Electrode active materials, electrode composite materials, and batteries

Abstract

To provide an electrode active material that undergoes small volumetric change upon charging and discharging.SOLUTION: The present disclosure provides an electrode active material having a silicon clathrate II type crystal phase, in which the five-membered ring size in the crystal phase is 3.752Å or more and 3.780Å or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to electrode active materials, electrode composite materials, and batteries. [Background technology]

[0002] In recent years, there has been a great deal of activity in battery development. For example, in the automotive industry, development is progressing on batteries used in electric vehicles (BEVs), plug-in hybrid vehicles (PHEVs), and hybrid electric vehicles (HEVs). Furthermore, silicon (Si) is known as an electrode active material used in batteries. For example, Patent Document 1 discloses an electrode active material having a silicon clathrate type II crystalline phase and having voids inside the primary particles. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-158004 [Overview of the project] [Problems that the invention aims to solve]

[0004] Si has a large theoretical capacity and is effective in increasing the energy density of batteries. On the other hand, Si undergoes a large volume change during charging and discharging. A large volume change during charging and discharging can lead to problems, such as a decrease in the functionality of the electrode active material when repeated charging and discharging is performed.

[0005] This disclosure has been made in view of the above circumstances, and its main purpose is to provide an electrode active material that exhibits small volume changes due to charging and discharging. [Means for solving the problem]

[0006] In order to solve the above problems, the inventors of the present invention conducted intensive research and found that when the electrode active material has a diamond-type silicon crystal phase in addition to the silicon class rate II-type crystal phase, the volume change during charge and discharge is suppressed. At the same time, the inventors of the present invention obtained a new finding that even when the ratio of the diamond-type silicon crystal phase in the electrode active material is the same, there are differences in the volume change during charge and discharge. When the inventors of the present invention examined in detail the cause of the above differences, they discovered that the 5-membered ring size of the silicon class rate II-type crystal phase has a great influence on the volume change during charge and discharge, and thus completed the following invention.

[0007] [1] An electrode active material having a silicon class rate II-type crystal phase, wherein the 5-membered ring size in the crystal phase is 3.752 Å or more and 3.780 Å or less, the electrode active material.

[0008] [2] The electrode active material according to [1], wherein the electrode active material has voids inside the primary particles.

[0009] [3] An electrode composite material containing the electrode active material according to [1] or [2] and at least one of a conductive material and a binder.

[0010] [4] A battery having a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer or the negative electrode layer contains the electrode composite material according to [3], the battery.

[0011] [5] The battery according to [4], wherein the electrolyte layer contains a solid electrolyte. [Effect of the Invention]

[0012] In the present disclosure, there is an effect that an electrode active material with a small volume change due to charge and discharge can be obtained.

Brief Description of the Drawings

[0013] [Figure 1] It is a schematic perspective view explaining the crystal phase of Si. [Figure 2] It is a schematic cross-sectional view illustrating the battery in the present disclosure. [Figure 3] It is the result of the volume expansion rate of the battery using the electrode active materials obtained in Examples 1 to 5 and Comparative Examples 1 to 3.

Modes for Carrying Out the Invention

[0014] Hereinafter, the electrode active material, electrode binder, and battery in the present disclosure will be described in detail.

[0015] A. Electrode Active Material The electrode active material in the present disclosure has a silicon clathrate II-type crystal phase. Further, the 5-membered ring size of the silicon clathrate II-type crystal phase is usually 3.752 Å or more and 3.780 Å or less.

[0016] According to the present disclosure, since the 5-membered ring size of the silicon clathrate II-type crystal phase is within a predetermined range, the electrode active material has a small volume change due to charge and discharge. As described above, Si has a large theoretical capacity and is effective for increasing the energy density of the battery. On the other hand, Si has a large volume change during charge and discharge. When the volume change during charge and discharge is large, for example, there are problems such as the function of the electrode active material being likely to deteriorate when charge and discharge are repeated. In response to such problems, the inventors have conducted intensive research and found that when the electrode active material has a diamond-type silicon crystal phase in addition to the silicon clathrate II-type crystal phase, the volume change during charge and discharge is suppressed.

[0017] At the same time, the inventors obtained a new finding: even if the proportion of the diamond-type silicon crystalline phase in the electrode active material is similar, differences occur in the volume change during charging and discharging. In other words, they obtained a new finding: there are phenomena that cannot be explained solely by the proportion of the diamond-type silicon crystalline phase. Therefore, the inventors investigated the cause of the above differences in detail and discovered that the size of the 5-membered rings in the silicon clathrate type II crystalline phase has a significant effect on the volume change during charging and discharging.

[0018] Specifically, the inventors have found that volume changes during charging and discharging can be suppressed by adjusting the size of the five-membered rings in the silicon clathrate type II crystalline phase to a predetermined range. The reason why volume changes can be suppressed is presumed to be that adjusting the size of the five-membered rings to a predetermined range makes the insertion and removal of Li through the five-membered rings smoother. On the other hand, it is presumed that if the size of the five-membered rings is too large or too small, distortion occurs in the five-membered rings themselves or in the six-membered rings adjacent to the five-membered rings, making it impossible to suppress volume changes due to charging and discharging.

[0019] Furthermore, the electrode active material in this disclosure has a silicon clathrate type II crystalline phase. As shown in Figure 1(a), in the silicon clathrate type II crystalline phase, polyhedra (cages) containing pentagons (5-membered rings) or hexagons (6-membered rings) are formed by multiple Si elements. These polyhedra have internal spaces that can encapsulate metal ions such as Li ions. By inserting metal ions into these spaces, volume changes due to charging and discharging can be suppressed. In particular, in all-solid-state batteries, it is generally necessary to apply high confinement pressure to suppress volume changes due to charging and discharging, but by using the electrode active material in this disclosure, the confinement pressure can be reduced, and as a result, the size of the confinement jig can be suppressed. On the other hand, as shown in Figure 1(b), in the diamond-type silicon crystalline phase, tetrahedra are formed by multiple Si elements. Since tetrahedra do not have internal spaces that can encapsulate metal ions such as Li ions, the diamond-type silicon crystalline phase is less able to suppress volume changes due to charging and discharging compared to the silicon clathrate type II crystalline phase. However, in some cases, the volume change due to charging and discharging can be suppressed if the electrode active material contains a small amount of the diamond-type silicon crystalline phase.

[0020] The electrode active material in this disclosure has a silicon clathrate type II crystalline phase. The five-membered ring size of the silicon clathrate type II crystalline phase is typically 3.752 Å or more and 3.780 Å or less, but may also be 3.755 Å or more and 3.775 Å or less. Having the five-membered ring size within a predetermined range results in an electrode active material with small volume changes due to charging and discharging. The five-membered ring size is determined by performing Rietveld analysis on XRD measurement results, creating a crystal model based on atomic position information, and calculating the interatomic distances in the crystal model. Specifically, the maximum length of the diagonal of the five-membered ring is defined as the five-membered ring size.

[0021] In this disclosure, the electrode active material preferably has a silicon clathrate type II crystalline phase as its main phase. "Main phase" refers to the peak belonging to that crystalline phase that has the highest diffraction intensity among the peaks observed in X-ray diffraction measurements. The proportion of silicon clathrate type II crystalline phase in the electrode active material is, for example, 80% by weight or more, may be 85% by weight or more, 90% by weight or more, or 95% by weight or more. Furthermore, the proportion of silicon clathrate type II crystalline phase in the electrode active material may be 100% by weight or less than 100% by weight. The proportion of the crystalline phase can be determined by performing Rietveld analysis on the XRD measurement results and using the RIR method (Reference Intensity Ratio method).

[0022] The electrode active material in this disclosure may or may not have a silicon clathrate type I crystalline phase. "Not having a crystalline phase" means that the peak of the crystalline phase is not detected in X-ray diffraction measurements.

[0023] The electrode active material in this disclosure may or may not have a diamond-type silicon crystalline phase. The proportion of the diamond-type silicon crystalline phase contained in the electrode active material may be, for example, 0% by weight, greater than 0% by weight, or 0.2% by weight or more. On the other hand, the proportion of the diamond-type silicon crystalline phase contained in the electrode active material may be, for example, 5% by weight or less, or 3% by weight or less.

[0024] The composition of the electrode active material in this disclosure is not particularly limited, but Na x Si 136 It is preferable that the expression be expressed as (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.

[0025] The electrode active material in this disclosure may be primary particles or secondary particles formed by aggregation of primary particles. The average particle size (D) of the electrode active material. 50 ) is not particularly limited, but for example, it may be 0.1 μm or more and 50 μm or less, or 0.5 μm or more and 30 μm or less. Average particle size (D 50 This can be calculated, for example, from measurements taken using a scanning electron microscope (SEM).

[0026] The electrode active material preferably has voids inside the primary particles. The void ratio is, for example, 4% or more, and may be 10% or more. Alternatively, the void ratio may be, for example, 40% or less, and may be 20% or less. The void ratio can be determined by the following procedure, for example. First, a cross-section is made of the electrode layer containing the electrode active material by ion milling. Then, the cross-section is observed with an SEM (scanning electron microscope) to obtain a photograph of the particles. From the obtained photograph, the silicon portion and the void portion are separated using image analysis software and binarized. The area of ​​the silicon portion and the void portion is determined, and the void ratio (%) is calculated from the following formula. Porosity (%) = 100 × (Area of ​​voids) / ((Area of ​​silicon) + (Area of ​​voids))

[0027] The electrode active material in this disclosure is typically used in batteries. The electrode active material in this disclosure may be a negative electrode active material or a positive electrode active material, but the former is preferred.

[0028] The method for producing the electrode active material is not particularly limited, but it is preferable to have an alloying step of reacting a Na source and a Si source to obtain a Na-Si alloy, and a sintering step of sintering the Na-Si alloy to reduce the amount of Na in the Na-Si alloy and generate a silicon clathrate type II crystalline phase.

[0029] The alloying process involves reacting a Na source and a Si source to obtain a Na-Si alloy. The Si source is, for example, elemental Si. Preferably, the Si source is porous Si, which has many voids inside the primary particles. On the other hand, the Na source contains at least Na. Examples of Na sources include metallic Na, NaH, and a metallic Na dispersion in which metallic Na particles are dispersed in oil.

[0030] One method for obtaining a Na-Si alloy by reacting a Na source and a Si source is to heat a mixture containing the Na source and the Si source. The heating temperature is, for example, 300°C or higher, but may also be 310°C or higher, 320°C or higher, or 340°C or higher. On the other hand, the heating temperature may be, for example, 800°C or lower, but may also be 600°C or lower, or 450°C or lower.

[0031] The Na-Si alloy preferably has a zintl phase, and more preferably has the zintl phase as the main phase. The composition of the Na-Si alloy is not particularly limited, however, Na z Si 136 It is preferable that the composition be expressed as (121 ≤ z ≤ 151).

[0032] The firing process involves firing the above Na-Si alloy to reduce the amount of Na in the alloy and generate a silicon clathrate type II crystalline phase. In the firing process, it is preferable to adjust the firing conditions so that the size of the five-membered rings of the silicon clathrate type II crystalline phase is between 3.752 Å and 3.780 Å.

[0033] The size of the five-membered ring may correlate with the crystallite size of the silicon clathrate type II crystal phase. Furthermore, the crystallite size can be controlled by adjusting the firing conditions. Specifically, the crystallite size can be adjusted by considering the balance between nucleation and nucleation growth during firing. This balance can be controlled, for example, by the firing temperature. Here, in order to form a silicon clathrate type II crystal phase from the jintol phase contained in the Na-Si alloy, firing at a relatively high temperature is necessary. Specifically, the Na-Si alloy needs to be fired at a temperature of 340°C or higher. On the other hand, when firing is performed at a temperature of 340°C or higher, nucleation growth of the silicon clathrate type II crystal phase takes precedence over nucleation of the silicon clathrate type II crystal phase, so the crystallite size of the silicon clathrate type II crystal phase tends to be larger. As a result, the size of the five-membered ring also tends to be larger.

[0034] In contrast, by firing at a temperature below 340°C before firing at a temperature above 340°C, nucleation takes precedence over nucleation growth, and the crystallite size can be reduced. As a result, the size of the five-membered rings also tends to be smaller. In other words, it is preferable that the firing process comprises at least a first firing treatment in which the Na-Si alloy is fired at a temperature below 340°C, and a second firing treatment in which the compound that has undergone the first firing treatment is fired at a temperature of 340°C or higher.

[0035] The first firing process involves firing the Na-Si alloy at a temperature of less than 340°C. In the first firing process, the scavenging agent described later may or may not be used. The firing temperature in the first firing process is usually less than 340°C, may be less than 310°C, or may be 300°C or lower. On the other hand, the firing temperature in the first firing process is, for example, 250°C or higher, may be 270°C or higher, or may be 280°C or higher. The firing time in the first firing process is, for example, 1 hour or more and 50 hours or less, or 5 hours or more and 30 hours or less.

[0036] The second calcination treatment is a process in which the compound that has undergone the first calcination treatment is calcined at a temperature of 340°C or higher. In the second calcination treatment, it is preferable to use a scavenging agent, which will be described later, and in particular, it is preferable to use AlF3. The calcination temperature in the second calcination treatment is usually 340°C or higher, but may also be 360°C or higher. On the other hand, the calcination temperature in the second calcination treatment may also be, for example, 450°C or lower. The calcination time in the second calcination treatment is, for example, 1 hour or more and 120 hours or less, and may also be 10 hours or more and 80 hours or less. It is preferable that the compound that has undergone the second calcination treatment has a silicon clathrate type II crystalline phase.

[0037] The calcination process may include a third calcination treatment in which the compound that has undergone the second calcination treatment is calcined at a temperature of 340°C or higher. In the third calcination treatment, it is preferable to use a scavenger described later, and in particular, it is preferable to use ZnCl2. The calcination temperature in the third calcination treatment is usually 340°C or higher, and may be 360°C or higher. On the other hand, the calcination temperature in the third calcination treatment may be, for example, 450°C or lower. The calcination time in the third calcination treatment is, for example, 1 hour or more and 120 hours or less, and may be 10 hours or more and 80 hours or less. It is preferable that the compound that has undergone the third calcination treatment has a silicon clathrate type II crystalline phase as its main phase.

[0038] In the firing process, it is preferable to use a scavenging agent that captures Na in the Na-Si alloy. An example of a scavenging agent is a Na getter agent that reacts with the Na vapor generated from the Na-Si alloy. The Na getter agent is positioned, for example, without contact with the Na-Si alloy. Examples of Na getter agents include SiO, MoO3, FeO, and Fe3O4. When using a Na getter agent, it is preferable to carry out the firing process in a reduced-pressure atmosphere.

[0039] Other examples of scavenging agents include Na trapping agents that directly react with Na-Si alloys to accept Na. The Na trapping agent is positioned, for example, in contact with the Na-Si alloy. Examples of Na trapping agents include CaCl2, AlF3, CaBr2, CaI2, Fe3O4, FeO, MgCl2, ZnO, ZnCl2, and MnCl2. When using a Na trapping agent, the firing process may be carried out under a reduced pressure atmosphere or under normal pressure.

[0040] Furthermore, the balance between nucleation and nucleation growth during firing can be controlled, for example, by the type, particle size, and amount of the scavenging agent. For instance, reducing the particle size of the Na trapping agent increases the contact area between the Na trapping agent and the Na-Si alloy. This makes it easier for Na to be extracted from the Na-Si alloy, prioritizing nucleation over nucleation growth, and allowing for adjustment to a smaller crystallite size. On the other hand, if the contact area between the Na trapping agent and the Na-Si alloy increases too much, it is presumed that a diamond-type silicon crystal phase, which is more stable than the silicon clathrate type II crystal phase, is more likely to form.

[0041] B. Electrode composite material The electrode composite material in this disclosure contains the above-described electrode active material and at least one of a conductive material and a binder.

[0042] According to this disclosure, by using the electrode active material described above, an electrode composite material with small volume changes due to charging and discharging is obtained.

[0043] The electrode mixture contains an electrode active material and at least one of a conductive material and a binder. The electrode active material is the same as described in "A. Electrode Active Material" above. The electrode active material may be a negative electrode active material or a positive electrode active material, but the former is preferred. That is, the electrode mixture may be a negative electrode mixture or a positive electrode mixture, but the former is preferred.

[0044] The proportion of electrode active material in the electrode mixture is, for example, 20% by weight or more, but may also be 30% by weight or more, or 40% by weight or more. If the proportion of electrode active material is too low, a sufficient energy density may not be obtained. On the other hand, the proportion of electrode active material is, for example, 80% by weight or less, but may also be 70% by weight or less, or 60% by weight or less. If the proportion of electrode active material is too high, the ionic conductivity and electronic conductivity of the electrode mixture may relatively decrease.

[0045] The electrode composite material contains at least one of a conductive material and a binder. Examples of conductive materials include carbon materials, metal particles, and conductive polymers. Examples of carbon materials include particulate carbon materials such as acetylene black (AB) and Ketjenblack (KB), and fibrous carbon materials such as carbon fibers, carbon nanotubes (CNTs), and carbon nanofibers (CNFs). Examples of binders include rubber-based binders and fluoride-based binders.

[0046] The electrode composite may further contain a solid electrolyte. Examples of solid electrolytes include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes, and 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. The sulfide solid electrolyte may further contain at least one of O and halogen elements. Examples of halogen elements include F, Cl, Br, and I. The sulfide solid electrolyte may 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. The electrode mixture may also contain a dispersion medium.

[0047] One method for preparing an electrode composite is to mix an electrode active material with at least one of a conductive material and a binder.

[0048] C.Battery Figure 2 is a schematic cross-sectional view illustrating a battery in this disclosure. The battery 10 shown in Figure 2 includes a positive electrode layer 1, a negative electrode layer 2, an electrolyte layer 3 disposed between the positive electrode layer 1 and the negative electrode layer 2, a positive electrode current collector 4 for collecting current from the positive electrode layer 1, and a negative electrode current collector 5 for collecting current from the negative electrode layer 2. In this disclosure, either the positive electrode layer 1 or the negative electrode layer 2 contains the electrode mixture described in "B. Electrode Mixture" above.

[0049] According to this disclosure, by using the electrode composite material described above, a battery with small volume changes due to charging and discharging can be obtained. As described above, the electrode composite material may be either a negative electrode composite material or a positive electrode composite material, but the former is preferred. The details of the battery will be described below in the case where the electrode composite material is a negative electrode composite material.

[0050] 1. Negative electrode layer The negative electrode layer in this disclosure contains the electrode mixture (negative electrode mixture) described above. The electrode mixture is the same as described in "B. Electrode Mixture" above, so its description is omitted here. The negative electrode layer may also contain an electrolyte as needed. The electrolyte is the same as described in "3. Electrolyte Layer". The thickness of the negative electrode layer is, for example, 0.1 μm or more and 1000 μm or less, and may be 0.1 μm or more and 500 μm or less, or 0.1 μm or more and 100 μm or less. As a method for forming the negative electrode layer, for example, a method of coating the electrode mixture (negative electrode mixture) onto the negative electrode current collector can be mentioned.

[0051] 2. Positive electrode layer The positive electrode layer is a layer containing at least a positive electrode active material. The positive electrode layer may also optionally contain at least one of an electrolyte, a conductive material, and a binder.

[0052] Examples of the positive electrode active material include oxide active materials. Examples of the oxide active materials include rock salt layer-structured active materials such as LiCoO2, LiMnO2, LiNiO2, LiVO2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 and the like, spinel-type active materials such as LiMn2O4, Li4Ti5O 12 、Li(Ni 0.5 Mn 1.5 )O4 and the like, and olivine-type active materials such as LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4.

[0053] A coating layer containing a Li-ion conductive oxide may be formed on the surface of the oxide active material. This is because it can suppress the reaction between the oxide active material and the solid electrolyte (especially a sulfide solid electrolyte). Examples of the Li-ion conductive oxide include LiNbO3. The thickness of the coating layer is, for example, 1 nm or more and 30 nm or less. Further, for example, Li2S can also be used as the positive electrode active material.

[0054] The electrolyte used for the positive electrode layer is the same as the content described in "3. Electrolyte layer". Further, since the conductive material and the binder used for the positive electrode layer are the same as the content described in the above "B. Electrode composite material", the description here is omitted. The thickness of the positive electrode layer is, for example, 0.1 μm or more and 1000 μm or less, may be 0.1 μm or more and 500 μm or less, or may be 0.1 μm or more and 100 μm or less.

[0055] 3. Electrolyte layer The electrolyte layer is a layer formed between the positive electrode layer and the negative electrode layer and contains at least an electrolyte. The electrolyte may be a solid electrolyte or a liquid electrolyte (electrolyte solution).

[0056] The solid electrolyte is the same as described in "B. Electrode Mixture" above, so it will not be described here. On the other hand, the electrolyte solution preferably contains a support salt and a solvent. A known electrolyte solution can be used as the electrolyte solution. The thickness of the electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less, and may be 0.1 μm or more and 500 μm or less, or 0.1 μm or more and 100 μm or less.

[0057] 4. Other configurations The battery in this disclosure preferably has a positive electrode current collector for collecting current from the positive electrode layer and a negative electrode current collector for collecting current from the negative electrode layer. Examples of materials for the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. On the other hand, examples of materials for the negative electrode current collector include SUS, copper, nickel, and carbon.

[0058] The battery in this disclosure may further include a restraining jig that applies restraining pressure along the thickness direction to the positive electrode layer, electrolyte layer, and negative electrode layer. In particular, when the electrolyte layer is a solid electrolyte layer, it is preferable to apply restraining pressure in order to form good ion conduction paths and electron conduction paths. The restraining pressure may be, for example, 0.1 MPa or more, 1 MPa or more, or 5 MPa or more. On the other hand, the restraining pressure may be, for example, 100 MPa or less, 50 MPa or less, or 20 MPa or less.

[0059] 5.Battery The type of battery described herein is not particularly limited, but is typically a lithium-ion battery. The battery described herein may be a liquid battery containing an electrolyte as the electrolyte layer, or an all-solid-state battery having a solid electrolyte layer. Furthermore, the battery described herein may be a primary battery or a secondary battery, but a secondary battery is preferred because it can be repeatedly charged and discharged, making it useful, for example, as an in-vehicle battery.

[0060] Applications of the battery include, for example, powering vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline cars, and diesel cars. It is particularly preferable for the battery to be used as a power source for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or battery electric vehicles (BEVs). The battery may also be used as a power source for other mobile devices (e.g., trains, ships, aircraft), or as a power source for electrical products such as information processing devices. Furthermore, the manufacturing method of the battery is not particularly limited, and known methods can be employed.

[0061] This disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of this disclosure and achieves similar effects is included within the technical scope of this disclosure. [Examples]

[0062] [Example 1] Under an Ar atmosphere, weigh out metallic Li and Si powder (manufactured by Kojun Kagaku Co., Ltd., SIEPB32) in a molar ratio of 4:1, and mix in a mortar for 1 hour. 15 A Li-Si alloy containing a Si4 phase was obtained. The obtained Li-Si alloy was reacted with ethanol under an Ar atmosphere. Subsequently, acetic acid was added, and the liquid and solid components were separated by filtration. The separated solid component was vacuum-dried at 120°C to obtain powdered porous Si.

[0063] The obtained porous Si and NaH, which is the Na source, were weighed in a molar ratio of NaH / porous Si = 1.1 / 1 and mixed using a cutter mill. The resulting mixture was placed in a reaction vessel and calcined under conditions of Ar atmosphere, 475°C, and 10 hours to obtain a Na-Si alloy.

[0064] The obtained Na-Si alloy was mixed with AlF3, a Na trapping agent. The AlF3 used was classified using a sieve with a mesh size of 35 μm and a sieve with a mesh size of 75 μm. The resulting mixture underwent a first calcination treatment under an Ar atmosphere at 290°C for 10 hours, followed by a second calcination treatment under an Ar atmosphere at 340°C for 40 hours. The resulting compound was then placed in a 6 wt% HNO3 aqueous solution and stirred for 1 hour. The stirred compound was then filtered, and the solid content was dried at 120°C for 12 hours to obtain a powder.

[0065] The obtained powder and zinc chloride (ZnCl2) were weighed in a molar ratio of powder:ZnCl2 = 6:1 and mixed using a cutter mill. The resulting mixture was subjected to a third calcination treatment under an Ar atmosphere at 345°C for 15 hours. Subsequently, the obtained compound was placed in a 6% by weight aqueous solution of HNO3 and stirred for 1 hour. After that, the stirred compound was filtered, and the solid content was dried at 120°C for 12 hours to obtain a powder.

[0066] The obtained powder was placed in a 3% by weight aqueous solution of hydrogen fluoride (HF) and stirred for 3 hours. The stirred compound was then filtered by suction, and the solids were dried at 120°C for 12 hours to obtain a powder. After drying, the obtained powder was placed in acetone, and coarse particles were removed using a resin sieve to obtain the electrode active material.

[0067] [Example 2] An electrode active material was obtained in the same manner as in Example 1, except that the second firing treatment was carried out under the conditions of an Ar atmosphere, 340°C, and 80 hours.

[0068] [Example 3] An electrode active material was obtained in the same manner as in Example 1, except that the second firing treatment was carried out under the conditions of an Ar atmosphere, 340°C, and 60 hours.

[0069] [Example 4] An electrode active material was obtained in the same manner as in Example 1, except that the first firing treatment was carried out under conditions of Ar atmosphere, 280°C, and 10 hours, and the second firing treatment was carried out under conditions of Ar atmosphere, 340°C, and 20 hours.

[0070] [Example 5] An electrode active material was obtained in the same manner as in Example 1, except that the first firing treatment was carried out under conditions of Ar atmosphere, 280°C, and 10 hours, and the second firing treatment was carried out under conditions of Ar atmosphere, 340°C, and 100 hours.

[0071] [Comparative Example 1] An electrode active material was obtained in the same manner as in Example 1, except that the first firing treatment was carried out under conditions of Ar atmosphere, 340°C, and 10 hours, and the second firing treatment was carried out under conditions of Ar atmosphere, 340°C, and 120 hours.

[0072] [Comparative Example 2] AlF3 was placed in a container with crushed balls (φ1 μm) and pulverized using a planetary ball mill (Fritsch) at 200 rpm for 3 hours. An electrode active material was obtained in the same manner as in Example 1, except that the first calcination treatment was carried out in an Ar atmosphere at 310°C for 10 hours, and the second calcination treatment was carried out in an Ar atmosphere at 340°C for 10 hours.

[0073] [Comparative Example 3] An electrode active material was obtained in the same manner as in Example 1, except that the first firing treatment was carried out under conditions of Ar atmosphere, 360°C, and 10 hours, and the second firing treatment was carried out under conditions of Ar atmosphere, 360°C, and 100 hours.

[0074] [evaluation] (XRD measurement) X-ray diffraction (XRD) measurements using CuKα radiation were performed on the electrode active materials obtained in Examples 1-5 and Comparative Examples 1-3. As a result, it was confirmed that all electrode active materials had a silicon clathrate type II crystalline phase as the main phase.

[0075] In the silicon clathrate type II crystalline phase, the intensity of peak A located around 2θ = 20.09° is defined as I A Let the intensity of peak B, located around 2θ = 31.72°, be I B Furthermore, the maximum intensity at 2θ = 22° to 23° was defined as I.M To, I A / I M and I B / I M This was determined. As a result, the electrode active materials obtained in Examples 1-5 and Comparative Examples 1-3 were all I A / I M If it is greater than 1, B / I M It was also greater than 1.

[0076] Rietveld analysis was performed using XRD analysis software (PDXL, RIGAKU Corporation). Furthermore, a crystal model based on atomic position information was created, and the interatomic distances in the crystal model were calculated. The maximum length of the diagonal of the five-membered ring was defined as the five-membered ring size of the silicon clathrate type II crystal phase. The results are shown in Table 1. In addition, the electrode active materials obtained in Examples 1-5 and Comparative Examples 1-3 all contained a small amount of diamond-type silicon crystal phase. The proportion of diamond-type silicon crystal phase (crystalline Si content) was determined using the Rietveld analysis results and the RIR method. The results are shown in Table 1.

[0077] (SEM observation) The average particle size (D) of the electrode active material obtained in Examples 1-5 and Comparative Examples 1-3 50 The average particle size D of all electrode active materials was determined by observation using a scanning electron microscope (SEM). As a result, the average particle size D of all electrode active materials was 50 The average particle size of the electrode active material (D 50 The particle size is preferably 0.5 μm or more and 5 μm or less.

[0078] (Measurement of volumetric expansion coefficient) All-solid-state batteries were fabricated using the electrode active materials obtained in Examples 1-5 and Comparative Examples 1-3 as negative electrode active materials. The fabrication methods are as follows.

[0079] (1) Fabrication of the negative electrode In a polypropylene container, the obtained electrode active material, a butyl butyrate solution containing a sulfide solid electrolyte (Li2S-P2S5 glass ceramic), a conductive material (VGCF), and a PVDF binder in a proportion of 5% by weight, and butyl butyrate were added and stirred for 30 seconds using an ultrasonic disperser (SMT UH-50). Next, the container was shaken for 30 minutes using a shaker (Shibata Scientific Co., Ltd., TTM-1). Using an applicator, the mixture was coated onto a negative electrode current collector (Cu foil, UACJ) by the blade method and dried on a hot plate at 100°C for 30 minutes. This yielded a negative electrode having a negative electrode current collector and a negative electrode layer.

[0080] (2) Preparation of the positive electrode A polypropylene container contains a positive electrode active material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 A butyl butyrate solution containing 5% by weight of O2 (average particle size 6 μm), sulfide solid electrolyte (Li2S-P2S5 glass ceramic), conductive material (VGCF), and PVDF binder, and butyl butyrate were added and stirred for 30 seconds using an ultrasonic disperser (SMT UH-50). Next, the container was shaken for 3 minutes using a shaker (Shibata Scientific Co., Ltd., TTM-1), then stirred again for 30 seconds using the ultrasonic disperser, and shaken again for 3 minutes using the shaker. Using an applicator, the solution was coated onto a positive electrode current collector (Al foil, Showa Denko) using the blade method and dried on a hot plate at 100°C for 30 minutes. This yielded a positive electrode having a positive electrode current collector and a positive electrode layer. The area of ​​the positive electrode was made smaller than the area of ​​the negative electrode.

[0081] (3) Preparation of the solid electrolyte layer A heptane solution containing a sulfide solid electrolyte (Li2S-P2S5 glass ceramic), a butylene rubber binder in a ratio of 5% by weight, and heptane were added to a polypropylene container and stirred for 30 seconds using an ultrasonic disperser (SMT UH-50). Next, the container was shaken for 30 minutes using a shaker (Shibata Scientific Co., Ltd., TTM-1). Using an applicator, the mixture was coated onto a release sheet (Al foil) using the blade method and dried on a hot plate at 100°C for 30 minutes. This yielded a transfer member having a release sheet and a solid electrolyte layer.

[0082] (4) Fabrication of all-solid-state batteries A solid electrolyte layer for bonding was placed on the positive electrode layer of the positive electrode, set in a roll press machine, and pressed at 100 kN / cm and 165°C. This yielded the first laminate.

[0083] Next, the negative electrode was placed in a roll press and pressed at 60 kN / cm and 25°C. This obtained a pressed negative electrode. Then, the solid electrolyte layer for bonding and the transfer member were placed in order from the negative electrode layer side. At this time, the solid electrolyte layer for bonding and the solid electrolyte layer in the transfer member were positioned to face each other. The resulting laminate was placed in a planar uniaxial press and pre-pressed at 100 MPa and 25°C for 10 seconds. After that, the release sheet was peeled off from the solid electrolyte layer. This obtained a second laminate.

[0084] Next, the solid electrolyte layer for bonding in the first laminate and the solid electrolyte layer in the second laminate were placed facing each other, set in a planar uniaxial press, and pressed for 1 minute at 200 MPa and 120°C. This resulted in obtaining an all-solid-state battery.

[0085] (5) Measurement of volume expansion coefficient The obtained all-solid-state batteries were charged, and their volume expansion rate was measured. The test conditions were a confinement pressure (standard size) of 5 MPa, a charge of 0.1 C, and a cut-off voltage of 4.55 V. The confinement pressure at 4.55 V was measured, and the increase in confinement pressure from the pre-charging state was determined to calculate the volume expansion rate. The results are shown in Table 1 and Figure 3. Note that the volume expansion rate results in Table 1 and Figure 3 are relative values ​​with the result of Comparative Example 1 set to 100.

[0086] [Table 1]

[0087] As shown in Table 1, although Example 3 and Comparative Example 1 had similar amounts of crystalline Si, there were significant differences in their volume expansion coefficients. Furthermore, as shown in Table 1 and Figure 3, it was confirmed that Examples 1-5 had smaller volume expansion coefficients compared to Comparative Examples 1-3. Thus, by keeping the 5-membered ring size within a predetermined range, a reduction in volume expansion coefficient was achieved. [Explanation of Symbols]

[0088] 1 ... Positive electrode layer 2 ... Negative electrode layer 3...electrolyte layer 4...Positive electrode current collector 5...Negative electrode current collector 10...battery

Claims

1. An electrode active material having a silicon clathrate type II crystalline phase, An electrode active material in which the size of the five-membered ring in the crystalline phase is 3.752 Å or more and 3.780 Å or less.

2. The electrode active material according to claim 1, wherein the electrode active material has voids inside the primary particles.

3. An electrode composite comprising the electrode active material according to claim 1 or claim 2, and at least one of a conductive material and a binder.

4. A battery having a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer, A lithium-ion battery comprising the positive electrode layer or the negative electrode layer containing the electrode composite material described in claim 3.

5. The lithium-ion battery according to claim 4, wherein the electrolyte layer contains a solid electrolyte.

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