JP3049892B2 - Positive electrode active material for non-aqueous electrolyte battery and non-aqueous electrolyte battery using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery,
In particular, the present invention relates to improvement of battery characteristics using a spinel-related manganese composite oxide containing copper for a positive electrode.

[0002]

2. Description of the Related Art In recent years, portable and cordless electronic devices such as AV devices and personal computers have been rapidly advanced, and there is a high demand for small, lightweight batteries having high energy density as power sources for driving these devices. In this respect, non-aqueous batteries, particularly lithium batteries, are expected to be particularly high-voltage, high-energy density batteries.

A spinel-related manganese composite oxide (LiMn ₂ O ₄ ) capable of inserting and extracting lithium as a positive electrode active material satisfying this demand.
Or layered compounds such as LiCoO ₂ , LiNiO ₂ (eg, US Pat. No. 4,302,518) and LiCo _x Ni _1-x
A composite oxide mainly composed of lithium and a transition metal (hereinafter, referred to as lithium composite oxide) such as O ₂ (x ≦ 0.27) (JP-A-62-264560) has been proposed. A high energy density secondary battery having a voltage of 4V class is being developed.

[0004]

SUMMARY OF THE INVENTION LiMn_TwoO_FourAnd LiC
oO_TwoIndicates a potential of 4 V or more with respect to lithium,
When used as an active material, secondary batteries with high energy density
Pond can be realized. However, such lithium composite oxidation
When the product is stored at a high temperature while being charged, its capacity is significantly reduced.
Problem. LiCoO_TwoHas a layered structure
The structure is safe due to lithium ions entering between the cage layers.
Has been standardized. Therefore, LiCoO _TwoThe positive electrode active material
When the battery is charged using the quality as a secondary battery,
When lithium ions are extracted between oxygen and cobalt
Is very unstable. As a result,
May be caused by crystal structure destruction during high temperature storage
Significant capacity degradation occurs. Mitigating such capacity deterioration
LiCoO_TwoWhen is used as a positive electrode active material
Depends on charging conditions or battery design._TwoIn
Extract about half of the lithium content and leave the remaining layer between layers.
Is used. High temperature in charged state by this method
Deterioration of storage capacity is alleviated, but utilization rate as an active material
A significant reduction in capacity due to halving
And On the other hand, LiMn_TwoO_FourHas a spinel structure
Is relatively more structurally stable than a layered structure
it is conceivable that. In actual charge, high temperature storage LiCo
O_TwoAlthough the capacity degradation is small compared to the case of
Absent. Further, LiMn_TwoO_FourCorresponds to two atoms of manganese
And only one atom of lithium can be used as 4V class
Therefore, the theoretical capacity per weight is LiCoO_TwoCompare with
Then it becomes quite small.

An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to provide a secondary battery which maintains a high operating voltage and has excellent charge / discharge characteristics and storage characteristics.

[0006]

In order to solve these problems, the present invention provides a spinel-related manganese oxide, C
By treating uMn ₂ O ₄ with an acid containing at least one of nitric acid, sulfuric acid and phosphoric acid, a part of copper is extracted from the crystal and Cu _x Mn ₂ O ₄ (provided that 0.05 ≦ x ≦ 0.3 ) Is used as a positive electrode active material, and is combined with a negative electrode made of lithium, a lithium alloy, a lithium-containing composite oxide or a carbonaceous material to form a nonaqueous electrolyte secondary battery. Alternatively, the spinel-related manganese oxide Cu
By treating Mn ₂ O ₄ with an acid containing at least one of nitric acid, sulfuric acid and phosphoric acid, a part of copper is extracted from the crystal and Cu _x Mn ₂ O ₄ (provided that 0.05 ≦ x ≦ 0.3 ) And further lithium addition with n-butyllithium, lithium iodide or lithium hydroxide to give Li
_y Cu _x Mn ₂ O ₄ (however, 0.05 ≦ x ≦ 0.3, 0.1 ≦
A non-aqueous electrolyte secondary battery is obtained by combining the composite oxide with y <2) as a positive electrode active material and a negative electrode made of lithium, a lithium alloy, a lithium-containing composite oxide or a carbonaceous material.

As the lithium salt used for the lithium addition, n-butyllithium, lithium iodide or lithium hydroxide is preferable.

[0008]

The spinel-related manganese oxide containing copper prepared by the method of the present invention is used as a positive electrode active material,
Significant capacity deterioration and cycle deterioration after high temperature storage in a charged state can be suppressed, and the battery discharge capacity can be increased as compared with the case where LiMn ₂ O ₄ is used. The elucidation of its mechanism of action is unclear at present, but it is speculated as follows.

When a battery using LiMn ₂ O ₄ or LiCoO ₂ as a positive electrode active material is stored at a high temperature in a charged state, the capacity and cycle characteristics of the battery after storage are extremely deteriorated. Although there are various factors in this, destruction of the crystal structure is considered to be an important factor, and suppressing such crystal destruction at a high potential is a very important point as a practical battery.
As one of the methods, as described above, there is a method in which the extraction of lithium from the active material is regulated by the charging conditions and the battery design, but this is not an essential improvement measure due to a significant decrease in the battery discharge capacity. . Since LiMn ₂ O ₄ has a spinel structure, it is more stable than a layered structure LiCoO ₂ , but is not sufficient. Cu _x M of the present invention
Since n ₂ O ₄ (where 0.05 ≦ x ≦ 0.3) allows copper to be inserted into the structure while maintaining the spinel crystal, the lithium ion insertion and desorption functions (battery active material Is maintained, and the crystal is stabilized. The amount of copper to be inserted will be described in the examples together with the experiment.
Up to mol% is good. This is thought to be because when more copper is inserted, the charge and discharge are repeated, whereby a part of the copper comes out of the crystal and deposits on the negative electrode to hinder the charge and discharge reaction of the negative electrode.

Cu _x Mn ₂ O ₄ (provided that 0.05 ≦ x ≦ 0.
In 3), the discharge capacity is increased as compared with LiMn ₂ O ₄ , and its action mechanism is speculated as follows. LiMn
_{When 2} O ₄ is used for the positive electrode, it is considered that the reaction shown in (Chem. 1) occurs by charging and discharging.

[0011]

Embedded image

When the value of y represented by Li _y Mn ₂ O ₄ is 0 <y
<1 indicates a potential of 4 V with respect to lithium, but 1 ≦ y <2
Is 3V. Therefore, when a 4V class battery is used, only the range of 0 <y <1 can be used. Since the voltage drop from 4 V to 3 V corresponds to the region where the crystal of the spinel changes from cubic to tetragonal, this falls from 4 V to 3 V.
It is considered to be a factor that causes V. Therefore, LiMn
_{In the} case of using ₂ O ₄ , lithium is 1 atom for 2 manganese at maximum. On the other hand, Li _y Cu _x Mn ₂ O ₄ (however, 0.0
In the case of 5 ≦ x ≦ 0.3, 0.1 ≦ y <2), the entry of copper affects the crystal change accompanying the reaction, and the area of cubic reaction increases, resulting in use as a 4V class battery. It is considered that the range (1 atom or more of lithium with respect to 2 atoms of manganese), that is, the discharge capacity can be increased.

Cu_xMn_TwoO_Four(However, 0.05 ≦ x ≦ 0.
3) Using the positive electrode active material as a positive electrode active material to constitute the positive electrode of a lithium
If Cu_xMn_TwoO_Four(However, 0.05 ≦ x ≦ 0.3)
Mix carbon material as conductive material and fluorine resin as binder
Dry at 250 ° C. under reduced pressure. Cu_xMn_TwoO_FourIs x
When the value of is 1, it is stabilized as a spinel crystal,
When copper is extracted by acid treatment, crystal stability decreases. One
In short, crystals are slightly broken when dried at 250 ° C under reduced pressure
Happens. To prevent this, spinel-related manganic acid
CuMn_TwoO_FourBy treating with acid
Is partially extracted from the crystal._xMn_TwoO_Four(However, 0.
05 ≦ x ≦ 0.3) and n-butyllithium
By adding lithium with a lithium salt such as Li_y
Cu_xMn _TwoO_Four(However, 0.05 ≦ x ≦ 0.3, 0.1 ≦
After setting y <2), the carbon material and the binder are mixed and reduced
If dried at 0 ° C., Li_yCu_xMn_TwoO_Four(However, 0.
05 ≦ x ≦ 0.3, 0.1 ≦ y <2) is the extracted copper
Instead of heat treatment because lithium stabilizes the crystal.
Active materials can be more effectively prevented
It is considered that it can be used in a typical way.

[0014]

The details and effects of the present invention will be described below with reference to examples.

(Embodiment 1) In the embodiment, the convenience of the test
Above, a coin-type battery was configured as a battery system and evaluated.
Was. FIG. 1 shows a vertical sectional view of the coin battery. In the figure
1 is an electrode formed by processing a stainless steel sheet resistant to organic electrolyte.
Pond case, 2 sealing plate made of the same material, 3 titanium
Welded on the inner surface of battery case 1
Have been. 4 is to deposit metallic lithium on the inner surface of the sealing plate 2.
Welded stainless steel expanded metal
The negative electrode is formed on the negative electrode current collector 5 of FIG. 6 is Cu_x
Mn_TwoO _Four7 parts by weight of carbon black for 100 parts by weight
Part, polytetrafluoroethylene resin powder 7 weight as binder
A predetermined amount of the mixture consisting of parts was molded on the positive electrode current collector 3
It is a positive electrode. Positive electrode at 250 ° C, negative electrode at 120 ° C
After drying under reduced pressure, it was used for battery assembly. 7 is made of micropore
Separator made of polypropylene, 8 is made of polypropylene
It is an insulating gasket. Ethylene carbonate is used as the electrolyte.
1: 1 mixed solvent of diethyl carbonate and diethyl carbonate
And 1 mol / L of lithium hexafluorophosphate as solute
What was dissolved at the concentration of The dimensions of this battery
The diameter is 20 mm and the total height of the battery is 1.6 mm.

Cu _x Mn ₂ O ₄ was prepared by the following method. First, manganese carbonate and copper carbonate are mixed so that the atomic ratio of manganese to copper becomes 2: 1. Then, the powder is press-molded and mixed in a mixed gas stream of the same volume of carbon dioxide and oxygen.
By calcination at 0 ° C. for 12 hours, CuMn ₂ O ₄ was synthesized. After pulverizing the fired product, 150 g of CuMn was added to 4 liters of water.
₂ O ₄ was added, and dilute sulfuric acid was added dropwise with stirring. At this time, the pH of the solution was changed from 1 to 5 and maintained at that pH for 1 hour. Since the amount of copper extracted from the crystal varies depending on the value of the retained pH, Cu _x Mn ₂ O ₄ having various values of x can be adjusted by changing the pH variously. The prepared Cu _x Mn ₂ O ₄ was used as a positive electrode active material in the above-described battery and evaluated.

The charge / discharge cycle test was performed at 20 ° C. under the conditions of a charge current of 0.5 mA, a charge end voltage of 4.2 V, a discharge current of 1 mA, and a discharge end voltage of 3.0 V. FIG. 2 shows the charge / discharge cycle characteristics after storage at a high temperature. Test 2
After 10 cycles of charge / discharge at 0 ° C., the battery was stored in a charged state at 60 ° C. for 2 weeks, and the charge / discharge cycle test was performed again. FIG. 2 shows the number of cycles when the discharge capacity of the 10th cycle before storage reached 50% of the discharge capacity in the cycle after storage, as Cu _x Mn ₂ O _4.
It is the figure plotted with respect to x of FIG. The point where the value of x is 0 is the case where conventionally used LiMn ₂ O ₄ is used as the positive electrode active material. From FIG. 2, it can be seen that, even after storage, the value of x is in the range of 0.05 to 0.3, the characteristics are 100 cycles or more, and the life is at least twice as long as that of the conventional LiMn ₂ O _4. I understand. When x exceeds 0.3, the cycle life is remarkably reduced.
It is considered that when there is copper exceeding the limit, part of the copper comes out of the crystal and precipitates on the negative electrode by repeating charge / discharge, thereby obstructing the charge / discharge reaction of the negative electrode. Therefore, the value of x is desirably 0.05 to 0.3. In this embodiment, lithium metal was used for the negative electrode, but lithium alloy or LiN
It may be a lithium composite oxide such as b ₂ O ₅ . When a carbonaceous material is used for the negative electrode, lithium metal is adhered in a dry state on the positive electrode or the negative electrode filled in the case,
The electrolyte is injected from above and short-circuited to allow lithium to be absorbed in the positive or negative electrode, and then the battery is assembled. The same result as that of the present example was obtained by making up for the shortage of lithium existing in the battery system by this method. As the electrolyte, a solution in which lithium hexafluorophosphate was dissolved at a concentration of 1 mol / liter as a solute in a 1: 1 equal volume mixed solvent of ethylene carbonate and diethyl carbonate was used. The same applies to an electrolyte in which a lithium salt is dissolved.

(Example 2) Next, CuMn ₂ O ₄ , which is a spinel-related manganese oxide, is treated with an acid.
A lithium-containing composite oxide, which is obtained by extracting a part of copper from the crystal to obtain Cu _x Mn ₂ O ₄ and further adding lithium with a lithium salt such as lithium iodide to obtain Li _y Cu _x Mn ₂ O _4, is used as a positive electrode active material. An example used in the description will be described.

A method for synthesizing Li _y Cu _x Mn ₂ O ₄ will be described. First, Cu _x Mn ₂ O ₄ having various values of x is synthesized by the same method as shown in the first embodiment. Next, lithium iodide is added and reacted at 150 ° C. in a nitrogen stream to obtain Li
synthesizing _y Cu _x Mn ₂ O _4. At this time, the value of y was variously changed depending on the amount of lithium iodide added. The same applies when lithium hydroxide is used as the lithium salt.
In the case of using n-butyllithium as the lithium salt, in this example, Cu _x Mn ₂ was added in dry hexane under a nitrogen atmosphere.
Li _y Cu _x Mn ₂ O ₄ was synthesized by adding O ₄ powder and n-butyl lithium and reacting for several days. The y value was changed by the amount of n-butyllithium added. A coin-shaped battery was prepared from the thus prepared active material in the same manner as in Example 1, and evaluated. The results are shown in Tables 1 to 3. Tables 1, 2, and 3 show that the lithium salts used for lithium addition were lithium iodide, lithium hydroxide,
of n-butyl lithium. Although the y value in the table is not an accurate value in terms of synthesis, a value close to this value was selected. The discharge capacity at the 10th cycle before storage in the table is shown by a ratio when the discharge capacity when LiMn ₂ O ₄ conventionally used is used as the positive electrode active material is set to 100. LiMn ₂
The characteristics using O ₄ are shown at the top of the table.
Example 1 shows the number of cycles until the capacity reaches 50% after storage.
This is the same evaluation method as that shown in.

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

[Table 3]

From the table, when any lithium salt is used,
Also, conventional when 0.05 ≦ x ≦ 0.3 and 0.1 ≦ y <2
LiMn used more_TwoO_FourCompared to using
The discharge capacity has increased and the cycle life after storage has also increased.
You can see that Also, Cu _xMn_TwoO_FourLithium added
2 and Table 1 are compared with the case where
As can be seen from the comparison, the cycle life after storage is increased.
You can see that it is doing. In this embodiment, lithium gold is used for the negative electrode.
Metals, but lithium alloy or LiNb _TwoO_FiveSuch
May be used as the lithium composite oxide. Carbonaceous material for negative electrode
If a positive electrode or negative electrode is used,
Attach the lithium metal on top of it in a dry state and remove the electrolyte.
Positive electrode or negative electrode
After assembling lithium into the battery, the battery is assembled. This way
To compensate for the lack of lithium in the battery system
Similar results were obtained. The electrolyte contains ethylene carbonate.
And diethyl carbonate in a 1: 1 equal volume mixed solution
1 mol / liter of lithium hexafluorophosphate as a solute
Dissolved at a concentration of Torr, but used in other solvents.
The same applies to an electrolytic solution in which a sodium salt is dissolved.

[0024]

As is apparent from the above description, according to the present invention, CuMn ₂ which is a spinel-related manganese oxide
By treating O ₄ with an acid, a part of copper is extracted from the crystal and Cu _x Mn ₂ O ₄ is used as the positive electrode active material, and lithium, lithium alloy, lithium-containing composite oxide, or carbonaceous material is used as the positive electrode active material. A non-aqueous electrolyte secondary battery combined with a negative electrode made of a material, or Cu _x Mn ₂ O ₄ (0.05 ≦ x ≦ 0.3), and then n-butyl lithium and lithium iodide Alternatively, a composite oxide having Li _y Cu _x Mn ₂ O ₄ (0.05 ≦ x ≦ 0.3, 0.1 ≦ y <2) obtained by adding lithium with lithium hydroxide is used as a positive electrode active material, and lithium is added. By combining a lithium alloy, a lithium-containing composite oxide, or a negative electrode made of a carbonaceous material with a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery having excellent cycle characteristics and high-temperature storage characteristics can be obtained. Can You.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a coin-type battery according to an embodiment of the present invention.

FIG. 2 is a diagram showing charge / discharge cycle characteristics after high-temperature storage.

[Description of Signs] 1 Battery case 2 Sealing plate 3 Positive electrode current collector 4 Negative electrode 5 Negative electrode current collector 6 Positive electrode 7 Separator 8 Insulating gasket

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-271365 (JP, A) JP-A-63-114064 (JP, A) JP-A-2-267861 (JP, A) M. Taracon et al. , "The Spinel Phase of LiMn Lower 2 O Lower 4 as a Cathode in Secondary Lithium Cells", Journal of the Electrochemical Society, 1991. 138, no. 10, p2859-2864 (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/50 H01M 4/48 H01M 10/40

Claims (6)

(57) [Claims] 1. Cu which is a spinel-related manganese oxide
By treating Mn ₂ O ₄ with an acid containing at least one of nitric acid, sulfuric acid and phosphoric acid, a part of copper is extracted from the crystal and Cu _x Mn ₂ O ₄ (provided that 0.05 ≦ x ≦ 0.3 The positive electrode active material for a non-aqueous electrolyte battery comprising the composite oxide described above. 2. Cu which is a spinel-related manganese oxide
By treating Mn ₂ O ₄ with an acid containing at least one of nitric acid, sulfuric acid and phosphoric acid, a part of copper is extracted from the crystal and Cu _x Mn ₂ O ₄ (provided that 0.05 ≦ x ≦ 0.3 A) a non-aqueous electrolyte battery comprising a positive electrode made of a composite oxide, a negative electrode made of lithium, a lithium alloy, a lithium-containing composite oxide or a carbonaceous material, and a non-aqueous electrolyte. 3. Cu which is a spinel-related manganese oxide
By treating Mn ₂ O ₄ with an acid containing at least one of nitric acid, sulfuric acid and phosphoric acid, a part of copper is extracted from the crystal and Cu _x Mn ₂ O ₄ (provided that 0.05 ≦ x ≦ 0.3 ), And further by adding lithium with a lithium salt, Li _y Cu _x Mn ₂ O ₄ (provided that 0.05 ≦ x ≦ 0.3,
A positive electrode active material for a non-aqueous electrolyte battery, wherein 0.1 ≦ y <2). 4. The positive electrode active material for a non-aqueous electrolyte battery according to claim 3, wherein the lithium salt is n-butyllithium, lithium iodide or lithium hydroxide. 5. A spinel-related manganese oxide, CuM
By treating n ₂ O ₄ with an acid containing at least one of nitric acid, sulfuric acid and phosphoric acid, a part of copper is extracted from the crystal and Cu _x Mn ₂ O ₄ (provided that 0.05 ≦ x ≦ 0.3 )age,
Further, by adding lithium with a lithium salt, Li is added.
_y Cu _x Mn ₂ O ₄ (however, 0.05 ≦ x ≦ 0.3, 0.1 ≦
y <2), a positive electrode made of a composite oxide, lithium,
A non-aqueous electrolyte battery comprising a negative electrode made of a lithium alloy, a lithium-containing composite oxide or a carbonaceous material, and a non-aqueous electrolyte. 6. The non-aqueous electrolyte battery according to claim 5, wherein the lithium salt is n-butyl lithium, lithium iodide or lithium hydroxide.