JP2009167100A - Lithium manganate, method for manufacturing the same, positive electrode sub-active material for lithium secondary battery, positive electrode active material for lithium secondary battery, and lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide lithium manganate useful as a positive electrode sub-active material for a lithium secondary battery showing no decrease in the capacity in normal use and capable of suppressing deterioration in performance due to over discharge, and to provide a method for manufacturing the same, a positive electrode sub-active material for the lithium secondary battery, a positive electrode active material for the lithium secondary battery, and the lithium secondary battery. <P>SOLUTION: The lithium manganate is expressed by general formula (1): Li<SB>x</SB>MnO<SB>2</SB>, wherein x is 0.9≤x≤1.1, and an X-ray diffraction analysis of the lithium manganate using a Cu-Kα ray as a ray source shows ≥0.25 of an intensity ratio (I<SB>24.6</SB>/I<SB>15.3</SB>) of a diffraction peak around 2θ=24.6°, and ≥0.70 of an intensity ratio (I<SB>45.0</SB>/I<SB>15.3</SB>) of a diffraction peak around 2θ=45.0°, each of which is with respect to a diffraction peak around 2θ=15.3°. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  In recent years, as home appliances have become portable and cordless, lithium ion secondary batteries have been put to practical use as power sources for small electronic devices such as laptop computers, mobile phones, and video cameras. Regarding this lithium ion secondary battery, in 1980, Mizushima et al. Reported that lithium cobalt oxide was useful as a positive electrode active material for lithium ion secondary batteries ("Material Research Bulletin" vol15, P783-789 (1980)). ) Has been actively researched and developed on lithium-based composite oxides, and many proposals have been made so far.

  However, a lithium secondary battery using a lithium-based composite oxide as a positive electrode active material and a carbon material or the like as a negative electrode has a problem that Li ions released by charging are taken into the negative electrode side and do not contribute to subsequent charge / discharge. is there. Therefore, the lithium-based composite oxide is always in a charged state in which Li ions are insufficient, and as a result, the positive electrode potential is high. Therefore, when the lithium ion secondary battery is placed in an overdischarged state, the copper foil used as the negative electrode current collector elutes in the electrolyte, and further, a part of it is deposited on the positive electrode, resulting in deterioration of charge / discharge characteristics. There is a problem that it is easy to do. For this reason, a method of preventing an overdischarge itself by providing an electric circuit for preventing overdischarge on the outside of the battery is used. However, since an electric circuit for preventing overdischarge exists, an apparatus or a battery using the battery Costs such as packs increase. Moreover, if the circuit does not operate properly, deterioration due to overdischarge can no longer be prevented.

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 secondary active material thereto has also been proposed (see, for example, Patent Document 1 and Patent Document 2; (Kaihei 6-349493, JP-A-2003-223898). The LiMnO ₂ of Patent Document 1 and Patent Document 2 is manufactured by firing MnO ₂ and lithium carbonate in an inert gas atmosphere, but LiMnO ₂ obtained by the manufacturing method of Patent Document 1 and Patent Document ₂ is used. Lithium secondary battery used as a positive electrode active material improves the overdischarge characteristics to some extent, but tends to cause problems such as a decrease in battery capacity, and can provide excellent battery performance. Development of was desired.

Patent Document 3 below discloses a lithium secondary battery using LiMnO ₂ produced by baking a mixture of Mn ₂ O ₃ and a lithium compound obtained by heat-treating MnO ₂ as a positive electrode active material, or the following patent: Reference 4 proposes a lithium secondary battery using LiMnO ₂ obtained by firing a mixture of LiOH and Mn ₂ O ₃ in vacuum at 600 to 800 ° C. as a positive electrode active material. Even when LiMnO ₂ of No. 3 or Patent Document 4 is used as a positive electrode secondary active material, there remain problems such as a decrease in battery capacity and insufficient overdischarge safety. In addition, LiMnO ₂ disclosed in Patent Document 4 is an X-ray diffraction diagram in which the intensity ratio of the diffraction peak at 2θ = 24.6 ° to the diffraction peak at 2θ = 15.3 ° (I _24.6 / I _{15. 3} ) is 0.11 to 0.25, but the intensity ratio of the diffraction peak at 2θ = 45.0 ° to the diffraction peak at 2θ = 15.3 ° (I _45.0 / I _15.3 ) is It is 0.73 or more when calculated.

  Here, the lithium secondary battery positive electrode secondary active material needs different characteristics from the positive electrode active material in various points. The positive electrode active material requires a high discharge voltage in order to achieve high output characteristics, and it can be said that the higher the discharge voltage, the better the positive electrode active material. On the other hand, since the positive electrode secondary active material is a material intended to supply Li ions, the lower the discharge voltage, the better. This is because when the discharge voltage is high, it contributes to charge and discharge without changing from the positive electrode active material, and Li is not supplied. In this respect, the performance required for the positive electrode active material and the positive electrode sub-active material is opposite.

  Moreover, it can be said that a positive electrode active material is so excellent that a discharge capacity is high. This is because the higher the discharge capacity, the longer it can be used. On the other hand, the positive electrode active material supplies Li ions, so the lower the discharge capacity, the better. A high discharge capacity means that Li ions are inserted, and Li ions are not supplied. In this respect as well, the performance required for the positive electrode active material and the positive electrode sub-active material is opposite.

  Furthermore, it can be said that the positive electrode active material is more excellent as the capacity deterioration and the discharge voltage drop associated with the charge / discharge cycle are smaller. This is because the higher the output characteristics and capacity characteristics are maintained, the longer it can be used even after repeated use. On the other hand, since the positive electrode secondary active material hardly captures Li ions even after discharging after releasing Li ions by charging, it is less necessary to consider capacity deterioration and a decrease in discharge voltage due to charge / discharge cycles. Conversely, when the discharge capacity increases or the discharge voltage increases with the charge / discharge cycle, it is necessary to suppress them. Also in this respect, the performance required for the positive electrode active material and the positive electrode sub-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 secondary active material are greatly different, even if LiMnO ₂ as a positive electrode active material known in the art is used as the positive electrode secondary active material, the battery capacity It is thought that the decrease in the temperature and sufficient overdischarge safety were not obtained. Therefore, development of LiMnO ₂ having characteristics suitable as a positive electrode secondary active material has been demanded.

JP-A-6-349493 JP 2003-223898 A JP 2002-151079 A JP-A-8-37027

  Accordingly, an object of the present invention is to provide lithium manganate useful as a secondary active material for a positive electrode of a lithium secondary battery capable of suppressing deterioration in performance due to overdischarge without a decrease in capacity during normal use, a method for producing the same, and An object of the present invention is to provide a lithium secondary battery sub-positive electrode active material, a lithium secondary battery positive electrode active material used, and a lithium secondary battery excellent in performance deterioration suppression effect due to overdischarge without a decrease in capacity in normal use.

As a result of intensive studies to solve these problems, the present inventors have (1) a diffraction peak near 2θ = 24.6 ° with respect to a diffraction peak near 2θ = 15.3 ° when X-ray diffraction analysis is performed. Intensity ratio (I _24.6 / I _15.3 ) of 0.25 or less, and the intensity ratio of diffraction peaks in the vicinity of 2θ = 45.0 ° (I _45.0 / I _15.3 ) of 0.70 or less. The lithium secondary battery using lithium manganate as a positive electrode secondary active material has no reduction in capacity during normal use, and is excellent in performance deterioration suppression effect due to overdischarge. (2) The lithium manganate is The present invention has been completed by finding out that it is obtained by firing a mixture of Mn ₂ O ₃ and a lithium compound obtained by heating MnO at a specific temperature or higher.

That is, the first invention to be provided by the present invention is the general formula (1); Li _x MnO ₂ (1)
(Wherein x represents 0.9 ≦ x ≦ 1.1), and when X-ray diffraction analysis is performed using Cu—Kα rays as a radiation source, 2θ = 15. The diffraction peak intensity ratio (I _24.6 / I _15.3 ) near 2θ = 24.6 ° with respect to the diffraction peak near 3 ° is 0.25 or less and the diffraction peak near 2θ = 45.0 ° The lithium manganate is characterized in that the intensity ratio (I _45.0 / I _15.3 ) is 0.70 or less.

In addition, according to a second invention to be provided by the present invention, MnO is heat-treated at 525 ° C. or higher to obtain Mn ₂ O ₃ , and then the obtained Mn ₂ O ₃ and a lithium compound are mixed, The mixture is fired to obtain the following general formula (1); Li _x MnO ₂ (1)
(Wherein x represents 0.9 ≦ x ≦ 1.1).

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

In addition, the fourth invention to be provided by the present invention includes a lithium secondary battery positive electrode secondary active material of the third invention, the following general formula (2); Li _a M _1-b A _b O _c (2 )
(Wherein M is at least one transition metal element selected from Co and Ni, A is at least one transition metal element selected from Mg, Al, Mn, Ti, Zr, Fe, Cu, Zn, Sn, In) A metal element, a is 0.9 ≦ a ≦ 1.1, b is 0 ≦ b ≦ 0.5, and c is 1.8 ≦ c ≦ 2.2.) It is a lithium secondary battery positive electrode active material characterized by containing.

  A fifth invention to be provided by the present invention is a lithium secondary battery using the positive electrode active material of the fourth invention.

  The lithium secondary battery using the lithium manganate of the present invention as the positive electrode active material is excellent in battery performance, particularly in the effect of suppressing deterioration in performance due to overdischarge without a decrease in capacity during normal use.

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

Hereinafter, the present invention will be described based on preferred embodiments thereof.
The lithium manganate of the present invention has the following general formula (1); Li _x MnO ₂ (1)
(Where x represents 0.9 ≦ x ≦ 1.1) and is distinguished from conventional lithium manganate by its X-ray diffraction characteristics. That is, the lithium manganate of the present invention has 2θ = 14.6 ° with respect to the diffraction peak near 2θ = 15.3 ° ((010) plane) when X-ray diffraction analysis is performed using Cu—Kα ray as a radiation source. ((011) plane) diffraction peak intensity ratio (I _24.6 / I _15.3 ) is 0.25 or less, preferably 0.10 to 0.25, more preferably 0.20 to 0.25. And the intensity ratio of the diffraction peak around 2θ = 45.0 ° ((120) plane) to the diffraction peak around 2θ = 15.3 ° ((010) plane) (I _45.0 / I _15.3 ) Is 0.70 or less, preferably 0.45 to 0.70, and more preferably 0.48 to 0.70. Incidentally, the diffraction surface means the diffraction plane obtained from the diffraction peak position of the lithium manganate (LiMnO ₂₎ of ASTM card 23-361. In addition, 2θ, d value, and plane index of lithium manganate (LiMnO ₂ ) shown in the ASTM card (23-361) are as shown in Table 1.

  In the present invention, the significance of expressing the two peak intensity ratios of the three peaks in the X-ray diffraction analysis will be described below. In X-ray diffraction analysis, each peak intensity and peak position change depending on the crystal space group, extinction rule, and measurement conditions. Therefore, under constant measurement conditions, structural changes are observed as changes in peak intensity and peak position. . Since each peak only has information on a specific surface, only information on a specific surface can be 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 about each of h, k, and l. Furthermore, in order to consider the mutual relationship between h, k and l, it is necessary to consider the relationship between the peaks having the 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. Corresponds to 3 strong lines. Therefore, using the peak corresponding to the three strong lines can reduce the error due to the measurement, and the peak has information on a plane parallel to the specific axis. The relationship can be determined, and therefore the structure can be determined accurately. In addition, the stability of the structure and the conductivity of electrons, which determine the quality of the secondary secondary battery as a secondary active material, are brought about by the three-dimensional connection of elements, and there is a difference for each surface. If there is a defect such as an element deviating beyond a certain permissible width, it may cause performance degradation such as structural instability and a decrease in electronic conductivity. Therefore, by obtaining the two peak intensity ratios of the three strong lines on the ASTM card, the permissible width and the structural state with respect to the respective axes of h, k, and l can be accurately grasped. On the other hand, for example, in the peak ratio of 24.6 ° and the intensity ratio of 15.3 ° disclosed in the conventional Japanese Patent Laid-Open No. 8-37027, information in the h-axis direction is missing, It is unclear whether a material with a dimensional structure 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, h The structure horizontal to the axis itself is not preferable in that the initial capacity is reduced as a secondary active material of the lithium secondary battery, and the capacity difference between the charge and discharge capacities is reduced. The diffraction peak intensity ratio (I _45.0 / I _15.3 ) has structural information in the h-axis direction and the k-axis direction, and when the intensity ratio exceeds 0.70, The horizontal surface structure itself is not preferable as a secondary active material of the lithium secondary battery in that the initial capacity is reduced and the capacity difference between the charge and discharge capacities is reduced.

  Since the lithium manganate according to the present invention has the above-described configuration, in a lithium secondary battery using the lithium manganate as a positive electrode secondary active material, there is no decrease in capacity, and an excellent battery that suppresses performance deterioration due to overdischarge. Performance can be imparted. Furthermore, in addition to the above characteristics, the lithium manganate of the present invention can apply a uniform electrode sheet when the average particle size is 1.0 to 20.0 μm, preferably 4 to 15 μm, and the concentration of current, etc. It is preferable at the point which can suppress the deterioration of the battery performance by, etc. The average particle diameter is determined by a laser particle size distribution measurement method. Hereinafter, the average particle diameter refers to a value obtained by this measurement method.

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 performance deterioration of the lithium secondary battery due to elution of Mn is suppressed, or the high rate is increased. This is particularly preferable in that Li can be supplied.

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

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

In the present invention, it is essential that the heat treatment of MnO be performed 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 becomes insufficient, and lithium secondary batteries using the lithium manganate thus obtained as a cathode secondary active material are usually used. This is because the capacity is reduced. The upper limit of the heat treatment temperature is not particularly limited as long as it is a temperature that can sufficiently convert MnO to Mn ₂ O ₃ , but in many cases it is 950 ° C., and when the heat treatment temperature exceeds 750 ° C. When the generated lithium manganate is used as a positive electrode secondary active material, the voltage at which Li is desorbed (charge voltage) tends to increase, and therefore the heat treatment temperature is particularly preferably 550 to 750 ° C. The time for the heat treatment is usually 1 to 20 hours, preferably 2 to 10 hours.

In the heat treatment atmosphere, if 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 sufficient to convert MnO into Mn ₂ O ₃ . It is preferable to carry out in an atmosphere containing fresh oxygen. Usually, it is preferably performed in the air or in an oxygen atmosphere. In the present invention, the heat treatment can be repeated as necessary.

In the present invention, Mn ₂ O ₃ prepared above and a lithium compound are uniformly mixed, and the resulting uniform mixture is fired to obtain the target lithium manganate represented by the general formula (1).

  Examples of the raw material lithium compound include lithium carbonate and lithium hydroxide. These lithium compounds can be used alone or in combination of two or more. The physical properties and the like of the lithium compound to be used are not limited, but it is preferable that the average particle diameter is 20 μm or less, preferably 3 to 10 μm, since the raw materials can be mixed uniformly.

The mixing ratio of the Mn ₂ O ₃ and the lithium compound is 0.95 to 1.05, particularly 0.98 to 0.3, in terms of the molar ratio (Li / Mn) of the Li atom in the lithium compound to the Mn atom of Mn ₂ O _3. 1.01 is particularly preferable because lithium manganate having a large Li supply capability can be synthesized.

  The mixing may be either a dry method or a wet method, but a dry method is preferred because the production is easy. In the case of dry mixing, it is preferable to use a blender or the like that uniformly mixes the raw materials.

As for the firing conditions, the firing temperature is 600 to 1000 ° C, preferably 700 to 850 ° C. This is because if the calcination temperature is less than 600 ° C., the reaction is insufficient and a suitable lithium manganate cannot be obtained, while if it exceeds 1000 ° C., it changes to lithium manganate with a low Li supply capacity. is there. The firing 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. At this time, as an inert gas to be used, nitrogen gas, helium gas, argon gas, or the like can be used. The firing time is usually 1 to 20 hours, preferably 2 to 10 hours. In the present invention, the firing may be repeated as necessary.

After firing, the mixture is appropriately cooled and pulverized as necessary to obtain lithium manganate represented by the general formula (1). The pulverization performed as necessary is appropriately performed when the lithium manganate obtained by baking is in a brittle and bonded block shape, and the lithium manganate particles themselves have a specific average particle diameter, BET It has a specific surface area. That is, the obtained 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 0.8. 4 to 1.0 m ² / g. Further, the lithium manganate is near 2θ = 24.6 ° with respect to the diffraction peak around 2θ = 15.3 ° ((010) plane) when X-ray diffraction analysis is performed using Cu—Kα ray as a radiation source ( (011) plane) diffraction peak intensity ratio (I _24.6 / I _15.3 ) is 0.25 or less, preferably 0.10 to 0.25, more preferably 0.20 to 0.25. And the intensity ratio (I _45.0 / I _15.3 ) of the diffraction peak near 2θ = 45.0 ° ((120) plane) to the diffraction peak near 2θ = 15.3 ° ((010) plane). Lithium manganate represented by the general formula (1) having a value of 0.70 or less, preferably 0.45 to 0.70, and more preferably 0.48 to 0.7 is preferable.

The lithium manganate concerning this invention can be used suitably as a lithium secondary battery positive electrode side active material used together with the lithium secondary battery positive electrode active material mentioned later. The positive electrode active material for a lithium secondary battery of the present invention comprises the lithium manganate, and the lithium secondary battery positive electrode active material of the present invention includes the auxiliary active material and the following general formula (2); Li _a M _1-b A _b O _c (2)
(Wherein M is at least one transition metal element selected from Co and Ni, A is at least one transition metal element selected from Mg, Al, Mn, Ti, Zr, Fe, Cu, Zn, Sn, In) A metal element, a is 0.9 ≦ a ≦ 1.1, b is 0 ≦ b ≦ 0.5, and c is 1.8 ≦ c ≦ 2.2.) In the normal use, the capacity is not reduced, and the lithium secondary battery is excellent in the effect of suppressing the performance deterioration due to overdischarge.

The type of the lithium composite oxide represented by the general formula (2) is not particularly limited, One example _{thereof, 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, these lithium composite oxides can be used singly or in combination. Among them, LiCoO ₂ is particularly preferred because it is widely used industrially and has a high synergistic effect with the lithium secondary battery positive electrode side active material of the present invention.

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

  The mixing ratio of the positive electrode secondary active material of the present invention is 5 to 30 parts by weight, preferably 10 to 20 parts by weight with respect to 100 parts by weight of the lithium composite oxide. The reason for this is that if the proportion of the positive electrode sub-active material is greater than 30 parts by weight, the discharge capacity of the battery will be small, while if it is less than 5 parts by weight, the effect of suppressing overdischarge will not be sufficiently obtained. The reason why the amount of the secondary active material of the present invention is preferably smaller than that of the lithium composite oxide is preferable because the terminal potential of charge / discharge is higher in the combined use than in the case of the lithium composite oxide alone. This is because, in the range, the secondary active material hardly contributes to charging / discharging, and a battery with a smaller capacity can produce a battery with a higher capacity.

  Such a positive electrode active material is produced by uniformly mixing a predetermined amount of the secondary active material and the lithium composite oxide. The mixing means is not particularly limited, and the mixing means is prepared by a mechanical means in which a strong shearing force is applied by a wet method or a dry method so as to obtain a uniform composition in the above ratio. The wet method is operated by an apparatus such as a ball mill, a disper mill, a homogenizer, a vibration mill, a sand grind mill, an attritor, and a powerful stirrer. On the other hand, in the dry method, apparatuses such as a high speed mixer, a super mixer, a turbo sphere mixer, a Henschel mixer, a nauter mixer, and a ribbon blender can be used. These uniform blending operations are not limited to the illustrated mechanical means. If desired, the particle size may be adjusted by grinding with a jet mill or the like.

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

  The positive electrode current collector is not particularly limited as long as it is an electronic conductor that does not cause a chemical change in the constituted battery. For example, stainless steel, nickel, aluminum, titanium, calcined carbon, aluminum, and stainless steel Examples of the surface include carbon, nickel, titanium, and silver surface-treated. The surface of these materials may be oxidized and used, or the current collector surface may be provided with irregularities by surface treatment. Examples of the current collector include foils, films, sheets, nets, punched ones, lath bodies, porous bodies, foam bodies, fiber groups, nonwoven fabric molded bodies, and the like. The thickness of the current collector is not particularly limited, but is preferably 1 to 500 μm.

  The conductive agent is not particularly limited as long as it is an electron conductive material that does not cause a chemical change in the constructed battery. For example, graphite such as natural graphite and artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, carbon black such as thermal black, conductive fibers such as carbon fiber and metal fiber, Examples include metal powders such as carbon fluoride, aluminum and nickel powder, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and conductive materials such as polyphenylene derivatives. Examples of graphite include scaly graphite, scaly graphite, and earthy graphite. These can be used alone or in combination of two or more. The blending ratio of the conductive agent is 1 to 50% by weight, preferably 2 to 30% by weight in the positive electrode mixture.

  Examples of the binder include starch, polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, regenerated cellulose, diacetylcellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer ( EPDM), sulfonated EPDM, styrene butadiene rubber, fluoro rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, fluorinated Vinylidene-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene Oroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetra Fluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer or its (Na +) ionic crosslinked product, ethylene-methacrylic acid copolymer or its (Na + ) Ionic crosslinked body, ethylene-methyl acrylate copolymer or its (Na +) ionic crosslinked body, ethylene-methyl methacrylate copolymer or its (Na +) ionic crosslinked body, polysaccharide such as polyethylene oxide, thermoplastic resin Polymers having rubber elasticity, and these may be used individually or in combination. In addition, when using the compound containing a functional group which reacts with lithium like a polysaccharide, it is preferable to add the compound like an isocyanate group and to deactivate the functional group, for example. 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 can be used as long as it does not cause a chemical change in the constructed battery. For example, olefinic polymers such as polypropylene and polyethylene, and fibers such as glass and carbon are used. Although the addition amount of a filler is not specifically limited, 0-30 weight% is preferable in a positive electrode mixture.

  The negative electrode is formed by applying and drying a negative electrode material on the negative electrode current collector. The negative electrode current collector is not particularly limited as long as it is an electronic conductor that does not cause a chemical change in the constituted battery, but the positive electrode potential (about 3.5 V vs. Li / The present invention is most effective for those which are oxidized and dissolved by Li +). Further, the surface of the material may be oxidized and used, or the surface of the current collector may be provided with irregularities by surface treatment. Examples of the current collector include foils, films, sheets, nets, punched ones, lath bodies, porous bodies, foam bodies, fiber groups, nonwoven fabric molded bodies, and the like. The thickness of the current collector is not particularly limited, but is preferably 1 to 500 μm.

The negative electrode material is not particularly limited, and examples thereof include carbonaceous materials, metal composite oxides, lithium metals, lithium alloys, silicon-based alloys, tin-based alloys, metal oxides, conductive polymers, and chalcogen compounds. And Li—Co—Ni-based materials. Examples of the carbonaceous material include non-graphitizable carbon materials and graphite-based carbon materials. Examples of the metal composite oxide include Sn _p M ¹ _1-p M ² _{q Or} (wherein M ¹ represents one or more elements selected from Mn, Fe, Pb and Ge, and M ² represents Al. , B, P, Si, one or more elements selected from Group 1, Group 2, Group 3 of the periodic table and halogen elements, 0 <p ≦ 1, 1 ≦ q ≦ 3, 1 ≦ r ≦ 8.), LixFe ₂ O ₃ (0 ≦ x ≦ 1), LixWO ₂ (0 ≦ x ≦ 1) and the like. As the metal _{oxide, 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 Bi ₂ O ₄ , Bi ₂ O _{5 and the} like. Examples of the conductive polymer include polyacetylene and poly-p-phenylene.

  As the separator, an insulating thin film having a large ion permeability and a predetermined mechanical strength is used. Sheets and non-woven fabrics made of olefin polymers such as polypropylene, glass fibers or polyethylene are used because of their organic solvent resistance and hydrophobicity. The pore diameter of the separator may be in a range generally useful for batteries, for example, 0.01 to 10 μm. The thickness of the separator may be in a range for a general battery, for example, 5 to 300 μm. In addition, when a solid electrolyte such as a polymer is used as the electrolyte described later, the solid electrolyte may also serve as a separator.

The non-aqueous electrolyte containing a lithium salt is composed of a non-aqueous electrolyte and a lithium salt. As the non-aqueous electrolyte, a non-aqueous electrolyte, an organic solid electrolyte, or an inorganic solid electrolyte is used. Examples of the non-aqueous electrolyte include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, and 2-methyl. Tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 3-methyl -2-oxazolidinone, 1,3-dimethyl-2
-Solvents obtained by mixing one or more aprotic organic solvents such as imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, diethyl ether, 1,3-propane sultone, methyl propionate, ethyl propionate, etc. It is done.

  Examples of the organic solid electrolyte include 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, polyphosphazene, polyaziridine, polyethylene sulfide, polyvinyl alcohol, polyvinylidene fluoride, Examples thereof include a polymer containing an ionic dissociation group such as polyhexafluoropropylene, and a mixture of a polymer containing an ionic dissociation group and the above non-aqueous electrolyte.

As the inorganic solid electrolyte, a nitride, halide, oxyacid salt, or the like of Li 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, and the like phosphorus sulfide compound.

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, lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenylborate, Examples thereof include a salt obtained by mixing one or more of imides.

  Moreover, the compound shown below can be added to a nonaqueous electrolyte for the purpose of improving discharge, a charge characteristic, and a flame retardance. For example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid 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, conductive polymer electrode active material monomer, triethylenephosphonamide, trialkylphosphine, morpholine, aryl compounds with carbonyl group, hexamethylphosphine Examples include hollic triamide and 4-alkylmorpholine, bicyclic tertiary amines, oils, phosphonium salts and tertiary sulfonium salts, phosphazenes, and carbonates. That. In order to make the electrolyte nonflammable, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride can be included in the electrolyte. In addition, carbon dioxide gas can be included in the electrolytic solution in order to make it suitable for high-temperature storage.

  The lithium secondary battery configured in this manner is a lithium secondary battery having excellent overdischarge characteristics, showing battery performance, particularly no decrease in capacity during normal use, showing a continuous voltage change during charging and discharging. . The shape of the battery may be any shape such as a button, a sheet, a cylinder, a corner, or a coin shape. In addition, the lithium secondary battery of the present invention includes, for example, a notebook computer, a laptop computer, a pocket word processor, a mobile phone, a cordless cordless handset, a portable CD player, a radio, an LCD TV, a backup power supply, an electric shaver, a memory card, a video movie. It can be suitably used for consumer electronic devices such as electronic devices such as automobiles, electric vehicles, and game devices.

  EXAMPLES Next, the present invention will be described more specifically with reference to examples. However, this is merely an example and does not limit the present invention.

(Preparation of MnO)
Commercially available MnCO ₃ having an average particle size of 8.1 μm was heat-treated at 650 ° C. for 10 hours in a nitrogen atmosphere. As a result of XRD analysis, the obtained heat-treated product was confirmed to be MnO having an average particle size of 7.6 μm.

Examples 1-8 and Comparative Example 1
The MnO prepared above was heat-treated at a temperature shown in Table 2 for 10 hours in the air to prepare each manganese oxide sample shown in Table 2. Among these heat-treated products, those having a heat treatment temperature of 500 ° C. were all confirmed to be Mn ₂ O ₃ by XRD analysis.

Using each of the manganese oxide samples prepared above, this was mixed with Li ₂ CO ₃ having an average particle diameter of 5 μm at a molar ratio of Li atom to Mn atom (Li / Mn) = 1.00, Each mixture was calcined at 800 ° C. for 10 hours in a nitrogen atmosphere to prepare each LiMnO ₂ sample. 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 that the molar ratio of Li / Mn was 1.00, and the mixture was mixed at 800 ° C. under a nitrogen atmosphere. A LiMnO ₂ sample was prepared by firing for 10 hours. The obtained LiMnO ₂ sample was confirmed to be LiMnO ₂ from the diffraction peak pattern of ASTM card 23-361.

Comparative Example 3
Commercially available MnO ₂ having an average particle size of 3.5 μm was fired at 1000 ° C. for 12 hours in the air to prepare Mn ₃ O ₄ . This Mn ₃ O ₄ was fired at 650 ° C. for 10 hours in the air to obtain Mn ₂ O ₃ . This Mn ₂ O ₃ and Li ₂ CO ₃ having an average particle diameter of 5 μm are mixed so that the molar ratio of Li / Mn is 1.00, and calcined at 800 ° C. for 10 hours in a nitrogen atmosphere to prepare a LiMnO ₂ sample. did. 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 size of 3.5 μm was fired in the atmosphere at 650 ° C. for 10 hours to prepare Mn ₂ O ₃ . This Mn ₂ O ₃ and lithium hydroxide having an average particle diameter of 10 μm are mixed so that the molar ratio of Li / Mn is 1.00, and calcined in vacuum at 800 ° C. for 12 hours to prepare a LiMnO ₂ sample. did. The obtained LiMnO ₂ sample was confirmed to be LiMnO ₂ from the diffraction peak pattern of ASTM card 23-361.

<Physical 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 the average particle diameter, BET specific surface area, and radiation source, and 2θ = 15.3. The intensity ratio of the diffraction peak near 2θ = 24.6 ° (I _24.6 / I _15.3 ) and the intensity ratio of the diffraction peak near 2θ = 45.0 ° (I _45.0 / I _15.3 ) was measured. The results are shown in Table 4. An X-ray diffraction diagram of LiMnO ₂ obtained in Example 4 is shown in FIG. In FIG. 1, the symbol a indicates a diffraction peak near 15.3 °, the symbol b indicates a diffraction peak near 24.6 °, and the symbol c indicates a diffraction peak near 45.0 °.

<Preparation of lithium secondary battery>
(1) Production of lithium secondary battery;
For each of the various LiMnO ₂ samples prepared in Examples 1 to 8 and Comparative Examples 1 to 4 described above, 85% by weight of the sample, 10% by weight of graphite powder, and 5% by weight of polyvinylidene fluoride were mixed to form a positive electrode material. This was dispersed in N-methyl-2-pyrrolidinone to prepare a kneaded paste. The kneaded paste was applied to an aluminum foil, dried, pressed and punched into a disk with a diameter of 15 mm to obtain a positive electrode plate.

Using this positive electrode plate, a lithium secondary battery was manufactured using each member such as a separator, a negative electrode, a positive electrode, a current collector plate, a mounting bracket, an external terminal, and an electrolytic solution. Of these, lithium metal was used for the negative electrode, copper was used for the current collector, and 1 mol of LiPF ₆ was dissolved in 1 liter of a 1: 1 kneaded solution of ethylene carbonate and methyl ethyl carbonate as the electrolyte.

(2) Initial discharge capacity, initial charge capacity, average charge voltage Charging is in CCCV mode, cutoff voltage is 4.25V, current value equivalent to 1C, cutoff current is 1/20 of 1C current value, charging is in CCCV mode, cut The initial discharge capacity, the initial charge capacity, and the average charge voltage were measured with an off voltage of 3.4 V and a current value equivalent to 1 C and a cut-off current of 1/20 of the 1 C current. The results are shown in Table 5.

In this test, a material having a large charge capacity and a small discharge capacity, that is, a material having a large difference in charge / discharge capacity indicates that the Li supply capacity as a positive electrode secondary active material is high. For example, LiCoO ₂ has a charge capacity of about 155 mAH / g with respect to a charge capacity of 160 mAH / g, and the capacity difference between the charge and discharge capacity is small. Moreover, the one where an average charging voltage is low shows that resistance is small at the time of discharge | release of Li, and shows that it is excellent as Li supply material. As is apparent from Table 5, the LiMnO ₂ of the present invention has a high initial charge capacity, a large charge / discharge capacity difference, and a low average charge voltage. It turns out that it is excellent in the usefulness as a positive electrode secondary active material for improving.

Examples 9 to 16 and Comparative Example 5
(Preparation of lithium composite oxide)
40.0 g of Co ₃ O ₄ having an average particle diameter of 5 μm and 8.38 g of Li ₂ CO ₃ having an average particle diameter of 5 μm were weighed, thoroughly mixed by a dry process, and then fired at 1000 ° C. for 5 hours. The fired product was pulverized and classified to obtain LiCoO ₂ . Various physical properties of this product are shown in Table 6.

<Preparation of lithium secondary battery>
<Battery performance test>
(1) Production of lithium secondary battery;
Using the LiMnO ₂ sample and the LiCoO ₂ prepared above, a positive electrode active material having the 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 prepare a positive electrode material, which was dispersed in N-methyl-2-pyrrolidinone to prepare a kneaded paste. The amount of the table 7 with respect to LiCoO 2 ₁₀₀ parts by weight, the formulation of the lithium manganate, 10 parts by weight, the mixing ratio of such positive electrode active material, in a positive electrode material, it is the inner seat. The kneaded paste was applied to an aluminum foil, dried, pressed and punched into a disk with a diameter of 15 mm to obtain a positive electrode plate. Using this positive electrode plate, a lithium secondary battery was manufactured using each member such as a separator, a negative electrode, a positive electrode, a current collector plate, a mounting bracket, an external terminal, and an electrolytic solution. Of these, artificial graphite was used for the negative electrode, copper was used for the current collector, and 1 mol of LiPF ₆ was dissolved in 1 liter of a 1: 1 kneaded solution of ethylene carbonate and methyl ethyl carbonate as the electrolyte.

<Battery performance test>
(1) Production of lithium secondary battery;
A positive electrode agent was prepared by mixing 91% by weight of the positive electrode active materials of Examples 9 to 16 and Comparative Example 5 prepared as described above, 6% by weight of graphite powder, and 3% by weight of polyvinylidene fluoride. A kneaded paste was prepared by dispersing in pyrrolidinone. The kneaded paste was applied to an aluminum foil, dried, pressed and punched into a disk with a diameter of 15 mm to obtain a positive electrode plate.

Using this positive electrode plate, a lithium secondary battery was manufactured using each member such as a separator, a negative electrode, a positive electrode, a current collector plate, a mounting bracket, an external terminal, and an electrolytic solution. Of these, artificial graphite was used for the negative electrode, copper was used for the current collector, and 1 mol of LiPF ₆ was dissolved in 1 liter of a 1: 1 kneaded solution of ethylene carbonate and methyl ethyl carbonate as the electrolyte.

(2) Overdischarge test About the battery using the positive electrode active material of Examples 9-16 and the comparative example 5, it charges to 4.2V with the electric current of 1C at 25 degreeC, and is charged for 3 hours with the constant voltage of 4.2V. After that, the discharge capacity when discharged to 2.0 V with a current of 1 C (hereinafter referred to as “initial discharge capacity”) was measured. Subsequently, it was left to stand at a constant voltage of 0 V for 2 days to perform overdischarge. After standing, the battery was recharged at a constant current and a constant voltage of 4.2 V at 1 C for 3 hours, and then a constant current discharge was performed at 1 C to 2.0 V, and the discharge capacity (hereinafter referred to as “recovery capacity”) was measured.
The ratio of the recovery capacity to the initial discharge capacity measured in the previous discharge test (hereinafter referred to as “capacity recovery rate”) was determined for this recovery capacity, and is shown in Table 8. Further, the battery after the test was disassembled and the positive electrode was observed to observe whether copper of the negative electrode current collector was deposited on the positive electrode. The results are shown in Table 8.

  From the results of 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 the positive electrode auxiliary active material.

Claims (9)

General formula (1); Li _x MnO ₂ (1)
(Wherein x represents 0.9 ≦ x ≦ 1.1),
When the X-ray diffraction analysis is performed using Cu-Kα ray as a radiation source, the intensity ratio of the diffraction peak near 2θ = 24.6 ° to the diffraction peak near 2θ = 15.3 ° (I _24.6 / I _{15. 3} ) is 0.25 or less, and the intensity ratio of diffraction peaks in the vicinity of 2θ = 45.0 ° (I _45.0 / I _15.3 ) is 0.70 or less. .   The lithium manganate according to claim 1, having an average particle diameter of 1 to 20 μm. The lithium manganate according to claim 1, wherein the BET specific surface area is 0.2 to 2.0 m ² / g. MnO was heat-treated at 525 ° C. or higher to obtain Mn ₂ O ₃ , then, the obtained Mn ₂ O ₃ and a lithium compound were mixed, the mixture was baked, and the following general formula (1);
Li _x MnO ₂ (1)
(Wherein x represents 0.9 ≦ x ≦ 1.1).   The method for producing lithium manganate according to claim 4, wherein the baking is performed at a temperature of 600 to 1000 ° C. in an inert gas atmosphere.   A lithium secondary battery positive electrode side active material comprising the lithium manganate according to any one of claims 1 to 3. And a lithium secondary battery positive electrode subsidiary active material of claim 6, wherein the following general formula _{(2); Li a M 1} -b A b O c (2)
(Wherein M is at least one transition metal element selected from Co and Ni, A is at least one transition metal element selected from Mg, Al, Mn, Ti, Zr, Fe, Cu, Zn, Sn, In) A metal element, a is 0.9 ≦ a ≦ 1.1, b is 0 ≦ b ≦ 0.5, and c is 1.8 ≦ c ≦ 2.2.) A positive electrode active material for a lithium secondary battery, comprising: The lithium secondary battery positive electrode active material according to claim 7, wherein the lithium composite oxide is LiCoO ₂ .   A lithium secondary battery comprising the lithium secondary battery positive electrode active material according to claim 8.