JP2001124762A - Method for quantitatively analyzing oxygen in oxide containing lithium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new dry method for quantitatively analyzing a quantity of oxygen in an oxide containing lithium directly and highly accurately. SOLUTION: A dissociation reaction of oxygen is promoted with the use of a metal tin and/or a tin alloy as a flux for a capsule container in the method for quantitatively analyzing a content of oxygen in the oxide including lithium. The capsule container formed of the tin or tin alloy and containing a sample is brought into a deoxidized graphite crucible kept to a predetermined temperature in a range of 1200-1700 deg.C. Quantities of formed carbon monoxide and carbon dioxide of a minute amount are directly measured by an infrared sensor, or measured by the infrared sensor after converted all to carbon monoxide. The content of oxygen is obtained by a calibration curve obtained by analyzing a metal oxide (e.g. lithium carbonate, yttrium oxide or the like) of a known content of oxygen.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates to a method for quantitatively analyzing oxygen in a lithium-containing oxide.

[0002] In recent years, lithium ion secondary batteries using a composite oxide of lithium and a transition metal, such as lithium cobalt oxide and lithium-containing manganese oxide, as a positive electrode active material have been developed for various electronic devices. Used as a power source for equipment. To reduce the size and weight of electronic devices,
It is extremely useful as a battery for these electronic devices.
Further improvement in safety, higher capacity, and longer life are required for batteries. The development of cathodes made of lithium-containing oxides is a key issue in the future, and the analysis of the amount of oxygen will be increasingly faster, easier and more accurate in R & D, manufacturing, and quality control of complex oxides with precise structural design. There is a need for a method. The present invention relates to a high-precision quantitative oxygen analysis technique in a lithium-containing oxide.

[0003] In order to measure the content of oxygen in a metal oxide containing no lithium, an inert gas melting method is usually used. A certain amount of the sample to be analyzed is weighed, automatically dropped into a graphite crucible from a sample holder that is shut off from the atmosphere, and heated to a high temperature of 2000 ° C or higher while flowing an inert gas such as an argon gas or a nitrogen gas as a carrier gas. In this method, oxygen that is decomposed or dissociated reacts with carbon by heating the carbon monoxide, carbon monoxide or carbon dioxide generated is quantified from the absorbance of infrared rays, and the oxygen content is determined from the measurement results. That is, the oxygen content in a metal oxide such as alumina, zirconia, silicon oxide, iron oxide, and manganese dioxide is quantitatively analyzed. In addition, there is a vacuum melting method in which oxygen is heated and separated in a vacuum, and carbon monoxide or carbon dioxide generated in the same manner is quantified from infrared absorbance. In these analysis methods, since the constituent metal elements such as aluminum, zirconium, silicon, iron, and manganese have a high boiling point, they are heated to a high-temperature region of 2000 ° C. or more necessary for dissociation of oxygen or promotion of reaction with carbon. Oxygen content can be relatively easily determined quantitatively by analyzing the product carbon monoxide and carbon dioxide, as the oxygen contained can react completely with the carbon. However, when the lithium-containing oxide is analyzed by the above-described method, it is dissociated into oxygen and metallic lithium, and while oxygen is converted into carbon monoxide and carbon dioxide, metallic lithium has a boiling point of 1336 ° C. and thus has a boiling point of 2000 ° C. or more. At a temperature of, it partially evaporates and reacts with the produced carbon dioxide, and at high temperatures it is chemically active and dissociated oxygen cannot be completely converted as carbon monoxide. When the temperature is 1400 ° C. or lower, the dissociation of oxygen from the oxide becomes insufficient. Presumably because of this contradictory phenomenon, quantitative analysis of oxygen in lithium-containing oxides
There are no methods for quantitative analysis of oxygen in lithium-containing oxides because the results of content measurement are extremely low, and the reproducibility of analysis values is poor, and the values are varied. In addition, a lithium-containing oxide is used as an aqueous solution, and the amount of oxygen that is electronically neutralized is determined from the amount of the metal element, its valence, and the amount of lithium by titration analysis. However, this method is an indirect method for analyzing the amount of oxygen using a complicated reagent, and is applicable only to a limited system. For example, in the case of a lithium-containing metal oxide to which several kinds of foreign metals are added, the valence of the added metal element is unknown, and a titration analysis method based on the ionic valence of a known metal element cannot be applied.
Therefore, at present, the establishment of a technology capable of directly and accurately and quickly analyzing the oxygen content in a novel lithium-containing oxide is an urgent problem to be solved.

[0004] The present invention relates to a conventional method for analyzing oxygen in metal oxides, such as an inert gas melting method or a vacuum melting method, or an indirect oxygen-containing method for titrating and analyzing constituent elements in an aqueous solution. An object of the present invention is to establish a direct and high-precision quantitative analysis method of oxygen in lithium-containing oxides, which is an alternative to the quantitative analysis method.

As a result of various studies on the above problems, the present inventors have found that tin and its alloys (solder, solder, etc.) having a low melting point and an ability to form an alloy with metallic lithium. Oxygen in the lithium-containing oxide is dissociated with good reproducibility by the addition of babbitt metal, britannia metal, wood metal, etc., and is converted to carbon monoxide with good selectivity, and there is metallic lithium generated by reduction. However, the present inventors have found a method capable of quantitatively analyzing with high precision, and have completed the present invention.

[Embodiment of the Invention] The present invention will be specifically described below. That is, the present invention provides:
First, a graphite crucible is set on an electrode in an argon stream or under vacuum, and a current is applied to the electrode by using a conventional apparatus such as an inert gas melting method or a vacuum melting method for oxygen analysis of metal oxides. At 3000 ° C., oxygen contained in the graphite crucible is removed. Although a crucible can be used even with a single bottom, it is preferable to form a double crucible by stacking an outer crucible and an inner crucible in order to reduce the variation in heating temperature and to make the oxygen reaction uniform. Next, the temperature is lowered to a temperature range of 1200 to 1700 ° C., which is an appropriate heating temperature of the sample, and maintained at a desired temperature. Below 1200 ° C., it becomes difficult to completely convert the contained oxygen to carbon monoxide or carbon dioxide even if the flux metal is tin or an alloy of tin. If the temperature exceeds 1700 ° C., scattering of lithium and a side reaction between lithium and oxygen are considered to be factors.
The oxygen content is low as compared to the appropriate temperature range. Preferably, it is a temperature range of 1300 to 1600 ° C. Dozens of mg of the lithium-containing oxide of the measurement sample, 5
It is accurately weighed to the order of magnitude and placed in a metal capsule (made of tin or tin alloy) acting as a flux, if necessary, together with a metal catalyst (nickel powder, tin powder, tin alloy powder, etc.). The sample is crushed using a pressure molding machine, pliers, nippers or the like so that the sample does not scatter from the capsule. This is put into the deoxygenated graphite crucible from the automatic supply device. Nickel, lead, iron, aluminum, and yttrium alone as fluxes cannot produce reproducible carbon monoxide and carbon dioxide for the purpose of the present invention in a temperature range where there is almost no effect of lithium metal evaporation. The specific action that is only in tin and alloys of tin is used. Measure the amount of carbon monoxide and a trace amount of carbon dioxide generated by the reaction of graphite and oxygen with an infrared sensor, and analyze the metal oxides with known oxygen content (eg lithium carbonate, yttrium oxide, etc.) to obtain The oxygen content is determined using the calibration curve obtained. The sample is heated under vacuum to make it completely dry, and the weighing is performed in a glove box or a dry room controlled to 0.2% RH or less. By removing the oxygen and water that easily adheres to the sample capsule, quantitative analysis of the oxygen amount in the lithium-containing oxide becomes possible.

[0007] The lithium-containing oxide of the present invention is not particularly limited.
ixCoO ₂ (where x represents a number satisfying 1.0 ≦ x ≦ 1.03), LixCoyMzO ₂ (where M is Ni, M
n, Cr, Fe, Al, In, Sn, Zr, Ga or the like, and x, y, and z are each 1.00 or more.
≦ x ≦ 1.10, y + z = 1. ), Li _x M
n _y M _z O ₄ (where M is Co, Cr, Ni, Al, Fe
X, y, and z each represent a number of 1.00 ≦ x ≦ 1.12 and y + z = 2. ),
LixNiyMzO ₂ (where M is Co, Mn, Cr, F
one or more selected from e, Al, Ga, Zr, etc .;
y and z are respectively 0.98 ≦ x ≦ 1.10 and y + z =
Represents the number of 1. ), Li _x V ₂ O ₅ (where x is 1.0
Represents the number 0 ≦ x ≦ 3.00. ), Li _X V ₃ O
₁₃ (where x represents a number satisfying 1.00 ≦ x ≦ 1.2), Li _x Ti _y O _z (where x, y, and z represent integers, for example, x = 4, y = 5, represents the number of z = 12.)
At least one selected from

The present invention will be described in detail below with reference to examples and comparative examples, but the scope of the present invention is not limited to these examples.

The coefficient of variation as a measure of analysis accuracy is 0.7% or less. Here, the standard deviation is obtained by squaring the deviation (difference between the measured value and the average value) and arithmetically averaging the squared values. That is, n measurement values are calculated as X ₁ , X
_{2, X} 3, ......, average value and Xn (Xa) is Xa
= (X ₁ + X ₂ + X ₃ +... + Xn) / n. Relationship between the sum (S _T ) of the square of the difference (Xi−Xa) between each measured value (Xi) and the average value (Xa), and the variance (V) obtained by dividing the value by the degree of freedom (n−1) _{is, V} = S T / from _{(n-1), V =} [(X 1 -X a) 2 + (X 2 -Xa) 2 + (X 3 -
Xa) ² + ‥ + (Xn−Xa) ² ] / (n−1). The square root of this variance (V) is the standard deviation (s). Therefore, s = √V The variation coefficient is defined by the following equation.

[Example 1] Using a model 416 _DR manufactured by LECO (USA), nickel, manganese and lithium elements were measured by atomic emission spectroscopy (ICP), and charge was calculated assuming that nickel ions were divalent. From LiN
i _0.1 Mn _1.9 O ₄ (oxygen amount 21.76 mmol /
The sample of g) is dried under vacuum at 150 ° C. for 6 hours, cooled in a desiccator, and then precisely weighed in a glove box with a stream of dry argon gas in an amount of 0.01000 to 0.05000 g. This is placed in a tin capsule container using tin as a flux metal and sealed with pliers. First, a graphite double crucible is set on an electrode in an argon stream or under vacuum, and an electric current is applied to remove oxygen contained in the graphite crucible at 3000 ° C. The temperature is kept at 1500 ° C., which is the appropriate heating temperature of the sample. The tin capsule containing the above sample is put into the deoxygenated graphite crucible from the automatic supply device. The amount of generated carbon monoxide and a small amount of carbon dioxide are measured by an infrared sensor, and the oxygen content is determined by a calibration curve obtained by analyzing lithium carbonate having a known oxygen content. The obtained result was 21.74 mm / g. The measurement was repeated 10 times, and the coefficient of variation was found to be 0.5%.

Embodiment 2 EMGA-650 Horiba, Ltd.
The analyzer is additionally equipped with a gas column equipped with a catalytic column unit that converts carbon dioxide to carbon monoxide. A manganese spinel of known composition, Li _1.07 Mn _2.00 O _4.03 (oxygen amount: 21.90 mmol / g) was dried at 120 ° C. under vacuum for 6 hours, cooled in a dry desiccator, and dried in a dry argon gas stream. Weigh accurately 0.01036 grams in glove box. This is placed in a tin capsule container using tin as a flux metal and sealed with pliers. First, a graphite double crucible is set on an electrode in an argon stream or under vacuum, and an electric current is applied to remove oxygen contained in the graphite crucible at 3000 ° C. The temperature is kept at 1450 ° C., which is the proper heating temperature of the sample. The tin capsule containing the above sample is put into the deoxygenated graphite crucible from the automatic supply device. The amount of carbon monoxide generated is measured by an infrared sensor, and the oxygen content is determined by a calibration curve obtained by analyzing lithium carbonate having a known oxygen content. The result obtained was 21.86 mmol / g. 10 measurements
The coefficient of variation was determined to be 0.3%.

[Comparative Example 1] Using the oxygen analyzer used in Example 1, a LiMn having a known concentration determined by charge calculation was used.
A sample of ₂ O ₄ is dried at 150 ° C. for 6 hours, cooled in a desiccator, and then precisely weighed in a dry argon gas stream glove box in a range of 0.01000 g to 0.03900 g. This is put in a nickel capsule used as a flux metal and sealed with pliers. The graphite double crucible is set on the electrode of the heating furnace, and a current is applied to remove the oxygen contained in the graphite crucible at 3000 ° C. Thereafter, the graphite crucible is heated to 1700 ° C. and maintained at a constant temperature. Thereafter, the nickel capsule containing the weighed sample is supplied to the graphite crucible from an automatic supply device completely shut off from the atmosphere. Hereinafter, the oxygen content was determined in the same manner as in Example 1. In this comparative example,
As a result of repeating the measurement 10 times, the average value of the analysis values was 2
9.00%, standard deviation 0.676, coefficient of variation 2.33%
Met. The analysis result of the oxygen content of the sample used here was a considerably low value as compared with 35.39% of the value obtained from the charge calculation. Further, the coefficient of variation, which is an index of the variation in the analysis, is large, and it was impossible to analyze the oxygen content in the spinel with high accuracy and high reproducibility.

[Comparative Example 2] Using the oxygen analyzer used in Example 1, the LiMn with a known concentration determined from the charge calculation was used.
A sample of ₂ O ₄ is dried at 150 ° C. for 6 hours, cooled in a desiccator, and then precisely weighed in a dry argon gas stream glove box in a range of 0.01000 g to 0.03900 g. This is put in a tin capsule using the flux metal as tin and sealed with pliers. A graphite double crucible was set on the electrode of the heating furnace, and an electric current was applied.
At 0 ° C., oxygen contained in the graphite crucible is removed.
Thereafter, the graphite crucible is heated to 1800 ° C. and maintained at a constant temperature. Thereafter, the capsule containing the weighed sample is supplied to the graphite crucible from an automatic supply device completely shut off from the atmosphere. Hereinafter, the oxygen content was determined in the same manner as in Example 1. The results of five measurements under these analysis conditions were 34.17%, 34.03%, and 33.35, respectively.
%, 34.61% and 33.84%. That is, the average value was 33.98%, the standard deviation was 0.429, and the variation coefficient was 1.26%. It was confirmed that when the analysis temperature was out of the appropriate temperature range as in the comparative example, the analysis value of oxygen became low.

[Effects of the Invention] According to the present invention, the oxygen content in the lithium-containing oxide is adjusted to a relative coefficient of variation of 0.3% to 0.1%.
The analysis time can be reduced to 5% and the required analysis time is about 2 to 3 minutes. A very quick and accurate direct oxygen content analysis method can be obtained. Research on new active materials for lithium ion secondary batteries It is expected to contribute to development, production of positive electrode active materials, and improvement of quality control technology.

Claims (2)

[Claims] 1. A pretreatment for removing oxygen-containing volatile components such as oxygen, carbon dioxide, and moisture adsorbed or adhered under vacuum from a lithium-containing oxide and a graphite crucible containing the lithium-containing oxide. A method for quantitatively analyzing the oxygen content in a lithium-containing oxide, wherein a dissociation reaction of oxygen is promoted by using metal tin and / or an alloy with tin as a flux. 2. LixCoO ₂ as a lithium-containing oxide
(Where x represents a number satisfying 1.0 ≦ x ≦ 1.10.), L
ixCoyMzO ₂ (where M is Ni, Mn, Cr, F
e, Al, In, Sn, Zr, Ga or the like, and x, y, and z are each 1.00 ≦ x ≦ 1.1.
0, y + z = 1. _{), Li x Mn y M z} O 4
(Where M is at least one selected from Co, Cr, Ni, Al, Fe, etc., and x, y, and z are each 1.00 ≦ x ≦
1.12, represents the number y + z = 2. ), Li _X NiyM
_Z O ₂ (where M is Co, Mn, Cr, Fe, Al, G
x, y, and z are numbers of 0.98 ≦ x ≦ 1.10 and y + z = 1, respectively, in at least one kind selected from a, Zr, and the like. 2. The method for quantitatively analyzing the oxygen content in a lithium-containing oxide according to claim 1, wherein at least one selected from the above) is used.