JP6928873B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

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

In recent years, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have been used for portable power sources such as personal computers and mobile terminals, and vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV). It is suitably used for driving power supplies and the like.

A general non-aqueous electrolyte secondary battery includes an electrode body in which a positive electrode and a negative electrode are laminated via a separator. This electrode body is roughly classified into a wound electrode body and a laminated electrode body.
As a non-aqueous electrolytic solution secondary battery including a wound electrode body, for example, Patent Document 1 is wound by superimposing a positive electrode having a positive electrode active material layer, a negative electrode having a negative electrode active material layer, and a separator having a heat resistant layer. A non-aqueous electrolyte secondary battery including a wound electrode body is disclosed. In Patent Document 1, the wound electrode ^body, it is described that the prepared wound at a tension of ^{0.35N / mm 2 ~4.3N / mm 2} (0.35MPa~4.3MPa).

Japanese Unexamined Patent Publication No. 2016-189261

As a result of diligent studies by the present inventor, in a non-aqueous electrolyte secondary battery provided with a wound electrode body including a separator having a heat-resistant layer, metallic lithium precipitation resistance during repeated charging and discharging and low-temperature output characteristics are exhibited at a high level. We found that there is room for improvement in achieving both.

Therefore, an object of the present invention is a non-aqueous electrolytic solution secondary battery including a wound electrode body including a separator having a heat-resistant layer, which has high resistance to metallic lithium precipitation during repeated charging and discharging and high low-temperature output characteristics. The purpose is to provide a water electrolyte secondary battery.

As a result of diligent studies by the present inventor, by making the heat-resistant layer of the separator face the positive electrode active material layer and appropriately controlling the tension of the wound electrode body, metallic lithium precipitation resistance during repeated charging and discharging and low-temperature output It was found that both the characteristics and the characteristics can be enhanced.
That is, the non-aqueous electrolyte secondary battery disclosed herein includes a wound electrode body in which a positive electrode, a negative electrode, and a separator are stacked and wound, a non-aqueous electrolyte solution, the wound electrode body, and the wound electrode body. A battery case for accommodating the non-aqueous electrolyte solution is provided. The separator has a heat resistant layer. The positive electrode has a positive electrode active material layer. The heat-resistant layer is in contact with the positive electrode active material layer. The tension acting on the wound electrode body is 12 MPa or more and 82 MPa or less.
According to such a configuration, it is a non-aqueous electrolytic solution secondary battery including a wound electrode body including a separator having a heat-resistant layer, and has high resistance to metal lithium precipitation during repeated charging and discharging and high low-temperature output characteristics. A non-aqueous electrolyte secondary battery can be provided.

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 a part of the laminated structure of the wound electrode body 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 non-aqueous electrolyte batteries that do not characterize the present invention) are , 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 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 charged and discharged repeatedly, 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 electrolyte solution (not shown) are housed in a flat square battery case (that is, an outer container) 30. It is a sealed battery 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 active material layer 54 is formed along the longitudinal direction on one side or both sides (here, both sides) of the elongated positive electrode current collector 52. The positive electrode sheet 50 and the negative electrode sheet 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 are two long sheets. It has a form in which it is overlapped with each other via a separator sheet 70 and wound in the longitudinal direction. The positive electrode active material layer non-formed portion 52a (that is, the positive electrode) formed so as to protrude outward from both ends of the winding electrode body 20 in the winding axis direction (referring to the sheet width direction orthogonal to the longitudinal direction). A portion where the positive electrode current collector 52 is exposed without forming the active material layer 54) and a portion 62a where the negative electrode active material layer is not formed (that is, a portion where the negative electrode current collector 62 is exposed without forming the negative electrode active material layer 64). ) Are joined to a positive electrode current collector plate 42a and a negative electrode current collector plate 44a, respectively.

As the positive electrode sheet 50 and the negative electrode sheet 60, the same ones used in the conventional lithium ion secondary battery can be used without particular limitation. A typical aspect is shown below.

Examples of the positive electrode current collector 52 constituting the positive electrode sheet 50 include aluminum foil and the like. Examples of the positive electrode active material contained in the positive electrode active material layer 54 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. The positive electrode active material layer 54 may contain components other than the active material, such as a conductive material and a binder. As the conductive material, 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.

Examples of the negative electrode current collector 62 constituting the negative electrode sheet 60 include copper foil and the like. As the negative electrode active material contained in the negative electrode active material layer 64, a carbon material such as graphite, hard carbon, or soft carbon can be used. The negative electrode active material 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.

In this embodiment, as shown in FIG. 3, a separator 70 having a heat-resistant layer (HRL) 72 is used. In FIG. 3, the separator 70 has a heat-resistant layer 72 and a base material layer (here, a porous resin sheet layer 74). The heat-resistant layer 72 is arranged so as to face the positive electrode 50, and as a result, the heat-resistant layer 72 is in contact with the positive electrode active material layer 54.
Since the heat-resistant layer 72 of the separator 70 faces the positive electrode 50 (is in contact with the positive electrode active material layer 54), the non-aqueous electrolyte solution is retained at the interface between the positive electrode 50 (positive electrode active material layer 54) and the separator 70. The property can be improved, whereby the diffusion resistance of lithium ions can be reduced and the low output characteristics can be improved.

The heat-resistant layer 72 may include a material usually used for the heat-resistant layer of a separator of a lithium ion secondary battery. Specifically, it may contain an inorganic filler, and if necessary, a binder, a thickener, and the like.
Examples of the inorganic filler include _{inorganic oxides such as alumina (Al 2} O ₃ ), magnesia (MgO), silica (SiO ₂ ), and titania (TiO ₂ ), nitrides such as aluminum oxide and silicon nitride, and calcium hydroxide. , Metal hydroxides such as magnesium hydroxide and aluminum hydroxide, clay minerals such as mica, talc, boehmite, zeolite, apatite and kaolin, glass fibers and the like. Of these, alumina, boehmite, and magnesia are preferably used.
Examples of the binder of the heat-resistant layer 72 include fluoropolymers such as polytetrafluoroethylene (PTFE), acrylic binders, styrene-butadiene rubber (SBR), and polyolefin-based binders. Examples of the thickener of the heat-resistant layer 72 include binders. For example, carboxymethyl cellulose (CMC), methyl cellulose (MC) and the like can be mentioned.

Examples of the resin constituting the porous resin sheet layer 74 include polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. The porous resin sheet layer 74 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 the PE layer).

In the present embodiment, the tension acting on the wound electrode body 20 is 12 MPa or more and 82 MPa or less.
If the tension acting on the wound electrode body 20 is too small, the force for maintaining the shape of the wound electrode body 20 (particularly the shape of the curved R portion) becomes weak, and the distance between the poles becomes non-uniform. Therefore, resistance unevenness due to the difference in the distance between the poles occurs, and a large current flows in a place where the distance between the poles is small. As a result, the current is concentrated at the boundary portion, and the metal lithium precipitation resistance during repeated charging and discharging deteriorates. Therefore, the tension acting on the wound electrode body 20 is 12 MPa or more, preferably 20 MPa or more, and more preferably 28 MPa or more.
On the other hand, if the tension acting on the wound electrode body 20 is too large, the viscosity of the non-aqueous electrolytic solution becomes high, particularly at a low temperature, so that the holding amount of the electrolytic solution of the wound electrode body 20 decreases, and lithium ions are diffused. Resistance increases. As a result, the low temperature output characteristics deteriorate. Therefore, the tension acting on the wound electrode body 20 is 82 MPa or less, preferably 70 MPa or less, and more preferably 60 MPa or less.
The tension acting on the wound electrode body 20 can be appropriately adjusted by changing the tension applied when the wound electrode body is manufactured.

As the non-aqueous electrolytic solution, the same one as that of 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 are used without particular limitation. Can be done. Specific examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl 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 type can be used alone, or two or more types can 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 electrolyte solution is a gas generating agent such as biphenyl (BP), cyclohexylbenzene (CHB) and the like; 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. , Vinylene carbonate (VC), fluoroethylene carbonate (FEC) and other film-forming agents; dispersants; thickeners and the like.

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 typically consists of a plurality of batteries connected 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 cylindrical lithium ion secondary battery, a laminated lithium ion secondary battery, or the like. Further, the technique disclosed herein can be applied to a non-aqueous electrolyte 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.

<Manufacturing of lithium-ion secondary battery for evaluation>
_{LiNi 1/3} Co _1/3 Mn _1/3 O ₂ (LNCM) as a positive electrode active material powder, AB as a conductive material, and PVDF as a binder are used as LNCM: AB: PVDF = 90: 8: 2. A slurry for forming a positive electrode active material layer was prepared by mixing with N-methylpyrrolidone (NMP) in a mass ratio of. This slurry was applied to both sides of a long aluminum foil in a strip shape while exposing one end of the aluminum foil, dried, and then pressed to prepare a positive electrode having a positive electrode active material layer.
Further, the natural graphite-based carbon material (C) as the negative electrode active material, the SBR as the binder, and the CMC as the thickener are mixed with ion-exchanged water at a mass ratio of C: SBR: CMC = 98: 1: 1. To prepare a slurry for forming a negative electrode active material layer. This slurry was applied to both sides of a long copper foil in a strip shape while exposing one end of the copper foil, dried, and then pressed to prepare a negative electrode having a negative electrode active material layer.

A separator in which a heat-resistant layer (HRL) made of an inorganic filler was formed on one side of a porous polyolefin substrate having a three-layer structure of PP / PE / PP was prepared.
The prepared positive electrode, the prepared negative electrode, and the two separators were superposed and wound to prepare a wound electrode body. At this time, in the evaluation lithium ion secondary batteries A1 to A4 and B1 to B2, the HRL of the separator was made to face the positive electrode so that the HRL was in contact with the positive electrode active material layer. In the evaluation lithium ion secondary batteries B3 to B8, the HRL of the separator was made to face the negative electrode so that the HRL was in contact with the negative electrode active material layer. Further, in the evaluation lithium ion secondary batteries A1 to A4 and B1 to B8, the tension at the time of winding was changed to change the tension acting on the wound electrode body. Table 1 shows the tensions acting on the wound electrodes of the evaluation lithium ion secondary batteries A1 to A4 and B1 to B8.

The prepared wound electrode body was housed in a battery case mainly made of aluminum. Subsequently, a non-aqueous electrolytic solution was injected through the opening of the battery case, and the opening was hermetically sealed to prepare lithium ion secondary batteries A1 to A4 and B1 to B8 for evaluation. The non-aqueous electrolyte solution is supported by a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of EC: EMC: DMC = 3: 4: 3. A salt _{prepared by dissolving LiPF 6} at a concentration of 1.0 mol / L was used.

<Cycle characterization>
The capacity of each of the prepared lithium secondary batteries for evaluation was measured and adjusted to 80% SOC (State of charge) in an environment of −10 ° C. Then, a square wave charge / discharge at 200 A for 10 seconds was carried out for 1000 cycles. Then, the capacity was measured, and the capacity retention rate (%) was obtained from (battery capacity after 1000 cycles of charging / discharging / battery capacity before 1000 cycles of charging / discharging) × 100. The results are shown in Table 1.

<Evaluation of low temperature output characteristics>
Each of the prepared lithium secondary batteries for evaluation was adjusted to SOC 27% and allowed to stand in an environment of −35 ° C. for 6 hours. After that, constant power output was performed under a plurality of conditions, and an output value reaching a predetermined voltage in a predetermined time was calculated. When the output value of the evaluation lithium secondary battery B1 was set to 100, the ratio of the output values of the other evaluation lithium secondary batteries to the evaluation lithium secondary battery B1 was determined. The results are shown in Table 1.

As can be seen from the results in Table 1, both the capacity retention rate and the low temperature output are high because the HRL faces the positive electrode (that is, the HRL contacts the positive electrode active material layer) and the tension acting on the wound electrode body is 12 MPa. This is the case of 82 MPa or less (that is, lithium ion secondary batteries A1 to A4). Since the decrease in the capacity retention rate during high-rate charging / discharging in an environment of −10 ° C. is mainly due to the precipitation of metallic lithium, the capacity retention rate is an index of the precipitation resistance of metallic lithium.
Therefore, according to the above-described embodiment, it is a non-aqueous electrolytic solution secondary battery including a wound electrode body including a separator having a heat-resistant layer, and has metal lithium precipitation resistance during repeated charging and discharging and low-temperature output characteristics. It can be seen that both can provide a high non-aqueous electrolyte secondary battery.

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

20 Winding 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 60 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 70 Separator sheet (separator)
72 Heat-resistant layer 74 Porous resin sheet layer 100 Lithium-ion secondary battery

Claims (1)

A wound electrode body in which a positive electrode, a negative electrode, and a separator are overlapped and wound.
With non-aqueous electrolyte
A battery case accommodating the wound electrode body and the non-aqueous electrolytic solution, and
A non-aqueous electrolyte secondary battery equipped with
The separator has a polyolefin porous base material and a heat-resistant layer.
The heat-resistant layer contains an inorganic filler and contains
The positive electrode has a positive electrode current collector and a positive electrode active material layer.
The positive electrode current collector is an aluminum foil.
The positive electrode active material layer contains lithium transition metal oxide, carbon black, and polyvinylidene fluoride.
The negative electrode has a negative electrode current collector and a negative electrode active material layer.
The negative electrode current collector is a copper foil.
The negative electrode active material layer contains graphite, styrene-butadiene rubber, and carboxymethyl cellulose, and contains
The heat-resistant layer is in contact with the positive electrode active material layer, and is in contact with the positive electrode active material layer.
The tension acting on the wound electrode body is 12 MPa or more and 60 MPa or less .
A non-aqueous electrolyte secondary battery characterized by this.

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