JP2009129747A - Secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a secondary battery which has a high energy density, and is excellent in cycling and conservation properties. <P>SOLUTION: The secondary battery includes a positive electrode containing lithium-nickel composite oxide with a moisture content of less than 300 ppm as a positive electrode active material, a negative electrode, and an electrolyte for secondary battery including at least an aprotonic solvent and disulfonic acid ester. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a secondary battery.

  Non-aqueous electrolyte lithium ion / lithium secondary battery using a composite oxide of lithium and transition metal for the positive electrode and carbon material, oxide, lithium alloy or lithium metal for the negative electrode can achieve high energy density. Has characteristics. For this reason, these secondary batteries are electric vehicles such as electric vehicles, hybrid vehicles, hybrid trains, hybrid buses, mobile electronic devices such as mobile phones and laptop computers, and stationary types such as UPS and backup power supplies. It is attracting attention as a power source for power supply devices.

  In this secondary battery, lithium cobaltate, lithium manganate, lithium nickelate, or composite oxides of these elements are used as the positive electrode active material. Among these, lithium-nickel composite oxides (hereinafter sometimes simply referred to as “lithium nickelate”) have a high energy density and are actively developed for the above applications that require long-time driving. . As a positive electrode active material, lithium nickelate doped with an element other than nickel in addition to nickel is known.

  On the other hand, in the secondary battery, a film called a protective film, SEI (Solid Electrolyte Interface), or a film (hereinafter sometimes referred to as “surface film”) is formed on the negative electrode surface. It has been known. Since this surface film has a great influence on charge / discharge efficiency, cycle life and safety, it is known that control of the surface film is indispensable for improving the performance of the negative electrode. In particular, when a carbon material or an oxide material is used as the negative electrode active material, it is necessary to reduce the irreversible capacity. When a lithium metal / alloy negative electrode is used, the charge / discharge efficiency decreases and dendrites (dendritic crystals) It was necessary to solve the safety problem due to generation.

Therefore, conventionally, various additives for electrolytic solutions have been applied in the secondary battery in order to form a stable surface film on the negative electrode surface. For example, the cyclic monosulfonic acid esters as shown in Patent Documents 1 to 3 are often used because they are excellent in film-forming ability on the electrode surface and can improve battery characteristics. Also, recently, when a cyclic disulfonic acid ester as shown in Patent Document 4 is used, cycle characteristics and storage characteristics (suppression of resistance increase and capacity retention rate) can be improved as compared with those using cyclic monosulfonic acid esters. Has been reported. This cyclic disulfonic acid ester can be synthesized by the method shown in Patent Document 5.
JP 63-102173 A JP 2000-3724 A JP 11-339850 A JP 2004-281368 A Japanese Patent Publication No. 5-44946

  As described above, in recent years, a lithium-nickel composite oxide has attracted attention as a positive electrode active material that has a high energy density and is expected to have excellent cycle characteristics. However, in the secondary battery using the lithium / nickel composite oxide as the positive electrode active material, disulfonic acid ester is used for the purpose of improving the cycle characteristics and storage characteristics (suppression of resistance increase and capacity retention rate) of the secondary battery. When used as an additive for an electrolytic solution, desired cycle characteristics and storage characteristics may not be improved with good reproducibility.

  As a result of studying this problem, the present inventor has found that deterioration of battery characteristics such as cycle characteristics and storage characteristics is a problem peculiar to the combined use of the above lithium / nickel composite oxide and disulfonic acid ester. It was. That is, as described above, the lithium / nickel composite oxide has been produced using a raw material such as lithium hydroxide which is highly reactive with moisture and easily forms a hydrate. For this reason, lithium / nickel composite oxides obtained from these raw materials are also likely to contain hydrates. As a result, it was considered that this moisture reacted with the Li salt to generate HF, which hindered improvement in battery characteristics.

  As described above, lithium nickelate as a positive electrode active material and disulfonic acid ester as an additive in an electrolytic solution have such characteristics that the characteristics of the secondary battery can be improved. When used in combination, the desired secondary battery characteristics may not be obtained depending on the battery material used, the usage conditions, and the like.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to use a lithium / nickel composite oxide as a positive electrode active material and a disulfonic acid ester as an electrolytic solution additive. It is an object of the present invention to provide a non-aqueous electrolyte secondary battery that suppresses deterioration of the battery and has excellent battery characteristics.

In order to solve the above problems, the present invention is characterized by having the following configuration.
1. A positive electrode obtained by applying a slurry containing a lithium / nickel composite oxide having a water content of less than 300 ppm as a positive electrode active material and a solvent on a positive electrode current collector, and then drying to remove the solvent; ,
A negative electrode,
An electrolyte solution for a secondary battery containing at least an aprotic solvent and a disulfonic acid ester;
Secondary battery equipped with.

  2. 2. The secondary battery according to 1 above, wherein the electrolyte for secondary battery further contains a lithium salt.

3. The lithium-nickel composite oxide is Liα (Ni _x M _1-x ) O ₂ (where M is one or more metals other than Ni, and 0.5 ≦ x ≦ 1 and 0 <α ≦ 1. 2. The secondary battery according to 1 or 2 above, wherein the secondary battery is a compound represented by 2).

  4). 4. The secondary battery according to claim 1, wherein the lithium / nickel composite oxide is a compound manufactured from a raw material containing lithium hydroxide and a Ni-containing hydroxide.

  5). 5. The secondary battery according to any one of 1 to 4 above, wherein the disulfonic acid ester contains a compound represented by the following general formula (1).

(However, in the said General formula (1), Q is an oxygen atom, a methylene group, or a single bond, A is a substituted or unsubstituted C1-C5 alkylene group, a carbonyl group, a sulfinyl group, C1-C5. At least one C—C bond in the polyfluoroalkylene group, a substituted or unsubstituted fluoroalkylene group having 1 to 5 carbon atoms, or a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms is a C—O—C bond A group in which at least one C—C bond in the polyfluoroalkylene group having 1 to 5 carbon atoms is a C—O—C bond, and a substituted or unsubstituted fluoroalkylene having 1 to 5 carbon atoms A group selected from a group in which at least one C—C bond in the group is a C—O—C bond, B is a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, carbon number 5 of polyfluoroalkylene group, and a substituted or unsubstituted group selected from fluoroalkylene group having 1 to 5 carbon atoms shown).

  6). 6. The secondary battery according to any one of 1 to 5 above, which contains a compound represented by the following general formula (2) as the disulfonic acid ester.

(However, in the said General formula (2), R < ₁ > and R < ₄ > is respectively independently a hydrogen atom, a substituted or unsubstituted C1-C5 alkyl group, a substituted or unsubstituted C1-C5. An alkoxy group, a substituted or unsubstituted fluoroalkyl group having 1 to 5 carbon atoms, a polyfluoroalkyl group having 1 to 5 carbon atoms, —SO ₂ X ₁ (wherein X ₁ is a substituted or unsubstituted carbon atom having 1 to 5 carbon atoms). alkyl group), - SY ₁ (Y ₁ is a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), - COZ (Z is a hydrogen atom, or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), And R ₂ and R ₃ each independently represents a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, or a substituted or unsubstituted carbon group having 1 to 5 carbon atoms. An alkoxy group, substituted or unsubstituted Noxy group, substituted or unsubstituted fluoroalkyl group having 1 to 5 carbon atoms, polyfluoroalkyl group having 1 to 5 carbon atoms, substituted or unsubstituted fluoroalkoxy group having 1 to 5 carbon atoms, 1 to 5 carbon atoms polyfluoroalkoxy group, a hydroxyl group, a halogen atom, -NX ₂ X ₃ (X ₂ and X ₃ are each independently a hydrogen atom, or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), and -NY ₂ CONY ₃ Y ₄ (Y _{2 to} Y ₄ are each independently an atom or group selected from a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms).

  7. The aprotic solvent is at least selected from the group consisting of cyclic carbonates, chain carbonates, aliphatic carboxylic acid esters, γ-lactones, cyclic ethers, chain ethers and their fluorinated derivatives. 7. The secondary battery according to any one of 1 to 6 above, which is one type of organic solvent.

8). The electrolyte solution for a secondary battery is obtained by adding at least a disulfonic acid ester in an aprotic solvent,
8. The secondary battery according to any one of 1 to 7 above, wherein a water content of the disulfonic acid ester before addition to the aprotic solvent is less than 300 ppm.

  9. The negative electrode includes at least one selected from the group consisting of a material capable of occluding and releasing lithium, a lithium metal, and a lithium alloy as a negative electrode active material. The secondary battery as described.

  10. 10. The secondary battery as described in any one of 1 to 9 above, wherein the negative electrode contains carbon as a negative electrode active material.

  11. 11. The secondary battery as described in 10 above, wherein the carbon is graphite.

  12 11. The secondary battery as described in 10 above, wherein the carbon is amorphous carbon.

  A secondary battery having a high energy density and excellent cycle characteristics and storage characteristics can be provided.

(Secondary battery)
Hereinafter, the configuration of the secondary battery of the present invention will be described.
The secondary battery of this invention is equipped with a positive electrode, a negative electrode, and the electrolyte solution for secondary batteries. This positive electrode is obtained by applying a slurry containing a lithium / nickel composite oxide having a water content of less than 300 ppm as a positive electrode active material and a solvent on the positive electrode current collector, and then drying to remove the solvent. It is a thing. Moreover, the electrolyte solution for secondary batteries contains at least an aprotic solvent and a disulfonic acid ester.

  The “water content” of the “lithium / nickel composite oxide having a water content of less than 300 ppm” represents the water content of the lithium / nickel composite oxide alone before manufacturing the slurry and the secondary battery.

  Here, in the conventional secondary battery, the battery characteristics were deteriorated by using the Li salt as the positive electrode active material and the disulfonic acid ester as the additive for the electrolyte solution for the secondary battery. The reason for this is that HF generated by the reaction of lithium-nickel composite oxide and water acts on the ester bond of the disulfonic acid ester to generate a product, which deteriorates the ionic conductivity in the electrolyte. It is thought that it was because of. That is, when the disulfonic acid ester is added to the electrolyte, the number of ester bonds is larger than that of the monosulfonic acid ester, so that a reaction product different from the case where the monosulfonic acid ester is added is generated. It is thought that it leads to the deterioration of characteristics.

  On the other hand, since the secondary battery of the present invention uses the lithium / nickel composite oxide having a water content of less than 300 ppm as the positive electrode active material, the positive electrode of the secondary battery is a secondary battery. The water content in the portion in contact with the battery electrolyte can be greatly reduced. As a result, it is difficult for HF to be generated by the reaction of the Li salt and water, and the reaction between the HF and the ester bond of the disulfonic acid ester and the decrease in ionic conductivity due to the reaction product do not occur. In addition, it is possible to provide a secondary battery that has high energy density, suppresses an increase in resistance of the positive electrode, and degrades due to decomposition of the electrolytic solution, and has excellent storage characteristics and cycle characteristics and suppresses an increase in resistance. In addition, it can be applied to uses such as secondary batteries for vehicles that require a maintenance-free state over a long period of time and that require high weight energy density and volume energy density.

  FIG. 1 is a schematic configuration diagram of an example of the secondary battery of the present invention. The secondary battery of the present invention has a structure as shown in FIG. 1, for example. In the positive electrode, a layer 12 containing a positive electrode active material is formed on the positive electrode current collector 11. In the negative electrode, a layer 13 containing a negative electrode active material is formed on a negative electrode current collector 14. The positive electrode and the negative electrode are disposed to face each other with the secondary battery electrolyte and the porous separator 16 in the secondary battery electrolyte. The porous separator 16 is disposed substantially parallel to the layer 13 containing the negative electrode active material.

In the secondary battery of FIG. 1, the layer 12 containing the positive electrode active material is formed using a lithium / nickel composite oxide having a water content of less than 300 ppm as the positive electrode active material. The composition formula of this lithium / nickel composite oxide is Liα (Ni _x M _1-x ) O ₂ , where M is one or more metals other than Ni, and 0.5 ≦ x ≦ 1 and 0 <α ≦ 1.2. This M is preferably at least one metal selected from the group consisting of Li, Mg, Ca, Sr, Al, Ti, Zr, Mn, Fe, Co, and Zn. Further, the lithium-nickel composite _{oxide, LiNi 0.8 Co 0.2 O 2,} Li 1.02 Ni 0.8 Co 0.15 Al 0.05 O 2, Li 1.02 Ni 1-xy Co x Al y O 2 (0 <x ≦ 0.20, 0 <y ≦ 0.10), Li _1.1 Ni _0.5 Mn _0.5 O ₂ is preferably used.

  For example, these positive electrode active materials are dispersed and kneaded in a solvent such as N-methyl-2-pyrrolidone (NMP) together with a conductive material such as carbon black and a binder such as polyvinylidene fluoride (PVDF). It can be obtained by applying it on a substrate such as an aluminum foil.

  The secondary battery shown in FIG. 1 has a negative electrode and a positive electrode laminated in a dry air or in an inert gas atmosphere, or after winding a laminated one, a battery can, a synthetic resin and a metal foil It is manufactured by impregnating an electrolytic solution for a secondary battery after being accommodated in an exterior body such as a flexible film made of a laminate. And a film | membrane can be formed on a negative electrode by charging after sealing or sealing an exterior body. In addition, as the porous separator 16, porous films, such as polyolefin, such as a polypropylene and polyethylene, a fluororesin, are used. The shape of the secondary battery is not particularly limited, and examples thereof include a cylindrical shape, a square shape, a laminate outer shape, and a coin shape.

(Positive electrode)
Hereinafter, the positive electrode active material and the positive electrode in the secondary battery of the present invention will be described. In the present invention, a lithium / nickel composite oxide having a water content of less than 300 ppm is used as the positive electrode active material when the positive electrode is manufactured. In the present invention, by using the lithium / nickel composite oxide having a low water content, the water content in the positive electrode of the secondary battery after production can be greatly reduced. Generation of HF due to the reaction between water and water is less likely to occur. For this reason, the reaction of this HF and the ester bond of the disulfonic acid ester contained in the electrolyte solution for secondary batteries and the decrease in ionic conductivity due to this reaction product do not occur. In addition, it is possible to provide a secondary battery that has high energy density, suppresses deterioration due to positive electrode resistance and decomposition of the electrolyte, has excellent storage characteristics and cycle characteristics, and suppresses resistance increase.

The water content of the lithium / nickel composite oxide can be adjusted by controlling the raw material of the lithium / nickel composite oxide, the production method, and the treatment method after the production (such as heat treatment). In general, nickel oxide (NiO) is highly hygroscopic and has a characteristic of easily containing crystal water, such as Ni ₂ O ₃ .nH ₂ O (n = 1, _{2, 3} , 4, 5, 6). It is known to have. The lithium / nickel composite oxide of the present invention also has characteristics close to that of nickel oxide and may have high hygroscopicity. When using such a lithium / nickel composite oxide as the positive electrode active material, be careful not to increase the moisture content because the moisture content will increase if left in a humid environment after heat treatment. Need to manage.

  The lithium / nickel composite oxide is not particularly limited as long as it has a water content of less than 300 ppm and contains nickel atoms and lithium atoms. The water content of the lithium / nickel composite oxide can be confirmed by measuring by a general Karl Fischer method. Further, as the positive electrode active material, it is preferable to use a lithium / nickel composite oxide of 200 ppm or less, and it is more preferable to use a lithium / nickel composite oxide of 100 ppm or less. By using a lithium-nickel composite oxide with a low water content in this way, a secondary battery with a high energy density, improved storage characteristics and cycle characteristics can be prevented more effectively. can do.

  Here, the lithium / nickel composite oxide is preferably a compound produced from a raw material containing lithium hydroxide and a Ni-containing hydroxide. Thus, when lithium hydroxide is used as the Li raw material and a hydroxide is selected as the Ni raw material, these raw materials can be reacted in the solution. As a result, the uniformity of the reaction is improved, and a lithium / nickel composite oxide having good quality and uniform characteristics can be obtained. In addition, a lithium / nickel composite oxide doped with other elements can be easily obtained, whereby a battery excellent in storage and cycle characteristics can be obtained.

A method for producing a lithium / nickel composite oxide in which a part of nickel is replaced with cobalt and aluminum will be described below as an example. First, lithium hydroxide (LiOH) is used as a Li raw material. Further, hydroxides, carbonates, oxides and the like can be used as Ni and Co raw materials. Furthermore, Al ₂ O ₃ , Al (OH) ₃ , aluminum nitrate, aluminum acetate, etc. can be used as the Al raw material for replacing Ni with Al. Alternatively, Ni—Co—Al composite hydroxide, Ni—Co—Al composite carbonate, Ni—Co—Al composite oxide, etc. prepared so as to contain Al at a predetermined ratio may be used.

  And the mixture of a desired composition ratio can be obtained by selecting the usage-amount of a starting material suitably. Next, this mixture is baked in air or oxygen in a temperature range of about 600 ° C. to 950 ° C., for example. Preferably, the firing temperature is about 700 ° C to 850 ° C. Finally, a lithium / nickel composite oxide having a desired composition can be stably obtained.

As the lithium-nickel composite oxide, Liα (Ni _x M _1-x ) O ₂ (where M is one or more metals other than Ni, and 0.5 ≦ x ≦ 1 and 0 <α ≦ 1. 2). M is preferably at least one metal selected from the group consisting of Mg, Ca, Sr, Al, Ti, Zr, Mn, Fe, Co, and Zn. Moreover, it is preferable that 0.5 ≦ α ≦ 1.2, more preferably 0.95 ≦ α ≦ 1.1.

More preferably, the lithium-nickel composite oxide _{LiNi 0.8 Co 0.2 O 2, Li} 1.02 Ni 0.8 Co 0.15 Al 0.05 O 2, Li 1.02 Ni 1-xy Co x Al y O 2 (0 <x ≦ 0.20, 0 <y ≦ 0.10), Li _1.1 Ni _0.5 Mn _0.5 O ₂ may be used. By using these compounds as the lithium / nickel composite oxide, higher cycle characteristics and higher energy density can be achieved.

The BET specific surface area of the lithium / nickel composite oxide is preferably 0.3 m ² / g or more. Further, BET specific surface area is preferably set to be lower than or equal to 2m ² / g, and more preferably to less 1 m ² / g. By setting the BET specific surface area in such a range, it is possible to reduce the amount of binder added necessary for electrode preparation. As a result, the energy density of the battery can be improved.
As the current collector for the positive electrode, aluminum, stainless steel, nickel, titanium, and alloys thereof can be used.

(Electrolyte for secondary battery)
The electrolyte solution for secondary batteries of the present invention contains at least an aprotic solvent and a disulfonic acid ester. As the disulfonic acid ester, a compound represented by the following general formula (1) is preferably used.

(However, in the said General formula (1), Q is an oxygen atom, a methylene group, or a single bond, A is a substituted or unsubstituted C1-C5 alkylene group, a carbonyl group, a sulfinyl group, C1-C5. At least one C—C bond in the polyfluoroalkylene group, a substituted or unsubstituted fluoroalkylene group having 1 to 5 carbon atoms, or a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms is a C—O—C bond A group in which at least one C—C bond in the polyfluoroalkylene group having 1 to 5 carbon atoms is a C—O—C bond, and a substituted or unsubstituted fluoroalkylene having 1 to 5 carbon atoms A group selected from a group in which at least one C—C bond in the group is a C—O—C bond, B is a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, carbon number 5 of polyfluoroalkylene group, and a substituted or unsubstituted group selected from fluoroalkylene group having 1 to 5 carbon atoms shown).

  In the present invention, by adding the compound represented by the general formula (1) as a disulfonic acid ester to the electrolytic solution, it is possible to have more excellent cycle characteristics and storage characteristics.

  In the general formula (1), the carbon number of A represents the number of carbons constituting the ring, and does not include the number of carbons contained in the side chain. When A is a substituted or unsubstituted C2-C5 fluoroalkylene group, A may have a methylene unit and a fluoromethylene unit, or may have only a fluoromethylene unit. Further, when the alkylene unit or the fluoroalkylene unit is bonded via an ether bond, the alkylene units may be bonded, the fluoroalkylene units may be bonded, or the alkylene unit and A fluoroalkylene unit may be bonded.

  In the compound represented by the general formula (1), A is a substituted or unsubstituted carbon atom having 1 to 5 carbon atoms from the viewpoint of stability of the compound, ease of synthesis of the compound, solubility in a solvent, price, and the like. At least a C-C bond in the alkylene group, a polyfluoroalkylene group having 1 to 5 carbon atoms, a substituted or unsubstituted fluoroalkylene group having 1 to 5 carbon atoms, and a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms. A group in which one site is a C—O—C bond, a group in which at least one C—C bond in a C 1-5 polyfluoroalkylene group is a C—O—C bond, and a substituted or unsubstituted group A group selected from a group in which at least one C—C bond in the fluoroalkylene group having 1 to 5 carbon atoms is a C—O—C bond is preferable. More preferred is a group selected from a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, a polyfluoroalkylene group having 1 to 5 carbon atoms, and a substituted or unsubstituted fluoroalkylene group having 1 to 5 carbon atoms. Alternatively, an unsubstituted alkylene group having 1 to 5 carbon atoms is more preferable, and a methylene group, an ethylene group, or a 2,2-propanediyl group is particularly preferable. The C1-C5 fluoroalkylene group preferably includes a methylene group and a difluoromethylene group, and more preferably includes a methylene group and a difluoromethylene group.

  For the same reason, B is preferably an alkylene group having 1 to 5 carbon atoms, more preferably a methylene group, a 1,1-ethanediyl group, or a 2,2-propanediyl group.

  Although the typical example of a compound shown by General formula (1) is specifically illustrated below, it is not limited to these. In addition, the following compounds may be used alone or in combination of two or more.

  It is preferable to use a compound represented by the following general formula (2) as the disulfonic acid ester.

(However, in the said General formula (2), R < ₁ > and R < ₄ > is respectively independently a hydrogen atom, a substituted or unsubstituted C1-C5 alkyl group, a substituted or unsubstituted C1-C5. An alkoxy group, a substituted or unsubstituted fluoroalkyl group having 1 to 5 carbon atoms, a polyfluoroalkyl group having 1 to 5 carbon atoms, —SO ₂ X ₁ (wherein X ₁ is a substituted or unsubstituted carbon atom having 1 to 5 carbon atoms). alkyl group), - SY ₁ (Y ₁ is a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), - COZ (Z is a hydrogen atom, or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), And R ₂ and R ₃ each independently represents a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, or a substituted or unsubstituted carbon group having 1 to 5 carbon atoms. An alkoxy group, substituted or unsubstituted Noxy group, substituted or unsubstituted fluoroalkyl group having 1 to 5 carbon atoms, polyfluoroalkyl group having 1 to 5 carbon atoms, substituted or unsubstituted fluoroalkoxy group having 1 to 5 carbon atoms, 1 to 5 carbon atoms polyfluoroalkoxy group, a hydroxyl group, a halogen atom, -NX ₂ X ₃ (X ₂ and X ₃ are each independently a hydrogen atom, or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), and -NY ₂ CONY ₃ Y ₄ (Y _{2 to} Y ₄ are each independently an atom or group selected from a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms).

  In the present invention, by adding the compound represented by the general formula (2) as a disulfonic acid ester to the electrolytic solution, it has a higher energy density and can obtain better cycle characteristics.

Preferred molecular structures of R ₁ and R _{4 in} the general formula (2) include ease of formation of a reactive film on the electrode, stability of the compound, ease of handling, solubility in a solvent, From the viewpoint of ease of synthesis, cost, etc., each independently represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, a halogen atom, and —SO ₂ X ₁ (X ₁ is a substituted or unsubstituted carbon atom having 1 to Atoms or groups selected from (5 alkyl groups), each independently preferably a hydrogen atom or an unsubstituted alkyl group having 1 to 5 carbon atoms, more preferably a hydrogen atom or a methyl group. Particularly preferred embodiments of R ₁ and R ₄ is where R ₁ and R ₄ are hydrogen atoms. This is because when R ₁ and R ₄ are hydrogen atoms, the methylene moiety sandwiched between the two sulfonyl groups is activated and a reaction film on the electrode is easily formed.

In R ₂ and R ₃ , from the viewpoints of stability of the compound, ease of synthesis of the compound, solubility in a solvent, price, and the like, each independently, a substituted or unsubstituted alkyl having 1 to 5 carbon atoms. A group, a substituted or unsubstituted alkoxy group having 1 to 5 carbon atoms, a substituted or unsubstituted phenoxy group, a hydroxyl group, a halogen atom, and —NX ₂ X ₃ (X ₂ and X ₃ are each independently a hydrogen atom; Or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, or substituted or unsubstituted. The alkoxy group having 1 to 5 carbon atoms is more preferable, and one or both of R ₂ and R ₃ are more preferably substituted or unsubstituted alkoxy groups having 1 to 5 carbon atoms. For the same reason, the substituted or unsubstituted alkyl group having 1 to 5 carbon atoms is preferably a methyl group or ethyl group, and the substituted or unsubstituted alkoxy group having 1 to 5 carbon atoms is a methoxy group or An ethoxy group is preferable.
Specific examples of the compound represented by the general formula (2) are specifically illustrated below, but are not limited thereto. In addition, the following compounds may be used alone or in combination of two or more.

  In addition, even if only the compound of General formula (1) is contained as a disulfonic acid ester in the electrolyte solution, or only the compound of General formula (2) is contained, General formula (1) and (2 ) May be included.

  The compounds represented by the general formulas (1) and (2) can be obtained, for example, using the production methods described in US Pat. No. 4,950,768 and JP-B-5-44946. The ratio of the total amount of the compounds of the general formulas (1) and (2) in the secondary battery electrolyte solution is not particularly limited, but is preferably 0.005 to 10% by mass with respect to the entire electrolyte solution. By setting the concentration of the compounds represented by the general formulas (1) and (2) to 0.005% by mass or more, a sufficient film effect can be obtained. The battery characteristics can be further improved by adding 0.01% by mass or more. Moreover, by setting it as 10 mass% or less, the raise of the viscosity of electrolyte solution and the increase in resistance accompanying this can be suppressed. The battery characteristics can be further improved by adding 5% by mass or less.

  The electrolyte solution for a secondary battery is obtained by adding at least a disulfonic acid ester to an aprotic solvent, and the water content of the disulfonic acid ester before addition to the aprotic solvent is less than 300 ppm. Preferably there is. Thus, when the water content of the disulfonic acid ester before addition to the electrolytic solution is less than 300 ppm, the reaction between the water in the disulfonic acid ester and the ester bond can be effectively suppressed. As a result, HF is less likely to be generated, and the reaction between the HF and the ester bond of the disulfonic acid ester and the decrease in ionic conductivity due to the reaction product do not occur. In addition, it is possible to provide a secondary battery that has excellent storage characteristics and cycle characteristics and suppresses an increase in resistance.

  The aprotic solvent contained in the secondary battery electrolyte includes cyclic carbonates, chain carbonates, aliphatic carboxylic acid esters, γ-lactones, cyclic ethers, chain ethers, and their fluorine. Preferably, the organic solvent is at least one organic solvent selected from the group consisting of fluorinated derivatives.

Specifically, the following substances can be used as the aprotic solvent.
Cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), vinylene carbonate (VC),
Chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dipropyl carbonate (DPC),
Aliphatic carboxylic acid esters such as methyl formate, methyl acetate, ethyl propionate,
γ-lactones such as γ-butyrolactone,
Chain ethers such as 1,2-ethoxyethane (DEE) and ethoxymethoxyethane (EME);
Cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran,
Dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylformamide, acetonitrile, propyl nitrile, nitromethane, ethyl monoglyme, phosphate triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl- 2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, N-methylpyrrolidone, fluorinated carboxylic acid ester, methyl-2,2,2-trifluoroethyl carbonate, methyl- 2,2,3,3,3-pentafluoropropyl carbonate, trifluoromethyl ethylene carbonate, monofluoromethyl ethylene carbonate, difluoromethyl ethylene Carbonate, 4,5-difluoro-1,3-dioxolan-2-one, monofluoroethylene carbonate These aprotic solvents may be used by mixing one or two or more.

  It is preferable that the electrolyte solution for secondary batteries further contains a sulfonyl compound. By including a sulfonyl compound in the electrolyte solution for a secondary battery, it is possible to further suppress the decomposition of the solvent molecules. Specific examples of the sulfonyl compound include sulfolane, 1,3-propane sultone, 1,4-butane sultone, alkane sulfonic acid anhydride (described in JP-A-10-189041, etc.), and γ-sultone compound (JP-A 2000). -Described in JP-A No. 235866), sulfolene derivatives (described in JP-A No. 2000-294278, etc.) and the like, but are not limited thereto.

  When adding this sulfonyl compound in the electrolyte solution for secondary batteries, it is preferable to add it so that it may become 0.005 mass% or more and 10 mass% or less with respect to electrolyte solution. By setting it as 0.005 mass% or more, a membrane | film | coat can be effectively formed in the negative electrode surface. More preferably, it can be 0.01 mass% or more. Preferably, the solubility of the sulfonyl compound is maintained and the increase in the viscosity of the electrolyte can be suppressed by setting the content to 10% by mass or less. More preferably, it can be 5 mass% or less.

  Moreover, it is preferable that the compound shown by following General formula (3) is included in the electrolyte solution for secondary batteries as a compound which has a sulfonyl group.

(However, in the above general formula (3), n is 0 to 2 integer. Also, R ₅ to R ₁₀ each independently represent a hydrogen atom, a substituted or unsubstituted alkyl having 1 to 12 carbon atoms An atom or group selected from a group, a substituted or unsubstituted fluoroalkyl group having 1 to 6 carbon atoms, and a polyfluoroalkyl group having 1 to 6 carbon atoms.
In the compound represented by the general formula (3), n is preferably 0 or 1, from the viewpoint of stability of the compound, ease of synthesis of the compound, solubility in a solvent, price, and the like, and R _{5 to} R ₁₀ Are preferably each independently an atom or group selected from a hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 12 carbon atoms, and a polyfluoroalkyl group having 1 to 5 carbon atoms. A hydrogen atom or a polyfluoroalkyl group having 1 to 5 carbon atoms is more preferable. More preferably, all of R _{5 to} R ₁₀ are hydrogen atoms, or one or two of R _{5 to} R ₁₀ are polyfluoroalkyl groups having 1 to 5 carbon atoms and the other is a hydrogen atom. As said C1-C5 polyfluoroalkyl group, a trifluoromethyl group is preferable.

  In addition to the compounds of the general formulas (1) and (2), the viscosity of the electrolytic solution can be easily adjusted by adding the compound having a sulfonyl group represented by the general formula (3). Moreover, the stability of the film on the negative electrode surface can be improved by a synergistic effect resulting from the combined use of compounds having a sulfonyl group. Furthermore, decomposition of solvent molecules can be suppressed, and the effect of removing moisture in the electrolyte can be increased.

  Thus, the electrolyte solution for a secondary battery of the present invention is preferably a compound of the general formulas (1) and (2), a sulfonyl compound, a lithium salt, or other additives as a disulfonate in an aprotic solvent. Can be obtained by dissolving or dispersing. By mixing these additives having different characteristics into the electrolyte, a film having different properties can be formed on the negative electrode surface, which is effective in improving battery characteristics.

  When the compound of the general formula (3) is added to the electrolytic solution, the content in the electrolytic solution is not particularly limited, but is contained in the electrolytic solution in the range of 0.5% by mass to 10.0% by mass. It is preferable. If the content is less than 0.5% by mass, the effect may not be sufficiently exerted on the film formation by the electrochemical reaction on the electrode surface. Moreover, when content exceeds 10.0 mass%, the viscosity of electrolyte solution may be enlarged.

The electrolyte for a secondary battery can further contain a lithium salt as an electrolyte. By including a lithium salt, lithium ions can be used as a mobile substance, so that battery characteristics can be improved. As the lithium salt, LiPF _6, LiBF _4, LiAsF ₆ and at least one lithium salt selected from the group consisting of LiSbF ₆ can be used. By using these lithium salts, the electrical conductivity can be increased and the performance of the secondary battery can be improved.

(Negative electrode)
The negative electrode active material used in the negative electrode of the present invention includes at least one selected from the group consisting of a material capable of inserting and extracting lithium, lithium metal, and a metal material capable of forming an alloy with lithium. Is preferred.

  As a material capable of inserting and extracting lithium ions, carbon or an oxide can be used, but carbon is preferably used. As this carbon material, graphite, amorphous carbon, diamond-like carbon, carbon nanotubes, and composite oxides of these materials that occlude lithium can be used. Of these materials, it is preferable to use graphite or amorphous carbon as carbon. Graphite has high electron conductivity, and is excellent in adhesion to a current collector made of a metal such as copper and voltage flatness. Further, since it is formed at a high processing temperature and contains few impurities, it is advantageous for improving the negative electrode performance. Therefore, it is preferably used as a negative electrode active material.

  As the oxide, it is preferable to use at least one oxide selected from the group consisting of silicon oxide, tin oxide, indium oxide, zinc oxide, lithium oxide, and a composite thereof. It is more preferable to use silicon oxide. This is because silicon oxide is stable and does not cause reaction with other compounds. Further, the silicon oxide is preferably in an amorphous state. This is because the amorphous structure does not lead to deterioration due to non-uniformity such as crystal grain boundaries and defects. As an oxide film formation method, a vapor deposition method, a CVD method, a sputtering method, or the like can be used.

  The lithium alloy is composed of lithium and a metal capable of forming an alloy with lithium. For example, it is composed of a binary or ternary alloy of metal such as Al, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, La and lithium. . As the lithium metal and lithium alloy, those having an amorphous structure are particularly preferable. This is because the amorphous structure hardly causes deterioration due to non-uniformity such as crystal grain boundaries and defects.

  The lithium metal and lithium alloy should be formed by an appropriate method such as a melt cooling method, a liquid quenching method, an atomizing method, a vacuum deposition method, a sputtering method, a plasma CVD method, a photo CVD method, a thermal CVD method, a sol-gel method, etc. Can do.

  Moreover, it is preferable that the complex which consists of a transition metal cation and an imide anion exists in the electrolyte solution for secondary batteries. By making the complex of transition metal cation and imide anion present at the interface between the negative electrode and the electrolyte for secondary batteries, the negative electrode is flexible with respect to volume change of metal and alloy phases, uniformity of ion distribution, physical / chemical Excellent in mechanical stability. As a result, dendrite formation and lithium atomization can be effectively prevented, and cycle efficiency and life are improved.

  In addition, when a carbon material or an oxide material is used as the negative electrode, dangling bonds existing on the surface have high chemical activity, and the solvent is easily decomposed. By adsorbing a complex composed of a transition metal cation and an imide anion on this surface, the decomposition of the solvent is suppressed and the irreversible capacity is greatly reduced, so that the charge / discharge efficiency can be kept high.

Furthermore, when the film breaks, lithium fluoride, which is a reactive product of lithium on the negative electrode surface and imide anion adsorbed on the negative electrode surface, has a function of repairing the film at the broken point. Even after the film is broken, it has the effect of leading to the formation of a stable surface compound.
Moreover, copper, stainless steel, nickel, titanium, or alloys thereof can be used as the current collector for the negative electrode.

(Creation of disulfonic acid ester)
As a disulfonic acid ester to be added to the electrolytic solution for a secondary battery, Compound No. The compound represented by 2 was used. This compound no. The disulfonic acid ester 2 was synthesized according to the method described in Patent Document 5. After the synthesis, the resulting crude product was purified by silica gel column chromatography using a mixed solvent of hexane: ethyl acetate = 1: 1 (volume ratio). Thus obtained compound No. When the water content of the disulfonic acid ester No. 2 was measured by the Karl Fischer method, it was 3000 ppm. Next, the moisture content after drying this disulfonic acid ester at 40 ° C. under reduced pressure for 12 hours was 500 ppm, the moisture content after drying for 18 hours was 300 ppm, and the moisture content after drying for 24 hours was 250 ppm. In the following examples, compound No. 1 having any one of the above water contents is used. 2 (disulfonic acid ester) was used.

(Creation of lithium / nickel composite oxide)
Li _1.02 Ni _0.8 Co _0.15 Al _0.05 O ₂ was used as the lithium / nickel composite oxide. When this lithium-nickel composite oxide was produced, lithium hydroxide and (Ni _0.8 Co _0.15 Al _0.05 ) hydroxide were used as starting materials. These starting materials were mixed so that the molar ratio was [LiOH] / [Ni _0.8 Co _0.15 Al _0.05 ] = 1.02 / 1. Next, the obtained mixed powder was fired at 750 ° C. in oxygen. The specific surface area at this time was 0.6 m ² / g. Moreover, the water content of the lithium / nickel composite oxide thus fired was 150 ppm, and the water content was 250 ppm when stored in an inert gas for 6 months. This lithium / nickel composite oxide having a water content of 250 ppm was used in the following examples.

Example 1
Li _1.02 Ni _0.8 Co _0.15 Al _0.05 O ₂ prepared as described above was used as the positive electrode active material of the battery . This positive electrode active material was dry-mixed with a conductivity imparting agent made of carbon, and uniformly dispersed in N-methyl-2-pyrrolidone (NMP) in which PVdF as a binder was dissolved to obtain a slurry. After applying this slurry on an aluminum metal foil having a thickness of 20 μm, NMP was evaporated to prepare a positive electrode sheet containing a positive electrode active material. At this time, the solid content ratio in the positive electrode was weight percent, and lithium / nickel composite oxide: conductivity imparting agent: PVdF = 89: 7: 4.

  Next, amorphous carbon was used as the negative electrode active material, and a slurry was uniformly dispersed in NMP in which PVdF as a binder was dissolved. The slurry was applied on a copper foil having a thickness of 15 μm. Then, the negative electrode sheet was produced by evaporating NMP. At this time, the solid content ratio in the negative electrode was set to amorphous carbon: PVdF = 90: 10 in weight percent.

Further, a mixed solvent of EC and DEC (volume ratio: 30/70) is used as an aprotic solvent for the electrolyte solution for the secondary battery, LiPF ₆ is dissolved in 1 mol / L as an electrolyte, and further as described above. Compound No. 2 prepared with a water content of 250 ppm. 2 disulfonic acid ester was added so that 1 mass% might be contained in electrolyte solution. And the negative electrode and the positive electrode were laminated | stacked through the separator which consists of polyethylene, and the secondary battery of a present Example was produced.

Battery Characteristic Evaluation Test The secondary battery obtained as described above was once charged, placed in a constant temperature bath at 60 ° C. in a state where it was discharged to a discharge depth of 50%, and left for one month. After leaving it to stand, it was discharged after returning to room temperature, and after charging and measuring the resistance of the battery, a second discharge was performed. The second discharge capacity was taken as the recovery capacity.

  Further, at a temperature of 20 ° C., a cycle test was performed at a charge rate of 0.05 C, a discharge rate of 0.1 C, a charge end voltage of 4.2 V, and a discharge end voltage of 3.0 V. The capacity retention rate (%) is a value obtained by dividing the discharge capacity (mAh) after 400 cycles by the discharge capacity (mAh) at the 10th cycle. These results are shown in Table 1.

(Example 2)
In the preparation example of the disulfonic acid ester, the compound No. 1 having a water content of 3000 ppm obtained without drying under reduced pressure was used. Two disulfonic acid esters were added into the electrolyte. A secondary battery was fabricated in the same manner as in Example 1 except for the above, and the same evaluation as in Example 1 was performed. The results are shown in Table 1.

(Comparative Example 1)
A secondary battery was produced in the same manner as in Example 1 except that a lithium / nickel composite oxide having a water content adjusted to 300 ppm was used, and the same evaluation as in Example 1 was performed. The results are shown in Table 1.

(Comparative Example 2)
A secondary battery was produced in the same manner as in Example 1 except that a lithium / nickel composite oxide having a moisture content adjusted to 1500 ppm was used, and the same evaluation as in Example 1 was performed. The results are shown in Table 1.

  As shown in Table 1, when the water content of the lithium / nickel composite oxide is 300 ppm or more, the capacity recovery rate is extremely reduced to about 89% or less, and the resistance increase ratio and cycle capacity maintenance rate are also deteriorated. I understand that.

It is a schematic block diagram showing an example of the secondary battery of this invention.

Explanation of symbols

11 Positive Electrode Current Collector 12 Layer Containing Positive Electrode Active Material 13 Layer Containing Negative Electrode Active Material 14 Negative Electrode Current Collector 15 Nonaqueous Electrolytic Solution 16 Porous Separator

Claims (12)

A positive electrode obtained by applying a slurry containing a lithium / nickel composite oxide having a water content of less than 300 ppm as a positive electrode active material and a solvent on a positive electrode current collector, and then drying to remove the solvent; ,
A negative electrode,
An electrolyte solution for a secondary battery containing at least an aprotic solvent and a disulfonic acid ester;
Secondary battery equipped with.   The secondary battery according to claim 1, wherein the secondary battery electrolyte further contains a lithium salt. The lithium-nickel composite oxide is Liα (Ni _x M _1-x ) O ₂ (where M is one or more metals other than Ni, and 0.5 ≦ x ≦ 1 and 0 <α ≦ 1. The secondary battery according to claim 1, wherein the secondary battery is a compound represented by 2).   The secondary battery according to claim 1, wherein the lithium / nickel composite oxide is a compound manufactured from a raw material containing lithium hydroxide and a Ni-containing hydroxide. 5. The secondary battery according to claim 1, comprising a compound represented by the following general formula (1) as the disulfonic acid ester.

(However, in the said General formula (1), Q is an oxygen atom, a methylene group, or a single bond, A is a substituted or unsubstituted C1-C5 alkylene group, a carbonyl group, a sulfinyl group, C1-C5. At least one C—C bond in the polyfluoroalkylene group, a substituted or unsubstituted fluoroalkylene group having 1 to 5 carbon atoms, or a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms is a C—O—C bond A group in which at least one C—C bond in the polyfluoroalkylene group having 1 to 5 carbon atoms is a C—O—C bond, and a substituted or unsubstituted fluoroalkylene having 1 to 5 carbon atoms A group selected from a group in which at least one C—C bond in the group is a C—O—C bond, B is a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, carbon number 5 of polyfluoroalkylene group, and a substituted or unsubstituted group selected from fluoroalkylene group having 1 to 5 carbon atoms shown). The secondary battery according to claim 1, comprising a compound represented by the following general formula (2) as the disulfonic acid ester.

(However, in the said General formula (2), R < ₁ > and R < ₄ > is respectively independently a hydrogen atom, a substituted or unsubstituted C1-C5 alkyl group, a substituted or unsubstituted C1-C5. An alkoxy group, a substituted or unsubstituted fluoroalkyl group having 1 to 5 carbon atoms, a polyfluoroalkyl group having 1 to 5 carbon atoms, —SO ₂ X ₁ (wherein X ₁ is a substituted or unsubstituted carbon atom having 1 to 5 carbon atoms). alkyl group), - SY ₁ (Y ₁ is a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), - COZ (Z is a hydrogen atom, or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), And R ₂ and R ₃ each independently represents a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, or a substituted or unsubstituted carbon group having 1 to 5 carbon atoms. An alkoxy group, substituted or unsubstituted Noxy group, substituted or unsubstituted fluoroalkyl group having 1 to 5 carbon atoms, polyfluoroalkyl group having 1 to 5 carbon atoms, substituted or unsubstituted fluoroalkoxy group having 1 to 5 carbon atoms, 1 to 5 carbon atoms polyfluoroalkoxy group, a hydroxyl group, a halogen atom, -NX ₂ X ₃ (X ₂ and X ₃ are each independently a hydrogen atom, or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms), and -NY ₂ CONY ₃ Y ₄ (Y _{2 to} Y ₄ are each independently an atom or group selected from a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms).   The aprotic solvent is at least selected from the group consisting of cyclic carbonates, chain carbonates, aliphatic carboxylic acid esters, γ-lactones, cyclic ethers, chain ethers and their fluorinated derivatives. The secondary battery according to claim 1, wherein the secondary battery is one type of organic solvent. The electrolyte solution for a secondary battery is obtained by adding at least a disulfonic acid ester in an aprotic solvent,
The secondary battery according to any one of claims 1 to 7, wherein a moisture content of the disulfonic acid ester before being added to the aprotic solvent is less than 300 ppm.   The said negative electrode contains at least 1 sort (s) selected from the group which consists of the material which can occlude and discharge | release lithium, a lithium metal, and a lithium alloy as a negative electrode active material. Secondary battery described in 1.   The secondary battery according to claim 1, wherein the negative electrode contains carbon as a negative electrode active material.   The secondary battery according to claim 10, wherein the carbon is graphite.   The secondary battery according to claim 10, wherein the carbon is amorphous carbon.

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