JP2006024413A - Substance, battery using the substance, and manufacturing method for the substance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high capacity battery, a substance suitable for electrode material of the battery, and a manufacturing method for the substance. <P>SOLUTION: A positive electrode active material layer 12B contains the substance whose composition ratio is Li<SB>a</SB>CoO<SB>b</SB>(0≤a<3.6, 1.4≤b<1.5). Valence of Co is reduced to 1 or less, 0 approximately, in electrochemical redox reaction between the substance and Li. Composition ratio b of oxygen of the substance is larger than that of Co<SB>3</SB>O<SB>4</SB>and smaller than that of Co<SB>2</SB>O<SB>3</SB>. Thereby quantity of lithium which can react electrochemically and reversibly can be increased resulting in high capacity of the battery. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a substance suitable as an electrode material, a battery using the same, and a method for producing the substance.

  The development and progress of portable electronic devices in recent years have been remarkable, and the demands for miniaturization, weight reduction and high capacity for the batteries used therein have increased rapidly. An example of a battery that meets such a requirement is a lithium secondary battery. Lithium secondary batteries can obtain a higher capacity than other batteries, but further improvements are desired, and one of them is the development of positive electrode materials.

Examples of the positive electrode material of the lithium secondary battery include Co ₃ O ₄ , Fe ₂ O ₃ , Ni ₂ O ₃ , CoFe ₂ O ₄ , cobalt phosphide, cobalt nitride, manganese vanadate, Li ₄ Ti ₅ O ₁₂ or There is a chalcogenite type such as Li ₆ Fe ₂ O ₃ (for example, see Patent Document 1). It has been known that some chalcogenite type materials have a very large capacity for a long time (see, for example, Non-Patent Document 1). However, conventionally, when lithium (Li) is occluded, the valence change of the metal element is controlled to be small so as to maintain the crystal structure, and the capacity remains very small. This is because the chalcogenite type material has poor cycle characteristics, and a large capacity is considered to be caused by an irreversible reaction.

  In contrast, Tarascon et al. Developed a special electrode structure by processing a chalcogenite-type material into a nano-size, which breaks the crystal structure when lithium is occluded, that is, intercalates lithium. Even if the material cannot be taken into the crystal, it is found that the metal element is reduced and cycled until the oxidation number becomes almost zero, and the large capacity of the chalcogenite type material is not due to an irreversible reaction. Prove that not.

As a result, research on chalcogenite-type materials has progressed, and in recent years, it has been confirmed that cycle characteristics are poor but reversible without processing into nano-size or a special electrode structure. Therefore, this chalcogenite type material is expected to give a capacity of 1600 Wh / l by future research, and is considered to be a necessary material for future batteries.
JP 2003-77544 A M. M. Shackray (MMThackeray), double. Ai. F. David (WIFDavid), Jay. Bee. JB Goodenough, “Mat. Res. Bull.”, 1982, No. 17, p. 785

  However, this material has a problem that a capacity that should be theoretically obtained has not yet been obtained.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a battery capable of obtaining a high capacity, a substance suitable as the material thereof, and a manufacturing method thereof.

The substance according to the present invention contains at least cobalt and oxygen among lithium (Li), cobalt (Co), and oxygen (O), and the composition ratio thereof is within the range shown in Chemical Formula 1.
(Chemical formula 1)
Li _a CoO _b
(In the formula, a and b are values within the range of 0 ≦ a <3.6 and 1.4 ≦ b <1.5.)

A battery according to the present invention includes an electrolyte together with a positive electrode and a negative electrode, and the positive electrode includes at least cobalt and oxygen among lithium, cobalt, and oxygen, and the composition ratio thereof is shown in chemical formula 2. It contains substances that are within.
(Chemical formula 2)
Li _a CoO _b
(In the formula, a and b are values within the range of 0 ≦ a <3.6 and 1.4 ≦ b <1.5.)

A method of manufacturing a substance according to the present invention is a process for manufacturing a substance containing at least cobalt and oxygen among lithium, cobalt, and oxygen, the composition ratio of which is within the range shown in Chemical Formula 3, This includes a step of using cobalt carbonate as a raw material and baking the cobalt carbonate at a temperature of 180 ° C. or higher and 250 ° C. or lower.
(Chemical formula 3)
Li _a CoO _b
(In the formula, a and b are values within the range of 0 ≦ a <3.6 and 1.4 ≦ b <1.5.)

  According to the substance of the present invention, the composition ratio b of oxygen is set in the range of 1.4 or more and less than 1.5, so that the amount of lithium that can react electrochemically and reversibly can be increased. it can. Therefore, for example, when used as a positive electrode material of a battery, the capacity can be improved.

  According to the method for producing a substance of the present invention, since cobalt carbonate is used as a cobalt raw material and is fired at 180 ° C. or higher and 250 ° C. or lower, the substance of the present invention can be easily obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

The substance according to one embodiment of the present invention contains cobalt and oxygen, or lithium, cobalt and oxygen, and the composition ratio thereof is within the range shown in Chemical Formula 4.
(Chemical formula 4)
Li _a CoO _b
(Wherein, a is a molar ratio of lithium to 1 mol of cobalt, b is a molar ratio of oxygen to 1 mol of cobalt, and values within the ranges of 0 ≦ a <3.6 and 1.4 ≦ b <1.5, respectively. is there.)

  This substance is a substance in which the valence of cobalt is reduced to 1 or less and substantially zero in an electrochemical redox reaction with lithium. That is, cobalt metal in a reduced state exists in an electrochemical redox reaction with lithium. Therefore, when this substance does not contain lithium, it exists as lithium cobaltate. When lithium is contained, depending on the amount of lithium, a lithium oxide phase, a cobalt metal phase, and a cobalt oxide phase are mixed. The state or the lithium oxide phase and the cobalt metal phase are mixed. In some cases, a lithium cobaltate phase may be present. However, the size of the cobalt metal phase is considered to be very small, about several nanometers, and since it is difficult to clearly distinguish each phase, it can be regarded as a compound of lithium, cobalt, and oxygen.

In this material, the composition ratio b of oxygen is larger than Co ₃ O ₄ and smaller than Co ₂ O ₃ , so that the amount of lithium that can be electrochemically reacted can be increased. It has become.

  The oxygen composition ratio b is the remaining weight obtained by electrochemically extracting lithium into cobalt oxide, analyzing the amount of cobalt contained in the cobalt oxide, and subtracting the weight of cobalt from the weight of cobalt oxide. Is the stoichiometric ratio obtained by determining the amount of oxygen assuming that all are oxygen, and dividing the amount of oxygen by the amount of cobalt.

This material can be, for example, the composition was calcined cobalt raw material After combining the cobalt oxide CoO _b, obtained by electrochemically reacting with lithium as needed. As a raw material of cobalt, cobalt carbonate (CoCO ₃ ) is preferable. This is because cobalt nitrate (CoNO ₃ ) or cobalt sulfate (CoSO ₄ ) or the like can be obtained only with a small oxygen composition ratio b. The firing temperature is preferably in the range of 180 ° C. or higher and 250 ° C. or lower. This is because the composition ratio b of oxygen can be controlled by adjusting the firing temperature, and the target composition ratio b can be obtained within this range. The atmosphere during firing is not particularly specified.

  This oxide is used, for example, in the following secondary battery as a positive electrode material.

  FIG. 1 shows a cross-sectional structure of a secondary battery using an oxide according to this embodiment. This secondary battery is a so-called coin-type battery. The disc-shaped positive electrode 12 accommodated in the outer can 11 and the disc-shaped negative electrode 14 accommodated in the outer cup 13 form the separator 15. Are stacked. The separator 15 is impregnated with an electrolytic solution that is a liquid electrolyte, and the outer peripheral portions of the outer can 11 and the outer cup 13 are sealed by caulking through a gasket 16. The outer can 11 and the outer cup 13 are made of, for example, a metal such as stainless steel or aluminum (Al).

  The positive electrode 12 includes, for example, a positive electrode current collector 12A and a positive electrode active material layer 12B provided on the positive electrode current collector 12A. The positive electrode current collector 12A is made of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil. The positive electrode active material layer 12B includes, for example, the material according to the present embodiment as a positive electrode active material, and is configured with a conductive agent such as carbon black or graphite and a binder such as polyvinylidene fluoride as necessary. Yes. Moreover, the other positive electrode active material may further be included.

  The negative electrode 14 includes, for example, a negative electrode current collector 14A and a negative electrode active material layer 14B provided on the negative electrode current collector 14A. The negative electrode current collector 14A is made of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil.

The negative electrode active material layer 14B includes, for example, one or more of a negative electrode material capable of inserting and extracting lithium, lithium metal, and a lithium alloy as a negative electrode active material. And a binder such as polyvinylidene fluoride. Examples of the anode material capable of inserting and extracting lithium include carbon materials, metal compounds, tin, tin alloys, silicon, silicon alloys, and conductive polymers, and any one or more of these are mixed. Used. Examples of the carbon material include graphite, non-graphitizable carbon, and graphitizable carbon, and examples of the metal compound include lithium titanium composite oxide (Li ₄ Ti ₅ O ₁₂ ) having a spinel structure, tungsten oxide (WO ₂ ), Oxides such as niobium oxide (Nb ₂ O ₅ ) or tin oxide (SnO), and examples of the conductive polymer include polyacetylene and polypyrrole. Among them, a carbon material is preferable because a change in crystal structure that occurs during charge and discharge is very small and good cycle characteristics can be obtained.

  The separator 15 separates the positive electrode 12 and the negative electrode 14 and allows lithium ions to pass through while preventing a short circuit of current due to contact between the two electrodes. The separator 15 is made of, for example, a porous film made of a synthetic resin made of polytetrafluoroethylene, polypropylene, polyethylene, or the like, or a porous film made of an inorganic material such as a ceramic nonwoven fabric. The porous film may be laminated.

The electrolytic solution is obtained by dissolving an electrolyte salt in a solvent, and exhibits ion conductivity when the electrolyte salt is ionized. Examples of the electrolyte salt include lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), lithium boron tetrafluoride (LiBF ₄ ), and trifluoromethanesulfonic acid. Examples thereof include lithium salts such as lithium (LiCF ₃ SO ₃ ) or bis (trifluoromethanesulfonyl) imide lithium (LiN (CF ₃ SO ₂ ) ₂ ). Any one electrolyte salt may be used alone, or two or more electrolyte salts may be mixed and used.

  Examples of the solvent include propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, γ-butyrolactone, sulfolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 2-methyltetrahydrofuran, 1,3-dioxolane, 3- Nonaqueous solvents such as methyl-1,3-dioxolane, methyl propionate, methyl butyrate, dimethyl carbonate, diethyl carbonate or dipropyl carbonate are preferred. Any one of the solvents may be used alone, or two or more may be mixed and used.

  This secondary battery can be manufactured, for example, as follows.

  First, for example, a positive electrode mixture is prepared by mixing the above-described oxide and, if necessary, a conductive agent and a binder, and dispersed in a solvent such as N-methyl-2-pyrrolidone to form a paste. The positive electrode current collector 12 </ b> A is applied to the solvent, and the solvent is dried. The positive electrode active material layer 12 </ b> B is formed by compression molding using a roll press or the like, and the positive electrode 12 is obtained.

  Next, for example, a negative electrode active material and, if necessary, a binder are mixed to prepare a negative electrode mixture, which is dispersed in a solvent such as N-methyl-2-pyrrolidone and pasted into a negative electrode current collector. It is applied to 14A, the solvent is dried, and compression molding is performed by a roll press or the like to form the negative electrode active material layer 14B. Further, for example, the negative electrode active material layer 14 </ b> B is formed on the negative electrode current collector 14 </ b> A by vapor deposition or plating to form the negative electrode 14.

  Subsequently, the negative electrode 14 and the separator 15 are placed in this order at the center of the outer cup 13, the electrolyte is poured from above the separator 15, and the outer can 11 containing the positive electrode 12 is covered and caulked through the gasket 17. Thereby, the secondary battery shown in FIG. 1 is formed.

  In this secondary battery, when discharged, for example, lithium ions are released from the negative electrode 14 or lithium metal is eluted as lithium ions and reacts with the positive electrode active material layer 12B through the electrolytic solution. When charging is performed, for example, lithium ions are released from the positive electrode active material layer 12B, and are inserted into the negative electrode 14 through the electrolytic solution or deposited as lithium metal. At that time, in the positive electrode active material layer 12B, an oxidation-reduction reaction with lithium occurs in the above-described substances, and during complete discharge, the cobalt valence is reduced to almost zero, which is 1 or less. Exists. As described above, since the composition ratio b of oxygen is adjusted in this substance, the amount of reactive lithium is increased.

  As described above, according to the present embodiment, the composition ratio b of oxygen is set within the range of 1.4 or more and less than 1.5, so that the amount of lithium that can be electrochemically and reversibly reacted is increased. can do. Therefore, when used as a positive electrode material of a battery, the capacity of the battery can be improved.

  In addition, since cobalt carbonate is used as a cobalt raw material and the raw material is fired at 180 ° C. or higher and 250 ° C. or lower, the oxide according to this embodiment can be easily obtained.

  Further, specific embodiments of the present invention will be described in detail.

(Examples 1-6)
First, cobalt carbonate powder was prepared as a cobalt raw material, and the cobalt carbonate powder was fired in air for 12 hours to obtain cobalt oxide powder. At that time, the firing temperature was changed to 250 ° C., 200 ° C., or 180 ° C. in Examples 1 to 6.

  About the obtained cobalt oxide powder of Examples 1-6, the composition ratio b of oxygen was investigated as follows. First, the obtained cobalt oxide powder was dissolved in concentrated hydrochloric acid, and the amount of cobalt was measured by a standard sample method using an ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy) apparatus. Next, the amount of oxygen was determined by taking all the remainder obtained by subtracting the weight of cobalt from the weight of the cobalt oxide powder as the weight of oxygen, and the value obtained by dividing the number of moles of oxygen by the number of moles of cobalt was defined as the oxygen composition ratio b. The obtained results are shown in Table 1. As a result, the composition ratio b of oxygen was in the range of 1.41 to 1.49. In this example, since lithium is not added, the amount of lithium is zero.

  Next, using the obtained cobalt oxide powders of Examples 1 to 6 as a positive electrode material, a coin-type battery as shown in FIG. 1 was prepared, the discharge capacity was measured, and the characteristics of the positive electrode material were evaluated.

  At that time, the positive electrode 12 was produced as follows. First, the produced cobalt oxide powder and polyvinylidene fluoride as a binder were mixed using N-methyl-2-pyrrolidone as a solvent to obtain a paste-like positive electrode mixture. The ratio of cobalt oxide to binder was set to cobalt oxide: binder = 9: 1 by mass ratio. Next, this positive electrode mixture was applied to a positive electrode current collector 12A made of copper foil and dried to form a positive electrode active material layer 12B. The positive electrode 12 was punched into a disk shape having a diameter of 16 mm.

A lithium metal plate punched into a disk shape with a diameter of 15 mm was used for the negative electrode 14, and LiPF ₆ was added at 1 mol / kg as a lithium salt in a solvent in which 1,3-dioxolane and 1,2-dimethoxyethane were mixed as the electrolyte. What was dissolved with the density | concentration of was used.

  The discharge capacity was measured by performing constant current discharge at 23 ° C. with a constant current of 1.0 mA until the battery voltage reached 0.9V. The results are shown in Table 1.

As Comparative Example 1 with respect to Examples 1 to 6, except that a commercially available Co ₃ O ₄ powder (manufactured by Aldrich) was used in place of the cobalt oxide powder produced as the positive electrode material, the others were as in Examples 1 to 6. A battery was prepared in the same manner as in Example 6, and the discharge capacity was determined. The results are also shown in Table 1. The composition of Co ₃ O ₄ used in Comparative Example 1 was not analyzed, but was considered to be almost Co ₃ O ₄ , and the oxygen composition ratio b was set to 1.33 and shown in parentheses in Table 1. It was.

  Further, as Comparative Examples 2 to 4, except that the firing temperature was changed to 850 ° C., 550 ° C., or 150 ° C., other than that, cobalt oxide powders were produced in the same manner as in Examples 1 to 6, and The composition ratio b of oxygen was examined. The obtained results are shown in Table 1. As a result, in Comparative Examples 2 and 3 in which the firing temperature was increased, the oxygen composition ratio b was smaller than 1.4, and in Comparative Example 4 in which the firing temperature was lowered, the oxygen composition ratio b was higher than 1.5.

  Further, as Comparative Examples 5 to 9, except that cobalt nitrate powder or cobalt sulfate powder was used as a raw material for cobalt, and the firing temperature was changed to 250 ° C., 550 ° C., or 850 ° C., other than Examples 1 to 6 Cobalt oxide powder was prepared in the same manner as above, and the oxygen composition ratio b was examined in the same manner. The obtained results are shown in Table 1. As a result, in Comparative Examples 5 to 7 using cobalt nitrate and Comparative Example 8 using cobalt sulfate, the oxygen composition ratio b was smaller than 1.4. Further, in Comparative Example 9 in which cobalt sulfate was used and the firing temperature was 550 ° C. lower than that of Comparative Example 8, an oxide having a spinel structure could not be obtained, and the oxygen composition ratio b could not be measured. .

  For these Comparative Examples 2 to 8, as in Examples 1 to 6, the obtained cobalt oxide powder was used as a positive electrode material to produce a battery and determine the discharge capacity. The results are also shown in Table 1.

  As shown in Table 1, according to Examples 1-6, a larger discharge capacity than Comparative Examples 1-8 could be obtained. FIG. 2 shows the relationship between the oxygen composition ratio b and the discharge capacity in Examples 1 to 6 and Comparative Examples 1 to 8. As can be seen from FIG. 2, the discharge capacity is greatly improved when the oxygen composition ratio b is in the range of 1.4 to less than 1.5.

  That is, if the oxygen composition ratio b is in the range of 1.4 to less than 1.5, the amount of lithium that can be reacted electrochemically and reversibly can be increased, and the capacity of the battery can be increased. It has been found that it can be improved. It was also found that cobalt carbonate is preferably used as the cobalt raw material, and the firing temperature is preferably in the range of 180 ° C. to 250 ° C.

  Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, in the above-described embodiments and examples, the case where an electrolytic solution that is a liquid electrolyte is used has been described, but another electrolyte may be used. Other electrolytes include, for example, a gel electrolyte in which an electrolytic solution is held in a polymer compound, a polymer electrolyte in which an electrolyte salt is dispersed in a polymer compound having ion conductivity, ion conductive ceramics, and ion conductive glass Or the inorganic solid electrolyte which consists of an ionic crystal etc., molten salt electrolyte, or what mixed these is mentioned.

Examples of the polymer compound of the gel electrolyte include polyvinylidene fluoride or a polymer thereof, or polyacrylonitrile or a polymer thereof. Examples of the polymer electrolyte include those obtained by dispersing LiSO ₃ CF ₃ in polyethylene oxide, and those using an ionomer. Furthermore, β ”-alumina, lithium nitride, NASiCON type compounds (“ HI CONDUCTIVITY SOLID IONIC CONDUCTORS-RECENT TRENDS AND APPLICATIONS ”“ TAKEHIKO TAKAHASHI ” TAKAHASHI) WORLD SCIENTIFIC, Singapore, 1989) or LISCON type compounds ("HIGH CONDUCTIVITY SOLID IONIC CONDUCTORS-RECENT TRENDS AND APPLICATIONS") (TAKEHIKO TAKAHASHI) World Scientific (WORLD SCIENTIFIC), Singapore, see 1989).

  In the above-described embodiments and examples, the coin-type secondary battery has been specifically described, but the present invention has other shapes such as a cylindrical shape having another structure, a button shape, or a square shape. The present invention can be similarly applied to a secondary battery or a secondary battery having another structure such as a winding structure. Furthermore, the present invention can be similarly applied to other batteries such as a primary battery.

It is sectional drawing showing the structure of the secondary battery using the oxide which concerns on one embodiment of this invention. It is a characteristic view showing the relationship between the oxygen composition ratio b and the discharge capacity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Outer can, 12 ... Positive electrode, 12A ... Positive electrode collector, 12B ... Positive electrode active material layer, 13 ... Outer cup, 14 ... Negative electrode, 14A ... Negative electrode collector, 14B ... Negative electrode active material layer, 15 ... Separator, 16 ... gasket.

Claims (5)

A substance comprising at least cobalt and oxygen among lithium (Li), cobalt (Co), and oxygen (O), the composition ratio of which is within the range shown in Chemical Formula 1.
(Chemical formula 1)
Li _a CoO _b
(In the formula, a and b are values within the range of 0 ≦ a <3.6 and 1.4 ≦ b <1.5.)   The substance according to claim 1, wherein the valence of cobalt is reduced to 1 or less in an electrochemical redox reaction with lithium. A battery comprising an electrolyte together with a positive electrode and a negative electrode,
The positive electrode contains a substance containing at least cobalt and oxygen among lithium (Li), cobalt (Co), and oxygen (O), the composition ratio of which is within the range shown in Chemical Formula 2. Battery characterized.
(Chemical formula 2)
Li _a CoO _b
(In the formula, a and b are values within the range of 0 ≦ a <3.6 and 1.4 ≦ b <1.5.)   The battery according to claim 3, wherein the substance is reduced to a cobalt valence of 1 or less in an electrochemical redox reaction with lithium. A method for producing a substance containing at least cobalt and oxygen among lithium (Li), cobalt (Co), and oxygen (O), the composition ratio of which is within the range shown in Chemical Formula 3,
A method for producing a substance comprising the step of using cobalt carbonate as a raw material of cobalt and baking the cobalt carbonate at a temperature of 180 ° C. or higher and 250 ° C. or lower.
(Chemical formula 3)
Li _a CoO _b
(In the formula, a and b are values within the range of 0 ≦ a <3.6 and 1.4 ≦ b <1.5.)

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