Electrode for all-solid-state secondary batteries, and all-solid-state secondary battery

Abstract

The present invention provides: an all-solid-state secondary battery which has a low internal resistance; and an electrode for constituting the all-solid-state secondary battery. An all-solid-state secondary battery according to the present invention relates to goals 3, 7, 11 and 12 of the SDGs.　An electrode for all-solid-state secondary batteries according to the present invention is used for an all-solid-state secondary battery which comprises a solid electrolyte layer, and is characterized by comprising a molded body of an electrode mixture that contains an electrode active material, a conductive assistant and a solid electrolyte, while being also characterized in that: the particle diameter D90 of the electrode active material is 1.5 µm or less; and if A (µm) is the average particle diameter D50 of the electrode active material and B (µm) is the average particle diameter D50 of the conductive assistant, the relational expression 0.4 ≤ B / A ≤ 1.5 is satisfied. In addition, an all-solid-state secondary battery according to the present invention comprises a positive electrode, a negative electrode, and a solid electrolyte layer that is interposed between the positive electrode and the negative electrode, and is characterized in that at least one of the positive electrode and the negative electrode is the above-described electrode for all-solid-state secondary batteries.

Description

[Technical Field]

[0001] The present invention relates to an all-solid-state secondary battery having low internal resistance and an electrode for constituting the all-solid-state secondary battery. [Background technology]

[0002] In recent years, with the development of portable electronic devices such as mobile phones and laptop personal computers, and the practical application of electric vehicles, there has been a growing demand for small, lightweight batteries with high capacity and high energy density.

[0003] Currently, lithium secondary batteries, particularly lithium ion secondary batteries, that can meet this demand use lithium-containing composite oxides such as lithium cobalt oxide (LiCoO) and lithium nickel oxide (LiNiO) as the positive electrode active material, graphite or the like as the negative electrode active material, and an organic electrolyte solution containing an organic solvent and a lithium salt as the non-aqueous electrolyte.

[0004] Furthermore, with the further development of devices that use lithium-ion secondary batteries, there is a demand for lithium-ion secondary batteries with longer life, higher capacity, and higher energy density, as well as a high demand for the reliability of these longer-life, higher-capacity, and higher-energy-density lithium-ion secondary batteries.

[0005] However, the organic electrolyte solution used in lithium-ion secondary batteries contains a flammable organic solvent, which can cause the organic electrolyte solution to generate excessive heat when an abnormality such as a short circuit occurs in the battery. In addition, with the recent trend toward higher energy density of lithium-ion secondary batteries and an increasing amount of organic solvent in the organic electrolyte solution, there is a demand for even greater reliability in lithium-ion secondary batteries.

[0006] In light of the above, all-solid-state lithium secondary batteries that do not use organic solvents (all-solid-state secondary batteries) are being considered. All-solid-state lithium secondary batteries use a molded body of a solid electrolyte that does not use an organic solvent instead of the conventional organic solvent-based electrolyte, and are therefore highly reliable with no risk of abnormal heat generation from the solid electrolyte.

[0007] Furthermore, all-solid-state secondary batteries are not only highly safe, but also highly reliable, environmentally resistant, and have a long lifespan, making them promising maintenance-free batteries that can contribute to social development while also continuing to contribute to safety and security. Providing all-solid-state secondary batteries to society will contribute to achieving Goal 3 (Ensure healthy lives and promote well-being for all at all ages), Goal 7 (Ensure access to affordable, reliable, sustainable, and modern energy for all), Goal 11 (Make cities inclusive, safe, resilient, and sustainable cities and human settlements), and Goal 12 (Ensure sustainable consumption and production patterns) of the 17 Sustainable Development Goals (SDGs) established by the United Nations.

[0008] In order to improve the characteristics of such secondary batteries, many attempts have been made to control the particle size of components such as active materials and conductive additives contained in the electrodes (Patent Documents 1 to 3, etc.). [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 10-199507 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-33641 [Patent Document 3] Patent Publication No. 2021-44195 Summary of the Invention [Problem to be solved by the invention]

[0010] Incidentally, in all-solid-state secondary batteries, it is desirable that the internal resistance be low in order to enhance various characteristics, and one way to achieve this is to reduce the resistance of the electrodes, for example.

[0011] In lithium-ion secondary batteries that use a non-aqueous electrolyte, effective means for shortening the diffusion distance of lithium ions inside the active material and reducing the resistance of the electrode include coating the active material with carbon or increasing the amount of conductive additive added to the electrode.

[0012] However, in all-solid-state secondary batteries in which lithium ions are not diffused using a liquid medium, the carbon coating layer on the surface of the active material and the conductive additive in the electrode inhibit ion conduction at the interface between the active material and the solid electrolyte in the electrode, and therefore, using such means ends up increasing the resistance of the electrode.

[0013] Therefore, in all-solid-state secondary batteries that do not use non-aqueous electrolytes, there is a need to develop a technology that reduces internal resistance by a means different from the above.

[0014] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an all-solid-state secondary battery having low internal resistance and an electrode for constituting the all-solid-state secondary battery. [Means for solving the problem]

[0015] The electrode for an all-solid-state secondary battery of the present invention is an electrode used in an all-solid-state secondary battery having a solid electrolyte layer, and has a molded body of an electrode mixture containing an electrode active material, a conductive additive, and a solid electrolyte, and has a particle diameter D of the electrode active material. 90 is 1.5 μm or less, and the average particle diameter D 50 is A (μm), and the average particle diameter D of the conductive additive 50 When B (μm) is used, the relationship 0.4≦B / A≦1.5 is satisfied.

[0016] The all-solid-state secondary battery of the present invention comprises a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, and at least one of the positive electrode and the negative electrode is the electrode for the all-solid-state secondary battery of the present invention. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide an all-solid-state secondary battery having low internal resistance and an electrode for constituting the all-solid-state secondary battery. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a cross-sectional view schematically illustrating an example of an all-solid-state secondary battery of the present invention. [Figure 2] FIG. 2 is a plan view schematically illustrating another example of the all-solid-state secondary battery of the present invention. [Figure 3] FIG. 3 is a cross-sectional view taken along line II in FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0019] <Electrode for all-solid-state secondary battery> The electrode for an all-solid-state secondary battery of the present invention (hereinafter sometimes simply referred to as "electrode") is used in an all-solid-state secondary battery having a solid electrolyte layer, and has a molded body of an electrode mixture containing an electrode active material, a conductive additive, and a solid electrolyte. 90 is 1.5 μm or less, and the average particle diameter D of the electrode active material 50 is A (μm), and the average particle diameter of the conductive additive is D 50 When B (μm) is used, the relationship 0.4≦B / A≦1.5 is satisfied.

[0020] In an electrode having a molded body of an electrode mixture containing an electrode active material, a conductive additive, and a solid electrolyte, when the volume-based particle size distribution of the electrode active material and the volume-based particle size distribution of the conductive additive are close to each other, that is, when the average particle diameter D 50 The A value and the average particle diameter D of the conductive additive 50The inventors' investigations have revealed that when the B value of the electrode mixture is relatively close to the B value of the electrode mixture, electron conductive paths and ion conductive paths can be formed satisfactorily in the electrode mixture compact.

[0021] On the other hand, it has also been found that even when the A value and the B value are relatively close to each other, if the particles of the electrode active material are large, it is difficult to reduce the resistance of the electrode.

[0022] Therefore, in the present invention, the D 90 The electrode resistance can be reduced by controlling the B / A value within a specific range while adjusting the B / A value to a specific value or less. Therefore, a battery using the electrode of the present invention (the all-solid-state secondary battery of the present invention) has low internal resistance and can exhibit excellent discharge characteristics.

[0023] Electrode active material particle diameter D 90 and D 50 The mean particle diameter D of the conductive additive is 90% and 50% of the volume-based cumulative fraction when calculating the integral volume from particles with small particle sizes. 50 The term also refers to the 50% diameter value in the volume-based cumulative fraction when calculating the integral volume from particles with small particle sizes.

[0024] D of the electrode active material in this specification 90 and D 50 The (A value) is a value determined by the following method (the numerical values ​​described in the examples are values ​​determined using the equipment and software described below). 90 and D 50The particle size distribution for determining the particle size distribution (D') was obtained by sampling all particles identified as electrode active material and not overlapping the edges of the image in scanning electron microscope (SEM) images (magnifications of 5,000x to 10,000x) of multiple arbitrary locations on the cross section of a sample piece prepared by focused ion beam (FIB) processing, or on the cross section of a compact of electrode mixture prepared by cross-section processing using an ion milling device (IM4000, Hitachi High-Tech Corporation) after cutting the battery. The number of observation fields was determined so that at least 3,000 particles of electrode active material were observed. The electrode active material particles in the SEM images could be identified by energy dispersive X-ray spectroscopy (EDS) mapping analysis, electron probe microanalysis (EPMA) analysis, or time-of-flight secondary ion mass spectrometry (TOF-SIMS) mapping analysis. The apparent particle size D'(n) of the nth particle of the electrode active material was defined as the diameter of a circle having an area equivalent to the cross section of the nth particle of the electrode active material. Considering that the average diameter of the cross-section of a sphere cut at any depth from the outermost surface is √(2 / 3) times the sphere diameter D, the particle size D(n) [=D'(n) / √(2 / 3)] of the nth particle of the electrode active material is calculated. A volume-based particle size distribution (histogram) can be created by multiplying the frequency of each particle size obtained by the volume V(n) of each particle and dividing the result by the sum of V(n).

[0025] Image analysis software can be used to sample electrode active material particles. Specifically, ImageJ is used to analyze the contrast histogram of the image, and the contrast region to which particles attributed to the electrode active material by the EDS mapping analysis or the like belong is selected and the image is binarized. The binarized image is then subjected to shrinkage and expansion processes twice in the order described above, once for Fill Halls processing, and once for shrinkage processing, after which adjacent particles are divided at the watershed. Analyze Particles is used to find particles with an area of ​​0.005 (μm 2 ) particles, more than 3,000 particles can be sampled (particles that hang over the edge of the image are excluded).

[0026] The particle size distribution of the electrode active material on a volume basis obtained in this way is plotted with particle size on the horizontal axis and cumulative frequency on the vertical axis, and D is calculated from the particle size at a cumulative frequency of 90% and that at a cumulative frequency of 50%. 90 and D 50 Ask for.

[0027] In addition, the conductive additive D 50 The (B value) is a value obtained by analyzing the binarized image in the same manner as for the electrode active material, except that the Fill Halls processing and the operation of dividing adjacent particles at watersheds are not performed on the binarized image, and the number of conductive additive particles sampled is 700 or more.

[0028] Electrode active material D 50 The A value and the D value of the conductive additive 50 If the ratio B / A of the B value (B) is too small, the solid electrolyte particles may easily penetrate between each other in the molded electrode mixture, preventing contact between them and hindering ion conduction. If the B / A value is too large, the short-distance path for electron conduction in the molded electrode mixture may be insufficient. Therefore, from the viewpoint of favorably forming ion conduction paths and electron conduction paths in the molded electrode mixture, the B / A value is 0.4 or more, preferably 0.5 or more, and 1.5 or less, preferably 1.4 or less.

[0029] Furthermore, if the electrode active material contained in the molded body of the electrode mixture is too large, local stress concentration occurs inside the molded body of the electrode mixture when the volume of the electrode active material changes due to charging and discharging of the battery, and there is a risk that the internal structure of the molded body will be destroyed, resulting in an increase in resistance. Furthermore, the larger the electrode active material, the longer the diffusion distance of ions inside the electrode active material, resulting in an increase in resistance. Therefore, from the viewpoint of suppressing the increase in resistance due to these factors, it is necessary to reduce the D of the electrode active material. 90is 1.5 μm or less, and preferably 1.2 μm or less. If the electrode active material contained in the molded body of the electrode mixture is too small, the active material particles may form agglomerates, which may reduce the effect of reducing resistance. Therefore, from the viewpoint of uniformly forming the interface between the solid electrolyte particles and the active material particles and more effectively exerting the effect of reducing resistance, the D of the electrode active material is 90 is preferably 0.3 μm or more, and more preferably 0.4 μm or more.

[0030] In addition, the A value of the electrode active material (D 50 ) is preferably 0.1 μm or more, more preferably 0.2 μm or more, from the viewpoint of forming a uniform interface between the solid electrolyte particles and the active material particles and more effectively exerting the effect of reducing resistance, and is preferably 1.1 μm or less, more preferably 0.9 μm or less, from the viewpoint of shortening the average diffusion length of ions inside the electrode active material and further reducing resistance. Furthermore, the B value (D 50 ) is preferably 0.04 μm or more, more preferably 0.08 μm or more, from the viewpoint of improving ion conduction between the solid electrolyte particles, and is preferably 1.65 μm or less, more preferably 1.35 μm or less, from the viewpoint of improving the formation of a short-distance conduction path for electrons within the electrode.

[0031] The electrode of the present invention has a molded body of an electrode mixture containing an electrode active material, a conductive additive, and a solid electrolyte, and examples thereof include an electrode consisting of only a molded body (pellet, etc.) of the electrode mixture, and an electrode having a structure in which a layer (electrode mixture layer) consisting of a molded body of the electrode mixture is formed on a current collector.

[0032] The electrode of the present invention can be used as a positive electrode of an all-solid-state secondary battery, and can also be used as a negative electrode of an all-solid-state secondary battery.

[0033] When using an electrode as the positive electrode of a all-solid-state secondary battery, as the particles of the electrode active material, particles of an active material capable of occluding and releasing lithium ions, similar to those used in conventionally known lithium-ion secondary batteries, can be used. Specifically, LiM r Mn 2-r O4 (where M is at least one element selected from the group consisting of Li, Na, K, B, Mg, Ca, Sr, Ba, Ti, V, Cr, Zr, Fe, Co, Ni, Cu, Zn, Al, Sn, Sb, In, Nb, Ta, Mo, W, Y, Ru, and Rh, and 0 ≦ r ≦ 1), spinel-type lithium manganese composite oxide represented by Li r Mn (1-s-r) Ni s M t O (2-u) F v (where M is at least one element selected from the group consisting of Co, Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr, and W, 0.8 ≦ r ≦ 1.2, 0 < s < 0.5, 0 ≦ t ≦ 0.5, u + v < 1, -0.1 ≦ u ≦ 0.2, 0 ≦ v ≦ 0.1), layered compound represented by LiCo 1-r M r O2 (where M is at least one element selected from the group consisting of Al, Mg, Ti, V, Cr, Zr, Fe, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, and Ba, and 0 ≦ r ≦ 0.5), lithium cobalt composite oxide represented by LiNi 1-r M r O2 (where M is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Fe, Co, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, and Ba, and 0 ≦ r ≦ 0.5), lithium nickel composite oxide represented by Li 1+s M 1-r N r PO4F s(wherein M is at least one element selected from the group consisting of Fe, Mn, and Co, and N is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, V, and Ba, and 0≦r≦0.5, 0≦s≦1), an olivine-type composite oxide represented by Li2M 1-r N r Examples of the positive electrode active material include one or more types of particles of various positive electrode active materials used in conventionally known non-aqueous electrolyte secondary batteries, such as a pyrophosphate compound represented by P2O7 (wherein M is at least one element selected from the group consisting of Fe, Mn, and Co, and N is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, V, and Ba, and 0≦r≦0.5).

[0034] When the electrode is a positive electrode, the electrode active material (positive electrode active material) may be provided with a reaction suppression layer on its surface to suppress reaction with the solid electrolyte, in order to more effectively suppress side reactions of the solid electrolyte.

[0035] The reaction suppression layer may be made of any material that has ion conductivity and can suppress the reaction between particles of the electrode active material (cathode active material) and the solid electrolyte. Examples of materials that can form the reaction suppression layer include oxides containing Li and at least one element selected from the group consisting of Nb, P, B, Si, Ge, Ti, Zr, Ta, and W. More specifically, Nb-containing oxides such as LiNbO3, Li3PO4, Li3BO3, Li2SO4, Li4SiO4, Li4GeO4, LiTiO3, LiZrO3, and Li2WO4 are examples. The reaction suppression layer may contain only one of these oxides, or two or more of them, or may even form a composite compound of two or more of these oxides. Among these oxides, Nb-containing oxides are preferred, and LiNbO3 is more preferred.

[0036] The reaction suppression layer is preferably present on the surface in an amount of 0.1 to 2.0 parts by mass per 100 parts by mass of the electrode active material, which allows for effective suppression of the reaction between the particles of the electrode active material and the solid electrolyte.

[0037] Examples of methods for forming a reaction suppression layer on the surface of an electrode active material include the sol-gel method, mechanofusion method, CVD method, PVD method, and ALD method.

[0038] When the electrode of the present invention is a negative electrode, examples of the negative electrode active material include carbon materials such as graphite; simple substances, compounds (oxides, etc.) containing elements such as Si, Sn, Ge, Bi, Sb, and In, and alloys thereof; lithium-containing nitrides or lithium-containing oxides (Li4Ti5O 12 Lithium-titanium oxides such as TiNb2O7, niobium composite oxides such as TiNb2O7, tungsten oxide, molybdenum oxide, vanadium oxide, etc.) and other compounds that can be charged and discharged at low voltages close to that of lithium metal.

[0039] In addition, whether the electrode is a positive electrode or a negative electrode, a niobium composite oxide (A) containing at least two elements selected from the group consisting of Cu, Zn, Al, W, Fe, and Ti can be used as the electrode active material. The niobium composite oxide is preferably of the monoclinic type, which is advantageous for improving the output characteristics of the electrode.

[0040] In addition, whether the electrode is a positive electrode or a negative electrode, a monoclinic niobium composite oxide (B) represented by the following general formula (1) can be used as the electrode active material, which is also advantageous in improving the output characteristics of the electrode.

[0041] A y M 1 αAl x- αNb 12-x-z M 2 z O 29- δ (1)

[0042] In the general formula (1), A is at least one element selected from Li and Na; M1 is at least one element selected from the group consisting of Fe, Mn, Zn, Cu, Ag, Mg, Ca, Sr, Ba, Co, Eu, Y, Bi, La, Ce, Nd, Sm and Gd; M 2 is at least one element selected from the group consisting of K, Ti, Ni, Zr, V, Mo, Ta and W, and 0 <x≦1.1、0≦y≦24、0≦z≦2、-1≦δ≦2、0<α≦0.4xである。

[0043] element M 1 is Fe(Fe 2+ ), Mn(Mn 2+ ), Zn(Zn 2+ ), Cu(Cu + , Cu 2+ ), Ag(Ag + ), Mg(Mg 2+ ), Ca(Ca 2+ ), Sr(Sr 2+ ), Ba(Ba 2+ ), Co(Co 2+ ), Eu(Eu 2+ ,EU 3+ ), Y(Y 3+ ), Bi(Bi 3+ ), La(La 3+ ), Ce(Ce 3+ , Ce 4+ ), Nd(Nd 3+ ), Sm(Sm 3+ ) and Gd(Gd 3+ ) is Nb(Nb 5+ ) and Al(Al 3+ ) has a larger effective ionic radius than AlNb 11 O 29 Based on Al, part of which is element M 1 By being substituted by AlNb 11 O 29 The lattice constant of the crystal is larger than that of the niobium composite oxide (B), and the diffusibility of the element A ions inside the crystal is increased. Therefore, in an all-solid-state secondary battery constructed using an electrode in which the niobium composite oxide (B) is used as an electrode active material, the output characteristics are improved.

[0044] In addition, AlNb11 O 29 In this case, Al has the effect of stabilizing the crystal structure, and a part of it is replaced by the element M. 1 It is thought that the stability of the crystal structure of the oxide may be impaired by the substitution, and as a result, it is expected that in an all-solid-state secondary battery configured with this oxide as an active material, the capacity may be more likely to decrease when charge and discharge are repeated (the charge and discharge cycle characteristics may be deteriorated).

[0045] However, contrary to this expectation, as represented by the general formula (1), the element M 1 If the amount of Al substituted by AlNb is within a certain range, the capacity decrease during repeated charge and discharge in an all-solid-state secondary battery configured with this oxide as the active material can be reduced by replacing AlNb 11 O 29 The reason is that the ionic radius of Nb (Nb 5+ ) and Al(Al 3+ ) larger than element M 1 By containing , the lattice constant of the oxide increases before the element A ions that act as carriers are inserted, and the space in which the element A ions are occluded expands, thereby improving the insertion length of the element A ions during charge and discharge. Detachment This is presumably because the volume change of the oxide (active material) during charging and discharging can be suppressed, making it possible to suppress deterioration of the electrode even when the all-solid-state secondary battery is repeatedly charged and discharged.

[0046] In this way, by using an electrode containing niobium composite oxide (B) as an electrode active material, it is possible to improve the output characteristics of an all-solid-state secondary battery while maintaining high charge-discharge cycle characteristics.

[0047] The niobium composite oxide (B) represented by the general formula (1) contains an element M 1 The alloy may contain only one element selected from Fe, Mn, Zn, Cu, Ag, Mg, Ca, Sr, Ba, Co, Eu, Y, Bi, La, Ce, Nd, Sm, and Gd, or may contain two or more elements selected from these elements M. 1Among these, Fe, Mn, Zn and Cu are preferred, and Zn and Cu are more preferred, because they are particularly easy to substitute for Al in terms of electron configuration and have a high effect of increasing the electronic conductivity of the niobium composite oxide (B).

[0048] The niobium composite oxide (B) represented by the general formula (1) contains an element M 1 For example, Fe 3+ / Fe 2+ and Cu 2+ / Cu + When the oxide represented by the general formula (1) contains an element having a plurality of valences, such as niobium, a large number of oxygen vacancies may occur (i.e., δ becomes larger than 0 in the general formula (1)), which further improves the electronic conductivity and ionic conductivity of the niobium composite oxide (B) represented by the general formula (1). 1 When Fe or Cu is contained as the cation, further improvement in the output characteristics of the all-solid-state secondary battery can be expected.

[0049] The niobium composite oxide (B) represented by the general formula (1) contains an element M which substitutes a part of Al. 1 and at least one element M selected from the group consisting of K, Ti, Ni, Zr, V, Mo, Ta and W. 2 These elements M 2 is a component that does not replace a portion of the Al constituting the crystal in the niobium composite oxide (B) represented by the general formula (1) and having a monoclinic crystal structure, but substitutes Nb, or is a component that is dissolved in the crystal or contained as an impurity. 2 The amount z may be 0, but the element M 2 When it is contained, it is permissible because it does not affect the performance of the niobium composite oxide (B) so long as the amount z is not more than 2. Furthermore, the niobium composite oxide (B) represented by the general formula (1) may contain water.

[0050] In the niobium composite oxide (B) represented by the general formula (1), Al is a component for enhancing the structural stability of the niobium composite oxide (B), and the action of Al improves the reversibility of the electrode active material during charge and discharge of the all-solid-state secondary battery.

[0051] In the niobium composite oxide (B) represented by the general formula (1), as described above, a part of Al is the element M. 1 The amount of Al and the element M 1 The sum of the amounts of Al and M is greater than 0. 1 From the viewpoint of better exerting the above-mentioned functions, the content of Al and element M in the niobium composite oxide (B) is preferably 0.8 or more. 1 If the amount of Al is too large, the amount of Nb in the niobium composite oxide (B) becomes too small, and there is a risk that the effect of the element M will not be exhibited well. 1 The sum x of the amount of is preferably 1.1 or less, and more preferably 1.05 or less.

[0052] In addition, in the niobium composite oxide (B) represented by the general formula (1), the element M 1 The amount α is greater than 0, and is preferably 0.05 or greater from the viewpoint of better ensuring the effect of improving the output characteristics of the all-solid-state secondary battery. However, in the niobium composite oxide (B) represented by the general formula (1), the element M 1 If the amount of element M is too large, the stability of the crystal structure decreases, and the charge-discharge cycle characteristics of the all-solid-state secondary battery tend to decrease. Therefore, from the viewpoint of improving the charge-discharge cycle characteristics of the all-solid-state secondary battery, it is preferable that the amount of element M in the oxide represented by the general formula (1) is too large. 1 The amount α is preferably 0.4x or less, more specifically, more preferably 0.44 or less, and even more preferably 0.4 or less.

[0053] In the niobium composite oxide (B) represented by the general formula (1), the element A is at least one of Li and Na, and is absorbed into or desorbed from the niobium composite oxide (B) by charging and discharging the all-solid-state secondary battery (i.e., functions as a carrier). The niobium composite oxide (B) may or may not contain the element A. In the case of a niobium composite oxide (B) that does not contain the element A, for example, by charging an all-solid-state secondary battery used as a negative electrode active material or by pre-doping with ions of element A before use in an all-solid-state secondary battery, ions of element A are inserted, and the niobium composite oxide (B) comes to contain the element A.

[0054] The niobium composite oxide (B ) The amount y of the element A in the formula (I) is preferably 0 or more and 24 or less.

[0055] In the niobium composite oxide (B) represented by the general formula (1), the amount of oxygen is originally AlNb 11 O 29 29 as well as element M 1 The value may vary depending on the presence of niobium composite oxide (B). Specifically, in the general formula (1), δ is preferably −1 or more, preferably 2 or less, and more preferably 1.95 or less. When δ in the general formula (1) is greater than 0, oxygen deficiency occurs in the oxide. In this case, the electronic conductivity and the conductivity of element A ions of the electrode active material containing the niobium composite oxide (B) are improved, and the use of such an active material makes it possible to further increase the energy density of the all-solid-state secondary battery.

[0056] In the niobium composite oxide (B) represented by the general formula (1), δ, which relates to the amount of oxygen, is determined by the amount of the element M that forms the cation. 1 , element M 2 The amount of Nb and Al is determined by the amount of oxygen that forms the anion.

[0057] Among the niobium composite oxide (A) and the niobium composite oxide (B), one of the more preferred forms is an oxide that satisfies the following general formula (2).

[0058] M 1 αAl 1-1.5 αNb 11+0.5 αO 29- δ (2)

[0059] The element M in the general formula (2) 1 is at least one of Zn and Cu, and 0<α≦0.4, 0≦δ≦0.5α. The element M in the general formula (2) 1 The amount α is preferably 0.05 or more, preferably 0.4 or less, and more preferably 0.35 or less. In addition, in the general formula (2), δ relating to the amount of oxygen is 0 or more and 0.5α or less, but as described above, 0<α≦0.4, so the value of δ is 0 or more and 0.2 or less.

[0060] When Li ions are inserted into an oxide satisfying the general formula (2), it comes to satisfy, for example, the following general formula (3).

[0061] Li y M 1 αAl 1-1.5 αNb 11+0.5 αO 29- δ (3)

[0062] In the general formula (3), the element M 1 The amount α and the amount of oxygen δ are the same as those in the general formula (2), and 0 <y≦22である。

[0063] Niobium composite oxide (A) and niobium composite oxide (B) can be used as either a positive electrode active material or a negative electrode active material, depending on the type of active material used in the counter electrode of the electrode containing them. Therefore, when the electrode of the present invention is a positive electrode, niobium composite oxide (A) and niobium composite oxide (B) can be used as a positive electrode active material, and when the electrode of the present invention is a negative electrode, niobium composite oxide (A) and niobium composite oxide (B) can be used as a negative electrode active material. Furthermore, lithium titanium oxide, which is exemplified as a negative electrode active material, can also function as a positive electrode active material depending on the type of active material contained in the counter electrode, and therefore can also be used as a positive electrode active material when the electrode of the present invention is a positive electrode.

[0064] In the case of the monoclinic niobium composite oxide (A) and niobium composite oxide (B), if the crystallites are too fine, there is a risk that polarization will increase at the end of discharge in an all-solid-state secondary battery using an electrode. Therefore, from the viewpoint of suppressing the occurrence of such problems and enabling the construction of an all-solid-state secondary battery with better characteristics, the monoclinic niobium composite oxide (A) and niobium composite oxide (B) are designed to have a crystallite size d (μm) in the b-axis direction and an average particle diameter D 50 That is, the ratio d / A to the A value is preferably 0.12 or more, and more preferably 0.15 or more. The upper limit of the d / A value is, for example, 0.7, from the viewpoint of suppressing plastic deformation of the electrode caused by differences in the magnitude of expansion and contraction for each crystal orientation.

[0065] [Method for producing niobium composite oxide (A) and niobium composite oxide (B)] The method for producing the niobium composite oxide (A) and the niobium composite oxide (B) is not particularly limited. For example, they can be synthesized and produced by a solid-phase reaction method in which various metal oxides of constituent elements such as Nb, Al, Cu, and Zn are mixed and fired, or a reaction method in which a mixture of metal compounds prepared by coprecipitating chloride salts, nitrates, and alkoxides of the respective metals in a liquid phase is used as a precursor.

[0066] In the solid-state reaction method, firing is preferably performed at a temperature of 800°C or higher, more preferably in the range of 900°C to 1100°C, to enhance the interdiffusion of various metal ions. The firing time is not particularly limited, but can be performed for 1 to 1000 hours. If the firing temperature exceeds 1100°C, oxygen is gradually released from the sample, resulting in the formation of crystal phases other than the monoclinic crystal phase, or the composition no longer satisfying, for example, the general formulas (1) and (2). Therefore, it is more preferable to hold the sample at 1100°C or higher for 10 hours or less. The cooling rate of the sample during firing is not particularly limited as long as a monoclinic crystal phase is obtained. However, to obtain a stable monoclinic crystal phase at this temperature, a cooling rate of 15°C / min to 60°C / min (including natural cooling) is preferred. Rapid cooling may also be performed at a cooling rate of 1°C / sec to 1000°C / sec.

[0067] [Method for determining the composition of niobium composite oxide (A) and niobium composite oxide (B)] The compositions of the niobium composite oxide (A) and the niobium composite oxide (B) can be analyzed, for example, using inductively coupled plasma atomic emission spectroscopy (ICP-AES). When quantification using ICP-AES is difficult because the niobium composite oxide (A) and the niobium composite oxide (B) are sintered with an oxide-based solid electrolyte, making it difficult to separate the individual components, the compositions can also be determined by a method that combines an SEM or a transmission electron microscope (TEM) with various elemental analysis methods such as an energy dispersive X-ray spectrometer (EDS) or a wavelength dispersive X-ray spectrometer (WDS).

[0068] [Method for confirming oxygen vacancies in niobium composite oxide (A) and niobium composite oxide (B)] The occurrence of oxygen defects in niobium composite oxide (A) and niobium composite oxide (B) can be confirmed by X-ray photoelectron spectroscopy (XPS) by the presence of a mixture of peaks attributable to pentavalent niobium and peaks attributable to tetravalent niobium in these composite oxides (confirmed by this method in the Examples described later). The C1s peak position of the contaminating hydrocarbon on the sample surface was set at 284.6 eV, and the binding energy of the spectrum was corrected for charge charging. An XPS spectrum was obtained in the binding energy range from 202 eV to 214 eV, and the background shape was estimated using the iterative Shirley method, and the background was removed from the spectrum. Peak fitting was performed on the obtained spectrum using a pseudo-Voigt function, and the Nb in Nb3d3 / 2 was identified. 5+ The area of ​​the peaks (obtained at binding energies of 209.8 eV to 210.2 eV) assigned to Nb 4+ Peaks attributed to (Nb 5+ The area of ​​the peak (a peak is obtained at a position 0.5 eV to 2 eV lower in binding energy than the peak position assigned to 3d3 / 2) is calculated, and the average valence of Nb is calculated. 5+ The area of ​​the peaks (obtained at binding energies of 206.6 eV to 207.1 eV) assigned to Nb 4+ Peaks attributed to (Nb 5+ The area of ​​the peak (a peak is obtained at a position 0.5 eV to 2 eV lower in binding energy than the peak position assigned to 3d5 / 2) is calculated, and the average valence of Nb is calculated. The average value of the average valence of Nb calculated from Nb3d3 / 2 and the average valence of Nb calculated from Nb3d5 / 2 is calculated, and the average valence of Nb contained in the active material is determined.

[0069] Similar to the average valence of Nb, the average valence of Cu can also be determined. XPS spectra were acquired in the binding energy range from 925 eV to 950 eV, and the Cu valence of Cu2p3 / 2 was determined. 2+ The area of ​​the peaks (obtained at binding energies of 932.7 eV to 934.6 eV) assigned to Cu + Peaks attributed to Cu 2+The area of ​​the peak (a peak is obtained at a position 0.5 eV to 2 eV lower in binding energy than the peak position assigned to 2p3 / 2) is calculated, and the average valence of Cu is determined.

[0070] Next, the amount of each metal element is quantified using Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). 5 mg of sample is placed in a platinum crucible, and 5 ml of hydrofluoric acid and 10 ml of 50% sulfuric acid are added. Heat decomposition is performed to obtain a mixture of concentrated sulfuric acid and various metal fluoride salts (the hydrofluoric acid turns into white smoke and is removed). 2 ml of 30% hydrogen peroxide is added to the resulting mixture, and the sample is then diluted to 100 ml with pure water using a measuring flask. The resulting sample solution and standard solutions with known metal concentrations are measured alternately three times, and the average values ​​are calculated. The amount of metal element in the sample is determined from the ratio of the signal intensity of the sample solution to that of the standard solution.

[0071] The average valence of Nb and Cu elements (Al is all Al) determined by XPS analysis. 3+ The total charge of the cations contained in the sample was calculated from the total charge of the cations (assumed to exist in the state of oxygen anions (O 2- The content of oxygen anions in the sample is calculated, and the difference between this content and the content of oxygen anions in the sample assuming no oxygen vacancies is defined as the amount of oxygen vacancies δ. That is, in the case of a niobium composite oxide represented by the general formula (2), Al, Cu, and Nb in the sample are respectively Al 3+ and Cu 2+ , Nb 5+ The difference between the oxygen content when it is assumed that the film is composed of the above and the oxygen content obtained by the above method is the amount of oxygen defects δ.

[0072] The oxygen content in a sample may also be directly determined by placing the sample in a graphite crucible, resistively heating it in a helium stream, and detecting the carbon dioxide produced with an infrared detector.

[0073] [Method for confirming the monoclinic structure of niobium composite oxide (A) and niobium composite oxide (B)] The crystal structures of niobium composite oxide (A) and niobium composite oxide (B) can be determined by measuring the powder X-ray diffraction (powder XRD) pattern using a Rigaku RINT2500VPC (X-rays used: CuKα radiation) and comparing it with the Powder Diffraction File (PDF) database, or by analyzing it using the Rietveld method. When comparing crystal lattice sizes between different samples, Si powder (Rigaku, a0 = 5.4308 Å at 298.1 K) is mixed as an internal reference when preparing the sample for powder XRD measurement, and the spectrum is corrected so that the peak attributed to the X-ray diffraction of the Si (111) plane is at 2θ = 28.442 degrees. The lattice constant (d 010 ) can be calculated by doubling the interplanar spacing determined from the peak attributable to the diffraction of the (020) plane, assuming an X-ray wavelength of 1.5418 Å. When niobium composite oxide (A) and niobium composite oxide (B) are contained in an electrode (negative electrode) as the negative electrode active material, a 1 kΩ resistor is connected to the battery and the battery is discharged at a constant resistance for 100 hours. After that, the negative electrode is removed from the battery and the surface of the electrode opposite to the surface bonded to the current collector is flattened so that it is parallel to the current collector. The surface is then fixed to a powder XRD sample stage, and a powder XRD pattern of the electrode can be obtained. When the niobium composite oxide (A) and the niobium composite oxide (B) are contained in the electrode (cathode) as the positive electrode active material, the battery is charged at a constant current of 10 μA with an upper limit voltage of 3 V, and then maintained at a constant voltage of 3 V for 100 hours. The positive electrode is then removed, and the surface of the electrode opposite to the surface that is in contact with the current collector is processed flat so that it is parallel to the current collector, as in the case of the negative electrode. The electrode is then fixed to a sample stage for powder XRD, and a powder XRD pattern of the electrode can be obtained.

[0074] When the niobium composite oxide (A) and the niobium composite oxide (B) are in a form sintered with a crystalline sulfide-based solid electrolyte or an oxide-based solid electrolyte, a sample piece is extracted from a compact of a sample containing the niobium composite oxide using FIB processing, mounted on a TEM sample stage, and then thinned to a thickness of 100 nm or less. A selected area electron diffraction (SAED) pattern is obtained using a TEM, and the monoclinic crystal structure can be confirmed by analyzing the pattern.

[0075] [Method for measuring crystallite size d in the b-axis direction of niobium composite oxide (A) and niobium composite oxide (B)] The crystallite size d in the b-axis direction of the niobium composite oxide (A) and the niobium composite oxide (B) is calculated by the Scherrer equation below, by determining the half-width of a specific peak from the powder X-ray diffraction pattern of the niobium composite oxide obtained by the above method.

[0076] d = Kλ / wcosθ

[0077] In the formula, d is the crystallite size, K is the Scherrer constant, λ is the wavelength of the X-ray, w is the half-width, and θ is the Bragg angle.

[0078] When the space group of the niobium composite oxide (A) and the niobium composite oxide (B) is C2 / m, the crystallite size d in the b-axis direction is determined from the peak of the (020) plane. When the space group of the niobium composite oxide is A2 / m, the crystallite size d in the b-axis direction is determined from the peak of the (020) plane. When the space group of the niobium composite oxide (A) and the niobium composite oxide (B) is I2 / m, the crystallite size d in the b-axis direction is determined from the peak of the (020) plane.

[0079] When the electrode is a positive electrode, the content of the electrode active material (positive electrode active material) in the electrode mixture (positive electrode mixture) is preferably 20 to 95 mass %.

[0080] When the electrode is a negative electrode, the content of the electrode active material (negative electrode active material) in the electrode mixture (negative electrode mixture) is preferably 10 to 99 mass %.

[0081] Specific examples of the conductive additive to be contained in the molded body of the electrode mixture include carbon materials such as graphite (natural graphite, artificial graphite), graphene, carbon black, carbon nanofibers, carbon nanotubes, etc. The content of the conductive additive particles in the electrode mixture is preferably 1 to 10 mass %.

[0082] In addition, when the cross-sectional aspect ratio of the conductive additive in the electrode mixture compact is large, this usually indicates that the particles of the conductive additive were crushed and oriented during the manufacturing of the electrode (during compression molding of the electrode mixture compact). In such cases, the conductive path in the thickness direction of the electrode mixture compact (the direction parallel to the compression direction during molding) may be broken, potentially reducing the effect of reducing the electrode resistance. Therefore, when using a conductive additive that does not have a long shape, such as graphite, graphene, or carbon black, the cross-sectional aspect ratio of the conductive additive in the electrode mixture compact is preferably 3 or less. The lower limit of the cross-sectional aspect ratio of the conductive additive in the electrode mixture compact is usually about 1.5, although it depends on the shape of the conductive additive used.

[0083] The cross-sectional aspect ratio of the conductive additive in the electrode mixture molded body can be determined by setting "Shape descriptors" when performing the "Analyze Particles" operation for the conductive additive particles, outputting the cross-sectional aspect ratio of each conductive additive particle, and calculating the average value (the values ​​described in the examples below were determined using this method).

[0084] The solid electrolyte to be contained in the electrode mixture compact is not particularly limited as long as it has Li ion conductivity, and for example, a sulfide-based solid electrolyte, a hydride-based solid electrolyte, a halide-based solid electrolyte, an oxide-based solid electrolyte, etc. can be used.

[0085] Examples of sulfide-based solid electrolytes include particles such as Li2S-P2S5, Li2S-SiS2, Li2S-P2S5-GeS2, and Li2S-B2S3-based glasses. In recent years, thio-LISICON-type materials [Li 10 GeP2S 12 、Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 and others, such as Li 12-12a-b+c+6d-e M 1 3+a-b-c-d M 2 b M 3 c M 4 d M 5 12-e X e (where M 1 is Si, Ge, or Sn, M 2 is P or V, M 3 is Al, Ga, Y, or Sb, M 4 is Zn, Ca, or Ba, M 5 is either S or S and O, X is F, Cl, Br, or I, 0 ≦ a < 3, 0 ≦ b + c + d ≦ 3, 0 ≦ e ≦ 3), or argyrodite-type materials [such as Li6PS5Cl, Li 7-k PS 6-k X k (where X represents one or more halogen elements, 0.2 < k < 2.0), Li 7-f+g PS 6-x Cl x+y (where 0.05 ≦ f ≦ 0.9, -3.0f + 1.8 ≦ g ≦ -3.0f + 5.7), Li 7-h PS 6-h Cl i Br j (where h = i + j, 0 < h ≦ 1.8, 0.1 ≦ i / j ≦ 10.0), etc.] can also be used.

[0086] Examples of hydride-based solid electrolytes include LiBH4, solid solutions of LiBH4 and the following alkali metal compounds (for example, those in which the molar ratio of LiBH4 to the alkali metal compound is 1:1 to 20:1). The alkali metal compound in the solid solution may be at least one selected from the group consisting of lithium halides (LiI, LiBr, LiF, LiCl, etc.), rubidium halides (RbI, RbBr, RbF, RbCl, etc.), cesium halides (CsI, CsBr, CsF, CsCl, etc.), lithium amide, rubidium amide, and cesium amide.

[0087] Examples of halide-based solid electrolytes include monoclinic LiAlCl4, defect spinel or layered structure LiInBr4, monoclinic Li 6-3m Y m X6 (However, 0 <m<2かつX=ClまたはBr , Y = yttrium ) and the like, and other known compounds described in, for example, WO 2020 / 070958 and WO 2020 / 070955 can also be used.

[0088] Examples of oxide-based solid electrolytes include Li2O-Al2O3-SiO2-P2O5-TiO2-based glass ceramics, Li2O-Al2O3-SiO2-P2O5-GeO2-based glass ceramics, Li3PO4-Li3BO3-Li2SO4-based glass, and garnet-type Li7La3Zr2O. 12 , NASICON type Li 1+O Al 1+O Ti 2-O (PO4)3, Li 1+p Al 1+p Ge 2-p (PO4)3, perovskite-type Li 3q La 2 / 3-q Examples include TiO3 and antiperovskite-type Li3HX (X=O, S, Se, Te).

[0089] Among these solid electrolytes, sulfide-based solid electrolytes are preferred due to their high Li-ion conductivity, sulfide-based solid electrolytes containing Li and P are more preferred, and argyrodite-type sulfide-based solid electrolytes are even more preferred due to their particularly high Li-ion conductivity and high chemical stability.

[0090] The average particle size of the solid electrolyte is preferably 0.1 μm or more, and more preferably 0.2 μm or more, from the viewpoint of reducing grain boundary resistance, while it is preferably 10 μm or less, and more preferably 5 μm or less, from the viewpoint of forming a sufficient contact interface between the positive electrode active material and the solid electrolyte.

[0091] The average particle diameter of the solid electrolyte in this specification is the 50% diameter value (D ) in the volume-based integrated fraction when the integrated volume is calculated from small particles using a particle size distribution analyzer (such as a Microtrac particle size distribution analyzer "HRA9320" manufactured by Nikkiso Co., Ltd.). 50 ) means

[0092] When the electrode is a positive electrode, the content of the solid electrolyte in the electrode mixture (positive electrode mixture) is preferably 4 to 80 mass %, and when the electrode is a negative electrode, the content of the solid electrolyte in the electrode mixture (negative electrode mixture) is preferably 4 to 85 mass %.

[0093] The compact of the electrode mixture can contain a binder. Specific examples include fluororesins such as polyvinylidene fluoride (PVDF). Note that, for example, when the compact of the electrode mixture contains a sulfide-based solid electrolyte, if good moldability can be ensured in forming the compact of the electrode mixture without using a binder, the compact of the electrode mixture does not need to contain a binder.

[0094] When a binder is required in the electrode mixture, the content thereof is preferably 6% by mass or less, and more preferably 0.5% by mass or more. On the other hand, when formability can be obtained without a binder, the content thereof is preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and even more preferably 0% by mass (i.e., no binder is contained).

[0095] When the electrode is a positive electrode and has a current collector, the current collector can be made of a metal such as aluminum, nickel, or stainless steel foil, punched metal, mesh, expanded metal, foamed metal, carbon sheet, etc. When the electrode is a negative electrode and has a current collector, the current collector can be made of a copper or nickel foil, punched metal, mesh, expanded metal, foamed metal, carbon sheet, etc.

[0096] The compact of the electrode mixture can be formed, for example, by compressing an electrode mixture prepared by mixing an electrode active material, a solid electrolyte, a conductive additive, etc., by pressure molding or the like.

[0097] In the case of an electrode having a current collector, it can be produced by bonding a molded body of the electrode mixture formed by the above-mentioned method to the current collector by, for example, pressing.

[0098] Alternatively, the electrode mixture may be mixed with a solvent to prepare an electrode mixture-containing composition, which may then be applied to a substrate such as a current collector or a solid electrolyte layer that faces an electrode, dried, and then pressed to form a molded body of the electrode mixture.

[0099] It is preferable to select a solvent for the electrode mixture-containing composition that is less likely to deteriorate the solid electrolyte. In particular, sulfide-based solid electrolytes and hydride-based solid electrolytes undergo chemical reactions with trace amounts of water, so that solvents such as hexane, heptane, octane, nonane, decane, decalin, toluene, xylene, MesityleneIt is preferable to use a nonpolar aprotic solvent, such as a hydrocarbon solvent such as tetralin. It is particularly preferable to use a highly dehydrated solvent with a water content of 0.001% by mass (10 ppm) or less. It is also possible to use fluorine-based solvents such as "Vertrel (registered trademark)" manufactured by Mitsui-DuPont Fluorochemicals Co., Ltd., "Zeorolla (registered trademark)" manufactured by Nippon Zeon Co., Ltd., and "Novec (registered trademark)" manufactured by Sumitomo 3M Company, Ltd., as well as nonaqueous organic solvents such as dichloromethane, diethyl ether, and anisole.

[0100] The thickness of the electrode mixture compact (in the case of an electrode having a current collector, the thickness of the electrode mixture compact per one side of the current collector; the same applies hereinafter) is usually 100 μm or more, but from the viewpoint of increasing the capacity of the all-solid-state secondary battery, it is preferably 200 μm or more. In addition, the thickness of the electrode mixture compact is usually 3000 μm or less.

[0101] In the case of an electrode produced by forming an electrode mixture layer on a current collector using an electrode mixture-containing composition containing a solvent, the thickness of the electrode mixture layer is preferably 10 to 1000 μm.

[0102] <All-solid-state secondary battery> The nonaqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, and at least one of the positive electrode and the negative electrode is an electrode for the all-solid-state secondary battery of the present invention. Regarding the components other than the electrode, various components employed in conventionally known all-solid-state secondary batteries can be applied.

[0103] A cross-sectional view schematically illustrating one example of the all-solid-state secondary battery of the present invention is shown in Fig. 1. The all-solid-state secondary battery 1 shown in Fig. 1 has a positive electrode 10, a negative electrode 20, and a solid electrolyte layer 30 interposed between the positive electrode 10 and the negative electrode 20 enclosed in an exterior body formed by an exterior can 40, a sealing can 50, and a resin gasket 60 interposed between them.

[0104] The sealing can 50 is fitted into the opening of the outer can 40 via a gasket 60, and the open end of the outer can 40 is tightened inward, causing the gasket 60 to abut against the sealing can 50, thereby sealing the opening of the outer can 40 and creating an airtight structure inside the battery.

[0105] The outer can and the sealing can can be made of stainless steel or other materials. The gasket can be made of polypropylene, nylon, or other materials. If heat resistance is required for the battery's intended use, a heat-resistant resin with a melting point exceeding 240°C can also be used. Examples of heat-resistant resins include fluororesins (e.g., tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA)), polyphenylene ether (PPE), polysulfone (PSF), polyarylate (PAR), polyethersulfone (PES), polyphenylene sulfide (PPS), and polyetheretherketone (PEEK). If the battery is intended for use in applications requiring heat resistance, a glass hermetic seal can be used for sealing.

[0106] 2 and 3 are diagrams showing schematic diagrams of other examples of the all-solid-state secondary battery of the present invention. Fig. 2 is a plan view of the all-solid-state secondary battery, and Fig. 3 is a cross-sectional view taken along line II in Fig. 2.

[0107] The all-solid-state secondary battery 100 shown in FIGS. 2 and 3 houses an electrode assembly 200 in a laminate film exterior body 500 made of two metal laminate films, and the laminate film exterior body 500 is sealed at its outer periphery by heat-sealing the upper and lower metal laminate films.

[0108] The electrode assembly 200 is configured by laminating a positive electrode, a negative electrode, and a solid electrolyte layer interposed between them.

[0109] In Figure 3, in order to avoid complicating the drawing, the layers that make up the laminate film exterior body 500 and the components (positive electrode, negative electrode, etc.) that make up the electrode body 200 are not distinguished from one another.

[0110] The positive electrode of the electrode body 200 is connected to a positive electrode external terminal 300 inside the battery 100, and although not shown, the negative electrode of the electrode body 200 is also connected to a negative electrode external terminal 400 inside the battery 100. One end of the positive electrode external terminal 300 and the negative electrode external terminal 400 is drawn out to the outside of the laminate film exterior body 500 so that they can be connected to external devices, etc.

[0111] (positive electrode) The electrode of the present invention can be used as the positive electrode of the all-solid-state secondary battery, but when the negative electrode is the electrode of the present invention, a positive electrode other than the electrode of the present invention can also be used. 90 Examples of such positive electrodes include a positive electrode having the same configuration as the electrode of the present invention except that it contains an electrode active material whose B / A value does not satisfy the above-mentioned value, and a positive electrode having the same configuration as the electrode of the present invention except that it contains an electrode active material whose B / A value does not satisfy the above-mentioned value.

[0112] (Negative electrode) The electrode of the present invention can be used as the negative electrode of the all-solid-state secondary battery, but when the positive electrode is the electrode of the present invention, a negative electrode other than the electrode of the present invention can also be used. 90 Examples of such negative electrodes include a negative electrode having the same configuration as the electrode of the present invention except that it contains an electrode active material whose B / A value does not satisfy the above-mentioned value, a negative electrode having the same configuration as the electrode of the present invention except that the B / A value does not satisfy the above-mentioned value, and a negative electrode having a lithium sheet or a lithium alloy sheet.

[0113] In the case of a negative electrode having a lithium sheet or a lithium alloy sheet, one consisting of only this sheet or one consisting of this sheet stuck to a current collector is used.

[0114] Examples of alloying elements for lithium alloys include aluminum, lead, bismuth, indium, and gallium, with aluminum and indium being preferred. The proportion of alloying elements in the lithium alloy (the total proportion when multiple alloying elements are included) is preferably 50 atomic % or less (in this case, the remainder is lithium and inevitable impurities).

[0115] In addition, in the case of a negative electrode having a lithium alloy sheet, a laminate can be used in which a layer containing an alloying element for forming a lithium alloy is laminated on the surface of a lithium layer (a layer containing lithium) composed of a metal lithium foil or the like by pressure bonding, and this laminate is brought into contact with a solid electrolyte in a battery to form a lithium alloy on the surface of the lithium layer, thereby forming a negative electrode. In such a negative electrode, a laminate having a layer containing an alloying element on only one side of the lithium layer may be used, or a laminate having a layer containing an alloying element on both sides of the lithium layer may be used. The laminate can be formed, for example, by pressure bonding a metal lithium foil and a foil composed of an alloying element.

[0116] The current collector can also be used when a lithium alloy is formed in a battery to form a negative electrode. For example, a laminate having a lithium layer on one side of the negative electrode current collector and a layer containing an alloying element on the side of the lithium layer opposite the negative electrode current collector may be used, or a laminate having lithium layers on both sides of the negative electrode current collector and a layer containing an alloying element on the side of each lithium layer opposite the negative electrode current collector may be used. A laminate may also be used. The negative electrode current collector and the lithium layer (metallic lithium foil) may be laminated by pressure bonding or the like.

[0117] The layer containing the alloying elements in the laminate to be used as the negative electrode can be, for example, a foil composed of these alloying elements. The thickness of the layer containing the alloying elements is preferably 1 μm or more, more preferably 3 μm or more, and is preferably 20 μm or less, more preferably 12 μm or less.

[0118] The lithium layer of the laminate for use as a negative electrode may be, for example, a metallic lithium foil. The thickness of the lithium layer is preferably 0.1 to 1.5 mm. In addition, the thickness of the sheet for the negative electrode having a lithium or lithium alloy sheet is also preferably 0.1 to 1.5 mm.

[0119] Furthermore, when a negative electrode having a lithium sheet or a lithium alloy sheet has a current collector, the same current collectors as those exemplified above as those usable when the electrode of the present invention is a negative electrode can be used as the current collector.

[0120] (Solid electrolyte layer) The solid electrolyte in the solid electrolyte layer interposed between the positive electrode and the negative electrode can be one or more of the various sulfide-based solid electrolytes, hydride-based solid electrolytes, halide-based solid electrolytes, and oxide-based solid electrolytes listed above as examples of usable electrodes. However, to improve battery characteristics, it is preferable to include a sulfide-based solid electrolyte, and it is more preferable to include an argyrodite-type sulfide-based solid electrolyte. It is even more preferable to include a sulfide-based solid electrolyte in all of the positive electrode, negative electrode, and solid electrolyte layer, and it is even more preferable to include an argyrodite-type sulfide-based solid electrolyte.

[0121] The solid electrolyte layer may have a porous body such as a resin nonwoven fabric as a support.

[0122] The solid electrolyte layer can be formed by a method of compressing a solid electrolyte by pressure molding or the like; or a method of applying a solid electrolyte layer-forming composition prepared by dispersing a solid electrolyte in a solvent onto a substrate (including a porous body serving as a support), a positive electrode, or a negative electrode, drying the composition, and, if necessary, performing pressure molding such as pressing.

[0123] It is desirable to select a solvent that is unlikely to deteriorate the solid electrolyte as the solvent used in the solid electrolyte layer-forming composition, and it is preferable to use the same solvents as those exemplified above as the solvents for the electrode mixture-containing composition.

[0124] The thickness of the solid electrolyte layer is preferably 10 to 500 μm.

[0125] (electrode body) The positive electrode and the negative electrode can be used in a battery in the form of a laminated electrode body in which the positive electrode and the negative electrode are laminated with a solid electrolyte layer interposed therebetween, or in the form of a wound electrode body in which this laminated electrode body is wound.

[0126] When forming the electrode body, it is preferable to pressure-mold the positive electrode, negative electrode, and solid electrolyte layer in a stacked state, from the viewpoint of increasing the mechanical strength of the electrode body.

[0127] (Battery type) The all-solid-state secondary battery may have a configuration having an exterior body composed of an exterior can, a sealing can, and a gasket as shown in FIG. 1, that is, a configuration generally referred to as a coin-type battery or a button-type battery, or a configuration having an exterior body composed of a resin film or a metal-resin laminate film as shown in FIGS. 2 and 3, or may have an exterior body having a metallic, bottomed, tubular (cylindrical or rectangular) exterior can and a sealing structure that seals the opening of the can. [Example]

[0128] The present invention will be described in detail below based on examples. However, the following examples do not limit the present invention. Note that the values ​​described below regarding the negative electrodes prepared in the examples and comparative examples, as well as the compositions and crystalline structures of the negative electrode active materials, were all determined by the methods described above.

[0129] Example 1 <Preparation of positive electrode> A coating solution for forming a reaction suppression layer was prepared by mixing 0.86 g of lithium and 38.7 g of pentaethoxyniobium in 394 g of dehydrated ethanol. Next, the coating solution for forming a reaction suppression layer was applied to 1,000 g of positive electrode active material (LiCoO2) at a rate of 2 g per minute using a coating device using a tumbling fluidized bed. The resulting powder was heat-treated at 350 °C to obtain a positive electrode material with a reaction suppression layer formed on its surface, consisting of 2 parts by mass of LiNbO3 per 100 parts by mass of positive electrode active material.

[0130] The cathode material, vapor-grown carbon fiber (conductive additive), and Li6PS5Cl (sulfide-based solid electrolyte) were mixed to prepare a cathode mixture. The mixture ratio of the cathode material, conductive additive, and sulfide-based solid electrolyte was 66:4:30 by mass. 112 mg of this cathode mixture was placed in a powder molding die with a diameter of 7.5 mm, and a pressure of 6000 kgf / cm was applied using a press. 2 The mixture was molded under a pressure of 1000 kJ / cm 2 to prepare a positive electrode mixture compact having a cylindrical shape.

[0131] <Formation of solid electrolyte layer> On top of the positive electrode mixture compact in the powder molding die, 8 mg of the same sulfide-based solid electrolyte as used for the positive electrode was placed, and a pressure of 1000 kgf / cm was applied using a press. 2 The positive electrode mixture compact was molded under a pressure of 1000 kJ / cm 2 , thereby forming a solid electrolyte layer on the positive electrode mixture compact.

[0132] <Formation of negative electrode and fabrication of laminated electrode body> Active materials were synthesized using a solid-state reaction method using various metal oxide powders (all obtained from Kojundo Chemical Co., Ltd.). Nb2O5 (purity: >99.9%) with an average particle size of 1 μm, α-Al2O3 (purity: >99.99%) with an average particle size of 1 μm, and CuO (purity: >99.99%) were weighed and mixed in amounts of 96.72 g, 2.34 g, and 1.04 g, respectively. The mixture of starting materials was added to a 500 ml zirconia container along with 70 g of ethanol and 300 g of 2 mm diameter YSZ balls. The mixture was mixed in a planetary ball mill (Fritsch "Planetary Mill Pulverisette 5") at 300 rpm for 6 hours. The zirconia balls were separated from the mixed sample, and the resulting slurry was dried to obtain a precursor powder for the negative electrode active material. The precursor powder was transferred to an alumina crucible, heated to 900°C at a rate of 16°C / min in an air atmosphere, and then calcined for 8 hours, followed by natural cooling to room temperature. The resulting powder was crushed in a mortar for 5 minutes and passed through a 150 μm mesh sieve to obtain a crude active material. 4 g of the crude active material was added to a zirconia container with an internal volume of 12.5 ml along with 4 g of ethanol and 30 g of 2 mm diameter YSZ balls, and crushed for 6 hours in the planetary ball mill at 300 rpm. The resulting slurry was dried overnight under reduced pressure at 60°C to obtain the negative electrode active material, Cu. 0.2 Al 0.74 Nb 11.05 O 27.89 particles were obtained.

[0133] The powder XRD pattern of the obtained negative electrode active material was measured, and it was confirmed that the negative electrode active material had a monoclinic crystal structure and belonged to the C2 / m space group.

[0134] The negative electrode active material, graphene (conductive additive), and sulfide-based solid electrolyte (Li6PS5Cl) were mixed in a mass ratio of 69:6.1:24.9 and kneaded in an automatic mortar ("Motor Grinder P-2" (trade name) manufactured by Fritsch) for 1 hour in an argon atmosphere to prepare a negative electrode mixture. Next, 62 mg of the negative electrode mixture was placed on top of the solid electrolyte layer in the powder molding die, and a pressure of 14,000 kgf / cm was applied using a press. 2 The mixture was molded under a pressure of 1000 MPa, and a negative electrode made of the negative electrode mixture molded body was formed on the solid electrolyte layer, thereby producing a laminated electrode body in which the positive electrode, the solid electrolyte layer, and the negative electrode were laminated.

[0135] In the obtained negative electrode (negative electrode mixture compact), the D 90 and D 50 (A value) are 0.67μm and 0.46μm, respectively, and the D 50 The B value was 0.55 μm, and the B / A value was 1.20. The cross-sectional aspect ratio of the conductive additive in the negative electrode was 2.6. The crystallite size d in the b-axis direction of the negative electrode active material was 81 nm, and the d / A value was 0.18.

[0136] <Assembly of all-solid-state secondary batteries> Flexible graphite sheet "PERMA-FOIL" (product name) manufactured by Toyo Tanso Co., Ltd. (thickness: 0.1 mm, apparent density: 1.1 g / cm 3 Two sheets of graphite sheet 10 were punched out to the same size as the laminated electrode body, and one of them was placed on the inner bottom surface of a stainless steel sealed can into which a polypropylene annular gasket had been fitted. Next, the laminated electrode body was placed on top of the graphite sheet with the negative electrode facing the graphite sheet side, and another graphite sheet was placed on top of that. A stainless steel outer can was then placed over the laminated electrode body, and the open edge of the outer can was crimped inward to seal it, thereby producing a flat all-solid-state secondary battery with a diameter of approximately 9 mm, in which the graphite sheets were placed between the inner bottom surface of the sealed can and the laminated electrode body, and between the inner bottom surface of the outer can and the laminated electrode body, respectively.

[0137] Example 2 A negative electrode active material was prepared in the same manner as in Example 1 except that the baking temperature of the negative electrode active material was changed to 950°C, and a flat all-solid-state secondary battery was prepared in the same manner as in Example 1 except that this negative electrode active material was used.

[0138] In addition, in the negative electrode (negative electrode mixture compact) of the laminated electrode body used in the battery of Example 2, the D 90 and D 50 (A value) are 0.77μm and 0.49μm, respectively, and the D 50 The B value was 0.52 μm, and the B / A value was 1.06. The cross-sectional aspect ratio of the conductive additive in the negative electrode was 2.7. The crystallite size d in the b-axis direction of the negative electrode active material was 78 nm, and the d / A value was 0.16.

[0139] Example 3 The negative electrode active material was produced in the same manner as in Example 1 except that the size of the YSZ balls added when mixing the mixture of starting materials was 5 mm in diameter, the conditions for mixing the mixture of starting materials were 250 rpm for 3 hours, and the firing conditions were holding at 1000°C for 4 hours, the size of the YSZ balls added when crushing the crude product was 5 mm in diameter, and the conditions for crushing the crude product were 250 rpm for 3 hours.The negative electrode mixture was prepared in the same manner as in Example 1 except that the composition was changed to a mass ratio of negative electrode active material:graphene:solid electrolyte=69:5.5:25.5, and a flat all-solid-state secondary battery was produced in the same manner as in Example 1 except that this negative electrode mixture was used.

[0140] In addition, in the negative electrode (negative electrode mixture compact) of the laminated electrode body used in the battery of Example 3, the D 90 and D 50 (A value) are 1.23 μm and 0.75 μm, respectively, and the D 50 The B value was 0.33 μm, and the B / A value was 0.44. The cross-sectional aspect ratio of the conductive additive in the negative electrode was 2.8. The crystallite size d in the b-axis direction of the negative electrode active material was 97 nm, and the d / A value was 0.13.

[0141] Comparative Example 1 An anode mixture was prepared in the same manner as in Example 3, except that the time for mixing the anode active material, the solid electrolyte, and the graphene was changed to 20 minutes. A flat all-solid-state secondary battery was fabricated in the same manner as in Example 1, except that this anode mixture was used.

[0142] In addition, in the negative electrode (negative electrode mixture compact) of the laminated electrode body used in the battery of Comparative Example 1, the D 90 and D 50 (A value) are 2.40 μm and 1.01 μm, respectively, and the D 50 The B value was 3.99 μm, and the B / A value was 3.95. The cross-sectional aspect ratio of the conductive additive in the negative electrode was 3.3. The crystallite size d in the b-axis direction of the negative electrode active material was 97 nm, and the d / A value was 0.10.

[0143] Comparative Example 2 The negative electrode active material was changed to that of Example 3, and the negative electrode mixture was changed to a composition of negative electrode active material:graphene:solid electrolyte=69:9.4:21.6 in mass ratio, except that the procedure was the same as in Example 1, and a flat all-solid-state secondary battery was fabricated in the same manner as in Example 1, except that the negative electrode mixture was used.

[0144] In addition, in the negative electrode (negative electrode mixture compact) of the laminated electrode body used in the battery of Comparative Example 2, the D 90 and D 50 (A value) are 1.38 μm and 0.78 μm, respectively, and the D 50 The B value was 1.44 μm, and the B / A value was 1.85. The cross-sectional aspect ratio of the conductive additive in the negative electrode was 2.6. The crystallite size d in the b-axis direction of the negative electrode active material was 97 nm, and the d / A value was 0.12.

[0145] <Impedance evaluation> The flat all-solid-state secondary batteries of the Examples and Comparative Examples were evaluated for internal resistance by measuring impedance using the following method. Each battery was charged at a constant current of 0.04 C until the voltage reached 3.2 V, then charged at a constant voltage of 0.01 C until the current reached 0.01 C, and then discharged at a constant current of 0.04 C until the voltage reached 1.0 V. Each battery was then charged at a constant current under the same conditions as above until it reached a capacity of 5 mAh, and its open circuit voltage was measured for 10 minutes. In this state, the impedance was measured at 1 Hz with an effective AC voltage of 10 mV.

[0146] <Output characteristic evaluation> After the impedance measurement, each battery was subjected to constant current charging at a current value of 0.04 C until the voltage reached 3.2 V, followed by constant voltage charging until the current reached 0.01 C. Then, the open circuit voltage was measured for 1 hour, followed by constant current discharging at a current value of 0.05 C until the voltage reached 1.0 V, thereby measuring the 0.05 C discharge capacity. Then, the open circuit voltage was measured for 1 hour, followed by constant current discharging at a current value of 0.01 C until the voltage reached 1.0 V, and the sum of the obtained discharge capacity and the 0.05 C discharge capacity was defined as the 0.01 C discharge capacity.

[0147] The output characteristics of the battery were evaluated by calculating the ratio of the 0.05C discharge capacity (0.05C / 0.01C discharge capacity maintenance rate) when the 0.01C discharge capacity was taken as 100%.

[0148] The physical properties of the components constituting the negative electrode are shown in Table 1, and the evaluation results are shown in Table 2.

[0149] [Table 1]

[0150] [Table 2]

[0151] As shown in Tables 1 and 2, the D 90The flat all-solid-state secondary batteries of Examples 1 to 3 having negative electrodes with appropriate B / A values ​​had lower impedance and reduced internal resistance than the batteries of Comparative Examples 1 and 2 having inappropriate values.

[0152] Furthermore, the flat all-solid-state secondary batteries of Examples 1 to 3 were superior to the batteries of Comparative Examples 1 and 2 in terms of output characteristics.

[0153] The present invention can be implemented in other forms without departing from the spirit of the present invention. The embodiments disclosed in this application are merely examples, and the present invention is not limited to these embodiments. The scope of the present invention shall be interpreted in accordance with the appended claims rather than the description in the above specification, and all modifications within the scope of the claims are included in the scope of the claims. [Industrial Applicability]

[0154] The all-solid-state secondary battery of the present invention has low internal resistance and excellent characteristics, and can be preferably used in applications requiring such characteristics, as well as in other applications in which conventionally known all-solid-state secondary batteries are used. The electrode for an all-solid-state secondary battery of the present invention can constitute the all-solid-state secondary battery of the present invention. [Explanation of symbols]

[0155] 1,100 All-solid-state secondary battery 10 positive electrode 20 negative electrode 30 Solid electrolyte layer 40 outer can 50 sealed cans 60 gaskets 200 Electrode body 300 Positive external terminal 400 Negative external terminal 500 Laminated film exterior

Claims

1. An electrode used in an all-solid-state secondary battery having a solid electrolyte layer, The electrode mixture includes a molded body containing an electrode active material, a conductive additive, and a solid electrolyte, The particle diameter D of the electrode active material 90 is 1.5 μm or less, The average particle diameter D of the electrode active material 50 is A (μm), and the average particle diameter D of the conductive additive 50 is B (μm), the relationship 0.4≦B / A≦1.5 is satisfied, An electrode for an all-solid-state secondary battery, comprising, as the electrode active material, a niobium composite oxide containing at least two elements selected from the group consisting of Cu, Zn, Al, W, Fe, and Ti.

2. The niobium composite oxide is a monoclinic crystal having a crystallite size d (μm) in the b-axis direction and an average particle diameter D 50 2. The electrode for an all-solid-state secondary battery according to claim 1, wherein a ratio d / A of A (μm) to d / A is 0.12 or more.

3. 2. The electrode for an all-solid-state secondary battery according to claim 1, wherein the electrode active material comprises a niobium composite oxide having a monoclinic crystal structure and satisfying the following general formula (1): A y M 1 aAl x- aNb 12-x-z M 2 z Oh 29- d (1) [In the general formula (1), A is at least one element selected from Li and Na; M 1 represents at least one element selected from the group consisting of Fe, Mn, Zn, Cu, Ag, Mg, Ca, Sr, Ba, Co, Eu, Y, Bi, La, Ce, Nd, Sm, and Gd; M 2 is at least one element selected from the group consisting of K, Ti, Ni, Zr, V, Mo, Ta, and W, and 0<x≦1.1, 0≦y≦24, 0≦z≦2, −1≦δ≦2, 0<α≦0.4x.

4. The niobium composite oxide has a crystallite size d (μm) in the b-axis direction and an average particle diameter D 50 4. The electrode for an all-solid-state secondary battery according to claim 3, wherein a ratio d / A of A (μm) to d / A is 0.12 or more.

5. An electrode for an all-solid-state secondary battery as described in claim 1, wherein the cross-sectional aspect ratio of the conductive additive is 3 or less.

6. An all-solid-state secondary battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode is the electrode for an all-solid-state secondary battery according to any one of claims 1 to 5.

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