JPH0562679A - Nonaqueous electrolyte lithium secondary battery and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a nonaqueous electrolyte lithium secondary battery which can be supplied stably at a low cost, gives no fear of environmental pollution, and can provide a high voltage and a high energy density, by using the beta-phase lithium ferrite as the main component of a positive electrode active material. CONSTITUTION:A nonaqueous electrolyte lithium secondary battery is composed of a positive electrode 1, a nonaqueous electrolyte, and a negative electrode 4, as the main components, and the beta-phase lithium ferrite is used as the main component of a positive electrode active material. Such a positive electrode active material is made by making the mixing ratio of at least one compound selected from iron oxide, iron hydroxide, iron oxalate, and iron ammonium oxalate, and a lithium salt, 0.8:1.0 to 1.2 in the mole ratio of the lithium and the iron, and manufactured by baking at the baking temperature 350 deg.C to 500 deg.C. Consequently, a nonaqueous electrolyte lithium secondary battery which can be supplied stably at a low cost, gives no fear of environmental pollution, and has a high voltage and a high energy density can be obtained easily.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte lithium secondary battery having a high voltage and a high energy density, which uses lithium or a lithium compound as a negative electrode.

[0002]

2. Description of the Related Art Non-aqueous electrolyte secondary batteries using lithium or a lithium compound as a negative electrode are expected to have high voltage and high energy density, and in recent years, research and development have been actively conducted.

Hitherto, as positive electrode active materials for non-aqueous electrolyte secondary batteries, LiCoO ₂ , LiMn ₂ O ₄ , V ₂ O ₅ and Cr have been used.
Oxides of transition metals such as ₂ O ₅ , MnO ₂ , TiS ₂ , MoS ₂ and chalcogen compounds are known. These positive electrode active materials form a layered structure or a tunnel structure,
It has a crystal structure that allows lithium ions to freely move in and out. In particular, LiCoO ₂ and LiMn ₂ O ₄ are attracting attention as a positive electrode active material for a non-aqueous electrolyte lithium secondary battery showing a voltage of 4V class.

[0004]

However, such a conventional positive electrode active material contains heavy metals such as Co, Mn, V, Cr and Mo and sulfur, and a non-aqueous electrolyte using these active materials. When the secondary battery is discarded, it may cause environmental pollution such as heavy metal pollution and sulfur oxide generation. Further, in terms of cost, these heavy metals are more expensive than iron, which makes the battery expensive. Furthermore, there are some concerns about the supply of raw materials, and there is a possibility that supply shortages due to changes in the world situation and price hikes may occur.

The present invention is intended to solve such a problem and is a non-aqueous electrolyte lithium secondary battery which is stably supplied at a low price, has no fear of environmental pollution, has a high voltage and a high energy density, and a method for producing the same. It is intended to provide.

[0006]

SUMMARY OF THE INVENTION The present invention is intended to solve such a problem and has a structure mainly composed of a positive electrode, a non-aqueous electrolyte and a negative electrode, and mainly composed of β-phase lithium ferrite as a positive electrode active material. It is a thing.

Further, iron oxide hydroxide, iron hydroxide, iron oxalate,
A positive electrode active material is prepared by firing a mixture mainly containing a lithium salt and at least one compound selected from ammonium iron oxalate.

The firing temperature is 350 ° C. to 500 ° C., and the mixing ratio of at least one compound selected from iron oxide hydroxide, iron hydroxide, iron oxalate, and ammonium iron oxalate to the lithium salt is lithium. And iron in a molar ratio of 0.8: 1.
It is set to be 0 to 1.2: 1.0.

[0009]

[Function] According to this structure, iron oxide hydroxide, iron hydroxide,
At least 1 selected from iron oxalate and ammonium iron oxalate
The compound obtained by firing a mixture of the seed compound and a lithium salt is a lithium-iron composite oxide. Since iron is a very abundant element, there are no worries on the supply side, and the cost is very low. Further, it is a positive electrode active material for non-aqueous electrolyte secondary batteries, which is optimal in terms of cost and environmental protection without problems such as environmental pollution. The charge composition is a molar ratio of lithium and iron of 0.8: 1.0 to 1.2: 1.0.
, Mainly lithium ferrite (LiFe
O ₂ ) is produced. LiFeO ₂ has a crystal structure of α, β,
The existence of three phases of γ has been confirmed, but the firing temperature is 3
As for the product at 50 ° C to 500 ° C, β phase is mainly produced.

When the electrode characteristics of each phase of LiFeO ₂ were examined, it was found that lithium was occluded and desorbed reversibly. Among them, the β phase had the highest capacity and the charge / discharge cycle characteristics were good. It is considered that this is because the β phase has the crystal structure in which lithium is most likely to enter and exit. β-phase LiFeO ₂ is α-phase or γ-phase LiFe
It can be obtained by synthesizing O ₂ and then heat-treating at around 400 ° C., but it requires a very long heat-treatment time. However, iron oxide hydroxide, iron hydroxide, ferrous oxalate, iron oxalate (II
I) β-phase LiFeO ₂ can be easily obtained in a short time by baking a mixture of at least one compound selected from ammonium and a lithium salt. Thus, by using β-phase LiFeO ₂ as the positive electrode active material, a non-aqueous electrolyte lithium secondary battery that is stably supplied at a low price, has no fear of environmental pollution, and has high voltage and high energy density is obtained. It will be possible.

[0011]

EXAMPLE A non-aqueous electrolyte lithium secondary battery of one example of the present invention and a method for manufacturing the same will be described below.

Example 1 In this example, a fired product obtained by using Li ₂ CO ₃ (lithium carbonate) and FeO (OH) (iron oxide hydroxide) as starting materials was used as a positive electrode active material.
A battery having a configuration in which lithium is used as the negative electrode active material will be described.

First, Li ₂ CO ₃ and FeO (OH) were mixed in such a manner that lithium and iron were mixed at a molar ratio of 1: 1 and pressure-molded, followed by firing in the atmosphere at 400 ° C. for 40 hours. This fired product is used as an active material a. As a comparative example, Li ₂ CO ₃ and F
e ₂ O ₃ (iron (III) oxide) was mixed with lithium and iron in a molar ratio of 1: 1 and pressure-molded, and the mixture was calcined in the air at 680 ° C. for 2 hours, then crushed and added. The calcined product obtained by pressure molding and calcining at 1000 ° C. for 5 hours in the atmosphere was mixed with active material b, Li ₂ CO ₃ and Fe ₂ O ₃ so that the molar ratio of lithium and iron was 1: 1. The pressure-formed product was fired in the air at 600 ° C. for 6 days, and the fired product was used as the active material c. As a result of X-ray diffraction, the active material a was mainly composed of β-phase lithium ferrite (LiFeO ₂ ),
The active material b is α phase LiFeO ₂ , and the active material c is γ phase LiFe
It was confirmed to be O ₂ .

Next, a positive electrode was produced using the active material obtained as described above. First, an active material, acetylene black as a conductive agent, and polyfluorinated ethylene resin as a binder are mixed in a weight ratio of 7: 2: 1,
The sufficiently dried product was used as the positive electrode mixture. 0.15 g of this positive electrode mixture was pressure-molded at ² ton / cm ² into a pellet having a diameter of 17.5 mm to obtain a positive electrode.

FIG. 1 shows the structure of a battery manufactured by using the electrode manufactured as described above. The positive electrode 1 was placed in the case 2, and the porous polypropylene film as the separator 3 was placed on the positive electrode 1. The negative electrode 4 has a thickness of 0.8.
A lithium plate having a diameter of 17.5 mm and a diameter of 17.5 mm was pressure-bonded to the sealing plate 7 provided with the polypropylene gasket 5 and the negative electrode current collector 6. As the non-aqueous electrolyte, propylene carbonate in which 1 mol / l lithium perchlorate was dissolved was used. After adding this on the separator 3, the positive electrode 1, and the negative electrode 4, respectively, the battery was sealed.

As described above, the charge / discharge characteristics were compared using the batteries using the active materials a, b and c as the positive electrode active materials. Charge / discharge conditions are a constant current of 2 mA and a voltage range of 3.
The voltage was regulated from 0V to 4.6V. Table 1 shows the initial discharge capacity and the discharge capacity at the 50th cycle of each battery. The battery using the active material a was battery A, the battery using the active material b was battery B, the battery using the active material c was battery C, and the number of samples n was 50 each.

[0017]

[Table 1]

As shown in (Table 1), the initial discharge capacity of Battery A was 14.91 mAh, and that of Battery B was 5.98 mAh.
It was found that Battery C had 9.03 mAh, and Battery A had the largest initial discharge capacity. Regarding the cycle characteristics, the discharge capacity at the 50th cycle was 14.6 for Battery A.
8 mAh, Battery B 4.41 mAh, Battery C 7.46
In mAh, the capacity retention rate of Battery A was the best. From the above results, the active material a has the most excellent characteristics,
As the positive electrode active material, it is desirable to use a fired product containing Li ₂ CO ₃ and Fe ₂ O ₃ as starting materials and mainly containing β-phase LiFeO ₂ .

In this embodiment, the case where lithium is used for the negative electrode has been described, but even when a lithium compound such as a carbon material or a lithium-aluminum alloy capable of reversibly taking in and out lithium is used for the negative electrode, The same effect can be obtained.

Example 2 In this example, a fired product obtained by using Li ₂ CO ₃ (lithium carbonate) and Fe (OH) ₃ (ferric hydroxide) as starting materials was used as a positive electrode active material. ,
A structure using lithium as the negative electrode active material will be described.

First, Li ₂ CO ₃ and Fe (OH) ₃ were mixed so that lithium and iron were mixed at a molar ratio of 1: 1 and pressure-molded, followed by firing in the atmosphere at 400 ° C. for 40 hours. This fired product is used as an active material d. As a comparative example, Li ₂ CO ₃ and F
Active materials b and c obtained by firing using e ₂ O ₃ in the same manner as in Example 1 were used. As a result of X-ray diffraction, it was confirmed that the active material a was mainly composed of β-phase LiFeO ₂ . Active material b
Is the α-phase LiFeO ₂ and the active material c is the γ-phase LiFeO ₂ .

Next, using the active material obtained as described above, a positive electrode and a battery were manufactured in the same manner as in Example 1.

Further, the charge / discharge characteristics of the batteries using the active materials d, b, and c as the positive electrode active materials were compared. Charge / discharge conditions are a constant current of 2 mA and a voltage range of 3.
The voltage was regulated from 0V to 4.6V. (Table 2) shows the initial capacity and the discharge capacity at the 50th cycle of each battery.
The battery using the active material d was battery D, the battery using the active material b was battery B, the battery using the active material c was battery C, and the number of samples n was 50 each.

[0024]

[Table 2]

As shown in (Table 2), the initial capacity is battery D
12.15 mAh for battery B and 5.98 mAh for battery B
The pond C has 9.03 mAh, and the battery D has the highest initial capacity.
Was found to be large. Also, regarding cycle characteristics
The discharge capacity at the 50th cycle is 11.83 mA for Battery D.
h, Battery B is 4.41 mAh, Battery C is 7.46 mAh
Therefore, the discharge capacity retention rate of the battery D is the best. More than
From the results, the active material d has the most excellent characteristics,
As a polar active material, Li₂CO₃And Fe (OH) ₃Depart
Mainly as a raw material β phase LiFeO₂Use a fired product containing
And is desirable.

In the present embodiment, the case where lithium is used for the negative electrode has been described. However, the negative electrode uses a lithium compound such as a carbon material or a lithium-aluminum alloy that can reversibly take in and out lithium. However, the same effect can be obtained.

The same thing can be obtained by using ferrous hydroxide instead of ferric hydroxide.

Example 3 In this example, Li ₂ CO ₃ (lithium carbonate) and FeC ₂ O ₄ .2H ₂ O were used as starting materials.
A battery having a configuration in which a fired product obtained by using (ferrous oxalate dihydrate) is used as the positive electrode active material and lithium is used as the negative electrode active material will be described.

Firstly, Li ₂ CO ₃ and FeC ₂ O ₄ · H 1 to ₂ O with lithium and iron molar ratio: 1 so as mixing those molded under pressure, the calcined 40 hours at 400 ° C. in air did.
This fired product is used as an active material e. As a comparative example, Li ₂ CO ₃
And active materials b and c obtained by firing with Fe ₂ O ₃ in the same manner as in Example 1 were used. As a result of X-ray diffraction, the active material e
Was confirmed to consist mainly of β-phase LiFeO ₂ . The active material b is α-phase LiFeO ₂ and the active material c is γ-phase LiFeO ₂ .

Next, using the active material obtained as described above, a positive electrode and a battery were manufactured in the same manner as in Example 1.

Further, the charge / discharge characteristics were compared using batteries using the active materials e, b, and c as the positive electrode active materials. Charge and discharge conditions were 2 mA constant current and voltage range 3.0.
The voltage was regulated from V to 4.6V. Table 3 shows the initial discharge capacity and the discharge capacity at the 50th cycle of each battery. The battery using the active material e was battery E, the battery using the active material b was battery B, the battery using the active material c was battery C, and the number of samples n was 50 each.

[0032]

[Table 3]

As shown in (Table 3), the initial capacity was 13.26 mAh for battery E, 5.98 mAh for battery B, and 9.03 mAh for battery C, indicating that battery E had the largest initial capacity. Regarding the charge / discharge cycle characteristics, the discharge capacity at the 50th cycle was 12.93 for Battery E.
mAh, Battery B is 4.41 mAh, Battery C is 7.46 m
With Ah, the capacity maintenance ratio of the battery E is the best. From the above results, the active material e has the most excellent characteristics, and as the positive electrode active material, Li ₂ CO ₃ and FeC ₂ O ₄ .2H ₂ O are used.
It is desirable to use a calcined product containing as a starting material and mainly containing β-phase LiFeO ₂ .

In this embodiment, a battery having a structure in which lithium is used for the negative electrode has been described, but a lithium compound such as a carbon material or a lithium-aluminum alloy capable of reversibly taking in and out lithium is used for the negative electrode. Even with the configuration, the same effect can be obtained.

The same effect can be obtained by using ferric oxalate instead of ferrous oxalate. Example 4 In this example, Li ₂ CO ₃ was used as a starting material.
(Lithium carbonate) and _{Fe (NH 4) 3 (C} 2 O 4) 3 · 3H 2
A battery having a structure in which a fired product obtained by using O (iron (III) oxalate ammonium trihydrate) is used as the positive electrode active material and lithium is used as the negative electrode active material will be described.

First, Li ₂ CO ₃ and Fe (NH ₄ ) ₃ (C ₂
O _{4) 3} · 3H 1 to ₂ O with lithium and iron molar ratio: 1 so as mixing those molded under pressure to and calcined 40 hours at 400 ° C. in air. This fired product is used as an active material f. As comparative examples, active materials b and c obtained by firing Li ₂ CO ₃ and Fe ₂ O ₃ in the same manner as in Example 1 were used. As a result of X-ray diffraction, it was confirmed that the active material f was mainly composed of β-phase LiFeO ₂ . Active material b is α-phase LiFeO ₂ , active material c
Is the γ-phase LiFeO ₂ .

Next, using the active material obtained as described above, a positive electrode and a battery were prepared in the same manner as in Example 1.

Further, the charge / discharge characteristics were compared using batteries using the active materials f, b, and c as the positive electrode active materials. Charge / discharge conditions are a constant current of 2 mA and a voltage range of 3.
The voltage was regulated from 0V to 4.6V. (Table 4) shows the initial discharge capacity and the discharge capacity at the 50th cycle of each battery. The battery using the active material f was battery F, the battery using the active material b was battery B, the battery using the active material c was battery C, and the number of samples n was 50 each.

[0039]

[Table 4]

As shown in (Table 4), the initial discharge capacity of the battery F was 13.84 mAh and that of the battery B was 5.98 mAh.
It was found that the battery C had 9.03 mAh, and the battery F had the largest initial capacity. Regarding the cycle characteristics, the discharge capacity at the 50th cycle was 13.01 m for Battery F.
Ah, battery B is 4.41 mAh, battery C is 7.46 mA
At h, the capacity retention rate of the battery F is the best. From the above results, the active material f has the most excellent characteristics, and as the positive electrode active material, Li ₂ CO ₃ and Fe (NH ₄ ) ₃ (C
_{2 O 4) 3 · 3H 2} O was used as a starting material mainly β phase LiFeO ₂
It is desirable to use a fired product containing.

In this embodiment, the structure using lithium for the negative electrode has been described. However, it is a structure using a lithium compound such as a carbon material or a lithium-aluminum alloy capable of reversibly taking in and out lithium in the negative electrode. However, the same effect can be obtained.

Example 5 In this example, α phase LiFeO 2 is used.
Β obtained by firing ₂ at 400 ° C. for a long time
A structure in which phase LiFeO ₂ is used as the positive electrode active material and lithium is used as the negative electrode active material will be described.

The α-phase LiFeO ₂ contains Li ₂ CO ₃ and Fe ₂ O.
₃ with using the active material b obtained by firing in the same manner as in Example 1, which was obtained β-phase LiFeO ₂ by firing 150 hours at 400 ° C. in air. This is designated as an active material g. When the firing time was 40 hours, the firing time was short and β-phase LiFeO ₂ could not be obtained.

Next, using the active material thus obtained, a positive electrode and a battery were produced in the same manner as in Example 1. Further, with respect to the active materials b and c obtained by firing in the same manner as in Example 1, a positive electrode and a battery were similarly prepared. The active material b is α-phase LiFeO ₂ and the active material c is γ
The phase is LiFeO ₂ .

The charge / discharge characteristics of the batteries using the above active materials g, b, and c as the positive electrode active materials were compared. Charge and discharge conditions were 2 mA constant current and voltage range 3.0.
The voltage was regulated from V to 4.6V. (Table 4) shows the initial capacity and the discharge capacity at the 50th cycle of each battery. The battery using the active material g was battery G, the battery using the active material b was battery B, the battery using the active material c was battery C, and the number of samples n was 50 each.

[0046]

[Table 5]

As shown in (Table 5), the initial capacity of the battery F was 10.53 mAh, the battery B was 5.98 mAh, and the battery C was 9.03 mAh, and it was found that the battery G had the largest initial capacity. Regarding the cycle characteristics, the discharge capacity at the 50th cycle was 9.85 mAh for Battery G,
Battery B is 4.41 mAh, Battery C is 7.46 mAh,
The capacity retention rate of the battery G is the best. From the above results, the active material g has the most excellent characteristics, and the α-phase Li
Even if β-phase LiFeO ₂ obtained by firing FeO ₂ at 400 ° C. for a long time is used, α-phase and γ-phase Li
It can be seen that it has better characteristics than the case of using FeO ₂ . However, mainly β-phase LiFeO ₂ obtained by firing a mixture of at least one compound selected from iron oxide hydroxide, iron hydroxide, ferrous oxalate, and iron (III) oxalate ammonium and a lithium salt. The characteristics are slightly inferior to the case where a fired product containing is used as the positive electrode active material. From this, as the positive electrode active material, a mixture of at least one compound selected from iron oxide hydroxide, iron hydroxide, ferrous oxalate, and ammonium iron (III) oxalate, and a lithium salt is fired. It is desirable to use the obtained fired product.

In the present embodiment, the structure using lithium for the negative electrode has been described, but a structure using a lithium compound such as a carbon material or a lithium-aluminum alloy capable of reversibly taking in and out lithium is also used for the negative electrode. , A similar effect is obtained.

As described above, iron oxide hydroxide, iron hydroxide, ferrous oxalate, iron oxalate (II
I) With ammonium and α-phase LiFeO ₂
A battery using a fired product containing β-phase LiFeO ₂ mainly obtained by firing at 400 ° C. for a long time as a positive electrode active material was described. From these results, as a property, the case where iron oxide hydroxide was used is the most excellent, and the iron (III) oxalate ammonium, ferrous oxalate,
The order is the case when iron hydroxide is used, both of which are α-phase LiF
It can be seen that it exhibits better properties than those obtained by firing eO ₂ at 400 ° C. for 150 hours.

(Embodiment 6) In this embodiment, the electrode characteristics of the product when the firing temperature and the mixing ratio of lithium and iron are variously changed will be described. The electrode characteristics are shown in Example 1.
The change in the initial discharge capacity of the lithium secondary battery manufactured by the same method as in (1) was investigated.

Li ₂ CO ₃ was used as a lithium source and FeO (OH) was used as an iron source. First, the mixing ratio was set to 1.0: 1.0 in terms of the molar ratio of lithium and iron, and the temperature was changed from 200 ° C to 600
The initial capacity was investigated when the product obtained by firing at a temperature within the range of ° C was used as the positive electrode active material. The lithium battery was manufactured in the same manner as in Example 1. The relationship between the firing temperature and the initial capacity is shown in FIG. From these results, it can be seen that good characteristics are exhibited when the mixing ratio of lithium and iron is 0.8: 1.0 to 1.2: 1.0 in terms of molar ratio. As a result of X-ray diffraction, the products in this mixing ratio range were mainly β-phase LiFeO ₂ . Next, when the firing temperature was set to 400 ° C. and the mixing ratio was changed in the molar ratio of lithium and iron within the range of 0.5: 1.0 to 1.5: 1.0, the product was used as the positive electrode active material. The change in the initial capacity of the above structure was investigated. The relationship between the mixing ratio of lithium and iron and the initial discharge capacity is shown in FIG. From this, the firing temperature is 350
It can be seen that good characteristics are exhibited at a temperature in the range of ℃ to 500 ℃. Also in this case, the product at the firing temperature in the range of 350 ° C. to 500 ° C. was mainly β-phase LiFeO ₂ .

As can be seen from the above results, the mixing ratio of lithium and iron is 0.8: 1.0 to 1.2: in molar ratio.
The range is 1.0 and the firing temperature is from 350 ° C to 50 ° C.
LiF synthesized under the synthesis conditions having a temperature in the range of 0 ° C
It is desirable to use eO ₂ as the positive electrode active material.

In this example, Li was used as a starting material.
_{Although the case where 2} CO ₃ and FeO (OH) are used has been described, the same effect can be obtained when any of iron hydroxide, iron oxalate, and ammonium iron oxalate is used as the iron source.

Although the structures using lithium carbonate as the lithium salt have been described in Examples 1 to 6, the same effect can be obtained when a lithium salt such as lithium hydroxide is used.

[0055]

As is apparent from the above description of the embodiments, in a lithium secondary battery comprising a positive electrode, a non-aqueous electrolyte and a negative electrode, β-phase lithium ferrite (LiFeO ₂ ) is mainly used as a positive electrode active material. As a result, it is possible to easily obtain a non-aqueous electrolyte lithium secondary battery that is stably supplied at a low price, has no fear of environmental pollution, and has high voltage and high energy density.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a non-aqueous electrolyte lithium secondary battery of Example 1 of the present invention.

FIG. 2 is a graph showing the relationship between the firing temperature of the active material and the discharge capacity of the battery used therein.

FIG. 3 is a diagram showing a relationship between a mixture ratio of lithium and iron as a starting material of the active material and a discharge capacity of a battery.

[Explanation of symbols]

 1 Positive Electrode 2 Case 3 Separator 4 Negative Electrode 5 Gasket 6 Negative Electrode Current Collector 7 Sealing Plate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiko Mito 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A non-aqueous electrolyte lithium secondary battery having a positive electrode, a non-aqueous electrolyte and a negative electrode as a main component, and a β-phase lithium ferrite as a main component as a positive electrode active material. 2. A positive electrode active material is prepared by firing a mixture containing at least one compound selected from iron oxide hydroxide, iron hydroxide, iron oxalate, and iron ammonium oxalate, and a lithium salt. Manufacturing method of water electrolyte lithium secondary battery. 3. A firing temperature of 350 ° C. to 500 ° C., iron oxide hydroxide, iron hydroxide, iron oxalate, ammonium iron oxalate,
The mixing ratio of at least one compound selected from the above and the lithium salt is 0.8: 1.0 to a molar ratio of lithium and iron.
The method for producing a non-aqueous electrolyte lithium secondary battery according to claim 2, wherein the ratio is 1.2: 1.0.