Positive electrode and power storage device

Abstract

The present invention provides a positive electrode having a positive electrode current collector and a positive electrode composite material layer, wherein the positive electrode composite material layer comprises a positive electrode active material and dielectric particles, wherein the dielectric particles comprise ion conductive particles and non-ion conductive particles. The present invention also provides a power storage device having the positive electrode, a negative electrode and an electrolyte.

Description

Technical Field

[0001] The invention relates to a positive electrode and an electricity storage device. Background Art

[0002] In the past, lithium-ion secondary batteries have been widely used as power storage devices with high energy density. Lithium-ion secondary batteries have the following structure: for example, a separator is present between the positive electrode and the negative electrode, and the separator is filled with an electrolyte. In addition, the positive electrode has the following structure: for example, a positive electrode composite material layer is formed on the positive electrode current collector.

[0003] Patent Document 1 describes that barium titanate particles having a relative dielectric constant of 500 or more and a particle size of 200 nm or less are dispersed in a positive electrode.

[0004] [Prior Technical Literature]

[0005] (Patent Document)

[0006] Patent Document 1: Japanese Patent Application Publication No. 2016-119180 Summary of the invention

[0007] [Problems to be solved by the invention]

[0008] However, since barium titanate particles with a particle size of less than 200 nm are used alone, the specific surface area of ​​the barium titanate particles is high and they are easily aggregated. As a result, there are the following problems: the contact area with the electrolyte is reduced, and even if the electric field generated inside the lithium ion secondary battery acts on the barium titanate particles, the dielectric polarization of the barium titanate particles does not sufficiently increase the dissociation degree of the supporting salt in the electrolyte, resulting in an increase in the initial single body resistance.

[0009] On the other hand, there is also a problem in that the positive electrode of the lithium ion secondary battery is corroded by the positive electrode active material or decomposed by the electrolyte, resulting in an increase in the cell resistance of the lithium ion secondary battery after endurance.

[0010] An object of the present invention is to provide a positive electrode capable of reducing the initial and endurance resistance of a power storage device.

[0011] [Technical means to solve the problem]

[0012] One aspect of the present invention is a positive electrode having a positive electrode current collector and a positive electrode composite material layer. The positive electrode composite material layer contains a positive electrode active material and dielectric particles. The dielectric particles include ion conductive particles and non-ion conductive particles.

[0013] The content of the dielectric particles in the positive electrode composite material layer may be 0.5 mass % or more and 5 mass % or less.

[0014] The ion conductive particles and the non-ion conductive particles may be oxide particles, respectively.

[0015] The ion conductive particles and the non-ion conductive particles may each have a relative dielectric constant of 30 or more.

[0016] The above-mentioned ion conductive particles can have a lithium ion conductivity of 1×10 -7 S / cm or more.

[0017] The non-ion conductive particles may have a median particle size of 0.07 μm or more and 0.5 μm or less.

[0018] The ion conductive particles may have a median particle size of 0.4 μm or more and 1.0 μm or less.

[0019] The dielectric particles may contain the non-ion conductive particles in an amount of 2% by mass or more and 50% by mass or less.

[0020] The dielectric particles may contain the ion conductive particles in an amount of 50% by mass or more and 98% by mass or less.

[0021] Another aspect of the present invention is an electricity storage device comprising the above-mentioned positive electrode, negative electrode and electrolyte.

[0022] (Effects of the Invention)

[0023] According to the present invention, it is possible to provide a positive electrode capable of reducing the initial and endurance resistance of an electric storage device. DETAILED DESCRIPTION

[0024] Hereinafter, embodiments of the present invention will be described.

[0025] <Positive electrode>

[0026] The positive electrode of this embodiment has a positive electrode current collector and a positive electrode composite material layer. The positive electrode composite material layer contains a positive electrode active material and dielectric particles, and the dielectric particles include ion conductive particles and non-ion conductive particles.

[0027] In addition, in the positive electrode of the present embodiment, the positive electrode composite material layer may be formed on one surface of the positive electrode current collector, or may be formed on both surfaces of the positive electrode current collector.

[0028] In the positive electrode of the present embodiment, since the positive electrode composite material layer contains ion conductive particles and non-ion conductive particles as dielectric particles, the non-ion conductive particles are not easily aggregated and are easily dispersed in the positive electrode composite material layer. As a result, if the electric field generated inside the power storage device acts on the non-ion conductive particles, the dielectric polarization of the non-ion conductive particles increases the dissociation degree of the supporting salt in the electrolyte, and the initial single body resistance of the power storage device is reduced.

[0029] Furthermore, since the positive electrode composite material layer contains non-ion conductive particles, it is possible to suppress the corrosion of the positive electrode active material or the decomposition of the electrolyte by capturing trace amounts of acid present in the electrolyte or by stabilizing the electrolyte through interaction with the electrolyte. As a result, the single body resistance of the battery device after durability is reduced.

[0030] In order to reduce the initial and endurance single-cell resistance of the power storage device, it is preferable to increase the relative dielectric constant of the ion conductive particles and the non-ion conductive particles.

[0031] The reason for the polarization principle of non-ion-conducting particles is that, for example, in BaTiO 3 In the case of , the displacement of the positive and negative charges of each atom when the external electric field is applied deviates compared to before the external electric field is applied. If the non-ion conductive particles can maintain the crystalline structure even when crushed, the effect on the dielectric polarization is small. Therefore, if the non-ion conductive particles are crushed, the surface area increases, and the relative dielectric constant increases accordingly. Therefore, it is preferred to micronize the non-ion conductive particles, for example, to make the median particle size less than 0.5 μm, so as to increase the contact area with the electrolyte.

[0032] On the other hand, if micronized non-ion conductive particles are used alone, the non-ion conductive particles aggregate with each other, and the contact area with the electrolyte solution decreases, resulting in an increase in the initial cell resistance of the power storage device.

[0033] On the other hand, the polarization principle of ion conductive particles is considered to be that when an external electric field is applied, ions diffuse and ions are offset inside the ion conductive particles. Therefore, if the median particle size of the ion conductive particles is reduced, the diffusion range of the ions is limited, and thus the relative dielectric constant of the ion conductive particles is reduced.

[0034] The pore diameter of the voids inside the positive electrode (positive electrode composite material layer) is mainly distributed in the range of 0.02 to 2 μm, and therefore, it is preferable to use ion conductive particles and non-ion conductive particles having a median diameter within the above range.

[0035] In the positive electrode of the present embodiment, the content of dielectric particles in the positive electrode composite material layer is preferably 0.5 mass% or more and 5 mass% or less, and more preferably 1.0 mass% or more and 2.0 mass% or less. If the content of dielectric particles in the positive electrode composite material layer is 0.5 mass% or more, the initial and endurance monomer resistance of the storage device is reduced; and if the content of dielectric particles in the positive electrode composite material layer is 5 mass% or less, the energy density of the storage device is improved.

[0036] [Ion-conductive particles]

[0037] The ion-conductive particles may be oxide particles.

[0038] Examples of the oxide constituting the oxide particles include Li 1.3 Al 0.3 Ti 1.7 P 3 O 12 , Li 0.33 La 0.55 TiO 3 、LiNbO 3 , Li 3 PO 4 wait.

[0039] The relative dielectric constant of the ion conductive particles is preferably 30 or more, and more preferably 40 or more. When the relative dielectric constant of the ion conductive particles is 30 or more, the initial cell resistance of the power storage device is reduced.

[0040] The lithium ion conductivity of the ion conductive particles at 25°C is preferably 1×10 -7 S / cm or more, more preferably 1×10 -4 S / cm or more. If the lithium ion conductivity of the ion conductive particles at 25°C is 1×10 -7 S / cm or more, the initial cell resistance of the power storage device is reduced.

[0041] The median particle size of the ion conductive particles is preferably 0.4 μm to 1.0 μm, more preferably 0.5 μm to 0.8 μm. When the median particle size of the ion conductive particles is 0.4 μm to 1.0 μm, the initial cell resistance of the power storage device is reduced.

[0042] The content of the ion conductive particles in the dielectric particles is preferably 50% by mass or more and 98% by mass or less, and more preferably 60% by mass or more and 70% by mass or less. If the content of the ion conductive particles in the dielectric particles is 50% by mass or more, the initial single cell resistance of the power storage device is reduced, and if the content of the ion conductive particles in the dielectric particles is 98% by mass or less, the single cell resistance of the power storage device after endurance is reduced.

[0043] [Non-ion conductive particles]

[0044] The non-ion conductive particles may be oxide particles.

[0045] Examples of the oxide constituting the oxide particles include BaTi 1-x Zr x O 3 (0≦X≦0.5), SrBi 2 Ta 2 O 9 ,(K 1-x Na x )NbO 3 (0≦X≦1), BiFeO 3 , CaCu 3 Ti 4 O 12 wait.

[0046] The relative dielectric constant of the non-ion conductive particles is preferably 30 or more, and more preferably 40 or more. When the relative dielectric constant of the non-ion conductive particles is 30 or more, the cell resistance of the power storage device after endurance testing is reduced.

[0047] The median particle size of the non-ion conductive particles is preferably 0.07 μm to 0.5 μm, more preferably 0.1 μm to 0.5 μm. If the median particle size of the non-ion conductive particles is 0.07 μm to 0.5 μm, the cell resistance of the power storage device after endurance testing is reduced.

[0048] The content of the non-ion conductive particles in the dielectric particles is preferably 2% by mass or more and 50% by mass or less, and more preferably 30% by mass or more and 40% by mass or less. If the content of the non-ion conductive particles in the dielectric particles is 2% by mass or more, the cell resistance of the power storage device after endurance is reduced, and if the content of the non-ion conductive particles in the dielectric particles is 50% by mass or less, the initial cell resistance of the power storage device is reduced.

[0049] [Positive electrode composite material layer]

[0050] The positive electrode composite material layer contains a positive electrode active material and dielectric particles, and may further contain other components.

[0051] Examples of other components include solid electrolytes, conductive additives, and binders.

[0052] The positive electrode active material is not particularly limited as long as it can absorb and release lithium ions, and examples thereof include LiCoO 2 、Li(Ni 5 / 10 Co 2 / 10 Mn 3 / 10 ) 2 、Li(Ni 6 / 10 Co 2 / 10 Mn 2 / 10 ) 2 、Li(Ni 8 / 10 Co 1 / 10 Mn 1 / 10 ) 2 、Li(Ni 0.8 Co 0.15 Al 0.05 ) 2 、Li(Ni 1 / 6 Co 4 / 6 Mn 1 / 6 ) 2 、Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 ) 2 、LiCoO 4 、LiMn 2 O 4 、LiNiO 2 、LiFePO 4 , lithium sulfide, sulfur, etc.

[0053] [Positive electrode current collector]

[0054] The positive electrode current collector is not particularly limited, and examples thereof include metal foil and the like.

[0055] Examples of the metal constituting the metal foil include aluminum and the like.

[0056] <Positive electrode manufacturing method>

[0057] The method for manufacturing the positive electrode of this embodiment is not particularly limited, and a common method in this technical field can be applied, for example, a method of coating a positive electrode composite material layer paste containing a positive electrode active material and dielectric particles on a positive electrode collector and then drying the paste.

[0058] After the positive electrode composite material layer is formed on the positive electrode current collector, a common method in the art can be applied. For example, the positive electrode current collector formed with the positive electrode composite material layer is pressed to obtain a positive electrode. In this case, the density of the positive electrode can be adjusted by pressing.

[0059] <Electricity storage device>

[0060] The power storage device of this embodiment includes the positive electrode, the negative electrode, and the electrolyte solution of this embodiment.

[0061] Examples of the power storage device include secondary batteries such as lithium ion secondary batteries and capacitors.

[0062] The negative electrode is not particularly limited, and a well-known negative electrode applicable to a power storage device can be used.

[0063] The electrolyte solution is not particularly limited, and a well-known electrolyte solution applicable to a power storage device can be used.

[0064] [Lithium-ion secondary battery]

[0065] The lithium ion secondary battery of the present embodiment includes the positive electrode of the present embodiment, a negative electrode, an electrolyte solution, and a separator located between the positive electrode and the negative electrode.

[0066] In the lithium ion secondary battery of this embodiment, two materials can be selected from materials that can constitute electrodes, the charge and discharge potentials of the two materials can be compared, and the material with a higher potential can be applied to the positive electrode and the material with a lower potential can be applied to the negative electrode to form an arbitrary battery.

[0067] The separator is not particularly limited, and a well-known separator applicable to lithium ion secondary batteries can be used.

[0068] [Example]

[0069] Hereinafter, examples of the present invention will be described, but the present invention is not limited to the examples.

[0070] [Dielectric particles]

[0071] After obtaining dielectric particles from Toshima Manufacturing Co., Ltd., the dielectric particles whose median particle size needs to be adjusted were pulverized by a ball mill using IPA (isopropyl alcohol).

[0072] Table 1 shows the properties of the ion conductive particles.

[0073] [Table 1]

[0074]

[0075] Table 2 shows the properties of the non-ion conductive particles.

[0076] [Table 2]

[0077]

[0078] [Measurement method of relative dielectric constant of powder]

[0079] After the powder is introduced into a tablet forming machine with a diameter (R) of 38 mm for measurement, the powder is compressed using a hydraulic press to a thickness (d) of 1 to 2 mm to form a pressed powder. powder The powder compact was formed so that the mass density of the powder compact / the true specific gravity of the powder × 100) was 40% or more. Then, the electrostatic capacitance C of the powder compact at 25°C and 1kHz was measured using an LCR meter by an automatic balancing bridge method. total , calculate the relative dielectric constant ε of the pressed powder total Next, the dielectric constant of vacuum ε 0 Set to 8.854×10 -12 , the relative dielectric constant ε of air air The relative dielectric constant ε of the powder (actual volume fraction) is calculated using the following equations (1) to (3): powder .

[0080] The contact area between the powder compact and the electrode is A = (R / 2) 2 ×π (1)

[0081] C total =ε total ×ε 0 ×(A / d) (2)

[0082] ε total =ε powder ×D powder +ε air ×(1-D powder ) (3)

[0083] [Method for measuring Li ion conductivity]

[0084] Au was sputtered on both sides of the powder compact to produce electrodes. Using the produced electrodes, an AC two-terminal method was used to measure the temperature of the powder compact at a voltage of 50 mV and a frequency of 1 to 10. 6 The Li ion conductivity is measured in the range of Hz. At this time, the real number at the point where the imaginary component of the impedance is 0 is obtained, and thus the Li ion conductivity k is calculated based on the resistance value Ri. Solatron 1260 / 1287 is used as the measuring device. If the area of ​​Au is set to A' and the thickness of the powder compact is set to l, the Li ion conductivity k is expressed by the following formula (4).

[0085] k=l / (Ri×A') (4)

[0086] [Median particle size of powder (D 50)]

[0087] The particle size distribution of the powder was measured using a particle size distribution measuring apparatus MT3000II (manufactured by Microtrac Inc.) using water as a solvent, a refractive index of 1.81, and a particle size value when the cumulative % was 50 as a median diameter.

[0088] <Examples 1 to 8, Comparative Examples 1 to 3>

[0089] [Production of positive electrode]

[0090] Dielectric particles, acetylene black (AB) as a conductive additive, polyvinylidene fluoride (PVDF) as a binder, and N-methyl-2-pyrrolidone (NMP) as a dispersion medium were pre-mixed and wet-mixed using a rotary mixer to obtain a pre-mixed slurry. 0.6 Co 0.2 Mn 0.2 O 2 After mixing (NCM622) with the premixed slurry, a planetary mixer was used to perform a dispersion treatment to obtain a positive electrode composite material layer paste. The mass ratio of each component in the positive electrode composite material layer paste is shown in Table 3. Here, the median particle size of NCM622 is 12 μm.

[0091] The positive electrode composite material layer paste was applied to the aluminum foil as the positive electrode current collector and then dried. Then, the dried positive electrode current collector was pressed by roller pressing and dried in a vacuum at 120°C to form a positive electrode composite material layer to obtain a positive electrode plate. The obtained positive electrode plate was punched into a size of 30 mm × 40 mm to make a positive electrode.

[0092] [Production of negative electrode]

[0093] A planetary mixer is used to pre-mix a carboxymethyl cellulose (CMC) aqueous solution as a binder and acetylene black (AB) as a conductive aid. Next, natural graphite (NG) as a negative electrode active material is mixed and pre-mixed using a planetary mixer. Next, after adding water as a dispersion medium and styrene-butadiene rubber (SBR) as a binder, a planetary mixer is used to perform a dispersion treatment to obtain a negative electrode composite material layer paste. The mass ratio of each component in the negative electrode composite material layer paste is NG:AB:CMC:SBR=96.5:1.0:1.0:1.5. The median particle size of NG is 12μm.

[0094] The negative electrode composite material layer paste was applied to the copper foil as the negative electrode current collector and then dried. Then, the dried negative electrode current collector was pressed by roller pressing and dried in a vacuum at 130°C to form a negative electrode composite material layer to obtain a negative electrode plate. The obtained negative electrode plate was punched into a size of 34 mm × 44 mm to make a negative electrode.

[0095] [Manufacturing of lithium-ion secondary batteries]

[0096] An aluminum laminate for secondary batteries (manufactured by Dai Nippon Printing Co., Ltd.) is heat-sealed and processed into a bag shape to obtain a container. Next, after the laminate with a separator sandwiched between the positive electrode and the negative electrode is introduced into the interior of the container, the electrolyte is injected into the interface of each electrode. Next, the container is sealed after the pressure is reduced to -95kPa to produce a lithium-ion secondary battery. As a separator, a polyethylene microporous membrane coated with aluminum oxide particles on one side with a thickness of about 5μm is used. In addition, as an electrolyte, the following solution is used: LiPF as an electrolyte salt is dissolved at a concentration of 1.2mol / L in a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a volume ratio of 30:30:40. 6 .

[0097] <Evaluation of initial performance of lithium-ion secondary batteries>

[0098] The lithium ion secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 3 were subjected to the following initial performance evaluation.

[0099] [Discharge capacity]

[0100] After the lithium-ion secondary battery is placed at the measurement temperature (25°C) for 1 hour, it is charged to 4.2V at a constant current of 8.4mA, and then charged to 4.2V at a constant voltage for 1 hour. Next, after the lithium-ion secondary battery is placed for 30 minutes, it is discharged to 2.5V at a current value of 8.4mA. Then, the above operation is repeated 5 times, and the discharge capacity at the 5th discharge is set as the discharge capacity (mAh). In addition, the current value that can complete the discharge of the obtained discharge capacity within 1 hour is set to 1C.

[0101] [Single resistor]

[0102] After the discharge capacity of the lithium-ion secondary battery is measured, it is placed at the measurement temperature (25°C) for 1 hour, and then constant current charging is performed at a charging rate of 0.2C, and the charging level (SOC (State of Charge)) is adjusted to 50%, and the battery is placed for 10 minutes. Next, pulse discharge is performed at a discharge rate of 0.5C for 10 seconds, and the voltage at the time of discharge for 10 seconds is measured. In addition, the horizontal axis is set to the current value, and the vertical axis is set to the voltage, and the voltage at the time of discharge for 10 seconds at a discharge rate of 0.5C is plotted. Next, after the lithium-ion secondary battery is placed for 10 minutes, auxiliary charging is performed to restore the SOC to 50%, and the lithium-ion secondary battery is placed for 10 minutes. Next, the above operation is performed at each discharge rate of 1.0C, 1.5C, 2.0C, 2.5C, and 3.0C, and the voltage at the time of discharge for 10 seconds at each discharge rate is plotted. In addition, the slope of the approximate straight line obtained from each plot using the least squares method is used as the single body resistance (mΩ).

[0103] <Evaluation of post-life performance of lithium-ion secondary batteries>

[0104] The lithium ion secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 3 were subjected to the following evaluation of post-durability performance.

[0105] [Discharge capacity]

[0106] In a constant temperature bath at 45°C, the lithium-ion secondary battery is charged to 4.2V at a charging rate of 1C and then discharged to 2.5V at a constant current at a discharge rate of 2C as one cycle, and the above operation is repeated 500 times. Then, the temperature of the constant temperature bath is changed to 25°C, and the lithium-ion secondary battery is placed for 24 hours. Then, constant current charging is performed to 4.2V at a charging rate of 0.2C, and then constant voltage charging is performed at a voltage of 4.2V for 1 hour. Then, after the lithium-ion secondary battery is placed for 30 minutes, constant current discharge is performed to 2.5V at a discharge rate of 0.2C, and the discharge capacity (mAh) is measured.

[0107] [Single resistor]

[0108] In the same manner as in the measurement of initial performance, the lithium ion secondary battery after the discharge capacity measurement was adjusted to a charge level (SOC (State of Charge)) of 50%, and then the cell resistance (mΩ) was determined.

[0109] [Capacity retention rate]

[0110] The ratio of the discharge capacity of the post-durability performance to the discharge capacity of the initial performance was calculated as the capacity retention rate (%).

[0111] [Resistance change rate]

[0112] The ratio of the single cell resistance of the performance after durability to the single cell resistance of the initial performance was calculated as the resistance change rate (%).

[0113] Table 3 shows the evaluation results of the initial performance and post-endurance performance of the lithium ion secondary battery.

[0114] [Table 3]

[0115]

[0116]

[0117] As can be seen from Table 3, the initial and post-endurance cell resistances of the lithium ion secondary batteries of Examples 1 to 8 are low.

[0118] In contrast, the lithium ion secondary battery of Comparative Example 1 has a higher monomer resistance after durability because the positive electrode composite material layer does not contain dielectric particles. In addition, the lithium ion secondary battery of Comparative Example 2 has a higher monomer resistance after durability because the positive electrode composite material layer does not contain non-ion conductive particles. In addition, the lithium ion secondary battery of Comparative Example 3 has a higher initial monomer resistance because it does not contain ion conductive particles.

Claims

1. A positive electrode having a positive electrode current collector and a positive electrode composite material layer, The positive electrode composite material layer comprises a positive electrode active material and dielectric particles, wherein the content of the dielectric particles is 1 mass % or more and 5 mass % or less. The dielectric particles include ion conductive particles and non-ion conductive particles, the content of the non-ion conductive particles is 2 mass % or more and 50 mass % or less, and the content of the ion conductive particles is 50 mass % or more and 98 mass % or less, The ion conductive particles are Li 0.33 La 0.55 TiO 3 Particles, LiNbO 3 Particles or Li 3 PO 4 particles, wherein the relative dielectric constant of the ion conductive particles is 30 or more, The aforementioned non-ion conductive particles are BaTi 1-x Zr x O 3 (0≦X≦0.5) particles, wherein the relative dielectric constant of the non-ion conductive particles is 30 or more.

2. The positive electrode according to claim 1, in, The non-ion conductive particles have a median particle size of 0.07 μm or more and 0.5 μm or less.

3. The positive electrode according to claim 1, in, The median particle size of the ion conductive particles is 0.4 μm or more and 1.0 μm or less. 4 . A power storage device comprising the positive electrode according to claim 1 , a negative electrode and an electrolyte solution.

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