cooled and solidified alloy obtained in the step (b) does not contain the Sn single phase, but the Sn single phase can be reduced by the next step or the like. It may contain phases. Therefore, when the content of the Sn single phase is small in the step (b), the step (c) is not necessarily required.

Step (c) is a heat treatment step for the purpose of homogenizing the structure of the cooled and solidified alloy obtained in step (b), improving the crystallinity, reducing the residual metal Sn, and the like. Step (c) can be performed in a rare gas and / or hydrogen gas atmosphere of 0.07 to 10 MPa in order to prevent oxidation of the cooled and solidified alloy and to improve the activity. When a mixed gas of a rare gas and hydrogen gas is used, a mixed gas containing 5% by volume or more of hydrogen gas is preferable. When the pressure of the atmosphere gas is under a high reduced pressure of less than 0.07 MPa, Sn in the alloy
Tends to precipitate on the surface by heat treatment, and when a battery is manufactured from such a material and evaluated, the cycle life tends to be reduced. In the step (c), the alloy cooled in the step (b) is kept in the above atmosphere in a temperature range of 100 to 1150 ° C. for 1 minute to 100 hours. If the heat treatment temperature is lower than 100 ° C., the diffusion of the residual metals Sn and Li is extremely unlikely to occur, and the effect of the heat treatment cannot be obtained. On the other hand, when the temperature exceeds 1150 ° C., the alloy itself is re-melted, so that the cooled and solidified alloys are welded to each other, so that the desired purpose cannot be achieved. The heat treatment time can be appropriately selected from the above range according to the structure, amount, shape, and the like of the alloy to be treated, the heat treatment apparatus to be used, and the like. If it is less than 1 minute, the effect of the heat treatment is not exhibited, and if it exceeds 100 hours, the economic efficiency is impaired.
Preferably it is 30 minutes to 48 hours.

When the alloy obtained in the step (b) contains a residual Sn single phase which adversely affects the cycle characteristics,
Although it can be reduced by (c), in order to further reduce the residual Sn single phase, a step (d) of sieving the alloy obtained in step (c) after pulverizing the alloy can also be performed. In the step (d), the pulverization can be performed by mechanical pulverization or the like. The reason that the Sn single phase can be removed from the pulverized alloy by sieving is that the ductility of the metal Sn is larger than the intermetallic compound in the alloy, so the intermetallic compound is preferentially pulverized, and the Sn single phase is removed. This is because the particle size increases. The standard of the particle size at the time of sieving is preferably 25 to 200 μm, particularly preferably 50 to 100 μm.

The negative electrode for a lithium ion secondary battery of the present invention contains the above-described negative electrode material of the present invention as an active material, and can be obtained according to any known method for producing an electrode. For example, a suitable binder is mixed with the powder of the negative electrode material of the present invention, and a suitable conductive powder is mixed as needed to improve conductivity. A solvent in which the binder is dissolved is added to the mixture, and if necessary, the mixture is sufficiently stirred with a homogenizer or the like to form a slurry. The obtained slurry is applied to an electrode substrate (current collector) such as a rolled copper foil or an electrolytic copper foil using a doctor blade or the like, dried, and then roll-rolled or the like to consolidate the electrode active material. Can be manufactured.

Examples of the binder include water-insoluble resins such as PVDF (polyvinylidene fluoride), PMMA (polymethyl methacrylate), and PTFE (polytetrafluoroethylene); CMC (carboxymethyl cellulose);
And water-soluble resins such as VA (polyvinyl alcohol). Examples of the solvent include an organic solvent such as NMP (N-methylpyrrolidone) and DMF (dimethylformamide), or water. Examples of the conductive powder include carbon materials such as acetylene black, Ketjen black, and graphite;
And the like. In particular, the carbon material is preferable because it can occlude Li between the layers, and can contribute to the charge and discharge capacity of the negative electrode in addition to the conductivity.

In producing the negative electrode of the present invention, the negative electrode material of the present invention used as an active material usually contains 50 to 50% in the active material.
It is preferable to contain 100% by weight, particularly 80 to 100% by weight. In particular, in the negative electrode material of the present invention, the alloy having the composition represented by the formula (1) does not contain Li, or
In the case of an alloy containing only less than the required initial irreversible component in the desired composition alloy, in addition to the negative electrode material of the present invention as an active material, metal Li, LiH (lithium hydride), Li ₃ A lithium source such as N (lithium nitride) can be included. By using such a lithium supply source, irreversible Li at the time of initial charge / discharge is compensated.However, if the content ratio of the lithium supply source in the negative electrode active material is too large, there may be a problem in handleability. There is. In addition, since the lithium source has a low density,
If the content ratio in the negative electrode active material is too large, the energy density of the battery will be reduced. Therefore, when a lithium supply source is used, the content ratio in the active material is less than 50% by weight, particularly considering the initial charge and discharge efficiency of the alloy composition,
Less than 20% by weight is preferred.

The lithium ion secondary battery of the present invention may be provided with the above-described negative electrode of the present invention, and usually includes, as its basic structure, the negative electrode of the present invention, a positive electrode, a separator and a non-aqueous electrolyte such as a polymer electrolyte. . These battery constituent materials can be configured by appropriately combining known materials except for the negative electrode. The shape of the secondary battery is not particularly limited,
Any of cylindrical, square, coin, and seal types may be used.

[0029]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto. still,
The raw materials used in the examples used materials of 99.5% or more.
Misch metal (Mm) is La: Ce: Nd: P in weight ratio.
r: A rare earth alloy manufactured by Santoku Co., Ltd. having an Sm of 28: 51: 16: 4: 1 was used. Preparation of negative electrode material alloy for lithium ion secondary batteries of Examples 1 to 20 and Comparative Examples 1 to 2 After high-frequency melting of a metal mixture constituting the composition shown in Table 1, the resulting molten metal was molded using a copper mold. Casting method (mold method)
Alternatively, a flake-shaped alloy piece was obtained by a strip casting method (SC method) in which a molten metal was poured into a rotating roll via a tundish. Next, the respective alloys obtained in Examples 2 to 5, 7, 9 to 13 and 15 were subjected to a heat treatment under the conditions shown in Table 1. Each alloy piece that had not been subjected to the heat treatment and each alloy piece that had been subjected to the heat treatment were pulverized by a mechanical pulverization method in an argon gas atmosphere, and classified using a sieve to 25 μm or less to produce a negative electrode material alloy. The production of the molten alloy and the cooling of the molten alloy were each performed in an argon gas atmosphere. Next, the composition of each of the obtained powder alloys was measured by elemental analysis, and it was confirmed that the composition was as shown in Table 1. Further, the constituent phases of each powder alloy were measured by powder X-ray diffraction (XRD), and the precipitation ratio of residual metal Sn in the constituent phases was defined as (W), which was calculated and evaluated according to the following equation. Table 1 shows the results. (W) = (Peak intensity of metal Sn (200) plane / strongest peak intensity among peaks derived from RSn ₃ ) × 100

Preparation of negative electrode for lithium ion secondary battery and
Charge / discharge test method: The above prepared alloy powder as the negative electrode active material, Ketjen black as a conductive additive, and PVDF as a binder were mixed at a weight ratio of 85: 5: 10, and an appropriate amount of NMP was added. After adding and kneading, apply to an electrolytic copper foil having a thickness of 18 μm,
After being preliminarily dried in a drier of No. 1, the powder was consolidated by a roller press. Punch it into a size of 1.0cm in diameter, 130
A test electrode was prepared by vacuum drying at ° C. The obtained test electrode, a polypropylene porous film as a separator, metallic lithium as a counter electrode, and a mixed solvent of ethylene carbonate (EC): dimethyl carbonate (DMC) = 1: 2 (volume ratio) as an electrolytic solution And a solution in which LiPF ₆ was dissolved at a concentration of 1 mol was prepared.
0-1 at a current density of 0.2 mA / cm ² in the cell temperature 25 ° C..
A constant current charge / discharge test was performed in the potential range of 0 V vs. Li / Li ⁺ . Further, a capacity retention ratio (S) as an index indicating how much the maximum discharge capacity was maintained at the 50th cycle was calculated and evaluated by the following formula. (S) = discharge capacity at 50th cycle / maximum discharge capacity × 100 (%) Furthermore, the initial charge / discharge efficiency (Z) as an index indicating the ratio of the initial discharge capacity to the initial charge capacity was calculated by the following equation. evaluated. (Z) = initial discharge capacity / initial charge capacity × 100 (%) The above results are shown in Table 1. The cell assembly and charge / discharge test were performed in a glove box under an argon gas atmosphere.

Comparative Example 3 A charge / discharge test was performed in the same manner as in Example 1 except that artificial graphite was used as a test electrode. Table 1 shows the results.

[0032]

[Table 1]

From Table 1, in LixRSn ₃ of Examples 1 to 20, R
In Examples 1 to 15 using Ce or Mm, the initial discharge capacity and initial charge / discharge efficiency are clearly superior to those in Examples 16 to 20 using other rare earth elements. In particular, Examples 6 and 7 show that heat treatment improves cycle life. In Comparative Examples 1 and 2 having a composition not containing a rare earth element,
It can be seen that both the discharge capacity and the cycle characteristics are low. The discharge capacity per weight of Examples 1 to 20 was 1.5 times or more higher than the graphite of Comparative Example 3, and the initial charge / discharge efficiency was also almost the same as that of graphite. It turns out that it shows a characteristic.

Examples 21-32 and Comparative Examples 4-5 Residual metal was prepared in the same manner as in Example 1 except that the alloy compositions were changed to the compositions shown in Table 2 and the heat treatment conditions for the alloy pieces were changed to the conditions shown in Table 2. Measurement of the precipitation ratio (W) of Sn, preparation of the cell, and charge / discharge test (initial discharge capacity and initial charge / discharge efficiency) were performed. Table 2 shows the results.

[0035]

[Table 2]

From Table 2, Examples 21 to 32 show that the substitution element (Ma)
It can be seen that the initial discharge capacity is clearly increased as compared with Comparative Examples 4 and 5 in which the ratio is out of the range of the present invention.

Examples 33 to 54 and Comparative Example 6 The same procedure as in Example 1 was carried out except that the alloy composition was changed to the composition shown in Table 3 and the heat treatment conditions for the alloy pieces were changed to the conditions shown in Table 3. The deposition ratio (W) was measured, the cell was prepared, and a charge / discharge test (initial charge / discharge efficiency and capacity retention at the 50th cycle) was performed. Table 3 shows the results.

[0038]

[Table 3]

From Table 3, it can be seen that Comparative Example 6, which has a substitution element other than the substitution element (Mb) in the present invention, has a clearly lower capacity retention ratio than Examples 33 to 54, which have the substitution element (Mb). I understand. Further, in the example in which the cycle life using the heat-treated alloy is improved, the intermetallic compound phase of the substitution element (Mb) and the rare earth (R) by the XRD measurement, the substitution element (Mb)
Intermetallic compound phase of Sn and Sn, RSn ₃ phase (R <0), substitution element (Mb)
It was confirmed that the simple substance was precipitated in a complex manner.

Examples 55-68 and Comparative Examples 7-8 Residual metals were prepared in the same manner as in Example 1 except that the alloy compositions were changed to the compositions shown in Table 4 and the heat treatment conditions for the alloy pieces were changed to the conditions shown in Table 4. Measurement of the precipitation ratio (W) of Sn, production of a cell, and charge / discharge test were performed. Table 4 shows the results.

[0041]

[Table 4]

In Examples 55 to 68 containing the substitution elements (Ma, Mb), the Sn content was lower than the range of the present invention, and the substitution element (Ma, Mb) content was higher than the range of the present invention. Comparative example
It turns out that it shows high initial discharge capacity compared with 7 and 8.

Examples 69 to 71 In the same manner as in Example 1, except that the alloy composition was changed to the composition shown in Table 5, and a Li source shown in Table 5 was added as a negative electrode active material at the time of producing a test electrode, Fabrication and charge / discharge tests were performed. Table 5 shows the results.

[0044]

[Table 5]

Examples 69 to 71 are compositions containing no Li in the alloy, and Example 72 is a composition having a low Li ratio.
It can be seen that the coexistence of H and LiN in the negative electrode active material provides a negative electrode having excellent initial discharge capacity, initial charge / discharge efficiency, and cycle characteristics.

Examples 73 to 74 Alloy pieces containing the amounts of oxygen and nitrogen shown in Table 6 were prepared in the same manner as in Example 1, and the deposition rate (W) of the residual metal Sn was measured. Was done. Table 6 shows the results.

[0047]

[Table 6]

[0048]

The negative electrode for a lithium ion secondary battery of the present invention uses the negative electrode material of the present invention containing an alloy having a specific composition as an active material, and thus has excellent initial charge / discharge efficiency and suppresses cycle deterioration accompanying charge / discharge. And a particularly good discharge capacity is achieved.
Further, the negative electrode material of the present invention is useful for producing such a negative electrode. Therefore, the negative electrode material and the negative electrode of the present invention can make a lithium ion secondary battery using a carbon material negative electrode that is currently in practical use higher in capacity and more compact, and extremely useful for industrial use. high.

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (Reference) H01M 4/02 H01M 4/02 D 4/38 4/38 Z 4/58 4/58 10/40 10/40 Z ( 72) Inventor Tetsuo Sakai 1-31-31 Midorioka, Ikeda-shi, Osaka F-term in the National Institute of Advanced Industrial Science and Technology (Reference) 4K018 AA13 AA40 BB04 BC06 FA03 JA01 KA38 5H029 AJ02 AJ03 AJ05 AJ14 AK11 AL11 AM05 AM07 CJ02 CJ28 DJ16 DJ17 EJ04 EJ12 HJ01 HJ02 HJ05 HJ13 HJ14 HJ15 5H050 AA02 AA07 AA08 AA19 BA17 CA17 CB11 EA02 EA10 EA11 EA21 EA23 EA24 FA17 FA19 GA02 GA05 GA17 GA27 HA01 HA02 HA05 HA13 HA14 HA15 HA20

Claims (15)

[Claims] 1. A negative electrode material for a lithium ion secondary battery comprising an alloy having a composition represented by the formula (1). (Li) x (R) y (Sn) z (Ma) w (Mb) v ・ ・ ・ (1) (where R is selected from the group consisting of elements from lanthanide series La to Lu including Y and Sc One or two or more, Ma is
B, C, Si, P, Al, Zn, V, Mn, Cu, Ag, In, Sb, Pb and
One or more selected from the group consisting of Bi, Mb is Ti,
V, Cr, Fe, Co, Ni, Cu, B, Mg, Zr, Hf, Nb, Ta and Mo
Ma ≠ Mb in at least one kind selected from the group consisting of
x, y, z are each a molar ratio, 0 ≦ x ≦ 13, 0.70 ≦ y ≦ 1.1
0, 2.20 ≦ z ≦ 3.50, 0 ≦ w ≦ 0.70, 0 ≦ v ≦ 0.70, 0 ≦ w + v ≦
It is 0.70. ) 2. R of the formula (1) is Ce alone, or 90 mol with Ce.
Lanthanide series La to L containing less than% Y and Sc other than Ce
2. The negative electrode material according to claim 1, comprising one or more selected from the group consisting of elements up to u. 3. The peak intensity of the Sn (200) plane in the powder X-ray diffraction of the alloy represented by the formula (1) has _three phases of RSn (R is the same as R in the formula (1)). 3. The negative electrode material according to claim 1, which has 30% or less of the strongest peak intensity among peaks derived from (1). 4. An alloy represented by the formula (1) is composed of Ma and a rare earth (R).
Intermetallic compound phase of Mb and rare earth (R), intermetallic compound phase of Ma and Sn, intermetallic compound phase of Mb and Sn, intermetallic phase of rare earth (R) and Sn At least one of the compound phases
The negative electrode material according to any one of claims 1 to 3, which has a kind of intermetallic compound phase. 5. The intermetallic compound phase of the rare earth (R) and Sn is represented by RS
5. The negative electrode material according to claim 4, wherein n _3-X (R is the same as R in the formula (1)), wherein X is a rational number and 0 <X <3. 6. The form of the alloy represented by the formula (1) is an average particle size.
The negative electrode material according to any one of claims 1 to 5, which is a powder of 0.1 to 25 µm. 7. The alloy represented by the formula (1) is capable of adding oxygen to 0.05 to 5
The negative electrode material according to any one of claims 1 to 6, wherein the negative electrode material comprises 0.1% by weight. 8. The alloy represented by the formula (1) contains nitrogen from 0.0005 to 0.0005.
The negative electrode material according to any one of claims 1 to 7, comprising 2% by weight. 9.A step (a) of producing a molten alloy having a composition represented by the formula (1), a step (b) of cooling and solidifying the produced molten alloy, and cooling and solidifying the alloy to a pressure of 0.07 to 10 MPa. The negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 8, including a step (c) of maintaining the composition in a rare gas and / or hydrogen gas at a temperature in a range of 100 to 1150 ° C for 1 minute to 100 hours. Manufacturing method. 10. The production method according to claim 9, wherein the production of the molten alloy in the step (a) is performed by a high-frequency melting method. 11. After grinding the alloy produced in step (c),
Sieving, comprising a step (d) of removing the Sn single phase portion or claim 9 or
10. The production method according to 10. A negative electrode for a lithium ion secondary battery, comprising the negative electrode material according to any one of claims 1 to 8 as an active material. 13. The active material further comprises one or more selected from the group consisting of metal Li, LiH and Li ₃ N.
The negative electrode as described. 14. The negative electrode according to claim 12, wherein a content ratio of the negative electrode material according to any one of claims 1 to 8 in the active material is 50% by weight or more. A lithium ion secondary battery comprising the negative electrode according to any one of claims 12 to 14.