WO2017164237A1

WO2017164237A1 - Positive-electrode active material for non-aqueous-electrolyte secondary cell and method for manufacturing same, positive-electrode material paste for non-aqueous-electrolyte secondary cell, and non-aqueous-electrolyte secondary cell

Info

Publication number: WO2017164237A1
Application number: PCT/JP2017/011450
Authority: WO
Inventors: 治朗岡田; 相田　平; 小向　哲史
Original assignee: 住友金属鉱山株式会社
Priority date: 2016-03-24
Filing date: 2017-03-22
Publication date: 2017-09-28

Abstract

The purpose of the present invention is to provide a positive-electrode active material for a non-aqueous-electrolyte secondary cell with which it is possible to improve the stability of a positive-electrode material paste when manufacturing a non-aqueous-electrolyte secondary cell, and with which it is possible to improve the cell capacity and output characteristics when configuring a secondary cell. The problem is addressed using a method for manufacturing a positive-electrode active material for a non-aqueous-electrolyte secondary cell, etc. provided with mixing of water with a firing powder comprising a lithium composite metal oxide having a layered structure crystalline structure, and drying of the mixture obtained by mixing; and for which the firing powder contains secondary particles formed by agglomerating primary particles, and the water is mixed in an amount such that when 5 g of the obtained positive-electrode active material is dispersed in 100 ml of purified water, and the supernatant liquid after standing still for 10 minutes is measured, the pH at 25°C is in the range of 11-11.9.

Description

Non-aqueous electrolyte secondary battery positive electrode active material and method for producing the same, non-aqueous electrolyte secondary battery positive electrode mixture paste, and non-aqueous electrolyte secondary battery

The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery and a method for producing the same, a positive electrode mixture paste for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery.

In recent years, with the widespread use of portable electronic devices such as mobile phones and notebook computers, the development of small and lightweight secondary batteries with high energy density is strongly desired. In addition, development of secondary batteries having excellent output characteristics and charge / discharge cycle characteristics is strongly desired as batteries for electric vehicles including hybrid cars.

As a secondary battery satisfying such requirements, a non-aqueous electrolyte secondary battery can be cited, and a lithium ion secondary battery can be cited as a typical non-aqueous electrolyte secondary battery. A lithium ion secondary battery is composed of a negative electrode, a positive electrode, an electrolyte, and the like, and an active material for the negative electrode and the positive electrode is made of a material that can desorb and insert lithium.

Lithium ion secondary batteries are currently being actively researched and developed. Among them, lithium ion secondary batteries using a layered or spinel type lithium metal composite oxide as a positive electrode material have a high 4V class. Since a voltage can be obtained, the practical application is progressing as a battery having a high energy density.

As positive electrode active materials that have been mainly proposed so far, lithium cobalt composite oxide (LiCoO ₂ ) that is relatively easy to synthesize, lithium metal composite oxide (LiNiO ₂ ) using nickel that is cheaper than cobalt, Examples thereof include lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) and lithium manganese composite oxide (LiMn ₂ O ₄ ) using manganese. In order to further improve the charge / discharge cycle characteristics, for example, it is effective to contain lithium in excess of the stoichiometric composition with respect to metal elements such as nickel, cobalt, and manganese.

By the way, the positive electrode of the nonaqueous electrolyte secondary battery is, for example, a positive electrode obtained by mixing a positive electrode active material, a binder such as polyvinylidene fluoride (PVDF), and a solvent such as normal methyl-2-pyrrolidone (NMP). It is formed by applying a composite paste to a current collector such as an aluminum foil. At this time, lithium liberated from the positive electrode active material in the positive electrode mixture paste may react with moisture contained in the binder to generate lithium hydroxide. The generated lithium hydroxide and the binder may react to cause gelation of the positive electrode mixture paste. Gelation of the positive electrode mixture paste causes poor operability and yield. This tendency becomes remarkable when the lithium in the positive electrode active material is in excess of the stoichiometric ratio and the ratio of nickel is high.

Some attempts have been made to suppress gelation of the positive electrode composite paste. For example, Patent Document 1 discloses Li _x Ni _1-y A _y O ₂ (0.98 ≦ x ≦ 1.06, 0.05 ≦ y ≦ 0.30, A is at least one of Co and Al). The positive electrode active material for a non-aqueous electrolyte secondary battery in which 5 g is stirred and mixed in 100 g of pure water for 120 minutes and then left to stand for 30 seconds, and the pH of the supernatant is 12.7 or less at 25 ° C. Has been proposed. It is described that this positive electrode active material has fluidity and excellent gelation resistance even after 24 hours have passed since the slurry (positive electrode mixture paste) was produced.

Patent Document 2 proposes a positive electrode composition for a non-aqueous electrolyte secondary battery including a positive electrode active material composed of a lithium transition metal composite oxide and additive particles composed of particles composed of acidic oxide particles. Yes. In this positive electrode composition, lithium hydroxide generated by reacting with moisture contained in the binder preferentially reacts with the acidic oxide, suppressing the reaction between the generated lithium hydroxide and the binder, It is described that gelation is suppressed. Further, the acidic oxide plays a role as a conductive agent in the positive electrode, lowers the resistance of the whole positive electrode, and contributes to the improvement of the output characteristics of the battery.

Patent Document 3 also provides a lithium transition metal oxide containing LiOH outside the composition as the positive electrode active material; grasping the molar amount P of LiOH contained per gram of the positive electrode active material; Prepare 0.05 mol or more of tungsten oxide in terms of tungsten atom per mol of LiOH with respect to the amount P; and knead the positive electrode active material and tungsten oxide together with the conductive material and the binder in an organic solvent. A method for producing a lithium ion secondary battery has been proposed.

On the other hand, some attempts have been made to obtain lithium ion secondary batteries excellent in output characteristics and charge / discharge cycle characteristics. For example, it is known that the positive electrode active material is excellent in output characteristics and charge / discharge cycle characteristics by being composed of particles having a small particle size and a narrow particle size distribution. This is because particles having a small particle size have a large specific surface area, and when used as a positive electrode active material, a sufficient reaction area with the electrolytic solution can be secured, and the positive electrode is made thin, This is because the movement distance between the positive electrode and the negative electrode can be shortened, so that the positive electrode resistance can be reduced. In addition, the particles having a narrow particle size distribution can equalize the voltage applied to the particles in the electrode, and therefore it is possible to suppress a decrease in battery capacity due to the selective deterioration of the fine particles.

In order to further improve the output characteristics and charge / discharge cycle characteristics, for example, it has been reported that it is effective to make the positive electrode active material have a hollow structure. Since such a positive electrode active material can increase the reaction area with the electrolyte compared to a solid positive electrode active material having the same particle size, the positive electrode resistance can be greatly reduced. .

For example, in Patent Document 4 and Patent Document 5, transition metal composite hydroxide particles serving as a precursor of a positive electrode active material are mainly divided into two stages: a nucleation process for mainly nucleation and a particle growth process for mainly particle growth. Discloses a method for producing by a crystallized reaction clearly separated. In these methods, the pH value of the aqueous reaction solution is adjusted to a particle temperature within a range of 12 or more (for example, 12.0 to 13.4 or 12.0 to 14.0) in the nucleation step, based on a liquid temperature of 25 ° C. In the process, it is controlled to be lower than the nucleation process and 12 or less (for example, 10.5 to 12.0). The reaction atmosphere is an oxidizing atmosphere at the initial stage of the nucleation step and the particle growth step, and is switched to a non-oxidizing atmosphere at a predetermined timing.

By these methods, the obtained transition metal composite hydroxide particles have a small particle size, a narrow particle size distribution, a low-density central portion composed of fine primary particles, and a high density composed of plate-like or needle-like primary particles. And the outer shell. Therefore, when such transition metal composite hydroxide particles are fired, the low density center portion is greatly contracted, and a space portion is formed inside. The particle properties of the composite hydroxide particles are inherited by the positive electrode active material. It is said that secondary batteries using these positive electrode active materials can improve capacity characteristics, output characteristics, and charge / discharge cycle characteristics.

Regarding the improvement of output characteristics, for example, Patent Document 6 discloses an alkaline solution in which a tungsten compound is dissolved in a lithium metal composite oxide powder composed of primary particles and secondary particles formed by aggregation of the primary particles. Adding and mixing the first step of dispersing W on the surface of the lithium metal composite oxide powder or the primary particles of the powder, the alkali solution in which the mixed tungsten compound is dissolved, and the lithium metal composite A positive electrode for a non-aqueous electrolyte secondary battery comprising a second step of forming fine particles containing W and Li on the surface of the lithium metal composite oxide powder or the surface of primary particles of the powder by heat-treating the oxide powder. A method for producing an active material has been proposed.

According to this proposal, it is said that a positive electrode active material for a non-aqueous electrolyte secondary battery capable of realizing high capacity and high output when used as a positive electrode material of a battery is obtained. However, although high power output has been studied, no investigation has been made on gelation suppression of the positive electrode mixture paste.

JP 2003-312222 A JP 2012-28313 A JP 2013-84395 A International Publication WO2012 / 131881 International Publication WO2014 / 181891 JP 2012-077944 A

However, the proposal of the above-mentioned Patent Document 1 merely provides a condition that allows a positive electrode active material for a lithium secondary battery that is stable for a long time in a slurry (positive electrode mixture paste) to be practically determined. It is insufficient as a measure for suppressing gelation of the composite paste. Moreover, in the proposal of the above-mentioned patent document 2, there is a fear that the separator is damaged and the safety is lowered due to the remaining acidic oxide particles. Moreover, it cannot be said that gelation suppression is sufficient. Further, even in the proposal of the above-mentioned Patent Document 3, it cannot be said that the problem regarding the breakage of the separator due to the remaining acidic oxide (for example, tungsten oxide) and the suppression of gelation are not solved.

Further, as proposed in Patent Document 4 and Patent Document 5 above, when the reaction area with the electrolyte is increased in order to improve output characteristics and charge / discharge cycle characteristics, gelation of the positive electrode mixture paste is promoted. New problems may arise. Furthermore, in the proposal of the above-mentioned Patent Document 6, although the output characteristics have been studied, no study has been made on the gelation suppression of the positive electrode mixture paste. Therefore, although some of the above proposals have been examined with regard to the suppression of gelation of the positive electrode mixture paste and the improvement of battery characteristics, it cannot be said that the problem has been sufficiently solved.

In view of the above-mentioned problems, the present invention improves the stability of the positive electrode mixture paste when producing a non-aqueous electrolyte secondary battery, and satisfies the output characteristics and cycle characteristics when the secondary battery is configured. It aims at providing the positive electrode active material for nonaqueous electrolyte secondary batteries which can improve discharge capacity simultaneously, and its manufacturing method. Another object of the present invention is to provide a positive electrode mixture paste using such a positive electrode active material and a non-aqueous electrolyte secondary battery.

In order to solve the above-mentioned problems, the present inventor has intensively studied on the gelation suppression and output characteristics of the positive electrode mixture paste for the non-aqueous electrolyte secondary battery. As a result, the present inventors used the positive electrode mixture paste as a positive electrode active material. The lithium metal composite oxide is greatly influenced by the pH of the lithium metal composite oxide and the form of the compound in which excess lithium is formed on the surface of the lithium metal composite oxide particles. It was found that the pH can be controlled and the reaction resistance of the positive electrode active material can be reduced to improve the output characteristics. Furthermore, the present invention was completed by obtaining the knowledge that the form of the compound formed by excess lithium can be controlled by mixing and drying water in the lithium metal composite oxide.

In a first aspect of the present invention, the method comprises mixing a fired powder made of a lithium metal composite oxide having a layered crystal structure and water, and drying the mixture obtained by the mixing. , baking powder, formula _{_{(1): Li s Ni 1}} -x-y-z Co x Mn y M 1 z O 2 ( however, 0.05 ≦ x ≦ 0.35,0 ≦ y ≦ 0.35 , 0 ≦ z ≦ 0.10, 0.95 ≦ s ≦ 1.50, M ¹ is represented by at least one element selected from V, Mg, Mo, Nb, Ti, W and Al), and primary The secondary particles formed by agglomeration of the particles contain water, and 5 g of the obtained positive electrode active material is dispersed in 100 ml of pure water, and the pH at 25 ° C. when measuring the supernatant after standing for 10 minutes is 25 ° C. A positive electrode active for a non-aqueous electrolyte secondary battery, in which an amount in the range of 11 to 11.9 is mixed. Method of manufacturing quality is provided.

Further, when mixing the calcined powder and water, it is preferable to add the water by spraying it to a droplet size of 1 to 2000 μm. Moreover, it is preferable to mix water in the range of 1 mass% or more and 35 mass% or less with respect to baked powder. Moreover, it is preferable to mix water in the range of 0.003 g / m ² or more and 0.025 g / m ² or less with respect to the surface area of the fired powder. Moreover, it is preferable to mix water in 1 mass% or more and 6 mass% or less with respect to baked powder. The fired powder preferably has an average particle size in the range of 3 μm to 15 μm, and [(d90−d10) / average particle size], which is an index indicating the spread of the particle size distribution, is 0.7 or less. Moreover, as for the baked powder, it is preferable that the area ratio which the space | gap measured by cross-sectional observation occupies is 4.5% or more and 60% or less with respect to the whole cross-sectional area of baked powder. Moreover, it is preferable to perform drying at 100 degreeC or more and 300 degrees C or less. The firing powder has the general formula _{_{(2): Li s Ni 1}} -x-y-z-t Co x Mn y M 2 z W t O 2 ( however, 0.05 ≦ x ≦ 0.35,0 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.10, 0.95 ≦ s ≦ 1.50, 0.0001 ≦ t ≦ 0.03, 0.0001 ≦ z + t ≦ 0.10, M ² is V, It is preferably represented by at least one element selected from Mg, Mo, Nb, Ti and Al.

According to a second aspect of the present invention, there is provided a positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium metal composite oxide powder having a layered crystal structure, wherein the lithium metal composite oxide powder has the general formula Li _s. Ni _1-xyz Co _x Mn _y M ¹ _z O ₂ (where 0.05 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.10, 0.95 ≦ s ≦ 1.50, M ¹ is represented by at least one element selected from V, Mg, Mo, Nb, Ti, W and Al), and includes secondary particles formed by aggregation of primary particles In addition, 5 g of the positive electrode active material is dispersed in 100 ml of pure water, and the pH at 25 ° C. when measuring the supernatant after standing for 10 minutes is 11 to 11.9, and the excess LiOH determined by the titration method mass ratio of excess _Li 2 CO ₃ (excess LiOH / surplus L ₂ CO ₃₎ is 0.45 or less, the positive electrode active material for a non-aqueous electrolyte secondary battery is provided.

The positive electrode active material preferably has a ratio of the amount of excess LiOH to excess Li ₂ CO ₃ of 0.3 or less. Further, the ratio of the amount of surplus LiOH and surplus Li ₂ CO ₃ is 0.18 or more, and the amount of surplus Li ₂ CO ₃ is 0.157 × 10 ⁻² g / m ^{2 with} respect to the surface area of the positive electrode active material. The following is preferable. The positive electrode active material has an average particle size in the range of 3 μm or more and 15 μm or less, and [(d90−d10) / average particle size], which is an index indicating the spread of the particle size distribution, is 0.7 or less. preferable. Moreover, it is preferable that the area ratio which the space | gap which is measured in the cross-sectional observation of lithium metal complex oxide powder occupies 4.5% or more and 60% or less with respect to the cross-sectional area of this lithium metal complex oxide particle whole. Further, the lithium metal composite oxide powder represented by the general formula _{_{_{Li s Ni 1-x-y}}} -z-t Co x Mn y M 2 z W t O 2 ( however, 0.05 ≦ x ≦ 0.35,0 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.10, 0.95 ≦ <s ≦ 1.50, 0.0001 ≦ t ≦ 0.03, 0.0001 ≦ z + t ≦ 0.10, M ² is V And at least one element selected from Mg, Mo, Nb, Ti and Al.

In the third aspect of the present invention, the positive electrode mixture paste for a non-aqueous electrolyte secondary battery includes the positive electrode active material for a non-aqueous electrolyte secondary battery.

In the fourth aspect of the present invention, a non-aqueous electrolyte secondary battery has a positive electrode containing the positive electrode active material for a non-aqueous electrolyte secondary battery.

According to the present invention, a positive electrode mixture slurry with high gel stability and high stability is obtained, and excellent output characteristics and cycle characteristics when used for a positive electrode material of a battery, and excellent charge / discharge capacity, It is possible to provide a positive electrode active material for a non-aqueous electrolyte secondary battery. Furthermore, the manufacturing method is easy and suitable for production on an industrial scale, and its industrial value is extremely large.

Drawing 1 is a figure showing an example of a manufacturing method of a cathode active material for nonaqueous system electrolyte rechargeable batteries of an embodiment. FIG. 2 is a schematic explanatory diagram of an impedance evaluation measurement example and an equivalent circuit used for analysis. FIG. 3 is a schematic cross-sectional view of a coin-type battery used for battery evaluation. FIG. 4 is a schematic explanatory diagram of a laminate cell used for battery evaluation. FIG. 5 is an example of a measurement result of ΔV by the current pause method used for low-temperature output evaluation.

Hereinafter, regarding the present embodiment, (1) a positive electrode active material for a non-aqueous electrolyte secondary battery, (2) a manufacturing method thereof, and (3) a positive electrode mixture paste for a non-aqueous electrolyte secondary battery using the positive electrode active material And (4) the non-aqueous electrolyte secondary battery will be described.

(1) Positive electrode active material for non-aqueous electrolyte secondary battery The non-aqueous electrolyte positive electrode active material of the present embodiment (hereinafter also referred to as “positive electrode active material”) is a lithium metal composite oxide powder having a layered crystal structure. (Hereinafter also referred to as “composite oxide powder”), and the lithium metal composite oxide powder has the general formula (1): Li _s Ni _1-xyZ Co _x Mn _y M ¹ _z O ₂ ( However, 0.05 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.10, 0.95 ≦ s ≦ 1.50, M ¹ is V, Mg, Mo, Nb, And at least one element selected from Ti, W, and Al), and includes secondary particles formed by aggregation of primary particles. Further, 5 g of the positive electrode active material is dispersed in 100 ml of pure water, and the pH at 25 ° C. when measuring the supernatant after standing for 10 minutes is 11 to 11.9, and excess LiOH determined by titration And the mass of surplus Li ₂ CO ₃ (surplus LiOH / surplus Li ₂ CO ₃ ) is 0.45 or less.

In the above general formula (1), s represents the atomic ratio of Li to the total of Ni, Co, Mn and M ^{1 in} the lithium metal composite oxide powder (Li / Me), and production of the lithium metal composite oxide powder The amount of Li added in the process is reflected. In the general formula (1), s satisfies 0.95 ≦ s ≦ 1.50, and preferably satisfies 1.00 <s <1.30. When the amount of Li is in the range of s, the battery capacity and output characteristics of the lithium metal composite oxide itself can be improved.

Composite oxide powder obtained by a normal production method (for example, lithium nickel composite oxide powder obtained by firing nickel composite hydroxide or nickel composite oxide and lithium compound) is a secondary particle. In addition, unreacted lithium compounds (surplus lithium compounds) exist on the surfaces of the primary particles. The surplus lithium compound may elute in the positive electrode mixture paste (hereinafter also referred to as “paste”) to raise the pH and cause the paste to gel. It is also conceivable that excess lithium is present inside the lithium metal composite oxide powder and is eluted into the paste to cause the paste to gel. In order to suppress gelation of the paste, the present inventors consider that it is important to suppress elution of excess lithium into the paste, and unreacted particles present on the surfaces of secondary particles and primary particles. We focused on the form of the lithium compound.

Examples of the surplus lithium compound existing on the surfaces of the secondary particles and the primary particles include unreacted LiOH (surplus LiOH) and unreacted Li ₂ CO ₃ (surplus Li ₂ CO ₃ ). Excess LiOH easily elutes into the paste and raises the pH of the paste to promote gelation. In addition, excessive lithium (Li) in the composite oxide powder may elute into the paste to form LiOH and raise the pH of the paste to cause gelation. Accordingly, surplus LiOH refers to a lithium source that can be in the form of LiOH during paste preparation, and includes secondary particles, unreacted LiOH on the surface of the primary particles, excess lithium inside the composite oxide powder, and the like. On the other hand, surplus Li ₂ CO ₃ is less likely to elute into the paste than LiOH and has a small effect of gelling the paste.

Therefore, the present inventors convert surplus LiOH into Li ₂ CO ₃ and immobilize it as surplus Li ₂ CO ₃ , thereby reducing elution of LiOH into the paste and suppressing paste gelation. The present invention has been completed on the basis of a novel idea that it may be possible. That is, the positive electrode active material of this embodiment has a mass ratio (LiOH / Li ₂ CO ₃ ) of surplus LiOH and surplus Li ₂ CO ₃ determined by a titration method of 0.45 or less, preferably 0.3. It is as follows. When LiOH / Li ₂ CO ₃ is in the above range, elution of lithium into the paste is reduced, gelation of the paste is suppressed, and reaction resistance of the positive electrode active material (hereinafter referred to as “positive electrode resistance”) ) Can be brought into a lower state, exhibiting better output and cycle characteristics and higher initial charge / discharge capacity. Note that the positive electrode active material of the present embodiment exhibits excellent characteristics not only at room temperature but also at a low temperature (eg, −20 ° C.). Further, the lower limit of LiOH / Li ₂ CO ₃ is preferably 0.10 or more, and more preferably 0.18 or more. When the lower limit is in the above range, it indicates that the LiOH is not excessively extracted and excessive Li ₂ CO ₃ is not generated, and the output characteristics and cycle characteristics are improved. It can be improved further. The reason for improving the battery characteristics as described above by converting surplus LiOH to Li ₂ CO ₃ and immobilizing it as surplus Li ₂ CO ₃ is not limited, but is considered as follows.

Surplus LiOH is normally thinly distributed on the secondary particle surface and primary particle surface of the composite oxide. Here, the surface of the primary particle means not only the surface of the primary particle exposed on the outer surface of the secondary particle, but also the space near and inside the surface of the secondary particle through which the electrolyte can penetrate through the outside of the secondary particle. It also includes the surface of the primary particles exposed to the surface. Furthermore, even if it is a grain boundary between primary particles, if the primary particle bonding is incomplete and the electrolyte solution can permeate, it is included in the primary particle surface.

Since elution of Li from surplus LiOH occurs at the contact surface (primary particle surface) with the electrolyte, the excess LiOH on the primary particle surface is converted to surplus Li ₂ CO ₃ and immobilized, thereby elution of Li. And the gelation of the paste can be suppressed.

In addition, excess LiOH present on the surface of the primary particles inhibits Li movement between the complex oxide crystal and the electrolytic solution. Therefore, by converting excess LiOH to excess Li ₂ CO ₃ and immobilizing it on the primary particle surface, by reducing the amount of excess LiOH, excess LiOH present on the primary surface or secondary particle surface is removed, and Li Is not hindered, and the charge / discharge capacity (hereinafter also referred to as “battery capacity”) when used in a battery can be improved.

Further, when the excess LiOH present on the primary particle surface is fixed as excess Li ₂ CO ₃ , it is once removed from the primary particle surface and eluted in the added water, and then as excess Li ₂ CO ₃ as the primary Li ₂ CO _3. It is thought that it aggregates on the particle surface. Therefore, the area of the surplus lithium compound (including surplus LiOH and surplus Li ₂ CO ₃ ) that covers the primary particle surface is reduced, the contact surface between the electrolyte and the primary particle surface is secured, and the movement of Li is promoted. Therefore, the positive electrode resistance is reduced, and further, the internal resistance of the secondary battery is reduced.

By reducing the resistance in the secondary battery, the voltage lost in the battery is reduced, and the voltage actually applied to the load side becomes relatively high, so a high output is obtained and the output characteristics are reduced. Can be improved. Note that the positive electrode active material of the present embodiment exhibits excellent characteristics not only at room temperature but also at a low temperature (eg, −20 ° C.). Further, since the voltage applied to the load side is increased, the insertion and extraction of lithium at the positive electrode is sufficiently performed, so that the battery capacity and cycle characteristics are improved. Furthermore, since the movement of Li becomes easy and the load received by the positive electrode active material during charge / discharge is reduced, the charge / discharge cycle characteristics are also excellent.

The amount of excess LiOH in the positive electrode active material is preferably 0.15% by mass or less, and more preferably 0.12% by mass or less with respect to the entire positive electrode active material. By reducing the amount of excess LiOH, gelation of the paste can be further suppressed and the battery capacity can be further improved.

The lower limit of the amount of excess LiOH is preferably 0.05% by mass or more with respect to the total amount of the positive electrode active material, from the viewpoint of suppressing deterioration of battery characteristics. When the excess LiOH becomes too small, it indicates that excessive lithium is extracted from the crystal of the lithium metal composite oxide particles when the excess LiOH is fixed as Li ₂ CO ₃ .

The amount of excess Li ₂ CO _{3 in} the positive electrode active material is preferably 0.200 × 10 ⁻² g / m ² or less with respect to the surface area of the positive electrode active material, preferably 0.157 × 10 ⁻² g / m ^2. It is more preferably ² or less, and further preferably 0.155 × 10 ⁻² g / m ² or less. By reducing the amount of surplus Li ₂ CO ₃ , the contact surface between the electrolytic solution and the primary particle surface is increased, the movement of Li is further promoted, and the positive electrode resistance can be further reduced. The lower limit of the amount of excess Li ₂ CO _{3 with} respect to the surface area of the positive electrode active material is not particularly limited, and is, for example, 0.100 × 10 ⁻² g / m ² or more.

The positive electrode active material of this embodiment has a pH of 11 or more and 11.9 or less at 25 ° C. when 5 g of the positive electrode active material is dispersed in 100 ml of pure water and the supernatant is measured after standing for 10 minutes. The degree of elution of the lithium into the paste is evaluated by dispersing 5 g of the positive electrode active material in 100 ml of pure water and measuring the pH of the supernatant after standing for 10 minutes.

In the positive electrode active material, the pH of the supernatant liquid at 25 ° C. (hereinafter, also simply referred to as “pH value of the positive electrode active material”) is controlled in the range of 11 or more and 11.9 or less, so that the paste becomes very gelled. To be suppressed. When the pH is less than 11, a large amount of excess Li ₂ CO ₃ is formed, and when lithium is extracted from the lithium metal composite oxide more than necessary, it is charged and discharged when used for the positive electrode of the battery. The capacity may decrease and the reaction resistance of the positive electrode may increase. From the viewpoint of further reducing lithium extraction and further reducing the positive electrode resistance, the lower limit of the pH value of the positive electrode active material is preferably 11.5 or more. On the other hand, when pH exceeds 11.9, it is in the state where there is much elution of lithium at the time of setting it as a paste, and it is difficult to suppress gelation of a paste. From the viewpoint of further suppressing elution of lithium and further suppressing gelation of the paste, the upper limit of the pH value of the positive electrode active material is preferably 11.8 or less.

The lithium metal composite oxide particles include secondary particles composed of aggregated primary particles. Further, the positive electrode active material may include primary particles present alone. The composite oxide particles can form lithium tungstate (LW compound) described later on the primary particle surfaces. Thereby, it is possible to improve the output characteristics while maintaining the charge / discharge capacity, and to obtain better cycle characteristics.

Lithium metal composite oxide powder represented by the general formula _{_{(2): Li s Ni 1}} -x-y-z-t Co x Mn y M 2 z W t O 2 ( however, 0.05 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.10, 0.95 ≦ s ≦ 1.50, 0.0001 ≦ t ≦ 0.03, 0.0001 ≦ z + t ≦ 0.10, M ² is It is preferable that it is represented by at least one element selected from V, Mg, Mo, Nb, Ti, and Al.

In the general formula (2), t represents the amount of tungsten (W) added to the lithium metal composite oxide. In the general formula (2), t is 0.0001 ≦ t ≦ 0.03, preferably 0.0003 ≦ t ≦ 0.02, and more preferably 0.0003 ≦ t ≦ 0.012. . When W is included in the above range t, in addition to improving the battery capacity and output characteristics of the lithium metal composite oxide itself, excess LiOH is converted to Li ₂ CO ₃ and immobilized on the surface of the primary particles. In this case, W eluted in the added water reacts with excess lithium eluted in the water, and lithium tungstate is formed, so that the positive electrode resistance can be reduced.

In the general formula (2), s represents the atomic ratio of Li to the total of Ni, Co, Mn, M ² and W (Li / Me) in the lithium metal composite oxide powder, and the lithium metal composite oxide powder This reflects the amount of Li added in the manufacturing process. S in the general formula (2) is preferably in the same range as s in the general formula (1).

The powder characteristics and particle structure of the positive electrode active material can also be selected from known lithium metal composite oxides according to the characteristics required for the battery. For example, the average particle diameter of the positive electrode active material is in the range of 3 μm or more and 15 μm or less, and [(d90−d10) / average particle diameter], which is an index indicating the spread of the particle size distribution, is preferably 0.7 or less. Thereby, filling property can be improved and the battery capacity per volume of a battery can be made higher. Further, the applied voltage between the lithium metal composite oxide particles can be made uniform, the load between the particles can be made uniform, and the cycle characteristics can be further improved.

The d10 means a particle size in which the number of particles in each particle size is accumulated from the smaller particle size side and the accumulated volume becomes 10% of the total volume of all particles. D90 means a particle diameter in which the number of particles is similarly accumulated and the accumulated volume is 90% of the total volume of all particles. The average particle diameter, d10 and d90 can be obtained from the volume integrated value measured with a laser light diffraction / scattering particle size analyzer. The average particle diameter Mv can be used as the average particle diameter, and can be determined using a laser light diffraction / scattering particle size analyzer in the same manner as d10 and d90.

In addition, the area ratio (porosity) occupied by the voids measured in the cross-sectional observation of the composite oxide powder is preferably 4.5% or more and 60% or less of the entire cross-sectional area of the secondary particles. When the porosity is in the above range, the positive electrode resistance reduction effect can be further increased while suppressing gelation of the paste. When the porosity is less than 4.5% of the entire cross-sectional area, a higher reduction effect of the positive electrode resistance may not be obtained. On the other hand, when the porosity exceeds 60%, the packing density may decrease, and the battery capacity per battery volume may not be sufficiently obtained. In addition, the whole cross-sectional area of a secondary particle is a cross-sectional area including the space | gap in a secondary particle.

The porosity can be measured by observing an arbitrary cross section of the secondary particles using a scanning electron microscope and analyzing the image. Specifically, a plurality of composite oxide particles are embedded in a resin, a cross-section polisher is used to prepare a cross-section sample, and the secondary electron cross-section can be observed with a scanning electron microscope, followed by image analysis. With software (for example, WinRoof 6.1.1 etc.), the void part in the secondary particle is detected in black for any 20 or more secondary particles, and the dense part in the contour of the secondary particle Is detected in white, the total area of the black part and the white part of the 20 or more secondary particles is measured, and the porosity is calculated by calculating the area ratio of [black part / (black part + white part)]. It can be calculated.

The specific surface area of the positive electrode active material is preferably 1 m ² / g or more and 50 m ² / g or less. When the specific surface area is less than 1 m ² / g, there is little contact with the electrolytic solution, and high output characteristics may not be obtained. Moreover, when a specific surface area exceeds 50 m < ² > / g, contact with electrolyte solution increases too much and suppression of gelatinization may not be enough. The specific surface area can be determined by the BET method using nitrogen gas adsorption.

The moisture content of the positive electrode active material is preferably 0.5% by mass or less, and more preferably 0.3% by mass or less. By controlling the moisture content of the positive electrode active material to 0.5% by mass or less, it is possible to suppress the formation of a film-like lithium compound on the surface by absorbing gas components including carbon and sulfur in the atmosphere, and an excellent battery. Characteristics can be obtained. In addition, the measured value of the said moisture rate is a measured value at the time of measuring with a Karl Fischer moisture meter on condition of vaporization temperature of 300 degreeC. In addition, the minimum of a moisture content is 0.01 mass% or more.

(2) Method for Producing Positive Electrode Active Material for Nonaqueous Electrolyte Secondary Battery The method for producing the positive electrode active material comprises mixing a fired powder made of a lithium metal composite oxide having a layered crystal structure and water ( Step S1) and drying the mixture obtained by the mixing (Step S2). Hereinafter, each step will be described with reference to the drawings.

FIG. 1 is a view showing an example of a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present embodiment (hereinafter also simply referred to as “a method for producing a positive electrode active material”). In addition, the following description is an example of a manufacturing method, Comprising: It does not limit to this method.

As shown in FIG. 1, in the method for producing a positive electrode active material, first, a fired powder made of a lithium metal composite oxide having a layered crystal structure and water are mixed (step S1). At this time, 5 g of the obtained positive electrode active material was dispersed in 100 ml of pure water, and the pH at 25 ° C. when the supernatant liquid after standing for 10 minutes was measured (hereinafter also simply referred to as “pH value of the positive electrode active material”). ) Is mixed with an amount of water in the range of 11 to 11.9.

In the mixing step (step S1), the fired powder and water are mixed so that the positive electrode active material has a pH value in the range of 11 to 11.9. In the mixing step, by mixing a predetermined amount of water, elution of lithium into the paste is suppressed in the paste using the obtained positive electrode active material. Although this reason is not limited, in the drying process (step S2) described later, surplus LiOH eluted in water reacts with carbon dioxide in the atmosphere to convert surplus LiOH in the fired powder into Li ₂ CO ₃ . Thus, it is considered that the excess LiOH-derived lithium is immobilized on the surface of the primary particles.

Further, from the viewpoint of further reducing lithium extraction and further reducing the positive electrode resistance, it is preferable to mix water so that the lower limit of the pH value of the positive electrode active material is 11.5 or more. On the other hand, from the viewpoint of further suppressing the elution of lithium and further suppressing the gelation of the paste, it is preferable to mix water so that the upper limit of the pH value is 11.8 or less.

The mixing of the fired powder and water can be performed, for example, by adding water to the fired powder and mixing. The amount of water added can be easily determined by collecting a small amount of the fired powder in advance and conducting a preliminary test to confirm the amount of water added. Moreover, if the manufacturing conditions of Li / Me and baked powder are stabilized, the pH value of the positive electrode active material can be controlled within the above-described range by the addition amount determined in the preliminary test.

The method for adding water is not particularly limited, and water may be added dropwise to the fired powder, or water may be added to the fired powder by spraying. In particular, it is preferable to add water by spraying the fired powder to a droplet size of 1 μm to 2000 μm. By adding water by spraying with fine droplets, water can be added uniformly by the calcined powder, the reaction between excess LiOH and carbon dioxide in the atmosphere can be made more uniform, and a higher output improvement effect and It becomes possible to obtain the gelation suppressing effect. Various sprays and ultrasonic humidifiers can be used as the water spraying method. The droplet size of water when spraying is preferably 1 μm or more and 2000 μm or less, and more preferably 5 μm or more and 1000 μm or less.

In addition, the mixture of the baked powder and water may be mixed after adding the baked powder water, or may be mixed while adding water, but in order to make the addition of water more uniform, water is added. It is more preferable to mix them.

The surplus LiOH amount varies depending on the atomic ratio of Li to the total of Ni, Co, Mn, and M (Li / Me) in the sintered powder of lithium metal composite oxide, or the production conditions of the sintered powder. The amount of water added may be an amount that allows the pH value of the positive electrode active material to be controlled within the above range by immobilizing these excess LiOH. Therefore, water may be added in a range where the pH value of the positive electrode active material is 11 or more and 11.9 or less.

The amount of water to be mixed in the mixing step (step S1) can be appropriately adjusted according to the powder characteristics and particle structure of the fired powder. It is preferable that Thereby, excess LiOH can be fixed and the elution of lithium can be further reduced. Further, with sufficient amount of water, the lithium metal composite oxide particles can be sufficiently permeated to the surface of primary particles inside the lithium metal composite oxide particles, and the fixation of surplus LiOH can be promoted uniformly between the lithium metal composite oxide particles. Capacity and output characteristics can be further improved. The amount of water mixed is more preferably 1% by mass or more and 6% by mass or less with respect to the fired powder. By optimizing the amount of water to be mixed, it is possible to further prevent lithium from being pulled out excessively while fixing excess LiOH, and to maximize the effect of improving the output characteristics at room temperature and low temperature. Is possible.

The surface area of the fired powder may vary depending on the composition of the fired powder and the manufacturing conditions. Accordingly, the surface area of the calcined powder to supply desired amounts of water may vary, it is more preferable to mix the water with 0.003 g / ^{m 2} or more 0.025 g / ^{m 2} or less of the range of the surface area.

Even when the pH value of the fired powder of the lithium metal composite oxide is 11 or more and 11.9 or less, by mixing water, aggregation by Li ₂ CO ₃ formation proceeds on the primary particle surface, and the paste The effect of stabilizing the battery capacity and improving the battery capacity and output characteristics can be obtained. In this case, water should just mix the quantity from which the pH of the positive electrode active material obtained becomes the range of 11-11. The mixing amount is not specifically limited, For example, 1 mass% with respect to baked powder, for example The above water can be mixed.

The calcined powder has the general formula (1): Li _s Ni _1-xyz Co _x Mn _y M ¹ _z O ₂ (where 0.05 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.10, 0.95 ≦ s ≦ 1.50, M is represented by at least one element selected from V, Mg, Mo, Nb, Ti, W and Al), and the primary particles are Secondary particles formed by aggregation are included. Since the powder characteristics and particle structure of the fired powder are inherited up to the positive electrode active material, the composition, powder characteristics, particle structure and the like of the fired powder can be the same as those of the positive electrode active material described above. Further, the fired powder is selected according to the positive electrode active material to be obtained.

Baking powder, formula _{_{(2): Li s Ni 1}} -x-y-z-t Co x Mn y M 2 z W t O 2 ( however, 0.05 ≦ x ≦ 0.35,0 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.10, 0.95 ≦ s ≦ 1.50, 0.0001 ≦ t ≦ 0.03, 0.0001 ≦ z + t ≦ 0.10, M is V, Mg, Mo And at least one element selected from Nb, Ti, and Al). In the general formula (2), t indicating the amount of tungsten (W) is 0.0001 ≦ t ≦ 0.03, preferably 0.0003 ≦ t ≦ 0.02, and more preferably 0.00. 0003 ≦ t ≦ 0.012. W added to the calcined powder is eluted in the water added in the mixing step and similarly reacts with lithium eluted in the water in the drying step to form lithium tungstate on the surface of the primary particles. Lithium tungstate reduces the positive electrode resistance and further improves the output characteristics.

As a preferred embodiment of the fired powder, like the positive electrode active material, the average particle diameter is in the range of 3 μm to 15 μm, and is an index indicating the spread of the particle size distribution [(d90−d10) / average particle diameter] is 0. .7 or less can be selected. The lower limit of [(d90−d10) / average particle diameter] is not particularly limited, but is about 0.25 or more. Moreover, it is preferable that the area ratio (void ratio) which the space | gap measured in the cross-sectional observation of baking powder occupies is 4.5% or more and 60% or less of the cross-sectional area of this lithium metal complex oxide particle.

An apparatus used for mixing the baked powder and water is not particularly limited, and a known apparatus can be used. For example, the mixing is performed using a mixer such as a shaker mixer, a Laedige mixer, a Julia mixer, or a V blender. It is only necessary that the calcined powder and moisture be sufficiently mixed.

Next, the mixture obtained by mixing is dried (step S2). This step dries the mixture of water and calcined powder, and removes excess LiOH (including excess lithium in the lithium metal composite oxide particles) dissolved in water in the mixture on the surface of the primary particles. To form fine aggregates. In this process, surplus LiOH reacts with carbon dioxide gas (CO ₂ ) in the atmosphere to become Li ₂ CO ₃ and is immobilized on the primary particle surface as surplus Li ₂ CO ₃ . Furthermore, since the surplus LiOH changes from a thin and widely distributed state on the primary particle surface to a state where surplus Li ₂ CO ₃ forms fine aggregates and is scattered, the primary particle surface and the electrolyte solution are changed. And the reaction field of Li ion intercalation reaction is increased. The removal of excess LiOH due to the dispersion of excess Li ₂ CO ₃ is confirmed by an increase in the specific surface area of the lithium metal composite oxide particles.

The drying temperature is preferably 450 ° C. or lower. When it exceeds 450 ° C., lithium may further be liberated from the crystal of the lithium metal composite oxide, and the gelation of the paste may not be sufficiently suppressed. From the viewpoint of drying more sufficiently and preventing the liberation of lithium from the lithium metal composite oxide, the drying temperature is more preferably 100 ° C. or higher and 300 ° C. or lower. The drying time is not particularly limited, but can be 1 hour or more and 24 hours or less.

In addition, the atmosphere during drying is decarboxylated air in which the content of carbon dioxide gas is controlled as necessary in order to avoid excessive reaction of moisture in the atmosphere and carbon and lithium on the surface of the lithium metal composite oxide particles, An inert gas or a vacuum atmosphere can be used, but an air atmosphere is preferable. The content of carbon dioxide gas is preferably 100 ppm to 500 ppm by volume. Furthermore, the pressure of the atmosphere during drying is preferably 1 atm or less. When the atmospheric pressure is higher than 1 atm, the water content of the positive electrode active material may not be sufficiently lowered. When the pressure of the atmosphere at the time of drying is a reduced pressure atmosphere (for example, about −90 kPa), the moisture content of the positive electrode active material can be further reduced, and the positive electrode resistance of the obtained secondary battery can be reduced.

(3) Positive electrode mixture paste for non-aqueous electrolyte secondary battery In the positive electrode mixture paste of this embodiment, elution of lithium from the positive electrode active material is reduced, and gelation of the paste is suppressed. Therefore, the positive electrode mixture paste has a high stability with little change in the viscosity of the paste even after long-term storage. By producing a positive electrode using such a paste, the positive electrode also has stable and excellent characteristics, and the characteristics of the finally obtained battery can be made stable and high.

The positive electrode mixture paste is characterized by containing the positive electrode active material, and the other constituent materials are the same as those of a normal positive electrode mixture paste. For example, when the total mass of the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material is 60 to 95 parts by mass in the same manner as the positive electrode of a general non-aqueous electrolyte secondary battery, It is preferable that the content of the conductive agent is 1 to 20 parts by mass and the content of the binder is 1 to 20 parts by mass.

Further, as the conductive agent, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black materials such as acetylene black, ketjen black, and the like can be used.

The binder plays a role of anchoring the active material particles. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluorine rubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin, polyacrylic, and the like. An acid or the like can be used.

If necessary, a positive electrode active material, a conductive agent, and activated carbon are dispersed, and a solvent that dissolves the binder is added to the positive electrode mixture. Specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent. Activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity.

A powdered positive electrode active material, a conductive agent, and a binder are mixed, and, if necessary, a target solvent such as activated carbon and viscosity adjustment is added and kneaded to prepare a positive electrode mixture paste.

(4) Non-aqueous electrolyte secondary battery The non-aqueous electrolyte secondary battery according to the present embodiment includes a positive electrode, a negative electrode, a non-aqueous electrolyte, and the like, and includes the same components as those of a general non-aqueous electrolyte secondary battery. . Note that the embodiment described below is merely an example, and the nonaqueous electrolyte secondary battery of the present embodiment can be variously modified based on the knowledge of those skilled in the art based on the embodiment described in the present specification. It can be implemented in an improved form. Further, the use of the nonaqueous electrolyte secondary battery of the present embodiment is not particularly limited.

(A) Positive electrode Using the positive electrode active material for a non-aqueous electrolyte secondary battery described above and the positive electrode mixture paste, for example, a positive electrode of a non-aqueous electrolyte secondary battery is produced as follows.

The positive electrode mixture paste is applied to, for example, the surface of a current collector made of aluminum foil and dried to disperse the solvent. If necessary, pressurization may be performed by a roll press or the like to increase the electrode density. In this way, a sheet-like positive electrode can be produced. The sheet-like positive electrode can be cut into an appropriate size or the like according to the target battery and used for battery production. However, the method for manufacturing the positive electrode is not limited to the illustrated one, and other methods may be used.

(B) Negative electrode A negative electrode mixture in which a negative electrode active material capable of occluding and desorbing lithium ions is mixed with a binder and an appropriate solvent is added to the negative electrode. Is applied to the surface of a metal foil current collector such as copper, dried, and compressed to increase the electrode density as necessary.

As the negative electrode active material, for example, natural graphite, artificial graphite, a fired organic compound such as phenol resin, and a powdery carbon material such as coke can be used. In this case, a fluorine-containing resin such as PVDF can be used as the negative electrode binder, as in the case of the positive electrode, and a solvent for dispersing these active materials and the binder can be N-methyl-2-pyrrolidone or the like. Organic solvents can be used.

(C) Separator A separator is interposed between the positive electrode and the negative electrode. The separator separates the positive electrode and the negative electrode and retains the electrolyte, and a thin film such as polyethylene or polypropylene and a film having many minute holes can be used.

(D) Non-aqueous electrolyte The non-aqueous electrolyte is obtained by dissolving a lithium salt as a supporting salt in an organic solvent.
Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, and dipropyl carbonate, tetrahydrofuran, 2- One kind selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesultone, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, etc. are used alone or in admixture of two or more. be able to.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , or a composite salt thereof can be used. Furthermore, the non-aqueous electrolyte solution may contain a radical scavenger, a surfactant, a flame retardant, and the like.

(E) Battery shape and configuration The shape of the non-aqueous electrolyte secondary battery of the present embodiment constituted by the positive electrode, the negative electrode, the separator and the non-aqueous electrolyte described above is a cylindrical type, a laminated type, etc. It can be various.

In any case, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolyte and communicated with the positive electrode current collector and the outside. The positive electrode terminal and the negative electrode current collector and the negative electrode terminal communicating with the outside are connected using a current collecting lead or the like and sealed in a battery case to complete a non-aqueous electrolyte secondary battery. .

(F) Characteristics The nonaqueous electrolyte secondary battery using the positive electrode active material of the present embodiment has a high capacity and a high output.
In particular, the non-aqueous electrolyte secondary battery using the positive electrode active material according to the present embodiment obtained in a more preferable form has a high value of 150 mAh / g or more when used for the positive electrode of the 2032 type coin battery described in the examples. An initial discharge capacity and a low positive electrode resistance are obtained.

In addition, it will be as follows if the measuring method of the positive electrode resistance in this embodiment is illustrated. When the frequency dependence of the battery reaction is measured by a general AC impedance method as an electrochemical evaluation method, the Nyquist diagram based on the solution resistance, the negative electrode resistance and the negative electrode capacity, and the positive electrode resistance and the positive electrode capacity is shown in FIG. Is obtained as follows.

The battery reaction at the electrode consists of a resistance component accompanying the charge transfer and a capacity component due to the electric double layer. When these are expressed as an electric circuit, it becomes a parallel circuit of resistance and capacity. It is represented by an equivalent circuit in which circuits are connected in series. Fitting calculation is performed on the Nyquist diagram measured using this equivalent circuit, and each resistance component and capacitance component can be estimated. The positive electrode resistance is equal to the diameter of the semicircle on the low frequency side of the obtained Nyquist diagram.

From the above, the positive electrode resistance can be estimated by performing AC impedance measurement on the manufactured positive electrode and performing fitting calculation with the equivalent circuit on the obtained Nyquist diagram.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. About the positive electrode active material obtained in this example, the positive electrode mixture paste using this positive electrode active material, and the non-aqueous electrolyte secondary battery, the performance (stability of paste, initial discharge capacity, positive electrode resistance, internal resistance, discharge) The capacity retention ratio was evaluated by the following method.

(Manufacture of coin-type battery and evaluation of battery characteristics)
32.5 mg of a positive electrode active material for a non-aqueous electrolyte secondary battery, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) were mixed and press-molded to a diameter of 11 mm and a thickness of 100 μm at a pressure of 100 MPa. The positive electrode 1 (electrode for evaluation) shown in FIG. The produced positive electrode 1 was dried at 120 ° C. for 12 hours in a vacuum dryer. Using this positive electrode 1, a 2032 type coin-type battery B was produced in a glove box in an Ar atmosphere in which the dew point was controlled at −80 ° C.
For the negative electrode 2, a negative electrode sheet in which a graphite powder punched into a disk shape with a diameter of 14 mm and an average particle diameter of about 20 μm and polyvinylidene fluoride are applied to a copper foil is used, and 1 M LiPF ₆ is used as the electrolyte for the electrolyte. An equivalent mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (manufactured by Toyama Pharmaceutical Co., Ltd.) was used. As the separator 3, a polyethylene porous film having a film thickness of 25 μm was used. The coin-type battery B has a gasket 4 and a wave washer 5, and the positive electrode can 6 and the negative electrode can 7 are assembled into a coin-shaped battery. The initial discharge capacity, the positive electrode resistance, and the cycle characteristics showing the performance of the manufactured coin battery B were evaluated as follows.

(Initial discharge capacity)
The initial discharge capacity is left for about 24 hours after the coin-type battery B is manufactured, and after the open circuit voltage OCV (Open Circuit Voltage) is stabilized, the current density with respect to the positive electrode is set to 0.1 mA / cm ² and the cut-off voltage 4 The capacity when the battery was charged to 3 V, discharged after a pause of 1 hour to a cutoff voltage of 3.0 V was defined as the initial discharge capacity.

(Positive electrode resistance)
Further, the positive electrode resistance is obtained by charging the coin-type battery B at 25 ° C. with a charging potential of 4.1 V and measuring the positive electrode resistance by the AC impedance method using a frequency response analyzer and a potentiogalvanostat (manufactured by Solartron, 1255B). The Nyquist plot shown in FIG. Since this Nyquist plot is represented as the sum of the solution resistance, the negative electrode resistance and its capacity, and the characteristic curve indicating the positive electrode resistance and its capacity, the fitting calculation was performed using an equivalent circuit based on this Nyquist plot, and the positive resistance The value of was calculated.
(Cycle characteristics)
The evaluation of the cycle characteristics (discharge capacity maintenance rate) was performed based on the capacity maintenance rate after the cycle test. The cycle test was held at 60 ° C. and paused for 10 minutes after the initial discharge capacity measurement, and the charge / discharge cycle was repeated 500 cycles (charge / discharge) including the initial discharge capacity measurement in the same manner as the initial discharge capacity measurement. The discharge capacity at the 500th cycle was measured, and the percentage of the discharge capacity at the 500th cycle with respect to the discharge capacity at the first cycle (initial discharge capacity) was determined as the capacity retention rate (%).

(Evaluation of low temperature output characteristics)
Using the laminate cell C, the low-temperature output characteristics were evaluated by measuring the battery internal resistance ΔV at low temperatures by the current pause method. The evaluation method is as follows.
A laminate cell C used for evaluation was produced as follows. After mixing a positive electrode active material, a conductive material (acetylene black), and a binder (PVDF) at a mass ratio of 85: 10: 5 to an aluminum current collector foil (thickness 0.02 mm), a solvent (NMP) was added. In addition, the positive electrode active material was made into a paste, applied while leaving a conductive part connected to the outside, and dried to prepare a positive electrode sheet 8 on which a positive electrode active material layer having a basis weight of 7 mg / cm ² was formed.
Also, carbon powder (acetylene black) was pasted as a negative electrode active material on a copper current collector foil (thickness 0.02 mm), and a negative electrode active material layer having a negative electrode active material weight of 5 mg / cm ² was formed in the same manner. A negative electrode sheet 9 was produced.
A laminated sheet was formed between the produced positive electrode sheet 8 and negative electrode sheet 9 with a separator 10 made of a polypropylene microporous film (thickness 20.7 μm, porosity density 43.9%) interposed therebetween. Then, the laminated sheet is sandwiched between two aluminum laminate sheets 11 (thickness 0.55 mm), and the three sides of the aluminum laminate sheet 11 are heat-sealed to form a heat-sealed portion HS, which is sealed. 4 was assembled.
Thereafter, 260 μl of an electrolyte made by Ube Industries, Ltd. in which LiPF ₆ (1 mol / L) was dissolved in a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (volume ratio 3: 3: 4) was injected, and the rest One side was heat-sealed to produce a laminate cell C shown in FIG.
The manufactured laminate cell C was charged to 4.2 V at a temperature of −20 ° C., then discharged to 0.2 V at 0.2 C, and the voltage change (ΔV) before and after the voltage was relaxed for 600 seconds was made open circuit. Calculated. When the current during discharge is the same, the difference in ΔV can be interpreted as a resistance difference as it is, that is, the smaller the ΔV, the lower the resistance, so the value of ΔV was evaluated as a direct current resistance under low temperature conditions. An example of the measurement result of the current pause method is shown in FIG.

(Viscosity stability of positive electrode mixture paste)
Positive electrode active material 25.0 g, carbon powder 1.5 g of conductive material, 2.9 g of polyvinylidene fluoride (PVDF), and N-methyl-2-pyrrolidone (NMP) were mixed by a planetary motion kneader. A paste was obtained. The amount of N-methyl-2pyrrolidone (NMP) added was adjusted so that the viscosity would be 1.5 to 2.5 Pa · s by a viscosity measurement method using a vibration viscometer specified in JIS Z 8803: 2011. The obtained paste was stored for 76 hours, and the viscosity ratio before and after storage (paste viscosity after storage for 76 hours / paste viscosity immediately after preparation) was evaluated. The viscosity was measured with a vibration viscometer (VM10A manufactured by Seconic).

(Moisture percentage)
The measurement was performed with a Karl Fischer moisture meter under the condition of a vaporization temperature of 300 ° C.

(Measurement of surplus LiOH amount and surplus Li ₂ CO ₃ amount)
The excess lithium amount was evaluated by titrating Li eluted from the positive electrode active material. After adding 10 ml of pure water to 1 g of the obtained positive electrode active material and stirring for 1 minute, the lithium elution from the neutralization point appearing by adding 1 mol / liter hydrochloric acid while measuring the pH of the filtered filtrate was performed. The compound state was analyzed to evaluate the excess lithium amount. Here, the first neutralization point (shoulder) from the high alkali side indicates the LiOH amount, and the second neutralization point indicates the Li ₂ CO ₃ amount.

Example 1
Lithium metal composite represented by Li _1.20 Ni _0.35 Co _0.35 Mn _0.30 O ₂ obtained by a known technique of mixing and baking oxide powder containing Ni as a main component and lithium hydroxide Baked oxide powder (average particle size: 5.07 μm, [(d90-d10) / average particle size]: 0.42, porosity: 14.2%: specific surface area 2.50 g / m ² ) It was. Water was added to the calcined powder used as a base material in an amount of 1.5% by mass with respect to the calcined powder, and further mixed. Then, the positive electrode active material was obtained by drying at 150 degreeC for 12 hours in an atmospheric condition. The production conditions of the positive electrode active material and the following measurement / evaluation results are shown in Tables 1 and 2. The specific surface area of the positive electrode active material was determined by a BET method using nitrogen gas adsorption.
[PH measurement]
5 g of the obtained positive electrode active material was dispersed in 100 ml of pure water, allowed to stand for 10 minutes, and the pH of the supernatant liquid at 25 ° C. was measured.
[Positive electrode paste]
Using the obtained positive electrode active material, the viscosity of the positive electrode mixture paste produced by the above method was measured.
[Battery evaluation]
Using the obtained positive electrode active material, the battery characteristics of the coin-type battery B and the laminate cell C having the positive electrode prepared by the above method were evaluated.

(Example 2)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the amount of water added was 3% by mass. The evaluation results are shown in Tables 1 and 2.
(Example 3)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the amount of water added was 5% by mass. The evaluation results are shown in Tables 1 and 2.
(Example 4)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the amount of water added was 7% by mass. The evaluation results are shown in Tables 1 and 2.
(Example 5)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the amount of water added was 14% by mass. The evaluation results are shown in Tables 1 and 2.
(Example 6)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the amount of water added was 30% by mass. The evaluation results are shown in Tables 1 and 2.
(Example 7)
The fired powder used as a base material is put in a vat, and 3% by mass of water is sprayed on the lithium metal composite oxide powder under the condition that the average droplet diameter is about 300 μm using a spray bottle. A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that mixing was performed while adding. The evaluation results are shown in Tables 1 and 2.
(Example 8)
Put the calcined powder as the base material into a Henschel mixer (FM20C / I manufactured by Nippon Coke Co., Ltd.) and stir and mix the calcined powder with stirring blades in the tank so that the average droplet diameter is about 300 μm. Under the conditions, 3 mass% water is sprayed and added to the lithium metal composite oxide powder using a spray, and then mixed, and then dried at 130 ° C. for 2 hours in a reduced pressure atmosphere of about −90 kPa. In the same manner as in Example 1, a positive electrode active material was obtained and evaluated. The evaluation results are shown in Tables 1 and 2.

Example 9
A calcined powder of a lithium metal composite oxide having a composition of Li _1.20 (Ni _0.35 Co _0.35 Mn _0.30 ) _0.995 W _0.005 O ₂ (average particle size: 4) A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that it was set to .97 μm, [(d90-d10) / average particle diameter] 0.41, and porosity: 15.6%). The evaluation results are shown in Tables 1 and 2. The above composition of the base material is such that the molar ratio of Ni, Co, and Mn (Ni: Co: Mn) is 0.35: 0.35: 0.30, and the sum of Ni, Co, and Mn, and W The molar ratio (Ni + Co + Mn: W) is 0.995: 0.005, and the molar ratio (Li: Me) of Li to Me (total of Ni, Co, Mn and W) is 1.20: 1. Indicates that
(Example 10)
A positive electrode active material was obtained and evaluated in the same manner as in Example 7 except that the amount of water added was 3% by mass. The evaluation results are shown in Tables 1 and 2.
(Example 11)
A positive electrode active material was obtained and evaluated in the same manner as in Example 7 except that the amount of water added was 5% by mass. The evaluation results are shown in Tables 1 and 2.
(Example 12)
A positive electrode active material was obtained and evaluated in the same manner as in Example 7 except that the amount of water added was 7% by mass. The evaluation results are shown in Tables 1 and 2.
(Example 13)
A positive electrode active material was obtained and evaluated in the same manner as in Example 7 except that the amount of water added was 14% by mass. The evaluation results are shown in Tables 1 and 2.
(Example 14)
A positive electrode active material was obtained and evaluated in the same manner as in Example 7 except that the amount of water added was 30% by mass. The evaluation results are shown in Tables 1 and 2.
(Example 15)
The fired powder used as a base material is put in a vat, and 3% by mass of water is sprayed on the lithium metal composite oxide powder under the condition that the average droplet diameter is about 300 μm using a spray bottle. A positive electrode active material was obtained and evaluated in the same manner as in Example 9 except that mixing was performed while adding. The evaluation results are shown in Tables 1 and 2.
(Example 16)
Put the calcined powder as the base material into a Henschel mixer (FM20C / I manufactured by Nippon Coke Co., Ltd.) and stir and mix the calcined powder with stirring blades in the tank so that the average droplet diameter is about 300 μm. Under the conditions, 3 mass% water is sprayed and added to the lithium metal composite oxide powder using a spray, and then mixed, and then dried at 130 ° C. for 2 hours in a reduced pressure atmosphere of about −90 kPa. Were evaluated in the same manner as in Example 9 while obtaining a positive electrode active material. The evaluation results are shown in Tables 1 and 2.

(Comparative Example 1)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the base material was directly used as the positive electrode active material. The evaluation results are shown in Tables 1 and 2.

(Comparative Example 2)
A positive electrode active material was obtained and evaluated in the same manner as in Example 7 except that the base material was directly used as the positive electrode active material. The evaluation results are shown in Tables 1 and 2.

(Evaluation results)
The secondary battery using the positive electrode active material of the example has an initial discharge capacity, a positive electrode resistance, a battery internal resistance, and a capacity maintenance ratio as compared with the secondary battery using the positive electrode active material of the comparative example in which water is not mixed. In either case, good results were obtained. In Examples 9 to 16 in which the lithium metal composite oxide containing W was used as the fired powder, the positive electrode resistance and the battery internal resistance were further reduced. In particular, the internal resistance of the battery showing output characteristics at low temperatures was significantly reduced.
Further, Examples 1 to 3, 7, 8, 9 to 11, 15 and 16 in which the amount of water to be mixed was optimized had a lithium extraction amount as compared with Examples 4 to 6 and 12 to 14 having the same composition. The output characteristics are improved as compared with the examples of the same composition while maintaining the low viscosity ratio of the positive electrode mixture paste. In particular, the output characteristics of Examples 7, 8, 15, and 16 to which water was added by spraying are further improved.
Further, in Examples 1 to 16 in which water was mixed, the content of surplus LiOH was reduced while the content of surplus Li ₂ CO ₃ was increased as compared with Comparative Examples 1 and 2 in which water was not mixed. , LiOH / Li ₂ CO ₃ was 0.45 or less. This is presumably because excess LiOH in the fired powder was converted to Li ₂ CO ₃ in the step of adding water and subsequent drying.
In addition, the positive electrode mixture paste using the positive electrode active material of the example has a lower viscosity ratio value and excellent viscosity stability than the positive electrode mixture paste of the comparative example.

As far as permitted by law, the contents of Japanese Patent Application Nos. 2016-060745, 2016-118644, 2016-248296, and all the references cited in the above-described embodiments are incorporated. As a part of the description of the text.

B …… Coin-type battery 1 …… Positive electrode (Evaluation electrode)
2 ... Negative electrode 3 ... Separator 4 ... Gasket 5 ... Wave washer 6 ... Positive electrode can 7 ... Negative electrode can C ... Laminate cell 8 ... Positive electrode sheet 9 ... Negative electrode sheet 10 ... Separator 11 ... Aluminum Laminate sheet HS ... Heat seal

Claims

Mixing a fired powder composed of a lithium metal composite oxide having a layered crystal structure and water, and drying the mixture obtained by mixing,
The calcined powder has the general formula (1): Li s Ni 1-xyz Co x Mn y M 1 z O 2 (where 0.05 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.35 , 0 ≦ z ≦ 0.10, 0.95 ≦ s ≦ 1.50, M 1 is represented by at least one element selected from V, Mg, Mo, Nb, Ti, W and Al), and primary Including secondary particles formed by aggregation of particles,
In the water, 5 g of the obtained positive electrode active material is dispersed in 100 ml of pure water and mixed in such an amount that the pH at 25 ° C. is in the range of 11 to 11.9 when the supernatant liquid after standing for 10 minutes is measured. The manufacturing method of the positive electrode active material for non-aqueous electrolyte secondary batteries characterized by the above-mentioned.
2. The non-aqueous electrolyte secondary according to claim 1, wherein when the fired powder and water are mixed, the fired powder is mixed by spraying water to a droplet size of 1 μm or more and 2000 μm or less. A method for producing a positive electrode active material for a battery.
The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the water is mixed in a range of 1% by mass to 35% by mass with respect to the fired powder.
The water, mixed with 0.003 g / m 2 or more 0.025 g / m 2 or less in the range of the surface area of the calcined powder, a non-aqueous electrolyte according to any one of claims 1 to 3 A method for producing a positive electrode active material for a secondary battery.
The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the water is mixed in a range of 1% by mass to 6% by mass with respect to the fired powder. Production method.
The fired powder has an average particle diameter in the range of 3 μm to 15 μm, and an index indicating the spread of the particle size distribution [(d90−d10) / average particle diameter] is 0.7 or less. The manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries as described in any one of Claims 5.
The area ratio of voids measured by cross-sectional observation of the fired powder is 4.5% or more and 60% or less with respect to the entire cross-sectional area of the fired powder. The manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries as described in any one of.
The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 7, wherein the drying is performed at 100 ° C or higher and 300 ° C or lower.
The calcined powder has the general formula (2): Li s Ni 1- xyzt Co x Mn y M 2 z W t O 2 (where 0.05 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.35,0 ≦ z ≦ 0.10,0.95 ≦ s ≦ 1.50,0.0001 ≦ t ≦ 0.03,0.0001 ≦ z + t ≦ 0.10, M 2 is, V, Mg The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 8, represented by: at least one element selected from Mo, Nb, Ti and Al) .
A positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium metal composite oxide powder having a layered crystal structure,
The lithium metal composite oxide powder has the general formula (1): Li s Ni 1-xyz Co x Mn y M 1 z O 2 (where 0.05 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.10, 0.95 ≦ s ≦ 1.50, M 1 is at least one element selected from V, Mg, Mo, Nb, Ti, W and Al) Including secondary particles formed by aggregation of primary particles,
5 g of the positive electrode active material was dispersed in 100 ml of pure water, and the pH at 25 ° C. when measuring the supernatant after standing for 10 minutes was 11 to 11.9,
A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein a mass ratio of surplus LiOH and surplus Li 2 CO 3 (surplus LiOH / surplus Li 2 CO 3 ) determined by a titration method is 0.45 or less.
The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 10, wherein a ratio of the amount of surplus LiOH to surplus Li 2 CO 3 (surplus LiOH / surplus Li 2 CO 3 ) is 0.3 or less.
The ratio of the amount of surplus LiOH to surplus Li 2 CO 3 (surplus LiOH / surplus Li 2 CO 3 ) is 0.18 or more, and the amount of surplus Li 2 CO 3 is 0. 0 relative to the surface area of the positive electrode active material. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 10 or 11, wherein the positive electrode active material is 157 × 10 −2 g / m 2 or less.
The average particle diameter is in the range of 3 μm or more and 15 μm or less, and [(d90−d10) / average particle diameter], which is an index showing the spread of the particle size distribution, is 0.7 or less. A positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1.
The area ratio occupied by voids measured in cross-sectional observation of the lithium metal composite oxide powder is 4.5% or more and 60% or less with respect to the cross-sectional area of the entire lithium metal composite oxide particle. Item 14. The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Items 13.
The lithium metal composite oxide powder represented by the general formula (2): Li s Ni 1 -x-y-z-t Co x Mn y M 2 z W t O 2 ( however, 0.05 ≦ x ≦ 0.35 , 0 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.10, 0.95 ≦ s ≦ 1.50, 0.0001 ≦ t ≦ 0.03, 0.0001 ≦ z + t ≦ 0.10, M 2 is The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 10 to 14, represented by: at least one element selected from V, Mg, Mo, Nb, Ti and Al). material.
A positive electrode mixture paste for a non-aqueous electrolyte secondary battery, comprising the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 10 to 15.
A non-aqueous electrolyte secondary battery having a positive electrode comprising the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 10 to 15.