JP5083743B2 - Lithium battery - Google Patents

Description

  The present invention relates to a lithium battery including a positive electrode into which lithium ions can be inserted, a negative electrode from which lithium ions can be removed, and a nonaqueous electrolytic solution in which a lithium salt is dissolved.

As electronic devices become more portable and multifunctional in recent years, higher performance is required for the discharge characteristics and long-term reliability of batteries used as power sources for electronic devices.
In particular, a lithium battery including a negative electrode active material capable of desorbing lithium ions, a positive electrode active material capable of inserting lithium ions, and a non-aqueous electrolyte in which a lithium salt is dissolved has high energy density and long-term reliability. Excellent in properties. For this reason, the demand for lithium batteries is growing rapidly.

Since the negative electrode active material of the lithium battery has a low potential, the electrolyte solution may be a simple substance such as propylene carbonate (PC), ethylene carbonate (EC), 1,2-dimethoxyethane (DME), or a mixed organic solvent thereof. In addition, a non-aqueous electrolyte solution in which a lithium salt such as LiClO ₄ or LiPF ₆ is dissolved is used, and an aqueous solution is not used.

Metal oxides such as MnO ₂ , LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ are used for the positive electrode active material of the lithium secondary battery. The negative electrode active material includes lithium metal, carbon materials such as graphite, metal materials such as Si, Sn, or Al, alloy materials including Ti—Si, Zr—Si, or Ni—Si, or Li ₄ Ti. A metal oxide such as ₅ O ₁₂ is used.

Manganese dioxide (MnO ₂ ) is used as the positive electrode active material for primary batteries, but it is disclosed that the wettability of the non-aqueous electrolyte can be improved by firing manganese dioxide with lithium hydroxide. (For example, refer to Patent Document 1).
JP 08-115728 A

  For the positive and negative electrodes, a positive electrode active material or a negative electrode active material of a lithium battery is mixed with a conductive additive such as carbon and a binder such as a fluororesin, and then pressure-molded. However, active material particles made of a metal oxide, a metal material, or an alloy material tend to agglomerate, and it has been difficult to uniformly mix with a conductive additive. Therefore, there has been a problem that due to the deterioration of the discharge characteristics and the expansion of the active material particles during charging / discharging, the current collecting property of the active material particles is decreased, and the discharge capacity is likely to decrease with repeated charging / discharging.

  Also, these active materials are usually hydrophilic because the surface is covered with a hydroxyl group, and when these are used for the electrode of a lithium battery, impregnation of the non-aqueous electrolyte into the electrode is not sufficient, There was a problem that the effective reaction area of the electrode was reduced.

Further, as described above, Patent Document 1 discloses that the wettability of the non-aqueous electrolyte is improved by firing manganese dioxide, which is a positive electrode active material for a primary battery, together with lithium hydroxide. Further, since the mixing before firing is solid phase mixing, unevenness in surface modification is likely to occur.
Accordingly, an object of the present invention is to provide a lithium battery excellent in discharge characteristics and charge / discharge cycle characteristics by improving electrode reactivity in order to solve the above-described conventional problems.

The present invention is a lithium battery comprising a positive electrode including a positive electrode active material capable of inserting lithium ions, a negative electrode including a negative electrode active material capable of detaching lithium ions, and a non-aqueous electrolyte solution in which a lithium salt is dissolved. In addition, at least one of the positive electrode active material and the negative electrode active material has an organic group on the surface.
Thereby, the intermolecular force between active material particles can be reduced and aggregation of particles can be suppressed. In addition, since the surface of the active material particles is hydrophobic, the electrode can be easily impregnated with the nonaqueous electrolytic solution.

The organic group is preferably an alkoxyl group.
Preferably it has a structure alkoxyl group represented by _{-O-C n H 2n + 1} (n = 3~10). Thereby, aggregation of particles can be suppressed and the particle surface is also hydrophobic.
Moreover, it is preferable that carbon number of an alkoxyl group is 3-10 (n = 3-10). When the number of carbon atoms of the alkoxyl group is 3 or more (n ≧ 3), the alkoxyl group layer becomes thick, aggregation of particles can be prevented, and the particle surface is also hydrophobic. Moreover, since the electronic conductivity of the particle | grain surface will fall when carbon number exceeds 10, it is preferable that carbon number of an alkoxy group is 10 or less (n <= 10).

An active material having —O—C _n H _{2n + 1} (n = 3 to 10) on the surface is obtained by thermally condensing HO—C _n H _{2n + 1} (n = 3 to 10) and the active material. can get. A dehydration reaction occurs between the hydroxyl group of HO—C _n H _{2n + 1 and} the hydroxyl group on the active material surface, and an organic group can be easily bonded to the active material surface.

According to the present invention, by bonding an organic group to the surface of an active material in a lithium battery, the aggregation of the active material is suppressed, and the active material and the conductive additive are easily mixed uniformly. In addition, since the surface of the active material has hydrophobicity, the impregnation property of the nonaqueous electrolyte solution of the electrode is improved.
When the lithium battery is a primary battery, the discharge characteristics are improved. When the lithium battery is a secondary battery, the discharge characteristics are improved and the charge / discharge cycle characteristics are improved.

The present invention comprises a positive electrode including a positive electrode active material into which lithium ions can be inserted, a negative electrode including a negative electrode active material from which lithium ions can be desorbed, and a non-aqueous electrolyte in which a lithium salt is dissolved. At least one of the substance and the negative electrode active material relates to a lithium battery having an organic group on the surface.
Thereby, the intermolecular force between the active material particles is reduced, the aggregation of the active material particles can be suppressed, and the active material particles and the conductive additive are easily mixed uniformly. In addition, since the surface of the active material particles is hydrophobic, the electrode can be easily impregnated with the nonaqueous electrolytic solution. Therefore, when the lithium battery is a primary battery, the discharge characteristics are improved. When the lithium battery is a secondary battery, the discharge characteristics are improved and the charge / discharge cycle characteristics are also improved.

The organic group is an alkoxyl group, —NH—R (R is an alkyl group), an ester group, an acyl group, —SO ₂ —R (R is an alkyl group), or —S—R (R is an alkyl group). Is preferred.
Furthermore, as each of the above functional groups, —O—C _n H _{2n + 1} (n = 3 to 10), —NH—C _n H _{2n + 1} (n = 3 to 10), —COO—C _n H _{2n + 1 (n = 2~9)} , - CO-C n H 2n + 1 (n = 2~9), - SO 2 -C n H 2n + 1 (n = 3~10), and -S- C _n H _{2n + 1} (n = 3 to 10) is preferable.
When the n value is in the above range, the effect of suppressing aggregation of the active material particles can be sufficiently obtained, and a sufficiently hydrophobic particle surface can be obtained. However, if the n value exceeds the above range, the organic group layer on the particle surface becomes too thick, and the electron conductivity on the particle surface decreases.

The active material particles having an organic group on the surface can be obtained, for example, by thermally condensing the active material particles and a modifying material containing a constituent site of the organic group.
In order to bond the organic group to the surface of the active material particles, the modifying material includes HO—C _n H _{2n + 1} (n = 3 to 10), C _n H _{2n + 1} —NH ₂ (n = _{3~10), C n H 2n +} 1 -COOH (n = 2~9), C n H 2n + 1 -CHO (n = 2~9), C n H 2n + 1 -SO 3 H (n = 3-10), and _{C n H 2n + 1 -SH (} n = 3~10) are used, respectively.

The positive electrode includes, for example, a positive electrode active material having an organic group on the surface, a conductive aid such as carbon black, and a binder such as a fluororesin.
The negative electrode includes, for example, a negative electrode active material having an organic group on the surface, a conductive aid such as graphite, and a binder such as polyacrylic acid.

When the lithium battery is a secondary battery, a positive electrode active material and a negative electrode active material capable of inserting and removing lithium ions are used.
As the positive electrode active material, for example, a metal oxide such as MnO ₂ , LiCoO ₂ , LiNiO ₂ , or LiMn ₂ O ₄ is used. Examples of the negative electrode active material include lithium materials, carbon materials such as graphite, metal materials such as Si, Sn, and Al, alloy materials such as Ti—Si, Zr—Ti, and Ni—Si, or Li ₄ Ti _5. A metal oxide such as O ₁₂ is used.
When the lithium battery is a primary battery, for example, manganese dioxide or the like is used as a positive electrode active material into which lithium can be inserted, and lithium metal or the like is used as a negative electrode active material from which lithium can be removed.

Nonaqueous electrolytes include, for example, propylene carbonate (PC), ethylene carbonate (EC), 1,2-dimethoxyethane (DME), or a mixed organic solvent such as LiClO ₄ or LiPF _6. What dissolved the salt is used.

The active material particles having an organic group on the surface can be produced, for example, using the apparatus shown in FIG.
FIG. 1 shows the configuration of the apparatus used in this embodiment. The tubular furnace 2 is provided with a thermocouple 3 for measuring the temperature in the tubular furnace 2. By controlling the heating of the tubular furnace 2 according to the temperature in the tubular furnace 2 measured by the thermocouple 3, the inside of the tubular furnace 2 is controlled to a predetermined temperature. A reaction tube 1 is inserted into the tubular furnace 2, and an active material having an organic group on the surface is generated in the reaction tube 1.

First, the raw material liquid is charged into the reaction tube 1. As the raw material liquid, a material obtained by dispersing active material powder and a modifying material containing a constituent site of an organic group such as alcohol to be bonded to the active material surface in distilled water is used.
This raw material liquid is adjusted to a target pressure according to the temperature in the tubular furnace 2. This pressure is calculated by a steam table assuming that the raw material liquid is pure water. For example, since the density of water at the reaction temperature 200 ° C. and the reaction pressure 30MPa is 0.88 g / cm ^3, if the reaction tube at 1 volume of 10 cm ^3, the raw material solution of 8.8 cm ³ into the reaction tube 1 .

After putting the raw material liquid into the reaction tube 1, the reaction tube 1 is inserted into the tubular furnace 2 and left for a predetermined reaction time (for example, about 5 to 20 minutes). After a predetermined time has elapsed, the reaction tube 1 is taken out of the tubular furnace 2 and placed in a cold water bath to quickly stop the reaction.
And after taking out the content of the reaction tube 1, filtering, and washing with water, the active material which has an organic group on the surface which is a reaction result product is obtained.
Hereinafter, embodiments of the present invention will be described in detail. However, this example shows an example of the present invention, and the present invention is not limited to the following example.

Example 1
The case where the lithium battery of the present invention is a primary battery is shown below.
(1) Production of Positive Electrode Active Material Having Organic Group on Surface Using the same apparatus as in FIG. 1, manganese dioxide particles having an alkoxyl group on the surface were produced. The reaction tube 1 was made of SUS316 having a volume of 5 cm ³ .
Manganese dioxide powder 0.1g as a cathode active material, CH of 1.5 × ^10- 8 mol as modified material containing portion constituting an organic group ₃ - (CH _{2) 7} distilled water and -OH dispersed 4.41 cm ³ was put into the reaction tube 1 and reacted in the tubular furnace 2 adjusted to 200 ° C. for 10 minutes. After the reaction, the reaction tube 1 was put into a water bath to stop the reaction.

(2) Preparation of positive electrode Manganese dioxide having an organic machine on the surface obtained above, carbon black as a conductive agent, and fluororesin as a binder are mixed at a weight ratio of 90: 5: 5, A positive electrode mixture was obtained. This positive electrode mixture was pressure-molded to produce a cylindrical positive electrode.

(3) Production of negative electrode A lithium rolled plate was punched into a disc shape to obtain a negative electrode.
(4) Preparation of non-aqueous electrolyte In a solvent obtained by mixing propylene carbonate (PC) and 1,2-dimethoxyethane (DME) at a volume ratio of 1: 1, 1 mol / liter of lithium perchlorate (LiClO ₄ ) was added. A non-aqueous electrolyte was obtained by dissolving 1 liter.

(5) Production of Battery A coin-shaped battery (primary battery) having an outer diameter of 20.0 mm and a thickness of 3.2 mm having the structure shown in FIG. It was produced by the procedure.
The negative electrode 5 was pressure bonded to the sealing plate 8 combined with the gasket 7. As the separator 6, a polypropylene non-woven fabric punched out in a circle was inserted into the sealing plate 8. Further, after the positive electrode 4 was inserted, an electrolytic solution was injected. After covering the battery case 9, the battery case 9 was sealed by placing it in a sealing mold and caulking the edge of the battery case 9 to the sealing plate 8 via the gasket 7 with a press. A carbon paint 10 was applied to the portion of the battery case 9 that contacts the positive electrode 4.

Example 2
A battery was fabricated in the same manner as in Example 1 except that CH ₃ — (CH ₂ ) ₇ —NH ₂ was used as the modifying material.

Example 3
A battery was fabricated in the same manner as in Example 1 except that CH ₃ — (CH ₂ ) ₆ —COOH was used as the modifying material.

Example 4
A battery was fabricated in the same manner as in Example 1 except that CH ₃ — (CH ₂ ) ₆ —CHO was used as the modifying material.

Example 5
A battery was fabricated in the same manner as in Example 1 except that CH ₃ — (CH ₂ ) ₇ —SO ₃ H was used as the modifying material.

Example 6
A battery was fabricated in the same manner as in Example 1 except that CH ₃ — (CH ₂ ) ₇ —SH was used as the modifying material.

Example 7
A battery was fabricated in the same manner as in Example 1 except that CH ₃ — (CH ₂ ) ₂ —OH was used as the modifying material.

Example 8
A battery was produced in the same manner as in Example 1 except that CH ₃ —OH was used as the modifying material.

Example 9
A battery was fabricated in the same manner as in Example 1 except that CH ₃ — (CH ₂ ) ₁₁ —OH was used as the modifying material.

<< Comparative Example 1 >>
A battery was produced in the same manner as in Example 1 except that untreated manganese dioxide (which did not bind organic groups to the surface) was used as the positive electrode active material.

Example 10
The case where the lithium battery of the present invention is a secondary battery is shown below.
(1) Preparation of positive electrode active material and negative electrode active material having organic group on surface Using LiCoO ₂ for the positive electrode active material, Si metal for the negative electrode active material, and using the same apparatus as in FIG. LiCoO ₂ powder and Si powder having a group were prepared by the following procedure. The reaction tube 1 was made of SUS316 having a volume of 5 cm ³ .
4.41 cm ³ of distilled water in which 0.1 g of LiCoO ₂ powder or Si powder and 1.5 × 10 ⁻⁸ mol of CH ₃ — (CH ₂ ) ₇ —OH were dispersed as a modifying material was added in the reaction tube 1. And reacted for 10 minutes in the tubular furnace 2 adjusted to 200 ° C. After the reaction, the reaction tube 1 was put into a water bath to stop the reaction.

(2) Production of positive electrode LiCoO ₂ having an organic group on the surface obtained above, carbon black as a conductive agent, and fluororesin as a binder are mixed in a weight ratio of 90: 5: 5 to obtain a positive electrode A mixture was obtained. This positive electrode mixture was pressure-molded to produce a cylindrical positive electrode.

(3) Production of negative electrode The above-obtained Si having an organic group on the surface, graphite as a conductive agent, and polyacrylic acid as a binder were mixed at a weight ratio of 70:20:10 to obtain a negative electrode composite. An agent was obtained. This negative electrode mixture was pressure-molded to produce a cylindrical negative electrode.

(4) Preparation of non-aqueous electrolyte In a solvent obtained by mixing propylene carbonate (PC) and 1,2-dimethoxyethane (DME) at a volume ratio of 1: 1, 1 mol / liter of lithium perchlorate (LiClO ₄ ) was added. A non-aqueous electrolyte was obtained by dissolving 1 liter.

(5) Production of Battery Using the positive electrode, negative electrode, and nonaqueous electrolyte obtained above, a coin-type battery (secondary battery) having an outer diameter of 20.0 mm and a thickness of 3.2 mm having the structure shown in FIG. ) Was prepared by the following procedure.
Lithium 12 punched out from a rolled plate into a disc shape was pressure-bonded to a sealing plate 16 combined with a gasket 15, and a negative electrode 13 was inserted. A separator 14 in which a polypropylene nonwoven fabric was punched out in a circle was inserted into the sealing plate 16. After the positive electrode 11 is inserted, an electrolytic solution is injected, and the battery case 17 is covered. Then, the battery case 17 is put in a sealing mold, and the edge of the battery case 17 is caulked to the sealing plate 16 via the gasket 15 by a press machine. As a result, the battery case 17 was sealed. A carbon paint 18 was applied to a portion of the battery case 17 that contacts the positive electrode 11 and a portion of the sealing plate 16 that contacts the lithium 12.

Example 11
A battery was produced in the same manner as in Example 10 except that LiNiO ₂ was used as the positive electrode active material.

Example 12
A battery was produced in the same manner as in Example 10 except that LiMn ₂ O ₄ was used as the positive electrode active material.

Example 13
A battery was produced in the same manner as in Example 10 except that Sn metal was used for the negative electrode active material.

Example 14
A battery was produced in the same manner as in Example 10 except that Al metal was used as the negative electrode active material.

Example 15
A Ti—Si alloy containing an A phase mainly composed of Si and a B phase composed of an intermetallic compound of Ti and Si was used as the negative electrode active material. The Ti—Si alloy was produced as follows.
Ti powder (purity 99.99%, particle size 100-150 μm) and Si powder (purity 99.9%, average particle size 3 μm) were mixed to obtain a mixed powder. At this time, the mixing ratio of the Si powder and the Ti powder is such that, when it is assumed that the B phase constitutes TiSi ₂ , the weight ratio of the A phase to the total weight of the A phase and the B phase in the generated alloy material is about 80%. % Was adjusted.

3.5 kg of the mixed powder is weighed and put into a vibration mill apparatus (manufactured by Chuo Kako Co., Ltd., model number FV-20). It was thrown to occupy. After the inside of the container was evacuated, Ar (purity 99.999%, manufactured by Nippon Oxygen Co., Ltd.) was introduced to make 1 atmosphere. And mechanical alloying operation was performed for 80 hours and Ti-Si alloy powder was obtained. The operating conditions of the mill apparatus during the mechanical alloying operation were an amplitude of 8 mm and a rotation speed of 1200 rpm.
A battery was fabricated in the same manner as in Example 10 except that the Ti—Si alloy obtained above was used as the negative electrode active material.

Example 16
Instead of Ti powder, Zr powder (purity 99.99%, particle size 100 to 150 μm) was used in the same manner as in Example 15 except that A phase mainly composed of Si and Zr And a Zr—Si alloy containing a B phase composed of an intermetallic compound of Si.
A battery was fabricated in the same manner as in Example 10 except that the Zr—Si alloy obtained above was used as the negative electrode active material.

Example 17
A phase mainly composed of Si as the negative electrode active material and Ni were obtained in the same manner as in Example 15 except that Ni powder (purity 99.99%, particle size 100 to 150 μm) was used instead of Ti powder. And a Ni-Si alloy containing a B phase composed of an intermetallic compound of Si.
A battery was fabricated in the same manner as in Example 10 except that the Ni—Si alloy obtained above was used as the negative electrode active material.

<< Comparative Example 2 >>
A battery was fabricated in the same manner as in Example 10 except that untreated LiCoO ₂ and untreated Si metal were used.

<< Comparative Example 3 >>
A battery was fabricated in the same manner as in Example 11 except that untreated LiNiO ₂ and untreated Si metal were used.

<< Comparative Example 4 >>
A battery was fabricated in the same manner as in Example 12 except that untreated LiMn ₂ O ₄ and untreated Si metal were used.

<< Comparative Example 5 >>
A battery was fabricated in the same manner as in Example 13 except that untreated LiCoO ₂ and untreated Sn metal were used.

<< Comparative Example 6 >>
A battery was fabricated in the same manner as in Example 14 except that untreated LiCoO ₂ and untreated Al metal were used.

<< Comparative Example 7 >>
A battery was fabricated in the same manner as in Example 15 except that untreated LiCoO ₂ and untreated Ti—Si alloy were used.

<< Comparative Example 8 >>
A battery was fabricated in the same manner as in Example 16 except that untreated LiCoO ₂ and untreated Zr—Si alloy were used.

<< Comparative Example 9 >>
A battery was fabricated in the same manner as in Example 17 except that untreated LiCoO ₂ and untreated Ni—Si alloy were used.

[Battery evaluation]
For the batteries of Examples 1 to 9 and Comparative Example 1 which are primary batteries, 10 batteries each were discharged to 2.0 V with a protective resistance of 15 kΩ.
Moreover, about the battery of Examples 10-17 which is a secondary battery, and Comparative Examples 2-9, it charges in the range of battery voltage 3.5-4.5V by the charge rate and the discharge rate 1C as a charging / discharging cycle test. And discharge were repeated alternately. And the capacity | capacitance maintenance factor at the time of 50 cycles was calculated | required from the following formula.
Capacity maintenance rate at 50 cycles (%)
= (Discharge capacity at 50 cycles / discharge capacity at 2 cycles) × 100
Table 1 shows the evaluation results of Examples 1 to 9 and Comparative Example 1 of the present invention.

  From Table 1, it was found that the batteries of Examples 1 to 9 of the present invention had a larger discharge capacity than the battery of Comparative Example 1 of the related art. This is because the manganese dioxide of the present invention has an organic group layer on the surface, so that aggregation between the manganese dioxide particles can be suppressed and can be uniformly mixed with the conductive assistant. Further, since the surface of the active material is hydrophobic, the electrode is easily impregnated with the electrolytic solution.

  Compared with the battery of Example 8, the battery of Example 7 had a larger discharge capacity. This is because the manganese dioxide used in Example 7 has a larger organic group molecular weight and a thick layer of alkoxyl groups on the surface of the manganese dioxide, so that the effect of preventing the aggregation of the active material particles and the surface of the active material are hydrophobic. This is thought to be due to the greater effect.

Moreover, the battery of Example 1 had a larger discharge capacity than the battery of Example 9. This is because the molecular weight of the alkoxyl group on the surface of manganese dioxide used in Example 9 is too large, so that the layer composed of the alkoxyl group on the surface of manganese dioxide becomes thick and the electron conduction on the surface of the active material particles is inhibited.
Next, Table 2 shows the evaluation results of Examples 10 to 17 and Comparative Examples 2 to 9 of the present invention.

  Compared with the batteries of Comparative Examples 2 to 9, the batteries of Examples 10 to 17 of the present invention have an organic group on the surface of the active material, so that the active material and the carbon as the conductive auxiliary agent are more uniformly dispersed. Since the current collecting property of the active material during charge / discharge was improved, the charge / discharge cycle characteristics were improved.

  The lithium battery of the present invention is suitably used as a power source for electronic devices such as portable devices and information devices.

It is a figure which shows the apparatus for producing the active material which has an organic group on the surface. It is a longitudinal cross-sectional view of the coin-type battery (primary battery) of the Example of this invention. It is a longitudinal cross-sectional view of the coin-type battery (secondary battery) of the other Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reaction tube 2 Tubular furnace 3 Thermocouple 4, 11 Positive electrode 5, 12 Lithium metal 6, 14 Separator 7, 15 Gasket 8, 16 Sealing plate 9, 17 Battery case 10, 18 Carbon paint 13 Negative electrode

Claims (5)

Lithium secondary comprising a positive electrode including a positive electrode active material capable of inserting / extracting lithium ions, a negative electrode including a negative electrode active material capable of inserting / extracting lithium ions, and a non-aqueous electrolyte in which a lithium salt is dissolved A battery,
The positive electrode active material is a metal oxide,
The negative electrode active material is one of a metal oxide, a metal, or an alloy,
At least one of the positive electrode active material and the negative electrode active material is obtained by bonding an alkoxyl group represented by —O—C _n H _{2n + 1} (n = 3 to 10) to the surface of lithium. Secondary battery. On the surface, Table with -O-C _n H _2n + 1 wherein active material alkoxyl group is bonded, represented by (n = 3 to 10) _{is, HO-C n H 2n +} 1 (n = 3~10) 2. The lithium secondary battery according to claim 1, wherein the lithium secondary battery is obtained by thermally condensing an alcohol and an active material. The lithium secondary battery according to claim 1, wherein the negative electrode active material or the positive electrode active material is a metal oxide. The lithium secondary battery according to claim 1, wherein the negative electrode active material is a metal. The lithium secondary battery according to claim 1, wherein the negative electrode active material is an alloy.

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