JP2023092776A - Electrode and secondary battery - Google Patents

Abstract

To provide a secondary battery capable of obtaining excellent cycle characteristics and excellent load characteristics.SOLUTION: A secondary battery includes an electrode and an electrolyte, and the electrode includes a current collector and an active material layer supported by the current collector. The active material layer includes an active material and a conductive agent, and has a first surface on a side far from the current collector and a second surface on a side close to the current collector. The conductive agent includes a fibrous carbon material and a particulate carbon material. When an existence area of the conductive agent is subjected to Raman mapping by Raman spectroscopic analysis of each of the first surface and the second surface, and the existence area of the conductive agent is separated into an existence area of the fibrous carbon material and an existence area of the particulate carbon material, a ratio of the abundance of the fibrous carbon material on the second surface to the abundance of the fibrous carbon material on the first surface is 0.81 or more and 0.93 or less, and a ratio of the abundance of the particulate carbon material on the second surface to the abundance of the particulate carbon material on the first surface is 0.54 or more and 0.88 or less.SELECTED DRAWING: Figure 2

Description

The present technology relates to electrodes and secondary batteries.

Due to the widespread use of various electronic devices such as mobile phones, secondary batteries are being developed as power sources that are compact and lightweight and can provide high energy density. This secondary battery has an electrode and an electrolyte, and the electrode contains an active material and a conductive agent.

Various studies have been made on the configuration of the secondary battery. Specifically, when the mixture layer of the electrode contains an active material and a conductive agent, and the conductive agent contains carbon nanotubes or the like, the distribution of the conductive agent in the mixture layer (cohesion degree, dispersion degree and volume ratio) are defined (see, for example, Patent Documents 1 to 4).

JP 2017-557426 A JP 2006-100222 A JP 2006-054174 A JP 2010-253406 A

Various studies have been made on the configuration of the secondary battery, but the cycle characteristics and load characteristics are still insufficient, and there is room for improvement.

Therefore, an electrode and a secondary battery capable of obtaining excellent cycle characteristics and excellent load characteristics are desired.

An electrode of one embodiment of the present technology includes a current collector and an active material layer supported by the current collector. The active material layer contains an active material and a conductive agent, and has a first surface far from the current collector and a second surface close to the current collector. Conductive agents include fibrous carbon materials and particulate carbon materials. By performing Raman spectroscopic analysis on each of the first surface and the second surface, the region where the conductive agent exists is Raman mapped, and the region where the conductive agent exists is divided into an existing region of the fibrous carbon material and an existing region of the particulate carbon material. and the ratio of the abundance of the fibrous carbon material on the second surface to the abundance of the fibrous carbon material on the first surface is 0.81 or more and 0.93 or less, and the particles on the first surface The ratio of the abundance of the particulate carbon material on the second surface to the abundance of the particulate carbon material is 0.54 or more and 0.88 or less.

A secondary battery of an embodiment of the present technology includes an electrode and an electrolytic solution, and the electrode has the same configuration and physical properties as the electrode of the embodiment of the present technology described above.

Here, each of the abundance of the fibrous carbon material and the abundance of the particulate carbon material is the analysis result of each of the first surface and the second surface using Raman spectroscopic analysis (Raman mapping), as described above. calculated based on The details of the procedures for calculating the abundance of the fibrous carbon material and the abundance of the particulate carbon material will be described later.

According to the electrode or secondary battery of one embodiment of the present technology, the conductive agent contained in the active material layer of the electrode contains the fibrous carbon material and the particulate carbon material. Further, when each of the first surface and the second surface of the active material layer is subjected to Raman spectroscopic analysis (Raman mapping), the ratio of the abundance of the fibrous carbon material is within the above range, and the abundance of the particulate carbon material is is within the range described above. Therefore, excellent cycle characteristics and excellent load characteristics can be obtained.

Note that the effects of the present technology are not necessarily limited to the effects described here, and may be any of a series of effects related to the present technology described below.

It is a sectional view showing composition of an electrode in one embodiment of this art. FIG. 2 is a diagram schematically showing the distribution of a conductive agent on the surface of the active material layer shown in FIG. 1; It is a perspective view showing composition of a secondary battery in one embodiment of this art. FIG. 4 is a cross-sectional view showing the configuration of the battery element shown in FIG. 3; FIG. 3 is a block diagram showing the configuration of an application example of a secondary battery;

Hereinafter, one embodiment of the present technology will be described in detail with reference to the drawings. The order of explanation is as follows.

1. Electrode 1-1. Configuration 1-2. Physical properties 1-3. Manufacturing method 1-4. Action and effect 2 . Secondary Battery 2-1. Configuration 2-2. Operation 2-3. Manufacturing method 2-4. Action and effect 3. Modification 4. Applications of secondary batteries

<1. Electrode>
First, an electrode according to an embodiment of the present technology will be described.

Since the use of this electrode is not particularly limited, it can be set arbitrarily. An example of the application of electrodes is an electrochemical device, and specific examples of the electrochemical device are secondary batteries, capacitors, and the like.

When an electrode is used in an electrochemical device, the electrode may be used as a positive electrode, a negative electrode, or both a positive electrode and a negative electrode.

A case where the electrode is used in a secondary battery will be described below. The secondary battery described here is a secondary battery in which battery capacity is obtained by utilizing the absorption and release of electrode reactants, and includes an electrolyte together with electrodes.

<1-1. Configuration>
FIG. 1 shows a cross-sectional configuration of an electrode 100, which is an electrode of one embodiment of the present technology. This electrode 100 includes a current collector 110 and an active material layer 120, as shown in FIG.

[Current collector]
The current collector 110 has a pair of surfaces on which the active material layer 120 is provided, and contains a conductive material such as a metal material. The type of conductive material can be arbitrarily selected according to the application (positive electrode or negative electrode) of the electrode 100, and the details of the conductive material will be described later.

[Active material layer]
Since the active material layer 120 is provided on the current collector 110 , it is supported by the current collector 110 . This active material layer 120 contains an active material and a conductive agent. However, the active material layer 120 may further contain one or more of other materials such as a binder.

Since the active material layers 120 are provided on both sides of the current collector 110 here, the electrode 100 includes two active material layers 120 . However, since the active material layer 120 is provided only on one side of the current collector 110 , the electrode 100 may include only one active material layer 120 . The method of forming the active material layer 120 is not particularly limited, but specifically, any one or two of a coating method, a vapor phase method, a liquid phase method, a thermal spraying method, a firing method (sintering method), and the like can be used. Kinds or more.

As shown in FIG. 1, the active material layer 120 has a surface F1 which is a first surface farther from the current collector 110 in the thickness direction T and a surface F1 which is a first surface farther from the current collector 110 in the thickness direction T and a side closer to the current collector 110 in the thickness direction T. and a back surface F2 which is the second surface of the .

The “thickness direction T” is the direction from the active material layer 120 toward the current collector 110, that is, the direction from the front surface F1 to the rear surface F2. FIG. 1 focuses on one of the two active material layers 120, more specifically, on the active material layer 120 disposed above the current collector 110, so that The thickness direction T is shown to be the direction toward .

(active material)
In order to occlude and desorb the electrode reactant, the active material contains one or more of electrode materials that occlude and desorb the electrode reactant. The type of electrode material can be arbitrarily selected according to the application (positive electrode or negative electrode) of the electrode 100, and the details of the electrode material will be described later.

(Conductive agent)
The conductive agent contains a conductive material to improve the conductivity of the active material layer 120. More specifically, two types of carbon materials (fibrous carbon material and particulate carbon material) are used as the conductive material. ).

A fibrous carbon material is a carbon material having an elongated fibrous shape. The type of fibrous carbon material is not particularly limited, but specifically, one or more of carbon nanotubes, carbon nanofibers, carbon nanohorns, and the like. This is because the physical property conditions of the electrode 100, which will be described later, are easily satisfied.

A particulate carbon material is a carbon material having a substantially particulate shape, unlike a fibrous carbon material. The type of particulate carbon material is not particularly limited, but specifically, one or more of carbon black, acetylene black, ketjen black, and the like. This is because the physical property conditions of the electrode 100, which will be described later, are easily satisfied.

The mixing ratio (weight ratio) of the fibrous carbon material and the particulate carbon material is not particularly limited, and can be arbitrarily set according to the use of the electrode 100 (positive electrode or negative electrode).

However, the conductive agent may further contain one or more of other conductive materials. The type of other conductive material is not particularly limited, but specifically includes metal materials, conductive polymer compounds, and the like.

(Binder)
The binder contains one or both of synthetic rubber and a polymer compound to bind the active material and the conductive agent together. The types of the synthetic rubber and polymer compound can be arbitrarily selected according to the use of the electrode 100 (positive electrode or negative electrode), etc. Details of the synthetic rubber and polymer compound will be described later.

<1-2. physical properties >
Regarding the physical properties of the electrode 100, the conditions described below are satisfied.

FIG. 2 schematically shows distribution of the conductive agent 122 on the surface F1 of the active material layer 120 shown in FIG.

In the following, the procedure for identifying the region where the conductive agent 122 exists on the front surface F1 of the active material layer 120 and the procedure for identifying the region where the conductive agent 122 exists on the back surface F2 of the active material layer 120 will be described. After explaining the procedure for calculating E1(F1) and E1(F2) and the procedure for calculating the amounts of particulate carbon material E2(F1) and E2(F2), the physical property conditions of the electrode 100 will be explained.

[Procedure for specifying region where conductive agent exists on surface of active material layer]
When identifying the region where conductive agent 122 exists on surface F1 of active material layer 120, Raman spectroscopic analysis is performed on surface F1 using Raman spectroscopic analysis, and a Raman spectrum (not shown), which is the analysis result, is obtained. get. In this case, an argon laser beam (wavelength=532 nm) is used as a light source for analysis. Also, by irradiating a part (portion P) of the surface F1 with laser light, the analysis range is set to 350 nm×500 nm.

In this Raman spectrum, a G' band peak is detected within a wavelength range of 2400 cm ^-1 to 2800 cm ^-1 . This peak is generated due to the presence of the conductive agent 122 containing two types of carbon materials (fibrous carbon material and particulate carbon material).

After that, by performing Raman mapping on the area where the conductive agent 122 exists, the distribution of the conductive agent 122 on the surface F1 is obtained as shown in FIG. This distribution is a map in which the abundance of the conductive agent 122 is color-coded according to the peak intensity. However, in FIG. 2 , in order to simplify the illustration, the presence area of the conductive agent 122 is shaded without color-coding the amount of the conductive agent 122 present.

Electrode 100 includes active material 121 and conductive agent 122 (fibrous carbon material and particulate carbon material) on surface F1, as shown in FIG. Existing. A binder may further exist around the active material 121 .

[Procedure for specifying region where conductive agent exists on back surface of active material layer]
Although not specifically illustrated here, the procedure for specifying the existing region of the conductive agent 122 on the back surface F2 of the active material layer 120 is to perform Raman spectroscopic analysis (Raman mapping) on the back surface F2 instead of the surface F1. The procedure is the same as that for identifying the region where the conductive agent 122 exists on the surface F1.

The preparation procedure for Raman spectroscopic analysis of the rear surface F2 is as described below. In the following, one of the two active material layers 120 shown in FIG. The other active material layer 120 arranged in 1 is set as a non-analysis target.

Specifically, after a double-sided tape is attached to the surface of the support base, the electrode 100 is placed on the double-sided tape. In this case, by adjusting the direction of the electrode 100 so that the active material layer 120 to be analyzed faces the double-sided tape, the surface F1 is adhered to the double-sided tape. Thereby, the electrode 100 is fixed to the support through the double-sided tape. After that, by pulling up the current collector 110 provided with the active material layer 120 that is not to be analyzed so as to move away from the active material layer 120 that is to be analyzed, current is collected from the active material layer 120 that is to be analyzed. The body 110 is exfoliated. As a result, the back surface F2 of the active material layer 120 to be analyzed is exposed, so that the back surface F2 can be analyzed.

[Procedures for calculating the abundance of the fibrous carbon material and the abundance of the particulate carbon material on the surface of the active material layer]
When calculating each of the abundance E1 (F1) of the fibrous carbon material and the abundance E2 (F1) of the particulate carbon material on the surface F1 of the active material layer 120, as a preliminary preparation, the procedure described below is performed. , separates the existing region of the conductive agent 122 on the surface F1 into the existing region of the fibrous carbon material and the existing region of the particulate carbon material.

In the distribution of the conductive agent 122 on the surface F1 shown in FIG. 2, the existing region of the conductive agent 122 can be specified, but the existing regions of the fibrous carbon material and the particulate carbon material cannot be specified.

Therefore, in order to calculate each of the abundances E1 (F1) and E2 (F1), the presence region of the conductive agent 122 is determined based on the intensity of the peak (step value that is a relative value described later). It separates into an existing region and an existing region of the particulate carbon material.

Specifically, the intensity of the peak is graded so as to have 101 graded values. In this case, since the intensity of the peak is the lowest in the first stage, the step value of the first stage is set to the minimum value (=0). Also, since the intensity of the peak is highest at the 101st stage, the step value at the 101st stage is set to the maximum value (=100).

As a result, the region in which the step value is 0 to 29 is defined as the presence region of the particulate carbon material, and the region in which the step value is 30 to 100 is defined as the presence region of the fibrous carbon material. In the region where the particulate carbon material exists, the larger the step value (= 0 to 29), the larger the amount of the particulate carbon material, and in the region where the fibrous carbon material exists, the step value (= 30 to 100 ), the greater the abundance of the fibrous carbon material.

Therefore, based on the step value set according to the intensity of the peak, the region where the conductive agent 122 exists is separated into the region where the fibrous carbon material exists and the region where the particulate carbon material exists.

When calculating the amount E1 (F1) of the fibrous carbon material existing on the surface F1, in the existing area of the fibrous carbon material separated from the existing area of the conductive agent 122, The existence amount E1 (F1) is calculated by counting the pixels that are included.

Further, when calculating the abundance E2 (F1) of the particulate carbon material on the surface F1, in the presence region of the particulate carbon material separated from the presence region of the conductive agent 122, the existence region of the particulate carbon material By counting the pixels contained in , its abundance E2 (F1) is calculated.

[Procedures for calculating the abundance of the fibrous carbon material and the abundance of the particulate carbon material on the back surface of the active material layer]
The procedure for calculating the abundance E1 (F2) of the fibrous carbon material and the abundance E2 (F2) of the particulate carbon material on the back surface F2 of the active material layer 120 is, except as described below, the abundance This is the same as the procedure for calculating E1(F1) and E2(F1). In order to calculate each of the abundances E1 (F2) and E2 (F2), instead of the area where the conductive agent 122 exists on the front surface F1, the area where the conductive agent 122 exists on the back surface F2 is specified, and then the conductive agent 122 is divided into a fibrous carbon material existing area and a particulate carbon material existing area. Also, abundances E1 (F2) and E2 (F2)) are calculated instead of abundances E1 (F1) and E2 (F1).

When calculating the abundance E1 (F2) of the fibrous carbon material on the back surface F2, in the existing region of the fibrous carbon material separated from the existing region of the conductive agent 122, The abundance E1 (F2) is calculated by counting the pixels that are included.

Further, when calculating the abundance E2 (F2) of the particulate carbon material on the back surface F2, in the presence region of the particulate carbon material separated from the presence region of the conductive agent 122, the existence region of the particulate carbon material By counting the pixels contained in , its abundance E2 (F2) is calculated.

[Physical properties of electrode]
The abundance ratio R1 is calculated based on the abundances E1(F1) and E1(F2) of the fibrous carbon material. Since this abundance ratio R1 is the ratio of abundance E1 (F2) to abundance E1 (F1), it is calculated based on the formula R1=E1 (F2)/E1 (F1).

Also, the abundance ratio R2 is calculated based on the abundances E2(F1) and E2(F2) of the particulate carbon material. Since this abundance ratio R2 is the ratio of abundance E2 (F2) to abundance E2 (F1), it is calculated based on the formula R2=E2 (F2)/E2 (F1).

The abundance ratio R1 is a parameter representing the degree of segregation of the fibrous carbon material on the front surface F1 and the back surface F2 of the active material layer 120, and the abundance ratio R2 is the particulate carbon material on the front surface F1 and the back surface F2 of the active material layer 120. is a parameter that represents the degree of segregation of However, each value of abundance ratios R1 and R2 is a value rounded off to the third decimal place.

Here, the abundance ratio R1 is 0.81 to 0.93, and the abundance ratio R2 is 0.54 to 0.88. Each of the existence ratios R1 and R2 is within the above-described range because the existence state of the conductive agent 122 in the active material layer 120, that is, the dispersed state of the fibrous carbon material and the dispersed state of the particulate carbon material are each appropriate. This is because As a result, the electron conductivity of the active material layer 120 is improved, so that the electrical resistance of the active material layer 120 is lowered, and the occlusion and release properties of the electrode reactant in the active material layer 120 are improved. The details of the reasons explained here will be described later.

<1-3. Manufacturing method>
In the following, as an example of the manufacturing method of the electrode 100, the case of using the coating method will be described.

When manufacturing the electrode 100, first, an active material and a conductive agent (fibrous carbon material and particulate carbon material) are mixed together to form a mixture. In this case, a binder may be further used to form a mixture containing the binder.

Subsequently, after the mixture is added to the solvent, the solvent is kneaded using a stirring device or the like to prepare a paste-like mixture slurry. This solvent may be an aqueous solvent or an organic solvent. Subsequently, the active material layer 120 is formed by applying the mixture slurry to both surfaces of the current collector 110 and then drying the mixture slurry.

Finally, the active material layer 120 may be compression molded using a press such as a roll press. In this case, the active material layer 120 may be heated, or compression molding may be repeated multiple times.

As a result, as shown in FIG. 1, active material layers 120 containing an active material and a conductive agent (fibrous carbon material and particulate carbon material) are formed on both sides of current collector 110, thus completing electrode 100. do.

When manufacturing this electrode 100, the conductive agent 122 (fibrous carbon material and Since the distribution of the particulate carbon material) changes, each of the abundance ratios R1 and R2 can be adjusted.

<1-4. Action and effect>
According to this electrode 100, the conductive agent contained in the active material layer 120 of the electrode 100 contains a fibrous carbon material and a particulate carbon material. Further, when the surface F1 and the back surface F2 of the active material layer 120 are subjected to Raman spectroscopic analysis (Raman mapping), the abundance ratio R1 of the fibrous carbon material is 0.81 to 0.93, and the abundance ratio R2 of the particulate carbon material is 0.81 to 0.93. is 0.54 to 0.88. Therefore, for the reasons described below, the secondary battery including the electrode 100 can have excellent cycle characteristics and excellent load characteristics.

When each of the abundance ratios R1 and R2 is within the above range, the conductive agent 122 is properly contained in the active material layer 120 compared to when each of the abundance ratios R1 and R2 is not within the above range. distributed. As a result, the distribution of the conductive agent 122 in the active material layer 120 , that is, the dispersed state of the fibrous carbon material and the dispersed state of the particulate carbon material are optimized in relation to the function of the conductive agent 122 .

Specifically, since the abundance ratio R1 is relatively larger than the abundance ratio R2, the fibrous carbon material is dispersed in the active material layer 120 so that the abundance is substantially uniform in the thickness direction T. be.

In this case, the fibrous carbon material tends to cling to the surface of each of the plurality of particulate active materials 121 . As a result, the active materials 121 are easily electrically connected to each other via the fibrous carbon material, and the active material 121 is easily electrically connected to the current collector 110 via the fibrous carbon material grains. . Therefore, the electronic conductivity between the active materials 121 is improved, and the electronic conductivity between the active materials 121 and the current collector 110 is improved. The occlusion and release properties of the electrode reactant in the material layer 120 are improved.

Moreover, since the abundance ratio R2 is relatively smaller than the abundance ratio R1, the particulate carbon material is dispersed in the active material layer 120 so that the abundance in the thickness direction T gradually decreases. That is, in the active material layer 120, the abundance of the particulate carbon material increases in the region near the front surface F1, and the abundance of the particulate carbon material decreases in the region near the back surface F2.

In this case, in the vicinity of the surface F1 of the active material layer 120 where it is difficult to collect current using the current collector 110, the active materials 121 are easily electrically connected to each other via the fibrous carbon material. Furthermore, the active materials 121 are easily electrically connected to each other through the particulate carbon material. Therefore, the electron conductivity between the active materials 121 is further improved, so that the electrical resistance of the active material layer 120 is further reduced, and the occlusion and release properties of the electrode reactant in the active material layer 120 are further improved.

From these facts, when each of the abundance ratios R1 and R2 is within the above range, the distribution of the conductive agent 122 (the dispersed state of the fibrous carbon material and the dispersed state of the particulate carbon material) in the active material layer 120 is be optimized. Therefore, the electrical resistance of the active material layer 120 is significantly reduced, and the occlusion and release properties of the electrode reactant are significantly improved, so that the secondary battery provided with the electrode 100 can have excellent cycle characteristics and excellent load characteristics. .

As a result, in the secondary battery including the electrode 100, even if the upper limit of the charging voltage is increased, more specifically, even if the upper limit of the charging voltage is increased to 4.45 V or higher, the cycle characteristics can be maintained. and load characteristics are guaranteed.

In particular, the fibrous carbon material contains one or more of carbon nanotubes, carbon nanofibers and carbon nanohorns, and the particulate carbon material is carbon black, acetylene black and ketjen black. If any one type or two or more types are included, the physical property conditions of the electrode 100 described above are likely to be satisfied. Therefore, the electrical resistance of the active material layer 120 is sufficiently lowered and the absorption/release property of the electrode reactant is sufficiently improved, so that a higher effect can be obtained.

<2. Secondary battery>
Next, a secondary battery according to an embodiment of the present technology using the electrodes described above will be described.

The secondary battery described here is a secondary battery in which the battery capacity is obtained by utilizing the absorption and release of the electrode reactant, as described above, and is provided with the electrolyte solution together with the electrodes.

The type of electrode reactant is not particularly limited, but specifically light metals such as alkali metals and alkaline earth metals. Examples of alkali metals are lithium, sodium and potassium, and examples of alkaline earth metals are beryllium, magnesium and calcium.

In the following, the case where the electrode reactant is lithium and the electrode is used as the positive electrode will be taken as an example. A secondary battery in which battery capacity is obtained by utilizing the intercalation and deintercalation of lithium is a so-called lithium ion secondary battery, and in the lithium ion secondary battery, lithium is intercalated and deintercalated in an ionic state.

In this secondary battery, the charge capacity of the negative electrode is larger than the discharge capacity of the positive electrode. That is, the electrochemical capacity per unit area of the negative electrode is set to be larger than the electrochemical capacity per unit area of the positive electrode. This is to prevent electrode reactants from depositing on the surface of the negative electrode during charging.

<2-1. Configuration>
FIG. 3 shows a perspective configuration of a secondary battery. FIG. 4 shows a cross-sectional configuration of the battery element 20 shown in FIG. However, FIG. 3 shows a state in which the exterior film 10 and the battery element 20 are separated from each other, and the cross section of the battery element 20 along the XZ plane is indicated by a broken line. In FIG. 4, only part of the battery element 20 is shown.

This secondary battery includes an exterior film 10, a battery element 20, a positive electrode lead 31, a negative electrode lead 32, and sealing films 41 and 42, as shown in FIGS. The secondary battery described here is a laminated film type secondary battery using a flexible or pliable exterior member (the exterior film 10).

[Exterior film and sealing film]
As shown in FIG. 3, the exterior film 10 is an exterior member that houses the battery element 20, and has a sealed bag-like structure with the battery element 20 housed therein. That is, the exterior film 10 accommodates the electrolytic solution together with the positive electrode 21 and the negative electrode 22 which will be described later.

Here, the exterior film 10 is a single film-like member and is folded in the folding direction FD. The exterior film 10 is provided with a recessed portion 10U (so-called deep drawn portion) for housing the battery element 20 .

Specifically, the exterior film 10 is a three-layer laminate film in which a fusion layer, a metal layer, and a surface protection layer are laminated in this order from the inside. The outer peripheral edges of the deposited layers are fused together. The fusible layer contains a polymer compound such as polypropylene. The metal layer contains a metal material such as aluminum. The surface protective layer contains a polymer compound such as nylon.

However, the configuration (number of layers) of the exterior film 10 is not particularly limited, and may be one layer, two layers, or four layers or more.

The sealing film 41 is inserted between the packaging film 10 and the positive electrode lead 31 , and the sealing film 42 is inserted between the packaging film 10 and the negative electrode lead 32 . However, one or both of the sealing films 41 and 42 may be omitted.

The sealing film 41 is a sealing member that prevents outside air from entering the exterior film 10 . Further, the sealing film 41 contains a polymer compound such as polyolefin having adhesiveness to the positive electrode lead 31, and a specific example of the polyolefin is polypropylene.

The configuration of the sealing film 42 is the same as the configuration of the sealing film 41 except that it is a sealing member having adhesiveness to the negative electrode lead 32 . That is, the sealing film 42 contains a polymer compound such as polyolefin that has adhesiveness to the negative electrode lead 32 .

[Battery element]
The battery element 20 is a power generation element including a positive electrode 21, a negative electrode 22, a separator 23, and an electrolytic solution (not shown), as shown in FIGS. It is

This battery element 20 is a so-called wound electrode body. That is, the positive electrode 21 and the negative electrode 22 are laminated with the separator 23 interposed therebetween, and are wound around the winding axis P, which is an imaginary axis extending in the Y-axis direction, facing each other with the separator 23 interposed therebetween. It is

The three-dimensional shape of the battery element 20 is not particularly limited. Here, since the battery element 20 is flat, the cross section of the battery element 20 intersecting the winding axis P (the cross section along the XZ plane) has a flat shape defined by the long axis J1 and the short axis J2. have. The major axis J1 is a virtual axis that extends in the X-axis direction and has a length greater than that of the minor axis J2. A virtual axis having a length smaller than the axis J1. Here, since the three-dimensional shape of the battery element 20 is a flat cylindrical shape, the cross-sectional shape of the battery element 20 is a flat, substantially elliptical shape.

(positive electrode)
The positive electrode 21 has the same configuration and physical properties as those of the electrode 100 . Specifically, the positive electrode 21 includes a positive electrode current collector 21A corresponding to the current collector 110 and a positive electrode active material layer 21B corresponding to the active material layer 120, as shown in FIG.

The positive electrode current collector 21A has a pair of surfaces on which the positive electrode active material layer 21B is provided. The positive electrode current collector 21A contains a conductive material such as a metal material, and a specific example of the conductive material is aluminum.

The positive electrode active material layer 21B contains a positive electrode active material that is the active material of the positive electrode 21 and a positive electrode conductive agent (fibrous carbon material and particulate carbon material) that is the conductive agent of the positive electrode 21 . However, the positive electrode active material layer 21B may further contain one or more of other materials such as a positive electrode binder that is a binder for the positive electrode 21 . The details of the method of manufacturing the positive electrode active material layer 21B are the same as those of the method of manufacturing the electrode 100 .

Here, the cathode active material layer 21B is provided on both surfaces of the cathode current collector 21A. However, the positive electrode active material layer 21B may be provided only on one side of the positive electrode current collector 21A on the side where the positive electrode 21 faces the negative electrode 22 . A method for forming the positive electrode active material layer 21B is not particularly limited, but specifically, one or more of coating methods and the like are used.

The kind of the positive electrode active material is not particularly limited, but specifically, it is a lithium-containing compound that intercalates and deintercalates lithium. This lithium-containing compound is a compound containing lithium and one or more transition metal elements as constituent elements, and may further contain one or more other elements as constituent elements. The type of the other element is not particularly limited as long as it is an element other than lithium and transition metal elements, but specifically, it is an element belonging to Groups 2 to 15 in the long period periodic table. The type of lithium-containing compound is not particularly limited, but specific examples include oxides, phosphoric acid compounds, silicic acid compounds and boric acid compounds.

_Specific examples _{of oxides} include _{LiNiO2 , LiCoO2 , LiCo0.98Al0.01Mg0.01O2 , LiNi0.5Co0.2Mn0.3O2} and _{LiMn2O4 .} Specific examples _of phosphoric acid compounds include _LiFePO4 , _{LiMnPO4 and LiFe0.5Mn0.5PO4} .

The positive electrode binder contains one or more of synthetic rubbers and polymer compounds. Specific examples of synthetic rubbers include styrene-butadiene rubber, fluororubber, and ethylene propylene diene. Specific examples of polymer compounds include polyvinylidene fluoride, polyimide and carboxymethylcellulose.

(negative electrode)
The negative electrode 22 includes a negative electrode current collector 22A and a negative electrode active material layer 22B, as shown in FIG.

The negative electrode current collector 22A has a pair of surfaces on which the negative electrode active material layer 22B is provided. The negative electrode current collector 22A contains a conductive material such as a metal material, and a specific example of the conductive material is copper.

The negative electrode active material layer 22B contains one or more of negative electrode active materials that intercalate and deintercalate lithium. However, the negative electrode active material layer 22B may further contain one or more of other materials such as a negative electrode binder and a negative electrode conductor.

Here, the negative electrode active material layer 22B is provided on both surfaces of the negative electrode current collector 22A. However, the negative electrode active material layer 22B may be provided only on one side of the negative electrode current collector 22A on the side where the negative electrode 22 faces the positive electrode 21 . The method of forming the negative electrode active material layer 22B is not particularly limited, but specifically, any one of a coating method, a vapor phase method, a liquid phase method, a thermal spraying method, a firing method (sintering method), or the like, or Two or more types.

The type of negative electrode active material is not particularly limited, but specifically, one or both of a carbon material and a metal-based material. This is because a high energy density can be obtained. Specific examples of carbon materials include graphitizable carbon, non-graphitizable carbon and graphite (natural graphite and artificial graphite). A metallic material is a material containing as constituent elements one or more of metallic elements and semi-metallic elements capable of forming an alloy with lithium. , silicon and tin. This metallic material may be a single substance, an alloy, a compound, a mixture of two or more of them, or a material containing two or more of these phases. Specific examples of metallic materials include TiSi ₂ and SiO _x (0<x≦2, or 0.2<x<1.4).

The details of the negative electrode binder and the negative electrode electrical conductor are the same as the details of the positive electrode binder and the positive electrode electrical conductor.

(separator)
The separator 23 is an insulating porous film interposed between the positive electrode 21 and the negative electrode 22, as shown in FIG. Allows lithium ions to pass through. This separator 23 contains a polymer compound such as polyethylene.

(Electrolyte)
The electrolytic solution is a liquid electrolyte. The electrolyte is impregnated into each of the positive electrode 21, the negative electrode 22 and the separator 23, and contains a solvent and an electrolyte salt.

Here, the solvent contains one or more of non-aqueous solvents (organic solvents), and the electrolytic solution containing the non-aqueous solvent is a so-called non-aqueous electrolytic solution. The non-aqueous solvents are esters, ethers, and the like, and more specifically, carbonate compounds, carboxylic acid ester compounds, lactone compounds, and the like.

The carbonate compounds include cyclic carbonates and chain carbonates. Specific examples of the cyclic carbonate include ethylene carbonate and propylene carbonate, and specific examples of the chain carbonate include dimethyl carbonate, diethyl carbonate and ethylmethyl carbonate. The carboxylic acid ester compound is a chain carboxylic acid ester or the like. Specific examples of chain carboxylic acid esters include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, ethyl trimethylacetate, methyl butyrate and ethyl butyrate. Lactone-based compounds include lactones. Specific examples of lactones include γ-butyrolactone and γ-valerolactone. Ethers may be 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, and the like.

The electrolyte salt contains one or more of light metal salts such as lithium salts. Specific examples of lithium salts include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium bis(fluorosulfonyl)imide (LiN ( _FSO2 ) ₂ ), bis(trifluoromethanesulfonyl _{)imidolithium (LiN(CF3SO2)2), lithium tris(trifluoromethanesulfonyl)methide (LiC(CF3SO2)3 ) , bis ( oxalato} )boron lithium oxide (LiB( _C2O4 ) ₂ ) and lithium difluoro( _oxalato )borate (LiB( _{C2O4 ) F2} ).

The content of the electrolyte salt is not particularly limited, but is specifically 0.3 mol/kg to 3.0 mol/kg with respect to the solvent. This is because high ionic conductivity can be obtained.

[Positive lead and negative lead]
The positive electrode lead 31 is a positive electrode terminal connected to the positive electrode current collector 21A of the positive electrode 21, as shown in FIGS. The positive electrode lead 31 contains a conductive material such as a metal material, and a specific example of the conductive material is aluminum. The shape of the positive electrode lead 31 is not particularly limited, but specifically, it is either a thin plate shape, a mesh shape, or the like.

The negative electrode lead 32 is a negative electrode terminal connected to the negative electrode current collector 22A of the negative electrode 22, as shown in FIGS. The negative electrode lead 32 contains a conductive material such as a metal material, and a specific example of the conductive material is copper. Here, details regarding the lead-out direction and shape of the negative electrode lead 32 are the same as those of the lead-out direction and shape of the positive electrode lead 31 .

<2-2. Operation>
During charging of the secondary battery, in the battery element 20, lithium is released from the positive electrode 21 and absorbed into the negative electrode 22 via the electrolyte. On the other hand, when the secondary battery is discharged, in the battery element 20, lithium is released from the negative electrode 22 and absorbed into the positive electrode 21 through the electrolyte. Lithium is intercalated and deintercalated in an ionic state during charging and discharging, respectively.

<2-3. Manufacturing method>
In the case of manufacturing a secondary battery, the positive electrode 21 and the negative electrode 22 are prepared according to an example procedure described below, and an electrolytic solution is prepared. A secondary battery is assembled, and the secondary battery after assembly is subjected to stabilization treatment.

[Preparation of positive electrode]
The positive electrode 21 is manufactured by the same procedure as the manufacturing procedure of the electrode 100 described above. Specifically, first, a paste-like positive electrode mixture slurry is prepared by putting a mixture (positive electrode mixture) in which a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder are mixed together into a solvent. This solvent may be an aqueous solvent or an organic solvent. Subsequently, the cathode active material layer 21B is formed by applying the cathode mixture slurry to both surfaces of the cathode current collector 21A. Finally, the cathode active material layer 21B is compression-molded using a roll press or the like. In this case, the positive electrode active material layer 21B may be heated, or compression molding may be repeated multiple times. As a result, the cathode active material layers 21B are formed on both surfaces of the cathode current collector 21A, so that the cathode 21 is produced.

[Preparation of negative electrode]
A negative electrode 22 is formed by substantially the same procedure as that of the positive electrode 21 described above. Specifically, first, a paste-like negative electrode mixture slurry is prepared by putting a mixture (negative electrode mixture) in which a negative electrode active material, a negative electrode conductor, and a negative electrode binder are mixed together into a solvent. Details regarding the solvent are given above. Subsequently, the anode active material layer 22B is formed by applying the anode mixture slurry to both surfaces of the anode current collector 22A. Finally, the negative electrode active material layer 22B is compression molded. As a result, the negative electrode 22 is manufactured because the negative electrode active material layers 22B are formed on both surfaces of the negative electrode current collector 22A.

[Preparation of electrolytic solution]
Add the electrolyte salt to the solvent. This disperses or dissolves the electrolyte salt in the solvent, thus preparing an electrolytic solution.

[Assembly of secondary battery]
First, a joining method such as welding is used to connect the positive electrode lead 31 to the positive electrode current collector 21A of the positive electrode 21, and a joining method such as welding is used to connect the negative electrode current collector 22A of the negative electrode 22 to the negative electrode. Connect lead 32 .

Subsequently, after the positive electrode 21 and the negative electrode 22 are laminated with the separator 23 interposed therebetween, the positive electrode 21, the negative electrode 22 and the separator 23 are wound to form a wound body (not shown). This wound body has the same structure as the battery element 20 except that the positive electrode 21, the negative electrode 22 and the separator 23 are not impregnated with the electrolytic solution. Subsequently, by pressing the wound body using a pressing machine or the like, the wound body is formed into a flat shape.

Subsequently, after the wound body is housed inside the hollow portion 10U, the exterior films 10 (bonding layer/metal layer/surface protective layer) are folded to face each other. Subsequently, by using an adhesion method such as a heat fusion method, the outer peripheral edges of two sides of the fusion layers facing each other are adhered to each other, so that the wound body is placed inside the bag-shaped exterior film 10. to accommodate.

Finally, after injecting the electrolytic solution into the inside of the bag-like exterior film 10, the outer peripheral edges of the remaining one side of the fusion layer are adhered to each other by using a bonding method such as a heat fusion method. In this case, a sealing film 41 is inserted between the packaging film 10 and the positive electrode lead 31 and a sealing film 42 is inserted between the packaging film 10 and the negative electrode lead 32 .

As a result, the wound body is impregnated with the electrolytic solution, so that the battery element 20, which is a wound electrode body, is produced. Accordingly, since the battery element 20 is enclosed inside the bag-shaped exterior film 10, the secondary battery is assembled.

[Stabilization of secondary battery]
The secondary battery after assembly is charged and discharged. Various conditions such as environmental temperature, number of charge/discharge times (number of cycles), and charge/discharge conditions can be arbitrarily set. As a result, films are formed on the respective surfaces of the positive electrode 21 and the negative electrode 22, so that the state of the secondary battery is electrochemically stabilized. Thus, a secondary battery is completed.

<2-4. Action and effect>
According to this secondary battery, the positive electrode 21 has the same configuration and physical properties as the electrode 100 described above. In this case, for the same reason as described for the electrode 100, the positive electrode active material layer 21B has a significantly reduced electrical resistance and a significantly improved lithium occlusion-release property, resulting in excellent cycle characteristics and excellent load characteristics. can be obtained. As a result, a sufficiently high discharge capacity can be obtained even after repeated charging and discharging, and rapid charging can be realized.

In particular, if the secondary battery is a lithium-ion secondary battery, a sufficient battery capacity can be stably obtained by utilizing the intercalation and deintercalation of lithium, so that a higher effect can be obtained.

Further, the positive electrode 21 has the same configuration and physical properties as the electrode 100 described above. Therefore, for the same reason as described for the electrode 100, the secondary battery using the positive electrode 21 can have excellent cycle characteristics and excellent load characteristics.

<3. Variation>
Next, modifications of the electrodes and secondary batteries described above will be described.

The configurations of the electrodes and the secondary battery can be changed as appropriate, as described below. However, any two or more of the series of modifications described below may be combined with each other.

[Modification 1]
The positive electrode 21 had the same configuration and physical properties as the electrode 100 . However, instead of the positive electrode 21 , the negative electrode 22 may have the same configuration and physical properties as the electrode 100 . Moreover, both the positive electrode 21 and the negative electrode 22 may have the same configuration and physical properties as those of the electrode 100 .

In the former case, the electrical resistance of the negative electrode active material layer 22B is remarkably lowered and the lithium intercalation/deintercalation property is remarkably improved, so that similar effects can be obtained. In the latter case, the electrical resistance of the positive electrode active material layer 21B and the negative electrode active material layer 22B is significantly reduced and the lithium absorption/desorption properties are significantly improved, so that a higher effect can be obtained.

[Modification 2]
A separator 23, which is a porous membrane, was used. However, although not specifically illustrated here, instead of the separator 23, a laminated separator including a polymer compound layer may be used.

Specifically, a laminated separator includes a porous membrane having a pair of surfaces and a polymer compound layer provided on one or both sides of the porous membrane. This is because the adhesiveness of the separator to each of the positive electrode 21 and the negative electrode 22 is improved, so that the winding misalignment of the battery element 20 is suppressed. As a result, even if a decomposition reaction of the electrolytic solution occurs, the secondary battery is less likely to swell. The polymer compound layer contains a polymer compound such as polyvinylidene fluoride. This is because polyvinylidene fluoride or the like has excellent physical strength and is electrochemically stable.

One or both of the porous film and the polymer compound layer may contain one or more of a plurality of insulating particles. This is because the safety (heat resistance) of the secondary battery is improved because the plurality of insulating particles promote heat dissipation when the secondary battery generates heat. The insulating particles include one or both of inorganic particles and resin particles. Specific examples of inorganic particles are particles such as aluminum oxide, aluminum nitride, boehmite, silicon oxide, titanium oxide, magnesium oxide and zirconium oxide. Specific examples of resin particles are particles of acrylic resins, styrene resins, and the like.

When producing a laminated separator, a precursor solution containing a polymer compound, a solvent, and the like is prepared, and then the precursor solution is applied to one or both surfaces of the porous membrane. In this case, instead of applying the precursor solution to the porous membrane, the porous membrane may be immersed in the precursor solution. Also, a plurality of insulating particles may be added to the precursor solution.

Even when this laminated separator is used, since lithium ions can move between the positive electrode 21 and the negative electrode 22, a similar effect can be obtained. In this case, particularly, as described above, the safety of the secondary battery is improved, so that a higher effect can be obtained.

[Modification 3]
An electrolytic solution, which is a liquid electrolyte, was used. However, although not specifically illustrated here, an electrolyte layer that is a gel electrolyte may be used instead of the electrolyte solution.

In the battery element 20 using the electrolyte layer, the positive electrode 21 and the negative electrode 22 are laminated with the separator 23 and the electrolyte layer interposed therebetween, and the positive electrode 21, the negative electrode 22, the separator 23 and the electrolyte layer are wound. This electrolyte layer is interposed between the positive electrode 21 and the separator 23 and interposed between the negative electrode 22 and the separator 23 . However, the electrolyte layer may be interposed only between the positive electrode 21 and the separator 23 or may be interposed only between the negative electrode 22 and the separator 23 .

Specifically, the electrolyte layer contains a polymer compound together with an electrolytic solution, and the electrolytic solution is held by the polymer compound. This is because leakage of the electrolytic solution is prevented. The composition of the electrolytic solution is as described above. Polymer compounds include polyvinylidene fluoride and the like. When forming the electrolyte layer, after preparing a precursor solution containing an electrolytic solution, a polymer compound, a solvent, and the like, the precursor solution is applied to one side or both sides of each of the positive electrode 21 and the negative electrode 22 .

Even when this electrolyte layer is used, lithium ions can move between the positive electrode 21 and the negative electrode 22 through the electrolyte layer, so that similar effects can be obtained. In this case, especially, as described above, leakage of the electrolytic solution is prevented, so that a higher effect can be obtained.

<4. Use of secondary battery>
Finally, the use (application example) of the secondary battery will be described.

Applications of the secondary battery are not particularly limited. A secondary battery used as a power source may be a main power source for electronic devices and electric vehicles, or may be an auxiliary power source. A main power source is a power source that is preferentially used regardless of the presence or absence of other power sources. The auxiliary power supply may be a power supply used in place of the main power supply, or may be a power supply switched from the main power supply.

Specific examples of uses of the secondary battery are as follows. Electronic devices such as video cameras, digital still cameras, mobile phones, laptop computers, headphone stereos, portable radios and portable information terminals. Backup power and storage devices such as memory cards. Power tools such as power drills and power saws. It is a battery pack mounted on an electronic device. Medical electronic devices such as pacemakers and hearing aids. It is an electric vehicle such as an electric vehicle (including a hybrid vehicle). It is a power storage system such as a home or industrial battery system that stores power in preparation for emergencies. In these uses, one secondary battery may be used, or a plurality of secondary batteries may be used.

The battery pack may be a single cell or an assembled battery. An electric vehicle is a vehicle that operates (runs) using a secondary battery as a drive power source, and may be a hybrid vehicle that also includes a drive source other than the secondary battery. In a home electric power storage system, electric power stored in a secondary battery, which is an electric power storage source, can be used to use electric appliances for home use.

Here, an example of the application of the secondary battery will be specifically described. The configuration described below is merely an example, and can be changed as appropriate.

FIG. 5 shows a block configuration of a battery pack, which is an application example of a secondary battery. The battery pack described here is a battery pack (a so-called soft pack) using one secondary battery, and is mounted in an electronic device such as a smart phone.

This battery pack includes a power supply 51 and a circuit board 52, as shown in FIG. This circuit board 52 is connected to the power supply 51 and includes a positive terminal 53 , a negative terminal 54 and a temperature detection terminal 55 .

Power supply 51 includes one secondary battery. In this secondary battery, the positive lead is connected to the positive terminal 53 and the negative lead is connected to the negative terminal 54 . The power source 51 is connected to the outside through a positive terminal 53 and a negative terminal 54, and thus can be charged and discharged. The circuit board 52 includes a control section 56 , a switch 57 , a thermal resistance element (so-called PTC element) 58 and a temperature detection section 59 . However, the PTC element 58 may be omitted.

Control unit 56 includes a central processing unit (CPU), a memory, and the like, and controls the operation of the entire battery pack. This control unit 56 detects and controls the use state of the power supply 51 as necessary.

When the voltage of the power supply 51 (secondary battery) reaches the overcharge detection voltage or the overdischarge detection voltage, the control unit 56 cuts off the switch 57 so that the charging current does not flow through the current path of the power supply 51. to The overcharge detection voltage is not particularly limited, but is specifically 4.20V±0.05V, and the overdischarge detection voltage is not particularly limited, but is specifically 2.40V±0.10V. is.

The switch 57 includes a charge control switch, a discharge control switch, a charge diode, a discharge diode, and the like, and switches connection/disconnection between the power supply 51 and the external device according to instructions from the control unit 56 . The switch 57 includes a field effect transistor (MOSFET) using a metal oxide semiconductor, etc., and the charge/discharge current is detected based on the ON resistance of the switch 57 .

The temperature detection unit 59 includes a temperature detection element such as a thermistor, measures the temperature of the power supply 51 using the temperature detection terminal 55 , and outputs the temperature measurement result to the control unit 56 . The measurement result of the temperature measured by the temperature detection unit 59 is used when the control unit 56 performs charging/discharging control at the time of abnormal heat generation and when the control unit 56 performs correction processing when calculating the remaining capacity.

An embodiment of the present technology will be described.

<Experimental Examples 1 to 5 and Comparative Examples 1 to 3>
As described below, after the secondary battery was produced, the characteristics of the secondary battery were evaluated.

[Production of secondary battery]
The secondary battery (laminate film type lithium ion secondary battery) shown in FIGS. 3 and 4 was produced by the procedure described below. In this case, the positive electrode 21 was configured to have the same configuration as the electrode 100 .

(Preparation of positive electrode)
First, a positive electrode active material (lithium cobalt oxide (LiCoO ₂ ) of 95 parts by mass, a positive electrode conductive agent of 2 parts by mass, and a positive electrode binder (polyvinylidene fluoride) of 3 parts by mass are mixed with each other to form a positive electrode mixture. As the positive electrode conductive agent, 1 part by mass of carbon nanotubes, which is a fibrous carbon material, and 1 part by mass of acetylene black (Denka Black, manufactured by Denka Co., Ltd.), which is a particulate carbon material, were used.

Subsequently, the positive electrode mixture is added to a solvent (N-methyl-2-pyrrolidone, which is an organic solvent), and the solvent containing the positive electrode mixture is kneaded to obtain a pasty positive electrode mixture slurry. prepared. Subsequently, the positive electrode mixture slurry is applied to both surfaces of the positive electrode current collector 21A (aluminum foil having a thickness of 12 μm) using a coating device, and then the positive electrode mixture slurry is dried to form a positive electrode active material layer. 21B. Subsequently, the positive electrode active material layer 21B was compression molded using a roll press (roll temperature=130° C., linear pressure=0.7 t/cm, press speed=10 m/min). Finally, the cathode current collector 21A on which the cathode active material layer 21B was formed was cut into strips (width=48 mm, length=300 mm). Thus, the positive electrode 21 was produced.

When producing this positive electrode 21, as described above, by changing each of the kneading conditions of the solvent in which the positive electrode mixture is introduced and the drying conditions of the positive electrode slurry, each of the abundance ratios R1 and R2 described later changed.

(Preparation of negative electrode)
First, 90 parts by mass of a negative electrode active material (artificial graphite that is a carbon material) and 10 parts by mass of a negative electrode binder (N-methyl-2-pyrrolidone solution containing polyimide (concentration = 20% by weight)) are mixed together. A negative electrode mixture slurry was prepared by kneading the negative electrode mixture. Subsequently, the negative electrode mixture slurry is applied to both surfaces of the negative electrode current collector 22A (copper foil having a thickness of 15 μm) using a bar coater (gap=35 μm), and then the negative electrode mixture slurry is dried (drying temperature= 80° C.). Subsequently, a coating film of the negative electrode mixture slurry is compression-molded using a roll press, and then the coating film is heated (heating temperature = 70°C, heating time = 3 hours) to form the negative electrode active material layer 22B. formed. Finally, the negative electrode current collector 22A on which the negative electrode active material layer 22B was formed was cut into strips (width=50 mm, length=310 mm). Thus, the negative electrode 22 was produced.

(Preparation of electrolytic solution)
After adding an electrolyte salt (lithium hexafluorophosphate) to a solvent (cyclic carbonate ethylene carbonate and chain carbonate ethylmethyl carbonate), the electrolyte salt-added solvent was stirred. In this case, the mixing ratio (weight ratio) of the solvent was set to ethylene carbonate:ethyl methyl carbonate=50:50, and the content of the electrolyte salt was set to 1 mol/l (=1 mol/dm ³ ) with respect to the solvent. . An electrolytic solution was thus prepared.

(Assembly of secondary battery)
First, the positive electrode lead 31 (aluminum foil) was welded to the positive electrode collector 21A of the positive electrode 21, and the negative electrode lead 32 (copper foil) was welded to the negative electrode collector 22A.

Subsequently, the positive electrode 21 and the negative electrode 22 are laminated with each other with a separator 23 (a microporous polyethylene film having a thickness of 15 μm) interposed therebetween, and then the positive electrode 21, the negative electrode 22 and the separator 23 are wound to obtain a winding. A circular body was produced. Subsequently, the wound body was molded into a flat shape by pressing the wound body using a pressing machine.

Subsequently, after folding the exterior film 10 (bonding layer/metal layer/surface protective layer) so as to sandwich the wound body housed inside the recess 10U, two sides of the bonding layer are folded. The wound body was housed inside the bag-shaped exterior film 10 by heat-sealing the peripheral edges to each other. The exterior film 10 includes a fusion layer (a polypropylene film with a thickness of 30 μm), a metal layer (aluminum foil with a thickness of 40 μm), and a surface protective layer (a nylon film with a thickness of 25 μm). Aluminum laminate films laminated in this order from the inside were used.

Finally, after the electrolytic solution was injected into the inside of the bag-shaped exterior film 10, the outer peripheral edges of the remaining one side of the fusion layer were heat-sealed to each other in a reduced pressure environment. In this case, a sealing film 41 (polypropylene film having a thickness of 5 μm) was inserted between the exterior film 10 and the positive electrode lead 31, and a sealing film 42 was inserted between the exterior film 10 and the negative electrode lead 32. (polypropylene film with thickness = 5 μm) was inserted.

As a result, the wound body was impregnated with the electrolytic solution, and the battery element 20 was produced. Accordingly, since the battery element was sealed inside the exterior film 10, the secondary battery was assembled.

(Stabilization of secondary battery)
The secondary battery was charged and discharged for one cycle in a normal temperature environment (temperature = 25°C). During charging, constant-current charging was performed at a current of 0.1C until the voltage reached 4.2V, and then constant-voltage charging was performed at the voltage of 4.2V until the current reached 0.05C. During discharge, constant current discharge was performed at a current of 0.1C until the voltage reached 3.0V. 0.1C is a current value that can fully discharge the battery capacity (a reference discharge capacity described later) in 10 hours, and 0.05C is a current value that fully discharges the battery capacity in 20 hours.

As a result, films were formed on the respective surfaces of the positive electrode 21 and the negative electrode 22, so that the state of the secondary battery was electrochemically stabilized. Thus, the secondary battery was completed.

[Calculation of abundance ratio]
Raman spectroscopic analysis (Raman mapping) was performed on each of the front surface F1 and the rear surface F2 of the positive electrode active material layer 21B by the procedure described above. Thereby, the abundance ratio R1 was calculated based on the existence region of the fibrous carbon material, and the abundance ratio R2 was calculated based on the existence region of the particulate carbon material. Table 1 shows the calculation results of the abundance ratios R1 and R2.

[Evaluation of battery characteristics]
When the cycle characteristics and load characteristics were evaluated according to the procedures described below, the results shown in Table 1 were obtained.

(Cycle characteristics)
First, the discharge capacity was measured by charging and discharging the secondary battery in a normal temperature environment (temperature = 25°C). During charging, constant current charging was performed at a current of 0.5 A until the voltage reached 4.50 V, and then constant voltage charging was performed at the voltage of 4.50 V until the current was reduced to 1/10. During discharge, constant current discharge was performed at a current of 0.2 A until the voltage reached 3.00V.

Subsequently, the secondary battery was charged and discharged in a high temperature environment (temperature = 45°C) to measure the discharge capacity at the second cycle. The charging/discharging conditions for the second cycle were the same as the charging/discharging conditions for the first cycle, except that the current during discharge was changed to 0.5C. 0.5C is a current value at which the battery capacity (reference discharge capacity obtained in the first cycle) can be discharged in 2 hours.

Subsequently, the secondary battery was repeatedly charged and discharged in the same environment until the number of cycles reached 300 cycles, thereby measuring the discharge capacity at the 300th cycle. The charging/discharging conditions were the same as the charging/discharging conditions for the second cycle.

Finally, the capacity retention rate, which is an index for evaluating cycle characteristics, was calculated based on the formula: cycle retention rate (%)=(discharge capacity at 300th cycle/discharge capacity at 2nd cycle)×100. .

(Load characteristics)
First, the discharge capacity in the first cycle was measured by charging and discharging the secondary battery in a room temperature environment (temperature = 25°C). During charging, constant current charging was performed at a current of 0.5 C until the voltage reached 4.50 V, and then constant voltage charging was performed at the voltage of 4.50 V until the current was reduced to 1/10. During discharge, constant current discharge was performed at a current of 0.2C until the voltage reached 3.00V. 0.2C is a current value that can discharge the battery capacity in 5 hours.

Subsequently, the secondary battery was charged and discharged in the same environment to measure the discharge capacity at the second cycle. The charge/discharge conditions for the second cycle were the same as the charge/discharge conditions for the first cycle, except that the current during discharge was changed to 1.0C. 1.0C is a current value that can discharge the battery capacity in 1 hour.

Finally, the load retention rate, which is an index for evaluating load characteristics, was calculated based on the formula: load retention rate (%) = (second cycle discharge capacity/first cycle discharge capacity) x 100. .

[Discussion]
As shown in Table 1, each of the cycle retention rate and the load retention rate fluctuated according to each of abundance ratios R1 and R2.

Specifically, when the appropriate conditions (R1 = 0.81 to 0.93, R2 = 0.54 to 0.88) are not satisfied for both abundance ratios R1 and R2 (Comparative Examples 1 to 3) decreased one or both of cycle retention rate and load retention rate.

On the other hand, when the appropriate conditions were met for both abundance ratios R1 and R2 (Examples 1 to 5), both the cycle retention rate and the load retention rate increased.

[summary]
From the results shown in Table 1, the conductive agent contained in the active material layer 120 of the electrode 100 contains a fibrous carbon material and a particulate carbon material, and the existence ratio R1 of the fibrous carbon material is 0.81. ∼0.93, and when the abundance ratio R2 for the particulate carbon material was 0.54 to 0.88, a high cycle retention rate and a high load retention rate were obtained. Therefore, excellent cycle characteristics and excellent load characteristics could be obtained in the secondary battery including electrode 100 .

Although the present technology has been described above with reference to one embodiment and example, the configuration of the present technology is not limited to the configuration described in the one embodiment and example, and can be variously modified.

Specifically, the case where the battery structure of the secondary battery is a laminated film type has been described. However, the battery structure of the secondary battery is not particularly limited, and may be cylindrical, rectangular, coin-shaped, button-shaped, or the like.

Also, the case where the element structure of the battery element is the wound type has been described. However, since the element structure of the battery element is not particularly limited, it may be a laminated type or a folded type. In this laminated type, the positive electrode and the negative electrode are stacked on each other, and in the ninety-nine fold type, the positive electrode and the negative electrode are folded in a zigzag pattern.

Furthermore, although the case where the electrode reactant is lithium has been described, the electrode reactant is not particularly limited. Specifically, the electrode reactants may be other alkali metals such as sodium and potassium, or alkaline earth metals such as beryllium, magnesium and calcium, as described above. Alternatively, the electrode reactant may be other light metals such as aluminum.

Since the effects described in this specification are merely examples, the effects of the present technology are not limited to the effects described in this specification. Accordingly, other advantages may be obtained with respect to the present technology.

DESCRIPTION OF SYMBOLS 21... Positive electrode, 21A... Positive electrode collector, 21B... Positive electrode active material layer, 22... Negative electrode, 22A... Negative electrode collector, 22B... Negative electrode active material layer, 100... Electrode, 110... Current collector, 120... Active material Layer, 121... active material, 122... conductive agent, T... thickness direction.

Claims (5)

Equipped with electrodes and electrolyte,
the electrode includes a current collector and an active material layer supported by the current collector;
The active material layer contains an active material and a conductive agent, and has a first surface far from the current collector and a second surface close to the current collector,
The conductive agent includes a fibrous carbon material and a particulate carbon material,
By performing Raman spectroscopic analysis on each of the first surface and the second surface, the existing region of the conductive agent is Raman mapped, and the existing region of the conductive agent is divided into the existing region of the fibrous carbon material and the particulate matter. When separated into the existing region of the carbon material,
A ratio of the abundance of the fibrous carbon material on the second surface to the abundance of the fibrous carbon material on the first surface is 0.81 or more and 0.93 or less,
The ratio of the abundance of the particulate carbon material on the second surface to the abundance of the particulate carbon material on the first surface is 0.54 or more and 0.88 or less.
secondary battery. The fibrous carbon material includes at least one of carbon nanotubes, carbon nanofibers and carbon nanohorns,
The particulate carbon material contains at least one of carbon black, acetylene black and ketjen black,
The secondary battery according to claim 1. the electrode is at least one of a positive electrode and a negative electrode;
The secondary battery according to claim 1 or 2. A lithium ion secondary battery,
The secondary battery according to any one of claims 1 to 3. comprising a current collector and an active material layer supported by the current collector;
The active material layer contains an active material and a conductive agent, and has a first surface far from the current collector and a second surface close to the current collector,
The conductive agent includes a fibrous carbon material and a particulate carbon material,
By performing Raman spectroscopic analysis on each of the first surface and the second surface, the existing region of the conductive agent is Raman mapped, and the existing region of the conductive agent is divided into the existing region of the fibrous carbon material and the particulate matter. When separated into the existing region of the carbon material,
A ratio of the abundance of the fibrous carbon material on the second surface to the abundance of the fibrous carbon material on the first surface is 0.81 or more and 0.93 or less,
The ratio of the abundance of the particulate carbon material on the second surface to the abundance of the particulate carbon material on the first surface is 0.54 or more and 0.88 or less.
electrode.

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