JP2007103134A - Lithium ion secondary battery and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery having a high output and high reliability, as well as its manufacturing method. <P>SOLUTION: The lithium ion secondary battery 100 is provided with a cathode active substance 153 and a cathode 155 composed of a high specific surface area carbon material 154 having a specific surface area of 100m<SP>2</SP>/g or more. A surface of the high specific surface area carbon material 154 is covered by carbonate 158. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a lithium ion secondary battery and a method for manufacturing the same.

  Lithium ion secondary batteries are attracting attention as power sources for portable devices and portable devices, and as power sources for electric vehicles and hybrid vehicles. However, in a lithium ion secondary battery, when charging / discharging is repeated or overcharged, a decomposition reaction of the electrolytic solution occurs on the surface of the positive electrode, and the surface of the positive electrode is covered with a compound generated by this reaction. There is a problem. With this coating, the IV resistance value (internal resistance) of the battery increases, and the output characteristics of the battery deteriorate. In recent years, various lithium ion secondary batteries and manufacturing methods thereof have been proposed in order to solve such problems (see, for example, Patent Documents 1 and 2).

Japanese Patent Laid-Open No. 7-245107 JP 2003-92146 A

  Patent Document 1 proposes a lithium ion secondary battery using a positive electrode active material in which the surface of lithium nickelate is coated with lithium carbonate. By covering the surface of the lithium nickelate with lithium carbonate, the contact surface between the lithium nickelate and the electrolytic solution is reduced, and the formation of a coating film caused by the decomposition reaction of the electrolytic solution is suppressed. Specifically, by leaving the baked lithium nickelate in a carbon dioxide gas atmosphere at 150 ° C. for 2 to 3 minutes, or by leaving the lithium nickelate in air at 200 ° C. for 10 minutes, The surface of is covered with lithium carbonate.

  Moreover, in patent document 2, while using spinel type lithium manganate as a positive electrode active material, the electrolyte solution which dissolved the carbon dioxide gas is inject | poured in a battery case. And after pouring, the film of the lithium carbonate produced | generated by reaction of the carbon dioxide gas dissolved in electrolyte solution and electrolyte solution is provided on the surface of spinel type lithium manganate. As a result, the contact surface between the spinel type lithium manganate and the electrolytic solution is reduced to suppress the decomposition reaction of the electrolytic solution.

However, in recent years, there has been an increasing demand for higher output for lithium ion secondary batteries, and the lithium ion secondary battery proposed in Patent Document 1 and Patent Document 2 and the manufacturing method thereof have met the demand. I couldn't respond.
This invention is made | formed in view of this present condition, Comprising: It aims at providing the high output and highly reliable lithium ion secondary battery, and a manufacturing method.

The solution is a lithium ion secondary battery comprising a positive electrode having a positive electrode active material and a high specific surface area carbon material having a specific surface area of 100 m ² / g or more, wherein the high specific surface area carbon material comprises carbonic acid. It is a lithium ion secondary battery whose surface is coated with a salt.

The positive electrode of the lithium ion secondary battery of the present invention has a high specific surface area carbon material having a specific surface area of 100 m ² / g or more. For this reason, the lithium ion secondary battery of this invention turns into a high output lithium ion secondary battery.

Moreover, the surface of the high specific surface area carbon material is coated with carbonate. Thus, by covering the surface of the high specific surface area carbon material with a carbonate (such as lithium carbonate), the contact between the high specific surface area carbon material and the electrolytic solution can be suppressed, and the decomposition reaction of the electrolytic solution can be suppressed. it can. Thereby, since generation | occurrence | production of the gas accompanying the decomposition reaction of electrolyte solution can be suppressed, it becomes a reliable battery. Furthermore, it can suppress that the film of the compound produced | generated by the decomposition reaction of electrolyte solution is formed in the positive electrode surface. Thereby, since the raise of IV resistance value (internal resistance) of a battery can also be suppressed, the fall of the output characteristic of a battery can also be suppressed.
As described above, the lithium ion secondary battery of the present invention is a lithium ion secondary battery with high output and high reliability.

Examples of the positive electrode active material include a LiNiO ₂ -based positive electrode active material and a LiCoO ₂ -based positive electrode active material. Examples of the LiNiO ₂ positive electrode active material include LiNiO ₂ and LiNi _0.81 Co _0.16 Al _0.03 O _{2 in} which a part of Ni is substituted with Co and Al. In addition, a material in which a part of Ni is substituted with at least one metal element selected from Mg, Ti, Cr, Mn, Fe, Cu, Zn, Ga, and Nb can be exemplified. As the positive electrode active material LiCoO ₂ system, in addition to LiCoO _2, the ratio of Li and Co (Li / Co) can be exemplified larger composition material than 1.
Also, as the positive electrode active material, it is also possible to use a material based on LiMnO ₂ (positive electrode active material LiMnO ₂ system).

  Further, the high specific surface area carbon material may be mixed in the positive electrode as a single high specific surface area carbon material separately from the positive electrode active material, or may be included in a form covering the surface of the positive electrode active material. Further, the surface of the positive electrode active material may be covered with a high specific surface area carbon material, and the high specific surface area carbon material may be separately mixed in the positive electrode.

  Furthermore, in the above lithium ion secondary battery, the positive electrode may be a lithium ion secondary battery in which at least a part of the high specific surface area carbon material covers the surface of the positive electrode active material.

In the positive electrode of the lithium ion secondary battery of the present invention, the surface of the positive electrode active material is coated with at least a part of the high specific surface area carbon material having a specific surface area of 100 m ² / g or more. Thus, by covering the surface of the positive electrode active material with the high specific surface area carbon material having a specific surface area of 100 m ² / g or more, the output characteristics of the battery can be particularly improved.

Moreover, as described above, the surface of the high specific surface area carbon material is coated with carbonate. That is, not only the surface of the high specific surface area carbon material that is not coated with the positive electrode active material but also the surface of the high specific surface area carbon material that covers the positive electrode active material is coated with the carbonate. Thereby, since generation | occurrence | production of the gas accompanying the decomposition reaction of electrolyte solution can be suppressed, it becomes a reliable battery. Furthermore, it can suppress that the film of the compound produced | generated by the decomposition reaction of electrolyte solution is formed in the positive electrode surface. Thereby, since the raise of IV resistance value (internal resistance) of a battery can also be suppressed, the fall of the output characteristic of a battery can also be suppressed.
As described above, the lithium ion secondary battery of the present invention is a lithium ion secondary battery with higher output and higher reliability.

  Furthermore, in the above lithium ion secondary battery, the positive electrode includes carbonate in an amount such that the weight of carbonate ions contained in the carbonate is 5 wt% or more based on the weight of the high specific surface area carbon material. A lithium ion secondary battery is preferably included.

  In the lithium ion secondary battery of the present invention, the surface of the high specific surface area carbon material is covered with carbonate in an amount that makes the weight of the carbonate ions 5 wt% or more based on the weight of the high specific surface area carbon material. Thereby, contact with a high specific surface area carbon material and electrolyte solution can be suppressed appropriately, and decomposition reaction of electrolyte solution can be controlled.

  Furthermore, in the above lithium ion secondary battery, the positive electrode has an amount such that the weight of carbonate ions contained in the carbonate is 5 wt% or more and 30 wt% or less based on the weight of the high specific surface area carbon material. A lithium ion secondary battery containing carbonate is preferable.

As the carbonate covering the carbon material is increased, the decomposition reaction of the electrolytic solution can be suppressed. However, if the amount of the carbonate covering the carbon material is excessively increased, the IV resistance value (internal resistance) is greatly increased by the carbonate, There is a risk of deteriorating the output characteristics. On the other hand, in the lithium ion secondary battery of the present invention, the amount of carbonate covering the high specific surface area carbon material is suppressed to an amount where the carbonate ion is 30 wt% or less of the weight of the high specific surface area carbon material. Yes. Thereby, the raise of IV resistance value (internal resistance) by carbonate can be suppressed.
Therefore, the lithium ion secondary battery of the present invention is a lithium ion secondary battery with high output and high reliability.

  Furthermore, in the above lithium ion secondary battery, the positive electrode has an amount such that the weight of carbonate ions contained in the carbonate is 10 wt% or more and 25 wt% or less based on the weight of the high specific surface area carbon material. A lithium ion secondary battery containing carbonate is preferable.

In the lithium ion secondary battery of the present invention, the surface of the high specific surface area carbon material is coated with carbonate in an amount that makes the weight of the carbonate ions 10 wt% or more based on the weight of the high specific surface area carbon material. Thereby, contact with a high specific surface area carbon material and electrolyte solution can be suppressed further, and decomposition reaction of electrolyte solution can be controlled.
In addition, the amount of carbonate covering the high specific surface area carbon material is suppressed to an amount such that the carbonate ions are 25 wt% or less of the weight of the high specific surface area carbon material. Thereby, the raise of IV resistance value (internal resistance) by carbonate can be suppressed further.
Therefore, the lithium ion secondary battery of the present invention is a lithium ion secondary battery that is particularly high output and highly reliable.

Another solution is a method for manufacturing a lithium ion secondary battery, which is a positive electrode active material, a high specific surface area carbon material having a specific surface area of 100 m ² / g or more, a positive electrode material containing an aqueous binder resin, water, A paste preparation step for preparing a paste containing an alkali compound generated by the reaction of the positive electrode active material and water, and a paste containing a cured product obtained by drying and curing the paste or a gas containing CO ₂ This is a method for producing a lithium ion secondary battery comprising a carbonate production step in which the alkali compound and CO ₂ are reacted by being exposed to an atmosphere to produce carbonate on the surface of the positive electrode material.

In the manufacturing method of the present invention, in the paste preparation step, a positive electrode active material, a high specific surface area carbon material having a specific surface area of 100 m ² / g or more, and a positive electrode material containing an aqueous binder resin and water are kneaded, and paste Is made. At this time, an alkaline compound, for example, a metal hydroxide (LiOH or the like) is generated by the reaction between the positive electrode active material and water, and therefore the alkali compound (LiOH or the like) is contained in the paste.

Furthermore, the carbonate generating step, the paste, by exposure to a gas atmosphere containing CO _2, an alkaline compound in paste (LiOH, etc.) is reacted with CO _2, (such as Li ₂ CO ₃₎ carbonate Can be generated. Thereby, the surface of a positive electrode material (a positive electrode active material or a high specific surface area carbon material) can be coat | covered with carbonate.

Moreover, since the paste is obtained by kneading the positive electrode material and water, the alkali compound (LiOH or the like) exists over the entire surface of the positive electrode material. In particular, many alkali compounds (such as LiOH) adhere to the surface of a high specific surface area carbon material having a large specific surface area. By exposing such paste to a gas atmosphere containing CO ₂ , the entire surface of the positive electrode material (positive electrode active material or high specific surface area carbon material), especially the surface of the high specific surface area carbon material, is covered with carbonate. can do.

Thereby, a contact with a positive electrode material and electrolyte solution, especially a contact with a high specific surface area carbon material and electrolyte solution can be suppressed, and the decomposition reaction of electrolyte solution can be suppressed. For this reason, generation | occurrence | production of the gas accompanying the decomposition reaction of electrolyte solution can be suppressed. Furthermore, since it can suppress that the film of the compound accompanying the decomposition reaction of the electrolytic solution is formed on the positive electrode surface, an increase in the IV resistance value (internal resistance) of the battery can also be suppressed.
Therefore, according to the manufacturing method of the present invention, a lithium ion secondary battery with high output and high reliability can be manufactured.

In addition, the paste may be exposed to a gas atmosphere containing CO ₂ in a state of being applied to the surface of the positive electrode substrate (which may be dried and cured thereafter), or before being applied to the surface of the positive electrode substrate. In addition, the paste alone may be exposed to a gas atmosphere containing CO ₂ .
Moreover, the high specific surface area carbon material may be mixed in the paste as a single high specific surface area carbon material separately from the positive electrode active material, or may be included in a form covering the surface of the positive electrode active material. Further, the surface of the positive electrode active material may be coated with a high specific surface area carbon material, and a single high specific surface area carbon material may be separately mixed in the paste.

Furthermore, it is a manufacturing method of said lithium ion secondary battery, Comprising: It has the application | coating process which apply | coats the said paste to a positive electrode base material, The said paste apply | coated to the said positive electrode base material in the said carbonate production | generation process, or A cured product obtained by drying and curing the paste applied to the positive electrode substrate may be a method for producing a lithium ion secondary battery in which the cured product is exposed to a gas atmosphere containing CO ₂ .

In the production method of the present invention, in the carbonate production step, the paste applied to the positive electrode substrate or the cured product obtained by drying and curing the paste applied to the positive electrode substrate is exposed to a gas atmosphere containing CO _2. ing. Thereby, the positive electrode by which the surface of a high specific surface area carbon material is coat | covered with carbonate can be produced appropriately and efficiently.

Alternatively, a method of preparing the lithium ion secondary battery, in the carbonate production step, the paste, by exposure to a gas atmosphere containing CO _2, by reacting with the alkali compound and CO _2, A method for producing a lithium ion secondary battery comprising a coating step in which a carbonate formed on the surface of the positive electrode material and a paste formed on the surface of the positive electrode material is applied to the positive electrode substrate is preferable. .

In the production method of the present invention, in the carbonate generation step, the paste is exposed to a gas atmosphere containing CO ₂ to generate carbonate on the surface of the positive electrode material, and then in the coating step, carbonate is applied to the surface of the positive electrode material. The produced paste is applied to the positive electrode substrate. By producing the positive electrode in such a procedure, corrosion of the positive electrode substrate (for example, aluminum foil) can be suppressed.

That is, since the paste produced in the paste production process contains a large amount of alkali compounds (such as LiOH), it becomes alkaline (pH of about 10 to 11). Therefore, when an alkaline paste is applied to the positive electrode substrate, the positive electrode substrate may be corroded. In contrast, the alkaline paste can be neutralized by exposing only the paste to a gas containing CO ₂ before applying the paste to the positive electrode substrate as in the production method of the present invention. For this reason, if this paste is subsequently applied to a positive electrode substrate (such as an aluminum foil), corrosion of the positive electrode substrate can be prevented.

  Furthermore, in any one of the above-described methods for producing a lithium ion secondary battery, the positive electrode is formed by covering at least a part of the high specific surface area carbon material with a surface of the positive electrode active material, and generating the carbonate. In the process, a method for producing a lithium ion secondary battery in which the surface of the high specific surface area carbon material is coated with the carbonate may be used.

  The surface of the positive electrode active material used in the production method of the present invention is coated with a high specific surface area carbon material. Thus, the output characteristic of a battery can be improved by using the positive electrode active material coat | covered with the high specific surface area carbon material.

In addition, in the carbonate generation step, as described above, the paste formed by kneading the positive electrode material and water, or the cured product thereof, is exposed to a gas atmosphere containing CO ₂ . As a result, not only the surface of the high specific surface area carbon material that does not cover the surface of the positive electrode active material but also the surface of the high specific surface area carbon material that covers the surface of the positive electrode active material are appropriately coated with carbonate. Can be coated. Thereby, since contact with a high specific surface area carbon material and electrolyte solution can be controlled, decomposition reaction of electrolyte solution can be controlled.
Therefore, according to the manufacturing method of the present invention, a lithium ion secondary battery with high output and high reliability can be manufactured.

Furthermore, in any one of the above-described methods for manufacturing a lithium ion secondary battery, the positive electrode active material includes at least one of a LiNiO ₂ -based positive electrode active material and a LiCoO ₂ -based positive electrode active material. A battery manufacturing method is preferable.

The LiNiO ₂ -based positive electrode active material and the LiCoO ₂ -based positive electrode active material are particularly likely to generate LiOH by reaction with water. Therefore, by using a positive electrode active material containing at least one of a LiNiO ₂ -based positive electrode active material and a LiCoO ₂ -based positive electrode active material, LiOH can be appropriately attached to the surface of the positive electrode material in the paste. . Thus, in the carbonate production step, it is possible to coat the Li ₂ CO ₃ to the surface of the cathode material.

Examples of the LiNiO ₂ positive electrode active material include LiNiO ₂ and LiNi _0.81 Co _0.16 Al _0.03 O _{2 in} which a part of Ni is substituted with Co and Al. In addition, a material in which a part of Ni is substituted with at least one metal element selected from Mg, Ti, Cr, Mn, Fe, Cu, Zn, Ga, and Nb can be exemplified. As the positive electrode active material LiCoO ₂ system, in addition to LiCoO _2, the ratio of Li and Co (Li / Co) can be exemplified larger composition material than 1.

Next, embodiments of the present invention will be described with reference to the drawings.
(Example)
First, the lithium ion secondary battery 100 according to the present embodiment will be described. As shown in FIG. 1, the lithium ion secondary battery 100 is a rectangular sealed battery including a rectangular parallelepiped battery case 110, a positive electrode terminal 120, and a negative electrode terminal 130.
The battery case 110 is made of metal, and includes a rectangular housing portion 111 that forms a rectangular parallelepiped housing space, and a metal lid portion 112. A wound body 150, a positive current collecting member 122, a negative current collecting member 132, and the like are accommodated in the battery case 110 (rectangular accommodation portion 111). The positive electrode current collecting member 122 and the negative electrode current collecting member 132 are elongated metal members, and are connected to the positive electrode terminal 120 and the negative electrode terminal 130, respectively.

  The wound body 150 is an oblong cross-section, and is a flat wound body formed by winding a sheet-like positive electrode 155, negative electrode 156, and separator 157. The wound body 150 is positioned at one end portion (right end portion in FIG. 1) in the axial direction (left and right direction in FIG. 1), and a positive electrode wound portion 155b in which only a part of the positive electrode 155 overlaps in a spiral shape, It is located at the other end (left end in FIG. 1), and has a negative electrode winding portion 156b in which only a part of the negative electrode 156 overlaps in a spiral shape. A positive electrode mixture containing a positive electrode active material is applied to the positive electrode 155 at a portion other than the positive electrode winding portion 155b. Similarly, the negative electrode 156 is coated with a negative electrode mixture containing a negative electrode active material at portions other than the negative electrode winding portion 156b.

Here, the positive electrode 155 will be described in detail with reference to FIG. As shown in FIG. 2, the positive electrode 155 includes a positive electrode base material 151 made of an aluminum foil, and a positive electrode mixture 152 applied to the surface of the positive electrode base material 151. The positive electrode mixture 152 contains a positive electrode active material 153 (in this embodiment, LiNi _0.81 Co _0.16 Al _0.03 O ₂ ). The surface of the positive electrode active material 153 is covered with a high specific surface area carbon material 154 (in this embodiment, ketjen black, specific surface area 1370 m ² / g). Further, the surface of the high specific surface area carbon material 154 is covered with a carbonate 158 (Li ₂ CO ₃ or the like).

Further, the positive electrode mixture 152 includes a high specific surface area carbon material 160 (active carbon in this example, specific surface area 1000 m ² / g) and a low specific surface area carbon material 159 (in this example) that do not cover the positive electrode active material 153. Acetylene black, specific surface area of 40 m ² / g) and a binder resin (not shown) (CMC, PTFE in this embodiment). These surfaces are also coated with carbonate 158 (such as Li ₂ CO ₃ ). Thus, the positive electrode 155 of the present example is a positive electrode in which the high specific surface area carbon materials 154 and 160 included therein are coated with a carbonate (Li ₂ CO ₃ or the like).

Next, the manufacturing method of the lithium ion secondary battery 100 of a present Example is demonstrated.
(Production of positive electrode)
First, positive electrode active material 153 (LiNi _0.81 Co _0.16 Al _0.03 O ₂ ) 84 wt%, high specific surface area carbon material 154 (Ketjen Black, specific surface area 1370 m ² / g) 4 wt%, high specific surface area carbon material 160 (activated carbon) Specific surface area 1000 m ² / g) 3 wt%, low specific surface area carbon material 159 (acetylene black, specific surface area 40 m ² / g) 6 wt%, CMC (binder resin) 2 wt%, PTFE (binder resin) 1 wt% The positive electrode material which consists of was produced.

  Specifically, as shown in FIG. 3, first, in the carbon coating step, the high specific surface area carbon material 154 was formed on the surface of the positive electrode active material 153 by using the high specific surface area carbon material 154 for 4 wt%. . Specifically, the surface of the positive electrode active material 153 was coated with the high specific surface area carbon material 154 by mechanochemical treatment using a known mechanofusion apparatus. Next, the positive electrode active material 153 coated with the high specific surface area carbon material 154, the high specific surface area carbon material 160 for 3 wt%, the low specific surface area carbon material 159 for 6 wt%, the CMC for 2 wt%, and 1 wt% Mineral PTFE was mixed to obtain a positive electrode material.

  Subsequently, it progressed to the paste preparation process, the positive electrode material obtained as mentioned above and water were knead | mixed, and the paste was produced. Subsequently, it progressed to the application | coating process and this paste was apply | coated to the surface of the positive electrode base material 151 (aluminum foil).

By the way, the paste contains an alkali compound (LiOH or the like) generated by a reaction between the positive electrode active material 153 (LiNi _0.81 Co _0.16 Al _0.03 O ₂ ) and water. In particular, since this paste is obtained by kneading a positive electrode material and water, an alkali compound (such as LiOH) is present over the entire surface of the positive electrode material. In particular, in this example, a LiNiO ₂ positive electrode active material (specifically, LiNi _0.81 Co _0.16 Al _0.03 O ₂ ) is used as the positive electrode active material. Since the LiNiO ₂ positive electrode active material easily generates LiOH by reaction with water, in this embodiment, a sufficient amount of LiOH can be attached to the surface of the positive electrode material in the paste.

Next, the positive electrode base material 151 to which the paste was applied was pressed and pressed to obtain a positive electrode sheet. Subsequently, this positive electrode sheet was vacuum-dried at 120 ° C. for 8 hours, and then cooled. Next, the process proceeds to a carbonate production step, and this positive electrode sheet was left for 1 hour in a chamber filled with a gas containing CO ₂ (specifically, a mixed gas of CO ₂ and N ₂ ). This makes it possible to the surface of the cathode material (such as high specific surface area carbon material), to generate a carbonate 158 (such as Li ₂ CO _3). Specifically, the entire surface of the positive electrode material (such as a high specific surface area carbon material) is covered with carbonate 158 by reacting an alkali compound (such as LiOH) existing over the entire surface of the positive electrode material with CO _2. can do.

In this example, the positive electrode sheet was placed in each of the chambers in which the CO ₂ concentration was changed to five types of 0.03%, 3%, 10%, 50%, and 99%, and left for 1 hour. did. In this manner, five types of positive electrodes 155 (referred to as positive electrode samples A1 to A5) with different production amounts (covering amounts) of carbonate 158 were obtained. Here, the CO ₂ concentration of 0.03% is a CO ₂ concentration equivalent to air (atmosphere). Therefore, the positive electrode (positive electrode sample A1) obtained by leaving in a chamber with a CO ₂ concentration of 0.03% for 1 hour is equivalent to the positive electrode obtained by leaving in air (atmosphere) for 1 hour. That is, the positive electrode sample A1 is equivalent to the positive electrode manufactured without being placed in a chamber filled with a gas containing CO ₂ (without performing a carbonate generation step).

(Production of battery)
Moreover, the paste which mixed the negative electrode active material (carbon powder) and binder resin was apply | coated to the surface of a negative electrode base material (copper foil), the press work was performed, and the negative electrode 156 was produced. Subsequently, the positive electrode 155, the negative electrode 156, and the separator 157 were laminated | stacked, this was wound, and the flat winding body 150 with a cross-sectional oval shape was formed. Next, the flat wound body 150 was connected to the external terminals (the positive electrode terminal 120 and the negative electrode terminal 130) and was accommodated in the rectangular accommodating portion 111. Thereafter, as shown in FIG. 1, the rectangular housing part 111 and the lid body 112 were welded to seal the battery case 110. Next, after pouring an electrolyte through a liquid injection port (not shown) provided in the lid 112, the liquid injection port is sealed, whereby the lithium ion secondary battery 100 of this embodiment is completed. In this example, five types of lithium ion secondary batteries (referred to as battery samples B1 to B5) each including positive electrode samples A1 to A5 were manufactured as positive electrodes.

Next, the ratio of carbonate ions (CO ₃ ²⁻ ) of carbonate contained in the positive electrode samples A1 to A5 was detected. Specifically, 0.1 g of the positive electrode mixture was scraped from the positive electrode samples A1 to A5 and dissolved in 0.1 liter of pure water. Next, this aqueous solution was filtered through a membrane filter having a pore size of 0.22 μm, 100 ml of the filtrate was injected into an ion chromatography apparatus, and the carbonate ion (CO ₃ ²⁻ ) concentration was measured.

Further, based on the measured carbonate ion concentration, the weight ratio of carbonate ions (CO ₃ ²⁻ ) based on the weight of the high specific surface area carbon material was calculated, and this was defined as the carbonate ion amount x (wt%). Specifically, since the positive electrode mixtures of the positive electrode samples A1 to A5 all contain 7 wt% of the high specific surface area carbon material, the weight ratio of carbonate ions based on the weight of the positive electrode mixture is calculated. By dividing this value by 0.07, the carbonate ion amount x (wt%) can be obtained. The results are shown in Table 1.

  In this example, DX-320 manufactured by Dionex was used as the ion chromatography apparatus. The column used was a weakly acidic column and the detector used was an electrical conductivity detector. Moreover, 0.3 mmol / liter octanesulfonic acid was used as a solution. As a regenerating solution, a mixed solution of 0.5 mmol / liter tetrabutylammonium hydroxide and 50 mmol / liter boric acid was used.

  As shown in Table 1, in the positive electrode samples A2 to A5 (the positive electrode according to the present invention), the amount of carbonate ions x (wt%) compared to the positive electrode sample A1 (the conventional positive electrode not subjected to the carbonate generation step). Can be greatly increased. Specifically, in the positive electrode sample A1, the carbonate ion amount x was as small as 2.9 wt%, whereas in the positive electrode samples A2 to A5, 10.0 wt%, 14.3 wt%, 21.4 wt%, It could be increased to 35.7 wt%. From this result, it can be said that in the positive electrode samples A2 to A5, more carbonates could be generated on the surface of the high specific surface area carbon material than in the positive electrode sample A1. Therefore, according to the carbonate production | generation process of a present Example, it can be said that the surface of a high specific surface area carbon material can be coat | covered with carbonate appropriately.

Moreover, as shown in Table 1, the sample exposed to the gas atmosphere having a higher CO ₂ concentration in the carbonate production step has a higher carbonate ion concentration in the positive electrode mixture and a larger carbonate ion amount x (wt%). I was able to confirm. From this result, it can be said that according to the production method of this example, the amount of carbonate produced (the amount of coating) can be adjusted by adjusting the CO ₂ concentration in the carbonate production step.

(Comparative example)
In addition, as a comparative example, a lithium ion secondary battery (referred to as battery sample B6) including a positive electrode in which Li ₂ CO ₃ powder was mixed in the positive electrode mixture instead of performing the carbonate generation step was manufactured. Specifically, a positive electrode material was prepared in the same manner as in the Examples, and then Li ₂ CO ₃ powder was mixed at a rate of 20 wt%. Next, as in the example, this mixture was made into a paste and applied to the surface of the positive electrode substrate (aluminum foil). Thereafter, press working is performed to form a positive electrode sheet by pressing, and this positive electrode sheet is vacuum-dried at 120 ° C. for 8 hours and then cooled, and the positive electrode of this comparative example (with positive electrode sample A6 and Obtained). In this comparative example, this positive electrode sample A6 was used to produce a lithium ion secondary battery (battery sample B6) in the same manner as in the example.

(Battery evaluation)
Next, IV resistance values were measured for battery samples B1 to B6, respectively.
Specifically, after each battery sample that had been subjected to predetermined initial charge / discharge was allowed to stand at 25 ° C. for 10 days, it was charged with constant current-constant voltage for 1.5 hours until the battery voltage reached 4.1V. did. Thereafter, discharging was performed at a current value of 1 C until the battery voltage reached 3V. When the discharge capacity at this time was defined as the battery capacity, all the samples were about 7 Ah.

  Next, each battery sample was charged with a constant current-constant voltage of 1 C for 1.5 hours until the battery voltage reached 3.72 V, and SOC (State Of Charge) was adjusted. Thereafter, charging and discharging were performed for 10 seconds at each current value of 1C, 2C, 3C, 5C, and 15C, and the amount of voltage drop was measured. The relationship between the current value (X axis) and the voltage (Y axis) at this time is represented as an IV diagram, and the IV resistance value (internal resistance) of each battery sample was calculated based on this IV diagram.

  Then, with respect to the IV resistance value of the battery sample B1, the ratio of the IV resistance value of the battery sample B2 to B6 with the IV resistance value of the battery sample B1 was calculated as the IV resistance ratio. The IV resistance ratios of the battery samples B2 to B6 were 0.95, 0.92, 0.93, 1.02, and 0.98 in this order. FIG. 4 shows a relationship diagram between the carbonate ion amount x and the IV resistance ratio produced based on this result. The series of tests described above is performed in a constant temperature bath at 25 ° C.

  Here, the relationship between the carbonate ion amount x (wt%) and the IV resistance ratio shown in FIG. 4 will be examined. As can be seen from the results of the examples, the IV resistance ratio decreases as the carbonate ion amount x increases with reference to the battery sample B1 (carbonate ion amount x = 2.9 wt%), but the predetermined carbonate ion amount x If it exceeds (about 18 wt%), the IV resistance value increases, and if the carbonate ion amount x becomes too large, the IV resistance ratio increases. That is, by covering the surface of the high specific surface area carbon material with carbonate, the IV resistance value can be reduced and the output of the battery can be improved. However, if the coating amount of the carbonate is increased too much, the IV resistance is rather increased. It can be seen that the value increases and the output characteristics deteriorate.

  As the amount of carbonate covering the surface of the high specific surface area carbon material increases, the contact between the high specific surface area carbon material and the electrolytic solution can be suppressed, and the decomposition reaction of the electrolytic solution can be suppressed. It is considered that if the amount of carbonate covering the specific surface area carbon material is excessively increased, the IV resistance value (internal resistance) is greatly increased by the carbonate, and the output characteristics are deteriorated.

In addition, in the battery sample B6 (comparative example), the IV resistance ratio is 0.98, which indicates that the IV resistance value is smaller than that in the battery sample B1 (a battery equivalent to the conventional battery not subjected to the carbonate generation step). . On the other hand, in the examples, in order to make the IV resistance ratio 0.98 or less, as shown in FIG. 4, it is understood that the carbonate ion amount x should be 5 wt% or more and 30 wt% or less. That is, in this example, by setting the carbonate ion amount x to 5 wt% or more and 30 wt% or less, lithium ions having higher output than the battery of the comparative example (battery in which Li ₂ CO ₃ powder is mixed in the positive electrode). It can be said that a secondary battery can be made.
Therefore, by coating the surface of the high specific surface area carbon material with an amount of carbonate in which the weight of carbonate ions contained in the carbonate is 5 wt% or more and 30 wt% or less, based on the weight of the high specific surface area carbon material, It can be said that it becomes a high output lithium ion secondary battery.

  Furthermore, as can be seen from FIG. 4, the IV resistance ratio can be reduced to 0.95 or less by setting the carbonate ion amount x to 10 wt% or more and 25 wt% or less. That is, by setting the carbonate ion amount x to 10 wt% or more and 25 wt% or less, the IV resistance value can be reduced by 5% or more compared to the battery sample B1 (battery equivalent to the conventional battery not subjected to the carbonate generation step). Can do. Therefore, by coating the surface of the high specific surface area carbon material with an amount of carbonate in which the weight of carbonate ions contained in the carbonate is 10 wt% or more and 25 wt% or less, based on the weight of the high specific surface area carbon material, In particular, it can be said to be a high-power lithium ion secondary battery.

  Next, each sample battery was subjected to a durability test, and the amount of gas generated in the durability test was measured. Specifically, a pressure sensor was attached to each sample battery, and each battery sample was charged to SOC 80% and then left at 60 ° C. for 60 days. Thereafter, for each battery sample, a pressure increase value was calculated from a value indicated by the pressure sensor, and a gas generation amount (ml) was calculated based on the pressure increase value. FIG. 5 shows a relationship diagram between the carbonate ion amount x (wt%) and the gas generation amount (ml) produced based on this result.

  From the results of the examples (battery samples B1 to B5) shown in FIG. 5, it can be seen that the gas generation amount decreases as the carbonate ion amount x (wt%) increases. Specifically, in the battery sample B1 (carbonate ion amount x = 2.9), the gas generation amount was as large as 11 ml, whereas in the battery sample B2 to B5 (carbonate ion amount x = 10.0-35.7). ) Can be greatly reduced to 6 ml, 5.5 ml, 5 ml, and 5 ml, respectively. That is, in the battery samples B2 to B5 (battery according to the present invention), the amount of gas generated could be greatly reduced as compared with the battery sample B1 (battery equivalent to the conventional battery not subjected to the carbonate generation step). From this result, it can be said that the amount of gas generation can be appropriately reduced by applying a carbonate generation step to coat the surface of the high specific surface area carbon material with carbonate. Therefore, the lithium ion secondary batteries (battery samples B2 to B5) of the present invention can be said to be highly reliable lithium ion secondary batteries.

Further, in the battery sample B6 (comparative example), the amount of gas generated was 9 ml. In this example, it can be seen that in order to reduce the amount of gas generated to 9 ml or less, the carbonate ion amount x should be 5 wt% or more as shown in FIG. That is, by setting the carbonate ion amount x to 5 wt% or more, it can be said that a lithium ion secondary battery with less gas generation is obtained as compared with the battery of the comparative example (battery in which Li ₂ CO ₃ powder is mixed in the positive electrode). . From this result, based on the weight of the high specific surface area carbon material, by covering the surface of the high specific surface area carbon material with an amount of carbonate in which the weight of the carbonate ions contained in the carbonate is 5 wt% or more, It can be said that the lithium ion secondary battery has high performance.

  Furthermore, as shown in FIG. 5, the gas generation amount can be decreased as the carbonate ion amount x (wt%) is increased, but when the carbonate ion amount x is 10 wt% or more, in particular, It can be seen that the amount of gas generation can be greatly reduced. That is, by setting the carbonate ion amount x to 10 wt% or more, it can be said that a lithium ion secondary battery with particularly low gas generation amount and high reliability can be obtained. Therefore, it can be said that the carbonate ion contained in the carbonate is more preferably 10 wt% or more based on the weight of the high specific surface area carbon material.

  As described above, according to the manufacturing method of this example, it can be said that a lithium ion secondary battery with high output and high reliability can be manufactured. In particular, based on the weight of the high specific surface area carbon material, the amount of carbonate ions contained in the carbonate is 5 wt% or more, preferably 5 wt% or more and 30 wt% or less, more preferably 10 wt% or more and 25 wt% or less. By covering the surface of the high specific surface area carbon material with carbonate, it can be said that a lithium ion secondary battery with high output and high reliability can be obtained.

(Modification)
In the above-described example, as shown in FIG. 3, the positive electrode was manufactured in the order of the carbon coating process, the paste manufacturing process, the coating process, and the carbonate generating process. However, as in this modification shown in FIG. 6, the positive electrode may be manufactured in the order of the carbon coating step, the paste preparation step, the carbonate generation step, and the coating step. That is, before applying the paste to the positive electrode substrate (aluminum foil), only the paste may be exposed to a gas containing CO ₂ and then the paste may be applied to the positive electrode substrate (aluminum foil).

By producing a positive electrode in such a procedure, corrosion of the aluminum foil which is a positive electrode base material can be suppressed. That is, since the paste produced in the paste production process contains a large amount of LiOH and the like, it becomes alkaline (pH is about 11). Therefore, when this paste is applied to an aluminum foil, the aluminum foil may be corroded. On the other hand, as in this modification, before applying the paste to the positive electrode substrate (aluminum foil), the paste that was alkaline can be neutralized by exposing only the paste to a gas containing CO _2. it can. For this reason, if this paste is subsequently applied to the positive electrode substrate (aluminum foil), corrosion of the aluminum foil can be prevented.

  In the above, the present invention has been described with reference to the embodiments and the modified examples. However, the present invention is not limited to the above-described embodiments and the like, and it can be applied as appropriate without departing from the gist thereof. Not too long.

It is sectional drawing of the lithium ion secondary battery 100 concerning an Example. 3 is an enlarged cross-sectional view of a positive electrode 155 of a lithium ion secondary battery 100. FIG. It is a block diagram which shows the flow of the manufacturing process of the positive electrode concerning an Example. It is a graph which shows the relationship between carbonate ion amount x and IV resistance ratio. It is a graph which shows the relationship between carbonate ion amount x and gas generation amount. It is a block diagram which shows the flow of the manufacturing process of the positive electrode concerning a modification.

Explanation of symbols

100 Lithium ion secondary battery 153 Positive electrode active material 154,160 High specific surface area carbon material 155 Positive electrode 158 Carbonate

Claims (9)

A positive electrode active material;
A high specific surface area carbon material having a specific surface area of 100 m ² / g or more;
A lithium ion secondary battery comprising a positive electrode having
The high specific surface area carbon material is a lithium ion secondary battery whose surface is coated with carbonate. The lithium ion secondary battery according to claim 1,
The positive electrode is
A lithium ion secondary battery in which at least a part of the high specific surface area carbon material covers the surface of the positive electrode active material. The lithium ion secondary battery according to claim 2,
The positive electrode is
A lithium ion secondary battery comprising carbonate in an amount such that the weight of carbonate ions contained in the carbonate is 5 wt% or more based on the weight of the high specific surface area carbon material. The lithium ion secondary battery according to claim 3,
The positive electrode is
A lithium ion secondary battery comprising carbonate in an amount such that the weight of carbonate ions contained in the carbonate is 5 wt% to 30 wt% based on the weight of the high specific surface area carbon material. A method for producing a lithium ion secondary battery, comprising:
A positive electrode active material, a high specific surface area carbon material having a specific surface area of 100 m ² / g or more, and a positive electrode material containing an aqueous binder resin and water are kneaded and produced by reaction of the positive electrode active material and water. A paste preparation step of preparing a paste containing an alkali compound;
The cured product obtained by drying and curing said paste or the paste, by exposure to a gas atmosphere containing CO _2, is reacted with the CO ₂ the alkaline compounds, carbonates to produce a carbonate on the surface of the cathode material The manufacturing method of a lithium ion secondary battery provided with a production | generation process. It is a manufacturing method of the lithium ion secondary battery according to claim 5,
An application step of applying the paste to the positive electrode substrate;
In the carbonate production step,
A method for producing a lithium ion secondary battery, wherein the paste applied to the positive electrode substrate or a cured product obtained by drying and curing the paste applied to the positive electrode substrate is exposed to a gas atmosphere containing CO ₂ . It is a manufacturing method of the lithium ion secondary battery according to claim 5,
In the carbonate production step,
By exposing the paste to a gas atmosphere containing CO ₂ , the alkali compound and CO ₂ are reacted to generate carbonate on the surface of the positive electrode material,
The manufacturing method of a lithium ion secondary battery provided with the application | coating process which apply | coats the paste formed on the surface of the said positive electrode material to the positive electrode base material. It is a manufacturing method of the lithium ion secondary battery as described in any one of Claims 5-7,
The positive electrode comprises at least a part of the high specific surface area carbon material covering the surface of the positive electrode active material,
The manufacturing method of the lithium ion secondary battery which coat | covers the surface of the said high specific surface area carbon material with the said carbonate in the said carbonate production | generation process. It is a manufacturing method of the lithium ion secondary battery as described in any one of Claims 5-8,
The method for manufacturing a lithium ion secondary battery, wherein the positive electrode active material includes at least one of a LiNiO ₂ positive electrode active material and a LiCoO ₂ positive electrode active material.

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