Nonaqueous electrolyte secondary battery

The present invention relates to the improvement of the negative electrode of a non-aqueous electrolyte secondary battery, and particularly to the improvement of graphite particles contained in the negative electrode active material layer.

In recent years, a non-aqueous electrolyte secondary battery has been widely used as a secondary battery having a high operating voltage and a high energy density as a power source for driving portable electronic devices such as mobile phones, notebook computers, and video camcorders. Recently, not only the above-mentioned small consumer applications but also high-power non-aqueous electrolyte secondary batteries for electric power storage and electric vehicles have been rapidly developed.

As the positive electrode active material of a lithium ion secondary battery, which is a typical non-aqueous electrolyte secondary battery, a lithium-containing composite oxide having a high potential of 4V class with respect to metallic lithium is used. For example, LiCoO with a hexagonal structure₂, LiNiO₂, And LiMn with spinel structure₂O₄Is a typical lithium-containing composite oxide. Among these, LiCoO has a high operating voltage and a high energy density.₂Is mainly used as a positive electrode active material.

Further, as the negative electrode active material, for example, a carbon material capable of occluding and releasing lithium ions is used. In particular, graphite particles are mainly used from the viewpoint of realizing a flat discharge potential and a high capacity. The higher the degree of graphitization, that is, the higher the graphite content, the higher the volume density of the carbon material.

Here, when the positive electrode and the negative electrode are manufactured, the positive electrode active material layer and the negative electrode active material layer are rolled. However, when the negative electrode active material layer containing graphite is rolled, the basal surface of graphite tends to be oriented in one direction. As a result, the edge surface of graphite, which is the inlet for lithium ions to be inserted, is not oriented toward the negative electrode surface side, and the reaction resistance between the positive and negative electrodes during the charge / discharge reaction tends to increase. When the reaction resistance becomes large, metallic lithium is deposited on the surface of the negative electrode, and the cycle life characteristic is deteriorated.

Therefore, Patent Document 1 proposes to use a negative electrode composed of a multilayer film having a graphite layer and an amorphous carbon layer. The amorphous carbon layer is arranged at a position where it easily comes into contact with the electrolytic solution.

<p><patcit num="1"><text>Japanese Unexamined Patent Publication No. 8-153514</text></patcit></p>

<p> When a multilayer film having a graphite layer and an amorphous carbon layer is used as in Patent Document 1, it is considered that the reaction resistance between the positive electrode and the negative electrode during the charge / discharge reaction can be reduced. However, since the amorphous carbon layer has a small capacity density, the battery capacity is greatly reduced. Further, since the amorphous carbon layer has a large irreversible capacity, the energy density of the battery decreases.</p><p> Therefore, the present invention maintains the battery capacity and suppresses the precipitation of lithium on the surface of the negative electrode active material layer, thereby achieving both the cycle life characteristic and the battery capacity in an excellent balance. The purpose is to provide batteries.</p>

<p> The present invention provides a positive electrode including a positive electrode current collector and a positive electrode active material layer, a negative electrode including a negative electrode current collector and a negative electrode active material layer, a porous insulating layer interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. Prepare, The negative electrode active material layer contains graphite particles, and the degree of graphitization of the graphite particles distributed on the surface side of the negative electrode active material layer is lower than the degree of graphitization of the graphite particles distributed on the negative electrode current collector side. The next battery is provided.</p><p> By distributing graphite particles having a low degree of graphitization on the surface side of the negative electrode active material layer, the reaction resistance during the charge / discharge reaction can be reduced. Therefore, the precipitation of lithium on the surface of the negative electrode active material layer is suppressed, and the irreversible capacitance of the electrode can be reduced. Therefore, the cycle life characteristics of the non-aqueous electrolyte secondary battery are greatly improved. Further, according to the present invention, since the orientation of the basal surface by rolling is unlikely to occur, it becomes easy to insert lithium ions into the negative electrode on the surface side of the negative electrode active material layer. As a result, good charge / discharge characteristics can be obtained even at a low temperature at which the viscosity of the non-aqueous electrolyte becomes high.</p><p> Further, since the graphite particles having a high degree of graphitization are distributed on the current collector side of the negative electrode active material layer, the battery capacity and the active material density can be maintained satisfactorily. That is, according to the present invention, it is possible to achieve both the cycle life characteristics of the non-aqueous electrolyte secondary battery and the battery capacity in an excellent balance.</p><p> Here, the surface side of the negative electrode active material layer means a region of 50% or less of the total thickness of the negative electrode active material layer from the surface of the negative electrode active material layer, and the current collector side of the negative electrode active material layer is the negative electrode active material. The region of less than 50% of the total thickness of the negative electrode active material layer from the contact surface of the material layer with the current collector.</p><p> As the graphite particles distributed on the surface side of the negative electrode active material layer, it is preferable that at least a part of the surface is amorphous. The degree of graphitization of the graphite particles may change stepwise or continuously in the thickness direction of the negative electrode active material layer. In this case, the degree of graphitization may increase from the surface side of the negative electrode active material layer toward the current collector side on average. The negative electrode of the present invention is the surface side of the negative electrode active material layer when the intensity of the peak of the G band is IG and the intensity of the peak of the D band is ID in Raman spectrum analysis using argon laser light having a wavelength of 5143 Å. The peak intensity ratio ID / IG in is 0.25 or more and 1.0 or less, and the peak intensity ratio ID / IG on the current collector side of the negative electrode active material layer is preferably 0.01 or more and less than 0.25.</p>

<p> According to the present invention, since the battery capacity is maintained and the precipitation of lithium on the surface of the negative electrode active material layer is suppressed, a non-aqueous electrolyte secondary battery having both cycle life characteristics and battery capacity in an excellent balance is achieved. Can be provided.</p>

<figref num="1">It is a vertical cross-sectional view schematically showing the cylindrical non-aqueous electrolyte secondary battery which concerns on one Embodiment of this invention.</figref>

The negative electrode of the non-aqueous electrolyte secondary battery includes a sheet-shaped negative electrode current collector and a negative electrode active material layer formed on one or both sides thereof. The negative electrode active material layer contains a negative electrode active material as an essential component and a binder or the like as an optional component. The negative electrode active material of the present invention contains graphite particles. Here, the graphite particles are a general term for particles including a region having a graphite structure. Therefore, the graphite particles include carbon particles having an arbitrary degree of graphitization in addition to natural graphite, artificial graphite, graphitized mesophase carbon particles and the like.

The negative electrode active material layer containing graphite particles is usually obtained by mixing a negative electrode mixture containing graphite particles and a liquid component, applying the obtained paste to a negative electrode current collector, drying the mixture, and rolling the mixture. Be done. In the negative electrode active material layer formed through such a rolling step, when the degree of graphitization of the graphite particles is large, the basal surface of graphite tends to be oriented parallel to the surface of the negative electrode current collector. Therefore, the reaction resistance during the charge / discharge reaction tends to increase. If the reaction resistance becomes excessively large, lithium may be deposited on the surface side of the negative electrode as the battery is charged and discharged, and the cycle life characteristics of the battery may be deteriorated.

On the other hand, when the graphitization degree of the graphite particles is excessively reduced in the negative electrode active material layer, it is effective in suppressing the precipitation of lithium, but the capacitance density of the negative electrode is reduced. Therefore, it is difficult to apply it to a non-aqueous electrolyte secondary battery that requires high capacity and high output.

Therefore, in the non-aqueous electrolyte secondary battery of the present invention, the degree of graphitization of the graphite particles distributed on the surface side of the negative electrode active material layer is the degree of graphitization of the graphite particles distributed on the negative electrode current collector side of the negative electrode active material layer. Is lower than.

By distributing the graphite particles having a low degree of graphitization on the surface side of the negative electrode active material layer, the orientation of the basal surface on the negative electrode surface is suppressed, and the lithium ions easily approach the edge surface of the graphite. Therefore, the reaction resistance during the charge / discharge reaction can be reduced, and the precipitation of lithium on the surface of the negative electrode active material layer can be suppressed. This improves the cycle life characteristics of the non-aqueous electrolyte secondary battery. Further, since the graphite particles having a high degree of graphitization are distributed on the current collector side of the negative electrode active material layer, the battery capacity and the active material density can be maintained at a high level.

The closer it is to the current collector side, the less likely it is that the basal surface will be oriented by rolling. Therefore, by increasing the graphitization degree of the graphite particles on the current collector side and decreasing the graphitization degree of the graphite particles on the surface side, the orientation of the basal surface can be efficiently controlled. In addition, it is possible to achieve both suppression of an increase in reaction resistance and high battery capacity at a high level.

For example, when a mixture of amorphous particles and graphite particles is distributed on the surface side of the negative electrode active material layer, the degree of graphitization becomes non-uniform on the entire surface on the surface side. In this case, a local voltage rise or the like occurs on the electrode surface, and the reaction becomes non-uniform. Further, since the basal surface of the graphite particles distributed on the surface side is oriented, there is a limit to the improvement of charge acceptability. Therefore, in the present invention, it is preferable to distribute the graphitized particles having a low degree of graphitization on the entire surface side of the negative electrode active material layer. The degree of graphitization of the graphite particles is preferably uniform over the entire surface of the outermost surface of the negative electrode active material layer.

The degree of graphitization only needs to be higher from the surface side of the negative electrode active material layer toward the negative electrode current collector side on average, and there is a region where the degree of graphitization is locally low inside the negative electrode active material layer. It may be included.

The negative electrode active material layer in which the graphitization degree of the graphite particles distributed on the surface side is lower than the graphitization degree of the graphite particles distributed on the negative electrode current collector side can be produced, for example, by the following method. Graphite particles having a predetermined degree of graphitization can be obtained by calcining a carbon material under predetermined conditions (temperature, pressure, etc.) or subjecting graphite particles to a predetermined amorphization treatment. The obtained graphite particles, a binder, and a liquid component are mixed to prepare a negative electrode active material paste. At this time, the graphitization degree of the graphite particles is changed to prepare a first negative electrode active material paste and a second negative electrode active material paste having different graphitization degrees.

A first negative electrode active material paste containing graphite particles having a high degree of graphitization is applied to a current collector and dried to form a first layer. Then, a second negative electrode active material paste containing graphite particles having a low degree of graphitization is applied to the first layer to form the second layer. As a result, a negative electrode active material layer in which the graphitization degree of the graphite particles distributed on the surface side is lower than the graphitization degree of the graphite particles distributed on the negative electrode current collector side can be obtained.

Graphite particles having different degrees of graphitization can be used, for example, by changing the temperature conditions when firing a carbon material, changing the pressure when firing a carbon material, and selecting a carbon material which is easy to crystallize and a carbon material which is difficult to crystallize. It can be obtained by using it together. Graphite particles with a low degree of graphitization lower the temperature when firing a carbon material, lower the pressure when firing a carbon material (for example, under vacuum), or use a carbon material that is difficult to crystallize. You can get it.

As a method for measuring the degree of graphitization of graphite particles, for example, Raman spectrum analysis can be mentioned. In Raman spectrum analysis using argon laser light with a wavelength of 5143 Å, when the intensity of the peak in the G band is IG and the intensity of the peak in the D band is ID, the peak intensity ratio R on the surface side of the negative electrode active material layer.₁(ID / IG) is preferably 0.25 or more and 1.0 or less, and more preferably 0.4 or more and 1.0 or less. In addition, the peak intensity ratio R on the current collector side of the negative electrode active material layer₂(ID / IG) is preferably 0.01 or more and less than 0.25. In the negative electrode active material layer showing such a peak intensity ratio, it can be said that the graphitization degree of the graphite particles distributed on the surface side is lower than the graphitization degree of the graphite particles distributed on the negative electrode current collector side. Since the negative electrode active material layer showing the above peak intensity ratio has a smaller reaction resistance during the charge / discharge reaction, the cycle life characteristics of the non-aqueous electrolyte secondary battery are greatly improved. Here, the intensity of the peak means the height of the peak.

The peak of the D band is about 1350 to 1370 cm^-1It is a peak appearing in the range of, and is a peak derived from a defect indicating the presence of carbon having low crystallinity. The peak of the G band is about 1580 to 1620 cm^-1It is a peak that appears in the range of, and is a peak derived from the graphite structure.

Peak intensity ratio R on the surface side of the negative electrode active material layer₁And the peak intensity ratio R on the current collector side₂Ratio with (R₁/ R₂) Is preferably 1.5 to 100, more preferably 3 to 20, from the viewpoint of improving the acceptability of lithium ions and the capacity of the active material.

The peak intensity ratio on the surface side of the negative electrode active material layer can be obtained by performing Raman spectrum analysis of the surface of the negative electrode active material layer that does not face the negative electrode current collector. The peak intensity ratio of the negative electrode active material layer on the current collector side can be obtained by peeling the negative electrode active material layer from the negative electrode current collector and then performing Raman spectrum analysis of the surface in contact with the current collector. Raman spectrum analysis may be performed using, for example, a commercially available laser Raman spectroscope (LabRAM HR-800 manufactured by HORIBA, Ltd., etc.).

At least a part of the surface of the graphite particles distributed on the surface side of the negative electrode active material layer is preferably amorphous, and more preferably almost the entire surface is amorphous. This randomizes the surface structure of the graphite particles and increases the number of lithium ion insertion sites. Therefore, the reaction resistance during the charge / discharge reaction can be made smaller.

The state in which at least a part of the graphite particles is amorphized can be confirmed by, for example, a commercially available laser Raman spectroscope (LabRAM HR-800 manufactured by HORIBA, Ltd., etc.).

Graphite particles in which at least a part of the surface is amorphous can be obtained, for example, by adhering an amorphous layer to the surface of the graphite particles. The method of adhering the amorphous layer to the surface of the graphite particles is not particularly limited, but for example, the surface of the natural graphite particles is coated with pitches such as a melt pitch. After that, the surface of the natural graphite particles whose surface is coated is calcined at a temperature of about 500 ° C. or higher and 2000 ° C. or lower and carbonized to obtain graphite particles in which at least a part of the surface is amorphous. Be done. The amorphous layer is not limited to that formed in such a liquid phase, and may be formed in a gas phase.

Further, by mechanically treating the graphite material, graphite particles having at least a part of the surface amorphous can be obtained. For the mechanical processing, for example, a ball mill or the like may be used.

In one embodiment of the present invention, the degree of graphitization of the graphite particles changes stepwise from the surface side of the negative electrode active material layer toward the current collector side. By lowering the graphitization degree on the surface side of the negative electrode active material layer where lithium ion acceptability is important and increasing the graphitization degree on the current collector side where orientation is unlikely to occur, the lithium ion acceptability and battery capacity Can be compatible at a high level. The degree of graphitization of the graphite particles may vary in three or more steps.

The negative electrode active material layer in which the degree of graphitization of the graphite particles changes stepwise in the thickness direction can be obtained, for example, by the following method. First, a plurality of negative electrode active material pastes containing graphite particles having different degrees of graphitization are prepared. The first negative electrode active material paste containing the graphite particles having the highest degree of graphitization is applied to the negative electrode current collector and dried to form the first layer. Next, a second layer is formed on the first layer by using the second negative electrode active material paste containing graphite particles having a lower degree of graphitization than the first negative electrode active material paste. After repeating the same process a predetermined number of times, rolling is performed. This makes it possible to prepare a negative electrode active material layer in which the degree of graphitization of the graphite particles changes stepwise in the thickness direction.

In another embodiment of the present invention, the degree of graphitization of the graphite particles continuously changes from the surface side of the negative electrode active material layer toward the current collector side. The degree of change in the degree of graphitization in the thickness direction of the negative electrode active material layer may or may not be constant. At this time, if the degree of graphitization decreases on average from the negative electrode current collector side to the surface side of the negative electrode active material layer, the degree of graphitization may be locally increased.

Examples of the shape of the graphite particles include scale-like, spherical, needle-like and the like. Of these, spherical graphite particles are preferable because they improve the filling property.

The average particle size of the graphite particles is preferably 5 to 50 μm, more preferably 15 to 25 μm in terms of improving the acceptability of lithium ions and the filling property of the graphite particles. Here, the average particle size of the graphite particles is the median diameter (D50) in the volume particle size distribution of the graphite particles. The volume particle size distribution of the graphite particles can be measured by, for example, a commercially available laser diffraction type particle size distribution measuring device.

From the viewpoint of increasing the capacity of the battery, the weight ratio of the graphite particles to the entire negative electrode active material layer is preferably, for example, 90% by weight or more, and more preferably 99% by weight or more. The amount of the binder is not particularly limited, but may be, for example, 0.5 to 7% by weight of the entire negative electrode active material layer. The thickness of the negative electrode active material layer is, for example, 90 to 220 μm, and the porosity of the negative electrode active material layer is, for example, 5 to 30%.

The binder for the negative electrode is not particularly limited, but for example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), vinylidene fluoride- Hexafluoropropylene copolymer and the like can be mentioned.

The negative electrode current collector is not particularly limited, and for example, a sheet or foil made of stainless steel, copper, or the like can be used.

The non-aqueous electrolyte secondary battery of the present invention includes the above-mentioned negative electrode, and other configurations are not particularly limited. The positive electrode includes, for example, a sheet-shaped positive electrode current collector and a positive electrode active material layer formed on one or both sides of the current collector. The positive electrode active material layer contains a positive electrode active material as an essential component, and contains a conductive material and a binder as optional components.

For the positive electrode, for example, a paste containing a positive electrode active material, a conductive agent such as carbon black, and a binder such as polyvinylidene fluoride is applied to a positive electrode current collector such as an aluminum foil, dried, and rolled. Obtained by As the positive electrode active material, a lithium-containing transition metal oxide is preferable. A typical example of a lithium-containing transition metal compound is LiCoO.₂, LiNiO₂, LiMn₂O₄, LiMnO₂, LiNi_1-yCo_yO₂(0 &lt;y &lt;1), LiNi_1-yzCo_yMn_zO₂(0 &lt;y + z &lt;1) etc. can be mentioned. As the binder for the positive electrode, for example, the same binder as those mentioned as the binder for the negative electrode can be used.

As the non-aqueous electrolyte, a liquid electrolyte composed of a non-aqueous solvent and a lithium salt dissolved therein is preferable. As the non-aqueous solvent, a mixed solvent of cyclic carbonates such as ethylene carbonate and propylene carbonate and chain carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate is generally used. In addition, γ-butyrolactone and dimethoxyethane are also used. Examples of the lithium salt include inorganic lithium fluoride and lithium imide compounds. As an inorganic lithium fluoride, LiPF₆, LIBF₄Etc., and LiN (CF) is an example of a lithium imide compound.₃SO₂)₂And so on.

As the porous insulating layer (separator), a microporous film made of polyethylene, polypropylene or the like is generally used. The thickness of the porous insulating layer is, for example, 10 to 30 μm.

The present invention can be applied to a non-aqueous electrolyte secondary battery having various shapes such as a cylindrical type, a flat type, a coin type, and a square type, and the shape of the battery is not particularly limited.

Next, the present invention will be specifically described with reference to Examples and Comparative Examples. However, the present invention is not limited to the following examples.

<p>&lt;&lt; Example 1 &gt;&gt; (a) Fabrication of negative electrode As the first graphite particles, spherical natural graphite having an average particle size of 20 μm was used. The first graphite particles, styrene-butadiene rubber (SBR) as a binder, and water were mixed to prepare a first negative electrode active material paste. Here, the amount of SBR was 1.0 part by weight per 100 parts by weight of the first graphite particles.</p><p> Further, the same spherical natural graphite as the first graphite particles described above was mechanically treated with a ball mill for 12 hours to prepare second graphite particles having an average particle size of 20 μm. When confirmed using LabRAM HR-800, a laser Raman spectroscope manufactured by HORIBA, Ltd., a part of the surface of the obtained second graphite particles was amorphized. The second graphite particles, SBR as a binder, and water were mixed to prepare a second negative electrode active material paste. Here, the amount of SBR was 1.0 part by weight per 100 parts by weight of the second graphite particles.</p><p> The first negative electrode active material paste was applied to both sides of an electrolytic copper foil (thickness 8 μm) which is a negative electrode current collector, and then dried at 110 ° C. to form a first layer. Next, the second negative electrode active material paste was applied onto the first layer and then dried at 110 ° C. to form the second layer. Then, rolling was performed to obtain a negative electrode having a thickness of 188 μm. The thickness of the negative electrode active material layer composed of the first layer and the second layer was 90 μm per side. The thickness of the first layer was 45 μm per side, and the thickness of the second layer was 45 μm per side.</p><p> Raman spectrum analysis was performed on the obtained negative electrode using argon laser light with a wavelength of 5143 Å, and the peak intensity ratio (ID / IG) between the intensity ID of the peak of the D band and the intensity IG of the peak of the G band was determined. .. Peak intensity ratio (R) on the surface side of the negative electrode active material layer₁) ID / IG is 0.5, and the peak intensity ratio (R) on the current collector side of the negative electrode active material layer₂) ID / IG was 0.15. From this, it was found that in the negative electrode of Example 1, the degree of graphitization of the graphite particles distributed on the surface side of the negative electrode active material layer was lower than the degree of graphitization of the graphite particles distributed on the negative electrode current collector side. It was. Peak intensity ratio R on the surface side of the negative electrode active material layer₁And the peak intensity ratio R on the current collector side₂Ratio with (R₁/ R₂) Was 3.3.</p><p>(b) Fabrication of positive electrode LiNi is the positive electrode active material_0.33Mn_0.33Co_0.33O₂Was used. A positive electrode active material paste was prepared by mixing 100 parts by weight of the positive electrode active material, 1.3 parts by weight of acetylene black as a conductive material, and an N-methyl-2-pyrrolidone (NMP) solution of PVDF as a binder. .. Here, the amount of PVDF was set to 1.0 part by weight per 100 parts by weight of the positive electrode active material.</p><p> The positive electrode active material paste was applied to both sides of the aluminum foil, which is a positive electrode current collector, dried at 110 ° C., and rolled. As a result, a positive electrode having a thickness of 155 μm was obtained. The thickness of the positive electrode active material layer formed on the positive electrode current collector was 70 μm per side.</p><p>(c) Preparation of non-aqueous electrolyte 5 wt% vinylene carbonate was added to a mixed solvent having a volume ratio of ethylene carbonate and dimethyl carbonate of 1: 3, and LiPF was added at a concentration of 1.4 mol / L.₆Was dissolved to obtain a non-aqueous electrolyte.</p><p>(d) Manufacture of cylindrical lithium ion secondary battery A cylindrical lithium-ion secondary battery as shown in Fig. 1 was manufactured by the following procedure.</p><p> An aluminum positive electrode lead 5a was attached to the current collector of the positive electrode 5, and a nickel negative electrode lead 6a was attached to the current collector of the negative electrode 6. Then, it was wound between the positive electrode and the negative electrode via a separator 7 made of a microporous film made of polyethylene having a thickness of 20 μm to form an electrode group.</p><p> Next, the upper insulating plate 8a and the lower insulating plate 8b were arranged at the upper and lower parts of the electrode group, respectively. The negative electrode lead 6a was welded to the inside of the battery case 1, and the positive electrode lead 5a was welded to the sealing plate 2 having the internal pressure actuated safety valve. The electrode group was housed inside the battery case 1, and the non-aqueous electrolyte was injected by a decompression method. Finally, a cylindrical lithium ion secondary battery was completed by crimping the open end of the battery case 1 to the sealing plate 2 via the gasket 3.</p><p>[Evaluation] (i) Battery capacity In a 25 ° C environment, the battery was charged with a constant current of 1.4A until the battery voltage reached 4.2V, and then charged with a constant voltage of 4.2V until the current value reached 50mA. Then, the battery was discharged at a constant current of 0.56 A until it reached 2.5 V, and the capacity of the obtained battery was determined. The results are shown in Table 1. Battery capacity is 2.4Ah, LiNi_0.33Mn_0.33Co_0.33O₂The active material capacity of was 150 mAh / g.</p><p>(ii) Cycle characteristics In a 25 ° C environment, the battery was charged with a constant current of 1.4A until the battery voltage reached 4.2V, and then charged with a constant voltage of 4.2V until the current value reached 50mA. After that, it was discharged to 2.5V with a constant current of 2.8A. This cycle was repeated for 500 cycles. The battery capacity at the first cycle was set to 100%, and the cycle capacity retention rate (%) was calculated from the battery capacity after 500 cycles. The results are shown in Table 1.</p><p><tables num="1"><img file="JP2010267540A_D0001.tif" /></tables></p><p>&lt;&lt; Comparative Example 1 &gt;&gt; The first negative electrode active material paste was prepared by mixing 100 parts by weight of spherical natural graphite similar to that in Example 1, SBR as a binder, and water. Here, the amount of PVDF was set to 1 part by weight per 100 parts by weight of the first graphite particles. Further, 50 parts by weight of non-graphitizable carbon having an average particle size of 20 μm, which is an amorphous material, 50 parts by weight of the above-mentioned spherical natural graphite, SBR as a binder, and water are mixed to obtain the first mixture. 2 Negative electrode active material paste was prepared. Here, the amount of SBR was set to 1 part by weight per 100 parts by weight of the total of non-graphitizable carbon and spherical natural graphite.</p><p> The first negative electrode active material paste was applied to both sides of an electrolytic copper foil (thickness 8 μm) which is a negative electrode current collector, and then dried at 110 ° C. to form a first layer. Then, the second negative electrode active material paste was applied on the first layer and then dried at 110 ° C. to form the second layer. Then, rolling was performed to obtain a negative electrode having a thickness of 188 μm. The thickness of the negative electrode active material layer composed of the first layer and the second layer was 90 μm per side. The thickness of the first layer was 45 μm per side, and the thickness of the second layer was 45 μm per side.</p><p> In the negative electrode active material layer of Comparative Example 1, the second layer contains a mixture of non-graphitizable carbon and spherical natural graphite, and the first layer and the second layer contain the same spherical natural graphite.</p><p> Raman spectrum analysis was performed on the obtained negative electrode using argon laser light with a wavelength of 5143 Å, and the peak intensity ratio (ID / IG) between the intensity ID of the peak of the D band and the intensity IG of the peak of the G band was determined. .. The peak intensity ratio ID / IG on the surface side of the negative electrode active material layer was 0.5, and the peak intensity ratio of the negative electrode active material layer on the current collector side was 0.15.</p><p> A cylindrical lithium ion secondary battery was produced in the same manner as in Example 1 except that the above negative electrode was used. The obtained battery was evaluated in the same manner as in Example 1. The results are shown in Table 1. The battery capacity was 2.3Ah.</p><p> Although the ID / IG ratios on the surface side and the current collector side of the negative electrode active material layer were the same between Example 1 and Comparative Example 1, there was a large difference in cycle life characteristics. Since the negative electrode of Example 1 has a substantially uniform degree of graphitization on the entire surface side, it is considered that the charge acceptability is improved and the irreversible capacity of the negative electrode is reduced as compared with the negative electrode of the comparative example. As a result, it is considered that the battery of Example 1 was able to realize high capacity and excellent cycle life characteristics.</p>

According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery having both a cycle life characteristic and a battery capacity in an excellent balance. The non-aqueous electrolyte secondary battery of the present invention is useful, for example, as a power source for consumer use, a power source for mounting on an automobile, a power source for large tools, and the like.

1 Battery case 2 Seal plate 3 Gasket 5 Positive electrode 5a positive electrode lead 6 Negative electrode 6a Negative lead 7 Separator 8a Top insulation plate 8b Lower insulation plate