WO2009139397A1 - Plate-like crystal grain and production method thereof, and secondary lithium battery - Google Patents

Abstract

Provided is a plate-like crystal grain which includes lithium manganate having Li and Mn as constituent elements in a spinel structure, has an aspect ratio of 1.5 to 20 and a thickness of 1 to 20mm, and includes, as a glowing face, a crystal face (111) having an amount of preferred orientation of 20% or more when measured by the Lotgering method.

Description

 Specification

 Invention title:

Plate-like crystal particles, method for producing the same, and lithium secondary battery

 Technical field

 The present invention relates to plate-like crystal particles useful as a positive electrode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery excellent in output characteristics and high-temperature cycle characteristics.

 Background art

 [0002] In recent years, portable electronic devices such as mobile phones, VTRs, notebook computers, and the like have been increasingly reduced in size and weight, and as a battery for power supplies, a positive electrode active material and a lithium transition metal composite oxide. Secondary batteries using an organic electrolytic solution in which a carbonaceous material is used as a negative electrode active material and an Li-ion electrolyte is dissolved in an organic solvent as an electrolytic solution are now being used.

 [0003] Such a secondary battery is generally called a lithium secondary battery or a lithium-ion battery, and has a feature of high energy density and high single battery voltage of about 4 V. In addition to portable electronic devices, the motor drive of electric vehicles (EVs) or hybrid electric vehicles (HEVs) that are actively popularized as low-emission vehicles against the background of recent environmental problems It is also attracting attention as a power source.

[0004] The battery characteristics of such a lithium secondary battery largely depend on the material characteristics of the positive electrode active material used. Specific examples of the lithium transition element composite oxide contained in the positive electrode active material include lithium cobaltate (L i Co 0 ₂ ), lithium nickelate (L i N i 0 ₂ ), and lithium manganate (L i M n ₂ 0 ₄ ) etc. Among these positive electrode active materials, lithium manganate having a spinel structure that is inexpensive and excellent in safety is being used mainly, but improvement in high-temperature characteristics is an issue.

[0005] As a factor that the high temperature characteristics of lithium manganate are not good, Mn is eluted by the free acid generated from the refining and causes the crystallinity of lithium manganate to decrease, and the eluted Mn is deposited on the surface of the negative electrode material such as graphite and adversely affects the negative electrode itself. This is considered. As measures for suppressing Mn elution, low specific surface area, large particle size, high crystallization of lithium manganate particles, and substantially octahedral shape of primary particles are known (for example, patents). (See references 1-3).

 Prior art documents

 Special δ dedication

 [0006] Patent Document 1: Japanese Patent Laid-Open No. 2 0 2 — 2 8 9 1 9 1

 Patent Document 2: Japanese Patent Laid-Open No. 2 0 0 6-2 5 2 9 4 0

 Patent Document 3: Japanese Laid-Open Patent Publication No. 2 0 0 7-2 9 4 1 1 9

 Summary of the Invention

 However, depending on the measures disclosed in Patent Documents 1 to 3, etc., the high temperature characteristics of lithium manganate cannot be sufficiently improved, and there is still room for improvement. Therefore, as a positive electrode and a substance capable of providing a lithium secondary battery having excellent output characteristics and small output decrease and capacity decrease with the passage of a high temperature cycle (that is, excellent cycle characteristics), and such a lithium secondary battery At present, useful lithium manganate crystal particles have not yet been found.

 [0008] The present invention has been made in view of the above-described problems of the prior art, and the object is to provide a lithium secondary battery excellent in output characteristics and high-temperature cycle characteristics. It is an object of the present invention to provide a plate-like crystal particle useful as a positive electrode active material and a method for producing the same. Another object of the present invention is to provide a lithium secondary battery excellent in output characteristics and high-temperature cycle characteristics.

 [0009] As a result of intensive studies to achieve the above-mentioned problems, the present inventors have found that the above-described problems can be achieved by adopting the following configuration, and have completed the present invention.

That is, according to the present invention, the following plate-like crystal particles and method for producing the plate-like crystal particles And a lithium secondary battery are provided.

 [0011] [1] It is composed of lithium manganate with a spinel structure containing Li and Mn as constituent elements, has an aspect ratio of 1.5 to 20 and a thickness of 1 to 20 m. As a plate-like crystal particle having a crystal face (1 1 1) having an orientation measured by the Lotgering method of 2 θο / ο or more.

 [0012] [2] The plate-like crystal particles according to [1], which are single crystal particles.

 [3] [3] The single crystal particle includes a plurality of single crystal particles, and the number of the single crystal particles substantially existing in the thickness direction is one, and the plurality of single crystal particles includes the crystal plane (1 1 1 ) Are aligned, the plate-like crystal particles according to [1], which are bonded to each other between the grain boundary portions of the single crystal particles.

 [4] The plate-like crystal particles according to any one of [1 :! to [3], wherein the lithium manganate is represented by the following general formula (1):

 (In the general formula (1), Μ is Li, Fe, 、 ί, Mg, Zn, Al, Co, Cr, Si, Sn, P, V, Sb, Nb. And one or more elements selected from the group consisting of Ta, Mo, and W, and two or more substitution elements including Ti, and X represents the number of substitutions of the substitution element M)

[5] The plate shape according to any one of [1] to [4], wherein a molar ratio between Li and Mn contained in the lithium manganate satisfies a relationship of Li / Mn> 0.5. Crystal particles.

 [0016] [6] The method for producing plate-like crystal particles according to any one of [1] to [5], wherein a molding material containing lithium manganate particles is molded and has a thickness of 30 mm or less. A molding step for obtaining a self-supporting sheet-shaped molded body, and a state in which the sheet-shaped molded body is adjacent to an inert layer that does not substantially react with the sheet-shaped molded body, or the sheet-shaped molded body remains as it is. A method for producing plate-like crystal particles, comprising: a firing step of firing in a state; and a grinding step of crushing and classifying the sheet-shaped formed body after firing.

[7] The firing temperature in the firing step is 650 to 1250 ° C. [6] The method for producing plate-like crystal particles according to [6].

[8] The method for producing plate-like crystal particles according to [6] or [7], wherein the median diameter of the lithium manganate particles is 1 to 60% of the thickness of the sheet-like molded body.

 [9] The method according to any one of [6] to [8], wherein the sheet-shaped molded body is fired in a volatilization-suppressed state capable of suppressing volatilization of a specific component contained in the sheet-shaped molded body. A method for producing plate-like crystal particles.

[10] The method for producing plate-like crystal particles according to [9], wherein the volatilization suppression state is a state in which the lithium manganate particles coexist with the sheet-like molded body.

 [1 1] The above pulverizing step is a step of pulverizing and classifying the sheet-like molded body after firing by passing through an opening of a predetermined size.

[10] The method for producing plate-like crystal particles according to any one of [1].

[0022] [1 2] The method for producing plate-like crystal particles according to [1 1], wherein an average opening diameter of the opening is 1. Omm or less.

[13] The sheet-like molded body after firing is pressed with a pressing member, and passed through a mesh having the opening, and the sheet-like molded body after firing is unwound and classified. ] The method for producing plate-like crystal particles according to any one of [1 2].

[0024] [14] A lithium secondary battery using the plate-like crystal particles according to any one of [1] to [5] as a positive electrode active material.

[0025] The plate-like crystal particles of the present invention can provide a lithium secondary battery excellent in output characteristics and high-temperature cycle characteristics, and are effective as a positive electrode active material.

 [0026] According to the method for producing plate-like crystal particles of the present invention, plate-like crystal particles useful as a positive electrode active material capable of providing a lithium secondary battery excellent in output characteristics and high-temperature cycle characteristics are produced. be able to.

[0027] The lithium secondary battery of the present invention has an effect of being excellent in output characteristics and high-temperature cycle characteristics. Brief Description of Drawings

 FIG. 1 is a perspective view schematically showing one embodiment of a plate-like crystal particle of the present invention.

 FIG. 2A is a perspective view schematically showing another embodiment of the plate-like crystal particle of the present invention.

 FIG. 2B is a perspective view schematically showing still another embodiment of the plate-like crystal particle of the present invention.

 FIG. 2G is a perspective view schematically showing still another embodiment of the plate-like crystal particle of the present invention.

 FIG. 3A is a side view showing an example of a calciner.

 FIG. 3B is an AA cross-sectional view of FIG. 3A.

 FIG. 4 is an explanatory view showing an example of a grinding process.

 FIG. 5 is a cross-sectional view schematically showing an example of the microstructure of the positive electrode plate.

 FIG. 6 is an electron micrograph showing the surface state (morphology) of the sheet-like molded body obtained in Example 8.

 FIG. 7 is an electron micrograph showing the cross-sectional state (morphology) of the sheet-like molded body obtained in Example 8.

 BEST MODE FOR CARRYING OUT THE INVENTION

 [0029] Hereinafter, modes for carrying out the present invention will be described. However, the present invention is not limited to the following embodiments, and the ordinary knowledge of those skilled in the art is within the scope of the present invention. Based on the above, it should be understood that modifications, improvements, and the like to the following embodiments are also included in the scope of the present invention.

 [0030] 1. Plate-like crystal particles:

FIG. 1 is a perspective view schematically showing one embodiment of the plate-like crystal particle of the present invention. As shown in FIG. 1, the plate-like crystal particles 10 of the present embodiment are single crystal particles made of lithium manganate having a spinel structure containing Li and Mn as constituent elements. The plate-like crystal particle 10 has a crystal plane (1 1 1) 2 as a development plane. When the plate-like crystal particle 10 of this embodiment having such a configuration is used as a positive electrode active material, a lithium secondary battery excellent in output characteristics and high-temperature cycle characteristics can be provided. As used herein, “developmental aspects” Of the crystal planes that make up the plate-like crystal grains, the plane with the widest area.

[0031] When the plate-like crystal particle of the present invention is used as a positive electrode active material, the reason why it is possible to provide a lithium secondary battery excellent in output characteristics and high-temperature cycle characteristics is as follows. In lithium crystal particles, lithium ion (L i +) de-insertion can occur on any crystal plane, while the dissolution rate of Mn may differ depending on the crystal plane. That is, the plate-like crystal particles of the present invention can smoothly remove and insert lithium ions (L i +), and the shape of the particles is plate-like. Since the diffusion distance of i +) is shorter than that of general isotropic particles of the same volume, it is presumed that a lithium secondary battery having excellent output characteristics can be provided. In addition, since the plate-like crystal particle of the present invention is a crystal particle having a crystal plane (1 1 1) with a slow Mn elution rate as a development plane, a lithium secondary battery excellent in high-temperature cycle characteristics is provided. It is estimated that

 [0032] The longest grain length Y of plate-like crystal grains 1 0 (see Fig. 1)! Is usually 50 m or less, preferably 30 / m or less, more preferably 20 m or less. The maximum particle length Y can be appropriately set according to the purpose. In addition, the aspect ratio of the plate-like crystal particle 10 represented by the ratio of the longest particle length Υ to the particle thickness (Y ZWJ is 1.5 to 20, 1.5 to 10 Preferably, it is 1.5 to 5. When the aspect ratio is in the above numerical range, the positive electrode active that can provide a lithium secondary battery excellent in output characteristics and high-temperature cycle characteristics. It can be a substance.

[0033] The grain thickness \ Λ of the plate-like crystal particle 10 is the thickness of the thickest portion of the plate-like crystal particle 10. The plate-like crystal particle 10 has a particle thickness W of 20 m or less, preferably 15 mm or less, and more preferably 1 O im or less. The particle thickness W is 1 mm or more, preferably 5 jUm or more. When the particle thickness is 1 m or more, the shape of the plate-like crystal particle 10 is easily maintained in a flat plate shape. If the grain thickness is 20 mm or less, the crystal plane (1 1 1) 2 The degree of orientation can be further increased.

 FIG. 2A is a perspective view schematically showing another embodiment of the plate-like crystal particle of the present invention. As shown in FIG. 2, the plate-like crystal particle 20 of the present embodiment includes a plurality of single crystal particles 1 2, and the plurality of single crystal particles 1 2 are developed into crystal planes (1 1 1 ) In the state where 2 are aligned, it is constituted by being bonded at the grain boundary portions 14 of the single crystal particles 1 2. That is, the plate-like crystal particle 20 has a shape in which a plurality of single crystal particles 12 having aligned crystal faces (1 1 1) 2 as a development plane are connected in a substantially two-dimensional manner. This “alignment of crystal planes (1 1 1) 2” means that the crystal planes (1 1 1) 2 of a plurality of single crystal particles 1 2 are on the same plane (Fig. 2A) If the crystal plane (1 1 1) 2 faces in the same direction (Figure 2B), and the crystal plane (1 1 1) 2 faces in the same direction When the crystal plane (1 1 1) 2 of the single crystal particle 1 2 is on the same plane, or the crystal plane (1 1 1) 2 is the same direction (Figure 2C), etc. The state of. In FIGS. 2B and 2C, reference numerals 30 and 40 denote plate-like crystal particles.

 [0035] The number of single crystal particles 12 substantially existing in the thickness direction of the plate crystal particles 20

 One. This “substantially the number of single crystal particles 1 2 existing in the thickness direction is 1” means that even if there is a part where the single crystal particles 1 2 overlap each other, most of the other single crystal particles 1 A state where the two do not overlap. The concept of “the number of single crystal particles substantially existing in the thickness direction” is substantially equal to the number of single crystal particles existing in the thickness direction in a narrow region such as an end. It is one, but in the wide area such as the center, it is not included if it is more than one

[0036] The plate-like crystal particles 20 (see FIG. 2A) are obtained by firing a sheet-like molded body obtained by molding a molding material containing lithium manganate particles, and crushing and classifying the fired molded body having grown grains. It can be obtained. That is, the number of single crystal grains 12 substantially existing in the thickness direction is one because the number of single crystal particles 12 existing in the thickness direction is limited when grains grow by firing. The grain growth in the surface direction Prompted. As a result, the flat single crystal particles 12 are arranged in the plane direction, and the crystal plane (1 1 1) which is a development plane is oriented. The plate-like crystal particles of the present invention may include single crystal particles that do not grow to the thickness of the sheet-like molded body, or single crystal particles having different crystal plane (1 1 1) orientations. For this reason, as shown in FIG. 2B and FIG. 2C, there may be local portions where the single crystal particles 1 2 overlap each other or where the crystal plane (1 1 1) 2 faces differently. However, a plurality of single crystal grains 12 are bonded at the grain boundary portion 14 with the crystal plane (1 1 1) 2 directions being substantially aligned.

 [0037] The number of single crystal particles 12 included in the plate crystal particles 20 in the thickness direction is 2

 The ratio of only one part is preferably 70% or more, more preferably 800/0 or more, and 90% or more with respect to the entire area of the plate-like crystal particles 20. Is particularly preferred. This area ratio can be calculated based on a SEM photograph taken by scanning electron microscope (SEM) observation with the plate crystal particles 20 dispersed as much as possible. This area ratio can also be predicted from the total area of the plate-like crystal particles 20 when the length in the plane direction of the plate-like crystal particles 20 is equal to or greater than the thickness of the plate-like crystal particles 20. . In this plate-like crystal particle 20, the portion where the single crystal particles 12 overlap is only a part of the whole (for example, 30% or less in area ratio). For this reason, it can be crushed relatively easily at the grain boundary part 14 where the single crystal grains 12 and 2 are bonded.

[0038] The longest grain length Y ₂ of the plate-like crystal particle 20 (see FIG. 2A) is usually 100 m or less, preferably 7 Ojt m or less, and more preferably 50 / m or less. The maximum particle length Y ₂ can be appropriately set according to the purpose. Further, with respect to particle Koatsumi W _2, § scan Bae transfected ratio of plate crystal grains 20, represented by the ratio of the particle maximum length Y ₂ (Y ₂ ZW ₂₎ is preferably 1. 5 to 20 2 to 15 is more preferable, and 2 to 10 is particularly preferable. When the aspect ratio is in the above numerical range, a positive electrode active material capable of providing a lithium secondary battery excellent in output characteristics and high-temperature cycle characteristics can be obtained. Note that if the aspect ratio exceeds 20, the rate characteristics may deteriorate. [0039] grain thickness W ₂ of the plate crystal grains 20 is a Thickness of the thickest portion of the plate crystal grains 20. The particle thickness W ₂ of the plate-like crystal particle 20 is preferably 2 OjUm or less, more preferably 15 // m or less, and particularly preferably 10 μm or less. Further, the particle thickness W ₂ is preferably 1 m or more, and more preferably 5 m or more. When the particle thickness W ₂ is 1 / m or more, the shape of the plate-like crystal particle 20 is easily maintained as a flat plate. In addition, when the particle thickness W ₂ is 20 m or less, the degree of orientation of the crystal plane (1 1 1) 2 can be further increased, and the ion diffusion distance in the particle is shortened, resulting in degradation of output characteristics. Is preferable because it is difficult to occur. The particle thickness W ₂ is usually substantially the same as the thickness of the single crystal particle.

 [0040] The aspect ratio of the plate-like crystal particles is calculated as follows. First, the particle thickness (W) is measured based on a SEM photograph taken using a scanning electron microscope (SEM). Next, a plate-like crystal particle is placed in a solvent such as alcohol so as to be 1 to 10% by mass, and a dispersion obtained by dispersing with ultrasonic waves is placed on the surface of the glass substrate at 1 000 to 4000. Spin coating is performed under the condition of r pm to prepare a measurement sample in which the particles do not overlap as much as possible and the plate surface of the particles is arranged parallel to the surface of the glass substrate. Using a scanning electron microscope (SEM), observe the plate surface of the particles in the field of view containing about 5 to 30 plate-like crystal particles in the manufactured sample for measurement, and take the plate from the SEM photograph taken. Measure the longest length (Y) of the crystal grains. At this time, the overlapping plate-like crystal particles are ignored. Then, assuming that the measured longest length (Y) is the particle size of the plate-like crystal particles, this particle size (Y) is divided by the particle thickness (W) to calculate Γ YZW for each plate-like crystal particle. The average of these values is referred to as “aspect ratio of plate-like crystal grains”.

[0041] The degree of orientation of the crystal plane (1 1 1) measured by the Lotgering method is 20% or more, preferably 50 <½ or more, more preferably 70 o / o or more, It is particularly preferable that it is 80% or more. This is because, when the orientation degree of the crystal plane (1 1 1) is 20% or more, the Mn elution suppression effect appears remarkably. [0042] A method for measuring the degree of orientation of the crystal plane (1 1 1) (Lottgering method) will be described. First, a plate-like crystal particle is put in a solvent such as alcohol so as to be 1 to 10% by mass, and a dispersion obtained by dispersing with ultrasonic waves is placed on the surface of a glass substrate under conditions of 1000 to 4000 rpm. The sample for measurement is prepared in such a manner that the particles are not overlapped as much as possible and the plate surface of the particles is arranged parallel to the surface of the glass substrate. Next, using an XRD diffractometer, measure the XRD diffraction pattern when the surface of the plate crystal particle in the prepared measurement sample is irradiated with X-rays. Using the peaks of (1 1 1), (31 1), (400), and (331) in the measured XRD diffraction pattern, the orientation of the crystal plane (1 1 1) from the following equation (2) The degree can be calculated.

[0043] [Equation 1]

_∑'I (HKL) _∑'I ₀ (HKL)

 „., ∑I (hkl) ∑I. (Hkl)

 Orientation degree (%) = ~ X 100 ---- (2)

₁ ∑'Io (HKL)

∑I ₀ (hkl)

In the above formula (2), ∑ I (h k I) represents the total sum of X-ray diffraction intensities of all crystal planes (h k I) measured with the plate-like crystal particles, and ∑ I. (hk I) is the sum of the X-ray diffraction intensities of all crystal planes (hk I) measured for the same composition as the plate-like crystal grains and non-oriented, and ∑ 'I (HKL) is , Shows the sum of X-ray diffraction intensities (in this case only (1 1 1) plane) of crystallographically equivalent specific crystal planes measured in plate-like crystal grains, and ∑ 'I 0 (HKL) is The sum of the X-ray diffraction intensities of the crystal plane (1 1 1) measured for the same composition as the plate-like crystal grains and for the non-oriented ones.

[0045] The thickness (single crystal particle thickness Z) of the single crystal particle 12 contained in the plate crystal particle 20 (see FIG. 2A) is preferably 2 Ojum or less, and 15 mm or less. More preferably, it is particularly preferably 10 / m or less. The single crystal particle thickness Z is preferably 1 mm or more, and more preferably 5 m or more. When the single crystal grain thickness Z is 1 jwm or more, It is easy to keep the shape of 20 flat. In addition, if the single crystal grain thickness Z is 2 O im or less, the grain growth in the thickness direction is limited even if inorganic particles that grow into isotropic and polyhedral crystal grains are included, Since the crystal growth of the single crystal particle 12 is further promoted in the plane direction of the plate crystal particle 20, the crystal plane (1 1 1) grows in the plane of the plate crystal particle 10, so that The specular ratio is large and the crystal plane (1 1 1) 2 has a high degree of orientation.

 [0046] The aspect ratio of the single crystal particle 12 contained in the plate crystal particle 20 (see FIG. 2A) expressed by the ratio of the single crystal particle longest length X to the single crystal particle thickness Z. The ratio (X / Z) is preferably 1 or more, more preferably 2 or more, and particularly preferably 4 or more. When the aspect ratio is 1 or more, the single crystal particles 12 are easily oriented, and the degree of orientation of the plate crystal particles 20 is also increased. The aspect ratio is preferably 50 or less. When the aspect ratio is 50 or less, it is easy to adjust the size (particle size) of the obtained plate-like crystal particles 20. The aspect ratio of the single crystal particles 12 can be calculated by a method similar to the method for calculating the aspect ratio of the plate-like crystal particles described above.

 [0047] The longest length of the single crystal particles 12 included in the plate-like crystal particles 20 (see FIG. 2A) (the longest single crystal particle length X) is preferably 5 O / m or less, It is more preferably 0 im or less, and particularly preferably 2 O im or less. When the longest single crystal particle length X is 50 m or less, the size (particle size) of the obtained plate-like crystal particle 20 can be easily adjusted.

[0048] The value of Y ₂ Ζ expressed by the ratio of the longest particle length Y _{2 to} the longest single crystal particle length X is preferably 3 to 100. If the value of Υ ₂ / Χ is 3 or more, it is easy to align the particle size. Also, if the value of Υ ₂以下 is less than 100, there are few grain boundary parts with weak mechanical strength, and it becomes difficult to break.

[0049] The plate-like crystal particles of the present invention are composed of lithium manganate. The stoichiometric composition of lithium manganate is usually represented by Li M n ₂ 0 ₄ , but the lithium manganate constituting the plate crystal particles of the present invention has such a stoichiometric composition. It is not limited to. Specifically, the manpage represented by the following general formula (1) Gansan lithium can also be used to similarly good suitable lithium manganate represented by L i M n ₂ 0 _4.

[0050] In the general formula (1), Μ is Li, Fe, Ni, Mg, Zn, Al, Co, Cr, Si, Sn, P, V, Sb. , Nb, Ta, Mo, and W, and one or more elements selected from the group consisting of W and two or more substitution elements including Ti, and X represents the number of substitutions of the substitution element M. L i is +1, F e, Mn, Ni, Mg, Z n is +2, B, A l, Co, and Cr are +3, S i, T i, and Sn are + Tetravalent, P, V, Sb, Nb, Ta are +5 valent, Mo, W are +6 valent ions, and both elements are theoretically fixed in Li M n ₂ 0 ₄ It melts. For Co and Sn, for +2, Val, for Fe, Sb and Ti, for +3, for Mn, +3, for +4, for Cr It can be +4 or +6. Therefore, the substitution element M may exist in a state having a mixed valence. Further, the amount of oxygen does not necessarily need to be 4 as represented by the theoretical chemical composition, and may be deficient or excessive in the range for maintaining the crystal structure. Absent.

[0051] When M n is substituted with Li (when Li is excessive), the Li i ZMn ratio (molar ratio) is (1 + X) (2- X). On the other hand, when M n is substituted with a substitution element M other than Li, 1 (2-X) is obtained. Therefore, in either case, L; 1 \ 10 ratio> 0.5. The molar ratio of Li to Mn (L i ZMn) contained in the lithium manganate constituting the plate crystal particle of the present invention is preferably more than 0.5. Using lithium manganate that satisfies the relationship L i ZM n> 0.5 further stabilizes the crystal structure compared to the case of using the stoichiometric composition (L i M n _z 0 ₄ ). Therefore, it is possible to obtain a lithium secondary battery with excellent high-temperature cycle characteristics.

 [0052] 2. Method for producing plate-like crystal particles:

Next, an embodiment of the method for producing plate-like crystal particles of the present invention will be described. The method for producing plate-like crystal particles of the present invention comprises (1) a composition containing lithium manganate particles. Molding process to form a self-supporting sheet-like molded body having a thickness of 30 m or less by molding a molding material, (2) the sheet-shaped molded body into an inert layer that does not substantially react with the sheet-shaped molded body A firing step of firing in an adjacent state or in a state of a sheet-like shaped body, and (3) a grinding step of crushing and classifying the fired sheet-like shaped body. Hereinafter, each process will be described.

[0053] (1) Molding process

The lithium manganate particles contained in the forming raw material include, for example, a mixture of raw material compounds containing various elements constituting lithium manganate (L i M n ₂ 0 ₄ ) in a predetermined ratio in an oxidizing atmosphere. It can be synthesized by calcining in the range of 50 ° C. to 1 250 ° C. for 2 hours to 50 hours. Here, the oxidizing atmosphere generally refers to an atmosphere having an oxygen partial pressure that causes an oxidation reaction of the in-furnace sample, and specifically includes an air atmosphere and an oxygen atmosphere.

 [0054] It is preferable that the obtained lithium manganate particles are further pulverized after provisional firing. In this pulverization, the particle size of the lithium manganate particles is preferably set to a particle size according to the thickness of the sheet-like molded body. Specifically, the median diameter (D 50) is preferably 1 to 60% of the thickness of the sheet-like molded body. When the median diameter of the lithium manganate particles is set to 1% or more of the thickness of the sheet-like molded product, pulverization is easy. On the other hand, when the content is 60% or less, the lithium manganate particles contained in the sheet-shaped molded body are more uniformly distributed, so that the thickness of the sheet-shaped molded body can be easily adjusted. In order to increase the size of the single crystal particles, it is preferable from the viewpoint of promoting grain growth to further reduce the median diameter (D 50) of the lithium manganate particles. The particle size of the lithium manganate particles can be measured by dispersing them in a dispersion medium such as an organic solvent or water using a laser diffraction / scattering particle size distribution analyzer. The lithium manganate is preferably wet pulverized using, for example, a pole mill, a bead mill, a trommel, an attritor or the like.

As the starting compound containing [0055] lithium, L i ₂ 0 is the oxide is not preferred for highly hygroscopic, difficult to handle. Therefore, chemically stable carbonate, hydrochloride Nitrate, sulfate, hydroxide, organic acid salt, halide and the like can be suitably employed, and these several types may be used in an appropriate combination. As raw material compounds containing other elements, salts and oxides of the respective elements (including substitution element M when Mn is substituted) can be suitably used. The salt of each element is not particularly limited, but it is preferable to use a raw material having a high purity and being inexpensive. Specifically, carbonates, hydroxides, and organic acid salts are preferably used, but nitrates, hydrochlorides, sulfates, and the like can also be used. In addition, as a molding material, for example, a raw material compound containing various elements constituting lithium manganate (L i M n ₂ 0 ₄ ) mixed in a predetermined ratio and pulverized may be used without being calcined. .

 [0056] The obtained molding material is molded to obtain a self-supporting sheet-like formed body (green sheet) having a thickness of 30 m or less. The “self-supporting sheet-like molded product” can be used to maintain the sheet shape by itself, or even if it cannot maintain the sheet shape by itself, it can be attached to a substrate or formed into a film. This includes those that can maintain the recite shape. Examples of the method for forming a sheet-like molded body include a doctor blade method using a forming raw material (slurry) containing lithium manganate particles, an extrusion method using a clay containing inorganic particles, and the like. .

[0057] When producing a sheet-like molded body by the doctor blade method, first, slurry is applied to a flexible plate (for example, an organic polymer plate such as a PET film). The sheet-like molded body formed by drying and solidifying the applied slurry can be removed from the plate to obtain a sheet-like molded body. When preparing a forming raw material such as slurry or clay, lithium manganate particles may be dispersed in an appropriate dispersion medium, and a binder, a plasticizer, or the like may be added as appropriate. Further, the viscosity of the slurry is preferably adjusted to 500 to 80 Om Pa s and preferably defoamed by reducing the pressure. The thickness of the sheet-like shaped body is 30 / m or less, preferably 20 jum or less, more preferably 15 m or less. When the thickness of the sheet-like compact is 3 Oim or less, the degree of orientation of the obtained plate-like crystal particles can be increased. In addition, if the thickness of the sheet-shaped molded body is 15 jum or less, The degree of orientation of the plate-like crystal particles can be further increased. Note that the thickness of the sheet-like molded body is preferably 1 im or more, and more preferably 5 m or more. If the thickness is 1 / m or more, the sheet-like molded body can be made self-supporting.

 [0058] In order to further increase the size of the plate-like crystal particles, it is preferable that the thickness of the sheet-like molded body is 15 to 3 O jum. Since the thickness of the plate-like crystal particles is defined by the thickness of the sheet-like molded product, the thickness of the sheet-like molded product may be appropriately set according to the use of the plate-like crystal particles. Other molding methods for sheet-like molded products include resin, glass, ceramics, or metal by high-speed spraying methods such as aerosol deposition, or vapor phase methods such as sputtering, CVD, and PVD. For example, there is a method of forming a film on a substrate, etc., and peeling it from the substrate. In the case of these forming methods, the density of the resulting sheet-like shaped product can be increased, and thus there are advantages such as low-temperature grain growth, prevention of volatilization of constituent elements, and high density of the obtained plate-like crystal particles. is there.

 [0059] (2) Firing process

 In the firing step, the sheet-like molded body is fired in a state where it is adjacent to an inert layer that does not substantially react with the sheet-like molded body, or in a state where the sheet-like molded body remains.

Specific examples of the “inert layer that does not substantially react with the sheet-like molded body” include a fired ceramic plate, a Pt plate, a carbon plate, a graphite plate, a molybdenum plate, a tungsten plate, and an organic sheet that burns during firing. Etc. It should be noted that the compact may be placed on a layer that is inactive at the firing temperature of the compact, such as alumina, zirconia, spinel, carbon, graphite, molybdenum, tungsten, or platinum, and fired. In addition, as an organic substance sheet combusted at the time of baking, the thing which does not have thermoplasticity, such as the paper synthesize | combined from a pulp, can be used.

[0060] In addition, a sheet-shaped molded body and an inert sheet may be stacked and rolled into a roll shape, or a sheet-shaped molded body may be formed on the inert layer, and the inert layer after firing. You may make it peel from. Alternatively, a sheet-like molded body may be formed on the inert layer, and the inert layer may be removed after firing. When using a graphite layer as an inert layer Alternatively, after firing in a non-oxidizing atmosphere such as a nitrogen atmosphere, the heat treatment may be performed again in an oxidizing atmosphere at a temperature equal to or lower than the firing temperature to burn the graphite layer. The thickness of the sheet-shaped compact is 30 m or less, and the grain growth in the thickness direction of the sheet-shaped compact is limited, and the grain growth in the surface direction of the sheet-shaped compact is promoted. 1 1 1) grows along the surface of the sheet-like molded body, and plate-like crystal grains having a large aspect ratio and a highly oriented crystal face (1 1 1) can be produced.

 [0061] It should be noted that a sheet-like molded body that has been crumpled or a sheet-shaped molded body that has been cut into a strip (ribbon) may be fired. Alternatively, the sheet-shaped molded body cut into a strip shape (ribbon shape) may be fired in a state of being randomly entangled so as to have a predetermined shape (for example, a spherical shape). In these cases, a plate-like crystal grain having a highly oriented crystal face (1 1 1) is obtained because most of the sheet-like molded body is fired while maintaining a self-supporting state without using a special inert layer. The child can be manufactured in large quantities. Further, for the purpose of preventing adhesion between sheets, it is also preferable to fire using a single-tally kiln (rotary furnace).

 [0062] In the firing step, it is preferable to fire the sheet-like molded body in a volatilization-suppressed state that suppresses the volatilization of specific components such as the Al force element contained in the sheet-like molded body. By suppressing the volatilization of a specific component such as an alkali element, it is possible to suppress the deviation of the composition of the obtained plate-like crystal particles. It is also preferable to fire in a state where lithium manganate particles coexist with the sheet-like molded body. That is, by volatilizing the specific component from the coexisting lithium manganate particles, volatilization of the specific component from the sheet-like molded product can be suppressed relatively easily. It is also preferable to place the sheet-shaped molded body in a sheath with a lid, etc., and fire it in a sealed state in which a co-molded molded body and other lithium manganate particles coexist. It is preferable to make it small. It is also preferable to use a molded body in which the lithium content is excessive in anticipation of the volatilization of the specific component.

[0063] However, the sheet-like molded body coexisting inside the sheath and another lithium manganate particle If the amount is too large, sintering and grain growth of the sheet-like molded product will become too active, resulting in undulation in the sheet-like molded product and a decrease in the aspect ratio of the plate-like crystal particles. There is a case. Therefore, it is important to appropriately set the volume inside the sheath, the amount of the sheet-like molded body, the amount of lithium manganate particles to be coexisted, etc. so that the atmosphere inside the sheath is in an optimal state. In addition, when firing the sheet-like molded article, it is preferable that lithium manganate particles having the same composition as the lithium manganate particles contained in the sheet-like molded article coexist, but the lithium manganate particles contained in the sheet-like molded article By allowing the specific component to be volatilized more easily than the coexisting material, the volatilized specific component can be replenished to the sheet-like molded body after firing.

[0064] Further, in the firing step, after firing at the first firing temperature in the sheath controlled to the first atmosphere, returning to room temperature, the first firing temperature in the sheath controlled to the second atmosphere The second baking temperature may be higher than that of the second baking temperature. The firing atmosphere may be in the air, but in consideration of the suppression of volatilization of the constituent elements and reactivity with the inert layer, etc., reduction in a neutral atmosphere such as an oxygen atmosphere or nitrogen, in the presence of hydrogen or hydrocarbons, etc. It may be in an atmosphere or vacuum. Further, from the viewpoint of promoting in-plane grain growth, weighted firing may be performed by hot pressing or the like.

 FIG. 3A is a side view showing an example of a calciner, and FIG. 3B is a cross-sectional view taken along the line AA in FIG. 3A. The calciner 5 is used when the sheet-like molded body 15 is fired in a firing furnace (not shown), and has been fired on which an unfired molded body (sheet-like molded body 15) is placed. Placed on ceramic plate setter 2 2, thick coexisting green compact 2 4, which contains lithium manganese oxide particles, and coexisting green compact 2 4 And a square plate 26 that is a fired ceramic plate that covers the upper portion of the sheet-like molded body 15. By enclosing the four sides of the sheet-like molded body 15 with the coexisting unfired molded body 24, the specific components are volatilized from the sheet-like molded body 15 to prevent the composition from changing.

[0066] The shape of the setter 2 2 shown in FIGS. 3A and 3B is a flat plate, but is a sheet. Sheet shape, such as a setter with a roughened surface on which the compact 15 is placed, a honeycomb-shaped setter having a plurality of through-holes on the surface on which the compact 15 is placed, a dimple processed setter, etc. It is preferable to use a setter that reduces the contact area with the molded body 15 and prevents the sheet-shaped molded body 15 from being welded. In addition, on the surface of the setter 2 2 on which the sheet-like molded body 15 is placed, an alumina powder or a zirconia powder that is stable even at the firing temperature of the sheet-like molded body 15 is laid, and on that surface. It is also preferable that the sheet-like molded body 15 is placed and fired.

 [0067] When the powder of lithium manganate coexists in the sheath instead of using the coexisting green compact, the setting method of the setter, the size of the setter, and the stacking in the sheath The atmosphere inside the sheath can be uniformly adjusted by appropriately adjusting the method and the location where the powder is disposed. Thereby, when a plurality of sheet-like molded bodies are fired simultaneously, the crystal grain structure of the fired sheet-like molded body can be made uniform.

[0068] The sheet-like molded body is 50 0-compared to the temperature at which a re-equilibrated crystal can be obtained by firing (for example, the temperature at which densification and grain growth occur by firing the bulk). Baking is preferably performed at a temperature as high as 200 ° C. By firing at such a temperature, grain growth can be sufficiently advanced. It is preferable to fire at a temperature that is high enough not to decompose the molding material contained in the sheet-like molded body. In particular, when the thickness of the sheet-like molded body is thinner, it is difficult to grow the grains. Therefore, it is preferable to raise the firing temperature. In order to increase the particle size of the obtained plate-like crystal particles, firing at a higher temperature is preferable. Also, in order to promote the grain growth of plate crystal grains may be added to the low melting oxides such as B i ₂ 0 ₃ as a sintering aid.

 [0069] (3) Grinding process

In the pulverization step, the fired sheet-like molded body is crushed and classified by passing through an opening of a predetermined size. In this step, for example, a mesh having an opening having an opening diameter that matches the particle size of the target plate crystal particle is used. The average opening diameter of the mesh used is usually 1. O mm It is as follows.

FIG. 4 is an explanatory diagram showing an example of a pulverization process. In the pulverization process, for example, a mesh 34 having an average opening diameter << 1 00 m, 70 m _% 45 m, 25 jU m, 20 m, 10 jU m, 5 jL <m or the like is used. be able to. The sheet-like molded body 32 after firing is brittle and relatively easy to disintegrate. For this reason, a sheet-like molded product after firing is obtained by sieving the mesh 3 4 while lightly pressing the fired sheet-like shaped product 3 2 placed on the mesh 34 with a spatula-shaped pressing member 36. The body can be crushed and classified at the same time, and plate-like crystal particles 1.5 can be obtained. In order to obtain plate-like crystal particles having a large particle size and a large aspect ratio, a mesh 34 having an opening with a large opening diameter may be used. On the other hand, in order to obtain plate-like crystal particles having a small particle size and a small aspect ratio, a mesh 34 having an opening having a small opening diameter may be used. That is, the characteristics of the obtained plate-like crystal particles can be changed by a simple selection of changing the opening diameter of the opening of the mesh 34.

 [0071] Note that, when firing at a high temperature of 800 ° C or higher, it is assumed that oxygen deficiency occurs and the performance as the positive electrode material deteriorates. Therefore, it is also preferable to supply oxygen by performing a heat treatment again in the atmosphere or in an oxygen * atmosphere at about 60 to 700 ° C.

 [0072] 3. Lithium secondary battery:

Next, an embodiment of the lithium secondary battery of the present invention will be described. The lithium secondary battery of the present invention is manufactured using the plate-like crystal particles described above as a positive electrode active material. Therefore, the lithium secondary battery of the present invention is excellent in output characteristics and high temperature cycle characteristics. Such excellent output characteristics and high-temperature cycle characteristics are particularly noticeable in a large-capacity secondary battery manufactured using a large amount of electrode active material. For this reason, the lithium secondary battery of the present invention is suitable as a power source for driving a motor of an EV or HEV, for example. However, the lithium secondary battery of the present invention is also suitable as a small capacity battery such as a coin battery. [0073] As a member (material) other than the positive electrode active material for constituting the lithium secondary battery of the present invention, various conventionally known materials can be used. For example, as the negative electrode active material, amorphous carbonaceous materials such as soft carbon and hard carbon, and highly graphitized carbon materials such as artificial graphite and natural graphite can be used. Among them, it is preferable to use a highly graphitized carbon material having a large lithium capacity.

 [0074] Organic solvents used in the non-aqueous electrolyte include carbonate solvents such as ethylene carbonate (EC), jetyl carbonate (DEC), dimethyl carbonate (DMC), propylene carbonate (PC), and r- A single solvent such as petit mouth lactone, tetrahydrofuran, or acetonitrile, or a mixed solvent thereof is preferably used.

[0075] Specific examples of the electrolyte include lithium hexafluorophosphate (L i PF ₆ ) and lithium borofluoride (L ί BFJ and other lithium complex fluorine compounds: lithium perchlorate (L i CI 0 ₄ ) It should be noted that one or more of these electrolytes are usually used by dissolving in the above-mentioned organic solvent among these electrolytes. It is preferable to use Li PF ₆ having high conductivity.

 [0076] Specific examples of the battery structure include a coin-type battery (coin cell) in which a separator is disposed between a plate-shaped positive electrode active material and a negative electrode active material and filled with an electrolytic solution, or a metal foil. A positive electrode plate formed by coating a positive electrode active material on the surface and a negative electrode plate formed by applying a negative electrode active material on the surface of a metal foil are wound or laminated with a separator used. Various types of cylindrical or box type batteries can be given.

[0077] Since the filling rate of the positive electrode active material constituting the positive electrode plate is an important factor for determining the capacity of the battery, it is desirable to employ particles having high filling properties as the positive electrode active material. It is preferable to use the above-mentioned plate-like crystal particles (plate-like crystal particles of the present invention) because it is easy to increase the filling rate of the positive electrode active material constituting the positive electrode plate. When crystal particles having a large particle size are used as the positive electrode active material, the filling property is improved. However, lithium manganate with a spinel structure is an octahedral angular particle. Since it tends to be a shape, it cannot be said that the filling property is good. On the other hand, since the plate-like crystal particles of the present invention are plate-like crystal particles having a flat surface spread, in particular, the particles can be easily filled by arranging them so that the directions of the particles are aligned. A high filling rate can be obtained.

 FIG. 5 is a cross-sectional view schematically showing an example of the microstructure of the positive electrode plate. In FIG. 5, the plate crystal particles 60 of the present embodiment are used as the positive electrode active material 65, and the positive electrode material (paste) containing the plate crystal particles 60 is used as a current collector plate (aluminum foil) 1 A positive electrode plate 110 obtained by coating on 0 0 is shown. In this way, by arranging the large number of plate-like crystal particles 60 of this embodiment in the same direction, it is possible to obtain the positive electrode plate 110 filled with the positive electrode active material 65 with a high filling rate. it can. Note that reference numeral 95 in FIG. 5 denotes a binder part containing acetylene black, polyvinylidene fluoride (P V D F), or the like.

 In addition, as shown in FIG. 5, the conventional equiaxed crystal particles 85 are used as the positive electrode active material 75 together with the plate crystal particles 60 of the present embodiment, that is, the plate crystal The positive electrode plate 110 can also be produced by mixing the particles 60 and the conventional equiaxed crystal particles 85 in an appropriate ratio. Further, it is not necessary to use only the same size and shape of the plate-like crystal particle 60, and it is also possible to use a mixture of particles having different sizes and shapes. The plate-like crystal particles of the present invention have a higher particle size homogeneity than the positive electrode active material particles produced by a conventional particle synthesis method. For this reason, it is preferable to use the plate-like crystal particles of the present invention as the positive electrode active material, because even when a large number of batteries are manufactured, a uniform battery with little variation in characteristics can be obtained.

 Example

 Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples.

[0081] (Example 1)

 (1) Synthesis of inorganic particles

L i ₂ C 0 ₃ powder (manufactured by Kanto Chemical Co., Inc.), so that the composition ratio of L i M n ₂ 0 ₄ And Mn0 ₂ powder (Kojundo Chemical Laboratory Co., Ltd.) were weighed placed in cylindrical jar made of resin, Jirukoniaboru, and ethanol further put as a dispersion medium, 1 6 hours at Po mill, wet mixing and The slurry was obtained by grinding. The obtained slurry was dried using an evaporator and a dryer, and then calcined at 800 ° C. for 24 hours to obtain a calcined powder. The obtained calcined powder was wet pulverized with a ball mill for 5 hours using zirconia balls and ethanol as a dispersion medium. Drying was performed using an evaporator and a drier to obtain L ίίη ₂ 0 ₄ powder (inorganic particles). The average particle size of the L ί Mn ₂ 0 ₄ powder (median diameter (D50) measured using water diffraction as a dispersion medium using a laser diffraction Ζscattering particle size distribution analyzer (model number “LA-750J” manufactured by HOR I BA) )) Was 0.6 0m.

[0082] (2) Molding process

Dispersion media 1 00 parts by weight to prepare a toluene and isopropanol by mixing equal amounts, L i Mn ₂ 0 ₄ powder 1 00 parts by mass of the resultant polyvinyl as a binder butyral (trade name Ganmabetamyu- 2 ", manufactured by Sekisui Chemical Co., Ltd. ) 10 parts by mass, plasticizer (trade name “DOP”, manufactured by Kurokin Kasei Co., Ltd.) 4 parts by mass, and dispersant (trade name “SP-O 30”, manufactured by Kao Co., Ltd.) 2 parts by mass, A slurry-like forming raw material was obtained. The obtained slurry-like forming raw material was stirred and degassed under reduced pressure, and its viscosity was adjusted to 500 to 700 mPa · s. The viscosity of the slurry molding raw material was measured using an LVT viscometer (manufactured by Brookfield). By using the doctor blade method, a slurry-like forming raw material whose viscosity was adjusted was formed on a PET film to obtain a sheet-like formed body. The thickness of the sheet-like molded body after drying was 5 / m.

 [0083] (3) Firing process

The sheet-like molded body peeled from the PET film was cut into 5 Omm squares with a cutter and placed in the center of a zirconia setter (dimensions: 7 Omm X 7 Omm X thickness 1 mm). To this setter, an unfired molded body (dimensions: 5mmX 40 mm, thickness 100 jU m) made of the same molding raw material as the slurry-shaped molding raw material used to obtain the sheet-shaped molded body was placed on the four sides of the sheet-shaped molded body. Outside the sheet-shaped molded body It was placed so as to surround. A zirconia square plate (dimensions: 7 Omm X 7 Omm, height 5 mm) was placed on the green body. In this way, the space in which the sheet-shaped molded body is placed is made as small as possible, and the same molding raw material is allowed to coexist, degreased at 600 ° C for 2 hours, and then fired at 900 ° C for 24 hours. The portion not welded to the setter of the subsequent sheet-like molded body was taken out.

[0084] (4) Grinding process

 The sheet-like shaped body after firing was placed on a sieve having an average mesh opening diameter of 25 μm, and pressed lightly with a spatula to crush and classify to obtain plate-like crystal particles (Example 1). It was.

[0085] (Examples 2 to 7)

 Except that the dried sheet-like molded product had the thickness shown in Table 1, and that the baked sheet-like molded product was crushed and classified using a sieve having a mesh average opening diameter shown in Table 1. In the same manner as in Example 1 described above, plate-like crystal particles (Examples 2 to 7) were obtained.

[0086] (Example 8)

 (1) Synthesis of inorganic particles

L i L ₀₅ Mn such that ₉₅ 0 ₄ composition ratio, L i ₂ C0 (manufactured by Kanto Chemical Co., Inc.) ₃ powder, and Mn0 ₂ powder (Kojundo Chemical Laboratory Co., Ltd.) were weighed to a resin cylinder and The mixture was placed in a wide-mouthed bottle, zirconia pol, and ethanol as a dispersion medium were further added, and wet-mixed and pulverized for 16 hours in a ball mill to obtain a slurry. The obtained slurry was dried using an evaporator and a dryer, and then calcined at 800 ° C. for 24 hours to obtain a calcined powder. The obtained calcined powder was wet pulverized with a pole mill for 5 hours using zirconia pole and ethanol as a dispersion medium. And dried using an evaporator and a dryer, L i, to obtain _{a. 05 Μ η ι. 95 0} 4 powder (inorganic particles). L i τ. ₀₅ Mn L ₉₅ 0 ₄ Average particle diameter measured using a laser diffraction Z-scattering particle size distribution analyzer (model number Γ LA-750, manufactured by HOR I BA) with water as the dispersion medium The median diameter (D 50) was 1.0 β m. [0087] (2) Molding process

Dispersion media 1 00 parts by weight to prepare a toluene and isopropanol by mixing equal amounts, the resulting _{L i!. 05 Mn n.} 95 0 4 powder 1 00 parts by mass, Po polyvinyl butyral as a binder (trade name ΓΒΜ- 2 ”, manufactured by Sekisui Chemical Co., Ltd.) 10 parts by mass, plasticizer (trade name“ DOP ”, manufactured by Kurokin Kasei Co., Ltd.) 4 parts by mass, and dispersant (trade name: Γ S P_O30, manufactured by Kao) 2 parts by mass The parts were mixed to obtain a slurry-like forming raw material. The resulting slurry-like forming raw material was stirred and degassed under reduced pressure, and its viscosity was set to 4 OO OmPa · s. The viscosity of the slurry molding raw material was measured using an LVT type viscometer (Brookfield). Using a doctor blade method, a slurry-like forming material with adjusted viscosity was formed on a PET film to obtain a sheet-like formed body. The thickness of the sheet-like molded body after drying was 17 jtim.

 [0088] (3) Firing step

 The sheet-like shaped product peeled from the PET film was cut into 5 Omm squares with a cutter and placed in the center of a zirconia setter (dimensions: 7 Omm X 7 Omm X thickness 1 mm). Place a set of 5 mm high Zirconia spacers at the four corners of this setter, and stack 10 sets of setters on which sheet-like molded bodies are placed in the same manner. Omm X height 6 Omm). Degrease at 600 ° C for 2 hours with the lid open, and further fire for 3 hours at 1100 ° C with the lid closed, and remove the part that is not welded to the setter of the fired sheet Removed. Fig. 6 shows an electron micrograph showing the surface condition (morphology) of the sheet-shaped molded article taken out. In addition, Fig. 7 shows an electron micrograph showing the cross-sectional state (morphology) of the sheet-like molded article taken out.

 [0089] (4) Grinding process

 The calcined sheet-shaped product after firing was placed on a sieve having an average mesh opening diameter of 50 jt / m, and was lightly pressed against the sieve with a spatula to be unraveled and classified.

 [0090] (5) Reheat treatment process

The particles obtained by crushing and classification are heat-treated at 700 ° C for 3 hours in an oxygen atmosphere. Thus, plate-like crystal particles (Example 8) were obtained.

 [0091] (Comparative example "! ~ 3)

L i ₂ C0 ₃ powder (manufactured by Kanto Chemical Co., Inc.),. And Mn0 ₂ powder (manufactured by High Purity Chemical Laboratory Co., Ltd.) are weighed so that the composition ratio of L i Mn ₂ 0 ₄ is obtained. The mixture was placed in a wide-mouthed bottle, and zirconia balls and ethanol as a dispersion medium were further added, and wet mixing and pulverization were performed for 16 hours in a ball mill to obtain a slurry. The obtained slurry was dried using an evaporator and a dryer, and then calcined at 800 ° C. for 24 hours to obtain a calcined powder. The obtained calcined powder was wet-ground by a ball mill for 5 hours using zirconia pollen and ethanol as a dispersion medium. Li Mn _{20 4} powder (inorganic particles) was obtained by drying using an evaporator and a dryer. Average particle diameter of Li Mn ₂ 0 ₄ powder (median diameter (D50)) measured using a laser diffraction / scattering particle size distribution analyzer (model number “LA-750J” manufactured by HOR I BA) with water as the dispersion medium ) Was 0.6.

[0,092] obtained L i Mn ₂ 0 ₄ powder was put into Jirukonia steel sheath, to obtain a L i Mn ₂ 0 ₄ powder was grain growth by heat treatment between 24 hours at 900 ° C. Jirukoniaporu, and using ethanol as a dispersion medium, L i Mn ₂ 0 ₄ powder obtained was wet pulverized to the desired particle size in Porumi Le. And dried using an evaporator and a dryer, the average particle diameter of 0. 6 im (comparative example 1), 3 / m of Comparative Example 2, and 1 Oum (comparative example 3) Works i Mn ₂ 0 ₄ not Regular crystal particles were obtained.

 [0093] (Example 9)

 (1) Synthesis and molding process of inorganic particles

. L i L τΜη τ ₉ 0 so that the _fourth composition ratio, L i ₂ C0 ₃ powder (Honjo Chemicals Le Co., fine grade, average particle size: 3jum), and Mn0 ₂ powder (trade name "electrolytic dioxide Manganese grade FMJ, manufactured by Tosohichi Co., Ltd., average particle size: 5〃m) is weighed and placed in a resin-made cylindrical wide-mouthed jar, zirconia balls, as well as toluene and isopropanol as a dispersion medium, etc. 100 parts by mass of the mixed liquid prepared by mixing the quantity was added to 100 parts by mass of the previous weighed product, and wet-mixed and pulverized with a ball mill for 16 hours. The dried powder was sampled and observed using a scanning electron microscope (SEM) (Model No. Γ J SM-6390, manufactured by JEOL Ltd.). The particle diameter of the powder was 1 m or less. Furthermore, polyvinyl petital (trade name “BM_2J, manufactured by Sekisui Chemical Co., Ltd.) 10 parts by mass, plasticizer (trade name“ DOP ”, manufactured by Kurokin Kasei Co., Ltd.) 4 parts by weight, and a dispersant (trade name“ SP ” —030 ”(manufactured by Kao Corporation) 2 parts by mass were mixed to obtain a slurry-like forming raw material. The obtained slurry-like forming raw material was stirred and degassed under reduced pressure, and the viscosity was adjusted to 400 OmPa · s. The viscosity of the slurry-like forming raw material was measured using an LVT viscometer (manufactured by Brookfield). Using a doctor blade method, a slurry-like forming raw material with adjusted viscosity was formed on a PET film to obtain a sheet-like formed body. The thickness of the sheet-like molded body after drying was 17 jt / m.

 [0094] (2) Firing process

 The sheet-like molded product peeled from the PET film was cut into 30 Omm squares with a force cutter and placed in an alumina sheath (dimensions: 9 Omm X 9 Omm X height 6 Omm) in a crumpled state. . Degreasing was performed at 600 ° C for 2 hours with the lid open, and further, baking was performed at 1050 ° C for 3 hours with the lid closed.

 [0095] (3) Grinding process

 The fired sheet-like molded body was placed on a sieve having a mesh average opening diameter of 5 Ojum, and pressed lightly with a spatula to be crushed and classified.

 [0096] (4) Reheating process

 Particles obtained by crushing and classification were heat-treated at 650 ° C. for 3 hours in the air to obtain plate-like crystal particles (Example 9).

 [Example 10]

_{... L i n 05 AI} o iMn, so as to have the composition ratio of the _{β 5} O ₄ AI ₂ 0 ₃ powder (trade name ΓΑΚΡ- 20J, manufactured by Sumitomo Chemical Co., Ltd., average particle size:: 0. 6 ym) further Plate-like crystal particles (Example 10) were obtained in the same manner as in Example 1 except that weighing was performed and the firing temperature was 110 ° C.

[Example 1 1] Implementation as described above, except that the thickness of the dried sheet-like molded body was set to 4 and the fired sheet-like shaped body was crushed and classified using a sieve having an average mesh opening of 5 jum. In the same manner as in Example 1, plate-like crystal particles (Example 11) were obtained.

 [0099] (Example 1 2)

 Example 1 described above, except that the firing temperature was set to 1 000 ° C, and the sheet-like molded product after firing was crushed and classified using a sieve having a mesh average opening diameter of 10 / m. In the same manner as in Example 1, plate-like crystal particles (Example 1 2) were obtained.

 [0100] (Comparative Example 4)

L i!. ₀₅ Mn such that ₉₅ 0 ₄ composition ratio, L i ₂ C0 (manufactured by Kanto Chemical Co., Inc.) ₃ powder, and Mn0 ₂ powder (Kojundo Chemical Laboratory Co., Ltd.) made of resin was weighed It was put into a cylindrical wide-mouth bottle, further added with zirconia balls and ethanol as a dispersion medium, and wet-mixed and pulverized with a ball mill for 16 hours to obtain a slurry. The obtained slurry was dried using an evaporator and a dryer, and then calcined at 800 ° C. for 24 hours to obtain a calcined powder. Using the zirconia balls and ethanol as the dispersion medium, the obtained calcined powder was wet pulverized with a pole mill for 5 hours. And dried using an evaporator and a dryer, to obtain _{L i!. 05 Mn 95 o} 4 powder (inorganic particles). The average particle diameter (median diameter (D) of Li Mn ₂ 0 ₄ powder measured using a laser diffraction / scattering particle size distribution analyzer (model number Γ LA-750) manufactured by HOR I BA with water as the dispersion medium. 50)) is at 0.6〃 m.

[0101] The obtained Li Mn ₂ 0 ₄ powder was put in a zirconia sheath and heat-treated at 1 100 ° o for 24 hours to obtain Li L ₀₅ Μη τ. ₉₅ 0 ₄ powder. It was. Zirconyl two apo Lumpur, and using ethanol as a dispersion medium, a _{L i L 05 Mn L 9 5} o 4 powder obtained by wet grinding with a ball mill, and further Drying with an evaporator and dryer A powder having an average particle size of 10 m was obtained. The obtained powder was heat-treated at 700 ° C. for 3 hours in an oxygen atmosphere to obtain amorphous crystal particles of _Li L ₀₅ η τ. _G5 0 ₄ (Comparative Example 4). [0102] (Comparative Example 5)

L i ₂ C0 ₃ powder (Made by Honjo Chemical Co., fine grade, average particle size: 3 im) and Mn 0 ₂ powder (trade name) so that the composition ratio of L i L τΜ η L ₉ 0 ₄

Weighed “Electrolytic Manganese Dioxide Grade FM”, manufactured by Tosohichi Co., Ltd., average particle size: 5 / m) into a plastic cylindrical wide-mouthed jar, and then added zirconia balls and ethanol as a dispersion medium. A slurry was obtained by wet mixing and grinding for 16 hours in a ball mill. The resulting slurry was dried using an evaporator and a dryer, 1 1 00 ° C, 24 hours heat treatment to grain grown L i tau., Was obtained Μ η τ. ₉ 0 ₄ powder. The obtained Li L τΜη!. _G 0 ₄ powder was wet-ground with a ball mill using zirconia pol and ethanol as a dispersion medium, and further dried using an evaporator and a dryer. A powder with a particle size of 1 O im was obtained. The obtained powder was heat-treated in the atmosphere at 650 ° C. for 3 hours to obtain amorphous crystal particles of _Li , _Mni . _{90 4} (Comparative Example 5).

[0103]

1]

[Orientation] 0.1 _g of particles was added to 2 _g of ethanol and dispersed for 30 minutes with an ultrasonic disperser (ultrasonic cleaner) to prepare a dispersion. Spin coating of the dispersion liquid at 2000 rpm on the surface of a 25 mm x 5 Omm glass substrate so that the particles do not overlap as much as possible and the plate surface of the particles is arranged parallel to the surface of the glass substrate Samples for measurement were prepared. Using the XRD diffractometer (model number “RAD—IB”, manufactured by Rigaku Corporation) The XRD diffraction pattern was measured when the line was irradiated. The orientation of the (1 1 1) plane by the Lotgering method using the peaks of the (1 1 1) plane, (31 1) plane, (400) plane, and (331) plane in the measured XRD diffraction pattern The degree was calculated from Equation (2) above. The results are shown in Table 2.

[0105] [Measurement of particle thickness]: Observation using a scanning electron microscope (SEM) (model number “J SM-6390”, manufactured by JEOL Ltd.) with particles randomly arranged on a conductive tape Then, the particles whose plate surface was arranged parallel to the observation direction (ie, particles standing in a vertical state) were selected, and the particle thickness (W) was measured. Table 2 shows the measurement results.

 [Calculation of aspect ratio]: 0.1 g of particles was added to 2 g of ethanol and dispersed for 30 minutes with an ultrasonic dispersing machine (ultrasonic cleaner) to prepare a dispersion. Spin coating the dispersion liquid at 2000 rpm on the surface of a 25mm x 5 Omm glass substrate, the particles are not overlapping as much as possible, and the particle plate surface is arranged parallel to the surface of the glass substrate Samples for measurement were prepared. Scanning electron microscope (SEM)

(Model No. “J SM-6390”, manufactured by JEOL Ltd.) is used to observe the plate surface of the particles in the field of view containing about 5 to 30 particles in the sample for measurement. The length (Y) was measured. Assuming that the longest length (Y) is the particle size of the particle, this particle size (Y) is divided by the particle thickness (W) to calculate the YZWJ value for each particle, and the average value is The aspect ratio of the plate-like crystal grains ”. The results are shown in Table 2. Also, with respect to the aspect ratio of the single crystal particles contained in the plate-like crystal particles, Γχ ”is calculated in the same manner as the above Γ 丫, and“ Z = W

Assuming J, Γχ ζ ”value was calculated. The average value of the calculated “χ ζ” values was defined as “aspect ratio of single crystal grains”. The results are shown in Table 2.

[Production of battery (coin cell)]: Acetylene black and polyvinylidene fluoride (PVDF) were added to each of the plate-like crystal particles of Examples 1 to 12 and the amorphous crystal particles of Comparative Examples 1 to 5. A positive electrode material was prepared by adding and mixing so that the ratio was 50: 2: 3. The prepared positive electrode material 0.02 g was press-molded into a disk shape having a diameter of 2 Omm ø at a pressure of 300 kg Zcm ² to produce a positive electrode. Product A positive electrode was manufactured, and ethylene carbonate (EC) and an electrolyte prepared by dissolving in a mixed organic solvent in an equal volume of oxygenate chill carbonate (DEC) and L i PF ₆ at a concentration of 1 mo I ZL A coin cell was fabricated using a carbon negative electrode and a separator.

[0108] [Measurement of capacity maintenance ratio]: With respect to the manufactured battery (coin cell), the test temperature was set to 45 ° C. (1) Charging up to 4.1 V with constant current and constant voltage of 1 C rate, and (2 ) Cyclic charge / discharge was repeated with a constant current of 1 C rate until discharge to 2.5 V. The capacity retention rate (%) was obtained by dividing the discharge capacity of the battery after the end of 100 cycles of charge / discharge by the discharge capacity of the first battery. The results are shown in Table 2. It can be evaluated that the larger the value of the capacity retention rate (%), the smaller the rate of decrease in the discharge capacity of the battery, and the more excellent the cycle characteristics.

[0109]

:

Industrial applicability

The plate crystal particles of the present invention are useful as a positive electrode active material, and can provide a lithium secondary battery excellent in output characteristics and high-temperature cycle characteristics. The lithium secondary battery of the present invention is excellent in output characteristics and high-temperature cycle characteristics. It is effectively used as a drive battery for hybrid electric vehicles, electrical equipment, communication equipment, etc.

Explanation of symbols

2: crystal plane (1 1 1), 5: calciner, 10, 20, 30, 40, 50, 60: plate crystal particles, 12: single crystal particles, 14: grain boundaries, 15: Sheet-shaped molded body, 22: Setter, 24: Unsintered green molded body, 26: Square plate, 32: Sintered molded body after firing, 34: Mesh, 36: Press member, 65, 75: Positive electrode active material, 85: equiaxed crystal grains, 95: binder part, 1 00: current collector plate (aluminum foil), 1 1 0: positive electrode plate, Wh W _2: the grain thickness, X: a single crystal grains longest length , Y, Υ ₂ : Maximum length of particle, ：: Single crystal particle thickness

Claims

The scope of the claims

 [Claim 1] It is composed of lithium manganate having a spinel structure containing L i and Mn as constituent elements, has an aspect ratio of 1.5 to 20, and a thickness of 1 to 20 m.

 Plate-like crystal grains having a crystal plane (1 1 1) having a degree of orientation of 20% or more as measured by the Lotgering method.

[Claim 2] The plate-like crystal particle according to claim 1, which is a single crystal particle.

 [Claim 3] comprising a plurality of single crystal particles,

 The number of the single crystal particles substantially existing in the thickness direction is one, and a plurality of the single crystal particles are bonded in a state where the crystal planes (1 1 1) are aligned. 2. Plate-like crystal particles according to 1.

[Claim 4] The lithium manganate is represented by the following general formula (1):

The plate-like crystal particle according to any one of to 3.

 (In the above general formula (1), 、 is Li, Fe, Ni, Mg, Zn, AI, Co, Cr, Si, Sn, P, V, Sb, Nb, T one or more elements selected from the group consisting of a, Mo, and W, and two or more substitution elements including Ti, and X represents the number of substitutions of the substitution element M)

[Claim 5] The molar ratio of Li to Mn contained in the lithium manganate is Li /

 The plate-like crystal particle according to any one of claims 1 to 4, which satisfies a relationship of Mn> 0.5.

 [Claim 6] The method for producing plate-like crystal particles according to any one of claims 1 to 5,

A molding step of molding a molding material containing lithium manganate particles to obtain a self-supporting sheet-like shaped body having a thickness of 3 OjUm or less, and the sheet-like shaped body substantially reacts with the sheet-like shaped body A firing step of firing in a state adjacent to the inert layer, or in the state of the sheet-like molded body, A crushing step of crushing and classifying the sheet-like shaped product after firing, and a method for producing plate-like crystal particles.

 7. The method for producing plate-like crystal particles according to claim 6, wherein a firing temperature in the firing step is 6500 to 1250 ° C.

8. The method for producing plate-like crystal particles according to claim 6 or 7, wherein a median diameter of the lithium manganate particles is 1 to 60 · ½ of a thickness of the sheet-like molded body.

 [Claim 9] The method according to any one of claims 6 to 8, wherein the sheet-shaped molded body is fired in a volatilization-suppressed state capable of suppressing volatilization of a specific component contained in the sheet-shaped molded body. A method for producing plate-like crystal particles.

 10. The method for producing plate-like crystal particles according to claim 9, wherein the volatilization suppression state is a state in which the lithium manganate particles coexist with the sheet-like molded body.

 [Claim 11] The pulverizing step is a step of pulverizing and classifying the sheet-like molded body after firing by passing through an opening of a predetermined size. The manufacturing method of the plate-shaped crystal particle as described in a term.

 12. The method for producing plate-like crystal particles according to claim 11, wherein an average opening diameter of the opening is 1. O mm or less.

[Claim 13] The sheet-shaped molded body after firing is pressed by a pressing member, and the mesh having the opening is passed through to crush and classify the sheet-shaped molded body after firing. 1. A method for producing plate-like crystal particles according to any one of 2 above.

 [Claim 14] A lithium secondary battery obtained by using the plate-like crystal particles according to any one of claims 1 to 5 as a positive electrode active material.