JP3079382B2 - Non-aqueous secondary battery - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a novel secondary battery, and more particularly to a secondary battery having excellent overdischarge characteristics.

[Prior Art] Conventionally, non-aqueous secondary batteries are expected to have higher voltage, higher energy density and better self-discharge than aqueous battery batteries. In particular, a composite oxide composed of lithium and a transition metal, and if necessary, a non-transition metal and the like disclosed in JP-A-55-13613, JP-A-62-90863, JP-A-63-299056 and the like. A non-aqueous secondary battery using a material as a positive electrode active material has a high electromotive force of 3 V or more, has an extremely high energy density, and is highly expected as a next-generation high-performance secondary battery. Further, as a feature when such a composite oxide is used as a positive electrode, a lithium composite oxide itself already contains lithium as an ion, and a battery system can be formed without necessarily using metal lithium as a negative electrode active material. It is also expected to be an excellent battery in terms of safety.

[Problems to be Solved by the Invention] As described above, a battery using a composite oxide of lithium and a transition metal, and if necessary, a non-transition metal as a positive electrode can be said to be a secondary battery that may have excellent characteristics. .

Normally, in the case of a nickel cadmium battery or a lead storage battery which is a conventional aqueous secondary battery, there is almost no problem even if overdischarge is performed.

On the other hand, in the case of a non-aqueous secondary battery, no matter how much the battery is charged when overdischarged to 0 V, it does not return to the original state. The reason is considered as follows.

Discharging until the voltage becomes 0 V means that either the capacity of the positive electrode or the capacity of the negative electrode runs out first, the potential is lowered or raised to the discharge potential of the other party, and the voltage of the entire battery is 0 V It is to become. First, considering the case where the capacity of the positive electrode is exhausted first, the potential of the positive electrode is reduced to the potential of the negative electrode when the discharge ends. In general, the inorganic compound used as a positive electrode active material of a non-aqueous secondary battery has a potential lower than a certain level, and is almost 1 V with respect to lithium. But it will not return.

Next, considering the case where the capacity of the negative electrode is exhausted first, the potential of the negative electrode is raised to the discharge potential of the positive electrode. In this case, it depends on the type of positive electrode
It will be raised to more than 3V, and in some cases up to near 4V. In this case, not only the negative electrode active material is deteriorated, but also the materials such as the negative electrode current collector, the can material, and the lead tab material are electrochemically dissolved. In particular, when the lithium composite oxide represented by the above-mentioned general formula LixMyNzO ₂ is used as a positive electrode, since the discharge potential is high, the influence is significantly affected. Further, as described above, a battery system using the lithium composite oxide as a positive electrode can be assembled in a state containing lithium ions at the time of its assembly, that is, in a discharge state. It can be used as an active material, or as another combination, it is possible to use a material capable of intercalating cations such as a conductive polymer or a carbonaceous material by the first charge thereof, which is a great advantage. I have. Therefore, particularly when a lithium composite oxide is used as the positive electrode, the difference in the current efficiency between the positive electrode and the negative electrode active material at the time of the first charge determines the charge capacity of each of the positive electrode and the negative electrode. In general, the current efficiency of the lithium composite oxide shows almost 100% even at the time of the first charge, and is usually larger than the current efficiency of the negative electrode. This means that the battery system repeats the charge-discharge cycle of the negative electrode capacity-limited. This fact also means that when the battery is overdischarged, that is, when the battery voltage becomes 0 V, the potential of the negative electrode is raised to the discharge potential of the positive electrode. That is, the latter case, that is, the case where the capacity of the negative electrode runs out first, causes deterioration of the battery performance.

Therefore, a battery using this lithium composite oxide as a positive electrode active material cannot be used in an overdischarged state like other non-aqueous secondary batteries, and this is a great limitation when using the battery.

An object of the present invention is to improve overdischarge characteristics of a battery using the lithium composite oxide as a positive electrode active material.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides LixMyNzO ₂ (M
Represents at least one transition metal, N represents at least one non-transition metal, and x, y, and z each represent 0.05 ≦ x ≦ 1.1.
It is a number of 0, 0.85 ≦ y ≦ 1.00, 0 ≦ z ≦ 0.10, and the value of y indicates the total value when two or more transition metals are used. ) Is used as a positive electrode main active material, a lithium / copper composite oxide is used as a positive electrode auxiliary active material, and a material capable of intercalating lithium ions is provided as a negative electrode.

[Operation] When the battery is overdischarged to 0 V as described above, the capacity of either the positive electrode or the negative electrode is exhausted first. If no countermeasures are taken, the capacity of the negative electrode will be exhausted first, causing the above-mentioned problem.

This means that the amount of lithium ions released by the positive-electrode anode reaction of the lithium composite oxide and the amount of the intercalation compound formed with the conductive polymer and the carbonaceous material by the negative-electrode cathode reaction of the lithium ions at the time of the first charge as described above. Arising from the imbalance of

In order to eliminate such imbalance, it is conceivable to release lithium ions from the secondary active material other than the lithium composite oxide at the time of the first charge.

As a characteristic required for such a sub-active material, the sub-active material itself does not have a discharge potential when releasing lithium ions, or has a discharge potential even if it has a discharge potential.
Those having a potential of 3 V or less, preferably 2.7 V or less are preferable.

The present inventors have conducted intensive studies on various substances,
It has been found that lithium / copper composite oxide is extremely useful as such a positive electrode sub-active material, and brings about a very remarkable effect.

General formula LixMyNzO ₂ used as a positive electrode main active material in the present invention
In the lithium composite oxide represented by, M represents at least one kind of transition metal, and N represents at least one kind of non-transition metal. M is not particularly limited, but examples thereof include Co, Ni, Fe, Mn, V, Mo and the like.
Is not particularly limited, but Al, In, Sn and the like can be mentioned. If a specific example is shown by a chemical formula in a state containing Li ions, that is, in a discharge state, LiCoO ₂ , LiNiO ₂ , LiCo _0.97 Sn
_0.03 O ₂ , LiCo _0.96 Al _0.05 O ₂ , LiCo _0.98 In _0.06 O ₂ , LiCo _0.75 N
i _0.23 O ₂ , LiCo _0.85 Fe _0.10 O ₂ , LiCo _0.80 Ni _0.17 Sn _0.02 O ₂ , Li
Co _0.85 Fe _0.10 Sn _0.05 O ₂ , LiCo _0.85 Mn _0.15 O ₂ , LiCo _0.85 V
_0.11 O ₂ , LiCo _0.83 Mo _0.15 O _{2 and the} like.

The value of x varies depending on the state of charge and the state of discharge, and the range is 0.05 ≦ x ≦ 1.10. That is, lithium ion dintercalation occurs due to charging, and the value of x becomes small, and in a fully charged state, the value of x reaches 0.05. Further, intercalation of lithium ions occurs due to the discharge, and the value of x increases. In a completely discharged state, the value of x reaches 1.10.

When two or more transition metals are used, the value of y indicates the total value. The value of y does not fluctuate due to charging and discharging, and is in the range of 0.85 ≦ y ≦ 1.00. The value of y is 0.85
If it is less than 1.00 or more than 1.00, phenomena such as a decrease in cyclability and an increase in overvoltage occur, so that sufficient performance as an active material for a secondary battery cannot be obtained, which is not preferable.

The value of z is in the range of 0 ≦ z ≦ 0.10, and the value of z is 0.
If it exceeds 10, the basic characteristics as an active material for a secondary battery are impaired, which is not preferable.

Such LixMyNzO ₂ can be obtained by a known method as described in JP-A-62-90863. That is, L
After mixing the oxides, hydroxides, carbonates, nitrates, organic acid salts, etc. of each metal of i, M and N, the mixture is heated to 600 to 950 ° C., preferably 700 to 900 ° C. in air or oxygen atmosphere. It is obtained by firing in a temperature range.

The lithium-copper composite oxide referred to in the present invention is a composite oxide composed of lithium and copper as main components, and other elements may be added as long as the essential structure is not changed.

LiCuO, Li ₂ CuO ₂ , Li ₃ CuO _{3 and the} like can be cited as specific examples of lithium-copper composite oxides. Such composite oxides include lithium compounds such as lithium carbonate, lithium hydroxide and lithium oxide. Obtained by mixing a copper compound such as copper carbonate, copper oxide, copper hydroxide and the like, and calcining the mixture in a temperature range of 450 ° C. to 1,200 ° C., preferably 600 ° C. to 1,000 ° C. under any conditions such as air or oxygen atmosphere. be able to.

Here, the compounding ratio of LixMyNzO _{2 as the main} active material and the lithium-copper composite oxide is not particularly limited, but considering over-discharge characteristics and discharge capacity, the lithium-copper composite oxide is 100 parts by weight of LixMyNzO ₂ . Is preferably not less than 1 part by weight and not more than 40 parts by weight. More preferably, 5 parts by weight or more, 2
5 parts by weight or less, more preferably 5 parts by weight or more and 20 parts by weight or less.

Although the action mechanism of the lithium / copper composite oxide is not yet clear, the compound itself has an excellent lithium ion releasing ability at the time of the first charge. Li
₂ CuO ₂ Is electrochemically occurring, and the amount of lithium ions released varies depending on conditions.
By charging at a potential of 4.2 V, the value of w reaches a value of 0.8 to 1.2. Characteristically, such initially charged, that is, intercalated, lithium-copper composite oxide has almost no discharge capability and discharge potential. That is, it is presumed that it works only as a lithium ion supply source at the time of the first charge.

Based on such characteristics, when the positive electrode main active material and the positive electrode sub-active material based on the composition of the present invention are used, for the above-described reason, at the time of overdischarge, that is, even when the battery voltage becomes 0 V, the negative electrode potential is conditioned. , But is maintained in the range of 1.5 V to 3.5 V, and the overdischarge characteristics are significantly improved.

The negative electrode active material used in the present invention is not particularly limited. Examples of the negative electrode active material include conductive polymer negative electrodes such as polyacetylene and poly-p-phenylene, pitch-based carbon, and carbonaceous materials such as vapor-grown carbon fiber. No.

As described above, excellent effects are exhibited when a substance capable of intercalating lithium ions such as a carbonaceous material is used for the negative electrode.

Basic components for assembling the non-aqueous secondary battery of the present invention include an electrode using the active material of the present invention, a separator, and a non-aqueous electrolyte. The separator is not particularly limited, and examples thereof include a woven fabric, a nonwoven fabric, a glass woven fabric, and a synthetic resin microporous membrane.
When a thin film and large area electrode are used, for example,
The microporous synthetic resin membrane disclosed in Japanese Patent No. 59072, particularly a polyolefin-based microporous membrane, is preferred in terms of thickness, strength, and membrane resistance.

 The electrolyte of the non-aqueous electrolyte is not particularly limited.
For example, LiClO_Four, LiBF_Four, LiAsF₆, CF_ThreeSO_ThreeLi, LiPF₆, Li
I, LiAlCl_Four, NaClO_Four, NaBF_Four, NaI, (n-Bu)_FourN ClO_Four, (N
−Bu)_FourN BF_Four, KPF₆And the like. In addition,
Examples of the organic solvent for the dissolution include ethers, ketones
, Lactones, nitriles, amines, amides, sulfur
Yellow compounds, chlorinated hydrocarbons, esters, carbonate
G, nitro compounds, phosphate compounds, sulfo
Run compounds can be used.
But ethers, ketones, nitriles, chlorinated hydrocarbons
Elements, carbonates and sulfolane compounds are preferred.
No. More preferred are cyclic carbonates.

Representative examples of these include tetrahydrofuran, 2-
Methyltetrahydrofuran, 1,4-dioxane, anisole, monoglyme, acetonitrile, propionitrile, 4-methyl-2-pentanone, butyronitrile, valeronitrile, benzonitrile, 1,2-dichloroethane, γ-butyrolactone, dimethoxyethane, methylphor Mate, propylene carbonate, ethylene carbonate, vinylene carbonate, dimethylformamide, dimethylsulfoxide, dimethylthioformamide, sulfolane, 3-methyl-sulfolane, trimethyl phosphate, trimethyl phosphate, and a mixed solvent of these can be given, but not necessarily. It is not limited to these.

If necessary, a battery is configured using components such as a current collector, a terminal, and an insulating plate. In addition, the structure of the battery is not particularly limited, but a positive electrode, a negative electrode, and, if necessary, a paper type battery having a single or multiple layers of separators, a laminated type battery, or a positive electrode, a negative electrode, For example, a form of a cylindrical battery or the like in which a separator is wound in a roll shape is given as an example.

[Effect of the Invention] The battery of the present invention has a remarkably improved overdischarge characteristic, which is a drawback of the conventional nonaqueous battery, and is extremely useful as a power source for consumer use such as small electronic devices, electric vehicles, and industrial use. is there.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

Production Example of Lithium-Copper Composite Oxide After mixing lithium carbonate and cupric oxide at a molar ratio of 2: 1, the mixture was calcined in air at 940 ° C. for 18 hours to produce Li ₂ Cu.
To give the O _2.

This Li ₂ CuO ₂ was pulverized with a ball mill to an average particle size of 15 μm and used in the following Examples and Comparative Examples.

Example 1 LiCoO ₂ was used as a positive electrode active material, Li ₂ CuO ₂ was used as a positive electrode sub-active material, graphite and acetylene black were used as conductive agents, and fluororubber was used as a binder. LiCoO ₂ : Li ₂ CuO ₂ : graphite: Acetylene black: fluoro rubber = 100: 1
A mixture mixed at a weight ratio of 2: 7.5: 2.5: 2 as a dimethylamide paste, a sheet coated and dried on an Al foil as a positive electrode, needle coke powder as a negative electrode active material, a fluoro rubber as a binder, a needle Coke: Fluorine rubber = 95: 5
The mixture shown in FIG. 1 was prepared as a dimethylformamide paste and applied to a Ni foil, and the dried sheet was used as a negative electrode and a Li metal was used as a reference electrode to produce a battery shown in FIG.

In addition, a polypropylene nonwoven fabric was used as the separator 3, and a liquid prepared by adjusting lithium borofluoride to a concentration of 1.0 M in a mixed solvent (volume ratio = 1: 1) of propylene carbonate and butyrolactone was used as an electrolytic solution.

After charging this battery at a constant voltage of 4.2 V for 5 hours, 1.0 mA / cm
^The battery was discharged at a constant current of ² and a cutoff voltage of 2.7 V. After repeating this charge / discharge cycle five times, an overdischarge standing test was performed. That is, the positive and negative terminals were left short-circuited for one week via a 5Ω resistor. Thereafter, the charge / discharge cycle under the above conditions was repeated five times. FIG. 2 shows a change in discharge capacity at this time, and FIG. 3 shows a voltage change during overdischarge. As is clear from FIG. 3, when the cell voltage becomes 0 V, the negative electrode potential becomes 2.
Showed 2V. As is apparent from FIG. 2, no reduction in capacity due to this overdischarge test was observed.

Comparative Example 1 LiCoO ₂ was used as a positive electrode main active material, graphite and acetylene black were used as conductive agents, and fluororubber was used as a binder. LiCoO ₂ : graphite: acetylene black:
A battery was manufactured in the same manner as in Example 1 except that a sheet obtained by applying a mixture of fluororubber at a weight ratio of 100: 7.5: 2.5: 2 to an Al foil as a dimethylformamide paste was used as a positive electrode, and the same evaluation was performed. went. The results are shown in Table 1, FIG. 4, and FIG.
Shown in the figure.

As is clear from FIG. 5, when the cell voltage at the time of overdischarge became 0 V, the negative electrode potential had increased to 3.9 V. In addition, as apparent from FIG. 4, the capacity was significantly reduced by this overdischarge test.

Examples 2 to 11 The same operation as in Example 1 was performed except that the mixing ratio of LiCoO ₂ and Li ₂ CuO ₂ was changed as shown in Table 1. The results are shown in Table 1.

Example 12 The same operation as in Example 1 was carried out except that LiCo _0.97 Sn _0.33 O ₂ was used instead of LiCoO ₂ .

Example 13 The same operation as in Example 1 was performed except that LiCo _0.7 Ni _0.3 O ₂ was used instead of LiCoO ₂ .

 The results are shown in Table 2.

Example 14 Example 1 was repeated except that a polyacetylene negative electrode was used as the negative electrode.
Performed exactly the same operation as. The method for preparing the polyacetylene negative electrode is as follows.

Under N ₂ atmosphere, toluene 50m in a glass container with an internal volume of 800ml
Then, 6 ml of tetrabutoxytitanium and 10 ml of triethylaluminum were added to prepare a catalyst. After cooling the vessel to −78 ° C., the system was evacuated, a catalyst liquid was applied to the vessel wall, and acetylene gas was introduced. Immediately, a film-like polyacetylene was formed on the wall surface, and the system was evacuated after standing for 15 minutes. After washing with toluene and washing with 0.5N-HCl-MeOH five times, the product was dried and taken out.

This film-like polyacetylene was used after heat treatment at 250 ° C. for 5 seconds.

 The results are shown in Table 3.

Comparative Example 2 Comparative Example 1 except that a polyacetylene negative electrode was used as the negative electrode.
Performed exactly the same operation as.

 The results are shown in Table 3.

[Brief description of the drawings]

FIG. 1 is a structural view of a battery used in Examples and Comparative Examples of the present invention. In the figure, 1 ... Positive electrode, 2 ... Negative electrode, 3,3 '... Current collecting rod, 4,4' ... SUS net, 5,5 '... External electrode terminal 6 ... Reference electrode, 7 ... ... Battery case, 8 ... Separator 9 ... Electrolyte FIG. 2 and FIG. 4 show the change in capacity before and after overdischarge evaluation in Examples and Comparative Examples of the present invention. FIG. 3 and FIG. 5 show potential changes during the overdischarge evaluation. a is the cell voltage, b is the positive electrode potential, c
Indicates a negative electrode potential.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-90863 (JP, A) JP-A-63-314778 (JP, A) JP-A-62-172662 (JP, A) JP-A-1- 163969 (JP, A) JP-A-1-161668 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/58 H01M 10/40 H01M 4/02

Claims (1)

(57) [Claims] (1) LixMyNzO ₂ (M represents at least one transition metal, N represents at least one non-transition metal, and x, y, and z each represent 0.05 ≦ x ≦ 1.10, 0.85 ≦ y ≦ 1.00, 0 ≦ z
≤0.10, and the value of y indicates the total value of two or more transition metals when used. ) Is used as a positive electrode main active material, a lithium-copper composite oxide is used as a positive electrode auxiliary active material, and a material capable of intercalating lithium ions is used as a negative electrode.