JP3518543B2 - Manufacturing method of secondary battery - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a secondary battery using a non-aqueous solvent-based electrolyte, particularly a lithium secondary battery,
It relates to an improved version of the negative electrode.

[0002]

2. Description of the Related Art With the miniaturization of electronic devices, there has been a demand for higher density batteries, and various new secondary batteries have been proposed to meet this demand. One of them is a non-aqueous electrolyte battery using lithium, which is being researched for practical use.

However, when the non-aqueous electrolyte battery is put into practical use, the following drawbacks associated with the use of metallic lithium for the negative electrode have become particularly problematic. That is, (1)
The cycle life is short, and (2) rapid chargeability is inferior. All of these are caused by metallic lithium itself, and are considered to be caused by morphological change of the lithium negative electrode due to repeated charging and discharging, formation of dendrite, passivation of lithium, and the like.

As a method for solving the above problems, it has been proposed to use lithium as a negative electrode by doping a carbonaceous material instead of using lithium alone. This is because the carbon intercalation compound of lithium can be easily formed electrochemically. For example, when a negative electrode made of a carbonaceous material is used and charging is performed in a non-aqueous electrolyte, lithium in the electrolyte is electrochemically doped into the carbon layer of the negative electrode, and lithium is removed from the carbon layer during discharge. Be doped.

The amount of electricity per unit weight of the carbonaceous material depends on the amount of lithium doped. Therefore,
In order to increase the charge / discharge capacity of the battery, it is desirable to increase the amount of lithium doped into the carbonaceous material as much as possible.

Conventionally, as a carbonaceous material used for the negative electrode of this type of battery, for example, a carbonaceous material obtained by carbonizing an organic material as shown in Patent Document 1 is known. However, the carbonaceous materials that have been known so far are in fact the fact that they show only about half the theoretical amount of electricity because the doping amount of lithium is insufficient.

Further, for example, a carbonaceous material having a pseudo-graphite structure obtained by carbonizing a coke, a hydrocarbon, or a polymer material, which has a lattice spacing (d00) by X-ray diffraction.
2) is larger than 3.40Å, and the size of the crystallite in the a-axis direction (La) and the size of the crystallite in the c-axis direction (Lc) are both less than 200Å are used for the negative electrode. A method of occluding and releasing lithium to form a negative electrode has been proposed. However, when the pseudo graphite material having such a disordered layer structure to some extent is used for the negative electrode, there are the following problems. That is, (1) the iron component, the calcium component, the aluminum component, the magnesium component, the titanium component, etc., which are contained as impurities in the raw material and the like react with lithium, so that the capacity is greatly reduced during storage. The amount of occlusion / release is small at 100 to 150 mAh / g.

Thus, the negative electrode using the carbonaceous material is
From the practical point of view, the originally expected performance has not yet been realized.

Further, as non-aqueous electrolyte secondary batteries provided with a negative electrode using a carbonaceous material, those described in Patent Documents 2 and 3 are known. The former is provided with a negative electrode configured by doping coke or the like with an alkali metal such as lithium, and the latter is a negative electrode configured by doping polyacene, which is a thermal decomposition polymer, with an alkali metal such as lithium. Be prepared. Such a secondary battery utilizes a doping phenomenon of alkali metal ions,
Since the dendrite like the lithium negative electrode is not generated even when the charge and discharge are repeated, the battery can have excellent charge and discharge cycle performance.

However, in such a secondary battery,
Since the doped alkali metal such as lithium is consumed at the beginning of the charge / discharge cycle, the lithium in the positive electrode is made excessive so that the consumed lithium can be supplemented. Therefore, there is a problem that the volume of the positive electrode increases and the energy density of the secondary battery per unit volume decreases. In addition, compared with a battery using metallic lithium for the negative electrode,
There was a problem that the self-discharge during standing was large and the capacity was greatly reduced due to storage.

[0011]

[Patent Document 1] Japanese Patent Laid-Open No. 62-268058

[Patent Document 2] JP-A-62-90863

[Patent Document 3] JP-A-58-209864

[Patent Document 4] Japanese Patent Laid-Open No. 4-184862

[Patent Document 5] Japanese Patent Laid-Open No. 4-206259

[0012]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a secondary battery having excellent cycle characteristics and self-discharge characteristics and high energy density.

[0013]

The present invention is designed to absorb lithium.
Manufactures secondary batteries using carbonaceous materials for storage and release
The method for producing a carbonaceous material for a negative electrode according to
The impurities are iron, calcium, and aluminum.
Of the titanium, magnesium, and titanium components
Carbon containing at least 1 in excess of 1% by weight
Each of the above components is controlled to 1% by weight or less from quality materials.
Controlled to obtain the above-mentioned carbonaceous material for negative electrode
It is characterized by being. As the above process
Can be subjected to acid treatment. Examples of each component that is an impurity include Fe ₂ O ₃ , CaO, Al ₂ O ₃ , and M.
gO, TiO ₂ and the like.

Impurities such as iron component, calcium component, aluminum component, magnesium component, and titanium component react with lithium that is occluded / released. Therefore, if a carbonaceous material containing these impurities is used for the negative electrode, it will be stored. Self-discharge of the battery occurs. In the present invention, since the concentration of these impurities is low, self-discharge is suppressed and the storage characteristics of the battery are improved. Especially, the impurity concentration is 1
Since the content is controlled to be less than or equal to weight%, the effect of suppressing self-discharge is great.

In the present invention, the carbonaceous material has a lattice spacing (d002) of 3.40 by X-ray diffraction.
Å or less, and the size of the crystallite in the a-axis direction (La)
And the crystallite size (Lc) in the c-axis direction is both 200Å
It is preferable to use the above. (D002) is larger than 3.40Å and both (La) and (Lc) are 2
If it is smaller than 00Å, the absorption / release amount of lithium is 100
It becomes as small as 150 mAh / g, and high energy density cannot be achieved. However, if (d002) is 3.40 Å or less and both (La) and (Lc) are 200 Å or more, the absorption / desorption amount of lithium is 200 mAh / g or more, and high energy density can be achieved. . Examples of such a carbonaceous material are not particularly limited, but for example, graphite, fibers made from pitch of coal or petroleum, and the like, graphitized by subjecting mesocarbon microbeads to heat treatment, And so on.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) FIG. 1 is a schematic view showing a lithium secondary battery of this embodiment. In the figure, 1 is a positive electrode, 2 is a negative electrode, 3 is a separator, 5 is a positive electrode current collector, and 6
Is a negative electrode current collector, 8 is a positive electrode outer casing, 9 is a negative electrode outer casing, 10
Is an insulating packing. The positive electrode 1 is Li which is an active material.
It is made by mixing CoO ₂ , carbon black which is a conductive agent, and fluororesin which is a binder, and is pressure-bonded to the positive electrode current collector 5 made of an aluminum net. The negative electrode 2 is formed by mixing powder of carbonaceous material and polyvinylidene fluoride as a binder, and is pressure-bonded to the negative electrode current collector 6 made of nickel net. The separator 3 is made of a polypropylene microporous membrane. The electrolytic solution is prepared by dissolving LiPF _{6 in} a mixed solvent of ethylene carbonate and diethyl carbonate.

The carbonaceous material used for the negative electrode 2 is natural graphite crushed to an average particle size of 10 μm and then acid-treated. The iron component, calcium component, aluminum component, magnesium component and titanium component which are impurities in this carbonaceous material are 0.5, 0.3, 0.3 and 0.2, respectively.
And 0.2% by weight. In addition, this carbonaceous material
When analyzed by the line diffraction method, the lattice spacing (d00
2) is 3.35Å, the crystallite size in the a-axis direction (La)
And the crystallite size (Lc) in the c-axis direction are both 1000
It was more than Å. The battery of this example is referred to as battery C1.

Comparative Examples 1 to 6 Batteries Z1 to Z6 of Comparative Examples 1 to 6 were produced in the same manner as in Example 1 except that the carbonaceous material used for the negative electrode 2 was different.

That is, as the carbonaceous material of the negative electrode 2 of each of the batteries Z1 to Z6, natural graphite crushed to an average particle size of 10 μm was used as it was without the acid treatment as in Example 1. When these carbonaceous materials were analyzed by X-ray diffraction, the lattice spacing (d002) was 3.35.
Å, the crystallite size in the a-axis direction (La) and the crystallite size in the c-axis direction (Lc) were both 1000 Å or more. As shown in Table 1, the iron component, calcium component, aluminum component, magnesium component, and titanium component that are impurities in the carbonaceous material are different for each battery Z1 to Z6. That is, in the batteries Z1 to Z5, only one component out of the five components as impurities was contained in an amount exceeding 1% by weight, and in the battery Z6, all five components were contained in an amount exceeding 1% by weight.

[0020]

[Table 1]

The initial capacities of the battery C1 of Example 1 and the batteries Z1 to Z6 of Comparative Examples 1 to 6 thus obtained were determined and compared. The test conditions were as follows. That is, the charging is constant current constant voltage charging, and the constant current has a current density of 1.0 mA /
cm ² , final voltage is 4.2 V, constant voltage charging voltage is 4.2
V, charging time is 5 hours, discharge is constant current discharge,
The current density was 1.0 mA / cm ² and the final voltage was 3.0V. The initial capacities of the battery C1 and the batteries Z1 to Z6 were all 18 mAh.

Further, the storage characteristics of the battery C1 and the batteries Z1 to Z6 were determined and compared. The test conditions were to repeat charging and discharging under the same conditions as the test conditions for obtaining the initial capacity 10 times, charge under the same conditions, store at 60 ° C., and measure the discharge capacity of the battery. As a result, the capacity remaining rate after 30 days was 95% in the battery C1, whereas it was 65, 63, 61, 63, 60, and in the batteries Z1, Z2, Z3, Z4, Z5, and Z6, respectively. It was 50%. As described above, the battery C1 of Example 1 in which all of the iron component, the calcium component, the aluminum component, the magnesium component, and the titanium component, which are impurities, were suppressed to 1% by weight or less has excellent storage characteristics.

[Study of Impurity Content] Iron component, calcium component, which are impurities in the carbonaceous material used for the negative electrode 2,
The relationship between the concentrations of the aluminum component, the magnesium component, and the titanium component and the self-discharge rate of the battery was investigated.

FIG. 2 shows the calcium component in the carbonaceous material,
The concentrations of aluminum component, magnesium component, and titanium component are 0.2, 0.2, 0.1, and 0.1, respectively.
FIG. 3 shows the relationship between the iron component concentration and the self-discharge rate of the battery in the case of weight%. FIG. 3 shows the concentrations of the iron component, aluminum component, magnesium component, and titanium component in the carbonaceous material, respectively. Fig. 4 shows the relationship between the concentration of the calcium component and the self-discharge rate of the battery when 3, 0.2, 0.1, and 0.1% by weight, and Fig. 4 shows the iron component in the carbonaceous material,
The relationship between the concentration of the aluminum component and the self-discharge rate of the battery when the concentrations of the calcium component, the magnesium component, and the titanium component are 0.3, 0.2, 0.1, and 0.1% by weight, respectively. 5 shows the concentrations of iron component, calcium component, aluminum component, and titanium component in the carbonaceous material of 0.3, 0.2, 0.2, and 0.
FIG. 6 shows the relationship between the concentration of the magnesium component and the self-discharge rate of the battery in the case of 1% by weight. FIG. 6 shows that the concentrations of the iron component, the calcium component, the aluminum component, and the magnesium component in the carbonaceous material are 0. .3, 0.2, 0.
It shows the relationship between the concentration of titanium component and the self-discharge rate of the battery in the case of 2 and 0.1% by weight. As can be seen from these figures, when the concentration of one impurity exceeds 1% by weight, the self-discharge rate becomes extremely large. Therefore, it is preferable that the concentration of each of the iron component, the calcium component, the aluminum component, the magnesium component, and the titanium component, which are impurities, be 1% by weight or less in view of the storage characteristics of the battery.

Example 2 Example 2 was repeated except that the carbonaceous material used for the negative electrode 2 was changed.
A battery C2 of this example was manufactured.

That is, the carbonaceous material used for the negative electrode 2 is obtained by firing anisotropic coal pitch in an argon atmosphere at a temperature of 2500 ° C., pulverizing it to an average particle size of 10 μm, and then treating it with an acid. The iron component, calcium component, aluminum component, magnesium component, and titanium component which are impurities in this carbonaceous material are 0.3, 0.2, 0.
2, 0.1, and 0.1% by weight. In addition, when this carbonaceous material was analyzed by an X-ray diffraction method, the lattice spacing (d002) was 3.38Å, the crystallite size in the a-axis direction (La) was 250Å, and the crystallite size in the c-axis direction. Sa (L
c) was 200Å.

Comparative Examples 7 to 12 Batteries Z7 to Z12 of Comparative Examples 7 to 12 were produced in the same manner as in Example 2 except that the carbonaceous material used for the negative electrode 2 was different.

That is, as the carbonaceous material for the negative electrode 2 of each of the batteries Z7 to Z12, anisotropic coal pitch was fired in an argon atmosphere at a temperature of 2500 ° C. and crushed to an average particle size of 10 μm. It was used as it was without performing the acid treatment as in Example 2. Analysis of these carbonaceous materials by an X-ray diffraction method revealed that the lattice spacing (d002) was 3.38Å and the crystallite size (La) in the a-axis direction was 25.
0Å, the crystallite size (Lc) in the c-axis direction was 200Å or more. The iron component, the calcium component, the aluminum component, the magnesium component, and the titanium component, which are impurities in the carbonaceous material, are shown in Table 2 for each battery Z.
7 to Z12 are different. That is, batteries Z7 to Z11
Then, out of the five impurities, only one component is 1% by weight.
In battery Z12, all five components are contained in an amount of more than 1% by weight.

[0029]

[Table 2]

The initial capacities of the battery C2 of Example 2 and the batteries Z7 to Z12 of Comparative Examples 7 to 12 thus obtained were determined and compared. The test conditions are the same as those for the battery C1 and the batteries Z1 to Z6. The initial capacities of the battery C2 and the batteries Z7 to Z12 were all 16 mAh.

Further, the storage characteristics of the battery C2 and the batteries Z7 to Z12 were determined and compared. The test conditions are the same as those for the battery C1 and the batteries Z1 to Z6. As a result, the capacity retention rate after 30 days was 95% for the battery C2, whereas the capacity storage ratio was 30% for the batteries Z7, Z8, Z9, Z10, Z11, and Z.
In No. 12, it was 68, 65, 61, 64, 60, and 51%, respectively. In this way, impurities iron component, calcium component, aluminum component, magnesium component,
The battery C2 of Example 2 in which both the titanium component and the titanium component were suppressed to 1% by weight or less has excellent storage characteristics.

(Example 3) The same procedure as in Example 1 was repeated except that the carbonaceous material used for the negative electrode 2 was different.
A battery C3 of this example was manufactured.

That is, the carbonaceous material used for the negative electrode 2 is obtained by firing anisotropic coal pitch in an argon atmosphere at a temperature of 1400 ° C., crushing it to an average particle size of 10 μm, and then treating it with an acid. The iron component, calcium component, aluminum component, magnesium component, and titanium component which are impurities in this carbonaceous material are 0.3, 0.2, 0.
2, 0.1, and 0.1% by weight. Moreover, when this carbonaceous material was analyzed by an X-ray diffraction method, the lattice spacing (d002) was 3.45Å, the crystallite size in the a-axis direction (La) was 34Å, and the crystallite size in the c-axis direction. Sa (L
c) was 20Å.

(Comparative Examples 13 to 18) Batteries Z13 to Z18 of Comparative Examples 13 to 18 were produced in the same manner as in Example 1 except that the carbonaceous material used for the negative electrode 2 was different.

That is, as the carbonaceous material of the negative electrode 2 of each of the batteries Z13 to Z18, anisotropic coal pitch was fired at a temperature of 1400 ° C. in an argon atmosphere, and the average particle diameter was 10 μm.
The pulverized product was used as it was without the acid treatment as in Example 2. When these carbonaceous materials were analyzed by an X-ray diffraction method, the lattice spacing (d002) was 3.45Å and the crystallite size (La) in the a-axis direction was 34.
Å, the crystallite size (Lc) in the c-axis direction was 20Å. The iron component, the calcium component, the aluminum component, the magnesium component, and the titanium component which are impurities in the carbonaceous material, as shown in Table 3, are used in the batteries Z13 to Z1.
Every 8 is different. That is, in the batteries Z13 to Z17,
Of the five components that are impurities, only one component is contained in excess of 1% by weight, and battery Z18 contains all five components in excess of 1% by weight.

[0036]

[Table 3]

The initial capacities of the battery C3 of Example 3 and the batteries Z13 to Z18 of Comparative Examples 13 to 18 thus obtained were determined and compared with the battery C2 of Example 2. The test conditions are the same as those for batteries Z1 to Z6. Initial capacity is battery C
2 was 16 mAh, whereas all of the batteries C3 and Z13 to Z18 were 10 mAh. It can be seen that the battery C2 of Example 2 is excellent in capacity.

The storage characteristics of the batteries Z13 to Z18 were determined and compared with the battery C2 of Example 2. The test conditions are the same as those for batteries Z1 to Z6. As a result, the capacity retention rate after 30 days was 95% for the battery C2, whereas the capacity storage ratio for the batteries Z13, Z14, Z15, Z16, Z17 was
And Z18 are 68, 65, 61, 64, 6 respectively.
0 and 51%. As described above, the battery C2 of Example 2 in which all of the iron, calcium, aluminum, magnesium, and titanium components as impurities were suppressed to 1% by weight or less has excellent storage characteristics.

As described above, the batteries C1 to C3 of Examples 1 to 3, which are the secondary batteries of the present invention, were particularly excellent in storage characteristics.

[Brief description of drawings]

FIG. 1 is a schematic view showing each secondary battery of Examples 1 to 3 and Comparative Examples 1 to 18.

FIG. 2 is a diagram showing changes in the self-discharge rate with respect to the concentration of an iron component that is an impurity in the secondary batteries according to Examples 1 to 3.

FIG. 3 is a diagram showing changes in the self-discharge rate with respect to the concentration of a calcium component that is an impurity in the secondary batteries according to Examples 1 to 3.

FIG. 4 is a diagram showing changes in the self-discharge rate with respect to the concentration of an aluminum component which is an impurity in the secondary batteries according to Examples 1 to 3.

FIG. 5 is a diagram showing changes in the self-discharge rate with respect to the concentration of a magnesium component that is an impurity in the secondary batteries according to Examples 1 to 3.

FIG. 6 is a diagram showing changes in the self-discharge rate with respect to the concentration of a titanium component that is an impurity in the secondary batteries according to Examples 1 to 3.

[Explanation of symbols]

2 Negative electrode

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-4-206259 (JP, A) JP-A-4-184862 (JP, A) JP-A-4-322056 (JP, A) JP-A-5- 307956 (JP, A) JP-A-6-290781 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/58 H01M 4/02 H01M 10/40 C01B 31/02

Claims (2)

(57) [Claims] 1. A carbonaceous material for negative electrode which absorbs and releases lithium.
In the method of manufacturing a secondary battery using a material, the step of manufacturing the carbonaceous material for a negative electrode is an impurity.
Iron component, calcium component, aluminum component, mug
At least one of a nesium component and a titanium component
From the carbonaceous material containing more than 1% by weight,
The above negative electrode in which each of the components is controlled to 1% by weight or less
Characterized by being treated to obtain a carbonaceous material for use
And a method of manufacturing a secondary battery. 2. The method according to claim 1, wherein the treatment is acid treatment.
Manufacturing method of secondary battery.