JP2016201231A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery in which discharge of nonaqueous electrolyte from a wound electrode body is suppressed.SOLUTION: A nonaqueous electrolyte secondary battery includes a wound electrode body 20 formed by winding a long positive electrode 50 having a positive electrode active material layer 54, a long separator 70, and a long negative electrode 60 having a negative electrode active material layer 64, in the longitudinal direction, while superposing. In at least one of the positive electrode active material layer 54, separator 70, and negative electrode active material layer 64, regions 56, 66, 76 containing a solid electrolyte are provided at the opposite ends in the winding axis direction orthogonal to the longitudinal direction.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

  Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries (lithium secondary batteries) are lighter and have higher energy density than existing batteries. It is used as a driving power source. Particularly, lithium ion secondary batteries that are lightweight and obtain high energy density are preferably used as high-output power sources for driving vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV). Yes.

  As a typical example of a non-aqueous electrolyte secondary battery, a long electrode sheet, a long negative electrode sheet, and a wound electrode body formed by winding a long separator sheet in the longitudinal direction are stacked. Things. When the non-aqueous electrolyte secondary battery in such a form is repeatedly charged and discharged at a high rate, the non-aqueous electrolyte that permeates the wound electrode body while the wound electrode body repeatedly expands and contracts is wound on the wound electrode body. A phenomenon (so-called “so-called“ amount of non-aqueous electrolyte ”that is discharged from the end portion (open end portion) of the axial direction (referred to as a direction orthogonal to the longitudinal direction; the same applies hereinafter) and the inside of the wound electrode body is insufficient. Liquid drainage ") may occur. When this liquid withering occurs, the battery performance deteriorates, such as a reduction in battery capacity.

  On the other hand, in Patent Document 1, when a plurality of secondary batteries having wound electrode bodies are constrained to form an assembled battery, a load is applied to a region where the flat electrode collecting terminals of the battery case are present. That is, a method for preventing discharge of the non-aqueous electrolyte from the wound electrode body by applying a load to the end region in the winding axis direction of the wound electrode body has been proposed.

JP 2012-230837 A

  However, according to the study by the present inventors, the discharge of the non-aqueous electrolyte from the wound electrode body when charging / discharging is repeated at a high rate is reduced by the method of Patent Document 1, and the deterioration of battery performance is reduced. However, it has been found that there is still room for improvement.

  Therefore, an object of the present invention is to provide a nonaqueous electrolyte secondary battery in which discharge of the nonaqueous electrolyte from the wound electrode body is highly suppressed.

As a result of intensive studies, the inventors have provided a region containing a solid electrolyte at both ends in the winding axis direction of at least one of the positive electrode active material layer, the separator, and the negative electrode active material layer constituting the wound electrode body. Thus, the solid electrolyte works as an obstacle to block the discharge of the non-aqueous electrolyte at the winding axial end of the wound electrode body, and discharges the non-aqueous electrolyte from the wound electrode body. We found that it can be highly controlled.
In other words, the non-aqueous electrolyte secondary battery disclosed herein has a long positive electrode having a positive electrode active material layer, a long separator, and a long negative electrode having a negative electrode active material layer superimposed on each other in the longitudinal direction. A wound electrode body that is wound is provided. In at least one of the positive electrode active material layer, the separator, and the negative electrode active material layer, regions including a solid electrolyte are provided at both ends in the winding axis direction orthogonal to the longitudinal direction.
According to such a configuration, it is possible to provide a non-aqueous electrolyte secondary battery in which discharge of the non-aqueous electrolyte from the wound electrode body is highly suppressed. In addition, since a solid electrolyte is used as a substance (obstacle) that suppresses discharge of the non-aqueous electrolyte at the winding axial end of the wound electrode body, the inside of the battery due to the inclusion of the substance (obstacle) An increase in resistance can be suppressed.

It is a perspective view which shows typically the external shape of the non-aqueous-electrolyte secondary battery which concerns on one Embodiment of this invention. It is a longitudinal cross-sectional view which shows typically the cross-sectional structure which follows the II-II line | wire in FIG. It is a schematic diagram which shows the structure of the wound electrode body used by the 1st aspect of one embodiment. It is a figure which shows typically a part of cross section of the wound electrode body used by the 1st aspect of one Embodiment. It is a figure which shows typically a part of cross section of the wound electrode body used by the 2nd implementation mode of one embodiment. It is a graph which shows the change of the capacity | capacitance maintenance factor with respect to the charging / discharging cycle of the battery of Example 1 and Example 2.

  Embodiments according to the present invention will be described below with reference to the drawings. Note that matters other than the matters specifically mentioned in the present specification and necessary for the implementation of the present invention (for example, a general configuration and manufacturing process of a battery that does not characterize the present invention) It can be grasped as a design matter of those skilled in the art based on the prior art. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. Moreover, in the following drawings, the same code | symbol is attached | subjected and demonstrated to the member and site | part which show | plays the same effect | action. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships.

  In the present specification, the “secondary battery” refers to a general power storage device that can be repeatedly charged and discharged, and is a term including a so-called storage battery such as a lithium ion secondary battery and a power storage element such as an electric double layer capacitor. Hereinafter, the present invention will be described in detail by taking a lithium ion secondary battery as an example. It should be noted that the present invention is not intended to be limited to the one described in the embodiment, and the technical idea of the present invention is that other secondary nonaqueous electrolyte solutions having other charge carriers (for example, sodium ions) are used. The present invention is also applied to a battery (for example, a sodium ion secondary battery).

  The lithium ion secondary battery 100 shown in FIG. 1 and FIG. 2 is accommodated in a flat rectangular battery case (that is, an exterior container) 30 having a flat wound electrode body 20 and a non-aqueous electrolyte (not shown). This is a sealed battery 100 constructed by the above. The battery case 30 is provided with a positive terminal 42 and a negative terminal 44 for external connection, and a thin safety valve 36 set so as to release the internal pressure when the internal pressure of the battery case 30 rises above a predetermined level. Yes. The positive and negative terminals 42 and 44 are electrically connected to the positive and negative current collectors 42a and 44a, respectively. As the material of the battery case 30, for example, a light metal material having good thermal conductivity such as aluminum is used.

  Here, first, general portions of the wound electrode body 20 will be described, and characteristic portions of the wound electrode body 20 will be described later. As shown in FIG. 2, the wound electrode body 20 includes a positive electrode sheet 50 in which a positive electrode active material layer 54 is formed on one or both surfaces (here, both surfaces) of a long positive electrode current collector 52 along the longitudinal direction. And the negative electrode 60 sheet in which the negative electrode active material layer 64 is formed along the longitudinal direction on one side or both sides (here, both sides) of the long negative electrode current collector 62 and two long separator sheets. 70 are overlapped via 70 and wound in the longitudinal direction. It should be noted that the positive electrode active material non-formed portion 52a formed so as to protrude outward from both ends in the winding axis direction of the wound electrode body 20 (that is, the positive electrode current collector 52 is formed without forming the positive electrode active material layer 54). The exposed portion) and the negative electrode active material layer non-formed portion 62a (that is, the portion where the negative electrode current collector 62 is exposed without forming the negative electrode active material layer 64) are the positive electrode current collector plate 42a and the negative electrode current collector plate, respectively. 44a is joined.

Examples of the positive electrode current collector 52 constituting the positive electrode sheet 50 include aluminum foil. Examples of the positive electrode active material include lithium transition metal oxides (for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNiO ₂ , LiCoO ₂ , LiFeO ₂ , LiMn ₂ O ₄ , LiNi _0.5 Mn _{1 .5} O ₄ etc.) and lithium transition metal phosphate compounds (LiFePO ₄ etc.). The positive electrode active material layer can include components other than the active material, such as a conductive material and a binder. As the conductive material, carbon black such as acetylene black (AB) and other (such as graphite) carbon materials can be suitably used. As the binder, polyvinylidene fluoride (PVDF) or the like can be used.

  Examples of the negative electrode current collector 62 constituting the negative electrode sheet 60 include copper foil. As the negative electrode active material, for example, a carbon material such as graphite, hard carbon, or soft carbon can be used. The negative electrode active material layer can contain components other than the active material, such as a binder and a thickener. As the binder, styrene butadiene rubber (SBR) or the like can be used. As the thickener, for example, carboxymethyl cellulose (CMC) can be used.

  As the separator sheet 70, for example, a porous sheet (film) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, polyamide or the like can be used. Preferably, a polyolefin resin (eg, PE, A porous sheet made of PP) is used. Such a porous sheet may have a single-layer structure or a laminated structure of two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer).

The non-aqueous electrolyte can be the same as the conventional lithium ion secondary battery, and typically, an organic solvent (non-aqueous solvent) containing a supporting salt can be used. . As the non-aqueous solvent, various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, lactones and the like used in electrolytes of general lithium ion secondary batteries are used without particular limitation. Can do. Specific examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and the like. Such a non-aqueous solvent can be used individually by 1 type or in combination of 2 or more types as appropriate. As the supporting salt, for example, a lithium salt such as LiPF ₆ , LiBF ₄ , LiClO ₄ (preferably LiPF ₆ ) can be suitably used. The concentration of the supporting salt is preferably 0.7 mol / L or more and 1.3 mol / L or less (for example, 1.0 mol / L).

  In the non-aqueous electrolyte, gas generation of components other than the above-mentioned non-aqueous solvent and supporting salt, for example, biphenyl (BP), cyclohexylbenzene (CHB), etc., is provided as long as the effects of the present invention are not significantly impaired. Agents; film forming agents such as oxalato complex compounds containing boron and / or phosphorus atoms, vinylene carbonate (VC), fluoroethylene carbonate (FEC); dispersants; thickeners; .

  Next, the characteristic part of the wound electrode body 20 will be described. The wound electrode body 20 is characterized in that in at least one of the positive electrode active material layer 54, the separator 70, and the negative electrode active material layer 64, regions including a solid electrolyte are provided at both ends in the winding axis direction. To do. When the lithium ion secondary battery 100 is repeatedly charged and discharged at a high rate, the nonaqueous electrolytic solution that has permeated the wound electrode body 20 is wound on the winding axial end of the wound electrode body 20 (the positive electrode active material layer 54, the separator 70, And the end surface of the negative electrode active material layer 64), the solid electrolyte obstructs the discharge of the non-aqueous electrolyte at the end of the wound electrode body 20 in the winding axis direction. As a role. Therefore, according to the lithium ion secondary battery having such characteristics, discharge of the non-aqueous electrolyte from the winding axial end of the wound electrode body 20 is prevented, and deterioration of battery performance can be suppressed. . Hereinafter, specific embodiments will be described in detail.

[First Embodiment]
In the first embodiment, in at least one of the positive electrode active material layer 54, the separator 70, and the negative electrode active material layer 64, the solid electrolyte is filled in the holes from the both ends in the winding axis direction to a predetermined position. Yes. Thereby, in at least one of the positive electrode active material layer 54, the separator 70, and the negative electrode active material layer 64, regions including the solid electrolyte are provided at both ends in the winding axis direction. Specific examples of the first embodiment are shown in FIGS.

  3 and 4, the positive electrode sheet 50, the separator 70, and the negative electrode sheet 60 are laminated, and the width of the separator (the length in the winding axis direction) is the width of the negative electrode active material layer 64 (the length in the winding axis direction). The width of the negative electrode active material layer 64 is larger than the width of the positive electrode active material layer 54 (length in the winding axis direction). A first region 56 containing a solid electrolyte is provided in the holes from both ends of the positive electrode active material layer 54 to a predetermined position. In addition, a second region 66 containing a solid electrolyte is provided in a hole from the both ends of the negative electrode active material layer 64 to a predetermined position. Further, a third region 76 containing a solid electrolyte is provided in the pores from both ends of the separator 70 to a predetermined position. Therefore, in the first embodiment, the regions 56, 66, and 76 including the solid electrolyte are formed from both ends in the winding axis direction of the positive electrode active material layer 54, the separator 70, and the negative electrode active material layer 64 inward. Has been. The solid electrolyte filled in the voids at both ends of the positive electrode active material layer 54, the separator 70, and the negative electrode active material layer 64 has a nonaqueous electrolyte solution of the positive electrode active material layer 54, the separator 70, and the negative electrode active material layer 64. It works as an obstacle to block the discharge from the end face, and suppresses the discharge of the non-aqueous electrolyte from the wound electrode body 20.

  In FIG. 4, in the positive electrode active material layer 54, the separator 70, and the negative electrode active material layer 64, the positions of the end points where the solid electrolyte is filled from the end portions to the holes are aligned, that is, the positive electrode active material layer 54, Although the pores are filled with the solid electrolyte from both ends of the separator 70 and the negative electrode active material layer 64 to the same position, the positions of the end points need not be aligned. When viewed in the winding axis direction, the distance D from the end of the portion where the positive electrode active material layer 54, the separator 70, and the negative electrode active material layer 64 overlap to the position of the end point is the width of the wound electrode body 20. It is preferable to be within a range of 0.1 to 10% of (the length in the winding axis direction).

  As a method of filling the solid electrolyte in the vacancies at the ends of the positive electrode active material layer 54, the separator 70, and the negative electrode active material layer 64, the positive electrode active material layer 54, the separator 70, and the negative electrode active material layer 64 are arranged in the longitudinal direction. After immersing the end portions in the orthogonal width direction in a slurry containing a solid electrolyte having a nano-order particle size smaller than the pores of the positive electrode active material layer 54, the separator 70, and the negative electrode active material layer 64, or A method of applying a slurry containing the solid electrolyte to the end and then drying to remove the solvent may be mentioned. In order to increase the filling rate of the solid electrolyte, the dipping or coating and drying operations may be repeated several times. As the solid electrolyte, a known solid electrolyte that can be used for a lithium ion secondary battery can be used without particular limitation. Examples of solid electrolytes include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes. Note that the slurry may contain a binder.

  In the examples of FIGS. 3 and 4, in all of the positive electrode active material layer 54, the separator 70, and the negative electrode active material layer 64, the solid electrolyte is filled in the holes from both ends to a predetermined position. If any of the positive electrode active material layer 54, the separator 70, and the negative electrode active material layer 64 is filled with a solid electrolyte, an effect of suppressing discharge of the non-aqueous electrolyte can be obtained. Therefore, for example, only the member having the lowest ventilation resistance among the positive electrode active material layer 54, the separator 70, and the negative electrode active material layer 64 may have its pores filled with a solid electrolyte, and the ventilation resistance The pores may be filled with a solid electrolyte for the lowest member and the second lowest member. For example, the solid electrolyte is filled in the holes from the both ends of the separator 70 and either the positive or negative active material layers 54 and 64 or both ends of the separator 70 and the positive or negative active material layers 64 and 64 to predetermined positions. Form may be sufficient.

[Second Embodiment]
In the second embodiment, a solid electrolyte is filled between the positive electrode current collector 52 and the negative electrode current collector 62. Thereby, in the positive electrode active material layer 54, the separator 70, and the negative electrode active material layer 64, the area | region 86 containing a solid electrolyte is provided in the both ends of the winding axis direction. A specific example of the second embodiment is shown in FIG.

  As shown in FIG. 5, between the positive electrode current collector 52 and the negative electrode current collector 62, the ends of the positive electrode active material layer 54, the separator 70, and the negative electrode active material layer 64 are connected to the negative electrode current collector 62. The solid electrolyte is filled to the end, and regions 86 containing the solid electrolyte are formed at both ends in the winding axis direction. Therefore, in the second embodiment, the region 86 including the solid electrolyte is formed outward from both ends of the positive electrode active material layer 54, the separator 70, and the negative electrode active material layer 64 in the winding axis direction. The solid electrolyte filled outside the ends of the positive electrode active material layer 54, the separator 70, and the negative electrode active material layer 64 is likely to be discharged from the end surfaces of the positive electrode active material layer 54, the separator 70, and the negative electrode active material layer 64. This acts as an obstacle to block the non-aqueous electrolyte, and prevents the non-aqueous electrolyte from being discharged outside the wound electrode body 20.

  In FIG. 5, the solid electrolyte is filled up to the end portion of the negative electrode current collector 62, but the solid formed outside the end portions of the positive electrode active material layer 54, the separator 70, and the negative electrode active material layer 64. As long as there is a region filled with the electrolyte, it is not necessary to fill the solid electrolyte up to the end 62 of the negative electrode current collector.

  As a method of forming the region 86 including the solid electrolyte, a method of filling the solid electrolyte from the side surface (that is, the opening end surface) in the winding axis direction of the wound electrode body 20 can be cited. In order to increase the filling rate, the solid electrolyte may be compressed during or after filling. Unlike the first embodiment, in the second embodiment, a solid electrolyte having a particle diameter larger than the pores of the positive electrode active material layer 54, the separator 70, and the negative electrode active material layer 64 can be used. .

  The lithium ion secondary battery 100 configured as described above can be used for various applications. In particular, it is advantageous to use as a large-sized battery, and suitable applications include driving power sources mounted on vehicles such as electric vehicles (EV), hybrid vehicles (HV), plug-in hybrid vehicles (PHV), and the like. . It can also be used as an industrial power source such as a household power source or a factory. The lithium ion secondary battery 100 can also be used in the form of an assembled battery formed by connecting a plurality of lithium ion secondary batteries 100 in series and / or in parallel.

  EXAMPLES Examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples.

<Example 1>
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (LNCM) as the positive electrode active material powder, AB as the conductive material, and PVDF as the binder are LNCM: AB: PVDF = 92: 5: 3 Was mixed with N-methylpyrrolidone (NMP) at a mass ratio of 2 to prepare a positive electrode active material layer forming slurry. The slurry was applied in a strip shape on both sides of a long aluminum foil (positive electrode current collector), dried, and then pressed to prepare a positive electrode.
Further, graphite (C) as a negative electrode active material, SBR as a binder, and CMC as a thickener are mixed with ion-exchanged water at a mass ratio of C: SBR: CMC = 98: 1: 1. A slurry for forming a negative electrode active material layer was prepared. The slurry was applied to both sides of a long copper foil (negative electrode current collector) in a strip shape, dried, and then pressed to prepare a negative electrode.
In addition, two separator sheets (porous polyolefin sheets) were prepared.

The produced positive electrode and negative electrode and two prepared separator sheets were superposed and wound to produce a wound electrode body. At this time, a separator was interposed between the positive electrode and the negative electrode.
Next, a slurry was prepared in which Li ₁₀ GeP ₂ S ₁₂ (sulfide-based ion conductive solid electrolyte) as a solid electrolyte and SBR as a binder were dispersed. One end of the wound electrode body in the winding axis direction was dipped in the slurry and dried. Subsequently, the other end of the wound electrode body in the winding axis direction was dipped in the slurry and dried. In this manner, the solid electrolyte is filled into the pores of the positive electrode active material layer, the separator sheet, and the negative electrode active material layer from both ends of the wound electrode body, and the wound electrode body has both ends in the winding axis direction. A region containing a solid electrolyte was formed.

As described above, the wound electrode body in which the regions including the solid electrolyte were provided at both ends in the winding axis direction of the positive electrode active material layer, the separator sheet, and the negative electrode active material layer was accommodated in the battery case. Subsequently, a non-aqueous electrolyte was injected from the opening of the battery case, and the opening was hermetically sealed to produce a non-aqueous electrolyte secondary battery according to Example 1. The non-aqueous electrolyte is supported by a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of EC: DMC: EMC = 1: 1: 1. of LiPF ₆ as a salt were used as dissolved at a concentration of 1.0 mol / L.

The non-aqueous electrolyte secondary battery according to Example 1 was charged with a constant current up to 4.1 V at a current value (charge rate) of C / 5, and then the current value during constant voltage charging was The battery was fully charged (SOC 100%) by performing constant voltage charging up to a point where C / 50 was reached. Thereafter, under a temperature condition of 25 ° C., a discharge capacity (initial battery capacity) was measured when discharging was performed at a constant current up to 3 V at a current value of C / 5. Here, 1C means a current value that can charge the battery capacity (Ah) predicted from the theoretical capacity of the positive electrode in one hour.
Subsequently, under a temperature condition of 60 ° C., charging and discharging in which constant current charging is performed to a voltage of 4.1 V at a charging rate of 2 C and then constant current discharging is performed to a voltage of 3 V at a discharging rate of 2 C is defined as one cycle. The cycle was repeated. The discharge capacity (battery capacity after cycle) was measured every 300 cycles of charge / discharge, and the value calculated from {(battery capacity after cycle) / (initial battery capacity)} × 100 was determined as the capacity retention rate (%). The results are shown in FIG.

<Example 2>
A wound electrode body was produced in the same manner as in Example 1. The wound electrode body was accommodated in the battery case without being immersed in the slurry in which the solid electrolyte was dispersed. Subsequently, a non-aqueous electrolyte was injected from the opening of the battery case, and the opening was hermetically sealed to produce a non-aqueous electrolyte secondary battery according to Example 2 (thus, the non-aqueous electrolyte according to Example 2). The electrolyte secondary battery is not provided with a region containing a solid electrolyte). The same nonaqueous electrolytic solution as used in Example 1 was used.
When producing an assembled battery in a region (end region in the winding axis direction of the wound electrode body) where the flat electrode collecting terminals of the battery case of the non-aqueous electrolyte secondary battery according to Example 2 are provided A load was applied using a restraining member.
Subsequently, the capacity retention rate (%) was measured in the same manner as in Example 1. The results are shown in FIG.

  As shown in FIG. 6, in the wound electrode body, the non-aqueous electrolyte solution 2 according to Example 1 in which the positive electrode active material layer, the separator, and the negative electrode active material layer are provided with regions containing a solid electrolyte at both ends in the winding axis direction. The secondary battery had a higher capacity retention rate than the nonaqueous electrolyte secondary battery according to Example 2 in which the region containing the solid electrolyte was not provided. From this, it can be seen that the region containing the solid electrolyte suppresses the discharge of the non-aqueous electrolyte from the end of the wound electrode body and suppresses the deterioration of the battery performance.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

20 wound electrode body 30 battery case 36 safety valve 42 positive electrode terminal 42a positive electrode current collector plate 44 negative electrode terminal 44a negative electrode current collector plate 50 positive electrode sheet (positive electrode)
52 Positive electrode current collector 52a Positive electrode active material layer non-formed portion 54 Positive electrode active material layer 56 First region 60 containing solid electrolyte Negative electrode sheet (negative electrode)
62 Negative electrode current collector 62a Negative electrode active material layer non-formed portion 64 Negative electrode active material layer 66 Second region 70 containing solid electrolyte Separator sheet (separator)
76 3rd area | region 86 containing a solid electrolyte Area | region 100 containing a solid electrolyte 100 Nonaqueous electrolyte secondary battery (lithium ion secondary battery)

Claims (1)

A non-aqueous electrolyte comprising a wound electrode body in which a long positive electrode having a positive electrode active material layer, a long separator, and a long negative electrode having a negative electrode active material layer are stacked and wound in the longitudinal direction. A secondary battery,
In at least one of the positive electrode active material layer, the separator, and the negative electrode active material layer, regions containing a solid electrolyte are provided at both ends in the winding axis direction orthogonal to the longitudinal direction. Electrolyte secondary battery.

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