JP5605614B2 - Method for manufacturing lithium secondary battery - Google Patents

Description

  The present invention relates to a lithium secondary battery and a method for manufacturing the same. Specifically, the present invention relates to a positive electrode plate of the secondary battery.

In recent years, secondary batteries such as lithium secondary batteries and nickel metal hydride batteries have become increasingly important as power sources mounted on vehicles using electricity as a drive source, or power sources mounted on personal computers, portable terminals, and other electrical products. . In particular, a lithium secondary battery (typically 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.
In a typical configuration of this type of lithium secondary battery, an electrode mixture layer (specifically, a positive electrode mixture layer and a negative electrode mixture layer) capable of reversibly inserting and extracting lithium ions corresponds. A positive electrode plate and a negative electrode formed on the surface of the electric body (that is, the positive electrode core material) are provided. For example, in the case of a positive electrode plate of a lithium secondary battery, a paste or slurry-like positive electrode composite prepared by mixing a positive electrode active material such as a lithium transition metal composite oxide with a conductive material and a binder with an appropriate solvent. The positive electrode mixture layer is formed by applying the material layer forming composition to the positive electrode current collector (that is, the positive electrode core material).

  An aqueous solvent may be used as a solvent to be mixed when preparing such a composition. A paste or slurry-like composition for forming a positive electrode mixture layer using an aqueous solvent (hereinafter, this type of composition is referred to as an “aqueous paste”) is a composition comprising an organic solvent (non-aqueous solvent). (Hereinafter, this type of composition is referred to as “non-aqueous paste”.) Since there is less organic solvent and associated industrial waste, and there is no equipment and processing costs for it, the overall environmental impact is reduced. Has the advantage of being reduced. Patent document 1 is mentioned as a prior art regarding the preparation method of the aqueous paste of such a lithium secondary battery. Patent Document 1 discloses a technique for suppressing fluctuations in fluidity of an aqueous paste whose viscosity tends to decrease over time by using an aqueous solvent whose pH is shifted to the alkali side in the preparation process of the aqueous paste. It is disclosed.

JP 2007-66823 A JP 2000-208135 A JP 2003-123764 A

By the way, in order to realize high output and high capacity of the lithium secondary battery, it is required to increase the density of the positive electrode active material on the positive electrode side. Since such a positive electrode active material has low electron conductivity, a conductive material is added to the positive electrode mixture layer formed using the active material as a main component to enhance electron conductivity. However, when a conductive material such as carbon powder is added to an aqueous solvent together with a positive electrode active material and kneaded when preparing an aqueous paste, it tends to be compressed from a bulky state by mechanical energy such as shearing force and the bulk tends to decrease. is there. When the volume of the conductive material is reduced, the ratio of the exposed positive electrode active material that is not coated with the conductive material to the surface of the positive electrode current collector (that is, the positive electrode core material) increases. Electrode conductivity between positive electrode active material existing between the positive electrode core material) -positive electrode mixture layer and the positive electrode plate surface is decreased, and the resistance is increased.
On the other hand, increasing the content of the conductive material to increase the proportion of the positive electrode active material coated with the conductive material requires a large amount of solvent during preparation of the aqueous paste, and the coating property is poor and uneven. An aqueous paste is prepared.
Patent Document 2 discloses a secondary battery having a layer made of a carbon material on the positive electrode plate, and Patent Document 3 discloses a secondary battery in which the ratio of the conductive material to the positive electrode active material in the positive electrode mixture layer is defined. Has been. However, none of them fully realize the increase in capacity and output of lithium secondary batteries. That is, as described above, no consideration is given to an increase in battery resistance when a positive electrode active material not coated with a conductive material is present on the surface of the positive electrode plate.

  Therefore, the present invention was created to solve such problems, and the object of the present invention is to reduce the proportion of the positive electrode active material that is not coated with the conductive material on the surface of the positive electrode plate. By providing the above, a lithium secondary battery having a positive electrode mixture layer excellent in electron conductivity and having excellent battery characteristics (for example, high rate characteristics or cycle characteristics) as a vehicle-mounted high-output power supply and a method for manufacturing the same are provided. For the purpose.

  In order to achieve the above object, the present invention provides a lithium secondary battery including a positive electrode plate in which a positive electrode mixture layer containing a positive electrode active material is formed on the surface of a positive electrode current collector (ie, positive electrode core material). In the lithium secondary battery disclosed herein, the positive electrode mixture layer includes the positive electrode active material, at least one binder dissolved or dispersed in an aqueous solvent, and a conductive material. The area ratio of the positive electrode active material in the positive electrode mixture layer exposed on the surface of the positive electrode plate with respect to the total area of the positive electrode mixture layer of the positive electrode plate satisfies 3% or more and 25% or less. It is characterized by.

In the present specification, the “lithium secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by movement of lithium ions between the positive and negative electrodes. In general, a secondary battery referred to as a lithium ion battery is a typical example included in the lithium secondary battery in this specification.
In the present specification, the “positive electrode active material” refers to an active material on the positive electrode side capable of reversibly occluding and releasing (typically inserting and removing) chemical species serving as charge carriers in the secondary battery. .

The positive electrode mixture layer of the lithium secondary battery according to the present invention includes a positive electrode active material, at least one binder material dissolved or dispersed in an aqueous solvent, and a conductive material. The positive electrode active material with low electron conductivity is coated with a conductive material on the surface through a binder, whereby the conductivity of the positive electrode plate is enhanced. However, when preparing a paste for forming a positive electrode mixture layer or a slurry-like composition for forming a positive electrode mixture layer (hereinafter, this type of composition is referred to as “aqueous paste”), When a conductive material is added to a solvent (here, an aqueous solvent) together with a positive electrode active material or a binder and kneaded, the conductive material tends to be compressed from a bulky state by mechanical energy such as shearing force. When the bulk of the conductive material is reduced by the compression, the ratio of the exposed positive electrode active material that is not coated with the conductive material increases, and as a result, the positive electrode current collector (that is, the positive electrode core material) and the positive electrode mixture The electron conductivity between the layers and between the positive electrode active materials existing on the surface of the positive electrode plate is reduced and the resistance is increased.
Therefore, the present inventor has focused on the area ratio of the positive electrode active material (in an exposed state in which the conductive material is not coated on the surface) in the positive electrode mixture layer present on the surface of the positive electrode plate. In the lithium secondary battery according to the present invention, with respect to the total area of the positive electrode mixture layer of the positive electrode plate, the conductive material, binder, and conductive material in the positive electrode mixture layer exposed on the surface of the positive electrode plate are on the surface. The area ratio of the exposed positive electrode active material (excluding the coated positive electrode active material) is 3% or more and 25% or less (typically 4% or more and 22% or less, particularly preferably 4% or more and 8% or less). Satisfies. In the lithium secondary battery configured to have such an area ratio, there is a conductive path between the positive electrode current collector (that is, the positive electrode core material) and the positive electrode mixture layer or between the positive electrode active materials existing on the surface of the positive electrode plate. This is done well and the internal resistance in the positive electrode plate is reduced. As a result, it is possible to provide a lithium secondary battery having a low resistance and excellent battery characteristics (high rate characteristics or cycle characteristics), and particularly good low temperature output characteristics under low temperature charge and discharge.

In a preferred embodiment of the lithium secondary battery disclosed herein, the positive electrode active material is composed of a lithium transition metal composite oxide containing at least lithium and nickel as constituent metal elements.
Nickel-based lithium transition metal composite oxides composed mainly of nickel have a large theoretical lithium ion storage capacity, and use of expensive metal materials such as cobalt-based lithium transition metal composite oxides (for example, LiCoO ₂ ) The amount can be reduced, and it is suitable as a battery for high output applications (for example, in-vehicle use).

Further, preferably, the positive electrode active material has the following general formula:
Li _x Ni _{1- y My} O ₂ (1)
(X and y in the formula (1) are
1 ≦ x ≦ 1.2,
0 ≦ y <0.5 is satisfied, and
M in the formula (1) is at least one element or two or more elements including at least one or two or more metal elements selected from the group consisting of Co, Mn and Al. )
A lithium transition metal composite oxide represented by
Among the lithium transition metal composite oxides, nickel-based lithium transition metal composite oxides represented by the above formula (1) further include cobalt (Co), manganese (Mn), and aluminum as the minutely contained metal element (M). By using a positive electrode active material that can contain at least one or two or more metal elements selected from the group consisting of (Al), a lithium secondary battery that can achieve higher output can be provided. .

In another preferred embodiment of the lithium secondary battery disclosed herein, the positive electrode mixture layer contains at least one water-soluble cellulose derivative as the binder.
The conductive material is coated on the surface of the positive electrode active material through the binder. However, if the binder is excessively attached to the surface of the positive electrode active material, the specific surface area of the positive electrode active material is reduced, and the portion where the binder is attached. Is not preferable because it becomes a reaction resistance at the time of lithium ion desorption. However, the water-soluble cellulose derivative is less likely to adhere to the surface of the positive electrode active material as compared with a binder that is soluble in an organic solvent. As a result, a wide reaction area of the positive electrode active material related to insertion and extraction of lithium ions is secured, and further increase in the output of the lithium secondary battery is expected.

Furthermore, in another preferable embodiment, when the total amount of the positive electrode active material, the binder, and the conductive material in the positive electrode mixture layer is 100% by mass, the content of the conductive material in the positive electrode mixture layer is 5 It is not less than 15% by mass.
If the content of the conductive material is too small, the proportion of the positive electrode active material whose surface is not coated with the conductive material in the positive electrode mixture layer increases. When the area ratio of the exposed positive electrode active material with respect to the total area of the positive electrode mixture layer of the positive electrode plate increases, it exists in the positive electrode current collector (ie, positive electrode core material) -positive electrode mixture layer or on the positive electrode plate surface. As a result, the electron conductivity between the positive electrode active materials is reduced and the resistance is increased. On the other hand, if the content ratio of the conductive material is too large, the conductive materials are aggregated, and thus a large amount of solvent (here, aqueous solvent) is required in the preparation of the aqueous paste. Since the aqueous paste prepared in this way has a low viscosity, the positive electrode active material is likely to settle, and the positive electrode mixture layer formed using such paste is not preferable because the distribution of the positive electrode active material can be biased. However, a positive electrode plate including a positive electrode mixture layer having a conductive material content in the above range has a positive electrode active material between the positive electrode current collector (ie, positive electrode core material) and the positive electrode mixture layer or on the surface of the positive electrode plate. A conduction path between substances is formed well, and an increase in resistance can be suppressed. As a result, a lithium secondary battery having excellent battery characteristics (high rate characteristics or cycle characteristics) as a high-output power supply can be provided.

  Moreover, this invention provides the method of manufacturing a lithium secondary battery as another side surface which implement | achieves the said objective. That is, the method for producing a lithium secondary battery provided by the present invention includes a lithium secondary battery including a positive electrode plate in which a positive electrode mixture layer containing a positive electrode active material is formed on the surface of a positive electrode current collector (ie, positive electrode core material). This is a method for manufacturing a secondary battery. The production method disclosed herein includes: 1) preparing an aqueous paste A by adding a conductive material and at least one binder dissolved or dispersed in an aqueous solvent to the aqueous solvent and kneading; ) Preparing the aqueous paste B by adding the positive electrode active material and at least one binder dissolved or dispersed in the aqueous solvent to the aqueous solvent and kneading; and 3) preparing the aqueous paste A described above. This includes preparing an aqueous paste C by mixing with the aqueous paste B, and applying the paste C to the surface of the positive electrode current collector (that is, the positive electrode core material) to form a positive electrode mixture layer. The area of the positive electrode active material in the positive electrode mixture layer exposed on the surface of the positive electrode plate satisfies 3% or more and 25% or less with respect to the total area of the positive electrode mixture layer of the positive electrode plate. And forming the positive electrode mixture layer.

At the time of preparing the aqueous paste, a conductive material made of a bulky material such as carbon powder tends to be compressed by mechanical energy such as shearing force to reduce the bulk when kneaded with a solvent (here, an aqueous solvent). When the volume of the conductive material is reduced, it becomes difficult to uniformly coat the surface of the positive electrode active material with the conductive material. Even when such an aqueous paste is applied to the positive electrode current collector (that is, the positive electrode core material), A positive electrode mixture layer containing a large amount of the exposed positive electrode active material that is not coated on the surface is formed. In particular, when a large amount of the exposed positive electrode active material is disposed on the surface portion of the positive electrode plate, the positive electrode existing between the positive electrode current collector (ie, positive electrode core material) and the positive electrode mixture layer or on the positive electrode plate surface. The electron conductivity between the active materials is reduced and the resistance is increased. Therefore, how to coat the surface of the positive electrode active material while keeping the conductive material bulky is a problem.
In the manufacturing method according to the present invention, the aqueous paste A containing the conductive material and the aqueous paste B containing the positive electrode active material are separately prepared and then mixed to prepare the aqueous paste C. According to this method, since the material for forming the positive electrode mixture layer (positive electrode active material, conductive material, binder, etc.) is not added at the same time, the load such as shearing force applied to the conductive material during kneading is reduced. be able to. By preparing the aqueous paste A containing the conductive material in advance, it is possible to cover the surface of the positive electrode active material while keeping the conductive material bulky. Furthermore, the area ratio of the positive electrode active material in the positive electrode mixture layer exposed to the positive electrode plate is 3% or more and 25% or less (typically 4% or more with respect to the total area of the positive electrode mixture layer of the positive electrode plate. 22% or less, particularly preferably 4% or more and 8% or less) by applying an aqueous paste C on the surface of the positive electrode current collector (ie, positive electrode core material) to form a positive electrode mixture layer, The conductive path between the positive electrode current collector (that is, the positive electrode core material) and the positive electrode mixture layer or between the positive electrode active materials on the positive electrode plate surface is satisfactorily performed, and the internal resistance in the positive electrode plate is reduced. As a result, it is possible to manufacture a lithium secondary battery having excellent battery characteristics (high rate characteristics or cycle characteristics) in which an increase in internal resistance is suppressed.

In a preferred embodiment of the production method disclosed herein, a lithium transition metal composite oxide containing at least lithium and nickel as constituent metal elements is used as the positive electrode active material.
Nickel-based lithium transition metal composite oxides composed mainly of nickel have a large theoretical lithium ion storage capacity, and use of expensive metal materials such as cobalt-based lithium transition metal composite oxides (for example, LiCoO ₂ ) Since the amount can be reduced, a lithium secondary battery capable of realizing high output can be manufactured by using such a composite oxide as a positive electrode active material.

Furthermore, preferably, as the positive electrode active material, the following general formula:
Li _x Ni _{1- y My} O ₂ (1)
(X and y in the formula (1) are
1 ≦ x ≦ 1.2,
0 ≦ y <0.5 is satisfied, and
M in the formula (1) is at least one element or two or more elements including at least one or two or more metal elements selected from the group consisting of Co, Mn and Al. )
A lithium transition metal composite oxide represented by
Among the lithium transition metal composite oxides, nickel-based lithium transition metal composite oxides represented by the above formula (1) further include cobalt (Co), manganese (Mn), and aluminum as the minutely contained metal element (M). A lithium secondary battery capable of realizing higher output is produced by using, as a positive electrode active material, a composite oxide that can contain at least one or two or more metal elements selected from the group consisting of (Al). be able to.

In another preferred embodiment of the production method disclosed herein, at least one water-soluble cellulose derivative is used as the binder in the positive electrode mixture layer.
When an aqueous paste is prepared using the water-soluble cellulose derivative, the derivative is less likely to adhere to the surface of the positive electrode active material. Therefore, it is possible to provide a lithium secondary battery in which a large reaction area of the positive electrode active material related to the insertion and extraction of lithium ions is ensured and a higher output is possible.

Furthermore, in another preferable embodiment, when the total amount of the positive electrode active material, the binder, and the conductive material in the positive electrode mixture layer is 100% by mass, the content of the conductive material in the positive electrode mixture layer is 5%. The positive electrode mixture layer is formed so as to be not less than 15% by mass and not more than 15% by mass.
If the content of the conductive material is too small, the proportion of the positive electrode active material whose surface is not coated with the conductive material in the positive electrode mixture layer increases. When the area ratio of the exposed positive electrode active material to the total area of the positive electrode mixture layer of the positive electrode plate is increased, the positive electrode plate is formed between the positive electrode current collector (that is, the positive electrode core material) and the positive electrode mixture layer. The electron conductivity between the positive electrode active materials present on the surface is reduced and the resistance is increased. On the other hand, when the content of the conductive material is too large, the conductive materials are aggregated. Therefore, a large amount of solvent (here, aqueous solvent) must be added to prepare an aqueous paste. Since the paste thus obtained has a low viscosity and the positive electrode active material tends to settle, it is difficult to uniformly apply to the surface of the positive electrode current collector (that is, the positive electrode core material). However, since the surface of the positive electrode plate can be coated with a suitable amount of the conductive material by setting the content of the conductive material in the above range, the positive electrode current collector (that is, the positive electrode core material) and the positive electrode mixture layer A conductive path between the positive electrode active material and the positive electrode active material on the positive electrode plate surface is well formed, and an increase in resistance can be suppressed. As a result, a lithium secondary battery having excellent battery characteristics (high rate characteristics or cycle characteristics) as a high-output power source can be manufactured.

More preferably, the aqueous paste A and the aqueous paste B are prepared such that the viscosity of the aqueous paste A is larger than the viscosity of the aqueous paste B.
By preparing the aqueous paste A containing the conductive material to have a higher viscosity than the aqueous paste B containing the positive electrode active material, the conductive material can be made bulky without over compressing the conductive material. An aqueous paste C coated on the surface can be prepared. As a result, a lithium secondary battery having excellent battery characteristics (high rate characteristics or cycle characteristics) as a high-output power supply can be provided.

  In addition, according to the present invention, there is provided a vehicle including any lithium secondary battery disclosed herein (or may be a lithium secondary battery manufactured by any method disclosed herein). The lithium secondary battery provided by the present invention may exhibit performance suitable as a secondary battery mounted on a vehicle (for example, high rate characteristics, cycle characteristics, or low temperature output characteristics). Therefore, such a lithium secondary battery can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile equipped with an electric motor such as a hybrid vehicle, an electric vehicle, and a fuel cell vehicle.

It is a perspective view which shows typically the external shape of the lithium secondary battery which concerns on one Embodiment. It is the II-II sectional view taken on the line in FIG. It is a perspective view which shows typically the state which winds and produces an electrode body. It is a side view which shows typically the vehicle (automobile) provided with the secondary battery which concerns on one Embodiment. It is a figure which shows the surface of the positive electrode plate of the sample A by EPMA. It is a figure which shows the surface of the positive electrode plate of the sample E by EPMA.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

As described above, in the lithium secondary battery (typically, a lithium ion battery) disclosed herein, the positive electrode mixture layer containing the positive electrode active material is formed on the surface of the positive electrode current collector (that is, the positive electrode core material). A positive electrode plate.
First, each component of the positive electrode plate of the lithium secondary battery according to the present embodiment will be described. The positive electrode mixture layer of the positive electrode plate includes a powdery (granular) positive electrode active material capable of occluding and releasing lithium ions serving as charge carriers, at least one binder dissolved or dispersed in an aqueous solvent, and a conductive material Including. As such a positive electrode active material, one or two or more kinds of substances conventionally used in lithium secondary batteries can be used without particular limitation as long as the object of the present invention can be realized. As a typical positive electrode active material, a lithium transition metal composite oxide containing lithium (Li) and at least one transition metal element can be given. For example, lithium nickelate (LiNiO ₂ ), lithium cobaltate (LiCoO ₂ ), lithium manganate (LiMn ₂ O ₄ ), or nickel / manganese-based LiNi _x Mn _1-x O ₂ (0 <x <1) _{LiNi x Mn 2-x O 4} (0 <x <2), LiNi x Co 1-x O 2 (0 <x <1) of the nickel-cobalt, LiCo of cobalt-manganese-based _x Mn _{1-x O 2} A so-called binary lithium transition metal composite oxide containing two kinds of transition metal elements other than lithium as represented by (0 <x <1) may be used. Alternatively, a ternary lithium transition metal composite oxide (typically LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) such as nickel / cobalt / manganese containing three kinds of transition metal elements may be used.
However, more preferably, it is a nickel-based lithium transition metal composite oxide having at least lithium and nickel as constituent metal elements. Such a complex oxide has a large theoretical lithium ion storage capacity, and is therefore suitable as a battery for high-power applications (for example, in-vehicle use).

Further, a more preferable positive electrode active material has the following general formula:
Li _x Ni _{1- y My} O ₂ (1)
(X and y in the formula (1) are
1 ≦ x ≦ 1.2,
0 ≦ y <0.5 is satisfied, and
M in the formula (1) is at least one element or two or more elements including at least one or two or more metal elements selected from the group consisting of Co, Mn and Al. ) Is a lithium transition metal composite oxide. Among the lithium transition metal composite oxides, the nickel-based lithium transition metal composite oxide represented by the above formula (1) further includes cobalt (Co), manganese (Mn), and aluminum (M) as the metal element (M). It may contain at least one or two or more metal elements selected from the group consisting of Al).

  Here, the lithium transition metal composite oxide represented by the above formula (1) is at least one or two or more selected from the group consisting of cobalt (Co), manganese (Mn), and aluminum (Al) as the M element. In addition to oxides containing the above metal elements, at least one element (that is, transition metal element and / or typical metal element other than the above-mentioned main constituent metal elements) is a minute constituent metal in a proportion smaller than the molar ratio of each main constituent metal element. It is meant to include oxides contained as elements. Examples of such minute constituent metal elements include chromium (Cr), vanadium (V), magnesium (Mg), titanium (Ti), zirconium (Zr), niobium (Nb), molybdenum (Mo), tungsten (W), Selected from the group consisting of copper (Cu), zinc (Zn), gallium (Ga), indium (In), tin (Sn), lanthanum (La), cerium (Ce), iron (Fe) and yttrium (Y) Can be one or more.

  In addition, as the positive electrode active material disclosed herein, for example, a lithium transition metal composite oxide powder prepared and provided by a conventionally known method can be used as it is. For example, the oxide can be prepared by mixing several raw material compounds appropriately selected according to the atomic composition at a predetermined molar ratio and firing by an appropriate means. In addition, a granular lithium transition metal composite oxide substantially constituted by secondary particles having a desired average particle size and / or particle size distribution by pulverizing, granulating and classifying the fired product by an appropriate means Can be obtained.

Furthermore, as the at least one binder that dissolves or disperses in the aqueous solvent contained in the positive electrode mixture layer, a polymer that is insoluble in the organic solvent and soluble or dispersible in the aqueous solvent can be selected. For example, polymers dissolved in an aqueous solvent include carboxymethyl cellulose (CMC; typically sodium salt), hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), methyl cellulose (MC), cellulose acetate phthalate (CAP), Examples thereof include cellulose derivatives such as hydroxypropylmethylcellulose (HPMC) and hydroxypropylmethylcellulose phthalate (HPMCP), and polyvinyl alcohol (PVA). Of these, cellulose derivatives (for example, CMC) can be particularly preferably used.
Polymers dispersed in the aqueous solvent include polyethylene oxide (PEO), polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer. Fluorine resin such as coalescence (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), vinyl acetate copolymer, styrene butadiene block copolymer (SBR), acrylic acid modified SBR resin (SBR latex), Arabic Examples thereof include rubbers such as rubber. Such a binder may be used individually by 1 type, and may be used in combination of 2 or more type. In addition to the function as a binder, the polymer material exemplified above may be used for the purpose of exhibiting the function as a thickener or other additive of the above composition.

  The aqueous solvent in which the binder is dissolved or dispersed is typically water, but may be any water-based solvent as a whole, that is, water or a mixed solvent mainly composed of water is preferably used. it can. As the solvent other than water constituting the mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used. For example, it is preferable to use a solvent in which about 80% by mass or more (more preferably about 90% by mass or more, more preferably about 95% by mass or more) of the aqueous solvent is water. A particularly preferred example is a solvent consisting essentially of water.

Moreover, as said electrically conductive material, electroconductive powder materials, such as carbon powder and carbon fiber, are used preferably. As the carbon powder, various carbon blacks such as acetylene black, furnace black, ketjen black, and graphite powder are preferable. In addition, conductive fibers such as carbon fibers and metal fibers, metal powders such as copper and nickel, and organic conductive materials such as polyphenylene derivatives can be contained alone or as a mixture thereof. In addition, only 1 type may be used among these, or 2 or more types may be used together.
Moreover, although the said material is not specifically limited, For example, bulk density (JIS K1469 conformity) is 0.1-0.25 g / cm < ³ > (preferably about 0.14-0.18 g / cm < ³ > suitably). A certain conductive powder material is particularly preferably used.

The ratio of the material constituting the positive electrode mixture layer is not particularly limited, but when the total amount of the positive electrode active material, the binder, and the conductive material is 100% by mass, the inclusion of the conductive material in the positive electrode mixture layer The rate can be, for example, about 3% by mass to 17% by mass, and it is more preferable that the positive electrode mixture layer is formed so that it is preferably about 5% by mass to 15% by mass. If the content of the conductive material is too small, the ratio of the exposed positive electrode active material in which the conductive material is not coated on the surface in the positive electrode mixture layer increases. Therefore, the area ratio occupied by the exposed positive electrode active material exposed on the surface of the positive electrode plate is larger than the total area of the positive electrode mixture layer of the positive electrode plate. In this case, the electron conductivity between the positive electrode current collector (that is, the positive electrode core material) and the positive electrode mixture layer or between the positive electrode active materials existing on the surface of the positive electrode plate is reduced, and the resistance is increased. On the other hand, if the content of the conductive material is too large, the conductive materials are aggregated, so that a large amount of solvent (here, aqueous solvent) is required in the preparation of the aqueous paste. Since the aqueous paste prepared in this way has a low viscosity, the positive electrode active material is likely to settle, and the positive electrode mixture layer formed using such paste is not preferable because the distribution of the positive electrode active material can be biased. However, a positive electrode plate including a positive electrode mixture layer having a conductive material content in the above range has a positive electrode active material between the positive electrode current collector (ie, positive electrode core material) and the positive electrode mixture layer or on the surface of the positive electrode plate. A conduction path between substances is formed well, and an increase in resistance can be suppressed.
The proportion of the positive electrode active material in the positive electrode mixture layer is preferably about 50% by mass or more (typically 50 to 95% by mass), and about 70 to 95% by mass (for example, 80 to 95% by mass). ) Is more preferable.
Furthermore, the ratio of the binder in the positive electrode mixture layer can be, for example, about 1 to 10% by mass, usually about 3 to 8% by mass, and more preferably 1 to 5% by mass.

  Moreover, the positive electrode mixture layer of the lithium secondary battery according to the present invention is formed on the surface of the positive electrode plate, and as described above, the positive electrode active material, and at least one binder dissolved or dispersed in an aqueous solvent, And conductive material. Here, the area ratio of the positive electrode active material in the positive electrode mixture layer exposed on the surface of the positive electrode plate to the total area of the positive electrode mixture layer of the positive electrode plate is 3% or more and 25% or less (typically 4% or more and 22% or less, and particularly preferably 4% or more and 8% or less). In a lithium secondary battery configured such that the area ratio of the positive electrode active material in the positive electrode mixture layer exposed on the surface of the positive electrode plate satisfies the above range, the positive electrode current collector (that is, the positive electrode core material) and the positive electrode composite Conductive paths between the material layers and between the positive electrode active materials are performed well, and the internal resistance of the positive electrode plate is reduced. As a result, a lithium secondary battery capable of high output with suppressed increase in internal resistance can be obtained.

  Here, in order to determine the area ratio of the positive electrode active material (in an exposed state where the conductive material is not coated on the surface) in the positive electrode mixture layer existing on the surface of the positive electrode plate, the positive electrode mixture layer was formed. The distribution state of the positive electrode plate surface can be analyzed by mapping with EPMA (Electron Probe Micro-Analysis). EPMA is an analysis in which the surface of a sample is irradiated with an electron beam focused to about 1 μm to detect characteristic X-rays generated by the interaction between the sample and the electron beam. The area ratio of the positive electrode active material present on the surface can be measured.

  In addition, as the positive electrode current collector (that is, the positive electrode core material) serving as the base material of the positive electrode plate, a conductive member made of a metal having good conductivity is preferably used. For example, aluminum or an alloy containing aluminum as a main component can be used. The shape of the positive electrode current collector (that is, the positive electrode core material) can vary depending on the shape of the lithium secondary battery, and is not particularly limited. Various shapes such as a rod shape, a plate shape, a sheet shape, a foil shape, and a mesh shape are available. It can be in the form of

Subsequently, the manufacturing method of a positive electrode plate is demonstrated as an example of the preferable aspect of the manufacturing method of the lithium secondary battery which concerns on this invention.
The manufacturing method disclosed herein is a method for manufacturing a lithium secondary battery including a positive electrode plate in which a positive electrode mixture layer containing a positive electrode active material is formed on the surface of a positive electrode current collector (that is, a positive electrode core material). .
1) Step of preparing an aqueous paste A by adding and kneading a conductive material and at least one binder dissolved or dispersed in an aqueous solvent to the aqueous solvent, 2) a positive electrode active material, and an aqueous solvent Step of preparing aqueous paste B by adding and kneading at least one binder that dissolves or disperses in an aqueous solvent, and 3) aqueous by mixing aqueous paste A and aqueous paste B prepared above. A step of preparing paste C and applying the paste C to the surface of a positive electrode current collector (ie, positive electrode core material) to form a positive electrode mixture layer. Hereafter, the manufacturing method of the positive electrode plate including the said process is demonstrated in detail.

  First, an aqueous paste A is prepared by adding a conductive material and at least one binder dissolved or dispersed in an aqueous solvent to the aqueous solvent and kneading them. The conductive material is easily agglomerated and bulky and difficult to disperse. However, by adding at least one binder (for example, CMC) that is dissolved or dispersed in the aqueous solvent, the binder adheres to the surface of the conductive material, and the affinity of the conductive material for water is improved. Therefore, the aqueous paste A can be prepared without aggregating the conductive material even when kneaded.

  Furthermore, in the production method disclosed herein, the aqueous paste B is prepared by adding a positive electrode active material and at least one binder dissolved or dispersed in an aqueous solvent to the aqueous solvent and kneading. And the aqueous paste C containing all the materials which comprise the positive mix layer is prepared by mixing the aqueous paste A and the aqueous paste B which were each prepared. According to this procedure, constituent materials for forming the positive electrode mixture layer (positive electrode active material, conductive material, binder, etc.) are not added at the same time, so that the load such as shearing force applied to the conductive material during kneading can be reduced. It is possible to coat the surface of the positive electrode active material while keeping the conductive material bulky.

  In addition, it is preferable to prepare the aqueous paste A and the aqueous paste B so that the viscosity of the aqueous paste A containing the conductive material is larger than the viscosity of the aqueous paste B containing the positive electrode active material. By preparing the aqueous paste A containing the conductive material to have a viscosity higher than that of the aqueous paste B containing the positive electrode active material, the aqueous paste A can be prepared without over compressing the conductive material. Furthermore, by mixing with an aqueous paste B containing a positive electrode active material having a viscosity lower than that of the aqueous paste A, an aqueous paste C having excellent coatability (performance to uniformly apply to the positive electrode current collector) is prepared. Can do.

  In addition, as long as it has the property melt | dissolved or disperse | distributed to an aqueous solvent as each binder used for preparation of the said aqueous paste A and the said aqueous paste B, it does not restrict | limit. For example, the same substances may be used among the binders listed above, or binders of different substances may be used. Moreover, when making the viscosity of the aqueous paste A larger than the viscosity of the aqueous paste B as described above, the amount of the aqueous solvent added at the time of preparation is increased or decreased, or binders having different thickening actions are used. It can be adjusted depending on the situation. For example, PEO may be used as the binder of the aqueous paste A containing the conductive material, and CMC having a smaller thickening action than PEO may be used as the binder of the aqueous paste B containing the positive electrode active material.

Next, the aqueous paste C prepared by mixing the aqueous paste A and the aqueous paste B prepared above was applied to the surface of the positive electrode current collector (that is, the positive electrode core material), and the solvent was volatilized and dried. After that, it is compressed (pressed). Thereby, the positive electrode plate of the lithium secondary battery in which the positive electrode mixture layer is formed on the surface of the positive electrode current collector (that is, the positive electrode core material) is obtained. In the manufacturing method disclosed herein, the area ratio of the positive electrode active material in the positive electrode mixture layer exposed on the surface of the positive electrode plate is 3% or more with respect to the total area of the positive electrode mixture layer of the positive electrode plate. The positive electrode mixture layer is formed so as to satisfy 25% or less (typically 4% or more and 22% or less, particularly preferably 4% or more and 8% or less). When a large amount of the positive electrode active material whose surface is not coated with the conductive material is disposed between the surface portion of the positive electrode plate and the positive electrode active material, the positive electrode current collector (that is, the positive electrode core material) and the positive electrode mixture layer In addition, the electron conductivity between the positive electrode active materials is reduced, and the resistance is increased. However, the positive electrode mixture layer is formed so that the area ratio of the positive electrode active material in the positive electrode mixture layer exposed on the surface of the positive electrode plate satisfies the above range with respect to the total area of the positive electrode mixture layer of the positive electrode plate. Thus, a conductive path between the positive electrode current collector (that is, the positive electrode core material) and the positive electrode mixture layer or between the positive electrode active materials is satisfactorily performed, and the internal resistance in the positive electrode plate is reduced. As a result, it is possible to manufacture a lithium secondary battery having excellent battery characteristics (high rate characteristics or cycle characteristics) in which an increase in internal resistance is suppressed.

  In addition, as a method of apply | coating the said aqueous paste C to a positive electrode electrical power collector (namely, positive electrode core material), the technique similar to a conventionally well-known method can be employ | adopted suitably. For example, the paste can be suitably applied to the positive electrode current collector (that is, the positive electrode core material) by using an appropriate application device such as a slit coater, a die coater, a gravure coater, or a comma coater. Moreover, when drying a solvent, it can dry favorably by using natural drying, a hot air, low-humidity air, a vacuum, infrared rays, far-infrared rays, and an electron beam individually or in combination. Furthermore, as a compression method, a conventionally known compression method such as a roll press method or a flat plate press method can be employed. In adjusting the thickness, the thickness may be measured with a film thickness measuring instrument, and the press pressure may be adjusted to compress a plurality of times until a desired thickness is obtained.

  Next, each component of the negative electrode of the lithium secondary battery disclosed here will be described. Such a negative electrode has a configuration in which a negative electrode mixture layer is formed on the surface of a negative electrode current collector (that is, a negative electrode core material). As the negative electrode current collector (that is, the negative electrode core material) serving as the negative electrode substrate, a conductive member made of a metal having good conductivity is preferably used. For example, copper or an alloy containing copper as a main component can be used. The shape of the negative electrode current collector (ie, the negative electrode core material) is not particularly limited because it may vary depending on the shape or the like of the lithium secondary battery. Various shapes such as a rod shape, a plate shape, a sheet shape, a foil shape, and a mesh shape are available. It can be in form. A copper foil having a thickness of about 5 to 100 μm is suitably used as a negative electrode current collector of a lithium secondary battery used as a high-output power source for mounting on a vehicle.

  The negative electrode mixture layer formed on the surface of the negative electrode current collector (that is, the negative electrode core material) contains a negative electrode active material capable of occluding and releasing lithium ions serving as charge carriers. As the negative electrode active material, one type or two or more types of materials conventionally used in lithium secondary batteries can be used without any particular limitation. An example is carbon particles. A particulate carbon material (carbon particles) containing a graphite structure (layered structure) at least partially is preferably used. Any carbon material of a so-called graphitic material (graphite), non-graphitizable carbon material (hard carbon), easily graphitized carbon material (soft carbon), or a combination of these materials is preferably used. obtain. Among these, graphite particles can be preferably used. Graphite particles (eg, graphite) are excellent in conductivity because they can suitably occlude lithium ions as charge carriers. Moreover, since the particle size is small and the surface area per unit volume is large, it can be a negative electrode active material suitable for higher rate charge / discharge.

  Moreover, the said negative electrode compound material layer can typically contain arbitrary components, such as a binder, as needed in addition to the said negative electrode active material as the structural component. As such a binder, the same binder as that used for the negative electrode of a general lithium secondary battery can be adopted as appropriate, and functions as the binder listed in the components of the positive electrode plate described above. Various polymer materials that can be used are preferably used. Alternatively, when a non-aqueous solvent (organic solvent) is used as a solvent during paste preparation, a water-insoluble polymer that is soluble in an organic solvent and insoluble in water may be used as a binder. it can. Examples of this type of polymer include polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyacrylonitrile (PAN), polypropylene oxide (PPO), and polyethylene oxide-propylene oxide copolymer (PEO-PPO). .

  Next, a method for manufacturing the negative electrode of the lithium secondary battery will be described. In order to form a negative electrode mixture layer on the surface of the negative electrode current collector (that is, the negative electrode core material), first, the negative electrode active material is mixed with the appropriate solvent (aqueous solvent or non-aqueous solvent) together with the binder and the like. Then, a paste or slurry-like composition for forming a negative electrode mixture layer (hereinafter referred to as “negative electrode mixture layer forming paste”) is prepared. What was illustrated by the component of the above-mentioned positive electrode plate can be used suitably for an aqueous solvent. Further, preferred examples of the non-aqueous solvent include N-methyl-2-pyrrolidone (NMP), methyl ethyl ketone, toluene and the like.

  In addition, as for the blending ratio of each constituent material, for example, the ratio of the negative electrode active material in the negative electrode mixture layer is preferably about 50% by mass or more, and about 85 to 99% by mass (for example, 90 to 97% by mass). It is more preferable that Further, the ratio of the binder in the negative electrode mixture layer can be, for example, about 1 to 15% by mass, and usually about 3 to 10% by mass is preferable. The paste thus prepared is applied to a negative electrode current collector (that is, a negative electrode core material), the solvent is volatilized and dried, and then compressed (pressed). Thereby, the negative electrode of the lithium secondary battery which has the negative electrode compound material layer formed using this paste on a negative electrode collector (namely, negative electrode core material) is obtained. In addition, the application | coating, drying, and the compression method can use a conventionally well-known means similarly to the manufacturing method of the above-mentioned positive electrode plate.

  Hereinafter, as one specific example of the lithium secondary battery according to the present invention, a square-shaped lithium secondary battery including a wound electrode body will be described. However, the present invention is not intended to be limited to such an example. Absent. Further, matters other than the matters specifically mentioned in the present specification and matters necessary for carrying out the present invention (for example, the configuration and manufacturing method of the electrode body, the configuration and manufacturing method of the separator, the lithium secondary battery, etc. General techniques related to battery construction, etc.) can be grasped as design matters of those skilled in the art based on conventional techniques in the field. In addition, in the following drawings, the same code | symbol is attached | subjected to the member and site | part which show | plays the same effect | action, and the overlapping description may be abbreviate | omitted or simplified. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships.

FIG. 1 is a perspective view schematically showing a rectangular lithium secondary battery according to an embodiment, and FIG. 2 is a cross-sectional view taken along line II-II in FIG. FIG. 3 is a perspective view schematically showing a state in which the electrode body is wound and manufactured.
As shown in FIGS. 1 and 2, the lithium secondary battery 100 according to the present embodiment includes a rectangular parallelepiped battery case 10 and a lid body 14 that closes the opening 12 of the case 10. A flat electrode body (wound electrode body 20) and an electrolyte can be accommodated in the battery case 10 through the opening 12. The lid 14 is provided with a positive terminal 38 and a negative terminal 48 for external connection, and a part of the terminals 38 and 48 protrudes to the surface side of the lid 14. Also, some of the external terminals 38 and 48 are connected to the internal positive terminal 37 or the internal negative terminal 47, respectively, inside the case.

  Next, the wound electrode body 20 according to the present embodiment will be described with reference to FIGS. 2 and 3. As shown in FIG. 3, the wound electrode body 20 includes a sheet-like positive electrode sheet 30 having a positive electrode mixture layer 34 on the surface of a long positive electrode current collector (that is, a positive electrode core material) 32, A sheet-like separator 50 and a sheet-like negative electrode sheet 40 having a negative electrode mixture layer 44 on the surface of a long negative electrode current collector (ie, negative electrode core material) 42 are configured. In the cross-sectional view in the winding axis direction R, the positive electrode sheet 30 and the negative electrode sheet 40 are laminated via two separators 50, and the positive electrode sheet 30, the separator 50, the negative electrode sheet 40, and the separator 50 are stacked. Are stacked in this order. The laminate is wound around a shaft core (not shown) in a cylindrical shape, and is formed into a flat shape by squashing the obtained wound electrode body 20 from the side surface direction.

Further, as shown in FIG. 3, the wound electrode body 20 according to the present embodiment has a positive electrode current collector (that is, a positive electrode core material) 32 at the center in the winding axis direction R. The formed positive electrode mixture layer 34 and the negative electrode mixture layer 44 formed on the surface of the negative electrode current collector (that is, the negative electrode core material) 42 are overlapped and densely stacked. Further, in a cross-sectional view in a direction along the winding axis direction R, the positive electrode current collector (that is, the positive electrode core material) 32 is exposed without forming the positive electrode mixture layer 34 at one end portion in the direction R. The portion (the positive electrode mixture layer non-forming portion 36) is laminated so as to protrude from the separator 50 and the negative electrode sheet 40 (or the dense laminated portion of the positive electrode mixture layer 34 and the negative electrode mixture layer 44). ing. That is, a positive current collector laminated portion (that is, a positive electrode core material) in which a positive electrode mixture layer non-forming portion 36 in a positive electrode current collector (namely, positive electrode core material) 32 is laminated at the end of the electrode body 20. (Stacked portion) 35 is formed. Further, the other end portion of the electrode body 20 has the same configuration as that of the positive electrode sheet 30, and the negative electrode mixture layer non-forming portion 46 in the negative electrode current collector (that is, the negative electrode core material) 42 is laminated, so A body laminate portion (that is, a negative electrode core laminate portion) 45 is formed.
Here, as the separator 50, a separator having a width larger than the width of the laminated portion of the positive electrode mixture layer 34 and the negative electrode mixture layer 44 and smaller than the width of the electrode body 20 is used, and a positive electrode current collector (that is, The positive electrode core material 32 and the negative electrode current collector 42 (that is, the negative electrode core material) 42 are arranged so as to be sandwiched between the stacked portions of the positive electrode mixture layer 34 and the negative electrode mixture layer 44 so as not to cause an internal short circuit. Has been.

The separator 50 is a sheet interposed between the positive electrode sheet 30 and the negative electrode sheet 40, and is disposed so as to be in contact with the positive electrode mixture layer 34 of the positive electrode sheet 30 and the negative electrode mixture layer 44 of the negative electrode sheet 40. And the short circuit prevention accompanying the contact of both the composite material layers 34 and 44 in the positive electrode sheet 30 and the negative electrode sheet 40, or the conduction path between electrodes by impregnating the electrolyte (non-aqueous electrolyte) in the pores of the separator 50 It plays a role of forming (conductive path).
As a constituent material of the separator 50, a porous sheet (microporous resin sheet) made of a resin can be preferably used. Particularly preferred are porous polyolefin resins such as polypropylene, polyethylene, and polystyrene.

  The lithium secondary battery according to the present embodiment can be constructed as follows. In the embodiment described above, the positive electrode plate (typically positive electrode sheet 30) and the negative electrode (typically negative electrode sheet 40) are stacked and wound together with two separators 50, and the wound electrode body 20 obtained is laterally oriented. It is formed into a flat shape by crushing and abating. An internal positive electrode terminal 37 is connected to the positive electrode mixture layer non-forming portion 36 of the positive electrode current collector (ie, positive electrode core material) 32, and an internal electrode is connected to the exposed end portion of the negative electrode current collector (ie, negative electrode core material) 42. The negative electrode terminal 47 is joined by ultrasonic welding, resistance welding or the like, and is electrically connected to the positive electrode sheet 30 or the negative electrode sheet 40 of the wound electrode body 20 formed in the flat shape. After the wound electrode body 20 obtained in this manner is accommodated in the battery case 10, the lithium secondary battery 100 of this embodiment can be constructed by injecting a non-aqueous electrolyte and sealing the inlet. . In particular, the structure, size, material (for example, can be made of metal or laminate film) of the battery case 10, and the structure of the electrode body (for example, a wound structure or a laminated structure) having the positive and negative electrodes as main components, etc. There is no limit.

As the non-aqueous electrolyte, the same non-aqueous electrolyte as conventionally used for lithium secondary batteries can be used without any particular limitation. Such a nonaqueous electrolytic solution typically has a composition in which a supporting salt is contained in a suitable nonaqueous solvent. Examples of the non-aqueous solvent include one or two selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and the like. More than seeds can be used. Examples of the supporting salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ). _3. Lithium compounds (lithium salts) such as LiI can be used. In addition, the density | concentration of the support salt in a nonaqueous electrolyte solution may be the same as that of the nonaqueous electrolyte solution used with the conventional lithium secondary battery, and there is no restriction | limiting in particular. An electrolyte containing an appropriate lithium compound (supporting salt) at a concentration of about 0.1 to 5 mol / L can be used.

  As described above, the lithium secondary battery 100 constructed in this manner can exhibit excellent battery characteristics (high rate characteristics, cycle characteristics, or low temperature output characteristics) as a vehicle-mounted high-output power supply. Therefore, the lithium secondary battery 100 according to the present invention can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile. Therefore, as schematically shown in FIG. 4, a vehicle including such a lithium secondary battery 100 (which may be in the form of an assembled battery formed by connecting a plurality of lithium secondary batteries 100 in series) as a power source. (Typically automobiles, in particular automobiles equipped with electric motors such as hybrid cars, electric cars, fuel cell cars) 1 are provided.

  In the following test examples, a lithium secondary battery (test battery) disclosed herein was constructed and its performance was evaluated. However, it is not intended to limit the present invention to those shown in the specific examples.

<Construction of lithium secondary battery: Sample A>
A lithium secondary battery according to Sample A was constructed as follows.
First, a positive electrode plate of a lithium secondary battery according to Sample A was produced. That is, when forming the positive electrode mixture layer in the positive electrode plate, a paste for forming the positive electrode mixture layer was prepared. 5 parts by weight of acetylene black (AB) having a bulk density of 0.14 to 0.18 g / cm ³ (conforming to JIS K1469) as a conductive material, and 1.7 parts by weight of carboxymethyl cellulose (CMC) as a binder An aqueous paste A was prepared by kneading in addition to 55 parts by weight of ion-exchanged water.
Further, 92 parts by weight of the positive electrode active material (LiNi _0.82 Co _0.15 Al _0.03 O ₂ ) and 0.3 parts by weight of carboxymethyl cellulose (CMC) are added to 30 parts by weight of ion-exchanged water and kneaded. An aqueous paste B was prepared.
Then, the prepared aqueous paste A and aqueous paste B were mixed, and further 1.3 parts by weight of polytetrafluoroethylene (PTFE) / water suspension having a solid content of 80% was added to prepare aqueous paste C. .
Next, the aqueous paste C was applied to the aluminum foil (thickness 15 μm) as the positive electrode current collector (that is, the positive electrode core material) so that the coating amount of the positive electrode active material per unit area was 86 mg / cm ^2. That is, it was applied to one side of (a positive electrode core material) and dried. After drying, the sheet was rolled into a sheet with a roller press to form a thickness of 58 μm, and the positive electrode mixture layer was slit so that the positive electrode mixture layer had a predetermined width (71 mm in this case) to prepare a positive electrode sheet.

Next, the negative electrode of the lithium secondary battery according to Sample A was produced. That is, when forming the negative electrode mixture layer in the negative electrode, a negative electrode mixture layer forming paste (negative electrode paste) was prepared. The paste was prepared by adding 98 parts by weight of graphite as a negative electrode active material, 1 part by weight of a styrene butadiene block copolymer (SBR) as a binder, and 1 part by weight of carboxymethyl cellulose (CMC) to ion-exchanged water. And mixing.
Then, the negative electrode paste is applied to the copper foil (thickness 10 μm) as the negative electrode current collector (that is, the negative electrode core material) so that the coating amount of the negative electrode active material per unit area becomes 6.4 mg / cm ^2. It applied to both surfaces of the electric body (namely, negative electrode core material), and was dried. After drying, it was rolled into a sheet with a roller press to form a thickness of 57 μm, and a negative electrode sheet was formed by slitting so that the negative electrode mixture layer had a predetermined width.

A lithium secondary battery according to Sample A was constructed using the prepared positive electrode sheet and negative electrode sheet. That is, a positive electrode sheet and a negative electrode sheet were laminated together with two separators, and this laminated sheet was wound to produce a wound electrode body. And this electrode body was accommodated in a container with electrolyte, and the (square) large sized battery (dimension (mm) about width 110x depth 14x height 90) was constructed | assembled. As an electrolytic solution, a non-aqueous electrolytic solution having a composition in which 1 mol / L LiPF ₆ was dissolved in a 1: 1 (volume ratio) mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) was used.

<Construction of lithium secondary battery: Sample B>
The lithium secondary battery according to Sample B was made of the same material as the lithium secondary battery according to Sample A, except that the positive electrode active material and the conductive material content in the positive electrode mixture layer were changed.
First, in preparing an aqueous paste for forming a positive electrode mixture layer, 10 parts by weight of AB as a conductive material and 1.7 parts by weight of CMC as a binder are added to 55 parts by weight of ion-exchanged water and kneaded. To prepare an aqueous paste A.
Further, 88 parts by weight of a positive electrode active material (LiNi _0.82 Co _0.15 Al _0.03 O ₂ ) and 0.3 parts by weight of CMC as a binder are added to 30 parts by weight of ion-exchanged water and kneaded. As a result, an aqueous paste B was prepared.
Then, the prepared aqueous paste A and aqueous paste B were mixed, and further 1.3 parts by weight of PTFE / water suspension having a solid content rate of 80% was added to prepare an aqueous paste C.
A positive electrode plate was produced by the same procedure as that of the lithium secondary battery according to Sample A, except that the content ratios of the positive electrode active material and the conductive material were changed. A lithium secondary battery according to Sample B was constructed using the positive electrode plate thus prepared and a negative electrode similar to the lithium secondary battery according to Sample A above.

<Construction of lithium secondary battery: Sample C>
The lithium secondary battery according to sample C was made of the same material as the lithium secondary battery according to sample A, except that the contents of the positive electrode active material and the conductive material in the positive electrode mixture layer were changed.
First, in preparing the aqueous paste for forming the positive electrode mixture layer, 15 parts by weight of AB as a conductive material and 1.7 parts by weight of CMC as a binder are added to 55 parts by weight of ion-exchanged water and kneaded. To prepare an aqueous paste A.
Further, 83 parts by weight of a positive electrode active material (LiNi _0.82 Co _0.15 Al _0.03 O ₂ ) and 0.3 part by weight of CMC as a binder are added to 30 parts by weight of ion-exchanged water and kneaded. As a result, an aqueous paste B was prepared.
Then, the prepared aqueous paste A and aqueous paste B were mixed, and further 1.3 parts by weight of PTFE / water suspension having a solid content rate of 80% was added to prepare an aqueous paste C.
A positive electrode plate was produced by the same procedure as that of the lithium secondary battery according to Sample A, except that the content ratios of the positive electrode active material and the conductive material were changed. A lithium secondary battery according to Sample C was constructed using the positive electrode plate thus prepared and a negative electrode similar to the lithium secondary battery according to Sample A.

<Construction of lithium secondary battery: Sample D>
The lithium secondary battery according to Sample D was made of the same material as the lithium secondary battery according to Sample A above, except that the contents of the positive electrode active material and the conductive material in the positive electrode mixture layer were changed.
First, in preparing the aqueous paste for forming the positive electrode mixture layer, 20 parts by weight of AB as a conductive material and 1.7 parts by weight of CMC as a binder are added to 55 parts by weight of ion-exchanged water and kneaded. To prepare an aqueous paste A.
Further, 78 parts by weight of a positive electrode active material (LiNi _0.82 Co _0.15 Al _0.03 O ₂ ) and 0.3 part by weight of CMC as a binder are added to 30 parts by weight of ion-exchanged water and kneaded. As a result, an aqueous paste B was prepared.
Then, the prepared aqueous paste A and aqueous paste B were mixed, and further 1.3 parts by weight of PTFE / water suspension having a solid content rate of 80% was added to prepare an aqueous paste C. Since the aqueous paste C prepared in this way did not have fluidity (high viscosity), it could not be applied to the positive electrode current collector (that is, the positive electrode core material). Therefore, sample D did not build a lithium secondary battery.

<Construction of lithium secondary battery: Sample E>
The lithium secondary battery according to Sample E was made of the same material as the lithium secondary battery according to Sample A, except that the paste preparation method was changed. That is, an aqueous paste was prepared by simultaneously adding materials for forming the positive electrode mixture layer.
First, in preparing an aqueous paste for forming a positive electrode mixture layer, 92 parts by weight of a positive electrode active material (LiNi _0.82 Co _0.15 Al _0.03 O ₂ ), AB 5 parts by weight as a conductive material, 2 parts by weight of CMC as a binder was added to 85 parts by weight of ion exchange water and kneaded. Further, 1.3 parts by weight of PTFE / water suspension having a solid content of 80% was added to prepare an aqueous paste.
A positive electrode plate was produced by the same procedure as the lithium secondary battery according to Sample A, except that the method for preparing the paste was changed. A lithium secondary battery according to Sample E was constructed using the positive electrode plate thus prepared and a negative electrode similar to the lithium secondary battery according to Sample A.

<Construction of lithium secondary battery: Sample F>
The lithium secondary battery according to Sample F was made of the same material as the lithium secondary battery according to Sample A, except that the paste preparation method and the solvent during paste preparation were changed. That is, a paste was prepared by simultaneously adding materials for forming the positive electrode mixture layer. Furthermore, a non-aqueous paste was prepared using a non-aqueous solvent N-methyl-2-pyrrolidone (NMP) without using an aqueous solvent.
That is, in preparing a non-aqueous paste for forming a positive electrode mixture layer, 92 parts by weight of a positive electrode active material (LiNi _0.82 Co _0.15 Al _0.03 O ₂ ), and 5 parts by weight of AB as a conductive material, A non-aqueous paste was prepared by adding and kneading 23 parts by weight of polyvinylidene fluoride (PVDF / NMP solution) having a solid content of 13% as a binder to 65 parts by weight of the non-aqueous solvent NMP.
A positive electrode plate was produced by the same procedure as that of the lithium secondary battery according to Sample A, except that the paste preparation method and the solvent during paste preparation were changed. A lithium secondary battery according to Sample E was constructed using the positive electrode plate thus prepared and a negative electrode similar to the lithium secondary battery according to Sample A.

<Construction of lithium secondary battery: Sample G>
The lithium secondary battery according to Sample G was made of the same material as that of the lithium secondary battery according to Sample A, except that the solvent used for preparing the paste was changed. That is, a non-aqueous paste was prepared using a non-aqueous solvent N-methyl-2-pyrrolidone (NMP) without using an aqueous solvent.
First, in preparing a non-aqueous paste for forming a positive electrode mixture layer, 10 parts by weight of AB as a conductive material and polyvinylidene fluoride (PVDF / NMP having a solid content of 13% as a binder are used. A non-aqueous paste A was prepared by adding 23 parts by weight of the solution) to 10 parts by weight of the non-aqueous solvent NMP and kneading.
Further, 88 parts by weight of a positive electrode active material (LiNi _0.82 Co _0.15 Al _0.03 O ₂ ) and a polyvinylidene fluoride (PVDF / PVD) having a solid content of 13% as a binder as a binder. NMP solution) 11.5 parts by weight was added to 10 parts by weight of non-aqueous solvent NMP and kneaded to prepare non-aqueous paste B.
And the prepared non-aqueous paste A and the non-aqueous paste B were mixed, and the non-aqueous paste C was prepared.
A positive electrode plate was produced by the same procedure as that of the lithium secondary battery according to Sample A, except that the solvent at the time of preparing the paste was changed. A lithium secondary battery according to sample G was constructed using the positive electrode plate thus prepared and a negative electrode similar to the lithium secondary battery according to sample A above.

  It shows in Table 1 about the structure (The content rate of a electrically conductive material, the kind of solvent, and the kneading | mixing method of a paste) of the positive electrode plate of the lithium secondary battery which concerns on the produced said samples AG.

[Area ratio of positive electrode active material]
About the positive electrode sheet of the lithium secondary battery which concerns on the produced said samples AG, the mapping by EPMA was performed and the distribution state of the positive electrode active material exposed to the surface of the positive electrode plate was analyzed. Then, the area ratio of the positive electrode active material in the positive electrode mixture layer exposed on the surface of the positive electrode plate was determined with respect to the total area of the positive electrode mixture layer of the positive electrode plate. Table 1 shows the area ratios of the positive electrode active materials according to Samples A to G. 5 and 6 show mapping images by EPMA for the positive electrode sheets of the lithium secondary batteries according to Sample A and Sample E.

[Battery evaluation]
Next, the resistance values of the lithium secondary batteries according to the samples A to G were measured by the following resistance measurement method.
That is, under a temperature condition of 25 ° C., the battery capacity was measured by charging to 4.1 V at a constant current of 5 A and then discharging at a constant current to 2.5 V at 5 A. Further, after a 30-minute pause, the battery was charged to 3.73 V with a maximum current of 5 A, and the charge was terminated when the current was attenuated to 100 mA while keeping the voltage constant. Thereafter, the battery adjusted to 3.73 V was subjected to constant current discharge at 20 A, the voltage after 4 seconds was measured, and the current (with the vertical axis representing the voltage after each charge / discharge and the horizontal axis representing the charge / discharge current ( I) The resistance value was determined from the slope of the linear approximation line of the voltage (V) plot value. Table 1 shows the results.

As shown in Table 1, the positive electrode sheet of the lithium secondary battery according to Sample E, in which the material for forming the positive electrode mixture layer was simultaneously added to prepare a paste (collective kneading), is the area ratio of the positive electrode active material Was as large as 72%, and the resistance value was the largest. Moreover, the positive electrode sheet of the lithium secondary battery according to Samples A to C, in which materials for forming the positive electrode mixture layer were separately added to prepare pastes (split kneading), the area ratio of the positive electrode active material was 4 to 4 The resistance value was small at 22%.
Further, when comparing the distribution state of the positive electrode active material existing on the surface of each of the positive electrode plates in FIG. 5 and FIG. 6, the positive electrode active material in FIG. 5 (sample A) is more than in FIG. 6 (sample E). It was confirmed that there were few white parts in the figure shown. Therefore, by separately adding materials for forming the positive electrode mixture layer and preparing a paste, the ratio of the positive electrode active material that is not coated with the conductive material on the surface is reduced, It was shown that the resistance value can be reduced.
Further, the positive electrode sheet of the lithium secondary battery according to Sample G using a non-aqueous solvent as a solvent at the time of preparing the paste had a smaller area ratio of the positive electrode active material of 11%, but the resistance value of Sample A was 0. It was 5mΩ larger. Here, the difference in resistance value of 0.5 mΩ seems not to be very different in terms of battery characteristics, but even under a temperature condition lower than this test (for example, 0 ° C. or less), even a difference in resistance value of 0.1Ω. It is known that battery characteristics are greatly affected. Therefore, it is estimated that the lithium secondary battery according to Sample G does not have the low temperature output characteristics as the lithium secondary battery according to Sample A under low temperature conditions. Therefore, it was confirmed that the resistance value of the battery can be further reduced by using an aqueous solvent as a solvent for preparing the paste.

  As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations and what changed and changed the above-mentioned specific example is contained in the invention disclosed here. For example, the type of battery is not limited to the lithium secondary battery described above, but may be batteries having various contents with different constituent materials and electrolytes for the electrode body. Further, the size and other configurations of the battery can be appropriately changed depending on the application (typically for in-vehicle use).

  In the lithium secondary battery according to the present invention, the ratio of the positive electrode active material that is not coated on the surface of the positive electrode active material on the surface of the positive electrode plate by covering the surface of the positive electrode active material while the conductive material is bulky To provide a lithium secondary battery having excellent battery characteristics (for example, high-rate characteristics, cycle characteristics, or low-temperature output characteristics) as a vehicle-mounted high-output power source having a positive electrode mixture layer excellent in electron conductivity Can do. Therefore, according to the present invention, as shown in FIG. 4, a vehicle 1 (typically) including such a secondary battery 100 (which may be in the form of an assembled battery formed by connecting a plurality of batteries 100) as a power source. Can provide automobiles, in particular automobiles equipped with electric motors such as hybrid cars and electric cars.

DESCRIPTION OF SYMBOLS 1 Vehicle 10 Battery case 12 Opening part 14 Cover body 20 Winding electrode body 30 Positive electrode sheet 32 Positive electrode collector (namely, positive electrode core material)
34 Positive electrode mixture layer 35 Positive electrode current collector layered portion (positive electrode core material layered portion)
36 Positive electrode mixture layer non-formation part 37 Positive electrode current collector terminal 38 External positive electrode current collector terminal 40 Negative electrode sheet 42 Negative electrode current collector (ie, negative electrode core material)
44 Negative electrode mixture layer 45 Negative electrode current collector layered portion (negative electrode core material layered portion)
46 Negative electrode mixture layer non-forming part 47 Negative electrode current collector terminal 48 External negative electrode current collector terminal 50 Separator 100 Lithium secondary battery R Winding axis direction

Claims (6)

A method for manufacturing a lithium secondary battery including a positive electrode plate in which a positive electrode mixture layer containing a positive electrode active material is formed on the surface of a positive electrode current collector, the following steps:
Preparing an aqueous paste A by adding a conductive material and at least one binder dissolved or dispersed in an aqueous solvent to the aqueous solvent and kneading;
Preparing an aqueous paste B by adding and kneading the positive electrode active material and at least one binder dissolved or dispersed in an aqueous solvent into an aqueous solvent;
An aqueous paste C is prepared by mixing the prepared aqueous paste A and aqueous paste B, and the paste C is applied to the surface of the positive electrode current collector to form a positive electrode mixture layer;
Including
Here, the positive electrode mixture layer is such that the area of the positive electrode active material exposed on the surface of the positive electrode plate satisfies 3% or more and 25% or less with respect to the total area of the positive electrode mixture layer of the positive electrode plate. The manufacturing method characterized by forming. Wherein as a positive electrode active material, using a lithium transition metal composite oxide as a constituent metal element at least lithium and nickel, The method according to claim 1. As the positive electrode active material, the following general formula:
Li _x Ni _{1- y My} O ₂ (1)
(X and y in the formula (1) are
1 ≦ x ≦ 1.2,
0 ≦ y <0.5 is satisfied, and
M in the formula (1) is at least one element or two or more elements including at least one or two or more metal elements selected from the group consisting of Co, Mn and Al. )
The manufacturing method of Claim 1 or 2 using the lithium transition metal complex oxide represented by these. The manufacturing method in any one of Claims 1-3 which uses at least 1 type of water-soluble cellulose derivative as a binder in the said positive electrode compound material layer. When the total amount of the positive electrode active material, the binder, and the conductive material in the positive electrode mixture layer is 100% by mass, the content of the conductive material in the positive electrode mixture layer is 5% by mass to 15% by mass. forming a positive-electrode mixture layer as method according to claim 1. The viscosity of the aqueous paste A is the to be greater than the viscosity of the aqueous paste B, and wherein the preparation of aqueous paste A and aqueous pastes B, according to claim 1 Production method.