JP6156823B2 - Binders, electrodes and electrochemical devices - Google Patents

Description

  The present invention relates to a binder, an electrode, and an electrochemical device.

  In recent years, electrochemical devices (for example, electric storage devices such as electrochemical capacitors and lithium ion secondary batteries) have been developed that are mounted on mobile phone devices and electric vehicles. These electrochemical devices can be charged and discharged, and can be charged and discharged with a large current. Among these, the electrochemical capacitor and the lithium ion secondary battery can be used for, for example, a power failure countermeasure device, a power failure compensation device, etc. in a hybrid vehicle. Since it is excellent, it is used for various power sources.

  The electrode constituting the electrochemical device is composed of an active material directly related to the storage of electric energy, a conductive auxiliary agent responsible for a conduction path between the active materials, a binder, and a current collector. The characteristics of electrochemical devices depend greatly on the electrodes, and are greatly influenced by the characteristics of each material itself and the way the materials are combined.

  In particular, the binder has a small abundance ratio in an electrode obtained from a composite material containing an active material, a conductive additive, and a binder, has excellent affinity with an electrolyte solution supplied to an electrochemical device, and an electrode. It is required that the electrical resistance can be minimized. In addition, stability to withstand high voltage operation is also important.

  This binder is roughly classified into an aqueous system or a non-aqueous system. Examples of the aqueous binder include styrene-butadiene rubber (SBR) aqueous dispersion (Patent Document 1, etc.) and carboxymethylcellulose (CMC) (Patent Documents 2-4, etc.). Moreover, the combined use of these binders has also been proposed as a prior art (Patent Documents 3, 5, 6, etc.). Since these water-based binders have relatively high adhesion to the active material and the conductive additive, there is an advantage that the content in the composite material can be reduced.

  Examples of the non-aqueous binder include polytetrafluoroethylene (PTFE) (Patent Documents 7 and 8, etc.) and an N-methyl-2-pyrrolidone (NMP) solution of polyvinylidene fluoride (PVdF) (Patent Documents 9 to 11 etc.). In particular, it has an advantage in that it works advantageously in a high-pressure operation type device.

  On the other hand, it is disclosed that sodium alginate, which is a polysaccharide-based natural polymer, is used as a binder for an electrode for a lithium ion secondary battery, and can be applied as a binder, and lithium ion using this binder It is described that the cycle durability of the secondary battery electrode is high (Non-Patent Document 1). It has also been proposed to apply a chitosan derivative as a binder using a similar natural polymer (Patent Document 12).

  Further, it has been discovered by the present inventors that a binder using alginic acid can be applied to an anode for an electricity storage device such as an electrochemical capacitor and a lithium ion secondary battery (Patent Documents 13 and 14, non-patent documents). Patent Document 2).

Japanese Patent No. 3101775 (issued on October 23, 2000) Japanese Patent No. 3968771 (issued August 29, 2007) Patent No. 4329169 (issued on September 9, 2009) Patent No. 4244401 (issued on March 25, 2009) Japanese Patent No. 3449679 (issued on September 22, 2003) Patent No. 3958781 (issued on August 15, 2007) Japanese Patent No. 3356021 (issued on December 9, 2002) Japanese Patent Laid-Open No. 7-326357 (released on December 12, 1995) Japanese Patent No. 3619711 (issued February 16, 2005) Japanese Patent No. 3619890 (issued February 16, 2005) Japanese Patent No. 3668579 (issued July 6, 2005) Japanese Patent No. 5284896 (issued on September 11, 2013) JP 2013-161832 A (released on August 19, 2013) JP 2013-197055 A (published September 30, 2013)

I. Kovalenko et al., Science, Vol. 75, pp. 75-79 (2011) M. Yamagata et al., RSC Advances, Vol. 3, pp. 1037-1040 (2013)

  However, the conventional binder has the following problems.

  First, in a composite material using SBR which is an aqueous binder, the active material and the conductive auxiliary agent become non-uniform and lack uniformity, so the performance reproducibility of the electricity storage device tends to be low. In addition, since CMC has poor adhesion to the active material and the conductive additive, it is necessary to increase the content of CMC in the electrode to 10% by weight or more. As a result, the content of the active material decreases. .

  In order to eliminate these disadvantages, it is necessary to use SBR and CMC in combination in practice. However, since SBR has a double bond in the main chain, when SBR is used for the positive electrode, it is oxidized along with charge / discharge of the device. Deterioration due to. Furthermore, SBR and CMC expand when in contact with the electrolyte. As a result, the active material peels off from the current collector and falls off, so that there is a problem that cycle durability and output characteristics are deteriorated in the electricity storage device using both SBR and CMC.

  Next, fluorine-based polymers such as PTFE and PVdF that are non-aqueous binders have a low intermolecular force on the active material, and thus there is a tendency that sufficient adhesive force cannot be exhibited. In order to compensate for insufficient adhesive strength, it is possible to ensure the strength of the electrode by increasing the binder content. In the case of a substance or the like, its active point is lost. Moreover, the content rate of an active material falls and the capacity | capacitance of an electrical storage device falls. Furthermore, PTFE and PVdF have (1) low reproducibility of the resulting electrode due to low affinity for carbon materials such as activated carbon, and (2) a dispersant is required for uniform mixing with the carbon material. There is a problem of becoming.

  Further, in Non-Patent Documents 1 and 2, and Patent Documents 13 and 14, applicability to a silicon-based negative electrode using a binder containing alginic acid, a carbon negative electrode for a lithium ion secondary battery, and the like has been confirmed. However, application of a binder containing alginic acid to the positive electrode has not been studied. The positive electrode is exposed to a higher potential atmosphere than the negative electrode. Therefore, the binder that can be used in the negative electrode is not always applicable to the positive electrode. The characteristics of the positive electrode using a binder containing alginic acid, particularly withstand voltage (electrochemical stability at high potential), is unknown.

  Furthermore, for a binder containing a chitosan derivative, it is essential to use a special solvent for improving the dispersibility in the slurry and the process of synthesizing the derivative, and applicable electrode materials are limited. Moreover, the operation | movement in the high voltage or high potential of the binder containing a chitosan derivative is not confirmed.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a binder that can be applied to a positive electrode of an electrochemical device and exhibits good charge / discharge characteristics at a high voltage and a high potential. There is.

  As a result of intensive studies to solve the above problems, the present inventors have realized a binder that exhibits good charge / discharge characteristics at high voltage and high potential by applying a binder containing alginic acid to the positive electrode of an electrochemical device. I found out that I can do it.

  One skilled in the art will understand how surprising this is. Polysaccharide-based natural polymers generally contain a large number of polar functional groups such as hydroxyl groups and carboxyl groups, and double bonds. Such polar functional groups and double bonds are easily broken down by oxidation. For this reason, it has been common technical knowledge in the technical field that a binder containing a natural polymer cannot withstand use at a high potential and a high voltage and is difficult to apply to a positive electrode that operates at a high potential. . The present inventors independently found that alginic acid, which is a kind of natural polymer, can be applied to the positive electrode of an electrochemical device, and completed the present invention.

  That is, the binder according to the present invention is characterized by containing alginic acid in a binder for connecting an active material, which is a material for a positive electrode for electrochemical devices, and a conductive additive, in order to solve the above-described problems.

  The binder has high affinity with the active material and the conductive additive, and the active material and the conductive additive are unlikely to peel off from the positive electrode for an electrochemical device using the binder. For this reason, in an electrochemical device provided with the said positive electrode, an electrode does not deteriorate easily and can provide the electrochemical device excellent in cycle durability. Moreover, since the said binder is excellent in affinity with an active material and a conductive support agent, in the said positive electrode for electrochemical devices, the interface resistance between each material is lower than the conventional electrode. For this reason, the electrochemical device provided with the positive electrode has excellent capacity development characteristics. Therefore, according to the said invention, it can apply to the positive electrode of an electrochemical device, Comprising: The binder which shows a favorable charging / discharging characteristic at a high voltage and a high potential can be provided.

  In the binder according to the present invention, the alginic acid is an alginate, and the alginate has a viscosity at 20 ° C. of a 1% (w / v) aqueous solution of alginate of 300 mPa · s or more and 2000 mPa · s or less. It is preferably 350 mPa · s or more and 1000 mPa · s or less.

  Thereby, the output characteristic by the positive electrode for electrochemical devices containing the said binder can be improved.

  Moreover, the positive electrode for electrochemical devices which concerns on this invention contains the said binder.

  The electrochemical device according to the present invention is an electrochemical device that includes a positive electrode and a negative electrode, and includes an electrolyte solution between the positive electrode and the negative electrode. The positive electrode is a positive electrode for an electrochemical device according to the present invention. It is.

  In the electrochemical device according to the present invention, the negative electrode contains a binder, and the binder may contain alginic acid.

  The binder of the present invention contains alginic acid in a binder that connects an active material, which is a material for a positive electrode for electrochemical devices, and a conductive additive.

  Therefore, the binder has a high affinity with the active material and the conductive auxiliary, and the active material and the conductive auxiliary are not easily separated from the positive electrode for an electrochemical device using the binder. For this reason, in an electrochemical device provided with the said positive electrode, an electrode does not deteriorate easily and can provide the electrochemical device excellent in cycle durability. Moreover, since the said binder is excellent in affinity with an active material and a conductive support agent, in the said positive electrode for electrochemical devices, the interface resistance between each material is lower than the conventional electrode. For this reason, the electrochemical device provided with the positive electrode has excellent capacity development characteristics. Therefore, according to the said invention, it is applicable to the positive electrode of an electrochemical device, and there exists an effect that the binder which shows a favorable charging / discharging characteristic at a high voltage and a high potential can be provided.

(A) is a graph which shows the charging / discharging curve in Example 1, (b) is a graph which shows the charging / discharging curve in the comparative example 1. FIG. 4 is a graph showing charge / discharge cycle characteristics according to Examples 1 to 4 and Comparative Example 1. 4 is a graph showing charge / discharge rate characteristics according to Example 1 and Comparative Example 1. It is a graph which shows the charging / discharging characteristic in the low temperature environment in Example 1 and Comparative Example 1. It is a graph which shows the result of internal resistance evaluation by the alternating current impedance method in Example 1 and Comparative Example 1. 6 is a graph showing charge / discharge cycle characteristics according to Example 5 and Comparative Example 2. 6 is a graph showing charge / discharge rate characteristics according to Example 5 and Comparative Example 2. 10 is a graph showing charge / discharge cycle characteristics according to Example 6;

  Hereinafter, although an example of an embodiment of the invention is explained in detail, the present invention is not limited to these. Unless otherwise specified in this specification, “A to B” indicating a numerical range means “A or more and B or less”.

[Positive electrode for electrochemical devices]
The positive electrode for electrochemical devices according to the present invention is composed of a composite material including an active material, a conductive additive and a binder, and a current collector. Each material contained in the positive electrode will be described.

<Binder>
The binder which concerns on this invention is a binder which connects the active material which is the material of the positive electrode for electrochemical devices, and a conductive support agent, and contains alginic acid.

  The binder which concerns on this invention connects an active material and a conductive support agent, exists so that an active material and a conductive support agent may be covered, and fixes a conductive support agent with respect to an active material. Alginic acid has a basic molecular structure of a high-molecular polysaccharide in which β-D-mannuronic acid and α-L-guluronic acid are linked by 1,4. The alginic acid is usually derived from brown algae plants such as kombu, wakame and kajime.

  Examples of alginic acid include non-crosslinked alginic acid (hereinafter also referred to as non-alginate alginate) and cross-linked alginic acid (hereinafter also referred to as alginate cross-linked product).

  Examples of the non-cross-linked alginate include non-ionized free alginic acid or monovalent salt of alginic acid. Examples of the monovalent salt of alginic acid include alginic acid alkali metal salts such as lithium alginate, potassium alginate, and sodium alginate; ammonium alginate and the like.

  Examples of the alginic acid cross-linked product include, for example, alginic acid polyvalent salt, which is a salt of free alginic acid or monovalent salt of alginic acid and a divalent or higher metal ion, free alginic acid or monovalent alginic acid salt, etc. Thing etc. are mentioned. Examples of the alginic acid polyvalent salt include calcium alginate and magnesium alginate.

  Alginic acid has a lower molecular weight and is more likely to adhere to the active material and the conductive additive, and can form a more uniform compound. However, the viewpoint of increasing the amount of active material that contributes to output characteristics is considered. Therefore, it is preferable to have a certain molecular weight.

  For convenience of use as a binder, the alginate preferably has a 1% (g / 100 ml) aqueous solution of alginic acid having a viscosity at 20 ° C. of 300 mPa · s to 2000 mPa · s, preferably 350 mPa · s. As mentioned above, what is 1000 mPa * s or less is more preferable. The viscosity is a value measured by a rotary viscometer (manufactured by Brookfield) using an RV-1 spindle at 20 ° C. under a rotation speed of 60 rpm and a measurement time of 1 minute.

  The alginic acid is preferably prepared using an aqueous solution of alginic acid monovalent salt or alginic acid polyvalent salt. The alginic acid is preferably prepared using an aqueous solution of 0.5% by weight or more and 5.0% by weight or less of an alginic acid monovalent salt or an alginic acid polyvalent salt, and is 2.0% by weight or more. More preferably, it is prepared using an aqueous solution of 3.0% by weight or less of an alginic acid monovalent salt or an alginic acid polyvalent salt. Alginic acid was prepared using an aqueous solution of alginic acid monovalent salt or alginic acid polyvalent salt of 0.5 wt% or more and 5.0 wt% or less, more preferably 2.0 wt% or more and 3.0 wt% or less. By being a thing, mixing of a compound material can be performed easily.

  The binder according to the present invention may contain alginic acid, but the content of alginic acid in the binder is preferably 50% by weight or more and 100% by weight or less, and is 70% by weight or more and 100% by weight or less. Is more preferably 90% by weight or more and 100% by weight or less, and most preferably 100% by weight. When the content of alginic acid is less than 100% by weight, binder components other than alginic acid include polyvinylidene fluoride (PVdF); a copolymer of PVdF and hexafluoropropylene (HFP), perfluoromethyl vinyl ether (PFMV) and tetra PVdF copolymer resins such as copolymers with fluoroethylene (TFE); fluorinated resins such as polytetrafluoroethylene (PTFE) and fluororubber; styrene-butadiene rubber (SBR), ethylene-propylene rubber (EPDM), Examples thereof include polymers such as styrene-acrylonitrile copolymers, and polysaccharides such as carboxymethyl cellulose (CMC), thermoplastic resins such as polyimide resins, and the like can be used together, but are not particularly limited.

  Further, the content ratio (% by weight) of the active material, the conductive auxiliary agent and the binder in the composite material is not particularly limited. For example, the active material: conductive auxiliary agent: binder = 80 to 97: 4 to 10: 2-15. In addition, the sum total of the content ratio of an active material, a conductive support agent, and a binder is 100. That is, the blending ratio of the binder in the positive electrode for electrochemical devices obtained from the composite material is preferably 2% by weight or more and 15% by weight or less. More preferably, it is 5 wt% or more and 10 wt% or less. If it is 2% by weight or more, it becomes easy to produce a composite material in which the active material, conductive additive and binder are uniformly mixed, and if it is 15% by weight or less, the active material is associated with an increase in the binder content. Decrease in the blending ratio can be prevented.

  The said compound material is obtained by mixing an active material, a conductive support agent, and alginic acid. You may mix | blend alginic acid in the state of aqueous solution. Moreover, you may add water etc. to a compound material for viscosity adjustment. The binder according to the present invention is characterized in that it has a high affinity with the active material and the conductive additive, and a very uniform composite material can be obtained, and an electrode excellent in design can be obtained.

<Active material>
The active material in the positive electrode is not particularly limited as long as it can insert or desorb lithium ions. For example, transition metal oxides such as CuO, Cu ₂ O, MnO ₂ , MoO ₃ , V ₂ O ₅ , CrO ₃ , MoO ₃ , Fe ₂ O ₃ , Ni ₂ O ₃ , CoO ₃ ; Li _x CoO ₂ , Li _{X NiO 2, Li X Mn 2} O 4, a lithium complex oxide containing lithium and a transition metal of LiFePO ₄ or the _{like; TiS 2, MoS 2, NbSe} 3 , etc. of metal chalcogenides; polyacene, polyparaphenylene, polypyrrole, polyaniline And the like, and the like.

Among them, a composite oxide of lithium and one or more kinds selected from transition metals such as cobalt, nickel, and manganese, which is generally called a high voltage system, is preferable in that lithium ions can be released and a high voltage can be easily obtained. . Specific examples of the composite oxide of cobalt, nickel, manganese and lithium include LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _X Co _(1-X) O ₂ , LiNi _X Mn _{(2-X )} O ₄ , LiMn _a Ni _b Co _c O ₂ (a + b + c = 1) and the like.

Also, those lithium composite oxides doped with a small amount of elements such as fluorine, boron, aluminum, chromium, zirconium, molybdenum, iron, etc., and the lithium composite oxide particle surface is made of carbon, MgO, Al ₂ O ₃ , those treated with SiO ₂ or the like can also be used. The above active materials may be used alone or in combination of two or more.

<Conductive aid>
Any electrically conductive material that does not adversely affect battery performance can be used as the conductive assistant. Usually, carbon black such as acetylene black and ketjen black is used, but natural graphite (scale-like graphite, scale-like graphite, earth-like graphite, etc.), artificial graphite, carbon whisker, carbon fiber powder, metal (copper, nickel, Conductive materials such as aluminum, silver, gold, etc.) powder, metal fibers, conductive ceramic materials, etc. may be used. These may be used alone or as a mixture of two or more.

<Current collector>
The positive electrode for an electrochemical device according to the present invention can be produced by applying a coating liquid comprising the above active material, conductive additive, binder, and the like to a current collector.

  As the current collector for the positive electrode, an electronic conductor that does not adversely affect the constructed battery can be used. For example, aluminum, titanium, stainless steel, nickel, baked carbon, conductive polymer, conductive glass, and the like can be given. For the purpose of improving adhesiveness, conductivity, oxidation resistance, etc., a positive electrode current collector in which the surface of aluminum or the like is treated with carbon, nickel, titanium, silver, or the like may be used.

  It is also possible to oxidize the surface of these positive electrode current collectors. In addition to the foil shape, the shape of the positive electrode current collector may be a film shape, a sheet shape, a net shape, a punched or expanded material, a lath body, a porous body, a foamed body or the like. Good. The thickness is not particularly limited, but a thickness of 1 μm or more and 100 μm or less is usually used.

<Method for producing electrode>
An example of obtaining the positive electrode will be described. The positive electrode coating liquid is applied to the positive electrode current collector at a desired thickness. As a coating method, a method of applying a coating liquid to a current collector and removing excess coating liquid with a doctor blade, a method of applying a coating liquid to a current collector and rolling the coating liquid with a roller, etc. A known coating method may be mentioned.

  The temperature at which the coating liquid is dried is not particularly limited, and may be appropriately changed depending on the blending ratio of each material in the coating liquid, but is usually 70 ° C. or higher and 100 ° C. or lower. Moreover, what is necessary is just to change the thickness of the obtained positive electrode suitably by the use of an electrochemical device.

[Electrochemical devices]
The electrochemical device according to the present invention includes a positive electrode and a negative electrode, and includes an electrolytic solution between the positive electrode and the negative electrode. And the said positive electrode is a positive electrode for electrochemical devices which concerns on this invention mentioned above. In addition, in an electrochemical device, a separator is disposed between the positive electrode and the negative electrode in order to prevent a short circuit between the positive electrode and the negative electrode. Each of the positive electrode and the negative electrode is provided with a current collector, and both current collectors are connected to a power source. Charging / discharging is switched by operating this power source.

  In addition, about the matter already demonstrated in the said [positive electrode for electrochemical devices], description is abbreviate | omitted below.

  Examples of the electrochemical device according to the present invention include an electrochemical capacitor, a lithium ion secondary battery, and the like, and further include a non-lithium ion battery, a lithium ion capacitor, a dye-sensitized solar cell, and the like. The electrochemical device can be used as an electricity storage device with high performance and high safety. Therefore, the electrochemical device according to the present invention is a small electronic device such as a mobile phone device, a notebook computer, a personal digital assistant (PDA), a video camera, and a digital camera; a mobile device such as an electric bicycle, an electric vehicle, and a train (vehicle) ); It may be mounted on power generation equipment such as thermal power generation, wind power generation, hydroelectric power generation, nuclear power generation, geothermal power generation.

<Anode for electrochemical devices>
The negative electrode for electrochemical devices is composed of a mixture containing an active material, a conductive additive and a binder, and a current collector, like the positive electrode for electrochemical devices described above. Each material contained in the negative electrode will be described.

  The active material is not particularly limited as long as it can insert or desorb metallic lithium or lithium ions. Examples thereof include carbon materials such as natural graphite, artificial graphite, non-graphitizable carbon, and graphitizable carbon. Moreover, metal materials, such as metallic lithium, an alloy, and a tin compound; lithium transition metal nitride; crystalline metal oxide; amorphous metal oxide; silicon material;

  The above active materials may be used alone or in combination of two or more. The amount of the active material varies depending on its use and is not particularly limited, but is usually 80% by weight or more and 100% by weight or less with respect to the total weight of the active material, the conductive auxiliary agent and the binder.

  In the present specification, a negative electrode containing 90% by weight or more and 100% by weight or less of a carbon material as an active material is called a carbon negative electrode. Since a carbon negative electrode has high versatility, it is easy to produce.

  As the conductive aid, the same conductive aid as that in the above-described positive electrode for electrochemical devices can be used, but it is not specifically limited. Further, the addition amount of the conductive assistant is preferably 1% by weight or more and 20% by weight or less, and more preferably 2% by weight or more and 10% by weight or less with respect to the total weight of the negative electrode.

  Examples of the binder contained in the negative electrode include polyvinylidene fluoride (PVdF); a copolymer of PVdF and hexafluoropropylene (HFP), a copolymer of perfluoromethyl vinyl ether (PFMV) and tetrafluoroethylene (TFE), and the like. PVdF copolymer resin; fluorinated resins such as polytetrafluoroethylene (PTFE) and fluororubber; polymers such as styrene-butadiene rubber (SBR), ethylene-propylene rubber (EPDM), styrene-acrylonitrile copolymer, etc. Polysaccharides such as carboxymethyl cellulose (CMC), thermoplastic resins such as polyimide resins, and the like can be used in combination, but the binder of the negative electrode is not limited to these specific examples.

  Moreover, the binder contained in a negative electrode may contain alginic acid similarly to the positive electrode for electrochemical devices. As alginic acid, the same thing as the alginic acid in the above-mentioned positive electrode for electrochemical devices can be used. In the case where the binder of the negative electrode contains alginic acid, the binder has high affinity with the active material and the conductive additive, and the active material and the conductive additive are not easily separated from the negative electrode for electrochemical devices using the binder. For this reason, in an electrochemical device provided with the said negative electrode, an electrode does not deteriorate easily and can provide the electrochemical device excellent in cycle durability.

  Moreover, since the said binder is excellent in affinity with an active material and a conductive support agent, in an electrochemical device provided with the said negative electrode, the interface resistance between each material in an electrode is lower than the conventional electrode. For this reason, the electrochemical device provided with the said negative electrode is excellent also in the output characteristic.

<Electrolyte>
The electrolyte solution is not particularly limited as long as a known one is used, but a non-aqueous electrolyte solution can be used. The non-aqueous electrolyte solution may be any non-aqueous electrolyte solution used in conventionally known electrochemical devices, and an ionic liquid can also be used.

  The “ionic liquid” here means a salt that exists in a liquid state even at room temperature. Examples of the cation of the ionic liquid include imidazolium, pyridinium, pyrrolidinium, piperidinium, tetraalkylammonium, pyrazolium, and tetraalkylphosphonium.

  Examples of the imidazolium include 1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, 1-ethyl-2,3-dimethylimidazolium, 1-allyl-3-methylimidazolium, Examples include 1-allyl-3-ethylimidazolium, 1-allyl-3-butylimidazolium, 1,3-diallylimidazolium, and the like.

  Examples of the pyridinium include 1-propylpyridinium, 1-butylpyridinium, 1-ethyl-3- (hydroxymethyl) pyridinium, 1-ethyl-3-methylpyridinium, and the like.

  Examples of the pyrrolidinium include N-methyl-N-propylpyrrolidinium, N-methyl-N-butylpyrrolidinium, N-methyl-N-methoxymethylpyrrolidinium, and the like.

  Moreover, as said piperidinium, N-methyl-N-propyl piperidinium etc. are mentioned, for example.

  Examples of the tetraalkylammonium include N, N, N-trimethyl-N-propylammonium and methyltrioctylammonium.

  Examples of the pyrazolium include 1-ethyl-2,3,5-trimethylpyrazolium, 1-propyl-2,3,5-trimethylpyrazolium, 1-butyl-2,3,5-trimethylpyrazo Examples include lithium.

In addition, examples of the anion that forms an ionic liquid in combination with the above cation include, for example, BF ₄ ⁻ , NO ₃ ⁻ , PF ₆ ⁻ , SbF ₆ ⁻ , CH ₃ CH ₂ OSO ₃ ⁻ , CH ₃ CO ₂ ⁻ , or ^{_{; CF 3 CO 2 -, CF}} 3 SO 3 -, (CF 3 SO 2) 2 N - [ bis (trifluoromethylsulfonyl) _{imide], (FSO 2) 2 N} - [ bis (fluoro sulfonyl) imide, ( Fluoroalkyl group-containing anions such as CF ₃ SO ₂ ) ₃ C ^— can be mentioned.

As the ionic liquid, a combination of at least one of these various anions and at least one of these various cations can be employed. When the electrochemical device is a lithium ion secondary battery, an ionic liquid containing an anion such as (FSO ₂ ) ₂ N ^— is preferable. These ionic liquids are (1) that the electrical characteristics of the electricity storage device are more excellent, and that the degradation of the electrical characteristics is suppressed, and (2) the electrical characteristics that the electrolyte solution has are easy to obtain. Is preferable in that it is more suppressed in the electricity storage device.

In view of easy handling in the air, an ionic liquid containing a fluorine-containing anion such as (FSO ₂ ) ₂ N ^— is preferable in the lithium ion secondary battery.

  Further, the ionic liquid is preferably an ionic liquid containing an imidazolium cation or a pyrrolidinium cation from the viewpoint of relatively low viscosity, excellent ionic conductivity, and excellent electrochemical stability.

  Specifically, the ionic liquid is preferably a salt of a bis (fluorosulfonyl) imide anion as an anion and a quaternary ammonium such as pyrrolidinium as a cation, and more specifically, an N, N-dialkylpyrrole. Dinium bis (fluorosulfonyl) imide is preferred. Further, tetraalkylammonium bis (fluorosulfonyl) imide and 1-ethyl-3-methylimidazolium bis (fluorosulfonyl) imide are also preferable non-aqueous electrolytes.

  The non-aqueous electrolyte solution is not limited to the “ionic liquid”, and may be an organic electrolyte solution used for the non-aqueous electrolyte solution of the electrochemical device. Such an organic electrolyte includes an electrolyte salt that serves as an ion carrier, and is composed of an organic solvent that dissolves the electrolyte salt.

  As the electrolyte salt, the ionic liquid, quaternary onium salt, alkali metal salt, alkaline earth metal salt, or the like can be used.

  Typical quaternary onium salts include tetraalkylammonium salts and tetraalkylphosphonium salts.

  Typical alkali metal salts and alkaline earth metal salts include lithium salts, sodium salts, potassium salts, magnesium salts, calcium salts, and the like.

Examples of the anion of the electrolyte salt include BF ₄ ⁻ , NO ₃ ⁻ , PF ₆ ⁻ , SbF ₆ ⁻ , CH ₃ CH ₂ OSO ₃ ⁻ , CH ₃ CO ₂ ⁻ , or CF ₃ CO ₂ ⁻ , CF ₃ SO ^{_{3 -, (CF 3 SO 2}} ) 2 N - [ bis (trifluoromethylsulfonyl) _{imide], (CF 3 SO 2)} 3 C - include fluoroalkyl group-containing anions such as.

In particular, as an electrolyte salt in a lithium ion secondary battery, for example, LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiPF ₄ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , LiCl, LiBr, CH ₃ SO ₃ Li, CF ₃ A lithium salt such as SO ₃ Li can be mentioned.

  Examples of the organic solvent include ethers, ketones, lactones, nitriles, amines, amides, sulfur compounds, chlorinated hydrocarbons, esters, carbonates, nitro compounds, and phosphate ester compounds. , Sulfolane compounds and the like can be used.

  Typical organic solvents include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, anisole, monoglyme, acetonitrile, propionitrile, 4-methyl-2-pentanone, butyronitrile, valeronitrile, benzonitrile, 1,2 -Dichloroethane, γ-butyrolactone, dimethoxyethane, methyl formate, propylene carbonate, ethylene carbonate, dimethyl carbonate, dimethylformamide, dimethyl sulfoxide, dimethylthioformamide, sulfolane, 3-methyl-sulfolane, trimethyl phosphate, triethyl phosphate and these And the like.

  Among these, propylene carbonate is preferable because it has a low viscosity, excellent ionic conductivity, and excellent electrochemical stability. The non-aqueous electrolyte may be used alone or in combination of two or more.

  Moreover, in a lithium ion secondary battery, you may use well-known polymer electrolytes, such as a polyethylene oxide, a polyacrylonitrile, a polymethylmethacrylate.

<Separator>
In the electrochemical device of the present invention, a separator is provided between them in order to prevent a short circuit between the positive electrode and the negative electrode. A known separator can be used, and is not particularly limited. Specifically, the separator is a microporous film of polyethylene or polypropylene film; a multilayer film of porous polyethylene film and polypropylene; polyester fiber, aramid fiber, glass fiber, or the like. Nonwoven fabrics may be mentioned, and more preferred are separators in which ceramic fine particles such as silica, alumina, titania and the like are attached to the surface thereof.

  The separator preferably has a porosity of 70% or more, more preferably 80% or more and 95% or less. The air permeability obtained by the Gurley test method is preferably 200 seconds / 100 cc or less.

Here, the porosity is a value calculated by the following equation from the apparent density of the separator and the true density of the solid content of the constituent material.
Porosity (%) = 100− (apparent density of separator / true density of solid material content) × 100
The Gurley air permeability is an air resistance according to a Gurley tester method defined in JIS P 8117.

  The separator contains 80% by weight or more of glass fibers having an average fiber diameter of 1 μm or less and less than 20% by weight of organic components containing fibrillated organic fibers, and the glass fibers are entangled with the fibrillated organic fibers. A wet papermaking sheet bonded to a porosity of 85% or more is particularly preferably used.

  The fibrillated organic fiber is formed by a device that disaggregates fibers, for example, a double disc refiner, and is subjected to the action of shearing force by beating and the like, and a single fiber is formed by very finely cleaving in the fiber axis direction. It is preferable that at least 50% by weight or more of fibril-containing fibers are fibrillated to a fiber diameter of 1 μm or less, and more preferably 100% by weight is fibrillated to a fiber diameter of 1 μm or less. preferable.

  As the fibrillated organic fiber, polyethylene fiber, polypropylene fiber, polyamide fiber, cellulose fiber, rayon fiber, acrylic fiber and the like can be used.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The present invention will be described more specifically based on Examples and Comparative Examples and FIGS. 1 to 7, but the present invention is not limited thereto. Those skilled in the art can make various changes, modifications, and alterations without departing from the scope of the present invention.

[Example 1]
A positive electrode for an electrochemical device was produced using the following materials.

Active material: LiNi _0.5 Mn _1.5 O ₄ (hereinafter also referred to as LNM)
Conductive aid: Mixture of carbon black (KB, manufactured by Lion Corporation) and vapor grown carbon fiber (VGCF (registered trademark), manufactured by Showa Denko KK) Binder: Magnesium alginate (Alg-Mg) (produced by Kimika Corporation) )
Current collector: Aluminum foil First, a 5 wt% magnesium alginate aqueous solution was prepared. Moreover, the active material and the conductive assistant were put in a mortar and mixed for about 10 minutes. Next, an aqueous magnesium alginate solution was added to the mixture of the active material and the conductive additive. Here, the active material, the conductive additive, and the magnesium alginate aqueous solution were mixed so that the weight ratio after drying (content ratio in the electrode) was 85: 8: 7 to prepare a slurry coating solution. The coating liquid was applied to the current collector by a doctor blade, and the coating liquid was heated on a hot plate at 80 ° C. for about 10 minutes. Thereafter, the coating liquid applied to the current collector was dried under a reduced pressure of 10 ⁻¹ Pa for 12 hours in a temperature atmosphere of 100 ° C. to obtain a target positive electrode. The obtained electrode was punched into a disk shape having a diameter of 12 mm for evaluation.

  Furthermore, this positive electrode and the following negative electrode were disposed on both sides, a separator was disposed between both electrodes, and an electrolyte was injected to produce a two-electrode half cell. The following materials were used as materials for the two-electrode half cell.

Electrolyte solution: 1.0 mol dm ⁻³ LiPF ₆ / EC + DMC (battery grade, manufactured by Kishida Chemical Co., Ltd.)
Separator: Ceramic coated polyethylene Negative electrode: Metallic lithium foil (Honjo Metal Co., Ltd.)
LiPF ₆ = lithium hexafluorophosphate EC + DMC = 1: 1 mixture of ethylene carbonate and dimethyl carbonate [Example 2]
A two-electrode half cell was prepared in the same manner as in Example 1 except that the following binder was used instead of magnesium alginate as the binder.

Binder: Sodium alginate (Alg-Na) (Kimika Co., Ltd.)
Example 3
A bipolar half cell was produced in the same manner as in Example 1 except that the following binder was used instead of magnesium alginate as the binder.

Binder: Lithium alginate (Alg-Li) (Kimika Co., Ltd.)
Example 4
A two-electrode half cell was prepared in the same manner as in Example 1 except that the following binder was used instead of magnesium alginate as the binder.

Binder: Ammonium alginate (Alg-NH ₄ ) (Kimika Co., Ltd.)
[Comparative Example 1]
A two-electrode half cell was prepared in the same manner as in Example 1 except that the following binder was used instead of magnesium alginate as the binder.

Binder: Polyvinylidene fluoride (PVdF) (used as N-methylpyrrolidone solution)
[Charge / discharge characteristics evaluation]
Using the two-electrode half cells obtained in Examples 1 to 4 and Comparative Example 1, charge / discharge characteristics were evaluated under the following conditions.

Charging: Constant current-constant voltage (CC-CV mode. Note that in CV mode, it ends when the current value becomes 1/10 of the set current value in CC mode.)
Discharge: Constant current (CC mode)
1 hour rate (1C rate) = 142.3 mA g ⁻¹
Voltage range: 3.5-4.9V
<Charge / discharge curve and charge / discharge cycle characteristics>
Under the above conditions, 100 cycles of charging and discharging were performed. In the first cycle, both charging and discharging were performed at a 0.1 C rate, and after the second cycle, both charging and discharging were performed at a 1.0 C rate.

  FIG. 1 shows the relationship between the discharge capacity and the electrode voltage when charge / discharge is performed for 1, 2, 10, 20, 50, 70 and 100 cycles. 1A is a graph showing a charge / discharge curve in Example 1, and FIG. 1B is a graph showing a charge / discharge curve in Comparative Example 1. FIG. In FIG. 1, the number attached to the curve represents the number of cycles. In FIG. 1A, the charge / discharge curves overlap, and it can be seen that the relationship between the discharge capacity and the electrode voltage in each cycle is stable. On the other hand, in FIG.1 (b), discharge capacity is falling with the increase in the number of cycles. This result shows that the system using the binder containing alginic acid has less change than the system using PVdF as the binder, and stable charging / discharging is possible. Moreover, in Example 1, it turns out that it is operate | moving stably also in the very high voltage range of 3.5-4.9V.

  FIG. 2 is a graph showing the charge / discharge cycle characteristics according to Examples 1 to 4 and Comparative Example 1, and shows the transition of the discharge capacity depending on the number of cycles. This result shows that the system using the binder containing alginic acid has less change than the system using PVdF as the binder, and stable charging / discharging is possible. Further, when ammonium alginate was used as the binder, an excellent effect was obtained as compared with the case where lithium alginate was used. Furthermore, the most excellent effect was obtained when magnesium alginate or sodium alginate was used as the binder.

<Charge / discharge rate characteristics>
Under the above conditions, the charge rate and discharge rate were 0.1 C, 1.0 C, 2.0 C, 3.0 C, 5.0 C, 8.0 C, 10.0 C, 20.0 C, 30.0 C, 50 The discharge capacity was measured at a setting of 0.0C. At each rate, 5 cycles of charge / discharge were performed.

  FIG. 3 is a graph showing charge / discharge rate characteristics according to Example 1 and Comparative Example 1, and shows changes in discharge capacity according to the rate and the number of cycles. In Example 1, fast charge / discharge at 8.0C and 10.0C was possible. Moreover, in Example 1, the change of the discharge capacity in 5 cycles in each rate is also small, and the stable charge / discharge can be maintained.

<Charge / discharge characteristics in low temperature environment>
Under the above conditions, 60 cycles of charge / discharge were performed. In addition, in 1-10 cycles, it charged / discharged at room temperature (25 degreeC), and in 11-60 cycles, it charged / discharged at low temperature (0 degreeC). In the first cycle, both charging and discharging were performed at a 0.1 C rate, and in the second and subsequent cycles, both charging and discharging were performed at a 1.0 C rate.

  FIG. 4 is a graph showing the charge / discharge characteristics under a low temperature environment in Example 1 and Comparative Example 1, and shows the transition of the discharge capacity depending on the temperature and the number of cycles. In Example 1, compared with Comparative Example 1, a high discharge capacity is maintained even in a low temperature environment. Therefore, when alginic acid is used, it turns out that the low temperature characteristic which exceeds the system using PVdF is shown.

[Evaluation of internal resistance by AC impedance method]
Using the two-electrode half cell obtained in Example 1 and Comparative Example 1, internal resistance was evaluated under the following conditions by the AC impedance method.

Frequency range: 500 kHz to 10 mHz
AC signal amplitude: 10 mV _p-0
FIG. 5 is a graph showing the results of internal resistance evaluation by the AC impedance method in Example 1 and Comparative Example 1. The result is shown as a Cole-Cole plot. In Example 1, it can be seen that the internal resistance is reduced as compared with Comparative Example 1. In other words, the use of alginic acid has succeeded in reducing internal resistance. The present invention can be said to be very effective especially for reducing the charge transfer resistance in the semicircular portion.

Example 5
A two-electrode full cell (practical cell) was produced in the same manner as the two-electrode half cell of Example 1 except that a graphite negative electrode was used instead of the metal lithium foil as the negative electrode. The following materials were used as materials for the graphite negative electrode.

Active material: Graphite Conductive auxiliary agent: Mixture of flaky graphite and vapor grown carbon fiber (VGCF (registered trademark), manufactured by Showa Denko KK) Binder: Magnesium alginate (manufactured by Kimika Co., Ltd.)
Current collector: Aluminum foil Specifically, first, a 5 wt% magnesium alginate aqueous solution was prepared. Moreover, the active material and the conductive assistant were put in a mortar and mixed for about 10 minutes. Next, an aqueous magnesium alginate solution was added to the mixture of the active material and the conductive additive. Here, the active material, the conductive additive, and the magnesium alginate aqueous solution were mixed so that the weight ratio after drying (content ratio in the electrode) was 91: 3: 6 to prepare a slurry coating solution. The coating liquid was applied to the current collector by a doctor blade, and the coating liquid was heated on a hot plate at 80 ° C. for about 10 minutes. Thereafter, the coating liquid applied to the current collector was dried in a temperature atmosphere of 100 ° C. under a reduced pressure of 10 ⁻¹ Pa for 12 hours to obtain a target negative electrode. The obtained electrode was punched into a disk shape having a diameter of 12 mm for evaluation.

  And the positive electrode obtained in Example 1 and the said negative electrode were arrange | positioned on both sides, the separator was arrange | positioned between both electrodes, electrolyte solution was inject | poured, and the 2 electrode type full cell was produced.

[Comparative Example 2]
A two-electrode full cell was produced in the same manner as in Example 5 except that the following binder was used instead of magnesium alginate as the binder.

Binder: Polyvinylidene fluoride (used as N-methylpyrrolidone solution)
(Charge / discharge characteristics)
Using the two-electrode full cell obtained in Example 5 and Comparative Example 2, charge / discharge characteristics were evaluated under the following conditions.

Charging: Constant current-constant voltage (CC-CV mode. Note that in CV mode, it ends when the current value becomes 1/10 of the set current value in CC mode.)
Discharge: Constant current (CC mode)
1 hour rate (1C rate) = 142.3 mA g ⁻¹
Voltage range: 3.5-4.9V
<Charge / discharge cycle characteristics>
Under the above conditions, 100 cycles of charging and discharging were performed. In the first cycle, both charging and discharging were performed at a 0.1 C rate, and after the second cycle, both charging and discharging were performed at a 1.0 C rate.

  FIG. 6 is a graph showing charge / discharge cycle characteristics according to Example 5 and Comparative Example 2, and shows a change in discharge capacity depending on the number of cycles. This result shows that in Example 5, there is less change than in Comparative Example 2, and stable charging / discharging is possible. In other words, by applying a binder containing alginic acid to the positive and negative electrodes of a practical cell, a battery that is more stable than a system using PVdF was successfully constructed.

<Charge / discharge rate characteristics>
Under the above conditions, the charge rate and discharge rate were set to 0.1 C, 1.0 C, 2.0 C, 3.0 C, 5.0 C, 8.0 C, 10.0 C, and the discharge capacity was measured. At each rate, 5 cycles of charge / discharge were performed.

  FIG. 7 is a graph showing the charge / discharge rate characteristics according to Example 5 and Comparative Example 2, and shows the change in discharge capacity according to the rate and the number of cycles. In Example 5, fast charge / discharge at 8.0C and 10.0C was possible. Moreover, in Example 5, the change of the discharge capacity in 5 cycles in each rate is also small, and stable charge / discharge can be maintained.

  From the above Examples and Comparative Examples, the binder according to the present invention can be applied to the positive electrode of the electrochemical device by containing alginic acid, and can be applied to a high voltage and a high potential (for example, 3.5 to 4.9 V). It can be seen that good charge / discharge characteristics are exhibited.

Example 6
A two-electrode half cell was produced in the same manner as in Example 1 except that the following electrolytic solution (ionic liquid) was used as the electrolytic solution.

Electrolyte solution: 1.46 mol dm ⁻³ LiFSI / MPPyFSI (Daiichi Kogyo Seiyaku Co., Ltd.)
LiFSI = lithium bis (fluorosulfonyl) imide MPPyFSI = N, N-methylpropylpyrrolidinium bis (fluorosulfonyl) imide [Charge / Discharge characteristics]
Under the same conditions as in Example 1, 100 cycles of charge / discharge at a charge 1.0C rate and a discharge 1.0C rate were performed, and charge / discharge cycle characteristics were evaluated.

  FIG. 8 is a graph showing the charge / discharge cycle characteristics according to Example 6, and shows the transition of the discharge capacity according to the number of cycles. As a result, it became clear that stable charging and discharging is possible even when the binder according to the present invention is combined with not only a conventional organic solvent electrolyte but also an ionic liquid electrolyte. .

  The present invention relates to a binder as a material for an electrochemical device, and can be used in the capacitor industry, the automobile industry, the battery industry, the home appliance industry, and the like.

Claims (5)

In the binder that connects the active material that is the material of the positive electrode for the electrochemical device and the conductive additive,
A binder comprising magnesium alginate. 1% magnesium upper Kia alginic acid (w / v) viscosity at 20 ° C. of the aqueous solution 300 mPa · s or more, the binder according to claim 1, characterized in that not more than 2000 mPa · s.   A positive electrode for electrochemical devices, comprising the binder according to claim 1. An electrochemical device comprising a positive electrode and a negative electrode, and containing an electrolyte solution between the positive electrode and the negative electrode,
The said positive electrode is a positive electrode for electrochemical devices of Claim 3, The electrochemical device characterized by the above-mentioned. The negative electrode includes a binder,
The electrochemical device according to claim 4, wherein the binder contains alginic acid.

Images