JP2018107118A - Nonaqueous electrolyte secondary battery, and method for manufacturing nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further improve the safety of a nonaqueous electrolyte secondary battery.SOLUTION: A nonaqueous electrolyte secondary battery comprises a positive electrode, a negative electrode and a nonaqueous electrolyte. In the nonaqueous electrolyte secondary battery, the positive electrode includes, as an active material, a first lithium transition metal composite oxide having an α-NaFeOstructure and represented by the general formula, LiMe1O(where Me1 is a transition metal element including Ni, Co and Mn), and a second lithium transition metal composite oxide having an α-NaFeOstructure and represented by the general formula, LiMe2O(where 0<α, and Me2 is a transition metal element including a combination of Ni and Mn or a combination of Ni, Mn and Co). As to the positive electrode, a diffraction peak is observed at or near 21° in an X-ray diffraction diagram with Cu Kα rays.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a non-aqueous electrolyte secondary battery and a method for manufacturing a non-aqueous electrolyte secondary battery.

Non-aqueous electrolyte secondary batteries represented by lithium secondary batteries have been increasingly used in recent years, and development of higher-capacity cathode materials has been demanded.
Conventionally, lithium transition metal composite oxides having an α-NaFeO ₂ type crystal structure have been studied as positive electrode active materials for non-aqueous electrolyte secondary batteries, and non-aqueous electrolyte secondary batteries using LiCoO ₂ have been widely put into practical use. Yes. The discharge capacity of LiCoO ₂ is about 120 to 130 mAh / g. As the transition metal (Me) constituting the lithium transition metal composite oxide, abundant Mn is used as an earth resource, and the molar ratio Li / Me of Li to the transition metal constituting the lithium transition metal composite oxide is approximately 1. In addition, a nonaqueous electrolyte secondary battery using a so-called “LiMeO ₂ type” active material having a Mn molar ratio Mn / Me in the transition metal of 0.5 or less has been put into practical use. For example, the discharge capacity of the positive electrode active material containing LiNi _1/2 Mn _1/2 O ₂ or LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is 150 to 180 mAh / g.
Generally, the charging voltage adopted for a non-aqueous electrolyte secondary battery using these so-called “LiMeO ₂ type” active materials is about 4.3 V, and the maximum potential reached at the positive electrode at this time is about 4. 4 V (vs. Li ^/ Li ⁺ ). This is because even if the charging voltage is further increased, a larger discharge capacity cannot be obtained.

  The standard stipulates that safety is ensured for non-aqueous electrolyte secondary batteries even when they are overcharged by mistake. As a technique for improving the safety of a non-aqueous electrolyte secondary battery, a technique for applying a specific additive to a non-aqueous electrolyte (electrolytic solution) is known (see, for example, Patent Document 1).

Patent Document 1 states that “a nonaqueous electrolyte secondary battery including a nonaqueous electrolyte, wherein the nonaqueous electrolyte includes a halogenated aromatic compound represented by the following general formula (1) and the following general formula (2 Non-aqueous electrolyte secondary battery comprising a nitrogen-containing heterocyclic compound represented by the formula (1)].
Examples include a positive electrode plate (paragraph [0063]) prepared using “LiNi _1/3 Mn _1/3 Co _1/3 O ₂ as a positive electrode active material” and “graphite (graphite as a negative electrode active material). ) ”And LiPF ₆ at a concentration of 1 mol / L in a mixed solvent of“ ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 30: 70 (volume ratio) ”(paragraph [0064]). 2-fluorotoluene (orthofluorotoluene) which is a halogenated aromatic compound represented by the general formula (1) and 3-methyl which is a nitrogen-containing heterocyclic compound represented by the general formula (2) Non-aqueous electrolyte with non-aqueous electrolyte (paragraph [0066]) prepared by adding 5.0 mass% and 4.0 mass% of 2-oxazolidone to the non-aqueous electrolyte, respectively On solution electrolyte secondary battery, it was subjected to the overcharge test (paragraph [0069], [0070]) have been described.

On the other hand, in recent years, among lithium transition metal composite oxides having an α-NaFeO ₂ type crystal structure, the Mn molar ratio Mn / Me in the transition metal (Me) exceeds 0.5, and Li to the transition metal (Me) So-called “lithium-rich” active materials having a molar ratio Li / Me of greater than 1 are known. This active material has a relatively flat potential change with respect to the amount of charge in the potential range of 4.5 to 5.0 V (vs. Li / Li ⁺ ) in the initial charging process after assembling the battery. In this case, the “LiMeO ₂ type” active material can be obtained by charging until the charging process in which the flat region is observed is completed, even if the subsequent charging potential is not so noble. It has attracted attention because it has a high discharge capacity compared to (see Patent Document 2).

Patent Document 2 states that “an active material for a lithium secondary battery including a solid solution of a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure, which includes Li, Co, Ni, and Mn contained in the solid solution. The composition ratio is Li _{1+ (1/3) x} Co _1-xy Ni _{(1/2) y} Mn _{(2/3) x + (1/2) y} (x + y ≦ 1, 0 ≦ y, 1−x −y = z), and the intensity ratio of the diffraction peaks of the (003) plane and the (104) plane by X-ray diffraction measurement is I ₍₀₀₃₎ / I _{( 104)} ≧ 1.56, and I ₍₀₀₃₎ / I ₍₁₀₄₎ > 1 at the end of discharge, exceeding 4.3 V (vs. Li / Li ⁺ ) and 4.8 V or less (vs. Li / Li) potential change appearing against amount of charge in the positive electrode potential range of ⁺⁾ is relatively flat region When passing through the step of performing at least throughout the initial charge, 4.3 V for a lithium secondary battery (vs.Li/Li ⁺⁾ electric quantity capable discharge in the following potential region is characterized to be a 177 mAh / g or more Active material "(Claim 3).

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

It is also known that a “LiMeO ₂ type” active material and a “lithium-excess type” active material are mixed and used as a positive electrode active material (see Patent Documents 3 and 4).
Patent Document 3 discloses that “having an α-NaFeO ₂ structure and containing Co, Ni and Mn as transition metals Me1, 1 <molar ratio Li / Me1 <1.5, molar ratio Mn / Me1> 0.5. lithium transition metal complex oxide a is represented by a composition formula LiMe2O ₂ (where, Me2 is Co, transition metal containing Ni and Mn, 0 <mole ratio Mn / Me2 ≦ 0.5) lithium transition metal complex represented by A mixed active material for a lithium secondary battery using a mixture of oxide B as an active material, the lithium transition metal composite oxide A being contained in the mixture in an amount of 50 to 85% by mass, and the lithium transition metal composite oxide A is the average particle diameter is smaller than the average particle diameter of the lithium transition metal composite oxide B, and the differential pore volume determined by the BJH method from the adsorption isotherm using the nitrogen gas adsorption method shows the maximum value. Pore diameter is 30 In the range of 40 nm, a mixed active material for a lithium secondary battery, wherein the peak differential pore volume is 0.85mm ³ / (g · nm) or more. "(Claim 1) is described.
And about the secondary battery (paragraph [0119]) which has the positive electrode using the mixed active material which concerns on an Example, and the negative electrode using metallic lithium, it used for the initial stage charge / discharge process under 25 degreeC. The constant current and constant voltage charging with a current of 0.1 CmA and a voltage of 4.6 V was performed, and the charge termination condition was set at the time when the current value was attenuated to 放電 The discharge was performed at a constant current of 0.1 CmA and a final voltage of 2.0 V. It was referred to as “current discharge. This charge / discharge was performed for two cycles”.

Patent Document 4 states that “compositional formula Li _x Ni _a Mn _b M _c O ₂ (1.09 <x <1.20, 0.21 <a <0.42, 0.42 <b <0.63, 0 ≦ c ≦ 0.02, x + a + b + c = 2.0, where M is an element represented by at least one of Co, V, Mo, W, Zr, Nb, Ti, Al, Fe, Mg, Cu, etc. One positive electrode active material particle and a compositional formula LiM′O ₂ (0.9 ≦ y ≦ 1.1, where M ′ is one or more metal elements including at least one of Ni and Co). And a positive electrode material for a lithium ion secondary battery, comprising positive electrode active material particles.
And about the prototype battery which has the positive electrode using the positive electrode material which concerns on an Example, and the negative electrode (paragraph [0038]) using metallic lithium, "The charge / discharge test was done. Charging is constant current constant voltage charge (CC-CV. The upper limit voltage was 4.5 V. The discharge was constant current discharge (CC mode) and the lower limit voltage was 3.0 V ”(paragraph [0040]).

JP-A-2006-46125 Japanese Patent No. 4877660 Japanese Patent Laid-Open No. 2006-119288 JP, 2006-62788, A

As described above, non-aqueous electrolyte secondary batteries have standards that ensure safety even if they are accidentally overcharged (for example, GB / T (China recommended national standard for automotive batteries). ) ”). As a method of evaluating the improvement in safety, assuming that the charge control circuit is broken, when the current is forcibly applied beyond the fully charged state (SOC 100%), the electrode potential rapidly increases. There is a method of recording the observed SOC. If no rapid increase in electrode potential is observed until a higher SOC is reached, it is evaluated that safety has improved.
Patent Document 1 discloses that a “LiMeO ₂ type” active material is used for a positive electrode and a specific additive is added to a nonaqueous electrolyte to improve safety by overcharging. However, there is a problem that such an additive causes a decrease in battery performance.
Patent Document 2 uses a “lithium-excess type” active material as a positive electrode, and Patent Documents 3 and 4 describe a mixture of a “LiMeO ₂ type” active material and a “lithium-excess type” active material to form a positive electrode active material. It is shown that the discharge capacity and the like can be improved by setting the initial charging potential for metallic lithium to 4.5 V or higher. However, there is no indication of safety during overcharging.
An object of this invention is to improve the safety | security of a nonaqueous electrolyte secondary battery more.

One aspect of the present invention is a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode has an α-NaFeO ₂ structure as an active material, and has a general formula LiMe1O ₂ (Me1 is A first lithium transition metal composite oxide represented by a transition metal element including Ni, Co, and Mn), an α-NaFeO ₂ structure, and a general formula Li _{1 + α} Me2 _1-α O ₂ (0 <α, Me2 includes a second lithium transition metal composite oxide represented by Ni and Mn, or a transition metal element including Ni, Mn, and Co), and the active material is 21 in an X-ray diffraction diagram using CuKα rays. This is a non-aqueous electrolyte secondary battery in which a diffraction peak is observed in the vicinity of °.

Another aspect of the present invention is a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode has an α-NaFeO ₂ structure as an active material, and has a general formula of LiMe1O ₂ ( Me1 has a first lithium transition metal composite oxide represented by Ni, Co, and Mn) and an α-NaFeO ₂ structure, and has the general formula Li _{1 + α} Me2 _1-α O ₂ (0 < α, Me2 includes a second lithium transition metal composite oxide represented by Ni and Mn, or a transition metal element including Ni, Mn, and Co), and the positive electrode potential is 5.0 V (vs. Li ^/ Li ⁺ ). When charging up to is performed, a region in which the potential change is relatively flat with respect to the amount of charge is observed in the positive electrode potential range of 4.5 to 5.0 V (vs. Li / Li ⁺ ). It is a water electrolyte secondary battery.

Another aspect of the present invention is a method of manufacturing a non-aqueous electrolyte secondary battery, wherein the initial charge / discharge step is performed at less than 4.5 V (vs. Li / Li ⁺ ). Is the method.

  ADVANTAGE OF THE INVENTION According to this invention, even when it overcharges accidentally, the nonaqueous electrolyte secondary battery which improved safety | security, and its manufacturing method can be provided.

X-ray diffraction pattern of positive electrode active material according to an embodiment of the present invention X-ray diffraction pattern of a positive electrode active material after overcharging a nonaqueous electrolyte secondary battery according to an embodiment of the present invention X-ray diffraction pattern of positive electrode active material according to comparative example of the present invention The figure which shows the electrical potential change with respect to the charge amount of electricity at the time of the overcharge of the positive electrode which concerns on embodiment and comparative example of this invention. It shows the potential change for the amount of charge to be observed "LiMeO ₂ Model" and "lithium-excess type" active material when charged and discharged at the positive electrode potential range of less than 4.5V (vs.Li/Li ⁺⁾ Shows the potential change for the amount of charge that is observed when the initial charge-discharge "LiMeO ₂ Model" and "lithium-excess type" active material 4.5V (vs.Li/Li ⁺⁾ or more positive electrode potential range The figure explaining "the area | region where an electric potential change is comparatively flat with respect to the amount of charge electricity" in the nonaqueous electrolyte secondary battery which concerns on embodiment of this invention The perspective view which shows one Embodiment of the nonaqueous electrolyte secondary battery which concerns on 1 aspect of this invention 1 is a schematic diagram illustrating a power storage device including a plurality of nonaqueous electrolyte secondary batteries according to one embodiment of the present invention.

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

The present inventor uses a so-called “LiMeO ₂ type” active material as a positive electrode and adopts a charging condition in which the maximum potential of the positive electrode during charging is 4.45 V (vs. Li / Li ⁺ ) or less. In a battery based on the assumption that the so-called “lithium-excess” active material is mixed with the positive electrode, the exothermic reaction when the state of charge (SOC) of the battery is intentionally increased beyond 100% is more The inventors have found that the effect observed at high SOC is achieved, and have reached the present invention.
A nonaqueous electrolyte secondary battery according to an embodiment of the present invention (hereinafter referred to as “this embodiment”) includes a first lithium transition metal composite oxide and a second lithium as a positive electrode active material. The active material is a non-aqueous electrolyte secondary battery that includes a transition metal composite oxide and has a diffraction peak observed at around 21 ° in an X-ray diffraction diagram using CuKα rays.
The nonaqueous electrolyte secondary battery according to the present embodiment includes the following first lithium transition metal composite oxide and second lithium transition metal composite oxide as the positive electrode active material, and the positive electrode potential is 5. 0V when performing charging leading to (vs.Li/Li ^+), in the positive electrode potential range of 4.5~5.0V (vs.Li/Li ^+), the potential change with respect to the charge electrical quantity is relatively It can also be said that the non-aqueous electrolyte secondary battery includes a positive electrode in which a flat region is observed.
Furthermore, the nonaqueous electrolyte secondary battery according to the present embodiment includes an aspect in which the positive electrode is combined with a nonaqueous electrolyte containing fluoroethylene carbonate (FEC) in a nonaqueous solvent. According to this aspect, it is possible to obtain a nonaqueous electrolyte secondary battery in which safety is further improved and internal resistance after the charge / discharge cycle is kept low.
Hereinafter, this embodiment will be described in detail.

<First lithium transition metal composite oxide>
The first lithium transition metal composite oxide is a so-called “LiMeO ₂ type” active material represented by the general formula LiMe1O ₂ (M1 is a transition metal element containing Ni, Co and Mn). In this active material, Li is exclusively located at the Li site, and theoretically Li / Me1 = 1. Therefore, it is typically represented by the composition formula LiNi _a Co _b Mn _c O ₂ (a + b + c = 1). The However, LiMe1O ₂ may be Li / Me1> 1 in terms of quantitative analysis when it is subjected to a process such that the charging amount of the Li raw material during synthesis is Li / Me1> 1. When it is oxidized (charged), Li / Me1 <1 in some quantitative analysis. However, in the lithium transition metal composite oxide represented by LiMe1O ₂ , even when Li / Me1 is not equal to 1, a part of Li is substantially not contained in the lithium-excess lithium transition metal composite oxide. Since it is not located at the transition metal site, it can be distinguished from the lithium-rich active material that is the second lithium transition metal composite oxide.
The molar ratio Ni / Me1 of Ni to the transition metal element Me1, that is, a is preferably set to 0.3 or more and 0.6 or less in order to improve the charge / discharge cycle performance of the nonaqueous electrolyte secondary battery.
The molar ratio Co / Me1 of Co to the transition metal element Me1, that is, b is preferably 0.1 or more and 0.4 or less in order to increase the conductivity of the active material particles.
The molar ratio of Mn to transition metal element Me1, Mn / Me1, that is, c is preferably 0.5 or less in order to improve charge / discharge cycle performance. Moreover, it is preferable to set it as 0.2 or more from a viewpoint of material cost.
The first lithium transition metal composite oxide according to the present embodiment is an alkali metal such as Na and K, an alkaline earth metal such as Mg and Ca, and 3d such as Fe, as long as the effects of the present invention are not impaired. It does not exclude inclusion of a small amount of other metals such as transition metals typified by transition metals.

The first lithium transition metal composite oxide according to this embodiment has an α-NaFeO ₂ structure. The lithium transition metal composite oxide after synthesis (before charge / discharge) and after charge / discharge are both attributed to R3-m. Note that “R3-m” should be represented by adding a bar “-” on “3” of “R3m”.

<Second lithium transition metal composite oxide>
The second lithium transition metal composite oxide according to the present embodiment has the general formula Li _{1 + α} Me2 _1-α O ₂ (0 <α, Me2 is a transition metal element containing Ni and Mn, or Ni, Mn and Co). It is a so-called “lithium-rich” active material. Typically, it can be expressed as Li _{1 + α} (Ni _β Co _γ Mn _δ ) _1-α O ₂ (β + γ + δ = 1). In order to increase safety during overcharge, the molar ratio Li / Me2 of Li to the transition metal element Me2, that is, (1 + α) / (1-α) is preferably 1.1 or more, and is 1.15 or more. More preferably. In order to suppress a decrease in discharge capacity, Li / Me2 is preferably 1.35 or less, and more preferably 1.3 or less.
The molar ratio of Mn to transition metal element Me2 Mn / Me2, that is, δ, preferably exceeds 0.5 from the viewpoint of stabilizing the layered structure. Further, from the viewpoint of charge / discharge capacity, Mn / Me2 is preferably 0.7 or less, and more preferably 0.65 or less.
In order to improve the charge / discharge cycle performance of the nonaqueous electrolyte secondary battery, the molar ratio Ni / Me2 of Ni with respect to the transition metal element Me, that is, β is preferably 0.2 or more and 0.5 or less.
The molar ratio Co / Me2 of Co to the transition metal element Me2, that is, γ increases the conductivity of the active material particles, but is preferably 0.0 or more and 0.3 or less in order to reduce the material cost.
Note that the second lithium transition metal composite oxide according to the present embodiment is also an alkali metal such as Na and K, an alkaline earth metal such as Mg and Ca, and 3d such as Fe, as long as the effects of the present invention are not impaired. It does not exclude inclusion of a small amount of other metals such as transition metals typified by transition metals.

The second lithium transition metal composite oxide according to this embodiment has an α-NaFeO ₂ structure. The lithium transition metal composite oxide after synthesis (before charge / discharge) is attributed to the space group P3 ₁ 12 and has a superlattice peak (Li) near 2θ = 21 ° on an X-ray diffraction diagram using a CuKα tube. [Li _1/3 Mn _2/3 ] O ₂ type monoclinic crystal peak) is confirmed. However, when the charge exceeding 4.5V (vs. Li / Li ⁺ ) is performed even once, this superlattice peak disappears because the symmetry of the crystal changes with the elimination of Li in the crystal. Thus, the lithium transition metal composite oxide is assigned to the space group R3-m. Here, P3 ₁ 12 is a crystal structure model in which the atomic positions of the 3a, 3b, and 6c sites in R3-m are subdivided, and when ordering is recognized in the atomic arrangement in R3-m, the P3 ₁ 12 model Is adopted.

The “lithium-excess type” active material that is the second lithium transition metal composite oxide is 4.5 to 5.0 V (vs) when charged so that the positive electrode potential reaches 5.0 V (vs. Li ^/ Li ⁺ ). .Li / Li ⁺ ), a region where the potential change is relatively flat with respect to the amount of charge is observed in the positive electrode potential range. However, when the charging until the end of the charging process in which the flat region is observed is performed even once, even if the charging reaches 5.0 V (vs. Li ^/ Li ⁺ ), the flat region is observed. The area is never reproduced.

<Positive electrode active material>
The positive electrode active material used for the non-aqueous electrolyte secondary battery according to this embodiment includes the first lithium transition metal composite oxide and the second lithium transition metal composite oxide.
When this positive electrode active material is subjected to X-ray diffraction using CuKα rays, a diffraction peak is observed in the vicinity of 21 ° in the X-ray diffraction diagram, or 4.5 V (vs. Li ^/ Li ⁺ ) or more. In the case of the positive electrode potential range, this can be confirmed by the appearance of a relatively flat region of potential change with respect to the amount of charged electricity.

X-ray diffraction measurement for the positive electrode active material used in the non-aqueous electrolyte secondary battery according to the present embodiment, and the active material included in the positive electrode included in the non-aqueous electrolyte secondary battery according to the present embodiment, and X-rays using CuKα rays In the diffractogram, confirmation that a diffraction peak is observed near 21 ° is performed according to the following procedure and conditions.
If the sample to be used for measurement is an active material powder before electrode preparation, it is used for measurement as it is. When a sample is collected from an electrode taken out by disassembling the battery, the battery is put into a discharged state by the following procedure before disassembling the battery. First, constant current charging is performed up to a battery voltage at which the positive electrode potential becomes 4.3 V (vs. Li ^/ Li ⁺ ) with a current of 0.1 C, and the current value decreases to 0.01 C at the same battery voltage. Charge the battery at a constant voltage until the end of charge. After a 30-minute pause, constant current discharge is performed at a current of 0.1 C until the battery voltage reaches a positive electrode potential of 2.0 V (vs. Li ^/ Li ⁺ ), and a discharge end state is obtained. If the battery uses a metal lithium electrode as the negative electrode, the battery may be disassembled after the battery is brought into the end-of-discharge state or the end-of-charge state, and the electrode may be taken out. In order to accurately control the positive electrode potential, after disassembling the battery and taking out the electrode, after assembling the battery using the metal lithium electrode as a counter electrode, the battery is adjusted to the end of discharge state according to the above procedure. The work from disassembly of the battery to measurement is performed in an argon atmosphere with a dew point of -60 ° C or lower. The positive electrode plate taken out is washed thoroughly with non-aqueous electrolyte attached to the electrode using dimethyl carbonate, dried at room temperature for a whole day and night, and then the mixture on the aluminum foil current collector is collected. The collected mixture is lightly loosened in an agate mortar and placed in an X-ray diffraction measurement sample holder for measurement.

FIG. 1 shows the positive electrode in the end-of-discharge state during normal use (4.45 V (vs. Li / Li ⁺ ) charging is defined as SOC 100%) for the nonaqueous electrolyte secondary battery according to Example 1-7 to be described later. FIG. 3 is an X-ray diffraction diagram measured by the above procedure. In FIG. 1, a diffraction peak is observed near 21 °.
On the other hand, FIG. 2 shows an overcharge corresponding to SOC 202% until the positive electrode potential reaches 5.0 V (vs. Li ^/ Li ⁺ ) with respect to the nonaqueous electrolyte secondary battery according to Example 1-7. It is an X-ray-diffraction figure measured by said procedure about the positive electrode in the end-of-discharge state after performing. Here, the diffraction peak near 21 ° disappears.
FIG. 3 shows the positive electrode in the end-of-discharge state during normal use (4.60 V (vs. Li / Li ⁺ ) charging is defined as SOC 100%) for the nonaqueous electrolyte secondary battery according to Comparative Example 1-3 to be described later. FIG. 3 is an X-ray diffraction diagram measured by the above procedure. That is, in Comparative Example 1-3, the diffraction peak near 21 ° has already disappeared during normal use.

FIG. 4 shows that for the nonaqueous electrolyte secondary batteries according to Examples 1-7 and Comparative Example 1-3, the positive electrode potential was 5.0 V (vs. Li / Li from the fully charged state during normal use. The charging curve is shown when overcharging up to ⁺ ) is performed. In Example 1-7, it has a relatively flat charging curve until the positive electrode potential suddenly rises at around 200% SOC, but in Comparative Example 1-3, as soon as the SOC exceeds 100%. A rapid increase in the positive electrode potential occurs.

The principle of the action mechanism of the present invention will be described with reference to FIGS. 5 and 6, the first lithium transition metal composite oxide (denoted as NCM) and the second lithium transition metal complex oxide (denoted as LR) were each used alone as the positive electrode active material. The nonaqueous electrolyte secondary battery provided with the positive electrode is assembled, and the potential change of the charge / discharge positive electrode performed first is shown. However, FIG. 5 shows that the maximum potential of the positive electrode during charging is 4.45 V (vs. Li / Li ⁺ ), and FIG. 6 shows that the maximum potential of the positive electrode during charging is 4.55 V (vs. Li / Li). Li ⁺ ).
A nonaqueous electrolyte secondary battery using the first lithium transition metal composite oxide alone as a positive electrode active material is charged at a maximum potential of less than 4.5 V (vs. Li ^/ Li ⁺ ) (see FIG. 5). However, even when charged at 4.5 V (vs. Li ^/ Li ⁺ ) or more (see FIG. 6), the potential gradually increases with respect to the amount of charged electricity, and a region where the potential change is flat does not appear. Even when the charging potential is 4.5 V (vs. Li / Li ⁺ ) or more, the discharge capacity is at most about 210 mAh / g.
On the other hand, the nonaqueous electrolyte secondary battery using the second lithium transition metal composite oxide alone as the positive electrode active material has a positive electrode potential range of 4.5 V (vs. Li ^/ Li ⁺ ) or higher. In the potential range of 4.5 to 5.0 V (vs. Li / Li ⁺ ), a region where the potential change is relatively flat with respect to the amount of charge is observed (see FIG. 6), and the flat region is By charging until the observed charging process is completed, a discharge capacity of about 300 mAh / g can be obtained. On the other hand, when charging is performed at a maximum potential of less than 4.5 V (vs. Li ^/ Li ⁺ ), the discharge capacity is a non-aqueous electrolyte that uses the first lithium transition metal composite oxide alone as the positive electrode active material. Below the secondary battery (see FIG. 5).
The non-aqueous electrolyte secondary battery according to one embodiment of the present invention uses the first lithium transition metal composite oxide and the second lithium transition metal composite oxide as a positive electrode active material by mixing them. The battery is completed without charging until the charging process in which the flat region is observed is completed. Furthermore, the nonaqueous electrolyte secondary battery according to an embodiment of the present invention is used under charging conditions in which charging is not performed until the charging process in which the flat region is observed is completed. Therefore, the non-aqueous electrolyte secondary battery according to an embodiment of the present invention is not charged until the charging process in which the flat region is observed once is completed from the manufacturing stage to the time of use. When overcharging is performed, a region in which the potential change is relatively flat with respect to the amount of charge is observed in the positive electrode potential range of 4.5 to 5.0 V (vs. Li / Li ⁺ ). The non-aqueous electrolyte secondary battery according to an embodiment of the present invention uses the behavior described above to reach a higher SOC in an overcharged state exceeding SOC 100% that is a fully charged state during normal use. Thus, it is possible to suppress the rapid increase in electrode potential and improve the safety against overcharge.

In the nonaqueous electrolyte secondary battery according to the present embodiment, the ratio of the second lithium transition metal composite oxide in the positive electrode active material is preferably 20% by mass or more from the viewpoint of safety against overcharging, More preferably, it is 30% by mass or more.
On the other hand, regarding the discharge capacity, when the battery is used for charging / discharging whose maximum potential is less than, for example, 4.5 V (vs. Li / Li ⁺ ), the first lithium transition metal composite oxide is more suitable for the second lithium transition. The discharge capacity is higher than that of the metal composite oxide (see FIG. 5).
Therefore, in order to increase the discharge capacity, the ratio of the first lithium transition metal composite oxide in the positive electrode active material is preferably 30% by mass or more, and more preferably 50% by mass or more.
That is, the mixing ratio of the first lithium transition metal composite oxide and the second lithium transition metal composite oxide is preferably 20:80 to 80:20, and 30:70 to 70:30. Is more preferable, and 50:50 to 70:30 is particularly preferable.
Here, when the positive electrode is “charged up to a positive electrode potential of 5.0 V (vs. Li ^/ Li ⁺ ), within a positive electrode potential range of 4.5 to 5.0 V (vs. Li ^/ Li ⁺ ). More specifically, “a region where the potential change is relatively flat with respect to the amount of charge is observed” means that “a non-aqueous electrolyte secondary battery is 4.5 V (vs. Li) at a current of 0.1 C. / Li ⁺⁾ maximum value of dSOC / dV of 5.0V (vs.Li/Li ⁺⁾ until the constant current charge was performed from judges in "to show more than 70. The maximum value of the dSOC / dV is preferably 90 or more, and more preferably 100 or more. dSOC / dV is the slope of the curve by reversing the horizontal and vertical axes of a normal charging curve plotted with the horizontal axis as the charge depth (SOC) and the vertical axis as the potential (V (vs. Li ^/ Li ⁺ )). (Refer to FIG. 7). The state of SOC 100% corresponds to the fully charged state when the battery to be confirmed is charged according to the charging conditions during normal use. In the specification of the present application, the normal use is a case where the nonaqueous electrolyte secondary battery is used under the charge / discharge conditions recommended or specified for the nonaqueous electrolyte secondary battery. When a charger for a non-aqueous electrolyte secondary battery is prepared, it means a case where the non-aqueous electrolyte secondary battery is used by applying the charger.

<Method for producing precursors of first and second lithium transition metal composite oxide>
Next, a method for producing the precursors of the first and second lithium transition metal composite oxides used for the active material for a nonaqueous electrolyte secondary battery according to this embodiment will be described.
The lithium transition metal composite oxide according to the present embodiment is basically a raw material containing a metal element (Li, Ni, Co, Mn) constituting the active material according to the composition of the target active material (oxide). It can be obtained by preparing and baking this.
In producing a composite oxide having a desired composition, a so-called “solid phase method” in which salts of Li, Ni, Co, and Mn are mixed and fired, or Ni, Co, and Mn are previously present in one particle. There is known a “coprecipitation method” in which a coprecipitation precursor is prepared, and a Li salt is mixed and fired therein. In the synthesis process by the “solid phase method”, especially Mn is difficult to uniformly dissolve in Ni and Co, so it is difficult to obtain a sample in which each element is uniformly distributed in one particle. In literatures and the like, many attempts have been made to dissolve Mn in a part of Ni or Co (LiNi _1-x Mn _x O ₂ etc.) by solid phase method, but the “coprecipitation method” is selected. It is easier to obtain a homogeneous phase at the atomic level. Therefore, the “coprecipitation method” is employed in the examples described later.

In the method for producing a precursor of a lithium transition metal composite oxide according to this embodiment, a raw material aqueous solution containing Ni, Co and Mn is dropped, and a compound containing Ni, Co and Mn is coprecipitated in the solution. It is preferable to prepare a precursor.
In producing a coprecipitation precursor, Mn is easily oxidized among Ni, Co, and Mn, and it is not easy to produce a coprecipitation precursor in which Ni, Co, and Mn are uniformly distributed in a divalent state. Uniform mixing at the atomic level of Ni, Co and Mn tends to be insufficient. Therefore, in the present invention, it is preferable to remove dissolved oxygen in order to suppress oxidation of Mn existing in the coprecipitation precursor. Examples of the method for removing dissolved oxygen include a method of bubbling a gas not containing oxygen. The gas not containing oxygen is not limited, but nitrogen gas, argon gas, carbon dioxide (CO ₂ ), or the like can be used.

Although the pH in the step of preparing a precursor by co-precipitation of a compound containing Ni, Co and Mn in a solution is not limited, an attempt is made to prepare the co-precipitation precursor as a co-precipitation hydroxide precursor. When doing, it can be set to 10.5-14. In 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. Furthermore, since the particle growth rate can be accelerated by setting the pH to 11.0 or less, the stirring continuation time after completion of dropping of the raw material aqueous solution can be shortened.
Moreover, when it is going to produce the said coprecipitation precursor as a coprecipitation carbonate precursor, it can be set as 7.5-11. By setting the pH to 9.4 or less, the tap density can be set to 1.25 g / cm ³ or more, and high-rate discharge performance can be improved. Furthermore, since the particle growth rate can be accelerated by setting the pH to 8.0 or less, the stirring continuation time after completion of dropping of the raw material aqueous solution can be shortened.

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

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

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

  The preferable stirring duration after the dropping of the raw material aqueous solution is influenced by the size of the reaction vessel, stirring conditions, pH, reaction temperature, etc., but 0.5 hours or more in order to grow the particles as uniform spherical particles 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 is not sufficient due to the particle size becoming too large, it is preferably 30 hours or less, more preferably 25 hours or less, and most preferably 20 hours or less.

<Method for producing first and second lithium transition metal composite oxide>
It is preferable that the manufacturing method of the 1st and 2nd active material for nonaqueous electrolyte secondary batteries which concerns on this embodiment is a method of mixing the said coprecipitation precursor and Li compound, and baking.
LiF, Li ₂ SO ₄ , or Li ₃ PO ₄ may be used as a sintering aid together with lithium hydroxide and lithium carbonate that 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. The total amount of the Li compound is preferably charged in an excess of about 1 to 5% in view of the disappearance of a part of the Li compound during firing.

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

On the other hand, if the firing temperature is too high, the structure changes from a layered α-NaFeO ₂ structure to a rock salt cubic structure, which is disadvantageous for lithium ion movement in the active material during the charge / discharge reaction, and the discharge performance decreases. . In the present invention, the firing temperature is preferably 1000 ° C. or lower. By setting it to 1000 ° C. or less, the charge / discharge cycle performance can be improved.
Therefore, when the positive electrode active material containing the lithium transition metal composite oxide according to one embodiment of the present invention is manufactured, the firing temperature is preferably 900 to 1000 ° C. in order to improve charge / discharge cycle performance.

<Negative electrode material>
The negative electrode material of the battery according to the present embodiment is not limited, and any battery material that can release or occlude lithium ions may be selected. For example, titanium-based materials such as lithium titanate having a spinel crystal structure typified by Li [Li _1/3 Ti _5/3 ] O ₄ , alloy-based materials such as Si, Sb, and Sn-based materials, lithium metal, lithium Alloys (lithium-containing alloys such as lithium-silicon, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and wood alloys), lithium composite oxide (lithium-titanium), oxidation In addition to silicon, alloys that can occlude and release lithium, carbon materials (eg, graphite, hard carbon, low-temperature fired carbon, amorphous carbon, etc.), and the like can be given.

<Positive electrode / Negative electrode>
The positive electrode active material and the negative electrode material are desirably powders having an average particle size of 100 μm or less. Particularly, the powder of the positive electrode active material is preferably 15 μm or less for the purpose of improving the high output characteristics of the nonaqueous electrolyte secondary battery, and preferably 10 μm or more in order to maintain the charge / discharge cycle performance. . In order to obtain the powder in a predetermined shape, a pulverizer or a classifier is used. For example, a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill or a sieve is used. At the time of pulverization, wet pulverization in the presence of water or an organic solvent such as hexane may be used. There is no particular limitation on the classification method, and a sieve, an air classifier, or the like is used as needed for both dry and wet methods.

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

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

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

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

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

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

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

<Nonaqueous electrolyte>
The nonaqueous electrolyte used in the nonaqueous electrolyte secondary battery according to one embodiment of the present invention is not limited, and those generally proposed for use in lithium batteries and the like can be used. Nonaqueous solvents used for nonaqueous electrolytes include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, vinylene carbonate or fluorides thereof; cyclic esters such as γ-butyrolactone and γ-valerolactone A chain carbonate such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; a chain ester such as methyl formate, methyl acetate, and methyl butyrate; tetrahydrofuran or a derivative thereof; 1,3-dioxane, 1,4-dioxane, Ethers such as 1,2-dimethoxyethane, 1,4-dibutoxyethane and methyldiglyme; Nitriles such as acetonitrile and benzonitrile; Dioxolane or derivatives thereof; Ethylene sulfide, sulfolane, sulfur Or a mixture of two or more thereof.
Among these, it is preferable to use a nonaqueous electrolyte containing FEC in which the nonaqueous solvent is a fluorinated cyclic carbonate. By combining the positive electrode including the first lithium transition metal composite oxide and the second lithium transition metal composite oxide with the nonaqueous electrolyte including FEC in the nonaqueous solvent, the safety is further improved and the charge is improved. A nonaqueous electrolyte secondary battery in which the internal resistance after the discharge cycle is kept low can be obtained.

  In this specification, the internal resistance is measured under the following conditions. Prior to measurement, the battery is brought to the end of charge under normal use conditions. Next, after performing constant-current discharge to a voltage that the closed circuit voltage between the terminals is expected to reach during normal use with a current of 0.2 C, the circuit is opened and left for 2 hours or longer. By the above operation, the nonaqueous electrolyte battery is brought into a discharged state. The resistance value between the positive and negative terminals is measured using an impedance meter of a system that applies 1 kHz alternating current (AC). An overcharged non-aqueous electrolyte battery or an over-discharged non-aqueous electrolyte battery should not be measured.

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

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

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

  The concentration of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol / L to 5 mol / L, more preferably 0.5 mol / L in order to reliably obtain a non-aqueous electrolyte secondary battery having high battery characteristics. -2.5 mol / L.

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

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

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

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

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

  Other battery components include a terminal, an insulating plate, a battery case, and the like, but these components may be used as they are.

<Nonaqueous electrolyte secondary battery>
A non-aqueous electrolyte secondary battery according to this embodiment is shown in FIG. FIG. 8 is a perspective view of the inside of a rectangular nonaqueous electrolyte secondary battery seen through. The nonaqueous electrolyte secondary battery 1 is assembled by injecting a nonaqueous electrolyte (electrolytic 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 including a positive electrode active material and a negative electrode including a negative electrode active material via a separator. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 4 ′, and the negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 5 ′.
The shape of the nonaqueous electrolyte secondary battery according to this embodiment is not particularly limited, and examples thereof include a cylindrical battery, a square battery (rectangular battery), a flat battery, and the like.

The non-aqueous electrolyte secondary battery according to this embodiment uses a positive electrode including a “LiMeO ₂ type” active material and a “lithium-excess type” active material, and is normally performed on a “lithium-excess type” active material. Manufacture and use without passing through the charging process until the end of the charging process in which the flat region observed in the positive electrode potential range of .5 to 5.0 V (vs. Li / Li ⁺ ) is observed. Is done.

As described above, the nonaqueous electrolyte secondary battery according to the present embodiment does not have a history of charging until the charging process in which the flat region is observed is taken out from the battery, X-ray diffraction is performed using CuKα rays, and in the X-ray diffraction diagram, a diffraction peak is observed near 21 °, or 4.5 V (vs. Li / Li ⁺⁾ at a current of 0.1 C with metal Li as a counter electrode. ) To 5 V (vs. Li / Li ⁺ ), and the maximum value of dSOC / dV is 70 or more (a region where the potential change is relatively flat with respect to the amount of charge is observed). Can be confirmed.

  The nonaqueous electrolyte secondary battery of this 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 illustrated in FIG. In FIG. 9, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of nonaqueous electrolyte secondary batteries 1. The power storage device 30 can be mounted as a power source for vehicles such as an electric vehicle (EV), a hybrid vehicle (HEV), and a plug-in hybrid vehicle (PHEV).

(Example 1-1)
<Preparation of first lithium transition metal composite oxide>
350.6 g of nickel sulfate hexahydrate, 375.0 g of cobalt sulfate heptahydrate, and 321.6 g of manganese sulfate pentahydrate were weighed, and all of these were dissolved in 4 L of ion-exchanged water, and Ni: Co: Mn A 1.0 M aqueous sulfate solution with a molar ratio of 1: 1: 1 was prepared. Next, 2 L of ion exchanged water was poured into a 5 L reaction tank, and Ar gas was bubbled for 30 minutes to remove oxygen contained in the ion exchanged water. The reaction vessel temperature is set to 50 ° C. (± 2 ° C.), and the reaction vessel is stirred at a rotational speed of 1500 rpm using a paddle blade equipped with a stirring motor so that sufficient convection occurs in the reaction layer. did. The aqueous sulfate solution was dropped into the reaction vessel at a rate of 3 mL / min. Here, during the period from the start to the end of dropping, a mixed alkaline solution consisting of 4.0 M sodium hydroxide, 0.5 M ammonia water, and 0.5 M hydrazine is appropriately dropped to thereby adjust the pH in the reaction vessel. Was controlled to always maintain 11.0 (± 0.1), and a part of the reaction solution was discharged by overflow, so that the total amount of the reaction solution was always controlled not to exceed 2 L. After completion of the dropwise addition, stirring in the reaction vessel was further continued for 3 hours. After stopping stirring, the mixture was allowed to stand at room temperature for 12 hours or more.
Next, using a suction filtration device, the hydroxide precursor particles generated in the reaction tank are separated, and further, sodium ions adhering to the particles are washed and removed using ion exchange water, and an electric furnace is used. Then, it was dried in an air atmosphere at 80 ° C. under normal pressure for 20 hours. Then, in order to arrange | equalize a particle size, it grind | pulverized for several minutes with the smoked automatic mortar. In this way, a hydroxide precursor was produced.

To 1.898 g of the hydroxide precursor, 0.896 g of lithium hydroxide monohydrate is added and mixed well using a smoked automatic mortar. The molar ratio of Li: (Ni, Co, Mn) is 1: A mixed powder was prepared so as to be 1. Using a pellet molding machine, molding was performed at a pressure of 6 MPa to obtain pellets having a diameter of 25 mm. The amount of the mixed powder subjected to pellet molding was determined by conversion so that the mass of the assumed final product was 2 g. One pellet was placed on an alumina boat having a total length of about 100 mm, placed in a box-type electric furnace (model number: AMF20), heated in air at atmospheric pressure and normal temperature to 900 ° C. over 10 hours, Firing at 900 ° C. for 5 hours. The box-type electric furnace has internal dimensions of 10 cm in length, 20 cm in width, and 30 cm in depth, and heating wires are inserted at intervals of 20 cm in the width direction. After firing, the heater was turned off and allowed to cool naturally with the alumina boat placed in the furnace. As a result, the temperature of the furnace decreases to about 200 ° C. after 5 hours, but the subsequent temperature decrease rate is somewhat moderate. After the passage of day and night, it was confirmed that the furnace temperature was 100 ° C. or lower, and then the pellets were taken out and pulverized for several minutes in a smoked automatic mortar in order to make the particle diameter uniform. Thus, lithium transition metal complex oxide LiNi _1/3 Co _1/3 Mn _1/3 O ₂ was produced.

<Preparation of second lithium transition metal composite oxide>
Nickel sulfate hexahydrate 315.6 g, cobalt sulfate heptahydrate 168.7 g, manganese sulfate pentahydrate 530.6 g were weighed, and all of these were dissolved in 4 L of ion-exchanged water, and Ni: Co: Mn A 1.0 M aqueous sulfate solution with a molar ratio of 30:15:55 was prepared.
Next, 2 L of ion exchanged water was poured into a 5 L reaction tank, and Ar gas was bubbled for 30 minutes to remove oxygen contained in the ion exchanged water. The reaction vessel temperature is set to 50 ° C. (± 2 ° C.), and the reaction vessel is stirred at a rotational speed of 1500 rpm using a paddle blade equipped with a stirring motor so that sufficient convection occurs in the reaction layer. did. The aqueous sulfate solution was dropped into the reaction vessel at a rate of 3 mL / min. Here, during the period from the start to the end of the dropping, a mixed alkali solution composed of 4.0 M sodium hydroxide, 0.5 M ammonia water, and 0.2 M hydrazine is appropriately dropped to adjust the pH in the reaction vessel. 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 was always controlled not to exceed 2 L. After completion of the dropwise addition, stirring in the reaction vessel was further continued for 3 hours. After stopping stirring, the mixture was allowed to stand at room temperature for 12 hours or more.
Next, using a suction filtration device, the hydroxide precursor particles generated in the reaction tank are separated, and further, sodium ions adhering to the particles are washed and removed using ion exchange water, and an electric furnace is used. Then, it was dried in an air atmosphere at 80 ° C. under normal pressure for 20 hours. Then, in order to arrange | equalize a particle size, it grind | pulverized for several minutes with the smoked automatic mortar. In this way, a hydroxide precursor was produced.
To 1.852 g of the hydroxide precursor, 0.971 g of lithium hydroxide monohydrate is added and mixed well using a smoked automatic mortar. The molar ratio of Li: (Ni, Co, Mn) is 110: A mixed powder was prepared so as to be 100. Using a pellet molding machine, molding was performed at a pressure of 6 MPa to obtain pellets having a diameter of 25 mm. The amount of the mixed powder subjected to pellet molding was determined by conversion so that the mass of the assumed final product was 2 g. One pellet was placed on an alumina boat having a total length of about 100 mm, placed in a box-type electric furnace (model number: AMF20), heated in air at atmospheric pressure and normal temperature to 900 ° C. over 10 hours, Firing at 900 ° C. for 5 hours. The box-type electric furnace has internal dimensions of 10 cm in length, 20 cm in width, and 30 cm in depth, and heating wires are inserted at intervals of 20 cm in the width direction. After firing, the heater was turned off and allowed to cool naturally with the alumina boat placed in the furnace. As a result, the temperature of the furnace decreases to about 200 ° C. after 5 hours, but the subsequent temperature decrease rate is somewhat moderate. After a day and night, after confirming that the furnace temperature was 100 ° C. or less, the pellets were taken out and lightly loosened with a smoked mortar to make the particle size uniform.
In this way, lithium transition metal composite oxide Li _1.1 (Ni _0.30 Co _0.15 Mn _0.55 ) _0.9 O ₂ was produced.

<Confirmation of crystal structure>
About said 1st and 2nd lithium transition metal complex oxide, the powder X-ray-diffraction measurement was performed using the X-ray-diffraction apparatus (the Rigaku company make, model name: MiniFlex II). It was confirmed that the first and second lithium transition metal composite oxides have an α-NaFeO ₂ structure.

<Preparation of positive electrode>
The active material which concerns on Example 1-1 containing 30 mass parts of 2nd lithium transition metal complex oxide with respect to 70 mass parts of 1st lithium transition metal complex oxide was produced.
Coating paste in which N-methylpyrrolidone is used as a dispersion medium, and the active material according to Example 1-1, acetylene black (AB) and polyvinylidene fluoride (PVdF) are kneaded and dispersed at a mass ratio of 90: 5: 5 Was made. The coating paste was applied to one side of an aluminum foil current collector having a thickness of 20 μm to produce a positive electrode according to Example 1-1. In addition, the mass and coating thickness of the active material applied per fixed area were unified so that the test conditions were the same for all non-aqueous electrolyte secondary batteries according to Examples and Comparative Examples described later.

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

<Assembly of nonaqueous electrolyte secondary battery>
Using the positive electrode according to Example 1-1, a nonaqueous electrolyte secondary battery was assembled by the following procedure.
As a non-aqueous electrolyte, LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) in a volume ratio of 6: 7: 7 so that the concentration would be 1 mol / L. Solution was used. As the separator, a polypropylene microporous film whose surface was modified with polyacrylate was used. A metal resin composite film made of polyethylene terephthalate (15 μm) / aluminum foil (50 μm) / metal-adhesive polypropylene film (50 μm) was used for the outer package. The positive electrode according to Example 1-1 and the negative electrode are accommodated in the exterior body through the separator so that the open ends of the positive electrode terminal and the negative electrode terminal are exposed to the outside, and the inner surfaces of the metal resin composite film are The non-electrolyte secondary battery was assembled by sealing the fusion allowance facing each other except for the portion serving as the injection hole, sealing the injection hole after sealing the non-aqueous electrolyte.

<Initial charge / discharge process>
The assembled nonaqueous electrolyte secondary battery was subjected to an initial charge / discharge step at 25 ° C. Charging was performed at a constant current and a constant voltage (CCCV) with a current of 0.1 C and a voltage of 4.45 V (vs. Li / Li ⁺ ), and the charge termination condition was the time when the current value was attenuated to 1/6. The discharge was a constant current discharge with a current of 0.1 C and a final voltage of 2.0 V (vs. Li ^/ Li ⁺ ). This charge / discharge was performed for two cycles. Here, a pause process of 30 minutes was provided after charging and after discharging, respectively, and the discharge capacity was confirmed.
The nonaqueous electrolyte secondary battery according to Example 1-1 was completed through the above manufacturing steps.

(Examples 1-2 to 1-9)
The first lithium transition metal composite oxide in Example 1-1 was used as the first lithium transition metal composite oxide (hereinafter, the first lithium transition metal composite oxide in Example 1-1 was referred to as “NCM”. ").
In the production process of the second lithium transition metal composite oxide in Example 1-1, the molar ratio Li of the transition metal element Me2 (Ni: Co: Mn = 30: 15: 55) to Li in the hydroxide precursor / Me2 is changed from 1.1 to 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, and 1.5 respectively. A lithium transition metal composite oxide was produced (hereinafter, the second lithium transition metal composite oxide is referred to as “LR”).
A non-aqueous electrolyte was produced in the same manner as in Example 1-1 except that the positive electrode active material according to Examples 1-2 to 1-9 containing 30 parts by mass of the above LR with respect to 70 parts by mass of NCM was prepared. The secondary battery was assembled and initially charged / discharged to complete the nonaqueous electrolyte secondary battery according to Examples 1-2 to 1-9.

(Comparative Example 1-1)
A nonaqueous electrolyte secondary battery was assembled and initially charged / discharged in the same manner as in Example 1-1 except that the NCM according to Example 1-1 was used alone as the positive electrode active material. Such a nonaqueous electrolyte secondary battery was completed.

<Safety confirmation test during overcharge>
Using the non-aqueous electrolyte secondary battery completed as described above, a constant current (CC) charge at a current of 0.1 C was performed without setting an upper limit of the voltage, and a rapid increase in the positive electrode potential with respect to the amount of charge was observed. The SOC (%) was recorded. Here, the charging depth when the constant current constant voltage (CCCV) charging of 4.45 V (vs. Li / Li ⁺ ) was performed was defined as SOC 100%.

Table 1 shows the discharge capacities of the nonaqueous electrolyte secondary batteries according to Examples 1-1 to 1-9 and Comparative Example 1-1, the SOC (%) in the safety confirmation test, and the dSOC / dV maximum value.
In Tables 1 to 3 below, the SOC delay effect is “◎” when the maximum value of dSOC / dV is 100 or more, “◯” when 70 or more, and “×” when less than 70. did.

According to Table 1, the non-aqueous electrolyte secondary battery according to Comparative Example 1-1 including the positive electrode using NCM alone as the active material has a positive electrode potential rapidly increased at 133% SOC in the safety confirmation test. doing. On the other hand, the non-aqueous electrolyte secondary batteries according to Examples 1-1 to 1-9 including the positive electrode containing NCM and LR as the active material have an SOC in which the positive electrode potential rapidly increases in the safety confirmation test. It is 175% or more, and it can be seen that the safety is improved as compared with Comparative Example 1-1.
Here, the dSOC / dV maximum value of the nonaqueous electrolyte secondary battery according to Comparative Example 1-1 is less than 70. That is, the positive electrode in Comparative Example 1-1 was within a positive electrode potential range of 4.5 to 5.0 V (vs. Li ^/ Li ⁺ ) when charged to 5.0 V (vs. Li ^/ Li ⁺ ). Furthermore, it does not have a relatively flat region of potential change with respect to the amount of charge. In contrast, the non-aqueous electrolyte secondary batteries according to Examples 1-1 to 1-9 have a dSOC / dV maximum value exceeding 70. That is, the positive electrodes in Examples 1-1 to 1-9 were 4.5 to 5.0 V (vs. Li ^/ Li ⁺ ) when charged to 5.0 V (vs. Li ^/ Li ⁺ ). Within the positive electrode potential range, there is a relatively flat region with respect to the amount of charged electricity.
The discharge capacity is maximum when the Li / Me2 ratio is 1.2, and it can be seen that the capacity tends to decrease when the ratio exceeds 1.2.

(Example 1-10, Comparative Example 1-2, 1-3)
Using the same positive electrode active material as that of the nonaqueous electrolyte secondary battery according to Example 1-3, the constant current and constant voltage (CCCV) charging voltages in the initial charge and discharge process were 4.50 V, 4.55 V, and 4. The nonaqueous electrolyte secondary batteries according to Example 1-10 and Comparative Examples 1-2 and 1-3 were the same as Example 1-3 except that the voltage was 60 V (both vs. Li ^/ Li ⁺ ). Completed and confirmed the discharge capacity.
Next, with respect to the nonaqueous electrolyte secondary batteries according to Example 1-10 and Comparative Examples 1-2 and 1-3, the voltage adopted in the constant current and constant voltage (CCCV) in each initial charge and discharge process A safety confirmation test at the time of overcharge was performed in the same manner as in Example 1-3, assuming that the charge depth when charging was SOC 100%.
The discharge capacity of the nonaqueous electrolyte secondary batteries according to Example 1-10 and Comparative Examples 1-2 and 1-3, the SOC (%) by the safety confirmation test, and the maximum value of dSOC / dV are shown in Example 1 3 and Comparative Example 1-1 are shown in Table 2.

According to Table 2, the non-aqueous electrolyte secondary battery according to Example 1-10 in which the initial charge / discharge process was performed at 4.5 V (vs. Li / Li ⁺ ) also rapidly increased in the positive electrode potential in the safety confirmation test. It can be seen that the SOC is improved as compared with Comparative Example 1-1, and the safety is improved. However, in the nonaqueous electrolyte secondary batteries according to Comparative Examples 1-2 and 1-3 in which the same positive electrode active material as in Example 1-10 was used and the initial charge / discharge process was performed at 4.55 V and 4.60 V, The SOC at which the positive electrode potential rapidly increases in the safety confirmation test is lower than that in Comparative Example 1-1, and safety is not improved.
Here, the nonaqueous electrolyte secondary battery according to Example 1-10 has a dSOC / dV maximum value of 70 or more. That is, when charging up to 5.0 V (vs. Li ^/ Li ⁺ ) in Example 1-10 was performed, charging was performed within the positive electrode potential range of 4.5 to 5.0 V (vs. Li ^/ Li ⁺ ). It has a relatively flat area with respect to the amount of electricity. On the other hand, the nonaqueous electrolyte secondary batteries according to Comparative Examples 1-2 and 1-3 have a high discharge capacity but a dSOC / dV maximum value of less than 70. That is, the positive electrode in the battery of Comparative Example 1-2 and 1-3, where a charge leading to ^{5.0V (vs.Li/Li +), 4.5~5.0V (} vs.Li/Li + ) Does not have a relatively flat region of potential change with respect to the amount of charge.

(Examples 1-11 and 1-12)
Except that the mass ratio of NCM and LR (Li / Me2 = 1.2) in Example 1-3 was changed from 70:30 to 50:50 and 30:70, respectively, in the same manner as Example 1-3. The nonaqueous electrolyte secondary batteries according to Example 1-11 and Example 1-12 were completed.
Table 3 shows the initial discharge capacity of the nonaqueous electrolyte secondary batteries according to Examples 1-11 and 1-12 and the SOC (%) by the safety confirmation test together with Example 1-3.

  According to Table 3, the nonaqueous electrolyte secondary battery according to Example 1-11 provided with a positive electrode in which the mass ratio of the first lithium transition metal composite oxide and the second lithium transition metal composite oxide was 50:50 In addition, the non-aqueous electrolyte secondary battery according to Example 1-12 provided with the positive electrode having a mass ratio of 30:70 was also compared with Comparative Example 1-1 in which the positive electrode potential rapidly increased in the safety confirmation test. It can be seen that the safety is improved. Moreover, it turns out that the fall of discharge capacity is also suppressed.

  For the nonaqueous electrolyte secondary batteries according to Examples 1-1 to 1-12, the positive electrode in the end-of-discharge state based on the above-described procedures and conditions before separately performing the safety confirmation test during overcharge. When X-ray diffraction measurement was performed, the positive electrode active material was confirmed to have a diffraction peak observed at around 21 ° in an X-ray diffraction diagram using CuKα rays. The same X-ray diffraction measurement was performed on the nonaqueous electrolyte secondary batteries according to Comparative Examples 1-2 and 1-3, but no diffraction peak near 21 ° was observed.

The following example is for confirming the influence of the nonaqueous electrolyte on the internal resistance after the charge / discharge cycle by including FEC in the nonaqueous solvent. For this reason, the Example using the nonaqueous electrolyte which does not contain FEC is described as a "reference example" here.
(Example 2-1 ₁ )
A positive electrode active material containing 20 parts by mass of LR in which the molar ratio Li / Me2 of the transition metal element Me2 (Ni: Co: Mn = 20: 20: 60) to Li is 1.43 with respect to 80 parts by mass of NCM is prepared. A positive electrode was produced in the same manner as in Example 1.

(Preparation of negative electrode)
A negative electrode mixture paste was prepared using graphite as the negative electrode active material, styrene-butadiene-rubber and carboxymethyl cellulose (CMC) as the binder, and water as the dispersion medium. Note that the mass ratio of the negative electrode active material, the binder, and the CMC was 97: 2: 1. This negative electrode mixture paste was applied to one side of a copper foil as a negative electrode substrate and dried at 100 ° C. to obtain a negative electrode.

As the non-aqueous electrolyte, a mixed solvent having an FEC / EMC volume ratio of 10:90 was used. A nonaqueous electrolyte secondary battery was assembled in the same manner as in Example 1 using the positive electrode, the negative electrode, and the nonaqueous electrolyte.
The initial charge / discharge of the assembled non-aqueous electrolyte secondary battery was charged at a constant current / constant voltage (CCCV) charge at 25 ° C. with a current of 0.1 C and a voltage of 4.25 V (when the current value was attenuated to 1/6). stop), and current 0.1 C, carried out at a constant current discharge termination voltage 2.0 V, thereby completing the non-aqueous electrolyte secondary cell according to example 2-1 _1.
The potential of the positive electrode during charging of the battery is about 4.35 V (vs. Li ^/ Li ⁺ ) because the potential of the graphite negative electrode is about 0.1 V (vs. Li ^/ Li ⁺ ).

(Example 2-1 ₂ )
Except that FEC and 3,3,3-trifluoro propylene methyl (FMP) was used a mixed solvent is a volume ratio 10:90 as a non-aqueous electrolyte, carried out in the same manner as in Example 2-1 ₁ case 2 It was completed a non-aqueous electrolyte secondary battery according to 1 _2.

(Reference Example 2-1)
Nonaqueous except that EC and EMC as electrolyte using a mixed solvent having a volume ratio of 30:70, thereby completing the non-aqueous electrolyte secondary cell according to comparative example 2-1 in the same manner as in Example 2-1 _1.

(Example 2-2 ₁ , 2-2 ₂ , Reference Example 2-2)
The mass ratio of NCM and LR of the positive electrode active material, 50: 50 and then other than the embodiment _2-1 1, 2-1 _2, and in the same manner as in Reference Example 2-1, Example _2-2 1, The nonaqueous electrolyte secondary battery according to 2-2 ₂ and Reference Example 2-2 was completed.

(Example 2-3, Reference Example 2-3)
The mass ratio of NCM and LR positive poling material, 70: except for using 30, in the same manner as in Example 2-1 ₁ and Reference Examples 2-1, according to Examples 2-3 and Reference Examples 2-3 A non-aqueous electrolyte secondary battery was completed.

(Comparative Examples 2-1 to 2-3)
The nonaqueous electrolyte 2 according to Comparative Examples 2-1 to _2-3 is the same as Example 2-1 ₁ , 2-1 ₂ and Reference Example 2-1, except that NCM is used alone as the positive electrode active material. The next battery was completed.

When the constant current and constant voltage (CCCV) charge of 4.25 V (the positive electrode potential is about 4.35 V (vs. Li / Li ⁺ )) is performed on the batteries of the above-described examples, reference examples, and comparative examples. Except that the charging depth was set to SOC 100%, the safety confirmation test at the time of overcharging was performed in the same manner as in Example 1, and the SOC (%) and the dSOC / dV maximum value were obtained.
In addition, as a charge / discharge cycle test, the battery before the safety confirmation test at the time of overcharge was subjected to CCCV charge (current value is 1 / C) at a current of 0.1 C and a voltage of 4.25 V at 45 ° C. 50), and constant current discharge with a current of 0.1 C and a final voltage of 2.0 V was performed for 50 cycles, and the internal resistance of the battery after the test was measured under the conditions described above.
Moreover, in each Example when the value of the said internal resistance measured in the battery which concerns on the battery which concerns on the reference example using the nonaqueous electrolyte which does not contain FEC between each battery from which only the composition of a nonaqueous electrolyte differs is set to 100. The ratio of the internal resistance of the battery was determined as “resistivity (%)”.
These results are shown in Table 4 below.

From Table 4, it can be seen that when the batteries according to Examples and Reference Examples having a positive electrode containing NCM and LR as positive electrode active materials are used at a potential of less than 4.5 V (vs. Li ^/ Li ⁺ ), 3 shows that it has the effect of high safety against overcharging. Further, the batteries according to Examples 2-1 to 2-3 in which the positive electrode containing LR and the non-aqueous electrolyte containing FEC were combined were used in Reference Examples 2-1 to 2-3 combined with the non-aqueous electrolyte not containing FEC. It can be seen that the battery has a small internal resistance after 50 cycles of charging and discharging, that is, FEC contained in the nonaqueous electrolyte has an effect of keeping the internal resistance after the charging and discharging cycle low.
On the other hand, the batteries according to Comparative Examples 2-1 and 2-2 in which the positive electrode not including LR and the nonaqueous electrolyte including FEC are combined are more than the battery according to Comparative Example 2-3 in which the nonaqueous electrolyte not including FEC is combined. Since the internal resistance after 50 cycles is large, it can be seen that the battery of the comparative example having the positive electrode containing no LR does not have the effect of keeping the internal resistance low due to the inclusion of FEC.

(Examples 2-4 and 2-5, Reference Examples 2-4 and 2-5)
Example 2-2 ₁ , 2 except that the charge in the initial charge / discharge process was a constant current constant voltage (CCCV) charge with a voltage of 4.35 V (positive electrode potential was about 4.45 V (vs. Li / Li ⁺ )). -3 and Reference Examples 2-2 and 2-3, the batteries according to Examples 2-4 and 2-5 and Reference Examples 2-4 and 2-5 were completed, respectively.

(Comparative Examples 2-4 and 2-5)
The charging in the initial charging / discharging process was performed in constant voltage and constant voltage (CCCV) with a voltage of 4.6 V (the positive electrode potential was about 4.7 V (vs. Li ^/ Li ⁺ )). In the same manner as in Example 2-4, batteries according to Comparative Examples 2-4 and 2-5 were completed, respectively.

The above embodiments 2-4 and 2-5, Reference Example 2-4 and 2-5, the non-aqueous electrolyte secondary cell according to comparative example 2-4 and 2-5, as in Example 2-1 ₁ A charge / discharge cycle test was performed, and the internal resistance after 50 cycles was measured. Moreover, in each Example when the value of the said internal resistance measured in the battery which concerns on the battery which concerns on the reference example using the nonaqueous electrolyte which does not contain FEC between each battery from which only the composition of a nonaqueous electrolyte differs is set to 100. The ratio of the internal resistance of the battery was determined as “resistivity (%)”. The results are shown in Table 5 below.

According to Table 5, in the batteries according to Comparative Examples 2-4 and 2-5 in which the initial charge / discharge process was performed at a potential of 4.5 V (vs. Li / Li ⁺ ) or higher, 4.5 V (vs. Li / Li) Compared with the batteries according to Examples 2-4 and 2-5 and Reference Examples 2-4 and 2-5 performed under less than ⁺ ), the resistance after 50 cycles is large, and in particular, FEC is contained in the nonaqueous electrolyte. It can be seen that the resistance of Comparative Example 2-4 is larger.
In contrast, 4.5V the initial charge-discharge process (vs.Li/Li ⁺⁾ less than 4.35V (positive electrode potential is about 4.45V (vs.Li/Li ⁺⁾⁾ in Examples and Reference Been In the example, the batteries according to Examples 2-4 and 2-5 using the nonaqueous electrolyte containing FEC are compared with the batteries according to Reference Examples 2-4 and 2-5 using the nonaqueous electrolyte not containing FEC. It can be seen that the resistance after 50 cycles is maintained at a low value. This is a non-aqueous electrolyte that does not contain FEC when the initial charge / discharge step shown in Table 4 was performed at 4.25 V (the positive electrode potential was about 4.35 V (vs. Li / Li ⁺ )). The effect is similar to that of the batteries according to Examples 2-2 ₁ and 2-3 using the nonaqueous electrolyte containing FEC for Reference Examples 2-2 and 2-3. In addition, when the battery according to the example and the reference example including the positive electrode containing NCM and LR as the positive electrode active material is used at a potential of less than 4.5 V (vs. Li ^/ Li ⁺ ), Similarly, it turns out that it has the effect that the safety | security with respect to an overcharge is high.

  In addition, from Table 4 and Table 5, battery sets that differ only in the charge voltage conditions in the initial charge / discharge step are extracted, and the charge voltage for each set of batteries with a charge voltage of 4.25 V is 4.35 V. Table 6 below shows the resistivity (which is different from the resistivity in Tables 4 and 5).

From Table 6, the batteries according to Reference Examples 2-2 to 2-5 using a non-aqueous electrolyte that does not contain FEC have a charge voltage of 4.25 V in the initial charge / discharge process (Reference Examples 2-2 and 2-3). ) To 4.35 V (Reference Examples 2-4 and 2-5), the resistance value after 50 cycles increases by about 1.5 to 3 times. Example 2 using a nonaqueous electrolyte containing FEC -2 ₁ , 2-3 to 2-5, the charging voltage is changed from 4.25 V (Example 2-2 ₁ , 2-3) to 4.35 V (Examples 2-4, 2-5). Even if it rises, it can be seen that the resistance value after 50 cycles is only about 30% higher.

(Example 2-6)
The solvent of the nonaqueous electrolyte, except that the volume ratio of the FEC / EMC was used a mixed solvent of 5:95, the same procedure as in Example 2-2 _1, the non-aqueous electrolyte secondary according to Example 2-6 Completed the battery.

(Example 2-7)
The solvent of the nonaqueous electrolyte, except that the volume ratio of the FEC / EMC was used a mixed solvent is 20:80, in the same manner as in Example 2-2 _1, the non-aqueous electrolyte secondary according to Examples 2-7 Completed the battery.

The resistance after 50 cycles of the nonaqueous electrolyte secondary battery according to Examples 2-6 and 2-7 was measured, and the ratio of the resistance of each example to the resistance of Reference Example 2-2 not including FEC was used as the resistivity. Asked. The results are shown in Table 7 below together with Example 2-2 ₁ in which the FEC / EMC volume ratio is 10:90 and Reference Example 2-2 not including FEC.

  From Table 6, it can be seen that FEC contained in the solvent of the nonaqueous electrolyte has a significant effect of maintaining low resistance after the charge / discharge cycle at least in the range of 5 to 20% by volume.

  The nonaqueous electrolyte secondary battery according to the present invention has high safety even when it is overcharged by mistake. Therefore, this non-aqueous electrolyte secondary battery is useful as a battery for hybrid vehicles (HEV), plug-in hybrid vehicles (PHEV), and electric vehicles (EV) that require high safety and charge / discharge cycle performance. High nature.

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

Claims (8)

A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte,
The positive electrode is an active material,
having an α-NaFeO ₂ structure,
A first lithium transition metal composite oxide represented by the general formula LiMe1O ₂ (Me1 is a transition metal element containing Ni, Co and Mn);
having an α-NaFeO ₂ structure,
A second lithium transition metal composite oxide represented by the general formula Li _{1 + α} Me2 _1-α O ₂ (0 <α, Me2 is a transition metal element including Ni and Mn, or Ni, Mn and Co);
The active material is a non-aqueous electrolyte secondary battery in which a diffraction peak is observed at around 21 ° in an X-ray diffraction diagram using CuKα rays. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte,
The positive electrode is an active material,
having an α-NaFeO ₂ structure,
A first lithium transition metal composite oxide represented by the general formula LiMe1O ₂ (Me1 is a transition metal element containing Ni, Co and Mn);
having an α-NaFeO ₂ structure,
A second lithium transition metal composite oxide represented by the general formula Li _{1 + α} Me2 _1-α O ₂ (0 <α, Me2 is a transition metal element including Ni and Mn, or Ni, Mn and Co);
When charging is performed until the positive electrode potential reaches 5.0 V (vs. Li ^/ Li ⁺ ), within the positive electrode potential range of 4.5 to 5.0 V (vs. Li ^/ Li ⁺ ) A non-aqueous electrolyte secondary battery in which a region with a relatively flat potential change is observed.   3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the first lithium transition metal composite oxide has a molar ratio of Mn to transition metal (Me1) of Mn / Me1 ≦ 0.5.   The nonaqueous electrolyte 2 according to any one of claims 1 to 3, wherein the second lithium transition metal composite oxide has a molar ratio of Mn to transition metal (Me2) of 0.5 <Mn / Me2. Next battery.   5. The non-aqueous electrolyte 2 according to claim 1, wherein the second lithium transition metal composite oxide has a molar ratio of Li to the transition metal (Me 2) of Li / Me 2 ≦ 1.35. Next battery. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 5, which is used at a potential of less than 4.5 V (vs. Li ^/ Li ⁺ ).   The nonaqueous electrolyte secondary battery according to claim 1, wherein the nonaqueous electrolyte contains fluoroethylene carbonate in a nonaqueous solvent. It is a manufacturing method of the nonaqueous electrolyte secondary battery of any one of Claims 1-7, Comprising ^{: The} non-aqueous water which performs an initial stage charging / discharging process with the electric potential of less than 4.5V (vs.Li/Li ^<+> ). Manufacturing method of electrolyte secondary battery.