JP2014011077A - Nonaqueous electrolyte secondary battery manufacturing method and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery manufacturing method which, while restraining the number of electrode defects, is also able to improve the peel strength of a mixture layer in an electrode in order to manufacture a nonaqueous electrolyte secondary battery having excellent high rate characteristic at low temperature, and a nonaqueous electrolyte secondary battery manufactured by this manufacturing method.SOLUTION: Provided is a method for manufacturing a lithium ion secondary battery 1 which is a nonaqueous electrolyte secondary battery containing CMC 3 in the mixture layer of an anode 10, the method including at least the steps of: producing a first kneaded body 5 by kneading graphite 2 which is a raw active material, CMC 3 which is a thickener and water 4 with stiff consistency; producing an anode paste 8 necessary to manufacture an electrode (anode 10) by adding water 4 to the first kneaded body 5 to dilute; applying a coating of the anode paste 8 to a current collector foil (copper foil 9); and drying and pressing the anode paste 8 coated to the copper foil 9 to form an anode 10, where the transparency of the 1% aqueous solution of the CMC 3 is 22 cm or more.

Description

  The present invention relates to a method for producing a nonaqueous electrolyte secondary battery and a technique for a nonaqueous electrolyte secondary battery produced by the production method.

A non-aqueous electrolyte secondary battery such as a lithium ion secondary battery used in a hybrid vehicle is required to have excellent high-rate characteristics at a low temperature, but a thickener contained in an electrode (for example, a negative electrode) It is known that when undissolved (so-called CMC gel) is generated in (for example, CMC), it adversely affects high rate characteristics at low temperatures.
That is, in order to obtain a non-aqueous electrolyte secondary battery excellent in high rate characteristics at low temperatures, it is effective to make defects in the electrodes less likely to occur, and the adhesion between the mixture layer and the current collector foil in the electrodes is improved. It is also effective to improve it.

  Conventionally, a technique for easily generating a paste for an electrode while suppressing undissolved residual gel thickener has been studied. For example, the technique is disclosed in Patent Document 1 shown below, and is well known. It has become.

In the prior art disclosed in Patent Document 1, it is possible to easily produce a paste for an electrode as an aqueous paste by adding a solvent after mixing active material particles in a powder state and CMC. I have to.
And in the prior art currently disclosed by patent document 1, after mixing the active material particle of a powder state, and CMC, in the structure which adds a solvent and produces a paste, the active material particle and the average particle diameter of CMC By prescribing the ratio, the aqueous paste is easily produced while suppressing the generation of CMC gel.

JP 2011-63673 A

However, as in the prior art disclosed in Patent Document 1, the amount of CMC gel in the paste cannot be controlled only by defining the average particle size ratio between the active material particles and CMC. In some cases, defects (through-through) derived from the CMC gel occurred in the layer.
Moreover, in the prior art currently disclosed by patent document 1, it is not mentioned about improving the peeling strength of the composite material layer in a negative electrode.

  Thus, in the past, in order to improve the high rate characteristics at low temperatures, a technique has been developed that makes it difficult for defects to occur in the electrode and improves the adhesion (that is, the peel strength) between the electrode mixture layer and the current collector foil. For this reason, there has been no technique for specifying the specifications of the thickener and the current collector foil from the viewpoint of improving the peel strength of the composite layer while suppressing the defects of the electrodes.

  The present invention has been made in view of such current problems, and in order to produce a nonaqueous electrolyte secondary battery excellent in high rate characteristics at low temperatures, the number of defects of the electrode is suppressed, and a composite material in the electrode It aims at providing the manufacturing method of the nonaqueous electrolyte secondary battery which improves the peeling strength of a layer, and the nonaqueous electrolyte secondary battery manufactured by this manufacturing method.

  The problem to be solved by the present invention is as described above. Next, means for solving the problem will be described.

  That is, in claim 1, an electrode is manufactured by solidifying a raw material active material, a thickener, and water to form a primary kneaded body, and adding and diluting water to the primary kneaded body. And a step of applying the paste to the current collector foil, and a step of drying and pressing the paste applied to the current collector foil to form the electrode. A method for producing a non-aqueous electrolyte secondary battery containing a thickener in the electrode mixture layer of the electrode, wherein the transparency of a 1% aqueous solution of the thickener is 22 cm or more.

  According to a second aspect of the present invention, the electrode is a negative electrode, and the current collector foil is a copper foil having a wettability index of 50 mN / m or more on the surface on which the paste is applied.

  In the present invention, the thickener is CMC.

  In claim 4, the electrode is the amount of Na on the surface side from the thickness method center of the mixture layer of the electrode, and the value obtained by dividing the amount of Na on the current collector foil side from the thickness method center of the mixture layer, 0.7 or more and 1.5 or less.

  In Claim 5, it has the said electrode manufactured with the manufacturing method of the nonaqueous electrolyte secondary battery as described in any one of the said Claims 1-4.

  As effects of the present invention, the following effects can be obtained.

  In claims 1 to 3, since the solubility of CMC in water is improved, it is possible to suppress the occurrence of defects due to the CMC gel.

  In Claim 4, the fault resulting from CMC gel can be suppressed and the adhesiveness of the compound material layer with respect to current collection foil can be improved.

  The present invention provides a nonaqueous electrolyte secondary battery excellent in high-rate characteristics at low temperature, in which defects due to CMC gel are suppressed and adhesion of the composite material layer to the current collector foil is improved. be able to.

The schematic diagram which shows the flow of the manufacturing method of the lithium ion secondary battery which concerns on one Embodiment of this invention. The schematic diagram which shows the condition of the negative electrode in the lithium ion secondary battery (Examples 1-3) which concerns on one Embodiment of this invention, (a) The figure which shows the spreading | diffusion condition of CMC in the compound material layer of a negative electrode, (b) Negative electrode The figure which shows the spreading | diffusion condition of Na in the compound material layer of. The figure which shows the measurement result of each characteristic in a lithium ion secondary battery. Schematic diagram showing the state of the negative electrode in a conventional lithium ion secondary battery, (a) a diagram showing the diffusion state of CMC in the composite layer of the negative electrode (in the case of Comparative Example 1), (b) negative electrode (in the case of Comparative Example 2) The figure which shows the diffusion condition of CMC in the composite material layer of (), (c) The figure which shows the diffusion condition of CMC in the composite material layer of the negative electrode (in the case of Comparative Example 3).

Next, embodiments of the invention will be described.
First, the flow of a method for manufacturing a nonaqueous electrolyte secondary battery according to an embodiment of the present invention will be described with reference to FIG.
As shown in FIG. 1, the method for manufacturing a nonaqueous electrolyte secondary battery according to an embodiment of the present invention is a method for manufacturing a lithium ion secondary battery 1 according to an embodiment of the present invention. First, a negative electrode 10 is manufactured. The process of producing | generating the negative electrode paste 8 for performing is implemented, the graphite 2 which is a negative electrode active material, CMC3 which is a thickener, and the water 4 which is a solvent are mixed and kneaded.
The kneading here is a process called primary kneading and can be carried out, for example, using a twin-screw extrusion kneader.

And in the manufacturing method of the lithium ion secondary battery 1 which concerns on one Embodiment of this invention, the transparency of CMC3 used here is prescribed | regulated, Specifically, CMC3 whose transparency is 22 cm or more is used. I have to.
In addition, "transparency" said here is in the state where a tube (transparency tube) for measuring transparency was placed (standing) on a thing (visual object) with black lines drawn at 1 mm intervals. A 1% aqueous solution of CMC3 is poured into the transparency tube, and is defined by the height of the liquid column (cm) when the black line of the object to be visually recognized cannot be recognized under a predetermined light source.
This method is a general method for evaluating “transparency”. If there is an insoluble part, unreacted cellulose, or the like, the numerical value of transparency becomes small.

In the method of manufacturing the lithium ion secondary battery 1 according to one embodiment of the present invention, a solvent (water 4) is further added to the material produced by solidification (hereinafter referred to as the primary kneaded body 5). Then, the primary kneaded body 5 is diluted to produce a slurry 6 in which particles of graphite 2 are dispersed in a medium composed of a solvent (water 4), CMC 3 and the like.
And SBR7 (binder) is added with respect to the slurry 6 after dispersion | distribution, and the negative electrode paste 8 is produced | generated.

  In this embodiment, when the weight of the graphite 2 is 98.6, the weight of the CMC3 is 0.7, and the weight of the SBR is 0.7, and the solid components of graphite 2, CMC3, and SBR7. Are mixed (that is, the weight percent of CMC3 with respect to the weight of all solid components is 0.7) to produce negative electrode paste 8.

  And the negative electrode paste 8 produced | generated on such conditions is apply | coated and dried on current collection foil (this embodiment copper foil 9), and negative electrode 10 (negative electrode plate) is passed through each processes, such as a press and a slit. To manufacture.

And in the manufacturing method of the lithium ion secondary battery 1 which concerns on one Embodiment of this invention, the wettability index | exponent of the copper foil 9 to be used is prescribed | regulated, Specifically, a wettability index | exponent is 50 mN / m or more. The copper foil 9 is used.
The “wetting index” here is obtained by measurement using a predetermined evaluation reagent. When a mixed liquid for wet tension evaluation is applied to the current collector foil (copper foil 9), It can be obtained from the repellent condition of the liquid.

  Then, the negative electrode 10 manufactured by defining the transparency of CMC 3 and the wettability index of the copper foil 9 is wound together with the positive electrode (not shown) and the separator (not shown) to form a wound body (not shown). Then, the wound body was housed in a case and sealed after injecting an electrolyte (not shown) to produce a lithium ion secondary battery 1 according to an embodiment of the present invention having a capacity of 4 Ah.

  Furthermore, in the method for manufacturing a nonaqueous electrolyte secondary battery according to an embodiment of the present invention, the CMC distribution in the negative electrode mixture layer is defined for the negative electrode to be used.

Here, a method for defining the CMC distribution will be described with reference to FIG.
FIG. 2A schematically shows the state of the negative electrode 10 before drying.
When the negative electrode 10 is formed using CMC3 having a transparency of 22 cm or more and a current collector foil (copper foil 9) having a wettability index of 50 mN / m or more, as shown in FIG. In the composite material layer 10a of the negative electrode 10, there is no insoluble content of CMC3 (CMC gel), and CMC3 is evenly distributed.

In this case, since the hydrophilic portion 3a of the CMC 3 is preferentially coordinated with the copper foil 9, the adhesion (that is, the peel strength) of the mixture layer 10a to the copper foil 9 is improved.
2A represents the hydrophilic portion 3a, and the whisker-shaped portion represents the hydrophobic portion 3b (FIGS. 4A, 4B, and 4C). The same applies to the above).
FIG. 2B illustrates an analysis result of the degree of uneven distribution of CMC 3 in the negative electrode 10.
Since CMC3 is often used as a Na salt, here, the distribution of CMC3 is obtained by analyzing the Na distribution in the negative electrode 10 (mixed material layer 10a).
The analysis of Na distribution can be performed using an apparatus such as SEM (Scanning Electron Microscope) and EDX (Energy Dispersive X-ray spectrumometer).
Then, by measuring the characteristic X-ray intensity of the cross section of the negative electrode 10 using these apparatuses, a distribution (map) of Na (that is, CMC3) as shown in FIG. 2B can be obtained. .

  And in the manufacturing method of the nonaqueous electrolyte secondary battery which concerns on one Embodiment of this invention, from the map shown in FIG.2 (b), 1/2 of the surface side of this map (the collector foil side from the center in the thickness direction) ), The Na intensity at 1/2 of the current collector foil side of the map (from the center in the thickness direction to the current collector foil side) is B, and an index L representing the distribution of Na from the value of B / A Is calculated.

  The index L approaches 1.0 if CMC3 is evenly distributed in the composite material layer 10a, and the index L is smaller than 1.0 if CMC3 is biased to the surface side. Further, if the CMC 3 is biased toward the current collector foil, the index L becomes larger than 1.0. Therefore, the quality of the negative electrode 10 is determined based on the index L (= B / A). .

  And in the manufacturing method of the lithium ion secondary battery 1 which concerns on one Embodiment of this invention, the range of the parameter | index L in the compound material layer 10a of the manufactured negative electrode 10 is prescribed | regulated, Specifically, the parameter | index L is 0. The lithium ion secondary battery 1 is manufactured using the negative electrode 10 that is 0.7 or more and 1.5 or less.

  Next, the characteristic of the lithium ion secondary battery 1 manufactured with the manufacturing method of the nonaqueous electrolyte secondary battery which concerns on one Embodiment of this invention is demonstrated using FIGS.

In FIG. 3, the result of having measured each characteristic in six types of lithium ion secondary batteries from which a manufacturing method differs is shown collectively.
And each lithium ion secondary battery of Examples 1-3 shown in FIG. 3 has a wettability index of the copper foil 9 of 50-54 mN / m, and the nonaqueous electrolyte secondary battery according to one embodiment of the present invention. The specified value (50 mN / m or more) of the wettability index of the current collector foil in this production method is satisfied.

  In addition, each of the lithium ion secondary batteries of Examples 1 to 3 shown in FIG. 3 has a CMC3 transparency of 22 to 25 cm, and the CMC of the nonaqueous electrolyte secondary battery manufacturing method according to one embodiment of the present invention. The specified value of transparency (22 cm or more) is also satisfied.

In addition, the lithium ion secondary battery according to Example 2 is different from the lithium ion secondary battery according to Example 1 in the wettability index of the copper foil 9 to be used, and is common in other configurations. Yes.
Further, the lithium ion secondary battery according to Example 3 differs from the lithium ion secondary battery according to Example 1 in the transparency of the CMC 3 used, and is common in other configurations.

  Further, each of the lithium ion secondary batteries of Examples 1 to 3 shown in FIG. 3 has a Na distribution index L of 0.7 or more and 1.5 or less, and the non-aqueous solution according to one embodiment of the present invention. The specified value (0.7 or more and 1.5 or less) of the Na distribution index L in the manufacturing method of the electrolyte secondary battery is also satisfied.

More specifically, since the map shown in FIG. 2B is that of the lithium ion secondary battery of Example 1 and has an index L = 1.0, the map according to one embodiment of the present invention is not shown. The specified value of the index L (0.7 or more and 1.5 or less) in the method for manufacturing a water electrolyte secondary battery is satisfied.
Further, as shown in FIG. 3, in the lithium ion secondary batteries of Examples 2 and 3, since the indices L are 1.5 and 0.7, respectively, the nonaqueous electrolyte according to one embodiment of the present invention The specified value (0.7 or more and 1.5 or less) of the index L in the manufacturing method of the secondary battery is satisfied.

That is, in the method for manufacturing a non-aqueous electrolyte secondary battery according to an embodiment of the present invention, the negative electrode 109 has a Na amount on the surface side from the thickness method center of the composite material layer 10a of the negative electrode 10, and the composite material layer 10a. The value obtained by dividing the amount of Na on the side of the current collector foil (copper foil 9) from the center of the thickness method is 0.7 or more and 1.5 or less.
With such a configuration, the solubility of CMC 3 in water 4 is improved, so that it is possible to suppress the occurrence of defects due to CMC gel 3c.

  And each lithium ion secondary battery of Examples 1-3 shown in FIG. 3 corresponds to what was manufactured with the manufacturing method of the nonaqueous electrolyte secondary battery which concerns on one Embodiment of this invention, and one implementation of this invention It corresponds to the lithium ion secondary battery 1 (refer FIG. 1) which concerns on a form.

On the other hand, in the lithium ion secondary battery of Comparative Example 1 shown in FIG. 3, the wettability index of the copper foil 9 is 54 mN / m, and the collection in the method for manufacturing the nonaqueous electrolyte secondary battery according to one embodiment of the present invention is performed. Although the specified value (50 mN / m or more) of the wettability index of the foil is satisfied, the transparency of CMC3 is 16 cm, and the specified value (22 cm or more) of CMC3 is not satisfied.
Furthermore, the lithium ion secondary battery of Comparative Example 1 shown in FIG. 3 has a Na distribution index L of 0.4, and Na in the method for manufacturing a nonaqueous electrolyte secondary battery according to one embodiment of the present invention. The specified value (0.7 or more and 1.5 or less) of the distribution index L is not satisfied.

Further, the lithium ion secondary battery of Comparative Example 2 shown in FIG. 3 has a CMC3 transparency of 25 cm, and the transparency value of CMC3 in the method for manufacturing a nonaqueous electrolyte secondary battery according to an embodiment of the present invention ( 22 cm or more), but the wettability index of the copper foil 9 is 34 mN / m, and the specified value (50 mN / m or more) of the wettability index of the current collector foil is not satisfied.
Furthermore, the lithium ion secondary battery of Comparative Example 2 shown in FIG. 3 has a Na distribution index L of 0.4, and Na in the method for manufacturing a nonaqueous electrolyte secondary battery according to one embodiment of the present invention. The specified value (0.7 or more and 1.5 or less) of the distribution index L is not satisfied.

Furthermore, the lithium ion secondary battery of Comparative Example 3 shown in FIG. 3 has a CMC3 transparency of 16 cm, and the transparency value of CMC3 in the method for manufacturing a nonaqueous electrolyte secondary battery according to an embodiment of the present invention ( 22 cm or more), the wettability index of the copper foil 9 is 34 mN / m, and the specified value (50 mN / m or more) of the wettability index of the current collector foil is not satisfied.
Furthermore, the lithium ion secondary battery of Comparative Example 3 shown in FIG. 3 has a Na distribution index L of 2.3, and Na in the method for manufacturing a nonaqueous electrolyte secondary battery according to one embodiment of the present invention. The specified value (0.7 or more and 1.5 or less) of the distribution index L is not satisfied.

  Therefore, the lithium ion secondary batteries of Comparative Examples 1 to 3 shown in FIG. 3 do not correspond to those manufactured by the method for manufacturing a nonaqueous electrolyte secondary battery according to one embodiment of the present invention (lithium ion secondary batteries). Not the next battery 1).

FIG. 3 shows the evaluation of the number of defects, peel strength, and capacity retention after low-temperature high-rate cycling.
As used herein, the “number of defects” is calculated as an average value of the number of “defects” in each of the five samples by preparing five samples obtained by cutting the negative electrode 10 after pressing into a size of 10 cm × 50 cm. .
Then, the average value of the number of defects was divided by the area of the sample (0.05 m ² ) to calculate the number of defects per unit area.
In addition, the “defect” mentioned here refers to a defect in which the undissolved portion of CMC 3 (CMC gel) adheres to the copper foil 9 and a portion where the graphite 2 is not locally attached (through) is generated. Yes.
In the present embodiment, a defective product having a defect count of 200 pieces / m ² or less is regarded as a non-defective product.

In addition, the “peel strength” herein refers to a sample prepared by cutting the pressed negative electrode 10 into a width of 15 mm and performing a 90 ° peel test on the sample to calculate the peel strength.
The method for calculating the peel strength will be described in more detail.
The coated surface of the sample obtained by cutting the negative electrode plate after pressing to a width of 15 mm is attached to the glass plate with a double-sided tape. And the intensity | strength (stress required for peeling) at the time of peeling from the said glass plate at a fixed speed | rate was measured, hold | maintaining the angle of 90 degree | times at the end of a negative electrode plate.
And the value which remove | divided the intensity | strength by 15 mm in width was made into peeling strength.
And in this embodiment, the thing whose peeling strength is 2 N / m or more was made into the non-defective product.

Further, the “capacity maintenance ratio after low-temperature high-rate cycle” here will be described.
In order to calculate the capacity retention rate after the low-temperature high-rate cycle, first, the initial capacity is confirmed.
This initial capacity is 5C after charging to 4.2V at 1C in an environment of 25 ° C, then discharging to 2.5V and resting for 5 minutes, at 1C rate, 0.01C cut, CCCV charge up to 4.2V and CCCV discharge up to 2.5V were performed to confirm the initial capacity.

Then, after confirming the initial capacity, a low temperature large current charge / discharge test is performed.
The low-temperature, large-current charge / discharge test was performed at 24 A (6 C) for 0.5 seconds in a -15 ° C. environment, then discharged at 0.24 A (about 0.06 C) for 50 seconds, and then 29.5 seconds. The process of stopping is defined as one cycle. And this process was implemented 2000 cycles and the low temperature large current charging / discharging test was done.

And, "capacity maintenance rate after low temperature high rate cycle" is the capacity after the test with respect to the initial capacity, after confirming the capacity after the test in the same manner as the initial capacity for the lithium ion secondary battery after the low temperature large current charge and discharge test, The capacity retention rate after low temperature high rate cycle was calculated.
And in this embodiment, the thing whose capacity maintenance rate after a low-temperature high-rate cycle is 95% or more was made into the quality product.

  Hereinafter, the consideration about evaluation of each lithium ion secondary battery shown in FIG. 3 is shown.

First, the characteristics of the lithium ion secondary batteries according to Examples 1 to 3 will be described.
In each of the lithium ion secondary batteries 1, 1, 1 according to Examples 1 to 3, the number of defects is 4 to 20 / m ^{2 as} shown in FIG. It has become.
Moreover, in each lithium ion secondary battery 1-1.1 which concerns on Examples 1-3, since peeling strength is 2.9-3.1 N / m, it is favorable also in evaluation of peeling strength, Furthermore, Since the capacity retention ratio after low-temperature high-rate cycle is 96 to 97%, the capacity retention ratio after low-temperature high-rate cycle is good in evaluation.

Next, the characteristics of the lithium ion secondary battery according to Comparative Example 1 shown in FIG. 3 will be described.
FIG. 4A schematically shows the state of the negative electrode 20 that is the negative electrode of the lithium ion secondary battery according to Comparative Example 1 before drying.
The negative electrode 20 of Comparative Example 1 is formed using CMC3 having a transparency of 16 cm and using a copper foil 9 having a wettability index of 54 mN / m (that is, 50 mN / m or more).

In this case, an insoluble component (CMC gel 3c) of CMC3 exists in the composite material layer 20a of the negative electrode 20, and therefore, the negative electrode 20 has a defect (slear) due to the CMC gel 3c.
In this case, the hydrophilic portion 3a of the CMC 3 is preferentially coordinated with respect to the copper foil 9, but the adhesion force of the composite layer 20a to the copper foil 9 (ie, peel strength) is equivalent to the presence of the CMC gel 3c. Decreases.

  As shown in FIG. 3, in the lithium ion secondary battery of Comparative Example 1, since the Na distribution index L is 0.4, the manufacture of the nonaqueous electrolyte secondary battery according to one embodiment of the present invention is performed. The specified value (0.7 or more and 1.5 or less) of the index L in the method is not satisfied.

In the lithium ion secondary battery according to Comparative Example 1 including such a negative electrode 20, as shown in FIG. 3, the number of defects is as large as 984 pieces / m ² , and it is determined to be defective in the evaluation of the number of defects. Moreover, it is inferior compared with each lithium ion secondary battery 1-1.1 of Examples 1-3.

  Moreover, in each lithium ion secondary battery which concerns on the comparative example 1, peeling strength is 1.8 N / m and it is judged that it is inferior also in peeling strength evaluation, Each lithium ion secondary battery 1 of Examples 1-3・ It is inferior to 1.1.

  Furthermore, in each lithium ion secondary battery according to Comparative Example 1, the capacity retention rate after low-temperature high-rate cycle was 93%, and it was determined that the capacity retention rate after low-temperature high-rate cycle was poor. It is inferior to each of the lithium ion secondary batteries 1.

Next, the characteristics of the lithium ion secondary battery according to Comparative Example 2 shown in FIG. 3 will be described.
FIG. 4B schematically shows the state of the negative electrode 30 that is the negative electrode of the lithium ion secondary battery according to Comparative Example 2 before drying.
The negative electrode 30 of Comparative Example 2 is formed using CMC3 having a transparency of 25 cm (ie, 22 cm or more) and using a copper foil 9 having a wettability index of 34 mN / m.

In this case, the insoluble content of CMC3 (CMC gel 3c) does not exist in the composite material layer 30a of the negative electrode 30, and therefore, in the negative electrode 30, the defect (slear) due to the CMC gel 3c is not present. It is hard to occur.
However, in this case, since the wettability index of the copper foil 9 is as low as 34 mN / m, the hydrophilic portion 3a of the CMC 3 gathers on the surface side of the mixture layer 30a, and as a result, the mixture layer 30a with respect to the copper foil 9 Adhesive strength (that is, peel strength) decreases.

  As shown in FIG. 3, in the lithium ion secondary battery of Comparative Example 2, since the Na distribution index L is 0.4, the manufacture of the nonaqueous electrolyte secondary battery according to one embodiment of the present invention is performed. The specified value (0.7 or more and 1.5 or less) of the index L in the method is not satisfied.

In the lithium ion secondary battery according to Comparative Example 2 including the negative electrode 30 having such a configuration, the number of defects is 8 / m ^{2 as} shown in FIG. This is equivalent to each of the lithium ion secondary batteries 1.

  However, in each lithium ion secondary battery according to Comparative Example 2 including the negative electrode 30, the peel strength is 1.9 N / m, and it is determined that the peel strength is poor. It is inferior to the secondary battery 1.

  Furthermore, in each lithium ion secondary battery according to Comparative Example 2, the capacity retention rate after low-temperature high-rate cycle was 94%, and it was determined that the capacity retention rate after low-temperature high-rate cycle was poor. It is inferior to each of the lithium ion secondary batteries 1.

Next, the characteristics of the lithium ion secondary battery according to Comparative Example 3 shown in FIG. 3 will be described.
FIG. 4C schematically shows the state of the negative electrode 40 that is the negative electrode of the lithium ion secondary battery according to Comparative Example 3 before drying.
The negative electrode 40 of Comparative Example 3 is formed using CMC3 having a transparency of 16 cm and using copper foil 9 having a wettability index of 34 mN / m.

In this case, insoluble material (CMC gel 3c) of CMC3 exists in the composite material layer 40a of the negative electrode 40, and therefore, in the negative electrode 40, a defect (slear) due to the CMC gel 3c occurs. Yes.
In this case, since the wettability index of the copper foil 9 is as low as 34 mN / m, the hydrophilic portion 3a of the CMC 3 gathers on the surface side of the composite material layer 40a, and the CMC gel 3c is also contained in the composite material layer 40a. Since it exists, as a result, the adhesive force (namely, peeling strength) of the compound material layer 40a with respect to the copper foil 9 falls.

  As shown in FIG. 3, in the lithium ion secondary battery of Comparative Example 3, since the Na distribution index L is 2.3, the manufacture of the nonaqueous electrolyte secondary battery according to one embodiment of the present invention is performed. The specified value (0.7 or more and 1.5 or less) of the index L in the method is not satisfied.

In the lithium ion secondary battery according to Comparative Example 3 including the negative electrode 40 having such a configuration, the number of defects is as large as 1172 / m ^{2 as} shown in FIG. These are inferior to the lithium ion secondary batteries 1.

  Moreover, in each lithium ion secondary battery which concerns on the comparative example 3 provided with the negative electrode 40, peeling strength is 1.0 N / m and it is judged that it is inferior also in peeling strength evaluation, Each lithium ion of Examples 1-3 It is inferior to the secondary battery 1.

  Furthermore, in each lithium ion secondary battery according to Comparative Example 3, the capacity retention rate after low-temperature high-rate cycle was 91%, and it was determined that the capacity retention rate after low-temperature high-rate cycle was poor. It is inferior to each of the lithium ion secondary batteries 1.

  That is, in the method for manufacturing a non-aqueous electrolyte secondary battery according to one embodiment of the present invention, the specified value of transparency of CMC3 (22 cm or more) and the specified value of wettability index of copper foil 9 (50 mN / m or more). If it is not satisfied at the same time (that is, in Comparative Examples 1 to 3), it can be seen that the high rate characteristics at low temperatures cannot be improved.

  On the other hand, the specified value of transparency of CMC3 (22 cm or more) and the specified value of wettability index of copper foil 9 (50 mN / m or more) in the method for manufacturing a nonaqueous electrolyte secondary battery according to one embodiment of the present invention are satisfied. In each of the lithium ion secondary batteries 1, 1, 1 of Examples 1 to 3, the high rate characteristics at a low temperature can be improved.

  That is, according to the results shown in FIG. 3, using CMC3 satisfying the prescribed value of transparency (22 cm or more) and using copper foil 9 satisfying the prescribed value of wettability index (50 mN / m or more). By using the manufactured negative electrode 10 to manufacture the lithium ion secondary battery 1, it is possible to provide a lithium ion secondary battery having excellent high rate characteristics at low temperatures.

That is, the method for producing a nonaqueous electrolyte secondary battery according to an embodiment of the present invention includes a step of producing a primary kneaded body 5 by kneading graphite 2 as a raw material active material, CMC 3 as a thickener, and water 4. The step of producing a negative electrode paste 8 as a paste for producing an electrode (negative electrode 10) by adding water 4 to the primary kneaded body 5 and diluting, and the negative electrode paste 8 as a current collector foil (copper foil 9) A non-aqueous solution containing CMC3 in the composite material layer 10a of the negative electrode 10 comprising at least a step of coating the negative electrode paste 8 applied to the copper foil 9 and a step of drying and pressing the negative electrode paste 8 applied to the copper foil 9 to form the negative electrode 10 A method for producing a lithium ion secondary battery 1 which is an electrolyte secondary battery, wherein the transparency of a 1% aqueous solution of CMC3 is set to 22 cm or more.
In the method for manufacturing a nonaqueous electrolyte secondary battery according to an embodiment of the present invention, the electrode is the negative electrode 10, and the current collector foil has a wettability index of 50 mN / m or more on the surface on which the negative electrode paste 8 is applied. The copper foil 9 is used.
Moreover, the manufacturing method of the nonaqueous electrolyte secondary battery which concerns on one Embodiment of this invention uses CMC3 as a thickener.
With such a configuration, defects due to the CMC gel 3c can be suppressed, and the adhesion (that is, the peel strength) of 10a to the copper foil 9 can be improved.

Moreover, the lithium ion secondary battery 1 which is the nonaqueous electrolyte secondary battery which concerns on one Embodiment of this invention has the negative electrode 10 manufactured with the manufacturing method of the nonaqueous electrolyte secondary battery which concerns on one Embodiment of this invention. Is.
With such a configuration, the non-aqueous electrolyte excellent in high-rate characteristics at low temperature, in which defects due to the CMC gel 3c are suppressed and the adhesion (peeling strength) of the composite material layer 10a to the copper foil 9 is improved. The lithium ion secondary battery 1 which is a secondary battery can be provided.

  In the present embodiment, it is the negative electrode that contains the thickener in the mixture layer, the thickener is CMC, and the current collector foil constituting the electrode is a copper foil. However, the present invention can also be applied to a non-aqueous electrolyte secondary battery having a structure in which a thickener is added to the positive electrode mixture layer, and the thickener may be other than CMC. The current collector foil may be other than copper foil.

1 Lithium ion secondary battery (non-aqueous electrolyte secondary battery)
2 Graphite 3 CMC (Thickener)
4 Water 5 Primary kneaded body 8 Negative electrode paste 9 Copper foil (current collector foil)
10 Negative electrode (electrode)
10a Compound material layer

Claims (5)

A step of producing a primary kneaded body by kneading raw material active material, thickener and water;
Producing a paste for producing an electrode by adding water to the primary kneaded body and diluting; and
Applying the paste to a collector foil;
Drying and pressing the paste applied to the current collector foil to form the electrode;
Comprising at least
A method for producing a non-aqueous electrolyte secondary battery containing a thickener in the composite layer of the electrode,
The transparency of a 1% aqueous solution of the thickener is 22 cm or more.
A method for producing a non-aqueous electrolyte secondary battery. The electrode is a negative electrode;
The current collector foil,
A copper foil having a wettability index of 50 mN / m or more on the surface to which the paste is applied,
The manufacturing method of the nonaqueous electrolyte secondary battery of Claim 1 characterized by the above-mentioned. The thickener is CMC,
The method for producing a non-aqueous electrolyte secondary battery according to claim 1, wherein: The electrode is
The value obtained by dividing the amount of Na on the current collector foil side from the thickness method center of the composite material layer by the amount of Na on the surface side from the thickness method center of the electrode composite layer is 0.7 or more and 1.5 or less To
The method for producing a nonaqueous electrolyte secondary battery according to claim 3. It has the electrode manufactured by the manufacturing method of the nonaqueous electrolyte secondary battery according to any one of claims 1 to 4.
A non-aqueous electrolyte secondary battery.

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