JP3403678B2 - Method for producing lithium secondary battery and wound electrode body - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a lithium secondary battery having excellent reliability, which uses a wound electrode body having good output characteristics by keeping a current collecting resistance low while ensuring homogeneity, and a lithium secondary battery having the same. The present invention relates to a method for manufacturing a wound electrode body.

[0002]

2. Description of the Related Art In recent years, lithium secondary batteries have come to be widely used as power source batteries for portable electronic devices such as mobile phones, VTRs, and notebook computers. In addition, since the lithium secondary battery has a cell voltage of about 4 V, which is higher than that of conventional secondary batteries such as lead storage batteries, and has a large energy density, not only the portable electronic device but also recent environmental problems. Against this background, electric vehicles (E
V) or a hybrid electric vehicle (HEV) as a motor drive power source.

In a lithium secondary battery, generally, a lithium transition metal composite oxide is used as a positive electrode active material, a carbonaceous material is used as a negative electrode active material, and an Li electrolyte is dissolved in an organic solvent as an electrolyte. There are various types of electrode bodies, such as a sandwich type, a wound type, and a laminated type, as an electrode body that is a part that performs a battery reaction.

Among these, in the lithium secondary battery having a relatively large capacity, which is preferably used for EV and the like,
As shown in 1, the positive and negative electrode plates 2 and 3 (the positive electrode plate 2, which functions as a lead wire for collecting current from the electrodes. Hereinafter referred to as “tab”) 5 are attached. A wound electrode body (hereinafter referred to as a "wound body") formed by winding the negative electrode plate 3) around the outer periphery of the hollow cylindrical winding core 6 with the separator 4 interposed therebetween so as not to contact each other. 1 is preferably used.

The electrode plates 2 and 3 are formed by forming an electrode active material layer on both surfaces of a metal foil, and the tabs 5 are electrode plates 2 and 3.
3 and the separator 4 may be attached to the exposed portions of the metal foil at the end portions of the electrode plates 2 and 3 at predetermined intervals by using a means such as ultrasonic welding during the work of winding around the winding core 6. it can.

The shape of the electrode plates 2 and 3 is determined in consideration of the resistance of the wound body 1 and the energy density, but the thickness of the metal foil used for the electrode plates 2 and 3 is determined. The thickness is about 10 to 50 μm, and the total thickness of the electrode plates 2 and 3 is often set to about 300 μm or less.

[0007]

As shown in FIG. 2, as a method for producing the wound body 1, two separators 4 are fixed to a winding core 6 using a double-sided tape or the like, and the winding core 6 is surrounded. When winding the separator 4, a method of winding the electrode plates 2 and 3 so as to be sandwiched between the separators 4 is preferably used.

In this case, the electrode plates 2 and 3 are not fixed to the winding core 6, but the electrode plates 2 and 3 are arranged so that their electrode active material layers face each other with the separator 4 interposed therebetween. , It is necessary to keep them parallel. Here, if the parallelism of the electrode plates 2 and 3 deviates at the beginning of winding on the winding core 6, the electrode plates 2 and 3 are thin as described above, and the curvature at the starting position of the winding is small. However, wrinkles may occur on the electrode plates 2 and 3 immediately.

The wrinkles formed on the electrode plates 2 and 3 penetrate the separator 4 and cause an internal short circuit. Further, peeling of the electrode active material easily occurs at the wrinkled portion, and the risk of an internal short circuit due to the peeled electrode active material increases. Furthermore, the occurrence of wrinkles causes variations in the current distribution, which partially deteriorates the electrode active material, causing various problems such as shortening the battery life.

When the cause of the occurrence of many wrinkles on the electrode plates 2 and 3 at the start of winding on the core 6 is examined, the position is closest to the core 6 shown in FIG. 2 described above. Tab (Tab at this position will be referred to as "Tab 5A"
Will be written. It has become clear that () causes a slight deviation in the positions of the electrode plates 2 and 3 and causes wrinkles in the electrode plates 2 and 3. Therefore, tab 5
Start winding the position A on the winding core 6 (ends of the electrode plates 2 and 3)
It is considered that if the distance from the tab 5A is increased, the influence of the tab 5A on the electrode plates 2 and 3 can be reduced to prevent the generation of wrinkles.

However, it is preferable that the tabs 5 be arranged at substantially constant intervals so that the currents flowing through the tabs are equal. In particular, in applications for EVs and HEVs that frequently discharge large currents, the non-uniformity of current collection affects the deterioration of tabs and electrode active materials due to the non-uniformity of current distribution,
It has a great influence on the life characteristics of the battery. Therefore, tab 5
If only A is arranged at a position far from the end portions of the electrode plates 2 and 3, the current collecting area of only the tab 5A becomes large, resulting in uneven current collection. On the other hand, if the distance between the other tabs is increased according to the position of the tab 5A, the number of tabs 5 to be arranged decreases,
This causes a problem that the resistance at the time of extracting the electric current becomes large.

[0012]

Means for Solving the Problems In view of the above-mentioned problems of the prior art, the present invention determines the positional condition and the geometrical condition of a tab to be mounted closest to the start of winding on a winding core. The lithium secondary battery was found in consideration of its shape as well, and it does not impair the uniformity of current collection and does not increase the current collection resistance, and it is a highly reliable lithium secondary battery that suppresses the generation of wrinkles on the electrode plate. The purpose is to provide.

That is, according to the present invention, the nonaqueous electrolytic solution is applied to the wound electrode body formed by winding the positive and negative electrode plates, each having a plurality of current collecting tabs attached thereto, around the outer circumference of the winding core through the separator. A lithium secondary battery that is impregnated, wherein
Times electrode body, the length from the winding start of the electrode plate to the first current collecting tab L (mm), the width of the electrode plate W (m
m), the outer diameter of the winding core R (mm), the thickness of the electrode plate T (μm), the thickness of the tab for the current collector t ([mu] m), before
When the width of the power collection tab is w (mm), L ≧ W.
been configured to meet the t · w / (R · T ) of the relationship
Lithium secondary battery, characterized and Nalco, is provided.

In this lithium secondary battery, the width (W) of the electrode plate is preferably in the range of 60 mm ≦ W ≦ 300 mm, and the thickness (T) of the electrode plate is 50 μm ≦.
It is preferably in the range of T ≦ 200 μm. The thickness (t) of the current collecting tab is preferably in the range of the current collecting substrate thickness of the electrode plate ≦ t ≦ 100 μm. Furthermore,
Between the width (w) of the current collecting tab and the outer diameter (R) of the winding core,
It is preferable that the relationship of w ≦ R is established.

[0015]

[0016]

Furthermore, according to the present invention as a method for producing a wound-type electrode body that is preferably used in the above-mentioned lithium secondary battery, according to the present invention, positive and negative electrode plates each having a plurality of current collecting tabs attached thereto are separated by a separator. the method for preparing wound turn and becomes wound electrode body in the core periphery Te, the length from the winding start of the electrode plate to the first current collecting tab L (mm), the <br/> electrode the width of the plate W (mm), the outer diameter of the winding core R (m
m), the thickness of the electrode plate T (μm), the thickness of the current collector tab t (μm), the width of the tabs for the collector w (mm)
And when, as relation of L ≧ W · t · w / (R · T) is established, a method for manufacturing a wound electrode body, wherein the attachment tabs for the collector to the electrode plate, Will be provided.

[0018]

Embodiments of the present invention will be described below with reference to the drawings, but it goes without saying that the present invention is not limited to the following embodiments.

The lithium secondary battery of the present invention has been previously described with reference to FIG.
As shown in, each of the positive and negative electrode plates (the positive electrode plate 2 and the negative electrode plate 3) having a plurality of current collecting tabs 5 (tabs) attached thereto
Is a lithium secondary battery in which a non-aqueous electrolyte solution is impregnated in a wound electrode body (rolled body) 1 formed by winding a sheet around a core 6 via a separator 4.

The positive electrode plate 2 is manufactured by applying a positive electrode active material on both surfaces of a current collecting substrate. As the current collector substrate, a metal foil such as an aluminum foil or a titanium foil having good corrosion resistance against a positive electrode electrochemical reaction is used, but a punching metal or a mesh (mesh) may be used instead of the foil.

As the positive electrode active material, lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNi
O ₂ ), lithium transition metal composite oxides such as lithium manganate (LiMn ₂ O ₄ ) are preferably used. In the present invention, particularly, lithium manganate having a cubic spinel structure (hereinafter, referred to as “LiMn ₂ O ₄ spinel ") is particularly preferably used. In this case, the resistance of the internal electrode body can be reduced as compared with the case where another electrode active material is used, which is preferable.

LiMn₂O_FourSpinel is like this
It is not limited to the stoichiometric composition, but the Mn
Part substituted with one or more other elements, general formula LiM _XMn
_2-XO_Four(M represents a substitution element and X represents a substitution amount)
Spinel is also preferably used. Such element substitution
Done LiMn₂O_FourIn spinel, Li / Mn ratio
Is over 0.5.

The substitutional element M is listed below by element symbols, but Li, Fe, Mn, Ni, Mg, Z
n, B, Al, Co, Cr, Si, Ti, Sn, P,
V, Sb, Nb, Ta, Mo, W can be mentioned,
Theoretically, Li is +1 valence, Fe, Mn, Ni, Mg, Zn
Is +2 valence, B, Al, Co and Cr are +3 valence, Si, T
i and Sn are +4 valence, P, V, Sb, Nb and Ta are +5
Valence, Mo, and W are +6 valent ions, and are elements that form a solid solution in LiMn ₂ O ₄ . However, for Co and Sn +
In the case of divalent, Fe, Sb, and Ti may be +3 valent, Mn may be +3 valent, +4 valent, and Cr may be +4 valent and +6 valent.

Therefore, various substitution elements M may exist in a state having mixed valences, and the amount of oxygen needs to be 4 as represented by the stoichiometric composition. Alternatively, it may be deficient or excessively present within the range for maintaining the crystal structure.

The coating of these various positive electrode active materials on the current collecting substrate (metal foil) is performed by using a roll coater method or the like to prepare a slurry or paste prepared by adding a solvent, a binder, etc. to the positive electrode active material powder. , Is applied to the current collecting substrate and dried, and then, if necessary, subjected to press treatment,
The thickness is adjusted. In forming the electrode active material layer, carbon fine powder such as acetylene black is added to these positive electrode active material powders as a conduction aid.

On the other hand, the negative electrode plate 3 can be manufactured in the same manner as the positive electrode plate 2. As the current collecting substrate of the negative electrode plate 3, a metal foil such as a copper foil or a nickel foil having a good corrosion resistance against a negative electrode electrochemical reaction is preferably used. As the negative electrode active material, an amorphous carbonaceous material such as soft carbon or hard carbon, or highly graphitized carbonaceous powder such as artificial graphite or natural graphite is used.

As the separator 4, micropores are used.
Having Li ion (Li ⁺) Permeable polyethylene fibers
Rum (PE film) with porous Li⁺Transparent poly
Three-layer structure sandwiched by propylene film (PP film)
The following are preferably used. This is the internal electrode body
When the temperature rises, the PE film softens at about 130 ° C.
And the micropores are crushed, Li⁺Movement of batteries
It also serves as a safety mechanism that suppresses And this
Clamps PE film between PP films with higher softening temperature
When the PE film softens due to
Even if the PP film retains its shape, the positive electrode plate 2 and the negative electrode plate
Prevents contact and short circuit of 3 and reliably suppresses battery reaction and safety
It is possible to secure the sex.

During the work of winding the electrode plates 2 and 3 and the separator 4 around the winding core 6, a portion of the electrode plates 2 and 3 on which the current collecting substrate not coated with the electrode active material is exposed, The tabs 5 are attached respectively. As the tab 5, a foil-like one made of the same material as the current collecting substrate of each of the electrode plates 2 and 3 is preferably used. Electrode plate 2 of tab 5
The attachment to 3 can be performed using ultrasonic welding, spot welding, or the like. At this time, as shown in FIG. 1, if the tabs 5 are attached so that the tabs of one electrode are arranged on one end surface of the internal electrode body 1, contact between the tabs 5 can be prevented, which is preferable. .

In assembling the battery, first, while maintaining electrical continuity between the terminal 5 for taking out an electric current and the tab 5, the produced internal electrode body 1 is inserted into the battery case and held at a stable position. To do. Then, after impregnating the non-aqueous electrolyte, the battery can be sealed by sealing the battery case.

As the non-aqueous electrolyte, lithium hexafluorophosphate (LiPF ₆ ) or lithium borofluoride (L
A lithium complex fluorine compound such as iBF ₄ ), or one or more electrolytes selected from lithium halides such as lithium perchlorate (LiClO ₄ ), ethylene carbonate (EC), diethyl carbonate (DEC), Those dissolved in a carbonate ester solvent such as dimethyl carbonate (DMC) or propylene carbonate (PC) or a single solvent such as γ-butyrolactone, tetrahydrofuran or acetonitrile, or a mixed solvent are preferably used.

Next, the conditions for producing the wound body 1 described above will be described in more detail. First, regarding the method of winding the electrode plates 2 and 3 and the separator 4, the same method as that described above with reference to FIG. 2 is used. A plan view of the expanded positive electrode plate 2 is shown in FIG. 3. Here, it is assumed that the winding is started from the left end surface of FIG. 3 on the winding core 6, and the first tab from the winding start of the positive electrode plate 2 (left end surface). The length up to 5 A is L (mm), and the width of the positive electrode plate 2 is W (mm). Also,
The outer diameter of the winding core 6 is R (mm), the thickness of the positive electrode plate 2 (the total thickness of the current collecting substrate and the positive electrode active material layer) is T (μm),
The thickness of the tab 5 (including the tab 5A. The same applies hereinafter) is t (μm), and the width of the tab 5 is w (mm). Such conditions also apply to the negative electrode plate 3.

Table 1 shows the results of examining the value of each parameter and the presence or absence of wrinkles when a wound body was manufactured by changing these parameters variously. Here, LiMn ₂ O ₄ spinel was used as the positive electrode active material, highly graphitized carbon powder was used as the negative electrode active material, aluminum foil with a thickness of 20 μm was used as the current collector substrate for the positive electrode plate, and current collector for the negative electrode plate was used. A copper foil having a thickness of 10 μm was used as each substrate. Each electrode active material is dispersed in an organic solvent in which PVDF (polyvinylidene fluoride) is dissolved as a binder to form a slurry, and the slurry is applied onto each current collecting substrate using a roll coater method and dried to prepare an electrode plate. did.

Then, 20 wound bodies were produced under each condition, and then wound and unwound, and a case where even one wrinkle was observed at the beginning of winding the electrode plate was marked with “x”, and no wrinkle was observed. The case was marked as "○". An electrode plate with a length of 3000 mm was used, and the tab width (w) was 8 m.
Fixed to m, the distance between tabs is the set length (L) (m
In consideration of m), the tabs are arranged at substantially equal intervals so that the current collecting areas of the tabs are equal to each other, and when the wound body is manufactured, the tabs are arranged in a substantially linear shape in the radial direction. . In addition, for all samples, other winding body manufacturing conditions, for example,
The winding speed and tension of the electrode plates were the same.

[0034]

[Table 1]

The conditions under which wrinkles are likely to occur on the electrode plate are:
If the width (W) of the electrode plate is wide, the thickness (t) of the tab is large, the width (w) of the tab is wide, the outer diameter (R) of the winding core is small, the thickness (T) of the electrode plate is There are five possible thin conditions. Of these conditions, for the former three, it is considered that the length (L) from the winding start of the electrode plate to the first tab 5A becomes longer as the value (W · t · w) becomes larger. And W · t · w can be assumed to be in a positive correlation (proportional relationship). On the other hand, regarding the latter two conditions, it is considered that the length (L) becomes longer as the value (R · T) becomes smaller, so that L and R ·
It can be assumed that T has a negative correlation (inverse proportion).

Therefore, as a result of associating the relationship between L and W · t · w / (R · T) with the occurrence of wrinkles shown in Table 1, L ≧ A · W · t · w / (R -T) (where A is a proportional coefficient, and in the case of Table 1, A = 1.0), it was revealed that no wrinkles were observed on the electrode plate. . This, on the contrary, suggests that the wound body needs to be manufactured so as to satisfy such conditions.

Considering each parameter in more detail, as the width (W) of the electrode plate becomes wider, wrinkles are more likely to occur, and the distance from the opposite side of the electrode plate to which the tab is not attached to the tab becomes longer. Therefore, the resistance increases and the current collection efficiency decreases. On the other hand, if the width (W) of the electrode plate is narrowed, the occurrence of wrinkles can be prevented, but in order to increase the electrode area, a long electrode plate is required, increasing the internal resistance and lowering the winding workability. Problems such as occur. In consideration of these merits and demerits, in the present invention,
The width (W) of the electrode plate is preferably in the range of 60 mm ≦ W ≦ 300 mm.

If the thickness (T) of the electrode plate is increased, wrinkles can be prevented, but the internal resistance of the electrode plate increases. On the other hand, if the electrode plate is made thin, the internal resistance is reduced, but wrinkles are likely to occur and the energy density is also lowered. Considering these characteristics,
In the present invention, the thickness (T) of the electrode plate is 50 μm ≦ T
It is preferable to set it in the range of ≦ 200 μm.

If a thin core is used, the curvature is small and wrinkles are likely to occur on the electrode plate, while if a thick core is used, the curvature is large and wrinkles are less likely to occur on the electrode plate. However, the wasted space such as the hollow portion of the winding core increases, leading to a reduction in energy density. Therefore, the outer diameter R of the winding core is preferably in the range of 6 mm ≦ R ≦ 20 mm.

When the thickness (t) of the tab is increased, the electrode plate is less likely to be deformed due to the curvature at the beginning of winding, and therefore wrinkles are significantly generated. On the other hand, if the thickness is reduced, the occurrence of wrinkles is suppressed, but the resistance of the tab increases, the current collection efficiency decreases, and there is a problem that attachment to the electrode plate by welding or the like becomes difficult. Considering these things,
The thickness (t) of the tab is such that the collector substrate thickness of the electrode plate ≦ t
It is preferable to set it in the range of ≦ 100 μm.

The occurrence of wrinkles on the electrode plate is considered to be greatly influenced by the width (w) of the tab, as described above. Particularly, in relation to the outer diameter (R) of the winding core,
It was confirmed that the occurrence of wrinkles changed. Table 2 shows the test results when the width (w) of the tab was changed by using the same method as the method for producing and evaluating the various samples described in Table 1 above.

[0042]

[Table 2]

From Table 2, even when the width (w) of the tab is changed, the relationship between L and W · t · w / (R · T) is L ≧
It can be seen that the occurrence of wrinkles on the electrode plate is avoided when W · t · w / (R · T) is satisfied. Further, focusing on the relationship between the outer diameter (R) of the winding core and the width (w) of the tab, it can be seen that wrinkles are prevented from being generated on the electrode plate when the relationship of w ≦ R is established.

Here, if the width (w) of the tab is widened,
Besides the occurrence of wrinkles, the outer diameter R of the winding core must be increased, which causes a problem of lowering the energy density. On the other hand, when the width (w) of the tab is narrowed, the resistance of the tab itself is increased. In addition, the welding area with the electrode plate is reduced and the current collecting resistance is increased. In consideration of these situations, the width (w) of the tab is preferably 5 mm ≦ w ≦ R.

Various conditions for the tab to be arranged closest to the winding core according to the present invention are as follows: a plurality of tabs are attached to one electrode plate, and The present invention is preferably applied to the production of a wound body having a substantially uniform charging area and a small current collecting resistance from the wound body, and at this time, the wrinkles on the electrode plate are remarkably avoided. That is, even if the present invention is adopted when the total number of tabs attached to the electrode plate is small, it is difficult to obtain a large effect. The present invention is particularly effective when the number of tabs attached to one electrode plate is 10 or more.

There are no restrictions on the shape of the battery constituent members other than the constituent members of the wound body, such as the battery case and the external terminals for connecting the battery to an external addition or the like.
The wound body having the above-mentioned parameter conditions is suitably used for a battery having a battery capacity of 2 Ah or more. This is because, when the battery capacity is large, the area of the electrode plate is naturally large, and therefore the parameter conditions (constituent conditions) of the wound body are restricted. On the contrary, the battery using the wound body having such a parameter condition has a small internal resistance and thus is excellent in charge / discharge characteristics and can have a large energy density. Furthermore, since wrinkles do not occur on the electrode plate, the risk of internal short circuit is avoided, and since the homogeneity of the wound body is ensured, the charge / discharge reaction is carried out uniformly, and the wrinkles of the electrode active material. Local peeling and deterioration progress are suppressed in the area of, and the reliability becomes excellent. Such characteristics show preferable characteristics as a power source for an electric vehicle or a hybrid electric vehicle, particularly as a power source battery for driving a motor.

[0047]

As described above, according to the method for producing a lithium secondary battery and a wound electrode body of the present invention, the wound electrode body is
Mutual in but the electrode plates, tabs and core constituting it
Since the dimensional relationship of the electrodes is configured to be appropriate, wrinkles on the electrode plate are prevented from occurring and the electrode plate is homogenized, and the resistance of the electrode plate and the current collecting resistance from the wound electrode body are also improved. It can be kept small and the energy density can be increased. That is, the present invention has a remarkable effect of contributing to the provision of a battery having excellent charge / discharge characteristics and reliability and a long service life.

[Brief description of drawings]

FIG. 1 is a perspective view showing a schematic structure of a wound electrode body used in a lithium secondary battery.

FIG. 2 is an explanatory view showing a state in which winding of an electrode plate or the like is started around a winding core in the production of a wound electrode body.

FIG. 3 is a development view of a positive electrode plate.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Winding type electrode body, 2 ... Positive electrode plate, 3 ... Negative electrode plate, 4 ... Separator, 5.5A ... Current collecting tab, 6 ... Core.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kennobu Kenshin No. 2-56 Suda-cho, Mizuho-ku, Nagoya-shi, Aichi Japan Insulator Co., Ltd. (56) Reference JP-A-12-251864 (JP, A) JP HEI 7-192717 (JP, A) JP H11-189419 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 10/04 H01M 4/04

Claims (6)

(57) [Claims] 1. A lithium-ion electrode obtained by impregnating a non-aqueous electrolyte solution into a wound electrode body obtained by winding positive and negative electrode plates, each having a plurality of current collecting tabs attached thereto, around the outer periphery of a winding core through a separator. a next cell, the wound electrode body, a length from the winding start of the electrode plate to the first current collecting tab L (mm), the width of the electrode plate W (mm), the winding the outer diameter of the core R (mm), the thickness of the electrode plate T (μm), the thickness of the current collector tab t (mu
m), the width of the tabs for the collector is taken as w (mm),
L ≧ W · t · w / structure to so that to satisfy the relationship of (R · T)
Lithium secondary battery which is characterized that you made are composed. 2. The width (W) of the electrode plate is in the range of 60 mm or more and 300 mm or less.
The lithium secondary battery described. 3. The lithium secondary battery according to claim 1, wherein the thickness (T) of the electrode plate is in the range of 50 μm or more and 200 μm or less. 4. The thickness (t) of the current collecting tab is in the range of not less than the thickness of the current collecting substrate forming the electrode plate and not more than 100 μm. The lithium secondary battery described. 5. The relationship of w ≦ R is established between the width (w) of the current collecting tab and the outer diameter (R) of the winding core, according to any one of claims 1 to 4. The lithium secondary battery according to item 1. 6. A method for producing a wound electrode body, comprising winding positive and negative electrode plates, each having a plurality of current collecting tabs attached thereto, around a winding core via a separator, wherein the electrode plate is wound. the length from the beginning up to the first current collecting tab L (mm), the width of the electrode plate W (mm), the outer diameter of the winding core R (mm), the thickness of the electrode plate T ([mu] m ),
The thickness of the tab for the current collector t (μm), the width of the tabs for the collector is taken as w (mm), L ≧ W · t · w / (R ·
As the relationship T) holds, a method for manufacturing a wound electrode body, wherein the mounting tabs for the collector to the collector <br/> plate.