JP2001325959A - Manufacturing method of lithium-manganese compound oxide for lithium secondary cell positive electrode active material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method which enables manufacturing lithium-manganese compound oxide that can be an effective positive electrode active material for a lithium secondary cell and has a spinel structure or a lamellar halite structure of good crystallinity in extremely short time and with lowered cost, and is well-suited for continuous and mass production. SOLUTION: The manufacturing method of lithium-manganese compound oxide comprises a precipitated process in which a compound oxide precursor is precipitated by mixing salt solution as manganese source, H2O2 solution of lithium hydroxide as lithium source, and, as necessity arises, salt solution of other elements substitutable with Mn site, and a maturing process which matures the precipitated precursor by irradiating an electromagnetic wave.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a lithium manganese composite oxide which can be used as a positive electrode active material of a lithium secondary battery by utilizing the occlusion and desorption of lithium ions.

[0002]

2. Description of the Related Art As mobile phones and personal computers become smaller,
Secondary batteries with high energy density are required, and lithium secondary batteries have come into widespread use in the fields of communication devices and information-related devices. In addition, demands for electric vehicles are increasing in the field of automobiles due to resource problems and environmental problems, and the development of lithium secondary batteries that are inexpensive, have large capacities, and have good cycle characteristics is urgently required.

At present, as a positive electrode active material of a lithium secondary battery, LiCoO ₂ having a layered rock salt structure has been adopted as a material capable of constituting a 4 V class secondary battery. Li
Since CoO ₂ is easy to synthesize and relatively easy to handle and has excellent charge-discharge cycle characteristics, secondary batteries using LiCoO ₂ as a positive electrode active material are currently the mainstream. .

[0004] However, cobalt is a scarce resource, and a secondary battery using LiCoO ₂ as a positive electrode active material is difficult to cope with future mass production and enlargement of automobile batteries, and is extremely expensive. It has to be expensive. Therefore, instead of cobalt, an attempt has been made to adopt a lithium manganese composite oxide containing manganese, which is abundant as a resource and inexpensive, as a constituent element as a positive electrode active material.

The lithium-manganese composite oxide is represented by a composition formula LiMn ₂ O ₄ having a crystal structure of a spinel structure or a composition formula of LiMnO ₂ having a hexagonal layered rock salt structure. Are known.
The crystal structure of the spinel structure is stable, and although the theoretical capacity is small, the amount of lithium that can be inserted and released reversibly is large.
A discharge capacity almost equivalent to that of oO ₂ is obtained. Further, those of layered rock salt structure of a hexagonal system has the same crystal structure as the LiCoO _2, has a LiCoO ₂ equal to or higher than the theoretical discharge capacity. Therefore, the lithium manganese composite oxide having a spinel structure or a layered rock salt structure is expected to be an effective cathode active material.

The method invented by the present inventors as a technique for synthesizing the lithium manganese composite oxide having a spinel structure or a layered rock salt structure is described in, for example, Japanese Patent Application No. 11-32.
8078 is the hydrothermal method. In this hydrothermal method, a manganese salt aqueous solution, a Me salt aqueous solution (Me is at least one selected from Al and Fe) and a lithium hydroxide H ₂ O ₂ aqueous solution are mixed to precipitate a composite oxide precursor, In this method, the precursor is aged at a temperature of 50 ° C. or more and 110 ° C. or less to obtain a lithium manganese composite oxide having the above structure. According to this hydrothermal method, the lithium manganese composite oxide having the above-described structure having excellent crystallinity can be synthesized at a relatively low temperature and in a short time as compared with the conventional solid-phase method.

[0007]

However, the aging step in the above-mentioned hydrothermal method involves heating the solution in which the composite oxide precursor is deposited, and therefore requires several hours to complete the aging. For this reason, it is difficult to perform continuous synthesis or mass synthesis of the lithium manganese composite oxide.

The present invention has been made to solve the above problems, and is a method for producing a lithium manganese composite oxide which can be used as an effective positive electrode active material for a lithium secondary battery, comprising a spinel structure having excellent crystallinity. Alternatively, a lithium manganese composite oxide having a layered rock salt structure can be produced in a very short time,
Another object of the present invention is to provide a manufacturing method which can be manufactured at low cost and is suitable for continuous and mass production.

[0009]

According to the present invention, there is provided a method for producing a lithium manganese composite oxide for a positive electrode active material of a lithium secondary battery, comprising the steps of: dissolving a manganese cation salt in water; water lithium and H ₂ O ₂ Li aqueous H ₂ O ₂ solution hydroxide dissolved in an aqueous solution, the metal element Me optionally (Me is Al, at least one or more selected from Fe) salt of a cation of And an aqueous solution of a Me salt dissolved in water to form a mixed solution. In the mixed solution, the composition formula Li _b Mn _{1-a / 2} Me _{a / 2} O ₂ .nH ₂ O (0 <b ≦
1.5, 0 ≦ a ≦ 0.1, 0.1 ≦ n ≦ 1) a precipitation step of precipitating a lithium manganese composite oxide precursor represented by the following formula, and applying an electromagnetic wave to the mixed solution in which the precursor is precipitated. By irradiation, the precursor is aged, and the composition formula Li _c Mn _2-a Me _a O ₄ (0 <c ≦ 1.3, 0 ≦ a ≦ 0.
And a ripening step of obtaining a lithium manganese composite oxide having a spinel structure represented by 1).

[0010] In the method of manufacturing a lithium secondary battery positive electrode active material for a lithium-manganese composite oxide of the present invention, the salt of the manganese cations and water-soluble manganese salt solution dissolved in water, lithium hydroxide H ₂ and O ₂ aqueous lithium aqueous H ₂ O ₂ solution hydroxide dissolved in the metal element is necessary Me
(Me is at least one or more selected from Al and Fe)
The salts of the cation and the mixed solution by mixing and Me salt aqueous solution prepared by dissolving in water, the composition formula Li _y in the mixed solution
Mn _1-x Me _x O ₂ .nH ₂ O (0 <y ≦ 1.5, 0.05
<X ≦ 0.2, 0.1 ≦ n ≦ 1) by depositing a lithium manganese composite oxide precursor represented by: and irradiating the mixed solution on which the precursor has been deposited with electromagnetic waves, The precursor is aged and the composition formula Li _z Mn
_1-x Me _x O ₂ (0 <z ≦ 1.2, 0.05 <x ≦ 0.
And a ripening step of obtaining a layered rock-salt structure lithium manganese composite oxide represented by 2).

That is, the method for producing a lithium manganese composite oxide according to the present invention comprises an aqueous solution of a salt serving as a manganese source, an aqueous H ₂ O ₂ solution of lithium hydroxide serving as a lithium source, and an Mn site mixed as required. Is mixed with an aqueous solution of a salt serving as another element capable of substituting the compound, a composite oxide precursor is precipitated in the mixed solution, and the deposited precursor is irradiated with electromagnetic waves to be matured.

In the above-mentioned precipitation step in the production method of the present invention, a composite oxide precursor having a generally hexagonal layered rock salt structure is precipitated in the mixed solution. This composite oxide precursor contains water of hydration and has low crystallinity, as shown by the above composition formula. Therefore, when this composite oxide precursor is aged by irradiating electromagnetic waves to form a lithium manganese composite oxide having a spinel structure, water of hydration is removed to change the crystal structure to a spinel structure, and a layered rock salt When a lithium manganese composite oxide having a structure is used, water of hydration is removed to enhance crystallinity.

In the production method of the present invention, the deposited composite oxide precursor is matured by irradiating it with electromagnetic waves. Although the action of the electromagnetic wave is not clear, it is considered that the aging is completed in a short time because the irradiated electromagnetic wave locally acts on the reaction field, that is, the complex oxide precursor itself.

In the method for producing a lithium-manganese composite oxide according to the present invention, the aging step for improving the crystallinity and dehydrating the hydration water is carried out by irradiating electromagnetic waves. A production method that can produce a manganese composite oxide in a short time and at low cost. Further, the method for producing a lithium manganese composite oxide of the present invention can be applied not only to a batch method but also to a continuous synthesis, so that the method is suitable for mass production.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for producing a lithium manganese composite oxide for a positive electrode active material of a lithium secondary battery according to the present invention will be described.
The precipitation step and the aging step will be described in this order, and then a lithium secondary battery that is a use form of the manufactured lithium manganese composite oxide will be described.

<Lithium-manganese composite oxide to be produced> The lithium-manganese composite oxide to be produced by the method for producing a lithium-manganese composite oxide of the present invention has a spinel structure and a layered rock salt structure. . The spinel-structured lithium manganese composite oxide has a composition formula of Li _c Mn
_2-a Me _a O ₄ (0 <c ≦ 1.3, 0 ≦ a ≦ 0.1), and the layered rock-salt structure lithium manganese composite oxide has a composition formula of Li _z Mn _1-x Me _x O ₂ ( 0 <z ≦ 1.2, 0.05 <
x ≦ 0.2).

One reason for replacing a part of the Mn site with another element Me is to improve the cycle characteristics of a lithium secondary battery using the same as a positive electrode active material by strengthening the crystal structure. Another reason is that it is difficult to produce a layered rock-salt structure by a production method such as precipitation and maturation without replacement with another element. It is considered that Al and Fe, which are substitution elements, have an ionic radius smaller than Mn, so that they easily take a layered rock salt structure with a small interlayer distance. This has been confirmed by experiments by the present inventors. The substitution element M
e is more preferably Al. This is because Al has a smaller ionic radius than Fe (Al ³⁺ = 0.68).
{Fe ²⁺ = 0.75 °, Fe ³⁺ = 0.69 °).

The substitution ratio of Me, that is, the values of a and x in the composition formula are 0 ≦ a ≦ 0.1 for a lithium manganese composite oxide having a spinel structure, and 0.05 for a lithium manganese composite oxide having a layered rock salt structure. <X ≦ 0.2.
In other words, when a spinel structure is obtained in the aging step, a = 0, that is, not replaced with Me, or the value of a may be set to 0.1 or less. When a layered rock salt structure is obtained in the aging step, the substitution ratio of Me may be further increased and the value of x may be set to be larger than 0.05.
However, when the value of x exceeds 0.2, since Al and Fe are stable in divalent and trivalent states, tetravalent Mn increases and trivalent Mn contributing to charge and discharge decreases, and lithium and lithium decrease. When a secondary battery is configured, its capacity is greatly reduced.

The proportion of Li in the crystal, that is, the values of c and z in the composition formula, are 0 <c ≦ 1.3 for a lithium manganese composite oxide having a spinel structure, and 0 for a lithium manganese composite oxide having a layered rock salt structure. 0 <z ≦ 1.2. In the present production method, the values of c and z can be changed by changing the ratio of the aqueous solution of manganese salt and the aqueous solution of lithium hydroxide H ₂ O ₂ mixed in the precipitation step. Incidentally, when used as a positive electrode active material, it is more preferable that 0.8 ≦ c ≦ 1.3 for a spinel structure and 0.7 ≦ z ≦ 1.2 for a layered rock salt structure. When c and z are smaller than 0.8 and 0.7, respectively, L
The absolute amount of i will be reduced too much, and 1.3,
Li that participates in charging and discharging even when it exceeds 1.2
Is excessively reduced, and the discharge capacity of the constituent lithium secondary battery is reduced.

It should be noted that the lithium-manganese composite oxide targeted by the present production method is not necessarily limited to one having a stoichiometric composition. For example, the cation elements of Li and Mn inevitably produced in production And those having a non-stoichiometric composition in which oxygen is deficient or oxygen element is deficient.

<Precipitation Step> In the precipitation step in the method for producing a lithium manganese composite oxide of the present invention, the manganese salt aqueous solution, the lithium hydroxide H ₂ O ₂ aqueous solution, and the Me salt aqueous solution are mixed to form a mixed solution. This is a step of precipitating a lithium manganese composite oxide precursor in the mixed solution.

In the manufacturing method of the present invention, the spinel structure
Deposition performed to obtain lithium manganese composite oxide
In the process, a salt with manganese as a cation was dissolved in water
Manganese salt aqueous solution and lithium hydroxide_TwoO_TwoIn aqueous solution
Dissolved lithium hydroxide H _TwoO_TwoAqueous solution and as needed
The metal element Me (Me is at least selected from Al and Fe
M) in which a salt having a cation as a cation is dissolved in water.
e mixed with an aqueous salt solution to form a mixed solution.
The composition formula Li_bMn_{1-a / 2}Me_{a / 2}O_Two・ NH_TwoO (0 <b
≦ 1.5, 0 ≦ a ≦ 0.1, 0.1 ≦ n ≦ 1)
For depositing lithium manganese composite oxide precursor
It is. Hereinafter, this step is referred to as a “precipitation-1” step.

In the production method of the present invention, the layered rock salt structure
Deposition performed to obtain lithium manganese composite oxide
In the process, a salt with manganese as a cation was dissolved in water
Manganese salt aqueous solution and lithium hydroxide_TwoO_TwoIn aqueous solution
Dissolved lithium hydroxide H _TwoO_TwoAqueous solution and metal element M
e (Me is at least one kind selected from Al and Fe
Me salt aqueous solution in which a salt with cation as above is dissolved in water
Are mixed to form a mixed solution, and the composition formula L
i_yMn_1-xMe_xO_Two・ NH_TwoO (0 <y ≦ 1.5, 0.
05 <x ≦ 0.2, 0.1 ≦ n ≦ 1)
This is the step of precipitating the manganese composite oxide precursor.
Hereinafter, this step is referred to as a “precipitation-2” step.

In both the [precipitation-1] and [precipitation-2] steps, manganese nitrate, manganese sulfate, manganese acetate and the like can be used as the salt having Mn as a cation. Similarly, as the salt having the metal element Me as a cation, a nitrate, a sulfate, an acetate, or the like can be used. Desirably, both the salt having Mn as a cation and the salt having metal element Me as a cation are nitrates. The use of nitrate is a strong acid which is desirable for the neutralization reaction and has the advantage that no ions remain in the product.

H is used as a solvent for dissolving lithium hydroxide.
_The use of an aqueous solution of ₂ O ₂ is because water-soluble Mn ²⁺ is
This is for oxidizing to n ³⁺ . The concentration of the H ₂ O ₂ aqueous solution is desirably 1 to 10 wt% in consideration of the safety of the reaction. The concentration of lithium hydroxide dissolved in aqueous solution of H ₂ O _2, in order to perform a uniform reaction, it is desirable that 0.2～5M.

In the [precipitation-1] step for producing a lithium manganese composite oxide having a spinel structure, an aqueous Me salt solution is not always necessary, and the lithium manganese composite oxide having a spinel structure can be prepared without mixing the aqueous Me salt solution. Can be generated. When mixing the Me salt aqueous solution, the mixing ratio between the manganese salt aqueous solution and the Me salt aqueous solution is such that the composition ratio of the lithium manganese composite oxide Li _c Mn _2-a Me _a O which is intended to obtain the molar ratio between Mn and Me. _It may be mixed so as to be 2-a: a according to ₄ . A manganese salt aqueous solution and M
The concentration of the aqueous salt solution e is desirably 0.2 to 5M.
This is because when less than 0.2M, the amount of precipitation is small,
If it exceeds 5M, the generation of oxygen increases, which may be dangerous.

The mixing ratio of the aqueous solution of manganese salt and the aqueous solution of lithium hydroxide H ₂ O _{2 with the} aqueous solution of Me salt depends on the composition Li _c Mn of the lithium manganese composite oxide to be obtained.
Change according to _2-a Me _a O ₄ . The value of b in the composition Li _b Mn _{1-a / 2} Me _{a / 2} O ₂ .nH ₂ O of the composite oxide precursor to be deposited is not the same as the value of c, and the mixing ratio of the solution (mixing (Existence ratio of Mn + Me and Li in solution)
And b and c do not have the same ratio. After the aging step, for example, when it is desired to precipitate a material in the range of 0.8 ≦ c ≦ 1.3, it is necessary to precipitate a precursor having approximately 1.0 ≦ b ≦ 1.5. For that, (Mn + M
e): Li may be mixed at a molar ratio of 1: 3 to 1:10.

In the [precipitation-2] step for producing the layered rock salt structure lithium manganese composite oxide, the mixing ratio of the manganese salt aqueous solution and the Me salt aqueous solution is such that the molar ratio of Mn to Me is to be obtained. depending on the composition _{Li z Mn 1-x Me x} O 2 manganese composite oxide, 1-x: may be mixed so that x. A manganese salt aqueous solution and M
The concentration of the salt aqueous solution is also 0.2 to 5M for the same reason.
It is desirable that

Also, a manganese salt aqueous solution and lithium hydroxide
Umm H_TwoO_TwoThe mixing ratio between the aqueous solution and the aqueous Me salt solution is
Composition Li of Lithium Manganese Composite Oxide_zMn
_1-xMe_xO_TwoChange according to. Complex oxide to be deposited
Precursor composition Li_yMn_1-xMe _xO_Two・ NH_TwoIn O
The value of y and the value of z above are not the same, and
(The proportion of Mn + Me and Li in the mixed solution)
Both y and z do not have the same ratio. After the aging process
Thus, for example, those having a range of 0.7 ≦ z ≦ 1.2 are deposited.
If it is intended to make
It is necessary to precipitate the body, for which (Mn + M
e): Li is in a molar ratio of 1: 3 to 1: 6.
Should be mixed.

[0030] The precipitation step includes [precipitation-1] and [precipitation-2].
Manganese salt aqueous solution, lithium hydroxide H ₂ O ₂
This is performed by uniformly mixing the aqueous solution and the aqueous Me salt solution. The method of mixing is not particularly limited. In order to ensure the uniformity of mixing, it is desirable to perform the mixing while stirring. The method of stirring is not particularly limited, and a known method of stirring a normal solution may be used.
The reaction temperature in the precipitation step is preferably from 10 ° C. to 30 ° C. because it involves an exothermic reaction. Further, the reaction time in the precipitation step may be 1 to 30 minutes, which is a relatively quick step.

In the precipitation step, an aqueous solution of manganese salt, an aqueous solution of lithium hydroxide H ₂ O _{2, and an} aqueous solution of Me salt are mixed, but an aqueous solution in which both manganese salt and Me salt are dissolved is prepared, and this aqueous solution is mixed with hydroxide. It is also possible to adopt a mode of mixing with an aqueous solution of lithium H ₂ O ₂ . Therefore, the mixing of the solution in the precipitation step means that this embodiment is also included.

If the composite oxide precursor deposited in the deposition step has a spinel structure, the composition formula is Li _b Mn _{1-a / 2} M
e _{a / 2} O ₂ · nH ₂ O, Li _y Mn for a layered rock salt structure
_1-x is represented by _{Me x O 2 · nH 2 O} (0.1 ≦ n ≦ 1), contains water of hydration, as is clear from the formula, the crystalline is low. The ratio of this hydration water, that is, the value of n in the composition formula, depends on the reaction conditions in the precipitation, and 0.1 ≦
It is not clear in the range of n ≦ 1. Regardless of the value of n in this range, it is removed in the subsequent aging step, and the final product, lithium manganese composite oxide, contains no water of hydration. By the way, 1M manganese nitrate aqueous solution and aluminum nitrate aqueous solution and LiOH 3wt% H
_{A 2} O ₂ aqueous solution was mixed with a molar ratio of (Mn + Al): Li = 1:
When the mixture is mixed to 5 and reacted at a temperature of 20 ° C. for 5 minutes, the value of n is about 0.6.

<Aging Step> In the aging step in the method for producing a lithium manganese composite oxide of the present invention, the composite oxide precursor deposited in the deposition step is aged by irradiating the mixed solution with electromagnetic waves in the deposited mixed solution. And obtaining a lithium manganese composite oxide.

In the manufacturing method of the present invention, the spinel structure
Aging performed to obtain lithium manganese composite oxide
The process is performed using the composition formula Li deposited in the deposition process._bMn_{1-a / 2}M
e_{a / Two}O_Two・ NH_TwoO (0 <b ≦ 1.5, 0 ≦ a ≦ 0.
1, a complex oxide precursor represented by 0.1 ≦ n ≦ 1)
By irradiating electromagnetic waves in the precipitated mixed solution
And aged, the composition formula Li_cMn_2-aMe_aO_Four(0 <c
≦ 1.3, 0 ≦ a ≦ 0.1)
This is a step of obtaining a titanium-manganese composite oxide.

In the production method of the present invention, the aging step performed to obtain the lithium manganese composite oxide having the layered rock salt structure includes the composition formula Li _y Mn deposited in the precipitation step.
_{1-x Me x O 2 ·} nH 2 O (0 <y ≦ 1.5,0.05 <x
≦ 0.2, 0.1 ≦ n ≦ 1), the composite oxide precursor is aged by irradiating the mixed solution with electromagnetic waves in the deposited mixed solution to obtain a composition formula Li _z Mn _1-x Me _x O
_This is a step of obtaining a layered rock-salt structure lithium manganese composite oxide represented by ₂ (0 <z ≦ 1.2, 0.05 <x ≦ 0.2).

The frequency of the electromagnetic wave is not particularly limited as long as the frequency of the electromagnetic wave can be increased by activating the molecular motion in the mixed oxide precursor and the mixed solution. In particular, from the viewpoint of directly raising the temperature of the composite oxide precursor itself, it is preferable to irradiate an electromagnetic wave having a frequency in the range of 0.3 to 300 GHz. Also, the output of the electromagnetic wave is not particularly limited, as in the case described above, and irradiation may be performed with a commonly used output. In particular, it is preferable to irradiate an electromagnetic wave whose output is in the range of 100 W to 1000 W from the viewpoint of making the heating rate appropriate.

The irradiation time of the electromagnetic wave varies depending on the frequency and output of the electromagnetic wave, the amount of the composite oxide precursor, and the like.
Therefore, an optimal irradiation time at which the aging reaction can be completely completed may be selected depending on the irradiation conditions of the electromagnetic wave and the like. Since aging after the completion of the reaction leads to elongation of the entire production process, it is preferable to set the time as short as possible. By the way, when ripening by the above-mentioned hydrothermal method, it is generally said that it is better to heat and hold for 6 hours or more. In the case of the manufacturing method of the present invention, it is sufficient to irradiate the electromagnetic wave for 1 to 30 minutes. Note that, as will be described later, the irradiation time of the electromagnetic wave is extremely short.

The aging step can be carried out, for example, in a batch system. In this case, the mixed solution obtained in the precipitation step is placed in a container having high electromagnetic wave permeability, and a predetermined frequency and output power are placed in the container containing the mixed solution. The electromagnetic wave is irradiated for a predetermined time, and then the temperature is lowered to around room temperature before being taken out. The container having high electromagnetic wave permeability is not particularly limited, and examples thereof include materials made of glass, Teflon (registered trademark), and the like.

For the purpose of continuous and mass production of the lithium manganese composite oxide, the ripening step comprises mixing the mixed solution obtained in the deposition step in a channel made of a material having high electromagnetic wave permeability. It is possible to adopt a mode in which the liquid is continuously supplied, and a part of the flow path is irradiated with electromagnetic waves to continuously ripen. For example, a glass tube, a Teflon tube, or the like can be used as the channel made of a material having high electromagnetic wave permeability. By performing the aging step continuously, mass production becomes possible, and in this case, the cost can be further reduced.

If the aging temperature is around 100.degree. C. or more than 100.degree. C., evaporation of the mixture itself becomes a problem. In that case, aging must be performed under pressure to prevent evaporation of the solution.

By the aging step performed as described above, the composite oxide precursor is further improved in crystallinity while further taking in lithium present in the mixed solution, and at the same time, hydration water contained therein is removed. It is produced as a highly crystalline lithium manganese composite oxide having a spinel structure or a layered rock salt structure.

The produced lithium manganese composite oxide is separated from the solution by filtration, washed with water, and dried to obtain a powder. The drying method in this case is not particularly limited, and is generally performed in a drying furnace or the like at a temperature of 50 to 120 ° C., as generally performed.
It may be performed for about 60 to 180 minutes.

<Lithium Secondary Battery> As one embodiment of the lithium secondary battery, a lithium manganese composite oxide produced by the method for producing a lithium manganese composite oxide according to the present invention is used as a positive electrode active material. A secondary battery can be configured. The lithium secondary battery in which the lithium manganese composite oxide produced by the production method of the present invention is used as a positive electrode active material has a high battery voltage of 4V class, a large discharge capacity, and a low cost. Next battery.

Hereinafter, the main structure of a lithium secondary battery using the lithium manganese composite oxide produced by the production method of the present invention as a positive electrode active material will be described. Generally, a lithium secondary battery includes a positive electrode and a negative electrode that occlude and release lithium ions, a separator that is interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte that moves lithium ions between the positive electrode and the negative electrode. Consists of Since the secondary battery of the present embodiment also follows this configuration, the following description will be made for each of these components.

The positive electrode is prepared by mixing a conductive material and a binder with a positive electrode active material capable of occluding and releasing lithium ions, adding an appropriate solvent as necessary, and forming a paste-like positive electrode mixture into aluminum or the like. On the surface of the metal foil current collector,
It can be formed by drying and then increasing the active material density by pressing.

In this embodiment, the positive electrode active material is
The composition formula Li obtained by the production method described above _cMn_2-bMe_bO_Fourso
Represented spinel-structured lithium manganese composite oxide
And the composition formula Li_zMn_1-xMe_xO_TwoLayered rock salt structure represented by
A lithium manganese composite oxide is used. Mn site
Varies depending on the type of other element Me that substitutes
Lithium manganese composite oxide can be a positive electrode active material
You. In the secondary battery of the present embodiment, one of these
Can be used as the positive electrode active material.
The above can be used in combination. In addition,
Lithium-manganese composite oxide, already known
Other positive electrode active materials, for example, LiCoO_Two, LiNiO_Twoetc
May be used in combination.

The conductive material used for the positive electrode is for ensuring the electrical conductivity of the positive electrode active material layer, and is made of a carbon material powder such as carbon black, acetylene black, and graphite.
A species or a mixture of two or more species can be used. The binder plays a role of binding the active material particles, and is made of polytetrafluoroethylene, polyvinylidene fluoride, a fluorine-containing resin such as fluororubber, polypropylene,
A thermoplastic resin such as polyethylene can be used.
An organic solvent such as N-methyl-2-pyrrolidone can be used as a solvent in which the active material, the conductive material, and the binder are dispersed.

The negative electrode in the present embodiment is made of lithium metal, which is an active material for the negative electrode, in the form of a sheet, as in the case of a general battery, or a sheet-like material obtained by forming a sheet of a current collector such as nickel or stainless steel. It is formed by pressing. As the negative electrode active material, a lithium alloy or a lithium compound can be used instead of metal lithium.

As another form of the negative electrode, the negative electrode can be constituted by using a carbon material capable of inserting and extracting lithium ions as the negative electrode active material. Examples of the carbon substance that can be used include natural or artificial graphite, fired organic compounds such as phenolic resins, and powders such as coke. In this case, the negative electrode active material can be formed by mixing a binder with the negative electrode active material, adding a suitable solvent to form a paste, and applying and drying the negative electrode mixture on the surface of a metal foil current collector such as copper. .

When a carbon material is used as the negative electrode active material, a fluorine-containing resin such as polyvinylidene fluoride or the like is used as the negative electrode binder and an organic solvent such as N-methyl-2-pyrrolidone is used as the solvent, similarly to the positive electrode. Can be.

The separator sandwiched between the positive electrode and the negative electrode separates the positive electrode and the negative electrode, holds the electrolytic solution and allows ions to pass therethrough, and uses a thin microporous film such as polyethylene or polypropylene. Can be.

The non-aqueous electrolyte is a solution in which an electrolyte is dissolved in an organic solvent. Examples of the organic solvent include aprotic organic solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and the like.
One kind of γ-butyrolactone, acetonitrile, dimethoxyethane, tetrahydrofuran, dioxolane, methylene chloride and the like, or a mixture of two or more kinds thereof can be used. As the electrolyte to be dissolved, LiI, LiCl which generates lithium ions when dissolved are used.
O ₄ , LiAsF ₆ , LiBF ₄ , LiPF _{6 and the} like can be used. Note that a solid electrolyte or the like can be used instead of the non-aqueous electrolyte.

The lithium secondary battery constituted as described above can be formed in various shapes such as a coin type, a stacked type and a cylindrical type. In any case, a separator is sandwiched between the positive electrode and the negative electrode to form an electrode body, and the electrode body is made to conduct from the positive electrode and the negative electrode to the positive electrode terminal and the negative electrode terminal communicating with the outside, respectively. Can be sealed in a battery case together with the non-aqueous electrolyte to complete the battery.

The embodiments of the method for producing a lithium manganese composite oxide and the lithium secondary battery according to the present invention described above are merely examples, and the production method of the present invention and the lithium manganese composite oxide produced thereby The lithium secondary battery using as a positive electrode active material can be implemented in various embodiments including various modifications and improvements based on the knowledge of those skilled in the art, including the above embodiment.

[0055]

EXAMPLES In order to confirm that a good lithium manganese composite oxide for a positive electrode active material can be produced by the above production method of the present invention, a lithium manganese composite oxide was produced by the following production method and evaluated. The production of the lithium manganese composite oxide and the identification and confirmation of the crystal structure of the produced lithium manganese composite oxide will be described below as examples.

<Production of Lithium-Manganese Composite Oxide> (1) Example 1 M Mn (NO ₃ ) ₂ aqueous solution and 1 M Al
(NO ₃ ) ₃ aqueous solution and Mn: Al in a molar ratio of 0.9:
30 ml of a mixed aqueous solution mixed so as to be 0.1 was prepared. While stirring the mixed aqueous solution with a stirrer, 150 ml of a 1 M aqueous solution of LiOH / 3 wt% H ₂ O ₂ was mixed, and then reacted for 5 minutes to precipitate a composite oxide precursor.

Next, this mixed oxide precursor was put into a glass beaker together with the mixed solution, and irradiated with an electromagnetic wave having a frequency of 2.45 GHz and an output of 600 W for 1 to 10 minutes to be aged. After aging, the mixture was allowed to reach room temperature, filtered, washed with water, and dried to obtain a lithium manganese composite oxide.

(2) Comparative Example A mixed solution was prepared in the same manner as in the above example, and a composite oxide precursor was deposited. Next, this mixed oxide precursor was put into a closed pressure vessel together with the mixed solution, and aged at a temperature of 80 ° C. for 1 to 24 hours under a saturated vapor pressure (hydrothermal method). After aging, the mixture was allowed to reach room temperature, filtered, washed with water, and dried to obtain a lithium manganese composite oxide.

<Specification of Crystal Structure of Lithium-Manganese Composite Oxide> X-ray diffraction analysis using CuKα ray was performed on each lithium manganese composite oxide produced based on each of the above Examples and Comparative Examples. FIG. 1 shows an X-ray diffraction pattern of the lithium manganese composite oxide of the example. FIG. 2 shows an X-ray diffraction pattern of the lithium manganese composite oxide of the comparative example.

According to the pattern shown in FIG. 1, when aging was performed by irradiating an electromagnetic wave, only 2 minutes
It can be seen that the peak near 64 ° (θ is the diffraction angle) is separated into two peaks. Therefore, it was confirmed that among the lithium manganese composite oxides of the examples, those aged by irradiating electromagnetic waves for 2 minutes or more had a hexagonal layered rock salt structure with high crystallization water removed. In addition, the electromagnetic wave
The crystal structure of the lithium manganese composite oxide hardly changed even after irradiation for 0 minutes, and thus it was confirmed that excessive irradiation did not affect the crystal structure.

On the other hand, as can be seen from the pattern of FIG.
It can be seen that a ripening time of 2 hours or more is required to separate a peak near 2θ = 64 ° (θ is a diffraction angle) into two peaks. In other words, it was found that the aging time was required to be 2 hours or more in order to obtain a hexagonal layered rock-salt structure lithium manganese composite oxide having high crystallinity and high crystallinity by removing the water of hydration by the hydrothermal method.

Therefore, it was confirmed that a lithium manganese composite oxide having a layered rock salt structure with high crystallinity can be produced in a very short time by aging by irradiation with electromagnetic waves.

<Confirmation of Crystal Structure of Lithium Manganese Composite Oxide by Charge / Discharge Curve> A lithium manganese composite oxide obtained by irradiating an electromagnetic wave for 2 minutes to ripen the lithium manganese composite oxide was used as a positive electrode active material. A lithium battery was fabricated, and the crystal structure of the lithium manganese composite oxide was confirmed from a charge / discharge curve.

The positive electrode of the battery was 10 mg of a positive electrode mixture prepared by mixing 70 parts by weight of the lithium manganese composite oxide with 25 parts by weight of a conductive additive (carbon black) and 5 parts by weight of a binder (Teflon). Was molded into a pellet having a diameter of 10 mm, and vacuum-dried at 200 ° C. for 10 hours before use. Metal lithium is used for the negative electrode, a polyethylene sheet having a thickness of 25 μm is used for the separator, and the non-aqueous electrolyte is
A solution obtained by dissolving LiPF ₆ at a concentration of 1 M in a mixed solvent obtained by mixing ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1 was used.

FIG. 3 shows that the current density was 0.4 mA at 20 ° C.
Was charged to 4.2V at a constant current of / cm ^2, the charge-discharge curve when discharged at a constant current density of 0.4 mA / cm ² until 2.5V - shows the (time voltage curve). As can be seen from this figure, the charge / discharge curve shows a discharge curve having no plateau region, which is peculiar to the layered rock salt structure. Water was removed, and it was confirmed that the layer had a highly crystalline layered rock salt structure. Further, when the discharge capacity was measured, it was confirmed that the discharge capacity was at a practical level of about 150 mAh / g.

[0066]

The method for producing a lithium manganese composite oxide according to the present invention is a method for producing a lithium manganese composite oxide having a spinel structure or a layered rock salt structure, wherein the composite is prepared in a mixed solution obtained by mixing an aqueous solution as a raw material. It comprises a deposition step of depositing an oxide precursor, and a ripening step of ripening the deposited precursor by irradiating it with electromagnetic waves.

According to the method for producing a lithium manganese composite oxide of the present invention, a lithium manganese composite oxide having a spinel structure or a layered rock salt structure having excellent crystallinity can be produced in a very short time and at low cost. Furthermore, according to the method for producing a lithium manganese composite oxide of the present invention,
The lithium manganese composite oxide can be easily produced by a continuous method as well as a batch method, and can be easily mass-produced.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction pattern of a lithium manganese composite oxide aged by irradiation with electromagnetic waves.

FIG. 2 is an X-ray diffraction pattern of a lithium manganese composite oxide aged by a hydrothermal method.

FIG. 3 is a charge / discharge curve of a lithium secondary battery using a lithium manganese composite oxide aged by performing electromagnetic wave irradiation for 2 minutes as a positive electrode active material.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yoshio Ukyo F-term in Toyota Central R & D Laboratories Co., Ltd. 1 41-cho, Yokomichi, Nagakute-cho, Aichi-gun, Aichi F-term (reference) 4G048 AA04 AB02 AB05 AC06 AD06 AE05 5H050 AA19 BA17 CA09 CB08 CB12 EA10 EA24 FA19 GA01 GA02 GA10 GA15 HA02 HA13

Claims (2)

[Claims] 1. A manganese salt aqueous solution in which a salt having manganese as a cation is dissolved in water; a lithium hydroxide H ₂ O ₂ aqueous solution in which lithium hydroxide is dissolved in an H ₂ O ₂ aqueous solution; A mixed solution is prepared by mixing an aqueous Me salt solution in which a salt having a metal element Me (Me is at least one selected from Al and Fe) as a cation is dissolved in water, and the composition formula Li _b Mn _{1-a / 2} Me _{a / 2} O ₂ .nH ₂ O
(0 <b ≦ 1.5, 0 ≦ a ≦ 0.1, 0.1 ≦ n ≦ 1)
A precipitation step of precipitating a lithium manganese composite oxide precursor represented by, and irradiating the mixed solution on which the precursor has been deposited with electromagnetic waves, to ripen the precursor and obtain a composition formula Li _c
Mn _2-a Me _a O ₄ (0 <c ≦ 1.3, 0 ≦ a ≦ 0.1)
A method for producing a lithium manganese composite oxide for a lithium secondary battery positive electrode active material, comprising: an aging step of obtaining a spinel-structured lithium manganese composite oxide represented by the formula: 2. A manganese and manganese salt solution the salt with cations dissolved in water, lithium hydroxide and H ₂ O ₂ Li aqueous H ₂ O ₂ solution hydroxide dissolved in an aqueous solution, a metal element Me ( Me is at least one selected from Al and Fe
(Or more than one species) as a cation is mixed with a Me salt aqueous solution in which water is dissolved in water to form a mixed solution, and the composition formula Li _y Mn _1-x Me _x O ₂ .nH ₂ O (0 <Y ≦ 1.5,
A precipitation step of depositing a lithium manganese composite oxide precursor represented by 0.05 <x ≦ 0.2, 0.1 ≦ n ≦ 1), and irradiating the mixed solution on which the precursor has been deposited with electromagnetic waves. The precursor is thereby aged, and the composition formula Li _z M
n _1-x Me _x O ₂ (0 <z ≦ 1.2, 0.05 <x ≦ 0.
A method for producing a lithium manganese composite oxide for a lithium secondary battery positive electrode active material, comprising: an aging step of obtaining a layered rock salt structure lithium manganese composite oxide represented by 2).