JP2845150B2 - Rechargeable battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery using an alkali metal, and more particularly to an increase in the capacity of a secondary battery.

[0002]

2. Description of the Related Art A secondary battery which is an object of the present invention comprises:
A battery characterized in that an active material containing an alkali metal or an alkali metal ion is used for a negative electrode. A typical example is a lithium secondary battery. Lithium secondary batteries that can store 2 to 3 times more electric energy per unit weight and unit volume than lead-acid batteries or nickel-cadmium batteries can be used to drive portable electric devices and portable computers. And as a power source for memory backup.

An active material composed of a metal oxide is often used for a positive electrode of a lithium secondary battery, and the metal oxide has a property of reversibly inserting and extracting alkali metal ions in a crystal lattice. It is. For the negative electrode, an active material such as an alkali metal, an alloy containing an alkali metal, or a compound obtained by intercalating an alkali metal ion is used. As the electrolyte, a non-aqueous electrolyte in which a salt of an alkali metal ion is dissolved, or a solid polymer containing a salt of an alkali metal ion is used.

[0004] Then, for the purpose of increasing the discharge capacity of the positive electrode active material, for example, Japanese Patent Application Laid-Open No.
In 5-290890, the technology of Li _x Co _y Ni _1-y O ₂ in which the transition metal ion in the positive electrode active material is replaced with a foreign metal ion is also described in JP-A-5-101828, a part of Co, such as _{1-x Mn x O 2 V} , Cr, techniques LiCoO ₂ was replaced with Cu is disclosed.

[0005]

[Problems to be solved by the invention] However,
The discharge capacity per weight or volume of the battery active material is small, and the weight or volume of the electrode occupying the battery is not satisfactory. That is, there remains a problem that the amount of electric energy that can be stored in a secondary battery using an alkali metal, that is, the energy density is increased.

Accordingly, it is an object of the present invention to increase the discharge capacity of a positive electrode active material per weight, improve the capacity density of a secondary battery using an alkali metal, and provide a high capacity secondary battery. is there.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a secondary battery comprising a positive electrode comprising a positive electrode active material containing an alkali metal ion, a negative electrode, and a non-aqueous electrolyte. Contains a different metal ion different from the alkali metal ion, and the different metal ion is a monovalent cation A ⁺ having an ion radius larger than that of the alkali metal ion, and is represented by the following formula (1). The standard equilibrium potential of the oxidation-reduction reaction for the different metal ion is less than or equal to the standard equilibrium potential of the redox reaction of oxygen represented by the formula (2), and
The standard equilibrium potential of the oxidation-reduction reaction for the foreign metal ion is achieved when the positive electrode active material is higher than the minimum operating potential for electrochemically absorbing and releasing the cation A ⁺ .

[0008] ^{A + + e - → A (} 1) O 2 + 4H + + 4e - → 2H 2 O (2) In addition, the positive electrode active _{material, Li 1-y Ag y CoO} 2 or Li _1-y Cu _y Co
It is also achieved by having the formula O ₂ , where y is in the range of 0.01 to 0.12.

[0009]

According to the above construction, the positive electrode active material contains alkali metal ions and dissimilar metal ions, so that a positive electrode active material having a large discharge capacity can be obtained. Density can be improved.

Hereinafter, a lithium secondary battery will be described as a typical example of a secondary battery using an alkali metal, and the operation of the present invention will be described in detail from a principle and a method. Positive electrode active materials used in lithium secondary batteries include α-NaFeO ₂ structural system LiCoO ₂ , LiNiO _{2 and the} like, spinel structure system LiMn ₂ O _{4 and the} like, and Co, Ni contained in their oxides. , Mn and the like are oxides obtained by partially substituting other transition metal ions. Li ⁺ of these positive electrode active materials is present in a layered region surrounded by O ²⁻ , and is occluded and released electrochemically.
In the present invention, included in the positive electrode active material of α-NaFeO ₂ structure system
By replacing a part of Li ⁺ with a foreign metal ion, the crystal site where Li ⁺ is intercalated is extended, and L ⁺
The i ⁺ storage capacity could be increased. Hereinafter, a transition metal ion that forms a layered structure with O ²⁻ is referred to as a host metal ion.

When Li ⁺ intercalates between the layers of the above-mentioned metal oxide, the volume of the oxide changes with an increase in the interval between layers composed of host metal ions and O ²⁻ . One of the reasons why the capacity of a battery cannot be increased by a charge / discharge cycle of a lithium secondary battery is that crystals easily collapse due to a change in volume of the positive electrode active material. Therefore,
If the change in the interlayer distance between LiCoO ₂ and LiNiO ₂ during charge and discharge can be suppressed, an increase in the capacity of the positive electrode active material can be expected.

According to the present invention, a positive electrode active material having an extended layer interval is intercalated between layers of a layered oxide such as LiCoO ₂ and LiNiO ₂ by intercalating a different metal ion having an ion radius larger than that of Li ^+. developed. With such a cathode active material, it is possible to reduce the volume change of the positive electrode active material during intercalation of Li ^+, it is easy to Li ⁺ diffusion in layers of active material, the change in the interlayer distance It is to be suppressed.

Next, the requirement of a different metal ion which is effective in extending the layer interval of the positive electrode active material will be described. The first requirement is that the foreign metal ion has a larger ionic radius than Li ^+, one of the alkali metal ions, and is a monovalent cation. Such a monovalent cation,
Li ^{+ of the} same valence intercalated in the positive electrode active material
Can be replaced with Also, even if monovalent ions intercalate between layers, the electrostatic repulsion on Li ⁺ is smaller than that of polyvalent ions. Therefore, the positive electrode active material substituted with monovalent ions can intercalate more Li ⁺ than the positive electrode active material substituted with multivalent ions.

The second requirement is that the standard equilibrium potential of the redox reaction of the foreign metal ion is lower than the standard equilibrium potential of the redox reaction of oxygen. This potential corresponds to 1.23 V based on the standard hydrogen electrode and 4.27 V based on the standard lithium electrode. Dissimilar metals satisfying this condition include, for example, Ag and Cu
The oxidation-reduction reaction of these metals and the equilibrium potential E ⁰ are shown below.

[0015] ^{Ag + + e - → Ag E} 0 = 0.7991 V (3.84 V) Cu + + e - → Cu E 0 = 0.521 V (3.56 V) , however, numerical values in parentheses shown in the right of the reaction equation above Is a value based on the equilibrium potential of the oxidation-reduction reaction of Li metal in the standard state. If the equilibrium potential of the redox reaction of the foreign metal is higher than the equilibrium potential of the redox reaction of oxygen, when the foreign metal ion is intercalated into the positive electrode active material, moisture in the atmosphere is reduced by the foreign metal ion. It is oxidized and foreign metal ions are reduced. Therefore, when the standard equilibrium potential of the redox reaction of the foreign metal ion is 1.23 V or more based on the standard hydrogen electrode, it becomes difficult to handle the foreign metal ion in the air, which is not preferable. As for the production cost of the positive electrode active material, a process capable of producing the positive electrode active material in the atmosphere can be reduced, and thus, Ag ⁺ and Cu ^{+ that} are chemically stable in the atmosphere can be said to be suitable.

The third requirement is to provide a condition for the lower limit of the standard equilibrium potential of the oxidation-reduction reaction of a foreign metal ion. That is, the standard equilibrium potential of the oxidation-reduction reaction for different metal ions is the operating potential (operating voltage) for the positive electrode active material to electrochemically occlude and release alkali metal ions.
Is higher than the lowest value of

The minimum value of the operating potential refers to the potential when the battery is discharged to its limit and the potential drops to the minimum.
This is also called a discharge termination potential (discharge termination voltage). Then, for example, Ag ^{+ +} e ^- → equilibrium potential of Ag is,
If the operating potential of the positive electrode is higher than the minimum value, Ag ⁺ is always maintained in a state of Ag in the positive electrode crystal.

Although a theoretical explanation of this condition cannot be given clearly yet, if a foreign metal ion satisfying this condition is intercalated between the layers of the positive electrode active material, some of the foreign metal ions are charged and discharged during positive electrode charging and discharging. It is presumed that the ions are reduced and hardly desorbed from the interlayer. For example, in the case of a lithium secondary battery having an operating voltage of 3 V or more, which is a target of the present invention, Ag ⁺ and Cu ⁺ taken up in the second requirement described above become dissimilar metal ions satisfying the third requirement. The inventor has obtained the above-mentioned knowledge. During discharging of the lithium secondary battery, the positive electrode potential may be near or below the equilibrium potential of Ag ⁺ and Cu ⁺ . At this time, the electron density of Ag ⁺ and Cu ⁺ intercalated between the layers may increase, and the ions may be partially reduced.

In the case of a secondary battery using lithium, the foreign metal ions satisfying the above three requirements are Ag ⁺ and Cu ⁺ .

These ions have an Li ⁺ ion radius of 0.073.
It has an ionic radius larger than that of Li ⁺ compared to nm, and the ionic radius of Cu ⁺ is 0.074 nm and that of Ag ⁺ is 0.116 nm. The redox potential of these dissimilar metal ions is close to or higher than the positive electrode operating potential, as described above, and is lower than the redox potential of oxygen. Therefore, these dissimilar metal ions can be intercalated between the layers of the positive electrode active material having a layered structure such as LiCoO ₂ and LiNiO ₂ instead of Li ⁺ , and the intercalated metal ions are converted to the positive electrode oxide. Enlarge the layers between.

As will be described in detail in the following examples, in the present invention, Ag ⁺ has the greatest effect of increasing the capacity. Since Ag ⁺ is partially reduced at a low potential, it is estimated that Ag ⁺ is most effective for increasing the capacity of the positive electrode active material. When the Ag ⁺ is partially reduced, the ionic radius of the Ag ⁺ increases, and the Li ⁺ diffusion between the layers becomes easy to spread the layers of the positive electrode active material, and the valence of Ag ⁺ decreases. Therefore, repulsion with Li ⁺ inserted into the crystal lattice is reduced. As a result, Li ⁺ diffusion in the positive electrode crystal becomes extremely easy, and the capacity reduction rate can be reduced even when the charge / discharge current of the positive electrode is increased.
That is, there is an effect that the rate characteristics of the battery are improved and the life of the battery is extended.

Further, even in the case of a positive electrode active material which electrochemically occludes and releases an alkali metal other than lithium metal, a foreign metal ion satisfying the above three requirements is replaced with a part of the alkali metal ion. By doing so, the capacity of the positive electrode can be increased. For example, in the case of a secondary battery using sodium metal, Ag ⁺ can be used because the ionic radius of Na ⁺ is 0.113 nm.

Based on the principle of the present invention, means for introducing a foreign metal ion into a positive electrode active material of a secondary battery using an alkali metal will be described. A typical example of a positive electrode active material having a layered structure is A _x BO ₂ when represented by a chemical formula. Here, A is an alkali metal, such as Li or Na. B is C
It is a transition metal such as o or Ni, and x is a numerical value of 0 or more.
B may be one in which Co or Ni is partially substituted with a transition metal such as Co, Ni, Mn, or V. For example, if y and z are 0
Given these numbers, A _x Co _1-y Ni _y O ₂ , A _x Ni _1-y Mn _y
O ₂ , A _x Co _1-yz Ni _y Mn _z O ₂ and the like. In order to substitute an alkali metal contained in these oxides with a different metal, a thermal decomposition method, an ion exchange method, or the like may be applied.

In the case of the thermal decomposition method, when synthesizing the positive electrode active material, a salt of a different metal is mixed with the raw material of the positive electrode active material, and the mixture is subjected to heat treatment, so that the different metal ions and alkali metal ions are randomly distributed between the layers. Ranked. For example, when synthesizing Li _1-x Ag _x CoO ₂ as a composition of silver ions, Li, Ag and Co are used so that the molar ratio is 1-x: x: 1.
Is mixed and heated in the air or in an oxygen stream. LiOH, Li ₂ CO ₃ , LiNO that can be used
₃ , LiClO _{4 and the} like, Ag salts include AgNO ₃ , AgCl, AgClO ₄ ,
CH ₃ COOAg, etc., and Co compounds include Co (NO ₃ ) ₃ , CoCl ₃ , C
o (OH) ₃ , Co ₂ O ₃ and the like.

When replacing Cu ⁺ , Cu ₂ CO ₃ , CuCl, C
Use uBr, CuI, CuSCN, etc. The thermal decomposition temperature depends on the decomposition temperature of the salt used, and when using nitrate,
Decomposition at a low temperature of about 250 to 500 ° C is possible. Also, C
When synthesizing a Ni-based positive electrode active material instead of an o-based positive electrode active material, oxides such as Li ₂ O and Ag ₂ O can be used for the Li salt and the Ag salt. When Li ⁺ is replaced with Cu ⁺ , Cu ₂ CO ₃ ,
Use CuCl, CuBr, CuI, CuSCN, etc. Ni (OH) ₃ or Ni ₂ O ₃ is used as the Ni oxide. Unless Ni-based oxides are synthesized in an atmosphere that is more oxidizing than Co-based oxides, trivalent Ni ³⁺ will not be generated. Therefore, a mixture of the above-described Li salt, Ag salt, and Ni oxide is placed in an oxygen stream. Synthesized at a high temperature of 600 ° C or higher.

When the ion exchange method is applied, LiCoO ₂ , Na
A cathode active material such as CoO ₂ , LiNiO ₂ , and NaNiO ₂ is prepared. When ion exchange is performed in a solution phase, the above-described positive electrode active material and a salt of a different metal are dissolved in water, or an alcohol such as methanol or ethanol, a ketone such as acetone, or a nitrile-based polar solvent such as acetonitrile and refluxed. . Salts of different metals that can be used here are Cu ₂ CO ₃ , CuCl,
In addition to CuBr and CuI, organometallic complexes such as CuN (CH ₃ ) ₄ can also be used.

In addition to the above method, there is an ion exchange method using a molten salt, which is a method in which a molten salt of a different metal is brought into contact with a positive electrode active material. Metal nitrates such as AgNO ₃ and CuNO ₃ are 150
Since it melts at a temperature of ℃ or higher, there is no need for high-temperature heating operation. Therefore, by heating a mixture of a metal nitrate and a positive electrode active material such as LiCoO ₂ or LiNiO ₂ and bringing the nitrate in a molten state into contact with the positive electrode active material, a part of the alkali metal in the positive electrode is replaced with a foreign metal ion. be able to. The above-described ion exchange method is effective when a high temperature is required by a thermal decomposition method and Ag ⁺ and Cu ⁺ are likely to become oxides having a high oxidation number. For example, LiNi
When a positive electrode active material in which Li ⁺ of O ₂ is replaced by Cu ⁺ is synthesized by a pyrolysis method, a high temperature of 600 ° C. or more is required, and Cu ⁺ is oxidized to Cu ²⁺ . In such a case, the ion exchange method is suitable.

[0028]

Embodiments Embodiments 1 to 5 will be described below.

Embodiment 1 FIG. 1 is a half sectional view of a cylindrical lithium secondary battery according to an embodiment of the present invention. First, LiCoO ₂ was produced by the method described below. LiNO ₃ and Co ₂ O ₃ are mixed in an equimolar ratio. At this time, if a small amount of pure water is added, uniform mixing can be achieved.
In addition to LiNO ₃ , LiOH, Li ₂ CO _{3 and the} like, and Li salts can also be used. When a mixture of LiNO ₃ and Co ₂ O ₃ is heat-treated at 400 to 500 ° C. for 5 hours in the atmosphere, a black powder is obtained. This powder
Is LiCoO _2, was used after classified by a sieve it. The chemical composition confirmed that the above chemical formula was correct by inductively coupled plasma emission analysis.

Then, a carbon powder and a binder were mixed with LiCoO ₂ , and the mixture was pressed against an aluminum current collector to produce a sheet-shaped positive electrode 1. On the other hand, graphite powder was used as the negative electrode active material, and a mixture obtained by mixing a binder with the powder was pressed on a copper current collector to produce a sheet-shaped negative electrode 2. An electrode group 4 having a polypropylene separator 3 sandwiched between sheets of the positive electrode 1 and the negative electrode 2 was wound. The electrode group 4 is housed in a metal battery case 6 with a polymer insulating sheet 5 laid on the bottom, and the negative electrode lead wire 7 is connected to the battery case 6.
Welded. Then, a mixed solvent of ethylene carbonate and diethyl carbonate in an equal volume ratio was mixed with a 1 molar equivalent of Li.
A non-aqueous electrolyte solution in which PF ₆ is dissolved is poured into the inside of the battery container 6, the insulating plate 8 is placed on the wound electrode group 4, and the positive electrode lead wire 9 is inserted through the center hole of the insulating plate 8 into the container lid 10. Connected to the positive electrode terminal 11 on the upper side. Finally, the container lid 10 and the battery container 6 were crimped to seal the container, thereby producing a cylindrical battery. Hereinafter, the battery manufactured as described above is referred to as Type 1.

Next, Li _0.99 Ag _0.01 CoO ₂ , Li _0.98 Ag
_0.02 CoO ₂ , Li _0.95 Ag _0.05 CoO ₂ , and Li _0.90 Ag _0.10 CoO ₂ were synthesized, and four types of cylindrical batteries using Ag-added positive electrode active materials were produced. To synthesize these four types of positive electrode active materials, 0.99: 0.01: 1, 0.98: 0.02: 1, 0.95: 0.0
LiNO ₃ , AgN mixed at a molar ratio of 5: 1, 0.90: 0.10: 1
O ₃ and Co ₂ O ₃ are heat-treated in air at 400-500 ° C. for 5 hours to obtain powdered L from each sample.
i _0.99 Ag _0.01 CoO ₂ , Li _0.98 Ag _0.02 CoO ₂ , Li _0.95 Ag _0.05 C
oO ₂ and Li _0.90 Ag _0.10 CoO ₂ were obtained. The powder was used after being classified by a sieve. The chemical composition of each positive electrode active material was confirmed by an induction plasma emission method.

From the powder X-ray diffraction pattern of the Ag-added cathode active material synthesized here, it was found that the interval between the layers composed of Co ³⁺ and O ²⁻ was larger than that of LiCoO ₂ . For example, in the case of Li _0.95 Ag _0.05 CoO ₂ , it was found that the layer spacing was increased by about 0.04 nm as compared with LiCoO ₂ . The result is Ag ⁺
Indicates that the layer is inserted between layers composed of Co ³⁺ and O ²⁻ .

The procedure for producing a cylindrical battery using four kinds of positive electrode active materials to which Ag is added is the same as that of Type 1. A carbon powder and a binder were mixed with each of the positive electrode active materials prepared by the above-described method, and the mixture was pressed on an aluminum current collector to prepare a sheet-shaped positive electrode 1 for each positive electrode active material.

However, the weight of the positive electrode active material contained in each positive electrode was the same as that of LiCoO ₂ used in Type 1. On the other hand, graphite powder was used as a negative electrode active material, and a mixture of the powder and a binder was pressed against a copper current collector to produce a sheet-shaped negative electrode 2. Positive electrode 1 and negative electrode 2
The electrode group 4 with the separator 3 interposed was wound between the sheets. The electrode group 4 was housed in a battery case 6 having an insulating sheet 5 laid on the bottom, and the negative electrode lead wire 7 was welded to the battery case 6. Then, LiPF ₆ equivalent to 1 molar concentration was added to a mixed solvent of ethylene carbonate and diethyl carbonate in an equal volume ratio.
Is injected into the battery container 6,
An insulating plate 8 was placed on the wound electrode group 4, and a positive electrode lead wire 9 was connected to a positive electrode terminal 11 on a container lid 10 through a hole in the insulating plate 8. Finally, the container lid 10 and the battery container 6 were crimped to seal the container, and a cylindrical battery having the same specifications as in Type 1 was produced. Hereinafter, Li _0.99 Ag _0.01 CoO ₂ , Li _0.98 Ag _0.02 Co
Batteries using O ₂ , Li _0.95 Ag _0.05 CoO ₂ , and Li _0.90 Ag _0.10 CoO ₂ are referred to as type 2, type 3, type 4, and type 5, respectively.

FIG. 2 is a diagram showing the relationship between the discharge capacity and the cycle number of the five types (types 1 to 5) of cylindrical batteries manufactured in Example 1. Battery operating voltage 3.0-4.2 V
The current value during charging and discharging was set to 100 mA.

In the case of type 1 containing 0% Ag, an average operating voltage of 3.6 V and a discharge capacity of 1250 mAh were obtained in the first cycle. The discharge capacity of this battery was almost constant up to 200 cycles, and a slight decrease in capacity was observed after 200 cycles. 500
The capacity reduction rate of the battery up to the cycle was 28% of the initial capacity.

In the case of Type 2 containing 1% of Ag, the average operating voltage was 3.6 V during the initial cycle.
Exactly the same as above, but the capacity was increased by about 50 mAh compared to type 1. This capacity increase is due to the addition of 1% Ag to LiCoO ₂ .

In the case of Type 3 and Type 4 in which the amount of Ag added was large, the average operating voltage was 3.6 V, but the capacity was of Type 2
Became bigger than. In particular, in the case of Type 4 in which the amount of Ag added was 5%, the discharge capacity was increased to 1400 mAh, and the capacity reduction rate was significantly reduced as compared with Type 1 in which Ag was not added. On the other hand, in the case of Type 5 in which the amount of Ag added was increased to 10%, the average operating voltage was 3.6 V, but the capacity was smaller than those of Type 2, Type 3, and Type 4. However, the discharge capacity of Type 5 was also larger than that of Type 1 with no Ag added.

As a result, it was confirmed that by replacing Li ⁺ of LiCoO ₂ with Ag ⁺ , the discharge capacity density of the positive electrode active material was increased, and the capacity reduction rate was also reduced.
Further, it was found that the addition percentage of Ag is preferably in the range of 1% to 12%. The addition% of Ag is a value expressed as a percentage (%) of the number of moles of Ag when Li is replaced with Ag with respect to the number of moles of Li contained in LiCoO ₂ . Therefore, the ratio of the number of moles of the different metal ions contained in the positive electrode active material to the number of moles of the alkali metal ions contained in the positive electrode active material,
The range is from 0.01 to 0.12. This means that by replacing a part of Li ⁺ contained in the positive electrode active material with Ag ⁺ , the crystal part where Li ⁺ is intercalated is expanded to increase the amount of Li ⁺ occlusion, If it is below, the replacement is too small and the expansion is not performed satisfactorily,
Further, it is considered that if the content is 0.12 or more, the amount of Ag to be replaced is too large, so that Li decreases and the original function of Li decreases.

Example 2 In Example 2, five kinds of Li _1-x Ag _x NiO ₂ having different amounts of added Ag were prepared by a pyrolysis method instead of Ni instead of Co, and these five kinds were used. The same thing as the cylindrical lithium secondary battery shown in FIG. 1 was produced. The x value in the second embodiment is 0,
They are 0.01, 0.02, 0.05 and 0.10.

First, LiOH and Ni (OH) ₂ were mixed at a molar ratio of 1: 1. The mixture was placed in a crucible and heated in an electric furnace through which oxygen was passed. The temperature of the heat treatment was 700 ° C., and the treatment time was 5 hours. A black powder was obtained after heat treatment. The powder was confirmed to be LiNiO ₂ by powder X-ray diffraction. This was sieved to make the particle size uniform and used as a positive electrode active material. This LiNiO ₂ powder was mixed with a carbon powder and a binder, and the mixture was pressed against an aluminum current collector to produce a sheet-shaped positive electrode 1.

On the other hand, graphite powder was used as a negative electrode active material, and a mixture of the powder and a binder was pressed against a copper current collector to produce a sheet-shaped negative electrode 2. An electrode group 4 having a separator 3 interposed between the sheets of the positive electrode 1 and the negative electrode 2 was wound. The electrode group 4 was housed in a metal battery case 6 having a polymer insulating sheet 5 laid on the bottom, and the negative electrode lead wire 7 was welded to the battery case 6. Next, a non-aqueous electrolyte solution in which LiPF ₆ equivalent to 1 molar concentration was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate in an equal volume ratio was injected into the inside of the battery container 6, and an insulating plate was placed on top of the wound electrode group 4. 8 and put the positive electrode lead wire 9 through the hole of the insulating plate 8 into the container lid 10.
It was connected to the positive terminal 11 on the top. Finally, the container lid 10
And the battery container 6 were caulked and the container was sealed to produce a cylindrical battery. The above battery is referred to as type 6.

Next, as a positive electrode active material, Li _0.99 Ag _0.01
NiO ₂ , Li _0.98 Ag _0.02 NiO ₂ , Li _0.95 Ag _0.10 NiO ₂ , Li _0.90
A cylindrical battery using Ag _0.10 NiO ₂ was fabricated. First, LiOH, Ag ₂ O and Ni (O
H) ₃ at 0.99: 0.01: 1, 0.98: 0.02: 1, 0.95: 0.05: 1,
They were mixed at a molar ratio of 0.90: 0.10: 1 and the mixture was placed in separate crucibles. A crucible containing the sample was placed in an electric furnace in which oxygen was passed, and heat-treated at 700 ° C. for 5 hours to obtain a black powder. As a result of examining the crystal structure and chemical composition of each sample by powder X-ray diffraction and inductively coupled plasma emission spectrometry, each sample was found to have the desired cathode active material, Li _0.99 Ag _0.01 NiO ₂ , Li _0.98 Ag _0.02 NiO ₂ , Li _0.95 Ag
It was confirmed that they were _0.10 NiO ₂ and Li _0.90 Ag _0.10 NiO ₂ .
Prior to use, the samples were sieved to a uniform particle size.

A carbon powder and a binder are mixed with the four types of Ag-added positive electrode active materials synthesized above, and the mixture is pressed on an aluminum current collector to form a sheet-shaped positive electrode 1 for each active material. did. The weight of the active material per positive electrode was the same as that of LiNiO ₂ used in Type 1. On the other hand, graphite powder was used as a negative electrode active material, and a mixture of the powder and a binder was pressed against a copper current collector to produce a sheet-shaped negative electrode 2. An electrode group 4 having a separator 3 interposed between the sheets of the positive electrode 1 and the negative electrode 2 was wound. The electrode group 4 was housed in a battery case 6 having an insulating sheet 5 laid on the bottom, and the negative electrode lead wire 7 was welded to the battery case 6. Then, a non-aqueous electrolyte solution in which LiPF ₆ equivalent to 1 molar concentration was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate at an equal volume ratio was injected into the inside of the battery container 6, and the upper part of the wound electrode group 4 was insulated. The plate 8 was placed, and the positive electrode lead wire 9 was connected to the positive electrode terminal 11 on the container lid 10 through the hole of the insulating plate 8. Finally, the container lid 10 and the battery container 6 were crimped to seal the container, and a cylindrical battery having the same specifications as the battery using LiNiO ₂ described above was produced. Below Li _0.99 Ag _0.01 NiO ₂ , Li _0.98 Ag _0.02 Ni
Cylindrical batteries using O ₂ , Li _0.95 Ag _0.10 NiO ₂ , and Li _0.90 Ag _0.10 NiO ₂ were converted to type 7, type 8, type 9,
Type 10.

Table 1 summarizes the discharge capacity reduction rates (rate characteristics) of types 6, 7, 8, 9, and 10 when the number of cycles is 10, 100, 200, and 500. The operating voltage of the battery is 3.0 to 4.2 V, and the current value during charging and discharging is 10
0 mA was set.

In the case of Type 6 containing no Ag, the discharge capacity at the 10th cycle was 1230 mAh. As for the discharge capacity of this battery, the capacity reduction was within 30% until 100 cycles, but the capacity reduction rates after 200 cycles and 500 cycles were 49% and 68%, respectively.

In the case of type 7, at the time of 10 cycles,
Capacity increased by 30 mAh compared to type 1. The capacity increase is the effect for the substitution of 1% of LiNiO ₂ Li ⁺ to Ag ^+. In the discharge capacity of type 7, the capacity reduction rate was within 13% up to 100 cycles, and the reduction rates after 200 and 500 cycles were 37% and 56%.

In the case of type 8 and type 9 having a larger amount of Ag ⁺ substitution, the discharge capacity was larger than that of type 6 in which the amount of Ag added was 1%. Capacity reduction is also suppressed compared to type 7,
The capacity reduction rate at 200 cycles was reduced to 7%, and the capacity reduction rate at 500 cycles was reduced to 20% or less. However, in the case of the type 10 using the positive electrode active material having an Ag ⁺ substitution amount of 10%, the capacity was smaller than those of the type 7, type 8, and type 9. However, the capacity reduction rate of type 10 is also Ag
^{+ It} was smaller than Type 1 without additive.

[0049]

[Table 1]

As a result, by replacing Li ⁺ of LiNiO ₂ with Ag ⁺ , the discharge capacity density of the positive electrode active material was increased, and the capacity reduction rate was also reduced.

On the other hand, the relationship between the discharge capacity and the discharge current of each of the five types of cylindrical batteries produced in Example 2, ie, the batteries of type 6, type 7, type 8, type 9, and type 10, was used. investigated.

FIG. 3 is a diagram showing the relationship between the discharge current value and the discharge capacity of the five types of cylindrical batteries manufactured in Example 2.

In this study, the operating voltage of the battery was 3.0 to 4.2 V
The charging current and the discharging current were equal. Ag addition amount 1
%, Type 8 with 2% Ag addition, and type 9 with 5% Ag addition also had larger discharge capacities than type 6 without Ag addition. In particular, the battery of type 9 had a larger discharge capacity than any of the batteries. In the case of type 10 in which the amount of Ag added was 10%, the discharge capacity was larger than that of type 6 in the region of a current density lower than 250 mA, but was approximately the same at higher current densities. Was.

From the above investigation results, it is presumed that the replacement of Li in LiNiO ₂ by Ag increased the diffusion rate of Li ions in the positive electrode active material. Therefore, Example 2 in which Co was replaced with Ni was used. In the same manner as in Example 1, it was found that higher capacity and improved rate characteristics of the secondary battery were obtained.
Example 1 wherein Li ions in LiCoO ₂ were replaced with Ag ions
For the rate characteristic of, the capacity reduction rate is read and confirmed along the horizontal axis in FIG.

Example 3 In Example 3, LiNiO ₂ was prepared in advance by the method described in Example 2, refluxed in an organic solvent in which AgClO ₄ , AgNO _{3 and the} like were dissolved, and LiNiO ₂ contained in LiNiO ₂ was refluxed. ⁺ Is replaced with Ag ⁺ . The solvents used in Example 3 are alcohols such as methanol and ethanol, ketones such as acetone, and nitrile solvents such as acetonitrile. After the ion exchange treatment, the contents were distilled, and the solid matter was washed and heat-treated at 400 ° C. This was pulverized and sieved to make the particle size uniform to obtain a black powder. This was analyzed by powder X-ray diffraction and inductively coupled plasma emission spectrometry to obtain Li _0.95 Ag _0.05 NiO ₂ obtained in Example 3.
It was confirmed that the compound had the same structure and the same chemical composition. By adjusting the Ag ⁺ concentration and reflux time, LiNiO
Oxides having different Ag ⁺ substitution amounts of ₂ are obtained.

Using Li _0.95 Ag _0.05 NiO ₂ obtained in Example 3, a cylindrical lithium secondary battery having the same shape as type 9 of Example 2 was produced according to the following procedure.

First, a carbon powder and a binder were mixed with Li _0.95 Ag _0.05 NiO ₂ , and the mixture was pressed against an aluminum current collector to produce a sheet-shaped positive electrode 1. Weight of positive electrode active material, was equal to Li0.95Ag0.05NiO ₂ used in type 9. On the other hand, graphite powder was used as a negative electrode active material, and a mixture of the powder and a binder was pressed against a copper current collector to produce a sheet-shaped negative electrode 2. An electrode group 4 having a separator 3 interposed between the sheets of the positive electrode 1 and the negative electrode 2 was wound. The electrode group 4 was housed in a battery case 6 having an insulating sheet 5 laid on the bottom, and the negative electrode lead wire 7 was welded to the battery case 6. Next, a non-aqueous electrolyte solution in which LiPF ₆ equivalent to 1 molar concentration was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate in an equal volume ratio was injected into the inside of the battery container 6, and an insulating plate was placed on top of the wound electrode group 4. 8 was placed, and the positive electrode lead wire 9 was connected to the positive electrode terminal 11 on the container lid 10 through the hole of the insulating plate 8. Finally, the container lid 10 and the battery container 6 were crimped to seal the container, thereby producing a cylindrical battery. Type 11 battery
And

Table 1 shows the results of the discharge capacity of Type 11 at the cycles of 10, 100, 200 and 500. The operating voltage of the battery was 3.0 to 4.2 V, and the charging current and discharging current were 100 mA. Discharge capacity of 1280 mAh for type 11 during 10 cycles
And the average output voltage was 3.6V. The rate of decrease in the discharge capacity of this battery was reduced to 3% or less after 100 cycles, 7% after 200 cycles, and 20% or less after 500 cycles.

Therefore, it was found that a lithium secondary battery having a small capacity reduction can be obtained even when the Ag-substituted LiNiO ₂ synthesized by the ion exchange method of Example 3 was used.

Example 4 In Example 4, Li _0.95 Ag _0.05 Co _0.9 Mn _0.1 O ₂ , Li _0.95
Ag _0.05 Ni _0.9 Mn _0.1 O ₂ , Li _0.95 Ag _0.05 Ni _0.9 Co _0.1 O ₂ Three types of positive electrode active materials represented by the chemical formulas are synthesized, and a lithium secondary battery using those active materials for the positive electrode is manufactured. did.

First, Li _0.95 Ag _0.05 Co _0.9 Mn _0.1 O ₂ is converted to LiO
H, AgNO ₃ , Co ₂ O ₃ , and MnCO ₃ in a molar ratio of 0.95: 0.05: 0.90:
The mixture was mixed at 0.10 and heat-treated at 400 to 500 ° C in air. In addition to the above lithium salts and silver salts, LiNO ₃ , Li ₂ CO ₃ , C
H ₃ COOAg can also be used. Pyrolysis time is 5
Time. After the powder obtained after the decomposition was classified by a sieve, it was used as a positive electrode active material.

Next, Li _0.95 Ag _0.05 Ni _0.9 Mn _0.1 O ₂ is converted to LiO
H, Ag ₂ O, Ni (OH) ₂ , MnCO ₃ in a molar ratio of 0.95: 0.05: 0.90:
The mixture was mixed at 0.10 and heat-treated at 700 ° C. in an oxygen stream. The thermal decomposition time was 5 hours. The powder obtained after the decomposition was classified by a sieve and then used as a positive electrode active material.

Then, similarly, Li _0.95 Ag _0.05 Ni _0.9 Co _0.1 O ₂
Is obtained by mixing LiOH, Ag ₂ O, Ni (OH) ₂ , and Co ₂ O ₃ with a molar ratio of 0.95: 0.0
The mixture was mixed at a ratio of 5: 0.90: 0.10 and heat-treated at 700 ° C. in an oxygen stream. The thermal decomposition time was 5 hours. After the powder obtained after the decomposition was classified by a sieve, it was used as a positive electrode active material.

The three kinds of positive electrode active materials were measured by powder X-ray diffraction method and inductively coupled plasma emission spectrometry in Example 4 of the present invention.
The three types of positive electrode active materials obtained in the above are hexagonal layered crystals like LiCoO ₂ and LiNiO ₂ , and the chemical composition is Li
_0.95 Ag _0.05 Co _0.9 Mn _0.1 O ₂ , Li _0.95 Ag _0.05 Ni _0.9 Mn _0.1 O ₂ ,
It was confirmed that the _{composition was} Li _0.95 Ag _0.05 Ni _0.9 Co _0.1 O ₂ .

Using the three types of positive electrode active materials prepared above, a battery similar to the cylindrical battery shown in FIG. 1 was prepared.
First, Li _0.95 Ag _0.05 Co _0.9 Mn _0.1 O ₂ was added to the type 1 of Example 1.
The same weight as that of LiCoO ₂ used in Example ₁ was collected, carbon powder and a binder were mixed with this powder, and the mixture was pressed against an aluminum current collector to produce a sheet-shaped positive electrode 1.

On the other hand, graphite powder was used as the negative electrode active material, and a mixture of the binder and the binder was pressed against a copper current collector to produce a sheet-shaped negative electrode 2. An electrode group 4 having a separator 3 interposed between the sheets of the positive electrode 1 and the negative electrode 2 was wound. The electrode group 4 is housed in a battery case 6 in which an insulating sheet 5 is spread on the bottom of the battery case.
Welded. Then, a mixed solvent of ethylene carbonate and diethyl carbonate in an equal volume ratio was mixed with a 1 molar equivalent of Li.
A non-aqueous electrolyte solution in which PF ₆ is dissolved is injected into the battery container 6, the insulating plate 8 is placed on the wound electrode group 4, and the positive electrode lead wire 9 is inserted into the container lid 10 through the hole of the insulating plate 8. It was connected to a certain positive electrode terminal 11. Finally, the container lid 10 and the battery container 6 were crimped to seal the container, thereby producing a cylindrical battery. Less than,
This battery is referred to as type 12.

Similarly, Li _0.95 Ag _0.05 Ni _0.9 Mn _0.1 O ₂ and Li _0.95 Ag _0.05 Ni _0.9 C of the same weight as LiNiO ₂ used in Example 3
o Two kinds of positive electrodes 1 were prepared using _0.1 O ₂ . Using each of the positive electrodes 1, a cylindrical battery having the same specifications as the type 12 was produced.

A battery using Li _0.95 Ag _0.05 Ni _0.9 Mn _0.1 O ₂ is referred to as type 13 and a battery using Li _0.95 Ag _0.05 Ni _0.9 Co _0.1 O ₂ is referred to as type 14.

Table 1 shows the results of the discharge capacities of the types 12, 13 and 14 at the cycles of 10, 100, 200 and 500. The operating voltage of the battery was 3.0 to 4.2 V, and the charging current and discharging current were 100 mA. In the case of type 12, the discharge capacity after 10 cycles was 1245 mAh. As for the discharge capacity of this battery, the capacity decrease was 13% until 100 cycles, and the capacity decrease rates after 200 cycles and 500 cycles were 27%, respectively.
% And 33%.

Compared with the type 6 of Example 2 in which the capacity increase was slight, Li _0.95 Ag _0.05 Co _0.9 Mn _0.1 O _{2 of the} present invention was used.
Is used, the capacity reduction rate can be significantly reduced.

In the case of type 13, the discharge capacity at the 10th cycle was 1212 mAh. The capacity reduction rate up to 100 cycles was 16%, and the capacity reduction rates after 200 cycles and 500 cycles were 20% and 23%, respectively. In the case of type 14, the discharge capacity was 1217 mAh at the 10th cycle, but the rate of decrease in the discharge capacity of the battery was 8% at 100 cycles. After 200 cycles, the capacity reduction rates after 500 cycles are 14% and 24%, respectively.

As a result, with the use of the positive electrode active material synthesized in Example 4, a decrease in discharge capacity could be significantly suppressed. In other words, it was found that the same effect as in Example 1 and the like can be obtained even if a transition metal containing Mn in addition to a single element of Co or Ni or containing two elements of Co and Ni is used. did.

Embodiment 5 In this embodiment 5, Cu ⁺ is employed as a foreign metal ion. A method for synthesizing a Cu-substituted positive electrode active material will be described. Cu
⁺ Is oxidized to Cu ²⁺ when heated at high temperature in the atmosphere.
Therefore, in order to avoid the oxidation of Cu ^+, the ion exchange method, and employs a method of exchanging the Li ⁺ and Cu ^+. First, according to the method described in the first and second embodiments, LiCoO ₂ and LiNiO ₂
Were synthesized. Each of these powders and CuC
l, reflux the organic solvent mixed with Cu ⁺ salt such as CuBr,
Li ⁺ contained in LiCoO ₂ or LiNiO ₂ was exchanged for Cu ⁺ . Solvents that can be used in Example 5 are alcohols such as methanol and ethanol, ketones such as acetone, and nitrile solvents such as acetonitrile.

After the ion exchange treatment, the contents were distilled, and the solid matter was washed and then heat-treated at 400 ° C. This was pulverized and sieved to make the particle size uniform to obtain a black powder. As a result of analyzing the above two types of samples by powder X-ray diffraction method and inductively coupled plasma emission spectrometry, the obtained sample has the same layered crystal structure as LiCoO ₂ and LiNiO ₂ and the chemical composition is Li _0.95 Cu _0.05 CoO ₂ and Li
It was confirmed to be _0.95 Cu _0.05 NiO ₂ .

A carbon powder and a binder were mixed into each of the above two types of samples, and the resulting mixture was pressed against an aluminum current collector to produce a sheet-shaped positive electrode 1 for each positive electrode active material. The weight of Li _0.95 Cu _0.05 CoO ₂ per positive electrode was equal to that of LiCoO ₂ used in Type 1 of Example 1. Similarly, the weight of Li _0.95 Cu _0.05 NiO ₂ per positive electrode was determined in Example 2.
LiNiO ₂ used in type 6 of the above. Graphite powder was used as the negative electrode active material, and a mixture of the binder and the binder was pressed against a copper current collector to produce a sheet-shaped negative electrode 2. An electrode group 4 having a separator 3 interposed between the sheets of the positive electrode 1 and the negative electrode 2 was wound. This electrode group 4 is housed in a battery container 6 having an insulating sheet 5 laid on the bottom, and a negative electrode lead wire 7 is provided.
Was welded to the battery container 6. Then, a non-aqueous electrolyte obtained by dissolving LiPF ₆ equivalent to 1 molar concentration in a mixed solvent of ethylene carbonate and diethyl carbonate in an equal volume ratio was placed in a battery container 6.
The insulating plate 8 was placed on top of the wound electrode group 4, and the positive electrode lead wire 9 was connected to the positive electrode terminal 11 above the container lid 10 through the center hole of the insulating plate 8. Finally, the container lid 10 and the battery container 6 were crimped to seal the container, thereby producing a cylindrical battery. Above Li _0.95 Cu _0.05 CoO ₂ , Li _0.95 Cu
Cylindrical batteries using _0.05 NiO ₂
5, type 16.

Table 1 shows the results of the discharge capacities of the types 15 and 16 at the cycles of 10, 100, 200 and 500. The operating voltage of the battery is 3.0 to 4.2 V, and the current value during charging and discharging is
100 mA. 10 for Cu-substituted LiCoO ₂ type 15
The discharge capacity during cycling was 1275 mAh. The capacity reduction rate of this battery is 7% at 100 cycles and 1 at 200 cycles.
9%, 27% after 500 cycles. Cu ⁺ substituted LiNiO ₂
The discharge capacity of Type 16 is also lower than that of Type 6 without Cu ^+.
The capacity reduction rate was 26% even after 500 cycles.

As a result, it was found that the same effect as that of Ag ⁺ was obtained even when Cu ⁺ was used as the dissimilar metal ion as in Example 5. Further, for the same reason as in the case of the addition% of Ag, it can be said that the ratio of the number of moles of different metal ions contained in the positive electrode active material to the number of moles of alkali metal ions is preferably in the range of 0.01 to 0.12.

[0078]

As described above, the use of the positive electrode active material containing a different metal ion different from the alkali metal ion has the effect of increasing the capacity and extending the life of the secondary battery using the alkali metal. can get.

Further, by increasing the capacity of the secondary battery, it is possible to obtain the effect of reducing the weight and size of portable electric equipment and the like.

[Brief description of the drawings]

FIG. 1 is a half sectional view of a cylindrical lithium secondary battery according to an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the discharge capacity and the number of cycles of five types of cylindrical batteries manufactured in Example 1.

FIG. 3 is a diagram showing a relationship between discharge current value and discharge capacity of five types of cylindrical batteries manufactured in Example 2.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... positive electrode, 2 ... separator, 3 ... negative electrode, 4 ... electrode group,
5 ... insulating sheet, 6 ... battery container, 7 ... negative electrode lead wire, 8
... an insulating plate, 9 ... a positive electrode lead wire, 10 ... a container lid, 11 ... a positive electrode terminal.

Continued on the front page (72) Inventor Masanori Yoshikawa 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Tatsuo Horiba 7-1-1, Omika-cho, Hitachi City, Ibaraki Stock Hitachi, Ltd. Hitachi Research Laboratories (72) Inventor Ren Muranaka 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Hitachi, Ltd. Hitachi Research Laboratories (56) References JP-A-5-190177 (JP, A) JP-A-2-139861 (JP, A) JP-A-5-242891 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01M 4/58 C01G 51/00 H01M 4/02 H01M 10/40

Claims (2)

(57) [Claims] 1. A secondary battery comprising a positive electrode made of a positive electrode active material containing an alkali metal ion, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode active material is Li _1-y Ag _y C
A secondary battery having a chemical formula of oO ₂ , wherein y is in a range of 0.01 to 0.12. Wherein the alkali metal consists of a positive electrode active material comprising an ion positive electrode, a secondary battery composed of a negative electrode, a nonaqueous electrolyte solution and the positive electrode active material, Li _1-y Cu _y C
A secondary battery having a chemical formula of oO ₂ , wherein y is in a range of 0.01 to 0.12.