JP6903900B2 - Manufacturing method of positive electrode for lithium ion secondary battery and manufacturing method of lithium ion secondary battery - Google Patents

Description

The present invention relates to a lithium ion secondary battery, particularly a lithium ion secondary battery using a lithium transition metal composite oxide as a positive electrode active material.

The lithium transition metal composite oxide having a layered rock salt type structure is a material expected as a positive electrode material for a lithium ion secondary battery having a high capacity and a high energy density. Further, as a negative electrode material used in combination with this, a carbon material and a material containing high-capacity silicon and silicon oxide are being studied.

A technique of a lithium ion secondary battery using such a positive electrode material and a negative electrode material is disclosed in the following documents.

According to Patent Document 1, it is possible to increase the capacity retention rate during the charge / discharge cycle by performing a reduction treatment in which an organic substance is mixed with a lithium iron-manganese-based composite oxide having a layered rock salt type structure and fired. Is shown.

Patent Document 2 describes that oxygen in a lithium transition metal composite oxide is extracted by mixing a reducing agent with a lithium transition metal composite oxide capable of storing and releasing lithium and firing the oxide. A deoxidized lithium transition metal composite oxide is shown, and it is described that this deoxidized lithium transition metal composite oxide is obtained through a reduction reaction. Then, the lithium transition metal composite oxide before withdrawing the oxygen has a layered rock-salt structure, _{specifically, LiNi 0.8 Co 0.15 Al 0.05 O} 2, LiNiO 2, LiNi 0.5 Mn 0.25 Co 0.25 O 2, LiNi _1/3 Co _1/3 Al _1/3 O ₂ , LiNi _0.7 Co _0.19 Al _0.01 O ₂ , and LiCo _{O 2} are used. Further, as an object of the invention, it is described that oxygen generation from the positive electrode is suppressed when the battery temperature rises such as when a short circuit occurs.

Japanese Unexamined Patent Publication No. 2015-415583 Japanese Unexamined Patent Publication No. 2014-86203

The reduction treatment described in Patent Document 1 aims to increase the capacity retention rate, and the reduction treatment described in Patent Document 2 aims to suppress the generation of oxygen. In these techniques, the performance of the positive electrode However, it was difficult to form a lithium ion secondary battery having a high energy density at a low cost.

An object of the present invention is to provide a lithium ion secondary battery having a high capacity, a high energy density, and can be manufactured at low cost.

According to one aspect of the invention
A lithium ion secondary battery containing a positive electrode containing a lithium transition metal composite oxide, a negative electrode, and an electrolyte.
The lithium transition metal composite oxide has a layered rock salt type structure and has the following formula (1):
Li _x M1 _(yp) Mn _p M2 _(zq) Fe _q O _(2- δ ₎ (1)
(Here, M1 is at least one element of Ti and Zr, M2 is at least one element selected from the group consisting of Co, Ni and Mn, 1.05 ≦ x ≦ 1.32, 0.33 ≦ y ≦ 0. .63, 0.06 ≤ z ≤ 0.50, 0 <p ≤ 0.63, 0 ≤ q ≤ 0.50, 0 ≤ δ ≤ 0.80, y ≥ p, z ≥ q)
Has a composition represented by
As the positive electrode, A1, A2, and the like, which are obtained by subjecting A0, which is one of the materials applicable to the above composition formula (1), to a reduction treatment having a different degree of reduction, respectively. .. .. Then, the materials A1, A2, which have been subjected to the reduction treatment. .. .. Including at least one of
The amount of oxygen (atomic number percentage) in the composition of the material (A1, A2, ...) After the above reduction treatment is 85% or more of the amount of oxygen in the composition of the material (A0) before the reduction treatment. Lithium ion secondary batteries are provided that are in the range of less than 100%.

According to another aspect of the invention
A lithium ion secondary battery containing a positive electrode containing a lithium transition metal composite oxide, a negative electrode, and an electrolyte.
The lithium transition metal composite oxide has a layered rock salt type structure and has the following formula (1):
Li _x M1 _(yp) Mn _p M2 _(zq) Fe _q O _(2- δ ₎ (1)
(Here, M1 is at least one element of Ti and Zr, M2 is at least one element selected from the group consisting of Co, Ni and Mn, 1.05 ≦ x ≦ 1.32, 0.33 ≦ y ≦ 0. .63, 0.06 ≤ z ≤ 0.50, 0 <p ≤ 0.63, 0 ≤ q ≤ 0.50, 0 ≤ δ ≤ 0.80, y ≥ p, z ≥ q)
Has a composition represented by
As the positive electrode, A1, A2, and the like, which are obtained by subjecting A0, which is one of the materials applicable to the above composition formula (1), to a reduction treatment having a different degree of reduction, respectively. .. .. Then, the materials A1, A2, which have been subjected to the reduction treatment. .. .. Including at least one of
The diffraction angle (2θ) of the (-3 3 1) peak of the material (A1, A2, ...) subjected to the above reduction treatment by X-ray diffraction is in the range of 64.9 ° to 65.1 °. Lithium ion secondary batteries are provided.

According to another aspect of the invention
A lithium ion secondary battery containing a positive electrode containing a lithium transition metal composite oxide, a negative electrode, and an electrolyte.
The lithium transition metal composite oxide has a layered rock salt type structure and has the following formula (1):
Li _x M1 _(yp) Mn _p M2 _(zq) Fe _q O _(2- δ ₎ Equation (1)
(Here, M1 is at least one element of Ti and Zr, M2 is at least one element selected from the group consisting of Co, Ni and Mn, 1.05 ≦ x ≦ 1.32, 0.33 ≦ y ≦ 0. .63, 0.06 ≤ z ≤ 0.50, 0 <p ≤ 0.63, 0 ≤ q ≤ 0.50, 0 ≤ δ ≤ 0.80, y ≥ p, z ≥ q)
Has a composition represented by
As the positive electrode, A1, A2, and the like, which are obtained by subjecting A0, which is one of the materials applicable to the above composition formula (1), to a reduction treatment having a different degree of reduction, respectively. .. .. Then, the materials A1, A2, which have been subjected to the reduction treatment. .. .. Including at least one of
Based on the results obtained by Rietveld analysis of the X-ray diffraction data of the materials (A1, A2, ...) that have undergone the above reduction treatment using a crystal model of the space group c2 / m, 4h sites, 4g sites, When the occupancy rate (g) of the transition metal at each site of the 2b site and the 2c site is g _4h , g _4g , g _2b , and g _2c , respectively, the following equation (2):
g _total = (2g _4h + g _2c ) / 3 + (2g _4g + g _2b ) / 3 Equation (2)
Provided is a lithium ion secondary battery having a transition metal occupancy sum (g _{total) of 0.72 or more calculated by.}

According to another aspect of the invention
A lithium ion secondary battery containing a positive electrode containing a lithium transition metal composite oxide, a negative electrode, and an electrolyte.
The lithium transition metal composite oxide has a layered rock salt type structure and has the following formula (1):
Li _x M1 _(yp) Mn _p M2 _(zq) Fe _q O _(2- δ ₎ (1)
(Here, M1 is at least one element of Ti and Zr, M2 is at least one element selected from the group consisting of Co, Ni and Mn, 1.05 ≦ x ≦ 1.32, 0.33 ≦ y ≦ 0. .63, 0.06 ≤ z ≤ 0.50, 0 <p ≤ 0.63, 0 ≤ q ≤ 0.50, 0 ≤ δ ≤ 0.80, y ≥ p, z ≥ q)
Has a composition represented by
As the positive electrode, A1, A2, and the like, which are obtained by subjecting A0, which is one of the materials applicable to the above composition formula (1), to a reduction treatment having a different degree of reduction, respectively. .. .. age,
B1, B2, and the like, which are the other materials B0 applicable to the above composition formula (1), which have been subjected to reduction treatments having different degrees of reduction, respectively. .. .. When
A1 and A0, A2 other than A1 ,. .. .. , B0, B1, B2 ,. .. .. A lithium ion secondary battery comprising a mixed material with at least one material selected from the group consisting of is provided.

According to the embodiment of the present invention, it is possible to provide a lithium ion secondary battery having a high capacity, a high energy density, and can be manufactured at low cost.

The figure which shows the relationship between the (3 3 1) peak angle (2θ) by X-ray diffraction of a positive electrode material, and the amount of oxygen. The figure which shows the relationship between the peak angle (2θ) by the X-ray diffraction of a positive electrode material, a reversible capacity, and an irreversible capacity (circle indicates a reversible capacity, and a triangle mark indicates an irreversible capacity). The figure which shows the relationship between the transition metal occupancy sum and the reversible capacity obtained by Rietveld analysis of the X-ray diffraction data of a positive electrode material. The figure which shows the lithium ion secondary battery by embodiment of this invention. FIG. 4A'A'cross-sectional view of FIG. The plan view which shows the current collector used for the positive electrode of the lithium ion secondary battery by embodiment of this invention. The plan view which shows the positive electrode of the lithium ion secondary battery by embodiment of this invention. FIG. 7A'A'cross-sectional view of FIG. The plan view which shows the current collector used for the negative electrode of the lithium ion secondary battery by embodiment of this invention. FIG. 9 is a cross-sectional view taken along the line AA'. The plan view which shows the negative electrode of the lithium ion secondary battery by embodiment of this invention. The figure which shows the laminated body of the positive electrode, the negative electrode, and a separator of the lithium ion secondary battery by embodiment of this invention.

The lithium ion secondary battery according to the embodiment of the present invention includes a positive electrode containing a lithium transition metal composite oxide, a negative electrode, and an electrolyte.
The lithium transition metal composite oxide has a layered rock salt type structure and has the following formula (1):
Li _x M1 _(yp) Mn _p M2 _(zq) Fe _q O _(2- δ ₎ (1)
(Here, M1 is at least one element of Ti and Zr, M2 is at least one element selected from the group consisting of Co, Ni and Mn, 1.05 ≦ x ≦ 1.32, 0.33 ≦ y ≦ 0. .63, 0.06 ≤ z ≤ 0.50, 0 <p ≤ 0.63, 0 ≤ q ≤ 0.50, 0 ≤ δ ≤ 0.80, y ≥ p, z ≥ q)
It has a composition represented by.

In the above composition, q is preferably in the range of 0.06 ≦ q ≦ 0.50. Further, it is more preferable that M2 contains Ni.

The positive electrode preferably satisfies at least one of the following constituent requirements (i), (ii) and (iii).

Configuration requirements (i)
As the positive electrode, A1, A2, and the like, which are obtained by subjecting A0, which is one of the materials applicable to the above composition formula (1), to a reduction treatment having a different degree of reduction, respectively. .. .. Then, the materials A1, A2, which have been subjected to the reduction treatment. .. .. Including at least one of
The amount of oxygen (percentage of atoms) in the composition of the material (A1, A2, ...) subjected to the above reduction treatment is 85% or more with respect to the amount of oxygen in the composition of the material (A0) before the reduction treatment. It is in the range of less than 100%.
Here, with respect to the material (A0) before the reduction treatment, it is preferable that δ in the composition formula (1) is 0.

Configuration requirements (ii)
As the positive electrode, A1, A2, and the like, which are obtained by subjecting A0, which is one of the materials applicable to the above composition formula (1), to a reduction treatment having a different degree of reduction, respectively. .. .. Then, the materials A1, A2, which have been subjected to the reduction treatment. .. .. Including at least one of
The diffraction angle (2θ) of the (-3 3 1) peak of the material (A1, A2, ...) subjected to the above reduction treatment by X-ray diffraction is in the range of 64.9 ° to 65.1 °.

Configuration requirements (iii)
As the positive electrode, A1, A2, and the like, which are obtained by subjecting A0, which is one of the materials applicable to the above composition formula (1), to a reduction treatment having a different degree of reduction, respectively. .. .. Then, the materials A1, A2, which have been subjected to the reduction treatment. .. .. Including at least one of
Based on the results obtained by Rietveld analysis of the X-ray diffraction data of the materials (A1, A2, ...) that have undergone the above reduction treatment using a crystal model of the space group c2 / m, 4h sites, 4g sites, When the occupancy rate (g) of the transition metal at each site of the 2b site and the 2c site is g _4h , g _4g , g _2b , and g _2c , respectively, the following equation (2):
g _total = (2g _4h + g _2c ) / 3 + (2g _4g + g _2b ) / 3 Equation (2)
The sum of transition metal occupancy (g _total ) calculated by is 0.72 or more.

Further, as another form, the above-mentioned positive electrode preferably contains a mixed material in which different positive electrode materials are combined as follows.
That is, as the positive electrode, A1, A2, and the like, which are obtained by subjecting A0, which is one of the materials applicable to the composition formula (1), to a reduction treatment having a different degree of reduction, respectively. .. .. age,
B1, B2, and the like, which are the other materials B0 applicable to the above composition formula (1), which have been subjected to reduction treatments having different degrees of reduction, respectively. .. .. When
A1 and A0, A2 other than A1 ,. .. .. , B0, B1, B2 ,. .. .. It is preferable to include a mixed material with at least one material selected from the group consisting of.

At that time, it is preferable that at least one of the following three conditions is satisfied between the two positive electrode materials contained in the mixed material.
Condition (a)
Among the materials forming the mixed material, the difference in the amount of oxygen in the composition differs by 5% or more with respect to A1 and at least one other material.
Condition (b)
Among the materials forming the mixed material, the difference in the diffraction angle (2θ) of the peak (3 3 1) by X-ray diffraction is 0.05 ° or more with respect to A1 and at least one other material. ..
Condition (c)
Based on the results obtained by Rietveld analysis of the X-ray diffraction data of each material forming the mixed material with a crystal model of the space group c2 / m, at each site of 4h site, 4g site, 2b site, and 2c site. The occupancy rate (g) of the transition metal is g _4h , g _4g , g _2b , g _{2c, respectively} ), and the following equation (2):
g _total = (2g _4h + g _2c ) / 3 + (2g _4g + g _2b ) / 3 Equation (2)
When the sum of transition metal occupancy rates (g _total ) is calculated by
_{Among the materials forming the mixed material, the difference in the sum of transition metal occupancy (g total} ) is 0.01 or more with respect to A1 and at least one other material.

The above negative electrode may contain silicon or silicon oxide as the negative electrode active material.

In the above lithium ion secondary battery, the electrolyte is preferably a non-aqueous electrolyte solution containing a non-aqueous solvent and an electrolyte salt. The non-aqueous solvent preferably contains at least one of a cyclic carbonate-based solvent and a chain carbonate-based solvent. Further, the non-aqueous solvent can include at least one fluorinated solvent selected from a fluorinated ether-based solvent, a fluorinated carbonate-based solvent, and a fluorinated phosphate ester.

Among the lithium transition metal composite oxides having a layered rock salt type structure, the present inventors perform reduction treatment on the lithium iron-manganese-based composite oxide represented by _{the composition formula Li 1.26} Mn _0.52 Fe _0.11 Ni _0.11 O _2. A unipolar laminate cell for evaluation of the positive electrode was prepared using a positive electrode containing the material after the reduction, a metallic lithium negative electrode, and a non-aqueous electrolyte solution, evaluated, and the following relationship was found and studied diligently. As a result, the present invention was completed.

(Relationship 1)
Relationship between the degree of reduction and the shift of the X-ray diffraction (XRD) peak position of the positive electrode material When the X-ray diffraction peaks of the positive electrode material (lithium iron-manganese-based composite oxide) before and after the reduction treatment were evaluated, the stronger the degree of reduction, the higher the degree of reduction. That is, it was found that the peak position of XRD shifts to the lower angle side as the amount of oxygen in the positive electrode material decreases.

FIG. 1 shows the amount of oxygen when the amount of oxygen in the positive electrode material is measured by the IR combustion method and the amount of oxygen before the reduction treatment is 1, and the peak angle (X-ray diffraction angle) of the XRD peaks (3 3 1). It is a plot of the relationship with 2θ). As shown in this figure, the stronger the degree of reduction (the smaller the amount of oxygen), the more the XRD peak angle linearly decreased to the lower angle side.

(Relationship 2)
Relationship between capacity (reversible capacity) and irreversible capacity and degree of reduction (XRD peak position) There are reversible capacity and irreversible capacity as the characteristics of the positive electrode, and the normal capacity is the reversible capacity. If the charge / discharge efficiency is 100%, all the lithium ions extracted from the crystal of the positive electrode during charging will return to their original state during discharge, but in reality there are lithium ions that cannot return to the positive electrode, and the capacity of that charge. Is the irreversible capacity. In particular, the irreversible capacity due to the initial charge / discharge is large.

FIG. 2 shows the relationship between the degree of reduction of the positive electrode material (horizontal axis: (3 3 1) peak angle (2θ), that is, the XRD peak position) and the capacity (vertical axis: reversible capacity and irreversible capacity).

When the degree of reduction is increased (the peak angle 2θ becomes smaller), the reversible capacitance increases, but when the degree of reduction is further increased, the reversible capacitance decreases, so the XRD peak position (X-ray diffraction angle 2θ) is set to around 65 °. There is a maximum value. In the positive electrode material at that time, the amount of oxygen in the composition of the positive electrode material after the reduction treatment is about 90% of the amount of oxygen in the composition of the material before the reduction treatment.

On the other hand, the irreversible capacity is the opposite of the reversible capacity, and decreases as the degree of reduction is increased. When the degree of reduction is further increased, the irreversible capacity increases, and the irreversible capacity becomes the minimum at the degree of reduction at which the reversible capacity is maximized.

From FIG. 2, in order for the reversible capacitance to be 240 mAh / g or more, the diffraction angle (2θ) of the (3 3 1) peak among the X-ray diffraction peaks after the reduction treatment is 64.9 ° to 65.1. It can be said that it needs to be in the range of °. This diffraction angle (2θ) is preferably in the range of 64.94 to 65.06 °, more preferably in the range of 64.95 to 65.05 °, from the viewpoint of obtaining a sufficient reduction treatment effect. , 64.96 to 65.04 °, more preferably.

Further, from FIG. 1, in order to obtain a material in the range of the diffraction angle (2θ), the amount of oxygen in the composition of the positive electrode material after the reduction treatment is 85% or more with respect to the amount of oxygen in the composition of the material before reduction. Turns out to be necessary. Since the amount of oxygen in the positive electrode material before the reduction treatment is 100%, the upper limit of the amount of oxygen in the composition of the positive electrode material after the reduction treatment is less than 100%. From the viewpoint of obtaining a sufficient reduction treatment effect, the amount of oxygen is preferably 97% or less on the upper limit side, more preferably 95% or less, further preferably 93% or less, and preferably 88% or more on the lower limit side. ..

(Relationship 3)
Relationship between reversible capacitance and transition metal occupancy at lithium sites in the crystal lattice By Rietveld analysis (fitting) of XRD data, information on crystal lattice parameters can be obtained. _{As a result of analyzing the material after the reduction treatment using the Li 2} MnO ₃ crystal structure model belonging to the C2 / m symmetric group as the fitting model, as shown in FIG. 3, the sum of the occupancy rates (g _total ) of the transition metals is large. It was found that the reversible capacity was large.
g _total is a value calculated by the following equation from the transition metal occupancy rates (g4h, g4g, g2b, g2c) at each site (4h site, 4g site, 2b site, 2c site) in the above crystal model.
g _total = (2g _4h + g _2c ) / 3 + (2g _4g + g _2b ) / 3

From FIG. 3, it can be seen that in order for the reversible capacity to be 240 mAh / g or more, the g _total after the reduction treatment must be 0.72 or more. From the viewpoint of obtaining a sufficient effect of the reduction treatment, the g _total after the reduction treatment is preferably 0.735 or more, more preferably 0.74 or more, and the g of the material subjected to the reduction treatment according to the degree of reduction that maximizes the reversible capacity. _{Since the total} was 0.75 or more, 0.75 or more is particularly preferable.

(Evaluation of lithium-ion secondary battery / battery capacity)
Next, based on the evaluation of the positive electrode material as described above, in order to obtain a cell having a high energy density, a lithium ion secondary battery is manufactured and evaluated using a high-capacity negative electrode containing silicon oxide as a main component. went.

Table 1 shows a comparison between the case where the positive electrode material (A0) before the reduction treatment is used and the case where the positive electrode material (A1) whose reversible capacity is maximized by the reduction treatment is used.

As shown in Table 1, it can be seen that by using the reduction-treated positive electrode material (A1), the cell capacity value is improved as compared with the case where the reduction-treated positive electrode material (A0) is used. ..

Looking at the capacity value of the positive electrode and the capacity value of the cell in Table 1, although the difference between the reversible capacity values of A0 and A1 is as much as 50 mAh / g, the difference in cell capacity due to the negative electrode using silicon oxide. Is only 5 mAh / g, and it can be seen that the improvement effect is small. This is because the negative electrode material also has an irreversible capacity, and in particular, the irreversible capacity of a high-capacity negative electrode containing silicon or silicon oxide is large.

The lithium ion secondary battery according to the embodiment of the present invention uses a low-cost material represented by the composition formula (1), and by reducing the material, the reversible capacity and the irreversible capacity are controlled, and the material after the reduction treatment. By forming the positive electrode using the above, it is possible to effectively obtain the battery performance in combination with a high-capacity negative electrode, for example, a negative electrode containing silicon or silicon oxide.

As one example, a material obtained by mixing a material (A1) having the maximum reversible capacity by the reduction treatment and a material (A0) before the reduction treatment is used as a positive electrode material, and a material containing silicon oxide is used as a negative electrode to form a cell. The results of evaluating the capacity are shown in Table 2 (corresponding to the results of Examples 1 to 3 described later).

Table 2 shows the results of changing the mixing ratio of A0 and A1 to 30%: 70%, 50%: 50%, and 70%: 30%. According to this result, the highest cell capacity (265 mAh / g) was obtained when the mixing ratio was 50%: 50%, and this value is the value when A0 or A1 is used alone as the positive electrode material (Table). It is larger than 1).

The most effective mixing ratio and degree of reduction vary depending on the characteristics of the negative electrode, mainly the irreversible capacity, but at least two types of materials are used as the positive electrode material to be mixed, and the reversible capacity value or irreversible capacity between the two materials is used. It is preferable that the difference between the values is sufficiently large, for example, 20 mAh / g or more.

The conditions for the difference between the reversible capacity value or the irreversible capacity value between the two materials to be sufficiently large, preferably 20 mAh / g or more, are the following three conditions (a), (a), described above, between the two materials. It is preferable to satisfy at least one of b) and (c).
(A) (-3 3 1) Difference in X-ray diffraction angle (2θ) of peak is 0.05 ° or more (b) Difference in oxygen amount is 5% or more (c) Sum of occupancy of transition metals (g _total ) The difference between the two materials is 0.01 or more, and the difference between the X-ray diffraction angles (2θ) of the two materials is more preferably 0.06 ° or more.
Regarding the condition (b), it is more preferable that the difference in the amount of oxygen is 6% or more.
Regarding the condition (c), it is more preferable that the difference in the _{sum of occupancy rates (g total) of the transition metals is 0.015 or more.}

According to FIG. 2, among the peaks of X-ray diffraction, when the difference in the X-ray diffraction angle (2θ) of the (-3 3 1) peak is 0.05 ° or more, a sufficient capacitance difference is obtained, and further, FIG. Therefore, a sufficient volume difference can be obtained when the difference in oxygen content is 5% or more, and from FIG. 3, a sufficient volume difference is obtained when the difference in the sum of occupancy rates (g _total ) of the transition metals is 0.01 or more. Can be obtained.
That is, more effective results can be obtained by using a material obtained by mixing at least two kinds of materials satisfying any of the above three conditions as the main component of the positive electrode.

The above example is the result of using a mixture of the material A1 having the maximum reversible capacity by the reduction treatment and the material A0 before the reduction treatment. However, if the material has been reduced, the reversible capacity is particularly high. It does not have to be the maximum. Further, in the above example, the material A0 before the reduction of A1 was used as the material to be mixed with A1, but another material (B0) before the reduction treatment satisfying the composition formula (1) and the material B1 obtained by the reduction treatment thereof. , B2 ,. .. .. May be mixed with.

That is, the material before the reduction treatment satisfying the composition formula (1) is A0, and the material after the reduction treatment is A1, A2 ,. .. .. Then, another material B0 before the reduction treatment and the material after the reduction treatment satisfying the composition formula (1) are referred to as B1 and B2. .. .. .. Then, A1 and A0, A2 ,. .. .. , B0, B1, B2 ,. .. .. An effective effect can be expected by using a mixed material with at least one material selected from the group consisting of the above as the main component of the positive electrode material.

In the above example, when the mixing ratio is 50%: 50%, the reversible capacity and the irreversible capacity of the mixed material are intermediate values between A0 and A1, but the degree of reduction is adjusted when A0 is reduced. Therefore, if the reversible capacity and the irreversible capacity are set to values close to this mixed material, the same characteristics can be obtained only with the material (A2) reduced by the degree of reduction.

Whether to use a mixed material or a single material having an adjusted degree of reduction can be determined by the cost of the reduction treatment.

For example, in many cases, when the cost of the reduction treatment largely depends on the amount of the material to be reduced and hardly depends on the degree of reduction, a mixed material having a mixing ratio of 50%: 50% can be used. Since the amount of the required reducing material is halved as compared with the case where the material having the adjusted degree of reduction is used alone, the cost required for the reduction treatment can be suppressed to halving.

(Effects of Embodiments of the present invention)
According to the embodiment of the present invention, even if a negative electrode material containing silicon or silicon oxide, which is difficult to use as it is because of its high capacity but large irreversible capacity, is used, the capacity of the original positive electrode is sufficiently sufficient. Can be demonstrated. Therefore, it is possible to provide a lithium ion secondary battery cell having a high energy density exceeding 300 Wh / kg.

Further, according to the embodiment of the present invention, it is possible to reduce the cost of the positive electrode and the negative electrode in the lithium ion secondary battery.

First, regarding the positive electrode, the material represented by the composition formula (1) is originally a material capable of extremely low cost. The reason is that it is possible to reduce the ratio of high-cost Co among the elements Mn, Ni, Fe, and Co contained as transition metals, and even if the Co content is zero, high-capacity lithium ion secondary This is because it is possible to form a battery. Further, as described above, if the mixed material is used, the cost required for the reduction treatment can be suppressed.

Regarding the cost of the negative electrode, techniques for reducing the irreversible capacity of the negative electrode material containing silicon and silicon oxide have been proposed, but they require additional treatment for the material, resulting in extra cost. However, according to the embodiment of the present invention, since it is not necessary to perform a special treatment, it is possible to suppress the cost of the negative electrode.

(Structure of lithium ion secondary battery and its manufacturing method)
Next, the lithium ion secondary battery according to the embodiment of the present invention and the method for manufacturing the lithium ion secondary battery will be further described with reference to the drawings.

FIG. 4 shows a lithium ion secondary battery according to an embodiment of the present invention, and FIG. 5 is a cross-sectional view taken along the line AA'of FIG.

In FIG. 4, reference numeral 410 indicates a positive electrode tab, reference numeral 420 indicates a negative electrode tab, and the positive electrode connected to the positive electrode tab, the negative electrode connected to the negative electrode tab, the separator arranged between them, and the electrolytic solution are metal laminated. It is packed by sheet 550.

In FIG. 5, reference numeral 510 is a positive electrode having positive electrode active material layers formed on both sides of the current collector, reference numeral 520 is a negative electrode having positive electrode active material layers formed on both sides of the current collector, and reference numeral 530 is a separator. .. The positive electrode active material layer contains a lithium transition metal composite oxide according to the embodiment of the present invention, and the negative electrode active material layer contains silicon oxide as a main component. The positive electrode and the negative electrode have a structure in which the positive electrode and the negative electrode are alternately laminated with a separator in between. The entire laminated structure of the positive electrode and the negative electrode is packed with a metal laminate sheet (550), and an electrolytic solution (540) is injected.

Next, a method of manufacturing a lithium ion secondary battery according to the present embodiment will be described with reference to FIGS. 6 to 12.

The positive electrode material (positive electrode active material) is obtained by subjecting a powdered lithium transition metal composite oxide (A0) satisfying the composition formula (1) to a reduction treatment.

The reduction treatment is possible, for example, by mixing an organic substance with the above powder and heat-baking. As the organic substance, for example, lithium acetate, sucrose, polyethylene glycol (PEG) and the like can be used. In this case, thermal firing can be performed in an atmosphere of an inert gas such as nitrogen or argon gas.

In this case, the degree of reduction is determined by the concentration of the organic matter to be mixed and the temperature of the heat firing. The higher the concentration of the organic matter and the higher the temperature of the heat firing, the higher the degree of reduction.

From FIG. 2, in order to obtain a positive electrode material having a reversible capacity of 240 mAh / g or more, among the X-ray diffraction peaks, the diffraction angle (2θ) of the (3 3 1) peak is 64.9 ° to 65.1. Must be °.
Further, from FIG. 1, in order to obtain a material in the range of the diffraction angle (2θ), the amount of oxygen in the composition of the material after the reduction treatment is 85% or more and 100% of the amount of oxygen in the composition of the material before the reduction. Must be in the range less than%.
Further, from FIG. 3 after the reduction treatment, in order for the reversible capacity to be 240 mAh / g or more, the transition metal occupancy sum (g _total ) obtained by Rietveld analysis of the X-ray diffraction data of the material after the reduction treatment. Must be 0.72 or higher.

Further, in order to obtain the material (A1) having the largest reversible capacity and the smallest irreversible capacity, the amount of oxygen in the composition after the reduction treatment is about 90% of the amount of oxygen in the composition before the reduction treatment. It is desirable to set the degree of reduction so as to be, for example, 88 to 97% is preferable, 88 to 95% is more preferable, and 89 to 93% is further preferable.
Of the X-ray diffraction peaks of the material A1, the position of the peak due to diffraction from the (-3 3 1) plane is preferably around 65 °, for example, 64.94 ° to 65.06 ° is preferable, and 64.95 ° is preferable. ° to 65.05 ° is more preferred, and 64.96 ° to 65.04 ° is even more preferred.
_{Further, the total} transition metal occupancy (g total) obtained by Rietveld analysis of the X-ray diffraction data is preferably 0.735 or more, more preferably 0.74 or more, and further preferably 0.75 or more. preferable.

The material A1 obtained above and the material A0 before the reduction treatment can be mixed and used as the main component of the positive electrode material. In this case, since the amount of oxygen in the composition of A1 is 90% of the amount of oxygen in the composition of A0, the difference in the amount of oxygen between A1 and A0 is 10% (= 100-90) under the above-mentioned desirable conditions. A certain condition (b) that the amount of oxygen has a difference of 5% or more is satisfied.

Further, among the X-ray diffraction peaks of the material A0 before the reduction treatment, the position of the peak due to diffraction from the (3 3 1) plane was 65.09 °, so that the (-3 3 1) peaks of A1 and A0 The difference in angle is 0.09 ° (= 65.09-65), which satisfies the above-mentioned desirable condition (a) of having a difference of 0.05 ° or more.

Further, when the X-ray diffraction data of the material powder _{was Rietveld analyzed by the Li 2} MnO ₃ crystal structure model belonging to the symmetric group C2 / m, the sum of the occupancy of the transition metals (g _total ) was obtained. _{While the g total of the} previous material (A0) was 0.72, that of the material (A1) after the reduction treatment increased to about 0.76, so that the occupancy of the transition metals between A1 and A0 The difference in sum (g _total ) is 0.04 (= 0.76-0.72), which satisfies the above-mentioned desirable condition (c) of 0.01 or more.

The above example is the case where A1 and A0 are used, but instead of A0, other materials having different degrees of reduction (A0, A2, ..., B0, B1, B2, ...) And A1 are used. be able to. For example, when A2 (a material obtained by reducing A0) is used instead of A0, the amount of oxygen in the composition of A2 (the number of atoms of the amount of oxygen in the composition of A2 relative to the amount of oxygen in the composition of A0 before the reduction treatment). Percentage) is preferably greater than 97%, more preferably 98% or more, and even more preferably 99% or more, from the viewpoint of satisfying the conditions (a), (b), and (c). Further, when a material (B1, B2, ...) obtained by reducing B0 (a material having a composition of the formula (1) but having a composition different from that of A0 before the reduction treatment) is used instead of A0, the amount of oxygen is also used. It is preferable to use a material having a large value (low degree of reduction).

The positive electrode can be formed, for example, as follows. First, a slurry of a positive electrode material is obtained by mixing a small amount of a binder and a conductive auxiliary agent with a positive electrode material (for example, a material obtained by mixing A1 and A0), mixing an organic solvent, and kneading. Polyvinylidene fluoride (PVDF) or the like can be used as the binder, and carbon black or the like can be used as the conductive auxiliary agent. The slurry is applied to both sides of the metal foil of the current collector 601 shown in FIG. 6 to form the positive electrode active material layer shown by reference numeral 701 in FIG. 7, and the positive electrodes shown in FIGS. 7 and 8 are obtained. FIG. 8 is a cross-sectional view taken along the line AA'in FIG. 7, in which positive electrode active material layers 801-1 and 801-2 are formed on both sides of the current collector 802.

The negative electrode can be formed, for example, as follows. First, a negative electrode material, for example, silicon oxide powder and a binder are mixed, and an organic solvent is mixed and kneaded to obtain a slurry of the negative electrode material. This slurry is applied to both sides of the metal foil of the current collector 902 shown in FIG. 9 to form a positive electrode active material layer shown by reference numeral 1001 in FIG. 10, and a negative electrode shown in FIGS. 10 and 11 is obtained. FIG. 11 is a cross-sectional view taken along the line AA'in FIG. 10, in which positive electrode active material layers 1101-1 and 1101-2 are formed on both sides of the current collector 1102.

Next, as shown in FIG. 12, the obtained negative electrode and the positive electrode are alternately laminated with the separator sandwiched between them to form a laminated body.

Next, the take-out portion of the positive electrode current collector and the take-out portion of the negative electrode current collector are collectively welded together with a metal tab by an ultrasonic welder. As shown in FIG. 4, the cell structure shown in FIG. 4 is formed by packing the entire tab with a metal laminate sheet (450) and injecting an electrolytic solution so that a part of the tab (410, 420) is exposed to the outside. Can be obtained.

As the above-mentioned positive electrode material, a material whose surface is partially coated with an oxide of at least one kind of metal can be used. At least a part thereof may be coated with an oxide of at least one kind of metal. This makes it possible to suppress the reaction between the positive electrode and the electrolytic solution during the charge / discharge cycle, suppress gas generation, and prevent a decrease in the capacity retention rate. The metal oxide includes an oxide of at least one metal selected from the group consisting of La, Pr, Nd, Sm, and Eu, or a group consisting of La, Pr, Nd, Sm, and Eu. A composite oxide of at least one metal selected and at least one metal selected from the group consisting of Ge, Mo, Zr, Al and V can be used.

An ionic liquid may be added to the electrolytic solution. As a result, it is possible to suppress gas generation during the charge / discharge cycle and further prevent a decrease in the capacity retention rate. As the ionic liquid, a pyridinium salt, an imidazolium salt, or the like can be used.

Hereinafter, embodiments of the present invention will be further described.

<Positive electrode>
As the positive electrode of the lithium ion secondary battery, one in which a positive electrode active material layer containing a positive electrode active material and a binder is formed on a positive electrode current collector can be used.

As the positive electrode active material, the above-mentioned positive electrode material (lithium transition metal composite oxide) is used. The positive electrode active material may be used alone or in combination of two or more.

A conductive auxiliary agent may be added to the positive electrode active material layer for the purpose of lowering the impedance. Examples of the conductive auxiliary agent include graphites such as natural graphite and artificial graphite, and carbon blacks such as acetylene black, ketjen black, furnace black, channel black, and thermal black. As the conductive auxiliary agent, a plurality of types may be appropriately mixed and used. The amount of the conductive auxiliary agent is preferably 1 to 10% by mass with respect to the positive electrode active material.

The binder for the positive electrode is not particularly limited, and examples thereof include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer and the like. Further, styrene-butadiene copolymer rubber, polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamideimide and the like may be used as the binder for the positive electrode. In particular, from the viewpoint of versatility and low cost, it is preferable to use polyvinylidene fluoride as a binder for the positive electrode. The amount of the positive electrode binder used is preferably 2 to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material from the viewpoint of "sufficient binding force" and "high energy", which are in a trade-off relationship. ..

As the positive electrode current collector, a general one can be arbitrarily used, and for example, an aluminum foil, a lath plate made of stainless steel, or the like can be used.

For the positive electrode, for example, a mixture of a positive electrode active material, a conductive auxiliary agent, and a binder, to which a solvent such as N-methylpyrrolidone is added and kneaded, is applied to a current collector by a doctor blade method, a die coater method, or the like. It can be produced by drying.

<Negative electrode>
As the negative electrode of the lithium ion secondary battery, for example, one in which a negative electrode polar active material layer containing a negative electrode polar active material and a binder is formed on a negative electrode electrode current collector can be used.

Examples of the negative electrode active material include lithium metal, a metal or alloy capable of alloying with lithium, an oxide capable of storing and releasing lithium, a carbon material, and a negative electrode active material containing silicon.

Examples of the metal or alloy that can be alloyed with lithium include lithium-silicon and lithium-tin. Examples of oxides capable of storing and releasing lithium include niobium pentoxide (Nb ₂ O ₅ ), titanium titanium composite oxide (Li _4/3 Ti _5/3 O ₄ ), and titanium dioxide (Tio _2). ) Etc. can be mentioned. Examples of the carbon material capable of occluding and releasing lithium include a carbonaceous material such as graphite material, carbon black, coke, mesocarbon microbeads, hard carbon, and graphite. Examples of the graphite material include artificial graphite and natural graphite. Examples of carbon black include acetylene black and furnace black.

Among the above-mentioned negative electrode active materials, a carbonaceous material is preferable because it has good cycle characteristics and safety, and also has excellent continuous charging characteristics. As the negative electrode active material, the above-mentioned one type may be used alone, or two or more types may be used in combination in any combination and ratio.

Further, in the present embodiment, a negative electrode active material containing silicon may be used. For example, examples of the negative electrode active material containing silicon include silicon and a silicon compound. Examples of silicon include simple substance silicon. Examples of the silicon compound include a compound of silicon and a transition metal such as a silicon oxide, a silicate, a nickel silicide, and a cobalt silicide.

The silicon compound is preferably used from the viewpoint of charge / discharge cycle characteristics because it relaxes the expansion / contraction of the negative electrode active material itself due to repeated charge / discharge. Further, depending on the type of silicon compound, there is a function of ensuring continuity between silicons. From this point of view, a silicon oxide is preferably used as the silicon compound of the negative electrode active material.

The silicon oxide is not particularly limited, but is represented by, for example, SiO _x (0 <x ≦ 2). The silicon oxide may contain lithium. Silicon oxide containing lithium is expressed by e.g. _{SiLi y O z (y> 0,2} >z> 0).

Further, the silicon oxide may contain a trace amount of metal element or non-metal element. The silicon oxide can contain, for example, 0.1 to 5% by mass of one or more elements selected from among nitrogen, boron and sulfur. By containing a trace amount of metal element or non-metal element in the silicon oxide, the electric conductivity of the silicon oxide can be improved. Further, the silicon oxide may be crystalline or amorphous.

Further, the negative electrode active material preferably contains a carbon material capable of occluding and releasing lithium ions in addition to silicon or silicon oxide. The carbon material can also be contained in a composite state with silicon or silicon oxide. Similar to silicon oxide, the carbon material has a function of alleviating expansion and contraction of the negative electrode active material itself due to repeated charging and discharging, and ensuring continuity between silicon, which is the negative electrode active material. The coexistence of silicon and / and silicon oxide with the carbon material provides better cycle characteristics.

As the carbon material, graphite, amorphous carbon, diamond-like carbon, carbon nanotubes and the like can be used alone or in combination. Graphite with high crystallinity has high electrical conductivity, and is excellent in adhesiveness to a positive electrode current collector made of a metal such as copper and voltage flatness. On the other hand, amorphous carbon having low crystallinity has a relatively small volume expansion, so that it has a high effect of alleviating the volume expansion of the entire negative electrode, and deterioration due to non-uniformity such as grain boundaries and defects is unlikely to occur. The content of the carbon material in the negative electrode active material is preferably 2% by mass or more and 50% by mass or less, and more preferably 2% by mass or more and 30% by mass or less.

When silicon oxide is used as the silicon compound, the negative electrode active material containing silicon and a silicon compound is produced, for example, by mixing simple silicon and silicon oxide and sintering them under high temperature and reduced pressure. be able to. When a compound of a transition metal and silicon is used as the silicon compound, for example, the elemental silicon and the transition metal are mixed and melted, or the surface of the elemental silicon is coated with the transition metal by vapor deposition or the like. Can be made.

In addition to the above-mentioned method for producing a negative electrode active material, a composite with carbon can also be combined. For example, in a high-temperature non-oxygen atmosphere, a coating layer containing carbon is formed around the core of elemental silicon and silicon oxide by introducing a mixed sintered product of elemental silicon and a silicon compound into the gas atmosphere of an organic compound. can do. Further, for example, by mixing a mixed sintered product of elemental silicon and silicon oxide and a carbon precursor resin in a high-temperature non-oxygen atmosphere, a coating layer composed of carbon is formed around the core of elemental silicon and silicon oxide. Can be formed. By forming a coating layer containing carbon around the cores of elemental silicon and silicon oxide in this way, it is possible to obtain the effect of suppressing volume expansion and further improving the cycle characteristics with respect to charge and discharge.

When silicon is used as the negative electrode active material, a composite containing silicon, a silicon oxide, and a carbon material (hereinafter, also referred to as “Si / SiO / C complex”) is preferable.

Further, the silicon oxide preferably has an amorphous structure in whole or in part. The amorphous structure silicon oxide can suppress the volume expansion of other negative electrode active materials such as carbon material and silicon. Although this mechanism is not clear, it is presumed that the amorphous structure of the silicon oxide has some effect on the formation of a film at the interface between the carbon material and the electrolytic solution. Further, it is considered that the amorphous structure has relatively few elements due to non-uniformity such as grain boundaries and defects.

It can be confirmed by X-ray diffraction measurement that all or part of the silicon oxide has an amorphous structure. When the silicon oxide does not have an amorphous structure, a peak peculiar to the silicon oxide is strongly observed in the X-ray diffraction measurement. On the other hand, when all or a part of the silicon oxide has an amorphous structure, the peak peculiar to the silicon oxide becomes broad in the X-ray diffraction measurement.

In the Si / SiO / C complex, it is preferable that all or part of silicon is dispersed in the silicon oxide. By dispersing at least a part of silicon in the silicon oxide, the volume expansion of the negative electrode as a whole can be further suppressed, and the decomposition of the electrolytic solution can also be suppressed. It should be noted that the fact that all or part of the silicon is dispersed in the silicon oxide can be confirmed by using the transmission electron microscope observation and the energy dispersive X-ray spectroscopy measurement together. Specifically, the cross section of the sample is observed with a transmission electron microscope, and the oxygen concentration of the silicon portion dispersed in the silicon oxide is measured by energy dispersive X-ray spectroscopy measurement. As a result, it can be confirmed that the silicon dispersed in the silicon oxide is not an oxide.

In the Si / SiO / C complex, for example, all or part of the silicon oxide has an amorphous structure, and all or part of the silicon is dispersed in the silicon oxide. Such a Si / SiO / C complex can be produced, for example, by a method as disclosed in Japanese Patent Application Laid-Open No. 2004-47404. That is, the Si / SiO / C complex can be obtained, for example, by performing a CVD treatment on a silicon oxide in an atmosphere containing an organic gas such as methane gas. The Si / SiO / C composite obtained by such a method has a form in which the surface of particles made of silicon oxide containing silicon is coated with carbon. In addition, silicon is nanoclustered in silicon oxide.

The ratio of silicon, silicon oxide, and carbon material in the Si / SiO / C complex is not particularly limited, but the composition is preferably as follows. The amount of silicon is preferably 5% by mass or more and 90% by mass or less, and more preferably 20% by mass or more and 50% by mass or less, based on the Si / SiO / C complex. The silicon oxide is preferably 5% by mass or more and 90% by mass or less, and more preferably 40% by mass or more and 70% by mass or less with respect to the Si / SiO / C complex. The carbon material is preferably 2% by mass or more and 50% by mass or less, and more preferably 2% by mass or more and 30% by mass or less with respect to the Si / SiO / C complex.

Further, the Si / SiO / C composite may be a mixture of elemental silicon, silicon oxide and carbon material, and may also be produced by mixing elemental silicon, silicon oxide and carbon material by mechanical milling. it can. For example, the Si / SiO / C complex can be obtained by mixing a simple substance silicon, a silicon oxide, and a carbon material in the form of particles.

For example, the average particle size of elemental silicon can be smaller than the average particle size of carbon materials and silicon oxides. In this way, elemental silicon with a large volume change has a relatively small particle size during charging and discharging, and carbon materials and silicon oxides with a small volume change have a relatively large particle size. Micronization of silicon is suppressed more effectively. Further, in the process of charging and discharging, lithium is occluded and released in the order of large particle size particles, small particle size particles, and large particle size particles, and from this point as well, residual stress and residual strain are generated. It is suppressed.

The average particle size of elemental silicon is preferably, for example, 20 μm or less, and more preferably 15 μm or less. Further, the average particle size of silicon oxide is preferably 1/2 or less of the average particle size of carbon material, and the average particle size of elemental silicon is 1/2 or less of the average particle size of silicon oxide. preferable. Furthermore, the average particle size of silicon oxide is 1/2 or less of the average particle size of carbon material, and the average particle size of elemental silicon is 1/2 or less of the average particle size of silicon oxide. preferable. If the average particle size is controlled within the above range, the effect of alleviating volume expansion can be obtained more effectively, so that a secondary battery having an excellent balance of energy density, cycle life and efficiency can be obtained. More specifically, graphite is used as the carbon material, the average particle size of silicon oxide is 1/2 or less of the average particle size of graphite, and the average particle size of elemental silicon is 1/1 of the average particle size of silicon oxide. It is preferably 2 or less. The average particle size of simple silicon, silicon oxide, etc. is measured by a measuring method such as a laser diffraction scattering method or a dynamic light scattering method.

Further, as the negative electrode active material, a material obtained by treating the surface of the above-mentioned Si / SiO / C complex with a silane coupling agent or the like may be used.

The active material layer of the negative electrode preferably contains the above-mentioned negative electrode active material capable of occluding and releasing lithium ions as a main component. Specifically, the content of the negative electrode active material is preferably 55% or more of the total weight of the active material layer containing the negative electrode active material, the binder for the negative electrode, and various auxiliary agents as needed. , 65% or more is more preferable.

The binder for the negative electrode is not particularly limited, but for example, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, and styrene-butadiene copolymer. Rubber (SBR), polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamideimide and the like can be used. Further, as the binder for the negative electrode, polyacrylic acid or carboxymethyl cellulose containing an alkali-neutralized lithium salt, sodium salt or potassium salt can be used. Of these, polyimide, polyamide-imide, SBR, and polyacrylic acid or carboxymethyl cellulose containing an alkali-neutralized lithium salt, sodium salt, and potassium salt are preferable because of their strong binding property. The amount of the negative electrode binder used is preferably 5 to 25 parts by mass with respect to 100 parts by mass of the negative electrode active material from the viewpoint of "sufficient binding force" and "high energy", which are in a trade-off relationship. ..

Any general material can be used as the material of the current collector of the negative electrode, and for example, a metal material such as copper, nickel, or stainless steel is used. Of these, copper is particularly preferable from the viewpoint of ease of processing and cost. Further, it is preferable that the surface of the current collector of the negative electrode is roughened in advance. Further, the shape of the current collector is arbitrary, and examples thereof include a foil shape, a flat plate shape, and a mesh shape. It is also possible to use a perforated type current collector such as expanded metal or punching metal.

The negative electrode was made into a slurry by adding a solvent to a mixture of the above-mentioned negative electrode active material, a binder, and various auxiliary agents as needed, as in the case of the positive electrode active material layer, and kneading the mixture. It can be produced by applying the coating liquid to the current collector and drying it.

<Non-aqueous electrolyte>
The electrolytic solution used in the lithium ion secondary battery according to the embodiment of the present invention mainly contains a non-aqueous organic solvent (also referred to as “non-aqueous solvent”) and an electrolyte salt.

As the non-aqueous solvent, a general solvent can be appropriately selected. For example, examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, chain esters, lactones, ethers, sulfones, nitriles, phosphate esters and the like. Among these, cyclic carbonates and chain carbonates are preferable.

Specific examples of cyclic carbonates include propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, vinyl ethylene carbonate and the like.

Specific examples of chain carbonates include dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, methylisopropyl carbonate, methylbutyl carbonate and the like.

Specific examples of chain esters include methyl formate, methyl acetate, methyl propionate, ethyl propionate, methyl pivalate, ethyl pivalate and the like.

Specific examples of lactones include γ-butyrolactone, δ-valerolactone, α-methyl-γ-butyrolactone and the like.

Specific examples of ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1, 2-Dibutoxyethane and the like can be mentioned.

Specific examples of sulfones include sulfolanes, 3-methylsulfolanes, 2,4-dimethylsulfolanes and the like.

Specific examples of nitriles include acetonitrile, propionitrile, succinonitrile, glutaronitrile, adiponitrile, and the like.

Specific examples of the phosphate esters include trimethyl phosphate, triethyl phosphate, tributyl phosphate, trioctyl phosphate and the like.

The non-aqueous solvent may be used alone or in combination of two or more. Examples of the combination of a plurality of types of non-aqueous solvents include a combination of cyclic carbonates and chain carbonates, cyclic carbonates and chain carbonates, and as a third solvent, chain esters, lactones, and ethers. , Nitriles, sulfones, and phosphate esters are added. Above all, in order to realize excellent battery characteristics, a combination containing at least cyclic carbonates and chain carbonates is more preferable.

Further, a fluorinated ether solvent, a fluorinated carbonate solvent, a fluorinated phosphate ester and the like may be added as a third solvent to the combination of the cyclic carbonates and the chain carbonates.

Examples of the fluorinated ether solvent include fluorinated ether represented by the following general formula (3).

(In the formula, R ¹ and R ² are independently alkyl groups or fluorine-containing alkyl groups, and ^{at least one of R 1} and R ² is a fluorine-containing alkyl group.)

Specific examples of the fluorinated ether-based solvent include CF ₃ OCH ₃ , CF ₃ OC ₂ H ₅ , F (CF ₂ ) ₂ OCH ₃ , F (CF ₂ ) ₂ OC ₂ H ₅ , F (CF ₂ ) ₃ OCH ₃ , F (CF ₂ ) ₃ OC ₂ H ₅ , F (CF ₂ ) ₄ OCH ₃ , F (CF ₂ ) ₄ OC ₂ H ₅ , F (CF ₂ ) ₅ OCH ₃ , F (CF ₂ ) ₅ OC ₂ H ₅ , F (CF ₂ ) ₈ OCH ₃ , F (CF ₂ ) ₈ OC ₂ H ₅ , F (CF ₂ ) ₉ OCH ₃ , CF ₃ CH ₂ OCH ₃ , CF ₃ CH ₂ OCHF ₂ , CF ₃ CF ₂ CH ₂ OCH ₃ , CF ₃ CF ₂ CH ₂ OCHF ₂ , CF ₃ CF ₂ CH ₂ O (CF ₂ ) ₂ H, CF ₃ CF ₂ CH ₂ O (CF ₂ ) ₂ F, HCF ₂ CH ₂ OCH ₃ , H (CF ₂ ) ₂ OCH ₂ CH ₃ , H (CF ₂ ) ₂ OCH ₂ CF ₃ , H (CF ₂ ) ₂ CH ₂ OCHF ₂ , H (CF ₂ ) ₂ CH ₂ O (CF ₂ ) ₂ H, H (CF ₂ ) ₂ CH ₂ O (CF ₂ ) ₃ H, H (CF ₂ ) ₃ CH ₂ O (CF ₂ ) ₂ H, H (CF ₂ ) ₄ CH ₂ O (CF ₂ ) ₂ H, (CF _{3) ) 2 CHOCH 3, (CF 3} ) 2 CHCF 2 OCH 3, CF 3 CHFCF 2 OCH 3, CF 3 CHFCF 2 OCH 2 CH 3, CF 3 CHFCF 2 CH 2 OCHF 2, CF 3 CHFCF 2 CH 2 OCH 2 CF 2 _{CF 3, H (CF 2)} 2 CH 2 OCF 2 CHFCF 3, CHF 2 CH 2 OCF 2 CFHCF 3, F (CF 2) 2 CH 2 OCF 2 CFHCF 3, CF 3 (CF 2) 3 fluorine such as OCHF ₂ Examples include ethers.

Examples of the fluorinated carbonate solvent include fluoroethylene carbonate, fluoromethylmethyl carbonate, 2-fluoroethylmethyl carbonate, ethyl- (2-fluoroethyl) carbonate, (2,2-difluoroethyl) ethyl carbonate, and bis (2). Examples thereof include fluorinated carbonates such as −fluoroethyl) carbonate and ethyl- (2,2,2-trifluoroethyl) carbonate.

As the fluorinated phosphate ester solvent, tris phosphate (2,2,2-trifluoroethyl), tris phosphate (trifluoromethyl), tris phosphate (2,2,3,3-tetrafluoropropyl) Fluorinated phosphoric acid esters such as.

Specific examples of the electrolyte salt used other than the pyridinium salt are not particularly limited, but LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ F) ₂ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO 2 CF 3) 2, LiN (SO ₂ C ₂ F ₅ ) ₂ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, LiAsF _{6 , LiAlCl 4} , LiSbF ₆ , LiPF ₄ (CF ₃ ) ₂ , LiPF ₃ (C ₂ F ₅ ) ₃ , LiPF ₃ (CF ₃ ) ₃ , (CF ₂ ) ₂ (SO ₂ ) ₂ NLi, (CF ₂ ) ₃ (SO ₂ ) ₂ Li, Lithium bis (oxate) boronate, Lithium oxa Examples thereof include lithium difluoro (oxalato) boronate. Among the above-mentioned electrolytes, LiPF ₆ , LiBF ₄ , LiN (SO ₂ F) ₂ , LiN (SO ₂ CF ₃ ) ₂ , and LiN (SO ₂ C ₂ F ₅ ) ₂ are particularly preferable. The above-mentioned electrolyte salts may be used alone or in combination of two or more.

The concentration of the above-mentioned electrolyte salt dissolved in the non-aqueous solvent in the non-aqueous electrolyte solution is preferably 0.1 to 3 M (mol / L) with respect to the non-aqueous solvent, and is 0.5 to 2 M. More preferably.

In addition, the non-aqueous electrolytic solution can optionally contain general components as other components. For example, vinylene carbonate, maleic anhydride, ethylene sulfate, boronic acid ester, 1,3-propanesulton, 1,5,2,4-dioxadithian-2,2,4,4-tetraoxide and the like are other components. Is listed as.

<Separator>
The separator is not particularly limited, but a polyolefin such as polypropylene or polyethylene, a single-layer or laminated porous film such as aramid or polyimide, or a non-woven fabric can be used. Further, as an inorganic material, a separator using glass fiber can be mentioned. Further, coating of different materials on polyolefin or laminated film can also be used. An example of coating a polyolefin with a different material is a polyolefin base material coated with a fluorine compound or inorganic fine particles. Moreover, as an example of the laminated film, the one in which the polyethylene base material and the polypropire layer are laminated, and the one in which the polyolefin base material and the aramid layer are laminated are mentioned.

The thickness of the separator is preferably 5 to 50 μm, more preferably 10 to 40 μm in terms of the energy density of the battery and the mechanical strength of the separator.

<Structure of lithium-ion secondary battery>
The structure of the lithium ion secondary battery is not particularly limited, and the above configuration can be used for a coin battery having a single-layer or laminated separator, a cylindrical battery, a laminated battery, and the like.

For example, as in the above-mentioned example shown in FIGS. 4 and 5, in the case of a laminated laminate type lithium ion battery, a positive electrode, a separator, and a negative electrode are alternately laminated, and each electrode is connected to a metal terminal called a tab. It can be put in a container made of a laminated film, which is an exterior body, and sealed by injecting an electrolytic solution.

The laminated film can be appropriately selected as long as it is stable in the electrolytic solution and has sufficient water vapor barrier properties. For example, aluminum, silica, polypropylene coated with alumina, polyethylene, or the like can be used as the laminate film. In particular, from the viewpoint of suppressing volume expansion, it is preferable to use it as a laminated film coated with aluminum.

A typical layer structure of the laminated film includes a structure in which a metal thin film layer and a heat-sealing resin layer are laminated. In addition, as a typical layer structure of the laminated film, a protective layer made of a film such as polyester or polyamide such as polyethylene terephthalate is further provided on the surface opposite to the heat-sealed resin layer of the metal thin film layer. A laminated layer structure can be mentioned. When sealing the battery element, the heat-sealing resin layers are opposed to each other to surround the battery element. As the metal thin film layer, for example, a foil having a thickness of 10 to 100 μm, such as Al, Ti, Ti alloy, Fe, stainless steel, or Mg alloy, is used.

The resin used for the heat-sealing resin layer of the laminated film is not particularly limited as long as it is a resin capable of heat-sealing. For example, polypropylene, polyethylene, an acid modified product of polypropylene or polyethylene, polyester such as polyphenylene sulfide and polyethylene terephthalate, polyamide, ethylene-vinyl acetate copolymer and the like are used as the heat-sealing resin layer. Further, an ethylene-methacrylic acid copolymer or an ionomer resin in which an ethylene-acrylic acid copolymer is intermolecularly bonded with a metal ion is also used as the heat-sealing resin layer. The thickness of the heat-sealing resin layer is preferably 10 to 200 μm, more preferably 30 to 100 μm.

Hereinafter, embodiments of the present invention will be specifically described with reference to examples.

(Example 1)
First, the positive electrode material (positive electrode active material) was obtained by subjecting a powdery lithium transition metal composite oxide (A0) satisfying the composition formula (1) to a reduction treatment.

As the material (A0), a powder of a lithium iron-manganese-based composite oxide represented by _{Li 1.26} Mn _0.52 Fe _0.11 Ni _0.11 O _{2 was prepared.}

An aqueous solution of an organic substance was prepared in order to carry out a reduction treatment. As an organic substance, polyethylene glycol was used, and an aqueous solution was prepared in which 6 parts by mass of polyethylene glycol was dissolved in 100 parts by mass of water with respect to 100 parts by mass of the composite oxide (A0).

This aqueous solution was mixed with the powder of the composite oxide (A0), stirred, dried, and then heat-calculated in a nitrogen atmosphere at 350 ° C. for 60 minutes. Thereby, the material (A1) having the largest reversible capacity and the smallest irreversible capacity can be obtained.

When the oxygen content of the powder before and after the reduction treatment was measured by the IR combustion method, the oxygen content (atomic number percentage) in the composition after the reduction treatment was reduced by about 10% as compared with that before the reduction treatment. The difference in the amount of oxygen in the compositions of A0 and A1 was 10%, which satisfied the above-mentioned desirable condition of having a difference in the amount of oxygen of 5% or more.

Further, when the powder before and after the reduction treatment was analyzed by X-ray diffraction, it was observed that the peak position (X-ray diffraction angle 2θ) after the reduction treatment was shifted to the low angle side, and among the peaks (3 3 1). The position of the peak due to diffraction from the plane was 65.09 ° for the material A0 before the reduction treatment, but decreased to 65.000 ° after the reduction treatment. The difference between the (-3 3 1) peak angles of A0 and A1 was 0.09 °, which satisfied the condition of having an angle difference of 0.05 ° or more, which is the above-mentioned desirable condition.

_{Further, when the X-ray diffraction data was Rietveld analyzed by the Li 2} MnO ₃ crystal structure model belonging to the symmetric group C2 / m, the sum of the occupancy rates (g _total ) of the transition metals was obtained. g _tota l of A0) whereas a 0.72, g _total material after the reduction treatment (A1) had increased to about 0.76. _{The difference in g total} between A0 and A1 was 0.04, which satisfied the above-mentioned desirable condition of having a difference in _{g total of 0.01 or more.}

The material A1 obtained above and the material A0 before the reduction treatment are mixed at a mass ratio of 1: 1, and 4% by mass of polyvinylidene fluoride (PVDF) and 4% by mass of carbon black are further added to the total mass. After mixing, N-methyl-2-pyrrolidone (NMP) was added, mixed and kneaded to obtain a slurry of positive electrode material. This slurry was applied onto a current collector of an aluminum foil having a thickness of 20 μm as shown in FIG. 6 and dried to form a positive electrode active material layer. The coating area was set to both sides of the area shown in FIG. 701, and the coating thickness was set to 50 μm on one side. By the above method, a positive electrode as shown in FIGS. 7 and 8 was formed.

Regarding the negative electrode, a slurry of a negative electrode material was prepared by mixing an organic solvent with a mixture of 85% by mass of silicon oxide (SiO) powder and 15% by mass of polyamic acid. This slurry was applied onto a current collector of a copper foil having a thickness of 10 μm as shown in FIG. The coating area was both sides of the area shown in 1001 of FIG. 10, and the coating thickness was 20 μm on one side. The negative electrode after coating was heat-treated at 350 ° C. for 3 hours in a nitrogen atmosphere to cure the polyamic acid, thereby forming the negative electrode as shown in FIGS. 10 and 11.

Next, as shown in FIG. 12, the obtained negative electrode and the positive electrode were alternately laminated with the separator sandwiched between them to form a laminated body. As the separator, a porous thin film made of polypropylene having a thickness of 25 μm was used.

Next, the taken-out portion of the positive electrode current collector and the taken-out portion of the negative electrode current collector of the laminated body were collectively welded together with a metal tab by an ultrasonic welding machine. As shown in FIG. 4, a part (410, 420) of the tabs of the positive electrode and the negative electrode is exposed to the outside, the whole is wrapped with a metal laminate sheet (450), an electrolytic solution is injected into the inside, and heat fusion is performed. The cell structure shown in FIG. 5 was obtained by sealing with. As the metal laminate sheet, an aluminum foil coated on both sides with polyethylene was used. _{As the electrolytic solution, a solution prepared by dissolving lithium hexafluorophosphate (LiPF 6} ) in a solvent of ethylene carbonate and diethyl carbonate at a concentration of about 1 mol / l was used.

<Activation treatment>
The lithium ion secondary battery before the activation treatment is charged to 4.5 V with a current of 20 mA / g per positive electrode material, and then discharged to 1.5 V with a current of 20 mA / g per positive electrode material, which is repeated four times. It was. Then, the sealing portion of the exterior body was once broken, the gas inside the secondary battery was released by reducing the pressure, and the lithium ion secondary battery was manufactured by resealing.

<Evaluation of lithium-ion secondary battery>
The lithium ion secondary battery was charged to 4.5 V with a constant current of 0.1 C in a constant temperature bath at 45 ° C., and further charged with a constant voltage of 4.5 V until the current reached 0.25 C. Then, the lithium ion secondary battery was discharged to 1.5 V with a current of 0.1 C to obtain the capacity of the secondary battery. The volume obtained was 265 mAh / g.

(Example 2)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the material A0 and the material A1 were mixed at a mass ratio of 3: 7 (A0: A1). When the capacity of the formed lithium ion secondary battery was measured, a value of 257 mAh / g was obtained.

(Example 3)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the material A0 and the material A1 were mixed at a mass ratio of 7: 3 (A0: A1). When the capacity of the formed lithium ion secondary battery was measured, a value of 255 mAh / g was obtained.

(Example 4)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that only A1 was used as the positive electrode active material (A0 was not used). When the capacity of the formed lithium ion secondary battery was measured, a value of 245 mAh / g was obtained.

(Comparative Example 1)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that only A0 was used as the positive electrode active material (A1 was not used). When the capacity of the formed lithium ion secondary battery was measured, a value of 240 mAh / g was obtained.

As shown in Table 3, Examples 1 to 4 using the positive electrode active material material (A1) subjected to the reduction treatment are compared with Comparative Example 1 using only the positive electrode active material material (A0) not subjected to the reduction treatment. , It can be seen that the capacity value is high.
Further, as in Examples 1 to 3, when the positive electrode active material (A1) subjected to the reduction treatment and the positive electrode active material (A0) not subjected to the reduction treatment were mixed, only the positive electrode active material material (A1) was used. It can be seen that the capacity value is further improved as compared with Example 4.

The reason why the capacity of the cell using the mixed positive electrode of A1 and A0 is larger than the capacity of the cell using the single positive electrode of A1 or A0 is related to the irreversible capacity of the SiO negative electrode, and is considered as follows.
A0 has a small reversible capacity and a large irreversible capacity. A part of this large irreversible capacitance becomes the irreversible capacitance of the SiO negative electrode. Therefore, in the cell using the A0 single positive electrode and the SiO negative electrode (Comparative Example 1), a capacity corresponding to the reversible capacity (240 mAh / g) of A0 can be obtained.
On the other hand, A1 has a large reversible capacity and a small irreversible capacity. Since the irreversible capacity is small, in addition to the irreversible capacity of A1, a part of Li ions corresponding to the reversible capacity is taken by the irreversible capacity of the SiO negative electrode. Therefore, the capacity of the cell (Example 4) using the A1 single positive electrode and the SiO negative electrode is smaller (245 mAh / g) than the reversible capacity (290 mAh / g) of A1.
In contrast to these cases, the positive electrode of the mixed system of A1 and A0 has a reversible capacity improved by mixing A1 as compared with A0 alone, and has a certain degree of irreversible capacity due to the presence of A0. When a certain amount of irreversible capacitance is present, the amount of Li ions corresponding to the reversible capacitance is not taken by the irreversible capacitance of the SiO negative electrode (Examples 1 and 3: the capacitance value of the positive electrode is the same as the capacitance value of the cell) or the amount taken is small. (Example 2: The capacity value of the cell is slightly smaller than the capacity value of the positive electrode). Therefore, in the cell using the mixed positive electrode of A1 and A0 and the SiO negative electrode (Examples 1 to 3), the effect of increasing the reversible capacity by mixing A1 is sufficiently reflected, and the single positive electrode of A1 or A0 is used. It is considered that the capacity of the cell is larger than that of the existing cell (Example 4, Comparative Example 1).

According to the embodiment of the present invention, it is possible to provide a lithium ion secondary battery having a high energy density, that is, a light weight and a high capacity, at a low cost. The lithium-ion secondary battery according to the present embodiment can be used, for example, in an electric vehicle that requires a long cruising range on a single charge, a drone that requires a long operating time, a robot, a mobile terminal, and the like.

701, 801-1, 801-2: Positive electrode active material layer 702, 802: Positive electrode current collector 1001, 1101-1, 1101-2: Negative electrode active material layer 902, 1002: Negative electrode current collector 510, 1210: Positive electrode 520 , 1220-1, 1220-2: Negative electrode 530, 1230-1, 1230-2: Separator 410: Positive electrode tab 420: Negative electrode tab 450, 550: Metal laminate sheet 540: Electrolyte

Claims (14)

A method for producing a positive electrode for a lithium ion secondary battery containing a positive electrode containing a lithium transition metal composite oxide, a negative electrode, and an electrolyte.
The lithium transition metal composite oxide has a layered rock salt type structure and has the following formula (1):
Li _x M1 _(y-p) Mn _p M2 _(z-q) Fe _q O _(2-δ) (1)
(Here, M1 is at least one element of Ti and Zr, M2 is at least one element selected from the group consisting of Co, Ni and Mn, 1.05 ≦ x ≦ 1.32, 0.33 ≦ y ≦ 0. .63, 0.06 ≤ z ≤ 0.50, 0 <p ≤ 0.63, 0 ≤ q ≤ 0.50, 0 ≤ δ ≤ 0.80, y ≥ p, z ≥ q)
Has a composition represented by
A1 materials subjected to different reduction treatment of reducing the degree to the material one A0 of true on SL composition formula (1), respectively, A2,. .. .. age,
B1, B2, and the like, which are the other materials B0 applicable to the above composition formula (1), which have been subjected to reduction treatments having different degrees of reduction, respectively. .. .. When
A1 and A0, A2 other than A1 ,. .. .. , B0, B1, B2 ,. .. .. Including the step of mixing with at least one or more materials selected from the group consisting of to form a mixed material.
Among the materials forming the mixed material, the difference in the amount of oxygen (percentage of atoms) in the composition differs by 5% or more with respect to at least one material other than A1.
The amount of oxygen in the composition of the material subjected to the reduction treatment (atomic number percentage) is in the range of 85% or more and less than 100% with respect to the amount of oxygen in the composition of the material before the reduction treatment. A method for manufacturing a positive electrode for a battery. Among the materials forming the mixed material, the difference in the diffraction angle (2θ) of the peak (3 3 1) by X-ray diffraction is 0.05 ° or more with respect to A1 and at least one other material. The method for manufacturing a positive electrode for a lithium ion secondary battery according to claim 1 . Based on the results obtained by Rietveld analysis of the X-ray diffraction data of each material forming the mixed material with a crystal model of the space group c2 / m, at each site of 4h site, 4g site, 2b site, and 2c site. The occupancy rate (g) of the transition metal is g _4h , g _4g , g _2b , g _{2c, respectively} ), and the following equation (2) :
g _total = (2g _4h + g _2c ) / 3 + (2g _4g + g _2b ) / 3 Equation (2)
When the sum of transition metal occupancy rates (g _total ) is calculated by
The material according to claim 1 or 2 , wherein _{the difference in the sum of transition metal occupancy (g total} ) is 0.01 or more with respect to A1 and at least one other material among the materials forming the mixed material. A method for manufacturing a positive electrode for a lithium ion secondary battery. Claims 1 to 3 in which the amount of oxygen (atomic number percentage) in the composition of the material A1 subjected to the reduction treatment is in the range of 88 to 95% with respect to the amount of oxygen in the composition of the material before the reduction treatment. The method for manufacturing a positive electrode for a lithium ion secondary battery according to any one of the above. A method for producing a positive electrode for a lithium ion secondary battery containing a positive electrode containing a lithium transition metal composite oxide, a negative electrode, and an electrolyte.
The lithium transition metal composite oxide has a layered rock salt type structure and has the following formula (1):
Li _x M1 _(y-p) Mn _p M2 _(z-q) Fe _q O _(2-δ) (1)
(Here, M1 is at least one element of Ti and Zr, M2 is at least one element selected from the group consisting of Co, Ni and Mn, 1.05 ≦ x ≦ 1.32, 0.33 ≦ y ≦ 0. .63, 0.06 ≤ z ≤ 0.50, 0 <p ≤ 0.63, 0 ≤ q ≤ 0.50, 0 ≤ δ ≤ 0.80, y ≥ p, z ≥ q)
Has a composition represented by
A0, A2, and the like, which are one of the materials applicable to the above composition formula (1) and which have been subjected to a reduction treatment having a different degree of reduction, respectively. .. .. age,
B1, B2, and the like, which are the other materials B0 applicable to the above composition formula (1), which have been subjected to reduction treatments having different degrees of reduction, respectively. .. .. When
A1 and A0, A2 other than A1 ,. .. .. , B0, B1, B2 ,. .. .. Including the step of mixing with at least one or more materials selected from the group consisting of to form a mixed material.
Among the materials forming the mixed material, the difference in the diffraction angle (2θ) of the peak (3 3 1) by X-ray diffraction is 0.05 ° or more with respect to A1 and at least one other material. ,
Manufacture of positive electrode for lithium ion secondary battery in which the diffraction angle (2θ) of the peak (2θ) by X-ray diffraction of the material subjected to the reduction treatment is in the range of 64.9 ° to 65.1 °. Method. The lithium ion according to claim 5, wherein the diffraction angle (2θ) of the (3 3 1) peak of the material A1 subjected to the reduction treatment by X-ray diffraction is in the range of 64.95 ° to 65.05 °. A method for manufacturing a positive electrode for a secondary battery. A method for producing a positive electrode for a lithium ion secondary battery containing a positive electrode containing a lithium transition metal composite oxide, a negative electrode, and an electrolyte.
The lithium transition metal composite oxide has a layered rock salt type structure and has the following formula (1):
Li _x M1 _(y-p) Mn _p M2 _(z-q) Fe _q O _(2-δ) (1)
(Here, M1 is at least one element of Ti and Zr, M2 is at least one element selected from the group consisting of Co, Ni and Mn, 1.05 ≦ x ≦ 1.32, 0.33 ≦ y ≦ 0. .63, 0.06 ≤ z ≤ 0.50, 0 <p ≤ 0.63, 0 ≤ q ≤ 0.50, 0 ≤ δ ≤ 0.80, y ≥ p, z ≥ q)
Has a composition represented by
A0, A2, and the like, which are one of the materials applicable to the above composition formula (1) and which have been subjected to a reduction treatment having a different degree of reduction, respectively. .. .. age,
B1, B2, and the like, which are the other materials B0 applicable to the above composition formula (1), which have been subjected to reduction treatments having different degrees of reduction, respectively. .. .. When
A1 and A0, A2 other than A1 ,. .. .. , B0, B1, B2 ,. .. .. Including the step of mixing with at least one or more materials selected from the group consisting of to form a mixed material.
Based on the results obtained by Rietveld analysis of the X-ray diffraction data of each material forming the mixed material with a crystal model of the space group c2 / m, at each site of 4h site, 4g site, 2b site, and 2c site. The occupancy rate (g) of the transition metal is g _4h , g _4g , g _2b , g _2c ), respectively, and the following (2):
g _total = (2g _4h + g _2c ) / 3 + (2g _4g + g _2b ) / 3 Equation (2)
When the sum of transition metal occupancy rates (g _total ) is calculated by
_{Among the materials forming the mixed material, the difference in the sum of transition metal occupancy (g total} ) is 0.01 or more with respect to A1 and at least one other material.
A method for producing a positive electrode for a lithium ion secondary battery, wherein the sum of transition metal occupancy (g _{total) of the material subjected to the reduction treatment is 0.72 or more.} The method for producing a positive electrode for a lithium ion secondary battery according to claim 7, wherein the sum of transition metal occupancy (g _{total) of the material A1 subjected to the reduction treatment is 0.74 or more.} The method for producing a positive electrode for a lithium ion secondary battery according to any one of claims 1 to 8, wherein the material (A0, B0) before the reduction treatment has δ in the composition formula (1) of 0. .. The positive electrode for a lithium ion secondary battery according to any one of claims 1 to 9, wherein the mixing ratio (mass ratio) of A1 and at least one other material is 3: 7 to 7: 3. Manufacturing method. The method for producing a positive electrode for a lithium ion secondary battery according to any one of claims 1 to 10, wherein the reduction treatment is carried out by mixing organic substances and heat firing. The method for producing a positive electrode for a lithium ion secondary battery according to claim 11, wherein the organic substance is polyethylene glycol. A method for manufacturing a lithium ion secondary battery containing a positive electrode containing a lithium transition metal composite oxide, a negative electrode, and an electrolyte.
A method for manufacturing a lithium ion secondary battery, which comprises a step of forming a positive electrode by the manufacturing method according to any one of claims 1 to 12. The method for manufacturing a lithium ion secondary battery according to claim 13, wherein the negative electrode contains silicon or silicon oxide as a negative electrode active material.

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