JP3212018B2 - Non-aqueous electrolyte secondary 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 non-aqueous electrolyte secondary battery using a substance capable of inserting and extracting lithium ions as an active material.

[0002]

2. Description of the Related Art In recent years, portable electronic devices such as video cameras, portable CDs, portable telephones, PDAs and notebook computers have been reduced in size, weight and performance. Power supplies for these portable electronic devices require secondary batteries with high capacity and heavy load characteristics and high safety. Sealed lead-acid batteries and nickel-cadmium batteries have been used as secondary batteries to meet such purposes, but nickel-metal hydride batteries and lithium-ion secondary batteries as non-aqueous electrolyte secondary batteries have higher energy densities. It has been put to practical use.

A non-aqueous electrolyte secondary battery uses a lithium salt dissolved in a non-aqueous solvent as an electrolyte, and uses metal lithium or an alloy of metal lithium and a metal such as Al, Sn, and Pb as a negative electrode active material. Lithium secondary batteries and lithium ion secondary batteries using carbonaceous materials such as carbon that can insert and remove lithium ions into and from the negative electrode active material are known. In these non-aqueous electrolyte secondary batteries, since water is not used for the electrolyte, it is possible to design a battery capable of charging and discharging at a high voltage higher than the electrolysis voltage of water, and there is an advantage that the energy density can be easily increased. .

An oxide or chalcogenide having a one-dimensional chain structure, a two-dimensional layer structure, a three-dimensional skeleton structure, an amorphous structure or the like capable of inserting and extracting lithium ions as a positive electrode active material of these nonaqueous electrolyte secondary batteries, or Conductive polymers and the like have been proposed. However, as a negative electrode active material,
In the case of using lithium metal, the dendrite-like lithium metal crystal grown by repeating charge and discharge breaks through the separator, causing a short circuit between the positive electrode and the negative electrode, which hinders practical application in terms of safety. When an alloy or nitride of lithium metal and another metal is used as a negative electrode active material in a nonaqueous electrolyte secondary battery, the energy density is smaller than that of lithium metal, and a carbon material is used as an active material. As compared with the case where the battery is used, the cycle characteristics are insufficient, so that it is currently used only for coin-type secondary batteries for memory backup. For this reason, most of the negative electrode active materials of non-aqueous electrolyte secondary batteries used as main power sources of portable electronic devices use carbonaceous materials.

However, while the theoretical energy density per unit weight of lithium metal is 3861 mAh / g, the theoretical energy density of a generally known carbonaceous material is 372 mAh / g. Therefore, when a carbonaceous material was used as the negative electrode active material, the weight energy density was lower than when metal lithium was used, and furthermore, there was a problem that the volume energy density was low because the actual carbon material was high. .

In order to answer such a problem, the present inventors have used a carbonaceous material capable of inserting and extracting lithium ions and / or various oxides such as silicon as a negative electrode active material, and have a composition represented by LiaTbLcOd as a positive electrode active material. A non-aqueous electrolyte secondary battery was prototyped and found to be able to provide a battery with high capacity and low internal resistance, which is disclosed in Japanese Patent Application Nos. 3-253921 and 4-162958. (T is Co, N
one or more transition metals selected from i, Mn, Fe, V, W, Nb, and Ti, L is B, Si, P, M
g, Zn, and Cu are at least one element selected from the group consisting of a, b, and c, where 0 <a <= 1.15;
0.8 <= b + c <= 1.3, 1.7 <= d <= 2.5
In a non-aqueous electrolyte secondary battery that actually uses these active materials, the active material, a conductive carbon material (such as graphite) and a binder are mixed to form a positive / negative electrode. Was used as an agent.
The thus obtained mixture is compression-molded in a coin-type battery, and is pelletized to constitute a battery. In a cylindrical or prismatic battery using a sheet electrode, a slurry in which the obtained mixture is dispersed in an appropriate solvent is applied to a foil-shaped metal thin film serving as a current collector, dried, and then rolled. -Used as a negative electrode.

[0007]

Conventionally, among the non-aqueous electrolyte secondary batteries manufactured with such a structure, the non-aqueous electrolyte secondary battery using a silicon oxide as a negative electrode active material is the first one. A phenomenon may occur that the first discharge capacity is smaller than the charge capacity. That is, all the lithium ions occluded in the active material by the first charge cannot be released by the next discharge. Such a decrease does not occur in the second and subsequent charging and discharging. If the difference between the first charge capacity and the discharge capacity (irreversible capacity) is large, the capacity of the positive electrode must be filled more than the capacity of the negative electrode to supply lithium equivalent to the irreversible capacity.
Otherwise, there is a problem that the capacity per volume is significantly reduced. In addition, there is a problem in that an attempt to correct the irreversible capacity at the time of manufacturing a battery increases an extra process, which causes an increase in cost.

[0008]

In order to solve the above-mentioned problems, the present invention relates to a non-aqueous electrolyte secondary battery using a material capable of inserting and extracting lithium ions as a positive electrode or a negative electrode active material. At least one of the negative electrode mixture, the active material and one or more metals that are unlikely to cause an alloying reaction with lithium selected from the conductive carbon material and the transition metal and their alloys, or a transition metal and It has a structure of a nitride of one or more elements selected from Groups 3B and 4B of the periodic table, or a mixture of both the metal and the nitride.

As a result, the irreversible capacity is reduced, and a non-aqueous electrolyte secondary battery having a large charge / discharge capacity in which the positive and negative electrodes are balanced can be easily manufactured at low cost.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Specific examples of one or more kinds of metals which are less likely to cause an alloy reaction with a transition metal and lithium selected from Group 3B and 4B elements of the periodic table are titanium, iron and the like. , Nickel, manganese, copper and the like.
The shape of these metals is preferably powder because it is easy to mix with the active material and the carbon material. The secondary particle size of the metal powder used in the present invention is preferably 50 μm or less, particularly preferably 15 μm or less.
It is good to make it below μm. The primary particle size is not particularly limited as long as it is equal to or smaller than the secondary particle size. Further, a metal that easily alloys with lithium easily deteriorates by repeating the charge / discharge reaction, which is not preferable because it is contrary to the gist of the present invention.

Examples of the transition metal and nitride of an element selected from Groups 3B and 4B of the periodic table in the present invention include:
Titanium nitride, silicon nitride, boron nitride, and the like are preferable.
The shape of these nitrides is preferably powder because it can be easily mixed with the active material and the carbon material. Further, the secondary particle size of the nitride used in the present invention is preferably 50 μm or less,
Particularly, the thickness is preferably 15 μm or less. The primary particle size is not particularly limited as long as it is equal to or smaller than the secondary particle size.

The metals and nitrides referred to in the present invention can be used as a mixture of two or more kinds of metals and nitrides or a mixture of a metal and a nitride. The positive electrode active material used in the present invention is not limited as long as it is capable of inserting and extracting lithium ions known as a positive electrode active material of a nonaqueous electrolyte secondary battery. In particular, a metal chalcogenite-based positive electrode active material used for a 4V-class lithium secondary battery is preferable. Li
CoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , or a combination of these with transition metal, semi-metal, boron, etc.
Alternatively, a mixture thereof is particularly preferable.

The negative electrode active material used in the present invention is not limited as long as it can absorb and release lithium ions known as a negative electrode active material of a non-aqueous electrolyte secondary battery. Preferably, an oxide of a transition metal and an element selected from the group 3B and 4B elements of the periodic table are preferable. Particularly, amorphous silicon oxide is particularly preferable.

The conductive carbon material referred to in the present invention may be any conductive carbon material. In particular, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, and the like, which hardly cause a reaction with an electrolytic solution in a battery reaction, are preferable, and a carbon material having a secondary particle size of 15 μm or less is particularly preferable.
These carbon materials may be used alone or as a mixture of two or more types.

When a coin-shaped, cylindrical, or square non-aqueous electrolyte secondary battery is manufactured using the mixture thus constituted, the difference between the charge capacity and the discharge capacity in the first cycle is reduced. Will decrease.

[0016]

【Example】

<Embodiment 1> One embodiment of the present invention will be described with reference to the drawings. In FIG. 1, SiO, which is an oxide of silicon, is used as a negative electrode active material, graphite is used as a conductive carbon material, a polyacrylic acid compound is used as a binder, and titanium having a particle size of 1 to 15 μm is used as a metal. 1 shows a structure of an embodiment of a coin-shaped battery according to the present invention manufactured using a mixture in which powder is mixed.

A working electrode (2) having a diameter of 8 is provided inside a nickel-plated stainless steel working electrode case (1).
The mixture formed into a pellet having a thickness of 2 mm was adhered to the mixture via a small amount of the conductive adhesive (3). On the inside of the counter electrode case (4), a counter electrode (5) having a thickness of 0.8 mm and a diameter of 14 mm is provided.
mm of disc-shaped metallic lithium was press-bonded, and a polypropylene gasket (6) was arranged around the counter electrode case (4) to prevent an electrical short circuit with the working electrode case (1). A separator (7) of a porous polypropylene film having a thickness of 40 μm was placed between the lithium metal counter electrode (5) and the working electrode (2), and 1 M / L of LiPF ₆ was used as an electrolyte.
Was added and a 1: 2 mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) was added to assemble a coin-shaped battery.

All of these battery assembling operations were performed in a glove box in an Ar gas atmosphere. The procedure for manufacturing the working electrode of the coin-type battery shown in this example is as follows.
First, a predetermined amount of an acrylic acid polymer as a binder is dissolved well using a suitable amount of water as a solvent until a uniform paste-like solution is obtained. Graphite, which is a conductive carbon material, is added to this solution so that the weight ratio with the acrylic acid polymer is 8: 3, and the mixture is kneaded well to form a uniform slurry. Thereafter, the solid is dried at 100 ° C. for 12 hours, and the obtained solid is crushed in an automatic mortar or the like.

Next, a mixture of SiO and titanium powder serving as the working electrode (2), the graphite and the acrylic acid polymer was weighed out to 21.5%, 23.5% and 55% by weight, and was The mixture was mixed in a mortar to make a mixture. Next, 20 mg of this mixture was weighed out, and using a hydraulic press device, a force of 1 ton was applied at a molding pressure of 8 mm in diameter and 0.2 m in thickness.
m pellets.

The pellet was attached to the working electrode case (1) with a conductive adhesive (3), and vacuum-dried at 100 ° C. for 8 hours to sufficiently remove water. FIG. 3 shows a charge / discharge curve of a nonaqueous electrolyte secondary battery using the titanium powder according to the present invention.

The charging and discharging are performed at a constant current of 0.1 mA, and the voltage range is from 2.0 V to 0.005 V. From this graph, the first charge capacity is 12.962 m.
Ah, and the first discharge capacity is 8.706 mAh. The irreversible capacity is 4.390 mAh. From this value, if the discharge capacity corresponding to the charge capacity is defined as the reversibility, 6
7.1%.

As a comparative example, without using titanium powder,
4% by weight of iO, graphite and acrylic acid polymer
A charge / discharge curve was also obtained for a battery prepared in the same manner as in Example 1 except for mixing at 5:40:15 under all other conditions. The result is shown in FIG. Charge capacity obtained from FIG.
962 mAh, discharge capacity 11.806 mAh, irreversible capacity 7.886 mAh, reversibility 59.1%,
Obviously, in Example 1, the irreversible capacity is reduced.

This embodiment shows an example of the nonaqueous electrolyte secondary battery according to the present invention, and includes a counter electrode (5) and a working electrode (2).
, The structure of the battery, the type and amount of the electrolyte and the electrolyte, the material and size of the separator (7), and the like are not specified. The metal powder added to the battery working electrode (2) together with the active material and the conductive carbon material is not limited to titanium, and transition of iron, nickel, manganese, copper, etc., which hardly causes an alloy reaction with lithium. Any material may be used as long as it is selected from metals or alloys thereof.

<Embodiment 2> This embodiment is a case where titanium nitride is used as the working electrode instead of the titanium powder used for the working electrode of the first embodiment. A similar battery was manufactured in the same manner as in Example 1 except that titanium nitride was used instead of titanium powder. The particle size of the titanium nitride used is 1 to 15 μm. FIG. 4 shows a charge / discharge curve of the coin-type non-aqueous electrolyte secondary battery of this example.

In this embodiment, the composition ratio between graphite and acrylic acid polymer is the same as in Embodiment 1, but the weight percentage of the active material and titanium nitride is 18.7 so that the molar ratio in a constant weight is the same. % And 26.3%. The conditions for charging and discharging are the same as in the first embodiment.

From FIG. 4, the first charge capacity is 12.03.
6 mAh, and the first discharge capacity was 8.041 mAh.
It is. The irreversible capacity is 3.995 mAh,
The reversibility is 66.8%. As a comparison, since titanium nitride itself may cause a charge / discharge reaction, titanium nitride and graphite were added to the working electrode (2) in the same manner as in this example.
A battery using an acrylic acid polymer mixture was also prepared. The charge / discharge curve at this time is shown in FIG.

From FIG. 5, the charge capacity is 1.642 mAh.
, Discharge capacity 1.113 mAh, irreversible capacity 0.529
The value of mAh is obtained. Since this value is sufficiently smaller than the value of the charge / discharge capacity of the present example or the comparative example of the prior art, it is understood that titanium nitride itself hardly contributes to the charge / discharge reaction. However, as shown in this embodiment, by mixing the active material, the conductive carbon material, and titanium nitride, a synergistic effect works, and the conventional problem can be solved.

<Embodiment 3> In this embodiment, the working electrode is used in combination with titanium nitride powder in addition to the titanium powder used for the working electrode of Embodiment 1. In addition to titanium powder,
All conditions except for the use of titanium nitride powder were as in Example 1.
In the same manner as in the above, a similar battery was produced. The particle size of the titanium nitride used is 1 to 15 μm. FIG. 6 shows a charge / discharge curve of the coin-type non-aqueous electrolyte secondary battery of this example.

In this embodiment, the composition ratio of graphite and acrylic acid polymer is the same as in Embodiment 1, but the weight percentages of the active material, titanium powder and titanium nitride are the same so that the molar ratio in a constant weight is the same. 20.0%, 11.0 respectively
% And 14.0%. The conditions for charging and discharging were as described in Example 1.
Is the same as

From FIG. 6, the first charge capacity is 12.81.
5 mAh, and the first discharge capacity was 8.928 mAh.
It is. The irreversible capacity is 3.887 mAh,
The reversibility is 69.7%. This value is the charge capacity 1 of the conventional example using the same volume of silicon oxide as the active material shown in FIG.
Compared with 9.962 mAh, discharge capacity 11.806 mAh, irreversible capacity 7.886 mAh, and reversibility 59.1%, the irreversible capacity is clearly reduced.

[0031]

The present invention is embodied in the form described above and has the following effects. That is, the present invention provides a non-aqueous electrolyte secondary battery in which a material capable of inserting and extracting lithium ions is used as a positive electrode or a negative electrode active material, wherein at least one of a positive electrode mixture and a negative electrode mixture has conductivity with the active material. One or more metals that are unlikely to cause an alloying reaction with lithium selected from carbon materials and transition metals and alloys thereof, or one or more elements selected from transition metals and groups 3B and 4B of the periodic table Nitride,
Alternatively, the structure is such that both the metal and the nitride are mixed.

Therefore, the capacity difference at the time of charge / discharge in the first cycle is reduced, and a high-capacity nonaqueous electrolyte secondary battery in which the positive and negative electrodes are balanced can be easily manufactured. Further, since the process of correcting the balance between the positive and negative electrodes can be omitted from the manufacturing process, the manufacturing cost of the non-aqueous electrolyte secondary battery can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a structural example of a coin-type battery according to the present invention.

FIG. 2 is a diagram showing charge / discharge bending of a coin-type battery according to a conventional example.

FIG. 3 is a diagram showing charge / discharge bending of a coin-shaped battery using titanium as a metal powder according to the present invention.

FIG. 4 is a diagram showing charge / discharge bending of a coin battery using titanium nitride as a nitride according to the present invention.

FIG. 5 is a diagram showing a charge / discharge curve of a coin-type battery using titanium nitride as an active material.

FIG. 6 is a diagram showing charge / discharge bending of a coin-type battery using titanium as a metal powder and titanium nitride as a nitride according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Working electrode case 2 Working electrode 3 Conductive adhesive 4 Counter electrode case 5 Counter electrode 6 Gasket 7 Separator

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Akifumi Sakata 1-8-1, Nakase, Mihama-ku, Chiba-shi, Chiba Seiko Electronic Industries Co., Ltd. (56) References JP-A-6-302315 (JP, A) JP-A Heisei 8-78018 (JP, A) JP-A-4-259764 (JP, A) JP-A-6-325765 (JP, A) JP-A-5-54889 (JP, A) (58) Fields investigated (Int. Cl ^7, DB name) H01M 4/02 -. 4/04 H01M 4/36 - 4/62 H01M 10/36 - 10/40

Claims (1)

(57) [Claims] 1. A non-aqueous electrolyte secondary battery comprising: a positive electrode mixture containing a substance capable of inserting and extracting lithium ions as a positive electrode active material; and a negative electrode mixture containing silicon oxide as a negative electrode active material. Are mainly composed of the negative electrode active material, a conductive carbon material, titanium, iron, nickel, manganese, copper, and these.
At least one type of gold selected from alloys
Powder or titanium nitride, silicon nitride, boron nitride
A non-aqueous electrolyte secondary battery comprising: a negative electrode mixture in which at least one kind of nitride powder selected from the group consisting of: a metal powder and a nitride powder are mixed.