Battery

Abstract

To provide a battery which generates suppressed heat.SOLUTION: In the present disclosure, the battery includes: a positive electrode layer containing a positive electrode active material; a negative electrode layer containing a negative electrode active material; and an electrolyte layer containing an electrolyte and arranged between the positive electrode layer and the negative electrode layer. The negative electrode layer includes an Si-based negative electrode active material as the negative electrode active material. The Si-based negative electrode active material includes a void in the inside of primary particles. The ratio of the negative electrode capacity to the positive electrode capacity is at least 2.5.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a battery.

Background Art

[0002] In recent years, the development of batteries has been actively carried out. For example, in the automotive industry, the development of batteries used in battery electric vehicles (BEVs), plug-in hybrid vehicles (PHEVs), or hybrid electric vehicles (HEVs) has been promoted. In addition, various studies have been conducted on the materials used for batteries.

[0003] For example, Patent Document 1 discloses a negative electrode material for a lithium-ion secondary battery containing silicon oxide. In addition, Patent Document 2 discloses a secondary battery using a silicon negative electrode active material.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Si is known as a high-capacity negative electrode active material. On the other hand, because Si has a high capacity, for example, when an internal short circuit occurs in a battery, the amount of heat generated tends to increase.

[0006] The present disclosure has been made in view of the above circumstances, and the main object thereof is to provide a battery with a suppressed amount of heat generation.

Means for Solving the Problems

[0007] [1] A battery having a positive electrode layer containing a positive electrode active material, a negative electrode layer containing a negative electrode active material, an electrolyte, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer, The negative electrode layer contains an Si-based negative electrode active material as the negative electrode active material, The Si-based negative electrode active material has voids inside the primary particles, A battery in which the ratio of the negative electrode capacity to the positive electrode capacity is 2.5 or more.

[0008] [2] The battery according to [1], wherein the ratio is 5.0 or less.

[0009] [3] The battery according to [1] or [2], wherein the Si-based negative electrode active material has a silicon clathrate-type crystal phase.

[0010] [4] The battery according to [3], wherein the Si-based negative electrode active material has a silicon clathrate II-type crystal phase as the crystal phase.

[0011] [5] The battery according to any one of [1] to [4], wherein the proportion of the Si-based negative electrode active material in the negative electrode layer is 45% by weight or more.

Advantages of the Invention

[0012] In the present disclosure, there is an effect that the heat generation amount of the battery can be suppressed.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0014] Hereinafter, the battery in the present disclosure will be described in detail. Since the Si-based negative electrode active material in the present disclosure has voids inside the primary particles, in this specification, the Si-based negative electrode active material may be denoted as porous Si (p-Si). Further, when the Si-based negative electrode active material (porous Si) in the present disclosure has a clathrate-type crystal phase, it may be denoted as porous clathrate Si (pc-Si).

[0015] FIG. 1 is a schematic cross-sectional view illustrating the battery in the present disclosure. The battery 10 shown in FIG. 1 includes a positive electrode layer 1 containing a positive electrode active material, a negative electrode layer 2 containing a negative electrode active material, and an electrolyte layer 3 containing an electrolyte and disposed between the positive electrode layer 1 and the negative electrode layer 2. Particularly in the present disclosure, in the battery 10, the negative electrode layer 2 contains a Si-based negative electrode active material as the negative electrode active material, and the Si-based negative electrode active material has voids inside the primary particles. Further, in the battery 10, the ratio of the negative electrode capacity to the positive electrode capacity is 2.5 or more. Although it will be described later, in the battery in the present disclosure, as shown in FIG. 1(a), the negative electrode layer 2 may be a single layer, or as shown in FIG. 1(b), the negative electrode layer 2 may be two layers (a first negative electrode layer 2A and a second negative electrode layer 2B).

[0016] According to the present disclosure, since the negative electrode layer contains a Si-based negative electrode active material having voids inside the primary particles as the negative electrode active material, and the ratio of the negative electrode capacity to the positive electrode capacity is 2.5 or more, a battery with suppressed heat generation is obtained.

[0017] Although Si is a high-capacity active material, a portion where the reaction with carrier ions such as Li ions tends to concentrate is likely to occur, and the reaction with carrier ions in the negative electrode active material may become non-uniform. When the reaction with carrier ions becomes non-uniform, that is, when there is a portion where the reaction concentrates, it is likely to become hot when an internal short circuit occurs.

[0018] In contrast, the Si-based negative electrode active material in the present disclosure has voids inside its primary particles. When such voids exist, the specific surface area of the active material increases, and the area where the electrolyte can contact the active material increases. Therefore, by using the Si-based negative electrode active material in the present disclosure, it is possible to suppress the concentrated reaction with carrier ions in a part of the active material. Further, in the battery of the present disclosure, the ratio of the negative electrode capacity to the positive electrode capacity (capacity ratio) is 2.5 or more. When the capacity ratio is sufficiently large, a sufficient amount of negative electrode active material exists in the negative electrode layer with respect to the carrier ions moving from the positive electrode. Therefore, it is possible to suppress the local reaction between the negative electrode active material and the carrier ions in the negative electrode layer, and the reaction can be made uniform over the entire negative electrode layer. As a result, heat generation of the battery can be suppressed.

[0019] Further, by setting the capacity ratio to 2.5 or more, an effect that the cycle characteristics become good can also be obtained as described in the examples described later.

[0020] 1. Negative electrode layer The negative electrode layer in the present disclosure contains a negative electrode active material. In particular, the negative electrode layer in the present disclosure contains a predetermined Si-based negative electrode active material.

[0021] (1) Si-based negative electrode active material The Si-based negative electrode active material may be a single Si, an alloy (Si alloy) containing Si as a main component, or a Si oxide. The ratio of the Si element in the Si alloy is, for example, 50 mol% or more and 95 mol% or less.

[0022] The Si-based negative electrode active material has voids inside the primary particles. Having voids can be confirmed by SEM (scanning electron microscope) observation. Also, the porosity is not particularly limited, but for example, it is 4% or more, and may be 10% or more. Further, the above porosity may be, for example, 40% or less, and may be 20% or less. The porosity can be obtained, for example, by the following procedure. First, a cross-section of the negative electrode layer containing the Si-based negative electrode active material is made by ion milling. Then, the cross-section is observed by SEM to obtain a photograph of the particles. Using image analysis software from the obtained photograph, the silicon part and the void part are distinguished and binarized. The areas of the silicon part and the void part are obtained, and the porosity (%) is calculated from the following formula. Porosity (%) = 100×(void area) / ((silicon area)+(void area))

[0023] Also, in porous Si, the void volume of voids with a pore diameter of 50 nm or less is, for example, 0.05 cc / g or more and 0.30 cc / g or less. Also, the BET specific surface area of porous Si is, for example, 20 m 2 / g or more and 200 m 2 / g or less.

[0024] As a method for producing porous Si, for example, a method of producing an alloy of Li and Si (LiSi alloy) and then removing Li from the LiSi alloy can be mentioned. The LiSi alloy can be obtained, for example, by mixing Li and Si. The ratio of Li to Si (Li / Si) is, for example, 1.0 or more, and may be 2.0 or more, may be 3.0 or more, or may be 4.0 or more. On the other hand, Li / Si is, for example, 8.0 or less. As a method for removing Li from the LiSi alloy, for example, a method of reacting the LiSi alloy with a Li extraction material can be mentioned. Examples of the Li extraction material include alcohols such as methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, and 1-hexanol; and acids such as acetic acid, formic acid, propionic acid, and oxalic acid.

[0025] Here, FIG. 2 is a schematic perspective view for explaining the crystal phase of Si. Generally, Si has a diamond-type crystal phase as shown in FIG. 2(a). In contrast, the Si-based negative electrode active material in the present disclosure may have a silicon clathrate-type crystal as shown in FIGS. 2(b) and (c). In the diamond-type crystal phase shown in FIG. 2(a), tetrahedrons are formed by a plurality of Si elements. The tetrahedron does not have a space inside that can enclose metal ions such as Li ions. On the other hand, the silicon clathrate type I and II crystal phases shown in FIGS. 2(b) and (c) have a cage-type structure (cage) for the skeletal atoms, and metal ions such as Li ions can enter therein, so the reaction of Li ions can be made more uniform. Therefore, in the Si-based negative electrode active material (pc-Si) having voids inside the primary particles and having a silicon clathrate-type crystal phase, the heat generation amount of the battery can be more suppressed.

[0026] The Si-based negative electrode active material may have a silicon clathrate type I crystal phase or a silicon clathrate type II crystal phase. In particular, it is preferably mainly composed of the silicon clathrate type II crystal phase. The "main phase" means that the peak belonging to the crystal phase has the largest diffraction intensity among the peaks observed by X-ray diffraction measurement. The proportion of the silicon clathrate type II crystal phase contained in the Si-based negative electrode active material is, for example, 80% by weight or more, may be 85% by weight or more, may be 90% by weight or more, or may be 95% by weight or more. Also, the proportion of the silicon clathrate type II crystal phase contained in the Si-based negative electrode active material may be 100% by weight or less than 100% by weight. The proportion of the crystal phase can be determined by using the RIR method (Reference Intensity Ratio method).

[0027] On the one hand, the Si-based negative electrode active material in the present disclosure may or may not have a crystal phase of diamond-type silicon (crystalline Si). "Not having a crystal phase" means that the peak of the crystal phase is not confirmed in X-ray diffraction measurement. The proportion of the crystal phase of diamond-type silicon contained in the active material is, for example, less than 3% by weight, may be 2.5% by weight or less, and may be 2% by weight or less. On the other hand, the proportion of the crystal phase of diamond-type silicon contained in the active material may be 0% by weight, may be more than 0% by weight, and may be 0.1% by weight or more.

[0028] As a method for producing porous class rate Si, for example, the above-mentioned porous Si and a Na source such as NaH are mixed and heated to produce a Na-Si alloy, and by heating the Na-Si alloy, the amount of Na in the Na-Si alloy is reduced to generate a silicon class rate type crystal phase. A method can be mentioned. For more specific methods, they will be described in the examples below.

[0029] The composition of the porous class rate Si is not particularly limited, but Na x Si 136 (0 ≦ x ≦ 24) is preferably represented. x may be 0, or may be greater than 0. On the other hand, x may be 20 or less, may be 10 or less, and may be 5 or less. The composition of the electrode active material can be determined by, for example, EDX, XRD, XRF, ICP or atomic absorption spectrometry. Also, the amount of Na in the active material may be 0% by weight, or may be more than 0% by weight. In the latter case, the amount of Na in the active material is, for example, 0.1% by weight or more, may be 0.5% by weight or more, and may be 1.0% by weight or more. On the other hand, the amount of Na in the active material is, for example, 10% by weight or less, may be 5% by weight or less, and may be 3% by weight or less.

[0030] The Si-based negative electrode active material in the present disclosure may be primary particles or secondary particles in which the primary particles are aggregated. The average particle diameter (D 50) is not particularly limited, but for example, it may be 0.1 μm or more and 50 μm or less, and may also be 0.5 μm or more and 30 μm or less. The average particle diameter (D 50 ) refers to the particle diameter corresponding to 50% by volume in cumulative measurement measured by a laser diffraction particle size distribution analyzer.

[0031] (2) Negative electrode layer In the battery according to the present disclosure, the ratio of the negative electrode capacity to the positive electrode capacity (capacity ratio) is 2.5 or more. The capacity ratio may be 3.0 or more, may be 3.2 or more, and may be 3.5 or more. On the other hand, the capacity ratio is, for example, 5.0 or less, may be 4.5 or less, may be 4.0 or less, and may be 3.8 or less. The capacity ratio can be calculated by the method described in the examples described later.

[0032] Further, the negative electrode layer may contain at least one of a conductive assistant, a binder, and an electrolyte as necessary. Examples of the conductive assistant include carbon materials, metal particles, and conductive polymers. Examples of the binder include fluorine-based binders, rubber-based binders, and acrylic-based binders. As for the electrolyte, the electrolyte described in "3. Electrolyte layer" described later can be mentioned.

[0033] The proportion of the Si-based negative electrode active material in the negative electrode layer is, for example, 45% by weight or more, may be 50% by weight or more, and may be 60% by weight or more. On the other hand, the proportion of the Si-based negative electrode active material is, for example, 80% by weight or less, and may be 70% by weight or less. Here, when the negative electrode layer contains a solid electrolyte, generally the negative electrode layer contains the Si-based negative electrode active material and the solid electrolyte as main components. Therefore, the proportion of the Si-based negative electrode active material can also be regarded as the proportion of the Si-based negative electrode active material to the total of the Si-based negative electrode active material and the solid electrolyte.

[0034] The thickness of the negative electrode layer is not particularly limited, but for example, it is 0.5 μm or more and 1000 μm or less.

[0035] As shown in FIG. 1(a), the negative electrode layer 2 may be a single layer. On the other hand, as shown in FIG. 1(b), the negative electrode layer 2 may have a first negative electrode layer 2A and a second negative electrode layer 2B disposed closer to the electrolyte layer 3 than the first negative electrode layer 2A in the thickness direction Dt. Further, in this case, the ratio of the Si-based negative electrode active material in the first negative electrode layer 2A is larger than the ratio of the Si-based negative electrode active material in the second negative electrode layer 2B. The ratio of the Si-based negative electrode active material in the first negative electrode layer and the second negative electrode layer is the same as the ratio of the Si-based negative electrode active material in the negative electrode layer. When the ratio of the Si-based negative electrode active material in the first negative electrode layer is X and the ratio of the Si-based negative electrode active material in the second negative electrode layer is Y, the ratio of X to Y (X / Y) is, for example, 1.1 or more and 1.5 or less.

[0036] 2. Positive electrode layer The positive electrode layer in the present disclosure contains at least a positive electrode active material.

[0037] Examples of the positive electrode active material include oxide active materials. Examples of the oxide active material include rock salt layer-type active materials such as LiCoO2, LiMnO2, LiNiO2, LiVO2, LiNi 0.33 Co 0.33 Mn 0.33 O2 and LiNi 0.8 Co 0.15 Al 0.05 O2; spinel-type active materials such as LiMn2O4, Li4Ti5O 12 and Li(Ni 0.5 Mn 1.5 )O4; and olivine-type active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4. Further, sulfur (S) may be used as the positive electrode active material.

[0038] Further, the positive electrode active material may be a coated positive electrode active material having a core particle, a first coating layer formed on the surface of the core particle, and a second coating layer formed on the surface of the first coating layer. The first coating layer contains, for example, an oxide solid electrolyte such as LiNbO3. The second coating layer contains, for example, a sulfide solid electrolyte such as Li2S-P2S5. The thicknesses of the first coating layer and the second coating layer are each, for example, 1 nm or more and 10 μm or less. Note that the positive electrode active material may be an active material having the core particle and the first coating layer without having the second coating layer.

[0039] The shape of the positive electrode active material is, for example, particulate. The average particle diameter (D 50 ) of the positive electrode active material (core particle) is not particularly limited, but is, for example, 10 nm or more and 50 μm or less, may be 1 μm or more and 10 μm or less, and may be 2.5 μm or more and 6.0 μm or less. The average particle diameter (D 50 ) is as described above.

[0040] Further, the positive electrode layer may contain at least one of a conductive assistant, a binder, and an electrolyte as necessary. The conductive assistant, the binder, and the electrolyte are the same as those described in "1. Negative electrode layer".

[0041] The proportion of the positive electrode active material in the positive electrode layer is, for example, 65% by weight or more and 85% by weight or less. Note that the proportion of the positive electrode active material can be regarded as the proportion of the positive electrode active material with respect to the total of the positive electrode active material and the solid electrolyte, similar to the proportion of the Si-based negative electrode active material described above.

[0042] The thickness of the positive electrode layer is not particularly limited, but is, for example, 0.5 μm or more and 1000 μm or less.

[0043] 3. Electrolyte layer The electrolyte layer in the present disclosure is a layer containing an electrolyte and disposed between the positive electrode layer and the negative electrode layer.

[0044] The electrolyte may be a solid electrolyte or a liquid electrolyte. The solid electrolyte may be an organic solid electrolyte such as a gel electrolyte, or an inorganic solid electrolyte such as a sulfide solid electrolyte or an oxide solid electrolyte. Among them, the solid electrolyte is preferably a sulfide solid electrolyte because of its high ionic conductivity. Here, generally, a battery having a solid electrolyte layer containing an inorganic solid electrolyte is called an all-solid-state battery.

[0045] The sulfide solid electrolyte usually contains at least Li element and S element. The sulfide solid electrolyte preferably further contains an M element (M is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, In). Also, the sulfide solid electrolyte may contain a halogen element such as F, Cl, Br, I.

[0046] On the other hand, the liquid electrolyte (electrolyte solution) contains, for example, a supporting salt such as LiPF6 and a solvent such as a carbonate-based solvent.

[0047] Also, the electrolyte layer may contain a non-woven fabric. Examples of the material of the non-woven fabric include polyester-based resins such as polyethylene terephthalate (PET), polyolefin-based resins such as polyethylene (PE), and polyamide-based resins such as nylon.

[0048] When the electrolyte layer contains the above non-woven fabric, the electrolyte is disposed inside the non-woven fabric. For example, the electrolyte can be disposed inside the non-woven fabric by coating a slurry containing the electrolyte on the non-woven fabric.

[0049] The thickness of the electrolyte layer is not particularly limited, but is, for example, 0.1 μm or more and 1000 μm or less, and may be 1 μm or more and 100 μm or less, may be 10 μm or more and 50 μm or less, or may be 15 μm or more and 30 μm or less.

[0050] 4. Battery As shown in Fig. 1, the battery in the present disclosure typically has a positive electrode current collector 4 that collects electrons from the positive electrode layer 1 and a negative electrode current collector 5 that collects electrons from the negative electrode layer 2. Examples of the material of the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. Further, the positive electrode current collector may be a current collector having a carbon layer containing alumina as described in the examples below, or a current collector having a resin coating layer formed on the surface of a metal foil. Examples of the material of the negative electrode current collector include SUS, copper, nickel, and carbon.

[0051] In addition, the battery in the present disclosure may have an exterior body that houses an electrode body including a positive electrode layer, an electrolyte layer, and a negative electrode layer. Examples of the exterior body include a case-type exterior body and a laminate-type exterior body.

[0052] The battery in the present disclosure is typically a lithium-ion secondary battery. Further, the battery in the present disclosure may be a liquid-based battery containing an electrolytic solution as an electrolyte, or a all-solid-state battery containing a solid electrolyte as an electrolyte. Examples of the applications of the 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. In addition, the battery in the present disclosure may be used as a power source for moving bodies other than vehicles (e.g., railways, ships, airplanes), or may be used as a power source for electrical products such as information processing devices.

[0053] Note that the present disclosure is not limited to the above-described embodiments. The above-described embodiments are examples, and any configuration that has substantially the same configuration as the technical idea described in the claims of the present disclosure and exhibits the same operational effects is included in the technical scope of the present disclosure.

Examples

[0054] [Example 1-1] (Preparation of Negative Electrode Active Material) By the following method, an active material (pc-Si) having voids inside the primary particles and a silicon clathrate-type crystal phase was produced as a negative electrode active material.

[0055] As the Si source, Si particles (Si powder without voids inside the primary particles, high-purity chemical SIE23PB) were prepared. Using this Si source and NaH as the Na source, a Na-Si alloy was produced. Note that as NaH, the one previously washed with hexane was used. The Na source and the Si source were weighed so that the molar ratio was 1.05:1, and these were mixed using a cutter mill. This mixture was heated in a heating furnace under an Ar atmosphere at 400 °C for 40 hours to obtain a powdery Na-Si alloy.

[0056] Using the obtained Na-Si alloy and further using AlF3 as a Na trap agent, a silicon clathrate formation step by a solid-phase method was performed. The Na-Si alloy and AlF3 were weighed so that the molar ratio was 1:0.35, and these were mixed using a cutter mill to obtain reaction raw materials. The obtained powdery reaction raw materials were put into a reaction vessel made of stainless steel and heated and reacted in a heating furnace under an Ar atmosphere at 310 °C for 60 hours. The obtained reaction product is considered to contain the target active material and NaF and Al as by-products. This reaction product was washed using a mixed solvent in which HNO3 and H2O were mixed at a volume ratio of 90:10. Thereby, the by-products in the reaction product were removed. After washing, filtration was performed, and the solid content separated by filtration was dried at 120 °C for 3 hours or more to obtain a powdery active material.

[0057] (Fabrication of negative electrode) The above active material (pc-Si), sulfide solid electrolyte (SE: Li2S-P2S5), conductive assistant (VGCF), PVDF-based binder, and butyl butyrate were stirred by an ultrasonic disperser to prepare a negative electrode composite material (negative electrode slurry). Here, in the negative electrode slurry, the weight ratio of the negative electrode active material to the sulfide solid electrolyte was 65:35. This negative electrode slurry was applied to a negative electrode current collector (Ni foil) by the blade method and dried at 100 °C on a hot plate for 30 minutes. Thereby, a negative electrode having a negative electrode layer and a negative electrode current collector was obtained.

[0058] (Fabrication of the positive electrode) As the positive electrode active material, a coated positive electrode active material having core particles (NCM: LiNi 0.33 Co 0.33 Mn 0.33 O2; average particle diameter 6.0 μm), a layer of LiNbO3 (first coating layer) formed on the surface of the core particles, and a layer of sulfide solid electrolyte (Li2S-P2S5) (second coating layer) formed on the surface of the first coating layer was prepared.

[0059] The above coated positive electrode active material, sulfide solid electrolyte (SE: Li2S-P2S5), conductive assistant (VGCF), PVDF-based binder, and butyl butyrate were stirred by an ultrasonic disperser to prepare a positive electrode slurry. Here, in the positive electrode slurry, the weight ratio of the positive electrode active material to the sulfide solid electrolyte was 80:20. This positive electrode slurry was applied to a positive electrode current collector by the blade method and dried at 100 °C on a hot plate for 30 minutes. Thereby, a positive electrode having a positive electrode layer and a positive electrode current collector was obtained. As the positive electrode current collector, a current collector foil (current collector foil α) having an Al foil and a carbon layer containing alumina (Al2O3) was used. The current collector foil α was prepared as follows. First, carbon, PVDF, and Al2O3 were mixed at a composition of 10:60:30 to prepare a slurry. This slurry was applied to a 15-μm Al foil and dried to form a carbon layer with a thickness of 1.5 μm on the Al foil.

[0060] In addition, in the production of the positive electrode and the negative electrode, the ratio of the negative electrode capacity to the positive electrode capacity (capacity ratio) was adjusted to be 2.5. The capacity ratio was determined from the following formula (1).

[0061] [Number]

[0062] (Production of Evaluation Battery) A sulfide solid electrolyte (Li2S-P2S5), a PVDF-based binder, and butyl butyrate were stirred by an ultrasonic disperser to prepare a solid electrolyte slurry. Here, the weight ratio of the sulfide solid electrolyte to the PVDF-based binder in the solid electrolyte slurry was adjusted to be 99.4:0.4. This solid electrolyte slurry was applied onto a substrate (Al foil) by the blade method and dried. Thereby, a transfer member having a sulfide solid electrolyte layer (film thickness: 30 μm) and a substrate was obtained.

[0063] The transfer member and the positive electrode were laminated and pressed so that the sulfide solid electrolyte layer and the positive electrode layer were in contact with each other, and the substrate (Al foil) of the transfer member was peeled off to obtain a laminate. Next, the laminate and the negative electrode were laminated and pressed so that the sulfide solid electrolyte layer and the negative electrode layer were in contact with each other. Thereby, an evaluation battery was produced.

[0064] [Example 1-2 and Example 1-3] An evaluation battery was produced in the same manner as in Example 1-1, except that the positive electrode and the negative electrode were produced so that the capacity ratio was the value shown in Table 1.

[0065] [Comparative Examples 1-1 to 1-3] An evaluation battery was produced in the same manner as in Examples 1-1 to 1-3, respectively, except that Si particles having a diamond-type crystal phase as the negative electrode active material (crystalline Si: Si powder having no voids inside the primary particles) were used.

[0066] [Evaluation 1] (Microscopic Observation) Photographs of the particles were obtained by observing the negative electrode active materials prepared in Examples 1-1 to 1-3 using SEM (scanning electron microscope). Specifically, cross-sectioning was performed on the negative electrode layer by ion milling, and SEM observation was performed on the cross-section. As a result, it was confirmed that voids exist inside the primary particles of the negative electrode active material.

[0067] (XRD measurement) X-ray diffraction (XRD) measurements using CuKα radiation were performed on the negative electrode active materials prepared in Examples 1-1 to 1-3. As a result, it was confirmed that all of the negative electrode active materials have a silicon class II-type crystal phase as the main phase.

[0068] (Nail penetration test) First, the fabricated evaluation battery was charged until the SOC reached 100%. Specifically, CC charging was performed at 1 / 3C up to 4.05V, and then CV charging was performed at 4.05V up to 1 / 100C. Next, a nail penetration test was performed on the charged battery. Specifically, a DISC test was performed while monitoring the battery voltage, nail potential, and inrush current, and the amount of heat generated was calculated from the changes in voltage and current during internal short circuit. The amount of heat generated in Example 1-1 was relatively evaluated with the amount of heat generated in Comparative Example 1-1 set as 100%. Similarly, Examples 1-2 and 1-3 were relatively evaluated with the amounts of heat generated in Comparative Examples 1-2 and 1-3 set as 100%, respectively. The results are shown in Table 1.

[0069] [Table 1]

[0070] As shown in Table 1, it was confirmed that the amount of heat generated was significantly suppressed in the battery according to the present disclosure.

[0071] [Comparative Example 1-4] An evaluation battery was fabricated in the same manner as in Example 1-1, except that the capacity ratio was changed to 2.4. A cycle test was performed on the fabricated evaluation battery. The conditions of the cycle test were CCCV charge and discharge at an upper limit voltage of 4.55 V and a lower limit voltage of 2.5 V, 0.1 C, and 50 cycles. The change in capacity based on the charge capacity of the first cycle was calculated. The results are shown in Figure 3.

[0072] As shown in Figure 3, the capacity at the 50th cycle decreased to about 65% of the capacity at the first cycle. Although not shown in the figure, when a cycle test was performed on the batteries of Examples 1-1 to 1-3, the capacity at the 50th cycle was 80% or more of the capacity at the first cycle in all cases.

[0073] [Example 2-1] An evaluation battery with a capacity ratio of 3.5 was fabricated as follows.

[0074] (Fabrication of negative electrode) A negative electrode slurry was prepared in the same manner as in Example 1-1, except that the weight ratio of the negative electrode active material (pc-Si) to the sulfide solid electrolyte was changed to 55:45. A negative electrode was prepared in the same manner as in Example 1-1, except that this negative electrode slurry was used.

[0075] (Fabrication of positive electrode) As the positive electrode active material, a coated positive electrode active material having the above first coating layer and not having the above second coating layer (core particles: NCA; LiNi 0.8 Co 0.15 Al 0.05 O2; average particle diameter 4.5 μm), a sulfide solid electrolyte (SE: Li2S-P2S5), a conductive assistant (VGCF), a PVdF-based binder, and butyl butyrate were stirred by an ultrasonic disperser to prepare a positive electrode slurry. Here, the weight ratio of the positive electrode active material to the sulfide solid electrolyte in the positive electrode slurry was 75:25. A positive electrode was prepared in the same manner as in Example 1-1, except that this positive electrode slurry was used.

[0076] An evaluation battery was fabricated in the same manner as in Example 1-1, except that the above negative electrode, positive electrode, and a transfer member having a sulfide solid electrolyte layer with a film thickness of 15 μm were used.

[0077] [Example 2-2] An evaluation battery was fabricated in the same manner as in Example 2-1, except that the film thickness of the electrolyte layer was changed to 30 μm.

[0078] [Example 2-3] A non-woven fabric made of polyester was placed on a substrate (Al foil), and the above solid electrolyte slurry was coated on the non-woven fabric by the blade method and dried. As a result, a transfer member containing the non-woven fabric and having a solid electrolyte layer with a film thickness of 30 μm was obtained. An evaluation battery was fabricated in the same manner as in Example 2-1, except that this transfer member was used.

[0079] [Example 2-4] A resin slurry was prepared by mixing a resin (polyethylene), a conductive aid (VGCF), and a solvent (butyl butyrate). The ratio (weight ratio) of the resin to the conductive aid was 80:20. This resin slurry was coated on Al foil and dried to produce a current collector (resin-coated Al foil) of resin-coated Al foil. An evaluation battery was fabricated in the same manner as in Example 2-1, except that the above resin-coated Al foil (current collector foil β) was used as the positive current collector.

[0080] [Example 2-5] As the positive electrode active material, an evaluation battery was fabricated in the same manner as in Example 2-1, except that a coated positive electrode active material having a first coating layer and a second coating layer (core particles: NCA; LiNi 0.8 Co 0.15 Al 0.05 O2; average particle diameter 3.0 μm) was used.

[0081] [Example 2-6] An evaluation battery was fabricated in the same manner as in Example 2-1, except that the weight ratio of the positive electrode active material to the sulfide solid electrolyte in the positive electrode slurry was changed to 70:30.

[0082] [Example 2-7] A resin (acrylic resin), a conductive aid (carbon black), a dispersant, and a solvent (water and isopropanol) were mixed to prepare a resin slurry. The ratio (weight ratio) of the resin, the conductive aid, and the dispersant was 70:25:5. This resin slurry was coated on an Al foil and dried to produce a resin-coated Al foil (current collector foil γ). A positive electrode was produced in the same manner as in Example 2-5 except that the current collector foil γ was used as the positive current collector.

[0083] A negative electrode having two negative electrode layers with different weight ratios of the negative electrode active material and the sulfide solid electrolyte was produced. Specifically, a negative electrode having a first negative electrode layer and a second negative electrode layer was produced from the negative electrode current collector side. Here, the weight ratio of the negative electrode active material and the sulfide solid electrolyte in the first negative electrode layer is 55:45, and the weight ratio of the negative electrode active material and the sulfide solid electrolyte in the second negative electrode layer is 45:55.

[0084] An evaluation battery was produced in the same manner as in Example 2-1 except that the above positive electrode and negative electrode were used.

[0085] [Example 2-8] A negative electrode was produced in the same manner as in Example 2-7. An evaluation battery was produced in the same manner as in Example 2-5 except that this negative electrode was used.

[0086] [Example 2-9] A negative electrode and an evaluation battery were produced in the same manner as in Example 2-7 except that the weight ratio of the negative electrode active material and the sulfide solid electrolyte in the first negative electrode layer was changed to 60:40.

[0087] [Example 2-10] An evaluation battery was produced in the same manner as in Example 2-9 except that the positive current collector was changed to current collector foil α.

[0088] [Evaluation 2] (Nail penetration test) For the fabricated evaluation battery, a nail penetration test was conducted in the same manner as in Evaluation 1, and the calorific value was evaluated. The calorific value of Example 2-1 was set as 100% and evaluated relatively. The results are shown in Table 2. In addition, Table 2 also describes the calorific values of Comparative Examples 1-1 to 1-3 compared with Example 2-1.

[0089]

Table 2

[0090] As shown in Table 2, it was confirmed that the calorific value was more suppressed by adjusting the conditions of the positive electrode layer and the positive electrode current collector, the conditions of the electrolyte layer, and the layer structure of the negative electrode layer. From this, it was suggested that there is a possibility that the calorific value can be synergistically suppressed by adjusting each condition of the battery.

Explanation of Symbols

[0091] 1... Positive electrode layer 2... Negative electrode layer 2A... First negative electrode layer 2B... Second negative electrode layer 3... Electrolyte layer 4... Positive electrode current collector 5... Negative electrode current collector 10... Battery

Claims

1. A battery having a positive electrode layer containing a positive electrode active material, a negative electrode layer containing a negative electrode active material, an electrolyte, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein the negative electrode layer contains an Si-based negative electrode active material as the negative electrode active material, the Si-based negative electrode active material has voids inside the primary particles, and a ratio of the negative electrode capacity to the positive electrode capacity is 2.5 or more.

2. The battery according to claim 1, wherein the ratio is 5.0 or less.

3. The battery according to claim 1, wherein the Si-based negative electrode active material has a silicon clathrate-type crystal phase.

4. The battery according to claim 3, wherein the Si-based negative electrode active material has a silicon clathrate II-type crystal phase as the crystal phase.

5. The battery according to any one of claims 1 to 4, wherein a ratio of the Si-based negative electrode active material in the negative electrode layer is 45% by weight or more.

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