JPH1012279A - Metal lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent damage of a separator and abnormal deposition of lithium, suppress internal short-circuiting and attain life extension of a battery, by storing lithium deposited in a negative electrode surface to a buffer void formed between a negative or positive electrode and the separator. SOLUTION: In a winding electrode of a metal lithium secondary battery, a spacer 4 is positioned in both ends in an axial direction of a separator 2 and a negative electrode 3, to be arranged in a belt shape along a lengthwise direction of the separator 2 and the negative electrode 3, between the separator 2 and the negative electrode 3, a buffer void 4a of almost fixed distance is formed. As a result, even when negative electrode lithium is fine granulated to expand the volume due to repetition of charge/discharge, till filling this buffer void 4a with the expanded deposition lithium, the deposited lithium, pressing the separator 2 and abnormally precipitating in its fine hole, is prevented from leading to a positive electrode 1. As a result, internal short- circuiting can be suppressed, a cycle life of the battery is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a metal lithium secondary battery having a structure in which a negative electrode using lithium or a lithium alloy as a negative electrode active material and a positive electrode made of a chargeable / dischargeable material are opposed to each other with a separator interposed therebetween. About.

[0002]

2. Description of the Related Art In recent years, with the spread of portable electric devices such as portable telephones, portable video cameras, and notebook computers, the need for a large capacity battery and a high energy density has rapidly increased. ing. Under such circumstances, as a new secondary battery replacing lead and nickel cadmium, metal lithium 2
Next battery is attracting attention. This is because, by adopting a high electromotive force of about 3 V and employing lithium metal having a low bulk density as an active material, the weight energy density is three to four times higher than that of a lead battery or NiCd battery having the same capacity. It is most suitable for the needs of high energy density.

However, this battery has a problem that the capacity is reduced due to the occurrence of a minute internal short circuit during repeated charging / discharging, resulting in a short cycle life. In particular, if the capacity is increased by adopting a long winding structure to meet the needs of portable electric equipment, this phenomenon becomes even more remarkable, and a short circuit occurs in the worst several cycles. At present, large-capacity lithium metal batteries have not yet been put to practical use because such problems have not been solved.

It is considered that the cause of the internal short circuit is that needle-shaped precipitated lithium generally called dendrite grows from the surface of the negative electrode upon charging, penetrates through the separator, and reaches the positive electrode. However, although various studies have been conducted on the detailed mechanism, such as how lithium precipitates in a needle shape, in terms of both material and structure, no definitive solution has been found yet.

Therefore, for example, Japanese Patent Application Laid-Open Nos. 4-104478 and 4-104479 disclose that a large-area electrode is divided into several small sections, and a section in which an internal short circuit occurs is burned out by a large current. There is disclosed an invention in which an adverse effect due to an internal short circuit is minimized by separating with a member (such as a fuse). However, the present invention does not suppress the internal short circuit itself, and causes an internal short circuit, and the electrode area is lost by the amount of the separated small section. As a result, the battery capacity decreases steadily. There is a problem in that it does not improve.

On the other hand, it is considered that the internal short-circuit is caused by remarkable volume expansion due to atomization of the negative electrode lithium by repeated charge and discharge. In other words, if the separator is compressed and becomes thin due to the volume expansion of the lithium deposited on the negative electrode side, the separator may be damaged in severe cases, or may be damaged, or may be abnormally deposited into the micropores of the separator in search of a space where lithium is deposited, and this may be the positive electrode. It is considered that the negative electrode and the positive electrode come into electrical contact with each other, resulting in a short circuit.

Therefore, a proposal has been made to prevent internal short circuit by suppressing volume expansion. For example,
Japanese Patent Application Laid-Open No. 52-5423 discloses a technique of employing a lithium-aluminum alloy as a negative electrode material, but has not yet been put to practical use. Japanese Patent Application Laid-Open No. 64-76668 discloses a technique of buffering the volume expansion by disposing an activated carbon fiber layer on the back side of the positive electrode of a coin-type battery. However, the present invention has a problem in that it can be used only for a battery having a single-layer structure such as a coin-type battery, and cannot be used for a multiplex structure such as a winding or a laminated structure.

[0008]

The present invention focuses on the fact that the above-mentioned internal short-circuit problem is caused by abnormal deposition in the micropores of the separator due to the volume expansion of lithium deposited on the negative electrode side and reaching the positive electrode. The problem to be solved is to prevent internal damage to the separator and abnormal deposition of lithium in a lithium metal secondary battery having a laminated electrode structure consisting of a positive electrode, a separator, and a negative electrode, to suppress an internal short circuit, and to prolong the life of the battery. It is assumed that.

[0009]

According to the first aspect of the present invention, there is provided a buffer gap formed between a negative electrode or a positive electrode and a separator by depositing lithium on a negative electrode surface. To prevent separator damage and abnormal deposition of lithium to prevent internal short circuits,
The life of the battery can be extended.

[0010] According to the means described in claim 2, which is a preferred embodiment, the buffer space for accommodating lithium precipitated on the surface of the negative electrode is reliably formed and held by the insulating structural member. In the case where the insulating structural member is disposed between the positive electrode and the separator and a buffer gap is formed between the positive electrode and the separator, when lithium is deposited on the negative electrode surface, the deposited lithium pushes the separator to press the buffer gap. Moves from the positive electrode side to the negative electrode side, and lithium deposited on the negative electrode surface is stored in a buffer space formed between the negative electrode and the separator. The configuration of arranging the insulating structural members in this way is
Since it is sufficient to arrange the insulating structure member not on the negative electrode made of metal lithium that cannot be handled in the air because it is oxidized, but on the positive electrode made of lithium manganese oxide that can be handled in the air, The production is much easier than in the case where the insulating structural member is arranged between the negative electrode and the separator.

According to a preferred aspect of the present invention, lithium deposited on the surface of the negative electrode is deposited and stored in holes or voids of the insulating structure member. The thickness of this insulating structural member is easy to control, and its manufacture is relatively easy. According to the means described in claim 4, which is a preferred embodiment, the buffer space for accommodating lithium deposited on the negative electrode surface is formed and held by the concave-convex structure of the separator, thereby avoiding an increase in the number of components. Can be easily manufactured.

According to the means described in claim 5, which is a preferred embodiment, buffer voids for accommodating lithium precipitated on the surface of the negative electrode are securely formed and held on both sides of the negative electrode by the insulating structural members. In the configuration in which the insulating structural members are arranged as described above, since the insulating structural members may be arranged for the two separators, the manufacturing is relatively easy. According to the means of claim 6, lithium precipitated on the surface of the negative electrode is stored in the pores of the porous layer of the separator, so that an internal short circuit can be suppressed and the life of the battery can be extended. Since there is no need to add new components to the conventional electrode configuration including the positive electrode, the separator, and the negative electrode,
It can be manufactured as easily as a conventional electrode.

According to the means described in claim 7, which is a preferred embodiment, an easy manufacturing method can be adopted for manufacturing the separator. Claims 8 and 9, which are preferred embodiments
According to the means described in (1), the capacity of the battery can be increased, and the internal short circuit can be suppressed by preventing the damage of the separator and abnormal deposition of lithium, and the life of the battery can be extended.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1 FIG. 1 is a perspective view of a winding electrode of a metal lithium secondary battery according to this embodiment, and FIG. 2 is a cross-sectional view of the winding electrode in a width direction.

1 and 2, reference numeral 1 denotes a positive electrode in which a positive electrode active material such as lithium manganese oxide is applied to both surfaces of a current collector made of aluminum foil by application or vapor deposition, and 2 denotes polyethylene or polypropylene. The separator 3 is a negative electrode having metallic lithium or an alloy thereof pressed on both sides of a current collector made of copper foil, and the separator 4 is a separator 2.
A spacer (insulating structure member) made of an insulating material inserted to provide a buffer space 4a between the anode and the negative electrode 3, 5 is a positive electrode lead for extracting current from the positive electrode 1, and 6 is a negative electrode lead for extracting current from the negative electrode 3. is there. Also, in FIG.
Reference numeral 7 denotes metallic lithium deposited on the surface of the negative electrode 3.

The winding electrode of this metal lithium secondary battery is composed of a set of electrode constituent units formed by sequentially laminating respective members of a separator 2, a positive electrode 1, a separator 2, a spacer 4, a negative electrode 3, and a spacer 4. It has a so-called spiral or wound electrode structure wound up in a long length. The spacers 4 are located at both axial ends of the separator 2 and the negative electrode 3, and are arranged in a strip shape along the longitudinal direction of the separator 2 and the negative electrode 3. Therefore, even when the four members of the positive electrode 1, the separator 2, the negative electrode 3, and the separator 2 are wound as one unit, a buffer space 4 a having a substantially constant distance is formed between the separator 2 and the negative electrode 3.

As a result, even if the negative electrode lithium is atomized by repeated charge and discharge and the volume is expanded, the deposited lithium presses the separator 2 or the separator 2 is not filled until the buffer space 4a is filled with the expanded precipitated lithium. Abnormal precipitation in the micropores does not reach the positive electrode 1. As a result, an internal short circuit can be suppressed, and the cycle life can be improved.

Actually, a trial production of a metallic lithium secondary battery having a cylindrical wound structure electrode with this configuration was performed, and the results of comparing the cycle life with a conventional structure (without a buffer gap) were shown in FIGS. 9 and 10.
Shown in The size of the electrode of the prototype battery is 50 mm wide × about 1200 mm long, and the outer diameter when wound is about 32 mm. Lithium manganese oxide was used as the positive electrode active material, metallic lithium was used as the negative electrode active material, and 30 μm thick polyethylene was used as the separator. The spacer 4 has a thickness of about 4
A 0 μm polypropylene tape was used.

FIG. 9 shows the results of the cycle characteristic test of the battery capacity in comparison with the design capacity. The test was performed under the conditions that the total capacity that can be taken out using the entire operating voltage range in the first cycle was measured, and then charging and discharging were repeated at 80% of the designed capacity in the second cycle and thereafter. FIG. 10 shows the charge / discharge efficiency, that is, the ratio between the discharge capacity and the charge capacity in each cycle. When a short circuit occurs, the difference between the charge capacity and the discharge capacity increases, so that the charge / discharge efficiency decreases.

9 and 10, the charge / discharge efficiency of the conventional structure, that is, the electrode battery without buffer voids (a), suddenly decreases due to an internal short circuit from the fifth cycle, and the capacity also sharply decreases in the eighth cycle. have done. On the other hand, the capacity and charge / discharge efficiency of the separator / negative-spacer-inserted battery (b) were reduced at least after 22 cycles, and the effect of improving the life was clearly observed.

Embodiment 2 FIG. 3 is a perspective view of a winding electrode of a lithium metal secondary battery according to this embodiment, and FIG. 4 is a cross-sectional view of the winding electrode in a width direction. The winding electrode of the metal lithium secondary battery of this embodiment is the same as that of the first embodiment.
(Insulating structural member) 4 for forming the buffer space 4a.
Is inserted not between the separator 2 and the negative electrode 3 but between the positive electrode 1 and the separator 2. In FIG. 4, 7 denotes metallic lithium deposited on the surface of the negative electrode 3 as in FIG.

In the structure of this embodiment, a gap is formed between the positive electrode 1 and the separator 2 at the beginning of assembly, but the separator 2 is bent toward the positive electrode 1 as shown in FIG. Thus, the expanded lithium can be stored between the separator 2 and the negative electrode 3.
The same effect as the separator / negative electrode spacer insertion structure as described above can be obtained.

The feature of this structure is that it is easier to manufacture than that of the first embodiment. That is, in the case of the first embodiment, the spacers 4 must be arranged on the negative electrode 3 of metallic lithium which can be handled only under an inert gas such as argon because it is oxidized in the air. Extremely difficult. However, in the case of this embodiment, since the spacers 4 may be arranged on the positive electrode 1 made of lithium manganese oxide or the like that can be handled in the air, the manufacture is much easier.

Also in this configuration, a metallic lithium secondary battery having a wound structure electrode was actually manufactured as a trial, and the cycle life was evaluated. The results are shown in FIGS. 9 and 10 (c). As can be seen from FIGS. 9 and 10, in this configuration, no significant reduction in the capacity and charge / discharge efficiency was observed even at 41 cycles, and the effect of improving the life over the structure of Example 1 was confirmed.

In the first embodiment and the second embodiment,
The method of inserting the spacer 4 between the separator 2 and the negative electrode 3 or the positive electrode 1 has been described. In these methods, what is actually used as the spacer 4 is an insulating tape having a thickness of several tens of μm. In addition to this, as shown in FIG. By doing
Spacers 4 protruding from the surface of the separator 2 can be integrally formed at both ends of the separator 2. In this case, the thickness dimension of the spacer 4 can be appropriately changed by folding the end of the separator 2 twice or more.

Further, the separator 2 having the uneven structure on one surface side by forming the spacer 4 in this manner is arranged such that the spacer 4 is located between the separator 2 and the negative electrode 3 in FIG. On the contrary, the spacer 4 may be arranged so as to be located between the separator 2 and the positive electrode 1. Further, as a method of securing a necessary buffer space by volume expansion at the time of depositing lithium as the aim of the present invention, the following method is further provided.

Embodiment 3 FIG. 6 is a perspective view of a winding electrode of a metal lithium secondary battery according to this embodiment, and FIG. 7 is a cross-sectional view of the winding electrode in a width direction. The winding electrodes of the metal lithium secondary battery of the present embodiment include a separator 2, a positive electrode 1, a separator 2, an insulating structural member 8, a negative electrode 3,
It has a structure in which a set of electrode constituent units formed by sequentially laminating the respective members of the insulating structural member 8 is elongated and wound. That is, a porous insulating structure member 8 such as a nonwoven fabric is inserted between the separator 2 and the negative electrode 3.

According to this configuration, lithium deposited on the surface of the negative electrode 3 can be stored in the innumerable voids in the insulating structural member 8. The feature of this configuration is that it is easier to manufacture and the thickness is easier to manage than the configuration in which the spacer 4 is inserted as in the first and second embodiments. Also in this configuration, a battery was actually manufactured and the cycle life was evaluated. The porous insulating structural member 8 has a thickness of about 24
A nonwoven fabric of 0 μm was used. The results are shown in FIG. 9 and FIG.
0 (d). In this configuration, although the capacity is slightly reduced, the charge / discharge efficiency is hardly reduced until at least 41 cycles, and it can be said that the effects of short-circuit suppression and life improvement can be confirmed.

Embodiment 4 FIG. 8 is a cross-sectional view in the width direction of a winding electrode of a lithium metal secondary battery according to this embodiment. In FIG. 8, reference numeral 4 denotes a separator 2 sandwiching the negative electrode 3.
It is a spacer that is inserted between the competitors and made of an insulating material thicker than the negative electrode 3. In the winding electrode of the present embodiment, the width of the negative electrode 3 is made smaller than that of the positive electrode 1, and the thickness of the negative electrode 3 and the separator 2 above and below the negative electrode 3 are interposed between the two separators 2 on the upper and lower sides of the negative electrode 3. In this configuration, spacers 4 having a thickness equal to the sum of the distances of the buffer voids 4 a provided therebetween are inserted on both outer sides of the negative electrode 3. That is, in this wound electrode, buffer voids 4a for accommodating metal lithium 7 deposited on the surface of the negative electrode 3 are provided on both sides of the negative electrode 3 disposed between the pair of positive electrodes 1 with the separator 2 interposed therebetween. Is formed.

When the lithium is deposited on the surface of the negative electrode 3, the wound electrode according to the present embodiment is in a state in which the lithium negative electrode 3, which has been expanded and thickened, is accommodated in a space between the two separators 2. Become. Therefore, the internal short circuit can be suppressed by preventing the separator 2 from being damaged and the lithium from being abnormally precipitated, and the life of the battery can be prolonged. In addition, the winding electrode of the present embodiment can be relatively easily manufactured because the spacers 4 may be disposed for the two separators 2.

Embodiment 5 FIG. 11 is a perspective view of a winding electrode of a lithium metal secondary battery according to this embodiment, and FIG.
FIG. 3 is a cross-sectional view in the width direction of the winding electrode. The winding electrode of the metal lithium secondary battery according to the present embodiment is formed by winding a set of electrode constituent units formed by laminating the respective members of the separator 2, the positive electrode 1, the separator 2, and the negative electrode 3 in order. It is of a structure. That is, the separator 2 having a buffer space for accommodating the deposited lithium is connected to the positive electrode 1 and the negative electrode 3.
The structure is the same as that of the conventional wound electrode except for the separator 2.

FIG. 13 shows a cross-sectional view of the separator 2 in the width direction and a distribution of the porosity which is the largest feature of the separator 2. The separator 2 has a base layer 2a having a low porosity (for example, about 30 to 40%) equivalent to that of a separator used in a normal lithium secondary battery on the positive electrode 1 side, and has a base layer 2a on the negative electrode 3 side. It has a porous layer 2b having a high porosity (about 80%) equivalent to that of the nonwoven fabric of Example 3. The portion of the porous layer 2b close to the base layer 2a is continuous with the base layer 2a such that the porosity gradually decreases as approaching the base layer 2a.

Thus, the base layer 2a on the positive electrode 1 side functions as a normal separator, and the pores in the porous layer 2b on the negative electrode 3 side precipitate on the surface of the negative electrode 3 as in the nonwoven fabric of Example 3. Functions as a buffer space for storing lithium.
Therefore, if such a separator 2 is used, no new component is added to the conventional electrode configuration including the positive electrode, the separator, and the negative electrode. The life can be improved.

As a method of manufacturing the separator 2 of this embodiment, a polyethylene or polypropylene sheet-like base material is formed by stretching a temperature gradient in the thickness direction, or in accordance with the porosity distribution. It is possible to adopt a method such as forming by stacking and forming while gradually changing the diameter of the fiber or the gap of the fiber used for the nonwoven fabric or the like.
Can be easily manufactured.

Further, the distribution of the porosity of the porous layer 2b does not necessarily have to be continuously continuous in a stepwise manner as in this embodiment, but may be changed stepwise as in the sixth embodiment. You may. [Embodiment 6] FIG. 14 is a cross-sectional view in the width direction of a separator 2 according to the present embodiment, and shows a distribution of porosity which is the greatest feature of the present separator 2 ".

The separator 2 of this embodiment is formed by laminating and integrating nonwoven fabrics having different porosity so that the porosity increases from the positive electrode side to the negative electrode side. That is,
On the positive electrode side, there is a base layer 2a having a low porosity (for example, about 30 to 40%) equivalent to that of a separator used in a normal lithium secondary battery, and on the negative electrode side, a void higher than the base layer 2a is provided. It has a porous layer 2b having a porosity. Porous layer 2b
Is one or several different porosity (e.g. 50
%, 70%, 80%) are arranged so that the porosity gradually increases from the positive electrode side to the negative electrode side.

Thus, the separator 2 of this embodiment is
The base layer 2a on the positive electrode side functions as a normal separator,
The porous layer 2b on the negative electrode side functions as a buffer space for accommodating lithium precipitated on the negative electrode surface. Therefore, even when such a separator 2 is used, similar to the fifth embodiment,
Since no new component is added to the conventional electrode configuration including the positive electrode, the separator, and the negative electrode, the fabrication is as easy as the conventional electrode, and the short circuit can be suppressed and the life can be improved.

As a method of manufacturing the separator 2 of the present embodiment, a method of fusing the boundary surfaces of the laminated non-woven fabrics having different porosity with heat or integrating them with an adhesive is adopted. Thus, the separator 2 can be easily manufactured. Although the embodiments of the wound electrode battery according to the present invention have been described above, the scope of the present invention is not limited thereto, and the present invention is basically applied to a laminated structure battery, a single-layer coin type battery or a sheet type battery. Since the basic cross-sectional structures are the same, the same effects can be obtained by applying them to them.

[Brief description of the drawings]

FIG. 1 is a perspective view of a winding electrode of a metal lithium secondary battery according to Embodiment 1 of the present invention.

FIG. 2 is a cross-sectional view in the width direction of a winding electrode of the metal lithium secondary battery according to Embodiment 1 of the present invention.

FIG. 3 is a perspective view of a winding electrode of the metal lithium secondary battery according to Embodiment 2 of the present invention.

FIG. 4 is a cross-sectional view in the width direction of a winding electrode of the lithium metal secondary battery according to Embodiment 2 of the present invention.

FIG. 5 is an explanatory view showing one embodiment of a method of manufacturing a spacer according to the present invention.

FIG. 6 is a perspective view of a wound electrode of a lithium metal secondary battery according to Embodiment 3 of the present invention.

FIG. 7 is a cross-sectional view in the width direction of a winding electrode of a lithium metal secondary battery according to Embodiment 3 of the present invention.

FIG. 8 is a cross-sectional view in the width direction of a winding electrode of a metal lithium secondary battery according to Example 4 of the present invention.

FIG. 9 is a graph showing the results of measuring the cycle characteristics of the capacity of the rechargeable metal lithium secondary battery in the test;
(A) is a conventional electrode battery (no void), (b) is a battery with a separator / negative electrode spacer inserted, (c) is a battery with a separator / positive electrode spacer inserted, and (d) is a measured result of a battery with a separator / negative electrode nonwoven fabric inserted. Is shown.

10 is a graph showing measurement results of cycle characteristics of charge and discharge efficiency of a roll-up type metal lithium secondary battery in a test, wherein (a), (b), (c), and (d) are the same as FIG. is there.

FIG. 11 is a perspective view of a wound electrode of a lithium metal secondary battery according to Embodiment 5 of the present invention.

FIG. 12 is a cross-sectional view in the width direction of a wound electrode of a lithium metal secondary battery according to Example 5 of the present invention.

FIG. 13 is an enlarged view of a cross section in a width direction of a separator according to Embodiment 5 of the present invention and a distribution diagram of porosity.

FIG. 14 is an enlarged view of a cross section in a width direction of a separator according to Example 6 of the present invention and a distribution diagram of porosity.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Positive electrode 2 ... Separator 2a ... Base layer 2b
... porous layer 3 ... negative electrode 4 ... spacer (insulating structural member) 4a ...
Buffer void 5 ... Positive electrode lead 6 ... Negative electrode lead 7 ... Metal lithium 8 ... Insulation structural member

Claims (9)

[Claims] 1. A metal lithium secondary battery in which a negative electrode using lithium or a lithium alloy as a negative electrode active material and a positive electrode made of a chargeable / dischargeable substance are arranged to face each other with a separator interposed therebetween, wherein: A rechargeable lithium metal battery having a buffer space for accommodating lithium deposited on the surface of the negative electrode between the separator and a separator. 2. The rechargeable lithium metal battery according to claim 1, wherein an insulating structural member for forming and holding the buffer gap is provided between the negative electrode or the positive electrode and the separator. 3. The rechargeable lithium metal battery according to claim 2, wherein the insulating structural member has many communicating holes and voids therein. 4. The metallic lithium secondary battery according to claim 1, wherein said separator has at least partially an uneven structure for forming and holding said buffer space on at least one of said negative electrode side and said positive electrode side. battery. 5. A structure in which two separators sandwiching the negative electrode have a wider width than the negative electrode, and an insulating structural member thicker than the negative electrode is inserted between both outer sides of the negative electrode and both ends of the separator. The metal lithium secondary battery according to claim 1, comprising: 6. A metal lithium secondary battery in which a negative electrode using lithium or a lithium alloy as a negative electrode active material and a positive electrode made of a chargeable / dischargeable material are arranged to face each other with a separator interposed therebetween. A metal lithium secondary battery, comprising a porous layer having a high porosity for storing lithium deposited on the surface of the negative electrode on a surface facing the negative electrode. 7. The rechargeable lithium metal battery according to claim 6, wherein the porous layer is formed such that the porosity gradually increases from the positive electrode side to the negative electrode side. 8. The rechargeable lithium metal battery according to claim 1, wherein the negative electrode, the separator, and the positive electrode have a spiral structure in which the negative electrode, the separator, and the positive electrode are stacked and wound. 9. The metal lithium secondary battery according to claim 1, wherein the negative electrode, the separator, and the positive electrode have a structure in which one or more layers are stacked.