Negative electrode layer

Abstract

To provide a negative electrode layer with low resistance in a high SOC region.SOLUTION: A negative electrode layer is used for an all-solid-state battery. The negative electrode layer contains Si-based particles having pores as negative electrode active material. A ratio of a particle diameter D90 of the Si particles to a particle diameter D50 of the Si-based particles (D90 / D50) is 37.9 or more. The Si-based particles have a peak A near 1050 cm-1 and a peak B near 1400 cm-1 in Fourier Transform Infrared Spectroscopy (FT-IR) measurement. A ratio of intensity D2 of the peak B to intensity D1 of the peak A (D2 / D1) is 0.30 or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a negative electrode layer used in an all-solid-state battery.

Background Art

[0002] An all-solid-state battery is a battery having a solid electrolyte layer between a positive electrode layer and a negative electrode layer, and has an advantage that simplification of a safety device is easy compared to a liquid-based battery having an electrolyte containing a flammable organic solvent. Further, Si is known as a negative electrode active material used in an all-solid-state battery. For example, Patent Document 1 discloses an all-solid-state battery in which a negative electrode active material layer has voids in a region of 0.3 μm around the surface of a Si-based negative electrode active material.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Si has a large theoretical capacity and is effective for increasing the energy density of an all-solid-state battery. On the other hand, since Si has a large volume change during charge and discharge, the restraint pressure of the all-solid-state battery may fluctuate. In this regard, although the volume change of Si can be suppressed by providing voids as in Patent Document 1, a new problem arises in that the battery resistance increases in a high SOC (State of Charge) region.

[0005] The present disclosure has been made in view of the above circumstances, and a main object thereof is to provide a negative electrode layer having low resistance in a high SOC region.

Means for Solving the Problems

[0006] In order to solve the above problems, in the present disclosure, there is provided a negative electrode layer for an all-solid-state battery, the negative electrode layer containing Si-based particles having pores as a negative electrode active material, the ratio (D90 / D50) of the particle diameter D90 of the Si particles to the particle diameter D50 of the Si-based particles being 37.9 or more, and the Si-based particles having, in Fourier transform infrared spectroscopy measurement (FT-IR), a peak A at around 1050 cm -1 and a peak B at around 1400 cm -1 such that the ratio (D2 / D1) of the intensity D2 of the peak B to the intensity D1 of the peak A is 0.30 or less.

[0007] According to the present disclosure, since the Si-based particles having pores have a predetermined particle diameter ratio and peak intensity ratio, a negative electrode layer having low resistance in a high SOC region is obtained.

Advantages of the Invention

[0008] In the present disclosure, there is an effect that a negative electrode layer having low resistance in a high SOC region can be provided.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0010] Hereinafter, the negative electrode layer in the present disclosure will be described in detail.

[0011] The negative electrode layer in the present disclosure is used in an all-solid-state battery and contains Si-based particles having pores as a negative electrode active material. The ratio (D90 / D50) of the particle diameter D90 of the Si particles to the particle diameter D50 of the Si-based particles is 37.9 or more. Further, the Si-based particles have a peak A near 1050 cm -1 and a peak B near 1400 cm -1 in Fourier transform infrared spectroscopy measurement (FT-IR), and the ratio (D2 / D1) of the intensity D2 of the peak B to the intensity D1 of the peak A is 0.30 or less.

[0012] According to the present disclosure, since the Si-based particles having pores have a predetermined particle diameter ratio and peak intensity ratio, a negative electrode layer having a low resistance in a high SOC region is obtained.

[0013] When Si provided with voids (pores) as described above is used, although the volume change during charge and discharge can be suppressed, the resistance in the high SOC region increases. In this regard, it is unclear what parameters of the Si-based particles having pores (also referred to as porous Si-based particles) contribute to the reduction of battery resistance, and there is room for performance improvement in all-solid-state batteries using porous Si-based particles as an active material. The inventors focused on the shape parameters and surface characteristic parameters of the porous Si-based particles and conducted repeated studies. As a result, it was found that the battery resistance can be reduced in the high SOC region by adjusting the particle diameter ratio and the peak intensity ratio obtained by FT-IR within a predetermined range.

[0014] In the present disclosure, although the exact reason for the resistance to decrease in the high SOC region is unknown, it is speculated as follows. In Si particles having pores (porous), for a certain amount of porosity, it is considered that the lithium diffusivity inside the active material (Si particles) is higher in particles with a larger particle size than in particles with a smaller particle size. Therefore, in Si-based particles, it is considered that the resistance can be reduced by making D90 / D50 sufficiently large. Also, on the surface of Si particles, it is considered that the resistance increases when the amount of Si-R bonds relative to Si-O bonds is large. Therefore, when D90 / D50 is 37.9 or more and D2 / D1 is 0.30 or less, it is considered that the resistance becomes smaller more synergistically.

[0015] 1. Negative electrode layer (1) Si-based particles The negative electrode layer contains Si-based particles having pores as the negative electrode active material. FIG. 1 is a schematic cross-sectional view showing an example of Si-based particles in the present disclosure. As shown in FIG. 1, the Si-based particles 1 have pores 2. Also, in the negative electrode layer, since the Si-based particles 1 are bonded to O element or a functional group R other than O element on their surfaces, they have peaks at predetermined positions in FT-IR described later.

[0016] The Si-based particles contain at least Si element. Examples of the Si-based particles include single Si particles, Si alloy particles, and Si oxide particles. The Si alloy preferably contains Si element as the main component. The proportion of Si element in the Si alloy is, for example, 50 at% or more, may be 70 at% or more, or may be 90 at% or more. Examples of the Si alloy include Si-Li-based alloy, Si-Al-based alloy, Si-Sn-based alloy, Si-In-based alloy, Si-Ag-based alloy, Si-Pb-based alloy, Si-Sb-based alloy, Si-Bi-based alloy, Si-Mg-based alloy, Si-Ca-based alloy, Si-Ge-based alloy, Si-Pb-based alloy, etc. The Si alloy may be a binary alloy or a multi-component alloy of three or more components. The Si alloy may be a Si-Li-based alloy. Also, examples of the Si oxide include SiO.

[0017] The Si-based particles have pores. By having pores, the volume change during charge and discharge can be suppressed. The porosity of the Si-based particles is not particularly limited, but for example, it is 5% or more and 50% or less. The porosity can be calculated from the following formula by observing a scanning electron microscope (SEM) image of the cross-section of the Si-based particles, for example. Porosity (%) = 100 × (pore area) / (particle area)

[0018] Also, the Si-based particles may have a predetermined BET specific surface area. The BET specific surface area of the Si-based particles is, for example, 20.0 m 2 / g or more, and may be 25.0 m 2 / g or more, may be 30.0 m 2 / g or more, may be 35.0 m 2 / g or more. On the other hand, the BET specific surface area of the Si-based particles is, for example, 60.0 m 2 / g or less, may be 55.0 m 2 / g or less, may be 50.0 m 2 / g or less, may be 45.0 m 2 / g or less, may be 40.0 m 2 / g or less. The BET specific surface area can be calculated from the BET method using, for example, a pore distribution measuring device.

[0019] In the Si-based particles, the ratio of the particle diameter D90 to the particle diameter D50 (D90 / D50) is within a predetermined range. The lower limit of D90 / D50 is usually 37.9 or more, may be 50.0 or more, and may be 100.0 or more. On the other hand, the upper limit of D90 / D50 is not particularly limited, but for example, it is 300.0 or less, may be 250.0 or less, may be 200.0 or less, and may be 150.0 or less. Note that the particle diameter D50 refers to the cumulative 50% particle diameter in the volume-based particle size distribution measured by a laser diffraction particle size distribution measuring device. Also, the particle diameter D90 refers to the cumulative 90% particle diameter in the volume-based particle size distribution measured by a laser diffraction particle size distribution measuring device.

[0020] The D50 of the Si-based particles is not particularly limited as long as it satisfies the above relationship. The D50 is, for example, 0.3 μm or more, and may be 0.4 μm or more, or may be 0.5 μm or more. On the other hand, the D50 is, for example, 1.0 μm or less, and may be 0.8 μm or less, or may be 0.6 μm or less.

[0021] The D90 of the Si-based particles is not particularly limited as long as it satisfies the above relationship. The D90 is, for example, 10 μm or more, and may be 30 μm or more, or may be 50 μm or more. On the other hand, the D90 is, for example, 100 μm or less, and may be 80 μm or less, or may be 60 μm or less.

[0022] In Fourier transform infrared spectroscopy measurement (FT-IR), the Si-based particles have a peak A around 1050 cm -1 and a peak B around 1400 cm -1 . The peak A is a peak derived from the Si-O bond on the surface of the Si-based particles. Also, the peak B is a peak derived from the Si-R bond (R is a functional group other than O) on the surface of the Si-based particles. The positions of the peak A and the peak B may shift back and forth within a range of ±100 cm -1 . Further, the Si-based particles in the present disclosure may further have typical peaks around 1560 cm -1 and around 870 cm -1 .

[0023] Also, for the Si-based particles, the ratio (D2 / D1) of the intensity D2 of the peak B to the intensity D1 of the peak A is within a predetermined range. The upper limit of D2 / D1 is usually 0.30 or less, and may be 0.25 or less, or may be 0.20 or less. On the other hand, the lower limit of D2 / D1 is not particularly limited, but is, for example, 0.10 or more, and may be 0.15 or more.

[0024] D1 at peak A is not particularly limited as long as it satisfies the above relationship. D1 is, for example, 0.0180 or more and 0.0250 or less. Also, D2 at peak B is not particularly limited as long as it satisfies the above relationship. D2 is, for example, 0.0020 or more and 0.0070 or less. D1 and D2 can be adjusted by changing the manufacturing conditions of the Si-based particles, as shown in the examples described later, for example.

[0025] The content of the Si-based particles in the negative electrode layer is, for example, 50% by weight or more and 95% by weight or less.

[0026] (2) Negative electrode layer The negative electrode layer may contain a solid electrolyte. Examples of the solid electrolyte include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes.

[0027] Examples of the sulfide solid electrolyte include solid electrolytes containing Li element, X element (X is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, In), and S element. Also, the sulfide solid electrolyte may further contain at least one of O element and halogen element. Examples of the halogen element include F element, Cl element, Br element, and I element. The sulfide solid electrolyte may be glass (amorphous) or glass ceramics. Examples of the sulfide solid electrolyte include Li2S-P2S5, LiI-Li2S-P2S5, LiI-LiBr-Li2S-P2S5, Li2S-SiS2, Li2S-GeS2, and Li2S-P2S5-GeS2.

[0028] The negative electrode layer may contain a conductive material. By using a conductive material, the electron conductivity in the negative electrode layer is improved. Examples of the conductive material include carbon materials. Examples of the carbon materials include particulate carbon materials such as acetylene black (AB) and ketjen black (KB), fibrous carbon materials such as carbon fiber, carbon nanotube (CNT), and carbon nanofiber (CNF).

[0029] The negative electrode layer may contain a binder. Examples of the binder include fluorine-containing binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). Further, the thickness of the negative electrode layer is, for example, 0.1 μm or more and 1000 μm or less.

[0030] 2. All-solid-state battery The negative electrode layer in the present disclosure is used in an all-solid-state battery. FIG. 2 is a schematic cross-sectional view showing an example of the all-solid-state battery in the present disclosure. The all-solid-state battery 10 shown in FIG. 2 includes a positive electrode layer 11, a negative electrode layer 12, and a solid electrolyte layer 13 disposed between the positive electrode layer 11 and the negative electrode layer 12. Further, the all-solid-state battery 10 includes a positive electrode current collector 14 that collects current from the positive electrode layer 11 and a negative electrode current collector 15 that collects current from the negative electrode layer 12. The negative electrode layer 12 is the negative electrode layer described above.

[0031] (1) Negative electrode layer Since the description of the negative electrode layer is the same as that described in "1. Negative electrode layer", the description here is omitted.

[0032] (2) Positive electrode layer The positive electrode layer contains at least a positive electrode active material. Further, the positive electrode layer may further contain at least one of a solid electrolyte, a conductive material, and a binder. Since the solid electrolyte, the conductive material, and the binder are the same as those described in "1. Negative electrode layer", the description here is omitted.

[0033] Examples of the positive electrode active material include oxide active materials. Examples of the oxide active materials include rock salt layer-type active materials such as LiCoO2, LiMnO2, LiNiO2, LiVO2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 3 / 5 Co 1 / 5 Mn 1 / 5 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, etc., spinel-type active materials such as LiMn2O4, Li4Ti5O 12 , Li(Ni 0.5 Mn1.5 )Spinel-type active materials such as O4, and olivine-type active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4 can be mentioned.

[0034] The thickness of the positive electrode layer is, for example, 0.1 μm or more and 1000 μm or less.

[0035] (3) Solid electrolyte layer The solid electrolyte layer is a layer containing at least a solid electrolyte, and may further contain a binder. Since the solid electrolyte and the binder are the same as those described in "1. Negative electrode layer", the description here is omitted. The thickness of the solid electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less.

[0036] (4) Other members The all-solid-state battery usually has a positive electrode current collector for collecting current from the positive electrode layer and a negative electrode current collector for collecting current from the negative electrode layer. Examples of the material of the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. On the other hand, examples of the material of the negative electrode current collector include SUS, copper, nickel, and carbon. Further, the all-solid-state battery in the present disclosure may have a battery case for housing the above-described negative electrode layer, positive electrode layer, and solid electrolyte layer.

[0037] (5) All-solid-state battery The all-solid-state battery is preferably an all-solid-state lithium battery. Examples of the applications of the all-solid-state battery include power sources for vehicles such as hybrid vehicles (HEV), plug-in hybrid vehicles (PHEV), battery electric vehicles (BEV), gasoline vehicles, and diesel vehicles. Further, the all-solid-state battery in the present disclosure may be used as a power source for moving bodies other than vehicles (for example, railways, ships, airplanes), and may also be used as a power source for electrical products such as information processing devices.

[0038] Note that the present disclosure is not limited to the above embodiments. The above embodiments are examples, and any structure that has substantially the same structure as the technical idea described in the claims of the present disclosure and exhibits the same effects is included in the technical scope of the present disclosure.

Example

[0039] [Example 1] (Preparation of Porous Si Particles) Particles of elemental Si (27.7 g) were pulverized by a ball mill to adjust the particle size. The conditions of the ball mill were 1000 rpm for 3 h. Next, the pulverized elemental Si particles and metallic Li (32.5 g) were added to a mortar and mixed at room temperature to obtain an LiSi alloy. The conditions of the mortar mixing were 50 rpm for 20 min. Then, the LiSi alloy was added to a mesitylene solvent (600 ml), and while stirring at room temperature and 250 rpm, ethanol at 0°C or lower was added dropwise at a constant rate (1 drop / 5 sec) for a total of 600 ml. Further, while stirring at 250 rpm, acetic acid was added dropwise for a total of 800 ml. The resulting solution was filtered under reduced pressure, and the powder was recovered. The recovered powder was vacuum dried (-0.1 MPa, for 12 h or more) to remove the solvent. Thereafter, further heat drying (160°C, 12 h) was performed. Thereby, Si-based particles having pores (porous Si particles) were obtained.

[0040] (Preparation of Negative Electrode) 50% by mass of the above porous Si particles, 37% by mass of a sulfide solid electrolyte (10LiI - 15LiBr - 75(0.75Li2S - 0.25P2S5)), 10% by mass of a conductive material (VGCF), and 3% by mass of a binder (PVdF) were put into a dispersion medium (heptane). Ultrasonic treatment was performed on this dispersion medium for 5 minutes using an ultrasonic homogenizer to obtain a negative electrode composite material. The negative electrode composite material was coated on both sides of a current collector foil (Ni foil, thickness 24 μm) and dried, and then roll-pressed at a linear pressure of 50 kN / cm. The current collector foil with the obtained negative electrode layer (thickness of each layer 45.3 μm) was punched out to φ11.3 mm (1 cm 2) As a result, a negative electrode having a negative electrode layer formed on both sides of the negative electrode current collector foil was obtained.

[0041] (Fabrication of Evaluation Battery) The positive electrode active material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2), 84.7 mass%, the sulfide solid electrolyte (10LiI - 15LiBr - 75(0.75Li2S - 0.25P2S5)), 13.4 mass%, the conductive material (VGCF), 1.3 mass%, and the binder (PVdF), 0.6 mass% were put into a dispersion medium (heptane). Ultrasonic treatment was performed on this dispersion medium using an ultrasonic homogenizer for 5 minutes to obtain a positive electrode mixture. The positive electrode mixture was applied to a current collector foil (Al foil, thickness 10 μm) and dried, and then roll-pressed at a linear pressure of 50 kN / cm. The current collector foil with the obtained positive electrode layer (thickness 70.0 μm) was punched out to φ11.3 mm (1 cm 2 ). As a result, a positive electrode having a positive electrode current collector foil and a positive electrode layer was obtained.

[0042] The sulfide solid electrolyte (10LiI - 15LiBr - 75(0.75Li2S - 0.25P2S5)), 99.5 mass%, and the binder (PVdF), 0.5 mass% were put into a dispersion medium (heptane). Ultrasonic treatment was performed on this dispersion medium using an ultrasonic homogenizer for 5 minutes to obtain a mixture. The obtained mixture was applied to a substrate (Al foil, thickness 20 μm) to a thickness of 15 μm and dried, and then punched out to φ11.3 mm (1 cm 2 ). As a result, a solid electrolyte layer (separator layer, thickness 15.0 μm) was obtained.

[0043] The above positive electrode, separator layer, and negative electrode were centered and stacked, and each layer was adhered with a surface pressure of 5 tons / cm 2 . Then, it was sealed with a tab laminate and constrained at 5 MPa. As a result, an evaluation battery (all-solid-state lithium battery) was fabricated. Note that the evaluation battery was fabricated so that its capacity would be 2 mAh. Also, the porosity of the positive electrode layer and the negative electrode layer was 3.7 g / cc and 1.8 g / cc, respectively.

[0044] [Comparative Example 1] In the production of the negative electrode of Example 1, a negative electrode and an evaluation battery were produced in the same manner as in Example 1, except that single-crystalline Si particles (Si-based particles having no voids) were used instead of the porous Si-based particles.

[0045] [Examples 2 to 6, Comparative Examples 2 to 8] The conditions of the ball mill were changed to adjust the particle size as shown in Table 1. Further, at least one of the amount of mesitylene, ethanol temperature, ethanol dropping rate, ethanol amount, and stirrer rotation speed was changed to produce porous Si-based particles having surface characteristic parameters as shown in Tables 1 and 2. A negative electrode and an evaluation battery were produced in the same manner as in Example 1, except that these porous Si-based particles were used.

[0046] [Evaluation] (Measurement of particle diameter and BET specific surface area) For the Si-based particles produced in each Example and each Comparative Example, D50 and D90 were measured. Specifically, the Si-based particles were dispersed in an aqueous solvent by a wet method and measured using a laser diffraction particle size distribution measuring device (manufactured by SHIMADZU, SALD-2300). The shape parameter (D90 / D50) was calculated from the obtained D50 and D90. The results are shown in Tables 1 and 2. In Tables 1 and 2, np-Si indicates Si-based particles having voids.

[0047] Also, the specific surface area of each Si-based particle was determined by the BET method using a specific surface area measuring device (manufactured by Anton Paar QuantaTec, Quantachrome Nova). The results are shown in Tables 1 and 2.

[0048] (FT-IR measurement) For the Si-based particles produced in each Example and each Comparative Example, FT-IR measurement was performed using a Fourier transform infrared spectrometer (manufactured by SHIMADZU, IRTracer-100), and the intensity D1 of peak A obtained in the vicinity of 1050 cm -1 and 1400 cm -1The intensity D2 of peak B obtained nearby was measured. Also, from the obtained values, the surface property parameter (D2 / D1) was calculated. The results are shown in Tables 1 and 2. In the FT-IR measurement, the smoothing points were set to around 15. Also, multi-point baseline correction was performed. Also, the ATR correction was set to 1583.560 cm -1 was set.

[0049] (Battery Resistance Measurement) For each of the evaluation all-solid-state batteries obtained in each example and each comparative example, DCIR measurement was performed under the following two conditions to obtain the charging resistance. The results are shown in Tables 1 and 2. Condition 1: Charge for 10 seconds at SOC 76% Condition 2: Charge for 10 seconds at SOC 40%

[0050] Also, for Examples 1 to 6 and Comparative Examples 2 to 8, the relationship between the shape parameter (D90 / D50) and the surface property parameter (D2 / D1) was summarized in Fig. 4.

[0051]

Table 1

[0052]

Table 2

[0053] As shown in Tables 1 and 2, it was confirmed that the larger the shape parameter (D90 / D50), the lower the DCIR. From this, it is estimated that a particle size distribution with a higher standard deviation is more effective in reducing resistance, and that if the total particle surface area is too large, it will affect the resistance. Also, it was confirmed that the smaller the surface property parameter (D2 / D1), the lower the DCIR. From this, it is estimated that if the amount of Si-R bonds relative to the Si-O bonds on the surface of the Si-based particles is large, it will affect the resistance.

[0054] Also, as shown in Table 1, Table 2, and FIG. 3, in Comparative Example 5, although the shape parameter is large, the surface characteristic parameter is also large, so the value of DCIR is large. In Comparative Example 3, although the surface characteristic parameter is small, the shape parameter is large, so the value of DCIR is large. From this, it was found that controlling both the shape parameter and the surface characteristic parameter in Si-based particles having pores has a high correlation with reducing battery resistance.

Explanation of Signs

[0055] 1 … Si-based particles 2 … Pores 10 … All-solid-state battery 11 … Positive electrode layer 12 … Negative electrode layer 13 … Solid electrolyte layer 14 … Positive electrode current collector 15 … Negative electrode current collector

Claims

**Claim 1**: A negative electrode layer containing a solid electrolyte, wherein the negative electrode layer contains Si-based particles having pores as a negative electrode active material, the ratio (D90 / D50) of the particle diameter D90 of the Si particles to the particle diameter D50 of the Si-based particles is 37.9 or more, The Si-based particles have peak A near 1050 cm －１ and peak B near 1400 cm －１ in Fourier transform infrared spectroscopy measurement (FT-IR). and the ratio (D2 / D1) of the intensity D2 of the peak B to the intensity D1 of the peak A is 0.30 or less. Negative electrode layer.

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