JP4576891B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a lithium ion secondary battery, and more particularly to a structure of a lithium ion secondary battery excellent in output characteristics.

  In recent years, electronic devices are rapidly becoming smaller and lighter, and there is an increasing demand for smaller, lighter, and higher capacity batteries as power sources. Batteries have been actively researched and developed and have been put to practical use.

  In addition to these small-sized consumer applications, technology development for large-capacity large-sized batteries such as those for power storage and electric vehicles has been accelerated. In particular, the development of lithium-ion secondary batteries for hybrid electric vehicles (HEVs) has been accelerated. It is advanced to. Furthermore, even for batteries that require a very high output such as a power source for driving an electric tool, development of a high-output type lithium ion secondary battery is urgently replacing the conventional nickel-cadmium battery and nickel-metal hydride battery.

  Here, a lithium ion secondary battery for power source for driving an electric tool is greatly different from that of a small-sized consumer application in use and required performance, and a high level output characteristic is required with a limited capacity. Therefore, it is necessary for the battery to minimize internal resistance as much as possible. Therefore, not only the development of active materials and electrolytes, but also the electrode by reducing the resistance of battery structural parts such as reviewing the electrode current collection structure and making the electrodes thinner and longer Significantly higher output is achieved by increasing the reaction area.

A conventional prismatic battery has a structure in which a single electrode plate group is accommodated in a rectangular battery case, and a current path is obtained from a single current collecting lead led out from a positive electrode and a negative electrode. However, batteries that require high output have a large capacity compared to small consumer applications, and the electrodes are thin and long, so a single current collector lead has high component resistance and cannot provide sufficient high output characteristics. There is a problem, and Patent Document 1 devises a method of taking a plurality of current collecting leads by housing a plurality of electrode plate groups in a rectangular case and connecting the plurality of groups in parallel.
JP 2003-31202 A

  However, the lithium secondary battery of the electrode plate group wound in a square shape is expanded and contracted by charging and discharging, and the expansion and contraction rate is particularly high in the central portion of the electrode plate group having a low tension rate. Stacked and accommodated electrode plate groups interact with each other in shape change due to expansion and contraction, resulting in lithium deposition due to non-uniform charge and discharge reaction due to the electrode plate buckling, reducing capacity deterioration and safety. .

  In view of the above-described conventional problems, an object of the present invention is to provide a battery that can reduce the internal resistance of the battery, obtain a high output, and further improve battery characteristics.

  In order to achieve the above object, the present invention provides a non-aqueous electrolyte secondary battery having an electrode plate group in which a positive electrode plate and a negative electrode plate on a sheet are wound through a separator, an electrolytic solution, and a battery case. In the battery case, a plurality of the electrode plate groups are stacked and accommodated in the battery case, the electrode plate groups are connected in parallel, and a spacer is provided between the adjacent electrode plate groups (spacer area / electrode axis of the electrode plate group). (Vertical cross-sectional area passing through the core) is 0.38 or more.

  The non-aqueous electrolyte secondary battery according to the present invention has the above-described structure, so that it can be connected in parallel, and a plurality of current collecting leads can be obtained. As a result, component resistance is reduced and high output characteristics are obtained. By having a spacer between the plate groups, expansion and contraction of the electrode plate group can be suppressed to prevent the electrode plate from buckling, and good battery characteristics can be obtained.

  The present invention provides a non-aqueous electrolyte secondary battery having a group of electrode plates formed by winding a positive electrode plate and a negative electrode plate on a sheet with a separator interposed therebetween, an electrolytic solution, and a battery case. A plurality of plate groups are stacked and accommodated in parallel, each electrode plate group is connected in parallel, and there is a spacer between adjacent electrode plate groups, (spacer area / vertical cross-sectional area passing through the axis of the electrode plate group) is 0. It is .38 or more, and it is possible to obtain a reduction in component resistance and high output characteristics and to suppress expansion of the electrode plate group.

  Further, at least a part of the spacer is joined to the battery case, whereby the spacer and the electrode plate group are fixed in place in the battery case. In addition, the joining method of a spacer and a battery case uses the method of joining by various weldings, such as resistance welding and laser welding, or the method of inserting a spacer by grooving a battery case.

  Furthermore, the spacer is opposed to the central part of the electrode plate group. In addition, the electrode plate group central part is a part shown as an electrode plate group central part 9 in FIG. 5, and the electrode plate group central part 9 has a center part length 11 in the height direction of electrode plate group height 10. It is preferable that the central portion length 13 in the width direction is 0.5 or more of the electrode plate group width 12, and the expansion and contraction of the electrode plate group due to charging / discharging is the most in the electrode plate group central portion having a low tension rate. Although large, it is possible to suppress the expansion and contraction of the electrode plate group by fixing the central part of the electrode plate group with a spacer.

  Moreover, it is preferable that the thickness of a spacer is 0.2 mm or more. This is because if the thickness of the spacer is less than 0 or 2 mm, the strength of the spacer is weak and it becomes insufficient to suppress the expansion and contraction of the electrode plate group.

  Further, the material of the spacer is preferably the same material as the battery case, and Fe, Al, etc. can be used. This is because when the battery case has a potential structure, the spacer having the joint portion with the case also has a potential. From the influence of the withstand voltage of the material, the battery case and the spacer are preferably made of the same material.

  The nonaqueous electrolyte secondary battery of the present invention will be further described below.

  The positive electrode is formed by providing a positive electrode mixture layer containing a positive electrode active material, a conductive material, a binder and the like on an aluminum foil as a current collector. First, a positive electrode active material, a conductive material, a binder, and a solvent are kneaded for the purpose of adjusting viscosity to prepare a positive electrode mixture paste, and the positive electrode mixture paste is applied to an aluminum foil current collector and dried. . Thereafter, the sheet is processed into a predetermined size by pressing and slitting as necessary to produce a sheet-like positive electrode.

Lithium metal composite oxides such as LiCoO ₂ , LiNiO ₂ and LiMn ₂ O ₄ are used for the positive electrode active material, but a part of the Co, Ni or Mn is further substituted with Co, Mn, Al or the like, Other element substitution types such as those substituted with Li can also be used, and these positive electrode active materials can be used as long as they are active materials capable of occluding and releasing lithium and capable of charge / discharge reactions. It is not limited to the above.

The conductive material is for enhancing electrical conductivity in order to efficiently perform the charge / discharge reaction of the positive electrode mixture, and is made of carbon material such as acetylene black (AB), ketjen black (KB), or graphite. It can be used alone or in combination.

  In addition, the binder is used to provide adhesion between the mixture and an adhesion function between the mixture and the core material, and uses an organic solvent such as polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVdF). PVdF is used when the solvent is used, and a water-soluble dispersion of PTFE is particularly used when water is the solvent.

  Further, a water-soluble polymer such as carboxymethyl cellulose (CMC) can be used as the thickener.

  In addition, a mixture paste is prepared by kneading these materials, and the mixture mixture ratio can be arbitrarily adjusted according to the suitability of the battery.

  On the other hand, the negative electrode is configured by providing a negative electrode active material and a negative electrode mixture layer such as a binder on a copper foil as a current collector. Is applied to a copper foil and dried, and then processed into a predetermined size by pressing and slitting as necessary to obtain a sheet-like negative electrode.

  Here, a material capable of inserting and extracting lithium ions is used for the negative electrode active material, and carbon materials such as natural graphite, artificial graphite, and coke can be used. Although metallic lithium can be used, there are problems such as poor charge / discharge efficiency.

  As the binder, PVdF, styrene butadiene rubber (SBR) or the like is used, and an organic solvent such as N-methyl-2-pyrrolidone (NMP) or water is used as a solvent for dispersing these active materials and the binder. Can be used.

  The separator has a function of insulating between the positive electrode and the negative electrode and further holding an electrolyte solution. The separator is made of a thin microporous film such as polyethylene (PE), polypropylene (PP), or a laminate thereof. However, the present invention is not limited to these as long as the necessary functions can be obtained.

The electrolytic solution is obtained by dissolving a lithium salt in an organic solvent. Examples of the organic solvent include cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), A chain carbonate such as ethyl methyl carbonate (EMC) or the like alone or in a mixed system is used. As the lithium salt, lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), or the like can be used.

As a specific embodiment according to the present invention, a rectangular battery manufactured using various spacers will be described below.
Example 1
For the positive electrode, lithium cobalt composite oxide (LiCoO ₂ ) was used as an active material, AB was used as a conductive agent, and PVdF was used as a binder. The active material, the conductive agent, and the binder were each adjusted at a solid weight ratio of 100: 2: 2, and kneaded with NMP as a solvent to prepare a positive electrode mixture paste. The mixture paste was applied to both surfaces of a 15 μm thick aluminum foil positive electrode current collector, dried, and then rolled and slitted to produce a positive electrode plate having a thickness of 0.115 mm, a mixture width of 65 mm, and a length of 335 mm.

For the negative electrode, artificial graphite was used as the active material, and SBR water-soluble dispersion was used as the binder. CMC is used as the thickener, and the active material, the binder, and the thickener are adjusted at a solid weight ratio of 100: 1: 1, respectively, and water is used as a solvent with respect to the solid weight. 100% was mixed and kneaded to prepare a negative electrode mixture paste. This was applied to both sides of a 10 μm thick copper foil, dried, and then rolled and slitted to produce a negative electrode plate having a thickness of 0.105 mm, a mixture width of 70 mm, and a length of 360 mm.

  Aluminum and nickel current collector leads were joined to the positive electrode and the negative electrode, and then dried in a drying furnace at 100 ° C. for 10 hours and 80 ° C. for 10 hours in order to remove residual moisture. Thereafter, an electrode plate group in which the positive electrode and the negative electrode were wound through a PE separator having a thickness of 25 μm was produced. The electrode plate group had a thickness of 2.7 mm, a height of 74 mm, and a width of 49 mm.

  Then, an Fe spacer having a thickness of 0.2 mm, a height of 74 mm, and a width of 49 mm is inserted into an Fe battery case having a thickness of 0.5 mm, a thickness of 14 mm, a height of 80 mm, and a width of 50 mm, at an interval of 3.1 mm. The case was laser welded to the side of the case. The bottom of the spacer is located 2.5 mm above the bottom of the case. The electrode plate group was inserted into this battery case. The gap in the height direction between the battery case and the electrode plate group was 2.5 mm above and below.

  Further, the ratio of the length in the height direction of the spacer facing the center part of the electrode plate group to the height of the electrode plate group is 1.0, and the ratio of the spacer facing the center part of the electrode plate group to the width of the electrode plate group is The length ratio in the width direction was 1.0.

  A total of four groups were accommodated in the battery case. The positional relationship between the electrode plate group and the spacer of this battery is shown in FIG.

The positive electrode lead derived from each electrode plate group was laser welded to the positive electrode connection terminal, and the negative electrode lead derived from each electrode plate group was resistance welded to the negative electrode connection terminal. The volume ratio of EC and EMC in Case 1: a solvent mixture in the mixing ratio of 3, after injecting an electrolyte solution prepared by dissolving at a concentration of 1 mol / dm ³ of LiPF ₆ as a solute, a case with the sealing plate was sealed A square battery was produced, and this battery was designated as battery A. When this battery was charged with a constant current and constant voltage with a voltage of 4.2 V and a current of 1 C, and discharged with a constant current of 2.5 V and a current of 0.2 C, the capacity was 3 Ah.

(Example 2)
A spacer having a thickness of 0.2 mm, a height of 37 mm, and a width of 37 mm is used, and the ratio of the length in the height direction of the spacer facing the center of the electrode plate group to the electrode plate group height is 0.5. Battery B was prepared in the same manner as Battery A except that the ratio of the length in the width direction of the spacer facing the center of the electrode plate group to the plate group width was 0.5. The positional relationship between the electrode plate group and the spacer of this battery is shown in FIG.

(Comparative Example 1)
A spacer having a thickness of 0.2 mm, a height of 37 mm, and a width of 27 mm is used, and the ratio of the length in the height direction of the spacer facing the center part of the electrode plate group to the electrode plate group height is 0.5. A battery C was prepared in the same manner as the battery A, except that the ratio of the length in the width direction of the spacer facing the center part of the electrode plate group to the plate group width was 0.3. The positional relationship between the electrode plate group and the spacer of this battery is shown in FIG.

(Comparative Example 2)
Using a spacer with a thickness of 0.2 mm, a height of 22.2 mm, and a width of 37 mm, the ratio of the length in the height direction of the spacer facing the center of the electrode plate group to the electrode plate group height is 0.3. A battery D was prepared in the same manner as the battery A, except that the ratio of the length in the width direction of the spacer facing the center part of the electrode plate group to the electrode plate group width was 0.5. The positional relationship between the electrode plate group and the spacer of this battery is shown in FIG.

(Comparative Example 3)
A spacer having a thickness of 0.2 mm, a height of 37 mm, and a width of 10 mm is used, and the ratio of the length in the height direction of the spacer facing the center of the electrode plate group to the electrode plate group height is 0, and the electrode plate group A battery E was prepared in the same manner as the battery A, except that the ratio of the length in the width direction of the spacer facing the center of the electrode plate group to the width was 0. The positional relationship between the electrode plate group and the spacer of this battery is shown in FIG.

(Comparative Example 4)
Battery F was prepared in the same manner as Battery A except that no spacer was used. The positional relationship between the electrode plate group and the spacer of this battery is shown in FIG.

  These batteries were subjected to a cycle life test with a charging condition of an upper limit voltage of 4.2 V and a constant current constant voltage charging with a maximum current of 1 C and a discharging condition of a lower limit voltage of 2.5 V and a constant current discharging of a current of 10 C. Table 1 shows the results of measuring the capacity retention rate at the 200th cycle when the charging conditions were the above conditions to confirm the capacity, the discharge conditions were a constant current discharge with a lower limit voltage of 2.5 V, and a current of 0.2 C. .

  The “area ratio” in Table 1 is “(spacer area / longitudinal sectional area passing through the axis of the electrode plate group)”, and “height ratio” is “(facing the center of the electrode plate group). The length in the height direction of the spacer) / (electrode plate group height) ”, and the“ width ratio ”means“ (the length in the width direction of the spacer facing the center of the electrode plate group) / (pole Board group width) ".

表１の結果より、電池Ａおよび電池Ｂは高い容量維持率が得られるが、電池Ｃ〜電池Ｆの容量維持率は低い結果となった。これらの電池を分解観察すると、電池Ｃ〜Ｆでは、極板の挫屈およびリチウム析出が観察されたが、電池Ａおよび電池Ｂでは極板の挫屈は観察されなかった。したがって、極板群の中央部にスペーサーを有することで極板群の膨張収縮を抑制して極板挫屈を防止し、良好な電池特性を得ることができる。

From the results shown in Table 1, although the battery A and the battery B have high capacity retention rates, the capacity retention rates of the batteries C to F were low. When these batteries were disassembled and observed, in the batteries C to F, electrode plate buckling and lithium deposition were observed, but in the batteries A and B, electrode plate buckling was not observed. Therefore, by having a spacer at the center of the electrode plate group, expansion and contraction of the electrode plate group can be suppressed to prevent electrode plate buckling, and good battery characteristics can be obtained.

Next, the thickness of the spacer is examined.
(Comparative Example 5)
A battery G was prepared in the same manner as Battery A except that a spacer having a thickness of 0.1 mm was used and the battery case thickness was 13.7 mm.

  A cycle life test was performed on the batteries A and G with the charging condition being a constant current constant voltage charging with an upper limit voltage of 4.2 V and a maximum current of 1 C, and the discharging condition being a constant voltage discharging with a voltage lower limit of 2.5 V and a current of 10 C. In addition, Table 2 shows the capacity maintenance rate at the 200th cycle in which the charging conditions are the above conditions and the discharging conditions are a constant voltage discharge with a voltage lower limit of 2.5 V and a current of 0.2 C in order to confirm the capacity.

スペーサーの厚みが０．２ｍｍである電池Ａは高い容量維持率が得られるが、スペーサーの厚みが０．１ｍｍである電池Ｇの容量維持率は低い結果となった。したがって、スペーサーの厚みが薄いと、スペーサーによる極板群の膨張収縮の抑制効果が低くなるため、０．２ｍｍ以上の厚みが効果的である。以上のことから本発明の形態により、特性の良好なリチウム二次電池を得ることができることがわかった。なお、スペーサーの厚みの上限値については、いずれの値であっても本発明の効果を奏することができた。

The battery A with a spacer thickness of 0.2 mm has a high capacity retention rate, but the battery G with a spacer thickness of 0.1 mm has a low capacity retention rate. Accordingly, if the spacer is thin, the effect of suppressing the expansion and contraction of the electrode plate group by the spacer is reduced, and therefore a thickness of 0.2 mm or more is effective. From the above, it was found that a lithium secondary battery with good characteristics can be obtained according to the embodiment of the present invention. In addition, about the upper limit of the thickness of the spacer, even if it was any value, the effect of this invention was able to be show | played.

  The non-aqueous electrolyte secondary battery of the present invention is useful as a high-power non-aqueous electrolyte secondary battery for electric tools, cordless vacuum cleaners, electric vehicles, and the like because high output characteristics are obtained and buckling of the electrode plate can be suppressed. It is.

The positive electrode terminal side cross-sectional view of the battery in embodiment of this invention Cross-sectional view of negative electrode terminal side of battery in an embodiment of the present invention BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view of a short side of a battery according to an embodiment of the present invention. Long side longitudinal sectional view of a battery in an embodiment of the present invention The longitudinal cross-sectional view of the electrode group in the embodiment of the present invention Vertical section of battery A Vertical section of battery B Vertical section of battery C Vertical section of battery D Vertical section of battery E Vertical section of battery F

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Battery case 2 Electrode plate group 3 Spacer 4 Positive electrode lead connection terminal 5 Positive electrode lead 6 Negative electrode lead connection terminal 7 Negative electrode lead 8 Junction part of a battery case and a spacer 9 Electrode plate group center part 10 Electrode plate group height 11 Electrode plate group center Length in the height direction of the part 12 Width of the electrode plate group 13 Length in the width direction of the center part of the electrode plate group

Claims (5)

In a non-aqueous electrolyte secondary battery having an electrode plate group in which a positive electrode plate and a negative electrode plate on a sheet are wound in a square shape with a separator interposed therebetween, an electrolyte, and a battery case, the electrode plate group is attached to the battery case. Are stacked and accommodated in parallel, and each electrode plate group is connected in parallel, and between adjacent electrode plate groups, there is a spacer having a strength that can suppress expansion and contraction of the electrode plate group. Non-aqueous electrolyte secondary battery having a surface area of the electrode plate group facing the spacer ) of 0.38 or more.   The nonaqueous electrolyte secondary battery according to claim 1, wherein at least a part of the spacer is joined to the battery case.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the spacer is opposed to a central part of the electrode plate group.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the spacer has a thickness of 0.2 mm or more.   The non-aqueous electrolyte secondary battery according to claim 1, wherein a material of the spacer is the same as a material of the battery case.

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