JP2014017073A - Nonaqueous electrolyte secondary battery and manufacturing method therefor - Google Patents

Abstract

To provide a non-aqueous electrolyte secondary battery capable of suppressing deterioration of battery characteristics even when a flat wound electrode body is used in a restrained manner.
A flat wound electrode body 1 in which a positive electrode, a negative electrode, and a separator are laminated and wound, and a sandwiching member 2 that sandwiches flat portions 5 and 6 of the wound electrode body 1 from both sides. 3 are provided. The negative electrode has a negative electrode mixture layer containing a negative electrode active material and a negative electrode current collector on which the negative electrode mixture layer is laminated. The negative electrode active material has a tap density of 0.92 g / cm ³ or more and 1.25 g / The material of cm ³ or less is used, the density of the negative electrode mixture layer 22 is 1.1 g / cm ³ or more and 1.52 g / cm ³ or less, and the density of the negative electrode mixture layer is the tap density of the negative electrode active material. The divided value is 1.07 to 1.26.
[Selection] Figure 1

Description

  The present invention relates to a non-aqueous electrolyte secondary battery and a method for manufacturing the same.

  One of the non-aqueous electrolyte secondary batteries is a lithium ion secondary battery. A lithium ion secondary battery is a secondary battery that can be charged and discharged by moving lithium ions in a non-aqueous electrolyte between a positive electrode and a negative electrode that occlude and release lithium ions.

  Patent Document 1 discloses a technique related to a non-aqueous electrolyte secondary battery that has excellent output characteristics and can maintain excellent output characteristics. In the technique disclosed in Patent Document 1, the flat packing portion of the wound electrode body has a filling density of the negative electrode of the flat wound electrode body included in the nonaqueous electrolyte secondary battery of 1.0 to 1.2 g / cc. The compression ratio of the separator is 11% or less, and the ratio of the thickness of the flat portion of the wound electrode body to the inner dimension of the rectangular exterior body is 94% or more.

JP 2010-238469 A

  In a non-aqueous electrolyte secondary battery using a flat wound electrode body, the flat part of the wound electrode body (see flat parts 5 and 6 in FIG. 1) is sandwiched from both sides to restrain the wound electrode body. May be used. However, when the wound electrode body is constrained and used in this way, a load is applied to the flat portion of the wound electrode body, but a curved portion sandwiched between the flat portions of the wound electrode body (FIG. 1). No load is applied to the curved portions 7 and 8). For this reason, while using the non-aqueous electrolyte secondary battery, the amount of deformation in the thickness direction of the negative electrode mixture layer varies between the flat portion where the load is applied and the curved portion where the load is not applied. That is, the thickness of the curved portion where the load is not applied is increased with respect to the flat portion where the load is applied, and the resistance of the negative electrode of the curved portion is increased. Thus, when the distribution of the resistance of the negative electrode occurs between the flat portion where the load is applied and the curved portion where the load is not applied, the battery characteristics such as lithium is deposited at a location where the resistance is high during charging and the capacity retention rate of the battery is reduced. There is a problem of lowering.

  In view of the above problems, an object of the present invention is to provide a non-aqueous electrolyte secondary battery and a method for manufacturing the same that can suppress deterioration of battery characteristics even when a flat wound electrode body is constrained and used. Is to provide.

A non-aqueous electrolyte secondary battery according to one aspect of the present invention is a flat wound electrode in which a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode are stacked and wound together. And a sandwiching member that sandwiches the flat part of the wound electrode body from both sides. The negative electrode includes a negative electrode mixture layer containing the negative electrode active material, and the negative electrode mixture layer laminated. A material having a tap density of 0.92 g / cm ³ or more and 1.25 g / cm ³ or less is used for the negative electrode active material, and the density of the negative electrode mixture layer is: 1.1 g / cm ³ or more and 1.52 g / cm ³ or less, and a value obtained by dividing the density of the negative electrode mixture layer by the tap density of the negative electrode active material is 1.07 or more and 1.26 or less.

  In the non-aqueous electrolyte secondary battery, the surface of the negative electrode active material may be coated with an amorphous material.

  In the non-aqueous electrolyte secondary battery, the negative electrode active material may be a material obtained by coating graphite with amorphous carbon.

  In the non-aqueous electrolyte secondary battery, the holding member may hold the wound electrode body with a load of 500 kgf or more.

  In the non-aqueous electrolyte secondary battery, a value obtained by dividing the density of the negative electrode mixture layer by the tap density of the negative electrode active material may be 1.07 or more and 1.23 or less.

  In the non-aqueous electrolyte secondary battery, a value obtained by dividing the density of the negative electrode mixture layer by the tap density of the negative electrode active material may be 1.07 or more and 1.19 or less.

  In the non-aqueous electrolyte secondary battery, a value obtained by dividing the density of the negative electrode mixture layer by the tap density of the negative electrode active material may be 1.07 or more and 1.12 or less.

A method for manufacturing a nonaqueous electrolyte secondary battery according to one embodiment of the present invention includes producing a positive electrode mixture containing a positive electrode active material, laminating the positive electrode mixture on a positive electrode current collector, forming a positive electrode, A negative electrode mixture containing a substance is prepared, the negative electrode mixture is laminated on a negative electrode current collector to form a negative electrode, and the positive electrode, the negative electrode, and a separator disposed between the positive electrode and the negative electrode, Is a method of manufacturing a non-aqueous electrolyte secondary battery, in which a flat wound electrode body is formed by stacking and winding each other, and the wound electrode body is sandwiched with a predetermined load using a sandwiching member. When forming the negative electrode, a material having a tap density of 0.92 g / cm ³ or more and 1.25 g / cm ³ or less is used for the negative electrode active material, and the density of the negative electrode mixture layer is 1.1 g / cm 3. ³ or more and 1.52 g / cm ³ or less, and the density of the negative electrode mixture layer is the tap density of the negative electrode active material. The value divided by degrees is set to 1.07 or more and 1.26 or less.

  In the method for manufacturing a non-aqueous electrolyte secondary battery, the surface of the negative electrode active material may be coated with an amorphous material.

  According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery and a method for manufacturing the same that can suppress deterioration of battery characteristics even when a flat wound electrode body is used in a restrained manner.

It is sectional drawing which shows the nonaqueous electrolyte secondary battery concerning embodiment. It is an enlarged view of the wound electrode body with which the nonaqueous electrolyte secondary battery concerning embodiment is provided. It is sectional drawing of the negative electrode of the wound electrode body with which the nonaqueous electrolyte secondary battery concerning embodiment is provided. (A) is sectional drawing of a flat part. (B) is sectional drawing of a curved part. It is a table | surface which shows the formation conditions and each test result of each sample. It is a figure which shows the relationship between the value (d2 / d1 value) which divided the density d2 of the negative mix layer by the tap density d1 of a negative electrode active material, and a capacity | capacitance maintenance factor. It is a figure which shows the relationship between the value (d2 / d1 value) which divided the density d2 of the negative mix layer by the tap density d1 of a negative electrode active material, and resistance ratio. It is sectional drawing of the negative electrode of the wound electrode body concerning a prior art. (A) is sectional drawing of a flat part. (B) is sectional drawing of a curved part.

Embodiments of the present invention will be described below.
FIG. 1 is a cross-sectional view showing a non-aqueous electrolyte secondary battery according to the present embodiment (hereinafter, a lithium ion secondary battery will be described as an example). As shown in FIG. 1, the lithium ion secondary battery according to the present embodiment includes a wound electrode body 1 and sandwiching members 2 and 3. The wound electrode body 1 includes flat portions 5 and 6 and curved portions (curved portions) 7 and 8 sandwiched between the flat portions 5 and 6. The holding members 2 and 3 hold the flat portions 5 and 6 of the wound electrode body 1 from both sides. Therefore, a load is applied to the flat portions 5 and 6 of the wound electrode body 1, but no load is applied to the curved portions 7 and 8 of the wound electrode body 1 (even if a load is applied, it is compared with the flat portions 5 and 6. And a small load).

  FIG. 2 is an enlarged cross-sectional view of a part of the wound electrode body 1. As shown in FIG. 2, the wound electrode body 1 has a structure in which a positive electrode 10, a negative electrode 20, and a separator 30 are stacked on each other. The positive electrode 10 includes a positive electrode current collector 11 and a positive electrode mixture layer 12 provided on both sides of the positive electrode current collector 11. The negative electrode 20 includes a negative electrode current collector 21 and a negative electrode mixture layer 22 provided on both sides of the negative electrode current collector 21.

The positive electrode mixture layer 12 included in the positive electrode 10 has a positive electrode active material. The positive electrode active material is a material capable of inserting and extracting lithium, for example, lithium cobaltate (LiCoO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium nickelate (LiNiO ₂ ), and nickel cobalt that is a mixture thereof. Lithium manganate or the like can be used. An example of the composition of lithium nickel cobalt manganate is LiNi _1/3 Co _1/3 Mn _1/3 O _{2 in} which each metal element is mixed and fired at an equal ratio.

  Moreover, the positive mix layer 12 may contain the electrically conductive material. As the conductive material, for example, carbon black such as acetylene black (AB) and ketjen black, and graphite (graphite) can be used.

  The positive electrode is, for example, kneaded with a positive electrode active material, a conductive material, a solvent, and a binder (binder), applied to the positive electrode current collector 11 after drying the kneaded positive electrode mixture, and then rolled. Can be produced. Here, as the solvent, for example, an NMP (N-methyl-2-pyrrolidone) solution can be used. As the binder, for example, polyvinylidene fluoride (PVdF), styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), or the like can be used. As the positive electrode current collector 11, aluminum or an alloy containing aluminum as a main component can be used.

  The negative electrode mixture layer 22 included in the negative electrode 20 has a negative electrode active material. The negative electrode active material is made of a material capable of inserting and extracting lithium. For example, the surface of the negative electrode active material is coated with an amorphous material. As the negative electrode active material, a material obtained by coating a powdery carbon material made of graphite or the like with an amorphous material (amorphous carbon) can be used. Then, like the positive electrode, a negative electrode active material, a solvent, and a binder are kneaded, and the kneaded negative electrode mixture is applied to the negative electrode current collector 21, dried, and then rolled to produce a negative electrode. Can do. Here, as the negative electrode current collector 21, for example, copper, nickel, or an alloy thereof can be used.

In the lithium ion secondary battery according to the present embodiment, a material having a tap density d1 of 0.92 g / cm ³ or more and 1.25 g / cm ³ or less is used as the negative electrode active material. Here, the tap density is a bulk density when a predetermined container is filled with a negative electrode active material and then tapped to reduce gaps between the negative electrode active materials to be densely filled with the negative electrode active material ( For example, the number of tappings is 250). That is, the larger the tap density value, the closer the negative electrode active material is packed.

Further, the density d2 of the negative electrode mixture layer 22 formed at this time is set to 1.1 g / cm ³ or more and 1.52 g / cm ³ or less. The density of the negative electrode mixture layer 22 can be adjusted, for example, by changing the pressure when rolling the negative electrode mixture.

  Furthermore, in the lithium ion secondary battery according to the present embodiment, a value obtained by dividing the density d2 of the negative electrode mixture layer by the tap density d1 of the negative electrode active material (hereinafter also referred to as d2 / d1 value) is 1.07. It is 1.26 or less, preferably 1.07 or more and 1.23 or less, more preferably 1.07 or more and 1.19 or less, and further preferably 1.07 or more and 1.12 or less.

  As the separator, for example, a porous polymer film such as a porous polyethylene film, a porous polypropylene film, a porous polyolefin film, or a porous polyvinyl chloride film can be used alone or in combination.

  A separator is interposed between the positive electrode and the negative electrode formed as described above, and a wound electrode body is formed by winding these laminates. And the wound electrode body 1 produced in this way is crushed from the side surface direction to obtain a flat wound electrode body 1.

  Thereafter, the wound electrode body 1 is accommodated in the battery container. For example, the battery container includes a flat rectangular parallelepiped battery container main body whose upper end is opened, and a lid that closes the opening. The material constituting the battery container is preferably a metal material such as aluminum or steel. Or the container which shape | molded resin materials, such as polyphenylene sulfide resin (PPS) and a polyimide resin, may be sufficient. On the upper surface (that is, the lid) of the battery container, a positive electrode terminal electrically connected to the positive electrode of the wound electrode body 1 and a negative electrode terminal electrically connected to the negative electrode of the wound electrode body 1 are provided. Yes.

  When the wound electrode body 1 is housed in the battery container, the holding members 2 and 3 that sandwich the flat portions 5 and 6 of the wound electrode body 1 from both sides are housed in the battery container together with the wound electrode body 1. May be. Further, the side walls of the battery container may be used as the holding members 2 and 3. In this case, since it is not necessary to accommodate a new member in the battery container, the lithium ion secondary battery can be reduced in size. The sandwiching members 2 and 3 sandwich the wound electrode body 1 with a load of 500 kgf or more, for example.

  And the positive electrode lead terminal and the negative electrode lead terminal are respectively provided in the portion where the positive electrode and the negative electrode of the wound electrode body 1 are exposed (the portion without the positive electrode mixture layer and the negative electrode mixture layer), Connect each one electrically. Then, the opening part of a container main body is sealed using a cover body, and nonaqueous electrolyte solution is inject | poured from the injection hole provided in the cover body. Finally, a lithium ion secondary battery can be produced by closing the liquid injection hole with a sealing cap.

The nonaqueous electrolytic solution is a composition in which a supporting salt is contained in a nonaqueous solvent. Here, as the non-aqueous solvent, one or two selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and the like. More than one type of material can be used. The supporting salts include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiI 1 type, or 2 or more types of lithium compounds (lithium salt) selected from these etc. can be used.

  Then, a conditioning process is performed on the lithium ion secondary battery manufactured as described above. The conditioning process can be performed by repeating the charging and discharging of the lithium ion secondary battery a predetermined number of times. Note that the charge rate, the discharge rate, the set voltage for charge / discharge, etc. when performing the conditioning process can be arbitrarily set.

  In large-capacity lithium ion secondary batteries mounted on electric vehicles and hybrid vehicles, it is possible to prevent wrinkles from forming on the positive electrode and negative electrode due to expansion and contraction of the wound electrode body, and expansion of the wound electrode body. In order to maintain the shape of the lithium ion secondary battery, for example, it is necessary to restrain the wound electrode body by applying a load of 500 kgf or more.

  Further, in a lithium ion secondary battery using a wound electrode body, the flat part of the wound electrode body may be sandwiched from both sides and the wound electrode body may be restrained for use. For example, a lithium ion secondary battery may be equipped with a pressure operation type CID (Current Interrupt Device) in order to ensure safety. The pressure operation type CID detects an abnormality by monitoring an increase in the internal pressure of the battery cell during overcharge. Therefore, it is necessary to increase the internal pressure of the battery cell at the time of abnormality, and for this reason, the wound electrode body may be restrained and used.

  However, when the wound electrode body is constrained in this way, a load is applied to the flat part of the wound electrode body, but a load is applied to the curved portion sandwiched between the flat parts of the wound electrode body. It does not take. For this reason, while using the non-aqueous electrolyte secondary battery, the amount of deformation in the thickness direction of the negative electrode mixture layer varies between the flat portion where the load is applied and the curved portion where the load is not applied. That is, the thickness of the curved portion where the load is not applied is increased with respect to the flat portion where the load is applied, and the resistance of the negative electrode of the curved portion is increased. Thus, when the distribution of the resistance of the negative electrode occurs between the flat portion where the load is applied and the curved portion where the load is not applied, the battery characteristics such as lithium is deposited at a location where the resistance is high during charging and the capacity retention rate of the battery is reduced. There was a problem of lowering.

  FIGS. 7A and 7B are views for explaining the prior art, and are cross-sectional views of the negative electrode of the wound electrode body. FIG. 7A is a cross-sectional view of the flat portion, and FIG. 7B is a cross-sectional view of the curved portion. 7A and 7B illustrate a case where the negative electrode mixture layer 122 is provided only on one side of the negative electrode current collector 121 for the sake of simplicity.

As shown in FIGS. 7A and 7B, the negative electrode included in the wound electrode body includes a negative electrode current collector 121 and a negative electrode mixture layer 122 containing a negative electrode active material. Since a load is applied to the negative electrode mixture layer in the flat portion of the wound electrode body, an increase in the thickness t _f of the negative electrode mixture layer can be suppressed as shown in FIG. However, since no load is applied to the negative electrode mixture layer at the curved portion of the wound electrode body, the thickness of the negative electrode mixture layer increases as shown in FIG. That is, the thickness of the negative electrode mixture layer is t _f at the flat portion where the load is applied in the wound electrode body, whereas the thickness of the negative electrode mixture layer is t _c (t _c at the curved portion where no load is applied. > T _f ), and unevenness occurs in the thickness of the negative electrode mixture layer between the flat portion where the load is applied and the curved portion where the load is not applied. As described above, when unevenness occurs in the thickness of the negative electrode mixture layer, there is a problem that the resistance of the negative electrode is distributed between the flat portion where the load is applied and the curved portion where the load is not applied, and the battery characteristics are deteriorated.

Therefore, in the lithium ion secondary battery according to the present embodiment, a material having a tap density d1 of 0.92 g / cm ³ or more and 1.25 g / cm ³ or less is used as the negative electrode active material. The density d2 of the negative electrode mixture layer formed at this time is set to 1.1 g / cm ³ or more and 1.52 g / cm ³ or less. Furthermore, the value (d2 / d1 value) obtained by dividing the density d2 of the negative electrode mixture layer by the tap density d1 of the negative electrode active material is set to 1.07 or more and 1.26 or less.

  Thus, in the lithium ion secondary battery according to the present embodiment, the ratio of the tap density d1 of the negative electrode active material used when forming the negative electrode mixture layer and the density d2 of the negative electrode mixture layer (d2 / By setting the (d1 value) to an optimal value, it is possible to suppress unevenness in the thickness of the negative electrode mixture layer between the flat portion where the load is applied and the curved portion where the load is not applied.

  3A and 3B are cross-sectional views of the negative electrode of the wound electrode body included in the lithium ion secondary battery according to the present embodiment. 3A is a cross-sectional view of the flat portion, and FIG. 3B is a cross-sectional view of the curved portion. 3A and 3B show the case where the negative electrode mixture layer 22 is provided only on one side of the negative electrode current collector 21 for the sake of simplicity.

As shown in FIG. 3 (a), in the flat portion of the wound electrode body 1, it is possible to suppress the increase in the thickness t _f of the negative electrode mixture layer 22 because the load is applied to the negative electrode mixture layer 22 . Further, as shown in FIG. 3B, in the lithium ion secondary battery according to the present embodiment, the value obtained by dividing the density d2 of the negative electrode mixture layer by the tap density d1 of the negative electrode active material (d2 / d1 value). Therefore, even in a curved portion where no load is applied, it is possible to suppress an increase in the thickness t _c of the negative electrode mixture layer 22. Therefore, it is possible to suppress unevenness in the thickness of the negative electrode mixture layer between the flat portion where the load is applied and the curved portion where the load is not applied.

  In particular, the invention according to this embodiment is effective when a negative electrode active material whose surface is coated with an amorphous material is used. When a negative electrode active material whose surface is coated with an amorphous material is used, the particles constituting the negative electrode active material are difficult to bind to each other, so the thickness of the negative electrode mixture layer at the curved portion where no load is applied increases. It becomes easy to do. However, like the lithium ion secondary battery according to the present embodiment, the negative electrode active material is configured by setting the relationship between the tap density d1 of the negative electrode active material and the density d2 of the negative electrode mixture layer as described above. Even when the particles are difficult to bind to each other, an increase in the thickness of the negative electrode mixture layer can be suppressed. For this reason, it can suppress that the nonuniformity produces in the thickness of a negative mix layer with the flat part to which a load is applied, and the curved part to which a load is not applied.

  Therefore, according to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery and a method for manufacturing the same that can suppress deterioration in battery characteristics even when a flat wound electrode body is used in a restrained manner. .

  Next, examples of the present invention will be described.

<Production of lithium ion secondary battery>
91% by weight of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ as a positive electrode active material, 6% by weight of acetylene black (AB) as a conductive material, and 3% by weight of polyvinylidene fluoride (PVdF) as a binder Were mixed using an NMP (N-methyl-2-pyrrolidone) solution as a solvent to prepare a positive electrode mixture. Thereafter, the positive electrode mixture was applied onto an aluminum foil, dried, and then rolled at a predetermined pressure. And the positive electrode electrical power collector which has a positive mix layer was cut | judged to the desired magnitude | size, and it was set as the positive electrode.

  98% by weight of graphite (coated with amorphous carbon) as a negative electrode active material, 1% by weight of styrene butadiene rubber (SBR) as a binder, and 1% by weight of carboxymethyl cellulose (CMC) as a thickener. The negative electrode mixture was prepared by kneading. Then, after apply | coating this negative electrode mixture on copper foil and drying, it rolled with the predetermined pressure and adjusted so that the density of the negative electrode mixture layer might become a predetermined density. And after adjusting the density of a negative mix layer, the negative electrode collector which has a negative mix layer was cut | judged to the desired magnitude | size, and it was set as the negative electrode.

  The tap density d1 of the negative electrode active material used at this time, the density d2 of the negative electrode mixture layer after adjustment, and the value d2 of the negative electrode mixture layer divided by the tap density d1 of the negative electrode active material (d2 / d1 value) As shown in FIG. In this example, samples having different d2 / d1 values were produced by changing the tap density d1 of the negative electrode active material and the density d2 of the negative electrode mixture, respectively. In this example, each sample was produced by the same method except that the tap density d1 of the negative electrode active material, the density d2 of the negative electrode mixture, and the d2 / d1 value were different.

  A separator was interposed between the positive electrode and the negative electrode formed as described above, and these laminates were wound to form a wound electrode body. The produced wound electrode body was formed into a flat shape. In addition, a positive electrode lead terminal and a negative electrode lead terminal are respectively provided in a portion where the positive electrode and the negative electrode of the wound electrode body are exposed (a portion where the positive electrode mixture layer and the negative electrode mixture layer are not provided), and provided on the lid of the battery container. The positive electrode terminal and the negative electrode terminal were electrically connected to each other. Thereafter, the holding electrode is used to hold the flat portion of the wound electrode body from both sides, the wound electrode body and the holding member are accommodated in the battery container, and the opening of the container body is sealed using the lid. Stopped. Thereafter, a non-aqueous electrolyte was injected from a liquid injection hole provided in the lid, and the liquid injection hole was closed with a sealing cap.

<Measurement of capacity retention>
Each sample produced as described above was charged with a constant current up to 4.1 V at a charge rate of 1 C, and then subjected to a constant voltage charge for 2 hours to perform a conditioning process. Then, discharged to 3V at a discharge rate of 0.3 C, and the discharge capacity at this time and the initial battery capacity W _0.

Then, performed cycle test by repeating charge and discharge at predetermined conditions for each sample were determined battery capacity W ₁ after 1000 cycles. Battery capacity _{W 1,} after each sample the SOC = 100%, was discharged to 3V at a discharge rate of 0.3 C, was determined from the discharge capacity at this time. And the capacity maintenance rate (%) after 1000 cycles was calculated | required using the following formula.
Capacity maintenance rate after 1000 cycles (%) = (battery capacity W ₁ / battery capacity W ₀ ) × 100

<Measurement of resistance ratio>
After 1000 cycles of charge and discharge, the IV resistance value (normal temperature) of each sample was measured. The IV resistance value was measured by first adjusting the SOC of each sample to 60%, and then alternately discharging and charging for 10 seconds under the conditions of 1C, 2C, 5C, and 10C at room temperature. The voltage value after 2 seconds was plotted, and the IV characteristic graph of each battery was created. And IV resistance value of each sample in normal temperature was calculated | required from the inclination of an IV characteristic graph. In this example, the IV resistance value of sample H was set to 100, and the resistance ratio of each sample was obtained.

  Moreover, after repeating 1000 cycles of charging / discharging, each sample was disassembled and the wound electrode body was observed, and it was confirmed whether lithium was deposited on the curved part of the wound electrode body.

<Test results>
FIG. 4 shows the tap density d1 of the negative electrode active material, the density d2 of the negative electrode mixture layer, the d2 / d1 value, the presence or absence of lithium precipitation, the capacity retention ratio, the resistance ratio, the energy density, and the evaluation of the samples. FIG. 5 shows the relationship between the d2 / d1 value and the capacity retention ratio, and FIG. 6 shows the relationship between the d2 / d1 value and the resistance ratio.

  As shown in FIGS. 4 and 5, in samples A to G having d2 / d1 values in the range of 1.03 to 1.26, the capacity retention rate after 1000 cycles was 90% or more. In particular, the capacity retention rate tended to increase as the d2 / d1 value decreased. On the other hand, in the samples H to J having a d2 / d1 value of 1.31 or more, the capacity retention rate was smaller than 90%, and lithium was deposited on the curved portion of the wound electrode body. Therefore, when considering the capacity retention rate, samples A to G having d2 / d1 values of 1.03 to 1.26 were good.

  Further, as shown in FIGS. 4 and 6, the resistance ratio was 98 to 108 in the samples B to I having the d2 / d1 value in the range of 1.07 to 1.32. On the other hand, in the sample A having a d2 / d1 value of 1.03, the resistance ratio was as high as 116. The reason for this is considered that the density d2 of the negative electrode mixture layer is reduced because the pressure when the negative electrode mixture layer is rolled on the negative electrode current collector was small. Further, even in the sample J having a d2 / d1 value of 1.44, the resistance ratio was as high as 120. In sample J, it is considered that the resistance of the negative electrode increased because the thickness of the negative electrode mixture layer increased. Therefore, when considering the resistance ratio, Samples B to I having d2 / d1 values of 1.07 to 1.32 were good.

  Considering the above points, lithium ions having a good capacity retention ratio and resistance ratio can be obtained by setting the d2 / d1 value of the negative electrode in the range of 1.07-1.26 (that is, corresponding to samples B to G). A secondary battery could be obtained. Further, the d2 / d1 value is 1.07 to 1.23 (corresponding to samples B to F), more preferably 1.07 to 1.19 (corresponding to samples B to E), and further preferably 1.07. By setting it to 1.12 or less (corresponding to samples B to D), a lithium ion secondary battery having a good capacity retention ratio and resistance ratio value could be obtained.

  Here, comparing Sample E and Sample H in which the tap density d1 of the negative electrode active material is the same, it can be said that precipitation of lithium can be suppressed by reducing the density d2 of the negative electrode mixture layer. However, when samples B, C, E, and I having the same negative electrode mixture layer density d2 are compared, there is a sample (sample I) in which lithium is deposited even if the negative electrode mixture layer density d2 is the same. It can be seen that the characteristics of the negative electrode cannot be evaluated only by the density d2 of the agent layer.

  Further, when samples F, H, and J having the same negative electrode mixture layer density d2 are compared, it can be said that the precipitation of lithium tends to be suppressed as the tap density d1 of the negative electrode active material increases. This is presumably because the larger the tap density d1, the easier it is for the particles constituting the negative electrode active material to bind to each other. However, when samples D, I, and J are compared, the presence or absence of lithium deposition varies depending on the density d2 of the negative electrode mixture layer even if the tap density d1 of the negative electrode active material is the same. That is, in Samples I and J, lithium is precipitated, whereas in Sample D, lithium is not precipitated. Similarly, when samples E and H are compared, the presence or absence of lithium deposition varies depending on the density d2 of the negative electrode mixture layer even if the tap density d1 of the negative electrode active material is the same. That is, in sample H, lithium is precipitated, whereas in sample E, lithium is not precipitated.

  Therefore, in the present invention, attention is paid to the d2 / d1 value that is the ratio of the density d2 of the negative electrode mixture layer and the tap density d1 of the negative electrode active material, and the capacity is maintained by setting this d2 / d1 value to an appropriate value. A lithium ion secondary battery having a good rate and resistance ratio value could be obtained.

For example, in samples D, I, and J, the tap density d1 of the negative electrode active material is a small value of 0.98 g / cm ^3, and it is considered that the particles constituting the negative electrode active material are difficult to bind to each other, but d2 / d1 By setting the value to an appropriate value, Sample D had good characteristics. Similarly, in Samples E and H, the tap density d1 of the negative electrode active material is a small value of 1.08 g / cm ³ and it is considered that the particles constituting the negative electrode active material are difficult to bind to each other. By setting the value to an appropriate value, the sample E had good characteristics.

  Therefore, even when a negative electrode active material whose surface is coated with an amorphous material (that is, a negative electrode active material in which particles are not easily bonded) is used, the d2 / d1 value should be an appropriate value. Thus, the increase in the resistance of the negative electrode could be suppressed.

  Further, as shown in FIG. 4, the energy density tends to increase as the density d2 of the negative electrode mixture layer increases. For example, in Sample G in which the density d2 of the negative electrode mixture layer is the largest, the energy density is 300 Wh / L, which is the largest value. On the other hand, in Sample D where the density d2 of the negative electrode mixture layer was the smallest, the energy density was 247 Wh / L, which was the smallest value.

  The present invention has been described with reference to the above-described embodiment and examples. However, the present invention is not limited only to the configurations of the above-described embodiment and examples. It goes without saying that various modifications, corrections, and combinations that can be made by those skilled in the art within the scope of the invention are included.

DESCRIPTION OF SYMBOLS 1 Winding electrode body 2, 3 Holding member 5, 6 Flat part 7, 8 Curved part 10 Positive electrode 11 Positive electrode collector 12 Positive electrode mixture layer 20 Negative electrode 21 Negative electrode collector 22 Negative electrode mixture layer

Claims (9)

A flat wound electrode body in which a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode are laminated and wound;
A holding member that holds the flat portion of the wound electrode body from both sides, and
The negative electrode has a negative electrode mixture layer containing the negative electrode active material, and a negative electrode current collector in which the negative electrode mixture layer is laminated,
A material having a tap density of 0.92 g / cm ³ or more and 1.25 g / cm ³ or less is used for the negative electrode active material,
The density of the negative electrode mixture layer is 1.1 g / cm ³ or more and 1.52 g / cm ³ or less,
A value obtained by dividing the density of the negative electrode mixture layer by the tap density of the negative electrode active material is 1.07 or more and 1.26 or less.
Non-aqueous electrolyte secondary battery.   The nonaqueous electrolyte secondary battery according to claim 1, wherein a surface of the negative electrode active material is coated with an amorphous material.   The non-aqueous electrolyte secondary battery according to claim 2, wherein the negative electrode active material is a material obtained by coating graphite with amorphous carbon.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the holding member holds the wound electrode body with a load of 500 kgf or more.   The nonaqueous electrolyte secondary according to any one of claims 1 to 4, wherein a value obtained by dividing the density of the negative electrode mixture layer by the tap density of the negative electrode active material is 1.07 or more and 1.23 or less. battery.   The nonaqueous electrolyte secondary according to any one of claims 1 to 4, wherein a value obtained by dividing the density of the negative electrode mixture layer by the tap density of the negative electrode active material is 1.07 or more and 1.19 or less. battery.   The nonaqueous electrolyte secondary according to any one of claims 1 to 4, wherein a value obtained by dividing the density of the negative electrode mixture layer by the tap density of the negative electrode active material is 1.07 or more and 1.12 or less. battery. A positive electrode mixture containing a positive electrode active material is prepared, and the positive electrode mixture is laminated on a positive electrode current collector to form a positive electrode.
A negative electrode mixture containing a negative electrode active material is prepared, and the negative electrode mixture is laminated on a negative electrode current collector to form a negative electrode.
The positive electrode, the negative electrode, and a separator disposed between the positive electrode and the negative electrode are stacked and wound to form a flat wound electrode body,
A method for producing a non-aqueous electrolyte secondary battery, wherein the wound electrode body is sandwiched with a predetermined load using a sandwiching member,
When forming the negative electrode,
A material having a tap density of 0.92 g / cm ³ or more and 1.25 g / cm ³ or less is used for the negative electrode active material,
The negative electrode mixture layer has a density of 1.1 g / cm ³ or more and 1.52 g / cm ³ or less,
A value obtained by dividing the density of the negative electrode mixture layer by the tap density of the negative electrode active material is 1.07 or more and 1.26 or less.
A method for producing a non-aqueous electrolyte secondary battery.   The method of manufacturing a nonaqueous electrolyte secondary battery according to claim 8, wherein a surface of the negative electrode active material is coated with an amorphous material.

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