KR100692733B1 - Nonaqueous electrolyte secondary cell - Google Patents

Abstract

The present invention relates to a nonaqueous electrolyte secondary battery having a positive electrode, a negative electrode containing a carbonaceous material capable of occluding and releasing lithium ions, and a nonaqueous electrolyte containing a nonaqueous solvent.

The non-aqueous solvent includes a sultone compound having at least one double bond in a ring,

The carbonaceous material has a specific surface area of 1.5 m ² / g or more and 10 m ² / g or less by BET method, and peaks derived from an interplanar spacing (d ₀₀₂ ) of 0.336 nm or less appear in powder X-ray diffraction measurements, and CuKα In the X-ray diffraction measurement using a line, peaks are detected at diffraction angles 2θ of 42.8 ° to 44.0 ° and 45.5 ° to 46.6 °, and Raman spectrum measurement shows that the R value is 0.3 or more in intensity ratio and 1 or more in area ratio. It is characterized by providing a nonaqueous electrolyte secondary battery containing.

Description

Non-aqueous electrolyte secondary battery {NONAQUEOUS ELECTROLYTE SECONDARY CELL}

The present invention relates to a nonaqueous electrolyte secondary battery.

In recent years, by miniaturizing and reducing the weight of electronic devices such as mobile communication devices, notebook computers, palm top computers, integrated video cameras, portable CD (MD) players, cordless phones, and the like, in particular, as power sources for these electronic devices, Small and large capacity batteries are required.

Examples of batteries that are popularized as power sources for these electronic devices include primary batteries such as alkaline manganese batteries and secondary batteries such as nickel cadmium batteries and lead acid batteries. Among these, nonaqueous electrolyte secondary batteries using lithium composite oxide for the positive electrode and carbonaceous materials capable of absorbing and releasing lithium ions for the negative electrode are small, lightweight, and have high unit cell voltage and high energy density. It is attracting attention in that it exists.

In the negative electrode, lithium or lithium alloy may be used instead of the carbonaceous material. In this case, however, the charge / discharge operation of the secondary battery is repeated, so that dissolution and precipitation of lithium are repeated to form a so-called dendrite that grows in a needle shape, and the dendrite penetrates a separator to form an internal portion. There is a problem that a short circuit may occur. On the other hand, the negative electrode containing carbonaceous material is less likely to form dendrites as compared with the negative electrode containing lithium or lithium alloy. In addition, by using the graphite material, the cathode capacity can be made close to 372 mAh / g of the theoretical capacity, and a high capacity lithium ion secondary battery can be realized. However, since the graphite material has high activity against most of the nonaqueous electrolytes used in the lithium ion secondary battery and causes decomposition of the nonaqueous electrolyte with the release of the material itself, the initial charge and discharge efficiency, discharge capacity and There is a problem that the cycle characteristics are lowered.

An object of the present invention is to provide a nonaqueous electrolyte secondary battery that satisfies initial charge and discharge efficiency, discharge capacity and cycle characteristics simultaneously.

According to the present invention, there is provided a nonaqueous electrolyte secondary battery having a positive electrode, a negative electrode containing a carbonaceous material capable of occluding and releasing lithium ions, and a nonaqueous electrolyte containing a nonaqueous solvent.

The non-aqueous solvent includes a sultone compound having at least one double bond in the ring,

The carbonaceous material has a specific surface area of 1.5 m ² / g or more and 10 m ² / g or less by the BET method, and peaks derived from a plane interval d ₀₀₂ of 0.336 nm or less appear in the powder X-ray diffraction measurement. In the X-ray diffraction measurement using CuKα rays, peaks are detected at diffraction angles 2θ of 42.8 ° to 44.0 ° and 45.5 ° to 46.6 °, and Raman spectrum measurement shows that the R value is 0.3 or more in intensity ratio and 1 or more in area ratio. A nonaqueous electrolyte secondary battery comprising a material is provided.

According to the present invention, there is also provided a nonaqueous electrolyte secondary battery having a positive electrode, a negative electrode containing a carbonaceous material capable of occluding and releasing lithium ions, and a nonaqueous electrolyte containing a nonaqueous solvent.

The non-aqueous solvent includes a sultone compound having at least one double bond in a ring,

The carbonaceous substance has a specific surface area of 1.5 m ² / g or more and 10 m ² / g or less according to the BET method, and peaks derived from the surface interval d _{002 of} 0.336 nm or less appear in powder X-ray diffraction measurement. A nonaqueous electrolyte secondary battery comprising a graphite material having a tetrahedral structure and having an R value of 0.3 or more in intensity ratio and 1 or more in area ratio by Raman spectrum measurement is provided.

1 is a perspective view showing a thin nonaqueous electrolyte secondary battery which is an example of a nonaqueous electrolyte secondary battery according to the present invention;

FIG. 2 is a partial cross-sectional view of the thin nonaqueous electrolyte secondary battery of FIG. 1 taken along line II-II; FIG.

3 is a partial cross-sectional view showing a cylindrical nonaqueous electrolyte secondary battery which is an example of a nonaqueous electrolyte secondary battery according to the present invention;

4 is a schematic diagram showing a diffraction pattern obtained by X-ray diffraction measurement using CuKα rays with respect to the graphite material of the nonaqueous electrolyte secondary battery of Example 1;

FIG. 5 is a characteristic diagram showing ¹ HNMR spectra of PRSs included in the nonaqueous electrolyte of the nonaqueous electrolyte secondary battery of Example 1. FIG.

Hereinafter, an example of the nonaqueous electrolyte secondary battery according to the present invention will be described.

The nonaqueous electrolyte secondary battery includes a container, an electrode group housed in the container and containing a positive electrode and a negative electrode, and a nonaqueous electrolyte held in the electrode group and containing a nonaqueous solvent.

The nonaqueous solvent contains a sultone compound having one or more double bonds in the ring, and the specific surface area of the carbonaceous material by the BET method is in the range of 1.5 m ² / g or more and 10 m ² / g or less.

Sultone compounds having at least one double bond in the ring can form a protective film on the surface of the carbonaceous material. By setting the specific surface area by the carbonaceous BET method to 1.5 m ² / g or more and 10 m ² / g as in the present invention, the uniformity of the distribution of the protective film formed on the carbonaceous material surface can be increased, and the charge and discharge Since it is possible to suppress the protective film from inhibiting the lithium intercalation reaction according to the present invention, it is possible to provide a nonaqueous electrolyte secondary battery that satisfies initial charge and discharge efficiency, discharge capacity, and cycle characteristics simultaneously.

Hereinafter, the electrode group, the positive electrode, the negative electrode, the separator, the nonaqueous electrolyte and the container will be described.

1) electrode group

The electrode group may, for example, be wound into a flat or vortex shape with a separator interposed between the positive electrode and the negative electrode, or (ii) a vortex shape with a separator interposed between the positive electrode and the negative electrode, and then Direction, or (b) bend or fold one or more times with a separator interposed between the positive electrode and the negative electrode, or (iii) be laminated with a separator interposed between the positive electrode and the negative electrode.

Although it is not necessary to press a electrode group, you may press in order to raise the integration strength of a positive electrode, a negative electrode, and a separator. Moreover, it is also possible to heat at the time of press.

2) anode

The positive electrode includes a current collector and a positive electrode layer supported on one or both sides of the current collector and containing an active material.

The anode layer includes a cathode active material, a binder, and a conductive agent.

Examples of the positive electrode active material include various oxides such as manganese dioxide, lithium manganese composite oxide, lithium-containing nickel oxide, lithium-containing cobalt oxide, lithium-containing nickel cobalt oxide, lithium-containing iron oxide, lithium-containing vanadium oxide, titanium disulfide, molybdenum disulfide, and the like. And chalcogen compounds. Among these, when a lithium-containing cobalt oxide (eg, LiCoO ₂ ), a lithium-containing nickel cobalt oxide (eg, LiNi _0.8 Co _0.2 O ₂ ) and a lithium manganese composite oxide (eg, LiMn ₂ O ₄ , LiMnO ₂ ) are used, a high voltage can be obtained. It is preferable because it can. As the positive electrode active material, one type of oxide may be used alone, or two or more types of oxides may be mixed and used.

As said conductive agent, acetylene black, carbon black, graphite, etc. are mentioned, for example.

The binder retains the active material in the current collector and also has a function of connecting the active materials. As the binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyethersulfone, ethylene propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR) and the like can be used. .

The blending ratio of the positive electrode active material, the conductive agent and the binder is preferably in the range of 80 to 95% by weight of the positive electrode active material, 3 to 20% by weight of the conductive agent, and 2 to 7% by weight of the binder.

As the current collector, a porous conductive substrate or a non-porous conductive substrate can be used. These conductive substrates can be formed of aluminum, stainless steel, or nickel, for example.

The positive electrode is produced by, for example, suspending a conductive agent and a binder in a positive electrode active material in a suitable solvent, applying the suspension to a current collector, drying, and pressing.

3) cathode

The negative electrode includes a current collector and a negative electrode layer supported on one or both sides of the current collector.

The negative electrode layer contains a carbonaceous substance and a binder that occlude and release lithium ions.

The specific surface area by the BET method of the said carbonaceous material exists in the range of 1.5 m <^2> / g or more and 10 m <^2> / g or less. That is, when the specific surface area is less than 1.5 m ² / g, the protective film derived from the sultone compound acts as a resistance component to the lithium intercalation reaction, so that the discharge capacity of the secondary battery decreases. On the other hand, when the specific surface area exceeds 10 m ² / g, the uniformity of the distribution of the protective film decreases, so that the initial charge and discharge efficiency, discharge capacity and charge and discharge cycle life of the secondary battery decrease. By setting the specific surface area within the range of 1.5 to 10 m ² / g, the protective coating by the cyclic sultone compound can be made uniform or thin, so that lithium intercalation is suppressed while suppressing side reactions caused by contact between the nonaqueous electrolyte and the negative electrode active material. It can run efficiently. The more preferable range of specific surface area is 1.5-10 m <^2> / g, and a more preferable range is 1.5-6 m <^2> / g.

The carbonaceous material preferably exhibits a peak derived from an interplanar spacing (d ₀₀₂ ) of 0.336 nm or less in the powder X-ray diffraction measurement. In other words, the carbonaceous material in which the peak derived from the surface spacing (d ₀₀₂ ) of 0.336 nm or less is not detected in the powder X-ray diffraction measurement causes decomposition reaction of nonaqueous solvent other than the sultone compound, so that the discharge capacity or cycle life may decrease. There is concern. The carbonaceous material in which the peak derived from the surface spacing (d ₀₀₂ ) of 0.336 nm or less in the powder X-ray diffraction measurement can narrow the decomposition potential width of the sultone compound. It can form, and the protective film formation reaction speed by a sultone compound can be made high. As a result, the charge and discharge cycle life of the secondary battery can be further improved. The plane spacing (d ₀₀₂₎ is the lower limit side of the plane (002) in a complete graphite crystal spacing (d _002), that is preferably set to 0.3354 nm. The carbonaceous material may also detect peaks derived from the surface interval d ₀₀₂ exceeding 0.336 nm.

The carbonaceous material preferably detects peaks at diffraction angles 2θ of 42.8 ° to 44.0 ° and 45.5 ° to 46.6 ° in X-ray diffraction measurement using CuKα rays. Since the carbonaceous material has a rhombohedral structure, the decomposition potential of the sultone compound can be narrowed, and the decomposition reaction of the solvent other than the sultone compound can be suppressed, thereby further improving the cycle life of the secondary battery. . In particular, the carbonaceous material having a rhombohedral structure and showing peaks derived from a surface spacing (d ₀₀₂ ) of 0.336 nm or less in powder X-ray diffraction measurement has an effect of promoting formation of a protective film derived from a sultone compound and Since the effect of suppressing the decomposition reaction of the nonaqueous solvent other than the compound can be made high, the initial charge and discharge efficiency and the discharge capacity of the secondary battery can be further improved.

(a) powder X-ray diffraction measurements show peaks from plane spacing (d ₀₀₂ ) of 0.336 nm or less, or (b) have a rhombohedral structure, or (a) and (b) both conditions. As the satisfactory carbonaceous material, for example, natural graphite that satisfies at least one of the conditions (a) and (b) can be used. In addition, such carbonaceous materials are subjected to heat treatment at, for example, coke, pitch, thermosetting resin, or the like at 2800 to 3000 ° C., or coke, pitch, thermosetting resin, etc. are added to natural graphite, It can be obtained by carrying out.

As for carbonaceous material, it is preferable that R value by Raman spectrum measurement is 0.3 or more in intensity ratio, and 1 or more in area ratio. Such carbonaceous material can have a low crystalline structure on part or all of the surface while maintaining the specific surface area and the internal graphite structure. As a result, since decomposition reaction of propylene carbonate (PC) can be suppressed, the initial charge / discharge efficiency when using a non-aqueous solvent containing PC can be improved, and a secondary battery excellent in both discharge capacity and cycle life can be realized. Can be. In addition, when the strength ratio is larger than 1.5 and the area ratio is larger than 4.0, the ratio of the low crystalline structure region in the carbonaceous substance is increased, so that decomposition reactions of solvents other than sultone compounds may be promoted. Therefore, it is preferable to set the upper limit of the intensity ratio to 1.5 and the upper limit of the area ratio to 4.0. The range with a more preferable intensity ratio is 0.3-1.5, and the range with a more preferable area ratio is 1.0-3.0.

Carbonaceous substance whose R value by Raman spectrum measurement is 0.3 or more in intensity ratio and 1 or more in area ratio is produced by the method demonstrated below, for example. That is, carbonaceous materials such as coke, pitch, and thermosetting resins or carbon precursors are finely pulverized in a liquid phase or pulverized, and then mixed with a molded graphite material, and then heat-treated at a temperature of 2500 ° C. or lower in an inert atmosphere. . Further, chemical vapor deposition may be performed on the graphite material using benzene, toluene or the like to deposit a carbon layer having a low crystallinity on the surface thereof.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), and the like. Can be used.

The blending ratio of the carbonaceous material and the binder is preferably in the range of 90 to 98% by weight of the carbonaceous material and 2 to 20% by weight of the binder.

As the current collector, a porous conductive substrate or a non-porous conductive substrate can be used. These conductive substrates can be formed of copper, stainless steel or nickel, for example.

The negative electrode is, for example, kneaded with carbonaceous material and a binder that occludes and releases lithium ions in the presence of a solvent, and the obtained suspension is applied to the current collector, dried, and then pressed once or at a target pressure of 2 to 5 times. It is produced by multi-stage pressing.

4) Separator

As the separator, a microporous membrane, a woven fabric, a nonwoven fabric, a laminate of the same material or different kinds of materials, and the like can be used. Examples of the material for forming the separator include polyethylene, polypropylene, ethylene-propylene copolymers, ethylene-butene copolymers, and the like. As the material for forming the separator, one kind or two or more kinds selected from the above kinds can be used.

It is preferable that the thickness of the said separator shall be 30 micrometers or less, and more preferable range is 25 micrometers or less. Moreover, it is preferable that the lower limit of thickness is 5 micrometers, and a more preferable lower limit is 8 micrometers.

The separator preferably has a thermal contraction rate of 20% or less at 120 ° C. for 1 hour. As for the said thermal contraction rate, it is more preferable to set it as 15% or less.

It is preferable that the separator has a porosity in the range of 30 to 60%. The more preferable range of porosity is 35 to 50%.

The separator preferably has an air transmittance of 600 seconds / 100 cm 3 or less. The air permeability refers to the time (seconds) required for 100 cm 3 of air to pass through the separator. The upper limit of the air permeability is preferably 500 seconds / 100 cm 3. In addition, the lower limit of the air permeability is preferably 50 seconds / 100 cm 3, and more preferably 80 seconds / 100 cm 3.

It is preferable to make the width of the separator wider than the width of the positive electrode and the negative electrode. By such a configuration, it is possible to prevent the positive electrode and the negative electrode from directly contacting each other without passing through the separator.

5) non-aqueous electrolyte

As the nonaqueous electrolyte, those having a liquid or gel form may be used. The gel nonaqueous electrolyte can reduce the risk that the nonaqueous electrolyte will leak to the outside when the container is broken by any external force. On the other hand, since the liquid nonaqueous electrolyte can have higher ionic conductivity than the gel nonaqueous electrolyte, the capacity when the nonaqueous electrolyte secondary battery is discharged at a large current and at the low temperature can be improved.

The said nonaqueous electrolyte is prepared by the method demonstrated to the following (I)-(VI), for example.

(I) A nonaqueous electrolyte is obtained by dissolving an electrolyte (for example, a lithium salt) in the above nonaqueous solvent (liquid nonaqueous electrolyte).

(II) An organic polymer compound and a lithium salt are dissolved in a solvent to prepare a polymer solution. Next, the polymer solution is applied or impregnated on an electrode (at least one of the positive electrode and the negative electrode), the separator, or both the electrode and the separator, and the solvent is evaporated to cast. Next, an electrode group is obtained through a separator between an anode and a cathode. This is accommodated in a container, the nonaqueous electrolyte is poured and retained in a cast polymer film to obtain a secondary battery having a gel nonaqueous electrolyte.

(III) In the above-mentioned method of (II), a crosslinked polymer may be used instead of the organic polymer compound. For example, (a) a prepolymer solution is prepared from a compound having a crosslinkable functional group, a lithium salt, and a solvent, which is coated or impregnated on an electrode (at least one of an anode and a cathode), a separator, or both an electrode and a separator. Thereafter, the compound having a crosslinkable functional group is crosslinked. Next, an electrode group is obtained through a separator between an anode and a cathode. The crosslinking step may be carried out before the solvent is volatilized, and in the case of crosslinking by heating, the crosslinking may be carried out while volatilizing the solvent. Or (b) a prepolymer solution is applied or impregnated to an electrode (at least one of the positive electrode and the negative electrode), the separator, or both the electrode and the separator, and then an electrode group is obtained by interposing a separator between the positive electrode and the negative electrode. It is also possible to perform a crosslinking process after that.

Although the method of crosslinking is not specifically limited, In consideration of the simplicity and cost of an apparatus, heat polymerization or photopolymerization by an ultraviolet-ray is preferable. In addition, when crosslinking is carried out by heating or ultraviolet irradiation, it is necessary to add a polymerization initiator suitable for the polymerization method to the prepolymer solution. Moreover, a polymerization initiator is not limited to one type, You may mix and use two or more types.

(IV) The organic polymer compound and the lithium salt are directly dissolved in the nonaqueous electrolyte to obtain a gel electrolyte. The gel electrolyte is coated or impregnated on an electrode (at least one of the positive electrode and the negative electrode), the separator, or both the electrode and the separator, and then a separator is interposed between the positive electrode and the negative electrode to obtain an electrode group, and the gel nonaqueous electrolyte is provided. Obtain a secondary battery.

(V) In the above-mentioned method of (IV), a crosslinked polymer can be used in place of the organic polymer compound. For example, a pre-gel solution is prepared from a compound having a crosslinkable functional group, a lithium salt, and an electrolyte, and coated or impregnated with an electrode (at least one of the positive electrode and the negative electrode), the separator, or both the electrode and the separator. Thereafter, the compound having a crosslinkable functional group is crosslinked. You may perform the said crosslinking process before producing an electrode group, or after preparation.

The method of crosslinking is not particularly limited, but heat polymerization or photopolymerization by ultraviolet rays is preferable in view of the simplicity and cost of the apparatus. Moreover, when crosslinking is performed by heating or ultraviolet irradiation, it is necessary to add the polymerization initiator suitable for a polymerization method to a pregel solution. In addition, a polymerization initiator is not limited to one type, You may mix and use two or more types.

(VI) An electrode group in which a separator is interposed between an anode and a cathode is accommodated in a container. Next, after impregnating the electrode group with the gel nonaqueous electrolyte of the above-mentioned (IV), the container is sealed and the secondary battery provided with the gel nonaqueous electrolyte is obtained. Or after impregnating the pregel solution of (V) in an electrode group, the pregel solution is bridge | crosslinked before or after sealing a container, and the secondary battery provided with a gel nonaqueous electrolyte is obtained.

As the above-mentioned organic polymer compounds of (II) and (IV), for example, polymers having an alkylene oxide such as polyethylene oxide and polypropylene oxide or derivatives thereof as a skeleton; Vinylidene fluoride, propylene hexafluoride, ethylene tetrafluoride, perfluoroalkyl vinyl ether, or copolymers thereof; Polyacrylate-based polymers having polyacrylonitrile or polyacrylonitrile as a main component and a copolymer of methyl acrylate, vinyl pyrrolidone, vinyl acetate or the like; Polyether polymers; Polycarbonate-based polymers; Polyacrylonitrile-based polymers; Polyester-based polymers based on polyethylene terephthalate, polybutylene terephthalate or derivatives thereof and copolymers with ethyl methacrylate, styrene, vinyl acetate, and the like; Fluorine resins; Polyolefin resin; Polyether resins; And the copolymer etc. which consist of these two or more types are mentioned. Moreover, the prepolymer solution (III) and pregel solution (V) which consist of a monomer and oligomer which become precursors of these polymers can be produced.

In the present invention, a sultone compound having one double bond is contained in the ring in the electrolyte.

Here, as the sultone compound having at least one double bond in the ring, sultone compound A represented by the following formula (1) or sultone compound B in which at least one H in sultone compound A is substituted with a hydrocarbon group can be used. In addition, in this application, sultone compound A or sultone compound B may be used independently, and both sultone compound A and sultone compound B may be used.

(In Formula 1,

C _m H _n is a straight chain hydrocarbon group,

m and n are two or more integers satisfying 2m> n.)

The sultone compound having a double bond in the ring can form a dense protective film on the surface of the negative electrode without opening the double bond when the reduction reaction with the negative electrode, the polymerization reaction occurs and does not involve gas generation. At this time, if EC and PC exist, a dense protective film excellent in lithium ion permeability can be formed.

Preferred among the sultone compounds are compounds in which m = 3, n = 4, ie 1,3-propenesultone (PRS), or compounds with m = 4, n = 6, ie 1,4-butylene Sulton (BTS). It is because the protective film derived from these compounds has the highest effect of suppressing the side reaction by the contact of Li <^+> and nonaqueous electrolyte in graphite material. As a sultone compound, 1, 3- propene sultone (PRS) or 1, 4- butylene sultone (BTS) may be used independently, and these PRS and BTS may be used together.

It is preferable to make the ratio of a sultone compound into 10 weight% or less. If the ratio of the sultone compound exceeds 10% by weight, the lithium ion permeability of the protective film is lowered, which may increase the impedance of the negative electrode and fail to obtain sufficient capacity or charge and discharge efficiency. In addition, in order to maintain the design capacity of the electrode and to maintain the initial charge / discharge efficiency, the ratio of the sultone compound is preferably 4% by weight or less. Moreover, in order to ensure the formation amount of a protective film sufficiently, it is preferable to ensure the ratio of a sultone compound at least 0.01 weight%. Moreover, when the ratio of a sultone compound is 0.1 weight% or more, the protective function, such as suppressing gas generation at the time of initial charge by a protective film, can be made sufficient.

It is preferable to contain other solvent other than a sultone compound in a nonaqueous solvent. Other solvents include, for example, cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), linear carbonates (e.g., methyl ethyl carbonate (MEC), diethyl carbonate). (DEC), dimethyl carbonate (DMC)), γ-butyrolactone (GBL), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), phenyl ethylene carbonate (phEC), γ Valerolactone (VL), methyl propionate (MP), ethyl propionate (EP), 2-methylfuran (2Me-F), furan (F), thiophene (TIOP), catecholcarbonate (CATC), Ethylene sulfite (ES), 12-crown-4 (Crown), tetraethylene glycol dimethyl ether (Ether), etc. are mentioned. The kind of other solvent can be made into one type or two types or more.

Among these, vinylene carbonate can enhance the compactness of a protective film without significantly reducing the lithium ion permeability of a carbonaceous material, and can further improve initial charge-discharge efficiency, discharge capacity, and cycle life.

It is preferable to make the weight ratio of the vinylene carbonate in a nonaqueous solvent into the range of 10 weight% or less. This is because when the weight ratio of vinylene carbonate is more than 10% by weight, the lithium ion permeability of the protective film on the surface of the negative electrode is lowered, which may significantly impair initial charge and discharge efficiency, discharge capacity or cycle life. The more preferable range of the weight ratio of vinylene carbonate is 0.01 to 5% by weight.

Preferred compositions of the non-aqueous solvent include (I) a cyclic carbonate, γ-butyrolactone (GBL), and a non-aqueous solvent containing a sultone compound, (II) EC, a straight carbonate comprising at least MEC, and Nonaqueous solvent comprising sultone compounds, (III) cyclic carbonate comprising at least EC and PC, sultone compound, and nonaqueous solvent comprising GBL, (IV) cyclic carbonate comprising at least EC and PC And a non-aqueous solvent containing a sultone compound.

It is preferable that EC is contained in the cyclic carbonate of nonaqueous solvent (I), and it is more preferable if PC is contained with EC. According to the nonaqueous solvent (I), the high temperature storage characteristics and the cycle life of the secondary battery can be further improved. If vinylene carbonate (VC) is further added to the non-aqueous solvent (I), the low-temperature discharge characteristics of the secondary battery can also be improved.

Methyl ethyl carbonate (MEC) is included as an essential component in the linear carbonate of the non-aqueous solvent (II), and only MEC may be used as the linear carbonate, or other linear carbonate may be used in combination with the MEC. good. According to the non-aqueous solvent (II), gas generation during initial charge and discharge can be suppressed, and low-temperature discharge characteristics and cycle life can be improved.

It is preferable that other linear carbonates used together with MEC have a low freezing point and a low viscosity. Moreover, the solvent with a relatively small molecular weight is preferable. This is because the discharge characteristics at low temperatures become good. As another linear carbonate, at least one of diethyl carbonate (DEC) and dimethyl carbonate (DMC) is preferable. Particularly, from the viewpoint of obtaining excellent charge and discharge cycle characteristics, linear carbonates containing MEC and DEC are preferred, while linear carbonates containing MEC and DMC are preferred from the viewpoint of obtaining excellent low temperature discharge characteristics. .

If vinylene carbonate (VC) is further added to the nonaqueous solvent (II), the cycle life of the secondary battery can be further improved.

The nonaqueous solvent (III) can reduce the amount of gas generated during the initial charge / discharge of the secondary battery and at the same time enhance the high temperature storage characteristics. The addition of vinylene carbonate (VC) to the nonaqueous solvent (II) can further improve the high temperature storage characteristics of the secondary battery.

The nonaqueous solvent (IV) can suppress the amount of gas generated at the time of initial charge and can also improve the initial charge and discharge efficiency. The addition of vinylene carbonate (VC) to the nonaqueous solvent (IV) can further improve the initial charge and discharge efficiency.

Examples of the electrolyte dissolved in the non-aqueous solvent include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoride (LiAsF ₆ ), and trifluorometasul acid lithium (LiCF ₃ SO _3), bis trimethyl-sulfonyl imide lithium fluoro _{[(LiN (CF 3 SO 2} ) 2], LiN (C 2 F 5 SO 2) there may be mentioned lithium salt of _2, and so on. The type of electrolyte used may be one kind or two or more kinds.

Among these, it is preferable to contain LiPF ₆ or LiBF ₄ . In _{addition, (LiN (CF 3 SO 2} ) 2 and _{LiN (C 2 F 5 SO 2} ) mixed salt containing a salt composed of the already deuyeom consisting of one or more of the _2, LiBF ₄ and LiPF least one of _six ( The use of A) or a mixed salt (B) containing LiBF ₄ and LiPF ₆ can further improve cycle life at high temperatures, and also improve the thermal stability of the electrolyte, which can be caused by self discharge during storage at high temperatures. The voltage drop can be suppressed.

The amount of the electrolyte dissolved in the nonaqueous solvent is preferably 0.5 to 2.5 mol / L. A more preferable range is 1 to 2.5 mol / L.

In order to improve the wettability with the separator, the liquid nonaqueous electrolyte may contain a surfactant such as trioctyl phosphate (TOP). 3% or less of the addition amount of surfactant is preferable, or it is preferable to carry out in 0.1 to 1% of range.

The amount of the liquid nonaqueous electrolyte is preferably 0.2 to 0.6 g per 100 mAh battery unit capacity. The more preferable range of the liquid nonaqueous mass is 0.25 to 0.55 g / 100 mAh.

6) Container (Storage Container)

The shape of the container can be, for example, a bottomed cylindrical shape, a bottomed rectangular cylinder shape, a bag shape, a cup shape or the like.

This container can be formed, for example, from the sheet | seat containing a resin layer, a metal plate, a metal film, etc.

The resin layer contained in the said sheet can be comprised, for example from polyolefin and polyamide.

The metal plate and the metal film may be formed from, for example, iron, stainless steel, and aluminum.

It is preferable that the thickness (wall thickness of a container) of a container shall be 0.3 mm or less. If the thickness is thicker than 0.3 mm, it is difficult to obtain a high weight energy density and a volume energy density. The preferred range of the container thickness is 0.25 mm or less, more preferably 0.15 mm or less, and the most preferred range is 0.12 mm or less. Moreover, when thickness is thinner than 0.05 mm, since it will become easy to deform or break, it is preferable that the lower limit of container thickness shall be 0.05 mm.

A thin lithium ion secondary battery and a cylindrical lithium ion secondary battery which are examples of the nonaqueous electrolyte secondary battery according to the present invention will be described in detail with reference to FIGS. 1 to 3.

1 is a perspective view showing a thin lithium ion secondary battery which is an example of a nonaqueous electrolyte secondary battery according to the present invention, FIG. 2 is an enlarged cross-sectional view of an essential part of the nonaqueous electrolyte secondary battery of FIG. 1, and FIG. 3 is a nonaqueous electrolyte secondary battery according to the present invention. It is a partial cut-away perspective view which shows the cylindrical nonaqueous electrolyte secondary battery which is an example of a battery.

First, a thin lithium ion secondary battery will be described with reference to FIGS. 1 and 2.

As shown in FIG. 1, the electrode group 2 is accommodated in the container main body 1 which consists of a long box-shaped cup shape. The electrode group 2 has a structure in which a laminate including an anode 3, a cathode 4, and a separator 5 disposed between the anode 3 and the cathode 4 is wound in a flat shape. The nonaqueous electrolyte is held in the electrode group 2. A part of the edge of the container main body 1 is wide, and functions as the cover plate 6. The container body 1 and the cover plate 6 are each composed of a laminate film. The laminate film comprises an outer protective layer 7 and an inner protective layer 8 containing a thermoplastic resin, and a metal layer 9 disposed between the outer protective layer 7 and the inner protective layer 8. The lid 6 is fixed to the container main body 1 by a heat seal using a thermoplastic resin of the inner protective layer 8, whereby the electrode group 2 is sealed in the container. The positive electrode tab 10 is connected to the positive electrode 3, and the negative electrode tab 11 is connected to the negative electrode 4, and each of them is drawn out of the container to serve as a positive electrode terminal and a negative electrode terminal.

Next, a cylindrical lithium ion secondary battery will be described with reference to FIG. 3.

In the bottomed cylindrical container 21 made of stainless steel, an insulator 22 is disposed at the bottom. The electrode group 23 is housed in the container 21. The electrode group 23 has a structure in which a belt-like material in which the anode 24, the separator 25, the cathode 26, and the separator 25 are laminated is wound in a spiral shape so that the separator 25 is located outside. have.

The nonaqueous electrolyte is accommodated in the container 21. The insulating paper 27 with the central portion open is disposed above the electrode group 23 in the container 21. The insulating sealing plate 28 is disposed in the upper opening of the container 21, and the sealing plate 28 is fixed to the container 21 by performing a process of tightly adhering the vicinity of the upper opening inward. The positive terminal 29 is fitted to the center of the insulating sealing plate 28. One end of the positive electrode lead 30 is connected to the anode 24 and the other end is connected to the anode terminal 29, respectively. The negative electrode 26 is connected to the container 21 which is a negative electrode terminal through a negative electrode lead (not shown).

The nonaqueous electrolyte secondary battery according to the present invention described above is a nonaqueous electrolyte secondary battery having a positive electrode, a negative electrode containing carbonaceous material capable of occluding and releasing lithium ions, and a nonaqueous electrolyte containing a nonaqueous solvent.

The non-aqueous solvent includes a sultone compound having at least one double bond in the ring, and the specific surface area of the carbonaceous material by the BET method is in the range of 1.5 m ² / g or more and 10 m ² / g or less. will be.

Thus, by using a carbonaceous material having a large specific surface area, the reactivity of the sultone compound can be optimized, thereby realizing a secondary battery that satisfies initial charge and discharge efficiency, discharge capacity, and cycle life at the same time.

In the carbonaceous substance, peaks derived from a surface spacing (d ₀₀₂ ) of 0.336 nm or less appear in powder X-ray diffraction measurement, or diffraction angles 2θ are 42.8 ° to 44.0 ° and 45.5 ° in X-ray diffraction measurement using CuKα rays. The appearance of a peak at ˜46.6 ° may promote the decomposition reaction of the sultone compound, thereby forming a protective film while suppressing side reactions with coexisting solvents. Therefore, the initial charge and discharge efficiency and the discharge capacity of the secondary battery can be further improved.

In addition, since the decomposition value of a solvent (particularly propylene carbonate) other than a sultone compound can be suppressed by setting the R value by the Raman spectrum measurement of carbonaceous material to 0.3 or more in intensity ratio and 1.0 or more in area ratio, initial charge and discharge of the secondary battery The efficiency can be further improved.

In particular, the carbonaceous material has a specific surface area of 1.5 m ² / g or more and 10 m ² / g or less, and peaks derived from an interplanar spacing (d ₀₀₂ ) of 0.336 nm or less appear in a powder X-ray diffraction measurement, and the Raman spectrum measurement In the X-ray diffraction measurement using a CuKα ray with an R value of 0.3 or more in intensity ratio or 1 or more in area ratio, peaks are detected at diffraction angles 2θ of 42.8 ° to 44.0 ° and 45.5 ° to 46.6 °, By using the graphite material having a structure, the charge and discharge cycle life of the secondary battery can be further improved.

Namely, the graphite material having the above-described surface spacing, specific surface area, and R value and the diffraction peak or rhombohedral structure described above preferentially reacts with the sultone compound to protect the protective film without damaging the lithium ion permeability on the surface of the cathode. Can be formed uniformly. By reacting with a sultone compound preferentially and forming a dense protective film at the time of initial charge, the decomposition reaction of cyclic carbonates such as PC can be suppressed, and the amount of gas generated at the time of initial charge can be reduced. As a result, the initial charge and discharge efficiency can be increased, so that the discharge capacity and the charge and discharge cycle life can be further improved.

Hereinafter, embodiments of the present invention will be described in detail with reference to the above-mentioned drawings.

(Example 1)

<Production of Anode>

First, 90% by weight of lithium cobalt oxide (Li _x CoO ₂ ; where X is 0 <X≤1), dimethylformamide (5% by weight of acetylene black and 5% by weight of polyvinylidene fluoride (PVdF)) DMF) solution was added and mixed, and the slurry was prepared. The slurry was applied to both surfaces of a current collector made of aluminum foil having a thickness of 15 µm, and then dried and pressed to prepare a positive electrode having a structure in which the positive electrode layer was supported on both sides of the current collector. Moreover, the thickness of the anode layer was 60 micrometers per side.

<Production of Cathode>

In powder X-ray diffraction, a peak at 0.3358 nm of the plane spacing (d ₀₀₂ ) of the (002) plane was detected, and in the X-ray diffraction measurement using CuKα rays, the diffraction angle 2θ was 43.35 ° (P4) and 46.19 ° ( Natural graphite having a peak at P5) was prepared. 4 shows the X-ray diffraction measurement results using CuKα rays of the graphite material used in Example 1. FIG. The surface spacing d ₀₀₂ of the (002) plane is a value obtained by the half value width midpoint method in the powder X-ray diffraction spectrum. At this time, scattering correction such as Lorentz scattering was not performed.

After the spheroidizing treatment was performed on the natural graphite, a chemical vapor deposition treatment was performed at 1000 ° C. under a benzene / N ₂ stream to obtain a graphite material.

The specific surface area and Raman R value by the BET method are measured by the method described below in the graphite material, and the results are shown in Table 1 below.

(Measurement of specific surface area by BET method)

Cantasorb used the brand name of Yuasa Ionics as a measuring apparatus. The sample amount was set to about 0.5 g, and the sample was degassed at 120 ° C for 15 minutes as a pretreatment.

(Measurement of R value)

The peak separation is performed on the Raman spectrum of the graphite material, and D (A1g) is a peak derived from the confusion of the structure of graphite near 1360 cm ⁻¹ , and D ′ (Alg): graphite around 1620 cm ^−1. A peak derived from the confusion of the structure of D, a peak derived from the confusion of the graphite structure of amorphous carbon, G (E2g): a peak derived from the graphite structure around 1580 cm ^-1 , and G: derived from the graphite structure of amorphous carbon A peak was obtained.

To calculate the intensity of each peak, and the one that I _D, and a ratio (I _D / I _G) with the one I _G sum the intensity of the peak derived from the G band sum the intensity of the peak derived from the D-band intensity ratio As shown in Table 1 below. In addition, calculating the area of each peak, and would be S _G ratio (S _D / S _G) with the total area value of the peak derived from one to S _D and G bands in total an area value of the peak derived from the D-band Is shown in Table 1 as the area ratio.

95% by weight of the obtained graphite material powder and 5% by weight of a dimethylformamide (DMF) solution of polyvinylidene fluoride (PVdF) were mixed to prepare a slurry. The said slurry was apply | coated on both surfaces of the electrical power collector which consists of copper foil of 12 micrometers in thickness, and it dried and pressed, and produced the negative electrode of the structure by which the negative electrode layer was carried by the electrical power collector. Moreover, the thickness of the cathode layer was 55 micrometers per side.

<Separator>

The separator which consists of a microporous polyethylene membrane of 25 micrometers in thickness was prepared.

<Preparation of nonaqueous electrolyte amount>

1,3-propenesultone (PRS) was 2 weights with respect to the mixed solution which mixed ethylene carbonate (EC) and (gamma) -butyrolactone (GBL) so that it may become 35:65 by volume ratio (EC: GBL). 1% by weight of vinylene carbonate (VC) and 0.5% by weight of trioctylphosphate (TOP) were added to prepare a non-aqueous solvent. Lithium tetrafluoroborate (LiBF ₄ ) was dissolved in the obtained nonaqueous solvent so as to have a concentration of 1.5 mol / L, and a liquid nonaqueous electrolyte was prepared.

<Production of electrode group>

Ultrasonic welding a positive electrode lead made of a strip-shaped aluminum foil (thickness 100 μm) to the current collector of the positive electrode, and ultrasonic welding the negative electrode lead made of strip-shaped nickel foil (thickness 100 μm) to the current collector of the negative electrode; An electrode group was produced by winding in a spiral shape between the positive electrode and the negative electrode through the separator.

The laminated film of thickness 100micrometer which covered both surfaces of aluminum foil with polyethylene was shape | molded in rectangular cup shape by the press, and the said electrode group was accommodated in the obtained container.

Next, the electrode group in a container was vacuum-dried at 80 degreeC for 12 hours, and the moisture contained in an electrode group and a laminated film was removed.

The liquid nonaqueous electrolyte was injected into the electrode group in the container so that the amount per 1Ah of the battery capacity was 4.8 g, and sealed by heat seal, and then the structure shown in FIGS. 1 and 2 described above was 3.6 mm in thickness and width. The 35 mm non-aqueous electrolyte secondary battery of 62 mm in height and nominal capacity of 0.65 Ah was assembled.

The following treatment was performed on the nonaqueous electrolyte secondary battery as an initial charge / discharge step. First, constant current and constant voltage charge were performed at 0.2 C to 4.2 V for 15 hours. Then, it discharged to 3.0V at 0.2 C at room temperature, and produced the nonaqueous electrolyte secondary battery.

Here, 1 C is a current value required for discharging the nominal capacity Ah in one hour. Therefore, 0.2 C is a current value required to discharge the nominal capacity Ah in 5 hours.

(Examples 2 to 5)

A thin nonaqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1 except that the composition of the nonaqueous solvent, the type and concentration of the electrolyte were changed as shown in Table 1 below.

(Example 6)

In powder X-ray diffraction, a peak at 0.3358 nm of the plane spacing (d ₀₀₂ ) of the (002) plane is detected, and a diffraction angle 2θ appears at 43.35 ° and 46.19 ° in an X-ray diffraction measurement using CuKα rays. Natural graphite was molded to obtain a graphite material.

The graphite material was measured in the same manner as described in Example 1 above, and the specific surface area and the Raman R value by the BET method were measured, and the results are shown in Table 1 below.

A negative electrode was produced in the same manner as described in Example 1 except for using such a graphite material.

Also, 2,% by weight of 1,3-propenesultone (PRS) and trioctyl to the mixed solution obtained by mixing ethylene carbonate (EC) and propylene carbonate (PC) in a volume ratio of 50:50. 0.5 weight% of phosphates (TOP) were added, and the nonaqueous solvent was prepared. Lithium hexafluorophosphate (LiPF ₆ ) was dissolved in the obtained non-aqueous solvent so as to have a concentration of 1 mol / L, and a liquid nonaqueous electrolyte was prepared.

A thin nonaqueous electrolyte secondary battery was produced in the same manner as described in Example 1 except that the obtained negative electrode and the nonaqueous electrolyte were used.

(Example 7)

In powder X-ray diffraction, a peak at 0.3358 nm of the plane spacing (d ₀₀₂ ) of the (002) plane was detected, and a peak derived from the rhombohedral system formed an undetected artificial graphite to obtain a graphite material. .

The graphite material was measured in the same manner as described in Example 1 above, and the specific surface area and the Raman R value by the BET method were measured, and the results are shown in Table 1 below.

A negative electrode was produced in the same manner as described in Example 1 except for using such a graphite material.

In addition, a liquid nonaqueous electrolyte was prepared in the same manner as described in Example 6 above.

A thin nonaqueous electrolyte secondary battery was produced in the same manner as described in Example 1 except that the obtained negative electrode and the nonaqueous electrolyte were used.

(Example 8)

In powder X-ray diffraction, a peak at which the plane spacing (d ₀₀₂ ) of the (002) plane is derived from 0.3362 nm is detected, and a peak derived from the rhombohedral system is prepared to prepare a spherical artificial graphite material having no detection. The graphite material was measured in the same manner as described in Example 1 above, and the specific surface area and the Raman R value by the BET method were measured, and the results are shown in Table 1 below.

A negative electrode was produced in the same manner as described in Example 1 except for using such a graphite material.

In addition, a liquid nonaqueous electrolyte was prepared in the same manner as described in Example 6 above.

A thin nonaqueous electrolyte secondary battery was produced in the same manner as described in Example 1 except that the obtained negative electrode and the nonaqueous electrolyte were used.

(Examples 9-11)

A thin nonaqueous electrolyte secondary battery was produced in the same manner as described in Example 1 except that the parameters of the graphite material and the composition of the nonaqueous electrolyte were set as shown in Table 1 below.

In addition, the graphite material used in Examples 9-11 was produced by the method demonstrated below, respectively.

In Example 9, the graphite material was obtained by pitch coating on the same natural graphite as described in Example 1, and then baking at 1500 ° C.

In Example 10, in the powder X-ray diffraction, the peak at which the plane spacing (d ₀₀₂ ) of the (002) plane originated from 0.3356 nm was detected, and the diffraction angle 2θ was 43.35 ° (P4) in the X-ray diffraction measurement using CuKα rays. ) And natural graphite with peaks at 46.19 ° (P5).

After the spheroidizing treatment on the natural graphite, a chemical vapor deposition treatment was carried out at 1000 ° C. under a benzene / N ₂ stream to obtain a graphite material.

In Example 11, after spheroidizing the same natural graphite as described in Example 10, it was pitch-coated and baked at 1000 ° C to obtain a graphite material.

(Comparative Example 1)

In the powder X-ray diffraction, a spherical artificial graphite in which the surface spacing (d ₀₀₂ ) of the (002) plane was detected at 0.3365 nm was prepared, and the artificial graphite was prepared in the same manner as described in Example 1 above. The specific surface area and the Raman R value were measured by the BET method, and the results are shown in Table 1 below.

A negative electrode was produced in the same manner as described in Example 1 except for using such artificial graphite.

Also, 1,3-propenesultone (PRS) was 0.5 in a mixed solution obtained by mixing ethylene carbonate (EC) and methyl ethyl carbonate (MEC) so that the volume ratio (EC: MEC) was 35:65. 0.5% by weight and vinylene carbonate (VC) were added to prepare a non-aqueous solvent. Lithium hexafluorophosphate (LiPF ₆ ) was dissolved in the obtained nonaqueous solvent so that the concentration was 1 mol / L, and a liquid nonaqueous electrolyte was prepared.

A thin nonaqueous electrolyte secondary battery was produced in the same manner as described in Example 1 except that the obtained negative electrode and the nonaqueous electrolyte were used.

(Comparative Examples 2 to 3)

A thin nonaqueous electrolyte secondary battery was prepared in the same manner as described in Comparative Example 1 except that the composition of the nonaqueous solvent, the type and concentration of the electrolyte were changed as shown in Table 2 below.

(Comparative Example 4)

A thin nonaqueous electrolyte secondary battery having the same structure as described in Comparative Example 1 was prepared except that the specific surface area of the carbonaceous material by the BET method was changed as shown in Table 2 below.

(Comparative Example 5)

In powder X-ray diffraction, a peak at 0.3358 nm of the plane spacing (d ₀₀₂ ) of the (002) plane is detected, and a diffraction angle 2θ is found at 43.35 ° and 46.19 ° in an X-ray diffraction measurement using CuKα rays. Natural graphite was prepared as a graphite material.

The graphite material was measured in the same manner as described in Example 1 above, and the specific surface area and the Raman R value by the BET method were measured, and the results are shown in Table 1 below.

A negative electrode was produced in the same manner as described in Example 1 except for using such a graphite material, and a thin nonaqueous electrolyte secondary battery having the same structure as described in Example 1 was prepared using the negative electrode. .

The initial charge / discharge efficiency, battery capacity, and charge / discharge cycle characteristics of the secondary batteries obtained in Examples 1 to 11 and Comparative Examples 1 to 5 were evaluated under the conditions described below, and the results are shown in Tables 1 to 2 below.

Initial charge and discharge efficiency

Each secondary battery was subjected to a charge and discharge test with a constant voltage charge of 0.2 C, a charge end voltage of 4.2 V, and a discharge cutting voltage of 3.0 V in an environment of a temperature of 20 ° C., to determine initial charge and discharge efficiency. It evaluates and shows the result in following Tables 1-2.

(Battery capacity)

The discharge capacity at the discharge cutting voltage 3.0V at the time of initial charge / discharge was compared as a battery capacity, and the result is shown to the following Tables 1-2.

(Charge / Discharge Cycle Characteristics)

Charge / discharge tests of charging and discharging rate 1 C, end-of-charge voltage 4.2 V, and end-of-discharge voltage 3.0 V were carried out on each secondary battery, and the discharge capacity retention rate after repeated 50 times and 300 times of charging and discharging in an environment at a temperature of 20 ° C ( The capacity of the first discharge is 100%), and the results are shown in Tables 1 and 2 below.

As is clear from Tables 1 to 2, the secondary batteries of Examples 1 to 11 using carbonaceous materials having a specific surface area of 1.5 m ² / g or more and 10 m ² / g or less by the BET method are initially charged and discharged. It was found that the efficiency, discharge capacity, and capacity retention rate at 300 cycles were all excellent. Among them, a peak derived from a plane spacing (d ₀₀₂ ) of 0.336 nm or less appears in the powder X-ray diffraction measurement, has a rhombohedral structure, and the R value by Raman spectrum measurement is 0.3 or more in intensity ratio and 1 or more in area ratio. In the secondary batteries of Examples 2 to 4 using the graphite material and the nonaqueous electrolyte containing EC, PRS and VC, both the discharge capacity and the capacity retention rate at 300 cycles are the highest.

On the other hand, in the secondary batteries of Comparative Examples 1 to 3 using carbonaceous substances having a specific surface area of less than 1.5 m ² / g by the BET method, both the discharge capacity and the capacity retention rate at 300 cycles were lowered, Could not execute the charge / discharge reaction. The secondary battery of Comparative Example 4 had a high capacity retention rate at 300 cycles but a low discharge capacity.

In addition, in the secondary batteries of Examples 1 to 5 and 9 to 11, the capacity retention rate at 50 cycles was higher than 90%, whereas in the secondary batteries of Examples 6 to 8, the capacity retention ratio at 50 cycles reached 90%. I couldn't. The main reason can be considered to be explained below.

In the secondary battery of Example 6, since the graphitization degree of the surface is high, in addition to the decomposition of PRS, the decomposition reaction of cyclic carbonates such as PC is caused, and the resistance of the protective film on the surface of the negative electrode increases with an initial cycle, and the capacity is increased. The capacity retention rate at the 50th cycle was lowered because of the sharp drop.

On the other hand, in the secondary batteries of Examples 7 and 8, since the graphite material having no rhombohedral structure is used, the decomposition reaction of PRS does not proceed preferentially, and the resistance of the protective film on the surface of the negative electrode increases along the initial cycle. As a result, the capacity retention rate at the 50th cycle was lowered because the capacity dropped sharply.

(Detection method of PRS and VC)

In the secondary battery of Example 1, after the initial charge / discharge process, the circuit was opened for at least 5 hours to sufficiently stabilize the potential, and the Ar concentration was 99.9% or more, and the dew point was -50 ° C or less. It disassembled in the glove box and the electrode group was taken out. The electrode group was filled into a centrifuge tube, sealed by adding dimethyl sulfoxide (DMSO) -d ₆ , taken out from the glove box, and centrifuged. Thereafter, the mixed solution of the electrolyte solution and the DMSO-d ₆ was collected from the centrifuge tube in the glove box. 0.5 ml of the said mixed solvent was put into the 5 mm diameter NMR sample tube, and NMR measurement was performed. The apparatus used for the NMR measurement was JNM-LA400WB manufactured by Nippon Electronics Co., Ltd., the observation nucleus was ¹ H, the observation frequency was 400 MHz, and the residual proton signal contained in the dimethyl sulfoxide (DMSO) -d ₆ was used as an internal reference. (2.5 ppm). Measurement temperature was 25 degreeC. ^{In the 1} HNMR spectrum, a peak corresponding to EC was found at around 4.5 ppm and a peak corresponding to VC was found at around 7.7 ppm. On the other hand, peaks corresponding to PRS were observed near 5.1 ppm (P ₁ ), near 7.05 ppm (P ₂ ) and near 7.2 ppm (P ₃ ) as shown in the spectrum shown in FIG. 5. From the above results, it can be confirmed that VC and PRS are included in the nonaqueous solvent present in the secondary battery of Example 1 after the initial charge and discharge process.

In addition, the observation frequency was 100 MHz, and ¹³ CNMR measurements of dimethyl sulfoxide (DMSO) -d ₆ (39.5 ppm) as an internal reference substance showed that the peak corresponding to EC was around 66 ppm and the peak corresponding to VC. The peaks corresponding to 133 ppm and PRS were observed at around 74 ppm, at around 124 ppm, and at about 140 ppm. From the results, VC and PRS were found in the nonaqueous solvent present in the secondary battery of Example 1 after the initial charge / discharge process. It was confirmed that it was included.

In addition, the ratio of the NMR integral intensity of VC to the NMR integral intensity of EC and the NMR integral intensity of PRS to the NMR integral intensity of EC in the ¹ HNMR spectrum was obtained. It was confirmed that all of the ratios are reduced than before the assembly of the secondary battery.

In addition, the present invention is not limited to the above embodiment, and can be similarly applied to the assembly of other types of anodes, cathodes, separators, and containers. In addition to the nonaqueous electrolyte secondary battery in which a container is formed from the laminator film as in the above embodiment, the present invention can be applied to a secondary battery having a cylindrical or rectangular container.

As described above, according to the present invention, it is possible to provide a nonaqueous electrolyte secondary battery that satisfies initial charge and discharge efficiency, discharge capacity, and charge and discharge cycle life at the same time.

Claims (13)

A nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode containing a carbonaceous material capable of occluding and releasing lithium ions, and a nonaqueous electrolyte containing a nonaqueous solvent, The non-aqueous solvent includes a sultone compound having at least one double bond in a ring, The carbonaceous material has a specific surface area of 1.5 m ² / g or more and 10 m ² / g or less by the BET method, and peaks derived from an interplanar spacing (d ₀₀₂ ) of 0.336 nm or less appear in powder X-ray diffraction measurements. In the X-ray diffraction measurement using a line, peaks are detected at diffraction angles 2θ of 42.8 ° to 44.0 ° and 45.5 ° to 46.6 °, and Raman spectrum measurement shows that the R value is 0.3 or more in intensity ratio and 1 or more in area ratio. Non-aqueous electrolyte secondary battery comprising a. In a nonaqueous electrolyte secondary battery having a positive electrode, a negative electrode containing a carbonaceous material capable of occluding and releasing lithium ions, and a nonaqueous electrolyte containing a nonaqueous solvent, The non-aqueous solvent includes a sultone compound having at least one double bond in a ring, The carbonaceous material has a specific surface area of 1.5 m ² / g or more and 10 m ² / g or less by BET method, and peaks derived from an interplanar spacing (d ₀₀₂ ) of 0.336 nm or less appear in powder X-ray diffraction measurements. A nonaqueous electrolyte secondary battery comprising a graphite material having a crystal structure and having an R value of 0.3 or more in intensity ratio and 1 or more in area ratio by Raman spectrum measurement. The method according to claim 1 or 2, The specific surface area is 1.5 m ² / g or more, 6 m ² / g or less nonaqueous electrolyte secondary battery, characterized in that. The method according to claim 1 or 2, The strength ratio of the R value is 0.3 or more, 1.5 or less non-aqueous electrolyte secondary battery, characterized in that. The method according to claim 1 or 2, The area ratio of the R value is 1 or more, 4 or less, characterized in that the nonaqueous electrolyte secondary battery. The method according to claim 1 or 2, The area ratio of the R value is 1 or more, 3 or less non-aqueous electrolyte secondary battery, characterized in that. The method according to claim 1 or 2, The sultone compound is a non-aqueous electrolyte secondary battery comprising at least one of 1,3-propenesultone (PRS) and 1,4-butylene sultone (BTS). The method according to claim 1 or 2, The non-aqueous solvent is a non-aqueous electrolyte secondary battery, characterized in that further comprises vinylene carbonate (VC). The method according to claim 1 or 2, The non-aqueous solvent is a non-aqueous electrolyte secondary battery further comprises a cyclic carbonate and γ-butyrolactone. The method according to claim 1 or 2, The nonaqueous solvent further comprises a linear carbonate comprising ethylene carbonate and at least methyl ethyl carbonate. The method according to claim 1 or 2, The non-aqueous solvent further comprises a cyclic carbonate containing at least ethylene carbonate and propylene carbonate, and γ-butyrolactone. The method according to claim 1 or 2, The nonaqueous solvent further comprises a cyclic carbonate containing at least ethylene carbonate and propylene carbonate. The method according to claim 1 or 2, The non-aqueous electrolyte secondary battery non-aqueous electrolyte, characterized in that it further comprises one or more of the lithium salt of LiPF ₆ and LiBF ₄ .

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