Battery

Abstract

The invention relates to a battery. The present invention solves the problem by providing a battery having 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 disposed between the positive electrode layer and the negative electrode layer, the negative electrode layer contains a Si-based negative electrode active material as the negative electrode active material, the Si-based negative electrode active material has voids inside primary particles, and the ratio of the negative electrode capacity to the positive electrode capacity is 2.5 or more.

Description

Technical Field

[0001] The present invention relates to batteries. Background Art

[0002] In recent years, battery development has been actively pursued. For example, in the automotive industry, development of batteries for battery electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), and hybrid electric vehicles (HEVs) is progressing. Furthermore, various research efforts are underway into materials used in batteries.

[0003] For example, Japanese Patent Application Laid-Open No. 2020-113547 discloses a negative electrode material for a lithium ion secondary battery containing silicon oxide, and Japanese Patent Application Laid-Open No. 2023-098419 discloses a secondary battery using a silicon negative electrode active material. Summary of the Invention

[0004] Si is known as a high-capacity negative electrode active material. However, due to its high capacity, Si tends to generate a large amount of heat when an internal short circuit occurs in the battery, for example.

[0005] The present invention has been made in view of the above-mentioned actual situation, and a main object of the present invention is to provide a battery with suppressed heat generation. [1]

[0007] A battery comprising 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 disposed between the positive electrode layer and the negative electrode layer, wherein:

[0008] The negative electrode layer contains a Si-based negative electrode active material as the negative electrode active material.

[0009] The Si-based negative electrode active material has voids inside the primary particles.

[0010] The ratio of the negative electrode capacity to the positive electrode capacity is 2.5 or more. [2]

[0012] The battery according to [1], wherein the ratio is 5.0 or less. [3]

[0014] The battery according to [1] or [2], wherein the Si-based negative electrode active material has a silicon inclusion compound type crystal phase. [4]

[0016] 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. [5]

[0018] The battery according to any one of [1] to [4], wherein the ratio of the Si-based negative electrode active material in the negative electrode layer is 45% by weight or more.

[0019] In the present invention, the effect of suppressing the amount of heat generated by the battery is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention are described below with reference to the accompanying drawings, wherein like symbols denote like elements.

[0021] Figure 1A This is a schematic cross-sectional view illustrating a battery according to the present invention.

[0022] Figure 1B This is a schematic cross-sectional view illustrating a battery according to the present invention.

[0023] Figure 2A It is a schematic perspective view illustrating the crystal phase of Si.

[0024] Figure 2B It is a schematic perspective view illustrating the crystal phase of Si.

[0025] Figure 2C It is a schematic perspective view illustrating the crystal phase of Si.

[0026] Figure 3 It is a graph showing the results of the cycle test in Comparative Example 1-4. DETAILED DESCRIPTION

[0027] The battery of the present invention is described in detail below. It should be noted that the Si-based negative electrode active material of the present invention has voids inside the primary particles. Therefore, in this specification, the Si-based negative electrode active material is sometimes described as porous Si (p-Si). In addition, when the Si-based negative electrode active material (porous Si) of the present invention has a clathrate-type crystal phase, it is sometimes described as porous clathrate Si (pc-Si).

[0028] Figure 1A 、 Figure 1B This is a schematic cross-sectional view illustrating a battery according to the present invention. Figure 1A 、 Figure 1B The battery 10 shown has 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 arranged between the positive electrode layer 1 and the negative electrode layer 2. In particular, in the battery 10 of the present invention, the negative electrode layer 2 contains a Si-based negative electrode active material as the above-mentioned negative electrode active material, and the above-mentioned Si-based negative electrode active material has voids inside the primary particles. In addition, in the battery 10, the ratio of the negative electrode capacity to the positive electrode capacity is 2.5 or more. It should be noted that in the battery of the present invention described later, the negative electrode layer 2 can be as follows Figure 1A The negative electrode layer 2 can also be as shown in FIG. Figure 1B Two layers (a first negative electrode layer 2A and a second negative electrode layer 2B) are shown.

[0029] According to the present invention, the negative electrode layer contains a Si-based negative electrode active material having voids inside 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, thereby achieving a battery with suppressed heat generation.

[0030] Although Si is a high-capacity active material, it is prone to forming areas where the reaction with carrier ions such as Li ions is concentrated, and the reaction with carrier ions may become uneven in the negative electrode active material. If the reaction with carrier ions becomes uneven, that is, if there are areas where the reaction is concentrated, it is easy to reach high temperatures when an internal short circuit occurs.

[0031] In this regard, the Si-based negative electrode active material of the present invention has voids inside its primary particles. If such voids exist, the specific surface area of the active material becomes larger, and the area in which the electrolyte and the active material can contact each other becomes larger. Therefore, by using the Si-based negative electrode active material of the present invention, it is possible to suppress the concentrated reaction with carrier ions in a part of the active material. In addition, in the battery of the present invention, the ratio of the negative electrode capacity to the positive electrode capacity (capacity ratio) is 2.5 or more. If the capacity ratio is large enough, a sufficient amount of negative electrode active material is present in the negative electrode layer relative to the carrier ions moving from the positive electrode. Therefore, it is possible to suppress the local reaction of the negative electrode active material with the carrier ions in the negative electrode layer, and to make the reaction of the entire negative electrode layer uniform. As a result, the heat generation of the battery can be suppressed.

[0032] Furthermore, by setting the capacity ratio to 2.5 or more, as described in the examples below, an effect of improving cycle characteristics can also be obtained.

[0033] 1. Negative electrode layer

[0034] The negative electrode layer of the present invention contains a negative electrode active material. In particular, the negative electrode layer of the present invention contains a predetermined Si-based negative electrode active material.

[0035] (1) Si-based negative electrode active materials

[0036] The Si-based negative electrode active material may be a single substance of Si, an alloy containing Si as a main component (Si alloy), or a Si oxide. The proportion of Si element in the Si alloy is, for example, 50 mol % or more and 95 mol % or less.

[0037] The Si-based negative electrode active material has voids inside the primary particles. The presence of voids can be confirmed by SEM (scanning electron microscope) observation. In addition, the porosity is not particularly limited, and is, for example, 4% or more, or 10% or more. In addition, the above-mentioned porosity is, for example, 40% or less, or 20% or less. The porosity can be calculated, for example, by the following steps. First, the negative electrode layer containing the Si-based negative electrode active material is exposed in cross section by ion milling. Then, the cross section is observed using SEM and a photograph of the particles is obtained. The silicon portion and the void portion are strictly distinguished from the obtained photograph using image analysis software, and binarization is performed. The areas of the silicon portion and the void portion are calculated, and the porosity (%) is calculated according to the following formula.

[0038] Void ratio (%) = 100 × (void area) / ((silicon area) + (void area))

[0039] In the porous Si, the void content 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. In addition, the BET specific surface area of the porous Si is, for example, 20 m 2 / g and above and 200m 2 / g or less.

[0040] As a method for producing porous Si, for example, the following method can be cited: an alloy of Li and Si (LiSi alloy) is produced, and then Li is removed from the LiSi alloy. The LiSi alloy is obtained, for example, by mixing Li and Si. The ratio of Li to Si (Li / Si) is, for example, greater than 1.0, may be greater than 2.0, may be greater than 3.0, or may be greater than 4.0. On the other hand, Li / Si is, for example, less than 8.0. As a method for removing Li from the LiSi alloy, for example, a method for reacting the LiSi alloy with a Li extraction material can be cited. As the Li extraction material, for example, 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 can be cited.

[0041] Here, Figure 2A 、 Figure 2B 、 Figure 2C This is a schematic three-dimensional diagram illustrating the crystal phase of Si. Generally, Si has the following Figure 2A In contrast, the Si-based negative electrode active material of the present invention may have a diamond-type crystal phase as shown. Figure 2B and Figure 2C The silicon inclusion type crystal phase shown. Figure 2A In the diamond-type crystal phase shown, a plurality of Si elements form tetrahedra. The interior of the tetrahedra does not have space that can accommodate metal ions such as Li ions. On the other hand, Figure 2B and Figure 2CIn the silicon clathrate type I and II crystal phases shown, the skeleton atoms have a cage-like structure (cage), which allows metal ions such as lithium ions to enter, thereby making the lithium ion reaction more uniform. Therefore, Si-based negative electrode active materials (pc-Si) with voids within the primary particles and a silicon clathrate crystal phase can further suppress battery heat generation.

[0042] The Si-based negative electrode active material may have a silicon inclusion compound type I crystal phase or a silicon inclusion compound type II crystal phase. It is particularly preferred to have a silicon inclusion compound type II crystal phase as the main phase. "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 inclusion compound type II crystal phase contained in the Si-based negative electrode active material is, for example, 80% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. In addition, the proportion of the silicon inclusion compound 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 obtained by using the RIR method (Reference Intensity Ratio method).

[0043] On the other hand, the Si-based negative electrode active material of the present invention may or may not have a crystal phase of diamond-type silicon (crystalline Si). "Not having a crystal phase" means that no peak of the crystal phase is confirmed in the 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 less than 2.5% by weight, or may be less than 2% by weight. 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 greater than 0% by weight, or may be more than 0.1% by weight.

[0044] As a method for producing porous Si inclusion complexes, for example, the following method can be cited: the porous Si is mixed with a Na source such as NaH and heated to produce a Na-Si alloy, and the Na-Si alloy is heated to reduce the amount of Na in the Na-Si alloy, thereby generating a silicon inclusion complex type crystal phase. A more specific method is described in the Examples described below.

[0045] The composition of the porous Si inclusion compound is not particularly limited, but is preferably composed of Na x Si 136(0≤x≤24). x may be 0 or greater than 0. On the other hand, x may be 20 or less, 10 or less, or 5 or less. The composition of the electrode active material can be determined, for example, by EDX, XRD, XRF, ICP, or atomic absorption spectrometry. In addition, the amount of Na in the active material may be 0 wt % or greater than 0 wt %. In the latter case, the amount of Na in the active material may be, for example, 0.1 wt % or more, 0.5 wt % or more, or 1.0 wt % or more. On the other hand, the amount of Na in the active material may be, for example, 10 wt % or less, 5 wt % or less, or 3 wt % or less.

[0046] The Si-based negative electrode active material of the present invention may be primary particles or secondary particles formed by aggregation of primary particles. The average particle size (D 50 ) is not particularly limited, and may be, for example, 0.1 μm or more and 50 μm or less, or 0.5 μm or more and 30 μm or less. 50 ) refers to the particle size corresponding to the cumulative 50 volume % measured by a laser diffraction particle size distribution analyzer.

[0047] (2) Negative electrode layer

[0048] In the battery of the present invention, 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, 3.2 or more, or 3.5 or more. On the other hand, the capacity ratio is, for example, 5.0 or less, 4.5 or less, 4.0 or less, or 3.8 or less. The capacity ratio can be calculated by the method described in the Examples below.

[0049] The negative electrode layer may contain at least one of a conductive additive, a binder, and an electrolyte, as needed. Examples of conductive additives include carbon materials, metal particles, and conductive polymers. Examples of binders include fluorine-based binders, rubber-based binders, and acrylic binders. Examples of electrolytes include those described in "3. Electrolyte Layer" below.

[0050] The proportion of Si-based negative electrode active material in the negative electrode layer is, for example, 45% by weight or more, 50% by weight or more, or 60% by weight or more. On the other hand, the proportion of Si-based negative electrode active material is, for example, 80% by weight or less, or 70% by weight or less. Here, in the case where the negative electrode layer contains a solid electrolyte, the negative electrode layer usually contains Si-based negative electrode active material and solid electrolyte as main components. Therefore, the above-mentioned proportion of Si-based negative electrode active material can also be understood as the ratio of Si-based negative electrode active material to the total of Si-based negative electrode active material and solid electrolyte.

[0051] The thickness of the negative electrode layer is not particularly limited, and is, for example, 0.5 μm or more and 1000 μm or less.

[0052] The negative electrode layer 2 may be Figure 1A On the other hand, the negative electrode layer 2 can also be as shown Figure 1B As shown, it has a first negative electrode layer 2A and a second negative electrode layer 2B arranged on the electrolyte layer 3 side relative to the first negative electrode layer 2A in the thickness direction Dt. In addition, in this case, the ratio of the above-mentioned Si-based negative electrode active material in the first negative electrode layer 2A is greater than the ratio of the above-mentioned 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 above-mentioned 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, greater than or equal to 1.1 and less than or equal to 1.5.

[0053] 2. Positive electrode layer

[0054] The positive electrode layer of the present invention contains at least a positive electrode active material.

[0055] Examples of positive electrode active materials include oxide active materials. Examples of oxide active materials include 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 and other rock salt layered active materials; LiMn2O4, Li4Ti5O 12 and Li(Ni 0.5 Mn 1.5 )O4 and other spinel active materials; and LiFePO4, LiMnPO4, LiNiPO4 and LiCoPO4 and other olivine active materials. In addition, sulfur (S) can be used as the positive electrode active material.

[0056] In addition, 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 thickness of the first coating layer and the second coating layer are, for example, greater than 1 nm and less than 10 μm, respectively. It should be noted that the positive electrode active material may be an active material having the core particle and the first coating layer without the second coating layer.

[0057] The shape of the positive electrode active material is, for example, a particle shape. The average particle size (D 50 ) is not particularly limited, and may be, for example, 10 nm or more and 50 μm or less, 1 μm or more and 10 μm or less, or 2.5 μm or more and 6.0 μm or less. 50 ), as described above.

[0058] The positive electrode layer may contain at least one of a conductive additive, a binder, and an electrolyte as needed. The conductive additive, the binder, and the electrolyte are the same as those described in "1. Negative Electrode Layer".

[0059] The ratio 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. It should be noted that, with respect to the ratio of the positive electrode active material, similarly to the ratio of the above-mentioned Si-based negative electrode active material, it can also be understood as the ratio of the positive electrode active material to the total of the positive electrode active material and the solid electrolyte.

[0060] The thickness of the positive electrode layer is not particularly limited, and is, for example, 0.5 μm or more and 1000 μm or less.

[0061] 3. Electrolyte layer

[0062] The electrolyte layer of the present invention is a layer containing an electrolyte and disposed between the positive electrode layer and the negative electrode layer.

[0063] The electrolyte can be either a solid electrolyte or a liquid electrolyte. The solid electrolyte can 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. Sulfide solid electrolytes are preferred as solid electrolytes due to their high ionic conductivity. Generally, batteries having a solid electrolyte layer containing an inorganic solid electrolyte are referred to as all-solid-state batteries.

[0064] Sulfide solid electrolytes typically contain at least Li and S. Sulfide solid electrolytes preferably also contain M (M is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In). Sulfide solid electrolytes may also contain halogen elements such as F, Cl, Br, and I.

[0065] On the other hand, the liquid electrolyte (electrolyte) contains, for example, a supporting salt such as LiPF 6 and a solvent such as a carbonate solvent.

[0066] The electrolyte layer may contain a nonwoven fabric. Examples of the material of the nonwoven fabric include polyester resins such as polyethylene terephthalate (PET), polyolefin resins such as polyethylene (PE), and polyamide resins such as nylon.

[0067] When the electrolyte layer includes the nonwoven fabric, the electrolyte is placed inside the nonwoven fabric. For example, the electrolyte can be placed inside the nonwoven fabric by applying a slurry containing the electrolyte to the nonwoven fabric.

[0068] The thickness of the electrolyte layer is not particularly limited, and may be, for example, 0.1 μm to 1000 μm, 1 μm to 100 μm, 10 μm to 50 μm, or 15 μm to 30 μm.

[0069] 4.Battery

[0070] like Figure 1A 、 Figure 1B As shown, the battery of the present invention generally has a positive electrode current collector 4 for collecting electrons from the positive electrode layer 1 and a negative electrode current collector 5 for collecting electrons from the negative electrode layer 2. Examples of materials for the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. Furthermore, the positive electrode current collector may be a current collector having a carbon layer containing aluminum oxide, as described in the embodiments below, or a current collector having a resin coating formed on the surface of a metal foil. Examples of materials for the negative electrode current collector include SUS, copper, nickel, and carbon.

[0071] The battery of the present invention may also include an outer casing that houses an electrode assembly including a positive electrode layer, an electrolyte layer, and a negative electrode layer. Examples of the outer casing include a shell-type outer casing and a laminate-type outer casing.

[0072] The battery of the present invention is typically a lithium ion secondary battery. In addition, the battery of the present invention may be a liquid battery containing an electrolyte as an electrolyte, or an all-solid-state battery containing a solid electrolyte as an electrolyte. As the use of the battery, for example, power sources for vehicles such as hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), electric vehicles (BEV), gasoline vehicles, and diesel vehicles can be listed. In addition, the battery of the present invention can also be used as a power source for mobile bodies other than vehicles (for example, trains, ships, and airplanes), and can also be used as a power source for electrical products such as information processing devices.

[0073] It should be noted that the present invention is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely illustrative, and any technical solution having substantially the same configuration and exhibiting the same effects as the technical concept described in the claims of the present invention is encompassed within the technical scope of the present invention.

[0074] [Example 1-1]

[0075] (Preparation of Negative Electrode Active Material)

[0076] An active material (pc-Si) having voids inside primary particles and a silicon clathrate-type crystal phase was prepared as a negative electrode active material by the following method.

[0077] As a Si source, Si particles (Si powder without voids inside the primary particles, high-purity chemical SIE23PB) are prepared. Using this Si source and using NaH as a Na source, a Na-Si alloy is produced. It should be noted that as NaH, NaH pre-washed with hexane is used. The Na source and the Si source are weighed in a molar ratio of 1.05:1 and mixed using a chopper. The mixture is heated in a heating furnace under an Ar atmosphere at 400°C for 40 hours to obtain a powdered Na-Si alloy.

[0078] The obtained Na-Si alloy is used, and AlF3 is further used as a Na capture agent to carry out a silicon inclusion compound formation process based on the solid phase method. The Na-Si alloy and AlF3 are weighed in a molar ratio of 1:0.35 and mixed using a chopper to obtain a reaction raw material. The obtained powdered reaction raw material is placed in a stainless steel reaction container and heated in an Ar atmosphere at 310°C for 60 hours using a heating furnace to react. It is believed that the obtained reaction product contains the target active material and NaF and Al as by-products. The reaction product is washed with a mixed solvent prepared by mixing HNO3 and H2O in a volume ratio of 90:10. In this way, the by-products in the reaction product are removed. After washing, filtration is carried out, and the filtered solid component is dried at 120°C for more than 3 hours to obtain a powdered active material.

[0079] (Fabrication of negative electrode)

[0080] The active material (pc-Si), sulfide solid electrolyte (SE: Li2S-P2S5), conductive additive (VGCF), PVDF binder, and butyl butyrate were stirred using an ultrasonic disperser to prepare a negative electrode composite material (negative electrode slurry). The weight ratio of the negative electrode active material to the sulfide solid electrolyte in the negative electrode slurry was set at 65:35. This negative electrode slurry was applied to a negative electrode current collector (Ni foil) using a doctor blade method and dried on a hot plate at 100°C for 30 minutes. This produced a negative electrode having a negative electrode layer and a negative electrode current collector.

[0081] (Production of positive electrode)

[0082] As the positive electrode active material, core particles (NCM: LiNi 0.33 Co 0.33 Mn 0.33O2; average particle size 6.0μm), a layer of LiNbO3 formed on the surface of the core particle (first coating layer) and a layer of sulfide solid electrolyte (Li2S-P2S5) formed on the surface of the first coating layer (second coating layer) coated positive electrode active material.

[0083] The coated positive electrode active material, sulfide solid electrolyte (SE: Li2S-P2S5), conductive additive (VGCF), PVDF-based binder and butyl butyrate are stirred using 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 is set to 80:20. The positive electrode slurry is applied to the positive electrode collector by a doctor blade method and dried on a hot plate at 100°C for 30 minutes. Thus, a positive electrode having a positive electrode layer and a positive electrode collector is obtained. As the positive electrode collector, a collector foil (collector foil α) having an Al foil and a carbon layer containing aluminum oxide (Al2O3) is used. The collector foil α is prepared as follows. First, carbon, PVDF and Al2O3 are mixed in a composition of 10:60:30 to prepare a slurry. The slurry is applied to a 15μm Al foil and dried to form a carbon layer with a thickness of 1.5μm on the Al foil.

[0084] In the preparation 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 2.5. The capacity ratio was obtained by the following formula (1).

[0085]

[0086] (Production of Evaluation Batteries)

[0087] A sulfide solid electrolyte (Li2S-P2S5), a PVDF-based binder, and butyl butyrate were stirred using an ultrasonic dispersing device to prepare a solid electrolyte slurry. The weight ratio of sulfide solid electrolyte to PVDF-based binder in the solid electrolyte slurry was adjusted to 99.4:0.4. This solid electrolyte slurry was applied to a substrate (Al foil) using a doctor blade method and allowed to dry. This produced a transfer member comprising a sulfide solid electrolyte layer (30 μm thick) and a substrate.

[0088] The transfer member and the positive electrode were stacked and pressed so that the sulfide solid electrolyte layer was in contact with the positive electrode layer. The substrate (Al foil) of the transfer member was peeled off to obtain a laminate. Next, the laminate and the negative electrode were stacked and pressed so that the sulfide solid electrolyte layer was in contact with the negative electrode layer. This produced an evaluation battery.

[0089] [Example 1-2 and Example 1-3]

[0090] A battery for evaluation was prepared in the same manner as in Example 1-1 except that the positive electrode and the negative electrode were prepared so that the capacity ratio became the value shown in Table 1.

[0091] [Comparative Examples 1-1 to 1-3]

[0092] Evaluation batteries were prepared in the same manner as in Examples 1-1 to 1-3, except that Si particles having a diamond-type crystal phase (crystalline Si: Si powder having no voids inside primary particles) were used as the negative electrode active material.

[0093] [Evaluation 1]

[0094] (Microscope observation)

[0095] The negative electrode active materials prepared in Examples 1-1 to 1-3 were observed using a scanning electron microscope (SEM) to obtain particle photographs. Specifically, a cross-section of the negative electrode layer was exposed by ion milling, and this cross-section was observed under the SEM. The results confirmed the presence of voids within the primary particles of the negative electrode active material.

[0096] (XRD measurement)

[0097] X-ray diffraction (XRD) measurement using CuKα radiation was performed on the negative electrode active materials prepared in Examples 1-1 to 1-3. It was confirmed that all of the negative electrode active materials had a silicon clathrate II-type crystal phase as a main phase.

[0098] (Nail penetration test)

[0099] First, the prepared evaluation battery was charged until the SOC reached 100%. Specifically, CC charging was performed at 1 / 3C to 4.05V, and then CV charging was performed at 4.05V to 1 / 100C.

[0100] Next, the charged battery was subjected to a nail penetration test. Specifically, a DISC test was performed while monitoring the battery voltage, nail potential, and sneak current. The heat generation was calculated from the changes in voltage and current during an internal short circuit.

[0101] The calorific value of Comparative Example 1-1 was set as 100% to evaluate the calorific value of Example 1-1. Similarly, Examples 1-2 and 1-3 were evaluated relative to each other, with the calorific value of Comparative Examples 1-2 and 1-3 set as 100%. The results are shown in Table 1.

[0102] [Table 1]

[0103]

[0104] As shown in Table 1, it was confirmed that the amount of heat generated was significantly suppressed in the battery of the present invention.

[0105] [Comparative Examples 1-4]

[0106] The evaluation battery was prepared 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 prepared evaluation battery. The cycle test conditions were set to CCCV charge and discharge with an upper limit voltage of 4.55V and a lower limit voltage of 2.5V, 0.1C, and 50 cycles. The capacity change was calculated based on the charge capacity of the first cycle. The results are shown in FIG. Figure 3 middle.

[0107] like Figure 3 As shown, the capacity at the 50th cycle decreased to approximately 65% relative to the capacity at the 1st cycle. Although not shown, cycle tests were conducted on the batteries of Examples 1-1 to 1-3, and the results showed that the capacity at the 50th cycle was at least 80% relative to the capacity at the 1st cycle.

[0108] [Example 2-1]

[0109] An evaluation battery having a capacity ratio of 3.5 was produced as follows.

[0110] (Fabrication of negative electrode)

[0111] 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.

[0112] (Production of positive electrode)

[0113] As the positive electrode active material, a coated positive electrode active material (core particle: NCA; LiNi 0.8 Co 0.15 Al 0.05 A positive electrode slurry was prepared by stirring a mixture of a sulfide solid electrolyte (Li2S-P2S5) (aluminum oxide; average particle size 4.5 μm), a conductive additive (VGCF), a PVdF-based binder, and butyl butyrate using an ultrasonic disperser. The weight ratio of the positive electrode active material to the sulfide solid electrolyte in the positive electrode slurry was set at 75:25. A positive electrode was prepared in the same manner as Example 1-1 using this positive electrode slurry, except for the above.

[0114] A battery for evaluation was prepared in the same manner as in Example 1-1 except that a transfer member having the above-mentioned negative electrode and positive electrode and a sulfide solid electrolyte layer having a thickness of 15 μm was used.

[0115] [Example 2-2]

[0116] A battery for evaluation was prepared in the same manner as in Example 2-1 except that the thickness of the electrolyte layer was changed to 30 μm.

[0117] [Examples 2-3]

[0118] A polyester nonwoven fabric was placed on a substrate (Al foil). The solid electrolyte slurry was applied to the nonwoven fabric using a doctor blade method and dried. This produced a transfer member having a 30 μm thick solid electrolyte layer containing the nonwoven fabric. Using this transfer member, an evaluation battery was fabricated in the same manner as in Example 2-1, except for the above.

[0119] [Examples 2-4]

[0120] A resin slurry was prepared by mixing a resin (polyethylene), a conductive additive (VGCF), and a solvent (butyl butyrate). The weight ratio of resin to conductive additive was set at 80:20. This resin slurry was applied to an aluminum foil and dried to produce a resin-coated aluminum foil current collector. An evaluation cell was prepared in the same manner as in Example 2-1, except that the resin-coated aluminum foil (collector foil β) was used as the positive electrode current collector.

[0121] [Examples 2-5]

[0122] As the positive electrode active material, a coated positive electrode active material (core particle: NCA; LiNi 0.8 Co 0.15 Al 0.05 O2; average particle size 3.0 μm), a battery for evaluation was prepared in the same manner as in Example 2-1 except that

[0123] [Examples 2-6]

[0124] An evaluation cell was prepared 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.

[0125] [Example 2-7]

[0126] A resin slurry was prepared by mixing a resin (acrylic resin), a conductive additive (carbon black), a dispersant, and a solvent (water and isopropyl alcohol). The weight ratio of resin to conductive additive to dispersant was set at 70:25:5. This resin slurry was applied to Al foil and dried to produce a resin-coated Al foil (collector foil γ). A positive electrode was produced in the same manner as in Example 2-5, except that this collector foil γ was used as the positive electrode current collector.

[0127] A negative electrode was prepared with two negative electrode layers having different weight ratios of negative electrode active material to sulfide solid electrolyte. Specifically, a negative electrode was prepared having a first negative electrode layer and a second negative electrode layer from the negative electrode current collector side. The weight ratio of negative electrode active material to sulfide solid electrolyte in the first negative electrode layer was 55:45, and the weight ratio of negative electrode active material to sulfide solid electrolyte in the second negative electrode layer was 45:55.

[0128] A battery for evaluation was prepared in the same manner as in Example 2-1 except that the above-mentioned positive electrode and negative electrode were used.

[0129] [Example 2-8]

[0130] A negative electrode was prepared in the same manner as in Example 2-7. A battery for evaluation was prepared in the same manner as in Example 2-5 except that this negative electrode was used.

[0131] [Example 2-9]

[0132] A negative electrode and an evaluation cell were prepared in the same manner as in Example 2-7, except that the weight ratio of the negative electrode active material to the sulfide solid electrolyte in the first negative electrode layer was changed to 60:40.

[0133] [Example 2-10]

[0134] A battery for evaluation was prepared in the same manner as in Example 2-9 except that the positive electrode current collector was changed to the current collector foil α.

[0135] [Evaluation 2]

[0136] (Nail penetration test)

[0137] The prepared evaluation batteries were subjected to a nail penetration test using the same method as in Evaluation 1 to evaluate their calorific value. The calorific value of Example 2-1 was set as 100% for relative evaluation. The results are shown in Table 2. Table 2 also shows the calorific value of Comparative Examples 1-1 to 1-3, which were compared with Example 2-1.

[0138] [Table 2]

[0139]

[0140] As shown in Table 2, it was confirmed that the heat generation can be further suppressed by adjusting the conditions of the positive electrode layer and positive electrode current collector, the conditions of the electrolyte layer, and the layer composition of the negative electrode layer. This suggests that the heat generation can be synergistically suppressed by adjusting various battery conditions.

Claims

1. A battery comprising 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 disposed between the positive electrode layer and the negative electrode layer, wherein: The negative electrode layer contains a 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. The 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 inclusion compound 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 The ratio of the Si-based negative electrode active material in the negative electrode layer is 45 wt % or more.

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