JP2015222646A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery superior in high-rate endurance characteristic.SOLUTION: A nonaqueous electrolyte secondary battery according to the present invention comprises: an electrode body of a laminate structure including a positive electrode 50 including a positive electrode active material layer 54, a negative electrode 60 including a negative electrode active material layer 64 and a separator 70 for electrically isolating the positive and negative electrodes from each other. In the nonaqueous electrolyte secondary battery, a micro bubble buildup region 80 where micro bubbles having an average diameter of 10 μm or less are built up is formed between the negative electrode active material layer 64 and the separator 70.

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.

JP 2009-289609 A International Publication No. 2013/108396

  Meanwhile, some non-aqueous electrolyte secondary battery applications (for example, power sources for driving a vehicle) are assumed to be used in such a manner that charging and discharging are repeated at a large charge rate (high rate). Such a battery is required to improve performance degradation (e.g., increase in battery resistance) that may occur due to repeated high-rate charge / discharge, that is, to improve durability against high-rate charge / discharge (high-rate durability characteristics).

  In a non-aqueous electrolyte secondary battery that has repeatedly performed high-rate charge / discharge, a portion of the non-aqueous electrolyte and salt that have permeated into the electrode body migrates within the electrode body, so that the salt concentration in the electrode body (charge carrier concentration, for example, lithium There may be a deviation in ion concentration) depending on the location (for example, a partial decrease in salt concentration). For example, since the charge carrier is released from the negative electrode active material during discharge, the volume of the negative electrode active material (negative electrode active material layer) is reduced. When the volume of the negative electrode active material is reduced, the volume of the negative electrode active material layer (negative electrode) In some cases, the non-aqueous electrolyte that has permeated into the electrode moves (for example, moves outside the negative electrode active material layer). In a portion where the salt concentration is relatively low, the battery reaction is relatively slow, and there is a possibility that the high-rate charge / discharge performance (for example, input / output characteristics) of the entire battery is lowered. Further, since the battery reaction concentrates at a portion where the salt concentration is relatively high, there is a possibility that deterioration of the portion is promoted. Any of these events can be a factor in reducing the high-rate endurance characteristics.

  Patent Document 1 describes a technique of forming a recess in a part of the negative electrode active material layer for the purpose of preventing the nonaqueous electrolyte from flowing out of the electrode body. According to the study by the present inventors, the non-aqueous electrolyte can be prevented from flowing out of the electrode body by such a technique, but the non-aqueous electrolyte in the electrode body (particularly, the surface facing the negative electrode active material layer and the separator). It was insufficient to suppress the movement of Therefore, from the viewpoint of improving the high-rate durability characteristics, there is room for improvement in suppressing salt concentration unevenness (for example, local decrease in salt concentration) in the negative electrode active material layer. Moreover, according to the technique described in Patent Document 1, there is a tradeoff in that the formation area of the negative electrode active material layer is reduced according to the formation area of the recess, and the battery capacity is reduced.

  The present invention has been made in view of the above points, and its main purpose is non-aqueous electrolysis excellent in high-rate durability characteristics (particularly, suppression of increase in battery resistance accompanying high-rate charge / discharge) without reducing battery capacity. It is to provide a liquid secondary battery.

  When the non-aqueous electrolyte solution (typically, the over-charge additive added to the non-aqueous electrolyte solution) is decomposed during overcharge, the present inventors have applied the surface of the negative electrode active material (negative electrode active material layer) to the surface. Attention was paid to the generated gas (see Patent Document 2). As a result of intensive studies, it has been found that the arrangement of microbubbles (bubbles) between the negative electrode active material layer and the separator is effective in suppressing the movement of the non-aqueous electrolyte in the negative electrode active material layer. The present invention has been completed.

  In order to achieve the above object, according to the present invention, there is provided an electrode body having a laminated structure of a positive electrode including a positive electrode active material layer, a negative electrode including a negative electrode active material layer, and a separator that electrically isolates the positive and negative electrodes. A nonaqueous electrolyte secondary battery, wherein a microbubble integration region in which microbubbles having an average diameter of 10 μm or less are integrated is formed between the negative electrode active material layer and the separator. A secondary battery is provided.

  With such a configuration, it is possible to suppress the movement of the non-aqueous electrolyte in the negative electrode active material layer without reducing the area where the negative electrode active material layer can be formed. In particular, in the facing surface where the negative electrode active material layer and the separator face each other, the non-aqueous electrolyte moves from the negative electrode active material layer in the direction perpendicular to the facing surface to the separator, and the facing surface It is possible to effectively suppress the movement of the non-aqueous electrolyte from the central portion of the electrode body, which is the horizontal direction, toward the end portion of the electrode body. Thereby, the deviation (for example, local fall of salt concentration) of the salt concentration (charge carrier concentration, for example, lithium ion concentration) in a negative electrode active material layer can be suppressed highly. Therefore, it is possible to provide a non-aqueous electrolyte secondary battery that can maintain both battery capacity and improve high-rate durability characteristics.

  Here, in the present specification, the microbubble means a fine bubble having a diameter of the order of a micrometer or less, and a diameter generated in the battery case is 10 μm or less (particularly preferably 5 μm or less). These bubbles are typical examples included in the microbubbles referred to herein. The lower limit of the diameter of the microbubbles is not particularly limited, but typically the diameter is 0.1 μm or more, and more preferably the diameter is 1 μm or more.

It is a longitudinal cross-sectional view which shows typically the internal structure of the nonaqueous electrolyte secondary battery which concerns on one Embodiment of this invention. It is sectional drawing which shows typically the laminated structure of the electrode body which concerns on one Embodiment of this invention. It is a graph which shows the voltage characteristic at the time of forming a microbubble integrated layer in the non-aqueous-electrolyte secondary battery concerning one Embodiment of this invention. It is an electron microscope (SEM) photograph of the electrode body cross section of the microbubble formation range in FIG. It is an electron micrograph (SEM) photograph of the electrode body cross section in the electrolytic solution decomposition range in FIG. It is a graph which shows the relationship between the frequency | count of each of the battery of one Example and one comparative example, and an internal resistance increase rate.

  Hereinafter, a suitable embodiment of the present invention will be described by taking a lithium ion secondary battery as an example, with appropriate reference to the drawings. Note that matters other than matters specifically mentioned in the present specification and necessary for implementation can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be implemented based on the contents disclosed in the present specification and common general technical knowledge in the field. Further, the lithium ion secondary battery is an example, and the technical idea of the present invention is also applied to other non-aqueous electrolyte secondary batteries (for example, sodium ion secondary batteries) provided with other charge carriers (for example, sodium ions). Is done.

  A lithium ion secondary battery 100 shown in FIG. 1 is roughly divided into a flat rectangular battery case (that is, an outer container) 30 in which a flat wound electrode body 20 and a nonaqueous electrolyte (not shown) are flat. Contained. The battery case 30 has a box-shaped (that is, bottomed rectangular parallelepiped) case main body 32 having an opening at one end (corresponding to the upper end in a normal use state of the battery), and the opening of the case main body 32 is sealed. And a lid 34 to be stopped. As a material of the battery case 30, for example, a light metal material having a good thermal conductivity such as aluminum, stainless steel, or nickel-plated steel can be preferably used.

  Further, as shown in FIG. 1, the lid 34 has positive and negative terminals 42 and 44 for external connection and the internal pressure of the battery case 30 at a predetermined level (for example, a set valve opening pressure of about 0.3 MPa to 1.0 MPa). A thin-walled safety valve 36 set so as to release the internal pressure when it rises above and an inlet (not shown) for injecting a non-aqueous electrolyte are provided. In addition, a current interrupt device (CID) that operates when the internal pressure of the battery case 30 is increased may be provided inside the battery case 30.

  As shown in FIGS. 1 and 2, the wound electrode body 20 disclosed herein includes a positive electrode active material layer along a longitudinal direction on one side or both sides (here, both sides) of an elongated positive electrode current collector 52. The negative electrode 60 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. The laminated body laminated | stacked through the elongate separator 70 is wound by the elongate direction, and is shape | molded by the flat shape. Such a wound electrode body can be formed into a flat shape by, for example, crushing and ablating the wound body obtained by winding the laminated body from the side surface direction.

  As shown in FIG. 1, a wound core portion (that is, a positive electrode active material layer 54 of the positive electrode 50, a negative electrode active material layer 64 of the negative electrode 60, and A laminated structure in which the separator 70 is laminated) is formed. In addition, at both ends in the winding axis direction of the wound electrode body 20, the positive electrode active material layer non-formed portion 52a and the negative electrode active material layer non-formed portion 62a partially protrude outward from the wound core portion. Yes. The positive electrode side protruding portion (positive electrode active material layer non-forming portion 52a) and the negative electrode side protruding portion (negative electrode active material layer non-forming portion 62a) are respectively provided with a positive electrode current collecting plate 42a and a negative electrode current collecting plate 44a. The terminal 42 and the negative terminal 44 are electrically connected to each other.

Examples of the positive electrode current collector 52 constituting the positive electrode 50 include an aluminum foil. The positive electrode active material layer 54 contains at least a positive electrode active material. Examples of the positive electrode active material include lithium composite metal oxides such as a layered structure and a spinel structure (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 , LiFePO _4, etc.). The positive electrode active material layer 54 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. PVDF or the like can be used as the binder.

  Such a positive electrode 50 can be produced as follows, for example. First, a positive electrode active material and a material used as necessary are dispersed in an appropriate solvent (for example, N-methyl-2-pyrrolidone) to prepare a paste-like (slurry) composition, and then the composition It can be formed by applying an appropriate amount of the product to the surface of the positive electrode current collector 52 and then removing the solvent by drying. Moreover, the properties (for example, average thickness, active material density, porosity, etc.) of the positive electrode active material layer 54 can be adjusted by performing an appropriate press treatment as necessary.

  Examples of the negative electrode current collector 62 constituting the negative electrode 60 include copper foil. The negative electrode active material layer 64 contains at least a negative electrode active material. As such a negative electrode active material, for example, a carbon material such as graphite, hard carbon, and soft carbon can be used. The negative electrode active material layer 64 can include 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, carbomethylcellulose (CMC) can be used.

  Such a negative electrode 60 can be produced, for example, in the same manner as in the case of the positive electrode 50 described above. That is, a negative electrode active material and materials used as necessary are dispersed in a suitable solvent (for example, ion-exchanged water) to prepare a paste (slurry) composition, and then an appropriate amount of the composition Is applied to the surface of the negative electrode current collector 62 and then the solvent is removed by drying. Further, the properties (for example, average thickness, active material density, porosity, etc.) of the negative electrode active material layer 64 can be adjusted by performing an appropriate press treatment as necessary.

  Examples of the separator 70 include a porous sheet (film) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. 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).

As shown in FIG. 2, the non-aqueous electrolyte secondary battery 100 disclosed herein has a surface facing the separator 70 of the negative electrode active material layer 64 (that is, between the negative electrode active material layer 64 and the separator 70). ), Preferably a microbubble integrated region 80 in which microbubbles having a diameter of 10 μm or less are integrated. By controlling the diameter of the microbubbles (the average diameter of the accumulated microbubbles) to 10 μm or less, the movement of the non-aqueous electrolyte in the negative electrode active material layer can be suppressed without inhibiting the progress of the battery reaction. it can.
The total amount (total volume) of the microbubbles constituting the microbubble accumulation region 80 is not particularly limited, but according to the study by the present inventors, 1% by volume of the nonaqueous electrolytic solution impregnated in the electrode body 20 The nonaqueous electrolyte secondary battery 100 provided with the microbubble accumulation region 80 in which microbubbles corresponding to the degree (volume) were accumulated was able to exhibit the effects of the present invention at a high level.

  Such a microbubble accumulation region 80 can be formed by charging a non-aqueous electrolyte secondary battery 100 including a non-aqueous electrolyte containing an overcharge additive to a predetermined charged state (FIG. 3). reference). Specifically, in a battery in a charged state (typically an overcharged state) in which the potential between the positive and negative electrodes is equal to or higher than a predetermined level, the overcharge additive in the non-aqueous electrolyte is oxidized at the positive electrode 50 (positive electrode active material surface). By being decomposed, and further, the decomposed product is reduced at the negative electrode 60 (negative electrode active material surface), gas is generated on the negative electrode active material layer 64 (negative electrode active material) surface. Typically, hydrogen ions are generated by oxidation of the overcharge additive in the positive electrode 50, and the hydrogen ions diffuse in the non-aqueous electrolyte and move to the vicinity of the negative electrode 60 and are reduced on the surface of the negative electrode 60. It becomes hydrogen gas. By appropriately controlling the generation of such gas, a microbubble integrated region 80 suitable for the implementation of the present invention can be formed.

  That is, as the nonaqueous electrolytic solution, typically, an organic solvent (nonaqueous solvent) containing a supporting salt and an overcharge additive 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 , or LiClO ₄ can be suitably used. Particularly preferred support salt include LiPF _6. The concentration of the supporting salt is preferably 0.7 mol / L or more and 1.3 mol / L or less.

The overcharge additive is particularly a compound that can generate gas (microbubbles) on the surface of the negative electrode active material layer 64 (typically, between the negative electrode active material layer 64 and the separator 70) in a predetermined charged state. Without limitation, one or two or more of those that can be used as an overcharge additive (gas generating agent) in a conventional non-aqueous electrolyte secondary battery can be used. Specific compounds (abbreviation and approximate oxidation potential (vs. Li / Li ⁺ ) of the compound) include biphenyl (BP; 4.4V), cyclohexylbenzene (CHB; 4.6V), methylphenyl carbonate ( MPhC; 4.8V), ortho-terphenyl (OTP; 4.3V) and the like. From the viewpoint of the formability of the microbubble integrated region 80, BP and CHB are particularly preferable. The oxidation potential of each compound can be measured by a measurement method using a conventionally known tripolar cell. The content of the overcharge additive is preferably 0.05% by mass or more and 5% by mass or less with respect to 100% by mass of the non-aqueous electrolyte, for example.

  Next, a method for forming the microbubble integrated region 80 will be described. As described above, the microbubble accumulation region 80 starts normal use of the battery by charging the non-aqueous electrolyte secondary battery 100 including the non-aqueous electrolyte containing the overcharge additive to a predetermined charged state. It can be formed in advance. For example, as shown in FIGS. 3 and 4, it can be formed by charging until the positive electrode potential reaches a predetermined value (typically, the oxidation potential of the overcharge additive contained in the non-aqueous electrolyte). It is. When the value of the predetermined charging potential (for example, positive electrode potential) is set too low, microbubbles (in FIG. 4, typically between the negative electrode active material layer 64 and the separator 70) are formed on the surface of the negative electrode active material layer 64. White spots are not generated, which is not preferable. On the other hand, if the predetermined charging potential (for example, positive electrode potential) is set too high, bubbles generated on the surface of the negative electrode active material layer 64 are united (bonded) to form huge bubbles as shown in FIG. This is not preferable. For example, it is preferable to set the predetermined charging potential (for example, the positive electrode potential) to a potential within a range that is equal to or higher than the oxidation potential of the overcharge additive to be used and is 0.2 V higher than the oxidation potential. Specifically, when BP is used as an overcharge additive, it is preferable to charge until the positive electrode potential is 4.4 V or higher (more preferably 4.45 V or higher) and 4.6 V or lower. A microbubble integrated region 80 can be formed. Alternatively, as shown in FIG. 3, the predetermined charging state may be a charging state of 80% to 90% of the positive electrode capacity.

  The microbubble integrated region 80 can be formed, for example, by a method (constant current charging, CC charging) in which charging is performed with a constant current from the start of charging until the predetermined charging state is reached. Charging at a charging rate that is too low may reduce the formation efficiency of the microbubble integrated region 80 (the time required to form the region will be long). On the other hand, when charging at a charging rate that is too high, there is a risk that the formation of microbubbles will be reduced (the decomposition reaction of the overcharge additive at the positive electrode and the gas generation reaction at the negative electrode will not proceed sufficiently). For this reason, it is preferable to set it as the charge rate of 3 C or more and 10 C or less (more preferably about 5 ± 1 C, for example, 5 C).

As a preferred method for forming the microbubble accumulation region 80, after the non-aqueous electrolyte secondary battery 100 is charged to the predetermined charging state, charging may be continued for a certain time at a relatively low charging rate. . A desired amount of microbubbles can be formed by such low rate charging. Such low-rate charging conditions can be appropriately set depending on the configuration of the non-aqueous electrolyte to be used and the amount of the electrolyte. For example, if the battery configuration is described in the examples below, the battery is in a predetermined charged state. After reaching (charged state of positive electrode potential 4.5V (vs. Li / Li ⁺ )), about 1 volume of non-aqueous electrolyte impregnated in the electrode body by charging for about 5 minutes at a charge rate of 1C. % Microbubbles can be formed.
Here, “1C” in this specification means a current value that can charge the battery capacity (Ah) predicted from the theoretical capacity in one hour. For example, when the battery capacity is 24 Ah, 1C = 24A. is there.

  Further, as a suitable method for forming the microbubble accumulation region 80, the nonaqueous electrolyte secondary battery 100 may be charged in a state where the nonaqueous electrolyte secondary battery 100 is restrained with an appropriate pressure. By this method, the microbubble integrated region 80 can be formed with high efficiency. For example, when the non-aqueous electrolyte secondary battery 100 disclosed herein is used as a unit cell constituting an assembled battery in which a plurality of unit cells are constrained at a predetermined restraining pressure, after the assembly of the assembled battery ( That is, it is preferable to form the microbubble integrated region 80 (that is, an appropriate charging process) after the cell is restrained. Alternatively, for example, a region (typically the central portion of the flat surface of the wound electrode body) in which a partial decrease in salt concentration (charge carrier concentration, for example, lithium ion concentration) is likely to occur is greater than the surrounding pressure. By forming the microbubbles in a restrained state (that is, an appropriate charging process), the microbubble integrated region 80 can be formed with a focus on the region. As a result, the microbubble integrated region 80 that can contribute to the improvement of the high-rate durability characteristics at a high level can be formed in a short time. In addition, the magnitude | size of the said restraint pressure can be made comparable as the conventional nonaqueous electrolyte secondary battery.

  The formation of the microbubble integrated region 80 can be performed following the initial charging process under the same conditions as those for manufacturing a conventional non-aqueous electrolyte secondary battery (for example, as part of the initial charging process). Alternatively, the microbubble integrated region 80 is again formed in the non-aqueous electrolyte secondary battery 100 whose internal resistance has been increased by use for an appropriate purpose (typically, use in an environment where high-rate charge / discharge is performed). By performing the formation (that is, the appropriate charging process), it is possible to replenish the microbubbles that have decreased due to the use of the battery. This makes it possible to maintain the effect of suppressing the movement of the non-aqueous electrolyte and the effect of suppressing the increase in battery resistance over a long period of time by a simple process of performing the recharging process (formation of the microbubble accumulation region). It becomes.

  The non-aqueous electrolyte secondary battery disclosed herein can be used for various applications, but is characterized by having excellent high-rate durability characteristics (particularly, suppression of increase in battery resistance associated with high-rate charge / discharge). Therefore, taking advantage of this feature, for example, it can be suitably used as a driving power source mounted on a vehicle such as a plug-in hybrid vehicle (PHV), a hybrid vehicle (HV), or an electric vehicle (EV).

  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.

  Lithium ion secondary batteries (nonaqueous electrolyte secondary batteries) according to Example 1 (Comparative Example) and Example 2 (Example) were constructed by the following materials and processes.

The positive electrode was produced by the following procedure. LiNi _0.33 Co _0.33 Mn _0.33 O ₂ (LNCM) as a positive electrode active material powder, AB as a conductive material, and PVDF as a binder, LNCM: AB: PVDF = 91: 6: 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 pressed to produce a positive electrode.

  The negative electrode was produced according to the following procedure. 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 to form a negative electrode A slurry for forming an active material layer was prepared. The slurry was applied in a strip shape on both sides of a long copper foil (negative electrode current collector), dried and pressed to prepare a negative electrode.

  The positive electrode and the negative electrode produced by the above method were overlapped in the longitudinal direction via two separators having a three-layer structure in which a porous polypropylene layer was formed on both sides of the porous polyethylene layer, and wound in the longitudinal direction. Later, flattened wound electrode bodies were fabricated by crushing and labbing.

Next, the wound electrode body is accommodated in the battery case, a nonaqueous electrolyte is injected from the opening of the battery case, the opening is hermetically sealed, and the battery assembly according to Example 1 and Example 2 Built. Here, in the construction of the battery assembly according to Example 1, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were used as the non-aqueous electrolyte. EC: DMC: EMC = 30 : A solution obtained by dissolving LiPF ₆ as a supporting salt at a concentration of 1.1 mol / L in a mixed solvent containing a volume ratio of 40:30 was used. On the other hand, in the construction of the battery assembly according to Example 2, 1.0 mass% of biphenyl was further contained as an overcharge additive in 100 mass% of the non-aqueous electrolyte in the non-aqueous electrolyte used in Example 1 above. A thing was used.

  The battery assemblies according to the examples constructed as described above were initially charged (including the formation of a microbubble integrated region) under a temperature condition of 25 ° C., and the nonaqueous electrolyte secondary batteries according to Examples 1 and 2 Was made. Specifically, first, constant current charging (CC charging) is performed until the voltage between the positive and negative terminals becomes 4.1 V at a charging rate (current value) of 1 C, and then the current value becomes 0.02 C. Constant voltage charging (CV charging) was performed. Then, CC charging was performed until the positive electrode potential became 4.5 V at a charging rate of 5 C, and then CC charging was further performed for 5 minutes at a charging rate of 1 C.

[High-rate endurance test]
About each battery concerning Example 1 and Example 2 produced as mentioned above, by measuring the internal resistance increase rate (%) after performing a high-rate endurance test (high load charge / discharge cycle test), high-rate endurance characteristics (high Load characteristics). Specifically, it was performed as follows.
First, for the batteries according to the above examples, the IV resistance (initial IV resistance) before the cycle test was measured under the following conditions. That is, after adjusting to a state of charge of SOC (State of Charge) 60% at 1 C under a temperature condition of 25 ° C., a constant current discharge is performed at 15 C for 10 seconds, and current (I) -voltage (V) at this time The IV resistance before the cycle test (initial IV resistance) was determined from the slope of the first-order approximate straight line of the plot values.
Next, charge and discharge were repeated 2500 cycles for the batteries according to the above examples. The charge / discharge conditions for one cycle are: constant current voltage discharge for 10 seconds at 20C under a temperature condition of 25 ° C, pause for 10 seconds, then constant current voltage charge for 40 seconds at 5C and pause for 10 seconds. there were. And about the battery concerning each example, IV resistance after a cycle test was measured by the method similar to the measurement of the said initial IV resistance for every 500 charging / discharging cycles.
Then, the internal resistance increase rate (%) was obtained from the following formula: internal resistance increase rate (%) = IV resistance after cycle test / initial IV resistance × 100; FIG. 6 shows a graph plotting the internal resistance increase rate (%) every 500 cycles in the battery according to each example.

As shown in FIG. 6, in the battery according to Example 1 (comparative example), the rate of increase in internal resistance continued to increase in proportion to the repetition of high-rate charge / discharge, and the rate of increase in internal resistance was 200% after 2500 cycles of charge / discharge. (That is, a resistance value that is twice the initial resistance). On the other hand, the rate of increase in internal resistance of the battery according to Example 2 (Example) was almost constant from 500 cycles after high-rate charge / discharge to 2500 cycles after charge / discharge, and the value was as low as 120% or less. . This is because, in the battery according to Example 2, a microbubble accumulation region in which microbubbles having a diameter of 10 μm or less are accumulated between the negative electrode active material layer and the separator, and thereby, in the negative electrode active material layer due to repeated high-rate charge / discharge. This is considered to be because the local decrease of the salt concentration (charge carrier concentration, for example, lithium ion concentration) in the negative electrode active material layer accompanying the movement of the non-aqueous electrolyte was suppressed.
From the above results, by forming a microbubble accumulation region in which microbubbles having a diameter of 10 μm or less are accumulated between the negative electrode active material layer and the separator, high high-rate durability characteristics (high load characteristics, typically associated with high-rate charging) It was confirmed that the suppression of increase in resistance can be realized.

  As described above, according to the technology disclosed herein, it is possible to provide a non-aqueous electrolyte secondary battery that achieves both maintenance of battery capacity and excellent durability characteristics (high load characteristics).

  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 Winding electrode body 30 Battery case 32 Battery case body 34 Cover body 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 52 Positive electrode current collector 52a Positive electrode active material layer non-formed part 54 Positive electrode Active material layer 60 Negative electrode 62 Negative electrode current collector 62a Negative electrode active material layer non-formed portion 64 Negative electrode active material layer 70 Separator 80 Microbubble integrated region 100 Nonaqueous electrolyte secondary battery (lithium ion secondary battery)

Claims (1)

A non-aqueous electrolyte secondary battery including an electrode body having a laminated structure of a positive electrode including a positive electrode active material layer, a negative electrode including a negative electrode active material layer, and a separator that electrically isolates the positive and negative electrodes,
A non-aqueous electrolyte secondary battery in which a microbubble accumulation region in which microbubbles having an average diameter of 10 μm or less are accumulated is formed between the negative electrode active material layer and the separator.