JP5820531B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to an electrode of a storage battery including a lithium ion secondary battery, and a storage battery having this electrode.

  In recent years, there has been a demand for energy conservation against the background of fossil fuel resource conservation and global warming. Among secondary batteries, large-capacity, small-sized lithium ion secondary batteries are an important power storage for realizing an energy-saving society. Expected as a device. For this reason, demand is expanding mainly in consumer applications as power sources for portable information terminals and cordless electronic devices, industrial applications such as power sources for power tools and power storage, and in-vehicle applications such as electric vehicles and hybrid electric vehicles. In addition, development for improving battery performance represented by high capacity is accelerating according to such various uses.

  In order to increase the capacity of lithium ion secondary batteries, efforts are being made to change the type of active material used for the electrodes. In the amorphous carbon typified by the negative electrode active material that has been used so far, the amount of expansion and contraction of the active material is not a problem in the lithium insertion / extraction process associated with charge / discharge. However, by changing the negative electrode active material to graphite having a higher capacity, the amount of expansion and contraction of the active material during charging / discharging becomes larger than that of amorphous carbon. By repeating the charge and discharge cycle, the volume of graphite expands by about 10 to 30%.

  On the other hand, efforts are being made to improve the mounting density of the electrode active material mixture in order to achieve higher capacity. However, by increasing the mounting density of the active material mixture, the internal stress applied to the electrode increases due to the expansion of the active material in the charge / discharge process. When the internal stress during the expansion of the electrode active material increases, the pores existing between the active materials are crushed, and the movement of lithium ions moving in the electrolyte filled in the pores is hindered. Decrease and battery performance degradation occur. In addition, the internal stress applied to the electrode causes the electrode to break or buckle, causing an internal short circuit and reducing the safety of the battery.

  For such a problem, there is JP 2011-8929 A (Patent Document 1) as a background art in this technical field. This publication states that “a resin that softens with at least one of a positive electrode plate and a porous insulator or between a negative electrode plate and a porous insulator with a non-aqueous electrolyte to relieve stress due to expansion and contraction of the electrode plate. To constitute an electrode group. "

  Patent Document 2 discloses that a “positive electrode plate having a positive electrode mixture layer formed on a positive electrode current collector and a negative electrode plate having a negative electrode mixture layer formed on a negative electrode current collector are wound through a separator. An electrode group, and at least one of the positive electrode plate and the negative electrode plate is an uncoated portion where a mixture layer is not formed on the current collector in a curved portion at the end of the electrode group in the major axis direction. And the exterior case is a laminate exterior ”.

JP 2011-8929 A JP2011-119145A

  In the lithium ion secondary battery described in Patent Document 1, since a resin that relaxes expansion and contraction is disposed on at least one of the positive electrode plate, the separator (porous insulator), and the negative electrode plate, internal stress applied to the electrode Can be mitigated. However, since the electrode volume is increased by the resin to be installed, the battery capacity in the battery volume is reduced. This makes it difficult to achieve the purpose of improving battery capacity. In addition, the number of parts increases, leading to an increase in cost.

  On the other hand, in the lithium ion secondary battery described in Patent Document 2, there is an uncoated portion where a mixture layer containing an active material is not formed on the current collector, particularly in a curved portion where internal stress increases. It is effective for the relaxation of internal stress applied to the electrode accompanying the expansion of the active material. However, the electrode area occupying the entire area of the current collector is small by having an uncoated part where the mixture layer is not formed on the current collector with respect to the electrode group occupied by the curved part such as a cylindrical battery. In the same manner, the capacity is reduced.

  The present invention has been made in view of the above points, and the object of the present invention is to add to the electrode by expansion of the electrode active material without increasing the cost due to the increase in the number of parts and reducing the capacity occupied in the battery volume. It is to provide a wound type lithium ion secondary battery having a high capacity and little deterioration by alleviating internal stress.

  In order to solve the above problems, for example, the configuration described in the claims is adopted.

  The present application includes a plurality of means for solving the above problems. To give an example, an electrode group in which an electrode plate is wound, a battery can in which the electrode group is accommodated, and a liquid injection into the battery can A lithium ion secondary battery having an electrolyte solution that is attached to the outer peripheral surface of the electrode group and maintains the wound state of the electrode group, and is deformed according to the radial expansion of the electrode group And holding means for allowing the expansion.

  According to the present invention, it is possible to relieve the internal stress applied to the electrode without increasing the number of parts, and the collapse of the electrode layer provided on the electrode plate can be avoided. By avoiding the collapse of the electrode layer, the pores between the active materials formed in the electrode layer can be prevented from being crushed and blocked, the movement of lithium ions in the electrolyte is not inhibited, Battery performance degradation can be suppressed. Further, since the electrode area is not reduced and the battery volume is not increased, the battery can be increased in capacity.

The top view which shows the structure of the lithium ion secondary battery which has a stretchable winding electrode group fixing tool which relieves the internal stress which stretches and applies to an electrode in 1st embodiment of this invention. The schematic diagram which shows the structure of the lithium ion secondary battery which has a stretchable wound electrode group fixing tool which relieves the internal stress applied to an electrode by expanding and contracting in the first embodiment of the present invention. The top view which shows the structure of the lithium ion secondary battery which has the soluble wound electrode group fixing tool which melt | dissolves in electrolyte solution gradually and lose | disappears in 2nd embodiment of this invention. The top view which shows the structure of the lithium ion secondary battery after electrode expansion in 2nd embodiment of this invention. The top view which shows the structure of the lithium ion secondary battery which has an expansion | swelling absorber which shrinks gradually with expansion | swelling of an electrode in 3rd embodiment of this invention. The schematic diagram which shows the usage method of the conventional winding electrode group fixing tool. The table | surface which shows the structure of a 18650 type cylindrical battery.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the following description shows the specific example of the content of this invention, and this invention is not limited to these description.

  Example 1 of the present invention is shown in the plan view of FIG. 1 and the schematic diagram of FIG. For comparison, FIG. 6 shows a schematic diagram of the conventional method.

  The lithium ion secondary battery C1 of Example 1 is a cylindrical lithium ion secondary battery, in which one stacked unit composed of a positive electrode plate, a separator 107, a negative electrode plate, and a separator 107 is wound around an axial core 109 to form an electrode group. 100 is formed and the battery can 101 is housed in this structure. In some cases, the shaft core 109 may be removed after the wound electrode group is created and does not exist.

  The outermost periphery of the electrode group 100 is wound so as to be covered with the separator 107, and the wound electrode group end portion 110, which is the end of the winding, is fixed with the tape 102 so that the winding cannot be unwound. It has become.

  The electrode group 100 fulfills a charge / discharge function as a battery electrode by mounting the positive electrode plate, the separator 107, the negative electrode plate, and the separator 107 in a state of being wound and in close contact with each other. The tape 102 is a necessary component for maintaining the adhesion when the electrode group 100 is formed, and is attached to the outer peripheral surface of the electrode group 100 to maintain the wound state of the electrode group 100. It has a function as a holding means that deforms according to the expansion in the direction and allows the expansion.

  One end of the tape 102 is attached to the wound electrode group end 110, the other end projects from the wound electrode group end 110, and the other end is attached to the outer peripheral surface of the electrode group 100. It has elasticity that expands and contracts along the winding direction of the electrode group according to expansion and contraction. And it is attached so that it may extend over the winding axis direction of the electrode group 100. FIG. Specific examples of the material of the tape 102 include a polypropylene tape and a polyester tape that have a higher elongation rate than polyimide, but are not limited thereto.

  The positive electrode plate (electrode plate) is configured by forming a positive electrode active material layer (electrode layer) 103 containing a positive electrode active material, a conductive additive, and a binder on a positive electrode current collector foil (current collector) 104. Similarly, the negative electrode plate (electrode plate) is configured by forming a negative electrode active material layer (electrode layer) 105 containing a negative electrode active material, a conductive additive, and a binder on a negative electrode current collector foil (current collector) 106. The Here, the positive electrode active material layer 103 and the negative electrode active material layer 105 may include an additive and the like in addition to the active material, the conductive additive, and the binder. The positive electrode active material layer 103 and the negative electrode active material layer 105 have pores through which the electrolytic solution can permeate between the active materials.

  In general, an aluminum foil is used for the positive electrode current collector foil 104, and a copper foil is used for the negative electrode current collector foil 106. However, a conductive material such as a nickel foil or a stainless steel foil may be used. It is not limited to.

  Examples of the active material of the positive electrode active material layer 103 include lithium cobaltate, lithium nickelate, and lithium manganate, but are not limited thereto and can be changed as appropriate. Two or more kinds of substances may be used. Examples of the active material of the negative electrode active material layer 105 include graphite and lithium titanate. However, the active material is not limited to this and can be changed as appropriate.

  The separator 107 is interposed between the positive electrode plate and the negative electrode plate to prevent direct contact between the positive electrode plate and the negative electrode plate and to maintain ionic conductivity. A porous material having a part is often used. Examples of the porous material include polyolefin, polyethylene, and polypropylene, but are not limited thereto.

An electrolytic solution (not shown) enters the pores of the separator 107, the positive electrode active material layer 103, and the negative electrode active material layer 105 and exists. Here, the electrolytic solution functions as an ionic conductive phase, and a non-aqueous electrolyte is used in the lithium ion secondary battery. The electrolytic solution is composed of a lithium salt such as LiPF ₆ , LiBF ₄ , and LiClO ₄ and a solvent such as ethylene carbonate or diethyl carbonate. Further, the electrolytic solution is not limited to a liquid or gel but may be a solid.

  The cylindrical lithium ion secondary battery C1 shown in FIG. 1 is characterized in that the tape 102 is made of a material that can expand and contract in accordance with the expansion and contraction of the electrode group 100 during the charge / discharge process. Furthermore, although the electrode group 100 expands due to the expansion of the positive electrode active material layer 103 and the negative electrode active material layer 105, the tape 102 is made of a material that gradually expands following the expansion.

  Usually, since there is a certain amount of space between the longitudinal battery ends and the battery can between the cylindrical battery electrode group and the battery can, this space is used as the expansion / contraction absorption section 108 to expand and contract the electrode. Can be absorbed. That is, the stretchable tape 102 expands in response to the expansion of the electrode group 100, and the electrode group 100 expands into the expansion / contraction absorption part 108 without crushing the pores between the active materials formed in the electrode layer. Can do.

  If the expansion / contraction absorption part 108 is excessively large, it leads to a reduction in capacity and cost increase in the battery volume, so that the expansion / contraction absorption part 108 only needs to be large enough to absorb the expansion of the electrode group 100. In particular, when graphite is used as the active material of the negative electrode active material layer 105, the electrode group 100 expands by about 10% to 30% due to expansion / contraction due to a lithium insertion / extraction process during charging.

  Here, as a typical example of the cylindrical lithium ion secondary battery, an 18650 type battery, that is, a cylindrical battery having a diameter of 18 mm and a length of 65 mm will be described. The configuration of the 18650 type battery is shown in the table of FIG. From the table shown in FIG. 7, the thickness of the negative electrode active material layer 105 in the radial direction is 0.56 mm × 2 = 1.12 mm. When the negative electrode active material expands by about 30%, the thickness increment of the electrode group 100 is 0.336 mm. Therefore, the expansion and contraction absorbing portion 108 in the radial direction may have a size of about 0.30 mm to 0.35 mm, and the capacity occupying the battery volume is reduced by slightly reducing the radius of the shaft core, the thickness of the separator, and the outer wall of the battery can. It is applicable without accompanying.

  Conventionally, as shown in FIG. 6, in order not to expand the electrode group 100 in the radial direction, the entire circumference in the circumferential direction is restrained and fixed by the rigid wound electrode group fixture 600 (a wound type fixing method). Here, the height of the rigid wound electrode group fixture 600 in the longitudinal direction is a tape having a width of about one third to one times the electrode height, but is not particularly limited. In addition, as a material of the rigid wound electrode group fixture 600, a polyimide tape having an insulating property and small stretchability is usually used.

  However, even if restrained by the rigid wound electrode group fixture 600, the active material expands due to repeated charge and discharge, and thus the thickness change in the radial direction of the electrode group 100 is suppressed. A strong compressive force is applied to the layers 103 and 105, and the pores between the active materials existing in the active material layers 103 and 105 are crushed. Here, when disassembling and observing the deteriorated battery after the charge / discharge cycle in the conventional product, the pores between the active materials at positions fixed by the rigid wound electrode group fixture 600 are mainly crushed. I found out that By crushing the pores between the active materials, as described above, the movement of lithium ions in the electrolytic solution is hindered, leading to battery capacity reduction and battery performance deterioration.

  Therefore, in this embodiment, as shown in FIG. 2, a configuration is adopted in which the wound electrode group end portion 110 is fastened with a stretchable tape 102. One end of the tape 102 is attached to the wound electrode group end 110, the other end projects from the wound electrode group end 110, and the other end is attached to the outer peripheral surface of the electrode group 100. It has elasticity that expands and contracts along the winding direction of the electrode group according to expansion and contraction.

  Accordingly, internal stress acting on the electrode group 100 due to the expansion of the electrode group 100 can be relaxed. As the electrode group 100 expands, the tape 102 expands along the winding direction as shown by an arrow in FIG. 1 to suppress the compressive force from acting on the active material layers 103 and 105, and the active material layer It can prevent that the pore which exists in 103,105 is crushed.

  According to the lithium ion secondary battery C1 of the present embodiment, since the tape 102 is attached so as to extend over the winding axis direction of the electrode group 100, when the electrode group 100 expands in the radial direction, the electrode The group 100 can be clamped with a uniform force over the winding axis direction. Therefore, it is possible to prevent a compressive force from acting locally on a part in the winding axis direction as in the prior art.

  Next, the configuration of the second embodiment is shown in FIG. Further, FIG. 4 shows a configuration after the expansion by repeating the charge / discharge cycle in FIG. Here, the description is abbreviate | omitted about the part which has the same code | symbol shown by already demonstrated FIG. 1, FIG. 2, and the part which has the same function.

  What is characteristic in this embodiment is that the electrode group 100 is externally fitted to the electrode group 100 instead of the tape 102 of the first embodiment, or is applied continuously to the outer peripheral surface of the electrode group 100 in a circumferential manner. The outer peripheral surface of the electrode assembly 100 is covered, and a soluble covering 300 is provided which gradually dissolves as the electrode group 100 expands in the radial direction due to permeation of the electrolyte, and the thickness gradually decreases.

  And when the electrode group 100 expand | swells to the magnitude | size which contacts the battery can 101, the coating body 300 may melt | dissolve completely and may lose | disappear. Furthermore, it is desirable that the covering 300 includes an additive that suppresses deterioration of the electrolytic solution due to repeated charge / discharge cycles.

  As described above, in the initial stage of battery use before the electrode group 100 expands, it is necessary to maintain the adhesion of the positive electrode plate, the separator 107, the negative electrode plate, and the separator 107 in the electrode group 100. However, as the charge / discharge cycle is repeated, the electrode group 100 gradually expands. Therefore, as shown in FIG. 4, the electrode group 100 comes into contact with the inner peripheral surface of the battery can 101 and the electrode group 100 becomes the battery can. In the stage held by 101, the covering 300 becomes an unnecessary part.

  Therefore, by adopting a material that gradually dissolves the covering 300 in the electrolytic solution as the electrode group 100 expands and does not deteriorate the performance of the electrolytic solution, The pores are not crushed and battery performance deterioration can be suppressed. Furthermore, by using the covering 300 that is dissolved by the electrolytic solution, high permeability of the electrolytic solution with respect to the electrode group 100 is exhibited, and the effect of improving the initial battery performance is also exhibited.

  The covering body 300 may be a cylinder that is externally fitted to the electrode group 100, or a coating material that is continuously applied to the outer peripheral surface of the electrode group 100 in a circumferential manner to cover the outer peripheral surface of the electrode group 100. . Specific examples of the material of the cover 300 include rubber adhesives, acrylic adhesives, silicone adhesives, and the like, and the solubility in the electrolytic solution is adjusted with a tackifier or the like. However, it is not limited to this.

  In addition, as an example of the structure of the covering 300 that dissolves in the electrolytic solution, an additive that suppresses the deterioration of the electrolytic solution is mounted in advance between the layers of the coating material that is continuously applied in a circumferential shape, and when the immersion is immersed in the electrolytic solution The additive dissolves in the electrolyte, and the battery life can be extended. Specific examples of the additive include vinylene carbonate which suppresses film growth and improves high temperature characteristics, but is not limited thereto. The covering body 300 is not limited to a cylindrical body or a coating material, and may be any adhesive body that can cover the electrode group 100, for example, an adhesive body that is attached to the outer peripheral surface of the electrode group 100.

  The configuration of Example 3 is shown in FIG.

  What is characteristic in the present embodiment is that the electrode group 100 is interposed between the outer peripheral surface of the electrode group 100 and the inner peripheral surface of the battery can 101 instead of the tape 102 of the first embodiment and the covering 300 of the second embodiment. In other words, the shrinkable expansion absorbent body 500 whose thickness gradually decreases in accordance with the expansion in the radial direction is provided.

  In this embodiment, the expansion / contraction absorption part 108 is not provided, but a contraction-type expansion absorber 500 is provided inside the battery can 101 to maintain the adhesion of the electrode group 100 and allow the electrode group 100 to expand. Shows how to do.

  Specifically, the expansion absorber 500 is configured with a porous film, and the expansion absorber 500 is configured to have flexibility such that the expansion absorber 500 gradually becomes thinner as the electrode group 100 expands. The porous film is made of a resin such as polyethylene, polypropylene or PPS, or a rubber such as EPDM. If more flexibility is required, one not reinforced with glass fiber is used. By being porous, the electrode assembly 100 can be flexibly deformed with respect to expansion. By adopting such a structure, since there is no space like the expansion / contraction absorption part 108, the displacement and vibration of the wound electrode group 100 inside the battery can 101 can be suppressed, and a longer life with higher safety. A battery can be obtained.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various designs can be made without departing from the spirit of the present invention described in the claims. It can be changed. For example, the above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to one having all the configurations described. Further, a part of the configuration of an embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of an embodiment. Furthermore, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

DESCRIPTION OF SYMBOLS 100 Electrode group 101 Battery can 102 Tape 103 Positive electrode active material layer 104 Positive electrode current collection foil (aluminum foil)
105 Negative electrode active material layer 106 Negative electrode current collector foil (copper foil)
107 Separator 108 Expansion / Shrink Absorption Portion 109 Axle Core 110 End of Winding Electrode Group (End of Firing)
300 Cover 500 Expansion Absorber 600 Rigid Winding Electrode Group Fixture C1 Lithium Ion Secondary Battery

Claims (3)

A lithium ion secondary battery comprising: an electrode group in which an electrode plate is wound; a battery can in which the electrode group is accommodated; and an electrolyte solution poured into the battery can,
A holding means that is attached to the outer peripheral surface of the electrode group and maintains the wound state of the electrode group, deforms according to the radial expansion of the electrode group, and allows the expansion;
The holding means is externally fitted to the electrode group or is continuously applied circumferentially to the outer peripheral surface of the electrode group to cover the outer peripheral surface of the electrode group, and by penetration of the electrolyte solution, A soluble coating that gradually dissolves with the radial expansion of the electrode group and the thickness gradually decreases,
The covering includes an additive that suppresses deterioration of the electrolytic solution,
The additive is gradually dissolved in the electrolytic solution as the covering is dissolved.   The lithium ion secondary battery according to claim 1, wherein the covering disappears by the dissolution. The electrode plate has a negative electrode plate in which a negative electrode active material layer is formed on the surface of a negative electrode current collector,
The lithium ion secondary battery according to claim 1 or 2 , wherein the negative electrode active material layer contains graphite as a negative electrode active material.

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