JP2004087487A - Positive electrode active material and non-aqueous electrolyte secondary battery containing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte secondary battery having high capacity at low cost. <P>SOLUTION: As for a non-aqueous electrolyte secondary battery comprising a negative electrode having a material or metallic lithium at least capable of absorbing and releasing lithium ion as a negative electrode activator, a positive electrode, and an electrolyte. As a positive electrode activator, an oxide, containing nickel and manganese element having a twinning in the primary particle and showing a superlattice structure of [ √3 x √3 ] R30° assuming R3, is used. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a positive electrode active material, particularly to a positive electrode active material used for a non-aqueous electrolyte secondary battery. Furthermore, the present invention relates to a high-capacity and inexpensive nonaqueous electrolyte secondary battery having a positive electrode containing a specific positive electrode active material.

In recent years, with the spread of cordless and portable AV devices, personal computers, and the like, there is an increasing demand for small, lightweight, and high-energy-density batteries as power sources for driving them. In particular, since a lithium secondary battery is a battery having a high energy density, it is expected as a next-generation main battery, and its potential market scale is large. Currently in most of the lithium secondary battery which is commercially available, although LiCoO ₂ is used with a high voltage of 4V as the positive electrode active material, since Co is expensive, a variety of positive electrode active material in place of LiCoO ₂ Has been studied. Among them, lithium-containing transition metal oxides have been energetically studied, LiNi _a Co _b O ₂ (a + b ≒ 1) is promising, and LiMn ₂ O ₄ having a spinel structure has been commercialized.

In addition, studies on nickel and manganese have been actively conducted as substitutes for expensive cobalt. For example, LiNiO ₂ having a layered structure is expected to exhibit a large discharge capacity. Since the crystal structure changes, the degree of deterioration is large. Therefore, it has been proposed to add an element capable of stabilizing the crystal structure during charge and discharge and suppressing deterioration to LiNiO ₂ . Specifically, elements such as cobalt, manganese, titanium, and aluminum are mentioned. Here, with respect to the composition of the composite oxide of Ni and Mn used as a positive electrode active material for a lithium secondary battery, those shown in Table 1 are cited as conventional techniques.

US Patent Publication and Japanese Patent composite oxide described in the Application Publication as described above, in order to improve the electrochemical characteristics such as cycle characteristics of all LiNiO _2, while leaving the characteristics of LiNiO _2, LiNiO ₂ Obtained by adding a trace amount of element. Therefore, the amount of Ni contained in the active material obtained after the addition is always higher than the amount of Mn, and a ratio of Ni: Mn = 0.8: 0.2 is preferable. Also, as the ratio with the largest Mn content, Ni: Mn = 0.55: 0.45 is disclosed. However, in these conventional techniques, LiNiO ₂ is separated from LiMnO ₂ , so that it is difficult to obtain a composite oxide having a single-phase crystal structure. This is considered to be because it is difficult to form a homogeneous oxide due to the properties of nickel and manganese oxidized in separate regions during coprecipitation.

Accordingly, research and development of LiNiO ₂ and LiMnO ₂ , which are high-capacity and low-cost cathode active materials having a similar layer structure while having a similar layer structure, have been carried out as alternative materials to LiCoO ₂ having a high voltage of 4 V which is currently commercially available. I have. However, the shape of the discharge curve of LiNiO ₂ is not flat and its cycle life is short. Furthermore, heat resistance is low, and there is a major problem in using LiNiO ₂ as a substitute for LiCoO ₂ . Attempts have been made to improve LiNiO ₂ by adding various elements, but the improvement is still insufficient. In addition, since LiMnO ₂ can obtain only a voltage of 3 V, research has begun on LiMn ₂ O ₄ having no layer structure and a low-capacity spinel structure. That is, a positive electrode active material having a voltage of 4 V equivalent to that of LiCoO ₂ , showing a flat discharge curve, and having a higher capacity and a lower price than LiCoO ₂ has been demanded.

On the other hand, Japanese Patent Application No. 2000-227858 (Japanese Patent Application Laid-Open No. 2002-42813) does not describe a technique of improving the characteristics of LiNiO ₂ and the characteristics of LiMnO ₂ by adding a new additive element, A positive electrode active material made of a nickel-manganese composite oxide that exhibits a new function by uniformly dispersing a nickel compound and a manganese compound at an atomic level to form a solid solution has been proposed. As described above, in the prior art, although many additional elements have been proposed, it has not been clarified technically which element is specifically preferable, whereas nickel and manganese have been proposed. A positive electrode active material capable of exhibiting a new function when combined at substantially the same ratio is provided.
Next, with regard to the crystal structure of the composite oxide and the morphology of the particles, there are the following conventional techniques.

As described above, regarding the particles of the composite oxide constituting the positive electrode active material, the particle size, pores, specific surface area, primary particles, secondary particles and their aggregates and the like are described, but with the focus of the present invention No detailed structure and crystal structure in the primary particles are disclosed. That is, no detailed study has been made on the structure and crystal structure of the primary particles of the composite oxide constituting the positive electrode active material.

Therefore, the present invention controls the composition of the nickel and manganese elements to form a solid solution, controls the crystal structure and the superlattice structure, and simultaneously controls the structure arrangement in the primary particles, thereby achieving high-rate rate characteristics and cycle characteristics. An object of the present invention is to provide an active material composed of a lithium-containing composite oxide having a long life.

The present invention relates to a positive electrode active material comprising a lithium-containing composite oxide containing at least a nickel element and a manganese element, comprising primary particles of the composite oxide having a twinning portion.
Preferably, the composite oxide has a layered crystal structure, and the arrangement of oxygen is a cubic close-packed structure.
Preferably, the composite oxide has a defective portion or a strained portion.

The composite oxide preferably has a superlattice arrangement of [√3 × √3] R30 ° assuming R3m.
It is preferable that the composite oxide contains nickel and manganese at substantially the same ratio.
The composite oxide preferably satisfies the relationship of integral intensity ratio (003) / (104) ≦ 1.2 at an X-ray diffraction peak assigned assuming R3m.
It is preferable that the composite oxide has extra spots or streaks in substantially all patterns in electron beam diffraction assuming R3m.

Preferably, the primary particles have at least one shape of a sphere and a rectangular parallelepiped.
It is preferable that the primary particles have a particle size of 0.1 to 2 μm, and further include secondary particles of the composite oxide having a particle size of 2 to 20 μm.
The composite oxide has the formula (1):
Li _{1 + y} [M _X (NiδMnγ) _1-X ] O ₂
(Where, -0.05 <y <0.05, M is one or more elements other than nickel and manganese, -0.1 ≦ x ≦ 0.3, δ = 0.5 ± 0.1, γ = 0.5 ± 0.1, and when M is cobalt, -0.1 ≦ x ≦ 0.5 is satisfied).

Preferably, M is trivalent in the oxidized state.
Further, it is preferable that M is at least one selected from the group consisting of aluminum and cobalt.
Further, it is preferable that M is at least one selected from the group consisting of magnesium, calcium, strontium, zirconium, yttrium, and ytterbium magnesium.
The present invention also provides a non-aqueous electrolyte comprising a negative electrode containing a material capable of inserting and extracting lithium and / or metallic lithium as a negative electrode active material, a positive electrode containing the positive electrode active material, and an electrolyte. Next battery.

According to the present invention, it is possible to provide a nonaqueous electrolyte secondary battery in which an inexpensive nickel-manganese composite oxide can be effectively used as a positive electrode active material, and which has high capacity, excellent rate characteristics, and excellent cycle life.

The present invention relates to a positive electrode active material comprising a lithium-containing composite oxide containing at least a nickel element and a manganese element, comprising primary particles of the composite oxide having a twining portion. Here, the twinning portion refers to an interface between a tissue and a domain.
In the present invention, the composite oxide has a layered crystal structure, the arrangement of oxygen is a cubic close-packed structure, and the composite oxide has a defect portion or a disordered portion. It is characterized by having. Note that in this specification, the positive electrode active material may be simply referred to as a material.

The present inventors have enthusiastically studied and developed a series of lithium-containing composite oxides containing nickel and manganese elements, and have found one that exhibits excellent functions as a positive electrode active material for a non-aqueous electrolyte secondary battery. . Further, based on these conventional techniques, it has been found that by controlling the morphology of the particles in addition to the control of the composition and the crystal structure, more excellent functions appear, and the present invention has been completed.
As for the composition, it is assumed that nickel and manganese are simultaneously contained, but it is important that the ratio is 1: 1 (the same ratio). In addition, these elements interfere with each other in the state of electrons in the oxide and exhibit a superlattice behavior. It is considered important that nickel and manganese elements are uniformly dispersed at the nano level in the crystal. From the viewpoint of the crystal structure, it has a layer structure, and the oxygen arrangement is a cubic close-packed structure having ABCABC stacking. The X-ray diffraction pattern is characterized in that the integrated intensity ratio of the X-ray diffraction pattern assigned by R3m satisfies (003) / (104) ≦ 1.2 irrespective of the layer structure.
As for the morphology, a more excellent active material is obtained by stepping further one step and controlling the morphology to the preferred morphology up to the structure and the grain boundaries within the primary particles.

Furthermore, the present inventors have also found that various additional functions can be further added by dissolving a different element in a solid solution. For example, doping with an aluminum element can improve the heat resistance of the crystal grains, slightly increase the potential, and flatten the shape of the charge / discharge curve. It is possible to improve the polarization characteristics by doping with cobalt element. Further, the electron conductivity of the crystal particles can be increased by doping with magnesium. Further, by changing the kind of the different element, the amount of gas generated by the reaction between the surface of the crystal particles and the electrolyte at a high temperature can be reduced or conversely increased.
In the following, the third element, cobalt, aluminum, and magnesium may be described as representatives. However, it is easily assumed that other functions are added, and the third element can be implemented.

(1) Particle Morphology and Crystal Structure of the Active Material of the Present Invention Hereinafter, the present invention is represented by LiNi _1/2 Mn _1/2 O ₂ and LiNi _1/3 Mn _1/3 Co _1/3 O _2. explain.
1 and 2 show TEM (transmission electron microscope) photographs of the lithium-containing composite oxide of the present invention. FIG. 1 is a TEM photograph of LiNi _1/2 Mn _1/2 O ₂ , and FIG. 2 is a TEM photograph of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ . From these photographs, it can be seen that the primary particle diameter of each composite oxide is 100 nm to 500 nm and 200 nm to 1000 nm. Although only representative portions are shown in the photograph, the particle diameter was in this range in almost all of the observed portions. Therefore, it is considered that the actual powder is composed of primary particles of 100 nm to 2000 nm.

Next, the structure in the primary particles will be described. FIG. 3 is a TEM photograph of typical primary particles of LiNi _1/2 Mn _1/2 O ₂ . As shown in this photograph, the particles of the composite oxide according to the present invention have a spherical shape (a) or a rectangular parallelepiped shape (b). FIG. 4 is a TEM photograph showing the structure of the structure in the primary particles of LiNi _1/2 Mn _1/2 O ₂ . From this photograph, it can be seen that a twining portion exists in the particles. The twinning portion means an interface between a grain and a domain in a primary particle.
As described above, the composite oxide constituting the positive electrode active material according to the present invention has the following features. 1) Most of the primary particles are spherical or rectangular parallelepipeds, and 2) Twining portions exist in the primary particles. By satisfying the above two points, an excellent effect is achieved.

In the currently used positive electrode active material having a layer structure such as LiCoO ₂ , a charge / discharge reaction is established by insertion / desorption of lithium ions. However, lithium ions are directed from a direction perpendicular to the layer surface, that is, from the c-axis direction. It is thought to come and go. Therefore, in such a material in the form of hexagonal prism particles, it is considered that lithium ions enter and exit only from a direction perpendicular to the layer surface, not from the entire surface of the particles. Further, with respect to such conventional materials, no study has been made on the direction of the structure in the particles, and there is no description in the prior art literature.
Although the positive electrode active material according to the present invention also has the same layer structure, lithium ions can enter and exit from all directions of the particles by satisfying the above 1) or 2), preferably, both. As a result, the polarization resistance relating to the mass transfer of lithium ions is greatly reduced, and as a result, an active material having excellent rate characteristics can be realized.

FIG. 5 is a TEM photograph showing the morphology of the structure in the primary particles of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ . The same particle morphology as LiNi _1/2 Mn _1/2 O ₂ was observed (a), and it was found that many twinning portions were observed (b).
FIG. 6 is a TEM photograph showing the oxygen arrangement of LiNi _1/2 Mn _1/2 O ₂ . It can be seen that the white portion in the frame in FIG. 6 is oxygen, and ABCABC is cubic densely packed in the layer direction. FIG. 7 is a TEM photograph showing the oxygen arrangement of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , and also shows that oxygen is arranged like ABCABC.

Next, FIGS. 8A and 8B are TEM photographs showing lattice defects of LiNi _1/2 Mn _1/2 O ₂ . (B) is an enlargement of (a). As can be seen from FIG. 8B, the tissue is the same in the upper right region and the lower left region, but a lattice defect is observed in the portion indicated by the arrow. FIG. 9 is a TEM photograph showing a lattice disorder included in LiNi _1/2 Mn _1/2 O ₂ .
These defects and distortions are important for obtaining a good active material according to the present invention. In the active material having these defects and strains, the lattice repeatedly expands and contracts with charge and discharge. The stress due to the expansion and contraction is one of the causes of breaking the lattice and shortening the cycle life. In the present invention, it is considered that the stress caused by the expansion and contraction of the lattice can be reduced by these defects and strains, and as a result, the cycle life is improved.

Next, the superlattice arrangement in the positive electrode active material according to the present invention will be described. FIG. 10 is an electron diffraction photograph of LiNi _1/2 Mn _1/2 O ₂ . FIG. 10 shows a part of the electron beam diffraction, but extra spots (a) or streaks (b) are observed in almost all electron beam diffraction patterns assuming R3m. This is very similar to that observed in the electron diffraction pattern of Li [Li _1/3 Mn _2/3 ] O ₂ assuming C2 / m. In addition, the strength of these extra spots or streaks differs depending on the particles, and further, it is considered that the strength varies depending on the above-mentioned twinning portion, the degree of the defect or the distortion, and the like.

These extra spots are considered to be due to the super lattice arrangement of [√3 × √3] R30 °. 11 and 12 show photographs of images analyzed using a Fourier transform technique in order to find superlattice regularity in a short range from TEM images. 11A and 12A are photographs showing the original TEM images, and FIGS. 11 and 12B are photographs of the converted TEM images. The images of FIGS. 11 and 12 (b) are obtained by subjecting the images of FIGS. 11 and 12 (a) to Fourier transform once to obtain an image excluding only the extra spots except for the basic spots, and then performing the Fourier transform again. It is a photograph of the image obtained by performing the conversion. Therefore, what is shown in the images of FIGS. 11 and 12 (b) is a short range, but shows only the regularity due to the superlattice arrangement. As is apparent from FIGS. 11 and 12B, an image showing periodicity is observed.

In order to obtain the above particle morphology and crystal structure, it is important to contain nickel and manganese at a ratio of 1: 1. LiNi _1/2 Mn _1/2 O ₂ and LiNi _1/3 Mn _1/3 Co _1/3 O ₂ are shown as typical examples, but the amount of Co added to LiNi _1/2 Mn _1/2 O ₂ The same tendency is observed in a range where satisfies 0 ≦ Co / (Ni + Mn) ≦ 2. Further, it is preferable to satisfy Co / (Ni + Mn) ≦ 1. Further preferably, formula (2):
LiCo _{x / 3} Ni _{((3-x) / 6)} Mn _{((3-x) / 6)} O ₂ (2)
(In the formula, 0 ≦ x ≦ 1), the above feature strongly appeared.

Next, FIG. 13B shows the X-ray diffraction pattern of LiNi _1/2 Mn _1/2 O ₂ . In the Miller index assuming a hexagonal crystal, the integrated intensity of the characteristic peaks of (104) and (003) is carefully measured, and the integrated intensity ratio is calculated for each value to obtain (003) / (104) = 0.847. Become. FIG. 13A also shows the case of LiNiO ₂ for comparison ((003) / (104) = 1.34). Generally, in the X-ray diffraction patterns of LiCoO ₂ and LiNiO ₂ having a layer structure, the peak intensity of the (003) plane is the strongest. Therefore, the value of (003) / (104) is always 1 or more.
The integrated intensity is indicated by the peak area, not the peak height. In the X-ray diffraction pattern shown in FIG. 13 (b), the integrated intensity of the (104) plane is the highest, and according to the knowledge obtained so far, transition metals fall into lithium sites in materials having such peaks. It was determined to be an undesired active material with a small salt volume and a large polarization, containing a salt-type structure.

On the other hand, in the X-ray diffraction pattern of LiNi _1/2 Mn _1/2 O ₂ in the present invention, (003) / (104) shows a value of 1 or less. The composition of the positive electrode active material can be said to be similar to the composition of the conventional material, but can be said to be completely different. FIG. 14 shows the peak intensities of FIGS. 13 (a) and (b).
FIG. 15 shows an X-ray diffraction pattern of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ . The layer structure was strongly observed by the addition of Co, and showed (003) / (104) = 1.15, which is a value of 1 or more. FIG. 16 shows the Miller index assuming R3m, the d value obtained from measurement or calculation, and the intensity ratio.
The present inventors have theoretically calculated that it is important to control the nickel element to be divalent, the manganese element to be tetravalent, and the cobalt element to be trivalent in these series of materials. It has been found from the analysis results by principle calculation) and X-ray absorption fine structure (XAFS) measurement, and it has been confirmed that these analysis results also apply to the active material of the present invention.

(2) Electrochemical Characteristics of Positive Electrode Active Material According to the Present Invention LiCoO _{2, which} is currently most widely used as a positive electrode active material for a lithium secondary battery, has a charge capacity of 140 to 145 mAh / g at 4.3 V with respect to lithium metal. Has electric capacity. Even when used in an actual battery using a carbon material for the negative electrode, the utilization rate is almost the same as this value. Therefore, if a capacity equal to or higher than that in this potential region cannot be secured, LiCoO ₂ becomes a material lacking in attractiveness.
The electrochemical characteristics of the positive electrode active material according to the present invention having the particle morphology and crystal structure described in (1) above were evaluated by manufacturing a coin-type battery. A coin-type battery was manufactured according to the following procedure. A positive electrode active material, acetylene black as a conductive material, and polyvinylidene fluoride resin (hereinafter, referred to as “PVDF”) as a binder were mixed at a weight ratio of 80:10:10 to obtain a sheet-like molded product. Then, this molded product was punched into a disk shape and dried at 80 ° C. for about 15 hours in a vacuum to obtain a positive electrode. In addition, a sheet-shaped lithium metal was punched into a disk to form a negative electrode. A microporous polyethylene membrane was used as the separator, and the electrolytic solution was prepared by dissolving 1 mol of LiPF ₆ in a 1: 3 (volume ratio) mixed solvent of EC (ethylene carbonate) and EMC (ethyl methyl carbonate). did. Using these, a coin type battery of 2016 size (diameter 20 mm, thickness 1.6 mm) was produced by a conventional method.

FIG. 17 shows a charge / discharge curve of LiNi _1/2 Mn _1/2 O ₂ when the lithium metal was charged at 4.3 V (constant voltage / constant current charging). FIG. 18 shows the discharge capacity of LiNi _1/2 Mn _1/2 O ₂ with respect to the number of charge / discharge cycles. From FIG. 18, it can be seen that a charge / discharge capacity of about 150 mAh / g can be obtained, and a single-stage discharge voltage can be obtained in the 4V class. Furthermore, in the case of LiCoO ₂ and LiNiO ₂ , charging was performed up to 4.6 V, which is considered to be substantially impossible in consideration of the stability of the crystal structure and the reactivity with the electrolytic solution. FIG. 19 shows a charge / discharge curve when charging was performed up to 4.6V. FIG. 20 shows the discharge capacity with respect to the number of charge / discharge cycles. FIG. 20 shows that a charge / discharge capacity of about 195 mAh / g can be obtained, and the cycle life is extremely good.
Similarly, for LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , charge / discharge curves and cycle life at 4.6 V charging are shown in FIGS. 21 and 22, respectively. From the figure, it can be seen that a charge / discharge capacity of about 200 mAh / g can be obtained and the cycle life is extremely good.
As described above, the present invention can provide an active material having higher capacity and superior cycle life as compared with conventional materials.

(3) Method for Producing Positive Electrode Active Material According to the Present Invention Next, a specific method for producing the positive electrode active material according to the present invention will be described. Here, a typical production method will be described. However, as described above, since the particle morphology is important in the present invention, if the particle morphology can be realized, the method is not limited to the method described below. Absent.
In the method for producing a positive electrode active material according to the present invention, an aqueous solution containing two or more transition metal salts or two or more aqueous solutions of different transition metal salts and an alkaline solution are simultaneously charged into a reaction vessel, and a reducing agent coexists. Step (a) of obtaining a hydroxide as a precursor by coprecipitation while allowing or passing an inert gas through, and drying the precursor at 300 to 500 ° C. to obtain a dried precursor (a) And baking and cooling the mixture of the precursor and the lithium compound to obtain a lithium-containing transition metal oxide (c).

First, regarding the step (a) by the coprecipitation method, the coprecipitation method is a method of obtaining a composite hydroxide mainly by simultaneously precipitating a plurality of elements by using a neutralization reaction in an aqueous solution. Taking nickel, manganese and cobalt as an example, manganese is very easily oxidized, and even a small amount of dissolved oxygen present in an aqueous solution is sufficiently oxidized to contain trivalent manganese ions. Therefore, the solid solution at the atomic level becomes incomplete. The point in this step is that nickel, manganese and cobalt elements are present without separation in the layered hydroxide having the same structure to generate double hydroxide or toy ripple hydroxide. Conventionally, in order to suppress such a situation, a method of removing dissolved oxygen by bubbling an inert gas such as nitrogen or argon into the aqueous solution, or adding a reducing agent such as hydrazine in the aqueous solution in advance. Has been taken. This is also important in the present invention.

Further, in the present invention, a sulfate is used as the aqueous solution containing the transition metal salt. Use of nitrates is not preferred because they can oxidize manganese in the presence of nickel ions. The present inventors prepared a mixed solution of a 1.2 mol / liter aqueous solution of NiSO _{4, an} aqueous solution of MnSO _{4 and an} aqueous solution of CoSO ₄ , a 4.8 mol / liter aqueous solution of NaOH, and a 4.8 mol / liter NH ₃ solution. , At a rate of 0.5 ml / min. Further, when the ratio of nickel and manganese is 1: 1 as in the composition of the positive electrode active material according to the present invention, the composition ratio is preferably strictly 1: 1.
FIG. 23 shows, for comparison, an X-ray diffraction pattern of a material having a composition ratio of nickel and manganese deviating from 1: 1. FIG. 23A shows the case where Ni: Mn = 1.02: 0.98, and FIG. 23B shows the case where Ni: Mn = 1.005: 0.995. FIG. 24 shows a charge / discharge curve when these materials were used. From FIG. 24, it can be seen that those having Ni: Mn = 1.005: 0.995 are superior to those having Ni: Mn = 1.02: 0.98 in initial capacity and cycle life. At this time, the X-ray diffraction patterns are almost identical and indistinguishable. Conventionally, the quality of the material has been discussed only with the composition and the X-ray diffraction pattern. However, it is understood that it is insufficient to evaluate the material only with these. Even when cobalt is added, it is preferable that the ratio of Ni: Mn be exactly 1: 1.

Next, the hydroxide as the precursor obtained in the step (A) is heated, calcined and dried to obtain a dried precursor. The heating temperature at this time is preferably 300 to 500 ° C., since the contained water is dehydrated by overheating, and is a temperature at which the dehydration is almost completed and the weight becomes constant. If the temperature exceeds 500 ° C., the crystallinity of the precursor is excessively increased, and the reactivity with lithium decreases, which is not preferable. The heating time is influenced by the filling amount of the powdery precursor to be dried and the like, but may be 1 to 10 hours from the viewpoint of completing the dehydration.

Next, in the step (c), the dried precursor and the lithium compound are mixed, and the obtained mixture is fired. As the lithium compound at this time, it is preferable to use lithium carbonate and / or lithium hydroxide. Especially, it is preferable to use lithium hydroxide. In the case of using lithium carbonate, it is possible to obtain a positive electrode active material composed of a target single-phase lithium-containing composite oxide. However, lithium hydroxide is used in terms of particle shape control and crystallinity. Is more advantageous. The nickel manganese cobalt hydroxide or oxide and lithium hydroxide are thoroughly mixed in a dry manner.

At this time, the lithium hydroxide and the nickel, manganese, and cobalt composite oxides may be mixed according to the composition of the cathode active material to be obtained, but the atomic ratio of Li, Ni, Mn, and Co is Li / ( Ideally, they are mixed so as to satisfy (Ni + Mn + Co) = 1. However, the atomic ratio can be slightly increased or decreased for controlling physical properties. For example, when the sintering temperature is high, when the primary particles after sintering are large, or when it is desired to further stabilize the crystal, lithium is mixed a little more. In this case, an increase or decrease of about 3% is preferable.

The atmosphere for firing the mixture of the dry precursor and the lithium compound may be an oxidizing atmosphere. Therefore, a normal atmosphere may be used. The hydroxide or oxide obtained by co-precipitation and lithium hydroxide are dry-mixed, and the oxidation reaction of the preferred elements such as nickel, manganese and cobalt occurs at the same time. It is preferred to fire at a temperature of ~ 1200 ° C.
Here, FIG. 25 shows the charging / discharging behavior depending on the firing temperature of LiNi _1/2 Mn _1/2 O ₂ . FIG. 25A is an X-ray diffraction pattern when fired at 750 ° C., and FIG. 25B is an X-ray diffraction pattern when fired at 1000 ° C. FIG. 26A shows a charge / discharge curve when firing at 750 ° C., and FIG. 26B shows a charge / discharge curve when firing at 1000 ° C. From FIG. 25 and FIG. 26, it is understood that firing at 1000 ° C. is more preferable for both the electric capacity and the cycle life. The firing time is preferably from 1 to 10 hours after reaching the set temperature.

In the method for producing a positive electrode active material according to the present invention, unprecedented control is performed during firing and cooling. As a basic concept, rapid heating and rapid cooling are performed in the present invention. It is preferable to perform rapid heating at a heating rate of 7 ° C./min or more and rapid cooling at a cooling rate of 5 ° C./min or more. Thereby, the structure in the obtained primary particles can be controlled as described above. In addition, when quenching is performed, it is considered that oxygen is likely to be lost. Therefore, it is preferable to perform heat treatment again at 700 to 750 ° C. in air for 1 to 5 hours.
To summarize the above, based on the conventional coprecipitation method for synthesizing the material of the present invention, mainly, 1) removal of dissolved oxygen, removal of nitrate ions, and thorough prevention of oxidation of Mn ions by adding a reducing agent 2) Increase the accuracy of the 1: 1 ratio of nickel and manganese elements, and 3) Perform rapid heating and rapid cooling in the firing step.

Note that the positive electrode active material according to the present invention substantially contains a transition metal such as nickel, manganese, and cobalt, and a new foreign element (additional element or dopant) is added to the crystal grains constituting the positive electrode active material. It is easy to predict that the added value will be obtained.
Therefore, the cathode active material of the present invention may contain other new different elements. In particular, since the crystal particles of the positive electrode active material comprising the lithium-containing transition metal oxide constituting the positive electrode active material are granular, it is practical to include such an additional element near the surface thereof. All of the positive electrode active materials having an additional function by such an additional element are also included in the present invention.

Examples of such different elements include aluminum, magnesium, calcium, strontium, zirconium, yttrium and ytterbium. By doping aluminum, the potential of the positive electrode active material is slightly increased, and at the same time, the thermal stability is improved. In this case, the precursor obtained in the above steps (a) and (a) is mixed with lithium hydroxide and calcined. At this time, an appropriate amount of an aluminum source such as aluminum hydroxide is simultaneously mixed. As a result, aluminum is not uniformly doped throughout the eutectic oxide particles, but the concentration of aluminum doped only in the vicinity of the surface is increased.
This can be confirmed by characteristic X-ray analysis of the crystal particles. Therefore, according to the doping, the parent of the crystal particles constituting the positive electrode active material maintains the effect of the crystal structure of the transition metal element, and the above-described effect can be added by changing only the surface state of the crystal particles.

効果 Because the effect of the crystal structure decreases as the amount of addition of aluminum or the like increases, it is more effective to make the surface slightly unevenly distributed. Strontium, zirconium, yttrium, calcium, ytterbium, and the like can also provide the effect of improving heat resistance. Further, by adding magnesium, the electron conductivity of the positive electrode active material can be improved by about one to two digits. In this case as well, magnesium hydroxide may be similarly mixed with the precursor and lithium hydroxide and fired. Sintering may be performed by the method described above. When the positive electrode active material thus obtained is used in a battery, the electron conductivity is extremely high, so that the capacity can be increased by reducing the amount of the conductive agent. It is effective that the addition amount of these different elements is in the range of 0.05 to 20 atomic% of the total of the three transition metals. If the content is less than 0.05 atomic%, a sufficient effect cannot be obtained, and if the content is more than 20 atomic%, a problem that the capacity is reduced occurs.

(4) Nonaqueous Electrolyte Secondary Battery Hereinafter, other constituent materials that can be used when producing a nonaqueous electrolyte (lithium) secondary battery using the positive electrode active material of the present invention will be described.
The conductive agent in the positive electrode mixture used for producing the positive electrode in the present invention is not particularly limited as long as it is an electron conductive material that does not cause a chemical change in the configured battery. For example, graphites such as natural graphite (such as flake graphite) and artificial graphite, carbon blacks such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black, and conductive materials such as carbon fiber and metal fiber. Conductive fibers, metal powders such as carbon fluoride, copper, nickel, aluminum and silver, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and organic materials such as polyphenylene derivatives Conductive materials and the like can be given. These can be used singly or arbitrarily in combination as long as the effects of the present invention are not impaired. Among these, artificial graphite, acetylene black and nickel powder are particularly preferred. The amount of the conductive agent is not particularly limited, but is preferably 1 to 50% by weight, and particularly preferably 1 to 30% by weight. For carbon and graphite, 2 to 15% by weight is particularly preferred.

A preferred binder in the positive electrode mixture of the present invention is a polymer having a decomposition temperature of 300 ° C or higher. For example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene- Perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE resin), polychlorotri Fluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer ( CTFE), vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene copolymer and vinylidene fluoride - perfluoromethylvinylether - and the like tetrafluoroethylene copolymer. These can be used singly or arbitrarily in combination as long as the effects of the present invention are not impaired.
Particularly, among these, polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) are most preferred.

The current collector of the positive electrode is not particularly limited as long as it is an electronic conductor that does not cause a chemical change in the configured battery. Examples of the material constituting the current collector include stainless steel, nickel, aluminum, titanium, various alloys, carbon, and the like, and a composite obtained by treating the surface of aluminum or stainless steel with carbon, nickel, titanium, or silver. Can also be used.
Particularly, aluminum or an aluminum alloy is preferable. The surface of these materials can be oxidized. Further, the surface of the current collector may be made uneven by surface treatment. The shape may be that employed in the field of batteries, for example, foil, film, sheet, net, punched, lath, porous, foam, fiber group, nonwoven fabric, and the like. . The thickness is not particularly limited, but a thickness of 1 to 500 μm is preferably used.

The negative electrode material used in the present invention may be any compound capable of inserting and extracting lithium ions, such as lithium, a lithium alloy, an alloy, an intermetallic compound, carbon, an organic compound, an inorganic compound, a metal complex, and an organic polymer compound. . These can be used alone or in any combination as long as the effects of the present invention are not impaired.
Examples of the lithium alloy include a Li-Al alloy, a Li-Al-Mn alloy, a Li-Al-Mg alloy, a Li-Al-Sn alloy, a Li-Al-In alloy, and a Li-Al-Cd alloy. , Li-Al-Te alloys, Li-Ga alloys, Li-Cd alloys, Li-In alloys, Li-Pb alloys, Li-Bi alloys, and Li-Mg alloys. In this case, the content of lithium is preferably 10% by weight or more.
Examples of the alloy and the intermetallic compound include a compound of a transition metal and silicon, a compound of a transition metal and tin, and a compound of nickel and silicon is particularly preferable.

Examples of carbonaceous materials include coke, pyrolytic carbons, natural graphite, artificial graphite, mesocarbon microbeads, graphitized mesophase spherules, vapor-grown carbon, glassy carbons, carbon fibers (polyacrylonitrile, pitch, Cellulose-based, vapor-grown carbon-based), amorphous carbon, and organically calcined carbon. These may be used alone or in any combination as long as the effects of the present invention are not impaired. Above all, graphite materials such as graphitized mesophase microspheres, natural graphite and artificial graphite are preferred.
The carbonaceous material may contain different compounds such as O, B, P, N, S, SiC and B4C, in addition to carbon. The content is preferably from 0 to 10% by weight.

Examples of the inorganic compound include a tin compound and a silicon compound, and examples of the inorganic oxide include a titanium oxide, a tungsten oxide, a molybdenum oxide, a niobium oxide, a vanadium oxide, and an iron oxide. .
Examples of the inorganic chalcogenide include, for example, iron sulfide, molybdenum sulfide, and titanium sulfide.
Examples of the organic polymer compound include polymer compounds such as polythiophene and polyacetylene, and examples of the nitride include cobalt nitride, copper nitride, nickel nitride, iron nitride, and manganese nitride.
These negative electrode materials may be used in combination, for example, a combination of carbon and an alloy or a combination of carbon and an inorganic compound.

The average particle size of the carbon material used in the present invention is preferably 0.1 to 60 μm. More preferably, it is 0.5 to 30 μm. The specific surface area is preferably from 1 to 10 m2 / g. In terms of crystal structure, graphite having a carbon hexagonal plane interval (d002) of 3.35 to 3.40 ° and a crystallite size (LC) in the c-axis direction of 100 ° or more is preferable.
In the present invention, since the positive electrode active material contains Li, a negative electrode material (such as carbon) containing no Li can be used. When a small amount of Li (about 0.01 to 10 parts by weight with respect to 100 parts by weight of the negative electrode material) is added to such a negative electrode material that does not contain Li, some of the Li reacts with the electrolyte or the like. Even if it becomes inactive, it can be replenished with Li contained in the negative electrode material, which is preferable.

As described above, in order to include Li in the negative electrode material, for example, a heated and melted lithium metal is applied on a current collector to which the negative electrode material has been pressed to impregnate the negative electrode material with Li, or the electrode Lithium metal may be adhered to the inside by pressure bonding or the like, and Li may be doped into the negative electrode material electrochemically in the electrolytic solution.
Similar to the conductive agent in the positive electrode mixture, the conductive agent in the negative electrode mixture is not particularly limited as long as it is an electron conductive material that does not cause a chemical change in the configured battery. When a carbonaceous material is used as the negative electrode material, the carbonaceous material itself has electronic conductivity, and thus may or may not contain a conductive agent.

(4) The binder in the negative electrode mixture may be either a thermoplastic resin or a thermosetting resin, but a preferred binder is a polymer having a decomposition temperature of 300 ° C. or higher. For example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE resin), polychlorotrifluoroethylene (PCTFE), fluorine Vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride Hexafluoropropylene - tetrafluoroethylene copolymer and vinylidene fluoride - perfluoromethylvinylether - may be mentioned, such as tetrafluoroethylene copolymer. More preferred are styrene butadiene rubber and polyvinylidene fluoride. Of these, styrene butadiene rubber is most preferred.

The current collector of the negative electrode is not particularly limited as long as it is an electronic conductor that does not cause a chemical change in the configured battery. As a material constituting the current collector, for example, in addition to stainless steel, nickel, copper, titanium, and carbon, a material obtained by treating the surface of copper or stainless steel with carbon, nickel, titanium, or silver, an Al-Cd alloy, or the like is used. Used. Particularly, copper or a copper alloy is preferable. The surface of these materials may be oxidized. Further, the surface of the current collector may be made uneven by surface treatment.
As the shape of the positive electrode, for example, a foil, a film, a sheet, a net, a punched material, a lath body, a porous body, a foam, a molded body of a fiber group, and the like are used as in the case of the positive electrode. The thickness is not particularly limited, but a thickness of 1 to 500 μm is preferably used.

As the electrode mixture, a filler, a dispersant, an ionic conductive agent, a pressure enhancer, and other various additives can be used in addition to the conductive agent and the binder. As the filler, any fibrous material that does not cause a chemical change in the configured battery can be used. Usually, fibers such as olefin polymers such as polypropylene and polyethylene, glass, and carbon are used. The amount of the filler added is not particularly limited, but is preferably 0 to 30% by weight.
The positive electrode and the negative electrode in the present invention are introduced for the purpose of improving the adhesion between the current collector and the mixture layer, the conductivity, the cycle characteristics, and the charge / discharge efficiency, in addition to the mixture layer containing the positive electrode active material or the negative electrode material. A protective layer introduced for the purpose of mechanical protection or chemical protection of the undercoat layer or the mixture layer. The undercoat layer and the protective layer can include a binder, conductive agent particles, and particles having no conductivity.

As the separator, an insulating microporous thin film having a high ion permeability, a predetermined mechanical strength, and an insulating property is used. Further, it preferably has a function of closing holes at 80 ° C. or higher to increase resistance. Sheets or non-woven fabrics made of olefin-based polymers such as polypropylene and polyethylene alone or in combination or glass fibers are used because of their organic solvent resistance and hydrophobicity.
The pore size of the separator is desirably in a range that does not allow the active material, the binder, the conductive agent, and the like detached from the electrode sheet to permeate, and for example, desirably 0.1 to 1 μm. Generally, the thickness of the separator is preferably 10 to 300 μm. The porosity is determined according to the electron and ion permeability, the material and the film pressure, but is generally preferably 30 to 80%. Further, the use of a flame-retardant material or a non-combustible material such as glass or a metal oxide film improves the safety of the battery.

The non-aqueous electrolyte in the present invention is composed of a solvent and a lithium salt dissolved in the solvent. Preferred solvents are esters alone or mixed esters. Among them, cyclic carbonate, cyclic carboxylate, acyclic carbonate, aliphatic carboxylate and the like are preferable. Further, a mixed solvent containing a cyclic carbonate and a non-cyclic carbonate, a mixed solvent containing a cyclic carboxylate, and a mixed solvent containing a cyclic carboxylate and a cyclic carbonate are preferable.
Specific examples of the solvent and other solvents used in the present invention are illustrated below.

Examples of the ester used for the non-aqueous solvent include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) and vinylene carbonate (VC), dimethyl carbonate (DMC), and diethyl carbonate (DEC). Acyclic carbonates such as ethyl methyl carbonate (EMC) and dipropyl carbonate (DPC), aliphatic carboxylic acids such as methyl formate (MF), methyl acetate (MA), methyl propionate (MP) and ethyl propionate (MA) And acidic carboxylic acid esters such as γ-butyrolactone (GBL).
EC, PC, VC and the like are particularly preferable as the cyclic carbonate, GBL and the like are particularly preferable as the cyclic carboxylate, and DMC, DEC and EMC are preferable as the non-cyclic carbonate. Further, if necessary, those containing an aliphatic carboxylic acid ester are also preferable. It is preferable that the aliphatic carboxylic acid ester is contained in an amount of not more than 30%, more preferably not more than 20% of the whole solvent weight.
Further, the solvent of the electrolytic solution of the present invention may contain a known aprotic organic solvent in addition to the above-mentioned ester in an amount of 80% or more.

Examples of lithium salts dissolved in these solvents include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , and LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiB ₁₀ Cl ₁₀ , lithium lower aliphatic carboxylate, lithium chloroborane, lithium tetraphenylborate, LiN (CF ₃ SO ₂ ) (C ₂ F ₅ SO ₂ ), LiN (CF _{3 SO 2) 2, LiN (} C 2 F 5 SO 2) 2, LiN (CF 3 SO 2) (C 4 F 9 SO 2) can be mentioned imides such. These can be used alone or arbitrarily in combination with the electrolytic solution or the like within a range that does not impair the effects of the present invention. Above all, it is particularly preferable to include LiPF ₆ .

A particularly preferred non-aqueous electrolyte in the present invention is an electrolyte containing at least ethylene carbonate and ethyl methyl carbonate, and containing LiPF ₆ as a lithium salt. Further, an electrolytic solution containing GBL as a main solvent is also preferable. In this case, an additive such as VC is added by several%, and LiBF ₄ other than LiPF ₆ and LiN (C ₂ F ₅ SO ₂ ) ₂ are used as lithium salts. It is preferable to use a mixed salt.
The amount of these electrolytes to be added to the battery is not particularly limited, but may be used in the required amount depending on the amounts of the positive electrode active material and the negative electrode material and the size of the battery. The amount of lithium salt dissolved in the non-aqueous solvent is not particularly limited, but is preferably 0.2 to 2 mol / liter. In particular, it is more preferably 0.5 to 1.5 mol / liter.
This electrolyte is usually used by impregnating or filling a separator such as a porous polymer, a glass filter, or a nonwoven fabric. Further, in order to make the electrolytic solution nonflammable, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride chloride can be contained in the electrolytic solution. In addition, carbon dioxide gas can be included in the electrolytic solution in order to provide suitability for high-temperature storage.

In addition to the liquid, the following solid electrolyte can be used. Solid electrolytes are classified into inorganic solid electrolytes and organic solid electrolytes.
Well-known inorganic solid electrolytes include nitrides, halides, and oxyacid salts of Li. Among _{them, Li 4 SiO 4, Li 4} SiO 4 -LiI-LiOH, xLi 3 PO 4 - (1-x) Li 4 SiO 4, Li 2 SiS 3, Li 3 PO 4 -Li 2 S-SiS 2, sulfide Phosphorus compounds are effective.
In the organic solid electrolyte, for example, polymer materials such as polyethylene oxide, polypropylene oxide, polyphosphazene, polyaziridine, polyethylene sulfide, polyvinyl alcohol, polyvinylidene fluoride, polyhexafluoropropylene, and derivatives, mixtures, and composites thereof are effective. is there.
Further, a gel electrolyte in which the above non-aqueous electrolyte is contained in an organic solid electrolyte can also be used. As the organic solid electrolyte, for example, polyethylene oxide, polypropylene oxide, polyphosphazene, polyaziridine, polyethylene sulfide, polyvinyl alcohol, polyvinylidene fluoride, polyhexafluoropropylene and the like, and derivatives, mixtures, and polymer matrices such as composites The material is effective. Particularly, a copolymer of vinylidene fluoride and hexafluoropropylene or a mixture of polyvinylidene fluoride and polyethylene oxide is preferable.

As the shape of the battery, any of coin type, button type, sheet type, cylindrical type, flat type, square type and the like can be applied. When the shape of the battery is a coin type or a button type, the mixture of the positive electrode active material and the negative electrode material is mainly used after being compressed into a pellet shape. The thickness and diameter of the pellet may be determined according to the size of the battery.
When the shape of the battery is a sheet type, a cylindrical type, or a square type, the mixture containing the positive electrode active material or the negative electrode material is mainly applied (coated) on a current collector, dried, and compressed for use. As a coating method, a general method can be used. Examples of the method include a reverse roll method, a direct roll method, a blade method, a knife method, an extrusion method, a curtain method, a gravure method, a bar method, a casting method, a dip method, and a squeeze method. Among them, the blade method, the knife method and the extrusion method are preferred.

Application is preferably performed at a speed of 0.1 to 100 m / min. At this time, by selecting the above-mentioned coating method in accordance with the solution physical properties and drying properties of the mixture, a good surface state of the coated layer can be obtained. The application of the mixture to the current collector may be performed on each side of the current collector, or may be performed simultaneously on both sides. Further, it is preferable to provide the coating layer on both sides of the current collector, and the coating layer on one surface may be composed of a plurality of layers including a mixture layer. The mixture layer contains a binder, a conductive material, and the like, in addition to a material related to insertion and release of lithium ions, such as a positive electrode active material or a negative electrode material. In addition to the mixture layer, a protective layer containing no active material, an undercoat layer provided on the current collector, an intermediate layer provided between the mixture layers, and the like may be provided. It is preferable that the layer containing no active material contains conductive particles, insulating particles, a binder, and the like.

The application method may be continuous, intermittent, or stripe. The thickness, length and width of the coating layer are determined by the size of the battery, and the thickness of the coating layer on one side is preferably 1 to 2000 μm in a compressed state after drying.
As a method for drying or dehydrating the pellets or sheets of the mixture, generally employed methods can be used. In particular, it is preferable to use hot air, vacuum, infrared rays, far infrared rays, electron beams, and low-humidity air alone or in combination.
The temperature is preferably in the range of 80 to 350C, particularly preferably in the range of 100 to 250C. The water content of the whole battery is preferably 2000 ppm or less, and the water content of each of the positive electrode mixture, the negative electrode mixture and the electrolyte is preferably 500 ppm or less from the viewpoint of cycleability.

As a method for pressing the sheet, a generally used method can be used, but a die pressing method or a calendar pressing method is particularly preferable. The press pressure is not particularly limited, but is preferably 0.2 to 3 t / cm ² . The press speed of the calender press method is preferably 0.1 to 50 m / min.
The pressing temperature is preferably from room temperature to 200 ° C. The width ratio of the positive electrode sheet to the negative electrode sheet is preferably 0.9 to 1.1. In particular, 0.95 to 1.0 is preferable. The content ratio between the positive electrode active material and the negative electrode material cannot be limited because it differs depending on the compound type and the mixture formulation, but those skilled in the art can set an optimal value from the viewpoint of capacity, cycleability and safety.
In addition, the wound body of the electrode in the present invention does not necessarily have to be a true cylindrical shape, and may have a prismatic shape such as a long cylindrical shape or a rectangular shape having an elliptical cross section.

Here, FIG. 27 shows a front view of a cross section of a part of a cylindrical battery manufactured in an example described later. An electrode plate group 4 in which a positive electrode plate and a negative electrode plate are spirally wound a plurality of times with a separator interposed therebetween is housed in the battery case 1. Then, the positive electrode lead 5 is drawn out from the positive electrode plate and connected to the sealing plate 2, and the negative electrode lead 6 is drawn out from the negative electrode plate and connected to the bottom of the battery case 1. For the battery case and the lead plate, a metal or an alloy having an organic electrolytic solution resistance and electron conductivity can be used. For example, metals such as iron, nickel, titanium, chromium, molybdenum, copper, and aluminum or alloys thereof are used. In particular, the battery case is preferably made of a stainless steel plate or an Al-Mn alloy plate, and the positive electrode lead is most preferably aluminum and the negative electrode lead is preferably nickel. Further, as the battery case, various types of engineering plastics and a combination thereof with a metal can be used to reduce the weight.

絶 縁 An insulating ring 7 is provided on each of the upper and lower portions of the electrode plate group 4. Then, an electrolyte is injected, and the battery case is sealed using a sealing plate. At this time, a safety valve can be provided on the sealing plate. In addition to the safety valve, various conventionally known safety elements may be provided. For example, a fuse, a bimetal, a PTC element, or the like is used as the overcurrent prevention element. In addition to the safety valve, as a countermeasure against an increase in the internal pressure of the battery case, a method of making a cut in the battery case, a method of cracking a gasket, a method of cracking a sealing plate, or a method of cutting with a lead plate can be used. Further, the charger may be provided with a protection circuit incorporating measures for overcharging and overdischarging, or may be connected independently.

As a measure against overcharging, a method of interrupting the current by increasing the internal pressure of the battery can be adopted. At this time, a compound for increasing the internal pressure can be contained in the mixture or the electrolyte. Examples of the compound raising the internal pressure and carbonates such as _{Li 2 CO 3, LiHCO 3,} Na 2 CO 3, NaHCO 3, CaCO 3 and MgCO ₃ and the like. As a method for welding the cap, the battery case, the sheet, and the lead plate, a known method (eg, DC or AC electric welding, laser welding, ultrasonic welding, or the like) can be used. Further, as the sealing agent for sealing, a conventionally known compound or mixture such as asphalt can be used.
Hereinafter, the present invention will be described by way of examples, but the present invention is not limited thereto.

A cylindrical battery having the structure shown in FIG. 27 was manufactured.
First, a positive electrode plate was produced as follows. 10 parts by weight of carbon powder as a conductive agent and 5 parts by weight of polyvinylidene fluoride resin as a binder were mixed with 85 parts by weight of the positive electrode active material powder of the present invention. These were dispersed in dehydrated N-methylpyrrolidinone to obtain a slurry, coated on a positive electrode current collector made of aluminum foil, dried and rolled, and then cut into a predetermined size.
The negative electrode plate is made of a carbonaceous material as a main material, and a mixture of this and a styrene-butadiene rubber-based binder in a weight ratio of 100: 5 is applied to both sides of a copper foil, dried, rolled, and then subjected to a predetermined process. And cut to size.
A polyethylene microporous film was used as a separator. As the organic electrolyte, a solution prepared by dissolving 1.5 mol / liter of LiPF ₆ in a mixed solvent of ethylene carbonate and ethyl methyl carbonate at a volume ratio of 1: 1 was used. The produced cylindrical battery had a diameter of 18 mm and a height of 650 mm.

As the positive electrode active material, Li [Li _0.03 (Ni _1/2 Mn _1/2 ) _0.97 ] O ₂ (Example 1-1) or Li [Li _0.03 (Ni _1/3 Mn _1/3 Co) according to the present invention is used. _1/3 ) _0.97 ] O ₂ (Example 1-2) was used. These materials were confirmed by TEM images and electron diffraction as described above to have a signal indicating a twinning portion in the particles and a superlattice arrangement.
Also, for comparison, instead of using the method for producing a positive electrode active material according to the present invention, lithium hydroxide, nickel hydroxide and manganese oxyhydroxide were used to obtain the same composition ratio as in Example 1. Mixed. All the steps after firing were performed by the method of the present invention. Using the material thus obtained, a cylindrical battery was produced in the same manner as in Example 1 (Comparative Example 1). From the TEM image and electron beam diffraction of this material, no signal indicating the above-mentioned twinning portion and superlattice was confirmed.

For comparison, a cylindrical battery was manufactured in the same manner using LiCoO ₂ as the positive electrode active material (Comparative Example 2).
Li [Li _0.03 (Ni _1/2 Mn _1/2 ) _0.97 ] O obtained by baking at 1000 ° C. without performing the quenching step, and gradually cooling to room temperature in 48 hours. ₂ (Example 1-3) and Li [Li _0.03 (Ni _1/3 Mn _1/3 Co _1/3 ) _0.97 ] O ₂ (Example 1-4), and the cylindrical mold was used in the same manner as in Example 1. A battery was prepared and evaluated.

[Evaluation]
The electric capacity, rate characteristics and cycle life of these batteries were evaluated.
1) Electric Capacity The battery was first charged with a constant current of 100 mA until it reached 4.2 V, and then charged and discharged with a constant current of 100 mA until it reached 2.0 V. This charge / discharge was repeated several cycles, and the capacity was confirmed when the battery capacity became almost constant.
The capacity was confirmed as follows. First, charging was performed at a constant voltage of 4.2 V, and the maximum current was 1 A. Charging was terminated when the current value reached 50 mA. Discharge was performed at a constant current of 300 mA to 2.5 V. The discharge capacity obtained at this time was defined as the electric capacity of the battery. The values of the electric capacity shown in Table 4 are shown as ratios when the electric capacity when the conventional LiCoO ₂ of Comparative Example ₂ is used is 100. The charge / discharge atmosphere was performed at 25 ° C.

2) Rate characteristics The capacity discharged to 2.5 V at a constant current of 1000 mA was measured, and the rate characteristic value was calculated by calculating the ratio (%) of (capacity at 1000 mA discharge) / (capacity at 300 mA discharge). . Therefore, a larger value indicates a battery with better rate characteristics.
3) Cycle Life A 500-cycle test was performed with this charge / discharge as one cycle. Since the capacities of the batteries of Example 1 and Comparative Examples 1 and 2 are different, Table 4 shows the capacity of each battery confirmed before performing the cycle life test as 100, and shows the capacity of the battery after 500 cycles as a ratio. . Therefore, this value is a number indicating the cycle deterioration rate, and the larger the value, the better the cycle life.

From the results in Table 4, it is understood that the battery using the positive electrode active material according to the present invention is excellent in electric capacity, rate characteristics, and cycle life. It can be seen that by performing the quenching step, the characteristics of the batteries of Examples 1 and 2 were all improved compared to the batteries of Examples 3 and 4. As described above, by applying the positive electrode active material according to the present invention to a lithium secondary battery, it is possible to provide a battery that is superior to a battery using LiCoO ₂ that has been mainly used conventionally.

(Material stability)
When Li is released from LiNiO ₂ by charging, LiNiO ₂ becomes very unstable and releases oxygen at a relatively low temperature to be reduced to NiO. This is fatal when used as a positive electrode active material of a battery, and it is expected that oxygen generated will lead to thermal runaway of the battery, that is, ignition or rupture.
The present inventors have proposed that such inconveniences can be improved by using an oxide obtained by dissolving nickel: manganese at a ratio of 1: 1 and nickel: manganese: cobalt at a ratio of 1: 1: 1. . Further, a positive electrode in which Li [Li _0.03 (Ni _1/2 Mn _1/2 ) _0.97 ] O ₂ or Li [Li _0.03 (Ni _1/3 Mn _1/3 Co _1/3 ) _0.97 ] O ₂ is doped with aluminum A battery using an active material has been similarly proposed.

It has been clarified that the heat resistance can be improved by doping aluminum or the like in the vicinity of the surface of the composite oxide having a precisely controlled particle morphology according to the present invention. It was confirmed by TEM and electron beam diffraction that the particle morphology of the material doped with aluminum or the like also had the above-mentioned features of the present invention. As the additive element, the amount of aluminum, calcium, strontium, zirconium, yttrium and ytterbium was set to 5 atomic% with respect to the total amount of nickel and manganese.
Using these materials, the battery shown in FIG. 27 was produced, overcharged to 4.8 V, and then disassembled to take out the positive electrode mixture. This positive electrode mixture was directly subjected to DSC (differential scanning calorimetry) measurement, and the exothermic peak (1st peak) observed at the lowest temperature at this time is shown in Table 5. The batteries of Examples 1 and 2 were similarly evaluated.

From Table 5, it can be seen that the exothermic temperature is higher in each case than in LiCoO ₂ . This can be considered as follows. For LiCoO _2, the entire grid LiCoO ₂ expands due to overcharging. As a result, the crystal structure becomes unstable and oxygen is easily released. When the temperature is increased in this state, an exothermic reaction which is considered to be caused by the released oxygen is observed. On the other hand, although not clear in the material of the embodiment of the present invention, the combination of the fact that the oxidation-reduction reaction with the organic substance (electrolyte) on the material surface is suppressed and the release of oxygen due to lattice expansion is suppressed are combined. It is thought that it was. Furthermore, when aluminum or the like is added, this effect is increased, and the temperature rise is large, so that the thermal stability of the positive electrode active material is dramatically improved. Examining the amount of addition, preferable results are obtained in the range of 0.05 to 20 atomic% of the total of transition metal elements. If the content is less than 0.05 atomic%, a sufficient effect cannot be obtained, and if the content exceeds 20 atomic%, the capacity is reduced.

(Electronic conductivity of material)
The additional function can be exhibited by doping a different element into Li [Li _0.03 (Ni _1/2 Mn _1/2 ) _0.97 ] O ₂ of the present invention, but the electron conductivity is greatly increased by adding magnesium. We have already suggested that it can be improved. It has been clarified that the electron conductivity can be improved by doping magnesium in the vicinity of the surface also in the case of the present invention in which the particle morphology is precisely controlled.
This makes it possible to reduce the amount of the conductive agent to be added to the positive electrode plate, so that the active material can be filled more by that amount, and as a result, the capacity can be increased.

In this example, 3 parts by weight of carbon powder as a conductive agent and 4 parts by weight of polyvinylidene fluoride resin as a binder were mixed with 93 parts by weight of the positive electrode active material powder. The electrode conductivity of the thus obtained electrode plate was measured. The measurement was performed by measuring a resistance value in a cross section direction of the electrode plate and converting it into an electron conductivity per cross section. The measurement results are shown in Table 6 as a ratio when the electronic conductivity of the electrode plate using Li [Li _0.03 (Ni _1/2 Mn _1/2 ) _0.97 ] O ₂ is 100. Using the positive electrode active material to which magnesium was added, the electronic conductivity of the electrode plate containing various amounts of the conductive agent was measured. The addition amount of magnesium was 2 atomic%.

Table 6 shows that when magnesium is doped, the electrode plate to which the conductive agent is added at 2% by weight has the same electronic conductivity as the conventional electrode plate to which the conductive agent is added at 3% by weight. The amount of addition was almost the same as in the case of aluminum. However, when the amount of addition was increased, undoped magnesium was detected as an impurity. Therefore, 0.05 to 10 atomic% is preferable.
In the examples, a carbonaceous material was used as the active material of the negative electrode in order to evaluate the performance of the positive electrode. However, the present invention is not limited to this. Objects can also be adopted. In the examples, as for the electrolytic solution, a solution obtained by dissolving 1.5 mol / l of LiPF ₆ in a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1: 1 was used. Instead, an organic or inorganic solid electrolyte may be employed.

It is a TEM photograph of LiNi _1/2 Mn _1/2 O ₂ which is the lithium-containing composite oxide of the present invention. It is a TEM photograph of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ which is the lithium-containing composite oxide of the present invention. 4 is a TEM photograph of typical primary particles of LiNi _1/2 Mn _1/2 O ₂ . 5 is a TEM photograph showing the morphology of a structure in primary particles of LiNi _1/2 Mn _1/2 O ₂ . LiNi _1/3 is a TEM photograph showing the morphology of a tissue of Mn _1/3 Co _1/3 the primary particles of the O _2. Is a TEM photograph showing the oxygen arrangement of LiNi _1/2 Mn _1/2 O _2. 4 is a TEM photograph showing the oxygen arrangement of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ . 5 is a TEM photograph showing lattice defects of LiNi _1/2 Mn _1/2 O ₂ . 5 is a TEM photograph showing lattice distortion included in LiNi _1/2 Mn _1/2 O _2. LiNi is an electron-ray diffraction photograph of _1/2 Mn _1/2 O _2. 5 is a photograph of an image analyzed using a Fourier transform technique to find superlattice regularity in a short range from a TEM image. 5 is a photograph of an image analyzed using a Fourier transform technique to find superlattice regularity in a short range from a TEM image. _{3 is} an X-ray diffraction pattern of LiNiO ₂ and LiNi _1/2 Mn _1/2 O ₂ . It is the peak intensity of (a) and (b) of FIG. _{3 is} an X-ray diffraction pattern of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ . 16 is a table showing Miller indices, d values, measured values and calculated values of the intensity ratio of the X-ray diffraction pattern in FIG. 15. It is a charge / discharge curve of LiNi _1/2 Mn _1/2 O ₂ when a 4.3 V charge (constant voltage constant current charge) is performed on lithium metal. It is a diagram showing a discharge capacity of LiNi _1/2 Mn _1/2 O ₂ with respect to the number of cycles. It is a charge / discharge curve of LiNi _1/2 Mn _1/2 O ₂ when a 4.6 V charge is performed on lithium metal. It is a diagram showing a discharge capacity of LiNi _1/2 Mn _1/2 O ₂ with respect to the number of cycles. For _{LiNi 1/3 Mn 1/3 Co 1/3 O 2} , a charge-discharge curve at 4.6V charging. For _{LiNi 1/3 Mn 1/3 Co 1/3 O 2} , a diagram showing the cycle life at 4.6V charging. 4 is an X-ray diffraction pattern of a material having a composition ratio of nickel and manganese deviating from 1: 1. 24 is a charge / discharge curve when a material having a composition ratio shown in FIG. 23 is used. It is an X-ray diffraction pattern by the firing temperature of the LiNi _1/2 Mn _1/2 O _2. A charge-discharge curve according to the firing temperature of LiNi _1/2 Mn _1/2 O _2. It is the front view which made a part of cylindrical type battery produced in an example a section.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Insulation packing 4 Electrode group 5 Positive electrode lead 6 Negative electrode lead 7 Insulation ring

Claims (14)

A positive electrode active material comprising a lithium-containing composite oxide containing at least a nickel element and a manganese element, comprising primary particles of the composite oxide having a twinning portion. The positive electrode active material according to claim 1, wherein the composite oxide has a layered crystal structure, and the arrangement of oxygen is a cubic close-packed structure. The positive electrode active material according to claim 1, wherein the composite oxide has a defective portion or a strained portion. 4. The positive electrode active material according to claim 1, wherein the composite oxide has a superlattice arrangement of [√3 × √3] R30 ° assuming R3m. 5. The positive electrode active material according to any one of claims 1 to 4, wherein the composite oxide contains a nickel element and a manganese element at substantially the same ratio. 6. The composite oxide according to claim 1, wherein an X-ray diffraction peak assigned assuming R3m satisfies a relationship of integral intensity ratio (003) / (104) ≦ 1.2. The positive electrode active material according to item 1. The positive electrode active material according to any one of claims 1 to 6, wherein the composite oxide has extra spots or streaks in substantially all patterns in electron beam diffraction assuming R3m. The positive electrode active material according to any one of claims 1 to 7, wherein the primary particles have at least one shape of a sphere and a rectangular parallelepiped. 9. The method according to claim 1, wherein the primary particles have a particle size of 0.1 to 2 [mu] m, and further include secondary particles of the composite oxide having a particle size of 2 to 20 [mu] m. Positive electrode active material. The composite oxide has the formula (1):
Li _{1 + y} [M _X (NiδMnγ) _1-X ] O ₂
(Where, -0.05 <y <0.05, M is one or more elements other than nickel and manganese, -0.1 ≦ x ≦ 0.3, δ = 0.5 ± 0.1, γ = 0.5 ± 0.1, and when M is cobalt, -0.1 ≦ x ≦ 0.5 is satisfied.) material. The positive electrode active material according to claim 10, wherein M is trivalent in an oxidized state. The cathode active material according to claim 10, wherein M includes at least one selected from the group consisting of aluminum and cobalt. The positive electrode active material according to claim 10, wherein M is at least one selected from the group consisting of magnesium, calcium, strontium, zirconium, yttrium, and ytterbium magnesium. A negative electrode comprising a material capable of inserting and extracting lithium and / or metallic lithium as a negative electrode active material, a positive electrode comprising the positive electrode active material according to any one of claims 1 to 13, and an electrolyte. Non-aqueous electrolyte secondary battery.