Lithium ion secondary battery and method for manufacturing the same

Abstract

To suppress precipitation of metal lithium Li on a negative electrode sheet of a lithium ion secondary battery.SOLUTION: A lithium ion secondary battery includes an electrode body in which a positive electrode sheet and a negative electrode sheet are stacked and wound through a separator 4, and a nonaqueous electrolyte solution is filled, the nonaqueous electrolyte solution being added with a film forming material containing a lithium salt. When a negative electrode mixture layer 22 of the negative electrode sheet contains Na, by providing a resistive layer, a resistance distribution is set according to the resistance distribution of the negative electrode mixture layer 22 for resistance [Ω] at each position of the separator 4 in a width direction orthogonal to the winding direction, and a combined resistance at each position of the negative electrode mixture layer 22 and the separator 4 is equalized.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a lithium ion secondary battery and a manufacturing method thereof, and more particularly to a lithium ion secondary battery that suppresses deposition of metallic lithium Li on a negative electrode plate and a manufacturing method thereof. [Background technology]

[0002] Lithium ion secondary batteries are lightweight, have high energy density, and are capable of inputting and outputting large currents, and therefore are preferably used as high-output power sources for driving vehicles and stationary power storage facilities.

[0003] FIG. 1 is a perspective view showing the appearance of a lithium ion secondary battery 10 of this embodiment. FIG. 2 is a schematic diagram showing an electrode body of the lithium ion secondary battery 10 of this embodiment. FIG. 14 is a schematic diagram showing the lithium ion Li when the conventional lithium ion secondary battery 10 is being charged. + FIG.

[0004] The lithium ion secondary battery 10 has a separator 4 holding a non-aqueous electrolyte 13 between a positive electrode plate 3 and a negative electrode plate 2, which are then laminated and wound to form an electrode assembly 12. Incidentally, in the lithium ion secondary battery 10, when the battery is initially charged after manufacture, a film of SEI (Solid Electrolyte Interface) is formed on the surface of the negative electrode active material 24 of the negative electrode mixture layer 22. The SEI film is present between the negative electrode active material 24 and the non-aqueous electrolyte solution 13, and the lithium ions Li + The SEI film facilitates the absorption and release of oxygen into and from the negative electrode, and also suppresses the decomposition of the non-aqueous electrolyte solution 13. For this reason, the SEI film is essential for maintaining good battery characteristics.

[0005] On the other hand, in the conventional lithium-ion secondary battery 10, the SEI film grows due to charging and discharging after production, and the resistance [Ω] increases. +and consumes the nonaqueous electrolyte 13. For this reason, an additive such as lithium bis(oxalato)borate (LiBOB) is sometimes added to suppress the growth of the SEI film.

[0006] However, when negative electrode mixture layer 22 contains Na, there is a problem in that the resistance [Ω] of central portion 22a in width direction W of negative electrode mixture layer 22 becomes large. When charging is performed in this state, current flows more easily through end portion 22b of negative electrode mixture layer 22, which has a smaller resistance than central portion 22a of negative electrode mixture layer 22 in the width direction W of negative electrode plate 2, and the current density [A / mm 2 As a result, local overcharging or the like occurs, and there is a problem in that metallic lithium Li is easily precipitated in negative electrode mixture layer 22.

[0007] In view of this, Patent Document 1 discloses an invention in which the amount of Na in the negative electrode mixture layer is adjusted to make the resistance distribution of the positive and negative electrodes uniform. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2023-43975 A Summary of the Invention [Problem to be solved by the invention]

[0009] However, there is a problem in that the adjustment of the Na content in negative electrode mixture layer 22 as in the invention described in Patent Document 1 cannot sufficiently uniformize the resistance distribution of the negative electrode. The problem to be solved by the lithium ion secondary battery and the method for producing the same of the present invention is to suppress the precipitation of metallic lithium Li on the negative electrode plate. [Means for solving the problem]

[0010] In order to solve the above problems, the lithium ion secondary battery of the present invention is a lithium ion secondary battery including an electrode body in which a positive electrode plate and a negative electrode plate are stacked and wound with a separator interposed therebetween and filled with a nonaqueous electrolyte, wherein a coating material containing a lithium salt is added to the nonaqueous electrolyte, and when the negative electrode composite layer of the negative electrode plate contains Na, a resistance [Ω] at each position in the width direction perpendicular to the winding direction of the separator is set to a resistance distribution according to the resistance distribution of the negative electrode composite layer, and a combined resistance of the negative electrode composite layer and the separator at each position is made uniform.

[0011] The separator may have a resistance value adjusted by forming a resistance layer at a position according to the set resistance distribution. The resistance layer may be formed on both end sides in the width direction of the separator except for the center part in the width direction. The resistance layer may be configured to include insulating particles and a binder. The insulating particles may be configured of boehmite or alumina.

[0012] The film-forming material having a lithium salt added to the non-aqueous electrolyte may be lithium bis(oxalato)borate (LiBOB, LiB(C2O4)2). In addition, in a method for producing a lithium ion secondary battery according to the present invention, a positive electrode plate and a negative electrode plate are laminated with a separator interposed therebetween, wound, and an electrode assembly filled with a nonaqueous electrolyte is provided, and a coating material containing a lithium salt is added to the nonaqueous electrolyte, When the negative electrode composite layer of the negative electrode plate contains Na, the resistance [Ω] at each position in the width direction perpendicular to the winding direction of the separator is set to a resistance distribution according to the resistance distribution of the negative electrode composite layer, and the combined resistance of the negative electrode composite layer and the separator at each position is made uniform.

[0013] The separator may have a resistance value adjusted by forming a resistance layer at a position corresponding to the set resistance distribution. The resistance layer may be formed on both end sides in the width direction of the separator except for a central portion in the width direction. Effect of the Invention

[0014] According to the lithium ion secondary battery and the manufacturing method thereof of the present invention, deposition of metallic lithium Li on the negative electrode plate can be suppressed. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a perspective view showing the appearance of a lithium-ion secondary battery 10 of the present embodiment. [Diagram 2] 1 is a schematic diagram showing an electrode body of a lithium-ion secondary battery 10 according to the present embodiment. [Diagram 3] 2 is a schematic diagram showing the state of movement of lithium ions during discharge of the lithium ion secondary battery of the present embodiment. FIG. [Figure 4] 4 is a graph showing the relationship between the position in the width direction W of the negative electrode mixture layer and the resistance RN [Ω] in the present embodiment. [Diagram 5] 4 is a graph showing the relationship between the position in the width direction W of the separator and the resistance RS [Ω] of the present embodiment. [Figure 6] 1 is a graph showing the relationship between the position in the width direction W of the separator and the negative electrode mixture layer and the combined resistance RS+RN [Ω] of the present embodiment. [Figure 7] 1 is a graph showing the relationship between the position in the width direction W of the negative electrode mixture layer and the resistance RN [Ω] when a conventional LiBOB is used. [Figure 8] 1 is a graph showing the relationship between the thickness [μm] of the resistive layer and the resistance RR [Ω / cm 2 ] of the resistive layer in this embodiment. [Figure 9] 4 is a graph showing the relationship between the position in the width direction W of the separator and the thickness [μm] of the resistance layer in this embodiment. [Figure 10] 1 is a graph showing the relationship between the position in the width direction W of the separator of this embodiment and the resistance RS [Ω] of the separator including a resistance layer. [Figure 11] 1 is a graph showing the relationship between the position in the width direction W of the separator and the negative electrode mixture layer and the combined resistance RS+RN [Ω] of the present embodiment. [Figure 12] FIG. 13 is a diagram showing a modified example of the resistive layer. [Figure 13] FIG. 13 is a diagram showing another modified example of the resistive layer. [Figure 14] It is a schematic diagram showing the state of lithium ion movement during charging of a conventional lithium ion secondary battery. [Figure 15] It is a graph showing the relationship between the position in the width direction W of a conventional negative electrode composite material layer and the resistance RN [Ω]. [Figure 16] It is a graph showing the relationship between the position in the width direction W of a conventional separator and the resistance RS [Ω].

Mode for Carrying Out the Invention

[0016] Hereinafter, regarding the lithium ion secondary battery and its manufacturing method of the present invention, taking an embodiment of the manufacturing method of the lithium ion secondary battery 10 as an example, it will be described with reference to FIGS. 1 to 14. <Principle of this Embodiment> First, the principle of suppressing the precipitation of metallic lithium Li in the negative electrode plate 2 of the lithium ion secondary battery 10 of this embodiment will be described.

[0017] As described in the background art, in the lithium ion secondary battery 10, unevenness may occur in the resistance distribution in the width direction W of the negative electrode composite material layer 22 for some reason. In this embodiment, it is characterized in that the combined resistance with the negative electrode composite material layer 22 is made uniform in the width direction W by the resistance layer 41 of the separator 4 with respect to such unevenness in the resistance distribution in the width direction W of the negative electrode composite material layer 22. Note that the cause of the unevenness in the resistance distribution in the width direction W of the negative electrode composite material layer 22 is not limited. In particular, it is remarkable when an additive such as lithium bisoxalate borate (LiBOB) is added to the negative electrode composite material layer 22 as a film inhibitor in the non-aqueous electrolyte 13 and the negative electrode composite material layer 22 contains Na. Therefore, in this embodiment, the present invention will be described taking such a case as an example.

[0018] <Relationship between LiBOB and Na> The SEI film is formed by the first charge immediately after the manufacture of the lithium ion secondary battery 10. The SEI exists between the negative electrode active material 24 and the non-aqueous electrolyte 13, and lithium ions Li +The SEI film facilitates the absorption and release of oxygen into and from the negative electrode, and also suppresses the decomposition of the non-aqueous electrolyte solution 13. For this reason, the SEI film is essential for maintaining good battery characteristics.

[0019] However, the SEI film is formed by decomposition products of the nonaqueous electrolyte 13 and additives, and the decomposition products during the formation process are lithium ions Li + The SEI film thickens when the battery is repeatedly charged and discharged or stored for a long period of time. This not only increases the internal resistance, but also increases the amount of lithium ions (Li + This may result in a decrease in battery capacity due to consumption of the electrolyte 13 and decomposition of the non-aqueous electrolyte solution 13.

[0020] To solve this problem, it has been proposed to add a film-forming material to the non-aqueous electrolyte 13 in advance. The film-forming material is a compound having a lithium salt, such as lithium bis(oxalato)borate (LiBOB, LiB(C2O4)2). According to this method, bis(oxalato)borate ions (BOB - ,BOB ion,B(C2O4)2 - ) is decomposed and polymerized, and a stable coating derived from BOB ions can be formed on the surface of the particles of the negative electrode active material 24. This makes it possible to suppress the growth of the SEI coating.

[0021] Incidentally, the material constituting the electrode body 12 used in the lithium ion secondary battery 10 may contain sodium salt. For example, the negative electrode mixture layer 22 is composed of a binder, a thickener, an additive, a solvent, and the like in addition to the negative electrode active material 24. Some of these use SBR (styrene butadiene copolymer) as the binder and CMC (carboxymethyl cellulose) as the thickener. SBR and CMC contain sodium salt. For this reason, the BOB ions BOB ionized from LiBOB may be dissolved in water. + is the sodium ion Na ionized from sodium salt + It also reacts with the negative electrode mixture layer 22 to form a NaBOB coating. The NaBOB coating becomes a part of the coating on the negative electrode mixture layer 22. This NaBOB coating has a relatively high resistance.

[0022] When the non-aqueous electrolyte 13 is poured into the battery case 11, the non-aqueous electrolyte 13 permeates the wound electrode assembly 12 from the end of the negative electrode plate 2. Sodium ions Na + The ion diffusion rate of NaBOB ions is faster than that of BOB ions. Therefore, a larger amount of the NaBOB coating is likely to be formed in the center portion 22a in the width direction W of the negative electrode mixture layer 22.

[0023] FIG. 15 shows the relationship between the position in the width direction W and the resistance R of a conventional negative electrode mixture layer 22. N 1 is a graph showing the relationship between the amount of coating and the resistance R [Ω]. N The resistance [Ω] becomes high, and resistance unevenness is formed in negative electrode mixture layer 22.

[0024] That is, for the above reasons, central portion 22a of negative electrode mixture layer 22 in this embodiment has a resistance R N [Ω] is getting larger. <Conventional separator 4> FIG. 16 shows the relationship between the position in the width direction W of the conventional separator 4 and the resistance R S Here, a conventional separator 4 will be described. As the separator 4, for example, a porous film made of a resin such as PP (polypropylene) or PE (polyethylene) is used. The separator 4 is a material that can absorb lithium ions Li + The separator 4 is required to have the functions of electrically insulating the positive electrode plate 3 and the negative electrode plate 2 while allowing the electrolyte 13 to pass therethrough, retaining the nonaqueous electrolyte 13, a shutdown function, and a short-circuit prevention function. In particular, the lithium-ion secondary battery 10 has a problem of the formation of dendrites due to the precipitation of metallic lithium Li caused by overcharging or the like in the negative electrode plate 2. If such dendrites break through the separator 4, a short circuit will occur.

[0025] In the conventional separator 4, the separator 4 is designed not to increase the internal resistance and to uniformly distribute the lithium ions Li +As shown in Figure 16, the resistance R is uniform across the width W. S It was common technical knowledge to write it as [Ω].

[0026] <Deposition of metallic lithium Li on the negative electrode plate 2> The deposition of metallic lithium Li in the negative electrode plate 2 is caused by a positional resistance R N This is caused by unevenness in the distribution of resistance [Ω]. Typically, this is the case where the resistance of the central portion 22a of the negative electrode mixture layer 22 is greater than that of the end portion 22b in the width direction W of the negative electrode plate 2 as described above. In this state, current easily flows through the end portion 22b of the negative electrode mixture layer 22, and the current density per unit area [A / mm 2 ] becomes larger. Then, local overcharging occurs on the surface of the negative electrode active material 24. As a result, the potential [V] of the surface of the negative electrode active material 24 becomes the potential [V] at which metallic lithium Li is deposited. Once metallic lithium Li is deposited, current flows more easily in that area, and metallic lithium Li grows as branched dendrites extending in the direction of the separator 4.

[0027] Therefore, measures against the formation of such dendrites have been considered. One approach would be to simply increase the mechanical strength of the separator 4. However, the approach in this embodiment aims to suppress the precipitation of metallic lithium Li itself, which is the essential cause of dendrites.

[0028] <Separator 4 of this embodiment> FIG. 3 shows the lithium ion Li when the lithium ion secondary battery 10 of this embodiment is being charged. + In the lithium ion secondary battery 10 of this embodiment, a resistance layer 41 is provided on both ends 4b in the width direction W of the surface of the separator 4 on the negative electrode plate 2 side. The resistance layer 41 is a portion in which insulating particles are fixed in a layer shape on the surface of the separator 4 with a binder. The insulating particles are a resistance R of the separator 4. S The change is proportional to the thickness [μm] of the resistance layer 41.

[0029] FIG. 4 shows the relationship between the position in the width direction W of the negative electrode mixture layer 22 and the resistance R N As described above, the negative electrode mixture layer 22 of the present embodiment has a higher resistance R in the central portion 22a than in the end portion 22b. N [Ω] is large. Therefore, in Figure 4, the center part of the graph is convex upward.

[0030] FIG. 5 shows the relationship between the position in the width direction W of the separator 4 and the resistance R S 4 is a graph showing the relationship between the resistance R [Ω] of the separator 4 of the present embodiment and the resistance R N To complement [Ω], the central portion 4a of the separator 4 has a resistance R S [Ω] is relatively small, but the resistance R S [Ω] is getting larger.

[0031] FIG. 6 shows the relationship between the position in the width direction W of separator 4 having resistance layer 41 of this embodiment and negative electrode mixture layer 22 and the combined resistance R S +R N 1 is a graph showing the relationship between the position in the width direction W of separator 4 having resistance layer 41 of the present embodiment and negative electrode mixture layer 22 and the combined resistance R S +R N As shown in Figure 6, [Ω] is the combined resistance R S +R N The value of [Ω] is uniform and the graph is a horizontal straight line. This is the ideal correction, but in reality, the effect can be achieved by simply moving the graph closer to a uniform one.

[0032] <Main Effects of This Embodiment> In this embodiment, such a resistance layer 41 is provided, and a combined resistance R S +R N The value of [Ω] is set to be uniform. As a result, current concentration at end 22b of negative electrode mixture layer 22 during charging can be avoided, and deposition of metallic lithium Li can be suppressed.

[0033] (Configuration of this embodiment) The lithium ion secondary battery 10 of this embodiment, which is provided with the separator 4 having the resistance layer 41 as described above, will be described in detail below.

[0034] <Configuration of lithium-ion secondary battery 10> 1 is a perspective view showing the outline of the external configuration of a lithium-ion secondary battery 10 according to the present embodiment. First, the configuration of the lithium-ion secondary battery 10 according to the present embodiment, which is one example of the present invention, will be described.

[0035] As shown in FIG. 1, the lithium ion secondary battery 10 illustrated in this embodiment is configured as a cell battery constituting a battery module housed in a battery pack that is a driving source for an automobile. The lithium ion secondary battery 10 includes a plate-shaped rectangular parallelepiped battery case 11 having an opening on the upper side. An electrode body 12 is housed inside the battery case 11. A nonaqueous electrolyte 13 is filled into the battery case 11 through a liquid filling hole. The battery case 11 is made of a metal such as an aluminum alloy, and forms a battery container sealed by a lid. The lithium ion secondary battery 10 also includes a positive electrode external terminal 14 and a negative electrode external terminal 15 used for charging and discharging power. The positive electrode external terminal 14 is electrically connected to a positive electrode current collector terminal 16 inside the battery case 11 via the lid. The negative electrode external terminal 15 is electrically connected to a negative electrode current collector terminal 17 inside the battery case 11 via the lid. The positive electrode current collector terminal 16 is electrically connected to a positive electrode current collector part 33 (see FIG. 2) of the electrode body 12. Moreover, the negative electrode current collector terminal 17 is electrically connected to the negative electrode current collector portion 23 of the electrode body 12 (see FIG. 2).

[0036] <Electrode body 12> 2 is a schematic diagram showing the configuration of the wound electrode body 12. The electrode body 12 is formed by stacking a negative electrode plate 2, a positive electrode plate 3, and a separator 4 arranged therebetween. The stacked negative electrode plate 2, positive electrode plate 3, and separator 4 are wound to form a flat shape. The negative electrode plate 2 has a negative electrode composite layer 22 formed on a negative electrode current collector 21 made of copper foil as a base material. A negative electrode current collector 23 is provided on one end side of a width direction W (winding axis direction) perpendicular to the winding direction (winding direction L). The negative electrode current collector 23 is configured such that the negative electrode composite layer 22 is not formed and the negative electrode current collector 21 is exposed.

[0037] In the positive electrode plate 3, a positive electrode composite layer 32 is formed on a positive electrode collector 31 made of aluminum foil as a base material. As shown in Fig. 2, a positive electrode collector 33 is provided on the other end side (opposite to the negative electrode collector 23) in a direction (width direction W) perpendicular to the direction in which the positive electrode collector 31 is wound (winding direction L). The positive electrode collector 33 does not have the positive electrode composite layer 32 formed thereon, and the metal of the positive electrode collector 31 is exposed.

[0038] <Layer structure of electrode body 12> As shown in FIG. 2, the basic configuration of an electrode assembly 12 of a lithium ion secondary battery 10 includes a negative electrode plate 2, a positive electrode plate 3, and a separator 4.

[0039] The negative electrode plate 2 includes a negative electrode mixture layer 22 on both sides of a negative electrode current collector 21 serving as a negative electrode base material. One end of the negative electrode current collector 21 serves as a negative electrode current collecting portion 23 where the metal is exposed. The positive electrode plate 3 includes a positive electrode mixture layer 32 on both sides of a positive electrode current collector 31 serving as a positive electrode base material. The other end of the positive electrode current collector 31 forms a positive electrode current collecting portion 33 where the metal is exposed.

[0040] The negative electrode plate 2 and the positive electrode plate 3 are stacked with a separator 4 interposed therebetween to form a laminate. As shown in Fig. 2, this laminate is wound in the longitudinal direction around the winding axis to form a wound-type electrode body 12 that is shaped flat as shown in Fig. 1.

[0041] <Nonaqueous electrolyte 13> The electrode body 12 of the lithium ion secondary battery 10 of this embodiment shown in FIG. 1 is impregnated with a nonaqueous electrolyte 13. The nonaqueous electrolyte 13 is a composition in which a lithium salt is dissolved in an organic solvent. As the lithium salt, LiClO4, LiPF6, LiAsF6, LiBF4, LiSO3CF3, etc. can be used. As the organic solvent, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate, ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butane sultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate can be used. As the nonaqueous electrolyte 13, one or more of these can be mixed and used. The composition of the nonaqueous electrolyte 13 is not limited to this.

[0042] As described above, the nonaqueous electrolyte 13 of this embodiment is previously added with a film-forming material containing Li. The film-forming material is, for example, lithium bis(oxalato)borate (LiBOB, LiB(C2O4)2). According to this method, bis(oxalato)borate ions (BOB - ,BOB ion,B(C2O4)2 - ) can be decomposed and polymerized to form a stable coating derived from BOB ions on the surface of the negative electrode active material particles.

[0043] <Components of electrode body 12> Next, the negative electrode plate 2, the positive electrode plate 3, and the separator 4, which are the components that make up the electrode assembly 12, will be described.

[0044] <Negative electrode plate 2> 2, negative electrode mixture layers 22 are formed on both sides of negative electrode current collector 21, which is a negative electrode base material, to form negative electrode plate 2. Negative electrode mixture layer 22 is formed by applying a negative electrode mixture paste to negative electrode current collector 21. After that, negative electrode plate 2 is completed through a drying process, a pressing process, and a cutting process.

[0045] <Negative electrode current collector 21> In this embodiment, the negative electrode current collector 21 is made of Cu foil. The negative electrode current collector 21 serves as a base for the aggregate of the negative electrode mixture layer 22, and also functions as a current collecting member that collects electricity from the negative electrode mixture layer 22. One end of the negative electrode current collector 21 serves as a negative electrode current collecting part 23 where the negative electrode mixture layer 22 is not formed and the metal surface is exposed. In other words, the negative electrode active material particles are electrically connected to the negative electrode external terminal 15 via the negative electrode current collector 21, the negative electrode current collecting part 23, and the negative electrode current collecting terminal 17.

[0046] <Negative electrode composite layer 22> In this embodiment, the negative electrode active material 24 shown in FIG. 3 is a powdered carbon material made of graphite or the like having a layered structure, and is used to charge and discharge lithium ions Li + It is a material that can absorb and release energy.

[0047] <Positive electrode plate 3> 2, the positive electrode plate 3 is composed of a positive electrode current collector 31, which is a positive electrode base material, and a positive electrode mixture layer 32 applied thereto. The positive electrode mixture layer 32 is formed by applying a positive electrode mixture paste to the positive electrode current collector 31. The positive electrode plate 3 is then completed through a drying process, a pressing process, and a cutting process.

[0048] <Positive electrode current collector 31> A positive electrode mixture layer 32 is formed on both sides of a positive electrode current collector 31, which is a positive electrode base material, to form a positive electrode plate 3. In this embodiment, the positive electrode current collector 31 is made of an Al foil. The positive electrode current collector 31 serves as a base for the aggregate of the positive electrode mixture layer 32, and also functions as a current collecting member that collects electricity from the positive electrode mixture layer 32.

[0049] First, the positive electrode base material constituting the positive electrode current collector 31 is exemplified as an Al foil, but may be made of a conductive material made of a metal having good conductivity. As a material having good conductivity, for example, in addition to Al foil, a material containing an Al alloy may be used. The configuration of the positive electrode current collector 31 is not limited to this.

[0050] <Positive electrode mixture layer 32> Positive electrode mixture layer 32 is formed by applying a positive electrode mixture paste to positive electrode current collector 31 and drying it. Positive electrode mixture layer 32 contains additives such as a conductive assistant, a binder, and a dispersant in addition to particles of a positive electrode active material as shown in FIG.

[0051] <Composition of positive electrode active material> The particles of the positive electrode active material contain a lithium transition metal oxide having a layered crystal structure. The lithium transition metal oxide contains one or more predetermined transition metal elements in addition to Li. The transition metal element contained in the lithium transition metal oxide is preferably at least one of Ni, Co, and Mn. The positive electrode active material of this embodiment is exemplified by a ternary system called NCM, which has a lithium transition metal oxide containing all of Ni, Co, and Mn.

[0052] The positive electrode active material of this embodiment is not limited to those having lithium transition metal oxides containing all of Ni, Co, and Mn. In addition, other than these, for example, compositions containing Al may be used. In addition, the positive electrode active material may be LiMnO4, LiFePO4, etc. Furthermore, it is not limited to these.

[0053] <Separator 4> The separator 4 is a highly insulating nonwoven fabric made of polypropylene or the like, which is a porous resin for holding the nonaqueous electrolyte 13 between the negative electrode plate 2 and the positive electrode plate 3. As the separator 4, 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.

[0054] The separator 4 of this embodiment is provided with the resistance layer 41 as described above. (Example) Next, the resistive layer 41 of this embodiment will be described in detail using examples.

[0055] <Configuration of Resistance Layer 41> FIG. 3 shows the lithium ion Li when the lithium ion secondary battery 10 of this embodiment is discharged. + 1 is a schematic diagram showing the state of movement of the separator 4. A thin layer-like resistance layer 41 is provided at both end portions 4b of the separator 4 of the lithium ion secondary battery 10 of this embodiment. The resistance layer 41 contains insulating particles. Examples of the insulating particles include ceramics obtained by sintering metal oxides, which have high insulation properties, high heat resistance, high mechanical strength, and high corrosion resistance. Specifically, particles of boehmite or alumina are used. Of course, any insulating material may be used, and particles of heat-resistant resin or the like may also be used. In this embodiment, boehmite is used as the insulating particles as an example.

[0056] A binder is also mixed in order to form a layer of insulating particles that adhere to the surface of the separator 4. A solvent is added and kneaded to disperse these mixtures homogeneously, but the solvent evaporates in the drying process and does not generally remain in the product.

[0057] <Boehmite> Boehmite is an aluminum hydroxide (γ-AlO(OH)) mineral and a component of the aluminum ore bauxite. It exhibits a vitreous to pearlescent luster, a Mohs hardness of 3-3.5, and a specific gravity of 3.00-3.07. It has high insulating, heat-resistant, and hardness properties, and industrially it can be used as an inexpensive flame-retardant additive for fire-resistant polymers.

[0058] Boehmite has the chemical composition AlO(OH) or Al2O3·H2O, and is generally a chemically stable alumina monohydrate produced by heating or hydrothermally treating alumina trihydrate in air. Boehmite has a high dehydration temperature of 450-530°C, and by adjusting the production conditions, it can be controlled into various shapes such as plate-like boehmite, needle-like boehmite, and hexagonal plate-like boehmite. In addition, the aspect ratio and particle size can be controlled by adjusting the production conditions.

[0059] In this embodiment, in order to avoid clogging of the separator 4, the average particle diameter (d 50) is 3 to 5 μm. The measurements are the average values ​​measured by laser diffraction. <Binding material> The binder may be, for example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyacrylic acid, polyacrylate, or the like.

[0060] <Separator 4 Configuration> The separator 4 can be a porous resin sheet made of a resin such as polyethylene (PE) or polypropylene (PP) to hold the non-aqueous electrolyte 13 while insulating the positive electrode plate 3 and the negative electrode plate 2 from each other. Such a porous resin sheet can have a single-layer structure using various materials alone, or a multi-layer structure combining various materials. For example, the porous resin sheet can be made of a surface layer made of PP with high heat resistance and an intermediate layer made of PE that shuts down when heated. In addition, the surface layer can be made of PP with high mechanical strength, and the average diameter (d 50 The average diameter (d 50 ) is the average diameter measured by mercury intrusion. 50 ) also determines the appropriate particle size.

[0061] The separator 4 in this embodiment has a width of 100 mm and a thickness of 15 to 19 μm. <Method of forming resistance layer 41> The resistive layer 41 is produced by adding a solvent to insulating particles and a binder and kneading them in a kneader to produce a resistive layer paste in a paste form. At this time, the composition (80 [wt%] in this embodiment), solid content NV (28 [wt%] in this embodiment), viscosity (3000 [Pa s] in this embodiment), etc. are adjusted.

[0062] While conveying the long uncut separator 4 in the length direction, the resistor layer paste is applied using a die nozzle (not shown). The die nozzle stores the resistor layer paste in an internal die, and pressurizes and discharges it from the nozzle.

[0063] <Arrangement of Resistance Layer 41> FIG. 9 is a graph showing the relationship between the position [mm] in the width direction W of the separator 4 and the thickness [μm] of the resistance layer 41 in this embodiment.

[0064] The nozzles are disposed at predetermined positions in the width direction W of the separator 4 (positions of 3.5 to 43.5 mm and 63.5 to 103.5 mm in this embodiment). The material is discharged from the nozzle at a predetermined width (40 mm in this embodiment) to the center 4a of the separator 4 at a predetermined gap (50 μm in this embodiment). At this time, the conveying speed of the separator 4 (1 m / s in this embodiment), the discharge amount (0.5 g / s in this embodiment), etc. are adjusted, and the basis weight (0.5 mg / cm in this embodiment) is adjusted. 2 [μm]), coating thickness (0.17 to 4.48 [μm] in this embodiment), etc. are adjusted. After coating, the resistance layer paste coated on both ends 4b of the separator 4 flows toward the center portion 4a of the separator 4 due to the fluidity of the resistance layer paste. As a result, a gradient in thickness [μm] of the resistance layer 41 is formed, with the resistance layer 41 being thin on the center portion 4a side of the separator 4 and thick on both ends 4b of the separator 4.

[0065] Although the nozzles can discharge the same amount of ink in the width direction W, it is also preferable to discharge more ink at the center of the width direction W and less ink at the ends, depending on the required resistance distribution. After the resistance layer paste is applied, the solvent is volatilized by hot air or infrared rays, and the paste is fixed onto the separator 4 .

[0066] Thereafter, the long separator 4 on which the resistance layer 41 is formed is cut to fit the product. <Resistance R of resistor layer 41 S [Ω] Settings> FIG. 8 shows the thickness [μm] of the resistive layer 41 and the resistance R R 1 is a graph showing the relationship between the resistance R of the resistive layer 41 and the surface area of ​​the insulating layer 42. R The resistance R of the resistive layer 41 can be adjusted by adjusting the thickness T of the resistive layer 41. R[Ω / cm2].

[0067] However, the resistance R is basically too high. S [Ω] is not preferable for the lithium ion secondary battery 10 as a whole. FIG. 7 shows the relationship between the position in the width direction W of the negative electrode composite layer and the resistance R when a conventional LiBOB is used. N 7 is a graph showing the relationship between the resistance R of negative electrode mixture layer 22 and the distance [mm] from the end (negative electrode current collecting portion 23) of negative electrode mixture layer 22. As shown in FIG. N [Ω] is the peak top with the highest resistance in the central portion 22a, which is approximately ΔR N = 31.9 [Ω], and the base of the end 22b with the lowest resistance is approximately ΔR N = 21 [Ω]. The difference ΔR N [Ω] is 10.9[Ω].

[0068] <Separator 4 resistance R S Adjustment > FIG. 10 shows the relationship between the position in the width direction W [mm] of the separator 4 of this embodiment and the resistance R of the separator 4 including the resistance layer 41. S 1 is a graph showing the relationship between the resistance R of the separator 4 as a whole including the resistance layer 41 and the resistance R of the separator 4 as a whole including the resistance layer 41. S The resistance layer 41 has a resistance R R The resistance [Ω] can be adjusted. On the other hand, the separator 4 itself has a uniform composition, and the resistance does not change depending on the position.

[0069] Therefore, in this embodiment, the resistance R of the separator 4 including the resistance layer 41 is S As shown in FIG. 10, the resistance R of the separator 4 is the lowest at the center 4a. S On the other hand, the R S The resistance is high, about 39 [Ω]. That is, the resistance difference ΔR between the center portion 4a and both ends 4b S [Ω] is 7[Ω].

[0070] <The combined resistance R in this example S +R N [Ω]> FIG. 11 shows the relationship between the position in the width direction W of the separator 4 and the negative electrode mixture layer 22 of this embodiment and the combined resistance R S +R N 1 is a graph showing the relationship between the position in the width direction W of the negative electrode composite layer and the resistance R [Ω] when a conventional LiBOB is used. N When compared with Figure 7, which shows the relationship between ΔR N [Ω] = 10.9 [Ω]. In comparison, the combined resistance R S +R N The maximum value of [Ω] is approximately 63 [Ω], and the minimum value is approximately 57 [Ω]. It can be seen that the difference between the maximum and minimum values ​​is approximately within 6 [Ω].

[0071] In other words, when the configuration of the conventional separator 4 is changed to the separator 4 having the resistance layer 41 of this embodiment, the combined resistance difference ΔR S +R N =10.9-6.0[Ω], which is a decrease in resistance difference of approximately 4.9.

[0072] In addition, the theoretically ideal combined resistance R S +R N [Ω] Maximum and minimum resistance difference ΔR S +R N However, it is desirable to set the value to 0 [Ω]. + The movement of the separator 4 is complicated, the precision of the formation of the resistance layer 41 is not necessarily high, and the resistance R S [Ω], etc., the resistance difference ΔR S +R N It is not possible to set = 0[Ω].

[0073] However, by reducing this difference, it is possible to improve the battery performance, such as expanding the battery capacity of the entire lithium ion secondary battery 10 and the range of usable SOC [%] in which Li precipitation is unlikely to occur.

[0074] <Manufacture of lithium ion secondary battery 10> The manufacturing process of the lithium ion secondary battery 10 of this embodiment will be briefly described below. First, in a manufacturing process, the elements of each battery are prepared. Specifically, the positive electrode plate 3, the negative electrode plate 2, and the separator 4 are prepared. At this stage, the separator 4 is formed by the above-mentioned method so as to have a resistance difference ΔR S [Ω] is adjusted. Next, the positive electrode plate 3, the negative electrode plate 2, and the separator 4 are laminated and wound. This wound body is pressed to a predetermined thickness by a press machine to shape it. A positive electrode collector terminal 16 and a negative electrode collector terminal 17 are attached to the electrode body 12 thus prepared. The electrode body 12 to which the positive electrode collector terminal 16 and the negative electrode collector terminal 17 are attached is housed in a battery case 11 to which an insulating film is attached. The upper opening of the battery case 11 is closed with a lid body and welded and sealed. Next, the battery case is heated to dry the inside and remove moisture. Once dry, nonaqueous electrolyte 13 is poured into the battery case and the pouring port is sealed. After that, when conditioning and aging are completed, inspection is performed and the cell battery as a product is completed. After that, a plurality of battery cells are combined to create a battery module. Furthermore, a plurality of battery modules are combined and housed in a case to become a battery pack for use in a vehicle.

[0075] (Action of this embodiment) In this embodiment, the resistance R of the negative electrode mixture layer 22 N The resistor layer 41 corresponds to the resistance distribution at each position of [Ω], and the composite resistance R S +R N The value of [Ω] is made uniform. As a result, current concentration at the end 22b of the negative electrode mixture layer 22 during charging is avoided. As a result, the potential [V] increases in the negative electrode active material 24 where the current concentrates, and deposition of metallic lithium Li can be suppressed. Therefore, the growth of dendrites is suppressed, the safety of the lithium ion secondary battery 10 is improved, and the battery life is extended.

[0076] (Effects of this embodiment) (1) According to the lithium ion secondary battery 10 and the manufacturing method thereof of the present embodiment, there is an advantage that deposition of metallic lithium Li on the negative electrode plate 2 can be suppressed.

[0077] (2) When a coating material containing a lithium salt is added to the nonaqueous electrolyte 13 and the negative electrode mixture layer 22 of the negative electrode plate 2 contains Na, the resistance R N Even in such a case, the resistance R S [Ω] is the resistance R of the negative electrode mixture layer 22 N The resistance distribution was set according to the resistance distribution [Ω], and the combined resistance at each position of the negative electrode mixture layer 22 and the separator 4 was made uniform. This has the effect of mitigating current concentration at the end of the negative electrode mixture layer 22, thereby suppressing the precipitation of metallic lithium Li.

[0078] (3) The separator 4 has a resistance layer 41 formed at a position according to the set resistance distribution to adjust the resistance value. Therefore, the resistance R S [Ω] can be adjusted.

[0079] (4) The resistance layer 41 is formed on both end portions 4b of the separator 4 in the width direction W, except for the central portion 4a in the width direction W. Therefore, the resistance R S This has the effect of increasing the resistance RS [Ω] of only the two end portions 4b without increasing the resistance [Ω].

[0080] (5) The resistance layer 41 contains insulating particles and a binder, and therefore has a stable resistance R S [Ω]. (6) In particular, the insulating particles are made of boehmite or alumina, which has the effect of making it possible to provide the resistance layer 41 at low cost and with stable quality.

[0081] (7) When the negative electrode composite layer 22 contains Na, the unevenness of the resistance RN [Ω] of the negative electrode composite layer 22 is alleviated by the resistance layer 41 of this embodiment. Therefore, there is an effect that lithium bis(oxalato)borate (LiBOB, LiB(C2O4)2) can be used as a film-forming material having a lithium salt that is highly effective as a film-forming material. As a result, there is an effect that the formation of a film in the SEI can be effectively suppressed and the battery performance can be improved.

[0082] (8) By effectively suppressing the precipitation of metallic lithium Li, it is possible to suppress the occurrence of short circuits due to dendrites, and this has the effect of making the lithium ion secondary battery 10 safer and longer-lasting.

[0083] (Another example) 12 is a diagram showing a modified example of the resistance layer 41. In this embodiment, as shown in FIG. 3, the resistance layer 41 is not provided in the central portion 4a of the separator 4, and the resistance layer 41 provided on both end portions 4b is formed so that the thickness T [μm] is thick on the both end portions 4b side and becomes thinner toward the central portion 4a side. However, the lithium ion secondary battery 10 of the present invention is not limited to such an embodiment.

[0084] Fig. 13 is a diagram showing another modified example of the resistance layer 41. As shown in Fig. 13, the resistance layer 41 may have a uniform thickness T [µm] at both ends 4b. With this configuration, in the coating process of the resistance layer 41, a resistance layer paste having a relatively high viscosity [Pa s] is discharged at a uniform amount [g / m 2 ], which simplifies the process.

[0085] 13 is a diagram showing another modified example of the resistance layer 41. In this modified example, the resistance layer 41 provided on both end portions 4b is formed so that the thickness T [μm] is thicker on the both end portions 4b side and becomes thinner toward the center portion 4a side. However, in this modified example, the resistance layers 41 on both end portions 4b are continuous with each other in the center portion 4a of the separator 4.

[0086] Although the lithium ion secondary battery 10 is illustrated as being for vehicle use, it can also be used as a stationary battery in a factory or a home. Although the lithium ion secondary battery 10 has a flat electrode body 12 as an example, the electrode body 12 may be cylindrical.

[0087] Although the resistance layer 41 is provided on one surface of the separator 4, it may be provided on both surfaces. It may also be applied to mesh holes of the separator 4. Alternatively, a film-like resistance layer 41 may be formed separately in advance and attached.

[0088] Although boehmite and alumina are exemplified as the insulating particles, the material is not important as long as the resistance value can be adjusted. For example, the insulating particles may be made of the same material as the separator 4, and the thickness may be increased before or after the fact.

[0089] Although the resistance layer 41 is formed by a coating process in the above example, the method is not limited thereto and may be spraying, impregnation, or the like. Furthermore, the configurations of the positive electrode plate 3, the negative electrode plate 2, the non-aqueous electrolyte 13, etc. are not limited to those illustrated.

[0090] The manufacturing process of the lithium ion secondary battery 10 is not limited to the process illustrated above. * The numerical values ​​and ranges of each dimension, weight, etc. are examples and can be optimized as appropriate by a person skilled in the art.

[0091] It goes without saying that those skilled in the art may add, delete or modify the configuration of the present invention without departing from the scope of the claims. [Explanation of symbols]

[0092] 10...Lithium-ion secondary battery 11…Battery case 12...Electrode body 13...Nonaqueous electrolyte 14…Positive external terminal 15...Negative external terminal 16…Positive current collecting terminal 17...Negative current collecting terminal 2...Negative electrode plate 21...Negative electrode current collector 22...Negative electrode composite material layer 23...Negative electrode current collector 24...Negative electrode active material 3…Positive electrode plate 31...Positive electrode current collector 32...Positive electrode mixture layer 33…Positive electrode current collector 4…Separator 41...Resistance layer

Claims

1. A lithium ion secondary battery having an electrode assembly in which a positive electrode plate and a negative electrode plate are stacked and wound with a separator interposed therebetween and filled with a nonaqueous electrolyte, A film-forming material having a lithium salt is added to the non-aqueous electrolyte solution, When the negative electrode mixture layer of the negative electrode plate contains Na, a resistance distribution of the resistance [Ω] at each position in a width direction perpendicular to the winding direction of the separator is set in accordance with a resistance distribution of the negative electrode mixture layer, and a combined resistance of the negative electrode mixture layer and the separator at each position is made uniform.

2. 2. The lithium ion secondary battery according to claim 1, wherein the separator has a resistance layer formed at a position corresponding to the set resistance distribution, thereby adjusting the resistance value.

3. 3. The lithium ion secondary battery according to claim 2, wherein the resistance layer is formed on both end sides in the width direction of the separator, except for a central portion in the width direction.

4. 3. The lithium ion secondary battery according to claim 2, wherein the resistance layer is configured to contain insulating particles and a binder.

5. 5. The lithium ion secondary battery according to claim 4, wherein the insulating particles are made of boehmite or alumina.

6. The film-forming material having a lithium salt added to the non-aqueous electrolyte is lithium bis(oxalato)borate (LiBOB, LiB(C ２ O ４ ) ２ 2. The lithium ion secondary battery according to claim 1, wherein

7. A method for manufacturing a lithium ion secondary battery including an electrode assembly in which a positive electrode plate and a negative electrode plate are stacked with a separator interposed therebetween and wound, and filled with a nonaqueous electrolyte, comprising the steps of: A film-forming material having a lithium salt is added to the non-aqueous electrolyte solution, When the negative electrode mixture layer of the negative electrode plate contains Na, a resistance distribution of the resistance [Ω] at each position in a width direction perpendicular to a winding direction of the separator is set in accordance with a resistance distribution of the negative electrode mixture layer, and a combined resistance of the negative electrode mixture layer and the separator at each position is made uniform.

8. 8. The method for producing a lithium ion secondary battery according to claim 7, wherein the separator has a resistance layer formed at a position corresponding to the set resistance distribution, thereby adjusting the resistance value.

9. 8. The method for producing a lithium ion secondary battery according to claim 7, wherein the resistance layer is formed on both end sides in the width direction of the separator except for the central portion in the width direction.

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