JPH04162357A - Nonaqueous secondary battery - Google Patents

Abstract

PURPOSE:To increase a proportion of active material in a positive electrode plied agent without worsening battery performance by using a specific compound metal oxide as a positive electrode active material, and adding two kinds of carbons of different means grain size as a conductive agent to specify a sum of two kinds of additive amounts. CONSTITUTION:A compound metal oxide, shown by an expression LixMyNzO2 with a mean grain size of 1mu or more and less than 10mu, is used as a positive electrode active material, and at one kind or more respectively of two kinds of carbons of 0.1 t0 10mu means grain size and 0.01 to 0.08mu mean grain size is added as a conductive auxiliary agent. In the expression, M shows at least one kind of transition metals, N shows at least one kind of non-transition metals, and x to z show a number of each 0.05<=x<=1.10, 0.85<=y<=1.00, 0<=z<=0.10. A sum of additive amounts of two kinds of carbons of this positive electrode plied agent is set to less than 6.5 pts.wt. and 2 pts.wt. or more relating to 100 pts.wt. the positive active material. In this way, battery performance is not decreased, and further density in the positive electrode plied agent can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a novel secondary battery, and more particularly to a small and lightweight secondary battery.

[Conventional technology]

In recent years, electronic devices have become smaller and lighter, and as a result, there is a strong demand for batteries that serve as power sources to be smaller and lighter. In the field of -secondary batteries, small and lightweight batteries such as lithium batteries have already been put into practical use, but because these are -secondary batteries, they cannot be used repeatedly, and their fields of application have been limited.

On the other hand, in the field of secondary batteries, lead batteries and nickel-cadmium batteries have conventionally been used, but both have major problems in terms of miniaturization and weight reduction.

From this point of view, non-aqueous secondary batteries have attracted much attention. Among these, there are those that use a new group of electrode active materials that utilize the intercalation or doping phenomenon of layered compounds, which is a reaction type that is essentially different from that of conventional nickel-cadmium batteries, lead-acid batteries, etc. Electrode active materials do not cause complex chemical reactions during electrochemical reactions during charging and discharging.
It has extremely excellent charge/discharge cycle performance. For example, JP-A No. 55-13613, JP-A No. 62-908
There are non-aqueous secondary batteries that use a composite oxide consisting of lithium, transition metals, and, if necessary, non-transition metals, as a positive electrode active material, as disclosed in Publication No. 63, Japanese Patent Application Laid-open No. 63-299056, etc. . These non-aqueous secondary batteries have a high electromotive force of 3 cm or more, have extremely high energy density, and are highly anticipated as next-generation high-performance secondary batteries. Furthermore, when such a composite oxide is used as a positive electrode, the lithium composite oxide itself already contains lithium as ions, and a battery system can be formed without necessarily using metallic lithium as the negative electrode active material. Due to its unique characteristics, it is expected to be an excellent battery in terms of safety.

[Problem to be solved by the invention]

As described above, a battery using a composite oxide of lithium and a transition metal, or, if necessary, a non-transition metal, as a positive electrode can be said to be a non-aqueous secondary battery that may have excellent characteristics.

However, in the positive electrode of these non-aqueous secondary batteries,
In terms of practical performance, it is necessary to add 6.5 to 30 parts by weight of the conductive additive per 100 parts by weight of the positive electrode active material, which is one of the obstacles to improving the capacity of a battery of the same volume.

In other words, this type of composite metal oxide, like other cathode active materials, does not have sufficient conductivity on its own, so if it is used without a conductive aid, the utilization rate will be low.

Overvoltage characteristics, cycle characteristics, etc. will be significantly deteriorated. Therefore,
Addition of a conductive aid is essential. On the other hand, the addition of such a conductive aid significantly reduces the battery capacity per volume. In particular, commonly used carbons such as graphite and acetylene black have smaller true and apparent densities than active materials, and in order to increase battery capacity, it is important to minimize the amount of such conductive additives added. It is.

When the active material of the present invention is used, the battery capacity changes significantly when 6 to 7 parts by weight of the conductive additive is added to 100 parts by weight of the active material. Therefore, in order to obtain a battery with a large battery capacity, it is necessary to limit the amount of the conductive additive to 6 to 7 parts by weight or less.

In addition, in the conventional technology, when the conductive auxiliary agent is reduced, stable current collection is possible by increasing the particle size of the active material particles and increasing the density of the positive electrode mixture. Diffusion resistance increases and overvoltage characteristics.

This will adversely affect output characteristics, etc.

The present invention solves the above-mentioned problem of the amount of conductive additive added in the composite metal oxide positive electrode, and improves battery performance, especially cyclability.
This was done in order to provide a positive electrode in which the proportion of active material in the positive electrode mixture is increased at the same time without deteriorating the utilization rate or overvoltage characteristics.

[Means to solve the problem]

In order to solve the above problems, the present invention uses a composite metal oxide represented by the following general formula (I) with an average particle diameter of 1 μ or more and less than 10 μ as a positive electrode active material, and as a conductive additive ( A) average particle size of 0.1 to 10μ and (B) average particle size of 0.1 to 10μ. In a positive electrode mixture in which at least one or more of two types of carbon of O1 to 0.08μ are added,
(A), (B) The total amount of the two types added is positive electrode active material 1
A non-aqueous secondary battery using a positive electrode mixture, characterized in that the amount of the positive electrode mixture is less than 6.5 parts by weight and 2 parts by weight or more based on 00 parts by weight.

(I): Lix stand yNzo□ (M represents at least one kind of transition metal, N represents at least one kind of non-transition metal, x, y, z are each 0.05≦x≦1.10
．． 0.85≦y≦1.00. The number is O≦2≦0.10. ).

The greater the total amount of conductive additives (A) and (B) added relative to the unit amount of active material, the more stable the battery performance will be. It becomes difficult to improve the capacity as

In the conventional technology, for practical performance, 6.5 parts by weight or more of the conductive additive is required for 100 parts by weight of the positive electrode active material.
It was difficult to reduce the addition ratio even further.

In other words, in any carbon-based system, a conductive agent is inserted between active material particles, and a micro current collection network is formed in which several to several tens of active materials are brought into electrical contact with each other in a complex manner. Furthermore, in order to simultaneously form a macro current collection network that brings these micro networks into contact with each other and enables electrical connection to the electrode terminal of the battery, at least 6
．． 5 parts by weight or more was required.

Therefore, the present inventor developed a conductive additive necessary for the above-mentioned micro current collection network with an average particle diameter of 0.01 to 0.
Carbon with an average particle size of 0.1 to 10μ is added as a conductive agent necessary for the macroscopic current collection network.
By using carbon, it was possible to reduce the total addition rate of the conductive auxiliary agent to less than 6.5 parts by weight based on 100 parts by weight of the positive electrode active material.

Here, the present inventor further found that this effect is more effectively expressed when the average particle diameter of the positive electrode active material is 1 to 10 μm, preferably 2 to 5 μm. That is,
When the average particle size of the active material is less than 1 μm, excellent battery performance will not be exhibited unless about 10 parts by weight is added, even in a mixed system, in order to sufficiently form a micro current collection network. In addition, when the average particle diameter of the active material is lθμ or more, the amount can be less than 6.5 parts by weight alone, but the solid phase diffusion resistance of the positive electrode active material itself affects overvoltage characteristics, output characteristics, utilization rate, etc. have a negative impact and are undesirable. On the other hand, in the case of a positive electrode active material with an average particle size of 1 to 10 μm or even 2 to 5 μm,
Even if the amount added is less than 665 parts by weight under the conductive additive addition conditions of the present invention, it is possible to increase the density of the active material in the positive electrode mixture without reducing battery performance. however,
If the amount is less than 2 parts by weight, it will be difficult to form the above-mentioned current collection network, and the battery performance will significantly deteriorate.

The conductive aid (A) of the present invention has an average particle size of 0.1 to 10
It is not particularly limited as long as it is carbon of μ,
Among them, graphite is preferred. The conductive aid (B) is
Carbon having an average particle diameter of 0.01 to 0.08μ,
For example, carbon blanks such as acetylene black, thermal black, channel blank, furnace black, etc. are preferable, and among them, furnace blanks having a high degree of stratification and acetylene black are particularly preferable.

Also, (A) / ([1) is (A) or (B)
Although it is effective under conditions where the ratio is not monotonous, the ratio is preferably 25/75 to 75/25, and more preferably 40/60 to 60/40.

Furthermore, when adding (A) and (B), it is not necessary to limit each type to one type of carbon, and depending on the correspondence with the active material particles, multiple carbons with different average particle sizes can be effectively combined and used. can do.

The positive electrode mixture of the present invention, which uses a composite metal oxide as an active material and has a new conductive agent addition ratio, has electrode performance equivalent to that of a positive electrode mixture with a high conductivity additive addition rate, that is, excellent cyclability. , utilization rate, and overvoltage characteristics, and exhibits excellent performance especially when used as a positive electrode for non-aqueous secondary batteries.

Next, a secondary battery using the positive electrode mixture of the present invention will be described.

General formula LixMyNz used as positive electrode active material in the present invention
In the lithium composite metal oxide represented by O□, M represents at least one type of transition metal, and N represents at least one type of non-transition metal. M is not particularly limited, but examples include Co, N+, Fe, Mn
, '/, tlo, etc., and N is also not particularly limited, but examples include An, In, Sn, etc. A specific example of this is shown by the chemical formula in a state containing Li ions, that is, in a discharge state.
iNi0z, LiCoo, qtsno', +
501LiCoo, qbA 12 o, osoz,
LiCoo, qsTno, 060g+LiC06
,75Nio,zsOt,'LiC0o,5sFe
o, +oOz+LiCoo, @oNio, +q';
No, ozoz.

LiCoe15Fe6.1oSno, osoz, L
iCoo, esMno, +501LiCoo, 5s
Vo, ++Oz, LiC0o, ssMno, +s
Examples include Oz.

Further, the value of X varies depending on the charging state and discharging state, and the range is 0.05≦x≦1.10. That is, charging causes deintercalation of lithium ions, and
The value of becomes small, and the value of X becomes 0 in a fully charged state.
．． Reach 05. Further, intercalation of lithium ions occurs due to discharge, and the value of X increases, and in a fully discharged state, the value of X reaches 1.10.

In addition, when two or more types of transition metals are used, the value of y indicates their total value, and the y value does not change due to charging and discharging, and is within the range of 0.85≦y≦1.00. be. If the value of y is less than 0.85 or greater than 1,00, phenomena such as a decrease in cycleability and an increase in overvoltage occur, making it impossible to obtain sufficient performance as an active material for a secondary battery, which is not preferable.

Further, the value of 2 is in the range of 0≦Z≦0.10, and when the value of Z exceeds 0.10, the basic characteristics as an active material for a secondary battery are impaired, which is not preferable.

Such LixMyNzOz can be obtained by a known method such as that described in Japanese Patent Application Laid-Open No. 62-90863.

That is, after mixing Li, M, N metal oxides, hydroxides, carbonates, nitrates, organic acid salts, etc.,
600-950°C1 in air or oxygen atmosphere
It is preferably obtained by firing at a temperature range of 700 to 900'C.

When using the positive electrode mixture for secondary batteries of the present invention, the mixture can be molded into any shape such as a sheet.

A common method for molding is to mix the active material with a powdered binder such as Teflon powder or polyethylene powder, and then compression mold the mixture.

Furthermore, another method includes a method of forming an electrode active material using an organic polymer dissolved and/or dispersed in a solvent as a binder.

Although the negative electrode is not particularly limited, metal Li or its alloy negative electrode, LixFe20s, LixPezO<;
Metal oxide negative electrodes such as t, i, Wo□, conductive polymer negative electrodes such as polyacetylene and polyP-phenylene, carbonaceous material negative electrodes such as vapor grown carbon fibers, pitch carbon, and polyacrylonitrile carbon fibers. etc.

As basic components when assembling the non-aqueous secondary battery of the present invention, an electrode using the positive electrode and the negative electrode of the present invention;
Further examples include separators and non-aqueous electrolytes. The separator is not particularly limited, but includes woven fabrics, non-woven fabrics, glass woven fabrics, synthetic resin microporous membranes, etc. As mentioned above, when using thin films and large-area electrodes, for example, A synthetic resin microporous membrane disclosed in No.
In particular, polyolefin microporous membranes are preferred in terms of thickness, strength, and membrane resistance.

The electrolyte of the non-aqueous electrolyte is not particularly limited, but an example is LiCj! Oa, LiBF4. L
iAsFa, CF35O+Li, LiPFa,
Lil+ LiA poor CI! ,4. NaC
j! 041NaBFa, Nal, (n-Bu)a
NI! 1cf04+ (n-Bu)aNΦBF4゜K
PF, etc. In addition, examples of organic solvents used in the electrolytic solution include ethers, ketones, lactones, nitriles, amines, amides, sulfur compounds, chlorinated hydrocarbons, esters, carbonates, nitro compounds, and phosphorus. Acid ester compounds, sulfolane compounds, etc. can be used, but among these, ethers, ketones, nitriles, chlorinated hydrocarbons, carbonate H, and sulfolane compounds are preferred. More preferably, cyclic Carbonate H.

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, methylformate, propylene carbonate, ethylene carbonate, vinylene carbonate, dimethylformamide, dimethylsulfoxide, dimethylthioborumamide,
Examples include, but are not limited to, sulfolane, 3-methyl-sulfolane, phosphoric acid, trimethyl, triethyl phosphate, and mixed solvents thereof.

Furthermore, if necessary, the battery is constructed using parts such as a current collector, a terminal, and an insulating plate. The structure of the battery is not particularly limited, but may include a paper type battery with a positive electrode, a negative electrode, and if necessary a separator in a single layer or multiple layers, a stacked battery, or a positive electrode, a negative electrode, and if necessary, a separator. An example is a cylindrical battery formed by winding a separator into a roll.

〔Effect of the invention〕

The battery of the present invention is small and lightweight, has particularly excellent cycle characteristics and self-discharge characteristics, and is extremely useful as a power source for small electronic devices, electric vehicles, power storage, etc.

〔Example〕

The average particle system was measured using a so-called electron microscopy method. i.e., randomly selected 50% of all particles in the electron microscope field containing at least 10 (I particles or more)
The arithmetic mean value of the randomly selected particles in the number or more was defined as the average diameter of the field of view, and the average of these values measured over at least three fields of view was defined as the average particle diameter of the powder. still,
The individual particle size is the average value of the longest and shortest diameters of the particle.

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

Example 1 1.05 mol of lithium carbonate, 1.90 mol of cobalt oxide, and 0.084 mol of tin oxide were mixed, calcined at 650°C for 5 hours, and then calcined in air at 850°C for 112 hours. , L++, 03COO, 56sno, o
A composite metal oxide having a composition of +202 was obtained. After pulverizing this composite metal oxide to an average size of 3 μm using a ball mill,
Dimethylformamide solution of polyacrylonitrile (concentration 2wt9+5) for 100 parts by weight of composite metal oxide
100 parts by weight and as a conductive auxiliary agent, average particle size of about 3
2.5 parts by weight of μ graphite, average particle size approximately 0.04
After mixing μ with 2.5 parts by weight of acetylene black,
15μm AI! A film thickness of 80 μm was applied to one side of the foil of 1 country x 5 countries.

Using this test piece as a positive electrode, lithium metal as a negative electrode, and a 1.0R (-L+Cff104-propylene carbonate solution) as an electrolyte, the battery shown in FIG. 1 was assembled.

After charging at a constant current of 25 mA (current density 5 mA/al) for 30 minutes, the battery was charged at a constant current of <25 mA for 3.8 minutes.
Discharge was performed to V. The end-of-charge voltage, open terminal voltage, and overvoltage at this time are 4.20V, respectively.4. +
They were 5V and 0.05V.

Thereafter, a cycle test was conducted under the same charging and discharging conditions, and the open terminal voltage and overvoltage in each cycle were as shown in Table 1, and showed almost no change.

Examples 2-7. Comparative Examples 1 to 5 The same procedure as in Example 1 was carried out except that the amounts of graphite and acetylene black with an average particle size of about 3 μm added to the composite metal oxide ground to an average particle size of 3 μm were changed to the amounts shown in Table 2. The operation was carried out to obtain various positive electrode test pieces.

(The following is a blank space) -17~ Table 2 This positive electrode test piece was assembled into a battery similar to that in Example 1 and evaluated. Table 3 shows the open terminal voltage and overvoltage at the 1st cycle and the 100th cycle.

(The following is a blank space) = 18 - Table 3 - 191 In Examples 1, 3, and 4.7, effects equivalent to those in Comparative Example 3.4 were found.

Examples 8-10. Comparative Examples 6, 7 In Examples 1, 3, 4 and Comparative Example 1.2, the battery evaluation was performed by performing the same operation except that the average crushed particle size of the composite metal oxide was changed to about 7μ. cycle and ten
The overvoltage in the 0th cycle is as shown in Table 4, and was not significantly different from that in the case of a pulverized average particle size of 3 μm.

(Leaving space below) Table 4 = 21 - Examples 11 to 13 The same operations as in Example 1 were performed except that the conductive additive addition conditions were changed as shown in Table 5, and battery evaluation was performed. The results were almost unchanged from those of Example 1.

Table 5 shows the overvoltages for 1 cycle and 100 cycles.

(Left below) -23 - Example 14.15, Comparative Examples 8 and 9 In Example 1, the average particle diameter of the composite metal oxide was
When the battery was evaluated using the same operation except for the changes shown in the table, the overvoltages for 1 cycle and 100 cycles were as shown in the chart. When the composite oxide average particle size was set to 14μ and 0.5μ, a decrease in performance was observed.

(Leaving space below) Table 6 Comparative Example 10.11 The same operation as in Comparative Example 8 was performed except that the conductive additive addition conditions were changed to those shown in Table 7, and battery evaluation was performed. There was a large difference from Example 1. If the average crushed particle size of the composite metal oxide is small, it is clear that it is necessary to add a large amount of the conductive additive. Table 7 shows the overvoltages for 1 cycle and 100 cycles.

(Leaving space below) Comparative Example 12 A battery was evaluated using the same operations as in Comparative Example 9 except that the conductive additive addition conditions were changed to only 20 parts by weight of graphite with an average particle size of 3 μm. The overvoltages were 0.11 V and 0.14 V, respectively, which were almost the same as the results of Comparative Example 9. When the average particle size of the composite metal oxide is large, no improvement in overvoltage is observed even if a large amount of conductive agent is added.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a configuration example of a secondary battery of the present invention. In Fig. 1, 1 is a positive electrode, 2 is a negative electrode, 3.3' is a current collector rod, 4.4' is an SUS net, 5.5' is an external electrode terminal,
6 is a battery case, 7 is a separator, and 8 is an electrolytic solution or solid electrolyte. Patent applicant: Asahi Kasei Industries, Ltd.

Claims (1)

[Claims] As a positive electrode active material, a composite metal oxide represented by the following general formula (I) having an average particle diameter of 1 μ or more and less than 10 μ is used, and as a conductive agent, (A) an average particle diameter of 0. 1-10
and (B) two types of carbon having an average particle diameter of 0.01 to 0.08μ. Less than 6.5 parts by weight based on 100 parts by weight of the positive electrode active material, 2
1. A non-aqueous secondary battery using a positive electrode mixture characterized by having a content of at least part by weight. (I): Li_xM_yN_zO_2 (M represents at least one type of transition metal, N represents at least one type of non-transition metal, x, y, z are each 0.05≦x≦1.
10, 0.85≦y≦1.00, 0≦z≦0.10. )