JP2015146269A - Method for producing positive electrode active material for lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a positive electrode active material for lithium ion secondary batteries which is high in capacity and easy to pass electric current therethrough at discharge.SOLUTION: A method for manufacturing a positive electrode active material for lithium ion secondary batteries comprises steps of (1) baking Li carbonate and/or hydroxide salt, and an oxide and others of at least two metals other than Li, thereby obtaining a lithium-containing metal oxide A satisfying the condition, 1≤M/M≤4, where Mrepresents the mole fraction of Li, and Mrepresents the mole fraction of the at least two metal elements other than Li, and (2) subsequently, mixing the lithium-containing metal oxide A thus obtained with a lithium compound B expressed by LiCOHinto a mixture and then, baking the mixture at a temperature lower than the highest baking temperature in the step (1), thereby obtaining one of a crystal C having a layer structure expressed by LiMeO, in which Li is arranged in a layered form, a crystal D having a Spinel structure expressed by LiMeO, and a crystal with the crystal C and the crystal D dissolved therein.

Description

  The present invention relates to a method for producing a positive electrode active material for a lithium ion secondary battery.

As interest in environmental technology has increased in recent years, there is an increasing expectation for storage devices for electrical energy generated by solar power generation and wind power generation and for battery applications in electric vehicles. In particular, lithium ion secondary batteries that are representative of power storage devices are required to be further improved in capacity, voltage, and durability.
However, as the positive electrode active material, the composition formula LiMeO ₂ {wherein Me is a transition metal element. } The actual capacity of a current lithium ion secondary battery using a layered lithium oxide crystal represented by the formula is about 160 mAh / g, and it is actually difficult to increase the capacity beyond this.
From the viewpoint of higher voltage and higher durability, lithium ion secondary batteries using lithium oxide crystals having a spinel structure represented by the composition formula LiMe ₂ O ₄ are also used, but the actual capacity is Currently, the application is limited because it is as low as about 120 mAh / g.
Since the capacity of the lithium ion secondary battery is governed by the lithium content in the positive electrode active material in the battery, it is necessary to develop a positive electrode active material with a high lithium content in order to increase the capacity of the lithium ion battery. It is said that.

As a positive electrode active material having a large amount of lithium, for example, in Patent Document 1 below, the layered lithium oxide crystal described by the above-described composition formula LiMeO ₂ and the lithium content of the same layered lithium oxide crystal are described. Compositional formula ωLiMeO ₂ · (1-ω) Li ₂ MnO ₃ {where 0 <ω <1 in which the layered lithium oxide crystal represented by a large compositional formula Li ₂ MnO ₃ is a solid solution. }, And a high capacity of about 200 mAh / g or more is reported as an actual capacity.

  In addition, in order for the positive electrode active material to exhibit a high capacity, the oxide crystals constituting the positive electrode active material require high element dispersibility, so various synthesis methods for achieving high element dispersibility Has been developed. For example, in Patent Document 2 below, as means for achieving high element dispersibility at the atomic level, a coprecipitation method for synthesizing a precursor of a positive electrode active material or a method for firing it into a lithium metal oxide Detailed reports have been made on the firing conditions and the like.

US Pat. No. 6,677,082 JP 2012-151084 A

However, the positive electrode active material whose lithium content has been increased for higher capacity tends to lower its element dispersibility when a specific crystal structure having a large amount of lithium is produced. The crystal represented by the formula Li ₂ MnO ₃ has a problem that the electrical resistance is large, that is, the crystal described by the composition formula Li ₂ MnO ₃ increases the electrical resistance of the positive electrode active material itself, and at the time of discharge Make it difficult to pass a large current.
Further, a layered lithium oxide crystal represented by the composition formula LiMeO ₂ , a lithium oxide crystal having a spinel structure described by the composition formula LiMe ₂ O ₄ , and a crystal in which they are solid-solved are also composed of Me from a plurality of kinds of elements. In the case of a multi-component system, when the lithium content is increased, the aggregation of a specific metal element occurs, the dispersibility of the element decreases, and the discharge characteristics such as the difficulty of flowing a large current occur. Performance may be reduced.
In view of such circumstances, the problem to be solved by the present invention is to provide a method for producing a positive electrode active material for a lithium ion battery having a high lithium content and high element dispersibility.

As a result of intensive studies and experiments conducted to solve the above problems, the present inventor has obtained a positive electrode active material containing at least two kinds of metal elements in addition to lithium in the following two steps:
(1) A step of firing a lithium-containing metal oxide having a high element dispersibility, which is made of an element constituting the positive electrode active material of the present invention and the molar ratio of the metal element to lithium is 1 or more and 4 or less; 2) The metal oxide obtained in the above step (2) and the lithium compound are mixed and baked at a temperature lower than the maximum calcination temperature in the step (1), so that lithium is additionally introduced into the metal oxide. The positive electrode active material having a high lithium content is obtained while substantially maintaining the particle shape of the lithium-containing metal oxide produced in step (1) and the dispersion state of the metal element inside the crystal. As a result, the present invention has been completed.

That is, the present invention is as follows.
[1] The following steps:
(1) Among carbonates and / or hydroxide salts of Li and oxides, carbonates, hydroxide salts, sulfates, nitrates, hydrochlorides, and acetates of two or more metals other than Li At least one is fired, Li and at least two kinds of metal elements other than Li are included, and the mole fraction of Li is M _L , and the mole fraction of two or more kinds of metal elements other than Li is M _M When the following formula (1):
1 ≦ M _M / M _L ≦ 4 (1)
And (2) the resulting lithium-containing metal oxide A and the following compositional formula (2):
Li _x C _a O _b H _c (2)
{In the formula, 1 ≦ x ≦ 2, 0 ≦ a ≦ 1, 1 ≦ b ≦ 3, and 0 ≦ c ≦ 2 are satisfied. } Is mixed and calcined at a temperature lower than the maximum calcining temperature in the step (1), and the following composition formula (3):
Li _{1 + j} MeO _α (3)
{Wherein Me is two or more metal elements other than Li, and 0 ≦ j ≦ 1 and 2 ≦ α ≦ 3. } The crystal C having a layered structure in which Li represented by the following formula is arranged, or the following composition formula (4):
Li _{1 + k} Me ₂ O _4-β (4)
{Wherein Me is two or more metal elements other than Li, and 0 ≦ k <1 and 0 ≦ β <1. A crystal D having a spinel structure represented by the following formula: or a crystal in which the crystal C and the crystal D are dissolved;
including,
A method for producing a positive electrode active material for a lithium ion secondary battery.

  [2] The method according to [1], further including a step of baking after the step (2) at a temperature higher than a maximum baking temperature in the step (2).

  [3] The method according to [1] or [2], wherein the lithium-containing metal oxide A has a spinel structure.

[4] The lithium-containing metal oxide A has the following composition formula (5):
Li _{1 + k} Mn _2-x M _x O _4-α (5)
{In the formula, M is one or more metal elements other than Mn and Li, and satisfies the relations 0 ≦ k <1, 0 <x ≦ 0.5, and 0 ≦ α <1. } The method as described in said [3] which has a spinel structure represented by these.

  [5] The method according to [4], wherein M is at least Ni.

  [6] The method according to any one of [1] to [3], wherein the Me is at least Mn and Ni.

  [7] The method according to any one of [1] to [6], wherein the lithium compound B includes at least lithium carbonate or lithium hydroxide.

  [8] A positive electrode active material for a lithium ion secondary battery produced by the method according to any one of [1] to [7].

  According to the present invention, it is possible to produce a positive electrode active material for a lithium ion secondary battery that has a high capacity and is easy to pass a large current during discharge.

Hereinafter, a mode for carrying out the present invention (hereinafter also referred to as “the present embodiment”) will be described in detail. The following embodiments are examples for explaining the present invention, and are not intended to limit the present invention to the following contents. The present invention can be implemented with appropriate modifications within the scope of the gist thereof.
As described above, the method for producing a positive electrode active material for a lithium ion secondary battery according to this embodiment includes the following steps:
(1) Among carbonates and / or hydroxide salts of Li and oxides, carbonates, hydroxide salts, sulfates, nitrates, hydrochlorides, and acetates of two or more metals other than Li At least one is fired, Li and at least two kinds of metal elements other than Li are included, and the mole fraction of Li is M _L , and the mole fraction of two or more kinds of metal elements other than Li is M _M When the following formula (1):
1 ≦ M _M / M _L ≦ 4 (1)
And (2) the resulting lithium-containing metal oxide A and the following compositional formula (2):
Li _x C _a O _b H _c (2)
{In the formula, 1 ≦ x ≦ 2, 0 ≦ a ≦ 1, 1 ≦ b ≦ 3, and 0 ≦ c ≦ 2 are satisfied. } Is mixed and calcined at a temperature lower than the maximum calcining temperature in the step (1), and the following composition formula (3):
Li _{1 + j} MeO _α (3)
{Wherein Me is two or more metal elements other than Li, and 0 ≦ j ≦ 1 and 2 ≦ α ≦ 3. } The crystal C having a layered structure in which Li represented by the following formula is arranged, or the following composition formula (4):
Li _{1 + k} Me ₂ O _4-β (4)
{Wherein Me is two or more metal elements other than Li, and 0 ≦ k <1 and 0 ≦ β <1. A crystal D having a spinel structure represented by the following formula: or a crystal in which the crystal C and the crystal D are dissolved;
including.

[Step (1)]
In the step (1), a carbonate and / or hydroxide salt of Li and an oxide, carbonate, hydroxide salt, sulfate, nitrate, hydrochloride, and acetate of two or more metals other than Li At least one of the above is fired, Li and at least two kinds of metal elements other than Li are included, and the mole fraction of Li is M _L , and the mole fraction of two or more kinds of metal elements other than Li Where _M is _M , the following formula (1):
1 ≦ M _M / M _L ≦ 4 (1)
The lithium-containing metal oxide A satisfying the following conditions is produced.
Here, the molar fraction M _L of lithium and the molar fraction M _M of a metal element other than lithium are relative to the total number of lithium atoms and the total number of metal atoms other than lithium in the lithium-containing metal oxide A. ,Each,
M _L = total number of lithium atoms / (total number of lithium atoms + total number of metal atoms other than lithium)
M _M = total number of metal atoms other than lithium / (total number of lithium atoms + total number of metal atoms other than lithium)
It is a value defined by.

When the value of M M _/ M _L is less than 1, aggregation of the same kind of metal is likely to occur in the lithium-containing metal oxide A, such aggregation unit lithium ion secondary reduce the element dispersibility This is not preferable because the performance of the battery is impaired. On the other hand, the value of M M _/ M _L is greater than 4, the aggregation of oxides containing no lithium in the lithium-containing metal oxide A is likely to occur undesirably.
The lithium-containing metal oxide A preferably has a crystal structure. The amorphous structure makes it difficult for lithium to move within the oxide, and it is difficult to pass a large current when a lithium ion secondary battery is formed.

The lithium-containing metal oxide A having a crystal structure is generally a powder composed of primary particles and secondary particles in which the primary particles are aggregated. The primary particles may be single crystals themselves, or may be a combination of a plurality of single crystals with different plane orientations. The secondary particles have a form where they can be isolated as one particle without any bonding point with other particles.
The average primary particle size, which is the average particle size of the primary particles, is not particularly limited, but if the average primary particle size becomes too large, the average of the positive electrode active material crystals obtained after going through step (2) described later As the primary particle size increases, the discharge characteristics such as difficulty in passing a large current occur. Therefore, the preferred average primary particle size is preferably 2 μm or less, more preferably 1 μm or less, and even more preferably 0.5 μm or less. It is. However, if the average primary particle size becomes too small, the durability (long-term storage characteristics, deterioration characteristics due to repeated charge / discharge) deteriorates as the battery. Therefore, the preferred average primary particle diameter of the lithium-containing metal oxide A is preferably Is 0.05 μm or more, more preferably 0.1 μm or more.

The lithium-containing metal oxide A produced in the step (1) is not particularly limited as long as it is an oxide crystal containing at least two kinds of metal elements other than lithium, but each metal element is uniform in the crystal. It is preferable that the same kind of metal element is not aggregated. When aggregation of the same kind of metal element occurs, the aggregated portion eventually decreases in element dispersibility, resulting in a structure different from the target crystal structure, thereby reducing the performance of the positive electrode active material.
As the positive electrode active material of the present embodiment, at least two kinds of metal elements constituting the lithium-containing metal oxide A are preferably Mn (manganese), nickel (Ni), cobalt (Co), titanium (Ti), and molybdenum. (Mo), tungsten (W), vanadium (V), iron (Fe), copper (Cu), and zirconium (Zr).
Among them, a metal element having a large effective nuclear charge in the 3d orbital is preferable in terms of improving the electromotive force of the lithium ion secondary battery, iron, cobalt and nickel having an effective nuclear charge of 6 or more are preferable, and the most effective nuclear charge is the most. Large nickel is particularly preferred.
In addition, from the viewpoint of easily developing a high capacity, the metal element is preferably a metal element that can take many valence states, particularly molybdenum or tungsten, which are Group 6 transition metal elements.

Furthermore, in the present invention, it is preferable to contain manganese as the metal element. By containing manganese, it is possible to facilitate the introduction (addition) of lithium into the crystal in the step (2).
The structure of the lithium-containing metal oxide A is not particularly limited, but the following composition formula (4):
Li _{1 + k} Me ₂ O _4−β {wherein Me is two or more metal elements other than Li, and 0 ≦ k <1 and 0 ≦ β <1. } Is one of the preferred forms. The spinel structure may be a disordered structure belonging to the space group Fd3-m, an order structure belonging to the space group P4 ₃ 32, or a mixture of both structures. Note that “Fd3-m” should be written by adding a bar “-” on “3” of “Fd3m”.

The structure of the lithium-containing metal oxide A may be, for example, a layered rock salt structure other than the spinel structure. In this case, a composition represented by LiMO _δ is adopted, and δ is a value slightly smaller than 2 or 2. The layered rock salt structure may be a structure belonging to the space group R3-m, a structure belonging to the space group P3 ₁ 12, or a mixture of both. Note that “R3-m” should be represented by adding a bar “-” on “3” of “R3m”.

  The structure of the lithium-containing metal oxide A may be a crystal structure other than those described above, for example, an olivine structure, or a crystal in which the lithium-containing metal oxide A does not function as a positive electrode active material, and is not particularly limited. However, in order to increase the capacity, it is necessary that the lithium-containing metal oxide obtained after the step (2) has a composition and structure that function as a positive electrode active material.

The step of producing the lithium-containing metal oxide A in the step (1) is not particularly limited as long as it undergoes the firing step, but preferably has high element dispersibility. There are three examples.
[Example 1]
In Example 1, as a raw material, a finely pulverized lithium salt (for example, lithium sulfate, lithium nitrate, lithium carbonate, lithium hydroxide, etc.) and two or more finely pulverized metal oxides are mixed and then fired. Is mentioned. At this time, the powder may be baked in a mixed state, may be compressed and formed into pellets, or may be baked by dispersing or dissolving the mixture in a liquid such as water. You may bake what was spray-dried by.

[Example 2]
In Example 2, lithium and two or more kinds of metal salts (for example, sulfate, nitrate, hydrochloride, acetate, etc.) are dissolved in water, a solvent such as ethylene glycol, propylene glycol, etc., and the solvent is dried up. The method of baking after performing is mentioned. In particular, it is preferable to use nitrate and acetate, and it is particularly preferable to use the mixture at a molar ratio of nitrate ion NO ₃ ^— and acetate ion CH ₃ COO ^— of 1: 3. At this time, a known complex-forming agent having a function of suppressing a reduction in element dispersibility by coagulating and bonding with metal ions to aggregate the same kind of metal elements during dry-up may be added. As such a complexing agent, citric acid, acetic acid, malic acid, acetylacetone, polyvinyl alcohol and the like can be used.

[Example 3]
In Example 3, an aqueous solution of two or more kinds of metal salts (for example, sulfate, nitrate, hydrochloride, acetate, etc.) and an alkaline aqueous solution (for example, sodium carbonate, sodium bicarbonate, sodium hydroxide, hydroxide) are used as raw materials. The lithium salt described above is added to particles of poorly soluble metal salts (for example, carbonates, hydroxide salts, oxyhydroxide salts, complex salts thereof, etc.) obtained by reacting with potassium, etc. The method of baking after mixing is mentioned.
In the above reaction, in order to prevent metal ions from being oxidized by dissolved oxygen in the aqueous solution, it is preferable to react by blowing nitrogen gas, argon gas, carbon dioxide (CO ₂ ), or the like. In the case of producing a carbonate, it is preferable to employ carbon dioxide because it provides an environment in which carbonate is more easily generated.
In addition, a known complex-forming agent may be added which has a function of coordinating with metal ions and suppressing aggregation of the same kind of metal elements in a poorly soluble metal salt to reduce element dispersibility. As such a complexing agent, ammonia, ammonium sulfate, ethylenediamine, ethylenediaminetetraacetic acid, bipyridine, diaminoethanol or the like can be used.

Among the above examples, Example 2 or Example 3 is preferable in terms of enhancing the element dispersibility of the lithium-containing metal oxide A, and Example 3 is preferable in terms of controlling the secondary particle size. Example 1 is preferable in terms of reducing the cost during synthesis.
The firing temperature in the step (1) is not particularly limited as long as it is a firing temperature at which the target lithium-containing metal oxide A can be obtained, but at least 300 in order for lithium and two or more kinds of metal elements to react uniformly with oxygen. ° C or higher is preferable, and 400 ° C or higher is more preferable. However, if the average primary particle size of the crystal becomes too large due to excessive crystallization accompanying firing, the discharge characteristics deteriorate as described above, and therefore, it is preferably 1000 ° C. or less, more preferably 950 ° C. or less.
In the step (1), the baking may be performed a plurality of times at the same or different temperatures. For example, the baking may be performed at 700 to 900 ° C. after baking at 400 to 600 ° C. Multiple firings may be performed continuously with the raw material in the furnace, or after firing at a certain temperature, the raw material is taken out of the furnace and subjected to processing such as mixing, crushing, and compression again. You may bake in a furnace.

  Whether or not the lithium-containing metal oxide A produced as described above has the target structure can be determined by a known X-ray crystallographic technique. The weight ratio of lithium and metal element in the lithium-containing metal oxide A can be determined by a known inductively coupled plasma emission analysis method (hereinafter abbreviated as ICP). In addition, the average primary particle size of the crystals constituting the lithium-containing metal oxide A is obtained by measuring a plurality of crystal particle sizes in an image using a scanning electron microscope (hereinafter abbreviated as SEM) and averaging them. Or by specific surface area measurement (hereinafter abbreviated as BET) for measuring the physical adsorption method amount of an inert gas. The average primary particle size obtained by BET is calculated on the assumption that the particles are true spheres.

[Step (2)]
In the step (2), the lithium-containing metal oxide A obtained in the step (1) and the following composition formula (2):
Li _x C _a O _b H _c (2)
{In the formula, 1 ≦ x ≦ 2, 0 ≦ a ≦ 1, 1 ≦ b ≦ 3, and 0 ≦ c ≦ 2 are satisfied. } Is mixed and calcined at a temperature lower than the maximum calcining temperature in the step (1), and the following composition formula (3):
Li _{1 + j} MeO _α (3)
{Wherein Me is two or more metal elements other than Li, and 0 ≦ j ≦ 1 and 2 ≦ α ≦ 3. } The crystal C having a layered structure in which Li represented by the following formula is arranged, or the following composition formula (4):
Li _{1 + k} Me ₂ O _4-β (4)
{Wherein Me is two or more metal elements other than Li, and 0 ≦ k <1 and 0 ≦ β <1. }, Or a crystal in which the crystal C and the crystal D are in solid solution.

Step (2) is a step of increasing the lithium content in the lithium-containing metal oxide constituting the positive electrode active material by additionally introducing (adding) lithium to the lithium-containing metal oxide A. The lithium material to be additionally introduced is not particularly limited as long as lithium diffuses into the crystal of the lithium-containing metal oxide A by reacting with the lithium-containing metal oxide A, but the above-described composition formula The lithium compound B represented by (2) is preferable because lithium can be efficiently introduced. Examples of the lithium compound B include lithium carbonate, lithium hydroxide, and a mixture thereof.
In addition to the lithium compound B represented by the composition formula (2), lithium nitrate, lithium sulfate, lithium chloride, etc. may be used alone or in combination as the lithium raw material to be additionally introduced, if necessary. May be.

  When mixing the lithium-containing metal oxide A and the lithium compound B, the lithium compound B refined by pulverization or the like may be used, or the lithium compound B dissolved or dispersed in a liquid such as water is used. May be. When dissolved in a liquid such as water, the liquid may be dried up before firing, or may be fired with the liquid remaining.

The firing temperature in the step (2) needs to be in the following two lower and upper temperature ranges.
The lower limit of the firing temperature is equal to or higher than the temperature at which lithium-containing metal oxide A and lithium compound B react and lithium starts to diffuse into the crystal of lithium-containing metal oxide A. Although this temperature varies depending on the types of the lithium-containing metal oxide A and the lithium compound B, since the above reaction is generally an endothermic reaction and is accompanied by weight loss of the mixture, thermogravimetric-differential thermal analysis (Thermogravimetric-Differential). Thermal Analysis (hereinafter abbreviated as TG-DTA) is performed, and the temperature can be set by measuring the temperature at which weight loss and endothermic reaction occur. More specifically, it is preferably in the range of −100 ° C. or higher and + 200 ° C. or lower, more preferably in the range of −50 ° C. or higher and + 150 ° C. or lower, with respect to the temperature at which the suggested heat reduction shows the minimum value while showing weight loss. is there.

The upper limit of the firing temperature is less than the maximum firing temperature of step (1). If the firing temperature exceeds this upper limit, crystal growth is accelerated rapidly due to the diffusion of lithium introduced into the crystal, and the average primary particle size is in a suitable range (preferable range is the lithium-containing metal in the present embodiment). It is the same as that of oxide A) and the discharge characteristics are deteriorated.
In addition, the firing temperature in the step (2) needs to be in the above temperature range, but it is often preferable to perform firing near the lower limit in the above temperature range. When the firing temperature in the step (2) is high, not only lithium but also metal elements diffuse simultaneously in the crystal of the lithium-containing metal oxide A. As a result, specific metal elements segregate and element dispersibility decreases. However, a positive electrode active material having a desired composition and crystal structure cannot be obtained. In the present invention, the target positive electrode having high element dispersibility is obtained by increasing the lithium content while maintaining the dispersion (distribution) state of the metal element in the lithium-containing metal oxide A produced in the step (1) as much as possible. In order to obtain an active material, it is possible to uniformly introduce lithium into the crystal of the lithium-containing metal oxide A in step (2) while suppressing diffusion of the metal element in the crystal of the lithium-containing metal oxide A as much as possible. desirable. Accordingly, although depending on the types of the lithium-containing metal oxide A and the lithium compound B, the firing temperature in the step (2) is preferably near the lower limit or slightly higher than the lower limit in the above temperature range.

  In the step (2), baking may be performed a plurality of times at the same or different temperatures within the above temperature range. Multiple firings may be performed continuously with the raw material in the furnace, or after firing at a certain temperature, the raw material is taken out of the furnace and subjected to processing such as mixing, crushing, and compression again. You may bake in a furnace. For example, after firing at 400 ° C. to 600 ° C., the mixture may be removed from the furnace, mixed and crushed, and then fired again at 400 ° C. to 600 ° C. The firing time at this time is not particularly limited, but is preferably 30 minutes or more, more preferably 1 hour or more in order to sufficiently complete the reaction between the lithium-containing metal oxide A and the lithium compound B. The upper limit time is not particularly limited. However, from the viewpoint of production cost, the firing time is preferably 24 hours or less, and more preferably 10 hours or less.

In step (2), when lithium is introduced into the crystal of lithium-containing metal oxide A and diffuses in the reaction between lithium-containing metal oxide A and lithium compound B, the crystal of lithium-containing metal oxide A The structure may remain retained, or part or all may be changed to another structure. The function as the positive electrode active material may be manifested by the change.
In the manufacturing method of the positive electrode active material for lithium ion secondary batteries in this embodiment, it has the process of further baking at the temperature higher than the highest baking temperature in a process (2) as needed after a process (2). May be. Thereby, you may adjust the average primary particle diameter of the crystal | crystallization which comprises a positive electrode active material to the suitable range (The suitable range is the same as that of the lithium containing metal oxide A).
In addition, the composition formula (3) below, which is different from the structure of the lithium-containing metal oxide A, is obtained through the above-mentioned further firing step.
Li _{1 + j} MeO _α (3)
{Wherein Me is at least two kinds of metal elements other than Li, and 0 ≦ j ≦ 1 and 2 ≦ α ≦ 3. } May be formed in the crystal of the lithium-containing metal oxide. As such a new crystal structure, for example, the following composition formula (6) having a large lithium content:
Li ₂ MeO _3-γ (6)
{Where 0 ≦ γ ≦ 1. }, There is no particular limitation, but there is no particular limitation.

Here, by using manganese or titanium as one of the metal elements constituting the lithium-containing metal oxide A, a structure represented by a composition of Li ₂ MeO _3-γ containing excessive lithium can be easily formed. The structure shown by the composition of Li ₂ MeO _3-γ where Me is composed of only manganese or titanium has high electrical resistance as described above, and if the firing temperature is too high, crystals where Me is composed of only manganese or titanium are generated and enlarged. Therefore, when a step of further baking is added after step (2), the baking temperature is preferably 1000 ° C. or lower, more preferably 950 ° C. or lower.
Note that the atmosphere during firing in both step (1) and step (2) may be in an oxygen atmosphere or a nitrogen atmosphere, and is not particularly limited. Moreover, although the temperature increase and temperature decrease rate of a baking process are not specifically limited, Preferably both are 1 degreeC / min-50 degreeC / min, More preferably, they are 1 degreeC / min-15 degreeC / min.

The positive electrode active material for a lithium ion secondary battery according to the present invention can be produced by the production method including the steps (1) and (2).
The positive electrode active material for a lithium ion secondary battery produced by the present invention has the following composition formula (3):
Li _{1 + j} MeO _α (3)
{Wherein Me is two or more metal elements other than Li, and 0 ≦ j ≦ 1 and 2 ≦ α ≦ 3. } The crystal C having a layered structure in which Li represented by the following formula is arranged, or the following composition formula (4):
Li _{1 + k} Me ₂ O _4-β (4)
{Wherein Me is two or more metal elements other than Li, and 0 ≦ k <1 and 0 ≦ β <1. } The crystal | crystallization D which has a spinel structure represented by these, or the crystal | crystallization where this crystal | crystallization C and this crystal | crystallization D dissolved.

The layered structure represented by the composition formula Li _{1 + j} MeO _α is from a LiMeO ₂ composition where j = 1 and α = 2 to a Li ₂ MeO ₃ composition where j = 2 and α = 3. Moreover, the thing of the state in which those multiple compositions were mixed in arbitrary ratios is contained.
The spinel structure represented by the composition formula Li _{1 + k} Me ₂ O _4-β also includes a crystal structure in which a plurality of compositions are mixed at an arbitrary ratio.
Furthermore, the thing of the crystal structure which the above-mentioned layered structure and spinel structure dissolved is contained.

As a specific example, one having a crystal structure in which the above-mentioned spinel structure and the above-described layered structure having the Li ₂ MeO _{3 -γ} composition are dissolved can be given. The positive electrode active material having such a crystal structure has high durability and high capacity due to a crystal structure in which a high crystal stability of a spinel structure and a layered structure of a Li ₂ MeO _3-γ composition with a high lithium content are dissolved. It is possible to achieve both, and it is easy to flow a large current by ensuring high element dispersibility.

Further, there can be mentioned those having a crystal structure in which the above-mentioned spinel structure and the above-described layered structure of the LiMeO ₂ composition are dissolved. By having such a crystal structure and maintaining high element dispersibility, it is possible to obtain a positive electrode active material having both characteristics of a high crystal stability of a spinel structure and a layered structure of a LiMeO ₂ composition that easily allows a large current to flow. Can do.

Further, there may be mentioned those having a crystal structure in which the layered structure of the above _Li 2 MeO _3-γ composition and layer structure of the aforementioned LiMeO ₂ composition in a solid solution state. By having such a crystal structure and maintaining high element dispersibility, it is possible to obtain a positive electrode active material that is easy to pass a large capacity and large current.

In addition, there may also be mentioned those made of a layered structure of the above _Li 2 MeO _3-γ composition. When Me is composed of two or more kinds of metal elements and maintains high element dispersibility, a positive electrode active material that is easy to pass a large capacity and a large current can be obtained.
Furthermore, in the spinel structure represented by the composition formula Li _{1 + k} Me ₂ O _4−β , one containing an excessive amount of lithium of k> 0 can be given. By having such a crystal structure and maintaining high element dispersibility, it is possible to obtain a positive electrode active material that is easy to pass a large capacity and large current.

[Lithium ion secondary battery]
An example of using the lithium ion-containing metal oxide in the present embodiment for a lithium ion secondary battery is shown below.
The lithium ion secondary battery includes a positive electrode, a negative electrode, an electrolytic solution, a separator, and an exterior body for housing them for electrical connection and insulation.
An example of the positive electrode and its manufacturing method is shown below. In general, the positive electrode preferably contains a conductive additive and a binder in addition to the positive electrode active material and the current collector foil. Here, the conductive auxiliary agent is not particularly limited as long as it is a known one that can conduct electrons, but a carbon material typified by graphite, acetylene black, and carbon black is preferable. The binder is not particularly limited as long as it can bind two or more kinds of constituent materials contained in the positive electrode, but is not limited to polyvinylidene fluoride (hereinafter abbreviated as PVDF), polytetrafluoroethylene (PTFE), polyacrylic. Polymer materials typified by acid, styrene butadiene rubber and fluoro rubber are preferred. These are used singly or in combination of two or more. Although it does not specifically limit as current collection foil, For example, metal foil, such as aluminum, titanium, stainless steel, an expanded metal, a punch metal, a foam metal, carbon cloth, carbon paper, etc. are suitable.

  A solvent such as N-methylpyrrolidone (hereinafter abbreviated as NMP) is prepared by mixing a lithium-containing metal oxide, which is a positive electrode active material, and, if necessary, a positive electrode mixture obtained by adding the above-described conductive additive or binder. To prepare a positive electrode mixture-containing paste. Next, this positive electrode mixture-containing paste is applied to a current collector foil and dried to form a positive electrode mixture layer, which is pressurized as necessary to adjust the thickness, thereby producing a positive electrode. In addition, a positive electrode active material can be used individually by 1 type or in combination of 2 or more types.

  An example of the negative electrode and the manufacturing method thereof is shown below. A negative electrode will not be specifically limited if it acts as a negative electrode of a lithium ion secondary battery, A well-known thing can be used. It is preferable that a negative electrode contains 1 or more types chosen from the group which consists of a material which can occlude and discharge | release lithium ion as a negative electrode active material. That is, the negative electrode is lithium metal, or a negative electrode active material containing an element capable of forming an alloy with lithium, such as a carbon negative electrode active material, a silicon alloy negative electrode active material, or a tin alloy negative electrode active material, and a silicon oxide negative electrode active material. It is preferable to contain at least one negative electrode active material selected from the group consisting of a material, a tin oxide negative electrode active material, and a lithium-containing compound typified by a lithium titanate negative electrode active material. These negative electrode active materials can be used alone or in combination.

  Examples of the carbon negative electrode active material include hard carbon, soft carbon, artificial graphite, natural graphite, graphite, pyrolytic carbon, coke, glassy carbon, fired body of organic polymer compound, mesocarbon microbead, carbon fiber, activated carbon , Graphite, carbon colloid, and carbon black. Examples of coke include pitch coke, needle coke, and petroleum coke. Moreover, the fired body of an organic polymer compound is obtained by firing and carbonizing a polymer material such as a phenol resin or a furan resin at an appropriate temperature.

  Examples of a material capable of inserting and extracting lithium ions include a negative electrode active material containing an element capable of forming an alloy with lithium. The negative electrode active material may be a single metal or metalloid, an alloy or a compound, and may have at least a part of one or more of these phases. Good. In the present specification, the “alloy” includes an alloy having one or more metal elements and one or more metalloid elements in addition to an alloy composed of two or more metal elements. Further, the alloy may contain a nonmetallic element as long as it has metal properties as a whole.

Examples of metal elements and metalloid elements include titanium, tin (Sn), lead (Pb), aluminum, indium (In), silicon (Si), zinc (Zn), antimony (Sb), bismuth (Bi), Examples include gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), hafnium (Hf), zirconium, and yttrium (Y).
Among these, metal elements and metalloid elements of Group 4 or Group 14 in the long-period periodic table are preferable, and titanium, silicon, and tin are particularly preferable.
Examples of the tin alloy include silicon, magnesium (Mg), nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium as the second constituent element other than tin. Examples thereof include those having one or more elements selected from the group consisting of (Cr).
Examples of the silicon alloy include, as the second constituent element other than silicon, a group consisting of tin, magnesium, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium. Those having one or more elements selected from the above are listed.
As a titanium compound, a tin compound, and a silicon compound, what has oxygen or carbon is mentioned, for example, In addition to titanium, tin, or silicon, you may have the above-mentioned 2nd structural element.

A negative electrode mixture-containing paste is prepared by dispersing, in a solvent, a negative electrode mixture prepared by adding a conductive additive, a binder, or the like to the negative electrode active material as necessary. The binder is not particularly limited as long as it can bind two or more constituent materials contained in the negative electrode. Among them, carboxymethyl cellulose, styrene-butadiene crosslinked rubber latex, acrylic latex, and polyvinylidene fluoride are preferable. These are used singly or in combination of two or more.
Next, this negative electrode mixture-containing paste is applied to a current collector and dried to form a negative electrode mixture layer, which is pressurized as necessary to adjust the thickness, thereby producing a negative electrode. The current collector in the negative electrode is made of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil. In addition, a negative electrode active material can be used individually by 1 type or in combination of 2 or more types.

The electrolytic solution is not particularly limited as long as it contains a lithium salt and a non-aqueous solvent and acts as an electrolytic solution of a lithium ion secondary battery, and a known one can be used.
From the viewpoint of ion conductivity, the lithium salt is preferably LiPF ₆ , LiCIO ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiOSO ₂ C _k F _{2k + 1} [k is an integer of 1 to 8], LiN (SO ₂ C _t F _{2t + 1} ) ₂ [t is an integer of 1 to 8], LiPF _n (C _t F _{2t + 1} ) _6-n [n is an integer of 1 to 5, t is an integer of 1 to 8], LiPF ₄ (C ₂ O _{2), LiPF 2 (C 2} O 2) 2, LiBF 4, LiAlO 4, LiAlCl 4, Li 2 B 12 F g H 12-g [g is an integer of from 0 to _{3], LiBF q (C s F 2s} + 1) _4-q [q is an integer of 1 to 3, s is an integer of 1 to 8], LiB (C ₂ O ₄ ) ₂ , LiBF ₂ (C ₂ O ₄ ), LiB (C ₃ O ₄ H ₂ ) ₂ , LiPF ₄ (C ₂ O ₂ ) etc. Particularly preferred is LiPF ₆ . These electrolytes can be used singly or in combination of two or more.

  Although various things can be used as a non-aqueous solvent, an aprotic polar solvent is preferable. Specific examples thereof include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, trifluoromethylethylene carbonate, fluoroethylene. Cyclic carbonates such as carbonate and 4,5-difluoroethylene carbonate; lactones such as γ-ptyrolactone and γ-valerolactone; cyclic sulfones such as sulfolane; cyclic ethers such as tetrahydrofuran and dioxane; ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, Methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, ethyl pro Chain carbonates such as pyr carbonate and methyl trifluoroethyl carbonate; Nitriles such as acetonitrile; Chain ethers such as dimethyl ether; Chain carboxylic acid esters such as methyl propionate; Chain ether carbonate compounds such as dimethoxyethane It is done. These can be used individually by 1 type or in combination of 2 or more types.

As the non-aqueous solvent, it is more preferable to use a carbonate-based solvent such as cyclic carbonate and chain carbonate from the viewpoint of ion conductivity. Further, it is more preferable to use a combination of a cyclic carbonate and a chain carbonate as the carbonate solvent. Various cyclic carbonates can be used, but ethylene carbonate, propylene carbonate, and fluoroethylene carbonate are preferable, and ethylene carbonate and propylene carbonate are more preferable. Various chain carbonates can be used, but ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate are preferred.
When the carbonate solvent includes a combination of a cyclic carbonate and a chain carbonate, the mixing ratio of the cyclic carbonate and the chain carbonate is 1:10 to 5: 1 in terms of volume ratio from the viewpoint of ion conductivity. Preferably, it is 1: 5 to 3: 1.
In the case of using a carbonate-based solvent, another nonaqueous solvent such as acetonitrile or sulfolane can be further added as necessary from the viewpoint of improving battery physical properties.

  As a separator that can be used in the present embodiment, a conventionally known separator used for a lithium ion secondary battery can be used, and is not particularly limited. Among them, an insulating thin film having high ion permeability and excellent mechanical strength is preferable. Examples of such a separator include a woven fabric, a nonwoven fabric, and a synthetic resin microporous membrane, and among these, a synthetic resin microporous membrane is preferable. As the synthetic resin microporous membrane, for example, a polyolefin microporous membrane such as a microporous membrane containing polyethylene or polypropylene as a main component or a microporous membrane containing both of these polyolefins is suitably used. As the non-woven fabric, a porous film made of a heat-resistant resin such as glass-containing ceramic, polyolefin, polyester, polyamide, liquid crystal polyester, or aramid is used. The separator may be a single microporous membrane or a laminate of a plurality of microporous membranes, or may be a laminate of two or more microporous membranes.

  A conventionally well-known thing can be used for the exterior body which can be used for this embodiment, and it does not restrict | limit in particular. The material of the outer package is not particularly limited, and examples thereof include metals such as stainless steel, iron, and aluminum, or a laminate film in which the surface of the metal is coated with a resin.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these Examples.
[Example 1]
<Step (1)>
Following _Sulfate: MnSO 4 · _5H 2 O (manufactured by Kanto Chemical Co., _{Ltd.) 79.6g, NiSO 4 · 6H 2} O ( manufactured by Kanto Chemical Co., Ltd.) 26.0 g, and FeSO ₄ · _7H 2 O (Kanto Chemical stock Aqueous solution A was prepared by dissolving 3.12 g (made by company) in pure water to a total of 220 ml. An aqueous solution B was prepared by dissolving 46.6 g of sodium carbonate Na ₂ CO ₃ (manufactured by Kanto Chemical Co., Ltd.) in pure water and adding 14.6 ml of 28% by mass ammonia water (manufactured by Kanto Chemical Co., Ltd.) to a total of 220 ml.
In a reaction tank having a stirring mechanism and a mechanism for bubbling an inert gas, an aqueous solution C in which sodium sulfate Na ₂ SO ₄ (manufactured by Kanto Chemical Co., Ltd.) is dissolved in pure water to make a total of 200 ml is added, and nitrogen gas is stirred while stirring. The aqueous solution A and the aqueous solution B were simultaneously dropped into the aqueous solution C at a rate of 5 ml / min. The liquid was extracted from the reaction tank 100 ml every 10 minutes, the dropping was stopped after 40 minutes, the liquid in the reaction tank was recovered, filtered, washed with water, and dried to obtain a precipitate D.

After thoroughly mixing 2.00 g of the dried precipitate D with 0.318 g of lithium carbonate Li ₂ CO ₃ (Honjo Chemical Co., Ltd.) pulverized to an average primary particle size <2 μm, the mixture was heated at 800 ° C. in the atmosphere. The lithium-containing metal oxide A was obtained by firing for 5 hours. X-ray structural analysis revealed that the lithium-containing metal oxide A has a spinel structure. This was acid-decomposed with microwaves (Analyte Jena, TOPwave (registered trademark)), and by ICP measurement (Perkin Elmer, Optima 8300), the composition ratio of the metal elements was Li: Mn: Ni: Fe = 0.33: 0.51: 0.14: 0.02.

<Step (2)>
After thoroughly mixing 1.41 g of the above lithium-containing metal oxide A and 0.286 g of the above-mentioned lithium carbonate Li ₂ CO ₃ , TG-DTA analysis was performed, and the weight loss and suggested heat from 425 ° C. It was found that the suggested decrease in heat takes a minimum value at 500 ° C. Therefore, this mixture was fired at 650 ° C. in the atmosphere for 5 hours, lithium was additionally introduced into the oxide, and then further fired at 800 ° C. for 5 hours to obtain a positive electrode active material.
X-ray structural analysis revealed that the positive electrode active material had a spinel structure and a composition of Li ₂ MeO _{3-γ that} could be assigned to a space group of approximately C2 / m. The composition ratio of the metal elements determined by ICP measurement was Li: Mn: Ni: Fe = 0.49: 0.39: 0.11: 0.01.

<Manufacture of lithium ion secondary batteries>
The positive electrode active material obtained as described above, graphite powder (TIMCAL, KS-6) and acetylene black powder (HS-100, manufactured by Denki Kagaku Kogyo Co., Ltd.), which are conductive assistants, and a binder A certain polyvinylidene fluoride solution (manufactured by Kureha, L # 7208) was mixed at a mass ratio of 80: 5: 5: 10 in terms of solid content. To the obtained mixture, NMP as a dispersion solvent was added so as to have a solid content of 30% by mass, and further mixed to prepare a slurry solution. This slurry solution was applied to one side of an aluminum foil having a thickness of 20 μm, and the solvent was removed by drying, followed by rolling with a roll press to obtain a positive electrode having a thickness of 64 μm.
LiPF ₆ was dissolved in a mixed solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 2 so as to be 1 mol / L to obtain an electrolytic solution.
A lithium metal foil (thickness 0.5 mm) punched out to a diameter of 16 mm as a negative electrode is inserted into a stainless steel disk-type battery case (exterior body), and a separator made of a microporous film made of polyethylene and glass fiber is formed thereon. The separator (ADVANTEC, GA-100, film thickness: about 500 μm) was inserted, and then a positive electrode punched to a diameter of 16 mm was inserted. Next, 1.0 mL of the above-described electrolytic solution was injected therein, and after immersing the positive electrode, the negative electrode, and the separator in the electrolytic solution, the battery case was sealed to manufacture a lithium ion secondary battery.

<Battery evaluation>
The obtained lithium ion secondary battery (hereinafter, also simply referred to as “battery”) is housed in a thermostatic chamber (manufactured by Futaba Kagaku Corporation, thermostatic chamber PLM-73S) set at 25 ° C., and a charge / discharge device (Asuka Electronics) It connected to the product made by Corporation | KK Co., Ltd. charge / discharge device ACD-01). Next, the battery was charged with a constant current of 0.1 C, reached 5.0 V, charged with a constant voltage of 5.0 V for 2 hours, and discharged to 2.0 V with a constant current of 0.1 C. When the discharge capacity was measured, a capacity of 230 mAh / g was obtained. 1C is a current value at which the battery is discharged in one hour.
Next, the battery was charged with a constant current of 0.3 C, reached 4.9 V, charged with a constant voltage of 4.9 V until the current became 0.05 mA or less, and then with a constant current of 2 C. When the discharge capacity when discharging to 2.0 V was measured, a capacity of 186 mAh / g was obtained.

[Comparative Example 1]
2.00 g of dried precipitate D produced in Example 1 and mixed well with 0.634 g of lithium carbonate Li ₂ CO ₃ pulverized to an average primary particle size <2 μm or less, then calcined at 850 ° C. for 5 hours, A positive electrode active material was obtained.
X-ray structural analysis revealed that the positive electrode active material had a spinel structure and a Li ₂ MeO _{3 -γ} composition that could be attributed to a C2 / m space group. The composition ratio of the metal elements determined by ICP was Li: Mn: Ni: Fe = 0.48: 0.41: 0.1: 0.01. A lithium ion secondary battery was manufactured in the same manner as in Example 1, and charged at a constant current of 0.1 C as in Example 1. After reaching 5.0 V, it was charged at a constant voltage of 5.0 V for 2 hours. When the discharge capacity when discharged to 2.0 V with a constant current of 0.1 C was measured, a capacity of 161 mAh / g was obtained. Next, when the discharge capacity at the time of discharging to 2.0 V with a constant current of 2 C as in Example 1 was measured, a capacity of 150 mAh / g was obtained.

  The manufacturing method of the positive electrode active material for lithium ion secondary batteries of this invention can be utilized suitably in manufacture of the power supply for various consumer devices, and the power supply for motor vehicles.

Claims (8)

The following steps:
(1) Among carbonates and / or hydroxide salts of Li and oxides, carbonates, hydroxide salts, sulfates, nitrates, hydrochlorides, and acetates of two or more metals other than Li At least one is fired, Li and at least two kinds of metal elements other than Li are included, and the mole fraction of Li is M _L , and the mole fraction of two or more kinds of metal elements other than Li is M _M When the following formula (1):
1 ≦ M _M / M _L ≦ 4 (1)
And (2) the resulting lithium-containing metal oxide A and the following compositional formula (2):
Li _x C _a O _b H _c (2)
{In the formula, 1 ≦ x ≦ 2, 0 ≦ a ≦ 1, 1 ≦ b ≦ 3, and 0 ≦ c ≦ 2 are satisfied. } Is mixed and calcined at a temperature lower than the maximum calcining temperature in the step (1), and the following composition formula (3):
Li _{1 + j} MeO _α (3)
{Wherein Me is two or more metal elements other than Li, and 0 ≦ j ≦ 1 and 2 ≦ α ≦ 3. } The crystal C having a layered structure in which Li represented by the following formula is arranged, or the following composition formula (4):
Li _{1 + k} Me ₂ O _4-β (4)
{Wherein Me is two or more metal elements other than Li, and 0 ≦ k <1 and 0 ≦ β <1. A crystal D having a spinel structure represented by the following formula: or a crystal in which the crystal C and the crystal D are dissolved;
including,
A method for producing a positive electrode active material for a lithium ion secondary battery.   The method according to claim 1, further comprising a step of firing after the step (2) at a temperature higher than a maximum firing temperature in the step (2).   The method according to claim 1 or 2, wherein the lithium-containing metal oxide A has a spinel structure. The lithium-containing metal oxide A has the following composition formula (5):
Li _{1 + k} Mn _2-x M _x O _4-α (5)
{In the formula, M is one or more metal elements other than Mn and Li, and satisfies the relations 0 ≦ k <1, 0 <x ≦ 0.5, and 0 ≦ α <1. } The method of Claim 3 which has a spinel structure represented by these.   The method of claim 4, wherein M is at least Ni.   The method according to claim 1, wherein Me is at least Mn and Ni.   The method according to claim 1, wherein the lithium compound B includes at least lithium carbonate or lithium hydroxide.   The positive electrode active material for lithium ion secondary batteries manufactured by the method of any one of Claims 1-7.