JP2020173906A - Positive electrode active material for all-solid battery - Google Patents

Abstract

To provide a positive electrode active material for all-solid battery ensuring good rate characteristics in an all-solid battery.SOLUTION: A positive electrode active material for all-solid battery contains a lithium nickel manganese oxide having a lamellar crystal structure of NaFeO2 type, represented by a constitution formula LiaNibMncO2 (0.90≤a≤1.15, 0.45≤b≤0.71, 0.28≤c≤0.55). In an electron diffraction image acquired by incoming radiation of an electron ray from (100) direction of the unit lattice of the lamellar crystal structure of the NaFeO2 type, the lithium nickel manganese oxide has a crystal structure where (i) a first diffraction spot group appearing in correspondence with the grating period of the unit lattice of the lamellar crystal structure of the NaFeO2 type, and (ii) a second diffraction spot group appearing in correspondence with a grating period two times that of the unit lattice in the c-axis direction appear.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to a positive electrode active material for an all-solid-state battery.

With the rapid spread of information-related devices such as personal computers, video cameras and mobile phones, and communication devices in recent years, the development of batteries used as their power sources has been emphasized. In addition, the automobile industry and the like are also developing high-output and high-capacity batteries for electric vehicles or hybrid vehicles.

Among the batteries used in the above-mentioned applications, the all-solid-state lithium-ion battery has a high energy density because it utilizes a battery reaction involving the movement of lithium ions, and is organic as an electrolyte interposed between the positive electrode and the negative electrode. Attention has been paid to the fact that a solid electrolyte is used instead of the electrolytic solution containing a solvent.

As positive electrode active materials used in such batteries, for example, in Patent Document 1, the formula (1): Li [Li _x (A _y B _1-y ) _1-x ] O ₂ (A and B in the formula are High capacity of non-aqueous electrolyte secondary battery by using positive electrode active material composed of different transition metal elements, crystal particles of lithium-containing oxide represented by 0 ≦ x ≦ 0.3 and 0 <y <1). It is disclosed that the charging / discharging efficiency can be improved. Patent Document 1 describes that it is important that the transition metals are solid-solved at the atomic level and that the number of the two transition metals is substantially the same.

Further, Patent Document 2 describes Li ₂ Ni _α M ¹ _β M ² _γ Mn _η O _4- for the purpose of suppressing the collapse of the crystal structure during charging and discharging and providing a positive electrode material having excellent safety. _ε (0.50 <α ≦ 1.33, 0.33 ≦ γ ≦ 1.1, 0 ≦ η ≦ 1.00, 0 ≦ β <0.67, 0 ≦ ε ≦ 1.00, M ¹ : Co , at least one selected from ^{Ga, M 2: Ge, Sn} , represented by at least one) selected from Sb, having a layered structure that includes a Li layer and the Ni layer, the crystal structure is a superlattice structure The positive electrode material is disclosed.
This technology improves safety by improving the packing property by combining the size of the unit lattice and the superlattice, thereby suppressing the collapse of the crystal structure during charging and discharging of the non-aqueous electrolyte secondary battery. Is.

International Publication No. 2002/078105 JP-A-2016-192309

In Example 2 of Patent Document 1, 2.5 to 4 non-aqueous electrolyte secondary batteries prepared by using a lithium-containing oxide represented by LiNi _1/2 Mn _1/2 O ₂ as a positive electrode active material are used. High-rate discharge represented by the capacity ratio (2C / 0.2C) of the discharge capacity at the current value of 2C rate to the discharge capacity at the current value of 0.2C rate when charging / discharging in the voltage range of 2V. The ratio is as high as 95%, indicating that good rate characteristics can be obtained.
However, the present researchers charge and discharge using the lithium-containing oxide (LiNi _1/2 Mn _1/2 O ₂ ) disclosed in Example 2 of Patent Document 1 as the positive electrode active material of the all-solid-state battery. When the above is performed, if the voltage range is changed to, for example, 2.5 to 4.5 V and the upper limit of the voltage value is raised, the discharge capacity under high rate conditions tends to decrease, and good rate characteristics cannot be obtained. I found out.

Further, even an all-solid-state battery using a positive electrode material disclosed in Patent Document 2 has a problem that the discharge capacity when charging / discharging under high rate conditions tends to decrease and the rate characteristics are low.

In view of the above circumstances, an object of the present disclosure is to provide a positive electrode active material for an all-solid-state battery, which can obtain good rate characteristics in the all-solid-state battery.

The positive electrode active material for the all-solid-state battery of the present disclosure has a composition formula Li _a Ni _b Mn _c O ₂ (0.90 ≦ a ≦ 1.15, 0.45 ≦ b ≦ 0.71, 0.28 ≦ c ≦. represented by 0.55), containing lithium nickel manganese oxide having a layered crystal structure of type ₂ NaFeO, the lithium nickel manganese oxide, [100] direction of the unit cell of the NaFeO ₂ type of layered crystal structure In the electron diffraction image obtained by injecting an electron beam from, (i) a first diffraction spot group appearing corresponding to the lattice period of the unit lattice of the NaFeO type ₂ layered crystal structure, and (ii). It is characterized by having a crystal structure in which a second diffraction spot group appearing corresponding to a lattice period twice the lattice period in the c-axis direction of the unit cell appears.

According to the present disclosure, it is possible to provide a positive electrode active material for an all-solid-state battery, which can obtain good rate characteristics in the all-solid-state battery.

FIG. 1A is a model diagram showing a unit cell of lithium nickel-manganese oxide contained in the positive electrode active material of the present disclosure, and FIG. 1B constitutes the unit cell shown in FIG. 1A. It is a figure which extracts one of the transition metal layers and schematically shows the atomic arrangement observed from the direction (001). FIG. 2A is a diagram showing a selected area diffraction pattern for the sample of Comparative Example 1, and FIG. 2B is a diagram showing a selected area diffraction pattern for the sample of Example 1. FIG. 3 (a) is a model diagram showing a unit cell of lithium nickel-manganese oxide contained in the positive electrode active material of the present disclosure, and FIG. 3 (b) shows the lattice shown in FIG. 3 (a) as a unit cell. FIG. 3 (c) is a diagram schematically showing an arrangement state of transition metal elements when a lithium nickel-manganese oxide having a crystal structure is observed from the direction (001). FIG. It is a schematic diagram for demonstrating the stacking period of the pore group which a contained lithium nickel manganese oxide has. FIG. 4A is a diagram showing an XRD spectrum of the sample of Example 1, and FIG. 4B is a diagram showing an enlarged XRD spectrum shown in FIG. 4A. FIG. 5A is a diagram showing an XRD spectrum of the sample of Comparative Example 1, and FIG. 5B is a diagram showing an enlarged XRD spectrum shown in FIG. 5A. It is a figure which shows an example of the layer structure of the all-solid-state battery provided with the positive electrode active material layer of this disclosure, and is the figure which shows typically the cross section cut in the stacking direction. It is a figure which shows the charge / discharge curve about the constant current charge and constant current discharge performed using the evaluation cell 1 of Example 1 and the evaluation cell 6 of Comparative Example 1. It is a figure which shows the charge / discharge curve about the constant current charge and constant current discharge with the current equivalent to 0.1C performed using the evaluation cell 5 of Example 5 and the evaluation cell 7 of Comparative Example 2. FIG. 9A is a diagram showing an SEM observation image of Comparative Example 1, and FIG. 9B is a diagram showing an SEM observation image of Example 1.

The positive electrode active material for the all-solid-state battery of the present disclosure has a composition formula Li _a Ni _b Mn _c O ₂ (0.90 ≦ a ≦ 1.15, 0.45 ≦ b ≦ 0.71, 0.28 ≦ c ≦. represented by 0.55), containing lithium nickel manganese oxide having a layered crystal structure of type ₂ NaFeO, the lithium nickel manganese oxide, [100] direction of the unit cell of the NaFeO ₂ type of layered crystal structure In the electron diffraction image obtained by injecting an electron beam from, (i) a first diffraction spot group appearing corresponding to the lattice period of the unit lattice of the NaFeO type ₂ layered crystal structure, and (ii). It is characterized by having a crystal structure in which a second diffraction spot group appearing corresponding to a lattice period twice the lattice period in the c-axis direction of the unit cell appears.

The positive electrode active material of the present disclosure contains a lithium nickel-manganese oxide represented by the composition formula of the following formula (1).

Li _a Ni _b Mn _c O ₂ formula (1)
(However, in the formula (1), 0.90 ≦ a ≦ 1.15, 0.45 ≦ b ≦ 0.71, 0.28 ≦ c ≦ 0.55.)

FIG. 1A is a model diagram showing a unit cell of lithium nickel-manganese oxide contained in the positive electrode active material of the present disclosure.
The unit cell shown in FIG. 1 (a) has a layered crystal structure of NaFeO type ₂ belonging to the space group R-3 m, and a layer parallel to the (001) plane is formed along the c-axis direction of the unit cell. Multiple layers are stacked.
As shown in FIG. 1 (a), Li (lithium) is present at the 3a site of the unit cell of the lithium nickel-manganese oxide contained in the positive electrode active material of the present disclosure, and a transition metal (Mn (manganese)) is present at the 3b site. ) And Ni (nickel)), and oxygen is present at the 6c site.

In the unit cell shown in FIG. 1 (a), a Li (lithium) layer, a transition metal layer, and an oxygen layer are laminated along the c-axis direction of the unit cell as a layer parallel to the above-mentioned (001) plane. There is.
The Li (lithium) layer is a layer containing Li (lithium) as a main component, and is substantially composed of Li (lithium). The transition metal layer is a layer containing a transition metal (Ni (nickel) and Mn (manganese)) as a main component, and is substantially composed of a transition metal (Ni (nickel) and Mn (manganese)). .. Further, the oxygen layer is a layer containing oxygen as a main component and is substantially composed of oxygen.
In the present disclosure, the main component means the component having the largest content ratio.

FIG. 1 (b) extracts one of the transition metal layers from the layers parallel to the (001) plane constituting the unit cell shown in FIG. 1 (a), and selects a transmission electron microscope from the direction (001). It is a figure which shows typically the atomic arrangement observed by selected area diffraction using.
The atomic arrangement shown in FIG. 1 (b) has a long-period structure expressed as √3 × √3 in Wood's notation. The part indicated by the dotted line in FIG. 1B indicates that the hole is a hole or a part where a different element different from the transition metal existing at the position indicated by the solid line exists.
The atomic arrangement shown in FIG. 1 (b) is formed by partially replacing a part of the transition metal forming a long-period structure of √3 × √3 with vacancies or transition metals with a predetermined regularity. In the following description, the part indicated by the dotted line may be referred to as a "vacancy" for convenience. Further, in the following description, a plurality of pores or a regular arrangement structure of different elements (see FIG. 1B) formed in each transition metal layer is referred to as a pore group.

The lithium nickel manganese oxide contained in the positive electrode active material of the present disclosure is found in an electron diffraction image obtained by injecting an electron beam from the [100] direction of the unit cell of the NaFeO type ₂ layered crystal structure. i) The first diffraction spot group appearing corresponding to the lattice period of the unit cell of the NaFeO type ₂ layered crystal structure, and (ii) corresponding to the lattice period twice the lattice period in the c-axis direction of the unit cell. It has a crystal structure in which a second diffraction spot group appears and appears.
In the following description, the "unit cell of NaFeO type ₂ layered crystal structure" is simply referred to as "unit cell".

Selected area diffraction measurements were performed on the lithium nickel-manganese oxides of Example 1 and Comparative Example 1 described later using a transmission electron microscope to obtain selected area diffraction figures. Selected area diffraction measurements were performed using a transmission electron microscope device (JEOL, ARM-200F) under the condition of an accelerating voltage of 200 kV.
FIG. 2A shows selected area diffraction obtained by injecting an electron beam from the [100] direction of the unit cell with a transmission electron microscope for the sample (lithium nickel manganese oxide) of Comparative Example 1 described later. FIG. 2B is a diagram showing a figure, in which an electron beam is incident on the sample (lithium nickel manganese oxide) of Example 1 described later from the [100] direction of the unit cell by a transmission electron microscope. It is a figure which shows the selected area diffraction figure acquired in.

In the selected area diffraction pattern of the sample of Comparative Example 1 shown in FIG. 2 (a), a group of first diffraction spots having high brightness (hereinafter referred to as) appearing corresponding to the lattice period of the unit cell of the lithium nickel manganese oxide. , Simply referred to as the first diffraction spot group) appears. In FIG. 2A, in the first diffraction spot group, the region represented by reference numeral P corresponds to one unit cell shown in FIG. 1A. The broken line circle in FIG. 2A is drawn for convenience in order to show the unit cell in the first diffraction spot group.

On the other hand, the selected area diffraction pattern of the sample of Example 1 shown in FIG. 2 (b) is also the selected area diffraction pattern of the sample of Comparative Example 1 (see FIG. 2 (a)). A first group of diffraction spots appearing corresponding to the lattice period of the unit cell of.

Further, in the selected area diffraction pattern shown in FIG. 2B, in addition to the above-mentioned first diffraction spot group, a second diffraction spot group having a lower brightness than the first diffraction spot group (hereinafter, simply the first). (Shown as a group of 2 diffraction spots) appears. The arrows in FIG. 2B are drawn for convenience to indicate the second diffraction spot group.
In the second diffraction spot group, each pore group (see FIG. 1B) existing in the basic crystal structure having the lattice shown in FIG. 1A as a unit lattice forms a regular stacking period. As a result, it appears in the selected area diffraction pattern. In the following description, a crystal structure in which each pore group existing in a basic crystal structure having a layered structure forms a regular stacking period is referred to as a superlattice structure. That is, the second diffraction spot group of the selected area diffraction pattern shown in FIG. 2B appears corresponding to the superlattice structure of the lithium nickel manganese oxide.
The second diffraction spot group is a diffraction spot that appears corresponding to a lattice period that is twice the lattice period in the c-axis direction of the unit cell shown in FIG. 2B, and the reason will be described in detail later.

The lamination period of the pore group of the lithium nickel-manganese oxide contained in the positive electrode active material of the present disclosure will be described below.

FIG. 3A is a model diagram showing a unit cell of lithium nickel-manganese oxide contained in the positive electrode active material of the present disclosure. The unit cell shown in FIG. 3A has three transition metal layers, and is laminated in the order of A layer, B layer, and C layer from the lower middle side of FIG. 3A. Therefore, each diffraction spot of the first diffraction spot group appearing in FIG. 2B appears corresponding to three transition metal layers (A layer, B layer, and C layer). The lithium nickel-manganese oxide of the present disclosure having the unit cell shown in FIG. 3 (a) has a basic crystal structure in which transition metal layers are laminated in three layers in the c-axis direction in one lamination period.
The model diagram shown in FIG. 3A is the same as that of FIG. 1A except that the transition metal layers existing in the unit cell are described as A layer, B layer, and C layer. It is a model diagram.

FIG. 3B schematically shows the arrangement state of transition metal elements when the lithium nickel-manganese oxide having a crystal structure having the lattice shown in FIG. 3A as a unit lattice is observed from the direction (001). It is a figure which shows. In FIG. 3B, the transition metal element existing in the A layer, the transition metal element existing in the B layer, and the transition metal element existing in the C layer are shown separately.

FIG. 3C is a schematic diagram for explaining the stacking cycle of the pore group of the lithium nickel-manganese oxide contained in the positive electrode active material of the present disclosure. Note that FIG. 3 (c) shows for convenience one of the pore groups existing in the observation area of the schematic diagram shown in FIG. 3 (b), and the arrow shown in FIG. 3 (c). In a, arrow b, and arrow c, in a crystal structure having the lattice shown in FIG. 3 (a) as a unit lattice, a group of pores having the arrangement shown in FIG. 1 (b) has a regular stacking period. It shows the stacking pattern that the pore group can form when it is formed and exists.
In FIG. 3C, arrow a is an arrow indicating a line connecting in the order of position α1, position α2, position α3, and position α1, and arrow b is connected in the order of position α1, position α2, position β3, and position β4. It is an arrow indicating a line, and the arrow c is an arrow indicating a line connected in the order of position α1, position α2, position α3, position γ4, position γ5, position γ6, and position γ7.

From the selected area diffraction pattern shown in FIG. 2 (b), the lithium nickel manganese oxide contained in the positive electrode active material of the present disclosure has the pores shown in FIG. 1 (b) indicated by arrows in the c-axis direction of the unit cell. It can be determined that the crystal structure (superlattice structure) that forms the laminated pattern shown in c is present. The reason will be explained below.
If it is assumed that the pore group shown in FIG. 1 (b) forms the laminated pattern shown by the middle arrow a in FIG. 3 (c), for example, the pores 10 constituting the pore group may be formed. , The laminated pattern is obtained from the position α1 in FIG. 3C, through the position α2 and the position α3, to the position α1. In this case, the stacking cycle of the pore group in the c-axis direction is one stacking cycle with three layers. In this case, in the selected area diffraction pattern acquired by injecting an electron beam from the [100] direction of the unit cell, the diffraction spot group appearing corresponding to the periodic laminated structure (super lattice structure) of the pore group is It is estimated that the unit lattice (see FIG. 3A) appears with substantially the same brightness as the first diffraction spot group that appears corresponding to the lattice period (one cycle of three transition metal layers in the c-axis direction). Will be done.

Further, if it is assumed that the pore group shown in FIG. 1B forms the laminated pattern shown by the arrow b in FIG. 3C, for example, the pores constituting the pore group Reference numeral 10 denotes a laminated pattern from position α1 in FIG. 3C, through position α2 and position β3, to position β4. In this case, the stacking cycle of the pore group in the c-axis direction is one stacking cycle with three layers. Also in this case, in the selected area diffraction pattern acquired by injecting an electron beam from the [100] direction of the unit cell, the diffraction spot group appearing corresponding to the periodic laminated structure (super lattice structure) of the pore group. Appears with substantially the same brightness as the first diffraction spot group appearing corresponding to the lattice period (one cycle of three transition metal layers in the c-axis direction) of the unit cell (see FIG. 3A). It is estimated to be.

Therefore, in the selected area diffraction pattern, the laminated pattern of the pore group of the lithium nickel-manganese oxide of Example 1 in which the second diffraction spot group having a lower brightness than the first diffraction spot group appears is indicated by arrow a. It can be determined that it does not correspond to the laminated pattern of and does not correspond to the laminated pattern of arrow b.

On the other hand, if it is assumed that the pore groups shown in FIG. 1 (b) are laminated in the stacking pattern indicated by the middle arrow c in FIG. 3 (c), for example, the pores constituting the pore group Reference numeral 10 denotes a laminated pattern from position α1 in FIG. 3C to position γ7 via position α2, position α3, position γ4, position γ5, and position γ6. In this case, the stacking cycle of the pore group in the c-axis direction is 6 layers, which is one stacking cycle. In this case, in the selected area diffraction pattern acquired by injecting an electron beam from the [100] direction of the unit cell, the diffraction spot group appearing corresponding to the periodic laminated structure (super lattice structure) of the pore group is When it appears at a lower brightness than the first diffraction spot group that appears corresponding to the lattice period (one cycle of three transition metal layers in the c-axis direction) of the unit cell (see FIG. 3A). Presumed.

Therefore, in the selected area diffraction pattern, the laminated pattern of the pore group of the lithium nickel-manganese oxide of Example 1 in which the second diffraction spot group having a lower brightness than the first diffraction spot group appears is indicated by the arrow c. It can be judged that it corresponds to the laminated pattern of.
From the above, the periodic stacking structure (superlattice structure) of the pore group corresponding to the second diffraction spot group shown in FIG. 2B has 6 layers in the c-axis direction and a stacking cycle of 1 cycle. It can be determined that the lamination period is twice the lattice period of the unit cell shown in FIG. 3A in the c-axis direction (one cycle of three transition metal layers in the c-axis direction).

The lithium nickel-manganese oxide contained in the positive electrode active material of the present disclosure is the c-axis of the unit cell as described above in the selected area diffraction pattern acquired by injecting an electron beam from the [100] direction of the unit cell. It has a crystal structure in which a second diffraction spot group appears corresponding to a lattice period twice the lattice period in the direction, and the second diffraction spot group has a periodic laminated structure of pore groups (super). It appears corresponding to the lattice structure). As described above, the positive electrode active material of the present disclosure containing lithium nickel-manganese oxide having a periodic laminated structure (super lattice structure) of pores in the basic crystal structure is a positive electrode active material containing the positive electrode active material. When an all-solid-state battery with a layer is charged and discharged and Li is extracted from the positive electrode, it is possible to suppress the occurrence of a phenomenon called cation mixing in which Ni diffuses into the Li site that has become an empty site. The state in which Ni is stably present at the 3b site can be maintained.
Therefore, even when charging / discharging is performed under high rate conditions, a high discharge capacity can be maintained and good rate characteristics can be obtained.

On the other hand, the selected area diffraction pattern of the sample (lithium nickel-manganese oxide) of Comparative Example 1 shown in FIG. 2A corresponds to the lattice period of the unit cell shown in FIG. 3C, as described above. Only the first diffraction spot group appears, and the second diffraction spot group corresponding to the periodic laminated structure (superlattice structure) of the pore group does not appear.
Therefore, in the lithium nickel-manganese oxide of Comparative Example 1, the pore groups do not form a periodic laminated structure (superlattice structure), and the pore groups are irregularly laminated. Presumed.
The positive electrode active material containing the lithium nickel manganese oxide of Comparative Example 1 is obtained when Li is extracted from the positive electrode by charging / discharging an all-solid-state battery provided with the positive electrode active material layer containing the positive electrode active material. In addition, Ni tends to diffuse to the Li site that has become an empty site, and it becomes difficult to maintain a state in which Ni is stably present at the 3b site. Therefore, it is presumed that when charging / discharging is performed under high rate conditions, it becomes difficult to maintain a high discharge capacity and the rate characteristics deteriorate.

As described above, the lithium nickel manganese oxide contained in the positive electrode active material of the present disclosure is represented by the composition formula (1), and a, b, and c represented by the composition formula (1) are respectively. , A is 0.90 ≦ a ≦ 1.15, b is 0.45 ≦ b ≦ 0.71, and c is 0.28 ≦ c ≦ 0.55.
By setting a, b, and c in the above numerical ranges in the composition formula (1), the lithium nickel-manganese oxide represented by the composition formula (1) is selected from the [100] direction of the unit cell. In the selected area diffraction pattern acquired by injecting a line, a crystal structure having the above-mentioned first diffraction spot group and second spot group can be stably obtained.

X-ray diffraction measurement (XRD measurement) was performed on the lithium nickel-manganese oxide prepared in Example 1 and Comparative Example 1. The measurement results of Example 1 are shown in FIGS. 4 (a) and 4 (b), and the measurement results of Comparative Example 1 are shown in FIGS. 5 (a) and 5 (b).
The XRD measurement conditions are as follows, for example.
X-ray diffraction measuring device Ultima IV (manufactured by Rigaku Co., Ltd.)
Characteristic X-ray CuKα ray Measurement range 2θ = 10-120 °
Measurement interval 0.02 °
Scanning speed 5 ° / min
Measurement voltage 50kV
Measurement current 300mA
Number of scans 3 times

As shown in FIG. 5B, the XRD spectrum obtained by the XRD measurement of the lithium nickel-manganese oxide of Comparative Example 1 does not have diffraction peaks at the positions of 2θ = 20.5 ° and 21.5 °. On the other hand, as shown in FIG. 4B, the XRD spectrum obtained by the XRD measurement of the lithium nickel-manganese oxide of Example 1 has diffraction peaks at the positions of 2θ = 20.5 ° and 21.5 °. ..
Therefore, the diffraction peaks at positions θ = 20.5 ° and 2θ = 21.5 ° appearing in the XRD spectrum shown in FIG. 4B appeared in the selected area diffraction pattern shown in FIG. 2B. It is presumed that it belongs to the periodic laminated structure (superlattice structure) of the pore group corresponding to the second spot group.
The position of the peak may be slightly deviated, and the deviation is ± 0. From the value of 2θ.
Allowed within a range of 5 °. “± 0.5 °” for the value of 2θ in the present disclosure is 2θ.
It means the allowable range of deviation of the value of.

From the above, the lithium nickel-manganese oxide contained in the positive electrode active material of the present disclosure has 2θ = 20.5 ° ± 0.5 ° and 21.5 in the XRD spectrum obtained by the XRD measurement performed under the above-mentioned measurement conditions. It is preferable to have a diffraction peak at a position of ° ± 0.5 °.

The shape of the positive electrode active material of the present disclosure is not particularly limited, and examples thereof include a particle-like shape and a film-like shape.

When the positive electrode active material of the present disclosure has a particulate shape, the surface of the lithium nickel manganese oxide particles contained in the positive electrode active material has a coating layer coated with a solid electrolyte having Li ion conductivity. You may. As the solid electrolyte having Li ion conductivity, for example, LiNbO ₃ can be used.

When the positive electrode active material is in the shape of particles, the average particle size of the particles is preferably, for example, 1 to 50 μm, particularly preferably 1 to 20 μm, particularly preferably 3 to 10 μm. If the average particle size of the positive electrode active material is too small, the handleability may deteriorate, and if the average particle size of the positive electrode active material is too large, it may be difficult to obtain a flat positive electrode active material layer. Is.
In the present disclosure, the average particle size of the particles is a value measured by laser diffraction / scattering type particle size distribution measurement. Further, in the present disclosure, the median diameter (D50) is a diameter at which the cumulative volume of the particles is half (50%) of the total volume when the particles are arranged in order from the particles having the smallest particle size.

Next, a method for producing the positive electrode active material of the present disclosure will be described.
The production method described below includes (1) a raw material preparation step and (2) a firing step. In addition, you may prepare the raw material prepared in advance. In that case, (1) the raw material preparation step may be omitted.

(1) Raw Material Preparation Step In the raw material preparation step, first, a precursor containing a transition metal is prepared by a coprecipitation method, and then the precursor and a lithium compound are mixed to prepare a raw material for a positive electrode active material. be able to.

The coprecipitation method is a powder synthesis method that utilizes the coprecipitation phenomenon. In the synthesis of the precursor by the coprecipitation method, the raw material aqueous solution and the alkaline aqueous solution are mixed to react the components contained in both aqueous solutions to produce a precursor which is a coprecipitate ((Ni, Mn) OH ₂ ). It can be done by letting it do. By synthesizing the precursor by the coprecipitation method, the metal elements can be uniformly mixed at the atomic level, so that more suitable performance can be obtained.

As the raw material aqueous solution, an aqueous solution containing Ni ions and an aqueous solution containing Mn ions can be used. Specifically, as the raw material aqueous solution, for example, an aqueous solution in which nickel nitrate, nickel sulfate or the like as a Ni source is dissolved in water, or an aqueous solution in which manganese nitrate, manganese sulfate or the like as a Mn source is dissolved in water can be used. ..
The raw material aqueous solution may be prepared by separately preparing an aqueous solution containing a Ni source and an aqueous solution containing an Mn source and then mixing these aqueous solutions, or the above-mentioned Ni source and Mn source are dissolved in water. It may be prepared as an aqueous solution. The ratio of the Ni source and the Mn source to be blended in the raw material aqueous solution may be appropriately adjusted so that the molar ratio of Ni and Mn contained in the raw material aqueous solution satisfies the ratio of the composition formula (1) described above. ..

As the alkaline aqueous solution, for example, a sodium hydroxide aqueous solution or the like can be used. Ammonia may be appropriately added to the alkaline aqueous solution as a chelating agent.

The precursor ((Ni, Mn) OH ₂ ) synthesized by the coprecipitation method may be calcined before being mixed with the lithium compound. The calcination of the precursor oxide precursor _{((Ni, Mn) O x} ) are obtained.
The precursor is preferably fired in a temperature range of, for example, 300 to 650 ° C. The firing time of the precursor is not particularly limited, but may be, for example, 10 to 15 hours.

As the lithium compound, for example, lithium carbonate, lithium hydroxide, lithium nitrate and the like can be used.

The precursor or the oxide of the precursor and the lithium compound can be mixed, for example, by a ball mill or the like.
The mixing ratio of the precursor or the oxide of the precursor and the lithium compound may be appropriately adjusted so that the molar ratio of Li, Ni and Mn contained in the mixture satisfies the ratio of the composition formula (1). .. However, in consideration of the fact that Li easily volatilizes when it is held at a high temperature in the firing step described later, the lithium compound is added so that the amount of Li is slightly larger than the ratio of Li contained in the final product. It may be mixed.

(2) Firing step The firing step can be performed by calcining the raw material of the positive electrode active material obtained in the (1) raw material preparation step and then annealing.
The firing treatment can be performed by firing the raw material of the positive electrode active material in an air atmosphere or an oxygen atmosphere in a first temperature range of 850 ° C. or higher and 1050 ° C. or lower. By firing in the above temperature range, the lithium nickel-manganese oxide represented by the composition formula (1) can be stably obtained.
The firing time may be, for example, in the range of 5 hours or more and 48 hours or less.

Further, the annealing treatment can be performed by lowering the temperature to a second temperature range lower than the first temperature range after the firing treatment and holding the temperature in this temperature range.
The second temperature range can be, for example, 500 ° C. or higher and 900 ° C. or lower. The annealing treatment time may be 10 hours or more and 50 hours or less.
The annealing treatment may be carried out by keeping the temperature in the above-mentioned temperature range and lower than the first temperature range constant, or by holding the temperature in the above-mentioned temperature range and lower than the first temperature range for a predetermined time. After that, it may be carried out by gradually lowering the holding temperature. By performing the annealing treatment in the temperature range of the second temperature described above and in the processing time described above, for example, each pore group existing in the basic crystal structure having the lattice shown in FIG. 1A as a unit lattice ( FIG. 1 (b)) shows that a lithium nickel-manganese oxide having a crystal structure (superlattice structure) forming a periodic laminated structure can be stably obtained.

In particular, the second treatment temperature is a temperature equal to or higher than the glass transition point in the c-axis direction of the unit cell of the lithium nickel-manganese oxide obtained by the firing treatment in the first temperature range and near the glass transition point. It is considered that the periodic laminated structure (super lattice structure) in which the pores are periodically laminated in the c-axis direction can be stably formed by the annealing treatment by setting the temperature range.

Since the diffusion coefficient in each transition metal layer constituting the NaFeO type ₂ layered crystal structure is extremely small and the distance between the layers of each transition metal layer is relatively large, a periodic laminated structure is formed in the c-axis direction. Considering that the energy gain due to the formation is small and the driving force for forming the periodic laminated structure is small, in order to stably obtain a crystal structure having a periodic laminated structure of pores, lithium is used. It is desirable to perform the annealing treatment by holding the nickel-manganese oxide at a temperature near the glass transition point for a certain period of time.

2. All-solid-state battery The all-solid-state battery of the present disclosure includes a positive electrode, a negative electrode, and a solid electrolyte layer arranged between the positive electrode and the negative electrode.

FIG. 6 is a diagram showing an example of the layer structure of the all-solid-state battery provided with the positive electrode active material layer of the present disclosure, and is a diagram schematically showing a cross section cut in the stacking direction. The all-solid-state battery of the present disclosure is not necessarily limited to this example.
The all-solid-state battery 100 is a solid sandwiched between a positive electrode 6 having a positive electrode active material layer 4 and a positive electrode current collector 2, a negative electrode 7 having a negative electrode active material layer 3 and a negative electrode current collector 5, and a positive electrode 6 and a negative electrode 7. It includes an electrolyte layer 1.

(Positive electrode)
The positive electrode used in the all-solid-state battery of the present disclosure includes a positive electrode active material layer, and if necessary, a positive electrode current collector and a positive electrode lead connected to the positive electrode current collector.

(Positive electrode active material layer)
The positive electrode active material layer used in the all-solid-state battery of the present disclosure contains the above-mentioned positive electrode active material for the all-solid-state battery of the present disclosure.
In the electron beam diffraction image obtained by injecting an electron beam from the [100] direction of the unit cell into the positive electrode active material layer, a crystal in which the above-mentioned first diffraction spot group and second diffraction spot group appear. By containing a positive electrode active material containing a lithium nickel-manganese oxide having a structure, an all-solid-state battery having a positive electrode having the positive electrode active material layer is charged and discharged at a higher rate than a conventional all-solid-state battery. The decrease in discharge capacity can be suppressed, and excellent rate characteristics can be obtained.

The proportion of the positive electrode active material of the present disclosure contained in the positive electrode active material layer is not particularly limited, but for example, the positive electrode when the total volume of the positive electrode active material and the solid electrolyte is 100% by volume. The proportion of the active material may be in the range of 50% by volume to 99% by volume.

The positive electrode active material layer may contain another positive electrode active material in addition to the positive electrode active material for the all-solid-state battery of the present disclosure described above.
Other positive electrode active materials include, for example, LiCoO ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNiPO ₄ , LiMnPO ₄ , LiNiO ₂ , LiMn ₂ O ₄ , LiComnO ₄ , Li ₂ Nimn ₃ O. ₈ , Li3Fe ₂ (PO ₄ ) ₃ and Li ₃ V ₂ (PO ₄ ) _{3 and the} like can be mentioned.
When the positive electrode active material layer contains the other positive electrode active material described above in the form of particles, the preferable range of the average particle size of the particles is the average particle size of the positive electrode active material for the all-solid battery of the present disclosure. It can be the same range as the preferable range of.

The positive electrode active material layer may contain only the positive electrode active material, or may contain at least one of a solid electrolyte, a conductive material, and a binder in addition to the positive electrode active material.

Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, halides and the like.
The sulfide solid electrolyte, for _{example, Li 2 S-P 2 S} 5, Li 2 S-P 2 S 5 -LiI, Li 2 S-P 2 S 5 -Li 2 O, Li 2 S-P 2 S 5 -Li ₂ O-LiI, Li ₂ S-SiS ₂ , Li ₂ S-SiS _2- LiI, Li ₂ S-SiS _2- LiBr, Li ₂ S-SiS _2- LiCl, Li ₂ S-SiS _2- B ₂ S _3- LiI, Li ₂ S-SiS _2- P ₂ S _5- LiI, Li ₂ SB ₂ S ₃ , Li ₂ SP ₂ S _5- Z _m S _n (where m and n are positive Number .Z is any of Ge, Zn, and Ga.), Li ₂ S-GeS ₂ , Li ₂ S-SiS ₂ -Li ₃ PO ₄ , Li ₂ S-SiS ₂ -Li _x MO _y (where x) , Y is a positive number. M is any of P, Si, Ge, B, Al, Ga, In.), 10LiI-15LiBr-75 (0.75Li ₂ S-0.25P ₂ S ₅ ), ( 75 [(0.75-x) Li ₂ S · 2/3 x Li ₃ N · 0.25P ₂ S ₅ )] · 10LiI · 15LiBr) and the like can be mentioned. The above description of "Li ₂ S-P ₂ S ₅ " means a sulfide solid electrolyte made by using a raw material composition containing Li ₂ S and P ₂ S _5, and the same applies to other descriptions. .. The sulfide solid electrolyte may further contain LiX (X is F, Cl, Br or I). Further, the solid electrolyte may be amorphous, crystalline, or glass ceramics.

The ratio of the solid electrolyte in the positive electrode active material layer is not particularly limited, but for example, the ratio of the solid electrolyte when the total volume of the positive electrode active material and the solid electrolyte is 100% by volume is one volume. It may be in the range of% to 50% by volume.
The solid electrolyte is not particularly limited, but may have a density of 1.9 to 2.5 g / cm ³ .

Examples of the binder used for the positive electrode active material layer include polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). The content of the binder in the positive electrode active material layer is not particularly limited as long as it can immobilize the positive electrode active material or the like.

The conductive material is not particularly limited as long as it can be used for the positive electrode of an all-solid-state battery.
The raw material of the conductive material may be, for example, at least one carbon-based material selected from the group consisting of carbon black such as acetylene black, ketjen black, furnace black, carbon nanotubes, and carbon nanofibers.
From the viewpoint of electron conductivity, it may be at least one carbon-based material selected from the group consisting of carbon nanotubes and carbon nanofibers, and the carbon nanotubes and carbon nanofibers are VGCF (gas phase carbon fibers). ) May be.
The content ratio of the conductive material in the positive electrode active material layer varies depending on the type of the conductive material, and is not particularly limited.

The method for producing the positive electrode active material layer for the all-solid-state battery according to the present disclosure is not particularly limited.

As a method for forming the positive electrode active material layer, preferably, the positive electrode active material, the solid electrolyte, the binder, the conductive material and the like are dispersed with a dispersion medium to prepare a paste for the positive electrode active material layer, and the positive electrode active material layer is formed on the positive electrode current collector. Examples include a method of applying and drying.
The dispersion medium is not particularly limited, and examples thereof include heptane, butyl butyrate, and the like. The dispersion method is not particularly limited, and examples thereof include a homogenizer, a bead mill, a share mixer, and a roll mill.
The method of applying the paste for the positive electrode active material layer, the method of drying, and the like can be appropriately selected. For example, examples of the coating method include a spray method, a screen printing method, a doctor blade method, a gravure printing method, and a die coating method. In addition, examples of the drying method include vacuum drying, heat drying, vacuum heating drying and the like. There are no restrictions on the specific conditions for vacuum drying and heat drying, which may be set as appropriate.
After forming the positive electrode active material layer, the positive electrode active material layer may be pressed by a roll press treatment or the like in order to improve the electrode density.

The thickness of the positive electrode active material layer of the present disclosure is not particularly limited, and may be appropriately determined according to the desired performance.

The positive electrode current collector has a function of collecting current from the positive electrode active material layer. Examples of the material of the positive electrode current collector include aluminum, SUS, nickel, iron and titanium, and among them, aluminum and SUS are preferable. Further, as the shape of the positive electrode current collector, for example, a foil shape, a plate shape, a mesh shape and the like can be mentioned, and the foil shape is particularly preferable.

(Negative electrode)
The negative electrode used in the all-solid-state battery of the present disclosure includes a negative electrode active material layer, and if necessary, a negative electrode current collector and a negative electrode lead connected to the negative electrode current collector.

(Negative electrode active material layer)
The negative electrode active material layer used in the present disclosure contains a negative electrode active material.
As the negative electrode active material, conventionally known materials can be used, and examples thereof include metallic lithium (Li), lithium alloys, carbon, Si, Si alloys, and Li ₄ Ti ₅ O ₁₂ (LTO).
Examples of the lithium alloy include LiSn, LiSi, LiAl, LiGe, LiSb, LiP, LiIn and the like.
Examples of the Si alloy include alloys with metals such as Li, and other alloys may be alloys with at least one metal selected from the group consisting of Sn, Ge, and Al.
The shape of the negative electrode active material is not particularly limited, but may be, for example, a particulate or a thin film.
When the negative electrode active material is in the shape of particles, the average particle size (D50) of the particles is preferably 1 nm or more and 100 μm or less, for example.
The content of the negative electrode active material in the negative electrode layer is not particularly limited, but is preferably 40% by mass or more and 100% by mass or less, for example.

The negative electrode active material layer may contain only the negative electrode active material, and may contain at least one of a solid electrolyte, a conductive material, and a binder in addition to the negative electrode active material. For example, when the negative electrode active material is in the form of a foil, it can be a negative electrode active material layer containing only the negative electrode active material. On the other hand, when the negative electrode active material is in the form of powder, it can be a negative electrode active material layer having a negative electrode active material and a binder.

As the conductive material used for the negative electrode active material layer, the same conductive material as the conductive material used for the positive electrode active material layer described above can be used. The content ratio of the conductive material in the negative electrode active material layer is not particularly limited.

As the binder used for the negative electrode active material layer, the same binder as that used for the positive electrode active material layer described above can be used. The content ratio of the binder in the negative electrode active material layer is not particularly limited.

The negative electrode active material layer may contain a solid electrolyte. As the solid electrolyte, the above-mentioned sulfide-based solid electrolyte, oxide-based solid electrolyte, and the like can be used. The content ratio of the solid electrolyte in the negative electrode active material layer is not particularly limited.

The thickness of the negative electrode active material layer is not particularly limited, and may be appropriately determined according to the desired performance.

(Negative electrode current collector)
As the material of the negative electrode current collector, the same material as the above-mentioned positive electrode current collector can be used. Further, as the shape of the negative electrode current collector, the same shape as that of the positive electrode current collector described above can be adopted.

The method for producing the negative electrode used in the present disclosure is not particularly limited as long as it is a method capable of obtaining the negative electrode. After forming the negative electrode active material layer, the negative electrode active material layer may be pressed in order to improve the electrode density.

(Solid electrolyte layer)
The solid electrolyte layer used in the present disclosure is held between the positive electrode and the negative electrode, and has a function of exchanging metal ions between the positive electrode and the negative electrode.
As the solid electrolyte contained in the solid electrolyte layer, a sulfide-based solid electrolyte that can be used in the positive electrode active material layer described above, an oxide-based solid electrolyte, or the like can be used.
Only one type of solid electrolyte may be used alone, or two or more types may be used in combination.
The content ratio of the solid electrolyte in the solid electrolyte layer is not particularly limited.
The solid electrolyte layer may contain a binder that binds the solid electrolytes to each other. As the binder contained in the solid electrolyte layer, a binder that can be used in the positive electrode active material layer described above can be used.

(Battery case)
The all-solid-state battery according to the present disclosure usually includes a battery case for accommodating the positive electrode, the negative electrode, the solid electrolyte layer, and the like. Specific examples of the shape of the battery case include a coin type, a flat plate type, a cylindrical type, and a laminated type.

1. 1. Production of positive electrode active material (Example 1)
(1) Production of Positive Electrode Active Material First, nickel nitrate and manganese nitrate were dissolved in pure water to obtain a raw material aqueous solution. Nickel nitrate and manganese nitrate were dissolved in pure water so that the ratio of nickel (Ni) and manganese (Mn) contained in the raw material aqueous solution was Ni: Mn = 1: 1 in terms of molar ratio. A precursor (coprecipitate) was obtained by mixing this raw material aqueous solution with a sodium hydroxide aqueous solution (1 mol / l, pH 13) as an alkaline aqueous solution. The ratio of nickel (Ni) and manganese (Mn) contained in the precursor (coprecipitate) was Ni: Mn = 1: 1 in terms of molar ratio.
The obtained precursor (coprecipitate) was calcined in the air at 600 ° C. for 12 hours to obtain an oxide of the precursor (coprecipitate). A raw material for the positive electrode active material was prepared by mixing the obtained precursor (coprecipitate) oxide and lithium carbonate using a ball mill. Lithium carbonate was mixed so as to be equivalent to 1.1 mol with respect to the total molar amount of nickel (Ni) and manganese (Mn) contained in the oxide of the precursor (coprecipitate).

Next, the obtained raw material of the positive electrode active material was calcined in the air at 1000 ° C. for 12 hours. Next, the obtained fired product was held at 850 ° C. for 10 hours, then at 700 ° C. for 10 hours, then at 550 ° C. for 10 hours, and then slowly cooled to room temperature to cool the positive electrode of Example 1. An active material (lithium nickel-manganese oxide) was obtained.

(Example 2)
An oxide of a precursor (coprecipitate) was prepared in the same manner as in Example 1. With respect to the oxide of the obtained precursor (coprecipitate), lithium carbonate was added to the total molar amount of nickel (Ni) and manganese (Mn) contained in the oxide of the precursor (coprecipitate). The raw materials for the positive electrode active material were prepared by mixing them so as to have an amount equivalent to 1.05 mol. The step after the preparation of the raw material of the positive electrode active material was carried out in the same manner as in Example 1 to obtain the positive electrode active material (lithium nickel manganese oxide) of Example 2.

(Example 3)
Examples except that the ratio of nickel (Ni) and manganese (Mn) contained in the raw material aqueous solution was changed from Ni: Mn = 1: 1 to Ni: Mn = 2: 1 in terms of molar ratio. A raw material aqueous solution was prepared in the same manner as in 1. Using this aqueous raw material solution, a precursor (coprecipitate) was obtained in the same manner as in Example 1. The ratio of nickel (Ni) and manganese (Mn) contained in the precursor (coprecipitate) was Ni: Mn = 2: 1 in terms of molar ratio. The obtained precursor (coprecipitate) and lithium carbonate were mixed using a ball mill to prepare a raw material for the positive electrode active material. Lithium carbonate was mixed so as to be equivalent to 1.05 mol with respect to the total molar amount of nickel (Ni) and manganese (Mn) contained in the precursor (coprecipitate).

Next, the obtained raw material of the positive electrode active material was calcined in the air at 900 ° C. for 12 hours. Next, the obtained fired product was held at 850 ° C. for 10 hours, then at 700 ° C. for 10 hours, then at 550 ° C. for 10 hours, and then slowly cooled to room temperature to cool the positive electrode of Example 3. An active material (lithium nickel-manganese oxide) was obtained.

(Example 4)
The positive electrode active material (lithium nickel manganese) of Example 4 is the same as in Example 3 except that the atmosphere when the raw material of the positive electrode active material is fired at 900 ° C. for 12 hours is changed from the atmospheric atmosphere to the oxygen atmosphere. Oxide) was obtained.

(Comparative Example 1)
A raw material for the positive electrode active material was prepared in the same manner as in Example 2.
Next, the obtained raw material of the positive electrode active material was calcined in the air at 1000 ° C. for 12 hours to obtain the positive electrode active material (lithium nickel manganese oxide) of Comparative Example 1.

(Example 5)
An oxide of a precursor (coprecipitate) was prepared in the same manner as in Example 1. With respect to the oxide of the obtained precursor (coprecipitate), lithium carbonate was added to the total molar amount of nickel (Ni) and manganese (Mn) contained in the oxide of the precursor (coprecipitate). The raw materials for the positive electrode active material were prepared by mixing them so as to have an amount equivalent to 1.05 mol. Next, the step after preparing the raw material of the positive electrode active material was carried out in the same manner as in Example 1 to obtain a lithium nickel manganese oxide.
Next, the surface of the obtained lithium nickel-manganese oxide was coated with LiNbO _{3 so as} to have a thickness of 10 nm using a rolling fluidizer. As a result, the positive electrode active material of Example 5 was obtained.

(Comparative Example 2)
A raw material for the positive electrode active material was prepared in the same manner as in Example 5. Next, the obtained raw material of the positive electrode active material was calcined in the air at 1000 ° C. for 12 hours and then cooled to obtain a lithium nickel manganese oxide. Next, the surface of the obtained lithium nickel-manganese oxide was coated with LiNbO _{3 so as} to have a thickness of 10 nm in the same manner as in Example 5. As a result, the positive electrode active material of Comparative Example 2 was obtained.

2. Manufacture of evaluation cell [Preparation of positive electrode]
Each positive electrode active material and sulfide-based solid electrolyte (75 [(0.75-x) Li ₂ S ・ 2/3 x Li ₃ N ・ 0.25P ₂ S) obtained in Examples 1 to 5 and Comparative Examples 1 and _{2 5} )], 10LiI, and 15LiBr) were weighed so that the positive electrode active material: sulfide-based solid electrolyte = 75:25, respectively, in terms of volume ratio, and this was put into a container for producing a positive electrode slurry.
Further, PVDF (manufactured by Kureha), which is a binder component, and an amount of 1.5 parts by mass with respect to 100 parts by mass of the positive electrode active material, which is 0.75 parts by mass with respect to 100 parts by mass of the positive electrode active material. VGCF (manufactured by Showa Denko Co., Ltd.), which is a conductive agent of the above, was weighed and put into a container for producing a slurry for a positive electrode.
Further, a mixture for a positive electrode was prepared by putting butyl butyrate (manufactured by Kishida Chemical Co., Ltd.) as a solvent into a container for producing a slurry for a positive electrode.
Next, the prepared positive electrode mixture was dispersed with an ultrasonic homogenizer (UH-50, manufactured by SMT Co., Ltd., the same applies hereinafter) for 1 minute to prepare a positive electrode slurry. The obtained positive electrode slurry is applied to the surface of an aluminum foil (manufactured by Showa Denko KK) as a positive electrode current collector using a doctor blade, air-dried at room temperature for 2 hours, and then at 110 ° C. for 30. After drying for a minute and further hot-roll pressing, a positive electrode having a positive electrode active material layer on an aluminum foil was prepared.

Next, a sulfide-based solid electrolyte powder (75 [(0.75-x) Li ₂ S ・ 2/3 x Li ₃ N ・ 0.25P ₂ S ₅ )] ・ 10LiI ・ 15LiBr) was applied at a load of 1 ton / cm ² . A solid electrolyte layer was prepared by uniaxial pressing.
Next, the obtained solid electrolyte layer and the positive electrode active material layer of the positive electrode obtained in [Preparation of positive electrode] are opposed to each other, and the solid electrolyte layer and the positive electrode are overlapped with each other, and a load is applied under room temperature conditions by a roll press method. Cold pressing was performed at 6 ton / cm ² to obtain a laminate of a positive electrode-solid electrolyte layer.
Next, the solid electrolyte layer laminated on the positive electrode active material layer and the Li metal foil are superposed, and cold-pressed by a roll press method under room temperature conditions at a load of 1 ton / cm ² to obtain an evaluation cell. It was.
In the following description, the evaluation cells prepared by using the positive electrode active materials obtained in Examples 1 to 5 are referred to as evaluation cells 1 to 5, respectively, and obtained in Comparative Examples 1 and 2. The evaluation cells prepared by using the positive electrode active material are shown as evaluation cells 6 to 7, respectively.

3. 3. Evaluation <Average composition of the entire positive electrode active material>
The Li / Ni / Mn molar ratio of the entire positive electrode active material was calculated by performing elemental analysis on each of the positive electrode active materials obtained in Examples 1 to 5 and Comparative Examples 1 and 2 by ICP emission spectroscopic analysis. The evaluation results are shown in Table 1.

<Selected area diffraction pattern>
Selected area diffraction measurements were performed on the positive electrode active materials obtained in Examples 1 to 5 and Comparative Examples 1 and 2 using a transmission electron microscope to obtain selected area diffraction figures. Selected area diffraction measurements were performed using a transmission electron microscope device (JEOL, ARM-200F) under the condition of an accelerating voltage of 200 kV.
Table 1 shows the presence or absence of the second diffraction spot in the obtained selected area diffraction pattern. Further, the selected area diffraction pattern for the positive electrode active material obtained in Comparative Example 1 is shown in FIG. 2 (a), and the selected area diffraction figure for the positive electrode active material obtained in Example 1 is shown in FIG. 2 (b). ).

<3.0C charge / discharge capacity and 0.1C charge / discharge capacity>
After the prepared evaluation cells 1 to 4 of Examples 1 to 4 and the evaluation cells 6 of Comparative Example 1 are constantly charged with a current equivalent to 0.1 C in a voltage range of 2.5V to 4.5V. , A constant current discharge was performed with a current equivalent to 0.1 C. Then, in the voltage range of 2.5V-4.5V, a constant current was charged with a current equivalent to 0.1C, and then a constant current was discharged with a current equivalent to 3.0C.
Table 1 shows the discharge capacity (mAh) at a current equivalent to 0.1 C and the discharge capacity (mAh) at a current equivalent to 3.0 C obtained for Examples 1 to 4 and Comparative Example 1, respectively.
Of these, FIG. 7 shows a charge / discharge curve for constant current charging and constant current discharging performed using the evaluation cell 1 of Example 1 and the evaluation cell 6 of Comparative Example 1.

<3.0C charge / discharge capacity and 0.1C charge / discharge capacity>
The prepared evaluation cell 5 of Example 5 and the evaluation cell 7 of Comparative Example 2 are constantly charged with a current equivalent to 0.1C in a voltage range of 2.5V-4.9V, and then 0.1C. A constant current was discharged with a considerable current. Then, in the voltage range of 2.5V-4.9V, a constant current was charged with a current equivalent to 0.1C, and then a constant current was discharged with a current equivalent to 3.0C.
Table 1 shows the discharge capacity (mAh) at a current equivalent to 0.1 C and the discharge capacity (mAh) at a current equivalent to 3.0 C obtained for Example 5 and Comparative Example 2, respectively.
Of these, FIG. 8 shows a charge / discharge curve for constant current charging and constant current discharge at a current equivalent to 0.1 C, which was performed using the evaluation cell 5 of Example 5 and the evaluation cell 7 of Comparative Example 2. ..

<SEM image>
The positive electrode active materials obtained in Example 1 and Comparative Example 1 were observed using an SEM (scanning electron microscope). The observation image of Comparative Example 1 is shown in FIG. 9A, and the observation image of Example 1 is shown in FIG. 9B.

3. 3. Discussion As shown in FIG. 7 and Table 1, the positive electrode active material (lithium nickel manganese oxide; Example 2 of Patent Document 1) of Comparative Example 1 in which the second diffraction spot group does not appear in the selected area diffraction pattern. In the all-solid-state battery using substantially the same composition), the discharge capacity at 0.1 C rate was 152 mAh / g, whereas the second diffraction spot group appeared in the selected area diffraction pattern. The all-solid-state battery using the positive electrode active material (lithium nickel-manganese oxide) of Example 1 had a discharge capacity of 176 mAh / g at a 0.1 C rate, which was higher than that of Comparative Example 1. Therefore, the all-solid-state battery using the positive electrode active material (lithium nickel-manganese oxide) of Example 1 suppresses a decrease in discharge capacity even when charged and discharged under a high voltage of 2.5 to 4.5 V. It was possible to achieve a high energy density.
This is because the positive electrode active material (lithium nickel-manganese oxide) of Comparative Example 1 does not have a crystal structure (superlattice structure) having a periodic laminated structure of pore groups, so Li is extracted from the positive electrode during charging. It is presumed that the discharge capacity was reduced due to the occurrence of so-called cation mixing in which Ni diffused into the vacant Li site.
On the other hand, since the positive electrode active material (lithium nickel-manganese oxide) of Example 1 has a crystal structure (super lattice structure) having a periodic laminated structure of pore groups, Li is pulled out from the positive electrode during charging and becomes empty. Since the diffusion of Ni to the Li site that became the site was suppressed, the state in which Ni was stably present at the 3b site was maintained, and even if charging and discharging were performed under a high voltage of 2.5 to 4.5 V. It is estimated that a high discharge capacity was obtained.
Comparing the SEM image of FIG. 9A (Comparative Example 1) with the SEM image of FIG. 9B (Example 1), the size of the primary particles of the positive electrode active material of Example 1 is No significant difference was observed as compared with the size of the primary particles of the positive electrode active material of Comparative Example 1. Therefore, it is presumed that the difference in effect between the positive electrode active material of Comparative Example 1 and the positive electrode active material of Example 1 as described above has a low correlation with the size of the positive electrode active material particles.
Further, the lithium nickel manganese oxide of Comparative Example 1 had a discharge capacity of 91 mAh / g at the 3C rate, whereas the lithium nickel manganese oxide of Example 1 had a discharge capacity of 129 mAh / g at the 3C rate. A higher discharge capacity than that of Comparative Example 1 was obtained, and even when charging and discharging were performed under high rate conditions of 3C rate, the decrease in discharge capacity was suppressed and good rate characteristics were obtained. The reason is presumed to be based on the same reason as described above.
Further, as shown in Table 1, in Comparative Example 1, the discharge capacity at the 0.1 C rate was 152 mAh / g, whereas in Examples 2 to 4, the discharge capacity at the 0.1 C rate was 170 to 170. A value of 185 mAh / g, which is higher than that of Comparative Example 1, was obtained, and in Examples 2 to 4, the discharge capacity decreased when charging and discharging were performed under a high voltage of 2.5 to 4.5 V. Was suppressed.
Further, as shown in Table 1, in Comparative Example 1, the discharge capacity of the 3C rate was 91 mAh / g, whereas in Examples 2 to 4, the discharge capacity of the 3C rate was 118 to 141 mAh / g. , A value higher than that of Comparative Example 1 was obtained, and in Examples 2 to 4, a decrease in discharge capacity was suppressed when charging / discharging was performed under a high rate condition of 3C rate, which is good. The rate characteristics were obtained.

Further, as shown in FIGS. 8 and 1, in the selected area diffraction pattern, the all-solid-state battery using the positive electrode active material of Comparative Example 2 in which the second diffraction spot group does not appear is discharged at a 0.1 C rate. The all-solid-state battery using the positive electrode active material of Example 5, in which the second diffraction spot group appears in the selected area diffraction pattern while the capacity was 121 mAh / g, was discharged at a 0.1 C rate. The capacity was 186 mAh / g, which was higher than that of Comparative Example 2. Therefore, the all-solid-state battery using the positive electrode active material of Example 5 has a high energy density because the decrease in discharge capacity is suppressed even when charging / discharging is performed under a high voltage of 2.5 to 4.5 V. I was able to realize it. The reason is presumed to be based on the same reason as described above.
Further, as shown in Table 1, the positive electrode active material of Comparative Example 2 had a discharge capacity of 3C rate of 85 mAh / g, whereas the positive electrode active material of Example 5 had a discharge capacity of 3C rate. A discharge capacity of 148 mAh / g, which is higher than that of Comparative Example 2, was obtained, and even when charging and discharging were performed under a high rate condition of 3C rate, a decrease in the discharge capacity was suppressed and good rate characteristics were obtained. .. The reason is presumed to be based on the same reason as described above.

1 Solid electrolyte layer 2 Positive electrode current collector 3 Negative electrode active material layer 4 Positive electrode active material layer 5 Negative electrode current collector 6 Positive electrode 7 Negative electrode 100 All-solid-state battery P unit lattice

Claims (1)

It is represented by the composition formula Li _a Ni _b Mn _c O ₂ (0.90 ≦ a ≦ 1.15, 0.45 ≦ b ≦ 0.71, 0.28 ≦ c ≦ 0.55), and is a layered NaFeO type _2. Contains lithium nickel-manganese oxide with a crystal structure,
The lithium nickel manganese oxide is obtained in an electron diffraction image obtained by injecting an electron beam from the [100] direction of the unit cell of the NaFeO type ₂ layered crystal structure.
(I) The first diffraction spot group appearing corresponding to the lattice period of the unit lattice of the NaFeO type ₂ layered crystal structure, and
(Ii) A positive electrode for an all-solid-state battery having a crystal structure in which a second diffraction spot group appearing corresponding to a lattice period twice the lattice period in the c-axis direction of the unit cell appears. Active material.