JP2001307768A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

(57) [Problem] To provide a non-aqueous electrolyte secondary battery in which a flame-retardant effect is sufficiently exerted and which is excellent in high-temperature charge / discharge cycle characteristics. SOLUTION: In a non-aqueous electrolyte secondary battery including a positive electrode containing a lithium transition metal composite oxide, a negative electrode capable of inserting and removing lithium ions, and a non-aqueous electrolyte, The solution contains 20-40% by volume of the solvent, tributyl phosphate (TBP) or triphenyl phosphate (TP).
P).

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 having excellent safety and charge / discharge characteristics, and more particularly to improvement of a solvent in a non-aqueous electrolyte.

[0002]

2. Description of the Related Art A battery using a non-aqueous electrolyte, particularly a lithium ion secondary battery has a high energy density and is therefore widely used as a power source for consumer electronic devices. As a non-aqueous electrolyte used for a lithium ion secondary battery, a solution in which LiPF ₆ is dissolved as an electrolyte in a carbonate-based solvent such as ethylene carbonate (EC) or diethyl carbonate (DEC) is generally used. However, these solvents are flammable and have a relatively low flash point, so there is a risk of ignition. Therefore, it has good charge / discharge cycle characteristics and
It has been reported that a phosphoric acid ester, which is a high flash point solvent, is used as an electrolyte in order to achieve flame retardancy.

[0003] Japanese Patent Application Laid-Open No. 8-88023 proposes that a phosphate ester be used in an amount of 1 to 20% by volume based on an electrolytic solution. However, in this example, the mixing ratio is limited to 20% by volume or less in order to satisfy good charge / discharge cycle characteristics, and the effect of flame retardancy cannot be expected as a practical problem.

Japanese Patent Application Laid-Open No. 11-40193 reports an example in which a trace amount of an ether having a halogen-substituted aromatic ring is added to an electrolytic solution containing 1 to 50% by volume of a phosphoric ester. This is because the use of a large amount of phosphoric acid ester is expected to have the effect of flame retardancy. The additive forms a stable film on the electrode surface and suppresses the reaction between the electrolyte and the electrode. It is considered that this was improved.
However, the inventors examined the above electrolyte, and found that this electrolyte had a large initial irreversible capacity (difference between charge capacity and discharge capacity at the time of first charge / discharge) and a small discharge capacity. The improvement effect was hardly recognized.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and provides a non-aqueous electrolyte secondary battery having a sufficient flame retardancy effect and excellent high-temperature charge / discharge cycle characteristics. It is intended to provide a battery.

[0006]

The present invention provides a non-aqueous electrolyte secondary comprising a positive electrode containing a lithium transition metal composite oxide, a negative electrode capable of inserting and removing lithium ions, and a non-aqueous electrolyte. In the battery, the non-aqueous electrolyte contains 20 to 20
A nonaqueous electrolyte secondary battery characterized in that 40% by volume is tributyl phosphate (TBP) or triphenyl phosphate (TPP).

The most remarkable point in the present invention is that the solvent of the non-aqueous electrolyte contains 20 to 40% by volume of a specific component such as tributyl phosphate (TBP) or triphenyl phosphate (TPP). That is. The above TBP and TPP can be contained alone, or both can be mixed and contained.

The flash points of the TBP and TPP are 146 ° C. and 210 ° C., respectively, which are relatively high. Therefore, the flame retardant effect can be enhanced as the content of these components is increased. And the above T
When the content of the specific components BP and TPP is less than 20% by volume of the solvent, there is a problem that a sufficient flame retardant effect cannot be obtained. On the other hand, if it exceeds 40% by volume, there is a problem that the viscosity of the non-aqueous electrolyte becomes high and the high-temperature charge / discharge cycle characteristics of the battery are extremely deteriorated.

As a solvent of the above-mentioned electrolytic solution, for example, EC, DE,
C or the like can be used. Examples of the supporting electrolyte for the electrolytic solution include LiPF ₆ , LiBF ₄ , LiClO ₄ , L
iAsF ₆ or the like, or a complex salt thereof can be used.

In the above positive electrode, as an active material,
Known lithium manganese spinel, lithium manganese spinel in excess of lithium, part of Mn is Ni, Al, C
Lithium manganese spinel substituted with a different metal such as o, Fe, Mg, and the like, and a mixture thereof can be used. Alternatively, a layered structure of LiCoO ₂ or LiNiO ₂ can be applied. As the negative electrode, for example, a carbon material can be used. In this case, as the carbon material,
Known natural graphite, artificial graphite, cokes, carbons obtained by calcining raw coke, and the like can be used.

Next, the operation and effect of the present invention will be described.
In the non-aqueous electrolyte secondary battery of the present invention, as described above, a non-aqueous electrolyte having a solvent containing the specific amount of the specific component TBP or TPP is used. Therefore, as described later, it is possible to obtain a very excellent flame retardant effect and high-temperature charge / discharge cycle characteristics. Although the reason for the improvement of the high-temperature charge / discharge cycle characteristics is not necessarily clear, as the battery is charged / discharged, the decomposition reaction of the phosphate ester is caused by the PO bond of POR (R: alkyl group, phenyl group). If so, it is presumed that when the carbon number of R is about 4 to 6, the PO bond becomes difficult to be broken, and an electrochemically stable structure may be obtained.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1 A non-aqueous electrolyte secondary battery according to an embodiment of the present invention is manufactured by a plurality of examples and a comparative example in which the configuration of the non-aqueous electrolyte is changed. Was subjected to a flame retardancy test and a high temperature charge / discharge cycle test. First, the prepared examples and comparative examples will be described.

(Example A1) The non-aqueous electrolyte of Example A1 was subjected to solvent distillation using EC (manufactured by Toyama Pharmaceutical Co., Ltd., battery grade, hereinafter the same), DEC (manufactured by Toyama Pharmaceutical Co., battery grade, the same as the following) Using TBP (manufactured by Tokyo Chemical Industry, the same applies hereinafter), the mixing ratio was 33% by volume, 42% by volume, and 25% by volume, respectively.
% By volume. LiPF ₆ is used for the electrolyte,
/ L. Using this non-aqueous electrolyte, a flame retardancy test described below was performed.

A non-aqueous electrolyte secondary battery for a high-temperature charge / discharge cycle test was prepared as follows using the above-mentioned non-aqueous electrolyte. The commercially available reagents Li ₂ CO ₃ and M
n ₃ O ₄ and Al (NO ₃ ) ₃ are mixed at a predetermined ratio,
Al-substituted M synthesized by heating at 900 ° C for 10 hours in air
n-type spinel powder LiAl _0.22 Mn _1.78 O ₄ (synthesized by the inventor, the same applies hereinafter) and LiNiO ₂ (manufactured by Fuji Chemical, Linilit
eCA-5, the same applies hereinafter) A powder blend material (80: 20% by weight) was used. Then, the PVA is added to the LiNiO ₂ powder and the artificial graphite powder so that the weight ratio of the blend material, the artificial graphite powder (KS8, manufactured by Lonza) and PVdF is 84: 10: 6.
An NMP solution of dF was added and kneaded for 3 hours to obtain a slurry. Next, the slurry was coated on both sides of an aluminum foil, and vacuum-dried at 200 ° C. for 10 hours to obtain a positive electrode sheet.

As the negative electrode material, spherical artificial graphite (manufactured by Osaka Gas Chemical Co., Ltd .; the same applies hereinafter) powder was used.
PVD is added to the graphite powder so that dF becomes a weight ratio of 95: 5.
An NMP solution of dF was added and kneaded for 3 hours to obtain a slurry. The slurry was coated on both sides of a copper foil.
After vacuum drying for a period of time, a negative electrode sheet was obtained.

A cylindrical battery having a diameter of 18 mm and a height of 65 mm was manufactured as follows using the above-mentioned positive electrode sheet, negative electrode sheet and electrolyte solution. First, the above-described positive electrode sheet and negative electrode sheet were laminated via a separator made of a 25 μm-thick polyethylene microporous membrane, and spirally wound. Then, the wound body was accommodated in a battery can, and the negative electrode and the bottom of the battery can were welded through a nickel lead wire, and the positive electrode and the battery can lid were welded through an aluminum lead wire. Next, the above-mentioned electrolyte was poured into a battery can, the battery lid was closed, and the battery can was caulked and sealed. As a result, a test battery was obtained.

Example A2 The non-aqueous electrolyte solution of Example A2 used as a solvent was EC, DEC, or distilled TPP (manufactured by Tokyo Chemical Industry, the same applies hereinafter), and the mixing ratio was 33% by volume and 42% by volume, respectively. , 25% by volume. Others are Example A
Same as 1. Also, a battery using this non-aqueous electrolyte was produced in the same manner as in Example A1.

(Comparative Example A1) The non-aqueous electrolyte of Comparative Example A1 used as a solvent was EC, DEC, and distilled trimethyl phosphate (TMP) (manufactured by Tokyo Kasei). %, 42% by volume, and 25% by volume. Others were the same as Example A1. Also, a battery using this non-aqueous electrolyte was produced in the same manner as in Example A1.

(Comparative Example A2) The non-aqueous electrolyte of Comparative Example A2 used EC, DEC, and distilled trioctyl phosphate (TOP) (manufactured by Tokyo Chemical Industry, hereinafter the same) as the solvent, and the mixing ratio was 33 vol. %, 42% by volume, and 25% by volume. Except for this, it was the same as Example A1. Also, a battery using this non-aqueous electrolyte was produced in the same manner as in Example A1.

(Comparative Example B1) The nonaqueous electrolyte solution of Comparative Example B1 used EC, DEC, and distilled TMP as solvents, and the mixing ratio was 33% by volume, 33% by volume, and 33% by volume, respectively. Others were the same as Example A1. A battery using this non-aqueous electrolyte was manufactured as follows. First,
The cathode materials include commercially available reagents Li ₂ CO ₃ and Mn ₃ O ₄ , and N 2
i (NO ₃ ) ₂ mixed at a predetermined ratio and heated in the air at 900 ° C. for 10 hours to obtain a Ni-substituted Mn-based spinel powder L
i _1.05 Ni _0.10 Mn _1.85 O ₄ and LiNiO ₂ powder blend material of (80:20 wt%) was used. Then, the PVA is added to the LiNiO ₂ powder and the artificial graphite powder so that the weight ratio of the blend material, the artificial graphite powder, and PVdF is 84: 10: 6.
An NMP solution of dF was added and kneaded for 3 hours to obtain a slurry. Next, the slurry was coated on both sides of an aluminum foil, and vacuum-dried at 200 ° C. for 10 hours to obtain a positive electrode sheet. Except for this, it was the same as Example A1.

(Comparative Example B2) The non-aqueous electrolyte of Comparative Example b2 used EC, DEC, and distilled TMP as solvents, and the mixing ratio was 33% by volume, 33% by volume, and 33% by volume, respectively. For the electrolyte, 4-fluoroanisole (4F
A) (manufactured by Tokyo Kasei, hereinafter the same) was added at 1% by weight. Except for this, it was the same as Comparative Example B1. Also, a battery using this non-aqueous electrolyte was produced in the same manner as in Example B1.

(Comparative Example B3) The nonaqueous electrolyte of Comparative Example B3 used EC, DEC, and distilled TMP as solvents, and the mixing ratio was 33% by volume, 33% by volume, and 33% by volume, respectively. 5% by weight of 4FA was added to the electrolyte. Except for this, it was the same as Comparative Example B1. Also, a battery using this non-aqueous electrolyte was produced in the same manner as in Example B1.

<Flame Retardancy Test> The flame retardancy test was performed as follows. A polyethylene separator {thickness 25 μm, width 6 mm, length 12 cm} was immersed in each of the above nonaqueous electrolytes. The upper end of the separator impregnated with the non-aqueous electrolyte was hung in the atmosphere with tweezers, and the match fire was brought closer to the lower end. The presence or absence of ignition and the combustion state of the separator when ignited were observed. The evaluation criteria were as follows: 場合 when no ignition occurred, △ when ignition occurred but most of the separator remained unburned, and X when ignition ignited and most of the separator burned off. Table 1 shows the test results.

<High Temperature Charge / Discharge Cycle Test> The high temperature charge / discharge cycle test was conducted at 60 ° C. under a current density of 1.1 mA / cm ^2.
Is performed up to an upper limit of 4.1 V, and then a constant current charge at a current density of 1.1 mA / cm ² is performed up to a lower limit of 3.0 V. This cycle is defined as one cycle, and this cycle is repeated. Is measured. Table 1
Table 2 shows the initial discharge capacity per positive electrode active material and the discharge capacity retention rate at 100 cycles. The discharge capacity retention ratio is a value obtained by dividing the discharge capacity in the cycle by the discharge capacity in the first cycle.

[0025]

[Table 1]

As can be seen from Table 1, the flame retardant effect was observed in all the samples when the phosphate was mixed with the electrolyte at 20% by volume or more. It has been found that the electrolyte of the present invention has a flame-retardant effect and has extremely excellent battery characteristics.

Embodiment 2 In this embodiment, a plurality of examples and comparative examples were newly prepared in addition to the embodiment 1, and a flame retardancy test and a high-temperature charge / discharge cycle test were performed. First, the prepared examples and comparative examples will be described.

(Example C1) The nonaqueous electrolytic solution of Example C1 used EC, DEC, and TPP as solvents, and the mixing ratio was 33% by volume, 27% by volume, and 40% by volume, respectively. Others were the same as Example A1. Further, a non-aqueous electrolyte secondary battery for a high-temperature charge / discharge cycle test was prepared as follows using the above-described non-aqueous electrolyte. For the cathode material,
LiNiO ₂ powder was used. Then, LiNiO ₂ powder, artificial graphite powder and polyvinylidene fluoride (PVdF)
An N-methyl-2-pyrrolidone (NMP) solution of PVdF was added to the LiNiO ₂ powder and the artificial graphite powder so that the weight ratio became 4: 10: 6, and the mixture was kneaded for 3 hours to obtain a slurry. Next, the slurry was coated on both sides of an aluminum foil, and vacuum-dried at 200 ° C. for 10 hours to obtain a positive electrode sheet.

As the negative electrode material, artificial graphite powder was used. The graphite powder was mixed with PVdF in a weight ratio of 96: 4.
An NMP solution of PVdF was added to the graphite powder and kneaded for 3 hours to obtain a slurry. The slurry was coated on both sides of a copper foil and vacuum dried at 120 ° C. for 10 hours to obtain a negative electrode sheet. Except for this, it was the same as Example A1.

(Example C2) The non-aqueous electrolyte of Example C2 used EC, DEC, and TPP as solvents, and the mixing ratio was 33% by volume, 33% by volume, and 33% by volume, respectively. Except for this, it was the same as Example C1. Also, a battery using this non-aqueous electrolyte was produced in the same manner as in Example C1.

(Example C3) The nonaqueous electrolyte of Example C3 used EC, DEC, and TPP as solvents, and the mixture was 33% by volume, 47% by volume, and 20% by volume, respectively. Except for this, it was the same as Example C1. Also, a battery using this non-aqueous electrolyte was produced in the same manner as in Example C1.

(Comparative Example C1) The non-aqueous electrolyte of Comparative Example C1 used EC, DEC, and distilled TMP as solvents, and the mixing ratio was 33% by volume, 33% by volume, and 33% by volume, respectively. Except for this, it was the same as Example C1. Also, a battery using this non-aqueous electrolyte was produced in the same manner as in Example C1.

(Comparative Example C2) The nonaqueous electrolytic solution of Comparative Example C2 used EC, DEC, and distilled TMP as solvents, and the mixing ratio was 33% by volume, 42% by volume, and 25% by volume, respectively. Except for this, it was the same as Example C1. Also, a battery using this non-aqueous electrolyte was produced in the same manner as in Example C1.

(Comparative Example C3) The nonaqueous electrolytic solution of Comparative Example C3 used EC, DEC, and distilled TMP as solvents, and the mixing ratio was 33% by volume, 47% by volume, and 20% by volume, respectively. Except for this, it was the same as Example C1. Also, a battery using this non-aqueous electrolyte was produced in the same manner as in Example C1.

(Comparative Example C4) The non-aqueous electrolyte of Comparative Example C4 used EC, DEC, and distilled TMP as solvents, and the mixing ratio was 33% by volume, 52% by volume, and 15% by volume, respectively. Except for this, it was the same as Example C1. Also, a battery using this non-aqueous electrolyte was produced in the same manner as in Example C1.

Next, a flame retardancy test and a high-temperature charge / discharge cycle test similar to those of the first embodiment were performed on these examples and comparative examples. Table 2 shows the results.

[0037]

[Table 2]

As can be seen from Table 2, the TMP was 15%
The flame retardant effect was not recognized only by mixing. T
Even when the mixing ratio of PP was changed from 20 to 40% by volume, the battery characteristics were found to be very excellent.

[0039]

As described above, according to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery in which the flame retardant effect is sufficiently exerted and which is excellent in high-temperature charge / discharge cycle characteristics.

Claims (1)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode containing a lithium transition metal composite oxide, a negative electrode into which lithium ions can be inserted and desorbed, and a non-aqueous electrolyte. A non-aqueous electrolyte secondary battery, wherein 20 to 40% by volume of the aqueous electrolyte is tributyl phosphate (TBP) or triphenyl phosphate (TPP).