KR20060102522A - Lithium manganate, process for preparing the same, positive electrode sub-active material of lithium secondary battery, positive electrode active material of lithium secondary battery and lithium secondary battery - Google Patents

Abstract

The present invention is a lithium manganate useful as a lithium secondary battery positive electrode activating material which can suppress deterioration of performance due to overdischarge without any decrease in capacity during normal use, a manufacturing method thereof, a lithium secondary battery positive electrode activating material, lithium secondary A battery positive electrode active material and a lithium secondary battery are provided.

Further, the present invention is lithium manganate represented by Li _x MnO ₂ (where x represents 0.9 ≦ x ≦ 1.1), and diffraction near 2θ = 15.3 ° when X-ray diffraction analysis is performed using Cu—Kα rays as the source. The intensity ratio (I _24.6 / I _15.3 ) of the diffraction peak near 2θ = 24.6 ° to the peak is 0.25 or less, and the intensity ratio (I _45.0 / I _15.3 ) of the diffraction peak near 2θ = 45.0 ° is 0.70 or less.

Lithium manganate, lithium secondary battery, positive electrode active material, positive electrode active material

Description

Lithium Manganate, Manufacturing Method thereof, Lithium Secondary Battery Positive Electrode Reactive Material, Lithium Secondary Battery Positive Electrode Active Material and Lithium Secondary Battery {Lithium Manganate, Process for Preparing the Same, Positive Electrode Sub-Active Material of Lithium Secondary Battery, Positive Electrode Active Material of Lithium Secondary Battery and Lithium Secondary Battery}

1 is an X-ray diffraction diagram of LiMnO ₂ obtained in Example 4. FIG.

[Patent Document 1] Japanese Unexamined Patent Publication No. 6-349493

[Patent Document 2] Japanese Patent Application Laid-Open No. 2003-223898

[Patent Document 3] Japanese Unexamined Patent Publication No. 2002-151079

[Patent Document 4] Japanese Patent Application Laid-Open No. 8-37027

The present invention relates to a lithium manganate, a method for producing the same, a lithium secondary battery positive electrode activating material, a lithium secondary battery positive electrode active material and a lithium secondary battery using the lithium manganate.

Background Art In recent years, as portable and wireless home appliances have been rapidly developed, lithium ion secondary batteries have been put into practical use as power sources for small electronic devices such as laptop personal computers, mobile phones, and video cameras. Regarding this lithium ion secondary battery, reports of lithium cobalate as a positive electrode active material of lithium ion secondary batteries by Mizushima et al. In 1980 ("Material Research Blutin" vol. 15, P783-789 (1980)) Since its inception, research and development on lithium-based composite oxides have been actively conducted, and many proposals have been made so far.

However, a lithium secondary battery having a lithium-based composite oxide as a positive electrode active material and having a carbon material or the like as a negative electrode has a problem in that Li ions emitted by charging are blown to the negative electrode side and do not contribute to subsequent charge and discharge. . Therefore, the lithium-based composite oxide is always in a charged state lacking Li ions, and as a result, the positive electrode potential becomes high. Therefore, when a lithium ion secondary battery is placed in an over-discharge state, the copper foil used as a negative electrode current collector elutes in electrolyte solution, and a part of it precipitates in a positive electrode, and there exists a problem that charge / discharge characteristics are easy to deteriorate. For this reason, a method of preventing an overdischarge itself by providing an electric circuit for preventing overdischarge is used outside of the battery. The cost is expensive. In addition, if the circuit does not operate properly, it is already impossible to prevent deterioration due to overdischarge.

On the other hand, a method of using a lithium-based composite oxide such as LiCoO ₂ as a main positive electrode active material and adding LiMnO ₂ as a sub-active substance to this is also proposed (for example, Patent Document 1, See Patent Document 2). LiMnO ₂ of Patent Document 1 and Patent Document 2 is produced by calcining MnO ₂ and lithium carbonate in an inert gas atmosphere. However, LiMnO ₂ obtained by LiMnO ₂ obtained by the production methods of Patent Document 1 and Patent Document 2 as a positive electrode active material is Although the overdischarge characteristic improves to some extent in a battery, it is easy to generate | occur | produce problems, such as a fall of a battery capacity, and the development of the lithium secondary battery positive electrode activating material which can provide the outstanding battery performance was desired.

Further, Patent Document 3 below discloses a lithium secondary battery using LiMnO ₂ produced by firing a mixture of Mn ₂ O ₃ and a lithium compound obtained by heating MnO ₂ as a positive electrode active material, or Patent Document 4 below discloses LiOH and Mn _2. Although a lithium secondary battery using LiMnO ₂ as a cathode active material obtained by firing a mixture with O ₃ at 600 to 800 ° C. in a vacuum has been proposed, LiMnO ₂ of Patent Document 3 and Patent Document 4 is used as a positive electrode activator. Also, problems such as a decrease in battery capacity and insufficient overdischarge safety have been left. Further, LiMnO ₂ disclosed in Patent Document 4 has an intensity ratio (I _24.6 / I _15.3 ) of the diffraction peak at 2θ = 24.6 ° to the diffraction peak at 2θ = 15.3 ° in the X-ray diffractogram, but is 0.11 to 0.25. , The intensity ratio (I _45.0 / I _15.3 ) of the diffraction peak of 2θ = 45.0 ° to the diffraction peak of 2θ = 15.3 ° is 0.73 or more when calculated from the figure.

Here, the lithium secondary battery positive electrode activating material requires different characteristics from the positive electrode active material in various respects. The positive electrode active material requires a high discharge voltage in order to achieve high output characteristics, and the higher the discharge voltage, the better the positive electrode active material. On the other hand, since the positive electrode activator is a material for supplying Li ions, the lower the discharge voltage is, the better. This is because a high discharge voltage does not change into a positive electrode active material and contributes to charging and discharging, and does not supply Li. In this respect, the performance required for the positive electrode active material and the positive electrode active material is opposite.

In addition, the higher the discharge capacity, the better the positive electrode active material. This is because the higher the discharge capacity is, the longer the use becomes possible. In contrast, the lower the discharge capacity, the better the cathode activating material is to supply Li ions. The high discharge capacity means that Li ions are inserted and Li ions are not supplied. In this respect, the performance required for the positive electrode active material and the positive electrode active material is opposite.

In addition, the smaller the capacity deterioration and the lower the discharge voltage caused by the charge / discharge cycle, the better the positive electrode active material. This is because the higher output characteristics and capacity characteristics can be maintained even after repeated use, so that they can be used for a long time. On the other hand, since the positive electrode activating material hardly takes in Li ions even after discharging the Li ions by charging, it is low to consider the capacity deterioration and the drop in the discharge voltage due to the charge / discharge cycle. On the contrary, it is necessary to suppress these when discharge capacity increases or discharge voltage rises with a charge-discharge cycle. Also in this respect, the performance required for the positive electrode active material and the positive electrode active material is different.

As described above, since the performance required for the positive electrode active material and the performance required for the positive electrode active material are significantly different, even when LiMnO ₂ as a positive electrode active material known in the art is used as the positive electrode active material, a decrease in battery capacity and sufficient It is thought that overdischarge safety was not obtained. Thus, there has been a demand for the development of LiMnO ₂ having suitable properties as a positive electrode activator.

Therefore, an object of the present invention is lithium manganate useful as a lithium secondary battery positive electrode activating material capable of suppressing deterioration in performance due to overdischarge without deterioration in capacity during normal use, a manufacturing method thereof, and a lithium secondary battery positive electrode using the same. It is an object to provide a lithium secondary battery which is excellent in an activating substance, a lithium secondary battery positive electrode active substance, and the capacity reduction at the time of normal use, and excellent in the effect of suppressing the performance degradation by over discharge.

As a result of intensive studies to solve these problems, the present inventors have (1) intensity ratio of diffraction peaks near 2θ = 24.6 ° to diffraction peaks near 2θ = 15.3 ° when analyzed by X-ray diffraction (I _24.6 / I _15.3 ) is a lithium secondary battery having lithium manganate as a positive electrode activating material whose intensity ratio (I _45.0 / I _15.3 ) of the diffraction peak near 2θ = 45.0 ° is 0.70 or less. It is also found that the effect of suppressing performance degradation due to overdischarge is excellent, and (2) the lithium manganate is obtained by calcining a mixture of Mn ₂ O ₃ and a lithium compound obtained by heating MnO above a specific temperature. Thus, the present invention has been completed.

That is, the first invention to be provided by the present invention is represented by the following formula (1), and when X-ray diffraction analysis using Cu-Kα rays as the source, near 2θ = 24.6 ° to the diffraction peak near 2θ = 15.3 ° The intensity ratio (I _24.6 / I _15.3 ) of the diffraction peak is 0.25 or less, and the lithium manganate is characterized in that the intensity ratio (I _45.0 / I _15.3 ) of the diffraction peak near 2θ = 45.0 ° is 0.70 or less.

Li _x MnO ₂

In the formula, x represents 0.9 ≦ x ≦ 1.1.

In addition, according to the second invention to be provided by the present invention, MnO is heat-treated at 525 ° C. or higher to obtain Mn ₂ O ₃ , then, the obtained Mn ₂ O ₃ and a lithium compound are mixed, and the mixture is calcined to give the following Chemical Formula 1 It is a method of manufacturing lithium manganate represented by.

<Formula 1>

Li _x MnO ₂

In the formula, x represents 0.9 ≦ x ≦ 1.1.

Further, a third invention to be provided by the present invention is a positive electrode activating material for a lithium secondary battery, comprising lithium manganate of the first invention.

In addition, a fourth invention to be provided by the present invention is a lithium secondary battery positive electrode active material characterized by containing the lithium secondary battery positive electrode activating material of the third invention and a lithium composite oxide represented by the following formula (2). .

Li _a M _{1 - b} A _b O _c

In the formula, M represents at least one transition metal element selected from Co, Ni, A represents at least one metal element selected from Mg, Al, Mn, Ti, Zr, Fe, Cu, Zn, Sn, In, a represents 0.9 ≦ a ≦ 1.1, b represents 0 ≦ b ≦ 0.5, and c represents 1.8 ≦ c ≦ 2.2.

 Moreover, the 5th invention which this invention intends to provide is the lithium secondary battery characterized by using the positive electrode active material of said 4th invention.

Best Mode for Carrying Out the Invention

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated based on preferable embodiment.

The lithium manganate of the present invention is represented by the following formula (1), and is distinguished from conventional lithium manganate by X-ray diffraction characteristics.

<Formula 1>

Li _x MnO ₂

In the formula, x represents 0.9 ≦ x ≦ 1.1.

That is, the lithium manganate of the present invention has a 2θ = 24.6 ° vicinity ((01) plane) with respect to the diffraction peak of 2θ = 15.3 ° near ((010) plane) when X-ray diffraction analysis is performed using Cu-Kα rays as the source. The intensity ratio (I _24.6 / I _15.3 ) of the diffraction peaks of _Nm ) is 0.25 or less, preferably 0.10 to 0.25, more preferably 0.20 to 0.25, with respect to the diffraction peak near 2θ = 15.3 ° (the (010) plane). The intensity ratio I _45.0 / I _15.3 of the diffraction peak near 2θ = 45.0 ° ((120) plane) has a value of 0.70 or less, preferably 0.45 to 0.70, and more preferably 0.48 to 0.70. In addition, the diffraction surface means the diffraction surface required at the diffraction peak position of lithium manganate (LiMnO ₂ ) of ASTM card 23-361. In addition, ₂ (theta), d value, and surface index of the lithium manganate (LiMnO2) displayed on ASTM card 23-361 are as Table 1 below.

In the present invention, the significance of what is represented by two peak intensity ratios by three peaks in the X-ray diffraction analysis will be described below. In the X-ray diffraction analysis, since each peak intensity and peak position change with the crystal group and the extinction side and the measurement conditions, a change in the structure is observed as a change in peak intensity or peak position under constant measurement conditions. Since each peak contains only information on a specific face, only information on a specific face is obtained from the specific peak. Therefore, in order to know the three-dimensional state of the entire crystal, it is necessary to judge a peak having information on each of h, k and l. In addition, in order to consider the mutual relations of h, k, and l, it is necessary to consider the relation between peaks having respective plane information.

The lithium manganate of the present invention has peaks near 15.3 °, 24.6 ° and 45.0 ° as described in ASTM card 23-361, and these peaks correspond to the three steel wires in the corresponding ASTM card. Therefore, using the peak corresponding to the three steel wires can reduce the error caused by the measurement. Since the peak has information of the plane that is horizontal with respect to a specific axis, the relationship between the specific two axes can be judged. Therefore, the determination of the structure can be assured. In addition, the stability of the structure and the conductivity of electrons, which determine the good and bad as an activating material of a lithium secondary battery, are caused by the relation of three-dimensional elements, and the elements are released beyond a certain allowable width for each surface. In the case of a defect such as the presence of a defect, it may cause deterioration in performance such as instability of a structure and a decrease in electronic conductivity. Therefore, if two peak intensity ratios by three steel wires on the said ASTM card are calculated | required, the allowable width | variety and structural state about each axis | shaft of h, k, and l can be grasped reliably. In contrast, for example, at the peak ratio of 24.6 ° and the intensity ratio of 15.3 ° disclosed in Japanese Unexamined Patent Application Publication No. Hei 8-37027, information in the h-axis direction is missing, and the material has a certain three-dimensional structure. It is unclear whether is good.

In the present invention, the intensity ratio I _24.6 / I _15.3 of the diffraction peak has structural information in the k-axis direction and the l-axis direction, and when the intensity ratio exceeds 0.25, the structure itself of the plane horizontal to the h axis is As an activating material of a lithium secondary battery, it is unpreferable since it is a structure in which initial stage capacity falls and the capacity difference of charge / discharge capacity is made small. In addition, the intensity ratio I _45.0 / I _15.3 of the diffraction peak has structural information in the h-axis direction and the k-axis direction, and when the intensity ratio exceeds 0.70, the structure itself of the plane parallel to the l-axis is lithium secondary. As a activating substance of a battery, it is unpreferable in that it is a structure in which initial stage capacity falls and the capacity difference of a charge / discharge capacity is made small.

The lithium manganate according to the present invention has the above constitution, so that the lithium secondary battery using the lithium manganate as a positive electrode activator material has no decrease in capacity, suppresses performance degradation due to overdischarge, and gives excellent battery performance. can do. In addition, the lithium manganate of the present invention can be coated with a uniform electrode sheet with an average particle diameter of 1.0 to 20.0 μm, preferably 4 to 15 μm, in addition to the above characteristics, and deterioration of battery performance due to concentration of current or the like. This is preferable at the point which can be suppressed. In addition, an average particle diameter is calculated | required by the laser method particle size distribution measuring method. Hereinafter, in the case of an average particle diameter, the value calculated | required by this measuring method is said.

Further, when the BET specific surface area is 0.2 to 2.0 m 2 / g, preferably 0.4 to 1.0 m 2 / g, the deterioration of the performance of the lithium secondary battery due to the elution of Mn can be suppressed or Li can be supplied at a high speed. Particularly preferred.

The lithium manganate having the above characteristics of the present invention can be obtained by mixing Mn ₂ O ₃ and a lithium compound obtained by heat-treating MnO at a specific temperature or higher, and calcining the obtained homogeneous mixture.

MnO which is a raw material used in the present invention is preferably a manganese compound obtained by heating a manganese carbonate or the like at low temperature. In this case, the heat treatment temperature varies depending on the type of manganese compound used, but in most cases, 1 to 1 in an inert gas atmosphere such as nitrogen gas, helium gas or argon gas at 500 to 800 ° C, preferably 550 to 700 ° C. By using a manganese compound obtained by heating for 20 hours, preferably 2 to 10 hours, lithium manganate useful as a lithium secondary battery positive electrode activating material having a large charge capacity and a low discharge capacity, that is, a large Li supply amount can be obtained. It is preferable at the point.

In the present invention, the heat treatment of the MnO is essential at 525 ° C or higher, preferably 550 ° C or higher. The reason for this is that when the heat treatment temperature is less than 525 ° C, the conversion of MnO to Mn ₂ O ₃ is insufficient, and the lithium secondary battery obtained using lithium manganate obtained as a positive electrode activating material has a lower capacity in normal use. to be. The upper limit of the heat treatment temperature is not particularly limited as long as it is a temperature capable of sufficiently converting MnO into Mn ₂ O ₃ , but in most cases, it is 950 ° C., and lithium manganate produced when the heat treatment temperature exceeds 750 ° C. is activated. Since the voltage (charge voltage) from which Li escapes when used as a soluble substance tends to be high, the heat treatment temperature is particularly preferably 550 to 750 ° C. The time for heat treatment is usually 1 to 20 hours, preferably 2 to 10 hours.

In the heat treatment atmosphere, when oxygen is insufficient, oxidation of MnO is insufficient, and impurities may be generated in addition to the target product. Therefore, the heat treatment atmosphere is an atmosphere containing oxygen sufficient to convert MnO to Mn ₂ O ₃ . It is preferable to carry out. Usually, it is preferable to carry out in air | atmosphere or oxygen atmosphere. In addition, in this invention, heat processing can be performed repeatedly as needed.

In the present invention, the Mn ₂ O ₃ prepared above and the lithium compound are uniformly mixed, and the obtained homogeneous mixture is calcined to obtain the desired lithium manganate represented by the formula (1).

As a lithium compound which is the said raw material, lithium carbonate, lithium hydroxide, etc. are mentioned, for example, These lithium compounds can be used 1 type or in 2 or more types. The physical properties and the like of the lithium compound to be used are not limited, but the average particle diameter is preferably 20 µm or less, preferably 3 to 10 µm, and therefore preferable mixing of the raw materials is possible.

The mixing ratio of the Mn ₂ O ₃ and the lithium compound is a molar ratio (Li / Mn) of Li atoms and Mn atoms of Mn ₂ O _{3 in} the lithium compound and is 0.95 to 1.05, particularly 0.98 to 1.01, lithium manganate having a large Li supply capacity. It is particularly preferable because it can synthesize.

Mixing may be either dry or wet, but dry is preferred because it is easy to manufacture. In the case of dry mixing, it is preferable to use a blender or the like in which the raw materials are mixed uniformly.

The firing conditions, the firing temperature is 600 to 1000 ℃, preferably 700 to 850 ℃. This is because if the firing temperature is less than 600 ° C, the reaction is insufficient and desirable lithium manganate is not obtained. On the other hand, if the firing temperature is higher than 1000 ° C, lithium manganate has a low Li supply capacity. The baking atmosphere is preferably an inert gas atmosphere because the produced lithium manganate is easily oxidized by oxygen and generates impurities such as LiMn ₂ O ₄ and Li ₂ MnO _{3 in} addition to the target product. Under the present circumstances, nitrogen gas, helium gas, argon gas, etc. can be used as an inert gas to be used. The firing time is usually 1 to 20 hours, preferably 2 to 10 hours. In addition, in this invention, baking can also be performed repeatedly as needed.

After firing, the mixture is cooled appropriately and ground as necessary to obtain lithium manganate represented by the formula (1). The grinding carried out as necessary is suitably performed in the case of a block form in which lithium manganate obtained by firing is bonded to a soft bond, but the particles of lithium manganate have a specific average particle diameter and a BET specific surface area. That is, the resulting lithium manganate has an average particle diameter of 1.0 to 20.0 µm, preferably 4.0 to 15.0 µm, and a BET specific surface area of 0.2 to 2.0 m 2 / g, preferably 0.4 to 1.0 m 2 / g. Further, the lithium manganate was near 2θ = 24.6 ° relative to the diffraction peak of 2θ = 15.3 ° ((010) plane) when X-ray diffraction analysis was performed using a Cu-Kα ray as a source. The intensity ratio (I _24.6 / I _15.3 ) of the diffraction peak of is 0.25 or less, preferably 0.10 to 25, more preferably 0.20 to 0.25, and 2θ to the diffraction peak near 2θ = 15.3 ° (plane (010)). The intensity ratio (I _45.0 / I _15.3 ) of the diffraction peak near = 45.0 ° ((120) plane) is represented by the formula (1) taking a value of 0.70 or less, preferably 0.45 to 0.70, more preferably 0.48 to 0.7. It is preferable that it is lithium manganate to become.

The lithium manganate according to the present invention can be suitably used as a lithium secondary battery positive electrode activating material to be used in combination with a lithium secondary battery positive electrode active material described later. The positive electrode activating material for a lithium secondary battery of the present invention includes the lithium manganate, and the lithium secondary battery positive electrode active material of the present invention contains the activating material and a lithium composite oxide represented by the following Formula 2, and when used normally There is no reduction in capacity, and the effect of suppressing deterioration of performance due to overdischarge of a lithium secondary battery is excellent.

<Formula 2>

Li _a M _{1 - b} A _b O _c

In the formula, M represents at least one transition metal element selected from Co, Ni, A represents at least one metal element selected from Mg, Al, Mn, Ti, Zr, Fe, Cu, Zn, Sn, In, a represents 0.9 ≦ a ≦ 1.1, b represents 0 ≦ b ≦ 0.5, and c represents 1.8 ≦ c ≦ 2.2.

As a kind of lithium compound oxide represented by the above formula (2) is not particularly limited, and represents the _{example, LiCoO 2, LiNiO 2, LiNi} 0 .8 Co 0 .2 O 2, LiNi 0 .8 Co 0 .1 Mn 0 _.1 O ₂ , LiNi _0.4 Co _0.3 Mn _0.3 O ₂ , and the like, and these lithium composite oxides may be used alone or in combination of two or more thereof. Among them, LiCoO ₂ is widely used industrially, and is particularly preferable in that the synergistic effect with the lithium secondary battery positive electrode activating material of the present invention is high.

The physical properties of the lithium composite oxide are not particularly limited, but the average particle diameter is preferably 1 to 30 µm, preferably 3 to 20 µm, in that polarization and poor conductivity can be suppressed. Further, the BET specific surface area is preferably 0.1 to 2.0 m 2 / g, preferably 0.2 to 1.0 m 2 / g, in terms of improving battery thermal stability.

The blending ratio of the positive electrode activator of the present invention is 5 to 30 parts by weight, preferably 10 to 20 parts by weight based on 100 parts by weight of the lithium composite oxide. This is because when the blending ratio of the positive electrode activating material is greater than 30 parts by weight, the discharge capacity of the battery becomes smaller, whereas when it is less than 5 parts by weight, the overdischarge suppressing effect is not sufficiently obtained, which is not preferable. The reason why it is preferable that the amount of the activating material of the present invention is smaller than that of the lithium composite oxide is because the case where the terminal potential of charge and discharge is used in combination with that of the lithium composite oxide alone is high. This is because a battery having a high capacity can be produced because it contributes little to discharge and has a small compounding amount.

Such a positive electrode active material is prepared by uniformly mixing a predetermined amount of the activating material and the lithium composite oxide. It does not restrict | limit especially as a mixing means, It is manufactured as a mechanical means by which the strong shear force by a wet method or a dry method acts so that it may become said relatively uniform composition mix. The wet process is operated with devices such as ball mills, disper mills, homogenizers, vibrating mills, sand grind mills, attritors and powerful stirrers. On the other hand, in a dry method, apparatuses, such as a high speed mixer, a super mixer, a turbo spare mixer, a Henschel mixer, a nuter mixer, and a ribbon blender, can be used. In addition, these uniform compounding operations are not limited to the illustrated mechanical means. In addition, it is also possible to grind | pulverize with a jet mill etc. and to adjust particle size as desired.

The lithium secondary battery according to the present invention uses the lithium secondary battery positive electrode active material, and includes a nonaqueous electrolyte containing a positive electrode, a negative electrode, a separator, and a lithium salt. The positive electrode is formed by, for example, coating and drying the positive electrode mixture on the positive electrode current collector, and the positive electrode mixture includes a positive electrode active material, a conductive agent, a binder, a filler added as necessary, and the like. In the lithium secondary battery according to the present invention, a mixture of the lithium composite oxide as the positive electrode active material and lithium manganate as the activating material is uniformly coated on the positive electrode. For this reason, the lithium secondary battery which concerns on this invention does not produce especially the fall of load characteristics and cycling characteristics.

The positive electrode current collector is not particularly limited as long as it is an electron conductor that does not cause chemical change in the battery configured, but for example, carbon, nickel, titanium, on the surface of stainless steel, nickel, aluminum, titanium, calcined carbon, aluminum or stainless steel, And surface-treated silver. The surface of these materials may be oxidized, or may be used by attaching irregularities to the surface of the current collector by surface treatment. Moreover, as a form of an electrical power collector, a foil, a film, a sheet, a net, a punched thing, a lath body, a porous body, a foam, a fiber group, the molded object of a nonwoven fabric, etc. are mentioned, for example. Although the thickness of an electrical power collector is not specifically limited, It is preferable to set it as 1-500 micrometers.

It will not specifically limit, if it is an electron conductive material which does not produce a chemical change in the battery comprised as a conductive agent. For example, graphite such as natural graphite and artificial graphite, carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, conductive fibers such as carbon fiber or metal fiber, fluorinated Conductive materials, such as metal powders, such as carbon, aluminum, and nickel powder, electroconductive whiskers, such as zinc oxide and potassium titanate, electroconductive metal oxides, such as titanium oxide, or a polyphenylene derivative, are mentioned, for example, as natural graphite, For example, scaly graphite, scaly graphite, earthy graphite, etc. are mentioned. These can be used 1 type or in combination or 2 or more types. The blending ratio of the conductive agent is 1 to 50% by weight, preferably 2 to 30% by weight in the positive electrode mixture.

As the binder, for example, starch, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, diacetyl cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, Ethylene-propylene-diene trimer (EPDM), sulfonated EPDM, styrenebutadiene rubber, fluororubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene Perfluoroalkyl vinyl ether copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, fluoride Vinylidene-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymerization , Ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinylether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer Or (Na +) ionic crosslinked product, ethylene-methacrylic acid copolymer or (Na +) ionic crosslinked product thereof, ethylene-methyl acrylate copolymer or (Na +) ion crosslinked product thereof, ethylene-methyl methacrylate copolymer or its Polysaccharides, such as a (Na +) ion crosslinked body and polyethylene oxide, a thermoplastic resin, a polymer which has rubber elasticity, etc. are mentioned, These can be used 1 type or in combination or 2 or more types. In addition, when using the compound containing a functional group, such as reacting with lithium like a polysaccharide, it is preferable to add a compound, such as an isocyanate group, and inactivate the functional group. The blending ratio of the binder is 1 to 50% by weight, preferably 5 to 15% by weight in the positive electrode mixture.

The filler suppresses the volume expansion of the positive electrode in the positive electrode mixture, and is added as necessary. As the filler, any fibrous material which does not cause chemical changes in the battery constructed can be used. For example, fibers such as olefin polymers such as polypropylene and polyethylene, glass and carbon are used. Although the addition amount of a filler is not specifically limited, 0-30 weight% is preferable in positive mix.

The negative electrode is formed by coating and drying a negative electrode material on a negative electrode current collector. The negative electrode current collector is not particularly limited as long as it is an electron conductor that does not cause chemical change in the battery configured. However, the negative electrode current collector is oxidized and dissolved at a positive electrode potential (about 3.5 V vs. Li / Li +) during overdischarge such as copper or a copper alloy. The invention is the most effective. In addition, the surface of the material may be oxidized or used, and unevenness may be attached to the surface of the current collector by surface treatment. Moreover, as a form of an electrical power collector, a foil, a film, a sheet, a net, a punched thing, a lath body, a porous body, a foam, a fiber group, the molded object of a nonwoven fabric, etc. are mentioned, for example. Although the thickness of an electrical power collector is not specifically limited, It is preferable to set it as 1-500 micrometers.

Although it does not restrict | limit especially as a negative electrode material, For example, a carbonaceous material, a metal complex oxide, lithium metal, a lithium alloy, a silicon type alloy, a tin type alloy, a metal oxide, a conductive polymer, a chalcogen compound, Li-Co- Ni type material etc. are mentioned. As a carbonaceous material, a non-graphitizing carbon material, a graphite type carbon material, etc. are mentioned, for example. Metal composite oxides include, for example, ^{_{Sn p M 1 1 - p M}} 2 q O r ( wherein, M ¹ represents at least one element selected from Mn, Fe, Pb, and Ge, M ² is Al, B, P, Si, at least one element selected from the group 1, 2, 3, and halogen elements of the periodic table, and represents 0 <p ≦ 1, 1 ≦ q ≦ 3, and 1 ≦ r ≦ 8. ), Li _x Fe ₂ O ₃ (0 ≦ _x ≦ 1), and Li _x WO ₂ (0 ≦ _x ≦ 1). Examples of the metal oxides include GeO, GeO ₂ , SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , Bi ₂ O ₃ , and the like _{Bi 2 O 4, Bi 2 O} 5. Examples of the conductive polymer include polyacetylene and poly-p-phenylene.

As the separator, an insulating thin film having a large ion permeability and having a predetermined mechanical strength is used. From the organic solvent resistance and hydrophobicity, the sheet | seat and nonwoven fabric which were made from olefinic polymers, such as polypropylene, glass fiber, polyethylene, etc. are used. As a pore size of a separator, it may be the range generally useful for a battery, for example, 0.01-10 micrometers. As thickness of a separator, it may be a general battery range, for example, 5-300 micrometers. In addition, when solid electrolytes, such as a polymer, are used as electrolyte mentioned later, a solid electrolyte may be what has a separator.

The nonaqueous electrolyte containing a lithium salt contains a nonaqueous electrolyte and a lithium salt. As the nonaqueous electrolyte, a nonaqueous electrolyte, an organic solid electrolyte, and an inorganic solid electrolyte are used. As the non-aqueous electrolyte, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyro Lactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, formic acid Methyl, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, propylenecar The solvent which mixed 1 type, or 2 or more types of aprotic organic solvents, such as a carbonate derivative, a tetrahydrofuran derivative, diethyl ether, 1, 3- propane sultone, methyl propionate, and ethyl propionate, is mentioned.

As the organic solid electrolyte, for example, a polyethylene derivative, a polyethylene oxide derivative or a polymer containing the same, a polypropylene oxide derivative or a polymer containing the same, a phosphate ester polymer, a polyphosphazene, a polyaziridine, a polyethylene sulfide, a poly Polymers containing ionic dissociation groups such as vinyl alcohol, polyvinylidene fluoride, polyhexafluoropropylene, polymers containing ionic dissociation groups, and mixtures of the above non-aqueous electrolyte solutions.

As the inorganic solid electrolyte, a nitride of Li, a halide, an oxyacid salt, or the like can be used. For example, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI -LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , phosphorus sulfide compounds, and the like.

As the lithium salt, those dissolved in the non-aqueous electrolyte are used, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiB ₁₀ Cl ₁₀ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic lithium carboxylate, lithium saphenyl borate The salt which mixed 1 type (s) or 2 or more types, such as Drew, is mentioned.

Moreover, the compound shown below can be added to a nonaqueous electrolyte in order to improve discharge, a charging characteristic, and a flame retardance. For example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone and N, N Substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, polyethylene glycol, pyrrole, 2-methoxyethanol, aluminum trichloride, monomer of conductive polymer electrode active material, triethylene phosphonamide, trialkylphosphine, mor Polline, aryl compounds having a carbonyl group, hexamethylphosphoric triamide and 4-alkylmorpholine, bicyclic tertiary amines, oils, phosphonium salts and tertiary sulfonium salts, phosphazenes, carbonate esters and the like. In addition, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be included in the electrolyte to render the electrolyte nonflammable. In addition, in order to make it suitable for high temperature storage, carbon dioxide gas can be included in electrolyte solution.

The lithium secondary battery configured as described above has no deterioration in battery performance, especially in normal use, exhibits a continuous voltage change during charge and discharge, and becomes a lithium secondary battery having excellent overdischarge characteristics. The shape of the battery may be any one of a button, a sheet, a cylinder, a square, a coin shape, and the like. In addition, the lithium secondary battery of the present invention is, for example, a laptop, a laptop personal computer, a pocket word processor, a mobile phone, a wireless handset, a portable CD player, a radio, a liquid crystal television, a backup power supply, an electric shaver. , Electronic devices such as memory cards and video movies, and commercial electronic devices such as automobiles, electric vehicles, and game devices.

<Example>

Next, the present invention will be described in more detail with reference to Examples, which are merely illustrative and do not limit the present invention.

(Manufacture of MnO)

Commercially available MnCO ₃ having an average particle diameter of 8.1 μm was heat-treated at 650 ° C. for 10 hours in a nitrogen atmosphere. The obtained heat-treated material confirmed that it was MnO of average particle diameter 7.6 micrometers as a result of XRD analysis.

<Examples 1 to 8 and Comparative Example 1>

The MnO prepared above was heat-treated in air for 10 hours at the temperature shown in Table 2 to prepare each manganese oxide sample shown in Table 2. Among these heat treated materials, it was confirmed that all of them were Mn ₂ O ₃ by XRD analysis except that the heat treatment temperature was 500 ° C.

Using each of the manganese oxide samples prepared above, this and Li ₂ CO ₃ having an average particle diameter of 5 μm were mixed at a molar ratio (Li / Mn) = 1.00 of Li atoms and Mn atoms, and then the mixture was mixed under a nitrogen atmosphere at 800 ° C. ℃ in firing, each for 10 hours LiMnO ₂ Samples were prepared. In addition, the obtained LiMnO ₂ sample was confirmed to be LiMnO ₂ from the diffraction peak pattern of ASTM card 23-361.

Comparative Example 2

Commercially available MnO ₂ having an average particle diameter of 3.5 µm and Li ₂ CO ₃ having an average particle diameter of 5 µm were mixed so as to have a molar ratio of Li / Mn = 1.00, and the mixture was calcined at 800 ° C. for 10 hours under a nitrogen atmosphere to form LiMnO. ₂ Samples were prepared. In addition, the obtained LiMnO ₂ The sample was confirmed to be the LiMnO ₂ from the diffraction peak pattern of the ASTM card 23-361.

Comparative Example 3

Commercially available MnO ₂ having an average particle diameter of 3.5 μm was calcined in the air at 1000 ° C. for 12 hours to prepare Mn ₃ O ₄ . This Mn ₃ O ₄ was calcined in the air at 650 ° C. for 10 hours to obtain Mn ₂ O ₃ . The Mn ₂ O ₃ and Li ₂ CO ₃ having an average particle diameter of 5 μm were mixed so as to have a molar ratio of Li / Mn = 1.00, and calcined at 800 ° C. for 10 hours in a nitrogen atmosphere to prepare a LiMnO ₂ sample. In addition, the obtained LiMnO ₂ sample was confirmed to be LiMnO ₂ from the diffraction peak pattern of ASTM card 23-361.

<Comparative Example 4>

Commercially available MnO ₂ having an average particle diameter of 3.5 μm was calcined in the air at 650 ° C. for 10 hours to prepare Mn ₂ O ₃ . The Mn ₂ O ₃ and lithium hydroxide having an average particle diameter of 10 µm were mixed so as to have a molar ratio of Li / Mn = 1.00, and then fired in vacuum at 800 ° C. for 12 hours to prepare a LiMnO ₂ sample. In addition, the obtained LiMnO ₂ sample was confirmed to be LiMnO ₂ from the diffraction peak pattern of ASTM card 23-361.

<Property evaluation>

The LiMnO ₂ samples obtained in Examples 1 to 8 and Comparative Examples 1 to 4 were subjected to X-ray diffraction analysis using Cu-Kα rays as average particle diameter, BET specific surface area and source, and diffraction peaks near 2θ = 15.3 °. The intensity ratio (I _24.6 / I _15.3 ) of the diffraction peak near 2θ = 24.6 ° and the intensity ratio (I _45.0 / I _15.3 ) of the diffraction peak near 2θ = 45.0 ° were measured. The results are shown in Table 4. In addition, the X-ray diffraction diagram of LiMnO ₂ obtained in Example 4 is shown in FIG. 1. In Fig. 1, symbol (a) shows a diffraction peak near 15.3 °, symbol (b) shows a diffraction peak near 24.6 °, and symbol (c) shows a diffraction peak near 45.0 °.

<Production of Lithium Secondary Battery>

(1) manufacture of a lithium secondary battery;

To each of the various LiMnO ₂ samples of Examples 1 to 8 and Comparative Examples 1 to 4 prepared above, 85 wt% of the sample, 10 wt% of the graphite powder, and 5 wt% of the polyvinylidene fluoride were mixed to form a positive electrode material. This was dispersed in N-methyl-2-pyrrolidinone to prepare a kneading paste. After apply | coating the said kneading paste to aluminum foil, it dried and pressed, it punched by the disk of diameter 15mm, and obtained the positive electrode plate.

Using this positive electrode plate, a lithium secondary battery was produced using each member such as a separator, a negative electrode, a positive electrode, a current collector plate, mounting hardware, an external terminal, and an electrolyte solution. Among them, lithium metal and copper were used for the current collector, and 1 mol of LiPF ₆ was dissolved in 1 L of a 1: 1 kneading solution of ethylene carbonate and methyl ethyl carbonate.

(2) initial discharge capacity, initial charge capacity, average charge voltage

In the CCCV mode, the cut-off voltage is 4.25 V, 1 C equivalent of the breaking current is 1/20 of the 1 C current value, and the charging is in the CCCV mode, the cut-off voltage 3.4 V, 1 C equivalent is the breaking current 1 Initial discharge capacity, initial charge capacity, and average charge voltage were measured as 1/20 of C current, and the results are shown in Table 5 below.

In this test, the charge capacity is large, and the material having a small discharge capacity, that is, the difference in the charge and discharge capacity, indicates that the Li supply ability as a positive electrode activating material is higher. In general, the positive electrode active material is, for example, a LiCoO ₂ charge capacity. With respect to 160 mAH / g, the capacity difference of the charge / discharge capacity is small about 155 mAH / g. In addition, a low average charging voltage indicates a small resistance when releasing Li, and indicates an excellent Li supply material. And, as is apparent from Table 5, LiMnO ₂ of the present invention has a high initial charge capacity, a large difference in capacity of charge and discharge capacity, and a low average charge voltage, so that it is useful as a positive electrode activator for improving safety during overdischarge. It can be seen that it is excellent in.

<Examples 9 to 16 and Comparative Example 5>

(Production of Lithium Composite Oxide)

Co ₃ O _{4 with an} average particle diameter of 5 μm 40.0 g of Li ₂ CO ₃ with an average particle diameter of 5 μm 8.38 g were weighed, thoroughly mixed dry and then calcined at 1000 ° C. for 5 hours. The calcined product was ground and graded to obtain LiCoO ₂ . Several materials of LiCoO ₂ are shown in Table 6 below.

<Production of Lithium Secondary Battery>

<Battery performance test>

(1) manufacture of a lithium secondary battery;

Using a LiMnO ₂ sample and LiCoO ₂ prepared above, a positive electrode active material having a composition shown in Table 7 was prepared. Next, 91% by weight of the positive electrode active material, 6% by weight of graphite powder, and 3% by weight of polyvinylidene fluoride were mixed to form a positive electrode material, which was dispersed in N-methyl-2-pyrrolidinone to prepare a kneading paste. In addition, to an amount shown in Table 7 is LiCoO ₂ 100 parts by weight blended 10 parts by weight of lithium manganese oxide with respect to a mixing ratio of such a positive electrode active material is represented by the percentage of the positive electrode material. After apply | coating the said kneading paste to aluminum foil, it dried and pressed, it punched by the disk of diameter 15mm, and obtained the positive electrode plate. Using this positive electrode plate, a lithium secondary battery was produced using each member such as a separator, a negative electrode, a positive electrode, a current collector, a cradle, an external terminal, and an electrolyte solution. Among them, artificial graphite and copper were used for the negative electrode, and 1 mol of LiPF ₆ was dissolved in 1 L of a 1: 1 kneading solution of ethylene carbonate and methyl ethyl carbonate.

<Battery performance test>

(1) manufacture of a lithium secondary battery;

91 wt% of the positive electrode active materials of Examples 9 to 16 and Comparative Example 5 prepared as described above, 6 wt% of graphite powder, and 3 wt% of polyvinylidene fluoride were mixed to form a positive electrode material, which was N-methyl-2. Kneading paste was prepared by dispersing in pyrrolidinone. After apply | coating the said kneading paste to aluminum foil, it dried and pressed, it punched by the disk of diameter 15mm, and obtained the positive electrode plate.

Using this positive electrode plate, a lithium secondary battery was produced using each member such as a separator, a negative electrode, a positive electrode, a current collector, a cradle, an external terminal, and an electrolyte solution. Among them, artificial graphite and copper were used for the negative electrode, and 1 mol of LiPF ₆ was dissolved in 1 L of a 1: 1 kneading solution of ethylene carbonate and methyl ethyl carbonate.

(2) over-discharge test

For the battery using the positive electrode active materials of Examples 9 to 16 and Comparative Example 5, at 25 ° C., it was charged to 4.2 V with a current of 1 C and charged for 3 hours at a constant voltage of 4.2 V, followed by a current of 1 C. The discharge capacity (hereinafter, referred to as "initial discharge capacity") at the time of discharge to 2.0 V was measured. Subsequently, it was left to stand for 2 days at the constant voltage of 0V, and overdischarge was performed. After standing, after recharging with a constant current constant voltage for 3 hours from 1 C to 4.2 V, constant current discharge was performed from 1 C to 2.0 V, and the discharge capacity (hereinafter, referred to as "recovery capacity") was measured.

About this recovery capacity, the ratio of recovery capacity with respect to the initial discharge capacity measured by the said discharge test (henceforth "capacitance recovery rate") was calculated | required, and it is shown in following Table 8. In addition, the battery after the test was dismantled, the positive electrode was observed, and it was observed whether copper of the negative electrode current collector was deposited on the positive electrode, and the results are shown in Table 8.

From the results in Table 8, it can be seen that the overdischarge characteristics of the lithium secondary battery can be improved by using the lithium manganate of the present invention as a positive electrode activating material.

The lithium secondary battery using the lithium manganate of the present invention as a positive electrode activator is excellent in battery performance, especially in the case of normal use, without any deterioration in capacity and in suppressing the performance deterioration effect due to overdischarge.

Claims (9)

The intensity ratio of the diffraction peak near 2θ = 24.6 ° to the diffraction peak near 2θ = 15.3 ° when X-ray diffraction analysis using Cu-Kα rays as a source is shown by the following formula (I _24.6 / I _15.3 ) Is 0.25 or less, and the intensity ratio (I _45.0 / I _15.3 ) of the diffraction peak near 2θ = 45.0 ° is 0.70 or less, lithium manganate. <Formula 1> Li _x MnO ₂ In the formula, x represents 0.9 ≦ x ≦ 1.1. The lithium manganate of claim 1, wherein the average particle diameter is 1 to 20 µm. The lithium manganate of Claim 1 or 2 whose BET specific surface area is 0.2-2.0 m <2> / g. MnO is heat-treated at 525 ° C. or higher to obtain Mn ₂ O ₃ , then, the obtained Mn ₂ O ₃ and a lithium compound are mixed, and the mixture is calcined to produce lithium manganate represented by the following formula (1). <Formula 1> Li _x MnO ₂ In the formula, x represents 0.9 ≦ x ≦ 1.1. The method for producing lithium manganate according to claim 4, wherein the calcination is performed at an inert gas atmosphere at a temperature of 600 to 1000 ° C. A lithium secondary battery positive electrode activating material comprising the lithium manganate according to any one of claims 1 to 3. A lithium secondary battery positive electrode active material according to claim 6, and a lithium composite oxide represented by the following general formula (2). <Formula 2> Li _a M _{1 - b} A _b O _c In the formula, M represents at least one transition metal element selected from Co, Ni, A represents at least one metal element selected from Mg, Al, Mn, Ti, Zr, Fe, Cu, Zn, Sn, In, a represents 0.9 ≦ a ≦ 1.1, b represents 0 ≦ b ≦ 0.5, and c represents 1.8 ≦ c ≦ 2.2. The lithium secondary battery positive electrode active material according to claim 7, wherein the lithium composite oxide is LiCoO ₂ . The lithium secondary battery positive electrode active material of Claim 8 was used, The lithium secondary battery characterized by the above-mentioned.

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