JP2005285707A - Organic electrolyte battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electrolyte battery, suppressing increase in the thickness of the battery, when the battery is exposed to a high temperature at voltages of a discharged state or lower than the discharged state over a long time, and also suppressing drop in charge/discharge cycles. <P>SOLUTION: In the organic electrolyte battery including a negative electrode, a positive electrode, and an organic electrolyte, a material capable of storing/releasing lithium is used as a negative active material, the negative electrode is constituted by forming a negative active material-containing coating on a conductive substrate, the contents of Zn and/or Cu in the negative active material-containing coating by ICP emission spectral analysis are/is set to 3-25 ppm. The contents of Zn and/or Cu are/is preferably 4 ppm or higher, more preferably 5 ppn or higher, and preferably 20 ppm or lower. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an organic electrolyte battery, and more particularly to an organic electrolyte battery that can suppress an increase in battery thickness when stored at a high temperature at a discharge state or a voltage equal to or lower than the discharge state, and has little cycle deterioration.

Organic electrolyte batteries represented by lithium ion secondary batteries are in high demand because of their high voltage and high energy density. Conventionally, in this organic electrolyte battery, a carbon material capable of occluding and releasing lithium such as graphite is used as a negative electrode active material, and the carbon material as the negative electrode active material is formed on a conductive substrate made of a metal foil together with a binder. What formed the active material containing coating film was used as a negative electrode.
JP 62-90863 A

  However, in recent years, even in this organic electrolyte battery, in order to achieve further increase in capacity, the filling rate of the positive electrode active material and the negative electrode active material has been increased. When exposed to a high temperature for a long time, there is a problem that the thickness of the battery increases due to gas generated in the battery.

  The present invention solves the problems in the conventional organic electrolyte battery as described above, and can suppress an increase in battery thickness when the battery is exposed to a high temperature for a long period of time at a voltage equal to or lower than a discharged state, and An object of the present invention is to provide an organic electrolyte battery with little cycle deterioration.

  The present invention has been made to achieve the above object, and in an organic electrolyte battery including a negative electrode, a positive electrode, and an organic electrolyte, a material capable of inserting and extracting lithium as a negative electrode active material is used. The negative electrode is formed by forming a negative electrode active material-containing coating film on a conductive substrate, and the zinc and / or copper content by ICP emission analysis in the negative electrode active material-containing coating film is 3 ppm or more and 25 ppm or less. The above-mentioned problem is solved.

  In the present invention, the content of zinc and / or copper in the negative electrode is measured by ICP emission analysis. The ICP emission analysis is carried out by accurately weighing about 5 g of the negative electrode active material-containing coating film of the negative electrode, and in a 200 ml beaker. And 100 ml of (1 + 1) hydrochloric acid was added, and the mixture was concentrated by heating to a liquid volume of about 20 to 25 ml, cooled, and then quantified filter paper No. manufactured by Advantech Co., Ltd. In 5B, solids such as the negative electrode active material were separated, and the filtrate and washings were placed in a 100 ml volumetric flask and diluted to a constant volume, and then measured using a sequential ICP emission analyzer IPIS1000 manufactured by Japan Jarrell Ash. It is.

  According to the present invention, it is possible to provide an organic electrolyte battery that can suppress an increase in battery thickness when the battery is exposed to a high temperature for a long period of time at a voltage equal to or lower than that of the discharged state, and has little cycle deterioration. Can do.

  In the present invention, the reason why the battery thickness increase when the battery is exposed to a high temperature for a long period of time at a voltage below the discharged state or the discharged state is not necessarily clear at present, but a small amount as described above The zinc and / or copper contained in the negative electrode active material-containing coating in a quantity forms a coating on the surface of the negative electrode at a voltage lower than the discharge state or the discharge state, or the zinc and / or copper is a gas This is thought to be due to the reaction with the source substance and the suppression of gas generation.

  In the present invention, examples of the material capable of occluding and releasing lithium as the negative electrode active material include carbon materials such as a carbonaceous material having a turbulent layer structure, natural graphite, artificial graphite, and glassy carbon. Some of them do not contain lithium at the time of manufacture, but when they act as a negative electrode active material, they are in a state containing lithium by chemical means, electrochemical means, or the like. In addition to the above carbon materials, examples of materials capable of inserting and extracting lithium that can be used as the negative electrode active material include lithium metal and lithium-containing compounds. Examples of the lithium-containing compounds include lithium alloys and other materials. There is something. Examples of the lithium alloy include alloys of lithium and other metals such as lithium-aluminum, lithium-lead, lithium-bismuth, lithium-indium, lithium-gallium, and lithium-indium-gallium.

  For example, a negative electrode is prepared by adding a binder to the negative electrode active material as necessary, and if necessary, adding an electron conduction assistant, further adding a solvent, and mixing to prepare a negative electrode active material-containing coating, The coating material is applied to a conductive substrate and dried to form a negative electrode active material-containing coating film. In preparing the negative electrode active material-containing paint, the binder is preferably used as a solution previously dissolved in an organic solvent, water, or an aqueous solution, and mixed with solid particles such as the negative electrode active material to prepare the paint.

  As the binder, for example, a polyvinylidene fluoride polymer (a polymer of a fluorine-containing monomer group containing 80% by mass or more of vinylidene fluoride as a main component monomer), a rubber polymer, a cellulose polymer, and the like are preferably used. It is done. You may use the said polymer in mixture.

  Examples of the fluorine-containing monomer group containing 80% by mass or more of vinylidene fluoride as a main component monomer in the synthesis of the polyvinylidene fluoride-based polymer include, for example, vinylidene fluoride alone, or vinylidene fluoride and other A mixture with at least one of the monomers may be mentioned. Examples of the other monomer include vinyl fluoride, trifluoroethylene, trifluorochloroethylene, tetrafluoroethylene, hexafluoropropylene, and fluoroalkyl vinyl ether.

  Examples of the rubber-based polymer include styrene butadiene rubber, ethylene propylene diene rubber, and fluorine rubber.

  Examples of the cellulose polymer include carboxymethyl cellulose, methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, and hydroxypropyl methyl cellulose.

  In this invention, it is preferable that a binder is 0.2-20 mass% in a negative electrode active material containing coating film, especially 0.5-10 mass%. When the binder content is less than the above range, the negative electrode active material-containing coating film may be insufficient in mechanical strength, and the negative electrode active material-containing coating film may be peeled off from the conductive substrate. When more than the said range, there exists a possibility that the negative electrode active material in a negative electrode active material containing coating film may reduce, and battery capacity may fall.

  In addition, as the electron conduction aid, for example, flaky graphite, carbon black, ketjen black, acetylene black, carbon fiber and the like are preferably used.

  In the present invention, various coating methods such as an extrusion coater, a reverse roller, a doctor blade, and an applicator can be employed as a coating method when the negative electrode active material-containing paint is applied to a conductive substrate. .

  Further, as the negative electrode conductive substrate, for example, a metal, a punched metal, a foam metal, a foil processed into a plate shape, or the like made of a metal conductive material such as aluminum, stainless steel, titanium, or copper is used.

  In the present invention, the negative electrode is required to have a zinc and / or copper content of 3 ppm or more and 25 ppm or less as measured by ICP emission analysis in the negative electrode active material-containing coating film. The content of 3 ppm to 25 ppm alone may be sufficient, the content of copper alone may be 3 ppm to 25 ppm, and the total amount of zinc and copper is 3 ppm to 25 ppm. May be.

  In the present invention, the content of zinc and / or copper by the ICP emission analysis in the negative electrode active material-containing coating film of the negative electrode is set to 3 ppm or more because when the zinc and / or copper content is less than 3 ppm, the battery This is because the increase in the thickness of the battery when exposed to a high temperature for a long period of time at a discharge state or a voltage below the discharge state cannot be sufficiently suppressed, and the zinc and / or copper content is 25 ppm or less. This is because the cycle characteristics deteriorate when the content of zinc and / or copper exceeds 25 ppm. And in order to suppress more appropriately the thickness increase of the battery when the battery is exposed to a high temperature for a long period of time at a voltage below the discharge state or the discharge state, the content of zinc and / or copper should be 4 ppm or more. Is preferable, and it is more preferable to set it as 5 ppm or more. Further, in order to keep the cycle characteristics in a more excellent state, it is preferable to set the content of zinc and / or copper to 20 ppm or less, and when considering zinc or copper alone, the content of zinc is 15 ppm or less, The copper content is preferably 15 ppm or less.

  In order to make the content of zinc and / or copper in the negative electrode active material-containing coating film as described above, the negative electrode active material capable of constituting the negative electrode active material-containing coating film with such a content of zinc and / or copper. Zinc by using a substance or adding zinc powder and / or copper powder to the negative electrode active material, or treating the negative electrode with a solution containing a zinc compound such as zinc chloride or a solution containing a copper compound such as copper chloride And / or copper content should just be 3 ppm or more and 25 ppm or less.

  Usually, as shown in Comparative Example 1 described later, the carbon material used as the negative electrode active material is refined to have a zinc or copper content below the detection limit (0.005 ppm) of the device in ICP emission analysis. However, with respect to zinc and copper, the content of the negative electrode active material-containing coating film of the negative electrode can be adjusted to the above-mentioned content by controlling the purification process.

In the present invention, in constituting a positive electrode serving as a counter electrode of the negative electrode, as the positive electrode active material, for example, lithium nickel oxide, lithium cobalt oxide, lithium manganese oxide (these are usually LiNiO ₂ , LiCoO ₂ , Although represented by LiMn ₂ O ₄ , the ratio of Li to Ni, the ratio of Li to Co, and the ratio of Li to Mn often deviate slightly from the stoichiometric composition, but such a slight deviation Lithium-containing composite metal oxides such as may be used alone or as a mixture of two or more thereof or as a solid solution thereof.

  The positive electrode includes, for example, the above-described positive electrode active material, and optionally includes an electron conduction assistant such as flaky graphite and carbon black, and further prepares a positive electrode active material-containing paint containing a binder, and the paint is made conductive. It is produced through a process of applying to a substrate and drying to form a coating film containing a positive electrode active material.

  In the production of this positive electrode, the same materials as in the case of the negative electrode can be used for the binder, the electron conduction auxiliary agent, the conductive substrate, and the negative electrode active material can be applied with respect to the coating method of the positive electrode active material-containing paint. The same method as in the case of applying the substance-containing paint can be employed.

In the present invention, an electrolytic solution in which an electrolyte such as a lithium salt is dissolved in an organic solvent is used. As the electrolyte, for example, a general formula LiMF _n (wherein M is P, As, Sb or B, and n is 6 when M is P, As or Sb, and 4 when M is B). These include inorganic lithium salts and fluorine-containing organic lithium imide salts. The electrolytes can be used alone or in combination of two or more.

  The concentration of the electrolyte in the electrolytic solution is preferably 0.4 mol / l to 1.6 mol / l as a whole even if two or more different types of electrolytes are included, and particularly 0.6 mol / l to 1 It is preferably 4 mol / l.

  Examples of the organic solvent used for dissolving the electrolyte include ethers such as 1,2-dimethoxyethane, 1.2-diethoxyethane, dimethoxypropane, 1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran. , Propylene carbonate, ethylene carbonate, γ-butyrolactone, esters such as diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate, and sulfolane are used alone or as a mixed solvent of two or more.

  Among the organic solvents, esters are preferable because they have little reactivity with the positive electrode active material even under a high voltage and have a large effect of improving storage characteristics. This ester is preferably 20% by volume or more in the total electrolytic solution solvent for the stability of the electrolytic solution during charging.

  As the separator, for example, a microporous polyethylene film or a microporous polypropylene film having a thickness of 10 to 50 μm and a porosity of 30 to 70% is preferably used.

  The battery is made of, for example, a spiral electrode body manufactured by winding a separator between a positive electrode and a negative electrode manufactured as described above, and aluminum, aluminum alloy, or nickel-plated iron. It is manufactured through a process of inserting into a battery case made of stainless steel or the like, injecting an electrolyte, and sealing. The battery usually incorporates an explosion-proof mechanism that discharges gas generated inside the battery to a certain pressure to the outside of the battery to prevent the battery from bursting under high pressure.

  Next, the present invention will be described more specifically with reference to examples. However, this invention is not limited only to those Examples.

Example 1
The negative electrode used in Example 1 was produced as follows.
First, 98 parts by mass of graphite having a specific surface area of 3.6 m ² / g as a negative electrode active material, a suspension of styrene-butadiene rubber as a binder, and a 1.5% by mass carboxymethylcellulose aqueous solution each having a solid content of 1 part by mass. A negative electrode active material-containing paint was prepared by mixing so as to be (2 parts by mass as a whole binder).

The obtained paint was applied onto a conductive substrate made of copper foil having a thickness of 8 μm using an applicator and dried at 100 ° C. to form a negative electrode active material-containing coating film. Moreover, the said coating material was apply | coated also to the back surface side of the electroconductive base | substrate which consists of said copper foil, and it dried and produced the electrode body. Thereafter, this electrode body was vacuum-dried at 100 ° C. for 10 hours and then roll-pressed to produce a sheet-like negative electrode. The total thickness of this negative electrode was 125 μm, and the density of the negative electrode active material-containing coating film was 1.7 g / cm ³ . Moreover, the zinc content by ICP emission analysis in the said negative electrode active material containing coating film was 5 ppm, and copper content was 7 ppm. However, in order to avoid the influence of the copper foil used as the conductive substrate, the content of copper described above is a coating containing a negative electrode active material formed by applying the negative electrode active material-containing paint onto a plastic sheet and drying it as described above. Measured on the membrane.

  A positive electrode serving as a counter electrode of the negative electrode was produced as follows. 96 parts by mass of lithium cobalt oxide, 1 part by mass of carbon black and scaly graphite as electron conduction assistants, and 2 parts by mass of polyvinylidene fluoride as a binder are mixed with an N-methylpyrrolidone solution. Thus, a positive electrode active material-containing paint was prepared.

And the obtained coating material was apply | coated using the applicator on the electroconductive base | substrate which consists of 15-micrometer-thick aluminum foil, and it dried at 100-120 degreeC, and formed the positive electrode active material containing coating film. In addition, the paint was applied to the back side of the conductive substrate made of the aluminum foil in the same manner as described above and dried to prepare an electrode body. The electrode body was vacuum-dried at 100 ° C. for 10 hours and then roll-pressed to produce a sheet-like positive electrode. The total thickness of the positive electrode at this time was 130 μm, and the density of the positive electrode active material-containing coating film was 3.8 g / cm ³ .

As the electrolytic solution, a solution obtained by dissolving LiPF ₆ at a concentration of 1.0 mol / l in a mixed solvent having a volume ratio of ethylene carbonate and methyl ethyl carbonate of 1: 2 was used.

  A current collecting tab is attached to each of the sheet-like positive electrode and the sheet-like negative electrode, and the sheet-like positive electrode and the sheet-like negative electrode are overlapped via a separator made of a microporous polyethylene film having a thickness of 20 μm and wound in a spiral shape. After turning, pressurize so that it is flattened to form an electrode laminate with a flat winding structure, and then attach an insulating tape, and a rectangular battery case with an outer dimension of 5 mm × 30 mm × 48 mm [thickness (depth) 5 mm , 30 mm wide and 48 mm high rectangular battery case], the lead body is welded, and the sealing lid plate is laser welded to the opening end of the battery case, and the electrolyte provided on the sealing lid plate After injecting the above electrolyte into the battery case from the inlet and sufficiently infiltrating the separator, etc., the electrolyte inlet is sealed and sealed, and then precharged and aged. 1 To produce an organic electrolyte secondary battery of prismatic having an appearance as shown in FIG. 2 in Suyo structure.

  The battery shown in FIGS. 1 and 2 will now be described. The positive electrode 1 and the negative electrode 2 are spirally wound through the separator 3 as described above, and then pressed so as to be flattened, thereby forming a flat winding structure. The electrode laminate 6 is housed in the rectangular battery case 4 together with the electrolyte solution. However, in FIG. 1, in order to avoid complication, a metal foil, an electrolytic solution, or the like as a conductive substrate used in manufacturing the positive electrode 1 and the negative electrode 2 is not illustrated.

  The battery case 4 is made of an aluminum alloy and constitutes a battery exterior material. The battery case 4 also serves as a positive electrode terminal. An insulator 5 made of a polytetrafluoroethylene sheet is disposed at the bottom of the battery case 4, and the positive electrode 1 and the negative electrode are formed from the flat electrode structure 6 made of the positive electrode 1, the negative electrode 2 and the separator 3. A positive electrode lead body 7 and a negative electrode lead body 8 connected to one end of each of the two are drawn out. A stainless steel terminal 11 is attached to an aluminum alloy cover plate 9 that seals the opening of the battery case 4 via a polypropylene insulating packing 10, and an insulator 12 is connected to the terminal 11. A stainless steel lead plate 13 is attached.

  And this cover plate 9 is inserted in the opening part of the said battery case 4, and the opening part of the battery case 4 is sealed by welding the junction part of both, and the inside of a battery is sealed.

  In the battery of Example 1, the battery case 4 and the cover plate 9 function as positive terminals by directly welding the positive electrode lead body 7 to the cover plate 9, and the negative electrode lead body 8 is welded to the lead plate 13, The terminal 11 functions as a negative electrode terminal by conducting the negative electrode lead body 8 and the terminal 11 through the lead plate 13, but depending on the material of the battery case 4, the sign may be reversed. There is also.

  FIG. 2 is a perspective view schematically showing the external appearance of the battery shown in FIG. 1. FIG. 2 is shown for the purpose of showing that the battery is a square battery. FIG. 1 schematically shows a battery, and only specific members of the battery are shown. Also in FIG. 1, the inner peripheral portion of the electrode body is not cross-sectional.

Example 2
The electrode body produced in Example 1 was immersed in a 1.0 mass% zinc chloride (ZnCl ₂ ) aqueous solution for 10 minutes, washed with water, vacuum-dried at 100 ° C. for 10 hours, roll-pressed, and sheet-shaped. A negative electrode was produced. The total thickness of this negative electrode was 125 μm, and the density of the negative electrode active material-containing coating film was 1.7 g / cm ³ . Further, the content of zinc in the negative electrode active material-containing coating film of the negative electrode by ICP emission analysis was 10 ppm, and the content of copper was 7 ppm. And the square organic electrolyte secondary battery was produced similarly to Example 1 except having used this negative electrode.

Example 3
The electrode body produced in Example 1 was immersed in a 1.0% by mass cupric chloride (CuCl ₂ ) aqueous solution for 10 minutes, washed with water, vacuum-dried at 100 ° C. for 10 hours, roll-pressed, and sheet A negative electrode was prepared. The total thickness of this negative electrode was 125 μm, and the density of the negative electrode active material-containing coating film was 1.7 g / cm ³ . Further, the content of zinc in the negative electrode active material-containing coating film of the negative electrode by an ICP emission analysis was 5 ppm, and the content of copper was 12 ppm. And the square organic electrolyte secondary battery was produced similarly to Example 1 except having used this negative electrode.

Example 4
A sheet-like negative electrode was produced in the same manner as in Example 1 except that graphite having a specific surface area of 4.0 m ² / g was used as the negative electrode active material. The total thickness of this negative electrode was 127 μm, and the density of the negative electrode active material-containing coating film was 1.67 g / cm ³ . Further, the content of zinc in the negative electrode active material-containing coating film of the negative electrode by ICP emission analysis was 5 ppm, and the content of copper was 5 ppm. And the square organic electrolyte secondary battery was produced similarly to Example 1 except having used this negative electrode.

Example 5
A sheet-like negative electrode was produced in the same manner as in Example 2 except that the electrode body produced in Example 4 was treated with the same zinc chloride solution as in Example 2. The total thickness of this negative electrode was 127 μm, and the density of the negative electrode active material-containing coating film was 1.67 g / cm ³ . Further, the content of zinc in the negative electrode active material-containing coating film of the negative electrode by ICP emission analysis was 14 ppm, and the content of copper was 5 ppm. And the square organic electrolyte secondary battery was produced similarly to Example 1 except having used this negative electrode.

Example 6
A sheet-like negative electrode was produced in the same manner as in Example 3 except that the electrode body produced in Example 4 was treated with the same copper chloride solution as in Example 3. The total thickness of this negative electrode was 127 μm, and the density of the negative electrode active material-containing coating film was 1.67 g / cm ³ . Further, the content of zinc in the negative electrode active material-containing coating film of the negative electrode by an ICP emission analysis was 5 ppm, and the content of copper was 15 ppm. And the square organic electrolyte secondary battery was produced similarly to Example 1 except having used this negative electrode.

Comparative Example 1
A sheet-like negative electrode was produced in the same manner as in Example 1 except that graphite having a specific surface area of 3.4 m ² / g was used as the negative electrode active material. The total thickness of this negative electrode was 125 μm, and the density of the negative electrode active material-containing coating film was 1.7 g / cm ³ . In addition, the content of zinc in the negative electrode active material-containing coating film of the negative electrode is not more than the detection limit (0.005 ppm) of the apparatus, and the copper content is also not more than the detection limit (0.01 ppm). Met. And the square organic electrolyte secondary battery was produced similarly to Example 1 except having used this negative electrode.

  For the batteries of Examples 1 to 6 and Comparative Example 1 manufactured as described above, when the charge / discharge current is indicated by C, a current limit circuit of 1 C is provided with 750 mA as 1 C, and the initial voltage is 4.2 V. The battery was charged and then discharged to 3.0V. In the repetition of charging and discharging at this time, after discharging for the 10th cycle, it was stored in a constant temperature bath at 80 ° C. for 100 days, and the increase in battery thickness due to storage was examined. The results are shown in Table 1.

  Table 1 shows the cycle characteristics (%) obtained by multiplying the value obtained by dividing the discharge capacity at the 500th cycle by the discharge capacity at the first cycle in the repetition of the charge / discharge.

  As shown in Table 1, the batteries of Examples 1 to 6 have less increase in battery thickness when stored at a high temperature in a discharged state than the battery of Comparative Example 1, and are almost equivalent to the battery of Comparative Example 1. The cycle deterioration due to inclusion of zinc and / or copper in the negative electrode active material-containing coating film was hardly observed.

It is a figure which shows typically an example of the organic electrolyte battery which concerns on this invention, (a) is the top view, (b) is the fragmentary longitudinal cross-sectional view. It is a perspective view of the organic electrolyte battery shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Battery case 5 Insulator 6 Electrode laminated body 7 Positive electrode lead body 8 Negative electrode lead body 9 Cover plate 11 Terminal 12 Insulator 13 Lead plate

Claims (4)

An organic electrolyte battery including a negative electrode, a positive electrode, and an organic electrolyte, wherein a material capable of inserting and extracting lithium is used as a negative electrode active material, and the negative electrode forms a negative electrode active material-containing coating film on a conductive substrate An organic electrolyte battery comprising a negative electrode active material-containing coating film, wherein the content of zinc and / or copper by ICP emission analysis is 3 ppm or more and 25 ppm or less. The organic electrolyte battery according to claim 1, wherein the content of zinc and / or copper is 4 ppm or more. The organic electrolyte battery according to claim 1, wherein the content of zinc and / or copper is 5 ppm or more. The organic electrolyte battery according to any one of claims 1 to 3, wherein the content of zinc and / or copper is 20 ppm or less.

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