JP5549321B2 - Positive electrode active material for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery and a non-aqueous electrolyte secondary battery. In particular, the present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery made of lithium manganate having a spinel structure with improved high-temperature storage characteristics and reduced battery resistance.

In recent years, portable devices such as VTRs, mobile phones, and notebook personal computers have been widely used and miniaturized, and non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have been used for power supplies. Furthermore, it has been attracting attention as a power battery for electric vehicles and the like due to recent environmental problems.

As a positive electrode active material for a lithium secondary battery, LiCoO ₂ (lithium cobaltate) is generally widely adopted as being capable of constituting a 4V class secondary battery.

However, lithium cobaltate contains cobalt in its raw material. Cobalt is a scarce resource and is expensive. Therefore, lithium manganate such as LiMn ₂ O ₄ using manganese, which is a relatively abundant resource, as a raw material has been studied.

Lithium manganate, like lithium cobaltate, can constitute a secondary battery of 4V class, but has a problem that the internal resistance of the battery increases and the battery characteristics deteriorate because of its low conductivity. As countermeasures, a method of reducing the internal resistance of the battery by adding a conductive material such as carbon black, or improving the characteristics of the positive electrode active material itself by covering the surface of lithium manganate with highly conductive tungsten oxide or the like. A technique (Patent Document 1) is used.

In addition, lithium manganate elutes into the electrolyte during charge / discharge or high temperature storage (especially 85 ° C. or more), resulting in deterioration of cycle characteristics. As a countermeasure, a technique (Patent Document 2) is used in which lithium manganate contains various elements other than Li and Mn, such as Cr, to reduce elution of Mn.

Japanese Patent Laying-Open No. 2005-320184

JP-A-11-071115

However, these conventional methods cannot achieve the effect of satisfying both the reduction of the internal resistance and the improvement of the high temperature storage characteristics of the lithium secondary battery, and the output characteristics and the cycle characteristics are not sufficient, so further improvement is necessary. there were. The present invention has been made in view of the above circumstances, and the object of the present invention is to provide a positive electrode active material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte with low raw material costs, reduced battery resistance, and improved high-temperature storage characteristics. An electrolyte secondary battery is provided.

In order to achieve the above object, the present inventors have conducted intensive studies and have completed the present invention. The present inventors have found that the presence of a lithium boron composite oxide and a lithium tungsten composite oxide in spinel lithium manganate reduces battery resistance and improves high-temperature storage characteristics. The features of the present invention are as follows. In the present invention, those obtained by substituting a part of manganese in lithium manganate with other elements are collectively referred to as lithium manganate.

(1) The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is a positive electrode active material for a non-aqueous electrolyte secondary battery made of spinel lithium manganate, wherein the lithium manganate includes a lithium boron composite oxide and lithium It has a tungsten composite oxide.

(2) The positive electrode active material for a nonaqueous electrolyte secondary battery according to the present invention is the positive electrode active material for a nonaqueous electrolyte secondary battery according to (1), wherein the lithium manganate has lithium boron at least on the surface of the particles. A composite oxide and a lithium tungsten composite oxide are present.

(3) The positive electrode active material for a nonaqueous electrolyte secondary battery according to the present invention is the positive electrode active material for a nonaqueous electrolyte secondary battery according to (1) or (2), wherein the lithium manganate is a secondary particle. And a lithium boron composite oxide and a lithium tungsten composite oxide are present on the surface and inside of the secondary particles.

(4) The positive electrode active material for a nonaqueous electrolyte secondary battery according to the present invention is the positive electrode active material for a nonaqueous electrolyte secondary battery according to any one of (1) to (3), wherein the lithium boron composite oxide is boron. The lithium tungsten composite oxide is lithium tungstate.

(5) The positive electrode active material for a nonaqueous electrolyte secondary battery of the present invention is the positive electrode active material for a nonaqueous electrolyte secondary battery according to (4), wherein the lithium borate is Li ₂ B ₄ O ₇ . The lithium tungstate is Li ₂ WO ₄ .

(6) The positive electrode active material for a nonaqueous electrolyte secondary battery according to the present invention is the positive electrode active material for a nonaqueous electrolyte secondary battery according to (1) to (5), wherein the manganese of the lithium manganate is It is substituted with at least one element selected from the group consisting of magnesium and aluminum.

(7) The positive electrode active material for a nonaqueous electrolyte secondary battery according to the present invention is the positive electrode active material for a nonaqueous electrolyte secondary battery according to any one of (1) to (6), and the composition of the lithium manganate is generally formula _{Li 1 + x M y Mn 2} -x-y O 4 · aLi 2 B 4 O 7 · bLi 2 WO 4
(However, M is at least one element selected from the group consisting of Mg and Al, 0 ≦ x ≦ 0.20, 0 ≦ y ≦ 0.5, 0.0001 ≦ a ≦ 0.005, 0.005 ≦ b. ≦ 0.1)
It is represented by.

(8) The nonaqueous electrolyte secondary battery according to the present invention includes a positive electrode active material layer using the positive electrode active material for a nonaqueous electrolyte secondary battery according to any one of (1) to (7). A belt-like positive electrode formed by forming on one side;
By forming a negative electrode active material layer using a metallic lithium, a lithium alloy, a carbon material capable of occluding and releasing lithium ions, or a compound capable of occluding and releasing lithium ions as a negative electrode active material on at least one side of a strip-shaped negative electrode current collector A configured negative electrode,
A strip separator,
A spiral-type winding in which the strip-shaped positive electrode and the strip-shaped negative electrode are wound a plurality of times in a state of being laminated via the strip-shaped separator, and the strip-shaped separator is interposed between the strip-shaped positive electrode and the strip-shaped negative electrode It is characterized by comprising a body.

Since the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention has the above-described characteristics, it can suppress elution of manganese during high-temperature storage and reduce battery resistance. In addition, by using the positive electrode active material of the present invention, it is possible to obtain a lithium secondary battery that satisfies both the reduction of the internal resistance of the battery and the improvement of the high temperature storage characteristics. Furthermore, since a positive electrode active material with a low cost can be obtained by the present invention, a nonaqueous electrolyte secondary battery that can be used in a harsh environment and is inexpensive can be obtained.

FIG. 1 is an X-ray diffraction diagram of Example 3 and Comparative Example 7. FIG. 2 is a conceptual diagram of the internal resistance obtained in the present invention. FIG. 3 is a scanning electron microscope (SEM) photograph of Example 1. FIG. 4 is a map of an electron beam microanalyzer (EPMA). FIG. 5 is a graph showing the relationship between the battery resistance and the b value of the positive electrode active material. FIG. 6 is a graph showing the relationship between the Mn elution amount and the b value of the positive electrode active material.

Hereinafter, the positive electrode active material of the present invention will be described in detail with reference to embodiments and examples. However, the present invention is not limited to these embodiments and examples.

The positive electrode active material of the present invention is a positive electrode active material composed of lithium manganate having a spinel structure having a lithium boron composite oxide and a lithium tungsten composite oxide. The lithium manganate preferably includes at least a lithium boron composite oxide and a lithium tungsten composite oxide on the surface of the particles, and has secondary particles, and the lithium boron composite oxide on the surfaces and inside of the secondary particles. More preferably, a lithium tungsten composite oxide is present. The lithium boron complex oxide is preferably lithium borate, and lithium borate is preferably lithium metaborate, lithium tetraborate, or lithium pentaborate, and tetraborate represented by Li ₂ B ₄ O ₇ Lithium is more preferred. The lithium tungsten composite oxide is preferably lithium tungstate, and more preferably Li ₂ WO ₄ . By firing a raw material mixture containing boron in a raw material containing lithium, manganese and tungsten, a lithium boron composite oxide and a lithium tungsten composite oxide are formed, battery resistance can be reduced, and storage at high temperatures Of manganese can be suppressed. On the other hand, when the raw material mixture is baked without containing boron in the raw material, a manganese tungsten composite oxide is formed. Therefore, the effect of reducing battery resistance and the effect of suppressing manganese elution during high temperature storage are very high. It gets smaller. In addition, the addition amount of lithium, manganese, tungsten, and boron in a raw material is adjusted so that the target lithium boron complex oxide and lithium tungsten complex oxide may be formed.

The lithium manganate has secondary particles that are primary particles and / or aggregates of primary particles. The primary particle diameter is preferably in the range of 0.1 to 5 μm, and is determined as the crystallite size by a line broadening method using an X-ray diffractometer. The secondary particle diameter is preferably in the range of 6 to 30 μm, and is determined as a 50% cumulative diameter in the particle size distribution in the volume distribution by a laser diffraction scattering method using a laser diffractometer. A preferable effect of the present invention is obtained in such a particle size range.

In the positive electrode active material of the present invention, a part of the manganese of the lithium manganate may be replaced with another metal element, for example, a metal element such as Mg, Al, Cr, Fe, Zr, Co, Ni, A total of 25 mol% of manganese can be substituted. If the substitution amount exceeds 25 mol%, the distortion of the spinel structure of lithium manganate becomes large, which is not preferable. Particularly preferred substitution elements are Mg and Al. By substitution with these elements, cycle characteristics and load characteristics can be improved.

The positive electrode active material of the present invention, the composition of the lithium manganate general formula _{Li 1 + x M y Mn 2} -x-y O 4 · aLi 2 B 4 O 7 · bLi 2 WO 4
(However, M is at least one element selected from the group consisting of Mg and Al, 0 ≦ x ≦ 0.20, 0 ≦ y ≦ 0.5, 0.0001 ≦ a ≦ 0.005, 0.001 ≦ b. ≦ 0.1) is particularly preferable. The lithium manganate having such a composition further improves the effect of reducing battery resistance and the effect of suppressing elution of manganese during high temperature storage. The x value is more preferably in the range of 0 ≦ x ≦ 0.15, the y value is more preferably in the range of 0 ≦ y ≦ 0.3, and further preferably in the range of 0 ≦ y ≦ 0.2. In this range, the effect is further increased. Since the value a is also related to the size of the primary particle diameter, the range of 0.0003 ≦ a ≦ 0.003 is more preferable. The b value is more preferably in the range of 0.005 ≦ b ≦ 0.05.

[Production of positive electrode active material]
The positive electrode active material of the present invention can be produced, for example, as follows.

A lithium compound, a manganese compound, a tungsten compound, a boron compound, and if necessary, a compound of a substituted metal element are weighed and mixed so as to have a target composition.

As the lithium compound, oxides, hydroxides, carbonates, nitrates, and the like can be used which are decomposed by heating to become oxides. For example, Li ₂ O, LiOH, Li ₂ CO ₃ , LiNO _{3 and the} like can be used.

As the manganese compound, oxides, hydroxides, carbonates, nitrates, and the like can be used which are decomposed by heating to become oxides. For example, such _{MnO 2, Mn 2 O 3,} Mn 3 O 4, Mn (OH) 2, MnCO 3 can be used.

Similarly, when a part of manganese is substituted with another metal element, oxides, hydroxides, carbonates, nitrates, and other substances that are decomposed by heating can be used. For example, when the substitution element is magnesium, MgO, Mg (OH) ₂ , MgCO ₃ , Mg (NO ₃ ) _2, etc. can be used, and when aluminum is used, Al ₂ O ₃ , Al (OH) ₃ , Al (NO _{3). 3} etc. can be used. Further, it is preferable to use a coprecipitated oxide obtained by dissolving manganese and a substituted metal element at the same time to form an aqueous solution, coprecipitating with a hydroxide or carbonate, and then thermally decomposing the precipitate.

As the tungsten compound, oxide, tungstic acid, tungstate, etc., for example, WO ₃ , H ₂ WO ₄ , Li ₂ WO _{4 and the} like can be used.

As the boron compound, oxides, boric acid, borates and the like, for example, B ₂ O ₃ , H ₃ BO ₃ , Li ₂ B ₄ O _{7 and the} like can be used. The boron compound also functions as a flux, and when the addition amount is large, the primary particle size becomes large. Therefore, the boron compound is 0.04 mol% to 2 mol%, more preferably 0.12 mol% to 1 based on the positive electrode active material in terms of boron. Add 2 mol%.

Next, the raw material mixture is fired. The firing temperature, time, atmosphere, etc. are not particularly limited, and can be appropriately determined according to the purpose. The firing temperature is preferably 650 ° C. or higher, and more preferably 700 ° C. or higher. If the firing temperature is too low, unreacted raw materials may remain in the positive electrode active material, and the original characteristics of the positive electrode active material may not be utilized. The firing temperature is preferably 1100 ° C. or lower, and more preferably 950 ° C. or lower. If the firing temperature is too high, the particle size of the positive electrode active material may become too large, and the charge / discharge characteristics may deteriorate. In addition, by-products such as Li ₂ MnO ₃ and LiMnO ₂ are likely to be generated, which may lead to a decrease in discharge capacity per unit weight, a decrease in cycle characteristics, and a decrease in operating voltage. The firing time is preferably 1 to 48 hours, and more preferably 6 to 30 hours. When the firing time is too short, the diffusion reaction between the raw material particles does not proceed. If the firing time is too long, energy is wasted and coarse particles may be formed by sintering.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[Preparation of positive electrode active material]

Aluminum sulfate and manganese sulfate are dissolved in pure water so that Al: Mn = 0.5: 9.5, and 12.5% by volume of ammonia water is added dropwise to adjust the pH to 8 or more. Next, carbon dioxide gas is blown to obtain a coprecipitated carbonate of aluminum and manganese. The obtained coprecipitated carbonate is separated, dried, and heat-treated at 560 ° C. for about 3 hours to obtain an aluminum-manganese coprecipitated oxide. Obtained aluminum-manganese coprecipitated oxide (0.095Al ₂ O ₃ .805Mn ₂ O ₃ ) 1.900 mol, lithium carbonate (Li ₂ CO ₃ ) 1.122 mol, tungsten oxide (WO ₃ ) 0.020 mol , And boric acid (H ₃ BO ₃ ) 0.008 mol are mixed to obtain a raw material mixture. The obtained raw material mixture is baked at 800 ° C. for 24 hours in an air atmosphere. Obtaining a positive electrode active material formula by grinding after firing is represented by _{Li 1.100 Al 0.095 Mn 1.805 O 4} · 0.001Li 2 B 4 O 7 · 0.01Li 2 WO 4. The composition of the positive electrode active material is determined by ICP emission spectroscopic analysis of a solution in which the positive electrode active material is dissolved with an acid.

Magnesium sulfate and manganese sulfate are dissolved in pure water so that Mg: Mn = 0.25: 9.75, and 12.5 vol% ammonia water is added dropwise to adjust the pH to 8 or more. Next, carbon dioxide gas is blown to obtain a coprecipitated carbonate of magnesium and manganese. The obtained coprecipitated carbonate is separated, dried, and heat-treated at 560 ° C. for about 3 hours to obtain a magnesium-manganese coprecipitated oxide. Magnesium-manganese coprecipitated oxide (0.095MgO · 1.8525Mn ₂ O ₃ ) 1.9475 mol, lithium carbonate (Li ₂ CO ₃ ) 1.122 mol, tungsten oxide (WO ₃ ) 0.020 mol, and boron 0.008 mol of acid (H ₃ BO ₃ ) is mixed to obtain a raw material mixture. The obtained raw material mixture is baked at 800 ° C. for 24 hours in an air atmosphere. Obtaining a positive electrode active material formula by grinding after firing is represented by _{Li 1.100 Mg 0.0475 Mn 1.8525 O 4} · 0.001Li 2 B 4 O 7 · 0.01Li 2 WO 4.

Manganese sulfate is dissolved in pure water, and 12.5% by volume of ammonia water is added dropwise to adjust the pH to 8 or more. Next, carbon dioxide gas is blown to obtain manganese carbonate. The obtained carbonate is separated, dried, and heat-treated at 560 ° C. for about 3 hours to obtain manganese oxide. Obtained manganese oxide (Mn ₂ O ₃ ) 1.900 mol, lithium carbonate (Li ₂ CO ₃ ) 1.122 mol, tungsten oxide (WO ₃ ) 0.020 mol, and boric acid (H ₃ BO ₃ ) 0.008 mol Are mixed to obtain a raw material mixture. The obtained raw material mixture is baked at 800 ° C. for 24 hours in an air atmosphere. A positive electrode active material represented by the general formula Li _1.100 Mn _1.900 O ₄ .0.001Li ₂ B ₄ O ₇ .0.01Li ₂ WO ₄ is obtained by pulverization after firing.

The same operation as in Example 3 was performed except that 3.800 mol of electrolytic manganese oxide (MnO ₂ ) was used instead of manganese oxide, and the general formula was Li _1.100 Mn _1.900 O ₄ .0.001Li _2. A positive electrode active material represented by B ₄ O ₇ · 0.01Li ₂ WO ₄ is obtained.

The same operation as in Example 3 was performed except that 3.800 mol of manganese hydroxide (Mn (OH) ₂ ) was used instead of manganese oxide, and the general formula was Li _1.100 Mn _1.900 O _{4 .0.} A positive electrode active material represented by .001Li ₂ B ₄ O ₇ · 0.01Li ₂ WO ₄ is obtained.

[Comparative Example 1]
Lithium carbonate (Li ₂ CO ₃ ) 1.100 mol and electrolytic manganese oxide (MnO ₂ ) 3.800 mol are mixed to obtain a raw material mixture. The obtained raw material mixture is baked at 800 ° C. for 24 hours in an air atmosphere. A positive electrode active material having a general formula of Li _1.100 Mn _1.900 O ₄ is obtained by pulverization after firing.

[Comparative Example 2]
Lithium carbonate (Li ₂ CO ₃ ) 1.120 mol, electrolytic manganese oxide (MnO ₂ ) 3.800 mol, and tungsten oxide (WO ₃ ) 0.020 mol are mixed to obtain a raw material mixture. The obtained raw material mixture is baked at 800 ° C. for 24 hours in an air atmosphere. A positive electrode active material having a general formula represented by Li _1.100 Mn _1.900 O ₄ .0.01MnWO ₄ is obtained by pulverizing after firing.

[Comparative Example 3]
The same operation as in Example 1 is performed to obtain an aluminum-manganese coprecipitated oxide. The obtained aluminum-manganese coprecipitated oxide (0.095Al ₂ O ₃ .805Mn ₂ O ₃ ) 1.900 mol, lithium carbonate (Li ₂ CO ₃ ) 1.102 mol and boric acid (H ₃ BO ₃ ) 0 0.008 mol is mixed to obtain a raw material mixture. The obtained raw material mixture is baked at 800 ° C. for 24 hours in an air atmosphere. A positive electrode active material having a general formula of Li _1.100 Al _0.095 Mn _1.805 O ₄ .0.001Li ₂ B ₄ O ₇ is obtained by pulverization after firing.

[Comparative Example 4]
The same operation as in Example 2 is performed to obtain a magnesium-manganese coprecipitated oxide. Magnesium-manganese coprecipitated oxide (0.095MgO · 1.8525Mn ₂ O ₃ ) 1.9475 mol, lithium carbonate (Li ₂ CO ₃ ) 1.102 mol and boric acid (H ₃ BO ₃ ) 0.008 mol were obtained. Mix to obtain a raw material mixture. The obtained raw material mixture is baked at 800 ° C. for 24 hours in an air atmosphere. Formula by grinding after firing to obtain a positive electrode active material represented by _{Li 1.100 Mg 0.0475 Mn 1.8525 O 4} · 0.001Li 2 B 4 O 7.

[Comparative Example 5]
The same operation as in Example 3 is performed to obtain a manganese oxide. 1.900 mol of the obtained manganese oxide (Mn ₂ O ₃ ), 1.102 mol of lithium carbonate (Li ₂ CO ₃ ) and 0.008 mol of boric acid (H ₃ BO ₃ ) are mixed to obtain a raw material mixture. The obtained raw material mixture is baked at 800 ° C. for 24 hours in an air atmosphere. The positive electrode active material represented by the general formula Li _1.100 Mn _1.900 O ₄ .0.001Li ₂ B ₄ O ₇ is obtained by grinding after firing.

[Comparative Example 6]
The same operation as in Example 3 is performed to obtain a manganese oxide. The resulting manganese oxide (Mn ₂ O ₃ ) 1.900 mol, lithium carbonate (Li ₂ CO ₃ ) 1.120 mol, and tungsten oxide (WO ₃ ) 0.020 mol are mixed to obtain a raw material mixture. The obtained raw material mixture is baked at 800 ° C. for 24 hours in an air atmosphere. A positive electrode active material having a general formula represented by Li _1.100 Mn _1.900 O ₄ .0.01MnWO ₄ is obtained by pulverizing after firing.

[Comparative Example 7]
The same operation as in Comparative Example 6 was performed except that 3.800 mol of manganese hydroxide (Mn (OH) ₂ ) was used instead of manganese oxide, and the general formula was Li _1.100 Mn _1.900 O _{4 .0.} A positive electrode active material represented by .01MnWO ₄ is obtained.

[Powder X-ray diffraction measurement of positive electrode active material]
The positive electrode active material obtained in Example 3 and Comparative Example 7 is measured for powder X-ray diffraction (XRD) using an X-ray diffractometer (RINT 2500V) manufactured by Rigaku Denki and using CuKα rays as an X-ray source. An X-ray diffraction diagram is shown in FIG. This figure shows that the positive electrode active material obtained in Example 3 and Comparative Example 7 is a positive electrode active material made of lithium manganate having a spinel structure. Further, it is confirmed that Li ₂ WO ₄ is present in the positive electrode active material obtained in Example 3, and that MnWO ₄ is present in the positive electrode active material obtained in Comparative Example 7. The presence of Li ₂ WO ₄ can be confirmed not only in Example 3 but also in the positive electrode active material obtained in other examples.

[SEM photograph of positive electrode active material]
A scanning electron microscope (SEM) photograph of the positive electrode active material obtained in Example 1 is shown in FIG. From this figure, it can be seen that the positive electrode active material of the present invention has secondary particles that are aggregates of primary particles.

[EPMA analysis of positive electrode active material]
About the positive electrode active material obtained in Example 1, the cross section of the secondary particle of a positive electrode active material was measured with the electron beam microanalyzer (EPMA) equipped with the wavelength dispersion type | mold X-ray-spectrometer made from JEOL (WDX). A map is shown in FIG. From this figure, it is confirmed that W element exists on the surface of the secondary particle of the positive electrode active material and the interface of the primary particle. Therefore, since the presence of Li ₂ WO ₄ from the powder X-ray diffraction measurement result is confirmed, it can be seen that Li ₂ WO ₄ is present on the surface and inside of the secondary particles.

[Elution test of positive electrode active material]
The positive electrode active material obtained in Example 3 is subjected to a dissolution test as follows. After adding 50 g of the positive electrode active material to 200 g of pure water and stirring for 8 hours, the slurry is subjected to solid-liquid separation, and the eluate is subjected to ICP spectroscopic analysis. Further, after adding 50 g of a positive electrode active material and 500 g of zirconia balls to 200 g of pure water and ball milling for 8 hours, the slurry is subjected to solid-liquid separation, and the eluate is subjected to ICP emission spectral analysis. Table 1 shows analysis values of the eluate and elution amounts of Li ₂ B ₄ O ₇ and Li ₂ WO ₄ . _Here, the elution amount of Li ₂ B 4 _{O 7} and _Li 2 WO ₄ (%) is, _Li 2 _B in the positive electrode active material obtained in Example 3 4 _{O 7} weight and _Li 2 WO ₄ weight respectively 100% This is the elution ratio.

From Table 1, it can be seen that the amount of Li ₂ B ₄ O ₇ and Li ₂ WO ₄ eluted is greater when ball milled than when only stirred. That is, in the case of only stirring, Li ₂ B ₄ O ₇ and Li ₂ WO ₄ are eluted mainly from the surface of the secondary particles of the positive electrode active material, but by ball milling, the secondary particles of the positive electrode active material It can be seen that Li ₂ B ₄ O ₇ and Li ₂ WO ₄ are eluted not only from the surface but also from the inside of the secondary particles.

Therefore, from the above measurement results, the positive electrode active material of the present invention has secondary particles, and spinel structure manganic acid in which Li ₂ B ₄ O ₇ and Li ₂ WO ₄ are present on the surface and inside of the secondary particles. It turns out that it is a positive electrode active material which consists of lithium.

[Production of lithium ion secondary battery]
Using the positive electrode active materials obtained in Examples 1 to 5 and Comparative Examples 1 to 7, lithium ion secondary batteries are prepared as follows and used for various evaluations.

  A paste is prepared by kneading 90% by weight of the positive electrode active material powder, 5% by weight of carbon powder as a conductive agent, and a normal methylpyrrolidone solution of polyvinylidene fluoride (5% by weight as the amount of polyvinylidene fluoride). Is applied to a positive electrode current collector and dried to obtain a positive electrode plate.

  A carbon material is used as the negative electrode active material, and a negative electrode plate is produced in the same manner as in the case of the positive electrode plate.

A porous propylene film is used as a separator, and a positive electrode plate, a negative electrode plate, and a separator are formed into a thin sheet shape, which is wound and accommodated in a metal cylindrical battery case. Into the battery case, a nonaqueous electrolytic solution prepared by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate / methyl ethyl carbonate = 3/7 (volume ratio) was injected to form a cylindrical lithium ion solution. Get the next battery.

[Evaluation of battery resistance (DC-IR)]
Measure current and potential as follows to determine battery resistance.

  At a measurement temperature of 25 ° C., constant voltage charging is performed at 4.2 V up to a charging depth of 50%, and pulse discharge is performed. The pulse time is 10 seconds and the pulse interval is 3 minutes. For currents 0.04A, 0.08A, 0.12A, 0.16A, and 0.20A during pulse discharge, the difference between the potential after charging and the potential during pulse discharge (potential difference) is divided by the current during pulse discharge. The battery resistance is the current at the time of pulse discharge during measurement. The battery resistance at the current during each pulse discharge is averaged and evaluated as the final battery resistance (DC-IR) (see FIG. 2).

[Evaluation of high-temperature storage characteristics]
The manganese elution amount from the positive electrode is measured in the following manner to evaluate the high temperature storage characteristics.

  After performing constant current-constant voltage charging to 4.2 V at a rate of 0.2 C, constant current discharging is performed to 2.75 V, and the initial discharge capacity is measured. Thereafter, the battery is charged at a constant voltage of 4.2 V to a charging depth of 40% and stored in a thermostatic bath at 80 ° C. for 3 days. After storage, the battery is taken out from the thermostatic chamber, discharged at a rate of 0.2 C to 2.75 V, charged to 4.2 V, and discharged to 2.75 V. After the final discharge, the negative electrode is taken out from the secondary battery, and manganese contained in the negative electrode is extracted with an HCl solution. After filtering the solution, the amount of manganese eluted by ICP emission spectrometry is analyzed.

Table 2 shows the compositions of the positive electrode active materials obtained in Examples 1 to 5 and Comparative Examples 1 to 7, and the evaluation results of the battery resistance (DC-IR) and high-temperature storage characteristics of the lithium ion secondary batteries.

From Table 2, the positive active materials of Examples 1 to 5 of the present invention because they contain _Li 2 _B 4 _{O 7} and _Li 2 WO _4, none of Li ₂ B 4 _{O 7} and _Li 2 WO ₄ and Comparative example 1 not containing, in comparison with the positive electrode active material of Comparative example 2-7 containing a Li ₂ B ₄ O ₇ or MnWO _4, it is possible to reduce the battery resistance, manganese during high-temperature storage It can be seen that elution can be suppressed.

Next, a lithium ion secondary battery is produced for each positive electrode active material obtained by changing the W amount of the raw material in Example 1, and battery resistance (DC-IR) and high-temperature storage characteristics are evaluated. Figure 5 shows the relationship between b value of the battery resistance and the positive electrode active material _(Li 2 WO ₄ volume). From this figure, it can be seen that the battery resistance is reduced when the b value of the positive electrode active material is in the range of 0.001 ≦ b ≦ 0.1, and is further reduced in the range of 0.005 ≦ b ≦ 0.05. FIG. 6 shows the relationship between the elution amount of Mn and the b value (Li ₂ WO ₄ amount) of the positive electrode active material. From this figure, it can be seen that the elution amount of Mn is small when the b value of the positive electrode active material is in the range of 0.005 ≦ b ≦ 0.1. Therefore, in order to satisfy both the reduction of the internal resistance and the improvement of the high temperature storage characteristics of the lithium ion secondary battery, the b value of the positive electrode active material is preferably in the range of 0.001 ≦ b ≦ 0.1, 0.005 It can be seen that the range of ≦ b ≦ 0.05 is more preferable.

Further, the a value (Li ₂ B ₄ O ₇ amount) of the positive electrode active material is related not only to battery resistance (DC-IR) and high-temperature storage characteristics but also to the size of the primary particle diameter. The range of ≦ a ≦ 0.005 is preferable, and the range of 0.0003 ≦ a ≦ 0.003 is more preferable.

Thus, the positive electrode active material of the present invention is a positive electrode active material composed of lithium manganate having a spinel structure having a lithium boron composite oxide and a lithium tungsten composite oxide, and by using the positive electrode active material of the present invention. Thus, it is possible to obtain a lithium secondary battery that satisfies both the reduction of the internal resistance of the battery and the improvement of the high-temperature storage characteristics. In addition, the positive electrode active material of the present invention can be expected to improve output characteristics because it can reduce battery resistance, and can be expected to improve cycle characteristics because it can suppress elution of manganese.

  By using the positive electrode active material of the present invention, a non-aqueous electrolyte secondary battery that can be used for a long time even in a harsh environment can be realized. The nonaqueous electrolyte secondary battery thus realized can be suitably used for portable devices such as VTRs, mobile phones, and notebook personal computers. Furthermore, since the battery resistance is low, it can be suitably used for high-power applications such as medium-sized devices such as electric tools and electric assist bicycles, and large devices such as electric vehicles and hybrid electric vehicles.

Claims (4)

In the positive electrode active material for a non-aqueous electrolyte secondary battery made of spinel lithium manganate, the lithium manganate is
General formula
_{Li 1 + x M y Mn 2} -x-y O 4 · aLi 2 B 4 O 7 · bLi 2 WO 4
(However, M is at least one element selected from the group consisting of Mg and Al, 0 ≦ x ≦ 0.20, 0 ≦ y ≦ 0.5, 0.0001 ≦ a ≦ 0.005, 0.005 ≦ b. ≦ 0.1)
A positive electrode active material for a non-aqueous electrolyte secondary battery, characterized in that it has secondary particles and has a lithium boron composite oxide and a lithium tungsten composite oxide on the surface and inside of the secondary particles . The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium boron composite oxide is lithium borate, and the lithium tungsten composite oxide is lithium tungstate. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 2 , wherein the lithium borate is Li ₂ B ₄ O ₇ and the lithium tungstate is Li ₂ WO ₄ . A positive electrode strip configured by a positive electrode active material layer using the positive electrode active material for non-aqueous electrolyte secondary battery according to claims 1 to 3, is formed on at least one surface of the strip-shaped cathode current collector,
By forming a negative electrode active material layer using a metallic lithium, a lithium alloy, a carbon material capable of occluding and releasing lithium ions, or a compound capable of occluding and releasing lithium ions as a negative electrode active material on at least one side of a strip-shaped negative electrode current collector A configured negative electrode,
A strip separator,
A spiral-type winding in which the strip-shaped positive electrode and the strip-shaped negative electrode are wound a plurality of times in a state of being laminated via the strip-shaped separator, and the strip-shaped separator is interposed between the strip-shaped positive electrode and the strip-shaped negative electrode A non-aqueous electrolyte secondary battery comprising a body.