JPH07130368A - Cathode material of lithium battery - Google Patents

Abstract

PURPOSE:To provide a cathode material with a large number of lithium ion insertion positions, chemical stability to an electrolyte, and high conductivity by containing a phase made of a specific formula of perovskite related structure. CONSTITUTION:A cathode material of a lithium battery contains a phase made of a formula of perovskite related structure represented by the general formula of Srn+1VnO3n+1 (n is 2, 3, or 4.). A system represented by the general formula of Srn+1VnO3n+1 contains several types of layered perovskite compound. Since deficiency or excess of oxygen atom in an oxygen atom position is usual, therefore, generally it is represented by the general formula of Srn+1VnO3n+1-delta. The quantity delta depends on (n), but practically delta/n is 0.3 to -0.02. The layered perovskite compounds in which n is 2-4 is capable of reversibly inserting or releasing lithium ions in or from the lattice, and show metallic resistance behavior.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to cathode materials for lithium batteries.

[0002]

2. Description of the Related Art Of lithium batteries, especially lithium secondary batteries
The voltage and capacity depend on the selection of the positive electrode active material (cathode material).
It is decided accordingly. Specifically, these positive electrode active materials include
The following properties are required. Do not dissolve in electrolyte etc. electrolytic
Must be chemically stable to quality. High electrical conductivity
To have. Multiple sites for inserting lithium ions
Have a number. However, the combination of these properties
The reality is that there are few compounds. Recently, Li _xCoO₂,
Li_xNiO₂Although materials such as
Since it has low electrical conductivity, it is a conductive material such as carbon black.
Adds and mixes quality as an aid to improve electrical conductivity
There is a need.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lithium battery having a large number of sites for inserting lithium ions and being chemically stable with respect to an electrolytic solution. It is to provide a conductive positive electrode active material (cathode material).

[0004]

The present invention relates to [outer 1] of a perovskite-related structure (n represents 2, 3 or 4).
The present invention relates to a cathode material for a lithium battery, characterized in that it contains a phase consisting of

The system represented by the general formula of Sr _{n + 1} V _n O _{3n + 1} includes various layered perovskite compounds. This is Sr ₂ V ₁ O ₄ when n = 1, and n = 2
Sr ₃ V ₂ O ₇ in the case of, and S in the case of n = 3
r ₄ V ₃ O ₁₀ , and when n = 4, Sr ₅ V ₄ O ₁₃
Is.

[0006] Here, "Sr _{n + 1} V _n O _{3n + 1} " is a conventional notation when describing ceramics having a so-called ABO ₃ type perovskite-related structure. Of course, it is usual that there is a deficiency or excess of oxygen atoms at the oxygen atom site. Therefore, among engineers in the ceramics industry,
Generally, it is also written as "[outer 1]". The number of δ depends on the value of n, but in reality, as the value of δ / n,
(0.3) to (-0.02).

Sr ₂ V ₁ O ₄ , Sr ₃ V ₂ O ₇ , Sr ₄
The perovskite-related structure itself having a structural formula of V ₃ O ₁₀ (the δ indicating the deficiency or excess amount of oxygen atoms is omitted) is a known chemical substance (Mat. Res. Bull. Vol. 26,
See pages 1-9, 1991, Solid State Communications V
ol.80, No. 8, 545-548, 1991).

The present inventor has found that Sr ₂ V ₁ O ₄ and Sr ₃ V ₂
Into the lattice of O ₇ , Sr ₄ V ₃ O ₁₀ , Sr ₅ V ₄ O ₁₃ ,
For the first time, we have discovered that lithium ions can be reversibly intercalated and that lithium ions can be extracted from these lattices. In addition, Sr ₃ V ₂ O ₇ , S
Although r ₄ V ₃ O ₁₀ and Sr ₅ V ₄ O ₁₃ have a slight difference in electric resistance, they show metallic electric resistance behavior. Also,
It was also confirmed that a lithium battery using this material as a cathode material can be discharged at a relatively high current density.

[0009]

EXAMPLES Specific experimental results will be described below. (Production of sample) Sr ₂ V ₁ O ₄ (n = 1), Sr ₃ V ₂
Each perovskite-related structure composed of O ₇ (n = 2) and Sr ₄ V ₃ O ₁₀ (n = 3) (each showing a target composition) was produced by a solid-phase reaction method. SrCO ₃ powder (purity 99.9%) and V ₂ O ₅ powder (purity 99.99)
%) And was stirred in ethanol. The molar ratio of Sr and V was a stoichiometric composition corresponding to each target composition.

Each mixed powder was calcined in air at 800 ° C. for 4 hours and then at 1150 ° C. for 12 hours. Each calcined product was crushed and press-formed under a pressure of 130 MPa to give a diameter of 10
mm and a thickness of 3 mm were obtained. The pellets were calcined in air for 6 hours at 1350 ° C. and allowed to cool to room temperature.

(Crystal structure of sample) The crystal phase was identified and the lattice constant was measured by a powder X-ray diffraction method using CuKα radiation. At this time, an Rigaku or Mac Science X-ray diffractometer equipped with a graphite monochromator was used. Silicon powder (5N) was used as an internal standard for the sample when measuring the lattice constant. For each sample, it was confirmed that a single phase was produced.

(Chemical composition) The molar ratio of each metal in the above sample was measured by the inductively coupled plasma spectroscopy (ICP) by the external standard method. The sample for analysis was manufactured as follows. A small amount of sample (about 10 mg) and 1 ml of concentrated hydrochloric acid (35% by weight) were enclosed in a Pyrex glass tube and kept at about 130 ° C for 1 to 3 hours to dissolve.

(Analysis of oxygen amount) The amount of oxygen in each sample was determined. Each sample was treated with 20 ml of oxygen flow at 200 ml / min.
Heated at 900 ° C for hours. During this oxidation process, V
If ⁺⁴ changes to V ^+5, the principle of electrical neutrality, V ⁺⁴
Corresponding to the number of mol changed from V ⁺⁵ to V ⁺⁵
l number of oxygen atoms are added to the perovskite related structure. The amount of increase in the weight of the perovskite-related structure before and after the oxidation step depends on the mo of the oxygen atom thus added.
It is determined by the number of l. Assuming that all V ⁺⁴ changes to V ⁺⁵ during the above oxidation process, the weight increase of the perovskite-related structure is measured to determine the mol number of V ⁺⁴ in each sample. As a result, the number of oxygen atoms is also determined.

As a result of this experiment,

[Outside 2] It was confirmed that a perovskite-related structure having each composition of was obtained.

(Experiment on Electrochemical Insertion of Lithium) Sr
Lithium ion was inserted into a sample composed of a perovskite-related structure having a composition of ₃ V ₂ O _6.88 and Sr ₄ V ₃ O _9.57 . Bipolar battery (Li / 1M Li
ClO ₄ PC in / each sample) was manufactured as a prototype. Here, lithium metal is the negative electrode active material, each of the above-mentioned samples is the cathode material (positive electrode active material), and (1M LiClO ₄
PC (polycarbonate) is the organic electrolyte.

Using this bipolar battery, lithium ions were electrochemically inserted into Sr ₄ V ₃ O _9.57 by a constant current method. As a comparative example, CaMnO ₃ having a perovskite structure was used as a cathode material. Figure 1
Shows the relationship between the amount of lithium inserted and the change in applied voltage.
As samples, it illustrates the results of using Sr ₄ V ₃ O _9.57.

In this case, it was possible to insert at least 0.6 lithium per metal at the B site. On the other hand, when CaMnO ₃ was used, it was difficult to insert lithium ions because manganese ions were too small.

The results show that the perovskite-related structure composed of Sr ₄ V ₃ O _9.57 can be used as a cathode material having a relatively large capacity. Also, Sr
Similar results were obtained when ₃ V ₂ O _6.88 was used as the cathode material in the bipolar battery described above.

(Measurement of Electric Resistance Value) In the same manner as above,
Sr ₄ V ₃ O _9.80 , Sr ₃ V ₂ O _6.88 , Sr ₂ V ₁ O _4-
Perovskite-related structures having respective compositions of δ were manufactured. The electrical resistance was measured by the standard four-terminal method in the temperature range of 2K to 300K. For each perovskite-related structure, a 2 mm × 2 mm × 10 mm sample was cut out. A thin gold film was applied to the sample by sputtering and used as an electrode. The result is shown in FIG.

As can be seen from FIG.

[Outside 3]In the case of, a behavior of a semiconductor resistance value is shown. Sr₃V
₂O_6.88In the case of (n = 2), the resistance value is almost metallic.
Shows behavior, Sr_FourV₃O_9.80In the case of (n = 4),
A behavior of a resistance value like a metal is shown. As you can see from this result
To Sr₂V₁O _Four-In the case of δ, as the cathode material
Has a large resistance value and is inappropriate.

A perovskite-related structure having a composition of Sr ₅ V ₄ O ₁₃ (n = 4) could not be manufactured by a usual solid phase reaction method because of a long atomic arrangement period.
In order to manufacture this, it was necessary to use a chemical vapor deposition method and a physical vapor deposition method. It was also confirmed that lithium ions can be inserted into Sr ₅ V ₄ O ₁₃ .

When n = 5 or more, the atomic arrangement period becomes very long. Such a long-period atomic array cannot exist physically or chemically even though the atomic array can be considered mathematically, the order of the atomic array is always disordered, and the number of n varies depending on the place. To do. In this case, in practice,
In the case of n = ∞ (SrVO ₃ ), it is considered that there is a partial deficiency, and therefore it is different from the compound defined in the present invention.

A lithium battery to which the cathode material of the present invention can be applied will be exemplified. As the lithium primary battery, manganese dioxide-lithium battery, fluorinated graphite-lithium battery,
Thionyl chloride-lithium batteries have been put to practical use. As this shape, a flat type having a single-layer structure, a flat type having a multi-layer structure, a thin type, a cylindrical shape having an inside-out structure, a cylindrical shape having a spiral structure, and a square shape are known.

In the lithium secondary battery, a room temperature organic electrolyte type lithium battery, a low temperature polymer electrolyte lithium battery,
High temperature type lithium batteries and the like are known. An organic electrolyte is used in a room temperature organic electrolyte type lithium battery. As the solute, LiPF ₆ , LiAsF ₆ , LiClO
₄ , LiBF ₄ , LiCF ₃ SO ₃ , LiCH ₃ SO ₃
Etc. are used. As the solvent, dimethyl sulfoxide, ethylene carbonate, propylene carbonate, sulfolane, gamma-butyrolactone, gamma-valerolactone, 1,2-diethoxyethane, 1,2-dimethoxyethane, 2-methyltetrahydrofuran, 1,
3-dioxolane, tetrahydrofuran, 1,2-dibutoxyethane or the like is used. Additives for organic electrolytes include crown ether, diglyme, THF, DM
Examples include F, decalin, paraffin, and hexadecane. Examples of the negative electrode active material in the room temperature organic electrolyte type lithium battery include lithium metal, Li / Al alloy, and Li / wood metal alloy. Further, a conductive polymer such as polyacetylene or various carbon materials capable of reversibly inserting and extracting lithium can be used. As the structure of the battery, there are a coin type, an AA type, a BC cell, a box type and the like.

In the low temperature polymer electrolyte lithium battery, the battery structure has a spiral structure, a laminated structure, a roll type, and the like, and usually a composite of a polymer compound and an electrolyte salt is used. As the polymer compound, PEO, crosslinked PEO, PMEEP, PMSEO, PPL, PMM
A, PMOEO, PVDF, etc. Examples of the electrolyte salt include LiClO ₄ , LiCF ₃ SO _{3, and the} like.

[0026]

As described above, a ceramic containing a phase composed of [outer 1] (n is 2, 3, or 4) of a perovskite-related structure is used as a cathode material having a relatively large capacity. It is possible. Moreover, this ceramic is a perovskite-related structure, is extremely chemically stable, has a metallic electric resistance, and can be used even at high temperatures.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a lithium insertion amount and a change in applied voltage.

FIG. 2 is a graph showing a temperature change of an electric resistance value of each perovskite-related structure.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication H01M 4/02 C (72) Inventor Tetsuro Nakamura 2-41-21 Fuji, Fujigaoka, Midori-ku, Yokohama-shi, Kanagawa Gaoka Residence 403

Claims (1)

[Claims] 1. A perovskite-related structure [1] (N represents 2, 3 or 4) A cathode material for a lithium battery, comprising a phase consisting of