JP2010044987A - Method for manufacturing cathode for lithium battery and lithium battery equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a cathode for a battery for suppressing coating film formation on the surface of a cathode active material. <P>SOLUTION: In the method for manufacturing the cathode for a lithium battery of a constitution in which a cathode mixture layer containing the cathode active material is retained by a cathode current collector, a process (step S20) of preparing slurry for cathode mixture layer formation is included in which the cathode active material is dispersed into a dispersion medium, and a process (step S30) of forming the cathode mixture layer by depositing the slurry for cathode mixture layer formation to the surface of the cathode current collector, and here in the preparation process of the slurry for the cathode mixture layer formation and a formation process of the cathode mixture layer, by measuring CO<SB>2</SB>concentration in working atmosphere or introducing gas in which the CO<SB>2</SB>concentration is controlled into the work atmosphere, the CO<SB>2</SB>concentration in the work atmosphere is kept at a prescribed value or less at least during a period from the slurry preparation process to the cathode mixture layer formation process. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a method for manufacturing a positive electrode for a battery having a structure in which a positive electrode mixture layer containing a positive electrode active material and a positive electrode active material is held by a positive electrode current collector, and a lithium battery including an electrode obtained by the manufacturing method. .

  In recent years, lithium secondary batteries such as lithium ion batteries have become increasingly important as power sources for mounting on vehicles or as power sources for personal computers and portable terminals. In particular, a lithium ion battery that is lightweight and obtains a high energy density is expected to be preferably used as a high-output power source mounted on a vehicle.

One typical configuration of a lithium secondary battery includes a positive electrode having a structure in which a positive electrode active material capable of reversibly occluding and releasing lithium ions is formed on a positive electrode current collector. For example, a lithium secondary battery using a positive electrode active material made of a lithium / nickel composite oxide (for example, lithium nickelate) is an example of such a battery. A positive electrode active material comprising such a lithium / nickel composite oxide is obtained by reacting a raw material compound, for example, a nickel-containing compound (for example, nickel hydroxide) and a lithium-containing compound (for example, lithium hydroxide) in the air. Can be synthesized. For example, Patent Document 1 is disclosed as a prior art of this type.
JP 2000-58053 A

  By the way, the positive electrode active material made of such a lithium / nickel composite oxide (for example, lithium nickelate) is liable to cause lithium ions to move between the active material and the electrolyte in the process of being held in the atmosphere. A film such as lithium carbonate may be formed that interferes (i.e. increases battery resistance). Such a surface film composed mainly of lithium carbonate or the like is not desirable because it causes a decrease in battery performance such as an increase in reaction resistance of the positive electrode active material. In order to remove such a film on the surface of the positive electrode active material, a technique for cleaning the positive electrode active material with acetone has been proposed. However, these cleaning processes may cause complexity of the process, resulting in productivity problems. In addition to obtaining, there is a possibility that a new film may be formed after the removal, which is not realistic.

This invention is made | formed in view of this point, The main objective is to provide the manufacturing method of the positive electrode for lithium batteries which can suppress the film | membrane production | generation in the positive electrode active material surface.
Moreover, the other objective is to provide a lithium battery provided with the positive electrode manufactured by such a manufacturing method.

As a result of intensive studies, the inventor has found that the formation of the surface film depends on the concentration of carbon dioxide (CO ₂ ) in the atmosphere, and has created the present invention.
That is, the manufacturing method provided by the present invention is a method for manufacturing a positive electrode for a battery having a configuration in which a positive electrode mixture layer containing a positive electrode active material is held by a positive electrode current collector. This method comprises a step of preparing a slurry for forming a positive electrode mixture layer formed by dispersing a positive electrode active material in a dispersion medium, and applying the prepared slurry for forming a positive electrode mixture layer to the surface of the positive electrode current collector. Forming the positive electrode mixture layer. And, by measuring the CO ₂ concentration in the working atmosphere in the positive electrode mixture layer forming slurry preparation step and the positive electrode mixture layer forming step, or introducing a gas having a controlled CO ₂ concentration into the working atmosphere, at least The CO ₂ concentration in the working atmosphere between the slurry preparation step and the positive electrode mixture layer formation step is maintained at a predetermined value or less.

According to the positive electrode manufacturing method having the above-described configuration disclosed herein, in the positive electrode mixture layer forming slurry preparation step and the positive electrode mixture layer formation step, the CO ₂ concentration in the working atmosphere is measured, and the slurry preparation step Since the series of steps from the positive electrode mixture layer formation step to the positive electrode mixture layer formation step are performed under an atmosphere control such that the CO ₂ concentration is a predetermined value or less, the positive electrode mixture layer is formed from the positive electrode mixture layer formation slurry. The amount of CO ₂ mixed in the slurry can be reduced, and the positive electrode active material in the slurry can be prevented from adsorbing CO ₂ . As a result, it is possible to suppress the formation of a film (for example, a surface film mainly composed of lithium carbonate) on the surface of the positive electrode active material due to the adsorption of CO ₂ , and the influence (for example, the surface of the positive electrode active material) In this case, an increase in reaction resistance due to inhibition of charge transfer of lithium ions or the like can be avoided. That is, according to the production method of the present invention, it is possible to provide a positive electrode for a battery that can suppress the formation of a film on the surface of the positive electrode active material and avoid a decrease in battery performance.

In a preferred embodiment of the positive electrode manufacturing method disclosed herein, the CO ₂ concentration in the working atmosphere is maintained at 400 ppm or less (for example, 300 to 400 ppm). By setting the upper limit of such CO ₂ concentration, it is possible to reduce the amount of CO ₂ to be mixed into a slurry to such an extent that does not affect the battery performance, In its CO ₂ adsorption (extension of the positive electrode active material Generation of a surface film such as lithium carbonate) can be effectively suppressed. Note that the CO ₂ concentration in the working atmosphere can be easily measured by, for example, commercially available CO ₂ sensors having various mechanisms.

In a preferred embodiment of the positive electrode manufacturing method disclosed herein, a lithium transition metal composite oxide containing lithium and one or more transition metal elements as constituent metal elements is used as the positive electrode active material. The lithium transition metal composite oxide has a property that when it reacts with surrounding moisture, it adsorbs CO ₂ and easily forms a surface film made of lithium carbonate or the like. Therefore, when the positive electrode active material is the lithium transition metal composite oxide, the CO ₂ concentration in the working atmosphere from the slurry preparation step to the positive electrode mixture layer formation step in order to suppress film formation on the surface of the positive electrode active material The effect of adopting the method of the present invention for controlling and managing the value below a predetermined value can be exhibited particularly well.

In a preferable embodiment of the positive electrode manufacturing method disclosed herein, the method further includes a step of synthesizing the positive electrode active material from a raw material compound. By or the CO ₂ concentration measured CO ₂ concentration in the working atmosphere at positive electrode active material synthesis step is introduced into the work atmosphere controlled gas, the positive-electrode mixture layer from at least the positive electrode active material synthesis step It is characterized in that the CO ₂ concentration in the working atmosphere until the forming step is kept at a predetermined value or less (preferably 400 ppm or less). According to this aspect, not only the generation of the positive electrode active material surface film due to the presence of CO ₂ mixed in the positive electrode mixture layer forming slurry is suppressed, but also in the atmosphere of the synthesis of the positive electrode active material (typically Can also suppress the formation of the positive electrode active material surface film due to the presence of CO _{2 in} the outside air).

  Embodiments according to the present invention will be described below with reference to the drawings. In the following drawings, members / parts having the same action are described with the same reference numerals. In addition, this invention is not limited to the following embodiment. Further, matters other than matters specifically mentioned in the present specification and matters necessary for carrying out the present invention (for example, manufacturing method of electrode active material, configuration and manufacturing method of separator and electrolyte, construction of batteries and other batteries) Can be grasped as a design matter of those skilled in the art based on the prior art in this field.

  Although not intended to be particularly limited, the configuration of the battery 100 and the electrode assembly 80 according to the present embodiment will be described below with reference to FIGS. 1 and 2 mainly using a lithium ion battery as an example. FIG. 1 is a cross-sectional view schematically showing a configuration of a lithium ion battery 100 according to the present embodiment, and FIG. 2 is an explanatory diagram schematically showing a configuration of an electrode body 80 according to the present embodiment.

  As shown in FIG. 1, a battery 100 disclosed herein is typically a predetermined battery constituent material (active material for each of positive and negative electrodes, current collector for each of positive and negative electrodes), like a conventional lithium ion secondary battery. , A separator, etc.) and a battery case 50 containing the electrode body 80 and an appropriate electrolytic solution.

  The battery case 50 includes a battery case main body 52 and a lid 54. The battery case main body 52 has a shape (here, a box shape) that can accommodate a wound electrode body 80 described later. The battery case main body 52 is provided with an opening (upper end opening in the drawing) at least at one end, and the electrode body 80 can be accommodated through the opening. The lid 54 is a member that closes the opening of the battery case main body 52. The material of the battery case main body 52 and the lid body 54 is preferably a lightweight metal material having good thermal conductivity. Examples of such a metal material include aluminum, stainless steel, nickel-plated steel, and the like.

  In the battery case 50, an electrode body 80 and an electrolytic solution (not shown) are accommodated. The electrode body 80 is a stacked electrode body in which the positive electrode 10 and the negative electrode 20 are stacked with a separator 30 interposed therebetween. In this embodiment, like the electrode body of a normal lithium ion secondary battery, the positive electrode sheet 10 and the negative electrode sheet 20 are laminated via two separator sheets 30a and 30b, and further wound. It is a laminated electrode body (winding electrode body).

  In the positive electrode sheet 10, a positive electrode mixture layer 14 containing a positive electrode active material is formed on both surfaces of a long sheet-like foil-like positive electrode current collector 12. However, the positive electrode mixture layer 14 was not attached to one side edge (lower side edge portion in the figure) along the edge in the sheet width direction, and the positive electrode current collector 12 was exposed with a certain width. A current collector exposed portion 16 is formed.

For the positive electrode current collector 12, an aluminum foil or other metal foil suitable for the positive electrode is preferably used. As the positive electrode active material, one or more of materials conventionally used in lithium ion batteries can be used without any particular limitation. As a preferred example, a material mainly composed of a lithium transition metal composite oxide containing lithium and one or more transition metal elements as constituent metal elements is preferably used. Preferred representative examples of such lithium transition metal composite oxides include lithium / nickel composite oxides, lithium / cobalt composite oxides, and lithium manganese composite oxides. In this embodiment, lithium nickelate (LiNiO ₂ ). For example, a suitable positive electrode sheet 10 can be obtained by forming a positive electrode mixture layer 14 mainly composed of a lithium transition metal composite oxide in a predetermined region on the surface of a long aluminum foil as a current collector. The positive electrode mixture layer 14 may include other positive electrode mixture layer forming components (for example, a conductive material and a binder) used as necessary.

  Similarly to the positive electrode sheet 10, the negative electrode sheet 20 has a negative electrode mixture layer 24 containing a negative electrode active material on both surfaces of a long sheet-like foil-shaped negative electrode current collector 22. However, the negative electrode mixture layer 24 is not attached to one side edge (upper side edge portion in the figure) along the edge in the sheet width direction, and the current collector 22 in which the negative electrode current collector 22 is exposed with a certain width. An electric body exposed portion 26 is formed.

  For the negative electrode current collector 22, a copper foil or other metal foil suitable for the negative electrode is preferably used. As the negative electrode active material, one or more of materials conventionally used in lithium ion batteries can be used without any particular limitation. Preferable examples include carbon-based materials such as graphite carbon and amorphous carbon, lithium transition metal composite oxides (lithium titanium composite oxides, etc.), lithium transition metal composite nitrides, and the like. For example, a suitable negative electrode sheet 20 can be obtained by forming the negative electrode mixture layer 24 mainly composed of graphite in a predetermined region on the surface of a long copper foil as a current collector by a conventional method.

  In manufacturing the wound electrode body 80, the positive electrode sheet 10 and the negative electrode sheet 20 are overlapped together with a total of two separator sheets 30a and 30b, and the positive electrode sheet 10 and the negative electrode sheet 20 are wound. At this time, the separator sheets 30a and 30b are arranged so that the current collector exposed portions 16 and 26 of the positive electrode sheet 10 and the negative electrode sheet 20 protrude outward (that is, the positive electrode mixture layer 14, the separator sheets 30a and 30b, and the negative electrode mixture). Superimposed so that layer 24 is opposite. A positive electrode lead terminal 42a and a negative electrode lead terminal 42b are attached to the current collector exposed portions 16 and 26, respectively. The positive electrode lead terminal 42 a and the negative electrode lead terminal 42 b are electrically connected to the positive electrode terminal 40 a and the negative electrode terminal 40 b for external connection that are provided on the lid 54 of the battery case 50. In this way, the battery 100 according to the present embodiment can be constructed.

  Next, a manufacturing method of the positive electrode sheet 10 according to the present embodiment and the battery 100 including the positive electrode sheet 10 will be described with reference to FIG.

  As described above, the positive electrode sheet 10 according to the present embodiment has a configuration in which the positive electrode mixture layer 14 containing the positive electrode active material is held by the positive electrode current collector 12. A method for producing the battery positive electrode 10 will be described.

First, in step S10, a positive electrode active material used for a battery positive electrode is prepared. Here, the positive electrode active material is synthesized from a raw material compound. As a method of synthesizing the positive electrode active material, a conventionally known general positive electrode active material synthesis method can be appropriately employed. In this embodiment, lithium nickelate (LiNiO ₂ ) is synthesized as the positive electrode active material. In addition, you may purchase the positive electrode active material used for the positive electrode for batteries, for example from an external manufacturer.

Next, in step S20, a positive electrode mixture layer forming slurry is prepared by dispersing the synthesized positive electrode active material in a dispersion medium. In this embodiment, the positive electrode active material (LiNiO ₂ ) powder and other positive electrode mixture layer forming components (for example, a conductive material and a binder) used as necessary are dispersed in a suitable dispersion medium (typically Are dissolved) and kneaded to prepare a paste-like positive electrode mixture layer forming slurry. The dispersion medium may be water or a mixed solvent mainly composed of water, or may be an organic medium such as a non-aqueous medium (for example, N-methylpyrrolidone). Dispersion and kneading of the positive electrode mixture layer forming slurry can be performed using, for example, a thin film swirling mixer (thin film swirling mixer).

  Next, in step S <b> 30, the prepared positive electrode mixture layer forming slurry is applied to the surface of the positive electrode current collector 12 to form the positive electrode mixture layer 14.

  In this embodiment, first, in Step S <b> 32, the prepared paste-like positive electrode mixture layer forming slurry is applied onto the positive electrode current collector 12. The application of the slurry for forming the positive electrode mixture layer is performed by, for example, forming a predetermined amount of the positive electrode mixture layer from above the positive electrode current collector 12 using an appropriate application device (slit coater, die coater, comma coater, etc.). The slurry can be coated to a uniform thickness.

  Next, in step S <b> 34, the dispersion medium in the positive electrode mixture layer forming slurry is removed by drying (typically 70 to 200 ° C.) the positive electrode mixture layer forming slurry by an appropriate drying means. By removing the dispersion medium from the slurry for forming the positive electrode mixture layer, the positive electrode mixture layer 14 containing the positive electrode active material is formed.

  In step S36, after drying, an appropriate press process (for example, a roll press process) is performed as necessary, so that the thickness and density of the positive electrode mixture layer 14 are appropriately adjusted. Thus, in step S40, the positive electrode sheet (battery positive electrode) 10 in which the positive electrode mixture layer 14 is held on the surface of the positive electrode current collector 12 can be obtained.

Here, in this embodiment, the concentration of CO ₂ in the working atmosphere is measured in the step of preparing the positive electrode mixture layer forming slurry (step S20) and the step of forming the positive electrode mixture layer (step S30), and at least the slurry preparation is performed. A treatment (CO that keeps the CO ₂ concentration in the working atmosphere between the process (step S20) and the positive electrode mixture layer forming process (step S30) below a predetermined value (typically based on the measured value). ₂ concentration management). Such treatment (CO ₂ concentration control), for example the various tasks to be performed during the period from the preparation process of the positive-electrode mixture layer slurry (step S20) until the positive-electrode mixture layer formation step (step S30), CO ₂ It can be easily performed by carrying out in a chamber (for example, in a glove box or a dry room) into which a gas having a controlled gas concentration is introduced. In this embodiment, the CO ₂ gas concentration is a predetermined value in various operations from the dispersion / kneading step (step S20) of the positive electrode mixture layer forming slurry to the application / drying step (step S34) of the positive electrode mixture layer forming slurry. The following operations are performed in a glove box into which a controlled gas is introduced, and various operations in the step of pressing the positive electrode mixture layer (step S36) are performed in a dry room in which the CO ₂ gas concentration is controlled. To do.
The method for measuring the CO ₂ concentration in the working atmosphere is not particularly limited, and can be easily performed using, for example, various commercially available carbon dioxide concentration meters (CO ₂ sensors). As a control method for keeping the CO ₂ concentration in the working atmosphere below a predetermined value based on the measured value, a conventionally known method for controlling the CO ₂ concentration in the working atmosphere can be appropriately employed. . For example, when the CO ₂ concentration in the working atmosphere is too high, an appropriate amount of CO ₂ gas in the working atmosphere may be removed using a general decarbonation treatment method. As a method of removing the CO ₂ gas, for example, a method of replacing the working atmosphere gas with a rare gas (for example, Ar gas) or the like, or an absorber that physically absorbs the CO ₂ gas (for example, a ceramic material such as zeolite or alumina). In a working atmosphere or an adsorbent that chemically adsorbs CO ₂ gas (for example, an organic liquid such as methylamine, aniline, toluidine, benzidine, N, N-dimethylpropan-2-amine). A method of installing inside may be adopted as appropriate.

In this embodiment, control is performed so that the CO ₂ concentration in the working atmosphere of the positive electrode active material synthesis step (step S10) also becomes a predetermined value or less. That is, the CO ₂ concentration in the working atmosphere in the positive electrode active material synthesis step was measured, the CO ₂ concentration in the working atmosphere during at least the positive electrode active material synthesis process based on the measured value to the positive-electrode mixture layer formation step A measure (CO ₂ concentration management) is performed to keep the value below a predetermined value. Such treatment (CO ₂ concentration management) is performed, for example, in various operations performed during the synthesis of the positive electrode active material (for example, operations in which raw material compounds are weighed, mixed and fired, etc.), and the CO ₂ gas concentration is controlled. It can be easily performed by carrying out in a separate chamber (for example, a glove box).

According to the positive electrode manufacturing method according to the present embodiment, the CO ₂ concentration in the working atmosphere is measured in the step of preparing the positive electrode mixture layer forming slurry and the step of forming the positive electrode mixture layer, and based on the measured value. Since a series of steps from the slurry preparation step to the positive electrode mixture layer forming step is performed under an atmosphere control such that the CO ₂ concentration is a predetermined value or less, the slurry for forming the positive electrode mixture layer is changed to the positive electrode mixture layer. When forming, the amount of CO ₂ mixed in the slurry can be reduced, and the positive electrode active material in the slurry can be suppressed from adsorbing CO ₂ . As a result, it is possible to suppress the formation of a film (for example, a surface film mainly composed of lithium carbonate) on the surface of the positive electrode active material due to the adsorption of CO ₂ , and the influence (for example, the surface of the positive electrode active material) due to the presence of the surface film In this case, an increase in reaction resistance due to inhibition of charge transfer of lithium ions or the like can be avoided. That is, according to the manufacturing method of the present embodiment, it is possible to provide a positive electrode for a battery that can suppress the formation of a film on the surface of the positive electrode active material and avoid a decrease in battery performance.

Under the above-described CO ₂ concentration control, the CO ₂ concentration is preferably maintained at 400 ppm or less, and more preferably 200 ppm or less. By setting the upper limit of such CO ₂ concentration, it is possible to reduce the amount of CO ₂ to be mixed into a slurry to such an extent that does not affect the battery performance, In its CO ₂ adsorption (extension of the positive electrode active material Generation of a surface film such as lithium carbonate) can be effectively suppressed.

In this embodiment, a lithium transition metal composite oxide (here, lithium nickelate) containing lithium and one or more transition metal elements as constituent metal elements is used as the positive electrode active material. These lithium composite oxides tend to generate a surface film made of lithium carbonate or the like by adsorbing CO ₂ when reacted with surrounding moisture. Therefore, when the positive electrode active material is the lithium transition metal composite oxide, the CO ₂ concentration in the working atmosphere from the slurry preparation step to the positive electrode mixture layer formation step in order to suppress film formation on the surface of the positive electrode active material The effect of adopting the method of the present embodiment for controlling the temperature can be exhibited particularly well.

In this embodiment, not only the CO ₂ concentration in the working atmosphere from the slurry preparation step to the positive electrode mixture layer forming step is controlled, but also in the working atmosphere of the positive electrode active material synthesis step (step S10). The CO ₂ concentration is also controlled to be a predetermined value or less. According to this aspect, not only the generation of the positive electrode active material surface film due to the presence of CO ₂ mixed in the positive electrode mixture layer forming slurry is suppressed, but also in the atmosphere of the synthesis of the positive electrode active material (typically Can also suppress the formation of the positive electrode active material surface film due to the presence of CO _{2 in} the outside air).

  Next, a process of building a battery using the battery positive electrode (here, positive electrode sheet) 10 obtained in step S40 will be described with reference to FIG. 1 and FIG.

  First, in step S50, the electrode body 80 is produced using the positive electrode sheet 10 obtained in step S40. In this embodiment, first, in step S52, the obtained positive electrode sheet 10 and the separately prepared negative electrode sheet 20 are overlapped and wound together via two separator sheets 30a and 30b, thereby winding the wound body. Next, in step S54, the obtained wound body is crushed from the side surface direction and ablated (pressed so as to have a flat shape) to produce a flat wound electrode body 80.

  Next, in step S <b> 60, the produced electrode body 80 is accommodated in the battery case 50 to construct the battery 100. In this embodiment, first, in step S62, the positive electrode lead terminal 42a and the negative electrode lead terminal 42b are respectively attached to the current collector exposed portions 16 and 26 of the wound electrode body 80 manufactured in step S50, and the positive electrode lead terminal 42a. The negative electrode lead terminal 42 b is welded to the positive electrode terminal 40 a and the negative electrode terminal 40 b of the lid 54. Next, in step S <b> 64, the wound electrode body 80 is accommodated in the battery case 50. In this embodiment, the wound electrode body 80 is accommodated through the upper end opening of the battery case main body 52, and the lid 54 is attached to the upper end opening by means such as welding. Next, in step S <b> 66, an electrolytic solution is supplied to the wound electrode body 80. In this embodiment, the electrolyte solution is supplied by injecting the electrolyte solution from the liquid injection port 58 of the lid 54. Then, the manufacturing flow of the battery 100 according to this embodiment is completed by sealing the liquid injection port 58 of the battery case 50 with the sealing plug 56 or the like (step S70).

Here, in this embodiment, the CO ₂ concentration in the working atmosphere is measured in the electrode body manufacturing process (step S50) and the battery construction process (step S60), and at least the electrode body manufacturing process (step A treatment (CO ₂ concentration management) is performed to keep the CO ₂ concentration in the working atmosphere between S50) and the battery construction step (step S60) below a predetermined value. Such treatment (CO ₂ concentration management) is performed, for example, in various operations performed between the electrode body preparation process (step S50) and the electrolyte solution injection process (step S66) in a dry room in which the CO ₂ concentration is controlled. (In this embodiment, it can be easily performed in a dry environment where the CO ₂ concentration is 400 ppm or less and the dew point is −30 ° C.).

Thus, not only the CO ₂ concentration in the working atmosphere of the battery positive electrode manufacturing process is controlled, but also in the working atmosphere during the electrode body manufacturing process (step S50) and the battery construction process (step S60), which are subsequent processes. By controlling the CO ₂ concentration to be equal to or less than the predetermined value, it is possible to suppress the formation of the positive electrode active material surface film due to the presence of CO ₂ during the production of the electrode body or during the battery construction. The influence can be avoided reliably.

Several preferred embodiments of the battery manufacturing method disclosed herein will be described below. That is, several test positive electrodes were produced by varying the CO ₂ gas concentration in the working atmosphere, and a test lithium ion battery using them was constructed. And the alternating current impedance measurement about each battery for a test was performed, and those reaction resistance was evaluated. The test lithium ion battery was produced as follows.

<Preparation of test positive electrode>
First, 87% by mass of lithium nickelate as a positive electrode active material is dispersed in an appropriate solvent (water) together with 10% by mass of acetylene black as a positive electrode conductive agent and 3% by mass of PTFE (solid content) as a positive electrode binder. The mixture was stirred for 1 hour with a biaxial stirrer to prepare a paste-form positive electrode mixture layer forming slurry. This paste slurry was applied and pressed onto a positive electrode current collector (aluminum foil) to volatilize the solvent, and a positive electrode for testing was prepared in which a positive electrode mixture layer was provided on one side of the positive electrode current collector. The test positive electrode was produced in a chamber in which the CO ₂ gas concentration was controlled to 164 ppm.

<Production of negative electrode>
On the other hand, 95% by mass of scaly graphite as a negative electrode active material is dispersed in an appropriate solvent (NMP) together with 5% by mass of PVDF (solid content) as a negative electrode binder, and stirred for 1 hour with a biaxial stirrer. A paste-form slurry for forming a negative electrode mixture layer was prepared. This slurry was applied to a negative electrode current collector (copper foil) and pressed to volatilize the solvent, thereby preparing a negative electrode in which a negative electrode mixture layer was provided on one side of the negative electrode current collector.

<Construction of test battery>
Subsequently, these test positive electrodes and negative electrodes were laminated through a separator made of fine porous polyethylene to prepare an electrode body. Next, the laminated electrode body thus obtained was accommodated in a battery case, and an electrolyte was injected into the battery case to construct a test battery. As the electrolytic solution, a solution obtained by dissolving about 1M LiPF ₆ in a 1: 1 (mass ratio) mixed solvent of ethylene carbonate and diethyl carbonate was used. The test battery was manufactured in a dry room in which the CO ₂ gas concentration was controlled to 164 ppm. The lithium ion battery thus produced was designated as Test Example 1.

In addition, as Test Examples 2 to 5, lithium ion secondary batteries were manufactured by varying the CO ₂ gas concentrations in the working atmosphere. Specifically, test batteries were produced by changing the CO ₂ gas concentration to 391 ppm, 452 ppm, 615 ppm, and 882 ppm in the order of Test Examples 2 to 5, respectively. It was produced under the same conditions as in Test Example 1 except that the CO ₂ gas concentration was changed.

<AC impedance measurement>
The alternating current impedance of the test batteries of Test Examples 1 to 5 produced as described above was measured, and their reaction resistance was evaluated. The AC impedance measurement conditions were an AC applied voltage of 250 mV and a frequency range of 10 μHz to 1 MHz. The impedance measurements were all performed on test batteries stored at 60 ° C. for 10 days. The results are shown in FIG. In FIG. 5, the horizontal axis represents the CO ₂ concentration (ppm) in the working atmosphere, and the vertical axis represents the reaction resistance value (mΩ) obtained from the impedance measurement result.

As is clear from the comparison between Test Examples 1 and 2 and Test Examples 3, 4, and 5, it was found that the reaction resistance decreases when the CO ₂ gas concentration in the working atmosphere is below 400 ppm. This is presumably because the formation of a film on the surface of the positive electrode active material due to CO ₂ adsorption could be suppressed by reducing the CO ₂ gas in the working atmosphere. From the above, by maintaining the CO ₂ concentration in the working atmosphere between the slurry preparation step and the positive electrode mixture layer forming step at 400 ppm or less, it is possible to suppress a decrease in battery performance due to film formation on the surface of the positive electrode active material. It was confirmed.

  As mentioned above, although this invention was demonstrated by suitable embodiment, such description is not a limitation matter and of course various modifications are possible. For example, the method for producing a positive electrode for a battery according to the present invention has been described so far mainly using a lithium ion secondary battery as an example, but a battery to which the present invention can be applied is not limited to a lithium ion secondary battery. For example, the production method of the present invention can be applied to preferably produce a positive electrode for a lithium ion primary battery.

  Since the battery including the positive electrode for a battery according to the present embodiment can suppress a decrease in battery performance due to film formation on the surface of the positive electrode active material as described above, it is particularly for a motor (electric motor) mounted on a vehicle such as an automobile. It can be suitably used as a power source. That is, a battery (typically an automobile, in particular a hybrid), in which the battery is arranged as a single battery in a predetermined direction, an assembled battery is constructed by restraining the single battery in the arrangement direction, and the assembled battery is used as a power source. An automobile equipped with an electric motor such as an automobile, an electric automobile, and a fuel cell automobile) can be provided.

In Patent Document 1 (Japanese Patent Laid-Open No. 2000-58053) described above, CO ₂ gas in the air reacts with lithium hydroxide that is a raw material of the positive electrode active material (lithium nickel-based composite oxide) to react with lithium carbonate. In order to suppress the generation of impurities such as the above, a technique for defining the CO ₂ gas concentration is disclosed. However, Patent Document 1 merely defines the carbon dioxide gas concentration in the working atmosphere at the time of synthesis. The configuration of the present invention, that is, the preparation process of the positive electrode mixture layer forming slurry and the formation of the positive electrode mixture layer About measuring the CO ₂ concentration in the working atmosphere in the process, and keeping the CO ₂ concentration in the working atmosphere at least from the slurry preparation step to the positive electrode mixture layer forming step based on the measured value below a predetermined value There is no disclosure or suggestion.

1 is a cross-sectional view schematically showing a configuration of a battery according to an embodiment of the present invention. Explanatory drawing which shows typically the structure of the electrode body which concerns on one Embodiment of this invention. The figure which shows the manufacture flow of the positive electrode for batteries which concerns on one Embodiment of this invention. The figure which shows the manufacture flow of the battery which concerns on one Embodiment of this invention. Graph showing the relationship between the CO ₂ concentration and reaction resistance.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Positive electrode 12 Positive electrode collector 14 Positive electrode mixture layer 16 Current collector exposed portion 20 Negative electrode 22 Negative electrode current collector 24 Negative electrode mixture layer 26 Current collector exposed portion 30a, 30b Separator 40a Positive electrode terminal 40b Negative electrode terminal 42a Positive electrode lead terminal 42b Negative electrode lead terminal 50 Battery case 52 Battery case main body 54 Lid 56 Seal plug 58 Injection port 80 Electrode body 100 Battery

Claims (5)

A method for producing a positive electrode for a lithium battery having a configuration in which a positive electrode mixture layer containing a positive electrode active material is held by a positive electrode current collector,
Preparing a slurry for forming a positive electrode mixture layer formed by dispersing a positive electrode active material in a dispersion medium;
Providing the prepared slurry for forming a positive electrode mixture layer on the surface of the positive electrode current collector to form the positive electrode mixture layer,
Here, in the positive electrode mixture layer forming slurry preparation step and the positive electrode mixture layer formation step, by measuring the CO ₂ concentration in the working atmosphere or introducing a gas having a controlled CO ₂ concentration into the working atmosphere A method for producing a positive electrode for a battery, wherein a CO ₂ concentration in a working atmosphere at least from the slurry preparation step to the positive electrode mixture layer formation step is maintained at a predetermined value or less. The manufacturing method according to claim 1, wherein a CO ₂ concentration in the working atmosphere is maintained at 400 ppm or less.   The production method according to claim 1 or 2, wherein a lithium transition metal composite oxide containing lithium and one or more transition metal elements as constituent metal elements is used as the positive electrode active material. Further, the method includes a step of synthesizing the positive electrode active material from the raw material compound, and measures the CO ₂ concentration in the working atmosphere in the positive electrode active material synthesizing step or introduces a gas having a controlled CO ₂ concentration into the working atmosphere. The CO ₂ concentration in the working atmosphere at least from the positive electrode active material synthesizing step to the positive electrode mixture layer forming step is maintained at a predetermined value or less by at least one of claims 1 to 3. The manufacturing method of the positive electrode for batteries as described in any one of.   A lithium battery comprising a battery positive electrode produced by the method according to claim 1.

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