Active material, negative electrode layer, battery, and method for manufacturing the same

Abstract

The main object of the present disclosure is to provide an active material having a small volume change due to charge and discharge. In the present disclosure, the above object is achieved by providing an active material having a Type II silicon clathrate crystal phase, having a pore inside a primary particle, and a pore volume of a pore having a pore diameter of 100 nm or less being 0.05 cc / g or more and 0.15 cc / g or less.

Description

[0001] This application is a divisional application of application number 202110308572.6, entitled "Active Material, Negative Electrode Layer, Battery and Method Thereof for Manufacturing Thereof", filed on March 23, 2021. Technical Field

[0002] This disclosure relates to active materials, negative electrode layers, batteries, and methods for manufacturing them. Background Technology

[0003] In recent years, battery development has been booming. For example, in the automotive industry, the development of batteries for electric or hybrid vehicles is being promoted. Furthermore, silicon (Si) is known as an active material used in batteries.

[0004] For example, Patent Document 1 discloses an all-solid-state battery system containing alloy-based negative electrode active material particles such as silicon particles. On the other hand, Patent Document 2 discloses that, according to calculations, silicon clathrate can be used as the negative electrode active material for lithium-ion batteries.

[0005] Existing technical documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2017-059534

[0007] Patent Document 2: U.S. Patent Application Publication No. 2012 / 0021283 Summary of the Invention

[0008] Si has a large theoretical capacity, which is effective for achieving high energy density in batteries. On the other hand, Si exhibits large volume changes during charging and discharging.

[0009] This disclosure is made in view of the above-mentioned circumstances, and its main purpose is to provide an active material with small volume change due to charging and discharging.

[0010] To address the aforementioned issues, this disclosure provides an active material having a type II silicon inclusion crystal phase, with pores within the primary particles, the porosity of which is 0.05 cc / g or more and 0.15 cc / g or less, and the pore diameter is less than 100 nm.

[0011] In addition, this disclosure provides a negative electrode layer containing the above-mentioned active material.

[0012] In addition, this disclosure provides a battery having a positive electrode layer, a negative electrode layer and an electrolyte layer formed between the positive electrode layer and the negative electrode layer, wherein the negative electrode layer is the negative electrode layer as described above.

[0013] In addition, this disclosure provides a method for manufacturing an active material, comprising: a preparation step in which an intermediate having a type II silicon inclusion crystal phase is prepared; an alloying step in which the intermediate and the Li-based material are alloyed such that the molar ratio (Li / Si) of Li contained in the Li-based material to Si contained in the intermediate is 3 or less to obtain an alloy compound; and a Li removal step in which Li is removed from the alloy compound to form pores inside the primary particles.

[0014] In addition, this disclosure provides a method for manufacturing a negative electrode layer, comprising: an active material manufacturing step in which an active material is manufactured using the aforementioned active material manufacturing method; and a negative electrode layer forming step in which the aforementioned active material is used to form a negative electrode layer.

[0015] In addition, this disclosure provides a method for manufacturing a battery, comprising: an active material manufacturing step in which an active material is manufactured using the above-described active material manufacturing method; and a negative electrode layer forming step in which a negative electrode layer is formed using the above-described active material.

[0016] In this disclosure, it is possible to obtain an active material with minimal volume change due to charging and discharging. Attached Figure Description

[0017] Figure 1 This is a simplified three-dimensional diagram illustrating the Si crystal phase.

[0018] Figure 2 This is a schematic cross-sectional view illustrating the battery in this disclosure.

[0019] Figure 3 This is a flowchart illustrating a method for manufacturing the active substance in this disclosure.

[0020] Figure 4 The results are obtained by XRD determination of the active substances obtained in Examples 1-3 and Comparative Examples 1 and 2.

[0021] Figure 5 This is a cross-sectional SEM image of the negative electrode layer (the negative electrode layer after rolling) obtained in Example 1.

[0022] Explanation of reference numerals in the attached figures

[0023] 1…Positive electrode layer, 2…Negative electrode layer, 3…Electrolyte layer, 4…Positive current collector, 5…Negative current collector, 10…Battery Detailed Implementation

[0024] The active material, negative electrode layer, battery, and manufacturing method thereof are described in detail below.

[0025] A. Active substances

[0026] The active material disclosed herein has a type II silicon inclusion complex crystal phase and pores within the primary particles, wherein the porosity of the pores with a diameter of less than 100 nm is greater than or equal to 0.05 cc / g and less than 0.15 cc / g.

[0027] The active material in this disclosure has a type II silicon inclusion compound crystal phase. For example... Figure 1 As shown in (a), in the crystal phase of the type II silicon inclusion compound, multiple Si elements form polyhedra (cages) including pentagons or hexagons. These polyhedra have spaces within them capable of containing metal ions such as Li ions. By inserting metal ions into these spaces, volume changes caused by charging and discharging can be suppressed. In particular, in all-solid-state batteries, a high binding voltage is generally required to suppress volume changes caused by charging and discharging; however, by using the active material of this disclosure, a reduction in binding voltage can be achieved, thereby suppressing the enlargement of the binding clamp.

[0028] On the other hand, ordinary Si has a diamond-type crystal phase. For example... Figure 1 As shown in (b), in the diamond-type Si crystal phase, tetrahedra are formed by multiple Si elements. Since the tetrahedra do not have spaces inside that can accommodate metal ions such as Li ions, it is difficult to suppress volume changes caused by charging and discharging. Therefore, durability is prone to deterioration.

[0029] Furthermore, the active material in this disclosure has pores within its primary particles. As described above, since the type II silicon inclusion complex crystal phase has cages capable of containing metal ions such as Li ions, it can suppress volume changes caused by charging and discharging. If the primary particles having this crystal phase have pores within them, these pores also contribute to suppressing volume changes, thus further suppressing volume changes caused by charging and discharging. Additionally, the active material in this disclosure has numerous micropores with a diameter of less than 100 nm. Therefore, it can uniformly mitigate volume changes caused by charging and discharging. Moreover, due to the presence of numerous micropores, it can suppress pore collapse caused by compression.

[0030] The active material of this disclosure has a type II silicon occlusion phase. Type II silicon occlusion phases typically belong to space group (Fd-3m). In X-ray diffraction using CuKα rays, the type II silicon occlusion phase exhibits typical peaks at 2θ = 20.09°, 21.00°, 26.51°, 31.72°, 36.26°, and 53.01°. These peak positions can shift within ±0.50°, ±0.30°, and ±0.10°, respectively.

[0031] The active material in this disclosure preferably has a type II silicon cladding phase as the main phase. "Having a type II silicon cladding phase as the main phase" means that, in the peaks observed by X-ray diffraction, the peaks belonging to the type II silicon cladding phase have the highest diffraction intensity. The definition of "main phase" is the same for other crystal phases.

[0032] In the crystal phase of type II silicon inclusion compounds, the peak located at 2θ = 20.09° ± 0.50° is designated as peak A, and the peak located at 2θ = 31.72° ± 0.50° is designated as peak B. Furthermore, the intensity of peak A is taken as I... A The intensity of peak B is used as I. B On the other hand, the maximum intensity at 2θ = 22° to 23° is taken as I. M At 2θ = 22° to 23°, this is typically the range where peaks of Si-related crystalline phases do not appear, and therefore can be used as a reference.

[0033] Preferred I A / I M The value of I is greater than 1. A / I M When the value is below 1, it can be determined that a type II silicon inclusion crystal phase has not actually formed. A / I M The value of can be 2 or higher, 5 or higher, or 7 or higher. On the other hand, I A / I M The upper limit of the value is not specifically limited (for example, sometimes I A / I M (The value is 1000 or higher). Furthermore, considering the results of the embodiments described later, I A / I M The value can be, for example, below 10.

[0034] Preferred I B / I M The value of I is greater than 1. B / I M When the value is below 1, it can be determined that a type II silicon inclusion crystal phase has not actually formed. B / I M The value of I can be, for example, 2 or higher, or 5 or higher. On the other hand, I B / I M The upper limit of the value is not specifically limited (for example, sometimes I B / I M (The value is 1000 or higher). Furthermore, considering the results of the embodiments described later, I B / I M The value can be, for example, below 10.

[0035] Furthermore, the active material in this disclosure preferably does not have a diamond-type Si crystal phase, but it may have a very small amount. In X-ray diffraction measurements using CuKα rays, the diamond-type Si crystal phase exhibits typical peaks at 2θ = 28.44°, 47.31°, 56.10°, 69.17°, and 76.37°. These peak positions can shift within ±0.50°, ±0.30°, and ±0.10°, respectively.

[0036] As a peak of the diamond-type Si crystal phase, when peak C is observed at 2θ = 28.44° ± 0.50°, the intensity of peak C is set as I. C I A / I C For example, a value greater than 1 could be 1.5 or greater, 2 or greater, or 3 or greater. B / I C The preferred range and I A / I C The preferred range is the same.

[0037] The active material in this disclosure preferably does not possess the crystalline phase of a type I silicon inclusion compound. The crystalline phase of a type I silicon inclusion compound typically belongs to space group (Pm-3n). In X-ray diffraction using CuKα rays, the crystalline phase of a type I silicon inclusion compound exhibits typical peaks at 2θ = 19.44°, 21.32°, 30.33°, 31.60°, 32.82°, 36.29°, 52.39°, and 55.49°. These peak positions can shift within ±0.50°, ±0.30°, and ±0.10°, respectively. "Not possessing a crystalline phase" can be confirmed by the presence of peaks whose crystalline phase is not identified in X-ray diffraction measurements.

[0038] The active material in this disclosure may take the form of, for example, liftable particles. The active material can be primary particles or secondary particles formed by the aggregation of primary particles. In either case, pores are typically present within the primary particles.

[0039] The active material of this disclosure has numerous micropores with a pore diameter of 100 nm or less. The porosity of these pores with a diameter of 100 nm or less is typically 0.05 cc / g or more, and can be 0.07 cc / g or more, or 0.10 cc / g or more. On the other hand, the aforementioned porosity is typically 0.15 cc / g or less. The porosity can be determined, for example, by mercury porosimetry, BET measurement, gas adsorption, 3D-SEM, or 3D-TEM.

[0040] The active material in this disclosure has pores within the primary particles. Its porosity is, for example, 4% or more, and can be 10% or more. Alternatively, the aforementioned porosity is, for example, 40% or less, and can be 20% or less. The porosity can be calculated, for example, in the following order: First, the electrode layer containing the active material is cross-sectionally cut by ion milling. Then, the cross-section is observed using SEM (scanning electron microscope) to obtain particle photographs. Image analysis software is used to distinguish the silicon portion and the pore portion from the obtained photographs and binarize them. The areas of the silicon portion and the pore portion are calculated, and the porosity (%) is calculated according to the following formula.

[0041] Porosity (%) = 100 × (pore area) / ((silicon area) + (pore area))

[0042] The specific image analysis and porosity calculation can be performed as follows. For example, using image analysis software, Fiji ImageJ bundled with Java 1.8.0_172 (hereinafter referred to as Fiji) is employed. Secondary electron images and reflected electron images of the same field of view are synthesized and converted to RGB color. Then, to remove noise from each pixel, the resulting RGB image is blurred using the "Median (filter size = 2)" function in Fiji. Next, using the "Weka Machine Learning" function in Fiji, a human assigns any number of regions in the noise-removed image as either silicon or porosity regions, creating teacher data that strictly distinguishes between silicon and porosity. Then, based on the created teacher data, within Fiji, the silicon and porosity regions are determined by machine, and the area ratio of the silicon and porosity regions is calculated.

[0043] Regarding RGB color image conversion, since both secondary electron images and reflected electron images are represented using grayscale levels, for example, the brightness x of each pixel in the secondary electron image is assigned a Red value, and the brightness y of the reflected electron image is similarly assigned a Green value. Thus, for example, for each pixel, RGB image conversion is performed as R = x, G = y, B = (x + y) / 2.

[0044] The detailed conditions in the "Weka Machine Learning" above are as follows. Gaussian blur, Hessian, Membrane projections, Mean, Maximum, Anisotropic diffusion, Sobel filter, Difference of gaussians, Variance, Minimum, and Median are selected as training features (focusing on the numerical features of the machine's images when creating teacher data in machine learning). Additionally, as other parameters, Membranethickness is set to 3, Membrane patch size is set to 19, Minimum sigma is set to 1.0, and Maximum sigma is set to 16.0.

[0045] The average particle size of primary particles is, for example, 50 nm or more, 100 nm or more, or 150 nm or more. On the other hand, the average particle size of primary particles is, for example, 3000 nm or less, 1500 nm or less, or 1000 nm or less. Furthermore, the average particle size of secondary particles is, for example, 1 μm or more, 2 μm or more, or 5 μm or more. On the other hand, the average particle size of secondary particles is, for example, 60 μm or less, or 40 μm or less. Moreover, the average particle size can be determined, for example, by observation using SEM. A large number of samples is preferred, for example, 20 or more, 50 or more, or 100 or more.

[0046] The composition of the active material in this disclosure is not particularly limited, but NaxSi is preferred. 136 (0≤x≤20) represents the expression. X can be 0 or greater than 0. On the other hand, x can be less than 10 or less than 5. Furthermore, the active material in this disclosure may contain unavoidable components (e.g., Li). The composition of the active material can be determined, for example, by EDX, XRD, XRF, ICP, or atomic absorption spectrometry. The composition of other compounds can also be determined in the same way.

[0047] The active material disclosed herein exhibits, in X-ray photoelectron spectroscopy (XPS) measurements, a peak X located at 99.2 eV ± 0.4 eV as a Si(2p) peak from Si, and a peak Y located at 103.6 eV ± 0.4 eV as a Si(2p) peak from SiO2. When the intensity of peak X is set to I... X And set the intensity of peak Y as I. Y In the case of I, it is preferred Y / I XSmall. Because this can suppress volume changes caused by silicon oxide. Y / I X For example, it can be below 1.30, below 1.23, or below 0.81. On the other hand, I Y / I X For example, it can be above 0.50, above 0.70, or above 0.76.

[0048] The active material disclosed herein is typically used in batteries. The active material in this disclosure can be a negative electrode active material or a positive electrode active material, but the former is preferred. This disclosure may also provide an electrode layer (negative electrode layer or positive electrode layer) having the aforementioned active material, and a battery having the electrode layer. As a method for manufacturing the active material, for example, the manufacturing method described in "D. Method for Manufacturing Active Material" described later can be cited.

[0049] B. Negative electrode layer

[0050] The negative electrode layer in this disclosure contains the aforementioned active material.

[0051] According to this disclosure, by using the above-mentioned active material, a negative electrode layer with small volume change due to charging and discharging can be formed.

[0052] The negative electrode layer is a layer containing at least a negative electrode active material. Regarding the negative electrode active material, the information described in "A. Active Material" above is the same, so it is omitted here. The proportion of the negative electrode active material in the negative electrode layer is, for example, 20% by weight or more, 30% by weight or more, or 40% by weight or more. If the proportion of the negative electrode active material is too low, sufficient energy density may not be obtained. On the other hand, the proportion of the negative electrode active material can be, for example, 80% by weight or less, 70% by weight or less, or 60% by weight or less. If the proportion of the negative electrode active material is too high, the ionic conductivity and electronic conductivity of the negative electrode layer may be relatively reduced.

[0053] The negative electrode layer may contain at least one of an electrolyte, a conductive material, and a binder, as needed. For example, the electrolyte described in "C. Battery 3. Electrolyte Layer" (described later) can be cited as an example. For example, the conductive material can be carbon material, metal particles, or a conductive polymer. For example, particulate carbon materials such as acetylene black (AB) and Ketjen black (KB), fibrous carbon materials such as carbon fibers, carbon nanotubes (CNTs), and carbon nanofibers (CNFs) can be cited as examples. Additionally, for example, rubber-based binders and fluoride-based binders can be cited as examples.

[0054] The thickness of the negative electrode layer is, for example, 0.1 μm or more and 1000 μm or less. The negative electrode layer in this disclosure is commonly used in batteries.

[0055] C. Battery

[0056] Figure 2 This is a schematic cross-sectional view illustrating the battery in this disclosure. Figure 2 The battery 10 shown includes: a positive electrode layer 1, a negative electrode layer 2, an electrolyte layer 3 formed between the positive electrode layer 1 and the negative electrode layer 2, a positive current collector 4 for collecting current in the positive electrode layer 1, and a negative current collector 5 for collecting current in the negative electrode layer 2. In this disclosure, the negative electrode layer 2 is the negative electrode layer described in "B. Negative Electrode Layer" above.

[0057] According to this disclosure, by using the above-described negative electrode layer, a battery with small volume change due to charging and discharging can be obtained.

[0058] 1. Negative electrode layer

[0059] Regarding the negative electrode layer in this disclosure, the content is the same as that described in "B. Negative Electrode Layer" above, so it is omitted here.

[0060] 2. Positive electrode layer

[0061] The positive electrode layer is a layer containing at least a positive electrode active material. Additionally, depending on the requirements, the positive electrode layer may also contain at least one of an electrolyte, a conductive material, and a binder.

[0062] Examples of positive electrode active materials include oxide active materials. Examples of oxide active materials include LiCoO2, LiMnO2, LiNiO2, LiVO2, and LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2 and other layered active substances in rock salt, LiMn2O4, Li4Ti5O 12 Li(Ni) 0.5 Mn 1.5 Spinel-type active substances such as O4, and olivine-type active substances such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4.

[0063] A coating layer containing a Li-ion-conducting oxide can be formed on the surface of the oxide active material. This suppresses the reaction between the oxide active material and the solid electrolyte (especially a sulfide solid electrolyte). Examples of Li-ion-conducting oxides include LiNbO3. The thickness of the coating layer is, for example, 1 nm or more and 30 nm or less. Alternatively, Li₂S can be used as a positive electrode active material, for example.

[0064] The shape of the positive electrode active material can be, for example, liftable particles. The average particle size (D) of the positive electrode active material... 50 There are no particular limitations; for example, it can be 10 nm or larger, or even 100 nm or larger. On the other hand, the average particle size (D) of the positive electrode active material...50 For example, it can be below 50 μm or below 20 μm. Average particle size (D) 50 For example, it can be calculated using a laser diffraction particle size analyzer or a scanning electron microscope (SEM).

[0065] The electrolyte, conductive material, and binder used in the positive electrode layer are the same as those described in "B. Negative Electrode Layer" above, so they are omitted here. The thickness of the positive electrode layer is, for example, 0.1 μm or more and 1000 μm or less.

[0066] 3. Electrolyte layer

[0067] The electrolyte layer is a layer formed between the positive electrode layer and the negative electrode layer, and it contains at least one electrolyte. The electrolyte can be a solid electrolyte or a liquid electrolyte (electrolyte).

[0068] Examples of solid electrolytes include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes, as well as organic polymer electrolytes such as polymer electrolytes. Examples of sulfide solid electrolytes include solid electrolytes containing Li, X (where X is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S. Additionally, sulfide solid electrolytes may also contain at least one of O and halogen elements. Examples of halogen elements include F, Cl, Br, and I. Sulfide solid electrolytes can be glass (amorphous) or glass ceramics. Examples of sulfide solid electrolytes include Li₂S-P₂S₅, LiI-Li₂S-P₂S₅, LiI-LiBr-Li₂S-P₂S₅, Li₂S-SiS₂, Li₂S-GeS₂, and Li₂S-P₂S₅-GeS₂.

[0069] The electrolyte preferably contains a supporting salt and a solvent. Examples of supporting salts (lithium salts) for electrolytes with lithium-ion conductivity include inorganic lithium salts such as LiPF6, LiBF4, LiClO4, and LiAsF6, and organic lithium salts such as LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(FSO2)2, and LiC(CF3SO2)3. Examples of solvents used in the electrolyte include cyclic esters (cyclic carbonates) such as ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (BC), and chain esters (chain carbonates) such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC). The electrolyte preferably contains two or more solvents.

[0070] The thickness of the electrolyte layer is, for example, greater than 0.1 μm and less than 1000 μm.

[0071] 4. Other structures

[0072] The battery disclosed herein preferably has a positive current collector for collecting current in the positive electrode layer and a negative current collector for collecting current in the negative electrode layer. Materials used as the positive current collector include, for example, SUS, aluminum, nickel, iron, titanium, and carbon. On the other hand, materials used as the negative current collector include, for example, SUS, copper, nickel, and carbon.

[0073] The battery disclosed herein may further include a binding clamp that applies binding pressure to the positive electrode layer, electrolyte layer, and negative electrode layer along the thickness direction. Particularly when the electrolyte layer is a solid electrolyte layer, applying binding pressure is preferable in order to form good ion conduction pathways and electron conduction pathways. The binding pressure may be, for example, 0.1 MPa or more, 1 MPa or more, or 5 MPa or more. On the other hand, the binding pressure may be, for example, 100 MPa or less, 50 MPa or less, or 20 MPa or less.

[0074] 5. Battery

[0075] The type of battery disclosed herein is not particularly limited, but lithium-ion batteries are typical. Furthermore, the battery in this disclosure can be a liquid battery containing an electrolyte layer as the electrolyte layer, or an all-solid-state battery having a solid electrolyte layer as the electrolyte layer. Additionally, the battery in this disclosure can be a primary battery or a secondary battery, with a secondary battery being preferred. Because it can be repeatedly charged and discharged, it is useful as, for example, a vehicle battery.

[0076] The battery disclosed herein can be a single cell or a stacked battery. The stacked battery can be a unipolar stacked battery (parallel-connected stacked battery) or a bipolar stacked battery (series-connected stacked battery). As for the shape of the battery, for example, it can be coin-shaped, laminated, cylindrical, or square.

[0077] D. Methods for manufacturing active substances

[0078] Figure 3 This is a flowchart illustrating a method for manufacturing the active substance in this disclosure. Figure 3 In the manufacturing method shown, firstly, a Zindle compound containing Na and Si and having at least a Zindle phase is prepared, and Na is removed from the Zindle compound, thereby preparing an intermediate having a type II silicon inclusion crystal phase (preparation step). Next, the intermediate and a Li-based material are alloyed in a predetermined ratio to obtain an alloy compound (alloying step). Next, Li is removed from the alloy compound, forming pores inside the primary particles (Li removal step). Thus, an active material having a type II silicon inclusion crystal phase is obtained.

[0079] According to this disclosure, it is possible to obtain an active material with small volume changes due to charging and discharging by forming pores inside a primary particle.

[0080] 1. Preparation process

[0081] The preparation process disclosed herein is a process for preparing an intermediate having a type II silicon inclusion compound crystalline phase. The method for preparing the intermediate is not particularly limited; for example, a method for removing Na from a Zindle compound containing Na and Si and having at least a Zindle phase can be cited.

[0082] (1) Zintel manufacturing

[0083] Zintl compounds possess a Zintl phase. In X-ray diffraction using CuKα rays, the Zintl phase exhibits typical peaks at 2θ = 16.10°, 16.56°, 17.64°, 20.16°, 27.96°, 33.60°, 35.68°, 40.22°, and 41.14°. These peak positions can shift within ±0.50° or ±0.30°. Preferably, the Zintl phase is the dominant phase in the Zintl compounds. Zintl compounds may or may not possess a type I silicon inclusion complex phase. Additionally, Zintl compounds may or may not possess a type II silicon inclusion complex phase.

[0084] The composition of the Zintel compound is not particularly limited, but NazSi is preferred. 136 The composition (121≤z≤151) represents this. z can be 126 or higher, or 131 or higher. On the other hand, z can be 141 or lower.

[0085] Zindle compounds can be obtained, for example, by heat treatment of a mixture of raw materials containing elemental Na and elemental Si. The ratio of elemental Na to elemental Si is not particularly limited; for example, the amount of elemental Na relative to 1 mole of elemental Si can be 0.8 moles or more, or 1 mole or more. On the other hand, the amount of elemental Na relative to 1 mole of elemental Si can be, for example, 1.5 moles or less, or 1.3 moles or less.

[0086] The heat treatment temperature is, for example, 500°C or higher and 1000°C or lower. The heat treatment time is, for example, 1 hour or higher and 50 hours or lower. In particular, heat treatment is preferably performed at approximately 700°C (e.g., 650°C or higher and 750°C or lower) and for approximately 20 hours (e.g., 15 hours or higher and 25 hours or lower).

[0087] (2)Na removal

[0088] As a method for removing Na from Zindle compounds, heat treatment is an example. The heat treatment temperature is, for example, 280°C or higher, and can be 300°C or higher. On the other hand, the heat treatment temperature is, for example, 500°C or lower. The heat treatment time is, for example, 1 hour or more and 50 hours or less. The heat treatment can be performed under an atmospheric pressure atmosphere or under a reduced pressure atmosphere. In the latter case, the pressure during heat treatment is, for example, 10 Pa or less, and can be 1 Pa or less, or 0.1 Pa or less. Alternatively, the heat treatment can be performed under an inert atmosphere such as Ar.

[0089] (3) Intermediate

[0090] The intermediate typically has a type II silicon inclusion complex phase. Preferably, the intermediate has a type II silicon inclusion complex phase as the main phase. The intermediate may or may not have a type I silicon inclusion complex phase. The intermediate preferably does not have a diamond-type Si phase, but it may have a very small amount. Furthermore, the composition of the intermediate is not particularly limited, but it is preferably composed of NaySi. 136 (0≤y≤24) represents the expression. y can be 0 or greater than 0. On the other hand, y can be less than 20 or less than 10.

[0091] 2. Alloying process

[0092] The alloying process in this disclosure involves alloying the intermediate and the Li-based material such that the molar ratio (Li / Si) of Li in the Li-based material to Si in the intermediate is 3 or less, thereby obtaining an alloy compound.

[0093] Li-based materials are not particularly limited as long as they can be alloyed with intermediates; they can be elemental Li or Li alloys. Li alloys are preferably Li-based alloys because they are easy to alloy with intermediates. Methods for alloying intermediates and Li-based materials include, for example, mixing the two and heat-treating them.

[0094] In the alloying process, it is preferable to alloy the intermediate and the Li-based material while setting the molar ratio (Li / Si) of Li in the Li-based material to Si in the intermediate within a predetermined range. The Li / Si ratio is, for example, 0.5 or more, and can be 0.75 or more, or 1 or more. If the Li / Si ratio is too small, pores may not form within the primary particles. On the other hand, the Li / Si ratio is typically 3 or less, and can be 2.5 or less, or 2 or less. If the Li / Si ratio is too large, it may be impossible to maintain the type II silicon inclusion complex crystal phase. Alloying with Li tends to reduce the crystallinity of Si, therefore controlling the Li / Si ratio is preferable.

[0095] 3. Li removal process

[0096] The Li removal process in this disclosure is a process of removing Li from the aforementioned alloy compound to form pores within the primary particles. By removing the Li (highly dispersed Li) contained in the alloy compound, nanoscale (nanoscale) pores can be formed.

[0097] One method for removing Li from alloy compounds is, for example, reacting a Li extractant with the alloy compound. The Li extractant is, for example, a liquid. Examples of Li extractants include primary alcohols such as methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, and 1-hexanol; secondary alcohols such as 2-propanol, 2-butanol, 2-pentanol, and 2-hexanol; tertiary alcohols such as tert-butanol; phenols such as phenol; diols such as 1,2-ethylene glycol and 1,3-butanediol; ethylene glycol ethers such as propylene glycol monomethyl ether and ethylene glycol monomethyl ether; pyranoses such as bD-glucopyranose; yellow sugars such as erythromycin; glucose; fructose; and polysaccharides. The Li extractant is preferably at least one selected from methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and 1-hexanol. In particular, the Li extractant preferably contains at least ethanol. Additionally, acids such as acetic acid, formic acid, propionic acid, and oxalic acid can also be used as Li extractants. In this disclosure, two or more Li extractants can be used. In this case, two or more Li extractants can be used in combination, or they can be used separately (as Li removal, more than two stages of treatment can be performed).

[0098] Li extractants preferably contain little water. Excessive water content can sometimes degrade the alloy compounds. The water content of the Li extractant can be, for example, below 100 ppm or even below 10 ppm.

[0099] The method for reacting the Li extractant with the alloy compound is not particularly limited. The Li extractant can be in direct contact with the alloy compound, or it can be in contact with a dispersion containing the alloy compound. Examples of dispersion media include saturated hydrocarbons such as n-heptane, n-octane, n-decane, 2-ethylhexane, and cyclohexane; unsaturated hydrocarbons such as hexene and heptene; ethers such as 1,3,5-trimethylbenzene, toluene, xylene, ethylbenzene, propylbenzene, isopropylbenzene, 1,2,4-trimethylbenzene, and 1,2,3-trimethylbenzene; and ethers such as n-butyl ether, n-hexyl ether, isopentyl ether, diphenyl ether, methylphenyl ether, and cyclopentylmethyl ether. The relative permittivity of the dispersion medium is, for example, 3.08 or less, and can be 3.00 or less. On the other hand, the relative permittivity of the dispersion medium is, for example, 1.50 or more, and can be 1.70 or more. The relative permittivity can be determined, for example, using the method described in JIS C 2565 (such as the void resonator method).

[0100] 4. Active substances

[0101] The active material obtained through the above processes has a type II silicon inclusion complex crystal phase. Furthermore, the active material contains pores within its primary particles. Regarding the preferred range of pore size in the active material, I... A / I M and I B / I M For the preferred scope and other matters, the contents described in “A. Active Substances” above may be appropriately cited.

[0102] E. Manufacturing method of negative electrode layer

[0103] In this disclosure, a method for manufacturing a negative electrode layer is provided, comprising: an active material manufacturing step of manufacturing an active material using the above-described active material manufacturing method; and a negative electrode layer forming step of forming a negative electrode layer using the above-described active material.

[0104] According to this disclosure, by using the aforementioned active material, a negative electrode layer with minimal volume change due to charging and discharging can be formed. The manufacturing process of the active material is the same as described in "D. Method for Manufacturing Active Material" above. Furthermore, the method for forming the negative electrode layer is not particularly limited, and known methods can be used. For example, a negative electrode layer formed on a negative electrode current collector can be obtained by coating a slurry containing at least the active material onto the negative electrode current collector and drying it. Regarding preferred embodiments of the obtained negative electrode layer, the description in "B. Negative Electrode Layer" above can be appropriately referenced.

[0105] F. Battery manufacturing method

[0106] In this disclosure, a method for manufacturing a battery is provided, comprising: an active material manufacturing step of manufacturing an active material using the above-described active material manufacturing method; and a negative electrode layer forming step of forming a negative electrode layer using the above-described active material.

[0107] According to this disclosure, by using the aforementioned active material, a battery with minimal volume change due to charging and discharging can be formed. The active material manufacturing process and the negative electrode layer formation process are the same as those described in "D. Method for Manufacturing Active Material" and "E. Method for Manufacturing Negative Electrode Layer" above. Furthermore, the method for forming the battery is not particularly limited, and known methods can be used. In addition to the active material manufacturing process and the negative electrode layer formation process, the battery manufacturing method of this disclosure may also include a positive electrode layer formation process for forming a positive electrode layer, an electrolyte layer formation process for forming an electrolyte layer, and a configuration process for sequentially configuring the positive electrode layer, the electrolyte layer, and the negative electrode layer. Regarding preferred embodiments of the obtained battery, the contents described in "C. Battery" above may be appropriately referenced.

[0108] Furthermore, this disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and all solutions that have the same technical concept as those described in the patent claims of this disclosure and that achieve the same effect are included within the technical scope of this disclosure.

[0109] [Example]

[0110] [Example 1]

[0111] (Synthesis of active substances)

[0112] Si and Na particles were mixed in a 1:1 molar ratio and placed in a crucible. The mixture was then sealed under an Ar atmosphere and heated to 700 °C to synthesize NaSi (Zinther compound). Na was then removed by heating under vacuum (approximately 1 Pa) at 340 °C to obtain an intermediate. This intermediate was weighed and mixed with Li metal at a Li / Si = 1 molar ratio in a mortar under an Ar atmosphere to obtain an alloy compound. The resulting alloy compound was reacted with ethanol under an Ar atmosphere to create pores within the primary particles, thus yielding the active material.

[0113] (Making the negative electrode)

[0114] The obtained active material, sulfide solid electrolyte (Li2S-P2S5 glass ceramic), conductive material (VGCF), butyl butyrate solution containing PVDF binder at a ratio of 5% by weight, and butyl butyrate were added to a polypropylene container and stirred for 30 seconds using an ultrasonic dispersion device (SMT UH-50). Next, the container was vibrated for 30 minutes using a vibrator (Shibata Scientific Co., Ltd., TTM-1). Using an applicator, the coating was applied to the negative electrode current collector (Cu foil, UACJ) using a doctor blade method and dried on a heating plate at 100°C for 30 minutes. This yielded a negative electrode with a negative electrode current collector and a negative electrode layer.

[0115] (The production of the positive electrode)

[0116] Add positive electrode active material (LiNi) to the polypropylene container 1 / 3 Co 1 / 3 Mn 1 / 3O2, an average particle size of 6 μm, a sulfide solid electrolyte (Li2S-P2S5 glass-ceramic), a conductive material (VGCF), a butyl butyrate solution containing PVDF-based binder at a ratio of 5% by weight, and butyl butyrate were stirred for 30 seconds using an ultrasonic dispersion device (SMT UH-50). Next, the container was vibrated for 3 minutes using a vibrator (Shibata Scientific Co., Ltd., TTM-1). Using a coating tool, the mixture was applied to the positive current collector (Al foil, Showa Denko) using a scraper method and dried on a heating plate at 100°C for 30 minutes. This yielded a positive electrode with a positive current collector and a positive electrode layer. Furthermore, the area of ​​the positive electrode was smaller than that of the negative electrode.

[0117] (Fabrication of the solid electrolyte layer)

[0118] A sulfide solid electrolyte (Li2S-P2S5-based glass ceramic), a heptane solution containing a butadiene rubber binder at a ratio of 5% by weight, and heptane were added to a polypropylene container, and the mixture was stirred for 30 seconds using an ultrasonic dispersion device (SMT UH-50). Next, the container was vibrated for 30 minutes using a vibrator (Shibata Scientific Co., Ltd., TTM-1). Using a coater, the coating was applied to a release sheet (Al foil) using a doctor blade method, and then dried on a hot plate at 100°C for 30 minutes. This yielded a transfer component with a release sheet and a solid electrolyte layer.

[0119] (The fabrication of an all-solid-state battery)

[0120] A solid electrolyte layer for bonding is disposed on the positive electrode layer of the positive electrode, and the mixture is placed in a roller press and pressed at 20 kN / cm (approximately 710 MPa) and 165 °C. Thus, the first layer stack is obtained.

[0121] Next, the negative electrode is placed in a roller press and pressed at 20 kN / cm (approximately 630 MPa) and 25°C. Then, a bonding solid electrolyte layer and a transfer member are sequentially arranged from the negative electrode layer side. At this time, the bonding solid electrolyte layer and the solid electrolyte layer in the transfer member are arranged opposite each other. The resulting laminate is placed in a planar uniaxial press and temporarily pressed at 100 MPa and 25°C for 10 seconds. Then, a release sheet is peeled off from the solid electrolyte layer. Thus, the second laminate is obtained.

[0122] Next, the solid electrolyte layer for bonding the first stack and the solid electrolyte layer for bonding the second stack are arranged opposite each other and placed on a planar uniaxial press, and pressed at 200 MPa and 135°C for 1 minute. Thus, an all-solid-state battery is obtained.

[0123] [Examples 2 and 3, Comparative Examples 1 and 2]

[0124] By changing the Li / Si ratio to the values ​​shown in Table 1, the active material was obtained in the same manner as in Example 1. Using the obtained active material, an all-solid-state battery was obtained in the same manner as in Example 1.

[0125] [evaluate]

[0126] (SEM-EDX measurement)

[0127] The intermediates and active substances obtained in Examples 1-3 and Comparative Examples 1 and 2 were analyzed by SEM-EDX (Scanning Electron Microscopy-Energy Dispersion X-ray Spectroscopy). The results confirmed that the active substances obtained in Examples 1-3 had nanoscale pores formed within the primary particles. Furthermore, the composition of the intermediates and active substances was determined based on the Na to Si ratio obtained from the EDX results. The results are shown in Table 1.

[0128] In addition, the cross-section of the negative electrode layer (the rolled negative electrode layer) obtained in Example 1 was observed using SEM. The results are shown below. Figure 5 .exist Figure 5 The study confirmed that the black areas corresponded to active materials, maintaining nanoscale pores even after rolling. This indicates that the presence of nanoscale pores can suppress pore collapse caused by pressing.

[0129] (XRD measurement)

[0130] The intermediates and active materials obtained in Examples 1-3 and Comparative Examples 1 and 2 were subjected to X-ray diffraction (XRD) measurements using CuKα rays. The results confirmed that all intermediates possessed a type II silicon inclusion compound crystal phase as the main phase. Furthermore, the XRD results of the obtained active materials are shown below. Figure 4 .

[0131] like Figure 4 As shown, it was confirmed that the active materials obtained in Examples 1-3 and Comparative Example 1 have a type II silicon inclusion complex crystal phase as the main phase and a diamond-type Si crystal phase as the secondary phase in their crystal phase. On the other hand, the active material obtained in Comparative Example 2 has very high amorphous properties, and no type II silicon inclusion complex crystal phase was confirmed.

[0132] Furthermore, the intensity of peak A, located near 2θ = 20.09° in the type II silicon inclusion crystal phase, is set as I. A And let the intensity of peak B, located near 2θ = 31.72°, be set as I. B Furthermore, the maximum intensity at 2θ = 22° to 23° is set as I. M Find I A / I M and I B / I MThe results are shown in Table 1.

[0133] (Determination of porosity)

[0134] The porosity (porosity of pores with a diameter of less than 100 nm) of the active substances obtained in Examples 1-3 and Comparative Examples 1 and 2 was determined. Porosity was measured using a mercury porosimeter. The measuring apparatus used was a Pore Master 60-GT (Quanta Chrom Ltd.). The analysis was conducted within a specified range. The Washburn method was used.

[0135] (Determination of the increase in restraint pressure)

[0136] The all-solid-state batteries obtained in Examples 1-3 and Comparative Examples 1 and 2 were charged, and the increase in binding pressure was measured. The test conditions were a binding pressure (constant magnitude) of 5 MPa, a charging rate of 0.1C, and a cutoff voltage of 4.55 V. The binding pressure at 4.55 V was measured, and the increase in binding pressure from the state before charging was calculated. The results are shown in Table 1. Furthermore, the results of the increase in binding pressure in Table 1 are relative values ​​with the result of Comparative Example 1 set to 100.

[0137] Table 1

[0138]

[0139] As shown in Table 1, it was confirmed that the increase in binding pressure in Examples 1-3 was smaller compared to Comparative Example 1. This is presumably because the active materials obtained in Examples 1-3 have numerous micropores with a diameter of less than 100 nm. On the other hand, it indicates that in Comparative Example 2, due to I... B / I M The value was below 1, so no type II silicon inclusion complex crystal phase was formed (collapse). In addition, the increase in binding pressure in Comparative Example 2 was also greater than that in Examples 1-3.

[0140] [Examples 4 and 5]

[0141] As Li extraction agents, 2-propanol and 1-propanol were used instead of ethanol, and the active material was obtained in the same manner as in Example 1. Using the obtained active material, an all-solid-state battery was obtained in the same manner as in Example 1.

[0142] [evaluate]

[0143] (XPS measurement)

[0144] X-ray photoelectron spectroscopy (XPS) was performed on the active materials obtained in Examples 1, 4, and 5. The results showed that peak X, representing the Si(2p) peak from Si, was observed at 99.2 eV ± 0.4 eV, and peak Y, representing the Si(2p) peak from SiO2, was observed at 103.6 eV ± 0.4 eV. The intensity of peak X was set as I... X Set the intensity of peak Y to I. Y Find I Y / I X The results are shown in Table 2.

[0145] (Determination of the increase in restraint pressure)

[0146] The all-solid-state batteries obtained in Examples 1, 4, and 5 were charged, and the increase in binding pressure was measured. The measurement method is as described above. The results are shown in Table 2. Furthermore, the results of the increase in binding pressure in Table 2 are relative values ​​when the result of Example 4 is set to 100.

[0147] Table 2

[0148]

[0149] As shown in Table 2, the increase in binding pressure in Examples 1 and 5 is smaller than that in Example 4. The reason for this is speculated as follows. Generally, the surface of Si is covered with an oxide film. This oxide film is usually around 100 nm, which is very thin, but it leads to a decrease in battery performance such as coulombic efficiency due to its reaction with Li. In addition, from the point of view of suppressing volume change, if Li, which should be contained by the type II silicon inclusion complex crystal phase, reacts with the oxide film, it will cause an expansion reaction. Therefore, a thin oxide film is preferred.

[0150] During the Li removal process, Si etching occurs, forming new Si surfaces. At this point, the oxide film formation on the Si surface varies depending on the type of Li extractant used. Specifically, it has been shown that using fast-reacting ethanol can suppress Si oxidation and inhibit the increase in binding pressure. This is presumably due to the fast reaction rate of ethanol. The reaction proceeds easily. After Si is etched, the reaction site is easily locally reduced by H2, thus inhibiting the formation of the oxide film. Alternatively, it may be due to the reaction occurring earlier than etching. The reaction is reduced, thus the amount of etching is decreased and the formation of the oxide film is inhibited.

Claims

1. An active material having a type II silicon inclusion compound crystalline phase as the main phase, wherein, Having a type II silicon inclusion compound phase as the main phase means that, among the peaks observed by X-ray diffraction, the peaks belonging to the type II silicon inclusion compound phase have the highest diffraction intensity. The interior of a primary particle contains pores. The porosity of pores with a diameter of less than 100 nm is greater than 0.05 cc / g and less than 0.15 cc / g. In X-ray photoelectron spectroscopy, a peak X, representing the Si(2p) ion from Si, was observed at 99.2 eV ± 0.4 eV, and a peak Y, representing the Si(2p) ion from SiO2, was observed at 103.6 eV ± 0.4 eV. Let the intensity of peak X be I. X And set the intensity of the peak Y as I. Y At that time, I Y / I X It is below 1.

30.

2. The active substance according to claim 1, In X-ray diffraction measurements using CuKα rays, peak A, located at 2θ = 20.09° ± 0.50° and peak B, located at 2θ = 31.72° ± 0.50°, were observed as the crystalline phase of the type II silicon inclusion compound. Set the intensity of peak A to I. A Set the intensity of peak B to I. B And let the maximum intensity of 2θ = 22°~23° be I. M At that time, I A / I M and I B / I M Each is 2 or more.

3. The active substance according to claim 1 or 2, wherein I Y / I X It is below 0.

81.

4. A negative electrode layer comprising the active substance as described in any one of claims 1 to 3.

5. A battery having a positive electrode layer, a negative electrode layer, and an electrolyte layer formed between the positive electrode layer and the negative electrode layer. The negative electrode layer is the negative electrode layer as described in claim 4.

6. A method for manufacturing the active substance according to claim 1, comprising: Preparation process, in which an intermediate having a type II silicon inclusion compound crystal phase is prepared; An alloying process in which the intermediate and the Li-based material are alloyed such that the molar ratio of Li in the Li-based material to Si in the intermediate (i.e., Li / Si) is 0.5 or more and 3 or less, to obtain an alloy compound; and The Li removal process removes Li from the alloy compound, creating pores within the primary particles.

7. The method for manufacturing the active substance according to claim 6, wherein in the Li removal step, ethanol is used to remove the Li from the alloy compound.

8. A method for manufacturing a negative electrode layer, comprising: An active substance manufacturing process, wherein the active substance is manufactured using the method for manufacturing the active substance as described in claim 6 or 7; and The negative electrode layer formation process uses the active material to form the negative electrode layer.

9. A method for manufacturing a battery, comprising: An active substance manufacturing process, wherein the active substance is manufactured using the method for manufacturing the active substance as described in claim 6 or 7; and The negative electrode layer formation process uses the active material to form the negative electrode layer.

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