JP2000012023A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase cycle discharge capacity of a lithium secondary battery using lithium manganese composite oxide represented by composition formula LixMn2-yMyO4, (M is a transition metal) in a positive electrode. SOLUTION: A lithium manganese composite oxide represented by the composition formula LixMn2-yMyO4 (M is transition metal, with x being in 1.15-1.25 range), having specific surface area of 0.05-0.5 m2/g is used as a positive active material. Cycle stability and thermal stability of a battery are increased, and cycle discharge capacity is also increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to an improvement in the performance of a non-aqueous electrolyte secondary battery using a lithium manganese composite oxide for a positive electrode.

[0002]

2. Description of the Related Art Since a lithium secondary battery has a large discharge capacity, a high voltage and a high energy density, a cylindrical or square type lithium secondary battery has already been put into practical use for a portable power supply. Developments are being pursued to obtain higher energy densities with the aim of applying it to power supplies for power storage.

[0003] At present, lithium cobalt oxide or the like has been put into practical use as a material suitable for the positive electrode active material of a lithium secondary battery. Since it is necessary to use a rare metal and it is costly and it is difficult to manufacture it at a low cost, adoption of lithium manganate which is abundant in resources and can be manufactured at low cost is being studied as a positive electrode active material.

However, when using a lithium manganese composite oxide as a positive electrode active material, the cycle discharge capacity characteristics are inferior to the case where lithium cobalt oxide is used, and the charge / discharge cycle characteristics of the battery deteriorate. It is pointed out that it is easy.

[0005] The cause of this is that the adhesion between the positive electrode active material made of LiMn ₂ O ₄ and the conductive agent or current collector decreases due to the repetition of expansion and contraction of the LiMn ₂ O ₄ crystal lattice accompanying the charge / discharge cycle. As a result, it is considered that the current collection efficiency is reduced and the cycle characteristics are deteriorated. It is also pointed out that LiMn ₂ O ₄ itself has low oxidation stability and thermal stability with an electrolytic solution.

As a countermeasure against such a cycle deterioration of the battery, Japanese Patent Application Laid-Open No. 8-69790 discloses that the specific surface area of the lithium manganese composite oxide is 0.05 to 5.0 m ^2.
It has been proposed to obtain a secondary battery having a high energy density and excellent cycle characteristics by regulating the content in the range of / g. Here, the upper limit of the specific surface area is 5.0 m ^2.
The reason for setting to / g is to suppress the miniaturization of the lithium manganese composite oxide. When the specific surface area exceeds 5.0 m ² / g, the particle diameter becomes small, and the miniaturization accompanying charge / discharge easily proceeds. It is described that this is because a large cycle reduction is caused. The lower limit is 0.05 m ²
/ G because the specific surface area of the positive electrode active material is 0.05 m
^It is described that when the content is less than ² / g, although the miniaturization of the positive electrode active material is suppressed, the heavy particle size becomes too large to deteriorate the heavy load characteristics and the battery capacity becomes small.

[0007]

However, as a result of intensive studies conducted by the present inventors, even when the specific surface area of the lithium manganese composite oxide is in the range of 0.05 to ⁵ m ² / g, It is not always possible to keep both the initial discharge capacity and the cycle discharge capacity retention rate high at the same time, but rather a narrow region (0.05 to 0.5) close to the lower limit of the range.
m ² / g) and good cycle discharge capacity characteristics cannot be obtained only by regulating the specific surface area. Other conditions include the molar ratio of lithium Li to manganese Mn. Must be in the proper range.

The present invention has been made in view of the above problems, and an object of the present invention is to optimize the Li: (Mn + M) ratio and the specific surface area of lithium manganate as a positive electrode active material, An object of the present invention is to provide a non-aqueous electrolyte secondary battery having improved cycle discharge capacity characteristics.

[0009]

Means for Solving the Problems The present inventors have added a composition formula Li _x Mn _{2- y My} O ₄ (M is a transition metal) to a positive electrode active material.
In the case of a battery using a lithium manganese composite oxide having a value of X in the range of 1.15 to 1.25 and a specific surface area in the range of 0.05 to 0.5 m ² / g, the cycle stability Also, it has been found that the thermal stability is improved.

That is, the non-aqueous electrolyte secondary battery of the present invention uses a material capable of doping and undoping lithium in the negative electrode, and uses the composition formula Li _x Mn _2-y My O ₄ (M is a transition metal) for the positive electrode. In a non-aqueous electrolyte secondary battery using a given lithium manganese composite oxide and a non-aqueous electrolyte obtained by dissolving an electrolyte in an organic solvent as an electrolyte, a lithium manganese composite oxide represented by the above composition formula Means that the value of X is 1.15
1.25 and a specific surface area of 0.05 to 0.1.
It is in the range of 5 m ² / g (Claim 1).

As the ratio X of Li increases from 1 in the stoichiometric ratio to lithium, the initial discharge capacity decreases. However, the cycle discharge capacity retention rate is improved. The reason for this is not clear, but a Li-rich phase (for example, Li ₄ Mn ₅ O ₁₂ or the like) grows by adding a large amount of Li, and the discharge capacity is relatively reduced in the LiMn _{2- y My} O ₄ phase. , It is speculated that this contributes to stabilization of the active material, that is, improvement of the cycle discharge capacity retention rate due to the reduction of expansion and contraction due to the coexistence of phases unrelated to the electrode reaction (X > 1.15). The reason why the lower limit of the value of X in the lithium manganese composite oxide is set to 1.15 is that if it is less than this, no improvement in the cycle discharge capacity retention rate is observed.

However, if the amount of Li is too large, the capacity of the battery is reduced. Therefore, it is necessary to consider the Li / Mn molar ratio of Li while balancing the stability of the active material (X <1. 25). The reason why the upper limit of the value of X in the lithium manganese composite oxide is set to 1.25 is that if it exceeds this value, the capacity of the battery will be reduced.

[0013] The value of X is 1.15 to 1.25, because the molar ratio of Li to Mn, Li: Mn = 0.9 to 0.1, disclosed in the prior art, for example, in JP-A-9-86933.
1.10: It is in a range deviating from the side larger than 2.00. The upper limit of y is preferably about 0.6, and the value of x is a value for Mn + M of 2, and there is no direct correlation between x and y.

In the present invention, the specific surface area of the lithium manganese composite oxide is 0.05 to 5.0 m, which is the conventional value.
^It is set to a narrow range of 0.05 to 0.5 m ² / g which is close to the lower limit of the range of ² / g. This is because the smaller the specific surface area of the active material is, the better the cycle discharge capacity retention rate is, in order to suppress the reaction with the electrolytic solution as much as possible (specific surface area <0.5 m ² / g). The upper limit of the specific surface area is 0.5 m ² /
The reason why the specific surface area is set to be less than 0.5 g is that if the specific surface area exceeds 0.5 m ² / g, the cycle discharge capacity retention rate is greatly reduced.

However, the specific surface area is so small that
If the surface area is less than 0.05 m ² / g, the initial discharge capacity is reduced because the electrode reaction area is small, so the lower limit of the specific surface area is 0.05 m ² / g (specific surface area> 0.05).
m ² / g).

It is desirable that at least one of the positive electrode conductive agents of the positive electrode mixture in this battery uses expanded graphite. The conductive agent to be used simultaneously includes carbon black, graphite, and metal. Graphite is not particularly limited, and various coke, natural graphite, artificial graphite, activated carbon, and various graphites can be used.

This will be described later, but LiCoO ₂ and L
Compared to iNiO ₂ active material, Li _{x has} lower bulk density.
Mn _2-y M _y O _4, for the expansion and contraction of the crystal lattice caused by the charge and discharge cycles, the adhesion between the conductive agent and the current collector tends to decrease. For this reason, the use of expanded graphite having a worm-like honeycomb structure not only ensures conductivity, but also the active material is entangled between the honeycombs during the rolling process when producing a positive electrode sheet, and as a binder, Since it also plays a role, this disadvantage can be solved.

The negative electrode may be made of any material capable of doping lithium, such as lithium metal, lithium alloy, artificial graphite such as natural graphite or coke, carbon fiber, glassy carbon, or the like.
Oxides such as Si and Sn are exemplified.

Examples of the electrolyte include cyclic carbonates such as propylene carbonate and ethylene carbonate, dimethoxyethane, tetrahydrofuran, γ-butyrolactone, dioxolan, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate and the like.

Further, in the non-aqueous electrolyte secondary battery according to the second aspect of the present invention, lithium hexafluorophosphate (hereinafter referred to as LiPF ₆ ) is used as an electrolyte and the amount of hydrogen fluoride in the electrolyte is reduced. To 50 ppm or less. Here, LiPF ₆ is used because it is preferable as an electrolyte.
₆ is hydrofluoric acid (hereinafter referred to as HF) by hydrolysis with water
Generate This HF causes great damage to lithium manganate. Therefore, the concentration of HF in the electrolytic solution should be as low as possible. Therefore, in the present invention, the amount of HF in the electrolyte is set to 50 ppm or less. However, this HF concentration is closely related to the specific surface area of lithium manganate. That is, when the specific surface area of lithium manganate is large, the area where HF causes large damage to lithium manganate also increases, resulting in capacity deterioration. For this reason, it is important to keep the HF concentration in the electrolytic solution low while reducing the specific surface area.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on the illustrated embodiment.

The following batteries are prepared using the positive electrode active material obtained in the present invention.

FIG. 1 is a sectional view of a non-aqueous electrolyte secondary battery. In FIG. 1, reference numeral 1 denotes a positive electrode plate, which is composed of an oxide mixture of a positive electrode active material, an expanded graphite having an average particle diameter of 10 μm as a conductive agent, and an aqueous dispersion of PTFE as a binder in a weight ratio of 85: 10: 5. After mixing at a ratio and kneading it into a paste with water, it was applied to both sides of a 30 μm-thick aluminum foil, dried, rolled, and cut into the largest predetermined size that would fit in a can. A belt-shaped positive electrode sheet was produced. The mixture was scraped off a part of the sheet perpendicularly to the longitudinal direction of the sheet, and a titanium positive electrode lead plate was attached to the current collector by spot welding. The ratio of the aqueous dispersion of PTFE in the mixing ratio of the above materials is the ratio of the solid content. At this time, the weight of the positive electrode active material was 4.7.
g.

As the negative electrode active material, carbon obtained by graphitizing pitch-based coke was used. Reference numeral 2 denotes a negative electrode carbon material electrode, which is obtained by kneading a carbonaceous powder and an aqueous dispersion of PTFE as a binder in a weight ratio of 100: 5 into a nickel expanded metal, followed by drying. Eight types were cut to produce strip-shaped negative electrode sheets. The mixture was scraped off a part of the sheet perpendicularly to the longitudinal direction of the sheet, and a nickel negative electrode lead plate was attached to the current collector by spot welding. In addition, the ratio of PTFE is a ratio of a solid content similarly to the above. The weight of the carbonaceous powder in the negative electrode was 2.1 g.

The positive electrode and the negative electrode are spirally wound through a microporous film separator 3 made of polypropylene, and inserted into the case 4. After insertion, use titanium lead 5
Is spot-welded to the sealing plate 6 made of stainless steel. Reference numeral 7 denotes an aluminum positive electrode cap / positive terminal, which has a sealing plate 6 in advance.
Spot welded. Further, the negative electrode lead plate 11 is spot-welded to the center position of the circular bottom surface of the case 4 also serving as the negative electrode terminal. Reference numeral 8 denotes a polypropylene insulating gasket. Reference numeral 10 denotes a safety valve attached so that the internal gas is released to the outside when an abnormality occurs in the battery and the internal pressure of the battery increases. 12 is a polypropylene insulating bottom plate,
A hole is formed to have the same area as the space A generated at the time of winding.

After the above operation, an electrolytic solution containing 1 mol of LiPF ₆ as an electrolyte in a mixed solvent (volume ratio 1: 1) with ethylene carbonate and diethyl carbonate (2.
3 ml) Inject and seal. The HF concentration in the electrolyte is 30
ppm. The size of the completed battery is AA (14.5)
φmm × 50 mm).

Using the battery prepared by the above method, at 20 ° C.
Constant temperature, constant current of 0.2C from 4.2V to 3.0
Charge and discharge to V. The ratio of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle, and the cycle discharge capacity retention rate were measured.

[0028] Of these prototype batteries, those of Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 1.

[0029]

[Table 1]

(Example 1) In the above-mentioned AA battery,
Electrolytic manganese dioxide and lithium carbonate (Li ₂ CO ₃ ) were added to lithium manganate as a positive electrode active material using Li / Mn.
Mix at a molar ratio of 1.15: 2, and in the atmosphere 700 to 800
What was heated at 20 degreeC for 20 hours was used. Table 1 shows the chemical analysis results, specific surface area (m ² / g), initial discharge capacity (mAh), and cycle discharge capacity maintenance rate (%) of the obtained compound.
Shown in The specific surface area of this battery was 0.2 m ² / g.

Example 2 As lithium manganate,
First, electrolytic manganese dioxide and lithium carbonate (Li ₂ C
O ₃ ) was mixed at a Li / Mn molar ratio of 1.15: 2, and heat-treated in the air at 700 to 800 ° C. for 20 hours. Further, 0.05 mol of Li was added, and the mixture was heated again at 650 ° C. A battery was manufactured in the same manner as in Example 1, except that an active material having a Li / Mn ratio of 1.2: 2 was used. Table 1 shows the results of chemical analysis, the specific surface area, the initial discharge capacity, and the cycle discharge capacity retention of the obtained compound.

Example 3 As lithium manganate,
First, electrolytic manganese dioxide and lithium carbonate (Li ₂ C
O ₃ ) was mixed at a Li / Mn molar ratio of 1.15: 2, and heat-treated in the air at 700 to 800 ° C. for 20 hours. Further, 0.10 mol of Li was added, and the mixture was heated again at 650 ° C. A battery was fabricated in the same manner as in Example 1, except that an active material having a Li / Mn ratio of 1.25: 2 was used. Chemical analysis results of the obtained compound, specific surface area, initial discharge capacity,
Table 1 shows the cycle discharge capacity retention rate.

Comparative Example 1 As lithium manganate,
Electrolytic manganese dioxide and lithium carbonate (Li ₂ CO ₃ ) were mixed at a Li / Mn molar ratio of 1.0: 2,
A battery was manufactured in the same manner as in Example 1, except that a material heated at 20 ° C. to 800 ° C. for 20 hours was used as an active material. Chemical analysis results of the obtained compound, specific surface area, initial discharge capacity,
Table 1 shows the cycle discharge capacity retention rate.

Comparative Example 2 As lithium manganate,
Electrolytic manganese dioxide and lithium carbonate (Li ₂ CO ₃ ) were mixed at a Li / Mn molar ratio of 1.1: 2,
A battery was fabricated in the same manner as in Example 1, except that the material heated at ８００800 ° C. for 20 hours was used as an active material. Table 1 shows the chemical analysis results, the specific surface area, the initial discharge capacity, and the cycle discharge capacity retention of the obtained compound.

Comparative Example 3 As lithium manganate,
First, electrolytic manganese dioxide and lithium carbonate (Li ₂ C
O ₃ ) was mixed at a Li / Mn molar ratio of 1.15: 2, and heat-treated in the air at 700 to 800 ° C. for 20 hours. Then, 0.15 mol of Li was further added, and the mixture was heated again at 650 ° C. A battery was fabricated in the same manner as in Example 1, except that an active material having a Li / Mn ratio of 1.30: 2 was used. Chemical analysis results of the obtained compound, specific surface area, initial discharge capacity,
Table 1 shows the cycle discharge capacity retention rate.

As shown in Table 1 above, in Examples 1 to 3, the initial discharge capacity was relatively large, 400 to 342 mA / h, and the cycle discharge capacity retention rate was 80% to 80%.
As high as 91%, good performance was exhibited. In contrast, those of Comparative Examples 1 and 2 had an initial discharge capacity of 415 mA /
h and 408 mA / h, which were relatively large, but the cycle discharge capacity retention ratio was as small as 50% and 62%. In Comparative Example 3, the cycle discharge capacity retention rate was as high as 85%, but the initial initial discharge capacity was originally as small as 302 mA / h.

From these results, the Li / Mn ratio having a large initial discharge capacity and a high cycle discharge capacity retention ratio is the same as that of Examples 1 to 3, that is, Li is 1.15 to 2 mol of Mn. It has been found that a ratio of １．２1.25 mol is preferable.

Next, in order to examine the influence of the difference in specific surface area, as shown in Table 2, the Li / Mn ratio was kept constant at 1.2: 2, and the batteries of Examples 4 to 6 described below and Comparative Examples The batteries of Examples 4 and 5 were prototyped.

[0039]

[Table 2]

Example 4 As lithium manganate,
First, electrolytic manganese dioxide and lithium carbonate (Li ₂ C
O ₃₎ with Li / Mn molar ratio 1.15: 2 were mixed, after 15 hours of heat treatment at 700 to 800 ° C. in air, and further heated with 0.05 moles added again 650 ° C. The Li, final A battery was fabricated in the same manner as in Example 1, except that the active material having a Li / Mn ratio of 1.2: 2 was used. Chemical analysis results of the obtained compound, specific surface area, initial discharge capacity,
Table 2 shows the cycle discharge capacity retention ratio. The specific surface area of lithium manganate in this battery was 0.48 m ² /
g.

Example 5 A battery was manufactured in the same manner as in Example 4, except that the firing time at 700 to 800 ° C. was 25 hours. Table 2 shows the chemical analysis results, specific surface area, initial discharge capacity, and cycle discharge capacity retention of the obtained compound.
Shown in The specific surface area of this battery was 0.01 m ² / g.

Example 6 A battery was manufactured in the same manner as in Example 4 except that the firing time at 700 to 800 ° C. was 35 hours. Table 2 shows the chemical analysis results, specific surface area, initial discharge capacity, and cycle discharge capacity retention of the obtained compound.
Shown in The specific surface area of lithium manganate in this battery was 0.05 m ² / g.

Comparative Example 4 A battery was manufactured in the same manner as in Example 4 except that the firing time at 700 to 800 ° C. was changed to 10 hours. Table 2 shows the chemical analysis results, specific surface area, initial discharge capacity, and cycle discharge capacity retention of the obtained compound.
Shown in The specific surface area of lithium manganate in this battery was 0.78 m ² / g.

Comparative Example 5 A battery was manufactured in the same manner as in Example 4, except that the firing time at 700 to 800 ° C. was changed to 50 hours. Table 2 shows the chemical analysis results, specific surface area, initial discharge capacity, and cycle discharge capacity retention of the obtained compound.
Shown in The specific surface area of lithium manganate in this battery was 0.012 m ² / g.

As can be seen from Table 2 above, those of Examples 4 to 6 have an initial discharge capacity of 382 to 330 mA / h.
And the cycle discharge capacity retention rate is 85%
It was as high as ~ 91%, showing good performance. On the other hand, in the case of Comparative Example 4, the initial discharge capacity was relatively large at 400 mA / h, but the cycle discharge capacity maintenance ratio was as small as 70%. In Comparative Example 5, the cycle discharge capacity retention rate was as high as 92%, but the original initial discharge capacity was 3%.
It was as small as 00 mA / h.

From these results, it can be seen that the initial discharge capacity is large and the cycle discharge capacity retention rate is high in Examples 4 to 5.
6, and the specific surface area is 0.05 to 0.5.
It has been found that a range of m ² / g is preferred.

Next, the influence of the HF concentration in the electrolytic solution was examined.
In Table 3, the Li / Mn ratio is the same as in Example 2, 1.2:
2, the heat treatment time was also 20 hours, which was the same as in Example 2, and H
The battery characteristics of Examples 7 and 8 and Comparative Examples 6 to 9 when the F concentration is changed are shown.

[0048]

[Table 3]

(Example 7) When the HF concentration of the electrolytic solution was 40 p
A battery was produced in the same manner as in Example 2 except that the battery was pm. Table 3 shows the chemical analysis results, the specific surface area, the initial discharge capacity, and the cycle discharge capacity retention of the obtained compound.

(Embodiment 8) The HF concentration of the electrolytic solution was 50 p
A battery was produced in the same manner as in Example 2 except that the battery was pm. Table 3 shows the chemical analysis results, the specific surface area, the initial discharge capacity, and the cycle discharge capacity retention of the obtained compound.

(Comparative Example 6) When the HF concentration of the electrolytic solution was 60 p
A battery was produced in the same manner as in Example 2 except that the battery was pm. Table 3 shows the chemical analysis results, the specific surface area, the initial discharge capacity, and the cycle discharge capacity retention of the obtained compound.

(Comparative Examples 7 to 9) When the HF concentration of the electrolytic solution was 7
A battery was fabricated in the same manner as in Example 2, except that the content was 0 ppm. Chemical analysis result of the obtained compound, specific surface area,
Table 3 shows the initial discharge capacity and the cycle discharge capacity retention rate.

As can be seen from Table 3, in Examples 2 and 7 and 8 in which the HF concentration was 50% or less, the initial discharge capacity was relatively large at 350 to 348 mA / h.
The cycle discharge capacity retention ratio was as high as 90% to 87%, indicating good performance. On the other hand, those of Comparative Examples 6 to 9 in which the HF concentration exceeds 50 have an initial discharge capacity of 348 to 368 mA / h, which is relatively large, but a cycle discharge capacity retention ratio of 80 to 50%. Was small.

From these results, it can be seen that the HF concentration is closely related to the cycle discharge capacity retention rate of the battery, and
It has been found that the HF concentration is preferably set to 50 ppm or less in order to increase the cycle discharge capacity retention rate. In addition, it was found that when an electrolytic solution having a high HF concentration was used, a larger specific surface area was more likely to be adversely affected.

Next, a study was carried out on a system in which a transition metal M was added in the composition formula Li _x Mn _{2- y My} O ₄ . Table 4 shows Examples 9 and 10 and Comparative Example 1 using Cr as the transition metal M.
The battery characteristics of Examples 0 and 11 and Examples 11 and 12 using Co, Examples 13 and 14 using Ni, and Example 16 using Al are shown.

[0056]

[Table 4]

Example 9 As lithium manganate,
First, electrolytic manganese dioxide and lithium carbonate (Li ₂ C
O ₃ ) and chromium oxide at a Li / Mn / Cr ratio of 1.15:
1.95: mixed at 0.05, in air at 700-800 ° C
After heating for 20 hours, 0.05 mol of Li was further added, and the mixture was heated again at 650 ° C. and finally Li / Mn / Cr
A battery was fabricated in the same manner as in Example 1, except that the active material having a ratio of 1.2: 1.95 / 0.05 was used. Chemical analysis results of the obtained compound, specific surface area, initial discharge capacity,
Table 4 shows the cycle discharge capacity retention ratio.

Example 10 First, electrolytic manganese dioxide and lithium carbonate (Li ₂ C) were used as lithium manganate.
O ₃ ) and chromium oxide at a Li / Mn / Cr ratio of 1.15:
1.9: 0.1 and mixed in air at 700-800 ° C.
After heat treatment for 0 hour, 0.05 mol of Li is further added, and the mixture is heated again at 650 ° C. to use an active material having a final Li / Mn / Cr ratio of 1.2: 1.9: 0.1 A battery was fabricated in the same manner as in Example 1 except for the above. Table 4 shows the chemical analysis results, specific surface area, initial discharge capacity, and cycle discharge capacity retention of the obtained compound.

(Example 11) As lithium manganate, electrolytic manganese dioxide and lithium carbonate (Li ₂ C
O ₃ ) and cobalt oxide in a Li / Mn / Co ratio of 1.1
5: 1.95: 0.05, 700-80 in air
After heat treatment at 0 ° C. for 20 hours, Li was further added to 0.05
Mol and heated again at 650 ° C. and finally Li / Mn /
A battery was fabricated in the same manner as in Example 1, except that the active material having a Co ratio of 1.2: 1.95 / 0.05 was used.
Table 4 shows the chemical analysis results, specific surface area, initial discharge capacity, and cycle discharge capacity retention of the obtained compound.

(Example 12) As lithium manganate, electrolytic manganese dioxide and lithium carbonate (Li ₂ C
O ₃ ) and cobalt oxide in a Li / Mn / Co ratio of 1.1
5: 1.9: 0.1, 700-800 ° C in air
After heating for 20 hours, 0.05 mol of Li was further added, and the mixture was heated again at 650 ° C., and finally Li / Mn / Co
A battery was fabricated in the same manner as in Example 1, except that the active material having a ratio of 1.2: 1.9 / 0.1 was used. Table 4 shows the chemical analysis results, specific surface area, initial discharge capacity, and cycle discharge capacity retention of the obtained compound.

(Example 13) As lithium manganate, electrolytic manganese dioxide and lithium carbonate (Li ₂ C
O ₃ ) and nickel oxide at a Li / Mn / Ni ratio of 1.1
5: 1.95: 0.05, 700-80 in air
After heat treatment at 0 ° C. for 20 hours, Li was further added to 0.05
Mol and heated again at 650 ° C. and finally Li / Mn /
A battery was fabricated in the same manner as in Example 1, except that an active material having a Ni ratio of 1.2: 1.95: 0.05 was used.
Table 4 shows the chemical analysis results, specific surface area, initial discharge capacity, and cycle discharge capacity retention of the obtained compound.

Example 14 As lithium manganate, first, electrolytic manganese dioxide and lithium carbonate (Li ₂ C
O ₃ ) and nickel oxide at a Li / Mn / Ni ratio of 1.1
5: 1.9: 0.1, 700-800 ° C in air
After heating for 20 hours, 0.05 mol of Li was further added, and the mixture was heated again at 650 ° C. and finally Li / Mn / Ni
A battery was fabricated in the same manner as in Example 1, except that the active material having a ratio of 1.2: 1.9: 0.1 was used. Table 4 shows the chemical analysis results, specific surface area, initial discharge capacity, and cycle discharge capacity retention of the obtained compound.

Example 15 As lithium manganate, first, electrolytic manganese dioxide and lithium carbonate (Li ₂ C
O ₃ ) and aluminum oxide in a Li / Mn / Al ratio of 1.15:
1.95: mixed at 0.05, in air at 700-800 ° C
After heating for 20 hours, 0.05 mol of Li was further added, and the mixture was heated again at 650 ° C. and finally Li / Mn / Al
A battery was fabricated in the same manner as in Example 1, except that the active material having a ratio of 1.2: 1.95: 0.05 was used. Chemical analysis results of the obtained compound, specific surface area, initial discharge capacity,
Table 4 shows the cycle discharge capacity retention ratio.

(Example 16) As lithium manganate, electrolytic manganese dioxide and lithium carbonate (Li ₂ C
O ₃ ) and aluminum oxide in a Li / Mn / Al ratio of 1.15:
1.9: 0.1 and mixed in air at 700-800 ° C.
After heat treatment for 0 hour, 0.05 mol of Li is further added, and the mixture is heated again at 650 ° C. to use an active material having a final Li / Mn / Al ratio of 1.2: 1.9: 0.1. A battery was fabricated in the same manner as in Example 1 except for the above. Table 4 shows the chemical analysis results, specific surface area, initial discharge capacity, and cycle discharge capacity retention of the obtained compound.

Comparative Example 10 As lithium manganate, first, electrolytic manganese dioxide and lithium carbonate (Li ₂ C
O ₃ ) and chromium oxide in a Li / Mn / Cr ratio of 1.1:
1.95: mixed at 0.05, in air at 700-800 ° C
For 20 hours, and finally Li / Mn / Cr
A battery was fabricated in the same manner as in Example 1, except that the active material having a ratio of 1.2: 1.95 / 0.05 was used. Chemical analysis results of the obtained compound, specific surface area, initial discharge capacity,
Table 4 shows the cycle discharge capacity retention ratio.

Comparative Example 11 As lithium manganate, first, electrolytic manganese dioxide and lithium carbonate (Li ₂ C
O ₃ ) and chromium oxide at a Li / Mn / Cr ratio of 1.15:
1.9: 0.05, and heat-treated in the air at 700-800 ° C. for 20 hours. Then, 0.15 mol of Li was further added, and the mixture was heated again at 650 ° C., and finally the Li / Mn / Cr ratio was changed. A battery was fabricated in the same manner as in Example 1, except that an active material having a ratio of 1.3: 1.95: 0.05 was used. Table 4 shows the chemical analysis results, specific surface area, initial discharge capacity, and cycle discharge capacity retention of the obtained compound.

As shown in Table 4, similar results were obtained in the system to which the transition metal M was added, as in the system to which M was not added. That is, a material capable of doping and undoping lithium is used for the negative electrode, and a lithium manganese composite oxide given by a composition formula Li _x Mn _{2- y My} O ₄ (M is a transition metal or the like) is used for the positive electrode. In a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte obtained by dissolving an electrolyte in an organic solvent, in the lithium manganese composite oxide represented by the composition formula, the value of X is 1.15 to 1.25. Examples 10 to 1 having a specific surface area of 0.05 to 0.5 m ² / g.
In No. 6, the initial discharge capacity showed a relatively high value of 335 to 368 mAh, and the cycle discharge capacity maintenance ratio also showed a high value of 87 to 90%. On the other hand, Comparative Example 1 below the lower limit of X in the range of 1.15 to 1.25.
In the case of No. 0, the initial discharge capacity was as large as 398 mA / h, but the cycle discharge capacity maintenance ratio was as small as 70%.
In Comparative Example 11, which exceeds the upper limit of the range of 1.15 to 1.25 of X, the cycle discharge capacity retention ratio was 84%.
%, But the initial discharge capacity is 310 mA /
h, which was not good as the battery characteristics. When Al or Cr is used as M, Mn can be replaced with Mn up to about 30%.

Next, the effect of expanded graphite as a conductive agent was examined. Table 5 shows Example 1 when the type of the conductive agent was changed.
7, 18 and Comparative Examples 12 to 14 are shown together with Example 2 using expanded graphite as a conductive agent.

[0069]

[Table 5]

Comparative Example 12 A battery was manufactured in the same manner as in Example 2 except that the type of the conductive agent was acetylene black (AB). Table 5 shows the initial discharge capacity and the cycle discharge capacity retention of the battery.

Comparative Example 13 A battery was manufactured in the same manner as in Example 2 except that the type of the electric agent was flaky graphite. Table 5 shows the initial discharge capacity and the cycle discharge capacity retention of the battery.

Comparative Example 14 A battery was manufactured in the same manner as in Example 2 except that the type of the conductive agent was fibrous carbon. Table 5 shows the initial discharge capacity and the cycle discharge capacity retention of the battery.

Example 17 A battery was manufactured in the same manner as in Example 2 except that the type of the conductive agent was a mixture of acetylene black and expanded graphite in a ratio of 1: 9. Table 5 shows the initial discharge capacity and the cycle discharge capacity retention rate of the battery.
Shown in

Example 18 A conductive agent was a mixture of fibrous graphite and expanded graphite mixed at a ratio of 1: 9.
A battery was produced in the same manner as in Example 2. Table 5 shows the initial discharge capacity and the cycle discharge capacity retention of the battery.

As can be seen from Table 5, the batteries of Comparative Examples 12 to 14, which had the same structure as in Example 2 except for the composition of the conductive agent but did not contain expanded graphite in the conductive agent, had an initial discharge capacity of Although relatively high at 340 to 352 mAh, the cycle discharge capacity retention rate is only 70 to 81%. On the other hand, when expanded graphite is included in the conductive agent as in Example 2 or Examples 17 to 18, the cycle discharge capacity retention ratio increases to 90 to 92%. That is, the use of expanded graphite as described above improved the cycle discharge capacity retention rate.

[0076]

As described above, according to the present invention, the following excellent effects can be obtained.

According to the non-aqueous electrolyte secondary battery of the first aspect, the composition formula Li _x Mn _{2- y My} O is used as the positive electrode active material.
₄ (M is a transition metal), the value of X is in the range of 1.15 to 1.25, and the specific surface area is in the range of 0.05 to 0.5 m ² / g. As a result, the cycle stability and thermal stability of the battery are improved, and the cycle discharge capacity characteristics are improved.

Further, according to the non-aqueous electrolyte secondary battery according to the second aspect, since lithium hexafluorophosphate is used for the electrolyte and the amount of hydrogen fluoride in the electrolyte is 50 ppm or less, The damage of lithium manganate due to hydrogen hydride is reduced, and a decrease in the cycle discharge capacity retention rate can be suppressed.

Further, according to the non-aqueous electrolyte secondary battery according to the third aspect, since expanded graphite is contained as a conductive agent for the positive electrode, the cycle discharge capacity retention rate is increased, and the cycle discharge capacity retention rate is increased. Can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery according to one embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 positive electrode plate 2 negative electrode carbon material electrode 3 microporous film separator 4 case 5 lead 6 sealing plate 7 positive electrode cap and positive electrode terminal 8 insulating gasket 10 safety valve 11 negative electrode lead plate 12 insulating bottom plate

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hidenori Nakura 5-36-11 Shimbashi, Minato-ku, Tokyo Fuji Electric Chemical Co., Ltd. F-term (reference) 5H003 AA02 AA04 BB05 BB15 BD00 BD05 BD06 5H014 AA02 HH00 HH08 5H029 AJ03 AJ05 AK03 AL06 AL12 AM03 AM07 BJ02 BJ14 HJ02 HJ07 HJ10

Claims (3)

[Claims] 1. A negative electrode made of a material capable of doping and undoping lithium, and a positive electrode having a composition formula of Li _x Mn _2-y M _y O
_{4 In} a non-aqueous electrolyte secondary battery using a lithium manganese composite oxide given by (M is a transition metal) and a non-aqueous electrolyte obtained by dissolving an electrolyte in an organic solvent as an electrolyte, The lithium manganese composite oxide represented is
A non-aqueous electrolyte secondary battery characterized in that the value of X is in the range of 1.15 to 1.25 and the specific surface area is in the range of 0.05 to 0.5 m ² / g. 2. The electrolyte according to claim 1, wherein lithium hexafluorophosphate is used as the electrolyte, and the amount of hydrogen fluoride in the electrolyte is 50%.
The non-aqueous electrolyte secondary battery according to claim 1, wherein the content is not more than ppm. 3. The lithium secondary battery according to claim 1, wherein the positive electrode contains expanded graphite as a conductive agent.