JP2018041657A - Positive electrode active material for lithium secondary battery, method for manufacturing the same, lithium secondary battery electrode, and lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the initial efficiency of a lithium secondary battery.SOLUTION: A positive electrode active material for a lithium secondary battery comprises particles of a lithium transition metal composite oxide. The lithium transition metal composite oxide particles have an α-NaFeOtype structure, and include Ni, Co and Mn as a transition metal (Me), in which the mole ratio Ni/Me of Ni to Me is given by Ni/Me≥0.4. The lithium transition metal composite oxide particles have two or more peaks in a particle size distribution, and have at least one peak on a particle diameter side larger than a diameter showing a maximum peak. A method for manufacturing the positive electrode active material for a lithium secondary battery comprises the steps of: mixing particles of a precursor of the transition metal compound including Ni, Co and Mn with a lithium compound, and a fluorine source including fluorine of 2.5 mol% or more to the precursor; and baking the resultant mixture at a temperature over 950°C, thereby manufacturing the lithium transition metal composite oxide particles.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a positive electrode active material for a lithium secondary battery, a method for producing the positive electrode active material, an electrode for a lithium secondary battery containing the positive electrode active material, and a lithium secondary battery including the electrode.

Conventionally, lithium transition metal composite oxides having an α-NaFeO ₂ type crystal structure have been studied as positive electrode active materials for lithium secondary batteries, and lithium secondary batteries using LiCoO ₂ have been widely put into practical use. However, LiCoO ₂ has a discharge capacity of about 120 to 130 mAh / g.

Nickel-based lithium transition metal oxides containing Ni, Co, Mn, etc. are known as positive electrode active materials that exhibit a high discharge capacity per unit mass compared to LiCoO ₂ . Since the packing density is low, the discharge capacity per unit volume is low, and as a result, the lithium secondary battery using this has a low discharge capacity (see paragraph [0004] of Patent Document 1).

A nickel-based lithium transition metal composite oxide containing fluorine is also known (see Patent Document 2). Example 11 of Patent Document 2 includes cobalt represented by “Ni _0.83 Co _0.17 (OH) _2. Co-precipitated nickel hydroxide powder, aluminum hydroxide, lithium tetraborate, and lithium fluoride have a molar ratio of Li: B: Al: F: Mn: (Ni + Co) of 1.05: 0.02: 0.02: 0. .05: 0.03: 0.95 A 3 mol / liter sodium hydroxide aqueous solution was added dropwise to a solution dispersed in a 3 mol / liter manganese nitrate aqueous solution so as to maintain a temperature of 40-60 ° C. The resulting product was reacted continuously with a 3 mol / liter lithium hydroxide aqueous solution so that the molar ratio of Li: (Ni + Co + Mn + Al + B + F) was 1.05: 0.95. After dripping and mixing well, while introducing an oxygen stream so that the oxygen concentration becomes 18% or more and 100% or less, it is sprayed in a reactor maintained at a temperature of 700 ° C., and the oxygen concentration is 95% or more. Then, heat treatment was performed for 5 hours at 800 ° C. while pressurizing up to 1 MPas, and the obtained product was measured by X-ray diffraction, Li _1.05 Ni _0.75 Co _0.15 Mn _0.03 Al _0.02 B _0.02 F _0.05 0 _1.95 ”(paragraph [0061]).

  As a method for increasing the packing density of the positive electrode active material, a technique of adding a fluorine-based additive at the time of firing the precursor and firing at a low temperature is known (see, for example, Non-Patent Document 1, Patent Documents 3 and 4).

In Non-Patent Document 1, LiOH.H ₂ O and LiF are mixed with a transition metal hydroxide that is a precursor, fired at 900 ° C., and Li [Ni _x Co _1-2x Mn _x ] O _2. Is obtained (Experimental column).

  Patent Document 3 states that “a positive electrode active material for a non-aqueous electrolyte secondary battery having at least a layered lithium transition metal composite oxide, wherein the lithium transition metal composite oxide is an aggregate of primary particles. A non-aqueous electrolyte secondary particle having secondary particles, wherein the secondary particles have a filling portion and a cavity portion inside the secondary particles, and the median diameter of the secondary particles is 3 μm or more The positive electrode active material for a battery. (Claim 3), "The lithium transition metal composite oxide has at least one selected from the group consisting of fluorine, vanadium and boron. "Positive electrode active material for liquid secondary battery" (Claim 6).

Patent Document 3 states that “the lithium transition metal composite oxide has at least one selected from the group consisting of fluorine, vanadium and boron, so that the size of the primary particles can be controlled even at low temperature firing. Therefore, the electrode plate filling property can be more effectively improved without hindering the improvement of the load characteristics ”(paragraph [0018]).
In Example 10, the precipitate containing cobalt, nickel and manganese was filtered, washed with water, heat-treated, mixed with lithium carbonate and lithium fluoride, and fired at 900 ° C. for 15 hours in the air. An electrode plate manufactured from a positive electrode active material represented by Li _1.00 Ni _0.33 Co _0.33 Mn _0.33 O ₂ F _0.0025 has a density of 3.15 g / ml. (Paragraph [0095], Table 1).

Patent Document 4 discloses that “the lithium-containing composite oxide is a compound represented by the following general formula (1):
_{Li a Ni x Mn y Co z} Me b O c F d ··· formula (1)
However, in the general formula (1), 1.02 ≦ a ≦ 1.12, 0 <x ≦ 1.0, 0 <y ≦ 1.0, 0 ≦ z ≦ 1.0, 0 ≦ b ≦ 0. 3, 0.90 ≦ x + y + z + b ≦ 1.05, 1.9 ≦ c ≦ 2.1, and 0 ≦ d ≦ 0.03, and Me is composed of Mg, Ca, Sr, Ba, Al, and Zr It is at least one selected from the group. (Claim 9) and "A lithium-containing composite oxide obtained by the method for producing a lithium-containing composite oxide according to claim 8 or 9" (Claim 10).

Patent Document 4 discloses in Example 2 that “200.00 g of a composite compound obtained in the same manner as in the method described in Example 1 and lithium carbonate (Li ₂ CO ₃ having a Li content of 26.96 mol / kg). Ex. 1 except that 83.59 g of SQM) and 0.06 g of lithium fluoride (LiF, manufactured by Wako Pure Chemical Industries, Ltd.) were mixed and baked at 910 ° C. for 8 hours in an air atmosphere. Similarly, a lithium-containing composite oxide having a charging composition of Li _1.014 Ni _0.495 Co _0.197 Mn _0.294 O _1.999 F _0.001 was obtained. The composition ratio of the lithium-containing composite oxide was 2.3 g / cm ³ (Table 2), and the composition ratio of the lithium-containing composite oxide was equal to the preparation ratio ”(paragraph [0102]). Lithium-containing composite oxidation It is also described that the electrode density of the electrode using the object is 3.01 g / cm ³ and the efficiency of the battery including the electrode is 88.2% (Table 3).

  As another method for increasing the packing density of the positive electrode active material, a technique of mixing a plurality of particles having different particle diameters is also known (see, for example, Patent Documents 5 and 6).

  Patent Document 5 states that “a negative electrode, a positive electrode obtained by coating and molding a composite oxide composed of lithium and a transition metal as a positive electrode active material, and a positive electrode active of a lithium secondary battery in which a separator is disposed and filled with a nonaqueous electrolyte. A non-aqueous lithium secondary battery, characterized in that the spherical particles have an average particle size of 1 to 20 μm, a maximum particle size of 50 μm or less, and a plurality of peaks in the particle size distribution (Claim 7), “In order to have a plurality of peaks in the particle size distribution of the spherical particles, the particle size is adjusted separately and powders having different particle sizes are mixed. The positive electrode active material for a non-aqueous lithium secondary battery according to claim 7. (Claim 8), "The particle size distribution of the spherical particles has two peaks, and the particle size ratio of the two peaks. 9 or more according to claim 7 or 8, Non-aqueous lithium secondary battery positive electrode active material "(Claim 9) is described.

In addition, in Patent Document 5, “... in addition, since the particle size distribution has two peaks, the gaps between the particles are filled with small particles, and the particles are more densely packed. As a result, the amount of the positive electrode material that can be filled into the battery can be increased, and a high capacity can be obtained as the battery. Since the contact property with the agent is improved and the electrical contact state is also improved, the cycle characteristics are also improved "(paragraph [0009]).
In the examples, the amorphous Li—Co composite oxide particles (Li: Co = 1: 1) having an average particle diameter of 3 μm are added to the spherical Li—Co composite oxide particles (Li: Co) having an average particle diameter of 18 μm. = 1: 1) manufactured using a positive electrode active material mixed at a ratio of 1: 1 shows an electrode density of 3.4 g / cm ³ , and a battery using the electrode has a discharge capacity of 524 mAh / cm ³ . (Paragraph [0019], Table 1).

Patent Document 6 includes “a mixture B of a large number of large particles having different particle diameters and a large number of small particles having different particle diameters, and the particle size of the particles contained in the mixture B. The function F (x) of x and its frequency F has the relationship of Formula 1 (where, in Formula 1, the median diameter μ _g in the aggregate of large particles is 10 μm ≦ μ _g ≦ 30 μm, and the standard deviation σ _g is 1.16 ≦ σ _g ≦ 1.65, the median diameter μ _h in the small particle aggregate is 0.1 μm ≦ μ _h <10 μm, and the standard deviation σ _h is 1.16 ≦ σ _h ≦ 1. .65, A _g + A _h = 1, 0 <A _g <1, 0 <A _h <1, and 1 ≦ A _g / A _h ≦ 9)), and the mixture B is 1.92 t / cm the particle size x of the particles contained in the mixture B 'after pressurizing with ² function E with its frequency E (x) has the relationship of equation 2 However, in Equation 2, a median diameter mu _'g is 10μm ≦ _{μ' g} ≦ 30μm in aggregates of large particles, the standard deviation sigma _'g is 1.16 ≦ _sigma' is _g ≦ 1.65, small particles The median diameter μ ′ _h in the aggregate is 0.1 μm ≦ μ ′ _h <10 μm, the standard deviation σ ′ _h is 1.16 ≦ σ ′ _h ≦ 1.65, and A ′ _g + A ′ _h = 1. 0 <A ′ _g <1, 0 <A ′ _h <1, and 1 ≦ A ′ _g / A ′ _h ≦ 9), and the rate of change of the median diameter μ ′ _g with respect to μ _g is 10% or less. The positive electrode active material for a lithium ion secondary battery, wherein the change rate of the median diameter μ ′ _h with respect to μ _h is 20% or more. (Claim 1), “The positive electrode active material is Li _p. a lithium composite oxide having a composition represented by a _{Ni x Co y Mn z M q} O r F a ( where, M is, Ni, Co and and at least one element selected from the group consisting of transition metal elements other than n, Al, and Group 2 elements, and p, x, y, z, q, r, and a are 0.9 ≦ p ≦ 1.5, 0 ≦ x ≦ 0.8, 0 ≦ y ≦ 1.0, 0 ≦ z ≦ 0.5, 0 ≦ q ≦ 0.1, 1.9 ≦ r ≦ 2.1, 0 ≦ a ≦ 0.1 is satisfied.) The positive electrode active material for a lithium ion secondary battery according to claim 1 or 2 ”(claim 3).

Patent Document 6 discloses a composite hydroxide powder having a composition of substantially spherical Ni _0.50 Co _0.20 Mn _0.30 (OH) ₂ having a median diameter of 16 μm and lithium carbonate powder in Example 1. After mixing, a large particle size lithium composite having a composition of Li _1.015 (Ni _0.50 Co _0.20 Mn _0.30 ) _0.985 O ₂ obtained by firing at 950 ° C. in an oxygen-containing atmosphere. After mixing the oxide powder and the composite hydroxide powder having a composition of hollow Ni _0.50 Co _0.20 Mn _0.30 (OH) ₂ having a median diameter of 5 μm and the lithium carbonate powder, oxygen A powder of a small particle size lithium composite oxide having a composition of Li _1.015 (Ni _0.50 Co _0.20 Mn _0.30 ) _0.985 O ₂ obtained by firing at 950 ° C. in a containing atmosphere, Large particle size by weight The positive electrode active material mixed at a ratio of lithium composite oxide: small particle size lithium composite oxide = 80: 20 exhibits a press density of 3.65 g / cm ³ , and a battery using the active material has a capacity of 620 mAh / cm. ³ (paragraphs [0051] to [0056]).

Japanese Patent Laying-Open No. 2015-18803 JP 2000-243394 A JP 2005-44722 A WO2014 / 175191 JP 2002-279984 A WO2013 / 191179

J. Electrochem. Soc., Jouanneau et al., 151, 1749 (2004)

In the technology described in Non-Patent Document 1, Patent Documents 3 and 4, and the low-temperature firing technique by adding a fluorine-based additive (LiF or the like) during firing, the packing density of the active material is improved, but at the same time the initial efficiency is reduced. The problem was that a battery having a high energy density could not be obtained.
The lithium transition metal composite oxide described in Patent Document 2 has a high Ni / Me ratio and uses LiF in the synthesis process. However, it uses a spray drying method and has an oxygen partial pressure of 95% or more. Since the firing is performed below, an active material having a high tap density cannot be obtained, and a material having a sharp particle size distribution is obtained. Therefore, the initial efficiency is low.

As described in Patent Documents 5 and 6, when a lithium transition metal composite oxide having a large particle size and a small particle size is mixed for the purpose of increasing the packing density of the electrode, the active material having a plurality of peaks in the particle size distribution And the discharge capacity per unit volume increases. However, in order to increase the packing density of the electrode by mixing a large particle size and a small particle size lithium transition metal composite oxide, the small particle size lithium transition metal composite oxide is exclusively Since the gaps in the transition metal composite oxide must be filled, inevitably, the cumulative volume of the lithium transition metal composite oxide having a small particle size is larger than that of the lithium transition metal composite oxide having a large particle size. Is smaller. For this reason, there is no peak on the larger particle size side than the particle size showing the maximum peak in the particle size distribution, and the initial efficiency is not improved as shown in a comparative example described later.
Further, in the case where the positive electrode active material containing Ni, Co, and Mn is a lithium transition metal composite oxide having a high Ni / Me ratio as described in Patent Documents 1 and 6, a high firing temperature (around 1000 ° C.) is used. When employed, the tap density is improved, but the initial efficiency is inferior.

  An object of the present invention is to improve initial efficiency in a lithium secondary battery.

In order to solve the above problems, one aspect of the present invention is “a positive electrode active material for a lithium secondary battery containing lithium transition metal composite oxide particles, wherein the lithium transition metal composite oxide particles are α- It has a NaFeO ₂ type structure, contains Ni, Co and Mn as transition metals (Me), the molar ratio of Ni to Me is Ni / Me ≧ 0.4, and two or more peaks in the particle size distribution And a positive electrode active material for a lithium secondary battery having at least one peak on the larger particle size side than the particle size exhibiting the maximum peak.

  According to another aspect of the present invention, “a precursor particle of a transition metal compound containing Ni, Co and Mn includes a lithium compound and a fluorine source containing 2.5 mol% or more of fluorine with respect to the precursor particle. The method for producing a positive electrode active material for a lithium secondary battery, wherein the lithium transition metal composite oxide particles are produced by mixing and firing at a temperature exceeding 950 ° C. ”.

  Another aspect of the present invention is a lithium secondary battery positive electrode including the lithium secondary battery positive electrode active material, and is a lithium secondary battery including the positive electrode.

  According to the present invention, the initial efficiency of the lithium secondary battery can be improved.

Schematic showing the peak of the particle size distribution of Example 3 Schematic showing the peak of the particle size distribution of Comparative Example 1 1 is an external perspective view showing a lithium secondary battery according to an embodiment of the present invention. 1 is a schematic diagram showing a power storage device in which a plurality of lithium secondary batteries according to an embodiment of the present invention are assembled.

  The configuration and operational effects of the present invention will be described with the technical idea. However, the action mechanism includes estimation, and the correctness does not limit the present invention. It should be noted that the present invention can be implemented in various other forms without departing from the spirit or main features thereof. For this reason, the following embodiments or experimental examples are merely examples in all respects and should not be interpreted in a limited manner. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

[Positive electrode active material]
In one embodiment of the present invention (hereinafter referred to as “this embodiment”), the lithium transition metal composite oxide particles contained in the positive electrode active material for a lithium secondary battery have an α-NaFeO ₂ type structure, Ni, Co, and Mn are included as transition metals (Me), and the molar ratio of Ni to Me, Ni / Me, is Ni / Me ≧ 0.4.

  Since various performances of the lithium secondary battery change depending on the ratio of Ni, Co, and Mn in the transition metal (Me), the respective molar ratios of Ni, Co, and Mn to Me are the secondary lithium to be produced. It is determined appropriately according to the performance characteristics required for the battery.

In order to improve the charge / discharge cycle performance of the lithium secondary battery and to make the discharge capacity per mass sufficient, the molar ratio of Ni to Me, Ni / Me, is 0.4 or more. Ni / Me is preferably 0.4 to 0.6.
In order to make the conductivity of the active material particles sufficient, and to control the high rate discharge performance of the lithium secondary battery, and considering the material cost, the molar ratio Co / Me to Me is 0.1 to 0.1. It is preferable to set it to 0.3.
In order to improve the charge / discharge cycle performance of the lithium secondary battery and considering the material cost, the molar ratio of Mn to Me, Mn / Me, is preferably 0.2 to 0.4.

The lithium transition metal composite oxide particles in the present embodiment are typically lithium transition metal composite oxides represented by the composition formula Li _{1 + x} Me _1-x O ₂ (Me: transition metal containing Ni, Co, and Mn). Particles of things. In order to obtain a lithium secondary battery having a high discharge capacity per volume, −0.1 <x <0.1 is preferable. More preferably, −0.05 ≦ x ≦ 0.09.

The lithium transition metal composite oxide particles preferably contain fluorine in terms of improving the tap density. The composition formula of the lithium transition metal composite oxide in this case is represented by, for example, Li _{1 + x} (Ni _a Co _b Mn _c ) _1-x O _{2 -y} F _y (a + b + c = 1).
The content of fluorine is preferably 2.5 to 10 mol%, and more preferably 2.5 to 5 mol%.
When the lithium transition metal composite oxide particles contain fluorine, since the fluorine is contained in the synthesis process, the existence state is not clear, but it can be removed by washing with dimethyl carbonate described later. Not. A material containing fluorine (LiPF ₆ , PVDF, etc.) may be used for the non-aqueous electrolyte and the binder, but when the sample is taken from the electrode taken out by disassembling the battery, the pretreatment described later Since the fluorine derived from these is removed by performing the above, it can be distinguished from the fluorine contained in the lithium transition metal composite oxide particles.

  The lithium transition metal composite oxide particles are typified by alkali metals such as Na and K, alkaline earth metals such as Mg and Ca, and 3d transition metals such as Fe and Zn as long as the effects of the present invention are not impaired. The inclusion of small amounts of other metals such as transition metals is not excluded.

In the positive electrode active material for a lithium secondary battery according to the present embodiment, the lithium transition metal composite oxide particles constituting the lithium active metal particles have two or more peaks in the particle size distribution, and are larger than the particle size exhibiting the maximum peak. It has at least one peak on the radial side.
Even if the lithium transition metal composite oxide particles have two or more peaks in the particle size distribution, if there is no peak on the larger particle size side than the particle size showing the maximum peak, a single peak is The initial efficiency is not improved compared to what it has. Moreover, the discharge capacity per volume of the lithium secondary battery using this is low.
When the lithium transition metal composite oxide particles have two or more peaks in the particle size distribution and at least one peak larger than the particle size showing the maximum peak, a lithium secondary battery using the lithium transition metal composite oxide particles As the discharge capacity per volume increases, the initial efficiency improves.
By including fluorine in the lithium transition metal composite oxide particles, the tap density is improved, but the initial efficiency is not improved when the particle size distribution has only a single peak.
When the lithium transition metal composite oxide particles have two or more peaks in the particle size distribution as shown in FIG. 1 and at least one peak larger than the particle size showing the maximum peak, The initial efficiency of a lithium secondary battery manufactured using this is improved as compared with that having only a single peak in the particle size distribution as shown in FIG.

The lithium transition metal composite oxide particles according to the present embodiment have a particle size distribution having a maximum peak size of D _Fre (μm) and a peak adjacent to the peak of D _Adj (μm) (where D _adj> when the _{D Fre),} it D adj _{/ D Fre} is 1.8 to 3.2 is preferred from the viewpoint of obtaining a high lithium secondary battery initial efficiency. The value of D _Adj / D _Fre is more preferably 2.0 to 3.0, and further preferably 2.0 to 2.8.

In addition, the lithium transition metal composite oxide particles according to the present embodiment have Fre (%) as the frequency of the maximum peak in the particle size distribution, and D ₁₀ (μm) particle sizes at which the cumulative volume in the cumulative particle size distribution is 10% and 90%, respectively. ) And D ₉₀ (μm), Fre / (D ₉₀ -D ₁₀ ) is preferably 0.42 or less from the viewpoint of obtaining a lithium secondary battery with high initial efficiency.

The lithium transition metal composite oxide particles (positive electrode active material) according to this embodiment are particularly preferably those having a tap density of 2.00 g / cm ³ or more. By using such a high tap density powder, the packing density in the electrode is improved, and a secondary battery having a high discharge capacity per unit volume can be obtained.

  The positive electrode active material for a lithium secondary battery according to the present embodiment may contain other positive electrode active materials in addition to the lithium transition metal composite oxide particles as long as the effects of the present invention are not impaired. The form also belongs to the technical scope of the present invention.

(Pretreatment of various measurement samples)
When various measurements described below are performed using lithium transition metal composite oxide particles as a sample, those in a powder state before electrode preparation are directly subjected to measurement. When a sample is collected from an electrode taken out by disassembling the battery, the battery is put into a discharged state by the following procedure before disassembling the battery. First, with a current of 0.1 CmA, constant current charging is performed up to a battery voltage at which the positive electrode potential becomes 4.3 V (vs. Li ^/ Li ⁺ ), and at the same battery voltage, the current value decreases to 0.01 CmA. Charge the battery at a constant voltage until the end of charge. After a pause of 30 minutes, constant current discharge is performed at a current of 0.1 CmA until the battery voltage reaches a positive electrode potential of 2.0 V (vs. Li ^/ Li ⁺ ), and a discharge end state is obtained. If the battery uses a metal lithium electrode as the negative electrode, the battery may be disassembled after the battery is brought into the end-of-discharge state or the end-of-charge state, and the electrode may be taken out. In order to accurately control the positive electrode potential, after disassembling the battery and taking out the electrode, after assembling the battery using the metal lithium electrode as a counter electrode, the battery is adjusted to the end of discharge state according to the above procedure. The work from disassembly of the battery to measurement is performed in an argon atmosphere with a dew point of −60 ° C. or lower. The taken-out positive electrode plate uses dimethyl carbonate to sufficiently wash the electrolytic solution adhering to the electrode, and after drying at room temperature for a whole day and night, the mixture on the aluminum foil current collector is collected. The mixture is heated in air at 600 ° C. for 4 hours using a small electric furnace to remove carbon as a conductive agent and PVdF binder as a binder, and take out lithium transition metal composite oxide particles.

(Measurement of particle size distribution of lithium transition metal composite oxide particles)
The particle size distribution of the lithium transition metal composite oxide particles is measured by the following method.
Microtrac (model number: MT3000) manufactured by Nikkiso Co., Ltd. was used as a measuring device. The measuring apparatus is composed of a computer equipped with an optical bench, a sample supply unit, and control software, and a wet cell equipped with a laser light transmission window is installed on the optical bench. The measurement principle is a method in which a wet cell in which a dispersion liquid in which a sample to be measured is dispersed in a dispersion solvent circulates is irradiated with laser light, and the scattered light distribution from the measurement sample is converted into a particle size distribution. The dispersion is stored in a sample supply unit and circulated and supplied to a wet cell by a pump. The sample supply unit is always subjected to ultrasonic vibration. Water was used as a dispersion solvent. Microtrac DHS for Win98 (MT3000) was used as measurement control software. For the `` substance information '' set and input to the measuring device, set 1.33 as the `` refractive index '' of the solvent, select `` TRANSPARENT '' as the `` transparency '', and set `` non-spherical '' as the `` spherical particle '' Selected. Prior to sample measurement, perform “Set Zero” operation. The “Set Zero” operation is an operation to subtract the influence of disturbance elements other than the scattered light from the particles (glass, dirt on the glass wall surface, glass irregularities, etc.) on the subsequent measurement. Only a certain amount of water is put in, a background measurement is performed in a state where only the water as the dispersion solvent is circulating in the wet cell, and the background data is stored in the computer. Subsequently, “Sample LD (Sample Loading)” operation is performed. The Sample LD operation is an operation for optimizing the sample concentration in the dispersion that is circulated and supplied to the wet cell during measurement, and manually reaches the optimum amount of the sample to be measured in the sample supply unit according to the instructions of the measurement control software. It is an operation to throw up. Subsequently, the measurement operation is performed by pressing the “Measure” button. The measurement operation is repeated twice, and the measurement result is output from the control computer as the average value. Measurement results, the particle size distribution, _and, D _{10, D} values of ₅₀ and _{D 90 (D 10, D 50} and _{D 90} 10% cumulative volume in the particle size distribution of secondary particles each 50% and 90% Obtained as a granularity). The division width of the particle size distribution is set as 0.01% on the vertical axis and 0.0376 on the common logarithm on the horizontal axis. For D _Fre , read the particle size of the largest peak in the particle size distribution, for D _Adj , read the particle size of the peak adjacent to the largest peak of the particle size distribution, and for Fre, the peak of the largest peak in the particle size distribution Each is obtained by reading the frequency of the top.

(Measurement of tap density of lithium transition metal composite oxide particles)
In this specification, the tap density of the lithium transition metal composite oxide particles is measured by the following method. ² g ± 0.2 g of the powder of the sample to be measured is put into a 10 ⁻² dm ³ graduated cylinder, and REI ELECTRIC CO. LTD. A value obtained by dividing the volume of the sample to be measured after counting 200 times by the input mass using a tapping device manufactured by the company is adopted.

(Qualitative analysis of fluorine contained in lithium transition metal composite oxide particles)
The qualitative analysis of F was performed using a scanning electron microscope (SEM) (manufactured by JEOL, model number JSM-6360) and energy dispersive X-ray analysis (EDX: Energy dispersive X) for lithium transition metal composite oxides. -ray spectrometry) apparatus (hereinafter, also referred to as “SEM-EDX apparatus”) is performed according to the following procedure. A conductive tape is attached to a stainless steel sample stage, and an appropriate amount of powder particles of a lithium transition metal composite oxide to be measured are collected with a spatula and held on the tape. Platinum deposition (deposition time: 5 min, current value: 10 mA) is performed on the surface, and set in the SEM-EDX apparatus. The working distance at the analysis position is 10 mm, and the acceleration voltage of the electron gun is 15 kV. At a plurality of measurement points, the molar concentration of F with respect to Ni is calculated by elemental analysis of SEM-EDX measurement. The active material containing F exhibits a molar concentration of 5 mol% or more with respect to Ni. Thereby, qualitative analysis of F is performed.

[Method for producing positive electrode active material]
The lithium transition metal composite oxide particles contained in the positive electrode active material for a lithium secondary battery according to the present embodiment are prepared in advance as precursor particles in which Ni, Co, and Mn are present in one particle. It can be suitably manufactured by a method of mixing and baking a Li salt and a fluorine source.
As a method for producing precursor particles, a co-precipitation method is used in which a raw material aqueous solution containing Ni, Co and Mn is dropped and a compound containing Ni, Co and Mn is co-precipitated in the solution. It is preferable to prepare a precursor.
In producing a coprecipitation precursor, Mn is easily oxidized among Ni, Co, and Mn, and it is not easy to produce a coprecipitation precursor in which Ni, Co, and Mn are uniformly distributed in a divalent state. Uniform mixing at the atomic level of Ni, Co and Mn tends to be insufficient. Therefore, in the present invention, it is preferable to remove dissolved oxygen in order to suppress oxidation of Mn existing in the coprecipitation precursor. Examples of the method for removing dissolved oxygen include a method of bubbling a gas not containing oxygen. The gas not containing oxygen is not limited, but nitrogen gas, argon gas, carbon dioxide (CO ₂ ), or the like can be used.

Although the pH in the step of preparing a precursor by co-precipitation of a compound containing Ni, Co and Mn in a solution is not limited, an attempt is made to prepare the co-precipitation precursor as a co-precipitation hydroxide precursor. When doing, it can be set to 10.5-14. In particular, since the particle growth can be promoted by setting the pH to 11.0 or less, the stirring continuation time after completion of dropping of the raw material aqueous solution can be shortened.
Moreover, when it is going to produce the said coprecipitation precursor as a coprecipitation carbonate precursor, it can be set as 7.5-11. In particular, by adjusting the pH to 8.0 or less, the particle growth rate can be accelerated, so that the stirring continuation time after completion of dropping of the raw material aqueous solution can be shortened.

  The raw material of the coprecipitation precursor is nickel hydroxide, nickel carbonate, nickel sulfate, nickel nitrate, nickel acetate or the like as the Ni compound, and cobalt sulfate, cobalt nitrate, cobalt acetate, or the like as the Mn compound as the Co compound. Examples thereof include manganese oxide, manganese carbonate, manganese sulfate, manganese nitrate, manganese acetate and the like.

  The dropping speed of the raw material aqueous solution greatly affects the uniformity of element distribution in one particle of the coprecipitation precursor to be generated. The preferred dropping rate is influenced by the reaction vessel size, stirring conditions, pH, reaction temperature, etc., but is preferably 30 ml / min or less. In order to improve the discharge capacity, the dropping rate is more preferably 10 ml / min or less, and most preferably 5 ml / min or less.

Further, when a complexing agent such as NH ₃ is present in the reaction tank and a certain convection condition is applied, by continuing the stirring after the dropwise addition of the raw material aqueous solution, the rotation of the particles and in the stirring tank are performed. Revolution is promoted, and in this process, particles collide with each other, and the particles grow into concentric spheres step by step. That is, the coprecipitation precursor undergoes a reaction in two stages: a metal complex formation reaction when the raw material aqueous solution is dropped into the reaction tank, and a precipitation formation reaction that occurs while the metal complex is retained in the reaction tank. It is formed. Therefore, coprecipitation precursor particles having a target particle diameter can be obtained by appropriately selecting a time for continuing stirring after the dropping of the raw material aqueous solution.

  The preferable stirring duration after completion of dropping of the raw material aqueous solution is influenced by the size of the reaction vessel, stirring conditions, pH, reaction temperature, etc., but 0.5 h or more is required to grow the particles as uniform spherical particles. Preferably, 1 h or more is more preferable. Further, in order to reduce the possibility that the output performance in the low SOC region of the battery is not sufficient due to the particle size becoming too large, 30 h or less is preferable, 25 h or less is more preferable, and 20 h or less is most preferable.

The Li compound to be mixed with the precursor particles, lithium hydroxide which is usually used, with lithium carbonate, as a sintering aid, LiF, _Li 2 SO _4, or it is preferable to use _Li 3 PO _4. Of these, LiF also acts as a fluorine source to be described later. The addition ratio of these sintering aids is preferably 1 to 10 mol% with respect to the total amount of the Li compound. The total amount of the Li compound is preferably charged in an excess of about 1 to 5% in view of the disappearance of a part of the Li compound during firing.

When mixing the Li compound as the lithium source with the precursor particles, the F compound as the fluorine source is mixed at the same time, and the metal element (Li, Ni, Co, Mn) and particles containing 2.5 mol% or more of fluorine with respect to the precursor particles are preferable. In this way, lithium transition metal composite oxide particles having two or more peaks in the particle size distribution and having at least one peak larger than the particle size showing the maximum peak are fired once. Therefore, the trouble of mixing a plurality of particles having different particle sizes can be saved.
By mixing and firing Li compound and F compound in the precursor particles, the particle size distribution has two or more peaks and at least one peak on the larger particle size side than the particle size showing the maximum peak. The reason why lithium transition metal composite oxide particles can be produced is not necessarily clear, but when a part of the produced lithium transition metal composite oxide particles were observed with a scanning electron microscope (SEM), the particle size was about Since 10 μm particles and particles having a particle size of 2 to 3 times were observed as distinguished from each other, some of the precursor particles (secondary particles) having a particle size of about 10 μm were 2 in the firing process. The present inventors speculate that this is due to the occurrence of a reaction in which three or three are associated.
The upper limit of the fluorine content is not particularly limited, but considering the effect of improving characteristics due to the increase in the content of the F compound and the increase in raw material cost, it is preferably 10 mol% or less with respect to the precursor particles. More preferably, it is 5.0 mol% or less.
In addition to LiF, ammonium fluoride, calcium fluoride, aluminum fluoride, barium fluoride, magnesium fluoride, sodium fluoride, potassium fluoride, and the like can be used as the fluorine compound.

Firing of the precursor particles containing fluorine is performed at a temperature exceeding 950 ° C.
When the firing temperature is 950 ° C. or lower, the particle size distribution of the obtained particles does not show two or more peaks, and the initial efficiency of a lithium secondary battery produced using the same decreases.
A preferable firing temperature is 1000 ° C. to 1100 ° C.

[Negative electrode active material]
The negative electrode material is not limited, and any negative electrode material may be selected as long as it can release or occlude lithium ions. For example, titanium-based materials such as lithium titanate having a spinel crystal structure represented by Li [Li _1/3 Ti _5/3 ] O ₄ , alloy-based materials such as Si, Sb, and Sn-based lithium metal, lithium alloys (Lithium metal-containing alloys such as lithium-silicon, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and wood alloys), lithium composite oxide (lithium-titanium), silicon oxide In addition, an alloy capable of inserting and extracting lithium, a carbon material (for example, graphite, hard carbon, low-temperature fired carbon, amorphous carbon, etc.) can be used.

[Production of positive electrode and negative electrode]
It is desirable that the positive electrode active material powder and the negative electrode material powder have an average particle size of 100 μm or less. In particular, the positive electrode active material powder is desirably 10 μm or less for the purpose of improving the high output characteristics of the non-aqueous electrolyte battery. In order to obtain the powder in a predetermined shape, a pulverizer or a classifier is used. For example, a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill or a sieve is used. At the time of pulverization, wet pulverization in the presence of water or an organic solvent such as hexane may be used. There is no particular limitation on the classification method, and a sieve, an air classifier, or the like is used as needed for both dry and wet methods.

  The positive electrode active material and the negative electrode material, which are the main components of the positive electrode and the negative electrode, have been described in detail above. In addition to the main components, the positive electrode and the negative electrode include a conductive agent, a binder, a thickener, and a filler. Etc. may be contained as other constituents.

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

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

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

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

  The positive electrode and the negative electrode are prepared by mixing the main components (positive electrode active material in the positive electrode, negative electrode material in the negative electrode) and other materials into a mixture and mixing them in an organic solvent such as N-methylpyrrolidone and toluene or water. After that, the obtained liquid mixture is applied on a current collector described in detail below, or pressed and heat-treated at a temperature of about 50 ° C. to 250 ° C. for about 2 hours. . About the application method, for example, it is desirable to apply to any thickness and any shape using means such as roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc. It is not limited.

  As the current collector, a current collector foil such as an Al foil or a Cu foil can be used. The positive electrode current collector foil is preferably an Al foil, and the negative electrode current collector foil is preferably a Cu foil. The thickness of the current collector foil is preferably 10 to 30 μm. Further, the thickness of the mixture layer is preferably 40 to 150 μm (excluding the current collector foil thickness) after pressing.

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

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

Furthermore, by mixing and using LiPF ₆ or LiBF ₄ and a lithium salt having a perfluoroalkyl group such as LiN (C ₂ F ₅ SO ₂ ) ₂ , the viscosity of the electrolyte can be further reduced. The low temperature characteristics can be further improved, and self-discharge can be suppressed, which is more desirable.

  Moreover, you may use normal temperature molten salt and an ionic liquid as a nonaqueous electrolyte.

  The concentration of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol / l to 5 mol / l, more preferably 0.5 mol / l to 2 in order to reliably obtain a non-aqueous electrolyte battery having high battery characteristics. .5 mol / l.

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

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

  The separator may be a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, polyvinylidene fluoride, and an electrolyte. Use of the non-aqueous electrolyte in the gel state as described above is preferable in that it has an effect of preventing leakage.

  Furthermore, it is desirable that the separator be used in combination with the above-described porous film, non-woven fabric, or the like and a polymer gel because the liquid retention of the electrolyte is improved. That is, by forming a film in which the surface of the polyethylene microporous membrane and the microporous wall are coated with a solvophilic polymer having a thickness of several μm or less, and holding the electrolyte in the micropores of the film, Gels.

  Examples of the solvophilic polymer include polyvinylidene fluoride, an acrylate monomer having an ethylene oxide group or an ester group, an epoxy monomer, a polymer having a monomer having an isocyanate group, and the like crosslinked. The monomer can be subjected to a crosslinking reaction using a radical initiator in combination with heating or ultraviolet rays (UV), or using an actinic ray such as an electron beam (EB).

[Configuration of lithium secondary battery]
Other battery components include a terminal, an insulating plate, a battery case, and the like, but these components may be used as they are.

  FIG. 3 shows an external perspective view of a rectangular lithium secondary battery 1 which is an embodiment of the lithium secondary battery according to the present invention. In the figure, the inside of the container is seen through. In the lithium secondary battery 1 shown in FIG. 3, the electrode group 2 is housed in a battery container 3. The electrode group 2 is formed by winding a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material via a separator. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 4 ′, and the negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 5 ′.

  The shape of the lithium secondary battery according to this embodiment is not particularly limited, and examples thereof include a cylindrical battery, a square battery (rectangular battery), a flat battery, and the like. The present invention can also be realized as a power storage device in which a plurality of the lithium secondary batteries are assembled. One embodiment of a power storage device is shown in FIG. In FIG. 4, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of lithium secondary batteries 1. The power storage device 30 can be mounted as a power source for vehicles such as an electric vehicle (EV), a hybrid vehicle (HEV), and a plug-in hybrid vehicle (PHEV).

Example 1
<Precursor production process>
Example In preparing an active material, a hydroxide precursor was prepared using a reaction crystallization method. First, 168.66 g of cobalt sulfate heptahydrate, 394.28 g of nickel sulfate hexahydrate and 216.97 g of manganese sulfate pentahydrate were weighed and dissolved in ion-exchanged water, and a molar ratio of Ni: Co: Mn was obtained. A 3 L aqueous sulfate solution with a ratio of 5: 2: 3 was prepared. Next, 2 L of ion exchange water was poured into a 5 L reaction tank, and argon gas was bubbled for 30 minutes to remove oxygen in the ion exchange water. The temperature of the reaction vessel was set to 50 ° C. (± 2 ° C.), and an aqueous sulfate solution was added to 1.5 mL / min in ion-exchanged water while stirring at a rotational speed of 1500 rpm using a paddle blade equipped with a stirring motor. It was dripped at a speed. At this time, an aqueous solution containing 4M sodium hydroxide, 0.5M ammonia and 0.29M hydrazine was appropriately added dropwise so that pH = 11 (± 0.1). A part of the reaction solution was discharged due to overflow, and the total amount of the reaction solution was controlled so as not to always exceed 2 L. After completion of the dropping, stirring in the reaction vessel was further continued for 2 hours or more.
Next, the particles of the obtained hydroxide precursor are separated using a suction filtration device, and after washing and removing sodium ions adhering to the particles using ion-exchanged water, in an air atmosphere, It was dried overnight at 80 ° C. under normal pressure. In this way, hydroxide precursor particles were produced.

<Baking process>
2.371 g of this hydroxide precursor particle was mixed well with 1.0911 g of lithium hydroxide monohydrate and 0.017 g of lithium fluoride using an agate mortar. At this time, the molar ratio of lithium to the transition metal (Ni, Co, Mn) was 1.0, and the ratio of fluorine to the hydroxide precursor particles was 2.5 mol%. Using a pellet molding machine, pellets having a diameter of 25 mm were produced at a pressure of 10 MPa. The amount of the mixture required for pellet molding was determined by conversion so that the mass of the expected final product was 2.5 g. The pellets were placed on an alumina boat and fired at 1000 ° C. under normal pressure in an air atmosphere using a box-type electric furnace (model: AMF20). The temperature rising time from room temperature was 10 hours, and the holding time at 1000 ° C. was 4 hours. The internal dimensions of the box-type electric furnace are 10 cm in length, 20 cm in width, and 30 cm in depth, and heating wires are inserted at intervals of 20 cm in the width direction. After firing, the heater was turned off, and the alumina boat was left in the furnace for natural cooling. After one day and night, after confirming that the temperature of the furnace is 100 ° C. or less, the pellets are taken out and pulverized, and LiNi _0.5 Co _0.2 Mn _0.3 O ₂ contains fluorine. Lithium transition metal composite oxide particles according to Example 1 were prepared.

(Example 2)
In the firing step, 2.3721 g of the hydroxide precursor particles are mixed with 1.0631 g of lithium hydroxide monohydrate and 0.0346 g of lithium fluoride, and the ratio of fluorine to the hydroxide precursor particles is 5.0 mol. % Lithium transition metal composite oxide particles according to Example 2 were produced in the same manner as in Example 1 except that the content was%.

(Example 3)
Example 3 was conducted in the same manner as in Example 1 except that 2.3721 g of the hydroxide precursor particles were mixed with 1.0911 g of lithium hydroxide monohydrate and 0.0247 g of ammonium fluoride in the firing step. Such lithium transition metal composite oxide particles were prepared. In addition, the ratio of the fluorine with respect to the hydroxide precursor particle in a present Example is 2.5 mol% similarly to Example 1. FIG.

Example 4
In the firing step, 2.3721 g of the hydroxide precursor particles are mixed with 1.0631 g of lithium hydroxide monohydrate and 0.0494 g of ammonium fluoride, and the ratio of fluorine to the hydroxide precursor particles is 5.0 mol. %, Lithium transition metal composite oxide particles according to Example 4 were produced in the same manner as in Example 1 except that the percentage was changed to%.

(Comparative Example 1)
In the firing step, except that 2.3721 g of the hydroxide precursor particles were mixed with 1.1190 g of lithium hydroxide monohydrate to make particles substantially free of fluorine, the same as in Example 1, Lithium transition metal composite oxide particles according to Comparative Example 1 were produced.

(Comparative Example 2)
In the firing step, 2.3721 g of the hydroxide precursor particles are mixed with 1.1078 g of lithium hydroxide monohydrate and 0.0069 g of lithium fluoride, and the ratio of fluorine to the hydroxide precursor particles is 1.0 mol. The lithium transition metal composite oxide particles according to Comparative Example 2 were produced in the same manner as in Example 1 except that the content was%.

(Comparative Example 3)
In the firing step, 2.3721 g of the hydroxide precursor particles are mixed with 1.1078 g of lithium hydroxide monohydrate and 0.0099 g of ammonium fluoride, and the ratio of fluorine to the hydroxide precursor particles is 1.0 mol. % Lithium transition metal composite oxide particles according to Comparative Example 3 were produced in the same manner as in Example 1 except that the content was%.

(Example 5)
In the precursor preparation step, 252.99 g of cobalt sulfate heptahydrate, 394.26 g of nickel sulfate hexahydrate and 144.65 g of manganese sulfate pentahydrate are weighed and dissolved in ion-exchanged water, and Ni: Co: Hydroxide precursor particles were prepared in the same manner as in Example 1 except that a 3 L sulfate aqueous solution having a Mn molar ratio of 5: 3: 2 was prepared.
Example 5 was repeated in the same manner as in Example 3 except that 2.3726 g of the hydroxide precursor particles were mixed with 1.0866 g of lithium hydroxide monohydrate and 0.0246 g of ammonium fluoride in the firing step. Such lithium transition metal composite oxide particles were prepared. In addition, the ratio of the fluorine with respect to the hydroxide precursor particle | grains in a present Example is 2.5 mol% similarly to Example 3. FIG.

(Comparative Example 4)
In the firing step, except that 2.3726 g of the hydroxide precursor particles were mixed with 1.1144 g of lithium hydroxide monohydrate to make particles substantially free of fluorine, the same as in Example 5, Lithium transition metal composite oxide particles according to Comparative Example 4 were produced.

(Comparative Example 5)
In the firing step, 2.3726 g of the hydroxide precursor particles are mixed with 1.1033 g of lithium hydroxide monohydrate and 0.0069 g of lithium fluoride, and the ratio of fluorine to the hydroxide precursor particles is 1.0 mol. %, Lithium transition metal composite oxide particles according to Comparative Example 5 were produced in the same manner as in Example 5.

(Example 6)
In the precursor preparation step, 84.33 g of cobalt sulfate heptahydrate, 394.26 g of nickel sulfate hexahydrate and 289.29 g of manganese sulfate pentahydrate are weighed and dissolved in ion-exchanged water, and Ni: Co: Hydroxide precursor particles were prepared in the same manner as in Example 1 except that a 3 L sulfate aqueous solution having a Mn molar ratio of 5: 1: 4 was prepared.
Example 6 was carried out in the same manner as in Example 3 except that 2.3715 g of the hydroxide precursor particles were mixed with 1.0956 g of lithium hydroxide monohydrate and 0.0248 g of ammonium fluoride in the firing step. Such lithium transition metal composite oxide particles were prepared. In addition, the ratio of the fluorine with respect to the hydroxide precursor particle | grains in a present Example is 2.5 mol% similarly to Example 3. FIG.

(Comparative Example 6)
In the firing step, except that 2.3715 g of the hydroxide precursor particles were mixed with 1.1237 g of lithium hydroxide monohydrate to make particles substantially free of fluorine, the same as in Example 6, Lithium transition metal composite oxide particles according to Comparative Example 6 were produced.

(Comparative Example 7)
In the firing step, 2.3715 g of the hydroxide precursor particles are mixed with 1.1124 g of lithium hydroxide monohydrate and 0.0099 g of ammonium fluoride, and the ratio of fluorine to the hydroxide precursor particles is 1.0 mol. The lithium transition metal composite oxide particles according to Comparative Example 7 were produced in the same manner as in Example 6 except that the content was%.

(Comparative Example 8)
In the firing step, 2.3715 g of the hydroxide precursor particles are mixed with 1.0956 g of lithium hydroxide monohydrate and 0.0174 g of lithium fluoride, and the ratio of fluorine to the hydroxide precursor particles is 2.5 mol. %, And a lithium transition metal composite oxide particle according to Comparative Example 8 was produced in the same manner as in Example 6 except that the firing temperature was 950 ° C.

(Comparative Example 9)
Lithium transition metal composite oxide particles according to Comparative Example 9 were produced in the same manner as in Comparative Example 1 except that the firing temperature was 800 ° C. in the firing step.

(Comparative Example 10)
In the precursor preparation step, particles of a large particle size lithium transition metal composite oxide were prepared in the same manner as in Comparative Example 9 except that stirring in the reaction vessel was continued for 12 hours after the completion of dropping. Further, after completion of the dropping, particles of a small-sized lithium transition metal composite oxide were produced in the same manner as in Comparative Example 9, except that stirring in the reaction vessel was continued for 3 hours. The obtained large particle size lithium transition metal composite oxide and small particle size lithium transition metal composite oxide are mixed at a mass ratio of 7: 3, and the lithium transition metal composite oxide has two or more peaks in the particle size distribution. Material mixed particles were prepared.

(Confirmation of α-NaFeO type ₂ crystal structure)
It was confirmed that the lithium transition metal composite oxides according to Examples 1 to 6 and Comparative Examples 1 to 10 had an α-NaFeO ₂ type crystal structure because the structural model and the diffraction pattern in the X-ray diffraction measurement coincided. .

(Measurement of particle size distribution of lithium transition metal composite oxide particles)
The particle size distribution of the lithium transition metal composite oxide particles according to Examples 1 to 6 and Comparative Examples 1 to 10 was measured according to the conditions and procedures described above. Then, Fre / (D ₉₀ -D ₁₀ ) was calculated from the obtained Fre (%), D ₁₀ (μm), and D ₉₀ (μm). In Examples 1 to 6, D _Adj / D _Fre was calculated from D _Fre (μm) and D _Adj (μm) obtained by the measurement of the particle size distribution.
As a typical example of lithium transition metal composite oxide particles having two or more peaks in the particle size distribution and having at least one peak larger than the particle size showing the maximum peak in FIG. Similar particle size distribution was also observed in other examples.
FIG. 2 shows the peak of the particle size distribution of Comparative Example 1 as a typical example of the lithium transition metal composite oxide particles having a single peak in the particle size distribution. In other Comparative Examples (except for Comparative Example 10), Similar particle size distribution was seen.

(Measurement of tap density of lithium transition metal composite oxide particles)
The tap densities of the lithium transition metal composite oxide particles according to Examples 1 to 6 and Comparative Examples 1 to 10 were measured according to the conditions and procedures described above.

[Production and evaluation of lithium secondary battery]
Using the lithium transition metal composite oxide particles according to Examples 1 to 6 and Comparative Examples 1 to 10 as positive electrode active materials, lithium secondary batteries were produced in the following procedure, and battery characteristics were evaluated.

  Using N-methylpyrrolidone as a dispersion medium, an active material, acetylene black (AB), and polyvinylidene fluoride (PVdF) were kneaded and dispersed at a mass ratio of 90: 5: 5. The coating paste was applied to one side of an aluminum foil current collector having a thickness of 20 μm to produce a positive electrode plate. In addition, the mass and coating thickness of the active material applied per fixed area were standardized so that the test conditions were the same among the lithium secondary batteries according to all the examples and comparative examples.

  A coating paste in which graphite, styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were kneaded and dispersed at a mass ratio of 96.7: 2.1: 1.2 was prepared using water as a dispersion medium. The coating paste was applied to one side of a 10 μm thick copper foil current collector to prepare a negative electrode plate. The coating amount of the coating paste was adjusted so that the battery capacity was not limited by the negative electrode when combined with the positive plate.

As an electrolytic solution, LiPF ₆ was dissolved in a mixed solvent in which ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) had a volume ratio of 6: 7: 7 so that the concentration was 1 mol / l. The solution was used. As the separator, a polypropylene microporous film whose surface was modified with polyacrylate was used. A metal resin composite film made of polyethylene terephthalate (15 μm) / aluminum foil (50 μm) / metal-adhesive polypropylene film (50 μm) is used for the exterior body, and the electrodes are exposed so that the open ends of the positive electrode terminal and the negative electrode terminal are exposed to the outside. The metal resin composite film was hermetically sealed with the fusion allowance where the inner surfaces of the metal resin composite films faced each other except for the portion serving as the injection hole, and the injection hole was sealed after the electrolyte solution was injected.

The lithium secondary battery produced by the above procedure was subjected to an initial charge / discharge process at 25 ° C. Charging was performed at a constant current and constant voltage with a current of 0.1 CmA and a voltage of 4.45 V, and the charge termination condition was when the current value was attenuated to 1/5. The discharge was a constant current discharge with a current of 0.1 CmA and a final voltage of 2.0 V. Here, a pause process of 10 minutes was provided after charging and discharging, respectively.
Further, the percentage of the amount of discharged electricity with respect to the amount of charged electricity in the first cycle of the initial charge / discharge process was recorded as “initial efficiency (%)”.

For each of the examples and comparative examples, the value of the discharge capacity (mAh / g) is multiplied by the value of the tap density (g / cm ³ ) to obtain a discharge capacity per volume of “0.1 C capacity ( mAh / cm ³ ) ”was calculated.

Ni / Co / Mn molar ratio of lithium transition metal composite oxides according to Examples 1 to 6 and Comparative Examples 1 to 8, usage conditions of additives (presence / absence of additive, type, added amount), firing temperature, particle size The number of distribution peaks, the value of D _Adj / D _Fre , the value of Fre / (D ₉₀ -D ₁₀ ) and the tap density, and the lithium secondary battery using the above lithium transition metal composite oxide as a positive electrode active material, respectively The test results are shown in Tables 1 to 3, respectively.

From Tables 1 to 3, the following can be understood.
Ni, Co, and Mn are included as transition metals (Me), the molar ratio of Ni to Me, Ni / Me, is Ni / Me ≧ 0.4, has two or more peaks in the particle size distribution, and shows the maximum peak Lithium secondary battery of Examples 1 to 4, lithium secondary battery of Example 5 using lithium transition metal composite oxide particles having at least one peak on the larger particle size side than the particle size as the positive electrode active material, implementation The lithium secondary battery of Example 6 is a lithium secondary battery of Comparative Examples 1 to 3 using Comparative Examples 1 to 4 using lithium transition metal composite oxide particles having a single particle size distribution as a positive electrode active material. It can be seen that the initial efficiency is improved and the capacity per volume is improved as compared with the lithium secondary battery and the lithium secondary batteries of Comparative Examples 6 to 8.

Moreover, when it sees about the case where a fluorine source is added to a precursor particle | grain with a lithium compound, like Comparative Examples 2-3 of Table 1, Comparative Example 5 of Table 2, and Comparative Example 7 of Table 3, a calcination temperature is 1000. Even when the ratio of fluorine is 1 mol% even when the temperature is ℃, as in Comparative Example 8 of Table 3, when the firing temperature is 950 ° C. even when the ratio of fluorine is 2.5 mol%, the lithium transition metal The composite oxide particles have only a single peak in the particle size distribution, and the initial efficiency is reduced and the capacity per volume is also reduced.
Therefore, a lithium transition metal having two or more peaks in the particle size distribution by adding a fluorine source together with a lithium compound to the precursor particles and at least one peak on the larger particle size side than the particle size exhibiting the maximum peak When the composite oxide particles are produced by single firing without mixing a plurality of particles having different particle size distributions, a fluorine source containing 2.5 mol% or more of fluorine is mixed with the precursor particles. At the same time, it is necessary to employ a firing temperature exceeding 950 ° C.

Ni / Co / Mn molar ratio of lithium transition metal composite oxides according to Comparative Examples 9 and 10, firing temperature, number of particle size distribution peaks, Fre / (D ₉₀ -D ₁₀ ) value and tap density, and each of the above Table 4 shows the test results of the lithium secondary battery using the lithium transition metal composite oxide as the positive electrode active material.

From Table 4, the particle size showing the maximum peak, although having two or more peaks in the particle size distribution, obtained by mixing the large particle size lithium transition metal composite oxide and the small particle size lithium transition metal composite oxide It can be seen that even when lithium transition metal composite oxide particles having no peak on the larger particle size side are used as the positive electrode active material, the initial efficiency of the lithium secondary battery is not improved.
In Comparative Examples 9 and 10, since the firing temperature is 800 ° C., the numerical value of the initial efficiency itself is high. On the other hand, the capacity per volume is very low. As shown in Comparative Example 1, when the firing temperature is 1000 ° C., the capacity per volume increases, but the initial efficiency decreases. In this case, even if mixed particles of a large particle size lithium transition metal composite oxide and a small particle size lithium transition metal composite oxide are used, the initial efficiency is not improved.

  As described above, in the present embodiment, lithium transition metal composite oxide particles having two or more peaks in the particle size distribution and having at least one peak on the larger particle size side than the particle size showing the maximum peak, By using it as a positive electrode active material for a lithium secondary battery, a lithium secondary battery with high initial efficiency can be obtained.

  By using the positive electrode active material containing the lithium transition metal composite oxide according to one aspect of the present invention, a lithium secondary battery having a large discharge capacity per unit volume and high initial efficiency can be provided. The lithium secondary battery is useful as a lithium secondary battery for hybrid vehicles and electric vehicles.

DESCRIPTION OF SYMBOLS 1 Lithium secondary battery 2 Electrode group 3 Battery container 4 Positive electrode terminal 4 'Positive electrode lead 5 Negative electrode terminal 5' Negative electrode lead 20 Power storage unit 30 Power storage device

Claims (7)

A positive electrode active material for a lithium secondary battery containing lithium transition metal composite oxide particles, wherein the lithium transition metal composite oxide particles have an α-NaFeO ₂ type structure, Ni as a transition metal (Me), Ni / Me molar ratio Ni / Me ≧ 0.4, including Co and Mn, Ni / Me ≧ 0.4, having two or more peaks in the particle size distribution, and larger than the particle size showing the maximum peak A positive electrode active material for a lithium secondary battery having at least one peak. When the particle size distribution showing the maximum peak is D _Fre (μm) and the particle size showing the peak adjacent to the peak is D _Adj (μm) (where D _Adj > D _Fre ), D _Adj / D _Fre is The positive electrode active material for a lithium secondary battery according to claim 1, wherein the positive electrode active material is 1.8 to 3.2. The lithium transition metal composite oxide particles have Fre (%) as the frequency of the maximum peak in the particle size distribution, and D ₁₀ (μm) and D ₉₀ (D ₉₀ (particle sizes) where the cumulative volume in the cumulative particle size distribution is 10% and 90%, respectively. when the _{μm), Fre / (D 90} -D 10) is 0.42 or less, the positive electrode active material for a lithium secondary battery according to claim 1 or 2.   The positive electrode active material for lithium secondary batteries according to any one of claims 1 to 3, wherein the lithium transition metal composite oxide particles contain fluorine.   Transition metal compound precursor particles containing Ni, Co and Mn are mixed with a lithium compound and a fluorine source containing 2.5 mol% or more of fluorine with respect to the precursor particles, and fired at a temperature exceeding 950 ° C. And the manufacturing method of the positive electrode active material for lithium secondary batteries in any one of Claims 1-4 which manufactures the said lithium transition metal complex oxide particle.   The positive electrode for lithium secondary batteries containing the positive electrode active material for lithium secondary batteries in any one of Claims 1-4.   A lithium secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the positive electrode comprises the positive electrode according to claim 6.

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