KR100464313B1 - lithuim manganese oxide, preparation thereof and lithium secondary battery employing the same as cathode active material - Google Patents

Abstract

The present invention relates to a lithium manganese oxide having a tetragonal structure represented by the following formula (1) or (2), a manufacturing method thereof, and a lithium secondary battery employing the same as an active material.

Li _x Me _y Mn _1-y O _2-z F _z (wherein Me is boron or gallium, x is 0.9 to 1.3, y is 0.02 to 0.25 and z is 0.05 to 0.2).

Lithium manganese oxide according to the present invention is excellent in ion conductivity and electrical conductivity and can be synthesized at low temperature using a low cost raw material. Moreover, the lithium secondary battery using this lithium manganese oxide as an active material has a high capacity and little capacity loss in the chemical conversion step. In addition, the Mars speed is high, and the high-rate charge and discharge characteristics and the initial charge and discharge characteristics as well as the overall charge and discharge characteristics are excellent. The lifetime characteristics are also excellent.

Description

Lithium manganese oxide, a method of manufacturing the same and a lithium secondary battery employing the same as an active material {lithuim manganese oxide, preparations and lithium secondary battery employing the same as cathode active material}

The present invention relates to a lithium manganese oxide, and more particularly, a lithium manganese oxide having a tetragonal structure with lattice defects and having excellent ion conductivity and electrical conductivity, a method of preparing the same, and a cathode active material thereof, which can be used as a cathode active material and have high initialization rate. The present invention relates to a lithium secondary battery having improved charge / discharge characteristics, lifetime characteristics, and the like.

The composite oxide of lithium-manganese-oxygen (Li-Mn-O) is useful as a cathode active material for rechargeable lithium secondary batteries because it is not toxic to the human body, environmentally friendly, and relatively inexpensive compared to lithium cobalt oxide (LiCoO ₂ ). Is one of.

Lithium manganese oxide is roughly classified into spinel-based LiMn ₂ O ₄ used as the cathode active material of a 4V class battery and tetragonal lambda -Li ₂ Mn ₂ O ₄ used as the cathode active material of a 3V class battery.

Tetragonal λ-Li ₂ Mn ₂ O ₄ has a theoretical capacity of 285 재료 h / g and is considerably higher than spinel-based LiMn ₂ O ₄ (theoretical capacity: 145㎃h / g). It is pointed out as a problem that there is difficulty in battery manufacturing due to instability.

The high temperature synthetic orthogonal lithium manganese oxide (LiMnO ₂ ; hereinafter referred to as high temperature lithium manganese oxide) developed by IJDavison et al. Of the National Research Institute of Canada can overcome the problems of the existing lithium manganese oxide and Osaka University of Japan. And low temperature synthetic tetragonal lithium manganese oxides (LiMnO ₂ ; hereinafter referred to as low temperature lithium manganese oxides) developed at the University of Simon Prasher University, Canada.

They have the advantage of being stable in the air and exhibiting high capacity.

However, the high temperature lithium manganese oxide is synthesized at a high temperature of about 1000 ° C. or higher, and thus has poor ion conductivity and electrical conductivity. In addition, the lithium secondary battery employing the same as an active material has a significant capacity loss in the initial chemical conversion stage, takes a long time to reach a fully chemical conversion stage, and a significant decrease in capacity during high-rate charging and discharging.

Low-temperature lithium manganese oxide has a disadvantage in that it is economical because expensive MnOOH must be used as a starting material. In addition, the lithium secondary battery employing the same as the active material has an excellent initial charging and discharging efficiency as compared to the lithium secondary battery employing the high temperature lithium manganese oxide as the active material. As with the lithium secondary battery used as the active material, the capacity during the high rate charge / discharge is significantly reduced and the lifespan characteristics are poor.

In addition, the biggest problem that is commonly pointed out in both the high-temperature and low-temperature lithium manganese oxide is that it is difficult to act as an active material of the battery because the insertion / deintercalation of lithium is not performed in the tetragonal structure.

When the above-described high-temperature and low-temperature lithium manganese oxides are employed as active materials for a lithium secondary battery, the lithium manganese oxides undergo irreversible phase transition from a tetragonal structure to a second phase (for example, a spinel like structure). The insertion / deinsertion of lithium occurs when

This irreversible phase transition generally occurs during the first charge and discharge process. However, most of the lithium ions removed during the phase transition process cannot be reinserted. Accordingly, as the number of charge and discharge cycles increases, the charge and discharge efficiency of the battery decreases rapidly and the life is greatly shortened.

The present invention is intended to overcome the above problems.

The technical problem to be achieved by the present invention is to provide a lithium manganese oxide having a tetragonal structure containing crystal defects.

Another technical problem to be achieved by the present invention is to provide a method for producing lithium manganese oxide as described above.

Another technical problem to be achieved by the present invention is to adopt a lithium manganese oxide having a tetragonal structure as the cathode active material as described above, not only a high capacity, but also a small capacity loss in the initial chemical conversion stage, and improved lithium speed and life characteristics. It is to provide a secondary battery.

1 is an X-ray diffraction analysis of lithium manganese oxide according to an embodiment of the present invention.

FIG. 2 is a graph of the charging and discharging stages of a lithium secondary battery employing lithium manganese oxide as a cathode active material according to an embodiment of the present invention.

3 is a graph showing the life characteristics of a lithium secondary battery employing a lithium manganese oxide as a cathode active material according to an embodiment of the present invention.

4 is a graph showing the life characteristics of a lithium secondary battery employing a lithium manganese oxide as a cathode active material according to another embodiment of the present invention.

5 is a graph showing the life characteristics of a lithium secondary battery employing a lithium manganese oxide as a cathode active material according to another embodiment of the present invention.

6 is a graph showing the life characteristics of a lithium secondary battery employing a conventional lithium manganese oxide as a cathode active material.

7 is a graph showing the life characteristics of a lithium secondary battery employing another conventional lithium manganese oxide as a cathode active material.

Technical problem of the present invention can be made by the lithium manganese oxide represented by the formula (1) or formula (2).

[Formula 1]

Li _x Me _y Mn _1-y O _2-z F _z

(In formula, Me is boron or gallium, x is 0.9-1.3, y is 0.02-0.25, z is 0.05-0.2).

Another technical problem of the present invention,

a) mixing and grinding lithium salt, manganese salt, boron salt or gallium salt, and lithium salt;

b) placing the mixture into a reactor and then removing oxygen gas from the reactor;

c) calcining the mixture at 400-650 ° C. for 10-24 hours; And

d) by the method of producing a lithium manganese oxide of the formula (1) comprising the step of heat-treating the resultant of step c) for 24 to 48 hours at 650 ~ 800 ℃.

[Formula 1]

Li _x Me _y Mn _1-y O _2-z F _z

(In formula, Me is boron or gallium, x is 0.9-1.3, y is 0.02-0.25, z is 0.05-0.2).

In the method for producing a lithium manganese oxide according to the present invention, the lithium salt is lithium carbonate (Li ₂ CO ₃ ), lithium hydroxide (LiOH H ₂ O) or lithium oxide (Li ₂ O), the manganese salt is manganese dioxide (β-MnO ₂ ), manganese trioxide (Mn ₂ O ₃ ) or manganese carbonate (MnCO ₃ ), and the boron or gallium salt is boron trioxide (B ₂ O ₃ ) or gallium hydroxide (Ga (OH) ₃ ), respectively. It is preferable. In addition, the lithium salt is preferably lithium fluoride.

Steps (b) and (d) are preferably carried out in the presence of nitrogen gas or argon gas.

On the other hand, if necessary, after the step (d) to further perform the grinding step to control the size of the lithium manganese oxide particles 1-30㎛, more preferably 1-15㎛.

Another technical problem according to the present invention,

A cathode comprising a lithium manganese oxide represented by the formula (1);

An anode comprising an active material selected from lithium metal, lithium alloy or carbon material; And

It can be made by a lithium secondary battery made of an electrolyte.

[Formula 1]

Li _x Me _y Mn _1-y O _2-z F _z

(In formula, Me is boron or gallium, x is 0.9-1.3, y is 0.02-0.25, z is 0.05-0.2).

Lithium manganese oxide according to the present invention is characterized by improving the conventional ion conductivity and electrical conductivity by adding boron or gallium in the synthesis and can be synthesized at a low temperature of less than 800 ℃ using a low-cost starting material is economical.

In addition, by replacing boron (or gallium) and fluorine with a part of manganese and oxygen atoms, respectively, and using more than one mole of lithium to maintain the oxidation value of manganese above trivalent, many crystal defects are formed from the starting phase. do.

These crystal defects promote the site shift of the manganese element, and as a result, many phases in the crystal structure during the primary charge generate many lithium ion reinsertion sites.

1 is an X-ray diffraction diagram of lithium manganese oxide to which boron and fluorine are added as an example of lithium manganese oxide according to the present invention.

1, it can be seen that boron according to the present invention, fluorine-added lithium manganese oxide has a tetragonal structure.

Meanwhile, although not shown in the X-ray diffractogram of FIG. 1, as the amount of boron added increases, boron salt increases, that is, conventional lithium manganese oxide (LiMnO ₂ ) having a tetragonal structure as a base matrix and lithium borate (Li ₂ B ₂ O ₄ ) is present as the secondary phase.

The exact position of the secondary phase lithium borate is unknown, but exists as crystal defects at the microcrystalline phase interface of the tetragonal lithium manganese oxide in the same particle and is involved in ion migration between the microcrystals.

In addition, a small amount of Mn ₃ O ₄ is present as a secondary phase, which is expected to be formed by an electron imbalance caused by the addition of boron and fluorine. This secondary phase also acts as a crystal defect, inducing the site shift of the manganese element and Creates a lot of reinsertion positions.

Therefore, when the lithium manganese oxide of the present invention having such a structure is used as a battery active material, not only a high capacity battery can be obtained but also the capacity of the battery can be prevented from being lost in the chemical conversion step. Moreover, this battery is excellent in charge / discharge characteristics and lifespan characteristics.

Lithium manganese oxide of the tetragonal structure according to the present invention can be prepared according to the following method.

First, the reactants are weighed, mixed and milled. The reactants may be lithium salts such as lithium carbonate (Li ₂ CO ₃ ), lithium hydroxide (LiOHH ₂ O) or lithium oxide (Li ₂ O), manganese dioxide (β-MnO ₂ ), manganese trioxide (Mn ₂ O ₃ ) or Manganese salts such as manganese carbonate (MnCO ₃ ), boron salts such as boron trioxide (B ₂ O ₃ ) or gallium salts such as gallium hydroxide (Ga (OH) ₃ ), and lithium salts such as lithium fluoride (LiF) .

Subsequently, the mixture is placed in an alumina container and placed in a reactor capable of controlling the atmosphere, and argon or nitrogen gas is injected for at least about 30 minutes to remove oxygen gas. At this time, if the oxygen gas is not sufficiently removed, spinel lithium manganese oxide is partly generated, so care should be taken.

Next, the mixture is calcined at 400-700 ° C. for 10-24 hours. In this case, the calcination temperature and time may vary depending on the type of lithium salt used as a reactant. For example, when lithium carbonate (Li ₂ CO ₃ ) is used as the lithium salt, calcination is performed at 600 to 650 ° C. for at least 10 hours. In the case of using lithium hydroxide (LiOH.H ₂ O) as the lithium salt, it is preferable to calcinate at 400 to 500 ° C for 10 hours or more.

Finally, the calcined mixture is heat treated at 650-800 ° C. for 24-48 hours. At this time, the heat treatment temperature and time is controlled according to the addition amount of boron or gallium salt, in general, the more the addition amount of the boron or gallium salt can be reduced in temperature and time.

On the other hand, if necessary, after the heat treatment step is further carried out a grinding step to control the size of the lithium manganese oxide particles to 1 to 30㎛, preferably 1 to 15㎛.

If the size of the particles is less than the above range, the productivity is lowered, while if the size exceeds the above range, the charge-discharge capacity, rate characteristic, etc. are all reduced, which is undesirable.

The method for producing a lithium secondary battery employing the lithium manganese oxide of the present invention thus obtained as a cathode active material is as follows.

First, the lithium manganese oxide according to the present invention (Li _x Me _y Mn _1-y O _2-z F _z ; wherein Me is boron or gallium, x is 0.9 to 1.3, y is 0.02 to 0.25, and z is 0.05 to 0.2), a conductive agent and a binder are mixed in a weight ratio of 85: 10: 5, and the mixture is mixed with a solvent to prepare a cathode active material slurry. The prepared cathode active material slurry is cast on a thin aluminum plate and then dried to prepare a cathode.

The anode electrode includes an active material for an anode electrode such as a lithium metal, a lithium alloy, or a carbon material, and may process the lithium metal into a predetermined size and shape to obtain an anode electrode, or by mixing a carbon material active material, a conductive agent, and a binder The obtained anode active material slurry may be cast on a thin copper plate, dried and processed into a predetermined form to obtain an anode electrode.

As the electrolyte, any one of an organic electrolyte prepared by dissolving lithium salt in a non-aqueous organic solvent or a solid electrolyte prepared by impregnating the organic electrolyte with a polymer matrix may be used as the electrolyte.

The non-aqueous organic solvent is propylene carbonate (PC), ethylene carbonate (EC), ethylmethyl carbonate, methyl acetate, γ-butyrolactone, 1,3-dioxolane (1,3-dioxolane), dimethoxyethane, dimethylcarbonate, diethylcarbonate, tetrahydrofuran (THF), dimethylsulfoxide and polyethylene glycol dimethyl ether Preference is given to using at least one solvent selected from glycol dimthylether.

In addition, the lithium salt is not particularly limited as long as it is a lithium compound that dissociates in an organic solvent to give lithium ions, and specific examples thereof include lithium perchlorate (LiClO ₄ ) and lithium tetrafluoroborate (LiBF ₄ ). , Lithium hexafluorophosphate (LiPF ₆ ), lithium trifluoromethansulfonate (LiCF ₃ SO ₃ ), lithium bistrifluoromethansulfonylamide, LiN (CF ₃ SO ₂ ) ₂ ) Etc., and the content thereof is at a normal level.

On the other hand, the polymer matrix is not particularly limited as long as the organic electrolyte solution impregnation rate is excellent and the lithium ion transport water is high. Examples of the polymer matrix most commonly used in the field of the present invention include vinylidene fluoride-based polymers. .

The obtained cathode electrode and the anode electrode as described above are assembled together with the electrolyte to prepare a lithium secondary battery.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

<Example 1>

0.9 moles of LiOH, 0.49 moles of Mn ₂ O ₃ , 0.02 moles of B ₂ O ₃ and 0.1 moles of LiF are added to an auto trigger, pulverized and mixed for at least 30 minutes, and the mixture is placed in an alumina crucible to control the atmosphere. This was put into a possible reactor. Subsequently, argon gas was injected into the reactor for about 30 minutes to remove oxygen present in the reactor. Next, the mixture was calcined at 450 ° C. for 10 hours and then heat treated at 650 ° C. for 24 hours under a nitrogen atmosphere. As a product, lithium manganese oxide (LiB _0.02 Mn _0.98 O _1.9 F _0.1 ) having an average particle diameter of 10 μm was obtained.

A 3% Kynar flex 2801 (trade name) solution (content of Kynar flex 2801) in which a mixed powder containing 85 g of lithium manganese oxide, 5 g of carbon, and 5 g of graphite was dissolved in N-methylpyrrolidone. It was mixed with to prepare an active material slurry. The obtained active material slurry was cast on a thin aluminum plate of 30 μm and placed in an oven at 60 ° C. for 1 hour to evaporate N-methylpyrrolidone and further dried in a vacuum oven at 120 ° C. for 1 hour. The dried film was pressed with a roller press to have a thickness of 90 μm, and then molded into a circular film having a radius of 5 mm using a jig.

Subsequently, an active material slurry obtained by mixing a mixture of MCMB (mesocarbon) and conductive super-P carbon (mixed weight ratio: 95: 5) with a 3% Kynaplex 2801 solution was cast on a copper sheet and the cathode electrode The anode electrode in the form of a circular disk having a radius of 6 mm was prepared by processing as in the manufacturing process of.

As the electrolyte, 1M LiPF ₆ / EC / EMC manufactured by Mitsubishi Corporation was used.

The battery was assembled using the cathode electrode, the anode electrode, and the electrolyte prepared as described above.

In order to activate the assembled battery, a low current (3.6 mA / g) was added to form the battery, and the current was increased to 36 mA / g, and the life characteristics were tested. The obtained charge and discharge curves are shown in FIG. 2 and the life test results are shown in FIG. 3.

<Example 2>

A lithium manganese oxide (LiGa _0.02 Mn _0.98 O _1.9 F _0.1 ) was prepared according to the same method as disclosed in Example 1 except that 0.02 mole of Ga (OH) ₃ was used instead of 0.02 mole of B ₂ O _3. .

Using the prepared lithium manganese oxide, a cathode electrode was prepared in the same manner as in Example 1, and then assembled together with the same anode electrode and electrolyte as in Example 1 to prepare a lithium secondary battery. The life characteristics of the manufactured lithium secondary battery were tested and the results are shown in FIG. 4.

<Example 3>

0.45 moles of Li ₂ CO ₃ , 0.98 moles of MnO ₂ , 0.02 moles of B ₂ O ₃ and 0.1 moles of LiF are weighed in an automatic mortar, pulverized and mixed for at least 30 minutes, and then the mixture is placed in an alumina crucible and placed in an atmosphere. It was placed in a controllable reactor.

Subsequently, argon gas was injected into the reactor for about 30 minutes to remove oxygen present in the reactor. The mixture was then calcined at 650 ° C. for 10 hours and then heat treated at 750 ° C. for 24 hours under a nitrogen atmosphere. The obtained product produced lithium manganese oxide (LiB _0.02 Mn _0.98 O _1.9 F _0.1 ) having an average particle diameter of 20 μm.

Using the prepared lithium manganese oxide, a cathode electrode was prepared in the same manner as in Example 1, and then assembled together with the same anode electrode and electrolyte as in Example 1 to prepare a lithium secondary battery. The life characteristics of the manufactured lithium secondary battery were tested and the results are shown in FIG. 5.

Comparative Example 1

Using a common high-temperature lithium manganese oxide (LiMnO ₂ ) to prepare a cathode electrode in the same manner as in Example 1 and assembling it with the same anode electrode and electrolyte as in Example 1 to prepare a lithium secondary battery. The life characteristics of the manufactured lithium secondary battery were tested and the results are shown in FIG. 6.

Comparative Example 2

Lithium manganese oxide (LiMnO _1.9 F _0.1 ) was prepared in the same manner as in Example 1 except that B ₂ O ₃ was not added.

Using the obtained lithium manganese oxide, a cathode electrode was prepared in the same manner as in Example 1, and was assembled together with the same anode electrode and electrolyte as in Example 1 to prepare a lithium secondary battery. The life characteristics of the manufactured lithium secondary battery were tested and the results are shown in FIG. 7.

3 to 7 showing the life characteristics of the lithium secondary battery prepared according to each embodiment and comparative example, in the case of the lithium secondary battery prepared according to the present invention (Fig. 3 to 5) the number of charge and discharge cycles It can be seen that even if is repeated there is almost no decrease in the discharge capacity compared to the initial capacity, but rather increased (Fig. 3).

In contrast, referring to FIGS. 6 and 7 showing the life characteristics of a lithium secondary battery employing a conventional lithium manganese oxide as a cathode active material, not only the initial capacity but also the cycle capacity is significantly lower than that of the battery of the present invention (FIG. 6). The initial capacity is very high, but as the number of cycles is repeated, the cycle capacity decreases rapidly (FIG. 7).

Lithium manganese oxide according to the present invention is excellent in ion conductivity and electrical conductivity and can be synthesized at low temperature using a low cost raw material. Moreover, the lithium secondary battery using this lithium manganese oxide as an active material has a high capacity and little capacity loss in the chemical conversion step. In addition, the Mars speed is high, and the high-rate charge and discharge characteristics and the initial charge and discharge characteristics as well as the overall charge and discharge characteristics are excellent. The lifetime characteristics are also excellent.

Claims (9)

Lithium manganese oxide of a tetragonal structure represented by the formula (1). [Formula 1] Li _x Me _y Mn _1-y O _2-z F _z (In formula, Me is boron or gallium, x is 0.9-1.3, y is 0.02-0.25, z is 0.05-0.2). a) mixing and grinding lithium salt, manganese salt, boron salt or gallium salt and lithium salt; b) placing the mixture into a reactor and then removing oxygen gas from the reactor; c) calcining the mixture at 400-650 ° C. for 10-24 hours; And d) a method of preparing lithium manganese oxide of Chemical Formula 1, comprising the step of heat-treating the product of step c) at 650-800 ° C. for 24-48 hours. [Formula 1] Li _x Me _y Mn _1-y O _2-z F _z (In formula, Me is boron or gallium, x is 0.9-1.3, y is 0.02-0.25, z is 0.05-0.2). The method of claim 2, wherein the lithium salt is lithium carbonate (Li ₂ CO ₃ ), lithium hydroxide (LiOH.H ₂ O) or lithium oxide (Li ₂ O). The method for producing lithium manganese oxide according to claim 2, wherein the manganese salt is manganese dioxide (β-MnO ₂ ), manganese trioxide (Mn ₂ O ₃ ) or manganese carbonate (MnCO ₃ ). The method of claim 2, wherein the boron salt and gallium salt are boron trioxide (B ₂ O ₃ ) and gallium hydroxide (Ga (OH) ₃ ), respectively. The method of claim 2, wherein the step (b) and (d) is carried out in the presence of nitrogen gas or argon gas. The method of claim 2, wherein after the step (d) further comprises a grinding step. A cathode comprising a lithium manganese oxide represented by the formula (1); An anode comprising an active material selected from lithium metal, lithium alloy or carbon material; And Lithium secondary battery consisting of an electrolyte. [Formula 1] Li _x Me _y Mn _1-y O _2-z F _z (In formula, Me is boron or gallium, x is 0.9-1.3, y is 0.02-0.25, z is 0.05-0.2). A lithium manganese oxide, a method for producing a lithium manganese oxide, and a lithium secondary battery according to claim 1, 2 and 8, wherein the particle size is 1 to 30 µm.