JP2020013747A - Positive electrode active material for lithium ion secondary battery and method of producing the same, positive electrode mixture paste for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

To provide: a positive electrode active material which is capable of suppressing a decrease in battery capacity and output characteristics and is also highly effective in the suppression of gelation of a positive electrode mixture paste during electrode manufacturing; and the like.SOLUTION: A positive electrode active material for a lithium ion secondary battery contains a lithium nickel composite oxide and amorphous LiBO. The lithium nickel composite oxide contains lithium, nickel, cobalt and an element M, and the ratio (molar ratio) of the material amount of each element is represented by Li:Ni:Co:M=a:(1-x-y):x:y (where, 0.95≤a≤1.10, 0.05≤x≤0.35 and 0≤y≤0.10 are satisfied, and M represents at least one element selected from among Mn, V, Mg, Mo, Nb, Ti, W, Zr and Al). At least part of the surface of the lithium nickel composite oxide is coated with amorphous LiBO, and the content of boron is 0.01 mass% or more and 0.1 mass% or less with respect to the entire positive electrode active material.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a positive electrode active material for a lithium ion secondary battery and a method for producing the same, a positive electrode mixture paste for a lithium ion secondary battery, and a lithium ion secondary battery.

  2. Description of the Related Art In recent years, with the spread of small information terminals such as smartphones and tablet PCs, development of small and lightweight secondary batteries having high energy density has been required. Further, development of a high-output secondary battery is also required as a secondary battery for an electric vehicle such as a hybrid vehicle. As a secondary battery satisfying such a demand, there is a lithium ion secondary battery. A lithium ion secondary battery is composed of a negative electrode, a positive electrode, an electrolyte, and the like, and a material capable of removing and inserting lithium is used as an active material of the negative electrode and the positive electrode.

Research and development of such lithium ion secondary batteries are being actively conducted at present, and among them, lithium ion secondary batteries using a layered or spinel-type lithium transition metal composite oxide as a positive electrode active material are among them. Since a secondary battery can obtain a high voltage of 4V class, it is being put to practical use as a battery having a high energy density. Materials mainly proposed so far include lithium-cobalt composite oxide (LiCoO ₂ ) which is relatively easy to synthesize, lithium-nickel composite oxide (LiNiO ₂ ) using nickel which is cheaper than cobalt, and lithium nickel Examples thereof include a cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) and a lithium manganese composite oxide using manganese (LiMn ₂ O ₄ ).

  Among them, in the battery using the lithium-cobalt composite oxide, many developments for obtaining excellent initial capacity characteristics and cycle characteristics have been performed so far, and various results have already been obtained. However, since the lithium-cobalt composite oxide uses an expensive cobalt compound as a raw material, the unit price per capacity of a battery using this lithium-cobalt composite oxide is significantly higher than that of a nickel-metal hydride secondary battery. Is quite limited. Therefore, not only for small secondary batteries for portable electronic devices, but also for large secondary batteries for electric power storage and electric vehicles, the cost of the positive electrode active material is reduced, and the production of cheaper lithium-ion secondary batteries is achieved. There is great expectation for making this possible, and its realization is of great industrial significance.

  As a new material of an active material for a lithium ion secondary battery, a lithium nickel composite oxide using nickel, which is cheaper than cobalt, can be given. This lithium nickel composite oxide is more expensive than a lithium cobalt composite oxide. Because of its low electrochemical potential, decomposition due to oxidation of the electrolyte is unlikely to be a problem, and a higher capacity can be expected. It is being actively developed as a substance.

  By the way, the positive electrode of a lithium ion secondary battery is prepared by mixing, for example, a positive electrode active material, a binder such as polyvinylidene fluoride (PVDF), and a solvent such as N-methyl-2-pyrrolidone (NMP). It is formed by forming a paste and applying it to a current collector such as an aluminum foil. At this time, when lithium is released from the positive electrode active material in the positive electrode mixture paste, it may react with moisture contained in the binder or the like to generate lithium hydroxide. The produced lithium hydroxide reacts with the binder, and the positive electrode mixture paste may gel. The gelation of the positive electrode mixture paste causes poor operability in a manufacturing process and a decrease in yield. This tendency is remarkable when lithium in the lithium transition metal composite oxide as the positive electrode active material is in excess of the stoichiometric ratio with respect to the transition metal, and the ratio of nickel in the transition metal is high.

  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. It has also been proposed to improve the battery characteristics by adding a compound containing boron to the lithium nickel cobalt composite oxide.

  Patent Document 1 discloses a positive electrode active material for a nonaqueous electrolyte secondary battery having at least a layered crystal structure of a lithium transition metal composite oxide, wherein the lithium transition metal composite oxide is at least A positive electrode active material for a non-aqueous electrolyte secondary battery having lithium borate on the surface of the particles has been proposed. According to Patent Document 1, the presence of lithium borate on the surface of the particles makes it possible to improve the thermal stability while maintaining the initial discharge capacity and the initial efficiency at the same level.

  Patent Document 2 discloses that at least one of a sulfate and a borate compound is applied to a composite oxide particle containing lithium (Li) and at least one of nickel (Ni) and cobalt (Co). And a step of heat-treating the composite oxide particles to which at least one of the sulfate and the boric acid compound is applied under an oxidizing atmosphere. Proposed. According to Patent Literature 2, it is described that a positive electrode active material capable of realizing high capacity of a secondary battery and improvement of charge / discharge efficiency can be manufactured.

  Some attempts have been made to suppress the gelation of the positive electrode mixture paste. For example, Patent Document 3 proposes a positive electrode composition for a nonaqueous electrolyte secondary battery including a positive electrode active material composed of a lithium transition metal composite oxide and additional particles composed of acidic oxide particles. In this positive electrode composition, lithium hydroxide generated by reacting with water contained in the binder reacts preferentially with the acidic oxide, and suppresses the reaction between the generated lithium hydroxide and the binder. It is said to suppress gelation. The acid oxide also plays a role as a conductive agent in the positive electrode, lowers the resistance of the entire positive electrode, and contributes to improving the output characteristics of the battery.

  Patent Literature 4 discloses a method for manufacturing a lithium ion secondary battery, in which a lithium transition metal oxide containing LiOH in addition to a composition is prepared as a positive electrode active material; To grasp the molar amount P; to prepare 0.05 mol or more of tungsten oxide in terms of tungsten atom per mol of LiOH with respect to the molar amount P of LiOH; and to make the positive electrode active material and tungsten oxide conductive. A method for producing a lithium ion secondary battery has been proposed, which comprises kneading an organic solvent together with a material and a binder to prepare a positive electrode paste.

JP 2004-335278 A JP 2009-146739 A JP 2012-028313 A JP 2013-084395 A

  In the proposals of Patent Documents 1 and 2, the battery characteristics such as output characteristics are both improved, but the addition of a boron compound causes a problem of gelation of the positive electrode mixture paste during electrode production. There is. Therefore, further improvement in gelation as well as improvement in battery characteristics such as output characteristics and battery capacity is desired.

  Further, in the proposal of Patent Document 3, there is a possibility that the acidic oxide particles remain in the positive electrode composition, which may cause breakage of the separator and a resultant decrease in thermal stability of the battery. Further, further suppression of gelation in the positive electrode mixture paste is required. It is considered that the gelation can be further suppressed by increasing the amount of the acidic oxide added. Increasing the weight ratio may decrease the battery capacity per unit mass.

  Also in the proposal of Patent Document 4, there is a possibility that the separator may be damaged due to the residual tungsten oxide. Further, further suppression of gelation in the positive electrode mixture paste is required. In addition, there is a problem that the addition of tungsten, which is a heavy element that does not contribute to charge and discharge, lowers the battery capacity per weight.

  The present invention has been made in view of the above problems, and when used in a lithium ion secondary battery, suppresses a decrease in battery capacity and output characteristics, and has an effect of suppressing gelation of a positive electrode mixture paste during electrode production. It is intended to provide a large positive electrode active material. Another object of the present invention is to provide a method for easily producing such a positive electrode active material in industrial scale production.

In a first aspect of the present invention, the lithium-nickel composite oxide includes lithium nickel composite oxide and amorphous LiBO ₂ , and the lithium-nickel composite oxide includes lithium, nickel, cobalt, and an element M; The ratio (molar ratio) of the substance amounts of the elements is Li: Ni: Co: M = a: (1-xy): x: y (where 0.95 ≦ a ≦ 1.10, 0.05 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.10, M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti, W, Zr, and Al), and lithium Lithium in which at least a part of the surface of the nickel composite oxide is coated with amorphous LiBO 2, and the content of boron is 0.01% by mass or more and 0.1% by mass or less based on the whole positive electrode active material. A positive electrode active material for an ion secondary battery is provided.

In the second aspect of the present invention, a lithium nickel composite oxide and a boron compound are mixed to obtain a mixture, and the mixture is heat-treated at a temperature of 300 ° C. or more and 500 ° C. or less in an oxygen atmosphere. Reacting the boron compound with lithium in the lithium-nickel composite oxide to form amorphous LiBO ₂ on at least a portion of the surface of the lithium-nickel composite oxide. The material contains lithium, nickel, cobalt, and the element M, and the ratio (molar ratio) of the amount of each element is Li: Ni: Co: M = a: (1-xy): x : Y (however, 0.95 ≦ a ≦ 1.10, 0.05 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.10, M is Mn, V, Mg, Mo, Nb, Ti, W, Zr and at least one element selected from Al) Wherein the mixture contains boron in the boron compound in an amount of 0.01% by mass or more and 0.1% by mass or less based on the whole mixture, and a method for producing a positive electrode active material for a lithium ion secondary battery is provided. .

Further, the boron compound preferably contains at least one selected from H ₃ BO ₃ and B ₂ O ₃ . Further, the lithium compound preferably contains lithium hydroxide. It is preferable that at least a part of the surface of the lithium nickel composite oxide is covered with LiBO ₂ .

  The boron compound has an amount of lithium hydroxide eluted when the positive electrode active material is dispersed in water, measured by a neutralization titration method, of 0.01% by mass or more based on the whole positive electrode active material. It is preferable to adjust so as to be less than 0.2% by mass.

  According to a third aspect of the present invention, there is provided a positive electrode mixture paste for a lithium ion secondary battery, comprising the positive electrode active material for a lithium ion secondary battery.

  According to a fourth aspect of the present invention, there is provided a lithium ion secondary battery including a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, the positive electrode including the positive electrode active material for a lithium ion secondary battery.

  Advantageous Effects of Invention According to the present invention, it is possible to suppress a decrease in battery capacity and output characteristics when used in a lithium ion secondary battery, and to suppress a gelation and obtain a highly stable positive electrode mixture slurry. A substance can be provided. Furthermore, the production method is easy and suitable for production on an industrial scale, and its industrial value is extremely large.

FIG. 1 is a diagram illustrating an example of a positive electrode active material for a lithium ion secondary battery according to an embodiment. FIG. 2A is a diagram illustrating an example of a method for manufacturing a positive electrode active material for a lithium ion secondary battery according to the embodiment. FIG. 2B is an explanatory diagram of a reaction between lithium and a boron compound contained in the lithium nickel composite oxide (raw material). FIG. 3 is a schematic explanatory diagram of a measurement example of impedance evaluation and an equivalent circuit used for analysis. FIG. 4 is a schematic diagram of a coin-type battery used for battery evaluation.

  Hereinafter, a positive electrode active material for a lithium ion secondary battery, a method for producing the same, a positive electrode mixture paste for a lithium ion secondary battery, and a lithium ion secondary battery according to an embodiment of the present invention will be described with reference to the drawings. The present invention is not limited to the following detailed description.

1. 1. Positive Electrode Active Material for Lithium Ion Secondary Battery FIG. 1 is a view showing an example of a positive electrode active material 100 for a lithium ion secondary battery according to the present embodiment (hereinafter, also referred to as “positive electrode active material 100”). As shown in FIG. 1, the positive electrode active material 100 is composed of a lithium nickel composite oxide 10 and amorphous LiBO ₂ (in FIG. 1, denoted by the symbol “LB”. Hereinafter, also referred to as “amorphous LiBO ₂ ”). )), And at least a part of the surface of the lithium-nickel composite oxide 10 is covered with amorphous LiBO ₂ . That is, the positive electrode active material 100 includes a coating layer (also referred to as a LiBO ₂ layer) in which amorphous LiBO ₂ covers at least a part of the surface of the lithium nickel composite oxide 10.

The present inventor has made intensive studies and found that the presence of amorphous LiBO ₂ on the particle surface of the lithium-nickel composite oxide 10 allows the battery capacity and output characteristics of a secondary battery using the positive electrode active material 100 to be used as a positive electrode. It has been found that it is possible to achieve both the suppression of the decrease in the temperature and the suppression of the gelation of the positive electrode mixture paste. Hereinafter, each configuration of the positive electrode active material 100 will be described.

(Lithium nickel composite oxide)
The lithium nickel composite oxide 10 includes lithium, nickel, cobalt, and the element M, and the ratio (molar ratio) of the amounts of these elements is Li: Ni: Co: M = a: (1 -Xy): x: y (however, 0.95 ≦ a ≦ 1.10, 0.05 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.10, M is Mn, V, Mg, Mo) , Nb, Ti, W, Zr, and Al) to form a layered crystal structure. Further, the lithium nickel composite oxide 10 includes secondary particles in which a plurality of primary particles are aggregated. In addition, the ratio of the substance amounts of the respective elements (contents of the respective elements) can be measured by ICP emission spectroscopy.

In the above molar ratio, the value of a indicates the ratio of the amount of Li (Li / Me) to the total amount of Ni, Co, and M (Me), and 0.95 ≦ a ≦ 1.10. is there. The value of a is a value including the amount of Li contained in the amorphous LiBO ₂ . As described later, the amorphous LiBO ₂ reacts with the boron compound B and lithium contained in the lithium nickel composite oxide 10a (raw material) in a heat treatment step (step S2, see FIG. 2A). (See FIG. 2B). Therefore, in consideration of the amount of Li contained in LiBO ₂ , the value of a may be 1 or more, or may exceed 1.

In the above molar ratio, (1-xy) indicating the amount of nickel satisfies 0.55 ≦ (1-xy) ≦ 0.95. Normally, a lithium-nickel composite oxide (positive electrode active material) containing a large amount of nickel tends to cause gelation of the positive electrode mixture paste, but the positive electrode active material 100 can be used even when the nickel amount is in the above range. By coating the surface of the lithium nickel composite oxide 10 with amorphous LiBO ₂ , it is possible to suppress gelation of the positive electrode mixture paste during electrode production.

  In the above molar ratio, x indicating the amount of cobalt satisfies 0.05 ≦ x ≦ 0.35. When the amount of cobalt is in the above range, the cycle characteristics are excellent while maintaining a high battery capacity.

  In the above molar ratio, M is at least one element selected from the group consisting of Mn, V, Mg, Mo, Nb, Ti, W, Zr, and Al, and the thermal stability of the positive electrode active material. From the viewpoint, it is preferable to contain Al. The value of y indicating the amount of M satisfies 0 ≦ y ≦ 0.10, and preferably satisfies 0.01 ≦ y ≦ 0.10.

Further, the lithium nickel composite oxide 10 represented by the general formula _{(1): Li a Ni 1} -x-y Co x M y O 2 + α ( although, 0.05 ≦ x ≦ 0.35,0 ≦ y ≦ 0.10 , 0.95 ≦ a ≦ 1.10, 0 ≦ α ≦ 0.2, M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti, W, Zr, and Al) May be represented by The technical significance and the preferred range of each element in the general formula (1) are the same as in the description of the molar ratio, and thus description thereof is omitted.

(Amorphous LiBO ₂ )
When the positive electrode active material 100 is used for a secondary battery, the battery capacity is reduced by coating at least a part of the surface of the lithium nickel composite oxide 10 with amorphous LiBO ₂ , and It is possible to achieve both suppression of a decrease in output characteristics due to an increase in the positive electrode resistance and suppression of gelling of the positive electrode mixture paste at the time of electrode preparation.

Normally, when covering the surface of the lithium nickel composite oxide 10 with a compound of different, but battery characteristics such as reaction resistance of the positive electrode (positive electrode resistance) may be decreased, amorphous LiBO ₂ lithium conductivity When the surface of the lithium-nickel composite oxide 10 is coated with amorphous LiBO ₂ , not only can the battery characteristics (eg, battery capacity) of the secondary battery be reduced, but also the positive electrode resistance can be reduced. can do.

Further, the lithium nickel composite oxide 10 coated with amorphous LiBO ₂ can suppress the gelation of the positive electrode mixture paste. The mechanism by which the gelation of the paste is suppressed in the lithium nickel composite oxide 10 coated with amorphous LiBO ₂ is unknown, but for example, the manufacturing process of the positive electrode active material 100 (see FIG. 2A) 2), as shown in FIG. 2 (B), the boron compound B used as a raw material is replaced with surplus lithium existing on the surface of the lithium nickel metal composite oxide 10a used as a raw material (eg, an unreacted lithium compound, It is considered that by reacting with lithium in the crystal to form amorphous LiBO ₂ , gelation of the paste is suppressed.

Incidentally, the positive electrode active material 100 may include LiBO ₂ other than lithium borate amorphous, but preferably includes an amorphous LiBO ₂ alone. The lithium borate coating the surface of the lithium nickel composite oxide 10 may be amorphous LiBO ₂ alone or may include lithium borate other than amorphous LiBO _2. More preferably, the surface of the oxide 10 is substantially covered only with amorphous LiBO ₂ . Examples of lithium borate other than amorphous LiBO ₂ include crystalline LiB (OH) _4, LiBO ₂ , and Li ₃ BO ₃ , but from the viewpoint of gel suppression, Li _{3 is} substantially used. it preferably contains no BO _3.

Note that the presence and crystallinity of lithium borate on the surface of the lithium nickel composite oxide 10 can be confirmed by Raman spectroscopy. Note that “substantially covered only by amorphous LiBO ₂ ” means that only broad peaks of LiBO ₂ are detected as peaks other than those derived from lithium nickel composite oxide 10 in Raman spectroscopy. And may contain a small amount of other lithium borate below the detection limit.

When the surface of the lithium nickel composite oxide 10 is coated with the amorphous LiBO ₂ alone, the positive electrode resistance can be further reduced, and the gelation of the positive electrode mixture paste can be suppressed. The surface of the lithium nickel composite oxide 10 can be coated with amorphous LiBO ₂ by, for example, a method for manufacturing a positive electrode active material described later (see FIG. 2A).

(Boron content)
The content of boron (B) contained in the positive electrode active material 100 is 0.01% by mass or more and 0.1% by mass or less, preferably 0.03% by mass or more and 0.06% by mass or less with respect to the whole positive electrode active material. % By mass or less. When the content of boron is in the above range, when the positive electrode active material 100 is used for a secondary battery, the battery capacity, and the suppression of a decrease in output characteristics and the suppression of gelation of the cathode mixture paste during electrode production. And compatibility can be achieved.

On the other hand, if the boron content is less than 0.01% by mass, the effect of suppressing gelation of the positive electrode mixture paste during electrode production cannot be sufficiently obtained. It is considered that this is because the lithium hydroxide remaining on the surface of the lithium nickel composite oxide 10 cannot be sufficiently removed. When the boron content exceeds 0.1% by mass, the battery characteristics of the secondary battery may deteriorate. Although the details of this reason are unclear, it is considered that the reason is that the amorphous LiBO ₂ layer formed on the surface of the lithium nickel composite oxide 10 becomes too thick and the reaction resistance of the positive electrode increases.

(Eluted amount of lithium hydroxide)

  A water-soluble lithium compound containing lithium hydroxide (LiOH) (hereinafter collectively referred to as “excess lithium”) is formed on the surface of a normal lithium nickel composite oxide (eg, reference numeral “10a” in FIG. 2B). Exists. When manufacturing a secondary battery, the positive electrode mixture paste may be gelled. This is because surplus lithium is eluted in the water contained in the positive electrode mixture paste and raises the pH value of the paste. It is thought to be because.

  The present inventors 1) Among the excess lithium remaining in the ordinary lithium-nickel composite oxide 10a, particularly, lithium that elutes as lithium hydroxide (LiOH) in the positive electrode mixture paste is a gel of the positive electrode mixture paste. And 2) when the amount of lithium eluted as lithium hydroxide (LiOH) is controlled to a specific range when the positive electrode active material 100 is dispersed in water, the positive electrode mixture paste It has been found that gelation can be suppressed.

The amount of the lithium nickel composite oxide 10 coated with the amorphous LiBO ₂ that elutes as lithium hydroxide when dispersed in water (hereinafter, also referred to as “excess lithium hydroxide amount”) is positive electrode activity. Preferably, it is less than 0.2% by mass, more preferably 0.15% by mass or less, more preferably 0.1% by mass or less, based on the whole substance 100. When the amount of surplus lithium hydroxide is in the above range, gelation of the positive electrode mixture paste can be suppressed, and deterioration of battery characteristics can be suppressed.

  On the other hand, when the amount of surplus lithium hydroxide is 0.2% by mass or more, the effect of suppressing the gelation of the paste may not be sufficiently obtained. The reason for this is considered to be that excess lithium hydroxide is large and promotes gelation. Further, the lower limit of the amount of excess lithium hydroxide is, for example, 0.01% by mass or more, may be 0.05% by mass or more, or 0.09% by mass or more based on the whole positive electrode active material 100. You may.

  In the present specification, the amount of excess lithium hydroxide refers to the amount of the acid used up to the first neutralization point, by neutralization titration, among lithium compounds eluted by dispersing the positive electrode active material 100 in water. The Li amount to be measured refers to a lithium compound neutralized by the first neutralization point when a barium chloride aqueous solution is added to the slurry in which the positive electrode active material 100 is dispersed to precipitate the carbonate once. All values are calculated assuming that they are derived from lithium hydroxide (LiOH).

Specifically, the amount of surplus lithium hydroxide can be measured by the following method. First, 15 g of the positive electrode active material is sufficiently dispersed in 75 ml of pure water and allowed to stand for 10 minutes to obtain an aqueous solution obtained by diluting the supernatant with 50 ml of pure water. Next, 5 mL of a 10% barium chloride aqueous solution is added to the aqueous solution. The amount of Li eluted in the aqueous solution thus obtained is measured by a neutralization titration method using an acid such as hydrochloric acid. During the neutralization titration, the pH of the aqueous solution obtained by diluting the supernatant decreases in two steps. And the 1st stage shows the pH which decreases by the neutralization of lithium hydroxide. Therefore, the amount of surplus lithium hydroxide is calculated assuming that the amount of Li calculated from the amount of acid used up to the first neutralization point is all derived from lithium hydroxide (LiOH) by neutralization titration. At the first neutralization point, for example, Li ₃ BO ₃ is also eluted, so that the excess amount of lithium hydroxide may include lithium derived from Li ₃ BO ₃ .

The amount of surplus lithium hydroxide in the lithium-nickel composite oxide 10 coated with amorphous LiBO ₂ is determined, for example, in the later-described production process of the lithium-nickel composite oxide 10 (see FIG. The above range can be controlled by appropriately adjusting the amount of the boron compound added in the mixing step (Step S1) and the heat treatment temperature in the heat treatment step (Step S2).

2. Next, with reference to FIGS. 2A and 2B, a method for manufacturing a positive electrode active material for a lithium ion secondary battery according to the present embodiment (hereinafter, referred to as “a positive electrode active material for a lithium ion secondary battery” Also referred to as “a method for producing a positive electrode active material”). FIG. 2A is a diagram illustrating an example of a method for manufacturing a positive electrode active material according to the present embodiment. FIG. 2B is an explanatory diagram of a reaction between lithium contained in the lithium nickel composite oxide 10a (raw material) and the boron compound B. By the method for producing a positive electrode active material according to the present embodiment, the positive electrode active material 100 including the lithium nickel composite oxide 10 having at least a part of the surface coated with amorphous LiBO ₂ as described above is produced on an industrial scale. It can be manufactured with high productivity.

The method for producing a positive electrode active material of the present embodiment includes the steps of mixing a lithium nickel composite oxide 10a (raw material) and a boron compound B to obtain a boron mixture (step S1), and adding the boron mixture to an oxygen atmosphere. Medium heat treatment at a temperature of 300 ° C. or more and 500 ° C. or less to obtain a lithium nickel composite oxide 10 coated with amorphous LiBO ₂ (step S2). Hereinafter, each step will be described.

[Mixing Step (Step S1)]
In the method for producing a positive electrode active material of the present embodiment, first, the boron compound B and the lithium nickel composite oxide 10a (raw material) are mixed to obtain a boron mixture (step S1).

As the boron compound B, a compound containing boron capable of reacting with lithium can be used. For example, boron oxide (B ₂ O ₃ ), boric acid (H ₃ BO ₃ ), ammonium tetraborate tetrahydrate ( _{(NH 4) 2B 4 O 7} · 4H 2 O), and the like pentaborate ammonium octahydrate _{((NH 4) 2 O ·} 5B 2 O 3 · 8H 2 O). These compounds have high reactivity with lithium salts, and are considered to form amorphous LiBO ₂ after a heat treatment step (step S2) described later. Among these compounds, it is preferable to use at least one selected from H ₃ BO and B ₂ O ₃ . H ₃ BO ₃ and B ₂ O ₃ are preferred as the boron compound B because they show acidity and have higher reactivity with Li.

  The boron compound B contains boron (B) in the boron compound B in an amount of 0.01% by mass or more and 0.1% by mass or less, preferably 0.03% by mass or more and 0.06% by mass or less with respect to the whole obtained positive electrode active material. It is mixed in an amount of not more than mass%.

Lithium nickel composite oxide 10a (raw material) is not particularly limited, can be a known, for example, the general formula _{(1): Li a Ni 1} -x-y Co x M y O 2 + α ( where 0.95 ≦ a ≦ 1.10, 0.05 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.10, 0 ≦ α ≦ 0.2, M is Mn, V, Mg, Mo, Nb, Ti , W, Zr and at least one element selected from Al).

  The amount of surplus lithium hydroxide in the lithium nickel composite oxide 10a (raw material) is, for example, 0.15% by mass or more and 0.25% by mass or less, and preferably 0% .15% by mass or more and 0.21% by mass or less.

  The amount of the boron compound B to be mixed is such that the upper limit of the surplus lithium hydroxide amount of the finally obtained positive electrode active material 100 is preferably less than 0.2% by mass, more preferably 0% by mass, based on the whole positive electrode active material 100. It is preferable to adjust the amount to be .15% by mass or less, more preferably 0.1% by mass or less. Further, the amount of the boron compound B to be mixed is preferably set to an amount such that the lower limit is, for example, 0.01% by mass or more based on the whole positive electrode active material 100.

  That is, in the manufacturing method of the present embodiment, the amount of lithium hydroxide measured by the neutralization titration method and eluted when the positive electrode active material 100 obtained after the heat treatment described later (step S2) is dispersed in water ( The amount and mixing of the lithium-nickel composite oxide 10a (raw material) are adjusted so that the amount of excess lithium hydroxide is in the range of 0.01% by mass or more and less than 0.2% by mass with respect to the entire positive electrode active material 100. It is preferred to adjust the amount of boron compound B. Thereby, the obtained positive electrode active material 100 can further suppress the gelation of the positive electrode mixture paste and can suppress the deterioration of the battery characteristics.

  In the mixing step (step S1), it is preferable that the boron compound B and the lithium nickel composite oxide 10a are sufficiently mixed. For mixing, a general mixer can be used. For example, a shaker mixer, a Lodige mixer, a Julia mixer, a V blender, or the like can be used, and the shape of the lithium nickel composite oxide particles is not destroyed. May be sufficiently mixed with the boron compound B.

[Heat treatment step (Step S2)]
Next, the boron mixture is heat-treated in an oxygen atmosphere at a temperature of 300 ° C. or more and 500 ° C. or less to obtain a lithium nickel composite oxide 10 coated with amorphous LiBO ₂ (step S2). By heat-treating the lithium nickel composite oxide 10 containing the boron compound B, the lithium hydroxide remaining on the surface of the lithium nickel composite oxide 10 reacts with the boron compound B as shown in FIG. Quality LiBO ₂ can be produced. Since boron hardly forms a solid solution in the lithium-nickel composite oxide 10, most of the boron added as the boron compound B is considered to form LiBO ₂ .

The heat treatment temperature is 300 ° C. or higher and 500 ° C. or lower, preferably 300 ° C. or higher and 450 ° C. or lower. When the firing temperature is in the above range, the surface of the lithium nickel composite oxide 10 can be uniformly coated in an amorphous state on the LiBO ₂ layer. When the firing temperature is 300 ° C. or higher, the hydroxyl group in LiB (OH) ₄ generated by the reaction between the boron compound B and the lithium hydroxide remaining on the surface of the lithium nickel composite oxide 10 is removed, and amorphous LiBO is formed. ₂ can be generated. Thus, the surface of the lithium nickel composite oxide 10 can be uniformly coated with the LiBO ₂ layer.

On the other hand, when the firing temperature is lower than 300 ° C., the removal of hydroxyl groups from LiB (OH) ₄ becomes insufficient, the lithium ion conductivity is low, and the battery characteristics are further reduced. When the sintering temperature exceeds 500 ° C., LiBO ₂ extracts lithium in the lithium-nickel composite oxide 10 to generate Li ₃ BO ₃ , thereby increasing the reaction resistance of the lithium-nickel composite oxide 10 and increasing the battery resistance. It is not preferable because the characteristics are deteriorated.

  The holding time at the heat treatment temperature is, for example, 0.5 to 5 hours, preferably about 1 to 3 hours, and may be, for example, 1 to 2 hours. The atmosphere during the heat treatment is an oxygen atmosphere, for example, an atmosphere having an oxygen concentration of 100% by volume is preferable.

The lithium nickel composite oxide 10 (positive electrode active material 100) according to the present embodiment can be obtained by the above-described manufacturing method. As described above, in the lithium nickel composite oxide 10 (positive electrode active material 100) coated with amorphous LiBO ₂ obtained in the present embodiment, the amount of excess lithium hydroxide measured by the neutralization titration method is positive. It is preferably less than 0.2% by mass, more preferably 0.15% by mass or less, more preferably 0.1% by mass or less based on the whole active material 100. When the amount of surplus lithium hydroxide is in the above range, gelation of the positive electrode mixture paste can be suppressed. Note that the lower limit of the amount of the surplus lithium hydroxide is preferably, for example, 0.01% by mass or more based on the entire positive electrode active material 100.

For example, the surplus lithium hydroxide amount (mass%) of the lithium nickel composite oxide 10 with respect to the entire positive electrode active material 100 is determined by the surplus lithium hydroxide amount (mass) of the lithium nickel composite oxide 10a (raw material) used as a raw material. %) May be 0.01% by mass or more, 0.02% by mass or more, or 0.05% by mass or more. As shown in FIG. 2B, excess lithium in the raw material is used as a Li source when amorphous LiBO ₂ is formed, and as a result, the amount of excess lithium hydroxide is considered to be reduced. Therefore, it is considered that the difference in the amount of excess lithium hydroxide between the lithium nickel composite oxide 10 and the raw material reflects the degree of the reaction or coating of the amorphous LiBO ₂ , and the difference in the amount of excess lithium is within the above range. In this case, it can be said that the amorphous LiBO ₂ is sufficiently formed on the surface of the lithium nickel composite oxide 10. The upper limit of the difference is not particularly limited, but is, for example, 0.15% by mass or less.

3. Next, a method for producing the positive electrode mixture paste for a lithium ion secondary battery according to the present embodiment (hereinafter, also referred to as “positive electrode mixture paste” or “paste”) will be described. I do. The paste of the present embodiment includes the lithium nickel composite oxide 10 (positive electrode active material 100) coated with amorphous LiBO ₂ . Therefore, elution of lithium from the lithium nickel composite oxide 10 (positive electrode active material 100) in the paste is reduced, and gelation of the paste is suppressed. Therefore, even when the paste is stored for a long time, the change in the viscosity of the paste is small, and the paste can have high stability. When a positive electrode is manufactured using such a paste, a positive electrode having excellent characteristics can be obtained stably, and the characteristics of a finally obtained secondary battery can be stably improved.

  The constituent material of the positive electrode mixture paste is not particularly limited except for the lithium nickel composite oxide 10, and a material equivalent to a known positive electrode mixture paste can be used. The positive electrode mixture paste contains, for example, the above-described lithium nickel composite oxide 10, a conductive material, and a binder. The positive electrode mixture paste may further contain a solvent. When the total mass of the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, for example, the positive electrode mixture paste has a positive electrode active material content of 60 to 95 parts by mass and a conductive material content of 1 to 100 parts by mass. 20 parts by mass and the content of the binder can be 1 to 20 parts by mass.

  As the conductive agent, for example, graphite (natural graphite, artificial graphite, expanded graphite, or the like), or a carbon black-based material such as acetylene black or Ketjen black can be used.

  The binder (binder) plays a role of binding the active material particles. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluoro rubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin And polyacrylic acid.

  Note that a conductive material and activated carbon may be dispersed in the positive electrode active material 100, and a solvent that dissolves a binder (binder) may be added as necessary. Specifically, an organic solvent such as N-methyl-2-pyrrolidone (NMP) 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. For the positive electrode mixture paste, for example, the powdered oxide, the conductive material, and the binder are mixed, and further, if necessary, activated carbon, a target solvent such as viscosity adjustment is added, and the mixture is kneaded. Can be made.

4. Lithium ion secondary battery The lithium ion secondary battery (hereinafter, also referred to as “secondary battery”) according to the present embodiment includes a positive electrode including the above-described positive electrode active material as a positive electrode material. The lithium ion secondary battery can be configured by the same components as those of a conventionally known lithium ion secondary battery, and includes, for example, a positive electrode, a negative electrode, and a non-aqueous electrolyte. In addition, the secondary battery may include, for example, a positive electrode, a negative electrode, and a solid electrolyte. Further, the secondary battery may be a secondary battery that performs charging and discharging by desorption and insertion of lithium ions, for example, may be a non-aqueous electrolyte secondary battery, and may be an all-solid lithium secondary battery. There may be. The embodiment described below is merely an example, and the lithium ion secondary battery of the present embodiment is based on the embodiment described in the present specification, based on the knowledge of those skilled in the art, various changes, It can be implemented in an improved form. The use of the lithium ion secondary battery of the present embodiment is not particularly limited.

[Components]
(Positive electrode)
First, the above-described positive electrode active material 100, a conductive material and a binder are mixed, and if necessary, activated carbon or a solvent for viscosity control or the like is added, and the mixture is kneaded to prepare a positive electrode mixture paste. . As the positive electrode mixture paste, the above-described positive electrode mixture paste of the present embodiment can be used.

  The obtained positive electrode mixture paste is applied to, for example, the surface of a current collector made of aluminum foil, dried, and the solvent is scattered. If necessary, pressure may be applied by a roll press or the like in order to increase the electrode density. Thus, a sheet-shaped positive electrode can be manufactured. The sheet-shaped positive electrode can be cut to an appropriate size according to the intended battery, and used for battery production. Note that the method for manufacturing the positive electrode is not limited to the above method, and may be another method.

(Negative electrode)
As the negative electrode, metallic lithium, a lithium alloy, or the like may be used. As the negative electrode, a negative electrode mixture obtained by mixing a binder with a negative electrode active material capable of inserting and extracting lithium ions and adding an appropriate solvent to form a paste is formed on the surface of a metal foil collector such as copper. May be applied, dried, and, if necessary, compressed to increase the electrode density.

  As the negative electrode active material, for example, an organic compound fired body such as natural graphite, artificial graphite and a phenol resin, and a powdered carbon material such as coke can be used. In this case, similarly to the positive electrode, a fluorine-containing resin such as PVDF can be used as the negative electrode binder, and an organic material such as N-methyl-2-pyrrolidone is used as a solvent for dispersing these active materials and the binder. Solvents can be used.

(Separator)
A separator is interposed between the positive electrode and the negative electrode as necessary. The separator separates the positive electrode and the negative electrode and retains the electrolyte, and may be a thin film such as polyethylene or polypropylene having a large number of fine pores.

(Non-aqueous electrolyte)
As the non-aqueous electrolyte, a non-aqueous electrolyte can be used. As the non-aqueous electrolyte, for example, a solution in which a lithium salt as a supporting salt is dissolved in an organic solvent may be used. Further, as the non-aqueous electrolyte, an ionic liquid in which a lithium salt is dissolved may be used. In addition, the ionic liquid refers to a salt composed of cations and anions other than lithium ions, and which is liquid even at normal temperature.

  Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate, and chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate and dipropyl carbonate, and further, tetrahydrofuran and 2-hydrogen carbonate. One compound selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate may be used alone or as a mixture of two or more. Can be used.

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

  Further, a solid electrolyte may be used as the non-aqueous electrolyte. The solid electrolyte has a property that can withstand a high voltage. Examples of the solid electrolyte include an inorganic solid electrolyte and an organic solid electrolyte.

  As the inorganic solid electrolyte, an oxide solid electrolyte, a sulfide solid electrolyte, or the like is used.

The oxide solid electrolyte is not particularly limited, and any oxide containing oxygen (O) and having lithium ion conductivity and electronic insulation can be used. The oxide-based solid electrolyte, for example, lithium phosphate _{(Li 3 PO 4), Li} 3 PO 4 N X, LiBO 2 N X, LiNbO 3, LiTaO 3, Li 2 SiO 3, Li 4 SiO 4 -Li 3 PO ₄ , Li ₄ SiO ₄ —Li ₃ VO ₄ , Li ₂ O—B ₂ O ₃ —P ₂ O ₅ , Li ₂ O—SiO ₂ , Li ₂ O—B ₂ O ₃ —ZnO, Li _{1 + X} Al _X Ti _2-X (PO ₄ ) ₃ (0 ≦ X ≦ 1), Li _{1 + X} Al _X Ge _2-X (PO ₄ ) ₃ (0 ≦ X ≦ 1), LiTi ₂ (PO ₄ ) ₃ , Li _3X La _{2 / 3-X} TiO ₃ (0 ≦ X ≦ 2/3), Li ₅ La ₃ Ta ₂ O ₁₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₆ BaLa ₂ Ta ₂ O ₁₂ , Li _3.6 Si _0.6 P _0.4 O ₄ etc. I can do it.

The sulfide-based solid electrolyte is not particularly limited, and any electrolyte containing sulfur (S) and having lithium ion conductivity and electronic insulation can be used. The sulfide-based solid electrolyte, for _{example, Li 2 S-P 2 S} 5, Li 2 S-SiS 2, LiI-Li 2 S-SiS 2, LiI-Li 2 S-P 2 S 5, LiI-Li 2 _{S-B 2 S 3, Li} 3 PO 4 -Li 2 S-Si 2 S, Li 3 PO 4 -Li 2 S-SiS 2, LiPO 4 -Li 2 S-SiS, LiI-Li 2 S-P 2 O _{5, LiI-Li 3 PO 4} -P 2 S 5 , and the like.

In addition, as the inorganic solid electrolyte, one other than the above may be used. For example, Li ₃ N, LiI, Li ₃ N—LiI—LiOH, or the like may be used.

  The organic solid electrolyte is not particularly limited as long as it is a polymer compound having ion conductivity, and for example, polyethylene oxide, polypropylene oxide, a copolymer thereof, or the like can be used. Further, the organic solid electrolyte may contain a supporting salt (lithium salt). When a solid electrolyte is used, the solid electrolyte may be mixed in the positive electrode material in order to ensure contact between the electrolyte and the positive electrode active material.

(Battery shape and configuration)
The configuration of the secondary battery is not particularly limited, and may be configured with a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, or the like as described above, or may be configured with a positive electrode, a negative electrode, a solid electrolyte, or the like. The shape of the secondary battery is not particularly limited, and may be various shapes such as a cylindrical shape and a stacked shape.

  For example, when the secondary battery is a non-aqueous electrolyte secondary battery, a positive electrode and a negative electrode are laminated via a separator to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolyte solution to form a positive electrode. Connect the current collector and the positive terminal connected to the outside and between the negative electrode current collector and the negative terminal connected to the outside using a current collecting lead or the like, seal the battery case, and seal the secondary battery. To complete.

(Characteristic)
After the coin-type battery CBA used in the example was manufactured, the initial discharge capacity was allowed to stand for about 24 hours after the open-circuit voltage OCV (Open Circuit Voltage) was stabilized, and the current density with respect to the positive electrode was 0.1 mA / cm ^2. It is a value obtained by measuring the capacity when the battery was charged to a cutoff voltage of 4.3 V, discharged after a one-hour pause, and then discharged to a cutoff voltage of 3.0 V.

  An example of the method for measuring the positive electrode resistance in the present embodiment is as follows. When the frequency dependence of the battery reaction is measured by a general AC impedance method as an electrochemical evaluation method, a Nyquist plot based on solution resistance, negative electrode resistance and negative electrode capacity, and positive electrode resistance and positive electrode capacity is shown in FIG. Is obtained. The battery reaction at the electrode consists of a resistance component due to charge transfer and a capacitance component due to the electric double layer.When these are represented by an electric circuit, a parallel circuit of resistance and capacitance is formed. It is represented by an equivalent circuit in which circuits are connected in series. A 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 plot. Therefore, the AC impedance of the secondary battery to be manufactured is measured, and the positive electrode resistance can be estimated by performing fitting calculation on the obtained Nyquist diagram with an equivalent circuit.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples of the present invention, but the present invention is not limited to these Examples. In addition, the Example and the comparative example evaluated by the measurement result using the following apparatus and method.

[Composition of whole positive electrode active material]
After dissolving the obtained positive electrode active material with nitric acid, it was measured with an ICP emission spectrometer (ICPS-8100, manufactured by Shimadzu Corporation).

[Compound species identification]
The obtained positive electrode active material was evaluated using an X-ray diffractometer (trade name: X'Pert PRO, manufactured by PANalytical) and a Raman spectrometer (trade name: DXR2, manufactured by Thermo Fisher Scientific).

[Viscosity stability of positive electrode mixture paste]
25.0 g of the positive electrode active material, 1.5 g of carbon powder of conductive material, 2.9 g of polyvinylidene fluoride (PVDF), and N-methyl-2-pyrrolidone (NMP) were mixed by a planetary kneader to mix the positive electrode mixture. A paste was obtained. The addition amount of N-methyl-2-pyrrolidone (NMP) was adjusted by a viscosity measurement method using a vibration viscometer specified in JIS Z 8803: 2011 so that the viscosity was 1.5 to 2.5 Pa · s. The obtained positive electrode mixture paste was stored for 76 hours, and the state of occurrence of gelation was visually evaluated. The case where gelation did not occur was evaluated as ○, and the case where gelation occurred was evaluated as ×.

[Measurement of surplus lithium hydroxide amount]
After 15 g of the obtained positive electrode active material was dispersed in 75 ml of pure water, the mixture was allowed to stand for 10 minutes, 10 ml of the supernatant was diluted with 50 ml of pure water, and 5 ml of a 10% barium chloride aqueous solution was added to the diluted solution. The amount of Li eluted in the aqueous solution was measured by a neutralization titration method in which 1 mol / liter of hydrochloric acid was added. In the neutralization titration, the pH of the aqueous solution of the supernatant is reduced in two stages. The amount of pH decrease in the first stage indicates excess lithium hydroxide (first neutralization point), and the amount of eluted Li (excess lithium hydroxide) is calculated from the amount of hydrochloric acid up to the first neutralization point. did. The amount of surplus lithium hydroxide is the amount of Li measured from the amount of hydrochloric acid up to the first neutralization point when a barium chloride aqueous solution is added to the slurry in which the positive electrode active material 100 is dispersed, and the carbonate is once precipitated. Was calculated as being derived from lithium hydroxide (LiOH).

[Evaluation of battery characteristics]
(Preparation of coin cell battery for evaluation)
20% by mass of acetylene black and 10% by mass of PTFE were mixed with 70% by mass of the obtained positive electrode active material, and 150 mg of the mixture was taken out to prepare a pellet, which was used as a positive electrode. Lithium metal is used as the negative electrode, and an electrolytic solution is a mixed solution of equal amounts of ethylene carbonate (EC) and diethyl carbonate (DEC) using 1M LiClO ₄ as a supporting salt (manufactured by Toyama Pharmaceutical Co., Ltd.). A 2032-type coin-type battery CBA as shown in FIG. The performance of the manufactured coin-type battery CBA was evaluated based on the initial discharge capacity and the like.

(Initial discharge capacity)
The initial discharge capacity was set at about 24 hours after the coin-type battery CBA was manufactured, and after the open circuit voltage OCV (open circuit voltage) became stable, the current density with respect to the positive electrode was 0.1 mA / cm ² , and the cut-off voltage was 4 The battery was charged to 0.3 V, and after a pause of 1 hour, the discharge capacity was measured when the battery was discharged to a cutoff voltage of 3.0 V, which was defined as the initial discharge capacity before exposure to the atmosphere.

(Positive electrode resistance)
When the coin-type battery CBA was charged at a charging potential of 4.1 V and the internal resistance was measured by an AC impedance method using a frequency response analyzer and a potentiogalvanostat (manufactured by Solartron, 1255B), the Nyquist plot shown in FIG. 3 was obtained. can get. The Nyquist plot is represented as a sum of characteristic curves indicating solution resistance, negative electrode resistance and its capacity, and positive electrode resistance and its capacity. A fitting calculation was performed using an equivalent circuit based on the obtained Nyquist plot, and the value of the positive electrode resistance was calculated.

(Example 1)
To the particles of the lithium-nickel composite oxide having an average particle diameter of 13 μm, an amount that makes the amount of boron 0.03% by mass based on the positive electrode active material from which the boron compound H ₃ BO ₃ (manufactured by Wako Pure Chemical Industries, Ltd.) is obtained, A boron mixture was formed. Mixing was performed using a shaker mixer device (TURBULA Type T2C, manufactured by Willy & Bacoffen (WAB)). The obtained mixture was baked (heat treated) at 300 ° C. (heat treatment temperature) for 1 hour in an oxygen stream (oxygen: 100% by volume), cooled, and sieved to obtain a positive electrode active material. The obtained positive electrode active material contains boron in an amount of 0.03% by mass with respect to the positive electrode active material, and is represented by the composition formula Li _1.03 Ni _0.82 Co _0.15 Al _0.03 O _2. It was a composite oxide.

When the obtained positive electrode active material was analyzed with a Raman spectrometer (trade name: DXR2, manufactured by Thermo Fisher Scientific), a broad peak of LiBO ₂ was detected, and LiBO ₂ was amorphous on the surface of the lithium nickel composite oxide. It was confirmed that it exists. Tables 1 and 2 show the evaluation results of the obtained positive electrode active materials and the like.

(Example 2)
A positive electrode active material and the like were obtained and evaluated in the same manner as in Example 1, except that H ₃ BO ₃ was added so that the boron content was 0.06% by mass with respect to the positive electrode active material. The evaluation results are shown in Tables 1 and 2.

(Example 3)
A positive electrode active material and the like were obtained and evaluated in the same manner as in Example 1 except that the heat treatment temperature was changed to 450 ° C. The evaluation results are shown in Tables 1 and 2.

(Example 4)
A cathode active material and the like were obtained in the same manner as in Example 1 except that H ₃ BO ₃ was added so that the boron content was 0.06% by mass with respect to the cathode active material, and the heat treatment temperature was 450 ° C. evaluated. The evaluation results are shown in Tables 1 and 2.

(Example 5)
A positive electrode active material and the like were obtained and evaluated in the same manner as in Example 1, except that the boron compound B ₂ O ₃ was added so that the boron content was 0.06% by mass based on the positive electrode active material. The evaluation results are shown in Tables 1 and 2.

(Comparative Example 1)
A positive electrode active material and the like were obtained and evaluated in the same manner as in Example 1 except that boric acid (boron compound) was not added. The evaluation results are shown in Tables 1 and 2.

(Comparative Example 2)
A positive electrode active material and the like were obtained and evaluated in the same manner as in Example 1, except that H ₃ BO ₃ was added so that the boron content was 0.005% by mass based on the positive electrode active material. The evaluation results are shown in Tables 1 and 2.

(Comparative Example 3)
A positive electrode active material and the like were obtained and evaluated in the same manner as in Example 1 except that the heat treatment temperature was changed to 600 ° C. The evaluation results are shown in Tables 1 and 2.

(Comparative Example 4)
A positive electrode active material and the like were obtained and evaluated in the same manner as in Example 1 except that the heat treatment temperature was set to 200 ° C. The evaluation results are shown in Tables 1 and 2.

(Comparative Example 5)
A positive electrode active material and the like were obtained and evaluated in the same manner as in Example 1, except that H ₃ BO ₃ was added so that the boron content was 0.2% by mass with respect to the positive electrode active material. The evaluation results are shown in Tables 1 and 2.

(Evaluation results)
When the X-ray diffractions of the positive electrode active materials obtained in Examples 1 to 5 and Comparative Examples 1 to 5 were measured, a peak of the lithium nickel composite oxide was detected. In Comparative Example 3, in addition to the peak of the lithium nickel composite oxide, a peak of Li ₃ BO ₃ was also detected. When the positive electrode active materials obtained in Examples 1 to 5 and Comparative Examples 2 and 5 were analyzed with a Raman spectrometer, a broad peak of LiBO ₂ was detected.

In Examples 1 to 5, amorphous LiBO ₂ was uniformly coated on the surface. Compared with Comparative Examples 1 to 5, when used for the positive electrode of the secondary battery, increase in the positive electrode resistance was suppressed. As a result, a high battery capacity was obtained. Further, in all of the positive electrode active materials obtained in Examples 1 to 5, gelation of the paste was suppressed. In Comparative Example 1, the amount of excess lithium hydroxide was large, and the paste gelled. On the other hand, in Comparative Example 2, since the amount of boron was small, the amount of excess lithium hydroxide was not sufficiently reduced, and the paste gelled. In Comparative Example 3, it is considered that lithium was extracted from the surface of the lithium-nickel composite oxide due to generation of Li ₃ BO ₃ , and the positive electrode resistance was increased. In Comparative Example 4, it was considered that LiBO ₂ was not generated and sufficient lithium ion conductivity was not obtained, so that the positive electrode resistance increased. In Comparative Example 5, it is considered that the coating layer of LiBO ₂ was thick, the initial discharge capacity decreased, and the positive electrode resistance increased.

  From the above results, the positive electrode active material of the present embodiment, by setting the heat treatment temperature and the addition amount of the boron raw material in an appropriate range, good output characteristics by reducing the positive electrode resistance, and high battery capacity, It is clear that a positive electrode active material that achieves both suppression of gelation of the paste during electrode production can be obtained.

  The positive electrode active material for a lithium ion secondary battery of the present invention can suppress the gelation of the positive electrode mixture paste and exhibit stable battery performance at low cost. Therefore, it is particularly suitable as a positive electrode active material of a lithium ion battery used as a power source for a hybrid vehicle or an electric vehicle.

100 positive electrode active material 10 lithium nickel composite oxide 10a lithium nickel composite oxide (raw material)
LB: Amorphous LiBO ₂
B: Boron compound CBA: Coin-type battery CA: Case PC: Positive electrode can NC: Negative electrode can GA: Gasket PE: Positive electrode NE: Negative electrode SE: Separator

Claims (7)

Including a lithium nickel composite oxide and amorphous LiBO ₂ ,
The lithium-nickel composite oxide contains lithium, nickel, cobalt, and an element M, and the ratio (molar ratio) of the amount of each element is Li: Ni: Co: M = a: (1-x -Y): x: y (where 0.95 ≦ a ≦ 1.10, 0.05 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.10, M is Mn, V, Mg, Mo, Nb) , Ti, W, Zr, and at least one element selected from Al)
Amorphous LiBO ₂ covers at least a part of the surface of the lithium nickel composite oxide,
The content of boron is 0.01% by mass or more and 0.1% by mass or less based on the whole positive electrode active material.
A positive electrode active material for lithium ion secondary batteries. Mixing a lithium nickel composite oxide and a boron compound to obtain a mixture,
The mixture is heat-treated at a temperature of 300 ° C. or more and 500 ° C. or less in an oxygen atmosphere to react the boron compound with lithium in the lithium nickel composite oxide, thereby forming a surface of the lithium nickel composite oxide. Forming amorphous LiBO ₂ at least in part of
The lithium-nickel composite oxide contains lithium, nickel, cobalt, and an element M, and the ratio (molar ratio) of the amount of each element is Li: Ni: Co: M = a: (1-x -Y): x: y (where 0.95 ≦ a ≦ 1.10, 0.05 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.10, M is Mn, V, Mg, Mo, Nb) , Ti, W, Zr, and at least one element selected from Al)
The mixture contains 0.01% by mass or more and 0.1% by mass or less of boron in the boron compound based on the entire mixture.
A method for producing a positive electrode active material for a lithium ion secondary battery. The boron compound, H ₃ BO ₃ and B contains at least one selected from ₂ O _3, method for producing a cathode active material for a lithium ion secondary battery as claimed in claim 2. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 2 or 3, wherein at least a part of the surface of the lithium nickel composite oxide is coated with amorphous LiBO ₂ .   The amount of lithium hydroxide eluted when the positive electrode active material obtained after the heat treatment is dispersed in water and measured by a neutralization titration method is 0.01% by mass or more to 0.2% by mass with respect to the whole positive electrode active material. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 2 to 4, wherein the method is adjusted to be in a range of less than mass%.   A positive electrode mixture paste for a lithium ion secondary battery, comprising the positive electrode active material for a lithium ion secondary battery according to claim 1.   A lithium ion secondary battery including a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the positive electrode includes the positive electrode active material according to claim 1.

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