JP2016103325A - Titanium oxide, negative electrode arranged by using the same as material, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode and a nonaqueous electrolyte secondary battery which enable the reduction in gas generation accompanying the use under a high-temperature environment, especially the repetition of charge and discharge under a high-temperature environment (high-temperature cycle)), thereby suppressing the decrease in battery capacity.SOLUTION: A negative electrode comprises at least titanium and oxygen and as an active material, a titanium complex oxide and/or titanium oxide, capable of reversibly occluding and releasing lithium ions. After performing an initial charging to a negative electrode potential and then, storing a secondary battery including the negative electrode in an atmosphere of 50°C or higher and under 80°C, the ratio of a peak area (A) of a lithium fluoride compound in X-ray photoelectron spectroscopy spectra of the negative electrode to a peak area (B) of a carbon compound is in a range given by: 0.3<A/B<3.0.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a titanium composite oxide and / or titanium oxide (hereinafter sometimes referred to as titanium oxide) that contains at least titanium and oxygen and can reversibly store and release lithium ions. The present invention also relates to a negative electrode using the titanium oxide or the like as an active material and a nonaqueous electrolyte secondary battery using the negative electrode. More specifically, in a non-aqueous electrolyte secondary battery using titanium oxide or the like as a negative electrode active material, a non-aqueous electrolyte capable of reducing gas generation accompanying use in a high-temperature environment and suppressing a decrease in battery capacity. The present invention relates to a secondary battery.

A nonaqueous electrolyte secondary battery is a secondary battery in which charging and discharging are performed by ions moving between a negative electrode and a positive electrode through the nonaqueous electrolyte, and a lithium ion secondary battery is representative. In recent years, nonaqueous electrolyte secondary batteries using titanium oxide or the like as a negative electrode active material have been developed. Titanium oxide and the like are compounds containing at least titanium and oxygen and capable of reversibly occluding and releasing lithium ions, and examples thereof include lithium titanate, monoclinic titanium oxide, and lithium hydrogen titanate. These titanium oxides generally have an advantage that the lithium occlusion potential has a large difference from the metal Li deposition potential, so that even when rapid charging is performed, metal lithium is essentially difficult to deposit. . Further, for example, Li ₄ Ti ₅ O ₁₂ has an advantage that the structure deterioration is extremely slow because there is almost no change in the volume of the crystal accompanying charging and discharging. Therefore, a battery using titanium oxide or the like as a negative electrode active material has high safety and excellent battery characteristics, particularly cycle life characteristics.

  In recent years, several techniques have been proposed in which a halogen element such as fluoride exists in titanium oxide or the like, which is a negative electrode active material. In Patent Document 1, the ratio of the peak appearing at 680 to 687 eV of F1s and the peak appearing at 280 to 290 eV of C1s in the X-ray photoelectron spectroscopy spectrum of the negative electrode including lithium titanate particles having a fluoride layer containing lithium fluoride on the surface Is 3.2 to 6, it is disclosed that a non-aqueous electrolyte secondary battery with high output and suppressed increase in battery resistance due to high-temperature storage can be obtained. In Patent Document 2, the maximum intensity of the peak appearing at 680 to 687 eV and the peak appearing at 280 to 290 eV in the X-ray photoelectron spectrum of the negative electrode including lithium titanate particles having a fluoride layer containing lithium fluoride on the surface are disclosed. It is disclosed that when the ratio of the maximum strength is 6 to 21, a nonaqueous electrolyte secondary battery excellent in the effect of suppressing the battery internal resistance and the cycle characteristics can be obtained.

  In Patent Document 3, a negative electrode active material mainly composed of lithium titanate is immersed or placed in an aqueous solution or atmosphere containing a halogen element, particularly a compound containing fluorine, at a predetermined temperature for a predetermined time. Describes producing a negative electrode active material in which a halogen element is present on a part of the surface of the negative electrode active material. Further, lithium titanate having a ratio of 1 s peak intensity of fluorine (peak intensity of 1 s of fluorine) / (peak intensity of 2p of titanium) of 0.01 or more and 1 or less is disclosed.

JP 2010-231960 A JP 2013-114809 A JP 2014-63702 A

  In Patent Documents 1, 2, and 3, the surface fluoride layer is specifically disclosed as a method for forming a secondary battery including a non-aqueous electrolyte containing hydrofluoric acid or water, It is a method of charging / discharging the secondary battery, or a method of using hydrofluoric acid or water, such as treating a negative electrode or an active material with a treatment solution to which hydrofluoric acid or water is added. When this is performed, gas generation that is considered to be caused by the remaining hydrofluoric acid or water is expected.

  As described above, a battery using titanium oxide or the like as a negative electrode active material has a problem that gas is easily generated when charging / discharging is performed in a high temperature environment, and battery capacity is likely to be reduced. When a large amount of gas is generated, there is a risk that the internal pressure of the battery increases and the battery swells, and when the battery capacity decreases, the life performance deteriorates. Particularly in recent years, with the expansion of applications of non-aqueous electrolyte secondary batteries, the demand for higher energy density of batteries has increased, and inside the battery, high-density filling of electrodes and reduction of the space in the battery have been performed. The problem has become apparent.

  Accordingly, an object of the present invention is to use a non-aqueous electrolyte secondary battery using titanium oxide or the like as a negative electrode active material in a high temperature environment, in particular, gas generation due to repeated charge / discharge (high temperature cycle) in a high temperature environment. An object of the present invention is to provide a titanium oxide, a negative electrode, and a nonaqueous electrolyte secondary battery capable of suppressing reduction and battery capacity reduction.

As a result of intensive studies to solve the above problems, the inventors of the present invention have an X-ray photoelectron spectrum measured using a single crystal spectrum Al—Kα ray as an excitation X-ray source that satisfies the following (formula 1): The present inventors have found that the above-mentioned problems can be achieved by using a titanium oxide containing a lithium fluoride compound and a carbon compound, and have reached the present invention.
0.3 <A / B <3.0 (Formula 1)
(In Formula 1, A is the peak area of F1s combined with Li appearing at 682 to 688 eV, and B is the peak area of C1s appearing at 280 to 294 eV.)

That is, the present invention (1) provides a single crystal spectroscopic Al-- as an excitation X-ray source on the surface of a titanium composite oxide and / or titanium oxide containing at least titanium and oxygen and capable of reversibly occluding and releasing lithium ions. It is a titanium oxide containing a lithium fluoride compound and a carbon compound whose X-ray photoelectron spectrum measured using Kα rays satisfies the following (formula 1).
0.3 <A / B <3.0 (Formula 1)
(In Formula 1, A is the peak area of F1s combined with Li appearing at 682 to 688 eV, and B is the peak area of C1s appearing at 280 to 294 eV.)

Moreover, this invention (2) is a titanium oxide as described in said (1) in which the X-ray photoelectron spectroscopy spectrum measured using the single-crystal-spectrum Al-K alpha ray as an excitation X-ray source satisfy | fills following (Formula 2). is there.
0.2 <A / T (Formula 2)
(In Formula 2, A is the peak area of F1s combined with Li appearing at 682 to 688 eV, and T is the peak area of Ti2p _3/2 appearing at 455 to 462 eV.)

Further, the present invention (3) includes at least titanium and oxygen, and includes, as an active material, a titanium composite oxide and / or titanium oxide capable of reversibly occluding and releasing lithium ions,
An X-ray photoelectron spectrum measured using a single crystal spectrum Al—Kα ray as an excitation X-ray source is a negative electrode satisfying the following (formula 3).
0.3 <A / B <3.0 (Formula 3)
(In Formula 3, A is the peak area of F1s combined with Li appearing at 682 to 688 eV, and B is the peak area of C1s appearing at 280 to 294 eV.)

Moreover, this invention (4) is a negative electrode as described in said (3) in which the X-ray photoelectron spectroscopy spectrum measured using the single crystal spectrum Al-K (alpha) ray as an excitation X-ray source satisfy | fills following (Formula 4).
0.2 <A / T (Formula 4)
(In Formula 4, A is the peak area of F1s combined with Li appearing at 682 to 688 eV, and T is the peak area of Ti2p _3/2 appearing at 455 to 462 eV.)

In addition, the present invention (5) includes a positive electrode, a negative electrode containing at least titanium and oxygen, a titanium composite oxide capable of reversibly occluding and releasing lithium ions and / or a titanium oxide as an active material, and the positive electrode. A non-aqueous electrolyte secondary battery comprising a separator disposed between the negative electrode and a non-aqueous electrolyte, wherein X is measured using single-crystal spectral Al-Kα rays as an excitation X-ray source of the negative electrode It is a nonaqueous electrolyte secondary battery whose linear photoelectron spectroscopy spectrum satisfies the following (formula 5).
0.3 <A / B <3.0 (Formula 5)
(In Formula 5, A is the peak area of F1s combined with Li appearing at 682 to 688 eV, and B is the peak area of C1s appearing at 280 to 294 eV.)

Moreover, this invention (6) is as described in said (5) with which the X-ray photoelectron spectroscopy spectrum measured using the single-crystal-spectrum Al-K (alpha) ray as an excitation X-ray source of the said negative electrode satisfy | fills following (Formula 6). It is a non-aqueous electrolyte secondary battery.
0.2 <A / T (Formula 6)
(In Formula 6, A is the peak area of F1s combined with Li appearing at 682 to 688 eV, and T is the peak area of Ti2p _3/2 appearing at 455 to 462 eV.)

By using the titanium oxide or the like of the present invention as an active material, use in a high temperature environment, particularly gas generation accompanying repeated charge / discharge (high temperature cycle) in a high temperature environment can be reduced, and a decrease in battery capacity can be suppressed. A possible non-aqueous electrolyte secondary battery can be provided. In particular, even when titanium oxide having a large specific surface area is used, gas generation can be sufficiently reduced, particularly gas generation accompanying a high temperature cycle can be remarkably reduced, and titanium oxide having a large specific surface area can be reduced. Taking advantage of this, good low temperature charge / discharge characteristics and large current charge / discharge characteristics can be imparted.
In addition, when the negative electrode of the present invention is used for a non-aqueous electrolyte secondary battery, gas generation associated with repeated use (high temperature cycle) of charge / discharge in a high temperature environment is reduced, and a decrease in battery capacity is suppressed. It is possible to provide a non-aqueous electrolyte secondary battery that can be used.

It is a characteristic view which shows the X-ray photoelectron spectroscopy spectrum (binding energy is 682-688 eV) of F1s of the negative electrode of Example 2. It is a characteristic view which shows the X-ray photoelectron spectroscopy spectrum (binding energy is 280-294 eV) of C1s of the negative electrode of Example 2. It is a characteristic view which shows the X-ray photoelectron spectroscopy spectrum (binding energy is 455-462 eV) of Ti2p3 _/ 2 of the negative electrode of Example 2.

The titanium oxide of the present invention contains at least titanium and oxygen and has a single crystal spectroscopic Al-Kα as an excitation X-ray source on the surface of a titanium composite oxide and / or titanium oxide capable of reversibly occluding and releasing lithium ions. There exists a lithium fluoride compound and a carbon compound whose X-ray photoelectron spectrum measured using a line satisfies the following (formula 1).
0.3 <A / B <3.0 (Formula 1)
(In Formula 1, A is the peak area of F1s combined with Li appearing at 682 to 688 eV, and B is the peak area of C1s appearing at 280 to 294 eV.)

The titanium oxide or the like is a compound containing at least titanium and oxygen, and is not particularly limited as long as it is a titanium composite oxide and / or titanium oxide capable of reversibly occluding and releasing lithium ions, and an arbitrary one is used. be able to. It may be a complex oxide with other elements such as lithium. Specific examples include lithium titanate having a spinel structure (Li _{4 + x} Ti ₅ O ₁₂ (x is a real number satisfying 0 ≦ x ≦ 3)), lithium titanate having a ramsdellite structure (Li _{2 + x} Ti ₃ O ₇ (x Is a real number satisfying 0 ≦ x ≦ 3)), monoclinic titanium oxide and lithium hydrogen titanate. Examples of the monoclinic titanium oxide include a monoclinic titanic acid compound represented by the general formula H ₂ Ti _n O _{2n + 1} (n is an even number of 4 or more. For example, H ₂ Ti ₁₂ O ₂₅ ), Monoclinic lithium titanate represented by the general formula Li ₂ Ti _n O _{2n + 1} (n is an even number of 4 or more, such as Li ₂ Ti ₁₈ O ₃₇ ) and bronze type titanium oxide (TiO ₂ (B)) Is included. Examples of the lithium hydrogen titanate include those obtained by substituting a part of the lithium element of the lithium titanate with hydrogen. For example, the general formula H _x Li _y-x Ti _z O ₄ (x, y, z is a real number satisfying y ≧ x> 0, 0.8 ≦ y ≦ 2.7, 1.3 ≦ z ≦ 2.2) For example, lithium hydrogen titanate represented by H _x Li _{4 / 3-x} Ti _5/3 O ₄ ) and lithium hydrogen titanate represented by the general formula H _2-x Li _x Ti _n O _{2n + 1} (n Is an even number greater than or equal to 4, and x is a real number satisfying 0 <x <2, for example, H _2−x Li _x Ti ₁₂ O ₂₅ ). In these chemical formulas, some of lithium, titanium, and oxygen may be substituted with other elements, and not only the stoichiometric composition but also non-stoichiometry in which some elements are deficient or excessive. It may be of composition. It may be a titanium oxide having a lithium-titanium composite oxides (e.g., TiO ₂₎ by charging and discharging. You may mix and use these. The upper limit of the lithium ion storage potential of the titanium oxide is not limited to this, but is preferably 2V.

As the titanium oxide or the like, a compound selected from Li _{4 + x} Ti ₅ O ₁₂ , Li _{2 + x} Ti ₃ O ₇ , a titanate compound represented by the general formula H ₂ Tin _n O _{2n + 1} , and bronze-type titanium oxide is preferable. The above x is a real number satisfying 0 ≦ x ≦ 3, and n is an even number of 4 or more.

Titanium oxide or the like is preferable when the lithium ion occlusion potential is 1.2 V (vs. Li / Li ⁺ ) or more because the effects of the present invention are particularly easily obtained. The lithium ion occlusion potential of the above-mentioned spinel lithium titanate, ramsdellite lithium titanate, monoclinic titanium oxide and lithium hydrogen titanate is 1.5 to 1.6 V vs. Li / Li ⁺ . . The lithium ion occlusion potential refers to a potential corresponding to the middle point of the capacity when a potential-capacity curve at the time of charging is drawn in capacity measurement according to a method described later.

  The titanium oxide or the like preferably has an average primary particle size of 2 μm or less. When the average primary particle size is 2 μm or less, an effective area contributing to the electrode reaction can be sufficiently secured, and good large current discharge characteristics can be obtained. Moreover, it is good also as a secondary particle which granulated the primary particle by the well-known method. The average particle diameter measured by the laser diffraction / scattering method is preferably 0.1 to 30 μm.

Further, the titanium oxide or the like preferably has a specific surface area of 1 to ²⁰ m ² / g. When the specific surface area is 1 m ² / g or more, an effective area contributing to the electrode reaction can be sufficiently secured, and good charge / discharge characteristics can be obtained. Even if the specific surface area is 20 m ² / g or more, the effect of the present invention can be obtained. However, in the production of the electrode, the dispersibility of the active material in the mixture slurry such as the negative electrode and the application of the mixture slurry to the current collector In order to avoid problems in handling such as workability and adhesion between the active material layer and the current collector, the specific surface area is preferably 20 m ² / g or less. The specific surface area such as titanium oxide, more preferably 3 to 20 m ² / g, more preferably 5 to 20 m ² / g. Usually, when a titanium oxide having a large specific surface area such as a specific surface area of 5 m ² / g or more is used, a large amount of gas is generated during charge / discharge cycles and storage, but if the present invention is applied, gas generation is reduced. It is possible, and gas generation accompanying a high temperature cycle can be significantly reduced. As a result, titanium oxide or the like having a large specific surface area can be used as the negative electrode active material, so that good low-temperature charge / discharge characteristics and large current charge / discharge characteristics can be imparted to the nonaqueous electrolyte secondary battery. The specific surface area can be determined by the BET single point method by nitrogen adsorption.

  The lithium fluoride compound and the carbon compound present on the surface of the titanium oxide or the like of the present invention are mainly composed of a fluoride component mainly composed of lithium fluoride and a carbon-based component mainly composed of the carbon compound. It is estimated that The state of these lithium fluoride compounds and carbon compounds can be expressed by the ratio of the peak area (A) of F bonded to Li and the peak area (B) of C1s using an X-ray photoelectron spectroscopy spectrum. By adjusting the ratio A / B of the peak areas of the lithium fluoride compound component A and the carbon compound component B to an appropriate range, gas generation occurs during use in a high temperature environment, particularly when charging and discharging are repeated (high temperature cycle) in a high temperature environment. And a decrease in battery capacity can be suppressed.

  When the ratio A / B between the peak area (A) of F bonded to Li and the peak area (B) of C1s in a titanium oxide or the like is smaller than 0.3, the lithium fluoride is reduced. It is considered that the thermal stability of the surface layer is degraded and the surface layer collapses due to decomposition at a high temperature and the like, and the decomposition of the nonaqueous electrolyte in the high temperature cycle cannot be suppressed, resulting in an increase in the amount of gas generated. When A / B is larger than 3.0, since there is too much lithium fluoride, the Li ion conductivity is deteriorated and the battery capacity is reduced due to an increase in battery resistance. Therefore, when 0.3 <A / B <3.0 is satisfied, the surface layer becomes stable even at high temperatures, and gas generation during high-temperature cycling can be suppressed and good cycle characteristics are exhibited. Li ion conductivity is in a trade-off relationship by using the present invention. A / B is preferably in the range of 0.5 <A / B <2.5, and more preferably in the range of 0.6 <A / B <2.2.

  Here, measurement by X-ray photoelectron spectroscopy (hereinafter referred to as XPS) will be described. In a 25 ° C. environment, the nonaqueous electrolyte secondary battery in which SOC is 0% by discharging to 0.2 V at 0.2 C is decomposed in an argon atmosphere and the negative electrode is taken out. The taken-out negative electrode is washed with MEC (methyl ethyl carbonate), dried, cut into an appropriate size, and used as a measurement sample. The measurement apparatus used was Quanta SXM manufactured by ULVAC-PHI, single-crystal spectroscopic Al-Kα ray (1486.6 eV) (25 W 15 kV) was used as the excitation X-ray, the analysis area was 300 μm × 800 μm, and the photoelectron extraction angle was 45 The charge neutralization is performed with electrons and floating ions, and an X-ray photoelectron spectrum is obtained. Charging correction of the obtained spectrum is performed with hydrocarbon (CHn: C1s, 285 eV).

  The peak area (A) of F bonded to Li of the lithium fluoride compound is calculated from the peak area of F1s bonded to Li appearing at 682 to 688 eV by separating the 1s peak of fluorine into two peaks having different energies. A specific example is shown in FIG. In FIG. 1, the low energy side (right side) is LiF-bonded F1s, and the high energy side (left side) is PF bond or CF bond F1s. Peak separation is performed using a curve fitting method using a nonlinear least square method. The peak area is obtained by performing background correction.

The C1s peak area (B) of the carbon compound can be calculated from the C1s peak area appearing at 280 to 294 eV. C1s is the sum of C—C appearing at 282 to 285 eV, CHn appearing at 285 eV, C—O appearing at 287 eV, O—C═O appearing at 289 eV, and the peak area of Li ₂ CO ₃ appearing at 290 eV. . A specific example is shown in FIG.

The titanium oxide and the like of the present invention preferably have an X-ray photoelectron spectroscopic spectrum measured using a single crystal spectroscopic Al-Kα ray as an excitation X-ray source that satisfies the following (formula 2).
0.2 <A / T (Formula 2)
(In Formula 2, A is the peak area of F combined with Li appearing at 682 to 688 eV, and T is the peak area of Ti2p _3/2 appearing at 455 to 462 eV.)

A in Formula 2 is the same as A in Formula 1, and T is considered to depend on the ratio of the surface portion of the titanium oxide where no lithium fluoride compound is present. The ratio of the lithium fluoride compound present on the surface is the ratio of the 2p _3/2 peak area (T) of titanium and the peak area (A) of F bonded to Li by X-ray photoelectron spectroscopy (XPS). Stipulate. The peak area of T is also obtained by performing background correction.

The peak area of _{2p 3/2} of titanium, using a peak area of _{2p 3/2} of titanium observed in 455～462EV. A specific example is shown in FIG. In FIG. 3, the peak on the low energy side (right side) is the peak of Ti2p _3/2 , and the peak on the high energy side (left side) is the peak of Ti2p _1/2 .

  As the value of A / T increases, it is estimated that the portion covered with the lithium fluoride compound increases. By setting A / T to a range larger than 0.2, it is assumed that a lithium fluoride compound is sufficiently present on the titanium oxide surface. Therefore, the thermal stability of the surface fluoride layer at a high temperature is increased, and the gas generation suppressing effect is further increased. A / T is more preferably greater than 0.3.

Next, the present invention includes at least titanium and oxygen, titanium composite oxide and / or titanium oxide capable of reversibly occluding and releasing lithium ions as an active material, and single crystal spectroscopic Al— as an excitation X-ray source. An X-ray photoelectron spectrum measured using Kα rays is a negative electrode satisfying the following (formula 3).
0.3 <A / B <3.0 (Formula 3)
(In Formula 3, A is the peak area of F1s combined with Li appearing at 682 to 688 eV, and B is the peak area of C1s appearing at 280 to 294 eV.)

  The negative electrode of the present invention includes at least a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is formed on one side or both sides of the negative electrode current collector. The negative electrode active material layer includes at least a negative electrode active material, and may include a conductive agent, a binder, and other materials as necessary. For the negative electrode current collector, for example, aluminum, an aluminum alloy, copper, or a copper alloy can be used.

  The negative electrode active material used for the negative electrode of the present invention uses titanium oxide or the like that contains at least titanium and oxygen and can reversibly store and release lithium ions, and the above-described lithium fluoride compound and carbon compound are present on the surface of titanium. It is preferable to use an oxide or the like. Only one kind of the above-described titanium oxide may be used, but two or more kinds may be mixed and used. The negative electrode may contain a known negative electrode active material other than titanium oxide, but titanium oxide or the like preferably occupies 50% or more of the negative electrode capacity, and more preferably 80% or more.

  A negative electrode containing titanium oxide or the like as an active material includes a fluoride component mainly composed of lithium fluoride and a carbon-based component mainly composed of a carbon compound. The state of this negative electrode can be represented by the ratio of the peak area (A) of F bonded to Li and the peak area (B) of C1s using an X-ray photoelectron spectroscopy spectrum. By adjusting the ratio A / B of the peak area of the carbon compound component B to an appropriate range, use in a high temperature environment, particularly reduction of gas generation due to repeated charge / discharge (high temperature cycle) in a high temperature environment, and battery capacity Reduction can be suppressed.

  When the ratio A / B of the peak area (A) of F bonded to Li and the peak area (B) of C1s in the negative electrode is smaller than 0.3, the lithium fluoride is reduced, so the thermal stability of the surface fluoride layer However, the surface layer is considered to be decomposed due to decomposition at a high temperature, and the decomposition of the nonaqueous electrolyte in the high temperature cycle cannot be suppressed, resulting in an increase in the amount of gas generated. When A / B is larger than 3.0, since there is too much lithium fluoride, the Li ion conductivity is deteriorated and the battery capacity is reduced due to an increase in battery resistance. Therefore, when 0.3 <A / B <3.0 is satisfied, the surface layer becomes stable even at high temperatures, and gas generation during high-temperature cycling can be suppressed and good cycle characteristics are exhibited. Li ion conductivity is in a trade-off relationship by using the present invention. A / B is preferably in the range of 0.5 <A / B <2.5, and more preferably in the range of 0.6 <A / B <2.2. For such a negative electrode, it is preferable to use a titanium oxide represented by Formula 1 of the present invention.

In the negative electrode of the present invention, it is preferable that an X-ray photoelectron spectrum measured using a single crystal spectrum Al—Kα ray as an excitation X-ray source satisfies the following (formula 4).
0.2 <A / T (Formula 4)
(A in Formula 4 is the same as A in Formula 3, and is the peak area of F1s combined with Li appearing at 682 to 688 eV, and T is the peak area of Ti2p _3/2 appearing at 455 to 462 eV. .)

  When the A / T value increases, it is estimated that the portion of the titanium oxide or the like in the negative electrode whose surface is covered with the fluoride layer increases. By setting A / T to a range larger than 0.2, it is assumed that lithium fluoride is sufficiently present on the surface of the titanium oxide in the negative electrode. Therefore, the thermal stability of the surface fluoride layer at a high temperature is increased, and the gas generation suppressing effect is further increased. A / T is more preferably greater than 0.3. Such a negative electrode preferably uses a titanium oxide represented by Formula 2 of the present invention.

  All of A, B, and T obtained from the XPS measurement and the XPS spectrum can be calculated by the method described above.

  The conductive agent is used for imparting conductivity to the negative electrode, and any material can be used as long as it is a conductive material that does not cause a chemical change in the constituted secondary battery. Examples include natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon-based materials such as carbon fiber, metal powders such as copper, nickel, aluminum, silver, or metal-based materials such as metal fiber, polyphenylene A conductive material including a conductive polymer such as a derivative, or a mixture thereof can be used.

  As the binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), or the like can be used.

  Examples of other materials that can be included in the negative electrode active material layer include various known additives.

  The mixing ratio of the negative electrode active material, the conductive agent and the binder is preferably in the range of 70 to 95% by mass of the negative electrode active material, 0 to 25% by mass of the conductive agent, and 2 to 10% by mass of the binder.

Next, the present invention provides a positive electrode, a negative electrode containing at least titanium and oxygen, and a titanium composite oxide and / or titanium oxide capable of reversibly occluding and releasing lithium ions as an active material, the positive electrode, and the negative electrode X-ray measured using a single crystal spectroscopic Al-Kα ray as an excitation X-ray source of the negative electrode. It is a non-aqueous electrolyte secondary battery whose photoelectron spectroscopy spectrum satisfies the following (formula 5).
0.3 <A / B <3.0 (Formula 5)
(In Formula 5, A is the peak area of F1s combined with Li appearing at 682 to 688 eV, and B is the peak area of C1s appearing at 280 to 294 eV.)

  The nonaqueous electrolyte secondary battery of the present invention uses the above negative electrode, and the ratio A / B of the peak area (A) of F bonded to Li and the peak area (B) of C1s in the negative electrode is: By making the range 0.3 <A / B <3.0, use of the non-aqueous electrolyte secondary battery in a high temperature environment, particularly gas generation accompanying repeated charge / discharge (high temperature cycle) in a high temperature environment And a decrease in battery capacity can be suppressed. A / B is preferably in the range of 0.5 <A / B <2.5, and more preferably in the range of 0.6 <A / B <2.2. For such a negative electrode, it is preferable to use a titanium oxide represented by Formula 1 of the present invention.

Moreover, it is preferable that the non-aqueous electrolyte secondary battery of this invention satisfy | fills the following (Formula 6) in the X-ray photoelectron spectrum which used the single crystal spectrum Al-K (alpha) ray as an excitation X-ray source of a negative electrode.
0.2 <A / T (Formula 6)
(A in Formula 6 is the same as A in Formula 5, and is the peak area of F combined with Li that appears at 682 to 688 eV, and T is the peak area of Ti2p _3/2 that appears at 455 to 462 eV. .)

The non-aqueous electrolyte secondary battery of the present invention uses the above negative electrode, and the ratio of the peak area (A) of F bonded to Li and the peak area (T) of Ti2p _{3/2 in} the negative electrode A / By setting T to a range of 0.2 <A / T, it is assumed that lithium fluoride is sufficiently present on the surface of the titanium oxide in the negative electrode. Therefore, when it is set as a nonaqueous electrolyte secondary battery, the SEI film at high temperature becomes more stable, and the gas generation suppression effect is further enhanced. A / T is more preferably greater than 0.3. For such a negative electrode, it is preferable to use a titanium oxide represented by Formula 2 of the present invention.

  The positive electrode includes at least a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer is formed on one or both surfaces of the positive electrode current collector, includes at least a positive electrode active material, and may include a conductive agent, a binder, and other materials as necessary. For the positive electrode current collector, for example, aluminum or an aluminum alloy can be used.

As a positive electrode active material, the well-known electrode active material which can function as a positive electrode with respect to the titanium oxide used as a negative electrode active material can be used. Specifically, an active material having a lithium ion storage potential larger than 1.6 V (vs. Li / Li ⁺ ) is preferable, and more preferably 2.0 V (vs. Li / Li ⁺ ) or more. As such an active material, various oxides and sulfides can be used. For example, manganese dioxide (MnO ₂ ), iron oxide, copper oxide, nickel oxide, lithium manganese composite oxide (eg, Li _x Mn ₂ O ₄ or Li _x MnO ₂ ), lithium nickel composite oxide (eg, Li _x NiO ₂ ) , lithium-cobalt composite oxide _(Li x _CoO 2), lithium nickel cobalt composite oxide (e.g., _{Li x Ni 1-y Co y} O 2), lithium manganese cobalt composite oxide _{(Li x Mn y Co 1-} y O 2 ), lithium nickel manganese cobalt composite oxide _{(Li x Ni y Mn z Co} 1-y-z O 2), lithium manganese nickel complex oxide having a spinel structure _{(Li x Mn 2-y Ni} y O 4), olivine Lithium phosphorus oxide having a structure (Li _x FePO ₄ , Li _x Fe _1-y Mn _y P O ₄ , Li _x CoPO ₄ , Li _x MnPO _4, etc.), lithium silicate (such as Li _2x FeSiO ₄ ), iron sulfate (Fe ₂ (SO ₄ ) ₃ ), vanadium oxide (eg, V ₂ O ₅ ), A solid solution based complex oxide represented by xLi ₂ MO _3. (1-x) LiM′O ₂ (M and M ′ are one kind or two or more kinds of metals) can be used. You may mix and use these. In the above, x, y and z are preferably in the range of 0 to 1, respectively.

  Further, conductive polymer materials such as polyaniline and polypyrrole, disulfide polymer materials, organic materials such as sulfur (S) and carbon fluoride, and inorganic materials can also be used as the positive electrode active material.

Among the positive electrode active materials, an active material having a high lithium ion storage potential is preferably used. For example, lithium manganese composite oxide (Li _x Mn ₂ O ₄ ) having a spinel structure, lithium nickel composite oxide (Li _x NiO ₂ ), lithium cobalt composite oxide (Li _x CoO ₂ ), lithium nickel cobalt composite oxide _{(Li x Ni 1-y Co} y O 2), lithium manganese cobalt composite oxide _{(Li x Mn y Co 1-} y O 2), lithium nickel manganese cobalt composite oxide _{(Li x Ni y Mn z Co} 1-y _-Z O ₂ ), lithium manganese nickel composite oxide having a spinel structure (Li _x Mn _{2 -y} Ni _y O ₄ ), lithium iron phosphate (Li _x FePO ₄ ), etc. are preferably used, and particularly lithium nickel manganese Cobalt composite oxide and lithium iron phosphate are preferably used. In the above, x, y and z are preferably in the range of 0 to 1, respectively.

  As the conductive agent, for example, acetylene black, carbon black, or graphite can be used.

  As the binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), or the like can be used.

  Examples of other materials that can be included in the positive electrode active material layer include various additives, such as dinitrile compounds, fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, and ethylene sulfite. .

  The mixing ratio of the positive electrode active material, the conductive agent, and the binder is preferably in the range of 80 to 95% by mass of the positive electrode active material, 3 to 18% by mass of the conductive agent, and 2 to 10% by mass of the binder.

  As the non-aqueous electrolyte, a normal electrolyte can be used, and a solution in which a lithium salt is dissolved in a non-aqueous solvent is preferably used. A non-aqueous organic solvent is used as the non-aqueous solvent used in the non-aqueous electrolyte, and serves as a medium through which ions involved in the electrochemical reaction of the lithium battery can move. As examples of such non-aqueous organic solvents, carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or other aprotic solvents can be used. The non-aqueous electrolyte may contain moisture as an impurity. However, it is preferable to reduce this moisture as much as possible, preferably 100 ppm or less in 1 L of the electrolytic solution, and more preferably 20 ppm or less. It is preferable that at least the nonaqueous electrolyte does not actively contain moisture.

  Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC), ethylene carbonate ( EC), propylene carbonate (PC), butylene carbonate (BC), and the like can be used.

  Examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone (GBL), decanolide, valerolactone, mevalonolactone, and caprolactone. (Caprolactone) or the like can be used.

  As the ether solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran and the like can be used.

  As the ketone solvent, cyclohexanone or the like can be used.

  As the alcohol solvent, ethyl alcohol, isopropyl alcohol, or the like can be used.

The other aprotic solvents, R-CN (R is, C ₂ -C ₂₀ linear, a hydrocarbon group branched or cyclic structure, a double bond, an aromatic ring or an ether bond Nitriles such as dimethylformamide, amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, and the like.

Examples of the lithium salt include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenide (LiAsF ₆ ), lithium perchlorate (LiClO ₄ ), lithium bistri Fluoromethanesulfonylimide (LiN (CF ₃ SO ₂ ) ₂ , LiTSFI) and lithium trifluorometasulfonate (LiCF ₃ SO ₃ ) are included. These may be used alone or in admixture of two or more.

  Moreover, the actual nonaqueous electrolyte secondary battery has a separator that separates the positive and negative electrodes, and an exterior member that houses these members. A separator is arrange | positioned between a positive electrode and a negative electrode, and prevents that a positive electrode and a negative electrode contact. The separator is made of an insulating material. The separator has a shape in which the electrolyte can move between the positive electrode and the negative electrode. Examples of the separator include a synthetic resin nonwoven fabric, a polyethylene porous film, a polypropylene porous film, and a cellulose separator.

  As the exterior member, a laminate film or a metal container can be used. As the laminate film, a multilayer film made of a metal foil covered with a resin film is used. As the resin forming the resin film, polymers such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET) can be used. The inner surface of the laminate film exterior member is formed of a thermoplastic resin such as PP and PE. The thickness of the laminate film is preferably 0.2 mm or less. In this way, a non-aqueous electrolyte secondary battery can be configured and applied to a lithium ion secondary battery or the like.

  From the viewpoint of preventing the deposition of metallic Li during charging, in the conventional nonaqueous electrolyte secondary battery using a negative electrode active material having a low lithium ion storage potential such as a carbon-based material, the negative electrode capacity is made larger than the positive electrode capacity and the positive electrode is regulated. . On the other hand, in the present invention, there is no problem regardless of whether the positive or negative electrode is used. When regulated by the negative electrode, the potential of the positive electrode is maintained at a relatively low level during normal use. Therefore, a film is formed on the positive electrode by the oxidation reaction of components of the electrolyte such as solvents, lithium salts, and additives in the non-aqueous electrolyte. Is less likely to occur, and the potential of the positive electrode does not become too high, so that the oxidative decomposition of the electrolyte is less likely to occur, and the amount of gas generated at the positive electrode is reduced. At the same time, since the potential of the positive electrode does not become excessively high, deterioration of the crystal structure of the positive electrode active material itself can be suppressed, so that it is possible to further suppress further reduction in gas generation and battery capacity due to a high temperature cycle.

The aforementioned positive electrode capacity is obtained by the following method. In dry argon, the positive electrode and the lithium metal foil, which have been shaped for coin cells, are opposed to each other with a separator interposed therebetween. These members are put in a coin cell, an electrolyte is poured, and the coin cell is sealed in a state where the separator and the electrode are sufficiently impregnated with the electrolyte. In the electrolyte solution, lithium hexafluorophosphate as an electrolyte was added to a mixed solvent in which ethylene carbonate (EC), propylene carbonate (PC) and methyl ethyl carbonate (MEC) were mixed at a volume ratio of 1: 3: 6. Use 1.0 mol / liter dissolved. For a manufactured coin cell, a sufficiently low current density in a 25 ° C. environment, for example, a current of about 0.2 C calculated from a theoretical capacity (for example, in the case of LiFePO ₄ , the current density is 9.4 mg / cm ^2. with it) if 0.28mA / cm ^2, the actual positive electrode potential limit contemplated for use in the nonaqueous electrolyte secondary battery (e.g., at a constant current until 3.8 V) if LiFePO ₄ After charging, the battery is discharged at a constant current until the cell voltage reaches 3.0 V at the same current density as that during charging. By dividing the electric capacity at the time of discharge by the area of the positive electrode active material layer of the coin cell, the actual electric capacity P (mAh / cm ² ) in a 25 ° C. environment per unit area of the positive electrode is calculated. The temperature environment for measuring the actual electric capacity is formed using a thermostatic chamber (Yamato Scientific Thermostatic Chamber Model number IN804).

Instead of the positive electrode, a coin cell is manufactured in the same manner except that the negative electrode having a shape adapted for coin cell is used. With respect to the produced coin cell, in a 25 ° C. environment, a sufficiently small current density, for example, a current of about 0.2 C calculated from the theoretical capacity (for example, Li ₄ Ti ₅ O ₁₂ , the amount of active material is 7.5 mg / cm ² Then, the current density may be 0.24 mA / cm ² ), and after charging with a constant current until the cell voltage reaches 1.0 V, the cell voltage reaches 3.0 V at the same current density as during charging. The battery was discharged at a constant current until By dividing the electric capacity at the time of discharge by the area of the negative electrode active material layer of the coin cell, the actual electric capacity N (mAh / cm ² ) in a 25 ° C. environment per unit area of the negative electrode is calculated. In the measurement of N, the side where lithium ions are occluded in the active material is referred to as charging, and the side where lithium ions are desorbed is referred to as discharging.

  Next, a method for producing the titanium oxide, negative electrode, and non-aqueous electrolyte secondary battery of the present invention will be described.

  Arbitrary production methods such as a physical method or an electrochemical method may be used to form a lithium fluoride compound and a carbon compound on the surface of titanium oxide or the like, but the titanium oxide of the present invention can be obtained by conditioning described below. A method for producing a negative electrode and a non-aqueous electrolyte secondary battery is preferable.

  In this manufacturing method, a negative electrode containing the positive electrode, titanium oxide or the like as an active material (hereinafter sometimes simply referred to as “negative electrode”) and a non-aqueous electrolyte are accommodated in an exterior member, and an opening of the exterior member is temporarily provided. A first step of sealing to obtain a temporary sealed secondary battery; a second step of storing the temporary sealed secondary battery in an atmosphere of 50 ° C. or higher and lower than 80 ° C. after initial charging; It includes a third step of opening the sealed secondary battery to discharge the internal gas, and then, if necessary, a fourth step of fully sealing the exterior member.

(First step)
In the first step, a temporarily sealed secondary battery is manufactured. First, the electrode group is accommodated in the exterior member. The electrode group includes a positive electrode, a negative electrode, and a separator. Specifically, for example, a positive electrode, a separator, a negative electrode, and a separator are sequentially stacked, and the stacked body is wound into a flat shape to form a flat electrode group. As another method, for example, the electrode group may be formed by laminating one set or a plurality of sets of the positive electrode and the negative electrode via a separator. If necessary, the electrode group may be wound and fixed with an insulating tape. You may add the process of heating and / or vacuum-drying an electrode group and each structural member after formation of an electrode group and / or before formation, and reducing adsorption | suction moisture.

  A belt-like positive electrode terminal is electrically connected to the positive electrode. A strip-like negative electrode terminal is electrically connected to the negative electrode. The positive and negative electrode terminals may be formed integrally with the positive and negative electrode current collectors, respectively. Alternatively, a terminal formed separately from the current collector may be connected to the current collector. The positive and negative electrode terminals may be connected to each of the positive and negative electrodes before winding the laminate. Or you may connect, after winding a laminated body.

  The laminate film exterior member is formed by extending or deep drawing the laminate film from the thermoplastic resin film side to form a cup-shaped electrode group housing portion, and then bending it 180 ° with the thermoplastic resin film side inside. And forming a lid. In the case of a metal container, it can be formed, for example, by drawing a metal plate. Below, the case where the laminated film exterior member is used as a representative example is demonstrated.

  An electrode group is arrange | positioned in the electrode group accommodating part of an exterior member, and a positive / negative terminal is extended to the container exterior. Next, the upper end portion where the positive and negative electrode terminals of the exterior member extend and one of the end portions orthogonal to the upper end portion are heat-sealed to form a sealing portion. Thereby, the exterior member in a state where one side is opened as an opening is formed. Here, you may add the process of heating and / or vacuum-drying each structural member and reducing adsorption | suction moisture.

  Next, a non-aqueous electrolyte is injected from the opening, and then the inside of the desiccator is decompressed to remove air bubbles in the battery. It is preferable that the injection of the electrolytic solution and the removal of bubbles by reducing the pressure are repeated a plurality of times to sufficiently impregnate the electrode group with the nonaqueous electrolytic solution. Here, when X is the holding time (min) of the degree of vacuum and P is the degree of vacuum (kPa), a reduced pressure state that satisfies 50 (kPa) ≧ P ≧ (10/9) X + 70/9 is at least once. Then, it is more preferable because the electrode group can be sufficiently impregnated with the nonaqueous electrolytic solution, and the titanium oxide and the negative electrode showing the specific XPS spectrum of the present invention are easily formed. Here, in order to promote the impregnation of the electrolytic solution, the battery may be stored under pressure in the thickness direction, or the electrolytic solution may be injected after the inside of the electrode is decompressed.

  Thereafter, the temporary sealing secondary battery in which the electrode group and the nonaqueous electrolyte impregnated in the electrode group are sealed is obtained by heat-sealing the opening to form a temporary sealing part. When conditioning is not performed, a sealed secondary battery is obtained by performing main sealing here.

(Second step)
Next, the second step is performed. Current is passed between the positive electrode terminal and the negative electrode terminal of the temporarily sealed secondary battery, and the initial charge is performed so that the negative electrode potential is in the range of potential higher than 0.8V and lower than 1.4V (vs. Li / Li ⁺ ). Is preferred. It is more preferable to perform initial charging so that the negative electrode potential is 350 mV or more lower than the lithium ion storage potential of the negative electrode active material.

When the battery is initially charged so that the negative electrode potential is 1.4 V or less (vs. Li / Li ⁺ ), it is preferable because gas generation associated with use in a high-temperature environment can be further reduced and battery capacity reduction can be further suppressed. , 1.2 V (vs. Li / Li ⁺ ) or less is more preferable. If the battery is initially charged until the negative electrode potential is 0.8 V or less (vs. Li / Li ⁺ ), it is estimated that an excessive film is formed on the negative electrode surface. Since it falls, it is not preferable. Further, when aluminum is used for the negative electrode current collector, it is not preferable that the negative electrode potential is lowered to 0.4 V or less (vs. Li / Li ⁺ ) because the current collector aluminum is alloyed with lithium.

  There is no restriction | limiting in particular in the period until it performs initial charge after preparation of the said temporary sealing battery, It can set arbitrarily according to a production schedule etc. For example, it is good as 1 hour-1 month. In addition, the initial charging and high-temperature storage described below are not limited to the initial charging after preparing the temporarily sealed battery, and charging and discharging and storage are performed once or a plurality of times as long as the gas can be discharged after opening. You may do it after doing.

Adjustment of the negative electrode potential is, for example, such that, in a cell having the same battery configuration, the negative electrode potential is higher than 0.8V and lower than 1.4V (vs. Li / Li ⁺ ) using the reference electrode. The amount of electricity charged can be calculated in advance, and the amount of electricity can be adjusted by charging the temporarily sealed battery. Alternatively, in a cell having the same battery configuration, charging is performed under the same conditions using the reference electrode until the negative electrode potential is higher than 0.8 V and reaches a desired potential in the range of 1.4 V or less (vs. Li / Li ⁺ ). The cell voltage can be adjusted in advance, and the initial charge end voltage of the temporary sealing battery can be adjusted to the value of the confirmed cell voltage. Another method may be as follows. A coin cell is manufactured by cutting out a positive electrode used for a nonaqueous electrolyte secondary battery as a working electrode, using a metal lithium foil as a counter electrode, and using the same type of electrolyte and separator as the battery. The coin cell is charged under the same C rate and temperature conditions as the initial charging of the battery, and a vertical axis: potential-horizontal axis: capacity charging curve is drawn. Also for the negative electrode, a Li-occlusion-side potential-capacity curve including a desired negative electrode potential is drawn by a method according to the positive electrode evaluation using the negative electrode cut out in the same dimensions as in the positive electrode evaluation as a working electrode. The potential-capacity curves of the positive electrode and negative electrode obtained in this way are superimposed on one figure, the potential of the positive electrode corresponding to the capacity when the negative electrode reaches the desired negative electrode potential is read, and the cell voltage is calculated from the difference between the positive and negative electrode potentials. The cell voltage is determined as the initial charge end voltage.

  When lithium nickel manganese cobalt composite oxide is used as the positive electrode active material, the cell voltage is preferably 2.7 to 3.3 V when adjusting the negative electrode potential of the temporary sealing battery. It is more preferable that the voltage be 9 to 3.3 V. When lithium iron phosphate is used as the positive electrode active material, it is preferable that the cell voltage be 2.1 to 2.7 V when adjusting the negative electrode potential of the temporary sealing battery. More preferably, the voltage is 7V.

  The temperature at which the initial charging is performed can be arbitrarily set, but is preferably about 20 to 45 ° C, and may be performed at room temperature (20 to 30 ° C). It is preferable to perform at room temperature because the equipment can be simplified.

  The charging current value can be set arbitrarily. If it is 1 C or less, the effect of suppressing gas generation under the high temperature environment of the present invention can be easily obtained, and it is more preferably 0.5 C or less. Further, the current value may be changed during charging, for example, CC-CV charging may be performed. Note that 1C capacity = nominal capacity of the battery.

  If the temporarily sealed secondary battery has a substantially flat shape, initial charging may be performed while pressing the battery body in the thickness direction. There is no particular limitation on the method of pressurization, for example, a method of performing the initial charge by pressing the battery, or storing the battery in a holder that can be fixed in contact with the front and back of the battery. Is mentioned.

  Next, it is preferable to store the temporarily sealed secondary battery initially charged to the negative electrode potential in an atmosphere having a temperature of 50 ° C. or higher and lower than 80 ° C.

  When the ambient temperature is less than 50 ° C., it is estimated that it is not industrial because it takes time to release water, carbon dioxide, and the like from the electrode group, and an appropriate film is not formed on the negative electrode surface. The high-temperature characteristics of are not sufficient. When the ambient temperature is 80 ° C. or higher, it is presumed that the reaction of the nonaqueous electrolyte on the surface of the positive electrode or the negative electrode is likely to occur, and an excessive film is formed. The decrease in the capacity maintenance rate of the battery also increases. A more preferable range of the atmospheric temperature is 50 to 70 ° C.

  The time for storing the temporarily sealed secondary battery in an atmosphere having a temperature of 50 ° C. or higher and lower than 80 ° C. may be a time for sufficiently releasing the gas from the negative electrode. Although it is not limited to this, For example, it can be set as 5 hours-10 days, Preferably it can be set as 1 day-8 days. This storage time may be adjusted according to the type of positive electrode active material. For example, when a lithium-transition metal composite oxide is used as the positive electrode active material, it can be 5 hours to 8 days, preferably 1 to 7 days. It can be. For example, when using lithium iron phosphate as a positive electrode active material, it can be set to 5 hours-10 days, Preferably it can be set to 5-8 days. There is no particular limitation on the time from the initial charging to the start of high-temperature storage, and any time can be set.

  When the temporarily sealed secondary battery is stored in an open circuit state during the high-temperature storage period, the negative electrode potential becomes higher due to self-discharge. Here, if the battery is stored at a constant potential by charging the battery substantially continuously during storage, the battery capacity is greatly reduced after storage, and therefore, storage at a constant potential, for example, trickle charge or float charge is not performed. Is preferred. In order to compensate for a part of the self-discharge capacity, charging of about 10% of the self-discharge amount may be intermittently performed during the storage, but it is most preferable to store in an open circuit state.

  In addition, “adjusting the negative electrode potential of the temporarily sealed secondary battery to a potential higher than 0.8V and lower than 1.4V and storing it in an atmosphere of 50 ° C. or higher and lower than 80 ° C.” means that during the high-temperature storage period, It does not mean that the negative electrode potential needs to be maintained in the above range, and includes the case where the negative electrode potential rises during the storage period and falls outside the above potential range if the end-of-charge potential is set as the above-mentioned potential range. . The negative electrode potential may rise to the lithium ion storage potential of titanium oxide or the like.

(Third step)
Next, a part of the exterior member is cut or a hole is formed, and the gas retained in the exterior member in the second step is discharged to the outside. For example, the exterior member can be opened by cutting the laminate film at any position of the opening portion that is the inside of the temporary sealing portion and is not heat-sealed. Opening is preferably performed under reduced pressure, and is preferably performed in an inert atmosphere or in dry air.

  After opening the exterior member, the nonaqueous electrolyte secondary battery may be in a reduced pressure atmosphere using a decompression chamber or the like, or gas may be sucked from the opening or hole of the exterior member using a suction nozzle. According to these methods, the gas inside the exterior member can be discharged more reliably. Here, when X is the holding time (min) of the degree of vacuum and P is the degree of vacuum (kPa), a reduced pressure state that satisfies 50 (kPa) ≧ P ≧ (10/9) X + 70/9 is at least once. Then, the electrode group can be sufficiently impregnated with the non-aqueous electrolyte, and the gas inside the exterior member can be sufficiently discharged, so that the titanium oxide and the negative electrode showing the specific XPS spectrum of the present invention are easily formed. preferable.

(Fourth process)
Next, after the gas is discharged, the main sealing portion is formed by heat-sealing the exterior member inside the cut portion of the opening portion, and the electrode group and the nonaqueous electrolyte are sealed again. Further, the opening part is cut outside the main sealing part. Thereby, a nonaqueous electrolyte secondary battery is obtained. At this time, it is preferable to seal under reduced pressure. Or you may affix an adhesive tape etc. on the location which made the hole of the exterior member, and may seal. Even when conditioning is not performed, opening, degassing, and resealing may be performed after the charging step.

  The obtained nonaqueous electrolyte secondary battery may be optionally charged and discharged one or more times. Moreover, you may store further at normal temperature or high temperature. The conditioning process (second step or second step + third step) may be performed a plurality of times.

In the case of conditioning, it is preferable to use ethylene carbonate as the non-aqueous solvent and LiPF ₆ and / or LiBF ₄ containing fluorine as the lithium salt. This is because when ethylene carbonate and fluorine-containing lithium salt are used in combination, even when titanium oxide or the like having a high potential is used as the negative electrode active material, it is maintained at a specific temperature after being set to a specific potential. By doing so, it is considered that a titanium oxide containing a lithium fluoride compound and a carbon compound exhibiting a specific XPS spectrum of the present invention is formed. If ethylene carbonate is 5 to 20% by volume of the whole non-aqueous solvent and the fluorine-containing lithium salt concentration is 0.5 to 2 mol / liter with respect to the non-aqueous electrolyte, a good lithium fluoride compound can be formed.

  Moreover, when performing the said conditioning, it is preferable to set it as the positive / negative electrode capacity ratio that a nonaqueous electrolyte secondary battery becomes negative electrode regulation. When regulated by the negative electrode, the potential of the negative electrode is likely to be lowered on the charging side, the desorption of water and carbon dioxide adsorbed during high temperature storage is promoted, and the formation of a film on the negative electrode surface can suppress gas generation. In addition, since the positive electrode potential at the initial charge can be suppressed from becoming too high, deterioration of the positive electrode can be suppressed. In particular, when the positive electrode actual electric capacity is P and the negative electrode actual electric capacity is N, the positive / negative electrode capacity ratio R = N / P is preferably 0.7 ≦ R <1.0. Even if R is less than 0.7, the effect of the present invention can be obtained, but the discharge capacity as a battery is lowered.

Including the lithium fluoride compound and the carbon compound in which the X-ray photoelectron spectrum using the single crystal spectrum Al—Kα ray as the excitation X-ray source satisfies 0.3 <A / B <3.0 by the above-described manufacturing method. Titanium oxide, etc.
Further, titanium oxide satisfying 0.2 <A / T in X-ray photoelectron spectrum using single crystal spectrum Al—Kα ray as an excitation X-ray source, etc.
An anode containing titanium oxide and the like as an active material, and an X-ray photoelectron spectrum using a single crystal spectrum Al—Kα ray as an excitation X-ray source satisfies 0.3 <A / B <3.0;
Furthermore, an X-ray photoelectron spectroscopic spectrum using a single crystal spectroscopic Al-Kα ray as an excitation X-ray source satisfies 0.2 <A / T,
A positive electrode, a negative electrode containing titanium oxide or the like as an active material, a separator disposed between the positive electrode and the negative electrode, a non-aqueous electrolyte,
A non-aqueous electrolyte secondary battery comprising: a non-electrolyte secondary battery having an X-ray photoelectron spectrum satisfying 0.3 <A / B <3.0 using a single-crystal spectroscopic Al-Kα ray as an excitation X-ray source of the negative electrode Water electrolyte secondary battery,
Furthermore, a non-aqueous electrolyte secondary battery using an X-ray photoelectron spectrum satisfying 0.2 <A / T, using a single crystal spectrum Al—Kα ray as an excitation X-ray source for the negative electrode,
Is obtained.

  By using the titanium oxide obtained by the above-described manufacturing method as a negative electrode active material, use in a high temperature environment, particularly reduction in gas generation due to repeated charge / discharge (high temperature cycle) in a high temperature environment, and reduction in battery capacity A non-aqueous electrolyte secondary battery that can be suppressed is obtained. In this manufacturing method, a titanium oxide or a negative electrode containing a lithium fluoride compound and a carbon compound exhibiting a specific XPS spectrum can be formed, and it is not necessary to use water or hydrofluoric acid. It is possible to reduce gas generation or corrosion of battery constituent members during high-temperature cycles caused by acid.

  Hereinafter, the present invention will be described specifically by way of examples.

Example 1
<Preparation of positive electrode>
84% by mass of lithium iron phosphate (LiFePO ₄ ) powder as a positive electrode active material, 10% by mass of acetylene black as a conductive additive, 6% by mass of polyvinylidene fluoride (PVdF) as a binder, and N-methylpyrrolidone (NMP) as a solvent ) Was prepared. This slurry was applied to both sides of a current collector made of an aluminum foil having a thickness of 20 μm so that the amount of active material per side was 9.4 mg / cm ² . After coating, the positive electrode was produced by drying and pressing so that the density of the composite material was 1.9 g / cm ³ . Thereafter, drying under reduced pressure was performed at 130 ° C. for 8 hours.

<Production of negative electrode>
Lithium titanium oxide having a spinel structure as a negative electrode active material (Li ₄ Ti ₅ O ₁₂ manufactured by Ishihara Sangyo, lithium occlusion potential = 1.55 V vs Li / Li ⁺ , specific surface area = 6.5 m ² / g, average particle size = 7. 3 μm), acetylene black as a conductive agent, and an N-methylpyrrolidone (NMP) solution of polyvinylidene fluoride (PVdF) in a mass ratio of Li ₄ Ti ₅ O ₁₂ : acetylene black: PVdF = 88: 5: 7 was mixed and NMP was added to prepare a negative electrode mixture slurry. This slurry was applied to both sides of a current collector made of an aluminum foil having a thickness of 20 μm so that the amount of active material per side was 7.7 mg / cm ² . After application, the negative electrode was prepared by drying and pressing so that the composite density was 1.8 to 2.0 g / cm ³ . Thereafter, drying under reduced pressure was performed at 130 ° C. for 8 hours. The average particle diameter of the active material was measured by a laser diffraction method (Laser diffraction / scattering particle size distribution measuring apparatus LA-950, manufactured by Horiba, Ltd.). About the specific surface area, it measured by the BET one-point method by nitrogen adsorption | suction using the specific surface area measuring apparatus (Monosorb: product made from Quantachrome Instruments).

<Production of electrode group>
The sheet-like positive electrode produced above, a separator made of rayon having a thickness of 50 μm, the sheet-like negative electrode produced above, and the separator were alternately laminated in this order and fixed with an insulating tape. After fixing, lead tabs made of aluminum foil having a thickness of 20 μm were welded to the positive electrode and negative electrode current collectors. The obtained electrode group was a flat electrode group having a width of 36 mm and a thickness of 3.9 mm. The obtained electrode group was accommodated in an exterior member made of a laminate film and vacuum-dried at 80 ° C. for 8 hours.

<Preparation of non-aqueous electrolyte>
In a mixed solvent of ethylene carbonate (EC), propylene carbonate (PC), and methyl ethyl carbonate (MEC) (mixing volume ratio 10:30:60), 1 mol / liter of lithium hexafluorophosphate (LiPF ₆ ) as a lithium salt. A solution dissolved to 1 liter was prepared.

<First step>
As a 1st process, the electrode group was accommodated in the state which the positive / negative terminal extended from the one side to the exterior member which consists of laminate films. The nonaqueous electrolyte is injected into the exterior member, and then the desiccator is depressurized to remove air bubbles in the battery and the electrolytic solution injection step is repeated to apply the nonaqueous electrolytic solution to the electrode group. Impregnated. The decompression condition at this time was maintained at a vacuum degree of 50 kPa for 2 minutes. Next, the laminate film was temporarily sealed by heat sealing and sealed to obtain a temporarily sealed secondary battery.

As a result of measuring the actual electrical capacity P of the positive electrode and the actual electrical capacity N of the negative electrode used in this temporary sealing battery by the method described in paragraphs 0072 and 0073, P = 1.42 mAh / cm ² and N = 1.28 mAh / cm ² . Therefore, this temporary sealing battery has a positive / negative electrode capacity ratio R = N / P = 0.9 and a design capacity of 50 mAh.

<Second step>
As a second step, after leaving the temporarily sealed secondary battery for 3 hours, a current is passed between the negative electrode terminal and the positive electrode terminal at room temperature until the negative electrode potential becomes 1.0 V at 0.2 C (10 mA). The battery was charged at 25 ° C. At the end of charging, the voltage of the secondary battery was 2.5V.

  Subsequently, the initially charged temporary sealed secondary battery was stored in an open circuit state for 168 hours in an atmosphere (constant temperature bath) having a temperature of 55 ° C.

<Third step>
As a third step, the temporarily sealed secondary battery after storage was cooled to room temperature, a part of the laminate film was cut out and placed in a vacuum chamber, and the gas was discharged. The degree of vacuum at this time was maintained at 50 kPa for 2 minutes.

<4th process>
Next, a part of the laminate film was sealed again (main sealing) by heat sealing. In this way, a non-aqueous electrolyte secondary battery having a width of 60 mm, a thickness of 2 mm, and a height of 80 mm, which was manufactured and conditioned by a temporary sealing battery, was produced.

(Example 2)
When the pressure inside the desiccator is reduced in Step 1 of Example 1 and the electrode group is impregnated with the non-aqueous electrolyte, and when the gas is discharged in the reduced pressure chamber in Step 3, the degree of vacuum is 20 kPa. Is the same as in Example 1 except that charging / discharging was performed at 55 ° C. (charging: 1 C—end voltage 2.5 V, pause: 30 minutes, discharge: 1 C—end voltage 1.0 V, pause: 30 minutes). A non-aqueous electrolyte secondary battery was manufactured by the method.

(Example 3)
Except when the pressure in the desiccator is reduced in Step 1 of Example 1 and the electrode group is impregnated with the nonaqueous electrolyte, and when the gas is discharged in the reduced pressure chamber in Step 3, the degree of vacuum is 60 kPa. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1.

(Comparative Example 1)
In Step 2 of Example 1, the same procedure as in Example 1 was applied except that the initially charged temporary-sealed secondary battery was stored in an open circuit state for 168 hours in an atmosphere (constant temperature bath) at a temperature of 25 ° C. Thus, a non-aqueous electrolyte secondary battery was manufactured.

<Experiment 1 X-ray photoelectron spectroscopy>
The nonaqueous electrolyte secondary batteries of Examples 1 to 3 and Comparative Example 1 were discharged to 1 V at 0.2 C in an environment of 25 ° C. to make SOC 0%. These batteries were decomposed in an argon atmosphere, the negative electrode was taken out, washed with MEC, dried, cut out into an appropriate size, and used as a measurement sample. For measurement of XPS spectrum, Quantara SXM manufactured by ULVAC-PHI was used. Single crystal spectroscopic Al-Kα ray (1486.6 eV) (25 W 15 kV) was used as the excitation X-ray, the analysis area was 300 μm × 800 μm, the photoelectron extraction angle was 45 °, and charge neutralization was performed with electrons and floating ions. . Spectral charge correction was performed with hydrocarbon (CHn: C1s, 285 eV) to obtain an X-ray photoelectron spectrum.

Using the XPS spectrum of the sample outermost surface obtained by the above measurement, the 1s peak of fluorine is separated into two peaks having different energies by the curve fitting method using the nonlinear least square method, and after performing background correction, The peak area A of F1s combined with Li appearing at 682 to 688 eV was determined. Similarly, the peak area B of C1s appearing at 280 to 294 eV was obtained. Similarly, the peak area T of 2p _3/2 of titanium observed at 455 to 462 eV was determined. 1 to 3 show XPS spectra of Example 2 in which charge correction, background correction, and peak separation are performed. A / B and A / T were calculated from the obtained A, B, and T. The results are shown in Table 1.

In addition, D / E described in JP 2010-231960 and F / G described in JP 2014-63702 were also calculated. Here, D is the maximum intensity of the peak appearing at 680 to 687 eV, and E is the maximum intensity of the peak appearing at 280 to 290 eV. F is the peak intensity of 1s of fluorine, and G is the peak intensity of 2p (sum of 2p _1/2 and 2p _3/2 ) of titanium. The results are shown in Table 1.

<Experiment 2 High-temperature cycle test>
The nonaqueous electrolyte secondary batteries manufactured in Examples 1 to 3 and Comparative Example 1 were stored in a constant temperature bath at a temperature of 25 ° C. and stabilized, and then discharged to SOC 0% once (1C, final voltage 1 .0V). After 30 minutes of rest, 1 C is charged with a constant current to 2.5 V, and after 30 minutes of rest, the capacity when discharged to 1 V at 1 C is defined as the discharge capacity. What measured the discharge capacity on these conditions was made into the initial capacity.
Next, the secondary battery was put into a constant temperature bath at a temperature of 55 ° C., and the same charge / discharge conditions as the capacity measurement (charge: 1C-end voltage 2.5 V, pause: 30 minutes, discharge: 1 C—end voltage 1.0 V , Pause: 30 minutes), 200 cycles of charge and discharge were performed. After 200 cycles, the discharge capacity was measured again to determine the post-cycle capacity, and the capacity retention ratio (= post-cycle capacity / initial capacity) was calculated. The results are shown in Table 1.

<Experiment 3 Gas Generation Measurement>
The nonaqueous electrolyte secondary batteries of Examples 1 to 3 and Comparative Example 1 were placed in a graduated cylinder containing 500 mL of water, and the volume of the battery was measured. The battery volume was measured before and after 200 cycles of the high-temperature cycle test, and the volume change was defined as the gas generation amount. The results are shown in Table 1.

  From Table 1, it was confirmed that Comparative Example 1 in which A / B = 0.24 had a larger gas generation amount and a lower capacity retention rate than Examples 1, 2, and 3. From this, it was found that by setting A / B> 0.3, gas generation accompanying the high-temperature cycle can be reduced and the capacity retention rate can be improved. In particular, it was confirmed that Examples 1 and 2 with A / T> 0.3 can further reduce gas generation and improve the capacity retention rate than Example 3 with A / T = 0.24. It was done. From this, it was found that by setting A / T> 0.3, it is possible to further reduce the gas generation accompanying the high-temperature cycle and improve the capacity retention rate.

  In JP 2010-231960, 3.2 ≦ D / E ≦ 6, in JP 2013-114809, 6 <D / E ≦ 21, and in JP 2014-63702, 0.01 ≦ F / G ≦ 1. Although lithium titanate satisfying the above requirements is disclosed, it was confirmed that D / E and F / G of the titanium oxide and the like of the present invention are not included in the scope of the prior art and are different.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

According to the present invention, a titanium oxide, a negative electrode, and a nonaqueous electrolyte capable of reducing gas generation due to use in a high temperature environment, in particular, repeated charging / discharging (high temperature cycle) in a high temperature environment, and suppressing a decrease in battery capacity. A secondary battery can be provided. The present invention can be applied to a non-aqueous electrolyte secondary battery using titanium oxide or the like as a negative electrode active material.
Therefore, the nonaqueous electrolyte secondary battery of the present invention can be used for various known applications. Specific examples include notebook computers, pen input computers, mobile computers, electronic book players, mobile phones, mobile faxes, mobile copy, mobile printers, headphone stereos, video movies, LCD TVs, handy cleaners, portable CDs, minidiscs, etc. , Walkie Talkie, Electronic Notebook, Calculator, Memory Card, Portable Tape Recorder, Radio, Backup Power Supply, Motor, Car, Bus, Train, Airplane, Bike, Motorbike, Bicycle, Lighting Equipment, Toy, Game Equipment, Clock, Electric Tool , Strobe, camera, power source for load leveling, natural energy storage power source, etc.

Claims (6)

X-rays measured using single crystal spectroscopic Al-Kα ray as an excitation X-ray source on the surface of titanium composite oxide and / or titanium oxide containing at least titanium and oxygen and capable of reversibly occluding and releasing lithium ions A titanium oxide containing a lithium fluoride compound and a carbon compound, the photoelectron spectrum of which satisfies the following (formula 1).
0.3 <A / B <3.0 (Formula 1)
(In Formula 1, A is the peak area of F1s combined with Li appearing at 682 to 688 eV, and B is the peak area of C1s appearing at 280 to 294 eV.) 2. The titanium oxide according to claim 1, wherein an X-ray photoelectron spectrum measured using a single crystal spectrum Al—Kα ray as an excitation X-ray source satisfies the following (formula 2).
0.2 <A / T (Formula 2)
(In Formula 2, A is the peak area of F1s combined with Li appearing at 682 to 688 eV, and T is the peak area of Ti2p _3/2 appearing at 455 to 462 eV.) Including at least titanium and oxygen, and a titanium composite oxide and / or titanium oxide capable of reversibly occluding and releasing lithium ions as an active material,
A negative electrode in which an X-ray photoelectron spectrum measured using a single crystal spectrum Al—Kα ray as an excitation X-ray source satisfies the following (formula 3).
0.3 <A / B <3.0 (Formula 3)
(In Formula 3, A is the peak area of F1s combined with Li appearing at 682 to 688 eV, and B is the peak area of C1s appearing at 280 to 294 eV.) The negative electrode according to claim 3, wherein an X-ray photoelectron spectrum measured using a single crystal spectral Al—Kα ray as an excitation X-ray source satisfies the following (formula 4).
0.2 <A / T (Formula 4)
(In Formula 4, A is the peak area of F1s combined with Li appearing at 682 to 688 eV, and T is the peak area of Ti2p _3/2 appearing at 455 to 462 eV.) A positive electrode;
A negative electrode containing at least titanium and oxygen, and a titanium composite oxide and / or titanium oxide capable of reversibly occluding and releasing lithium ions as an active material;
A separator disposed between the positive electrode and the negative electrode;
A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte,
A non-aqueous electrolyte secondary battery in which an X-ray photoelectron spectrum measured using a single crystal spectrum Al—Kα ray as an excitation X-ray source of the negative electrode satisfies the following (formula 5).
0.3 <A / B <3.0 (Formula 5)
(In Formula 5, A is the peak area of F1s combined with Li appearing at 682 to 688 eV, and B is the peak area of C1s appearing at 280 to 294 eV.) The non-aqueous electrolyte secondary battery according to claim 5, wherein an X-ray photoelectron spectrum measured using a single crystal spectral Al—Kα ray as an excitation X-ray source of the negative electrode satisfies the following (formula 6).
0.2 <A / T (Formula 6)
(In Formula 6, A is the peak area of F1s combined with Li appearing at 682 to 688 eV, and T is the peak area of Ti2p _3/2 appearing at 455 to 462 eV.)

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