JP2008108464A - Secondary battery and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a secondary battery in which improvement is applied to the surface structure of a negative electrode current collector and which is capable of maintaining a desired output by suppressing self-discharging in an initial period after forming the secondary battery. <P>SOLUTION: In the secondary battery, a main body of the negative electrode current collector 40 is constituted of metal. An oxide layer 43 composed of the oxide of the metal is formed in a part 42 of the surface of the negative electrode current collector in which the negative electrode active material layer 45 is not formed. The oxide layer of the same characteristic state as that of the oxide layer is not formed at a negative electrode active material layer forming part of the negative electrode current collector. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a secondary battery and a method for manufacturing the same. More specifically, the present invention relates to a surface treatment technique for a metal negative electrode current collector used in a lithium ion battery or other secondary battery.

The demand for lithium-ion batteries and other secondary batteries that are lightweight and provide high output is expected to increase further in the future as a power source for mounting on vehicles, or a power source for personal computers and portable terminals.
The secondary battery is disposed as a basic component between a positive electrode current collector having a positive electrode active material layer on the surface, a negative electrode current collector having a negative electrode active material layer on the surface, and the positive and negative electrode current collectors. With electrolyte. In order to construct a secondary battery with higher reliability over a long period of time, it is important to improve these basic components, particularly the properties of the positive and negative electrode current collectors, in detail. For example, the following Patent Documents 1 to 4 describe various ingenuity regarding a positive electrode current collector and / or a negative electrode current collector provided in a secondary battery such as a lithium ion battery.

JP 2005-78963 A JP 2004-63344 A JP-A-4-269466 JP-A-4-237955

Meanwhile, suppressing self-discharge in a secondary battery such as a lithium ion battery is important from the viewpoint of improving battery reliability, for example, maintaining output over a long period of time. However, no example has been found in which the surface structure of the positive and negative electrode current collectors has been studied in detail from the viewpoint of suppressing self-discharge.
Therefore, the object of the present invention is to improve the surface structure of the negative electrode current collector equipped in the lithium ion battery and other secondary batteries, and to suppress the self-discharge in the initial stage after the secondary battery is constructed and to achieve a desired output. It is to provide a secondary battery that can be maintained, and to provide a method capable of suitably manufacturing such a secondary battery.

The present inventor has found out that in the initial stage after the secondary battery is constructed, when the metal constituting the negative electrode current collector body is eluted in the electrolyte, a secondary battery with relatively large self-discharge can be formed by the dissolution. In order to suppress self-discharge, the surface structure of the negative electrode current collector was examined, and the present invention was completed.
That is, the secondary battery provided by the present invention is disposed between a positive electrode current collector having a positive electrode active material layer on the surface, a negative electrode current collector having a negative electrode active material layer on the surface, and the positive and negative electrode current collectors. A secondary battery. Here, the negative electrode current collector main body is made of a predetermined metal, and an oxide made of an oxide of the constituent metal is formed in a portion of the surface portion of the negative electrode current collector where the negative electrode active material layer is not formed. A layer is formed. And the oxide layer of the same property as the said oxide layer is not formed in the negative electrode active material layer formation part of the said negative electrode collector, It is characterized by the above-mentioned.

In this specification, the “secondary battery” generally refers to a power storage device that can be repeatedly charged, such as a lithium ion battery, a metal lithium secondary battery, a nickel hydride battery, a so-called storage battery such as a nickel cadmium battery, and an electric double layer capacitor. Includes power storage elements.
The “same property” with respect to the “oxide layer” is a term indicating that the property and state of the oxide layer are equal. Therefore, the chemical formula (structural formula) of the oxide itself as understood by the relationship between the intentionally formed oxide layer and the oxide layer naturally generated in the atmosphere (that is, the production process is different) is the same. However, in the case where the density or thickness (that is, the depth from the surface of the current collector main body) is different from each other, both of them are typical examples that cannot be included in the “oxide layer having the same property”. It is.

In the secondary battery disclosed here, the current collector is configured in a portion of the surface portion of the negative electrode current collector where the negative electrode active material layer is not formed (that is, the surface portion of the current collector body made of metal). While an oxide layer of a metal (for example, copper) is formed, an oxide layer having the same properties as the oxide layer (typically having a relatively same density or higher density) in the negative electrode active material layer forming portion. The oxide layer is not formed.
And as a result of such an oxide layer being formed on the surface portion of the negative electrode active material layer unformed portion of the negative electrode current collector, immediately after the secondary battery such as a lithium ion battery is constructed, for example, the secondary battery First charging step (for example, pre-charging in the case of a lithium ion battery) after the step of placing the electrolyte between the positive and negative electrode current collectors when constructing the battery (the injection step when the electrolyte is liquid) is completed Until the (conditioning) step) is started, the metal constituting the negative electrode current collector body can be prevented from being eluted and self-discharge can be prevented. In addition, it is possible to prevent the metal ions eluted in the electrolyte from being deposited on the surface of the current collector (particularly the surface of the negative electrode active material layer) and forming a plating during charging. Such plating formation is not preferable because it causes self-discharge and, in addition, causes the plating to peel off during repeated charge / discharge cycles and deteriorates various battery characteristics. For example, in a secondary battery equipped with a typical separator, the above-mentioned plating strip released into the electrolyte (electrolytic solution) may cause clogging of the separator and may cause a decrease in output.

On the other hand, in the secondary battery disclosed herein, the negative electrode active material layer forming portion has the same property as that of the negative electrode active material layer non-formed portion (typically relatively the same density). Or a higher density oxide layer) is not formed. For this reason, it is possible to prevent an increase in electrical resistance between the negative electrode active material layer and the current collector body (surface) due to the interposition of the oxide layer, and it is possible to prevent a decrease in output.
As described above, according to the present invention, it is possible to reduce the self-discharge level by preventing the elution of the metal constituting the negative electrode current collector main body while maintaining the desired output, thereby providing a highly reliable secondary battery. can do.

It is preferable that the thickness (depth) of the oxide layer in a portion where the negative electrode active material layer is not formed is 1 nm or more and 10 nm or less.
When the thickness of the oxide layer in the portion where the negative electrode active material layer is not formed is within the above range, both output maintenance and self-discharge prevention capability can be achieved at a high level. When the thickness of the oxide layer is less than 1 nm, the metal elution preventing action is not sufficient, and conversely, when the thickness of the oxide layer is more than 10 nm, the negative electrode current collector (negative electrode active material layer) The electrical resistance between the non-formed part) and the connection terminal outside the battery becomes too large, resulting in a decrease in output, which is not preferable.

A preferred embodiment of the secondary battery disclosed herein is a lithium ion battery. In the secondary battery of this embodiment, the positive electrode current collector and the negative electrode current collector are configured as a positive electrode current collector and a negative electrode current collector for a lithium ion battery, respectively. Typically, the electrolyte is any non-aqueous electrolyte for lithium ion batteries.
ADVANTAGE OF THE INVENTION According to this invention, it can prevent that a negative electrode collector main body structure metal elutes in a non-aqueous electrolyte, and self-discharge occurs, and can provide a reliable lithium ion battery.

As another aspect of the present invention, a method for suitably manufacturing the secondary battery disclosed herein is provided.
That is, the secondary battery manufacturing method of the present invention is arranged between a positive electrode current collector having a positive electrode active material layer on the surface, a negative electrode current collector having a negative electrode active material layer on the surface, and the positive and negative electrode current collectors. A process for forming a negative electrode active material layer on a part of a surface of a negative electrode current collector made of a predetermined metal, and a negative electrode having a negative electrode active material layer formed thereon A step of forming an oxide layer made of the metal oxide having a predetermined thickness and density only on a portion of the current collector where the negative electrode active material layer is not formed, and a negative electrode on which the oxide layer is formed A step of constructing a predetermined secondary battery using the current collector together with the positive electrode current collector and the electrolyte.
In this way, first, a negative electrode active material layer is formed on a part of the surface of the negative electrode current collector, and then the oxide formation step is performed, thereby oxidizing the portion where the negative electrode active material layer is not formed to a predetermined thickness and density. While the physical layer is formed, the secondary battery of the present invention can be suitably manufactured, wherein an oxide layer having the same property is not formed in the negative electrode active material layer forming portion.

In a preferred embodiment, the negative electrode active material layer forming step includes a step of applying a negative electrode active material layer forming material to the negative electrode current collector and a step of drying the coated material. In the oxide layer forming step, the negative electrode current collector on which the negative electrode active material layer is formed is heated to a temperature higher than the temperature at which the coated material is dried in an oxidizable atmosphere such as air. Done.
According to such a method, an oxide layer having a predetermined thickness and density can be suitably formed only on a portion where the negative electrode active material layer is not formed without adversely affecting the formation of the negative electrode active material layer. It is preferable to form an oxide layer having a thickness (depth) of 1 nm to 10 nm in a portion where the negative electrode active material layer is not formed.

  Moreover, the preferable one aspect | mode of the secondary battery manufacturing method disclosed here is a lithium ion battery manufacturing method. That is, in a preferred embodiment of the lithium ion battery manufacturing method disclosed herein, the positive electrode current collector and the negative electrode current collector are configured as a positive electrode current collector and a negative electrode current collector for a lithium ion battery, respectively. A lithium ion secondary battery is constructed using any non-aqueous electrolyte suitable for a lithium ion battery as an electrolyte.

In the process of constructing a lithium ion secondary battery using a negative electrode current collector in which an oxide layer is formed together with a positive electrode current collector and a non-aqueous electrolyte solution, the present inventors have established a non-aqueous system between the positive and negative electrode current collectors. It has been found that the output of the battery can be improved by providing a predetermined holding time from the placement (injection) of the electrolytic solution to the start of the precharging process.
Therefore, the secondary battery manufacturing method of a particularly preferable aspect disclosed herein is a lithium ion battery manufacturing method, in which a nonaqueous electrolytic solution is disposed (injected) between the positive and negative electrode current collectors, and then precharged. A predetermined holding time is provided until the processing is started. The holding time is particularly preferably at least 24 hours.

On the other hand, if the holding time is too long, the current collector main body constituent metal (for example, copper) may start to elute from the negative electrode active material layer forming portion (that is, the portion where the oxide layer is not formed) of the negative electrode current collector. Is not preferable. It is preferable that the holding time from when the non-aqueous electrolyte solution is disposed (injected) between the positive and negative electrode current collectors to start the precharging process is within 3 days (72 hours), for example, within 70 hours. .
Therefore, in a particularly preferred embodiment of the secondary battery manufacturing method disclosed herein, a step of constructing a lithium ion battery using the negative electrode current collector formed with the oxide layer together with the positive electrode current collector and the non-aqueous electrolyte solution The pre-charging process is performed when the holding time set to 24 hours or more and 70 hours or less has elapsed since the non-aqueous electrolyte solution was disposed between the positive and negative electrode current collectors. According to the method having such a configuration, it is possible to manufacture a lithium ion battery that can achieve both high output maintenance and self-discharge prevention capability as described above.

Hereinafter, preferred embodiments of the present invention will be described. It should be noted that matters other than the matters specifically mentioned in the present specification (for example, the material of the negative electrode current collector to be used and the formation method of the oxide layer) and matters necessary for carrying out the present invention (for example, the positive electrode, The structure and manufacturing method of the negative electrode and the separator, the preparation of electrode materials (a mixture of pastes and the like for forming the active material layer, and the mounting method on the vehicle) are grasped as design matters of those skilled in the art based on the conventional technology in this field. Can be done. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.
As described above, the secondary battery provided by the present invention can suppress self-discharge and maintain a desired output. Due to such characteristics, the secondary battery (particularly preferably lithium ion battery) according to the present invention can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile. Therefore, as schematically shown in FIG. 11, the present invention provides a vehicle having a secondary battery 10 (typically, an assembled battery formed by connecting a plurality of secondary batteries 10 in series) as a power source ( An automobile, in particular an automobile equipped with an electric motor such as a hybrid vehicle, an electric vehicle, and a fuel cell vehicle) 1 is provided.

As described above, the present invention is characterized by forming an oxide layer having a property capable of suppressing self-discharge on a predetermined portion of the surface portion of the metal negative electrode current collector. Can be widely applied to secondary batteries having a structure capable of forming For example, a lithium ion battery, a metal lithium secondary battery, and a nickel metal hydride secondary battery can be given. Application to a lithium ion battery is particularly suitable. Since the lithium ion battery is a secondary battery that can achieve a high output with a high energy density, it can be suitably used as, for example, a vehicle-mounted battery (battery module).
A positive electrode current collector having a positive electrode active material layer on the surface; a negative electrode current collector having a negative electrode active material layer on the surface; an electrolyte disposed between the positive and negative electrode current collectors; A secondary battery provided with a separator separating the current collector (which may be unnecessary when the electrolyte is fixed) may be used, and the structure of the outer container (for example, a metal housing or a laminate film structure) There are no particular restrictions on the size, size, or structure of the electrode body (eg, a wound structure or a laminated structure) having a positive and negative current collector as a main component.

For example, as one embodiment of the secondary battery provided by the present invention, there is a secondary battery 10 as schematically shown in FIGS.
As shown in the figure, the secondary battery 10 according to the present embodiment includes a metal (resin or laminate film) casing (outer container) 12. Inside, a wound electrode body 20 configured by laminating a long sheet-like positive electrode current collector 30, a separator 50A, a negative electrode current collector 40, and a separator 50B in this order and then winding in a flat shape is accommodated. Is done.
The positive electrode current collector 30 may preferably be made of a sheet material (typically a metal foil such as an aluminum foil) made of a metal such as aluminum, nickel, or titanium. On the other hand, as the negative electrode current collector 40, a sheet material (typically a metal foil such as a copper foil) made of a metal such as copper can be used.
Moreover, as separator 50A, 50B used by overlapping with a positive / negative electrode collector, the porous film which consists of polyolefin resin, such as polyethylene and a polypropylene, can be used conveniently, for example.

The above configuration is a configuration that can be used in various secondary batteries. The composition of the active material layer of the positive and negative electrodes (in other words, the positive and negative electrode mixture used for forming the active material layer) and the composition of the electrolyte are as follows. By changing according to the kind of secondary battery, the secondary battery of the desired content can be constructed | assembled. Hereinafter, materials, methods, and the like suitable for constructing a lithium ion battery preferable for application of the present invention will be described.
As the positive electrode active material, an oxide-based positive electrode active material having a layered structure used for a general lithium ion battery, an oxide-based positive electrode active material having a spinel structure, or the like can be preferably used. For example, the main component is lithium cobalt complex oxide (typically LiCoO ₂ ), lithium nickel complex oxide (typically LiNiO ₂ ), lithium manganese complex oxide (LiMn ₂ O ₄ ), or the like. A positive electrode active material can be used.

  An active material layer forming paste (positive electrode mixture) prepared by mixing such a positive electrode active material with a conductive material and a binder (binder) as described later is applied to the surfaces of both sides of the positive electrode current collector 30. The positive electrode active material layer 35 is formed at desired sites on the surfaces of both sides of the current collector 30 by applying and then drying the applied material at an appropriate temperature (typically 70 to 150 ° C.). (Fig. 2). Although it does not specifically limit, the usage-amount of the electrically conductive material with respect to 100 mass parts of positive electrode active materials can be made into the range of 1-20 mass parts (preferably 5-15 mass parts), for example. Moreover, the usage-amount of the binder with respect to 100 mass parts of positive electrode active materials can be made into the range of 0.5-10 mass parts, for example.

  On the other hand, as a negative electrode active material for a lithium ion battery, a carbon material containing a graphite structure (layered structure) at least partially can be suitably used. Any carbon material of a so-called graphitic material (graphite), non-graphitizable carbon material (hard carbon), easily graphitized carbon material (soft carbon), or a combination of these can be used. . For example, natural graphite, mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), etc. can be used. As in the case of the positive electrode, an active material layer forming paste (negative electrode) prepared by mixing such a negative electrode active material with a binder and, if necessary, a conductive material (same as the positive electrode side can be used). The mixture is applied to the surfaces of both sides of the negative electrode current collector 40, and then the coated material is dried at an appropriate temperature (typically 70 to 150 ° C.). The negative electrode active material layer 45 can be formed at a desired site on the surface (FIGS. 2 and 4). Although it does not specifically limit, the usage-amount of the binder with respect to 100 mass parts of negative electrode active materials can be made into the range of 0.5-10 mass parts, for example. In addition, since the technique itself which forms the active material layers 35 and 45 in the collectors 30 and 40 of each positive and negative electrode is well-known in the said field | area, further detailed description is abbreviate | omitted.

  In addition, as a binder used with the above active materials in order to form the positive electrode active material layer 35 and the negative electrode active material layer 45, if it is conventionally used for construction of this kind of secondary battery Well, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), styrene butadiene block copolymer (SBR), carboxymethyl cellulose (CMC), etc. Can be suitably used. As the conductive material, various carbon blacks (acetylene black, furnace black, ketjen black, etc.), carbon powder such as graphite powder, metal powder such as nickel powder, and the like can be used. These are merely examples and do not limit the practice of the invention.

As shown in FIG. 2, the paste (compound) is not applied to one end portion along the longitudinal direction of the positive electrode current collector 30 and the negative electrode current collector 40, and thus the active material layers 35 and 45 are not formed. Portions, that is, portions 32 and 42 where no active material layer is formed are formed.
Thus, when the positive and negative electrode current collectors 30 and 40 are overlapped with the two separators 50A and 50B, both the active material layers 35 and 45 are overlapped, and at the same time, the positive electrode active material layer non-formed portion 32 and the negative electrode active material The positive and negative electrode current collectors 30 and 40 are slightly shifted and overlapped so that the material layer-unformed portion 42 is separately disposed at one end and the other end along the longitudinal direction (FIG. 2). In this state, a total of four sheets 30, 40, 50 </ b> A, 50 </ b> B are wound, and then the obtained wound body is crushed from the side direction to be ablated, thereby obtaining the flat wound electrode body 20.

Next, the wound electrode body 20 obtained is accommodated in the housing 12, and the positive electrode active material layer non-formed part 32 and the negative electrode active material layer non-formed part 42 are partially arranged outside the housing 12. The external connection positive terminal 14 and the external connection negative terminal 16 are electrically connected.
Then, a suitable liquid electrolyte or solid (or gel) electrolyte, here a suitable non-aqueous electrolyte (for example, a non-aqueous electrolyte such as a mixed solvent of diethyl carbonate and ethylene carbonate containing a suitable amount of lithium salt such as LiPF ₆₎ Liquid) is disposed (injected) in the casing 12, and the opening of the casing 12 is sealed by welding or the like between the casing and the corresponding lid member 13, and the lithium ion secondary according to the present embodiment Construction (assembly) of the battery 10 is completed. In addition, the sealing process of the housing | casing 12 and an electrolyte arrangement | positioning (liquid injection) process may be the same as the method currently performed by manufacture of the conventional lithium ion battery, and do not characterize this invention.

In the secondary battery manufacturing method of the present invention, before the secondary battery construction step as described above (here, the electrode body assembly step including the winding step and the step of housing the obtained electrode body together with the electrolyte in the housing) An oxide layer 43 as shown in FIG. 4 is formed on the surface portion (surface layer portion) of the active material layer-unformed portion 42 of the negative electrode current collector 40.
Typically, after applying and drying the paste (composite material), in an oxidizable atmosphere (typically, preferably in the air or a gas having a higher oxygen concentration) than the temperature at the time of drying. Heat to a high temperature (for example, a temperature higher by 50 ° C. or more than the temperature during drying) As a result, a relatively high density oxide layer is formed only on the surface portion of the active material layer unformed portion while promoting oxidation, and it is naturally generated on a metal surface that is typically left in the atmosphere at room temperature. An oxide layer having a higher density than the oxide can be preferably formed. Preferably, an oxide layer (metal oxide coating layer) having a thickness (depth) of 1 nm to 10 nm is formed.

For example, when the constituent metal of the negative electrode current collector is copper, a layer made of copper oxide can be formed quickly. Although it does not specifically limit, For example, it is substantially homogeneous metal oxide over the whole by heating at about 160 to 290 degreeC (preferably about 180 to 220 degreeC) for 5 to 60 second in air | atmosphere. The layer can be formed on the surface portion of the negative electrode current collector where the active material layer is not formed. For example, in the above-described embodiment, the paste (compound) is applied to a part of the surface of the negative electrode current collector body and dried, and then heat treatment for forming the oxide layer is performed, and then the above-described winding is performed. It is good to carry out a process.
Thus, the negative electrode due to the high temperature during the formation of the oxide layer is provided by differentiating the drying step and the oxide layer forming step when forming the negative electrode active material layer and providing the oxide layer forming step after the drying step is completed. It is possible to avoid an adverse effect on the formation of the active material layer (for example, a decrease in capacity retention rate due to uneven distribution (precipitation) of binder contained in the mixture) on the surface.

Alternatively, the oxide layer forming step can be easily performed by oxygen ion implantation instead of the heat treatment. For example, the surface of the portion where the active material layer of the negative electrode current collector is not formed is irradiated with an oxygen ion beam having an energy of about 1 to 10 MeV for 1 to several hours to achieve a desired thickness (for example, 1 nm to 10 nm). A high-density oxide layer can be formed. For example, a desired oxide layer can be formed at a predetermined position and depth by using a commercially available ion implantation apparatus capable of implanting oxygen ions into a material such as a Si wafer under appropriate operation conditions.
For example, by performing oxygen ion beam irradiation for about 2 hours at room temperature under an oxygen ion beam energy of 8 MeV, the thickness of the surface of the negative electrode active material layer unformed portion of the negative electrode current collector (for example, made of copper foil) is increased. An oxide layer (for example, a copper oxide film) of about 1 nm to 10 nm can be easily formed.

A negative electrode in which an oxide layer 43 having a desired thickness and density is formed only in a portion 42 where the negative electrode active material layer 45 is not formed as shown in FIG. A current collector 40 is obtained. According to the secondary battery constructed by adopting the negative electrode current collector 40, it is effective that the metal constituting the negative electrode current collector 40 is eluted into the electrolyte (typically, a non-aqueous electrolyte). Can be prevented.
In particular, after the battery is constructed (that is, after the electrolyte and the electrode body are arranged at a predetermined position of the outer container), the initial charge of the negative electrode current collector constituting metal is initially performed until the first charge (for example, a precharge process in a lithium ion battery) is performed. Elution can be prevented and excessive self-discharge can be suppressed. On the other hand, in the secondary battery disclosed herein, as shown in FIG. 4, the same property as that formed in the portion 42 where the negative electrode active material layer 45 is not formed in the portion where the negative electrode active material layer 45 is formed. The oxide layer 43 (typically a relatively higher or the same level of density oxide layer) is not formed. For this reason, it is possible to prevent an increase in electrical resistance between the negative electrode active material layer 45 and the current collector body (surface) due to the interposition of the oxide layer 43, and to prevent a decrease in output. Accordingly, it is possible to reduce the self-discharge level by preventing elution of the metal constituting the main body of the negative electrode current collector while maintaining the desired output, and as a result, provide a highly reliable secondary battery (particularly a lithium ion battery). can do.

The lithium ion battery constructed by the method disclosed herein preferably has a holding time (left to stand) of at least about 24 hours from the completion of the nonaqueous electrolyte injection to the start of the precharging step (conditioning step). Time). As a result, the output of the battery can be improved.
Although it is not necessary to clarify the reason for improving the output in carrying out the present invention, as one factor, a minute amount of water (typically, the negative electrode active material layer) contained in the negative electrode current collector after several hours from immediately after the liquid injection process In the non-aqueous electrolyte solution. Thus, it is conceivable that the leached water reacts with the lithium salt contained in the nonaqueous electrolytic solution, and the reaction product contributes to the improvement in output.
On the other hand, when the holding time is too long (for example, 3 days or more), the electrolyte solution penetrates into the entire negative electrode active material layer before the preliminary charging step (conditioning step) is performed. As a result, the negative electrode current collector is obtained. This is not preferable because the constituent metals may be eluted from the surface of the active material layer forming portion (that is, self-discharge is induced).
Although not particularly limited, in order to prevent the electrolyte solution from penetrating into the entire anode active material layer, the holding time is suitably 70 hours or less. Accordingly, the holding time is preferably 24 hours or longer and 70 hours or shorter.

  Hereinafter, experimental examples relating to the present invention will be described. However, the present invention is not intended to be limited to the specific examples.

The negative electrode active material layer is prepared by mixing these materials and water so that the mass ratio of natural graphite, styrene butadiene rubber and carboxymethyl cellulose is 98.5: 0.5: 1 and the solid content concentration is 45 mass%. A forming paste (compound) was prepared.
Then, a copper foil having a length of 2 m, a width of 12 cm and a thickness of 15 μm is used as the negative electrode current collector body, the negative electrode active material layer forming paste is applied to a predetermined region of the surface, and dried under any of the conditions described later. Processed. Thereby, a negative electrode current collector in which a negative electrode active material layer was formed on both surfaces of the copper foil was produced.

  The negative electrode current collector on which the negative electrode active material layer was formed by the above treatment was subjected to oxide layer formation treatment under any of the conditions described below.

  Thus, a total of 7 negative electrode current collectors (samples A to G) shown in Table 1 were produced. Specifically, the drying process was performed for 10 seconds under a temperature condition of 120 ° C. (samples A, B, D, E, F, G) or 180 ° C. (sample C). The oxide layer forming step was performed at a temperature of 180 ° C. for 3 seconds (sample D), 8 seconds (sample E), 12 seconds (sample B), 20 seconds (sample F), or 30 seconds (sample G). . Note that Sample A and Sample C are not subjected to an oxide layer forming step independent of the drying step.

On the other hand, these materials and water are mixed so that the mass ratio of lithium cobaltate, graphite, polytetrafluoroethylene, and carboxymethylcellulose is 93: 5: 1: 1 and the solid content concentration is 45% by mass. A positive electrode active material layer forming paste (mixture) was prepared.
Then, an aluminum foil having a length of 1.9 m, a width of 12 cm, and a thickness of 10 μm is used as the positive electrode current collector body, and the positive electrode active material layer forming paste is applied to a predetermined region of the surface by the same method as in the case of the negative electrode. It was applied and dried. This produced the positive electrode electrical power collector in which the positive electrode active material layer was formed on both surfaces of the aluminum foil.

The above-obtained positive electrode current collector and any of the negative electrode current collectors were wound together with a polypropylene separator sheet (2 sheets) having a length of 2.1 m, a width of 12 cm, and a thickness of 30 μm, and then crushed between the flat surfaces A total of 7 types of wound electrode bodies having a thickness of 30 mm were prepared corresponding to each of the above 7 types of negative electrode current collectors.
The external connection terminals of the positive and negative electrodes were welded to the manufactured wound electrode body and accommodated in a box-shaped container having a shape corresponding to the wound electrode body. The container contains 50 mL of electrolyte (specifically, a nonaqueous electrolyte in which LiPF ₆ having a concentration of 1 M as a lithium salt is dissolved in a mixed solvent of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate having a mass ratio of 1: 1: 1. ) Was injected and sealed. As a result, a total of seven types of lithium ion batteries corresponding to each of the seven types of negative electrode current collectors (see Table 1) were prepared. Hereinafter, the batteries themselves are also referred to as Samples A to G in correspondence with the negative electrode current collectors used.
In the following test examples, the effects of the present invention were evaluated by using the lithium ion battery produced as described above.

<Test Example 1: Self-discharge measurement (1)>
The degree of self-discharge of each lithium ion battery was measured. That is, an appropriate conditioning process (for example, a constant current charge for 3 hours at a charge rate of 1/10 C, then a charge at a constant current constant voltage up to 4.1 V at a charge rate of 1/3 C; After the initial charge and discharge process of repeating the constant current discharge operation to 3.0V at a discharge rate 2 to 3 times), the battery is charged at a constant current and a constant voltage after a constant current discharge to 3.0V under a temperature condition of 60 ° C. And adjusted to SOC 80%. After the initial voltage was measured at this stage, the battery was stored in a constant temperature bath at 60 ° C.
The voltage after 7 days from the start of storage was measured. And the value which pulled the initial voltage from the voltage after a preservation | save, ie, the self-discharge voltage difference (mV), was measured as a parameter | index of the voltage fall by self-discharge. The results are shown in FIG. 5 (samples A, B, C) and FIG. 6 (samples B, D, E, F, G).
As is clear from the values shown in these graphs, in the sample in which a dense oxide layer is formed with an appropriate thickness by the oxide layer forming process, Sample A and Sample in which such an oxide layer is not formed Compared with D, self-discharge was remarkably suppressed. Table 2 shows the relationship between the thickness (nm) of the oxide layer and the self-discharge voltage difference (mV), which was clarified from the test examples.

<Test Example 2: Low temperature output characteristics (1)>
Next, the output characteristics of each lithium ion battery under low temperature conditions were examined. That is, after an appropriate conditioning treatment, after a constant current discharge up to 3.0 V under a temperature condition of 25 ° C., the battery was charged with a constant current and a constant voltage to be adjusted to SOC 40%. Thereafter, the current was appropriately changed at −30 ° C., the voltage 10 seconds after the start of discharge was measured, and an IV characteristic graph of the sample battery was created. The discharge cut voltage was 2.0V. The maximum output value (W) was obtained from the IV characteristic graph. The results are shown in FIG. 7 (samples A, B, C) and FIG. 8 (samples B, D, E, F, G).
As is apparent from the values shown in these graphs, when the oxide layer is formed only on the portion where the negative electrode active material layer is not formed and the thickness of the oxide layer is 10 nm or less (samples B, D, E) , F), good low-temperature output characteristics were maintained. On the other hand, in the sample G in which the thickness of the oxide layer exceeds 10 nm and the sample C in which the oxide layer is also formed in the portion where the negative electrode active material layer is not formed, the low-temperature output characteristics are deteriorated. Table 3 shows the relationship between the thickness (nm) of the oxide layer and the low-temperature output (W), which was clarified from the test examples.

<Test Example 3: Self-discharge measurement (2)>
Next, a plurality of batteries (oxide layer thickness: 5 nm) of sample B were manufactured, and self-discharge was performed when the holding time until the preliminary charging (conditioning) was performed after the electrolyte injection process was changed. The effect was investigated.
That is, a plurality of batteries (n = 4) of sample B are used, and the holding time (hr) until the preliminary charging (conditioning) is performed after the step of injecting the electrolytic solution is 5, 10, 24, 40, The self-discharge voltage difference (mV) in each case was examined by the same method as in Test Example 1 and set in seven ways of 55, 70, and 85 hours. The results are shown in FIG.
As is clear from the results shown in the graph, the same self-discharge voltage difference (9 to 10 mV) was maintained from 5 hours to 70 hours. However, when the holding time was 85 hours, a high self-discharge voltage difference (about 18 mV) was shown. This is because when the holding time is 3 days or more, the electrolyte solution sufficiently penetrates into the negative electrode active material layer. As a result, the negative electrode current collector structure is formed from the portion where the oxide layer is not formed. This indicates that copper (copper ion), which is a metal, is eluted.

<Test Example 4: Low temperature output characteristics (2)>
Next, a plurality of batteries of sample B were manufactured, and the influence on the low-temperature output characteristics when the holding time until the preliminary charging (conditioning) was performed after the injection process of the electrolytic solution was examined.
That is, in the same manner as in Test Example 3, a plurality of Sample B batteries were used, and the holding time was set in seven ways: 5, 10, 24, 40, 55, 70, and 85 hours. The characteristic (W) was examined by the same method as in Test Example 2. The results are shown in FIG.
As is clear from the results shown in the graph, it was confirmed that the output value can be drastically improved by providing the holding time of 24 hours or more. It was confirmed that the holding time was particularly good for about 40 to 70 hours (about 2 to 3 days).

  As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations, What included various deformation | transformation and change of the above-mentioned specific example is included in the invention disclosed here. For example, the means for forming an oxide layer with a desired thickness and a higher density than a naturally occurring oxide in the active material layer-unformed portion of the negative electrode current collector is not limited to the above-described method, and an oxide layer is formed. Any possible means may be employed.

It is a perspective view which shows typically the external shape of the lithium ion battery which concerns on one Embodiment. It is a partially broken top view which shows the positive / negative electrode electrical power collector and separator which comprise the winding electrode body which concerns on one Embodiment. It is the III-III sectional view taken on the line in FIG. It is sectional drawing of the partial fracture | rupture which shows typically the formation part of the oxide layer of the negative electrode collector which concerns on one Embodiment. It is a graph which shows the self-discharge characteristic of some lithium ion batteries produced as an Example, a horizontal axis is a sample name and a vertical axis | shaft is a self-discharge voltage difference (mV). It is a graph which shows the self-discharge characteristic of some lithium ion batteries produced as an Example, a horizontal axis is the thickness (nm) of an oxide layer, a vertical axis is a self-discharge voltage difference (mV), and the symbol in a graph is This is the name of the plotted sample. It is a graph which shows the low-temperature output characteristic of some lithium ion batteries produced as an Example, a horizontal axis is a sample name and a vertical axis | shaft is an output value (W). It is a graph which shows the low temperature output characteristic of some lithium ion batteries produced as an Example, the horizontal axis is the thickness (nm) of the oxide layer, the vertical axis is the output value (W), and the symbols in the graph are plotted. Sample name. It is a graph which shows the influence which the holding time after performing the injection process of the sample B (lithium ion battery) produced as an example until it precharges on a self-discharge characteristic, a horizontal axis is holding time (hr), a vertical axis | shaft Is a self-discharge voltage difference (mV). It is a graph which shows the influence which the holding time after performing the injection process of sample B (lithium ion battery) produced as an example until it performs preliminary charge on low temperature output characteristics, a horizontal axis is holding time (hr), and a vertical axis Is an output value (W). It is a side view which shows typically the vehicle (automobile) provided with the secondary battery of this invention.

Explanation of symbols

1 Vehicle (Automobile)
10 Secondary battery (lithium ion battery)
DESCRIPTION OF SYMBOLS 12 Case 20 Winding electrode body 30 Positive electrode collector 35 Positive electrode active material layer 40 Negative electrode collector 42 Negative electrode active material layer non-formation part 43 Oxide layer 45 Negative electrode active material layer 50A, 50B Separator

Claims (7)

A secondary battery comprising a positive electrode current collector having a positive electrode active material layer on a surface, a negative electrode current collector having a negative electrode active material layer on a surface, and an electrolyte disposed between the positive and negative electrode current collectors,
The negative electrode current collector body is made of a predetermined metal,
An oxide layer made of the metal oxide is formed on a portion of the surface of the negative electrode current collector where the negative electrode active material layer is not formed, and the oxide layer has the same properties as the oxide layer. The physical layer is a secondary battery in which a negative electrode active material layer forming portion of the negative electrode current collector is not formed.   The secondary battery according to claim 1, wherein a thickness of the oxide layer in a portion where the negative electrode active material layer is not formed is 1 nm or more and 10 nm or less. Method for manufacturing a secondary battery comprising a positive electrode current collector having a positive electrode active material layer on a surface, a negative electrode current collector having a negative electrode active material layer on a surface, and an electrolyte disposed between the positive and negative electrode current collectors Because
Forming a negative electrode active material layer on a part of the surface of the negative electrode current collector made of a predetermined metal;
Forming an oxide layer made of the metal oxide having a predetermined thickness and density only on a portion of the negative electrode current collector on which the negative electrode active material layer is formed, where the negative electrode active material layer is not formed, and ,
A step of constructing a predetermined secondary battery using the negative electrode current collector formed with the oxide layer together with the positive electrode current collector and an electrolyte;
Including a secondary battery. The negative electrode active material layer forming step includes a step of applying a negative electrode active material layer forming material to the negative electrode current collector and a step of drying the applied material.
The oxide layer forming step is performed by heating the negative electrode current collector on which the negative electrode active material layer is formed to a temperature higher than a temperature at which the coated material is dried in an oxidizable atmosphere. Item 4. The manufacturing method according to Item 3.   The manufacturing method according to claim 3 or 4, wherein the oxide layer having a thickness of 1 nm to 10 nm is formed in a portion where the negative electrode active material layer is not formed. The positive electrode current collector and the negative electrode current collector are configured as a positive electrode current collector and a negative electrode current collector for a lithium ion battery, respectively, and any non-aqueous electrolyte solution for a lithium ion battery is used as the electrolyte. To build a lithium-ion battery
Here, in the step of constructing a lithium ion battery using the negative electrode current collector on which the oxide layer is formed together with the positive electrode current collector and the non-aqueous electrolyte solution, a non-aqueous electrolyte solution is provided between the positive and negative electrode current collectors. The manufacturing method according to claim 5, wherein the precharging process is performed when a holding time set to 24 hours or more and 70 hours or less has elapsed since the placement.   A vehicle comprising the secondary battery according to claim 1.