JPH10270023A - Manufacture of electrode for nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve adhesion between an electrode mixture layer and a conductor and electric characteristics. SOLUTION: In manufacturing an electrode for a nonaqueous electrolyte secondary battery, electrode mixture paste is layered and dried several times. Then, each layer is thinner and a time required for drying is shorter, thus to improve productivity. The deviation of binder concentration per unit layer is reduced, thus to improve adhesion between a collector and an electrode mixture layer as well as electric characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrode for a non-aqueous electrolyte secondary battery having an electrode mixture layer formed on a current collector, and a method for producing the same.

[0002]

2. Description of the Related Art For example, a non-aqueous electrolyte secondary battery which performs charging and discharging by a reversible reaction of absorbing lithium ions released from one between a positive electrode and a negative electrode into the other has the following structure. It is known. For example, an electrode mixture containing a lithium-containing oxide of a transition metal is laminated on a metal aluminum foil as a current collector to produce a sheet-like electrode for a positive electrode, and a copper foil as a current collector is coated on a carbon foil having a layered structure. An electrode mixture containing a material is laminated to produce a sheet-like electrode for a negative electrode. Then, by winding these positive and negative electrodes with a separator interposed therebetween, an electrode body having a spiral multilayer structure is manufactured, and this is housed in a battery can together with a non-aqueous electrolyte.

In order to laminate the electrode mixture on each of the electrodes, a paste coating apparatus such as a direct coater is conventionally used to collect the electrode mixture paste obtained by kneading the raw material powder of the electrode mixture together with a binder and a solvent. The paste is applied to an electric body so as to have a predetermined thickness, and then the paste surface is dried by blowing hot air thereon, and the sheet is wound up by pressing or the like as necessary.

[0004]

However, when the paste is manufactured by the above-mentioned conventional method, there is a problem that it takes a long time to dry the paste and the productivity cannot be sufficiently improved. On the other hand, if the temperature of the hot air is increased or the amount of air is increased in order to dry in a short time, there arises a problem that the manufactured electrode mixture layer is easily separated from the current collector. According to the study of the present inventors, the reason why the adhesion between the electrode mixture layer and the current collector is reduced by drying for a short time is as follows. That is, when the temperature of the hot air is increased or the air volume is increased, the solvent is rapidly evaporated on the surface of the mixture paste applied on the current collector, and the binder concentration increases. Then, the solvent in which the binder is dissolved from the lower layer due to the evaporation of the solvent near the surface rises near the surface due to the capillary phenomenon, where it evaporates and the binder concentration near the surface further increases. As a result, the binder concentration decreases in the electrode mixture layer near the current collector, and the adhesion between the electrode mixture layer and the current collector decreases. In order to avoid such a decrease in adhesion, the amount of the binder added may be increased in advance. However, since the binder is an insulator, an increase in the amount of the binder may cause an increase in the electrical capacity such as a decrease in battery capacity. This leads to deterioration of characteristics.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a non-aqueous solution that can improve the adhesion between the electrode mixture layer and the current collector and the electrical characteristics while increasing the productivity. An object of the present invention is to provide a method for manufacturing an electrolyte secondary battery.

[0006]

The invention according to claim 1 is
A method for producing an electrode for a non-aqueous electrolyte secondary battery, in which an electrode mixture paste obtained by kneading an electrode raw material powder together with a binder and a solvent is laminated on a current collector to form an electrode mixture layer. It is characterized in that it is laminated and dried on the current collector a plurality of times.

The invention according to claim 2 is characterized in that in each paste laminating step, an electrode mixture paste having the same composition is used. According to a third aspect of the present invention, two paste laminating steps are performed. In the first paste laminating step, the electrode mixture having a thickness of 10 to 70% of the total thickness of the electrode mixture layer. It is characterized in that a layer is formed.

[0008]

Since the electrode mixture paste is laminated and dried in a plurality of times, the lamination thickness per time is reduced. When the lamination thickness per operation is reduced, the time required for drying is reduced, and the productivity can be increased. Moreover, since the bias of the binder concentration in each unit layer divided into a plurality of times is reduced, the distribution of the binder in the entire electrode mixture layer can be made more uniform than before, and the amount of added binder is not increased. In both cases, the adhesion between the current collector and the electrode mixture layer and the electrical characteristics can be improved. In addition, since the electrode mixture paste is laminated a plurality of times, the lamination and drying steps are required for the number of times. However, if the lamination thickness of the electrode mixture paste is １ ／, for example, the required drying time is about ４. Therefore, even if two lamination and drying steps are required, it is about 約 of the conventional thickness. It takes time. Further, in the case where the electrode mixture layer is formed in two lamination steps, if the electrode mixture layer having a layer thickness of 10 to 70% is formed in the first lamination step, it is difficult to form the electrode mixture layer with the current collector. It is preferable because the adhesion is improved (the invention of claim 3). This is because when the thickness is 10% or less, the time required for the second and subsequent drying steps is long and the effect of improving the productivity is small, and when it exceeds 70%, the binder concentration distribution tends to decrease on the current collector side.

According to the second aspect of the present invention, since the electrode mixture pastes having the same composition are used, the laminating step can be repeatedly performed by, for example, the same coating apparatus, and the production equipment is simplified.

[0010]

【Example】

<Examples 1 to 10> Examples 1 to 10 relating to the production of a negative electrode of a so-called lithium ion nonaqueous electrolyte secondary battery will be described. In all of these examples, the electrode mixture layer was divided into upper and lower layers and laminated and dried to manufacture.
First, a carbon material as an electrode raw material powder, polyvinylidene fluoride as a binder, and N-methyl- as a solvent
2-Pyrrolidone was mixed to prepare two types of electrode mixture pastes in which the ratio of the binder amount to the electrode raw material was 10% by weight and 8% by weight. (First Laminating Step) These pastes were uniformly applied onto a 20 μm-thick copper foil using a direct coater, dried, and press-formed to form a lower electrode mixture layer.
The thickness of each electrode mixture layer after press molding is shown in Table 1 for each example.
As shown in FIG. (Second Laminating Step) Next, an electrode mixture paste having the same composition as that of the first laminating step is uniformly applied on the lower electrode mixture layer using the same direct coater, and dried. Press forming was performed to form an upper electrode mixture layer. The thickness of the upper layer is adjusted so that the total thickness of the upper and lower layers is 150 μm.

As Comparative Examples 1 and 2, two types of electrode mixture pastes in which the ratio of the binder amount to the electrode raw material was 10% by weight and 8% by weight were laminated on a copper foil having a thickness of 20 μm.
After drying, the thickness of the electrode mixture layer after press molding is 150 μm
Thus, a single-layer negative electrode was prepared. In the press molding, the porosity of the electrode mixture layer was set to 30% in each of Examples 1 to 10 and Comparative Examples 1 and 2. (Evaluation) Each of these electrodes was assembled as a coin-type test cell using metallic lithium as a counter electrode, and as an electrolyte,
A solution prepared by dissolving 1 mol / liter of lithium hexafluorophosphate in a mixed solvent of ethylene carbonate and diethyl carbonate was used. After discharging these test cells to 0 V at a constant current corresponding to the current density of the negative electrode plate of 0.5 mA / cm 2, the cells were charged to 1.2 V at the same current, and then discharged to discharge them per unit weight of the carbon material. The discharge capacity was examined. Further, the adhesion was judged by the presence or absence of peeling observed when the electrode after press molding was wound around a cylinder having a diameter of 2 mm. Table 1 shows these results.

[0012]

[Table 1]

As shown in Table 1, in Comparative Example 2 in which the binder amount was 10% by weight, no peeling of the electrode mixture layer was observed in the adhesion test, but Comparative Example 1 in which the binder amount was 8% by weight.
Then, peeling of the electrode mixture layer occurs. On the contrary,
In Examples 1 to 5 having the two-layer structure, even when the amount of the binder is 8% by weight, which is the same as that in Comparative Example 1, the electrode mixture layer does not peel. It is considered that the reason for this is that when the thickness of the electrode mixture paste applied is thin, the solvent in which the binder is dissolved evaporates while remaining near the current collector without moving near the surface when the coating film is dried. As a result, the bias of the binder concentration in the electrode mixture layer is reduced, and the adhesion between the current collector and the electrode mixture layer is improved.

In the fifth embodiment in which the amount of the binder is 8% by weight and the thickness of the lower layer is 125 μm (83% of the whole electrode mixture layer), the electrode mixture layer peels off in the peeling test. This is considered to be due to the non-uniformity of the binder concentration distribution due to the underlayer being too thick. However, since the electrode mixture paste is laminated and dried in two parts, the entire drying time can be shortened, and the intended object of the present invention of improving productivity can be achieved. When the amount of the binder is 8% by weight, the thickness of the lower layer is preferably 70% or less of the entire electrode mixture layer in order to improve not only productivity but also adhesion. .

On the other hand, when comparing Examples 1 to 5 and Examples 6 to 10 in which the thicknesses of the upper layer and the lower layer are the same and only the binder amount is different, the former having a binder amount of 8% by weight is 10% by weight. The discharge capacity is larger than some of the latter. This is naturally expected from the fact that the ratio of the insulator (binder) in the electrode mixture layer is small, and the electrode material increases accordingly. However, while using the mixture paste having the same binder amount, Examples 6 to 10 were compared with Comparative Example 2.
Has a larger discharge capacity. In addition, the discharge capacity tends to increase as the thickness of the lower layer decreases. The reason is,
In Examples 6 to 10 in which the electrode mixture paste is laminated and dried in two parts, the current collector and the electrode mixture layer are compared with Comparative Example 2 in which the electrode paste is laminated and dried only once. This is presumably because the adhesion between them is improved, and thus, a conductive path between the current collector and the electrode mixture layer is more securely secured. Further, in Examples 6 to 10, the reason why the discharge capacity increases when the thickness of the lower electrode mixture layer is reduced is also considered that the improvement in adhesion contributes to the improvement in discharge capacity.

As described above, it is better to increase the amount of binder in terms of adhesion, but it is preferable to decrease the amount of binder in terms of discharge capacity. Coating with a single layer as before
After drying, at least 10% by weight of the binder was required to make the current collector and the electrode mixture layer adhere to each other. However, if the electrode mixture paste is applied and dried in a plurality of times as in the present invention, the binder amount can be reduced to 8% by weight. As a result, a battery having excellent adhesion and a large discharge capacity can be manufactured. In addition, since the drying time per layer becomes shorter, the effect that the productivity is also excellent is exhibited.

<Examples 11 to 20> This example relates to a positive electrode of a so-called lithium ion type non-aqueous electrolyte secondary battery, in which the electrode mixture layer is divided into upper and lower two layers as in Examples 1 to 10. It is manufactured by laminating and drying. LiCoO2 powder as an electrode raw material powder, polyvinylidene fluoride as a binder, and 2-methyl-2 as a solvent
-Pyrrolidone was mixed to prepare two types of electrode mixture pastes in which the ratio of the binder amount to the electrode raw material was 10% by weight and 8% by weight. It is manufactured in exactly the same manner as in Examples 1 to 10 except that the current collector is an aluminum foil having a thickness of 20 μm. That is, in Comparative Examples 3 and 4, a single-layer coated positive electrode was prepared such that the thickness of the electrode mixture layer was 150 μm, and in Examples 11 to 20, the upper and lower layers were divided into upper and lower layers as shown in Table 2. A positive electrode having a thickness of the entire electrode mixture layer of 150 μm was manufactured by a drying process.

Each of these electrodes was assembled as a coin-type test cell also using metallic lithium as a counter electrode, and 1 mol / liter of lithium hexafluorophosphate was used as an electrolytic solution in a mixed solvent of ethylene carbonate and diethyl carbonate. The dissolved one was used. These test cells were charged to a constant current corresponding to a current density of 0.5 mA / cm 2 of the negative electrode plate to 4.3 V, and then discharged to 3.0 V at the same current to obtain a discharge capacity per unit weight of LiCoO 2. In addition to the examination, the same peel test as in Examples 1 to 10 was performed. The evaluation results are as shown in Table 2, and the same results as those of the negative electrode were obtained.

[0019]

[Table 2]

<Other Embodiments> The present invention is not limited to the embodiments described above and described with reference to the drawings. For example, the following embodiments are also included in the technical scope of the present invention.
Further, various modifications other than those described below can be made without departing from the scope of the invention. (1) In the above embodiment, the electrode mixture layer is formed in two layers, but is not limited to this, and may be formed in three or more layers.

(2) In the above embodiment, the electrode mixture layer having the same binder concentration as the lower layer is used as the upper layer. However, the present invention is not limited to this, and electrode mixture pastes having different concentrations may be laminated.

(3) In each of the above embodiments, the mixture paste was laminated on the current collector by the direct coater, but it is needless to say that the present invention is not limited to this. Further, the electrode materials, electrolytes, binders, or solvents shown in the respective embodiments are merely examples, and are not limited thereto. Other materials can be selected as necessary. The desired object of the present invention can be achieved by laminating and drying the current collector on a plurality of times.

Claims (3)

[Claims] 1. A method for producing an electrode for a non-aqueous electrolyte secondary battery, wherein an electrode mixture paste obtained by kneading an electrode raw material powder together with a binder and a solvent is laminated on a current collector to form an electrode mixture layer. A method for manufacturing an electrode for a non-aqueous electrolyte secondary battery, comprising laminating and drying the electrode mixture paste on the current collector a plurality of times. 2. The method for producing an electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein in each paste laminating step, an electrode mixture paste having the same composition is used. 3. Laminating and laminating the electrode mixture paste in two parts.
Drying, wherein in the first paste laminating step, an electrode mixture layer having a thickness of 10 to 70% of the total thickness of the electrode mixture layer is formed. 3. The method for producing an electrode for a non-aqueous electrolyte secondary battery according to 1 or 2.