WO1999031746A1 - Nonaqueous battery electrode and battery using the electrode - Google Patents

Abstract

The electrolyte resistance of an electrode for a battery using nonaqueous electrolyte is improved and a useful secondary battery with the excellent charge/discharge characteristics and heat-resistant properties is obtained by employing the electrode. A binder including polyvinyl alcohol is used to bind electrode activating material and to form an electrode so as to produce the nonaqueous battery electrode which has the resisting properties against the nonaqueous electrolyte. The battery which has the electrodes and the electrolyte layer has the excellent charge/discharge characteristics and heat-resistant properties.

Description

 Description Electrode for non-aqueous battery and battery using the same

 The present invention relates to a non-aqueous battery electrode and a non-aqueous battery using the same. More specifically, the present invention relates to an electrode formed using a binder and a battery using the electrode. Background art

 There is a great demand for smaller and lighter portable electronic devices, but in order to achieve this, it is essential to improve the performance and size of batteries, and various battery developments and improvements are currently being promoted. I have. Characteristics required for batteries include high voltage, high energy density, and reliability. Non-aqueous batteries have attracted attention because satisfying such demands is impossible with conventional batteries using a common aqueous electrolyte. Among them, the lithium-ion battery is a secondary battery that is expected to achieve the highest voltage and the highest energy density among batteries to date, and improvements are being actively made at present. Conventionally, as binders for electrodes for non-aqueous batteries such as lithium ion batteries, for example, as disclosed in Japanese Patent Application Laid-Open No. 63-121262, polyvinyl fluoride and polyvinylidene fluoride are disclosed. And fluoropolymers such as copolymers thereof.

When preparing an electrode, according to Japanese Patent Application Publication No. 63-112212, the above polymer is dissolved, for example, N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP). It is obtained by forming a paste together with such an organic solvent, applying the paste on a current collector, and drying. In particular, Japanese Patent Application Laid-Open No. Sho 63-121212 discloses an example in which PVDF Koborimar is used as a binder. This solves the problem that PVDF homopolymer is soluble only in limited solvents such as NMP by using PVDF copolymer.

 As mentioned above, PVDF and its copolymers have been used as binders for non-aqueous battery electrodes.However, PVDF and its copolymers dissolve or swell in electrolyte at high temperatures. However, a battery using such an electrode has a problem that the charge / discharge characteristics are deteriorated at a high temperature.

 In addition, as shown in Japanese Patent Publication No. 63-112121, the use of PVDF copolymer for the binder is more effective than the use of PVDF homopolymer for the electrolyte. On the other hand, there is a problem of melting or swelling.

 The present invention has been made to solve the above problems, and has good electrical contact between electrode active materials without the electrode binder dissolving or swelling in the electrolytic solution even at a high temperature. An object of the present invention is to form an electrode body, thereby obtaining a practical non-aqueous battery with high reliability, high charge / discharge characteristics, and high heat resistance at low cost and efficiency. Disclosure of the invention

 A first non-aqueous battery electrode according to the present invention is a non-aqueous battery electrode having an electrode active material bound with a binder, wherein the binder contains polyvinyl alcohol.

 A second non-aqueous battery electrode according to the present invention is the above-mentioned first non-aqueous battery electrode, wherein the degree of saponification of polyvinyl alcohol is 97% or more.

The third non-aqueous battery electrode according to the present invention includes the first non-aqueous battery electrode. In the electrode, the degree of polymerization of polyvinyl alcohol is 170 or more.

 A fourth nonaqueous battery electrode according to the present invention is the third nonaqueous battery electrode, wherein the degree of saponification of polyvinyl alcohol is 97% or more.

 A first battery according to the present invention is a battery including an electrode laminate including an electrolyte layer and an electrode for a non-aqueous battery having an electrode active material bound by a binder containing polyvinyl alcohol.

 A second battery according to the present invention is the first battery, wherein the degree of saponification of polyvinyl alcohol is 97% or more.

 A third battery according to the present invention is the first battery, wherein the degree of polymerization of polyvinyl alcohol is 170 or more.

 A fourth battery according to the present invention is the above-described third battery, wherein the degree of saponification of polyvinyl alcohol is 97% or more.

 A fifth battery according to the present invention is a battery according to the first battery, having a plurality of layers of the electrode laminate.

 As described above, according to the present invention, since the binder contains polyvinyl alcohol, it is possible to realize high heat resistance, excellent electrolyte solution resistance of the electrode active material layer in a wide temperature range, and high battery charge / discharge characteristics. In addition, a reliable battery can be obtained over a wide temperature range, and the charge / discharge characteristics are high, so that a practical battery can be obtained.

 Further, by setting the degree of saponification of polyvinyl alcohol to 97% or more, the battery charge / discharge characteristics can be further improved.

Also, by setting the degree of polymerization of polyvinyl alcohol to 170 or more, the battery charge / discharge characteristics can be improved. BRIEF DESCRIPTION OF THE FIGURES

 FIG. 1 is a schematic cross-sectional view illustrating one embodiment of a battery according to the present invention. FIGS. 2, 3, and 4 illustrate other embodiments of the battery according to the present invention. It is a principal part cross section schematic diagram. BEST MODE FOR CARRYING OUT THE INVENTION

 The present inventors have conducted intensive studies on a non-aqueous battery having excellent charge / discharge characteristics and heat resistance and an electrode thereof, and as a result, have reached the present invention.

 That is, as shown in FIGS. 1 to 4, the present invention provides a positive electrode 1 having a positive electrode active material layer 3 in which a positive electrode active material is bound to a positive electrode current collector 2 by a binder, and a negative electrode A negative electrode 4 having a negative electrode active material layer 6 to which an active material is bound; and an electrolyte layer 9 between the positive electrode 1 and the negative electrode 4, i.e., a separator 7 holding a non-aqueous electrolyte. Battery. Although the adhesive layer 8 shown in the figure is not required, the structure in which the positive electrode 1 and the negative electrode 4 are joined to the separator 7 with the adhesive layer 8 eliminates the need for a strong outer can, and is lightweight, thin, and of any shape. Battery is obtained. In FIG. 1, the battery case 10 and the current collector 11 are further provided, and the electrode active material layers 3 and 6 and the separator 7 bound by a binder contain a non-aqueous electrolyte.

 A feature of the present invention is that the positive electrode active material and the negative electrode active material (both are referred to as electrode active materials) are bound to form the electrode active material layers 3 and 6, and the active material layers 3 and 6 and the current collector 2 are combined. The composition of the binder that bonds 5 and 5 is in the composition.

The present inventors have conducted various studies on a secondary battery that has been studied as to how thin and reliable the battery can be, and that the charge / discharge efficiency is increased. As a result, the binder contains polyvinyl alcohol in the binder. It has been found that the use of a non-aqueous battery ensures high reliability, high charge / discharge efficiency, and high heat resistance, and has completed the present invention. That is, the present inventors have accumulated various researches and found that polyvinyl alcohol is excellent in electrolytic solution resistance and exhibits strong adhesive strength as a binder for forming the electrode binder, that is, the positive electrode 1 and the negative electrode 4. However, they have found that an electrode body having good electrical contact between electrode active materials can be formed and maintained without dissolving or swelling in an electrolytic solution even at a high temperature.

 Examples of the polar organic solvent contained in the electrolyte include propylene carbonate, acetyl lactone, ethylene carbonate, tetrahydrofuran, 2-tetrahydrofuran, 1,3-dioxolan, and 4,4-dimethyl-1,3— Use dioxolane, getylcarbonate, dimethylcarbonate, sulfolane, 3-methylsulfolane, tert-butylethyl, iso-butylethyl, 1,2-dimethyloxetane, 1,2-ethoxymethoxetane, etc. Can be.

 The form of the battery using the non-aqueous battery electrode obtained by the present invention is not particularly limited. In addition to a conventional liquid battery, a positive electrode, a negative electrode and a negative electrode as shown in FIG. An electrode stack comprising a single layer of an electrode stack consisting of an electrolyte layer (separator). As shown in Fig. 2, an electrode stack with a positive electrode and a negative electrode alternately arranged in a separated separator overnight. A positive electrode and a negative electrode were alternately arranged between the rolled-up separators as shown in FIGS. 3 and 4 to form a plurality of layers of an electrode laminate. Examples include a wound battery and a polymer gel battery using a polymer gel containing an electrolyte as an electrolyte.

When the binder of the present invention is used, a method in which an electrode active material is dispersed in a binder solution obtained by dissolving the binder in a solvent is used as a coating liquid. A method of applying a solution or a dispersion of the binder is mentioned as an example. The amount of the binder to be used is not particularly limited. 0.1 to 20 parts by weight, preferably 0.5 to 10 parts by weight. Examples of the solvent for dissolving the binder include N-methyl-2-pyrrolidone and dimethyl sulfoxide.

Is not particularly limited electrode active material used in the present invention, if example embodiment, Mn_〇 _{2, Mo 0 3, V 2} 0 5, V 6 〇 _{13, F e 2 0 3,} F e 3 〇 _{4 , L - x) C o 0} 2, L i (1 - x) N i 0 2, N I_〇 _{2, T i S 2, Mo} S 3, F e S 2, CuF 2, N i F 2 , etc. Inorganic compounds, fluorinated carbon, graphite, vapor grown carbon fiber and / or its crushed material, polyacrylonitrile-based carbon fiber and / or its crushed material, pitch-based carbon fiber and / or its crushed material Examples include conductive materials such as carbon materials, polyacetylene, and poly (p-phenylene).

 The method of manufacturing the electrode will be described using a lithium ion secondary battery as an example. That is, the binder of the present invention, the electrode active material, and a solvent for dissolving the binder in a non-aqueous system are uniformly mixed, and the obtained paste is prepared by a conventionally known method such as a copper foil, an aluminum foil or a stainless steel foil as a current collector. The electrode film is uniformly applied to the metal foil and dried by heating at 60 to 150 ° C. for 3 to 120 minutes to form an electrode film in which the electrode active material is bound to the metal foil by the binder.

 Examples of the solvent for dissolving the binder used to obtain the above paste include N-methyl-2-pyrrolidone, dimethyl sulfoxide, γ-butyrolactone, and a mixed solvent obtained by combining these. be able to.

As the separator used during the production of the battery, any material having sufficient strength, such as a porous film made of an electrically insulating material, a net, and a nonwoven fabric, can be used. The material is not particularly limited, but a single porous film or a laminated porous film of polyethylene or polypropylene is preferable from the viewpoint of battery performance. Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

Example 1

 <Creation of positive electrode>

L i C o 0 ₂ 9 1 part by weight, 6 parts by weight of graphite powder, a polymerization degree of 3 0 3 parts by weight of a saponification degree of 9 7% polyvinyl alcohol in 0, N-methyl-2-pyrrolidone 9 5 parts by weight The positive electrode active material paste prepared by heating and mixing was adjusted to a thickness of 300 μm by the doctor blade method to form an active material thin film. An aluminum foil with a thickness of 30 μm serving as the positive electrode current collector is placed on the upper part, and the thickness of the aluminum foil is adjusted to 300 / zm by a dough-blade method to apply the positive electrode active material paste. Applied. This was left to dry in a dryer at 60 ° C for 60 minutes. A positive electrode was produced by rolling the produced laminate to 400 μm.

 <Creation of negative electrode>

95 parts by weight of mesophase microbeads (made by Osaka Gas), 5 parts by weight of polyvinyl alcohol with a degree of polymerization of 300 and a saponification degree of 97%, and 95 parts by weight of N-methyl-2-pyrrolidone The negative electrode active material paste prepared by mixing was applied to a thickness of 300 / zm while adjusting the thickness to 300 / zm by a docu-blade method to form an active material thin film. A 20-m-thick strip-shaped copper foil serving as a negative electrode current collector is placed on the upper part, and the upper part is adjusted to a thickness of 300 // m by a dough-blade method to apply the negative-electrode active material paste. Applied. This was left to dry in a dryer at 60 ° C for 60 minutes. A negative electrode was fabricated by rolling the fabricated laminate to 400 m.

 <Evaluation of Electrolyte Resistance of Electrode>

Cut the positive and negative electrodes obtained as described above into 1 cm x 5 cm, and ethylene carbonate: getylcapone-1: 1: 1 (weight ratio) Immersed in a mixed solvent at 23 ° C and 80 ° C for 30 days.Examine the peeling of the active material thin film from the metal foil and the solvent resistance.The results are shown in Table 1 and the results are shown in Table 1. Was.

 In Table 1,

〇: No change in active material thin film

 : Indicates that any of the following phenomena occurs in the active material thin film: peeling, cracking, swelling, and dissolution.

 <Battery preparation and charge / discharge characteristics evaluation>

 The positive and negative electrodes obtained as described above were cut into 5 cm x 5 cm, and assembled as shown in Fig. 1 to assemble a battery. The charge / discharge characteristics of the assembled battery were measured under the following conditions, for example, by the method described in the Battery Handbook (Battery Handbook Editing Committee, published by Maruzen 1990).

 Charging: constant current + constant voltage method, upper limit voltage 4.2 V

 Discharge: Constant current method Lower limit voltage 2.5 V

 Battery electrode capacity: 100 mAh

 Charge / discharge current value: 100 mA

 Charge / discharge efficiency (%) = Discharge electric capacity ÷ Charge electric capacity X 100

 The charge / discharge was repeated at 100 cycles at 25 ° C. and 80 ° C. The charge / discharge characteristics at the first cycle and at the 100th cycle were determined based on the following criteria (A) and (X). The results are shown in Table 1.

 In Table 1,

 〇: Charge and discharge efficiency is 90% or more

 △: Charge and discharge efficiency is 70% or more

 X: Charge / discharge efficiency is less than 70% or charge / discharge is not possible

Is shown.

Example 2. In place of the polyvinyl alcohol having a degree of polymerization of 300 and a degree of saponification of 97% used in Example 1 above, polyvinyl alcohol having a degree of polymerization of 1,000 and a degree of saponification of 97% was used, and the other conditions were the same as in Example 1. .

Example 3.

 In place of the polyvinyl alcohol having a degree of polymerization of 300 and a degree of saponification of 97% used in Example 1 above, polyvinyl alcohol having a degree of polymerization of 1700 and a degree of saponification of 97% was used. did.

Example 4.

 In place of the polyvinyl alcohol having a polymerization degree of 300 and a saponification degree of 97% used in Example 1 above, polyvinyl alcohol having a polymerization degree of 2400 and a saponification degree of 97% was used, and the other conditions were the same as in Example 1. I made it.

Example 5.

 In place of the polyvinyl alcohol having a polymerization degree of 300 and a saponification degree of 97% used in Example 1 above, polyvinyl alcohol having a polymerization degree of 300 and a saponification degree of 85% was used, and the other conditions were the same as in Example 1. did.

Example 6.

 In place of the polyvinyl alcohol having a polymerization degree of 300 and a saponification degree of 97% used in Example 1 above, a polyvinyl alcohol having a polymerization degree of 1 000 and a saponification degree of 85% was used. Same as.

Example 7.

 In place of the polyvinyl alcohol having a polymerization degree of 300 and a saponification degree of 97% used in Example 1 above, polyvinyl alcohol having a polymerization degree of 1700 and a saponification degree of 85% was used, and the other conditions were the same as in Example 1. did.

Example 8.

Instead of the polyvinyl alcohol having a degree of polymerization of 300 and a degree of saponification of 97% used in Example 1 above, the polymer having a degree of polymerization of 2400 and a degree of saponification of 85% was used. The same operation as in Example 1 was performed except for using vinyl alcohol.

Embodiment 9.

 A battery having a plurality of layers of the electrode laminate shown in FIG. 2 was produced using the positive electrode and the negative electrode of Examples 1 to 8 described above.

 <Production of battery>

 An NMP solution in which 3 wt% of the same polyvinyl alcohol as that used for the binder was dissolved was applied to one side of a porous polypropylene sheet (Celgard # 2400, manufactured by Hoechst) used as two separators 7. . Then, before the adhesive was dried, the positive electrode 1 (or the negative electrode) produced above was sandwiched between the separators and adhered to each other, bonded together, and dried at 80 ° C. The separator where the positive electrode 1 (or the negative electrode) is bonded is punched into a predetermined size, the NMP solution is applied to one surface of the separated separator, and the negative electrode 4 is punched into a predetermined size. (Or the positive electrode), and then apply the above NMP solution to one surface of another separator that has been punched to a predetermined size, and then apply the coated surface of this separate separator first. 4 (or the positive electrode). This step was repeated to form a battery body having 10 layers of electrode laminates, and this battery body was dried while being pressurized, thereby producing a flat laminated battery body as shown in FIG.

 The positive and negative electrode current collectors of the flat plate-shaped laminated battery body and the current collecting tabs connected to the ends of the positive and negative electrode current collectors are spot-welded to each other between the positive electrode and the negative electrode. Connected in parallel.

The tabular laminated structure cell body, (a molar ratio of 1: 1) mixed solvent of ethylene carbonate and Jimechiruka one Boneto. 1 to 6 Futsui spoon lithium phosphate O mo electrolyte dissolved in concentration of 1 / dm ³ After being immersed in the solution, the battery was sealed by heat fusion in a bag made of an aluminum laminate film.

Example 10 A battery having a plurality of layers of the electrode laminate shown in FIG. 3 was manufactured using the positive electrode and the negative electrode of Examples 1 to 8 described above.

 <Production of battery>

 The same polyvinyl alcohol as that used for the binder was applied to one side of each of two strip-shaped separators made of porous polypropylene sheet (Selgard # 2400) made by Hoechst. A 3 wt% NMP solution is applied, and a band-shaped positive electrode 1 (or negative electrode) is sandwiched between the coated surfaces, adhered and adhered, and then placed in a hot air drier at 80 ° C for 2 hours. The NMP was evaporated.

 Apply the above NMP solution to one side of the strip-shaped separator with the positive electrode 1 (or the negative electrode) joined between them. Bend one end of this separator a certain amount, and fold the negative electrode 4 (or positive electrode) at the fold. We sandwiched them and put them on Lamine overnight. Subsequently, the NMP solution was applied to the other surface of the strip-shaped separator, and another negative electrode (or positive electrode) was attached to a position opposite to the negative electrode (or positive electrode) sandwiched between the folds, and then separated. The evening is rolled up in an elliptical shape, and the process of rolling up the separator while adhering another negative electrode (or positive electrode) is repeated to form a battery body having a plurality of electrode laminates, and drying while pressing this battery body Then, a flat wound type laminated structure battery body as shown in FIG. 3 was produced.

 The current collector tabs connected to the respective ends of the positive electrode and the negative electrode current collector of the flat plate-shaped laminated battery body are spot-welded to each other between the positive electrode and the negative electrode, thereby electrically connecting the plate-shaped laminated battery element. Connected in parallel.

The tabular laminated structure cell body, (a molar ratio of 1: 1) mixed solvent of ethylene carbonate and Jimechiruka one Boneto. To 6 lithium Futsuihirin acid 1 O mo 1 / dm ³ of the electrolytic solution and dissolved at a concentration After soaking, the battery was sealed by heat sealing in a bag made of an aluminum laminate film. In this embodiment, the negative electrode 4 (or the positive electrode) may be interposed between the separators while the band-shaped separator in which the positive electrode 1 (or the negative electrode) is joined is folded.

Example 11 1.

 A battery having a plurality of layers of the electrode laminate shown in FIG. 4 was manufactured using the positive electrode and the negative electrode of Examples 1 to 8 described above.

 <Production of battery>

 The strip-shaped positive electrode 1 (or negative electrode) is placed between two strip-shaped separators made of a porous polypropylene sheet (Celgard # 2400, manufactured by Hoechst) to be used as separator 7 overnight. The negative electrode 4 (or the positive electrode) is placed so as to protrude outside of one of the separators by a certain amount. An NMP solution containing 3 wt% of the same polyvinyl alcohol as that used for the binder was applied to the inner surface of each separator and the outer surface of the separator where the negative electrode 4 (or positive electrode) was placed. 4 (or positive electrode), two separators, and positive electrode 1 (or negative electrode) are overlapped and passed through the laminator, and then the above NMP solution is applied to the outer surface of the other separator. A protruding negative electrode 4 (or positive electrode) is folded over this coated surface and attached, and a separator laminated so that the bent negative electrode 4 (or positive electrode) is wrapped inside is rolled up in an elliptical shape, and multiple layers are formed. A battery body having an electrode laminate was formed, and the battery body was dried while being pressurized, thereby producing a flat wound-type laminated structure battery body.

 The positive and negative electrode current collectors connected to the ends of the positive and negative electrode current collectors of this flat plate-shaped laminated battery body are spot-welded to each other between the positive electrode and the negative electrode, so that the flat laminated battery element is electrically connected. Were connected in parallel.

This plate-shaped laminated structure battery was prepared by adding lithium 6-phosphate to a mixed solvent of ethylene carbonate and dimethyl carbonate (molar ratio: 1: 1). After being immersed in an electrolyte solution dissolved at a concentration of O mo 1 / dm ³ , the battery was sealed by heat fusion in a bag made of an aluminum laminate film;

As a result of variously changing the number of stacked layers in the batteries of Examples 9 to 11, a battery capacity proportional to the number of stacked layers was obtained.

Comparative Example 1.

 Polyvinylidene fluoride was used in place of the polyvinyl alcohol having a degree of polymerization of 300 and a degree of saponification of 97% used in Example 1 above, and was otherwise the same as Example 1.

Comparative example 2.

 'Instead of the polyvinyl alcohol having a degree of polymerization of 300 and a degree of saponification of 97% used in Example 1 above, polyvinylidene fluoride-polyhexafluorofluorovinylene copolymer (polyvinylidene fluoride: polyhexafluoropropylene = 6: 4 (molar ratio)), and the other conditions were the same as in Example 1.

Electrolyte resistance Charging / discharging characteristics Positive electrode Negative electrode 1 cycle 100 cycles

23 ° C 80 ° C 23 ° C 80 ° C 23 ° C 80 ° C 23 ° C 80 ° C Actual 1 〇 〇 〇 〇 〇 〇 〇 ΔApplication 2 〇 〇 〇 〇 〇 〇 〇 〇 Example 3 O 〇 〇 〇 〇 〇 0 〇

4 〇 〇 〇 〇 〇 〇 〇 〇

5 〇 〇 〇 〇 〇 〇 Δ Δ

6 o 〇 〇 〇 〇 〇 〇 Δ

7 〇 〇 〇 〇 〇 〇 〇 〇

8 〇 〇 〇 〇 〇 〇 0 比 Ratio 1 〇 X 〇 X 〇 Δ Ο X Compare 2 〇 X 〇 X 〇 X 〇 X Example As clearly shown in the results of Table 1 above, in Comparative Examples 1 and 2, the electrolytic solution resistance and the charge / discharge characteristics were good at a temperature of 23 ° C, but the temperature was 80 ° C. In this case, sufficient characteristics were not obtained in both the electrolyte resistance and the charge / discharge characteristics. On the other hand, according to Examples 1 to 8, at both 23 ° C. and 80 ° C., both the positive electrode and the negative electrode have excellent electrolytic solution resistance of the active material layer and excellent battery charge / discharge characteristics. Battery is obtained. Industrial applicability

 It is used as a secondary battery for portable electronic devices such as mobile personal computers and mobile phones, and can be made smaller, lighter, and arbitrarily shaped as well as improving battery performance.

Claims

The scope of the claims

1. A non-aqueous battery electrode having an electrode active material bound by a binder, wherein the binder contains polyvinyl alcohol.

 2. The electrode for a non-aqueous battery according to claim 1, wherein the degree of saponification of polyvinyl alcohol is 97% or more.

 3. The electrode for a non-aqueous battery according to claim 1, wherein the degree of polymerization of polyvinyl alcohol is 170 or more.

 4. The electrode for a non-aqueous battery according to claim 1, wherein the degree of saponification of polyvinyl alcohol is 97% or more.

 5. A battery comprising an electrode laminate including an electrolyte layer and an electrode for a non-aqueous battery having an electrode active material bonded with a binder containing polyvinyl alcohol.

 6. The battery according to claim 5, wherein the degree of saponification of polyvinyl alcohol is 97% or more.

 7. The battery according to claim 5, wherein the degree of polymerization of polyvinyl alcohol is 170 or more.

 8. The battery according to claim 7, wherein the degree of saponification of polyvinyl alcohol is 97% or more.

 9. The battery according to claim 5, comprising a plurality of layers of the electrode laminate.