JP2006012788A - Lithium ion secondary battery and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery enhancing safety against danger derived from internal short circuit and overcharge. <P>SOLUTION: In the lithium ion secondary battery equipped with a positive electrode comprising a composite lithium oxide, a negative electrode, a separator, and a nonaqueous electrolyte, at least one of the positive electrode and the negative electrode has a porous film containing inorganic oxide fillers and a binder on the surface facing the other electrode, and the surface of the electrode partially has a projecting part. The projecting part may be a projecting part installed in the porous film itself, or may be a projecting part formed by installing the projecting part in a mix layer. Furthermore, the separator can be installed. Instead of the above porous film, a porous film can be installed in the separator. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a lithium ion secondary battery excellent in thermal stability during overcharge and a method for producing the same.

  In recent years, small and light portable devices have been widely used, and lithium ion secondary batteries used as power sources have been required to have high safety and reliability in combination with high energy density. .

  If a lithium ion battery is pierced with sharp conductive projections, such as nails, or if foreign particles with conductivity, such as large iron powder, are mixed in the manufacturing process, an internal short circuit of the battery will occur and its energy density Overheating occurs because of the height. Here, when only a microporous thin film sheet made of polyolefin such as polyethylene is used alone as a separator considering only the retention of the electrolytic solution, the microporous thin film sheet is thermally shrunk at a relatively low temperature, The short circuit part expands and the malfunction of inducing further overheating arises.

Therefore, as a technique for improving safety related to short circuit, a method of forming a porous film on an electrode has been proposed (see Patent Document 1). It has also been proposed to improve the discharge capacity by causing the porous film to function as an electrolyte solution holding layer (see Patent Document 2).
Japanese Patent Laid-Open No. 7-220759 JP 2002-8730 A

  When a conventional porous membrane is used in combination with a microporous thin film sheet, overheating due to an internal short circuit can be suppressed. However, it does not prevent overheating when overcharging exceeding the design capacity is performed.

Here, overcharge will be described in detail. If the charging power supply circuit breaks down, the battery will not stop charging even if it exceeds the design capacity, causing an overcharge reaction. Due to the overcharge reaction, excess lithium is released from the positive electrode active material. In particular, in the case of LiCoO ₂ , since the crystal structure of the active material collapses and generates intense heat, overheating of the entire battery is significantly promoted.

  There are two main methods for suppressing overheating due to overcharging. One is a method in which the pores of the separator are closed by melting at a relatively low temperature to lose ionic conductivity. The other is a method in which a partial short-circuit portion is intentionally formed between the positive and negative electrodes, and the apparent overcharge current is replaced with a short-circuit current. In order to embody the latter method, it is necessary to deposit conductive chemical species, specifically lithium needle crystals (dendrites) deposited from the negative electrode, or transition metals dissolved from the positive electrode active material and deposited on the negative electrode. Will be utilized.

  However, since the conventional porous film is uniformly formed on the surface of the flat electrode active material, the reactivity of the electrode becomes uniform. Although it is a preferred form in the normal charge and discharge range, from the viewpoint of suppressing the overcharge reaction, after the overcharge reaction of all the parts of the electrode has progressed considerably, the formation of a short-circuited portion due to the conductive precipitate occurs, It is impossible to suppress overheating.

  The present invention solves the above-mentioned problem, and improves the safety related to internal short circuit, and deposits the above-mentioned conductive chemical species at a stage where the progress of overcharge reaction is shallow, thereby preventing the progress of overcharge. An object is to provide an ion secondary battery.

The present invention provides a positive electrode made of a composite lithium oxide, a negative electrode made of a material capable of reversibly occluding and releasing lithium, and a non-aqueous electrolyte, and a lithium separator provided with a normal separator that separates the positive electrode and the negative electrode. The present invention relates to a secondary battery and a lithium secondary battery not provided with a separator, wherein at least one of the positive electrode and the negative electrode has a porous film containing an inorganic oxide filler and a binder on the surface facing the other electrode. And the electrode surface partially has a convex portion.
Furthermore, the present invention is a lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte comprising a composite lithium oxide, wherein at least one surface on the separator is bound with an inorganic oxide filler. It has the porous film containing an agent, The said porous film has the convex part formed partially, It is characterized by the above-mentioned.

The present invention also provides a lithium secondary battery including a normal separator that separates the positive electrode and the negative electrode, and a lithium ion battery that does not include a separator. In the secondary battery, one of the positive electrode and the negative electrode has a flat porous film containing an inorganic oxide filler and a binder on the surface facing the other electrode, and the mixture layer of the other electrode is Provided is a lithium ion secondary battery characterized in that a convex portion is partially provided on a surface facing the one electrode.
Furthermore, the present invention is a lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte made of composite lithium oxide, wherein at least one side of the separator has an inorganic oxide filler and a binder. The lithium ion secondary battery is characterized in that the electrode mixture layer facing the porous film has a convex part on the surface thereof.

  ADVANTAGE OF THE INVENTION According to this invention, the lithium ion secondary battery which improved the safety | security regarding both an internal short circuit and overcharge can be provided.

  In the lithium ion secondary battery of the present invention, at least one of the positive electrode and the negative electrode has a porous film containing an inorganic oxide filler and a binder on the surface facing the other electrode, and the surface of the electrode is partially Has a convex part.

In preferable embodiment, the said convex part consists of a convex part partially formed in the surface of the said porous film.
A method for producing such an electrode includes a step of applying a porous film-forming coating on the surface of an electrode mixture layer containing an electrode active material, a conductive agent and a binder, and drying to form a porous film, and On the porous film, there is a step of forming a convex portion by applying a porous film-forming paint in a certain pattern and drying.
Another method for producing such an electrode is to apply a coating for forming a porous film on the surface of an electrode mixture layer containing an electrode active material, a conductive agent and a binder by partially increasing the discharge rate. It has the process of forming the porous film which has a convex part partially by a construction method, for example, a die coater construction method.

In another preferred embodiment, the mixture layer of the electrode having the porous film partially has a convex portion.
The method of manufacturing this electrode includes a step of marking a convex portion on the surface of an electrode mixture layer containing an electrode active material, a conductive agent and a binder, and a porous surface on the surface of the electrode mixture layer stamped with the convex portion. A step of forming a porous film by applying and drying a film-forming coating material;

  In another embodiment of the present invention, one of the positive electrode and the negative electrode has a flat porous film containing an inorganic oxide filler and a binder on the surface facing the other electrode, and the mixture of the other electrode The layer partially has a convex portion on a surface facing the one electrode.

According to the present invention, a gap is formed between the convex portion of the porous film or electrode and the opposing electrode. Since this gap can hold more electrolytic solution than other parts, the exchange of ions is activated. At this site, the overcharge reaction proceeds intensively at the time of overcharge, and conductive chemical species are deposited before the overcharge as the whole battery progresses too much. For this reason, it is possible to suppress the progress of overcharging and avoid the problem of overheating.
Furthermore, if a material that generates a conductive polymer due to a high potential or temperature during overcharge is added to the inside of the battery, the timing of deposition of the conductive chemical species can be further advanced.
In addition, the effect mentioned above is similarly expressed even if the porous film is formed not on the electrode but on the separator.

Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.
First, the porous membrane which is the main component of the present invention will be described.
An insulating inorganic oxide is used as a filler in the porous film. Various resin fine particles are also generally used as fillers. However, as described above, heat resistance is required, and in addition, it is necessary to maintain high electrochemical stability within the range of use of the lithium ion battery and high resistance to dissolution in the electrolytic solution. An inorganic oxide is selected as a material that satisfies these requirements and is suitable for coating. Specific examples include alumina powder and silica powder. In particular, alumina is preferable from the viewpoint of electrochemical stability.

  The content of the inorganic oxide in the porous film is preferably 50% by weight or more and 99% by weight or less. When the content of the inorganic oxide is excessively less than 50% by weight, it is difficult to control the pore structure constituted by the gaps between the inorganic oxide particles. When the content of the inorganic oxide exceeds 99% by weight, the adhesiveness of the porous film to the electrode is lowered, and thus loss of function due to dropping off is caused. A plurality of these inorganic oxides may be mixed and used. Alternatively, the porous film may be multilayered and different inorganic oxides may be used for each. In particular, the use of a mixture of the same kind of inorganic oxides having different median diameters is one of preferred embodiments for obtaining a denser porous film.

The binder for fixing the porous membrane filler is not particularly limited as long as it is stable at the electrode potential for forming the porous membrane, and those usually used for the positive electrode or the negative electrode can be used.
The thickness of the porous film is not particularly limited, but when the separator is not provided between the positive and negative electrodes, it is preferably 0.5 to 30 μm from the viewpoint of maintaining the design capacity while exhibiting the effect of the porous film described above. More preferably, it is 1-20 micrometers. Moreover, when providing a separator, it is preferable that the total thickness of a separator and a porous membrane is 5.5-60 micrometers, More preferably, it is 9-45 micrometers. The thickness of the porous film referred to here is an average value excluding the convex portion when the porous film itself has a partial convex portion. The thickness can be measured by a thickness gauge, a surface roughness measuring machine, an SEM photograph of an electrode cross section, or the like.

  In order to improve the overcharge stability, which is an effect of the present invention, it is necessary to provide a gap between the electrodes that can hold the electrolytic solution more than other parts. The gap appears due to a partial convex portion, and the height is preferably 1 to 20 μm. The implementation measures are as follows.

  The first method is a method in which a porous film having a convex portion is bonded and formed on at least one of a positive electrode and a negative electrode or a separator. As a method for forming convex portions partially on the porous film, after forming a normal flat porous film by a method such as a die coater or gravure coater, the die coater or gravure coater, or intaglio transfer printing or screen This is a method of forming a convex portion on a porous film using printing or the like. Alternatively, a method of forming a porous film partially having a convex part by applying a porous film paint on a flat electrode mixture layer or separator by increasing the discharge amount in a pulse manner with a die coater. is there.

  The second method is to form a convex part on at least one of the positive electrode and negative electrode electrode mixture layers, and to form a porous membrane-integrated electrode having a convex part. In this method, a porous film having substantially the same thickness is formed by bonding. Examples of a method for forming a convex part partially on the electrode mixture layer include rolling or engraving using a rotating roller having a surface provided with irregularities. The unevenness of the rotating roller includes, for example, a textured surface, a rough surface, a groove (with a groove such as parallel, perpendicular or oblique to the rotation direction), embossing, a honeycomb shape, and a protrusion. Examples of the material of the rolling roller surface include metals, ceramics, and rubber. Furthermore, an intaglio film can be installed between a roller and an electrode, and a convex part can also be formed partially.

  The third method is a method in which a flat porous film is bonded and formed on one of the positive electrode and the negative electrode or on the separator, and a convex portion is partially formed on the electrode mixture layer facing the porous film. As a method for forming a flat porous film, the first method can be used. The second method can be used as a method of partially forming a convex portion in the electrode mixture layer.

  The ratio of the convex part pattern to the convex part and the relatively concave part may be large. Further, any position, shape, and pattern on the electrode plate plane may be used. A specific uneven pattern is shown in FIGS.

  The electrode plate 10 shown in FIGS. 1A and 1B is an example in which a porous film 14 having convex portions 15 is formed on the surface of the electrode mixture layer 13. As described above, after forming the porous film, the convex portion may be formed, or the porous film may be formed integrally with the convex portion. Here, the convex portions 15 are provided at equal intervals in the longitudinal direction of the electrode plate. 11 represents an electrode core, and 12 represents a current collecting lead.

The electrode plate 20 shown in FIGS. 2A and 2B is an example in which a convex portion 27 is provided on an electrode mixture layer 23 and a porous film 24 having substantially the same thickness is formed on the mixture layer 23. A portion 25 corresponding to the convex portion of the mixture layer 23 is a convex portion.
The electrode plate 30 shown in FIGS. 3A and 3B is an example in which a porous film 34 having convex portions 35 extending in the longitudinal direction of the electrode is formed on the mixture layer 13.
The electrode plate 40 shown in FIGS. 4A and 4B is an example in which a convex portion 47 extending in the longitudinal direction is formed on the mixture layer 43 and a porous film 44 is formed on the mixture layer. A portion corresponding to the convex portion of the mixture layer 43 is a convex portion 45.

  The electrode plate 50 shown in FIGS. 5A and 5B is obtained by providing convex portions 57 on the mixture layer 53 at equal intervals in the longitudinal direction. As shown in FIG. 6, this electrode plate 50 uses an electrode plate 60 in which a uniform porous film 64 is formed on a mixture layer 63 as a counter electrode. In FIG. 6, 61 is an electrode core, and 62 is a current collecting lead.

  As the positive electrode active material used in the present invention, lithium cobaltate and a modified product thereof, for example, a solid solution of aluminum or magnesium, lithium nickelate and a modified product thereof, for example, a part of nickel substituted with cobalt, Examples include composite oxides such as lithium manganate and modified products thereof. Examples of the binder include polytetrafluoroethylene, modified acrylonitrile rubber particle binder (for example, BM-500B manufactured by Nippon Zeon Co., Ltd.), carboxymethyl cellulose having a thickening effect, polyethylene oxide, soluble modified acrylonitrile rubber (for example, Japan BM-720H manufactured by Zeon Co., Ltd.) and the like, and a single polyvinylidene fluoride having both binding properties and thickening properties and a modified product thereof may be used alone or in combination. As the conductive agent, acetylene black, ketjen black, and various graphites may be used alone or in combination.

  As the negative electrode active material, various natural graphites and artificial graphites, silicon-based composite materials such as silicide, and various alloy composition materials including tin can be used. As the binder, various binders such as polyvinylidene fluoride and modified products thereof can be used. From the viewpoint of improving lithium ion acceptability, it is more preferable to use SBR and a modified product thereof together with a cellulose resin such as carboxymethyl cellulose or to add a small amount.

About a separator, if it is a composition which can endure the use range of a lithium ion battery, it will not specifically limit. Generally, a microporous film of an olefin resin such as polyethylene or polypropylene is used singly or in combination. The thickness of the separator is not particularly limited, but is preferably 5 to 30 μm from the viewpoint of maintaining the design capacity while exhibiting the effect of the porous film described above. More preferably, it is 8-25 micrometers.
In addition, in order to form a short circuit part, an overcharge additive such as a cycloalkylbenzene derivative is added to the electrolyte so that a decomposition product having conductivity in an overcharged state is generated and this causes a slight short circuit through the separator. It is more effective if it is done together.

The electrolyte may be any of various lithium salts such as LiPF ₆ and LiBF ₄ as a solute. As the solvent, ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, or the like can be used alone or in combination. Furthermore, in order to form a good film on the positive and negative electrodes, it is also possible to add vinylene carbonate or a modified product thereof.

  Here, in order to improve the overcharge safety that is a feature of the present invention, cyclohexylbenzene, biphenyl, diphenyl ether, cyclopentylbenzene, pyrrole, N-methylpyrrole, thiophene, furan, indole, 3-chlorothiophene, 3-bromothiophene. , 3-fluorothiophene, 1,2-dimethoxybenzene, 1-methyl-3-pyridinium tetrafluoroborate, cumene, 1,3-diisopropylbenzene, 1,4-diisopropylbenzene, 1-methylpropylbenzene, 1,3 It is effective to add -bis (1-methylpropyl) benzene, 1,4-bis (1-methylpropyl) benzene or the like to the electrolytic solution. These compounds are preferable from the viewpoint of making the effects of the present invention remarkable because they have an action of decomposing during overcharge and promoting the precipitation of conductive chemical species between the positive and negative electrodes.

Examples of the present invention will be described below.
<< Comparative Example 1 >>
First, the positive electrode plate was produced as follows.
3 kg of lithium cobaltate, 1 kg of a solution of polyvinylidene fluoride in N-methyl-2-pyrrolidone (hereinafter referred to as NMP) (PVDF # 1320 manufactured by Kureha Chemical Co., Ltd., 12 wt% solids), 90 g of acetylene black and an appropriate amount of NMP At the same time, the mixture was stirred with a double-arm kneader to prepare a positive electrode mixture paint. This paint is applied to both sides of a 15 μm thick aluminum foil, dried, rolled to a total thickness of 160 μm, and then inserted into a case of an 18650 cylindrical battery having a diameter of 18 mm and a height of 65 mm. The positive electrode plate was obtained by cutting and processing into lengths.

  On the other hand, the negative electrode plate comprises 3 kg of artificial graphite, 75 g of styrene-butadiene copolymer rubber particle binder (BM-400B (solid content: 40% by weight) manufactured by Nippon Zeon Co., Ltd.), 30 g of carboxymethyl cellulose and an appropriate amount of water. The mixture was stirred with a double arm kneader to prepare a negative electrode paint. This paint is applied to both sides of a 10 μm thick copper foil, dried, rolled to a total thickness of 180 μm, cut into a width and length that can be inserted into a 18650 cylindrical battery case, and processed into a negative electrode plate. Got.

These positive and negative electrode plates were spirally wound together with a separator made of a polyethylene microporous film having a thickness of 20 μm and inserted into the battery case. Next, 5.5 g of an electrolytic solution in which 1 mol / l of LiPF ₆ was dissolved in a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1: 3 was injected and sealed, and a 18650 cylindrical lithium ion battery was obtained. Produced.

<< Comparative Example 2 >>
970 g of alumina having a median diameter of 0.3 μm was stirred with a double-arm kneader together with 375 g of a polyacrylonitrile-modified rubber binder (BM-720H (solid content 8 wt%) manufactured by Nippon Zeon Co., Ltd.) and an appropriate amount of NMP. Then, a porous film paint was prepared. As shown in FIG. 6, this paint was applied to the positive electrode mixture of Comparative Example 1 by a gravure coater with a thickness of 5 μm on one side and dried. A battery was fabricated in the same manner as in Comparative Example 1 except for the above.

<< Comparative Example 3 >>
The porous film coating material of Comparative Example 2 was applied to the negative electrode mixture of Comparative Example 1 by a gravure coater and dried 5 μm thick on each side. A battery was fabricated in the same manner as in Comparative Example 1 except for the above.

Example 1
On the positive electrode produced in Comparative Example 2 and coated with a porous film, the porous film paint is further intermittently applied at a thickness of 5 μm, a width of 1 cm, and a coating pitch of 10 cm, as shown in FIGS. 1A and 1B. Thus, the porous film in which the convex part was partially formed was formed. A battery was fabricated in the same manner as in Comparative Example 1 except that this positive electrode was used.

Example 2
1A and 1B are shown in FIG. 1B by intermittently applying the porous film paint with a thickness of 5 μm, a width of 1 cm, and a coating pitch of 10 cm on the negative electrode prepared in Comparative Example 3 and coated with the porous film. Thus, the porous film in which the convex part was partially formed was formed. A battery was fabricated in the same manner as in Comparative Example 1 except that this negative electrode was used.

Example 3
By applying the porous film paint on the negative electrode produced in Comparative Example 1 with a die coater while increasing the discharge amount in a pulse manner, as shown in FIG. 1A and FIG. The formed porous film was formed. A battery was fabricated in the same manner as in Comparative Example 1 except that this negative electrode was used.

Example 4
When rolling the positive electrode plate produced in Comparative Example 1, by using a grooved rotary rolling roller, a convex portion having a height of about 5 μm was formed on the mixture layer as shown in FIGS. 2A and 2B. . The width of the convex portion was 1.5 cm, and the pitch was 9.5 cm. On top of that, the porous film paint was applied in a thickness of 5 μm to partially form convex portions. A battery was fabricated in the same manner as in Comparative Example 1 except that this positive electrode plate was used.

Example 5
When rolling the negative electrode plate produced in Comparative Example 1, by using a grooved rotary rolling roller, a convex portion having a height of about 7 μm was formed in the mixture layer as shown in FIGS. 2A and 2B. . The width of the convex portion was 1.5 cm, and the pitch was 9.5 cm. On top of that, the porous film paint was applied in a thickness of 5 μm to partially form convex portions. A battery was fabricated in the same manner as in Comparative Example 1 except that this negative electrode plate was used.

Example 6
As shown in FIG. 6, as shown in FIGS. 5A and 5B, using a positive electrode plate coated with a flat porous film as in Comparative Example 2 and a rotary rolling roller with a groove as in Example 4, A battery was fabricated in the same manner as in Comparative Example 1 except that a negative electrode plate having convex portions with a height of about 7 μm formed on the mixture layer was used.

Example 7
As in Comparative Example 3, a negative electrode plate coated with a flat porous film layer and a grooved rotary rolling roller as in Example 3 were used to form a convex portion having a height of about 5 μm on the mixture layer. A battery was produced in the same manner as in Comparative Example 1 except that the plate was used.

<< Examples 8 to 14 >>
A battery was produced using the electrode plate produced in the same manner as in Examples 1-7. However, as the electrolytic solution, 0.5 wt% cyclohexylbenzene and 1 mol / l LiPF ₆ were dissolved in a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1: 3. These batteries are referred to as Examples 8 to 14, respectively.

Example 15
The porous film paint of Comparative Example 2 was applied on the negative electrode mixture of Comparative Example 1 to a thickness of 10 μm on one side with a gravure coater and dried. On the formed porous film, the same porous film paint as described above was applied as shown in FIGS. 1A and 1B in the same manner as in Example 2 to partially form convex portions. A battery was fabricated in the same manner as in Comparative Example 1 except that this negative electrode was used and no separator was used.

Example 16
A battery was fabricated in the same manner as in Example 15 except that the thickness of the porous film was changed to 15 μm on one side.
Example 17
A battery was fabricated in the same manner as in Example 15 except that the thickness of the porous film was changed to 20 μm on one side.
Example 18
A battery was fabricated in the same manner as in Example 15 except that the thickness of the porous film was changed to 20 μm on one side.
Example 19
A battery was fabricated in the same manner as in Example 15 except that the thickness of the porous film was changed to 30 μm on one side.

Example 20
A battery was fabricated in the same manner as in Example 5, except that the thickness of the porous film to be coated on the negative electrode mixture layer on which the convex portion was formed was 20 μm on one side and the separator was removed.

<< Example 21 >>
The thickness of the porous film formed by applying and drying on the positive electrode mixture of Comparative Example 2 was changed to a thickness of 20 μm on one side. On the positive electrode, the same porous film paint as described above was applied to form a convex part partially. A battery was fabricated in the same manner as in Comparative Example 1 except that this positive electrode was used and no separator was used.

Example 22
The porous film paint of Comparative Example 2 was applied onto a separator made of a polyethylene microporous film having a thickness of 20 μm and dried with a gravure coater so as to have a thickness of 20 μm only on one side. On the porous film of this separator, the same porous film paint as described above is intermittently applied with a thickness of 5 μm, a width of 1 cm, and a coating pitch of 10 cm, whereby a porous film partially formed with convex portions is obtained. Formed. A battery was fabricated in the same manner as in Comparative Example 1 except that this separator was interposed between the positive and negative electrodes so that the porous film was opposed to the positive electrode and wound in a spiral shape.
The separator porous film may be opposed to the negative electrode.

<< Example 23 >>
The porous film paint of Comparative Example 2 was applied onto a separator made of a polyethylene microporous film having a thickness of 20 μm, and dried with a gravure coater so as to have a thickness of 20 μm only on one side. Further, a battery was fabricated in the same manner as in Comparative Example 1 except that the positive electrode plate having the convex portion prepared in Example 7 was used and the separator porous film was wound in a spiral shape so as to face the positive electrode.

The thicknesses of the recesses and the porous film of the electrodes used in the above comparative examples and examples were determined from SEM images obtained by polishing and photographing a cross section obtained by embedding an electrode plate in an epoxy resin. The capacity of the 18650 cylindrical battery produced as described above was about 1750 mAh.
Each of the batteries described above was charged and discharged for 3 cycles in a voltage range of 3.0 to 4.2 V at a constant current of 350 mA. The battery was subjected to an overcharge test while being discharged to 3.0V. In the test, overcharging was continuously performed for 3 hours at a constant current of 1225 mA at an environmental temperature of 25 ° C. In a commercially available battery, a sealing plate having a current interruption mechanism (CID) that operates by temperature, internal pressure, etc. is used as one of safety mechanisms. The effect was compared by the presence or absence of the CID operation, the charging depth at which the voltage drop started, and the maximum temperature of the battery under test. The results are shown in Table 1.

  An example of voltage behavior and temperature behavior during the 3-hour continuous overcharge test will be described with reference to FIG. Compared with the battery of Comparative Example 1, the battery of Example 1 has an internal short circuit where the overcharge depth is shallow and a voltage drop has begun. As described above, this is evidence that conductive chemical species are deposited between the positive and negative electrodes, causing an internal short circuit. Thus, an excessive increase in battery temperature can be suppressed by intentionally causing an internal short circuit during overcharging. Therefore, it is possible to avoid the high voltage and high temperature region that promotes the decomposition of the electrolytic solution, and it is possible to guarantee overcharge safety in a state where the final means of physical circuit disconnection called CID is left.

The results in Table 1 show this difference, and the maximum attainable temperature of Examples 1 to 14 was approximately 55 ° C. or less, so that CID operation could be avoided, whereas the maximum attainment temperature of Comparative Examples 1 to 3 was avoided. Since the temperature generally exceeded 65 ° C., overcharge was forced to be stopped with the help of the last means of CID.
From these results, it became clear that the present invention can provide a lithium ion secondary battery with improved safety and reliability during overcharge.

  The lithium ion secondary battery of the present invention is particularly useful as a portable power source that requires a high level of safety.

It is a top view of the electrode plate in one Example of this invention. 1B is a cross-sectional view taken along line 1B-1B 'of FIG. 1A. It is a top view of the electrode plate in the other Example of this invention. It is 2B-2B 'sectional view taken on the line of FIG. 2A. It is a top view of the electrode plate in the further another Example of this invention. It is 3B-3B 'sectional view taken on the line of FIG. 3A. It is a top view of the electrode plate in the other Example of this invention. FIG. 4B is a sectional view taken along line 4B-4B ′ of FIG. 4A. It is a top view of the electrode plate in the further another Example of this invention. FIG. 5B is a cross-sectional view taken along line 5B-5B 'of FIG. 5A. It is a top view of the electrode plate in the further another Example of this invention. It is a graph which shows the time-dependent change of the battery voltage and charging current in the overcharge test of the battery of the Example of this invention, and a comparative example.

Explanation of symbols

11, 61 Electrode plate core material 12, 62 Current collecting leads 13, 23, 43, 53, 63 Mixture layers 14, 24, 34, 44, 64 Porous membranes 15, 25, 35, 45 Protrusions 27, 47, 57 Convex part of the mixture layer

Claims (11)

  A lithium ion secondary battery comprising a positive electrode comprising a composite lithium oxide, a negative electrode, and a non-aqueous electrolyte, wherein at least one of the positive electrode and the negative electrode faces the other electrode and an inorganic oxide filler A lithium ion secondary battery comprising a porous film containing a binder and the electrode surface partially having a convex portion.   The lithium ion secondary battery according to claim 1, further comprising a separator between the positive electrode and the negative electrode.   The lithium ion secondary battery according to claim 1, wherein the convex portion is a convex portion partially formed on a surface of the porous film.   The lithium ion secondary battery according to claim 1 or 2, wherein a mixture layer of the electrode having the porous film partially has a convex portion.   A lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte comprising a composite lithium oxide, wherein at least one surface of the separator has a porous film containing an inorganic oxide filler and a binder. And the said porous film has a convex part formed partially, The lithium ion secondary battery characterized by the above-mentioned.   A lithium ion secondary battery comprising a positive electrode comprising a composite lithium oxide, a negative electrode, and a non-aqueous electrolyte, wherein one of the positive electrode and the negative electrode is bonded to an inorganic oxide filler on the surface facing the other electrode. A lithium ion secondary battery comprising a porous film containing an adhesive, wherein the mixture layer of the other electrode has a convex portion partially on a surface facing the one electrode.   The lithium ion secondary battery according to claim 6, further comprising a separator between the positive electrode and the negative electrode.   A lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte comprising a composite lithium oxide, wherein at least one surface of the separator has a porous film containing an inorganic oxide filler and a binder. The lithium ion secondary battery is characterized in that the electrode mixture layer facing the porous film has a convex portion partially on the surface thereof.   A step of forming a porous film by applying a coating material for forming a porous film on the surface of an electrode mixture layer containing an electrode active material, a conductive agent and a binder, and drying, and forming a porous film on the porous film The method for producing a lithium ion secondary battery according to claim 3, further comprising a step of applying a paint in a certain pattern and drying to form a convex portion.   Porous partly having a convex part by a die coater method in which a coating for forming a porous film is applied by partially increasing the discharge amount on the surface of an electrode mixture layer containing an electrode active material, a conductive agent and a binder. The method for producing a lithium ion secondary battery according to claim 3, wherein a film is formed. A step of imprinting convex portions on the surface of the electrode mixture layer containing an electrode active material, a conductive agent and a binder, and a porous film-forming paint is applied to the surface of the electrode mixture layer imprinted with the convex portions and dried. The method for producing a lithium ion secondary battery according to claim 4, further comprising a step of forming a porous film.

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