JPH11214001A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

(57) [Problem] To provide a non-aqueous electrolyte secondary battery having a high energy density capable of exhibiting good cycle characteristics even when a graphite material is applied to a negative electrode. SOLUTION: In a non-aqueous electrolyte secondary battery comprising at least a positive electrode made of a transition metal oxide containing lithium, a negative electrode made of a graphite material, and a non-aqueous electrolyte containing lithium ions, the graphite material of the negative electrode is used. And a non-aqueous electrolyte is a vinyl sulfone represented by the following formula (1) and a vinyl ester represented by the following formula (2): At least one selected from 1 to 10 (vol%) is contained. Formula 1: CH ₂ ＣＨCHSO ₂ R1 (R1 is a methyl group or an ethyl group) Formula 2: CH ₂ ＣＨCHCO ₂ R2 (R2 is a methyl group or an ethyl group)

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 in which capacity deterioration accompanying progress of a charge / discharge cycle is improved.

[0002]

2. Description of the Related Art A non-aqueous electrolyte secondary battery comprising a positive electrode made of a transition metal oxide containing lithium, a negative electrode made of a carbonaceous material, and a non-aqueous electrolyte containing lithium ions is a conventional secondary battery. Lead-acid battery, nickel-
Attention has been paid to higher energy density compared to cadmium batteries. For example, if a secondary battery is composed of a positive electrode containing a sufficient amount of lithium, a carbonaceous material, and a non-aqueous electrolyte containing lithium ions via a separator, the secondary battery is completely assembled in a discharged state. Will do. Therefore, this type of secondary battery does not enter a dischargeable state unless charged after assembly. When such a secondary battery is charged in the first cycle, lithium in the positive electrode is electrochemically doped between layers of the negative carbonaceous material, and when discharged, the lithium is doped. Lithium is undoped and returns to the positive electrode again.

[0003] In this case, the electric capacity per unit weight (mAh / g) of the carbonaceous material is determined by the capacity capable of occluding and releasing lithium. Therefore, in such a negative electrode, electrochemical reversible occlusion of lithium is performed. It is desirable to make the amount as large as possible. When an intercalation compound of lithium and carbon is electrochemically generated in a battery (corresponding to a charging operation) as in this type of battery, theoretically, a ratio of one lithium atom to six carbon atoms is used. The occluded state becomes the upper limit, that is, the saturated composition of the intercalation compound between lithium and the carbonaceous material.

[0004] As a negative electrode carbonaceous material satisfying such conditions, a material obtained by carbonizing or graphitizing a certain organic polymer compound or a composite thereof by various methods has conventionally been used. Also, naturally occurring carbonaceous substances such as natural graphite are being studied. Among them (00
2) A graphite material having a plane spacing d (002) of 3.38 angstroms or less not only has a high true density and can improve the volume energy density when applied to a battery, but also has a particularly high current density. When inserting and extracting lithium (equivalent to quick charge and heavy load discharge in the operation of the battery), the amount of lithium that can be inserted and extracted, that is, the capacity when the battery is constructed, is large. It is possible to increase the energy density of the electrolyte secondary battery.

[0005]

However, when a carbon material having a high degree of crystallinity, in other words, a high degree of graphitization, is applied as a negative electrode material, lithium is doped in the charging process and simultaneously participates in this electrochemical reaction. There is a problem that a part of the lithium is consumed by reductive decomposition accompanied by gas generation of the non-aqueous electrolyte. That is, charge and discharge are repeated with the capacity reduced over the entire subsequent cycle.

[0006] The charge / discharge reaction is performed by moving lithium ions from the positive electrode side to the negative electrode side and from the negative electrode side to the positive electrode side. Therefore, the amount of movable lithium is the charge / discharge capacity of the battery. However, as described above, in the charging process of each cycle, the movable amount continues to decrease, so that there is a problem that the battery capacity decreases as the charge / discharge cycle progresses. That is, if a carbon material having a high degree of graphitization is applied to a non-aqueous electrolyte secondary battery,
While there is an advantage that high energy density can be achieved, there is also a disadvantage that the capacity of the battery decreases as the cycle progresses because it easily reacts with the non-aqueous electrolyte.

The present invention has been made to solve the above problems, and has as its object to provide a non-aqueous electrolyte secondary battery having a high energy density capable of exhibiting good cycle characteristics even when a graphite material is applied to a negative electrode. Is to provide.

[0008]

In order to achieve the above object, the present invention provides at least a positive electrode comprising a transition metal oxide containing lithium, a negative electrode comprising a graphite material, and a nonaqueous electrolyte containing lithium ions. In the nonaqueous electrolyte secondary battery, the graphite material of the negative electrode has a surface spacing d of the (002) plane.
(002) is equal to or less than 3.38 angstroms, and the nonaqueous electrolyte contains 1 to 10 (vol%) of at least one selected from vinyl sulfone represented by the following formula 1 and vinyl ester represented by the following formula 2: It is characterized by having been done. Formula 1: CH ₂ ＣＨCHSO ₂ R1 (R1 is a methyl group or ethyl group) Formula 2: CH ₂ ＣＨCHCO ₂ R2 (R2 is a methyl group or ethyl group)

[0009] The spacing d (002) of the (002) plane of the carbonaceous material is specified to be 3.38 angstroms or less because the carbon material has a high true density as described above and the Not only can improve the volumetric energy density when applied to lithium batteries, but also especially when lithium is absorbed and released at high current densities (battery operation corresponds to rapid charge and heavy load discharge, respectively) This is because the amount of lithium that can be inserted and extracted, that is, the capacity when a battery is formed, is large. Examples of such a high-crystallinity carbon material include certain organic polymer compounds or composites thereof, pyrolytic carbon, mesophase pitch-based carbon fibers, and various cokes at least 2500 ° C.
Preferable examples include artificial graphite graphitized at a high temperature of 2800 ° C. or higher, and in some cases, a high temperature and a high pressure, or natural graphite having a highly developed crystal, and the (002) plane of the carbonaceous material. This is not true if the interval d (002) is equal to or less than 3.38 angstroms.

In the vinyl sulfone represented by the above formula (1), CH ₂ １CHSO ₂ R1 has a name in the case where R1 is a methyl group, and a name in the case where R1 is an ethyl group, a vinylethyl sulfone. . In addition, the expression 2
Is a vinyl ester represented by CH ₂ ＣＨCHCO ₂ R2, wherein when R2 is a methyl group, the name is vinyl acetate;
When R2 is an ethyl group, the name is vinyl propionate.

The excellent effect can be confirmed particularly when the amount of the vinyl sulfone or vinyl ester added to the nonaqueous electrolyte is 1 to 10 (vol%). When the addition amount is 1 (vol%) or less, the effect of suppressing the decomposition of the non-aqueous electrolyte accompanying the gas generation that occurs on the graphite particle surface is insufficient. On the other hand, when the addition amount is 10 (vol%) or more, the conductivity of the non-aqueous electrolyte decreases with the progress of the charge / discharge cycle, and the electrochemical reaction performed between the positive and negative electrodes during charge / discharge. The addition amount is particularly preferably 1 to 10 (vol%), since the cycle characteristics are deteriorated due to the inhibition of the reaction and the smooth movement of lithium ions in the non-aqueous electrolyte.

According to the present invention, the plane distance d (00)
The decomposition reaction of the non-aqueous electrolyte, which had been a problem when a carbon material having an extremely high degree of graphitization of 3.38 angstroms or less was used as the negative electrode, was converted into the above-mentioned vinyl sulfone and vinyl ester by the non-aqueous electrolyte. Is added to reduce the cycle characteristics of the battery.
Therefore, regarding the positive electrode material, the added non-aqueous electrolyte, and the like, it is possible to use the technology of the non-aqueous electrolyte secondary battery that has been reported or put into practical use without any particular limitation.

In this case, the positive electrode material may be any material as long as it is used in this type of battery. In particular, an oxide comprising at least one or more transition metals containing a sufficient amount of lithium is used. It is preferable to use a material. For example, a composite metal oxide represented by LiMn ₂ O ₄ or a general formula LiMO ₂ (where M represents at least one of Co and Ni; for example, LiCoO and LiCoNiO ₂ ) and an interlayer compound containing lithium are preferable. is there.

The non-aqueous electrolyte is prepared by appropriately combining an organic solvent and an electrolyte, and any of these organic solvents and electrolytes can be used as long as they are used for this type of battery. For example, as the organic solvent, propylene carbonate, ethylene carbonate, 1,2-
Dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolan, 4-methyl-
1,3-dioxolan, diethyl ether, sulfolane, and the like. LiClO ₄ , LiAs as the electrolyte
F ₆ , LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , L
iCl and the like.

As described above, the battery to which the present invention is applied is:
The battery is composed of a positive electrode containing a sufficient amount of lithium, a carbonaceous material, and a non-aqueous electrolyte containing lithium ions, and this type of battery is completely assembled in a discharged state. Therefore, if the battery is not charged after assembly, the battery cannot be discharged. When the battery is charged in the first cycle, lithium in the positive electrode is electrochemically doped between layers of the negative carbonaceous material. Then, when discharging is performed, the doped lithium is undoped and returns to the positive electrode again. Equation 1 and Equation 2
When vinyl sulfone and vinyl ester represented by are added to the non-aqueous electrolyte, it is considered that in the charging process of the first cycle, a stable lithium ion conductive film is formed on the surface of the negative electrode carbon material. . The presence of this film eliminates the direct contact between the edge of the graphite material and the electrolyte, and also makes it possible to suppress the decomposition of the electrolyte during the charging process of the subsequent charge / discharge cycle. It is considered that the cycle characteristics of the battery were improved.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a non-aqueous electrolyte secondary battery according to the present invention will be described below in detail with reference to the accompanying drawings along with comparative examples.

[Preparation of Battery and Charge / Discharge Test] FIG. 1 shows the structure of an AA wound lithium secondary battery according to Examples and Comparative Examples of the present invention. It is a very general thing. That is, in the figure, reference numeral 1 denotes a positive electrode plate, and LiCoO as a positive electrode active material.
An aluminum foil having a thickness of 30 μm is obtained by kneading a mixture obtained by mixing ₂ with a carbon powder of a conductive material and an aqueous dispersion of PTFE as a binder at a weight ratio of 100: 10: 10, and further kneading the mixture into a paste with water. Was coated on both sides of the current collector, dried, rolled, and cut into a predetermined size to produce a belt-shaped positive electrode sheet. This positive electrode sheet was scraped off a part of the mixture perpendicularly to its longitudinal direction to expose the current collector, and a titanium positive electrode lead plate was attached thereto by spot welding. The active material LiCoO ₂ is made of cobalt oxide (Co
O) and lithium carbonate (Li ₂ CO ₃ ) in a molar ratio of 2: 1.
And heated in air at 900 ° C. for 9 hours. The ratio of the aqueous dispersion of PTFE in the mixing ratio of the above materials is the ratio of the solid content.

Reference numeral 2 denotes a negative electrode plate made of a carbon material. A mixture obtained by kneading graphite powder and an aqueous dispersion of PTFE as a binder in a weight ratio of 100: 5 is used as a nickel expanded metal current collector. Press-fit, dry and cut to a predetermined size to produce a strip-shaped sheet. On this negative electrode sheet, a part of the mixture is scraped off perpendicular to the longitudinal direction to form an exposed part of the current collector Then, a nickel negative electrode lead plate was attached thereto by spot welding. In addition, the ratio of PTFE is a ratio of a solid content similarly to the above.

The positive electrode plate 1 and the negative electrode plate 2 are spirally wound through a porous film separator 3 made of polypropylene and inserted into a case 4, and after the insertion, a titanium lead 5 is attached to a stainless steel sealing plate 6. Spot welding.
Reference numeral 7 denotes an aluminum positive electrode cap and positive electrode terminal, which is spot-welded to the sealing plate 6 in advance. The negative electrode lead plate 11 was spot-welded to the center of the circular bottom surface of the case 4 which also served as the negative electrode terminal.

Reference numeral 8 denotes a polypropylene insulating plate, and 9
Is an insulating gasket also made of polypropylene. 1
Reference numeral 0 denotes a safety valve attached so that the internal gas is released to the outside when the battery internal pressure increases due to an abnormality in the battery. Reference numeral 12 denotes an insulating bottom plate made of polypropylene, which has a hole so as to have the same area as the space A generated at the time of winding.
After the above operation, an electrolytic solution (2.3 ml) is injected and sealed. The electrolyte used was one in which LiPF ₆ was dissolved to 1 (mol / l) in a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1. The size of the completed battery is AA type (14.5 mm x 50 mm).

The battery thus produced was charged at a constant current / constant voltage of 600 mA at an upper limit voltage of 4.2 V and a lower limit voltage of 2.5 V for 3 hours, and discharged at a constant current of 200 mA. Then, the above charge / discharge cycle is set to 10
Repeated until 0 cycle.

[Production of Graphite and Its Physical Properties and Battery Characteristics] The graphite powder used for the negative electrode was produced as follows. That is, commercially available coal-based pitch coke was pulverized with a ball mill and classified with a mesh to 22 μm or less. Thereafter, the pulverized material is placed in an electric furnace, and the pulverized product is placed in a nitrogen stream at 70.degree.
The temperature was raised to a predetermined temperature at a temperature rising rate of ° C./min, and the temperature was maintained for 5 hours, followed by cooling to room temperature. Here, the predetermined temperature is 23
00 ° C, 2500 ° C, 2700 ° C, 2900 ° C, 300
Five types of graphites of Samples A to E were prepared by setting each of the five types at 0 ° C. to obtain respective powders.

The sample A thus obtained is
To E in the graphite powder (002) plane d (0
02) was calculated from a measurement chart of X-ray wide-angle diffraction according to a method prescribed by the Japan Society for the Promotion of Science 117 committee. The slit used was 1/6 ° for the spectral slit, 1/6 ° for the scattering slit, 0.15 mm for the light receiving slit, the scanning speed of the counter tube was 0.25 ° / min, and the output of the X-ray was 30 k.
V, 15 mA, and the X-ray diffractometer is a Geigerflex type (117th Committee of the Japan Society for the Promotion of Science, Carbon, 25,
(No. 36), 1963).

When the graphite material was in the form of a block, the graphite block was roughly pulverized by a stamp mill and then finely pulverized by a jet mill to obtain a graphite powder of 200 mesh (Tyler standard sieve) or less. When the graphite material was in the form of powder, only the powder that passed through 200 mesh (Tyler standard sieve) was used. 30 parts are added to 80 parts by weight of the graphite powder.
20 parts by weight of ultrahigh-purity (99.999%) silicon powder of 0 mesh were mixed to obtain a measurement sample, and subjected to X-ray wide-angle diffraction measurement by a diffractometer method.
The plane distance d (002) was calculated from the peak near 7 °. The maximum temperature reached during the heat treatment and d (00
Table 1 below shows the measurement results of 2).

Using each of the graphite samples A to E, the batteries of the comparative examples (that is, the batteries of these comparative examples were prepared by adding vinyl sulfone and vinyl ester to the non-aqueous electrolyte solution in accordance with the above-described procedure. No.) was prepared, and a predetermined charge / discharge cycle test was performed. As the test results, the capacities obtained after the first cycle and the 100th cycle and the capacity retention rates after the 100th cycle calculated from the values are also shown in Table 1. The capacity retention ratio is a ratio of the capacity obtained in the 100th cycle to that in the first cycle.

[0026]

[Table 1]

As is apparent from Table 1, batteries (samples C to E) using a graphite material having a (002) plane spacing d (002) of 3.38 angstroms or less are used.
It was found that the capacity of graphite material within the scope of the present invention was large at the beginning of the cycle, but the cycle deterioration was large. As the heat treatment temperature increases, d (00
It was found that the value of 2) increased, and the battery capacity at the beginning of the cycle also increased.

[Addition of Vinyl Sulfone and Vinyl Ester to Nonaqueous Electrolyte and Its Effect] Next, as an additive to the nonaqueous electrolyte, the following formula: CH ₂ ＣＨCHSO ₂ R1 (R1 is a methyl group or ethyl R1 of vinyl sulfone represented by
Contains vinylmethylsulfone, which is a methyl group, R1 contains vinylethylenesulfone, which is an ethyl group, and formula 2: CH ₂ ＣＨCHCO ₂ R2
When R2 of the vinyl ester represented by (R2 is a methyl group or an ethyl group) contains vinyl acetate of a methyl group,
In the case where vinyl propionate in which R2 was an ethyl group was added, the addition amount was changed to various ratios and added to the non-aqueous electrolyte, and a battery was manufactured using graphite sample E. A charge / discharge cycle test was performed on these batteries in the same manner, and the capacity retention ratio was calculated. The results are shown in Tables 2 to 5. In the tables, those marked with an asterisk (*) indicate that the amount of addition is 1 to 10 (vol.
%), Which corresponds to an embodiment of the present invention.

[0029]

[Table 2]

[0030]

[Table 3]

[0031]

[Table 4]

[0032]

[Table 5]

As can be seen from Tables 2 to 5, vinyl methyl sulfone, vinyl ethyl sulfone, vinyl acetate,
When the amount of vinyl propionate added to the non-aqueous electrolyte is 1 to 10 (vol%), the capacity after 100 cycles is 90% or more, indicating a high value. Similar experiments were performed on graphites C and D. As a result, the initial capacity was 450 mAh or more and the capacity retention ratio was 90% or more.

From the above experiment, the spacing d of the (002) plane was obtained.
Even when a carbon material having a very high degree of graphitization, in which (002) is not more than 3.38 angstroms, is used as the negative electrode, the nonaqueous electrolytic solution contains vinyl sulfone represented by the following formula 1 and vinyl ester represented by the following formula 2 It has been found that a non-aqueous electrolyte secondary battery to which at least one selected from (1) to (1) (vol%) is added has a large initial capacity and can exhibit good cycle characteristics. Formula 1: CH ₂ ＣＨCHSO ₂ R1 (R1 is a methyl group or an ethyl group) Formula 2: CH ₂ ＣＨCHCO ₂ R2 (R2 is a methyl group or an ethyl group)

[0035]

As described in detail above, a nonaqueous electrolyte comprising at least a positive electrode made of a transition metal oxide containing lithium, a negative electrode made of a graphite material, and a nonaqueous electrolyte containing lithium ions. In the secondary battery, (00
2) A carbon material having a very high degree of graphitization with a plane spacing d (002) of 3.38 angstroms or less is used, and a nonaqueous electrolyte has a chemical formula of CH ₂ ＣＨCHSO ₂ R1 (R1 is a methyl group or ethyl). Group) and 1 to 10 (vol%) of at least one selected from vinyl esters represented by vinyl sulfone represented by 2CH ₂ ＣＨCHCO ₂ R2 (R2 is a methyl group or an ethyl group). ADVANTAGE OF THE INVENTION According to the nonaqueous electrolyte secondary battery of this invention, an initial capacity is large and favorable cycle characteristics can be exhibited.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a general structure of an AA wound lithium secondary battery according to an example of the present invention and a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode plate 2 Negative carbon material electrode 3 Porous film separator 4 Case 5 Titanium lead 6 Stainless steel sealing plate 7 Positive electrode cap and positive electrode terminal 8 Insulating plate 9 Insulating gasket 10 Safety valve 11 Negative electrode lead plate 12 Insulating bottom plate

Claims (1)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising at least a positive electrode made of a transition metal oxide containing lithium, a negative electrode made of a graphite material, and a non-aqueous electrolyte containing lithium ions. The material is a plane spacing d (00) of the (002) plane.
2) is 3.38 angstroms or less, and the nonaqueous electrolyte contains 1 to 10 (vol%) of at least one selected from vinyl sulfone represented by the following formula 1 and vinyl ester represented by the following formula 2 A non-aqueous electrolyte secondary battery characterized in that: Formula 1: CH ₂ ＣＨCHSO ₂ R1 (R1 is a methyl group or an ethyl group) Formula 2: CH ₂ ＣＨCHCO ₂ R2 (R2 is a methyl group or an ethyl group)