JPH08190933A - Secondary battery having nonaqueous solvent electrolyte - Google Patents

Abstract

PURPOSE: To provide a secondary battery with high energy density, high rate discharge and quick charge capability, long charge/discharge life, and low cost. CONSTITUTION: A secondary battery has a negative electrode 2 capable of charging/discharging a lithium ion, a positive electrode 6 capable of conducting reversible electrochemical reaction with a lithium ion, and an electrolyte 3 prepared by dissolving an ion dissociative lithium salt in a nonaqueous solvent. In this secondary battery, a positive active material which requires charging end voltage of 3.5V or higher is used in the positive electrode 6, as the nonaqueous solvent of the electrolyte 3, a mixture of ethylene carbonate and ester or ether having lower viscosity than the ethylene carbonate is used, and the volume mixing ratio is more than 5:5 but less than 0:10. As the example of the ester or ether, di-lower alkyl carbonate and 1,2-di-lower alkoxy ethane are used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery having a non-aqueous solvent electrolyte having a high voltage, a high energy density and a large charge / discharge capacity.

[0002]

2. Description of the Related Art As portable electronic devices have become smaller and lighter, (1) they have a high voltage and a high energy density as their power sources, and (2) they can be rapidly charged with a large current discharge due to their intended use.
(3) A charge / discharge life is long, and (4) an inexpensive secondary battery is required. As a battery that meets such demands, development of a high-performance secondary battery having a negative electrode capable of charging and discharging lithium ions and a positive electrode capable of charging and discharging lithium ions, that is, a lithium secondary battery is expected. The nickel-cadmium batteries, nickel-hydrogen batteries, and lead-acid batteries that are currently commercially available as secondary batteries have the characteristics that they can be rapidly charged, but their battery voltage and energy density are low, and the requirements currently demanded. Can't answer. On the other hand, a so-called lithium-ion battery using an intercalation compound of carbon doped with lithium ions or a graphite intercalation compound as a negative electrode material is a nickel-cadmium battery,
It has higher voltage and higher energy density than nickel-metal hydride batteries and lead storage batteries. However, this lithium ion battery has the following four problems to be solved. (Problem 1) It is inferior in both voltage and energy density as compared with a lithium secondary battery using metallic lithium for the negative electrode. (Problem 2) Since diffusion of lithium ions in the negative electrode is slow, high-current discharge rapid charging cannot be performed. (Problem 3) If only the negative electrode is changed to metallic lithium in order to increase the voltage and energy density, the charge / discharge efficiency of the negative electrode is particularly low, which shortens the charge / discharge cycle life and requires optimization of each material. Furthermore, (Problem 4)
The manufacture of lithium-ion batteries involves a special process, which makes the cost of manufacturing large-capacity batteries very high.

[0003]

The present invention has been made by paying attention to the above-mentioned four problems, that is, a positive electrode, a negative electrode,
An object of the present invention is to provide a lithium secondary battery which has a high energy density, is capable of high-current discharge rapid charging, has a long charge / discharge life, and is inexpensive with an optimal combination of electrolytic solutions.

[0004]

The present invention will be described in brief. The present invention relates to a secondary battery having a non-aqueous solvent electrolyte, wherein the negative electrode is capable of charging and discharging lithium ions, and reversible with lithium ions. Positive electrode capable of electrochemical reaction, and a secondary battery having an electrolytic solution in which a non-aqueous solvent contains an ion-dissociative lithium salt dissolved therein, the positive electrode active material requiring a charge end voltage of 3.5 V or more as the positive electrode. Is used for the positive electrode,
As the non-aqueous solvent of the electrolytic solution, a mixed solvent of ethylene carbonate and an ester or ether having a viscosity lower than the ethylene carbonate is used, and the volume mixing ratio exceeds 5: 5,
It is characterized in that it is less than 0:10.

According to the present invention, a positive electrode active material requiring a cut-off voltage of 3.5 V or more, particularly Li _x Mn _{2- y My.}
O ₄ (M = Na, Mg, Sc, Y, Fe, Co, Ni,
Cu, Zn, Al, Pb, Sb, 0 ≦ x ≦ 1.2, 0 ≦
composite oxide mainly composed of y ≦ 0.7) or Mn ₂ O
A compound oxide mainly composed of ₄ is used for the positive electrode, a negative electrode material capable of charging and discharging lithium ions, particularly metallic lithium or a lithium metal alloy is used, and ethylene carbonate (EC) is used as a solvent for the non-aqueous solvent electrolytic solution. Large current discharge and rapid charging by using a solvent having a viscosity lower than EC, especially a mixed solvent with at least one selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc. It is possible to provide a secondary battery having a non-aqueous solvent electrolytic solution that enables the above. In the present invention, examples of ethers having a viscosity lower than EC include 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-ethoxymethoxyethane.

As the negative electrode material capable of charging and discharging lithium ions, (1) a lithium metal negative electrode, (2) a lithium alloy negative electrode capable of charging and discharging lithium ions, for example, L
A lithium alloy mainly composed of i and Al, Li and Cd, I
Lithium alloys such as n, Pb and Bi, (3) Negative electrode mainly composed of a negative electrode active material holder capable of charging and discharging lithium ions,
For example, various carbon materials, Nb ₂ O ₅ , WO ₂ , Fe ₂
Examples thereof include metal oxides such as O ₃ and polymer compounds such as polythiophene and polyacetylene.

As the electrolyte of the electrolytic solution, LiClO ₄ , L
_{iPF 6, LiAsF 6, LiBF 4} , LiAlC
l ₄ , LiCF ₃ SO ₃ , LiSbF ₆ , LiSCN,
LiCl, LiC ₆ H ₅ SO ₃ , LiN (CF ₃ S
O ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiCF ₃ SO
Lithium salts such as ₃ can be used alone or in admixture of two or more. These lithium salts are 0.5 to 1.5
It is preferably used at a concentration of mol / liter.

The secondary battery having the non-aqueous solvent electrolyte of the present invention has the following features. That is, as a positive electrode active material, Li _x Mn _{2- y My} O ₄ (M = Na, Mg,
Sc, Y, Fe, Co, Ni, Cu, Zn, Al, P
b, Sb, 0 ≦ x ≦ 1.2, 0 ≦ y ≦ 0.7) and Mn
A battery using a complex oxide mainly composed of ₂ O ₄ is characterized by being inexpensive and having a long cycle life. Further, as a positive electrode active material, Li _x Mn _{2- y My} O ₄ (M = Na, Mg,
Sc, Y, Fe, Co, Ni, Cu, Zn, Al, P
b, Sb, 0 ≦ x ≦ 1.2, 0 ≦ y ≦ 0.7) is used as a battery, and a battery using a composite oxide is Li _x Mn ₂ O ₄ (0
By substituting a part of transition metal for Mn of ≦ x ≦ 1.2), the crystal structure is particularly stable and the charge / discharge life is extended. Further, as a positive electrode active material, Li _x CoO ₂ (0 ≦ x ≦
The battery using the complex oxide mainly composed of 1.2) is characterized by high voltage and high energy density. Further, as a positive electrode active material, Li _x NiO ₂ (0 ≦ x ≦
The battery using the complex oxide mainly composed of 1.2) has the characteristics of large charge / discharge capacity and large energy density. Further, as a positive electrode active material, Fe ₂ (SO ₄ ) ₃
A battery using a complex sulfate mainly composed of is characterized by being inexpensive and lightweight.

As described above, a high voltage and a high energy density can be obtained by using a positive electrode active material that requires 3.5 V or more as the final charge voltage for the positive electrode, and the lithium ion interface can be obtained. Curation,
It is suitable for high-current discharge rapid charging due to the rapid diffusion of deintercalation. The negative electrode can have a high energy density by using metal lithium or a lithium metal alloy, and there is no need for lithium ion intercalation or deintercalation, which causes a problem of lithium ion diffusion. Therefore, it is suitable for high-current discharge rapid charging, and no cost is required because no special process is required for producing the negative electrode.
EC with a very high dielectric constant is used as the electrolyte.
By mixing with a lower viscosity solvent, a high dielectric constant can be obtained by an additive effect. This enabled high-current discharge rapid charging. Also, this EC and EC
An electrolytic solution mixed with a lower viscosity solvent exhibits high charge / discharge efficiency of a lithium electrode, and thus a long charge / discharge life can be achieved.

[0010]

EXAMPLES The effects of the present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

Example 1 (2: 8) FIG. 1 is a sectional view of a secondary battery having a non-aqueous solvent electrolyte according to the present invention. In FIG. 1, 1 is a negative electrode case made of stainless steel. Reference numeral 2 denotes a negative electrode, which is obtained by punching out a lithium foil having a predetermined thickness to a diameter of 16 mm and press-bonding it to 1. Reference numeral 3 is an electrolytic solution using a non-aqueous solvent, in which 1 mol / liter of lithium hexafluorophosphate LiPF ₆ was dissolved in a mixed solvent of EC and DMC in a volume ratio of 2: 8. 4 is a separator made of a polypropylene or polyethylene porous film. 5 is a positive electrode case made of stainless steel. 6 is LiMn _1.9 Co _0.1 O
It is a positive electrode configured by using ₄ . This is prepared by mixing the above positive electrode active material with a conductive agent and a binder to form a slurry, applying the slurry to a predetermined thickness on a SUS foil, and drying it. It was cut into the size of. Reference numeral 7 denotes a gasket, which maintains electrical insulation between the negative electrode case 1 and the positive electrode case 5, and at the same time, the opening edge of the negative electrode case is bent inward and caulked to seal and seal the battery contents. .
A secondary battery having this non-aqueous solvent electrolytic solution is used in the range of 3.3V to 4.V.
A charging / discharging cycle test was performed in the voltage range of 3 V under the specifications of a large current discharge with a charging current of 1 mA / cm ² and a discharging current of 3 mA / cm ² , and rapid charging. Table 1 shows the charge / discharge capacity and cycle life. As is clear from this, this secondary battery was repeatedly charged and discharged stably, had a large charge and discharge capacity, and had a very long cycle life of 1400 times. The cycle life was the number of cycles when the capacity became half of the capacity during repeated stable charge and discharge, and the charge and discharge capacity was the average value up to the cycle life.

[0012]

[Table 1]

Example 2 (1: 9) In the secondary battery of Example 1, 1 mol / mol of LiPF ₆ was used as the electrolytic solution in a mixed solvent of EC and DMC in a volume mixing ratio of 1: 9.
A battery was prepared in the same manner as in Example 1 except that the one dissolved in liter was used, and this battery was subjected to a charge / discharge cycle test under the same charge / discharge conditions as in Example 1. Table 1 shows the charge / discharge capacity and cycle life. As is clear from this, this secondary battery was repeatedly charged and discharged stably, had a large charge and discharge capacity, and had a very long cycle life of 1200 times.

Example 3 (3: 7) In the secondary battery of Example 1, 1 mol / mol of LiPF ₆ was used as the electrolytic solution in a mixed solvent of EC and DMC in a volume mixing ratio of 3: 7.
A battery was prepared in the same manner as in Example 1 except that the one dissolved in liter was used, and this battery was subjected to a charge / discharge cycle test under the same charge / discharge conditions as in Example 1. Table 1 shows the charge / discharge capacity and cycle life. As is clear from this, this secondary battery was repeatedly charged and discharged stably, had a large charge and discharge capacity, and had a very long cycle life of 1200 times.

Example 4 (4: 6) In the secondary battery of Example 1, 1 mol / mL of LiPF ₆ was used as the electrolytic solution in a mixed solvent of EC and DMC in a volume mixing ratio of 4: 6.
A battery was prepared in the same manner as in Example 1 except that the one dissolved in liter was used, and this battery was subjected to a charge / discharge cycle test under the same charge / discharge conditions as in Example 1. Table 1 shows the charge / discharge capacity and cycle life. As is clear from this, this secondary battery was repeatedly charged and discharged stably, had a large charge and discharge capacity, and had a very long cycle life of 1100 times.

Comparative Example 1 (0:10) For comparison, in the secondary battery of Example 1, the electrolyte solution was changed to D
A battery was prepared in the same manner as in Example 1 except that 1 mol / liter of LiPF ₆ dissolved in a single solvent of MC was used, and this battery was subjected to a charge / discharge cycle test under the same charge / discharge conditions as in Example 1. Table 1 shows the charge / discharge capacity and cycle life. As is clear from this, the cycle life of this secondary battery was 650 times, which was much shorter than in Examples 1 to 4.

Comparative Example 2 (5: 5) For comparison, in the secondary battery of Example 1, the electrolytic solution was E.
LiPF ₆ was added to a mixed solvent of C and DMC at a volume mixing ratio of 5: 5.
A battery was prepared in the same manner as in Example 1 except that 1 mol / liter of was dissolved in Example 1.
A charge / discharge cycle test was performed under the same charge / discharge conditions as above. Table 1 shows the charge / discharge capacity and cycle life. As is clear from this, the cycle life and charge / discharge capacity of this secondary battery were much lower than those of Examples 1 to 4.

Example 5 Mn _{2 In the} secondary battery of Example 1, the positive electrode was LiMn _1.9 Co.
_A battery was prepared in the same manner as in Example 1 except that _0.1 O ₄ was used instead of LiMn ₂ O ₄ , and EC and D
A charge / discharge cycle test was performed under the same charge / discharge conditions using 10 kinds of electrolytic solutions having a volume mixing ratio of MC of 0:10 to 9: 1. Table 2 shows each charge / discharge capacity and cycle life. As is clear from this, in the electrolytic solution in which the volume mixing ratio of EC and DMC was 1: 9 to 4: 6, the cycle life of this secondary battery was long and the charge / discharge capacity was large.

[0019]

[Table 2]

Example 6 DEC In the secondary battery of Example 1, the electrolytic solution was LiPF in a mixed solvent of EC and DEC in a volume mixing ratio of 0:10 to 9: 1.
_A battery was produced in the same manner as in Example 1 except that ₆ was dissolved in 1 mol / liter, and a charge / discharge cycle test was performed under the same charge / discharge conditions. Table 3 shows each charge / discharge capacity and cycle life. As is clear from this, EC
In the electrolytic solution in which the volume mixing ratio of and DEC was 1: 9 to 4: 6, the cycle life of this secondary battery was long and the charge / discharge capacity was large.

[0021]

[Table 3]

Example 7 EMC In the secondary battery of Example 1, the electrolyte solution was mixed with EC and EMC in a mixed solvent having a volume mixing ratio of 0:10 to 9: 1, and LiPF.
_A battery was produced in the same manner as in Example 1 except that ₆ was dissolved in 1 mol / liter, and a charge / discharge cycle test was performed under the same charge / discharge conditions. Table 4 shows each charge / discharge capacity and cycle life. As is clear from this, EC
In the electrolytic solution in which the volume mixing ratio of EMC and 1: 9 to 4: 6, the cycle life of this secondary battery was long and the charge / discharge capacity was large.

[0023]

[Table 4]

Example 8 LiClO _{4 In the} secondary battery of Example 1, the electrolyte solution LiPF ₆ was added to L
A battery was prepared in the same manner as in Example 1 except that iClO ₄ was used, and the same charge was used for the battery using 10 kinds of electrolytic solutions having a volume mixing ratio of EC and DMC of 0:10 to 9: 1. A charge / discharge cycle test was conducted under discharge conditions. Table 5 shows each charge / discharge capacity and cycle life. As is clear from this, in an electrolytic solution using LiClO ₄ and a volume mixing ratio of EC and DMC of 1: 9 to 4: 6, the secondary battery has a long cycle life and a large charge / discharge capacity. became.

[0025]

[Table 5]

Example 9 LiAsF _{6 In the} secondary battery of Example 1, the electrolyte solution LiPF ₆ was changed to L.
A battery was prepared in the same manner as in Example 1 except that iAsF ₆ was used, and the same charge was used for this battery using 10 kinds of electrolytic solutions having a volume mixing ratio of EC and DMC of 0:10 to 9: 1. A charge / discharge cycle test was conducted under discharge conditions. Table 6 shows each charge / discharge capacity and cycle life. This As is clear from, using LiAsF _6, the volume mixing ratio of EC and DMC 1: 9 to 4: In 6 and the electrolyte, the cycle life of the secondary battery is long, as the charge-discharge capacity greater became.

[0027]

[Table 6]

[0028]

As described above, the present invention has 3.5
A positive electrode active material that requires a cut-off voltage of charge of V or more is used for the positive electrode, a mixed solvent of EC and a solvent having a viscosity lower than EC is used as the nonaqueous solvent of the electrolytic solution, and a solvent having a viscosity lower than that of EC is used. By increasing the volume mixing ratio, it is possible to provide a secondary battery having a high energy density, capable of high-current discharge rapid charging, long charge / discharge life, and inexpensive non-aqueous solvent electrolyte.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a battery of the present invention.

[Explanation of symbols]

1: Stainless steel negative electrode case, 2: Negative electrode, 3: Electrolyte using non-aqueous solvent, 4: Separator, 5: Stainless steel positive electrode case, 6: Positive electrode, 7: Gasket

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Junichi Yamaki 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (6)

[Claims] 1. A negative electrode capable of charging and discharging lithium ions,
In a secondary battery having a positive electrode capable of performing a reversible electrochemical reaction with lithium ions and an electrolytic solution in which an ion dissociative lithium salt is dissolved in a non-aqueous solvent, the positive electrode may be 3.5
A positive electrode active material that requires a cut-off voltage of charge of V or more is used for the positive electrode, a mixed solvent of ethylene carbonate and an ester or ether having a viscosity lower than the ethylene carbonate is used as a non-aqueous solvent of the electrolytic solution, and a volume mixing ratio is set. Is more than 5: 5 and less than 0:10, a secondary battery. 2. The secondary battery according to claim 1, wherein metallic lithium or a lithium metal alloy is used as a negative electrode active material for the negative electrode. 3. Li _x Mn _2-y M as the positive electrode active material
_y O ₄ (M = Na, Mg, Sc, Y, Fe, Co, N
i, Cu, Zn, Al, Pb, Sb, 0 ≦ x ≦ 1.2,
The secondary battery according to claim 1 or 2, wherein a composite oxide mainly composed of 0 ≦ y ≦ 0.7) and Mn ₂ O ₄ is used. 4. A non-aqueous solvent for the electrolytic solution, which comprises a mixture of ethylene carbonate and at least one selected from dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate as a solvent having a viscosity lower than that of ethylene carbonate. It uses, The secondary battery in any one of Claims 1-3. 5. LiP as a lithium salt for the electrolytic solution
0.5% of F ₆ , LiAsF ₆ or LiClO ₄
The secondary battery according to claim 1, wherein the secondary battery is used at a concentration of 1.5 mol / liter. 6. The volume mixing ratio of ethylene carbonate and dimethyl carbonate as the non-aqueous solvent is 3: 7 to.
Li _x Mn _2-y Co _y O ₄ (0 ≦ x ≦ 1.2, 0 ≦ _y was used as a positive electrode active material, using an electrolytic solution as a mixed solvent of 1: 9.
≦ 0.7) was used, The secondary battery according to claim 1.