WO2014128946A1

WO2014128946A1 - Lithium-ion secondary cell negative electrode, lithium-ion secondary cell using lithium-ion secondary cell negative electrode, and method for manufacturing said electrode and said cell

Info

Publication number: WO2014128946A1
Application number: PCT/JP2013/054653
Authority: WO
Inventors: 孝明鈴木
Original assignee: 株式会社日立製作所
Priority date: 2013-02-25
Filing date: 2013-02-25
Publication date: 2014-08-28

Abstract

Provided are a lithium-ion secondary cell negative electrode having excellent service life characteristics such as cycle characteristics and high-temperature storage characteristics, a lithium-ion secondary cell in which the lithium-ion secondary cell negative electrode is used, and a method for manufacturing the electrode and cell. A lithium-ion secondary cell electrode including a negative electrode and a negative-electrode mixture layer formed on the negative electrode, wherein the lithium-ion secondary cell negative electrode is characterized in that the negative-electrode mixture layer is composed of a negative-electrode first mixture layer formed in the center in the electrode width direction, and a negative-electrode second mixture layer formed at both ends of the negative-electrode first mixture layer, the negative-electrode first mixture layer including a large-grain-size negative-electrode active substance, and a small-grain-size negative-electrode active substance, the negative-electrode second mixture layer comprising a large-grain-size negative-electrode active substance or a small-grain-size negative-electrode active substance, both negative-electrode active substances being a graphite-based material, and the average grain size of the small-grain-size negative-electrode active substance being smaller than the average grain size of the large-grain-size negative-electrode active substance.

Description

Lithium ion secondary battery negative electrode, lithium ion secondary battery negative electrode using lithium ion secondary battery negative electrode, and production method thereof

The present invention relates to a lithium ion secondary battery negative electrode, a lithium ion secondary battery using a lithium ion secondary battery negative electrode, and a method for producing the same.

In recent years, development of lithium ion secondary batteries has been actively promoted. Patent Document 1 discloses a structure in which a negative electrode active material layer is composed of a strip-shaped edge portion located at both ends in the width direction perpendicular to the longitudinal direction of the strip-shaped electrode, and a central portion located at the center of the edge portion. Thus, a technique is described in which the central portion is made lower in resistance than the end edge portion, thereby preventing metallic lithium from precipitating during charging and suppressing the decrease in battery capacity due to practical use.

JP 2011-70976 A

In Patent Document 1, active material particles having an average particle size smaller than that of the edge portion are arranged in a central region in the width direction orthogonal to the longitudinal direction of the strip electrode. Since particles having a small particle size have a large specific surface area, it is considered that the surface reaction on the particle surface increases. Therefore, when the ratio of the central region in which the particles are arranged increases in the electrode width direction, high high temperature holding characteristics may not be expected. The present invention provides a lithium ion secondary battery negative electrode having excellent life characteristics such as high temperature storage characteristics and cycle characteristics, a lithium ion secondary battery using a lithium ion secondary battery negative electrode, and a method for producing the same. Objective.

The features of the present invention for solving the above-described problems are as follows. A negative electrode mixture layer is provided on the surface of the negative electrode, and the negative electrode mixture is orthogonal to the winding direction of the negative electrode in a lithium ion secondary battery having negative electrode active material particles capable of occluding and releasing lithium ions. Negative electrode active material contained in the negative electrode first mixture layer, having a negative electrode first mixture layer at the center in the width direction and having negative electrode second mixture layers at both ends in the width direction of the negative electrode first mixture layer. The material is a mixture of a negative electrode active material having a large particle size and a negative electrode active material having a small particle size, and the negative electrode active material contained in the negative electrode second mixture layer is a negative electrode active material having a large particle size or a small particle size. It is a lithium ion secondary battery which is a negative electrode active material.

Further, the negative electrode active material having a large particle size has an average particle size of 15 μm or more and 45 μm or less, and the negative electrode active material having a small particle size has an average particle size of 5 μm or more and less than 15 μm. is there.

As a manufacturing method, for example, (1) a negative electrode active material slurry containing a negative electrode active material having a large particle size or a negative electrode active material having a small particle size is applied to the edge region on the negative electrode, dried, pressed and processed After the step of forming a negative electrode mixture layer in the edge region and the step (1), a negative electrode mixture slurry containing a negative electrode active material having a large particle size and a negative electrode active material having a small particle size is applied, dried, and further pressed. And what has the process in which a negative mix layer is formed in a center area | region is employable.

According to the present invention, a negative electrode for a lithium ion secondary battery having excellent life characteristics such as cycle characteristics and high-temperature storage characteristics, a lithium ion secondary battery using a negative electrode for a lithium ion secondary battery, and a method for producing the same Can be provided. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

The single-side longitudinal cross-sectional view which shows the whole structure of one Embodiment of the secondary battery with which the electrode for lithium ion secondary batteries which concerns on this invention is applied. The figure which shows the basic composition of one Embodiment of the electrode for lithium ion secondary batteries which concerns on this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description shows specific examples of the contents of the present invention, and the present invention is not limited to these descriptions. Various modifications by those skilled in the art are within the scope of the technical idea disclosed in this specification. Changes and modifications are possible. In all the drawings for explaining the present invention, components having the same function are denoted by the same reference numerals, and repeated description thereof may be omitted.

FIG. 1 shows an overall configuration of an embodiment of a secondary battery to which an electrode for a lithium ion battery according to the present invention is applied.

The secondary battery 1100 includes a positive electrode 16 and a negative electrode 13 that reversibly occlude and release lithium ions, a separator 17 interposed between the positive electrode 16 and the negative electrode 13, and an organic solution in which an electrolyte containing lithium ions is dissolved. The electrolytic solution 115 is generally configured. Here, the positive electrode 16 is generally composed of a positive electrode 14 and a positive electrode mixture layer 15 disposed on both surfaces thereof, and one end of a positive electrode lead 18 is welded to the positive electrode 14 in order to collect the positive electrode 16. Yes. The negative electrode 13 is generally composed of the negative electrode 11 and the negative electrode mixture layer 12 disposed on both sides thereof, and one end of the negative electrode lead 19 is welded to the negative electrode 11 in order to collect the negative electrode 13. .

Next, an embodiment of the negative electrode for a lithium ion secondary battery according to the present invention will be described with reference to FIG. FIG. 2 shows a basic configuration of an embodiment of the negative electrode for a lithium ion secondary battery according to the present invention. The negative electrode for a lithium ion secondary battery shown in FIG. 2 has an electrode mixture layer on one side of the electrode, but an electrode mixture layer can also be provided on both sides of the electrode as shown in FIG.

The principle will be described with reference to FIG.

In one embodiment of the present invention, the negative electrode first mixture layer is provided in the center region in the width direction orthogonal to the winding direction of the electrode, and the negative electrode second mixture layer is formed at both ends of the negative electrode first mixture layer in the width direction. Is provided. The negative electrode first mixture layer includes a negative electrode active material having a large particle size and a negative electrode active material having a small particle size, and the negative electrode second mixture layer includes the negative electrode active material having a large particle size or the negative electrode active material having a small particle size. Contains one of the active materials. With this configuration, it is possible to improve cycle characteristics and high temperature holding characteristics.

For high temperature retention characteristics, it is important to reduce the surface reaction on the surface of the negative electrode active material during storage. As one of the countermeasures, it is conceivable to lower the specific surface area and reduce the reaction area. As a method for reducing the specific surface area, it is possible to improve the high-temperature holding characteristics by disposing a negative electrode active material having a relatively large particle size.

On the other hand, a negative electrode active material having a small particle size is considered effective for cycle life characteristics. The shape of natural graphite particles that are usually pressed is deformed into an ellipse, for example. As a result, the graphite particles expand and contract in the film thickness direction of the negative electrode mixture layer by charging and discharging. Considering the amount of displacement of the graphite particles at that time, it is considered that the smaller the particle size, the smaller the amount of displacement. An advantage of a small particle size is that the binding point can be increased. By disposing a negative electrode active material with a small particle diameter having the above-mentioned merit, cycle life characteristics can be improved.

Therefore, in the present invention, it is possible to achieve both cycle characteristics and high-temperature holding characteristics by disposing the negative electrode first mixture layer 12A containing the active material having a different particle diameter on the negative electrode 11.

Also, depending on the battery design conditions, the region near the center with respect to the width direction of the electrode is likely to be affected by a cycle life test in which charge and discharge are repeated and is likely to deteriorate. In the present invention, it is possible to reduce the life deterioration of this region by disposing the first mixture layer in the central region and using the first mixture layer as a mixed layer of particles having different particle diameters.

By mixing two types of particles having different median diameters (D ₅₀ ) in the first negative electrode mixture layer, a negative electrode active material having a small particle diameter effective for cycle characteristics and a particle diameter effective for high-temperature storage characteristics A life characteristic as a battery can be improved by mixing a large negative electrode active material. Moreover, the characteristic which raises the adhesive force with an electrode is mentioned. The median diameter (D ₅₀ ) is smaller than the median diameter (D ₅₀ ), and by mixing them, small particles are arranged in the gaps between the large particles. It is considered that the binding property is improved. In addition, since an anchor-like effect of particles having a large particle size can be expected, there is a possibility of increasing the binding force between the electrode and the active material.

Furthermore, by mixing particles having different particle diameters, it becomes possible to make the void size uniform in the negative electrode first mixture layer and increase the number of voids. As a result, it is considered that the permeability of the electrolytic solution becomes higher and it is possible to reduce the depletion of the electrolytic solution. When particles having different particle sizes are mixed, the larger the difference in particle size, the wider the particle size distribution.

Furthermore, it is preferable that the first negative electrode mixture layer 12A is disposed in a central region in the width direction orthogonal to the winding direction of the electrode considered to be easily affected by the cycle life test. When the surface of the negative electrode after the cycle life test is observed, deterioration near the center in the width direction perpendicular to the winding direction is observed. In the present invention, it is possible to improve cycle life characteristics by arranging a mixture layer having active materials having different particle diameters in the above-described region.

Further, if necessary, the negative electrode first mixture layer is formed slightly thicker than the negative electrode second mixture layer, so that deterioration due to the cycle life test can be reduced.

Commercially available graphite can be used for the two types of active materials contained in the first negative electrode mixture layer 12A. Among these, graphite having a particle size of 45 μm or less is used, and the median diameter (D ₅₀ ) is 5 μm or more and 15 μm or less for graphite having a small particle size, and is larger than 15 μm and 45 μm or less, preferably 15 μm for graphite having a large particle size. A size larger than 35 μm is used. When the median diameter (D ₅₀ ) is larger than 35 μm, influences such as a decrease in dispersibility in the coating slurry and a decrease in discharge capacity density can be considered. On the other hand, when the particle size is smaller than 5 μm, there may be a problem that a special manufacturing method is required for powder production, or that the difficulty of preparing a coating negative electrode mixture slurry is increased.

The larger the particle size difference between the large particle size particle and the small particle size, the higher the effect. The larger the particle size difference is, the larger the particle size, the larger the particle size of the active material. Further, it is conceivable that the contact between the particles is reduced due to the expansion and contraction of the particles having a large particle size accompanying the charging and discharging of the battery, and the conductivity is lowered. Since particles having a small particle diameter serve as an electron bridge, a decrease in conductivity can be prevented. For this reason, it is preferable that the negative electrode active material having a small particle diameter is 5 to 10 μm with respect to the median diameter (D ₅₀ ) of 20 to 40 μm having a large particle size. Furthermore, in consideration of the volume of the space generated when particles having a large particle diameter are densely packed, the negative electrode active material having a small particle diameter with respect to the medium diameter (D ₅₀ ) of 30 to 40 μm having a large particle diameter. The median diameter (D ₅₀ ) is preferably 5 to 8 μm. The average particle size of the negative electrode active material having a large particle size is 1.5 times or more, preferably 2.5 times or more, more preferably 3.0 times or more than the average particle size of the negative electrode active material having a small particle size.

Since the negative electrode first mixture layer includes a negative electrode active material having a large particle size and a negative electrode active material having a small particle size, a negative electrode active material having a large particle size and a particle size are included in the production process of the negative electrode first mixture layer. The process of mixing a small negative electrode active material of this, and manufacturing a slurry is included. This step may be a step of simultaneously mixing a binder or the like and two types of negative electrode active materials, a step of mixing two types of negative electrode active materials in advance, and a mixture of two types of negative electrode active materials with a binder or the like. The mixing process may be divided, and the order and timing of mixing are not particularly limited. Moreover, you may add a electrically conductive material to the said mixture layer as needed.

A negative electrode second mixture layer containing either one of a negative electrode active material having a large particle diameter or a negative electrode active material having a small particle diameter is disposed on both edges of the negative electrode first mixture layer. For example, when emphasizing the high-temperature holding characteristics as the battery specifications, the characteristics can be improved by using an active material having a median diameter (D ₅₀ ) larger than 15 μm and not larger than 35 μm. Further, when the cycle life characteristics are regarded as important, the use of an active material having a median diameter (D ₅₀ ) of 5 μm or more and 15 μm or less can further improve the respective characteristics.

Also, as one of the effects of disposing the negative electrode second mixture layer on both edges, the electrolyte penetration into the electrode center can be considered. For example, by disposing a negative electrode second mixture layer of particles having a larger particle diameter or smaller particle diameter than the negative electrode first mixture layer at both ends of the negative electrode first mixture layer. Since the void ratio between the particles increases, it is considered that the electrolyte solution can be easily supplied to the negative electrode first mixture layer disposed near the center in the electrode width direction.

The ratio of the negative electrode first mixture layer in the central region to the electrode width is 30% or more including the center, desirably 30 to 80% or less. This is because if the proportion of the negative electrode first mixture layer is less than 30%, it is difficult to compensate for the area that is damaged in the cycle life test. Moreover, it is because possibility that the effect which arrange | positions an above described negative electrode 2nd mixture layer will reduce will be considered when it becomes 80% or more.

<Negative electrode active material>
In one embodiment of the present invention, a graphite-based material such as natural graphite is used for the negative electrode active material. Since natural graphite has higher crystallinity than artificial graphite, a high capacity close to the theoretical capacity can be obtained. In addition, it has been put into practical use with features such as low initial charge irreversible capacity and low price. On the other hand, it has problems such as insufficient cycle characteristics.

Therefore, the negative electrode 13 having both high capacity, cycle characteristics, and high temperature holding characteristics by disposing the negative electrode first mixture layer 12A mixed with active materials having different particle sizes, such as one embodiment of the present invention. Is obtained. Further, by using the negative electrode 13 described above, it is possible to provide a lithium ion secondary battery having a high capacity and excellent cycle characteristics and high temperature holding characteristics. Natural graphite having various surface modifications may be used. Furthermore, crystalline artificial graphite or highly crystalline graphite close to natural graphite may be used as the graphite material.

In addition, as the negative electrode active material used for the negative electrode first mixture layer 12A and the negative electrode first mixture layer 12B, workability is improved by using the same type of negative electrode active material. In particular, when producing a negative electrode by one press working, the same kind is desirable. Moreover, it is desirable to make it the same kind also from a viewpoint of battery characteristics.

As a manufacturing method of the negative electrode 13, a method of simultaneously applying and drying the negative electrode first mixture layer 12 A and the second negative mixture layer 12 B on the negative electrode 11 using a die coater or the like having a necessary number of discharge ports is press-processed. Can be used. Further, the negative electrode first mixture layer and the negative electrode second mixture layer are separately applied and dried, that is, the negative electrode first mixture layer is applied and dried on the negative electrode 11, and then the negative electrode second mixture layer is formed. A method of applying, drying and pressing the mixture layer can also be employed. Moreover, the process of apply | coating a negative electrode 1st mixture layer and the process of apply | coating a negative electrode 2nd mixture layer separately, and drying and press-processing after that can also be used. Furthermore, a manufacturing method in which the negative electrode first mixture layer and the negative electrode second mixture layer are separately applied, dried, and pressed can be used. From the viewpoint of simplifying the production process, a production method in which the negative electrode first mixture layer and the negative electrode second mixture layer are simultaneously applied, dried and pressed is preferred.

<Positive electrode active material>
As the positive electrode active material used in the present invention, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ can be generally used. In addition, LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , Li ₄ Mn ₅ O ₁₂ , LiMn _{2 -x} M _x O ₂ (where M = Co, Ni, Fe, Cr, Zn, Ta, where x = 0.01 to 0.2), Li ₂ Mn ₃ MO ₈ (where M = Fe, Co, Ni, Cu, Zn), Li _1-x A _x Mn ₂ O ₄ (where A = Mg, B, Al, Fe, Co, Ni, Cr, Zn, Ca, and x = 0.01) 0.1), LiNi _1-x M _x O ₂ (where M = Co, Fe, Ga and x = 0.01-0.2), LiFeO ₂ , Fe ₂ (SO ₄ ) ₃ , _{_{_{LiCo 1-x M x O 2}}} ( however, M = Ni, Fe, a Mn, x = 0.01 ~ 0.2) , LiNi 1-x M x O 2 However, M = Mn, Fe, Co , Al, Ga, Ca, a Mg, x = 0.01 ~ 0.2) , Fe (MoO 4) 3, FeF 3, using, for example, LiFePO _4, LiMnPO ₄ can do.

<Binder>
The type of binder used in each electrode mixture layer is not particularly limited, and is generally high, such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl pyridine, etc., which are generally used for preparing electrodes of lithium ion batteries. Any one or more of the molecular materials can be used. Further, an aqueous binder capable of using, as a diluent, water represented by any one or more of styrene-butadiene rubber (SBR), polyacrylate and the like may be used.

The binder contained in each electrode mixture layer has an optimum composition depending on the type of binder, but in the case of an aqueous binder represented by styrene-butadiene rubber (SBR), if the binder concentration is less than 0.8% by weight. In addition, the binding force between the active materials may be reduced, which may adversely affect the production of the electrode. If the binder concentration is more than 2.0% by weight, the resistance between the electrodes is increased, so that the binder concentration is less than 0.2%. The content is desirably 8 to 2.0% by weight. Further, when styrene-butadiene rubber (SBR) is used, carboxymethyl cellulose (CMC) is used in an amount equivalent to SBR as a viscosity modifier.

<Separator>
The separator used for this invention can use the separator currently used for the well-known lithium ion battery. Examples thereof include microporous films made of polyolefin such as polyethylene and polypropylene, and nonwoven fabrics. From the viewpoint of increasing the capacity of the battery, the thickness of the separator is preferably 30 μm or less, and more preferably 18 μm or less.

<Production of negative electrode>
Hereinafter, description will be made with reference to FIGS. 1 and 2.

A negative electrode mixture layer 12 A and a negative electrode mixture layer 12 B were formed on the copper foil of the negative electrode 11. Specifically, natural graphite having a median diameter (D ₅₀ ) = 20 μm and natural graphite having a median diameter (D ₅₀ ) = 10 μm as a negative electrode active material of the negative electrode first mixture layer, a negative electrode Natural graphite having a median diameter (D ₅₀ ) = 20 μm was used as the negative electrode active material of the second mixture layer. Styrene-butadiene rubber (SBR) as a binder and carboxymethyl cellulose (CMC) as a viscosity modifier were used in an amount equivalent to SBR. Graphite and binder were mixed at a mixing ratio of 98.0: 2.0, and water was added for viscosity adjustment to prepare two types of negative electrode mixture slurry. Next, this negative electrode mixture slurry is applied on the negative electrode 11 of a copper foil having a thickness of 10 μm, dried with hot air at 110 ° C., and then the negative electrode mixture layer 12 is formed on the back using the negative electrode mixture slurry. did. In this example, the negative electrode first mixture layer 12A and the negative electrode second mixture layer were applied simultaneously. The coating was performed using a coating apparatus provided with three discharge ports and two containers for storing slurry.

The negative electrode mixture layer 12 formed on both surfaces of the electrode was pressed by roll rolling to adjust the single-sided film thickness of the negative electrode mixture layer 12 to 55 μm, and the negative electrode mixture layer 12 was produced.

<Preparation of positive electrode>
LiMn _1/3 Ni _1/3 Co _1/3 O ₂ was used as the positive electrode active material. Carbon black (CB1) and graphite (GF2) were dry mixed as the positive electrode active material and the electronic conductive material. A mixture of the mixture and polyvinylidene fluoride (PVDF) as a binder and N-methylpyrrolidone (NMP) as a solvent were added and mixed to prepare a positive electrode mixture slurry. Incidentally, these solid weight ratio after drying of _{_{_{_{LiMn 1/3 Ni 1/3 Co 1/3 O 2}}}} : CB1: GF2: PVDF = 86: 9: 2: was blended so that 3. Next, the positive electrode mixture slurry was applied to both surfaces of the positive electrode 14 made of an aluminum foil having a thickness of 15 μm, dried at 120 ° C., and then pressed by roll rolling to produce the positive electrode 16.

<Winding / Assembly>
For the separator of this example, a microporous film made of polyethylene was used.

Also, ethylene carbonate (EC), vinylene carbonate (VC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are prepared, and the volume composition ratio thereof is EC: VC: DMC: EMC = 19.8: 0 as a solvent. .2: 40: 40 was used, and 1M was dissolved using LiPF6 as a solute lithium salt to prepare an electrolytic solution 115 (organic electrolytic solution).

A separator 17 was sandwiched between the positive electrode 16 and the negative electrode 13 manufactured by the manufacturing method, and a wound group was formed and inserted into the negative battery can 113. Then, one end of a nickel (Ni) negative electrode lead 19 was welded to the negative electrode 11 and the other end was welded to the battery can 113 in order to collect the negative electrode 13. In addition, one end of an aluminum (Al) positive electrode lead 18 is welded to the positive electrode 14 in order to collect current from the positive electrode 16, and the other end is subjected to current interruption welding, and further via a current interruption valve (not shown). The positive electrode battery lid 112 was electrically connected. Then, the electrolytic solution 115 is poured into the battery can 113, the positive electrode 16, the negative electrode 13, and the separator 17 are immersed in the electrolytic solution 115, and the opening of the battery can 113 is caulked by a caulking machine or the like. A rechargeable secondary battery 1100 was manufactured. In FIG. 1, 110 is a positive electrode insulating material, 111 is a negative electrode insulating material, and 114 is a gasket.

The wound type battery of this example was manufactured by the method described below.
<Production of negative electrode>
A negative electrode mixture layer 12 A and a negative electrode mixture layer 12 B were formed on the copper foil of the negative electrode 11. Specifically, natural graphite having a median diameter (D ₅₀ ) = 8 μm and natural graphite having a median diameter (D ₅₀ ) = 30 μm measured by a particle size distribution measurement method as a negative electrode active material of the negative electrode first mixture layer 12A. Natural graphite having a median diameter (D ₅₀ ) = 8 μm was used as the negative electrode active material of the negative electrode second mixture layer 12B. Styrene-butadiene rubber (SBR) as a binder and carboxymethyl cellulose (CMC) as a viscosity modifier were used in an amount equivalent to SBR. Graphite and binder were mixed at a mixing ratio of 97.6: 2.4, and water was added to adjust the viscosity to adjust the viscosity, thereby preparing two types of negative electrode mixture slurry. Next, each negative electrode mixture slurry was applied onto a copper foil negative electrode 11 having a thickness of 10 μm, dried with hot air at 110 ° C., and then the negative electrode mixture layer 12 was formed on the back using the negative electrode mixture slurry. did. Pressing by roll rolling was performed so that the single-sided film thickness of the negative electrode mixture layer 12 was adjusted to 50 μm.

The positive electrode 16 and the wound secondary battery 1100 were manufactured in the same manner as in Example 1.

The wound type battery of this example was manufactured by the method described below.
<Production of negative electrode>
A negative electrode mixture layer 12 A and a negative electrode mixture layer 12 B were formed on the copper foil of the negative electrode 11. Specifically, natural graphite having a median diameter (D ₅₀ ) = 8 μm and natural graphite having a median diameter (D ₅₀ ) = 30 μm measured by a particle size distribution measurement method as a negative electrode active material of the negative electrode first mixture layer 12A. Natural graphite having a median diameter (D ₅₀ ) = 8 μm was used as the negative electrode active material of the negative electrode second mixture layer 12B. Polyvinylidene fluoride (PVDF) as a binder is blended so that the solid content weight ratio upon drying is natural graphite: PVDF = 95: 5, and N-methylpyrrolidone (NMP) is added as a solvent, and a negative electrode mixture slurry Was made. Next, each negative electrode mixture slurry was applied onto a copper foil negative electrode 11 having a thickness of 10 μm, dried with warm air at 120 ° C., and then the negative electrode mixture layer 12 was formed on the back using the negative electrode mixture slurry. did. Pressing by roll rolling was performed so that the single-sided film thickness of the negative electrode mixture layer 12 was adjusted to 50 μm.

The positive electrode 16 and the wound secondary battery 1100 were manufactured in the same manner as in Example 1.

[Comparative Example 1]
In Comparative Example 1, natural graphite having a median diameter (D ₅₀ ) = 20 μm was used, and only the negative electrode second mixture layer 12B was applied to both surfaces of the electrode 11 as a single layer. In addition, the negative electrode 13 was made to be the same as the manufacturing method of the negative electrode second layer 12B of Example 1. The positive electrode 16 and the wound-type secondary battery 1100 were manufactured in the same manner as in Example 1.

[Comparative Example 2]
In Comparative Example 2, a single layer coating of only the negative electrode second mixture layer 12 B on both surfaces of the electrode 11 using natural graphite having a median diameter (D ₅₀ ) = 8 μm. In addition, the negative electrode 13 was made to be the same as the manufacturing method of the negative electrode second layer 12B of Example 1. The positive electrode 16 and the wound-type secondary battery 1100 were manufactured in the same manner as in Example 1.

[Comparative Example 3]
Comparative Example 3 uses the natural graphite having a median diameter (D ₅₀ ) = 10 μm for the negative electrode first mixture layer and the natural graphite having the median diameter (D ₅₀ ) = 20 μm for the negative electrode second mixture layer. It was coated on both sides. In addition, the negative electrode 13 was made to be the same as the manufacturing method of the negative electrode second layer 12B of Example 1. The positive electrode 16 and the wound-type secondary battery 1100 were manufactured in the same manner as in Example 1.

[Comparative Example 4]
Comparative Example 4 uses a natural graphite having a median diameter (D ₅₀ ) = 30 μm for the negative electrode first mixture layer and a natural graphite having a median diameter (D ₅₀ ) = 8 μm for the negative electrode second mixture layer. It was coated on both sides. In addition, the negative electrode 13 was made to be the same as the manufacturing method of the negative electrode second layer 12B of Example 1. The positive electrode 16 and the wound-type secondary battery 1100 were manufactured in the same manner as in Example 1.

Cycle characteristics (life characteristics) of the wound lithium ion secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 4 manufactured by the above manufacturing method were evaluated using a cycle test. The cycle test conditions were as follows: the secondary battery was charged to 4.1 V with a charging current of 1 A (1 C), charged to a constant voltage of 4.2 V, stopped for 15 minutes, and then discharged with a discharging current of 1 A (1 C). The battery was discharged to 3.0 V and the operation was stopped for 15 minutes. This charging / discharging was performed 500 cycles, and the capacity change of the secondary battery before and after the cycle test was verified.

Table 1 shows the cycle test of the wound type lithium ion secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2 and the results of high temperature storage characteristics at 50 ° C.

The capacity retention ratios in the table are values when the discharge capacity before the cycle test of each wound battery is 100 and the capacity before storage at 50 ° C. is 100.

As shown in Table 1, as a result of the cycle test, the capacity retention rate after the elapse of 500 cycles in the lithium ion secondary batteries of Examples 1 to 3 was 82 to 88%. Further, the capacity retention rate after the elapse of 500 cycles in the secondary batteries of Comparative Examples 1 and 2 was 57 to 70%.

Further, the capacity retention rate of the storage characteristics at 50 ° C. in the lithium ion secondary batteries of Examples 1 to 3 was 85 to 93%. Further, the capacity retention ratio% of the storage characteristics at 50 ° C. in the secondary batteries of Comparative Examples 1 and 2 was 59 to 68%.

In comparison between Examples 1 to 3 and the secondary batteries of Comparative Examples 3 and 4, since the negative electrode first mixture layer is an active material having one kind of particle size, Comparative Example 3 has high temperature storage characteristics. A decrease was seen. In Comparative Example 4, the cycle characteristics were lower than in the example. It was found that it is difficult to satisfy both cycle characteristics and storage characteristics with a single particle alone.

From the above results, in the lithium ion secondary batteries of Examples 1 to 3, the negative electrode first mixture layer made of large and small negative electrode active materials having different particle diameters was formed in the central region in the width direction perpendicular to the electrode winding direction. The capacity of the secondary battery after cycle is maintained by disposing a negative electrode second mixture layer made of an active material having a large particle size or a small particle size at both ends so as to be in contact with the negative electrode first mixture layer. It has been demonstrated that the rate has improved significantly. Further, regarding the high temperature storage characteristics at 50 ° C., the effect of reducing the specific surface area to reduce the reaction area could be achieved, and as a result, it was demonstrated that the capacity retention rate of the high temperature storage characteristics was greatly improved.

The present invention is not limited to the first to third embodiments described above, and includes various modifications. For example, the first to third embodiments described above are described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described.
Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Furthermore, it is possible to add, delete, and replace other configurations for some of the configurations of the first to sixth embodiments.

DESCRIPTION OF SYMBOLS 11 Negative electrode 12 Negative electrode mixture layer 12A Negative electrode 1st mixture layer 12B Negative electrode 2nd mixture layer 13 Negative electrode 14 Positive electrode 15 Positive mix layer 16 Positive electrode 17 Separator 18 Positive electrode lead 19 Negative electrode lead 110 Positive electrode insulating material 111 Negative electrode insulating material 112 Positive battery cover 113 Battery can 114 Gasket 115 Electrolytic solution 1100 Secondary battery

Claims

A negative electrode mixture layer is provided on the surface of the negative electrode,
The negative electrode mixture is a lithium ion secondary battery having negative electrode active material particles capable of occluding and releasing lithium ions.
The negative electrode has a first negative electrode mixture layer at the center in the width direction perpendicular to the winding direction of the negative electrode,
The negative electrode has a negative electrode mixture layer at both ends in the width direction of the negative electrode mixture layer,
The negative electrode active material contained in the negative electrode first mixture layer is a mixture of a negative electrode active material having a large particle size and a negative electrode active material having a small particle size,
The lithium ion secondary battery, wherein the negative electrode active material contained in the negative electrode second mixture layer is the negative electrode active material having a large particle size or the negative electrode active material having a small particle size.
In claim 1,
The negative electrode for a lithium ion secondary battery, wherein the negative electrode active material having a large particle size has an average particle size of 15 μm or more and 45 μm or less, and the negative electrode active material having a small particle size has an average particle size of 5 μm or more and less than 15 μm.
In claim 2,
The negative electrode for a lithium ion secondary battery, wherein the negative electrode active material having a large particle size has an average particle size of 20 μm or more and 40 μm or less, and the negative electrode active material having a small particle size has an average particle size of 5 μm or more and less than 10 μm.
In any one of Claims 1 to 3,
The proportion of the negative electrode first mixture layer in the width direction perpendicular to the winding direction of the negative electrode is relative to the total width of the negative electrode first mixture layer and the negative electrode second mixture layer. A lithium ion secondary battery that is 30% or more.
In claim 4,
The proportion of the negative electrode first mixture layer in the width direction perpendicular to the winding direction of the negative electrode is relative to the total width of the negative electrode first mixture layer and the negative electrode second mixture layer. A lithium ion secondary battery that is 30% to 80%.
In any one of Claims 1 thru | or 6,
The negative electrode active material is a lithium ion secondary battery that is graphite.
In any one of Claims 1 to 2,
The lithium ion secondary battery includes a step of mixing a negative electrode active material having a large particle size and a negative electrode active material having a small particle size in the manufacturing process of the negative electrode first mixture layer.
In any one of Claims 1 thru | or 7,
The negative electrode first mixture layer or the negative electrode second mixture layer has a binder,
The negative electrode for a lithium ion secondary battery, wherein the binder is a binder capable of using water as a diluent.
In claim 8,
The binder is a negative electrode for a lithium ion secondary battery, wherein the binder is at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene, and polyvinylpyridine.
A method for producing a negative electrode for a lithium ion secondary battery according to any one of claims 1 to 9, comprising the following steps (1) and (2): .
(1) The edge region on the negative electrode is coated with a negative electrode active material having a large particle diameter or a negative electrode mixture slurry containing a negative electrode active material having a small particle diameter, dried, and pressed to form the edge. Forming a negative electrode mixture layer in the region;
(2) After the step (1), a negative electrode mixture slurry containing the negative electrode active material having a large particle size and the negative electrode active material having a small particle size is applied, dried, and further pressed to form a negative electrode in the central region. A step in which a mixture layer is formed.
A method for producing a negative electrode for a lithium ion secondary battery according to any one of claims 1 to 9,
A negative electrode mixture slurry containing the negative electrode active material having a large particle size and the negative electrode active material having a small particle size is applied to a central region in the width direction of the negative electrode, and the negative electrode active material having a large particle size is applied to both end regions. Or the manufacturing method of the negative electrode for lithium ion secondary batteries which has the process of apply | coating the negative mix slurry containing either of the said negative electrode active materials with a small particle size, and drying after that.
A method for producing a negative electrode for a lithium ion secondary battery according to any one of claims 1 to 9,
A step of applying a negative electrode mixture slurry containing the negative electrode active material having a large particle size and the negative electrode active material having a small particle size to a central region in the width direction of the negative electrode, and a negative electrode having a large particle size in regions at both ends thereof The manufacturing method of the negative electrode for lithium ion secondary batteries which has the process of performing simultaneously the process of apply | coating the negative mix slurry containing either an active material or the said negative electrode active material with a small particle size, and drying after that.
In any one of Claims 1 thru | or 9,
The lithium ion secondary battery includes a positive electrode,
A separator interposed between the positive electrode and the negative electrode;
An organic electrolyte that immerses the positive electrode, the negative electrode, and the separator;
A lithium ion secondary battery comprising: