JP2019220375A - Positive electrode active material for nonaqueous electrolyte secondary battery, method for manufacturing the same, positive electrode containing the active material, nonaqueous electrolyte secondary battery having the positive electrode, and method for manufacturing the nonaqueous electrolyte secondary battery - Google Patents

Abstract

To provide a positive electrode active material for a nonaqueous electrolyte secondary battery, which shows an excellent initial coulomb efficiency and a superior high-rate discharge performance when used at an electric potential under 4.5 V (vs.Li/Li), and a nonaqueous electrolyte secondary battery.SOLUTION: A positive electrode active material for a nonaqueous electrolyte secondary battery comprises a lithium transition metal composite oxide. The lithium transition metal composite oxide has an α-NaFeOtype crystalline structure, where the mole ratio Li/Me of Li to a transition metal(Me) is 1<Li/Me. The lithium transition metal composite oxide contains Ni, Co and Mn, or Ni and Mn as the transition metal(Me), and the mole ratio Mn/Me of Mn to Me is Mn/Me≥0.45. As to the positive electrode active material, the ratio a/b of a discharge capacity (a) of 4.35 V (vs.Li/Li) to 3.0 V (vs.Li/Li) to a discharge capacity (b) of 3.0 V (vs.Li/Li) to 2.0 V (vs.Li/Li) satisfies 17≤a/b≤25.SELECTED DRAWING: Figure 1

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 containing the active material, a non-aqueous electrolyte secondary battery including the positive electrode, and production of the non-aqueous electrolyte secondary battery About the method.

2. Description of the Related Art In recent years, non-aqueous electrolyte secondary batteries typified by lithium ion batteries having high energy density and high output performance have been strongly demanded for use in vehicles such as hybrid vehicles.
Conventionally, as a positive electrode active material for a non-aqueous electrolyte secondary battery, a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure has been studied, and a non-aqueous electrolyte secondary battery using LiCoO ₂ has been widely put into practical use. I have. The discharge capacity of LiCoO ₂ is about 120 to 130 mAh / g. As the transition metal (Me) constituting the lithium transition metal composite oxide, Mn, which is abundant as an earth resource, is used, and the molar ratio Li / Me of Li to the transition metal constituting the lithium transition metal composite oxide is approximately 1. In addition, a non-aqueous electrolyte secondary battery using a so-called “LiMeO ₂ type” active material in which the molar ratio Mn / Me of Mn in the transition metal is 0.5 or less has also been put to practical use. For example, the discharge capacity of the positive electrode active material containing LiNi _1/2 Mn _1/2 O ₂ or LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is 150 to 180 mAh / g.

On the other hand, among lithium transition metal composite oxides having an α-NaFeO ₂ type crystal structure, the molar ratio of Mn in the transition metal (Me) is large, and the molar ratio of Li to transition metal (Me), Li / Me, is 1 More so-called "lithium-rich" active materials are known. This active material has a relatively flat potential change with respect to the amount of charged electricity within a potential range of 4.5 to 5.0 V (vs. Li / Li ⁺ ) in a charging process performed first after a battery is assembled. The initial charge up to the flat area allows a higher discharge capacity compared to the “LiMeO ₂ type” active material even if the subsequent charge potential is not so noble. Therefore, it has attracted attention (see Patent Document 1).

Patent Literature 1 discloses an active material for a lithium secondary battery including a solid solution of a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure, wherein Li, Co, Ni, and Mn contained in the solid solution are contained. The composition ratio is Li1 _{+ (1/3) xCo1 -} xyNi _(1/2) yMn _{(2/3) x + (1/2) y} (x + y≤1, 0≤y, 1-x −y = z), expressed by..., And the intensity ratio of the diffraction peaks of the (003) plane and the (104) plane measured by X-ray diffraction is I ₍₀₀₃₎ / I _{( 104)} ≧ 1.56, and I ₍₀₀₃₎ / I ₍₁₀₄₎ > 1 at the end of discharge, exceeding 4.3 V (vs. Li ^/ Li ⁺ ) and 4.8 V or less (vs. Li ^/ Li ⁺ ). ) In the positive electrode potential range, where the potential change that appears with respect to the amount of charged electricity is relatively flat When passing through the step of performing initial charging reaching even without, 4.3V (vs.Li/Li ⁺⁾ or less of the lithium secondary battery electric quantity capable discharge in potential region is characterized to be a 177 mAh / g or more Active material. "(Claim 3).

The paragraph [0062] states that the maximum active potential of the positive electrode during charging is 4.3 V (vs. Li ^/ Li ⁺ ) or less when the active material for a lithium secondary battery according to the present invention is used. In order to manufacture a lithium secondary battery capable of taking out a sufficient discharge capacity even if a charging method as described above is adopted, the following is a characteristic of the active material for a lithium secondary battery according to the present invention. It is important to provide a charging step in consideration of the behavior in 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 as the positive electrode and the constant current charging is continued, A region where the potential change is relatively flat is observed over a relatively long period in the range of the potential of 4.3 V to 4.8 V. The charging conditions adopted here are that the current is 0.1 ItA and the voltage ( Positive electrode potential) 4.5 V (vs. Li / L ⁺⁾ Of is a constant-current constant-voltage charging, setting even higher charging voltage, the potential flat region over the relatively long period of time, when the value of x was used 1/3 of the material rarely observed. Conversely, a material value of x exceeds 2/3, becomes shorter even if the potential change is relatively flat areas observed. Further, the conventional Li [Co _{1- 2x Ni} x Mn _x] O ₂ this behavior in _{(0 ≦ x ≦ 1/2} ) material is not observed. this behavior is characteristic of the active material for a lithium secondary battery according to the present invention. " It is described.

On the other hand, when the battery using the “lithium-excess type” active material is used through an initial charging process of 4.5 V (vs. Li ^/ Li ⁺ ) or more, it is compared with the battery using the “LiMeO ₂ type” active material. It is known that the initial coulomb efficiency is low and the high rate discharge performance is inferior.
Therefore, acid treatment of a positive electrode active material is known as a technique for improving the initial coulomb efficiency and high-rate discharge performance of a battery using a “lithium-excess type” active material. (Patent Documents 2 to 6)

Patent Document 2, "the general _{formula: Li 1 + u Ni x Co} y Mn z A t O 2 + α (0.1 ≦ u <0.3,0.03 ≦ x ≦ 0.25,0.03 ≦ y ≦ 0 .25, 0.4 ≦ z <0.6, x + y + z + u + t = 1, 0 ≦ α <0.3, 0 ≦ t <0.1, A is a metal having any valence from divalent to hexavalent A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising a lithium-excess metal composite oxide composed of secondary particles in which primary particles are aggregated. A mixing step of obtaining a lithium mixture by mixing a lithium compound with secondary particles in which primary particles made of at least one of hydroxides, oxyhydroxides, oxides, and carbonates containing cobalt and manganese are aggregated, The lithium mixture is placed in an oxidizing atmosphere at 800 A baking step of baking at a temperature of ５０1050 ° C. to obtain a baked product, and a lithium removal rate obtained by dividing the difference in lithium content of the baked product before and after pickling by the lithium content of the baked product before pickling is 10 to 10. An acid pickling step in which the pickled slurry is subjected to pickling by controlling the pH of the pickled slurry at 30 ° C. at the end of the pickling at 25 ° C. to be 1 to 4 to 1 to 4 and then washed with water; A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: a heat treatment step of heat-treating the fired product after the step at a temperature of 200 to 600 ° C. in an oxidizing atmosphere. ” ) Is described.
Then, "The acid used for this pickling is preferably an acid showing a strong acidity with a high dissociation constant, more preferably one of inorganic acids such as hydrochloric acid, nitric acid and sulfuric acid, and one of hydrochloric acid and sulfuric acid. (Paragraph [0073]), "If a strong acid is not used, it is difficult to extract lithium from the crystal structure, and it is not possible to cause dissolution to form fine irregularities on the surface of primary particles. In some cases, the interfacial resistance cannot be reduced. ”(Paragraph [0074]), and the evaluation of the positive electrode active material was performed by preparing a coin-type battery using Li metal for the negative electrode and performing initial charge / discharge. The charging and discharging were performed at 0.05 C, 4.8 V charging and 2.5 V discharging, and the ratio of the discharging capacity to the charging capacity was defined as the initial charging / discharging efficiency. Using the discharge capacity at the time of charging as a denominator, the load efficiency is defined as the ratio (%) when the discharge capacity at the time of charging and discharging at 0.1 C of charge and 2 C of discharge is taken as the numerator (paragraph [ 0096] to [0101], [0103]).

Patent Literature 3 discloses “a positive electrode active material for a lithium secondary battery including a lithium transition metal composite oxide having an α-NaFeO ₂ structure, wherein the lithium transition metal composite oxide contains the transition metal (Me). A diffraction peak of 2θ = 44 ± 1 ° in an X-ray diffraction pattern using a CuKα radiation source, containing Co, Ni and Mn, wherein the molar ratio Mn / Me of Mn in the transition metal is Mn / Me ≧ 0.5. A positive electrode active material for a lithium secondary battery, wherein the half-value width is 0.265 ° or more and contains a P element. ”(Claim 1) The positive electrode active material for a lithium secondary battery according to claim 1, wherein P is contained by heat treatment after the acid treatment. ”(Claim 3).
Then, a lithium secondary battery using the active material according to each example, which was heat-treated after the above-described phosphoric acid treatment, was manufactured. After performing two cycles of constant current discharge at a final voltage of 2.0 V, a constant current constant voltage charge of a current of 0.2 C and a voltage of 4.3 V and a constant current discharge of a current of 0.5 C and a final voltage of 2.0 V are performed. It describes that a discharge test was performed for 30 cycles, and the discharge capacity at the 30th cycle was recorded as a 0.5C discharge capacity at the 30th cycle (paragraphs [0075] to [0085] and [0123] to [0130]).

Patent Literature 4 discloses “a positive electrode active material for a lithium secondary battery containing a lithium transition metal composite oxide, wherein the lithium transition metal composite oxide has an α-NaFeO ₂ structure, and a transition metal (Me ) Contains Co, Ni and Mn, the molar ratio Li / Me of lithium (Li) to the transition metal is greater than 1.2 and less than 1.6, and the BJH method Has a pore volume of 0.055 cc / g or more and 0.08 cc / g or less in a pore region in which the pore diameter showing the maximum value of the differential pore volume obtained in the above is up to 60 nm, and has a space at 1000 ° C. (Claim 1), "Precursor preparation for preparing a precursor containing Co, Ni and Mn as transition metal elements, showing a single phase belonging to group R3-m". Process, the precursor and L The lithium transition metal composite oxide is produced through a firing step of mixing a salt and heat-treating the mixture at a temperature of 800 ° C. or higher to produce an oxide, and an acid treatment step of treating the oxide with an acid. The method for producing a positive electrode active material for a lithium secondary battery according to any one of Claims 1 to 6. (Claim 9), "The acid treatment step uses sulfuric acid. Method for producing positive electrode active material for lithium secondary battery "(Claim 13).
Further, as the above-described example, a lithium secondary battery using a lithium transition metal composite oxide, sulfuric acid treatment, and drying was used as a positive electrode, and a lithium secondary battery using metal lithium as a negative electrode. As a process, constant-current constant-voltage charging at a current of 0.1 C and a voltage of 4.6 V, and constant-current discharging at a current of 0.1 C and a final voltage of 2.0 V are performed in two cycles. It is described that constant-current constant-voltage charging of 3 V and constant-current discharging at a current of 1 C and a final voltage of 2.0 V were performed, and the amount of discharged electricity was recorded as a 1 C capacity (paragraphs [0076] to [0087]. [0108] to [0115]).

Patent Literature 5 discloses “a positive electrode active material including a lithium transition metal composite oxide having an α-NaFeO ₂ structure, in which the transition metal (Me) is Co, Ni, and Mn. When the molar ratio of Li and transition metal (Me) (Li / Me) is 1 <Li / Me, and the molar ratio of Mn and transition metal (Me) (Mn / Me) is 0.5 <Mn / Me. And a positive electrode active material for a lithium secondary battery characterized by containing Ce ”(Claim 1), and as Examples 1 to 5,“ Lithium transition metal composite oxide Li _{1. 18} Co _0.10 Ni _0.17 Mn _0.55 O ₂ ”was charged into a cerium sulfate solution having a pH of 1.6 and heat-treated at 400 ° C. to produce a lithium-transition metal composite oxide containing Ce. Is described (paragraph [0079] to [0082]). Then, a battery was prepared in which the lithium transition metal composite oxide was used as a positive electrode active material and the negative electrode was metallic lithium, subjected to an initial charge / discharge step of 0.1 C, 4.6 V-2.0 V, and charged to a discharge capacity. Using the value (%) divided by the quantity of electricity as the initial efficiency, 30 cycles of constant current constant voltage charging at 0.2 C and 4.45 V and constant current discharging at 0.5 C and 2.0 V are performed, and the first cycle discharge is performed. Table 1 shows the results of evaluation of the battery with the ratio (%) of the discharge capacity at the 30th cycle to the capacity as the discharge capacity retention ratio (paragraphs [0090] to [0097]).

Patent Document 6 discloses that “including a step of acid-treating a perlithiated metal oxide and a step of doping the acid-treated perlithiated metal oxide with a metal cation, The method for producing a composite cathode active material containing a compound represented by the following Chemical Formula 4 is a method for preparing a composite cathode active material comprising the compound represented by the following Chemical Formula 4: xLi ₂ MO _3- (1-x) LiM′O ₂ , M is at least one metal selected from 4-period and 5-period transition metals having an average oxidation number +4, and M ′ is selected from 4-period and 5-period transition metals having an average oxidation number +3. At least one metal, and 0 <x <1 ”(claim 13). Then, as an _example, after adding a substance of _{0.55Li 2 MnO 3 -0.45LiNi 0.5 Co 0.2} Mn 0.3 O 2 composition in HNO ₃ aqueous solution, the acid treatment and drying at 80 ° C. Then, the acid-treated substance was put into 500 mL of an aqueous solution of nitrate such as Al, and heat-treated at 300 ° C. for 5 hours to obtain an active material doped with a metal cation (paragraphs [0137] to [0147]. ), In the case of the LiNi _0.5 Co _0.2 Mn _0.3 O ₂ active material, the charge-discharge curve does not change under the acid treatment conditions, and Li ions are not desorbed by the reaction with the acid solution. Li ₂ MnO ₃ is the discharge curve by substitution of ^{H +} and Li ⁺ ions in acid solution to the acid treatment has changed significantly (paragraph [0159]), a negative electrode as lithium metal, 0.1 C the initial charge and discharge The initial efficiency was evaluated by charging and discharging at a constant current of 4.7 to 2.5 V, and the charging and discharging currents of 0.5 C, 4.6 V constant voltage and constant current were respectively 0.2, 0.33, 1, 2, and It describes that a constant current discharge of 3 C and 2.5 V was performed to evaluate the rate characteristics (paragraphs [0165] to [0166]).

Japanese Patent No. 4877660 JP 2015-122235 A JP 2016-15298 A International Publication 2015/083330 JP-A-2006-126935 JP 2014-170739 A

As described in Patent Documents 2 to 6, a lithium-rich type active material is used for a positive electrode, and a positive electrode potential is 4.5 V (Li / Li ⁺ ) or higher for initial charge and discharge (hereinafter, also referred to as “overcharge formation”). In a non-aqueous electrolyte secondary battery that is supposed to be used after passing through, the “Lithium-excess type” active material is treated with hydrochloric acid, phosphoric acid, sulfuric acid, nitric acid, or the like. Although it is known that the discharge performance is improved, only the effect when treated with a strong acid is shown, and the effect when overcharging is not performed is unknown.

By the way, non-aqueous electrolyte secondary batteries are required to ensure safety if they are charged more than the full charge state (SOC 100%) by mistake (for example, “GB / T (Chinese Recommended National Standard) ”). As a method of evaluating the improvement in safety, assuming that the charge control circuit is broken, when a current is forcibly applied beyond the full charge state, a sharp increase in the battery voltage is observed. There is a way to record. If no sharp increase in battery voltage is observed until a higher SOC is reached, the safety is evaluated to be improved.
Here, the SOC is an abbreviation of State of Charge, and represents the state of charge of the battery as a ratio of the remaining capacity at that time to the capacity at the time of full charge, and the full charge state is described as "SOC 100%". . In addition, the “first time” charge / discharge in this specification refers to the first charge / discharge performed after injecting a nonaqueous electrolyte. “Initial” charge / discharge refers to one or more times of charging and discharging performed in a manufacturing process before shipment of a battery after injecting a non-aqueous electrolyte.
The potential change appearing with respect to the amount of charge in the positive electrode potential range of more than 4.3 V (vs. Li ^/ Li ⁺ ) and 4.8 V or less (vs. Li ^/ Li ⁺ ) described in Patent Document 1 is compared. The “flat region” is characteristically observed in the “lithium-rich” active material. If charging is performed once even in a region where the potential change is relatively flat, the flat region is not observed even when charging up to 4.8 V is performed next. Therefore, the positive electrode contains a “lithium-excess type” active material, does not perform the initial charge / discharge in which the above-mentioned region where the change in potential is relatively flat is observed, and the above-mentioned change in potential changes the full charge (SOC 100%) in normal use. A non-aqueous electrolyte secondary battery with a positive electrode potential where no flat region is observed was proposed. When the battery is further charged with the SOC exceeding 100%, a region where the potential change is relatively flat is observed for the first time, and no rapid increase in the battery voltage is observed until the battery reaches a higher SOC.

However, the initial coulomb efficiency and high-rate discharge performance when the “lithium excess” active material is used without passing a charge potential of 4.5 V (vs. Li ^/ Li ⁺ ) or more including the initial charge and discharge. It has not been studied so far, and its relationship with acid treatment was unknown.
Therefore, the present invention provides a positive electrode active material for a non-aqueous electrolyte secondary battery, which exhibits excellent initial coulomb efficiency and high rate discharge performance when used at a potential lower than 4.5 V (vs. Li ^/ Li ⁺ ). It is an object to provide a manufacturing method, a positive electrode for a non-aqueous electrolyte secondary battery containing the positive electrode active material, a non-aqueous electrolyte secondary battery including the positive electrode, and a method for manufacturing the non-aqueous electrolyte secondary battery. .

One aspect of the present invention 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 has an α-NaFeO ₂ type crystal structure, The molar ratio Li / Me of Li to the transition metal (Me) is 1 <Li / Me, and the transition metal (Me) contains Ni, Co and Mn, or Ni and Mn, and the molar ratio of Mn to Me is Mn / Me. Is Mn / Me ≧ 0.45, and the positive electrode active material has a discharge capacity (a) from 4.35 V (vs. Li ^/ Li ⁺ ) to 3.0 V (vs. Li ^/ Li ⁺ ) and A nonaqueous electrolyte secondary battery in which the ratio a / b of the discharge capacity (b) from 0 V (vs. Li ^/ Li ⁺ ) to 2.0 V (vs. Li ^/ Li ⁺ ) is 17 ≦ a / b ≦ 25. Positive electrode active material.

Another aspect of the present invention is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide, which has an α-NaFeO ₂ type crystal structure and has a transition metal (Me ), The molar ratio of Li / Me is 1 <Li / Me, and the transition metal (Me) contains Ni, Co and Mn, or Ni and Mn, and the molar ratio of Mn to Me, Mn / Me, is Mn / Me. The lithium transition metal composite oxide with ≧ 0.45 is treated with an acid having a pKa ₁ of 3.1 or more to change from 4.35 V (vs. Li ^/ Li ⁺ ) to 3.0 V (vs. Li ^/ Li ⁺ ). ) And the ratio a / b of the discharge capacity (b) from 3.0 V (vs. Li ^/ Li ⁺ ) to 2.0 V (vs. Li ^/ Li ⁺ ) is 17 ≦ a / b. A positive electrode for a non-aqueous electrolyte secondary battery, producing a positive electrode active material satisfying ≦ 25 It is a method of manufacturing the substance.

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

Still another aspect of the present invention includes the positive electrode for a nonaqueous electrolyte secondary battery, wherein the positive electrode active material contained in the positive electrode is in a range of 20 to 22 ° in an X-ray diffraction diagram using CuKα rays. This is a nonaqueous electrolyte secondary battery in which a diffraction peak is observed. Alternatively, the battery includes the positive electrode for a non-aqueous electrolyte secondary battery, and the positive electrode is charged to reach a positive electrode potential of 5.0 V (vs. Li ^/ Li ⁺ ), and is 4.5 to 5.0 V (vs. This is a non-aqueous electrolyte secondary battery in which a region where the change in potential is relatively flat with respect to the amount of charged electricity is observed within the positive electrode potential range of (Li / Li ⁺ ).

Another aspect of the present invention is the method for manufacturing a nonaqueous electrolyte secondary battery described above, wherein a 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 the nonaqueous electrolyte secondary battery.

According to the present invention, when used at a potential of less than 4.5 V (vs. Li ^/ Li ⁺ ), a positive electrode active material for a nonaqueous electrolyte secondary battery exhibiting excellent initial coulomb efficiency and high rate discharge performance, A manufacturing method, a positive electrode containing the positive electrode active material, a nonaqueous electrolyte secondary battery including the positive electrode, and a method for manufacturing the nonaqueous electrolyte secondary battery can be provided.

The figure explaining that "a diffraction peak is observed in the range of 20 to 22 degrees" in the X-ray diffraction measurement of the lithium-rich type positive electrode active material used for the nonaqueous electrolyte secondary battery. The figure explaining that "the diffraction peak is not observed in the range of 20 to 22 degrees" in the X-ray diffraction measurement of the lithium-rich type positive electrode active material used for the nonaqueous electrolyte secondary battery. The figure which shows the electric potential change with respect to the charge electric quantity of a lithium excess type positive electrode active material. Diagram for explaining “region where potential change is relatively flat with respect to charged electricity amount” External perspective view of a nonaqueous electrolyte secondary battery according to the present embodiment Schematic diagram of a power storage device including a plurality of nonaqueous electrolyte secondary batteries according to the present embodiment

  The configuration, operation and effect of the present invention will be described together with technical ideas. However, the mechanism of action includes an estimation, and its correctness does not limit the present invention. Note that the present invention can be embodied in various other forms without departing from its essential characteristics or main features. Therefore, the embodiments or examples described below are merely examples in all aspects and should not be interpreted in a limited manner. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

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, wherein the lithium transition metal composite oxide has an α-NaFeO ₂ type crystal structure. The molar ratio of Li to transition metal (Me) is 1 <Li / Me, and the transition metal (Me) contains Ni, Co and Mn, or Ni and Mn, and the molar ratio of Mn to Me is Mn / Me is Mn / Me ≧ 0.45, and the positive electrode active material has a discharge capacity (a) from 4.35 V (vs. Li ^/ Li ⁺ ) to 3.0 V (vs. Li ^/ Li ⁺ ) and 3 Non-aqueous electrolyte secondary, wherein the ratio a / b of the discharge capacity (b) from 0.0 V (vs. Li ^/ Li ⁺ ) to 2.0 V (vs. Li ^/ Li ⁺ ) is 17 ≦ a / b ≦ 25 It is a positive electrode active material for batteries.

Another embodiment of the present invention is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which has an α-NaFeO ₂ type crystal structure, and has a molar ratio Li / Li / metal transition metal (Me). A lithium transition where Me is 1 <Li / Me, Ni, Co and Mn, or Ni and Mn as transition metals (Me), and the molar ratio of Mn to Me Mn / Me is Mn / Me ≧ 0.45. The metal composite oxide is treated with an acid having a pKa ₁ of 3.1 or more, and a discharge capacity (a) from 4.35 V (vs. Li ^/ Li ⁺ ) to 3.0 V (vs. Li ^/ Li ⁺ ). And a positive electrode active material having a discharge capacity (b) ratio a / b of 17 ≦ a / b ≦ 25 from 3.0 V (vs. Li ^/ Li ⁺ ) to 2.0 V (vs. Li ^/ Li ⁺ ). This is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery to be produced.

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

  Still another embodiment of the present invention includes the positive electrode for a non-aqueous electrolyte secondary battery, wherein the positive electrode active material contained in the positive electrode has a range of 20 to 22 ° in an X-ray diffraction diagram using CuKα radiation. This is a nonaqueous electrolyte secondary battery in which a diffraction peak is observed.

Still another embodiment of the present invention includes the positive electrode for a non-aqueous electrolyte secondary battery, wherein the positive electrode is charged when the positive electrode potential reaches 5.0 V (vs. Li ^/ Li ⁺ ). This is a non-aqueous electrolyte secondary battery in which a region where a change in potential relative to the amount of charged electricity is relatively flat is observed within a positive electrode potential range of 0.5 to 5.0 V (vs. Li / Li ⁺ ).
The above non-aqueous electrolyte secondary battery is preferably used at a potential of less than 4.5 V (vs. Li ^/ Li ⁺ ).

Yet another embodiment of the present invention is the above-described method for producing a 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 ⁺ ). The method for producing a non-aqueous electrolyte secondary battery described above.

  The above-described positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention (hereinafter, referred to as “the positive electrode active material according to the present embodiment”), and 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”), a positive electrode for a nonaqueous electrolyte secondary battery according to still another embodiment of the present invention ( Hereinafter, “the positive electrode for a non-aqueous electrolyte secondary battery according to the present embodiment”), a non-aqueous electrolyte secondary battery according to still another embodiment of the present invention (hereinafter, “a non-aqueous electrolyte according to the present embodiment”) A method for manufacturing a nonaqueous electrolyte secondary battery according to still another embodiment of the present invention (hereinafter, referred to as a "method for manufacturing a nonaqueous electrolyte secondary battery according to this embodiment"). Will be described in detail below.

<Composition of lithium transition metal composite oxide>
The lithium transition metal composite oxide (hereinafter, referred to as “lithium transition metal composite oxide according to the present embodiment”) contained in the positive electrode active material according to the present embodiment has a general formula Li _{1 + α} Me _1−α O ₂ ( 0 <α, Me is a so-called “lithium-rich” active material represented by Ni and Mn or a transition metal element containing Ni, Mn and Co). Typically, it can be represented as _{Li 1 + α (Ni x Co} y Mn z) 1-α O 2 (x + y + z = 1). In order to prevent a sudden increase in the battery voltage from being observed when the SOC exceeds 100% and the SOC is further increased to a higher SOC, the molar ratio of Li to the transition metal element Li / Me, that is, (1 + α) / (1− α) is preferably at least 1.05, more preferably at least 1.10. In order to suppress a decrease in the discharge capacity, Li / Me is preferably 1.4 or less, more preferably 1.35 or less.
The molar ratio Mn / Me of Mn to the transition metal element Me, that is, z, is 0.45 or more from the viewpoint of stabilization of the layered structure. Further, from the viewpoint of charge / discharge capacity, Mn / Me is preferably 0.65 or less, more preferably 0.6 or less.
The molar ratio Ni / Me of Ni to the transition metal element Me, that is, x, is preferably 0.2 or more and 0.5 or less in order to improve the charge / discharge cycle performance of the nonaqueous electrolyte secondary battery. Is preferred.
The molar ratio Co / Me of Co to the transition metal element Me, that is, y, is preferably 0.03 or more in order to increase the conductivity of the active material particles. In order to reduce the material cost, it is preferably 0.40 or less, more preferably 0.30 or less.
Note that the lithium transition metal composite oxide according to the present embodiment is converted into 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 within a range that does not impair the effects of the present invention. It does not preclude the inclusion of small amounts of other metals, such as the typical transition metals.

<Crystal structure of lithium transition metal composite oxide>
The lithium transition metal composite oxide according to the present embodiment has an α-NaFeO ₂ type crystal structure. The lithium transition metal complex oxide, (before charge and discharge of the active material) after the synthesis, with belonging to the space group P3 1 _12, drawing X-ray diffraction using a CuKα tube, the 2 [Theta] = 20 to 22 ° A superlattice peak (a peak observed in a monoclinic Li [Li _1/3 Mn _2/3 ] O ₂ type) is confirmed in the range. This peak does not disappear unless charging is performed at a potential of 4.5 V (vs. Li ^/ Li ⁺ ) or higher (see FIG. 1). However, once charging is performed at a potential of 4.5 V (vs. Li / Li ⁺ ) or more, the superlattice peak disappears because the symmetry of the crystal changes with the elimination of Li in the crystal. Then, the lithium transition metal composite oxide comes to belong to the space group R3-m (see FIG. 2). Here, P3 ₁ 12 is a crystal structure model obtained by subdividing the atomic positions of the 3a, 3b, and 6c sites in R3-m. When order is recognized in the atomic arrangement in R3-m, the P3 ₁ 12 model Is adopted. Note that “R3-m” is originally described by adding a bar “−” to “3” of “R3m”.

<How to confirm diffraction peaks>
Confirmation that the positive electrode active material according to this embodiment has a diffraction peak observed in the range of 20 to 22 ° in an X-ray diffraction diagram using CuKα radiation is performed according to the following procedure and conditions. Further, “observed” means the maximum value of the intensity within 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 within the diffraction angle of 17 to 19 °. The ratio of the difference (I ₂₁ ) from the minimum value, that is, the value of “I ₂₁ / I ₁₈ ” is in the range of 0.001 to 0.1.
If the sample to be subjected to the measurement is an active material powder before preparation of the positive electrode (powder before charge and discharge), the sample is subjected to the measurement as it is. When a sample is collected from an electrode taken out after disassembly of a battery, a voltage specified by a current value (A) that is one-tenth of a nominal capacity (Ah) of the battery before disassembly of the battery. The battery is discharged at a constant current until the battery voltage reaches the lower limit of the above, and the battery is brought to a discharge end state. As a result of disassembly, if the battery uses a metal lithium electrode as the negative electrode, the additional work described below is not performed, and the positive electrode mixture collected from the positive electrode plate is measured. When the battery is not a battery using a metal lithium electrode as the negative electrode, in order to accurately control the positive electrode potential, after disassembling the battery and taking out the electrode, a battery using the metal lithium electrode as a counter electrode is assembled, and 10 mA per 1 g of the positive electrode mixture is obtained. At a current value of, a constant current discharge is performed until the potential of the positive electrode becomes 2.0 V (vs. Li ^/ Li ⁺ ), adjusted to a discharge end state, and then disassembled. The removed positive electrode plate is sufficiently washed with dimethyl carbonate to adhere the electrolytic solution to the electrodes, dried at room temperature for 24 hours, and then the mixture on the aluminum foil current collector is collected. The collected mixture is lightly loosened in an agate mortar, placed in a sample holder for X-ray diffraction measurement, and provided for measurement. The operations from the disassembly to re-disassembly of the battery, and the washing and drying operations of the positive electrode are performed in an argon atmosphere having a dew point of −60 ° C. or less.

<X-ray diffraction measurement>
In this specification, X-ray diffraction measurement is performed under the following conditions. The 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 divergence slit width is 0.625 deg, the light receiving slit is open, and the scattering slit is 8.0 mm.

FIG. 1 shows that the charging upper limit potential of the nonaqueous electrolyte secondary battery using the positive electrode active material (lithium-excess type positive electrode active material) according to the present embodiment is 4 mA at a current value of 10 mA per 1 g of the positive electrode mixture. Non-aqueous electrolyte secondary battery according to the present embodiment in a discharge end state after performing initial charge / discharge at 35 V (vs. Li ^/ Li ⁺ ) and a discharge lower limit potential of 2.0 V (vs. Li / Li ⁺ ). FIG. 5 is an X-ray diffraction diagram of the active material powder contained in the positive electrode measured by the above procedure. In FIG. 1, diffraction peaks are observed in the range of 20 to 22 °.
FIG. 2 shows that, for a nonaqueous electrolyte secondary battery using the same positive electrode active material as described above, the charging upper limit potential was 4.6 V (vs. Li ^/ Li ⁺ ) at a current value of 10 mA per 1 g of the positive electrode mixture, The active material powder contained in the positive electrode of the non-aqueous electrolyte secondary battery in the discharge end state after charging / discharging at a discharge lower limit potential of 2.0 V (vs. Li / Li ⁺ ) was measured by the above procedure. It is an X-ray diffraction diagram. In FIG. 2, no diffraction peak is observed in the range of 20 to 22 °. That is, in the battery charged at 4.6 V (Li / Li ⁺ ), the diffraction peak in the range of 20 to 22 ° of the lithium-excess type positive electrode active material disappears.
For a non-aqueous electrolyte secondary battery using the same positive electrode active material as described above, the charging upper limit potential was set to 4.6 V (vs. Li ^/ Li ⁺ ) and the discharge lower limit potential was set to 10 mA per 1 g of the positive electrode mixture. as 2.0V (vs.Li/Li ^+), after charge and discharge for the first time, further charging upper limit potential 4.35V (vs.Li/Li ^+), the discharge lower limit voltage 2.0V (vs.Li/ When the active material powder contained in the positive electrode of the non-aqueous electrolyte secondary battery in the discharge end state charged and discharged as Li ⁺ ) was measured by the above procedure, an X-ray diffraction diagram similar to that in FIG. 2 was obtained. . That is, once charging is performed to a potential of 4.5 V or more, 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.

<Discharge capacity ratio of positive electrode active material>
The positive electrode active material according to this embodiment further has a discharge capacity (a) from 4.35 V (vs. Li ^/ Li ⁺ ) to 3.0 V (vs. Li ^/ Li ⁺ ) and a discharge capacity (a) of 3.0 V (vs. Li / Li ⁺ ). / Li ⁺⁾ ratio a / b from 2.0V (vs.Li/Li ⁺⁾ to the discharge capacity (b) is 17 ≦ a / b ≦ 25.

The discharge capacity ratio a / b is determined as follows.
When the evaluation target is an active material, N-methylpyrrolidone is used as a dispersion medium, and an active material, acetylene black (AB) and polyvinylidene fluoride (PVdF) are prepared as a paste for application in a ratio of 90: 5: 5, The coating paste is applied to one surface of an aluminum foil current collector having a thickness of 20 μm to prepare a positive electrode plate, and a nonaqueous electrolyte secondary battery for evaluation is assembled using lithium metal as a counter electrode. At a current value of 15 mA per 1 g of the positive electrode mixture, constant-current constant-voltage charging is performed with a charging upper limit potential of 4.35 V (vs. Li / Li ⁺ ) and a charge termination condition at a time when the current value attenuates to 1/5. . After providing a break of 10 minutes, a discharge lower limit voltage at the same current value is 2.0V (vs.Li/Li ^+), was treated with constant current discharge, the discharge start 3.0V (vs.Li/Li ⁺ ) And the ratio a / b of the discharge capacity (b) from 3.0 V (vs. Li ^/ Li ⁺ ) to 2.0 V (vs. Li ^/ Li ⁺ ).
When the evaluation target is a secondary battery, a constant current discharge is performed at a current value (A) that is 1/10 of the nominal capacity (Ah) of the battery until the battery voltage reaches the lower limit of the specified voltage. Perform the discharge end state. After disassembling the battery in an argon atmosphere having a dew point of −60 ° C. or less and obtaining a positive electrode plate, a nonaqueous electrolyte secondary battery for evaluation using metal lithium as a counter electrode is assembled. The produced battery is discharged at a constant current of 2.0 V (vs. Li ^/ Li ⁺ ) at a current value of 15 mA per 1 g of the positive electrode mixture. Thereafter, constant-current constant-voltage charging is performed with the same current value, a charging upper-limit potential of 4.35 V (vs. Li / Li ⁺ ), and a condition for terminating the charging at a time when the current value attenuates to 1/5. After a pause of 10 minutes, a constant current discharge is performed to 2.0 V (vs. Li ^/ Li ⁺ ) at the same current, and a / b is similarly evaluated.
According to the experimental example described later, when the discharge capacity ratio a / b is 17 ≦ a / b ≦ 25, the positive electrode active material excellent in the initial coulomb efficiency and the high-rate discharge performance, and the present active material containing this positive electrode active material It was found that the positive electrode for a nonaqueous electrolyte secondary battery according to the embodiment and the nonaqueous electrolyte secondary battery according to the present embodiment including the positive electrode were obtained.

<Behavior of non-aqueous electrolyte secondary battery when charged over 4.5 V (vs. Li ^/ Li ⁺ )>
The nonaqueous electrolyte secondary battery according to the present embodiment includes a positive electrode containing the above positive electrode active material, and the positive electrode active material has a peak in the range of 20 to 22 ° in an X-ray diffraction diagram using CuKα radiation. As can be observed, the non-aqueous electrolyte secondary battery according to the present embodiment has a non-aqueous electrolyte secondary battery according to the present embodiment in which the maximum ultimate potential of the positive electrode in the initial charge / discharge step is less than 4.5 V (vs. Li ^/ Li ⁺ ). It is manufactured by a method for manufacturing a water electrolyte secondary battery. In addition, the non-aqueous electrolyte secondary battery according to the present embodiment does not go through a charging process of 4.5 V (vs. Li ^/ Li ⁺ ) or more during normal use. Therefore, when the charge exceeds 4.5 V (vs. Li ^/ Li ⁺ ) and reaches 5.0 V (vs. Li ^/ Li ⁺ ), “4.5 to 5.0 V (vs. .Li / Li ⁺ ) in the positive electrode potential range, a region where the potential change is relatively flat with respect to the amount of charged electricity (hereinafter also referred to as a “region where the potential change is flat”) is observed (FIG. 3). See solid line). Due to the presence of the flat region, in the nonaqueous electrolyte secondary battery according to the present embodiment, a rapid increase in battery voltage is not observed until a higher SOC is reached.

The solid line in FIG. 3 shows the charge when the charge up to 4.6 V (vs. Li ^/ Li ⁺ ) is initially performed on the nonaqueous electrolyte secondary battery including the positive electrode containing the lithium-rich type active material. An example of a curve is shown. Here, the capacity was converted to SOC based on the capacity from the start of charging until reaching 4.35 V (vs. Li / Li ⁺ ) (SOC 100%). It has a relatively flat charging curve until the positive electrode potential rises sharply when the SOC is around 200%. On the other hand, the dashed line in FIG. 3 indicates that after discharging the non-aqueous electrolyte secondary battery charged up to 4.6 V (vs. Li ^/ Li ⁺ ) to 2.0 V (vs. Li ^/ Li ⁺ ), It is a charging curve when the upper limit potential is again set to 4.6 V (vs. Li ^/ Li ⁺ ) and charging is performed. As can be seen from the figure, in a positive electrode that has undergone a charge history of 4.5 V (vs. Li ^/ Li ⁺ ) or more even once, a region where the potential change is flat does not appear.

<Confirmation method of area where potential change is flat>
Here, the following procedure confirms that a region where the potential change is flat is observed. A test battery was prepared in which the positive electrode taken out of the disassembly was used as a working electrode and a lithium metal as a 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 pause of 30 minutes is performed. Thereafter, constant current charging is performed to 5.0 V (vs. Li ^/ Li ⁺ ) at 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 reaching 4.45 V (vs. Li / Li ⁺ ) from the start of charging is Z (= Y / X * 100 (%)). ). The dZ / dV curve is obtained by taking dZ / dV, where the horizontal axis represents the potential, the vertical axis represents the difference in potential change using the denominator, and the numerator the difference in capacitance ratio change.
The solid line in FIG. 4 indicates that a nonaqueous electrolyte secondary battery including a positive electrode using a lithium-rich type active material as a positive electrode active material and a negative electrode using lithium metal was assembled, and the first charge was 4.5 V (vs. Li). / Li ⁺⁾ for a non-aqueous electrolyte secondary battery according to the present embodiment is less than an example of dZ / dV curve when performing charging leading to 4.6V (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 a dZ / dV value when the potential change is large with respect to the capacitance ratio change. The value decreases. In the charging process of the lithium-rich type active material in a potential region exceeding 4.5 V (vs. Li ^/ Li ⁺ ), the value of dZ / dV increases when a region where the potential change is flat starts to be seen. Thereafter, when the region where the potential change is flat ends and the potential rises again, the value of dZ / dV decreases. 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 that it will be. On the other hand, the broken line is a battery having the same configuration as the above-described nonaqueous electrolyte secondary battery, and initially has an upper limit of 4.6 V (vs. Li ^/ Li ⁺ ) and a lower limit of 2.0 V (vs. Li ^/ Li ⁺ ). It is a dZ / dV curve when charging and discharging are performed, and after a pause of 10 minutes, charging is performed with the upper limit of the second charging being 4.6 V (vs. Li / Li ⁺ ). In the broken line, a peak like the solid line is not observed. That is, when a non-aqueous electrolyte secondary battery provided with a positive electrode containing a lithium-rich type active material is charged at least once until the region where the potential change of 4.5 V (vs. Li ^/ Li ⁺ ) is flat is completed, 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 normal use is a case where the nonaqueous electrolyte secondary battery is used by adopting recommended or specified charge / discharge conditions for the nonaqueous electrolyte secondary battery. When a charger for a non-aqueous electrolyte secondary battery is provided, it refers to a case where the non-aqueous electrolyte secondary battery is used by applying the charger.

<Method for producing precursor of lithium transition metal composite oxide>
The method for producing a positive electrode active material according to the present embodiment basically involves converting the metal elements (Li, Ni, Co, Mn) constituting the lithium transition metal composite oxide contained in the active material into the desired composition. It can be obtained by preparing a raw material to be contained and baking it.
In preparing a lithium transition metal composite oxide having a desired composition, a so-called “solid phase method” in which powders of the respective compounds of Li, Ni, Co, and Mn are mixed and fired, or Ni, Co, and Mn are previously mixed with one another A “coprecipitation method” is known in which a coprecipitation precursor that has been present in particles is prepared, and a Li salt is mixed with the precursor and calcined. In the synthesis process using the “solid phase method”, Mn is particularly difficult to uniformly dissolve in Ni and Co, so that it is difficult to obtain a sample in which each element is uniformly distributed in one particle. Previously in such literature, but attempts to solid solution Mn in a part of Ni or Co by the solid phase method _(such as _{LiNi 1-x Mn x O 2} ) have been made a large number, select "coprecipitation method" It is easier to obtain a homogeneous phase at the atomic level. Therefore, in the examples described later, the “coprecipitation method” was adopted.

In the method for producing a positive electrode active material according to this embodiment, the production of the precursor of the lithium transition metal composite oxide is performed by dropping a raw material aqueous solution containing Ni, Co, and Mn, and containing Ni, Co, and Mn in the solution. It is preferable to prepare a precursor by co-precipitating the compound to be formed.
In preparing a coprecipitated precursor, Mn of Ni, Co, and Mn is easily oxidized, and it is not easy to prepare a coprecipitated precursor in which Ni, Co, and Mn are uniformly distributed in a divalent state. , Ni, Co, and Mn at the atomic level tend to be insufficient. Therefore, in the present invention, it is preferable to remove dissolved oxygen in order to suppress the oxidation of Mn distributed in the coprecipitated precursor. As a method of removing dissolved oxygen, a method of bubbling a gas containing no oxygen can be used. Examples of the gas containing no oxygen include, but are not limited to, nitrogen gas, argon gas, carbon dioxide (CO ₂ ), and the like.

The pH in the step of preparing a precursor by coprecipitating a compound containing Ni, Co and Mn in a solution is not limited, but it is intended to prepare the coprecipitated precursor as a coprecipitated hydroxide precursor. In this case, it can be set to 10.5 to 14. In order to increase the tap density, it is preferable to control the pH. By setting the pH to 11.5 or less, the tap density can be 1.00 g / cm ³ or more, and high-rate discharge performance can be improved. Further, by setting the pH to 11.0 or less, the particle growth can be promoted, so that the stirring continuation time after the completion of the dropwise addition of the raw material aqueous solution can be shortened.
When the coprecipitated precursor is to be prepared as a coprecipitated carbonate precursor, the pH can be adjusted to 7.5 to 11. By adjusting the pH to 9.4 or less, the tap density can be increased to 1.25 g / cc or more, and high-rate discharge performance can be improved. Further, by adjusting the pH to 8.0 or less, the particle growth can be promoted, so that the stirring continuation time after completion of the dropwise addition of the raw material aqueous solution can be reduced.

  The raw materials of the coprecipitation precursor include nickel hydroxide, nickel carbonate, nickel sulfate, nickel nitrate, nickel acetate and the like as a Ni source, cobalt sulfate, cobalt nitrate, cobalt acetate and the like as a Co source, and a Mn source. Examples thereof include manganese oxide, manganese carbonate, manganese sulfate, manganese nitrate, manganese acetate and the like.

  The dropping rate of the raw material aqueous solution greatly affects the uniformity of element distribution within one particle of the generated coprecipitated precursor. The preferred dropping rate is affected by the size of the reaction tank, 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 speed is more preferably 10 mL / min or less, most preferably 5 mL / min or less.

Further, when a complexing agent such as NH ₃ is present in the reaction tank and a certain convection condition is applied, after the completion of the dropping of the raw material aqueous solution, the stirring is further continued, so that the rotation of the particles and the rotation in the stirring tank are performed. The revolution is promoted, and in this process, the particles gradually grow concentrically spherically while colliding with each other. That is, the coprecipitation precursor undergoes a two-stage reaction of a metal complex formation reaction when the raw material aqueous solution is dropped into the reaction tank, and a precipitation formation reaction in which the metal complex is generated while the metal complex stays in the reaction tank. It is formed. Therefore, a coprecipitation precursor having a target particle diameter can be obtained by appropriately selecting the time during which stirring is continued after the completion of the dropwise addition of the raw material aqueous solution.

  The preferable duration of stirring after completion of the dropwise addition of the raw material aqueous solution is affected by the size of the reaction tank, stirring conditions, pH, reaction temperature, and the like, but is preferably 0.5 hour or more in order to grow the particles as uniform spherical particles. Is preferable, and 1 hour 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, the time is preferably 30 hours or less, more preferably 25 hours or less, and most preferably 20 hours or less.

<Production method of lithium transition metal composite oxide>
In the method for producing a positive electrode active material according to the present embodiment, it is preferable that the lithium transition metal composite oxide is synthesized by mixing the coprecipitated precursor and a Li compound, followed by firing.
LiF, Li ₂ SO ₄ , or Li ₃ PO ₄ may be used as a sintering aid together with lithium hydroxide and lithium carbonate, which are commonly used as Li compounds. The addition ratio of these sintering aids is preferably 1 to 10 mol% based on the total amount of the Li compound. Note that the total amount of the Li compound is preferably charged in excess of about 1 to 5% in view of the fact that part of the Li compound disappears during firing.

The firing temperature affects the reversible capacity of the active material.
If the firing temperature is too low, crystallization does not proceed sufficiently and the electrode characteristics tend to deteriorate. In one embodiment of the present invention, the firing temperature is preferably 900 ° C. or higher. By setting the temperature to 900 ° C. or higher, active material particles having a high degree of sintering can be obtained, and charge / discharge cycle performance can be improved.

On the other hand, when the firing temperature is too high, a structural change occurs from the layered α-NaFeO ₂ type crystal structure to the rock salt type cubic structure, which is disadvantageous to the movement of lithium ions in the active material during the charge / discharge reaction, and the discharge performance is reduced. descend. In the present invention, the firing temperature is preferably set to 1000 ° C. or less. By controlling the temperature to 1000 ° C. or lower, the charge / discharge cycle performance can be improved.
Therefore, in the method for manufacturing a positive electrode active material according to the present embodiment, the firing temperature is preferably set to 900 to 1000 ° C. in order to improve the charge / discharge cycle performance.

<Acid treatment of positive electrode active material>
In the method for manufacturing a positive electrode active material according to the present embodiment, the positive electrode active material having the discharge capacity ratio a / b of 17 ≦ a / b ≦ 25 is a lithium transition metal composite oxide synthesized by the above method. Can be produced by treating with an acid having a pKa ₁ of 3.1 or more. Acids having a pKa ₁ of 3.1 or more include boric acid (pKa ₁ = 9.14), citric acid (pKa ₁ = 3.1), tartaric acid (pKa ₁ = 3.2), and malic acid (pKa ₁ = 3.4), acetic acid (pKa ₁ = 4.74) and the like. By pKa ₁ is surface treated with lithium-excess active material used at the right concentrations 3.1 or more acid, under conditions that do not overcharge chemical, the active material and discharge capacity was improved than an equivalent or untreated In addition, the initial coulomb efficiency and the high rate discharge performance can be improved.

Detailed mechanism of action of acid treatment in the manufacturing method of the active material in accordance with this embodiment is unknown, the above-mentioned acids, since pKa ₁ is 3.1 or more, the lithium ions in the active material and hydrogen ion The possibility of substitution is low, and it is unlikely that the molar ratio Li / Me of lithium and the transition metal of the active material fluctuates greatly. Therefore, the acid treatment with a strong acid such as hydrochloric acid, phosphoric acid, or sulfuric acid having a small pKa ₁ replaces lithium ions with hydrogen ions (Li has been removed), whereby the above molar ratio Li of the active material before and after the treatment is reduced. It is presumed that a mechanism different from the examples described in Table 1 of Patent Document 2 and Table 1 of Patent Document 3 in which / Me is reduced and the description in paragraph [0159] of Patent Document 6 is working.
According to the experimental examples described below, the active material subjected to the acid treatment according to the present embodiment has a voltage of 4.35 V (vs. Li ^/ Li ⁺ ) to 3.0 V (vs. Li / li ⁺⁾ ratio a / b of the discharge capacity up to (a) and 3.0 V (discharge capacity from vs.Li/Li ⁺⁾ to 2.0V (vs.Li/Li ⁺⁾ (b) is reduced (The discharge capacity b was relatively increased), and the specific surface area was moderately increased. Since it is known that the discharge capacity b appears characteristically in the spinel structure, this acid treatment brings about an appropriate spinel-like crystal structure on the surface of the lithium-rich type active material, thereby making it irreversible during the first charge / discharge. It is presumed that the capacity is reduced to improve the initial coulomb efficiency.
In addition, it is speculated that the increase in the BET specific surface area resulted in moderate irregularities on the particle surface, promoting electrolyte penetration and lithium ion diffusion, improving initial coulombic efficiency, and improving high-rate discharge performance. . The BET specific surface area is preferably 6 m ² / g or less.

The specific procedure of the acid treatment is as follows.
5.0 g of the lithium transition metal composite oxide is added to 200 mL of a predetermined acid aqueous solution having a predetermined hydrogen ion concentration, and the temperature of the aqueous solution is maintained at 50 ° C. and stirred at 400 rpm for 2 hours using a stirrer. After stirring, the lithium transition metal composite oxide is filtered using a suction device, washed with ion-exchanged water, and dried at 80 ° C. overnight under normal pressure.

<Negative electrode material>
The material of the negative electrode to be combined with the positive electrode for a nonaqueous electrolyte secondary battery according to the present embodiment is not limited, and a material that can release or occlude 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 ] O ₄ , an alloy-based material such as Si, Sb, Sn-based, lithium metal, lithium Alloys (lithium-silicon, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, wood alloys and other lithium metal-containing alloys), lithium composite oxides (lithium-titanium), oxidation In addition to silicon, alloys capable of occluding and releasing lithium, carbon materials (for example, graphite, hard carbon, low-temperature fired carbon, amorphous carbon, and the like) are included.

<Positive electrode / negative electrode>
The positive electrode active material and the negative electrode material are preferably powders having 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 for the purpose of improving the high output characteristics of the nonaqueous electrolyte battery, and is preferably 10 μm or more for maintaining the charge / discharge cycle performance. In order to obtain the powder in a predetermined shape, a pulverizer or a classifier is used. For example, mortars, ball mills, sand mills, vibrating ball mills, planetary ball mills, jet mills, counter jet mills, swirling air jet mills, sieves and the like are used. At the time of pulverization, wet pulverization in which an organic solvent such as water or hexane coexists can be used. The classification method is not particularly limited, and a sieve, an air classifier, or the like is used as needed in both dry and wet methods.

  The positive electrode and the negative electrode, in addition to the positive electrode active material and the negative electrode material that are the main components, in addition to the main components, a conductive agent, a binder, a thickener, a filler, and the like, as other components It may be contained.

  The conductive agent is not limited as long as it is an electron conductive material that does not adversely affect battery performance. Usually, natural graphite (scale graphite, flake graphite, earth graphite, etc.), artificial graphite, carbon black, acetylene black, Conductive materials such as Ketjen black, carbon whiskers, carbon fibers, metal (copper, nickel, aluminum, silver, gold, etc.) powders, metal fibers, and conductive ceramic materials can be included as one type or a mixture thereof. .

  Among these, acetylene black is preferred as the conductive agent from the viewpoints of electron conductivity and coatability. The amount of the conductive agent to be added is preferably 0.1% by weight to 50% by weight, particularly preferably 0.5% by weight to 30% by weight based on the total weight of the positive electrode or the negative electrode. In particular, it is preferable to use acetylene black after being pulverized into ultrafine particles of 0.1 to 0.5 μm because the required carbon amount can be reduced. These mixing methods are physical mixing, and ideally, homogeneous mixing. Therefore, a powder mixer such as a V-type mixer, an S-type mixer, a grinder, a ball mill, and a planetary ball mill can be dry- or wet-mixed.

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

  The filler is not limited as long as it does not adversely affect 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 is preferably 30% by weight or less based on the total weight of the positive electrode or the negative electrode.

  The positive electrode and the negative electrode are prepared by kneading the main constituent components (a positive electrode active material in the positive electrode, a negative electrode material in the negative electrode) and other materials to form a mixture, and mixing the mixture with an organic solvent such as N-methylpyrrolidone and toluene or water. After that, the obtained liquid mixture is applied onto a current collector described in detail below, or is pressed and pressed, and is heated at a temperature of about 50 ° C. to about 250 ° C. for about 2 hours to be suitably prepared. . For the application method, for example, roller coating such as an applicator roll, screen coating, doctor blade system, spin coating, it is preferable to apply to any thickness and any shape using a bar coater or the like, It is not limited.

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

<Non-aqueous electrolyte>
The non-aqueous electrolyte used for the non-aqueous electrolyte secondary battery according to the present embodiment is not limited, and those generally proposed for use in a lithium battery or the like can be used. As the non-aqueous solvent used for the non-aqueous electrolyte, propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, cyclic carbonates such as vinylene carbonate; γ-butyrolactone, cyclic esters such as γ-valerolactone; dimethyl carbonate; Chain carbonates such as diethyl carbonate and ethyl methyl carbonate; chain esters such as methyl formate, methyl acetate and methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxy Ethers such as ethane, 1,4-dibutoxyethane and methyldiglyme; nitriles such as acetonitrile and benzonitrile; dioxolane or its derivatives; ethylene sulfide, sulfolane, sultone or its derivatives and the like Or a mixture of two or more thereof, but is not limited thereto.

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, and NaBr. , KClO ₄ , KSCN, etc., an inorganic ion salt containing one kind 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-male _{te, (C 2 H 5)} 4 N-benzoate, (C 2 H 5) 4 N-phthalate, lithium stearyl sulfonate, lithium octyl sulfonate, organic ion salts of lithium dodecyl benzene sulfonate, and the like. These May 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 reduced. It is more preferable that the low-temperature characteristics can be further improved 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 from 0.1 mol / L to 5 mol / L, more preferably from 0.5 mol / L to 2 mol / L in order to reliably obtain a non-aqueous electrolyte battery having high battery characteristics. 0.5 mol / L.

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

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

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

  Further, it is preferable to use the separator in combination with the above-described porous membrane, nonwoven fabric, or the like and a polymer gel because the liquid retention of the electrolyte is improved. That is, by forming a film in which the surface and the micropore wall of the polyethylene microporous membrane are coated with a solvophilic polymer having a thickness of several μm or less and holding an electrolyte in the micropores of the film, the lipophilic polymer is formed. Gels.

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

  Other components of the battery include a terminal, an insulating plate, a battery case, and the like. These components may be the same as those conventionally used.

<Non-aqueous electrolyte secondary battery>
FIG. 5 shows an example of the appearance of the nonaqueous electrolyte secondary battery according to the present embodiment. FIG. 5 is a perspective view of the inside of the container of the rectangular non-aqueous electrolyte secondary battery as seen through. The non-aqueous electrolyte secondary battery 1 is assembled by injecting the non-aqueous electrolyte into the battery container 3 in which the electrode group 2 is stored. The electrode group 2 is formed by winding a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material via a separator. The positive electrode is electrically connected to the positive terminal 4 via a positive electrode lead 4 ', and the negative electrode is electrically connected to the negative terminal 5 via a negative electrode lead 5'.
The shape of the nonaqueous electrolyte secondary battery according to this embodiment is not particularly limited, and examples thereof include a cylindrical battery, a square battery (rectangular battery), and a flat battery.

In the non-aqueous electrolyte secondary battery according to the present embodiment, the charging process in which the region where the potential change is relatively flat within the positive electrode potential range of 4.5 to 5.0 V (vs. Li / Li ⁺ ) is observed. It is manufactured and used without going through the charging process until it is completed.
The non-aqueous electrolyte secondary battery according to the present embodiment does not have a history of charging until the charging process in which the region where the potential change is relatively flat is observed is a positive electrode active material of the battery. However, in the X-ray diffraction diagram using the CuKα ray, a diffraction peak is observed in a range of 20 to 22 °, or the positive electrode of the battery has a positive electrode potential of 5.0 V (vs. Li ^/ Li ⁺ ). When charging was performed up to the range of 4.5 to 5.0 V (vs. Li / Li ⁺ ), a region where the potential change was relatively flat with respect to the amount of charged electricity was observed in the positive electrode potential range. You can check. The details of these confirmation methods are as described above.

  The non-aqueous electrolyte secondary battery of the present embodiment can also be realized as a power storage device in which a plurality of batteries are assembled. FIG. 6 illustrates an example of a power storage device. In FIG. 6, power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of nonaqueous electrolyte secondary batteries 1. The power storage device 30 can be mounted as a power source for vehicles such as an electric vehicle (EV), a hybrid vehicle (HEV), and a plug-in hybrid vehicle (PHEV).

(Example 1)
<Preparation of lithium transition metal composite oxide>
284 g of nickel sulfate hexahydrate, 303 g of cobalt sulfate heptahydrate, and 443 g of manganese sulfate pentahydrate were weighed and dissolved in 4 L of ion-exchanged water, and the molar ratio of Ni: Co: Mn was 27: A 1.0 M aqueous sulfate solution at 27:46 was prepared.
Next, 2 L of ion-exchanged water was poured into a 5 L reaction tank, and oxygen contained in the ion-exchanged water was removed by bubbling Ar gas for 30 minutes. The temperature of the reaction vessel was set to 50 ° C (± 2 ° C), and the inside of the reaction vessel was stirred at a rotation speed of 1500 rpm using a paddle blade equipped with a stirring motor, so that convection occurred sufficiently in the reaction layer. did. The sulfate aqueous solution was dropped into the reaction tank at a rate of 3 mL / min. Here, during the period from the start to the end of the dropping, a mixed alkali solution consisting of 4.0 M sodium hydroxide, 0.5 M ammonia water, and 0.2 M hydrazine is appropriately added dropwise to adjust the pH in the reaction tank. Was controlled to always maintain 9.8 (± 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 completion of the dropwise addition, stirring in the reaction tank was continued for another 3 hours. After stopping the stirring, the mixture was allowed to stand at room temperature for 12 hours or more.
Next, using a suction filtration device, the hydroxide precursor particles generated in the reaction tank are separated, and further, sodium ions adhering to the particles are washed and removed using ion-exchanged water, and an electric furnace is used. Then, it was dried at 80 ° C. for 20 hours under normal pressure in an air atmosphere. Then, in order to make the particle size uniform, the mixture was ground for several minutes in an automatic mortar made of agate. Thus, a hydroxide precursor was produced.

To 1.852 g of the hydroxide precursor, 0.971 g of lithium hydroxide monohydrate was added and mixed well using an agate automatic mortar, and the molar ratio of Li: (Ni, Co, Mn) was 130: A mixed powder was prepared so as to be 100. Using a pellet molding machine, the mixture was molded at a pressure of 6 MPa to obtain a pellet having a diameter of 25 mm. The amount of the mixed powder used for the pellet molding was determined by converting the mass of the assumed final product to 2 g. One of the pellets was placed on an alumina boat having a total length of about 100 mm, placed in a box-type electric furnace (model number: AMF20), and heated from normal temperature to 900 ° C. in an air atmosphere under normal pressure for 10 hours. It was baked at 900 ° C. for 5 hours. The inner dimensions of the box-type electric furnace are 10 cm in length, 20 cm in width, and 30 cm in depth, and heating wires are inserted at intervals of 20 cm in the width direction. After firing, the heater was turned off and the alumina boat was allowed to cool naturally while being kept in the furnace. As a result, the temperature of the furnace drops to about 200 ° C. after 5 hours, but the rate of cooling thereafter is somewhat slow. After one day and night, it was confirmed that the temperature of the furnace was 100 ° C. or lower, and then the pellets were taken out and lightly loosened with an agate mortar to make the particle diameter uniform.
Thus, a lithium transition metal composite oxide Li _1.13 Ni _0.235 Co _0.235 Mn _0.40 O ₂ was produced.

<Acid treatment of active material>
5.0 g of the above-mentioned lithium transition metal composite oxide was added to 200 mL of an aqueous citric acid solution having a hydrogen ion concentration of 0.05 M, and the temperature of the aqueous solution was maintained at 50 ° C., and stirred at 400 rpm for 2 hours using a stirrer. After stirring, the positive electrode active material was filtered using a suction device, washed with ion-exchanged water, and then dried at 80 ° C. overnight under normal pressure to prepare an acid-treated active material according to Example 1. . The BET specific surface area was 5.8 m ² / g.

(Examples 2 and 3)
Examples 2 and 3 were performed in the same manner as in Example 1 except that the acid treatment of the active material was performed using a boric acid aqueous solution having a hydrogen ion concentration of 0.05 M or a tartaric acid aqueous solution having a hydrogen ion concentration of 0.05 M instead of citric acid. did. BET specific surface area were respectively 4.6m ² /g,5.5m ² / g.

(Comparative Example 1)
An active material according to Comparative Example 1 was produced in the same manner as in Example 1, except that the active material was not subjected to an acid treatment. The BET specific surface area was 2.3 m ² / g.

(Comparative Examples 2 to 5)
Active materials according to Comparative Examples 2 to 4 in the same manner as in Example 1 except that the acid treatment of the active material was performed using a sulfuric acid aqueous solution having a hydrogen ion concentration of 0.05 M, 0.03 M, and 0.01 M, respectively. Was prepared, and an active material according to Comparative Example 5 was produced in the same manner as in Comparative Example 4 except that the acid treatment time was changed to 10 minutes. The BET specific surface area of Comparative Example 2 was 7.4 m ² / g.

(Comparative Examples 6 to 8)
Active materials according to Comparative Examples 6 and 7 were prepared in the same manner as in Example 1, except that the acid treatment of the active material was performed using a phosphoric acid aqueous solution having a hydrogen ion concentration of 0.1 M and 0.01 M, respectively. An active material according to Comparative Example 8 was produced in the same manner as in Comparative Example 7, except that the acid treatment time was changed to 10 minutes. The BET specific surface area of Comparative Example 6 was 5.7 m ² / g.

(Comparative Examples 9, 10)
Active materials according to Comparative Examples 9 and 10 were produced in the same manner as in Example 1, except that the acid treatment of the active material was performed using aqueous tartaric acid solutions having hydrogen ion concentrations of 0.1 M and 0.05 M, respectively. BET specific surface area were respectively 7.1m ² /g,6.5m ² / g.

(Examples 4, 5 and Comparative Example 11)
A hydroxide precursor having a molar ratio of Ni: Co: Mn of 40: 5: 55 was prepared, and a mixed powder was prepared such that a molar ratio of Li: (Ni, Co, Mn) was 120: 100. Except that, the active materials according to Examples 4, 5 and Comparative Example 11 were produced in the same manner as Examples 1 and 2 and Comparative Example 1, respectively.

(Example 6 and Comparative Example 12)
Example 6 and Comparative Example 12 were carried out in the same manner as Example 4 and Comparative Example 11, respectively, except that the mixed powder was prepared such that the molar ratio of Li: (Ni, Co, Mn) was 130: 100. An active material was prepared.

(Comparative Examples 13 to 15)
A hydroxide precursor having a molar ratio of Ni: Co: Mn of 35:25:40 is prepared, and a mixed powder is prepared such that a molar ratio of Li: (Ni, Co, Mn) is 120: 100. Except that, the active materials according to Comparative Examples 13 to 15 were produced in the same manner as in Examples 1 and 2 and Comparative Example 1, respectively.

(Comparative Examples 16 and 17)
Except that a mixed powder of the hydroxide precursor according to Example 4 and lithium hydroxide monohydrate was prepared such that the molar ratio of Li: (Ni, Co, Mn) was 100: 100. In the same manner as in Example 4 and Comparative Example 11, active materials according to Comparative Examples 16 and 17 were produced.

(Comparative Examples 18 to 20)
A hydroxide precursor having a molar ratio of Ni: Co: Mn of 33:33:33 was prepared, and the hydroxide precursor and lithium hydroxide monohydrate were combined with Li: (Ni, Co, Except that the mixed powder was prepared such that the molar ratio of Mn) was 100: 100, active materials according to Comparative Examples 18 to 20 were produced in the same manner as in Examples 1 and 2 and Comparative Example 1, respectively.

<Confirmation of crystal structure>
The active materials according to the above Examples and Comparative Examples were subjected to powder X-ray diffraction measurement using an X-ray diffractometer (manufactured by Rigaku, model name: MiniFlex II). The active materials according to all Examples and Comparative Examples had an α-NaFeO ₂ type crystal structure. In addition, it was confirmed that the diffraction peaks were observed in the range of 20 to 22 ° for the active materials (“lithium-excess type” active materials) according to all Examples and Comparative Examples except Comparative Examples 16 to 20.

<Preparation of positive electrode>
Coating in which N-methylpyrrolidone is used as a dispersion medium and the active materials, acetylene black (AB) and polyvinylidene fluoride (PVdF) according to the above Examples and Comparative Examples are kneaded and dispersed at a mass ratio of 90: 5: 5. Paste was prepared. The coating paste was applied to one surface of a 20-μm-thick aluminum foil current collector to produce positive electrodes according to Examples and Comparative Examples. In addition, the mass and applied thickness of the active material applied per fixed area were unified so that the test conditions were the same for all the non-aqueous electrolyte secondary batteries according to Examples and Comparative Examples described later.

<Preparation of negative electrode>
A negative electrode was prepared by disposing a metallic lithium foil on a nickel current collector. The amount of the metallic lithium was adjusted so that the capacity of the battery was not limited by the negative electrode when combined with the positive electrode plate.

<Assembly of non-aqueous electrolyte secondary battery>
Using the positive electrodes according to the respective examples and comparative examples, a non-aqueous electrolyte secondary battery was assembled in the following procedure.
As an electrolytic solution, LiPF ₆ was dissolved in a mixed solvent having a volume ratio of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) of 6: 7: 7 so that the concentration became 1 mol / L. The solution was used. A polypropylene microporous membrane surface-modified with polyacrylate was used as a separator. A metal resin composite film composed of polyethylene terephthalate (15 μm) / aluminum foil (50 μm) / metal adhesive polypropylene film (50 μm) was used for the outer package. The positive electrode according to each of the examples and the comparative examples, and the negative electrode are housed in the exterior body through the separator so that the open ends of the positive terminal and the negative terminal are exposed to the outside, and the inner surface of the metal-resin composite film. The non-aqueous electrolyte secondary battery was assembled by sealing hermetically sealed portions except for the portion serving as a liquid injection hole, except for the portion that would be a liquid injection hole, and after injecting the electrolytic solution, sealing the liquid injection hole.

<Confirmation of initial coulomb efficiency>
The assembled non-aqueous electrolyte secondary battery was subjected to an initial charge / discharge step at 25 ° C. to confirm initial coulomb efficiency. Charging was performed at a constant current and constant voltage with a current value of 15 mA (corresponding to 0.1 C) per gram of the positive electrode mixture and an upper limit potential of 4.35 V (vs. Li / Li ⁺ ). / 5. The discharge was a constant current discharge at the same current value and a lower limit potential of 2.85 V (vs. Li ^/ Li ⁺ ). Here, a pause process of 10 minutes was provided after charging and after discharging, respectively, the charge capacity and the discharge capacity (0.1 C discharge capacity) were confirmed, and the ratio of the discharge capacity to the charge capacity was defined as the initial coulomb efficiency.

<Measurement of discharge capacity ratio a / b>
Next, the discharge capacity ratio a / b was measured. Charging was performed at a constant current and constant voltage with a current value of 15 mA (corresponding to 0.1 C) per gram of the positive electrode mixture and an upper limit potential of 4.35 V (vs. Li / Li ⁺ ). / 5. A pause process of 10 minutes was provided, and the discharge was a constant current discharge of 2.0 V (vs. Li ^/ Li ⁺ ) at the same current value. Here, 4.35V (vs.Li/Li ⁺⁾ from the 3.0V (vs.Li/Li ⁺⁾ to the discharge capacity (a) and 3.0V (vs.Li/Li ⁺⁾ 2.0V ( vs. Li ^/ Li ⁺ ) to determine the ratio a / b of the discharge capacity (b).
In this example and the comparative example, when the above-mentioned discharge capacity ratio a / b was evaluated, even if the charge / discharge was performed at 0.1 C, the same a / b as in the case of the charge / discharge at 0.02 C was obtained. After confirming that it was obtained, the above measurement conditions were set.

<Confirmation of high rate discharge performance>
Furthermore, high rate discharge performance was confirmed. Charging was performed at a current value of 15 mA per 1 g of the positive electrode mixture and at a constant current and constant voltage with an upper limit potential of 4.35 V (vs. Li / Li ⁺ ). did. A pause process for 10 minutes was provided, and the discharge was a constant current discharge at a cutoff voltage of 2.85 V at a current of 300 mA (corresponding to 2 C) per gram of the positive electrode mixture. The ratio of the discharge capacity (2C discharge capacity) at this time to the above 0.1C discharge capacity was defined as high-rate discharge performance (2C / 0.1C).

<Confirmation of diffraction peak of positive electrode active material>
Based on the above-described method for confirming the diffraction peak, the nonaqueous electrolyte secondary battery according to the example in the discharge state was disassembled, the positive electrode mixture was taken out, and X-ray diffraction measurement using CuKα radiation was performed. In all the examples, diffraction peaks were observed in the range of 20 to 22 °.

  Table 1 shows the above measurement results.

From Table 1, it can be seen from the comparison between Examples 1 and 2 and Comparative Example 1 that the lithium-rich active material was acid-treated with citric acid (pKa ₁ = 3.1) or boric acid (pKa ₁ = 9.14). The non-aqueous electrolyte secondary batteries according to Examples 1 and 2 subjected to charge and discharge of less than 4.5 V (vs. Li / Li ⁺ ) using the positive electrode active material according to Comparative Example 1 not subjected to the acid treatment. It can be seen that the initial coulomb efficiency and the high rate discharge performance are improved while maintaining the 0.1 C capacity as compared to the battery. The batteries according to Examples 1 and 2 had a discharge capacity (a) from 4.35 V (vs. Li ^/ Li ⁺ ) to 3.0 V (vs. Li ^/ Li ⁺ ) and a discharge capacity (a) of 3.0 V (vs. Li ^/ Li ⁺ ). ⁺ ) To 2.0 V (vs. Li ^/ Li ⁺ ), the ratio a / b of the discharge capacity (b) was in the range of 17 to 25, whereas the battery according to Comparative Example 1 had a / B was greater than 25. The active materials of Examples 1 and 2 had a larger specific surface area than the active material of Comparative Example 1.

Comparative Examples 2 to 5 show the characteristics of the battery when the acid species was changed to sulfuric acid (pKa ₁ = −3) and the acid treatment was performed at various hydrogen ion concentrations and / or treatment times, and the 0.1 C capacity was shown. In both cases, the initial coulomb efficiency and the high-rate discharge performance did not exceed Comparative Example 1 in comparison with Comparative Example 1 in which no acid treatment was performed. The discharge capacity ratio a / b was smaller than 17 or larger than 25.

In Comparative Examples 6 to 8, the acid species was changed to phosphoric acid (pKa ₁ = 2.12), and the lithium-excess type active material was subjected to acid treatment by changing the hydrogen ion concentration and / or the treatment time, and used the positive electrode active material. 4 shows the characteristics of the battery in the case. Again, the 0.1 C capacity was lower than Comparative Example 1 in which none of the acid treatment was performed, and both the initial coulomb efficiency and the high-rate discharge performance did not exceed Comparative Example 1. The discharge capacity ratio a / b was smaller than 17 or larger than 25.

Example 3 and Comparative Examples 9 and 10 are examples relating to a battery having a positive electrode active material that was acid-treated with tartaric acid (pKa ₁ = 3.2) having a different hydrogen ion concentration.
In Example 3, the capacity of 0.1 C was substantially the same as that of Comparative Example 1 not treated with an acid, and the initial coulomb efficiency and the high-rate discharge performance were improved. Although the Coulomb efficiency was improved as compared with Example 3, the 0.1 C capacity shown in Comparative Example 1 could not be maintained, and the high rate discharge performance was not improved from Comparative Example 1. The discharge capacity ratio a / b was in the range of 17 or more and 25 or less in the battery of Example 3 having the positive electrode active material treated with tartaric acid having a low hydrogen ion concentration. Batteries of Comparative Examples 9 and 10 having positive electrodes treated with high tartaric acid were smaller than 17. The active material of Example 3 had a smaller specific surface area than the active materials of Comparative Examples 9 and 10.
From the above, it can be seen that even when an acid treatment with a pKa ₁ of 3.1 or more is performed, it is necessary to appropriately select the hydrogen ion concentration of the acid solution and satisfy a predetermined discharge capacity ratio a / b.

In Examples 4 and 5 and Comparative Example 11, the composition (Li / Me = 1.3, Mn / Me = 0.48) of the lithium-rich type active material according to Examples 1 and 2 and Comparative Example 1 Example 6 and Comparative Example 12 correspond to Examples 4 and 11 in which the composition ratio was changed to another composition having a larger composition ratio (Li / Me = 1.2, Mn / Me = 0.55). This corresponds to an example in which the Li ratio was changed (Li / Me = 1.3, Mn / Me = 0.55) without changing Mn / Me of the above composition.
The characteristics of the batteries according to Examples 4 and 5 were such that the active material had the same composition and all of the 0.1 C discharge capacity, the initial Coulomb efficiency, and the high-rate discharge performance were higher than those of Comparative Example 11 in which the acid treatment was not performed. This indicates that the discharge capacity ratio a / b is in the range of 17 or more and 25 or less. The characteristics of the battery according to Example 6 also exceeded those of Comparative Example 12 in which the active material had the same composition and was not subjected to the acid treatment, and the discharge capacity ratio a / b was 17 or more and 25 or more. It turns out that it is in the following ranges. Therefore, it can be seen that even in an active material having a composition range where Mn / Me is larger, the specification of a / b is related to an improvement in battery characteristics.

In Comparative Examples 13 to 15, the compositions (Li / Me = 1.3, Mn / Me = 0.48) of the lithium-excess type active materials according to Examples 1 and 2 and Comparative Example 1 were more changed. This corresponds to an example in which the composition is changed to another small composition (Li / Me = 1.2, Mn / Me = 0.40).
Regarding the characteristics of the batteries according to Comparative Examples 13 and 14 subjected to the acid treatment, only the initial coulomb efficiency was improved compared to Comparative Example 15 not subjected to the acid treatment, and the high-rate discharge performance was not improved.
Therefore, even when the discharge capacity ratio a / b satisfies 17 or more and 25 or less as in the active material according to Comparative Example 13, the effect of the present invention is not exhibited when Mn / Me is too small.

  Comparative Examples 16 and 17 are not active materials having a lithium-rich composition in which lithium is excessive with respect to the transition metal, but the composition ratio of Mn was increased (Li / Me = 1, Mn / Me = 0). .55), both of which have a 0.1 C capacity, a low high rate discharge performance, and a discharge capacity ratio a / b outside the range of the present invention.

  Comparative Examples 18 to 20 are examples in which a lithium transition metal composite oxide of Li / Me = 1 and Ni: Co: Me = 33: 33: 33, which has already been put to practical use, was used as the positive electrode active material. Comparative Example 19, which was treated with boric acid, had better battery characteristics than Comparative Example 20, which was not treated with acid. Comparative Example 18, which was treated with citric acid, had a discharge capacity of 0.1 C and a high rate discharge performance. And the correlation between each battery characteristic and the discharge capacity ratio a / b is not observed.

The active material for a non-aqueous electrolyte secondary battery according to the present invention exhibits excellent initial Coulomb efficiency and high-rate discharge performance when used in a potential range of less than 4.5 V (vs. Li ^/ Li ⁺ ). Therefore, this non-aqueous electrolyte secondary battery is used as a battery for a hybrid vehicle (HEV), a plug-in hybrid vehicle (PHEV), and an electric vehicle (EV) that require high safety, efficiency, and high output. , High usefulness.

DESCRIPTION OF SYMBOLS 1 Non-aqueous electrolyte secondary battery 2 Electrode group 3 Battery container 4 Positive terminal 4 'Positive lead 5 Negative terminal 5' Negative lead 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,
having an α-NaFeO ₂ type crystal structure,
The molar ratio Li / Me of Li to the transition metal (Me) is 1 <Li / Me;
Ni, Co and Mn, or Ni and Mn as transition metals (Me); the molar ratio of Mn to Me Mn / Me is Mn / Me ≧ 0.45;
The positive electrode active material has a discharge capacity (a) of 4.35 V (vs. Li ^/ Li ⁺ ) to 3.0 V (vs. Li ^/ Li ⁺ ) and a discharge capacity of 3.0 V (vs. Li ^/ Li ⁺ ) of 2 V. The ratio a / b of the discharge capacity (b) up to 0.0 V (vs. Li / Li ⁺ ) is 17 ≦ a / b ≦ 25;
Cathode active material for non-aqueous electrolyte secondary batteries. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide,
having an α-NaFeO ₂ type crystal structure,
The molar ratio Li / Me of Li to the transition metal (Me) is 1 <Li / Me;
A lithium transition metal composite oxide containing Ni, Co and Mn, or Ni and Mn as a transition metal (Me) and having a molar ratio Mn to Me of Mn / Me of Mn / Me ≧ 0.45, and pKa ₁ of 3 Discharge capacity (a) from 4.35 V (vs. Li ^/ Li ⁺ ) to 3.0 V (vs. Li ^/ Li ⁺ ) and 3.0 V (vs. Li / Li) ⁺ ) For a non-aqueous electrolyte secondary battery for producing a positive electrode active material having a discharge capacity (b) ratio a / b of 17 ≦ a / b ≦ 25 from 2.0 V (vs. Li ^/ Li ⁺ ). A method for producing a positive electrode active material.   A positive electrode for a non-aqueous electrolyte secondary battery, comprising 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, wherein the positive electrode active material contained in the positive electrode has a diffraction peak in a range of 20 to 22 ° in an X-ray diffraction diagram using CuKα radiation. , Non-aqueous electrolyte secondary batteries. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 3, wherein the positive electrode has a positive electrode potential of 5.0 V (vs. Li ^/ Li ⁺ ) when charged to 4.5 to 5.0 V ( vs. Li ^/ Li ⁺ ), a non-aqueous electrolyte secondary battery in which a region where the change in potential is relatively flat with respect to the amount of charged electricity is observed in the positive electrode potential range of Li ^/ Li ⁺ ). The nonaqueous electrolyte secondary battery according to claim 4, which is used at a potential of less than 4.5 V (vs. Li ^/ Li ⁺ ). The method for producing a nonaqueous electrolyte secondary battery according to any one of claims 4 to 6, wherein a maximum ultimate 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.