Electrode active material, electrode mixture and battery

Abstract

To provide an electrode active material that undergoes small volumetric change upon charging and discharging.SOLUTION: An electrode active material has a silicon clathrate II type crystalline phase, and the electrode active material has a zeta potential of -110 mV or more and -35 mV or less, obtained by measurement using diisobutyl ketone.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an electrode active material, an electrode mixture, and a battery. [Background technology]

[0002] In recent years, the development of batteries has been actively pursued. For example, in the automotive industry, development of batteries for use in electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), or hybrid electric vehicles (HEVs) is underway. In addition, 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 II type crystalline phase and having voids inside the primary particles. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-158004 Summary of the Invention [Problem to be solved by the invention]

[0004] Silicon has a large theoretical capacity and is effective in increasing the energy density of batteries. However, its volume changes significantly during charging and discharging. This large volume change can lead to problems such as a deterioration in the functionality of the electrode active material after repeated charging and discharging.

[0005] The present disclosure has been made in view of the above circumstances, and has as its main object to provide an electrode active material that undergoes little volume change upon charge and discharge. [Means for solving the problem]

[0006] [1] An electrode active material having a silicon clathrate II type crystalline phase, The electrode active material has a zeta potential of −110 mV or more and −35 mV or less, as determined by measurement using diisobutyl ketone.

[0007] [2] The electrode active material has voids inside the primary particles. [1]

[0008] [3] An electrode mixture comprising the electrode active material according to [1] or [2] and at least one of a conductive material and a binder.

[0009] [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, The battery, wherein the positive electrode layer or the negative electrode layer contains the electrode mixture according to [3].

[0010] [5] The battery according to [4], wherein the electrolyte layer contains a solid electrolyte. [Effects of the Invention]

[0011] The present disclosure has an effect of being able to obtain an electrode active material that undergoes little volume change upon charge and discharge. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a schematic perspective view illustrating the crystalline phase of Si. [Figure 2] FIG. 1 is a schematic cross-sectional view illustrating a battery according to the present disclosure. [Figure 3] 1 shows the results of the volume expansion rate of batteries using the electrode active materials obtained in Examples 1 to 4 and Comparative Examples 1 and 2. DETAILED DESCRIPTION OF THE INVENTION

[0013] The electrode active material, electrode mixture, and battery according to the present disclosure will be described in detail below.

[0014] A. Electrode active material The electrode active material according to the present disclosure has a silicon clathrate II crystal phase. Furthermore, the zeta potential of the electrode active material, as measured using diisobutyl ketone, is typically −110 mV or more and −35 mV or less.

[0015] According to the present disclosure, since the zeta potential of the electrode active material is within a predetermined range, the electrode active material exhibits small volume change upon charge and discharge. As described above, Si has a large theoretical capacity and is effective in increasing the energy density of batteries. On the other hand, Si exhibits large volume change upon charge and discharge. If the volume change upon charge and discharge is large, there is a problem that the function of the electrode active material is likely to deteriorate when the electrode active material is repeatedly charged and discharged.

[0016] Here, the electrode active material according to the present disclosure has a silicon clathrate II crystalline phase. As shown in FIG. 1(a), in the silicon clathrate II crystalline phase, multiple Si elements form polyhedra (cages) containing pentagons or hexagons. These polyhedra have spaces inside that can encapsulate metal ions such as Li ions. The insertion of metal ions into these spaces can suppress volumetric changes due to charge and discharge. In particular, in all-solid-state batteries, a high confining pressure is generally required to suppress volumetric changes due to charge and discharge. However, the use of the electrode active material according to the present disclosure can reduce the confining pressure, thereby suppressing the need for a large confining jig.

[0017] On the other hand, a Na-Si alloy containing Na and Si is used as a precursor of an electrode active material having a silicon clathrate II crystalline phase, for example. By removing Na from the Na-Si alloy while firing the Na-Si alloy, a silicon clathrate II crystalline phase is generated. If a large amount of Na remains in the electrode active material, Na remains in the cages of the silicon clathrate II crystalline phase, reducing the space available for encapsulating metal ions such as Li ions. Therefore, it is preferable that the amount of Na remaining in the electrode active material is small. Meanwhile, the present inventors have discovered a new finding that even when the amount of Na remaining in electrode active materials is similar, differences occur in volume change during charge and discharge. In other words, they have discovered a phenomenon that cannot be explained solely by the amount of Na remaining in the electrode active material. Therefore, the present inventors have conducted a detailed investigation into the cause of this difference and discovered that the zeta potential of the electrode active material has a significant impact on volume change during charge and discharge.

[0018] Specifically, the inventors have found that adjusting the zeta potential of an electrode active material within a predetermined range can suppress volume change during charge and discharge. It is believed that the reason for this suppression of volume change is that adjusting the zeta potential of the electrode active material within a predetermined range can suppress reaction unevenness due to aggregation. Here, the zeta potential is an index for evaluating the charged state (surface charge state) of particle surfaces. If the zeta potential of an electrode active material is too low, particles of the electrode active material tend to aggregate. On the other hand, if the zeta potential of an electrode active material is too low, the electrode active material and other compounds (e.g., solid electrolytes) tend to aggregate. In contrast, in the present disclosure, adjusting the zeta potential of the electrode active material within a predetermined range can suppress aggregation. As a result, it is possible to suppress a decrease in the dispersibility of each component in the electrode mixture, thereby enabling the production of a uniform electrode layer and suppressing an increase in volume change during charge and discharge due to reaction unevenness.

[0019] As shown in Figure 1(a), in the crystalline phase of silicon clathrate II, multiple Si elements form polyhedra (cages) including pentagons and hexagons. On the other hand, as shown in Figure 1(b), in the crystalline phase of diamond-type silicon, multiple Si elements form tetrahedra. Because tetrahedra do not have internal spaces that can encapsulate metal ions such as Li ions, the crystalline phase of diamond-type silicon is less able to suppress volume changes during charge and discharge than the crystalline phase of silicon clathrate II. Therefore, electrode active materials having a crystalline phase of silicon clathrate II have the advantage of being more able to suppress volume changes during charge and discharge than electrode active materials having a crystalline phase of diamond-type silicon.

[0020] The electrode active material according to the present disclosure has a zeta potential, as determined by measurement using diisobutyl ketone, of typically −110 mV or more and −35 mV or less, and may also be −95 mV or more and −45 mV or less. The method for measuring the zeta potential will be described in the Examples below.

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

[0022] The electrode active material in the present disclosure may or may not have a silicon clathrate I crystalline phase. "Not having a crystalline phase" means that no peak of the crystalline phase is confirmed in X-ray diffraction measurement. Similarly, the electrode active material in the present disclosure may or may not have a diamond-type silicon crystalline phase.

[0023] The composition of the electrode active material in the present disclosure is not particularly limited, but may include Na x Si 136 It is preferably 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. The Na content in the electrode active material may be 0 wt % or more. In the latter case, the Na content in the electrode active material may be, for example, 0.1 wt % or more, 0.5 wt % or more, or 1.0 wt % or more. On the other hand, the Na content in the electrode active material may be, for example, 10 wt % or less, 5 wt % or less, or 3 wt % or less.

[0024] The electrode active material in the present disclosure may be in the form of primary particles or secondary particles formed by aggregation of primary particles. 50 The average particle size (D) is not particularly limited, but may be, for example, 0.1 μm or more and 50 μm or less, or 0.5 μm or more and 30 μm or less. 50 ) can be calculated, for example, from measurements using a scanning electron microscope (SEM).

[0025] 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. The void ratio is, for example, 40% or less, and may be 20% or less. The void ratio can be determined, for example, by the following procedure. First, a cross section of an electrode layer containing the electrode active material is obtained by ion milling. The cross section is then observed with a scanning electron microscope (SEM) to obtain a photograph of the particles. From the obtained photograph, the silicon portion and the void portion are clearly distinguished using image analysis software and binarized. The areas of the silicon portion and the void portion are determined, and the void ratio (%) is calculated using the following formula. Porosity (%) = 100 × (area of ​​void part) / ((area of ​​silicon part) + (area of ​​void part))

[0026] The electrode active material of the present disclosure is generally used in batteries. The electrode active material of the present disclosure may be either a negative electrode active material or a positive electrode active material, but the former is preferred. Furthermore, the electrode active material preferably does not have a coating layer that covers the silicon clathrate II crystal phase.

[0027] The method for producing the electrode active material is not particularly limited, but preferably includes an alloying step in which a Na source and a Si source are reacted to obtain a Na-Si alloy, and a firing step in which the Na-Si alloy is fired to reduce the amount of Na in the Na-Si alloy and produce a silicon clathrate type II crystalline phase.

[0028] The alloying step is a step of reacting a Na source and a Si source to obtain a Na-Si alloy. The Si source is, for example, elemental Si. The Si source is preferably porous Si having many voids inside the primary particles. On the other hand, the Na source contains at least Na. Examples of the Na source include metallic Na, NaH, and a metallic Na dispersion in which metallic Na particles are dispersed in oil.

[0029] A method for obtaining a Na-Si alloy by reacting a Na source and a Si source includes, for example, heating a mixture containing a Na source and a Si source. The heating temperature is, for example, 300°C or higher, or may be 310°C or higher, 320°C or higher, or 340°C or higher. On the other hand, the heating temperature is, for example, 800°C or lower, or may be 600°C or lower, or may be 450°C or lower.

[0030] The Na-Si alloy preferably has a Zintl phase, and preferably has the Zintl phase as the main phase. The composition of the Na-Si alloy is not particularly limited, but z Si 136 It is preferable that the composition be represented by (121≦z≦151).

[0031] The calcination step is a step of calcining the Na-Si alloy to reduce the amount of Na in the Na-Si alloy and generate a silicon clathrate II crystalline phase. In the calcination step, it is preferable to adjust the calcination conditions so that the zeta potential of the electrode active material is −110 mV or more and −35 mV or less.

[0032] The zeta potential of the electrode active material may be correlated with the Na desorption rate. Specifically, the zeta potential tends to decrease as the Na desorption rate increases. For example, the zeta potential tends to decrease when the firing temperature is increased, the firing time is extended, or the amount of a scavenger (described later) is increased. The firing temperature of the Na-Si alloy is, for example, 300°C or higher and 400°C or lower. The firing time of the Na-Si alloy is, for example, 5 hours or higher and 120 hours or lower.

[0033] In the firing step, it is preferable to use a scavenger that captures Na in the Na-Si alloy. One example of the scavenger is a Na getter agent that reacts with Na vapor generated from the Na-Si alloy. The Na getter agent is disposed, for example, without contacting the Na-Si alloy. Examples of the Na getter agent include SiO, MoO, and FeO. When a Na getter agent is used, it is preferable to perform the firing step in a reduced pressure atmosphere.

[0034] Another example of a scavenger is a Na-trapping agent that directly reacts with the Na-Si alloy to receive Na. The Na-trapping agent is placed in contact with the Na-Si alloy. Examples of the Na-trapping agent include CaCl2, AlF3, CaBr2, CaI2, Fe3O4, FeO, MgCl2, ZnO, ZnCl2, and MnCl2. When using a Na-trapping agent, the firing process may be performed in a reduced pressure atmosphere or in an atmospheric pressure atmosphere.

[0035] B. Electrode composite material The electrode mixture in the present disclosure contains the above-described electrode active material and at least one of a conductive material and a binder.

[0036] According to the present disclosure, by using the above-described electrode active material, an electrode mixture that undergoes small volume change upon charging and discharging is obtained.

[0037] 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 that described above in "A. Electrode Active Material." The electrode active material may be either a negative electrode active material or a positive electrode active material, with the former being preferred. That is, the electrode mixture may be either a negative electrode mixture or a positive electrode mixture, with the former being preferred.

[0038] The proportion of the electrode active material in the electrode mixture is, for example, 20% by weight or more, or may be 30% by weight or more, or may be 40% by weight or more. If the proportion of the electrode active material is too low, sufficient energy density may not be obtained. On the other hand, the proportion of the electrode active material is, for example, 80% by weight or less, or may be 70% by weight or less, or may be 60% by weight or less. If the proportion of the electrode active material is too high, the ionic conductivity and electronic conductivity of the electrode mixture may relatively decrease.

[0039] The electrode mixture 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 ketjen black (KB), and fibrous carbon materials such as carbon fiber, carbon nanotubes (CNT), and carbon nanofibers (CNF). Examples of binders include rubber-based binders and fluoride-based binders.

[0040] The electrode mixture may further contain a solid electrolyte. Examples of the solid electrolyte include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes, and organic polymer electrolytes such as polymer electrolytes. Examples of the sulfide solid electrolyte 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 a halogen element. Examples of the halogen element 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 further contain a dispersion medium.

[0041] The electrode mixture may be prepared, for example, by mixing an electrode active material with at least one of a conductive material and a binder.

[0042] C.Battery Fig. 2 is a schematic cross-sectional view illustrating a battery according to the present disclosure. The battery 10 shown in Fig. 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 that collects current from the positive electrode layer 1, and a negative electrode current collector 5 that collects current from the negative electrode layer 2. In the present disclosure, the positive electrode layer 1 or the negative electrode layer 2 contains the electrode mixture described above in "B. Electrode mixture."

[0043] According to the present disclosure, by using the above-described electrode mixture, a battery with small volume change due to charging and discharging is obtained. As described above, the electrode mixture may be a negative electrode mixture or a positive electrode mixture, but the former is preferable. Below, details of the battery when the electrode mixture is a negative electrode mixture will be described.

[0044] 1. Negative electrode layer The negative electrode layer in the present disclosure contains the above-described electrode mixture (negative electrode mixture). The electrode mixture is the same as that described above in "B. Electrode mixture," and therefore will not be described here. The negative electrode layer may contain an electrolyte, if necessary. The electrolyte is the same as that 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, or 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. The negative electrode layer may be formed, for example, by coating the electrode mixture (negative electrode mixture) on a negative electrode current collector.

[0045] 2. Positive electrode layer The positive electrode layer is a layer containing at least a positive electrode active material, and may also contain at least one of an electrolyte, a conductive material, and a binder, as necessary.

[0046] Examples of the positive electrode active material include oxide active materials, such as LiCoO2, LiMnO2, LiNiO2, LiVO2, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc., rock salt layered active materials, LiMn2O4, Li4Ti5O 12 , Li(Ni 0.5 Mn 1.5 )O4, and olivine type active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4.

[0047] 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). An example of the Li-ion conductive oxide is LiNbO3. The thickness of the coating layer is, for example, 1 nm or more and 30 nm or less. Furthermore, Li2S, for example, can also be used as the positive electrode active material.

[0048] The electrolyte used in the positive electrode layer is the same as that described in "3. Electrolyte Layer." The conductive material and binder used in the positive electrode layer are the same as those described in "B. Electrode Composite" above, and therefore will not be described here. The thickness of the positive electrode layer is, for example, 0.1 μm or more and 1000 μm or less, or 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.

[0049] 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 (electrolytic solution).

[0050] The solid electrolyte is the same as that described above in "B. Electrode Composite Material," and therefore will not be described here. The electrolyte preferably contains a supporting salt and a solvent. A known electrolyte can be used as the electrolyte. The thickness of the electrolyte layer is, for example, 0.1 μm to 1000 μm, or may be 0.1 μm to 500 μm, or may be 0.1 μm to 100 μm.

[0051] 4. Other configurations The battery according to the present disclosure preferably includes a positive electrode current collector that collects current from the positive electrode layer and a negative electrode current collector that collects current from the negative electrode layer. Examples of materials for the positive electrode current collector include stainless steel, aluminum, nickel, iron, titanium, and carbon. On the other hand, examples of materials for the negative electrode current collector include stainless steel, copper, nickel, and carbon.

[0052] The battery of the present disclosure may further include a restraining jig that applies a restraining pressure to the positive electrode layer, the electrolyte layer, and the negative electrode layer in the thickness direction. In particular, when the electrolyte layer is a solid electrolyte layer, it is preferable to apply a restraining pressure to form good ion conduction paths and electron conduction paths. The restraining pressure is, for example, 0.1 MPa or more, or may be 1 MPa or more, or may be 5 MPa or more. Meanwhile, the restraining pressure is, for example, 100 MPa or less, or may be 50 MPa or less, or may be 20 MPa or less.

[0053] 5.Battery The type of battery in the present disclosure is not particularly limited, but is typically a lithium-ion battery. The battery in the present disclosure may be a liquid battery containing an electrolytic solution as an electrolyte layer, or an all-solid-state battery having a solid electrolyte layer as an electrolyte layer. The battery in the present disclosure may be a primary battery or a secondary battery, but a secondary battery is preferred because it can be repeatedly charged and discharged and is useful, for example, as an on-board battery.

[0054] Examples of uses of the battery include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles. In particular, it is preferable that the battery be used as a driving power source for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or electric vehicles (BEVs). The battery may also be used as a power source for mobile objects other than vehicles (for example, trains, ships, and aircraft), or as a power source for electrical appliances such as information processing devices. The method for manufacturing the battery is not particularly limited, and known methods can be used.

[0055] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Example]

[0056] [Example 1] Metallic Li and Si powder (SIEPB32, manufactured by Kojundo Kagaku Co., Ltd.) were weighed out at a molar ratio of 4:1 and mixed in a mortar under an Ar atmosphere at room temperature for 30 minutes to obtain Li4Si (Li-Si alloy). The resulting Li-Si alloy was reacted with ethanol under an Ar atmosphere. The liquid and solid components were then separated by filtration. The separated solid component was dried at 120°C for 3 hours to obtain powdered porous Si.

[0057] The resulting porous Si and NaH (Na source) were weighed to 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 fired at 475°C for 10 hours in an Ar atmosphere to obtain a Na-Si alloy.

[0058] The resulting Na-Si alloy and AlF3, a sodium trapping agent, were weighed to a molar ratio of Na-Si alloy:AlF3 = 1:0.4 and mixed using a cutter mill. The resulting mixture was placed in a stainless steel reaction vessel and fired in a heating furnace under an Ar atmosphere at 310°C for 60 hours. The resulting reaction product is believed to contain the target electrode active material and by-products (NaF and Al). This reaction product was washed using a mixed solvent of HNO3 and HO in a volume ratio of 90:10. The washed reaction product was filtered, and the solid was dried at 120°C for 3 hours to obtain a powder. The resulting powder was then added to a 3 wt% aqueous hydrogen fluoride (HF) solution and stirred for 3 hours. The stirred mixture was then suction filtered, and the solid was dried at 120°C for 3 hours to obtain an electrode active material.

[0059] [Example 2] An electrode active material was obtained in the same manner as in Example 1, except that the molar ratio of Na-Si alloy and AlF3 was changed to Na-Si alloy:AlF3 = 1:0.35, and the firing conditions were changed to an Ar atmosphere, 320°C, and 60 hours.

[0060] [Example 3] An electrode active material was obtained in the same manner as in Example 1, except that the firing conditions were changed to an Ar atmosphere, 360° C., and 20 hours.

[0061] [Example 4] An electrode active material was obtained in the same manner as in Example 1, except that the firing conditions were changed to an Ar atmosphere, 340° C., and 40 hours.

[0062] [Comparative Example 1] An electrode active material was obtained in the same manner as in Example 1, except that the molar ratio of Na-Si alloy and AlF3 was changed to Na-Si alloy:AlF3 = 1:0.35, and the firing conditions were changed to an Ar atmosphere, 310°C, and 80 hours.

[0063] Comparative Example 2 An electrode active material was obtained in the same manner as in Example 1, except that the molar ratio of Na-Si alloy and AlF3 was changed to Na-Si alloy:AlF3 = 1:0.5, and the firing conditions were changed to an Ar atmosphere, 340°C, and 80 hours.

[0064] [evaluation] (XRD measurement) X-ray diffraction (XRD) measurements using CuKα radiation were performed on the electrode active materials obtained in Examples 1 to 4 and Comparative Examples 1 and 2. As a result, it was confirmed that all of the electrode active materials had a silicon clathrate type II crystalline phase as the main phase.

[0065] The intensity of peak A located near 2θ=20.09° in the silicon clathrate II crystal phase is I A The intensity of peak B located near 2θ = 31.72° is I B The maximum intensity at 2θ = 22° to 23° was defined as I M And I A / I M and I B / I M As a result, the electrode active materials obtained in Examples 1 to 4 and Comparative Examples 1 and 2 all had I A / I M is greater than 1 and I B / I M was also greater than 1.

[0066] (Zeta potential measurement) The zeta potential of the electrode active materials obtained in Examples 1 to 4 and Comparative Examples 1 and 2 was measured. Specifically, 5 mg of the electrode active material powder was placed in 5 cc of diisobutyl ketone, dispersed for 10 minutes using an ultrasonic cleaner, and measured using a zeta potential meter (Anton Paar Litesizer 500). The zeta potential of the electrode active material was calculated as an average value. Specifically, the zeta potential was measured 10 times, and the highest, second highest, lowest, and second lowest values ​​were excluded to calculate the average value of the six values. The results are shown in Table 1.

[0067] (SEM observation) The electrode active materials obtained in Examples 1 to 4 and Comparative Examples 1 and 2 were subjected to SEM-EDX (scanning electron microscope-energy dispersive X-ray spectroscopy) measurement to measure Na / Si. Na / Si was calculated from the atomic ratio based on the signal intensity ratio of Na and Si obtained by EDX analysis. The Na amount (wt%) was calculated from Na / Si. The results are shown in Table 1.

[0068] In addition, the average particle size (D 50 ) was determined by observation using a scanning electron microscope (SEM). As a result, the average particle diameter D 50 The average particle size (D 50 ) is preferably 0.5 μm or more and 5 μm or less.

[0069] (Measurement of volume expansion rate) All-solid-state batteries were fabricated using the electrode active materials obtained in Examples 1 to 4 and Comparative Examples 1 and 2 as negative electrode active materials, respectively, by the following fabrication method.

[0070] (1) Preparation of the negative electrode The resulting electrode active material, sulfide solid electrolyte (Li2S-P2S5-based glass ceramic), conductive material (VGCF), and butyl butyrate solution containing 5 wt% PVDF-based binder, and butyl butyrate were added to a polypropylene container and stirred for 30 seconds using an ultrasonic disperser (UH-50, manufactured by SMT). The container was then shaken for 30 minutes using a shaker (TTM-1, manufactured by Shibata Scientific Co., Ltd.). The mixture was applied to a negative electrode current collector (Cu foil, manufactured by UACJ) using an applicator by the blade method and dried on a hot plate at 100 °C for 30 minutes. This resulted in a negative electrode comprising a negative electrode current collector and a negative electrode layer.

[0071] (2) Preparation of the positive electrode The positive electrode active material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3A butyl butyrate solution containing 5 wt% PVDF binder (O2, average particle size 6 μm), a sulfide solid electrolyte (Li2S-P2S5-based glass ceramic), a conductive material (VGCF), and butyl butyrate were added and stirred for 30 seconds using an ultrasonic disperser (UH-50, manufactured by SMT). The container was then shaken for 3 minutes using a shaker (TTM-1, manufactured by Shibata Scientific Co., Ltd.), followed by another 30 seconds of stirring using the ultrasonic disperser and another 3 minutes of shaking using the shaker. The mixture was applied to a positive electrode current collector (Al foil, manufactured by Showa Denko KK) using an applicator by the blade method and dried for 30 minutes on a hot plate at 100 °C. This resulted in a positive electrode comprising a positive electrode current collector and a positive electrode layer. The area of ​​the positive electrode was smaller than that of the negative electrode.

[0072] (3) Preparation of solid electrolyte layer A sulfide solid electrolyte (Li2S-P2S5-based glass ceramic), a heptane solution containing 5 wt% butylene rubber binder, and heptane were added to a polypropylene container and stirred for 30 seconds using an ultrasonic disperser (UH-50, manufactured by SMT). The container was then shaken for 30 minutes using a shaker (TTM-1, manufactured by Shibata Scientific Co., Ltd.). The mixture was applied to a release sheet (Al foil) using an applicator by the blade method and dried on a hot plate at 100°C for 30 minutes. This resulted in a transfer member having a release sheet and a solid electrolyte layer.

[0073] (4) Fabrication of all-solid-state batteries A solid electrolyte layer for bonding was placed on the positive electrode layer of the positive electrode, and the resulting mixture was set in a roll press and pressed at 100 kN / cm and 165° C. This produced a first laminate.

[0074] Next, the negative electrode was set in a roll press and pressed at 60 kN / cm and 25°C. This resulted in a pressed negative electrode. Thereafter, a solid electrolyte layer for bonding and a transfer member were arranged in this order from the negative electrode layer side. At this time, the solid electrolyte layer for bonding and the solid electrolyte layer on the transfer member were arranged so as to face each other. The obtained laminate was set in a planar uniaxial press and temporarily pressed at 100 MPa and 25°C for 10 seconds. Then, the release sheet was peeled off from the solid electrolyte layer. This resulted in a second laminate.

[0075] Next, the bonding solid electrolyte layer of the first laminate and the solid electrolyte layer of the second laminate were arranged to face each other, and then set in a flat uniaxial press and pressed at 200 MPa and 120°C for 1 minute, thereby obtaining an all-solid-state battery.

[0076] (5) Measurement of volume expansion rate The obtained all-solid-state battery was charged, and the volume expansion rate was measured. The test conditions were a confining pressure (constant size) of 5 MPa, a charge of 0.1 C, and a cutoff voltage of 4.55 V. The confining pressure at 4.55 V was measured, and the increase in confining pressure from the state before charging was determined, thereby calculating the volume expansion rate. The results are shown in Table 1 and FIG. 3. The volume expansion rate results in Table 1 and FIG. 3 are relative values, with the result of Comparative Example 1 set to 100.

[0077] [Table 1]

[0078] As shown in Table 1, Example 4 and Comparative Example 2 had similar amounts of Na, but there was a large difference in the volume expansion coefficient. Furthermore, as shown in Table 1 and Fig. 3, it was confirmed that Examples 1 to 4 had smaller volume expansion coefficients than Comparative Examples 1 and 2. In this way, by keeping the zeta potential within a predetermined range, the volume expansion coefficient was reduced. [Explanation of symbols]

[0079] 1...Positive electrode layer 2...Anode layer 3...electrolyte layer 4 …Positive current collector 5 … Negative current collector 10 … batteries

Claims

1. An electrode active material having a silicon clathrate II type crystalline phase, The electrode active material has a zeta potential of −110 mV or more and −35 mV or less, as determined by measurement using diisobutyl ketone.

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

3. An electrode mixture comprising the electrode active material according to claim 1 or 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 battery, wherein the positive electrode layer or the negative electrode layer contains the electrode mixture according to claim 3 .

5. The battery of claim 4 , wherein the electrolyte layer comprises a solid electrolyte.

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