negative electrode layer

Abstract

To provide a negative electrode layer with good coulombic efficiency.SOLUTION: A negative electrode layer 20 used in an all-solid-state battery contains a negative electrode active material 10 and a solid electrolyte 11. The negative electrode active material 10 includes Si-based particles and a metal thin film covering the Si-based particles and containing a metal element having a Young's modulus lower than that of Si element.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a negative electrode layer. [Background technology]

[0002] An all-solid-state battery is a battery having a solid electrolyte layer between a positive electrode layer and a negative electrode layer, and has the advantage that safety devices can be easily simplified compared to liquid-based batteries that use an electrolyte solution containing a flammable organic solvent. Si is known as an anode active material used in all-solid-state batteries. For example, Patent Document 1 describes a battery using anode active material fine particles (e.g., silicon fine particles) with a theoretical capacity of 800 mAh / g or more and an electron conductivity of 1.0 × 10 3 Patent Document 2 discloses a negative electrode composite containing conductive fine particles having a conductivity of 100 S / cm or more and inorganic solid electrolyte fine particles. Patent Document 2 also discloses a negative electrode composite having a first negative electrode active material containing a carbon matrix and fine particles containing Si or Sn elements dispersed in the carbon matrix. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-192093 [Patent Document 2] Japanese Patent Application Publication No. 2017-027886 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 all-solid-state batteries. However, because Si undergoes large volume changes during charging and discharging, cracks are likely to occur in the anode layer. When cracks occur in the anode layer, the ionic and electronic conduction paths are severed, resulting in a decrease in Coulomb efficiency.

[0005] The present disclosure has been made in view of the above circumstances, and has as its main object to provide a negative electrode layer having good Coulomb efficiency. [Means for solving the problem]

[0006] The present disclosure provides an anode layer for use in an all-solid-state battery, the anode layer containing an anode active material and a solid electrolyte, the anode active material having Si-based particles and a metal thin film that coats the Si-based particles and contains a metal element having a Young's modulus lower than that of Si element.

[0007] According to the present disclosure, by using a negative electrode active material in which Si-based particles are coated with a predetermined metal thin film, a negative electrode layer with good Coulomb efficiency is obtained. [Effects of the Invention]

[0008] The present disclosure has an effect of providing a negative electrode layer having good Coulomb efficiency. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a schematic cross-sectional view illustrating an example of a negative electrode layer in the present disclosure. [Figure 2] 1 is a schematic cross-sectional view illustrating an example of a negative electrode active material according to the present disclosure. [Figure 3] FIG. 1 is a schematic cross-sectional view illustrating an example of an all-solid-state battery according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] The negative electrode layer in the present disclosure will be described in detail below.

[0011] FIG. 1 is a schematic cross-sectional view illustrating an example of a negative electrode layer in the present disclosure. The negative electrode layer 20 shown in FIG. 1 has a negative electrode active material 10, a solid electrolyte 11, and a conductive material 12. The negative electrode active material 10 and the solid electrolyte 11 are in contact with each other. Similarly, the negative electrode active material 10 and the conductive material 12 are also in contact with each other. FIG. 2 is a schematic cross-sectional view illustrating an example of a negative electrode active material in the present disclosure. The negative electrode active material 10 shown in FIG. 2 has Si-based particles 1 and a metal thin film 2 that covers the Si-based particles 1. The metal thin film 2 contains a metal element having a lower Young's modulus than that of Si element.

[0012] According to the present disclosure, a negative electrode layer with good Coulombic efficiency is obtained by using a negative electrode active material in which Si-based particles are coated with a predetermined metal thin film. Si undergoes large volume changes during charge and discharge, which makes it prone to cracking in the negative electrode layer. When cracks occur in the negative electrode layer, the ionic and electronic conduction paths are severed, resulting in a decrease in Coulombic efficiency. For example, when cracks occur between the negative electrode active material and the solid electrolyte, the ionic conduction paths are severed, increasing internal resistance and resulting in a decrease in capacity and output. Similarly, when cracks occur between the negative electrode active material and the conductive material, the electronic conduction paths are severed, increasing internal resistance and resulting in a decrease in capacity and output.

[0013] In contrast, the present disclosure uses a negative electrode active material in which Si-based particles are coated with a metal thin film containing a metal element with a Young's modulus lower than that of Si. Because the metal thin film contains a metal element with a Young's modulus lower than that of Si, the adhesion between the negative electrode active material and the solid electrolyte is improved during charging (when the volume of the negative electrode active material increases). Therefore, it is believed that peeling between the negative electrode active material and the solid electrolyte can be suppressed during subsequent discharging (when the volume of the negative electrode active material decreases). As a result, it is believed that the Coulomb efficiency is improved.

[0014] The negative electrode layer in the present disclosure contains at least a negative electrode active material and a solid electrolyte. The negative electrode layer may also contain a conductive material. The negative electrode layer may also contain a binder.

[0015] 1.Negative electrode active material The negative electrode active material according to the present disclosure includes Si-based particles and a metal thin film that coats the Si-based particles and contains a metal element having a Young's modulus lower than that of elemental Si.

[0016] (1)Si-based particles The Si-based particles in the present disclosure contain at least Si element. Examples of Si-based particles include particles of simple Si, Si alloy particles, and Si oxide particles. The Si alloy preferably contains Si element as a main component. The proportion of Si element in the Si alloy is, for example, 50 at% or more, or may be 70 at% or more, or may be 90 at% or more. Examples of Si oxides include SiO.

[0017] Average particle size of Si-based particles (D 50 ) is not particularly limited, but is, for example, 30 μm or less, may be 10 μm or less, or may be 5 μm or less. If the average particle size of the Si-based particles is too large, cracks are likely to occur in the negative electrode layer due to volume changes during charge and discharge. On the other hand, the average particle size (D 50 ) is, for example, 0.1 μm or more, and may be 0.5 μm or more. If the average particle size of the Si-based particles is too small, it may be difficult to manufacture the Si-based particles. 50 ) can be calculated, for example, from measurements using a laser diffraction particle size distribution analyzer or a scanning electron microscope (SEM).

[0018] (2) Metallic thin film The metal thin film in the present disclosure coats Si-based particles and contains a metal element having a lower Young's modulus than Si element. The metal thin film preferably has Li-ion conductivity that allows it to donate Li ions to the Si-based particles. The metal thin film may be a thin film of a metal element or a thin film of a metal alloy. The metal element in the present disclosure also includes so-called semimetal elements (B, Si, Ge, As, Sb, and Te).

[0019] In this disclosure, a metal element having a Young's modulus lower than that of Si may be referred to as the metal element Me. The metal thin film contains at least the metal element Me. Examples of the metal element Me include Al, Cd, In, Sn, Sb, and Pb. The Young's moduli of these metal elements are shown in Table 1.

[0020] [Table 1]

[0021] The metal thin film may contain only one type of metal element Me, or may contain two or more types. The metal thin film preferably contains at least one of Al, In, and Sn as the metal element Me. The metal thin film may or may not contain a metal element other than the metal element Me (Si element or a metal element with a higher Young's modulus than Si element). The proportion of the metal element Me in the metal thin film is, for example, 50 at% or more, or may be 70 at% or more, or may be 90 at% or more.

[0022] The thickness of the metal thin film is, for example, 10 nm or more, or may be 15 nm or more, or may be 100 nm or more. If the metal thin film is too thin, good Coulomb efficiency may not be obtained. On the other hand, the thickness of the metal thin film is, for example, 1000 nm or less, or may be 500 nm or less. If the metal thin film is too thick, the amount of Li available to react with the Si-based particles may decrease.

[0023] The metal thin film covers at least a portion of the Si-based particles. The metal thin film may completely cover the Si-based particles. Alternatively, the metal thin film may incompletely cover the Si-based particles. That is, the negative electrode active material may have exposed portions where the Si-based particles are exposed from the metal thin film. The coverage of the metal thin film is, for example, 50% or more, or may be 70% or more, or may be 90% or more.

[0024] (3) Negative electrode active material The negative electrode active material according to the present disclosure is a negative electrode active material for use in an all-solid-state battery, and includes the above-described Si-based particles and metal thin film. A compound (e.g., an intermetallic compound) containing the Si element of the Si-based particles and the metal element Me of the metal thin film may be formed at the interface between the Si-based particles and the metal thin film.

[0025] The negative electrode active material of the present disclosure can be obtained, for example, by forming a metal thin film on the surface of Si-based particles. Examples of methods for forming a metal thin film on the surface of Si-based particles include PVD methods such as vacuum deposition, sputtering, and ion plating.

[0026] The proportion of the negative electrode active material contained in the negative electrode layer is, for example, 30% by weight or more, or may be 40% by weight or more, or 50% by weight or more, while the proportion of the negative electrode active material contained in the negative electrode layer is, for example, 80% by weight or less.

[0027] 2.Solid electrolyte The negative electrode layer contains 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. In particular, the negative electrode layer preferably contains a sulfide solid electrolyte. This is because sulfide solid electrolytes have excellent ion conductivity.

[0028] The sulfide solid electrolyte preferably contains, for example, Li, X (X is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S. The sulfide solid electrolyte may also contain at least one of Cl, Br, and I as a halogen element. The sulfide solid electrolyte may also contain O.

[0029] The sulfide solid electrolyte may be a glass-based sulfide solid electrolyte, a glass-ceramic-based sulfide solid electrolyte, or a crystalline sulfide solid electrolyte. When the sulfide solid electrolyte has a crystalline phase, examples of the crystalline phase include a Thio-LISICON-type crystalline phase, an LGPS-type crystalline phase, and an Argyrodite-type crystalline phase.

[0030] Furthermore, a compound (for example, sulfide) containing the metal element Me in the metal thin film and the S element in the sulfide solid electrolyte may be formed at the interface between the metal thin film in the negative electrode active material and the sulfide solid electrolyte.

[0031] 3. Negative electrode layer The negative electrode layer may contain a conductive material. The use of the conductive material improves the electronic conductivity of the negative electrode layer. Examples of the conductive material 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).

[0032] The negative electrode layer may contain a binder. Examples of the binder include fluorine-containing binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). The thickness of the negative electrode layer is, for example, 0.1 μm or more and 1000 μm or less.

[0033] The present disclosure can also provide an all-solid-state battery having the above-described anode layer. Fig. 3 is a schematic cross-sectional view illustrating an example of an all-solid-state battery according to the present disclosure. The all-solid-state battery 30 shown in Fig. 3 includes a positive electrode layer 21, a negative electrode layer 20, a solid electrolyte layer 22 disposed between the positive electrode layer 21 and the negative electrode layer 20, a positive electrode current collector 23 that collects current from the positive electrode layer 21, and a negative electrode current collector 24 that collects current from the negative electrode layer 20.

[0034] The positive electrode layer contains at least a positive electrode active material. Typical examples of the positive electrode active material include oxide active materials, such as LiCoO2, LiMnO2, LiNiO2, LiVO2, and LiNi. 4 / 5 Co 1 / 10 Al 1 / 10 O2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc., rock salt layered active materials, LiMn2O4, Li(Ni 0.5 Mn 1.5 Examples of suitable positive electrode active materials include spinel-type active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCuPO4, and olivine-type active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCuPO4. The surface of the positive electrode active material may be covered with a protective layer. The protective layer can prevent the positive electrode active material from reacting with the solid electrolyte (particularly, a sulfide solid electrolyte). The protective layer preferably contains a Li-containing oxide such as LiNbO3, Li3PO4, or LiPON.

[0035] The positive electrode layer may contain at least one of a solid electrolyte, a conductive material, and a binder, as necessary. These materials are as described above. The thickness of the positive electrode layer is, for example, 0.1 μm or more and 1000 μm or less.

[0036] The solid electrolyte layer is a layer disposed between the positive electrode layer and the negative electrode layer, and contains at least a solid electrolyte. The solid electrolyte layer may further contain a binder, if necessary. The solid electrolyte and the binder are as described above. The thickness of the solid electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less.

[0037] The all-solid-state battery may have a restraining jig that applies a restraining pressure to the positive electrode layer, the solid electrolyte layer, and the negative electrode layer in the thickness direction. By applying the restraining pressure, good ion conduction paths and electron conduction paths are formed. The restraining pressure is, for example, 0.1 MPa or more, or may be 1 MPa or more, or 5 MPa or more. On the other hand, the restraining pressure is, for example, 100 MPa or less, or may be 50 MPa or less, or may be 20 MPa or less. The type of the restraining jig is not particularly limited, but examples include restraining jigs that apply restraining torque using bolts.

[0038] The all-solid-state battery in the present disclosure is typically an all-solid-state lithium-ion secondary battery. Applications of the all-solid-state battery include, for example, power sources for vehicles such as hybrid electric vehicles (HEVs), electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles. The all-solid-state battery in the present disclosure may also be used as a power source for mobile objects other than vehicles (e.g., railways, ships, and aircraft), and may also be used as a power source for electrical appliances such as information processing devices.

[0039] 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]

[0040] [Example 1] (Fabrication of positive electrode structure) Positive electrode active material (LiNi 4 / 5 Co 1 / 10 Al 1 / 10O2, average particle size 10 μm), sulfide solid electrolyte (10LiI·15LiBr·75(0.75Li2S·0.25P2S5), average particle size 0.5 μm), conductive material (VGCF-H), and binder (PVDF) were weighed and mixed in a weight ratio of 85.4:12.7:1.3:0.6 for positive electrode active material:sulfide solid electrolyte:conductive material:binder. The resulting mixture was dispersed using an ultrasonic homogenizer (UH-50, manufactured by SMT Corporation) to obtain a positive electrode slurry. The resulting positive electrode slurry was applied to a positive electrode current collector (Al foil, 15 μm thick) by blade coating using an applicator and dried at 100°C for 30 minutes. Afterwards, a 1 cm 2 The sheet was punched out to a size of 100 mm to obtain a positive electrode structure having a positive electrode layer and a positive electrode current collector.

[0041] (Fabrication of negative electrode structure) A 15-nm-thick thin film of In was formed on the surface of silicon particles (average particle size 4 μm) by vacuum deposition to obtain anode active material. The resulting anode active material, a sulfide solid electrolyte (10LiI·15LiBr·75 (0.75LiS·0.25P2S5), average particle size 0.5 μm), a conductive material (VGCF-H), and a binder (SBR) were weighed out in a weight ratio of anode active material:sulfide solid electrolyte:conductive material:binder = 62.1:31.7:5.0:1.2 and mixed with a dispersion medium (diisobutyl ketone). The resulting mixture was dispersed using an ultrasonic homogenizer (UH-50, manufactured by SMT Corporation) to obtain anode slurry. The obtained negative electrode slurry was applied to a negative electrode current collector (Ni foil, thickness 22 μm) by a blade coating method using an applicator, and dried for 30 minutes at 100° C. The applicator gap at this time was 1 cm when the capacity of the positive electrode active material was 207 mAh / g and the capacity of the negative electrode active material was 3579 mAh / g. 2 The weight of the negative electrode active material per 1 cm was adjusted so that the ratio of the positive electrode capacity to the negative electrode capacity (positive electrode capacity / negative electrode capacity) was 3. 2 The negative electrode structure having the negative electrode layer and the negative electrode current collector was obtained by punching out the negative electrode layer into a size of 100 mm.

[0042] (Fabrication of solid electrolyte layer) A sulfide solid electrolyte (10LiI·15LiBr·75(0.75Li2S·0.25P2S5), average particle size 2.0 μm) and a binder (SBR) were weighed out so that the weight ratio of sulfide solid electrolyte to binder was 99.6:0.4, and mixed with a dispersion medium (diisobutyl ketone). The resulting mixture was dispersed using an ultrasonic homogenizer (UH-50, manufactured by SMT Corporation) to obtain a slurry for the solid electrolyte layer. The resulting slurry was applied to an Al foil (thickness 15 μm) by blade coating using an applicator and dried at 100°C for 30 minutes. After that, a 1 cm 2 A solid electrolyte layer having an Al foil was obtained by punching out the aluminum foil into a size of 100 mm.

[0043] (Fabrication of all-solid-state batteries) The obtained solid electrolyte layer was placed opposite the cathode layer of the cathode structure, and pressed by a roll press method at a linear pressure of 1.6 t / cm. Thereafter, the Al foil was peeled off from the solid electrolyte layer, thereby transferring the solid electrolyte layer onto the cathode layer of the cathode structure. Next, the transferred solid electrolyte layer was placed opposite the anode layer of the anode structure, and pressed by a uniaxial press at a surface pressure of 5.0 t / cm. 2 The electrode assembly was pressed with a pressure of 1000 kJ / cm 2 to obtain an electrode assembly. Next, current collecting tabs were attached to the positive electrode current collector and the negative electrode current collector of the obtained electrode assembly. Next, the electrode assembly with the attached tabs was sealed with a laminate film to obtain an all-solid-state battery.

[0044] [Comparative Example 1] An all-solid-state battery was obtained in the same manner as in Example 1, except that Si particles were used as the negative electrode active material.

[0045] Comparative Example 2 An all-solid-state battery was obtained in the same manner as in Example 1, except that in the preparation of the negative electrode active material, Si was used instead of In to form a metal thin film.

[0046] [evaluation] A charge / discharge test was conducted on the all-solid-state batteries obtained in Example 1 and Comparative Examples 1 and 2. Specifically, constant current charge / discharge was performed under the conditions of a voltage range of 2.5 V to 4.05 V, a rate of 0.1 C, and a temperature of 25°C. The ratio of the initial discharge capacity to the initial charge capacity was calculated as the Coulomb efficiency. The results are shown in Table 2. In addition, the first peak position (V) obtained in the curve (dQ / dV) obtained by differentiating the charge curve during the initial charge with respect to the voltage was calculated. The results are shown in Table 2. The first peak position was calculated as a relative value when the result of Comparative Example 1 was set to 1.00.

[0047] [Table 2]

[0048] As shown in Table 2, Example 1 had better Coulombic efficiency during the initial charge / discharge than Comparative Examples 1 and 2. This is presumably because the metal thin film contained a metal element with a lower Young's modulus than Si, which improved the adhesion between the negative electrode active material and the solid electrolyte during charging (when the volume of the negative electrode active material increases), and prevented peeling between the negative electrode active material and the solid electrolyte during subsequent discharge (when the volume of the negative electrode active material decreases).

[0049] Furthermore, as shown in Table 2, the first peak position (relative value) in Example 1 was less than 1. The reason for this is presumably that the internal resistance was reduced due to improved adhesion between the negative electrode active material and the solid electrolyte during charging. As in Example 1 and Comparative Example 1, negative electrode active materials that were similar except for the presence or absence of a metal thin film were prepared, and when the first peak position (V) of the negative electrode active material without a metal thin film is designated as P1 and the first peak position (V) of the negative electrode active material with a metal thin film is designated as P2, the ratio of P2 to P1 (P2 / P1) is preferably less than 1, and more preferably 0.98 or less.

[0050] [Example 2] LiNi as the positive electrode active material 1 / 3 Co 1 / 3 Mn 1 / 3An all-solid-state battery was obtained in the same manner as in Example 1, except that O2 (average particle size 10 μm) was used and Sn was used instead of In to form a metal thin film in the preparation of the negative electrode active material.

[0051] [Example 3] An all-solid-state battery was obtained in the same manner as in Example 2, except that in the preparation of the negative electrode active material, Al was used instead of In to form a metal thin film.

[0052] Comparative Example 3 An all-solid-state battery was obtained in the same manner as in Example 2, except that Si particles were used as the negative electrode active material.

[0053] Comparative Example 4 An all-solid-state battery was obtained in the same manner as in Example 2, except that in the preparation of the negative electrode active material, Si was used instead of In to form a metal thin film.

[0054] [evaluation] Charge and discharge tests were conducted on the all-solid-state batteries obtained in Examples 2 and 3 and Comparative Examples 3 and 4. Specifically, constant current charge and discharge were performed under the conditions of a voltage range of 3.0 V to 4.35 V, a rate of 0.1 C, and a temperature of 25°C. The ratio of the initial discharge capacity to the initial charge capacity was calculated as the Coulomb efficiency. The results are shown in Table 3. In addition, the first peak position (V) obtained in the curve (dQ / dV) obtained by differentiating the charge curve during the initial charge with respect to the voltage was calculated. The results are shown in Table 3. The first peak position was calculated as a relative value when the result of Comparative Example 3 was set to 1.00.

[0055] [Table 3]

[0056] As shown in Table 3, Examples 2 and 3 had better Coulombic efficiencies during the initial charge / discharge than Comparative Examples 3 and 4. Furthermore, the first peak positions in Examples 2 and 3 were less than 1. That is, the same effects as those of Example 1 described above were confirmed in Examples 2 and 3 as well. [Explanation of symbols]

[0057] 1 ...Si-based particles 2…metallic film 10 ...Negative electrode active material 11 …Solid Electrolyte 12 ...conductive materials 20 ...negative electrode layer 21 ...positive electrode layer 22 ...Solid electrolyte layer 23 ...positive electrode current collector 24 ...Negative electrode current collector 30 ...all-solid-state batteries

Claims

[Claim 1] A negative electrode layer for use in an all-solid-state battery, the negative electrode layer contains a negative electrode active material and a sulfide solid electrolyte, the negative electrode active material includes Si-based particles and a metal thin film that coats the Si-based particles and contains Sn, The thickness of the metal thin film is 10 nm or more and 15 nm or less.

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