JP5838952B2 - Non-aqueous electrolyte secondary battery and manufacturing method thereof - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery and a method for manufacturing the same.

  One of the techniques for improving the safety of a nonaqueous electrolyte secondary battery (for example, a lithium ion secondary battery) is a CID (Current Interrupt Device) mechanism. In general, when a lithium ion secondary battery is overcharged, the electrolyte is electrolyzed to generate gas and heat. The CID mechanism is a current interruption mechanism that stops the charging of the lithium ion secondary battery by detecting gas and heat generated during overcharging. Patent Document 1 describes a non-aqueous electrolyte secondary battery having a pressure-type current interruption mechanism, in which a gas generating agent is added to an electrolytic solution.

JP 2006-324235 A

  The non-aqueous electrolyte secondary battery described in Patent Document 1 is an excellent battery that can stop charging during overcharge without using a PTC (Positive Temperature Coefficient) thermistor. However, when the battery includes a high-density positive electrode plate, the amount of gas generated during overcharge may not be ensured.

  As in Patent Document 1, in a secondary battery having a pressure type current interruption mechanism and a gas generating agent as a battery safety mechanism, gas is generated by causing a decomposition reaction on the positive electrode plate during overcharge. The internal pressure in the secondary battery is increased to activate the pressure type current interrupting mechanism. Therefore, it is necessary that there is a reaction field where the decomposition reaction of the gas generating agent proceeds, and that the generated gas is efficiently discharged out of the electrode body.

  On the other hand, there is a case where the positive electrode plate is densified for the purpose of reducing resistance or the like, but when the positive electrode plate is densified, the gap of the positive electrode plate becomes small. In a secondary battery including such a high-density positive electrode, when a pressure-type current interrupt mechanism and a gas generating agent are used, the amount of decomposition reaction gas generated by the gas generating agent decreases.

  The present invention has been made to solve such a problem, and aims to secure the amount of gas generated during overcharge while ensuring the battery characteristics of the nonaqueous electrolyte secondary battery. . More specifically, an object of the present invention is to provide a non-aqueous electrolyte secondary battery that has both a battery performance and a safety during overcharge while having a high-density positive electrode plate.

  A non-aqueous electrolyte secondary battery of the present invention includes a positive electrode plate having a positive electrode active material and a conductive material, a negative electrode plate, and a non-aqueous electrolyte containing a gas generating additive that generates gas by decomposing reaction in the positive electrode plate; And a current interrupting unit that interrupts an electric current according to the generated gas.

The positive electrode active material has a DBP oil absorption of 21.5 to 32.5 ml / 100 g, and the conductive material has carbon black and 50 to 200 parts by mass of graphite with respect to 100 parts by mass of carbon black. The positive electrode plate has a density of 2.6 to 3.0 g / cm ³ . The DBP oil absorption is preferably 24.6 to 27.7 ml / 100 g.

The paste containing the positive electrode active material and the conductive material preferably has a viscosity of 2.0 to 8.0 (Pa · sec) when stirred at a shear rate of 2 (/ sec), from 2.563 to 3.875 (Pa · sec) is particularly preferable.
The solid content of the paste including the positive electrode active material and the conductive material is preferably 65 to 71%. It is preferable that the change rate in 5 days of the solid content rate of the paste containing the positive electrode active material and the conductive material is −5 to + 5%.

  The positive electrode plate includes 6 parts by mass of the conductive material and 3 parts by mass of a binder with respect to 91 parts by mass of the positive electrode active material, and the conductive material includes carbon black and carbon black of 100 parts by mass. On the other hand, it is preferable to consist of 50-100 mass parts graphite. The carbon black is preferably acetylene black.

  The manufacturing method of the non-aqueous electrolyte secondary battery of the present invention includes carbon black and a conductive material containing 50 to 200 parts by mass of graphite with respect to 100 parts by mass of carbon black, and a DBP oil absorption of 21.5 to 32.32. A kneading step of kneading a positive electrode active material of 5 ml / 100 g; and a forming step of forming a positive electrode plate having the kneaded material.

The manufacturing method further includes a rolling process for rolling the positive electrode plate so that the density of the positive electrode plate is 2.6 to 3.0 g / cm ³ , and gas generation that generates gas by decomposition reaction in the positive electrode plate. An addition step of adding an additive to the non-aqueous electrolyte, an assembly step of assembling the positive electrode plate, the negative electrode plate, the non-aqueous electrolyte, and a current interrupting unit that interrupts a current according to the generated gas; Is provided.

  By this invention, the gas generation amount at the time of overcharge can be ensured, ensuring the battery characteristic of a nonaqueous electrolyte secondary battery.

It is a graph showing the relationship between oil absorption amount and paste viscosity. It is a graph showing the relationship between oil absorption amount and ultimate SOC. It is a schematic diagram of the positive electrode plate concerning an Example. It is a schematic diagram of the positive electrode plate concerning a comparative example. It is a graph showing the relationship between oil absorption amount and electrical resistance. It is a schematic diagram of the positive electrode plate concerning a comparative example. It is a schematic diagram of the positive electrode plate concerning an Example. It is a schematic diagram of the positive electrode plate concerning a comparative example. It is a graph showing the relationship between oil absorption amount and paste viscosity. It is a graph showing the relationship between oil absorption and the sedimentation property of a paste.

  Hereinafter, a non-aqueous electrolyte secondary battery (hereinafter simply referred to as a battery) according to an embodiment of the present invention will be described. The lithium ion secondary battery according to the present embodiment includes a positive electrode plate, a negative electrode plate, a nonaqueous electrolyte, and a current interrupting unit.

<Positive electrode plate>
The positive electrode plate has a positive electrode active material, a conductive material, and a binder (binder). The conductive material has a first conductive material and a second conductive material.

The positive electrode active material is a material capable of inserting and extracting lithium. For example, lithium cobaltate (LiCoO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium nickelate (LiNiO ₂ ), and the like can be used. _{It may} also be a material obtained by mixing LiCoO 2, LiMn ₂ O _4, the LiNiO ₂ at an arbitrary ratio. In order to ensure battery output, it is preferable to use LiNi _1/3 Co _1/3 Mn _1/3 O ₂ .

  As the positive electrode active material, for example, a material having a particle size of D50 = 4.0 to 7.0 μm can be used. D50 is a volume-based or number-based median diameter, and so on. The particle diameter can be measured, for example, by a laser diffraction / scattering method using a Microtrack MT3000II manufactured by Nikkiso Co., Ltd. The positive electrode active material is not limited to these materials, and any material can be used as long as it is a material capable of inserting and extracting lithium.

The positive electrode active material preferably has a predetermined DBP oil absorption as a structural feature. The predetermined DBP oil absorption is preferably 21.5 to 32.5 ml / 100 g, and particularly preferably 24.6 to 27.7 ml / 100 g.
When the DBP oil absorption amount is within the upper limit range, even in a high-density positive electrode plate, it is possible to suppress a decrease in gas generation amount generated from a gas generation additive described later.

Moreover, when the DBP oil absorption amount is within the lower limit range, the electrical resistance at a low SOC (State of Charge) of 20% or less is reduced, and a decrease in output at a low SOC can be suppressed.
The positive electrode active material can be selected from the materials prepared according to known methods by measuring the DBP oil absorption. As a measuring method, for example, the A method defined in JIS K-6217 (Testing method for basic performance of carbon black for rubber) can be used.

  As the first conductive material, it is preferable to use carbon black (CB). As the carbon black, it is preferable to use one or more carbon blacks selected from the group consisting of acetylene black (AB), ketjen black (registered trademark, KB), and high black (HB). It is preferable to use acetylene black. By using the first conductive material, the amount of gas generated during overcharge can be ensured.

  As the second conductive material, graphite (graphite) is preferable, natural graphite is more preferable, and scaly graphite is particularly preferable. As the scaly graphite, one or more selected from the group consisting of KS4 and KS6 manufactured by Timcal Graphite and Carbon, and J-SP, SP-5030, and SP-270 manufactured by Nippon Graphite Industries Co., Ltd. Things can be used.

  The amount of the conductive material is preferably 50 to 200 parts by mass of graphite as the second conductor with respect to 100 parts by mass of carbon black as the first conductive material. By using the conductive material, the conductivity of the positive electrode is ensured.

  The positive electrode mixture may contain a dispersant. As the dispersant, for example, a polyvinyl acetal-based dispersant (binder-type dispersant) can be used. The polyvinyl acetal-based dispersant does not decompose (a small amount even if decomposed), and does not deposit on the positive electrode (a small amount even if deposited). Can be suppressed.

  Examples of the polyvinyl acetal dispersant include polyvinyl butyral, polyvinyl formal, polyvinyl acetoacetal, polyvinyl benzal, polyvinyl phenyl acetal, and copolymers thereof.

  As the binder (binder), for example, polyvinylidene fluoride (PVdF), styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC) and the like can be used. PVdF is preferable because a preferable paste viscosity can be obtained.

  Moreover, as a positive electrode electrical power collector (positive electrode core material), the material which consists of an alloy which has aluminum or aluminum as a main component can be used. It is preferable to form the current collector foil by thinly stretching the material and cutting it into a desired shape.

  In producing the positive electrode according to the present embodiment, first, a positive electrode active material, a first conductive material, a second conductive material, and a binder (binder) are kneaded. Each amount including the amount of the conductive material when kneading is 6 parts by mass of the first conductive material and the second conductive material with respect to 91 parts by mass of the positive electrode active material, and the binder is 3 parts by mass. It is preferable to do. It is particularly preferable that the first conductive material is 3 parts by mass and the second conductive material is 3 parts by mass.

In order to knead the above materials and adjust the solid content or viscosity of the paste (mixture), it is preferable to use a predetermined solvent. As the predetermined solvent, N-methyl-2-pyrrolidone (NMP) is preferable.
The solid content of the paste is preferably 65 to 71%, and particularly preferably 68%. When the positive electrode active material has the DBP oil absorption amount described above and the solid content of the paste is in the above range, the viscosity of the paste described later can be optimized.

  The viscosity of the paste is preferably 2.0 to 8.0 (Pa · sec) when stirred at a shear rate of 2 (/ sec), and preferably 2.563 to 3.875 (Pa · sec). It is particularly preferred that The paste having the predetermined viscosity can be selected using a viscoelasticity measuring device (rheometer).

When the paste viscosity is within the upper limit, kneading is facilitated, and the application work to the current collector foil can be performed efficiently. Moreover, when the paste viscosity is within the lower limit range, the change in solid content with time is reduced, and the stability of the paste is improved.
Moreover, as a time-dependent change of a solid content rate, it is preferable that the rate of change in 5 days is −5 to + 5%, more preferably −2 to + 4%, and −2 to + 1%. Particularly preferred. The production efficiency of the battery is improved when the solid content ratio is within a range that changes with time.

Next, the kneaded positive electrode mixture paste is applied onto the positive electrode core material and dried. Next, it adjusts so that a positive electrode plate may become a predetermined density by rolling. The predetermined density is preferably 2.6 to 3.0 g / cm ³ . By setting the density, the capacity of the battery is improved.

<Negative electrode plate>
The negative electrode active material is preferably a material capable of occluding and releasing lithium, and particularly preferably a powdery carbon material made of graphite. The graphite is preferably amorphous (amorphous) coated.

Similarly to the positive electrode plate, the negative electrode plate is prepared by kneading a negative electrode active material, a thickener, and a binder in a predetermined ratio, and applying the kneaded mixture onto the negative electrode current collector and drying. Can do. The negative electrode plate is preferably rolled to have a predetermined density. The predetermined density is preferably 1.1 to 1.3 g / cm ³ . By setting the density, the capacity of the battery is improved.

  As the thickener, carboxymethyl cellulose Na salt (CMC) is preferable. As the binder, styrene butadiene rubber (SBR) is preferable. As a predetermined ratio, it is preferable that CMC is 1 part by mass and a binder is 1 part by mass with respect to 98 parts by mass of the negative electrode active material. As the negative electrode current collector, for example, copper, nickel, or an alloy thereof can be used.

<Nonaqueous electrolyte>
The nonaqueous electrolyte is a composition in which a supporting salt is contained in a nonaqueous solvent. Here, as the non-aqueous solvent, one or two selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and the like. More than one type of material can be used.
From the viewpoint of increasing the battery output, it is preferable to use a ternary solvent system composed of EC, DMC and EMC, and it is preferable to use a mixture in a volume ratio of EC / DMC / EMC = 30/40/30.

The supporting salts include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiI 1 type, or 2 or more types of lithium compounds (lithium salt) selected from these etc. can be used. From the viewpoint of increasing the battery output, LiPF ₆ is preferably used. The concentration of the supporting salt is preferably 1.1M.

  Moreover, the non-aqueous electrolyte of the lithium ion secondary battery according to the present embodiment includes a gas generating additive that generates gas by decomposing at the positive electrode during overcharge. Here, as the gas generating additive, for example, cyclohexylbenzene (CHB), biphenyl (BP), or a mixture thereof can be used.

  The addition amount is preferably 4 parts by mass with respect to 100 parts by mass of the non-aqueous electrolyte from the viewpoint of securing the amount of gas generated necessary for current interruption. The gas generating additive is not limited to these materials, and any material may be used as long as it is a material that generates gas by a decomposition reaction at the positive electrode during overcharge.

<Separator>
Moreover, the lithium ion secondary battery according to the present embodiment may include a separator. As a separator, a porous polymer film such as a porous polyethylene film (PE), a porous polypropylene film (PP), a porous polyolefin film, and a porous polyvinyl chloride film, or a lithium ion or ion conductive polymer electrolyte film Can be used alone or in combination.
From the viewpoint of increasing the battery output, it is preferable to use a three-layer coated separator in which PE is sandwiched between two upper and lower PP layers.

<Current interrupter>
The current interrupting unit operating as a CID mechanism interrupts the current according to the gas generated by the decomposition reaction of the gas generating additive at the positive electrode during overcharge. That is, the current interrupting unit stops charging the lithium ion secondary battery when the pressure inside the lithium ion secondary battery becomes equal to or higher than a predetermined value due to the gas generated during overcharging.

  As the current interrupting unit, for example, a mechanism that interrupts the current supplied to the lithium ion secondary battery by deforming the container of the lithium ion secondary battery when the internal pressure of the lithium ion secondary battery increases is used. be able to. As such a mechanism, for example, a mechanism in which charging is stopped by disconnecting a wiring that supplies current to at least one of a positive electrode and a negative electrode of the lithium ion secondary battery by deforming a container of the lithium ion secondary battery. Can be used.

  In addition, a sensor that detects deformation of the container of the lithium ion secondary battery and a circuit that stops charging according to the measurement result of the sensor are provided, and when the deformation of the container is detected by the sensor, the lithium ion secondary battery You may comprise so that charge may be stopped. In addition, when a pressure sensor that detects the internal pressure of the container of the lithium ion secondary battery and a circuit that stops charging according to the measurement result of the pressure sensor are provided, and the internal pressure of the container exceeds a predetermined pressure Alternatively, the charging of the lithium ion secondary battery may be stopped.

<Manufacture of batteries>
The material and the amount for production are as described above. In manufacturing the battery, the positive electrode active material, the first conductor, the second conductor, and the binder are kneaded to prepare a positive electrode mixture paste (kneading step). The positive electrode mixture paste is applied to the positive electrode core material to form a positive electrode plate (forming step). It rolls so that the density of this positive electrode plate may be 2.6-3.0 g / cm < ³ > (rolling process). On the other hand, a gas generating additive is added to the non-aqueous electrolyte (addition process).

  A positive electrode plate, a negative electrode plate, a non-aqueous electrolyte, and a current interrupting unit that interrupts current according to the generated gas are assembled into a battery (assembly process). After laminating with the separator interposed between the positive electrode and the negative electrode produced as described above, the laminated body is flattened (winded electrode body). Then, the wound electrode body and the current interrupting portion are accommodated in a container having a shape that can accommodate the wound electrode body. The container includes a flat rectangular parallelepiped container body having an open upper end and a lid that closes the opening.

As a material constituting the container, a metal material such as aluminum or steel can be used. Further, for example, a container formed by molding a resin material such as polyphenylene sulfide resin (PPS) or polyimide resin may be used.
The shape of the container is not particularly limited. When mounted on an automobile, a rectangular shape is preferable from the viewpoint of increasing mounting efficiency. Moreover, when mounting in a motor vehicle, it may be a large cell.

The upper surface (that is, the lid) of the container is provided with a positive electrode terminal electrically connected to the positive electrode of the wound electrode body and a negative electrode terminal electrically connected to the negative electrode of the wound electrode body. You may attach the above-mentioned electric current interruption | blocking part to these terminals integrally with these.
In addition, a non-aqueous electrolyte is accommodated inside the container.

<Description of effects>
The effect of the configuration of the battery according to the present embodiment will be described with reference to FIG. Electric vehicles (EV) or plug-in hybrid vehicles (PHV) require high capacity batteries. For this reason, it is necessary to roll a positive electrode plate having a high-weight positive electrode mixture layer to form a positive electrode plate having a high density of 2.6 to 3.0 g / cm ³ .

  Further, when a pressure type CID mechanism is mounted on the battery, it is necessary to generate gas from the gas generating additive added to the non-aqueous electrolyte at the time of overcharging on the positive electrode surface. However, when the density of the positive electrode plate is high, the reactivity with the gas generating additive is deteriorated, and there is a case where the gas generation amount necessary for operating the CID mechanism in a desired overcharge state, that is, a desired SOC, cannot be secured. is there.

  In this Embodiment, in order to suppress the fall of said gas generation amount, attention was paid to the three-dimensional structure of the positive electrode active material particles. Moreover, the DBP oil absorption was adopted as a standard for defining the three-dimensional structure. The DBP oil absorption affects the viscosity of the mixture paste. Based on this, the DBP oil absorption amount of the positive electrode active material is plotted on the horizontal axis, the paste viscosity during stirring at a shear rate of 2 (/ sec) is plotted on the vertical axis, and the battery performance is evaluated in the regions I to V. FIG. 1 shows the results evaluated separately.

In the battery according to FIG. 1, a paste containing 3 parts by mass of the first conductive material, 3 parts by mass of the second conductive material, and 3 parts by mass of the binder is collected with respect to 91 parts by mass of the positive electrode active material at a solid content of 68%. A positive electrode plate was prepared by applying to a foil. The density of the positive electrode plate is 2.6 to 3.0 g / cm ³ . The battery according to each embodiment is represented by a square in the coordinate system of FIG.

  In region III, the DBP oil absorption is 21.5 to 32.5 (ml / 100 g) and the paste viscosity is 2.0 to 8.0 (Pa · sec). Batteries included in region III are represented by hatched squares, and those not included are represented by white squares. In region III, a decrease in gas generation amount is suppressed, while a decrease in battery output is suppressed. Moreover, productivity is also favorable.

In region I where the DBP oil absorption is greater than 32.5 (ml / 100 g), the amount of gas generated during overcharge is reduced. On the other hand, in the region II where the DBP oil absorption is smaller than 21.5 (ml / 100 g), the battery output decreases.
Further, in region IV where the paste viscosity is 2.0 (Pa · sec) or less, the stability of the paste is lowered. On the other hand, in the region V where the paste viscosity is 8.0 (Pa · sec) or more, the kneading property and the coating property are deteriorated. Further, in the region V, there is a concern about an increase in filter pressure when the paste is filtered and deterioration of paste transportability.

Further, in the region V, in order to obtain a desired solid content rate, excess NMP must be introduced, which may cause a decrease in productivity. For this reason, it is preferable that the DBP oil absorption amount of a positive electrode active material is 32.5 (ml / 100g) or less.
As another method for obtaining a desired solid content rate, it is conceivable to reduce the amount of the conductive material. However, in this case, the battery output may be reduced. Another possible method is to reduce the molecular weight of the binder. However, in this case, the migration state of the binder may be deteriorated. In addition, there is a limit to controlling the solid content with a conductive material or a binder.

  The above will be described in more detail in the verification of the effect of the embodiment. The battery of the present embodiment can be mounted on a transport machine such as an electric vehicle (EV) or a plug-in hybrid vehicle (PHV) and used as a drive power source. Note that the present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention.

[Example 1]
<Preparation of positive electrode plate>
The positive electrode plate according to Example 1 was produced as follows. When the entire positive electrode mixture was 100% by weight, 91.0% by weight of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ was used as the positive electrode active material. In addition, 3.0% by weight of acetylene black (AB, manufactured by Denki Kagaku Kogyo Co., Ltd .: HS100) was used as the first conductive material, and 3.0% by weight of graphite was used as the second conductive material.

  Furthermore, 3.0% by weight of polyvinylidene fluoride (PVdF) (manufactured by Kureha Co., Ltd .: # 1300) was used as a binder. The DBP oil absorption of the positive electrode active material was 27.7 (ml / 100 g).

  First, a binder (PVdF) was added to NMP (N-methyl-2-pyrrolidone) and mixed. Thereafter, acetylene black (AB) and a graphite-based material were further added and kneaded to prepare a positive electrode mixture paste. The solid content ratio (NV) of the positive electrode mixture paste was 68 (% by weight). The positive electrode mixture paste may be kneaded by previously mixing acetylene black (AB) and a graphite-based material, and then adding NMP to which a binder (PVdF) is added.

Thereafter, the positive electrode material mixture paste prepared as described above was applied on a 15 μm-thick aluminum foil serving as a positive electrode current collector at a basis weight of 27.0 mg / cm ² . After applying the positive electrode mixture paste, it was dried under conditions of a temperature of 150 ° C. and a wind speed of 5 m / sec. Finally, it was rolled with a rolling press and adjusted to a density of 2.6 to 3.0 g / cm ³ to obtain a positive electrode plate.

<Preparation of negative electrode plate>
Natural graphite powder, SBR (styrene butadiene rubber), and CMC (carboxymethylcellulose) were kneaded with water so that the mass ratio of these materials was 98: 1: 1 to prepare a negative electrode mixture paste. Thereafter, this negative electrode mixture paste was applied to a copper foil (negative electrode current collector) having a thickness of 10 μm and dried. Finally, it was rolled with a rolling press and adjusted to a density of 1.1 to 1.3 g / cm ³ to obtain a negative electrode plate.

<Current interruption mechanism>
A current interruption mechanism (CID mechanism) serving as a current interruption portion was provided as follows. First, a diaphragm-shaped current interruption mechanism made of metal foil was produced. The edge of the current interruption mechanism was electrically connected to the external negative terminal. Further, the vicinity of the center of the current interrupt mechanism was electrically connected to the internal negative terminal.

  When the SOC rises due to overcharging of the battery, the gas generating additive reacts to generate gas. When the pressure in the housing formed from the battery case and the sealing body is increased by the generated gas, the diaphragm-shaped current interruption mechanism is pushed into the sealing body by the pressure. As a result, the connection between the internal negative terminal and the current interrupt mechanism is disconnected, and the internal negative terminal and the external negative terminal are insulated. Moreover, it produced similarly also on the positive electrode side.

<Battery assembly>
The positive electrode and the negative electrode produced by the above method were laminated via two separators. The separator used was a three-layer coated separator in which PE was sandwiched between two upper and lower PP layers. This laminated body was accommodated in a rectangular battery container together with a nonaqueous electrolyte and a current interruption mechanism, and the opening of the battery container was sealed airtight.
As the non-aqueous electrolyte, a mixed solvent containing EC, EMC, and DMC in a volume ratio of 3: 3: 4 and containing LiPF ₆ as a supporting salt at a concentration of about 1.1 mol / liter was used. . In addition, 4% by weight of cyclohexylbenzene (CHB) was added as a gas generating additive.

[Example 2]
A battery was fabricated in the same manner as in Example 1, except that the DBP oil absorption amount of the positive electrode active material was 27.7 (ml / 100 g).
[Example 3]
A battery was fabricated in the same manner as in Example 1, except that the first conductive material was 3 wt%, the second conductive material was 3 wt%, and the DBP oil absorption amount of the positive electrode active material was 27.2 ml / 100 g.

[Example 4]
A battery was fabricated in the same manner as in Example 3, except that the first conductive material was 4% by weight and the second conductive material was 2% by weight. The amount of NMP was the same as in Example 3, and the solid content rate was not adjusted.
[Example 5]
A battery was fabricated in the same manner as in Example 3, except that the first conductive material was 2% by weight and the second conductive material was 4% by weight. The amount of NMP was the same as in Example 3, and the solid content rate was not adjusted.

[Comparative Example 1]
A battery was produced in the same manner as in Example 1 except that the DBP oil absorption amount of the positive electrode active material was 39.5 (ml / 100 g).
[Comparative Example 2]
A battery was produced in the same manner as in Example 1 except that the DBP oil absorption amount of the positive electrode active material was 33.4 (ml / 100 g).

[Comparative Example 3]
A battery was fabricated in the same manner as in Example 1 except that the DBP oil absorption amount of the positive electrode active material was 17.6 (ml / 100 g).
[Comparative Example 4]
A battery was produced in the same manner as in Example 1 except that the DBP oil absorption amount of the positive electrode active material was 20.0 (ml / 100 g).

[Comparative Example 5]
A battery was fabricated in the same manner as in Example 3, except that the first conductive material was 6% by weight and the second conductive material was not mixed. The amount of NMP was the same as in Example 3, and the solid content rate was not adjusted.
[Comparative Example 6]
A battery was fabricated in the same manner as in Example 3, except that the first conductive material was not mixed and the second conductive material was 6 wt%. The amount of NMP was the same as in Example 3, and the solid content rate was not adjusted.

[Comparative Example 7]
A battery was fabricated in the same manner as in Example 3, except that the first conductive material was 3% by weight, the second conductive material was 2% by weight, and the positive electrode active material was increased by 1% by weight. The amount of NMP was the same as in Example 3, and the solid content rate was not adjusted.
[Comparative Example 8]
A battery was fabricated in the same manner as in Example 3, except that the first conductive material was 4 wt%, the second conductive material was not mixed, and the positive electrode active material was increased by 2 wt%. The amount of NMP was the same as in Example 3, and the solid content rate was not adjusted.

[Verification of effects on DBP oil absorption]
<Operation of CID mechanism>
The test was started at an environmental temperature of 25 ° C. and a current rate of 1 C, and the SOC (%) at which the CID mechanism was operated was measured. The target range was determined to be SOC 165 (%) or less, and those operating with SOC within the target range were regarded as acceptable.
As shown in the black diamonds in Table 1 and FIG. 2, Examples 1 and 2 and Comparative Examples 3 and 4 were acceptable. On the other hand, as shown in the white diamonds of Table 1 and FIG. 2, Comparative Examples 1 and 2 were unacceptable.

^*比較例４の電気抵抗を１としたときの各実施例の電気抵抗の比を表す。

^* Represents the ratio of the electrical resistance of each example when the electrical resistance of Comparative Example 4 is 1.

The above results are explained as follows. 3, 4, and 6 to 8, the positive electrode active material 1, the conductive material surrounding the positive electrode active material, and the binder 2 are disposed and formed as a mixture layer on the current collector foil 3. As shown in FIG. 3, the positive electrode plate of the battery that passed the test has the positive electrode active material 1 having an appropriate internal space. The structure of such a positive electrode active material corresponds to the DBP oil absorption being in an appropriate range.
Even if the density of the positive electrode is increased, the shape of the positive electrode active material 1 is maintained to some extent. For this reason, the diffusion path of the gas generating additive retained in the positive electrode plate is not significantly hindered, the reactivity can be ensured, and the amount of gas generated is sufficient.

On the other hand, the positive electrode plate of the battery which has been rejected has the positive electrode active material 1 having a large internal space, as shown in FIG. The structure of the positive electrode active material corresponds to the DBP oil absorption amount being in an excessive range.
When the density of such a positive electrode is increased, the crushing rate of the positive electrode active material having an internal space increases, so that the shape of the positive electrode active material 1 becomes flat. For this reason, the diffusion path of the gas generating additive retained in the positive electrode plate is inhibited, the reaction efficiency is deteriorated, and the amount of gas generated is insufficient.
From the regression line analysis of the graph of FIG. 2, it was found that if the DBP oil absorption amount of the positive electrode active material is 32.5 (ml / 100 g) or less, a sufficient gas generation amount can be secured for the CID mechanism to operate.

<Battery characteristics at low charge>
The electric resistance of the battery was measured at an environmental temperature of 25 ° C. and SOC of 20%. Those having a resistance value within a predetermined range were regarded as acceptable. As shown in the black diamonds of Table 1 and FIG. 5, Examples 1 and 2 and Comparative Examples 1 and 2 were acceptable. On the other hand, as shown in the white rhombuses of Table 1 and FIG. 5, Comparative Examples 3 and 4 were unacceptable.

The above results are explained as follows. That is, as shown in FIG. 6, the positive electrode plate of the batteries according to Comparative Examples 1 and 2 does not change the shape of the active material even when the positive electrode has a high density. Therefore, it is difficult to secure a conductive path, and the electrical resistance increases. Battery characteristics deteriorated.
On the other hand, as shown in FIG. 7, the positive electrode plate of the batteries according to Examples 1 and 2 slightly changes the shape of the active material when the positive electrode has a high density, but an increase in electric resistance is suppressed because a conductive path can be secured. The deterioration of the battery characteristics was suppressed.

Furthermore, as shown in FIG. 8, the positive electrode plate of the batteries according to Comparative Examples 3 and 4 has a flat active material shape when the positive electrode has a high density, and a conductive path can be secured. The deterioration of characteristics was suppressed.
From the regression line analysis of the graph of FIG. 5, it was found that when the DBP oil absorption amount of the positive electrode active material is 21.5 (ml / 100 g) or more, battery characteristics that can provide sufficient output even at low charge can be secured.

<Paste viscosity>
The paste viscosity when stirring at a shear rate of 2 (/ sec) was measured. For measurement of the viscosity, a rheometer MCR301 manufactured by Anton Paar was used. The target range of the paste viscosity was determined to be 2.0 to 8.0 (Pa · sec), and the one within the target range was regarded as acceptable. Examples 1 and 2 passed as shown in Table 1 and the black diamonds in FIG. On the other hand, as shown in Table 1 and the white diamonds in FIG. 9, Comparative Examples 1 to 4 were unacceptable.
It was found that when the DBP oil absorption amount of the positive electrode active material is in the predetermined range and the paste solid content rate is about 68%, a desired paste viscosity can be secured.

<Paste sedimentation>
The rate of change was determined by measuring the initial solid content immediately after the paste was prepared, and the solid content of the supernatant of the paste after 5 days of standing. MS70 manufactured by A & D was used for the measurement of the solid content. Note that the greater the sedimentation, the greater the rate of change and the poorer the paste stability.

The rate of change ± 5% was taken as the target range, and those within the target range were accepted. As shown in the black diamonds of Table 1 and FIG. 10, Examples 1 and 2 and Comparative Examples 1 and 2 were acceptable. On the other hand, as shown in Table 1 and the white diamond in FIG. 10, Comparative Examples 3 and 4 were unacceptable.
It was found that when the DBP oil absorption amount of the positive electrode active material is in the predetermined range and the paste solid content is about 68%, desired paste stability can be ensured.

[Verification of effects on the amount of conductive material]
<Solid content>
The initial solid content rate immediately after the preparation of the paste was measured. A solid content ratio of 68 ± 1 (%) was set as a target range, and a solid content rate within the target range was determined as acceptable.

  As shown in Table 2, Examples 3 to 5 and Comparative Examples 7 and 8 were acceptable, but Comparative Examples 5 and 6 were unacceptable. If the amount of the conductive material of the first conductor and the second conductor is in the predetermined range and the DBP oil absorption amount of the positive electrode active material is about 27.2 (ml / 100 g), a solid content rate of about 68% is secured. I knew it was possible.

^*表１の比較例４の電気抵抗を１としたときの各実施例の電気抵抗の比を表す。

^* Represents the ratio of the electrical resistance of each example when the electrical resistance of Comparative Example 4 in Table 1 is 1.

<Operation of CID mechanism>
The operation of the CID mechanism was measured as described above. The target range is the same as above. As shown in Table 2, Examples 3 to 5 and Comparative Examples 5 and 6 were acceptable, but Comparative Examples 7 and 8 were unacceptable.
If the amount of the conductive material of the first conductor and the second conductor is in the predetermined range and the DBP oil absorption amount of the positive electrode active material is about 27.2 (ml / 100 g), it is sufficient for the CID mechanism to operate. It was found that a sufficient amount of gas was generated.

<Battery characteristics at low charge>
The battery characteristics at the time of low charge amount were measured in the same manner as described above. As shown in Table 2, Examples 3 to 5 and Comparative Examples 5, 7 and 8 were acceptable, but Comparative Example 6 was unacceptable.
If the amount of the conductive material of the first conductor and the second conductor is in the predetermined range and the DBP oil absorption amount of the positive electrode active material is about 27.2 (ml / 100 g), sufficient output can be obtained even at low charge. It turned out that the battery characteristic to exhibit can be ensured.

  As described above, the present invention is not limited to the configurations of the above-described embodiments or examples, and various modifications, corrections, and combinations that can be made by those skilled in the art within the scope of the invention of the claims of the claims of the present application. Of course.

DESCRIPTION OF SYMBOLS 1 Positive electrode active material 2 Conductive material and binder 3 Current collection foil (positive electrode core material)

Claims (9)

A positive electrode plate having a positive electrode active material and a conductive material;
A negative electrode plate;
A non-aqueous electrolyte containing a gas generating additive that generates a gas by decomposing in the positive electrode plate;
A current interrupting unit that interrupts current according to the generated gas,
The positive electrode active material has a DBP oil absorption of 21.5-32.5 ml / 100 g,
The conductive material has carbon black and 50 to 200 parts by mass of graphite with respect to 100 parts by mass of carbon black,
The positive electrode plate has a density of 2.6 to 3.0 g / cm ³ .
Non-aqueous electrolyte secondary battery.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the DBP oil absorption is 24.6 to 27.7 ml / 100 g. The positive electrode plate includes 6 parts by mass of the conductive material and 3 parts by mass of a binder with respect to 91 parts by mass of the positive electrode active material,
3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the conductive material is made of carbon black and 50 to 100 parts by mass of graphite with respect to 100 parts by mass of carbon black. The carbon black is acetylene black, non-aqueous electrolyte secondary battery according to any one of claims 1-3. A kneading step of kneading carbon black and a conductive material containing 50 to 200 parts by mass of graphite and a positive electrode active material having a DBP oil absorption of 21.5 to 32.5 ml / 100 g with respect to 100 parts by mass of carbon black. When,
Forming a positive electrode plate having the kneaded material; and
A rolling step of rolling the positive electrode plate so that the density of the positive electrode plate is 2.6 to 3.0 g / cm ³ ;
An addition step of adding, to the non-aqueous electrolyte, a gas generating additive that generates gas by decomposing in the positive electrode plate;
An assembly process for assembling the positive electrode plate, the negative electrode plate, the non-aqueous electrolyte, and a current interrupting unit that interrupts current according to the generated gas. The paste obtained by kneading the positive electrode active material and the conductive material has a viscosity of 2.0 to 8.0 (Pa · sec) when stirred at a shear rate of 2 (/ sec). The manufacturing method of the nonaqueous electrolyte secondary battery as described in any one of. The method for producing a nonaqueous electrolyte secondary battery according to claim 5 or 6, wherein a solid content of a paste formed by kneading the positive electrode active material and the conductive material is 65 to 71%. The non-aqueous electrolyte 2 according to any one of claims 5 to 7, wherein the change rate of the solid content of the paste obtained by kneading the positive electrode active material and the conductive material in 5 days is -5 to + 5%. A method for manufacturing a secondary battery. The method for producing a non-aqueous electrolyte secondary battery according to claim 6, wherein the viscosity is 2.563 to 3.875 (Pa · sec).

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