JP4283566B2 - Non-aqueous electrolyte and lithium secondary battery using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous electrolyte and a lithium secondary battery using the same.
[0002]
[Prior art]
Lithium secondary batteries have the advantages of high energy density and less self-discharge. Therefore, in recent years, it has been widely used as a power source for consumer mobile devices such as mobile phones, notebook computers, and PDAs. The electrolyte for a lithium secondary battery is composed of a lithium salt as a supporting electrolyte and a non-aqueous organic solvent. The non-aqueous organic solvent is required to have a high dielectric constant for dissociating the lithium salt, to exhibit high ionic conductivity in a wide temperature range, and to be stable in the battery. Since it is difficult to achieve these requirements with a single solvent, usually a combination of a high boiling point solvent typified by propylene carbonate and ethylene carbonate and a low boiling point solvent such as dimethyl carbonate and diethyl carbonate is used. Yes.
[0003]
In order to improve initial capacity, rate characteristics, cycle characteristics, high temperature storage characteristics, low temperature characteristics, trickle charge characteristics, self-discharge characteristics, overcharge prevention characteristics, etc., various additives are often added to the electrolyte. Have been reported. For example, as a method for improving cycle characteristics, it has been reported that a divalent sulfonate compound such as 1,4-butanediol dimethanesulfonate or propylene glycol dimethanesulfonate is added (for example, see Patent Documents 1 and 2).
[0004]
[Patent Document 1]
JP 2000-133304 A
[Patent Document 2]
JP 2001-313071 A
[0005]
[Problems to be solved by the invention]
However, in recent years, the demand for higher performance of lithium secondary batteries has been increasing. Some of these are associated with increased opportunities for outdoor use as lithium secondary batteries expand their applications. That is, mobile devices such as mobile phones, PDAs, and notebook personal computers may be exposed to high temperatures of 60 to 90 ° C. such as being left in midsummer cars. Accordingly, there are strict requirements for the storage characteristics of lithium secondary batteries, particularly at high temperatures. In recent years, it has been widely studied to use lithium nickel composite oxide instead of lithium cobalt composite oxide as a positive electrode active material in order to further increase the capacity. While an increase in capacity was achieved, there was a problem that a large amount of gas was generated during high-temperature storage. Since the bare cell of a lithium secondary battery swells somewhat due to gas generation when stored under high temperature conditions, it is usually housed in a slightly larger case so that there is no change in appearance even if it swells. If the amount of gas generated is large, it will be necessary to store it in a larger case, which reduces the energy density of the entire battery pack and offsets the merit of using lithium nickel composite oxide, which is a high-capacity active material. Will be. Moreover, if the amount of gas generated becomes large, there is even a risk that the case will burst. Therefore, suppressing the generation of gas during high-temperature storage has been an important issue in using the lithium nickel composite oxide.
[0006]
In addition, improvement of continuous charging characteristics has recently been particularly demanded with the growing demand for office notebook computers. When using a laptop computer in the office, the AC adapter is used as the power source in most cases, and the secondary battery in the computer is constantly charged. During such continuous charging, gas is generated by decomposition of the electrolyte. In a cylindrical battery that detects an internal pressure and activates a safety valve when there is an abnormality such as overcharging, if there is a large amount of gas generated, the safety valve will operate during continuous charging. In addition, in a rectangular battery without a safety valve, when the amount of gas is large, it is necessary to store the bare cell in a larger case so that there is no change in appearance, leading to a decrease in the energy density of the entire battery pack. Furthermore, if the generation of gas is large, there is a risk that the case will burst. Therefore, especially as a continuous charge characteristic, it is strongly required to suppress generation of gas. When lithium cobalt composite oxide is used as the positive electrode active material, the amount of gas generated during high temperature storage is relatively small, but the amount of gas generated during long-term continuous charging is large, and improvement has been required.
[0007]
[Means for Solving the Problems]
As a result of intensive studies to solve the above-mentioned problems, the present inventor has incorporated a specific compound into a non-aqueous electrolyte solution, thereby maintaining a high capacity and recovering a capacity when stored under high temperature conditions. The inventors have found that the gas generation is significantly reduced even when the battery is continuously charged for a long time, and the present invention has been completed.
[0008]
That is, the gist of the present invention is that a lithium salt is dissolved in a non-aqueous organic solvent. For lithium secondary battery A non-aqueous electrolyte solution, wherein the non-aqueous organic solvent is a polyvalent sulfonate compound represented by the following general formula (1): 0.01 to 15% by weight of the non-aqueous electrolyte for a lithium secondary battery It is characterized by containing For lithium secondary battery Non-aqueous electrolyte.
[0009]
[Chemical formula 2]
[0010]
(In the formula, L is composed of a carbon atom and a hydrogen atom. The number of carbon atoms is 3-12 Represents a Z-valent linking group, R is It is selected from an alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, an aryl group having 6 to 9 carbon atoms, and an aralkyl group having 7 to 8 carbon atoms. Represents a hydrocarbon group, Z is 3 Or 4 Is)
The other gist of the present invention is as described above. For lithium secondary battery The present invention resides in a lithium secondary battery using a nonaqueous electrolytic solution.
[0011]
When the electrolytic solution containing the above polyvalent sulfonate compound is used, the high-temperature storage characteristics and the continuous charge characteristics are improved while maintaining a high capacity. Specifically, gas generation during high temperature storage and continuous charging is suppressed and the recovery capacity after storage is improved. In particular, in a lithium secondary battery using a positive electrode containing a lithium nickel composite oxide that generates a large amount of gas, the amount of gas generated can be greatly reduced. As described above, divalent sulfonate compounds such as 1,4-butanediol dimethanesulfonate and propylene glycol dimethanesulfonate, which have been reported to improve the cycle characteristics as described above, improve the cycle characteristics. It is not a significant improvement. Therefore, it was completely unpredictable that the above polyvalent sulfonate compound greatly improved the storage characteristics at high temperatures. Although the details of the reason why the electrolytic solution containing the polyvalent sulfonate compound brings about improvement in storage characteristics are unknown, the SEI (interface protective film) formed on the negative electrode at the initial stage of charging is thermally stable. And that the polyvalent sulfonate compound covers the base point of the positive electrode. If the SEI that suppresses the reaction between lithium in the negative electrode and the electrolytic solution is thermally unstable, the reaction between the lithium and the electrolytic solution proceeds to generate gas. Non-aqueous solvents such as carbonates are reduced at the initial stage of charging to form SEI. However, the above polyvalent sulfonate compounds are partially reduced and incorporated into SEI, making SEI stronger. It is estimated to be. In addition, the polyvalent sulfonate remaining without being reduced at the initial stage of charging acts as an acid, and covers the base point of the positive electrode active material, so that the decarboxylation reaction of the carbonate solvent can be suppressed, and the generation of gas such as carbon dioxide is prevented. It is thought that it is suppressing.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
The non-aqueous electrolyte solution according to the present invention is a solution in which a lithium salt is dissolved in a non-aqueous organic solvent and a polyvalent sulfonate compound represented by the following general formula (I) is further contained.
[0013]
[Chemical 3]
[0014]
(In the formula, L is composed of a carbon atom and a hydrogen atom, 3 to 12 carbon atoms Represents a Z-valent linking group, R represents a hydrocarbon group, and Z represents 3 Or 4 Is)
In the general formula (1), R represents a hydrocarbon group. Examples of the hydrocarbon group include an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group, an isopropyl group, and a butyl group, and an alkenyl having 2 to 4 carbon atoms such as a vinyl group, an isopropenyl group, and an allyl group. Group, phenyl group, tolyl group, ethylphenyl group, dimethylphenyl group, trimethylphenyl group and other aryl groups having 6 to 9 carbon atoms, benzyl group, phenethyl group and other aralkyl groups having 7 to 8 carbon atoms, and the like. Preferred are alkyl groups having 1 to 2 carbon atoms such as methyl group and ethyl group, aryl groups having 6 to 9 carbon atoms such as phenyl group, tolyl group, ethylphenyl group, dimethylphenyl group and trimethylphenyl group, and more preferred. Are a methyl group and a tolyl group.
[0015]
Z Is 3 Or 4. L is composed of carbon atoms and hydrogen atoms, 3 to 12 carbon atoms Represents a Z-valent linking group. Number of carbon atoms constituting the linking group L Is More preferably, it is 3-8.
Some examples in which Z is 3, that is, L is a trivalent linking group composed of a carbon atom and a hydrogen atom are exemplified below.
[0016]
[Formula 4]
[0017]
[Chemical formula 5]
[0018]
[Chemical 6]
[0019]
[Chemical 7]
[0020]
[Chemical 8]
[0021]
[Chemical 9]
[0022]
Examples of the case where Z is 4, ie, L is a tetravalent linking group composed of a carbon atom and a hydrogen atom, include the following.
[0023]
[Chemical Formula 10]
[0024]
Embedded image
[0025]
Embedded image
[0026]
Examples of the polyvalent sulfonate compound of the general formula (1) include 1,2,3-propanetriol trimethanesulfonate, 1,2,3-propanetrioltriethanesulfonate, 1,2,3-propanetrioltripropanesulfonate. 1,2,3-propanetriol tributanesulfonate, 1,2,3-propanetriol tribenzenesulfonate, 1,2,3-propanetriol tri-p-toluenesulfonate, 1,2,3-propanetriol tri- 1,2,3-propanetriol trisulfonates such as 4-ethylbenzenesulfonate, 1,2,3-propanetriol tris-3,5-dimethylbenzenesulfonate, 1,2,3-propanetriol tri-2-mesitylenesulfonate 1,2,3-bu Ntrioltrimethanesulfonate, 1,2,3-butanetrioltriethanesulfonate, 1,2,3-butanetrioltripropanesulfonate, 1,2,3-butanetrioltributanesulfonate, 1,2,3-butane Triol tribenzene sulfonate, 1,2,3-butanetriol tri-p-toluenesulfonate, 1,2,3-butanetriol tri-4-ethylbenzenesulfonate, 1,2,3-butanetriol tris-3,5-dimethyl 1,2,3-butanetriol trisulfonates such as benzenesulfonate, 1,2,3-butanetrioltri-2-mesitylenesulfonate, 1,2,4-butanetrioltrimethanesulfonate, 1,2,4-butane Triol triethane sulfonate 1,2,4-butanetriol tripropanesulfonate, 1,2,4-butanetrioltributanesulfonate, 1,2,4-butanetrioltribenzenesulfonate, 1,2,4-butanetrioltri-p-toluenesulfonate 1,2,4-butanetriol tri-4-ethylbenzenesulfonate, 1,2,4-butanetrioltris-3,5-dimethylbenzenesulfonate, 1,2,4-butanetrioltri-2-mesitylenesulfonate, etc. 1,2,4-butanetriol trisulfonates, 1,2,5-pentanetriol trimethanesulfonate, 1,2,5-pentanetrioltriethanesulfonate, 1,2,5-pentanetrioltripropanesulfonate, 1, 2,5-pentanetriol 1,2,5-pentanetriol trisulfonates such as tribenzenesulfonate, 1,2,5-pentanetriol tri-p-toluenesulfonate, 1,2,6-hexanetrioltrimethanesulfonate, 1,2,6- 1,2,6, such as hexanetriol triethanesulfonate, 1,2,6-hexanetrioltripropanesulfonate, 1,2,6-hexanetrioltribenzenesulfonate, 1,2,6-hexanetrioltri-p-toluenesulfonate 6-hexanetriol trisulfonates, 1,2,3-heptanetrioltrimethanesulfonate, 1,2,3-heptanetrioltriethanesulfonate, 1,2,3-heptanetrioltripropanesulfonate, 1,2,3- Heptane trio 1,2,3-heptanetriol trisulfonates such as tribenzenesulfonate, 1,2,3-heptanetriol tri-p-toluenesulfonate, 1,2,7-heptanetrioltrimethanesulfonate, 1,2,7- 1,2,7, such as heptane triol triethane sulfonate, 1,2,7-heptane triol tripropane sulfonate, 1,2,7-heptane triol tribenzene sulfonate, 1,2,7-heptane triol tri-p-toluene sulfonate 7-heptanetriol trisulfonates, 1,2,8-octanetriol trimethanesulfonate, 1,2,8-octanetrioltriethanesulfonate, 1,2,8-octanetrioltripropanesulfonate, 1,2,8- Octantrio 1,2,8-octanetriol trisulfonates such as lutribenzenesulfonate, 1,2,8-octanetrioltri-p-toluenesulfonate, trimethylolethanetrimethanesulfonate, trimethylolethanetriethanesulfonate, trimethylolethanetri Propane sulfonate, trimethylol ethane tributane sulfonate, trimethylol ethane tribenzene sulfonate, trimethylol ethane tri-p-toluene sulfonate, trimethylol ethane tri-4-ethylbenzene sulfonate, trimethylol ethane tris-3,5-dimethylbenzene sulfonate, Trimethylolethane trisulfonates such as trimethylolethanetri-2-mesitylenesulfonate, trimethylolpropane trimethyl Tansulfonate, trimethylolpropane triethanesulfonate, trimethylolpropane tripropanesulfonate, trimethylolpropane tributanesulfonate, trimethylolpropane tribenzenesulfonate, trimethylolpropane tri-p-toluenesulfonate, trimethylolpropane tri-4-ethylbenzenesulfonate , Trimethylolpropane tri-3,5-dimethylbenzenesulfonate, trimethylolpropane trisulfonate such as trimethylolpropane tri-2-mesitylenesulfonate, 3-methylpentane-1,3,5-trioltrimethanesulfonate, 3- Methylpentane-1,3,5-trioltriethanesulfonate, 3-methylpentane-1,3,5-trioltriple Pansulfonate, 3-methylpentane-1,3,5-trioltributanesulfonate, 3-methylpentane-1,3,5-trioltribenzenesulfonate, 3-methylpentane-1,3,5-trioltri-p -Toluenesulfonate, 3-methylpentane-1,3,5-trioltri-4-ethylbenzenesulfonate, 3-methylpentane-1,3,5-trioltri-3,5-dimethylbenzenesulfonate, 3-methylpentane- 3-methylpentane-1,3,5-triol trisulfonates such as 1,3,5-trioltri-2-mesitylenesulfonate, 1,2,4-benzenetriol trimethanesulfonate, 1,2,4-benzene Triol triethanesulfonate, 1,2,4-benzenetri Trivalent sulfonates such as 1,2,4-benzenetriol trisulfonates, 1,2,4-benzenetriol tribenzenesulfonate, 1,2,4-benzenetriol tri-p-toluenesulfonate, etc. 1,2,3,4-butanetetrol tetramethanesulfonate, 1,2,3,4-butanetetrol tetraethanesulfonate, 1,2,3,4-butanetetroltetrapropanesulfonate, 1,2, 3,4-butanetetrol tetrabenzenesulfonate, 1,2,3,4-butanetetrol tetra-p-toluenesulfonate, 1,2,3,4-butanetetrol tetra-4-ethylbenzenesulfonate, 1,2, , 3,4-Butanetetrol tetrakis-3,5-dimethylbenzenes 1,2,3,4-butanetetrol tetrasulfonates such as sulfonate, pentaerythritol tetramethanesulfonate, pentaerythritol tetraethanesulfonate, pentaerythritol tetrapropanesulfonate, pentaerythritol tetrabenzenesulfonate, pentaerythritol tetra-p-toluenesulfonate And tetravalent sulfonates such as pentaerythritol tetrasulfonates such as pentaerythritol tetra-4-ethylbenzenesulfonate and pentaerythritol tetrakis-3,5-dimethylbenzenesulfonate.
[0027]
Preferably 1,2,3-propanetriol trimethanesulfonate, 1,2,3-propanetrioltriethanesulfonate, 1,2,3-propanetrioltribenzenesulfonate, 1,2,3-propanetrioltri-p- 1,2,3-propanetriol trisulfonates such as toluenesulfonate, 1,2,3-butanetrioltrimethanesulfonate, 1,2,3-butanetrioltriethanesulfonate, 1,2,3-butanetrioltribenzene 1,2,3-butanetriol trisulfonates such as sulfonate, 1,2,3-butanetrioltri-p-toluenesulfonate, 1,2,4-butanetrioltrimethanesulfonate, 1,2,4-butanetriol Trietanesulfonate, 1,2 1,2,4-butanetriol trisulfonates such as 4-butanetriol tribenzenesulfonate, 1,2,4-butanetrioltri-p-toluenesulfonate, trimethylolpropane trimethanesulfonate, trimethylolpropane triethanesulfonate, Trimethylolpropane trisulfonates such as trimethylolpropane tribenzenesulfonate, trimethylolpropane tri-p-toluenesulfonate, 3-methylpentane-1,3,5-trioltrimethanesulfonate, 3-methylpentane-1,3, 5-trioltriethanesulfonate, 3-methylpentane-1,3,5-trioltribenzenesulfonate, 3-methylpentane-1,3,5-trioltri-p-toluenesulfonate Trimethyl sulfonates such as 3-methylpentane-1,3,5-triol trisulfonates, 1,2,3,4-butanetetrol tetramethanesulfonate, 1,2,3,4-butanetetrol 1,2,3,4-butanetetrol tetra such as tetraethanesulfonate, 1,2,3,4-butanetetrol tetrabenzenesulfonate, 1,2,3,4-butanetetrol tetra-p-toluenesulfonate Sulfonates, tetravalent sulfonates such as pentaerythritol tetrasulfonates such as pentaerythritol tetramethanesulfonate, pentaerythritol tetraethanesulfonate, pentaerythritol tetrabenzenesulfonate, and pentaerythritol tetra-p-toluenesulfonate.
[0028]
More preferably 1,2,3-propanetriol trimethanesulfonate, 1,2,3-propanetriol tri-p-toluenesulfonate, 1,2,3-butanetrioltrimethanesulfonate, 1,2,3-butanetriol Tribenzenesulfonate, 1,2,3-butanetriol tri-p-toluenesulfonate, 1,2,4-butanetrioltrimethanesulfonate, 1,2,4-butanetrioltri-p-toluenesulfonate, trimethylolpropane tri 3 such as methanesulfonate, trimethylolpropane tri-p-toluenesulfonate, 3-methylpentane-1,3,5-trioltrimethanesulfonate, 3-methylpentane-1,3,5-trioltri-p-toluenesulfonate Methanesulfuric acid It is sulphonates and p- toluenesulfonic sulphonates.
[0029]
These sulfonate compounds may be used as a mixture of two or more.
The amount of the polyvalent sulfonate compound added to the non-aqueous organic solvent in which the lithium salt is dissolved is not particularly limited, but usually the sulfonate compound is 0.01% by weight or more, preferably 0.1% by weight of the non-aqueous electrolyte. Try to occupy the above. The upper limit is usually 15% by weight or less, preferably 7% by weight or less, and most preferably 3% by weight or less. If the amount added is too large, the ionic conductivity tends to decrease and battery characteristics such as rate characteristics tend to deteriorate. When the amount added is too small, no improvement in storage characteristics is observed.
[0030]
The lithium salt used as the supporting electrolyte in the present invention is not particularly limited. For example, LiPF ₆ , LiAsF ₆ , LiBF _Four , LiSbF ₆ LiAlCl _Four LiClO _Four , CF _Three SO _Three Li, C _Four F ₉ SO _Three Li, CF _Three COOLi, (CF _Three CO) ₂ NLi, (CF _Three SO ₂ ) ₂ NLi, (C ₂ F _Five SO ₂ ) ₂ Examples include lithium salts such as NLi. In particular, LiPF that is easily soluble in a solvent and has a high degree of dissociation ₆ , LiBF _Four , CF _Three SO _Three Li and (CF _Three SO ₂ ) ₂ A lithium salt selected from the group consisting of NLi is preferably used. The concentration of the lithium salt in the non-aqueous electrolyte is usually preferably in the range of 0.5 to 2 mol / L.
[0031]
The non-aqueous organic solvent used in the present invention is not particularly limited as long as the lithium salt can be dissolved. Among them, as a solvent that expresses high ionic conductivity, dimethyl carbonate (DMC), diethyl carbonate (DEC) are usually used. ), Chain carbonates such as ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate, cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC), vinylene carbonate, vinyl Unsaturated carbonates such as ethylene carbonate, ethers such as 1,2-dimethoxyethane and tetrahydrofuran, cyclic esters such as γ-butyrolactone and γ-valerolactone, methyl formate, methyl acetate, propylene A chain ester such as methyl onate is preferably used.
[0032]
These organic solvents are usually used as a mixture so that the electrolytic solution exhibits appropriate physical properties. In general, the chain carbonates and the cyclic carbonates are preferably used in combination. Of the chain carbonates, asymmetric carbonates such as ethyl methyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate are particularly preferable. Among them, ethyl methyl carbonate is preferably used because it has a low viscosity and thus not only enhances lithium mobility, but also has a relatively high boiling point and is difficult to volatilize and is easy to handle and has low reactivity with Li. Unsaturated carbonates such as vinylene carbonate and vinyl ethylene carbonate are preferable because they are easily reduced during initial charging and contribute to the formation of a stable interface protective film (SEI). These unsaturated carbonates are contained in the non-aqueous organic solvent in an amount of usually 0.01% by weight or more, preferably 0.05% by weight or more. The upper limit is usually 10% by weight or less, preferably 8% by weight or less.
[0033]
In preparing the non-aqueous electrolyte solution according to the present invention, each raw material of the non-aqueous electrolyte solution is preferably dehydrated in advance. The water content is usually 50 ppm or less, preferably 30 ppm or less. If a large amount of water is present, water electrolysis, reaction with lithium metal, and lithium salt hydrolysis may occur. The means for dehydration is not particularly limited, but in the case of a liquid such as a solvent, a molecular sieve or the like may be used. In the case of a solid such as a lithium salt, it may be dried at a temperature lower than the temperature at which decomposition occurs.
[0034]
The non-aqueous electrolyte solution according to the present invention is useful as an electrolyte solution for a lithium secondary battery. Hereinafter, the lithium secondary battery according to the present invention using this non-aqueous electrolyte will be described.
The basic configuration of this lithium secondary battery is the same as that of a conventionally known lithium secondary battery, and the positive electrode and the negative electrode are accommodated in the case via the porous film and the nonaqueous electrolyte solution according to the present invention. The external shape of the lithium secondary battery is not particularly limited, and may be any conventionally known coin-type battery, cylindrical battery, rectangular battery, or the like. What is necessary is just to select the active material of a positive electrode and a negative electrode suitably according to the kind of battery.
[0035]
Examples of the positive electrode active material include oxides having transition metals such as Fe, Co, Ni, and Mn, composite oxides of these with lithium, and inorganic compounds such as sulfides. Specifically, MnO, V ₂ O _Five , V ₆ O ₁₃ TiO ₂ Transition metal oxides such as, lithium nickel composite oxide, lithium cobalt composite oxide, lithium manganese composite oxide and other composite oxides of lithium and transition metal, TiS ₂ And transition metal sulfides such as FeS. You may mix and use multiple types of said active material. Among them, lithium and transition metal composite oxides such as lithium nickel composite oxide, lithium cobalt composite oxide, and lithium manganese composite oxide are preferably used because they have both high capacity and high cycle characteristics.
[0036]
The nonaqueous electrolytic solution according to the present invention improves the storage characteristics of the lithium secondary battery regardless of the type of the positive electrode active material, but the effect is particularly great when a positive electrode containing a lithium nickel composite oxide is used. It brings about significant improvement in properties such as suppressing gas generation during high temperature storage.
The lithium nickel composite oxide is an oxide containing at least lithium, nickel and oxygen, for example, LiNiO. ₂ , Li ₂ NiO ₂ , LiNi ₂ O _Four Among others, LiNiO ₂ Is preferred. Further, the lithium nickel composite oxide may be one in which a part of the site occupied by Ni is substituted with an element other than Ni. By substituting a part of the Ni site with another element, the stability of the crystal structure can be improved, and a decrease in capacity caused by a part of the Ni element moving to the Li site during repeated charging and discharging. Since it is suppressed, cycle characteristics are also improved. Furthermore, by replacing a part of the Ni site with an element other than Ni, the runaway reaction of the lithium nickel composite oxide when the temperature of the battery rises is also suppressed, resulting in an improvement in safety.
[0037]
Examples of the element (hereinafter referred to as “substitution element”) when substituting a part of the site occupied by Ni with an element other than Ni include, for example, Al, Ti, V, Cr, Mn, Fe, Co, Li, Cu, Zn, Mg, Ga, Zr etc. are mentioned. Al, Cr, Fe, Co, Li, Mg, Ga, and Mn are preferable, and Al and Co are more preferable. The Ni site may be substituted with two or more other elements.
[0038]
When the Ni site is substituted by a substitution element, the ratio is usually 2.5 mol% or more of Ni element, preferably 5 mol% or more, and usually 50 mol% or less, preferably 20 mol% or less of Ni element. is there. If the replacement ratio is too small, the effect of improving the cycle characteristics and the like may not be sufficient, and if it is too large, the capacity of the battery may be reduced.
[0039]
The specific surface area of the positive electrode active material is usually 0.1 m. ² / G or more, preferably 0.2 m ² / G or more, usually 10m ² / G or less, preferably 5.0 m ² / G or less. If the specific surface area is too small, the rate characteristics and capacity may be reduced. If the specific surface area is too large, an undesirable reaction with the electrolytic solution or the like may be caused, and the cycle characteristics may be deteriorated. In particular, lithium nickel composite oxide has a high reactivity with the electrolytic solution, so it is usually 5.0 m. ² / G or less, preferably 2.0 m ² / G or less.
[0040]
The average secondary particle size of the positive electrode active material is usually 0.2 μm or more, preferably 0.5 μm or more, usually 30 μm or less, preferably 20 μm or less. If the average secondary particle size is too small, the cycle deterioration of the battery may be increased or a safety problem may occur. If the average secondary particle size is too large, the internal resistance of the battery may be increased and output may be difficult to output.
[0041]
Lithium metal and lithium alloy can be used as the negative electrode active material, but in terms of good cycle characteristics and safety, such as coke, acetylene black, mesophase microbeads, and graphite that can occlude and release lithium ions. It is particularly preferred to use a carbonaceous material. The particle size of the granular negative electrode active material is usually about 1 to 50 μm, preferably about 15 to 30 μm, from the viewpoint of excellent battery characteristics such as initial efficiency, rate characteristics, and cycle characteristics.
[0042]
In addition, a material obtained by mixing and baking the carbonaceous substance with an organic substance or the like, or a material in which amorphous carbon is formed on at least a part of the surface using the CVD method or the like as compared with the carbonaceous substance is also carbonaceous. It can be suitably used as a substance.
Examples of the organic matter include coal tar pitch from soft pitch to hard pitch; heavy coal oil such as dry distillation liquefied oil; straight heavy oil such as atmospheric residual oil and vacuum residual oil; heat of crude oil, naphtha, etc. Examples include petroleum heavy oils such as cracking heavy oils (for example, ethylene heavy end) that are by-produced during cracking. Moreover, what grind | pulverized the solid residue obtained by distilling these heavy oils at 200-400 degreeC to 1-100 micrometers can also be used. Furthermore, a vinyl chloride resin and these resin precursors which become a phenol resin or an imide resin by firing can also be used.
[0043]
Examples of the binder that can be used for the positive electrode or the negative electrode include various materials from the viewpoint of weather resistance, chemical resistance, heat resistance, flame retardancy, and the like. Specifically, inorganic compounds such as silicate and glass, alkane polymers such as polyethylene, polypropylene and poly-1,1-dimethylethylene; unsaturated polymers such as polybutadiene and polyisoprene; polystyrene, polymethylstyrene, Polymers having rings such as polyvinyl pyridine and poly-N-vinyl pyrrolidone; polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, polyethyl acrylate, polyacrylic acid, polymethacrylic acid, poly Acrylic derivative polymers such as acrylamide; Fluorine resins such as polyvinyl fluoride, polyvinylidene fluoride, and polytetrafluoroethylene; CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide; Polyvinyl alcohol polymers such as polyvinyl alcohol; polyvinyl chloride, halogen-containing polymers such as polyvinylidene chloride; and conductive polymers such as polyaniline can be used. Further, a mixture such as the above-mentioned polymer, a modified product, a derivative, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer, and the like can be used. The weight average molecular weight of these resins is usually 10,000 to 3,000,000, preferably about 100,000 to 1,000,000. If the molecular weight is too low, the strength of the electrode tends to decrease. On the other hand, if the molecular weight is too high, the viscosity becomes high and it may be difficult to form an electrode. Preferred binder resins are fluororesins and CN group-containing polymers.
[0044]
The usage-amount of a binder is 0.1 weight part or more normally with respect to 100 weight part of active materials, Preferably it is 1 weight part or more, and is 30 weight part or less normally, Preferably it is 20 weight part or less. If the amount of the binder is too small, the strength of the electrode tends to decrease, and if the amount of the binder is too large, the ionic conductivity tends to decrease. Furthermore, in order to improve the electroconductivity and mechanical strength of an electrode, you may contain the additive, powder, filler, etc. which express various functions, such as an electroconductive material and a reinforcing material. The conductive material is not particularly limited as long as it can impart conductivity by mixing an appropriate amount of the above active material. Usually, carbon powder such as acetylene black, carbon black, graphite, various metal fibers, Examples include foil. As the reinforcing material, various inorganic, organic spherical and fibrous fillers can be used.
[0045]
The electrode can be formed by applying and drying a paint containing a component such as an active material or a binder and a solvent. The thickness of the electrode is usually 1 μm or more, preferably 10 μm or more, more preferably 20 μm or more, most preferably 40 μm or more, and usually 200 μm or less, preferably 150 μm or less, more preferably 100 μm or less. If it is too thin, the coating becomes difficult and it becomes difficult to ensure uniformity, and the battery capacity may be too small. On the other hand, if it is too thick, the rate characteristics may be deteriorated too much.
[0046]
At least one of the positive electrode and the negative electrode is usually formed on a current collector. Various types of current collectors can be used, but usually metals and alloys are used. Specifically, examples of the positive electrode current collector include aluminum, nickel, and SUS, and examples of the negative electrode current collector include copper, nickel, and SUS. Preferably, aluminum is used as the positive electrode current collector, and copper is used as the negative electrode current collector. In order to improve the binding effect with the positive and negative electrode layers, it is preferable that the surfaces of these current collectors are roughened in advance. Current roughening methods include a method of rolling with a blasting process or a rough roll, a polishing cloth with a fixed abrasive particle, a grinding wheel, emery buff, a wire brush with a steel wire, etc. Examples thereof include a mechanical polishing method for polishing the surface, an electrolytic polishing method, and a chemical polishing method.
[0047]
Further, in order to reduce the weight of the battery, that is, to improve the weight energy density, a perforated current collector such as an expanded metal or a punching metal can be used. In this case, the weight can be freely changed by changing the aperture ratio. In addition, when an active material is present on both sides of such a hole-type current collector, the rivet effect of the coating film through this hole tends to make the coating film more difficult to peel off, but the aperture ratio is too high. When it becomes high, the contact area between the coating film and the current collector becomes small, so that the adhesive strength may be lowered.
[0048]
The thickness of the current collector is usually 1 μm or more, preferably 5 μm or more, and is usually 100 μm or less, preferably 50 μm or less. If it is too thick, the capacity of the entire battery will be too low. Conversely, if it is too thin, handling may be difficult.
The non-aqueous electrolyte solution of the present invention may be gelled with a polymer to form a semi-solid. The amount of the non-aqueous electrolyte used in the semisolid electrolyte is usually 30% by weight or more, preferably 50% by weight or more, more preferably 75% by weight or more based on the total amount of the semisolid electrolyte. 99.95% by weight or less, preferably 99% by weight or less, more preferably 98% by weight or less. If the amount used is too large, it is difficult to retain the electrolyte solution and liquid leakage tends to occur. Conversely, if the amount is too small, the charge / discharge efficiency and capacity may be insufficient.
[0049]
A porous spacer is preferably provided between the positive electrode and the negative electrode to prevent a short circuit. That is, in this case, the electrolytic solution is used by being impregnated into a porous spacer. As a material for the spacer, polyolefin such as polyethylene or polypropylene, polytetrafluoroethylene, polyethersulfone, or the like can be used, and polyolefin is preferable. The thickness of the spacer is usually 1 μm or more, preferably 5 μm or more, more preferably 10 μm or more, and usually 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less. If the porous film is too thin, the insulation and mechanical strength may be deteriorated. If the porous film is too thick, not only the battery performance such as the rate characteristic is deteriorated, but also the energy density of the whole battery may be lowered. The porosity of the spacer is usually 20% or more, preferably 35% or more, more preferably 45% or more, and usually 90% or less, preferably 85% or less, more preferably 75% or less. If the porosity is too small, the membrane resistance increases and the rate characteristics tend to deteriorate. On the other hand, if it is too large, the mechanical strength of the film tends to decrease and the insulating property tends to decrease. The average pore diameter of the spacer is usually 0.5 μm or less, preferably 0.2 μm or less, and usually 0.05 μm or more. If it is too large, a short circuit tends to occur, and if it is too small, the film resistance increases and the rate characteristics may deteriorate.
[0050]
【Example】
EXAMPLES Hereinafter, although an Example is given and the specific aspect of this invention is further demonstrated, this invention is not limited by these Examples, unless the summary is exceeded.
Example 1
[Production of positive electrode]
Lithium nickel composite oxide (LiNi _0.82 Co _0.15 Al _0.03 O ₂ ) Mix 90% by weight, 5% by weight of polyvinylidene fluoride (PVdF) and 5% by weight of acetylene black, add N-methylpyrrolidone to form a slurry, and apply and dry on both sides of the current collector made of aluminum. Thus, a positive electrode was obtained.
[0051]
[Manufacture of negative electrode]
90% by weight of graphite powder and 10% by weight of PVdF were mixed, and a slurry obtained by adding N-methylpyrrolidone was applied to one side of a current collector made of copper and dried to obtain a negative electrode.
[Preparation of electrolyte]
LiPF ₆ Is obtained by adding 2 parts by weight of vinylene carbonate to 100 parts by weight of a mixed solvent of ethylene carbonate and ethyl methyl carbonate (mixing volume ratio 1: 3) containing 1.25 mol / L of the base electrolyte solution. 1 part by weight of 1,2,4-butanetriol trimethanesulfonate was added to obtain an electrolytic solution.
[0052]
[Manufacture of lithium secondary batteries]
After applying and impregnating the electrolyte solution to the positive electrode, the negative electrode, and a biaxially stretched porous film made of polyethylene having a film thickness of 16 μm, a porosity of 45%, and an average pore diameter of 0.05 μm, respectively, the negative electrode, separator, positive electrode, The separator and the negative electrode were laminated in this order. The battery element thus obtained was first sandwiched between PET films, and then sealed in a vacuum while sheeting positive and negative terminals on a laminate film in which both surfaces of an aluminum layer were covered with a resin layer, and sheet-like lithium secondary A battery was produced. In order to further improve the adhesion between the electrodes, a sheet battery is sandwiched between silicon rubber and a glass plate, and then 0.35 kg / cm. ² Was pressurized. FIG. 1 shows a schematic cross-sectional view of a secondary battery.
[0053]
[Capacity evaluation]
The discharge amount per hour of the lithium nickel composite oxide was set to 180 mAh / g, the discharge rate was determined from this and the amount of the active material of the positive electrode of the lithium secondary battery, and the rate was set. After charging to 2V, it was discharged to 3V at 0.2C, and the initial formation was performed. Subsequently, after charging to 4.2V at 0.5C, it was discharged again to 3V at 0.2C, and the 0.2C discharge capacity was determined. The cut current during charging was set to 0.05C.
[0054]
[Evaluation of storage characteristics]
After the capacity evaluation test was completed, the battery was charged to 4.2 V at 0.5 C, and then stored in a constant temperature bath at 85 ° C. for 1 day, and the amount of gas generated was immersed in an ethanol bath to measure the buoyancy (Archimedes's Principle). In addition, in order to evaluate the capacity deterioration after storage, charge to 0.5V at 4.2V, then discharge at 0.2C, measure the 0.2C discharge capacity after storage, and the capacity recovery rate according to the following formula Asked. The results are shown in Table 1.
[0055]
[Expression 1]
Capacity recovery rate (%) =
After storage 0.2C discharge capacity (mAh / g) /0.2C discharge capacity (mAh / g)
[0056]
Example 2
A lithium secondary battery was produced in the same manner as in Example 1 except that an electrolytic solution in which the amount of 1,2,4-butanetrioltrimethanesulfonate added was 3 parts by weight was used. A characteristic test was carried out. The results are shown in Table 1.
[0057]
Example 3
A lithium secondary battery was produced in the same manner as in Example 1 except that an electrolyte solution containing 5 parts by weight of 1,2,4-butanetrioltrimethanesulfonate was used. A characteristic test was carried out. The results are shown in Table 1.
Example 4
LiPF ₆ 1 part by weight of 1,2,4-butanetriol trimethanesulfonate to 100 parts by weight of a mixed solvent of ethylene carbonate and diethyl carbonate (mixing volume ratio 1: 1) containing 1.0 mol / L A lithium secondary battery was produced in the same manner as in Example 1 except that was used as the electrolytic solution, and the same battery characteristic test as in Example 1 was performed. The results are shown in Table 1. Regardless of the electrolyte composition, the amount of gas generation is reduced, and the effect of improving the storage characteristics is seen.
[0058]
Comparative Example 1
A lithium secondary battery was produced in the same manner as in Example 1 except that an electrolyte without adding 1,2,4-butanetrioltrimethanesulfonate was used, and a battery characteristic test similar to that in Example 1 was performed. The results are shown in Table 1. It can be seen that the capacity recovery rate is low, a large amount of gas is generated, and the storage characteristics are greatly inferior.
[0059]
Comparative Example 2
A lithium secondary battery was produced in the same manner as in Example 1 except that an electrolyte solution in which 1,4-butanediol dimethanesulfonate was added instead of 1,2,4-butanetrioltrimethanesulfonate as an additive was used. Then, the same battery characteristic test as in Example 1 was performed. The results are shown in Table 1. Although the capacity recovery rate is improved, the effect of suppressing gas generation is insufficient.
[0060]
Example 5
[Production of positive electrode]
Lithium cobalt composite oxide (LiCoO ₂ ) 90% by weight, PVdF 5% by weight, and acetylene black 5% by weight were mixed, and N-methylpyrrolidone was added to form a slurry, which was applied to both surfaces of an aluminum current collector and dried to obtain a positive electrode.
[0061]
[Manufacture of negative electrode]
A mixture of 87.4% by weight of graphite powder, 9.7% by weight of PVdF and 2.9% by weight of acetylene black, added with N-methylpyrrolidone to form a slurry, and applied to one side of a copper current collector. Thus, a negative electrode was obtained.
[Preparation of electrolyte]
LiPF ₆ Is obtained by adding 2 parts by weight of vinylene carbonate to 100 parts by weight of a mixed solvent of ethylene carbonate and ethyl methyl carbonate (mixing volume ratio 1: 3) containing 1.25 mol / L of the base electrolyte solution. 1 part by weight of 1,2,4-butanetriol trimethanesulfonate was added to obtain an electrolytic solution.
[0062]
[Manufacture of lithium secondary batteries]
After applying and impregnating the electrolyte solution to the positive electrode, the negative electrode, and a biaxially stretched porous film made of polyethylene having a film thickness of 16 μm, a porosity of 45%, and an average pore diameter of 0.05 μm, respectively, the negative electrode, separator, positive electrode, The separator and the negative electrode were laminated in this order. The battery element thus obtained was first sandwiched between PET films, and then sealed in a vacuum while sheeting positive and negative terminals on a laminate film in which both surfaces of an aluminum layer were covered with a resin layer, and sheet-like lithium secondary A battery was produced. In order to further improve the adhesion between the electrodes, a sheet battery is sandwiched between silicon rubber and a glass plate, and then 0.35 kg / cm. ² Was pressurized.
[0063]
[Capacity evaluation]
The discharge amount per hour of the lithium cobalt composite oxide was set to 138 mAh / g, and the rate was set by obtaining the discharge rate 1 C from this and the amount of the active material of the positive electrode of the lithium secondary battery. After charging to 2V, it was discharged to 3V at 0.2C, and the initial formation was performed. Subsequently, after charging to 4.2V at 0.5C, it was discharged again to 3V at 0.2C, and the 0.2C discharge capacity was determined. The cut current during charging was set to 0.05C.
[0064]
[Evaluation of storage characteristics]
After the capacity evaluation test is completed, the battery is charged to 4.2 V at 0.5 C and stored in a thermostatic bath at 85 ° C. for 1 day, and then the amount of gas generated is determined by immersing the battery in an ethanol bath and measuring the buoyancy. It was. In addition, in order to evaluate the capacity deterioration after storage, after charging to 4.2 V at 0.5 C, discharge at 0.2 C and measure the 0.2 C discharge capacity after storage, and the capacity recovery rate is calculated according to the above formula. Asked. The results are shown in Table 1.
[0065]
Comparative Example 3
A lithium secondary battery was produced in the same manner as in Example 5 except that an electrolytic solution to which 1,2,4-butanetrioltrimethanesulfonate was not added was used, and a battery characteristic test similar to that in Example 5 was performed. The results are shown in Table 1. Since lithium cobalt composite oxide is used as the positive electrode active material, the amount of gas generated after storage is at a low level, but capacity recovery is insufficient.
[0066]
[Table 1]
[0067]
As can be seen from Table 1 above, the use of the non-aqueous electrolyte according to the present invention improves the high-temperature storage characteristics while maintaining a high capacity. In particular, it is effective in suppressing the amount of gas generated during storage, and in particular, the effect of suppressing gas generation is great in a lithium secondary battery using a positive electrode containing a lithium nickel composite oxide.
[0068]
Example 6
[Continuous charging evaluation]
LiPF ₆ 1,2 and 4-butanetriol triol in 100 parts by weight of a mixed solvent of ethylene carbonate and ethyl methyl carbonate (mixing volume ratio 1: 3) and 2 parts by weight of vinylene carbonate. A lithium secondary battery was produced in the same manner as in Example 5 except that an electrolyte prepared by adding 1 part by weight of methanesulfonate was used, and a capacity evaluation test similar to that in Example 5 was performed. Next, this battery was placed in a constant temperature bath at 60 ° C., charged at a constant current of 0.7 C, and switched to constant voltage charging when it reached 4.25V. After charging for 7 days, the battery was immersed in an ethanol bath to measure buoyancy, and the amount of gas generated was calculated from the buoyancy. The results are shown in Table 2.
[0069]
Comparative Example 4
A lithium secondary battery was produced in the same manner as in Example 6 except that an electrolytic solution in which 1,3-propane sultone was added instead of 1,2,4-butanetrioltrimethanesulfonate as an additive was used. A battery characteristic test similar to that in Example 6 was performed. The results are shown in Table 2.
[0070]
Comparative Example 5
A lithium secondary battery was produced in the same manner as in Example 6 except that an electrolytic solution to which 1,2,4-butanetrioltrimethanesulfonate was not added was used, and a battery characteristic test similar to that in Example 6 was performed. The results are shown in Table 2.
[0071]
[Table 2]
[0072]
As apparent from Table 2 above, the amount of gas generated during continuous charging can be suppressed by using the non-aqueous electrolyte solution according to the present invention.
[0073]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, a lithium secondary battery with a high capacity | capacitance, a high temperature storage characteristic, and a favorable continuous charge characteristic can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing the structure of a lithium secondary battery embodying the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 PET film 5 Silicon rubber 6 Glass plate 7 Laminate film 8 Lead with sealing material

Claims (6)

A non-aqueous electrolyte for a lithium secondary battery in which a lithium salt is dissolved in a non-aqueous organic solvent, wherein the non-aqueous organic solvent is a polyvalent sulfonate compound represented by the following general formula (1) : A non-aqueous electrolyte for a lithium secondary battery , comprising 0.01 to 15% by weight of the non-aqueous electrolyte for a battery .
(In the formula, L is composed of a carbon atom and a hydrogen atom and represents a Z-valent linking group having 3 to 12 carbon atoms , and R is an alkyl group having 1 to 4 carbon atoms and 2 to 4 carbon atoms. (Represents a hydrocarbon group selected from an alkenyl group, an aryl group having 6 to 9 carbon atoms, and an aralkyl group having 7 to 8 carbon atoms , and Z is 3 or 4 ) The non-aqueous electrolyte for a lithium secondary battery according to claim 1, wherein the lithium secondary battery includes a positive electrode active material, and the positive electrode active material is a composite oxide of lithium and a transition metal. The nonaqueous electrolytic solution for a lithium secondary battery according to claim 1, wherein the nonaqueous organic solvent contains an unsaturated carbonate. The nonaqueous electrolytic solution for a lithium secondary battery according to any one of claims 1 to 3, wherein the nonaqueous organic solvent contains an asymmetric carbonate. A lithium secondary battery using the non-aqueous electrolyte solution for a lithium secondary battery according to any one of claims 1 to 4.   The lithium secondary battery according to claim 5, wherein a positive electrode containing a lithium nickel composite oxide is used as an active material.