JP3223051B2 - Lithium secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly to an improvement in a positive electrode material for providing a high voltage and high capacity lithium secondary battery.

[0002]

2. Description of the Related Art In recent years,
Lithium secondary batteries using lithium-transition metal composite oxides such as LiCoO ₂ , LiNiO ₂ , and LiMnO ₂ for the positive electrode and a carbon material capable of occluding and releasing lithium ions for the negative electrode have cycle characteristics. It is noted for its superiority.

[0003] However, the capacity per unit weight of the lithium-transition metal composite oxide is smaller than that of the carbon material used for the negative electrode. For this reason, conventional lithium secondary batteries of this type have room for improvement in terms of battery capacity.

As a solution to this problem, a lithium secondary battery comprising a positive electrode using an interlayer compound obtained by doping an anion between graphite layers as a positive electrode material and a negative electrode using graphite doped with lithium in advance as a negative electrode material. A battery has been proposed (Japanese Patent Laid-Open No. Hei 5-21070). This battery has a high capacity because the capacity per unit weight of the positive electrode active material is larger than that of a positive electrode using a conventional lithium-transition metal composite oxide.

[0005] However, the above-mentioned interlayer compound is produced by anodizing graphite in a solution in which a salt containing an anion to be doped is dissolved. In the anodic oxidation in such a solution, the applied voltage during anodic oxidation cannot be higher than the decomposition voltage of the solvent. For this reason, the publication only discloses anions that can be doped at a voltage lower than the decomposition voltage of the solvent, and does not disclose an intercalation compound capable of inserting and extracting lithium ions at a high positive electrode potential. That is, the battery disclosed in the publication has a problem that it is difficult to extract a high voltage.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a high-voltage, high-capacity lithium secondary battery.

[0007]

According to the first aspect of the present invention, there is provided a lithium secondary battery (hereinafter referred to as a "first battery") in a charged state immediately after battery assembly. , Between the layers of the carbon material having a layered structure, the following formula (I)
Alternatively, an interlayer compound doped with an anion of an organic acid lithium salt represented by the following formula (II) is used as a positive electrode material.

[0008]

Embedded image

[0009] [In formula (I), R ¹ is a phenyl group, a tolyl group or an alkyl group having 1 to 5 carbon atoms, in formula (II), R ²
Is a phenyl group, a tolyl group or an alkyl group having 1 to 4 carbon atoms. ]

In order to achieve the above object, a third aspect of the present invention is provided.
The lithium secondary battery according to the invention described above is in a discharged state immediately after battery assembly (hereinafter, referred to as a “second battery”).
Is used as a cathode material, an interlayer compound obtained by doping an anion and a lithium ion of an organic acid lithium salt represented by the following formula (I) or (II) between layers of a carbon material having a layered structure. It becomes. In the following, the first battery and the second battery may be collectively referred to as the battery of the present invention.

[0011]

Embedded image

[0012] [In formula (I), R ¹ is a phenyl group, a tolyl group or an alkyl group having 1 to 5 carbon atoms, in formula (II), R ²
Is a phenyl group, a tolyl group or an alkyl group having 1 to 4 carbon atoms. ]

As the carbon material having a layered structure, graphite,
Examples include coke and a fired organic material. These carbon materials, powder may be used as it is, if necessary,
It may be used after pretreatment such as purification treatment, heat treatment (500 to 3000 ° C.), acid treatment, alkali treatment, and expansion treatment.

Examples of the lithium organic acid salt include lithium benzoate, lithium p-toluate and its isomers, lithium acetate, lithium propionate, lithium n-butyrate and its isomers, lithium n-valerate and its isomers, n-
Lithium hexanoate and its isomers, lithium benzenesulfonate, lithium p-toluenesulfonate and its isomers, lithium methanesulfonate, lithium ethanesulfonate, lithium 1-propanesulfonate and its isomers, 1-butanesulfonic acid Lithium and its isomers are exemplified.

The positive electrode material in the battery of the present invention is obtained by doping an anion of the organic acid lithium salt represented by the above formula (I) or the above formula (II), or an anion and a lithium ion between carbon material layers. It is an intercalation compound.

In the first battery, an interlayer compound doped with an anion between carbon material layers is used for the positive electrode. In this case, the positive electrode is produced, for example, by the following method.

First, a carbon material and a binder (eg, polyvinylidene fluoride) are mixed with a solvent (eg, N-methylpyrrolidone).
Into a slurry, and this slurry is applied to the positive electrode current collector. Next, this is heated and dried under vacuum, connected to the anode of the electrolytic cell, and immersed in a molten lithium salt of an organic acid, is subjected to constant potential oxidation (anodic oxidation) to dope anions between carbon material layers. I do.

In the second battery, an interlayer compound obtained by doping anions and lithium ions between carbon material layers is used for the positive electrode. In this case, the positive electrode is produced, for example, by the following method.

An anion is doped between carbon material layers in the same manner as in the above-described method for producing the positive electrode of the first battery. Next, by inverting the polarity of both terminals of the electrolytic cell and performing a constant potential reduction (cathode reduction), lithium ions are further doped between the carbon material layers in addition to the anions. By the way,
The anion of the organic acid lithium salt doped between the carbon material layers by the above-mentioned constant potential oxidation is not undoped during the subsequent constant potential reduction.

In the first battery, a negative electrode material is, for example, a lithium alloy such as a Li--Al alloy or a Li--Sn alloy, and metallic lithium. In the second battery, the negative electrode material is, for example, graphite, coke, or an organic material. A carbon material such as a body is preferably used.

As described above, the battery of the present invention comprises, as a positive electrode material, an anion of a lithium salt of an organic acid represented by the above formula (I) or (II), or an anion of a lithium salt of an organic acid and lithium ion. It is characterized in that an interlayer compound doped between carbon material layers is used. Therefore, for other components constituting the battery such as a non-aqueous electrolyte and a separator (when a liquid electrolyte is used), various materials which have been conventionally used or proposed for lithium secondary batteries must be used. Can be.

[0022]

In the battery of the present invention, as the positive electrode material, an anion of the organic acid lithium salt represented by the above formula (I) or (II), or the anion and lithium, between the layers of the carbon material having a layered structure. Since the intercalation compound doped with ions is used, the potential of the positive electrode increases and the charge / discharge capacity of the positive electrode increases. The reason why the charge / discharge capacity of the positive electrode is increased is considered that the anion of the organic acid lithium salt having a large molecular structure spreads between the carbon material layers and is orderly doped between the layers, thereby increasing the doping amount of lithium ions. Can be

[0023]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and the present invention may be practiced by appropriately changing the gist of the invention. Is possible.

Example 1 [Preparation of Positive Electrode] 1.8 g of graphite powder and 0.2 g of polyvinylidene fluoride (PVdF) as a binder were mixed.
The slurry was dispersed in N-methylpyrrolidone to prepare a slurry positive electrode mixture. The slurry-like positive electrode mixture was applied on both sides of an aluminum foil as a positive electrode current collector by a doctor blade method, and then dried in vacuum at 150 ° C. for 2 hours. Next, using an electrolysis cell, constant potential oxidation (anodic oxidation) is performed at an applied voltage of 4.5 V, and anions (benzoate ions) are obtained.
Was doped between graphite layers to produce an interlayer compound. In the constant potential oxidation, the current density flowing in the circuit of the electrolytic cell is 10 μm.
The process was completed when the A / cm ² was reached.

FIG. 1 is a partial cross-sectional view of an electrolytic cell C used for constant potential oxidation.
(Reference electrode), aluminum foil 2 coated with a positive electrode mixture (working electrode), platinum electrode 3 (counter electrode), 240 of lithium benzoate
It consists of a melt 4, a container 5, an ammeter 6, a voltmeter 7, etc.

Next, the polarity of both terminals of the electrolytic cell is reversed, and a constant potential reduction (cathode reduction) is performed at an applied voltage of 2.75 V, and lithium ions as counter ions of anions are doped between graphite layers. A positive electrode doped with an anion and its counter ion between graphite layers was produced. Constant potential reduction also
The current density flowing in the circuit of the electrolytic cell is 10 μA / cm ²
It ended when it became.

[Preparation of negative electrode] 1.8 g of graphite powder and 0.2 g of polyvinylidene fluoride as a binder were mixed.
The slurry was dispersed in N-methylpyrrolidone to form a slurry. The slurry was applied to both surfaces of a copper foil as a negative electrode current collector by a doctor blade method, and then vacuum dried at 150 ° C. for 2 hours to produce a negative electrode.

[Preparation of Electrolyte Solution] A non-aqueous electrolyte solution was prepared by dissolving 1 mol / l of LiPF ₆ in an equal volume mixed solvent of ethylene carbonate (EC) and 1,2-dimethoxyethane (DME).

[Assembly of Battery] Using the positive and negative electrodes and the nonaqueous electrolyte described above, an AA size cylindrical battery (second battery) BA1 of the present invention was assembled. Note that a polypropylene microporous membrane was used as a separator, and this was impregnated with the nonaqueous electrolyte.

FIG. 2 is a sectional view of the assembled battery BA1 of the present invention. The illustrated battery BA1 of the present invention includes a positive electrode 11, a negative electrode 12, a separator 13, a positive electrode lead 14, a negative electrode lead 15, and a positive electrode It comprises an external terminal 16, a negative electrode can 17, and the like.

The positive electrode 11 and the negative electrode 12 are housed in a negative electrode can 17 while being spirally wound through a separator 13 impregnated with a non-aqueous electrolyte. The positive electrode external terminal 16 and the negative electrode 12
Is connected to a negative electrode can 17 via a negative electrode lead 15 so that chemical energy generated inside the battery can be taken out of the positive electrode external terminal 16 and the negative electrode can 17 as electric energy.

Example 2 As a lithium salt of an organic acid, lithium p-toluate (the above formula) was used in place of lithium benzoate.
Except that R ¹ in (I) was used as one) a p- tolyl group in the same manner as in Example 1 to prepare a present battery BA2.

Example 3 As a lithium salt of an organic acid, lithium acetate (R in the above formula (I)) was used in place of lithium benzoate.
^A battery BA3 of the present invention was produced in the same manner as in Example 1, except that ¹ was a methyl group).

Example 4 As a lithium salt of an organic acid, lithium propionate (the above formula) was used in place of lithium benzoate.
A battery BA4 of the present invention was produced in the same manner as in Example 1 except that (I) was used, in which R ¹ was an ethyl group.

Example 5 Example ¹ was repeated except that lithium n-butyrate (in which R ¹ in the above formula (I) was a propyl group) was used instead of lithium benzoate as the lithium salt of an organic acid. In the same manner as in the above, a battery BA5 of the present invention was produced.

Example 6 As a lithium salt of an organic acid, lithium n-valerate (the above formula (I)) was used in place of lithium benzoate.
Battery BA6 of the present invention was produced in the same manner as in Example 1 except that R1 in the formula ( ¹⁾ was a butyl group.

Example 7 As a lithium salt of an organic acid, lithium n-hexanoate (the above formula) was used in place of lithium benzoate.
A battery BA7 of the present invention was produced in the same manner as in Example 1 except that (I) in which R ¹ was a pentyl group).

Example 8 Example 1 was repeated except that lithium benzenesulfonate (in which R ^{2 in the} above formula (II) was a phenyl group) was used instead of lithium benzoate as the lithium organic acid salt. Similarly, battery BA8 of the present invention was produced.

Example 9 As a lithium salt of an organic acid, except that lithium p-toluenesulfonate (where R ² in the above formula (II) is a p-tolyl group) was used instead of lithium benzoate. In the same manner as in Example 1, a battery BA9 of the present invention was produced.

Example 10 As a lithium salt of an organic acid,
The battery BA10 of the present invention was prepared in the same manner as in Example 1 except that lithium methanesulfonate (in which R ² in the above formula (II) was a methyl group) was used instead of lithium benzoate.
Was prepared.

Example 11 As a lithium salt of an organic acid,
The battery BA11 of the present invention was prepared in the same manner as in Example 1 except that lithium benzoate (in which R ² in the above formula (II) was an ethyl group) was used instead of lithium benzoate.
Was prepared.

Example 12 As a lithium salt of an organic acid,
Battery B of the present invention was prepared in the same manner as in Example 1 except that lithium 1-propanesulfonate (in which R ² in the above formula (II) was a propyl group) was used instead of lithium benzoate.
A12 was produced.

Example 13 As a lithium salt of an organic acid,
The battery BA1 of the present invention was prepared in the same manner as in Example 1 except that lithium 1-butanesulfonate (in which R ² in the above formula (II) was a butyl group) was used instead of lithium benzoate.
3 was produced.

Comparative Example LiCoO ₂ as a positive electrode material
1.8 g of graphite as a conductive agent and 0.2 g of graphite as a conductive agent were dispersed in an N-methylpyrrolidone solution containing 5% by weight of polyvinylidene fluoride as a binder to prepare a slurry-type positive electrode mixture. The slurry-like positive electrode mixture was applied to both surfaces of an aluminum foil as a positive electrode current collector by a doctor blade method, and then dried under vacuum at 150 ° C. for 2 hours to produce a positive electrode. A comparative battery BC1 was produced in the same manner as in Example 1 except that this positive electrode was used as the positive electrode.

(Charge / Discharge Test) The battery BA1 of the present invention and the comparative battery BC1 were charged at 200 mA to a cut-off voltage of 5.0 V, and then discharged at 200 mA to a cut-off voltage of 2.0 V, and the charge / discharge characteristics of each battery were examined. Was. The results are shown in FIG.

FIG. 3 is a graph showing the battery voltage (V) on the ordinate and the charge / discharge capacity (mAh) on the abscissa. According to FIG. 3, the battery BA1 of the present invention uses LiCoO ₂ as a cathode material. It can be seen that the voltage is higher and the charge / discharge capacity is larger than that of the comparative battery BC1 used as the battery.

The batteries BA2 to BA13 of the present invention also
The charge / discharge characteristics of each battery were examined in the same manner as described above. Tables 1 and 2 show BA1 to BA13 and comparative battery B
Battery voltage (V) and discharge capacity (m) after 50% discharge of C1
Ah) is shown together with the type of the organic acid lithium salt used.

[0048]

[Table 1]

[0049]

[Table 2]

As shown in Tables 1 and 2, the batteries BA1 to B of the present invention were
It can be seen that A13 has a higher battery voltage after 50% discharge and a larger discharge capacity than the comparative battery BC1.

In the above embodiment, the second battery has been described as an example, but the same result was obtained with the first battery.

In the above embodiment, a specific example in which the present invention is applied to a cylindrical lithium secondary battery has been described. However, the shape of the battery is not particularly limited. The present invention can be applied to lithium secondary batteries of various shapes, such as a battery type, a film type, and an elliptic cylinder type.

Further, in the above embodiment, a liquid electrolyte is used, but a solid electrolyte can be used. By using solid electrolyte, there is no worry about liquid leakage,
A position-free and highly reliable battery can be obtained.

[0054]

According to the battery of the present invention, an anion of a specific organic acid lithium salt or an interlayer compound obtained by doping an anion and lithium ion is used as a cathode material between carbon material layers. And high capacity.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of an electrolytic cell used in an example.

FIG. 2 is a cross-sectional view of a cylindrical lithium secondary battery (battery of the present invention) assembled in an example.

FIG. 3 is a graph showing charge / discharge characteristics of a battery of the present invention and a comparative battery.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Toshihiko Saito 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (56) References JP-A-62-143370 (JP, A) 61-6567 (JP, A) JP-A-1-307157 (JP, A) JP-A-6-243868 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10 / 40 H01M 4/02-4/04 H01M 4/58

Claims (4)

(57) [Claims] (1) The following formula is provided between carbon material layers having a layered structure.
(I) or an interlayer compound obtained by doping an anion of a lithium salt of an organic acid represented by the following formula (II) is used as a cathode material, and the state immediately after battery assembly is a charged state. Lithium secondary battery. Embedded image [In the formula (I), R ¹ represents a phenyl group, a tolyl group,
And R ² is a phenyl group, a tolyl group or an alkyl group having 1 to 4 carbon atoms in the formula (II). ] 2. The method according to claim 1, wherein the lithium salt of the organic acid is lithium benzoate, lithium p-toluate or isomer thereof, lithium acetate, lithium propionate, lithium n-butyrate or isomer thereof, n-lithium valerate or isomer thereof. Isomer, lithium n-hexanoate or isomer thereof, lithium benzenesulfonate, lithium p-toluenesulfonate or isomer thereof, lithium methanesulfonate, lithium ethanesulfonate, lithium 1-propanesulfonate or isomer thereof, or The lithium secondary battery according to claim 1, which is lithium, 1-butanesulfonate or an isomer thereof. 3. The method according to claim 1, wherein the carbon material has a layered structure.
(I) or an anion of an organic acid lithium salt represented by the following formula (II) and an interlayer compound obtained by doping a lithium ion,
A lithium secondary battery in a discharged state immediately after battery assembly, wherein the lithium secondary battery is used as a positive electrode material. Embedded image [In the formula (I), R ¹ represents a phenyl group, a tolyl group,
And R ² is a phenyl group, a tolyl group or an alkyl group having 1 to 4 carbon atoms in the formula (II). ] 4. The lithium salt of an organic acid is lithium benzoate, lithium p-toluate or isomer thereof, lithium acetate, lithium propionate, lithium n-butyrate or isomer thereof, n-lithium valerate or isomer thereof. Isomer, lithium n-hexanoate or isomer thereof, lithium benzenesulfonate, lithium p-toluenesulfonate or isomer thereof, lithium methanesulfonate, lithium ethanesulfonate, lithium 1-propanesulfonate or isomer thereof, or The lithium secondary battery according to claim 3, which is lithium 1-butanesulfonate or an isomer thereof.