JP2007035552A - Electrode for lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for a lithium secondary battery which has an electrode layer having chemical resistance and high wettability with an electrolyte as well. <P>SOLUTION: The electrode for a lithium secondary battery is composed of a collector and an electrode layer which is formed on the above collector and contains fluorine resin as an active material and binding agent, and the surface of the above electrode layer has a hydroxyl group. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrode for a lithium secondary battery having an electrode layer that has both chemical resistance and good wettability with respect to an electrolytic solution.

  With the miniaturization of personal computers, video cameras, mobile phones, etc., in the fields of information-related equipment and communication equipment, lithium secondary batteries have been put into practical use because of their high energy density as the power source used for these equipment. It has become widespread. On the other hand, in the field of automobiles, the development of electric vehicles has been urgently caused by environmental problems and resource problems, and lithium secondary batteries have been studied as power sources for the electric vehicles.

  Such a lithium secondary battery generally includes an electrode body in which a positive electrode and a negative electrode are stacked via a separator, an electrolytic solution in which an electrolyte is dissolved in an organic solvent, and a battery that houses the electrode body and the electrolytic solution. And a case. An electrode used for a positive electrode or a negative electrode includes a current collector and an electrode layer having an active material and a binder.

  The binder is used to hold the active material on the current collector, and a fluorine-based resin is generally used from the viewpoint of excellent chemical resistance and long life of the lithium secondary battery. It is used for. However, since the fluororesin has low surface energy, the wettability with respect to the electrolytic solution is poor, and as a result, the internal resistance of the electrode body increases and the charge / discharge characteristics at high current density are poor.

  In order to solve such a problem, a binder using a hydrophilic polymer having good wettability to an electrolytic solution has been proposed. For example, in Patent Document 1, an electrode for a lithium secondary battery using a binder containing a hydrophilic binder made of a cellulose derivative and a lyophilic binder containing a polyether structure in the chemical structure is disclosed. It is disclosed. However, since such a hydrophilic binder has low chemical resistance as compared with a fluorine-based resin, it has been deteriorated by an electrolytic solution, and it has been difficult to extend the life of a lithium secondary battery.

JP 2003-249225 A Japanese Patent Laid-Open No. 1-116091 Japanese Patent Laid-Open No. 3-71556 JP-A-11-317217 JP-A-8-31404

  The present invention has been made in view of the above problems, and it is a main object of the present invention to provide an electrode for a lithium secondary battery having an electrode layer having both chemical resistance and good wettability with respect to an electrolytic solution. It is what.

  In order to achieve the above object, in the present invention, a lithium secondary battery comprising a current collector and an electrode layer formed on the current collector and containing a fluororesin as an active material and a binder Provided is an electrode for a lithium secondary battery, wherein the electrode layer has a hydroxyl group on the surface of the electrode layer.

  According to the present invention, since the surface of the electrode layer has a hydroxyl group, the electrode for a lithium secondary battery having good wettability with respect to the electrolytic solution can be obtained. Furthermore, the electrode for a lithium secondary battery of the present invention can be excellent in chemical resistance because the electrode layer contains a fluorine-based resin as a binder.

  Moreover, in the said invention, it is preferable that 5 mol% or more of hydroxyl groups exist in the surface of the said electrode layer. This is because when the hydroxyl group is present above the above value, improvement in wettability with respect to the electrolytic solution is recognized.

  Moreover, in this invention, the lithium secondary battery characterized by using the said electrode for lithium secondary batteries is provided.

  According to the present invention, by using the lithium secondary battery electrode for at least one of the positive electrode and the negative electrode, a lithium secondary battery excellent in durability and charge / discharge characteristics at high current density can be obtained. it can.

  In the present invention, an electrode forming material comprising a current collector and an electrode layer formed on the current collector and containing a fluorine-based resin as an active material and a binder is used for the electrode layer. On the other hand, the present invention provides a method for producing an electrode for a lithium secondary battery, characterized by performing a hydrophilic treatment.

  According to the present invention, the electrode layer containing a fluorine-based resin is subjected to a hydrophilic treatment, and by introducing a hydroxyl group on the surface of the electrode layer, chemical resistance and good wettability with respect to an electrolyte solution, Thus, an electrode for a secondary battery having an electrode layer having both of the above can be obtained.

  In the above invention, the hydrophilic treatment is preferably oxygen plasma treatment. This is because a hydroxyl group can be easily introduced into the surface of the electrode layer by using oxygen plasma treatment.

  In this invention, there exists an effect that the electrode for lithium secondary batteries which has an electrode layer which has chemical-resistance and favorable wettability with respect to electrolyte solution can be provided.

  Hereinafter, the manufacturing method of the electrode for lithium secondary batteries of this invention, a lithium secondary battery, and the electrode for lithium secondary batteries is demonstrated in detail.

A. First, an electrode for a lithium secondary battery of the present invention will be described. An electrode for a lithium secondary battery according to the present invention is an electrode for a lithium secondary battery comprising a current collector and an electrode layer formed on the current collector and containing a fluororesin as an active material and a binder. And the surface of the said electrode layer has a hydroxyl group, It is characterized by the above-mentioned.

  According to the present invention, since the surface of the electrode layer has a hydroxyl group, the electrode for a lithium secondary battery having good wettability with respect to the electrolytic solution can be obtained. Furthermore, the electrode for a lithium secondary battery of the present invention can be excellent in chemical resistance because the electrode layer contains a fluorine-based resin as a binder. That is, an electrode for a lithium secondary battery having both chemical resistance and good wettability with respect to the electrolytic solution can be obtained. Since the wettability to the electrolytic solution is good, the internal resistance of the electrode body can be reduced by using the electrode for the lithium secondary battery of the present invention, and the charge / discharge characteristics at high current density can be improved. it can.

  Moreover, the electrode for lithium secondary batteries of this invention can be used for both a positive electrode and a negative electrode. Here, the positive electrode is defined as including a positive electrode and a positive electrode, and the negative electrode is defined as including a negative electrode and a negative electrode. Therefore, the lithium secondary battery electrode of the present invention can be used as a positive electrode or a negative electrode by appropriately selecting the type of active material or current collector. Further, as described in “B. Lithium secondary battery” described later, a lithium secondary battery using a positive electrode or a negative electrode is preferable, and in particular, lithium using both a positive electrode and a negative electrode. A secondary battery is more preferable.

Next, the electrode for a lithium secondary battery of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing an example of an electrode for a lithium secondary battery of the present invention. The electrode 3 for a lithium secondary battery of the present invention includes a current collector 1, an electrode layer 2 formed on the current collector 1 and containing a fluorine-based resin as an active material and a binder, and the surface of the electrode layer 2 And a hydroxyl group present in
Hereinafter, each structure of the electrode for lithium secondary batteries of this invention is demonstrated.

1. Electrode Layer First, the electrode layer used in the present invention will be described. The electrode layer used in the present invention contains a fluororesin as at least an active material and a binder. Furthermore, the electrode layer used in the present invention has a hydroxyl group on the surface.

(1) Binder First, the binder used in the present invention will be described. The binder used in the present invention is used for holding the active material on the current collector. In the present invention, a fluororesin is used from the viewpoint of excellent chemical resistance. Such a fluororesin is not particularly limited as long as it has excellent chemical resistance, and specific examples include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and the like. Of these, polytetrafluoroethylene (PTFE) is preferred.

  Further, the content of the binder in the electrode layer is not particularly limited as long as an electrode layer having desired charge / discharge characteristics and the like can be formed, but the electrode for the lithium secondary battery of the present invention is not limited. When used as a positive electrode, it is preferably in the range of 2 to 10% by mass, and more preferably in the range of 3 to 6% by mass. The same applies when the lithium secondary battery electrode of the present invention is used as a negative electrode. If the above range is exceeded, there is a possibility that the migration of lithium ions may be inhibited, and if it is less than the above range, the active material may not be retained.

(2) Active material Next, the active material used for this invention is demonstrated. The active material used in the present invention has a function of releasing and occluding lithium ions. In this invention, the said active material can be divided roughly into the positive electrode active material used for the electrode for positive electrodes, and the negative electrode active material used for the electrode for negative electrodes.

The positive electrode active material is not particularly limited as long as it can release lithium ions during charging and occlude during discharge, and a known positive electrode active material can be used. Examples of such positive electrode active materials include Li _(1-x) MnO ₂ , Li _(1-x) Mn ₂ O ₄ , Li _(1-x) CoO ₂ , and Li _(1-x) NiO ₂ . A compound can be mentioned. Here, x represents 0-1. Among them, in the present invention, LiMn ₂ O ₄ , LiCoO ₂ , and LiNiO ₂ are preferable from the viewpoint of excellent diffusion performance of electrons and lithium ions, and in particular, LiMn ₂ O ₄ is more preferable from the viewpoint of low material cost. preferable. In the present invention, a mixture of the above compounds may be used as the positive electrode active material. Further, at least one or more kinds of transition metal elements such as LiMn ₂ O ₄ and LiNiO ₂ such as Li _(1-x) Mn _{(2 + x)} O ₄ and LiNi _(1-x) Co _x O ₂ may be used. A transition metal element or a material replaced with Li may be used as the positive electrode active material.

  In addition, the content of the positive electrode active material in the electrode layer is not particularly limited as long as an electrode layer having desired charge / discharge characteristics and the like can be formed. For example, in the range of 70 to 90% by mass, Especially, it is preferable to exist in the range of 80-90 mass%.

  The negative electrode active material is not particularly limited as long as it can occlude lithium ions during charging and can be released during discharge, and known negative electrode active materials can be used. Examples of such a negative electrode active material include carbon particles such as highly crystalline natural graphite and artificial graphite, metal particles such as metal lithium, lithium alloy, and tin compounds, and conductive polymers.

  Further, the content of the negative electrode active material in the electrode layer is not particularly limited as long as an electrode layer having desired charge / discharge characteristics and the like can be formed. For example, the content in the range of 85 to 97% by mass, In particular, it is preferably in the range of 90 to 95% by mass.

(3) Additive The electrode layer used in the present invention may contain an additive in addition to the binder and the active material. Such additives are not particularly limited, and examples thereof include a conductive agent. The conductive agent can be used, for example, to improve the electrical conductivity of the positive electrode. Specifically, the conductive agent is a mixture of one or more carbon materials such as carbon black, acetylene black, and graphite. Etc.

(4) Electrode layer Moreover, the electrode layer used for this invention has a hydroxyl group on the surface. The ratio of the hydroxyl group present on the surface of the electrode layer is not particularly limited as long as the wettability with respect to the electrolytic solution is improved. Specifically, the hydroxyl group is preferably 5 mol% or more on the surface of the electrode layer. This is because when the hydroxyl group is present above the above value, improvement in wettability with respect to the electrolytic solution is recognized. Furthermore, in this invention, it is preferable that a hydroxyl group exists in the surface of the said electrode layer within the range of 5-60 mol%, especially within the range of 15-30 mol%. It is because it can be set as the electrode layer excellent in chemical resistance and the wettability with respect to electrolyte solution, without reducing the intensity | strength of fluororesin if it is in the said range. In addition, the ratio of the hydroxyl group which exists on the surface of an electrode layer can be measured using a commercially available measuring apparatus.

  The electrode layer preferably has good wettability with respect to the electrolytic solution. That is, it is preferable that the contact angle of the electrolyte droplet is small. Although it does not specifically limit as said contact angle, Specifically, it is preferable to exist in the range of 0-30 degrees, and especially in the range of 0-10 degrees.

  The contact angle of the droplet is determined by dropping a 2 mm diameter water droplet on the electrode layer and measuring the contact angle between the electrode layer and the water droplet. Measurement was made with a contact angle meter DROPMASTER100 manufactured by Kyowa Interface Science Co., Ltd.

As the density of the electrode layer used in the present invention, but are not particularly limited, specifically in the range of 1.5 to 4 g / cm ^3, within the scope inter alia of 2 to 3 g / cm ³ Preferably there is.

2. Current Collector Next, the current collector used in the present invention will be described. The current collector used in the present invention is used for receiving electrons generated in the electrode layer and taking them out. In the present invention, the current collector can be roughly divided into a positive electrode current collector used for a positive electrode and a negative electrode current collector used for a negative electrode.

  The positive electrode current collector is not particularly limited, and a known positive electrode current collector can be used. Specifically, a foil obtained by processing a metal such as aluminum or stainless steel into a plate shape can be given. The negative electrode current collector is not particularly limited, and a known negative electrode current collector can be used. Specifically, the foil etc. which processed metals, such as copper and nickel, in plate shape can be mentioned.

3. Method for Producing Lithium Secondary Battery Electrode The method for producing an electrode for lithium secondary battery of the present invention is not particularly limited as long as it is a method capable of obtaining an electrode for lithium secondary battery having the above characteristics. For example, the method described in “C. Method for producing electrode for lithium secondary battery” described later can be used.

B. Next, the lithium secondary battery of the present invention will be described. The lithium secondary battery of the present invention is characterized by using the above electrode for a lithium secondary battery.

  According to the present invention, by using the lithium secondary battery electrode for at least one of the positive electrode and the negative electrode, a lithium secondary battery excellent in durability and charge / discharge characteristics at high current density can be obtained. it can. The lithium secondary battery of the present invention can be used as a power source for information-related devices such as personal computers, communication-related devices such as mobile phones, electric vehicles, and hybrid vehicles.

Next, the lithium secondary battery of the present invention will be described with reference to the drawings. FIG. 2 is a schematic cross-sectional view showing an example of the lithium secondary battery of the present invention. The lithium secondary battery of the present invention accommodates an electrode body 7 in which a positive electrode 4 and a negative electrode 5 are laminated via a separator 6, an electrolytic solution 8 in which an electrolyte is dissolved in an organic solvent, an electrode body 7 and the electrolytic solution 8. The battery case 9 is provided. The positive electrode 4 is formed on the positive electrode current collector 10, the positive electrode current collector 10, a positive electrode active material and a positive electrode layer 11 containing a fluorine resin as a binder and having a hydroxyl group on the surface, And a positive electrode extraction electrode 12. On the other hand, the negative electrode 5 is formed on the negative electrode current collector 13, the negative electrode current collector 13, and contains a negative electrode active material and a fluorine-based resin as a binder, and a negative electrode layer 14 having a hydroxyl group on the surface, Negative electrode extraction electrode 15.
Hereinafter, each configuration of the lithium secondary battery of the present invention will be described.

1. Electrode Body First, the electrode body used in the present invention will be described. The electrode body used in the present invention is obtained by laminating a positive electrode and a negative electrode with a separator interposed therebetween. In the present invention, the positive electrode includes a positive electrode and a positive electrode extraction electrode installed on the surface of the positive electrode current collector of the positive electrode. Moreover, in this invention, a negative electrode is equipped with the electrode for negative electrodes, and the extraction electrode for negative electrodes installed in the negative electrode collector surface of the said electrode for negative electrodes.

  In addition, the electrode body used in the present invention is obtained by using the electrode for the lithium secondary battery described in the above “A. Electrode for lithium secondary battery” for at least one of the electrode for positive electrode and the electrode for negative electrode. It is. Especially, in this invention, it is preferable that the electrode for positive electrodes and the electrode for negative electrodes are the said electrodes for lithium secondary batteries. This is because the internal resistance of the electrode body can be further reduced.

  The electrode for the lithium secondary battery used in the present invention is the same as that described in the above-mentioned “A. Electrode for lithium secondary battery”, and thus the description thereof is omitted here. Moreover, the extraction electrode used for this invention is not specifically limited, A well-known extraction electrode can be used.

  Moreover, the separator used for this invention has a function which isolate | separates a positive electrode and a negative electrode, and hold | maintains electrolyte solution. The separator used in the present invention is not particularly limited as long as it has the above function, and a known separator can be used. Specific examples include porous films such as polyethylene (PE) and polypropylene (PP).

  Further, the shape of the electrode body used in the present invention is not particularly limited, and examples thereof include a sheet-like electrode body. Furthermore, the sheet-like electrode body is preferably wound and used. This is because a lithium secondary battery with high power generation efficiency can be obtained by winding the sheet-like electrode body. In the present invention, it is particularly preferable to use an electrode body wound in a flat shape from the viewpoint of excellent volume efficiency.

2. Electrolytic Solution Next, the electrolytic solution used in the present invention will be described. The electrolytic solution used in the present invention is obtained by dissolving an electrolyte in an organic solvent. Although it does not specifically limit as said electrolyte, For example, inorganic lithium salt, organic lithium salt, etc. can be mentioned. Examples of the inorganic lithium salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCl, LiBr, LiI, LiAlCl ₄ , NaClO ₄ , NaBF ₄ , Nal, etc., among which LiPF ₆ , LiBF ₄ , LiClO ₄ and LiAsF ₆ are preferable. On the other hand, examples of the organic lithium salt include LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , and the like.

Although it does not specifically limit as a density | concentration of the said electrolyte in electrolyte solution, For example, it is preferable to exist in the range of 0.7-1.5 mol / dm < ³ >. When the concentration in the electrolytic solution is less than 0.7 mol / dm ³ , a sufficient current density may not be obtained, and when it exceeds 1.5 mol / dm ³ , the viscosity increases and the conductivity of the electrolytic solution decreases. This is because

  In addition, the organic solvent is not particularly limited as long as it is an organic solvent used in an electrolyte solution of a normal lithium secondary battery. For example, a carbonate compound, a lactone compound, an ether compound, a sulfolane compound, a dioxolane compound, a ketone compound, A nitrile compound, a halogenated hydrocarbon compound, etc. can be mentioned, A carbonate compound is especially preferable. Examples of the carbonate compound include carbonates such as dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, ethylene glycol dimethyl carbonate, propylene glycol dimethyl carbonate, ethylene glycol diethyl carbonate, and vinylene carbonate. .

3. Battery Case Next, the battery case used in the present invention will be described. The battery case used in the present invention is used for housing the electrode body and the electrolytic solution.
The battery case used in the present invention is not particularly limited as long as it can prevent leakage of the electrolyte, and a known battery case can be used. Moreover, a lithium secondary battery having a desired shape can be obtained by appropriately selecting the shape of the battery case used in the present invention. Specifically, lithium secondary batteries such as a sheet type, a coin type, a cylindrical type, and a square type can be given.

C. Next, the manufacturing method of the electrode for lithium secondary batteries of this invention is demonstrated. The method for producing an electrode for a lithium secondary battery according to the present invention includes an electrode forming material comprising a current collector and an electrode layer formed on the current collector and containing a fluorine-based resin as an active material and a binder. The electrode layer is subjected to a hydrophilic treatment.

  According to the present invention, the electrode layer containing a fluorine-based resin is subjected to a hydrophilic treatment, and by introducing a hydroxyl group on the surface of the electrode layer, chemical resistance and good wettability with respect to an electrolyte solution, Thus, an electrode for a secondary battery having an electrode layer having both of the above can be obtained.

1. First, the electrode forming material used in the present invention will be described. The electrode forming material used in the present invention includes a current collector and an electrode layer formed on the current collector and containing a fluorine-based resin as an active material and a binder.

  The current collector used in the present invention, and the active material and the binder constituting the electrode layer are the same as those described in the above-mentioned “A. Electrode for lithium secondary battery”. Is omitted.

  Further, the method for obtaining the electrode forming material is not particularly limited. For example, an electrode layer forming composition is prepared by mixing an active material and a binder in a predetermined amount. The electrode layer-forming composition is applied onto a current collector using a commercially available coater or the like, dried, and then the density of the electrode layer is improved using a roll press or the like, with a desired film thickness. The method of adjusting etc. can be mentioned.

2. Next, the hydrophilic treatment in the present invention will be described. In the present invention, the electrode layer of the electrode forming material is subjected to a hydrophilic treatment to introduce a hydroxyl group on the surface of the electrode layer.

  The hydrophilization treatment in the present invention is not particularly limited as long as it is a method capable of introducing a hydroxyl group to the surface of the electrode layer, and examples thereof include an oxygen plasma treatment. This is because a hydroxyl group can be easily introduced into the surface of the electrode layer by using oxygen plasma treatment.

An example of an oxygen plasma processing apparatus for performing the oxygen plasma processing is shown in FIG. As a method for performing the oxygen plasma treatment, for example, the electrode forming material 18 is placed in the chamber where the electrode 16 and the counter electrode 17 are placed so that the electrode layer is on the upper side, and the inside of the chamber is used using a rotary pump. Next, a vacuum is applied, and then oxygen is introduced from the O ₂ cylinder to a predetermined pressure to bring the chamber into an oxygen atmosphere, and then a high frequency is applied to cause glow discharge to introduce hydroxyl groups on the surface of the electrode layer. And the like. At this time, the strength and the like at the time of performing the oxygen plasma treatment are not particularly limited, but the contact angle of the droplet of the electrolytic solution in the electrode layer is the same as that in the above-mentioned “A. Oxygen plasma treatment is preferably performed so as to be within the stated range.

3. Electrode for lithium secondary battery The characteristics of the electrode for lithium secondary battery obtained by the present invention are not particularly limited, but have the characteristics described in "A. Electrode for lithium secondary battery" above. Preferably there is.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

Hereinafter, the present invention will be described in more detail with reference to examples.
[Example]
(Manufacture of positive electrode)
A PTFE aqueous solution having a solid content ratio of about 50% as a binder, using 87% by mass of lithium nickel oxide as a positive electrode active material and 10% by mass of acetylene black (product number: HS-100, manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material. The dispersion was added so that the solid content of PTFE was 3% by mass, and the mixture was stirred for 1 hour with a biaxial stirrer. The paste thus obtained was applied on one side with a coater to an aluminum foil serving as a positive electrode current collector with a basis weight of 6.51 (mg / cm ² ). Next, the member was passed through a roll press and a load of linear pressure 740 (kg / cm) was applied to form an electrode layer having an electrode density of 2.20 (g / cm ³ ). Next, the above member is cut to a width of 5.4 (cm) and a length of 9.0 (cm), and an electrode layer for a length of 0.5 (cm) is scraped off as a lead tab weld for the positive electrode extraction electrode. A positive electrode forming material was obtained. The effective reaction area of the electrode layer is 5.4 (cm) × 8.5 (cm) = 45.9 (cm ² ).

  Next, the positive electrode-forming material obtained by the above method was set in a plasma processing apparatus, the inside of the chamber was evacuated, oxygen was introduced, and the pressure was set to 13 Pa. Thereafter, a high frequency of 200 W and 13.56 MHz was applied to generate glow discharge. In this state, oxygen plasma treatment for 10 minutes was performed to obtain a positive electrode. The electrode layer of the positive electrode had a hydroxyl group of 15 mol% on the surface. Moreover, a 2 mm diameter water droplet was dripped at electrode layer shape, and the contact angle measured with Kyowa Interface Science Co., Ltd. contact angle meter DROPMASTER100 was 10 degrees.

(Manufacture of negative electrode)
Using 92.5% by mass of scaly graphite as the negative electrode active material, PTFE aqueous dispersion having a solid content ratio of about 50% as a binder was added so that the solid content of PTFE was 7.5% by mass. Stir for 1 hour with a shaft stirrer. The paste thus obtained was applied on one side with a coater to a copper foil as a negative electrode current collector at a basis weight of 3.74 (mg / cm ² ). Next, the member was passed through a roll press and a load of linear pressure 250 (kg / cm) was applied to form an electrode layer having an electrode density of 1.25 (g / cm ³ ). Next, the member is cut to a width of 5.6 (cm) and a length of 9.5 (cm), and an electrode layer of 0.5 (cm) length is scraped off as a lead tab weld for the negative electrode take-out electrode. A negative electrode forming material was obtained. The effective reaction area of the electrode layer is 5.6 (cm) × 9.5 (cm) = 53.2 (cm ² ). Next, the electrode forming material for a negative electrode obtained by the above method was subjected to oxygen plasma treatment under the same conditions as the electrode forming material for a positive electrode to obtain a negative electrode. The electrode layer of the negative electrode had a hydroxyl group of 15 mol% on the surface. Moreover, a 2 mm diameter water droplet was dripped at electrode layer shape, and the contact angle measured with Kyowa Interface Science Co., Ltd. contact angle meter DROPMASTER100 was 10 degrees.

(Production of lithium secondary battery)
The extraction electrode was welded to the sheet-like electrode for the positive electrode and the electrode for the negative electrode obtained by the above method, respectively, to obtain a positive electrode and a negative electrode. Thereafter, the positive electrode and the negative electrode were closely adhered to the laminating film through a separator made of a microporous polyethylene film having a thickness of 25 μm to form a laminated electrode body. Next, LiPF6 as an electrolyte was dissolved in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7 at a rate of 1 mol / L to prepare an electrolytic solution. Thereafter, an electrolytic solution was injected into the laminate type electrode body, and the film was sealed and sealed. By the above procedure, a laminated film type lithium secondary battery of about 60 mm × 100 mm was obtained.

(Evaluation)
Various characteristics of the lithium secondary battery obtained by the above method were measured by the following measuring methods.
(1) Initial battery capacity Initial charge is constant current-constant voltage charge (CC-CV charge) up to 4.1 (V) with charge current 12 (mA) and up to 3.0 (V) with discharge current 17 (mA) Constant current discharge (CC discharge) was performed. Next, CC-CV charge is performed up to 4.1 (V) at a charge current of 50 (mA), and CC discharge is performed four times up to 3.0 (V) at a discharge current of 50 (mA). ) To 4.1 (V), and CC discharge to 3.0 (V) at a discharge current of 17 (mA), and the charge / discharge capacity at this time was defined as the initial battery capacity. The measurement was performed in an atmosphere at 25 ° C.

(2) Room temperature output After the initial discharge capacity measurement, the temperature was kept at 25 ° C., and the battery was CC-CV charged to 3.750 V (charged state: SOC 60%) at a charging current of 50 mA. After that, discharging for 10 seconds and charging for 10 seconds in the order of 15 mA, 45 mA, 135 mA, 270 mA, and 400 mA are repeated, and each current value and closed circuit battery voltage are linearly approximated, and the current at the point where the straight line intersects with 3.0 V The output was obtained by reading the value and multiplying the current value by 3V. Note that. All measurements were performed at 25 ° C.

(3) Low temperature output After the initial discharge capacity measurement, the temperature was kept at 25 ° C., and the battery was CC-CV charged to 3.618 V (charged state: SOC 40%) at a charging current of 50 mA. Then, discharge for 10 seconds in each order of 5 mA, 10 mA, 15 mA, 20 mA, 30 mA, and 50 mA and charge for 10 seconds, measure the current value of each point and the closed circuit battery voltage, and connect the two points around 3.0V The output value was obtained by reading the current value at the point where the straight line intersects 3.0V and multiplying the current value by 3V. Note that. All measurements were performed at -30 ° C.

(4) Evaluation of high-temperature cycle characteristics The battery whose initial capacity was evaluated was charged / discharged at a constant current of 2.2 mA / cm ² and a battery electrode voltage between 4.1 V and 3 V in a constant temperature bath at 60 ° C. Was repeated. Then, the ratio of the charge / discharge capacity at the 500th cycle to the charge / discharge capacity at the first cycle, that is, the post-cycle capacity retention rate was determined.

(5) Results As a result of the above tests (1) to (4), the initial discharge capacity was 46 mAh, the room temperature output was 1.80 W, the low temperature output was 0.07 W, and the post-cycle capacity maintenance ratio was 81.5%. there were.

[Comparative example]
A laminate film type lithium secondary battery was obtained in the same manner as in the above example, except that the oxygen plasma treatment was not performed during the production of the positive electrode and the negative electrode. Further, as a result of the same test as in the above example, the initial discharge capacity was 46 mAh, the room temperature output was 1.30 W, the low temperature output was 0.02 W, the capacity retention rate after cycling was 81.8%, and the room temperature output and low temperature were low. The output was lower than that of the example.

It is a schematic sectional drawing which shows an example of the electrode for lithium secondary batteries of this invention. It is a schematic sectional drawing which shows an example of the lithium secondary battery of this invention. It is explanatory drawing which shows an example of an oxygen plasma processing apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Current collector 2 ... Electrode layer 3 ... Electrode for lithium secondary batteries 4 ... Positive electrode 5 ... Negative electrode 6 ... Separator 7 ... Electrode body 8 ... Electrolyte 9 ... Battery case

Claims (5)

An electrode for a lithium secondary battery comprising a current collector and an electrode layer formed on the current collector and containing a fluororesin as an active material and a binder, wherein the surface of the electrode layer has a hydroxyl group An electrode for a lithium secondary battery, comprising: 2. The electrode for a lithium secondary battery according to claim 1, wherein 5 mol% or more of a hydroxyl group is present on the surface of the electrode layer. A lithium secondary battery using the electrode for a lithium secondary battery according to claim 1 or 2. Using an electrode forming material comprising a current collector and an electrode layer formed on the current collector and containing a fluororesin as an active material and a binder, the electrode layer is subjected to a hydrophilic treatment. The manufacturing method of the electrode for lithium secondary batteries characterized by performing. The method for producing an electrode for a lithium secondary battery according to claim 4, wherein the hydrophilization treatment is an oxygen plasma treatment.

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