JP2003142093A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery capable of preventing swelling and an increase in internal resistance of the battery occurring due to gas generation. SOLUTION: The battery has a positive electrode active material made from a lithium containing metallic oxide having a single maximum diffraction peak in the region 10 deg.<2θ<20 deg. measured by the X-ray diffraction method using the CuKα line, and the intensity of a peak in the region 30 deg.<2θ<35 deg. being less than 1/1000 of the maximum diffraction peak. Accordingly, generation of carbon dioxide gas attributable to impurity lithium carbonate an is suppressed. Thereby, the non-aqueous electrolyte secondary battery capable of preventing swelling and an increase in internal resistance can be provided.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art Conventionally, a non-aqueous electrolyte secondary battery which is charged and discharged by a reversible reaction in which one of the positive and negative electrodes occludes lithium ions emitted by the other is charged with high voltage and high energy density. Widely used as a power source for consumer electronic devices. In such a battery,
A lithium-containing transition metal oxide such as lithium cobalt oxide, lithium manganate, or lithium nickel oxide is used as a positive electrode active material that absorbs and releases lithium ions.

[0003]

However, in such a non-aqueous electrolyte secondary battery, gas is generated in the battery during charging and discharging, so that the battery swells and the internal resistance of the battery increases. There was a problem. The cause of the generation of this gas is conventionally considered to be, for example, the decomposition of the electrolytic solution, and various countermeasures have been proposed.
It is not sufficient yet, and further improvement is required.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a non-aqueous electrolyte secondary battery capable of preventing the battery from swelling and the internal resistance from increasing due to the generation of gas. is there.

[0005]

Means for Solving the Problems The present inventor has conducted earnest research to provide a non-aqueous electrolyte secondary battery capable of preventing the battery from swelling and increasing the internal resistance due to the generation of gas. Heading out, the present invention has been completed.

Lithium carbonate may be contained as an impurity in the lithium-containing transition metal oxide. As a cause of this, it is considered that lithium carbonate derived from the raw material remains as an impurity. Further, when lithium hydroxide is used as a raw material, if left in the atmosphere during the synthesis, the absorbed lithium hydroxide may react with carbon dioxide in the air to generate lithium carbonate. Further, it is considered that lithium in the oxide diffuses to the surface and reacts with carbon dioxide in the air to generate lithium carbonate. This lithium carbonate is easily oxidized to generate carbon dioxide gas. Therefore, if a lithium-containing transition metal oxide containing a large amount of lithium carbonate is used as the positive electrode active material, the lithium carbonate is oxidized at the positive electrode to generate carbon dioxide gas, which may cause swelling of the battery and increase in internal resistance. It is thought to invite. In particular, in the case of a lithium-nickel composite oxide, lithium is likely to be diffused to the surface and react with carbon dioxide to easily generate lithium carbonate, and this problem becomes remarkable.

Therefore, in order to suppress the generation of carbon dioxide gas, it is considered necessary to increase the purity of the lithium-containing transition metal oxide and reduce the content of lithium carbonate. Here, as an index of the ratio of lithium carbonate to the lithium-containing transition metal oxide, the intensity ratio of the peak obtained by the X-ray diffraction method can be used. The inventor has found that the intensity ratio of the maximum diffraction peak of lithium carbonate to the maximum diffraction peak of the lithium-containing transition metal oxide is 1 / x by the X-ray diffraction method using CuKα ray as the characteristic X-ray.
It has been found that if it is less than 1000, the generation of gas can be effectively suppressed.

According to the X-ray diffraction method using CuKα rays as the characteristic X-ray, the maximum diffraction peak of the lithium-containing transition metal oxide appears as a single peak at 10 ° <2θ <20 °. On the other hand, the maximum diffraction peak of lithium carbonate appears at 30 ° <2θ <35 °. Therefore, 10 ° <
30 for the maximum diffraction peak appearing at 2θ <20 °
If the ratio of the intensities of the peaks appearing at ° <2θ <35 ° is less than a certain value, it can be determined that the content of lithium carbonate in the lithium-containing transition metal oxide is less than the predetermined value.

That is, the present invention is a non-aqueous electrolyte secondary battery using a lithium-containing transition metal oxide as a positive electrode active material, wherein the lithium-containing transition metal oxide has a characteristic X
Has a maximum diffraction peak as a single peak at 10 ° <2θ <20 ° by an X-ray diffraction method using CuKα ray as a line, and the intensity of the peak present at 30 ° <2θ <35 ° is the maximum diffraction peak. The peak intensity is less than 1/1000.

Here, the lithium-containing transition metal oxide is not particularly limited as long as it is one usually used as a positive electrode active material of a non-aqueous electrolyte secondary battery, and examples thereof include lithium manganese composite oxide and lithium nickel composite oxide. Materials, lithium cobalt composite oxides, and the like can be used. All of these oxides are X-rays using CuKα rays as characteristic X-rays.
Maximum diffraction peak by line diffraction method is 10 ° <2θ <20 °
It has a single peak at.

These lithium-containing transition metal oxides are
It is synthesized by mixing a lithium source and a transition metal source and firing. As the lithium source, for example, lithium carbonate, lithium hydroxide or the like can be used. Further, as the transition metal source, for example, cobalt oxide, nickel hydroxide, manganese dioxide or the like can be used. The conditions for obtaining a product in which the intensity ratio of the maximum diffraction peak of lithium carbonate to the maximum diffraction peak by X-ray diffraction is less than 1/1000 depends on the types of the lithium source and the transition metal source that are the raw materials, and is generally Although not limited, for example, the molar ratio of lithium and transition metal in the charged raw material (lithium / transition metal)
Is 0.97 to 1.00 when synthesizing layered LiCoO ₂ or LiNiO _2, and 1.97 to 2.00 when synthesizing spinel type LiMn ₂ O ₄ , and the firing temperature is 70.
It is preferable to bake at 0 ° C. to 800 ° C. for 6 hours or more.

[0012]

According to the present invention, Cu
The maximum diffraction peak by the X-ray diffraction method using Kα rays is 10
Exists as a single peak at ° <2θ <20 °, and 30
Generation of carbon dioxide gas derived from lithium carbonate is suppressed by using, as a positive electrode active material, a lithium-containing metal oxide having an intensity of a peak existing at ° <2θ <35 ° of less than 1/1000 of the maximum diffraction peak. However, it is possible to provide a non-aqueous electrolyte secondary battery capable of preventing the battery from swelling and increasing the internal resistance.

[0013]

EXAMPLES The present invention will be described in more detail with reference to examples.

<Example 1> 1. Synthesis of transition metal oxide containing lithium 1) Synthesis of lithium cobalt oxide Li ₂ CO ₃ (> 99.9%) and Co ₃ O ₄ (> 99.9)
%) Was weighed so that Li / Co = 1.00, mixed, and then baked at 750 ° C. in the atmosphere for 12 hours to synthesize lithium cobalt oxide. The synthesized sample was naturally cooled and then stored in a cool and dark place in the atmosphere.

2) X-ray diffraction analysis The lithium cobalt oxide synthesized in 1) above was subjected to X-ray diffraction analysis. At the time of measurement, C as characteristic X-ray
uKα ray, X-ray intensity 12kW (current 300m
A, voltage 40 kV), set slit width is divergence slit (DR), light receiving slit (RS), scattering slit (S
S) were set to 0.5 °, 0.5 mm, and 0.15 °, respectively. The distance between the sample surface and the X-ray detector (NaI scintillation counter) was 185 mm. The scanning range is 5 ° <2θ <80 ° in 2θ of the θ-2θ method,
The number of measurement steps was set to 0.02 ° / step.

2. Preparation of Lithium Ion Secondary Battery 1) Preparation of Positive Electrode The lithium cobalt oxide obtained in step 1 was used as a positive electrode active material, and polyvinylidene fluoride as a binder and acetylene black as a conductive agent were mixed with the positive electrode active material at a weight ratio of 87: 8: 5 to prepare a positive electrode mixture. An agent paste was prepared. This paste was uniformly applied on both sides of a current collector made of an aluminum foil having a thickness of 20 μm, dried, pressed, and then cut to prepare a strip-shaped positive electrode sheet.

2) Preparation of Negative Electrode Graphite is used as the negative electrode active material, and polyvinylidene fluoride is used as a binder with respect to this graphite in a weight ratio of 8
The mixture was mixed at a ratio of 6:14 to prepare a negative electrode mixture paste. This paste was uniformly applied to both sides of a current collector made of a copper foil having a thickness of 10 μm, and a strip-shaped negative electrode sheet was produced by the same method as that for the positive electrode sheet.

3) Preparation of Electrolyte Solution Ethylene carbonate and diethyl carbonate were mixed in a volume ratio of 3: 7 to prepare a non-aqueous solvent. In this non-aqueous solvent, L as a lithium salt as an electrolyte
iPF ₆ was added at a concentration of 1.2 mol / l to prepare a non-aqueous electrolytic solution.

4) Preparation of Battery A positive electrode sheet, a polyethylene separator, a negative electrode sheet, and a polyethylene separator were laminated in this order to form a power generating element, which was housed in a rectangular battery can. The battery can was filled with the electrolytic solution prepared in (3) above, and the battery can was sealed with a battery lid with an insulator interposed therebetween to assemble a rectangular battery by a known method. The battery can was made of an aluminum plate having a thickness of 0.2 mm, and the assembled battery had a thickness of 4.2 mm, a width of 29 mm, and a height of 48 mm.

3. Left test For the battery prepared by the above method, after charging to 4.3 V with a constant current of 600 mA, charging with a constant voltage of 4.3 V for 3 hours from the start of charging, 2.75 V with a constant current of 600 mA Was discharged until the initial discharge capacity was measured.
Also, the internal resistance of the battery was measured.

Next, this battery was charged at a constant current of 600 mA to 4.3 V and then charged at a constant voltage of 4.3 V for 3 hours from the start of charging. After charging, this battery was left for 30 days under a temperature atmosphere of 60 ° C. The battery after standing was discharged to 2.75 V at a constant current of 600 mA, and the remaining discharge capacity, internal resistance, and battery thickness were measured.

Example 2 LiOH (> 99.9%) and Ni (OH) ₂ (> 99.9%) were added to Li / Ni = 1.0.
It was weighed so as to be 0, mixed, and then baked at 750 ° C. in an oxygen stream for 12 hours to synthesize lithium nickelate. A battery was prepared from this lithium nickelate in the same manner as in Example 1, and a charge / discharge test was performed to measure the discharge capacity, internal resistance, and thickness of the battery.

<Comparative Example 1-1> Lithium cobalt oxide was synthesized in the same manner as in Example 1 except that Li ₂ CO ₃ and Co ₃ O ₄ were weighed so that Li / Co = 1.05. . Using this lithium cobalt oxide, a battery was prepared in the same manner as in Example 1, and a charge / discharge test was performed to measure the discharge capacity, internal resistance, and battery thickness.

<Comparative Example 1-2> Lithium cobalt oxide was synthesized in the same manner as in Example 1 except that the firing temperature was set to 600 ° C. Using this lithium cobalt oxide, a battery was prepared in the same manner as in Example 1, and a charge / discharge test was performed to measure the discharge capacity, internal resistance, and battery thickness.

<Comparative Example 2-1> LiOH and Ni (OH)
₂ was weighed so that Li / Ni = 1.05,
Lithium nickelate was synthesized in the same manner as in Example 2. Using this lithium nickel oxide, a battery was prepared in the same manner as in Example 1, and a charge / discharge test was performed to measure the discharge capacity, internal resistance, and battery thickness.

<Comparative Example 2-2> Lithium nickelate was synthesized in the same manner as in Example 2 except that the firing temperature was set to 600 ° C. Using this lithium nickel oxide, a battery was prepared in the same manner as in Example 1, and a charge / discharge test was performed to measure the discharge capacity, internal resistance, and battery thickness.

<Results and Discussion> 1. In lithium cobalt oxide Example 1 and Comparative Examples 1-1 and 1-2,
The maximum diffraction peaks of lithium cobalt oxide are 2θ =
Appeared near 19 °. Further, a peak of an impurity that is considered to be derived from lithium carbonate appeared near 2θ = 32 °. Table 1 shows the ratio I ₁ of the peak intensity I ₁ of lithium carbonate to the maximum diffraction peak intensity I ₀ of lithium cobalt oxide.
/ I ₀ is shown.

[0028]

[Table 1]

Table 2 shows the results of Examples and Comparative Examples.
The change in battery thickness before and after leaving is shown.

[0030]

[Table 2]

From Tables 1 and 2, the peak intensity ratio I ₁ /
When I ₀ was 1/1200, the thickness of the battery after being left was increased by 0.9 mm as compared with that before being left. This bulge is
It is considered that this is mainly due to oxidation and reductive decomposition of the electrolytic solution. On the other hand, when the peak intensity ratio I ₁ / I ₀ is 1/500 and 1/100, the battery thickness is 2.
It was increased by 1 mm and 3.1 mm. It was considered that this swelling was due to the oxidation and reductive decomposition of the electrolytic solution and the generation of gas due to the oxidation of lithium carbonate contained in the positive electrode active material when left at high temperature.

Table 3 shows the results of Examples and Comparative Examples.
The change in internal resistance of the battery before and after leaving is shown.

[0033]

[Table 3]

From Tables 1 and 3, the peak intensity ratio I ₁ /
When I ₀ was 1/1200, the difference in internal resistance of the battery after standing was small as compared with that before standing. On the other hand, when the peak intensity ratio I ₁ / I ₀ is 1/500 and 1/100, the internal resistance of the battery is 110 mΩ and 210, respectively.
It was increased by mΩ.

Table 4 shows the results of Examples and Comparative Examples.
The change in discharge capacity of the battery before and after leaving is shown.

[0036]

[Table 4]

From Tables 1 and 4, the peak intensity ratio I ₁ /
When I ₀ was 1/1200, the discharge capacity of the battery after being left was 50 mAh lower than that before being left. On the other hand, when the peak intensity ratio I ₁ / I ₀ is 1/500 and 1/100, the discharge capacity of the battery is 200 mAh and 3 respectively.
It was decreased by 00 mAh.

2. Lithium nickelate Example 2 and Comparative Examples 2-1 and 2-2,
The maximum diffraction peak of lithium nickelate is 2θ =
Appeared near 19 °. Further, a peak of an impurity that is considered to be derived from lithium carbonate appeared near 2θ = 32 °. Table 5 shows the ratio I ₁ of the peak intensity I ₁ of lithium carbonate to the maximum diffraction peak intensity I ₀ of lithium nickelate.
/ I ₀ is shown.

[0039]

[Table 5]

In Table 6, Example 2 and Comparative Example 2-1,
The change in the thickness of the battery before and after leaving in Comparative Example 2-2 is shown.

[0041]

[Table 6]

From Table 5 and Table 6, the peak intensity ratio I₁/
I₀When is 1/1100, the thickness of the battery after standing is
It was a little compared with before leaving. On the other hand, the peak intensity ratio I₁
/ I ₀Is 1/600 and 1/100, the battery
The thickness of the
In the same manner as in the case of lithium carbonate, the lithium carbonate contained in the positive electrode active material
It was thought that the gas had evolved into gas.

In Table 7, Example 2 and Comparative Example 2-1,
The change in the internal resistance of the battery before and after leaving in Comparative Example 2-2 is shown.

[0044]

[Table 7]

From Tables 5 and 7, the difference in the internal resistance of the battery was small when the peak intensity ratio I ₁ / I ₀ was 1/1100, as in the case of lithium cobalt oxide. When the peak intensity ratio I ₁ / I ₀ was 1/600 and 1/100, it was greatly increased.

In Table 8, Example 2 and Comparative Example 2-1,
The change in the discharge capacity of the battery before and after leaving in Comparative Example 2-2 is shown.

[0047]

[Table 8]

From Tables 5 and 8, as for the discharge capacity, the peak intensity ratio I is the same as in the case of lithium cobalt oxide.
_{When 1} / I ₀ was 1/1100, the decrease was slight, but when the peak intensity ratio I ₁ / I ₀ was 1/600 and 1/100, the decrease was large.

As is clear from the above results, lithium cobalt oxide or lithium nickel oxide in which the intensity ratio I ₁ / I ₀ of the maximum diffraction peak of lithium carbonate to the maximum diffraction peak by X-ray diffraction is less than 1/1000 is used. By using it as a positive electrode active material, it is possible to provide a battery having good discharge characteristics by suppressing swelling of the battery and increase in internal resistance due to generation of gas.

The technical scope of the present invention is not limited to the above-described embodiment, but extends to an equivalent range.

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Claims (2)

[Claims] 1. A non-aqueous electrolyte secondary battery using a lithium-containing transition metal oxide as a positive electrode active material, wherein the lithium-containing transition metal oxide is C as characteristic X-rays.
The maximum diffraction peak by the X-ray diffraction method using uKα ray is 1
It has a single peak at 0 ° <2θ <20 °, and 3
A non-aqueous electrolyte secondary battery, wherein the intensity of the peak existing at 0 ° <2θ <35 ° is less than 1/1000 of the intensity of the maximum diffraction peak. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium-containing transition metal oxide is a lithium nickel composite oxide.