WO2017119410A1

WO2017119410A1 - Lithium-copper composite oxide

Info

Publication number: WO2017119410A1
Application number: PCT/JP2017/000017
Authority: WO
Inventors: タイタスニャムワロマセセ; 鹿野　昌弘; 栄部　比夏里; 博妹尾; 光佐野
Original assignee: 国立研究開発法人産業技術総合研究所
Priority date: 2016-01-05
Filing date: 2017-01-04
Publication date: 2017-07-13
Also published as: JPWO2017119410A1; JP6857361B2; TW201736269A; TWI790197B

Abstract

Provided is a novel compound that is useful as a cathode active material for a lithium ion secondary battery. A lithium-copper composite oxide represented by formula (1): Li_mCu_yX¹O_n. In formula (1), X¹ represents Si or Ge, y is 0.8-1.2, m is 1.5-2.5 and n is 3.9-4.1.

Description

Lithium copper complex oxide

The present invention relates to a lithium copper based composite oxide.

Lithium ion secondary batteries occupy the most important position among energy storage devices, and in recent years, their uses such as automobile batteries for plug-in hybrids are expanding.

Currently, positive electrode active materials such as LiCoO ₂ and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ are mainly used for positive electrodes of lithium ion secondary batteries (Non-patent Documents 1 and 2). However, the positive electrode material containing these positive electrode active materials is expensive because it contains a large amount of rare metals such as cobalt and nickel, and is also a factor causing a heat generation accident and the like because of its strong combustion resistance. .

Therefore, as a positive electrode active material that can solve these problems, iron-based poly (oxo) that uses iron, which is an element abundant in nature, and has a strong polyanionic acid skeleton to significantly reduce the combustion resistance. ) Anionic materials, especially LiFePO _4, are attracting attention (Non-patent Document 3).

However, since the positive electrode material such as LiFePO ₄ described above has a polyanion unit that does not participate in the charge / discharge reaction in the structure, it is more than a simple oxide positive electrode material such as LiCoO ₂ having a theoretical capacity of 274 mAh / g. In addition, the tap density is inevitably lowered due to the formation of fine particles and the combination with carbon in practical use.

The present invention has been made in view of such a current situation, and an object thereof is to provide a novel compound useful as a positive electrode active material for a lithium ion secondary battery.

The present inventors have intensively studied to solve the above-described problems of the present invention. As a result, we succeeded in synthesizing lithium copper complex oxide having a specific composition. Furthermore, it has been found that the lithium copper-based composite oxide can insert and desorb lithium ions and exhibits a theoretical charge / discharge capacity that is high enough to be used as a positive electrode active material for a lithium ion secondary battery. The present inventors have completed the present invention by conducting further research based on these findings.

That is, the present invention typically includes the subject matters described in the following sections.
Item 1.
Composition formula (1):
Li _m Cu _y X ¹ O _n
[In the composition formula (1), X ¹ represents Si or Ge. y represents 0.8 to 1.2. m represents 1.5 to 2.5. n represents 3.9 to 4.1. ]
Lithium copper-based composite oxide represented by
Item 2.
Item 2. The lithium copper-based composite oxide according to Item 1, having a monoclinic structure.
Item 3.
Item 3. The lithium copper based composite oxide according to Item 1 or 2, wherein the average particle size is 0.1 to 100 μm.
Item 4.
Item 4. The method for producing a lithium-copper composite oxide according to any one of Items 1 to 3, further comprising a step of heating a mixture containing lithium, copper, silicon or germanium, and oxygen.
Item 5.
Item 5. The method according to Item 4, wherein the heating temperature is 600 ° C or higher.
Item 6.
Composition formula (2):
Li _m Cu _y X ² O _n
[In the composition formula (2), X ² represents Si, Ti or Ge. y represents 0.8 to 1.2. m represents 1.5 to 2.5. n represents 3.9 to 4.1. ]
The positive electrode active material for lithium ion secondary batteries containing the lithium copper type complex oxide represented by these.
Item 7.
The positive electrode for lithium ion secondary batteries containing the positive electrode active material for lithium ion secondary batteries of said claim | item 6.
Item 8.
Furthermore, the positive electrode for lithium ion secondary batteries of the said claim | item 7 containing a conductive support agent.
Item 9.
A lithium ion secondary battery comprising the positive electrode for a lithium ion secondary battery according to Item 7 or 8.

Since the lithium copper based composite oxide of the present invention can insert and desorb lithium ions, it can be used as a positive electrode active material for lithium ion secondary batteries. In particular, by using the lithium copper-based composite oxide of the present invention as a positive electrode active material, a lithium ion secondary battery exhibiting high charge / discharge capacity can be obtained.

₂ is a diagram showing an X-ray diffraction pattern of Li ₂ CuSiO ₄ obtained in Example 1. FIG. The X-ray diffraction pattern of Li ₂ CuSiO ₄ obtained when the firing temperature was set to 900 ° C. in Example 1, CuO as a raw material compound, and Li ₂ CO ₃ and SiO ₂ as raw material compounds produced it is a diagram showing a ₂ result of comparison of the X-ray diffraction pattern of the SiO _3. Is a diagram showing the observation results by the scanning electron microscope of Example 1 _Li 2 CuSiO ₄ that the firing temperature was obtained when the 900 ° C. In (SEM). 6 is a diagram showing an X-ray diffraction pattern of Li ₂ CuGeO ₄ obtained in Example 2. FIG. Is a diagram showing the observation results by the scanning electron microscope of _Li 2 CuGeO ₄ obtained when a 900 ° C. The calcination temperature in Example 2 (SEM). 3 is a cross-sectional view of a test cell used in Examples 3 and 4. FIG. It is a figure which shows the measurement result of the open circuit potential performed in Example 3. It is a figure which shows the measurement result (C / 20 rate) of the charging / discharging characteristic performed in Example 3. FIG. It is a figure which shows the measurement result (C / 50 rate) of the charging / discharging characteristic performed in Example 3. FIG. It is a figure which shows the charging / discharging result of only carbon and PVdF. It is a figure which shows the measurement result of the open circuit potential performed in Example 4. It is a figure which shows the measurement result (C / 50 rate) of the charging / discharging characteristic performed in Example 4. FIG.

Hereinafter, the present invention will be described in detail. In the present specification, when a numerical range is indicated, the numerical range includes both numerical values.

1. Lithium copper-based composite oxide The lithium copper-based composite oxide of the present invention has a composition formula (1):
Li _m Cu _y X ¹ O _n
[In the composition formula (1), X ¹ represents Si or Ge. y represents 0.8 to 1.2. m represents 1.5 to 2.5. n represents 3.9 to 4.1. ]
It is a compound represented by these. Hereinafter, the compound may be referred to as “a compound represented by the composition formula (1)”.

In the composition formula (1), X ¹ is silicon (Si) or germanium (Ge).

In the composition formula (1), y is 0.8 to 1.2, and 0.8 to 1.0 is preferable from the viewpoint of increasing the capacity.

In the composition formula (1), m is 1.5 to 2.5, and preferably 1.75 to 2.25 from the viewpoint of easy insertion and desorption of lithium ions, capacity and potential. In the above general formula (1), n is 3.9 to 4.1, and 3.95 to 4.05 is considered from the viewpoint of easy insertion and removal of lithium ions, capacity and potential. preferable.

Specific examples of the compound represented by the composition formula (1) include Li ₂ CuSiO ₄ and Li ₂ CuGeO ₄ . Among these, Li ₂ CuSiO ₄ is preferable from the viewpoint of performance (particularly capacity improvement) when used as a positive electrode active material for a lithium ion secondary battery described later.

The crystal structure of the compound represented by the composition formula (1) is preferably a monoclinic structure. In particular, the compound represented by the composition formula (1) preferably has a monoclinic crystal structure as the main phase. In the compound represented by the compositional formula (1), the abundance of the crystal structure as the main phase is not particularly limited, and is 80 mol% or more based on the whole compound represented by the compositional formula (1). Is preferable, and it is more preferable that it is 90 mol% or more. For this reason, the compound represented by the composition formula (1) can be a material having a single-phase crystal structure, or a material having another crystal structure as long as the effects of the present invention are not impaired. You can also The crystal structure of the compound represented by the composition formula (1) can be confirmed by X-ray diffraction measurement.

The compound represented by the composition formula (1) has peaks at various positions in the X-ray diffraction pattern by CuKα rays.

For example, Li ₂ CuSiO ₄ has a diffraction angle 2θ of 18.3 to 19.3 °, 26.3 to 27.0 °, 27.1 to 28.0 °, 28.8 to 29.6 °, 29. 9-30.5 °, 32.3-32.9 °, 35.5-36.7 °, 38.6-39.9 °, 40.8-42.0 °, 43.6-45.2 °, 45.7 to 46.8 °, 47.1 to 48.3 °, 48.5 to 49.8 °, 50.8 to 52.7 °, 53.7 to 55.2 °, 55.6 It preferably has peaks at -58.2 °, 62.3-63.4 °, 63.8-65.1 °, 68.6-71.0 °, and the like.

Also, for example, Li ₂ CuGeO ₄ has a diffraction angle 2θ of 17.9 to 19.2 °, 24.9 to 27.0 °, 31.6 to 33.4 °, 35.0 to 39.2 °, 41.2 to 43.4 °, 49.2 to 51.5 °, 53.2 to 55.4 °, 56.9 to 58.7 °, 60.1 to 62.7 °, 63.7 to 65 It preferably has peaks at .2 °, 66.5 to 68.5 °, 69.9 to 71.7 °, 72.7 to 75.5 °, 76.9 to 78.4 °, and the like.

The average particle size of the compound represented by the composition formula (1) is not particularly limited, and is preferably 0.1 to 100 μm, and preferably 0.1 to 50 μm from the viewpoint of shortening the Li ⁺ diffusion path. More preferably. In addition, the average particle diameter of the compound represented by the composition formula (1) can be confirmed by a scanning electron microscope (SEM).

2. Method for Producing Lithium Copper Complex Oxide In the method for producing a compound represented by the above composition formula (1), as a raw material compound for obtaining a mixture containing lithium, copper, silicon or germanium, and oxygen, Finally, lithium, copper, silicon or germanium, and oxygen may be contained in the mixture in a predetermined ratio. For example, lithium-containing compound, copper-containing compound, silicon-containing compound or germanium-containing compound, oxygen A containing compound or the like can be used.

The type of each compound such as a lithium-containing compound, a copper-containing compound, a silicon-containing compound, a germanium-containing compound, and an oxygen-containing compound is not particularly limited. One type of each element of lithium, copper, silicon, germanium, and oxygen It is also possible to use a mixture of four or more kinds of compounds including a compound containing two or more elements at the same time among lithium, copper, silicon or germanium, and oxygen as a part of the raw material. A mixture of less than four compounds can also be used.

As these raw material compounds, lithium, copper, silicon or germanium, and compounds containing no metal elements other than oxygen (particularly rare metal elements) are preferable. Moreover, it is preferable that elements other than each element of lithium, copper, silicon or germanium, and oxygen contained in the raw material compound are separated or volatilized by the heat treatment described later.

Specific examples of such raw material compounds include the following compounds.

Examples of the lithium-containing compound include metallic lithium (Li); lithium bromide (LiBr); lithium oxalate (Li ₂ C ₂ O ₄ ); lithium fluoride (LiF); lithium iodide (LiI); lithium sulfate (Li ₂ ). SO ₄ ); methoxy lithium (LiOCH ₃ ); ethoxy lithium (LiOC ₂ H ₅ ); lithium hydroxide (LiOH); lithium nitrate (LiNO ₃ ); lithium chloride (LiCl); lithium carbonate (Li ₂ CO ₃ ), etc. Can be mentioned.

Examples of the copper-containing compound include metal copper (Cu); copper oxide (CuO); copper hydroxide (Cu (OH) ₂ ); copper carbonate (CuCO ₃ ); copper oxalate (CuC ₂ O ₄ ); copper sulfate (CuSO) ₄ ); copper chloride (CuCl ₂ ); copper iodide (CuI); copper acetate (Cu (CH ₃ COO) ₂ ) and the like.

Silicon-containing compounds include silicon (Si); silicon oxide (SiO ₂ ); tetraethoxysilane (SiOC ₂ H ₅ ); tetramethoxysilane (SiOCH ₃ ); silicon tetrabromide (SiBr ₄ ); silicon tetrachloride (SiCl) ₄ ) and the like.

Germanium compounds include germanium (Ge); germanium oxide (GeO ₂ ); germanium tetrachloride (GeCl ₄ ); germanium tetrabromide (GeBr ₄ ); germanium tetraiodide (GeI ₄ ); germanium tetrafluoride (GeF ₄₎ ); Germanium disulfide (GeS ₂ ) and the like.

Examples of the oxygen-containing compound include lithium hydroxide (LiOH); lithium carbonate (Li ₂ CO ₃ ); copper oxide (CuO); copper hydroxide (Cu (OH) ₂ ); copper carbonate (CuCO ₃ ); copper oxalate ( CuC ₂ O ₄ ); silicon oxide (SiO ₂ ); germanium oxide (GeO ₂ ) and the like.

In addition, a hydrate can also be used for these raw material compounds.

In addition, as the raw material compound used in the production method of the present invention, a commercially available product can be used, or it can be appropriately synthesized and used. The synthesis method in the case of synthesizing each raw material compound is not particularly limited, and can be carried out according to a known method.

The shape of these raw material compounds is not particularly limited. From the viewpoint of ease of handling and the like, a powder form is preferable. From the viewpoint of reactivity, it is preferable that the particles are fine, and the average particle diameter is more preferably 1 μm or less (preferably about 10 to 500 nm, particularly preferably about 60 to 80 nm). . In addition, the average particle diameter of a raw material compound can be measured with a scanning electron microscope (SEM).

A mixture containing lithium, copper, silicon or germanium, and oxygen can be obtained by mixing necessary materials among the above-described raw material compounds.

The mixing ratio of each raw material compound is not particularly limited, and it is preferable to mix so that the composition of the compound represented by the above composition formula (1) which is the final product is obtained. The mixing ratio of the raw material compounds is preferably such that the ratio of each element contained in the raw material compound is the same as the ratio of each element in the compound represented by the composition formula (1) to be generated.

The method for preparing a mixture containing lithium, copper, silicon or germanium, and oxygen is not particularly limited, and a method capable of uniformly mixing each raw material compound can be employed. For example, mortar mixing, mechanical milling treatment, coprecipitation method, a method of mixing after each raw material compound is dispersed in a solvent, a method of dispersing each raw material compound at once in a solvent and mixing, etc. can be adopted. . Among these, a mixture can be obtained by a simple method by employing mortar mixing, and a uniform mixture can be obtained by employing a coprecipitation method.

Further, when performing mechanical milling as the mixing means, for example, a ball mill, a vibration mill, a turbo mill, a disk mill, or the like can be used as the mechanical milling device, and a ball mill is preferable. Moreover, when performing a mechanical milling process, it is preferable to perform mixing and a heating simultaneously.

The atmosphere during mixing and heating is not particularly limited. For example, an inert gas atmosphere such as argon or nitrogen, a hydrogen gas atmosphere, or the like can be employed. Further, mixing and heating may be performed under reduced pressure such as vacuum.

When heating a mixture containing lithium, copper, silicon or germanium and oxygen, the heating temperature is not particularly limited, and the crystallinity of the compound represented by the above composition formula (1) and the electrode obtained From the viewpoint of further improving the characteristics (capacity and potential), it is preferably 600 ° C. or higher, more preferably 700 ° C. or higher, further preferably 800 ° C. or higher, and particularly preferably 900 ° C. or higher. preferable. The upper limit of the heating temperature is not particularly limited as long as the temperature is such that the compound represented by the composition formula (1) can be easily produced (for example, about 1500 ° C.). In other words, the heating temperature is preferably 600 to 1500 ° C., more preferably 700 to 1500 ° C., further preferably 800 to 1500 ° C., and particularly preferably 900 to 1500 ° C. .

3. Positive electrode active material for lithium ion secondary battery Since the compound represented by the above composition formula (1) has the above composition and crystal structure, it can insert and desorb lithium ions. It can be used as a positive electrode active material. Therefore, this invention includes the positive electrode active material for lithium ion secondary batteries containing the compound represented by the said composition formula (1).

Further, not only the compound represented by the composition formula (1) but also the composition formula (2):
Li _m Cu _y X ² O _n
[In the composition formula (2), X ² represents Si, Ti or Ge. y represents 0.8 to 1.2. m represents 1.5 to 2.5. n represents 3.9 to 4.1. ]
Lithium copper-based composite oxides can also be used as positive electrode active materials for lithium ion secondary batteries because lithium ions can be inserted and removed. Hereinafter, the lithium copper-based composite oxide represented by the composition formula (2) may be referred to as “a compound represented by the composition formula (2)”. Therefore, this invention includes the positive electrode active material for lithium ion secondary batteries containing the compound represented by the said composition formula (2).

In the following, a positive electrode active material for a lithium ion secondary battery containing a compound represented by the composition formula (1) and a positive electrode active material for a lithium ion secondary battery containing a compound represented by the composition formula (2) May be collectively described as “the positive electrode active material for a lithium ion secondary battery of the present invention”.

In the composition formula (2), X ² is silicon (Si), titanium (Ti), or germanium (Ge).

In the composition formula (2), y is 0.8 to 1.2, and 0.8 to 1.0 is preferable from the viewpoint of increasing the capacity.

In the above composition formula (2), m is 1.5 to 2.5, and preferably 1.75 to 2.25 from the viewpoint of easy insertion and desorption of lithium ions, capacity and potential. n is 3.9 to 4.1, and is preferably 3.95 to 4.05 from the viewpoint of easy insertion and removal of lithium ions, capacity and potential.

Specific examples of the compound represented by the composition formula (2) include Li ₂ CuSiO ₄ , Li ₂ CuTiO ₄ , and Li ₂ CuGeO ₄ . Among these, Li ₂ CuSiO ₄ is preferable from the viewpoint of performance (particularly capacity improvement) when used as a positive electrode active material for a lithium ion secondary battery.

The crystal structure of the compound represented by the composition formula (2) is preferably a monoclinic structure. In particular, the compound represented by the composition formula (2) preferably has a monoclinic crystal structure as the main phase. In the compound represented by the composition formula (2), the amount of the crystal structure that is the main phase is not particularly limited, and is 80 mol% or more based on the whole compound represented by the composition formula (2). Is preferable, and it is more preferable that it is 90 mol% or more. For this reason, the compound represented by the composition formula (2) can be a material having a single-phase crystal structure, or a material having another crystal structure as long as the effects of the present invention are not impaired. You can also. The crystal structure of the compound represented by the composition formula (2) can be confirmed by X-ray diffraction measurement.

The compound represented by the composition formula (2) has peaks at various positions in the X-ray diffraction pattern by CuKα rays.

The average particle size of the compound represented by the composition formula (2) is not particularly limited, and is preferably 0.1 to 100 μm, and preferably 0.1 to 50 μm from the viewpoint of shortening the Li ⁺ diffusion path. It is more preferable. In addition, the average particle diameter of the compound represented by the composition formula (2) can be confirmed by a scanning electron microscope (SEM).

Method for producing a compound represented by the formula (2) include lithium, copper, and the X ^2, the step of heating a mixture comprising oxygen.

Lithium-containing compounds, copper-containing compounds, X ² containing compound is not particularly limited about the kind of each compound such as oxygen-containing compounds, lithium, copper, four or comprises one by one each element of X ^2, and oxygen It is also possible to use a mixture of more compounds, and a compound containing two or more elements of lithium, copper, X ² and oxygen at the same time is used as a part of the raw material, and less than four kinds A mixture of compounds can also be used.

As these raw material compounds, compounds containing no metal elements other than lithium, copper, X ² , and oxygen (particularly rare metal elements) are preferable. Moreover, it is preferable that elements other than each element of lithium, copper, X ² , and oxygen contained in the raw material compound are separated or volatilized by a heat treatment described later.

Examples of the lithium-containing compound include lithium oxalate (Li ₂ C ₂ O ₄ ); lithium hydroxide (LiOH); lithium nitrate (LiNO ₃ ); lithium chloride (LiCl); lithium carbonate (Li ₂ CO ₃ ) and the like. .

Examples of the copper-containing compound include metal copper (Cu); copper oxide (CuO); copper hydroxide (Cu (OH) ₂ ); copper carbonate (CuCO ₃ ); copper oxalate (CuC ₂ O ₄ ); cupric chloride (CuCl ₂ ); cupric sulfate (CuSO ₄ ); cupric nitrate (Cu (NO ₃ ) ₂ ); cupric sulfate (CuSO ₄ ) and the like.

Examples of the titanium-containing compound include titanium tetrachloride (TiCl ₄ ) and titanium hydroxide (Ti (OH) ₂ ). Examples of the silicon-containing compound include silicon (Si); silicon oxide (SiO ₂ ) and the like.

Examples of the germanium compound include germanium (Ge); germanium oxide (GeO ₂ ) and the like.

Examples of the oxygen-containing compound include lithium hydroxide (LiOH); lithium carbonate (Li ₂ CO ₃ ); copper oxide (CuO); copper hydroxide (Cu (OH) ₂ ); copper carbonate (CuCO ₃ ); copper oxalate ( CuC ₂ O ₄ ); silicon oxide (SiO ₂ ); titanium oxide (TiO ₂ ); titanium hydroxide (Ti (OH) ₂ ); germanium oxide (GeO ₂ ) and the like.

In addition, a hydrate can also be used for these raw material compounds.

In addition, as the raw material compound used in the method for producing the compound represented by the composition formula (2), a commercially available product can be used, or it can be synthesized and used as appropriate. The synthesis method in the case of synthesizing each raw material compound is not particularly limited, and can be carried out according to a known method.

The shape of these raw material compounds is not particularly limited. From the viewpoint of ease of handling and the like, a powder form is preferable. Further, from the viewpoint of reactivity, it is preferable that the particles are fine, and it is more preferable that the particles have a mean particle size of 1 μm or less (preferably about 10 to 100 nm, particularly preferably about 60 to 80 nm). . In addition, the average particle diameter of a raw material compound can be measured with a scanning electron microscope (SEM).

Lithium, and copper, and X ^2, mixture comprising oxygen can be obtained by mixing the necessary materials of the feed compounds described above.

The mixing ratio of each raw material compound is not particularly limited, and it is preferable to mix so as to have a composition possessed by the compound represented by the composition formula (2) which is the final product. The mixing ratio of the raw material compounds is preferably such that the ratio of each element contained in the raw material compound is the same as the ratio of each element in the compound represented by the composition formula (2) to be generated.

Lithium, and copper, and X ^2, not particularly limited as methods for preparing the mixture comprising oxygen, it is possible to employ a method of each raw material compound can be uniformly mixed. For example, mortar mixing, mechanical milling treatment, coprecipitation method, a method of mixing after each raw material compound is dispersed in a solvent, a method of dispersing each raw material compound at once in a solvent and mixing, etc. can be adopted. . Among these, a mixture can be obtained by a simple method by employing mortar mixing, and a uniform mixture can be obtained by employing a coprecipitation method.

Lithium, and copper, and X ^2, when heating a mixture comprising oxygen, crystallinity and electrode characteristics of heating is not particularly limited as temperature, the compound represented by the obtained above composition formula (2) From the viewpoint of further improving (capacity and potential), it is preferably 600 ° C. or higher, more preferably 700 ° C. or higher, further preferably 800 ° C. or higher, and particularly preferably 900 ° C. or higher. . The upper limit of the heating temperature is not particularly limited as long as the temperature is such that the compound represented by the composition formula (2) can be easily produced (for example, about 1500 ° C.). In other words, the heating temperature is preferably 600 to 1500 ° C., more preferably 700 to 1500 ° C., further preferably 800 to 1500 ° C., and particularly preferably 900 to 1500 ° C. .

The positive electrode active material for a lithium ion secondary battery of the present invention includes a compound represented by the above composition formula (1) or a compound represented by the composition formula (2) and a carbon material (for example, carbon black such as acetylene black) And a material) may form a composite. Thus, since the carbon material suppresses particle growth during firing, it is possible to obtain a fine electrode positive electrode active material for a lithium ion secondary battery having excellent electrode characteristics. In this case, the content of the carbon material is preferably 1 to 30% by mass, more preferably 3 to 20% by mass, and particularly preferably 5 to 15% by mass in the positive electrode active material for a lithium ion secondary battery of the present invention. is there.

The positive electrode active material for a lithium ion secondary battery of the present invention contains the compound represented by the above composition formula (1) or the compound represented by the composition formula (2). The positive electrode active material for a lithium ion secondary battery of the present invention may be composed of only the compound represented by the composition formula (1) or the compound represented by the composition formula (2), or the composition described above. In addition to the compound represented by the formula (1) or the compound represented by the composition formula (2), an unavoidable impurity may be included. Examples of such inevitable impurities include the raw material compounds described above. The content of inevitable impurities is 10 mol% or less, preferably 5 mol% or less, more preferably 2 mol% or less, as long as the effects of the present invention are not impaired.

4). Positive electrode for lithium ion secondary battery and lithium ion secondary battery The positive electrode material for lithium ion secondary battery and lithium ion secondary battery of the present invention are the compound represented by the above composition formula (1) or the composition formula (2). The basic structure is the known positive electrode for non-aqueous electrolyte (non-aqueous) lithium ion secondary battery and non-aqueous electrolyte (non-aqueous) lithium ion, except that the compound represented by A configuration similar to that of the secondary battery can be employed. For example, the positive electrode, the negative electrode, and the separator can be disposed in the battery container such that the positive electrode and the negative electrode are separated from each other by the separator. Thereafter, the lithium ion secondary battery of the present invention can be manufactured by, for example, sealing the battery container after filling the battery container with the nonaqueous electrolytic solution. The lithium ion secondary battery of the present invention may be a lithium secondary battery. In the present specification, “lithium ion secondary battery” means a secondary battery using lithium ions as carrier ions, and “lithium secondary battery” means a secondary that uses lithium metal or a lithium alloy as a negative electrode active material. Means battery.

The positive electrode for a lithium ion secondary battery of the present invention has a structure in which a positive electrode active material containing a compound represented by the above composition formula (1) or a compound represented by the composition formula (2) is supported on a positive electrode current collector. Can be adopted. For example, a positive electrode material containing the compound represented by the above-described composition formula (1) or the compound represented by the composition formula (2), a conductive auxiliary agent, and a binder as necessary is used as a positive electrode current collector. It can be manufactured by coating.

As the conductive aid, for example, carbon materials such as acetylene black, ketjen black, carbon nanotube, vapor grown carbon fiber, carbon nanofiber, graphite, coke, etc. can be used. The shape of the conductive auxiliary agent is not particularly limited, and for example, a powder form can be adopted.

As the binder, for example, fluorine resins such as polyvinylidene fluoride resin and polytetrafluoroethylene can be used.

The content of various components in the positive electrode material is not particularly limited, and can be appropriately determined from a wide range. For example, the compound represented by the composition formula (1) or the compound represented by the composition formula (2) is 50 to 95% by volume (particularly 70 to 90% by volume), and the conductive assistant is 2.5 to 25%. It is preferable to contain volume% (especially 5 to 15 volume%) and 2.5 to 25 volume% (particularly 5 to 15 volume%) of a binder.

Examples of the material constituting the positive electrode current collector include aluminum, platinum, molybdenum, and stainless steel. Examples of the shape of the positive electrode current collector include a porous body, a foil, a plate, and a mesh made of fibers.

It should be noted that the amount of the positive electrode material applied to the positive electrode current collector is not particularly limited, and is preferably determined appropriately according to the use of the lithium ion secondary battery.

Examples of the negative electrode active material constituting the negative electrode include lithium metal; silicon; silicon-containing acrylate compound; lithium alloy; M ¹ M ² ₂ O ₄ (M ¹ : Co, Ni, Mn, Sn, etc., M ² : Mn, Ternary or quaternary oxides represented by Fe, Zn, etc .; M ³ ₃ O ₄ (M ³ : Fe, Co, Ni, Mn, etc.), M ⁴ ₂ O ₃ (M ⁴ : Fe, Co, Ni) , Mn, etc.), MnV ₂ O ₆ , M ⁵ O ₂ (M ⁵ : Sn, Ti etc.), M ⁶ O (M ⁶ : Fe, Co, Ni, Mn, Sn, Cu etc.) Oxides; graphite, hard carbon, soft carbon, graphene; carbon materials described above; organic systems such as Li ₂ C ₆ H ₄ O ₄ , Li ₂ C ₈ H ₄ O ₄ , Li ₂ C ₁₆ H ₈ O ₄ Compounds and the like.

Examples of lithium alloys include alloys containing lithium and aluminum as constituent elements, alloys containing lithium and zinc as constituent elements, alloys containing lithium and lead as constituent elements, alloys containing lithium and manganese as constituent elements, lithium and bismuth. Alloys containing lithium and nickel as constituent elements, alloys containing lithium and antimony as constituent elements, alloys containing lithium and tin as constituent elements, alloys containing lithium and indium as constituent elements; metal (scandium) , Titanium, vanadium, chromium, zirconium, niobium, molybdenum, hafnium, tantalum, and the like) and carbon containing MXene alloy, M ⁷ _x BC ₃ alloy (M ⁷ : Sc, Ti, V, Cr, Zr, Nb, Mo, Hf Ta, etc.) quaternary layered carbide or nitride compounds such like.

The negative electrode can be composed of a negative electrode active material, and a configuration in which a negative electrode material containing a negative electrode active material, a conductive additive, and a binder as required is supported on the negative electrode current collector is adopted. You can also. When adopting a configuration in which the negative electrode material is supported on the negative electrode current collector, a negative electrode mixture containing a negative electrode active material, a conductive additive, and a binder as necessary is applied to the negative electrode current collector. Can be manufactured.

When the negative electrode is composed of a negative electrode active material, the above negative electrode active material has a shape suitable for an electrode (plate shape, etc.)
It can be obtained by molding.

In addition, when adopting a configuration in which the negative electrode material is supported on the negative electrode current collector, the types of the conductive auxiliary agent and the binder, and the negative electrode active material, the conductive auxiliary agent, and the binder content are those of the positive electrode described above. Can be applied. Examples of the material constituting the negative electrode current collector include aluminum, copper, nickel, and stainless steel. Examples of the shape of the negative electrode current collector include a porous body, a foil, a plate, and a mesh made of fibers. In addition, it is preferable to determine suitably the application quantity of the negative electrode material with respect to a negative electrode collector according to the use etc. of a lithium ion secondary battery.

The separator is not limited as long as it is made of a material that can separate the positive electrode and the negative electrode in the battery and can hold the electrolyte solution to ensure the ionic conductivity between the positive electrode and the negative electrode. For example, polyolefin resin such as polyethylene, polypropylene, polyimide, polyvinyl alcohol, terminal aminated polyethylene oxide; fluorine resin such as polytetrafluoroethylene; acrylic resin; nylon; aromatic aramid; inorganic glass; Materials in the form of a membrane, nonwoven fabric, woven fabric, etc. can be used.

The non-aqueous electrolyte is preferably an electrolyte containing lithium ions. Examples of such an electrolytic solution include a lithium salt solution, an ionic liquid composed of an inorganic material containing lithium, and the like.

Examples of the lithium salt include lithium halides such as lithium chloride, lithium bromide and lithium iodide; lithium inorganic salts such as lithium perchlorate, lithium tetrafluoroborate, lithium hexafluorophosphate and lithium hexafluoroarsenate Compound: Lithium organic salt compounds such as bis (trifluoromethylsulfonyl) imide lithium, bis (perfluoroethanesulfonyl) imide lithium, lithium benzoate, lithium salicylate, lithium phthalate, lithium acetate, lithium propionate, Grignard reagent, etc. Can be mentioned.

Examples of the solvent include carbonate compounds such as propylene carbonate, ethylene carbonate, dimethol carbonate, ethylmethyl carbonate, and diethyl carbonate; lactone compounds such as γ-butyrolactone and γ-valerolactone; tetrahydrofuran, 2-methyltetrahydrofuran, diethyl Ether compounds such as ether, diisopropyl ether, dibutyl ether, methoxymethane, glyme, dimethoxyethane, dimethoxymethane, diethoxymethane, diethoxyethane, propylene glycol dimethyl ether; acetonitrile; N, N-dimethylformamide; N-propyl-N- And methylpyrrolidinium bis (trifluoromethanesulfonyl) imide.

Further, a solid electrolyte can be used instead of the non-aqueous electrolyte. Examples of the solid electrolyte include lithium ion conductors such as Li ₁₀ GeP ₂ S ₁₂ , Li ₇ P ₃ S ₁₁ , Li ₇ La ₃ Zr ₂ O ₁₂ , La _0.51 Li _0.34 TiO _{2.94, and the} like. Enumerated.

In such a lithium ion secondary battery of the present invention, since the compound represented by the composition formula (1) or the compound represented by the composition formula (2) is used, the oxidation-reduction reaction (charge / discharge reaction) is performed. A higher potential and energy density can be ensured, and safety (polyanion skeleton) and practicality are excellent. Therefore, the lithium ion secondary battery of the present invention can be suitably used, for example, for devices that are required to be downsized and high performance.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.

Example _1: A synthetic material powder of _{_{Li 2 CuSiO 4, Li 2 CO}} 3 ( manufactured by Rare Metallic Co.; 99.9% (3N)), CuO ( Kojundo Chemical Laboratory Co., Ltd.; 99.99% (4N )), And precipitated amorphous SiO ₂ (manufactured by Kanto Chemical Co .; 3N). Li ₂ CO ₃ , CuO, and SiO ₂ were weighed so that the ratio of lithium: copper: silicon (molar ratio) was 2: 1: 1, and placed in a chrome steel container together with zirconia balls (15 mmΦ × 10 pieces). The mixture was pulverized and mixed for 24 hours at 400 rpm in a planetary ball mill (manufactured by Fritsch, trade name: P-6). Then, after removing acetone under reduced pressure, the recovered powder was pelleted by hand pressing and calcined at 600 ° C., 700 ° C., 800 ° C., 900 ° C., or 1000 ° C. for 1 hour under an argon stream. At this time, the temperature rising rate was 400 ° C./h. The cooling rate was set to 100 ° C./h up to 300 ° C., and thereafter, the mixture was naturally cooled to room temperature. Each obtained product (Li ₂ CuSiO ₄ ) was confirmed by powder X-ray diffraction (XRD). The results are shown in FIG.

Further, X-rays of Li ₂ CuSiO ₄ obtained when the firing temperature is set to 900 ° C., CuO as the raw material compound, and Li ₂ SiO ₃ generated from the raw material compounds Li ₂ CO ₃ and SiO ₂ The result of comparing the diffraction patterns is shown in FIG.

In addition, for powder X-ray diffraction (XRD) measurement, an X-ray diffraction measurement device (manufactured by Rigaku Corporation, trade name: RINT2200) was used, and the X-ray source was CuKα monochromatized with a monochromator. Data were collected under the measurement conditions of a tube voltage of 5 kV and a tube current of 300 mA. At this time, the scanning speed was set so that the intensity was about 10,000 counts. The sample used for measurement was sufficiently pulverized so that the particles were uniform. Rietveld analysis was performed for the structural analysis, and JANA-2006 was used as the analysis program.

FIG. 1 confirms that when the firing temperature is 800 ° C. or higher, a plurality of main peaks are observed at least at 2θ values of 15 to 70 °. Further, since the peak observed at 2θ value of 15 to 70 ° is stronger as the firing temperature is higher, it was found that a higher firing temperature is preferable.

From FIG. 1, the plurality of main peaks confirmed at 2θ values of 15 to 70 ° correspond to single-phase Li ₂ CuSiO ₄ , and thus single-phase Li ₂ CuSiO ₄ is obtained as a product. I understood. Further, from FIG. 2, CuO which is a raw material compound, and from the fact that peaks derived from _Li 2 SiO ₃ generated from _Li 2 CO ₃ and SiO ₂ which is a raw material compound is not verified, the single-phase Li ₂ It was found that CuSiO ₄ was obtained.

Also, from FIG. 1, the Li ₂ CuSiO ₄ crystals obtained when the firing temperature was set to 900 ° C. had a diffraction angle expressed by 2θ of 18.31 to 19 in an X-ray diffraction pattern by powder X-ray diffraction. .24 °, 26.39 to 26.96 °, 27.22 to 27.39 °, 28.90 to 29.59 °, 38.65 to 39.82 °, 40.88 to 41.92 °, 43 63 to 45.12 °, 45.72 to 46.70 °, 47.21 to 48.23 °, 48.56 to 49.71 °, 50.87 to 52.69 °, 53.81 to 55. It was found to have peaks at 14 °, 55.66-58.17 °, 62.40-63.33 °, 63.88-65.04 °, and 68.67-70.90 °. From the results, the obtained crystal of Li ₂ CuSiO ₄ has a monoclinic structure (space group C2 / m), the lattice constant is a = 6.457-6.484４８, b = 3.340-3 .345Å, c = 9.504 ~ 11.183Å, a β = 93.65 ~ 121.78 °, the unit cell volume (V) was found to be crystalline is 205.1 ~ 206.0Å ³ .

Furthermore, Li ₂ CuSiO ₄ obtained when the firing temperature was 900 ° C. was observed with a scanning electron microscope (SEM). The results are shown in FIG. In FIG. 3, the scale bar indicates 11.7 μm. From FIG. 3, it was found that Li ₂ CuSiO ₄ having a particle diameter of about 3 to 10 μm was obtained.

Further, when the chemical composition of the product obtained when the firing temperature was 900 ° C. was measured by ICP-AES method (measuring device: iCAP6500, manufactured by Thermo Fisher Scientific), Li _2.08 Cu _{1.05 was obtained.} It was found to be Si _1.00 O ₄ .

Example 2 Li ₂ CO ₃ (manufactured by Rare Metallic; 99.9% (3N)), CuO (manufactured by High-Purity Chemical Laboratories ); 99.99% (4N) as a synthetic raw material powder of Li ₂ CuGeO ₄ )), And GeO ₂ (manufactured by Kanto Chemical Co .; 99.99% (4N)). Li ₂ CO ₃ , CuO, and GeO ₂ were weighed so that the ratio of lithium: copper: germanium (molar ratio) was 2: 1: 1, placed in a chromium steel container together with zirconia balls (15 mmΦ × 10), and acetone The mixture was pulverized and mixed for 24 hours at 400 rpm in a planetary ball mill (manufactured by Fritsch, trade name: P-6). Then, after removing acetone under reduced pressure, the collected powder was pelleted by hand and baked at 700 ° C., 800 ° C., or 900 ° C. for 1 hour under an argon stream. At this time, the temperature rising rate was 400 ° C./h. The cooling rate was set to 100 ° C./h up to 300 ° C., and thereafter, the mixture was naturally cooled to room temperature. Each obtained product (Li ₂ CuGeO ₄ ) was confirmed by powder X-ray diffraction (XRD) in the same manner as in Example 1. The results are shown in FIG.

From FIG. 4, it was confirmed that when the firing temperature was 700 ° C. or higher, a plurality of main peaks were observed at least at 2θ values of 15 to 80 °. These peaks, since it corresponds to the _Li 2 CuGeO ₄ single-phase, _Li 2 CuGeO ₄ single-phase is found to be obtained as a product. Further, since the peak observed at the 2θ value of 15 to 80 ° is stronger as the firing temperature is higher, it was found that a higher firing temperature is preferable.

Also, from FIG. 4, the Li ₂ CuSiO ₄ crystals obtained when the firing temperature was set to 700 ° C. had a diffraction angle of 17.94 to 19 expressed by 2θ in the X-ray diffraction pattern by powder X-ray diffraction. .15 °, 24.96 to 26.91 °, 31.65 to 33.32 °, 35.07 to 39.17 °, 41.30 to 43.39 °, 49.29 to 51.44 °, 53 24 to 55.30 °, 56.92 to 58.63 °, 60.16 to 62.63 °, 63.79 to 65.19 °, 66.57 to 68.44 °, 69.92 to 71. It was found to have peaks at 64 °, 72.80-75.41 °, and 76.94-78.33 °. From the results, the obtained crystal of Li ₂ CuGeO ₄ has a monoclinic structure (space group C2 / m), the lattice constants are a = 5.491 to 5.552５５, and b = 9.645 to 9 .691Å, c = 5.491 ~ 5.552Å, a β = 119.69 ~ 120.75 °, the unit cell volume (V) was found to be crystalline is 256.1 ~ 256.6Å ³ .

Furthermore, Li ₂ CuGeO ₄ obtained when the firing temperature was 900 ° C. was observed with a scanning electron microscope (SEM). The results are shown in FIG. In FIG. 5, the scale bar indicates 27.0 μm. From FIG. 5, it was found that Li ₂ CuGeO ₄ having a particle diameter of about 1 to 50 μm was obtained.

Further, when the chemical composition of the product obtained when the firing temperature was 900 ° C. was measured by the EDX method (measuring device: JSM-7800F, manufactured by JEOL Ltd.), the mass ratio of Cu and Ge was 1: It was found to be 0.956.

Example _3: Li 2 to make measurements discharge measurements of the charge and discharge characteristics of CuSiO _{_4,} _Li 2 CuSiO ₄ were obtained when the firing temperature 900 ° C. In the first embodiment, polyvinylidene fluoride (PVDF), and Acetylene black (AB) was mixed in an agate mortar so that the volume ratio was 85: 7.5: 7.5, and the resulting slurry was applied onto an aluminum foil (thickness 20 μm) as a positive electrode current collector, This was punched into a circle with a diameter of 8 mm to obtain a positive electrode. Further, in order to prevent the sample from being peeled off from the positive electrode current collector, it was pressure-bonded at 30 to 40 mPa.

Metal lithium punched out at 14 mmφ was used for the negative electrode, and two porous membranes (trade name: celgard 2500) cut out at 18 mmφ were used as the separator. The electrolytic solution is an electrolytic solution (manufactured by Kishida Chemical Co., Ltd.) in which LiPF ₆ is dissolved at a concentration of 1 mol / dm ³ as a supporting electrolyte in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 1: 2. used. The battery was produced in Globe Books under an argon atmosphere because of the use of metallic lithium and the cause of increased resistance when water was mixed in the electrolyte. As the cell, a CR2032-type coin cell shown in FIG. 6 was used. Prior to the charge / discharge test, the potential in a state where no current was applied to the electrode (ie, open circuit potential) was measured. The constant current charge / discharge measurement was started from charging by using a voltage switch, setting a C / 20 rate or C / 50 rate, a current of 10 mA / g, an upper limit voltage of 4.8 V, and a lower limit voltage of 1.5 V. Moreover, the charge / discharge measurement was performed in a state where the cell was placed in a 55 ° C. constant temperature bath. FIG. 7 shows the measurement results of the open circuit potential, FIG. 8 shows the measurement results of the charge / discharge characteristics at the C / 20 rate (relationship between each cycle and the discharge capacity), and the measurement results of the charge / discharge characteristics at the C / 50 rate. As shown in FIG. The C rate means a current density necessary for charging / discharging the theoretical capacity from the electrode active material in one hour.

From FIG. 7, it was found that the open circuit potential of Li ₂ CuSiO ₄ was about 3.0V. Further, from FIG. 8, it was found that the initial charge capacity withdrawn at the C / 20 rate was about 110 mAh / g. The theoretical capacity is 316 mAh / g, and the initial charge / discharge capacity of Li ₂ CuSiO ₄ corresponds to about one third of the theoretical capacity. Further, as shown in FIG. 8, since the voltage (average operating voltage) at the intersection of the charging curve and the discharging curve was about 3.3 V, Li ₂ CuSiO ₄ was used as a positive electrode material having a high potential and a high capacity. It turned out to be useful.

Furthermore, from FIG. 9, it was confirmed that the initial charge capacity of Li ₂ CuSiO ₄ was 220 mAh / g (capacity corresponding to about 70% of the theoretical capacity) at the C / 50 rate. Also from this, Li ₂ CuSiO ₄ is expected as a high capacity material.

Further, a positive electrode was produced in the same manner as described above except that Li ₂ CuSiO ₄ was not used, and a charge / discharge test was performed at a C / 20 rate under the same conditions as described above. The results are shown in FIG.

From FIG. 10, it was confirmed that charge / discharge capacity could not be obtained with an electrode that did not use Li ₂ CuSiO ₄ . By comparing FIG. 8 with FIG. 10, it was found that the high charge / discharge capacity shown in FIG. 8 was derived from Li ₂ CuSiO ₄ .

Example _4: Li 2 to make measurements discharge measurements of the charge and discharge characteristics of CuGeO _4, the example _Li 2 CuGeO ₄ were obtained when the firing temperature 900 ° C. at 2, polyvinylidene fluoride (PVDF), and Acetylene black (AB) was mixed in an agate mortar so that the volume ratio was 85: 7.5: 7.5, and the resulting slurry was applied onto an aluminum foil (thickness 20 μm) as a positive electrode current collector, This was punched into a circle with a diameter of 8 mm to obtain a positive electrode. Further, in order to prevent the sample from being peeled off from the positive electrode current collector, it was pressure-bonded at 30 to 40 mPa.

Metal lithium punched out at 14 mmφ was used for the negative electrode, and two porous membranes (trade name: celgard 2500) cut out at 18 mmφ were used as the separator. The electrolytic solution is an electrolytic solution (manufactured by Kishida Chemical Co., Ltd.) in which LiPF ₆ is dissolved at a concentration of 1 mol / dm ³ as a supporting electrolyte in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 1: 2. used. The battery was produced in Globe Books under an argon atmosphere because of the use of metallic lithium and the cause of increased resistance when water was mixed in the electrolyte. As the cell, a CR2032-type coin cell shown in FIG. 6 was used. Prior to the charge / discharge test, the potential in a state where no current was applied to the electrode (ie, open circuit potential) was measured. The constant current charge / discharge measurement was started from charging by using a voltage switch, setting a C / 50 rate, a current of 10 mA / g, an upper limit voltage of 4.8 V, and a lower limit voltage of 1.5 V. Moreover, the charge / discharge measurement was performed in a state where the cell was placed in a 55 ° C. constant temperature bath. FIG. 11 shows the measurement result of the open circuit potential, and FIG. 12 shows the measurement result of the charge / discharge characteristics (relationship between each cycle and the discharge capacity).

From FIG. 11, it was found that the open circuit potential of Li ₂ CuGeO ₄ was about 2.7V. Also, from FIG. 12, it was found that the initial extraction capacity was about 120 mAh / g. The theoretical capacity is 250 mAh / g, and the initial charge / discharge capacity of Li ₂ CuGeO ₄ corresponds to about one half of the theoretical capacity. From the above results, it was found that Li ₂ CuGeO ₄ is useful as a positive electrode material having a high potential and a high capacity.

DESCRIPTION OF SYMBOLS 1 Lithium ion secondary battery 2 Negative electrode terminal 3 Negative electrode 4 Separator impregnated with electrolyte 5 Insulation packing 6 Positive electrode 7 Positive electrode can

Claims

Composition formula (1):
Li m Cu y X 1 O n
[In the composition formula (1), X 1 represents Si or Ge. y represents 0.8 to 1.2. m represents 1.5 to 2.5. n represents 3.9 to 4.1. ]
Lithium copper-based composite oxide represented by
The lithium copper-based composite oxide according to claim 1, having a monoclinic structure.
3. The lithium copper based composite oxide according to claim 1, wherein the average particle size is 0.1 to 100 μm.
The method for producing a lithium copper-based composite oxide according to any one of claims 1 to 3, further comprising a step of heating a mixture containing lithium, copper, silicon or germanium, and oxygen.
The method according to claim 4, wherein the heating temperature is 600 ° C. or higher.
Composition formula (2):
Li m Cu y X 2 O n
[In the composition formula (2), X 2 represents Si, Ti or Ge. y represents 0.8 to 1.2. m represents 1.5 to 2.5. n represents 3.9 to 4.1. ]
The positive electrode active material for lithium ion secondary batteries containing the lithium copper type complex oxide represented by these.
The positive electrode for lithium ion secondary batteries containing the positive electrode active material for lithium ion secondary batteries of Claim 6.
Furthermore, the positive electrode for lithium ion secondary batteries of Claim 7 containing a conductive support agent.
The lithium ion secondary battery containing the positive electrode for lithium ion secondary batteries of Claim 7 or 8.