JP2013131338A - Deterioration evaluation method of positive electrode active material and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a deterioration evaluation method of a positive electrode active material in the relationship with change of the crystal structure thereof, and to provide a deterioration evaluation method of a lithium ion secondary battery.SOLUTION: The deterioration evaluation method of a positive electrode active material consisting of LiNiMO(M is at least one kind of element selected from an element group of Mn, Co, Cr, Al, Mg, Ti and B) and used for the electrode plate 4 of a lithium ion secondary battery 1 includes a step measuring two peaks of first intensity A and second intensity B which are observed by irradiating the positive electrode active material with a soft X-ray RT that is rendered monochromatic to energy resolution of E/ΔE≥2000 while changing the energy, and performing XANES measurement for the Ni-Labsorption end, a step for calculating the absorption intensity ratio B/A, and a step for calculating the rate of change in the intensity ratio C from the initial absorption intensity ratio B/Aand the absorption intensity ratio B/A according to formula (1). C(%)=(B/A)/(B/A)×100 ... (1).

Description

  The present invention relates to a method for evaluating deterioration of a positive electrode active material and a lithium ion secondary battery, and more particularly, to a method for evaluating deterioration of a positive electrode active material and a lithium ion secondary battery using soft X-rays.

Lithium ion secondary batteries are used on the other side of vehicles such as hybrid vehicles, plug-in hybrid vehicles and electric vehicles, household electric devices such as notebook computers, and industrial devices such as impact drivers.
Examples of the positive electrode active material used for the positive electrode of such a lithium ion secondary battery (hereinafter also simply referred to as a battery) include, for example, LiNi _y M _1-y O, which is a nickel-based lithium composite oxide described in Patent Document 1. ₂ (M is at least one element selected from the group consisting of Mn, Co, Cr, Al, Mg, Ti and B) may be used.

This positive electrode active material has a layered structure in which Ni, M, and O are layered in an octahedral structure of NiO ₆ and MO ₆ and Li is inserted between the layers. And in the Li ion secondary battery using this positive electrode active material, the battery is charged and discharged by removing and inserting Li between layers.

JP 2003-346806 A

  By the way, if the battery is continuously used, the internal resistance of the battery may be deteriorated. As one of the factors, a change in the crystal structure of the positive electrode active material can be considered, but this could not be detected and evaluated appropriately.

  The present invention has been made in view of such problems, and provides a method for evaluating the deterioration of a positive electrode active material and a method for evaluating the deterioration of a lithium ion secondary battery in relation to a change in the crystal structure of the positive electrode active material. The purpose is to provide.

One aspect for solving the problem is that LiNi _y M _1-y O ₂ (M is Mn, Co, Cr, Al, Mg, Ti and B) used for the positive electrode plate of the lithium ion secondary battery. A method for evaluating the deterioration of a positive electrode active material comprising at least one element selected from the group of elements), wherein soft X-rays monochromatized with an energy resolution of E / ΔE ≧ 2000 change the energy of the positive electrode active material while changing its energy. Absorption intensity of two peaks observed when XANES measurement is performed on the Ni-L ₃ absorption edge by irradiating the substance (the absorption intensity of the low energy side peak is the first intensity A, the absorption intensity of the high energy side Is defined as a second intensity B.), a step of calculating an absorption intensity ratio B / A obtained by dividing the second intensity B by the first intensity A, and an initial absorption intensity ratio B ₀ / A ₀ and the absorption intensity ratio B / From, calculating the intensity ratio change rate C by the following equation (1), a positive electrode active deterioration evaluation method for a substance with a.
C (%) = (B / A) / (B ₀ / A ₀ ) × 100 (1)

When a battery using a positive electrode active material made of LiNi _y M _1-y O ₂ as a positive electrode plate is used, the crystal structure of the positive electrode active material gradually changes, which is one of the causes of the deterioration of the internal resistance of the battery. It has been found that Specifically, the X-ray absorption near edge structure (XANES) measurement of the Ni-L ₃ absorption edge is performed by irradiating soft X-rays with varying energy on the positive electrode active material of variously deteriorated batteries. When this is done, the peak of absorption intensity at which soft X-ray energy is observed near 852 eV (the absorption intensity of this peak is defined as the first intensity A) and the peak of absorption intensity observed at around 854 to 855 eV. Two (the absorption intensity of this peak is defined as the second intensity B) are observed. The change in the ratio (absorption intensity ratio) between the first intensity A and the second intensity B is considered to indicate a change in the structural distortion of the octahedral structure formed by (Ni, M) O ₆ .
And when it sees about the change from the initial stage of this absorption intensity ratio B / A, it has become clear that the magnitude | size changes according to deterioration of a positive electrode active material.
Therefore, the method for evaluating deterioration of the positive electrode active material according to the present invention includes a step of calculating the absorption intensity ratio B / A and a step of calculating the intensity ratio change rate C by the equation (1).
Thereby, it can evaluate appropriately about deterioration (structure change) of a positive electrode active material, and the raise of the internal resistance of a battery by this.

As the initial absorption intensity ratio B ₀ / A ₀ , the absorption intensity ratio A / B obtained for the positive electrode active material used in the battery before use may be used.

  Further, in the above-described method for evaluating the deterioration of the positive electrode active material, the soft X-ray is a method for evaluating the deterioration of the positive electrode active material that is monochromatized by a non-uniform spacing grating spectrometer (VLSPG) and a slit. good.

  By using a non-uniformly spaced diffraction grating spectrometer (VLSPG) and a slit, it is possible to easily obtain a monochromatic soft X-ray with a high resolution up to energy resolution E / ΔE ≧ 2000.

In another embodiment, a positive electrode active material made of LiNi _y M _1-y O ₂ (M is at least one element selected from the element group of Mn, Co, Cr, Al, Mg, Ti, and B) is used for the positive electrode plate. A method for evaluating deterioration of a lithium ion secondary battery used, wherein the positive electrode active material of the secondary battery is irradiated with monochromatic soft X-rays having energy resolution E / ΔE ≧ 2000 while changing the energy. Then, the absorption intensity of two peaks observed when XANES measurement is performed on the Ni-L ₃ absorption edge (the absorption intensity of the low energy side peak is the first intensity A, and the absorption intensity of the high energy side is the second Intensity B.), calculating the absorption intensity ratio B / A obtained by dividing the second intensity B by the first intensity A, and the initial absorption intensity ratio B ₀ / A ₀ and From the absorption intensity ratio B / A, strong Calculating a ratio change rate C by the following equation (1), a deterioration evaluating method of a lithium ion secondary battery comprising a.
C (%) = (B / A) / (B ₀ / A ₀ ) × 100 (1)

As described above, when the change from the initial stage of the absorption intensity ratio B / A is seen, it has been found that the magnitude thereof changes according to the deterioration of the positive electrode active material.
Accordingly, the secondary battery deterioration evaluation method of the present invention includes a step of calculating the absorption intensity ratio B / A and a step of calculating the intensity ratio change rate C by the equation (1).
Thereby, it can evaluate appropriately about the deterioration (increase of internal resistance) of the battery accompanying the structural change of a positive electrode active material.

  Furthermore, in the above-described method for evaluating deterioration of a lithium ion secondary battery, the soft X-ray is deteriorated in a lithium ion secondary battery that is monochromatized by a non-uniformly spaced grating spectrometer (VLSPG) and a slit. It should be an evaluation method.

  By using a non-uniformly spaced diffraction grating spectrometer (VLSPG) and a slit, it is possible to easily obtain a monochromatic soft X-ray with a high resolution up to energy resolution E / ΔE ≧ 2000.

It is explanatory drawing explaining the measurement system concerning embodiment and performing a XANES measurement. It is a graph which shows the relationship between the energy and the absorption intensity | strength of the soft X-ray which irradiated the active material sample by the XANES measurement about the initial sample 1 which has not performed the deterioration test. It is a graph which shows the relationship between the energy and the absorption intensity | strength of the soft X-ray which irradiated to the active material sample by XANES measurement about sample 2,3,4 which performed the deterioration test. It is a graph concerning samples 2 to 4 and showing the relationship between the intensity ratio change rate and the resistance increase rate. 1 is a perspective view of a lithium ion secondary battery used for evaluation according to an embodiment. 1 is a perspective view of a positive electrode plate of a lithium ion secondary battery used for evaluation according to an embodiment.

(Embodiment)
First, a battery 1 that is an object of evaluation according to the embodiment will be described with reference to FIGS. 5 and 6.
The battery 1 is a lithium ion secondary battery in which a wound electrode body 2 is housed in a battery case 3. A transparent insulating film (not shown) made of resin and bent in a box shape is interposed between the battery case 3 and the electrode body 2.

The electrode body 2 is formed by winding a strip-like positive electrode plate 4 and a negative electrode plate 5 into a flat shape via a strip-like separator 6. The positive electrode plate 4 and the negative electrode plate 5 of the electrode body 2 are respectively joined to a plate-like positive electrode current collector member 7 or a negative electrode current collector member 8 bent in a crank shape. The separator 6 made of porous polyethylene is impregnated with an electrolyte solution (not shown) obtained by adding a solute (LiPF ₆ ) to a mixed organic solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC). Has been.

  Among the electrode bodies 2, the negative electrode plate 5 is a thin strip-shaped copper negative electrode foil (not shown) and two negative electrode active material layers (not shown) arranged in a strip shape on both main surfaces of the negative electrode copper foil. And have.

Further, as shown in FIG. 6, the thin strip-like positive electrode plate 4 has a strip-like positive electrode foil 41 made of aluminum, and positive electrode active material layers 42 respectively formed on both main surfaces 41 a of the positive electrode foil 41. . Among these, the positive electrode active material layer 42 includes positive electrode active material particles made of nickel-based lithium composite oxide made of LiNi _1/3 Co _1/3 Mn _1/3 O _2, conductive particles made of acetylene black, and It consists of a resin binder (both not shown).

Next, evaluation of the positive electrode active material forming the battery 1 and the positive electrode plate 4 will be described with reference to FIGS. First, a battery (sample 1) subjected to only initial charging is prepared. In addition, the same batteries (samples 2, 3, and 4) as this battery were prepared, and these were stored for 130 days in an environment of 25 ° C., 40 ° C., and 60 ° C. in an SOC of 80%. For the batteries of Samples 2, 3, and 4, the resistance was measured before and after storage.
Thereafter, the batteries of Samples 1 to 4 were disassembled, and the positive electrode active material (active material sample SP) for each of Samples 1 to 4 was collected.
In addition, the resistance measurement of the battery was calculated from the voltage drop after discharging at 60 A for 10 seconds.
Moreover, the active material sample SP about each sample 1-4 was produced by wash | cleaning with EMC (methyl ethyl carbonate) after disassembling a battery in Ar glove box.

Next, XANES measurement (XAFS measurement) will be described with reference to FIG.
First, a continuous X-ray R radiated from the X-ray source 11 is interposed between two slit plates 12 and 13 each having a slit SS, and a VLSPG (unequal line spacing grating spectrometer) 14 is interposed. Thus, a monochromatic soft X-ray RT is generated.
As the X-ray source 11, there can be used Spring 8, Photon Factory and other synchrotron radiation facilities, and an X-ray generated by bremsstrahlung by irradiating an aluminum foil with an electron beam.
In addition, the energy resolution of the monochromatic soft X-ray RT is set to E / ΔE ≧ 2000. By doing in this way, two peaks of A and B can be observed in the XANES measurement for the Ni-L ₃ absorption edge described below.
Further, in the present embodiment, by using the VLSPG 14 and the slits 12 and 13, it is possible to easily obtain a monochromatic soft X-ray whose resolution is increased to energy resolution E / ΔE ≧ 2000.

The monochromatic soft X-ray RT is irradiated to the active material sample SP. The photocurrent generated in the active material sample SP is discharged to the ground potential through the ammeter 16.
The XANES measurement results for the Ni-L ₃ absorption edge out of the X-ray absorption intensities of the active material samples SP relating to the samples 1 to 4 thus obtained are shown in the graphs of FIGS. Among these, FIG. 2 shows the result of Sample 1 that was not subjected to the degradation test, in FIG. 3, the thick line shows the result of Sample 2 stored at 25 ° C. for 130 days, and the thin line shows Sample 3 stored at 40 ° C. for 130 days. The one-dot chain line shows Sample 4 stored at 60 ° C. for 130 days.

According to the graphs of FIGS. 2 and 3, a peak of absorption intensity is observed in the vicinity of X-ray energy of 852 to 855 eV. More specifically, each of the samples 1 to 4 has two peaks, one of which has soft X-ray energy observed in the vicinity of 852 eV. Further, an absorption intensity peak is also observed in the vicinity of 854 to 855 eV on the higher energy side (right side in the figure). Therefore, the absorption intensity of the peak on the low energy side (near 852 eV) is the first intensity A, and the absorption intensity on the high energy side (near 854 to 855 eV) is the second intensity B.
Then, it turns out that the magnitude | size of 1st intensity | strength A and 2nd intensity | strength B and the position (absorption peak) of the energy of the X-ray which shows a peak change with deterioration of a positive electrode active material.

Therefore, the first intensity A and the second intensity B are acquired from the graph of FIG. Next, the absorption intensity ratio A / B is calculated. Further, the initial absorption intensity ratio A / B (sample 1) is defined as the initial absorption intensity ratio A ₀ / B _0, and the peak intensity ratio A / B applied to the samples 2, 3 and 4 is defined as the initial absorption intensity ratio A _0. The intensity change rate C is calculated by the equation (1) divided by / B ₀ .
(C (%) = (B / A) / (B ₀ / A ₀ ) × 100) (1)

Further, for the batteries of Samples 2, 3 and 4, as described above, the resistance R ₀ of the battery before storage and the battery R after storage are measured, so the resistance change rate R / R ₀ is calculated. did.
These results are shown in Table 1. In addition, the relationship between the intensity ratio change rate C and the resistance change rate R / R ₀ is shown in FIG.

From the results shown in Table 1 and FIG. 4, with respect to the deteriorated batteries 1 to 4 of the samples, the resistance change rate R / R ₀ increases as the positive electrode active material deteriorates due to durability by storing at high temperature. The tendency to do is understood. From this, it is understood that the deterioration of the positive electrode active material can be evaluated by setting an appropriate threshold value using the strength change rate C as an index of battery deterioration (resistance increase) or positive electrode active material deterioration.

(Deformation)
In the above-described embodiment, the batteries 1 of Samples 1 to 4 were prepared, disassembled to create the active material sample SP, and XANES measurement was performed.
However, in this modification, the XANES measurement is performed using the battery 1 as it is as the battery sample SP.
That is, using a measurement system similar to that of the embodiment shown in FIG. 1, the XANES measurement is directly performed on the positive electrode active material applied to the positive electrode plate 4 in the battery 1, and the intensity change rate C is obtained as in the embodiment. And used as an index for evaluating the deterioration of the battery 1 (the positive electrode active material used therein).
In this case, there is an advantage that the battery 1 is nondestructive and the deterioration of the battery 1 (the positive electrode active material used therein) can be evaluated.
Note that, similarly to the embodiment, by using the VLSPG 14 and the slits 12 and 13, it is possible to easily obtain monochromatic soft X-rays with high resolution up to energy resolution E / ΔE ≧ 2000.

In the above, the positive electrode active material and the battery degradation evaluation method of the present invention have been described in accordance with the embodiment and the modification. However, the present invention is not limited to the embodiments and the like, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist thereof.
For example, in the embodiment, as shown in FIG. 5, the example applied to the battery 1 having the flat wound electrode body 2 is shown. However, any battery using a positive electrode active material such as a cylindrical type or a laminated type may be used. Either can be applied.
In the embodiments and the like, an example in which a nickel-based lithium composite oxide composed of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is used as the positive electrode active material has been described. However, LiNi _y M _1-y The present invention can be applied to a lithium composite oxide having a nickel-based layered structure made of O ₂ .

1 battery (secondary battery)
4 Positive electrode plate 11 X-ray source R Continuous X-ray RT Monochromatic soft X-rays 12 and 13 Slit plate SS Slit 14 VLSPG
SP active material sample, battery sample

Claims (4)

From LiNi _y M _1-y O ₂ (M is at least one element selected from the group consisting of Mn, Co, Cr, Al, Mg, Ti and B) used for the positive electrode plate of the lithium ion secondary battery A method for evaluating deterioration of a positive electrode active material, comprising:
Observed when XANES measurement is performed on the Ni-L ₃ absorption edge by irradiating the positive electrode active material while changing the energy of soft X-rays monochromatized to energy resolution E / ΔE ≧ 2000. Measuring the absorption intensity of the two peaks (the absorption intensity of the low energy side peak is the first intensity A, and the absorption intensity of the high energy side peak is the second intensity B);
Calculating an absorption intensity ratio B / A obtained by dividing the second intensity B by the first intensity A;
A method for evaluating the deterioration of the positive electrode active material, comprising: calculating an intensity ratio change rate C from the initial absorption intensity ratio B ₀ / A ₀ and the absorption intensity ratio B / A according to the following equation (1).
C (%) = (B / A) / (B ₀ / A ₀ ) × 100 (1) It is a deterioration evaluation method of the positive electrode active material according to claim 1,
The soft X-ray is a method for evaluating deterioration of a positive electrode active material, which is monochromatized by a non-uniformly spaced grating spectrometer (VLSPG) and a slit. Lithium ion 2 using a positive electrode active material made of LiNi _y M _1-y O ₂ (M is at least one element selected from the group consisting of Mn, Co, Cr, Al, Mg, Ti and B) for the positive electrode plate. A secondary battery deterioration evaluation method,
XANES measurement is performed on the Ni-L ₃ absorption edge by irradiating the positive active material of the secondary battery with soft X-rays monochromatized to energy resolution E / ΔE ≧ 2000 while changing the energy. Measuring the absorption intensity of the two peaks observed in the case of the low-energy peak (the absorption intensity of the low energy side peak is the first intensity A, and the absorption intensity of the high energy side peak is the second intensity B);
Calculating an absorption intensity ratio B / A obtained by dividing the second intensity B by the first intensity A;
A method for evaluating deterioration of a lithium ion secondary battery, comprising: calculating an intensity ratio change rate C from the initial absorption intensity ratio B ₀ / A ₀ and the absorption intensity ratio B / A according to the following equation (1).
C (%) = (B / A) / (B ₀ / A ₀ ) × 100 (1) A method for evaluating deterioration of a lithium ion secondary battery according to claim 3,
The soft X-ray is a method for evaluating deterioration of a lithium ion secondary battery in which the soft X-rays are monochromatized by a non-uniformly spaced grating spectrometer (VLSPG) and a slit.

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