JP7054440B2 - Secondary battery - Google Patents

Description

The present invention relates to a secondary battery.

Secondary batteries such as lithium-ion secondary batteries are lighter in weight and have a higher energy density than existing batteries, and have been used in recent years as so-called portable power sources for personal computers and mobile terminals and power sources for driving vehicles. In particular, lithium-ion secondary batteries, which are lightweight and have high energy density, will become more and more popular as high-output power sources for driving vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV). It is expected to continue.

A so-called liquid-based secondary battery typically has a configuration in which an electrode body having positive and negative electrodes and an electrolytic solution are housed in a battery case. The electrode typically has a configuration in which an electrode mixture layer containing an electrode active material is provided on an electrode current collector foil (see, for example, Patent Documents 1 and 2). The electrode mixture layer has voids between the particles of the electrode active material, and the electrolytic solution can be held in the voids.

International Publication No. 2012/1246887 Pamphlet JP-A-2015-0433304

In recent years, secondary batteries are required to have a higher energy density. As a measure for increasing the energy density of the secondary battery, increasing the density or the basis weight of the electrode mixture layer can be mentioned. However, when the density or the amount of the electrode mixture layer is increased, the electrolytic solution is extruded from the electrode body due to the expansion and contraction of the electrode when charging and discharging are repeated at a high rate, and the extruded electrolytic solution is used as the electrode. I can't get back to my body. As a result, there is a problem that the amount of the electrolytic solution impregnated in the electrode body is reduced and the resistance is increased.

Therefore, an object of the present invention is to provide a secondary battery in which an increase in resistance is suppressed when charging and discharging are repeated at a high rate.

The secondary battery disclosed herein includes an electrode body having positive and negative electrodes, a non-aqueous electrolytic solution, and a battery case for accommodating the electrode body and the non-aqueous electrolytic solution. At least one of the electrodes has an electrode current collector foil and an electrode mixture layer formed on the electrode current collector foil. The electrode current collector foil has a recess continuous from the end on the surface on which the electrode mixture layer is formed. The electrode mixture layer contains an electrode active material. The ratio (A / B) of the width A of the recess to the average particle diameter B of the electrode active material satisfies 0.2 <A / B <0.8. The ratio of the cross-sectional area of the solid component constituting the positive electrode mixture layer that has entered the recess to the cross-sectional area of the recess is 0.6 or less.
According to such a configuration, the recess can function as a flow path for the non-aqueous electrolytic solution. Therefore, when the electrode expands and contracts and the electrolytic solution is extruded from the electrode body when the secondary battery is repeatedly charged and discharged at a high rate, the extruded electrolytic solution returns to the inside of the electrode body through the recess. Therefore, it is possible to suppress a decrease in the amount of the electrolytic solution impregnated in the electrode body. As a result, it is possible to suppress a decrease in resistance due to a decrease in the amount of the electrolytic solution impregnated in the electrode body.

It is sectional drawing which shows typically the internal structure of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is a schematic diagram which shows the structure of the winding electrode body of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is a schematic diagram which shows the interface of the positive electrode current collector foil of the positive electrode of the positive electrode of the lithium ion secondary battery which concerns on one Embodiment of this invention and a positive electrode mixture layer, and the vicinity thereof. It is a schematic diagram which shows the form of the recess provided in the positive electrode current collector foil of the positive electrode of the positive electrode of the lithium ion secondary battery which concerns on one Embodiment of this invention.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings. It should be noted that matters other than those specifically mentioned in the present specification and necessary for carrying out the present invention (for example, general configurations and manufacturing processes of secondary batteries that do not characterize the present invention) are said to be relevant. It can be grasped as a design matter of a person skilled in the art based on the prior art in the field. The present invention can be carried out based on the contents disclosed in the present specification and the common general technical knowledge in the art. Further, in the following drawings, members / parts having the same action are described with the same reference numerals. Further, the dimensional relations (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relations.

In the present specification, the "secondary battery" generally refers to a power storage device that can be repeatedly charged and discharged, and is a term that includes 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 flat-angle type lithium ion secondary battery as an example, but the present invention is not intended to be limited to those described in such embodiments.

In the lithium ion secondary battery 100 shown in FIG. 1, a flat wound electrode body 20 and a non-aqueous electrolytic solution (not shown) are housed in a flat square battery case (that is, an outer container) 30. It is a closed-type lithium ion secondary battery 100 to be constructed. The battery case 30 is provided with a positive electrode terminal 42 and a negative electrode terminal 44 for external connection, and a thin-walled safety valve 36 set to release the internal pressure when the internal pressure of the battery case 30 rises above a predetermined level. There is. Further, the battery case 30 is provided with an injection port (not shown) for injecting a non-aqueous electrolytic solution. The positive electrode terminal 42 is electrically connected to the positive electrode current collector plate 42a. The negative electrode terminal 44 is electrically connected to the negative electrode current collector plate 44a. As the material of the battery case 30, for example, a lightweight metal material having good thermal conductivity such as aluminum is used.

In the wound electrode body 20, as shown in FIGS. 1 and 2, a positive electrode mixture layer 54 is formed along the longitudinal direction on one side or both sides (here, both sides) of the long positive electrode current collector foil 52. The positive electrode sheet 50 and the negative electrode sheet 60 in which the negative electrode mixture layer 64 is formed along the longitudinal direction on one side or both sides (here, both sides) of the long negative electrode current collector foil 62 are two long sheets. It has a form of being overlapped with each other via a separator sheet 70 and wound in the longitudinal direction. The positive electrode mixture layer non-formed portion 52a (that is, the positive electrode combination) formed so as to protrude outward from both ends of the winding electrode body 20 in the winding axis direction (that is, the sheet width direction orthogonal to the longitudinal direction). A portion where the positive electrode current collector foil 52 is exposed without forming the material layer 54) and a portion 62a where the negative electrode mixture layer is not formed (that is, a portion where the negative electrode mixture layer 64 is not formed and the negative electrode current collector foil 62 is exposed). A positive electrode current collector plate 42a and a negative electrode current collector plate 44a are joined to each of the above.

FIG. 3 schematically shows the interface between the positive electrode current collector foil 52 of the positive electrode sheet 50 and the positive electrode mixture layer 54 and its vicinity.
Examples of the positive electrode current collector foil 52 constituting the positive electrode sheet 50 include an aluminum foil and the like.
The positive electrode mixture layer 54 contains the positive electrode active material 56. Examples of the positive electrode active material 56 include lithium transition metal oxides (eg, 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.), lithium transition metal phosphate compounds (eg, LiFePO ₄ etc.) and the like can be used. The average particle size of the positive electrode active material 56 is, for example, 1 μm or more and 25 μm or less, preferably 2 μm or more and 20 μm or less. In the present specification, the "average particle size" means a particle size (D50) corresponding to a cumulative 50% in the volume-based particle size distribution obtained by a general laser diffraction / light scattering method. Further, the positive electrode active material 56 may exist in the form of primary particles or may form secondary particles.
The positive electrode mixture layer 54 may contain components other than the positive electrode active material 56, such as a conductive material 58 and a binder (not shown). As the conductive material 58, for example, carbon black such as acetylene black (AB) or other carbon material (eg, graphite or the like) can be preferably used. As the binder, for example, polyvinylidene fluoride (PVDF) or the like can be used.

As shown in FIG. 3, the positive electrode current collector foil 52 has a recess 53 on the surface on which the positive electrode mixture layer 54 is formed. As shown in FIG. 4, the recess 53 is formed continuously from the end of the positive electrode current collector foil 52. That is, the recess 53 is formed in a groove shape from the end of the positive electrode current collector foil 52.
Here, the width of the recess is A, and the average particle size of the positive electrode active material 56 is B. In the present embodiment, the ratio (A / B) of the width A of the recess 53 to the average particle diameter B of the positive electrode active material 56 satisfies 0.2 <A / B <0.8.
The ratio of the cross-sectional area of the solid component constituting the positive electrode mixture layer 54 that has entered the recess 53 to the cross-sectional area of the recess 53 is 0.6 or less.
According to such a configuration, the groove-shaped recess 53 can function as a flow path for the non-aqueous electrolytic solution. That is, when the ratio (A / B) is 0.2 or less, the recess 53 is likely to be blocked by a component having a small particle diameter such as the conductive material 58, and does not sufficiently function as a flow path. When the ratio (A / B) is 0.8 or more, the recess 53 is blocked by a positive electrode active material 56 having a relatively small particle size, and does not sufficiently function as a flow path. Further, the positive electrode mixture layer 54 may contain a solid component (eg, conductive material 58, binder, etc.) in addition to the positive electrode active material 56. When the ratio of the cross-sectional area of the solid component (that is, the positive electrode active material 56, the conductive material 58, the binder, etc.) constituting the positive electrode mixture layer 54 that has entered the recess 53 to the cross-sectional area of the recess 53 exceeds 0.6. The recess 53 is blocked by the solid component, and does not function sufficiently as a flow path.
When the lithium ion secondary battery 100 is repeatedly charged and discharged at a high rate, the positive electrode 50 and the negative electrode 60 expand and contract, and when the non-aqueous electrolyte solution is extruded from the electrode body 20, the extruded non-aqueous electrolysis The liquid can return into the positive electrode mixture layer 54 through the recess 53. That is, since the non-aqueous electrolytic solution extruded from the electrode body 20 can return to the electrode body 20, it is possible to suppress a decrease in the amount of the non-aqueous electrolytic solution impregnated in the electrode body 20, which is a result. The decrease in resistance can be suppressed.

In the present embodiment, the cross-sectional shape of the recess 53 is rectangular as shown in FIG. However, the cross-sectional shape of the recess 53 is not limited to this. The cross-sectional shape of the recess 53 may be V-shaped, U-shaped, semicircular or the like.

In the present embodiment, the recess 53 is continuous from one end to the other end of the positive electrode current collector foil 52 as shown in FIG. However, the form of the recess 53 is not limited to this. The recess 53 may be provided from one end to the center of the positive electrode current collector foil 52. The recess 53 may be provided only in the vicinity of the end portion of the positive electrode current collector foil 52. However, the longer the length of the continuous recess 53 (that is, the groove) is, the easier it is for the non-aqueous electrolytic solution to return to the inside of the positive electrode mixture layer 54, so that the effect of the present invention is enhanced.
The recess 53 may be continuously provided from any end of the electrode current collector foil, but in the present embodiment, since the electrode body 20 is a wound electrode body, the recess 53 is an electrode body. It is preferable that the electrode current collector foil is continuously formed from the end portion of the electrode current collector foil which is the open end portion of the above.

Such a positive electrode 60 can be manufactured, for example, as follows.
A positive electrode current collector foil 52 having a recess (that is, a groove) continuous from the end on at least one main surface is prepared. At this time, the width A of the groove is selected so that the ratio (A / B) of the width A of the recess 53 to the average particle diameter B of the positive electrode active material 56 satisfies 0.2 <A / B <0.8. ..
A positive electrode paste is prepared by dispersing the positive electrode active material 56, the conductive material 58, and the binder in an appropriate solvent (for example, N-methylpyrrolidone). At this time, the solid content concentration (NV) of the positive electrode paste is C, and the solid content concentration (NV) when the torque is maximized when the oil absorption is measured using the positive electrode active material 56 and the conductive material 58 is D. In this case, it is preferable to select the solid content concentration of the positive electrode paste so as to satisfy -5% <CD <8%. If the CD is −5% or less, the fluidity of the positive electrode paste becomes too high, and the groove may be filled with a conductive material having a small particle size. On the other hand, if CD is 8% or more, there is a possibility that the positive electrode paste cannot be formed.
This positive electrode paste is applied on the grooved surface of the positive electrode current collector foil 52 except for the portion that becomes the positive electrode mixture layer non-forming portion 52a. This is dried to remove the solvent to form the positive electrode mixture layer 54. If necessary, a pressing process is performed to adjust the density of the positive electrode mixture layer. In this way, the positive electrode 60 can be manufactured.

Examples of the negative electrode current collector foil 62 constituting the negative electrode sheet 60 include a copper foil and the like. As the negative electrode active material contained in the negative electrode mixture layer 64, a carbon material such as graphite, hard carbon, or soft carbon can be used. The negative electrode mixture layer 64 may contain components other than the active material, such as a binder and a thickener. As the binder, for example, styrene butadiene rubber (SBR) or the like can be used. As the thickener, for example, carboxymethyl cellulose (CMC) or the like can be used.

Although not shown in the present embodiment, the negative electrode 60 side also has the above-mentioned configuration. That is, the negative electrode current collector foil 62 has a recess continuous from the end on the surface on which the negative electrode mixture layer 64 is formed. The ratio (A'/ B') of the width A'of the recess to the average particle diameter B'of the negative electrode active material satisfies 0.2 <A'/ B'<0.8. The ratio of the cross-sectional area of the solid component constituting the negative electrode mixture layer 64 that has entered the recess to the cross-sectional area of the recess is 0.6 or less.
Therefore, even on the negative electrode 60 side, the recess functions as a flow path for the non-aqueous electrolytic solution, and even if the non-aqueous electrolytic solution is pushed out from the electrode body 20 when the lithium ion secondary battery 100 is repeatedly charged and discharged at a high rate. The non-aqueous electrolytic solution extruded through the recess on the negative electrode 60 side can return to the electrode body 20. As a result, it is possible to suppress a decrease in the amount of the non-aqueous electrolytic solution impregnated in the electrode body 20, and it is possible to suppress a decrease in resistance due to this.
In this embodiment, both the positive electrode 50 and the negative electrode 60 have a configuration in which a predetermined recess is formed in the electrode current collector foil. However, only one of the positive electrode 50 and the negative electrode 60 may have a configuration in which a predetermined recess is formed in the electrode current collector foil described above.

Examples of the separator 70 include a porous sheet (film) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. The 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). A heat resistant layer (HRL) may be provided on the surface of the separator 70.

As the non-aqueous electrolytic solution, the same as the conventional lithium ion secondary battery can be used, 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 and lactones used in the electrolytic solution of a general lithium ion secondary battery shall be used without particular limitation. Can be done. As specific examples, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), Examples thereof include monofluoromethyldifluoromethyl carbonate (F-DMC) and trifluorodimethyl carbonate (TFDMC). As such a non-aqueous solvent, one kind may be used alone, or two or more kinds may be used in combination as appropriate. As the supporting salt, for example, a lithium salt (preferably LiPF ₆ ) such as LiPF ₆ , LiBF ₄ , and LiClO ₄ can be preferably used. The concentration of the supporting salt is preferably 0.7 mol / L or more and 1.3 mol / L or less.

The non-aqueous electrolytic solution is, for example, a gas generator such as biphenyl (BP), cyclohexylbenzene (CHB); an oxalate complex compound containing a boron atom and / or a phosphorus atom, as long as the effect of the present invention is not significantly impaired. , A film-forming agent such as vinylene carbonate (VC); a dispersant; various additives such as a thickener.

The lithium ion secondary battery 100 configured as described above can be used for various purposes. Suitable applications include drive power supplies mounted on vehicles such as electric vehicles (EVs), hybrid vehicles (HVs), and plug-in hybrid vehicles (PHVs). The lithium ion secondary battery 100 can also be used in the form of an assembled battery, which is typically formed by connecting a plurality of lithium ion secondary batteries in series and / or in parallel.

As an example, a square lithium ion secondary battery 100 including a flat wound electrode body 20 has been described. However, the lithium ion secondary battery can also be configured as a lithium ion secondary battery including a laminated electrode body. The lithium ion secondary battery can also be configured as a cylindrical lithium ion secondary battery. Further, the technique disclosed herein can be applied to a secondary battery other than the lithium ion secondary battery.

Hereinafter, examples relating to the present invention will be described, but the present invention is not intended to be limited to those shown in such examples.

<Preparation of electrode sample>
[Preparation of positive electrode samples a1, a2, b1 and b2]
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (LNCM) as a positive electrode active material, AB as a conductive material, and PVDF as a binder are used in LNCM: AB: PVDF = 90: 8: 2. It was mixed with N-methylpyrrolidone (NMP) by mass ratio to prepare a paste for forming a positive electrode mixture layer. This paste was applied to both sides of an aluminum foil (current collector foil) in a band shape, dried, and pressed to prepare a positive electrode. The basis weight of the positive electrode mixture layer was 42 mg / cm ² , and the density was 2.8 g / cm ³ .
At this time, a current collector foil having grooves on both sides was used. The groove width A (μm) and the average particle size (D50) B of the active material were changed as shown in Table 1. The solid content concentration (NV) of the electrode paste is C, and the solid content concentration (NV) when the torque is maximized when the oil absorption is measured using the active material and the conductive material is C. The values of −D (%) are also shown in Table 1.
[Preparation of negative electrode samples a3, a4, b3 and b4]
Further, graphite (C) as a negative electrode active material, CMC as a thickener, and SBR as a binder are mixed with ion-exchanged water at a mass ratio of C: CMC: SBR = 98: 1: 1. , A paste for forming a negative electrode mixture layer was prepared. This paste was applied to both sides of a copper foil (current collector foil) in a band shape, dried, and pressed to prepare a negative electrode. The basis weight of the negative electrode mixture layer was 18.5 mg / cm ² , and the density was 1.5 g / cm ³ .
At this time, a current collector foil having grooves on both sides was used. The groove width A (μm) and the average particle size (D50) B of the active material were changed as shown in Table 1. The solid content concentration (NV) of the electrode paste is C, and the solid content concentration (NV) when the torque is maximized when the oil absorption is measured using the active material and the solvent is C-. The values of D (%) are also shown in Table 1.

<Evaluation of groove formation>
The cross section of the prepared electrode was observed using an electron microscope to evaluate whether or not a groove was formed (that is, whether or not a groove of the current collector foil remained). specifically. The image obtained by observing the cross section of the electrode with an electron microscope was analyzed, and the value of (cross section of the solid content of the electrode paste that entered the groove / cross section of the entire groove) was obtained. The value of (cross-section of solid content of electrode paste that has entered the groove / cross-section of all grooves) is less than 0.6 as "○", and the value of 0.6 or more is "x". .. The results are shown in Table 1.

<Preparation of battery samples A1 to A4 and C1>
In addition to the above-mentioned prepared electrodes, a positive electrode and a negative electrode were made by the same method as above, using a current collector foil having no groove.
A porous sheet having a three-layer structure of PP / PE / PP and a thickness of 24 μm was prepared as a separator.
An electrode body was prepared by laminating a positive electrode, a negative electrode, and a separator so that the separator was interposed between the positive and negative electrodes. The number of positive electrodes and negative electrodes was 65 each.
At this time, the electrodes shown in Table 2 were used. When a current collector foil having a groove was used, the groove communicated from one end of the electrode body to the other end in the electrode body.
The prepared electrode body was housed in a battery case. Subsequently, a non-aqueous electrolytic solution was injected through the opening of the battery case, and the opening was hermetically sealed to prepare a lithium ion secondary battery. The non-aqueous electrolytic solution is supported by a mixed solvent containing ethylene carbonate (EC), ethylmethyl carbonate (EMC) and dimethyl carbonate (DMC) in a volume ratio of EC: EMC: DMC = 3: 3: 4. A solution of LiPF ₆ as a salt at a concentration of 1.0 mol / L was used.

<Evaluation of battery sample>
For each of the obtained battery samples, constant current constant voltage (CCCV) charging / discharging was repeated under the conditions of rate: 2C, voltage range: SOC (State of charge) 15% to SOC 90%, under a temperature environment of 0 ° C. , High-rate charge / discharge test was performed. The battery resistance was measured before and after the test according to a conventional method, and the resistance increase rate (%) was obtained from (resistance after test / resistance before test-1) × 100. The results are shown in Table 2.

The battery samples A1 to A4 are battery samples within the range of the secondary battery according to the present embodiment, and the battery sample C1 is a battery sample outside the range of the secondary battery according to the present embodiment. As the results in Table 2 show, it can be seen that the resistance increase rate of the battery samples A1 to A4 is significantly lower than that of the battery sample C1. By providing a predetermined groove in the current collecting foil, the electrolytic solution extruded from the electrode body when high-rate charging / discharging is repeated can return to the electrode body, whereby the electrolytic solution in the electrode body can be returned. It is considered that this is because the increase in resistance due to the decrease in the amount could be suppressed.
Therefore, from the above results, it can be seen that the secondary battery according to the present embodiment can suppress an increase in resistance when charging and discharging are repeated at a high rate.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The techniques described in the claims include various modifications and modifications of the specific examples exemplified above.

20 (Turning) Electrode body 30 Battery case 36 Safety valve 42 Positive electrode terminal 42a Positive current collector plate 44 Negative electrode terminal 44a Negative electrode current collector plate 50 Positive electrode (sheet)
52 Positive electrode current collector foil 52a Positive electrode mixture layer non-formed portion 53 Recess 54 Positive electrode mixture layer 56 Positive electrode active material 58 Conductive material 60 Negative electrode (sheet)
62 Negative electrode current collector foil 62a Negative electrode mixture layer non-formed portion 64 Negative electrode mixture layer 70 Separator (sheet)
100 lithium ion secondary battery

Claims (1)

An electrode body with positive and negative electrodes and
With non-aqueous electrolyte
A battery case for accommodating the electrode body and the non-aqueous electrolytic solution,
It is a secondary battery equipped with
The negative electrode has a negative electrode current collector foil and a negative electrode mixture layer formed on the negative electrode current collector foil.
The negative electrode current collector foil has a recess continuous from the end on the surface on which the negative electrode mixture layer is formed.
The negative electrode mixture layer contains a negative electrode active material and has a negative electrode mixture layer.
The ratio (A / B) of the width A of the recess to the average particle diameter B of the negative electrode active material satisfies 0.2 <A / B <0.8.
The ratio of the cross-sectional area of the solid component constituting the negative electrode mixture layer that has entered the recess to the cross-sectional area of the recess is 0.6 or less.
Secondary battery.

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