JP2018113188A - Method for manufacturing lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a lithium ion secondary battery, by which the corrosion of a positive electrode collector plate can be prevented, and the increase in resistance in a battery arranged by use of a positive electrode plate can be suppressed.SOLUTION: A method for manufacturing a secondary battery 1 in which an electrode body 20 is encased in a battery container 10, wherein the electrode body is arranged by use of a positive electrode collector plate 22 made of aluminum and a positive electrode plate 21 having a positive electrode active material layer 23 including positive electrode active material particles including, in its composition, Liand Mn, comprises: a coating step S2 of coating the positive electrode collector plate with aqueous positive electrode paste of pH10.0 or less; a drying step S3 of drying the undried positive electrode active material layer to form the positive electrode plate; a step S4 of forming the electrode body by use of the positive electrode plate and others; a step S5 of encasing the electrode body in the battery container; a vacuum drying step S6 of evacuating the battery container containing the electrode body to dry the electrode body including the positive electrode plate under a vacuum condition; a step S7 of injecting an electrolyte solution into the battery container; and a step S9 of hermetically sealing an opening of the battery container. The vacuum drying step is executed for a length of time within 12 hours at a temperature of 60-75°C under a reduced pressure of 0.03 kPa or less in vacuum degree.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing a lithium ion secondary battery using a positive electrode plate having a positive electrode active material layer containing positive electrode active material particles containing Li ⁺ and Mn ⁴⁺ in its composition.

  In manufacturing a lithium ion secondary battery (hereinafter also simply referred to as a battery), an electrode body (assembly) in which a positive electrode plate, a negative electrode plate, and a separator are wound or stacked is accommodated in a battery case body, and then a vacuum drying apparatus is used. Then, the electrode body accommodated in the battery case body is vacuum-dried. Thereafter, an electrolytic solution is injected, sealed, and subjected to initial charge and predetermined inspection, thereby completing a battery (see Patent Documents 1 and 2).

JP 2007-227310 A Japanese Patent Laid-Open No. 2006-173974

By the way, as a positive electrode active material of a battery, a Li transition metal composite oxide containing Li ⁺ and Mn ⁴⁺ in its composition including LiNiMn spinel has been proposed. The positive electrode active material of LiNiMn spinel has an advantage that the positive electrode potential at the time of full charge can be relatively high as compared with a layered lithium metal oxide such as LiCoO ₃ .

On the other hand, from the viewpoint of environmental problems and the like, it is desired to use water as a solvent instead of a non-aqueous solvent such as NMP as a solvent contained in the positive electrode active material paste.
However, since the positive electrode active material paste containing the positive electrode active material particles and water containing Li ⁺ in the composition exhibits strong alkalinity due to the action of water and Li ^+, it is applied to a positive electrode current collector plate made of aluminum and dried. When the positive electrode active material layer is formed, the positive electrode current collector plate may be corroded by the positive electrode paste, resulting in problems such as a decrease in adhesion (adhesiveness) of the positive electrode active material layer to the positive electrode current collector plate.

Therefore, there is a problem that the positive electrode current collector plate made of coated aluminum is corroded by adding a pH adjuster such as polyacrylic acid (PAA) showing acidity to set the pH of the positive electrode active material paste to pH 10.0 or lower. It is conceivable to suppress the occurrence.
However, when the pH of the positive electrode active material paste is adjusted to pH 10.0 or lower in this way, a relatively large amount of H ⁺ is present in the solvent (water) as compared with the case where the pH is more than 10.0. . Then, due to an exchange reaction between H ⁺ in the solvent and Li ⁺ on the surface of the positive electrode active material particles, a large number of H ⁺ is attached to the surface of the positive electrode active material particles.

Further, when the positive electrode plate in this state is assembled into an electrode body and exposed to a high temperature in the vacuum drying process described above, O ions constituting the positive electrode active material are combined with H ⁺ adhering to the surface of the positive electrode active material particles. And desorbed as H ₂ O. At that time, Mn ⁴⁺ forming the active material is reduced to Mn ³⁺ on the surface of the active material particles.
However, when the Mn ions forming the active material are Mn ³⁺ on the surface of the positive electrode active material particles, the resistance of the positive electrode active material layer, and thus the battery, is increased as compared with the case of normal Mn ^4+. I understand that.

  The present invention has been made in view of such knowledge, and it is possible to prevent corrosion of a positive electrode current collector plate made of aluminum as a positive electrode plate and to suppress an increase in resistance in a battery using the positive electrode plate. A manufacturing method is provided.

The solution includes a positive electrode current collector plate made of aluminum, and a positive electrode active material layer containing positive electrode active material particles containing Li ⁺ and Mn ⁴⁺ in its composition, applied to the positive electrode current collector plate and dried. A method for producing a lithium ion secondary battery in which a positive electrode plate, a negative electrode plate, and an electrode body using a separator are hermetically accommodated in a battery container, wherein the positive electrode active material particles, the pH adjuster, and the solvent are water. An aqueous positive electrode paste having a pH of 10.0 or less is applied to the positive electrode current collector plate to form an undried positive electrode active material layer, and the undried positive electrode active material layer is dried, A drying step for forming the positive electrode plate having a positive electrode active material layer; an electrode body forming step for forming an electrode body using the positive electrode plate, the negative electrode plate, and the separator; and the electrode body in the battery container. The housing process for housing and the above A vacuum drying step of evacuating the battery body containing the polar body and vacuum-drying the electrode body including the positive electrode plate, a pouring step of injecting an electrolyte into the battery container, and the battery container The vacuum drying step is a method for producing a lithium ion secondary battery performed within 12 hours at a temperature of 60 to 75 ° C. under a reduced pressure with a vacuum degree of 0.03 kPa or less. is there.

In this manufacturing method, in the coating step, an aqueous positive electrode paste having a pH of 10.0 or less is applied to the positive electrode current collector plate to form an undried positive electrode active material layer. Therefore, the positive electrode current collector plate made of aluminum is an aqueous positive electrode. It can prevent being corroded by the paste. However, since there relatively often H ⁺ in the solvent (water), the exchange reaction between Li ⁺ on the surface of the H ⁺ and the positive electrode active material particles in a solvent, a number of the surface of the positive electrode active material particles H ⁺ Will be attached.
However, in this manufacturing method, the vacuum drying step is performed within 12 hours at a temperature of 60 to 75 ° C. under a reduced pressure with a degree of vacuum of 0.03 kPa or less. That is, when the electrode body in the battery container is vacuum-dried, the degree of vacuum is set to 0.03 kPa or less, the drying is accelerated, and the drying time is set within 12 hours. Thereby, the time of a vacuum drying process can be shortened, reducing the residual moisture amount in a positive electrode active material layer to such an extent that the gas generation by a residual moisture can be suppressed.
Moreover, in this manufacturing method, the drying temperature is set to a low 60 to 75 ° C. Thus, in order to dry at a low temperature while shortening the time required for the vacuum drying process, H ⁺ and the O ions forming the positive electrode active material adhere to the surface of the positive electrode active material particles together with the vacuum drying. By combining and desorbing as H ₂ O, it is possible to suppress the production of Mn ³⁺ by reducing Mn ⁴⁺ forming the active material on the surface of the positive electrode active material particles. And it can suppress that the resistance of a positive electrode active material layer and a battery increase.

Examples of “positive electrode active material particles containing Li ⁺ and Mn ⁴⁺ in the composition” include, for example, LiNiMn spinel. LiNiMn-based spinel is a positive electrode active material that mainly contains Li at the A site and Ni, Mn at the B site and has a spinel crystal structure. Examples thereof include Li (Ni, Mn) ₂ O ₄ .

  Examples of the “pH adjuster” include substances that exhibit acidity in a solvent (water). In addition to polymers exhibiting acidity such as polyacrylic acid that also functions as a binder, sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, etc. Inorganic acids and organic acids such as acetic acid, carboxylic acid and acrylic acid can also be used.

Further, in the water-based positive electrode paste, in addition to the positive electrode active material particles, a conductive material such as carbon black (for example, acetylene black, furnace black, ketjen black) or carbon powder such as graphite powder can be used as the solid content. . You may use together 1 type, or 2 or more types among these electrically conductive materials.
A thickener such as carboxymethyl cellulose (CMC) can also be included. As a thickener that can be included, a polymer material that is dissolved or dispersed in water can be preferably employed. Examples of the water-soluble (water-soluble) polymer material include cellulose polymers such as carboxymethyl cellulose (CMC), methyl cellulose (MC), cellulose acetate phthalate (CAP), and hydroxypropyl methyl cellulose (HPMC), and polyvinyl alcohol (PVA). And the like.

As an electrode body using a positive electrode plate, a negative electrode plate, and a separator, the form of a known electrode body can be adopted. For example, a strip-shaped positive electrode plate and a strip-shaped negative electrode plate are alternately stacked with a pair of strip-shaped separators and wound, or a plurality of positive electrode plates and a plurality of negative electrode plates are alternately sandwiched via separators. A laminated electrode body that is laminated may be mentioned.
In the vacuum drying process, the entire battery container with the electrode hole containing the electrode body is placed in a vacuum chamber, and the inside and outside of the battery container are evacuated to perform the vacuum drying process. Or the like, and the vacuum drying process can be performed with the inside of the battery container being evacuated.

In addition, in the manufacturing method of the above-mentioned lithium ion secondary battery, a vacuum drying process is the manufacturing method of the lithium ion secondary battery performed within 60 hours at the temperature of 60-70 degreeC under the pressure reduction of 0.03 kPa or less of vacuum. It is more preferable.
This is because the production of Mn ^{3+ on} the surface of the positive electrode active material particles can be reliably suppressed, and the reaction resistance of the battery can be lowered.

In addition, in the above-described method for manufacturing a lithium ion secondary battery, the vacuum drying step is performed within 12 hours at a temperature of 65 to 70 ° C. under a reduced pressure with a degree of vacuum of 0.03 kPa or less. The method is more preferable.
This is because the reaction resistance of the battery can be lowered and the amount of residual moisture in the positive electrode active material layer can be sufficiently reduced, so that problems such as gas generation due to residual moisture can be reliably suppressed.

1 is a perspective view of a lithium ion secondary battery according to an embodiment. It is a longitudinal cross-sectional view of the lithium ion secondary battery which concerns on embodiment. It is sectional drawing of the electrode body of the battery which concerns on embodiment. It is a top view of the positive electrode plate according to the embodiment. It is a top view of the negative electrode plate which concerns on embodiment. 4 is a flowchart illustrating a battery manufacturing process according to the embodiment. It is a graph which shows the relationship between the drying temperature at the time of vacuum drying, and a residual moisture content ratio. It is a graph which shows the relationship between the drying temperature at the time of vacuum drying, and reaction resistance ratio. It is a graph which shows the relationship between the vacuum degree at the time of vacuum drying, and the drying time until the residual water content ratio becomes 110%.

  Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 show a perspective view and a longitudinal sectional view of a lithium ion secondary battery 1 according to this embodiment. FIG. 3 shows a cross-sectional view of the electrode body 20. FIG. 4 shows a top view of the positive electrode plate 21. FIG. 5 shows a top view of the inner negative electrode plate 31C. In the following description, the battery thickness direction BH, the battery lateral direction CH, and the battery vertical direction DH of the battery 1 are defined as the directions shown in FIGS. 1 and 2.

  The battery 1 is a rectangular and sealed lithium ion secondary battery mounted on a vehicle such as a hybrid car, a plug-in hybrid car, or an electric car. The battery 1 includes a battery case 10, a stacked electrode body 20 accommodated therein, a positive terminal member 50 and a negative terminal member 60 supported by the battery case 10 (FIGS. 1 and 2). reference). In addition, a non-aqueous electrolyte 19 is accommodated in the battery case 10, and a part thereof is impregnated in the electrode body 20.

  Of these, the battery case 10 has a rectangular parallelepiped box shape and is made of metal (aluminum in the first embodiment). The battery case 10 is composed of a bottomed rectangular tube-shaped case main body member 11 that is open only on the upper side, and a rectangular plate-shaped case lid member 13 that is welded in a form that closes the opening of the case main body member 11. The A positive terminal member 50 made of aluminum is fixed to the case lid member 13 while being insulated from the case lid member 13. The positive electrode terminal member 50 is connected to and electrically connected to the positive electrode current collector 21m of the positive electrode plate 21 of the electrode body 20 in the battery case 10, and extends through the case lid member 13 to the outside of the battery. Further, a negative electrode terminal member 60 made of copper is fixed to the case lid member 13 while being insulated from the case lid member 13. The negative electrode terminal member 60 is connected to the negative electrode current collecting portion 31m of the negative electrode plate 31 of the electrode body 20 in the battery case 10 to be conductive, and extends through the case lid member 13 to the outside of the battery.

  The electrode body 20 (see also FIG. 3) has a substantially rectangular parallelepiped shape, the stacking direction EH (vertical direction in FIG. 3) of the electrode body 20 coincides with the battery thickness direction BH, and the electrode body lateral direction FH (in FIG. 3). , The horizontal direction) is accommodated in the battery case 10 in such a posture that the battery horizontal direction CH coincides with the electrode body vertical direction GH (see FIGS. 1 and 2) coincides with the battery vertical direction DH. In the present embodiment, among the stacking direction EH, in FIG. 3, the upper side is defined as one side EH1 in the stacking direction, and the lower side is defined as the other side EH2 in the stacking direction. Further, in FIG. 3, the left side of the electrode body lateral direction FH is defined as one lateral side FH <b> 1 and the right side is defined as the other lateral side FH <b> 2.

  This electrode body 20 includes a plurality of rectangular positive electrode plates 21 (see FIG. 4) and a plurality of rectangular negative electrode plates 31 (see FIG. 5) with a rectangular separator 41 made of a resin porous film. And alternately stacked in the stacking direction EH.

Each of the plurality of positive electrode plates 21 (see FIGS. 4 and 3) exposes a part (left side in FIG. 4) of one side FH1 in the lateral direction of the positive electrode current collector foil 22 made of a rectangular aluminum foil. Thus, the positive electrode current collector portion 21m is formed, and the positive electrode active material layers 23 and 23 are provided in a rectangular shape on both surfaces of the remaining portion (the other lateral side FH2). The positive electrode current collector 21m of each positive electrode plate 21 is bundled in the stacking direction EH (see FIG. 3) and welded to the positive electrode terminal member 50 described above. In the positive electrode plate 21, the positive electrode active material layers 23 and 23 each include, in addition to positive electrode active material particles, a conductive additive (acetylene black), a binder (polyacrylic acid), and a thickener (CMC). The positive electrode active material particles contained in the positive electrode active material layer 23 are particles of LiNiMn spinel (lithium nickel manganate, Li (Ni, Mn) ₂ O ₄ ).

  Next, the negative electrode plate 31 will be described (see FIGS. 5 and 3). The negative electrode plate 31 is divided into an uppermost negative electrode plate 31A positioned on the one side EH1 in the stacking direction, a lowermost layer negative electrode plate 31B positioned on the other side EH2 in the stacking direction, and an inner negative plate 31C positioned therebetween. First, the inner negative electrode plate 31C will be described. The inner negative electrode plate 31C (see FIG. 5) is such that a part of the other side FH2 in the lateral direction (right side in FIG. 5) of the negative electrode current collector foil 32 made of a rectangular copper foil is exposed. On the other hand, the negative electrode active material layers 33 and 33 are provided in a rectangular shape on both surfaces of the remaining portion (one side FH1 in the lateral direction) as the current collector 31m. The negative electrode active material layer 33 is formed larger over the entire circumference than the positive electrode active material layer 23 of the positive electrode plate 21 opposed via the separator 41. The negative electrode active material layer 33 includes a negative electrode active material, a binder, and a thickener. In the present embodiment, graphite particles are used as negative electrode active material particles, styrene butadiene rubber (SBR) is used as a binder, and carboxymethyl cellulose (CMC) is used as a thickener. The negative electrode active material layer 33 is provided by applying to the current collector foil 32 and drying.

  On the other hand, the uppermost layer negative electrode plate 31A (see FIG. 3) has a configuration in which the negative electrode active material layer 33 on one side EH1 in the stacking direction (upward in FIG. 3) is removed from the above-described inner negative electrode plate 31C, as indicated by a broken line. It is. Further, the lowermost layer negative electrode plate 31B (see FIG. 3) has a form in which the negative electrode active material layer 33 on the other side EH2 in the stacking direction (downward in FIG. 3) is removed from the above-described inner negative electrode plate 31C as indicated by a broken line. It is.

  The negative electrode current collector 31m of these negative electrode plates 31 (the uppermost negative electrode plate 31A, the lowermost negative electrode plate 31B, and the inner negative electrode plate 31C) is bundled in the stacking direction EH (see FIG. 3), and the negative electrode terminal member 60 described above. It is welded to.

  Next, the manufacture of the positive electrode plate 21 and the manufacture of the battery 1 will be described with reference to FIG. First, in the positive electrode paste manufacturing step S1, a positive electrode paste is manufactured. Specifically, LiNiMn spinel powder of positive electrode active material particles, CMC as a thickener, acetylene black as a conductive auxiliary agent, polyacrylic acid as a binder, and water as a solvent (dispersion medium). And kneading with a planetary mixer to produce a positive electrode paste.

  By the way, when LiNiMn spinel forming positive electrode active material particles is mixed with water as a solvent, Li ions are ionized while generating hydrogen, and the solvent itself and the positive electrode paste containing the same exceed pH 10.0 (pH = 12). .0) (strongly alkaline). When this positive electrode paste is applied to the positive electrode current collector foil 22, the resistance between the positive electrode current collector foil 22 and the positive electrode active material layer 23 may increase. Aluminum forming the positive electrode current collector foil 22 may be corroded under an alkali. In particular, corrosion is likely to occur under a strong alkali exceeding pH 10.0. For this reason, when a strong alkaline positive electrode paste is applied to the positive electrode current collector foil 22, the applied portion of the positive electrode current collector foil 22 is corroded and the surface becomes rough before the positive electrode paste is dried. In addition, due to hydrogen generated due to corrosion, the degree of adhesion between the positive electrode current collector foil 22 and the positive electrode active material layer 23 decreases, and the resistance between the positive electrode current collector foil 22 and the positive electrode active material layer 23 decreases. It is expected to rise.

On the other hand, in this embodiment, polyacrylic acid is added to the positive electrode paste as a binder. When polyacrylic acid is dispersed in water as a solvent, H ⁺ of the carboxyl group (COOH) is ionized, so that it also functions as an acidic pH adjuster. For this reason, the positive electrode paste to which this binder (pH adjuster) is added has reduced alkalinity caused by the positive electrode active material particles. In the positive electrode paste of the present embodiment, pH is 10.0 or less, specifically, pH 10.0. If this positive electrode paste is applied to the positive electrode current collector foil 22, it is possible to suppress the occurrence of problems such as a decrease in adhesion due to corrosion of the positive electrode current collector foil 22.
Therefore, in the application step S2, a positive electrode paste is applied to both surfaces of the positive electrode current collector foil 22 having a thickness of 20 μm using a coater to form an undried positive electrode active material layer.

  Further, as the drying step S3, the undried positive electrode active material layer is dried by hot air drying at 140 ° C. to form the positive electrode active material layer 23. In addition, as shown with a broken line in FIG. 6, the application | coating process S2 and the drying process S3 are repeated, the positive electrode active material layers 23 and 23 are formed on both surfaces of the positive electrode current collection foil 22, and the positive electrode plate 21 is completed.

  Thereafter, in the stacking step S4, in addition to the positive electrode plate 21, negative electrode plates 31 (the lowermost negative electrode plate 31B, the inner negative electrode plate 31C, and the uppermost negative electrode plate 31A) formed by a known method are alternately arranged via the separators 41. The stacked electrode body 20 is formed by stacking.

In the subsequent accommodating step S5, a case lid member 13 in which the positive electrode terminal member 50 and the negative electrode terminal member 60 are fixed in advance is prepared, and the positive electrode current collector 21m of each positive electrode plate 21 of the electrode body 20 is connected to the positive electrode terminal 21m. While welding the member 50, and the negative electrode current collection part 31m of each negative electrode plate 31, the negative electrode terminal member 60 is welded. And the electrode body 20 is accommodated in the case main body member 11, and the case main body member 11 and the case cover member 13 are welded airtightly.
As shown in FIGS. 1 and 2, the case lid member 13 has a liquid injection hole 13h, and the battery case 10 is not sealed at this point.

  Next, vacuum drying in the battery case 10 is performed in a vacuum drying step S6. In this vacuum drying step S6, the moisture adhering to the inner wall of the battery case 10 and the moisture adhering to or remaining in the positive electrode plate 21, the negative electrode plate 31 and the separator 41 constituting the electrode body 20 are evaporated. It is removed through the liquid hole 13h. If much moisture remains, it will cause gas generation during charging / discharging of the battery 1, and this is to suppress this.

  Specifically, the unsealed battery 1 is placed in a chamber of a vacuum dryer (not shown), the pressure inside the chamber is reduced to a predetermined vacuum level, and heated to a predetermined temperature with an infrared heater from around the chamber. Leave it alone. Accordingly, moisture (vapor) can be released and removed from the inner wall of the battery case 10 and the electrode body 20 (the positive electrode plate 21, the negative electrode plate 31, and the separator 41). In this embodiment, the inside of the chamber of the vacuum dryer was set to a vacuum degree of 0.03 kPa and a drying temperature of 60 ° C. and left for 12 hours.

Accordingly, moisture can be removed from the inner wall of the battery case 10, the negative electrode plate 31, and the separator 41, and residual moisture can also be removed from the positive electrode active material layer 23 of the positive electrode plate 21. Specifically, the residual moisture content of the positive electrode active material layer 23 of the positive electrode plate 21 is expressed as a residual moisture content ratio based on the case where the moisture content is dried at 0.03 kPa, 80 ° C., 12 hrs (Comparative Example 3 described later). And an amount corresponding to 110%.
The residual water content of the positive electrode active material layer 23 is obtained by removing the positive electrode plate 21 from the battery 1 after the vacuum drying step S6, heating a sample of 30 mm □ to 120 ° C., and using the released water content as Karl Fischer. Measured by the method.

  It has been found that when the residual moisture content of the positive electrode active material layer 23 is 110% or less as shown in the residual moisture content ratio described later, gas generation due to moisture remaining in the positive electrode active material layer 23 can be suppressed. Therefore, according to the vacuum drying step S6 of the present embodiment, gas generation due to moisture remaining in the positive electrode active material layer 23 can be suppressed.

Next, in a liquid injection step S7, a predetermined amount of the non-aqueous electrolyte 19 is injected into the battery case 10 through the liquid injection hole 13h.
Thereafter, initial charging is performed in the initial charging step S <b> 8, and the liquid injection hole 13 h is hermetically sealed using the sealing member 15 in the sealing step S <b> 9. Thus, the battery 1 is completed.

  Further, the battery resistance of the battery 1 was measured, and the reaction resistance of the battery 1 was calculated by impedance analysis using a Cole-Cole plot or the like. The size is the same as that of the battery 1 of the present embodiment, and the negative electrode plate 31 and the separator 41 are the same, but the positive electrode active material layer of the positive electrode plate was formed under drying conditions of 0.03 kPa, 80 ° C., and 12 hrs. Compared to the reaction resistance of the standard battery, the size was 84% (16% decrease).

This is because the reference battery was subjected to the vacuum drying step S6 at a relatively high temperature (80 ° C.) as described above, so that Mn ³⁺ was generated on the surface of the positive electrode active material particles, and the positive electrode active material It is considered that the reaction resistance in the layer was increased, and as a result, the reaction resistance of the battery was increased. On the other hand, in the battery 1 of this embodiment, in the vacuum drying step S6, the degree of vacuum was set to 0.03 kPa, the heating was kept at a relatively low temperature of 60 ° C., and the drying was performed for 12 hours. In addition, the elimination reaction of O ions from the positive electrode active material can be suppressed, the generation of Mn ^{3+ on} the surface of the positive electrode active material particles can be suppressed, and the reaction resistance of the battery can be increased. This is thought to be due to the suppression.

Moreover, since the degree of vacuum is set to 0.03 kPa in the vacuum drying step S6, 12 hours is sufficient for the residual water content to be 110% in the residual water content ratio, and the time required for the vacuum drying step S6 can be shortened. In addition to this, the time during which the positive electrode plate 21 is heated can be reduced, the period during which Mn ³⁺ is generated can be shortened, and the amount of Mn ³⁺ generated can be suppressed.

(Examples and Comparative Examples)
Next, the results of investigating the difference in reaction resistance and the difference in the residual water content ratio in the positive electrode active material layer 23 when the drying temperature in the vacuum drying step S6 is changed will be described (Table 1, FIG. 7, FIG. 8). reference).
Here, the unsealed batteries (Comparative Examples 1 to 5 and Examples 1 to 4) manufactured in the same manner as the above-described embodiment up to the housing process S5 are manufactured by changing only the drying temperature in the vacuum drying process S6. (Vacuum degree 0.03 kPa, drying time 12 hours) For each battery, the battery resistance was measured to calculate the reaction resistance, and the residual moisture content of the positive electrode active material layer 23 after the vacuum drying step S6 was measured. The residual water content ratio was calculated. The results are shown in Table 1, FIG. 7 and FIG. The battery 1 of the above-described embodiment corresponds to the battery of Example 1.

  In Table 1, the reaction resistance of each example is the same as that of the battery 1 of the above-described embodiment, and the negative electrode plate 31 and the separator 41 are the same, but the positive electrode active material layer of the positive electrode plate is 0.03 kPa, 80 ° C., The reaction resistance ratio of the battery of Comparative Example 3 formed by vacuum drying at 12 hrs was displayed as a reference (100%) reaction resistance ratio (see also FIG. 7).

  Also, in Table 1, as in the embodiment, the residual moisture content of the positive electrode active material layer 23 is obtained by removing the positive electrode plate 21 from the battery 1 after the vacuum drying step S6 and heating a sample having a size of 30 mm □ to 120 ° C. The amount of water released was measured by the Karl Fischer method. Furthermore, the residual moisture content in each example was also a ratio of the residual moisture content based on the residual moisture content of the positive electrode plate used in the battery of Comparative Example 3 that was vacuum-dried at 0.03 kPa, 80 ° C., 12 hrs (100%). Displayed (see also FIG. 7).

First, the reaction resistance ratio of each example shows that when the drying temperature exceeds 75 ° C., the reaction resistance ratio increases almost linearly with the drying temperature. On the other hand, when the drying temperature is 75 ° C. or less, the reaction resistance is almost the same regardless of the drying temperature (see also FIG. 8).
As described above, in the positive electrode active material layer 23 of the positive electrode plate 21 dried in the drying step S3, H ⁺ in the solvent (water) and Li ^{+ on} the surface of the positive electrode active material particles are formed on the surface of the positive electrode active material particles. Due to the exchange reaction, a large number of H ⁺ is attached to the surface of the positive electrode active material particles.

For this reason, when the drying temperature exceeds 75 ° C., which is relatively high, O ions constituting the positive electrode active material are combined with H ⁺ adhering to the surface of the positive electrode active material particles together with vacuum drying and H _2. By desorbing as O, Mn ⁴⁺ forming the active material is reduced to produce Mn ³⁺ . Since Mn ³⁺ has lower conductivity than Mn ⁴⁺ , the reaction resistance is increased on the surface of the positive electrode active material particles, and it is considered that the reaction resistance of the positive electrode active material layer 23 and thus the reaction resistance of the battery is increased. . It can also be understood that the above-described reaction proceeds as the temperature increases.
If the drying temperature is 75 ° C. or lower, the desorption of O ions is suppressed during vacuum drying, so that the generation of Mn ³⁺ is sufficiently suppressed. For this reason, it is considered that an increase in the reaction resistance of the positive electrode active material layer 23 and, consequently, the reaction resistance of the battery could be suppressed. Further, if the drying temperature is 75 ° C. or lower, the elimination reaction of O ions can be suppressed. Therefore, in Examples 1 to 4 where the drying temperature is 75 ° C. or lower, the reaction resistance ratio is considered to be substantially the same.
From these, it can be understood that the drying temperature is preferably 75 ° C. or lower. It can also be seen that when the drying temperature is 65 to 70 ° C., the elimination reaction of O ions can be reliably suppressed and the reaction resistance of the battery can be further reduced.

Next, the residual moisture content ratio will be examined. When the drying temperature is in the range of 65 to 75 ° C. (Examples 2 to 4), the residual moisture content ratio does not change much. Considering together the relationship between the degree of vacuum and the residual moisture content described below, when the drying temperature is in the range of 65 to 75 ° C., the influence of the drying temperature on the residual moisture content is relatively small and the influence of the vacuum degree is large. I understand. It can also be seen that if the drying temperature is set to 65 ° C. or higher, almost all of the water that can be removed in an environment with a degree of vacuum of 0.03 kPa can be removed.
On the other hand, when the drying temperature is less than 65 ° C. (Example 1, Comparative Examples 1 and 2), it can be seen that the residual moisture content increases rapidly as the drying temperature decreases. This is probably because the evaporation of residual moisture is suppressed when the drying temperature is low.
In addition, if the residual water content ratio of the positive electrode active material layer 23 exceeds 110%, gas may be generated due to the reaction between the non-aqueous electrolyte and water after the injection.
From these, it can be seen that the drying temperature is preferably 60 ° C. or higher. Furthermore, it can be understood that when the drying temperature is set to 65 ° C. or higher, a change in the amount of residual moisture due to variation in the drying temperature can be suppressed, which is more preferable.

In the judgment column of Table 1, “○” marks indicate those having a residual moisture content ratio of 110% or less and less than 100% reaction resistance ratio, and “x” marks indicate other things.
As can be seen from the determination column, when the degree of vacuum was 0.03 kPa and the drying time was 12 hours, “◯” was determined when the drying temperature was in the range of 60 to 75 ° C. (Examples 1 to 4). In this range, it is possible to suppress the generation of Mn ^{3+ on} the surface of the positive electrode active material particles, and it is possible to suppress an increase in battery resistance.
Furthermore, it can be understood that the drying temperature is preferably 60 to 70 ° C. In this way, the production of Mn ^{3+ on} the surface of the positive electrode active material particles can be reliably suppressed, and the reaction resistance of the battery can be further lowered.
Furthermore, it can be understood that the drying temperature is particularly preferably 65 to 70 ° C. This is because the reaction resistance of the battery can be lowered as described above, and the amount of residual moisture in the positive electrode active material layer can be sufficiently reduced, and problems such as gas generation due to residual moisture can be reliably suppressed.

(Vacuum level and drying time)
Next, the results of investigating the drying time until the residual water content in the positive electrode active material layer 23 reaches a predetermined amount when the degree of vacuum is changed will be described (see Table 2 and FIG. 9).
Also here, an unsealed battery manufactured in the same manner as in the previous embodiment is prepared up to the housing step S5, the drying temperature is set to 75 ° C. or 60 ° C., and the degree of vacuum is varied to make the vacuum drying step S6. Then, the residual moisture content of the positive electrode active material layer 23 after this vacuum drying step S6 was measured to obtain a drying time in which the residual moisture content ratio was 110%. The results are shown in Table 2 and FIG. In addition, the battery 1 of the embodiment described above corresponds to an example in which the residual water content ratio becomes 110% after a degree of vacuum of 0.03 kPa, a drying temperature of 60 ° C., and a drying time of 12 hours.

As can be understood from Table 2 and FIG. 9, the drying time until the residual moisture content ratio becomes 110% is higher as the degree of vacuum is higher (the numerical value is smaller) in both cases where the drying temperature is 75 ° C. and 60 ° C. It can be seen that it can be shortened.
Therefore, in Table 2, “○” marks indicate that the drying time until the residual water content ratio reaches 110% is within 12 hours, and “X” marks indicate that it takes longer than this. According to Table 2 and FIG. 9, when the drying temperature is 75 ° C. or 60 ° C., if the degree of vacuum is 0.03 kPa or less, the drying time until the residual moisture content ratio becomes 110% is 12 hours. It can be seen within.

However, the higher the degree of vacuum, the higher the cost because it requires a high-performance vacuum pump and the like, and it takes time to reach the target degree of vacuum.
Therefore, it can be seen that if the drying time is 12 hours or less, the degree of vacuum is preferably 0.03 kPa regardless of whether the drying temperature is 75 ° C. or 60 ° C.

  In addition, when the case where the drying temperature is 75 ° C. and the drying temperature is 60 ° C. is compared, it can always be seen that the drying time can be shortened when the drying temperature is 75 ° C. This is because, in addition to the degree of vacuum, the drying temperature is a factor in the removal of moisture remaining in the positive electrode active material layer 23, and the higher the drying temperature, the easier it is to evaporate.

In the above, the present invention has been described with reference to the embodiments and examples. However, the present invention is not limited to the above-described embodiments and the like, and can be applied with appropriate modifications without departing from the gist thereof. Not too long.
In the battery 1 of the embodiment, an example in which a stacked electrode body is used as the electrode body 20 is shown. However, the present invention can also be applied to the manufacture of a wound battery containing a belt-shaped positive electrode plate, a negative electrode plate, and a wound electrode body wound with a separator.

1 Battery 10 Battery Case (Battery Container)
19 Non-aqueous electrolyte 20 Electrode body 21 Positive electrode plate 22 Positive electrode current collector foil (positive electrode current collector plate)
23 positive electrode active material layer 31 negative electrode plate 41 separator S1 positive electrode paste preparation step S2 coating step S3 drying step S4 laminating step (electrode body forming step)
S5 Accommodation process S6 Vacuum drying process S7 Injection process S8 Initial charging process S9 Sealing process

Claims (1)

Positive electrode current collector plate made of aluminum, and positive electrode plate having a positive electrode active material layer containing positive electrode active material particles containing Li ⁺ and Mn ⁴⁺ in its composition, applied to the positive electrode current collector plate and dried, and negative electrode A method for producing a lithium ion secondary battery in which a plate and an electrode body using a separator are hermetically accommodated in a battery container,
An application step of forming an undried positive electrode active material layer by applying an aqueous positive electrode paste having a pH of 10.0 or less, including water as the positive electrode active material particles, a pH adjuster and a solvent, to the positive electrode current collector plate; ,
Drying the undried positive electrode active material layer to form the positive electrode plate having the positive electrode active material layer;
An electrode body forming step of forming an electrode body using the positive electrode plate, the negative electrode plate, and the separator;
A housing step of housing the electrode body in the battery container;
A vacuum drying step of evacuating the battery body containing the electrode body and vacuum drying the electrode body including the positive electrode plate;
A liquid injection step of injecting a non-aqueous electrolyte into the battery container;
A sealing step of sealing the battery container in an airtight manner,
The vacuum drying step
A method for producing a lithium ion secondary battery, which is carried out at a temperature of 60 to 75 ° C. within 12 hours under a reduced pressure of a vacuum degree of 0.03 kPa or less.

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