JP2002340821A - Method of evaluating precision crystal structure of positive electrode material for lithium battery using neutron diffracting method and magnetic measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a precision structure evaluating method aiming at the development of a lithium secondary battery, especially the development of a positive electrode material appropriate for a lithium secondary battery. SOLUTION: A neutron diffracting method using a high resolution neutron diffracting device and a magnetic measuring method using a super-conducting quantum interferometer are combined to obtain the accurate information related to lithium and oxygen in the structure of the electrode material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating the precise structure of a positive electrode material of a lithium secondary battery by combining a neutron diffraction method and a magnetic measurement method.

[0002]

2. Description of the Related Art Lithium secondary batteries are widely used in various fields as power sources for portable equipment because of their light weight and high energy density.

[0003] Since the characteristics such as the energy density of a battery are mainly determined by the electrode material, development is being actively conducted with the aim of realizing a higher performance electrode material. Among them, the positive electrode material is one of the important R & D factors because it occupies a large weight in terms of cost reduction and high energy density in the battery system.

At present, proposals have been made to replace commercially available lithium cobalt oxides with low-cost materials such as lithium nickel oxide and lithium manganese oxide, and some of them have been put to practical use as power supplies for portable equipment. .

[0005] In a large power source for a power source for a moving body, etc., lithium manganese oxide is a promising candidate as an electrode material, and development as a drive power source for an electric vehicle is actively carried out and put into practical use. Is coming.

However, in order to be widely used as portable power supply devices, it is necessary to satisfy the requirements for characteristics such as cycle characteristics and long life, which are superior to those of portable device power supplies, as well as electrode materials. Need to be improved.

[0007] In particular, lithium manganese spinel oxide has a serious problem in practical use that battery characteristics deteriorate during high-temperature storage. Development is an important issue.

[0008] Previous studies have suggested that the elution of manganese from the structure of the battery has a complicated effect on battery characteristics by examining the electrolyte and the surface of the negative electrode. Few studies directly examined structural changes.

In order to suppress the deterioration of the battery characteristics during high-temperature storage and to realize the strict required characteristics accompanying the increase in size, changes in the crystal structure of the positive electrode material itself during high-temperature storage and during cycling are examined in detail. It is essential to elucidate the cause and precisely control the crystal structure based on it.

For this purpose, it is necessary to develop a measurement and evaluation method capable of analyzing the coordinates and occupancy of each constituent element in the structure of the positive electrode material with high accuracy and speed. In particular, the development of a method capable of accurately detecting a slight structural change is important for elucidating the problems of materials and developing an improved positive electrode material. Further, extraction of problems using a practical battery is also very important.

Conventionally, for example, X-ray diffraction measurement has been used as a method of examining the structural change of lithium manganese spinel after storage at a high temperature. With this method, only information on the change in lattice constant affected by the sample surface can be obtained.
Accurate information on the occupancy and coordinates of the light elements lithium and oxygen in the structure was not obtained, and in particular, information on the occupancy of lithium and oxygen was not obtained.

The XAFS method (X-ray absorption fine structure analysis method) is known for examining the electronic state and local structure of a transition metal. XANES (X-ray absorption edge structure) is disclosed in Japanese Patent Application Laid-Open No. 10-255801. ) Have been proposed to develop a long-life lithium secondary battery, but both methods have a small change in spectrum and low detection sensitivity.

On the other hand, neutron diffraction can provide information on elements such as lithium and oxygen that have a large effect on the cathode material. Examples of studies using neutron diffraction to detect oxygen deficiency in lithium manganese spinel oxide include R. Kanno et al., J. Power Sources,
81-82, (1999) 542-546. However, this method only reports the crystal structure analysis of a normal oxide, and does not report the relationship between the crystal structure and battery characteristics.

As a method for examining the coordination state and electronic state of a transition metal in a structure, a magnetic measurement method is known. Further, a material evaluation method for quickly estimating the charge / discharge capacity and operating voltage of a battery is proposed in Japanese Patent Application Laid-Open No. 9-180722, but mention is made of a method for estimating the coordination state of a transition metal. Not.

As described above, there is an example in which the magnetic measurement method is examined as a material evaluation method of an electrode material, but is not associated with the structural evaluation. In addition, the neutron diffraction method only analyzes the structure of the material. Therefore, information obtained using these methods is not reflected in the development of practical batteries.

[0016]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for evaluating a precise structure which enables the development of a lithium secondary battery, particularly a positive electrode material suitable for a lithium secondary battery. .

[0017]

Means for Solving the Problems The present inventor combines neutron diffraction using a high-resolution neutron diffractometer and magnetic measurement using a superconducting quantum interferometer to form lithium or lithium in an electrode material structure. It has become possible to obtain accurate information on oxygen, and as a result, has found a method capable of elucidating a structural factor of characteristic deterioration of a battery electrode material.

That is, the present invention is as follows. Item 1. A precise structure evaluation method for a positive electrode material for a lithium battery using a combination of a neutron diffraction method using a high-resolution neutron diffractometer and a magnetic measurement method using a superconducting quantum interferometer. Item 2. The high-resolution neutron diffractometer, a neutron conduit to guide the neutrons generated in the neutron source between the neutron source and the measurement sample to the sample, and a neutron detector three-dimensionally spread around the measurement sample Item 3. The method according to Item 1, comprising: Item 3. The detector is a detector having a scattering angle of 150 to 175 degrees,
Item 3. The method according to Item 2, wherein the detector is apart from the sample by 2 to 2.5 m. Item 4. The neutron diffraction method was performed for 0.1 to 10 at 50 millisecond intervals.
Item 4. The method according to any one of Items 1 to 3, wherein the method is performed by generating white pulse neutrons having a wavelength distribution of Å. Item 5. Item 5. The method according to any one of Items 1 to 4, wherein the magnetic measurement is performed in a magnetic field range of 0 to 1 T and a temperature range of 5 to 350 K.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, measurement and evaluation of electrode materials are performed using a high-resolution neutron diffractometer and a superconducting quantum interferometer. As a high-resolution neutron diffractometer,
For example, an apparatus known as "Sirius (registered trademark)" can be used.

Since neutrons are electrically neutral, they are scattered by nuclei without being affected by the strong Coulomb potential in matter. For this reason, the neutron scattering length (nuclear scattering amplitude) varies greatly depending on the nuclide, but is independent of the atomic number, and gives detailed information even for a light element.

Therefore, by irradiating neutrons to the lithium-containing cathode material to be the cathode material of the lithium secondary battery, it is possible to obtain detailed information of lithium, which greatly affects the structure and physical properties, and to determine the structure more accurately. .

In addition, since the neutron scattering length of oxygen indicates a positive scattering length, it is easy to distinguish oxygen and cations from a combination of elements having a negative scattering length such as lithium and manganese. By utilizing this feature, it is possible to perform precise crystal structure evaluation using a high-resolution neutron diffractometer.

The magnetic properties are closely related to the coordination state and valence state of the transition metal. Particularly in oxides, the bond between the transition metal and oxygen has been qualitatively studied as a super-exchange interaction.

In particular, magnetic measurement data under a low temperature of 100 K or less and a low magnetic field of 0.1 T or less reflect slight structural changes and changes in valence states caused by transition metals.
Recently known. Using this feature, the temperature dependence of the magnetic susceptibility and the magnetic field dependence of the magnetization are measured, and the structure evaluation can be performed by comparing and examining the shapes and relative values of the obtained curves.

The linear part obtained from the temperature (T) dependence of the reciprocal (χ _m ⁻¹ ) of the molar susceptibility is expressed by the Curie-Weiss rule (χ _m ⁻¹ = (T−θ) / C _m ). Structural evaluation can also be performed by comparative study using the effective magnetic moment and Weiss temperature obtained by analysis based on the base.

As the cathode material to be measured, for example,
Examples include, but are not limited to, lithium manganese spinel oxide.

Examples of the lithium source material used in the present invention include oxides, water-soluble salts, and hydroxides.
Transition metal source materials include water-soluble salts (nitrates, sulfates,
Chloride), hydroxide, oxide hydroxide (MnOOH and the like), metal manganese and the like, but are not limited thereto. The lithium source material and the transition metal source material may be used alone or in combination of two or more.

The conditions for synthesizing the electrode material used in the present invention are such that the raw material mixture ratio (element composition ratio) is 0.4 to 0.8, preferably 0.5 to 0.6, when expressed as lithium source / transition metal source. Two or more transition metal elements may be used in combination as the transition metal source. The firing temperature is usually about 773 to 1273K, more preferably about 973 to 1173K, and it is preferable to repeat firing for 24 hours in air or in an oxygen atmosphere several times.

The high-resolution neutron diffraction measurement method is an apparatus (for example, hereinafter referred to as "Sirius") installed at a neutron source capable of generating white pulse neutrons having a wavelength distribution of about 0.1 to 10 ° at intervals of 50 milliseconds. ) Can be performed.

Since neutrons have different velocities depending on the wavelength,
If the detector is located far enough, the time at which the neutrons arrive at the detector will depend on the wavelength. Therefore, the wavelength can be known by checking the time of arrival at the detector.

In the evaluation of the structure of the positive electrode material for a lithium secondary battery using “Sirius”, the detector was used to measure the sample from 2 to 2.5
m and a detector having a scattering angle of about 150 to 175 degrees is preferably used. It is preferable to use 0.8 to 5 ° as a wavelength range for data analysis. The measurement temperature may be room temperature.

The neutrons generated from the neutron source are incident on the sample (cathode material), and the crystal structure of the battery cathode material can be examined in detail by examining the wavelength at which Bragg diffraction occurs in the sample.

However, in the conventional apparatus, sufficient diffraction intensity suitable for quick evaluation of battery electrode materials has not been obtained. Measurement time of 5 hours or more is required to collect data of sufficient strength for structural evaluation, and it is not necessarily suitable for structural evaluation of many samples with changed preparation conditions and charge / discharge conditions. Did not.

"Sirius" introduces a neutron conduit between a neutron source and a sample, guides neutrons to the sample without loss, and further lays a neutron detector three-dimensionally so as to surround the sample. Diffraction intensity one order higher than that of the conventional device can be obtained. That is, data suitable for structural evaluation can be collected in a measurement time of about 30 minutes.

"Sirius" has very high performance not only in diffraction intensity but also in precision in examining the crystal structure. For example, the resolution is “Sirius” for two devices of the same type installed at the Japan Atomic Energy Research Institute, for Δd / d = 0.4% and 0.2%.
Is 0.09%. The resolution indicates the degree of separation of Bragg diffraction lines, and a smaller value indicates that Bragg diffraction lines can be separated more.

[0036] In addition, the wave number region Q is for the two former is Q = 7Å ^-1, "Sirius" is a 30Å ^-1. Since the number of Bragg diffraction lines is proportional to the cube of the wavenumber range, the number of reflections is large.
s "can provide an extremely large amount of information necessary for precisely examining the crystal structure.

The sample (battery electrode material) is preferably filled in a vanadium container, set in "Sirius", evacuated to a vacuum, and then neutrons are incident. Neutrons detected by the detector can be immediately preprocessed and structurally analyzed by a computer.

The magnetic measurement was performed using SQUID. SQUID
Is an element in which one Josephson junction is arranged on a superconductor formed in a ring shape. When the magnetic flux in the ring penetrates, the element characteristics change at the cycle of the magnetic flux quantum due to the quantum exchange effect, so the SQUID is used as a sensitive magnetometer.

For example, the measurement conditions are as follows.
300mg, magnetic field range 0 ~ 1T, measurement temperature range 5
About 350K can be exemplified. As the measurement mode, it is necessary to measure the temperature dependence of magnetization and the magnetic field dependence of magnetization.

In order to obtain accurate data, the measurement sample must be
It is preferable to increase the number of data points under the measurement conditions of about 30 to 150 mg and the range of the magnetic field is about 0 to 0.3 T, and measure.
For measurement of temperature dependence of magnetization, measurement temperature range is 5 to 150K
The degree is preferred.

In the present invention, the electrode characteristics are evaluated by using a lithium ion secondary battery such as a coin type or an 18650 type cylindrical type, but the battery used for the evaluation is not limited to these.

In a coin-type battery, it is preferable to mix a conductive agent, a binder, and the like with an evaluation sample and knead the mixture to form a mixture. In the case of the 18650 type cylindrical type, it is preferable to mix a conductive agent, a binder, and the like with an evaluation sample, knead the paste, apply the paste uniformly to, for example, an aluminum foil, and then dry the paste to obtain a positive electrode.

In any case, the conductive agent is exemplified by acetylene black, Ketjen black and the like, and the binder is exemplified by tetrafluoroethylene and polyvinylidene fluoride, but is not particularly limited.

The amount of the conductive agent in the mixture is not particularly limited, but is usually 1 to 30% by weight, preferably 5 to 15% by weight of the mixture.
The range of weight% is good.

Although the amount of the binder is not particularly limited, it is usually in the range of 0 to 30% by weight, preferably 3 to 10% by weight.

According to the present invention, data such as the occupancy of light elements such as lithium and oxygen obtained by neutron diffraction, and data such as the coordination state and average valence of transition metals such as Mn obtained by magnetic measurement. By combining the above, even a slight structural change of the obtained cathode material can be detected, and it can be evaluated whether the material is suitable for the cathode material of the battery.

More specifically, as shown in the following Examples and Test Examples, for example, a positive electrode material as a raw material and a positive electrode material taken out of a battery after storage at room temperature and at a high temperature are considered as targets.
Perform neutron diffraction and magnetic measurements. By analyzing changes in lattice constants and the like obtained by neutron diffraction and changes in magnetic susceptibility and the like obtained by magnetic measurement, the stability of the cathode material,
That is, suitability as a positive electrode material can be evaluated.

[0048]

EXAMPLES Example 1 Li _{1 + x} Mn _2-x O ₄ (x = 0.3,0.5,0.8,1.0) was carbonated such that the molar ratio of lithium to manganese was in the range of 0.51 to 0.57. It was produced by completely mixing lithium (Li ₂ CO ₃ ) and manganese oxide (Mn ₃ O ₄ ). After baking in air at 1023K for 24 hours, it was gradually cooled in a furnace.

All of the obtained samples were confirmed by neutron diffraction measurement to be a single phase having a spinel structure and to have no trace of impurities. In the neutron diffraction measurement, the scattering angle is 150 to 1
Neutron detection was performed using a 75-degree detector in the wavelength range of 0.8 to 5 mm.

The powder sample used for the measurement was about 5 g, the measurement was performed at room temperature, and the measurement time was about 40 minutes each. From the results of the structural analysis, it was directly determined that the crystal phase of the measurement sample substantially matched the charged composition.

In the evaluation of the magnetic characteristics, a powder sample (50 mg) was used, and the measurement was performed using a SQUID as a magnetic characteristic evaluation device. To measure the temperature dependence of magnetic susceptibility, increase the temperature of the sample continuously from 5K to 300K under zero magnetic field, apply a 0.1T magnetic field, and continuously lower the temperature from 300K to 5K. Was performed.

The measurement of the magnetic field dependence of the magnetization is performed by
The test was performed by continuously changing the magnetic field in the order of 0T → 0.1T → −0.1T → 0.1T at a temperature of 5K. From the data of temperature dependence of magnetic susceptibility measured by magnetism, it was observed that the magnetic susceptibility increased and the cusp around 20K became clearer with the increase of lithium composition.

Further, from the data on the magnetic field dependence of the magnetization, greater hysteresis was shown as the lithium composition increased. This suggested an increase in the ferromagnetic component of Mn ⁴⁺ -O-Mn ⁴⁺ , and a slight increase in the average valence of Mn in the structure was detected.

Example 2 As a measurement sample, 5 g of lithium manganese spinel represented by a composition formula of Li _1.03 Mn _1.97 O ₄ was mixed with Ethyl so that LiPF ₆ became 1M.
6 g at 80 ° C in 12 g of an organic electrolyte dissolved in a mixed solvent (1: 1) of encarbonate (EC) and 1,2-diethoxycarbonate (DEC).
It was prepared by storing for days.

In the neutron diffraction measurement, a neutron was detected using a detector having a scattering angle of about 150 to 175 degrees, and data analysis was performed in a wavelength range of 0.8 to 5 °. The powder sample used for the measurement was about 5 g, the measurement was performed at room temperature, and the measurement time was about 40 minutes each.

Using the diffraction data obtained at room temperature by "Sirius", the crystal structure was determined by the Rietveld method. FIG. 1 shows the measured neutron diffraction pattern.

As a result of neutron structure analysis, the lattice constant before storage at high temperature was 8.24282 (3) Å, and the lattice constant after storage at high temperature was 8.23938.
(5) Å, a slight decrease in lattice constant was observed.

This decrease is due to the fact that the lattice constant before storage, which was obtained by X-ray diffraction, was 8.23849 (7) Å, and the lattice constant after storage at high temperature, 8.23
Since the change was smaller than the change to 052 (12) Å, it became clear that it was possible to detect the change of the lattice constant with high accuracy without being affected by the sample surface.

According to the results of the structural analysis, the information that the lithium in the structure slightly increased (Mn decreased) and the occupancy of oxygen atoms did not change in the sample stored at 80 ° C. Could be obtained directly from the material.

In the evaluation of the magnetic characteristics, a powder sample (50 mg) was measured using a SQUID as a magnetic characteristic evaluation device.
Measurement of temperature dependence of magnetic susceptibility from 5K to 300K under zero magnetic field
After the temperature was continuously increased to 0.1K, a magnetic field of 0.1T was applied, and the temperature was continuously decreased from 300K to 5K. The measurement of the magnetic field dependence of magnetization was performed by continuously changing the magnetic field in the order of 0T → 0.1T → −0.1T → 0.1T at a temperature of 5K.

From the data on the temperature dependence of the magnetic susceptibility obtained by the magnetic measurement, the sample in which Li _1.03 Mn _1.97 O ₄ was stored at 80 ° C. showed a lower value than the raw material Li _1.03 Mn _1.97 O ₄ shown in Example 1. It was detected that the susceptibility increased and the cusp around 20K became clear. FIG. 2 shows a temperature dependence curve of the magnetic susceptibility.

[0062] In addition, the high-temperature storage before 4.37μ _B, high-temperature storage after 4.3
Effective magnetic moment of 1 [mu] _B is obtained from the data of 160～300K. The reduction of the effective magnetic moment is due to Mn in the structure
^This suggested an increase in the ⁴⁺ component.

From the data on the magnetic field dependence of magnetization,_1.03Mn
_1.97O_FourWas stored at 80 ° C. _1.05Mn_1.95O_Four Than
It showed large hysteresis. This is Mn⁴⁺-O-Mn⁴⁺of
The average value of Mn in the structure suggests an increase in ferromagnetic components
A slight increase in the number was detected. Figure 3 shows the magnetic field dependence of magnetization.
1 shows a sex curve.

From these magnetic measurement data, Li _1.03 Mn
_In a sample in which _1.97 O ₄ was stored at 80 ° C., Li _1.05 Mn _1.95 O ₄
And the susceptibility of Li _1.08 Mn _1.92 O ₄ and that no significant change was observed in the shape of the susceptibility curve. From this result, it became clear that the coordination state of Mn in the crystal structure did not change significantly, and that the average valence of Mn changed between them.

For the first time, a subtle change in the coordination state of manganese was detected by examining the low-temperature magnetism.

From the results obtained in this example, the occupancy of lithium and oxygen is directly determined by neutron diffraction, and the magnetization curves (temperature dependence of magnetic susceptibility and magnetic field dependence of magnetization) Gender) was found.

Since the result of neutron diffraction and the result of magnetization measurement show a good correspondence, it is clear that high-precision information such as lithium and oxygen can be obtained by combining neutron diffraction and magnetic measurement. Became.

Further, it has been clarified that the crystal structure of a sample can be quickly evaluated by mainly using simple magnetic measurement and by using neutron diffraction for an arbitrary sample.

Example 3 In order to confirm the characteristics of the positive electrode in a practical battery, Li _1.03
Mn _1.97 O ₄ positive electrode material lithium manganese spinel represented by the composition formula, mesocarbon microbeads (MCMB) a negative electrode material, a mixed solvent of EC and DEC as LiPF ₆ is 1M in the electrolytic solution (1: 1 The 18650 type cylindrical battery was fabricated using the organic electrolyte dissolved in the above (1).

In the positive electrode, an electrode obtained by mixing 4% of acetylene black as a conductive additive, 10% of a binder (PVDF), and 86% of a positive electrode active material to reduce the influence on neutron diffraction measurement was used. Produced.

The batteries stored for one month at room temperature and the batteries that were charged or discharged for 6 days at 80 ° C. were disassembled after complete discharge after the test, and the positive electrode was peeled off from the current collector. The material, lithium manganese spinel, was recovered. The positive electrode material was subjected to measurement after washing with DEC and vacuum drying at room temperature. All the above dismantling operations were performed in the dry room.

In the neutron diffraction measurement, a neutron was detected using a detector having a scattering angle of 150 to 175 degrees, and data analysis was performed in a wavelength range of 0.8 to 5 °. 5g powder sample used for measurement
The measurement was performed at room temperature, and the measurement time was about 40 minutes each.

The crystal structure was determined using the diffraction data obtained by the measurement at room temperature with "Sirius". As a result of neutron structure analysis, it was found that the lattice constant after high-temperature storage was greatly reduced.

The lattice constant before storage at high temperature was 8.24282 (3) Å, and the lattice constant after storage at room temperature for one month was 8.23950 (2) Å. No remarkable change in lattice constant was observed after one month storage at room temperature. Was.

However, the lattice constant after storage at 80 ° C. for 6 days in the charged state and the discharged state is 8.15519 (3), respectively.
{, 8.16310 (8)}, a smaller lattice constant was observed in the charged sample, but no oxygen deficiency occurred in any of the samples.

The magnetic properties were evaluated by measuring 50 mg of a powder sample using SQUID as a magnetic property evaluation device. Measurement of the temperature dependence of magnetic susceptibility is performed by continuously raising the temperature of the sample from 5K to 300K under zero magnetic field, applying a magnetic field of 0.1T, and continuously lowering the temperature from 300K to 5K. went.

The measurement of the dependence of the magnetization on the magnetic field was performed by measuring the sample.
This was performed by continuously changing the magnetic field in the order of 0T → 0.1T → −0.1T → 0.1T at a temperature of 5K.

From the data on the temperature dependence of the magnetic susceptibility obtained by the magnetic measurement, an increase in magnetic susceptibility of 8 to 10 times was observed as compared with the raw material Li _1.03 Mn _1.97 O ₄ shown in Example 1. This value is
Compared with the magnetic susceptibility of Li _1.1 Mn _1.9 O ₄ shown in Example 1, the magnetic susceptibility shows a large value, indicating that a large composition change has occurred.

On the other hand, since no significant change is observed in the shape of the magnetic susceptibility curve, it is apparent that the average valence is not significantly changed but is significantly increased in the crystal structure. Became.

For the first time, a subtle change in coordination state of manganese was detected by examining low-temperature magnetism.

For the first time, the results obtained in this example
The occupancy of lithium and oxygen is directly determined by neutron diffraction in the cathode material whose battery characteristics have been evaluated in the electrode state of a practical battery, and the magnetization curves (temperature dependence of susceptibility and magnetization Magnetic field dependence) was found.

Since the results of neutron diffraction and the results of magnetization measurement show good correspondence, it has been clarified that accurate information on lithium, oxygen, etc. can be obtained by combining neutron diffraction and magnetic measurement. .

Further, after a measurement sample is measured by using a magnetic measurement method, a sample arbitrarily extracted from the measured sample is measured by using a neutron diffraction method, whereby a rapid and precise crystal structure of the sample is obtained. It became clear that evaluation was possible.

Further, there is no example in the development of battery materials so far, in which the precision structure evaluation method of the present invention and the practical battery prototype device are combined and feedback is applied to each other to develop battery electrode materials. This is an extremely effective method for developing high-performance electrode materials.

Test Example 1 The measurement samples obtained in Examples 1 and 2 were subjected to EC so that the positive electrode material, the negative electrode were lithium metal, and the organic electrolyte was LiPF ₆ at 1M.
A coin-type battery was prepared using an electrolytic solution dissolved in a mixed solvent (1: 1) of and DEC, and charge / discharge cycle characteristics were measured at a current density of 0.2 mA / cm ² .

As the positive electrode mixture, a mixture of a sample, acetylene black and Teflon (registered trademark) in a ratio of 85: 10: 5 was used.

FIG. 4 shows a charge / discharge pattern in the first cycle. Four.
It showed an initial discharge capacity of 101 mAh / g at a cutoff potential of 4 to 3.0 V. This is the initial discharge capacity of raw material Li _1.03 Mn _1.97 O ₄ 129m
A decrease in capacity was observed compared to A / g, and the charge / discharge efficiency was 0.9.
It dropped from 8 to 0.94.

The deterioration of the battery characteristics corresponds to the decrease in Mn and the increase in magnetic susceptibility in the structure observed in Example 2, and the coordination state of Mn and the value of magnetic susceptibility before and after high-temperature storage were changed. It was clarified that by synthesizing a sample with a small change, a lithium manganese spinel electrode material with suppressed deterioration during high-temperature storage could be obtained.

Test Example 2 Using the cylindrical battery obtained in Example 3, the charge / discharge cycle characteristics were measured at a charge of 1 / 6C. 4.4-2.5V for cylindrical batteries
And a discharge capacity of 1000 mAh. When stored in a discharged state at 80 ° C. for 6 days, almost no discharge capacity was exhibited.

This deterioration in battery characteristics corresponds to the decrease in Mn and the increase in magnetic susceptibility in the structure observed in Example 3, and the coordination state of Mn and the value of magnetic susceptibility before and after high-temperature storage changed. It was clarified that by synthesizing a sample having a small value, a lithium manganese spinel electrode material with suppressed deterioration during high-temperature storage could be obtained.

[0091]

By using the precise structure evaluation method combining the neutron diffraction method and the magnetic measurement method according to the present invention, it is possible to obtain information on the structure of the cathode material which has not been obtained conventionally.

Furthermore, by using this precise structure evaluation method to evaluate various batteries produced by a practical battery prototype, it is possible to efficiently develop materials.

[Brief description of the drawings]

FIG. 1 is a diagram showing a neutron diffraction pattern of a reaction product measured in Example 2 of the present invention.

FIG. 2 is a diagram showing the temperature dependence of the magnetic susceptibility of a reaction product measured in Example 2 of the present invention.

FIG. 3 is a diagram showing the magnetic field dependence of magnetization of a reaction product measured in Example 2 of the present invention.

FIG. 4 is a diagram showing charge / discharge cycle characteristics of a lithium ion secondary battery using the reaction products of Examples 1 and 2 of the present invention as a positive electrode material.

Continuing from the front page (72) Inventor Hironori Kobayashi 1-8-31 Midorioka, Ikeda-shi, Osaka Inside the National Institute of Advanced Industrial Science and Technology Kansai Center (72) Inventor Kenichi Kawamoto 1--8-3 Midorioka, Ikeda-shi, Osaka 31 Kansai Center, National Institute of Advanced Industrial Science and Technology (72) Inventor Sakabe Hinatsuri 1-38, Midorioka, Ikeda-shi, Osaka Prefecture Kansai Center, National Institute of Advanced Industrial Science and Technology (72) Inventor Mitsuharu Tabuchi 1-38-31 Midorigaoka, Ikeda-shi, Osaka Independent administrative institution Kansai Center, National Institute of Advanced Industrial Science and Technology (72) Inventor Tetsuo Sakai 1-38-31 Midorigaoka, Ikeda-shi, Osaka Independent administrative agency Sangyo (72) Inventor Susumu Ikeda 1-1-1 Oho, Tsukuba City, Ibaraki Prefecture High-energy Accelerator Research Organization Material Structure Science Laboratory (72) Inventor Takashi Kamiyama 1-1-1, Oho Tsukuba-city, Ibaraki Prefecture High Energyー Accelerator Research Organization Within the Science Research Institute (72) Inventor Ryoji Kanno 1-1-1 Oho, Tsukuba City, Ibaraki Prefecture High Energy Accelerator Research Organization In-house Research Institute for Materials Structure (72) Inventor Kenichi Oikawa 1-1-1, Oho 1 Tsukuba City, Ibaraki Research into High Energy Accelerators 2G001 AA04 BA18 CA04 GA01 GA13 KA08 LA02 NA17 2G053 AA08 AB06 AB14 BA02 BA04 BA15 BB17 BC10 CA10 5H050 AA19 BA15 BA16 CA09 CB12 DA02 GA28 HA04 HA14 HA16 HA20

Claims (5)

[Claims] 1. A method for evaluating the precise structure of a positive electrode material for a lithium battery using a combination of a neutron diffraction method using a high-resolution neutron diffractometer and a magnetic measurement method using a superconducting quantum interferometer. 2. The high-resolution neutron diffractometer is laid three-dimensionally between a neutron source and a measurement sample so as to surround a measurement sample with a neutron conduit for guiding neutrons generated by the neutron source to the sample. The method of claim 1, comprising a neutron detector. 3. The method according to claim 2, wherein the detector is a detector having a scattering angle of 150 to 175 degrees, and the detector is 2 to 2.5 m away from the sample. 4. The method of claim 1, wherein the neutron diffraction method is performed at intervals of 50 milliseconds.
The method according to any one of claims 1 to 3, wherein the method is performed by generating white pulse neutrons having a wavelength distribution of 0.1 to 10 °. 5. The method according to claim 1, wherein the magnetic measurement method is performed in a magnetic field range of 0 to 1T.
The method according to any one of claims 1 to 4, wherein the method is performed in a temperature range of ~ 350K.