JP2005158627A - Lithium ion battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium ion battery which is superior in safety, along with being a large-capacity and high-output battery. <P>SOLUTION: In a lithium ion secondary battery, a spinel lithium manganese composite oxide is used for the positive-electrode active material, and amorphous carbon is used for the negative-electrode active material. In a positive-electrode mixture, a predetermined quantity of Fe-Cu alloy powder is intentionally made contained. A separator is made of polyethylene and has a thickness of 40μm. By dividing the alloy powder which depends according to the particle size, the ratio a / b is made 0.75 or larger, when the diameter size of the alloy powder is represented by (a), and the thickness of the separator is represented by b. The alloy powder desorbs or is eluted from the positive-electrode mixture by being overcharged, deposits as dendrites on the negative electrode, and penetrates the separator. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a lithium ion battery, and more particularly to a lithium ion battery in which a positive electrode having a positive electrode mixture containing a lithium transition metal composite oxide and a negative electrode are disposed via a separator and infiltrated with a non-aqueous electrolyte.

  Lithium ion batteries are mainly used in portable devices such as VTR cameras, notebook computers and mobile phones, taking advantage of the high energy density. On the other hand, in the automobile industry, in order to cope with environmental problems, development of electric vehicles using a motor as a power source and hybrid electric vehicles using both an internal combustion engine and a motor is underway. Some have already been put to practical use. In addition, as the demand for electric power increases, the demand gap between daytime and nighttime and seasons is widening, and the development of electric power storage technology is being promoted to alleviate this. In particular, in recent years, research and development of large-sized lithium ion batteries intended for use in electric vehicles and power storage have become active.

  In the case of lithium ion batteries, the higher the capacity and output, the lower the safety. Therefore, large lithium ion batteries are required to have high capacity and high output, as well as improved safety. Yes. For example, when a large lithium secondary battery is used as a power source for an electric vehicle, safety can be ensured even when the battery is abnormal when the charge control system for monitoring the charge state of the battery fails and becomes overcharged. As a matter of course, it has become an important issue to minimize damage to automobiles by ensuring the safety, that is, the behavior when the battery is abnormal does not damage the human body.

  However, since a battery used for a power source for automobiles is charged with a large current and discharged with a large current, in response to a rise in the internal pressure of the battery, which is generally adopted for a small (for example, 18650 type) lithium ion battery. When an operating current interrupting mechanism (current disconnecting switch) is provided inside the battery, the mechanism itself becomes an electrical resistance, leading to a voltage drop during charging and discharging. For this reason, it is practically impossible to employ a current interruption mechanism in a large-sized lithium ion battery that places importance on reducing internal resistance. In order to ensure the safety of a lithium ion battery, for example, a technique in which at least one of positive and negative electrodes contains a flaky metal is disclosed (see Patent Document 1).

JP 2001-273902 A

  However, in the battery of Patent Document 1, the flaky metal prevents ionic conduction in the electrode and suppresses the reaction of the active material to prevent heat generation when the battery is abnormal. Therefore, it is effective for a small lithium ion battery. However, since a large lithium ion battery has a large electrode itself and a rapid reaction when the battery is abnormal, a sufficient effect cannot be expected. In particular, when a large lithium-ion battery is overcharged, the reaction of the non-aqueous electrolyte and active material under high voltage generates a rapid and large amount of gas, which may cause the battery behavior to become severe. There is.

  An object of the present invention is to provide a lithium-ion battery that has a high capacity, a high output, and an excellent safety.

  In order to solve the above problems, the present invention provides a lithium ion battery in which a positive electrode having a positive electrode mixture containing a lithium transition metal composite oxide and a negative electrode are disposed via a separator and infiltrated into a non-aqueous electrolyte. The positive electrode mixture contains a predetermined amount of metal or alloy particles containing at least one of elements of Fe, Cu, Ag, and Au, which are deposited in a dendrite shape on the negative electrode due to overcharge, When the particle diameter is a and the thickness of the separator is b, a / b ≧ 0.75 is satisfied.

  In the present invention, particles of metal or alloy containing at least one element of Fe, Cu, Ag, and Au intentionally contained in the positive electrode mixture are desorbed or eluted from the positive electrode mixture by overcharging, and the negative electrode Since it deposits in a dendrite form and penetrates the separator, a minute short circuit between the positive and negative electrodes is promoted during overcharge. When the particle diameter is a and the separator thickness is b, a / b ≧ 0.75 may cause dendrite precipitation that penetrates the separator and promotes a micro short circuit between the positive and negative electrodes. it can. Therefore, according to the present invention, the safety of the lithium ion battery can be ensured during overcharge. In this case, the separator is preferably made of a polyolefin material.

  According to the present invention, metal or alloy particles containing at least one of the elements of Fe, Cu, Ag, and Au intentionally contained in the positive electrode mixture are desorbed or eluted from the positive electrode mixture by overcharging. In addition, since it deposits in the form of dendrites on the negative electrode and penetrates the separator, a minute short-circuit between the positive and negative electrodes is promoted during overcharge, and when a particle diameter is a and a separator thickness is b, a / b ≧ By setting 0.75, it is possible to cause dendrite precipitation that penetrates the separator and promotes a micro short circuit between the positive and negative electrodes, so that the safety of the lithium ion battery can be ensured during overcharge. Can be obtained.

  Embodiments of a large cylindrical lithium ion secondary battery to which the present invention is applied will be described below with reference to the drawings.

(Negative electrode)
A slurry obtained by adding 10 parts by weight of polyvinylidene fluoride (PVDF) as a binder to 90 parts by weight of the amorphous carbon powder of the negative electrode active material, and adding and kneading N-methylpyrrolidone (NMP) as a dispersion solvent thereto. It apply | coated on both surfaces of the 10-micrometer-thick rolled copper foil. At this time, an uncoated part was left on one side edge in the negative electrode longitudinal direction. Then, the negative electrode was obtained by drying, pressing, and cutting. A notch was left in the uncoated part left on the side edge, and the remaining notch was used as a lead piece.

(Positive electrode)
5 parts by weight of carbon powder as a conductive material and 5 parts by weight of PVDF as a binder are added to 90 parts by weight of the spinel-based lithium manganese composite oxide powder of the positive electrode active material, and NMP is added thereto as a dispersion solvent. Added and kneaded. Furthermore, a predetermined amount (for example, 1 ppm) of a metal powder or alloy powder containing at least one element of Fe, Cu, Ag, and Au was added and kneaded almost uniformly to prepare a positive electrode mixture slurry. The metal powder or alloy powder is classified so that the ratio a / b is 0.75 or more (a / b ≧ 0.75), where a is the particle size and b is the thickness of the separator described later. Using. The obtained positive electrode mixture slurry was applied almost uniformly on both sides of an aluminum foil having a thickness of 20 μm. At this time, an uncoated part was left on one side edge in the positive electrode longitudinal direction. Thereafter, drying, pressing and cutting were performed to obtain a positive electrode. A notch was left in the uncoated part left on the side edge, and the remaining notch was used as a lead piece. The amount of metal powder or alloy powder added was determined by the thickness and size of the positive electrode mixture.

(Battery assembly)
As shown in FIG. 1, the prepared positive and negative electrodes are placed around an axis 11 serving as a winding center through a separator made of polyethylene and having a microporous thickness b of 40 μm so that the two electrodes do not directly contact each other. The wound group 6 was produced by winding. At this time, the lead pieces 9 for the positive electrode and the negative electrode were respectively positioned on the opposite end surfaces of the wound group 6. The length of the negative electrode is the length of the positive electrode so that the positive electrode does not protrude from the negative electrode in the winding direction at the innermost periphery of the winding group 6 and the positive electrode does not protrude from the negative electrode in the winding direction at the outermost periphery. 18 cm longer than the length. The width of the negative electrode active material application part was made 5 mm longer than the width of the positive electrode active material application part so that the positive electrode active material application part did not protrude from the negative electrode active material application part even in the direction orthogonal to the winding direction.

  After the lead pieces 9 led out from the positive electrode are deformed and all of them are gathered and brought into contact with the vicinity of the peripheral surface of the flange 7 integrally projecting from the periphery of the positive electrode external terminal 1 substantially on the extension line of the shaft core 11 The lead piece 9 and the flange 7 peripheral surface were ultrasonically welded to connect and fix the lead piece 9 to the flange 7 peripheral surface. Further, the connection operation between the negative electrode external terminal 1 ′ and the lead piece 9 led out from the negative electrode was performed in the same manner as the connection operation between the positive electrode external terminal 1 and the lead piece 9 led out from the positive electrode.

  An insulating coating 8 was applied to the entire circumference of the collar 7 peripheral surface of the positive external terminal 1 and the negative external terminal 1 ′. This insulating coating 8 also exerted on the entire outer periphery of the wound group 6. For the insulating coating 8, an adhesive tape in which the base material was polyimide and an adhesive made of hexamethacrylate was applied on one side thereof was used. This adhesive tape was wound several times from the peripheral surface of the collar portion 7 to the outer peripheral surface of the wound group 6 to form an insulating coating 8. Adjust the number of turns so that the maximum diameter portion of the wound group 6 is the insulation coating 8 existing portion, and make it a cylindrical shape with a diameter of 65 mm and a height of 390 mm and slightly smaller than the inner diameter of the battery container 5 made of SUS, The wound group 6 was inserted into the battery container 5.

A second ceramic washer 3 ′ made of alumina having a thickness of 2 mm, an inner diameter of 16 mm, and an outer diameter of 25 mm at the portion in contact with the back surface of the disk-shaped battery lid 4 is formed as a pole column constituting the positive electrode external terminal 1 and the tip is disposed outside the negative electrode. Each was fitted into a pole column constituting the terminal 1 ′. Further, a flat plate-like first ceramic washer 3 made of alumina and having a thickness of 2 mm, an inner diameter of 16 mm, and an outer diameter of 28 mm is placed on the battery lid 4, and the positive electrode external terminal 1 and the negative electrode external terminal 1 ′ are respectively connected to the first ceramic. Passed through washer 3. Thereafter, the peripheral end surface of the battery lid 4 was fitted into the opening of the battery container 5 and the entire contact portions were laser welded. At this time, the positive electrode external terminal 1 and the negative electrode external terminal 1 ′ pass through a hole formed in the center of the battery cover 4 and protrude outside the battery cover 4. Then, the first ceramic washer 3 and the metal washer 14 smoother than the bottom surface of the metal nut 2 were fitted into the positive external terminal 1 and the negative external terminal 1 ′ in this order. The battery lid 4 is provided with a plate-shaped cleavage valve 10 made of an aluminum alloy that is cleaved in response to an increase in the internal pressure of the battery. The cleavage pressure of the cleavage valve 10 was about 9 × 10 ⁵ Pa.

  Next, the nut 2 is screwed to the positive electrode external terminal 1 and the negative electrode external terminal 1 ′, and the battery lid 4 is connected to the flange portion 7 via the second ceramic washer 3 ′, the first ceramic washer 3, and the metal washer 14. The nut 2 was fixed by tightening. The tightening torque value at this time was 7 N · m. Note that the metal washer 14 did not rotate until the tightening operation was completed. In this state, the power generation element inside the battery container 5 is blocked from the outside air by the compression of the rubber (EPDM) O-ring 16 interposed between the back surface of the battery lid 4 and the flange portion 7.

  Cylindrical lithium ions having a capacity of 90 Ah and an output of 1000 W or more are injected by injecting a predetermined amount of non-aqueous electrolyte into the battery container 5 from the injection port 15 provided in the battery lid 4 and then sealing the injection port 15. The secondary battery 20 was assembled. As the non-aqueous electrolyte, a solution obtained by dissolving 1 mol / liter of lithium hexafluorophosphate in a mixed solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a volume ratio of 1: 1: 1 was used.

  Next, an example of the lithium ion secondary battery 20 produced by changing the material of the metal powder or alloy powder and the particle size a according to the present embodiment will be described. In addition, it describes together about the battery of the comparative example produced for the comparison.

(Example 1)
As shown in Table 1 below, in Example 1, an alloy powder with a material of Cu—Fe and a particle size of 30 μm was used. At this time, the ratio a / b is 0.75.

(Example 2 to Example 7)
As shown in Table 1, Examples 2 to 7 were the same as Example 1 except that the material of the metal powder or alloy powder was changed. Example 2 is Au powder, Example 3 is Fe—Ni alloy powder, Example 4 is Fe—Cr—Ni alloy powder, Example 5 is Fe—Mn—Ni alloy powder, and Example 6 is Fe—Al—Si. Alloy powder, Ag powder in Example 7, was used.

(Example 8 to Example 9)
As shown in Table 1, Examples 8 to 9 were the same as Example 1 except that the particle size of the Cu-Fe powder was changed. In Example 8, the particle size was 32 μm, and in Example 9, the particle size was 38 μm. The ratio a / b is 0.80 in Example 8 and 0.95 in Example 9.

(Example 10)
As shown in Table 1, in Example 10, it carried out similarly to Example 7 except the particle size of Ag powder having been 36 micrometers. The ratio a / b is 0.90.

(Comparative Example 1)
As shown in Table 1, in Comparative Example 1, a cylindrical lithium ion secondary battery was assembled without including the metal powder and the alloy powder in the positive electrode mixture.

(Comparative Example 2 to Comparative Example 3)
As shown in Table 1, Comparative Examples 2 to 3 were the same as Example 1 except that the particle size of the Cu-Fe powder was changed. In Comparative Example 2, the particle size was 20 μm, and in Comparative Example 3, the particle size was 28 μm. The ratio a / b is 0.50 in Comparative Example 2 and 0.70 in Comparative Example 3.

(Comparative Example 4 to Comparative Example 5)
As shown in Table 1, Comparative Examples 4 to 5 were the same as Example 7 except that the particle size of the Ag powder was changed. In Comparative Example 4, the particle diameter was 16 μm, and in Comparative Example 5, the particle diameter was 24 μm. The ratio a / b is 0.40 in Comparative Example 4 and 0.60 in Comparative Example 5.

(Comparative Example 6)
As shown in Table 1, Comparative Example 6 was the same as Example 3 except that the particle size of the Fe—Ni powder was 28 μm. The ratio a / b is 0.70.

(Comparative Example 7)
As shown in Table 1, Comparative Example 7 was the same as Example 6 except that the particle size of the Fe—Al—Si powder was 26 μm. The ratio a / b is 0.65.

(Overcharge test)
Each lithium ion secondary battery of an Example and a comparative example was charged to a charge condition (SOC) 100% on the following charge conditions at 25 degreeC. Thereafter, an overcharge test was performed in which the battery was continuously charged at a constant current of 25 ° C. and 40 A, the abnormal phenomenon was observed, and the highest temperature reached on the battery surface was measured. When an abnormality occurred, the battery surface temperature at that time was defined as the highest temperature reached. Table 2 below shows the test results of the overcharge test.
Charging conditions: 4.2V constant voltage, limiting current 80A, 3.5h

  As shown in Table 2, in the battery of Comparative Example 1 produced without containing the metal powder and the alloy powder in the positive electrode mixture, an abnormal phenomenon of rupture and ignition was observed, and the maximum temperature reached when the abnormality occurred was 500 °. C or higher. Further, although the positive electrode mixture contained metal powder or alloy powder, no abnormal phenomenon was observed in each of the batteries of Comparative Examples 2 to 7 where the ratio a / b was less than 0.75, but it reached the highest level. The temperature increased to 93-188 ° C. On the other hand, in each battery of Examples 1 to 10 in which the ratio a / b was 0.75 or more, no abnormal phenomenon was observed, and the maximum temperature reached was as low as 62 to 66 ° C. Therefore, even when the SOC 100% battery is continuously charged, it has been found that the battery has a gentle behavior and excellent safety.

  In the lithium ion secondary battery 20 of the present embodiment, the positive electrode mixture intentionally contains a metal powder or an alloy powder that is desorbed or eluted by overcharging and precipitates in a dendrite form on the negative electrode. For this reason, when the lithium ion secondary battery 20 is overcharged, the metal powder or the alloy powder deposits dendrites and penetrates the separator, thereby facilitating a minute short circuit between the positive and negative electrodes. As a result, the charge that is originally overcharged to the battery is not accumulated beyond a certain level, and the promotion of the reaction between the non-aqueous electrolyte and the active material during overcharge is suppressed. The safety of the ion secondary battery can be ensured. Therefore, since it is excellent in safety when the battery is overcharged, it is suitable for a power source for an electric vehicle that requires high output and safety.

  Further, when the ratio a / b is less than 0.75, even if the metal powder or alloy powder is detached or eluted from the positive electrode mixture due to overcharge, the dendrite deposition on the negative electrode is insufficient, so that the separator can be penetrated. It will not be reached. In the lithium ion secondary battery 20 of this embodiment, since the ratio a / b is set to 0.75 or more, it is possible to cause dendrite precipitation that penetrates the separator and promotes a micro short circuit.

  Furthermore, in the present embodiment, a polyethylene microporous separator having a thickness of 40 μm is used. For this reason, while allowing the passage of lithium ions during normal charging and discharging, the positive and negative electrodes can be arranged close to each other, so that the energy density per unit volume of the battery can be increased. On the other hand, at the time of overcharge, since the separator is made of resin, it can be damaged by dendrite precipitation of metal powder or alloy powder, and a minute short circuit between the positive and negative electrodes can be caused.

  Furthermore, in the lithium ion secondary battery 20 of the present embodiment, the metal particles or alloy particles contain at least one element of Fe, Cu, Ag, and Au. These elements elute due to the high voltage when the lithium ion secondary battery is overcharged and precipitate in a dendrite shape, whereas dendrite precipitation is suppressed during normal charging and discharging because the voltage is lower than during overcharging. Therefore, charging / discharging of a lithium ion secondary battery can be performed without trouble.

  In the present embodiment, a cylindrical lithium ion secondary battery having a capacity of 90 Ah and an output of 1000 W or more is exemplified, but the present invention is not limited to the shape of the battery. For example, a rectangular or polygonal shape may be used, and the internal structure of the battery may be a stacked electrode group instead of a wound electrode group. Moreover, there is no restriction | limiting in particular also about a capacity | capacitance and an output, It can apply to the lithium ion secondary battery of a general capacity | capacitance and an output.

  In the present embodiment, a polyethylene film having a thickness of 40 μm is exemplified as the separator, but the present invention is not limited to this. Examples of the material of the separator used other than the present embodiment include a polyolefin-based material such as polypropylene, and a polyethylene film and a polypropylene film may be laminated and used. Further, the thickness is not particularly limited.

Furthermore, in this embodiment, although the example using spinel type lithium manganese complex oxide as a positive electrode active material was shown, this invention is not limited to this. For example, lithium cobalt composite oxide or lithium nickel composite oxide may be used, and a part of lithium site or manganese site of lithium manganese composite oxide (LiMn ₂ O ₄ ) is replaced with another metal element. Or doped, for example, represented by the chemical formula Li _{1 + x} M _y Mn _2−xy O ₄ (M is Li, Co, Ni, Fe, Cu, Al, Cr, Mg, Zn, V, Ga, B, F). The material to be used may be used. Further, the crystal structure is not limited to the spinel crystal structure, and may be a layered crystal structure.

  Furthermore, although amorphous carbon is exemplified as the negative electrode active material, the present invention is not limited to this, and a material capable of occluding and releasing lithium or metallic lithium may be used. Examples of the negative electrode active material other than the present embodiment include carbonaceous materials such as natural graphite, artificial graphite, and coke, and the particle shape is not particularly limited.

  Furthermore, in the present embodiment, polyvinylidene fluoride is exemplified as the binder, but the present invention is not limited to this. For example, polytetrafluoroethylene (PTFE), polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile Polymers such as rubber, styrene / butadiene rubber, polysulfide rubber, ditrocellulose, cyanoethyl cellulose, various latexes, acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride, chloroprene fluoride, and mixtures thereof can also be used.

In the present embodiment, the nonaqueous electrolytic solution is exemplified by a solution of LiPF ₆ dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a volume ratio of 1: 1: 1. However, the present invention is limited to this. Is not to be done. For example, a solution obtained by dissolving a general lithium salt in a solvent in which an organic solvent such as carbonate, sulfolane, ether, or lactone is used alone or in combination can be used. Examples of lithium salts that can be used in other embodiments include LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, and CF ₃ SO ₃ Li. Can do. Examples of the organic solvent include propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, Mention may be made of diethyl ether, sulfolane, methyl sulfolane, acetonitrile, propionitrile.

  The lithium ion battery according to the present invention has high capacity, high output, and excellent safety, and thus contributes to production and sales and can be used industrially.

It is sectional drawing of the cylindrical lithium ion secondary battery of embodiment to which this invention is applied.

Explanation of symbols

6 Winding group 20 Cylindrical lithium ion secondary battery (lithium ion battery)

Claims (2)

  In a lithium ion battery in which a positive electrode having a positive electrode mixture containing a lithium transition metal composite oxide and a negative electrode are disposed via a separator and infiltrated into a non-aqueous electrolyte, the negative electrode is overcharged in the positive electrode mixture. Contains a predetermined amount of metal or alloy particles containing at least one of the elements Fe, Cu, Ag and Au that are precipitated in a dendritic form, wherein the particle size of the particles is a, and the thickness of the separator is b. A lithium ion battery that satisfies a / b ≧ 0.75.   The lithium ion battery according to claim 1, wherein the separator is made of a polyolefin material.