JP2013073832A - Positive electrode active material for lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material for a lithium ion secondary battery suffering only a small reduction in discharge capacity in charge and discharge cycle, and suffering only a small reduction in capacity even in cycles at a high charge and discharge rate.SOLUTION: There is provided a positive electrode active material for a lithium ion secondary battery containing: a lithium-nickel composite oxide represented by the formula (1) LiNiMO, where M represents one or more kinds of elements selected from Co, Fe, and Al, 0<x<1.5, and 0≤y<0.2; and an amorphous material containing lithium, silicon, and oxygen. The lithium-nickel composite oxide has the crystallite diameter in the range of 30 to 100 nm, and the positive electrode active material for a lithium ion secondary batter contains the amorphous material in the range of 1 to 10 mass% in terms of silicon. A lithium ion secondary battery using the positive electrode active material for a lithium ion secondary battery is also provided.

Description

  The present invention relates to a positive electrode active material for lithium ion secondary batteries containing nickel. More specifically, the present invention relates to a positive electrode active material for a lithium ion secondary battery including a lithium-nickel composite oxide and an amorphous material containing lithium, silicon, and oxygen.

  Nonaqueous electrolyte secondary batteries, particularly lithium ion secondary batteries, are widely used in mobile phones, portable personal computers and the like. Moreover, the nonaqueous electrolyte secondary battery is adopted as a power tool power source, and has great expectations as a power source for future hybrid vehicles. Therefore, a non-aqueous electrolyte secondary battery having a higher capacity is desired.

  By the way, during the 10 years since the start of mass production of lithium ion secondary batteries in 1991, the battery structure has been improved, and the technology for high-density filling has greatly advanced. However, the basic configuration in which the positive electrode active material is a lithium-cobalt composite oxide such as lithium cobaltate and the negative electrode active material is graphite is still mainstream. Under such circumstances, further improvement in performance and cost reduction of the lithium ion secondary battery are desired, and the need for a new positive electrode material replacing the lithium-cobalt composite oxide is increasing.

  As promising positive electrode materials that can replace lithium-cobalt composite oxides, lithium-containing transition metal oxides containing nickel, manganese, and iron have been actively studied. Among them, the lithium-nickel composite oxide has a higher capacity than the lithium-cobalt composite oxide, and is expected to be applied to a positive electrode material.

However, in the case of a lithium-nickel composite oxide such as lithium nickelate, since the ion radii of Li ⁺ and Ni ²⁺ are almost equal, Ni ²⁺ tends to be mixed into the site that should be originally occupied by Li ⁺ . For this reason, the crystal structure is often different from that of LiNiO ₂ having a stoichiometric composition at the time of synthesis, and as a result, there are problems such as a large reduction in discharge capacity during charge / discharge cycles (when charge / discharge is repeated). .

In response to the problem, for example, a method of containing Co, Mn, Al, Si, or the like in M or N of LiNi _1-xy M _x N _y O ₂ (see, for example, Patent Document 1) or an active material A method of coating the particle surface with carbon, SiO ₂ , a polymer compound or the like (for example, see Patent Document 2 and Patent Document 3), a method for controlling the particle diameter of the active material (for example, see Patent Document 4), and the like. It is disclosed. Although it has been reported that the decrease in the discharge capacity during the charge / discharge cycle is suppressed to some extent by these methods, a further improvement in performance is desired.

  In addition, the positive electrode material is required not only to have a small decrease in discharge capacity during the charge / discharge cycle, but also to have a small decrease in capacity even at a high charge / discharge rate. It has been demanded.

JP 2008-293661 A JP 2003-059491 A JP 2009-078991 A JP 2000-030893 A

  In view of these problems, it is an object of the present invention to provide a positive electrode active material for a lithium ion secondary battery in which a decrease in discharge capacity during a charge / discharge cycle is small and a decrease in capacity is small even at a high charge / discharge rate. .

  As a result of intensive studies to solve the above problems, the inventors of the present invention have developed a lithium-nickel composite oxide having a specific crystallite size, lithium, silicon, and a positive electrode material of a lithium ion secondary battery. And a non-crystalline substance containing oxygen, and the use of a positive electrode active material in which the content of the non-crystalline substance is within a specific range, reduces a decrease in discharge capacity during a charge / discharge cycle. In addition, the present inventors have found that the capacity reduction can be reduced even at a high charge / discharge rate, and have completed the present invention.

That is, the present invention
(1) including a lithium-nickel composite oxide represented by the following general formula (1) and an amorphous substance containing lithium, silicon, and oxygen,
The crystallite diameter of the lithium-nickel composite oxide is 30 to 100 nm,
The positive electrode active material for a lithium ion secondary battery, wherein the content of the amorphous material is 1 to 10% by mass in terms of silicon;
The general formula _{(1) ··· Li x Ni 1} -y M y O 2
[Wherein, M represents one or more elements selected from Co, Fe, and Al, 0.5 <x <1.5, and 0 ≦ y <0.2. ],
(2) The positive electrode active material for a lithium ion secondary battery according to (1), wherein the amorphous material is a compound represented by the following general formula (2):
General formula (2) ... Li _a Si _b O
[Wherein, a and b are each independently a positive real number. ],
(3) The lithium ion according to (1) or (2), wherein the amorphous substance is present between the crystals in at least a part of the crystals of the lithium-nickel composite oxide. Positive electrode active material for secondary battery,
(4) A lithium ion secondary battery obtained by using the positive electrode active material for a lithium ion secondary battery according to any one of (1) to (3),
Is to provide.

  ADVANTAGE OF THE INVENTION According to this invention, the positive electrode active material for lithium ion secondary batteries containing nickel with little capacity | capacitance fall by repeated charging / discharging, and little capacity | capacitance fall by a high charging / discharging speed | rate is provided.

2 is a diagram showing measurement conditions and results of a powder X-ray diffraction pattern of the positive electrode active material A obtained in Example 1. FIG. 3 is a transmission electron micrograph of positive electrode active material B obtained in Example 2. FIG. It is a chart of the energy dispersive X-ray spectroscopy of the substance A in FIG. It is a chart of the energy dispersive X-ray spectroscopy of the substance B in FIG.

<Positive electrode active material for lithium ion secondary battery>
The positive electrode active material for a lithium ion secondary battery of the present invention (hereinafter referred to as the positive electrode active material of the present invention) is composed of a lithium-nickel composite oxide and an amorphous material containing lithium, silicon and oxygen (hereinafter referred to as lithium silicate). The crystallite diameter of the lithium-nickel composite oxide is 30 to 100 nm, and the content of the amorphous substance is 1 to 10% by mass in terms of silicon. The reason why the positive electrode active material for a lithium ion secondary battery of the present invention has the effect of reducing the discharge capacity during charge / discharge cycles and the capacity reduction at a high charge / discharge rate is not clear, but the crystallite diameter The lithium-nickel composite oxide with a specific size contains lithium silicate in a specific ratio, so that the lithium silicate, which is an ionic conductor (electrolyte), promotes the diffusion of lithium ions in the active material. As a result, it is surmised that the charge / discharge rate is increased, and the capacity reduction when the charge / discharge rate is high is suppressed.

[Lithium-nickel composite oxide]
The lithium-nickel composite oxide contained in the positive electrode active material of the present invention is represented by the following general formula (1). In the following general formula (1), M represents one or more elements selected from Co, Fe, and Al, 0.5 <x <1.5, and 0 ≦ y <0.2.
The general formula _{(1) ··· Li x Ni 1} -y M y O 2

  When the amount of lithium ions in the lithium-nickel composite oxide is excessive, movement of Li ions between the positive and negative electrodes during charge / discharge may be hindered and the performance as the positive electrode material may be reduced. Therefore, in the general formula (1), x is a positive real number that satisfies 0.5 <x <1.5. The lithium-nickel composite oxide used in the present invention preferably satisfies 0.8 <x <1.3, and more preferably 0.95 <x <1.15.

In general formula (1), y is 0 ≦ y <0.2. When y is 0, the lithium-nickel composite oxide is Li _x Ni ₁ O ₂ . Since y is less than 0.2, the positive electrode active material of the present invention can contain a sufficient amount of Ni, and the decrease in the discharge capacity of the positive electrode material obtained using the positive electrode active material of the present invention is suppressed. The In the present invention, y may be 0, but from the viewpoint of suppressing a decrease in capacity during charge / discharge by stabilizing the crystal structure, 0 <y <0.2 is preferable, and 0.01 ≦ y <0.2 is more preferable, 0.01 ≦ y ≦ 0.1 is still more preferable, and 0.02 ≦ y ≦ 0.06 is still more preferable.

  In general formula (1), M is at least one element selected from cobalt, iron, and aluminum. That is, the lithium-nickel composite oxide may be a compound consisting of only one of cobalt, iron, or aluminum as M, and M is a compound containing two or more of the above element groups. May be. As the lithium-nickel composite oxide used in the present invention, among the above elements, aluminum having an oxidation number of only 3 that exists stably in the atmosphere is particularly preferable.

  The crystallite diameter of the lithium-nickel composite oxide in the positive electrode active material of the present invention is 30 nm to 100 nm. When the crystallite size of the positive electrode active material of the present invention is too small, the size of the primary particles (the primary particles in the present invention are composed of lithium-nickel composite oxide crystals and lithium silicate) is too small. As a result, the grain boundary increases, and the lithium ion diffusibility between the particles may be significantly reduced. On the other hand, when the crystallite diameter of the positive electrode active material of the present invention is too large, lithium deficiency is likely to be generated in the crystal structure of the lithium-nickel composite oxide in the positive electrode active material. Lithium vacancies cause crystal phase transitions during charge / discharge, and therefore repeated charge / discharge increases the crystal structure that is not electrochemically active and decreases the capacity.

The crystallite diameter of the lithium-nickel composite oxide in the positive electrode active material of the present invention is measured as follows by measuring the X-ray diffraction pattern (XRD) of the powder sample of the positive electrode active material. Is required. That is, the lithium-nickel composite oxide represented by the general formula (1) has a layered rock salt type crystal structure called α-NaFeO ₂ type (space group R-3m), and when XRD is measured, A diffraction peak “P104” attributed to the (104) plane appears at 2Θ = 43 to 44 °. Using the measured half width of P104, the crystallite diameter of the lithium-nickel composite oxide can be calculated by the following Scherrer equation. In the Serrer equation, D is the crystallite size (nm) of the lithium-nickel composite oxide, K is the Serrer constant (0.9), λ is the wavelength of the diffracted X-ray (nm), and β is P104 Is the half-value width (rad) of, and θ is the diffraction angle (°) of P104.
D = Kλ / (βcosΘ) (Sherler equation) Note that the half-width of the diffraction peak P104 used in the above equation uses a powder X-ray diffractometer, uses a monochromated CuKα ray as an X-ray source, and scans the goniometer. XRD can be measured and determined with the mode as continuous.

In XRD of the lithium-nickel composite oxide in the positive electrode active material of the present invention, in addition to the diffraction peak “P104” attributed to the (104) plane at 2Θ = 43 to 44 °, 2Θ = 18 to 19 °. And has a peak “P003” attributed to the (003) plane. The integral intensity ratio [I003 / I104] of the integral intensity “I003” of P003 and the integral intensity “I104” of P104 depends on the arrangement of Li ⁺ and Ni ³⁺ in the crystal structure of the lithium-nickel composite oxide, Since it reflects the amount of Li ⁺ site in the layered rock salt structure of the lithium-nickel composite oxide, it is an indicator of the discharge capacity of the lithium-nickel composite oxide (for example, P. Kalyani, N. Kalaiselvi, Adv. Mater. Vol. 6, p689 (2005).). [I003 / I104] is preferably 1.2 or more, because the crystal of the lithium-nickel composite oxide is sufficiently grown and exhibits a high capacity as the positive electrode active material. [I003 / I104] is preferably as large as possible because it has a higher capacity, but the actual synthesizable value is 2.0 or less.

  The higher the lithium-nickel composite oxide content in the positive electrode active material of the present invention, the higher the capacity, which is preferable. However, the lithium silicate content that has the effect of suppressing the decrease in capacity at a high charge / discharge rate is preferable. In order to ensure, it is preferable that it is 80 mass%-95 mass%, and it is more preferable that it is 90 mass%-95 mass%.

  The positive electrode active material of the present invention is preferably one in which lithium silicate is present between the crystals in at least some of the crystals of the lithium-nickel composite oxide. In the positive electrode active material, lithium silicate is present in the gap between the crystals of the lithium-nickel composite oxide, thereby obtaining a higher effect of the present invention (an excellent capacity reduction suppressing effect at a high charge / discharge rate). be able to. This is because lithium silicate, which is an ionic conductor (electrolyte), fills the gaps between the crystals of the lithium-nickel composite oxide, so that the diffusion of lithium ions in the active material is further promoted and the charge / discharge rate is increased. It is guessed.

  The lithium-nickel composite oxide having a crystallite diameter of 30 nm to 100 nm and [I003 / I104] of 1.2 or more is obtained by, for example, using a nickel precursor such as nickel hydroxide or nickel carbonate at 350 to 500 ° C. After firing, a lithium source such as lithium hydroxide can be mixed at a molar ratio of nickel to lithium of 1 to 1.2 and fired at 600 to 700 ° C. for 1 to 5 hours.

[Lithium silicate]
The lithium silicate contained in the positive electrode active material of the present invention is an amorphous material containing lithium, silicon, and oxygen. The composition of lithium silicate is not particularly limited, and examples thereof include a compound represented by the following general formula (2). In the following general formula (2), a and b are positive real numbers.
General formula (2) ... Li _a Si _b O

The lithium silicate represented by the general formula (2) is preferably a substance in which a and b satisfy 1 <a / b <6. By setting a / b within the above range, the lithium content in the lithium silicate is sufficient to exhibit the performance as an ion conductor more effectively, and the diffusion of lithium ions is not hindered. A more preferable amount can be obtained. In addition, in the lithium silicate represented by the general formula (2), when a / b becomes too large, the cost becomes high, which is not preferable from the viewpoint of manufacturing cost. Examples of the lithium silicate represented by the general formula (2) include Li ₄ SiO ₄ , Li ₂ SiO ₃ , Li ₆ Si ₂ O ₇ , and a mixture thereof.

  The content of lithium silicate in the positive electrode active material of the present invention can be appropriately determined in consideration of physical properties such as the crystallite diameter of the lithium-nickel composite oxide, the capacity of the desired positive electrode active material, and the like. In the present invention, the content of lithium silicate in the positive electrode active material is 1 to 10% by mass in terms of silicon (Si), preferably 1 to 6% by mass, and preferably 1 to 3% by mass. Is more preferable. By including lithium silicate in an amount of 1% by mass or more in terms of silicon (Si), a positive electrode active material with less decrease in capacity can be obtained even at a high charge / discharge rate. However, when the content of lithium silicate in the positive electrode active material of the present invention is too large, the content of the lithium-nickel composite oxide is relatively lowered, and thus the desired performance may not be exhibited.

[Average particle size of primary particles]
The positive electrode active material of the present invention forms primary particles in which lithium silicate enters between crystals of a lithium-nickel composite oxide. The lower limit of the average particle diameter of the primary particles is substantially larger than the crystallite diameter of the lithium-nickel composite oxide in the positive electrode active material of the present invention. The average particle diameter of the primary particles is preferably 30 to 200 nm. By making the average particle diameter of the primary particles 200 nm or less, lithium ions can move more easily between particles during charging and discharging, so that a higher capacity can be obtained even at a high charge / discharge rate (C rate). In the positive electrode active material of the present invention, the particle size of the secondary particles is not particularly limited.

<Method for producing positive electrode active material for lithium ion secondary battery>
The positive electrode active material of the present invention may be manufactured by any manufacturing method. As a preferred method for producing the positive electrode active material of the present invention, for example, a coprecipitate containing nickel and silicon is produced by a coprecipitation method, the coprecipitate is baked at a specific temperature, a lithium salt is added, and the reprecipitation is performed. The method of manufacturing by baking at temperature is mentioned. By using this production method, the crystallite diameter of the lithium-nickel composite oxide is controlled within the range of 30 nm to 100 nm, [I003 / I104] is set to 1.2 or more, and the content of lithium silicate in terms of silicon It is easy to disperse the lithium silicate relatively uniformly in the lithium-nickel composite oxide without making the lithium silicate unevenly distributed in the obtained positive electrode active material. Specifically, the manufacturing method includes the following coprecipitation step, first firing step, lithium mixing step, and second firing step.

[Co-precipitation process]
First, an aqueous solution containing a nickel compound (hereinafter referred to as a nickel compound solution) and an aqueous solution containing a silicon compound (hereinafter referred to as a silicon compound solution) are mixed, and the nickel compound and the silicon compound are reacted in the obtained mixed solution. A coprecipitate comprising nickel and silicon is obtained.

  The nickel compound in the nickel compound solution is not particularly limited as long as it is a water-soluble nickel compound. Moreover, the aqueous solution containing 1 type of nickel compounds may be sufficient, and the aqueous solution containing 2 or more types of nickel compounds may be sufficient. Specific examples of the nickel compound in the nickel compound solution include water-soluble nickel compounds such as nickel carbonate, nickel sulfate, and nickel nitrate, and mixtures thereof, and nickel sulfate is particularly preferable.

  The silicon compound in the silicon compound solution is not particularly limited as long as it is a water-soluble silicon compound. Moreover, the aqueous solution containing 1 type of silicon compounds may be sufficient, and the aqueous solution containing 2 or more types of silicon compounds may be sufficient. Specific examples of the silicon compound in the silicon compound solution include water-soluble silicon compounds such as silica, water glass, and colloidal silica, and mixtures thereof, and colloidal silica is particularly preferable.

  The nickel compound solution is preferably an acidic aqueous solution, preferably has a pH of 1 to 3, and more preferably has a pH of 1 to 2. On the other hand, the silicon compound solution is preferably a basic aqueous solution, preferably has a pH of 9 to 11, and more preferably has a pH of 9 to 10. In any aqueous solution, the pH can be adjusted to a preferred range using an acid or ammonia.

  Moreover, an alkali carbonate can also be mixed with a silicon compound solution. An alkali carbonate solution may be further added to the mixed solution obtained by mixing the silicon compound solution and the nickel compound solution. By carrying out the reaction in the presence of alkali carbonate, a coprecipitate containing nickel and silicon can be obtained more efficiently. The alkali carbonate is preferably mixed so that the molar ratio of nickel to the alkali carbonate is 0.7 to 1.0 in the mixed solution of the nickel compound solution and the silicon compound solution. Examples of the alkali carbonate include sodium carbonate.

  The nickel compound solution and the silicon compound solution are mixed so that the ratio of the number of moles of silicon contained in the mixed solution to the number of moles of nickel contained in the mixed solution after mixing is 0.05 to 0.3. It is preferable that the mixing is performed so that the amount is 0.06 to 0.27, and it is further preferable that the mixing is performed so that the amount is 0.07 to 0.25. When the molar ratio of nickel and silicon in the mixed solution is within the above range, a coprecipitate is likely to be produced when the reaction is performed in the mixed solution, and the coprecipitate can be obtained with a good yield.

  The pH of the mixture of the nickel compound solution and the silicon compound solution is preferably in the range of 6-9, more preferably in the range of 6-8, and in the range of 6.5-7.5. More preferably. If the pH of the mixed solution is within the range, a coprecipitate is likely to be produced when the reaction is performed in the mixed solution, and the coprecipitate can be obtained with a good yield.

  Next, by holding the obtained mixed liquid at 70 to 90 ° C., the nickel compound and the silicon compound are reacted to obtain a coprecipitate containing nickel and silicon. After mixing the nickel compound solution and the silicon compound solution, the obtained mixed solution may be heated to 70 to 90 ° C, but after the nickel compound solution and the silicon compound solution are preheated to 70 to 90 ° C, It is preferable to mix both solutions.

  The reaction time can be appropriately determined in consideration of the contents of the nickel compound and silicon compound in the mixed solution, the reaction temperature, and the like. Further, during the reaction, the mixed solution may be allowed to stand or may be stirred. For example, a coprecipitate containing nickel and silicon can be obtained by stirring the mixed solution at 70 to 90 ° C. for about 0.5 to 2 hours.

  The coprecipitate obtained is preferably dried after filtration and washing with water. The drying process may be any method that can remove water contained in the coprecipitate to some extent. For example, the solid (coprecipitate) after washing with water can be dried by drying at a temperature of about 100 to 150 ° C. by a known method.

[First firing step]
Next, the coprecipitate obtained by the coprecipitation step is fired. The firing temperature is preferably 350 to 500 ° C, and more preferably 350 to 450 ° C. By setting the firing temperature to 350 ° C. or higher, nickel oxide can be obtained efficiently, and by setting it to 500 ° C. or lower, the sintering of nickel oxide can be sufficiently suppressed. As a result, the finally obtained lithium-nickel composite oxide is easily crystallized with high “I003 / I104” by XRD.

  The firing time is not particularly limited as long as it is sufficient for the oxide to be synthesized from nickel or silicon in the coprecipitate, and is appropriately determined in consideration of the firing temperature and the amount of the coprecipitate. it can. For example, it is preferably 0.5 to 3 hours, and preferably 0.5 to 2 hours.

  Through the above steps, a mixture of “nickel oxide” and “silicon oxide”, which is a raw material of the positive electrode active material of the present invention (hereinafter, sometimes simply referred to as “calcined product after coprecipitation”). Is manufactured. In this method, silicon does not enter the nickel oxide crystals in the fired product after coprecipitation.

[Lithium mixing process]
Next, a lithium raw material is mixed with the obtained co-precipitated fired product. As the lithium raw material, lithium nitrate, lithium carbonate, lithium hydroxide and the like can be used, and lithium hydroxide is preferable.

  The mixing method of the calcined product and lithium raw material after co-precipitation is not particularly limited, and the calcined product and lithium raw material after co-precipitation may be physically mixed. Also good. When physically mixing, for example, after pulverizing the calcined product after coprecipitation, adding a lithium raw material and mixing thoroughly while grinding in a mortar to obtain a uniform mixture of the calcined product and lithium raw material after coprecipitation Can do.

  Lithium in the lithium raw material is incorporated into nickel oxide and silicon oxide in the fired product after coprecipitation, whereby the positive electrode active material of the present invention containing a lithium-nickel composite oxide and lithium silicate is produced. For this reason, 1 to 1.2 times the number of moles of nickel contained in the fired product after co-precipitation and the number of moles of silicon contained in the fired product after co-precipitation It is preferable to mix a lithium raw material containing lithium in an amount corresponding to the total number of moles of 3 to 6 times, preferably 4 to 6 times the number of moles.

[Second firing step]
After the coprecipitation, the mixture of the fired product and the lithium raw material is fired at 600 to 700 ° C. By setting the firing temperature to 600 ° C. or higher, the lithium-nickel composite oxide crystal represented by the general formula (1) can be synthesized, and by setting it to 700 ° C. or lower, lithium volatilization can be prevented. it can. As a result, the finally obtained lithium-nickel composite oxide is easily crystallized with high “I003 / I104” by XRD.

  The fired product obtained by the second firing step is the positive electrode active material of the present invention. In this production method, the positive electrode active material of the present invention is produced by firing a coprecipitate obtained by coprecipitation of nickel and silicon and then supporting lithium on the obtained fired product after coprecipitation. In the fired product after coprecipitation, nickel oxide and silicon oxide are relatively close to each other. For this reason, by supporting lithium in the fired product after coprecipitation, It is presumed that a positive electrode active material in which crystals and lithium silicate are relatively close to each other is obtained.

  A product obtained by pulverizing the fired product obtained in the second firing step is the primary particle of the positive electrode active material of the present invention. The pulverization method is not particularly limited, and may be crushed with a mortar or the like, or pulverized using a pulverizer such as a ball mill.

[Positive electrode active material containing metal M]
As a lithium-nickel composite oxide, when manufacturing a positive electrode active material containing a compound represented by the general formula (1) where 0 <y <0.2, that is, as the metal M, cobalt, iron And a positive electrode active material containing at least one element selected from aluminum, cobalt, iron, or aluminum is dissolved in at least one of the silicon compound solution and the nickel compound solution in the coprecipitation step. It is preferable that after coprecipitation of these atoms with nickel and silicon, the obtained coprecipitate is fired in the first firing step. By coprecipitating a metal M such as cobalt together, a silicon oxide and a nickel composite oxide in which the metal M is incorporated in a lattice of nickel oxide (Ni _{1- y My} O ₂ , 0 <y <0 .2) can be obtained. Most of the metal M enters the crystal of the nickel oxide and exists in a state where it is replaced with nickel atoms in the crystal. Thereafter, lithium is mixed in the obtained post-coprecipitation fired product by the above-described lithium mixing step, and further fired to obtain a lithium-nickel composite oxide containing metal M (Li _x Ni _{1- y My).} A positive electrode active material containing O ₂ , 0 <y <0.2) crystals and lithium silicate is obtained. By containing these metals by coprecipitation, lithium, nickel, and metal M (aluminum, cobalt, iron) can be more uniformly dispersed in the crystal.

  When cobalt is contained as the metal M, compounds such as cobalt sulfate, cobalt nitrate, and cobalt carbonate can be used as the cobalt raw material. Moreover, when iron is contained, iron sulfate, iron nitrate, iron carbonate, or the like can be used as an iron raw material. When aluminum is contained, aluminum nitrate, aluminum sulfate, aluminum hydroxide, boehmite, or the like can be used as the aluminum raw material. These raw materials for the metal M are preferably dissolved in a silicon compound solution or a nickel compound solution which is an acidic aqueous solution. Further, an acidic solution containing the metal M raw material may be coprecipitated after being added to the mixed solution of the silicon compound solution and the nickel compound solution.

  Further, among the compounds represented by the general formula (1), the positive electrode active material containing a compound satisfying 0 <y <0.2 is obtained as a metal M raw material after obtaining a coprecipitate containing no metal M. It can also be produced by adding. For example, the powdered metal M raw material may be physically mixed into the coprecipitate after the drying treatment, and then the steps after the first firing step may be performed, or the post-coprecipitation fired product after the first firing step. In addition, after the powdered metal M raw material is physically mixed with the lithium raw material, a second baking step described later may be performed, and the metal M raw material together with the lithium raw material is added to the fired product after coprecipitation after the first baking step. After the impregnation, a second baking step described later may be performed. As a metal M raw material, what was illustrated as a metal M raw material added to a silicon compound solution or a nickel compound solution can be used.

<Lithium ion secondary battery>
The lithium ion secondary battery of the present invention is obtained using the positive electrode active material of the present invention.
A lithium ion secondary battery includes a positive electrode formed by binding a positive electrode active material to a positive electrode current collector, a negative electrode formed by binding a negative electrode active material to a negative electrode current collector, and lithium in a non-aqueous solvent such as an organic solvent. A non-aqueous electrolyte obtained by dissolving an electrolyte such as a salt is a main component.
The lithium ion secondary battery of this invention can be manufactured by a conventional method except using the positive electrode active material of this invention as a positive electrode active material.

The positive electrode active material to be bound to the positive electrode current collector may be only the positive electrode active material of the present invention, or a combination of the positive electrode active material of the present invention and another positive electrode active material. Moreover, as a negative electrode active material, carbon materials, such as graphite and coke, metal lithium, etc. can be used, for example. As the positive electrode current collector, plate-like aluminum or the like is used, and as the negative electrode current collector, plate-like copper or the like is used. As the non-aqueous solvent, cyclic carbonates such as ethylene carbonate, chain carbonates such as dimethyl carbonate, and mixed solvents thereof can be used. As the electrolyte, a lithium salt such as LiPF ₆ can be used.

For the positive electrode or the negative electrode, for example, a positive electrode active material or a negative electrode active material, a conductive additive, a binder, a dispersant, and the like are mixed to produce an active material paste adjusted to an appropriate viscosity, and this active material paste is used as a current collector. It can be coated and pressed.
The shape of the lithium ion secondary battery of the present invention is not particularly limited, and may be a coin type, a cylindrical type, a square type, or a polymer type (wrapped with a laminate film). It may be of a square shape).

  EXAMPLES Next, although an Example is shown and this invention is demonstrated further in detail, this invention is not restrict | limited at all by these examples.

[Example 1]
To 1 L of ion-exchanged water, 126.5 g of Ni (SO ₄ ) ₂ · 6H ₂ O (manufactured by Wako Pure Chemical Industries) and 1.24 g of boehmite AP-3 (manufactured by Catalytic Chemical Industry) are added, and the mixture is heated to 80 ° C. to be acidic. A nickel compound solution was obtained. 3 L of colloidal silica Snowtex XS (Nissan Chemical) and 59.4 g of sodium carbonate were added to 1 L of ion-exchanged water separately prepared, and heated to 80 ° C. to obtain a basic silicon compound solution. While maintaining the nickel compound solution and the silicon compound solution at 80 ° C., the silicon compound solution was continuously added to the nickel compound solution for 30 minutes and stirred for 1 hour to carry out a coprecipitation reaction. The pH of the mixed solution when the whole amount of the silicon compound solution was added to the nickel compound solution was 7.1.
The precipitate in the mixed solution was collected by filtration, washed with 4 L of ion exchange water, and dried at 120 ° C. for 12 hours to obtain a coprecipitate a.
Subsequently, the coprecipitate a was baked at 400 ° C. for 1 hour. Thereafter, 3.004 g of the calcined coprecipitate a and 2.917 g of lithium hydroxide (manufactured by Kanto Kagaku) were mixed and kneaded in a mortar for 20 minutes. The resulting mixture A was calcined for 3 hours at 660 ° _C., to obtain a _{Li x Ni 1-y Al y} O 2 positive active material A consisting of lithium silicate. _{Li x Ni 1-y Al y} O 2 in the x, y in the positive electrode active material A from the results of elemental analysis were respectively 1.14,0.038. Moreover, the lithium silicate in the positive electrode active material A was estimated to be Li ₄ SiO ₄ from the result of elemental analysis.
Table 1 shows the results of measuring the amount of silicon in the obtained positive electrode active material A by elemental analysis. This measured value almost coincided with the value calculated from the charged amount.
The powder X-ray diffraction pattern of the obtained positive electrode active material A was measured under the following conditions. Measurement conditions and results are shown in FIG. From this measurement result, the crystallite diameter was calculated by the Scherrer equation described above. The results are shown in Table 1. Table 1 also shows the intensity ratio I003 / I104 of the (003) plane / (104) plane of the Li _x Ni _1-y Al _y O ₂ crystal.

(XRD measurement conditions)
Powder X-ray diffractometer: RINT-2500V (Rigaku),
X-ray ::
Monochromatic: CuKα line, tube voltage: 50 kV, tube current: 150 mA,
Goniometer: Vertical detector: Scintillation counter Scan axis: 2θ / θ
Scan mode: Continuous scan ::
Scan step: 0.002 °, scan speed: 0.25 ° / min
slit::
Fixed slit: used, divergent slit: 1 °, scattering slit: 1 °, light receiving slit: 0.15 mm

0.2258 g of the positive electrode active material A obtained as described above was mixed with 0.01257 g of ketjen black and 0.01261 g of polyvinylidene fluoride (PVdF) and kneaded in a mortar for 30 minutes. Thereafter, 300 μL of N-methyl-2-pyrrolidone (NMP) was added to the kneaded product, applied to an aluminum foil, and dried to prepare a coated electrode used for the positive electrode of a coin cell battery. The prepared coated electrode had a diameter of 14 mm and the active material thickness was 13 μm. Using this coated electrode as a positive electrode and metallic lithium as a negative electrode, a 2032 coin cell of a lithium ion battery was produced in an inert gas atmosphere.
This coin cell was loaded into a charge / discharge evaluation apparatus (Hokuto Denko, product name: HJ1001-SD8), and the charge / discharge characteristics of the positive electrode active material A were evaluated in an inert gas atmosphere at 25 ° C. This evaluation is performed in a constant current mode with current values corresponding to 0.1 C and 1 C in terms of C rate, and a cutoff potential of 3 V to 4.3 V vs. Performed with Li / Li ⁺ .

[Example 2]
To 1 L of ion-exchanged water, 126.5 g of Ni (SO ₄ ) ₂ · 6H ₂ O (manufactured by Wako Pure Chemical Industries) and 1.24 g of boehmite AP-3 (manufactured by Catalytic Chemical Industry) are added, and the mixture is heated to 80 ° C. to be acidic. A nickel compound solution was obtained. To 1 L of ion-exchanged water separately prepared, 17.0 g of colloidal silica Snowtex XS (Nissan Chemical) and 59.4 g of sodium carbonate were added and heated to 80 ° C. to obtain a basic silicon compound solution. While maintaining the nickel compound solution and the silicon compound solution at 80 ° C., the silicon compound solution was continuously added to the nickel compound solution for 30 minutes and stirred for 1 hour to carry out a coprecipitation reaction. The pH of the mixed solution when the whole amount of the silicon compound solution was added to the nickel compound solution was 7.2.
The precipitate in the mixed solution was collected by filtration, washed with 4 L of ion exchange water, and dried at 120 ° C. for 12 hours to obtain a coprecipitate b.
Subsequently, the coprecipitate b was fired at 400 ° C. for 1 hour. Thereafter, 3.001 g of the calcined precursor b and 2.490 g of lithium hydroxide (manufactured by Kanto Chemical) were mixed and kneaded in a mortar for 20 minutes. Then, the mixture B was calcined for 3 hours at 660 ° _C., to obtain a _{Li x Ni 1-y Al y} O 2 positive active material B consisting of lithium silicate. Note that x and y in Li _x Ni _1-y Al _y O ₂ in the positive electrode active material B were 1.11 and 0.036, respectively, from the results of elemental analysis. Further, the lithium silicate in the positive electrode active material B was estimated to be Li ₄ SiO ₄ from the result of elemental analysis. The charge / discharge characteristics of this positive electrode active material B were evaluated under the same conditions as in Example 1.

The primary particles in the positive electrode active material B were observed with a transmission electron microscope and energy dispersive X-ray spectroscopy. A photograph of a transmission electron microscope is shown in FIG. 2, and measurement results of energy dispersive X-ray spectroscopy of substance A and substance B in FIG. 2 are shown in FIGS.
As shown in FIG. 2, two types of substances having different shades of images were confirmed from a transmission electron micrograph. The substance that appears dark is in the form of particles (substance A in FIG. 2), and there is a thin substance with a sharp outline around the particulate substance (substance B in FIG. 2). It was inferred that the dense particulate material was Li _x Ni _1-y Al _y O ₂ crystals, and the thin material was amorphous lithium silicate. Therefore, the substance A and substance B in FIG. 2 were measured by energy dispersive X-ray spectroscopy. As a result, the substance A contained a lot of nickel and the substance B contained a lot of silicon. Was a crystal of Li _x Ni _1-y Al _y O ₂ , and the substance B was confirmed to be lithium silicate (FIGS. 3 and 4).
That is, from the transmission electron micrograph of the positive electrode active material B, in the positive electrode active material of the present invention, amorphous lithium silicate exists between the crystals of the lithium-nickel composite oxide. confirmed.

[Example 3]
The mixture A obtained in Example 1 was baked at 680 ° C. for 3 hours to obtain a positive electrode active material C composed of Li _x Ni _1-y Al _y O ₂ and lithium silicate. _{Incidentally, Li x Ni 1-y Al} y O 2 in the x, y in the positive electrode active material C from the results of elemental analysis were respectively 1.10,0.038. Further, the lithium silicate in the positive electrode active material C was estimated to be Li ₄ SiO ₄ from the result of elemental analysis. The charge / discharge characteristics of this positive electrode active material C were evaluated under the same conditions as in Example 1.

[Example 4]
To 1 L of ion-exchanged water, 126.5 g of Ni (SO ₄ ) ₂ · 6H ₂ O (manufactured by Wako Pure Chemical Industries) and 0.72 g of boehmite AP-3 (manufactured by Catalyst Kasei Kogyo) are added, and heated to 80 ° C. to become acidic. A nickel compound solution was obtained. 3 L of colloidal silica Snowtex XS (Nissan Chemical) and 59.4 g of sodium carbonate were added to 1 L of ion-exchanged water separately prepared, and heated to 80 ° C. to obtain a basic silicon compound solution. While maintaining the nickel compound solution and the silicon compound solution at 80 ° C., the silicon compound solution was continuously added to the nickel compound solution for 30 minutes and stirred for 1 hour to carry out a coprecipitation reaction. The pH of the mixed solution when the whole amount of the silicon compound solution was added to the nickel compound solution was 7.1.
The precipitate in the mixture was collected by filtration, washed with 4 L of ion exchange water, and dried at 120 ° C. for 12 hours to obtain a coprecipitate d made of a nickel compound.
Subsequently, the coprecipitate d was baked at 400 ° C. for 1 hour. Thereafter, 3.004 g of calcined coprecipitate d and 2.917 g of lithium hydroxide (manufactured by Kanto Chemical) were mixed and kneaded in a mortar for 20 minutes. The resulting mixture D was calcined for 3 hours at 660 ° _C., to obtain a _{Li x Ni 1-y Al y} O 2 positive active material D consisting of lithium silicate. X and y in Li _x Ni _1-y Al _y O ₂ in the positive electrode active material D were 1.10 and 0.024, respectively, from the results of elemental analysis. Moreover, the lithium silicate in the positive electrode active material D was estimated to be Li ₄ SiO ₄ from the result of elemental analysis. The charge / discharge characteristics of this positive electrode active material D were evaluated under the same conditions as in Example 1.

[Comparative Example 1]
To 1 L of ion-exchanged water, 126.5 g of Ni (SO ₄ ) ₂ · 6H ₂ O (manufactured by Wako Pure Chemical Industries) and 1.24 g of boehmite AP-3 (manufactured by Catalyst Kasei Kogyo) are added, heated to 80 ° C., nickel A compound solution was obtained. 4.9 g of colloidal silica Snowtex XS (Nissan Chemical) and 59.4 g of sodium carbonate were added to 1 L of ion-exchanged water separately prepared, and heated to 80 ° C. to obtain a silicon compound solution. While maintaining the nickel compound solution and the silicon compound solution at 80 ° C., the silicon compound solution was continuously added to the nickel compound solution for 30 minutes and stirred for 1 hour to carry out a coprecipitation reaction. The pH of the mixed solution when the whole amount of the silicon compound solution was added to the acidic solution was 7.2.
The precipitate in the liquid mixture was collected by filtration, washed with 4 L of ion exchange water, and dried at 120 ° C. for 12 hours to obtain a coprecipitate e.
Subsequently, the coprecipitate e was baked at 400 ° C. for 1 hour. Thereafter, 3.002 g of the calcined precursor e and 1.985 g of lithium hydroxide (manufactured by Kanto Chemical) were mixed and kneaded in a mortar for 20 minutes. Then, the mixture E was calcined for 3 hours at 660 ° _C., to obtain a _{Li x Ni 1-y Al y} O 2 positive active material E consisting of lithium silicate. Note that x and y in Li _x Ni _1-y Al _y O ₂ in the positive electrode active material E were 1.10 and 0.038, respectively, from the results of elemental analysis. Further, the lithium silicate in the positive electrode active material E was estimated to be Li ₄ SiO ₄ from the result of elemental analysis. The charge / discharge characteristics of this positive electrode active material E were evaluated under the same conditions as in Example 1.

[Comparative Example 2]
To 1 L of ion-exchanged water, 126.5 g of Ni (SO ₄ ) ₂ · 6H ₂ O (manufactured by Wako Pure Chemical Industries) and 1.24 g of boehmite AP-3 (manufactured by Catalyst Kasei Kogyo) are added, heated to 80 ° C., nickel A compound solution was obtained. To 1 L of ion exchange water prepared separately, 86.6 g of colloidal silica Snowtex XS (Nissan Chemical) and 59.4 g of sodium carbonate were added and heated to 80 ° C. to obtain a silicon compound solution. While maintaining the nickel compound solution and the silicon compound solution at 80 ° C., the silicon compound solution was continuously added to the nickel compound solution for 30 minutes and stirred for 1 hour to carry out a coprecipitation reaction. The pH of the mixed solution when the whole amount of the silicon compound solution was added to the acidic solution was 7.2.
The precipitate in the mixed solution was collected by filtration, washed with 4 L of ion exchange water, and dried at 120 ° C. for 12 hours to obtain a coprecipitate f.
Subsequently, the coprecipitate f was baked at 400 ° C. for 1 hour. Thereafter, the fired precursor f3.002 g and lithium hydroxide (manufactured by Kanto Chemical) 1.985 g were mixed and kneaded in a mortar for 20 minutes. Then, the mixture F was calcined for 3 hours at 660 ° _C., to obtain a _{Li x Ni 1-y Al y} O 2 positive active material E consisting of lithium silicate. The lithium silicate in the positive electrode active material E was estimated to be Li ₄ SiO ₄ from the result of elemental analysis. The charge / discharge characteristics of this positive electrode active material E were evaluated under the same conditions as in Example 1.

[Comparative Example 3]
The mixture A obtained in Example 1 was baked at 750 ° C. for 10 hours to obtain a positive electrode active material G composed of Li _x Ni _1-y Al _y O ₂ and lithium silicate. Note that the lithium silicate in the positive electrode active material G was estimated to be Li ₄ SiO ₄ from the results of elemental analysis. The charge / discharge characteristics of this positive electrode active material G were evaluated under the same conditions as in Example 1.

[Comparative Example 4]
The mixture A obtained in Example 1 was baked at 570 ° C. for 10 hours to obtain a positive electrode active material H composed of Li _x Ni _1-y Al _y O ₂ and lithium silicate. Note that the lithium silicate in the positive electrode active material H was estimated to be Li ₄ SiO ₄ from the results of elemental analysis. The charge / discharge characteristics of this positive electrode active material H were evaluated under the same conditions as in Example 1.

As shown in Table 1, the content of lithium silicate in the positive electrode active material is 1 to 10% by mass in terms of silicon, and the crystallite diameter of Li _x Ni _1-y Al _y O ₂ is 30 to 100 nm. The positive electrode active materials A to D (Examples 1 to 4) are reduced in the discharge capacity at the 30th cycle relative to the discharge capacity at the 1st cycle in the charge / discharge cycle in the constant current mode at a current value corresponding to 0.1C The amount (the amount of decrease in discharge capacity during the charge / discharge cycle in the constant current mode at a current value corresponding to 0.1 C) was small. Further, the ratio of the discharge capacity at the 30th cycle in the constant current mode at a current value corresponding to 0.1 C and the constant current mode at a current value corresponding to 1 C ([constant current mode at a current value corresponding to 1 C) 30th cycle discharge capacity] / [30th cycle discharge capacity in constant current mode at a current value corresponding to 0.1 C]) (hereinafter, discharge capacity ratio [1C / 0.1C]) is 80 The discharge capacity decreased little even at a high charge / discharge rate.

  The positive electrode active material E (Comparative Example 1) in which the content of lithium silicate in the positive electrode active material is less than 1% by mass in terms of silicon is a charge / discharge cycle in a constant current mode at a current value corresponding to 0.1C. Although the amount of decrease in the discharge capacity was as small as that of the positive electrode active materials A to D, the discharge capacity ratio [1C / 0.1C] was 45%, which was clearly lower than that of the positive electrode active materials A to D.

  The positive electrode active material F (Comparative Example 2) in which the content of lithium silicate in the positive electrode active material is more than 10% by mass in terms of silicon is obtained during the charge / discharge cycle in the constant current mode at a current value corresponding to 0.1C. Although both the decrease in the discharge capacity and the discharge capacity ratio [1C / 0.1C] were similar to the positive electrode active materials A to D, the discharge capacity itself was clearly lower than the positive electrode active materials A to D. .

  In the positive electrode active material G (Comparative Example 3) in which the crystallite diameter was larger than 100 nm, the discharge capacity ratio [1C / 0.1C] was slightly smaller than that of the positive electrode active materials A to D. The amount of decrease in the discharge capacity during the charge / discharge cycle in the constant current mode at a current value corresponding to was clearly greater than that of the positive electrode active materials A to D.

  In the positive electrode active material H (Comparative Example 4) whose crystallite diameter was smaller than 30 nm, [I003 / I104] was smaller than 1.2. Moreover, the amount of decrease in discharge capacity and the discharge capacity ratio [1C / 0.1C] during the charge / discharge cycle in the constant current mode at a current value corresponding to 0.1 C of the positive electrode active material H are the positive electrode active materials A to D. The discharge capacity itself was clearly lower than that of the positive electrode active materials A to D.

Claims (4)

A lithium-nickel composite oxide represented by the following general formula (1) and an amorphous substance containing lithium, silicon and oxygen,
The crystallite diameter of the lithium-nickel composite oxide is 30 to 100 nm,
Content of the said amorphous substance is 1-10 mass% in conversion of silicon, The positive electrode active material for lithium ion secondary batteries characterized by the above-mentioned.
The general formula _{(1) ··· Li x Ni 1} -y M y O 2
[Wherein, M represents one or more elements selected from Co, Fe, and Al, 0.5 <x <1.5, and 0 ≦ y <0.2. ] The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the amorphous material is a compound represented by the following general formula (2).
General formula (2) ... Li _a Si _b O
[Wherein, a and b are each independently a positive real number. ]   3. The positive electrode active for a lithium ion secondary battery according to claim 1, wherein the amorphous substance is present between the crystals in at least some of the crystals of the lithium-nickel composite oxide. material.   It obtains using the positive electrode active material for lithium ion secondary batteries as described in any one of Claims 1-3, The lithium ion secondary battery characterized by the above-mentioned.