Electrode active material, battery, and method for manufacturing electrode active material

Abstract

The invention relates to an electrode active material, a battery, and a method for manufacturing the electrode active material. The electrode active material according to the present disclosure has a characteristic in which, in an X-ray diffraction pattern thereof, the half-value width of a diffraction peak having a peak top at 2 [theta] = 64.8-65.4 degrees among diffraction peaks derived from an O2-type structure is less than 0.79 degrees.

Description

TECHNICAL FIELD

[0001] The present application discloses an electrode active material, a battery, and a method for manufacturing an electrode active material. BACKGROUND

[0002] As an electrode active material, an electrode active material having an O2-type structure (O: Octahedral) is known. As disclosed in Japanese Patent Application Publication No. 2010-092824, an electrode active material having an O2-type structure can be obtained by ion-exchanging at least a part of Na of a Na-containing transition metal oxide having a P2-type structure with Li. SUMMARY

[0003] The conventional electrode active material having an O2-type structure has room for improvement in terms of simultaneously achieving high capacity and low resistance.

[0004] The present application discloses the following multiple modes as a means for solving the above-described problems.

[0005] <Mode 1>

[0006] An electrode active material is an electrode active material having an O2-type structure,

[0007] In the X-ray diffraction pattern of the above-described electrode active material, the half-value width of a diffraction peak having a peak top at 2θ = 64.8° to 65.4° among the diffraction peaks derived from the above-described O2-type structure is less than 0.79°.

[0008] <Mode 2>

[0009] The electrode active material according to Mode 1 has a half-value width of 0.66° or less.

[0010] <Mode 3>

[0011] The electrode active material according to Mode 1 or 2 has a chemical composition represented by Li a Na b Mn x-p Ni y-q Co z-r M p+q+r O2 (here, 0.70 < a ≤ 1.40, 0 ≤ b ≤ 0.20, x + y + z = 1, 0 ≤ p + q + r < 0.17, M is at least one element selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W).

[0012] <Mode 4>

[0013] A battery having the electrode active material described in any one of Modes 1 to 3.

[0014] <Mode 5>

[0015] A method for producing an electrode active material, including the following steps:

[0016] obtaining a Na-containing transition metal oxide having a P2-type structure;

[0017] obtaining a Li-containing transition metal oxide having an O2-type structure by ion exchange of at least a part of Na of the Na-containing transition metal oxide to Li; and

[0018] doping Li to the Li-containing transition metal oxide by contacting a reducing solution containing Li ions with the Li-containing transition metal oxide,

[0019] the time for contacting the reducing solution with the Li-containing transition metal oxide is 10 minutes or more and 120 minutes or less,

[0020] the temperature for contacting the reducing solution with the Li-containing transition metal oxide is 10°C or more and 50°C or less.

[0021] The electrode active material of the present disclosure has an O2-type structure and easily realizes both high capacity and low resistance. BRIEF DESCRIPTION OF DRAWINGS

[0022] Features, advantages, and technical and industrial significance of exemplary embodiments of the present application will be described below with reference to the accompanying drawings, wherein the same reference numerals denote the same elements throughout the specification.

[0023] Figure 1 An example of a flow of a method for producing an electrode active material is shown.

[0024] Figure 2 An example of a configuration of a battery is schematically shown.

[0025] Figure 3 X-ray diffraction patterns of the respective electrode active materials of Example 1, Comparative Example 1, and Comparative Example 3 are shown.

[0026] Figure 4 A relationship between a half-value width of an X-ray diffraction peak and a normalized resistance value is shown. DETAILED DESCRIPTION

[0027] 1. Electrode active material

[0028] The electrode active material of one embodiment has an O2-type structure. In the X-ray diffraction chart of the electrode active material, the half-value width of the diffraction peak having a peak top at 2Θ = 64.8° to 65.4° among the diffraction peaks derived from the O2-type structure is less than 0.79°.

[0029] 1.1 Crystal structure

[0030] The electrode active material has an O2-type structure (belongs to space group P63mc). The electrode active material can have one or both of an O2-type structure (belongs to space group P63mc) and an O6-type structure (belongs to space group R-3m, the c-axis length is longer than or equal to 2.5 nm and shorter than or equal to 3.5 nm, and is typically longer than or equal to 2.9 nm and shorter than or equal to 3.0 nm) in addition to the O2-type structure, for example. The electrode active material can be an active material having an O2-type structure as a main phase or an active material having a crystal structure other than the O2-type structure as a main phase. An active material having an O2-type structure as a main phase is particularly preferable.

[0031] In the case where the X-ray diffraction chart of the electrode active material of one embodiment is obtained, the X-ray diffraction chart includes a diffraction peak derived from the O2-type structure. In one embodiment, one feature is that the half-value width of the diffraction peak having a peak top at 2Θ = 64.8° to 65.4° among the diffraction peaks derived from the O2-type structure is less than 0.79°.

[0032] In the X-ray diffraction chart of the electrode active material, the diffraction peak derived from the O2-type structure having a peak top at 2Θ = 64.8° to 65.4° is present, which means that the electrode active material has little Li deficiency and contains a large amount of Li in the crystal structure of the electrode active material. If described more specifically, the following is given. First, the diffraction peak having a peak top at 2Θ = 64.8° to 65.4° among the diffraction peaks derived from the O2-type structure is considered to correspond to a diffraction peak derived from the (110) plane of the O2-type structure, for example. Here, the X-ray diffraction peak derived from the (110) plane of the O2-type structure shifts in proportion to the amount of Li in the electrode active material. Specifically, the X-ray diffraction peak derived from the (110) plane of the O2-type structure is a diffraction peak having a peak top at 2Θ = 65° in the case where the molar ratio of Li contained in the electrode active material (a in the chemical composition described later) is 1.0.

[0033] As described later, in the conventional method, the molar ratio of Li contained in the electrode active material having the O2-type structure (a in the chemical composition described later) is only 0.7 or less, and the capacity potential of the electrode active material is not sufficiently exerted. In contrast, in the present embodiment, in the X-ray diffraction pattern of the electrode active material, there is a diffraction peak derived from the O2-type structure having a peak top at 2Θ = 64.8° to 65.4°, and thus it can be said that a large amount of Li is intercalated in the electrode active material, and the molar ratio of Li contained in the electrode active material (a in the chemical composition described later) is increased to more than 0.7 (for example, around 1.0). Thus, the capacity of the electrode active material having the O2-type structure is easily increased.

[0034] On the other hand, if the intercalation state of Li in the O2-type structure is not uniformized, excessive intercalation of Li easily occurs, for example, Li easily intercalates into a position not in the interlayer of the O2-type structure, and as a result, the resistance easily increases. Here, if the intercalation state of Li in the O2-type structure is not uniformized, the diffraction peak having a peak top at 2Θ = 64.8° to 65.4° described above is widened, and the half-value width becomes large. In contrast, in the present embodiment, the half-value width of the diffraction peak having a peak top at 2Θ = 64.8° to 65.4° among the diffraction peaks derived from the O2-type structure is small, and it is less than 0.79°. That is, in the electrode active material of the present embodiment, the uniformity of the intercalation state of Li in the O2-type structure is high, Li is difficult to intercalate into a position not in the interlayer of the O2-type structure, and as a result, it is easy to become an electrode active material having a low resistance. In particular, in the case where the half-value width is 0.66° or less, the resistance can be further significantly reduced. The lower limit value of the half-value width is not particularly limited. The half-value width may, for example, be 0.58° or more, 0.60° or more, or 0.62° or more.

[0035] Further, in the present application, the "X-ray diffraction pattern" and the "half-value width of the diffraction peak" refer to the X-ray diffraction pattern and the half-value width of the diffraction peak obtained under the following conditions. That is, for the electrode active material, an X-ray diffractometer (Rigaku Corporation, SmartLab, full-automatic multifunctional X-ray diffractometer) was used, CuKα was used as the ray source, 2Θ / θ scanning was performed under the conditions of a tube voltage of 245 kV, a tube current of 200 mA, a step of 0.02°, and a scanning speed of 1° / minute, and the X-ray diffraction pattern was obtained. In the X-ray diffraction pattern, the diffraction peak derived from the O2-type structure having a peak top at 2Θ = 64.8° to 65.4° was determined, and after the background value in the vicinity of the diffraction peak was subtracted, the half-value width of the diffraction peak was determined.

[0036] In the electrode active material of one embodiment, the size of the microcrystal having the O2-type structure is not particularly limited. In the electrode active material of one embodiment, one particle can be formed of one microcrystal or one particle can be formed of a plurality of microcrystals. In other words, the electrode active material of one embodiment can be (1) an electrode active material in which single-crystal particles exist independently, (2) an agglomerate (secondary particle) of a plurality of single-crystal particles, (3) a polycrystal particle including a plurality of microcrystals, or (4) an agglomerate (secondary particle) of a plurality of polycrystal particles. In particular, in the case where the electrode active material is a polycrystal particle, especially in the case where the polycrystal particle is a spherical polycrystal particle as described later, higher performance can be easily ensured as the electrode active material. The electrode active material of one embodiment can be obtained by ion-exchanging at least part of Na in a Na-containing oxide having a P2-type structure with Li, as described later. Here, the P2-type structure is hexagonal, the diffusion coefficient of Na ions is large, and crystal growth in a specific direction is easy. Thus, a microcrystal having a P2-type structure is usually a microcrystal in which the growth direction of the crystal is biased in a specific direction (e.g., a plate shape). In the case where Na ions in a P2-type microcrystal in which the growth direction of the crystal is biased in a specific direction are ion-exchanged with Li to obtain a microcrystal having an O2-type structure, the end portion of the microcrystal having the O2-type structure (the end portion in the growth direction of the crystal described above) is likely to serve as an entrance and an exit of intercalation. In other words, in the case where the electrode active material is a polycrystal particle, the following effects can be expected: the effect of increasing the number of entrances and exits of intercalation in one particle and thus reducing the reaction resistance, the effect of reducing the diffusion resistance of lithium ions because the movement distance of lithium ions is short, the effect of reducing the expansion and contraction amount of the entire particle during charge and discharge, and the like.

[0037] As described above, a microcrystal of a Na-containing oxide having a P2-type structure is likely to have a plate shape. That is, the Na-containing oxide having a P2-type structure can be a plate-shaped particle or small plate-shaped microcrystals can be connected to each other to be a spherical particle. In other words, one electrode active material particle can be a single-crystal particle having a plate shape or a polycrystal particle having a spherical shape. The polycrystal particle having a spherical shape has a plurality of microcrystals on the surface thereof. It is thought that in the case where the electrode active material is a polycrystal particle having a spherical shape, the degree of bending is reduced by the spherical shape, and the resistance to lithium ion conduction is reduced. Thus, for example, the rate characteristics of a battery are improved, and the reversible capacity is likely to be large. Note that in this specification, a "spherical particle" means a particle with a circularity of 0.80 or more. The circularity of a particle can be 0.81 or more, 0.82 or more, 0.83 or more, 0.84 or more, 0.85 or more, 0.86 or more, 0.87 or more, 0.88 or more, 0.89 or more, or 0.90 or more. The circularity of a particle is given by 4πS / L 2Definition. Here, S is a normal projection area of the particle, and L is a circumference of a normal projection image of the particle. The circularity of the particle can be found by observing the appearance of the particle using a scanning electron microscope (SEM), a transmission electron microscope (TEM), or an optical microscope.

[0038] 1.2 Chemical composition

[0039] The chemical composition of the electrode active material is not particularly limited as long as it can maintain the O2-type structure described above and satisfy the requirements related to the half-value width described above. The electrode active material can be an active material containing at least one element selected from Mn, Ni, and Co, Li, and O as constituent elements. In particular, in the case where at least Mn, at least one selected from Ni and Co, Li, and O are contained as constituent elements, and especially in the case where at least Li, Mn, Ni, Co, and O are contained as constituent elements, higher performance is easily ensured. However, the molar concentration of Li can also approach zero up to the limit, for example, when Li is substantially completely released by charging. In addition, the electrode active material can contain Na as a constituent element due to the manufacturing process described later. In addition, the electrode active material can contain a prescribed element M. In addition, the electrode active material can contain other impurity elements. For example, the electrode active material can contain components resulting from the manufacturing process described later as impurities. Specifically, the electrode active material can contain components derived from a reducing solution (aromatic compounds, ethers, etc.).

[0040] The electrode active material of one embodiment can have a composition represented by Li a Na b Mn x-p Ni y-q Co z-r M p+q+rO2 (here, 0.70 < a ≤ 1.40, 0 ≤ b ≤ 0.20, x + y + z = 1, 0 ≤ p + q + r < 0.17, M is at least one element selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W.) indicates a chemical composition. In the chemical composition, a is greater than 0.70, can be 0.75 or more, 0.80 or more, 0.85 or more, 0.90 or more, or 0.95 or more, and is 1.40 or less, can be 1.35 or less, 1.30 or less, 1.25 or less, 1.20 or less, 1.15 or less, 1.10 or less, 1.05 or less, or 1.00 or less. In addition, b is 0 or more, can be greater than 0, and is 0.20 or less, can be 0.15 or less, 0.10 or less, 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less, or 0.01 or less. In addition, x is 0 or more, can be 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, or 0.50 or more, and is 1.00 or less, can be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, or 0.50 or less. In addition, y is 0 or more, can be 0.10 or more or 0.20 or more, and is 1.00 or less, can be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, 0.30 or less, or 0.20 or less. In addition, z is 0 or more, can be 0.10 or more, 0.20 or more, or 0.30 or more, and is 1.00 or less, can be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, or 0.30 or less. The element M contributes little to charge and discharge. In this regard, in the above chemical composition, by p + q + r being less than 0.17, a high charge and discharge capacity is easily ensured. p + q + r can be 0.15 or less, 0.13 or less, 0.11 or less, 0.09 or less, 0.07 or less, 0.06 or less, 0.05 or less, or 0.04 or less. On the other hand, by containing the element M, the O2 type structure is easily stabilized. In this regard, in the above chemical composition, p + q + r is 0 or more, can be more than 0, 0.01 or more, 0.02 or more, or 0.03 or more. The composition ratio of O is approximately 2, but is not necessarily exactly 2.0, and is indefinite. Furthermore, in the above chemical composition, in the case where the valence number of the element M is denoted as +n, the relationship 3.0 ≤ 4(x - p) + 2(y - q) + 3(z - r) + n(p + q + r) ≤ 3.5 can also be satisfied. This means that the total valence number of the metals in the Li-containing transition metal oxide is in a range close to 3.33 valence (charge neutrality in the case where a is 0.67).The Li-containing transition metal oxide having an O2-type structure is synthesized from a Na-containing transition metal oxide having a P2-type structure, but at this time, the Na content is in a range of 0.5 or more and 1.0 or less, and the charge neutrality corresponds to a case where the above relationship is satisfied.

[0041] 1.3 Other

[0042] The electrode active material of one embodiment can be a solid particle, can be a hollow particle, or can be a particle having a void. The size of the particle of the electrode active material is not particularly limited, but it is considered that a small size is advantageous. For example, the average particle diameter (D50) of the particle of the electrode active material can be 0.1 μm or more and 10 μm or less, 1.0 μm or more and 8.0 μm or less, or 2.0 μm or more and 6.0 μm or less. Furthermore, the average particle diameter (D50) means a particle diameter (D50, median diameter) at which the cumulative value of 50 % in a particle size distribution on a volume basis obtained by a laser diffraction-scattering method corresponds. The electrode active material of one embodiment can be a positive electrode active material.

[0043] 2. Method for manufacturing electrode active material

[0044] As Figure 1 illustrated in FIG. 1, the method for manufacturing the electrode active material of one embodiment includes the following steps.

[0045] obtaining a Na-containing transition metal oxide having a P2-type structure (step S1);

[0046] replacing at least part of Na of the Na-containing transition metal oxide with Li by ion exchange to obtain a Li-containing transition metal oxide having an O2-type structure (step S2); and

[0047] doping Li to the Li-containing transition metal oxide by bringing a reduction solution containing Li ions into contact with the Li-containing transition metal oxide (step S3).

[0048] Here, by controlling the contact time and the contact temperature in step S3, the electrode active material of one embodiment described above can be manufactured. For example, in the method for manufacturing the electrode active material of one embodiment, the time during which the reduction solution is brought into contact with the Li-containing transition metal oxide can be 10 minutes or more and 120 minutes or less, and the temperature at which the reduction solution is brought into contact with the Li-containing transition metal oxide can be 10 °C or more and 50 °C or less.

[0049] 2.1 Step S1

[0050] In the step S1, the Na-containing transition metal oxide having a P2-type structure can be obtained, for example, by forming a precursor containing Na and a transition metal element, optionally pre-firing, and then performing a main firing.

[0051] In the step S1, the precursor can be, for example, a precursor obtained by mixing a transition metal source and a Na source. The transition metal source can be, for example, a transition metal salt such as a carbonate, a sulfate, a nitrate, an acetate, or the like, and can be a transition metal compound such as a transition metal hydroxide. The transition metal element can be at least one of Mn, Ni, and Co. The transition metal source can be a salt represented by Me(C03) x (Me is at least one transition metal element among Mn, Ni, and Co, and x depends on the valence number of Me), a salt represented by Me(S04) x (Me is at least one transition metal element among Mn, Ni, and Co, and x depends on the valence number of Me), a salt represented by Me(S04) x (Me is at least one transition metal element among Mn, Ni, and Co, and x depends on the valence number of Me), a salt represented by Me(S04) x (Me is at least one transition metal element among Mn, Ni, and Co, and x depends on the valence number of Me), a salt represented by Me(S04) x (Me is at least one transition metal element among Mn, Ni, and Co, and x depends on the valence number of Me), a salt represented by Me(S04) In the step S1, the Na-containing transition metal oxide having a P2-type structure can be obtained, for example, by forming a precursor containing Na and a transition metal element, optionally pre-firing, and then performing a main firing.

[0052] In the step S1, the precursor can be, for example, a precursor obtained by mixing a transition metal source and a Na source. The transition metal source can be, for example, a transition metal salt such as a carbonate, a sulfate, a nitrate, an acetate, or the like, and can be a transition metal compound such as a transition metal hydroxide. The transition metal element can be at least one of Mn, Ni, and Co. The transition metal source can be a salt represented by Me(C03)

[0053] In step S1, the precursor can be, for example, a precursor obtained by using an ion source capable of forming a precipitate with transition metal ions in aqueous solution and a transition metal compound to obtain a precipitate, followed by mixing the precipitate, a Na source, and optionally an element M source. Examples of ion sources capable of forming precipitates with transition metal ions include sodium salts such as sodium carbonate and sodium nitrate, sodium hydroxide, and sodium oxide. Examples of transition metal compounds include salts such as nitrates, sulfates, carbonates, acetates, and hydroxides. In step S1, the precipitate can be obtained by adding and mixing the solutions after preparing solutions of the ion source and the transition metal compound separately. Various sodium compounds can be used as the base, and ammonia solution can be added to adjust the alkalinity. More specifically, in step S1, a precipitate containing at least one transition metal element among Mn, Ni, and Co can also be obtained as the precipitate. The precipitate can be obtained, for example, by using a solution method such as coprecipitation or sol-gel method. In the case of coprecipitation, for example, by preparing Me(SO4)... x An aqueous solution of sodium hydroxide and an aqueous solution of sodium nitrate are added dropwise and mixed to obtain a precipitate. This precipitate can be recovered and then mixed with a sodium source. The amount of sodium source to be mixed with the precipitate can be determined by considering the sodium loss during subsequent calcination. Alternatively, the surface of the particles composed of the precipitate can be coated with sodium salt to obtain coated particles as a precursor. The coating ratio and other parameters of the coated particles are as described above.

[0054] In step S1, the pre-firing of the precursor obtained as described above can be carried out at a temperature below the formal firing temperature. For example, pre-firing can be carried out at a temperature below 700°C. There is no particular limitation on the pre-firing time. Alternatively, pre-firing can be omitted.

[0055] In step S1, the formal firing of the precursor can be carried out at a temperature of 700°C or higher and 1100°C or lower, preferably 800°C or higher and 1000°C or lower. If the formal firing temperature is too low, Na doping will not occur; if the formal firing temperature is too high, structures other than the P2 type structure are easily formed. The temperature rise conditions from the pre-firing temperature to the formal firing temperature are not particularly limited. The formal firing time is also not particularly limited, for example, it can be 30 minutes or more and 10 hours or less. The formal firing atmosphere is also not particularly limited, for example, it can be an oxygen-containing atmosphere such as atmospheric atmosphere or an inactive gas atmosphere.

[0056] In the step S1, the Na-containing transition metal oxide having the P2-type structure can be doped with the element M after the above-described main calcination. That is, the Na-containing transition metal oxide having the P2-type structure which does not contain the element M can be synthesized, and then the oxide can be doped with the element M. The doping of the element M can be performed by ion exchange, for example.

[0057] The Na-containing transition metal oxide obtained by the step S1 can be, for example, a Na-containing transition metal oxide containing at least one element selected from Mn, Ni, and Co, Na, and O as constituent elements. In particular, in the case where at least Na, Mn, at least one selected from Ni and Co, and O are contained as constituent elements, and especially in the case where at least Na, Mn, Ni, Co, and O are contained as constituent elements, the performance of the positive electrode active material is easily further increased. More specifically, the Na-containing transition metal oxide obtained by the step S1 can be a Na-containing transition metal oxide having a chemical composition represented by Na c Mn x-p Ni y-q Co z-r M p+q+r O2(wherein, 0 < c < 1.00, x + y + z = 1, and 0 < p + q + r < 0.17, and the element M is at least one selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W.) is represented. In the case where the Na-containing transition metal oxide has such a chemical composition, the P2-type structure is easily maintained. In the above-described chemical composition, c is greater than 0, and can be 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, 0.50 or more, or 0.60 or more, and is 1.00 or less, and can be 0.90 or less, 0.80 or less, or 0.70 or less. As for the composition ratio of x, y, z, p, q, and r, and O, the same as described above, the description is omitted here.

[0058] 2.2 Step S2

[0059] In the process S2, at least a part of Na of the Na-containing transition metal oxide obtained in the process S1 is replaced with Li by ion exchange, and a Li-containing transition metal oxide having an O2-type structure is obtained. In the process S2, for example, at least a part of Na of the Na-containing transition metal oxide can be replaced with Li by ion exchange using a lithium salt. For example, at least a part of Na can be replaced with Li by ion exchange by mixing the Na-containing transition metal oxide having a P2-type structure and a lithium salt, and heating to a temperature above the melting point of the lithium salt to melt the lithium salt. The lithium salt can be, for example, a lithium halide. The lithium halide is preferably at least one of lithium chloride, lithium bromide, and lithium iodide. Alternatively, the lithium salt can be lithium nitrate. Alternatively, the lithium salt can be a mixed salt of a lithium halide and lithium nitrate.

[0060] In the process S2, at least a part of Na of the Na-containing transition metal oxide obtained in the process S1 is replaced with Li by ion exchange, and a Li-containing transition metal oxide having an O2-type structure is obtained. In the process S2, for example, at least a part of Na of the Na-containing transition metal oxide can be replaced with Li by ion exchange using a lithium salt. For example, at least a part of Na can be replaced with Li by ion exchange by mixing the Na-containing transition metal oxide having a P2-type structure and a lithium salt, and heating to a temperature above the melting point of the lithium salt to melt the lithium salt. The lithium salt can be, for example, a lithium halide. The lithium halide is preferably at least one of lithium chloride, lithium bromide, and lithium iodide. Alternatively, the lithium salt can be lithium nitrate. Alternatively, the lithium salt can be a mixed salt of a lithium halide and lithium nitrate.

[0061] The temperature in the process S2 (for example, the heating temperature in the case where ion exchange is performed by heating and melting after bringing the lithium salt into contact with the Na-containing transition metal oxide particles) can be, for example, 600°C or lower, 500°C or lower, 400°C or lower, 350°C or lower, 300°C or lower, 280°C or lower, 250°C or lower, 230°C or lower, 200°C or lower, 170°C or lower, or 150°C or lower, and can be room temperature or higher or 100°C or higher. If the temperature is too high, the O2-type structure is not obtained, and the O3-type structure, which is a stable phase, is easily generated. In the case where the lithium salt is melted, as described above, the heating is performed to a temperature of the melting point of the lithium salt or higher. The time in the process S2 (for example, the heating time in the case where ion exchange is performed by heating and melting after bringing the lithium salt into contact with the Na-containing transition metal oxide) can be adjusted so that most of Na of the Na-containing transition metal oxide particles is replaced with Li. From the viewpoint of ensuring a sufficient time for melting of the lithium salt, and the like, the time in the process S2 can be, for example, 10 minutes or more or 60 minutes or more, and can be 12 hours or less or 6 hours or less. The atmosphere in the process S2 is not particularly limited, and can be, for example, an oxygen-containing atmosphere such as an atmospheric air atmosphere, or a non-reactive gas atmosphere. After the ion exchange, the Li-containing transition metal oxide having the O2-type structure can be subjected to some post-treatment such as washing.

[0062] The Li-containing transition metal oxide having the O2-type structure obtained by the ion exchange in the process S2 can be a Li-containing transition metal oxide containing, as constituent elements, at least one element selected from Mn, Ni, and Co, Li, and O. In particular, in the case where at least Mn, at least one element selected from Ni and Co, Li, and O are contained as constituent elements, and especially in the case where at least Li, Mn, Ni, Co, and O are contained as constituent elements, higher performance is easily ensured. In addition, the Li-containing transition metal oxide having the O2-type structure obtained by the ion exchange can contain Na as a constituent element due to the above-described manufacturing process. In addition, the Li-containing transition metal oxide having the O2-type structure obtained by the ion exchange can contain the above-described element M. In addition, the Li-containing transition metal oxide having the O2-type structure obtained by the ion exchange can contain other impurity elements. The chemical composition of the Li-containing transition metal oxide having the O2-type structure obtained by the ion exchange of the process S2 can be represented by Li a Na b Mn x-p Ni y-q Co z-r M p+q+rO2 (here, 0 < a < 0.70, 0 < b < 0.20, x + y + z = 1, and 0 < p + q + r < 0.17, and the element M is at least one selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W.) is represented. In the chemical composition, a is greater than 0, and can be 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, 0.50 or more, or 0.60 or more. In addition, b is 0 or more, and can be greater than 0, and is 0.20 or less, and can be 0.15 or less, 0.10 or less, 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less, or 0.01 or less. Regarding the composition ratios of x, y, z, p, q, and r, and O, the same as described above, the explanation is omitted here.

[0063] 2.3 Step S3

[0064] By going through the above-described steps S1 and S2, a Li-containing transition metal oxide having an O2-type structure can be obtained. However, according to the present inventors' confirmation, by only going through the above-described steps S1 and S2, the amount of Li contained in the Li-containing transition metal oxide is difficult to be made sufficient, and an electrode active material satisfying the above-described requirements of the peak top position and the half-value width cannot be obtained. For example, in the above-described ion exchange, the molar ratio of Li (the above-described a) in the Li-containing transition metal oxide is only 0.70 or less, and the potential of the capacity of the O2-type positive electrode active material cannot be sufficiently exerted.

[0065] On the contrary, in the step S3, by further doping Li to the Li-containing transition metal oxide obtained by the above-described step S2 with a process separate from the above-described ion exchange, the molar ratio of Li (the above-described a) in the Li-containing transition metal oxide can be increased to more than 0.70. Specifically, in the step S3, by bringing a reducing solution containing Li ions into contact with the Li-containing transition metal oxide, the Li-containing transition metal oxide is further doped with Li with a process separate from the ion exchange. The "reducing solution" means a solution having a reducing property, and for example, can be a solution containing an electrophile. The reducing solution can be obtained, for example, by dissolving an electrophile and a Li source in a solvent. The solvent can employ various organic solvents capable of dissolving the electrophile and the Li source.

[0066] The solvent constituting the reducing solution can be, for example, an ether. In other words, the reducing solution can be a solution containing an ether. The ether is, for example, preferably at least one selected from tetrahydrofuran (tetrahydrofuran, 2-methyltetrahydrofuran, and the like) which can have a substituent, dialkyl ether (dibutyl ether and the like), and alkylene glycol dialkyl ether (dimethoxyethane and the like).

[0067] The electrophilic agent can be various substances that are dissolved in the above-mentioned solvent. The electrophilic agent contained in the reduction solution can be, for example, an aromatic compound. In other words, the reduction solution can be a solution containing an aromatic compound. In this case, in the case where the aromatic compound is a compound having a plurality of benzene rings, the electron density in the structure decreases, the electrons embedded in the structure of the aromatic compound are stabilized, and a higher effect can be expected. In addition, in the case where the aromatic compound has an electron-withdrawing group as a substituent, the electron density in the benzene ring decreases by the electron-withdrawing group attracting electrons, the electrons embedded in the structure of the aromatic compound are stabilized, and a higher effect can be expected. The "electron-withdrawing group" is a group having relatively high electronegativity, and refers to a group containing halogen, oxygen, and / or nitrogen. Specifically, the electron-withdrawing group can be at least one selected from the group consisting of a halogen group, a carbonyl group, and a nitro group, and the like. As the aromatic compound of the electrophilic agent, for example, at least one selected from the group consisting of biphenyls (e.g., biphenyl, 2-methylbiphenyl, and the like) that can have a substituent, fluorenones (e.g., 9-fluorenones, and the like) that can have a substituent, naphthalenes (e.g., naphthalene, fluoronaphthalene, bromonaphthalene, nitronaphthalene, and the like) that can have a substituent, anthracenes (e.g., anthracene, 9-bromoanthracene, and the like) that can have a substituent, tetracenes that can have a substituent, pentacenes that can have a substituent, tetraphenylcyclopentadienones that can have a substituent, and the like is preferable.

[0068] The Li source can be various substances that generate Li ions by being dissolved in the above-mentioned solvent. The Li source can be metallic lithium, or a Li compound.

[0069] The concentrations of the electrophilic agent and the Li ions contained in the reduction solution are appropriately determined depending on the target doping amount. For example, in the case where the above-mentioned Li-containing transition metal oxide is immersed in the reduction solution, the molar ratio of the Li ions contained in the reduction solution to the Li-containing transition metal oxide immersed in the reduction solution (Li ions / Li-containing transition metal oxide) can be 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, or 0.8 or more, and can be 2.0 or less, 1.5 or less, 1.0 or less, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, or 0.2 or less. In particular, in the case where the molar ratio (Li ions / Li-containing transition metal oxide) is 0.2 or more and 0.6 or less, and particularly 0.3 or more and 0.5 or less, a positive electrode active material having excellent performance is easily obtained. The molar ratio of the electrophilic agent to the Li ions contained in the reduction solution (electrophilic agent / Li ions) is not particularly limited, and can be, for example, 0.5 or more and 2.0 or less, 0.7 or more and 1.5 or less, or 0.9 or more and 1.1 or less.

[0070] In step S3, for example, Li can be further doped onto the Li-containing transition metal oxide simply by contacting it with the aforementioned reducing solution. The contact mode between the reducing solution and the Li-containing transition metal oxide is not particularly limited. For example, the Li-containing transition metal oxide can be immersed in the reducing solution, or the reducing solution can be sprayed onto the Li-containing transition metal oxide in a mist state. The inventors have confirmed that, in step S3, by controlling the contact time and contact temperature between the Li-containing transition metal oxide and the reducing solution, the electrode active material of the above-described embodiment can be manufactured. Specifically, the contact time between the reducing solution and the Li-containing transition metal oxide can be 10 minutes or more and 120 minutes or less, and the contact temperature between the reducing solution and the Li-containing transition metal oxide can be 10°C or more and 50°C or less. The term "contact time" is, for example, considered to be the same as the "immersion time" from the time the Li-containing transition metal oxide is immersed in the reducing solution until it is removed, and the same as the "spraying time" when the Li-containing transition metal oxide is sprayed onto the Li-containing transition metal oxide in a mist state. The term "contact temperature" refers to the temperature of the "reducing solution" in contact with Li-containing transition metal oxides.

[0071] In step S3, after Li doping using a reducing solution, a cleaning and drying process can be performed as appropriate. The amount of impurities (derived from the reducing solution) in the electrode active material can be controlled through these cleaning and drying processes.

[0072] 3. Battery

[0073] One embodiment of the battery includes the electrode active material of this disclosure described above. The electrode active material of this disclosure can, for example, be used as the positive electrode active material of a lithium-ion battery. Figure 2 As shown, a battery 100 according to one embodiment has a positive electrode active material layer 10, an electrolyte layer 20, and a negative electrode active material layer 30. In the battery 100, for example, the positive electrode active material layer 10 may contain the electrode active material of this disclosure. The battery 100 may include a positive electrode current collector 40 and a negative electrode current collector 50. The battery 100 may be a solid-state battery or a liquid-based battery. Furthermore, a solid-state battery refers to a battery containing a solid electrolyte, which allows the presence of liquid. The battery 100 may also be a completely solid-state battery that substantially does not contain liquid. Regarding the battery configuration, except for the use of the electrode active material of this disclosure, it can be the same as conventional batteries. Detailed descriptions are omitted here.

[0074] As described above, the embodiment of the electrode active material and the like of the present disclosure has been described, but the electrode active material and the like of the present disclosure can be changed to a manner other than the above-described embodiment in a range not departing from the gist thereof. Hereinafter, an example is shown, and the technology of the present disclosure is further described in detail, but the technology of the present disclosure is not limited to the example below.

[0075] 1. Production of electrode active material

[0076] 1.1 Co-precipitation synthesis of transition metal source

[0077] MnSO4·5H2O, NiSO4·6H2O, and CoSO4·7H2O were weighed in a composition ratio to be targeted, dissolved in distilled water in a concentration of 1.2 mol / L, and a first liquid was obtained. In another container, Na2CO3 was dissolved in distilled water in a concentration of 1.2 mol / L, and a second liquid was obtained. Next, 500 mL each of the first liquid and the second liquid described above were added dropwise at a rate of about 4 mL / min to a reaction vessel into which 1000 mL of pure water was previously charged. After the addition was completed, stirring was performed at a stirring rate of 150 rpm for 1 hour at room temperature. The precipitate was washed with pure water, and solid-liquid separation was performed with a centrifugal separator. The obtained precipitate was dried at a temperature of 120°C for one night, pulverized using a mortar, and then particulate matter was removed by air classification, and a mixed salt particle containing Mn, Ni, and Co (transition metal source) was obtained.

[0078] 1.2 Mixing of transition metal source and Na source (Na coating)

[0079] After Na2CO3 and distilled water were weighed in a manner to be 1150 g / L, the mixture was stirred using a stirrer until completely dissolved, whereby an aqueous Na2CO3 solution was produced. By mixing the mixed salt particle described above into the aqueous Na2CO3 solution, a slurry was prepared. The Na2CO3 and the mixed salt particle described above were mixed in a manner such that the composition of Mn, Ni, and Co after drying became 1:1:1. The obtained slurry was dried by spray drying. Specifically, using a spray drying device DL410, the surface of the mixed salt particle described above was coated with Na2CO3 under conditions of a slurry feed rate of 30 mL / min, an inlet temperature of 200°C, a circulating air volume of 0.8 m 0.7 Mn 0.5 Ni 0.2 Co 0.3 O2. The obtained slurry was dried by spray drying. Specifically, using a spray drying device DL410, the surface of the mixed salt particle described above was coated with Na2CO3 under conditions of a slurry feed rate of 30 mL / min, an inlet temperature of 200°C, a circulating air volume of 0.8 m 3 / minute, a spray air pressure of 0.3 MPa, and a precursor particle was obtained.

[0080] 1.3 Calcination of precursor particle

[0081] The precursor particles were subjected to the "first temperature raising process", the "pre-sintering process", the "second temperature raising process", the "main sintering process", and the "in-furnace cooling process" shown in Table 1 below, and then, the sintered product was taken out of the electric furnace at a temperature of 250°C, pulverized using a mortar in a dry atmosphere having a dew point of -30°C or lower, whereby a Na-containing transition metal oxide having a P2-type structure (Na 0.7 Mn 0.5 Ni 0.2 Co 0.3 O2).

[0082] Table 1

[0083]

[0084] 1.4 Ion exchange

[0085] LiNO3 and LiCl were weighed so as to be in a molar ratio of 50:50, and mixed with the above Na-containing transition metal oxide in a molar ratio of 10 times the minimum amount of Li required for ion exchange, whereby a mixture was obtained. Next, under an atmospheric atmosphere (humidity of 50% or more), using an alumina crucible, sintering was performed at a temperature of 280°C for 1 hour. The salt remaining after sintering was washed with pure water, and solid-liquid separation was performed by vacuum filtration. The obtained precipitate was dried at a temperature of 120°C for one night, whereby a Li-containing transition metal oxide having an O2-type structure was obtained.

[0086] 1.5 Li doping

[0087] Naphthalene was mixed and dissolved in tetrahydrofuran (THF) in a glove box (Ar atmosphere) so as to be 1 mol / L, whereby a naphthalene solution was obtained. To the naphthalene solution, the same molar amount of Li foil as the naphthalene was further added, and stirred for 2 hours, whereby a reduction solution containing 1 mol / L of Li ions was obtained. To the obtained reduction solution, the above Li-containing transition metal oxide was added and immersed, and stirring was performed at the time and temperature shown in Table 2 below. Here, the molar ratio of the Li ions contained in the reduction solution to the Li-containing transition metal oxide immersed in the reduction solution (Li ions / Li-containing transition metal oxide) was set to 0.4. After stirring, the Li-containing transition metal oxide was washed with THF, and solid-liquid separation was performed by vacuum filtration. The obtained precipitate was dried at a temperature of 120°C for one night, whereby each of the electrode active materials of Examples 1 to 3 and Comparative Examples 1 to 3 (the electrode active materials obtained by further doping Li to the above Li-containing transition metal oxide) was obtained.

[0088] Table 2

[0089]

[0090] 2. Determination of chemical composition of electrode active material

[0091] The chemical composition was determined by ICP analysis for each of the electrode active materials of Examples 1 to 4 and Comparative Examples 1 to 3. Each of the electrode active materials of Examples 1 to 4 and Comparative Examples 1 to 3 had a chemical composition represented by Li X Mn 0.5 Ni 0.2 Co 0.3 O2, that is, the composition ratio of transition metals was the same, and on the other hand, the composition ratio of Li was different. The composition ratio of Li (value of X in the above chemical composition) of each of the electrode active materials of Examples 1 to 4 and Comparative Examples 1 to 3 is shown in Table 3 below.

[0092] 3. Obtaining X-ray diffraction pattern of electrode active material

[0093] X-ray diffraction measurement was performed on each of the electrode active materials of Examples 1 to 4 and Comparative Examples 1 to 3, and an X-ray diffraction pattern was obtained, and the crystal structure of each of the electrode active materials was determined. As a result, each of the electrode active materials had an O2-type structure. In each of the X-ray diffraction patterns, the peak top position of the X-ray diffraction peak derived from the (110) plane of the O2-type structure was determined. In addition, the half-value width was determined after subtracting the background value for the X-ray diffraction peak derived from the (110) plane of the O2-type structure. In Table 3 below, the above peak top position and half-value width are shown with respect to each of the electrode active materials of Examples 1 to 4 and Comparative Examples 1 to 3. In addition, the X-ray diffraction patterns of each of the electrode active materials of Examples 1, Comparative Example 1, and Comparative Example 3 are shown in Figs. 1, 2, and 3, respectively. Figure 3

[0094] 4. Production and evaluation of coin cell

[0095] A coin cell (CR2032) was produced using each of the electrode active materials of Examples 1 to 4 and Comparative Examples 1 to 3. The production steps of the coin cell were as follows.

[0096] (1) The above electrode active material, acetylene black (AB) as a conductive aid, and polyvinylidene fluoride (PVdF) as a binder were weighed so as to become electrode active material: AB: PVdF = 85: 10: 5 by mass ratio, and were dispersed and mixed in N-methyl-2-pyrrolidone to obtain a positive electrode mixture slurry. The positive electrode mixture slurry was coated on an aluminum foil, and vacuum dried at a temperature of 120°C for one night, thereby obtaining a positive electrode as a laminate of a positive electrode active material layer and a positive electrode current collector.

[0097] ​(2) LiPF6 was dissolved in a mixed solvent in which trifluoropropylencarbonate (TFPC) and trifluoroethyl methyl carbonate (TFEMC) were mixed at a ratio of TFPC:TFEMC = 30 vol%:70 vol% to obtain an electrolyte solution.

[0098] (3) A metal lithium foil was prepared as a negative electrode.

[0099] (4) A coin cell (CR2032) was produced using the positive electrode, the electrolyte solution, and the negative electrode.

[0100] Charge and discharge of the coin cell was performed at a voltage range of 2 to 4.8 V and a rate of 0.1C (1C = 240 mA / g) in a thermostat maintained at 25°C. Then, in a thermostat maintained at 25°C, a current equivalent to 3C was applied for 10 seconds in an SOC 50% state, whereby the DCIR resistance was measured. The coin cell having the lowest resistance value among the coin cells of Examples 1 to 4 and Comparative Examples 1 to 3 was taken as a reference (100), and the resistance values of the other coin cells were standardized. The results are shown in Table 3 and Figure 4 .

[0101] 5. Evaluation results

[0102] Table 3

[0103]

[0104] As shown in Table 3 and Figure 3 , it can be said that the electrode active material having an O2-type structure and in which a diffraction peak having a peak top at 2θ = 64.8° to 65.4° derived from the O2-type structure is confirmed in an X-ray diffraction pattern of the electrode active material (Examples 1 to 4 and Comparative Examples 1 to 3) has a high capacity by doping Li. Further, it is also clear from the prior application of the present applicant (Japanese Patent Application No. 2023-200071) that the capacity as an electrode active material is improved by further doping Li to the O2-type Li-containing transition metal oxide after ion exchange.

[0105] In addition, as shown in Table 3 and Figure 4 , it is known that the electrode active material having an O2-type structure and in which the half-value width of the diffraction peak having a peak top at 2θ = 64.8° to 65.4° among the diffraction peaks derived from the O2-type structure is less than 0.79° (Examples 1 to 4) has a low resistance compared to Comparative Examples 1 to 3.

[0106] Further, in the above-described embodiments, the electrode active material having a specific chemical composition is exemplified, but the chemical composition of the electrode active material is not limited to the above-described chemical composition. It is considered that by satisfying the peak top position and the half-value width described above, the electrode active material realizes both a high capacity and a low resistance regardless of the type of transition metal constituting the electrode active material.

Claims

1. An electrode active material is an electrode active material having an O2-type structure. In the X-ray diffraction pattern of the electrode active material, the half-value width of the diffraction peak having a peak top at 2θ = 64.8° to 65.4° among the diffraction peaks derived from the O2-type structure is less than 0.79°.

2. The electrode active material according to claim 1, wherein the half-value width is 0.66° or less.

3. The electrode active material according to claim 1, wherein it is made of Li a Na b Mn x-p Ni y-q Co z-r M p+q+r O2 represents the chemical composition, in which, 0.70 < a ≤ 1.40, 0 ≤ b ≤ 0.20, x + y + z = 1, 0 ≤ p + q + r < 0.17, and M is at least one element selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W.

4. A battery having the electrode active material according to any one of claims 1 to 3.

5. A method for manufacturing an electrode active material, comprising the following steps: Obtaining a Na-containing transition metal oxide having a P2-type structure; Replacing at least a part of Na in the Na-containing transition metal oxide with Li by ion exchange to obtain a Li-containing transition metal oxide having an O2-type structure; and Doping the Li-containing transition metal oxide with Li by bringing a reducing solution containing Li ions into contact with the Li-containing transition metal oxide, The time for bringing the reducing solution into contact with the Li-containing transition metal oxide is 10 minutes or more and 120 minutes or less, The temperature for bringing the reducing solution into contact with the Li-containing transition metal oxide is 10°C or more and 50°C or less.

Images