JP2013051148A - Negative electrode active material for nonaqueous electrolytic secondary battery, and nonaqueous electrolytic secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolytic secondary battery having an enhanced initial discharge capacity.SOLUTION: The negative electrode active material comprises zinc and a metal which serves as a negative electrode active material and which does not react with lithium; the zinc is coated with the metal. The formation of zinc oxide on the surface of the zinc particle caused by oxygen in the air can be suppressed by coating the zinc with the metal which never reacts with lithium. The oxygen included in the zinc oxide causes the following reaction at the times of charge and discharge: O+2 Li→LiO. Since the reaction is irreversible, the initial discharge capacity of the zinc particle is reduced. However, coating the zinc with the metal which never reacts with lithium, the surface of the zinc particle is not oxidized, and therefore the irreversible reaction is not caused. Consequently, a high initial discharge capacity can be obtained.

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 using the same.

  Graphite (Patent Document 1) conventionally used as a negative electrode active material is excellent in chemical durability and structural stability, and has high reversibility of lithium insertion and release reactions. Furthermore, there is an advantage that the operating potential is low and the flatness of the charge / discharge curve is excellent, and it is widely used for power supplies for mobile devices.

JP2009-245613

  However, graphite has a problem that the initial discharge capacity is not sufficiently high. The main object of the present invention is to increase the initial discharge capacity of the nonaqueous electrolyte secondary battery.

  A negative electrode active material for a non-aqueous electrolyte secondary battery according to one aspect of the present invention includes zinc coated with a metal that does not react with lithium. A nonaqueous electrolyte secondary battery according to one aspect of the present invention includes a positive electrode, a negative electrode, and a nonaqueous electrolyte, and the negative electrode includes a negative electrode active material containing zinc coated with a metal that does not react with lithium. It is characterized by.

  According to the present invention, the initial discharge capacity of the nonaqueous electrolyte secondary battery can be increased.

Schematic diagram of the cell

  The negative electrode active material for a non-aqueous electrolyte secondary battery used in the present invention contains zinc coated with a metal that does not react with lithium. It is preferable that 10-90 mass% of zinc is contained with respect to the total amount of a negative electrode active material. The metal is preferably copper or nickel. The metal is preferably contained in an amount of 0.05 to 10.0% by mass with respect to the total amount of zinc. As a method for coating copper or nickel, a method in which zinc is mixed in a weak acid or weak alkali aqueous solution and zinc oxide on the zinc surface is removed, and then a copper or nickel salt aqueous solution is dropped.

  The negative electrode active material preferably further contains graphite. Moreover, it is preferable that 10 to 90 mass% of graphite is contained with respect to the total amount of a negative electrode active material.

  As the positive electrode active material used in the present invention, a positive electrode active material conventionally used in non-aqueous electrolyte secondary batteries can be used. Examples thereof include lithium cobalt composite oxide, lithium manganese composite oxide, lithium nickel composite oxide, and lithium iron phosphate.

  As the non-aqueous electrolyte used in the present invention, a non-aqueous electrolyte conventionally used in non-aqueous electrolyte secondary batteries can be used. Examples thereof include ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate.

  The non-aqueous electrolyte used in the present invention includes lithium salts conventionally used in non-aqueous electrolyte secondary batteries. Examples thereof include lithium hexafluorophosphate and lithium tetrafluoroborate.

  Here, the non-aqueous electrolyte includes an electrolytic solution obtained by dissolving a supporting salt in a non-aqueous solvent, or a solid electrolyte containing the electrolytic solution.

  In the nonaqueous electrolyte secondary battery of the present invention, battery constituent members used in conventional nonaqueous electrolyte secondary batteries can be used as necessary.

  Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples. In addition, the present invention can be appropriately changed and implemented without changing the gist.

Example 1
[Coating of zinc particles]
In order to remove zinc oxide on the surface of the zinc particles, 35 g of zinc particles having an average particle diameter of about 20 μm were added to an aqueous solution A in which 0.5 ml of acetic acid was added to 1 L of water, and mixed for 1 minute. Thereafter, an aqueous solution B in which 1.76 g of CuSO ₄ was dissolved in 50 ml of water was dropped into the aqueous solution A and mixed for 2 minutes to obtain zinc particles coated with copper. As a result of quantifying the amount of copper covering the zinc particles, 2% by mass of copper was contained with respect to the total amount of zinc. At this time, copper does not form a solid solution with zinc.

  In the present application, a laser diffraction particle size distribution measuring device (SALAD-2000 manufactured by Shimadzu Corporation) was used for measuring the average particle diameter, and an atomic absorption method (AA-640-13 manufactured by Shimadzu Corporation) was used for measuring the coating amount. .

[Production of negative electrode]
The obtained zinc particles and graphite particles having an average particle diameter of 25 μm were mixed using a mortar so that the mass ratio was 30:70 to prepare a negative electrode active material. The obtained negative electrode active material and polyvinylidene fluoride as a binder were mixed so that the mass ratio was 90:10. Thereafter, N-methyl-2-pyrrolidone was added to the mixture 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, and dried at 80 ° C. to produce an electrode. After rolling the obtained electrode using a rolling roller, it cut out and produced the working electrode 1. FIG.

[Production of cell]
A cell A1 shown in FIG. 1 was produced using the working electrode 1, the counter electrode 2, the reference electrode 3, the separator 4, the nonaqueous electrolytic solution 5, and the container 6 under an argon atmosphere. Note that lithium metal was used for the counter electrode 2 and the reference electrode 3. As the separator 4, a polyethylene separator was used. Non-aqueous electrolyte 5 is prepared by dissolving lithium hexafluorophosphate so as to have a concentration of 1 mol / liter in a solvent in which ethylene carbonate and ethyl methyl carbonate are mixed in a volume ratio of 3: 7. Using. The container 6 was an aluminum laminate container. A current collecting tab 7 is attached to each of the working electrode 1, the counter electrode 2 and the reference electrode 3.

(Example 2)
Except for using 1.85g of NiSO ₄ instead of CuSO ₄ was prepared cell A2 in the same manner as in Example 1. In addition, as a result of quantifying the amount of nickel coating the zinc particles after the coating treatment, 2% by mass of nickel was included with respect to the total amount of zinc.

(Comparative Example 1)
A cell X was produced in the same manner as in Example 1 except that zinc particles that were not coated were used.

(Comparative Example 2)
A cell Y was produced in the same manner as in Example 1 except that only graphite particles were used as the negative electrode active material.

[Charge / discharge test]
For the cells A1, A2, X, and Y, the following charge / discharge test was performed at room temperature. After charging at a constant current of 0.75 mA / cm ² until reaching 0V (lithium metal standard), resting 1 minute, then charged until reaching again 0V (lithium metal standard) with a constant current of 0.25 mA / cm ² The battery was rested for 1 minute and charged at a constant current of 0.1 mA / cm ² until it reached 0 V (lithium metal reference) again. Thereafter, the battery was discharged at a constant current of 0.25 mA / cm ² until reaching 1.0 V (lithium metal reference). Table 1 shows the initial discharge capacity of each cell at this time.

  From Table 1, the cells A1 and A2 including the negative electrode active material containing zinc coated with a metal that does not react with lithium are compared with the cell X including a negative electrode active material including zinc that is not coated with a metal that does not react with lithium. Thus, it can be seen that the initial discharge capacity is high.

The reason is considered as follows. When zinc is not coated with a metal that does not react with lithium, zinc oxide is generated on the surface of the zinc particles by oxygen in the air. Oxygen contained in the zinc oxide causes a reaction of O + 2Li → Li ₂ O during charge / discharge, and this reaction is irreversible, so that the initial discharge capacity of the zinc particles is reduced. On the other hand, when zinc is coated with a metal that does not react with lithium, the surface of the zinc particles is not oxidized, and the above irreversible reaction does not occur. For this reason, a high initial discharge capacity is obtained. In addition, when the metal that does not react with lithium is copper or nickel, these metals are difficult to oxidize, and even when oxidized, the metal has conductivity, and therefore, between the negative electrode active material particles and between the negative electrode active material particles and the current collector. Contact resistance with the body is reduced. For this reason, a high initial discharge capacity is obtained. Even when copper or nickel is oxidized, the above irreversible reaction does not occur.

  It can be seen that the cell A1 including the negative electrode active material containing zinc coated with copper has a higher initial discharge capacity than the cell A2 including the negative electrode active material including zinc coated with nickel. This is probably because copper has higher conductivity than nickel.

  Further, from Table 1, the cells A1 and A2 provided with the negative electrode active material containing zinc coated with a metal that does not react with lithium have a higher initial discharge capacity than the cell Y using only graphite as the negative electrode active material. I understand that.

(Examples 3 to 9)
Cells B1 to B7 were produced in the same manner as in Example 1 except that the amount of CuSO ₄ was 0.044 g, 0.088 g, 0.44 g, 0.88 g, 3.52 g, 5.28 g, and 7.04 g. did. In addition, as a result of quantifying the amount of copper coating the zinc particles after the coating treatment, copper was 0.05, 0.1, 0.5, 1.0, 5.0, 7 with respect to the total amount of zinc, respectively. And 10.0% by mass.

  A charge / discharge test was performed in the same manner as described above using the cells B1 to B7. The results are shown in Table 2.

  From Table 2, it can be seen that the initial discharge capacity is increased when the copper coating amount is 0.05 to 10.0% by mass with respect to the total amount of zinc. It can also be seen that the initial discharge capacity is particularly high when the copper coating amount is 0.10 to 7.50 mass% with respect to the total amount of zinc.

(Examples 10 to 14)
Test cells C1 to C5 were prepared in the same manner as in Example 1 except that the mixing ratio of zinc particles and graphite particles was 10:90, 50:50, 65:35, 80:20, and 90:10. Produced.

  A charge / discharge test was performed in the same manner as described above using the cells C1 to C5. The results are shown in Table 3.

  From Table 3, it can be seen that the initial discharge capacity increases when the negative electrode active material contains 10 to 90 mass% of graphite. It can also be seen that the initial discharge capacity is particularly high when the negative electrode active material contains 35 to 90 mass% of graphite.

DESCRIPTION OF SYMBOLS 1 ... Working electrode 2 ... Counter electrode 3 ... Reference electrode 4 ... Separator 5 ... Non-aqueous electrolyte 6 ... Container 7 ... Current collection tab

Claims (6)

  A negative electrode active material for a non-aqueous electrolyte secondary battery, comprising zinc coated with a metal that does not react with lithium.   The negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the metal is copper or nickel.   The negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the metal is contained in an amount of 0.05 to 10.0% by mass with respect to the total amount of the zinc.   The negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, further comprising graphite.   5. The negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the graphite is contained in an amount of 10 to 90% by mass with respect to the total amount of the negative electrode active material. A nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein the negative electrode comprises the negative electrode active material according to claim 1.