JP2003168474A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte secondary battery, which the decomposing of the electrolysis liquid under preservation is suppressed and the swelling of it under the high temperature environment or prolonged preservation does not occur also. <P>SOLUTION: In the non-aqueous electrolyte secondary battery, which is constituted with a positive electrode, which consists of a substance that stores/releases lithium ions, a negative electrode, which consists of a substance that stores/ releases lithium ions, and a non-aqueous electrolyte, the non-aqueous electrolyte contains the benzene derivative, which has t-butyl group and hydroxy group. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery having excellent storage performance.

[0002]

2. Description of the Related Art In recent years, with the rapid miniaturization and diversification of consumer mobile phones, portable electronic devices, personal digital assistants, etc., the power source of batteries has become smaller, lighter and higher in energy density. There is a strong demand for the development of secondary batteries that can be repeatedly charged and discharged for a long period of time.

Among them, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have been put to practical use as secondary batteries satisfying these requirements, as compared with lead batteries and nickel-cadmium batteries using aqueous electrolytes. , Active research is being conducted.

Such a non-aqueous electrolyte secondary battery is, for example,
Positive electrode active material that absorbs and releases lithium ions as a current collector
Holds the positive electrode plate, which absorbs and releases lithium ions
A negative electrode plate in which the negative electrode active material
LiBF in organic solvent _FourAnd LiPF₆Such as Richi
Holds the electrolyte solution in which the um salt is dissolved and also holds the positive electrode plate
Is it a separator that exists between the negative electrode plate and the negative electrode plate to prevent a short circuit?
It is composed of

As an electrolyte for a non-aqueous electrolyte secondary battery, generally, LiB is used as a mixed solvent of a high dielectric constant solvent such as ethylene carbonate or propylene carbonate and a low viscosity solvent such as dimethyl carbonate or diethyl carbonate.
A solution in which a supporting salt such as F ₄ or LiPF ₆ is dissolved is used.

Positive electrode active materials for non-aqueous electrolyte secondary batteries include titanium disulfide, vanadium pentoxide, and the general formula Li _x MO.
Various compounds represented by ₂ (where M is one or more transition metals) have been studied.

Among them, lithium cobalt composite oxides, lithium nickel composite oxides, lithium manganese composite oxides and the like charge and discharge at an extremely noble potential of 4 V (vs. Li ^/ Li ⁺ ) or more, so that they are positive electrode active. By using it as a substance, a non-aqueous electrolyte secondary battery having a high discharge voltage can be realized.

Materials capable of inserting and extracting lithium ions, such as alloys containing lithium, have been studied as negative electrode active materials for non-aqueous electrolyte secondary batteries. Of non-aqueous electrolyte secondary battery having a long life and high safety, it is now in practical use.

Recently, such a non-aqueous electrolyte secondary battery has been increasingly used not only in a room temperature environment but also in an electronic device used in a wide temperature range environment. For example, in a notebook personal computer, the temperature inside the personal computer has risen along with the speeding up of the central processing unit, and the battery has been used for a long time in a high temperature environment. In addition, mobile phones and portable devices are often used in high temperature environments. Therefore, there has been a strong demand for improvement in storage performance of the non-aqueous electrolyte secondary battery used in such a high temperature environment.

[0010]

In a non-aqueous electrolyte secondary battery, since the electrolyte is insufficient in electrical and chemical stability, it has been stored in a high temperature environment or in a charged state for a long time. In some cases, depending on storage conditions, the decomposition reaction of the electrolyte proceeds, the generated gas fills the battery, the internal pressure of the battery rises, and as a result, the battery swells and the battery thickness increases. It was

An object of the present invention is to provide a non-aqueous electrolyte secondary battery which suppresses decomposition of an electrolytic solution during storage in the non-aqueous electrolyte secondary battery and does not swell even in a high temperature environment or during long-term storage. It is in.

[0012]

The invention according to claim 1 is composed of a positive electrode made of a substance which absorbs and releases lithium ions, a negative electrode which is made of a substance which absorbs and releases lithium ions, and a non-aqueous electrolyte. In non-aqueous electrolyte secondary battery,
Characterized in that it comprises a benzene derivative which said non-aqueous electrolyte and a t- butyl group _{((CH 3) 3} C-) and hydroxy group (-OH).

According to the invention of claim 1, since the electrolyte contains a benzene derivative having a t-butyl group and a hydroxy group, the gas generation reaction due to the decomposition of the electrolytic solution on the positive electrode is suppressed, and the battery swells. By preventing the above phenomenon and suppressing the increase in the thickness of the battery, it is possible to obtain a non-aqueous electrolyte secondary battery in which the characteristics are not deteriorated even in a high temperature environment or after long-term storage.

According to a second aspect of the present invention, in the above non-aqueous electrolyte secondary battery, the benzene derivative having a t-butyl group and a hydroxy group is at least one of dibutylhydroxytoluene or dibutylhydroxybenzene. .

According to the second aspect of the present invention, the gas generation reaction due to the decomposition of the electrolytic solution on the positive electrode can be suppressed more effectively.

According to a third aspect of the present invention, in the above non-aqueous electrolyte secondary battery, the content of the benzene derivative having a t-butyl group and a hydroxy group contained in the non-aqueous electrolyte is such that the t-butyl group and the hydroxy group are contained. The amount is 0.001 to 3 wt% with respect to the weight of the electrolyte other than the benzene derivative having a group.

According to the third aspect of the present invention, the amount of the benzene derivative having a t-butyl group and a hydroxy group contained in the electrolyte is set to an optimum range, so that the benzene having a t-butyl group and a hydroxy group can be obtained. An excellent effect can be realized by adding the derivative.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is a non-aqueous electrolyte secondary composed of a positive electrode made of a substance which absorbs and releases lithium ions, a negative electrode which is made of a substance which absorbs and releases lithium ions, and a non-aqueous electrolyte. In the battery, the non-aqueous electrolyte contains a benzene derivative having a t-butyl group and a hydroxy group.

In the present invention, compounds (1) to (4) shown in Chemical formula 1 are used as the benzene derivative having a t-butyl group and a hydroxy group.

[0020]

[Chemical 1]

However, in the chemical formula 1, the substituents R, R ₁ and R ₂ represent a linear alkyl group, a branched alkyl group, a phenyl group, a cycloalkyl group and the like. Further, the substitution positions of the substituents R, R ₁ , R ₂ , t-butyl group and hydroxy group in the chemical formula 1 include those which are changed to arbitrary positions other than the positions shown in the chemical formula 1.

The benzene derivative having a t-butyl group and a hydroxy group reduces the progress of oxidative decomposition of the electrolyte solvent in a kinetic manner by suppressing radical reaction especially on the positive electrode. Therefore, it is considered that the gas generation reaction due to the decomposition of the electrolyte solvent on the positive electrode is suppressed, and as a result, the increase in the internal pressure of the battery is suppressed, and the increase in the battery thickness is suppressed.

In the present invention, since the decomposition of the electrolyte solvent is suppressed by the action of the benzene derivative having a t-butyl group and a hydroxy group on the positive electrode in this manner, the type of solvent used for the electrolyte is Not limited.

In the present invention, the benzene derivative having a t-butyl group and a hydroxy group may be used alone or in admixture of two or more. Moreover, the position of the substituent in the benzene molecule is not particularly limited.

In the present invention, at least one of dibutylhydroxytoluene and dibutylhydroxybenzene is used as the benzene derivative having a t-butyl group and a hydroxy group. These compounds are readily available and extremely easy to handle.

Further, in the present invention, the content of the benzene derivative having a t-butyl group and a hydroxy group contained in the non-aqueous electrolyte is such that the weight of the electrolyte other than the benzene derivative having a t-butyl group and a hydroxy group is the same. As opposed to
The range is 0.001 to 3 wt%.

When the content of the benzene derivative having a t-butyl group and a hydroxy group is less than 0.001 wt%, the effect of suppressing the decomposition of the electrolytic solution solvent at the positive electrode is poor, and the t-butyl group and When the content of the benzene derivative having a hydroxy group is more than 3 wt%, discharge characteristics are deteriorated, such as an increase in internal resistance of the battery and a decrease in capacity retention rate.

Positive electrode active material for non-aqueous electrolyte secondary battery of the present invention
As Li_xMO_Two, Li_yM _TwoO_Four(However, M
Represents one or more transition metals, 0 ≦ x ≦ 1, 0 ≦ y ≦ 2)
Complex oxides, tunnel structure or layered structure gold
Group chalcogenides, metal oxides and metal sulfides alone
Or two or more kinds can be used in combination. That
As a specific example, LiCoO_Two, LiCo_xNi_1-x
O_Two, LiMnO_Four, LiMn_TwoO_Four, LiFeP
O_Four, MnO_Two, TiO_Two, V_TwoO₅, FeS_Two, Ti
S_Two, Li_{1 + x}NiO_Two, LiNi_xMn_2-xO_Four
And so on. Especially, due to the high discharge voltage,
It is preferable to use Co, Ni, Mn as the genus M.
Yes. Also, as an organic compound such as polyaniline,
Examples include conductive polymers and sulfur compounds.

Examples of the negative electrode active material of the non-aqueous electrolyte secondary battery of the present invention include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, carbon fibers, Al, Si, Active materials mainly containing Pb, Sn, Zn, Cd, Sb, etc., or alloys of these with lithium, L
iFe ₂ O ₃ , WO ₂ , MoO ₂ , SiO, SiO ₂ ,
_{CuO, SnO, SnO 2, Nb} 3 O 5, Li x Ti
_2- xO ₄ (0 ≦ x ≦ 1), metal oxides such as PbO ₂ and PbO ₅ , metal sulfides such as SnS and FeS ₂ , metal lithium, lithium alloys, polyacene, polythiophene, L
_{i 5 (Li 3 N))} , Li 7 MnN 4, Li 3 Fe
Lithium nitride such as N ₂ , Li _2.5 Co _0.5 N, Li ₃ CoN, etc., or a composite of these and carbon can be used alone or in combination of two or more, but in particular,
It is desirable to use a carbonaceous material because of its high safety.

Solvents for the non-aqueous electrolyte include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, trifluoropropylene carbonate, γ-butyrolactone, 2-methyl-γ-butyrolactone, acetyl-γ-butyrolactone and γ-valerolactone. , Sulfolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran,
2-methyltetrahydrofuran, dimethyltetrahydrofuran, 3-methyl-1,3-dioxolane, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, dimethyl carbonate, diethyl carbonate,
Ethyl methyl carbonate, dipropyl carbonate,
Methyl propyl carbonate, ethyl isopropyl carbonate, dibutyl carbonate, dimethylformamide, dimethylacetamide, methyl acetate, acetonitrile and the like can be used alone or in admixture of two or more. In particular, a mixed system of cyclic carbonic acid ester and chain carbonic acid ester is preferable from the viewpoint of stability against oxidation and reduction.

The electrolyte dissolves the supporting salt in these non-aqueous solvents.
To use. LiClO as supporting salt_Four, LiAsF
₆, LiPF₆, LiBF_Four, LiCF_ThreeSO_Three, Li
CF _ThreeCF_TwoSO_Three, LiCF_ThreeCF_TwoCF_TwoSO_Three,
LiN (CF_ThreeSO_Two)_Two, LiN (C_TwoF₅SO_Two)
_Two, LiPF_Three(CF_Three)_Three, LiCF_ThreeCO_Two, Li
A single lithium salt such as Cl, LiBr, LiSCN, etc.
Alternatively, two or more kinds can be mixed and used. Supporting salt
Especially as LiPF₆Is preferably used.

Instead of such a liquid electrolyte, an ion conductive polymer electrolyte and an organic electrolyte can be used in combination. Specific examples of the ion conductive polymer electrolyte, polyethylene oxide, polyether such as polypropylene oxide, polyolefin such as polyethylene and polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, polyvinyl chloride, polyvinylidene chloride, Polymethyl methacrylate, polymethyl acrylate, polyvinyl alcohol, polymethacrylonitrile, polyvinyl acetate, polyvinylpyrrolidone, polycarbonate, polyethylene terephthalate, polyhexamethylene acipamide, polycaprolactam, polyurethane, polyethyleneimine, polybutadiene, polystyrene, polyisoprene and these These derivatives can be used alone or as a mixture.

Further, a polymer containing various monomers constituting the above polymer may be used. In addition to the polymer electrolyte, it is possible to use an inorganic solid electrolyte, a mixed material of an organic polymer electrolyte and an inorganic solid electrolyte, or an inorganic solid powder bound by an organic binder.

The non-aqueous electrolyte secondary battery of the present invention is composed of a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte as its constitution.
A woven fabric, a non-woven fabric, a polyolefin-based material such as polyethylene or polypropylene, a polyimide, a porous polymer membrane such as a porous polyvinylidene fluoride membrane, or an ion conductive polymer electrolyte membrane can be used alone or in combination.

Further, the shape of the battery is cylindrical, prismatic,
Various shapes such as a coin type, a button type, and a laminated type can be used. As the material of the battery case, stainless steel, nickel-plated iron, aluminum, titanium or alloys thereof and plated products can be used. As a material for the laminated resin film, aluminum, aluminum alloy, titanium foil or the like can be used. The material of the heat-welded portion of the metal laminated resin film may be any material as long as it is a thermoplastic polymer material such as polyethylene, polypropylene or polyethylene terephthalate. Further, each of the metal laminate resin layer and the metal foil layer is not limited to one layer and may be two or more layers.

[0036]

EXAMPLES Specific examples to which the present invention is applied will be described. However, the present invention is not limited to these examples, and various modifications may be made without departing from the scope of the invention.

A schematic cross section of a prismatic non-aqueous electrolyte secondary battery (battery thickness 5.0 mm) used in the present invention is shown in FIG. Figure 1
1, 1 is a non-aqueous electrolyte battery, 2 is a power generation element, 3 is a positive electrode plate, 4 is a negative electrode plate, 5 is a separator, 6 is a battery case,
7 is a battery lid, 8 is a safety valve, 9 is a positive electrode terminal, and 10 is a positive electrode lead.

In FIG. 1, the non-aqueous electrolyte secondary battery 1 is
A non-aqueous electrolyte solution was prepared by using a positive electrode 3 formed by coating a positive electrode mixture containing a positive electrode active material on an aluminum current collector and a negative electrode 4 formed by coating a negative electrode mixture containing a negative electrode active material on a copper current collector. The wound type power generating element 2 wound via the injected separator 5 is housed in a battery case 6 made of nickel plated with iron. A battery cover 7 provided with a safety valve 8 is attached to the battery case 6 by laser welding, and the positive electrode terminal 9
Is connected to the positive electrode 3 via the positive electrode lead 10, and the negative electrode 4 is connected to the inner wall of the battery case 6 by contact.

The positive electrode was made of LiCoO ₂ 90w as an active material.
t% and 5 wt% of acetylene black as a conductive agent
And 5 wt% of polyvinylidene fluoride as a binder were mixed to form a positive electrode mixture, which was then dispersed in N-methyl-2-pyrrolidone to prepare a slurry. This slurry was uniformly applied to both sides of an aluminum current collector having a thickness of 20 μm to a thickness of 180 μm, dried, and then compression molded by a roll press.

For the negative electrode, a slurry was prepared by mixing 90 wt% of the negative electrode active material and 10 wt% of polyvinylidene fluoride as a binder to prepare a negative electrode mixture and dispersing it in N-methyl-2-pyrrolidone. This slurry was uniformly applied on both sides of a copper current collector having a thickness of 10 μm to a thickness of 180 μm, dried, and then compression molded by a roll press.

As the separator, a microporous polyethylene film having a thickness of 25 μm was used. The electrolyte also contains
Ethylene carbonate (EC) and ethylmethyl carbonate (EMC) were mixed at a volume ratio of 1: 1 and an electrolyte solution in which LiPF ₆ as a lithium salt was dissolved at 1.0 mol / l was used.

Therefore, the electrolytic solution (LiPF ₆ / EC +)
A battery using only EMC) (this is referred to as battery A), and seven types of batteries containing 0.0005 to 10 wt% of dibutylhydroxytoluene (BHT) in the above-mentioned electrolytic solution (referred to as batteries B to H). ), And 0.0005 to 10 wt% of dibutylhydroxybenzene (BHB) in the electrolyte solution.
7 types of batteries containing (this is referred to as batteries I to O)
Was produced.

Next, a storage test of these batteries was conducted. The condition of the storage test is that each battery is 1C at 25 ° C.
The battery was charged at a constant current of 4.2 V to 4.2 V, and further at a constant voltage of 4.2 V for a total of 3 hours, and then discharged to 2.75 V at a constant current of 1 C to obtain the discharge capacity at the first cycle. . Next, charge under the same conditions as the first cycle,
Store in a charged state at 80 ° C for 5 days, then store the battery at 25 ° C
Then, discharge was performed under the same conditions as in the first cycle, and the discharge capacity in the second cycle was obtained.

Then, the thickness of the battery after storage at 80 ° C. for 5 days in a charged state was measured. Further, the ratio (%) of the discharge capacity of the second cycle to the discharge capacity of the first cycle was defined as "capacity retention rate".

Table 1 shows the amount of dibutylhydroxytoluene or dibutylhydroxybenzene added to the electrolytic solution, the thickness of the battery after storage for 5 days at 80 ° C. and the capacity retention rate. In addition, in Table 1, in the "Additives" column, BHT represents dibutylhydroxytoluene,
BHB represents dibutylhydroxybenzene. Also,
The “content” column is the weight ratio (%) of dibutylhydroxytoluene or dibutylhydroxybenzene to the total weight of LiPF ₆ / EC + EMC.

[0046]

[Table 1]

From the results of the storage test shown in Table 1, the contents of dibutylhydroxytoluene (BHT) and dibutylhydroxybenzene (BHT) in the electrolytic solution were found to be BHT and B
In the batteries (batteries C to G, J to N) using the non-aqueous electrolyte solution that is 0.001 to 3 wt% with respect to the weight of the electrolyte other than HB, the batteries using the non-aqueous electrolyte solution containing none of these are used. Compared to A, the capacity retention was large, the discharge performance after leaving was not deteriorated, and the swelling of the battery was reduced, and the storage characteristics were improved.

The content of BHT or BHB is 0.00
When the amount is as small as 05 wt% (Batteries B and I), the swelling and capacity retention of the battery are almost the same as those of Battery A, and the effect of adding BHT or BHB to the electrolytic solution is almost the same. I couldn't do it.

Further, the content of BHT or BHB is 10w.
When it is as high as t% (batteries H and O), it can be inferred that the discharge characteristic is deteriorated due to an increase in internal resistance and the capacity retention rate is lowered.

Similar results are obtained when an electrolyte solution other than LiPF ₆ / EC + EMC is used, or when a benzene derivative having a t-butyl group and a hydroxy group other than dibutylhydroxytoluene or dibutylhydroxybenzene is contained. Was obtained.

[0051]

INDUSTRIAL APPLICABILITY In the non-aqueous electrolyte secondary battery according to the present invention, the benzene derivative having a -butyl group and a hydroxy group contained in the electrolyte suppresses the radical reaction particularly on the positive electrode and is Since the progress of oxidative decomposition is reduced kinetically, the gas generation reaction due to the decomposition of the electrolyte on the positive electrode is suppressed, the increase in internal pressure of the battery is suppressed, and the increase in battery thickness is suppressed.

According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery in which the degree of increase in battery thickness is reduced without causing deterioration in discharge performance after storage.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional structure of a prismatic non-aqueous electrolyte secondary battery.
Fig.

[Explanation of symbols]

1 Non-aqueous electrolyte secondary battery 2 power generation elements 3 Positive plate 4 Negative plate 5 separator 6 battery case 7 Battery lid 8 safety valve 9 Positive terminal 10 Positive electrode lead

Claims (3)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode made of a substance that occludes and releases lithium ions, a negative electrode made of a substance that occludes and releases lithium ions, and a non-aqueous electrolyte. A non-aqueous electrolyte secondary battery in which the electrolyte contains a benzene derivative having a t-butyl group and a hydroxy group. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the benzene derivative having a t-butyl group and a hydroxy group is at least one of dibutylhydroxytoluene and dibutylhydroxybenzene. 3. The content of the benzene derivative having a t-butyl group and a hydroxy group contained in the non-aqueous electrolyte is 0 relative to the weight of the electrolyte other than the benzene derivative having a t-butyl group and a hydroxy group. It is 0.001 to 3 wt%, The non-aqueous electrolyte secondary battery of Claim 1 or 2 characterized by the above-mentioned.