JP4365572B2 - Positive electrode material composite containing poly (3,4-ethylenedioxythiophene) and lithium secondary battery having a positive electrode made of the composite - Google Patents

Description

【００６７】
【表２】

【００６８】
以上の結果から明らかなように、本発明の無機活物質複合体を用いた実施例の電池の場合、本発明の無機活物質複合体を用いていない比較例の電池の場合に比べ、放電容量が大きくなり、充放電サイクルに伴なう放電容量の低下が小さい。
【００６９】
したがって、本発明が放電容量の増加と充放電サイクル特性の改善に有効であることがわかる。
【００７０】
【発明の効果】
本発明のＰＥＤＯＴを含有する無機活物質複合体をリチウム二次電池の正極材料として用いることにより、エネルギー密度が高く、サイクル特性および成形加工性に優れたリチウム二次電池を提供することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a positive electrode material composite containing poly (3,4-ethylenedioxythiophene) and a lithium secondary battery having a positive electrode made of the composite.
[0002]
[Prior art]
Due to advances in electronics technology, mobile electronic devices such as mobile phones and wireless devices, and portable electronic devices such as notebook computers and video cameras have been reduced in size and weight, and their functions and reliability have been improved, resulting in widespread use. Have been doing.
[0003]
Under such circumstances, the battery is also referred to as the “heart” of the electronic device, and since it has an important meaning that determines the size, weight, and performance of the entire electronic device, it is strongly desired to increase the energy density of the battery. . In particular, lithium ion secondary batteries and lithium secondary batteries having high voltage and high energy density are attracting attention, and the cycle characteristics, molding processability, and higher energy density of the positive electrode are important issues. .
[0004]
In general, examples of the positive electrode active material constituting the positive electrode include metal oxides and conductive polymers. However, since only metal oxides have poor conductivity and self-formability, conductive agents and binders. Need to be added in large quantities. Therefore, it is difficult to obtain the expected energy density. Therefore, development of a positive electrode material made of a conductive polymer that is excellent in workability, flexibility, and light weight is in progress.
[0005]
Examples of the conductive polymer include polyacetylene, polyaniline, polypyrrole, polythiophene and the like, and have advantages such as high cycle characteristics. However, since the theoretical capacity includes the doping rate and the weight of the dopant, the actual energy capacity per weight is small, and the density is lower than the metal oxide, so the energy density per volume is low. .
[0006]
A composite electrode of a conductive polymer and a metal oxide has been proposed as a method of making up for the disadvantages of the metal oxide and the conductive polymer, taking advantage of them, and solving the problem (for example, non-patented). Reference 1). In addition, a method for improving cycle characteristics by coating the surface of an inorganic active material has been proposed (for example, see Non-Patent Document 2).
[0007]
[Non-Patent Document 1]
GR Goward, et. Al., Electrochim. Acta, 43, 1307 (1998)
[Non-Patent Document 2]
Masaru Sugita, Hideyuki Noguchi, Yasunori Soejima, Masayuki Yoshio, Electrochemistry, 68, 587 (2000)
[0008]
[Problems to be solved by the invention]
However, in the case of the composite electrode of conductive polymer and metal oxide developed so far, the cycle characteristics are improved and the capacity is increased as compared with the metal oxide electrode, but the cycle deterioration is still completely suppressed. The capacity that is close to the theoretical capacity cannot be extracted.
[0009]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors have added poly (3,4-ethylenedioxythiophene) during the preparation of the positive electrode material and added poly (3,4-ethylene in the positive electrode material. The positive electrode material composite containing dioxythiophene) can solve the above problems, and can provide a lithium secondary battery with high energy density and excellent cycle characteristics and moldability. As a result, the present invention has been completed.
[0010]
That is, the present invention
Poly in the positive electrode material was added to poly (3,4-ethylenedioxythiophene) in the preparation of the cathode material (3,4-ethylenedioxythiophene) are contained, the poly (3,4-ethylenedioxythiophene ) Is a lithium secondary battery in which a positive electrode material composite having a content of 10 to 150% by weight with respect to the inorganic active material contained in the positive electrode material is used as a positive electrode,
Lithium secondary battery wherein an average particle diameter of the inorganic substance is 1 to 100 [mu] m (claim 1)
About.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The positive electrode material composite of the present invention is obtained by adding poly (3,4-ethylenedioxythiophene), which is a conductive polymer, at the time of preparation of the positive electrode material, poly (3,4-ethylenedioxythiophene), the positive electrode material, It is a complex. It is considered that the conductive polymer contained in the positive electrode material is usually present near the surface of the inorganic active material contained in the positive electrode material.
[0012]
When the positive electrode material composite is used for the production of a positive electrode of a lithium secondary battery, the energy density can be made higher than the case where the positive electrode material is produced alone and the capacity deterioration with respect to the charge / discharge cycle can be suppressed. . This improvement effect is achieved by adding poly (3,4-ethylenedioxythiophene) (hereinafter also referred to as PEDOT) to impart electrical conductivity to the inorganic active material contained in the positive electrode material, and thereby redox the inorganic active material. (Charge / discharge) It is considered that the volume change and the collapse of the crystal structure accompanying the reaction are suppressed, and the characteristic deterioration caused by repeatedly performing the redox reaction is reduced.
[0013]
Usually, examples of the conductive polymer used in the positive electrode material composite include polyanilines, polypyrroles, polythiophenes, and polyacetylenes, but the conductive polymer used in the present invention has excellent heat resistance, PEDOT with high environmental stability and high electrical conductivity is selected.
[0014]
There is no particular limitation on the molecular weight of PEDOT used in the positive electrode material composite, and it can be used as long as it is generally called PEDOT. Those having high electrical conductivity.
[0015]
The conductivity of PEDOT is generally 0.01 to 300 S / cm. However, in order to use it as a conductive material such as an electrode, the conductivity is preferably as high as possible, and the conductivity is preferably 1 S / cm or more.
[0016]
In order to increase the conductivity of the PEDOT, doping is usually performed. As a kind and a doping rate of a dopant used for doping, a dopant generally used for a conductive polymer, generally a conductive polymer is used. A doping rate (about 0.1 to 0.5) can be adopted.
[0017]
The heat resistance of PEDOT has heat resistance that does not change in weight up to 200 ° C. in thermogravimetric analysis, and has sufficient heat resistance to be used as a positive electrode material.
[0018]
PEDOT can be produced by a known polymerization method such as a chemical polymerization method or an electrolytic polymerization method. However, in the production by the electrolytic polymerization method, the polymer is obtained as a film on the electrode, but requires a lot of electric energy, Therefore, it is preferable to use a chemical polymerization method.
[0019]
When PEDOT is produced by a chemical polymerization method, for example, a method in which an oxidant is added to an organic solvent solution of EDOT to polymerize, or a liquid in which EDOT is emulsified in a liquid containing a surfactant is prepared. It can be produced by a method in which an aqueous solution is added for polymerization. The latter case is preferable because PEDOT with high yield and high electrical conductivity can be obtained even at a low oxidizing agent concentration.
[0020]
PEDOT is added at the time of preparation of the positive electrode material and contained in the positive electrode material to form a positive electrode material composite.
[0021]
The content of PEDOT is preferably 10 to 150%, more preferably 14 to 50% with respect to the inorganic active material contained in the positive electrode material. When the content of PEDOT is too small, a sufficient effect due to the inclusion of PEDOT cannot be obtained. When the content is too large, there is a possibility that the battery capacity is reduced when a lithium secondary battery is used.
[0022]
Examples of the inorganic active material include transition metal cargoogen compounds such as TiS ₂ , MoS ₂ , Co ₂ S ₆ , FeS ₂ , NbS ₂ , ZrS ₂ , VSe ₂ , V ₂ O ₅ , MoO ₃ , MnO ₂ , CoO _2. And metal oxides such as cobalt, manganese, nickel, iron, and the like, and composite oxides containing lithium as constituent elements. These may be used alone or in combination of two or more. Among these, composite oxides containing cobalt and lithium as constituent elements (for example, lithium cobaltate), composite oxides containing nickel and lithium as constituent elements (eg, lithium nickelate), V ₂ O ₅ (vanadium oxide) ) And MoO ₃ (molybdenum oxide) are preferable from the viewpoint of a large theoretical capacity. Furthermore, V ₂ O ₅ and MoO ₃ are preferable because they have a flat portion of the discharge curve in the vicinity of the potential causing the electrochemical redox reaction of the conductive polymer.
[0023]
The inorganic active material preferably has an average particle size of 0.1 to 150 μm, more preferably 0.5 to 120 μm, and particularly preferably 1 to 100 μm. As the average particle size decreases, the surface area increases and the initial battery capacity increases, so that an average particle size that is too large is not practical. On the other hand, when the average particle size becomes too small, problems such as a problem that the battery capacity is reduced during the charge / discharge cycle and a problem that the dispersibility in preparing the electrode is deteriorated easily occur.
[0024]
In the present invention, as a method for producing a positive electrode material composite containing PEDOT, for example, an inorganic active material contained in the positive electrode material, PEDOT, a conductive agent, and a binder are mixed and stirred in an organic solvent and uniformly dispersed. It can manufacture by removing the solvent of the made composition.
[0025]
The conditions for drying the dispersion are not particularly limited, but it is preferable that the solvent is completely removed.
[0026]
Examples of the conductive agent include acetylene black, graphite, and carbon. Among these carbon materials, although acetylene black is slightly inferior in conductivity, crystals of 0.1 μm or less are connected in the shape of a bunch of grapes, so that it efficiently contacts an inorganic active material having a size of 0.1 to 150 μm. Since it is possible, it is used as a general conductive agent in the positive electrode material. Since the average particle diameter of the inorganic active material used in the present invention is in the range of 0.1 to 150 μm, it is preferable to use acetylene black as the conductive agent.
[0027]
Examples of the binder include polyvinylidene fluoride and polytetrafluoroethylene. Generally, a polymer that can maintain high conductivity of the positive electrode by strongly binding the positive electrode active material and the conductive agent is used.
[0028]
As the organic solvent, a solvent that is a good solvent for the conductive polymer and the binder, such as N-methyl-2-pyrrolidone and dimethylformamide, is generally used.
[0029]
The amount of the organic solvent used is not particularly limited as long as the composition containing the solvent can be uniformly stirred, but there is a step of drying the electrode (removing the solvent). When N-methyl-2-pyrrolidone is used, since it is difficult to volatilize, it is preferable to make it as small as possible (for example, about 100 to 200 parts per 10 parts by weight of the binder (hereinafter referred to as “parts”)).
[0030]
There are no particular limitations on the temperature, time, and the like when the inorganic active material, PEDOT, conductive agent, and binder are mixed and stirred in an organic solvent for uniform dispersion.
[0031]
Further, the conditions for drying the organic solvent are not particularly limited, but it is preferable that the solvent is completely removed.
[0032]
As the ratio of each component in the composition excluding the solvent composed of an inorganic active material composite (a mixture of a predetermined amount of an inorganic active material and PEDOT), a conductive agent and a binder, the inorganic active material composite is 60 to 60%. 100%, more preferably 70 to 95%, conductive agent is 0 to 30%, further 5 to 25%, binder is 0 to 20%, further preferably 0 to 15%. When the proportion of the inorganic active material composite is too small, the battery capacity tends to decrease. Moreover, when there are too many ratios of the said electrically conductive agent, shaping | molding of an electrode will become difficult or an energy density will fall easily. Furthermore, when the ratio of the binder is too large, electron conduction due to the insulating properties of the binder tends to be poor.
[0033]
In addition, since the conductive polymer (PEDOT) contained in the inorganic active material composite can also serve as the binder and conductive agent of the inorganic active material, the electrode can be produced without adding the binder and conductive agent, In the present invention, a method of preparing a positive electrode material by adding a binder and a conductive agent to the inorganic composite is preferable in consideration of sufficiently extracting the characteristics of the electrode.
[0034]
The lithium secondary battery of this invention has a positive electrode manufactured using the said positive electrode material composite as a positive electrode of a lithium secondary battery, and there is no special limitation except a positive electrode.
[0035]
The positive electrode manufactured using the positive electrode material composite is usually obtained by uniformly mixing a composition comprising the inorganic active material composite or the inorganic active material and PEDOT with a conductive agent, a binder, and a solvent. It is an electrode obtained by molding the positive electrode material composite obtained by removing together with the current collector.
[0036]
Examples of the current collector include meshes, foils, and plates made of nickel, aluminum, stainless steel, titanium, copper, gold, platinum, and the like.
[0037]
The conditions for molding the positive electrode are not particularly limited, and may be molded according to a conventional method. Therefore, the shape of the positive electrode is not particularly limited.
[0038]
Examples of the negative electrode material of the lithium secondary battery to which the positive electrode is attached include the same materials that can occlude / release lithium, such as metal lithium and lithium-aluminum alloy, which have been used conventionally.
[0039]
The non-aqueous electrolyte used in the lithium secondary battery of the present invention is not particularly limited, and the same non-aqueous electrolyte as conventionally used, for example, an electrolyte solution in which a salt that is an electrolyte is dissolved in an organic solvent, A solid electrolyte can be used.
[0040]
As the electrolyte salt, a lithium salt such as LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) _3, or the like is used. Can do. These may be used alone or in combination of two or more.
[0041]
Examples of the organic solvent include ethylene carbonate, propylene carbonate, diethyl carbonate, dimethoxyethane, γ-butyrolactone, sulfolane, dimethyl sulfoxide, and the like. These may be used alone or in combination of two or more as a mixed solvent.
[0042]
When an electrolyte solution is used as the nonaqueous electrolyte, there is no particular limitation as long as the electrolyte solution does not substantially cause a chemical reaction with the electrode. The concentration of the electrolyte in the electrolyte solution is not particularly limited, and may be appropriately set in consideration of the type of electrolyte to be used and the solvent. Usually, the thing of the range of 0.001-10M and also 0.01-2M is used.
[0043]
On the other hand, when a solid electrolyte is used as the non-aqueous electrolyte, a lithium secondary battery that is not deformed, leaks, generates gas, is resistant to deformation, and has high reliability can be manufactured.
[0044]
Examples of the solid electrolyte include a composite in which a polymer material such as polyethylene oxide, polypropylene oxide, polyvinylidene fluoride, and polyacrylamide is used as a matrix, and a salt that is the aforementioned electrolyte dissolved in the matrix, and a gel of the composite Cross-linked products, those obtained by grafting ion dissociation groups such as low molecular weight polyethylene oxide and crown ether onto the polymer main chain, and high molecular weight polymers in the gel state containing the electrolyte solution described above.
[0045]
In the lithium secondary battery of the present invention, the effect of the present invention is not impaired even if a separator is used as necessary.
[0046]
Examples of the separator include a nonwoven fabric and a woven fabric manufactured from one or more materials selected from polyethylene, polypropylene, polyester, glass, polytetrafluoroethylene, and the like.
[0047]
As described above, the lithium secondary battery of the present invention is a poly (3,4-ethylenedioxythiophene), which is less likely to cause a problem that the crystal structure is collapsed and the energy density is lowered during repeated charge / discharge cycles. As a result, the structure of the inorganic active material in the charge / discharge cycle is stabilized, the discharge capacity is increased, and the charge / discharge cycle characteristics are improved. It will be a thing.
[0048]
【Example】
Next, the present invention will be described more specifically based on examples, but the present invention is not limited thereto.
[0049]
Example 1
In this example, a simple three-electrode cell was used as a laboratory-level experiment. The working electrode was manufactured using a composite containing PEDOT in an inorganic active material, and the counter electrode and the reference electrode were manufactured using a metal lithium foil. In addition, as a nonaqueous electrolyte, a solution in which LiClO ₄ was dissolved in propylene carbonate was used, and the battery characteristics were evaluated.
[0050]
First, PEDOT was manufactured by adding an oxidizing agent aqueous solution to an emulsion obtained by emulsifying EDOT in a surfactant aqueous solution from the viewpoint of high electrical conductivity.
[0051]
Ferric sulfate (Fe ₂ (SO ₄ ) ₃ ) was used as the oxidizing agent, and sodium dodecylbenzenesulfonate was used as the surfactant.
[0052]
In 200 ml of a 0.012M aqueous solution of a surfactant, 0.05M of 3,4-ethylenedioxythiophene monomer (Baitlon M manufactured by Bayer) was mixed and emulsified. To this was added 50 ml of an aqueous solution in which 0.05 M of an oxidizing agent was dissolved, and after stirring at room temperature for 1 day, acetone was added to precipitate the product, which was separated by filtration, washed (water / acetone), dried, and PEDOT (powder )
[0053]
The obtained PEDOT had a conductivity of 10 S / cm, and the heat resistance was a polymer having excellent stability that did not change in weight until 200 ° C. by thermogravimetric analysis.
[0054]
Next, a working electrode (positive electrode) was produced.
[0055]
PEDOT 50 mg, inorganic active material vanadium oxide (manufactured by Taiyo Mining Co., Ltd., V ₂ O ₅ , average particle size 100 μm) 350 mg, polyvinylidene fluoride (PVDF) (manufactured by Aldrich) 50 mg, and acetylene black 50 mg (manufactured by Denki Kagaku Kogyo Co., Ltd.) was mixed in an appropriate amount of N-methyl-2-pyrrolidone (hereinafter referred to as NMP), stirred for 1 day, and dried at 70 ° C.
[0056]
The obtained electrode material was sandwiched between nickel meshes (100 mesh, 10 × 10 × 0.1 mm), pressurized at about 29.4 MPa (300 kg / cm ² ), and then vacuum dried at room temperature overnight or more. It was the pole. In this example, the amount of active material was 5 to 10 mg.
[0057]
Next, a simple triode cell was assembled using the working electrode. As the counter electrode and the reference electrode, metallic lithium foil (manufactured by Asahi East Metal Industry Co., Ltd., thickness 0.2 mm) was used. As a nonaqueous electrolyte, a solution in which LiClO ₄ was dissolved in propylene carbonate at a concentration of 1M was used. All these operations were performed in a dry box in an argon atmosphere.
[0058]
The obtained simple triode cell was evaluated by the following method. The results are shown in Table 1.
[0059]
Examples 2-3
In this embodiment, the charge amount at the time of producing a positive electrode material, V ₂ O ₅ 320 mg and PEDOT 80 mg (Example 2), except for changing each of V ₂ O ₅ 267 mg and PEDOT 133 mg (Example 3) is performed In the same manner as in Example 1, a working electrode and then a simple triode cell were produced and evaluated. The results are shown in Table 1.
[0060]
Examples 4-6
In this example, a working electrode was produced using molybdenum oxide (MoO ₃ manufactured by Taiyo Mining Co., Ltd., average particle size of 1 to 5 μm) as an inorganic active material.
[0061]
The amount charged when the working electrode was produced was changed to 320 mg MoO ₃ and 80 mg PEDOT (Example 4), 300 mg MoO ₃ and 100 mg PEDOT (Example 5), 267 mg MoO _{3 and} 133 mg PEDOT (Example 6), respectively. A working electrode was produced in the same manner as in Example 1, and then a simple triode cell was produced and evaluated. The results are shown in Table 2.
[0062]
Comparative Examples 1-2
A working electrode was produced in the same manner as in Example 1 except that 400 mg of the inorganic active material alone was used without adding PEDOT, and then a simple tripolar cell was produced and evaluated. The results are shown in Tables 1 and 2.
[0063]
The case where vanadium oxide is used is Comparative Example 1, and the case where molybdenum oxide is used is Comparative Example 2.
[0064]
Comparative Example 3
A working electrode was produced in the same manner as in Example 1 except that 400 mg of PEDOT alone was used without using an inorganic active material, and then a simple tripolar cell was produced and evaluated. The results are shown in Tables 1 and 2.
[0065]
(Evaluation of lithium battery)
Using the obtained simple triode cell, the charge / discharge cycle test was performed 10 cycles at room temperature. A charge / discharge measuring device (HJ-101SM6 type manufactured by Hokuto Denko Co., Ltd.) was used for the test. The cycle conditions differed depending on the active material, and the following two conditions A and B were used properly.
Condition A: Lithium secondary battery containing V ₂ O _{5 in the} electrode active material is discharged to a battery voltage of 2.5 V at a constant current of 20 mA / g → paused for 1 minute → charged to a battery voltage of 4.0 V at a constant current of 20 mA / g → 1-minute rest condition B: Lithium secondary battery containing MoO _{3 in the} electrode active material is discharged to a battery voltage of 2.0 V at a constant current of 20 mA / g → paused for 1 minute → charged to a battery voltage of 4.0 V at a constant current of 20 mA / g → Pause for 1 minute [0066]
[Table 1]

[0067]
[Table 2]

[0068]
As is clear from the above results, in the case of the battery of the example using the inorganic active material composite of the present invention, the discharge capacity was compared with the case of the battery of the comparative example not using the inorganic active material composite of the present invention. And the decrease in discharge capacity accompanying the charge / discharge cycle is small.
[0069]
Therefore, it can be seen that the present invention is effective in increasing the discharge capacity and improving the charge / discharge cycle characteristics.
[0070]
【The invention's effect】
By using the inorganic active material composite containing PEDOT of the present invention as a positive electrode material of a lithium secondary battery, a lithium secondary battery having high energy density and excellent cycle characteristics and molding processability can be provided.

Claims (1)

Poly in the positive electrode material was added to poly (3,4-ethylenedioxythiophene) in the preparation of the cathode material (3,4-ethylenedioxythiophene) are contained, the poly (3,4-ethylenedioxythiophene ) Is a lithium secondary battery in which a positive electrode material composite having a content of 10 to 150% by weight with respect to the inorganic active material contained in the positive electrode material is used as a positive electrode,
The average particle size of the inorganic substance is 1 to 100 μm
A lithium secondary battery characterized by that .