JP7043989B2 - 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 provided with the positive electrode, and a method for producing the non-aqueous electrolyte secondary battery. - Google Patents

Description

The present invention comprises 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 provided with the positive electrode, and the non-aqueous electrolyte secondary battery. Regarding the method.

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 in-vehicle applications such as hybrid automobiles.
Conventionally, as a positive electrode active material for a non-aqueous electrolyte secondary battery, a lithium transition metal composite oxide having an α-NaFeO type ₂ crystal structure has been studied, and a non-aqueous electrolyte secondary battery using LiCoO ₂ has been widely put into practical use. There is. The discharge capacity of LiCoO ₂ is about 120 to 130 mAh / g. Mn, which is abundant as an earth resource, is used as the transition metal (Me) constituting the lithium transition metal composite oxide, and the molar ratio of Li to the transition metal constituting the lithium transition metal composite oxide is approximately 1. There is also a non-aqueous electrolyte secondary battery using a so-called "LiMeO type ₂ " active material in which the molar ratio Mn / Me of Mn in the transition metal is 0.5 or less. For example, the discharge capacity of the positive electrode active material containing LiNi _1/2 Mn _1/2 O ₂ and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is 150 to 180 mAh / g.

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

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

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

On the other hand, when a battery using a "lithium excess type" active material is used after an initial charging process of 4.5 V (vs. Li / Li ⁺ ) or higher, it is compared with a battery using a "LiMeO type ₂ " active material. Therefore, 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)

In Patent Document 2, "general formula: Li _{1 + u} Ni _{x Coy Mn z At} 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 a valence from divalent to hexavalent. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which is represented by at least one of the elements) and is composed of a lithium excess metal composite oxide composed of secondary particles in which primary particles are aggregated, and is at least nickel. , A mixing step of mixing a lithium compound with a secondary particle in which primary particles consisting of at least one of a hydroxide containing cobalt and manganese, an oxyhydroxide, an oxide, and a carbonate are aggregated to obtain a lithium mixture. The difference in the lithium content of the calcined product before and after pickling and the calcining step of calcining the lithium mixture at a temperature of 800 to 1050 ° C. in an oxidizing atmosphere to obtain a calcined product is the difference between the calcined product before pickling. The calcined product was subjected to pickling by controlling the lithium removal rate divided by the lithium content to be 10 to 30% and the pH of the pickled slurry at the end of pickling to be 1 to 4 based on 25 ° C. For non-aqueous electrolyte secondary batteries, which comprises a pickling step of washing with water and a heat treatment step of heat-treating the calcined product that has undergone the pickling step at a temperature of 200 to 600 ° C. in an oxidizing atmosphere. A method for producing a positive electrode active material. ”(Claim 5) is described.
Then, "The acid used for this pickling is preferably an acid having a high dissociation constant and showing strong acidity, more preferably any of inorganic acids such as hydrochloric acid, nitrate and sulfuric acid, and preferably either hydrochloric acid or sulfuric acid. It is more preferable. ”(Paragraph [0073]),“ Therefore, when a strong acid is not used, it is difficult to extract lithium from the crystal structure, and it is not possible to cause dissolution that forms fine irregularities on the surface of the primary particles. , It may not be possible to reduce the interfacial resistance. ”(Paragraph [0074]). The charge and discharge were performed at 0.05 C, 4.8 V charge and 2.5 V discharge, and the ratio of the discharge capacity to the charge capacity was taken as the initial charge / discharge efficiency, and the charge / discharge was performed at 0.1 C in the voltage range of 2.0 to 4.55 V. It is described that the load efficiency is the ratio (%) when the discharge capacity at the time is used as the denominator and the discharge capacity when charging / discharging is performed with charge 0.1C and discharge 2C as the molecule (paragraph [9006). ] To [0101], [0103]).

Patent Document 3 states that "a positive electrode active material for a lithium secondary battery containing a lithium transition metal composite oxide having an α-NaFeO ₂ structure, wherein the transition metal (Me) is used as the lithium transition metal composite oxide. The molar ratio Mn / Me of Mn in the transition metal containing Co, Ni and Mn is Mn / Me ≧ 0.5, and the diffraction peak of 2θ = 44 ± 1 ° in the X-ray diffraction pattern using the CuKα radiation source. (Claim 1), "The lithium transition metal composite oxide is phosphorus, which is characterized by having a half-price range of 0.265 ° or more and containing P element." The positive electrode active material for a lithium secondary battery according to claim 1 or 2, 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 embodiment heat-treated after the above phosphoric acid treatment was produced, and the current was 0.1 C, the constant current constant voltage charge of 4.6 V, and the current was 0.05 C. After performing two cycles of constant current discharge with a cutoff voltage of 2.0 V, charging with a constant current constant current of 0.2 C and a voltage of 4.3 V and charging of a constant current discharge with a current of 0.5 C and a cutoff voltage of 2.0 V. It is described that the discharge test was performed for 30 cycles and the discharge capacity at the 30th cycle was recorded as the 0.5C discharge capacity at the 30th cycle (paragraphs [0075] to [985], [0123] to [0130]).

Patent Document 4 states that "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 is a transition metal (Me). ) Contains Co, Ni and Mn, and the molar ratio Li / Me of lithium (Li) to the transition metal is larger than 1.2 and smaller than 1.6. It has a pore volume of 0.055 cc / g or more and 0.08 cc / g or less in a pore region having a pore diameter within the range of up to 60 nm, which indicates the maximum value of the differential pore volume obtained in 1. Preparation of a precursor for producing a precursor containing Co, Ni and Mn as transition metal elements, showing a single phase belonging to group R3-m and showing a positive electrode active material for a lithium secondary battery (claim 1). The lithium transition metal composite oxidation is carried out through a step, a firing step of mixing the precursor and a Li salt and heat-treating at a temperature of 800 ° C. or higher to produce an oxide, and an acid treatment step of acid-treating the oxide. The method for producing a positive electrode active material for a lithium secondary battery according to any one of claims 1 to 6 for producing a product. ”(Claim 9),“ The acid treatment step uses sulfuric acid, claims 9 to 9. 12. A method for producing a positive electrode active material for a lithium secondary battery according to any one of 12 ”(claim 13).
Further, as an example described above, a lithium secondary battery using an active material obtained by treating a lithium transition metal composite oxide with sulfuric acid and then drying it as a positive electrode and using metallic lithium as a negative electrode is produced, and initial charge / discharge is performed. As a step, a constant current constant voltage charge with a current of 0.1 C and a voltage of 4.6 V, and a constant current discharge of a current of 0.1 C and a cutoff voltage of 2.0 V are performed for two cycles, and then a current of 0.1 C and a voltage of 4. It is described that a constant current constant voltage charge of 3 V and a constant current discharge of a current of 1 C and a cutoff voltage of 2.0 V were performed, and this discharge electric amount was recorded as a 1 C capacity (paragraphs [0076] to [0087], [0108] to [0115]).

Patent Document 5 states that "a positive electrode active material containing a lithium transition metal composite oxide having an α-NaFeO ₂ structure, wherein the transition metal (Me) is Co, Ni and Mn in the lithium transition metal composite oxide. Including, the molar ratio (Li / Me) of Li and the transition metal (Me) is 1 <Li / Me, and the molar ratio (Mn / Me) of Mn and the transition metal (Me) is 0.5 <Mn / Me. A positive electrode active material for a lithium secondary battery, which is characterized by containing Ce. ”(Claim 1) is described, and as Examples 1 to 5,“ Lithium transition metal composite oxide Li _{1. As a starting material. 18} Co _0.10 Ni _0.17 Mn _0.55 O ₂ ”was added to a cerium sulfate solution having a pH of 1.6 and heat-treated at 400 ° C. to prepare a lithium transition metal composite oxide containing Ce. Is described (paragraphs [0079] to [0082]). Then, a battery in which these lithium transition metal composite oxides are used as the positive electrode active material and the negative electrode is made of metallic lithium is produced and subjected to an initial charge / discharge step of 0.1C, 4.6V-2.0V to charge the discharge capacity. The initial efficiency is the value (%) divided by the amount of electricity, and 30 cycles of 0.2C, 4.45V constant current constant voltage charging and 0.5C, 2.0V constant current discharge are performed, and the first cycle is discharged. Table 1 shows the results of evaluating the battery with the ratio (%) of the discharge capacity at the 30th cycle to the capacity as the discharge capacity retention rate (paragraphs [0090] to [097]).

Patent Document 6 includes "a step of acid-treating the hyperlithiated metal oxide and a step of doping the acid-treated superlithiated metal oxide with a metal cation." The perlithiated metal oxide is a method for producing a composite positive electrode active material containing a compound represented by the following chemical formula 4. [Chemical formula 4] xLi ₂ MO _3- (1-x) LiM'O ₂ By the above formula. , M is at least one metal selected from 4-cycle and 5-cycle transition metals with an average oxidation number of +4, and M'is selected from 4-cycle and 5-cycle transition metals with an average oxidation number of +3. It is at least one metal, and 0 <x <1. ”(Claim 13) is described. Then, as an example thereof, an acid treatment of 0.55Li ₂ MnO _{3-0.45LiNi 0.5} Co _0.2 Mn _0.3 O ₂ composition is added to the HNO ₃ aqueous solution and then dried at 80 ° C. Then, the acid-treated substance was put into 500 mL of a nitrate aqueous solution such as Al, and heat-treated at 300 ° C. for 5 hours to obtain an active material doped with metal cations (paragraphs [0137] to [0147]. ), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ In the case of the active material, there is no change in the charge / discharge curve under the acid treatment conditions, and Li ions are not desorbed by the reaction with the acid solution. In Li ₂ MnO ₃ , the discharge curve changed significantly due to the replacement of H ⁺ and Li ⁺ ions in the acid solution during acid treatment (paragraph [0159]), the negative electrode was lithium metal, and the initial charge / discharge was 0.1C, 4 .7-2.5V constant current charge / discharge to evaluate initial efficiency, 0.5C, 4.6V constant current constant current charge, discharge current 0.2, 0.33, 1, 2, and 3C, respectively. , 2.5 V constant current discharge was performed to evaluate the rate characteristics (paragraphs [0165] to [0166]).

Japanese Patent No. 4877660 Japanese Unexamined Patent Publication No. 2015-122235 Japanese Unexamined Patent Publication No. 2016-15298 International release 2015/0833330 Japanese Unexamined Patent Publication No. 2016-126935 Japanese Unexamined Patent Publication No. 2014-170739

As described in Patent Documents 2 to 6, an "lithium excess type" active material is used for the positive electrode, and the initial charge / discharge with a positive electrode potential of 4.5 V (Li / Li ⁺ ) or more (hereinafter, also referred to as "overcharge chemical formation"). In a non-aqueous electrolyte secondary battery that is supposed to be used after passing through the above), if the "lithium excess type" active material is acid-treated with hydrochloric acid, phosphoric acid, sulfuric acid, nitric acid, etc., the initial Coulomb efficiency and high rate will be increased. It is known that the discharge performance is improved, but the effect when treated with a strong acid is only shown, and the effect when not overcharged is not known.

By the way, it is a standard for non-aqueous electrolyte secondary batteries to ensure safety if they are accidentally charged beyond the fully charged state (SOC 100%) (for example, "GB / GB / for automobile batteries". T (China Recommended National Standard) ”). As a method of evaluating the improvement in safety, assuming that the charge control circuit is broken, the SOC in which a sudden rise in battery voltage is observed when a current is forcibly applied beyond the fully charged state is observed. There is a way to record. If no spike in battery voltage is observed up to a higher SOC, then safety is assessed as improved.
Here, SOC is an abbreviation for System of Charge, and the state of charge of the battery is expressed by the ratio of the remaining capacity at that time to the capacity at the time of full charge, and the fully charged state is expressed as "SOC 100%". .. Further, the "first time" charging / discharging in the present specification refers to the first charging / discharging performed after injecting a non-aqueous electrolyte. "Initial" charging and discharging refers to one or more charging and discharging performed in the pre-shipment manufacturing process of a battery after injecting a non-aqueous electrolyte.
Comparison of potential changes appearing with respect to the amount of charging electricity in the positive electrode potential range of "4.3 V (vs. Li / Li ⁺ ) and 4.8 V or less (vs. Li / Li ⁺ )" described in Patent Document 1. A "flat region" is characteristically observed in "lithium-rich" active materials. Once the charging in which the region where the potential change is relatively flat is observed is performed even once, the flat region is not observed even if the charging up to 4.8V is performed next. Therefore, the positive electrode contains a "lithium-excessive" active material, and the above-mentioned potential change is not performed in the initial charge / discharge where the above-mentioned potential change is observed in a relatively flat region, and the above-mentioned potential change is carried out in the normal use full charge (SOC 100%). We have proposed a non-aqueous electrolyte secondary battery with a positive electrode potential in which a flat region is not observed. When this battery exceeds 100% SOC and is further charged, the region where the potential change is relatively flat is observed for the first time, and no rapid increase in battery voltage is observed until a higher SOC is reached.

However, regarding the initial coulomb efficiency and high rate discharge performance when the "lithium excess type" active material is used without passing through a charging potential of 4.5 V (vs. Li / Li ⁺ ) or higher including the initial charge / discharge. , It has not been examined so far, and its relationship with acid treatment was unknown.
Therefore, the present invention is 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 of less than 4.5 V (vs. Li / Li ⁺ ). It is an object of the present invention 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 provided with 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 type ₂ crystal structure. The molar ratio of Li to the transition metal (Me) Li / Me is 1 <Li / Me, and the transition metal (Me) contains Ni, Co and Mn, or Ni and Mn, and the molar ratio of Mn to Me is Mn / Me. 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 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. It is a positive electrode active material for use.

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 type ₂ crystal structure and is a transition metal (Me). ), The molar ratio of Li to Li / Me is 1 <Li / Me, the transition metal (Me) contains Ni, Co and Mn, or Ni and Mn, and the molar ratio of Mn to Me is Mn / Me. The lithium transition metal composite oxide having ≧ 0.45 is treated with an acid having pKa ₁ of 3.1 or more, and is treated from 4.35 V (vs. Li / Li ⁺ ) to 3.0 V (vs. Li / Li ⁺ ). The ratio a / b of the discharge capacity (a) up to) and the discharge capacity (b) from 3.0 V (vs. Li / Li ⁺ ) to 2.0 V (vs. Li / Li ⁺ ) is 17 ≦ a / b. This is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which produces a positive electrode active material having ≦ 25.

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

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

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

According to the present invention, a positive electrode active material for a non-aqueous electrolyte secondary battery exhibiting excellent initial Coulomb efficiency and high rate discharge performance when used at a potential of less than 4.5 V (vs. Li / Li ⁺ ). It is possible to provide a manufacturing method, a positive electrode containing the positive electrode active material, a non-aqueous electrolyte secondary battery provided with the positive electrode, and a method for manufacturing the non-aqueous electrolyte secondary battery.

The figure explaining that "diffraction peak is observed in the range of 20-22 °" in the X-ray diffraction measurement of the lithium excess type positive electrode active material used for the non-aqueous electrolyte secondary battery. The figure explaining that "diffraction peak is not observed in the range of 20-22 °" in the X-ray diffraction measurement of the lithium excess type positive electrode active material used for the non-aqueous electrolyte secondary battery. The figure which shows the potential change with respect to the charge electric energy of a lithium excess type positive electrode active material The figure explaining "the region where the potential change is relatively flat with respect to the charge electric energy" External perspective view of the non-aqueous electrolyte secondary battery according to this embodiment Schematic diagram of a power storage device including a plurality of non-aqueous electrolyte secondary batteries according to this embodiment.

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

One embodiment of the present invention is a positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide, and the lithium transition metal composite oxide has an α-NaFeO type ₂ crystal structure. , The molar ratio of Li to the transition metal (Me) Li / Me is 1 <Li / Me, and the transition metal (Me) contains Ni, 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 in which 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 type ₂ crystal structure and has a molar ratio of Li to a transition metal (Me) Li /. Lithium transition in which Me is 1 <Li / Me, the transition metal (Me) contains Ni, Co and Mn, or Ni and Mn, and the molar ratio of Mn to 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 the discharge capacity (a) is from 4.35 V (vs. Li / Li ⁺ ) to 3.0 V (vs. Li / Li ⁺ ). And a positive electrode active material in which 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 ≦ 25. This is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery.

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

Yet another embodiment of the present invention comprises the positive electrode for the non-aqueous electrolyte secondary battery, and the positive electrode active material contained in the positive electrode is in the range of 20 to 22 ° in an X-ray diffraction diagram using CuKα rays. It is a non-aqueous electrolyte secondary battery in which a diffraction peak is observed.

Yet another embodiment of the present invention includes the positive electrode for the non-aqueous electrolyte secondary battery, and when the positive electrode is charged to a positive electrode potential of 5.0 V (vs. Li / Li ⁺ ), 4 It is a non-aqueous electrolyte secondary battery in which a region where the potential change is relatively flat with respect to the amount of charging electricity is observed within the positive electrode potential range of .5 to 5.0 V (vs. Li / Li ⁺ ).
The above-mentioned non-aqueous electrolyte secondary electricity is preferably used at a potential of less than 4.5 V (vs. Li / Li ⁺ ).

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

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

<Composition of Lithium Transition Metal Composite Oxide>
The lithium transition metal composite oxide contained in the positive electrode active material according to the present embodiment (hereinafter referred to as “lithium transition metal composite oxide according to the present embodiment”) is a general formula Li _{1 + α} Me _1-α O ₂ (hereinafter referred to as “lithium transition metal composite oxide according to the present embodiment”). 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 expressed as Li _{1 + α} (Ni _{x Coy} Mn _z ) _1-α O ₂ (x + y + z = 1). The molar ratio of Li to the transition metal element Me, Li / Me, i.e. (1 + α) / (1- α) is preferably 1.05 or more, and more preferably 1.10 or more. In order to suppress the decrease in discharge capacity, Li / Me is preferably 1.4 or less, and more preferably 1.35 or less.
The molar ratio of Mn to the transition metal element Me, Mn / Me, that is, z, is 0.45 or more from the viewpoint of stabilizing the layered structure. Further, from the viewpoint of charge / discharge capacity, Mn / Me is preferably 0.65 or less, and more preferably 0.6 or less.
The molar ratio of Ni to the transition metal element Me, Ni / Me, that is, x, is preferably 0.2 or more, preferably 0.5 or less, in order to improve the charge / discharge cycle performance of the non-aqueous electrolyte secondary battery. Is preferable.
The molar ratio of Co to the transition metal element Me, Co / Me, that is, y, is preferably 0.03 or more in order to enhance the conductivity of the active material particles. In order to reduce the material cost, it is preferably 0.40 or less, and more preferably 0.30 or less.
The lithium transition metal composite oxide according to the present embodiment can be used as an alkali metal such as Na and K, an alkaline earth metal such as Mg and Ca, and a 3d transition metal such as Fe, as long as the effect of the present invention is not impaired. It does not preclude the inclusion of small amounts of other metals such as typified transition metals.

<Crystal structure of lithium transition metal composite oxide>
The lithium transition metal composite oxide according to this embodiment has an α-NaFeO type ₂ crystal structure. The lithium transition metal composite oxide is assigned to the space group P3 ₁₁₂ after synthesis (before charging / discharging as an active material), and is 2θ = 20 to 22 ° on an X-ray diffraction diagram using a CuKα tube. A superlattice peak (a peak found in Li [Li _1/3 Mn _2/3 ] _O2 type monochromatic crystals) 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, if charging is performed at a potential of 4.5 V (vs. Li / Li ⁺ ) or higher even once, this superlattice peak disappears because the symmetry of the crystal changes with the desorption of Li in the crystal. Then, the lithium transition metal composite oxide is assigned to the space group R3-m (see FIG. 2). Here, P3 ₁ 12 is a crystal structure model in which the atomic positions of 3a, 3b, and 6c sites in R3-m are subdivided, and the P3 ₁ 12 model is when order is recognized in the atomic arrangement in R3-m. Is adopted. In addition, "R3-m" is originally described by adding a bar "-" on "3" of "R3m".

<Diffraction peak confirmation method>
It is confirmed that the positive electrode active material according to the present embodiment has a diffraction peak in the range of 20 to 22 ° in the X-ray diffraction diagram using CuKα rays according to the following procedure and conditions. Further, "observed" means the maximum value of the intensity in the range of the diffraction angle of 20 to 22 ° with respect to the difference (I ₁₈ ) between the maximum value and the minimum value of the intensity in the range of the diffraction angle of 17 to 19 °. It means that the ratio of the difference (I ₂₁ ) 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 measured is the active material powder (powder before charging / discharging) before the positive electrode is prepared, it is used as it is for the measurement. When a sample is taken from an electrode taken out by disassembling the battery, the voltage specified by the current value (A), which is 1/10 of the nominal capacity (Ah) of the battery, is used before disassembling the battery. A constant current discharge is performed up to the battery voltage, which is the lower limit of the above, and the state is set to the end of discharge state. As a result of dismantling, if the battery uses a metallic lithium electrode as the negative electrode, the positive electrode mixture collected from the positive electrode plate is targeted for measurement without performing the additional work described below. If the battery does not use a metallic lithium electrode as the negative electrode, in order to accurately control the positive electrode potential, after disassembling the battery and taking out the electrode, assemble a battery with the metallic lithium electrode as the counter electrode, and 10 mA per 1 g of the positive electrode mixture. With the current value of, constant current discharge is performed until the potential of the positive electrode reaches 2.0 V (vs. Li / Li ⁺ ), adjusted to the discharge end state, and then disassembled again. The removed positive electrode plate is thoroughly washed with dimethyl carbonate to thoroughly wash the electrolytic solution adhering to the electrode, dried at room temperature for a whole day and night, and then the mixture on the aluminum foil current collector is collected. Lightly loosen the collected mixture in an agate mortar and place it in a sample holder for X-ray diffraction measurement for measurement. The work from dismantling to re-disassembling the battery, and the cleaning and drying work of the positive electrode are performed in an argon atmosphere having a dew point of −60 ° C. or lower.

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

FIG. 1 shows a non-aqueous electrolyte secondary battery using the positive electrode active material (lithium excess type positive electrode active material) according to the present embodiment, with a current value of 10 mA per 1 g of the positive electrode mixture and a charge upper limit potential of 4. The non-aqueous electrolyte secondary battery according to the present embodiment in the discharge end state after the first charge / discharge with 35 V (vs. Li / Li ⁺ ) and the lower discharge potential of 2.0 V (vs. Li / Li ⁺ ). It is an X-ray discharge chart measured by the above-mentioned procedure about the active material powder contained in the positive electrode of. In FIG. 1, diffraction peaks are observed in the range of 20 to 22 °.
FIG. 2 shows a non-aqueous electrolyte secondary battery using the same positive electrode active material as described above, with a current value of 10 mA per 1 g of the positive electrode mixture and a charge upper limit potential of 4.6 V (vs. Li / Li ⁺ ). The active material powder contained in the positive electrode of the non-aqueous electrolyte secondary battery in the discharge end state after charging / discharging with the lower discharge 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, it can be seen that in a battery charged with 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 above, the charge upper limit potential is 4.6 V (vs. Li / Li ⁺ ) and the discharge lower limit potential is set at a current value of 10 mA per 1 g of the positive electrode mixture. After the first charge and discharge at 2.0 V (vs. Li / Li ⁺ ), the charge upper limit potential is 4.35 V (vs. Li / Li ⁺ ) and the discharge lower limit potential is 2.0 V (vs. Li / Li /). When the active material powder contained in the positive electrode of the non-aqueous electrolyte secondary battery in the end-discharged state of being 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 the battery is charged to a potential of 4.5 V or higher, the peak in the range of 20 to 22 ° disappears, and the diffraction peak in the range of 20 to 22 ° does not appear again.

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

The discharge capacity ratio a / b is obtained as follows.
When the evaluation target is an active material, N-methylpyrrolidone is used as a dispersion medium, and the active material, acetylene black (AB) and polyvinylidene fluoride (PVdF) are prepared in a ratio of 90: 5: 5 to prepare a coating paste. The coating paste is applied to one side of an aluminum foil current collector having a thickness of 20 μm to prepare a positive electrode plate, and a non-aqueous electrolyte secondary battery for evaluation is assembled using metallic lithium as a counter electrode. A constant current constant voltage charge is performed with a current value of 15 mA per 1 g of the positive electrode mixture, a charge upper limit potential of 4.35 V (vs. Li / Li ⁺ ), and a charge termination condition when the current value is reduced to 1/5. .. After a 10-minute pause, constant current discharge is performed with the same current value and a discharge lower limit potential of 2.0 V (vs. Li / Li ⁺ ), and 3.0 V (vs. Li / Li ⁺ ) from the start of discharge. ) 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, constant current discharge is performed up to the battery voltage, which is the lower limit of the specified voltage, with the current value (A), which is 1/10 of the nominal capacity (Ah) of the battery. This is done, and the state is set to the end of discharge. The battery is disassembled in an argon atmosphere with a dew point of -60 ° C. or lower to obtain a positive electrode plate, and then a non-aqueous electrolyte secondary battery for evaluation is assembled using metallic lithium as a counter electrode. The produced battery is constantly discharged to 2.0 V (vs. Li / Li ⁺ ) at a current value of 15 mA per 1 g of the positive electrode mixture. After that, constant current constant voltage charging is performed with the same current value, the upper limit potential of charging is 4.35 V (vs. Li / Li ⁺ ), and the charge termination condition is the time when the current value is reduced to 1/5. After a 10-minute pause, a constant current discharge of 2.0 V (vs. Li / Li ⁺ ) with the same current is performed, and a / b is evaluated in the same manner.
According to the experimental example described later, when the discharge capacity ratio a / b is 17 ≦ a / b ≦ 25, the present implementation contains a positive electrode active material excellent in initial Coulomb efficiency and high rate discharge performance, and this positive electrode active material. It was found that a positive electrode for a non-aqueous electrolyte secondary battery according to the embodiment and a non-aqueous electrolyte secondary battery according to the present embodiment provided with the positive electrode can be obtained.

<Behavior when the non-aqueous electrolyte secondary battery is charged to exceed 4.5 V (vs. Li / Li ⁺ )>
The non-aqueous electrolyte secondary battery according to the present embodiment includes a positive electrode containing the above-mentioned positive electrode active material, and the positive electrode active material has a peak in the range of 20 to 22 ° in an X-ray diffraction diagram using CuKα rays. As observed, the non-aqueous electrolyte secondary battery according to the present embodiment has a non-hydrolyte 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 the manufacturing method of a water electrolyte secondary battery. Further, the non-aqueous electrolyte secondary battery according to the present embodiment has not undergone a charging process of 4.5 V (vs. Li / Li ⁺ ) or more in normal use. Therefore, when the charge exceeds 4.5 V (vs. Li / Li ⁺ ) and reaches 5.0 V (vs. Li / Li ⁺ ), the positive electrode is charged with "4.5 to 5.0 V (vs). Within the positive electrode potential range of Li / Li ⁺ ), a region in which the potential change is relatively flat with respect to the amount of charging electricity (hereinafter, also referred to as a “region in which the potential change is flat”) is observed (FIG. 3). See solid line). Due to the presence of this flat region, no spike in battery voltage is observed in the non-aqueous electrolyte secondary battery according to this embodiment until a higher SOC is reached.

The solid line in FIG. 3 shows the charge when the non-aqueous electrolyte secondary battery equipped with the positive electrode containing the lithium excess type active material is initially charged to 4.6 V (vs. Li / Li ⁺ ). An example of a curve is shown. Here, the capacity is converted into SOC based on the capacity from the start of charging to the arrival of 4.35 V (vs. Li / Li ⁺ ) (SOC 100%). It has a relatively flat charge curve until the positive electrode potential rises sharply around 200% SOC. On the other hand, the broken line in FIG. 3 shows the above-mentioned non-aqueous electrolyte secondary battery charged to 4.6 V (vs. Li / Li ⁺ ) after being discharged to 2.0 V (vs. Li / Li ⁺ ). This is a charging curve when charging is performed with the upper limit potential set to 4.6 V (vs. Li / Li ⁺ ) again. As can be seen from the figure, in the positive electrode having 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.

<How to check the area where the potential change is flat>
Here, confirmation that a region where the potential change is flat is observed is performed by the following procedure. A test battery was prepared in which the positive electrode taken out by disassembly was used as the working electrode and the lithium metal was used as the counter electrode, and the test battery was discharged to 2.0 V (vs. Li / Li ⁺ ) at a current value of 10 mA per 1 g of the positive electrode mixture. After that, a 30-minute rest is performed. After that, constant current charging is performed up to 5.0 V (vs. Li / Li ⁺ ) with a current value of 10 mA per 1 g of the positive electrode mixture. Here, the ratio of the capacity X (mAh) at the time of reaching 4.45 V (vs. Li / Li ⁺ ) from the start of charging to the capacity Y (mAh) at each potential is Z (= Y / X * 100 (%)). ). The horizontal axis is the potential, the vertical axis is the difference in the potential change, and the numerator is the difference in the volume ratio change, and dZ / dV is taken to obtain a dZ / dV curve.
The solid line in FIG. 4 is an assembly of a non-aqueous electrolyte secondary battery equipped with a positive electrode using a lithium excess type active material as a positive electrode active material and a negative electrode using a lithium metal, and the initial charge is 4.5 V (vs. Li). This is an example of a dZ / dV curve when the non-aqueous electrolyte secondary battery according to the present embodiment having a value of less than / Li ⁺ ) is charged to 4.6 V (vs. Li / Li ⁺ ). As can be seen from the calculation formula, the dZ / dV curve has a large dZ / dV value when the potential change is small with respect to the capacitance ratio change, and dZ / dV when the potential change is large with respect to the capacitance ratio change. The value becomes smaller. In the charging process of the lithium excess type active material in the potential region exceeding 4.5 V (vs. Li / Li ⁺ ), the value of dZ / dV becomes large when the region where the potential change is flat begins to be seen. After that, when the region where the potential change is flat ends and the potential rises again, the value of dZ / dV becomes smaller. That is, a peak is observed in the dZ / dV curve. Here, when the maximum value of dZ / dV in the range of 4.5 V (vs. Li / Li ⁺ ) to 5.0 V (vs. Li / Li ⁺ ) is 150 or more, a region where the potential change is flat is observed. Judge to be done. On the other hand, the broken line is a battery having the same configuration as the above-mentioned non-aqueous electrolyte secondary battery, with an upper limit of 4.6 V (vs. Li / Li ⁺ ) and a lower limit of 2.0 V (vs. Li / Li ⁺ ) for the first time. It is a dZ / dV curve when charging and discharging are performed, a pause of 10 minutes is inserted, and then charging is performed with the upper limit of 4.6 V (vs. Li / Li ⁺ ) for the second charge. In the broken line, no peak like the solid line is observed. That is, when a non-aqueous electrolyte secondary battery equipped with a positive electrode containing a lithium excess type active material is charged even once until the region where the potential change of 4.5 V (vs. Li / Li ⁺ ) is flat is completed, the battery is charged. In the subsequent charging step at a potential of 4.5 V (vs. Li / Li ⁺ ) or higher, no peak is observed in the dZ / dV curve. In the present specification, the term "normal use" refers to the case where the non-aqueous electrolyte secondary battery is used by adopting the charge / discharge conditions recommended or specified for the non-aqueous electrolyte secondary battery. When a charger for a non-aqueous electrolyte secondary battery is prepared, it means a case where the charger is applied to use the non-aqueous electrolyte secondary battery.

<Manufacturing method of precursor of lithium transition metal composite oxide>
The method for producing a positive electrode active material according to the present embodiment basically comprises using metal elements (Li, Ni, Co, Mn) constituting the lithium transition metal composite oxide contained in the active material according to the desired composition. It can be obtained by preparing the raw material to be contained and baking it.
In producing a lithium transition metal composite oxide having the desired composition, the so-called "solid phase method" in which powders of Li, Ni, Co, and Mn compounds are mixed and fired, or Ni, Co, and Mn are used in advance. A "coprecipitation method" is known in which a coprecipitation precursor present in a particle is prepared, and a Li salt is mixed and fired with the coprecipitation precursor. In the synthesis process by the "solid phase method", it is difficult to obtain a sample in which each element is uniformly distributed in one particle, because Mn is particularly difficult to dissolve uniformly in Ni and Co. In the literature, many attempts have been made to dissolve Mn in a part of Ni or Co by the solid phase method (LiNi _1-x Mn _x O ₂ etc.), but the "coprecipitation method" is selected. It is easier to obtain a uniform 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 the present embodiment, in the production of a precursor of a lithium transition metal composite oxide, a raw material aqueous solution containing Ni, Co and Mn is dropped, and Ni, Co and Mn are contained in the solution. It is preferable to co-precipitate the compound to prepare a precursor.
In producing a coprecipitation precursor, Mn among Ni, Co, and Mn is easily oxidized, and it is not easy to produce a coprecipitation precursor in which Ni, Co, and Mn are uniformly distributed in a divalent state. , Ni, Co, Mn at the atomic level tends to be inadequate. Therefore, in the present invention, it is preferable to remove dissolved oxygen in order to suppress the oxidation of Mn distributed and present in the coprecipitation precursor. Examples of the method for removing dissolved oxygen include a method of bubbling a gas containing no oxygen. The gas containing no oxygen is not limited, but nitrogen gas, argon gas, carbon dioxide (CO ₂ ) and the like can be used.

The pH in the step of coprecipitating a compound containing Ni, Co and Mn in a solution to prepare a precursor is not limited, but an attempt is made to prepare the coprecipitated precursor as a coprecipitated hydroxide precursor. If so, it can be 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 set to 1.00 g / cm ³ or more, and the high rate discharge performance can be improved. Further, since the particle growth can be promoted by setting the pH to 11.0 or less, the stirring continuation time after the completion of dropping the raw material aqueous solution can be shortened.
Further, when the coprecipitation precursor is to be prepared as a coprecipitation carbonate precursor, the pH can be 7.5 to 11. By setting the pH to 9.4 or less, the tap density can be 1.25 g / cc or more, and the high rate discharge performance can be improved. Further, since the particle growth can be promoted by setting the pH to 8.0 or less, the stirring continuation time after the completion of dropping the raw material aqueous solution can be shortened.

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

The dropping rate of the raw material aqueous solution greatly affects the uniformity of the element distribution within one particle of the produced coprecipitation precursor. The preferable dropping rate is affected by the size of the reaction vessel, stirring conditions, pH, reaction temperature and the like, but is preferably 30 mL / min or less. In order to improve the discharge capacity, the dropping rate is more preferably 10 mL / min or less, and most preferably 5 mL / min or less.

In addition, when a complexing agent such as NH ₃ is present in the reaction vessel and certain convection conditions are applied, the particles rotate and in the stirring vessel by continuing stirring after the dropping of the raw material aqueous solution is completed. Revolution is promoted, and in this process, the particles gradually grow into convective spheres while colliding with each other. That is, the coprecipitation precursor undergoes a two-step reaction: a metal complex forming reaction when the raw material aqueous solution is dropped into the reaction vessel, and a precipitation forming reaction that occurs while the metal complex stays in the reaction vessel. It is formed. Therefore, a coprecipitation precursor having a target particle size can be obtained by appropriately selecting a time for further stirring after the completion of dropping of the raw material aqueous solution.

The preferable stirring duration after the completion of dropping the aqueous solution of the raw material is affected by the size of the reaction vessel, stirring conditions, pH, reaction temperature, etc., but is 0.5 hours 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, 30 hours or less is preferable, 25 hours or less is more preferable, and 20 hours or less is most preferable.

<Manufacturing method of lithium transition metal composite oxide>
In the method for producing a positive electrode active material according to the present embodiment, the lithium transition metal composite oxide is preferably synthesized by mixing the coprecipitation precursor and the Li compound and firing them.
LiF, Li ₂ SO ₄ or Li ₃ PO ₄ may be used as the sintering aid together with lithium hydroxide and lithium carbonate which are usually used as Li compounds. The addition ratio of these sintering aids is preferably 1 to 10 mol% with respect to the total amount of the Li compound. It is preferable that the total amount of the Li compound is excessively charged by about 1 to 5% in anticipation that a part of the Li compound will disappear during firing.

The firing temperature affects the reversible capacity of the active material.
If the firing temperature is too low, crystallization does not proceed sufficiently and the electrode characteristics tend to deteriorate. In one aspect 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, if the firing temperature is too high, the structure changes from the layered α-NaFeO type ₂ crystal structure to the rock salt type cubic crystal structure, which is disadvantageous for the movement of lithium ions in the active material during the charge / discharge reaction, resulting in poor discharge performance. descend. In the present invention, the firing temperature is preferably 1000 ° C. or lower. By setting the temperature to 1000 ° C. or lower, the charge / discharge cycle performance can be improved.
Therefore, in the method for producing a positive electrode active material according to the present embodiment, it is preferable to set the firing temperature 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 producing a positive electrode active material according to the present embodiment, the positive electrode active material having a discharge capacity ratio a / b of 17 ≦ a / b ≦ 25 is a lithium transition metal composite oxide synthesized by the above manufacturing method. Can be produced by treating with an acid having pKa ₁ of 3.1 or more. Acids with a pKa ₁ of 3.1 or higher 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 surface-treating the lithium-rich active material with an acid having a pKa ₁ of 3.1 or higher at an appropriate concentration, the discharge capacity equal to or higher than that of the untreated active material can be obtained under conditions where overcharge formation does not occur. While having it, the initial Coulomb efficiency and high rate discharge performance can be improved.

The detailed mechanism of action of the acid treatment in the method for producing an active substance according to the present embodiment is unknown, but since the above acid has a pKa ₁ of 3.1 or more, the lithium ion in the active material is a hydrogen ion. The possibility of substitution is low, and it is unlikely that the molar ratio Li / Me of the active material lithium and the transition metal will fluctuate significantly. Therefore, the acid treatment with a strong acid such as hydrochloric acid, phosphoric acid, or sulfuric acid having a small pKa ₁ replaced the lithium ions with hydrogen ions (Li was removed), so that the molar ratio Li of the active material before and after the treatment was Li. 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 matters described in paragraph [0159] of Patent Document 6 is working.
According to the experimental examples described later, the active material subjected to the acid treatment according to the present embodiment is 4.35 V (vs. Li / Li ⁺ ) to 3.0 V (vs. Li /) as compared with the untreated active material. The ratio a / b of the discharge capacity (a) up to Li ⁺ ) and the discharge capacity (b) from 3.0 V (vs. Li / Li ⁺ ) to 2.0 V (vs. Li / Li ⁺ ) decreases. The cage (discharge capacity b increased relatively), and the specific surface area increased moderately. Since the discharge capacity b is known to appear characteristically in the spinel structure, this acid treatment provides an appropriate spinel-like crystal structure on the surface of the lithium-rich active material, so that it is irreversible at the time of initial charge / discharge. It is presumed that the capacity will be reduced and the initial Coulomb efficiency will be improved.
In addition, it is presumed that the increase in the BET specific surface area brings about appropriate unevenness on the particle surface, promotes the permeation of the electrolyte and the diffusion of lithium ions, improves the initial Coulomb efficiency, and improves the high rate discharge performance. .. The BET specific surface area is preferably 6 m ² / g or less.

The specific acid treatment procedure 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, the temperature of the aqueous solution is maintained at 50 ° C., and the mixture is stirred at 400 rpm for 2 hours using a stirrer. After stirring, the lithium transition metal composite oxide is filtered using a suction device, further washed with ion-exchanged water, and then dried under atmospheric pressure at 80 ° C. overnight.

<Negative electrode material>
The material of the negative electrode to be combined with the positive electrode for the non-aqueous electrolyte secondary battery according to the present embodiment is not limited, and a material capable of releasing or occluding lithium ions can be appropriately selected. For example, titanium-based materials such as lithium titanate having a spinel-type crystal structure represented by Li [Li _1/3 Ti _5/3 ] _O4 , alloy-based materials such as Si, Sb, and Sn, lithium metals, and lithium. Alloys (lithium metal-containing alloys such as lithium-silicon, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and wood alloys), lithium composite oxides (lithium-titanium), oxidation In addition to silicon, alloys capable of storing and releasing lithium, carbon materials (for example, graphite, hard carbon, low-temperature calcined carbon, amorphous carbon, etc.) and the like can be mentioned.

<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 non-aqueous electrolyte battery, and preferably 10 μm or more for maintaining the charge / discharge cycle performance. A crusher or a classifier is used to obtain the powder in a predetermined shape. For example, a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counterjet mill, a swirling airflow type jet mill, a sieve, or the like is used. At the time of pulverization, wet pulverization in which water or an organic solvent such as hexane coexists can also be used. The classification method is not particularly limited, and a sieve, a wind power classifier, or the like is used as needed for both dry type and wet type.

In the positive electrode and the negative electrode, in addition to the positive electrode active material and the negative electrode material which are the main constituents thereof, in addition to the main constituents, a conductive agent, a binder, a thickener, a filler and the like are used as other constituents. It may be contained.

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

Among these, acetylene black is preferable as the conductive agent from the viewpoint of electron conductivity and coatability. The amount of the conductive agent added is preferably 0.1% by 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 pulverize acetylene black into ultrafine particles of 0.1 to 0.5 μm and use it because the required carbon amount can be reduced. These mixing methods are physical mixing, and the ideal is uniform mixing. Therefore, it is possible to mix powder mixers such as V-type mixers, S-type mixers, scouring machines, ball mills, and planetary ball mills in a dry or wet manner.

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

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

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

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

<Non-water electrolyte>
The non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery according to the present embodiment is not limited, and those generally proposed for use in lithium batteries and the like can be used. Examples of the non-aqueous solvent used for the non-aqueous electrolyte include cyclic carbonate esters such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate, Chain carbonates such as diethyl carbonate and ethylmethyl carbonate; Chain esters such as methyl formate, methyl acetate and methyl butyrate; tetrahydrofuran or its derivatives; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxy Ethers such as ethane, 1,4-dibutoxyethane, methyl diglyme; nitriles such as acetonitrile and benzonitrile; dioxolane or its derivatives; ethylene sulfide, sulfolane, sulton or its derivatives, etc. alone or two or more thereof. Mixtures and the like can be mentioned, but the present invention 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, NaBr. , KClO ₄ , KSCN and other inorganic ionic salts containing one of lithium (Li), sodium (Na) or potassium (K), LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ ) SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , ( CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (n-C ₄ H ₉ ) ₄ NClO ₄ , (n-C) ₄ H ₉ ) ₄ NI, (C ₂ H ₅ ) ₄ N-malate, (C ₂ H ₅ ) ₄ N-benzoate, (C ₂ H ₅ ) ₄ N-phthate, lithium stearyl sulfonate, lithium octyl sulfonate, Examples thereof include organic ionic salts such as lithium dodecylbenzenesulfonate, and these ionic compounds can be used alone or in combination of two or more.

Furthermore, 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 because the low temperature characteristics can be further enhanced and self-discharge can be suppressed.

Further, a room temperature molten salt or an ionic liquid may be used as the non-aqueous electrolyte.

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

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

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

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

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

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

Other components of the battery include terminals, insulating plates, battery cases, etc., but these parts may be the same as those conventionally used.

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

The non-aqueous electrolyte secondary battery according to the present embodiment has a charging process in which a region in which the potential change is relatively flat is observed within the positive electrode potential range of 4.5 to 5.0 V (vs. Li / Li ⁺ ). It is manufactured and used without going through a charging process until it is completed.
The fact that the non-aqueous electrolyte secondary battery according to the present embodiment has no history of being charged until the end of the charging process in which the region where the potential change is relatively flat is observed is that the positive electrode active material of the battery is used. However, in the X-ray diffraction diagram using the CuKα ray, a diffraction peak is observed in the range of 20 to 22 °, or the positive electrode of the battery has a positive electrode potential of 5.0 V (vs. Li / Li ⁺ ). By observing a region where the potential change is relatively flat with respect to the amount of charged electricity within the positive electrode potential range of 4.5 to 5.0 V (vs. Li / Li ⁺ ) when charging up to 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. An example of the power storage device is shown in FIG. In FIG. 6, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of non-aqueous electrolyte secondary batteries 1. The power storage device 30 can be mounted as a power source for an electric vehicle (EV), a hybrid vehicle (HEV), a plug-in hybrid vehicle (PHEV), or the like.

(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 all of them were dissolved in 4 L of ion-exchanged water, and the molar ratio of Ni: Co: Mn was 27: A 1.0 M sulfate aqueous solution having a ratio of 27:46 was prepared.
Next, 2 L of ion-exchanged water was poured into a 5 L reaction vessel, and Ar gas was bubbled for 30 minutes to remove oxygen contained in the ion-exchanged water. The temperature of the reaction vessel is set to 50 ° C (± 2 ° C), and convection is sufficiently generated in the reaction layer while stirring the inside of the reaction vessel at a rotation speed of 1500 rpm using a paddle blade equipped with a stirring motor. did. The aqueous sulfate solution was added dropwise to the reaction vessel at a rate of 3 mL / min. Here, the pH in the reaction vessel is adjusted by appropriately dropping a mixed alkaline solution consisting of 4.0 M sodium hydroxide, 0.5 M aqueous ammonia, and 0.2 M hydrazine from the start to the end of the dropping. 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 dropping was completed, stirring in the reaction vessel was continued for another 3 hours. After the stirring was stopped, the mixture was allowed to stand at room temperature for 12 hours or more.
Next, the hydroxide precursor particles generated in the reaction vessel are separated using a suction filtration device, and the sodium ions adhering to the particles are washed and removed using ion-exchanged water, and an electric furnace is used. Then, the particles were dried at 80 ° C. for 20 hours under normal pressure in an air atmosphere. Then, in order to make the particle size uniform, it was crushed in an automatic agate mortar for several minutes. In this way, a hydroxide precursor was prepared.

To 1.852 g of the hydroxide precursor, 0.971 g of lithium hydroxide monohydrate was added and mixed well using an automatic agate mortar, and the molar ratio of Li :( Ni, Co, Mn) was 130 :. A mixed powder was prepared so as to be 100. It was molded at a pressure of 6 MPa using a pellet molding machine to obtain pellets having a diameter of 25 mm. The amount of the mixed powder used for pellet molding was determined by converting so that the assumed mass of the final product was 2 g. One of the pellets was placed on an alumina boat having a total length of about 100 mm, installed in a box-type electric furnace (model number: AMF20), and heated in an air atmosphere under normal pressure from room temperature to 900 ° C. over 10 hours. It was fired at 900 ° C. for 5 hours. The internal dimensions of the box-type electric furnace are 10 cm in length, 20 cm in width, and 30 cm in depth, and heating wires are inserted at intervals of 20 cm in the width direction. After firing, the heater was switched off and the alumina boat was allowed to cool naturally while still in the furnace. As a result, the temperature of the furnace drops to about 200 ° C. after 5 hours, but the subsequent temperature decrease rate is rather gradual. After a day and night, after confirming that the temperature of the furnace was 100 ° C. or lower, the pellets were taken out and lightly loosened in an agate mortar to make the particle size uniform.
In this way, 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 substances>
5.0 g of the above lithium transition metal composite oxide was added to 200 mL of a citric acid aqueous solution having a hydrogen ion concentration of 0.05 M, the temperature of the aqueous solution was maintained at 50 ° C., and the mixture was stirred at 400 rpm for 2 hours using a stirrer. After stirring, the positive electrode active material was filtered using a suction device, further washed with ion-exchanged water, and then dried under normal pressure at 80 ° C. 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 are the same 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 0.025 M instead of citric acid. did. The BET specific surface area was 4.6 m ² / g and 5.5 m ² / g, respectively.

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

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

(Comparative Examples 6 to 8)
The 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 carried out using phosphoric acid aqueous solutions having hydrogen ion concentrations of 0.1 M and 0.01 M, respectively. The active material according to Comparative Example 8 was prepared in the same manner as in Comparative Example 7 except that the acid treatment time was set to 10 minutes. The BET specific surface area of Comparative Example 6 was 5.7 m ² / g.

(Comparative Examples 9 and 10)
The active materials according to Comparative Examples 9 and 10 were prepared in the same manner as in Example 1 except that the acid treatment of the active material was carried out using a tartaric acid aqueous solution having a hydrogen ion concentration of 0.1 M and 0.05 M, respectively. The BET specific surface areas were 7.1 m ² / g and 6.5 m ² / g, respectively.

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

(Example 6 and Comparative Example 12)
The present invention relates to Example 6 and Comparative Example 12 in the same manner as in Example 4 and Comparative Example 11, except that the mixed powder was prepared so that the molar ratio of Li: (Ni, Co, Mn) was 130: 100. The active material was prepared.

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

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

(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, The active materials according to Comparative Examples 18 to 20 were prepared in the same manner as in Examples 1 and 2, respectively, except that the mixed powder was prepared so that the molar ratio of Mn) was 100: 100.

<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 material according to all the examples and comparative examples had an α-NaFeO type ₂ crystal structure. In addition, it was confirmed that diffraction peaks were observed in the range of 20 to 22 ° in all the active materials (“lithium excess type” active materials) according to all Examples and Comparative Examples except Comparative Examples 16 to 20.

<Manufacturing of positive electrode>
A coating in which N-methylpyrrolidone is used as a dispersion medium and the active materials according to the above Examples and Comparative Examples, acetylene black (AB) and polyvinylidene fluoride (PVdF), are kneaded and dispersed in a mass ratio of 90: 5: 5. Made a paste for. The coating paste was applied to one surface of an aluminum foil current collector having a thickness of 20 μm to prepare positive electrodes according to each Example and Comparative Example. The mass and coating thickness of the active material applied per fixed area were unified so that the test conditions would be the same for all the non-aqueous electrolyte secondary batteries according to the examples and comparative examples described later.

<Manufacturing of negative electrode>
A negative electrode was prepared by arranging 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 each Example and Comparative Example, a non-aqueous electrolyte secondary battery was assembled by the following procedure.
As the electrolytic solution, LiPF ₆ was dissolved in a mixed solvent having an ethylene carbonate (EC) / ethylmethyl carbonate (EMC) / dimethyl carbonate (DMC) volume ratio of 6: 7: 7 so as to have a concentration of 1 mol / L. The solution was used. As a separator, a polypropylene micropore membrane surface-modified with polyacrylate was used. For the exterior body, a metal resin composite film made of polyethylene terephthalate (15 μm) / aluminum foil (50 μm) / metal-adhesive polypropylene film (50 μm) was used. The positive electrode and the negative electrode according to each Example and Comparative Example are housed in the exterior body so that the open ends of the positive electrode terminal and the negative electrode terminal are exposed to the outside through the separator, and the inner surface of the metal resin composite film is provided. The fusion allowance facing each other was hermetically sealed except for the portion to be the injection hole, the electrolytic solution was injected, and then the injection hole was sealed to assemble a non-aqueous electrolyte secondary battery.

<Confirmation of initial Coulomb efficiency>
The assembled non-aqueous electrolyte secondary battery was subjected to the initial charge / discharge process at 25 ° C., and the initial Coulomb efficiency was confirmed. Charging is a constant current constant voltage charge with an upper limit potential of 4.35 V (vs. Li / Li ⁺ ) with a current value of 15 mA (equivalent to 0.1 C) per 1 g of the positive electrode mixture, and the charge termination condition is a current value of 1. It was set as the time when it was attenuated to / 5. The discharge was a constant current discharge with a lower limit potential of 2.85 V (vs. Li / Li ⁺ ) at the same current value. Here, a rest process of 10 minutes was provided after charging and after discharging, and the charging capacity and the discharging capacity (0.1C discharge capacity) were confirmed, and the ratio of the discharging capacity to the charging 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 is a constant current constant voltage charge with an upper limit potential of 4.35 V (vs. Li / Li ⁺ ) with a current value of 15 mA (equivalent to 0.1 C) per 1 g of the positive electrode mixture, and the charge termination condition is a current value of 1. It was set as the time when it was attenuated to / 5. A 10-minute pause process was provided, and the discharge was a constant current discharge of 2.0 V (vs. Li / Li ⁺ ) at the same current value. Here, the discharge capacity (a) from 4.35 V (vs. Li / Li ⁺ ) to 3.0 V (vs. Li / Li ⁺ ) and the discharge capacity (a) from 3.0 V (vs. Li / Li ⁺ ) to 2.0 V (vs. Li / Li +). The ratio a / b of the discharge capacity (b) up to vs. Li / Li ⁺ ) was determined.
In this example and the comparative example, in evaluating the above discharge capacity ratio a / b, even if charging / discharging is performed at 0.1C, the same a / b as in the case of charging / discharging at 0.02C is obtained. After confirming that it was obtained, the above measurement conditions were set.

<Confirmation of high rate discharge performance>
Furthermore, the high rate discharge performance was confirmed. Charging is a constant current constant voltage charge with an upper limit potential of 4.35 V (vs. Li / Li ⁺ ) with a current value of 15 mA per 1 g of positive electrode mixture, and the charge termination condition is when the current value is reduced to 1/5. did. A 10-minute pause process was provided, and the discharge was a constant current discharge with a final voltage of 2.85 V at a current of 300 mA (corresponding to 2C) per 1 g 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 the high rate discharge performance (2C / 0.1C).

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

The above measurement results are shown in Table 1.

From Table 1, in comparison with Examples 1 and 2 and Comparative Example 1, the lithium excess type active material was acid-treated with citric acid (pKa ₁ = 3.1) or boric acid (pKa ₁ = 9.14). The non-aqueous electrolyte secondary battery according to Examples 1 and 2 subjected to charging / discharging of less than 4.5 V (vs. Li / Li ⁺ ) using the positive electrode active material according to Comparative Example 1 without 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 with the battery. The batteries according to Examples 1 and 2 have a discharge capacity (a) from 4.35 V (vs. Li / Li ⁺ ) to 3.0 V (vs. Li / Li ⁺ ) and 3.0 V (vs. Li / Li). The ratio a / b of the discharge capacity (b) from ⁺ ) to 2.0 V (vs. Li / Li ⁺ ) was in the range of 17 or more and 25 or less, whereas the battery according to Comparative Example 1 was a. / B was greater than 25. The active materials of Examples 1 and 2 had a larger specific surface area than the active materials of Comparative Example 1.

Comparative Examples 2 to 5 show the characteristics of the battery when the acid type is changed to sulfuric acid (pKa ₁ = -3) and the acid treatment is performed at various hydrogen ion concentrations and / or treatment times, and the capacity is 0.1 C. Both were lower than Comparative Example 1 without acid treatment, and both the initial Coulomb efficiency and the high rate discharge performance were not higher than those of Comparative Example 1. The discharge capacity ratio a / b was less than 17 or greater than 25.

In Comparative Examples 6 to 8, a positive acid active material in which the acid type was changed to phosphoric acid (pKa ₁ = 2.12) and the lithium excess type active material was acid-treated by changing the hydrogen ion concentration and / or the treatment time was used. The characteristics of the battery in the case are shown. Again, the 0.1C capacity was lower than that of Comparative Example 1 which was not subjected to the acid treatment, and both the initial Coulomb efficiency and the high rate discharge performance were not higher than those of Comparative Example 1. The discharge capacity ratio a / b was less than 17 or greater than 25.

Example 3 and Comparative Examples 9 and 10 are examples relating to a battery having a positive electrode active material acid-treated with tartaric acid (pKa ₁ = 3.2) having a different hydrogen ion concentration.
In Example 3, the acid-untreated Comparative Example 1 showed a capacity of 0.1 C, which was almost the same as that of Comparative Example 1, and the initial coulomb efficiency and high-rate discharge performance were improved. Although the Coulomb efficiency was improved from 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. Further, 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 acid-treated with tartrate acid having a low hydrogen ion concentration, whereas the hydrogen ion concentration was high. The batteries of Comparative Examples 9 and 10 having a positive electrode acid-treated with high tartrate 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 pKa ₁ is subjected to acid treatment of 3.1 or more, 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, 5 and Comparative Example 11, the composition (Li / Me = 1.3, Mn / Me = 0.48) of the lithium excess type active material according to Examples 1, 2 and Comparative Example 1 was determined by Mn. Corresponding to an example in which the composition ratio was changed to another composition (Li / Me = 1.2, Mn / Me = 0.55) having a larger composition ratio, Example 6 and Comparative Example 12 corresponded to Example 4 and Comparative Example 11. This corresponds to an example in which the Li ratio was changed (Li / Me = 1.3, Mn / Me = 0.55) without changing the Mn / Me of the above composition.
The characteristics of the batteries according to Examples 4 and 5 are 0.1C discharge capacity, initial Coulomb efficiency, and high rate discharge performance, as compared with Comparative Example 11 in which the active materials have the same composition and are not subjected to acid treatment. It can be seen that the discharge capacity ratio a / b is in the range of 17 or more and 25 or less. The characteristics of the batteries according to Example 6 are also higher than those of Comparative Example 12 in which the active materials have the same composition and are not subjected to the acid treatment, and the discharge capacity ratio a / b is 17 or more and 25. It can be seen that it is within the following range. Therefore, it can be seen that the identification of a / b is related to the improvement of the battery characteristics even in the active material having a composition range in which Mn / Me is larger.

In Comparative Examples 13 to 15, the composition ratio of Mn is higher than the composition of the lithium excess type active material (Li / Me = 1.3, Mn / Me = 0.48) according to Examples 1 and 2 and Comparative Example 1. It corresponds to the example of changing to another small composition (Li / Me = 1.2, Mn / Me = 0.40).
The characteristics of the batteries according to Comparative Examples 13 and 14 subjected to the acid treatment show only an improvement in the initial coulomb efficiency as compared with Comparative Example 15 not subjected to the acid treatment, but the high rate discharge performance is not improved.
Therefore, it can be seen that even when the discharge capacity ratio a / b is 17 or more and 25 or less as in the active material according to Comparative Example 13, if Mn / Me is too small, the effect of the present invention is not exhibited.

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 is increased (Li / Me = 1, Mn / Me = 0). .55) This is an example, both of which have a low 0.1C capacity and high rate discharge performance, and the discharge capacity ratio a / b is also outside the scope of the present invention.

Comparative Examples 18 to 20 are examples in which a lithium transition metal composite oxide having Li / Me = 1 and Ni: Co: Me = 33: 33: 33, which has already been put into practical use, is used as the positive electrode active material. The boric acid-treated Comparative Example 19 has improved battery characteristics as compared with the acid-untreated Comparative Example 20, but the citric acid-treated Comparative Example 18 has a 0.1 C discharge capacity and a high rate discharge performance. There is no correlation between each battery characteristic and the discharge capacity ratio a / b.

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 can be used as a battery for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and electric vehicles (EVs) that require high safety, efficiency, and high output. , Highly useful.

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 is
It has an α-NaFeO type ₂ crystal structure and has an α-NaFeO type 2 crystal structure.
The molar ratio of Li to the transition metal (Me), Li / Me, is 1 <Li / Me.
The transition metal (Me) contains Ni, Co and Mn, or Ni and Mn, and the molar ratio of Mn to Me, Mn / Me, is Mn / Me ≧ 0.45.
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 discharge capacity (a) from 3.0 V (vs. Li / Li ⁺ ) to 2. The ratio a / b of the discharge capacity (b) up to 0.0 V (vs. Li / Li ⁺ ) is 17 ≦ a / b ≦ 25.
Non-aqueous electrolyte Positive electrode active material for 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.
It has an α-NaFeO type ₂ crystal structure and has an α-NaFeO type 2 crystal structure.
The molar ratio of Li to the transition metal (Me), Li / Me, is 1 <Li / Me.
Lithium transition metal composite oxide containing Ni, Co and Mn, or Ni and Mn as the transition metal (Me) and having a molar ratio of Mn to Me of Mn / Me of Mn / Me ≧ 0.45, 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) treated with 1 or more acids. For non-aqueous electrolyte secondary batteries that produce positive electrode active materials with a ratio a / b of discharge capacity (b) from ⁺ ) to 2.0 V (vs. Li / Li ⁺ ) of 17 ≦ a / b ≦ 25. A method for producing a positive electrode active material. The positive electrode for a non-aqueous electrolyte secondary battery containing the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 3 is provided, and a diffraction peak is observed in the range of 20 to 22 ° in an X-ray diffraction diagram using CuKα rays for the positive electrode active material contained in the positive electrode. , Non-aqueous electrolyte secondary battery. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 3 is provided, and the positive electrode is charged to 4.5 V (vs. Li / Li ⁺ ) with a positive electrode potential of 4.5 to 5.0 V (vs. Li / Li +). A non-aqueous electrolyte secondary battery in which a region in which the potential change is relatively flat with respect to the amount of charging electricity is observed within the positive electrode potential range of vs. Li / Li ⁺ ). The non-aqueous electrolyte secondary battery according to claim 4 or 5, which is used at a potential of less than 4.5 V (vs. Li / Li ⁺ ). The method for manufacturing a non-aqueous electrolyte secondary battery according to any one of claims 4 to 6, wherein the maximum potential of the positive electrode in the initial charge / discharge step is less than 4.5 V (vs. Li / Li ⁺ ). A method for manufacturing a non-aqueous electrolyte secondary battery.

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