JP2017091673A - Lithium ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion battery from which a large current can be taken out easily, while ensuring a high energy density.SOLUTION: The collector 11A of the positive electrode plate 11 of a lithium ion battery is a porous collector of porous structure, the porous collector 11A is filled with a positive electrode active material, a conductive material and a binder composing a positive electrode active material layer 11B, and on the surface of the porous collector 11A, a carbon coat layer 17 contributive to reduction of electrical resistance between the porous collector 11A and positive electrode active material layer 11B is provided.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a lithium ion battery.

A lithium ion battery has been proposed in which a porous aluminum current collector is used as a positive electrode so that a larger amount of active material can be filled than when a metal foil is used (for example, Patent Document 1, 2). However, it is difficult to extract a large current, and the application is limited.
Further, in a lithium ion battery using a metal foil for the positive electrode, a layer containing conductive particles is applied to one or both sides of the metal foil so that the coverage of the conductive particles is 50 to 100%, and this layer is included. The structure which provided the layer containing an electrode active material in the surface is proposed (for example, patent document 3). However, when a high energy density is obtained and thick coating is performed, the characteristic change is remarkable, and it is difficult to increase the energy density beyond a certain level.

JP2013-140745A JP, 2014-022150, A Special table 2012-096189 gazette

  Therefore, an object of the present invention is to provide a lithium ion battery that can easily extract a large current and can achieve high energy density.

  In order to achieve the above object, the present invention provides a lithium ion battery using an electrode having a current collector and an active material layer, wherein the current collector is a porous current collector having a porous structure, and the porous The current collector is filled with an active material, a conductive material, and a binder constituting the active material layer, and a conductive layer is provided in advance on the surface of the porous current collector. It is characterized by.

In the above configuration, the porous current collector may have a three-dimensional porous structure.
In the above structure, the conductive layer may be a carbon coat layer.

  In the present invention, a current collector of an electrode of a lithium ion battery is a porous current collector having a porous structure, and the porous current collector includes an active material, a conductive material, and a binder constituting an active material layer. Since a conductive layer is provided in advance on the surface of the porous current collector, a large current can be easily taken out and a high energy density can be achieved.

It is the figure which showed typically the electrode group structure of the lithium ion battery which concerns on embodiment of this invention, (A) is sectional structure of an electrode group, (B) is the elements on larger scale of FIG. 1 (A). .

FIG. 1 is a diagram schematically showing a configuration of an electrode group of a lithium ion battery according to an embodiment of the present invention. FIG. 1 (A) is a sectional structure of the electrode group, and FIG. 1 (B) is a diagram of FIG. It is the figure which expanded a part of.
The lithium ion battery 10 includes a positive electrode (hereinafter “positive electrode plate”) 11, a negative electrode (hereinafter “negative electrode plate”) 13, and a separator interposed between the positive electrode plate 11 and the negative electrode plate 13. 15. The positive electrode plate 11 is a slurry in which a positive electrode active material, a conductive material, and a binder constituting the positive electrode active material layer 11B are dispersed in a solvent in a porous current collector 11A having a porous structure (hereinafter referred to as “positive electrode slurry”). ) To form a high filling electrode. The negative electrode plate 13 has a negative electrode active material, a conductive material and a binder constituting the negative electrode active material layer 13B dispersed in a solvent on the surface of a current collector 13A made of a metal foil based on a metal material such as copper. Formed on an electrode provided with a slurry (hereinafter referred to as “negative electrode slurry”).

The positive electrode plate 11 has a carbon coat layer 17 in advance between the porous current collector 11A and the positive electrode slurry constituting the positive electrode active material layer 11B.
The manufacturing process of the positive electrode plate 11 will be described in chronological order. A layer forming step for forming a carbon coat layer 17 functioning as a conductive layer on the surface of the porous current collector 11A, and a carbon coat layer 17 are formed. Filling the pores of the porous current collector 11A with the positive electrode slurry constituting the positive electrode active material layer 11B, the drying step for drying the porous current collector 11A, and pressing the porous current collector 11A Press step.

  According to studies by the inventors, the drying step causes a concentration gradient in the abundance ratio of the conductive material and the binder in the positive electrode active material layer 11B, and the positive electrode active material layer 11B and the porous current collector 11A Adverse effects may occur during For example, the abundance ratio of the conductive material and the binder tends to be relatively high in a region away from the porous current collector 11A due to drying. In addition, since it is difficult to reliably contact the porous current collector 11A and the positive electrode active material layer 11B, the conductivity between the porous current collector 11A and the positive electrode active material layer 11B is present when there is no contact. Disadvantageous.

  On the other hand, since the lithium ion battery 10 of this embodiment has the carbon coat layer 17 on the surface of the porous current collector 11A, the carbon coat layer 17 is composed of the porous current collector 11A and the positive electrode active material layer 11B. It is located in between, and contributes to a reduction in electrical resistance between the porous current collector 11A and the positive electrode active material layer 11B. Accordingly, it is possible to reduce the electric resistance and to easily flow a large current. In addition, since the porous current collector 11A is used, it is possible to fill a large amount of the positive electrode active material and the like, and it is easy to achieve high energy density. Accordingly, the lithium ion battery 10 of the present embodiment is easy to extract a large current and is suitable for increasing the energy density.

Here, if the porous current collector 11A is simply filled with the positive electrode slurry, the required coating film density cannot be obtained, and the output / cycle characteristics may be deteriorated.
According to the study by the inventors, when the carbon coat layer 17 is provided on the surface of the porous current collector 11A, the following knowledge has been obtained.
Compared with an electrode in which an active material or the like is coated on a general aluminum foil, the characteristics can be maintained even if the coating is made thicker. Further, the characteristics can be maintained even if the ratio of the conductive material in the positive electrode slurry is lowered. Further, the characteristics can be maintained even when the ratio of the binder in the positive electrode slurry is lowered, and the characteristics can be maintained without increasing the coating film density. Therefore, it is easy to suppress a decrease in output / cycle characteristics.

Hereinafter, the production method and properties of the positive electrode plate 11 will be described in detail.
1.1 (Porous current collector of positive electrode plate)
As the porous current collector 11A, for example, a porous aluminum current collector based on an aluminum alloy is used.
This porous current collector 11A is formed by press-molding a mixed powder of aluminum powder (corresponding to a base metal powder) mixed with a predetermined volume ratio and a supporting powder with an aluminum plate (corresponding to a base metal plate). After that, the molded body is heat-treated in an inert atmosphere to form a liquid phase from the aluminum powder or the aluminum plate, and the aluminum powder and the aluminum powder and the aluminum plate are joined together, and finally the supporting powder is removed. It is obtained by.
As a result, the porous current collector 11A has a three-dimensional porous structure including a large number of voids from which the support powder has been removed, and bonded metal powder walls of joined aluminum powder that form the periphery of the voids. Moreover, many fine holes are formed in the bonded metal powder wall. Thereby, it becomes an open cell type structure in which voids are connected by these fine holes.

  The porosity of the porous current collector 11A is set to 80% or more and 95% or less, preferably 85% or more. By setting it in this range, a large number of positive electrode slurries can be filled in the pores of the porous current collector 11A, which is advantageous for increasing the output and capacity of the battery.

The supporting powder has a melting point higher than that of the aluminum powder, and a material that can be finally removed is applied. When the mixed powder is combined with an aluminum plate, a supporting powder having a melting point higher than the lower melting point of the aluminum powder and the aluminum plate is used. As such a supporting powder, a water-soluble salt is preferable, and sodium chloride and potassium chloride are preferably used from the viewpoint of availability. Since the space formed by removing the support powder becomes the pores of the porous current collector 11A, the particle size of the support powder is reflected in the pore diameter.
The particle size of the support powder is preferably in the range of 100 to 1000 μm. The particle size of the support powder is defined by the opening of the sieve. Therefore, the porous current collector 11A having the uniform pore diameter can be obtained by aligning the particle diameter of the support powder by classification.

  For the aluminum plate, a net-like body such as a wire net, an expanded metal, or a punching metal is used. The aluminum plate serves as a support, and the strength of the porous aluminum current collector is improved and the conductivity is further improved. As the strength of the porous current collector 11A is higher, porous aluminum is not lost in the electrode manufacturing process, and a sufficient battery function can be exhibited. As the material of the aluminum plate, pure aluminum or aluminum alloy is used. As the aluminum alloy, an aluminum-titanium alloy, an aluminum-manganese alloy, an aluminum-iron alloy, an aluminum-nickel alloy, or the like is preferably used.

  The compounding of the mixed powder and the aluminum plate refers to an integrated state in which, for example, when a metal mesh is used for the aluminum plate, the mesh is covered with the mixed powder while the mixed powder is filled in the mesh. If the positive electrode active material is filled into porous aluminum provided with bonded metal powder walls on both sides of the aluminum plate, even if the aluminum plate is a porous network, it can be filled from one side of the region divided by the aluminum plate, The other area can be filled. Therefore, the aluminum plate is preferably a net-like body. Here, the term “porous” refers to a mesh portion of a net-like body and a gap portion between fibers of metal fibers.

1.2 (Layer formation step)
The carbon coat layer 17 is formed on the surface of the porous current collector 11A by physical vapor deposition (PVD: Physical Vapor Deposition) or the like. The carbon coat layer 17 may be provided uniformly on the surface, and is not limited to PVD. For example, a known thin film forming method such as chemical vapor deposition (CVD) or liquid phase growth can be applied. is there.
The carbon coat layer 17 may be formed using a carbon material. The carbon material to be used is preferably a material having an electric resistance as low as possible.

1.3 (filling step and drying step)
The porous current collector 11A on which the carbon coat layer 17 is formed is immersed in a positive electrode slurry in which a positive electrode active material, a conductive material, and a binder constituting the positive electrode active material layer 11B are dispersed in a solvent.
The positive electrode active material is not particularly limited as long as it can be used for a non-aqueous electrolyte secondary battery. For example, lithium metal oxide such as lithium cobaltate, lithium manganate, lithium nickelate, nickel cobalt lithium manganate, etc. You can list things. The conductive material is not particularly limited, and a known or commercially available material can be used. Examples thereof include carbon black such as acetylene black and ketjen black, activated carbon, graphite and the like.

  A binder is not specifically limited, A well-known or commercially available thing can be used. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinylpyrrolidone (PVP), polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, styrene butadiene rubber (SBR), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC) and the like.

  The positive electrode active material, the conductive material, and the binder are filled in the porous current collector 11A in the state of a positive electrode slurry dispersed in a solvent. The mixing ratio of the positive electrode active material, the conductive material, and the binder is preferably selected as appropriate so as to obtain a desired effect. Further, the concentration of each component in the positive electrode slurry is not limited. The solvent for the positive electrode slurry is not particularly limited, and for example, N-methyl-2-pyrrolidone, water and the like are preferably used. When using polyvinylidene fluoride as a binder, it is preferable to use N-methyl-2-pyrrolidone as a solvent. When using polytetrafluoroethylene, polyvinyl alcohol, carboxymethylcellulose, or the like as a binder, water is used. It is preferable to use it as a solvent.

The positive electrode slurry in which the positive electrode active material, the conductive material, and the binder are dispersed in a solvent may be filled into the porous current collector 11A by a known method such as a press-fitting method. In the case of the press-fitting method, the positive electrode slurry is arranged on one side with the porous current collector 11A as the diaphragm, and the other side is the permeate side of the positive electrode slurry. Then, the positive electrode active material, the conductive material, and the binder are filled in the holes of the porous current collector 11A by reducing the pressure on the other permeate side and allowing the positive electrode slurry to pass therethrough.
Alternatively, by pressurizing the positive electrode slurry disposed on one side, the positive electrode slurry in which the positive electrode active material, the conductive material and the binder are dispersed in the solvent is filled in the pores of the porous current collector 11A. good. In place of the press-fitting method, the porous current collector 11A is immersed in a positive electrode slurry in which a positive electrode active material, a conductive material, and a binder are dispersed in a solvent, and the positive electrode active material, the conductive material, and the binder are made porous. You may employ | adopt the method (equivalent to an "immersion method") to diffuse to the hole of the mass collector 11A.
The positive electrode plate 11 in which the positive electrode slurry in which the positive electrode active material, the conductive material, and the binder are dispersed in a solvent is filled in the pores of the porous current collector 11A is dried by scattering the solvent at a temperature within 50 to 200 ° C. Is done.

1.4 (press step)
The positive electrode plate 11 after the drying step is pressed using a press such as a roll press or a flat press to improve the electrode density of the active material. In particular, it is preferable to press with a flat plate press. This is because the porous current collector 11A may be distorted in press processing using a roll press.
Further, according to the study by the inventors, it was preferable that the electrode density of the positive electrode plate 11 be 2.75 g / cc or near 2.75 g / cc. When not pressed, the coating film density of the positive electrode plate 11 was 2.0 g / cc. However, each value may be appropriately changed within a range where desired characteristics can be obtained.

2. (Example)
Examples will be described. In the following description, in order to make the description easy to understand, the same members as those shown in FIG.
2.1 (Preparation of positive electrode plate)
The porous current collector 11A of the positive electrode plate 11 was made of an aluminum alloy as a base material. This porous current collector 11A was prepared by adjusting the mixing ratio of the aluminum powder and the support powder so that the porosity was 85%. A carbon coat layer 17 having a thickness of 2 μm was formed on the surface of the porous current collector 11A by an immersion method. The materials used for forming the carbon coat layer 17 were Denka Black (registered trademark), PVDF # 1100, and N-methyl-2-pyrrolidone at 3: 2: 95, respectively, and dispersed for 1 hour using a homogenizer. Produced.
As the positive electrode active material, lithium nickel cobalt manganate (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) was used. The composition was positive electrode active material: conductive material: binder = 90: 5: 5, and a positive electrode slurry was prepared by dispersing N-methyl-2-pyrrolidone in these materials using a kneader. Then, the porous current collector 11A on which the carbon coat layer 17 is formed is immersed in the positive electrode slurry using an immersion method, and the pressure is reduced (in this example, −0.1 MPa) to form the porous current collector 11A. The positive electrode slurry was filled.

After filling, surplus slurry adhered to the front and back surfaces of the porous current collector 11A was scraped off using a spatula. Next, the porous current collector 11A was placed in a drying apparatus and dried at 80 ° C. for 2 hours. The electrode coating amount after drying was 1000 g / square m.
Subsequently, the porous current collector 11A was pressed with a flat plate press at a pressure of 0.50 ton / square cm, sized to a predetermined size so that an uncoated portion remained on at least one side, and the electrode after sizing A positive electrode tab 11 was obtained by welding a positive electrode tab to an uncoated portion.

2.2 (Preparation of negative electrode plate)
A copper foil was used for the current collector 13 </ b> A of the negative electrode plate 13. The negative electrode active material was 90 parts by weight of artificial graphite powder having an average particle diameter of 20 μm and a maximum particle diameter of 81 μm, and the binder was 10 parts by weight of polyvinylidene fluoride resin. N-methylpyrrolidone as a solvent was blended with these negative electrode active material and binder, and the mixture was stirred and mixed with a disperser to prepare a slurry for coating a negative electrode active material mixture. The maximum particle size and the average particle size indicate a volume-based median diameter (D50) in particle size distribution measurement by a laser light diffraction method. The maximum particle size is the maximum value in the measurement.

  Next, the negative electrode active material mixture coating slurry is continuously applied to the current collector 13A using a die coater (thin film coating tool), and dried in an oven to remove the solvent. A negative electrode active material mixture coating film (corresponding to the negative electrode active material layer 13B) was formed on the current collector 13A. Subsequently, pressing was performed, sizing to a predetermined size so that an uncoated portion remained on at least one side, and a negative electrode tab was welded to the uncoated portion of the sized electrode, thereby obtaining the negative electrode plate 13.

2.3 (Battery assembly)
Using a plurality of electrode plates composed of the positive electrode plate 11 and the negative electrode plate 13 described above, these electrode plates and the separator 15 made of a microporous film are separated into a separator / negative electrode plate / separator / positive electrode plate / separator / negative electrode plate. The electrode group (also referred to as a power generation element) was prepared so that the positive electrode plate 11 and the coating surface of the negative electrode plate 13 faced the positive electrode plate 11, and the positive electrode tab and the negative electrode tab were opposed to each other.
Next, the positive electrode terminal and the negative electrode terminal were welded to tabs attached to the positive electrode plate 11 and the negative electrode plate 13 of the electrode group, respectively, and stored in the recesses formed by drawing the laminated film serving as the battery case. A flat aluminum laminate film having the same dimensions as that of the aluminum laminate film in which the concave portion was formed was superposed, and two sides through which each terminal passes and the other one side were heat-sealed.
At this time, for the purpose of preventing a short circuit between each terminal and the aluminum substrate, the terminal portion was sealed through a sheet film made of a synthetic resin to produce a dry cell.

  Subsequently, an electrolytic solution in which lithium hexafluorophosphate was dissolved in a mixed solvent of ethylene carbonate and ethyl methyl carbonate having a weight mixing ratio of 3: 7 so as to be 1.3 mol / L was added from one side where the dry cell was opened. After injecting and depressurizing the inside of the cell, the part was heat sealed to seal the cell. Next, this was initially charged until it was fully charged with a current of 0.1 CA, and stored for a predetermined time. Thereafter, the cell was discharged at a current of 0.2 CA until the cell voltage reached 2.75 V, and an activation process was performed. After completion of the activation treatment, the discharged gas is discharged, and the sealed portion at the time of pouring is opened, the inside of the cell is decompressed, and then heat-sealed for the final sealing. Produced.

3. (Comparative example)
Instead of the porous current collector 11A having the carbon coat layer 17 formed on the surface of the aluminum alloy substrate of the example, a known porous collector made of an aluminum alloy substrate having no carbon coat layer formed on the surface is used. The electric body was used as a positive electrode plate. The other conditions were all the same as those in the example, and a comparative lithium ion battery was produced.

4). (test)
4.1 (Discharge capacity test)
The discharge capacity test of the battery produced by the Example and the comparative example was implemented.
The contents of the test are as follows. The produced battery was charged to 4.2 V at a current value of 0.2 C, and after reaching 4.2 V, charging was performed until it dropped to a current value equivalent to 0.05 C at a constant voltage. After charging, discharging was performed at a constant current of 0.2 C until a voltage of 2.75 V was reached, and 0.2 C discharge capacities of the batteries of Examples and Comparative Examples were obtained.
Furthermore, charging was performed under the same conditions as described above, and discharging was performed at a constant current of 1.0 C until a voltage of 2.75 V was reached, thereby obtaining 1.0 C discharge capacities of the batteries of Examples and Comparative Examples. . Table 1 shows the test results.

  As shown in Table 1, the discharge capacity retention rate of the battery of the example was 90%, and the discharge capacity retention rate of the battery of the comparative example was 50%. Therefore, it can be seen that the battery of the example has a larger discharge capacity at the time of high rate discharge than the battery of the comparative example.

4.2 (Capacity maintenance rate at cycle test rate)
A cycle test was conducted on the batteries prepared in the examples and comparative examples.
The cycle test was performed at an environmental temperature of 25 ° C., a charge and discharge current value of 0.5 C, and a voltage setting of 2.75 to 4.2 V. Table 2 shows the discharge capacity at the first cycle of the cycle test, the discharge capacity at the 1000th cycle, and the maintenance rate, respectively.

  As shown in Table 2, the discharge capacity retention rate of the battery of the example was 80.2%, and the discharge capacity retention rate of the battery of the comparative example was 70.5%. Therefore, it can be seen that the battery of the example is superior in capacity retention rate in the cycle test as compared with the battery of the comparative example.

  As described above, the positive electrode plate 11 of the lithium ion battery 10 according to the present embodiment uses the porous current collector 11A having a porous structure, and the porous current collector 11A constitutes the positive electrode active material layer 11B. A positive electrode slurry in which a positive electrode active material, a conductive material, and a binder are dispersed in a solvent is filled, and the surface of the porous current collector 11A is between the porous current collector 11A and the positive electrode active material layer 11B. A carbon coat layer 17 having conductivity that contributes to a reduction in electrical resistance is provided in advance. The carbon coat layer 17 makes it easy to take out a large current, and the porous current collector 11A can be filled with a large amount of a positive electrode active material, which is advantageous for increasing the energy density.

  As a result, due to the drying step or the like, the abundance ratio of the conductive material and the binder in the vicinity of the porous current collector 11A is relatively lower than the abundance ratio in the region away from the vicinity of the porous current collector 11A. However, it is easy to extract a large current and a high energy density can be achieved. Therefore, it is possible to reduce the number of separators 15 and the number of electrodes while obtaining desired battery performance, which is advantageous for reducing the number of parts and cost, and further reducing the size of the lithium ion battery 10.

  In addition, the porous current collector 11A can be efficiently filled with a large amount of positive electrode active material and the like, which is advantageous in increasing the energy density. Furthermore, since the conductive layer is the carbon coat layer 17, it can be manufactured using a widely distributed carbon material, and desired performance can be easily obtained by selecting the carbon material. In addition, it is easy to procure materials and it is easy to suppress an increase in material costs.

The present invention is not limited to the above-described embodiment, and various modifications and changes can be made based on the technical idea of the present invention.
For example, in the above-described embodiment, the case where the porous current collector 11A is used for the positive electrode plate 11 of the lithium ion battery 10 and the carbon coat layer 17 is provided on the surface of the porous current collector 11A is applied. A porous current collector may be used for the plate 13 and a carbon coat layer may be provided on the surface of the porous current collector. Also in this case, it is easy to take out a large current, and it is advantageous for increasing the energy density. That is, the present invention is applicable to both the positive electrode plate 11 and the negative electrode plate 13.

  In the above-described embodiment, the case where the carbon coat layer 17 is provided has been described. However, the carbon coat layer 17 is not limited thereto. A conductive layer other than the coat layer may be provided.

10 Lithium ion battery 11 Positive electrode plate (electrode for lithium ion battery)
11A Porous current collector 11B Positive electrode active material layer 13 Negative electrode plate (electrode for lithium ion battery)
13B Negative electrode active material layer 15 Separator 17 Carbon coat layer

Claims (3)

In a lithium ion battery using an electrode having a current collector and an active material layer,
The current collector is a porous current collector having a porous structure, and the porous current collector is filled with an active material, a conductive material, and a binder constituting the active material layer,
A lithium ion battery characterized in that a conductive layer is provided in advance on the surface of the porous current collector.   The lithium ion battery according to claim 1, wherein the porous current collector has a three-dimensional porous structure.   The lithium ion battery according to claim 1, wherein the conductive layer is a carbon coat layer.

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