JPH06187989A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To provide a nonaqueous electrolyte battery having favorable cycle life characteristics and a large discharge capacity by developing carbon material capable of storing/discharging large quantity of lithium in the case of charging/ discharging at a high current density and having favorable reversibility. CONSTITUTION:Carbon material of a nonaqueous electrolyte secondary battery is obtained in an oil furnace method using creosote oil as material. The carbon black satisfy all the numerical characteristics of a spacing d002 of 3.55-3.70Angstrom for a face 002 as measured in an X-ray diffraction method, a size Lc of a cristal lattice in a C-axis direction within a range of 10-20Angstrom , a DBP oil absorption quantity within a range of 50-200ml/100g, and a nitrogen adsorption specific surface area of 30-300m<2>/g as determined in a BET method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to lithium-doped
The present invention relates to a non-aqueous electrolyte secondary battery in which an anode carbonaceous material to be dedoped is improved.

[0002]

2. Description of the Related Art Lithium metal or an alloy of lithium and a low melting point metal capable of melting lithium is used as a negative electrode material of a lithium secondary battery. However, with the practical use of this battery, the following drawbacks become a particular problem. That is, the charging time is long and the quick charging property is poor. Short cycle life. Etc.

All of these are problems caused by lithium, and the morphological changes of the lithium (or lithium alloy) negative electrode such as embrittlement and disintegration due to charge and discharge, formation of dendrites by electrodeposition of metallic lithium, and electrolysis of metallic lithium and electrolysis. The cause of this is the formation of a passive film due to the reaction with the liquid.

As one of the means for solving the above problems, it is proposed to use, as a negative electrode material, a material such as a carbonaceous material, which can reversibly occlude and release lithium at a base potential. And is about to be put to practical use.
This utilizes the fact that an intercalation compound of lithium and a carbonaceous material is easily and reversibly formed by an electrochemical operation.

For example, when a battery is composed of a positive electrode containing a sufficient amount of lithium, a carbonaceous material negative electrode, and a non-aqueous electrolyte and charged, lithium is electrochemically electrochemically separated from the negative electrode carbonaceous material. Is stored in. When the battery is discharged, lithium is released from the carbonaceous material layer and returns to the positive electrode.

[0006]

By the way, since the electric capacity (mAh / g) of carbon per unit weight of carbon at this time is determined by the amount of lithium that can be occluded / released, in such a negative electrode, lithium electrochemical It is desirable to maximize the reversible storage capacity as much as possible. Theoretically, the upper limit is the state of being occluded at a ratio of one lithium atom to six carbon atoms, that is, the saturated composition of the intercalation compound of lithium and the carbonaceous material.

As a negative electrode carbonaceous material satisfying such conditions, a carbonized or graphitized material of an organic polymer compound or a composite thereof has been conventionally used.

However, in the conventional carbonaceous material, the capacity is largely deteriorated due to the inactivation of lithium during the charge / discharge cycle, and the amount of lithium that can be occluded / released, that is, the capacity when a battery is constructed is unsatisfactory. In reality, when the charge and discharge were performed at a high density (1 mAh / cm ² or more), the amount of electrochemical reversible occlusion was only half or less of the theoretical value.

The present invention replaces the above-mentioned conventional carbonaceous material with a carbonaceous material excellent in reversibility, which has a large lithium occluding / releasing amount particularly when charging / discharging at a high current density. The object of the present invention is to provide a non-aqueous electrolyte secondary battery having excellent cycle life characteristics and a large discharge capacity.

[0010]

In order to achieve the above object, the carbonaceous material of the non-aqueous electrolyte secondary battery according to the present invention is carbon black obtained by an oil furnace method using creosote oil as a raw material. In the carbon black, (A) the interplanar spacing d002 of the 002 plane measured by the X-ray wide-angle diffraction method is 3.55 to 3.70 (angstrom), and the size Lc of the crystal lattice in the C-axis direction is 1.
0 to 20 (Angstrom), (B) DB
P oil absorption is 50 ~ 200ml / 100g,
(C) The nitrogen adsorption specific surface area determined by the BET method is 30.
It is one that satisfies all the conditions of being ~ 300 m ² / g.

Next, the reasons for limiting the above numerical values will be described.

Reason for limiting numerical values of (A): When the carbonaceous material used for the negative electrode is carbon black obtained by an oil furnace method using creosote oil as a raw material,
This carbon black has a surface spacing d002 of 002 planes.
The size Lc of the crystal lattice in the C-axis direction, the degree of development of the "structure" obtained in the thermal decomposition process ("structure"
This will be explained in the section “(B) Reason for limiting numerical values” below. ), And the size of the specific surface area, it has been clarified that the electrochemical characteristics depend on the following numerical values.

First, the surface spacing d002 of the 002 surface is below the lower limit of the numerical range of 3.55 (angstrom), and the size Lc in the C-axis direction is the upper limit of 20 (angstrom). 0.15 if exceeded
When lithium is doped / dedoped at a relatively low current density of mA / cm ² or less, the electrode potential is excellent in flatness at the beginning of the cycle, but lithium that becomes inactive appears every time the charge / discharge cycle is repeated. Not only does the amount of lithium that can be doped / dedoped reduced, but the flatness of the electrode potential cannot be maintained. The deactivated lithium refers to lithium that has been doped with carbon and cannot be electrochemically dedoped.

It is generally known that carbon doped with lithium has an interlayer distance (distance between 002 planes) d002 of 3.7 (angstrom). When carbon black with such a narrow spacing is doped with lithium, it is considered that the lithium is strongly pressed by the layers on both sides, and this force stabilizes the first doped lithium between the layers, resulting in inactivity. It is presumed that it will be converted (cannot be dedoped).

When lithium is doped / dedoped at a relatively high current density of 0.5 mA / cm ² or more, not only the amount of lithium that can be doped / dedoped becomes extremely small, but The electrode potential changes greatly depending on the doping or dedoping of lithium.

The main reason for this is, although the details are unknown, since the interlayer distance d002 is small in the above numerical values, it is difficult for lithium to be doped and dedoped, and the inactivated lithium is present as described above. It is presumed that the polarization becomes large as a result of the inability to maintain the fast reaction rate.

Next, contrary to the above, the surface spacing d of the 002 surface is d.
When 002 exceeds the upper limit of 3.7 (angstrom) of the present invention and the size Lc of the crystal lattice in the C-axis direction is lower than the lower limit of 10 (angstrom) of the present invention, charging / discharging is performed at a high current density. The amount of lithium that can be doped and dedoped is larger than that of the former, and its reversibility is excellent. However, although the amount of doped lithium can be reversibly undoped, each time the charge / discharge cycle is repeated,
The same amount of lithium as in the previous cycle cannot be doped.

Although the details are not clear, the main reason for this is thought to be that the layer structure of carbon black is destroyed during dedoping of lithium. In fact, it has been confirmed that when the carbon black having the above-mentioned numerical value is used, the amount of lithium that can be occluded in each cycle is reduced and the cycle life characteristics are reduced.

Therefore, from the above, the carbon black suitable for the lithium secondary battery can be obtained by using the 002 plane spacing d.
002 has a lower limit of 3.55 (Angstrom),
The upper limit is 3.70 (angstrom), and the size Lc of the crystal lattice in the C-axis direction is limited to a lower limit of 10 (angstrom) and an upper limit of 20 (angstrom).

Reason for limiting numerical values of (B): Carbon black has a chain-like or tuft-like appearance in which individual particles are fused together, and each agglomeration unit is integral as viewed from the internal structure. Are known. Chain-like aggregates of such particles are conventionally referred to as "structures."

It is considered that the structure is basically one in which microscopic droplets of condensed polycyclic polynuclear aromatic hydrocarbons collide with each other and solidify by fusion at the stage of particle formation in the reaction furnace. It can be controlled almost freely. In order to evaluate the structure, it is most common to densely fill the agglomerated particles of carbon black and to indicate the oil absorption amount with the amount of oil that replaces the voids as a scale. Here, an absorption meter is used, and the oil absorption amount per 100 g obtained from 70% of the maximum torque when DBP (dibutyl phthalate) is added to carbon black is defined as the DBP oil absorption amount.

For example, when the DBP oil absorption is larger than 200 ml / 100 g which is the upper limit of the present invention, the amount of lithium that can be absorbed and released by this carbon black greatly depends on the shape of the current collector. That is, such carbon black swells due to lithium doping / dedoping accompanying charging / discharging due to the inclusion of the electrolytic solution, which deteriorates the contact state of individual particles and causes poor current collection. As a result, the conductivity of the carbon black electrode is lowered and the polarization progresses, so that the amount of lithium that can be doped and dedoped decreases. After that, the swollen carbon black may be isolated in the electrode, making it impossible to dope and dedope lithium, and in some cases, it may drop from the current collector.

Therefore, for example, Japanese Patent Laid-Open No. 62-10846.
As disclosed in Japanese Patent Laid-Open No. 2 (1998), a plurality of reticulated current collectors are stacked to form a three-dimensional network structure, and carbon black is supported on the network to suppress swelling, or a conductive filler is added to carbon black. Some have taken measures such as mixing them, but even if these measures are taken, they are still insufficient.

Further, the bulk density of carbon black is closely related to the degree of structure development, and the more developed the structure, the smaller the bulk density. Therefore D
Carbon black having a larger BP oil absorption amount is also disadvantageous in terms of volume energy density because the amount that can be filled in the limited space is smaller.

On the other hand, contrary to the above, when the DBP oil absorption amount is smaller than the lower limit value of 50 ml / 100 g of the present invention, the bulk density is large, but the structure is not developed, so that the electrolyte solution The permeation deteriorates the contact state of individual particles, causing poor current collection, and the capacity deteriorates when the charge / discharge cycle is repeated.

From the above, the DBP oil absorption is 50 to 2
It is limited to the range of 00 ml / 100 g.

Reason for limiting numerical values of (C): It has been found that the specific surface area of carbon black also has a strong influence on the electrochemical characteristics of the negative electrode using this as a carbonaceous material. Generally, when repeating absorption and desorption of lithium in a carbonaceous material, the ratio of the amount that can be dedoped is not 100% with respect to the amount of lithium doped in the first cycle, although the degree varies depending on the electrolytic solution. , Some of them remain in the carbon black and become inactive, and do not participate in the subsequent cycles. When the deactivated lithium is referred to as a loss capacity in the first cycle, it goes without saying that the battery performance can be improved by reducing the loss capacity as much as possible.

Based on this premise, as a result of repeating various experiments, in the case of carbon black obtained by the oil furnace method using creosote oil as a raw material, the loss capacity in the first cycle is strongly dependent on the size of its specific surface area. It turned out to be involved. That is, the larger the value of the nitrogen adsorption specific surface area, the larger the loss capacity in the first cycle. In particular, for those exceeding the upper limit of 300 m ² / g of the present invention, this value is extremely large, and the subsequent amount of lithium that can be doped or dedoped becomes extremely small.

Although the details of the cause have not been clarified yet, the loss capacity in the first cycle depends on the formation of an irreversible compound of carbon black and reduced lithium, or the solvent as a competitive reaction. It is considered that the irreversible compounds generated by decomposition cover the surface of carbon black, and it is presumed that these products interfere with the doping and dedoping of lithium.

On the contrary, when the nitrogen adsorption specific surface area of carbon black is less than the lower limit value of 30 m ² / g of the present invention, the capacity decreases each time the lithium absorption / desorption cycle is repeated. However, it is unsuitable for use as a carbonaceous material for lithium secondary batteries.

From the above, the nitrogen adsorption specific surface area is 30
Limited to ~ 300 m ² / g.

Therefore, the lithium secondary battery constructed by using the carbon black satisfying all of the above numerical characteristics (A) to (C) has a high current density even if the lithium is doped and dedoped. It gives good results.

Next, a method of manufacturing a lithium secondary battery using the carbon black having the above characteristics will be described.

Kneading is performed by mixing the carbon black satisfying all the numerical characteristics (A) to (C) described above with a binder.
While forming a negative electrode by granulating, an oxide capable of inserting and extracting lithium as a positive electrode and containing lithium,
A lithium secondary battery can be obtained by using a sulfide and combining it with a separator and a non-aqueous electrolyte. The form of the battery may be flat or spiral.

As the positive electrode material, any material used in this type of battery can be used, but it is particularly preferable to use a material containing a sufficient amount of lithium.
For example, LiMn ₂ O ₄ and the general formula LiMO ₂ (however,
M represents at least one or a mixture of Co and Ni,
LiCoO ₂ and LiCo _0.8 Ni _0.2 O _{2 and the} like) are preferable, and an intercalation compound containing lithium and a composite metal oxide.

The non-aqueous electrolyte is prepared by appropriately combining an organic solvent and an electrolyte, and any of these organic solvents and electrolytes can be used as long as they are used in this type of battery. .

Examples of the organic solvent include propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl. Examples include -1,3-dioxolane, diethyl ether and sulfolane.

As the electrolyte, LiClO ₄ , LiAs
F ₆ , LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , L
iCl etc. are listed.

[0039]

The lithium secondary battery using carbon black having the above morphological parameters has a small loss capacity in the first cycle. Further, even if charging and discharging are repeated, the discharge capacity is less deteriorated. Further, the volume energy density is also set appropriately. On the contrary, the morphological parameters can be modeled according to the goals such as suppression of loss capacity in the first cycle, prevention of deterioration of discharge capacity, and optimization of volumetric energy density.

[0040]

The preferred embodiments of the present invention will be described in detail below. The carbon black used for the positive electrode was obtained by the oil furnace black method using creosote oil as a raw material. Table 1 shows the characteristics of the samples of 19 kinds of carbon blacks A to S in which the respective numerical characteristics are within the scope of the present invention and those which are not within the scope of the present invention.

[0041]

[Table 1] In Table 1, the interplanar spacing d002 of each carbon black and the crystal lattice size Lc in the C-axis direction were determined by the X-ray wide-angle diffraction method based on the Gakushin method.

The DBP oil absorption was determined as an oil absorption per 100 g obtained from 70% of the maximum torque when DBP was added to carbon black, using an absorber meter.

The nitrogen adsorption specific surface area was determined by the BET method.

The apparent density of carbon black is
It was calculated as the tap density. Tap density is 1 cm inside diameter, 12 cm high in a glass measuring cylinder, 1.000 g of precisely weighed carbon black is put into the measuring cylinder to seal the opening of the measuring cylinder, and after vibrating 100 times with a rubber rod, carbon is added. The black deposition height was read from the scale of the graduated cylinder, and the density was calculated from the volume to obtain it.

FIG. 1 shows the structure of a CR2016 flat type lithium secondary battery type test cell using the carbon black having the above various characteristics. This lithium secondary battery basically has a power generation element with a separator 3 in which a polypropylene non-woven fabric and a polypropylene microporous film are superposed between the positive electrode 1 and the negative electrode 2 in pellet form, as in the conventional case. The negative electrode 2 side is formed and connected to the negative electrode can 5 via the SUS net 4 constituting the current collector, and the positive electrode 1 side is connected to the positive electrode terminal plate 7 via the titanium net 6.
It is completed by injecting the non-aqueous electrolyte solution and then caulking between the negative electrode can 5 and the positive electrode terminal plate 7 via the sealing gasket 8.

For the negative electrode 2, 4 parts by weight of PTFE resin was added to 96 parts by weight of the carbon black, kneaded, and 8 mg was weighed after granulation. The mixture was put in a molding die having an inner diameter of 11 mm and 3 t / cm ^2. It is formed into a disk shape under the pressure of.

The positive electrode 1 is made of LiCoO ₂ which is a positive electrode active material.
Relative to 80 parts by weight, PTFE10 parts, acetylene black powder 10 parts by weight as a conductive material kneaded, weighed 100mg after granulating, it was placed in a mold having an inner diameter of 11mm at a pressure of 3t / cm ² It is formed into a disc shape.

As the non-aqueous electrolyte, a solution prepared by dissolving 1 mol / l lithium perchlorate (LiClO ₄ ) in a propylene carbonate-dimethoxyethane mixed solvent (volume ratio 1: 1) was used. The amount of active material in the test cell is
The electrochemical equivalent was positive electrode >> negative electrode, and the battery capacity was set to regulate the negative electrode.

After the above test cell assembly, the current density is 0.5.
The upper limit cut-off voltage is 4.05V and the lower limit cut-off voltage is 2.8V at constant current of mA.
It went up to the cycle. The first cycle obtained as a result,
The values of the discharge capacity at the 100th cycle and the loss capacity at the first cycle are also shown in Table 1 above.

From Table 1, the relationship between the value of d002 and the discharge capacity in the first cycle, the relationship between the value of d002 and the discharge capacity in the 100th cycle, the relationship between the DBP oil absorption and the tap density, and the specific surface area The relationship with the loss capacity in the first cycle was obtained. The results are shown in FIGS.

FIG. 2 shows the relationship between d002 and the discharge capacity in the first cycle. When the value of d002 is within the range of the present invention, the discharge capacity in the first cycle is 120.
Although it is as large as mAh / g or more, if the value of d002 is less than 3.55 (angstrom) (sample I, J, K) or exceeds 3.70 (angstrom) (sample G, P, L, M), The discharge capacity in one cycle is small. Further, FIG. 3 shows the relationship between the value of d002 and the discharge capacity at the 100th cycle. As is clear from FIG. 3, those which are not included in the scope of the present invention are repeatedly charged and discharged. The discharge capacity deteriorates.

Even if the value of d002 is within the range of the present invention, the samples Q, R and S having a DBP oil absorption of more than 200 ml / 100 g, and the DBP oil absorption of 50 ml / 1.
Samples D and E smaller than 00 g have a deteriorated discharge capacity after repeated charging and discharging.

Further, as shown in FIG. 4, the larger the DBP oil absorption, the smaller the tap density, and especially when it exceeds 200 ml / 100 g, it cannot be said to be a practical material considering the volumetric energy density of the battery.

Furthermore, as is apparent from FIG. 5, the loss capacity in the first cycle is related to the size of the specific surface area, and the larger this value, the larger the loss capacity in the first cycle. Especially for those with a specific surface area of more than 300 m ² / g, this value is extremely large, and the lithium equivalent to this loss capacity will eventually be supplemented from the positive electrode side. Therefore, consider the volumetric energy density of the battery. Then it is very disadvantageous. On the other hand, as in Samples D, E, and J, when the nitrogen adsorption specific surface area is 30 m ² / g or less, the discharge capacity deteriorates with each cycle.

As can be seen from the above examples, the batteries to which the present invention was applied, that is, samples A, B, C, F, of carbon black satisfying all the above-mentioned numerical characteristics were satisfied.
It was confirmed that only G and H significantly improved the discharge capacity, and the cycle deterioration could be set to be much smaller than the conventional one.

[0056]

As described in detail above, according to the present invention, charging / discharging was performed at a particularly high current density by setting the morphological parameters of the carbonaceous material used for the negative electrode within an appropriate range. In this case, it is possible to obtain a carbonaceous material having a large amount of lithium occlusion / release and excellent reversibility, and using such a carbonaceous material as a negative electrode, the discharge capacity is large and the cycle life is long. A water electrolyte secondary battery can be provided.

[Brief description of drawings]

FIG. 1 is a half sectional view showing a structure of a flat type non-aqueous electrolyte secondary battery in an example.

FIG. 2 is a graph showing the relationship between the value of d002 and the discharge capacity in the first cycle.

FIG. 3 is a graph showing the relationship between the value of d002 and the discharge capacity at the 100th cycle.

FIG. 4 is a graph showing the relationship between DBP oil absorption and tap density.

FIG. 5 is a graph showing the relationship between the nitrogen adsorption specific surface area and the loss capacity in the first cycle.

[Explanation of symbols]

 1 Positive electrode 2 Negative electrode 3 Separator 4 SUS net 5 Negative electrode can 6 Titanium net 7 Positive electrode terminal plate 8 Sealing gasket

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hidenori Nagura, 5-3-11 Shimbashi, Minato-ku, Tokyo Fuji Electric Chemical Co., Ltd. (72) Takashi Suzuki 5-36-11, Shimbashi, Minato-ku, Tokyo Fuji Electrochemical Co., Ltd.

Claims (1)

[Claims] 1. A non-aqueous electrolyte secondary battery using a carbonaceous material as a negative electrode, wherein the carbonaceous material is carbon black obtained by an oil furnace method using creosote oil as a raw material. Is the following (A)
To (C) have all the physical property values shown in (C). (A) The interplanar spacing d002 of the 002 plane measured by the X-ray wide-angle diffraction method is 3.55 to 3.70 (angstrom), and the size Lc of the crystal lattice in the C-axis direction is 10 to 20.
(Angstrom). (B) The DBP oil absorption is 50 to 200 ml / 100 g. (C) The nitrogen adsorption specific surface area determined by the BET method is 30.
~ 300 m ² / g.