JP7031108B2 - Manufacturing method of positive electrode active material for non-aqueous electrolyte secondary battery, positive electrode active material for non-aqueous electrolyte secondary battery, production of positive electrode for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery Method - Google Patents

Description

The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, a method for producing the same, a positive electrode for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery, and a method for producing the battery thereof.

Non-aqueous electrolyte secondary batteries represented by lithium secondary batteries have been increasingly used in recent years, and the development of higher-capacity positive electrode materials is required.
Conventionally, as a positive electrode active material for a non-aqueous electrolyte secondary battery, a lithium transition metal composite oxide having an α-NaFeO type ₂ crystal structure has been studied, and a non-aqueous electrolyte secondary battery using LiCoO ₂ has been widely put into practical use. There is. The discharge capacity of LiCoO ₂ is about 120 to 130 mAh / g. Mn, which is abundant as an earth resource, is used as the transition metal (Me) constituting the lithium transition metal composite oxide, and the molar ratio of Li to the transition metal constituting the lithium transition metal composite oxide is approximately 1. There is also a non-aqueous electrolyte secondary battery using a so-called "LiMeO type ₂ " active material in which the molar ratio Mn / Me of Mn in the transition metal is 0.5 or less. For example, the discharge capacity of the positive electrode active material containing LiNi _1/2 Mn _1/2 O ₂ and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is 150 to 180 mAh / g.
Generally, the charging voltage adopted for a non-aqueous electrolyte battery using these so-called "LiMeO type ₂ " active materials is about 4.3V, and the maximum ultimate potential of the positive electrode at this time is about 4.4V (. vs. Li / Li ⁺ ). This is because even if the charging voltage is raised further, more discharge capacity cannot be taken out.

On the other hand, among the lithium transition metal composite oxides having an α-NaFeO type ₂ crystal structure, the molar ratio of Mn in the transition metal (Me) is large, and the molar ratio of Li to the transition metal (Me), Li / Me, is 1. So-called "lithium-rich" active materials that exceed are known. In this active material, in the initial charging process after assembling the battery, the potential change is relatively flat with respect to the amount of charged electricity within the potential range of 4.5 to 5.0 V (vs. Li / Li ⁺ ). By performing the initial charge to reach the flat region, even if the subsequent charging potential is not so precious, the discharge capacity is as high as or higher than that of the "LiMeO type ₂ " active material. (See Patent Document 1).

Patent Document 1 describes "an active material for a lithium secondary battery containing a solid solution of a lithium transition metal composite oxide having an α-NaFeO type ₂ crystal structure, and Li, Co, Ni and Mn contained in the solid solution. The composition ratio is Li _{1+ (1/3) x} Co _1-x-y Ni _{(1/2) y} Mn _{(2/3) x + (1/2) y} (x + y ≦ 1, 0 ≦ y, 1-x). -Y = z) is satisfied, and the intensity ratio of the diffraction peaks of the (003) plane and the (104) plane by the X-ray diffraction measurement is I ₍₀₀₃₎ / I ₍ before charging / discharging). ₁₀₄₎ ≧ 1.56, I ₍₀₀₃₎ / I ₍₁₀₄₎ > 1 at the end of discharge, exceeding 4.3V (vs.Li / Li ⁺ ) and 4.8V or less (vs.Li / Li ⁺ ). ), A potential region of 4.3 V (vs. Li / Li ⁺ ) or less when the initial charge is performed so that the potential change appearing with respect to the amount of charging electricity reaches at least a relatively flat region in the positive potential range of). The active material for a lithium secondary battery, characterized in that the amount of electricity that can be discharged is 177 mAh / g or more. ”(Claim 3).

Then, in paragraph [0062], "using the active material for a lithium secondary battery according to the present invention, the maximum ultimate potential of the positive electrode at the time of charging is 4.3 V (vs. Li / Li ⁺ ) or less at the time of use. In order to manufacture a lithium secondary battery capable of taking out a sufficient discharge capacity even if such a charging method is adopted, the active material for a lithium secondary battery according to the present invention described below is characteristic. It is important to provide a charging process in consideration of the behavior during the manufacturing process of the lithium secondary battery. That is, when the active material for the lithium secondary battery according to the present invention is used for the positive electrode and constant current charging is continued, the positive electrode is used. In the range of potential 4.3V to 4.8V, a region where the potential change is relatively flat is observed over a relatively long period of time .... The charging conditions adopted here are current 0.1ItA, voltage ( Positive potential) 4.5V (vs. Li / Li ⁺ ) constant current constant voltage charging, but even if the charging voltage is set higher, the value of x is the value of x in the potential flat region over this relatively long period. It is rarely observed when a material of 1/3 or less is used. On the contrary, in a material having an x value of more than 2/3, even if a region where the potential change is relatively flat is observed, it is short. Further, this behavior is not observed even with the conventional Li [Co _{1-2 x} Ni _x Mn _x ] O ₂ (0 ≦ x ≦ 1/2) -based material. This behavior is the lithium secondary battery according to the present invention. It is characteristic of active materials. "

On the other hand, the initial Coulomb efficiency, rate characteristics, and cycle life characteristics when the initial charging process exceeding 4.5 V (vs. Li / Li ⁺ ) is performed by substituting the oxygen sites of the "lithium excess type" active material with F. (See Patent Documents 2 to 5).

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（請求項１）が記載されている。
そして、Ｍｎ及びＮｉを含む活物質の実施例として、「Ｌｉ_１．２Ｎｉ_０．２Ｍｎ_０．６Ｏ_１．９Ｆ_０．１」、「Ｌｉ_１．２Ｎｉ_０．２Ｍｎ_０．６Ｏ_１．８Ｆ_０．２」、「Ｌｉ_１．２Ｎｉ_０．２Ｍｎ_０．６Ｏ_１．７Ｆ_０．３」、「Ｌｉ_１．２Ｎｉ_０．２Ｍｎ_０．６Ｏ_１．６Ｆ_０．４」、「Ｌｉ_１．２Ｎｉ_０．４Ｍｎ_０．４Ｏ_１．８Ｆ_０．２」、比較例として、「Ｌｉ_１．２Ｎｉ_０．２Ｍｎ_０．６Ｏ_２」、「Ｌｉ_１．２Ｎｉ_０．２Ｍｎ_０．６Ｏ_１．９５Ｆ_０．０５」、「Ｌｉ_１．２Ｎｉ_０．２５Ｍｎ_０．５５Ｏ_１．９Ｆ_０．１」が記載され、４．６Ｖまでの充電による初回充電容量と、充電状態から２．０Ｖまでの放電による初回放電容量から、初回クーロン効率を求めたことが記載されている（段落［００７２］～［００７８］）。 In Patent Document 2, "a positive electrode active material for a non-aqueous electrolyte secondary battery represented by the general formula Li (Li _a Mn _b Ni _{c Code} Fe _e ) O _2-x F _x , which is described in the above general formula. In a, b, c, d, e and x, 0 <a ≦ 0.33, 0 <b ≦ 0.67, 0 ≦ c <1, 0 ≦ d <1, 0 ≦ e <1, 0. A positive electrode active material for a non-aqueous electrolyte secondary battery having a value of 1 <x ≦ 1-b and satisfying the following formula (1).

"
(Claim 1) is described.
Then, as an example of the active material containing Mn and Ni, "Li _1.2 Ni _0.2 Mn _0.6 O _1.9 F _0.1 " and "Li _1.2 Ni _0.2 Mn _0.6 " O _1.8 F _0.2 ”,“ Li _1.2 Ni _0.2 Mn _0.6 O _1.7 F _0.3 ”,“ Li _1.2 Ni _0.2 Mn _0.6 O _1.6 ” "F _0.4 ", "Li _1.2 Ni _0.4 Mn _0.4 O _1.8 F _0.2 ", as a comparative example, "Li _1.2 Ni _0.2 Mn _0.6 O ₂ ", "Li _1.2 Ni _0.2 Mn _0.6 O _1.95 F _0.05 " and "Li _1.2 Ni _0.25 Mn _0.55 O _1.9 F _0.1 " are described and 4 It is described that the initial Coulomb efficiency was obtained from the initial charge capacity by charging up to .6 V and the initial discharge capacity by discharging from the charged state to 2.0 V (paragraphs [0072] to [0078]).

Patent Document 3 states that "it is composed of a lithium metal composite compound containing an excess of lithium including Li ₂ MnO ₃ having a layered structure, the fluoro compound is doped, and the FWHM (full width at half maximum) value is in the range of 0.164 ° to 0.185 °. The positive electrode active material inside. ”(Claim 1) is described.
Then, as an example, 0.82 mol of the transition metal hydroxide precursor having a Ni: Co: Mn molar ratio of 2: 2: 6 and 1.18 mol of Li ₂ CO ₃ and Li F in total (LiF is A mixture of 0.02 to 0.06 mol) was fired to obtain a positive electrode active material, and the battery characteristics were evaluated by charging and discharging 2.5V to 4.6V to obtain high rate characteristics and life characteristics. It is stated that the evaluation was made (paragraphs [0054] to [0064], [0073]).

Patent Document 4 includes "a Li element and at least one transition metal element selected from Ni, Co, and Mn (however, the molar amount of the Li element is 1 with respect to the total molar amount of the transition metal element." A method for producing a positive electrode active material for a lithium ion secondary battery, which comprises contacting a lithium-containing composite oxide with a fluorine gas. ”(Claim 1) is described.
Then, as an example, a lithium-containing composite oxide having the composition “Li (Li _0.2 Ni _0.137 Co _0.125 Mn _0.538 ) O ₂ ” was treated with fluorine to obtain a positive electrode active material (paragraph). [0082]-[0092]), in the battery evaluation, the initial capacity was evaluated by charging / discharging of 4.8V to 2.5V, and the cycle characteristics were evaluated by the charging / discharging cycle of 4.5 to 2.5V. It is described (paragraphs [0101], [0102]).

Patent Document 5 describes an electrically active composition comprising a crystalline material approximately represented by the composition formula Li _{1 + x} Ni _α Mn _β Co _γ A _δ O _2-z F _z , where x is about. It is 0.02 to about 0.19, α is about 0.1 to about 0.4, β is about 0.35 to about 0.869, and γ is about 0.01 to about 0.2. Δ is 0.0 to about 0.1, z is about 0.01 to about 0.2, and A is Mg, Zn, Al, Ga, B, Zr, Ti, Ca, Ce. , Y, Nb, or a combination thereof, an electroactive composition. ”(Claim 1).
Then, as Example 1, a metal carbonate powder containing Ni, Co, and Mn and an appropriate amount of Li ₂ CO ₃ and Li F powder are mixed and fired in two steps to form Li _1.2 Ni _{0. 175} Co _0.10 Mn _0.525 O _{2-F FF} (F = 0.05, 0.01, 0.02, 0.05, 0.1, or 0.2) lithium composite oxide obtained (Paragraphs [0064] to [0069]), as Example 2, an oxide was produced without using LiF, and this oxide was mixed with NH ₄ HF ₂ and heated to Li _1.2 Ni. _0.175 Co _0.10 Mn _0.525 O _{2-F FF} , Li 1.167 Ni _0.219 Co _0.125 Mn _0.490 O _{2-F FF ,} Li _1.130 Ni _0.266 Co Obtained a lithium composite oxide of _0.152 Mn _0.451 O _{2-F FF} or Li _1.090 Ni _0.318 Co _0.182 Mn _0.409 O _{2-F FF} (paragraph [0070 [0070]). ], [0071]), a coin cell was manufactured using these lithium composite oxides as a positive electrode active material, and a charge / discharge cycle was performed between 2.0 and 4.6 V to obtain data on the specific discharge capacity. It is described (paragraphs [0072] to [0078]).

There is also a prior art in which the electrochemical properties of the positive electrode active material are evaluated by evaluating the Raman spectrum.
In Patent Document 6, "an anode containing an anode current collector and an anode active material arranged on the anode current collector, and arranged on the cathode current collector and the cathode current collector, xLi ₂ MO ₃ ·. (1-x) A battery cell comprising a cathode comprising a cathode active material having a composition represented by LiCo _y M' _(1-y) O _2. "(Claim 1). As Example 1, the cathode active material is "a composition represented by 0.02Li ₂ MnO _3. 0.98 LiNi _0.021 Co _0.979 O ₂ ", and its Raman spectrum is shown in FIG. (Paragraphs [0026] to [0029]).
Further, as other examples, it is represented by "0.04Li ₂ MnO _{3.0.96LiCoO 2} " and "0.01Li ₂ MnO _{3.0.99LiNi 0.01} Mn _0.01 Co _0.98 O ₂ ". Compositions are described (paragraphs [0030], [0036]).

In Patent Document 7, "It is a lithium-based positive electrode active material of the following chemical formula 1, and the ratio of the peak intensity of the A 1 _g vibration mode of the spinel structure to the peak intensity of the A 1 _g vibration mode of the hexagonal structure is 1 in Raman spectral analysis. : 0.1 to 1: 0.4, and the ratio of the peak intensity of the A _{1 g} vibration mode to the peak intensity of the E _g vibration mode of the hexagonal structure is 1: 0.9 to 1: 3.5. Positive active material having a spinel structure in which the ratio of the peak intensity of A _{1 g} vibration mode to the peak intensity of F _{2 g} vibration mode is 1: 0.2 to 1: 0.4.
[Chemical formula 1]
Li _x Coy M _{1-y A 2}
In the above formula, 0.95 ≦ x ≦ 1.0, 0 ≦ y
≦ 1 and M is selected from the group consisting of Ni, Fe, Pb, Mg, Al, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn and Cr. At least one element, and A is an element selected from the group consisting of O, F, S and P. (Claim 1), since the lithium-based positive electrode active material has only a hexagonal structure before battery production, when Raman spectroscopic analysis is performed, a peak (593 cm ^-1 A _{1 g} ) due to two vibration modes is performed. A spectrum showing only the mode and 484 cm ^-1 _Eg mode) is obtained, and it is described that after the battery is made, the lithium-based positive electrode active material will have a spinel structure in addition to the hexagonal system. (Paragraphs [0017], [0018], FIGS. 1 and 2).

Non-Patent Document 1 describes NCMs (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) with increased Li ratio, Li _1.1 Ni _1/3 Co _1/3 Mn _1/3 O ₂ and high energy. xLi ₂ MnO ₃ · (1-x) LiMO ₂ (M = Ni, Co, Mn; x = 0.5)) has a peak A of _{1 g} near 600 cm ^-1 corresponding to the MeO ₆ vibration mode in the Raman spectrum. , Having a peak Eg peak near 500 cm ^-1 corresponding to the O-Me-O vibration mode, Li ₂ MnO ₃ having a peak such as 612 cm ^-1 (A _g 1), 493 cm ^-1 and _xLi . ₂ MnO ₃ · (1-x) LiMO ₂ (x = 0.5) has a peak that Li ₂ MnO ₃ has without LiNi _1/3 Co _1/3 Mn _1/3 O ₂ . In particular, it is described that the peak of 496 cm ^-1 and the shoulder of 569 cm ^-1 are remarkable. Further, it is described that _NCMs maintain a layered _{LiMO 2} similar structure before charging / discharging even after charging / discharging in that they have peaks corresponding to typical Eg and Ag1 before and after charging / discharging. (Page 206, right column, lines 2-5, page 208, left column to page 209, right column, "3.2. Ex situ Raman investigation" full text).

Japanese Patent No. 4877660 Japanese Unexamined Patent Publication No. 2012-89470 Japanese Unexamined Patent Publication No. 2014-107269 Japanese Unexamined Patent Publication No. 2014-75177 Special Table 2012-504316 Gazette Special Table 2016-517615 Gazette Special Table 2005-44785

P. Lanz, et al. Electrochimica Acta, 130, 206-212 (2014)

It is a standard for non-aqueous electrolyte secondary batteries to ensure safety if they are accidentally charged beyond the fully charged state (SOC 100%) (for example, "GB / T (for example) for automobile batteries". It is stipulated by the National Standards of the People's Republic of China) ”). As a method of evaluating the improvement in safety, assuming that the charge control circuit is broken, the SOC in which a sudden rise in battery voltage is observed when a current is forcibly applied beyond the fully charged state is observed. There is a way to record. If no spike in battery voltage is observed up to a higher SOC, then safety is assessed as improved.
Here, SOC is an abbreviation for System of Charge, and the state of charge of the battery is expressed by the ratio of the remaining capacity at that time to the capacity at the time of full charge, and the fully charged state is expressed as "SOC 100%". .. Further, the "first time" charging / discharging in the present specification refers to the first charging / discharging performed after injecting a non-aqueous electrolyte. "Initial" charging and discharging refers to one or more charging and discharging performed in the pre-shipment manufacturing process of a battery after injecting a non-aqueous electrolyte.

Comparison of potential changes appearing with respect to the amount of charging electricity in the positive electrode potential range of "4.3 V (vs. Li / Li ⁺ ) and 4.8 V or less (vs. Li / Li ⁺ )" described in Patent Document 1. A "flat region" is characteristically observed in "lithium-rich" active materials. Hereinafter, in the present specification, it is referred to as "overcharge area". The flat region is observed even when charging up to 4.8 V is performed even once after charging (hereinafter referred to as "overcharge chemical formation") in which the above-mentioned potential change is observed in a relatively flat region. There is no such thing. Therefore, the positive electrode contains a "lithium-excessive" active material, and the above-mentioned potential change is not performed in the initial charge / discharge where the above-mentioned potential change is observed in a relatively flat region, and the above-mentioned potential change is carried out in the normal use full charge (SOC 100%). We have proposed a non-aqueous electrolyte secondary battery with a positive electrode potential in which a flat region is not observed. When this battery exceeds 100% SOC and is further charged, the region where the potential change is relatively flat is observed for the first time, and no rapid increase in battery voltage is observed until a higher SOC is reached.
However, if a non-aqueous electrolyte secondary battery is manufactured without going through the charging process until the end of the overcharge area and is used without charging until the end of the overcharge area, the conventional method is used. The lithium-rich active material has a problem that the discharge capacity is small.
On the other hand, the non-aqueous electrolyte secondary batteries containing the lithium excess type active material described in Patent Documents 1 to 5 in the positive electrode are all charged until the overcharge region is completed. It is different from the above non-aqueous electrolyte secondary battery.
Since the active material described in Patent Document 6 has a low Mn content, it is not the original lithium-rich active material, and the active material described in Patent Document 7 is not a lithium-rich active material, so that the above problem arises. do not have.

The present inventor changes the crystal structure of the precursor, the composition of the lithium excess type active material, the crystallinity, etc., so that the amount of electricity charged per mass in the overcharge region is large and overcharge formation is not performed. However, we have found that a high discharge capacity per mass can be obtained.
However, the lithium excess type active material has a problem that the powder density is smaller than that of the LiMeO type ₂ active material and the discharge capacity per volume is still small.
The present invention provides a positive electrode active material for a non-aqueous electrolyte secondary battery having a large amount of charging electricity per volume and a large discharge capacity per volume in an overcharge region, a method for producing the positive electrode active material, and the positive electrode active material. An object of the present invention is to provide a non-aqueous electrolyte secondary battery containing the battery.

One aspect of the present invention for solving the above problems is a positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide, wherein the lithium transition metal composite oxide is α-NaFeO. It has a type ₂ crystal structure, the molar ratio of Li to the transition metal (Me) is 1 <Li / Me, and the transition metal (Me) contains Ni and Mn, or Ni, Co and Mn, and is Me. The molar ratio of Mn to Mn / Me is 0.3 ≦ Mn / Me <0.55, and the maximum value I ₆₀₀ in the range of 550 to 650 cm ^-1 in the Raman spectrum is in the range of 450 to 520 cm ^-1 . It is a positive electrode active material for a non-aqueous electrolyte secondary battery having a ratio of a maximum value of I ₄₉₀ (hereinafter referred to as “I ₄₉₀ / I ₆₀₀ ”) of 0.45 or more.

Another aspect of the present invention is the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which comprises Ni and Mn, or Ni, Co and Mn, and has a molar ratio of Mn to Me, Mn / Me. A lithium transition metal composite oxide having a molar ratio of Li / Me of 1 <Li / Me is produced by mixing a Li compound with a transition metal compound of 0.3 ≦ Mn / Me <0.55 and firing. This is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, to which a sintering aid is added.

Yet another aspect of the present invention is a positive electrode for a non-aqueous electrolyte secondary battery containing the positive electrode active material for the non-aqueous electrolyte secondary battery.
Further, the positive electrode active material provided with the positive electrode for the non-aqueous electrolyte secondary battery has a diffraction peak observed in the range of 20 to 22 ° in an X-ray diffraction diagram using CuKα rays, which is non-water. It is an electrolyte secondary battery. Alternatively, when the positive electrode for the non-aqueous electrolyte secondary battery is provided and the positive electrode potential reaches 5.0 V (vs. Li / Li ⁺ ), the battery is charged to 4.5 to 5.0 V (vs. Li / Li ⁺ ). ) Is a non-aqueous electrolyte secondary battery in which a region where the potential change is relatively flat with respect to the amount of charging electricity is observed within the positive electrode potential range.

Yet another aspect of the present invention is the method for manufacturing the non-aqueous electrolyte secondary battery, wherein the maximum ultimate potential of the positive electrode in the initial charge / discharge step is less than 4.5 V (vs. Li / Li ⁺ ). This is a method for manufacturing a non-aqueous electrolyte secondary battery.

INDUSTRIAL APPLICABILITY According to the present invention, a positive electrode active material for a non-aqueous electrolyte secondary battery having a large amount of charging electricity per volume and a large discharge capacity per volume in an overcharge region, a method for producing the positive electrode active material, and the positive electrode active material thereof are provided. It is possible to provide a positive electrode contained therein, a non-aqueous electrolyte secondary battery provided with the positive electrode thereof, and a method for producing the same.

A conceptual diagram showing a typical charge curve and an overcharge region when a positive electrode using a lithium excess type active material is initially charged with an SOC of more than 100%. The figure which shows the _A1g and Eg vibration modes of the lithium transition metal composite oxide which has the α- _NaFeO type ₂ crystal structure. LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , Li _1.1 Ni _1/3 Co _1/3 Mn _1/3 O _2.1, xLi ₂ MnO ₃・ (1-x) LiMO ₂ (M) = Ni, Co, Mn; x = 0.5), and the Raman spectrum of Li ₂ MnO ₃ before charging and discharging. Raman spectrum and Raman peak intensity ratio I ₄₉₀ / I ₆₀₀ before and after charging and discharging the positive electrode active material according to the embodiment of the present invention. Explain that "a diffraction peak is observed in the range of 20 to 22 °" in the X-ray diffraction measurement of the positive electrode active material contained in the positive electrode of the non-aqueous electrolyte secondary battery to which the initial charge / discharge condition 1 of the example is applied. figure Explain that "a diffraction peak is not observed in the range of 20 to 22 °" in the X-ray diffraction measurement of the positive electrode active material contained in the positive electrode of the non-aqueous electrolyte secondary battery to which the initial charge / discharge condition 2 of the example is applied. figure External perspective view showing a non-aqueous electrolyte secondary battery according to an embodiment of the present invention. The figure explaining "the region where the potential change is relatively flat with respect to the amount of charge electricity" in the non-aqueous electrolyte secondary battery which concerns on this embodiment. Conceptual diagram of the device used to measure the press density for calculating the discharge capacity per volume and the amount of charge electricity. Schematic diagram showing a power storage device including a plurality of non-aqueous electrolyte secondary batteries according to an embodiment of the present invention. Raman spectrum according to an example and a comparative example of the present invention. A graph showing the relationship between the Raman peak intensity ratio I ₄₉₀ / I ₆₀₀ of the lithium excess type active material according to the examples and comparative examples of the present invention and the discharge capacity per volume.

The configuration and action / effect of the present invention will be described with reference to technical ideas. However, the mechanism of action includes estimation, and its correctness does not limit the present invention. It should be noted that the present invention can be carried out in various other forms without departing from its essence or main features. Therefore, the embodiments or examples described below are merely examples in all respects and should not be construed in a limited manner. Further, all modifications and modifications that fall within the equivalent scope of the claims are within the scope of the present invention.

One embodiment of the present invention is a positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide, and the lithium transition metal composite oxide has an α-NaFeO type ₂ crystal structure. , The molar ratio of Li to the transition metal (Me) Li / Me is 1 <Li / Me, and the transition metal (Me) contains Ni and Mn or Ni, Co and Mn, and the molar ratio of Mn to Me is Mn / Me is 0.3 ≤ Mn / Me <0.6, and the ratio of the maximum value I ₄₉₀ in the range of 450 to 520 cm ^-1 to the maximum value I ₆₀₀ in the range of 550 to 650 cm ^-1 in the Raman spectrum ( It is a positive electrode active material for a non-aqueous electrolyte secondary battery having an I ₄₉₀ / I ₆₀₀ ) of 0.45 or more.
According to the above embodiment of the present invention, there is provided a positive electrode active material having a large amount of charging electricity per volume in an overcharged region and a large discharge capacity per volume.

Another embodiment of the present invention is the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which comprises Ni and Mn, or Ni, Co and Mn, and has a molar ratio of Mn to Me, Mn / Me. By mixing a Li compound with a transition metal compound having a molar ratio of 0.3 ≦ Mn / Me <0.55 and firing, a lithium transition metal composite oxide having a molar ratio of Li / Me of 1 <Li / Me is obtained. This is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, to which a sintering aid is added at the time of production.
According to the other embodiment of the present invention, there is provided a method for producing a positive electrode active material having a large discharge capacity per volume.

Yet another embodiment of the present invention is a positive electrode for a non-aqueous electrolyte secondary battery containing the positive electrode active material for the non-aqueous electrolyte secondary battery.

Yet another embodiment of the present invention comprises the positive electrode for a non-aqueous electrolyte secondary battery, and the positive electrode active material contained in the positive electrode is in the range of 20 to 22 ° in an X-ray diffraction diagram using CuKα rays. It is a non-aqueous electrolyte secondary battery in which a diffraction peak is observed.
Further, when the positive electrode for the non-aqueous electrolyte secondary battery is provided and the positive electrode potential is charged to 5.0 V (vs. Li / Li ⁺ ), it is 4.5 to 5.0 V (vs. Li / Li ⁺ ). ) Is a non-aqueous electrolyte secondary battery in which a region where the potential change is relatively flat with respect to the amount of charging electricity is observed within the positive electrode potential range.
According to this embodiment, there is provided a non-aqueous electrolyte secondary battery in which a rapid increase in battery voltage is not observed until a higher SOC is observed because the amount of electricity charged per volume in the overcharge region is large.

The above non-aqueous electrolyte secondary battery is preferably used at a potential of less than 4.5 V (vs. Li / Li ⁺ ). When used at a potential of less than 4.5V (vs. Li / Li ⁺ ), it is possible to achieve both a large discharge capacity per volume and no observation of a sharp rise in battery voltage up to a higher SOC. ..

Yet another embodiment of the present invention is the method for manufacturing the non-aqueous electrolyte secondary battery, wherein the maximum potential of the positive electrode in the initial charge / discharge step is less than 4.5 V (vs. Li / Li ⁺ ). , A method for manufacturing a non-aqueous electrolyte secondary battery.
According to this embodiment, when charging is performed so that the positive electrode potential reaches 5.0 V (vs. Li / Li ⁺ ), it is within the positive electrode potential range of 4.5 to 5.0 V (vs. Li / Li ⁺ ). In addition, by observing a region where the potential change is relatively flat with respect to the amount of charging electricity, a non-aqueous electrolyte secondary battery in which a rapid increase in battery voltage is not observed up to a higher SOC is manufactured.
Non-aqueous electrolyte according to one embodiment of the present invention The positive electrode active material for a secondary battery (hereinafter referred to as “positive electrode active material according to the present embodiment”), the non-aqueous electrolyte according to another embodiment of the present invention. A method for producing a positive electrode active material for a secondary battery (hereinafter referred to as "a method for producing a positive electrode active material according to the present embodiment"), and a positive electrode for a non-aqueous electrolyte secondary battery according to still another embodiment of the present invention (hereinafter referred to as "a method for producing a positive electrode active material according to the present embodiment"). Hereinafter, "positive electrode for non-aqueous electrolyte secondary battery according to the present embodiment"), non-aqueous electrolyte secondary battery according to still another embodiment of the present invention (hereinafter, "non-aqueous electrolyte according to the present embodiment"). "Secondary battery"), a method for manufacturing a non-aqueous electrolyte secondary battery according to still another embodiment of the present invention (hereinafter, referred to as "a method for manufacturing a non-aqueous electrolyte secondary battery according to the present embodiment"). Will be described in detail below.

<Lithium transition metal composite oxide>
The lithium transition metal composite oxide contained in the positive electrode active material according to the present embodiment (hereinafter referred to as “lithium transition metal composite oxide according to the present embodiment”) has a composition formula Li _{1 + α} Me _1-α O ₂ (hereinafter referred to as “lithium transition metal composite oxide according to the present embodiment”). α>0; Me is a so-called “lithium-rich” active material that can be described as Ni and Mn, or Ni, Co and Mn). In the above composition formula, the molar ratio Li / Me of Li to the transition metal element Me represented by (1 + α) / (1-α) is 1 <Li / Me. Li / Me is preferably 1.05 or more, and more preferably 1.1 or more, in that the amount of charging electricity per volume in the overcharge region can be increased. Further, it is preferably less than 1.4, more preferably 1.3 or less. Within this range, the discharge capacity per volume of the positive electrode active material when manufactured and used in a potential range lower than the overcharge region is improved.
The molar ratio of Mn to the transition metal element Me, Mn / Me, is 0.3 or more and 0.55 or less. When it is 0.3 or more, the amount of charging electricity per volume in the overcharged region can be increased. Further, when it is 0.55 or less, the discharge capacity per volume when manufactured and used in a potential range lower than the overcharge region is improved. The molar ratio of Mn / Me is more preferably 0.5 or less, and even more preferably 0.45 or less.
Co contained in the lithium transition metal composite oxide is an optional component having an effect of improving the initial efficiency, but it is a rare resource and therefore costly. Therefore, the molar ratio Co / Me of Co to the transition metal element Me is preferably 0.35 or less, and may be 0.
The molar ratio of Ni to the transition metal element Me, Ni / Me, is preferably 0.2 or more, more preferably 0.3 or more. Further, 0.6 or less is preferable, and 0.55 or less is more preferable. Within this range, the polarization in charge / discharge becomes smaller, so that the discharge capacity becomes larger when used at a potential of less than 4.5 V (vs. Li / Li ⁺ ).
By using the lithium transition metal composite oxide having such a composition as the positive electrode active material, the amount of charge electricity per volume in the overcharge region is large, and it is manufactured without going through the charging process until the end of the overcharge region. Moreover, when used without charging until the end of the overcharge region, a non-aqueous electrolyte secondary battery having a large discharge capacity per volume can be obtained.
The lithium transition metal composite oxide according to the present embodiment can be used as an alkali metal such as Na and K, an alkaline earth metal such as Mg and Ca, and a 3d transition metal such as Fe, as long as the effects of the present invention are not impaired. It does not preclude the inclusion of small amounts of other metals such as typified transition metals.

The lithium transition metal composite oxide according to the present embodiment is the ratio of the maximum value I ₄₉₀ in the range of 450 to 520 cm ^-1 to the maximum value I ₆₀₀ in the range of 550 to 650 cm ^-1 in the Raman spectrum (I ₄₉₀ /). I ₆₀₀ ) is 0.45 or more.
By setting I ₄₉₀ / I ₆₀₀ to 0.45 or more, the amount of charging electricity per volume in the overcharge region becomes large, and the discharge capacity per volume becomes large.
In the present invention, the significance of specifying I ₄₉₀ / I ₆₀₀ as 0.45 or more is presumed as follows.
The lithium transition metal composite oxide according to the present embodiment can be represented as a solid solution of LiMeO ₂ (including M = Ni and Mn, or Ni, Co and Mn) and Li ₂ MnO ₃ . Although LiMeO ₂ and Li ₂ MnO ₃ have a peak A _{1 g} near 600 cm ^-1 corresponding to the MeO ₆ vibration mode and a peak E _g near 490 cm ^-1 corresponding to the O-Me-O vibration mode in the Raman spectrum. , Li ₂ MnO ₃ is known to have a particularly remarkable peak _Eg (see Non-Patent Document 1). FIG. 2 is a reproduction of FIG. 2 of Patent Document 7 for explaining the vibration mode, and FIG. 3 shows Fig. 4 is reprinted.
A large I ₄₉₀ / I ₆₀₀ means that the lithium transition metal composite oxide according to the present embodiment has a relatively large amount of Li ₂ MnO ₃ components because the O—Me—O vibration is relatively large. .. Since Li ₂ MnO ₃ is a component that contributes to increasing the amount of charge electricity in the overcharge region, a value of 0.45 or more for I ₄₉₀ / I ₆₀₀ causes a sharp rise in battery voltage up to a higher SOC. Is never observed.
On the other hand, the fact that I ₄₉₀ / I ₆₀₀ is small means that the LiMeO ₂ component is relatively large in the lithium transition metal composite oxide according to the present embodiment because the MeO ₆ vibration is relatively large. LiMeO ₂ has a higher density and a higher capacity than Li ₂ MnO ₃ . However, in the positive electrode active material containing the lithium transition metal composite oxide according to the present embodiment, when the density is increased by the sintering aid, the ratio of LiMeO ₂ units is considered to be relatively small I ₄₉₀ /. It was found that the active material having an I ₆₀₀ of 0.45 or more unexpectedly had a larger discharge capacity per volume than the active material having an I 600 of less than 0.45. The reason why I ₄₉₀ / I ₆₀₀ is reduced by the sintering aid is that the valence of the transition metal is reduced due to oxygen deficiency in the active material, or the disproportionation during active material synthesis (3LiMeO ₂ → LiMn ₂ ). It is considered that the elimination of O ₄ + Li ₂ MnO ₃ ) increases the ratio of LiMeO ₂ units to Li ₂ MnO ₃ units in the active material. However, for the above reason, in order to increase the discharge capacity per volume, it is preferable that I ₄₉₀ / I ₆₀₀ is not too large, and it is preferably 0.85 or less.

Further, the lithium transition metal composite oxide contained in the "lithium excess type" positive electrode active material according to the present embodiment belongs to the space group P3 ₁₁₂ after synthesis (before charging / discharging) and uses CuKα rays. On the X-ray diffraction diagram, a superlattice peak (peak seen in Li [Li _1/3 Mn _2/3 ] _O2 type monoclinic crystals) is confirmed in the range of 2θ = 20 to 22 °. Here, "observed" means the maximum value of the intensity in the range of the diffraction angle of 20 to 22 ° with respect to the difference (I ₁₈ ) between the maximum value and the minimum value of the intensity in the range of the diffraction angle of 17 to 19 °. It means that the ratio of the difference (I ₂₁ ) between the minimum value and the minimum value, that is, the value of "I ₂₁ / I ₁₈ " is in the range of 0.001 to 0.1. This superlattice peak (hereinafter referred to as "peak of 20 to 22 °") does not disappear even if charging / discharging is performed in a potential region of less than 4.5 V (vs. Li / Li ⁺ ). However, if charging is performed to a potential at which the overcharge region of 4.5 V (vs. Li / Li ⁺ ) or higher ends even once, the symmetry of the crystal changes with the desorption of Li in the crystal. The peak of 20 to 22 ° disappears, and the lithium transition metal composite oxide is assigned to the space group R3-m. Here, P3 ₁ 12 is a crystal structure model in which the atomic positions of 3a, 3b, and 6c sites in R3-m are subdivided, and the P3 ₁ 12 model is when order is recognized in the atomic arrangement in R3-m. Is adopted. In addition, "R3-m" is originally described by adding a bar "-" on "3" of "R3m".

The sample to be used for Raman spectrum measurement and X-ray diffraction measurement is prepared according to the following procedure and conditions.
If the sample to be measured is the active material powder (powder before charging / discharging) before the positive electrode is prepared, it is used as it is for the measurement. When a sample is taken from an electrode taken out by disassembling the battery, the voltage specified by the current value (A), which is 1/10 of the nominal capacity (Ah) of the battery, is used before disassembling the battery. A constant current discharge is performed up to the battery voltage, which is the lower limit of the above, and the state is set to the end of discharge state. As a result of dismantling, if the battery uses a metallic lithium electrode as the negative electrode, the positive electrode mixture collected from the positive electrode plate is used as the measurement target without performing the additional work described below. If the battery does not use a metallic lithium electrode as the negative electrode, in order to accurately control the positive electrode potential, after disassembling the battery and taking out the electrode, assemble a battery with the metallic lithium electrode as the counter electrode, and 10 mA per 1 g of the positive electrode mixture. With the current value of, constant current discharge is performed until the potential of the positive electrode reaches 2.0 V (vs. Li / Li ⁺ ), adjusted to the discharge end state, and then disassembled again. The removed positive electrode plate is thoroughly washed with dimethyl carbonate to thoroughly wash the non-aqueous electrolyte adhering to the electrode, dried at room temperature for 24 hours, and then the mixture on the aluminum foil current collector is collected. The sample to be used for X-ray diffraction measurement is lightly loosened with a mortar and pestle, and placed in a sample holder for X-ray diffraction measurement for measurement. For the sample to be used for Raman spectrum measurement, this mixture was calcined at 600 ° C. for 4 hours in a small electric furnace to remove carbon as a conductive agent and PVdF binder as a binder, and a lithium transition metal composite oxide. The particles are taken out and subjected to the above measurement as an active material powder (powder after charging / discharging).
The work from dismantling to re-disassembling the battery, and the cleaning and drying work of the positive electrode plate are performed in an argon atmosphere having a dew point of −60 ° C. or lower.

<Measurement method of Raman spectrum>
The Raman spectrum is measured under the following conditions.
Raman spectroscopy is performed using "LabRAM HR Revolution" manufactured by HORIBA, Ltd. A 100x lens is used as the objective lens, and the measurement is performed with the laser focused on the active material powder prepared as described above. At that time, the measurement is performed under the conditions of a wavelength of 532 nm (YAG laser), a grating of 600 g / mm, an exposure time of 30 seconds, two integrations, and a measurement wavelength of 100 cm ^-1 to 4000 cm ^-1 . In the spectrum obtained by the above measurement, the ratio of the maximum value I ₄₉₀ in the range of 450 cm ^-1 or more and 520 cm ^-1 or less to the maximum value I ₆₀₀ in the range of 550 cm ^-1 or more and 650 cm ^-1 or less (I ₄₉₀ / I). ₆₀₀ ) is calculated.

FIG. 4 is a Raman spectrum obtained by measuring the pre-charge / discharge powder and the post-charge / discharge powder of the lithium transition metal composite oxide according to Example 2 described later by the above procedure. The lithium transition metal composite oxide according to the present embodiment maintains a Raman spectrum before and after charging and discharging in a powder state.
In addition, Fig. 4 (before charging / discharging), Fig. It is shown that the Raman spectrum hardly changes even at 5 (after charging / discharging).

<Measurement method of X-ray diffraction>
In the present specification, the X-ray diffraction measurement is performed under the following conditions. The radioactive source is CuKα, the acceleration voltage is 30 kV, and the acceleration current is 15 mA. The sampling width is 0.01 deg, the scan speed is 1.0 deg / min, the divergent slit width is 0.625 deg, the light receiving slit is open, and the scattering slit is 8.0 mm.

FIG. 5 shows a current value of 10 mA per 1 g of the positive electrode mixture and a charge upper limit potential of 4.35 V (vs. Li / Li ⁺ ) for the non-aqueous electrolyte secondary battery using the positive electrode active material according to the present embodiment. ), The non-aqueous electrolyte secondary in the discharge end state after the first charge / discharge (corresponding to the first charge / discharge condition 1 of the examples described later) with the lower discharge potential set to 2.0 V (vs. Li / Li ⁺ ). FIG. 5 is an X-ray discharge diagram measured by the above procedure for an active material powder contained in a positive electrode of a battery (a non-aqueous electrolyte secondary battery according to the present embodiment). In FIG. 5, diffraction peaks are observed in the range of 20 to 22 °.
FIG. 6 shows a current value of 10 mA per 1 g of the positive electrode mixture and a charge upper limit potential of 4.6 V (vs. Li / Li) for a non-aqueous electrolyte secondary battery using the positive electrode active material according to the same embodiment. ⁺ ), With the lower limit potential of discharge set to 2.0 V (vs. Li / Li ⁺ ), the non-aqueous electrolyte 2 in the discharge end state after the first charge / discharge (corresponding to the first charge / discharge condition 2 of the examples described later). It is an X-ray discharge chart which measured the active material powder contained in the positive electrode of the next battery by the above-mentioned procedure. In FIG. 6, no diffraction peak is observed in the range of 20 to 22 °.
In addition, in the initial charge / discharge condition 2 of the embodiment described later, in order to investigate the amount of charge electricity per volume in the overcharge region of the positive electrode active material according to the present embodiment, the upper limit charge potential is 4.6 V (vs. Li). Since it is / Li ⁺ ), the non-aqueous electrolyte secondary battery after applying the initial charge / discharge condition 2 is not the non-aqueous electrolyte secondary battery according to the present embodiment.
For a non-aqueous electrolyte secondary battery using the positive electrode active material according to the same embodiment, the charge upper limit potential is 4.6 V (vs. Li / Li ⁺ ) and the discharge lower limit potential is 2.0 V (vs. Li /). After the first charge / discharge as Li ⁺ ), the charge / discharge was performed with the charge upper limit potential of 4.35 V (vs. Li / Li ⁺ ) and the discharge lower limit potential of 2.0 V (vs. Li / Li ⁺ ). When the active material powder contained in the positive electrode of the non-aqueous electrolyte secondary battery in the end-discharged state was measured by the above procedure, an X-ray diffraction diagram similar to that in FIG. 6 was obtained. That is, as described above, once the battery is charged to a potential of 4.5 V or higher, the peak in the range of 20 to 22 ° disappears, and the diffraction peak in the range of 20 to 22 ° does not appear again.
In the non-aqueous electrolyte secondary battery according to the present embodiment, a diffraction peak in the range of 20 to 22 ° is observed in the X-ray diffraction diagram of the positive electrode active material even in the X-ray diffraction measurement after charging / discharging by the above procedure. It can be seen that the non-aqueous electrolyte secondary battery according to the present embodiment is a battery used at a potential of less than 4.5 V (vs. Li / Li ⁺ ) including the initial charge / discharge.

<Manufacturing method of lithium transition metal composite oxide>
In the method for producing a positive electrode active material according to the present embodiment, the lithium transition metal composite oxide contains Ni and Mn, or Ni, Co and Mn, and the molar ratio of Mn to Me, Mn / Me, is 0.3 ≦ Mn /. It can be produced by mixing a Li compound with a transition metal compound having Me <0.55 and firing it. At the time of the firing, it is preferable to add a sintering aid.

The transition metal compound is a transition metal hydroxide precursor produced by a coprecipitation method in which a raw material compound containing Ni and Mn or Ni, Co and Mn is reacted in an aqueous solution having a pH of 10.2 or less. Is more preferable. By setting the pH to 10.2 or less, particle growth can be promoted, so that the stirring duration after the completion of dropping the aqueous solution of the raw material can be shortened, and a crystal structure containing αMe (OH) ₂ and βMe (OH) ₂ can be obtained. A precursor having can be produced. A precursor having a crystal structure containing αMe (OH) ₂ and βMe (OH) ₂ has a tap density higher than that of a precursor having a crystal structure of αMe (OH) ₂ single phase or βMe (OH) ₂ single phase. Can be made larger. An electrode made of a precursor having a high tap density can increase the press density, so that the resistance of the electrode can be reduced. If the pH is too low, it becomes a precursor of αMe (OH) ₂ single phase, so that the reaction pH preferably exceeds 9.

When producing a hydroxide precursor, an alkaline solution containing an alkali metal hydroxide, a complexing agent, and a reducing agent is added to a reaction vessel kept alkaline in addition to a solution containing a transition metal (Me). Therefore, it is preferable to co-precipitate the transition metal hydroxide.
As the complexing agent, ammonia, ammonium sulfate, ammonium nitrate and the like can be used, and ammonia is preferable. A precursor with a higher tap density can be produced by a crystallization reaction using a complexing agent.
It is preferable to use a reducing agent together with the complexing agent. As the reducing agent, hydrazine, sodium borohydride and the like can be used, and hydrazine is preferable.
Sodium hydroxide, lithium hydroxide or potassium hydroxide can be used as the alkali metal hydroxide (neutralizing agent).

Of Ni, Co, and Mn, Mn is easily oxidized, and it is not easy to prepare a coprecipitate in which Ni, Mn, or Ni, Co, and Mn are uniformly distributed in a divalent state. Therefore, Ni, Mn, Alternatively, uniform mixing of Ni, Co, and Mn at the atomic level tends to be inadequate. In the method for producing a positive electrode active material according to the present embodiment, since the molar ratio of Mn to Me in the composition range of the transition metal compound, Mn / Me, is 0.3 or more, it is important to remove the dissolved oxygen in the aqueous solution. Is. Examples of the method for removing dissolved oxygen include a method of bubbling a gas containing no oxygen. The gas containing no oxygen is not limited, but nitrogen gas, argon gas, carbon dioxide (CO ₂ ) and the like can be used.

The raw material of the transition metal compound is manganese oxide, manganese carbonate, manganese sulfate, manganese nitrate, manganese acetate or the like as the Mn source, and nickel hydroxide, nickel carbonate, nickel sulfate, nickel nitrate, nickel acetate or the like as the Ni source. As an example of the Co source, cobalt sulfate, cobalt nitrate, cobalt acetate and the like can be mentioned.

While the raw material aqueous solution of the transition metal compound is dropped and supplied, a mixed alkaline solution containing an alkali metal hydroxide (neutralizing agent) such as sodium hydroxide, a complexing agent such as ammonia, and a reducing agent such as hydrazine is prepared. A method of appropriately dropping is preferable. The concentration of the alkali metal hydroxide to be dropped is preferably 1.0 to 8.0 M. The concentration of the complexing agent is preferably 0.4 M or more, more preferably 0.6 M or more. Further, it is preferably 2.0 M or less, more preferably 1.6 M or less, and further preferably 1.5 M or less. The concentration of the reducing agent is preferably 0.05 to 1.0 M, more preferably 0.1 to 0.5 M. By lowering the pH of the reaction vessel and setting the concentration of ammonia (complexing agent) to 0.6 M or more, the tap density of the hydroxide precursor can be increased.

The dropping rate of the raw material aqueous solution greatly affects the uniformity of the element distribution within one particle of the produced hydroxide precursor. In particular, it should be noted that Mn does not easily form a uniform element distribution with Ni and Co. The preferable dropping rate is affected by the size of the reaction vessel, stirring conditions, pH, reaction temperature and the like, 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 ammonia is present in the reaction tank and certain convection conditions are applied, the particles rotate and revolve in the stirring tank by continuing stirring after the dropping of the raw material aqueous solution is completed. In this process, the particles gradually grow into concentric spheres while colliding with each other. That is, the hydroxide precursor undergoes a two-step reaction: a metal complex forming reaction when the raw material aqueous solution is dropped into the reaction vessel, and a precipitation forming reaction that occurs while the metal complex stays in the reaction vessel. It is formed through. Therefore, a hydroxide precursor having a target particle size can be obtained by appropriately selecting a time for further stirring after the completion of dropping of the raw material aqueous solution.

The preferable stirring duration after the completion of dropping the aqueous solution of the raw material is affected 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. It is preferable, 1h or more is more preferable. Further, in order to reduce the possibility that the output performance in the low SOC region of the battery becomes insufficient due to the particle size becoming too large, 15 hours or less is preferable, 10 hours or less is more preferable, and 5 hours or less is most preferable.

Further, the cumulative volume of the secondary particles of the hydroxide precursor and the lithium transition metal composite oxide in the particle size distribution is preferably 13 μm or less, which is the particle size of 50%. For that purpose, for example, when the pH is controlled to 9.1 to 10.2, the stirring duration is preferably 1 to 3 hours.

When the particles of the hydroxide precursor are prepared by using a sodium compound such as sodium hydroxide as a neutralizing agent, it is preferable to wash and remove the sodium ions adhering to the particles in the subsequent washing step. For example, when the produced hydroxide precursor is suction-filtered and taken out, a condition can be adopted such that the number of washings with 500 mL of ion-exchanged water is 6 times or more.

A lithium transition metal composite oxide is produced by mixing a Li compound with the hydroxide precursor (transition metal compound) produced as described above and firing the compound.
As the Li compound to be mixed with the transition metal compound, lithium hydroxide, lithium nitrate, lithium carbonate, lithium acetate and the like can be used.

When the transition metal compound and the Li compound are mixed and fired, it is preferable to add a sintering aid. Examples of the sintering aid include lithium fluoride (LiF), lithium carbonate (Li ₂ CO ₃ ), sodium fluoride (NaF), sodium chloride (NaCl), lithium sulfate (Li ₂ SO ₄ ), and lithium phosphate (Li). ₃ It is preferable to use PO ₄ ), lithium chloride (LiCl), magnesium chloride (MgCl ₂ ) or calcium chloride (CaCl ₂ ). As described above, lithium carbonate is used as a Li compound for producing a lithium transition metal composite oxide, but when lithium hydroxide is used as the lithium compound as described in Examples described later, lithium carbonate is used. Lithium carbonate functions as a sintering aid. The addition ratio of these sintering aids is preferably 1 to 10 mol% with respect to the total amount of the Li compound. It is preferable that the total amount of the Li compound is excessively charged by about 1 to 5% in anticipation that a part of the Li compound will disappear during firing.

The firing temperature affects the reversible capacity of the active material.
If the firing temperature is too high, the obtained active material will disintegrate with an oxygen release reaction, and in addition to the hexagonal crystal of the main phase, it will become a monoclinic Li [Li _1/3 Mn _2/3 ] O ₂ type. The defined phase tends to be observed as a phase-separated phase rather than as a solid solution phase. If too much of such a phase separation is contained, the reversible capacity of the active material is reduced, which is not preferable. In such a material, impurity peaks are observed near 35 ° and around 45 ° on the X-ray diffraction pattern. Therefore, the firing temperature is preferably lower than the temperature affected by the oxygen release reaction of the active material. The oxygen release temperature of the active material varies slightly depending on the composition of the active material, and the positive electrode active material according to the present embodiment is generally 1000 ° C. or higher, but the oxygen release temperature of the active material should be confirmed in advance. Is preferable. In particular, it has been confirmed that the oxygen release temperature of the hydroxide precursor shifts to the lower temperature side as the amount of Co contained in the sample increases, so caution is required. As a method for confirming the oxygen release temperature of the active material, a mixture of a hydroxide precursor and a lithium compound may be subjected to thermogravimetric analysis (TG-DTA measurement) in order to simulate the firing reaction process. However, in this method, the platinum used in the sample chamber of the measuring instrument may be corroded by the volatilized Li component and damage the instrument. Therefore, a firing temperature of about 500 ° C. was adopted in advance to promote crystallization to some extent. The composition should be subjected to thermogravimetric analysis.

On the other hand, if the firing temperature is too low, crystallization does not proceed sufficiently and the electrode characteristics tend to deteriorate. Sufficient crystallization can reduce the resistance of grain boundaries and promote smooth lithium ion transport.
Therefore, the preferable firing temperature varies depending on the oxygen release temperature depending on the composition of the active material, but in the method for producing the positive electrode active material according to the present embodiment, in order to obtain an active material having a sufficient discharge capacity per volume, the firing temperature is used. Is preferably 800 to 1000 ° C, more preferably 850 to 950 ° C.

<Positive electrode>
The positive electrode for a non-aqueous electrolyte secondary battery according to the present embodiment contains the powder containing the above-mentioned positive electrode active material as a main component. As other components, a conductive agent, a binder, a thickener, a filler and the like may be contained.

The powder of the positive electrode active material preferably has an average particle size of 100 μm or less. In particular, the powder of the positive electrode active material is preferably 15 μm or less in terms of improving the high output characteristics of the non-aqueous electrolyte battery. In order to obtain the powder in a predetermined shape, there are a method of producing a precursor having a predetermined size, a method of using a crusher, a classifier and the like. For pulverization, 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 airflow type jet mill, a sieve, or the like is used. At the time of pulverization, wet pulverization in which water or an organic solvent such as hexane coexists can also be used. The classification method is not particularly limited, and a sieve, a wind power classifier, or the like is used as needed for both dry and wet types.

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

Among these, acetylene black is preferable as the conductive agent from the viewpoint of electron conductivity and coatability. The amount of the conductive agent added is preferably 0.1% by mass to 50% by mass, particularly preferably 0.5% by mass to 30% by mass, based on the total mass of the positive electrode. In particular, it is preferable to pulverize acetylene black into ultrafine particles of 0.1 to 0.5 μm and use it because the required carbon amount can be reduced. These mixing methods are physical mixing, and the ideal is uniform mixing. Therefore, it is possible to mix by a dry type or a wet type by using a powder mixer such as a V-type mixer, an S-type mixer, a stirring machine, a ball mill, and a planetary ball mill.

Examples of the binder include thermoplastic resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene and polypropylene, ethylene-propylene-dienter polymer (EPDM), sulfonated EPDM and styrene butadiene. A polymer having rubber elasticity such as rubber (SBR) and fluororubber can be used as one kind or a mixture of two or more kinds. The amount of the binder added is preferably 1 to 50% by mass, particularly preferably 2 to 30% by mass, based on the total mass of the positive electrode.

The filler is not limited as long as it is a material that does not adversely affect the battery performance. Usually, olefin polymers such as polypropylene and polyethylene, amorphous silica, alumina, zeolite, glass, carbon and the like are used. The amount of the filler added is preferably 30% by mass or less with respect to the total mass of the positive electrode.

<Negative electrode>
The negative electrode active material used for the negative electrode to be combined with the above positive electrode is not limited. Any form that can occlude and release lithium ions can be appropriately selected. For example, a titanium-based material such as lithium titanate having a spinel-type crystal structure represented by Li [Li _1/3 Ti _5/3 ] _O4 , an alloy-based material such as Si, Sb, Sn, lithium metal, and a lithium alloy. (Lithium-silicon, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and lithium metal-containing alloys such as wood alloys), lithium composite oxide (lithium-titanium), silicon oxide In addition, alloys capable of storing and releasing lithium, carbon materials (for example, graphite, hard carbon, low temperature fired carbon, amorphous carbon, etc.) and the like can be mentioned.
The negative electrode active material is used as a powder like the positive electrode active material, and the negative electrode may contain other components like the positive electrode.

<Manufacturing of positive and negative electrodes>
For the positive electrode and the negative electrode, the main components (each active material) and other materials are kneaded to form a mixture, which is mixed with an organic solvent such as N-methylpyrrolidone or toluene or water, and then the obtained mixed solution is described below. It is suitably produced by applying it on a current collector to be described in detail, crimping it, and heat-treating it at a temperature of about 50 ° C. to 250 ° C. for about 2 hours. Regarding the above-mentioned coating method, for example, it is preferable to apply the coating to an arbitrary thickness and an arbitrary shape by using a means such as a roller coating such as an applicator roll, a screen coating, a doctor blade method, a spin coating, and a bar coater. Not limited.

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

<Non-water electrolyte>
The non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery is not limited, and generally, those proposed for use in lithium secondary batteries and the like can be used. Examples of the non-aqueous solvent used for the non-aqueous electrolyte include cyclic carbonate esters such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate and vinylene carbonate; cyclic esters such as γ-butylolactone and γ-valerolactone; dimethyl carbonate, Chain carbonates such as diethyl carbonate and ethylmethyl carbonate; Chain esters such as methyl formate, methyl acetate and methyl butyrate; tetrahydrofuran or its derivatives; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxy Ethers such as ethane, 1,4-dibutoxyetane, methyl diglyme; nitriles such as acetonitrile and benzonitrile; dioxolane or derivatives thereof; ethylene sulfide, sulfolane, sulton or derivatives thereof alone or two or more thereof. Examples include, but are not limited to, mixtures.

Examples of the electrolyte salt used for the non-aqueous electrolyte include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr. , KClO ₄ , KSCN and other inorganic ionic 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-malate, (C ₂ H ₅ ) ₄ N-benzoate, (C ₂ H ₅ ) ₄ N-phthate, lithium stearylsulfonate, lithium octylsulfonate, Examples thereof include organic ionic salts such as lithium dodecylbenzenesulfonate, and these ionic compounds can be used alone or in combination of two or more.

Further, by using a mixture of 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 lowered. It is more preferable because the low temperature characteristics can be further enhanced and self-discharge can be suppressed.
Further, a room temperature molten salt or an ionic liquid may be used as the non-aqueous 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 surely obtain a non-aqueous electrolyte battery having high battery characteristics. It is .5 mol / L.

<Separator>
As the separator of the non-aqueous electrolyte secondary battery, it is preferable to use or use a porous membrane, a non-woven fabric, or the like exhibiting excellent high rate discharge performance alone or in combination. Examples of the material constituting the separator for a non-aqueous electrolyte battery include a polyolefin resin typified by polyethylene and polypropylene, a polyester resin typified by polyethylene terephthalate and polybutylene terephthalate, and vinylidene fluoride and vinylidene fluoride-hexa. Fluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, foot Vinylidene-hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene Examples thereof include a copolymer, vinylidene fluoride-ethylene-tetrafluoroethylene copolymer and the like.

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

Further, as the separator, a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinylpyrrolidone, polyvinylidene fluoride and the like and an electrolyte may be used. It is preferable to use the non-aqueous electrolyte in the gel state as described above because it has an effect of preventing liquid leakage.

Further, it is preferable to use the separator in combination with the above-mentioned porous membrane, non-woven fabric or the like and the polymer gel because the liquid retention property of the electrolyte is improved. That is, the pro-solvent polymer is formed by forming a film coated with a pro-solvent polymer having a thickness of several μm or less on the surface of the polyethylene micropore membrane and the micropore wall surface, and retaining the electrolyte in the micropores of the film. Gells.

Examples of the pro-solvent polymer include polyvinylidene fluoride, an acrylate monomer having an ethylene oxide group and an ester group, an epoxy monomer, a polymer having a crosslinked monomer such as an isocyanato group, and the like. The monomer can be subjected to a cross-linking reaction by irradiation with an electron beam (EB), heating by adding a radical initiator, or irradiation with ultraviolet rays (UV).

<Structure of non-aqueous electrolyte secondary battery>
The configuration of the non-aqueous electrolyte secondary battery is not particularly limited, and examples thereof include a cylindrical battery having a positive electrode, a negative electrode, and a roll-shaped separator, a square battery (rectangular battery), and a flat battery. Be done.
FIG. 7 shows an external perspective view of the rectangular non-aqueous electrolyte secondary battery 1 according to the embodiment of the present invention. The figure is a perspective view of the inside of the container. In the non-aqueous electrolyte secondary battery 1 shown in FIG. 7, the electrode group 2 is housed in the battery container 3. The electrode group 2 is formed by winding a positive electrode having a positive electrode active material and a negative electrode having 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 non-aqueous electrolyte secondary battery according to the present embodiment includes a positive electrode containing the above-mentioned positive electrode active material, and the positive electrode active material contained in the positive electrode is in the range of 20 to 22 ° in an X-ray diffraction diagram using CuKα rays. When a diffraction peak is observed or the positive electrode potential is charged to 5.0 V (vs. Li / Li ⁺ ), the positive electrode is 4.5 to 5.0 V (vs. Li / Li ⁺ ). It is a battery in which a region where the potential change is relatively flat with respect to the amount of charging electricity is observed within the potential range.
In the non-aqueous electrolyte secondary battery in which the diffraction peak of the positive electrode active material contained in the above positive electrode is observed in the range of 20 to 22 °, the maximum ultimate potential of the positive electrode in the initial charge / discharge step is 4.5 V (vs. Li). Since it is manufactured by a method of less than / Li ⁺ ) (a method for manufacturing a non-aqueous electrolyte secondary battery according to the present embodiment), a region where the potential change is relatively flat is observed.
Since the above-mentioned potential change has a relatively flat region, the amount of charging electricity per volume in the overcharge region becomes large, so that a rapid increase in the battery voltage is not observed until a higher SOC is reached.

<How to check the area where the potential change is flat>
Confirmation that "a region where the potential change is relatively flat with respect to the amount of charging electricity" (hereinafter referred to as "a region where the potential change is flat") is observed is by the following procedure. A test battery was prepared using the positive electrode plate taken out after disassembly as the working electrode and the Li metal as the counter electrode, and the test battery was discharged to 2.0 V (vs. Li / Li ⁺ ) at a current value of 10 mA per 1 g of the positive electrode mixture. After that, a 30-minute rest is performed. After that, constant current charging is performed up to 5.0 V (vs. Li / Li ⁺ ) with a current value of 10 mA per 1 g of the positive electrode mixture. Here, the ratio of the capacity Y (mAh) at each potential to the capacity X (mAh) when 4.45 V (vs. Li / Li ⁺ ) is reached from the start of charging is Z (= Y / X * 100 (%)). And. The horizontal axis is the potential, the vertical axis is the difference in the potential change, and the numerator is the difference in the volume ratio change, and dZ / dV is taken to obtain a dZ / dV curve.
The solid line in FIG. 8 shows a non-aqueous electrolyte secondary battery equipped with a positive electrode using a lithium excess type active material as a positive electrode active material and a negative electrode using a Li metal, and the initial charge is 4.5 V (vs. Li). This is an example of a dZ / dV curve when the non-aqueous electrolyte secondary battery according to the present embodiment having a value of less than / Li ⁺ ) is charged to 4.6 V (vs. Li / Li ⁺ ). As can be seen from the calculation formula, the dZ / dV curve has a large dZ / dV value when the potential change is small with respect to the capacitance ratio change, and dZ / dV when the potential change is large with respect to the capacitance ratio change. The value becomes smaller. In the charging process of the lithium excess type active material in the potential region exceeding 4.5 V (vs. Li / Li ⁺ ), the value of dZ / dV becomes large when the region where the potential change is flat begins to be seen. After that, when the region where the potential change is flat ends and the potential starts to rise again, the value of dZ / dV becomes small. That is, a peak is observed in the dZ / dV curve. Here, when the maximum value of dZ / dV in the range of 4.5 V (vs. Li / Li ⁺ ) to 5.0 V (vs. Li / Li ⁺ ) is 150 or more, a region where the potential change is flat is observed. Judge to be done. On the other hand, the broken line is a battery having the same configuration as the above-mentioned non-aqueous electrolyte secondary battery, with an upper limit of 4.6 V (vs. Li / Li ⁺ ) and a lower limit of 2.0 V (vs. Li / Li ⁺ ) for the first time. The dZ / dV curve when the non-aqueous electrolyte secondary battery that has been charged and discharged is charged with a pause of 10 minutes and then the second charge is set to the upper limit of 4.6 V (vs. Li / Li ⁺ ). Is. In the broken line, no peak like the solid line is observed. That is, the non-aqueous electrolyte secondary battery provided with the positive electrode containing the lithium excess type active material is charged until the region where the potential change of 4.5 V (vs. Li / Li ⁺ ) or more is flat is completed even once. In the subsequent charging step at a potential of 4.5 V (vs. Li / Li ⁺ ) or higher, no peak is observed in the dZ / dV curve. In the present specification, the term "normal use" refers to the case where the non-aqueous electrolyte secondary battery is used by adopting the charge / discharge conditions recommended or specified for the non-aqueous electrolyte secondary battery. When a charger for a non-aqueous electrolyte secondary battery is prepared, it means a case where the charger is applied to use the non-aqueous electrolyte secondary battery.

<Calculation method of discharge capacity and charge electricity amount per volume>
In the present specification, the measurement conditions of the press density are as follows. The measurement is performed in the air at room temperature of 20 ° C. or higher and 25 ° C. or lower. FIG. 9 shows a conceptual diagram of the device used for measuring the press density. Prepare a pair of measurement probes 1A and 1B. The measuring probes 1A and 1B have measuring surfaces 2A and 2B obtained by flattening one end of a stainless steel (SUS304) cylinder having a diameter of 8.0 mm (± 0.05 mm) and a pedestal 3A made of stainless steel at the other end. The cylinder is vertically fixed to 3B. A side body 6 provided with a through hole 7 whose inner diameter is adjusted and polished so that the stainless steel cylinder can naturally and slowly descend in the air by gravity is prepared at the center of the acrylic cylinder. The upper surface and the lower surface of the side body 6 are smoothly polished.
One of the measuring probes 1A is placed on a horizontal desk so that the measuring surface 2A faces upward, and the cylindrical portion of the measuring probe 1A is placed in the through hole 7 of the side body 6 so as to cover the side body 6 from above. insert. The other measuring probe 1B is inserted from above the through hole 7 with the measuring surface 2B facing down, and the distance between the measuring surfaces 2A and 2B is set to zero. At this time, the distance between the pedestal 3B of the measuring probe 1B and the pedestal 3A of the measuring probe 1A is measured using a caliper.

Next, the measurement probe 1B is pulled out, 0.3 g of the powder of the sample to be measured (positive electrode active material powder) is charged from the upper part of the through hole 7 with a spatula, and the measurement probe 1B is again placed with the measurement surface 2B facing down. It is inserted from above the through hole 7. Using a manual hydraulic press equipped with a pressure gauge, pressurize from above the measuring probe 1B until the pressure scale of the press reaches 2 MPa. After the scale reaches 2 MPa, no additional pressurization is performed even if the value indicated by the scale decreases. In this state, that is, in a state where the sample to be measured is pressurized until it reaches 400 N, the distance between the pedestal 3B of the measurement probe 1B and the pedestal 3A of the measurement probe 1A is measured again using a caliper. The density of the sample to be measured in a pressurized state from the difference (cm) from the distance before the sample to be measured, the area of the measurement surface (0.5024 cm ² ) and the amount of the sample to be measured (0.3 g). Is calculated, and this is used as the press density (g / cm ³ ).
The discharge capacity and charge electricity amount per volume are calculated by multiplying the press density of the positive electrode active material powder measured as described above by the discharge capacity per mass and the charge electricity amount.

<Configuration of power storage device>
A power storage device in which a plurality of the above-mentioned non-aqueous electrolyte secondary batteries are assembled is also included in one embodiment of the present invention. The power storage device 30 shown in FIG. 10 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of non-aqueous electrolyte secondary batteries 1. The power storage device 30 can be mounted as a power source for an electric vehicle (EV), a hybrid vehicle (HEV), a plug-in hybrid vehicle (PHEV), or the like.

The non-aqueous electrolyte secondary battery according to the present embodiment is manufactured without undergoing a charging process until the end of the overcharge region, and is used without charging until the end of the overcharge region. It is assumed that it will be done. It is preferable that the charging voltage adopted during the charging process during manufacturing and during use is set so that the maximum ultimate potential reached by the positive electrode due to the charging, that is, the upper limit charging potential is equal to or lower than the potential at which the overcharge region starts. The upper limit potential for charging in the initial charge / discharge step and the upper limit potential for charging during use are preferably less than 4.5 V (vs. Li / Li ⁺ ). The upper limit potential for charging can be, for example, 4.40 V (vs. Li / Li ⁺ ). The upper charge potential may be 4.38 V (vs. Li / Li ⁺ ), 4.36 V (vs. Li / Li ⁺ ), or 4.34 V (vs. Li / Li ⁺ ). ), And may be 4.32 V (vs. Li / Li ⁺ ).

First, Examples 1 to 10 and Comparative Example 1 in which the transition metal compounds having the same composition are used and the production conditions of the lithium transition metal composite oxide are changed are shown.

<Preparation of Lithium Transition Metal Composite Oxide>
(Example 1)
In the preparation of the lithium transition metal composite oxide, a hydroxide precursor was prepared by using a reaction crystallization method. First, 578.3 g of nickel sulfate hexahydrate, 56.2 g of cobalt sulfate heptahydrate, and 385.7 g of manganese sulfate pentahydrate were weighed, and all of these were dissolved in 4 L of ion-exchanged water to dissolve Ni: Co. A 1.0 M sulfate aqueous solution having a molar ratio of Mn of 55: 5: 40 was prepared. Next, 2 L of ion-exchanged water was poured into a 5 L reaction vessel, and _N2 gas was bubbled for 30 minutes to remove oxygen contained in the ion-exchanged water. The temperature of the reaction vessel is set to 50 ° C (± 2 ° C), and convection is sufficiently generated in the reaction layer while stirring the inside of the reaction vessel at a rotation speed of 1500 rpm using a paddle blade equipped with a stirring motor. did. The sulfate stock solution was added dropwise to the reaction vessel at a rate of 1.3 mL / min for 50 hours. Here, from the start to the end of the dropping, the pH in the reaction vessel is adjusted by appropriately dropping a mixed alkaline solution consisting of 4.0 M sodium hydroxide, 1.25 M ammonia, and 0.1 M hydrazine. It was controlled to always maintain 10.20 (± 0.1), and a part of the reaction solution was discharged by overflow so that the total amount of the reaction solution did not always exceed 2 L. After the dropping was completed, stirring in the reaction vessel was continued for another 1 hour. After the stirring was stopped, the mixture was allowed to stand at room temperature for 12 hours or more. Next, the hydroxide precursor particles generated in the reaction vessel are separated using a suction filtration device, and the sodium ions adhering to the particles are washed and removed using ion-exchanged water, and an electric furnace is used. Then, the particles were dried at 80 ° C. for 20 hours under normal pressure in an air atmosphere. Then, in order to make the particle size uniform, it was crushed in an agate automatic mortar for several minutes. In this way, a hydroxide precursor having a molar ratio of Ni: Co: Mn of 55: 5: 40 was prepared.

To 2.264 g of the hydroxide precursor, 1.264 g of lithium hydroxide monohydrate and 0.015 g of lithium fluoride were added and mixed well using an automatic agate mortar, and Li :( Ni, Co, Mn. ) Was prepared as a mixed powder having a molar ratio of 120: 100. The addition ratio of lithium fluoride is 2 mol% with respect to the total amount of the Li compound. It was molded at a pressure of 6 MPa using a pellet molding machine to obtain pellets having a diameter of 25 mm. The amount of the mixed powder used for pellet molding was determined by converting so that the assumed mass of the final product was 2.5 g. One of the pellets was placed on an alumina boat having a total length of about 100 mm, installed in a box-type electric furnace (model number: AMF20), and heated in an air atmosphere under normal pressure from room temperature to 900 ° C. over 10 hours. It was fired at 900 ° C. for 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 switched off and the alumina boat was allowed to cool naturally while still in the furnace. As a result, the temperature of the furnace drops to about 200 ° C. after 5 hours, but the subsequent temperature decrease rate is rather gradual. After a day and night, after confirming that the temperature of the furnace was 100 ° C. or lower, the pellets were taken out and crushed in an automatic agate mortar for several minutes in order to make the particle size uniform. In this way, the lithium transition metal composite oxide according to Example 1 was produced.

(Examples 2 to 5, Comparative Example 1)
The addition ratio of lithium fluoride in the mixed powder of hydroxide precursor, lithium hydroxide monohydrate, and lithium fluoride was 5, 8, 10, and 20 mol% with respect to the total amount of Li compound, respectively. The lithium transition metal composite oxides according to Examples 2 to 4 and Comparative Example 1 were prepared in the same manner as in Example 1.
Further, the lithium transition metal composite oxide according to Example 5 was prepared in the same manner as in Example 1 except that lithium fluoride was not added.

(Example 6)
Lithium transition metal composite oxidation according to Example 6 in the same manner as in Example 2 except that the mixed powder of the hydroxide precursor, lithium hydroxide monohydrate, and lithium fluoride was fired at 950 ° C. I made a thing.

(Example 7)
Same as Example 2 except that the molar ratio of Li: (Ni, Co, Mn) in the mixed powder of the hydroxide precursor, lithium hydroxide monohydrate, and lithium fluoride was changed to 130: 100. The lithium transition metal composite oxide according to Example 7 was prepared.

(Examples 8 to 10)
Example 8 is the same as in Example 2 except that a mixed powder in which lithium carbonate, sodium fluoride, and sodium chloride are added in place of lithium fluoride in an amount of 5 mol% with respect to the total amount of the lithium compound is prepared. Lithium transition metal composite oxides according to 10 were prepared.

Next, Examples 11 to 14 and Comparative Example 2 in which the transition metal compound having a different composition is used and the production conditions of the lithium transition metal composite oxide are changed are shown.
(Example 11)
A hydroxide precursor was prepared by changing the molar ratio of Ni: Co: Mn to 40:15:45, and a mixed powder of the hydroxide precursor, lithium hydroxide monohydrate, and lithium fluoride was prepared. The lithium transition metal composite oxide according to Example 11 was prepared in the same manner as in Example 2 except that the molar ratio of Li: (Ni, Co, Mn) was changed to 110: 100.

(Examples 12 to 14)
The procedure was carried out in the same manner as in Example 11 except that a mixed powder was prepared by adding lithium carbonate, sodium fluoride, and sodium chloride in place of lithium fluoride in an amount of 5 mol% based on the total amount of the lithium compound. Lithium transition metal composite oxides according to Examples 12 to 14 were prepared.

(Comparative Example 2)
According to Comparative Example 2 in the same manner as in Example 11 except that the addition ratio of lithium fluoride in the mixed powder of the hydroxide precursor, lithium hydroxide monohydrate, and lithium fluoride was set to 20 mol%. A lithium transition metal composite oxide was prepared.

Further, Examples 15 to 17 and Comparative Examples 3 to 7 in which the production conditions of the lithium transition metal composite oxide are changed by using a transition metal compound having a different composition are shown.
(Example 15)
The lithium transition metal composite oxide according to Example 15 was prepared in the same manner as in Example 2 except that the molar ratio of Ni: Mn was changed to 60:40 to prepare a hydroxide precursor.

(Example 16)
A hydroxide precursor was prepared by changing the molar ratio of Ni: Co: Mn to 35:15:50, and a mixed powder of the hydroxide precursor, lithium hydroxide monohydrate, and lithium fluoride was prepared. The lithium transition metal composite oxide according to Example 16 was prepared in the same manner as in Example 2 except that the molar ratio of Li: (Ni, Co, Mn) was changed to 110: 100.

(Example 17)
A hydroxide precursor was prepared by changing the molar ratio of Ni: Co: Mn to 33:33:33, and a mixed powder of the hydroxide precursor, lithium hydroxide monohydrate, and lithium fluoride was prepared. The lithium transition metal composite oxide according to Example 17 was prepared in the same manner as in Example 2 except that the molar ratio of Li: (Ni, Co, Mn) was changed to 110: 100.

(Comparative Example 3)
The lithium transition metal composite oxide according to Comparative Example 3 was prepared in the same manner as in Example 2 except that the molar ratio of Ni: Co: Mn was changed to 30:15:55 to prepare a hydroxide precursor. ..

(Comparative Example 4)
A hydroxide precursor was prepared by changing the molar ratio of Ni: Co: Mn to 30:10:60, and a mixed powder of the hydroxide precursor, lithium hydroxide monohydrate, and lithium fluoride was prepared. The lithium transition metal composite oxide according to Comparative Example 4 was prepared in the same manner as in Example 2 except that the molar ratio of Li: (Ni, Co, Mn) was changed to 130: 100.

(Comparative Examples 5 and 6)
A hydroxide precursor was prepared by changing the molar ratio of Ni: Co: Mn to 33:33:33, and lithium fluoride was added to the mixed powder of the hydroxide precursor and lithium hydroxide monohydrate. Lithium transition according to Comparative Examples 5 and 6 in the same manner as in Example 2 except that the molar ratio of Li: (Ni, Co, Mn) was changed to 100: 100 with or without addition of each. A metal composite oxide was prepared.

(Comparative Example 7)
Except for changing the molar ratio of Li: (Ni, Co, Mn) in the mixed powder of the hydroxide precursor, lithium hydroxide monohydrate, and lithium fluoride according to Example 1 to 100: 100. The lithium transition metal composite oxide according to Comparative Example 7 was prepared in the same manner as in Example 2.

<Confirmation of crystal structure of lithium transition metal composite oxide>
It was confirmed that the lithium transition metal composite oxide according to the above Examples and Comparative Examples had an α-NaFeO type ₂ crystal structure by matching the diffraction pattern with the structural model in the X-ray diffraction measurement.

<Evaluation of I ₄₉₀ / I ₆₀₀ >
Further, the Raman spectrum of the lithium transition metal composite oxide according to the above Examples and Comparative Examples was measured, and the maximum value in the range of 450 to 520 cm ^-1 was compared with the maximum value I ₆₀₀ in the range of 550 to 650 cm ^-1 . The ratio of I ₄₉₀ (I ₄₉₀ / I ₆₀₀ ) was evaluated. The Raman spectra of the lithium transition metal composite oxides according to Examples 1 to 5 and Comparative Example 1 are shown in FIG.

<Manufacturing of positive electrode for non-aqueous electrolyte secondary battery>
Using the lithium transition metal composite oxide according to the above Examples and Comparative Examples as the positive electrode active material, positive electrodes for non-aqueous electrolyte secondary batteries according to Examples and Comparative Examples were prepared by the following procedure.

Using N-methylpyrrolidone as a dispersion medium, a coating paste in which the positive electrode active material, acetylene black (AB) and polyvinylidene fluoride (PVdF) were kneaded and dispersed at a mass ratio of 90: 5: 5 was prepared. The coating paste was applied to one side of an aluminum foil current collector having a thickness of 20 μm to prepare a positive electrode plate. In addition, the coating thickness of the active material applied per fixed area is set so that the test conditions for obtaining the charge electricity amount and the discharge capacity are the same among the non-aqueous electrolyte secondary batteries according to all the examples and the comparative examples. It was adjusted.

<Manufacturing of non-aqueous electrolyte secondary battery>
A part of the positive electrode for a non-aqueous electrolyte secondary battery produced as described above was cut out, and a test battery, which is a non-aqueous electrolyte secondary battery, was produced by the following procedure.
For the purpose of accurately observing the single behavior of the positive electrode, metallic lithium was used in close contact with the nickel foil current collector for the counter electrode, that is, the negative electrode. Here, a sufficient amount of metallic lithium was placed on the negative electrode so that the capacity of the non-aqueous electrolyte secondary battery was not limited by the negative electrode.

As a non-aqueous electrolyte, LiPF ₆ was dissolved in a mixed solvent having an ethylene carbonate (EC) / ethylmethyl carbonate (EMC) / dimethyl carbonate (DMC) volume ratio of 6: 7: 7 so as to have a concentration of 1 mol / L. The solution was used. As a separator, a polypropylene micropore membrane surface-modified with polyacrylate was used. For the exterior body, a metal resin composite film made of polyethylene terephthalate (15 μm) / aluminum foil (50 μm) / metal-adhesive polypropylene film (50 μm) was used. The electrodes are housed so that the open ends of the positive electrode terminal and the negative electrode terminal are exposed to the outside, and the fusion margin where the inner surfaces of the metal resin composite film face each other is hermetically sealed except for the portion to be the liquid injection hole. After injecting the non-aqueous electrolyte, the injection holes were sealed.

<Initial charge / discharge process>
The non-aqueous electrolyte secondary battery assembled by the above procedure is completed through the initial charge / discharge step. Here, in the initial charge / discharge step, the group was divided into a first group to which the initial charge / discharge condition 1 is applied and a second group to which the initial charge / discharge condition 2 is applied.

(Calculation of discharge capacity per volume)
Using the first group of batteries, the following initial charge / discharge condition 1 was applied and subjected to the initial charge / discharge step. Under 25 ° C., the charge was a constant current constant voltage charge with a current of 0.1 C and a voltage of 4.35 V (vs. Li / Li ⁺ ), and the charge termination condition was the time when the current value decreased to 0.02 C. The charging electricity amount at this time was set to "4.35V charging electricity amount" (mAh / g). The discharge was a constant current discharge with a current of 0.1 C and a final voltage of 2.5 V (vs. Li / Li ⁺ ). This charge / discharge was performed for one cycle. A 10-minute rest process was provided after charging.
The discharge capacity per mass at this time was defined as "4.35 V charge discharge capacity" (mAh / g). On the other hand, the press density of the positive electrode active material powder is measured under the above-mentioned conditions, and the measured press density (g / cm ³ ) is multiplied by the "4.35 V charge discharge capacity" (mAh / g) to per volume. The discharge capacity "4.35V charge discharge capacity" (mAh / cm ³ ) was calculated. Here, the "4.35V charge discharge capacity" (mAh / cm ³ ) is manufactured without going through the charging process until the overcharge area ends, and the charge until the overcharge area ends. It is an index showing the discharge capacity when used in a lower potential range without performing.

(Calculation of the amount of electricity charged per volume)
Using the second group of batteries, the following initial charge / discharge condition 2 was applied and subjected to the initial charge / discharge step. Under 25 ° C., the charge was a constant current constant voltage charge with a current of 0.1 C and a voltage of 4.6 V (vs. Li / Li ⁺ ), and the charge termination condition was the time when the current value decreased to 0.02 C. The discharge was a constant current discharge with a current of 0.1 C and a final voltage of 2.0 V (vs. Li / Li ⁺ ). This charge / discharge was performed for one cycle. A 10-minute rest process was provided after charging.
The difference between the charging electricity amount (mAh / g) at this time and the above-mentioned "4.35V charging electricity amount" (mAh / g) is "the charging electricity amount between 4.35 and 4.6V" (mAh / g). It was calculated as g). By multiplying the above press density (g / cm ³ ) and "charging electricity amount between 4.35 and 4.6V" (mAh / g), the charging electricity amount per volume is "4.35 to 4.6V". The amount of electricity charged during the period ”(mAh / cm ³ ) was calculated. Here, "the amount of electricity charged between 4.35 and 4.6 V" (mAh / cm ³ ) is an index representing the amount of electricity charged in the overcharged region.

The above results are shown in Table 1. Further, FIG. 12 shows the relationship between I ₄₉₀ / I ₆₀₀ and the discharge capacity per volume, in which 1 <Li / Me and Mn / Me <0.55 are ● (compared with Examples 1 to 17). Examples 1 and 2) are shown by ◇ (Comparative Examples 3 and 4), and Li / Me = 1.0 is shown by Δ (Comparative Examples 5 to 7). From FIG. 12, it can be seen that in the composition of 1 <Li / Me and Mn / Me <0.55, there is a correlation between the Raman peak intensity ratio and the discharge capacity per volume. On the other hand, no correlation was found in the compositions of Li / Me = 1.0 and 0.55 ≦ Mn / Me.

The lithium transition metal composite oxides (positive electrode active materials) according to Examples 1 to 5 all have the same composition of transition metal compounds (hydroxyl precursors) containing Ni, Co, and Mn, and also have a Li / Me ratio. Although they are the same, the presence or absence or amount of addition of lithium fluoride, which is a sintering aid, is different. The larger the amount added, the more I ₄₉₀ / I ₆₀₀ tend to decrease, but all of them exceed 0.45, and the discharge capacity per volume at 4.35 V charge exceeds 450 mAh / cm ³ in the overcharge region. It can be seen that the amount of charging electricity per volume exceeds 110 mAh / cm ³ . On the other hand, in Comparative Example 1 in which the amount of lithium fluoride added was 20 mol% with respect to the total amount of the lithium compound, I ₄₉₀ / I ₆₀₀ was less than 0.45, per 4.35 V charge volume. It can be seen that the discharge capacity and the amount of charge electricity per volume in the overcharge region cannot be sufficiently obtained.

Examples 6 and 7 correspond to the example in which the firing temperature of the mixed powder was changed or the Li / Me ratio was changed in Example 2. In both cases, I ₄₉₀ / I ₆₀₀ exceeds 0.45, the discharge capacity per volume when charging at 4.35 V exceeds 450 mAh / cm ³ , and the amount of electricity charged per volume in the overcharge region is 110 mAh / cm ³ . You can see that it exceeds.

Examples 8 to 10 correspond to examples in which the type of sintering aid in Example 2 is changed, and in each case, I ₄₉₀ / I ₆₀₀ exceeds 0.45 and discharge per volume during 4.35 V charging. It can be seen that the capacity and the amount of charge electricity per volume in the overcharge region are high.
Further, comparing Examples 1 to 4, 6 to 10 with Example 5, the positive electrode active materials of Examples 1 to 4, 6 to 10 to which the sintering aid was added did not add the sintering aid. It can be seen that I ₄₉₀ / I ₆₀₀ is smaller than the positive electrode active material of Example 5 and is 0.85 or less, and the discharge capacity per volume at the time of 4.35 V charging is high. Therefore, in order to increase the discharge capacity per volume during 4.35 V charging, it is preferable to set I ₄₉₀ / I ₆₀₀ to 0.45 or more and 0.85 or less.

Examples 11 to 14 and Comparative Example 2 correspond to an example in which the composition of the lithium transition metal composite oxide is changed from Example 2, and Examples 12 to 14 further indicate the type of sintering aid in Example 11. Corresponds to the example of changing. In each case, I ₄₉₀ / I ₆₀₀ is 0.45 or more, and it can be seen that the discharge capacity per volume at the time of 4.35 V charging and the charge electricity amount per volume in the overcharge region are high.
Comparative Example 2 corresponds to an example in which the amount of the sintering aid added in Example 11 was increased. I ₄₉₀ / I ₆₀₀ was less than 0.45, and the discharge capacity per volume when charging at 4.35 V was 389 mAh / cm ³ , which was not sufficient.

Examples 15 to 17 and Comparative Examples 3 to 7 correspond to examples in which the composition of the lithium transition metal composite oxide is further changed from Example 2. From Examples 15 to 17, if the Mn / Me ratio is 0.33 to 0.50, under the condition that I ₄₉₀ / I ₆₀₀ is 0.45, when charging at 4.35 V exceeding 450 mAh / cm ³ . It can be seen that an active material having a discharge capacity per volume and a charge electricity amount per volume in the overcharge region exceeding 110 mAh / cm ³ was obtained.
On the other hand, from Comparative Examples 3 and 4, when the Mn / Me ratio is 0.55 or more, even if I ₄₉₀ / I ₆₀₀ is 0.45 or more, the volume per sufficient 4.35 V charge. It can be seen that the discharge capacity of is not obtained.
Comparative Examples 5 to 7 are active substances in the case of Li / Me = 1, which is not the subject of the present invention. Both I ₄₉₀ / I ₆₀₀ were less than 0.45, and no active material was obtained in which both the discharge capacity per volume at 4.35 V charge and the charge electricity amount per volume in the overcharge region were sufficient.

When the positive electrode active material containing the lithium transition metal composite oxide according to the present invention is used, the charge capacity per volume in the overcharge region is large, a rapid increase in battery voltage is not observed until a higher SOC is observed, and the battery voltage is not observed to increase rapidly. It is possible to provide a non-aqueous electrolyte secondary battery having a large discharge capacity. Therefore, this non-aqueous electrolyte secondary battery is useful as a non-aqueous electrolyte secondary battery for hybrid vehicles, electric vehicles, plug-in hybrid vehicles, and the like.

1 Non-aqueous electrolyte secondary battery 2 Electrode group 3 Battery container 4 Positive electrode terminal 4'Positive lead 5 Negative terminal 5'Negative lead 1A, 1B Measurement probe 2A, 2B Measurement surface 3A, 3B Pedestal 6 Side body 7 Through hole 20 Power storage unit 30 Power storage device

Claims (7)

A positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide.
The lithium transition metal composite oxide is
It has an α-NaFeO type ₂ crystal structure and has an α-NaFeO type 2 crystal structure.
The molar ratio of Li to the transition metal (Me), Li / Me, is 1 <Li / Me.
The transition metal (Me) contains Ni and Mn, or Ni, Co and Mn, and the molar ratio of Mn to Me is Mn / Me of 0.3≤Mn / Me <0.55.
The ratio (I ₄₉₀ / I ₆₀₀ ) of the maximum value I ₄₉₀ in the range of 450 to 520 cm ^-1 to the maximum value I ₆₀₀ in the range of 550 to 650 cm ^-1 in the Raman spectrum is 0.45 or more.
Non-aqueous electrolyte Positive electrode active material for secondary batteries. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, which contains Ni and Mn, or Ni, Co and Mn, and has a molar ratio of Mn to Me of Mn / Me of 0.3 ≦. When a Li compound is mixed with a transition metal compound having Mn / Me <0.55 and fired to produce a lithium transition metal composite oxide having a molar ratio of Li / Me of 1 <Li / Me, A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, to which a sintering aid is added. The positive electrode for a non-aqueous electrolyte secondary battery containing the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 3 is provided, and a diffraction peak is observed in the range of 20 to 22 ° in an X-ray diffraction diagram using CuKα rays for the positive electrode active material contained in the positive electrode. , Non-aqueous electrolyte secondary battery. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 3 is provided, and when charging is performed up to a positive electrode potential of 5.0 V (vs. Li / Li ⁺ ), 4.5 to 5.0 V (vs. Li). A non-aqueous electrolyte secondary battery in which a region where the potential change is relatively flat with respect to the amount of charging electricity is observed within the positive electrode potential range of / Li ⁺ ). The non-aqueous electrolyte secondary battery according to claim 4 or 5, which is used at a potential of less than 4.5 V (vs. Li / Li ⁺ ). The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 4 or 5, wherein the maximum ultimate potential of the positive electrode in the initial charge / discharge step is less than 4.5 V (vs. Li / Li ⁺ ). How to manufacture a secondary battery.

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