JPH04155776A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To obtain a battery having a high voltage and a high capacity by forming negative electrode by use of a compound carbonic material consisting of both a graphite material obtained by carrying out heat treatment on coke and a vapor phase growing-related carbon fiber. CONSTITUTION:Paste obtained by mixing acetylene black, graphite and a fluororesin- related binding agent into Co O2 synthesized by mixing Li2CO3 and Co CO3 is applied and dried on both surfaces of an aluminum foil so as to form a positive electrode plate having the thickness of 0.19mm. Meanwhile, a negative electrode plate can be formed in such a way that coke obtained by carrying out heat treatment at 2800 deg.C and VGCF obtained by carrying out heat treatment at 2200 deg.C are mixed, that 10 weight part of fluororesin-related binding agent is mixed into 100 weight part of this carbonic material, and that it is suspended in an aqueous solution of carboxymethyl celulose so as to form a paste condition. After this paste is applied to both surfaces of a copper foil having the thickness of 0.02mm and dried, an electrode plate having the thickness of 0.20mm, the width of 40mm and the length of 270mm can be formed by means of rolling. By constituting a battery by use of such a positive electrode plate and a negative electrode plate, the battery having a high voltage and a high capacity can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a novel compact and lightweight secondary battery.

BACKGROUND OF THE INVENTION In recent years, consumer electronic devices have rapidly become portable and cordless. Along with this, there is an increasing demand for small, lightweight, and high energy density secondary batteries that serve as driving power sources. From this point of view, non-aqueous secondary batteries, especially lithium secondary batteries, have high expectations as batteries with particularly high voltage and high energy density, and their development is urgently needed.

Conventionally, manganese dioxide, vanadium pentoxide, titanium disulfide, and the like have been used as positive electrode active materials for lithium secondary batteries. These positive electrodes, a lithium negative electrode, and an organic electrolyte constituted a battery, which was repeatedly charged and discharged. However, in general, secondary batteries that use lithium metal for the negative electrode,
Issues such as internal short circuits caused by dendrite-like lithium generated during charging and side reactions between the active material and electrolyte are major obstacles to the development of secondary batteries. Furthermore, no material has been found that satisfies the high rate charge/discharge characteristics and overdischarge characteristics. In recent years, the safety of lithium batteries has been under strict scrutiny, and it is extremely difficult to ensure safety in battery systems that use lithium metal or lithium alloys for the negative electrode.

On the other hand, a new type of electrode active material that utilizes the intercalation reaction of layered compounds is attracting attention, and graphite intercalation compounds have been used as electrode materials for secondary batteries for a long time.

In particular, graphite intercalation compounds incorporating anions such as ClO4-1PF6-1BF and - ions are used as positive electrodes, while graphite intercalation compounds incorporating cations such as Ll+ and Na+ are considered as negative electrodes. However, graphite intercalation compounds incorporating cations are extremely unstable;
When natural graphite or artificial graphite is used as a negative electrode, the battery usually lacks stability and has a low capacity. Furthermore, since it involves decomposition of the electrolyte, it cannot be used as a substitute for a lithium negative electrode.

Recently, it has been discovered that cation-doped pseudographite materials obtained by carbonizing various hydrocarbons or polymeric materials are effective as negative electrodes, and have relatively high utilization rates and excellent stability as batteries. Ta. Research is being actively conducted on small, lightweight secondary batteries using this material.

On the other hand, with the use of carbon materials for the negative electrode, the positive electrode active materials include LiCoO2 and LiMn2O4, which are compounds that have a higher voltage and contain Li, or some of these Co and Mn with other elements, For example, Fe, Co,
It has been proposed to use a composite oxide substituted with NiXMn or the like.

Problems to be Solved by the Invention When a pseudographite material having a certain degree of turbostratic structure as described above is used as a negative electrode material, the amount of intercalation and desorption of lithium was determined to be 100 to 150 ■Ah/g carbon.
However, the polarization of the carbon electrode increases during charging and discharging.

Therefore, when combined with a positive electrode such as Li Co 02, it is difficult to obtain satisfactory capacity and voltage.On the other hand, when a highly crystalline graphite material is used as the negative electrode material, the graphite electrode It has been reported that gas generation occurs due to decomposition of the electrolyte on the surface, making it difficult for the intercalated carbon reaction of lithium to proceed.
0 to 250 mAh/g). However, due to the large expansion and contraction of graphite in the C-axis direction during charging and discharging, the molded body swells and cannot maintain its original shape. Therefore, there is a problem with cycle characteristics.

In addition, because the graphite electrode has poor wettability with the electrolyte, the reaction is uneven during initial charging, and not all of the lithium is intercalated, and metallic lithium is partially deposited on the electrode surface. There was a problem.

The present invention solves the conventional problems as described above, and
The purpose of the present invention is to provide a non-aqueous electrolyte secondary battery with high capacity and excellent cycle characteristics.

Means for Solving the Problems In order to solve these problems, the present invention uses graphite material heat-treated with coke and vapor-grown carbon fiber (hereinafter referred to as V
It is abbreviated as GCF. ) By using a composite carbon material consisting of
This improves the wettability of the electrode.

Generally, it has been reported that the upper limit of the amount of lithium that can be chemically intercalated between graphite layers is C6Li, a first-stage graphite intercalation compound in which one lithium atom is inserted for every six carbon atoms. Active material is 372mA
It has a capacity of h/g. When pseudographite materials such as those described above are used, the amount of lithium that can be intercalated is small because the layered structure of graphite is underdeveloped, and the charge/discharge reaction is around 1.0 μ, which is more negative than metal lithium. It was not suitable as a negative electrode material because it progresses at a potential of . When a high-temperature fired body of coke is used as the negative electrode,
Although it is known that the initial capacity can be increased to 200 to 250*Ah/g, the capacity deterioration due to cycling increases because the molded body swells. Also, it has poor wettability with electrolyte.

On the other hand, when VGCF is used for the negative electrode, almost no swelling of the molded product is observed and the wettability is good. However, since the bulk density is very low compared to other carbon materials such as coke, when considering an electrode plate in which carbon paste is applied to a long core material as shown in the example, the filling amount (filling amount) density) becomes extremely small.

Therefore, the capacity of the battery decreases. Therefore, the present inventors have solved the above-mentioned problems by making use of the features of both to create a composite carbon material.

In that case, the mixing ratio of the high-temperature calcined coke and VGCF is important, and the amount of VGCF added is preferably 5% by weight or more and 20% by weight or less, more preferably 5% by weight or more and 10% by weight.
It is as follows. If it is less than 5% by weight, the effect of VGCF cannot be utilized and the cycle characteristics deteriorate. If it exceeds 20% by weight, the packing density of the carbon material on the electrode plate decreases, resulting in a decrease in battery capacity. Furthermore, the degree of graphitization is an important factor for both the graphite material and VGCF used in the present invention, and the distance between the 002 planes (dO02) is 3.4.
0 people, and is required to be 3.45 Å or less. When a carbon material having a spacing greater than the above is used, the capacity is small and the polarization of the carbon electrode becomes large, as in the case of other pseudographite materials.

On the other hand, the positive electrode contains Li, a compound containing lithium ions.
C002, LiMn2O4, and both Co or M
A part of n is replaced by other elements, such as Co.

Composite oxides substituted with Mn, Fe, Ni, etc. can be used. The above composite oxide can be easily obtained by using carbonates or oxides of lithium or cobalt as raw materials, mixing and firing according to the desired composition.

Of course, the same synthesis can be performed using other raw materials.

Usually, the firing temperature is set between 650°C and 1200°C.

The electrolytic solution and separator are not particularly limited, and any conventionally known ones can be used.

Function: The composite carbon material of the high-temperature calcined coke and VGCF according to the present invention takes advantage of the features of both.

Like carbon black, VGCF is a carbon fiber produced by thermally decomposing hydrocarbons in a gas phase, and thus has good wettability with an electrolyte. In addition, carbon/carbon fiber composite materials are generally used as materials with high strength and high elastic modulus when considering carbon materials as structural materials, and the present invention applies this concept to battery electrode materials. This is what I did. As a result, by using the composite carbon material, it was possible to prevent swelling and destruction of the electrode plate due to charging and discharging, and further improve the wettability of the electrode plate. Therefore, by combining it with a positive electrode made of a lithium-containing composite oxide, it is possible to obtain a secondary battery with high voltage, high capacity, and excellent cycle characteristics.

Example Hereinafter, the present invention will be described in detail with reference to Examples.

FIG. 1 shows a longitudinal cross-sectional view of the cylindrical battery used in this example. In the figure, 1 is a battery case made of organic electrolyte-resistant stainless steel plate, 2 is a sealing plate provided with a safety valve, and 3 is an insulating backing. Reference numeral 4 denotes a group of electrode plates, in which a positive electrode and a negative electrode are wound a plurality of times with a separator in between and housed therein. A positive electrode lead 5 is drawn out from the positive electrode and connected to the sealing plate 2, and a negative electrode lead 6 is drawn out from the negative electrode and connected to the bottom of the battery case 1. Insulating rings 7 are provided at the top and bottom of the electrode plate group, respectively. The pressure, negative electrode plate, electrolyte, etc. will be explained in detail below.

The positive electrode is a mixture of Li2Co3 and CoC0, heated at 900℃.
CoO2 powder synthesized by baking for 10 hours
To the weight part, 3 parts by weight of acetylene black, 4 parts by weight of graphite, and 7 parts by weight of a fluororesin binder were mixed, and the mixture was suspended in a carboxymethyl cellulose aqueous solution to form a paste. This paste was applied to both sides of aluminum foil with a thickness of 0.03 mm, and after drying, it was rolled to a thickness of 0.19 mm and a width of 4 mm.
0mm.

The electrode plate had a length of 250 mm.

The negative electrode is made of coke (d002
= 3.38 people) and VGCF subjected to heat treatment at 2200℃
(d002 = 3.42 people) at the mixing ratio shown in Table 1, 100 parts by weight of carbon material, 10 parts by weight of fluororesin binder, suspended in carboxymethyl cellulose aqueous solution, and paste. It was made into a shape. This paste was applied to both sides of a copper foil having a thickness of 0.02 mm, and after drying, it was rolled to obtain an electrode plate having a thickness of 0.20 mm, a width of 40 mm, and a length of 270 mm.

Then, attach the leads to each of the positive and negative electrode plates, and make sure that the thickness is 0.
．． 025 mm, width 46 mm, length 700 mm, wound through a polypropylene separator, diameter 13.8 m.
It was housed in a battery case with a height of 50 mm. The electrolyte contains an equal volume mixed solvent of propylene carbonate and ethylene carbonate,
Table 1 A solution prepared by dissolving rum at a ratio of 1 mol/l was used.

Before sealing this battery, a charging/discharging operation was performed, and the generated gas was sufficiently degassed under vacuum, and then the battery was sealed to obtain a test battery.

These test batteries were then subjected to a charge/discharge current of 100 mAh, a charge end voltage of positive charge IV, and a discharge end voltage of 3. A constant current charge/discharge test was conducted under OV conditions. A comparison of the cycle characteristics is shown in Figure 2. Although the battery 1 that does not use VGCF has a large initial capacity of 500 mAh or more, the capacity deteriorates significantly with cycles.

On the other hand, it can be seen that in Batteries 2 and 3 containing 5% or 10% by weight of vGCF, the capacity deterioration due to cycling is extremely small while maintaining high capacity. VGCF
Battery 4 and Battery 5 with 25% by weight and 100% by weight have good cycle characteristics, but have extremely low capacity. This is because VCCF became dominant and the amount of the mixture filled decreased.

The average discharge voltage was about 3.7v in both cases.

Further, after sealing test batteries 1 to 5 constructed under the same conditions, the test was stopped after the first cycle of charging was completed, the batteries were disassembled, and the negative electrode plates were observed. As a result, in Battery 1, the electrode plates and the electrolyte were insufficiently wetted, and there was a completely unwetted and unreacted area in the center, and a small amount of metallic lithium was observed to be deposited around this area. In Batteries 2 to 5, the electrode plates were sufficiently wetted and reacted uniformly, and no noticeable changes such as precipitation of lithium were observed.

Comparative Example 1 All the configurations were the same as in the example except that a composite carbon material containing 5% by weight of commercially available acetylene black (d002 = 3.48 people) was used as the negative electrode material instead of vGCF. A battery of Comparative Example 1 was obtained.

Comparative Example 2 In the example, the heat treatment temperature of VCCF was 1200'C.
(d002=3.55 people), and a battery of Comparative Example 2 was prepared under the same conditions as in Example except that 5% by weight was mixed.

A charge/discharge test was conducted on the batteries of Comparative Examples 1 and 2 under the same conditions as in the Example. In all cases, the wettability of the electrode plate was good, but the capacity was small at 400 mAh or less, and the average discharge voltage was low at 3.5 V. This is due to the insufficient degree of graphitization of acetylene black and VGCF (processed at 1200°C).

Effects of the Invention As is clear from the above explanation, the non-aqueous electrolyte secondary battery according to the present invention, which uses a composite carbon material consisting of a high-temperature fired body of coke and vapor-grown carbon fibers for the negative electrode, can achieve high voltage, This has the effect of providing a non-aqueous electrolyte secondary battery with high capacity and excellent cycle characteristics.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a cylindrical battery in an example of the present invention, and FIG. 2 is a diagram showing a comparison of cycle characteristics. DESCRIPTION OF SYMBOLS 1... Battery case, 2... Sealing plate, 3... Insulating backing, 4... Electrode plate group, 5... Positive electrode lead, 6...
... Negative electrode lead, 7... Insulating ring, 8... Battery case, 9... Lithium metal, 10... Electrolyte. Name of agent: Patent attorney Akira Koebushi and 2 others +-, /
li＞twaT、s#j 2 Figure trill & (times) Procedural amendment 2 Name of the invention Non-aqueous electrolyte secondary battery 3 Relationship with the person making the amendment Case Patent applicant Location Kadoma City, Osaka Prefecture Oaza Kadoma 1006 address name (
582) Matsushita Electric Industrial Co., Ltd. Representative Akio Tanii 4 Agent 571 Address 6, Matsushita Electric Industrial Co., Ltd., 1006 Oaza Kadoma, Kadoma City, Osaka Contents of the amendment (1) Page 2 of the specification, No. 8 Correct "rechargeable battery" in the row to "rechargeable battery". (2) ", 8..." on page 16, line 1 to page 16, line 2
...-Battery N10... Electrolyte" is deleted.

Claims (4)

[Claims] (1) In a non-aqueous electrolyte secondary battery comprising a positive electrode made of a lithium-containing composite oxide, a non-aqueous electrolyte, and a rechargeable negative electrode; A non-aqueous electrolyte secondary battery characterized by being made of a composite carbon material made of a grown carbon fiber. (2) The non-aqueous electrolyte secondary battery according to claim 1, wherein the mixing ratio of the vapor-grown carbon fiber in the composite carbon material is 20% or less by weight relative to the graphite material. . (3) The above graphite material is 002 by X-ray wide-angle diffraction method.
The nonaqueous electrolytic method according to claim 1 or 2, wherein the interplanar spacing (d002) of the planes is 3.40 Å or less, and the vapor-grown carbon fiber has a (d002) of 3.45 Å or less. Liquid secondary battery. (4) The above positive electrode is LiCoO_2, LiMn_2O_
2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is at least one selected from the group consisting of 4, or a composite oxide in which Co and Mn are partially replaced with other elements.