JP2011204459A - Positive electrode plate for nonaqueous electrolyte secondary battery, manufacturing method of positive electrode plate for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode plate for nonaqueous electrolyte secondary battery which has an electrode active material layer constituted without existence of a resin binder and has high output and input characteristics, and provide a manufacturing method of a current collector having the electrode active material layer in which the active material is adhered excellently on the surface of the current collector without using a resin binder and which is hardly separated, and thereby to realize a nonaqueous electrolyte secondary battery having high output and input characteristics.SOLUTION: The electrode active material layer has an active material fixed on the surface of the current collector by jointing the active materials containing lithium and iron as metal elements without using a resin binder.

Description

  The present invention relates to a positive electrode plate used for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, a method for producing the positive electrode plate, and a non-aqueous electrolyte secondary battery.

  A non-aqueous electrolyte secondary battery represented by a lithium ion secondary battery has a high energy density and a high voltage, and has a memory effect during charging / discharging (when the battery is charged before it is completely discharged, Since there is no phenomenon in which the capacity decreases, it is used in various fields such as portable devices and large devices. In recent years, the use of secondary batteries has attracted attention in fields where high input / output characteristics are required, such as electric vehicles, hybrid vehicles, and power tools.

  The non-aqueous electrolyte secondary battery includes a positive electrode plate, a negative electrode plate, a separator, and an organic electrolyte. And as said positive electrode plate and negative electrode plate, what is equipped with the electrode active material layer formed by apply | coating the coating composition for electrode active material layer formation to collector surfaces, such as metal foil, is generally used. .

  The electrode active material layer-forming coating composition comprises an active material capable of inserting and releasing lithium ions, a resin binder, and a conductive material (provided that the conductive material is omitted when the active material also exhibits a conductive effect). Or, if necessary, other materials may be used and kneaded and / or dispersed in an organic solvent to prepare a slurry. A method of producing an electrode plate having an electrode active material layer by applying a coating composition for forming an electrode active material layer on the surface of a current collector to form a coating film, then drying and pressing is common. (For example, Patent Document 1 paragraphs [0019] to [0026], Patent Document 2 [Claim 1], paragraphs [0051] to [0055]).

  At this time, the active material contained in the electrode active material layer-forming coating composition is a particulate compound dispersed in the solution, and the current collector surface is simply applied to the current collector surface. Even if the electrode active material layer forming coating composition that does not easily adhere to the resin and does not contain a resin binder is applied to a current collector to form a coating film and then dried to form a film, the film is not collected. It easily peels off from the electric body. That is, the electrode active material is bound via the resin binder and is fixed to the surface of the current collector to form an electrode active material layer. Therefore, the resin binder is essentially an essential component.

  Moreover, the said electrically conductive material is used in order to ensure the electronic conductivity between each active material and collector in an electrode active material layer favorable, and to reduce the volume resistivity of electrode active material layer itself.

JP 2006-310010 A JP 2006-107750 A

  As described above, in recent years, development of large-capacity secondary batteries has been promoted particularly for fields that require high input / output characteristics such as electric vehicles, hybrid vehicles, and power tools. Even in the case of a secondary battery used in a relatively small device of a mobile phone, since the device tends to be multifunctional, improvement in input / output characteristics is expected. On the other hand, in order to improve the input / output characteristics of the secondary battery, it is necessary to reduce the impedance of the battery. This is because a battery with high impedance has a problem that its capacity cannot be fully utilized during high-speed charging.

  In order to reduce the impedance of the secondary battery, it is effective to reduce the impedance of the electrode plate. To date, a method of increasing the electrode area by thinning the electrode active material layer formed on the electrode plate is known. ing. In addition, since non-aqueous electrolytes used for lithium ion secondary batteries generally have higher resistance than aqueous electrolytes, they are thin and wide-area electrodes compared to other batteries such as lead-acid batteries from the beginning of development. A form has been developed in which the distance between the positive electrode and the negative electrode is shortened.

  However, considering the presence of components other than the active material in the electrode active material layer, there is a limit in reducing the thickness of the layer, and the lower limit of the thickness of the electrode active material layer is substantially up to several tens of μm. It was.

  The present inventors paid attention to the presence of a resin binder in the electrode active material layer as one of the factors that make it difficult to reduce the thickness of the electrode active material layer. As described above, the resin binder has been used as an essential component of the electrode active material layer until now, but the presence of the resin binder increases the volume of the electrode active material layer and physically This resulted in an increase in the thickness of the electrode active material layer. Furthermore, the present inventors have a problem that the movement distance of lithium ions and electrons becomes longer due to the presence of the resin binder between the active materials, and the permeability of the electrolytic solution in the electrode active material layer. It has been found that there is a problem that the contact area between the electrolytic solution and the active material becomes small. And it was guessed that the resin binder which causes these problems is one of the negative factors for the high input / output of the electrode plate.

  In view of the above-described situation, the present invention has been achieved particularly for the positive electrode plate among the electrode plates, and has an electrode active material layer configured without depending on the presence of the resin binder, and has high input / output characteristics. A positive electrode plate for a water electrolyte secondary battery is provided, and an active material layer adheres well to the surface of the current collector without using a resin binder, and an electrode active material layer that is difficult to peel off is provided on the current collector surface. It is an object of the present invention to provide a method for manufacturing a positive electrode plate for a non-aqueous electrolyte secondary battery, and to provide a non-aqueous electrolyte secondary battery with high input / output characteristics.

  The inventors of the present invention can further reduce the thickness of the electrode active material layer that is formed by adhering the active materials directly to each other by bonding directly to each other regardless of the presence of the resin binder. It has been found that a positive electrode plate for a non-aqueous electrolyte secondary battery capable of exhibiting very high input / output characteristics can be realized, and a positive electrode plate for a non-aqueous electrolyte secondary battery and the same are used. The present invention which is a non-aqueous electrolyte secondary battery was completed.

  In addition, the present inventors have disclosed a lithium element-containing compound and an iron element-containing compound as one of means for fixing the active material to the current collector surface by bonding the active materials without using a resin binder. According to the present invention, a lithium iron-based composite compound exhibiting a lithium ion insertion / release reaction on the current collector surface is produced as an active material by applying a solution in which the solution is dissolved on the current collector surface and heating. And found that the produced lithium iron-based composite compound can be at least partially and directly bonded to each other and fixed to the surface of the current collector to form a coating film that is difficult to peel off. The invention of the manufacturing method of a board was completed.

That is, the present invention
(1) A positive electrode plate for a nonaqueous electrolyte secondary battery comprising a current collector and an electrode active material layer composed of an active material on at least a part of the surface of the current collector,
The electrode active material layer is composed of an active material containing at least lithium and iron as metal elements, and has a structure in which the active materials are partially joined and the active material is continuously present. A porous layer having voids through which liquid can penetrate;
A positive electrode plate for a non-aqueous electrolyte secondary battery, wherein at least a part of the active material contained in the electrode active material layer is bonded to the current collector,
(2) The non-aqueous electrolyte 2 according to (1) above, wherein the active material constituting the electrode active material layer is a lithium iron-based composite oxide or a lithium iron-based composite phosphate compound. Positive plate for secondary battery,
(3) The positive electrode plate for a nonaqueous electrolyte secondary battery according to (1), wherein the electrode active material layer is composed of an active material containing lithium iron phosphate (LiFePO ₄ ),
(4) Measure the particle diameters of 20 arbitrarily selected active material particles, and use the arithmetic average value of 5 points selected in ascending order of the particle diameter as the average minimum particle diameter of the active material. When the arithmetic average value for the five points selected in descending order is the average maximum particle size of the active material,
Any one of (1) to (3) above, wherein the average minimum particle size of the active material is 5 nm or more and less than 20 nm, and the average maximum particle size is 20 nm or more and less than 150 nm. The positive electrode plate for a non-aqueous electrolyte secondary battery according to the description,
(5) Measure the particle diameters of 20 arbitrarily selected active material particles, and use the arithmetic average value of 5 points selected in ascending order of the particle diameter as the average minimum particle diameter of the active material. When the arithmetic average value for the five points selected in descending order is the average maximum particle size of the active material,
The non-aqueous electrolyte 2 according to any one of (1) to (4) above, wherein the active material has a value of (average maximum particle size−average minimum particle size) of 40 nm or less. Positive plate for secondary battery,
(6) The positive electrode for a nonaqueous electrolyte secondary battery according to any one of (1) to (4) above, wherein the electrode active material layer has a thickness of 300 nm to 10 μm. Board,
(7) The above-mentioned (1), wherein the discharge capacity retention rate is 50% or more at a discharge rate of 50C or more, assuming that the discharge capacity retention rate when discharged at a discharge rate of 1C is 100%. To the positive electrode plate for a non-aqueous electrolyte secondary battery according to any one of (5),
(8) preparing an electrode active material layer forming solution containing lithium and iron as metal elements;
The electrode active material layer forming solution is applied onto at least a part of the current collector surface to form a coating film, and then a heat source is installed on the coating film surface side with respect to the current collector on which the coating film is formed. In this state, an electrode active material layer is formed by generating a lithium iron-based composite oxide exhibiting a lithium ion insertion / release reaction on the current collector surface by performing a heat treatment comprising heating at a temperature of 150 ° C. or higher. Forming a positive electrode plate for a non-aqueous electrolyte secondary battery,
(9) An electrode active material layer forming solution containing lithium and iron as metal elements and containing phosphorus element is prepared,
The electrode active material layer forming solution is applied onto at least a part of the current collector surface to form a coating film, and then a heat source is installed on the coating film surface side with respect to the current collector on which the coating film is formed. In this state, a lithium iron-based composite phosphorus exhibiting a lithium ion insertion / desorption reaction on the surface of the current collector by performing a heat treatment comprising heating at a temperature of 200 ° C. or higher in an inert gas or reducing gas atmosphere Forming an electrode active material layer by generating an acid compound, a method for producing a positive electrode plate for a non-aqueous electrolyte secondary battery,
(10) After the heat treatment is performed by installing the heat source on the coating film surface side and heating the current collector on which the coating film is formed, the heat source is further installed on both surfaces of the current collector. The method for producing a positive electrode plate for a non-aqueous electrolyte secondary battery according to the above (8) or (9), characterized in that the treatment is a subsequent heating process,
(11) A nonaqueous electrolyte secondary battery comprising at least a positive electrode plate, a negative electrode plate, a separator provided between the positive electrode plate and the negative electrode plate, and an electrolyte solution containing a nonaqueous solvent,
The gist of the non-aqueous electrolyte secondary battery is characterized in that the positive electrode plate is the positive electrode plate for a non-aqueous electrolyte secondary battery according to any one of (1) to (7) above. Is.

  The positive electrode plate for a non-aqueous electrolyte secondary battery of the present invention can exhibit very high input / output characteristics. It is surmised that at least one of the factors enabling the high input / output of the positive electrode plate for a non-aqueous electrolyte secondary battery of the present invention is as follows. That is, the electrode active material layer in the positive electrode plate of the present invention is fixed to the current collector surface by bonding the active materials containing at least lithium and iron as metal elements to each other regardless of the presence of the resin binder. ing. For this reason, it is considered that the movement distance of lithium ions and electrons is shortened and the input / output characteristics are improved as compared with the conventional electrode active material layer using a resin binder. Moreover, the positive electrode plate of the present invention has good film adhesion of the electrode active material layer to the current collector, as in the case of the electrode plate using the conventional resin binder, and thus the film of the electrode active material layer. Good formability.

  Furthermore, the electrode active material layer in the present invention does not have a resin binder that allows the electrolytic solution to permeate well and adversely affect the behavior of lithium ions due to the presence of appropriate voids. Therefore, it is considered that lithium ions can move smoothly, and as a result, high input / output characteristics can be exhibited. In addition, the conduction of electrons between the current collector and the active material is smooth.

  In addition, the production method of the present invention, which is a method for producing a positive electrode plate for a non-aqueous electrolyte secondary battery, disperses an active material in advance in an electrode active material layer-forming coating composition as in the prior art. Unlike the method of applying to the surface of the electric conductor, drying, and pressure bonding, a method of applying an electrode active material layer forming solution containing at least lithium and iron as metal elements to the surface of the current collector and heating is employed. According to this method, a lithium iron-based composite compound that is an active material exhibiting a lithium ion insertion / release reaction is generated on the surface of the current collector. Moreover, at this time, the active materials are bonded to each other at least partially and directly and fixed to the current collector, so that the electrode active material layer is formed without using a resin binder.

  And if it is a nonaqueous electrolyte secondary battery comprised using the positive electrode plate for nonaqueous electrolyte secondary batteries of the said invention, the improvement of the input / output characteristic of a positive electrode plate will improve the input / output characteristic as a battery. As a result, a non-aqueous electrolyte secondary battery with improved input / output characteristics is provided.

It is a graph which shows the result of the X-ray-diffraction apparatus (XRD) of the positive electrode active material layer in Example 1 of this invention.

[Positive electrode plate for non-aqueous electrolyte secondary battery]
The positive electrode plate for a non-aqueous electrolyte secondary battery of the present invention (hereinafter sometimes simply referred to as “the positive electrode plate of the present invention”) includes a current collector and at least a part of the active material on the surface of the current collector. An electrode active material layer configured to be fixed by direct bonding is provided. Below, the form of the positive electrode plate for nonaqueous electrolyte secondary batteries of this invention is demonstrated.

(Current collector)
The current collector used in the present invention is not particularly limited as long as it is generally used as a positive electrode current collector of a positive electrode plate for a nonaqueous electrolyte secondary battery. For example, aluminum foil or nickel foil is preferably used.

  The thickness of the current collector is not particularly limited as long as it is a thickness that can generally be used as a current collector for a positive electrode plate for a nonaqueous electrolyte secondary battery, but is preferably 10 to 100 μm, and preferably 15 to 50 μm. It is more preferable.

(Electrode active material layer)
In the electrode active material layer in the present invention, a layer made of a particulate active material is formed on at least a part of the surface of the current collector, and the active materials are partially and directly joined to each other. The porous layer is formed as a porous layer having a layer structure in which the active material is continuously present and having voids through which the electrolytic solution can permeate. Further, at least a part of the active material contained in the electrode active material layer is bonded to the current collector. These states can be confirmed by scanning electron microscope (SEM) observation at a magnification of about 10,000 to 50,000 times. That is, the positive electrode plate for a non-aqueous electrolyte secondary battery in which the electrode active material layer of the present invention is formed on the current collector surface is cut in a direction perpendicular to the current collector surface, and the cut surface is scanned with an electron microscope (SEM). Thus, a layer made of a particulate active material forming an electrode active material layer is observed on the surface of the current collector by observing a photograph at a magnification of about 50,000 times. Further, it is observed from the photograph that at least a part of the active material contained in the electrode active material layer is directly attached to and bonded to the current collector.

  With respect to the electrode active material layer, “a void through which the electrolyte can permeate” is a void formed around the active material by partially and directly joining each other, and is 50,000 times larger in an electron microscope. When observed at a magnification, it means a void that is observable with the naked eye.

  The electrode active material layer can be analyzed using an X-ray diffractometer (XRD) to analyze the content of the lithium transition metal composite compound contained therein.

  FIG. 1 shows the result of analyzing the electrode active material layer using an X-ray diffractometer (XRD) taking Example 1 described later as an example. From FIG. 1, it was confirmed that the electrode active material layer was comprised from the lithium iron type complex compound.

  The active material constituting the electrode active material layer in the present invention is a metal compound that exhibits a lithium ion insertion / release reaction, and is composed of a lithium iron-based composite compound containing at least lithium and iron. In addition to compounds containing only lithium and iron as metal elements, the lithium iron-based composite compound contains lithium, iron and other metals (for example, cobalt, nickel, manganese, etc.) to the extent that they do not impair the effects of the present invention. It may be a compound contained as

  Examples of the lithium iron-based composite compound include a lithium iron-based composite oxide or a lithium iron-based composite phosphate compound.

As the lithium iron-based composite oxide, in addition to lithium iron oxide (LiFe _x O ₂ (0.7 ≦ x ≦ 1.3), some of the iron atoms in the crystal structure of the lithium iron oxide may be replaced with other metals. Those substituted with atoms, for example, an aluminum-substituted oxide in which a part of iron of lithium iron oxide is substituted with aluminum (LiFe _a Al _b O ₂ (0.7 ≦ a ≦ 1.2, 0.1 ≦ b ≦ 0.3).

Examples of the lithium iron-based composite phosphate compound include lithium iron phosphate (LiFe _y PO ₄ (0.7 ≦ y ≦ 1.3)) and other iron atoms in the crystal structure of lithium iron phosphate. For example, a manganese-substituted phosphate compound in which a part of iron of lithium iron phosphate is substituted with manganese (LiFe _c Mn _d PO ₄ (0.7 ≦ c ≦ 1.2,. 1 ≦ d ≦ 0.3)).

  When the active material is lithium iron phosphate, the active material can be generated at a relatively low temperature. Therefore, the lithium iron phosphate preferably has an olivine structure.

  In the present invention, the active material means a compound that exhibits a lithium ion insertion / release reaction. Whether or not the lithium iron-based composite compound constituting the electrode active material layer exhibits a lithium ion insertion / release reaction is evaluated by performing charge / discharge rate characteristic evaluation described later using the manufactured positive electrode plate. When it shows, it can be judged that lithium ion insertion elimination reaction is shown.

  Since the electrode active material layer in the present invention is formed by bonding the active materials to each other and adhering to the surface of the current collector without using a resin binder, the electrode active material layer is compared with the thickness of the conventional electrode active material layer. It can be formed very thin. More specifically, the electrode active material layer in the present invention can be formed to a thickness of 300 nm or more and 10 μm or less. However, the above description does not exclude the formation of the electrode active material layer in the positive electrode plate of the present invention with a thickness exceeding 10 μm. Further, when it is desired to increase the capacity, the thickness of the electrode active material layer can be appropriately determined. In addition, when forming the electrode active material layer in this invention in thickness exceeding 10 micrometers, it is desirable to add a electrically conductive material to an electrode active material layer formation solution. The thickness of the electrode active material layer is measured by measuring the thickness of the electrode active material layer at 10 points at any location using a micrometer and calculating the average value.

  In the positive electrode plate of the present invention, as described above, the electrode active material layer can be thinned. When the electrode active material layer is thin in this way, the movement distance of electrons moving between the electrode active material particles and the current collector in the electrode active material layer is shortened. This is desirable because it can contribute to the improvement of the input / output characteristics. Moreover, since there is no resin binder in the electrode active material layer in the present invention, compared with the conventional electrode active material layer in which the resin binder is used, the unit volume per unit volume of the electrode active material layer The weight of the active material is increasing. Therefore, even when the electrode active material layer is thinned, it is possible to maintain a good electric capacity.

  The particle size of the active material constituting the electrode active material layer is determined by using an electron micrograph taken at the time of electron microscope observation. That is, the particle size of the active material particles constituting the electrode active material layer is determined from the electron micrograph obtained by the electron microscope observation using image analysis type particle size distribution measurement software (manufactured by Mount Tech Co., Ltd., MAC VIEW). Can do. About the average particle diameter of active material particle | grains, a particle diameter can be measured about 20 particle | grains and it can specify by the arithmetic average value. At this time, 20 particles are arbitrarily selected. In addition, for the average minimum particle size and average maximum particle size of the active material particles, the average maximum particle size is 5 points in order of decreasing particle size, based on the measured values of 20 particle sizes arbitrarily selected. The particle size is calculated by calculating the arithmetic average for each of 5 points in order of increasing particle size. In addition, a 50,000 times magnified photograph is used for the electron micrograph used when calculating the particle size of an active material.

  The size of the particles of the active material constituting the electrode active material layer in the present invention is not particularly limited, but it is smaller than the particle size of a general active material constituting the conventional electrode active material layer. be able to. In order to increase the input / output of the positive electrode plate, it is preferable that the particle size is small. From this viewpoint, the active material has an average minimum particle size of 5 nm or more and less than 20 nm, and an average maximum particle size of 20 nm or more. It is preferable that it is less than 150 nm. In addition, according to the manufacturing method of the positive electrode plate for nonaqueous electrolyte secondary batteries of this invention mentioned later, an electrode active material layer can be easily comprised with the very small particle size shown above. The minimum average particle size and the maximum average particle size are obtained by measuring 20 particles using an image analysis type particle size distribution measurement software (manufactured by MAC VIEW, Inc., MAC VIEW), and measuring the particle size as an average minimum particle size. It is obtained by selecting 5 points in order of increasing diameter and selecting 5 points in order of increasing particle size as the average maximum particle size, and calculating the arithmetic average for each. In the image analysis type particle size distribution measurement software, the particle to be measured is recognized based on the image of the electron microscope observation photograph, the maximum diameter of the recognized particle is measured, and the maximum particle diameter of each of the 20 particles is measured. The value is measured. Furthermore, among these, the five largest values are selected in order and the average maximum particle size is specified by arithmetically averaging those values, and the five smallest values are selected in order and the arithmetic average is calculated. Thus, the average minimum particle size is specified. Specifically, in the example of Example 1 described later, the average particle size of the particles constituting the electrode active material layer was 12 nm and the average maximum particle size was 23 nm.

  For the uniformity of the particle size of the active material constituting the electrode active material layer, the average minimum particle size and the average maximum particle size obtained above are used, and the difference between these values (average maximum particle size−average minimum particle size). The diameter can be evaluated by obtaining. For example, for the electrode active material layer of Example 1 to be described later, the value of the average minimum particle size and the average maximum particle size (average minimum particle size−average maximum particle size) is 11 nm. Compared to 1, 2 and the like, the particle size of the active material was excellent in uniformity. That is, the electrode active material layer having a partial and direct bonding structure between the active materials as described above is made of an active material containing lithium and iron as a gold electrode element. The uniformity of the particle diameter of the substance is improved.

  Further, as described above, according to the present invention in which the particle size of the active material constituting the electrode active material layer can be reduced as compared with the conventional one, the total surface area of the active material per unit volume in the electrode active material layer can be conventionally increased. It can be increased in comparison. Since the total surface area is understood as a contact area between the active material and the electrolytic solution, an increase in the total surface area means that high input / output of the positive electrode plate is promoted, which is preferable.

(Other materials)
The electrode active material layer can be composed of only the active material described above, but may contain further additives within a range not departing from the gist of the present invention. For example, the electrode active material layer of the present invention may appropriately contain a conductive material. In general, by including a conductive material in the electrode active material layer, it is possible to ensure better electronic conductivity between each electrode active material and the current collector in the electrode active material layer, and the volume of the electrode active material layer itself. The resistivity can be lowered efficiently. Even when a conductive material is added, the thickness of the electrode active material layer can be 10 μm or less. Further, by adding the conductive material and increasing the amount of the active material, the thickness of the electrode active material layer may be formed to a thickness exceeding 10 μm. In this case, the thickness of the positive electrode plate of the present invention is easily increased. Capacity can be increased.

  As the conductive material, those usually used for a positive electrode plate for a non-aqueous electrolyte secondary battery can be used, and examples thereof include carbon materials such as carbon black such as acetylene black and ketjen black. The average particle size of the conductive material is preferably about 20 nm to 50 nm. The average particle size is obtained by an arithmetic average obtained from actual measurement using an electron microscope, as in the method of measuring the particle size of the active material. Carbon fiber (VGCF) is known as a different conductive material. The carbon fiber can conduct electricity very well in the length direction and can improve the fluidity of electricity. The fiber length is about 1 μm to 20 μm. Therefore, in addition to the particulate conductive material such as acetylene black described above, the effect of adding the conductive material can be improved by using carbon fiber together. When using a conductive material, it is necessary to keep in mind that the voids in the void-forming layer are maintained to such an extent that the electrolyte solution can penetrate.

  In addition, the electrode active material layer of this invention is improving the electroconductivity of an electron compared with the conventional electrode active material layer by not using a resin binder. Therefore, in the electrode active material layer according to the present invention, it is possible to reduce the blending amount of the conductive material as compared with the conventional case, or an embodiment in which no conductive material is used is possible. Thus, in the electrode active material layer in which the blending amount of the conductive material is small or the conductive material is not blended practically, the weight of the active material per unit volume in the electrode active material layer is increased.

  As another optional additive, in order to further improve the adhesion between the current collector and the active material, a metal oxide that does not function as an active material may be included in the electrode active material layer. The metal oxide as the additive is not particularly limited, and examples thereof include cobalt oxide, nickel oxide, titanium oxide, zirconium oxide, tin oxide, and manganese oxide.

(Method for evaluating charge / discharge rate characteristics of electrode)
The input / output characteristics of the positive electrode plate of the present invention can be evaluated by determining the discharge capacity retention rate (%). That is, the discharge capacity retention rate is an evaluation of discharge rate characteristics, and it is generally understood that in a positive electrode plate with improved discharge rate characteristics, the charge rate characteristics are also improved. Therefore, when a desirable discharge capacity retention ratio is indicated, it is evaluated that the charge / discharge rate characteristics are improved, and as a result, the input / output characteristics are evaluated as improved. More specifically, the discharge rate 1C is set such that the theoretical value of the discharge capacity (mAh / g) of the active material is completed in 1 hour, and the discharge actually measured at the set discharge rate of 1C. The capacity (mAh / g) is set to a discharge capacity maintenance rate of 100%. The discharge capacity (mAh / g) when the discharge rate is further increased is measured, and the discharge capacity retention ratio (%) can be obtained from the calculation formula shown in the following equation 1.

  In the present invention, it is desirable that a discharge capacity maintenance rate of 50% or more is exhibited at a discharge rate of 50C or more. More preferably, it is desirable that a discharge capacity maintenance rate of 50% or more is exhibited at a discharge rate of 100C or more. However, if the discharge rate is 2000 C or higher, a system that can withstand a large current is required, which is not desirable.

  From another point of view, it is desirable that the discharge capacity maintenance rate is high. When the discharge rate is 50 C, the discharge capacity maintenance rate is 50% or more, or 80% or more, and even 100%. It is desirable that the rate be indicated.

  In addition, the said discharge capacity is calculated | required by measuring the discharge capacity of electrode itself with a tripolar coin cell.

[Method for producing positive electrode plate for non-aqueous electrolyte secondary battery]
Next, a method for producing a positive electrode plate for a non-aqueous electrolyte secondary battery of the present invention (hereinafter also simply referred to as “the production method of the present invention”) will be described. In the production method of the present invention, an electrode active material layer forming solution is prepared by dissolving a compound serving as a precursor of an active material in a solvent, and this is applied to the surface of the current collector, and then heated to collect the current. An active material that is a lithium iron-based composite compound is generated on the surface of the body to form an electrode active material layer, and a positive electrode plate for a non-aqueous electrolyte secondary battery is manufactured. Specific examples of the lithium iron-based composite compound include a lithium iron-based composite oxide and a lithium iron-based composite phosphate compound. In any case, since the generated compound needs to act as an active material, it shows a lithium ion insertion / release reaction.

One feature of the production method of the present invention is that the resin binder is not substantially added to the electrode active material layer forming solution, and an active material is generated on the surface of the current collector in the production process. . At this time, a film in which the active material is fixed to the surface of the current collector is formed by utilizing the fact that the particles of the generated active material are partially directly bonded to each other and are in close contact with the current collector surface. It is. Here, in the electrode active material layer forming coating composition used in the conventional manufacturing method, since the resin binder was blended in addition to the active material, when the particle size of the active material to be used becomes small, The phenomenon that the viscosity of the coating composition for forming an electrode active material layer increased and the coating property deteriorated was observed, which was an adverse effect of thinning the electrode active material layer. However, since it is not necessary to add a resin binder to the electrode active material layer forming solution used in the production method of the present invention, the viscosity of the electrode active material layer forming solution may increase and the applicability may decrease. There is no. Therefore, the amount of application to the current collector can be easily set, and the electrode active material layer can be formed in a desired thickness. Therefore, it is easy to reduce the thickness of the electrode active material layer. That is, the film thickness of the electrode active material layer in the positive electrode plate produced in the present invention is not particularly limited, but when a thinner film thickness is desired, it can be formed to a film thickness of 300 nm or more and 10 μm or less. is there.

  Another feature of the production method of the present invention is that, as described above, the particle size of the active material generated on the surface of the current collector is very small. More specifically, the average minimum particle size may be 5 nm or more and less than 20 nm, and the average maximum particle size may be 20 nm or more and less than 150 nm. Reducing the particle size of the active material is effective as an approach for improving the high input / output characteristics of the positive electrode plate. By reducing the particle size of the active material, the total amount of the surface area of the active material contained in the electrode active material layer is increased, and the movement distance of lithium ions inserted and desorbed in the active material in the active material is reduced. Can be small. For this reason, the behavior of lithium ions becomes smoother, and as a result, improvement of the input / output characteristics can be realized. By the way, in the manufacture of a conventional positive electrode plate, a slurry-like coating composition for forming an electrode active material layer in which a resin binder and active material particles are blended is used. There was a tendency for the viscosity of the electrode active material layer forming coating composition to increase as it decreased. This tendency was particularly observed when active material particles having an average particle diameter of 11 μm or less or even smaller were used. Therefore, since the size of the active material particles that can be used is substantially limited, it has been disadvantageous for the above-described thinning of the electrode active material layer or optimization of the behavior of lithium ions. On the other hand, in the present invention, as described in the positive electrode plate, even the maximum average particle diameter can be formed much smaller than 11 μm. Therefore, in the positive electrode plate manufactured by the manufacturing method of the present invention, the total surface area of the active material per unit volume in the electrode active material layer can be sufficiently increased, and the input / output characteristics are improved.

  Another feature of the production method of the present invention is that the particle size of the active material produced on the current collector surface is relatively uniform as described above. More specifically, the electrode active material layer can be formed by generating the active material to such an extent that the difference between the average minimum particle size and the average maximum particle size falls within the range of 40 nm or less. When the active material is generated on the current collector as in the present application, the particle size of the active material in the electrode active material layer tends to be non-uniform. However, in the manufacturing method of the present invention, an electrode active material layer containing an active material excellent in uniformity can be formed. This further improves the input / output characteristics of the positive electrode plate manufactured by the manufacturing method shown in the present invention.

(Active material precursor)
The electrode active material layer forming solution is a solution containing a metal element constituting the active material, that is, a solution containing at least lithium and iron as metal elements. The electrode active material layer forming solution can be prepared by using a metal element-containing compound containing a metal constituting the active material generated on the current collector surface as a precursor of the active material and dissolving it in a solvent. it can. As the metal element-containing compound, a lithium element-containing compound and an iron element-containing compound are used.

  Examples of the metal element-containing compound include chlorides, nitrates, sulfates, perchlorates, acetates, bromates and the like containing specific metal elements. Among them, in the present invention, chloride, nitrate, and acetate are preferably used because they are easily available as general-purpose products. In particular, nitrate is preferably used because it has good film forming properties for a wide variety of current collectors.

  Examples of the lithium element-containing compound include lithium citrate tetrahydrate, lithium perchlorate trihydrate, lithium acetate dihydrate, and lithium nitrate.

  Examples of the iron element-containing compound include iron (II) chloride tetrahydrate, iron (III) citrate, iron (II) acetate, iron (II) oxalate dihydrate, iron nitrate (III) nine water Examples thereof include Japanese, iron (II) lactate trihydrate, and iron (II) sulfate heptahydrate.

  When a lithium iron-based composite phosphate compound is produced as an active material, the electrode active material layer forming solution is a solution containing at least lithium and iron as metal elements and a phosphorus element.

  In preparing the electrode active material layer forming solution, when using a metal element-containing compound such as a lithium element-containing compound and an iron element-containing compound that does not contain a phosphorus element, a lithium element is contained in the electrode active material layer forming solution. In addition to the containing compound and the iron element-containing compound, it is necessary to further blend a phosphorus element-containing compound. The phosphorus element-containing compound is a compound containing at least a phosphorus element. Therefore, the phosphorus element-containing compound may contain a volatile element as an element other than the phosphorus element. Here, the volatile element indicates an element that is vaporized by applying a heating history at a predetermined temperature or higher, and preferably includes a nonmetallic element such as hydrogen, oxygen, or nitrogen. Phosphorous element-containing compounds can include phosphoric acid compounds, phosphorous acid compounds, etc., phosphoric acid compounds can include phosphoric acid and salts thereof, and phosphorous acid compounds include phosphorous acid. And salts thereof. Examples of the phosphorus element-containing compound may include, but are not limited to, phosphoric acid, phosphorous acid, hypophosphorous acid, diisopropyl phosphite, ammonium phosphate, ammonium phosphite, ammonium hypophosphite, and the like. .

  When producing a lithium iron-based composite phosphate compound and preparing an electrode active material layer forming solution, when using a lithium element-containing compound or an iron element-containing compound containing a phosphorus element, an electrode active material The composition of the phosphorus element-containing compound in the layer forming solution is arbitrary.

  The phosphorus element-containing compound mentioned here excludes a metal element-containing compound that can be used when producing a lithium iron-based composite phosphate compound and contains a phosphorus element. That is, the phosphorus element-containing compound excludes a compound containing a phosphorus element and a lithium element or an iron element.

  Examples of the metal element-containing compound containing phosphorus element include lithium phosphate for lithium element-containing compounds, and iron phosphate for iron element-containing compounds.

  The combination ratio of the lithium element-containing compound and the iron element-containing compound used as the main raw material (Li: Fe = X: 1) is not particularly limited, but in the molar ratio of the metal elements contained, 0.8 ≦ X <1.2 It is preferable that 1 ≦ X ≦ 1.2.

  The total concentration of the lithium element and the other metal elements in the solution containing the lithium element-containing compound and the other metal element-containing compound (such as an iron element-containing compound) is 0.01 to 5 mol / L, 0.1-2 mol / L is particularly preferable. By setting the concentration to 0.01 mol / L or more, the current collector and the active material generated on the surface of the current collector can be satisfactorily adhered, and the active material can be fixed. In addition, by setting the concentration to 5 mol / L or less, it is possible to maintain a viscosity sufficient to allow the electrode active material layer forming solution to be applied to the current collector surface, and to form a uniform coating film. can do.

(Other additives)
In addition to the metal element-containing compound described above, other additives may be added to the electrode active material layer forming solution without departing from the spirit of the present invention. The said electrically conductive material can use the thing similar to the content described in description of the electrode active material layer of this invention.

  When the conductive material is added to the electrode active material layer forming solution, the added amount of the conductive material is 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the active material generated on the current collector surface. Is desirable. In addition, although the above is not the meaning which excludes adding a conductive material exceeding 20 weight, the electrode active material layer in this invention exhibits electroconductivity fully by use of a 20 weight part or less conductive material. The idea is that you can.

(solvent)
As the solvent used for dissolving the lithium element-containing compound and the metal element-containing compound containing other metals, as long as it can dissolve the metal element-containing compound including the lithium element-containing compound, in particular Although not limited, for example, lower alcohols having a total carbon number of 5 or less, such as methanol, ethanol, isopropyl alcohol, propanol, butanol, diketones such as acetylacetone, diacetyl, benzoylacetone, ethyl acetoacetate, ethyl pyruvate, ethyl benzoylacetate And ketoesters such as ethyl benzoylformate, toluene, and mixed solvents thereof, or those diluted with water.

  Next, the electrode active material layer forming solution prepared as described above is applied to any region of the current collector surface by a conventionally known coating method such as printing, spin coating, dip coating, bar coating, spray coating, etc. To form a coating film. In addition, when the current collector surface is porous, has a large number of irregularities, or has a three-dimensional structure, it can be manually applied in addition to the above method. Note that the current collector used in the present invention is preferable because corona treatment, oxygen plasma treatment, and the like can be performed in advance as necessary to further improve the film forming property of the electrode active material layer.

  The amount of the electrode active material layer forming solution applied to the current collector can be arbitrarily determined according to the use of the positive plate to be produced, etc., but the electrode active material layer in the present invention is very Since it can be formed thinly, when it is desired to reduce the thickness, the electrode active material layer after heating may be thinly applied so as to have a thickness of about 300 nm to 10 μm. As described above, a coating film for forming an electrode active material layer containing a metal element-containing compound that is a precursor of an active material is formed by applying an electrode layer forming solution to a current collector.

  Next, the current collector on which the electrode active material layer-forming coating film is formed is heated. At this time, a lithium iron-based composite compound that is an active material is generated on the surface of the current collector by performing a heating step of heating at a temperature equal to or higher than the decomposition temperature of the metal element-containing compound dissolved in the solution. When the electrode active material layer forming coating film does not contain a phosphorus source material such as the phosphorus element-containing compound described above, a lithium iron-based composite oxide can be generated as the lithium iron-based composite compound. Lithium iron-based composite phosphate compound is produced as a lithium iron-based composite compound when the electrode active material layer coating film contains a phosphorus element-containing compound as described above that serves as the source of the phosphorus element constituting the phosphate group. can do. The generated active material is substantially free of resin binder, but is bonded to each other and fixed to the current collector surface, so that an electrode active material layer having good adhesion to the current collector can be obtained. . In this manufacturing method, in order to form the said electrode active material layer appropriately, a heat source is installed in the coating-film surface side for the said electrode active material layer formation, It is characterized by the above-mentioned. The method for installing the heat source is not particularly limited, but the heat source device may be installed on the surface side of the electrode active material layer forming coating film, or on a hot plate heated to an appropriate temperature. You may heat by installing in the position which the surface and the coating film surface for electrode active material layer formation contact | connect. The heating method is not particularly limited, and in addition to the case where a hot plate is used as a heat source device, as the heat source device, for example, an oven, a heating furnace, an infrared heater, a halogen heater, a hot air blower, or the like is used, or The method of using 2 or more in combination can be mentioned. When the current collector used is planar, it is preferable to use a heating furnace, a hot plate, or the like.

  In this manufacturing method, after heating the coating-film surface side of a collector as mentioned above, you may heat the both surfaces side of a collector in the temperature range of 150 to 800 degreeC further. When heating the both sides, the position where the heat source is installed is, for example, a mode in which a heat source device is installed on the both sides, or a collection in which a coating film for forming an electrode active material layer is laminated in a heating furnace or the like. It includes a mode in which an electric body is installed and both sides are heated in the same environment.

  In addition, the atmosphere in the said heating process is not specifically limited. However, when the generated active material is a lithium iron-based composite oxide, the metal element contained in the active material precursor is thermally melted by carrying out the heating process of the present invention in the air atmosphere. It is preferable because it is easy to oxidize. When producing a lithium iron-based composite oxide as an active material, the heating step may be performed in an atmosphere having a low oxygen concentration or no oxygen, such as a hydrogen atmosphere or a nitrogen atmosphere. In the case of producing the element, it is necessary that the compound blended in the electrode active material layer forming solution contains a substance (oxygen element-containing compound) that is a source of oxygen element that can be used for metal oxidation. It is.

  On the other hand, when producing a lithium iron-based composite phosphate compound as an active material, it is desirable to carry out the heating step in an inert gas atmosphere or a reducing gas atmosphere. In an inert gas atmosphere or a reducing gas atmosphere, the contact between the coating film made of the electrode active material layer forming solution and oxygen is further regulated, and the formation of the lithium iron-based composite phosphate compound is further ensured. In this case, by further blending an oxygen element supply source in the electrode active material layer forming solution, phosphorus derived from the phosphorus element-containing compound contained in the electrode active material layer forming solution and the metal element-containing compound derived A lithium iron-based composite phosphate compound can be easily generated with a metal element (at least lithium and iron) and oxygen of an oxygen element-containing compound. Note that argon or nitrogen can be used as the inert gas. As the reducing gas, hydrogen or carbon monoxide can be used.

  Although the heating temperature at the time of implementing the said heating process changes with kinds of metal element containing compound used, when producing | generating a lithium iron type complex oxide as an active material, it is 150 degreeC-800 degreeC normally in an atmospheric condition. By heating to a temperature range, the metal element-containing compound is favorably decomposed and an active material is generated. Moreover, when producing | generating a lithium iron type complex phosphate compound as an active material, it is normally heated in a temperature range of 200 ° C. to 800 ° C. in an atmosphere of an inert gas or a reducing gas. Decomposition takes place and an active material is produced.

[Nonaqueous electrolyte secondary battery]
A nonaqueous electrolyte secondary battery is generally configured by providing a positive electrode plate and a negative electrode plate, and a separator such as a porous film made of polyolefin such as polyethylene between them. It is manufactured by being sealed in a state where it is housed in a container and filled with a non-aqueous electrolyte.

(Electrode plate)
The non-aqueous electrolyte secondary battery of the present invention is particularly characterized in that the positive electrode plate for a non-aqueous electrolyte secondary battery of the present invention described above is used as the positive electrode plate. Conventionally, when the negative electrode plate is made of a carbonaceous material, it has been common to add a large amount of conductive material to the positive electrode plate in order to increase the conductivity of the positive electrode plate accordingly. In addition, since the porosity of the positive electrode plate is reduced and the permeability of the electrolyte solution is reduced, it is difficult to increase the input / output characteristics of the battery. However, since the positive electrode plate of the present invention has excellent input / output characteristics, the non-aqueous electrolyte secondary battery of the present invention using the positive electrode plate as a positive electrode plate does not use a large amount of conductive material as in the prior art, or is conductive. Good conductivity and high input / output characteristics can be exhibited without using any material.

  On the other hand, as a negative electrode plate used for the nonaqueous electrolyte secondary battery of the present invention, a known negative electrode plate used for a conventionally known nonaqueous electrolyte secondary battery can be appropriately selected and used. For example, a copper foil such as an electrolytic copper foil or a rolled copper foil having a thickness of about 5 to 50 μm is used as the current collector, and the electrode active material layer forming coating composition in the negative electrode plate is formed on at least a part of the current collector surface. Is formed by coating, drying, and pressing as necessary. The coating composition for forming an electrode active material layer in the negative electrode plate is generally made of natural graphite, artificial graphite, amorphous carbon, carbon black, or a carbonaceous material obtained by adding a different element to these components. Active materials, or active materials such as lithium metal and its alloys, tin, silicon, and alloys thereof, materials that can insert and desorb lithium ions, resin binders, conductive materials as necessary, etc. It is common for other additives to be dispersed and mixed.

(Non-aqueous electrolyte)
The non-aqueous electrolyte used in the present invention is not particularly limited as long as it is generally used as a non-aqueous electrolyte for a non-aqueous electrolyte secondary battery, but a lithium salt is dissolved in an organic solvent. A non-aqueous electrolyte is preferably used.

Examples of the lithium salt include inorganic lithium salts such as LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiCl, and LiBr; LiB (C ₆ H ₅ ) ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiC ( Organic compounds such as SO ₂ CF ₃ ) ₃ , LiOSO ₂ CF ₃ , LiOSO ₂ C ₂ F ₅ , LiOSO ₂ C ₄ F ₉ , LiOSO ₂ C ₅ F ₁₁ , LiOSO ₂ C ₆ F ₁₃ , and LiOSO ₂ C ₇ F ₁₅ Typical examples include lithium salts.

  Examples of the organic solvent used for dissolving the lithium salt include cyclic esters, chain esters, cyclic ethers, and chain ethers.

  Examples of the cyclic esters include propylene carbonate, butylene carbonate, γ-butyrolactone, vinylene carbonate, 2-methyl-γ-butyrolactone, acetyl-γ-butyrolactone, and γ-valerolactone.

  Examples of the chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl butyl carbonate, methyl propyl carbonate, ethyl butyl carbonate, ethyl propyl carbonate, butyl propyl carbonate, propionic acid alkyl ester, Examples include malonic acid dialkyl esters and acetic acid alkyl esters.

  Examples of the cyclic ethers include tetrahydrofuran, alkyltetrahydrofuran, dialkyltetrahydrofuran, alkoxytetrahydrofuran, dialkoxytetrahydrofuran, 1,3-dioxolane, alkyl-1,3-dioxolane, and 1,4-dioxolane.

  Examples of the chain ethers include 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl ether, ethylene glycol dialkyl ether, diethylene glycol dialkyl ether, triethylene glycol dialkyl ether, and tetraethylene glycol dialkyl ether. It is done.

  As a structure of the non-aqueous electrolyte secondary battery manufactured using the positive electrode plate, the negative electrode plate, the separator, and the non-aqueous electrolyte solution, a conventionally known structure can be appropriately selected and used. For example, the structure which winds a positive electrode plate and a negative electrode plate in the shape of a spiral via the separator like a polyethylene porous film, and accommodates in a battery container is mentioned. As another aspect, a structure in which a positive electrode plate and a negative electrode plate cut into a predetermined shape are stacked and fixed via a separator, and this is housed in a battery container may be employed. In any structure, after the positive electrode plate and the negative electrode plate are stored in the battery container, the lead wire attached to the positive electrode plate is connected to the positive electrode terminal provided in the outer container, while the lead wire attached to the negative electrode plate Is connected to a negative electrode terminal provided in the outer container, and the battery container is further filled with a nonaqueous electrification solution and then sealed to produce a nonaqueous electrolyte secondary battery.

Example 1
An aluminum plate having a thickness of 15 μm was prepared as a current collector, and an electrode active material layer prepared as follows on one side of the current collector in an amount such that the thickness of the finally obtained electrode active material layer was 1 μm The forming solution was applied with a Miya bar to form a coating film for forming an electrode active material layer.

<Preparation of electrode active material layer forming solution>
10.2 g of Li (CH ₃ COO) · 2H ₂ O [molecular weight: 102.02] and 40 of Fe (NO ₃ ) ₃ · 9H ₂ O [molecular weight: 404] as raw materials (solutes) for generating the active material .4 g, 9.8 g of H ₃ PO ₄ [molecular weight: 98] and 2 g of polyethylene glycol 400 (manufactured by Kanto Chemical Co., Inc.), and these raw materials are mixed with water so that the weight ratio is water: methanol = 2: 1. And mixed with 50 g of a solution (solvent) prepared by mixing methanol and methanol, stirred with a bioshaker at a temperature of 70 ° C. and a rotation speed of 200 rpm for 1 hour, and allowed to stand at room temperature for 24 hours to form an electrode active material layer A forming solution was prepared.

<Heating process>
Next, from the side on which the electrode active material-forming coating film was formed on the hot plate heated to 250 ° C. in a nitrogen gas atmosphere, the current collector having the electrode active material layer-forming coating film formed on the surface. Gently approached and held for 2 minutes. After returning to room temperature, the temperature was raised to 550 ° C. over 5 hours in a firing furnace (manufactured by Koyo Thermo Co., Ltd.) filled with nitrogen gas, and then kept at 550 ° C. for 1 hour. I waited until I came back. When the temperature reached room temperature, the sample was taken out by opening it to the atmosphere to obtain a positive electrode plate for a non-aqueous electrolyte secondary battery of the present invention in which an appropriate electrode active material layer was laminated as a positive electrode active material layer on a current collector. . Then, the positive electrode plate was drawn out to a predetermined size (a disk having a diameter of 15 mm), and the positive electrode body obtained thereby was defined as Example 1. In addition, the above-mentioned heating is a muffle as an electric furnace for heating from both sides of the hot plate (manufactured by ASONE) and then the current collector to heat the side on which the coating film for forming the electrode active material layer is formed. A furnace (D90, P90) was used.

<Evaluation of film formability>
In preparing Example 1, the positive electrode plate for a nonaqueous electrolyte secondary battery obtained above was processed to a predetermined size. In this processing operation, the electrode active material layer was peeled off, etc. Thus, the working electrode used in the charge / discharge test described later could be formed. From this, it was confirmed that the film forming property of the electrode active material layer was good. The results are shown in Table 1. Also in the examples and comparative examples described below, the favorable film forming property means that the positive electrode plate can be pulled out without any trouble as described above. On the other hand, when a part of the electrode active material layer is peeled off in the above-mentioned punching process, or the electrode active material falls from the current collector and a disc that can be used as a working electrode of a tripolar coin cell is not formed. It is assumed that the film forming property of the electrode active material layer is poor. In Table 1, in the column showing the evaluation of film forming property, “◯” indicates “film forming property is good” and “x” indicates “film forming property is bad”.

<Electron microscope observation, electrode active material layer thickness, particle size measurement, X-ray diffraction>
When the electrode active material layer was observed at a magnification of 50,000 times using the scanning electron microscope (SEM) and the X-ray diffractometer (XRD) using Example 1, the entire thickness direction of the electrode active material layer was observed. On the other hand, it was confirmed that a layer structure was formed in which the active materials were partially and directly joined to each other and a void was formed around the active material. From these results, it was confirmed that the active material was lithium iron phosphate (LiFePO ₄ ). The results of XRD analysis are shown in FIG.

  Furthermore, when a cross section cut in a direction perpendicular to the current collector surface was observed at a magnification of 10000 times with an SEM using Example 1, a film thickness of 1 μm as an electrode active material layer was formed on the current collector surface. It was confirmed that this layer was formed. The magnification of 10,000 times was selected as a magnification at which the entire electrode active material layer can be observed.

  In addition, the particle size of the particles constituting the electrode active material layer is determined from the electron micrograph (magnified 50,000 times) obtained by the electron microscope observation, and the image analysis particle size distribution measurement software (manufactured by Mount Tech Co., Ltd., MAC VIEW). 20 points were measured using the above, and the arithmetic average was determined for the average minimum particle size of 5 points in ascending order of particle size and the average maximum particle size of 5 points in order of increasing particle size. The particle size was 12 nm and the average maximum particle size was 23 nm. (Table 1).

  Using Example 1, the uniformity was evaluated as follows. The results are shown in Table 1.

<Evaluation of particle size uniformity of active material of positive electrode plate>
The particle size uniformity of the active material of the positive electrode plate was evaluated by the difference value between the maximum average particle size and the minimum average particle size calculated above. In Example 1, (maximum average particle diameter-minimum average particle diameter) was 11 nm (Table 1).

Tripolar coin cell production:
Lithium hexafluorophosphate (LiPF ₆ ) is added as a solute to a mixed solvent of ethylene carbonate (EC) / dimethyl carbonate (DMC) (volume ratio = 1: 1), and the concentration of LiPF _{6 as} the solute is 1 mol. The non-aqueous electrolyte was prepared by adjusting the concentration to be / L. Then, Example 1 (15 mm diameter disc, weight of positive electrode active material contained: 0.6 mg / 1.77 cm ² ) prepared as described above as a positive electrode plate was used as a working electrode as a counter electrode plate and a reference electrode plate. A tripolar coin cell was assembled using a metallic lithium plate, the non-aqueous electrolyte prepared above as the electrolyte, and a porous polyethylene sheet as the separator, and this was designated as Example Test Cell 1. The example test cell 1 was subjected to the following charge / discharge test.

<Charge / discharge test>
In the example test cell 1, which is a tripolar coin cell prepared as described above, in order to evaluate the charge / discharge rate characteristics of the working electrode, the example test cell 1 was first fully charged as in the following charging test.

Charging test:
The test cell 1 was charged at a constant current (45 μA) under a 25 ° C. environment until the voltage reached 3.9 V. After the voltage reached 3.9 V, the voltage was 3.9 V. The current (discharge rate: 1C) was decreased until the current became 5% or less, and the battery was charged at a constant voltage, fully charged, and then suspended for 10 minutes. Here, the “1C” means a current value (current value reaching the discharge end voltage) at which constant current discharge is performed using the tripolar coin cell and discharge is completed in one hour. The constant current was set so that a theoretical discharge amount of 150 mAh / g of lithium iron phosphate as an active material was discharged in one hour at the working electrode in Example Test Cell 1.

Discharge test:
Thereafter, the fully charged example test cell 1 was subjected to a constant current (45 μA) (discharged) in an environment of 25 ° C. until the voltage changed from 3.9 V (full charge voltage) to 2.5 V (discharge end voltage). A constant current discharge at a rate of 1 C), the cell voltage (V) on the vertical axis, the discharge time (h) on the horizontal axis, a discharge curve is created, and the working electrode (electrode plate for positive electrode of Example 1) The discharge capacity (mAh) was determined and converted to the discharge capacity (mAh / g) per unit weight of the working electrode.

  Subsequently, with a constant current discharge test at a constant current (45 μA) (discharge rate: 1 C, discharge end time: 1 hour) carried out as described above, a constant current (0.23 mA) of 5 times (discharge rate: 5C, discharge end time: 12 minutes), 10 times constant current (0.45 mA) (discharge rate: 10 C, discharge end time: 6 minutes), 50 times constant current (2.25 mA) (discharge rate: 50 C, At the end of discharge: 1.2 minutes), a constant current discharge test was conducted in the same manner to determine the discharge capacity (mAh) of the working electrode at each discharge rate. From this, the discharge capacity per unit weight (mAh / g) ) Was converted.

<Calculation of discharge capacity maintenance rate (%)>
In order to evaluate the output characteristics (discharge rate characteristics) of the working electrode, the discharge capacity (mAh / g) per unit weight at each discharge rate obtained as described above is used, and the calculation formula of Formula 1 shown above is used. The discharge capacity retention rate (%) was determined. The discharge capacity (mAh / g) and discharge capacity retention rate (%) per unit weight obtained by the above discharge test are all shown in Table 2.

<Measurement of DC resistance of positive electrode plate>
Using the example test cell 1, the DC resistance value of the positive electrode plate was calculated as follows. When a discharge test is performed under the condition of a discharge rate of 1C, a voltage value (V1) (mV) 10 seconds after the start of discharge is measured. Furthermore, also when the discharge test is performed under the condition of a discharge rate of 10 C, the voltage value (V10) (mV) 10 seconds after the start of discharge is measured. Based on these measured values (V1, V10) and the constant current values (I1, I10) (mA) corresponding to the discharge rates 1C, 10C, the DC resistance value ( Ω) is calculated. The results are shown in Table 1.

  Specifically, the positive electrode plate of Example 1 is calculated as follows. The voltage values (V1, V10) (mV) 10 seconds after the start of discharge when the discharge test was performed under the conditions of the discharge rates of 1C and 10C were 3440 mV and 3435 mV, respectively. The constant current values (I1, I10) (mA) corresponding to the discharge rates 1C and 10C are 0.045 mA and 0.45 mA. Therefore, the DC resistance value (Ω) is 12Ω by (3440-3435) / (0.45-0.045).

  Based on the DC resistance value thus calculated, the smoothness of the flow of both electrons and lithium ions is evaluated. When the resistance value is small in this test, it is evaluated that the flow of electrons and lithium ions is smooth, and the input / output characteristics of the working plate are improved.

(Example 2 and Example 3)
The application amount of the electrode active material layer forming solution on the current collector is changed so that the film thickness of the electrode active material layer formed on the current collector becomes the value shown in Table 1, and the heating step is performed with nitrogen gas. A positive electrode body was prepared in the same manner as in Example 1 except that it was changed to be carried out in a mixed gas (hydrogen concentration: 4% (volume percentage)) atmosphere of Example 2 and Example 2. It was set to 3.

About Example 2 and Example 3, film-forming evaluation, electron microscope observation, the film thickness measurement of an electrode active material layer, a particle size measurement, and X-ray diffraction were performed similarly to Example 1. FIG. In the electron microscope observation, it was confirmed that the electrode active material layer was formed on the current collector as in Example 1. Further, it was confirmed by X-ray diffraction that the compound constituting the electrode active material layer was LiFePO ₄ . Other results are shown in Table 1.

  In addition, the uniformity of the particle size of the active material of the positive electrode plates of Example 2 and Example 3 was evaluated in the same manner as in Example 1. The results are shown in Table 1.

  Similar to Example Test Cell 1, Example Test Cell 2 and Example Test Cell 3 were prepared using Examples 2 and 3, respectively. Then, the charge test and the discharge test were performed in the same manner as in the example test cell 1 except that the constant current at each discharge rate was changed to the values shown in Table 2 using the example test cell 2 and the example test cell 3. Then, the discharge capacity (mAh) of the working electrode at each discharge rate was determined, and the discharge capacity per unit weight (mAh / g) was converted from this. For Example Test Cell 2 and Example Test Cell 3, the discharge capacity retention rate (%) was determined using the calculation formula (Equation 1) in the same manner as Example Test Cell 1. The results are summarized in Table 2.

  Moreover, DC resistance values were calculated for the positive plates of Example 2 and Example 3 in the same manner as Example 1 except that Example Test Cell 2 and Example Test Cell 3 were used. The results are shown in Table 1.

(Comparative Example 1)
80 parts by weight of LiFePO ₄ powder having an average particle diameter of 1 μm as a raw material for the positive electrode active material, 10 parts by weight of acetylene black (Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive agent, and polyvinylidene fluoride (PVDF) as a resin binder (Kureha, KF # 1100) 10 parts by weight of organic solvent N-methylpyrrolidone (NMP) (Mitsubishi Chemical Co., Ltd.) is added and dispersed to excel so that the solid concentration is 55% by weight. The slurry was stirred for 15 minutes at a rotation speed of 5000 rpm with an autohomogenizer (Nippon Seiki Seisakusho Co., Ltd.) to prepare a slurry-like coating composition for forming a positive electrode active material layer. And the application amount of the coating composition for positive electrode active material layer formation after drying on the aluminum plate of thickness 15 micrometers used for the positive electrode active material layer formation coating composition prepared above as a positive electrode collector. It apply | coated so that it might be set to 50 g / m < ² >, It was made to dry in 120 degreeC air | atmosphere atmosphere using an oven for 20 minutes, and the electrode active material layer for positive electrodes was formed on the collector surface. Furthermore, after pressing using a roll press machine so that the coating density of the formed electrode active material layer is 2.0 g / cm ³ (thickness of the positive electrode active material layer: 25 μm), a predetermined size ( And was vacuum-dried at 120 ° C. for 12 hours to produce an electrode plate for a non-aqueous electrolyte secondary battery positive electrode, which was referred to as Comparative Example 1. For Comparative Example 1, film forming properties were evaluated in the same manner as in Example 1. The results are shown in Table 1.

<Production of tripolar coin cell>
A tripolar coin cell was assembled in the same manner as Example Test Cell 1 except that Comparative Example 1 produced as described above was used as the working electrode, and this was designated as Comparative Example Test Cell 1.

<Charge test and discharge test>
About the comparative example test cell 1, except having changed the constant current in each discharge rate into the value shown in Table 2, a charge test and a discharge test are implemented like the example test cell 1, and the working electrode in each discharge rate is carried out. The discharge capacity (mAh) was determined, and the discharge capacity (mAh / g) per unit weight was converted from this. Similarly to the example test cell 1, the discharge capacity retention rate (%) was obtained using the calculation formula (Equation 1). The results are summarized in Table 2.

(Comparative Example 2)
A positive electrode plate was prepared in the same manner as in Comparative Example 1 except that the compounding amount of PVDF, which is a resin binder, was changed to 7% by weight with respect to the total solid components, and Comparative Example 2 was obtained. In Comparative Example 2, the film forming property was evaluated in the same manner as in Example 1. The results are shown in Table 1.

<Production of tripolar coin cell>
A tripolar coin cell was assembled in the same manner as Example Test Cell 1 except that Comparative Example 2 produced as described above was used as the working electrode, and this was designated as Comparative Example Test Cell 2.

<Charge test and discharge test>
About the comparative example test cell 2, except having changed the constant current in each discharge rate into the value shown in Table 2, a charge test and a discharge test are implemented like the example test cell 1, and the working electrode in each discharge rate is carried out. The discharge capacity (mAh) was determined, and the discharge capacity (mAh / g) per unit weight was converted from this. Similarly to the example test cell 1, the discharge capacity retention rate (%) was obtained using the calculation formula (Equation 1). The results are summarized in Table 2.

(Comparative Example 3)
A positive electrode plate was prepared in the same manner as in Comparative Example 1 except that no resin binder was used, and this was used as Comparative Example 3. However, in Comparative Example 3, a part of the electrode active material layer was peeled off when drawn out into a disk having a predetermined size, and the film forming property was poor (Table 1). As a result, the charge / discharge test could not be carried out.

(Reference Example 1)
Using the electrode active material layer forming solution for Reference Example 1 prepared as described below, the current collector (aluminum plate having a thickness of 15 μm) was added in such an amount that the thickness of the electrode active material layer finally obtained was 5 μm. ) A coating film for forming an electrode active material layer was formed in the same manner as in Example 1 except that it was applied to one surface side.

<Preparation of electrode active material layer forming solution for Reference Example 1>
As _{Li (CH 3 COO) · 2H} 2 O [ molecular weight: 102.02] raw material (solute) which generates an active material 10.2 g, and NiCl ₂ · _{6H 2} O [molecular weight: 237.69] a 23.8g , 2 g of Co (NO ₃ ) ₂ · 6H ₂ O [molecular weight: 291.03] and 5 g of polyethylene glycol 400 (manufactured by Kanto Chemical Co., Ltd.), and these raw materials were water: ethanol = 2: 1 by weight ratio. In addition to 50 g of the mixed solution, the mixture was dissolved, stirred for 1 hour at a temperature of 70 ° C. and a rotation speed of 200 rpm with a bioshaker, and allowed to stand at room temperature for 24 hours to prepare an electrode active material layer forming solution for Reference Example 1. did.

<Heating process>
Next, the current collector having the electrode active material layer-forming coating film formed on the surface thereof is mixed in an atmosphere of a mixed gas of oxygen gas and nitrogen gas (oxygen gas 30% by volume percentage, nitrogen gas 70%). A hot plate heated to 0 ° C. was brought into close contact with the electrode active material-forming coating film from the side where it was formed, and held for 5 minutes. After returning to room temperature, the temperature was raised to 580 ° C. over 5 hours in a baking furnace (manufactured by Koyo Thermo Co.) filled with oxygen gas, and then kept at 580 ° C. for 1 hour. I waited until I came back. When the temperature reaches room temperature, the sample is taken out by opening it to the atmosphere, and an appropriate electrode active material layer as a positive electrode active material layer on the current collector (the active material is based on the crystal structure of lithium nickelate as a part of nickel atoms). A positive electrode plate for a non-aqueous electrolyte secondary battery according to the present invention was obtained, in which the one substituted with cobalt atoms) was laminated. Then, the positive electrode plate was drawn out to a predetermined size (a disk having a diameter of 15 mm), and the positive electrode body thus obtained was used as Reference Example 1. For Reference Example 1, film formation was evaluated in the same manner as in Example 1. The results are shown in Table 1.

  Further, in the same manner as in Example 1, the evaluation of the uniformity of the particle size of the active material of the positive electrode plate of Reference Example 1 and the direct current resistance value of the positive electrode plate were carried out. The results are shown in Table 1.

<Production of tripolar coin cell>
A tripolar coin cell was assembled in the same manner as in Example Test Cell 1 except that Reference Example 1 produced as described above was used as the working electrode, and this was designated as Reference Example Test Cell 1.

<Charge test and discharge test>
About the reference example test cell 1, except having changed the constant current in each discharge rate into the value shown in Table 2, a charge test and a discharge test are implemented similarly to the example test cell 1, and the working electrode in each discharge rate is measured. The discharge capacity (mAh) was determined, and the discharge capacity (mAh / g) per unit weight was converted from this. Similarly to the example test cell 1, the discharge capacity retention rate (%) was obtained using the calculation formula (Equation 1). The results are summarized in Table 2.

  In addition, the direct current resistance value was calculated for the positive electrode plate of Reference Example 1 in the same manner as in Example 1 except that the reference example test cell 1 was used. The results are shown in Table 1.

(Reference Example 2)
Using the electrode active material layer forming solution for Reference Example 2 prepared as described below, the current collector (aluminum plate having a thickness of 15 μm) was added in such an amount that the thickness of the electrode active material layer finally obtained was 1 μm. ) A coating film for forming an electrode active material layer was formed in the same manner as in Example 1 except that it was applied to one surface side.

<Preparation of electrode active material layer forming solution for Reference Example 2>
LiNO ₃ [molecular weight: 68.95] as a starting material (solute) which generates an active material 6.9 g, and _{Co (NO 3) 2 · 6H} 2 O [ molecular weight: 291.03] using 29g of, these materials Electrode active material layer forming solution for Reference Example 2 by adding 0.2 g of polyethylene glycol 400 and further kneading with an Excel auto homogenizer (Nihon Seiki Seisakusho Co., Ltd.) at a rotation speed of 5000 rpm for 15 minutes. Was prepared.

<Heating process>
Next, from the side on which the electrode active material layer-forming coating film was formed on the hot plate heated to 400 ° C. in an atmospheric pressure atmosphere, the current collector having the electrode active material layer-forming coating film formed on the surface. Slowly approached and held for 10 minutes. Next, it is installed in an electric furnace at room temperature, heated up to the target temperature of 600 ° C. over 5 hours, then heated at 600 ° C. for 1 hour and taken out from the electric furnace, on the current collector A positive electrode plate for a non-aqueous electrolyte secondary battery of the present invention was obtained in which an appropriate electrode active material layer was laminated as a positive electrode active material layer. The electrode plate was cut into a predetermined size (a disk having a diameter of 15 mm) to obtain Reference Example 2. For Reference Example 2, film formation was evaluated in the same manner as in Example 1. The results are shown in Table 1.

  In addition, the uniformity of the particle size of the active material of the positive electrode plate of Reference Example 2 was evaluated in the same manner as in Example 1. The results are shown in Table 1.

<Production of tripolar coin cell>
A tripolar coin cell was assembled in the same manner as Example Test Cell 1 except that Reference Example 2 produced as described above was used as the working electrode, and this was designated as Reference Example Test Cell 2.

<Charge test and discharge test>
About the reference example test cell 2, a charge test and a discharge test were carried out in the same manner as in the example test cell 1 except that the discharge rate and the constant current at each discharge rate were changed to the values shown in Table 2, and at each discharge rate. The discharge capacity (mAh) of the working electrode was determined, and the discharge capacity per unit weight (mAh / g) was converted from this. Similarly to the example test cell 1, the discharge capacity retention rate (%) was obtained using the calculation formula (Equation 1). The results are summarized in Table 2.

  Further, the direct current resistance value was calculated for the positive electrode plate of Reference Example 2 in the same manner as in Example 1 except that the reference example test cell 2 was used. The results are shown in Table 1.

  Comparing Example 1 and Comparative Example 1, Example 1 is different in that the discharge capacity retention rate is also significantly higher. This difference is larger than the difference due to the difference in the amount of resin binder added as in Comparative Examples 1 and 2. Further, as shown in Comparative Example 3, when the same method as in Comparative Example 1 is used without simply adding the addition amount of the resin binder, the electrode active material layer itself can no longer be formed. End up. That is, an electrode active material layer having excellent input / output characteristics similar to that of Example 1 cannot be formed by simply reducing the resin binder or adding no resin binder using a conventional manufacturing method. . In this regard, in Example 1, an electrode active material layer having excellent input / output characteristics (that is, excellent discharge capacity retention ratio) can be formed without requiring a resin binder.

  In any of Examples 1 to 3, compared with Reference Examples 1 and 2, the particle size of the active material was generally reduced, and the average maximum particle size was as small as about 30 μm or less. In each of Examples 1 to 3, the difference between the average maximum particle size and the average minimum particle size is smaller than those in Reference Examples 1 and 2, and in Examples 1 to 3, the particle size of the active material is uniform. It was shown that an excellent electrode active material layer was formed.

  In Examples 1 to 3, the DC resistance value was smaller than those in Reference Examples 1 and 2, and it was confirmed that the electrode active material layer containing the lithium iron-based composite compound as an active material can be efficiently discharged and charged. . This indicates that the non-aqueous electrolyte secondary battery using the electrode of the present invention has high charge / discharge performance.

Claims (11)

A positive electrode plate for a non-aqueous electrolyte secondary battery comprising a current collector and an electrode active material layer composed of an active material on at least a part of the surface of the current collector,
The electrode active material layer is composed of an active material containing at least lithium and iron as metal elements, and has a structure in which the active materials are partially joined and the active material is continuously present. A porous layer having voids through which liquid can penetrate;
A positive electrode plate for a non-aqueous electrolyte secondary battery, wherein at least part of the active material contained in the electrode active material layer is bonded to a current collector.
2. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the active material constituting the electrode active material layer is a lithium iron-based composite oxide or a lithium iron-based composite phosphate compound. Board.
The positive electrode plate for a non-aqueous electrolyte secondary battery according to claim 1, wherein the electrode active material layer is composed of an active material containing lithium iron phosphate (LiFePO ₄ ).
The particle diameters of 20 arbitrarily selected active material particles are measured based on observation of an electrode active material layer by an electron microscope, and the arithmetic average value of 5 points selected in order of decreasing particle diameter is the average of the active material. When the average maximum particle size of the active material is set to the minimum particle size, and the arithmetic average value for 5 points selected in order of increasing particle size,
The average minimum particle size of the active material is 5 nm or more and less than 20 nm, and the average maximum particle size is 20 nm or more and less than 150 nm. Positive electrode plate for water electrolyte secondary battery.
The particle diameters of 20 arbitrarily selected active material particles are measured based on observation of an electrode active material layer by an electron microscope, and the arithmetic average value of 5 points selected in order of decreasing particle diameter is the average of the active material. When the average maximum particle size of the active material is set to the minimum particle size, and the arithmetic average value for 5 points selected in order of increasing particle size,
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the active material has a value of (average maximum particle size-average minimum particle size) of 40 nm or less. Positive electrode plate.
6. The positive electrode plate for a non-aqueous electrolyte secondary battery according to claim 1, wherein the electrode active material layer has a film thickness of 300 nm or more and 10 μm or less.
6. The discharge capacity maintenance ratio is 50% or more at a discharge rate of 50C or more, assuming that the discharge capacity maintenance ratio when discharging at a discharge rate of 1C is 100%. A positive electrode plate for a non-aqueous electrolyte secondary battery according to claim 1.
Prepare an electrode active material layer forming solution containing lithium and iron as metal elements,
Applying the electrode active material layer forming solution on at least a part of the current collector surface to form a coating film,
Next, the current collector on which the coating film has been formed is subjected to a heat treatment comprising heating at a temperature of 150 ° C. or higher in a state where a heat source is installed on the coating film side, and lithium is formed on the surface of the current collector. A method for producing a positive electrode plate for a non-aqueous electrolyte secondary battery, wherein an electrode active material layer is formed by producing a lithium iron-based composite oxide exhibiting an ion insertion / release reaction.
Prepare an electrode active material layer forming solution containing lithium and iron as metal elements and phosphorus element,
The electrode active material layer forming solution is applied onto at least a part of the current collector surface to form a coating film, and then a heat source is applied to the coating film surface side of the current collector on which the coating film is formed. Lithium iron-based composite that exhibits a lithium ion insertion / desorption reaction on the surface of the current collector by performing a heat treatment comprising heating at a temperature of 200 ° C. or higher in an inert gas or reducing gas atmosphere in the installed state A method for producing a positive electrode plate for a non-aqueous electrolyte secondary battery, wherein an electrode active material layer is formed by forming a phosphoric acid compound.
After the heat treatment is performed by heating the current collector on which the coating film is formed by installing a heat source on the coating film side, the heat source is further installed on both sides of the current collector and subsequently heated. The method for producing a positive electrode plate for a non-aqueous electrolyte secondary battery according to claim 8 or 9, wherein the method is a treatment.
A non-aqueous electrolyte secondary battery comprising at least a positive electrode plate, a negative electrode plate, a separator provided between the positive electrode plate and the negative electrode plate, and an electrolyte containing a non-aqueous solvent,
The said positive electrode plate is a positive electrode plate for nonaqueous electrolyte secondary batteries of any one of Claim 1 to 7, The nonaqueous electrolyte secondary battery characterized by the above-mentioned.

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