JP5779452B2 - Negative electrode active material for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a negative electrode active material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery.

  Nonaqueous electrolyte secondary batteries are used as power sources for portable electronic devices such as personal computers and mobile phones. In recent years, with the reduction in size and weight of these portable devices, there is an increasing demand for higher capacity and higher energy density of nonaqueous electrolyte secondary batteries. There is also a need for improved cycle characteristics of nonaqueous electrolyte secondary batteries.

  For example, Patent Document 1 proposes a lithium-ion secondary battery with improved capacity and excellent cycle characteristics, in which graphite used for the negative electrode active material is improved.

JP 2009-245613 A

  The main object of the present invention is to provide a negative electrode active material capable of increasing the capacity of a non-aqueous electrolyte secondary battery and improving cycle characteristics, and a non-aqueous electrolyte secondary battery.

The negative electrode active material of the nonaqueous electrolyte secondary battery of the present invention includes graphite and a zinc alloy. The zinc alloy is represented by a general formula: M _x Zn _1-x . In the general formula, M represents at least one selected from the group consisting of Ni, Cu and Fe. In the general formula (1), x satisfies the relationship 0 <x <1.

  The zinc alloy is preferably polycrystalline.

  In the general formula, M is preferably Ni.

  In the general formula, x preferably satisfies the relationship 0 <x ≦ 0.01.

  In the general formula, x preferably satisfies the relationship 0 <x ≦ 0.0015.

  The zinc alloy is preferably contained in the negative electrode active material in the range of 1% by mass to 80% by mass.

  The zinc alloy is preferably contained in the negative electrode active material in the range of 10% by mass to 50% by mass.

  The nonaqueous electrolyte secondary battery of the present invention includes a negative electrode including a negative electrode active material of the nonaqueous electrolyte secondary battery of the present invention, a positive electrode, and a nonaqueous electrolyte.

  ADVANTAGE OF THE INVENTION According to this invention, the negative electrode active material which can make a nonaqueous electrolyte secondary battery high capacity | capacitance, and can improve cycling characteristics can be provided, and a nonaqueous electrolyte secondary battery.

It is a schematic sectional drawing of the test cell produced in the Example.

  Hereinafter, an example of a preferred embodiment of the present invention will be described. However, the following embodiment is merely an example. The present invention is not limited to the following embodiments.

[Negative electrode active material]
In the present embodiment, the negative electrode active material of the nonaqueous electrolyte secondary battery includes graphite and a zinc alloy.

  Examples of graphite include natural graphite, artificial graphite, and mesophase carbon microspheres.

  The shape of the graphite is not particularly limited, but is preferably a powder.

  The average particle diameter of the graphite is preferably about 5 μm to 30 μm, and more preferably about 10 μm to 25 μm. In the present invention, the average particle diameter of graphite is a value measured using a laser diffraction particle size distribution analyzer (SALAD-2000) manufactured by Shimadzu Corporation.

  Graphite is preferably contained in the negative electrode active material in a range of about 20% by mass to 99% by mass, and more preferably in a range of about 50% by mass to 90% by mass.

  Only one type of graphite may be contained in the negative electrode active material, or two or more types may be used.

  The zinc alloy is a compound represented by the following general formula (1).

M _x Zn _1-x (1)

  In the general formula (1), M is at least one selected from the group consisting of Ni, Cu and Fe. M is preferably Ni.

  Although the shape of a zinc alloy is not specifically limited, It is preferable that it is a powder form.

  The average particle diameter of the zinc alloy is preferably about 5 μm to 25 μm, and more preferably about 10 μm to 20 μm. In addition, in this invention, the average particle diameter of a zinc alloy is the value measured using the Shimadzu Corporation laser diffraction type particle size distribution measuring apparatus (SALAD-2000).

  The zinc alloy is preferably polycrystalline.

  In the general formula (1), x satisfies the relationship 0 <x <1. In the general formula (1), x preferably satisfies the relationship 0 <x ≦ 0.01, more preferably satisfies the relationship 0 <x ≦ 0.0015, and the relationship 0 <x ≦ 0.0005. It is particularly preferable to satisfy The lower limit value of x is more preferably 0.00001.

  In general formula (1), when x satisfies the relationship x ≦ 0.01, zinc and M (at least one selected from the group consisting of Ni, Cu and Fe) can be easily alloyed. it can.

  The zinc alloy represented by the general formula (1) can be obtained by a known method such as a gas atomizing method or a water atomizing method.

  The zinc alloy is preferably included in the negative electrode active material in the range of about 1% by mass to 80% by mass, and more preferably in the range of about 10% by mass to 50% by mass.

  There may be only one type of zinc alloy contained in the negative electrode active material, or two or more types.

  The negative electrode active material can be obtained by mixing graphite and a zinc alloy. The mixing ratio of graphite and zinc alloy (graphite: zinc alloy) is preferably in the range of about 99: 1 to 20:80 by mass ratio, and more preferably in the range of about 90:10 to 50:50. preferable.

  The method for mixing graphite and zinc alloy is not particularly limited as long as it can be mixed so that graphite and zinc alloy are uniformly dispersed in the negative electrode active material.

[Negative electrode]
The negative electrode active material is mixed with a binder, a solvent, and the like, and integrated with the negative electrode current collector, whereby the negative electrode of the nonaqueous electrolyte secondary battery can be obtained. More specifically, a slurry containing a negative electrode active material, a binder and a solvent is prepared, applied to the negative electrode current collector, dried, rolled using a rolling roller, and non-aqueous electrolyte secondary It can be a negative electrode of a battery.

[Nonaqueous electrolyte secondary battery]
The nonaqueous electrolyte secondary battery includes the above-described negative electrode, positive electrode, and nonaqueous electrolyte.

  The positive electrode includes a positive electrode active material. The positive electrode active material is mixed with a binder, a solvent, and the like, and integrated with the positive electrode current collector, whereby the positive electrode of the nonaqueous electrolyte secondary battery can be obtained.

As the positive electrode active material, known materials generally used in non-aqueous electrolyte secondary batteries can be used. Examples of the positive electrode active material include lithium-cobalt composite oxide (for example, LiCoO ₂ ), lithium-nickel composite oxide (for example, LiNiO ₂ ), lithium-manganese composite oxide (for example, LiMn ₂ O ₄ , LiMnO ₂ ), lithium Nickel-cobalt composite oxide (for example, LiNi _1-x Co _x O ₂ ), lithium-manganese-cobalt composite oxide (for example, LiMn _1-x Co _x O ₂ ), lithium-nickel-cobalt-manganese composite oxide ( For example, LiNi _x Co _y Mn _z O ₂ (x + y + z = 1)), lithium-nickel-cobalt-aluminum composite oxide (for example, LiNi _x Co _y Al _z O ₂ (x + y + z = 1)), Li-containing transition metal oxide, etc. Is mentioned. The positive electrode active material may be composed of only one type or a mixture of two or more types.

  Examples of the binder contained in the positive electrode include polyvinylidene fluoride.

  Examples of the solvent contained in the positive electrode include aprotic solvents such as N-methyl-2-pyrrolidone.

  As the nonaqueous electrolyte, those generally used in known nonaqueous electrolyte secondary batteries can be used. As the non-aqueous electrolyte, for example, a non-aqueous electrolyte solution in which a solute is dissolved in a non-aqueous solvent can be used.

As the non-aqueous solvent, a non-aqueous electrolyte generally used in known non-aqueous electrolyte secondary batteries can be used. Examples of non-aqueous solvents include cyclic carbonates and chain carbonates. As the cyclic carbonate, for example, ethylene carbonate, propylene carbonate, vinylene carbonate and the like can be used. Examples of the chain carbonate include dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate. The non-aqueous solvent may consist of only one type or a mixture of two or more types.

As the solute, a non-aqueous electrolyte generally used in known non-aqueous electrolyte secondary batteries can be used. Examples of the solute include LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , LiClO ₄ , Li ₂ B ₁₀ Cl ₁₀ , Li ₂ B ₁₂ Cl _{12 and the} like. The solute may consist of only one type or a mixture of two or more types.

  Further, as the non-aqueous electrolyte, a gel polymer electrolyte obtained by impregnating a non-aqueous electrolyte solution with a polymer electrolyte such as polyethylene oxide or polyacrylonitrile can be used.

  In the nonaqueous electrolyte secondary battery of the present embodiment, when the zinc alloy contained in the negative electrode active material is an alloy of zinc and Ni, Cu, or Fe, the zinc alloy tends to be polycrystalline. In particular, in the case of an alloy of zinc and Ni, the zinc alloy tends to be polycrystalline. When the zinc alloy contained in the negative electrode active material is polycrystalline, the active surface of the electrode reaction increases. Therefore, when the zinc alloy contained in the negative electrode active material is an alloy of zinc and Ni, Cu or Fe, particularly when the zinc alloy is an alloy of zinc and Ni, the capacity of the nonaqueous electrolyte secondary battery is further increased. And high energy density.

In the nonaqueous electrolyte secondary battery of the present embodiment, the zinc alloy represented by the general formula (1): M _x Zn _1-x preferably satisfies the relationship of 0 <x ≦ 0.01. This is because alloying becomes easy. Further, when x satisfies the relationship of 0 <x ≦ 0.0015, the nonaqueous electrolyte secondary battery can have a higher capacity and higher energy density, and the relationship of x is 0 <x ≦ 0.0005. When satisfying the above, it is possible to increase the capacity and the energy density of the nonaqueous electrolyte secondary battery.

  Furthermore, in the non-aqueous electrolyte secondary battery of this embodiment, in addition to graphite, zinc alloy is contained in the negative electrode active material in the range of 1% by mass to 80% by mass. The battery can be increased in capacity and energy density. In particular, when the zinc alloy is contained in the range of 10% by mass to 50% by mass, the nonaqueous electrolyte secondary battery can be further increased in capacity and energy density.

  Hereinafter, the present invention will be described in more detail on the basis of specific examples. However, the present invention is not limited to the following examples, and may be appropriately modified and implemented without departing from the scope of the present invention. Is possible.

Example 1
[Preparation of zinc alloy powder]
As a zinc alloy powder, a nickel zinc alloy (Ni _0.00050 Zn _0.99950 ) powder having an average particle size of about 20 μm was prepared by a water atomization method. The average particle size of the nickel zinc alloy was measured using SALAD-2000 manufactured by Shimadzu Corporation as a laser diffraction particle size distribution measuring device, and the powder resistance was measured using PD-41 manufactured by Mitsubishi Chemical Corporation as a powder resistance measuring system. .

[Production of negative electrode]
As the negative electrode active material, the nickel-zinc alloy obtained as described above and artificial graphite having an average particle diameter of about 25 μm were used. The nickel zinc alloy and the artificial graphite were mixed using a mortar so that the mass ratio (nickel zinc alloy: artificial graphite) was 30:70. Next, polyvinylidene fluoride as a binder was mixed with the obtained mixture so that the mass ratio of the negative electrode active material to the binder (negative electrode active material: binder) was 90:10. Further, N-methyl-2-pyrrolidone was added as a solvent and kneaded to prepare a negative electrode mixture slurry.

  The obtained negative electrode mixture slurry was applied onto a negative electrode current collector made of a copper foil having a thickness of 10 μm. After drying this at 80 degreeC, it rolled using the rolling roller, the current collection tab was attached, and the negative electrode was produced.

[Production of test cell]
Using the above negative electrode, a test cell 1 as shown in FIG. 1 was produced in a glove box under an argon atmosphere. The negative electrode was used as the working electrode 2, and metallic lithium was used as the counter electrode 3 and the reference electrode 4. Electrode tabs 8 were attached to the working electrode 2, the counter electrode 3, and the reference electrode 4, respectively. A polyethylene separator 5 is interposed between the working electrode 2 and the counter electrode 3, and between the working electrode 2 and the reference electrode 4, and enclosed in a laminate container 7 made of an aluminum laminate together with a non-aqueous electrolyte 6. Thus, a test cell A1 of Example 1 was obtained.

In addition, as a non-aqueous electrolyte solution 6, lithium hexafluorophosphate (LiPF ₆ ) is mixed to a mixed solvent in which ethylene carbonate and ethyl methyl carbonate are mixed at a volume ratio of 3: 7 so that the concentration becomes 1 mol / liter. What was dissolved was used.

(Example 2)
Test cell A2 was produced in the same manner as in Example 1 except that Cu _0.00050 Zn _0.99950 was used instead of Ni _0.00050 Zn _0.99950 as the zinc alloy powder.

(Example 3)
Test cell A3 was produced in the same manner as in Example 1 except that Fe _0.00050 Zn _0.99950 was used instead of Ni _0.00050 Zn _0.99950 as the zinc alloy powder.

(Comparative Example 1)
The test cell X of Comparative Example 1 was _{prepared in the same} manner as in Example 1 except that artificial graphite was not added as the negative electrode active material and only zinc alloy powder Ni _0.00050 Zn _0.99950 was used as the negative electrode active material. Produced.

(Comparative Example 2)
A test cell Y of Comparative Example 2 was produced in the same manner as in Example 1 except that artificial graphite was not added as the negative electrode active material and only pure zinc powder was used as the negative electrode active material.

(Comparative Example 3)
A test cell Z of Comparative Example 3 was produced in the same manner as in Example 1 except that only artificial graphite was used as the negative electrode active material.

[Charge / discharge test]
The following charge / discharge tests were performed on the test cells A1 to A3 prepared in Examples 1 to 3 and the test cells X to Z prepared in Comparative Examples 1 to 3 prepared as described above.

For each test cell, at room ^temperature, 0.75 mA / cm 2, at the constant current of 0.25 mA / cm ² and 0.1 mA / cm ^2, were charged to the respective reaches 0V (vs.Li/Li ⁺⁾ The battery was discharged at a constant current of 0.25 mA / cm ² until the potential reached 1.0 V (vs. Li / Li ⁺ ), and the initial discharge capacities at the first and sixth cycles were obtained. The results are shown in Table 1.

  From the results shown in Table 1, in test cells A1 to A3 in which artificial graphite and zinc alloy (nickel zinc alloy, copper zinc alloy or iron zinc alloy) are used as the negative electrode active material, pure zinc or artificial graphite is used alone as the negative electrode active material. It can be seen that the initial discharge capacity and the sixth cycle discharge capacity are larger than those of the test cells Y and Z used in FIG. Moreover, test cell A1-A3 shows that an initial stage discharge capacity and a 6th cycle discharge capacity are large compared with the test cell X which uses only a nickel zinc alloy as a negative electrode active material. In particular, for the sixth cycle discharge capacity, the test cells A1 to A3 are significantly larger than the test cells X to Z.

  In addition, it turns out that the zinc alloy used by test cell A1-A3 and X is polycrystallized from the value of the powder resistance of a negative electrode active material. It can be seen that in the nickel-zinc alloys of test cells A1 and X, polycrystallization is particularly advanced.

Example 4
As zinc _alloy, Ni except for using _{Ni 0.00010} Zn _.99990 instead of _{0.00050 Zn .99950,} to prepare a test cell A4 in the same manner as in Example 1. The powder resistance of the zinc alloy was 1.20 Ω / cm ³ .

(Example 5)
As zinc _alloy, Ni except for using _{Ni 0.00025} Zn _0.99975 instead of _{0.00050 Zn .99950,} to prepare a test cell A5 in the same manner as in Example 1. The powder resistance of the zinc alloy was 1.30 Ω / cm ³ .

(Example 6)
As zinc _alloy, Ni except for using _{Ni 0.00075} Zn _.99925 instead of _{0.00050 Zn .99950,} to prepare a test cell A6 in the same manner as in Example 1. The powder resistance of the zinc alloy was 1.45 Ω / cm ³ .

(Example 7)
As the zinc alloy _powder, Ni except for using _{Ni 0.00100} Zn _0.99900 instead of _{0.00050 Zn 0.99950,} to prepare a test cell A7 in the same manner as in Example 1. The powder resistance of the zinc alloy was 1.30 Ω / cm ³ .

(Example 8)
As zinc _alloy, Ni except for using _{Ni 0.00150} Zn _0.99850 instead of _{0.00050 Zn .99950,} to prepare a test cell A8 in the same manner as in Example 1. The powder resistance of the zinc alloy was 1.10 Ω / cm ³ .

[Charge / discharge test]
About each test cell A4-A8 produced in Examples 4-8, it carried out similarly to Examples 1-3 and Comparative Examples 1-3, the charge / discharge test was done, and the initial stage discharge capacity was measured. The results are shown in Table 2 together with the results of the test cell A1 of Example 1.

From the results shown in Table 2, it can be seen that when a zinc alloy satisfying the relationship of 0 <x ≦ 0.0015 is used, _x of Ni _x Zn _1-x exhibits a high initial discharge capacity. When a zinc alloy satisfying a relationship of 0 <x ≦ 0.001 is used for _x of Ni _x Zn _1-x, a higher initial discharge capacity is exhibited, and x satisfies a relationship of 0 <x ≦ 0.0005. It can be seen that when a zinc alloy is used, a particularly high initial discharge capacity is exhibited.

Example 9
The negative electrode active material was the same as in Example 1 except that the mixing ratio of the nickel zinc alloy and the artificial graphite was 5:95 instead of 30:70 (nickel zinc alloy: artificial graphite) in mass ratio. Thus, a cell A9 was produced.

(Example 10)
The negative electrode active material was the same as in Example 1 except that the mixing ratio of the nickel zinc alloy and the artificial graphite was 10:90 instead of 30:70 (nickel zinc alloy: artificial graphite) in mass ratio. Thus, a cell A10 was produced.

(Example 11)
The negative electrode active material was the same as Example 1 except that the mixing ratio of the nickel zinc alloy and artificial graphite was 50:50 instead of 30:70 (nickel zinc alloy: artificial graphite) in mass ratio. Thus, a cell A11 was produced.

(Example 12)
The negative electrode active material was the same as in Example 1 except that the mixing ratio of the nickel zinc alloy and artificial graphite was 65:35 instead of 30:70 (nickel zinc alloy: artificial graphite) in mass ratio. Thus, a cell A12 was produced.

(Example 13)
In the negative electrode active material, the mixing ratio of the nickel zinc alloy and the artificial graphite was the same as that of Example 1 except that the mixing ratio was 80:20 instead of 30:70 (nickel zinc alloy: artificial graphite). Thus, a cell A13 was produced.

[Charge / discharge test]
About each test cell A9-A13 produced in Examples 9-14, it carried out similarly to Examples 1-3 and Comparative Examples 1-3, the charge / discharge test was done, and the initial stage discharge capacity was measured. The results are shown in Table 3 together with the results of the test cell A1 of Example 1.

  From the results shown in Table 3, it can be seen that high initial discharge capacity can be obtained when the zinc alloy powder is contained in the negative electrode active material in the range of 5 to 80% by mass. It can be seen that a particularly high initial discharge capacity can be obtained when the negative electrode active material contains zinc alloy powder in the range of 10 to 50 mass%.

DESCRIPTION OF SYMBOLS 1 ... Test cell 2 ... Working electrode 3 ... Counter electrode 4 ... Reference electrode 5 ... Separator 6 ... Non-aqueous electrolyte 7 ... Laminate container 8 ... Electrode tab

Claims (7)

Graphite,
General formula: M _x Zn _1-x (wherein M represents at least one selected from the group consisting of Ni, Cu and Fe. X satisfies the relationship 0 <x < 0.01 ). A zinc alloy represented,
A negative electrode active material for a non-aqueous electrolyte secondary battery.   The negative electrode active material of the nonaqueous electrolyte secondary battery according to claim 1, wherein the zinc alloy is polycrystalline.   The negative electrode active material of the nonaqueous electrolyte secondary battery according to claim 1, wherein M is Ni in the general formula. 4. The negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 , wherein x in the general formula satisfies a relationship of 0 <x ≦ 0.0015. 5. The said zinc alloy is a negative electrode active material of the nonaqueous electrolyte secondary battery as described in any one of Claims 1-4 contained in the range of 1 mass%-80 mass% in the said negative electrode active material. The said zinc alloy is a negative electrode active material of the nonaqueous electrolyte secondary battery of Claim 5 contained in the range of 10 mass%-50 mass% in the said negative electrode active material. A negative electrode comprising the negative electrode active material according to any one of claims 1 to 6 ,
A positive electrode;
A non-aqueous electrolyte,
A non-aqueous electrolyte secondary battery.

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