JP2012038562A - Precursor, method for manufacturing active material, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a precursor of an active material having high capacity and excellent durability for operating cycles at high potential.SOLUTION: An active material obtained by firing the precursor has a layer structure and is represented by a formula (1) below. The precursor shows an endothermic peak temperature of 550°C or lower when the temperature of the precursor is increased from 300°C to 800°C in a thermal differential analysis of the precursor in the air. LiNiCoMnMOF(1) [in the formula (1), an element M is at least one kind of element selected from a group consisting of Al, Si, Zr, Ti, Fe, Mg, Nb, Ba, and V, 1.9≤(a+b+c+d+y)≤2.1, 1.0≤y≤1.3, 0<a≤0.3, 0≤b≤0.25, 0.3≤c≤0.7, 0≤d≤0.1, 1.9≤(x+z)≤2.0, and 0≤z≤0.15].

Description

  The present invention relates to an active material precursor, a method for producing an active material, and a lithium ion secondary battery.

  In recent years, various electric vehicles are expected to be widely used for solving environmental and energy problems. As an in-vehicle power source such as a motor driving power source that holds the key to practical application of these electric vehicles, lithium ion secondary batteries have been intensively developed. However, in order for a battery to be widely used as an in-vehicle power source, it is necessary to make the battery high performance and make it cheaper. In addition, it is necessary to make the one-mile travel distance of an electric vehicle closer to a gasoline engine vehicle, and a higher energy battery is desired.

In order to increase the energy density of the battery, it is necessary to increase the amount of electricity stored per unit mass of the positive electrode and the negative electrode. A so-called solid solution positive electrode has been studied as a positive electrode material (positive electrode active material) that may meet this demand. Among them, the solid solution of the electrochemically inactive layered Li ₂ MnO ₃ and the electrochemically active layered LiAO ₂ (A is a transition metal such as Co or Ni) exceeds 200 mAh / g. It is expected as a candidate for a high-capacity positive electrode material that can exhibit a large electric capacity (for example, see Patent Document 1 below).

JP-A-9-55211

However, the solid solution positive electrode using Li ₂ MnO ₃ described in Patent Document 1 has a large discharge capacity, but when used at a high charge / discharge potential, the cycle characteristics are easily deteriorated by repeated charge / discharge. There was a problem. For this reason, even a lithium ion battery using such a solid solution positive electrode has a problem in that it has poor cycle durability under high capacity use conditions, and deteriorates immediately when charging / discharging at a high potential.

  The present invention has been made in view of the above-described problems of the prior art, and is a precursor of an active material having a high capacity and excellent charge / discharge cycle durability at a high potential. An object is to provide a secondary battery.

In order to achieve the above object, the precursor according to the present invention is a precursor of an active material, and the active material obtained by firing the precursor has a layered structure, and is represented by the following composition formula (1): In the suggested thermal analysis of the precursor in the atmosphere, the endothermic peak temperature exhibited by the precursor when the temperature of the precursor is increased from 300 ° C. to 800 ° C. is 550 ° C. or less.
_{Li y Ni a Co b Mn c} M d O x F z (1)
In the above formula (1), the element M is at least one element selected from the group consisting of Al, Si, Zr, Ti, Fe, Mg, Nb, Ba, and V, and 1.9 ≦ (a + b + c + d + y) ≦ 2 0.1, 1.0 ≦ y ≦ 1.3, 0 <a ≦ 0.3, 0 ≦ b ≦ 0.25, 0.3 ≦ c ≦ 0.7, 0 ≦ d ≦ 0.1, 1.9 ≦ (x + z) ≦ 2.0, 0 ≦ z ≦ 0.15.

  The manufacturing method of the active material which concerns on this invention comprises the process of heating the said precursor of this invention at 500-1000 degreeC.

  In the lithium ion secondary battery according to the present invention, the positive electrode active material layer contains an active material obtained by the active material manufacturing method according to the present invention.

  In the present invention, the upper limit of the temperature at which the precursor exhibits an endothermic peak in the temperature range of 300 to 800 ° C is 550 ° C. A lithium ion secondary battery including an active material obtained by firing a precursor exhibiting such temperature characteristics in a positive electrode active material layer has a high capacity and suppresses deterioration in a charge / discharge cycle at a high potential. .

The specific surface area of the precursor according to the present invention is preferably 0.5 to 6.0 m ² / g. Thereby, the charge / discharge cycle durability is easily improved.

  ADVANTAGE OF THE INVENTION According to this invention, the precursor of the active material excellent in the charge / discharge cycle durability with high capacity | capacitance and high potential, the manufacturing method of an active material, and a lithium ion secondary battery can be provided.

FIG. 1 is a schematic cross-sectional view of a lithium ion secondary battery including a positive electrode active material layer including an active material formed from a precursor according to an embodiment of the present invention. FIG. 2 (a) is a photograph of an active material having a uniform composition formed from the precursor of Example 2 of the present invention, taken with a transmission electron microscope (TEM), and FIG. 2 (b) shows a TEM-EDS. FIG. 2C is a distribution diagram of oxygen in the region shown in FIG. 2A measured by TEM, and FIG. 2C is a distribution diagram of manganese in the region shown in FIG. 2A measured by TEM-EDS. (D) is a distribution diagram of cobalt in the region shown in FIG. 2 (a) measured by TEM-EDS, and FIG. 2 (e) is nickel in the region shown in FIG. 2 (a) measured by TEM-EDS. FIG. FIG. 3A is a photograph of an active material having a non-uniform composition formed from the precursor of Comparative Example 4, taken by TEM, and FIG. 3B is a photograph of FIG. 3A measured by TEM-EDS. 3 (c) is a distribution map of carbon in the region shown in FIG. 3 (c), FIG. 3 (c) is a distribution diagram of oxygen in the region shown in FIG. 3 (a) measured by TEM-EDS, and FIG. 3A is a distribution diagram of manganese in the region shown in FIG. 3A measured by EDS, and FIG. 3E is a distribution diagram of cobalt in the region shown in FIG. 3A measured by TEM-EDS. 3 (f) is a distribution diagram of nickel in the region shown in FIG. 3 (a) measured by TEM-EDS. FIG. 4 is an endothermic peak of the precursor of Example 2. FIG. 5 is an endothermic peak of the precursor of Comparative Example 3. FIG. 6 is an X-ray diffraction pattern of the active material of Example 2 formed by firing the precursor of Example 2 of the present invention in the atmosphere at 900 ° C. for 10 hours.

  Hereinafter, an active material, an active material precursor, a precursor and a method for producing an active material, and a lithium ion secondary battery according to an embodiment of the present invention will be described. In addition, this invention is not limited to the following embodiment.

(Active material)
The active material of the present embodiment is a lithium-containing composite oxide having a layered structure and represented by the following composition formula (1).
_{Li y Ni a Co b Mn c} M d O x F z (1)
In the above formula (1), the element M is at least one element selected from the group consisting of Al, Si, Zr, Ti, Fe, Mg, Nb, Ba, and V, and 1.9 ≦ (a + b + c + d + y) ≦ 2 0.1, 1.0 ≦ y ≦ 1.3, 0 <a ≦ 0.3, 0 ≦ b ≦ 0.25, 0.3 ≦ c ≦ 0.7, 0 ≦ d ≦ 0.1, 1.9 ≦ (x + z) ≦ 2.0, 0 ≦ z ≦ 0.15.

The layered structure here is generally expressed as LiAO ₂ (A is a transition metal such as Co, Ni, Mn, etc.), and is a structure in which a lithium layer, a transition metal layer, and an oxygen layer are laminated in a uniaxial direction. Typical examples include those belonging to the α-NaFeO ₂ type such as LiCoO ₂ and LiNiO ₂ , which are rhombohedral, and are attributed to the space group R (−3) m due to their symmetry. LiMnO ₂ is orthorhombic and is attributed to the space group Pm2m due to its symmetry. Li ₂ MnO ₃ can also be expressed as Li [Li _1/3 Mn _2/3 ] O ₂ , which is monoclinic Although belonging to the space group C2 / m, it is a layered compound in which a Li layer, a [Li _1/3 Mn _2/3 ] layer and an oxygen layer are laminated. The active material of this embodiment is a solid solution of a lithium transition metal composite oxide represented by LiAO ₂ and is a system that also allows Li as a metal element occupying a transition metal site. The “solid solution” is distinguished from a mixture of compounds. For example, even if a mixture such as LiNi _0.5 Mn _0.5 O ₂ powder or LiNi _0.33 Co _0.33 Mn _0.34 O ₂ powder apparently satisfies the composition formula (1), Not included in “solid solution”. In the case of a simple mixture, the peak position corresponding to each lattice constant observed when X-ray diffraction measurement is performed is different, so that one peak splits into two or three. On the other hand, in the “solid solution”, one peak is not split. Therefore, the “solid solution” and the mixture can be distinguished by the presence or absence of the split of the peak of the X-ray diffraction measurement. Hereinafter, a case where the active material has a rhombohedral space group R (−3) m structure will be described.

(precursor)
The precursor of the present embodiment is a precursor of the active material of the present embodiment. That is, the active material of the present embodiment is obtained by sintering the precursor of the present embodiment. The precursor of the present embodiment includes, for example, Li, Ni, Co, Mn, M, O, and F. Like the composition formula (1), the precursors of Li, Ni, Co, Mn, M, O, and F are included. A mixture having a molar ratio of y: a: b: c: d: x: z. As specific examples of the precursor, compounds of Li, Ni, Co, Mn, and M (for example, salts), a compound containing O and a compound containing F are blended so as to satisfy the above molar ratio, and if necessary, It is a mixture obtained by heating. One of the compounds contained in the precursor may be composed of a plurality of elements selected from the group consisting of Li, Ni, Co, Mn, M, O, and F. In addition, since the molar ratio of O and F in the precursor varies depending on the firing conditions of the precursor (for example, atmosphere, temperature, etc.), the molar ratio of O and F in the precursor is outside the numerical ranges of x and z above. Also good.

  The reason why the lithium-containing composite oxide obtained from the precursor of the present embodiment is excellent in charge / discharge cycle durability at a high capacity and at a high potential is not necessarily clear, but the present inventors consider as follows. It is done. However, the effect which concerns on the precursor of this invention is not limited to the following.

  The present inventors use a sintered body obtained by sintering a precursor exhibiting an endothermic peak at 550 ° C. or lower when the temperature is raised from 300 ° C. to 800 ° C. as a positive electrode active material. It has been found that the characteristics (discharge capacity, charge / discharge cycle characteristics) are good. That is, the precursor of this embodiment shows an endothermic peak at 550 ° C. or lower when the temperature is increased from 300 ° C. to 800 ° C. in the suggested thermal analysis in the atmosphere. In order to obtain a lithium-containing composite oxide having a layered structure represented by the above composition formula (1), X-ray diffraction measurement of the precursor at each temperature while raising the temperature of the precursor in the air in 5 ° C steps. As a result of measuring the crystallization temperature of the precursor, the present inventors confirmed that the lowest crystallization temperature was 395 ° C. Therefore, the lower limit of the temperature when the precursor becomes a layered structure compound is about 395 ° C.

  Implicit thermal analysis (DTA) is a method of measuring the temperature difference between a sample and a reference material as a function of temperature while changing the temperature of the sample and the reference material according to a certain program. . The temperature difference between the sample and the reference material is measured as an electromotive force corresponding to the temperature difference by a differential thermocouple. In the suggested thermal analysis, when a chemical reaction occurs in the sample, the temperature difference between the sample and the reference material increases. Therefore, the temperature at which a chemical reaction occurs in the sample can be detected as the maximum value (endothermic peak) of the temperature difference between the sample and the reference material.

  The temperature increase rate of the precursor in the suggested thermal analysis is about 10 ° C./min. The atmosphere of the precursor in the suggested thermal analysis is air. Alumina powder is used as the standard sample used for the suggested thermal analysis. The temperature range of the precursor in the suggestive thermal analysis needs to be a temperature range in which the sintering reaction of the precursor is expected to proceed, and is about 300 to 800 ° C. In the present embodiment, the endothermic peak of the precursor means an endothermic peak having a size of 5 μV · sec / mg or more.

In this embodiment, the endothermic peak temperature of the precursor when the temperature is raised from 300 ° C. to 800 ° C. means that the precursor crystallization proceeds at a low temperature of 550 ° C. or less. It is thought that there is. For example, when the precursor contains a hydroxide or nitrate as a raw material compound, even if the temperature of the precursor is 550 ° C. or less, a dehydration reaction of a hydroxyl group contained in the precursor or an oxidation reaction of a NO group proceeds. It is considered that the crystallization of the precursor proceeds as the generated water, NO _{2 and the} like are desorbed from the precursor. In addition, the present inventors consider that the endothermic peak temperatures differ depending on differences in the composition of the precursor, the type of raw materials (Li salt, metal salt), the specific surface area of the precursor, the mixed state, and the like. The present inventors consider that the endothermic peak temperature of the precursor becomes 550 ° C. or lower only when the precursor has the composition represented by the composition formula (1). Further, the present inventors consider that the endothermic peak temperature of the precursor tends to be 550 ° C. or less because the precursor has an appropriate specific surface area or mixed state. When the endothermic peak temperature of the precursor is 550 ° C. or lower, an active material having a uniform composition distribution and less segregation can be obtained by firing the precursor. By using such an active material, the discharge capacity and charge / discharge cycle durability of the battery are improved.

  When the endothermic peak temperature of the precursor is higher than 550 ° C., the discharge capacity of the battery using the active material obtained from the precursor is lowered, and the charge / discharge cycle durability is deteriorated.

The specific surface area of the precursor according to the present invention is preferably 0.5 to 6.0 m ² / g. Thereby, the endothermic peak temperature of the precursor tends to be 550 ° C. or less, and the charge / discharge cycle durability is easily improved. When the specific surface area of the precursor is smaller than 0.5 m ² / g, the particle size of the precursor after firing (the particle size of the active material) tends to be large, and the composition distribution of the active material tends to be non-uniform. Moreover, when the specific surface area of a precursor is larger than 6.0 m < ² > / g, the water absorption amount of a precursor increases and a baking process becomes difficult. When the water absorption amount of the precursor is large, it is necessary to prepare a dry environment, which increases the cost of manufacturing the active material. The specific surface area can be measured with a known BET type powder specific surface area measuring device.

(Precursor production method)
A precursor is obtained by mix | blending the following compound so that the molar ratio shown to the said composition formula (1) may be satisfy | filled. Specifically, the precursor can be produced from the following compound by a method such as pulverization / mixing, thermal decomposition mixing, precipitation reaction, or hydrolysis. In particular, a method of mixing, stirring, and heat-treating a liquid raw material in which a Mn compound, a Ni compound, a Co compound, and a Li compound are dissolved in a solvent such as water is preferable. By drying this, it becomes easy to produce a composite oxide (precursor) having a uniform composition and an endothermic peak temperature of 550 ° C. or lower as a precursor.

Li compound: Lithium hydroxide monohydrate, lithium carbonate, lithium nitrate, lithium chloride and the like.
Ni compound: nickel sulfate hexahydrate, nickel nitrate hexahydrate, nickel chloride hexahydrate and the like.
Co compound: cobalt sulfate heptahydrate, cobalt nitrate hexahydrate, cobalt chloride hexahydrate and the like.
Mn compounds: manganese sulfate pentahydrate, manganese nitrate hexahydrate, manganese chloride tetrahydrate, manganese acetate tetrahydrate, and the like.
M compound: Al source, Si source, Zr source, Ti source, Fe source, Mg source, Nb source, Ba source, V source (oxide, fluoride, etc.). For example, aluminum nitrate nonahydrate, aluminum fluoride, iron sulfate heptahydrate, silicon dioxide, zirconium nitrate dihydrate, titanium sulfate hydrate, magnesium nitrate hexahydrate, niobium oxide, barium carbonate , Vanadium oxide and the like.
In addition, you may add fluorine sources, such as lithium fluoride and aluminum fluoride, to the raw material mixture of a precursor as needed.

  A raw material mixture prepared by adding sugar to a solvent in which the above compound is dissolved may be further mixed, stirred and heat-treated. In addition, if necessary, an acid may be added to the raw material mixture in order to adjust the pH. The kind of sugar is not limited, but glucose, fructose, sucrose and the like are preferable in view of availability and cost. Sugar acid may also be added. The type of sugar acid is not limited, but ascorbic acid, glucuronic acid and the like are preferable in view of availability and cost. Sugar and sugar acid may be added simultaneously. Furthermore, you may add the synthetic resin soluble in warm water like polyvinyl alcohol.

  In this embodiment, the total value (Ms) of the sugar and sugar acid contents in the precursor raw material mixture is 0.08 to 2.20 mol% with respect to the number of moles of the active material obtained from the precursor. It is preferable to adjust to. That is, the total value of the content of sugar and sugar acid in the precursor is preferably 0.08 to 2.20 mol% with respect to the number of moles of the active material obtained from the precursor. The sugar added to the precursor raw material mixture is converted into a sugar acid by the acid, forming a complex with the metal ion in the precursor raw material mixture. Also, when sugar acid itself is added, the sugar acid forms a complex with the metal ion. By heating and stirring the raw material mixture to which sugar or sugar acid is added, each metal ion is uniformly dispersed in the raw material mixture. By drying this, it becomes easy to obtain a precursor having a uniform composition distribution. When Ms is smaller than 0.05%, the effect of making the precursor composition distribution uniform tends to be small. When Ms is larger than 2.20%, it is difficult to obtain an effect corresponding to the amount of sugar or sugar acid added. Therefore, when Ms is large, the production cost is simply increased.

(Method for producing active material)
The active material of the present embodiment can be obtained by firing the precursor produced by the above method at about 500 to 1000 ° C. The firing temperature of the precursor is preferably 700 ° C. or higher and 980 ° C. or lower. If the firing temperature of the precursor is less than 500 ° C., the sintering reaction of the precursor does not proceed sufficiently, and the crystallinity of the resulting active material is lowered, which is not preferable. When the firing temperature of the precursor exceeds 1000 ° C., the amount of Li evaporation from the sintered body (active material) increases. As a result, there is a tendency that an active material having a composition lacking lithium tends to be generated, which is not preferable.

  The firing atmosphere of the precursor is preferably an atmosphere containing oxygen. Specific examples of the atmosphere include a mixed gas of an inert gas and oxygen, and an atmosphere containing oxygen such as air. The firing time of the precursor is preferably 30 minutes or longer, and more preferably 1 hour or longer.

  The average particle diameter of the active material powder (positive electrode material and negative electrode material) is preferably 100 μm or less. In particular, the average particle diameter of the positive electrode active material powder is preferably 10 μm or less. In a non-aqueous electrolyte battery using such a fine positive electrode active material, high output characteristics are improved.

  In order to obtain an active material powder having a desired particle size and shape, a pulverizer or a classifier is used. For example, a mortar, a ball mill, a bead mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill, a sieve, or the like is used. At the time of pulverization, wet pulverization in which an organic solvent such as water or hexane coexists can be used. The classification method is not particularly limited, and a sieve, an air classifier, or the like is used as needed for both dry and wet methods.

(Lithium ion secondary battery)
As shown in FIG. 1, a lithium ion secondary battery 100 according to the present embodiment is disposed adjacent to each other between a plate-like negative electrode 20 and a plate-like positive electrode 10 facing each other, and the negative electrode 20 and the positive electrode 10. A plate-like separator 18, an electrolyte solution containing lithium ions, a case 50 containing these in a sealed state, and one end of the negative electrode 20 being electrically connected. A negative electrode lead 62 whose other end protrudes outside the case, and a positive electrode lead 60 whose one end is electrically connected to the positive electrode 10 and whose other end protrudes outside the case are provided. .

  The negative electrode 20 includes a negative electrode current collector 22 and a negative electrode active material layer 24 formed on the negative electrode current collector 22. The positive electrode 10 includes a positive electrode current collector 12 and a positive electrode active material layer 14 formed on the positive electrode current collector 12. The separator 18 is located between the negative electrode active material layer 24 and the positive electrode active material layer 14.

The positive electrode active material contained in the positive electrode active material layer 14 has a layered structure and is represented by the following composition formula (1). This positive electrode active material is formed by firing the precursor of the present embodiment. In addition, as a positive electrode active material contained in the positive electrode active material layer 14, LiMn ₂ O ₄ having a spinel structure or LiFePO ₄ having an olivine structure are used as an active material formed by firing the precursor of the present embodiment. For example, a mixture of materials having other crystal structures may be used.

As a negative electrode active material used for the negative electrode of the nonaqueous electrolyte battery, any material can be selected as long as it can deposit or occlude lithium ions. For example, titanium-based materials such as lithium titanate having a spinel crystal structure represented by Li [Li _1/3 Ti _5/3 ] O ₄ , alloy-based materials such as Si, Sb, and Sn-based lithium metal, lithium alloys (Lithium metal-containing alloys such as lithium-silicon, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and wood alloys), lithium composite oxide (lithium-titanium), silicon oxide In addition, an alloy capable of inserting and extracting lithium, a carbon material (for example, graphite, hard carbon, low-temperature fired carbon, amorphous carbon, etc.) can be used.

  The positive electrode active material layer 14 and the negative electrode active material layer 24 may contain a conductive agent, a binder, a thickener, a filler, and the like as other components in addition to the main components.

  The conductive agent is not limited as long as it is an electron conductive material that does not adversely affect the battery performance. Usually, natural graphite (such as scaly graphite, scaly graphite, earthy graphite), artificial graphite, carbon black, acetylene black, Examples thereof include conductive materials such as ketjen black, carbon whisker, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) powder, metal fiber, and conductive ceramic material. These conductive agents may be used alone, or a mixture thereof may be used.

  In particular, as the conductive agent, acetylene black is preferable from the viewpoints of electron conductivity and coatability. The addition amount of the conductive agent is preferably 0.1% by weight to 50% by weight and more preferably 0.5% by weight to 30% by weight with respect to the total weight of the positive electrode active material layer or the negative electrode active material layer. In particular, acetylene black is preferably used after being pulverized into ultrafine particles of 0.1 to 0.5 μm because the required carbon amount can be reduced. These mixing methods are physical mixing, and the ideal is uniform mixing. Therefore, powder mixers such as V-type mixers, S-type mixers, crackers, ball mills, and planetary ball mills can be mixed dry or wet.

  The binder is usually a thermoplastic resin such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber. A polymer having rubber elasticity such as (SBR) or fluororubber can be used as one kind or a mixture of two or more kinds. The amount of the binder added is preferably 1 to 50% by weight and more preferably 2 to 30% by weight with respect to the total weight of the positive electrode active material layer or the negative electrode active material layer.

  As the thickener, polysaccharides such as carboxymethylcellulose and methylcellulose can be used as one kind or a mixture of two or more kinds. Moreover, it is preferable that the thickener which has a functional group which reacts with lithium like a polysaccharide deactivates the functional group by methylation etc., for example. The addition amount of the thickener is preferably 0.5 to 10% by weight, more preferably 1 to 2% by weight based on the total weight of the positive electrode active material layer or the negative electrode active material layer.

  As the filler, any material that does not adversely affect the battery performance may be used. Usually, olefin polymers such as polypropylene and polyethylene, amorphous silica, alumina, zeolite, glass, carbon and the like are used. The addition amount of the filler is preferably 30% by weight or less with respect to the total weight of the positive electrode active material layer or the negative electrode active material layer.

  The positive electrode active material layer or the negative electrode active material layer is prepared by kneading main constituent components and other materials into a mixture, mixing in an organic solvent such as N-methylpyrrolidone and toluene, and collecting the resulting mixture. It is preferably produced by applying on the body or pressing and heat-treating at a temperature of about 50 ° C. to 250 ° C. for about 2 hours. As for the application method, for example, it is preferable to apply to any thickness and any shape using means such as roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc. Is not to be done.

  As the current collector of the electrode, iron, copper, stainless steel, nickel and aluminum can be used. Moreover, a sheet | seat, a foam, a mesh, a porous body, an expanded lattice, etc. can be used as the shape. Further, the current collector can be used with a hole formed in an arbitrary shape.

  As the nonaqueous electrolyte, those generally proposed for use in lithium batteries and the like can be used. Nonaqueous solvents used for the nonaqueous electrolyte include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate, Chain carbonates such as diethyl carbonate and ethyl methyl carbonate; chain esters such as methyl formate, methyl acetate and methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxy Ethers such as ethane, 1,4-dibutoxyethane and methyldiglyme; Nitriles such as acetonitrile and benzonitrile; Dioxolane or derivatives thereof; Ethylene sulfide, sulfolane, sultone or derivatives thereof Examples thereof include a conductor alone or a mixture of two or more thereof, but are not limited thereto.

Furthermore, it can use combining electrolyte solution and a solid electrolyte. As the solid electrolyte, a crystalline or amorphous inorganic solid electrolyte can be used. As the crystalline inorganic solid electrolyte, LiI, Li ₃ N, Li _{1 + x} M _x Ti _2-x (PO ₄ ) ₃ (M = Al, Sc, Y, La), Li _0.5-3x R _{0.5 + x} Thio LISICON typified by TiO ₃ (R = La, Pr, Nd, Sm) or Li _4-x Ge _1-x P _x S ₄ can be used. Examples of the amorphous inorganic solid electrolyte include LiI—Li ₂ O—B ₂ O ₅ series, Li ₂ O—SiO ₂ series, LiI—Li ₂ S—B ₂ S ₃ series, LiI—Li ₂ S—SiS _2. System, Li ₂ S—SiS ₂ —Li ₃ PO ₄ system, or the like can be used.

Examples of the electrolyte salt used for the non-aqueous electrolyte include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, and NaBr. , KClO ₄ , KSCN, and other inorganic ion salts containing one of lithium (Li), sodium (Na), or potassium (K), LiCF ₃ SO ₃ , 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 ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , ( CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (n-C ₄ H ₉ ) ₄ NClO ₄ , (nC ₄ H ₉ ) ₄ NI, (C ₂ H ₅ ) ₄ N-maleate, (C ₂ H ₅ ) ₄ N-benzoate, (C ₂ H ₅ ) ₄ N-phthalate, Examples thereof include organic ion salts such as lithium stearyl sulfonate, lithium octyl sulfonate, and lithium dodecylbenzene sulfonate. These ionic compounds can be used alone or in admixture of two or more.

Further, it is preferable to use a mixture of LiPF ₆ and a lithium salt having a perfluoroalkyl group such as LiN (C ₂ F ₅ SO ₂ ) ₂ . As a result, the viscosity of the electrolyte can be further reduced, so that the low-temperature characteristics can be further improved and self-discharge can be suppressed.

  A room temperature molten salt or ionic liquid may be used for the non-aqueous electrolyte.

  The concentration of the electrolyte salt in the nonaqueous electrolyte is preferably 0.1 mol / l to 5 mol / l, and more preferably 0.5 mol / l to 2.5 mol / l. Thereby, the nonaqueous electrolyte battery which has a high battery characteristic can be obtained reliably.

  As a separator for a nonaqueous electrolyte battery, it is preferable to use a porous film or a non-woven fabric exhibiting excellent high rate discharge performance alone or in combination. Examples of the material constituting the separator for a nonaqueous electrolyte battery include polyolefin resins typified by polyethylene and polypropylene, polyester resins typified by polyethylene terephthalate and polybutylene terephthalate, polyvinylidene fluoride, and vinylidene fluoride-hexa. Fluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, fluorine Vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride - tetrafluoroethylene - hexafluoropropylene copolymer, vinylidene fluoride - ethylene - can be mentioned tetrafluoroethylene copolymer.

  The porosity of the non-aqueous electrolyte battery separator is preferably 98% by volume or less from the viewpoint of strength. Further, the porosity is preferably 20% by volume or more from the viewpoint of charge / discharge characteristics.

  As the separator for a nonaqueous electrolyte battery, for example, a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, and polyvinylidene fluoride and an electrolyte may be used. Use of a nonaqueous electrolyte in a gel state has an effect of preventing leakage.

  As mentioned above, although one suitable embodiment of the present invention was described in detail, the present invention is not limited to the above-mentioned embodiment.

  For example, the shape of the nonaqueous electrolyte secondary battery is not limited to that shown in FIG. For example, the shape of the nonaqueous electrolyte secondary battery may be a square, an ellipse, a coin, a button, a sheet, or the like.

  The active material of this embodiment can also be used as an electrode material for electrochemical devices other than lithium ion secondary batteries. As such an electrochemical element, other than lithium ion secondary batteries such as a metal lithium secondary battery (an electrode containing an active material obtained by the present invention is used as a positive electrode and metal lithium is used as a negative electrode). Examples include secondary batteries and electrochemical capacitors such as lithium capacitors. These electrochemical elements can be used for power sources such as self-propelled micromachines and IC cards, and distributed power sources arranged on or in a printed circuit board.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

(Example 2)
[Precursor preparation]
To a precursor raw material mixture obtained by dissolving 12.70 g of lithium nitrate, 3.10 g of cobalt nitrate hexahydrate, 24.60 g of manganese nitrate hexahydrate, and 7.55 g of nickel nitrate hexahydrate in distilled water, 0.3 g and 1 ml of nitric acid were added, and 15 ml of polyvinyl alcohol (1 wt% aqueous solution) was further added. A black powder (precursor of Example 2) was obtained by stirring the raw material mixture on a hot plate heated to 200 ° C. until distilled water evaporated. That is, the precursor of Example 2 was obtained by evaporating and drying the raw material mixture. In addition, the number of moles of Li, Ni, Co, and Mn contained in the precursor is adjusted to 0.00 by adjusting the blending amounts of lithium nitrate, nickel nitrate hexahydrate, cobalt nitrate, and manganese acid hexahydrate in the raw material mixture. It was adjusted to correspond to _{Li 1.2 Ni 0.17 Co 0.08 Mn 0.55} O 2 of 15 mol. That is, the number of moles of each element in the precursor was adjusted so that 0.15 mol of Li _1.2 Ni _0.17 Co _0.08 Mn _0.55 O ₂ was generated from the precursor of Example 2. . 0.3 g (0.00167 mol) of glucose added to the raw material mixture was 1.11 mol% with respect to 0.15 mol of the active material obtained from the precursor of Example 2.

[BET specific surface area of precursor]
The specific surface area of the precursor was adjusted by grinding the precursor of Example 2 in a mortar for about 10 minutes. The BET specific surface area of the precursor of Example 2 after pulverization was 2.0 m ² / g. The BET specific surface area was measured using an AMS8000 type fully automatic powder specific surface area measuring device manufactured by Okura Riken. In the measurement, nitrogen was used for the adsorption gas and helium was used for the carrier gas, and the BET one-point method by the continuous flow method was adopted. Specifically, the powdery precursor was heated and deaerated with a mixed gas at a temperature of 150 ° C. Next, the precursor was cooled to liquid nitrogen temperature, and the mixed gas was adsorbed on the precursor. After adsorption of the mixed gas, the precursor was warmed to room temperature with water. By this heating, the adsorbed nitrogen gas was desorbed, the amount of desorbed nitrogen gas was detected by a thermal conductivity detector, and the specific surface area of the precursor was calculated therefrom.

[Suggested thermal analysis of precursors]
The endothermic peak temperature of the precursor of Example 2 was measured by suggestive thermal analysis. The endothermic peak temperature of the precursor of Example 2 was 470 ° C.

In addition, TG-8120 made from Rigaku Corporation was used as the suggestion thermal analysis apparatus. The suggested thermal analysis was performed under the following conditions.
Mass of precursor of Example 2 used for suggested thermal analysis: 30 mg.
Measurement temperature range: 25.00-950 ° C.
Measurement atmosphere: Air flow.
Temperature increase rate of the precursor: 10 ° C./min.
Standard sample: Alumina powder.

[Production of active material]
The precursor was baked in the air at 900 ° C. for 10 hours to obtain an active material of Example 2. The crystal structure of the active material of Example 2 was analyzed by a powder X-ray diffraction method. The active material of Example 2 was confirmed to have a main phase having a rhombohedral space group R (-3) m structure. Further, in the X-ray diffraction pattern of the active material of Example 2, a diffraction peak peculiar to the Li ₂ MnO ₃ type monoclinic space group C2 / m structure was observed at 2θ of around 20 to 25 ° ( (See FIG. 6).

As a result of the composition analysis by inductively coupled plasma method (ICP method), it was confirmed that the composition of the active material of Example 2 was Li _1.2 Ni _0.17 Co _0.08 Mn _0.55 O ₂ . It was confirmed that the molar ratio of each metal element in the active material of Example 2 coincided with the molar ratio of each metal element in the precursor of Example 2. That is, it was confirmed that the composition of the active material obtained from the precursor can be accurately controlled by adjusting the molar ratio of the metal elements in the precursor.

[Production of positive electrode]
A positive electrode paint was prepared by mixing the active material of Example 2, a conductive additive, and a solvent containing a binder. The positive electrode coating material was applied to an aluminum foil (thickness 20 μm) as a current collector by a doctor blade method, dried at 100 ° C., and rolled. This obtained the positive electrode comprised from a positive electrode active material layer and a collector. As the conductive assistant, carbon black (DAB50, manufactured by Denki Kagaku Kogyo Co., Ltd.) and graphite were used. As a solvent containing a binder, N-methyl-2-pyrrolidinone (KF7305, manufactured by Kureha Chemical Industry Co., Ltd.) in which PVDF was dissolved was used.

[Production of negative electrode]
A negative electrode paint was prepared in the same manner as the positive electrode paint except that natural graphite was used in place of the active material of Example 2 and only carbon black was used as the conductive additive. The negative electrode coating material was applied to a copper foil (thickness: 16 μm) as a current collector by a doctor blade method, dried at 100 ° C., and rolled. This obtained the negative electrode comprised from a negative electrode active material layer and a collector.

[Production of lithium ion secondary battery]
The positive electrode, negative electrode, and separator (polyolefin microporous membrane) produced above were cut into predetermined dimensions. The positive electrode and the negative electrode were provided with portions to which no electrode paint was applied in order to weld the external lead terminals. A positive electrode, a negative electrode, and a separator were laminated in this order. When laminating, a small amount of hot melt adhesive (ethylene-methacrylic acid copolymer, EMAA) was applied and fixed so that the positive electrode, the negative electrode, and the separator did not shift. An aluminum foil (width 4 mm, length 40 mm, thickness 100 μm) and nickel foil (width 4 mm, length 40 mm, thickness 100 μm) were ultrasonically welded to the positive electrode and the negative electrode, respectively, as external lead terminals. Polypropylene (PP) grafted with maleic anhydride was wrapped around this external lead terminal and thermally bonded. This is to improve the sealing performance between the external terminal and the exterior body. An aluminum laminate material composed of a PET layer, an Al layer, and a PP layer was used as a battery outer package enclosing a battery element in which a positive electrode, a negative electrode, and a separator were stacked. The thickness of the PET layer was 12 μm. The thickness of the Al layer was 40 μm. The thickness of the PP layer was 50 μm. PET is polyethylene terephthalate and PP is polypropylene. In producing the battery outer package, the PP layer was disposed inside the outer package. A battery element was placed in the outer package, an appropriate amount of electrolyte was added, and the outer package was vacuum-sealed to produce a lithium ion secondary battery of Example 2. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ at a concentration of 1 M in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) was used. The volume ratio of EC to DMC in the mixed solvent was EC: DMC = 30: 70.

[Measurement of electrical characteristics]
The battery of Example 2 was charged at a constant current of up to 4.6 V at a current value of 30 mA / g, and then discharged at a constant current of 2.0 mA at a current value of 30 mA / g. At this time, the discharge capacity of Example 2 was 230 mAh / g. A cycle test was repeated for 100 cycles of this charge / discharge cycle. The test was conducted at 25 ° C. Assuming that the initial discharge capacity of the battery of Example 2 was 100%, the discharge capacity after 100 cycles was 90%. Hereinafter, the ratio of the discharge capacity after 100 cycles when the initial discharge capacity is 100% is referred to as cycle characteristics. A high cycle characteristic indicates that the battery is excellent in charge / discharge cycle durability.

(Examples 1 to 3 and Comparative Examples 2 and 3)
In Examples 1 to 3 and Comparative Examples 2 and 3, precursor raw material mixtures were prepared so that the composition of the active material obtained after firing was as shown in Table 1. Except for this matter, the precursors, active materials and lithium ion secondary batteries of Examples 1, 3 to 5 and Comparative Examples 2 and 3 were produced in the same manner as in Example 2.

  In the same manner as in Example 2, the endothermic peak temperatures of the precursors of Examples 1, 3 to 5 and Comparative Examples 2 and 3 were measured. In the same manner as in Example 2, the compositions and crystal structures of the active materials of Examples 1, 3 to 5 and Comparative Examples 2 and 3 were analyzed. In the same manner as in Example 2, the discharge capacities and cycle characteristics of the batteries of Examples 1, 3 to 5 and Comparative Examples 2 and 3 were evaluated. The results are shown in Table 1. The composition shown in the table below is the composition of each active material, and is the overall average composition (prepared composition) of the precursor of each active material. In the table below, a battery having a capacity of 210 mAh / g or more and a cycle characteristic of 85% or more is evaluated as “A”. A battery having a capacity of less than 210 mAh / g or a cycle characteristic of less than 85% is evaluated as “F”.

(Example 29)
In Example 29, a precursor raw material mixture was prepared so that the composition of the active material obtained after firing was as shown in Table 1. That is, in Example 29, only 12.70 g of lithium nitrate, 26.20 g of manganese nitrate hexahydrate, and 8.80 g of nickel nitrate hexahydrate were used as metal salts to be included in the precursor raw material mixture. Moreover, in Example 29, the specific surface area of the precursor was adjusted to 2.0 m < ² > / g by grind | pulverizing the obtained precursor for about 10 minutes with a mortar.

  A precursor, an active material, and a lithium ion secondary battery of Example 29 were produced in the same manner as in Example 2 except for the above items.

  In the same manner as in Example 2, the endothermic peak temperature of the precursor of Example 29 was measured. In the same manner as in Example 2, the composition and crystal structure of the active material of Example 29 were analyzed. In the same manner as in Example 2, the discharge capacity and cycle characteristics of the battery of Example 29 were evaluated. The results are shown in Table 1.

(Comparative Example 4)
In Comparative Example 4, a precursor having a composition corresponding to the active material represented by Li _1.2 Ni _0.17 Co _0.08 Mn _0.55 O ₂ was produced by the following coprecipitation method.

  In the coprecipitation method, first, 0.5 liter of water was placed in the reaction tank. Furthermore, 32% sodium hydroxide aqueous solution was added to water so that pH might become 11-11.5. Next, water was heated with an external heater while stirring, and the temperature of the solution in the reaction vessel was kept at 50 ° C. Separately, nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate pentahydrate are added so that the molar ratio of Ni, Co, and Mn is 0.17: 0.08: 0.55. The dissolved raw material solution was prepared. This raw material solution was continuously dropped into the reaction vessel at a flow rate of about 3 ml / min. Further, a 32% aqueous sodium hydroxide solution was intermittently charged into the reaction vessel so as to maintain the pH at 11 to 11.5. Further, the temperature of the solution in the reaction vessel was intermittently controlled with a heater so as to be constant at 50 ° C. After dropwise addition of the total amount of the raw material solution, stirring and heating were stopped and the contents of the reaction vessel were allowed to stand overnight. Next, a slurry of the precipitate was collected from the reaction vessel. The collected slurry was washed with water, filtered, and dried at 110 ° C. overnight to obtain a dry powder of coprecipitated hydroxide. The obtained dry powder was mixed with a predetermined amount of lithium hydroxide monohydrate powder to obtain a precursor of Comparative Example 4.

  A precursor, an active material, and a lithium ion secondary battery of Comparative Example 4 were produced in the same manner as in Example 2 except for the above items.

  In the same manner as in Example 2, the endothermic peak temperature of the precursor of Comparative Example 4 was measured. In the same manner as in Example 2, the composition and crystal structure of the active material in Comparative Example 4 were analyzed. In the same manner as in Example 2, the discharge capacity and cycle characteristics of the battery of Comparative Example 4 were evaluated. The results are shown in Table 1. In addition, as shown in Table 1 below, the crystallization temperature of Comparative Example 4 was higher than that of the Examples. This is because the composition of Li, Ni, Co, and Mn in the precursor of Comparative Example 4 became non-uniform because the precursor of Comparative Example 4 was prepared by a coprecipitation method different from that of the Example. The present inventors think that.

(Examples 6, 7, 27, 28)
In Example 6, instead of pulverizing the precursor with a mortar, the mass of the precursor after evaporation to dryness was roughly pulverized to adjust the specific surface area of the precursor to the value shown in Table 2. In Example 7, instead of grinding the precursor with a mortar, the specific surface area of the precursor was adjusted to the values shown in Table 2 by grinding with a bead mill. In Example 27, since the precursor after evaporation to dryness was not crushed, the specific surface area of the precursor was a value shown in Table 2. In Example 28, instead of pulverizing the precursor with a mortar, the specific surface area of the precursor was adjusted to the values shown in Table 2 by pulverizing with a planetary ball mill.

Except for the above, the precursors, active materials, and lithium ion secondary batteries of Examples 6, 7, 27, and 28 were produced in the same manner as in Example 2. In the same manner as in Example 2, the endothermic peak temperatures of the precursors of Examples 6, 7, 27, and 28 were measured. In the same manner as in Example 2, the composition and crystal structure of the active materials of Examples 6, 7, 27, and 28 were analyzed. In the same manner as in Example 2, the discharge capacity and cycle characteristics of the batteries of Examples 6, 7, 27, and 28 were evaluated. The results are shown in Table 2. The compositions of the active materials in Examples 6, 7, 27, and 28 are all Li _1.2 Ni _0.17 Co _0.08 Mn _0.55 O ₂ as in Example 2.

(Examples 8 to 19, 30 and Comparative Example 7)
In Example 8, aluminum nitrate nonahydrate was used as the Al source in the precursor raw material mixture. In Example 9, silicon dioxide was used as the Si source in the precursor raw material mixture. In Example 10, zirconium nitrate oxide dihydrate was used as the Zr source in the precursor raw material mixture. In Example 11, titanium sulfate hydrate was used as a Ti source in the precursor raw material mixture. In Example 12, magnesium nitrate hexahydrate was used as the Mg source in the precursor raw material mixture. In Example 13, niobium oxide was used as the Nb source in the precursor raw material mixture. In Example 14, barium carbonate was used as the Ba source in the precursor raw material mixture. In Example 15, vanadium oxide was used as a V source in the precursor raw material mixture. In Example 30, iron sulfate heptahydrate was used as the Fe source in the precursor raw material mixture. In Example 19 and Comparative Example 7, lithium fluoride was used as the F source in the precursor raw material mixture.

  In Examples 8 to 19, 30 and Comparative Example 7, precursor raw material mixtures were prepared so that the composition of the active material obtained after firing was as shown in Table 3. Except for the above items, the precursors, active materials, and lithium ion secondary batteries of Examples 8 to 19, 30 and Comparative Example 7 were produced in the same manner as in Example 2.

  In the same manner as in Example 2, the endothermic peak temperatures of the precursors of Examples 8 to 19, 30 and Comparative Example 7 were measured. The compositions and crystal structures of the active materials of Examples 8 to 19, 30 and Comparative Example 7 were analyzed in the same manner as in Example 2. In the same manner as in Example 2, the discharge capacities and cycle characteristics of the batteries of Examples 8 to 19, 30 and Comparative Example 7 were evaluated. The results are shown in Table 3.

It was confirmed that the composition of the active material of each Example shown in Tables 1 to 3 is within the range of the following composition formula (1). It was confirmed that the endothermic peak temperatures of the precursors in each Example were 550 ° C. or lower. It was confirmed that each active material formed from the precursor of each example had a rhombohedral space group R (-3) m structure.
_{Li y Ni a Co b Mn c} M d O x F z (1)
In the above formula (1), the element M is at least one element selected from the group consisting of Al, Si, Zr, Ti, Fe, Mg, Nb, Ba, and V, and 1.9 ≦ (a + b + c + d + y) ≦ 2 0.1, 1.0 ≦ y ≦ 1.3, 0 <a ≦ 0.3, 0 ≦ b ≦ 0.25, 0.3 ≦ c ≦ 0.7, 0 ≦ d ≦ 0.1, 1.9 ≦ (x + z) ≦ 2.0, 0 ≦ z ≦ 0.15.

  And in any battery of the examples, it was confirmed that the discharge capacity was 210 mAh / g or more and the cycle characteristics were 85% or more.

  It was confirmed that each active material formed from the precursor of each comparative example has a rhombohedral space group R (-3) m structure. However, in the case of the comparative example, it was confirmed that the endothermic peak temperature of the precursor exceeded 550 ° C., or the composition of the active material obtained from the precursor was out of the range of the composition formula (1). . As a result, it was confirmed that any of the batteries of the comparative examples had a capacity of less than 210 mAh / g or a cycle characteristic of less than 85%.

DESCRIPTION OF SYMBOLS 10 ... Positive electrode, 20 ... Negative electrode, 12 ... Positive electrode collector, 14 ... Positive electrode active material layer, 18 ... Separator, 22 ... Negative electrode collector, 24 ... Negative electrode Active material layer, 30 ... power generation element, 50 ... case, 60, 62 ... lead, 100 ... lithium ion secondary battery.

Claims (4)

An active material precursor,
The active material obtained by firing the precursor has a layered structure and is represented by the following composition formula (1):
In the suggested thermal analysis of the precursor in the atmosphere, the endothermic peak temperature exhibited by the precursor when the temperature of the precursor is increased from 300 ° C. to 800 ° C. is 550 ° C. or less.
precursor.
_{Li y Ni a Co b Mn c} M d O x F z (1)
[In the above formula (1), the element M is at least one element selected from the group consisting of Al, Si, Zr, Ti, Fe, Mg, Nb, Ba and V, and 1.9 ≦ (a + b + c + d + y) ≦ 2.1, 1.0 ≦ y ≦ 1.3, 0 <a ≦ 0.3, 0 ≦ b ≦ 0.25, 0.3 ≦ c ≦ 0.7, 0 ≦ d ≦ 0.1, 9 ≦ (x + z) ≦ 2.0, 0 ≦ z ≦ 0.15. ] The specific surface area is 0.5 to 6.0 m ² / g,
The precursor according to claim 1. It comprises a step of heating the precursor according to claim 1 or 2 at 500 to 1000 ° C.
A method for producing an active material. The positive electrode active material layer contains an active material obtained by the method for producing an active material according to claim 3,
Lithium ion secondary battery.