JP3971096B2 - Lithium secondary battery - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a lithium secondary battery, and more particularly to a lithium secondary battery having a flat plate shape.
[0002]
[Prior art]
A high energy density lithium secondary battery that has been developed in recent years has a high risk of ignition, smoke, etc. due to misuse of the battery or failure of equipment used due to its high energy density. Against this background, in recent years, development of battery design technology in which a safety function is added to the lithium secondary battery itself has been actively promoted. That is, ensuring the safety of lithium secondary batteries is one of the indispensable issues in current battery designs with higher energy density.
[0003]
In ensuring the safety of batteries, ensuring safety especially against overcharging is one of the important issues. This is because when a certain amount of electricity flows for some reason when charging a lithium secondary battery, the battery becomes overcharged, an internal short circuit occurs due to precipitation of lithium dendrite, etc., and the battery temperature rises. This is because there is an extremely high risk of causing accidents such as smoke and fire.
[0004]
In general, when a lithium secondary battery is overcharged, gas is first generated due to decomposition of an electrolytic solution or the like. When gas is generated, not only does the battery rupture, leakage, etc., but this state continues, the battery temperature eventually rises and may even lead to accidents such as smoke and fire. From such a viewpoint, various methods for preventing overcharge have been proposed.
[0005]
Specific methods for preventing overcharge are generated by a shutdown method using melting of the separator due to battery temperature rise, a control method using an electronic circuit attached to the outside of the battery, and decomposition of the electrolyte during overcharge. A mechanical current interruption method using a safety valve using gas is known.
However, the shutdown method using a separator has a rapid runaway reaction at the time of overcharge, and it is actually difficult to sufficiently function as overcharge protection.
[0006]
In addition, the control method using an electronic circuit and the mechanical current interruption method using a safety valve have design limitations such as the fact that a control device such as an electronic circuit or a safety valve cannot be installed due to the design of the battery, and also has the disadvantage of increasing the cost of the battery. is there. Furthermore, even if these control devices can be installed, there is a risk of malfunction due to malfunction of the circuit, misuse of the charger, etc., and risk of delay of battery shutdown due to sudden overcharge runaway reaction due to high current charging etc. And this is not always an adequate overcharge protection measure.
[0007]
Under such circumstances, in the above overcharge prevention measures, in recent years, from the trend of battery design to give a safety function to the battery itself, an organic substance is added to the electrolyte and the chemicals at the time of overcharge are added. A method utilizing a reaction has attracted attention, and various additives have been proposed.
The basic concept of overcharge prevention measures using organic additives is to add an organic compound having an oxidation potential that is nobler than the positive electrode potential at full charge to the electrolyte so that the positive electrode potential is increased in an overcharged state. When it rises, it causes an oxidation reaction of the organic additive to suppress the runaway reaction in the battery during overcharge.
[0008]
Conventionally proposed methods can be classified into two methods depending on the physical properties of the oxidation product of the additive. The first method uses an organic additive in which the oxidant of the organic additive is soluble in the electrolyte and has good reversibility of the oxidation-reduction reaction, and the additive reciprocates between the positive and negative electrodes in an overcharged state. Thus, the overcharge current is consumed (redox shuttle method). On the other hand, in the second method, current interruption occurs due to the formation of a film on the positive electrode by oxidative polymerization of the additive in an overcharged state, and the generated gas generated at that time is used to reliably operate the safety valve of the battery. (Aromatic compound oxidative polymerization method). The latter method can be said to be an overcharge prevention method by a combination of a method using a mechanical current interruption and a method using a polymerization reaction during overcharging of an organic additive. The former method is described in JP-A-7-302614, JP-A-9-17447, JP-A-9-50822, JP-A-9-231976, and the like. No. 106835, JP-A-9-171840, JP-A-9-23001, and the like.
[0009]
[Problems to be solved by the invention]
The conventional redox shuttle method and aromatic compound oxidative polymerization method may have sufficient functions to prevent adverse effects such as ignition and smoke for low current overcharge. Since the runaway reaction becomes rapid, control by the chemical reaction of the additive is not in time and often does not function as overcharge protection.
[0010]
For example, the Redox shuttle method has low stability of the oxidant of the additive, especially when the battery temperature rises, such as overcharge, and the additive is deteriorated. There is a possibility of losing. Furthermore, this method often cannot suppress the generation of gas during overcharge, and problems such as leakage of corrosive gas and toxic gas due to battery pressure during overcharge and damage to the equipment used due to battery swelling still remain. Has been.
[0011]
On the other hand, in the aromatic compound oxidative polymerization method, as an actual mechanism of action, in combination with the overcharge control by the safety valve, the safety valve of the battery is reliably operated using the generated gas generated during the polymerization reaction. It is said that there is. That is, since this method is also effective for the first time in combination with the mechanical current interrupting device, not only is there a restriction on the design described above, but also gas is actively generated during overcharge. Deficiencies such as corrosion of equipment used due to the generated gas and leakage of toxic gases such as organic gas remain.
[0012]
That is, in the battery design that attempts to give a safety function to the battery itself, there has always been a problem of gas generation, resulting in a problem of battery swelling. In particular, in a flat type battery, since the battery tends to swell in the thickness direction, the problem due to gas generation is more serious.
The present invention has been made in view of the above circumstances, and its purpose is to suppress leakage of corrosive gas and toxic gas at the time of overcharging of the battery and swelling of the battery by suppressing the swelling of the battery at the time of overcharging. It is an object of the present invention to provide a battery that prevents damage to equipment used due to the above and improves safety against overcharging of the battery reliably and effectively.
[0013]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that the trigger of the runaway reaction in the battery at the time of overcharging is in the initial swelling of the battery. In addition to being able to suppress gas generation and prevent damage to equipment used due to battery swelling and leakage of corrosive and toxic gases from the battery, it is also possible to prevent smoke and ignition of the battery due to battery temperature rise. The headline and the present invention were completed.
[0014]
That is, the gist of the present invention is as follows.
(1) A lithium secondary battery in which a battery element having a positive electrode and a negative electrode is sealed with an exterior materialThe battery element is formed by laminating a plurality of flat unit battery elements in the thickness direction, and a part of the positive electrode and a part of the negative electrode of each unit battery element are bundled between the unit battery elements. The positive electrode terminal portion and the negative electrode terminal portion, the entire battery element side surface from the positive electrode terminal portion to the negative electrode terminal portion is covered and fixed with an insulating material, andIn the following overcharge test, gas does not leak out of the battery, and the battery thickness (A) immediately after the test is equal to the battery thickness before the test.190% Lithium secondary battery.
  Overcharge test
  The battery having a battery voltage of 3V is continuously charged with a current of 1.8C for 200 minutes within a range where the upper limit voltage is 10V. However, 1C is a current value for discharging the capacity obtained by charging the battery voltage from 2.7V to 4.2V constant voltage until the current value becomes 0 in one hour.
[0015]
(2) The total thickness (B) of the battery element immediately after the overcharge test is equal to the total thickness of the battery element before the test.190%The lithium secondary battery as described in (1) below.
(3) The lithium secondary battery according to (1) or (2), wherein the difference between the battery thickness (A) immediately after the overcharge test and the total thickness (B) of the battery elements is 2 mm or less..
[0016]
(4) A film-shaped exterior material forms a joining piece part formed by joining the peripheral parts of the film and an encapsulating part that encapsulates the battery element, and at least a part of the joining piece part is formed in the covered part. (1) to () bent along the packet part3). The lithium secondary battery according to any one of
[0017]
(5) The joining piece is fixed to the enveloping part (4Lithium secondary battery according to (1).
(6) The thickness of the exterior material is 0.2 mm or less (1) to (5). The lithium secondary battery according to any one of
(7) The thickness of the battery is 2 mm or more (1) to (6). The lithium secondary battery according to any one of
[0018]
(8) The battery capacity is 100 mAh or more (1) to (7). The lithium secondary battery according to any one of
(9(1) to (1) to (1) to (1) to (1) are made of a laminate film in which a synthetic resin layer and a metal layer are laminated8). The lithium secondary battery according to any one of
(10) The electrolyte has a non-flowable electrolyte (1) to (9). The lithium secondary battery according to any one of
[0019]
(11) The electrolyte is LiPF₆Comprising (1) to (10). The lithium secondary battery according to any one of
(12) The positive electrode contains lithium cobalt oxide and / or lithium nickelate (1) to (11). The lithium secondary battery according to any one of
[0020]
DETAILED DESCRIPTION OF THE INVENTION
As a result of the overcharge test, the lithium secondary battery of the present invention does not leak gas to the outside of the battery, and is caused by the thickness of the battery immediately after the test (A; the thickness of the exterior material, the thickness of the battery element, or swelling) The thickness of the entire battery, including the thickness due to voids with1 of90% or less. Here, in the overcharge test, a battery having a battery voltage of 3V is continuously charged with a current of 1.8C for 200 minutes within a range where the upper limit voltage is 10V. However, 1C discharges the capacity obtained by charging the battery voltage from 2.7 V to 4.2 V at a constant voltage until the current value becomes 0 (hereinafter sometimes simply referred to as “battery capacity”) in 1 hour. Therefore, 1.8C is 1.8 times the current value of 1C. By using such a battery, leakage of corrosive gas and toxic gas when the battery is overcharged and damage to the equipment used due to battery bulge are prevented, and the safety against battery overcharge is improved reliably and effectively. A battery having an intrinsically safe function can be realized. In addition, such a lithium secondary battery having a small swelling due to the overcharge test has an advantage that it is safer even when exposed to more severe overcharge conditions.
[0021]
However, since it is not realistic to obtain a lithium secondary battery that does not swell at all in the overcharge test, the battery thickness (A) immediately after the test is usually 101% or more of the battery thickness before the test, Preferably it is 110% or more, More preferably, it is 120% or more. In order to obtain such a lithium secondary battery, it is important to suppress the initial gas generation during overcharge. In other words, it is important that the swelling of the battery element after the overcharge test is not caused by an increase in the gap due to the gas generation itself, but is caused by the swelling of the battery element itself. In this regard, the lithium secondary battery according to the present invention has a total thickness (B) of the battery element after the overcharge test before the test.1 of90% or less. However, in this case as well, it is not realistic to obtain a lithium secondary battery that does not swell at all in the overcharge test. Therefore, the thickness (B) of the battery element immediately after the test is usually the same as that of the battery element before the test. It is 101% or more of the thickness, preferably 110% or more, more preferably 120% or more.
[0022]
The total thickness of the lithium secondary battery before the overcharge test is usually 5 mm or less, preferably 4.5 mm or less, more preferably 4 mm or less. The effect of the present invention is particularly great for such a thin lithium secondary battery. However, a battery that is too thin may have a capacity that is too small or difficult to manufacture, and the problems due to overcharging are not relatively large. Therefore, it is usually 0.5 mm or more, preferably 1 mm or more, more preferably 2 mm or more. It is.
[0023]
In addition, as described above, the swelling of the battery element after the overcharge test is not caused by an increase in the gap due to the gas generation itself, but is caused by the swelling of the battery element itself. The difference between the thickness of the whole battery after the end of the charging test and the total thickness of the battery elements is preferably 1.5 mm or less, more preferably 1.2 mm or less, further preferably 1 mm or less, and most preferably 0.5 mm or less. . However, not only is it difficult to actually obtain a lithium secondary battery with the above difference being extremely small, but the thickness of the exterior material is present, so that the thickness is usually 0.01 mm or more, preferably 0.05 mm or more.
[0024]
When the battery capacity is not so large, the problem due to overcharging is alleviated. Therefore, in the present invention, it is remarkable that the battery capacity is set to 100 mAh or more, particularly 200 mAh or more. However, since it is difficult to actually obtain a battery with a very large capacity, it is usually set to 2000 mAh or less.
The exterior material that stores the battery element preferably has shape variability. As a result, not only is it easy to create batteries of various shapes, but when the exterior material is sealed under vacuum, it can be given a function to strengthen the bonding between the electrodes of the battery element, and as a result Battery characteristics such as cycle characteristics can be improved. As the thickness of the exterior material is thinner, the volume energy density and the weight energy density of the battery are increased, which is not only preferable, but the strength itself is relatively low, so the effect of the present invention is particularly remarkable. The thickness of the exterior material is usually 0.2 mm or less, preferably 0.15 mm or less. However, if the thickness is too thin, the strength is insufficient and moisture and the like are easily transmitted. Therefore, the thickness is usually 0.01 mm or more, preferably 0.02 mm or more.
[0025]
As the material of the exterior material, aluminum, nickel-plated iron, copper or other metal, synthetic resin, or the like can be used. Preferably, a laminate film in which a metal and a synthetic resin are laminated is used. By using this laminate film, the case member can be made thinner and lighter, and the capacity of the entire battery can be improved.
[0026]
As the laminate film, as shown in FIG. 12A, a laminate of a metal layer 40 and a synthetic resin layer 41 can be used. The metal layer 40 prevents moisture from entering or maintains shape retention, and is made of a single metal such as aluminum, iron, copper, nickel, titanium, molybdenum, or gold, an alloy such as stainless steel or hastelloy, or a metal such as aluminum oxide. It may be an oxide. In particular, aluminum having excellent workability is preferable.
[0027]
The metal layer 40 can be formed using a metal foil, a metal vapor deposition film, a metal sputtering, or the like.
The synthetic resin layer 41 is used for protecting the case member or preventing the contact with the electrolyte, preventing contact between the metal layer and the battery element, etc., or protecting the metal layer. The elastic modulus and tensile elongation of the resin are not limited. Therefore, the synthetic resin in the present invention includes what is generally called an elastomer.
[0028]
As the synthetic resin, thermoplastic plastics, thermoplastic elastomers, thermosetting resins, and plastic alloys are used. These resins include those in which fillers such as fillers are mixed.
In addition, as shown in FIG. 12B, the laminate film is provided with a synthetic resin layer 41 for functioning as an outer protective layer on the outer surface of the metal layer 40, and corrosion and metal layers on the inner surface and the battery element on the inner surface. A three-layer structure in which a synthetic resin layer 42 that functions as an inner protective layer for preventing contact with the metal layer and protecting the metal layer can be obtained.
[0029]
In this case, the resin used for the outer protective layer is preferably a resin excellent in chemical resistance and mechanical strength, such as polyethylene, polypropylene, modified polyolefin, ionomer, amorphous polyolefin, polyethylene terephthalate, and polyamide.
As the inner protective layer, a chemical-resistant synthetic resin is used. For example, polyethylene, polypropylene, modified polyolefin, ionomer, ethylene-vinyl acetate copolymer, and the like can be used.
[0030]
Further, as shown in FIG. 13, the composite material can also be provided with an adhesive layer 43 between the metal layer 40, the protective layer forming synthetic resin layer 41, and the corrosion resistant layer forming synthetic resin layer 42. Furthermore, in order to adhere the case members to each other, an adhesive layer made of a resin such as polyethylene or polypropylene that can be welded to the innermost surface of the composite material can be provided. A case is formed using these metals, synthetic resins, or composite materials. The case may be formed by fusing the periphery of a film-like body, or the sheet-like body may be drawn by vacuum forming, pressure forming, press forming or the like. It can also be formed by injection molding a synthetic resin. In the case of injection molding, the metal layer is usually formed by sputtering or the like.
[0031]
Providing the housing portion formed of a recess in the exterior material can be performed by drawing or the like.
As the exterior material, it is preferable to use a film-like material because it is easy to process.
In order to obtain a lithium secondary battery with less blistering with respect to the overcharge test, it is important to provide means for preventing the battery from expanding at the initial stage of overcharge.
[0032]
That is, the swelling of the battery at the time of overcharging is mainly caused by the generation of gas due to the distortion of the electrode, the expansion of the electrode (active material) and the decomposition reaction of the electrolytic solution at the time of overcharging. Among these, the distortion of the electrode at the time of overcharge and the gas generation in the battery are not yet clear, but can be suppressed by applying pressure between the electrodes at the time of overcharge. In the present invention, it is preferable to use a method of applying pressure between the electrodes during overcharging as a specific method of preventing battery swelling. Here, since the load between the electrodes leads to harmful effects such as a short circuit of the battery in a normal use range, a method in which pressure is strongly applied between the electrodes only in an overcharged state is preferable. Usually, at the time of overcharge, the thickness of the electrode remarkably increases especially from the vicinity of the charging depth at which the dedoping of lithium ions from the positive electrode is completed. Specific examples of such a method include, for example, firmly attaching an exterior material that houses the battery element so as to suppress swelling, or fixing a portion of the battery element in the vicinity of a portion from which current is easily extracted, which is particularly easily swollen. Can be mentioned. In particular, the former method is preferable because the electrode can be strongly pressed only in the overcharged state where the expansion of the electrode is most remarkable by suppressing the deformation of the exterior material during overcharging as much as possible.
[0033]
In addition, a method of encapsulating a packaging material with a heat-shrinkable polymer material, a method of using a high-strength packaging material, and the like are also included.
Furthermore, these methods can be combined with an overcharge prevention measure using a known overcharge inhibitor. As a result, safety against overcharging can be further improved.
[0034]
For example, as an organic additive, an organic compound having a π electron orbit having a molecular weight of 500 or less and having a reversible oxidation-reduction potential at a potential nobler than the positive electrode potential at the time of full charge (JP-A-7-302614) Aromatic compounds having a halogen atom and a methoxy group (Japanese Patent Laid-Open No. 9-17447); Aromatic compounds that polymerize at a battery voltage equal to or higher than the voltage at full charge (Japanese Patent Laid-Open No. 9-106835 and Japanese Patent Laid-Open No. 171840); and at least one aromatic hydrocarbon selected from naphthalene, anthracene and phenanthrene (Japanese Patent Laid-Open Nos. 9-231976 and 9-23001).
[0035]
Preferably, as the overcharge preventing agent, an organic compound having an oxidation potential that is nobler than the positive electrode potential during full charge and lower than the oxidation potential of the electrolyte used is present in the battery. Specific examples of such an organic compound include substituted anisoles, alkylbenzenes, diphenylalkanes, biphenyl, naphthalene, anthracene, esters having a substituted aromatic ring, and the like. In these, the compound which does not generate | occur | produce gas by the oxidation reaction at the time of overcharge is used suitably. When using a compound that generates a gas during overcharge, it is preferable to control its abundance such that the amount generated is extremely small.
[0036]
Hereinafter, a lithium secondary battery in which a battery element formed by laminating a plurality of flat unit battery elements each having a positive electrode, a negative electrode, and a non-fluidic electrolyte in the thickness direction is hermetically sealed by a film-like packaging material is taken as an example. The specific configuration of the lithium secondary battery will be described in more detail.
FIG. 1 is an exploded perspective view of a battery according to an embodiment, FIG. 2 is a cross-sectional view of a main part of the battery, FIG. 3 is a schematic perspective view of a battery element, and FIG. 4 is a perspective view of the battery.
[0037]
In this battery, after the battery element 1 is accommodated in the recess of the exterior material 3, an insulating material 5 such as epoxy resin or acrylic resin is injected in the vicinity of the terminal portions (tabs 4 a and 4 b) of the battery element 1, and then the exterior material 2. Is covered with the exterior material 3, and the peripheral portions 2a and 3a of the exterior materials 2 and 3 are joined by vacuum sealing.
As shown in FIG. 1, the exterior material 2 has a flat plate shape. The outer packaging material 3 is a shallow, open box-like box having a housing portion 3b formed of a rectangular box-shaped concave portion and a peripheral edge portion 3a projecting outwardly in a flange shape from the four peripheral edges of the housing portion 3b.
[0038]
As shown in FIG. 3, the battery element 1 is formed by laminating a plurality of unit battery elements in the thickness direction. The tab 4a or 4b is pulled out from the unit battery element. The tabs 4a from the positive electrode are bundled (that is, overlapped with each other), and the positive electrode lead 21 is joined to form the positive electrode terminal portion. The tabs 4b from the negative electrode are also bundled together, and the negative electrode lead 21 is joined to form a negative electrode terminal portion.
[0039]
After the battery element 1 is accommodated in the accommodating portion 3b of the exterior material 3, the insulating material 5 is injected in the vicinity of the tabs 4a and 4b, and the battery element side surfaces in the vicinity of the positive electrode terminal portion and the negative electrode terminal portion are covered with the insulating material, The exterior material 2 is covered. The pair of leads 21 extending from the battery element 1 are drawn out through the mating surfaces of the peripheral edges 2a and 3a on one side of the exterior materials 2 and 3, respectively. Thereafter, the peripheral edges 2a, 3a of the four peripheral edges of the outer packaging materials 2, 3 are hermetically joined by a technique such as thermocompression bonding or ultrasonic welding in a reduced pressure (preferably vacuum) atmosphere. 3 is enclosed. Thereafter, the insulating material 5 is subjected to a curing process by heating or the like, and the insulating material 5 is completely fixed in the vicinity of the terminal portion. Since the exterior material is sealed before being completely fixed, the shape of the battery hardly changes at the time of fixing.
[0040]
Joining piece parts 4A, 4F, and 4G are formed by joining peripheral parts 2a and 3a. The joining piece portions 4A, 4F, and 4G project outward from the encapsulating portion 4B that encapsulates the battery element 1. Therefore, the joining piece portions 4A, 4F, and 4G are bent along the enveloping portion 4B and fastened (fixed) to the side surface of the encapsulating portion 4B with an adhesive, an adhesive tape (not shown), or the like. .
[0041]
As said insulating material 5, a synthetic resin is suitable and an epoxy resin, an acrylic resin, a silicone resin etc. are illustrated, but an epoxy resin or an acrylic resin is especially suitable because the curing time is short. In particular, an acrylic resin is most preferable because it has a low possibility of adversely affecting battery performance. The insulating material is supplied to the vicinity of the terminal portion in an uncured and fluid state, and is completely fixed in the vicinity of the terminal portion by curing.
[0042]
In FIG. 1, the insulating material is separately supplied to the positive electrode terminal portion and the negative electrode terminal portion. However, in the present invention, in order to further improve safety during overcharge, the positive electrode terminal portion to the negative electrode terminal portion. It is preferred to cover the entire side of the battery element.
In FIG. 1, the exterior materials 2 and 3 are separate bodies. However, in the present invention, the exterior materials 2 and 3 may be integrated as a series as shown in FIG. 5. In FIG. 5, one side of the exterior material 3 and one side of the exterior material 2 are connected, and the exterior material 2 has a lid shape that is connected to the exterior material 3 so as to be bendable. A concave portion of the accommodating portion 3b is formed from one side where the exterior materials 2 and 3 are continuous, and the same configuration as the joining piece portion is provided except that the joining piece portion is not formed on this one side.
[0043]
Also in the case of FIG. 5, after the battery element 1 is accommodated in the accommodating portion 3b, an insulating material is injected in the vicinity of the tabs 4a and 4b of the battery element 1.
In FIGS. 1 and 5, the exterior material 3 having the accommodating portion 3 b and the flat exterior material 2 are shown. However, in the present invention, as shown in FIG. 6, the shallow box-like accommodating portions 6 b and 7 b and Alternatively, the battery element 1 may be encapsulated by the exterior members 6 and 7 having the peripheral portions 6a and 7a protruding from the four peripheral edges of the housing portions 6b and 7b. In FIG. 6, the exterior materials 6 and 7 are a series of bodies, but these may be separate bodies as in FIG.
[0044]
In the configurations of FIGS. 1, 5, and 6, since the battery element housing portion is formed in advance, the battery element can be housed more compactly, and the housing itself is easy.
In the above description, after the battery element is accommodated in the accommodating portion, the insulating material is injected in the vicinity of the terminal portion. In this case, the insulating material is provided between the mating surface of the peripheral portion or between the battery element and the exterior material. Adhesion and inflow may interfere with the joining of the peripheral part, or the battery shape may not be as designed. Therefore, the above problem can be avoided by accommodating the battery element in the accommodating portion after supplying the insulating material in the vicinity of the terminal portion of the battery element. In particular, in the case of FIG. 6, even if the insulating material is supplied after the battery element is accommodated, the insulating material cannot be supplied to the substantially upper half of the battery element, so this manufacturing method is preferable. On the other hand, in this method, since it is necessary to transport a battery element that is not easy to handle in a state where an insulating material is supplied and arrange it on an exterior material, care must be taken during manufacture. In this respect, it can be said that the former method is preferable.
[0045]
In the present invention, as shown in FIG. 7, one flat sheet-shaped exterior material 8 is folded back into two along the central side 8a to form two pieces, a first piece 8A and a second piece 8B, The battery element 1 is interposed between the first piece 8A and the second piece 8B, and the battery element 1 is sealed by joining the peripheral portions 8b of the first piece 8A and the second piece 8B as shown in FIG. May be.
Also in this case, before or after the insulating material is attached to the vicinity of the tabs 4a, 4b of the battery element 1, the battery element 1 is enclosed by overlapping the first piece 8A and the second piece 8B of the outer packaging material 8. Further, the joining piece portion is bent and fastened along the enveloping portion.
[0046]
In the battery configured in this way, the joining piece portion is bent along the encapsulated portion, and further fixed with an adhesive or an adhesive tape. Can be effectively prevented, and the strength and rigidity of the side of the battery are high. Of course, the bent joining piece part is also prevented from separating from the encapsulating part. In addition, since the strength and rigidity of the side surface of the battery are high, it is possible to prevent the active material from peeling even when the side surface receives an impact.
[0047]
Further, since the insulating material 5 is filled in the vicinity of the terminal portions (tabs 4a and 4b), the battery element can be effectively prevented from being swollen at the initial stage of overcharging, and further, a short circuit is prevented.
In covering the side surface of the battery element in the vicinity of the terminal portion, it is particularly preferable to provide a larger spacer between the positive electrode and the negative electrode, and to stick the protruding portions of the spacer to each other.
[0048]
That is, in the battery element, for example, as shown in FIG. 18, the spacer 13 slightly protrudes from the positive electrode 11 and the negative electrode 13 to form a protruding portion 13 a to prevent a short circuit between the positive electrode 11 and the negative electrode 13. Yes. By fixing the protruding portions 13a to each other with an insulating material, the battery elements are constrained in the stacking direction. Therefore, even when overcharged, the battery elements are prevented from swelling and thermal runaway of the battery is prevented. Of course, the insulating material can be supplied over the entire side of the battery element and is preferred.
In order to inject the insulating material, it is preferable to insert the nozzle 51 of the insulating material injection device 50 into the exterior material 3 as shown in FIG. 17 and inject the insulating material into the side end face of the battery element 1.
[0049]
In this case, as shown in FIGS. 14, 15 and 16, both corners R of the side end face provided with the tab 4a or 4b.₁, R₆And both sides R of the base of each tab 4a, 4b₂, R_Three, R_Four, R_FiveThus, it is preferable to inject an insulating material into a plurality of locations. The injected insulating material penetrates the entire side including the positive electrode terminal portion and the negative electrode terminal portion through the action of capillarity or the like on the side surface of the battery element. The injection device 50 includes a plurality (six nozzles) of nozzles and can inject a plurality of insulating materials at a time.
[0050]
In addition, as shown in FIG. 16, when an insulating material is injected into the base portions on both sides of the tabs 4a and 4b, the injection point (center of the injection nozzle 51) is preferably within 2 mm from the tab 4a or 4b. Thus, when the insulating material is injected into the bases on both sides of the tabs 4a and 4b, the insulating material not only fixes the protruding portions 13a to each other, but also the positive terminal portion and the negative terminal portion as in the case of FIG. A configuration in which at least a part of is covered with the insulating material 5 is also obtained.
[0051]
In the above configuration, the joining piece portion formed by bonding the film-like exterior material is bent along the encapsulating portion encapsulating the battery element, more preferably from the root of the encapsulating portion. Bend it. In this case, the joining piece part may be bent only once at the base of the enveloping part, or may be bent multiple times. When bending multiple times, it is preferable that the leading edge of the joint piece is bent so as to be interposed between the joint piece and the encapsulating part. Thereby, the front-end edge of a joining piece part is isolated from external air, and penetration | invasion of a water | moisture content, air, etc. can be prevented from a front-end edge.
[0052]
Examples of the adhesive that can be used to fasten the joining piece part to the encapsulated part include an epoxy adhesive, an acrylic adhesive, a urethane adhesive, a hot melt adhesive, or a synthetic rubber adhesive. Although it is mentioned, the hot-melt-type adhesive which hardens | cures easily in the environment with a short curing time and the low dew point used at the time of manufacture of a non-aqueous battery is preferable.
[0053]
In order to suppress gas generation in the battery during overcharge, it is preferable to apply a load between the electrodes, but the load per unit area applied between the electrodes is, when lithium cobaltate is used for the positive electrode, Usually 0.2kg / cm²Or more, preferably 0.4 kg / cm²More preferably, 0.55 kg / cm²That's it.
The battery element can be a flat plate type battery element formed by laminating a plurality of flat unit battery elements having a positive electrode, a negative electrode, and a spacer in the thickness direction. Hereinafter, a preferred configuration of the unit battery element will be described.
[0054]
FIG. 9 shows a preferred example of the unit battery element of the lithium secondary battery element. This unit battery element is formed by laminating a positive electrode composed of a positive electrode current collector 22 and a positive electrode active material layer 23, a spacer (electrolyte layer) 24, and a negative electrode composed of a negative electrode active material layer 25 and a negative electrode current collector 26. . In order to suppress precipitation of lithium dendrite, the negative electrode is made larger than the positive electrode. In order to prevent short circuit, the spacer 24 is made larger than the positive electrode and the negative electrode. By making the spacer larger than the positive and negative electrodes, as described above, the protruding portions of the spacers of the unit battery element can be fixed.
A plurality of unit battery elements are stacked to form a battery element. In this stacking, unit battery elements in a normal posture (FIG. 9) with the positive electrode on the upper side and the negative electrode on the lower side are opposite to this. Unit battery elements in a reverse posture (not shown) with the positive electrode on the lower side and the negative electrode on the upper side are alternately stacked. That is, the unit cell elements adjacent in the stacking direction are stacked so that the same polarity faces each other (that is, the positive electrodes and the negative electrodes) face each other.
[0055]
A positive electrode tab 4 a extends from the positive electrode current collector 22 of the unit battery element, and a negative electrode tab 4 b extends from the negative electrode current collector 26.
As shown in FIG. 10, instead of a unit battery element in which a positive electrode active material layer, a spacer, and a negative electrode active material layer are laminated between a positive electrode current collector and a negative electrode current collector as shown in FIG. A positive electrode 11 and a negative electrode 12 are prepared by laminating a positive electrode active material layer 11a or a negative electrode active material layer 12a on both sides of a 15a or negative electrode current collector 15b as a core material. As described above, the battery cells may be alternately stacked via the spacers (electrolyte layers) 13 to form unit battery elements. In this case, a combination of a pair of positive electrode 11 and negative electrode 12 (strictly speaking, from the center in the thickness direction of current collector 15a of positive electrode 11 to the center in the thickness direction of current collector 15b of negative electrode 12) is a unit cell element. It corresponds to.
[0056]
The planar shape of the electrode is arbitrary, and can be a square, a circle, a polygon, or the like.
As shown in FIGS. 9 and 11, the current collectors 22, 26 or 15a, 15b are usually provided with lead coupling tabs 4a, 4b. When the electrode is square, a tab 4a protruding from the positive electrode current collector is formed near the side of one side of the electrode, as shown in FIG. 3, and the tab 4b of the negative electrode current collector is formed near the other side. To do.
[0057]
Laminating a plurality of unit cell elements is effective in increasing the capacity of the battery. At this time, the tab 4a and the tab 4b from each unit cell element are usually coupled in the thickness direction. Thus, terminal portions of the positive electrode and the negative electrode are formed. As a result, a large capacity battery element 1 can be obtained.
As shown in FIG. 2, a lead 21 made of a flaky metal is coupled to the tabs 4a and 4b. As a result, the lead 21 and the positive electrode and negative electrode of the battery element are electrically coupled. The coupling between the tabs 4a and 4b and the coupling between the tabs 4a and 4b and the lead 21 can be performed by resistance welding such as spot welding, ultrasonic welding, or laser welding.
[0058]
In the present invention, it is preferable to use an annealed metal as at least one of the positive electrode lead and the negative electrode lead 21, preferably both. As a result, a battery excellent in not only strength but also bending durability can be obtained.
Generally, aluminum, copper, nickel, SUS, or the like can be used as the type of metal used for the lead. A preferred material for the positive electrode lead is aluminum. A preferred material for the negative electrode lead is copper.
[0059]
The thickness of the lead 21 is usually 1 μm or more, preferably 10 μm or more, more preferably 20 μm or more, and most preferably 40 μm or more. If it is too thin, the mechanical strength of the lead such as tensile strength tends to be insufficient. The lead thickness is usually 1000 μm or less, preferably 500 μm or less, and more preferably 100 μm or less. If it is too thick, the bending durability tends to deteriorate, and the battery element tends to be difficult to seal with the case. The advantage of using an annealed metal to be described later for the lead is more conspicuous as the lead is thicker.
[0060]
The width of the lead is usually 1 mm or more and 20 mm or less, particularly about 1 mm or more and 10 mm or less, and the exposed length of the lead to the outside is usually about 1 mm or more and 50 mm or less. The battery element to be used is a flat plate type battery in which the flat unit battery elements as described above are stacked in the thickness direction.TheIt is preferable that a spacer is interposed between the positive electrode and the negative electrode, which is larger than the positive and negative electrodes.. ElectricLithium secondary battery as a pond elementInuse. Hereinafter, materials used for the lithium secondary battery will be described.
[0061]
As the positive electrode current collector, various metals such as aluminum, nickel, and SUS can be used, and aluminum is preferable. The thickness of the current collector is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and usually 30 μm or less, preferably 25 μm or less, more preferably 20 μm or less. The thinner the thickness, the better from the viewpoint of volume energy density and weight energy density. However, too thin is likely to be difficult to handle in terms of strength and the like. The current collector may have a plate shape such as a normal metal foil or a mesh shape such as punching metal. The surface of the current collector can be roughened as necessary.
[0062]
As an active material that can be used for a positive electrode of a lithium secondary battery, an inorganic compound or an organic compound can be used as a compound capable of occluding and releasing lithium ions. Examples of inorganic compounds include oxides of transition metals such as Fe, Co, Ni, and Mn, composite oxides of lithium and transition metals, and transition metal sulfides. Specifically, MnO, V as the transition metal oxide₂O_Five, V₆O₁₃TiO₂Examples of the composite oxide of lithium and transition metal include lithium nickelate, lithium cobaltate, and lithium manganate, and TiS as the transition metal sulfide.₂And FeS. Examples of the organic compound include conductive polymers such as polyaniline. Moreover, the method of mixing arbitrary amounts of these arbitrary inorganic compounds and organic compounds, and using as a positive electrode active material is also used suitably. Preferably, it is a complex oxide containing lithium and a transition metal, in particular, a complex oxide containing at least one transition metal oxide selected from the group consisting of manganese, nickel and cobalt and lithium. In particular, when a composite oxide containing cobalt and lithium or a composite oxide containing nickel and lithium is used, dendrites are likely to be generated during overcharge, and the effect of the present invention is particularly remarkable. The particle size of the positive electrode active material is usually 1 to 30 μm, preferably 1 to 10 μm, because battery characteristics such as the rate characteristics and cycle characteristics are improved.
[0063]
As the negative electrode current collector, various metals such as copper, nickel, and SUS can be used, and copper is preferable. The thickness of the current collector is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and usually 30 μm or less, preferably 25 μm or less, more preferably 20 μm or less. The thinner the thickness, the better from the viewpoint of volume energy density and weight energy density. However, too thin is likely to be difficult to handle in terms of strength and the like. The current collector may have a plate shape such as a normal metal foil or a mesh shape such as punching metal. The surface of the current collector can be roughened as necessary.
[0064]
As the active material that can be used for the negative electrode, various compounds that can occlude and release lithium can be used in addition to lithium metal. Specific examples include lithium metal; lithium alloys such as lithium-aluminum alloy, lithium-bismuth-cadmium alloy, and lithium-tin-cadmium alloy; and carbon materials such as graphite and coke. In addition, oxides such as silicon, tin, zinc, manganese, iron, nickel, and lead sulfate can also be used. When lithium metal or a lithium alloy is used, dendrites are likely to be generated during charging, and the safety during overcharging tends to decrease. Carbon materials such as graphite and coke are preferred. The particle size of the negative electrode active material is usually 1 to 50 μm, preferably 15 to 30 μm, because battery characteristics such as initial efficiency, rate characteristics, and cycle characteristics are improved.
[0065]
The active material layer usually contains a binder in addition to the active material. The binder to be used needs to be stable with respect to the electrolytic solution and the like, and weather resistance, chemical resistance, heat resistance, flame retardancy and the like are desired. As the binder, inorganic compounds such as silicate and glass, and various resins mainly composed of polymers can be used. Examples of the resin include alkane polymers such as polyethylene, polypropylene and poly-1,1-dimethylethylene; unsaturated polymers such as polybutadiene and polyisoprene; polystyrene, polymethylstyrene, polyvinylpyridine, poly-N-vinylpyrrolidone and the like. Polymer having a ring; acrylic derivative polymer such as polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, polyethyl acrylate, polyacrylic acid, polymethacrylic acid, polyacrylamide; polyvinyl fluoride Fluorine resins such as polyvinylidene fluoride and polytetrafluoroethylene; CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide; Polyvinyl acetate and polyvinyl alcohol Alkenyl alcohol-based polymers; polyvinyl chloride, halogen-containing polymers such as polyvinylidene chloride; and conductive polymers such as polyaniline can be used. Further, a mixture such as the above-mentioned polymer, a modified product, a derivative, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer, and the like can be used. The molecular weight of these resins is preferably 10,000 to 3,000,000, more preferably 100,000 to 1,000,000. If it is too low, the strength of the active material layer will decrease, and if it is too high, the viscosity will increase and it will be difficult to form an electrode.
[0066]
As a compounding quantity of the binder with respect to 100 parts of active materials, Preferably it is 0.1-30 parts, More preferably, it is 1-20 parts. If the amount of the binder is too small, the strength of the electrode may decrease, and if it is too large, the ionic conductivity tends to decrease.
The active material layer may contain powders, fillers, and the like that exhibit various functions such as a conductive material and a reinforcing material, if necessary. The conductive material is not particularly limited as long as it is capable of imparting conductivity by mixing an appropriate amount of the above active material. Usually, carbon powder such as acetylene black, carbon black, graphite, and various metal fibers and foils are used. Etc. The DBP oil absorption amount of the carbon powder conductive material is preferably 120 cc / 100 g or more, and more preferably 150 cc / 100 g or more because the electrolyte solution is retained. As the reinforcing material, various inorganic, organic spherical and fibrous fillers can be used.
[0067]
The electrode can be manufactured by applying and drying a paint containing the material constituting the active material layer on the current collector. Thereafter, the active material layer can be subjected to a consolidation treatment. The volume fraction of the binder in the active material layer can be controlled by controlling the composition of the paint, the drying conditions, the compaction conditions, and the like.
In order to improve the adhesion between the active material layer and the current collector, an undercoat primer layer can be provided between them as necessary.
[0068]
When the undercoat primer layer is used, examples of the composition include a resin to which conductive particles such as carbon black, graphite, and metal powder are added, and a conductive organic conjugated resin. Preferably, carbon black or graphite that can also function as an active material is used for the conductive particles. As the resin, polyaniline, polypyrrole, polyacene, a disulfide compound, a polysulfide compound, or the like that can function as an active material is preferably used because the capacity is not reduced. In the case of a composition mainly composed of a resin to which conductive particles are added, the ratio of the resin to the conductive particles is preferably 1 to 300% by weight. If it is too low, the strength of the coating film is lowered, and when the battery is used, peeling on the process occurs, which is not preferable. If it is too high, the conductivity is lowered and the battery characteristics are lowered. Most preferably, it is 5-100 weight%. The film thickness of the undercoat primer layer is usually 0.05 to 10 μm, preferably 0.1 to 1 μm. If it is too thin, coating becomes difficult and uniformity cannot be ensured. If it is too thick, the volume capacity of the battery is impaired.
[0069]
An ion mobile phase is usually formed in the positive electrode and the negative electrode. The higher the proportion of the ion mobile phase in the electrode, the easier the ion movement, and this is preferable in terms of rate characteristics, while the lower one is higher in capacity. Preferably it is 10-50 volume%. As the material of the ion mobile phase, the same materials as those in the electrolyte layer described later can be used.
The positive electrode active material layer and the negative electrode active material layer are preferably thicker in terms of capacity and thinner on the rate. The film thickness is usually 20 μm or more, preferably 30 μm or more, more preferably 50 μm or more, and most preferably 80 μm or more. The film thickness of the positive electrode and the negative electrode is usually 200 μm or less, preferably 150 μm or less.
[0070]
An electrolyte is present in the electrolyte layer between the positive electrode and the negative electrode. The electrolyte is usually also present in the electrode as an ion mobile phase.
An electrolyte used for a lithium secondary battery usually has an electrolytic solution obtained by dissolving a lithium salt, which is a supporting electrolyte, in a non-aqueous solvent.
As the non-aqueous solvent, a solvent having a relatively high dielectric constant is preferably used. Specifically, cyclic carbonates such as ethylene carbonate and propylene carbonate, acyclic carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, glymes such as tetrahydrofuran, 2-methyltetrahydrofuran and dimethoxyethane, γ-butyllactone, etc. Lactones, sulfur compounds such as sulfolane, nitriles such as acetonitrile, and the like. Among them, it is preferable to use a high boiling point solvent having a boiling point of 150 ° C. or higher, particularly 200 ° C. or higher. Examples of such a high boiling point solvent include propylene carbonate, ethylene carbonate, butylene carbonate, and γ-butyrolactone. Among them, it is preferable to use propylene carbonate, ethylene carbonate, or γ-butyrolactone as a high boiling point solvent.
[0071]
The above non-aqueous solvent can use multiple types together. When the high boiling point solvent is used, the ratio of the high boiling point solvent to the non-aqueous solvent used is preferably 60% by volume or more, more preferably 70% by volume or more, more preferably 80% by volume or more, and most preferably 90%. Volume% or more. Moreover, it is preferable that the boiling point as the whole non-aqueous solvent when using several solvent together shall be 200 degreeC or more. By using the high boiling point solvent, even if the lithium secondary battery element is housed in the shape-variable case, the shape change (deformation) of the battery at a high temperature or the like can be suppressed. “Boiling point X ° C. or higher” means that the vapor pressure does not exceed 1 atm even when heated from room temperature to X ° C. under a pressure of 1 atm. That is, when heated from room temperature to 200 ° C. under a pressure of 1 atm, it means that the vapor pressure is always 1 atm or less.
[0072]
The non-aqueous solvent preferably has a viscosity of 1 mPa · s or more.
The lithium salt that is the supporting electrolyte used for the electrolyte is LiPF.₆, LiAsF₆, LiSbF₆, LiBF_FourLiClO_Four, LiI, LiBr, LiCl, LiAlCl, LiHF₂, LiSCN, LiSO_ThreeCF₂Etc. Of these, LiPF in particular₆And LiClO_FourIs preferred. LiPF₆Is a compound that is most preferable in terms of battery performance but easily decomposes, and as a result, a compound that easily generates gas during overcharge, and thus the effect of the present invention is particularly great. The content of these supporting electrolytes in the electrolytic solution is usually 0.5 to 2.5 mol / l.
[0073]
The electrolyte preferably has non-fluidity. As a result, even when the battery element is housed in a case having shape variability, leakage of the electrolyte can be effectively prevented. Specific examples of such a non-flowable electrolyte include a so-called polymer electrolyte in which the electrolyte solution is held by a polymer in addition to a completely solid electrolyte. The polymer electrolyte usually exhibits a gel state by holding the non-aqueous electrolyte with a polymer. The concentration of the polymer with respect to the electrolytic solution is usually 0.1 to 30% by weight, although it depends on the molecular weight of the polymer used. If the concentration is too low, it is difficult to form a gel, and the retention of the electrolytic solution is lowered, which may cause problems of flow and liquid leakage. On the other hand, when the concentration is too high, the viscosity becomes too high, resulting in difficulty in the process, and the ratio of the electrolytic solution is lowered, the ionic conductivity is lowered, and the battery characteristics such as the rate characteristics tend to be lowered. Various polymers having the above functions, such as an alkylene oxide polymer having an alkylene oxide unit and a fluorine polymer such as polyvinylidene fluoride or a vinylidene fluoride-hexafluoropropylene copolymer, can be used as a polymer for holding an electrolyte. Can be mentioned.
[0074]
As a method of forming a non-fluidic electrolyte, a method of non-fluidizing an electrolyte paint in which a polymer is previously dissolved in an electrolyte solution, or a method of cross-linking an electrolyte paint containing a polymerizable gelling agent in the electrolyte solution It is possible to adopt materials and manufacturing methods as needed.
When the non-fluidic electrolyte is formed by a method in which a coating containing a polymerizable gelling agent in the electrolytic solution is subjected to a crosslinking reaction, a polymer is formed by performing a polymerization treatment such as ultraviolet curing or heat curing. A paint is prepared by adding a monomer as a polymerizable gelling agent to the electrolyte.
[0075]
Examples of the polymerizable gelling agent include those having an unsaturated double bond such as acryloyl group, methacryloyl group, vinyl group and allyl group. Specifically, for example, acrylic acid, methyl acrylate, ethyl acrylate, ethoxyethyl acrylate, methoxyethyl acrylate, ethoxyethoxyethyl acrylate, polyethylene glycol monoacrylate, ethoxyethyl methacrylate, methoxyethyl methacrylate, ethoxyethoxyethyl methacrylate, polyethylene Glycol monomethacrylate, N, N-diethylaminoethyl acrylate, N, N-dimethylaminoethyl acrylate, glycidyl acrylate, allyl acrylate, acrylonitrile, N-vinylpyrrolidone, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, Polyethylene glycol diacrylate, diety Glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, polyalkylene glycol diacrylate, polyalkylene glycol dimethacrylate, trimethylolpropane alkoxylate triacrylate, pentaerythritol alkoxylate triacrylate, penta Examples include erythritol alkoxylate tetraacrylate, ditrimethylolpropane alkoxylate tetraacrylate, and the like, and these can be used in combination. Of these, diacrylates and triacrylates containing a plurality of ethylene oxide groups are particularly preferred. The content of the polymerizable gelling agent in the electrolytic solution is not particularly limited, but is preferably 1% by weight or more. When the content is low, the formation efficiency of the polymer is lowered, and it is difficult to make the electrolyte non-fluid. On the other hand, if it is too much, residual unreacted monomer and operability as an electrolyte coating are deteriorated.
[0076]
In the method of making a non-fluidic electrolyte non-fluidized with an electrolyte coating containing a polymer in advance, it is preferable to use a polymer that dissolves in an electrolytic solution at high temperature and forms a gel electrolyte at normal temperature. That is, the polymer dissolved in the electrolyte at high temperature is brought to room temperature to obtain a gel electrolyte. As temperature at the time of high temperature, it is 50-200 degreeC normally, Preferably it is 100-160 degreeC. If it seems to dissolve at too low a temperature, the stability of the non-fluidized electrolyte is reduced. If the melting temperature is too high, decomposition of the electrolyte component, polymer, etc. may be caused. As a non-fluidization method, it is preferable to leave the electrolytic solution at room temperature, but forced cooling can also be performed. Examples of polymers that can be used include polymers having rings such as polyvinyl pyridine and poly-N-vinyl pyrrolidone; polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, polyethyl acrylate, poly Acrylic derivative polymers such as acrylic acid, polymethacrylic acid and polyacrylamide; Fluorine resins such as polyvinyl fluoride and polyvinylidene fluoride; CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide; polyvinyl acetate, polyvinyl alcohol, etc. Polyvinyl alcohol polymers such as: halogen-containing polymers such as polyvinyl chloride and polyvinylidene chloride. Of these, polymethyl methacrylate, polyacrylonitrile, polyethylene oxide, or modified products thereof are preferably used. Mixtures, modified products, derivatives, random copolymers, alternating copolymers, graft copolymers, block copolymers, and the like of the above polymers can also be used. The weight average molecular weight of these polymers is preferably in the range of 10,000 to 5,000,000. If the molecular weight is low, it is difficult to form a gel. On the other hand, if the molecular weight is too high, the viscosity becomes too high and handling becomes difficult.
[0077]
Various additives can be added to the electrolyte as needed to improve battery performance. Although it does not specifically limit as an additive which expresses such a function, Trifluoropropylene carbonate, 1,6-dioxaspiro [4,4] nonane-2,7-dione, 12-crown-4-ether, vinylene Examples thereof include carbonate, catechol carbonate, and succinic anhydride.
[0078]
As described above, an overcharge inhibitor can be contained in the battery, but these overcharge inhibitors are usually present in the electrolyte.
The electrolyte layer is usually formed by impregnating an electrolyte in a spacer made of a porous sheet.
The thickness of the electrolyte layer is usually 1 to 200 μm, preferably 5 to 100 μm.
[0079]
Specifically, a porous sheet having a thickness of usually 1 μm or more, preferably 5 μm or more, and usually 200 μm or less, preferably 100 μm or less, more preferably 50 μm or less is used. The porosity is usually 10 to 95%, preferably about 30 to 85%. As a material for the porous sheet, polyolefin or polyolefin in which a part or all of hydrogen atoms are fluorine-substituted can be used. Specifically, a microporous film, a nonwoven fabric, a woven fabric or the like formed using a synthetic resin such as polyolefin can be used. Moreover, the thin film which consists of powder and a binder can be used.
[0080]
【Example】
EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited at all by the following Example, In the range which does not change the summary, it can change suitably and can implement. In addition, the part in a composition shows a weight part.
Positive electrode production example 1
90 parts of lithium cobaltate, 5 parts of acetylene black, 5 parts of polyvinylidene fluoride and 80 parts of N-methyl-2-pyrrolidone were kneaded with a kneader for 2 hours to obtain a positive electrode paint 1.
[0081]
Next, the positive electrode paint 1 is applied to an aluminum current collector base material having a thickness of 20 μm by an extrusion type die coating and dried, and consists of a porous film in which the active material is bound on the current collector by a binder. An active material layer was formed. Subsequently, after compacting using a roll press (calendar), it was cut into the positive electrode 1.
  Positive electrode production example 2
  A positive electrode 2 was obtained in the same manner as the positive electrode production example 1 except that the positive electrode paint 2 using 45 parts of lithium cobaltate and 45 parts of lithium nickelate was used instead of 90 parts of lithium cobaltate.
  Negative electrode production example
  90 parts of graphite (particle size 15 μm), 10 parts of polyvinylidene fluoride andN-100 parts of methyl-2-pyrrolidone was kneaded with a kneader for 2 hours to obtain a negative electrode paint 1.
[0082]
Next, the negative electrode paint 1 is coated on a 20 μm thick copper current collector substrate by extrusion die coating and dried, and an active material comprising a porous film in which the active material is bound on the current collector by a binder. A material layer was formed. Subsequently, after compaction using a roll press (calendar), it was cut to obtain a negative electrode 1.
Electrolytic paint preparation example 1
1M LiPF₆925 parts of a mixed liquid of ethylene carbonate, propylene carbonate and phenyl ether (volume ratio; ethylene carbonate: propylene carbonate: phenyl ether = 7.3: 7.3: 1), 44 parts of tetraethylene glycol diacrylate, 22 parts of polyethylene oxide triacrylate, 2 parts of a polymerization initiator, and 9 parts of an additive (succinic anhydride) were mixed and dissolved under stirring to obtain an electrolyte coating 1.
Electrolytic paint preparation example 2
An electrolyte paint 2 was prepared in the same manner as in the electrolyte paint production example 1 except that the mixing ratio of ethylene carbonate, propylene carbonate and phenyl ether was 6.2: 6.2: 1 by volume.
Example 1
After applying the electrolyte coating 1 to the positive electrode 1 and the negative electrode 1 and laminating the polyethylene porous film soaked in the electrolyte coating 1 between them, the electrolyte is made non-fluidized by heating at 90 ° C. for 10 minutes, A flat unit cell element having a positive electrode, a negative electrode, and a non-fluidizing electrolyte as shown in FIG. 9 was prepared.
[0083]
After stacking the obtained unit battery elements, the terminal portions of the positive electrodes and the negative electrodes were bundled, and leads for taking out current were connected to the respective terminal portions. Then, after accommodating a laminate film having a resin layer on both sides of the aluminum layer and having a thickness of about 100 μm in a facing material as shown in FIG. 5, 133 parts of tetraethylene glycol diacrylate, 67 parts of polyethylene oxide triacrylate, polymerization An appropriate amount of an insulating material composed of 1 part of an initiator was injected in the vicinity of the positive electrode terminal part and the negative electrode terminal part as shown in FIGS. 14 to 17 to cover the entire battery element side surface from the positive electrode terminal part to the negative electrode terminal part. After the laminate film was sealed with a vacuum seal, the joining piece part excluding the side from which the lead was taken out was bent along the encapsulated part. Thereafter, the battery was heated at 90 ° C. for 3 minutes to fix the terminal portion with an insulating material. The bent joining piece part was adhered to the side surface of the exterior material encapsulating part with a commercially available epoxy adhesive to prepare a flat battery A. The battery capacity of the battery thus prepared was 650 mAh.
[0084]
An overcharge test was performed on the flat battery A.
That is, charging and discharging between nominal operating voltages were performed for 3 cycles at a constant current of 0.65A. The thickness of the discharged battery was 3.9 mm (the total thickness of the battery elements was 3.7 mm). Next, the upper limit voltage was set to 10 V, and the battery was continuously charged from a 3 V state at a constant current of 1.8 C (1.17 A) for 200 minutes. As a result, the thickness of the battery after overcharging was 5.9 mm (of the battery element The total thickness was 5.7 mm. Further, no gas leakage during overcharging was observed, and the maximum temperature on the battery surface was 108 ° C. In such a battery, no gas leakage due to tearing of the exterior material was observed even when pressure was applied to the battery after overcharging.
[0085]
Subsequently, using the flat battery A, the upper limit voltage was set to 10 V, and the battery was continuously charged from the discharged state at a constant current of 1.95 A for 120 minutes or at a constant current of 3 A for 80 minutes. The maximum temperatures are 136 ° C. and 165 ° C., respectively, and no smoke or ignition of the battery in an overcharged state is observed, and the above battery is a highly safe battery that can withstand overcharge under a high current. understood.
Example 2
A flat battery B was prepared in the same manner as in the production of the flat battery A of Example 1 except that the electrolyte paint 2 was used instead of the electrolyte paint 1. The battery capacity of the battery thus prepared was 650 mAh.
[0086]
The flat battery B was charged and discharged between operating voltages at a constant current of 0.65 A for 3 cycles. The thickness of the discharged battery was 3.7 mm (the total thickness of the battery elements was 3.5 mm). Next, the upper limit voltage was set to 10 V, and the battery was continuously charged from a 3 V state at a constant current of 1.8 C (1.17 A) for 200 minutes. As a result, the thickness of the battery after overcharging was 6.4 mm (battery element The total thickness was 5.9 mm). Further, no gas leakage at the time of overcharging was observed, and the maximum temperature on the battery surface was 107 ° C. In such a battery, no gas leakage due to tearing of the exterior material was observed even when pressure was applied to the battery after overcharging.
[0087]
Subsequently, using the flat battery B, the upper limit voltage was set to 10 V, and the battery was continuously charged from the discharged state at a constant current of 1.95 A for 120 minutes or at a constant current of 3 A for 80 minutes. The maximum temperatures are 117 ° C. and 130 ° C., respectively, and no smoke or ignition of the battery in the overcharged state is observed, and the battery B is a highly safe battery that can withstand overcharge under a high current. I found out.
Example 3
A flat battery C was prepared in the same manner as in Example 1 except that the positive electrode 2 was used instead of the positive electrode 1. The battery capacity of the battery thus prepared was 700 mAh.
[0088]
Flat batteryCThe battery was charged and discharged between operating voltages at a constant current of 0.7 A for 3 cycles. The thickness of the discharged battery was 3.90 mm (the total thickness of the battery elements was 3.7 mm). Next, the upper limit voltage was set to 10 V and the battery was continuously charged from a 3 V state with a constant current of 1.8 C (1.26 A) for 200 minutes. As a result, the thickness of the battery after overcharging was 6.9 mm (of the battery element The total thickness was 6.4 mm). Further, no gas leakage during overcharging was observed, and the maximum temperature on the battery surface was 117 ° C. In such a battery, no gas leakage due to tearing of the exterior material was observed even when pressure was applied to the battery after overcharging.
  Example 4
  A flat battery D was prepared in the same manner as in Example 3 except that the sealing part (joining piece part) was not bent and the fixing to the enveloping part was not performed. The battery capacity of the battery thus prepared was 700 mAh.
[0089]
The flat battery D was charged and discharged between operating voltages at a constant current of 0.7 A for 3 cycles. The thickness of the discharged battery was 3.9 mm (the total thickness of the battery elements was 3.7 mm). Next, the upper limit voltage was set to 10 V, and the battery was continuously charged from a 3 V state at a constant current of 1.8 C (1.26 A) for 200 minutes. As a result, the thickness of the battery after overcharging was 7.3 mm (of the battery element The total thickness was 6.8 mm). Further, no gas leakage at the time of overcharging was observed, and the maximum temperature on the battery surface was 123 ° C. In such a battery, no gas leakage due to tearing of the exterior material was observed even when pressure was applied to the battery after overcharging.
Comparative Example 1
A flat battery E was produced in the same manner as in Example 1 except that the terminal part was not fixed and the seal part was not adhered to the encapsulated part. The battery capacity of the battery thus prepared was 650 mAh.
[0090]
The obtained flat battery E was charged and discharged between nominal operating voltages at a constant current of 0.65 A for 3 cycles. The thickness of the discharged battery was 3.9 mm (the total thickness of the battery elements was 3.7 mm). Next, the upper limit voltage was set to 10 V, and the battery was continuously charged from a 3 V state at a constant current of 1.8 C (1.17 A) for 200 minutes. As a result, the battery swelled during overcharging and smoked after 72 minutes. Gas leakage during charging was observed. At that time, the maximum temperature of the battery surface was 140 ° C.
[0091]
Moreover, as a result of using the flat battery E and setting the upper limit voltage to 10 V and continuing to charge the battery at a constant current of 1.95 A from the discharged state, the battery ignited after 38 minutes.
Comparative Example 2
A flat battery F was prepared in the same manner as in Comparative Example 1 except that the electrolyte paint 2 was used instead of the electrolyte paint 1. The battery capacity of the battery thus prepared was 650 mAh.
[0092]
The obtained flat battery F was charged and discharged between operating voltages at a constant current of 0.65 A for 3 cycles. The thickness of the discharged battery was 3.9 mm (the total thickness of the battery elements was 3.7 mm). Next, the upper limit voltage was set to 10 V, and the battery was continuously charged from a 3 V state at a constant current of 1.8 C (1.26 A) for 200 minutes. As a result, the thickness of the battery after overcharging was 17.1 mm (battery element The total thickness was 6.3 mm). The maximum temperature on the surface of the battery was 92 ° C., and no gas leakage during overcharging was observed. However, when such a battery was crushed by hand with an overcharged battery, the exterior material was broken and gas leakage occurred. Was observed.
Comparative Example 3
A flat battery G was prepared in the same manner as in Comparative Example 1 except that the positive electrode 2 was used instead of the positive electrode 1. The battery capacity of the battery thus prepared was 700 mAh.
[0093]
The obtained flat battery G was charged and discharged between operating voltages at a constant current of 0.70 A for 3 cycles. The thickness of the discharged battery was 3.8 mm (the total thickness of the battery elements was 3.6 mm). Next, the upper limit voltage was set to 10V, and as a result of continuously charging the battery from the 3V state at a constant current of 1.8C (1.26A) for 200 minutes, the thickness of the battery after overcharging was 15.0 mm (battery element The total thickness was 6.5 mm). The maximum temperature on the surface of the battery was 115 ° C., and no gas leakage during overcharging was observed. However, when such a battery was crushed by hand with an overcharged battery, the exterior material was broken and gas leakage occurred. Was observed.
[0094]
【The invention's effect】
According to the present invention, elucidation of a problem inherent to lithium secondary batteries, particularly safety during overcharge, and suppressing swelling of the battery during overcharge, damage of equipment used during overcharge and It is possible to provide a lithium secondary battery that prevents corrosion of used equipment due to the generated gas and leakage of toxic gases such as organic gas and improves the safety of the battery. Therefore, a lithium secondary battery having an intrinsic safety function is realized, and a safe lithium secondary battery can be obtained without taking other measures against overcharge. Moreover, it can be set as a safer lithium secondary battery by using together with another countermeasure against overcharge.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view of a battery according to an embodiment.
FIG. 2 is a cross-sectional view of a main part of the battery according to the embodiment.
FIG. 3 is a perspective view showing a battery element of the battery according to the embodiment.
FIG. 4 is a perspective view of a battery according to an embodiment.
FIG. 5 is a perspective view in the middle of manufacturing a battery according to another embodiment.
FIG. 6 is a perspective view in the middle of manufacturing a battery according to still another embodiment.
FIG. 7 is a perspective view in the middle of manufacturing a battery according to another embodiment.
FIG. 8 is a plan view in the middle of production of the implementation of FIG. 7;
FIG. 9 is a schematic cross-sectional view of a unit battery element.
FIG. 10 is a schematic cross-sectional view of a positive electrode or a negative electrode.
FIG. 11 is a schematic cross-sectional view of a battery element.
FIGS. 12A and 12B are longitudinal sectional views showing an example of a composite material constituting an exterior material.
FIG. 13 is a longitudinal sectional view showing another example of a composite material constituting an exterior material.
FIG. 14 is a perspective view in the middle of manufacturing a battery according to another embodiment.
15 is a plan view schematically showing the state of FIG.
16 is an enlarged view of a main part of FIG.
FIG. 17 is a cross-sectional view showing an injection state of an insulating material.
FIG. 18 is an enlarged cross-sectional view of a tab portion of a battery element.
[Explanation of symbols]
1 Battery element
2, 3, 6, 7, 8 Exterior material
4a, 4b tab
4A, 4F Joint piece
4B, 4G encapsulation
5 Insulation material
11 Positive electrode
11a Cathode active material
12 Negative electrode
12b Negative electrode active material
13 Non-fluidic electrolyte layer
15a Positive electrode current collector
15b Negative electrode current collector
21 Lead
22 Positive current collector
23 Cathode active material
24 Spacer (electrolyte layer)
25 Negative electrode active material
26 Negative electrode current collector
40 metal layers
41, 42 Synthetic resin layer
43 Adhesive layer
50 Infusion device
51 nozzles

Claims (12)

A battery element having a positive electrode and a negative electrode is a lithium secondary battery sealed with an exterior material , and the battery element is formed by laminating a plurality of flat unit battery elements in the thickness direction. Part of the positive electrode and part of the negative electrode are bundled together between the unit battery elements to form the positive electrode terminal part and the negative electrode terminal part, and the entire battery element side surface from the positive electrode terminal part to the negative electrode terminal part is covered with an insulating material. secured to it with and without gas leaking into the battery out by the following overcharge test, the lithium, wherein the thickness of the battery after the test (a) is less than 190% of the thickness of the battery before the test Secondary battery.
Overcharge test A battery having a battery voltage of 3V is continuously charged with a current of 1.8C for 200 minutes in a range where the upper limit voltage is 10V. However, 1C is a current value for discharging the capacity obtained by charging the battery voltage from 2.7 V to a 4.2 V constant voltage until the current value becomes 0 in one hour. The lithium secondary battery according to claim 1, wherein the total thickness (B) of the battery element immediately after the overcharge test is 190 % or less of the total thickness of the battery element before the test.  The lithium secondary battery according to claim 1 or 2, wherein the difference between the battery thickness (A) immediately after the overcharge test and the total thickness (B) of the battery elements is 2 mm or less.  A film-shaped exterior material forms a joining piece formed by joining the peripheral edges of the film and an enveloping part encapsulating the battery element, and at least a part of the joining piece is encapsulated. The lithium secondary battery according to claim 1, wherein the lithium secondary battery is bent along the portion. The lithium secondary battery according to claim 4 , wherein the joining piece is fixed to the enveloping part. The lithium secondary battery according to any one of claims 1 to 5 , wherein a thickness of the exterior material is 0.2 mm or less. The lithium secondary battery according to any one of claims 1 to 6 the thickness of the battery is 2mm or more. The lithium secondary battery according to any one of claims 1 to 7 capacity of the battery is not less than 100 mAh. The lithium secondary battery according to any one of claims 1 to 8 , wherein the exterior material is a laminate film in which a synthetic resin layer and a metal layer are laminated. The lithium secondary battery according to the electrolyte, any one of claims 1 to 9 having a non-flowable electrolyte. The lithium secondary battery according to the electrolyte, any one of claims 1 to 10 comprising a LiPF _6. The lithium secondary battery according to any one of claims 1 to 11 , wherein the positive electrode contains lithium cobaltate and / or lithium nickelate.

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