Composite particle and battery

Abstract

To provide composite particles that can suppress the amount of volume change of an electrode.SOLUTION: There is provided a composite particle that contains a binder and multiple active materials each containing Si or Sn element, and has a zeta potential of -30 mV or higher in water.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to composite particles and batteries. [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 vehicles (PHEVs), and hybrid electric vehicles (HEVs) is underway. Furthermore, development of components and materials for use in these batteries is also underway.

[0003] For example, Patent Document 1 discloses a negative electrode layer that contains composite particles having a binder and a plurality of particles containing Si or Sn elements, and has a porosity of 15% or less. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-121557 Summary of the Invention [Problem to be solved by the invention]

[0005] Si and Sn have a large theoretical capacity and are effective in increasing the energy density of batteries. However, they have a large volume change during charge and discharge, which may result in a large volume change (amount of expansion and contraction) in the electrode layer using Si or Sn. For example, if the volume change of the electrode layer is large, the ion conduction path may be cut, resulting in an increase in battery resistance. In this regard, as in Patent Document 1, it has been studied to absorb the expansion of the composite particles by providing voids in the negative electrode layer. However, there is room for further improvement in suppressing the volume change of the electrode.

[0006] The present disclosure has been made in view of the above circumstances, and has as its main object to provide composite particles that can suppress the amount of volume change of an electrode. [Means for solving the problem]

[0007] [1] A battery comprising a plurality of active materials each containing an Si element or an Sn element and a binder, Composite particles having a zeta potential in water of -30 mV or more.

[0008] [2] The composite particles according to [1], wherein the zeta potential is −10 mV or less.

[0009] [3] The composite particles according to [1] or [2], wherein the ratio of the binder to the active material is 3% by weight or more and 20% by weight or less.

[0010] [4] The composite particles according to any one of [1] to [3], wherein the active material contains the Si element and has voids inside the primary particles.

[0011] [5] The composite particles according to any one of [1] to [4], wherein the active material contains the Si element and has a silicon clathrate II type crystal phase.

[0012] [6] The composite particles according to any one of [1] to [5], wherein the binder contains elemental fluorine.

[0013] [7] A battery having a positive electrode active material layer, a negative electrode active material layer, and an electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, A battery in which the negative electrode active material layer contains the composite particles according to any one of [1] to [6]. [Effects of the Invention]

[0014] The composite particles of the present disclosure have the effect of suppressing the amount of volume change of the electrode. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 2 is a diagram illustrating the crystalline phase of a Si-based active material according to the present disclosure. [Figure 2] FIG. 1 is a schematic cross-sectional view illustrating a battery according to the present disclosure. [Figure 3] 1 is a graph showing the relationship between the zeta potential and the amount of electrode expansion in Examples and Comparative Examples. [Figure 4] 1 shows the results of microscopic observation (SEM observation) in Examples and Comparative Examples. [Figure 5] 1 shows the results of particle size distribution in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0016] The composite particles and batteries according to the present disclosure will be described in detail below.

[0017] A. Composite particles The composite particles of the present disclosure contain multiple active materials containing Si or Sn and a binder, and have a zeta potential in water of -30 mV or more. Herein, an active material containing Si may be referred to as an Si-based active material, and an active material containing Sn may be referred to as an Sn-based active material. The zeta potential in water may also be simply referred to as the zeta potential.

[0018] The composite particles of the present disclosure contain a predetermined active material and a binder, and have a zeta potential of −30 mV or higher in water, so that when used in a battery, the amount of volume change in the electrode and battery can be suppressed.

[0019] Composite particles having voids are known, as in Patent Document 1 mentioned above. In this regard, the present inventors discovered that in a battery state, the shape of the composite particles may collapse and the void volume may decrease. After detailed investigation of this phenomenon, the present inventors discovered that the zeta potential of the composite particles is related to the maintenance of the shape and void volume of the composite particles. Furthermore, they discovered that a zeta potential of -30 mV or higher can maintain the shape of the composite particles well and further suppress the amount of electrode expansion, leading to the completion of the present invention. It is presumed that a zeta potential of less than -30 mV increases the repulsive force between the particles constituting the composite particles, making it difficult to maintain the shape. In contrast, the composite particles in the present disclosure have a sufficiently large zeta potential of -30 mV or higher, which reduces the repulsive force and therefore presumably maintains the particle shape well. As a result, it is presumed that the void volume in the composite particles is maintained and the volume change of the electrode is suppressed.

[0020] The composite particles of the present disclosure have a zeta potential in water of -30 mV or higher. The zeta potential may be -25 mV or higher, or even -20 mV or higher. On the other hand, the zeta potential may be, for example, -10 mV or lower, or even -15 mV or lower. Here, "zeta potential" is also called interfacial potential, and refers to the portion of the potential difference at the interface between a solid and a liquid that effectively affects the interfacial electrokinetic phenomenon. The zeta potential in this specification is measured by the laser Doppler method, which is an electrophoretic light scattering method.

[0021] The zeta potential can be adjusted by changing the type of active material (primary particles), the type of binder, and the binder ratio. For example, organic polymer materials generally tend to have a higher zeta potential than the surface of inorganic particles. Therefore, for example, increasing the binder ratio in the composite particles can increase the zeta potential of the entire composite particles.

[0022] The composite particles of the present disclosure contain a plurality of active materials containing Si or Sn elements and a binder. Here, the composite particles can also be regarded as aggregates of the active materials (Si-based active materials or Sn-based active materials) aggregated by the binder. The active materials may be primary particles or secondary particles formed by aggregation of primary particles.

[0023] The active material containing Si element (Si-based active material) may be simple Si, an alloy containing Si as a main component (Si alloy), or a Si oxide. The proportion of Si element in the Si alloy is, for example, 50 mol % or more and 95 mol % or less.

[0024] The Si-based active material may have voids inside the primary particles. A Si-based active material having voids is referred to as porous Si. The presence of voids can be confirmed by observation with a scanning electron microscope (SEM). The porosity is not particularly limited, but may be, for example, 4% or more, or 10% or more. The porosity may be, for example, 40% or less, or 20% or less. The porosity can be determined, for example, by the following procedure. First, a cross-sectional image of the Si-based active material is obtained using an SEM. From the obtained image, 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 porosity (%) is calculated using the following formula: Porosity (%) = 100 × (area of void part) / ((area of silicon part) + (area of void part))

[0025] In porous Si, the pore volume of pores with a pore diameter of 50 nm or less is, for example, 0.05 cc / g or more and 0.30 cc / g or less. The BET specific surface area of porous Si is, for example, 20 m 2 / g or more, 200m 2 / g or less.

[0026] Porous Si can be produced, for example, by preparing an alloy of Li and Si (LiSi alloy) and then removing Li from the LiSi alloy. The LiSi alloy can be obtained, for example, by mixing Li and Si. Li can be removed from the LiSi alloy by reacting the LiSi alloy with a Li extractant. Examples of Li extractants include alcohols such as methanol and acids such as acetic acid.

[0027] FIG. 1 is a schematic perspective view illustrating the crystalline phase of Si. Generally, Si has a diamond-type crystalline phase as shown in FIG. 1(a). In contrast, the Si-based active material of the present disclosure may have a silicon clathrate-type crystalline phase as shown in FIGS. 1(b) and 1(c). In the diamond-type crystalline phase shown in FIG. 1(a), multiple Si elements form tetrahedra. The tetrahedra do not have internal spaces that can accommodate metal ions such as Li ions. On the other hand, in the silicon clathrate I and II crystalline phases shown in FIGS. 1(b) and 1(c), the skeletal atoms have cage-like structures, allowing metal ions such as Li ions to enter, thereby further suppressing the expansion and contraction of the composite particles and, consequently, the expansion and contraction of the electrode layer. A Si-based active material having a silicon clathrate-type crystalline phase is referred to as clathrate Si or crystalline Si. In particular, a Si-based active material having the above-mentioned voids and a clathrate-type crystalline phase is referred to as porous clathrate Si.

[0028] The Si-based active material may have a silicon clathrate I crystalline phase or a silicon clathrate II crystalline phase. It is particularly preferable for the Si-based active material to have a silicon clathrate II crystalline phase as the main phase. The "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 Si-based active material is, for example, 80% by weight or more, 85% by weight or more, 90% by weight or more, or even 95% by weight or more. The proportion of the silicon clathrate II crystalline phase contained in the Si-based active material may be 100% by weight or less. The proportion of the crystalline phase can be determined using the RIR (Reference Intensity Ratio) method.

[0029] Crystalline Si can be produced, for example, by mixing Si and a Na source such as NaH and heating the mixture to produce a Na-Si alloy, which is then heated to reduce the amount of Na in the Na-Si alloy and generate a silicon clathrate crystalline phase.Porous clathrate Si can be produced by using the porous Si described above as the Si.

[0030] The active material containing Sn element (Sn-based active material) may be Sn alone, an alloy containing Sn as a main component (Sn alloy), or Sn oxide. The proportion of Sn element in the Sn alloy is, for example, 50 mol % or more and 95 mol % or less.

[0031] The proportion of the Si-based active material or Sn-based active material in the composite particles is, for example, 90% by weight or more and 99% by weight or less.

[0032] The binder in the present disclosure is not particularly limited. Examples of binders include fluorine-containing fluorine-based binders and non-fluorine-based binders that do not contain fluorine. Examples of fluorine-based binders include fluoride-based binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). Examples of non-fluorine-based binders include polyimide-based binders; rubber-based binders such as amine-modified butadiene rubber (ABR), butadiene rubber (BR), and styrene-butadiene rubber (SBR); cellulose-based binders such as carboxymethyl cellulose (CMC); and acrylic binders such as polyacrylic acid, polyacrylates, and polyacrylic acid esters. Among these, fluorine-based binders are preferred, and polyvinylidene fluoride is particularly preferred. This is because they can further suppress battery resistance. Only one type of binder may be used, or multiple types may be mixed and used.

[0033] In the composite particles, the ratio of the binder to the active material is, for example, 3% by weight or more, and may be 5% by weight or more. On the other hand, the ratio of the binder is, for example, 25% by weight or less, may be 20% by weight or less, may be 15% by weight or less, or may be 10% by weight or less. If the ratio of the binder is too low, the adhesion between the active materials may be too weak, and the composite particles may not be able to maintain their shape well. If the ratio of the binder is too high, the electronic conductivity of the composite particles may decrease, and the battery resistance may increase.

[0034] Average particle diameter of composite particles (D 50 ) is, for example, 1 μm or more and 100 μm or less. 50 ) refers to the volume cumulative particle size measured by a laser diffraction scattering particle size distribution measurement method. 50 ) is, for example, 0.1 μm or more and 3 μm or less. The number of the active material particles contained in the composite particles is, for example, 10 or more and 150 or less.

[0035] The present disclosure can also provide an electrode layer containing the composite particles described above. The electrode layer may be a positive electrode active material layer containing the composite particles as a positive electrode active material, or a negative electrode active material layer containing the composite particles as a negative electrode active material, with the latter being preferred. This is because a high-voltage battery can be obtained. Furthermore, the electrode layer may further contain at least one of a conductive additive, a binder, and an electrolyte, as necessary. The conductive additive, the binder, and the electrolyte are described in "B. Batteries."

[0036] B.Battery Fig. 2 is a schematic cross-sectional view illustrating a battery according to the present disclosure. The battery 10 shown in Fig. 2 has a positive electrode active material layer 1, a negative electrode active material layer 2, and an electrolyte layer 3 disposed between the positive electrode active material layer 1 and the negative electrode active material layer 2. The negative electrode active material layer 2 in the battery 10 contains the composite particles according to the present disclosure described above.

[0037] In the battery of the present disclosure, the negative electrode active material layer contains the above-described composite particles, and therefore the amount of volume change in the negative electrode active material layer can be suppressed, and as a result, the amount of volume change in the battery is suppressed.

[0038] 1.Negative electrode active material layer The negative electrode active material layer contains the above-described composite particles. The composite particles are the same as those described in "A. Composite particles." The negative electrode active material layer contains the above-described composite particles as the negative electrode active material.

[0039] The negative electrode active material layer may further contain at least one of a conductive additive, a binder, and an electrolyte, as required.

[0040] The proportion of the composite particles in the negative electrode active material layer is not particularly limited, but may be, for example, 50% by weight or more, 70% by weight or more, or 90% by weight or more, while the proportion of the composite particles may be, for example, 99% by weight or less, or 95% by weight or less.

[0041] Examples of the conductive additive include carbon materials. Examples of the carbon material 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). The proportion of the conductive additive in the negative electrode active material layer is, for example, 0.01% by weight or more and 10% by weight or less, and may be 0.1% by weight or more and 5% by weight or less.

[0042] Examples of the binder include those described in "A. Composite Particles." The binder in the composite particles and the binder in the negative electrode active material layer may be the same type or different types. The proportion of the binder in the negative electrode active material layer is, for example, 0.5% by weight to 10% by weight, and may be 1% by weight to 5% by weight.

[0043] The negative electrode active material layer preferably contains a solid electrolyte as an electrolyte. Examples of solid electrolytes include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, and halide solid electrolytes. The sulfide solid electrolyte preferably contains sulfur (S) as the main anion element. The oxide solid electrolyte preferably contains oxygen (O) as the main anion element. The halide solid electrolyte preferably contains halogen as the main anion element. Among these, the sulfide solid electrolyte is preferred.

[0044] The sulfide solid electrolyte preferably contains Li, M (wherein M is at least one of P, Sn, Al, Zn, In, Ge, Si, Sb, Ga, and Bi), and S. The sulfide solid electrolyte may also contain a halogen element such as F, Cl, Br, or I. In the sulfide solid electrolyte, a portion of the S element may be substituted with O.

[0045] The sulfide solid electrolyte may be a glass-based (amorphous) sulfide solid electrolyte, a glass-ceramic sulfide solid electrolyte, or a crystalline sulfide solid electrolyte. Examples of the crystalline phase contained in the sulfide solid electrolyte include an LGPS-type crystalline phase, a Thio-LISICON-type crystalline phase, and an argyrodite-type crystalline phase.

[0046] Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-GeS2, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-P2S5-LiI-LiBr, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z m S n (where m and n are positive numbers. Z is Ge, Zn, or Ga.), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (where x and y are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, and In.)

[0047] The proportion of the solid electrolyte in the negative electrode active material layer is, for example, 30% by weight or more and 80% by weight or less, and may be 40% by weight or more and 70% by weight or less.

[0048] The thickness of the negative electrode active material layer is not particularly limited, but is, for example, 0.1 μm or more and 1000 μm or less.

[0049] 2.Cathode active material layer The positive electrode active material layer contains at least a positive electrode active material, and optionally contains at least one of a conductive additive, a binder, and an electrolyte. The conductive additive, the binder, and the electrolyte are the same as those described in "1. Negative electrode active material layer."

[0050] The positive electrode active material is not particularly limited as long as it has a higher reaction potential than the composite particles. Examples of the positive electrode active material include oxide active materials. Examples of oxide active materials include LiCoO2 and LiNi 0.8 Co 0.15 Mn 0.05 O2 and LiNi 0.33 Co 0.33 Mn 0.33 O2, etc., rock salt layered active materials, LiMn2O4, Li4Ti5O 12 Examples of the shape of the positive electrode active material include spinel-type active materials such as LiFePO4 and olivine-type active materials such as LiFePO4. The positive electrode active material may be in the form of particles. The average particle diameter (D 50 ) is, for example, 0.5 μm or more and 50 μm or less. 50 ) is as above.

[0051] The thickness of the positive electrode active material layer is not particularly limited, but is, for example, 0.1 μm or more and 1000 μm or less.

[0052] 3. Electrolyte layer The electrolyte layer contains an electrolyte. The electrolyte is preferably a solid electrolyte. The solid electrolyte is the same as that described in "1. Negative electrode active material layer." The electrolyte layer may contain a binder as needed. The binder is the same as that described in "1. Negative electrode active material layer." Generally, a battery having a solid electrolyte layer containing an inorganic solid electrolyte is called a solid-state battery. Solid-state batteries include semi-solid-state batteries and all-solid-state batteries. Generally, a battery in which the entire electrolyte constituting the solid electrolyte layer is made of an inorganic solid electrolyte is called an all-solid-state battery.

[0053] 4. Other configurations As shown in Fig. 2, a battery 10 according to the present disclosure typically includes a positive electrode current collector 4 that collects electrons from a positive electrode active material layer 1 and a negative electrode current collector 5 that collects electrons from a negative electrode active material layer 2. Examples of materials for the positive electrode current collector include stainless steel, aluminum, nickel, iron, titanium, and carbon. Examples of materials for the negative electrode current collector include stainless steel, copper, nickel, and carbon.

[0054] The battery according to the present disclosure may also include an exterior body that houses the above-described components. Examples of the exterior body include a laminate-type exterior body and a case-type exterior body. The battery according to the present disclosure may also include a restraining jig that applies a restraining pressure in the thickness direction to the above-described components. A known jig can be used as the restraining jig. The restraining pressure may be, for example, 0.1 MPa or more and 50 MPa or less, or 1 MPa or more and 20 MPa or less.

[0055] 5.Battery The battery in the present disclosure is typically a lithium-ion secondary battery. Furthermore, the battery in the present disclosure is preferably a solid-state battery, and particularly preferably an all-solid-state battery. 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 automobiles, and diesel-powered automobiles. Furthermore, the battery in the present disclosure may 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.

[0056] 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]

[0057] [Example 1] (Preparation of composite particles) A slurry was prepared by adding and mixing an Si-based active material into a binder solution containing an organic solvent and a non-fluorinated binder (SBR). Composite particles containing the Si-based active material and the binder were prepared by spray drying using this slurry. The Si-based active material was an active material having a silicon clathrate II type crystalline phase as the main phase (crystalline Si: average particle diameter (D 50 )0.5μm) was used.

[0058] (Preparation of negative electrode active material layer) The composite particles, binder (PVDF), conductive additive (VGCF), and sulfide solid electrolyte (Li2S-P2S5-based sulfide solid electrolyte) were added to an organic solvent and kneaded using an ultrasonic homogenizer. This produced a negative electrode slurry. The negative electrode slurry was then applied to a negative electrode current collector (Cu foil) and dried. This resulted in a negative electrode comprising a negative electrode current collector and a negative electrode active material layer.

[0059] (Preparation of positive electrode active material layer) The organic solvent contains a binder (PVDF), a conductive additive, a sulfide solid electrolyte, and a positive electrode active material (NCM: LiNi 0.8 Co 0.15 Mn 0.05 O2) was added. After addition, the mixture was kneaded using an ultrasonic homogenizer to obtain a positive electrode slurry. The obtained positive electrode slurry was applied to a positive electrode current collector (Al foil) and dried. This resulted in a positive electrode having a positive electrode current collector and a positive electrode active material layer.

[0060] (Preparation of evaluation battery) A binder (PVDF) and a sulfide solid electrolyte (Li2S-P2S5-based sulfide solid electrolyte) were added to an organic solvent and kneaded using an ultrasonic homogenizer. This resulted in a composite slurry. The composite slurry was applied to a substrate (Al foil) and dried. This resulted in a transfer member having a substrate and a solid electrolyte layer.

[0061] The prepared positive electrode, negative electrode, and transfer member were each molded into a strip shape. Next, the positive electrode and transfer member were stacked so that the positive electrode active material layer and the solid electrolyte layer faced each other, and roll-pressed at 165°C and a pressure of 50 kN / cm. The substrate was then peeled off to obtain a positive electrode member. The negative electrode and transfer member were stacked so that the negative electrode active material layer and the solid electrolyte layer faced each other, and roll-pressed at 25°C and a pressure of 50 kN / cm. The substrate was then peeled off to obtain a negative electrode member. Next, the negative electrode member was punched out to a diameter of 13.00 mm, and the positive electrode member was punched out to a diameter of 11.28 mm. A sulfide solid electrolyte powder was placed on the solid electrolyte layer of the punched negative electrode member, and uniaxial pressing was performed. Next, the negative electrode member and positive electrode member were stacked so that the solid electrolyte layers faced each other, and current extraction tabs were attached to the positive and negative electrodes. The battery was then sealed in an aluminum laminate using a vacuum lamination sealer and constrained at a pressure of 5 MPa, thereby producing an evaluation battery (all-solid-state battery).

[0062] [Examples 2 to 10 and Comparative Examples 1 to 8] Composite particles were produced by changing at least one of the presence or absence of composite, the type of primary particles, the type of binder, and the binder ratio, as shown in Table 1. A test battery was produced in the same manner as in Example 1, except that these composite particles were used.

[0063] [evaluation] (zeta potential measurement) The zeta potential of each example and comparative example was measured in water by the laser Doppler method. The results are shown in Table 1.

[0064] (electrode expansion amount) Each test battery was charged, and the increase in confining pressure measured using a load cell was evaluated as the amount of electrode expansion. The results are shown in Table 1. Comparative Examples 2 to 4 and Examples 1 to 5 were evaluated relative to the result of Comparative Example 1, and Comparative Examples 6 to 8 and Examples 6 to 10 were evaluated relative to the result of Comparative Example 5. The relationship between the zeta potential and the amount of electrode expansion is shown in Figures 3(a) and (b). Figure 3(a) shows the results of Comparative Examples 1 to 4 and Examples 1 to 5, and Figure 3(b) shows the results of Comparative Examples 5 to 8 and Examples 6 to 10.

[0065] As shown in Table 1 and Figures 3(a) and (b), it was confirmed that the amount of electrode expansion was significantly suppressed when the zeta potential was -30 mV or higher.

[0066] [Table 1]

[0067] (SEM observation and particle size distribution measurement) The composite particles produced in Comparative Example 2, Example 5, Comparative Example 6, and Example 10 were subjected to SEM observation, and the results are shown in Figure 4. Note that Figure 4(a) shows the results of Comparative Example 2, Figure 4(b) shows the results of Example 5, Figure 4(c) shows the results of Comparative Example 6, and Figure 4(d) shows the results of Example 10.

[0068] Furthermore, the particle size distribution of the composite particles produced in Comparative Example 2, Example 5, Comparative Example 6, and Example 10 was measured using a particle size distribution analyzer. The results are shown in Figure 5. Note that Figure 5(a) shows the results of Comparative Example 2, Figure 5(b) shows the results of Example 5, Figure 5(c) shows the results of Comparative Example 6, and Figure 5(d) shows the results of Example 10.

[0069] As shown in Figures 4 and 5, the examples (Figures 4(b), (d) and Figures 5(b), (d)) maintained good particle shape and had a wide particle size distribution compared to the comparative examples (Figures 4(a), (c) and Figures 5(a), (c)). From this, it is inferred that the composite particles of the present disclosure are able to maintain good shape even in the battery state.

[0070] (Measurement of specific surface area) The BET specific surface area of the active materials of Comparative Example 1 (crystalline Si) and Comparative Example 5 (porous Si) was calculated by the BET method using a pore size distribution measuring device. As a result, the specific surface area of Comparative Example 1 was 5.1 m 2 / g, and the specific surface area of Comparative Example 5 was 60.8 m 2 / g. It is presumed that in composite particles using porous Si, the primary particles (active material) themselves have voids that can absorb expansion, which can further suppress the amount of expansion of the electrode.

[0071] (Battery resistance evaluation) The voltage of the test batteries prepared in Examples 1 and 2 was adjusted to 3.7 V. Then, the resistance was calculated from the voltage drop after 5 seconds of discharging at a 5 C rate. As a result, the battery resistance was significantly reduced in Example 1, which used a fluorine-containing binder (PVdF). This suggests that using a binder containing elemental fluorine is preferable from the viewpoint of reducing battery resistance. [Explanation of symbols]

[0072] 1...Cathode active material layer 2...Negative electrode active material layer 3...electrolyte layer 4...Positive electrode current collector 5...Negative electrode current collector 10...battery

Claims

1. The battery includes a plurality of active materials each containing an Si element or an Sn element, and a binder, Composite particles having a zeta potential in water of -30 mV or more.

2. 2. The composite particle according to claim 1, wherein the zeta potential is −10 mV or less.

3. 2. The composite particle according to claim 1, wherein the ratio of the binder to the active material is 3% by weight or more and 20% by weight or less.

4. The composite particle according to claim 1 , wherein the active material contains the Si element and has voids inside the primary particles.

5. The composite particle according to claim 1 , wherein the active material contains the Si element and has a silicon clathrate II type crystal phase.

6. The composite particle according to claim 1 , wherein the binder contains elemental fluorine.

7. A battery having a positive electrode active material layer, a negative electrode active material layer, and an electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, A battery, wherein the negative electrode active material layer contains the composite particles according to any one of claims 1 to 6.

Images