WO2022137359A1 - All-solid-state secondary battery - Google Patents

Abstract

Provided is an all-solid-state secondary battery in which charge/discharge characteristics such as discharge capacity are significantly improved. This all-solid-state secondary battery comprises: a positive electrode layer including a porous sintered plate configured from a lithium composite oxide having a layered rock salt structure; a negative electrode layer including a porous sintered plate configured from a negative electrode active material; and a solid electrolyte that is interposed as a separator layer between the positive electrode layer and the negative electrode layer, the solid electrolyte also filling the pores of the porous sintered plates in the positive electrode layer and the negative electrode layer. The lithium composite oxide contains Ni, Co, and Mn at a mole ratio that satisfies 0.19≤Ni/(Ni+Co+Mn)≤0.41, 0.49≤Co/(Ni+Co+Mn)≤0.71, and 0.09≤Mn/(Ni+Co+Mn)≤0.11.

Description

All-solid-state secondary battery

The present invention relates to an all-solid-state secondary battery, particularly an all-solid-state lithium-ion secondary battery.

As a positive electrode active material layer for a lithium ion secondary battery, it is obtained by kneading and molding a powder of a lithium composite oxide (typically, a lithium transition metal oxide) and an additive such as a binder or a conductive agent. Powder-dispersed positive electrodes are widely known. Since the powder-dispersed positive electrode contains a relatively large amount (for example, about 10% by weight) of a binder that does not contribute to the capacity, the packing density of the lithium composite oxide as the positive electrode active material is low. Therefore, there is a lot of room for improvement in the powder dispersion type positive electrode in terms of capacity and charge / discharge efficiency. Therefore, attempts have been made to improve the capacity and charge / discharge efficiency by forming the positive electrode or the positive electrode active material layer with a lithium composite oxide sintered plate. In this case, since the positive electrode or the positive electrode active material layer does not contain a binder, it is expected that a high capacity and good charge / discharge efficiency can be obtained by increasing the packing density of the lithium composite oxide.

Further, in a lithium ion secondary battery, a liquid electrolyte (electrolyte solution) using a flammable organic solvent as a diluting solvent has been conventionally used as a medium for transferring ions. In a battery using such an electrolytic solution, problems such as leakage of the electrolytic solution, ignition, and explosion may occur. In order to solve such problems, in order to ensure intrinsic safety, solid-state batteries are being developed in which solid electrolytes are used instead of liquid electrolytes and all other elements are made of solids. ing. Since the electrolyte of such an all-solid-state battery is solid, there is no concern about ignition, liquid leakage does not occur, and problems such as deterioration of battery performance due to corrosion are unlikely to occur.

Various all-solid-state batteries using sintered electrodes and solid electrolytes have been proposed. For example, Patent Document 1 (WO2019 / 093222A1) contains an oriented positive electrode plate which is a lithium composite oxide sintered plate having a void ratio of 10 to 50%, Ti, and 0.4 V (against Li / Li ^+). ) As described above, an all-solid lithium battery including a negative electrode plate capable of inserting and removing lithium ions and a solid electrolyte having a melting point lower than the melting point or decomposition temperature of the oriented positive electrode board or the negative electrode plate is disclosed. In this document, as solid electrolytes with such a low melting point, Li ₃ OCl, xLiOH · yLi ₂ SO ₄ (in the formula, x + y = 1, 0.6 ≦ x ≦ 0.95) (eg 3LiOH ·. Various materials such as Li ₂ SO ₄ ) are disclosed. Such a solid electrolyte can be permeated into the voids of the electrode plate as a melt, and strong interfacial contact can be realized. As a result, it is said that the battery resistance and the rate performance at the time of charging / discharging can be remarkably improved, and the yield of battery manufacturing can be significantly improved. Further, in Patent Document 2 (WO2015 / 151566A1), Li _p (Ni _x , Coy, Mn _z ) O ₂ (in the formula, 0.9 ≦ p ≦ 1.3, 0 <x <0.8, ₀ ) An oriented positive electrode plate having a layered rock salt structure having a basic composition represented by <y <1, 0≤z≤0.7, x + y + z = 1), a Li-La-Zr-O ceramic material and / or lithium phosphate. Disclosed is an all-solid lithium battery comprising a solid electrolyte layer made of an oxynitride (LiPON) ceramic material and a negative electrode layer. The positive electrode composition actually evaluated in Patent Document 2 has a molar ratio of Ni: Co: Mn of 5: 2: 3 or 1: 1: 1.

WO2019 / 093222A1 WO2015 / 151566A1

The present inventors have obtained the finding that among the above-mentioned low melting point solid electrolytes, the LiOH / Li ₂ SO ₄ system solid electrolytes such as 3 LiOH / Li ₂ SO ₄ exhibit high lithium ion conductivity. However, a lithium composite oxide sintered plate having a Ni: Co: Mn molar ratio of 5: 2: 3 as conventionally used is used as a positive electrode, and a LiOH / Li ₂ SO ₄ system such as 3 LiOH / Li ₂ SO ₄ is used. When a cell was constructed with a solid electrolyte and the battery was operated, it was found that the discharge capacity was lower than the theoretical capacity assumed from the amount of active material.

The present inventors have recently constructed an all-solid-state secondary battery using a porous sintered plate of a lithium composite oxide containing Ni, Co and Mn in a molar ratio within a predetermined range as a positive electrode layer, thereby forming a discharge capacity. It was found that the charge / discharge characteristics such as the above can be significantly improved.

Therefore, an object of the present invention is to provide an all-solid-state secondary battery having significantly improved charge / discharge characteristics such as discharge capacity.

According to one aspect of the present invention, Ni, Co and Mn
0.19 ≤ Ni / (Ni + Co + Mn) ≤ 0.41,
0.49 ≤ Co / (Ni + Co + Mn) ≤ 0.71 and 0.09 ≤ Mn / (Ni + Co + Mn) ≤ 0.11
A positive electrode layer containing a porous sintered plate composed of a lithium composite oxide having a layered rock salt structure containing a molar ratio satisfying the above conditions.
A negative electrode layer including a porous sintered plate composed of a negative electrode active material, and
A solid electrolyte that is interposed between the positive electrode layer and the negative electrode layer as a separator layer and is also filled in the pores of the porous sintered plate of the positive electrode layer and the negative electrode layer.
An all-solid-state secondary battery is provided.

All-solid-state secondary battery The all-solid-state secondary battery of the present invention includes a positive electrode layer, a negative electrode layer, and a solid electrolyte. The positive electrode layer contains a porous sintered plate composed of a lithium composite oxide having a layered rock salt structure. The negative electrode layer contains a porous sintered plate composed of a negative electrode active material. The solid electrolyte is interposed between the positive electrode layer and the negative electrode layer as a separator layer, and is also filled in the pores of the porous sintered plate of the positive electrode layer and the negative electrode layer. The lithium composite oxide contains Ni, Co and Mn in an amount of 0.19 ≦ Ni / (Ni + Co + Mn) ≦ 0.41, 0.49 ≦ Co / (Ni + Co + Mn) ≦ 0.71 and 0.09 ≦ Mn. / (Ni + Co + Mn) ≤ 0.11 is included in a molar ratio. In this way, by forming an all-solid-state secondary battery using a porous sintered plate of a lithium composite oxide containing Ni, Co, and Mn in a molar ratio within a predetermined range as a positive electrode layer, charging and discharging of the discharge capacity and the like can be performed. The characteristics can be greatly improved.

As described above, an all-solid lithium battery impregnated with a low melting point solid electrolyte such as a LiOH / Li ₂ SO ₄ system solid electrolyte is known (see, for example, Patent Document 1), and the solid electrolyte is used as a melt in the electrode plate. Interfacial contact can be achieved by penetrating into the voids. As a result, it is possible to improve the battery resistance and the rate performance at the time of charging / discharging, and also improve the yield of battery manufacturing. However, a lithium composite oxide sintered plate having a Ni: Co: Mn molar ratio of 5: 2: 3 as conventionally used is used as a positive electrode, and a LiOH / Li ₂ SO ₄ system such as 3 LiOH / Li ₂ SO ₄ is used. When a cell was constructed with a solid electrolyte and the battery was operated, it was found that the discharge capacity was lower than the theoretical capacity assumed from the amount of active material. This problem can be conveniently solved by using a porous sintered plate of a lithium composite oxide containing Ni, Co and Mn in a molar ratio within the above range as a positive electrode layer. It is considered that this is because the expansion / contraction or the volume change due to the charge / discharge of the lithium composite oxide containing Ni, Co and Mn is small in the molar ratio within the above range. In fact, when the all-solid-state battery after charging and discharging whose performance was deteriorated was analyzed, the solid electrolyte impregnated in the positive electrode sintered plate of Ni: Co: Mn = 5: 2: 3 and the positive electrode sintered plate are formed. There was a gap between the positive electrode active material particles and the particles. That is, since the conventionally used lithium composite oxide particles of Ni: Co: Mn = 5: 2: 3 have the property of shrinking during charging, the stress associated with the particle shrinkage causes the positive electrode plate and the solid electrolyte to shrink. It is considered that the discharge capacity of the all-solid-state battery decreased due to the peeling and the suppression of the diffusion of Li ions. In this respect, since the porous sintered plate composed of the lithium composite oxide in the above composition range of the present invention has a small expansion / contraction or volume change during charging / discharging, the above-mentioned problems are unlikely to occur, and as a result, the discharge capacity and the like are filled. It is considered to bring about a significant improvement in discharge characteristics.

(1) Positive Electrode Layer The positive electrode layer contains a porous sintered plate composed of a lithium composite oxide having a layered rock salt structure as a positive electrode active material. In other words, the porous sintered plate has a structure in which a plurality of primary particles composed of a lithium composite oxide having a layered rock salt structure are bonded. This lithium composite oxide contains Ni, Co and Mn at 0.19 ≦ Ni / (Ni + Co + Mn) ≦ 0.41, 0.49 ≦ Co / (Ni + Co + Mn) ≦ 0.71 and 0.09 ≦ Mn / ( A molar ratio that satisfies Ni + Co + Mn) ≤0.11, more preferably 0.29≤Ni / (Ni + Co + Mn) ≤0.31, 0.59≤Co / (Ni + Co + Mn) ≤0.61, and 0.09≤Mn. / (Ni + Co + Mn) ≤ 0.11 is included in a molar ratio. As described above, the composition (molar ratio) within the above range brings about a great improvement in charge / discharge characteristics such as discharge capacity. In this respect, the lithium composite oxide containing Ni, Co and Mn (hereinafter abbreviated as NCM) has a different behavior of volume change during charging and discharging depending on the composition, particularly the molar ratio of Ni, Co and Mn. If the composition (molar ratio) is within the range, the expansion / contraction or volume change of the NCM porous sintered plate due to charging / discharging is small, and depending on the composition, there is a case where almost no volume change occurs during charging / discharging (for example, Ni). : Co: Mn = 3: 6: 1). Therefore, it is considered that the peeling between the NCM porous sintered plate and the solid electrolyte is suppressed, and the charge / discharge characteristics such as the discharge capacity are significantly improved. Specific examples of the NCM composition (molar ratio) within the above range include Ni: Co: Mn = 2: 7: 1, 3: 6: 1, and 4: 5: 1, and Ni: Co is particularly preferable. : Mn = 3: 6: 1. As described above, when the molar ratio of Co is increased, the volume change of the NCM porous sintered plate is less likely to occur during charging and discharging. On the other hand, lithium composite oxides with a small molar ratio of Co, such as Ni: Co: Mn = 5: 2: 3 and 8: 1: 1, have a large change in the volume of the NCM porous sintered plate during charging and discharging. do.

The NCM porous sintered plate has a ratio of the diffraction intensity I _[003] due to the (003) plane to the diffraction intensity I _[104] due to the (104) plane in the XRD profile measured by X-ray diffraction (XRD). The degree of orientation I _[003] / I _[104] defined as is 1.2 to 3.6, preferably 1.2 to 3.5, and more preferably 1.2 to 3.0. , More preferably 1.2 to 2.6. Within such a range, the volume change of the NCM porous sintered plate during charging and discharging is more likely to occur, the peeling between the sintered plate and the solid electrolyte is suppressed, and the discharge capacity and the like are more effectively filled. The discharge characteristics can be improved. Here, in the lithium composite oxide having a layered rock salt type crystal structure such as NCM, a plane other than the crystal plane ((003) plane) where lithium ions are satisfactorily transferred in and out, for example, a plane (101) or a plane (104). ) Side) and the other side (003) side. In the present specification, each diffraction intensity of the (003) plane and the (104) plane by XRD is conveniently used as an index for calculating the degree of orientation.

The reason why the charge / discharge characteristics such as the discharge capacity are improved when the degree of orientation I _[003] / I _[104] within the above range can be considered as follows. First, as a premise, orientation / non-orientation will be described. When the NCM is in the form of powder (that is, in the form of not a sintered body), the arrangement of particles is random, so that the orientation of the crystal plane is not biased. This is called non-oriented. On the other hand, in the form of a sintered plate, the arrangement of particles is fixed, so that the direction of the crystal plane tends to be biased, and it is said that such a state is oriented. In this regard, if the NCM porous sintered plate has an orientation degree I [003] / I [104] within the above range, the orientation degree I _{[003] /} I _{[ 104]} of the NCM powder, which is a guideline for non-orientation, ( For example, the values are equal to or close to 1.4 (Ni: Co: Mn = 5: 2: 3 composition) and 2.3 (Ni: Co: Mn = 3: 6: 1 composition), so that they are not oriented. It can be said that it is close to (random), that is, it is essentially unoriented (or not very oriented). NCM primary particles have anisotropy in expansion and contraction behavior during charge and discharge (this tendency is particularly remarkable in NCM with Ni: Co: Mn = 3: 6: 1), but it is close to non-oriented (random). In the case of an NCM porous sintered plate, the anisotropy of expansion and contraction of the NCM primary particles constituting the NCM porous sintered plate is offset or alleviated by the randomness of the crystal orientation, so that the expansion and contraction of the entire NCM porous sintered plate is reduced. As a result, the volume change of the NCM porous sintered plate during charging / discharging is less likely to occur, the peeling between the sintered plate and the solid electrolyte is suppressed, and the charging / discharging characteristics such as the discharge capacity are more effectively improved. it is conceivable that.

The porosity of the NCM porous sintered plate is 10 to 40%, preferably 15 to 38%, more preferably 18 to 36%, and even more preferably 20 to 33%. Within such a range, when the battery is manufactured, the pores can be sufficiently filled with the solid electrolyte, and the proportion of the positive electrode active material in the positive electrode increases, so that the high energy density of the battery can be achieved. It can be realized. As used herein, the "porosity" is the volume ratio of pores in a sintered plate. This porosity can be measured by image analysis of a cross-sectional SEM image of the sintered plate. For example, after the sintered plate is embedded with resin and the cross section is polished by ion milling, the polished cross section is observed with an SEM (scanning electron microscope) to obtain a cross section SEM image (for example, a magnification of 500 to 1000 times), and the obtained SEM is obtained. By analyzing the image, the ratio (%) of the area filled with the resin to the total area of the part of the electrode active material and the part filled with the resin (the part that was originally a pore) is calculated and fired. The pore ratio (%) of the knot may be calculated. If the measurement can be performed with a desired accuracy, the porosity may be measured without embedding the sintered plate with resin. For example, the porosity of a sintered plate (positive electrode plate taken out from an all-solid secondary battery) in which the pores are filled with the solid electrolyte can be measured with the solid electrolyte still filled.

The average primary particle size of the NCM porous sintered plate is preferably 0.4 to 5.0 μm, more preferably 0.5 to 4.0 μm, still more preferably 0.6 to 3.0 μm, and particularly preferably 0. It is 0.8 to 2.5 μm, most preferably 1.0 to 2.2 μm. Within such a range, it is possible to more effectively improve the charge / discharge characteristics such as the discharge capacity. It is considered that this is because the primary particles are small as described above, so that the anisotropy of expansion and contraction of the lithium composite oxide primary particles due to charge and discharge is reduced. In the present specification, the "average primary particle diameter" is an average value of the diameters of the primary particles contained in the sintered plate of the electrode. This average primary particle size can be measured by image analysis of a cross-sectional SEM image of the sintered plate. Specifically, the cross-sectional SEM image (for example, a magnification of 5000 times) obtained in the same manner as the porosity measurement described above can be analyzed, and the average primary particle size can be calculated by the section method as follows. First, a straight line (line segment) having a total length L is randomly drawn in an SEM image having a magnification of 5000 times, and the number n _L of intersections between the line segment and the grain boundary of the primary particle is obtained, and D ₁ = 1.5 × The average primary particle diameter D ₁ is obtained by the formula of L / n _L. The same operation as described above is performed twice by changing the position each time, and the average primary particle diameters D ₂ and D ₃ are calculated, respectively. The average values of the obtained average primary particle diameters D ₁ , D ₂ and D ₃ are calculated and used as the average primary particle diameter D of the porous sintered plate. If the measurement can be performed with a desired accuracy, the average primary particle size may be measured without embedding the sintered plate with resin. For example, the measurement of the average primary particle size of a sintered plate (positive electrode plate taken out from an all-solid secondary battery) in which the pores are filled with the solid electrolyte can be performed with the solid electrolyte still filled. ..

The average pore diameter of the NCM porous sintered plate is preferably 0.5 μm or more, more preferably 0.5 to 15.0 μm, still more preferably 0.7 to 15.0 μm, and particularly preferably 0.8 to 10.0 μm. Most preferably, it is 0.9 to 8.0 μm. Within such a range, the number of solid electrolyte portions (solid electrolyte portions located at a distance from the interface) that are less susceptible to deterioration due to side reactions between the solid electrolyte and the sintered plate increases. Therefore, it is considered that the element diffusion between the solid electrolyte and the sintered plate is suppressed, and the separation between the sintered plate and the solid electrolyte due to the deterioration of the solid electrolyte is suppressed. In the present specification, the "average pore diameter" is an average value of the diameters of pores contained in the sintered plate of the electrode. Such "diameter" is typically the length of a line segment (Martin diameter) that divides the projected area of the pore into two equal parts. In the present invention, the "mean value" is preferably calculated on the basis of the number of pieces. This average pore diameter can be measured by image analysis of a cross-sectional SEM image of the sintered plate. For example, the SEM image obtained by the above-mentioned porosity measurement is analyzed, and the portion of the sintered plate that is filled with the electrode active material and the portion filled with the resin (the portion that was originally the pores) is separated and then filled with the resin. The maximum Martin diameter of each region may be obtained in the region of the portion, and the average value thereof may be used as the average pore diameter of the sintered plate. If the measurement can be performed with a desired accuracy, the average pore diameter may be measured without embedding the sintered plate with resin. For example, the average pore diameter of a sintered plate (positive electrode plate taken out from an all-solid-state secondary battery) in which the pores are filled with the solid electrolyte can be measured with the solid electrolyte still filled.

The thickness of the NCM porous sintered plate is preferably 30 to 200 μm, more preferably 50 to 200 μm, and even more preferably 80 to 200 μm from the viewpoint of improving the energy density of the battery.

The NCM porous sintered plate may be manufactured by any method, and may be appropriately manufactured with reference to a known method for manufacturing a lithium composite oxide porous sintered body. For example, Ni, Co and Mn are 0.19 ≤ Ni / (Ni + Co + Mn) ≤ 0.41, 0.49 ≤ Co / (Ni + Co + Mn) ≤ 0.71, and 0.09 ≤ Mn / (Ni + Co + Mn) ≤ 0. An NCM green sheet may be produced using an NCM raw material powder contained in a molar ratio satisfying 11, and the NCM green sheet may be produced by firing. Various characteristics such as porosity, average primary particle size, and average pore size of the NCM porous sintered plate control the particle size of the NCM raw material powder, or a mixed powder of two or more types of NCM raw material powder having different particle size distributions. It can be appropriately controlled by using it or adjusting the firing conditions.

(2) Negative electrode layer The negative electrode layer includes a porous sintered plate made of a negative electrode active material. As the negative electrode active material, a negative electrode active material generally used for a lithium secondary battery can be used. Examples of such general negative electrode active materials include carbon-based materials, metals or metalloids such as Li, In, Al, Sn, Sb, Bi, Si, or alloys containing any of these. .. In addition, an oxide-based negative electrode active material may be used.

A particularly preferable negative electrode active material contains a material capable of inserting and removing lithium ions at 0.4 V (vs. Li / Li ⁺ ) or higher, and preferably contains Ti. The negative electrode active material satisfying such conditions is preferably an oxide containing at least Ti, that is, a titanium-containing oxide. Preferred examples of such a negative electrode active material include lithium titanate Li ₄ Ti ₅ O ₁₂ (hereinafter, may be referred to as LTO), niobium titanium composite oxide Nb ₂ TIO ₇ , and titanium oxide TIO ₂ . LTO and Nb ₂ TiO ₇ are preferable, and LTO is more preferable. Although LTO is typically known to have a spinel-type structure, other structures may be adopted during charging / discharging. For example, LTO reacts in a two-phase coexistence of Li ₄ Ti ₅ O ₁₂ (spinel structure) and Li ₇ Ti ₅ O ₁₂ (rock salt structure) during charging and discharging. Therefore, LTO is not limited to the spinel structure.

Since the porous sintered plate made of the negative electrode active material does not need to contain an electron conduction aid or a binder, the energy density of the negative electrode can be increased. The pores of the porous sintered plate are filled with a solid electrolyte.

The porosity of the negative electrode active material or its sintered plate is preferably 20 to 45%, more preferably 20 to 40%, and even more preferably 25 to 35%. If the porosity is within such a range, the pores in the negative electrode active material can be sufficiently filled with the solid electrolyte, and the proportion of the negative electrode active material in the negative electrode increases, so that the energy density of the battery is high. Can be realized.

The thickness of the negative electrode active material or its sintered plate is preferably 40 to 270 μm, more preferably 65 to 270 μm, still more preferably 100 to 270 μm, and particularly preferably 107 to 270 μm from the viewpoint of improving the energy density of the battery. be.

(3) Solid Electrolyte The solid electrolyte is not particularly limited as long as it can be applied to an all-solid-state secondary battery, particularly an all-solid-state lithium secondary battery. Examples thereof include garnet-based ceramic materials, nitride-based ceramic materials, perovskite-based ceramic materials, phosphoric acid-based ceramic materials, sulfide-based ceramic materials, borosilicate-based ceramic materials, lithium-halide-based materials, and polymer-based materials. Be done. Examples of garnet-based ceramic materials include Li-La-Zr-O-based materials (specifically, Li ₇ La ₃ Zr ₂ O ₁₂ and the like) and Li-La-Ta-O-based materials (specifically, Li-La-Ta-O-based materials). Li ₇ La ₃ Ta ₂ O ₁₂ etc.). An example of a nitride _- based ceramic material is Li 3N. Examples of perovskite-based ceramic materials include Li-La-Zr-O-based materials (specifically, LiLa _1-x Ti _x O ₃ (0.04 ≦ x ≦ 0.14) and the like). Examples of phosphoric acid-based ceramic materials include lithium phosphate, nitrogen-substituted lithium phosphate (LiPON), Li-Al-Ti-PO, Li-Al-Ge-PO, and Li-Al-Ti-. Examples thereof include Si—P—O (specifically, Li _{1 + x + y} Al _x Ti _2-x Si _y P _3-y O ₁₂ (0 ≦ x ≦ 0.4, 0 <y ≦ 0.6), etc.). Examples of sulfide-based ceramic materials include LiOH-Li ₂ SO ₄ and Li ₃ BO ₃ -Li ₂ SO ₄ -Li ₂ CO ₃ . Examples of the borosilicate ceramic material include Li _2O -B _{2O 3} -SiO ₂ . Examples of lithium-halide materials include Li ₃ OX (in the formula, X is Cl and / or Br), Li ₂ (OH) _{1-a Fa} Cl (in the formula, 0 ≦ a ≦ 0. 3) and Li ₂ OHX (where X is Cl and / or Br).

A preferred solid electrolyte is a LiOH / Li ₂ SO ₄ system solid electrolyte. The LiOH / Li ₂ SO ₄ system solid electrolyte is a composite compound of LiOH and Li ₂ SO ₄ , and the typical composition is the general formula: xLiOH / yLi ₂ SO ₄ (in the formula, x + y = 1, 0.6 ≦ x). (≦ 0.95), and as a typical example, 3LiOH · Li ₂ SO ₄ (composition of x = 0.75 and y = 0.25 in the above general formula) can be mentioned. Preferably, the LiOH / Li ₂ SO ₄ system solid electrolyte contains a solid electrolyte identified as 3 LiOH / Li ₂ SO ₄ by X-ray diffraction. This preferred solid electrolyte contains 3LiOH · Li ₂ SO ₄ as the main phase. Whether or not 3LiOH / Li ₂ SO ₄ is contained in the solid electrolyte can be confirmed by identifying the X-ray diffraction pattern using 032-0598 of the ICDD database. Here, "3LiOH / Li ₂ SO ₄ " refers to a crystal structure that can be regarded as the same as 3LiOH / Li ₂ SO ₄ , and the crystal composition does not necessarily have to be the same as 3LiOH / Li ₂ SO ₄ . That is, as long as it has a crystal structure equivalent to that of 3LiOH / Li ₂ SO ₄ , those whose composition deviates from LiOH: Li ₂ SO ₄ = 3: 1 are also included in "3 LiOH / Li ₂ SO ₄ ". Therefore, even if the solid electrolyte contains a dopant such as boron (for example, 3LiOH / Li ₂ SO ₄ in which boron is dissolved and the X-ray diffraction peak is shifted to the high angle side), the crystal structure is 3LiOH / Li ₂ SO. As long as it can be regarded as the same as ₄ , it is referred to herein as 3LiOH · Li ₂ SO ₄ . Similarly, the solid electrolyte used in the present invention also allows the inclusion of unavoidable impurities.

Therefore, the LiOH / Li ₂ SO ₄ system solid electrolyte may contain a different phase in addition to the main phase of 3LiOH / Li ₂ SO ₄ . The heterogeneous phase may contain a plurality of elements selected from Li, O, H, S and B, or may consist only of a plurality of elements selected from Li, O, H, S and B. May be. Examples of the heterogeneous phase include LiOH, Li ₂ SO ₄ and / or Li ₃ BO ₃ derived from the raw material. Regarding these heterogeneous phases, it is considered that unreacted raw materials remained when forming _3LiOH / Li2SO4 _, but since they do not contribute to lithium ion conduction _, the amount is smaller except for _Li3BO3 . desirable. However, the heterogeneous phase containing boron, such as Li ₃ BO ₃ , may be contained in a desired amount because it can contribute to the improvement of the lithium ion conductivity maintenance after holding at a high temperature for a long time. However, the solid electrolyte may be composed of a single phase of 3LiOH / Li ₂ SO ₄ in which boron is dissolved.

The LiOH / Li ₂ SO ₄ system solid electrolyte (particularly 3 LiOH / Li ₂ SO ₄ ) preferably further contains boron. By further containing boron in the solid electrolyte identified as 3LiOH / Li _{2SO 4} , it is possible to significantly suppress the decrease in lithium ion conductivity even after holding at a high temperature for a long time. Boron is presumed to be incorporated into one of the sites of the crystal structure of _3LiOH / _Li2SO4 and improve the stability of the crystal structure with respect to temperature. The molar ratio (B / S) of boron B to sulfur S contained in the solid electrolyte is preferably more than 0.002 and less than 1.0, more preferably 0.003 or more and 0.9 or less, still more preferably. It is 0.005 or more and 0.8 or less. When the B / S is within the above range, it is possible to improve the maintenance rate of lithium ion conductivity. Further, when the B / S is within the above range, the content of the unreacted heterogeneous phase containing boron is low, so that the absolute value of the lithium ion conductivity can be increased.

The LiOH / Li ₂ SO ₄ system solid electrolyte may be a green compact of a powder obtained by crushing a melt-solidified body, but a melt-solidified body (that is, one solidified after being heated and melted) is preferable.

The LiOH / Li ₂ SO ₄ system solid electrolyte is filled in the pores of the porous sintered plate of the positive electrode layer and the negative electrode layer by melting, but the remaining portion is a separator layer (separator layer) between the positive electrode layer and the negative electrode layer. Intervenes as a solid electrolyte layer). The thickness of the separator layer (excluding the portion that has entered the pores of the positive electrode layer and the negative electrode layer) is preferably 1 to 500 μm, more preferably 3 to 50 μm, and more preferably 3 to 50 μm from the viewpoint of charge / discharge rate characteristics and the insulating property of the solid electrolyte. It is preferably 5 to 40 μm.

(4) Intermediate layer It is preferable that the intermediate layer is provided at the interface between at least one of the positive electrode active material and the negative electrode active material and the solid electrolyte. By providing the intermediate layer, the discharge capacity can be further improved (compared to the one without the intermediate layer). Although the detailed mechanism for improving the discharge capacity is not clear, it is speculated that the presence of the intermediate layer may suppress the deterioration of the solid electrolyte due to the reaction between the solid electrolyte and the active material. It is more preferable that the intermediate layer is present at the interface between the positive electrode active material and the solid electrolyte, but the intermediate layer may be present at the interface between the negative electrode active material and the solid electrolyte. The intermediate layer may be present at both the interface between the positive electrode active material and the solid electrolyte and the interface between the negative electrode active material and the solid electrolyte. The thickness of the intermediate layer is not particularly limited as long as the desired effect of improving the discharge capacity can be obtained, but is preferably 0.001 to 1 μm, more preferably 0.005 to 0.2 μm, and further preferably 0.01 to 0.1 μm. Is.

The intermediate layer is a lithium composite oxide containing Li and at least one selected from the group consisting of Ti, La, Zr, Al, W, Nb, Sn, Ce, Mn, Y, and Ta, and / or Y. It is preferably composed of an oxide of ₍ typically _Y2O3 ). Preferred examples of such lithium composite oxides are Li and Ti oxides (typically Li ₂ TiO ₃ ), Li, La and Zr or Li, La, Zr and Al oxides (typically). Is an oxide of Li 7-3 x Al _x La ₃ Zr ₂ O ₁₂ ( _0≤x <0.4, more typically 0.02 <x <0.4)), Li, La and Ti (typical). Li _0.33 La _0.55 TiO ₃ ), Li and W oxides (typically Li ₂ WO ₄ ), Li and Al oxides (typically LiAlO ₂ ), Li and Nb. Oxides (typically LiNbO ₃ or LiNb 3O ₈ ), Li and Sn oxides (typically _{LiSnO 3 )} , Li and Ce oxides (typically Li ₈ CeO ₆ ), Li, La and Nb oxides (typically Li ₅ La ₃ Nb ₂ O ₁₂ ), Li and Mn oxides (typically LiMnO ₂ ), Li and Y oxides (typically LiYO ₂ ). , Li and Ta oxides (typically LiTaO ₃ ), and any combination thereof, more preferably Li and Ti oxides (typically Li ₂ TiO ₃ ), Li, La, Oxides of Zr and Al (typically Li _6.7 Al _0.1 La ₃ Zr ₂ O ₁₂ ), and oxides of Li, La and Ti (typically Li _0.33 La _0.55 TIO). ₃ ) can be mentioned.

To form the intermediate layer, a solution is prepared by mixing a metal alkoxide of one or more metal elements constituting the intermediate layer and a metal salt such as nitrate with alcohol such as ethanol or water at a predetermined molar ratio to prepare an electrode active material. This can be done by immersing (preferably a sintered plate or particles) in this solution, then taking it out and allowing it to stand in the air to hydrolyze the alkoxide or dry the solvent. In the case of a sintered plate, it is preferable to infiltrate the inside of the solution by dipping it in a solution under reduced pressure, and it is preferable to repeat the work from the dipping to standing in the air a plurality of times (for example, 1 to 20 times). preferable. It is preferable to heat-treat the electrode active material (preferably sintered plate or particles) on which the intermediate layer is formed at 400 to 700 ° C. for 5 to 60 minutes. When a metal alkoxide is used, it is preferable to carry out the work from preparation to immersion of the solution in an atmosphere having a dew point of −30 ° C. or lower so that the solution does not deteriorate due to hydrolysis or the like.

Manufacture of all-solid-state secondary battery The manufacture of all-solid-state secondary battery is, for example, i) forming an intermediate layer and a current collector (with an intermediate layer and a current collector formed as needed) and a positive electrode (with an intermediate layer and a current collector formed as needed). This can be done by preparing the negative electrode and ii) sandwiching a solid electrolyte between the positive electrode and the negative electrode and applying pressure, heating, or the like to integrate the positive electrode, the solid electrolyte, and the negative electrode. The positive electrode, the solid electrolyte, and the negative electrode may be bonded by other methods. In this case, as an example of the method of forming a solid electrolyte between the positive electrode and the negative electrode, a method of placing a solid electrolyte molded body or powder on one of the electrodes, and a method of screen-printing a paste of the solid electrolyte powder on the electrode. Examples thereof include a method of colliding and solidifying a solid electrolyte powder by an aerosol disposition method or the like using an electrode as a substrate, and a method of depositing a solid electrolyte powder on an electrode by an electrophoresis method to form a film.

The present invention will be described in more detail with reference to the following examples. In the following description, a lithium composite oxide having a layered rock salt structure containing Li, Ni, Co and Mn such as (Ni _0.3 Co _0.6 Mn _0.1 ) O ₂ is abbreviated as "NCM". , Li ₄ Ti ₅ O ₁₂ shall be abbreviated as "LTO".

First, as shown below, NCM raw material powders 1 to 6 for producing a positive electrode plate were prepared. Table 1 shows a summary of the methods for producing these raw material powders.

[Preparation of NCM raw material powder 1]
Commercially available (Ni _0.5 Co _0.2 Mn _0.3 ) (OH) ₂ powder (average particle size 9 to 10 μm) and Li weighed so that the molar ratio of Li / (Ni + Co + Mn) is 1.15. ₂ CO ₃ powder (average particle size 3 μm) was mixed. The obtained mixed powder was held at 750 ° C. for 10 hours, the volume standard D50 particle size was adjusted to about 5.5 μm by wet pulverization with a ball mill, and then dried to obtain NCM raw material powder 1.

[Preparation of NCM raw material powder 2]
Commercially available (Ni _0.3 Co _0.6 Mn _0.1 ) (OH) ₂ powder (average particle size 7 to 8 μm) and Li weighed so that the molar ratio of Li / (Ni + Co + Mn) is 1.15. ₂ CO ₃ powder (average particle size 3 μm) was mixed. The obtained mixed powder was held at 850 ° C. for 10 hours to obtain NCM raw material powder 2. The volume-based D50 particle size of this powder was about 6.5 μm.

[Preparation of NCM raw material powder 3]
The volume-based D50 particle size of the NCM raw material powder 2 was adjusted to about 4.3 μm by wet pulverization with a ball mill, and then dried to obtain the NCM raw material powder 3.

[Preparation of NCM raw material powder 4]
Commercially available (Ni _0.2 Co _0.7 Mn _0.1 ) (OH) ₂ powder (average particle size 7 to 8 μm) and Li weighed so that the molar ratio of Li / (Ni + Co + Mn) is 1.15. ₂ CO ₃ powder (average particle size 3 μm) was mixed. The obtained mixed powder was held at 850 ° C. for 10 hours, the volume standard D50 particle size was adjusted to about 4.5 μm by wet pulverization with a ball mill, and then dried to obtain NCM raw material powder 4.

[Preparation of NCM raw material powder 5]
Commercially available (Ni _0.4 Co _0.5 Mn _0.1 ) (OH) ₂ powder (average particle size 8-9 μm) and Li weighed so that the molar ratio of Li / (Ni + Co + Mn) is 1.15. ₂ CO ₃ powder (average particle size 3 μm) was mixed. The obtained mixed powder was held at 850 ° C. for 10 hours, the volume standard D50 particle size was adjusted to about 4.6 μm by wet pulverization with a ball mill, and then dried to obtain NCM raw material powder 5.

[Preparation of NCM raw material powder 6]
Commercially available (Ni _0.3 Co _0.6 Mn _0.1 ) (OH) ₂ powder (average particle size 7 to 8 μm) and Li weighed so that the molar ratio of Li / (Ni + Co + Mn) is 1.15. ₂ CO ₃ powder (average particle size 3 μm) was mixed. The obtained mixed powder was held at 750 ° C. for 10 hours, the volume standard D50 particle size was adjusted to about 0.4 μm by wet pulverization with a ball mill, and then dried to obtain NCM raw material powder 6.

Using the above raw material powders 1 to 6, positive electrode plates and batteries were prepared as shown below, and various evaluations were performed.

Example 1 (comparison)
(1) Preparation of positive electrode plate (1a) Preparation of NCM green sheet First, the NCM raw material powder 1 shown in Table 1 was prepared. This NCM raw material powder 1 was mixed with a solvent for tape molding, a binder, a plasticizer, and a dispersant. After adjusting the viscosity of the obtained paste, an NCM green sheet was produced by molding it into a sheet on a PET (polyethylene terephthalate) film. The thickness of the NCM green sheet was adjusted so that the thickness after firing was 100 μm.

(1b) Preparation of NCM Sintered Plate The NCM green sheet peeled off from the PET film was punched out into a circle with a diameter of 11 mm and placed in a firing sheath. Baking was performed by raising the temperature to 920 ° C. at a heating rate of 200 ° C./h and holding it for 10 hours. The thickness of the obtained sintered plate was about 100 μm as observed by SEM. An Au film (thickness 100 nm) was formed as a current collector layer on one side of this NCM sintered plate by sputtering. In this way, a positive electrode plate was obtained.

(1c) Film formation of intermediate layer Tetra-i-propoxytitanium: lithium ethoxydo: ethanol was mixed so as to have a molar ratio of 0.0225: 0.045: 1 to prepare a solution for forming an intermediate layer. .. The NCM sintered plate prepared in (1b) above was immersed in this solution to reduce the pressure, and the pores of the positive electrode plate were impregnated with the solution. The above-mentioned work was performed in a glove box in an Ar atmosphere with a dew point of −50 ° C. or lower. Then, the NCM sintered plate was taken out from the glove box and allowed to stand in the air for 10 minutes to form an intermediate layer. After that, the above series of operations was repeated 7 times (that is, a total of 8 times was formed). Finally, the NCM sintered plate was heat-treated at 400 ° C. for 30 minutes to obtain a positive electrode plate on which an intermediate layer was formed.

(2) Preparation of negative electrode plate (2a) Preparation of LTO green sheet Commercially available TiO ₂ powder (average particle size 1 μm or less) and Li ₂ CO ₃ powder weighed so that the molar ratio of Li / Ti is 0.84. After mixing (average particle size 3 μm), the mixture was held at 1000 ° C. for 2 hours to obtain a powder composed of LTO particles. This powder was adjusted to an average particle size of about 2 μm by wet grinding with a ball mill, and then mixed with a solvent for tape forming, a binder, a plasticizer, and a dispersant. After adjusting the viscosity of the obtained paste, an LTO green sheet was prepared by molding this paste into a sheet on a PET film. The thickness of the LTO green sheet was adjusted so that the thickness after firing was 130 μm.

(2b) Preparation of LTO Sintered Plate The LTO green sheet peeled off from the PET film was punched out into a circle with a diameter of 11 mm and placed in a firing sheath. Baking was performed by raising the temperature to 850 ° C. at a heating rate of 200 ° C./h and holding it for 2 hours. The thickness of the obtained sintered plate was about 130 μm according to SEM observation. An Au film (thickness 100 nm) was formed as a current collector layer on one side of this LTO sintered plate by sputtering. In this way, a negative electrode plate was obtained.

(3) Preparation of solid electrolyte (3a) Preparation of raw material mixed powder Li ₂ SO ₄ powder (commercially available, purity 99% or more), LiOH powder (commercially available, purity 98% or more), and Li ₃ BO ₃ (commercially available product) , Purity 99% or more) was mixed so as to have Li ₂ SO ₄ : LiOH: Li ₃ BO ₃ = 1: 2.6: 0.05 (molar ratio) to obtain a raw material mixed powder. These powders were handled in a glove box in an Ar atmosphere, and sufficient care was taken not to cause deterioration such as moisture absorption.

(3b) Melt synthesis The raw material mixed powder was put into a crucible made of high-purity alumina in an Ar atmosphere. This crucible was set in an electric furnace and heat-treated at 430 ° C. for 2 hours in an Ar atmosphere to prepare a melt. Subsequently, the melt was cooled at 100 ° C./h in an electric furnace to form a solidified product.

(3c) Mortar crushing The obtained coagulated product was crushed in a mortar in a glove box in an Ar atmosphere to obtain a solid electrolyte powder having a volume-based D50 particle size of 5 to 50 μm.

(4) Preparation of all-solid-state battery A solid electrolyte powder was placed on a positive electrode plate, and a negative electrode plate was placed on the solid electrolyte powder. Further, a weight was placed on the negative electrode plate and heated at 400 ° C. for 45 minutes in an electric furnace. At this time, the solid electrolyte powder was melted, and after the subsequent solidification, a solid electrolyte layer was formed between the electrode plates. A battery was manufactured using the cell composed of the obtained positive electrode plate / solid electrolyte / negative electrode plate.

(5) Evaluation (5a) Degree of Orientation XRD (X-ray diffraction) measurement was performed on the positive electrode plate produced in (1) above. This measurement was performed by measuring the XRD profile when the plate surface of the positive electrode plate was irradiated with X-rays using an XRD device (RIGKU Co., Ltd., RINT-TTR III). From this XRD profile, it is the ratio of the diffraction intensity (peak height) I _[003] caused by the (003) plane to the diffraction intensity (peak height) I _{[ 104]} caused by the (104) plane of the NCM. _003] / I _[104] was calculated and used as the degree of orientation.

(5b) Measurement of thickness and porosity The positive electrode plate (NCM sintered plate without solid electrolyte) produced in (1) above and the negative electrode plate (without solid electrolyte) produced in (2) above. The thickness and porosity (% by volume) of each of the LTO sintered plates in the state were measured as follows. First, the positive electrode plate (or the negative electrode plate) was embedded with resin, and then the cross section was polished by ion milling, and then the polished cross section was observed by SEM to obtain a cross section SEM image. The thickness was calculated from this SEM image. The SEM images for porosity measurement were images with a magnification of 1000 times and a magnification of 500 times. The obtained image is binarized using image analysis software (Image-Pro Premier manufactured by Media Cybernetics), and the positive electrode active material (or negative electrode active material) in the positive electrode plate (or negative electrode plate) is subjected to binarization treatment. Porosity of the positive electrode plate (or negative electrode plate) by calculating the ratio (%) of the area filled with resin to the total area of the part filled with resin and the part filled with resin (the part that was originally pores). It was set to (%). The threshold value for binarization was set using Otsu's binarization as a discriminant analysis method. The porosity of the positive electrode plate is as shown in Table 2, and the porosity of the negative electrode plate was 38%.

(5c) Measurement of average pore diameter Using the SEM image used for the above porosity measurement, the average pore diameter was measured as follows. Image analysis software (Image-Pro Premier manufactured by Media Cybernetics) is used to perform a binarization process, and the positive electrode plate (or negative electrode plate) is filled with a portion of the positive electrode active material (or negative electrode active material) and a resin. The part (the part that was originally a pore) was cut out. Then, in the region of the portion filled with the resin, the maximum Martin diameter of each region was obtained, and the average value thereof was taken as the average pore diameter (μm) of the positive electrode plate (or the negative electrode plate). The average pore diameter of the positive electrode plate is as shown in Table 2, and the average pore diameter of the negative electrode plate was 2.1 μm.

(5d) Average primary particle size The average primary particle size was calculated by the section method as follows using the SEM image (magnification 5000 times) obtained in the same manner as in the above porosity measurement. First, a straight line (line segment) having a total length L was randomly drawn in an SEM image having a magnification of 5000 times, and the number n _L of intersections between the line segment and the grain boundary of the primary particle was obtained. Using the line segment length L and the number of intersections between the line segment and the grain boundaries of the primary particles n _L , the following equation:
D ₁ = 1.5 × L / n _L
The average primary particle diameter D ₁ was obtained from the above. The same operation as described above was performed twice by changing the position each time, and the average primary particle diameters D ₂ and D ₃ were calculated, respectively. The average values of the obtained average primary particle diameters D ₁ , D ₂ and D ₃ were calculated and used as the average primary particle diameter D of the positive electrode plate. The average primary particle diameter D of the positive electrode plate was as shown in Table 2.

(5e) Measurement of molar ratio of metal elements in the positive electrode plate The molar ratio of each element to the total content of Ni, Co and Mn in the positive electrode plate produced in (1) above Ni / (Ni + Co + Mn), Co / (Ni + Co + Mn) , And Mn / (Ni + Co + Mn) were calculated from the measurement results of metal element analysis by inductively coupled plasma emission spectroscopic analysis (ICP-AES method). The results were within ± 0.01 of the molar ratio shown in Table 2.

(5f) Identification of solid electrolyte by XRD When the LiOH / Li ₂ SO ₄ system solid electrolyte obtained in (3c) above was analyzed by X-ray diffraction (XRD), it was identified as 3LiOH / Li ₂ SO ₄ .

(5g) Charge / Discharge Evaluation With respect to the battery manufactured in (4) above, the discharge capacity of the battery at an operating temperature of 150 ° C. was measured in a voltage range of 2.5V-1.5V. This measurement was performed by charging with a constant current and constant voltage until the battery voltage reached the upper limit of the voltage range, and then discharging until the lower limit of the voltage range was reached. At this time, the discharge capacity of Example 1 was regarded as 100, and the discharge capacity of Examples 2 to 9 described later was used as a reference for indicating a relative value.

Example 2
In the production of the positive electrode plate of (1) above, the positive electrode plate and the battery were produced in the same manner as in Example 1 except that the NCM raw material powder 3 shown in Table 1 was used instead of the NCM raw material powder 1. Evaluation was performed.

Example 3
In the production of the positive electrode plate of (1) above, the positive electrode plate and the battery were produced in the same manner as in Example 1 except that the NCM raw material powder 4 shown in Table 1 was used instead of the NCM raw material powder 1. Evaluation was performed.

Example 4
In the production of the positive electrode plate of (1) above, the positive electrode plate and the battery were produced in the same manner as in Example 1 except that the NCM raw material powder 5 shown in Table 1 was used instead of the NCM raw material powder 1. Evaluation was performed.

Example 5
In the production of the positive electrode plate of (1) above, the positive electrode plate and the battery were produced in the same manner as in Example 1 except that the NCM raw material powder 6 shown in Table 1 was used instead of the NCM raw material powder 1. Evaluation was performed.

Example 6
In the production of the positive electrode plate of (1) above, instead of 1) NCM raw material powder 1, NCM mixed powder A containing NCM raw material powders 2 and 6 shown in Table 1 in a blending ratio (weight ratio) of 90:10 is used. A positive electrode plate and a battery were produced in the same manner as in Example 1 except that they were used and 2) the firing temperature was set to 950 ° C., and various evaluations were performed.

Example 7
In the production of the positive electrode plate of (1) above, instead of 1) NCM raw material powder 1, NCM mixed powder A containing NCM raw material powders 2 and 6 shown in Table 1 in a blending ratio (weight ratio) of 90:10 is used. A positive electrode plate and a battery were produced in the same manner as in Example 1 except that they were used and 2) the firing temperature was set to 900 ° C., and various evaluations were performed.

Example 8
In the preparation of the positive electrode plate of (1) above, instead of 1) NCM raw material powder 1, NCM mixed powder B containing NCM raw material powders 2 and 6 shown in Table 1 at a blending ratio (weight ratio) of 70:30 is used. A positive electrode plate and a battery were produced in the same manner as in Example 1 except that they were used and 2) the firing temperature was set to 950 ° C., and various evaluations were performed.

Example 9
In the production of the positive electrode plate of (1) above, instead of 1) NCM raw material powder 1, NCM mixed powder C containing NCM raw material powders 2 and 6 shown in Table 1 in a blending ratio (weight ratio) of 95: 5 is used. A positive electrode plate and a battery were prepared in the same manner as in Example 1 except that they were used and 2) the firing temperature was set to 970 ° C., and various evaluations were performed.

Results Table 2 shows the specifications of the positive electrode plates produced in each example and the evaluation results of the cells. As described above, the charge / discharge characteristics were compared under the same rate conditions, the discharge capacity measured in Example 1 (comparison) was regarded as 100, and the relative value with respect to this was calculated and shown in Table 2.

 

Claims (11)

1. Ni, Co and Mn,
   0.19 ≤ Ni / (Ni + Co + Mn) ≤ 0.41,
   0.49 ≤ Co / (Ni + Co + Mn) ≤ 0.71 and 0.09 ≤ Mn / (Ni + Co + Mn) ≤ 0.11
   A positive electrode layer containing a porous sintered plate composed of a lithium composite oxide having a layered rock salt structure containing a molar ratio satisfying the above conditions.
   A negative electrode layer including a porous sintered plate composed of a negative electrode active material, and
   A solid electrolyte that is interposed between the positive electrode layer and the negative electrode layer as a separator layer and is also filled in the pores of the porous sintered plate of the positive electrode layer and the negative electrode layer.
   All-solid-state secondary battery with.
2. The lithium composite oxide contains Ni, Co and Mn.
   0.29 ≤ Ni / (Ni + Co + Mn) ≤ 0.31,
   0.59 ≤ Co / (Ni + Co + Mn) ≤ 0.61 and 0.09 ≤ Mn / (Ni + Co + Mn) ≤ 0.11
   The all-solid-state secondary battery according to claim 1, which comprises a molar ratio that satisfies.
3. The porous sintered plate has a ratio of the diffraction intensity I _[003] due to the (003) plane to the diffraction intensity I _[104] due to the (104) plane in the XRD profile measured by X-ray diffraction (XRD). The all-solid secondary battery according to claim 1 or 2, wherein the degree of orientation I _[003] / I _[104] is 1.2 to 3.6.
4. The all-solid-state secondary battery according to any one of claims 1 to 3, wherein the porous sintered plate has an average primary particle diameter of 0.4 to 5.0 μm.
5. The all-solid-state secondary battery according to any one of claims 1 to 4, wherein the porous sintered plate has an average pore diameter of 0.5 to 15 μm.
6. The all-solid-state secondary battery according to any one of claims 1 to 5, wherein the porous sintered plate has a porosity of 10 to 40%.
7. The all-solid secondary battery according to any one of claims 1 to 6, wherein the solid electrolyte is a LiOH / Li ₂ SO ₄ system solid electrolyte.
8. The all-solid secondary battery according to claim 7, wherein the LiOH / Li ₂ SO ₄ system solid electrolyte contains a solid electrolyte identified as 3 LiOH / Li ₂ SO ₄ by X-ray diffraction.
9. The all-solid-state secondary battery according to claim 7 or 8, wherein the LiOH / Li ₂ SO ₄ system solid electrolyte further contains boron.
10. The all-solid-state secondary battery according to any one of claims 1 to 9, wherein the negative electrode active material is a titanium-containing oxide.
11. The all-solid-state secondary battery according to claim 10, wherein the titanium-containing oxide is lithium titanate.