JP2009158335A - Negative pole plate for non-aqueous electrolyte secondary cell, manufacturing method therefor, and non-aqueous electrolyte secondary cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative pole plate for a non-aqueous electrolyte secondary cell excellent in cycle characteristics, a manufacturing method therefor, and a non-aqueous electrolyte secondary cell. <P>SOLUTION: The negative pole plate for a non-aqueous electrolyte secondary cell is formed with a negative pole mixture layer that includes a negative active substance composed of a carbonaceous material, on the surface of a negative pole axis body, wherein the negative pole mixture layer includes at least two layers, a negative pole mixture layer of a first layer on the negative pole axis body side contains lithium with higher concentration than that of a negative pole mixture layer of another layer, and the volume shared by the negative pole mixture layer of the first layer is 30 to 65 percent of that of the entire negative pole mixture layer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a negative electrode plate for a nonaqueous electrolyte secondary battery having good cycle characteristics, a method for producing the same, and a nonaqueous electrolyte secondary battery using the negative electrode plate.

  Non-aqueous electrolyte secondary typified by lithium-ion secondary battery with high energy density and high capacity as a driving power source for portable electronic devices such as mobile phones, portable personal computers, portable music players, etc. Batteries are widely used. Among these, nonaqueous electrolyte secondary batteries using particles of a carbonaceous material such as graphite as a negative electrode active material are widely used because of their high safety and high capacity.

  By the way, in a device in which this type of non-aqueous electrolyte secondary battery is used, the space for accommodating the battery is often a square (flat box shape), so the power generation element is accommodated in a rectangular outer can. The formed rectangular nonaqueous electrolyte secondary battery is often used. Such a rectangular non-aqueous electrolyte secondary battery is generally manufactured as follows.

  That is, a negative electrode plate in which a negative electrode mixture containing a negative electrode active material is applied to both sides of a negative electrode core made of a long sheet-like copper foil, and a positive electrode on both sides of a positive electrode core made of a long, thin sheet-like aluminum foil A positive electrode plate coated with a positive electrode mixture containing an active material is prepared. A separator made of a microporous polyethylene film or the like is disposed between the negative electrode plate and the positive electrode plate, and the negative electrode plate and the positive electrode plate are insulated from each other by the separator in a spiral shape on a cylindrical core. A cylindrical wound electrode body is produced by winding. Next, the cylindrical electrode body is crushed with a press machine and formed into a shape that can be inserted into a rectangular battery outer can. Then, the cylindrical electrode body is accommodated in the rectangular outer can, and an electrolytic solution is poured into the rectangular non-aqueous battery. It is an electrolyte secondary battery.

  The configuration of such a conventional rectangular nonaqueous electrolyte secondary battery will be described with reference to the drawings. FIG. 1 is a perspective view showing a rectangular nonaqueous electrolyte secondary battery disclosed in Patent Document 1 below, cut in the vertical direction. In this nonaqueous electrolyte secondary battery 10, a flat wound electrode body 14 in which a positive electrode plate 11 and a negative electrode plate 12 are wound via a separator 13 is accommodated in a rectangular battery outer can 15. The battery outer can 15 is sealed with a sealing plate 16. The wound electrode body 14 is wound so that the positive electrode plate 11 is exposed at the outermost periphery, and the exposed outermost positive electrode plate 11 is formed on the inner surface of the battery outer can 15 that also serves as a positive electrode terminal. Direct contact and electrical connection. The negative electrode plate 12 is formed at the center of the sealing plate 16 and is electrically connected to a negative electrode terminal 18 attached via an insulator 17 via a current collector 19.

  Since the battery outer can 15 is electrically connected to the positive electrode plate 11, in order to prevent a short circuit between the negative electrode plate 12 and the battery outer can 15, the upper end of the wound electrode body 14 and the sealing plate The insulating spacer 20 is inserted between the negative electrode plate 12 and the battery outer can 15 so as to be electrically insulated. In this rectangular nonaqueous electrolyte secondary battery, after the wound electrode body 14 is inserted into the battery outer can 15, the sealing plate 16 is laser welded to the opening of the battery outer can 15, and then the electrolyte injection hole 21. The nonaqueous electrolytic solution is injected from the above, and the electrolytic solution injection hole 21 is sealed. Such a rectangular non-aqueous electrolyte secondary battery has an excellent effect that there is little wasted space during use, and the battery performance and battery reliability are high.

  As a negative electrode active material used in this non-aqueous electrolyte secondary battery, carbonaceous materials such as graphite and amorphous carbon are widely used. The reason is that the carbonaceous material has a discharge potential comparable to that of lithium metal or lithium alloy, but has high safety because dendrites do not grow, and further has excellent initial efficiency and good potential flatness. Moreover, it is because it has the outstanding property that density is also high.

As a positive electrode active material in this nonaqueous electrolyte secondary battery, Li _x MO ₂ capable of reversibly inserting and extracting lithium ions (where M is at least one of Co, Ni, and Mn) A lithium transition metal composite oxide represented by: LiCoO ₂ , LiNiO ₂ , LiNi _y Co _1-y O ₂ (y = 0.01 to 0.99), LiMnO ₂ , LiMn ₂ O ₄ , LiCo _x Mn _y Ni _z O ₂ (x + y + z = 1), LiFePO ₄ or the like is used singly or in combination.
JP 2001-273931 A

  These nonaqueous electrolyte secondary batteries can achieve higher capacity and higher energy density than other types of batteries. However, due to the demand for higher performance, smaller size, and lighter weight of the portable electronic device as described above, further increase in capacity is desired. As a method for increasing the capacity of this non-aqueous electrolyte secondary battery, there is a method for increasing the packing density of the mixture layer containing the active material. However, when the packing density of the mixture layer containing the active material is increased, voids in the mixture layer containing the active material are reduced, and the amount of electrolyte that can be held in the mixture layer containing the active material is reduced. . In particular, on the core side of the mixture layer containing the active material, the supply amount of the electrolytic solution is smaller than the surface of the mixture layer containing the active material, so that the concentration of lithium ions decreases near the surface of the core body. The battery reaction in the mixture layer containing the active material becomes non-uniform and appears as deterioration of cycle characteristics. Such a decrease in the concentration of lithium ions in the vicinity of the surface of the core appears more greatly in the case of a negative electrode mixture containing a negative electrode active material having a density lower than that of the positive electrode active material because the degree of rolling is higher. .

  The inventor has conducted various experiments to solve the problems of the prior art, and as a result, can be solved by adding a large amount of lithium salt to the negative electrode mixture layer on the negative electrode core body side during the production of the negative electrode plate. As a result, the present invention has been completed.

  That is, an object of the present invention is to provide a negative electrode plate from which a nonaqueous electrolyte secondary battery having good cycle characteristics can be obtained, a method for producing the same, and a nonaqueous electrolyte secondary battery using the negative electrode plate.

In order to achieve the above object, the negative electrode plate for a non-aqueous electrolyte secondary battery of the present invention is a non-aqueous electrolyte secondary battery in which a negative electrode mixture layer containing a negative electrode active material made of a carbonaceous material is formed on the surface of a negative electrode core. In the negative electrode plate for secondary batteries,
The negative electrode mixture layer comprises at least two layers,
The first negative electrode mixture layer on the negative electrode core side contains a higher concentration of lithium salt than the other negative electrode mixture layers, and the volume occupied by the first negative electrode mixture layer is It is 30% or more and 65% or less of the volume of the whole negative electrode mixture layer.

  The negative electrode plate for a non-aqueous electrolyte secondary battery of the present invention has a negative electrode mixture layer containing a negative electrode active material made of a carbonaceous material formed on the surface of a negative electrode core, having at least a two-layer structure. The first negative electrode mixture layer contains a lithium salt having a higher concentration than the other layers. The carbonaceous material is conventionally used as a negative electrode active material of a nonaqueous electrolyte secondary battery, but has a density lower than that of the positive electrode active material. For this reason, the negative electrode mixture layer containing a negative electrode active material made of a carbonaceous material is rolled at a high rate in order to increase the packing density, so that the retention property of the electrolytic solution is reduced.

  However, according to the negative electrode plate for a non-aqueous electrolyte secondary battery of the present invention, a high-concentration lithium salt is contained in advance in the negative electrode mixture layer on the negative electrode core side. Even if charging / discharging is repeated, the lithium ion is present at a high concentration in the vicinity of the negative electrode core, so that the cycle characteristics are good. In addition, when charging / discharging is repeated, the lithium compound in the non-aqueous electrolyte of the non-aqueous electrolyte secondary battery and the lithium compound in the negative electrode mixture layer are mixed with each other. However, even after charging / discharging for about 500 cycles, A state in which the lithium ion concentration in the first negative electrode mixture layer is high can be maintained.

  In the negative electrode plate for a non-aqueous electrolyte secondary battery of the present invention, the volume occupied by the first negative electrode mixture layer is 30% or more and 65% or less of the volume of the total negative electrode mixture layer. ing. If the volume ratio of the first negative electrode mixture layer is less than 30%, the cycle characteristics decrease in proportion to the decrease in the ratio, and if it exceeds 30%, the effect of improving the cycle characteristics is saturated, If it exceeds 65%, the cycle characteristics deteriorate. In the negative electrode plate for a non-aqueous electrolyte secondary battery of the present invention, the negative electrode mixture layer formed on the surface of the first negative electrode mixture layer may be one layer or two or more layers. Good. Furthermore, these negative electrode mixture layers may be formed only on one side of the negative electrode core or on both sides.

In the negative electrode plate for a nonaqueous electrolyte secondary battery of the present invention, as the lithium _{salt, LiPF 6, LiBF 4, LiCF} 3 SO 3, LiN (CF 3 SO 2) 2, LiN (C 2 F 5 SO _{2) 2, LiN (CF 3} SO 2) (C 4 F 9 SO 2), LiC (CF 3 SO 2) 3, LiC (C 2 F 5 SO 2) 3, LiAsF 6, LiClO 4, Li 2 B 10 It is preferable to include at least one selected from Cl ₁₀ and Li ₂ B ₁₂ Cl ₁₂ .

  These lithium salts are conventionally used as solutes in the non-aqueous electrolyte solution of the non-aqueous electrolyte secondary battery. In the present invention, any of these lithium salts can be used to achieve a predetermined effect. Can be played.

  In the negative electrode plate for a nonaqueous electrolyte secondary battery of the present invention, the lithium salt is dissolved in a gelled organic solvent (nonaqueous solvent) in the first negative electrode mixture layer. It is preferable that it is contained.

  When lithium salt is contained in the gelled organic solvent and contained in the first negative electrode mixture layer, even if charge and discharge are repeated, the first negative electrode mixture layer The lithium salt is difficult to diffuse into the other layers of the negative electrode mixture layer and the non-aqueous electrolyte. Therefore, according to the negative electrode plate for a nonaqueous electrolyte secondary battery of the present invention, the cycle characteristics are further improved.

Furthermore, the method for producing a negative electrode plate for a nonaqueous electrolyte secondary battery according to the present invention is a nonaqueous electrolyte secondary battery in which a negative electrode mixture layer containing a negative electrode active material made of a carbonaceous material is formed on the surface of a negative electrode core. In the manufacturing method of the negative electrode plate for
Forming a first negative electrode mixture layer on the surface of the negative electrode core;
Applying and impregnating an organic solvent solution containing a lithium salt on the surface of the first negative electrode mixture layer;
At least one negative electrode mixture layer is formed on the surface of the first negative electrode mixture layer impregnated with the organic solvent solution containing the lithium salt, and the volume occupied by the first negative electrode mixture layer is the entire volume. Forming the negative electrode mixture layer so as to be 30% to 65% of the volume of the negative electrode mixture layer;
Next, a step of rolling so as to have a predetermined thickness,
It is characterized by providing.

  When an organic solvent solution containing a lithium salt is applied to the surface of the negative electrode mixture layer, this non-aqueous electrolyte gradually permeates into the negative electrode mixture layer. Therefore, according to the method for manufacturing a negative electrode plate for a non-aqueous electrolyte secondary battery of the present invention, the first negative electrode mixture layer on the negative electrode core side easily has a higher concentration than the other negative electrode mixture layers. Thus, it is possible to produce a negative electrode plate for a non-aqueous electrolyte secondary battery that can easily produce the above effects.

  Moreover, in the manufacturing method of the negative electrode plate for nonaqueous electrolyte secondary batteries of this invention, it is preferable that the nonaqueous electrolyte containing the said lithium salt contains the gelatinizer.

  Since the gelation reaction takes time, the gelation is completed after the nonaqueous electrolyte applied to the surface of the first negative electrode mixture layer penetrates into the first negative electrode mixture layer. . Therefore, according to the method for manufacturing a negative electrode plate for a nonaqueous electrolyte secondary battery of the present invention, the lithium salt is easily dissolved in the gelled organic solvent in the first negative electrode mixture layer. The negative electrode plate for a non-aqueous electrolyte secondary battery contained in can be produced.

  In the method for producing a negative electrode plate for a non-aqueous electrolyte secondary battery of the present invention, the concentration of the lithium salt in the organic solvent solution containing the lithium salt is the non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery. It is preferable that it is higher than the lithium salt concentration in the electrolytic solution.

  If the concentration of the lithium salt in the first negative electrode mixture layer is high, the battery reaction can occur uniformly in the negative electrode mixture layer for a longer time. Therefore, according to the method for producing a negative electrode plate for a nonaqueous electrolyte secondary battery of the present invention, a negative electrode plate for a nonaqueous electrolyte secondary battery that can achieve better cycle characteristics can be produced.

Furthermore, the non-aqueous electrolyte secondary battery of the present invention includes a negative electrode plate in which a negative electrode mixture layer including a negative electrode active material made of a carbonaceous material is formed on the surface of a negative electrode core and a positive electrode mixture layer including a positive electrode active material. In a non-aqueous electrolyte secondary battery comprising a positive electrode plate formed on the surface of a positive electrode core and an electrode body wound or laminated with a separator interposed therebetween, and a non-aqueous electrolyte solution,
The negative electrode plate includes at least two negative electrode mixture layers,
The first negative electrode mixture layer on the negative electrode core side contains a higher concentration of lithium salt than the other layers, and the volume occupied by the first negative electrode mixture layer is the total negative electrode mixture layer. It is characterized by being 30% or more and 65% or less of the volume.

  As described above, the nonaqueous electrolyte secondary battery of the present invention is repeatedly charged and discharged because the first negative electrode mixture layer on the negative electrode core side contains a high concentration of lithium salt in advance. However, since lithium ions are present at a high concentration in the vicinity of the negative electrode core, a non-aqueous electrolyte secondary battery with good cycle characteristics is obtained. The nonaqueous electrolyte secondary battery of the present invention can be applied to either a wound electrode body in which a negative electrode plate and a positive electrode plate are wound with a separator interposed therebetween or a laminated electrode body laminated. is there. Of these, the wound electrode body may be not only cylindrical but also flat.

As the positive electrode active material in the nonaqueous electrolyte secondary battery of the present invention, Li _x MO ₂ capable of reversibly occluding and releasing lithium ions (where M is at least Co, Ni, Mn) lithium transition metal composite oxide represented by one kind of), _{i.e., LiCoO 2, LiNiO 2, LiNi} y Co 1-y O 2 (y = 0.01~0.99), LiMnO 2, LiMn 2 O ₄ , LiCo _x Mn _y Ni _z O ₂ (x + y + z = 1), LiFePO ₄ or the like can be used singly or in combination.

  In the nonaqueous electrolyte secondary battery of the present invention, carbonates, lactones, ethers, esters and the like can be used as the organic solvent constituting the nonaqueous electrolyte solution. A mixture of the above can also be used. Among these, carbonates, lactones, ethers, ketones, esters and the like are preferable, and carbonates are more preferably used.

  Specific examples include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), cyclopentanone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, 3-methyl. -1,3-oxazolidine-2-one, dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), methyl propyl carbonate, methyl butyl carbonate, ethyl propyl carbonate, ethyl butyl carbonate, dipropyl carbonate, γ -Butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, 1,4-dio Xanthan can be mentioned.

In addition, as a solute of the nonaqueous electrolyte solution in the present invention, a lithium salt generally used as a solute in a nonaqueous electrolyte secondary battery can be used. Such lithium salts include LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , LiAsF ₆ , LiClO ₄ , Li ₂ B ₁₀ Cl ₁₀ , Li ₂ B ₁₂ Cl ₁₂ , and mixtures thereof Illustrated. Among these, LiPF ₆ (lithium hexafluorophosphate) is preferably used. The amount of solute dissolved in the non-aqueous solvent is preferably 0.5 to 2.0 mol / L.

  In the nonaqueous electrolyte secondary battery of the present invention, it is preferable that the lithium salt is made of the same compound as the solute in the nonaqueous electrolyte solution.

  According to the nonaqueous electrolyte secondary battery of the present invention, it is not necessary to prepare a plurality of particularly different lithium salts, and thus a nonaqueous electrolyte secondary battery that can be produced economically is obtained.

  In the non-aqueous electrolyte secondary battery of the present invention, it is preferable that the lithium salt is contained in the first negative electrode mixture layer in a state dissolved in a gelled organic solvent.

  When lithium salt is contained in the gelled organic solvent and contained in the first negative electrode mixture layer, even if charge and discharge are repeated, the first negative electrode mixture layer The lithium salt is difficult to diffuse into the other layers of the negative electrode mixture layer and the non-aqueous electrolyte. Therefore, according to the nonaqueous electrolyte secondary battery of the present invention, a nonaqueous electrolyte secondary battery with better cycle characteristics is obtained.

  Hereinafter, the best mode for carrying out the present invention will be described in detail using examples and comparative examples. However, the following examples illustrate a negative electrode plate for a non-aqueous electrolyte secondary battery, a manufacturing method thereof, and a non-aqueous electrolyte secondary battery for embodying the technical idea of the present invention. The invention is not intended to be specified in this embodiment, and the present invention can be equally applied to various modifications without departing from the technical idea shown in the claims. .

[Example 1]
The nonaqueous electrolyte secondary battery of Example 1 was produced as follows.

[Production of positive electrode]
90 parts by mass of lithium cobaltate (LiCoO ₂ ) as a positive electrode active material, 5 parts by mass of graphite as a conductive agent, and 5 parts by mass of polyvinylidene fluoride (PVdF) as a binder are N-methyl-2-pyrrolidone To prepare a positive electrode active material slurry. Next, the positive electrode active material slurry was applied to both surfaces of a positive electrode core made of an aluminum foil having a thickness of 15 μm so as to have a uniform thickness by a doctor blade method. The electrode plate was passed through a dryer to remove the organic solvent, and then rolled to a thickness of 125 μm using a roll press to produce a positive electrode plate.

[Production of negative electrode]
A slurry was prepared by dispersing 95 parts by mass of graphite powder as a negative electrode active material and 5 parts by mass of PVdF in water and mixing them uniformly. The slurry was applied to both surfaces of a negative electrode core made of a copper foil having a thickness of 10 μm with a uniform thickness, and then passed through a dryer to remove moisture to form a first negative electrode mixture layer. Then, a non-aqueous mixed solvent was prepared so as to be EC 10% by volume, PC 10% by volume, and MEC 80% by volume. The concentration of 2000 g of the mixed solvent was 1 g of polyalkylene oxide as a gelling agent and LiPF ₆ as a lithium salt. Was dissolved to 1.3 mol / L to obtain an organic solvent solution containing a lithium salt. Next, the organic solvent solution containing the lithium salt was mixed with a predetermined amount of an organic peroxide as a gelation catalyst, and then applied to the surface of the first negative electrode mixture layer by a doctor blade method. After the absorption, the organic solvent solution containing lithium salt was gelled by allowing it to stand for 2 hours in a constant temperature bath maintained at 45 ° C. and drying.

  Further, a slurry in which 95 parts by mass of graphite powder as a negative electrode active material and 5 parts by mass of PVdF are dispersed in water and uniformly mixed on the surface of the first negative electrode mixture layer is mixed with the negative electrode mixture of the second layer. It was applied by a doctor blade method so that the volume of the agent layer was 70% of the volume of the entire negative electrode mixture layer (that is, the volume of the first negative electrode mixture layer was 30% of the entire volume). However, an organic solvent solution containing a lithium salt is not applied to the surface of the second negative electrode mixture layer. Therefore, the first negative electrode mixture layer on the negative electrode core side contains a higher concentration of lithium salt than the second negative electrode mixture layer. Thereafter, the electrode plate was passed through a dryer to remove the organic solvent, and then rolled to a thickness of 120 μm using a roll press to produce a negative electrode plate. As for the amount of the negative electrode mixture applied, the charge capacity ratio (negative electrode charge capacity / positive electrode charge capacity) at the portion where the positive electrode and the negative electrode face each other is 1.1 at the charge voltage (4.2 V) as the design standard. Adjusted as follows.

[Preparation of non-aqueous electrolyte]
A non-aqueous mixed solvent was prepared so as to be EC 10% by volume, PC 10% by volume, and MEC 80% by volume, and LiPF ₆ dissolved therein at a ratio of 1.0 mol / L was used as a non-aqueous electrolyte.

[Preparation of flat wound electrode body]
The positive electrode, negative electrode, and microporous membrane separator made of olefin resin prepared as described above are wound by a winder, and an insulating anti-winding tape is attached to the end of the winding and pressed to make it flat. A spirally wound electrode body was completed.

[Example 1 Production of Battery]
The flat wound electrode body and non-aqueous electrolyte prepared as described above are inserted into a rectangular outer can having the same configuration as that of the conventional example described above, and the sealing plate is aligned with the opening of the outer can. The nonaqueous electrolyte secondary battery according to Example 1 having a height of 45 mm, a width of 54 mm, and a thickness of 5.0 mm was manufactured by laser welding.

[Example 2]
In the nonaqueous electrolyte secondary battery of Example 2, the volume of the first negative electrode mixture layer in [Preparation of negative electrode] was 65% of the volume of the total negative electrode mixture layer (second negative electrode mixture layer) The volume was made in the same manner as in Example 1 except that the volume of the volume was 35% of the total volume).

[Comparative Example 1]
In the non-aqueous electrolyte secondary battery of Comparative Example 1, the negative electrode mixture layer of the second layer was not added to the first negative electrode mixture layer without containing an organic solvent containing lithium salt in [Preparation of negative electrode]. It was produced in the same manner as in Example 1 except that it was formed (that is, the volume of the second negative electrode mixture layer was 100% of the total volume).

[Comparative Example 2]
In the nonaqueous electrolyte secondary battery of Comparative Example 2, the volume of the first negative electrode mixture layer in [Preparation of negative electrode] was 15% of the volume of the total negative electrode mixture layer (second negative electrode mixture layer) The volume was made in the same manner as in Example 1 except that the volume of the sample was 75% of the total volume).

[Comparative Example 3]
In the nonaqueous electrolyte secondary battery of Comparative Example 3, the volume of the first negative electrode mixture layer in [Preparation of negative electrode] was 70% of the total volume of the negative electrode mixture layer (second negative electrode mixture layer) The volume was made in the same manner as in Example 1 except that the volume of was 30% of the total volume).

[Measurement of cycle characteristics]
About each battery of Example 1, 2 and Comparative Examples 1-3, it charges until a battery voltage will be 4.20V with a constant current of 900 mA at 25 degreeC, and an electric current will be 45 mA with a constant voltage of 4.20V after that. The battery was then discharged at 25 ° C. with a constant current of 900 mA until the battery voltage reached 2.75V. The discharge capacity at this time was determined as the discharge capacity of the first cycle. Subsequently, the above charge / discharge cycle was repeated 500 times, and the 500th discharge capacity was determined as the 500th cycle discharge capacity. And the cycle characteristic was calculated | required with the following formulas. The results are summarized in Table 1.
Cycle characteristics (%)
= (Discharge capacity at 500th cycle / discharge capacity at the first cycle) × 100

  From the results shown in Table 1, the following can be understood. That is, according to the results of Comparative Examples 1 and 2 and Example 1, the volume occupied by the first negative electrode mixture layer is less than 30% of the total volume of the negative electrode mixture layer (Comparative Examples 1 and 2). Then, the cycle characteristics are reduced in proportion to the decrease in the ratio. Further, according to the results of Example 1 and Example 2, the cycle characteristics are improved when the volume occupied by the first negative electrode mixture layer is 30% or more and 65% or less of the total volume of the negative electrode mixture layer. The effect is saturated. Furthermore, according to the results of Example 2 and Comparative Example 3, when the volume occupied by the first negative electrode mixture layer exceeds 65% (Comparative Example 3), the cycle characteristics begin to deteriorate. Therefore, it can be seen that the volume occupied by the first negative electrode mixture layer is preferably 30% to 65%.

  The reason why such a phenomenon occurs is estimated as follows. That is, if the proportion of the first negative electrode mixture layer is 30% or more, even if lithium ions near the negative electrode core are consumed by the battery reaction, lithium ions diffuse smoothly from the surroundings. Since the battery reaction in the negative electrode mixture layer is made uniform, good cycle characteristics can be obtained. In addition, when the proportion of the first negative electrode mixture layer is less than 30%, lithium ions do not smoothly diffuse from the surroundings even when lithium ions near the negative electrode plate are consumed by the battery reaction. The battery reaction in the layer becomes non-uniform and appears as a decrease in cycle characteristics. Further, when the ratio of the first negative electrode mixture layer exceeds 65%, the interface resistance between the negative electrode mixture layer and the electrolyte solution decreases, but conversely moves in the negative electrode mixture layer. Since the conductivity of the lithium ions is reduced, the resistance of the negative electrode plate as a whole is increased, resulting in a reduction in cycle characteristics.

  In the negative electrode plates for non-aqueous electrolyte secondary batteries of Examples 1 and 2, the negative electrode mixture layer formed on the surface of the first negative electrode mixture layer is an example of one layer. However, it may be two or more layers. That is, the effect of the present invention occurs when the lithium salt concentration in the first negative electrode mixture layer on the negative electrode core side is higher than the lithium salt concentration in the other layers. This is because the layer structure of another negative electrode mixture layer formed on the surface of the agent layer is not affected.

It is a perspective view which cut | disconnects and shows the conventional square nonaqueous electrolyte secondary battery to the vertical direction.

Explanation of symbols

10: Non-aqueous electrolyte secondary battery 11: Positive electrode plate 12: Negative electrode plate 13: Separator 14: Flat wound electrode body 15: Rectangular battery outer can 16: Sealing plate 17: Insulator 18: Negative electrode terminal 19 : Current collector 20: Insulating spacer 21: Electrolyte injection hole

Claims (9)

In the negative electrode plate for a non-aqueous electrolyte secondary battery in which a negative electrode mixture layer containing a negative electrode active material made of a carbonaceous material is formed on the surface of the negative electrode core,
The negative electrode mixture layer comprises at least two layers,
The first negative electrode mixture layer on the negative electrode core side contains a higher concentration of lithium salt than the other negative electrode mixture layers, and the volume occupied by the first negative electrode mixture layer is A negative electrode plate for a non-aqueous electrolyte secondary battery, wherein the negative electrode plate has a volume of 30% to 65% of the total volume of the negative electrode mixture layer. The lithium salt includes LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , LiAsF ₆ , LiClO ₄ , Li ₂ B ₁₀ Cl ₁₀ , Li ₂ B ₁₂ Cl ₁₂ The negative electrode plate for a non-aqueous electrolyte secondary battery according to claim 1.   The non-aqueous electrolyte secondary according to claim 1, wherein the lithium salt is contained in the first negative electrode mixture layer in a state dissolved in a gelled organic solvent. Negative electrode plate for batteries. In the method for producing a negative electrode plate for a non-aqueous electrolyte secondary battery in which a negative electrode mixture layer containing a negative electrode active material made of a carbonaceous material is formed on the surface of the negative electrode core,
Forming a first negative electrode mixture layer on the surface of the negative electrode core;
Applying and impregnating an organic solvent solution containing a lithium salt on the surface of the first negative electrode mixture layer;
At least one negative electrode mixture layer is formed on the surface of the first negative electrode mixture layer impregnated with the organic solvent solution containing the lithium salt, and the volume occupied by the first negative electrode mixture layer is the entire volume. Forming the negative electrode mixture layer so as to be 30% to 65% of the volume of the negative electrode mixture layer;
Next, a step of rolling so as to have a predetermined thickness,
A method for producing a negative electrode plate for a non-aqueous electrolyte secondary battery.   The method for producing a negative electrode plate for a non-aqueous electrolyte secondary battery according to claim 4, wherein the organic solvent solution containing the lithium salt contains a gelling agent.   6. The lithium salt concentration in the organic solvent solution containing the lithium salt is higher than the lithium salt concentration in the non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery. The manufacturing method of the negative electrode plate for nonaqueous electrolyte secondary batteries as described. A negative electrode plate in which a negative electrode mixture layer including a negative electrode active material made of a carbonaceous material is formed on the surface of the negative electrode core, and a positive electrode plate in which a positive electrode mixture layer including a positive electrode active material is formed on the surface of the positive electrode core In a non-aqueous electrolyte secondary battery comprising an electrode body wound or laminated with a separator interposed therebetween, and a non-aqueous electrolyte solution,
The negative electrode plate includes at least two negative electrode mixture layers,
The first negative electrode mixture layer on the negative electrode core side contains a higher concentration of lithium salt than the other layers, and the volume occupied by the first negative electrode mixture layer is the total negative electrode mixture layer. A nonaqueous electrolyte secondary battery characterized by being 30% or more and 65% or less of the volume of the battery.   The non-aqueous electrolyte secondary battery according to claim 7, wherein the lithium salt is made of the same compound as a solute in the non-aqueous electrolyte.   The non-aqueous electrolyte secondary according to claim 7 or 8, wherein the lithium salt is contained in the first negative electrode mixture layer in a state dissolved in a gelled organic solvent. battery.

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