JPH1145712A - Nonaqueous electrolytic secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide battery performance which has a high discharge potential, a large discharge capacity, and is excellent in safety and cycle characteristics, by constituting negative electrode active material with a compound oxide which contains Sn, Zn, and P. SOLUTION: Composition ratio of Zn and P to Sn is important to provide noncrystalline compound oxide containing Sn, Zn, and P, and this is compound oxide represented by a formula SnZnh PiOj (where, 0.01<=h<=1.0, 0.1<=i<=2.0, 2.0<=j<=5.0). In order to provide further noncrystallization, it is more preferably 0.02<=h<=0.2, 0.25<=i<=1.5, 2.0<=j<=4.0. In negative electrode active material, preferably in respect of noncrystallization, component other than Sn, Zn, P, or O is at least one kind selected in a group of F, Al, Cu, Ni, Mn, Co, Fe, Bi, Sb, Cr, Ti, Zr, In, and Ga. Total amount of these components is preferably not more than 20 atom% to Sn, more preferably not more than 10 atom%.

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 secondary battery using a negative electrode active material which is excellent in charge / discharge characteristics such as discharge potential, discharge capacity and charge / discharge cycle life and has high safety.

[0002]

2. Description of the Related Art As a negative electrode active material for a non-aqueous electrolyte secondary battery, a lithium metal or a lithium alloy which has been studied since the beginning of commercialization of a lithium secondary battery is typical. It grows dendritic and shorts inside,
There was a risk of fire.

On the other hand, fired carbonaceous materials that can store and release lithium have been put to practical use to enhance safety. However, since such a carbonaceous material itself has conductivity, there is a risk that dendritic lithium metal is deposited on the carbonaceous material when overcharged or rapidly charged. As a countermeasure at present, a system for preventing a charger and overcharging has been introduced. However, the charge / discharge capacity of the carbonaceous material has been limited. Also,
Since the carbonaceous material has a low density, there is a disadvantage that the capacity per unit volume is small.

[0004] On the other hand, many studies have been made on a negative electrode active material for practical use of a non-aqueous electrolyte secondary battery which is highly safe and has a high discharge potential and a high discharge capacity. Recently, Sn oxides and composite oxides containing Sn have been proposed as negative electrode materials (JP-A-6-3383).
25, JP-A-7-122274, JP-A-7-28812
3, JP-A-8-138653, JP-A-8-20352
7). However, even when these oxides and composite oxide-based materials are used as the negative electrode active material, the cycle characteristics are not sufficient, and the charge / discharge cycle characteristics are more excellent, and have higher discharge potential and higher discharge capacity. A negative electrode active material for obtaining a non-aqueous electrolyte secondary battery is desired.

[0005]

SUMMARY OF THE INVENTION The present invention provides a non-aqueous electrolyte secondary battery having high safety, high discharge potential, high discharge capacity, and excellent cycle characteristics by examining a negative electrode active material. It is intended to provide a battery.

[0006]

SUMMARY OF THE INVENTION The present invention provides a positive electrode, a negative electrode,
And a non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte containing a lithium salt, wherein the active material of the negative electrode is a composite oxide containing Sn, Zn, and P. Provide batteries.

The present inventors have conducted intensive studies on the negative electrode active material of the non-aqueous electrolyte secondary battery, and found that adding Zn to the composite oxide of Sn and P as the negative electrode active material is secondary. It has been found that there is a remarkable effect in improving the cycle characteristics of the battery and achieving higher performance.

[0008] Although the reason is not clear, the amount of lithium that can be stored and released in the composite oxide of Sn and P is 8 equivalents, but by adding Zn to this composite oxide, it is possible to store and release lithium. It is considered that the amount of lithium increases to about 10 equivalents, and as a result, the capacity of the secondary battery increases and the performance increases. It is also considered that the addition of Zn stabilizes the structure of the composite oxide of Sn and P in a state where lithium is absorbed, and as a result, the cycle characteristics are improved. In the present specification, the expression “A equivalent of lithium is occluded in the composite oxide of Sn and P” means that the number of lithium atoms occluded with respect to Sn1 atoms in the composite oxide is A
Indicates that this is, for example, in the SnZn _h P _i O _j means that the _{Li A SnZn h P i O j} .

The composite oxide containing Sn, Zn, and P used in the present invention is required to be amorphous in order to exhibit high performance and high durability when used as a negative electrode active material for a non-aqueous electrolyte secondary battery. Preferably, it is quality. The term amorphous here means C
In X-ray diffraction using uKα ray, a small amount of crystalline peak may be present, but as a whole, 20 to 7 in 2θ value.
A substance that gives a broad scattering band over the entire range of 0 degrees.

In the present invention, Sn, Zn, and P
May have a crystalline peak in the range of 2 to 30 degrees in the 2θ value, and the peak intensity of the broad scattering band in the range of 20 to 40 degrees in the 2θ value is as follows. It is preferable that the intensity is not more than three times the intensity of the peak of the mountain.

In the synthesis of the composite oxide containing Sn, Zn, and P in the present invention, Sn, Z
It is preferable to use each oxide of n and P. Here, the oxide of the raw material includes a compound which becomes an oxide by a chemical treatment, a heat treatment, or the like, for example, a hydroxide, a salt of a carbonate, a nitrate, or the like.

As the Sn compound as a raw material, SnO,
Basically, any of SnO ₂ , Sn hydroxide, and Sn compound which becomes an oxide by thermal decomposition can be used.
Carbonates, nitrates, organic salts, halogen salts and the like,
Specific examples include tin carbonate and tin oxalate. The valence of Sn of the Sn compound as a raw material is preferably divalent, and particularly preferably SnO, from the viewpoints of amorphization and structural stability of the obtained composite oxide.

In the present invention, Zn promotes amorphization. As the Zn compound as a raw material, basically any oxide, hydroxide, or compound that becomes zinc oxide by thermal decomposition can be used, and examples thereof include zinc carbonate and zinc oxalate. Among them, zinc oxide is particularly preferred. Examples of the P compound as a raw material include phosphorus pentoxide,
Phosphorus pentachloride, orthophosphoric acid and the like.

In the present invention, in order to make the composite oxide containing Sn, Zn and P amorphous, Z
The composition ratio of n and P is important, and is preferably represented by Formula 1. SnZn _h P _i O _j ··· Formula 1 However, in the formula 1, 0.01 ≦ h ≦ 1.0,0.1
≤ i ≤ 2.0 and 2.0 ≤ j ≤ 5.0. In order to promote the amorphization, in Expression 1, 0.02 ≦ h ≦ 0.2,
More preferably, 0.25 ≦ i ≦ 1.5 and 2.0 ≦ j ≦ 4.0.

In the present invention, the negative electrode active material is S
Although a composite oxide consisting of only n, Zn, P, and O may be used,
Components other than Sn, Zn, P, and O may be contained in an amount of 20 atomic% or less based on Sn. Components other than Sn, Zn, P, and O include F, Al, Cu, Ni, Mn, Co, Fe, and B.
From the viewpoint of amorphization, at least one selected from the group consisting of i, Sb, Cr, Ti, Zr, In and Ga is preferable. These components are preferably 20 atomic% or less, and more preferably 10 atomic% or less, based on Sn in total.

Al, Cu, Ni, Mn, Co, Fe, B
As raw materials for i, Sb, Cr, Ti, Zr, In and Ga, in addition to metal oxides, any compounds that can be converted to oxides by chemical treatment and heat treatment, such as carbonates, halides, and organic salts, are used. it can. In the case of F, use of tin fluoride is preferred.

The composite oxide containing Sn, Zn and P used in the present invention is preferably obtained by mixing the raw materials, drying and then melting and firing. Regarding the mixing of the raw materials, they can be dispersed in water and wet-mixed, or when all the raw materials are solid, they may be mixed as they are with a jet mill or a rotary stirrer. In the case of wet mixing, drying is performed by heat treatment under normal pressure or reduced pressure. Drying and baking can also be performed sequentially using a melting furnace.

The melting and firing conditions are as follows.
It is preferable that the temperature is 1500C. The firing atmosphere is
An air atmosphere or an inert atmosphere such as nitrogen or argon may be used, but an inert atmosphere is preferable because Sn is easily maintained in a divalent state. The melt-fired product is flake-like amorphous composite oxide by being ruptured or flown on a water-cooled roller and rapidly cooled. This is pulverized using a pulverizer such as a ball mill until the average particle size becomes about several tens μm to about several μm, and further classified appropriately for use. Further, the shape of the pulverized material is preferably uniform, and more preferably spherical, and can be uniformly applied when applied on the current collector, and the battery performance is stabilized.

As the positive electrode active material used in the nonaqueous electrolyte secondary battery of the present invention, a lithium-containing metal oxide is preferable, and Li _x CoO ₂ , LiNiO ₂ , LiMnO _2
2 , LiMn ₂ O ₄ , Li _y Co _a Ni _1-a O ₂ (where 0.7 ≦ x ≦ 1.2, 0.7 ≦ y ≦ 1.2, 0.1
≤ a ≤ 0.9).

The positive electrode and the negative electrode used in the non-aqueous electrolyte secondary battery of the present invention can be produced by coating a positive electrode mixture or a negative electrode mixture on a current collector or molding them into pellets. At this time, as the negative electrode material, various carbon materials conventionally used for the composite oxide containing Sn, Zn, and P of the present invention, for example, coke, resin fired body, graphite, graphitized mesocarbon microbeads and the like are used. Can be included. Further, the positive electrode mixture or the negative electrode mixture may contain, in addition to the positive electrode active material or the negative electrode active material, respectively, a conductive agent, a binder, a dispersant, a filler, an ionic conductive agent, a pressure enhancer, and various additives. Can be.

The negative electrode active material used in the present invention can store Li in advance before assembling as a battery. Specifically, lithium metal, lithium alloy (Li-
Al) and a lithium compound (such as n-butyllithium) chemically and electrochemically. Preferably, it is a method in which metallic lithium is kneaded or pressure-bonded in the presence of an electrolytic solution used in a battery. The amount of occlusion can be up to about 1 to 12 equivalents to Sn in the negative electrode material, but is preferably 1 to 6 equivalents.

Graphite, acetylene black, carbon black and the like can be used as a conductive agent for the positive electrode and the negative electrode that can be used in the present invention. As a binder for the positive electrode and the negative electrode that can be used in the present invention, polytetrafluoroethylene (hereinafter, referred to as PTFE), polyvinylidene fluoride, propylene-tetrafluoroethylene copolymer, propylene-
A tetrafluoroethylene-vinylidene fluoride copolymer or the like can be used.

In the present invention, aluminum, nickel, titanium and the like can be used as the current collector of the positive electrode, and copper, nickel, gold and the like can be used as the current collector of the negative electrode. As the separator interposed between the positive electrode and the negative electrode, a polyolefin-based material can be preferably used, and specifically, a porous film of polypropylene or polyethylene can be preferably used.

In the non-aqueous electrolyte of the present invention, the solvent is propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, 1,2-
Dimethoxyethane and the like can be used. As electrolytes, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃
CO ₂ or the like can be used.

[0025]

EXAMPLES Examples and comparative examples of the present invention will be described below, but the present invention is not limited to the examples. In each of the following examples, the negative electrode active material in the present invention was used as the positive electrode active material in view of the potential because Li metal was used as the active material of the opposing electrode. For the relative evaluation of the performance of the active material with respect to the charge and discharge characteristics, the discharge capacity and the cycle characteristics were evaluated.

Example 1 (Example) 310 of SnO was placed in a 1-liter glass three-necked flask equipped with a stirrer.
6 g, 15.2 g of ZnO, and 300 g of pure water were added, and 283.0 g of orthophosphoric acid was added dropwise with stirring at room temperature over 1 hour. The obtained slurry was dried at 120 ° C. to obtain a raw material mixture. This raw material mixture was put in a quartz crucible, melted and fired in an argon atmosphere at 1000 to 1100 ° C. for 1 hour, and the melt was flowed on a water-cooled rotary roller to form a flake-like amorphous compound. Obtained. The composition of this compound was SnP _1.06 Zn _0.08 O _3.8 . This was coarsely pulverized by a ball mill and subsequently pulverized by a jet mill to obtain a fine powder having an average particle diameter of 5 μm.

The above fine powder, acetylene black, and P
TFE was mixed at a weight ratio of 80/16/4. This mixture is formed into a sheet by a roller press,
Heat-treated at 0 ° C, the sheet (thickness 0.2mm)
An electrode was punched out to 2.7 mm.

The obtained electrode was used as a positive electrode, a lithium foil was used as a negative electrode, and a mixed solvent of ethylene carbonate and diethyl carbonate (weight ratio of 1/1/1) was used as an electrolytic solution.
Using a solution in which 1 mol / l of LiPF ₆ was dissolved in 1), a closed pressure type two-electrode cell (J. Electroche) was used.
m. Soc. , 136, 3169 (1989)) and a charge / discharge test was performed. The discharge cut voltage was 0.02 V and the charge voltage was 2.5 V. 2
Table 1 shows the discharge capacity after the cycle, after the 20th cycle, and after the 100th cycle. FIG. 1 shows charge / discharge characteristics and cycle characteristics based on charge / discharge potential curves at the second cycle and the 20th cycle.

Examples 2 to 5 (Examples) In the same manner as in Example 1, the following amorphous compounds were obtained. The mixing ratio of the raw materials is an atomic ratio. In Example 1, Sn: P: Zn: Ni =
100: 106: 8: 2, Example 2: Sn: P: Zn: C
o = 100: 106: 8: 2, and in Example 3, Sn: P: Z
n: In = 100: 106: 8: 2, and in Example 4, Sn:
P: Zn: F = 100: 106: 8: 2, and Ni, Co, In, F
iO, Co ₃ O ₄ , In ₂ O ₃ , and SnF ₂ were used. For Examples 2 to 5, the cycle characteristics were measured in the same manner as in Example 1,
The results are shown in Table 1.

Example 2: SnP _1.06 Zn _0.08 Ni _0.02 O _4.0 , Example 3: SnP _1.06 Zn _0.08 Co _0.02 O _4.0 , Example 4: SnP _1.06 Zn _0.08 In _0.02 O _4.0 , Example 5: SnP _1.06 Zn _0.08 F _0.02 O _3.8 .

Examples 6 to 9 (Comparative Examples) In the same manner as in Example 1, the following amorphous compounds were obtained. The mixing ratio of the raw materials is an atomic ratio. In Example 6, Sn: P = 100: 10
6, Sn: P: B = 10: 6: 4 in Example 7, S in Example 8
n: P = 10: 3, and in Example 9, Sn: B = 10: 3 were mixed, and B ₂ O ₃ was used as a raw material of B. The cycle characteristics of Examples 6 to 9 were measured in the same manner as in Example 1,
The results are shown in Table 1.

Example 6: SnP _1.06 O _3.2 , Example 7: SnP _0.6 B _0.4 O _3.1 , Example 8: SnP _0.3 O _m , Example 9: SnB _0.3 O _n . However, in Example 8, 1.75 ≦ m ≦ 2.05,
In Example 9, 1.45 ≦ n ≦ 1.75.

When the composite oxide containing Sn, Zn, and P in the present invention is used as a positive electrode active material, it has a large discharge capacity and a high capacity retention rate after a charge / discharge cycle test. Therefore, even when these composite oxides are used as a negative electrode active material, a secondary battery having a large discharge capacity and excellent charge / discharge cycle characteristics can be obtained.

[0034]

[Table 1]

[0035]

According to the present invention, a non-aqueous electrolyte secondary battery having a large discharge capacity and good cycle characteristics can be provided.

[Brief description of the drawings]

FIG. 1 is a graph of charge and discharge characteristics at the second cycle and the 20th cycle in Example 1.

Claims (4)

[Claims] 1. A nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a nonaqueous electrolyte containing a lithium salt, wherein the active material of the negative electrode is a composite oxide containing Sn, Zn, and P. Characteristic non-aqueous electrolyte secondary battery. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein said composite oxide is amorphous. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the active material of the negative electrode is a composite oxide represented by Formula 1. SnZn _h P _i O _j ··· Formula 1 (where in Formula 1, 0.01 ≦ h ≦ 1.0,0.
1 ≦ i ≦ 2.0 and 2.0 ≦ j ≦ 5.0. ) 4. An active material for a negative electrode comprising F, Al, Cu, Ni,
Mn, Co, Fe, Bi, Sb, Cr, Ti, Zr, I
4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery contains at least one element selected from the group consisting of n and Ga in a total amount of 20 atomic% or less based on Sn.