JP2011251874A - Method for producing lithium-containing composite oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a lithium-containing composite oxide which is used as a positive electrode active mateiral of a nonaqueous electrolyte secondary battery.SOLUTION: The method includes steps of: dissolving raw materials in a solvent to prepare a solution; gelling the resulting solution; adding conductive carbon particles to the resulting gel followed by pulverizing the gel; and firing the resulting gel. LiMPXO(1), wherein M is at least one element selected from the group consisting of Fe, Ni, Mn, Zr, Sn, Al and Y; X is at least one selected from the group consisting of Si and Al; 0<x≤2, 0.8≤y≤1.2, and 0≤z≤1.

Description

  The present invention relates to a method for producing a lithium-containing composite oxide, and more particularly to a method for producing a lithium-containing composite oxide used as a positive electrode active material for a non-aqueous electrolyte secondary battery.

  As a non-aqueous electrolyte secondary battery, a lithium secondary battery has been put into practical use and is widely spread. Further, in recent years, lithium secondary batteries are attracting attention not only as small-sized batteries for portable electronic devices but also as large-capacity devices for on-vehicle use and power storage. Therefore, demands for safety, cost, life, etc. are higher.

  The lithium secondary battery has a positive electrode, a negative electrode, an electrolytic solution, a separator, and an exterior material as main components. The positive electrode includes a positive electrode active material, a conductive material, a current collector, and a binder (binder).

In general, a layered transition metal oxide typified by lithium cobaltate (LiCoO ₂ ) is used as the positive electrode active material. However, the layered transition metal oxide easily causes oxygen desorption at a relatively low temperature of about 150 ° C. in a fully charged state, and the thermal desorption reaction of the battery can occur due to the oxygen desorption. Therefore, when a battery having such a positive electrode active material is used for a portable electronic device, there is a risk that an accident such as heat generation or ignition of the battery may occur.

For this reason, a lithium-containing composite oxide, such as lithium iron phosphate (LiFePO ₄ ), which has a stable olivine structure and has an olivine structure that is safer than LiCoO ₂ is expected. Since lithium iron phosphate does not contain cobalt having a low crustal abundance, there is also an advantage that it is relatively inexpensive. In addition, lithium iron phosphate has an advantage that it is structurally more stable than the layered transition metal oxide.

  However, since lithium iron phosphate has a large electric resistance, there is a problem that a sufficient discharge capacity cannot be obtained. On the other hand, a method for improving the conductivity of lithium iron phosphate by coating the surface of lithium iron phosphate particles with carbon has been proposed (for example, Patent Document 1). In the method of Patent Document 1, a resin-encapsulated mixture containing a mixed precipitate containing a raw material is heat-treated at a temperature of 600 ° C. to 800 ° C. in a reducing atmosphere to obtain lithium iron phosphate.

JP 2005-530676 Gazette

  However, the method of Patent Document 1 has a problem in that the production cost increases because the firing temperature must be increased due to the need to carbonize the resin. Moreover, in the method of patent document 1, although it is necessary to grind | pulverize in order to control the magnitude | size of the secondary particle of lithium iron phosphate, there exists a problem that the crystallinity of lithium iron phosphate falls by grinding | pulverization. In addition, the carbon coating film is peeled off during pulverization, resulting in a problem that the conductivity is lowered.

  Accordingly, an object of the present invention is to provide a method for producing a lithium-containing composite oxide that can be fired at a lower temperature and can improve conductivity without lowering crystallinity.

In order to solve the above problems, a method for producing a lithium-containing composite oxide of the present invention is a method for producing a lithium-containing composite oxide represented by the following general formula (1), wherein a raw material is dissolved in a solvent. A step of preparing a solution, a step of gelling the obtained solution, a step of adding and pulverizing conductive carbon particles to the obtained gel, and a step of firing the obtained gel. Features.
_{Li x M y P 1-z} X z O 4 (1)
(Wherein, M is at least one element selected from the group consisting of Fe, Ni, Mn, Zr, Sn, Al and Y, and X is at least one selected from the group consisting of Si and Al) Seeds, 0 <x ≦ 2, 0.8 ≦ y ≦ 1.2, 0 ≦ z ≦ 1.)

  In the present invention, M in the general formula (1) is preferably Fe and Zr, and X is preferably Si.

  Moreover, in this invention, it is preferable to add the said conductive carbon particle so that it may become 1 to 40 weight% of the lithium containing complex oxide to produce | generate.

According to the present invention, unlike the case where the precipitation of the raw material is generated as in Patent Document 1, since the raw material element can be uniformly dispersed in the gel, it can be fired at a lower temperature.
In addition, the conductive carbon particles not only improve the conductivity of the finally obtained lithium-containing composite oxide, but also have the effect of suppressing the aggregation of the primary particles, thereby suppressing the coarsening of the secondary particles. You can also. Therefore, since it is not necessary to grind the lithium-containing composite oxide after firing for particle size control, the crystallinity of the lithium-containing composite oxide does not deteriorate. Further, in the present invention, since conductive carbon particles are used, there is no need to carbonize the resin as in Patent Document 1, so that the firing temperature can be further lowered.

3 is an X-ray diffraction pattern showing the structure of a lithium-containing composite oxide obtained in Example 1. FIG. 3 is an X-ray diffraction pattern showing the structure of a lithium-containing composite oxide obtained in Example 2. FIG.

  Hereinafter, embodiments of the present invention will be described in detail.

(1) Lithium-containing composite oxide The lithium-containing composite oxide that is the production target of the present invention is represented by the following general formula (1).
_{Li x M y P 1-z} X z O 4 (1)

  In the formula, M is at least one element selected from the group consisting of Fe, Ni, Mn, Zr, Sn, Al, and Y. By selecting M from this group, it is possible to prevent physical stress (volume shrinkage expansion) of the lithium-containing composite oxide that accompanies repeated charge / discharge (insertion / desorption of Li). Can provide. Furthermore, it is preferable that M contains Fe. By including Fe, a cheaper raw material can be used for the production of the lithium-containing composite oxide. In addition, in the element which can take various valences, the valence for prescribing “y” in the general formula (1) means an average value.

  X is at least one selected from the group consisting of Si and Al. Therefore, two types may be selected simultaneously. By selecting X from this group, it is possible to prevent physical stress (volume shrinkage expansion) of the lithium-containing composite oxide that accompanies repeated charge / discharge (Li insertion / desorption), so that the positive electrode active material having a longer lifespan Can provide. Furthermore, it is preferable to select at least Si that is more ionic than Al. By selecting Si, the bond between the metal M constituting the lithium-containing composite oxide and oxygen can be further strengthened, so that a positive electrode active material that is more resistant to physical stress can be provided.

  X is in the range of 0 <x ≦ 2. Further, x increases or decreases depending on the type of other elements constituting the lithium-containing composite oxide, charging, or discharging. Preferably, the range of x is 0.8 ≦ x ≦ 1.2.

  Moreover, y is in the range of 0.8 ≦ y ≦ 1.2. If it is this range, the lithium containing complex oxide which has the olivine structure which can be charged / discharged can be provided. Preferably, the range of y is 0.9 ≦ y ≦ 1.1.

  Z is in the range of 0 ≦ z ≦ 1. If it is this range, the lithium containing complex oxide which has the olivine structure which can be charged / discharged can be provided. Preferably, the range of z is 0.1 ≦ z ≦ 0.5.

As a specific example of the lithium-containing composite oxide,
Li _x Fe _y P _1-z O ₄
(0.8 ≦ x ≦ 1.2, 0.8 ≦ y ≦ 1.2, z = 0),
_{Li x Ni y P 1-z} O 4
(0.8 ≦ x ≦ 1.2, 0.8 ≦ y ≦ 1.2, z = 0),
_{Li x Mn y P 1-z} O 4
(0.8 ≦ x ≦ 1.2, 0.8 ≦ y ≦ 1.2, z = 0),
_{Li x (Fe, Ni) y} P 1-z O 4
(0.8 ≦ x ≦ 1.2, 0.8 ≦ y ≦ 1.2, z = 0),
_{Li x (Fe, Mn) y} P 1-z O 4
(0.8 ≦ x ≦ 1.2, 0.8 ≦ y ≦ 1.2, z = 0),
_{Li x (Fe, Zr) y} P 1-z O 4
(0.8 ≦ x ≦ 1.2, 0.8 ≦ y ≦ 1.2, z = 0),
Li _x (Fe, Sn) _y P _1-z O ₄
(0.8 ≦ x ≦ 1.2, 0.8 ≦ y ≦ 1.2, z = 0),
_{Li x (Fe, Y) y} P 1-z O 4
(0.8 ≦ x ≦ 1.2, 0.8 ≦ y ≦ 1.2, z = 0),
_{Li x (Fe, Ni) y} P 1-z Si z O 4
(0.8 ≦ x ≦ 1.2, 0.8 ≦ y ≦ 1.2, 0 <z ≦ 0.5),
_{Li x (Fe, Mn) y} P 1-z Si z O 4
(0.8 ≦ x ≦ 1.2, 0.8 ≦ y ≦ 1.2, 0 <z ≦ 0.5),
_{Li x (Fe, Zr) y} P 1-z Si z O 4
(0.8 ≦ x ≦ 1.2, 0.8 ≦ y ≦ 1.2, 0 <z ≦ 0.5),
_{Li x (Fe, Sn) y} P 1-z Si z O 4
(0.8 ≦ x ≦ 1.2, 0.8 ≦ y ≦ 1.2, 0 <z ≦ 0.5),
_{Li x (Fe, Y) y} P 1-z Si z O 4
(0.8 ≦ x ≦ 1.2, 0.8 ≦ y ≦ 1.2, 0 <z ≦ 0.5),
Etc. When M is composed of a plurality of elements, the value of each atomic% can take any value in the range of more than 0 atomic% and less than 100 atomic% with respect to the total amount of M.

From the viewpoint of use as a positive electrode active material, a particularly preferred lithium-containing composite oxide is
_{Li x (Fe, Zr) y} P 1-z Si z O 4
(0.8 ≦ x ≦ 1.2, 0.8 ≦ y ≦ 1.2, 0 <z ≦ 0.5),
_{Li x (Fe, Sn) y} P 1-z Si z O 4
(0.8 ≦ x ≦ 1.2, 0.8 ≦ y ≦ 1.2, 0 <z ≦ 0.5),
_{Li x (Fe, Y) y} P 1-z Si z O 4
(0.8 ≦ x ≦ 1.2, 0.8 ≦ y ≦ 1.2, 0 <z ≦ 0.5),
_{Li x (Fe, Ti) y} P 1-z Si z O 4
(0.8 ≦ x ≦ 1.2, 0.8 ≦ y ≦ 1.2, 0 <z ≦ 0.5),
_{Li x (Fe, Nb) y} P 1-z Si z O 4
(0.8 ≦ x ≦ 1.2, 0.8 ≦ y ≦ 1.2, 0 <z ≦ 0.5),
_{Li x (Fe, V) y} P 1-z Si z O 4
(0.8 ≦ x ≦ 1.2, 0.8 ≦ y ≦ 1.2, 0 <z ≦ 0.5),
It is.

  The lithium-containing composite oxide is usually used in the form of particles. The particle size of the primary particles is 1 μm or less, preferably 10 nm to 1 μm, in order to increase the efficiency of lithium ion insertion / extraction. The lower limit of the primary particle size is about 10 nm, which is realistic in view of the efficiency of insertion / desorption and the manufacturing cost. The particle size of the primary particles can be measured by direct observation with an SEM and a particle size distribution measuring device by a laser diffraction / scattering method.

  The particle size of the secondary particles is 100 μm or less, preferably 10 nm to 100 μm, in order to increase the efficiency of lithium ion insertion / extraction. The particle size of the secondary particles can be measured by direct observation with an SEM and a particle size distribution measuring device by a laser diffraction / scattering method.

(2) Method for Producing Lithium-Containing Composite Oxide The present invention includes a step of dissolving a raw material in a solvent (hereinafter referred to as a dissolution step) and a step of gelling the obtained solution (hereinafter referred to as a gelation step). The method includes at least a step of adding conductive carbon particles to the obtained gel and crushing, and a step of firing the obtained gel (hereinafter referred to as a firing step). In addition, as needed, the process (henceforth a drying process) which removes a solvent from the gel obtained by the gelatinization process, the process (henceforth a carbon source) which mixes the substance used as a carbon source with the gel before baking. A mixing step).

(I) Dissolution process The lithium source, the element M source, the phosphorus source, and the element X source as raw materials are not particularly limited as long as they are substances that can be dissolved in a solvent. These substances are preferably substances that can dissolve 10 mmol or more in 100 g of a solvent.

(Lithium source)
As the lithium source, inorganic lithium salts, hydroxides, organic acid salts, metal alkoxides, and hydrates of these salts can be used. Specifically, as the inorganic salt, lithium carbonate (Li ₂ CO ₃ ) which is a salt with a weak acid (hereinafter referred to as a weak acid salt), lithium nitrate (hereinafter referred to as a strong acid salt) with a strong acid. LiNO ₃ ) and lithium chloride (LiCl) can be mentioned. Examples of organic salts include weak acetates such as lithium acetate (LiCH ₃ COO) and lithium oxalate (COOLi) ₂ . The metal alkoxide is lithium methoxide (LiOCH _3), lithium ethoxide (LiOC ₂ H _5), lithium -n- propoxide _{(LiO-n-C 3 H} 7), lithium -i- propoxide (LiO _-i-C 3 _H 7), lithium -n- butoxide _{(LiO-n-C 4 H} 9), lithium -t- butoxide _{(LiO-t-C 4 H} 9), lithium -sec- butoxide (LiO-sec -C ₄ H _9), and the like. Hydrate may be sufficient about an inorganic salt and organic salt. Among these, a weak acid salt or a strong acid salt is preferable from the viewpoint of being easy to produce a uniform solution in an air atmosphere and being inexpensive, and among them, lithium acetate or lithium nitrate is preferable. In the present invention, the “homogeneous solution” refers to a state where no precipitate is observed by visual observation and the phase is not separated into two or more phases.

Hereinafter, the case where ethanol is used as a solvent will be described.
When an anhydride of a weak acid salt is used as the lithium source, since the solubility in ethanol is low, it is preferable to dissolve after dissolving the hydrate of the iron source salt or the zirconium source salt. When the iron source salt hydrate or the zirconium source salt hydrate is dissolved before being added, it is preferably dissolved in water in advance. Alternatively, an amount of water required to dissolve the weak acid salt anhydride may be added to ethanol. The amount of water in which the anhydride of the weak acid salt is dissolved is preferably 1 to 100 times the number of moles of Li, more preferably 4 to 20 times.

  Moreover, even if the anhydride of a weak acid salt is dissolved in an arbitrary order in an arbitrary combination of an iron source, a zirconium source, and a silicon source, a uniform solution can be obtained. After the obtained uniform solution is reacted in advance, the remaining raw materials may be added. It is preferable that the anhydride of the weak acid salt is previously reacted with the hydrate of the iron source salt. By reacting the anhydride of the weak acid salt and the hydrate of the iron source salt in advance, it is possible to suppress the formation of a precipitate when phosphoric acid is added.

  The anhydride of the weak acid salt is preferably reacted in advance with tetramethoxysilane or tetraethoxysilane, and particularly preferably reacted with tetramethoxysilane. As a mixing procedure at this time, it is preferable to dissolve the anhydride of the weak acid salt in water, add ethanol, and then add tetramethoxysilane or tetraethoxysilane. The reaction can be further promoted by heating from 30 ° C. to 60 ° C. after mixing them. The heating time is not particularly limited, but about 30 minutes to 12 hours is appropriate. By reacting the weak acid salt anhydride with the silicon source in advance, generation of impurities after firing and substitution of Fe into Li sites in the lithium composite oxide can be suppressed.

(Iron source)
As the iron source substance, inorganic iron salts, hydroxides, organic acid salts, metal alkoxides, and hydrates of these salts can be used. As an iron source, as an inorganic salt, iron (II) carbonate (Fe (CO ₃ )) which is a weak acid salt, iron nitrate (II) (Fe (NO ₃ ) ₂ ) which is a strong acid salt, iron (III) nitrate ( Mention may be made of Fe (NO ₃ ) ₃ ), iron (II) chloride (FeCl ₂ ) and iron (III) chloride (FeCl ₃ ). Moreover, as an organic salt, iron (II) oxalate (FeC ₂ O ₄ ), iron (III) oxalate (Fe ₂ (C ₂ O ₄ ) ₃ ), iron (II) acetate (Fe) which are weak acid salts. (CH ₃ COO) ₂ ) and iron (III) acetate (Fe (CH ₃ COO) ₃ ). A strong acid salt hydrate is preferable, and iron (III) nitrate nonahydrate is more preferable.

Hereinafter, the case where ethanol is used as a solvent will be described.
Even if the strong acid salt hydrate is dissolved in any order in any combination of a lithium source, a zirconium source and a silicon source, a uniform solution can be obtained. After the obtained uniform solution is reacted in advance, the remaining raw materials may be added. It is preferable to add the strong acid salt hydrate to the solvent prior to phosphoric acid. Since the formation of impurities after calcination can be suppressed by reacting only the strong acid salt hydrate in advance, the strong acid salt hydrate is precipitated after dissolving only the strong acid salt hydrate in ethanol. You may make it react previously by applying heat to such an extent that a thing does not arise.

(Zirconium source)
As the zirconium source, inorganic salts of zirconium, organic acid salts, metal alkoxides, and hydrates of these salts can be used. The zirconium source, inorganic salts, zirconium chloride (ZrCl ₄₎ zirconium halides, zirconium bromide (ZrBr _4), zirconium iodide _(ZrI 4), an oxy zirconium salts, zirconium oxychloride (ZrOCl ₂₎ And zirconium oxynitrate (ZrO (NO ₃ ) ₂ ). Examples of the metal alkoxide include zirconium methoxide (Zr (OCH ₃ ) ₄ ), zirconium ethoxide (Zr (OC ₂ H ₅ ) ₄ ), zirconium-n-propoxide (Zr (On-C ₃ H _{7). 4} ), zirconium-i-propoxide (Zr (O-i-C ₃ H ₇ ) ₄ ), zirconium-n-butoxide (Zr (On-C ₄ H ₈ ) ₄ ), zirconium-t-butoxide (Zr (Ot-C ₄ H ₈ ) ₄ ), zirconium-sec-butoxide (Zr (Ot-C ₄ H ₈ ) ₄ ), and the like. Zirconium halides are preferable, and among them, zirconium chloride is preferable.

  Zirconium halide can obtain a uniform solution even if it is dissolved in any order in any combination of a lithium source, an iron source, and a silicon source. Zirconium halide is preferably reacted in advance with an iron source comprising a strong acid salt hydrate. By previously reacting the zirconium halide with an iron source comprising a strong acid salt hydrate, it is possible to suppress the formation of impurities such as zirconia and zirconium phosphate after firing. The zirconium halide is preferably reacted in advance with tetramethoxysilane or tetraethoxysilane, particularly preferably with tetramethoxysilane. By reacting the zirconium halide with the silicon source in advance, generation of impurities after firing and substitution of Fe with Li sites in the lithium composite oxide can be suppressed.

(Phosphorus source)
Examples of the phosphorus source substance include phosphoric acid (H ₃ PO ₄ ), ammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), and the like. . Among these, phosphoric acid is preferable.

Hereinafter, a method for dissolving a phosphorus source will be described in the case where ethanol is used as a solvent.
Phosphoric acid needs to be added after at least a lithium source, an iron source and a zirconium source are dissolved. This is because when phosphoric acid is mixed with lithium weak acid anhydride or zirconium halide, a precipitate is formed. When adding phosphoric acid, phosphoric acid may be added in excess. By adding phosphoric acid in excess, generation of impurities after firing and substitution of Fe with Li sites in the lithium composite oxide can be suppressed. When phosphoric acid is added excessively, it can be added excessively in the range of 5 to 20% by weight, more preferably in the range of 5 to 15% by weight with respect to the stoichiometric ratio of phosphoric acid.

(Silicon source)
As the silicon source material, silicon metal alkoxide can be used. Specific examples include tetraethoxysilane (Si (OC ₂ H ₅ ) ₄ ), tetramethoxysilane (Si (OCH ₃ ) ₄ ), methyltriethoxysilane (CH ₃ Si (OC ₂ H ₅ ) ₃ ), methyltri Various types such as methoxysilane (CH ₃ Si (OCH ₃ ) ₃ ), ethyl methoxysilane (C ₂ H ₅ Si (OCH ₃ ) ₃ ), ethyltriethoxysilane (C ₂ H ₅ Si (OC ₂ H ₅ ) ₃ ), etc. The silicon alkoxide can be mentioned. Tetraethoxysilane or tetramethoxysilane is preferable.

Hereinafter, a method for dissolving a silicon source will be described in the case where ethanol is used as a solvent.
Silicon alkoxide can obtain a uniform solution even if it is dissolved in an arbitrary order in any combination of a lithium source, an iron source and a zirconium source. Water may be added to promote the reaction of silicon alkoxide. The amount of water added is 1 to 100 times, more preferably 2 to 20 times the number of moles of silicon. By adding water, hydrolysis proceeds and the reaction can be promoted. Silicon alkoxide can be pre-reacted with phosphoric acid. When using tetraethoxysilane, it is preferable to make it react at 40 to 80 degreeC, More preferably, it is made to react at 50 to 80 degreeC. When using tetramethoxysilane, it is preferable to make it react at 20 to 60 degreeC. When tetramethoxysilane is reacted with a weak acid anhydride serving as a lithium source, it is preferable that (number of moles of Li as a lithium source / number of moles of Si as a silicon source) ≧ 2.

  As the solvent, at least one alcohol selected from the group consisting of methanol, ethanol, n-propanol, isopropanol, and n-butanol can be used. Ethanol is preferable. In addition, in order to dissolve the raw material substance having low solubility in alcohol, a mixed solvent with water may be used as necessary. The amount of the solvent is not particularly limited as long as all raw materials can be dissolved. However, in consideration of the solvent recovery cost, the amount of the solvent is in the range of 1 to 100 times the molar ratio, more preferably in the range of 2 to 15 times the molar ratio with respect to the total moles of all raw materials. .

(Dissolution method)
In the dissolving step, a precipitate may be generated depending on the order of dissolving the raw material, and a uniform solution may not be obtained. Therefore, the order of dissolving the raw material is important. As described above, when phosphoric acid is mixed with a zirconium source, a precipitate is formed. However, when iron ions are present, zirconium ions are stabilized and the formation of precipitates is suppressed. Therefore, in the present invention, it is necessary to dissolve the phosphorus source in a solvent in which at least the iron source and the zirconium source are dissolved. The silicon source may be dissolved before the phosphorus source is dissolved, or may be dissolved after the phosphorus source is dissolved.
In the present invention, the order of dissolving the raw material substances refers to the order of the raw material substances to be charged when the raw material substances are sequentially added to the solvent, but the solution in which a plurality of raw material substances are dissolved in the solvent in advance is used. When preparing and mixing the solution, it refers to the order of mixing.

  The order of preparing the solvent in which the iron source and the zirconium source are dissolved is not particularly limited as long as the zirconium ions can be stabilized by the iron ions. As a method of stabilizing zirconium ions with iron ions, after dissolving a strong acid salt hydrate of iron in a solvent, a method of dissolving a zirconium halide, or after dissolving a zirconium halide in a solvent, And a method of dissolving an iron strong acid salt hydrate and a zirconium halide simultaneously in a solvent. In addition, the order of melt | dissolution of an iron source and a zirconium source is not specifically limited, Either may melt | dissolve first or may melt | dissolve both simultaneously.

  In addition, when a salt anhydride such as lithium acetate is used as the lithium source, it does not dissolve unless water is contained in the solvent. Therefore, when an anhydrous salt is used as the lithium source, it is preferable to dissolve the iron salt hydrate and zirconium salt hydrate after dissolving them in a solvent.

  When the raw material is dissolved in the solvent, it may be heated to room temperature or higher. As heating temperature, it is the range of the boiling point of the solvent to be used from room temperature, Preferably it is 30 to 80 degreeC, More preferably, it is 30 to 60 degreeC. In the present invention, room temperature means a range of 20 ± 10 ° C.

  In the description of the melting step, an example in which iron and zirconium are used as the element M and silicon is used as the element X has been described. However, the elements M and X included in the general formula (1) are all raw material substances. There is no particular limitation as long as it is a combination that can be uniformly dissolved in a solvent.

(Ii) Gelation step In this step, the solution obtained in the dissolution step is gelled. Gelation is a group of aggregates in which raw material elements such as Li, Fe, Zr, P and Si are bonded through oxygen atoms, and these aggregates are formed as fine particles having a particle diameter of several to several tens of nm in the gel. The inventors believe that the precipitation is carried out by increasing the viscosity of the solution.

  In the gelation method, the solution may be left still or the solution may be stirred. Moreover, in order to accelerate | stimulate gelatinization, you may heat to the temperature more than room temperature. The heating temperature is in the range from room temperature to the boiling point of the solvent used, preferably 30 ° C to 80 ° C, more preferably 40 ° C to 60 ° C. The heating time is 10 minutes to 48 hours, preferably 30 minutes to 24 hours.

(Iii) Drying step In this step, the remaining solvent is removed from the gelled gel. As a method for removing the solvent, a method of standing at room temperature, a method of removing the solvent by heating to 30 to 80 ° C., a gel is placed in a chamber using a rotary pump, and the solvent is removed by reducing the pressure. A method or the like can be used. Alternatively, the solvent may be removed by the same method as described above after performing solvent exchange with a solvent having higher volatility than the solvent used at the time of preparing the solution or a solvent having a different surface tension. Examples of the solvent used for solvent exchange include toluene, benzene, hexane, tetrahydrofuran, isopropanol, and mixed solvents thereof. The solvent can also be removed by immersing the gel obtained in this step in carbon dioxide in a supercritical state and extracting the solvent. These removed solvents are preferably recovered and reused from an industrial viewpoint.

(Iv) Grinding step In this step, the size of the secondary particles is controlled by adding conductive carbon particles to the obtained gel and mechanically grinding. The pulverization method is not particularly limited, and examples thereof include a method of heating, cooling and controlling the atmosphere as necessary.

  Examples of the pulverization method include, but are not limited to, a planetary ball mill, a ball mill, a bead mill, a vibration mill, a pin mill, an atomizer, a homogenizer, a rotor mill, a roller mill, a hammer mill, and a jet mill.

  Use carbon black such as acetylene black, channel black, ketjen black, natural graphite, artificial graphite, needle coke, carbon fiber, vapor grown carbon fiber, carbon nanotube, carbon nan fiber, etc. as conductive carbon particles Can do. Acetylene black and vapor grown carbon fiber are preferred. Two or more of these conductive carbon particles may be used. The addition amount of the conductive carbon particles is 1 to 40% by weight of the lithium-containing composite oxide that is a predicted product. The average particle size of the conductive carbon particles is 50 nm to 100 μm.

(V) Carbon source mixing step Sugars, fats and synthetic resin materials may be mixed with the crushed gel. These compounds are carbonized during firing, thereby forming a carbon coating on the surface of the positive electrode material and improving the conductivity of the positive electrode material. As the saccharide, sucrose, fructose and the like can be used. As the synthetic resin material, polyethers such as polyethylene glycol and polypropylene glycol, polyvinyl alcohol, polyacrylamide, carboxymethyl cellulose, polyvinyl acetate, and the like can be used as the polyether.

(Vi) Firing step In this step, the obtained gel is fired to obtain a lithium-containing composite oxide. Firing is performed at a temperature range of 400 to 700 ° C., preferably 400 to 600 ° C., for 1 to 24 hours. As an atmosphere during firing, an inert atmosphere (an atmosphere such as argon, nitrogen, or vacuum) or a reducing atmosphere (an atmosphere such as a hydrogen-containing inert gas or carbon monoxide) can be used. In order to perform uniform firing, the gel may be agitated, and if a toxic gas such as NO _x , SO _x , or chlorine is generated during firing, a removal device may be provided.

(Vii) Other steps The obtained lithium-containing composite oxide may be adjusted to a desired particle size by subjecting it to a pulverization step and / or a classification step, if necessary.

(3) Use The obtained lithium containing complex oxide can be used for the positive electrode active material of a non-aqueous electrolyte secondary battery. The positive electrode active material, in addition to the above-mentioned lithium-containing complex _{oxide, LiCoO 2, LiNiO 2, LiFeO} 2, LiMnO 2, LiMn 2 O 4, Li 2 MnO 3, LiCoPO 4, LiNiPO 4, LiMnPO 4, LiFePO 4 , etc. Other oxides may be included.

The non-aqueous electrolyte secondary battery has a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator. Hereinafter, each constituent material will be described.
(A) Positive electrode A positive electrode is producible using a well-known method. For example, a positive electrode active material, a conductive material, and a binder can be kneaded and dispersed using an organic solvent to obtain a paste, and the paste can be applied to a current collector. Note that when the obtained lithium-containing composite oxide has sufficiently high conductivity, the conductive material is not necessarily added.

  As binders, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, ethylene propylene diene polymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluororubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose, styrene Butadiene rubber or the like can be used. If necessary, a thickener such as carboxymethylcellulose can also be used.

  As the conductive material, acetylene black, natural graphite, artificial graphite, needle coke, or the like can be used.

  As the current collector, foamed (porous) metal having continuous pores, metal formed in a honeycomb shape, sintered metal, expanded metal, non-woven fabric, plate, perforated plate, foil, and the like can be used.

  As the organic solvent, N-methyl-2-pyrrolidone, toluene, cyclohexane, dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, methyl acrylate, diethyltriamine, N, N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc. are used. be able to. When a water-soluble binder is used, water can be used as a solvent.

  The thickness of the positive electrode is preferably about 0.01 to 20 mm. If it is too thick, the conductivity is lowered, and if it is too thin, the capacity per unit area is lowered. The positive electrode obtained by coating and drying may be compacted by a roller press or the like in order to increase the packing density of the active material.

(B) Negative electrode A negative electrode can be produced by a known method. For example, a negative electrode active material, a binder, and a conductive material are mixed, the obtained mixed powder is formed into a sheet shape, and the obtained molded body is pressure-bonded to a current collector, for example, a mesh current collector made of stainless steel or copper. Can be produced. Moreover, it can be produced using the method using the paste as described in the above (a) positive electrode. In that case, the negative electrode active material, the conductive material, and the binder are kneaded and dispersed using an organic solvent to obtain a paste. The paste can be produced by applying it to a current collector.

  A known material can be used as the negative electrode active material. In order to constitute a high energy density battery, it is preferable that the potential at which lithium is inserted / desorbed is close to the deposition / dissolution potential of metallic lithium. A typical example is a carbon material such as natural or artificial graphite in the form of particles (scale-like, lump-like, fibrous, whisker-like, spherical, pulverized particles, etc.).

  Examples of the artificial graphite include graphite obtained by graphitizing mesocarbon microbeads, mesophase pitch powder, isotropic pitch powder, and the like. Also, graphite particles having amorphous carbon attached to the surface can be used. Among these, natural graphite is preferable because it is inexpensive and close to the redox potential of lithium and can constitute a high energy density battery.

Further, lithium transition metal oxide, lithium transition metal nitride, transition metal oxide, silicon oxide, and the like can be used as the negative electrode active material. Among these, Li ₄ Ti ₅ O ₁₂ is preferable because it has high potential flatness and a small volume change due to charge and discharge.

(C) Nonaqueous electrolyte As the nonaqueous electrolyte, for example, an organic electrolyte, a gel electrolyte, a polymer solid electrolyte, an inorganic solid electrolyte, a molten salt, or the like can be used.

  Examples of the organic solvent constituting the organic electrolyte include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and butylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate, and dipropyl carbonate. Chain carbonates such as γ-butyrolactone (GBL), lactones such as γ-valerolactone, furans such as tetrahydrofuran and 2-methyltetrahydrofuran, diethyl ether, 1,2-dimethoxyethane, 1,2-diethoxy Examples include ethers such as ethane, ethoxymethoxyethane, dioxane, dimethyl sulfoxide, sulfolane, methyl sulfolane, acetonitrile, methyl formate, methyl acetate, and the like. Can.

  Moreover, since cyclic carbonates such as PC, EC and butylene carbonate are high-boiling solvents, they are suitable as solvents to be mixed with GBL.

Examples of the electrolyte salt constituting the organic electrolyte include lithium borofluoride (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium trifluoroacetate (LiCF ₃ COO) ), Lithium salts such as lithium bis (trifluoromethanesulfone) imide (LiN (CF ₃ SO ₂ ) ₂ ), and a mixture of one or more of these can be used. The salt concentration of the electrolytic solution is preferably 0.5 to 3 mol / l.

(D) Separator As the separator, a known material such as a porous material or a nonwoven fabric can be used. As a material for the separator, a material that does not dissolve or swell in the organic solvent in the electrolytic solution is preferable. Specific examples include polyester polymers, polyolefin polymers (for example, polyethylene and polypropylene), ether polymers, and glass fibers.

(E) Other members Various other known materials can be used for other members such as battery containers, and there is no particular limitation.

(F) Manufacturing method of secondary battery The secondary battery includes a laminate including, for example, a positive electrode, a negative electrode, and a separator sandwiched therebetween. The laminate may have, for example, a strip-like planar shape. In the case of producing a cylindrical or flat battery, the laminate may be wound to form a wound body.

  One or more of the laminates are inserted into the battery container. Usually, the positive electrode and the negative electrode are connected to the external conductive terminal of the battery. Thereafter, the battery container is sealed to block the positive electrode, the negative electrode, and the separator from the outside air.

  In the case of a cylindrical battery, the sealing method is generally a method in which a lid having a resin packing is fitted into the opening of the battery container and the battery container and the lid are caulked. In the case of a square battery, a method of attaching a lid called a metallic sealing plate to the opening and performing welding can be used. In addition to these methods, a method of sealing with a binder and a method of fixing with a bolt via a gasket can also be used. Furthermore, a method of sealing with a laminate film in which a thermoplastic resin is attached to a metal foil can also be used. An opening for electrolyte injection may be provided at the time of sealing. When using an organic electrolyte, the organic electrolyte is injected from the opening, and then the opening is sealed. Gas generated by energization before sealing may be removed.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example, this invention is not limited to a following example.

Example 1.
<I. Dissolution process>
The following were dissolved in the solvent in the order of iron source, lithium source, zirconium source, silicon source, and phosphorus source.
Fe (NO ₃ ) ₃ .9H ₂ O as an iron source was weighed in 30 times the molar amount of ethanol with respect to the molar amount of Li and stirred until it was completely dissolved. After confirming complete dissolution, LiCH ₃ COO is weighed as a lithium source, ZrCl ₄ is measured as a zirconium source, Si (OC ₂ H ₅ ) ₄ is weighed as a silicon source, and dissolved in order. Prepared. Finally, H ₃ PO ₄ (85 wt%) was weighed as a phosphorus source and stirred until a uniform solution was obtained. LiCH ₃ COO which is a lithium source is 0.9899 g, and Li: Fe: Zr: P: Si = 1: 0.875: 0.125: 0.75: 0.25 (molar ratio). The raw material was weighed.

<Ii. Gelation process>
The uniform solution stirred at room temperature for 1 hour was stored in a thermostatic bath at 60 ° C. for 24 hours to perform gelation. At the time of gelation, the container was covered to suppress evaporation of the solvent.

<Iii. Drying process>
In the gelation step, the lid of the obtained gel container was opened, and the solvent was volatilized by allowing it to stand in a constant temperature bath at 60 ° C. overnight.

<Iv. Grinding process>
Acetylene black was added to the precursor obtained by drying the gel in an amount of 10% by weight with respect to the weight of the lithium-containing composite oxide in a yield of 100%, and pulverized using a planetary ball mill. As the conditions of the planetary ball mill, zirconia balls with a diameter of 10 mm were used, and the treatment was performed for 1 hour at a rotational speed of 400 rpm.

<V. Carbon source mixing process>
A carbon source in which the ground precursor was dissolved in water was added. Sucrose was used as the carbon source. The amount added was 15% by weight based on the weight of the precursor. The precursor to which sucrose was added was dried and pulverized in a mortar.

<Vi. Firing step>
The precursor obtained by the pulverization step was calcined at 550 ° C. for 12 hours. As a firing process, first, the inside of the furnace was evacuated, then nitrogen was flowed, and the furnace was heated at a temperature rising rate of 200 ° C./h. The cooling rate was furnace cooling.

(Measurement of powder X-ray diffraction pattern)
About the obtained complex oxide, the powder X-ray-diffraction pattern was measured using the powder X-ray-diffraction apparatus MiniFlex II by Rigaku Corporation. The results are shown in FIG. It was confirmed that a crystal phase having an olivine type structure was generated and that there were no peaks attributed to impurities such as raw material and ZrO ₂ .

(Characteristic evaluation of battery)
About 1 g of the obtained positive electrode active material was weighed and pulverized in an agate mortar. As a conductive agent, about 10% by weight of acetylene black (trade name: “DENKA BLACK”, Denki Kagaku Kogyo) And a polyvinylidene fluoride resin powder of about 10% by weight with respect to the positive electrode active material as a binder. This mixture was dispersed in a solvent such as N-methyl-2-pyrrolidone to form a slurry, which was applied to both surfaces of an aluminum foil having a thickness of 20 μm by a doctor blade method. The coating amount was about 5 mg / cm ² . The electrode was dried and then pressed to obtain a positive electrode.

Approximately 30 ml of an electrolyte having a 1: 2 ratio of ethylene carbonate and diethyl carbonate in which 1 mol / l LiPF ₆ was dissolved in a 50 ml beaker was injected, and a lithium metal was used as a reference electrode together with a 2 cm × 2 cm positive electrode. A beaker cell was produced using metallic lithium as the counter electrode.

  The battery thus fabricated was charged for the first time in an environment of 25 ° C. The charging current was 0.1 mA, and the charging was terminated when the battery potential reached 4V. After charging was completed, discharging was performed at 0.1 mA. When the battery potential reached 2.0 V, discharging was terminated, and the measured capacity of the battery was obtained. These results are shown in Table 1. In this example, a high capacity of 96.0 mAh / g was obtained.

Example 2
In the dissolution step, polyethylene glycol 200 having an average molecular weight of 200 is added to a uniform solution in which all raw materials are dissolved, and the pulverization method in the pulverization step is a planetary ball mill, and acetylene black is obtained at a yield of 100% during pulverization. A lithium-containing composite oxide was obtained in the same manner as in Example 1 except that 10% by weight was added to the weight of the lithium-containing composite oxide and the carbon source mixing step was omitted. The amount of polyethylene glycol 200 added was 15% by weight with respect to the weight of the lithium-containing composite oxide at a yield of 100%. As the conditions of the planetary ball mill, zirconia balls with a diameter of 10 mm were used, and the treatment was performed for 1 hour at a rotational speed of 400 rpm.

(Measurement of powder X-ray diffraction pattern)
About the obtained complex oxide, the powder X-ray-diffraction pattern was measured like Example 1. FIG. The results are shown in FIG. It was confirmed that a crystal phase having an olivine type structure was generated and that there were no peaks attributed to impurities such as raw material and ZrO ₂ .

(Characteristic evaluation of battery)
A battery was produced by the same method as in Example 1 and the battery characteristics were evaluated. The results are shown in Table 1. In this example, a high capacity of 94.5 mAh / g was obtained.

Comparative Example 1
A battery was produced in the same manner as in Example 1 except that acetylene black was not added during the pulverization step, and the amount of acetylene black was changed to 20% by weight during the production of the positive electrode, and battery characteristics were evaluated. The results are shown in Table 1. In this comparative example, only a capacity of about 75.4 mAh / g could be obtained.

Claims (3)

A method for producing a lithium-containing composite oxide represented by the following general formula (1): a step of preparing a solution by dissolving a raw material in a solvent; a step of gelling the obtained solution; A method for producing a lithium-containing composite oxide, comprising: a step of adding conductive carbon particles to the obtained gel and pulverizing; and a step of firing the obtained gel.
_{Li x M y P 1-z} X z O 4 (1)
(Wherein, M is at least one element selected from the group consisting of Fe, Ni, Mn, Zr, Sn, Al and Y, and X is at least one selected from the group consisting of Si and Al) Seeds, 0 <x ≦ 2, 0.8 ≦ y ≦ 1.2, 0 ≦ z ≦ 1.)   The production method according to claim 1, wherein M in the general formula (1) is Fe and Zr, and X is Si.   The manufacturing method of Claim 1 or 2 which adds the said conductive carbon particle so that it may become 1 to 40 weight% of the lithium containing complex oxide to produce | generate.

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