Solid electrolyte powder, solid electrolyte layer, and lithium-ion all-solid-state battery

Abstract

The present invention relates to a solid electrolyte powder to be used in a lithium-ion all-solid-state battery, the volumetric grain size distribution in the solid electrolyte powder having a first peak within the grain size range of 0.5-0.7 μm and having a second peak within the grain size range of 1-3 μm.

Description

Technical Field

[0001] The present invention relates to a solid electrolyte powder, a solid electrolyte layer, and a lithium ion all-solid-state battery. More specifically, it relates to a solid electrolyte powder having excellent lithium ion conductivity, which is used in a lithium ion all-solid-state battery, a solid electrolyte layer containing the powder, and a lithium ion all-solid-state battery containing the solid electrolyte layer.

Background Art

[0002] Lithium ion secondary batteries are widely used in portable electronic devices such as mobile phones and notebook computers.

[0003] Conventionally, liquid electrolytes have been used in lithium ion secondary batteries. However, from the viewpoints of improving safety and enabling high-speed charge and discharge, lithium ion all-solid-state batteries (hereinafter also referred to as solid batteries) using solid electrolytes as the electrolytes of lithium ion secondary batteries have attracted attention.

[0004] As a technology related to solid batteries, for example, Patent Document 1 discloses a technology of using a ball group composed of two or more types of balls having different diameters when manufacturing a sulfide-based solid electrolyte using a ball mill.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Since a liquid electrolyte easily penetrates into the inside of the positive electrode and the negative electrode, an interface between the active material contained in the positive electrode and the negative electrode and the electrolyte solution is easily formed, and the performance as a battery can be easily improved.

[0007] On the other hand, solid electrolytes have inferior penetration into the positive and negative electrodes compared to liquid electrolytes. Therefore, efforts are being made to improve battery performance by reducing the particle size to form more interfaces with the active material. Furthermore, with the need for lighter solid batteries, there is a demand for thinner or sheet-like solid electrolyte layers. To prevent short circuits in the electrolyte layer, it is necessary to reduce the particle size of the solid electrolyte.

[0008] However, if the particle size of the solid electrolyte becomes too small, it can easily lead to a decrease in crystallinity and distortion or disorder of the crystal structure, resulting in poor lithium-ion conductivity.

[0009] In order to provide a solid electrolyte powder with excellent lithium ion conductivity, the inventors focused on the particle size distribution of the solid electrolyte powder and conducted diligent research. As a result, they found that a solid electrolyte powder having peaks in two specific different particle size ranges in its volume-based particle size distribution has excellent lithium ion conductivity.

[0010] Therefore, the present invention provides a solid electrolyte powder having excellent lithium ion conductivity. [Means for solving the problem]

[0011] The solid electrolyte powder according to an embodiment of the present invention is a solid electrolyte powder used in a lithium-ion all-solid-state battery, wherein the volume-based particle size distribution of the solid electrolyte powder has a first peak in the particle size range of 0.5 to 0.7 μm and a second peak in the particle size range of 1 to 3 μm.

[0012] Furthermore, in one embodiment of the present invention, the solid electrolyte powder may have a ratio of p2 / p1 of 0.4 or more and 2.5 or less, where p1 is the peak frequency of the first peak and p2 is the peak frequency of the second peak.

[0013] Furthermore, the solid electrolyte powder according to one aspect of the present invention may have a 50% diameter (D50) of 0.7 to 2.5 μm in its volume-based cumulative particle size distribution.

[0014] Furthermore, the solid electrolyte powder according to one aspect of the present invention may have a 99% diameter (D99) of 3 to 10 μm in its volume-based cumulative particle size distribution.

[0015] Furthermore, the solid electrolyte powder according to one aspect of the present invention may be a sulfide-based solid electrolyte powder.

[0016] The solid electrolyte layer according to the embodiment of the present invention includes the above-mentioned solid electrolyte powder.

[0017] A lithium-ion all-solid-state battery according to an embodiment of the present invention includes the solid electrolyte layer, a positive electrode, and a negative electrode. [Effects of the Invention]

[0018] The solid electrolyte powder according to the embodiment of the present invention has excellent lithium-ion conductivity, and therefore can provide a lithium-ion all-solid-state battery with high battery performance. [Brief explanation of the drawing]

[0019] [Figure 1] Figure 1 shows the volume-based particle size distribution of the solid electrolyte powder in the example. [Modes for carrying out the invention]

[0020] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be modified and implemented as appropriate without departing from the spirit of the invention. Furthermore, the "~" indicating a numerical range is used to mean that the numbers written before and after it are included as the lower limit and upper limit.

[0021] <Solid electrolyte powder> The solid electrolyte powder according to the embodiment of the present invention is used in lithium-ion all-solid-state batteries. This solid electrolyte powder is characterized in that its volume-based particle size distribution has a first peak in the particle size range of 0.5 to 0.7 μm and a second peak in the particle size range of 1 to 3 μm.

[0022] A solid electrolyte refers to a solid electrolyte that can move ions inside it. In the present invention, the type of the solid electrolyte is not particularly limited as long as it is particles containing a solid electrolyte having lithium ion conductivity, and known solid electrolytes can be used. For example, inorganic solid electrolytes such as sulfide-based solid electrolytes, oxide-based solid electrolytes, lithium nitride, and lithium iodide can be mentioned. These solid electrolytes may be used alone or in combination of multiple types.

[0023] Among them, from the viewpoint of lithium ion conductivity, at least one of a sulfide-based solid electrolyte and an oxide-based solid electrolyte having excellent lithium ion conductivity is preferable, and a sulfide-based solid electrolyte is more preferable.

[0024] The sulfide-based solid electrolyte is not particularly limited as long as it is a sulfide-based one, and those containing sulfur (S) and having lithium ion conductivity can be preferably used. Such a sulfide-based solid electrolyte may contain at least one of a crystalline phase and an amorphous phase.

[0025] The crystalline phase or the amorphous phase is not particularly limited as long as it contains Li, P, and S, and known ones can be applied. The sulfide-based solid electrolyte may contain at least one of the crystalline phase and the amorphous phase, and may contain both.

[0026] Among them, it is preferable from the viewpoint of lithium ion conductivity that at least one of the crystalline phase and the amorphous phase contains Ha in addition to Li, P, and S. Ha is at least one element selected from the group consisting of F, Cl, Br, and I.

[0027] Examples of the crystal structure of the crystalline phase include, for example, Li 10 GeP2S 12 、Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 and other LGPS types, Li6PS5Cl, Li 5.4 PS 4.4 Cl 1.6、 Li 5.6PS 4.4 Cl 0.8 Br 0.8 Li6PS5Cl 0.5 Br 0.5 Examples of argyrodite types include Li7P3S. 11 Examples include LPS crystallized glass, and crystallized glass having a composition containing Ha in addition to Li, P, and S. The phase structure of the crystalline phase and amorphous phase may be one type or two or more types.

[0028] If a crystalline phase is present, it is preferable from the viewpoint of symmetry of the crystalline structure that the crystalline structure includes an argyrodite type. Crystals with high symmetry are preferable when the lithium ion conduction path is spread in three dimensions, which is desirable when the powder is molded. Furthermore, it is also preferable from the viewpoint of easily maintaining lithium ion conductivity when obtaining powder by grinding.

[0029] To obtain an argyrodite-type crystal structure, the crystalline phase contains Ha in addition to Li, P, and S. Ha more preferably contains at least one of Cl and Br, even more preferably contains Cl, and still more preferably elemental Cl or a mixture of Cl and Br.

[0030] Argyrodite-type crystals can be defined as containing Li, P, S, and Ha, and having peaks at 2θ = 15.7 ± 0.5° and 30.2 ± 0.5° in their X-ray powder diffraction (XRD) patterns. In addition to the above, it is preferable that the XRD pattern also has a peak at 2θ = 18.0 ± 0.5°, and more preferably at 2θ = 25.7 ± 0.5°.

[0031] Argyrodite crystals are Li a PS b Ha cWhen expressed by [parameters], it is preferable that the relationships 5 < a < 7, 4 < b < 6 and 0 < c < 2 are satisfied because the crystal is likely to be of the alurgite type. It is more preferable that such an elemental ratio satisfies the relationships 5.1 < a < 6.3, 4 < b < 5.3 and 0.7 < c < 1.9, and it is even more preferable that it satisfies the relationships 5.2 < a < 6.2, 4.1 < b < 5.2 and 0.8 < c < 1.8.

[0032] That is, for a, 5 < a < 7 is preferable, 5.1 < a < 6.3 is more preferable, and 5.2 < a < 6.2 is even more preferable.

[0033] For b, 4 < b < 6 is preferable, 4 < b < 5.3 is more preferable, and 4.1 < b < 5.2 is even more preferable.

[0034] For c, 0 < c < 2 is preferable, 0.7 < c < 1.9 is more preferable, and 0.8 < c < 1.8 is even more preferable.

[0035] In this specification, the "elemental ratio" means the ratio of the content (at%) of elements.

[0036] In the case of an alurgite-type crystal, a preferable crystal structure is a cubic crystal such as F-43m, etc., but there may be hexagonal, tetragonal, orthorhombic, monoclinic, etc. with reduced symmetry, or even triclinic, etc. with further reduced symmetry.

[0037] When Ha constituting the alurgite-type crystal contains Cl and Br, when the content of Cl in the alurgite-type crystal is x (at%) and the content of Br is y (at%), the ratio represented by (x / y) is preferably 0.1 or more, more preferably 0.3 or more, and even more preferably 0.5 or more. Also, the ratio represented by (x / y) is preferably 10 or less, more preferably 3 or less, and even more preferably 1.6 or less.

[0038] When the ratio expressed as (x / y) satisfies the above range, the interaction between lithium ions and halide ions weakens, and the lithium ion conductivity of sulfide-based solid electrolytes tends to improve. This is thought to be due to the mixed anion effect, which weakens the interaction between cations and anions by mixing bromide ions, which have a larger ionic radius than chloride ions. In addition, when the ratio expressed as (x / y) satisfies the above range, the cycle characteristics of lithium-ion secondary batteries tend to improve.

[0039] Furthermore, if Ha contains Cl and Br, the ratio of the element content (at%) that constitutes the argyrodite type crystal is Li a -PS b -Cl c1 -Br c2 When expressed as such, c1 is preferably 0.1 or greater, more preferably 0.3 or greater, and even more preferably 0.5 or greater. c1 is preferably 1.5 or less, more preferably 1.4 or less, and even more preferably 1.3 or less.

[0040] c2 is preferably 0.1 or higher, more preferably 0.3 or higher, and even more preferably 0.5 or higher. c2 is preferably 1.9 or lower, more preferably 1.6 or lower, and even more preferably 1.4 or lower.

[0041] By satisfying the above ranges for c1 and c2, the proportion of halide ions in the crystal is optimized, and a stable argyrodite-type crystal is obtained while reducing the interaction between anions and lithium ions in the crystal. This tends to result in good lithium ion conductivity of the solid electrolyte. In addition, the above ranges for c1 and c2 tend to improve the cycle characteristics of lithium-ion secondary batteries.

[0042] Here, it is preferable that a, b, and (c1+c2) satisfy the same relationship as a, b, and c described above.

[0043] From the viewpoint of obtaining good lithium-ion conductivity when the crystal phase is formed into a battery, a smaller crystallite size is preferable. Specifically, a crystallite size of 1000 nm or less is preferable, 500 nm or less is more preferable, and 250 nm or less is even preferable. There is no particular lower limit to the crystallite size, but it is usually 5 nm or more.

[0044] Crystallite size can be calculated using the full width at half maximum (FMAX) of the peaks in the XRD pattern and Scherrer's formula.

[0045] In this embodiment, the crystalline phase of the sulfide-based solid electrolyte has counter-anions fixed within its crystalline structure. Furthermore, the amorphous phase of the sulfide-based solid electrolyte can also form an anionic structure within its structure by adjusting its composition.

[0046] The pair anion or anionic structure varies depending on the structure, such as the crystal structure, but on PS4 3- , P2S6 4- , P2S7 4- , O 2- S 2- , Se 2- F - Cl - , Br - , I - These are some examples.

[0047] In particular, the PS4 has a tetrahedron structure. 3- Including this is preferable from the viewpoint of improving the heat resistance of the crystal and providing thermodynamic stabilization effects.

[0048] Furthermore, if the argyrodite-type crystal is Li6PS5Cl, the counter anions that make up Li6PS5Cl are PS4. 3- It is a tetrahedron. In addition, the anti-anion is PS4 3- Examples of tetrahedral crystalline phases include LGPS-type crystals and LPS-type crystallized glass.

[0049] The structure of the counter-anions in the crystalline phase can be confirmed by structural analysis performed from XRD patterns. Furthermore, the anion structure in the amorphous phase can be confirmed by Raman spectroscopy or nuclear magnetic resonance (NMR) spectroscopy.

[0050] In this embodiment, the sulfide-based solid electrolyte may contain, in addition to crystalline and amorphous phases containing Li, P, and S, anions such as counteranions and oxide anions that are substituted at sites that take on anionic structures, as well as Li3PS4, Li4P2S6, Li2S, LiHa (where Ha is at least one halogen element selected from F, Cl, Br, and I).

[0051] In sulfide-based solid electrolytes, the total content of elements constituting the crystalline and amorphous phases, including Li, P, and S, is preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, from the viewpoint of achieving high ionic conductivity. Furthermore, there is no particular upper limit to the total content, and it may be 100% by mass. In addition, if two or more types of crystalline and amorphous phases are present, it is preferable that their total content be within the above range.

[0052] The total content of elements constituting the crystalline and amorphous phases can be determined by compositional analysis using methods such as ICP emission spectrometry, atomic absorption spectrometry, and ion chromatography. The proportion of the crystalline phase can be calculated by adding an internal standard, measuring it using XRD or neutron scattering, and then comparing the peak intensity with that of the internal standard.

[0053] The oxide-based solid electrolyte is not particularly limited as long as it is an oxide-based material, and those containing oxygen (O) and having lithium-ion conductivity can be preferably used.

[0054] For example, lithium-containing perovskite oxides, lithium-containing garnet oxides, lithium phosphate (Li3PO4), lithium niobate (LiNbO3), LAGP (Li) with a NASICON structure. 1+x Al x Ge 2-x(PO4)3(0≦x≦1)), LATP(Li) in a NASICON structure 1+x Al x Ti 2-x (PO4)3(0≦x≦1)), LZP(Li) in NASICON structure 1+4x Zr 2-x (PO4)3 (0≦x≦0.4, some of the metal elements in LZP may be replaced with other metal elements, or doping with other metal elements may be performed. Examples of other metal elements include Na, Sr, Ca, Mg, La, Y, Sc, Ce, In, Al, Ge, Ti, V, etc.). These may be used individually or in combination of several types.

[0055] Lithium-containing perovskite oxides are oxides represented by ABO3 having a perovskite crystal structure, wherein the A site preferably contains Li and at least one element selected from the group consisting of La, Sr, Ba, Na, Ca, and Nd, and the B site preferably contains at least one element selected from the group consisting of Ti, Ta, Cr, Fe, Co, Ga, and Nb.

[0056] Specifically, as a perovskite-type oxide, lithium lanthanum titanate Li 3x La 2 / 3-x TiO3 (0 ≤ x ≤ 1 / 6, also called LLTO), lithium lanthanum niobate (Li x La (1-x) / 3 Examples include NbO3)(0≦x≦1), etc. Note that some of the elements constituting lithium titanate lanthanum may be replaced with other elements, or it may be doped with other elements. Examples of other elements include Na, K, Rb, Ag, Tl, Mg, Sr, Ca, Ba, Nb, Ta, W, Ru, Cr, Mn, Fe, Co, Al, Ga, Si, Ge, Zr, Hf, Pr, Nd, Sm, Gd, Dy, Y, Eu, Tb, etc. Specifically, La (2 / 3)-x Sr x Li x TiO3, Li x La 2 / 3 Ti 1-x Al x Examples include O3.

[0057] Examples of garnet-type oxides include Li7La3Zr2O 12 Li5La3Nb2O 12 Li5La3Ta2O 12 , and Li6La2BaTa2O 12 These are some examples.

[0058] Furthermore, oxide-based solid electrolytes are not limited to crystalline materials, but may also be amorphous materials. For example, oxide-based solid electrolytes may be compounded with amorphous materials such as Li4SiO4, Li3PO4, Li3BO3, SiO2, B2O3, etc.

[0059] The solid electrolyte powder of this embodiment has a volume-based particle size distribution with a first peak in the particle size range of 0.5 to 0.7 μm and a second peak in the particle size range of 1 to 3 μm. Here, "peak" refers to a peak that can be separated by the nonlinear least squares method unless otherwise specified.

[0060] The inventors have discovered that having peaks in two specific different particle size ranges in the particle size distribution of a solid electrolyte powder improves its lithium ion conductivity. The reason for this is not entirely clear, but possible explanations include the fact that larger particles tend to maintain their crystalline structure, thus suppressing the decrease in lithium ion conductivity associated with grinding, and that larger particles act as nuclei, making it easier for smaller particles to come into contact with them, increasing the number of contact points and thus reducing interfacial resistance. Furthermore, it is possible that solid electrolyte powders with peaks in different particle size ranges may form a close-packed structure, and it is speculated that these factors contribute to the improvement of lithium ion conductivity.

[0061] The volume-based particle size distribution and volume-based cumulative particle size distribution in the solid electrolyte powder of this embodiment can be measured using a laser diffraction particle size analyzer. For example, the Microtrac MT3300EX II manufactured by Microtrac-Bell can be used.

[0062] In this embodiment, when the peak frequency of the first peak located in the particle size range of 0.5 to 0.7 μm is p1 (%) and the peak frequency of the second peak located in the particle size range of 1 to 3 μm is p2 (%), it is preferable that p2 / p1 is between 0.4 and 2.5.

[0063] When p2 / p1 is within the above range, lithium-ion conductivity is improved. Specifically, a p2 / p1 of 0.4 or higher prevents a single peak around 0.6 μm. This suppresses the decrease in conductivity caused by excessively fine particle size.

[0064] Furthermore, having a p2 / p1 ratio of 2.5 or less prevents the formation of a single peak around 2-3 μm. This suppresses the increase in interfacial resistance when assembling a battery due to the large particle size, leading to lower resistance and also preventing short circuits in the electrolyte layer.

[0065] Here, "peak frequency" refers to the proportion (%) of particle size present at the peak.

[0066] A p2 / p1 ratio of 0.5 or higher is more preferable, 0.7 or higher is even more preferable, and 0.8 or higher is particularly preferable.

[0067] Furthermore, p2 / p1 is more preferably 2.0 or less, even more preferably 1.4 or less, and particularly preferably 1.1 or less.

[0068] In this embodiment, the solid electrolyte powder preferably has a 50% diameter (D50) of 0.7 to 2.5 μm in the volume-based cumulative particle size distribution.

[0069] Because the D50 particle size is 2.5 μm or less, the particle size is small, allowing for the formation of more interfaces with the active material, thus improving battery performance. Furthermore, the continuity between solid electrolyte powders is easily ensured, suppressing an increase in interfacial resistance. Additionally, the electrolyte layer becomes denser, further suppressing the increase in interfacial resistance. to do This leads to... Furthermore, it makes it easier to prevent short circuits.

[0070] Because D50 is 0.7 μm or larger, the particle size does not become too small, thus preserving the crystallinity of the solid electrolyte powder and resulting in good lithium ion conductivity.

[0071] D50 is preferably 0.8 μm or larger, and more preferably 1.0 μm or larger. Furthermore, D50 is more preferably 1.5 μm or smaller, and even more preferably 1.2 μm or smaller.

[0072] In this embodiment, the solid electrolyte powder preferably has a 99% diameter (D99) of 3 to 10 μm in its volume-based cumulative particle size distribution.

[0073] Because the D99 particle size is 10 μm or less, the particle size is small, allowing for the formation of more interfaces with the active material, thus improving battery performance. Furthermore, the continuity between solid electrolyte powders is easily ensured, suppressing an increase in interfacial resistance. Additionally, the electrolyte layer becomes denser, further suppressing the increase in interfacial resistance. to do This leads to... Furthermore, it makes it easier to prevent short circuits.

[0074] Because the D99 size is 3 μm or larger, the particle size does not become too small, thus preserving the crystallinity of the solid electrolyte powder and resulting in good lithium ion conductivity.

[0075] D99 is more preferably 3.5 μm or larger. Furthermore, D99 is more preferably 8 μm or smaller, even more preferably 6 μm or smaller, and particularly preferably 4 μm or smaller.

[0076] In this embodiment, the solid electrolyte powder preferably has a 10% diameter (D10) of 0.1 to 0.6 μm in the volume-based cumulative particle size distribution.

[0077] Because D10 is 0.6 μm or less, the particle size is small, allowing for the formation of more interfaces with the active material, thus improving battery performance. Furthermore, the continuity between solid electrolyte powders is easily ensured, suppressing an increase in interfacial resistance. Additionally, the electrolyte layer becomes denser, further suppressing the increase in interfacial resistance. to do This leads to... Furthermore, it makes it easier to prevent short circuits.

[0078] Because D10 is 0.1 μm or larger, the particle size does not become too small, thus preserving the crystallinity of the solid electrolyte powder and resulting in good lithium ion conductivity.

[0079] D10 is more preferably 0.2 μm or larger. Furthermore, D10 is more preferably 0.5 μm or smaller, even more preferably 0.4 μm or smaller, and particularly preferably 0.3 μm or smaller.

[0080] In this embodiment, the solid electrolyte powder preferably has a 90% diameter (D90) of 1.5 to 6 μm in its volume-based cumulative particle size distribution.

[0081] Because the D90 particle size is 6 μm or less, the particle size is small, allowing for the formation of more interfaces with the active material, thus improving battery performance. Furthermore, the continuity between solid electrolyte powders is easily ensured, suppressing an increase in interfacial resistance. Additionally, the electrolyte layer becomes denser, further suppressing the increase in interfacial resistance. to do This leads to... Furthermore, it makes it easier to prevent short circuits. D90 is more preferably 2 μm or larger. Furthermore, D90 is more preferably 5 μm or smaller, and even more preferably 3 μm or smaller.

[0082] In the solid electrolyte powder of this embodiment, the conductivity is preferably 4 mS / cm or higher, more preferably 5 mS / cm or higher, and even more preferably 6 mS / cm or higher. Here, "conductivity" refers to lithium ion conductivity, which is measured by the method shown in the examples described later.

[0083] In this embodiment, a compacted powder was obtained by applying a pressure of 382 MPa to the solid electrolyte powder. The density of the compacted powder at this time was 1.65 to 1.75 g / cm³. 3 The compacted powder density is within the above range, especially 1.70 g / cm³. 3 As a result, the number of contact points between the particles of the compacted material increases, making it suitable for measuring conductivity. Here, the "density of the compacted material when a pressure of 382 MPa is applied" is measured by the method shown in the examples described later.

[0084] The method for producing the solid electrolyte powder in this embodiment is not particularly limited, but in addition to homogenization using a mortar and pestle, mechanical milling can be performed using a planetary mill, ball mill, vibratory mill, bead mill, etc.

[0085] In particular, from the viewpoint of obtaining a solid electrolyte powder having peaks in the two specific different particle size ranges mentioned above, it is preferable to produce the solid electrolyte powder by mechanical milling using a ball mill.

[0086] More specifically, in order to ensure that the particle size distribution of the solid electrolyte powder in this embodiment has peaks in two specific different particle size ranges, it is preferable to manufacture the solid electrolyte powder by grinding using a planetary ball mill or the like, or by impact grinding, compression grinding, or shear grinding using a bead mill or the like.

[0087] In grinding and crushing, an object is sandwiched between two or more relative moving work surfaces. The movement of the work surfaces generates friction between the object and the work surfaces, causing small pieces to be progressively scraped off from the surface of the object. These small pieces are thought to form the first peak with a particle size of 0.5-0.7 μm, while the core portion from which the surface is peeled off is thought to form the second peak with a particle size of 1-3 μm.

[0088] Specifically, for example, when using 1 mm alumina balls as the media, if grinding is performed for a certain period of time or longer, the D50 will reach a point where it can no longer be ground down to a finer particle size (saturation state) at around 0.5 to 0.7 μm, resulting in a single peak with a peak at a particle size of 0.5 to 0.7 μm. Therefore, in order to obtain the two different peaks mentioned above, it is necessary to stop grinding before reaching the saturation state, thereby obtaining peaks not only at a particle size of 0.5 to 0.7 μm but also at a particle size of 1 to 3 μm.

[0089] Furthermore, for example, when using 3mm alumina balls as the media, the ball diameter is relatively large, resulting in relatively large gaps between the balls, and some particles will not come into contact with the balls. Therefore, it is presumed that saturation is reached at a particle size of approximately 1 μm. In that case, since not all of the nuclei particles have been completely broken down, two different peaks are obtained, one at a particle size of 0.5-0.7 μm and another at a particle size of 1-3 μm.

[0090] Furthermore, in impact pulverization, compression pulverization, and shear pulverization, a hammer, ball, or other object moving at high speed instantaneously impacts the object, causing it to pulverize due to the impact force. The shattered fragments are thought to form a first peak with a particle size of 0.5-0.7 μm, while the core portion that is being pulverized is thought to form a second peak with a particle size of 1-3 μm.

[0091] Specifically, for example, when using 0.5 mm alumina balls as the media, as grinding continues, the peak of the particle size distribution shifts towards smaller particle sizes. Subsequently, the smaller peak remains at a particle size of 0.5-0.7 μm, and the other peak remains at a particle size of 1-3 μm, resulting in the first and second peaks. If grinding is continued in this manner, it will result in a single peak where the peaks are clustered at approximately 0.5 μm. Therefore, in order to obtain two peaks in different particle size ranges, it is necessary to stop grinding before reaching a saturation state, thereby obtaining peaks not only at 0.5-0.7 μm but also at 1-3 μm.

[0092] As described above, by appropriately adjusting the grinding means, the type and size of the media used for grinding, the grinding time, etc., the solid electrolyte powder of this embodiment having peaks in the two specific different particle size ranges mentioned above can be produced.

[0093] There are no particular restrictions on the material or size of the balls used in the ball mill; conventionally known materials can be used. Examples of ball materials used in the ball mill include alumina, zirconia, glass, and silicon nitride. The size of the balls is, for example, 0.5 to 4 mm. The grinding time is, for example, 30 to 120 minutes.

[0094] <Solid electrolyte layer> The solid electrolyte layer according to this embodiment contains the above-mentioned solid electrolyte powder and is used in a lithium-ion all-solid-state battery. A binder may also be included as needed.

[0095] The content of the solid electrolyte powder in the solid electrolyte layer is not particularly limited and can be appropriately determined according to the performance of the battery to be used. For example, assuming the entire solid electrolyte layer is 100% by mass, the content of the solid electrolyte powder is preferably 80% by mass or more, and more preferably 90% by mass or more.

[0096] Examples of binders that can be contained in the solid electrolyte layer include butadiene rubber (BR), acrylate butadiene rubber (ABR), styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF), and polytetrafluoroethylene (PTFE). The binder content in the solid electrolyte layer can be the same as in conventional methods.

[0097] The thickness of the solid electrolyte layer is not particularly limited and can be appropriately determined according to the desired performance of the battery. For example, it is preferably 10 μm or more, and more preferably 20 μm or more. If the thickness of the solid electrolyte layer is 10 μm or more, the mechanical strength will increase, making it resistant to stresses such as vibration and bending, and a highly reliable solid electrolyte layer can be obtained.

[0098] Furthermore, the thickness of the solid electrolyte layer is preferably 50 μm or less, and more preferably 30 μm or less. By making the solid electrolyte layer thin to 50 μm or less, the ionic conductivity between the positive and negative electrodes can be increased, and the energy density of the battery can also be increased.

[0099] The method for forming the solid electrolyte layer is not particularly limited. For example, the components constituting the solid electrolyte layer described above can be dispersed or dissolved in a solvent to form a slurry, which can then be coated in layers (sheets), dried, and optionally pressed to form the solid electrolyte layer. If necessary, heat may be applied to remove the binder. The thickness of the solid electrolyte layer can be easily adjusted by adjusting the amount of slurry applied.

[0100] Alternatively, instead of the wet molding described above, the solid electrolyte layer may be formed by dry press molding of solid electrolyte powder or the like on the surface of the object on which the solid electrolyte layer is to be formed (positive electrode, negative electrode, etc.). Alternatively, the solid electrolyte layer may be formed on another substrate and then transferred to the surface of the object on which the solid electrolyte layer is to be formed. From the viewpoint of being able to industrially and stably form a strong solid electrolyte layer on the surface of the object on which the solid electrolyte layer is to be formed, it is preferable to form the solid electrolyte layer on the surface of the object by wet molding using a solvent.

[0101] <Lithium-ion all-solid-state battery> The lithium-ion all-solid-state battery according to this embodiment includes the solid electrolyte layer, a positive electrode, and a negative electrode. Conventionally known positive and negative electrodes are used. Specific examples are shown below, but the invention is not limited to these.

[0102] (positive electrode) The positive electrode contains at least a positive electrode current collector and a positive electrode active material.

[0103] The positive electrode current collector can be any conductive plate material; for example, a thin metal sheet (metal foil) made of aluminum or an alloy thereof, or stainless steel can be used. These are preferable because they have excellent resistance to electrolytes and oxidation.

[0104] The positive electrode active material may be a lithium ion intercalation or a lithium ion counter anion (e.g., PF6) that intercalates or removes lithium ions. -The cathode active material is not particularly limited as long as the doping and dedoping of the material can be carried out reversibly, and any known cathode active material can be used. Examples of the cathode active material include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2), lithium nickel manganese oxide, and Li(Ni x Co y Mn z M a A composite metal oxide represented by O2(x+y+z+a=1, 0≦x≦1, 0≦y≦1, 0≦z≦1, 0≦a≦1, where M is at least one selected from Al, Mg, Nb, Ti, Cu, Zn, Cr), Li a M b (PO4) c Examples include polyanion olivine type cathodes represented by (1≦a≦4, 1≦b≦2, 1≦c≦3, and M is at least one selected from Fe, V, Co, Mn, Ni, VO), etc.

[0105] The positive electrode may have a binder that binds the positive electrode active materials together, as well as a binder that binds the positive electrode active materials to the positive electrode current collector. Conventional binders can be used.

[0106] Furthermore, the positive electrode may contain known conductive additives for positive electrodes, such as carbon-based materials like graphite and carbon black, metals like copper, nickel, stainless steel, and iron, and conductive oxides like indium tin oxide (ITO).

[0107] (Negative electrode) The negative electrode contains at least a negative electrode current collector and a negative electrode active material.

[0108] The negative electrode current collector can be any conductive plate material; for example, thin metal sheets (metal foils) such as copper or aluminum can be used. These are preferable because they have excellent resistance to electrolytes and oxidation.

[0109] The negative electrode active material is not particularly limited; any material capable of inserting and removing lithium ions may be used. For example, lithium metal, carbon-based materials, silicon, silicon alloys, tin, etc., can be used.

[0110] The negative electrode active material may be a lithium ion intercalation or a lithium ion counter anion (e.g., PF6) that intercalates or removes lithium ions. - The negative electrode active material is not particularly limited as long as the doping and dedoping of the material can be carried out reversibly, and any known negative electrode active material can be used. Examples of the negative electrode active material include carbon materials such as graphite, hard carbon, and soft carbon; metals that can form alloys with lithium such as aluminum, silicon, and tin; amorphous oxides such as silicon oxide and tin oxide; and lithium titanate (Li4Ti5O4). 12 Examples include:

[0111] In addition, the negative electrode may have a binder that binds the negative electrode active materials together, as well as a binder that binds the negative electrode active materials to the negative electrode current collector. Conventional known binders can be used.

[0112] Furthermore, the negative electrode may have a known conductive additive for negative electrodes, and the same type as the conductive additive for positive electrodes described above can be used.

[0113] The components of the lithium-ion all-solid-state battery, such as the solid electrolyte layer, positive electrode, and negative electrode, are housed in a battery casing. While conventionally known materials can be used for the battery casing, specific examples include nickel-plated iron, stainless steel, aluminum or its alloys, nickel, titanium, resin materials, and film materials.

[0114] Lithium-ion solid-state batteries come in various shapes, including coin-type, sheet-type (film-type), foldable-type, wound-type with a closed bottom, and button-type, and can be selected appropriately depending on the application.

[0115] The lithium-ion all-solid-state battery according to this embodiment can achieve good lithium-ion conductivity. [Examples]

[0116] The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto.

[0117] <Preparation of Solid Electrolyte Powder> The solid electrolyte powders of Examples 1 to 5 were prepared by the following method. Examples 1 to 4 are examples, and Example 5 is a comparative example.

[0118] (Example 1) First, sulfide-based solid electrolyte pellets (argyrodite-type crystal structure, composition: Li 5.6 PS 4.4 Cl 0.8 Br 0.8 Coarse powder obtained by crushing (AGC Corporation) with a cutter mill was then ground in a mortar and pestle (coarse grinding), and sulfide-based solid electrolytes smaller than 150 μm were selected using a sieve that passed through a 150 μm mesh. Next, a solvent for fine grinding was prepared. The solvent was a mixed solvent (100g) of 62.5g of heptane (manufactured by Kanto Chemical Co., Ltd., special grade (dehydrated -Super-)) and 37.5g of dibutyl ether (manufactured by Tokyo Chemical Industry Co., Ltd., stabilized with BHT). The mixed solvent was left to stand overnight or longer, and the pre-dehydrated product was used. Next, 100g of the above mixed solvent, 25g of the above-selected sulfide-based solid electrolyte, and 400g of 1mm diameter high-purity alumina balls (AS ONE AL9 series) were placed in a 500mL zirconia container (manufactured by Ito Seisakusho Co., Ltd.). The container was then set in an Ito Seisakusho LP-4 medium-sized planetary ball mill, and wet grinding was performed at a rotation speed of 150rpm for 30 minutes while maintaining a temperature of approximately 13°C with a spot cooler. After grinding, the mixture was passed through a stainless steel sieve with a mesh size of 150μm to recover the 1mm diameter high-purity alumina balls. After standing for 3-5 hours, the supernatant was removed, and the slurry was placed in a bottle and then into a separable flask inserted into a mantle heater located in a glove box. The solvent was dried by heating while flowing nitrogen gas, and a dried powder was obtained. The dried powder was then loosened in a mortar and passed through a stainless steel sieve with a 150 μm mesh to obtain the solid electrolyte powder of Example 1.

[0119] (Example 2) Coarse-grained product obtained by crushing sulfide-based solid electrolyte pellets with a cutter mill (argyrodite-type crystal structure, composition: Li 5.6 PS 4.4 Cl 0.8 Br 0.8 Dry powder (manufactured by AGC Inc.) was ground in a mortar and pestle (coarse grinding), and sulfide-based solid electrolytes smaller than 150 μm were selected using a sieve that passed through a 150 μm mesh. The solid electrolyte powder of Example 2 was obtained in the same manner as in Example 1, except that the size of the high-purity alumina balls of the AL9 series was set to a diameter of 3 mm and the wet grinding time was set to 60 minutes.

[0120] (Example 3) First, we crushed sulfide-based solid electrolyte pellets with a cutter mill to obtain coarse grains (argyrodite-type crystal structure, composition: Li 5.6 PS 4.4 Cl 0.8 Br 0.8 Dry powder (manufactured by AGC Inc.) was ground by hand in a mortar and pestle (coarse grinding), and sulfide-based solid electrolytes smaller than 100 μm were selected using a sieve that passed through a 100 μm mesh opening. Next, a solvent for fine grinding was prepared. The solvent was a mixed solvent (253 g) of heptane (manufactured by Kanto Chemical Co., Ltd., special grade (dehydrated -Super-)) 158.1 g and dibutyl ether (manufactured by Tokyo Chemical Industries, Ltd., stabilized with BHT) 94.9 g. Molecular sieves 4A 1 / 16 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were added to the mixed solvent and left to stand overnight or longer, and the pre-dehydrated product was used. Next, 48.2 g of the selected sulfide-based solid electrolyte (solid content concentration 16 wt%) and 288 g of 0.5 mm diameter high-purity alumina balls (AL9 series, manufactured by AS ONE) were added to 253 g of the above mixed solvent (packing rate 80 vol%), and wet grinding was performed for 10 minutes at a peripheral speed of 8 m / sec and a slurry flow rate of 300 mL / min using a bead mill type (LMZ015, manufactured by Ashizawa Finetech). After that, it was dried in the same manner as in Example 1, loosened in a mortar, and passed through a sieve with a mesh size of 150 μm to obtain the solid electrolyte powder of Example 3.

[0121] (Example 4) The solid electrolyte powder of Example 4 was obtained using the same method as in Example 2, except that the grinding time was set to 30 minutes.

[0122] (Example 5) First, we crushed sulfide-based solid electrolyte pellets with a cutter mill to obtain coarse grains (argyrodite-type crystal structure, composition: Li 5.6 PS 4.4 Cl 0.8 Br 0.8 Dry powder (manufactured by AGC Inc.) was ground by hand in a mortar and pestle (coarse grinding), and sulfide-based solid electrolytes smaller than 150 μm were selected using a sieve with a 150 μm mesh size. Next, a solvent for fine grinding was prepared. The solvent was a mixed solvent (8g) of 5g of heptane (manufactured by Kanto Chemical Co., Ltd., special grade (dehydrated -Super-)) and 3g of dibutyl ether (manufactured by Tokyo Chemical Industries, Ltd., stabilized with BHT). Molecular sieves 4A 1 / 16 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were added to the mixed solvent and left to stand overnight or longer, and the pre-dehydrated product was used. Next, 8g of the above mixed solvent, 2g of the above-selected sulfide-based solid electrolyte, and 40g of 2mm diameter high-purity alumina balls (AS ONE AL9 series) were placed in a 45mL zirconia container (manufactured by Ito Seisakusho Co., Ltd.). The container was then set in an Ito Seisakusho LP-M4 small planetary ball mill, and the first wet grinding was performed at 25°C and 200rpm for 20 minutes. The mixture was passed through a stainless steel sieve with a 150μm mesh to recover the 2mm diameter high-purity alumina balls, and in their place, 40g of 0.3mm diameter high-purity alumina balls (AS ONE AL series) were added. The container was then set in an Ito Seisakusho LP-M4 planetary ball mill, and the second wet grinding was performed at 25°C and 200rpm for 105 minutes. This mixture was passed through a stainless steel sieve with a 150 μm mesh opening to recover high-purity alumina balls with a diameter of 0.3 mm, dried using the same drying method as in Example 1, loosened in a mortar, and passed through a 150 μm mesh opening sieve to obtain the solid electrolyte powder of Example 5.

[0123] The conditions for preparing the solid electrolyte powders in Examples 1-5 described above are summarized in Tables 1 and 2 below.

[0124] [Table 1]

[0125] [Table 2]

[0126] [Methods for measuring particle size and particle size distribution] The D10, D50, D90, and D99 values ​​in the volume-based cumulative particle size distribution, as well as the first and second peak frequencies p1 and p2 in the volume-based particle size distribution, were measured using a Microtrac MT3300EX II laser diffraction particle size analyzer manufactured by Microtrac-Bell, using a wet method. The results are shown in Table 3 and Figure 1.

[0127] [Conductivity] The lithium-ion conductivity of the solid electrolyte powders in Examples 1-5 was measured using the AC impedance method. Specifically, in a glove box with a dew point of -50°C or lower, a manual Newton press NT-50H (Kenis Corporation) was used to place the sulfide-based solid electrolyte powders of Examples 1-5 into a cylinder with an inner diameter of 1 cm, and a pressure of up to 30 kN was applied to compact them into a powder. Subsequently, the lithium-ion conductivity was measured using an electrochemical measurement system VSP (Biologic Corporation) under the conditions of applied voltage of 100 mV, measurement temperature of 25°C, and measurement frequency range of 100 Hz to 1 MHz by applying AC impedance. The results are shown in Table 3.

[0128] [Compacted powder density] The thickness of the pellets obtained during the conductivity measurement described above, i.e., the pellets compressed under a pressure of 382 MPa, was measured, and the pellet density, i.e., the compacted powder density, was determined from the weight of the electrolyte powder and the pellet volume. The results are shown in Table 3.

[0129] [Table 3]

[0130] As shown in Table 3 and Figure 1, the solid electrolyte powders of Examples 1-4, which have a first peak in the 0.5-0.7 μm particle size range and a second peak in the 1-3 μm particle size range in their volume-based particle size distribution, were found to have higher conductivity and better performance compared to the solid electrolyte powder of Example 5, which does not have a second peak in the 1-3 μm particle size range.

[0131] Although various embodiments have been described above with reference to the drawings, it goes without saying that the present invention is not limited to these examples. It is clear to those skilled in the art that various modifications or alterations can be conceived within the scope of the claims, and these will naturally also fall within the technical scope of the present invention. Furthermore, the components of the above embodiments may be combined in any way without departing from the spirit of the invention.

[0132] This application is based on Japanese Patent Application No. 2021-161464 filed on September 30, 2021, and its contents are incorporated herein by reference.

Claims

1. A solid electrolyte powder used in lithium-ion all-solid-state batteries, The volume-based particle size distribution of the solid electrolyte powder has a first peak in the particle size range of 0.5 to 0.7 μm and a second peak in the particle size range of 1 to 3 μm. The characteristic is that when the peak frequency of the first peak is p1 (%) and the peak frequency of the second peak is p2 (%), p2 / p1 is 0.4 or more and 2.5 or less. Solid electrolyte powder.

2. The solid electrolyte powder according to claim 1, wherein the 50% diameter (D50) in the volume-based cumulative particle size distribution is 0.7 to 2.5 μm.

3. The solid electrolyte powder according to claim 1, wherein the 99% diameter (D99) in the volume-based cumulative particle size distribution is 3 to 10 μm.

4. The solid electrolyte powder according to claim 1, wherein the solid electrolyte powder is a sulfide-based solid electrolyte powder.

5. A solid electrolyte layer comprising the solid electrolyte powder described in any one of claims 1 to 4.

6. A lithium-ion all-solid-state battery comprising a solid electrolyte layer according to claim 5, a positive electrode, and a negative electrode.

Images