JP2000164206A - Nonaqueous electrolyte secondary battery for assembled battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance safety in overcharging and reliability of each unit cell by arranging a conductive intermediate which is converted into a high resistant body in overcharging between a current collector and an active material containing layer of a positive electrode used together with a negative electrode, a separator, and a nonaqueous electrolyte. SOLUTION: Specific resistance of a conductive intermediate layer arranged between a current collector made of aluminum foil or mesh and a lithium- transition metal composite oxide of a positive electrode is for example 1 >.cm or less in normal use, but is increased to 100 times or more in overcharging exceeding voltage in full charging. The conductive intermediate layer having the specified thickness is prepared by mixing a binder of 10 wt.% or more but less than 100 wt.% based on the weight of carbonaceous conductive particles such as carbon black having good thin film forming capability and suitable specific resistance and adhesion to the current collector is ensured. Connection of a PTC element to a positive electrode or a negative electrode is useful, and current is surely shut off by heat generation of the conductive intermediate layer converted into a high resistance body by overcharge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery for an assembled battery.

[0002]

2. Description of the Related Art In recent years, non-aqueous electrolyte secondary batteries typified by lithium ion secondary batteries have a high energy density.
It is receiving attention as a power source for cordless portable electronic devices such as players, personal computers, portable information data terminals, and mobile phones.

[0003] In particular, a nonaqueous electrolyte secondary battery has a wide potential window for an electrolyte solution and can extract a high voltage with a single cell. Therefore, demand for a small and lightweight portable electronic device is growing.

The non-aqueous electrolyte secondary battery is used not only in the form of a single cell but also as a battery pack connected in series and / or in parallel. Since such a battery pack has a high voltage and a high capacity, a high-output power supply is usually used for its charger. When the battery pack is charged by a charger having a high-output power supply, overcharging is likely to occur.

[0005] For this reason, various protection elements are provided inside the battery to ensure safety during overcharge. For example, Japanese Patent Application Laid-Open No. 2-112151 discloses providing a current cutoff valve that cuts off a circuit by using internal pressure during overcharge. JP-A-1-197963 discloses that a carbon-containing resin film whose resistance increases at a high temperature is provided between a battery terminal and a terminal plate, and the current is cut off by increasing the contact resistance between the terminals by utilizing heat generated during overcharging. It is disclosed. Japanese Patent Application Laid-Open No. 9-320568 discloses that an electrode and a current collector are separated from each other by using heat generated during overcharging to cut off current.

[0006]

However, an element that interrupts current by using internal pressure requires a space inside the battery, which hinders an increase in capacity.

In a safety mechanism for interrupting current by utilizing heat generated during overcharge, a current interrupt mechanism is used when the temperature of the element becomes high due to Joule heat generated by energization or heat of decomposition reaction of the electrolyte during overcharge. Operates, but the Joule heat fluctuates due to the charging current value and the internal resistance of the battery, and the operation timing becomes uneven.

In particular, when a rechargeable battery is configured using a rechargeable battery having a safety mechanism for interrupting the current by utilizing heat generation, for example, when a total of nine rechargeable batteries of three, three and three are combined, The temperature of a battery located at the center of the battery becomes higher due to the influence of heat generated by the surrounding batteries. For this reason, this battery preferentially operates the safety mechanism. As a result, the current path flows through the left and right batteries that are connected in parallel with this battery, and a behavior occurs in which one of the safety mechanisms operates similarly.
In other words, the operation of the safety mechanism varies from cell to cell,
In some cases, leakage or gas ejection may occur, leading to a decrease in reliability.

An object of the present invention is to provide a non-aqueous electrolyte secondary battery for a battery pack that can improve the safety and reliability of each battery when overcharged when used as a battery pack. is there.

[0010]

According to the present invention, there is provided a non-aqueous electrolyte secondary battery for an assembled battery according to the present invention, comprising a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte. An electrolyte secondary battery, wherein the positive electrode has a structure in which a conductive intermediate layer that changes into a high-resistance body during overcharge is disposed between a current collector and an active material-containing layer. is there.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a non-aqueous electrolyte secondary battery for an assembled battery according to the present invention will be described in detail.

This non-aqueous electrolyte secondary battery has a positive electrode, a negative electrode,
It includes a separator and a non-aqueous electrolyte.

Next, the positive electrode, the negative electrode, the separator and the non-aqueous electrolyte will be described.

1) Positive Electrode This positive electrode has a structure in which a conductive intermediate layer that changes into a high-resistance body during overcharge is disposed between the current collector and the active material-containing layer.

Examples of the current collector include an aluminum foil and an aluminum mesh material.

The active material-containing layer contains, for example, an active material and a binder. Examples of the active material include LiCo.
O ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiCo _(1-x) Ni _x
O ₂ (x denotes an 0 <x <1), LiCo (1-y) M y O
₂ (M is a metal other than Co and Ni, for example, In, Sn
And y represents 0 <y <0.1).
A transition metal composite oxide can be given. These lithium-transition metal composite oxides can also be used in a mixture of two or more.

The conductive intermediate layer is a conductor in a normal charged state and a discharged state, and the current at the time of use is not limited. However, when the charge is further continued beyond 100% charge (full charge), the conductive intermediate layer becomes high. It has the property of becoming a resistor. For example, in a normal battery use state, the specific resistance is 1 Ω · cm or less, but in an overcharged state, the specific resistance is 100 times or more.

Preferably, the conductive intermediate layer contains, for example, carbonaceous conductive particles and a binder.

Examples of the carbonaceous conductive particles include carbon blacks such as furnace black, acetylene black, and Ketjen black; graphites such as powdered graphite and powdered expanded graphite; ground carbon fiber; and graphitized carbon fiber. Pulverized materials and the like can be mentioned. In particular, carbon blacks are suitable because they have excellent thin film moldability, high conductivity during normal use, and excellent resistance increasing function during overcharge.

The particle size of the carbonaceous conductive particles is not particularly limited. However, from the viewpoint of reducing the thickness of the conductive intermediate layer and increasing the resistance of the conductive intermediate layer at the time of overcharging, it is preferable that the carbonaceous conductive particles have a particle size of 0.1.
It is desirable that the particle size is from 0.01 to 10 μm, more preferably from 0.04 to 1 μm.

As the binder, for example, a thermoplastic elastomer resin such as a fluorine resin, a polyolefin resin, a styrene resin, and an acrylic resin, or a rubber resin such as a fluorine rubber can be used. Specifically, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polyacrylonitrile, nitrile rubber, polybutadiene, butyl rubber, polystyrene, styrene-butadiene rubber, hydrogenated styrene-butadiene rubber, polysulfide rubber, nitrocellulose , Cyanoethylcellulose, carboxymethylcellulose and the like. Among these binders, an elastomer, a crosslinked rubber or a modified substance having a polar group introduced therein is useful for improving the adhesion between the current collector and the active material layer and the effect of increasing the resistance during overcharge. Is preferred.

[0022] In the conductive intermediate layer, the binder may be 10% by weight or more and 100% by weight based on the carbonaceous conductive particles.
It is preferable that the amount is less than that. If the amount of the binder is less than 10% by weight, the adhesion of the conductive intermediate layer to the current collector may be reduced. On the other hand, when the blending amount of the binder is 100% by weight or more, the conductivity of the conductive intermediate layer is impaired, the specific resistance becomes 1 Ω · cm or more, the internal resistance of the common positive electrode increases, or the overcharge occurs. The effect of increasing the resistance at the time is also reduced. More preferably, the compounding amount of the binder to the carbonaceous conductive particles is 20 to 70% by weight.

The conductive intermediate layer has a thickness of 0.1 to 30 μm,
More preferably, it has a thickness of 0.5 to 10 μm. When the thickness of the conductive intermediate layer is less than 0.1 μm, a bypass portion where the current collector and the active material layer are directly joined is locally formed, and the resistance of the conductive intermediate layer portion during overcharge is reduced. The current cutoff effect due to the increase may be insufficient. On the other hand, when the thickness of the conductive intermediate layer exceeds 30 μm, the ratio of the conductive intermediate layer in the positive electrode increases, and the ratio of the active material-containing layer relatively decreases, which may cause a reduction in capacity. There is.

[0024] The conductive intermediate layer, 1 to 30 g / m ² with respect to the current collector, more preferably 1.5~10g / m ²
Is desirable.

The above-mentioned positive electrode can be manufactured, for example, by the following method.

First, a current collector such as an aluminum thin film is coated with a dispersant containing carbonaceous conductive particles and a binder by a gravure roll coater, a blade coater, a roll coater, a bar coater or the like, and dried to form a conductive material. An intermediate layer is formed.
Subsequently, a paste containing an active material and a binder is applied on the conductive intermediate layer, and dried to form an active material-containing layer, thereby producing a positive electrode. In the step of forming such a conductive intermediate layer, the binder and the carbonaceous conductive particles are uniformly dispersed while avoiding the formation of a so-called film tension, in which the binder gathers on the surface during application and drying. Is preferred.

2) Negative Electrode The negative electrode is not particularly limited, but may be graphite, coke, or carbon which reversibly occupies and releases lithium ions or intercalates / deintercalates lithium ions during charge / discharge. A paste obtained by holding a paste containing a carbonaceous material such as polyacene on a current collector such as a copper foil can be used.

3) Non-aqueous electrolyte This non-aqueous electrolyte has a composition in which an electrolyte is dissolved in a non-aqueous solvent.

The electrolyte is not particularly limited, but from the viewpoint of increasing the resistance of the conductive intermediate layer during overcharging,
Fluorine-containing lithium salts are preferred. As the fluorine-containing lithium salt, for example, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium trifluoromethanesulfanylimide and the like can be used.

The non-aqueous solvent is not particularly limited, but preferably contains a cyclic ester from the viewpoint of increasing the resistance of the conductive intermediate layer during overcharge. Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate,
Vinylene carbonate, γ-butyrolactone, valerolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 3-dioxolan, sulfolane and the like can be mentioned. In particular, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate are preferred.

The non-aqueous solvents used in combination with the cyclic esters include ethers, ketones, nitriles, amides, sulfone compounds, chain carbonates, chain esters, aromatic hydrocarbons and the like. One or two selected
Mixtures of more than one species can be mentioned. Of these, ethers, ketones, chain carbonates, and chain esters are preferred.

Specific examples of the non-aqueous solvent used in combination with the cyclic carbonates include dimethoxyethane, anisole, 1,4-dioxane, 4-methyl-2-pentanone, cyclohexane, acetonitrile, propionitrile, and butyronitrile. Dimethylformamide, dimethylsulfoxide, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, ethyl propionate and the like.

As the separator, polyethylene,
A porous film made of a synthetic resin such as polypropylene is used.

In the non-aqueous electrolyte secondary battery according to the present invention, the connection of the PTC element to the positive electrode or the negative electrode is permitted.

Next, a non-aqueous electrolyte secondary battery according to the present invention, for example, a prismatic lithium ion secondary battery will be described with reference to FIG.

An outer can 1 made of a metal and having a bottomed rectangular cylindrical shape and made of, for example, aluminum, also serves as a positive electrode terminal, for example, and has an insulating film 2 disposed on the inner surface of the bottom.
The electrode body 3 as a power generation element is housed in the outer can 1. When the outer can is made of stainless steel or iron, it also serves as the negative electrode terminal. The electrode body 3 is manufactured by spirally winding the negative electrode 4, the separator 5, and the positive electrode 6 such that the positive electrode 6 is located at the outermost periphery, and then press-molding the flat electrode into a flat shape. A spacer 7 made of, for example, a synthetic resin and having a lead extraction hole near the center is disposed on the electrode body 3 in the outer can 1.

The metal lid 8 is hermetically joined to the upper end opening of the outer can 1 by, for example, laser welding. In the vicinity of the center of the lid 8, a hole 9 for taking out a negative electrode terminal is opened. The negative electrode terminal 10 is hermetically sealed in the hole 9 of the lid 8 via an insulating material 11 made of glass or resin. A lead 12 is connected to the lower end surface of the negative electrode terminal 10, and the other end of the lead 12 is connected to the negative electrode 4 of the electrode body 3.

The upper insulating paper 13 covers the entire outer surface of the lid 8. The lower insulating paper 15 having the slit 14 is disposed on the bottom surface of the outer can 1. PTC element (Positive Temperature Coe)
fficient) 16 has one surface interposed between the bottom surface of the outer can 1 and the lower insulating paper 15, and the other surface extending outside the insulating paper 15 through the slit 14. . The outer tube 17 is disposed so as to extend from the side surface of the outer can 1 to the periphery of the insulating papers 13 and 15 on the upper and lower surfaces, and the upper insulating paper 13 and the lower insulating paper 1 are arranged.
5 is fixed to the outer can 1. Due to such an arrangement of the outer tube 17, the other surface of the PTC element 16 extended to the outside is bent toward the bottom surface of the lower insulating paper 15.

The above-described nonaqueous electrolytic secondary battery for a battery pack according to the present invention includes a positive electrode, a negative electrode, a separator, and a nonaqueous electrolytic solution, and the positive electrode is overcharged between the current collector and the active material-containing layer. It has a structure in which a conductive intermediate layer that sometimes changes to a high-resistance body is provided, so that stable current interruption can be performed at the time of overcharge.

That is, a secondary battery provided with a negative electrode and a positive electrode containing a lithium-transition metal composite oxide having reversibility during charge and discharge as an active material has a voltage of 100% charge, that is, a voltage of full charge. It has a high energy density at 4 V or more. When a battery pack is constructed by combining a plurality of secondary batteries with high energy density, a large amount of energy is accumulated at the time of overcharging, so it is required to exhibit a more reliable current interruption function more reliably at the time of overcharging. You.

According to the present invention, by using a positive electrode in which a conductive intermediate layer that becomes a high-resistance element at the time of overcharge is disposed between the current collector and the active material-containing layer, the conductive intermediate layer due to a voltage increase can be formed. The current can be reduced and cut off by changing to a high-resistance body. The reason why such a conductive intermediate layer becomes a high-resistance body during overcharge is presumed to be that when the conductive intermediate layer enters a highly oxidized state, the conductive intermediate layer itself causes an electrochemical oxidation reaction and the resistance is significantly increased. . As a result, when a high-energy-density battery whose full-charge voltage is 4 V or more is used as an assembled battery, some batteries, such as a conventional battery equipped with a safety mechanism that cuts off current against heat generation, are used. Current can be stably cut off for all batteries without being locally cut off. Therefore, it is possible to provide a safe and highly reliable non-aqueous electrolytic secondary battery for an assembled battery in which leakage or gas ejection is prevented.

When the PTC element is connected to the positive electrode or the negative electrode, and the conductive intermediate layer of the positive electrode becomes a high-resistance body during overcharge, heat is generated. Operate. As a result, the current interruption can be more reliably performed as compared with the case where only the positive electrode having the conductive intermediate layer is used, and the current interruption can be quickly performed following the increase in the resistance of the conductive intermediate layer. It becomes possible.

[0043]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to a rectangular sealed battery as shown in FIG.

(Example 1) <Preparation of Positive Electrode> First, a predetermined amount of carbonaceous conductive particles was added to a solution in which a binder shown in Table 1 below was dissolved in a mixed solvent of toluene and xylene at a concentration of 7 to 10% by weight. The mixture was added, and the mixture was stirred and mixed with a ball mill all day and night to prepare nine types of coating liquids. Then, apply these coating liquids to a thickness of 20μ.
m, a 570 mm wide Al foil was coated on both sides by gravure coating and dried to form a conductive intermediate layer having the coating amount and thickness shown in Table 1 below.

Next, 89 parts by weight of LiCoO ₂ powder having an average particle diameter of 3 μm as an active material, 8 parts by weight of graphite powder (trade name, KS6, manufactured by Lonza) as a conductive filler, and polyvinylidene fluoride resin as a binder ( An active material-containing paste was prepared by mixing and mixing 3 parts by weight of N-methylpyrrolidone with 25 parts by weight of N-methylpyrrolidone using a dissolver and a bead mill.
This paste is applied onto the conductive intermediate layer coated on both sides of the Al foil as the current collector, and then dried, further pressed and slit to give a 180 μm thick
A kind of reel-shaped positive electrode was produced.

<Preparation of Negative Electrode> First, styrene / butadiene latex (trade name, L1571 manufactured by Asahi Kasei Corporation) was added to 100 parts by weight of graphite (trade name, KS15, manufactured by Rozan Co., Ltd.).
4.2 parts by weight of solid content (48% by weight), 130 parts by weight of an aqueous solution (1% by weight of solid content of BSH12) of carboxymethylcellulose (Daiichi Pharmaceutical Co., Ltd .; BSH12) and 20 parts by weight of water are added, mixed and paste is added. Was prepared. Subsequently, this paste was applied to a copper foil having a thickness of 10 μm and a width of 570 mm, dried, and then pressed and slit to a thickness of 1 μm.
A 60 μm reel-shaped negative electrode was produced.

Next, after a polyethylene microporous membrane is sandwiched between the positive and negative electrodes, it is spirally wound by a winding machine.
Subsequently, the cylindrical material was compressed at a pressure of 10 kg / cm ² to produce a flat electrode body (power generation element). Subsequently, the flat electrode body was inserted into the outer can, and the electrolyte of lithium hexafluorophosphate was mixed with a mixed solvent of ethylene carbonate and dimethyl carbonate (mixing ratio: 1: 2) at 1 mol / l.
After injecting the dissolved non-aqueous electrolyte, the sealing body is laser-welded to the opening of the outer can to form a non-aqueous electrolyte secondary having a structure similar to that shown in FIG. A battery (lithium ion secondary battery) was assembled.

Comparative Example 1 Example 1 was repeated except that an active material-containing layer was directly coated on both sides of an Al foil as a positive electrode.
As in the case of Nos. 1 to 9, a nonaqueous electrolyte secondary battery (lithium ion secondary battery) having the structure shown in FIG.

The full-charge voltages of the obtained Examples 1 to 9 and Comparative Example 1 are also shown in Table 1 below.

In each of Examples 1 to 9 and Comparative Example 1, P
After charging the rechargeable battery with the TC element to 4.2 V at full charge, the battery was further charged with a current of 1500 mA using a power supply of a maximum of 10 V, and when the battery blew and ignited, the gas was blown up to that point. If not reached, the power was kept on for 8 hours. The situation at the time of overcharging of such a single cell is shown in Table 2 below. FIG. 2 shows the relationship between the charging time and the battery voltage in Example 1 and Comparative Example 1.

Further, the secondary batteries without the PTC element of each of Examples 1 to 9 and Comparative Example 1 were
A total of nine batteries were connected in parallel to make a battery pack. These battery packs were overcharged at 3000 mA for a maximum of 8 hours with a power supply of a maximum of 15 V. At this time, the discharge capacity, the condition of the unit cell, and the condition of the assembled battery were examined. The results are shown in Table 2 below.

[0052]

[Table 1]

[0053]

[Table 2]

As is clear from Table 2 above, Examples 1 to 9
It can be seen that the secondary battery of No. 1 is a battery pack and has stable current suppression and current interrupting performance when overcharged, as compared with the secondary battery of Comparative Example 1.

Further, as is apparent from FIG. 2, in the secondary battery of Example 1 in which the PTC element is incorporated, the PTC element operates due to the heat generated due to the increase in the resistance of the conductive intermediate layer of the positive electrode, and the current flows. It can be seen that it can be reduced effectively.

In the above embodiment, the prismatic non-aqueous electrolyte secondary battery has been described as an example, but the present invention is not limited to this. For example, the present invention can be similarly applied to cylindrical, coin, flat, and paper secondary batteries.

[0057]

As described above in detail, according to the present invention, it is possible to improve the safety and reliability at the time of overcharging of each unit cell when used as an assembled battery, and to cut off the current which causes an increase in space. A high-capacity non-aqueous electrolyte secondary battery for an assembled battery that does not require a valve can be provided.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing a prismatic lithium ion secondary battery as an example of a nonaqueous electrolyte secondary battery according to the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a charging time, a battery voltage, and a current at the time of overcharging in Example 1 and Comparative Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Outer can, 3 ... Electrode body, 4 ... Negative electrode, 5 ... Separator, 6 ... Positive electrode 8 ... Lid, 14 ... PTC element.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H022 AA09 CC12 CC16 CC21 EE05 KK01 5H029 AJ12 AK03 AL06 AL07 AL12 AM03 AM04 AM05 AM07 DJ06 DJ07 DJ08 DJ16 EJ04 HJ01 HJ18

Claims (7)

[Claims] 1. A non-aqueous electrolyte secondary battery for an assembled battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the positive electrode is provided between a current collector and an active material-containing layer when overcharged. A non-aqueous electrolyte secondary battery for an assembled battery, having a structure in which a conductive intermediate layer that changes into a high-resistance body is arranged. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the conductive intermediate layer contains carbonaceous conductive particles and a binder. 3. The assembled battery according to claim 2, wherein the conductive intermediate layer contains the binder in an amount of 10% by weight or more and less than 100% by weight based on the carbonaceous conductive particles. For non-aqueous electrolyte secondary batteries. 4. The non-aqueous electrolyte secondary battery for an assembled battery according to claim 2, wherein the carbonaceous conductive particles are carbon blacks. 5. The non-aqueous electrolyte for an assembled battery according to claim 1, wherein the non-aqueous electrolyte contains a fluorine-containing lithium salt as an electrolyte and a cyclic ester as a non-aqueous solvent. Water electrolyte secondary battery. 6. The non-aqueous solution for an assembled battery according to claim 1, wherein the positive electrode active material is made of a lithium-transition metal composite oxide, and has a voltage of 4 V or more when fully charged. Electrolyte secondary battery. 7. The non-aqueous electrolyte secondary battery for an assembled battery according to claim 1, further comprising a PTC element connected to the positive electrode or the negative electrode.