Method for manufacturing a lithium-ion secondary battery, lithium-ion secondary battery

Abstract

To provide a lithium ion secondary battery which enhances Li precipitation resistance, and a method for manufacturing the same.SOLUTION: A method for manufacturing a lithium ion secondary battery includes: a first applying step (S21) of applying a first paste including a negative electrode active material on a metal negative electrode substrate of a negative electrode plate; a second applying step (S22) of applying a second paste including a negative electrode active material but not including Na over the first paste; and an orientation step (S23) of orienting particles of a negative electrode active material of the first paste along a magnetic field by applying the magnetic field on the first paste applied in the first applying step. Thereby, the method can effectively suppress the formation of, for example, NaBOB (sodium salt of oxalateborate complex) which is derived from Na, has high resistance and is slightly soluble, and the like on the surface of the negative electrode plate when a nonaqueous electrolyte is impregnated.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a lithium-ion secondary battery and a lithium-ion secondary battery. Specifically, the present invention relates to a method for manufacturing a lithium-ion secondary battery with good Li deposition resistance and a lithium-ion secondary battery.

Background Art

[0002] Since the deposition of metallic Li that occurs during high-current charging can also cause a short circuit, it is desired to suppress the generation of metallic Li. One of the causes of the deposition of metallic Li is attributed to the uneven current distribution on the negative electrode due to the uneven resistance value of the negative electrode. The reasons for this uneven resistance value are as follows. For example, CMC-Na (carboxymethyl cellulose sodium) may be contained as a constituent of the binder. Also, LiBOB (lithium bisoxalate borate) as a film-forming agent for the negative electrode may be added to the non-aqueous electrolyte. In such a case, when the electrolyte impregnates the separator from the end of the wound body, Na ions may be transferred and concentrated to the central part of the wound body by the electrolyte. Then, a film of BOB containing Na may be formed at the central part of the wound body. As a result, the resistance of the negative electrode at the central part of the wound body may increase. When the LiBOB film becomes non-uniform, the current density becomes non-uniform due to the resistance difference caused by the film thickness, and the lithium deposition resistance decreases in a part. As a result, the Li deposition resistance of the part where the charging current of the secondary battery decreases is limited, and the performance of the entire battery may decrease.

[0003] As described above, it can be said that it is not preferable to use an electrode binder for a lithium battery containing Na such as CMC. Therefore, in the invention disclosed in Patent Document 1, in a sheet-like electrode for forming an electrode active material layer on the surface of a metal foil, CMC-Li (carboxymethyl cellulose lithium) was used as a binder not containing Na. Therefore, undesirable side reactions are suppressed, and thus the charge-discharge cycle life is less affected, and it is possible to obtain a sheet-like electrode for a non-aqueous battery having very high adhesion between the metal foil surface and the electrode active material layer.

[0004] In the invention disclosed in Patent Document 1, by substituting CMC containing Na with Li to obtain CMC-Li not containing Na, it has become possible to cope with the problem of an increase in local resistance in the negative electrode caused by Na.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the invention disclosed in Patent Document 1, although the problem caused by Na is solved, there is another problem. FIG. 15(a) shows a manufacturing method of forming a negative electrode composite layer 104 by applying a paste containing CMC-Na to a negative electrode substrate 103 of a conventional negative electrode plate 102. When applying a paste containing CMC containing Na to the negative electrode substrate 103 as in the prior art, the paste was uniformly applied from a nozzle 132 to the negative electrode substrate 103 conveyed by a conveying roller 131.

[0007] However, on the other hand, there was a problem that the thickener containing CMC-Li in Patent Document 1 was likely to aggregate. In the case of CMC-Na or the like, it could be uniformly coated as shown in Fig. 15(a), but when CMC-Li was used, as shown in Fig. 15(b), the paste aggregated during coating. Then, defects were likely to occur, such as the occurrence of streak-like thickness non-uniformity 104a in the transport direction of the negative electrode plate 102. Therefore, when CMC-Li was used, even if the problems caused by Na were solved, as a result, due to the non-uniformity during coating caused by aggregation for another reason, the problem that the Li precipitation resistance deteriorated occurred.

[0008] The problem to be solved by the method for manufacturing a lithium-ion secondary battery and the lithium secondary battery of the present invention is to provide a lithium-ion secondary battery with good Li precipitation resistance.

Means for Solving the Problems

[0009] To solve the problems of the present invention, in the method for manufacturing a lithium-ion secondary battery of the present invention, a first coating step of coating a first paste containing a negative electrode active material on a metal negative electrode substrate of a negative electrode plate, a second coating step of coating a second paste containing a negative electrode active material but not containing Na on top of the first paste, and an orientation step of applying a magnetic field to the first paste coated in the first coating step before or after the second coating step to orient the particles of the negative electrode active material of the first paste along the magnetic field are provided.

[0010] The negative electrode active material may include particles made of graphite. The second paste may contain CMC-Li (lithium carboxymethyl cellulose), and the first paste may contain CMC (carboxymethyl cellulose) or CMC-Na (sodium carboxymethyl cellulose).

[0011] Further, the second coating step is performed before the alignment step, and it is preferable that the viscosity of the first paste is lower than that of the second paste. In this case, it is desirable that the viscosity of the first paste is adjusted to 300 to 2000 mPa·s, and the viscosity of the second paste is adjusted to 7000 to 40000 mPa·s.

[0012] In the alignment step, it is desirable that a magnetic field with a magnetic flux density of 0.5 T or more and an application time of 5 seconds or more is applied from a direction perpendicular to the coated surface of the negative electrode substrate. In the first coating step, a first paste is coated on the conveyed negative electrode substrate by a first die nozzle facing the conveying roller of the negative electrode substrate, and a second die nozzle arranged at a distance in the conveying direction from the first die nozzle by the second coating step coats a second paste on top of the first paste on the conveyed negative electrode substrate. This is also desirable.

[0013] The lithium ion secondary battery of the present invention is a lithium ion secondary battery including a battery case, a plate group in which a negative electrode plate, a positive electrode plate, and a separator are laminated and wound and housed in the battery case, and a non-aqueous electrolyte filled in the battery case. The negative electrode plate includes a first negative electrode composite layer containing a negative electrode active material formed on a metal negative electrode substrate, and a second negative electrode composite layer containing a negative electrode active material containing no Na formed on the first negative electrode composite layer. In the first negative electrode composite layer, the negative electrode active material is oriented in a direction perpendicular to the negative electrode substrate.

[0014] The negative electrode active material may include particles made of graphite. The second negative electrode composite layer may contain CMC-Li (lithium carboxymethyl cellulose), and the first negative electrode composite layer may contain CMC (carboxymethyl cellulose) or CMC-Na (sodium carboxymethyl cellulose).

Advantages of the Invention

[0015] The manufacturing method of the lithium ion secondary battery of the present invention, and the lithium secondary battery can be a lithium ion secondary battery with good Li precipitation resistance.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

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Figure 7

Figure 8

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Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Embodiments for Carrying Out the Invention

[0017] With reference to FIGS. 1 to 14, the lithium ion secondary battery and its manufacturing method according to the present invention will be described by taking an embodiment of the manufacturing method of the lithium ion secondary battery 10 as an example. (Outline of the First Embodiment) First, the principle by which the lithium ion secondary battery of the present embodiment can improve the Li precipitation resistance will be described.

[0018] FIG. 1 is a perspective view of a lithium ion secondary battery 10 that is a premise of the first embodiment. The lithium ion secondary battery 10 of the first embodiment includes a battery case 11 and a group of electrode plates 20 housed therein. The group of electrode plates 20 is configured by laminating and winding a negative electrode plate 2, a positive electrode plate 21, and a separator 23. The battery case 11 is filled with a non-aqueous electrolytic solution 25.

[0019] FIG. 4 is a schematic diagram showing the structure after the orientation step (FIG. 7·S23) of the negative electrode 2 of the first embodiment. The negative electrode plate 2 has a negative electrode composite layer 4 formed on a negative electrode substrate 3 made of a copper foil. The negative electrode composite layer 4 consists of a first negative electrode composite layer 4a and a second negative electrode composite layer 4b. The negative electrode composite layer 4 contains negative electrode active materials 6a and 6b made of graphite provided on the negative electrode substrate 3. It includes a first negative electrode composite layer 4a containing Na and a second negative electrode composite layer 4b containing a negative electrode active material 6 not containing Na formed on the first negative electrode composite layer 4a. In the first negative electrode composite layer 4a, the grains of the first negative electrode active material 6a are oriented in a direction perpendicular to the negative electrode substrate 3 in their major axis direction. Thus, when the negative electrode active material 6a of the first negative electrode composite layer 4a is oriented in a direction perpendicular to the negative electrode substrate 3, the negative electrode active material 6a is oriented in a direction orthogonal to the impregnation direction of the non-aqueous electrolyte 25. Therefore, the number of "meandering paths" with many detours increases and the impregnation rate decreases. On the other hand, the second negative electrode composite layer 4b formed by overlapping on the first negative electrode composite layer 4a has a configuration that does not contain Na such as CMC-Li. Also, in the second negative electrode composite layer 4b, in the coating process, the major axis direction of the second negative electrode active material 6b is generally oriented in a direction parallel to the impregnation direction of the non-aqueous electrolyte 25 by the second nozzle 33. Therefore, it is difficult to hinder the impregnation rate of the non-aqueous electrolyte 25, and the impregnation rate of the non-aqueous electrolyte 25 in the second negative electrode composite layer 4b becomes relatively faster than that in the first negative electrode composite layer 4a.

[0020] FIG. 5 is a schematic diagram showing the impregnation state of the non-aqueous electrolyte 25 in the non-aqueous electrolyte injection step (FIG. 6·S7) of the negative electrode plate 2 of the first embodiment. Due to such a configuration, the flow path 25b of the non-aqueous electrolyte 25 impregnating the second negative electrode composite layer 4b is relatively fast, and the non-aqueous electrolyte 25 impregnates so as to cover the non-aqueous electrolyte 25 impregnating the first negative electrode composite layer 4a advancing through the flow path 25b. As a result, the non-aqueous electrolyte 25 impregnating the first negative electrode composite layer 4a does not transfer Na ions to the surface side, that is, the separator 23 side, even if Na ions are eluted here. As a result, a film derived from Na that increases the resistance of the negative electrode is not formed.

[0021] The configuration of the negative electrode plate 2 of the lithium-ion secondary battery 10 in such a first embodiment can be achieved by a manufacturing method as described below. FIG. 7 is a flowchart showing the coating process (FIG. 6·S2) of the lithium-ion secondary battery of the first embodiment. The manufacturing method of the lithium-ion secondary battery 10 of the first embodiment is as follows. First, a first coating step (S21) of coating a first paste 5a containing a first negative electrode active material 6a on the negative electrode substrate 3 is performed. Next, a second coating step (S22) of coating a second paste 5b containing a second negative electrode active material 6b but not containing Na on top of the first paste 5a is performed. Then, by applying a magnetic field to the coated first paste 5a, an orientation step (S23) of selectively orienting only the particles of the first negative electrode active material 6a of the first paste 5a along the magnetic field is performed. In this case, the first paste 5a is prepared to have a viscosity of 300 to 2000 mPa·s. On the other hand, the second paste 5b is prepared to have a viscosity of 7000 to 40000 mPa·s. Therefore, when a magnetic field is applied, only the particles of the first negative electrode active material 6a in the first paste 5a with a low viscosity are selectively oriented along the magnetic field. On the other hand, the orientation of the particles of the second negative electrode active material 6b in the second paste 5b with a high viscosity does not change and they are not oriented.

[0022] (Configuration of the First Embodiment) Hereinafter, the configuration of the lithium-ion secondary battery 10 of the first embodiment and its manufacturing method will be described in detail.

[0023] <Lithium-Ion Secondary Battery of the First Embodiment> As shown in FIG. 1, the lithium-ion secondary battery 10 of the first embodiment is configured as a single cell battery. It includes a rectangular parallelepiped battery case 11 having an opening on the upper side. The battery case 11 includes a lid 12 for sealing the battery case 11. An electrode plate group 20 is housed inside the battery case 11. A non-aqueous electrolyte 25 is injected into the battery case 11 through a liquid injection hole (not shown). The battery case 11 and the lid 12 are made of a metal such as an aluminum alloy. The lithium-ion secondary battery 10 forms a sealed battery tank by attaching the lid 12 to the battery case 11. Further, the lithium-ion secondary battery 10 is provided with two external terminals 13 used for charging and discharging electric power on the lid 12.

[0024] FIG. 2 is a schematic diagram showing the configuration of the electrode plate group 20 before being wound. The electrode plate group 20 is formed by flatly winding a positive electrode plate 21, a negative electrode plate 2, and a separator 23 disposed therebetween. The electrode plate group 20 has a positive electrode plate 21 with a positive electrode substrate 21a protruding from one end side in a direction (winding axis direction) orthogonal to the winding direction, and a negative electrode plate 2 with a negative electrode substrate 3 protruding from the other end side. The winding axis direction is the vertical direction in FIG. 2.

[0025] A negative electrode composite material layer 4 is formed on the negative electrode substrate 3 of the negative electrode plate 2. A positive electrode composite material layer 22b is formed on the positive electrode substrate 21a of the positive electrode plate 21. <Positive electrode plate 21> The positive electrode plate 21 has a positive electrode composite material layer 21b formed on the surface of the positive electrode substrate 21a. The positive electrode composite material layer 21b contains a positive electrode active material. The positive electrode active material is a material capable of occluding and releasing lithium, and for example, lithium cobaltate (LiCoO2), lithium manganate (LiMn2O4), lithium nickelate (LiNiO2), etc. can be used. Also, a material obtained by mixing LiCoO2, LiMn2O4, and LiNiO2 at an arbitrary ratio may be used.

[0026] Also, the positive electrode composite material may contain a conductive material. As the conductive material, for example, carbon black such as acetylene black (AB) and ketjen black, or graphite can be used.

[0027] The positive electrode plate 21 is manufactured, for example, by kneading a positive electrode active material, a conductive material, a solvent, and a binder, applying the kneaded positive electrode mixture to a positive electrode substrate, and drying it. 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), etc. can be used. Further, as the positive electrode substrate serving as a current collector, a thin film made of aluminum or an alloy mainly composed of aluminum can be used.

[0028] <Negative electrode plate 2> A negative electrode mixture layer 4 is formed on the surface of the negative electrode substrate 3 to constitute the negative electrode plate 2. The negative electrode substrate 3 is composed of a copper foil in the first embodiment. The negative electrode substrate 3 serves as a base for the aggregate of the negative electrode active material 6 and has a function of a current collecting member that collects electricity from the negative electrode active material 6. The negative electrode plate 2 has a negative electrode mixture layer 4 formed on a metal negative electrode substrate 3. In the first embodiment, the negative electrode active material 6 is a material capable of occluding and releasing lithium ions, and a powdery carbon material made of graphite or the like is used.

[0029] As shown in the conventional negative electrode plate 102 shown in FIG. 16, conventionally, the negative electrode mixture layer 104 was a single layer and had a uniform structure as a whole. Therefore, the binder and the additive were uniformly dispersed throughout the negative electrode mixture layer 104.

[0030] <Features of the negative electrode plate 2 of the first embodiment> FIG. 4 is a schematic diagram showing the structure of the negative electrode plate 2 of the first embodiment. The feature of the negative electrode plate 2 of the first embodiment is that the negative electrode mixture layer 4 is composed of a first negative electrode mixture layer 4a and a second negative electrode mixture layer 4b. The first negative electrode mixture layer 4a is disposed by applying a paste 5a so as to be in contact with the negative electrode substrate 3. The grains of the first negative electrode active material 6a in the first negative electrode mixture layer 4a are oriented in a direction perpendicular to the negative electrode substrate 3, that is, in a direction perpendicular to the impregnation direction of the non-aqueous electrolyte 25.

[0031] Further, the second negative electrode composite material layer 4b is formed by applying a paste 5b so as to be superposed on the first negative electrode composite material layer 4b. The second negative electrode active material 6b of the second negative electrode composite material layer 4b is in a direction generally parallel to the surface of the negative electrode substrate 3 although it is random.

[0032] Note that the active material and the like are in the form of pastes 5a and 5b during coating, but are dried and cured after coating to form the negative electrode composite material layer 4 for the first time. However, for convenience of explanation, both the paste-like state after coating and the cured one may be referred to as the negative electrode composite material layer 4, the first negative electrode composite material layer 4a, and the second negative electrode composite material layer 4b.

[0033] The first negative electrode active material 6a and the second negative electrode active material 6b of the first embodiment are composed of the same graphite particles that are not perfect circles having a major axis and a minor axis. The only difference is the arrangement, i.e., whether it is arranged in the first negative electrode composite material layer 4a or the second negative electrode composite material layer 4b. Sometimes they are collectively referred to as the negative electrode active material 6.

[0034] The negative electrode plate 2 is manufactured by kneading a negative electrode active material 6, a solvent, and a binder to prepare a paste 5, and applying and drying the paste 5 on the negative electrode substrate 3. In the first embodiment, the first paste 5a for forming the first negative electrode composite material layer 4a contains a binder. The binder of the first paste 5a has a sodium salt, and examples thereof include CMC-Na (sodium carboxymethyl cellulose). Further, the binder of the second paste 5b for forming the second negative electrode composite material layer 4b does not contain a sodium salt. Examples thereof include CMC-Li (lithium carboxymethyl cellulose). Therefore, when the negative electrode plate 2 is immersed in the non-aqueous electrolyte 25, Na ions are released from the first negative electrode composite material layer 4a.

[0035] <Non-aqueous electrolyte 25> The non-aqueous electrolyte 25 is a composition in which a supporting salt is contained in a non-aqueous solvent. Here, as the non-aqueous solvent, ethylene carbonate (EC) can be used. Also, it may be one or more materials selected from the group consisting of propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), etc. Further, as the supporting salt, one or more lithium compounds (lithium salts) selected from LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC4F9SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, LiI, etc. can be used.

[0036] Also, in the lithium-ion secondary battery 10 according to the first embodiment, LiBOB (lithium bisoxalate borate) as a lithium salt as an additive which is a film-forming agent is added to the non-aqueous electrolyte 25. For example, LiBOB is added to the non-aqueous electrolyte 25 so that the concentration of LiBOB in the non-aqueous electrolyte 25 becomes 0.001 to 0.1 [mol / L].

[0037] <Separator 23> The separator 23 is a non-woven fabric made of polypropylene or the like for holding the non-aqueous electrolyte 25 between the positive electrode plate 21 and the negative electrode plate 22. Also, as the separator 23, a porous polymer membrane such as a porous polyethylene membrane, a porous polyolefin membrane, and a porous polyvinyl chloride membrane, or a lithium ion or ion-conductive polymer electrolyte membrane can be used alone or in combination. When the non-aqueous electrolyte 25 is immersed in the electrode plate group 20, the non-aqueous electrolyte penetrates from the end portion to the central portion of the separator 23. At this time, the penetration rate varies depending on the component due to the affinity with the negative electrode plate 2 and the molecular size. As described above, LiBOB added to the non-aqueous electrolyte 25 has a slower penetration rate than Na ions released from the negative electrode. Therefore, conventionally, as shown in FIG. 17, Na ions were transferred to the central portion of the separator 23 by the non-aqueous electrolyte 25, and a film with high resistance derived from Na ions was formed on the surface of the negative electrode plate 2.

[0038] <Method for manufacturing a lithium-ion secondary battery 10> FIG. 6 is a flowchart for explaining the overall flow of a method for manufacturing a lithium-ion secondary battery. Here, the overall flow of the method for manufacturing the lithium-ion secondary battery 10 according to the first embodiment will be briefly explained. Since the positive electrode and the negative electrode have different raw materials but the same manufacturing process, only the negative electrode will be described, and the description of the positive electrode will be omitted.

[0039] First, in the electrode mixture preparation step (S1), a first paste 5a and a second paste 5b made of a negative electrode mixture composed of a plurality of wet granulated bodies obtained by mixing a negative electrode active material 6, a binder, and a solvent, which are materials for the negative electrode mixture of the negative electrode plate 2, are prepared.

[0040] Here, for the first paste 5a used for the first negative electrode mixture layer 4a, a negative electrode active material 6 made of graphite is kneaded with CMC-Na as a binder together with a solvent for preparation. Also, for the second paste 5b used for the second negative electrode mixture layer 4b, a negative electrode active material 6 made of graphite is kneaded with CMC-Li as a binder together with a solvent for preparation.

[0041] Subsequently, in the coating step (S2), the pastes 5a and 5b, which are positive electrode mixtures, are coated on the positive electrode substrate 21a for the positive electrode in a film shape to form a first negative electrode mixture layer 4a and a second negative electrode mixture layer 4b having a predetermined thickness. The coating step (S2) of the first embodiment will be described in detail later.

[0042] When the coating step (S2) is completed, it is dried by the drying step (S3) to cure the negative electrode mixture layer 4. The negative electrode mixture layer 4 is cured to a predetermined hardness in the drying step (S3).

[0043] FIG. 10 is a molding machine used in the shaping step. In the shaping step (S4), the coated negative electrode mixture layer 4 is brought into contact with the surface of the negative electrode plate 2 while being pressed by a pair of press rolls 35, 35 as shown in FIG. 10 to shape the negative electrode plate 2. When the shaping step (S4) is completed, the components of the electrode plate group are completed.

[0044] Subsequently, in the electrode group assembly step (S5), as shown in FIG. 2, the completed negative electrode plate 2, the positive electrode plate 21 fabricated in the same manner, and the separator 23 are overlapped and wound to fabricate the electrode group 20 as shown in FIG. 1.

[0045] Then, in the battery assembly step (S6), as shown in FIG. 1, the electrode group 20 is inserted into the battery case 11, and external terminals 13 and the like are attached. When the assembly of the battery is completed, the non-aqueous electrolyte is injected into the battery case 11 and sealed in the non-aqueous electrolyte injection step (S7). At this time, the non-aqueous electrolyte 25 penetrates into the interior along the separator 23 from both ends of the electrode group 20. Thus, the cell of the lithium-ion secondary battery 10 is completed. After that, conditioning such as initial charging is performed to complete the lithium-ion secondary battery 10.

[0046] <Coating step (S2) of the first embodiment> FIG. 7 is a flowchart showing the details of the procedure of the coating step (S2) of the first embodiment. Next, the coating step (S2) of the first embodiment will be described in detail with reference to FIG. 7.

[0047] <First coating step (S21)> FIG. 8 is a perspective schematic view showing a coating apparatus 30 for performing the first coating step (S21) and the second coating step (S22).

[0048] The coating apparatus 30 includes a transport roller 31 that transports the negative electrode substrate 3 of the negative electrode plate 2 in the transport direction in a horizontal state. Note that auxiliary rollers, guides, etc. for horizontally supporting the negative electrode substrate 3 are not shown.

[0049] Above this conveying roller 31, a first nozzle 32 is arranged with the negative electrode substrate 3 to be conveyed sandwiched therebetween. The first nozzle 32 includes a die 32a that stores a first paste 5a therein and a nozzle 32b that discharges the first paste 5a at its lower end. The first paste 5a is supplied from a supply unit such as a tank (not shown) to the die 32a of the first nozzle 32 through a supply pipe. The nozzle 32b has a discharge port at its tip portion facing the surface of the negative electrode substrate 3. The discharge port is spaced apart from the surface of the negative electrode substrate 3. The nozzle 32b extends in a horizontal direction orthogonal to the conveying direction, and the discharge port is provided so as to correspond to the coating region on the surface of the negative electrode substrate 3. Inside the die 32a, the first paste 5a is pressurized, and the first paste 5a is discharged onto the coating region on the surface of the negative electrode substrate 3. The first nozzle 32 is controlled by a control unit (not shown) such that the discharge amount per unit time is controlled. At this time, the first negative electrode active material 6a in the first paste 5a is extended and coated as the first paste 5a is extended. Therefore, although it is random, the direction of its major axis generally becomes parallel to the coating surface of the negative electrode substrate 3.

[0050] <The first paste 5a> Here, the first paste 5a to be coated will be described. The first paste 5a is prepared to have a viscosity of 300 to 2000 mPa·s. The viscosity can be adjusted by a solvent or the like. Compared with the normal viscosity, it is considerably low. This is to make it easier to align the direction of the first negative electrode active material 6a in the first paste 5a by applying a magnetic field in the alignment step (S23).

[0051] <The second coating step (S22)> The second coating step is performed by a second nozzle 33 arranged spaced apart from the first nozzle 32 in the conveying direction. The second paste 5b is coated on top of the first paste 5a already coated by the first nozzle 32 on the conveyed negative electrode substrate 3.

[0052] The second nozzle 33 has the same basic configuration as the first nozzle 32. The second nozzle 33 includes a die 33a and a nozzle 33b. In the horizontal position, the second nozzle 33 is higher than the first nozzle 32. It is arranged higher by the thickness of the second negative electrode composite layer 4b formed from the negative electrode substrate 3.

[0053] <The second paste 5b> Here, the second paste 5b to be applied will be described. The second paste 5b is prepared to have a viscosity of 7000 - 40000 mPa·s. The viscosity can be adjusted with a solvent or the like. Compared with the first paste 5a, the viscosity is considerably higher. This is to prevent the orientation of the second negative electrode active material 6b in the second paste 5b from changing even when a magnetic field is applied during the orientation step (S23).

[0054] <Orientation step (S23)> FIG. 3 is a schematic diagram showing the structure of the negative electrode before the orientation step of the first embodiment. As shown in FIG. 3, at the time when the first coating step (S21) and the second coating step (S22) are completed, the first negative electrode active material 6a in the first negative electrode composite layer 4a and the second negative electrode active material 6b in the second negative electrode composite layer 4b are not oriented. That is, the first paste 5a discharged from the first nozzle 32 and the second paste 5b discharged from the second nozzle 33 are both subject to the tensile force due to coating. Therefore, although somewhat random as schematically shown in FIG. 3, they are generally in a direction parallel to the surface of the negative electrode substrate 3.

[0055] FIG. 9 is a perspective schematic view showing an aligning device 34 that performs an aligning step (S23). The negative electrode plate 2 has a first negative electrode composite layer 4a formed on the negative electrode substrate 3 in the first coating step (S21) and the second coating step (S22), and a second negative electrode composite layer 4b further formed thereon. A magnetic field generating device 34a is disposed below the negative electrode plate 2. The magnetic field generating device 34a generates a magnetic field with a predetermined intensity in the direction of the arrow by a control device and a driving device (not shown). The magnetic field application conditions in the first embodiment are that the magnetic flux density is 0.5 T or more and the application time is 5 seconds or more. When such a magnetic field is generated by the magnetic field generating device 34a, the first negative electrode active material 6a of the first negative electrode composite layer 4a and the second negative electrode active material 6b of the second negative electrode composite layer 4b of the negative electrode plate 2 are affected by the magnetic field. That is, the major axis of the first negative electrode active material 6a is oriented in the direction along the magnetic field lines. The second negative electrode active material 6b is also affected by the magnetic field, but since the viscosity of the second paste 5b is adjusted to 7000 to 40000 mPa·s, its posture does not change. For this purpose, an excessive magnetic field should not be applied.

[0056] FIG. 4 shows the structure of the negative electrode plate 2 after the aligning step (S23) of the first embodiment. The major axis direction of the first negative electrode active material 6a of the first negative electrode composite layer 4a of the negative electrode plate 2 is oriented in the direction perpendicular to the negative electrode substrate 3 along the magnetic field lines. On the other hand, the second negative electrode active material 6b of the second negative electrode composite layer 4b is not oriented, and its major axis direction remains substantially parallel to the negative electrode substrate 3.

[0057] (Operation of the First Embodiment) <Suppression of Transfer of Na Ions during Infiltration with Non-Aqueous Electrolyte> The manufacturing method of the lithium ion secondary battery 10 of the first embodiment includes the above-described coating step (S2), and a non-aqueous electrolyte injection step (S7) is performed.

[0058] FIG. 5 is a schematic view showing the state of infiltration of the non-aqueous electrolyte 25 in the non-aqueous electrolyte injection step (S7) in the negative electrode plate 2. After the alignment step (S23), in the first negative electrode composite layer 4a of the negative electrode plate 2, the major axis direction of the first negative electrode active material 6a is aligned in a direction perpendicular to the negative electrode substrate 3 along the magnetic field lines. On the other hand, in the second negative electrode composite layer 4b of the second negative electrode active material 6b, without being affected by the magnetic field lines, the major axis direction is aligned in a direction along the surface of the negative electrode substrate 3.

[0059] After such an alignment step (S23), a non-aqueous electrolyte injection step (S7) is performed. In the non-aqueous electrolyte injection step (S7), when the non-aqueous electrolyte 25 is injected from the injection hole (not shown) of the battery case 11, the non-aqueous electrolyte 25 is impregnated along the separator 23 from the end of the electrode plate group 20.

[0060] In the first negative electrode composite layer 4a in which the major axis direction is aligned in a direction perpendicular to the negative electrode substrate 3, when viewed from the impregnation direction of the non-aqueous electrolyte 25, that is, the direction along the surface of the negative electrode substrate 3, the projected area of the first negative electrode active material 6a becomes large. In other words, since the non-aqueous electrolyte 25 to be impregnated has many "detours" that block the path in its traveling direction, the flow path becomes long and the flow path resistance is also large.

[0061] On the other hand, in the second negative electrode composite layer 4b in which the major axis direction is aligned in a direction along the surface of the negative electrode substrate 3, when viewed from the impregnation direction of the non-aqueous electrolyte 25, that is, the direction along the surface of the negative electrode substrate 3, the projected area of the second negative electrode active material 6b becomes small. In other words, since the non-aqueous electrolyte 25 to be impregnated has few "detours" in its traveling direction, the flow path is relatively short and the flow path resistance is also low.

[0062] FIG. 12 is a graph showing the relationship between the tortuosity [%] and the penetration rate [mm / min]. The tortuosity [%] is the ratio of the tortuous area / the opening area in the traveling direction. If there are many detours, the non-aqueous electrolyte 25 has to detour and cannot go straight. Looking at how the penetration rate [mm / min] of the non-aqueous electrolyte 25 actually changes with the tortuosity [%], it is clear that as the tortuosity [%] increases, the penetration rate [mm / min] decreases.

[0063] Then, the non-aqueous electrolyte 25 is slowly impregnated in the first negative electrode composite material layer 4a and is also slowly impregnated in the second negative electrode composite material layer 4b. As shown in FIG. 5, the non-aqueous electrolyte 25 impregnating the first negative electrode composite material layer 4a impregnates the first flow path 25a, while the non-aqueous electrolyte 25 impregnating the second negative electrode composite material layer 4b impregnates the second flow path 25b. At this time, the non-aqueous electrolyte 25 impregnating the first flow path 25a is a non-aqueous electrolyte 25 containing Na ions derived from CMC-Na contained in the first negative electrode composite material layer 4a. On the other hand, the non-aqueous electrolyte 25 impregnating the second flow path 25b is a non-aqueous electrolyte 25 not containing Na ions due to CMC-Li contained in the second negative electrode composite material layer 4b. Then, the non-aqueous electrolyte 25 impregnating the second flow path 25b, which has a faster impregnation rate than this, precedes and first wraps around the first negative electrode composite material layer 4a. Thereafter, the non-aqueous electrolyte 25 of the first flow path 25a, which has been impregnated later, flows in such a way as to penetrate into the non-aqueous electrolyte 25 impregnating the second flow path 25b, and the transfer of Na ions to the separator 23 side is suppressed.

[0064] <Improvement in lithium precipitation resistance> FIG. 12 is a graph showing the relationship between the width position [mm] in the width direction from one end of the electrode plate group 20 in the negative electrode plate 2 and the resistance [Ω]. The resistance [Ω] of the lithium ion secondary battery 10 by the manufacturing method of the lithium ion secondary battery 10 as described above is not much different in the vicinity of the end portion compared with the resistance [Ω] of the lithium ion secondary battery by the conventional manufacturing method. However, it can be seen that there is a significant difference in the central portion (40 to 80 mm).

[0065] From the results, it can be understood that it is possible to effectively suppress the formation of hardly soluble NaBOB (sodium salt of oxalate borate complex) with a high resistance value derived from Na, for example, on the surface of the negative electrode plate 2, where there is almost no Na ion. Examples of NaBOB include sodium bisoxalatoborate · Na(B(C2O4)2). So to speak, since Na ions are confined in the first negative electrode composite layer 4a, even if NaBOB is generated in the first negative electrode composite layer 4a close to the negative electrode substrate 3, it has almost no influence on the resistance value between the negative electrode plate 2 and the positive electrode plate 21. As a result, unevenness in the current distribution of the negative electrode does not occur due to unevenness in the resistance value of the negative electrode plate 2. If unevenness in the current distribution of the negative electrode does not occur, precipitation of metallic Li caused by this is also less likely to occur.

[0066] As a result, the Li precipitation resistance of the portion where precipitation of metallic Li has occurred is not restricted, and the performance of the entire lithium-ion secondary battery 10 can be improved. <Improvement in capacity retention rate [%]> FIG. 13 is a graph comparing the capacity retention rate [%] of the lithium-ion secondary battery 10 manufactured by the manufacturing method of the first embodiment and a conventional lithium-ion secondary battery. As described above, in the lithium-ion secondary battery 10 manufactured by the manufacturing method of the first embodiment, precipitation of metallic Li is also less likely to occur, so the occurrence of minute internal short circuits is also suppressed. As a result, when the capacity retention rate [%] of the conventional lithium-ion secondary battery was 90%, the capacity retention rate [%] of the lithium-ion secondary battery 10 manufactured by the manufacturing method of the first embodiment exceeded 93%, and the effect was confirmed.

[0067] (Effect of the first embodiment) According to the manufacturing method of the lithium-ion secondary battery 10 of the first embodiment, the following effects can be achieved.

[0068] (1) In the manufacturing method of the lithium-ion secondary battery 10 according to the first embodiment, a first coating step (S21) of coating a first paste 5a containing a first negative electrode active material 6a on a negative electrode substrate 3 of a negative electrode plate 2 is provided. Further, a second coating step (S22) of coating a second paste 5b containing a second negative electrode active material 6b but not containing Na on top of the first paste 5a is provided. Then, after the second coating step, an orientation step (S23) of applying a magnetic field to the first paste 5a coated in the first coating step (S21) to orient the particles of the negative electrode active material of the first paste along the magnetic field is provided. Therefore, the first negative electrode active material 6a in the first negative electrode composite layer 4a can be oriented so that the tortuous paths of the non-aqueous electrolyte 25 increase, and the impregnation rate of the non-aqueous electrolyte 25 can be slowed down. Therefore, the first flow path 25a of the non-aqueous electrolyte 25 in the first negative electrode composite layer 4a with a slow speed flows so as to be covered by the second flow path 25b of the non-aqueous electrolyte 25 that impregnates the second negative electrode composite layer 4b with a relatively fast speed without such orientation. As a result, almost no Na ions exist on the surface of the negative electrode plate 2. Therefore, the variation in the resistance of the surface of the negative electrode plate 2 is suppressed, and the Li precipitation resistance can be enhanced.

[0069] (2) Since the negative electrode active material 6 contains particles made of graphite, it can be easily oriented when a magnetic field is applied. (3) Since the second paste 5b contains CMC-Li (lithium carboxymethyl cellulose), the Na component is excluded from the second paste 5b, and Na ions cannot be eluted into the non-aqueous electrolyte 25 flowing into the second negative electrode composite layer 4b.

[0070] (4) On the other hand, since the first paste 5a contains CMC (carboxymethyl cellulose) or CMC-Na (sodium carboxymethyl cellulose), aggregation hardly occurs, and the first negative electrode composite layer 4a can be formed uniformly. Therefore, even if a difference in thickness due to aggregation occurs in the second negative electrode composite layer 4b, this can be compensated for.

[0071] (5) The second coating step (S22) is performed before the orientation step (S23), and the first paste 5a has a lower viscosity than the second paste 5b. Therefore, when the second negative electrode composite material layer 4b is stacked on the first negative electrode composite material layer 4a, only the first negative electrode active material 6a of the first negative electrode composite material layer 4a can be selectively oriented by utilizing the viscosity difference.

[0072] (6) In the first embodiment, the first paste 5a is prepared to have a viscosity of 300 to 2000 mPa·s, and the second paste 5b is prepared to have a viscosity of 7000 to 40000 mPa·s. Therefore, in the orientation step (S23), only the first negative electrode active material 6a can be surely and selectively oriented.

[0073] (7) In the orientation step (S23) of the first embodiment, a magnetic field with a magnetic flux density of 0.5 T or more and an application time of 5 seconds or more is applied from a direction perpendicular to the coating surface of the first paste 5a by the magnetic field generating device 34a of the orientation device 34. Therefore, the particles of the negative electrode active material of the first paste can be effectively oriented along the magnetic field.

[0074] (8) In the first embodiment, in the first coating step (S21), the first paste 5a is coated on the conveyed negative electrode substrate 3 by the first nozzle 32 facing the conveying roller 31 of the negative electrode substrate 3. At the same time, in the second coating step (S22), the second paste 5b is coated on the first paste 5a on the conveyed negative electrode substrate 3 by the second nozzle 33 arranged at a distance from the first nozzle 32 in the conveying direction. Therefore, efficient production can be achieved by the second coating step (S22) continuous with the first coating step (S21).

[0075] (9) According to the manufacturing method of the lithium-ion secondary battery 10 of the first embodiment, the negative electrode plate 2 includes a first negative electrode composite material layer 4a containing a first negative electrode active material 6a formed on a negative electrode substrate 3 made of metal. Further, it includes a second negative electrode composite material layer 4b that contains a second negative electrode active material 6b formed on the first negative electrode composite material layer 4a and does not contain Na. And the first negative electrode composite material layer 4a can manufacture the lithium-ion secondary battery 10 in which the first negative electrode active material 6a is oriented in a direction perpendicular to the negative electrode substrate 3.

[0076] (Second Embodiment) <Coating Process (S2) of the Second Embodiment> In the coating process (S2) of the first embodiment, after the first coating process (S21), the second coating process (S22) was performed, and then the orientation process (S23) was performed.

[0077] In the coating process (S2) of the second embodiment, it is different in that after the first coating process (S121), the orientation process (S122) is performed, and then the second coating process (S123) is performed. The following will explain the second embodiment in detail, but the explanations of the points common to the first embodiment will be omitted.

[0078] <First Coating Process (S121)> When starting the coating process (S2), the first coating process (S121) is performed. Basically, it is the same as the first coating process (S21) of the embodiment. The difference is that the second coating process (S123) is performed independently without being continuous. Therefore, instead of the coating device 30 shown in FIG. 7, it can be implemented using a general-purpose coating device 101 that has been conventionally used as shown in FIG. 15(a). Here, as in the prior art, a paste using CMC-Na is coated on the negative electrode substrate 3 of the negative electrode plate 2 to form the first negative electrode composite material layer 4a. When coating the first paste 5a containing CMC containing Na as in the prior art on the negative electrode substrate 3, the paste is uniformly coated on the negative electrode substrate 3 conveyed to the conveying roller 131 from the nozzle 132. In the conventional coating device 101, the nozzle 132 is single, and a general-purpose device from the prior art can be utilized.

[0079] <First paste 5a> Here, the first paste 5a to be applied will be described. In the first embodiment, the first paste 5a was prepared to have a viscosity of 300 to 2000 mPa·s. The viscosity can be adjusted with a solvent or the like. Compared with the normal viscosity, it is considerably lower. This is because in the alignment step (S23), a magnetic field is applied to the first negative electrode active material 6a in the first paste 5a to make it easier to align the orientation. However, this viscosity is not limited in the second embodiment. That is, by increasing the viscosity until the shape is stable and increasing the magnetic flux density of the applied magnetic field or lengthening the application time in the alignment step (S122), it is possible to apply the paste at a higher viscosity than in the first embodiment. Also, the blending of the solvent can be reduced to improve the dimensional accuracy. Furthermore, it is also possible to shorten the curing time by drying.

[0080] <Alignment step (S122)> The alignment step (S122) of the second embodiment is the same process as the alignment step (S23) of the first embodiment. However, as described above, the magnetic flux density of the applied magnetic field can be increased or the application time can be lengthened to be compatible with the adjustment of the viscosity of the first paste 5a.

[0081] <Second coating step (S123)> The second coating step (S123) of the second embodiment is not performed continuously with the first coating step (S21) like the second coating step (S22) of the first embodiment, but is performed independently.

[0082] Therefore, similar to the first coating step (S121), it can be carried out using a general-purpose coating apparatus 101 that has been conventionally used as shown in Fig. 15(a). Here, the second paste 5b is applied on top of the first negative electrode composite layer 4a formed by applying the first paste 5a in the first coating step (S121). Therefore, the gap between the conveying roller 131 and the nozzle 132 in the second coating step (S123) is set wider by the thickness of the first negative electrode composite layer 4a than in the case of the first coating step (S121).

[0083] Here, the second paste 5b is applied on top of the first negative electrode composite material layer 4a. The second paste 5b is a paste using CMC-Li that does not contain Na. It is possible.

[0084] <The second paste 5b> Here, the second paste 5b to be applied will be described. In the first embodiment, the viscosity of the second paste 5b was adjusted to 7000 - 40000 mPa·s. This is because an orientation step (S22) is performed on the first negative electrode composite material layer 4a and the second negative electrode composite material layer 4b superimposed thereon, and only the first negative electrode active material 6a of the first negative electrode composite material layer 4a is oriented, so a difference in viscosity is provided.

[0085] In the second embodiment, before the second coating step (S123), in the orientation step (S122), the first negative electrode active material 6a of the first negative electrode composite material layer 4a has already been oriented. Therefore, in the second embodiment, it is not necessary to increase the viscosity so that the second negative electrode active material 6b contained in the second paste 5b is not oriented in the orientation step (S122).

[0086] On the other hand, the second paste 5b does not contain CMC or CMC-Na, and only CMC-Li is blended. This can effectively suppress the formation of lithium bisoxalatoborate·Na (B(C2O4)2) etc. derived from Na ions.

[0087] However, CMC-Li tends to aggregate, and streaks are formed in the conveying direction during the coating process, and there is a problem that non-uniformity is likely to occur in the thickness of the composite material layer. For this reason, in the second embodiment, unlike the first embodiment, since there is no viscosity limit, the viscosity of the second paste 5b can be freely adjusted. Also, if it does not contain Na, it can be blended with other binders etc. The viscosity can be adjusted with a solvent or the like.

[0088] (Function of the second embodiment) In the second embodiment, although the manufacturing method is different from that of the first embodiment, basically, the configuration of the negative electrode plate 2 shown in FIG. 4 can be obtained. Therefore, the same operation as in the first embodiment occurs.

[0089] That is, as shown in FIG. 5, the non-aqueous electrolyte 25 that infiltrates the first negative electrode composite material layer 4a infiltrates the first flow path 25a, while the non-aqueous electrolyte 25 that infiltrates the second negative electrode composite material layer 4b infiltrates the second flow path 25b. At this time, the non-aqueous electrolyte 25 that infiltrates the first flow path 25a becomes a non-aqueous electrolyte 25 containing Na ions due to CMC-Na contained in the first negative electrode composite material layer 4a. On the other hand, the non-aqueous electrolyte 25 that infiltrates the second flow path 25b becomes a non-aqueous electrolyte 25 that does not contain Na ions due to CMC-Li contained in the second negative electrode composite material layer 4b. Then, the non-aqueous electrolyte 25 that infiltrates the second flow path 25b, which has a faster infiltration rate than this, precedes and first wraps the first negative electrode composite material layer 4a. After that, the non-aqueous electrolyte 25 of the first flow path 25a that infiltrates later has a flow that dives into the non-aqueous electrolyte 25 that infiltrates the second flow path 25b, and the flow out to the separator 23 side is suppressed.

[0090] As a result, it is possible to effectively suppress the formation of hardly soluble NaBOB (sodium salt of oxalate borate complex) having a high resistance value derived from Na, for example, with almost no Na ions on the surface of the negative electrode plate 2. Examples of NaBOB include sodium bisoxalatoborate · Na(B(C2O4)2). In other words, since Na ions are confined in the first negative electrode composite material layer 4a, even if NaBOB is generated in the first negative electrode composite material layer 4a close to the negative electrode substrate 3, it has almost no influence on the resistance value between the negative electrode plate 2 and the positive electrode plate 21. As a result, unevenness in the current distribution of the negative electrode does not occur due to unevenness in the resistance value of the negative electrode plate 2. If unevenness in the current distribution of the negative electrode does not occur, precipitation of metallic Li caused by this is also unlikely to occur.

[0091] As a result, without being limited to the Li deposition resistance of the portion where the deposition of metallic Li occurred, the performance of the entire lithium-ion secondary battery 10 can be improved. (Effect of the Second Embodiment) The effects of the second embodiment are as follows in addition to the effects (1) to (4), (7), and (9) of the first embodiment.

[0092] (10) The first coating step (S121) and the second coating step (S123) can be performed by a conventional general-purpose coating apparatus as illustrated in FIG. 15(a). The equipment can be simplified and the production cost can be reduced.

[0093] (11) The first paste 5a and the second paste 5b are not in a selective orientation process of orienting only the first negative electrode active material and not orienting the second negative electrode active material as in the first embodiment. Therefore, the viscosity and composition of the first paste 5a can be determined independently of the second paste 5b.

[0094] (12) The second paste 5b of the second embodiment contains CMC-Li and is likely to aggregate and cause streaks during coating. In the second embodiment, the second paste 5b can have a viscosity that prevents non-uniformity in thickness from occurring during the coating process, regardless of the orientation step (S122).

[0095] (Other Alternative Examples) ○ In the embodiment, the first negative electrode active material 6a and the second negative electrode active material 6b are exemplified as the same graphite particles, but for example, those having different particle sizes, aspect ratios, shapes, etc. may be used separately.

[0096] ○ The binders exemplified are CMC, CMC-Na, CMC-Li, etc., but are not limited thereto. 〇 The film-forming agent exemplified is BOB, but is not limited thereto.

[0097] ○Although the electrode group of the present embodiment is exemplified as a wound type, it may also be a laminated type electrode group. Further, each raw material is an example and is not limited thereto. ○The exemplified lithium ion secondary battery 10 includes a plate-shaped case, but its shape is not limited, such as a cylindrical shape.

[0098] ○The flowcharts shown in FIGS. 6, 7, and 14 are examples, and the procedures can be added, deleted, changed, or the order can be changed and still implemented. ○The manufacturing method of the lithium ion secondary battery of the present embodiment is one embodiment of the invention, and it goes without saying that it is not limited to the embodiment and can be implemented by those skilled in the art by adding, deleting, or changing its configuration without departing from the scope of the claims.

Explanation of Reference Numerals

[0099] 2... Negative electrode plate 3... Negative electrode substrate 4... Negative electrode composite layer 4a... First negative electrode composite layer 4b... Second negative electrode composite layer 5... Paste 5a... First paste 5b... Second paste 6... Negative electrode active material (graphite) 6a... First negative electrode active material 6b... Second negative electrode active material 10... Lithium ion secondary battery 11... Battery case 12... Cover 13... External terminal 20... Electrode group 21... Positive electrode plate 21a... Positive electrode substrate 21b... Positive electrode composite layer 23... Separator 25... Non-aqueous electrolyte 25a... Flow path 1 25b... Flow path 2 30... Coating device 31... Conveyor roller 32... First nozzle 33... Second nozzle 34... Alignment device 34a... Magnetic field generating device 35... Press roll

Claims

1. A first coating step of coating a first paste containing a negative electrode active material containing particles made of graphite and CMC-Na (sodium carboxymethyl cellulose) on a metal negative electrode substrate of a negative electrode plate; A second coating step of coating a second paste containing the negative electrode active material and CMC-Li (lithium carboxymethyl cellulose) not containing Na on top of the first paste; Before or after the second coating step, by applying a magnetic field to the first paste coated in the first coating step from a direction perpendicular to the coated surface of the negative electrode substrate, the particles of the negative electrode active material in the first paste are oriented along the magnetic field, and the second paste is provided with an orientation step of not orienting the particles of the negative electrode active material in a direction perpendicular to the negative electrode substrate. A method for manufacturing a lithium-ion secondary battery, characterized in that.

2. The second coating step is performed before the orientation step, The method for manufacturing a lithium-ion secondary battery according to claim 1, wherein the first paste has a lower viscosity than the second paste.

3. The method for manufacturing a lithium-ion secondary battery according to claim 2, wherein the first paste is prepared to have a viscosity of 300 to 2000 mPa·s, and the second paste is prepared to have a viscosity of 7000 to 40000 mPa·s.

4. The method for manufacturing a lithium-ion secondary battery according to any one of claims 1 to 3, wherein in the orientation step, a magnetic field is applied with a magnetic flux density of 0.5 T or more and an application time of 5 seconds or more.

5. In the first coating step, the first paste is coated on the conveyed negative electrode substrate by a first nozzle facing the conveying roller of the negative electrode substrate, and the second coating step is spaced apart from the first nozzle in the conveying direction. The method for manufacturing a lithium-ion secondary battery according to any one of claims 2 to 4, wherein a second paste is coated on top of the first paste on the conveyed negative electrode substrate by a second nozzle arranged in such a manner.

6. A lithium-ion secondary battery comprising a battery case, a group of electrode plates in which a negative electrode plate, a positive electrode plate, and a separator are laminated and wound and housed in the battery case, and a non-aqueous electrolyte filled in the battery case. The negative electrode plate includes a first negative electrode composite layer containing a negative electrode active material including particles made of graphite formed on a metal negative electrode substrate and CMC-Na (sodium carboxymethyl cellulose), and a second negative electrode composite layer formed on the first negative electrode composite layer and containing the negative electrode active material and CMC-Li (lithium carboxymethyl cellulose) not containing Na. The first negative electrode composite layer is characterized in that the negative electrode active material is oriented in a direction perpendicular to the negative electrode substrate, and the second negative electrode composite layer is characterized in that the negative electrode active material is not oriented in a direction perpendicular to the negative electrode substrate. A lithium ion secondary battery.

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