JP6501129B2 - Electrode structure of lithium ion battery - Google Patents

Description

  The present invention relates to an electrode structure of a lithium ion battery, and more particularly to an electrode structure for preventing ignition of a lithium ion battery.

  Conventionally, lithium ion batteries having high energy density have been used for consumer mobile devices and the like. Lithium ion batteries have excellent charge and discharge characteristics and can form a large capacity light weight, so in recent years, they are mounted on vehicles and are also used as power sources of electric motors for running the vehicles.

  In lithium ion batteries, when the temperature rises abnormally due to an overcharge, or when a part of the electrodes shorts due to an impact etc., there is a risk that the electrolyte containing the organic compound may be vaporized. . When the vaporized electrolyte is oxidized, the temperature further rises, and there is a risk that the lithium ion battery may ignite. In particular, it is necessary to mount an ignition prevention function on an on-vehicle lithium ion battery that may be subjected to an impact due to a collision of a vehicle or the like.

  Therefore, for example, as in Patent Document 1, microcapsules containing an electrode corrosion solution are compounded in the positive electrode active material mixture layer constituting the positive electrode of a lithium ion battery, and the microcapsules are decomposed by the potential during overcharge. There is known a technique of releasing an electrode corrosive solution and interrupting the electrical connection by corrosion of the electrode to prevent ignition. In addition, as in Patent Document 2, a solid flame retardant is compounded in the negative electrode active material mixture layer that constitutes the negative electrode of a lithium ion battery, and the electrolytic solution in which the flame retardant decomposed by heat during abnormal heat generation is vaporized Techniques for preventing ignition by preventing oxidation are known.

JP, 2016-62872, A JP, 2016-62855, A

  However, the technique of Patent Document 1 can not prevent the ignition of the lithium ion battery when the positive and negative electrodes are shorted by impact. In addition, even if a solid flame retardant is blended in the negative electrode active material mixture layer as in Patent Document 2, since the flame retardant is in contact with the electrolytic solution, a side reaction usually occurs during use to inhibit migration of lithium ions. Therefore, there is a problem that the charge and discharge performance of the lithium ion battery is lowered, and there is a problem that the capacity of the lithium ion battery is rapidly reduced with repeated charge and discharge. It is necessary to suppress such performance deterioration because the lithium ion battery for vehicle use has a large input / output compared with a consumer mobile device etc., and has a long service life and many repetitions of charge and discharge.

  An object of the present invention is to provide an electrode structure of a lithium ion battery capable of suppressing the performance deterioration and preventing the ignition.

  According to a first aspect of the present invention, in the electrode structure of a lithium ion battery including a current collector made of metal foil, an electrode active material electrically connected to the current collector on a surface of at least one side of the current collector. While a mixture layer is formed, a flame retardant assembly is formed in a predetermined pattern on a part of the surface, and the flame retardant assembly is decomposed at a predetermined temperature with a plurality of particulate flame retardants to form a gas. A plurality of particulate foaming agents to be generated are formed to be covered by a binder which melts at or near the predetermined temperature, and the electrode active material mixture layer comprises an active material, a conductive aid and the binder. And is formed to cover the current collector and the flame retardant assembly.

  According to the above configuration, normally, the flame retardant in the flame retardant collecting part does not touch the electrolytic solution or the active material. When the lithium ion battery abnormally generates heat due to overcharge or impact, the binder of the flame retardant assembly melts at the portion reaching the predetermined temperature of the electrode and the foaming agent generates gas to make the flame retardant an electrode active material It disperse | distributes to the electrolyte solution infiltrated in the mixture layer. Therefore, since the side reaction by a flame retardant does not arise at the time of normal use, and movement of lithium ion is not inhibited, the performance fall of a lithium ion battery can be suppressed. Further, during abnormal heat generation, the flame retardant is dispersed in the electrolytic solution to suppress oxidation of the vaporized electrolytic solution, so that ignition of the lithium ion battery can be prevented.

  In a second invention according to the first invention, the flame retardant is a phosphazene compound, the foaming agent is baking soda or azodicarbonamide, the binder is polyvinylidene fluoride, and the flame retardant aggregate is A thin film is formed by applying a mixture containing the flame retardant, the foaming agent, the binding agent, and N-methyl-2-pyrrolidone as a solvent to the current collector.

  According to the above configuration, it is possible to easily form a homogeneous flame retardant assembly covered with a binder on the surface of the current collector.

  The third invention is characterized in that, in the first or second invention, the active material is made of a carbon material.

  According to the above configuration, heat can be rapidly transmitted to the electrode active material mixture layer and the flame retardant assembly portion by utilizing the excellent thermal conductivity of the carbon material, so that the flame retardant can be produced immediately upon occurrence of abnormal heat generation. Can be dispersed in the electrolyte.

  According to the present invention, it is possible to provide an electrode structure of a lithium ion battery capable of suppressing the performance deterioration and preventing the ignition.

It is a principal part disassembled figure of the lithium ion battery which concerns on the Example of this invention. It is a principal part disassembled view of the winding body and insulating film of FIG. It is a principal part schematic diagram of the electrode which comprises the winding body of FIG. It is the IV-IV line | wire cross-section schematic diagram of the electrode of FIG. It is a cross-sectional schematic diagram which shows the reaction at the time of the abnormal heat generation of the electrode of FIG. It is a cross-sectional schematic diagram which shows the state after reaction of FIG.

  Hereinafter, the form for carrying out the present invention is explained based on an example.

First, the entire configuration of the lithium ion battery 1 will be described.
As shown in FIG. 1, the lithium ion battery 1 has a positive and negative electrode inside a rectangular parallelepiped case formed by a box-like case main body 2 with an open top and a lid member 3 for closing the opening. A wound winding body 10 is accommodated. An electrolytic solution (not shown) for immersing the wound body 10 is filled in the case.

  The case body 2 and the lid member 3 are formed of, for example, an aluminum material, and an insulating film (not shown) is formed on the inner wall surface of the case body 2 and the cover member 3. The positive electrode terminal 4 and the negative electrode terminal 5 for connecting to the external apparatus respectively connected to the positive / negative electrode of the accommodated winding body 10 at the cover member 3 are arrange | positioned in the shape of protrusion upwards. The lid member 3 and the case body 2 are joined, for example, by welding or the like, and sealed so that the electrolyte does not leak.

Next, the wound body 10 will be described.
As shown in FIG. 2, the wound body 10 is wound via a strip-like separator having substantially the same width as the positive electrode 11 and the negative electrode 12 so that the strip-like positive electrode 11 and the negative electrode 12 having substantially the same width do not contact each other. It is done. The separator is composed of a first separator 13 and a second separator 14.

  The wound body 10 has, for example, a strip-shaped first separator 13 having a width of 14 cm and a length of 18 m, a positive electrode 11, a second separator 14 and a negative electrode 12 stacked in this order, with the width direction being the winding axis direction. The winding body 10 is formed by winding 90 times flatly so that the negative electrode 12 is the outermost layer. The sizes of the positive electrode 11 and the negative electrode 12, the sizes of the first and second separators 13 and 14, the number of turns, and the like are not limited to the above, and are appropriately set according to the specifications of the lithium ion battery 1. An insulating film 15 covering the wound body 10 along the winding direction is disposed on the outer periphery of the wound body 10, and the wound state of the wound body 10 is maintained, and the outermost negative electrode 12 and the case contact To prevent

Next, the separator will be described.
The first and second separators 13 and 14 are insulators for preventing contact between the positive electrode 11 and the negative electrode 12. The first and second separators 13 and 14 are formed in a porous shape having a large number of pores with a diameter of about 0.1 to 1 μm to allow the electrolyte to infiltrate and lithium ions are allowed to pass through the pores. Can pass through the first and second separators 13 and 14. The first and second separators 13 and 14 are formed, for example, in the shape of a strip having a thickness of 20 to 30 μm by a synthetic resin material such as polyethylene or polypropylene.

Next, the positive electrode 11 will be described.
As shown in FIGS. 2 to 4, the strip-shaped positive electrode 11 has a plurality of flame retardant aggregation portions 20 and a positive electrode active material mixture layer as an electrode active material mixture layer on both sides of the current collector 11 a made of metal foil. 11b is provided over substantially the entire length of the current collector 11a. The flame retardant assembly 20 is periodically formed on both sides of the current collector 11a so as to cover a part of the surface of the current collector 11a in a predetermined pattern. The positive electrode active material mixture layer 11 b is formed on both sides of the current collector 11 a so as to cover the surface of the current collector 11 a except the flame retardant assembly 20 and the outer peripheral portion of the current collector 11 a. The positive electrode active material mixture layer 11 b is formed in a porous shape in which the electrolytic solution can infiltrate.

  The current collector 11a is, for example, a strip-like aluminum foil having a thickness of 10 to 20 μm. The flame retardant assembly 20 is formed to a thickness of, for example, 10 to 30 μm. The positive electrode active material mixture layer 11 b is formed to have a thickness of, for example, 40 to 100 μm.

  As shown in FIG. 4, the flame retardant assembly 20 has a plurality of particulate flame retardants 21 represented by white circles and a plurality of particulate foaming agents 22 represented by black circles, which are covered by the binding agent 23 and connected. It is done. The flame retardant assembly 20 uniformly disperses a plurality of particles of the flame retardant 21 and a plurality of particles of the foaming agent 22 in a solvent (N-methyl-2-pyrrolidone, hereinafter also referred to as NMP) in which the binder 23 is dissolved. The slurry (mixture) is applied in a thin film on the current collector 11a in a predetermined pattern, and then dried. The total mass of the flame retardant 21 contained in the positive electrode 11 is set in the range of 1 to 18 wt% with respect to the total mass of the positive electrode active material 24 described later contained in the positive electrode active material mixture layer 11 b.

  The foaming agent 22 is, for example, particles of sodium bicarbonate or azodicarbonamide having a particle diameter of 3 to 5 μm, and is decomposed at a predetermined temperature (for example, 130 to 140 ° C.) to generate a gas such as carbon dioxide. The flame retardant 21 is, for example, particles of a phosphazene compound having a particle size of 5 to 10 μm, and is decomposed at a temperature higher than the predetermined temperature to capture surrounding oxygen and prevent oxidation. The binding agent 23 is, for example, polyvinylidene fluoride, and melts at or near the predetermined temperature.

  The predetermined pattern is a periodic pattern for arranging the flame retardant assembly 20 at a predetermined interval so as to expose the surface of the current collector 11a. For example, a linear flame retardant assembly 20 having a width of 40 μm and a length approximately equal to the width of the positive electrode active material mixture layer 11 b is extended in the width direction of the current collector 11 a and in the longitudinal direction of the current collector 11 a A plurality of stripe patterns are formed periodically at intervals of 160 .mu.m in the longitudinal direction of the current collector 11a.

  It is also possible to use stripe patterns other than the above, or dot patterns or lattice patterns periodically formed. Such a predetermined pattern is set, for example, so that the area of the flame retardant assembly 20 per unit area of the current collector 11a is in the range of 10 to 30%, and the positive electrode active material mixture layer 11b and the current collector The influence on the electrical conduction between 11a is reduced.

  As shown in FIG. 4, the positive electrode active material mixture layer 11 b formed on the current collector 11 a includes a plurality of particulate positive electrode active materials 24, a plurality of particulate conductive aids 25, and a plurality of particles as active materials. The binding agent 26 is The positive electrode active material 24, the conductive additive 25, and the current collector 11 a are connected by the binder 26 in a state where they are in contact with each other, and the positive electrode active material mixture layer 11 b and the current collector 11 a are electrically connected.

  In the positive electrode active material mixture layer 11b, a mixture slurry in which the positive electrode active material 24 and the conductive support agent 25 are uniformly dispersed in NMP of a solvent in which the binder 26 is dissolved is applied to the current collector 11a and then dried. It is formed. A planarization process may be performed by a roller or the like.

  The formed positive electrode active material mixture layer 11 b contains, for example, 90 wt% of the positive electrode active material 24, 5 wt% of the conductive additive 25, and 5 wt% of the binding agent 26. The positive electrode active material 24 is, for example, a particulate lithium oxide having a particle diameter of 20 to 40 μm, and known lithium oxides such as lithium manganate and lithium nickelate can be used. The conductive support agent 25 is a particulate carbon material having a particle diameter of 1 to 10 μm, in which a plurality of particles such as graphite and acetylene black, for example, are linked. The binding agent 26 is, for example, an elongated particulate polyvinylidene fluoride having a length of 20 to 50 μm, and melts at or near the predetermined temperature. The material, the particle size, the content ratio, and the like included in the positive electrode active material mixture layer 11b described above are one example and are not limited to the above, and are appropriately set according to the specification of the lithium ion battery 1 and the like. Be done.

Next, the negative electrode 12 will be described.
As shown in FIGS. 2 to 4, the strip-shaped negative electrode 12 has a plurality of flame retardant aggregation portions 30 and a negative electrode active material mixture layer as an electrode active material mixture layer on both sides of a current collector 12 a made of metal foil. 12b is provided over substantially the entire length of the current collector 12a. The flame retardant assembly 30 is periodically formed on both sides of the current collector 12a so as to cover a part of the surface of the current collector 12a in a predetermined pattern. The negative electrode active material mixture layer 12 b is formed on both sides of the current collector 11 a so as to cover the surface of the current collector 11 a excluding the flame retardant assembly 30 and the outer peripheral portion of the current collector 12 a. The negative electrode active material mixture layer 12 b is formed in a porous shape in which the electrolytic solution can infiltrate.

  The current collector 12a is, for example, a strip-like copper foil having a thickness of 10 to 20 μm. The flame retardant assembly 30 is formed to a thickness of, for example, 10 to 30 μm. The negative electrode active material mixture layer 12 b is formed to a thickness of, for example, 40 to 100 μm. In the portion corresponding to the outer peripheral surface of the wound body 10 of the current collector 12a, the formation of the flame retardant assembly portion 20 and the negative electrode active material mixture layer 12b may be omitted.

  As shown in FIG. 4, the flame retardant assembly portion 30 has a plurality of particulate flame retardants 31 represented by white circles and a plurality of particulate foaming agents 32 represented by black circles, which are covered by the binder 33 and connected. It is done. The flame retardant 31, the foaming agent 32 and the binder 33 are equivalent to the flame retardant 21, the foaming agent 22 and the binder 23 of the positive electrode 11, respectively, and the other components of the flame retardant assembly 30 are those of the positive electrode 11. Since it is the same as the flame retardant assembly part 20, the description is omitted.

  The negative electrode active material mixture layer 12b formed on the current collector 12a includes a plurality of particulate negative electrode active materials 34, a plurality of particulate conductive aids 35, and a plurality of particulate binders 36 as active materials. Have. The negative electrode active material 34 is, for example, a carbon material such as particulate graphite having a particle diameter of 20 to 40 μm. The conductive assistant 35 and the binder 36 are equivalent to the conductive assistant 25 and the binder 26 of the positive electrode active material mixture layer 11 b, and the other constitution of the negative electrode active material mixture layer 12 b is a positive electrode active material composite layer Since it is the same as the agent layer 11b, the description is omitted.

  Similar to the positive electrode active material mixture layer 11b, for example, 90 wt% of the negative electrode active material 34 and 5 wt% of the conductive support agent 35 are formed on the negative electrode active material mixture layer 12b formed by applying to the current collector 12a. The binder 36 is contained at a ratio of 5 wt%. In addition, the material, the particle size, the content ratio, and the like included in the above-described negative electrode active material mixture layer 12 b are one example, and are not limited to the above, and are appropriately set according to the specifications of the lithium ion battery 1, etc. Be done.

Next, the electrolytic solution will be described.
The electrolytic solution is, for example, an electrolytic solution in which a lithium salt such as lithium hexafluorophosphate or lithium borofluoride is dissolved in a solvent obtained by mixing a high viscosity cyclic ester and a low viscosity chain ester, but is not limited thereto. A known non-aqueous electrolyte can be used. The electrolytic solution is filled in the case, and infiltrates into the first and second separators 13 and 14, the positive electrode active material mixture layer 11b, and the negative electrode active material mixture layer 12b.

Next, the operation and effects of the electrode structure of the lithium ion battery 1 of the present embodiment will be described.
As shown in FIG. 4, since the particulate flame retardants 21 and 31 contained in the flame retardant assembly portions 20 and 30 of the positive electrode 11 and the negative electrode 12 which are the electrodes are covered with the binding agents 23 and 33, usually Sometimes it does not contact the electrolyte and the active material. Therefore, the side reaction by the flame retardants 21 and 31 does not occur, and the movement of lithium ions is not inhibited. In addition, since the flame retardant assembly portions 20 and 30 are not on the lithium ion migration path between the positive electrode active material mixture layer 11 b and the negative electrode active material mixture layer 12 b, the movement of lithium ions is not hindered. Therefore, the performance deterioration of the lithium ion battery 1 can be suppressed.

  When the lithium ion battery 1 abnormally generates heat due to overcharge or impact, as shown in FIG. 5, the binder 23 of the flame retardant assembly 20, 30 at a portion where the predetermined temperature of the positive electrode 11 and the negative electrode 12 or its adjacent temperature is reached. 33 melts. In addition, bubbles (not shown) in the electrolytic solution infiltrated into the positive electrode active material mixture layer 11 b and the negative electrode active material mixture layer 12 b by the decomposition of the foaming agents 22, 32 that have reached a predetermined temperature to generate gas. Is formed. The formation of the foam and the movement of the formed foam are the driving force for moving the particulate flame retardant 21 and 31, and the flame retardant 21 and 31 can be dispersed in the electrolyte as shown in FIG. it can.

  When the temperature further rises due to abnormal heat generation, the dispersed flame retardants 21 and 31 are decomposed to exhibit an oxidation preventing function. Thereby, even if the electrolytic solution is vaporized, the oxidation is suppressed, so that the ignition of the lithium ion battery 1 can be prevented. The binders 26, 36 of the positive electrode active material mixture layer 11b and the negative electrode active material mixture layer 12b also melt when they reach a predetermined temperature or a temperature near the predetermined temperature, and do not prevent the dispersion of the flame retardants 21, 31.

  Further, a phosphazene compound is used as the flame retardant 21, 31, the foaming agent 22, 32 is sodium bicarbonate or azodicarbonamide, and the binding agent 23, 33 is polyvinylidene fluoride. The flame retardant assembly portions 20, 30 coat the current collectors 11a, 12a with a mixture containing the flame retardants 21, 31, the foaming agents 22, 32, the binders 23, 33, and the solvent N-methyl-2-pyrrolidone. Since it is formed by adhesion, it is possible to easily form the homogeneous thin film-like flame retardant assembly 20, 30 covered with the binding agents 23, 33 on the surface of the current collectors 11a, 12a.

  Although the flame retardant assembly portions 20 and 30 are formed on both the positive electrode 11 and the negative electrode 12, in particular, the flame retardant assembly portion 30 is formed on the current collector 12 a of the negative electrode 12 to form the anode active material mixture layer 12 b. As the heat can be rapidly transmitted to the negative electrode active material mixture layer 12b and the flame retardant assembly 30 by utilizing the excellent thermal conductivity of the carbon material which is the negative electrode active material 34 which occupies most of the components, abnormal heat generation occurs. As soon as it occurs, the flame retardant 31 can be dispersed in the electrolyte.

Next, an example in which the embodiment is partially changed will be described.
[1] A lithium ion battery having an electrode structure in which a flame retardant assembly is formed on only one of positive and negative electrodes may be configured. Manufacturing of a lithium ion battery having an ignition prevention function substantially equivalent to that of the lithium ion battery 1 in which the flame retardant assembly portions 20 and 30 are formed on both the positive and negative electrodes can be facilitated.
[2] The wound body 10 may be formed by being stacked in the order of the positive electrode 11, the first separator 13, the negative electrode 12, and the second separator 14 so that the second separator 14 becomes the outermost periphery. At this time, the insulating film 15 covering the outer periphery of the wound body 10 may be omitted.
[3] The lithium ion battery may be formed of a laminate in which a plurality of positive electrodes 11 and negative electrodes 12 having an electrode structure provided with the flame retardant assembly portions 20 and 30 are alternately stacked via a separator.
[4] In addition, those skilled in the art can implement the embodiment in various modifications without departing from the spirit of the present invention, and the present invention includes such modifications. It is.

DESCRIPTION OF SYMBOLS 1 lithium ion battery 10 winding body 11 positive electrode 11a current collector 11b positive electrode active material mixture layer 12 negative electrode 12a current collector 12b negative electrode active material mixture layer 20, 30 flame retardant aggregation part 21, 31 flame retardant 22, 32 foaming Agent 23, 33, binder 24, positive electrode active material 25, 35, conductive assistant 26, 36, binder 34, negative electrode active material

Claims (3)

In an electrode structure of a lithium ion battery provided with a current collector made of metal foil,
An electrode active material mixture layer electrically connected to the current collector is formed on the surface of at least one side of the current collector, and a flame retardant assembly is formed in a predetermined pattern on part of the surface. Formed
The flame retardant assembly is covered with a plurality of particulate flame retardants and a plurality of particulate foaming agents which are decomposed at a predetermined temperature to generate a gas by a binder which melts at or near the predetermined temperature. Formed
The electrode active material mixture layer includes an active material, a conductive support agent, and the binding agent, and is formed to cover the current collector and the flame retardant assembly portion. Construction. The flame retardant is a phosphazene compound, the foaming agent is sodium bicarbonate or azodicarbonamide, and the binder is polyvinylidene fluoride.
The flame retardant assembly is formed into a thin film by applying a mixture containing the flame retardant, the foaming agent, the binder, and N-methyl-2-pyrrolidone as a solvent to the current collector. The electrode structure of a lithium ion battery according to claim 1, characterized by:   The electrode structure of a lithium ion battery according to claim 1 or 2, wherein the active material is made of a carbon material.