JP2005190785A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte secondary battery having a large battery capacity and capable of preventing deposition of lithium. <P>SOLUTION: In the battery, the size of a positive electrode active material layer and the size of a negative electrode active material layer are identical in substance and the size of a separator is larger than that of the positive electrode active material layer, and the separator has a transmission prevention region 31 where the micropores are closed beforehand. When the mass of the positive electrode active material in the positive electrode active material layer directly opposed to the separator of the positive electrode current collector is made m (g/m<SP>2</SP>), and the separator and the positive electrode plate are overlapped so as to cover the positive electrode active material layer, the straight line distance t1 between the outer circumference line 3a of the positive electrode active material layer and the inner circumference line 3b of the transmission prevention region satisfies 0.5≤t1≤12.3-0.03 m (mm), and the straight line distance t2 between the positive electrode outer circumference line 3a and the outer circumference line 3c of the transmission prevention region 31 satisfies 0.5≤t2 (mm). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an improvement in a non-aqueous electrolyte secondary battery for the purpose of increasing the battery capacity and improving safety.

  A non-aqueous electrolyte secondary battery represented by a lithium ion secondary battery has a high energy density and a high capacity, and thus is useful as a driving power source for mobile information terminals and the like.

 For example, a lithium secondary battery using a wound-type electrode body in which a positive electrode plate and a negative electrode plate are wound via a separator has a large opposing area between the positive and negative electrodes, and it is easy to take out a large current. Widely used in information terminals and the like.

  In such a wound electrode body, a separator is interposed between the positive and negative electrodes, and the center lines in the width direction of each electrode plate and the separator are overlapped with each other and then wound by a winder. It is produced by. Although this winding process is precisely controlled, there is a possibility that a slight winding deviation may occur. As shown in FIG. 6, when winding deviation (L 1, L 2) occurs, the negative electrode non-facing positive electrode in which the opposing negative electrode plate (negative electrode active material layer) 202 does not exist at the end of the positive electrode plate (positive electrode active material layer) 201. Region 205 is created. In this state, the movement of lithium ions 204 from the negative electrode non-opposing positive electrode region 205 is concentrated on the end portion of the negative electrode plate 202 (the portion surrounded by a circle in FIG. 6), and the amount of lithium ions that can be occluded by the end portion of the negative electrode plate 202 Over. For this reason, lithium dendrite is deposited at the end, which penetrates the separator and conducts with the positive electrode, causing an internal short circuit.

 4A to 4D, the size of the negative electrode plate 102 is larger than that of the positive electrode plate 101 and the size of the separator 103 is larger than that of the negative electrode plate 102. In order to prevent internal short-circuiting due to lithium deposition, a negative electrode non-opposing positive electrode region does not occur even when winding deviation (L1 <L2) occurs.

However, since the amount of the positive electrode active material in the positive electrode plate is reduced by this technique, it is not possible to meet the demand for higher capacity of the battery.
On the other hand, when the size of the positive electrode plate is increased to the size of the negative electrode plate, a problem arises in safety for the reason described above.

  Therefore, in order to prevent lithium deposition on the negative electrode, a technique has been proposed in which a part of the separator is blocked to partially prevent lithium ions from passing therethrough (Patent Documents 1 to 3).

JP-A-6-76860 (abstract) JP-A-11-307128 (abstract) JP 2000-285896 A (abstract)

  Patent Document 1 is a technique for improving safety by forming a separator with a porous body and crushing a hole in a portion facing the peripheral edge of a positive electrode plate of the separator to prevent permeation of lithium ions. is there. However, since this technique suppresses the charge / discharge reaction at the peripheral edge of the positive electrode plate, the battery capacity is reduced.

  Patent Document 2 discloses that a non-porous blocking portion for blocking lithium ion migration between the negative electrode side lead wire connecting portion and the other end portion of the positive electrode plate is formed. This technique is a technique for preventing lithium from being deposited on the negative electrode side lead wire connecting portion. Therefore, the examination from the viewpoint of increasing the amount of active material has not been made.

  Patent Document 3 discloses a technique for setting the porosity of the edge portion of the separator relatively lower than the porosity of the central portion of the separator sandwiched between the electrodes. However, this technique prevents the active material peeled off at the edge of the separator from entering the edge of the separator and prevents the separator from becoming highly conductive. Therefore, the examination from the viewpoint of increasing the amount of active material has not been made.

  The inventors have conducted intensive research to solve the above problems, and even if the size of the positive electrode plate is the same as the size of the negative electrode plate, the separator is previously blocked at a predetermined position so as not to transmit lithium ions. It was found that a battery having a high capacity and high safety can be obtained by forming the permeation blocking region.

  The present invention has been completed based on the above findings, and an object thereof is to provide a nonaqueous electrolyte secondary battery having a large battery capacity and excellent safety.

The present invention provides a strip-like positive electrode plate having a positive electrode active material layer coated on a positive electrode current collector, a strip-like negative electrode plate having a negative electrode active material layer, and a lithium ion interposed between the positive and negative electrode plates. In a non-aqueous electrolyte secondary battery comprising a strip-shaped separator having fine pores that permeate, an electrode body, and a non-aqueous electrolyte, the size of the positive electrode active material layer and the size of the negative electrode active material layer are Substantially the same, the separator has a size larger than the size of the positive electrode active material layer, and the separator has a permeation blocking region 31 formed by previously closing the micropores, and the positive electrode current collector has the When the mass of the positive electrode active material in the positive electrode active material layer directly facing the separator is m (g / m ² ) and the separator and the positive electrode plate are overlapped so as to cover the positive electrode active material layer, the positive electrode active material Material layer perimeter 3 And a linear distance t1 between the permeation prevention region 31 and the inner peripheral line 3b satisfies 0.5 ≦ t1 ≦ 12.3-0.03 m (mm), and the positive electrode outer peripheral line 3a and the outer perimeter line of the permeation prevention region 31 The linear distance t2 with 3c satisfies 0.5 ≦ t2 (mm).

  Here, “substantially the same” does not mean completely the same thing, but means that there may be a manufacturing error, and the error range is preferably 5% or less, more preferably Is 3% or less, more preferably 1% or less.

  According to the present invention, the permeation prevention region of the separator may be formed by heating the separator to a melting point or higher before melting the electrode body to melt the fine pores of the separator.

  According to the present invention, as shown in FIGS. 1 and 2, permeation blocking regions 31 are formed in the inner and outer regions of the separator around the outer peripheral line 3 a of the positive electrode active material layer. For this reason, when winding deviation occurs, the lithium ions 4 in the negative electrode non-opposing positive electrode region 5 bypass the permeation blocking region 31 as shown by the arrows in FIG. 3 at the time of charging, and the positive electrode plate (positive electrode active material layer) 1 To the negative electrode plate (negative electrode active material layer) 2. A part of the lithium ions 4 passes through the separator 3 and is occluded by the negative electrode plate before reaching the end of the negative electrode plate. Therefore, lithium deposition at the end of the negative electrode plate is suppressed, and a battery having a high capacity and excellent safety can be obtained.

  Here, the linear distance t1 between the outer peripheral line 3a of the positive electrode active material layer and the permeation prevention region inner peripheral line 3b and the linear distance t2 between the outer peripheral line 3a of the positive electrode active material layer and the permeation prevention region outer peripheral line 3c are 0.5 mm or more. It is preferable that On the other hand, as shown in FIG. 8, when the linear distance t1 between the outer peripheral line 403a of the positive electrode active material layer and the permeation blocking area inner peripheral line 403b is smaller than 0.5 mm, the size of the permeation blocking area is too small. The effect of preventing the occlusion of excessive lithium ions at the end of the plate is small, and lithium is deposited at the end of the negative electrode plate. The same applies to the case where the linear distance t2 between the outer peripheral line of the positive electrode active material layer and the permeation prevention region outer peripheral line is smaller than 0.5 mm.

Further, when the mass of the positive electrode active material in the positive electrode active material layer directly facing the separator is m (g / m ² ), the linear distance t1 between the outer peripheral line 3a of the positive electrode active material layer and the permeation blocking region inner peripheral line 3b. Is preferably 12.3-0.03 m or less. On the other hand, as shown in FIG. 7, when t1 is larger than 12.3-0.03 m, most of the lithium ions 304 from the positive electrode plate 301 facing the permeation blocking region 331 reach the end of the negative electrode plate 302. Before, a new problem arises in that excess lithium ions 304 are occluded in the negative electrode plate 302 in the vicinity of the permeation prevention region inner peripheral line 303b, and lithium is deposited in the portion.

  Moreover, although the upper limit of t2 is not particularly restricted, it should be noted that the volume energy density decreases as the separator size increases.

  In addition, when the size of the positive electrode active material layer and the mass of the positive electrode active material are designed, the position and size of the permeation blocking region are also determined accordingly, so that the portion is heated to the melting point or more of the separator before the electrode body is manufactured. The permeation blocking region can be produced by simple means. Therefore, it is easy to produce.

  The best mode for carrying out the present invention will be described in detail below based on the embodiments. The present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within a range that does not change the gist thereof.

(Embodiment)
Hereinafter, a method for manufacturing a battery according to the present invention will be described.

<Preparation of positive electrode>
90 parts by mass of a positive electrode active material composed of lithium cobaltate (LiCoO ₂ ), 5 parts by mass of a conductive agent composed of acetylene black, 5 parts by mass of a binder composed of polyvinylidene fluoride (PVdF), and N-methyl-2 -Pyrrolidone (NMP) was mixed to obtain an active material slurry.

  The active material slurry is uniformly applied to both surfaces of a positive electrode core made of an aluminum foil having a thickness of 20 μm by a doctor blade, and then passed through a dryer to be dried, thereby removing the organic solvent necessary for slurry preparation. did. Subsequently, the positive electrode plate 1 was produced by rolling and cutting this electrode plate with a roll press so as to have a predetermined filling density.

<Preparation of negative electrode>
An active material slurry was prepared by mixing 90 parts by mass of a negative electrode active material made of graphite, 10 parts by mass of a binder made of polyvinylidene fluoride (PVdF), and N-methyl-2-pyrrolidone (NMP). This active material slurry is uniformly applied to both sides of a negative electrode core made of a copper foil having a thickness of 20 μm by a doctor blade, and then passed through a dryer to dry, thereby removing an organic solvent necessary for slurry preparation. did. Next, the electrode plate was rolled and cut with a roll press so that the thickness was 0.14 mm, whereby a negative electrode plate 2 was produced. As shown in FIGS. 1A, 1B, and 1D, the positive electrode plate (positive electrode active material layer) 1 and the negative electrode plate (negative electrode active material layer) 2 have the same size. did.

<Preparation of separator>
The polyolefin microporous membrane was cut to a required size, and a certain portion of the membrane was pressed against a hot plate at 140 ° C. for 10 seconds to melt and close the micropore, thereby forming the permeation blocking region 31 shown in FIG. Separator 3 was produced. As shown in FIGS. 1C and 1D, the size of the separator 3 was made larger than the size of the positive electrode plate 1 and the size of the negative electrode plate 2.

<Preparation of electrolyte>
LiPF ₆ as an electrolyte salt was dissolved in a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed so as to have a volume ratio of 5: 5 to 1 M (mol / liter) to prepare an electrolytic solution.

<Production of electrode body>
The separator was interposed between the positive and negative electrode plates produced above, and the center lines in the width direction of each electrode plate were made to coincide with each other. Then, it wound with the winder and taped the outermost periphery, and produced the spiral electrode body.

 The electrode body was inserted into an outer can, an electrolyte solution was injected, and the opening was sealed to produce a cylindrical battery having a diameter of 18 mm and a height of 65 mm.

 In the above embodiment, the slurry is applied by the doctor blade, but a die coater may be used. Further, an active material paste can be used in place of the active material slurry, and it can be applied by a roller coating method. Moreover, it can produce similarly even if it uses an aluminum mesh instead of an aluminum foil.

(Examples A1 to A6, Comparative Examples X1 to X5)
As shown in Table 1 below, a battery was fabricated in the same manner as in the above embodiment, except that the linear distances t1 and t2 of the transmission blocking region were changed. In Comparative Example X1, as described in the background art, the positive electrode was made 2 mm smaller than the negative electrode. Further, the mass m (g / m ² ) of the positive electrode active material on one side is 150.

(Examples B1 to B7, Comparative Examples Y1 to Y4)
As shown in Table 2 below, a battery was fabricated in the same manner as in the above embodiment except that the linear distances t1 and t2 of the transmission blocking region were changed. In Comparative Example Y1, as described in the background art, the positive electrode was made 2 mm smaller than the negative electrode. Further, the mass m (g / m ² ) of the positive electrode active material on one side is 200.

(Examples C1-C6, Comparative Examples Z1-Z5)
As shown in Table 3 below, a battery was fabricated in the same manner as in the above embodiment, except that the linear distances t1 and t2 of the transmission blocking region were changed. In Comparative Example Z1, as described in the background art, the positive electrode was made 2 mm smaller than the negative electrode. Further, the mass m (g / m ² ) of the positive electrode active material on one side is 250.

Capacity measurement test After charging at a constant current of 2000 mA, a constant voltage of 4.2 V, a final current of 50 mA and 25 ° C.,
The discharge capacity when discharged at a constant current of 1 It (first charge capacity), a final voltage of 2.75 V and 25 ° C. was measured.

Confirmation of lithium deposition After charging and discharging once under the above conditions, each charged battery was disassembled, and lithium deposition was visually confirmed.

With respect to t1 in Tables 1 to 3, the case where lithium was precipitated was plotted in FIG. As a result of linear function fitting of this result, when the mass of the positive electrode active material on one side is m (g / m ² ), it is within the range of 0.5 ≦ t1 ≦ 12.3-0.03 m (mm). It turned out to be preferable.

It will be discussed below that the above results were obtained. When the value of t1 is less than 0.5 mm (X3, Y3, Z3), when the negative electrode non-facing positive electrode region 405 is generated due to winding misalignment or the like, it is formed in the separator 403 interposed therebetween as shown in FIG. The permeation blocking region 431 that is set is too small. Therefore, more lithium ions than can be occluded move to the end of the negative electrode plate, and lithium is deposited at the end of the negative electrode plate.
If the value of t1 is larger than 12.3-0.03 m (X4, X5, Y4, Z4, Z5), the permeation blocking region 331 of the negative electrode non-facing positive electrode region 305 is excessive as shown in FIG. The lithium ions 304 that have moved around the permeation-preventing region 331 are occluded by the negative electrode before moving to the end of the negative electrode plate 302 (mainly in the vicinity of the permeation-preventing region inner peripheral line 3b), and the lithium ion occlusion amount in that portion. Becomes excessive, and lithium is deposited.
On the other hand, when the value of t1 is 0.05 or more and 12.3-0.03 m (mm) or less (A1 to A6, B1 to B7, C1 to C6), as shown in FIG. The amount of movement to the end of the negative electrode plate 2 by bypassing 31 is properly maintained, the safety is improved, and the size of the positive electrode active material layer can be made larger than that of the conventional technology, so that the battery capacity is increased. Therefore, it is preferable to satisfy 0.5 ≦ t1 ≦ 12.3-0.03 m.

Moreover, it turned out that it is preferable that t2 is 0.5 mm or more. This is because when t2 is less than 0.5 mm (X2, Y2, Z2), the permeation blocking region formed in the separator is too small, and the same phenomenon as when t1 is less than 0.5 mm occurs. it is conceivable that.
It is not necessary to set an upper limit for t2, but it should be noted that the volume energy density decreases when the separator size is excessive.

  In addition, from Tables 1 to 3, the present invention batteries A1 to A6, B1 to B7, and C1 to C6 are compared with the conventional technique in which a positive and negative electrode gap (a difference in size between the positive electrode plate and the negative electrode plate) is provided. It can be seen that the battery capacity is larger by 64 to 83 mAh than the batteries X1, Y1, and Z1. This is presumably because the positive and negative electrode gaps are not provided, so that the size of the positive electrode plate is increased and the amount of the positive electrode active material is increased.

[Other matters]
In the above embodiment, a cylindrical outer can is used, but it is natural that various shapes such as a square shape and a laminate outer can be used.

  Further, as the positive electrode active material, one kind of compound selected from lithium-containing transition metal composite oxides, or a mixture of two or more kinds of compounds can be used. For example, lithium cobaltate, lithium nickelate, manganate Lithium, lithium ferrate, or an oxide obtained by substituting part of the transition metal contained in these oxides with another element can be used.

  Further, as the negative electrode active material, natural graphite, carbon black, coke, glassy carbon, carbon fiber, or a carbonaceous material such as a fired body thereof can be used.

  In addition, as the non-aqueous solvent used for the electrolyte, a kind of compound selected from carbonates, lactones, ethers, ketones, nitriles, amides, sulfone compounds, esters, aromatic hydrocarbons, Or it can use in mixture of 2 or more types. Among these, carbonates, lactones, ethers, ketones, and nitriles are preferable, and carbonates are more preferable. Specific examples thereof include ethylene carbonate, propylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, anisole, 1,4-dioxane, 4-methyl. -2-pentanone, cyclohexanone, acetonitrile, propionitrile, dimethylformamide, sulfolane, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, ethyl propionate and the like.

The electrolyte salt is selected from lithium salts such as LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiCF ₃ SO ₃ , LiPF ₆ , LiBF ₄ , LiAsF ₆ and LiClO _4. These compounds can be used alone or in combination of two or more. The amount of electrolyte salt dissolved in the non-aqueous solvent is preferably 0.5 to 2.0 mol / liter.

As is apparent from the above results, according to the present invention, there is an excellent effect that a nonaqueous electrolyte secondary battery having excellent safety and large capacity can be provided. Therefore, industrial applicability is great.

1 is a drawing showing sizes of a positive electrode active material layer, a negative electrode active material layer, and a separator according to the present invention. It is drawing which shows the permeation | transmission prevention area | region of the separator based on this invention. It is a conceptual diagram which shows the movement of the lithium ion of the nonaqueous electrolyte secondary battery which concerns on this invention. 6 is a diagram illustrating sizes of a positive electrode active material layer, a negative electrode active material layer, and a separator according to a conventional technique. It is a conceptual diagram which shows the movement of the lithium ion of the nonaqueous electrolyte secondary battery which concerns on a prior art. It is a conceptual diagram which shows the movement of the lithium ion of the nonaqueous electrolyte secondary battery of the other form which concerns on a prior art. It is a conceptual diagram which shows the movement of the lithium ion of the nonaqueous electrolyte secondary battery which concerns on X4, X5, Y4, Z4, Z5. It is a conceptual diagram which shows the movement of the lithium ion of the nonaqueous electrolyte secondary battery which concerns on X3, Y3, Z3. It is a graph which shows the relationship between the linear distance of a permeation | transmission prevention area | region, positive electrode active material density, and the presence or absence of lithium precipitation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode plate 2 Negative electrode plate 3 Separator 31 Transmission prevention area | region 4 Lithium ion 5 Negative electrode non-opposing positive electrode area | region

Claims (2)

A finely striped positive electrode plate having a positive electrode active material layer coated on a positive electrode current collector, a strip-like negative electrode plate having a negative electrode active material layer, and a fine electrode that is interposed between the positive and negative electrode plates and transmits lithium ions. An electrode body comprising a strip-shaped separator having holes;
A non-aqueous electrolyte,
In a non-aqueous electrolyte secondary battery comprising:
The size of the positive electrode active material layer and the size of the negative electrode active material layer are substantially the same,
The size of the separator is larger than the size of the positive electrode active material layer,
The separator has a permeation prevention region (31) formed by previously closing the micropores;
The positive electrode active material layer in the positive electrode active material layer directly facing the separator of the positive electrode current collector is defined as m (g / m ² ), and the separator and the positive electrode plate are overlapped so as to cover the positive electrode active material layer. When combined, the linear distance t1 between the outer peripheral line (3a) of the positive electrode active material layer and the inner peripheral line (3b) of the permeation blocking region (31) is 0.5 ≦ t1 ≦ 12.3-0.03m ( mm), and a linear distance t2 between the positive electrode outer peripheral line (3a) and the outer peripheral line (3c) of the transmission blocking region (31) satisfies 0.5 ≦ t2 (mm).
A non-aqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery according to claim 1,
The permeation blocking region (31) is formed by heating the separator to a melting point or higher before being interposed between the positive and negative electrodes to melt and close the fine pores of the separator,
A non-aqueous electrolyte secondary battery.

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