JP5154104B2 - Lithium ion secondary battery and method of manufacturing positive electrode plate thereof - Google Patents

Description

  The present invention relates to a method for producing a lithium ion secondary battery and a method for producing the positive electrode plate, and more particularly to a preferred production process for a positive electrode paste.

  In recent years, as a representative of lithium ion secondary batteries used in portable electronic and communication devices such as mobile phones and laptop computers, carbon materials that can occlude and release lithium ions are used as negative electrode active materials, and lithium selected metals. A lithium ion secondary battery using a composite oxide as a positive electrode active material has been put into practical use.

  A positive electrode active material such as a lithium-containing metal oxide, a conductive material, a binder, and a thickener are added, kneaded and dispersed to form a paste.

  For example, as an example of the above-mentioned battery electrode plate preparation means, in the method disclosed in Patent Document 1, an alkaline component in a paste prepared by kneading a positive electrode active material and a thickener is pH 7 to 7 with carbon dioxide gas. 11, the paste was applied to the surface of the current collector, dried and rolled to obtain a positive electrode plate.

In the method disclosed in Patent Document 2, the positive electrode active material and carbon dioxide are dry-mixed in a sealed mixer to neutralize the alkali component in the positive electrode active material, and then the thickener and the binder. The paste paste is added to the surface of the current collector and dried to form a positive electrode plate. For these reasons, the paste is made to have a pH of 7 to 11, when a strong alkali paste is applied to the aluminum foil of the current collector, the aluminum foil is corroded, and hydrogen gas is generated at the interface between the foil and the active material. This is because the substance drops off from the foil or floats to reduce the yield of the coating process.
Japanese Patent Laid-Open No. 8-67991 Japanese Patent Laid-Open No. 11-204108

  However, when a positive electrode active material, a conductive agent, a binder, and a thickener are kneaded to form a paste, carbon dioxide gas is injected and the paste is bubbled to neutralize, so that the pH is in the range of 7 to 11. Since the bubbling with carbon dioxide gas in the paste, bubbles are easily caught in the paste, and cracks may occur on the surface of the electrode plate after coating and drying, leading to a decrease in the yield of the coating process. there were.

  Further, when the active material and carbon dioxide gas are dry-mixed in a hermetically sealed mixer to neutralize the alkali component in the positive electrode active material, the active material and the neutralizing gas are brought into contact until the pH is in the range of 7 to 11. At this time, since only the active material solid surface layer portion can be in contact with the neutralizing gas, it is difficult to uniformly neutralize the inside, and when the paste is applied to the aluminum foil of the current collector, the aluminum foil is corroded, Hydrogen gas is generated at the interface between the active material and the active material, and the active material may fall off from the foil or float up, which may reduce the yield of the coating process.

  For this reason, a large amount of carbon dioxide gas is required for neutralization, and the neutralization treatment time required several hours, so that it cannot have high productivity as a positive electrode material of a lithium ion secondary battery. There was also a point.

  The present invention has been made in view of such a technical background, and can be carried out by a simple process without causing corrosion to the aluminum foil when the paste is applied to the aluminum foil of the current collector. An object of the present invention is to provide a method for uniformly neutralizing an alkali component in a positive electrode active material that can be produced without reducing productivity.

In order to achieve the above-described object, a method for producing a positive electrode plate for a lithium ion secondary battery according to the present invention includes a mixing step of preparing a mixed powder of a conductive material and a positive electrode active material, and carbonation with respect to the mixed powder. A neutralization step of neutralizing the alkaline component of the lithium composite oxide, which is a positive electrode active material, by contacting the gas , and a thickener and a binder are added to the neutralized positive electrode active material and kneaded. a kneading step of preparing a paste, Nurigi the prepared paste aluminum foil surface to be positive electrode current collector, seen at least including the formation step of forming a dried positive electrode active material layer, carbonate used in the neutralization step When the volume of the gas is V1, and the volume of the mixed powder obtained from the bulk density of the positive electrode active material and the conductive material is V2, the ratio of V1 and V2 (V1 / V2) is 2 or more and 30 or less .

  According to the method for producing a positive electrode paste for a lithium secondary battery according to the present invention, the neutralization gas is adsorbed on the surface of the conductive material by bringing the neutralized gas into contact with the mixed powder of the conductive material and the positive electrode active material in advance. As a result, the contact time and contact probability between the surface of the positive electrode active material and the neutralization gas are increased, and the neutralization process can be performed in a shorter amount of gas and in a shorter time. The yield can be improved.

  The gist of the present invention is that in the neutralization step, the neutralized gas is previously brought into contact with the mixed powder of the conductive material and the positive electrode active material, and then a thickener is added and kneaded. The paste prepared by neutralizing efficiently can be applied to the surface of the current collector.

  In this neutralization step, it is not necessary to prepare a mixed powder of the conductive material and the positive electrode active material in advance, and the conductive material and the positive electrode active material may be mixed simultaneously with the contact with the neutralizing gas. It is also preferable that the neutralizing gas, the positive electrode active material, and the conductive material are put into a mixer and mixed. When mixed in advance, powder separation due to a difference in specific gravity is likely to occur, and the dispersibility may be significantly impaired.

  Further, the neutralizing gas includes sulfuric acid, nitric acid, hydrochloric acid, and the like, but carbon dioxide gas is suitable because it has little corrosion resistance to the equipment and corrosion reaction to the active material due to the residue generated by the gas reaction.

  Further, when carbon dioxide is used as the neutralizing gas, V1 represents the volume of carbon dioxide used in the neutralization step, and V1 represents the volume of the mixed powder obtained from the bulk density of the positive electrode active material and the conductive material. The ratio of V2 to V2 (V1 / V2) is preferably 2 or more and 30 or less.

  If the ratio is 2 or less, the absolute amount necessary for neutralization is insufficient, and if it is 30 or more, excess gas remains as bubbles in the paste, causing pinholes.

  According to the manufacturing method described above, the conductivity is improved because there is no current collector exposure of the positive electrode plate, and by using these positive electrode plates, a lithium ion secondary battery with improved battery characteristics can be realized.

  Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS.

Example 1
The lithium ion secondary battery of the present invention is a cylindrical lithium ion secondary battery as shown in FIG. 1 and comprises an electrode plate group, an electrolytic solution, and a battery case that houses them.

  The electrode plate group includes a sheet-like positive electrode plate 5, a sheet-like negative electrode plate 6, a sheet-like separator 7 that insulates between the positive electrode plate 5 and the negative electrode plate 6, a positive electrode lead 3, a negative electrode lead 9, and an upper portion. It consists of an insulating plate 4 and a lower insulating plate 10. The positive electrode plate 5 is formed by coating on both surfaces of an aluminum foil.

  The separator 7 is a porous polypropylene film, and these are overlapped and wound in a spiral shape. The separator 7 is tightly accommodated in the cylindrical case body 8 and sealed by the sealing plate 1. A battery having a diameter of 17 mm and a height of 50 mm was produced.

  First, the manufacturing method of the positive electrode plate 5 is demonstrated in detail using sectional drawing of the battery used for this invention of FIG.

First, 50 parts by weight of LiCoO ₂ powder (bulk density 2.5 g / cm ³⁾ as a positive electrode active material powder, acetylene black as a conductive material powder (bulk density 0.03 g / cm ³⁾ 1.5 parts by weight additive To do.

  V2 (total volume of the mixed powder of positive electrode active material powder and conductive material powder) and V1 (volume of carbon dioxide gas) were obtained as follows.

  First, since the volume of the powder is obtained by dividing the powder input amount by the bulk density, the volume when the positive electrode active material powder input amount is M is M (input amount) /2.5 (bulk density). )

  Similarly to the positive electrode active material powder, the volume of the conductive material is also obtained by dividing the input amount of the conductive material by the bulk density. Here, since the input amount of the conductive material is 1.5 parts by mass (3% of the positive electrode active material powder) with respect to 50 parts by mass of the positive electrode active material, the positive electrode active material powder input amount M In this case, the conductive material powder input amount is 0.03 × M, and therefore the volume of the conductive material powder is determined by 0.03 × M / 0.03 (bulk density).

  V2 obtained by adding the positive electrode active material powder and the conductive material powder volume obtained as described above is M / 2.5 + 0.03 × M / 0.03 = 1.4 × M.

  When the volume V1 of the carbon dioxide gas is a ratio V1 / V2 = S (ratio value) of the total volume V2 obtained from the bulk density of the positive electrode active material powder and the conductive material powder, V1 = V2 × S. Therefore, the volume V1 of the carbon dioxide gas can be obtained as V1 = 1.4 × M × S, and the ratio numerical value S obtained from the ratio of V1 / V2 of the present invention is converted to S = V1 / 1.4 × M. be able to.

  From this equation, when the input amount of the positive electrode active material powder is fixed, the ratio numerical value S can be arbitrarily adjusted by changing the input volume of carbon dioxide gas.

In this example, the positive electrode active material powder input amount is set to M = 20 kg, the volume of carbon dioxide gas to be input is set to 420 cm ³ , and the mixture is sealed in a mixer sealed so that V1 / V2 = 15 for 2 minutes. Mixing was performed to obtain a mixed powder. Here, carbon dioxide gas was measured using a commercially available flow meter so that the required volume was obtained.

Then, using carboxymethylcellulose as a thickener, an aqueous solution in which 1 part by weight of the thickener was dissolved in 99 parts by weight of water was prepared, and this aqueous solution was used as a solvent. An aqueous paste 1 obtained by adding 50 parts by mass of polytetrafluoroethylene (PTFE) and 3 parts by mass of an aqueous solution as an agent to the mixed powder after the neutralization step and kneading and dispersing for 10 minutes was prepared. Next, the positive electrode paste of the present invention is applied to a 20 μm-thick aluminum foil used as a current collector with a die coater so that one side has a thickness of 180 μm, both sides are applied and dried, and the melting temperature of PTFE. The positive electrode plate was heated at 200 to 300 ° C. Thereafter, it was rolled to a thickness of 0.18 mm and cut to prepare a positive electrode plate. The surface state of the positive electrode plate obtained at this time was confirmed. The above positive electrode plate was used as the electrode plate 1 of this example.

Next, a method for manufacturing the negative electrode plate 6 will be described. First, 50 parts by mass of flaky graphite powder, 5 parts by mass of styrene butadiene rubber as a binder, and 23 parts by mass of an aqueous solution dissolved in 99 parts by mass of water with respect to 1 part by mass of carboxymethyl cellulose as a thickener were mixed and dispersed. Thus, a negative electrode paste was obtained. The obtained negative electrode paste was applied and dried on both sides of a negative electrode current collector made of a copper foil having a thickness of 40 μm using a die coater, rolled to a thickness of 0.2 mm, and cut to produce a sheet-like negative electrode plate 6. did. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / liter in a mixed solution of ethylene carbonate 30 vol%, diethyl carbonate 50 vol%, and propionate methyl 20 vol% at 25 ° C. was used. This electrolytic solution is accommodated in the battery case, impregnated in the positive electrode active material layer and the negative electrode active material layer, and in the battery reaction, the Li between the positive electrode plate 5 and the negative electrode plate 6 passes through the minute holes of the porous separator 7. Responsible for the movement of ions.

  The battery case includes a case main body 8 obtained by deep drawing an organic electrolyte resistant stainless steel plate, a sealing plate 1, and an insulating gasket 2 that insulates the sealing plate 1 from the case main body 8.

  A battery was produced in this way, and its initial discharge capacity and cycle characteristics were confirmed. Moreover, before producing a battery, the mass of the positive electrode plate used for the battery was measured and compared with the initial discharge capacity. The above battery was designated as battery 1 of this example.

(Example 2)
The positive electrode plate produced under the same conditions as in Example 1 was used as the electrode plate 2 of Example 2 except that the volume of carbon dioxide gas to be added was adjusted to 56 cm ³ so that V1 / V2 = 2. A battery using this was designated as a battery 2 of Example 2.

(Example 3)
The positive electrode plate produced under the same conditions as in Example 1 was used as the electrode plate 3 of Example 3 except that the volume of carbon dioxide gas input was adjusted to 840 cm ³ so that V1 / V2 = 30. A battery using this was designated as a battery 2 of Example 2.

(Comparative Example 1)
A positive electrode plate produced under exactly the same conditions as in Example 1 except that carbon dioxide gas was not added was used as the electrode plate 1 of Comparative Example 1, and a battery using this was used as the battery 1 of this Comparative Example 1.

  In this comparative example, V1 = 0 because no carbon dioxide gas was added, and thus the ratio value of V1 / V2 is also 0.

(Comparative Example 2)
Except for charging the conductive material powder, the mixture was sealed in a sealed mixer so that the ratio of V1 / V2 would be 20 and then mixed for 2 minutes, under exactly the same conditions as in Example 1 of the present invention. The produced positive electrode plate was used as an electrode plate 2 of a comparative example, and a battery using this was used as a battery 2 of this comparative example.

However, in this comparative example, since the conductive material powder is not added, V2 is the volume of the positive electrode active material powder alone, and it is considered that V2 = M / 2.5 + 0 = M / 2.5. The volume of carbon dioxide gas to be added was adjusted to 160 cm ³ so that the ratio of V1 / V2 was 20.

(Comparative Example 3)
A positive electrode plate produced under exactly the same conditions as in Example 1 was used as the electrode plate 3 of Comparative Example 3, except that the volume of carbon dioxide gas to be added was adjusted to 28 cm ³ so that V1 / V2 = 1. The battery using this was designated as Battery 3 of Comparative Example 3.

(Comparative Example 4)
The positive electrode plate produced under the same conditions as in Example 1 is used as the electrode plate 4 of Comparative Example 4, except that the volume of carbon dioxide gas to be added is adjusted to 1120 cm ³ so that V1 / V2 = 40. A battery using this was designated as a battery 4 of Comparative Example 4.

  The positive plates obtained in Examples 1, 2, 3 and Comparative Examples 1, 2, 3, and 4 were evaluated as described below. Agglomerates and pinholes present on the surface of the positive electrode plate 1000 cm 2 were visually counted and are shown in Table 1.

  When neutralization is insufficient, the aluminum foil is corroded, and hydrogen gas is generated at the interface between the foil and the active material to generate pinholes. Also, under non-uniform neutralization conditions, the mixture and dispersion in the binder and conductive material become insufficient, and agglomerates are likely to be generated. Therefore, measuring these numbers is worth evaluating this effect. It is.

  As shown in Table 1, the neutralization gas was mixed with the neutralization gas under predetermined conditions for the bulk density of the positive electrode active material powder and the conductive material powder as in Examples 1, 2, and 3. Since it is sufficiently neutralized as compared with Comparative Example 1 that is not charged and Comparative Example 2 in which only the positive electrode active material powder and the neutralizing gas are mixed, the corrosion of the aluminum foil is suppressed, and the foil and the active material It is difficult for hydrogen gas to be generated at the interface, and the yield of the coating process is improved without the active material falling off or floating from the foil.

  On the other hand, when V1 / V2 = 1 as shown in Comparative Example 3, neutralization is not sufficient, and when V1 / V2 exceeds 40 as shown in Comparative Example 4, the neutralization gas becomes excessive, Pinholes increased. In addition, cracks occurred from there, and the active material fell off.

  FIG. 2 shows the cycle life characteristics of a battery using the positive electrode plate and the product of the present invention.

  Charging was performed at a constant current of 500 mA. When the voltage reached 4.1 V, charging was replaced with constant voltage charging of 4.1 V, and charging was performed for a total of 2 hours. Discharge was performed at 20 ° C. and 720 mA, and when the discharge potential reached 3.0 V, the discharge was terminated and the next charge was started.

  FIG. 2 is a diagram showing the relationship between the capacity retention rate of the battery used in the example of the present invention and the number of cycles, and compares the cycle life characteristics.

  As is apparent from the figure, the batteries of Examples 1, 2, and 3 (101 to 103 in FIG. 2) are more charged than Comparative Examples 1, 2, 3, and 4 (104 to 107 in FIG. 2). It was found that even when the discharge was repeated, the capacity was hardly deteriorated and the cycle characteristics were excellent.

  This is because in the battery of this example, corrosion of the aluminum foil is suppressed, hydrogen gas is not easily generated at the interface between the foil and the active material, and the active material does not fall off or float up from the foil. Since the adhesion of the agent to the current collector has been improved, even during expansion and contraction of the mixture during charge and discharge, the mixture is difficult to peel off from the current collector, and the current collection of the active material is maintained, improving battery characteristics. It is thought.

  According to the present invention, the current collector is not exposed and the yield of the positive electrode plate is improved. Further, since there is no current collector exposure of the positive electrode plate, a lithium ion secondary battery with improved conductivity and battery characteristics can be realized. Therefore, it is useful as a power source for portable electric devices.

Sectional view of the battery used in the examples of the present invention The figure which shows the relationship between the capacity maintenance rate of the battery used in the Example of this invention, and the cycle number.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sealing plate 2 Insulation gasket 3 Positive electrode lead 4 Upper insulating plate 5 Positive electrode plate 6 Negative electrode plate 7 Separator 8 Case body 9 Negative electrode lead 10 Lower insulating plate

Claims (2)

A mixing step for preparing a mixed powder of a conductive material and a positive electrode active material, and neutralization for neutralizing an alkali component of a lithium composite oxide that is a positive electrode active material by bringing carbon dioxide gas into contact with the mixed powder A kneading step of adding a thickener and a binder to the neutralized positive electrode active material and kneading to prepare a paste; and applying the prepared paste to the surface of the aluminum foil serving as the positive electrode current collector wear, at least it viewed including the formation step of forming a dried positive electrode active material layer,
When the volume of carbon dioxide used in the neutralization step is V1, and the volume of the mixed powder obtained from the bulk density of the positive electrode active material and the conductive material is V2, the ratio of V1 and V2 (V1 / V2) is 2 or more. The manufacturing method of the positive electrode plate for lithium ion secondary batteries characterized by being 30 or less . The lithium ion secondary battery which comprised the positive electrode plate obtained by the manufacturing method of the positive electrode plate for lithium ion secondary batteries of Claim 1 .

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