JP3974012B2 - Electrolytes for electrochemical devices, electrolytes or solid electrolytes thereof, and batteries - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention has excellent cycle characteristics are utilized for electrochemical devices of the lithium battery and lithium-ion batteries, the electrolyte shows the storage characteristics, the electrolyte solution or solid electrolyte, and a lithium battery and a lithium ion battery using the same.
[0002]
[Prior art]
With the development of portable devices in recent years, the development of electrochemical devices using electrochemical phenomena such as batteries and capacitors as a power source has become active. Further, as an electrochemical device other than the power source, an electrochromic display (ECD) in which a color change is caused by an electrochemical reaction can be given.
[0003]
These electrochemical devices are generally composed of a pair of electrodes and an ionic conductor filling them. As the ionic conductor, a solution in which a salt (AB) composed of a cation (A ⁺ ) and an anion (B ⁻ ) called an electrolyte is dissolved in a solvent, a polymer, or a mixture thereof is used. When this electrolyte is dissolved, it dissociates into a cation and an anion, and conducts ions. In order to obtain the ionic conductivity necessary for the device, it is necessary that this electrolyte is dissolved in a sufficient amount in a solvent or a polymer. Actually, a solvent other than water is often used as a solvent, and there are currently only a few types of electrolytes having sufficient solubility in such organic solvents and polymers. For example, as an electrolyte for a lithium battery, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ) and LiCF ₃ SO ₃ only. The cation portion is often determined by the device, such as the lithium ion of a lithium battery, but the anion portion can be used if the condition that the solubility is high is satisfied.
[0004]
However, existing electrolytes have various problems, and an electrolyte having a novel anion portion is desired. Specifically, ClO ₄ ions are explosive and AsF ₆ ions are toxic and cannot be used for safety reasons. The only practically used LiPF ₆ also has problems such as heat resistance and hydrolysis resistance. LiN (CF ₃ SO ₂ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ) and LiCF ₃ SO ₃ have high stability and ionic conductivity. Although it is an excellent electrolyte because it is high, it is difficult to use because the aluminum current collector in the battery is corroded in a state where a potential is applied (Non-patent Documents 1 and 2).
[0005]
In addition, as the application range of devices is diversified, optimum electrolytes for each application are being searched for. However, since there are few types of anions in existing electrolytes, optimization has reached the limit. Therefore, we are searching for an electrolyte composition that combines the characteristics of individual electrolytes by mixing several types of the above existing electrolytes, and on the other hand, we are developing new electrolytes aiming at further enhancement of functionality. Is the current status (Non-patent Document 3, Patent Document 1, Patent Document 2).
[0006]
[Non-Patent Document 1]
K. Kinoshita et al, Electrochemical and Solid-State Letters, 4, A42 (2001)
[Non-Patent Document 2]
RTAtanasoski et al, J. Power Sources, 68, 320 (1997)
[Non-Patent Document 3]
L. Peter and J. Arai, J. Applied Electrochemistry, 29, 1053 (1999)
[Patent Document 1]
JP 2001-110450 A
[Patent Document 2]
JP 2001-143750 A
[0007]
[Means for solving problems]
As a result of intensive studies in view of the problems of the prior art, the present inventors have found a system in which several kinds of electrolytes having novel chemical structural characteristics are combined and have reached the present invention.
[0008]
That is, the present invention provides a lithium battery and an electrolyte for a lithium ion battery including at least a compound comprising the chemical structural formula represented by the general formula (1) and a compound comprising the chemical structural formula represented by the general formula (2).
[0009]
[Chemical formula 2]
[0010]
Where M is B or P, A ^{a +} is lithium ion, a is 1, b is 1, p is 1, m is 1 or 2 when M is B, and 1 when M is P 2, or 3 , n represents 0 or 2 when M is B, 0, 2, or 4 when M is P , q represents 0 or 1, respectively, and R ¹ and R ² are each independently , H, halogen, C ₁ -C ₁₀ alkyl, or C ₁ -C ₁₀ halogenated alkyl, R ³ is C ₁ -C ₁₀ alkylene, C ₁ -C ₁₀ halogenated alkylene, C ₆ -C ₂₀ arylenes, or C ₆ -C ₂₀ halogenated arylenes, R ⁴ is halogen, or X ² R ⁷ , X ¹ is O, or NR ⁵ , X ² is O, R ⁵ is C _1- alkyl of C ^{_10, X} 3 is O, ^{R 7} _is a halogenated alkyl of C 1 _{-C 10} A lithium battery and a lithium ion battery electrolyte each of which represents a lithium battery comprising a solution of the electrolyte in a non-aqueous solvent, a lithium ion battery electrolyte or a lithium battery comprising the electrolyte dissolved in a polymer, and a lithium battery Provided are a solid electrolyte for an ion battery, and at least a positive electrode, a negative electrode, an electrolytic solution or a solid electrolyte, and a lithium battery and a lithium ion battery containing the electrolyte in the electrolytic solution or the solid electrolyte.
[0011]
The alkyl, alkyl halide, aryl, and aryl halide used in the present invention include those having other functional groups such as a branch, a hydroxyl group, and an ether bond.
[0012]
Hereinafter, the present invention will be described in more detail.
[0013]
Here, specific examples of the compound represented by the general formula (1) and the compound represented by the general formula (2) used in the present invention are shown below.
[0014]
[Chemical 3]
[0015]
[Formula 4]
[0016]
Here, lithium ions are exemplified as A ^{a +} .
[0017]
Lithium ions are preferred when considering applications such as electrochemical devices. The valence ^a of the cation of A ^{a +} is preferably 1 to 3. If it is larger than 3, the crystal lattice energy becomes large, which causes a problem that it becomes difficult to dissolve in a solvent. Therefore, when solubility is required, 1 is more preferable. Similarly, the valence b of the anion is preferably 1 to 3, and more preferably 1. The constant p representing the ratio of cation to anion is inevitably determined by the valence ratio b / a of both.
[0018]
The electrolyte of the formula which is part of the configuration of the present invention (1) and the general formula (2) has taken an ionic metal complex structure, M serving as its center, a B or P,. In the case of B 2 or P, in addition to the ease of synthesis, it has excellent properties in all aspects such as low toxicity, stability and cost.
[0019]
Next, the part of the ligand that is characteristic of the electrolyte (ionic metal complex) represented by the general formula (1) and the general formula (2) will be described. Hereinafter, the organic or inorganic part bonded to M is referred to as a ligand.
[0020]
In the general formula (1) and the general formula (2), X ¹ is O, or NR ⁵ , X ² is O , and is bonded to M through these heteroatoms. Here, it is not impossible to combine other than O, S, and N, but it is very complicated in synthesis. Since this compound has a bond with M by a carboxyl group (—COO—) other than X ¹ in the same ligand, these ligands constitute a chelate structure with M. Due to the effect of this chelate, the heat resistance, chemical stability, and hydrolysis resistance of this compound are improved. The constant q in this ligand is 0 or 1. Particularly, 0 is preferable because this chelate ring is a five-membered ring, so that the chelate effect is exerted most strongly and the stability is increased. Further, the negative charge of M at the center is dispersed due to the electron withdrawing effect by the carboxyl group, and the electrical stability of the anion is increased. Therefore, ion dissociation becomes very easy, and the solubility in the solvent, the ionic conductivity, and the like increase. In addition, other heat resistance, chemical stability, and hydrolysis resistance are also improved.
[0021]
R ¹ and R ² are each independently selected from the group consisting of H, halogen, C ₁ -C ₁₀ alkyl, or C ₁ -C ₁₀ halogenated alkyl, preferably at least R ¹ and R ² One is a fluorinated alkyl, and more preferably at least one of R ¹ and R ² is a trifluoromethyl group. The presence of electron-withdrawing halogen or alkyl halide in R ¹ and R ² disperses the negative charge of the center M and increases the electrical stability of the anion. Solubility, ionic conductivity, catalytic activity, etc. increase. In addition, other heat resistance, chemical stability, and hydrolysis resistance are also improved. In particular, when the halogen is fluorine, the effect is greater, and when the halogen is a trifluoromethyl group, the effect is greatest.
[0022]
R ³ consists of _one selected from C ₁ -C ₁₀ alkylene, C ₁ -C ₁₀ halogenated alkylene, C ₆ -C ₂₀ arylene, or C ₆ -C ₂₀ halogenated arylene, preferably When a chelate ring is formed with the central M, one that forms a 5- to 10-membered ring is preferable. When it is larger than the 10-membered ring, the chelate effect is reduced, which is not preferable. Further, when R ³ has a hydroxyl group or a carboxyl group in the structure, it is possible to further form a bond at the center M at this portion.
[0023]
R ⁴ is made of halogen or X ² R ⁷ , and preferably fluorine.
[0024]
R ⁵ consists of _one selected from C ₁ -C ₁₀ alkyl. Unlike other parts, this part does not require an electron-withdrawing group. When an electron-withdrawing group is introduced here, the electron density on N is lowered and cannot be coordinated to M at the center.
[0025]
R ⁷ is composed of one selected from C _{1 to} C ₁₀ halogenated alkyls, preferably C _{1 to} C ₁₀ fluorinated alkyls. The presence of an electron-withdrawing alkyl halide in R ⁷ disperses the negative charge of the center M and increases the electrical stability of the anion, which makes it very easy to dissociate ions, solubilities in the solvent and ions Conductivity increases. In addition, other heat resistance, chemical stability, and hydrolysis resistance are also improved. In particular, the effect is greater when the alkyl halide is a fluorinated alkyl. Further, constants m and n relating to the number of ligands described thus far, Ru der what comes determined by the type of M of the center.
[0026]
As described above, even when these electrolytes are used alone, practically sufficient battery characteristics are exhibited. However, in a state where the battery is charged by mixing both or the same general electrolytes, for example, 40 It has been found by the present invention that when stored for a long time in a high temperature environment of at least ° C., the self-discharge amount is reduced and the storage characteristics are improved. Although the details of the principle are not clear, a part of both electrolytes are positively and slightly decomposed on the negative electrode surface during the first charge to form a film made of the ligand. It is presumed to prevent decomposition and electrode activity deterioration.
[0027]
The use ratio of these electrolytes is preferably in the following range in consideration of the cycle characteristics and storage stability improvement effect of lithium batteries and lithium ion batteries . The electrolyte of the general formula (1) and the general formula (2) are mixed, or the electrolytes of the same general formula are mixed. The molar ratio of each electrolyte is 1:99 to 99: 1, preferably 5:95 to 95: 5.
[0028]
When an electrochemical device is constituted using the electrolyte of the present invention, its basic components are composed of an ion conductor, a negative electrode, a positive electrode, a current collector, a separator, a container, and the like.
[0029]
As the ionic conductor, a mixture of an electrolyte and a non-aqueous solvent or polymer is used. If a non-aqueous solvent is used, this ionic conductor is generally called an electrolytic solution, and if a polymer is used, it becomes a polymer solid electrolyte. The polymer solid electrolyte includes those containing a non-aqueous solvent as a plasticizer.
[0030]
The non-aqueous solvent is not particularly limited as long as it is an aprotic solvent capable of dissolving the electrolyte of the present invention, and examples thereof include carbonates, esters, ethers, lactones, nitriles, amides, sulfones. Can be used. Moreover, not only a single solvent but 2 or more types of mixed solvents may be sufficient. Specific examples include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, dimethoxyethane, acetonitrile, propionitrile, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide. , Sulfolane, and γ-butyrolactone.
[0031]
However, when two or more kinds of mixed solvents are used, in the case of an electrolyte in which A ^{a +} in the formula is Li ion, an aprotic solvent having a dielectric constant of 20 or more and a dielectric constant of 10 or less among these nonaqueous solvents It is preferable to prepare an electrolytic solution by dissolving in a mixed solvent composed of aprotic solvent. In particular, lithium salts have low solubility in aprotic solvents having a dielectric constant of 10 or less, such as diethyl ether and dimethyl carbonate, so that sufficient ionic conductivity cannot be obtained by themselves, and conversely aprotic having a dielectric constant of 20 or more. In the solvent alone, the solubility is high, but the viscosity is high, so that the ions are difficult to move, and sufficient ionic conductivity cannot be obtained. If these are mixed, appropriate solubility and mobility can be ensured, and sufficient ionic conductivity can be obtained.
[0032]
The polymer mixed with the electrolyte is not particularly limited as long as it is an aprotic polymer capable of dissolving the compound. Examples thereof include polymers having polyethylene oxide in the main chain or side chain, homopolymers or copolymers of polyvinylidene fluoride, methacrylic acid ester polymers, polyacrylonitrile and the like. When a plasticizer is added to these polymers, the above-mentioned aprotic non-aqueous solvent can be used. Mixing the electrolyte concentration of the present invention in these ion conductors in the, 0.1 mol / dm ³ or more, the saturation concentration or less, preferably, 0.5 mol / dm ³ or more and 1.5 mol / dm ³ or less. If the concentration is lower than 0.1 mol / dm ³ , the ion conductivity is low, which is not preferable.
[0033]
Although it does not specifically limit as a negative electrode material, In the case of a lithium battery, the alloy and intermetallic compound of lithium metal, lithium, and another metal are used. In the case of a lithium ion battery, a material that uses a phenomenon called intercalation such as carbon, natural graphite, or metal oxide obtained by firing a polymer, an organic material, pitch, or the like is used .
[0034]
As the cathode material is not particularly limited, a lithium battery and a lithium ion battery, for _{example, LiCoO 2, LiNiO 2, LiMnO} 2, lithium-containing oxides such as _{LiMn 2 O 4, TiO 2,} V 2 O 5, MoO Oxides such as ₃ , sulfides such as TiS ₂ and FeS, or conductive polymers such as polyacetylene, polyparaphenylene, polyaniline, and polypyrrole are used .
[0035]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited by this Example.
[0036]
Example 1
In a mixed solvent of 50% by volume of ethylene carbonate and 50% by volume of dimethyl carbonate,
[0037]
[Chemical formula 5]
[0038]
0.99 mol / dm ^{3 of a} lithium borate derivative having the following structure:
[Chemical 6]
[0040]
An electrolytic solution in which 0.01 mol / dm ^{3 of a} lithium borate derivative having the following structure is dissolved is prepared. Using this electrolytic solution, a cell is manufactured using LiCoO ₂ as a positive electrode material and natural graphite as a negative electrode material. A charge / discharge test of the battery was performed. The test cell was produced as follows.
[0041]
To 90 parts by weight of LiCoO ₂ powder, 5 parts by weight of polyvinylidene fluoride (PVDF) as a binder and 5 parts by weight of acetylene black as a conductive material were mixed, and N, N-dimethylformamide was further added to form a paste. The paste was applied on an aluminum foil and dried to obtain a test positive electrode body. Further, 90 parts by weight of natural graphite powder was mixed with 10 parts by weight of polyvinylidene fluoride (PVDF) as a binder, and N, N-dimethylformamide was further added to form a slurry. This slurry was applied on a copper foil and dried at 150 ° C. for 12 hours to obtain a test negative electrode body. Then, the electrolyte was immersed in a polyethylene separator to assemble the cell.
[0042]
Next, a storage test was performed under the following conditions. First, 10 cycles of charge / discharge were performed at an environmental temperature of 25 ° C., and the battery was stored for 120 hours in a thermostatic chamber that was charged at the end and maintained at 60 ° C. At this time, the current density during charging and discharging was 0.35 mA / cm ² , the charging was 4.2 V, and the discharging was performed up to 3.0 V (vs. Li / Li ⁺ ). After storage, the battery was naturally cooled to 25 ° C. and discharged under the same conditions to examine the self-discharge rate. Subsequently, 1 cycle charge / discharge was implemented and the discharge capacity recovery rate was investigated. As a result, the self-discharge rate was 20% and the discharge capacity recovery rate was 86%.
[0043]
Example 2
In the same manner as in Example 1 in a mixed solvent of ethylene carbonate 50 vol% and diethyl carbonate 50 vol%
[Chemical 7]
[0045]
The lithium borate derivative having the structure: 0.90 mol / dm ³
[Chemical 8]
[0047]
An electrolyte solution prepared by dissolving 0.10 mol / dm ^{3 of a} lithium borate derivative having the following structure was prepared. Using this electrolyte solution, LiCoO ₂ was used as a positive electrode material and natural graphite was used as a negative electrode material in the same manner as in Example 1. A cell was prepared and a storage test was conducted in the same manner as in Example 1. As a result, the self-discharge rate was 15% and the discharge capacity recovery rate was 90%.
[0048]
Example 3
In a mixed solvent of ethylene carbonate 50 vol% and ethyl methyl carbonate 50 vol%,
[0049]
[Chemical 9]
[0050]
The lithium borate derivative having the structure: 0.80 mol / dm ³
[Chemical Formula 10]
[0052]
An electrolyte solution in which 0.20 mol / dm ^{3 of a} lithium borate derivative having the following structure was dissolved was prepared. Using this electrolyte solution, LiCoO ₂ was used as a positive electrode material and natural graphite was used as a negative electrode material in the same manner as in Example 1. A cell was prepared and a storage test was conducted in the same manner as in Example 1. As a result, the self-discharge rate was 17% and the discharge capacity recovery rate was 88%.
[0053]
Example 4
In a mixed solvent of ethylene carbonate 50 vol% and ethyl methyl carbonate 50 vol%,
[0054]
Embedded image
[0055]
The lithium borate derivative having the structure: 0.80 mol / dm ³
Embedded image
[0057]
An electrolyte solution in which 0.20 mol / dm ^{3 of a} lithium borate derivative having the following structure was dissolved was prepared. Using this electrolyte solution, LiCoO ₂ was used as a positive electrode material and natural graphite was used as a negative electrode material in the same manner as in Example 1. A cell was prepared, and a constant current charge / discharge test was performed under the following conditions. Charging and discharging were performed at an environmental temperature of 60 ° C. at a current density of 0.35 mA / cm ^2. Charging was performed at 4.2 V and discharging was performed up to 3.0 V (vs. Li / Li ⁺ ). As a result, charging / discharging was repeated 500 times, but the 500th capacity was 93% of the first time.
[0058]
Comparative Example 1
In a mixed solvent of 50% by volume of ethylene carbonate and 50% by volume of dimethyl carbonate,
[0059]
Embedded image
[0060]
An electrolytic solution in which 1.0 mol / dm ³ of a lithium borate derivative having the following structure was dissolved was prepared, and a cell using LiCoO ₂ as a positive electrode material and natural graphite as a negative electrode material was used in the same manner as in Example 1 using this electrolytic solution. And a storage test was conducted in the same manner. As a result, the self-discharge rate was 30% and the discharge capacity recovery rate was 80%.
[0061]
Comparative Example 2
In a mixed solvent of 50 vol% ethylene carbonate and 50 vol% diethyl carbonate,
[0062]
Embedded image
[0063]
An electrolytic solution in which 1.0 mol / dm ³ of a lithium borate derivative having the following structure was dissolved was prepared, and a cell using LiCoO ₂ as a positive electrode material and natural graphite as a negative electrode material was used in the same manner as in Example 1 using this electrolytic solution. And a storage test was conducted in the same manner. As a result, the self-discharge rate was 28% and the discharge capacity recovery rate was 78%.
[0064]
Comparative Example 3
In a mixed solvent of ethylene carbonate 50 vol% and ethyl methyl carbonate 50 vol%,
[0065]
Embedded image
[0066]
An electrolyte solution in which 1.0 mol / l of a lithium borate derivative having the structure of 1 was dissolved was prepared, and a cell using LiCoO ₂ as a positive electrode material and natural graphite as a negative electrode material was prepared in the same manner as in Example 1. The constant current charge / discharge test was performed under the same conditions as in No. 4. As a result, charging / discharging was repeated 500 times, but the 500th capacity was 25% of the first time.
[0067]
【The invention's effect】
The present invention is an electrolyte having excellent cycle characteristics and high-temperature storage characteristics as compared with conventional electrolytes used for electrochemical devices such as lithium batteries, lithium ion batteries, and electric double layer capacitors. An electrolyte and a battery using these are made possible.

Claims (5)

An electrolyte for a lithium battery and a lithium ion battery comprising at least a compound having a chemical structural formula represented by the general formula (1) and a compound having a chemical structural formula represented by the general formula (2).
Where M is B or P,
A ^{a +} is lithium ion,
a is 1,
b is 1,
p is 1,
m is 1 or 2 when M is B, 1, 2 or 3 when M is P ;
n is 0 or 2 when M is B, 0, 2, or 4 when M is P ;
q represents 0 or 1 respectively;
R ¹ and R ² are each independently H, halogen, C _{1 to} C ₁₀ alkyl, or C _{1 to} C ₁₀ halogenated alkyl,
R ³ is C ₁ -C ₁₀ alkylene, C ₁ -C ₁₀ halogenated alkylene, C ₆ -C ₂₀ arylene, or C ₆ -C ₂₀ halogenated arylene ,
R ⁴ is halogen or X ² R ⁷ ,
X ¹ is O or NR ⁵ , X ² is O,
R ⁵ is C ₁ -C ₁₀ alkyl,
X ³ is O,
R ⁷ represents a C _{1 to} C ₁₀ halogenated alkyl, respectively.   An electrolyte solution for lithium batteries and lithium ion batteries, comprising at least the electrolyte according to claim 1 dissolved in a non-aqueous solvent.   3. The electrolysis for lithium battery and lithium ion battery according to claim 2, wherein the non-aqueous solvent is a mixed solvent comprising an aprotic solvent having a dielectric constant of 20 or more and an aprotic solvent having a dielectric constant of 10 or less. liquid.   A solid electrolyte for a lithium battery and a lithium ion battery, comprising at least the electrolyte according to claim 1 dissolved in a polymer. A lithium battery and a lithium ion battery comprising at least a positive electrode, a negative electrode, an electrolytic solution, or a solid electrolyte, wherein the electrolytic solution or the solid electrolyte includes the electrolyte according to claim 1.