Lithium ion secondary battery and method of manufacturing the same

Abstract

To suppress a deterioration in a positive electrode plate of a lithium ion secondary battery.SOLUTION: In a lithium ion secondary battery including an electrode body formed by laminating and winding a positive electrode plate and a negative electrode plate with a separator 4 interposed therebetween, a resistance part 41 is formed, along a winding direction, in a central part 4a of the separator 4 in a width direction, and when ΔRP [Ω] represents a resistance difference in a thickness direction between an end part 32b and a central part 32a of a positive electrode mixture layer 32 of the positive electrode plate of the electrode body in a width direction, and ΔRN [Ω] represents a resistance difference in a thickness direction between an end part and a central part of a negative electrode mixture layer 22 of the negative electrode plate in a width direction W, and also when ΔRS [Ω] represents a resistance difference in a thickness direction between an end part 4b and the central part 4a of the separator 4 in the width direction, a resistance difference ΔRS [Ω] of the resistance part 41 is set such that a value of (ΔRN+ΔRS-ΔRP) is equal to or more than 0 [Ω] and is equal to or less than a threshold for suppressing Li precipitation at the negative electrode plate.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 with less deterioration of a positive 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 vehicles and stationary power storage facilities.

[0003] FIG. 1 is a perspective view showing an outline of the external configuration of a lithium ion secondary battery 10 of this embodiment. FIG. 2 is a schematic diagram showing the configuration of a wound electrode body 12. In one example of such a lithium ion secondary battery 10, a positive electrode plate 3 and a negative electrode plate 2 are insulated by a separator 4 and stacked, and the electrode body 12 wound into an elliptical cylinder is housed in one battery case 11. In such a lithium ion secondary battery 10, lithium ions Li are generated from the positive electrode active material of the positive electrode mixture layer 32 of the positive electrode plate 3 during charging. + The negative electrode mixture layer 22 of the negative electrode plate 2 is filled with lithium ions Li + In order to allow for ample storage of the negative electrode mixture layer 22, the dimension of the negative electrode mixture layer 22 is designed to be wider than the dimension in the width direction of the positive electrode mixture layer 32.

[0004] In such lithium ion secondary battery 10, the resistance [Ω] at the center in width direction W of positive electrode mixture layer 32 may be large due to its structure. During discharge of the lithium ion secondary battery 10, lithium ions Li are transferred from the negative electrode mixture layer 22 to the positive electrode mixture layer 32. + At this time, in the positive electrode mixture layer 32 in which the resistance [Ω] in the width direction central portion is large, lithium ions Li are released in the central portion. + As a result, the crystal structure of the positive electrode active material changes and the nonaqueous electrolyte undergoes reductive decomposition in the central portion, leading to the progression of degradation. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2010-201327 A Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, in the invention described in Patent Document 1, the amount of Na contained in the additive is adjusted to match the resistance distribution in the width direction W of the negative electrode mixture layer 22 with the resistance distribution of the positive electrode mixture layer 32. + An invention has been proposed that controls the movement of lithium ions Li+ to match the acceptability of the positive electrode active material. With such an invention, the deterioration of the positive electrode active material can be suppressed by reducing the resistance difference between the positive electrode mixture layer 32 and the negative electrode mixture layer 22.

[0007] However, the resistance distribution of the negative electrode changes depending on the additive composition of the nonaqueous electrolyte, the amount of electrolyte injected into the battery cell, and the conditioning and aging conditions, so it has been difficult to match the resistance distribution of the negative electrode mixture layer 22 to the resistance distribution of the positive electrode mixture layer 32 by simply adjusting the Na content.

[0008] 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 deterioration of the electrode body of the lithium ion secondary battery. [Means for solving the problem]

[0009] In order to solve the above problems, in the lithium ion secondary battery of the present invention, in a lithium ion secondary battery having an electrode assembly in which a positive electrode plate and a negative electrode plate are laminated and wound with a separator interposed therebetween, a resistance portion is formed along the winding direction in the center portion in the width direction of the separator, and a resistance difference in the thickness direction between the end portion and the center portion in the width direction of the positive electrode mixture layer of the positive electrode plate of the electrode assembly is defined as ΔR P [Ω], and the difference in resistance in the thickness direction between the end and center in the width direction of the negative electrode mixture layer of the negative electrode plate is ΔRN [Ω], and the difference in resistance between the end and center in the thickness direction of the separator in the width direction is ΔR S [Ω], (ΔR N +ΔR S -ΔR P ) is set to a value equal to or less than a threshold value for suppressing Li deposition in the negative electrode plate. S The characteristic of this method is that it is set to [Ω].

[0010] In this case, the above (ΔR N +ΔR S -ΔR P ) is set to a value equal to or greater than a threshold value for suppressing deterioration of the positive electrode active material in the positive electrode plate. S [Ω] can be set.

[0011] In addition, the above (ΔR N +ΔR S -ΔR P The resistance difference ΔR of the separator is set to 13 [Ω] or less. S [Ω] can be set. In addition, the above (ΔR N +ΔR S -ΔR P ) is set to 0 [Ω] or more. S [Ω] can be set.

[0012] The resistor portion may be made of a material containing insulating particles. In this case, the insulating particles forming the resistor portion may be boehmite or alumina. In addition, in the method for producing a lithium ion secondary battery of the present invention, a method for producing a lithium ion secondary battery including an electrode assembly in which a positive electrode plate and a negative electrode plate are stacked and wound with a separator interposed therebetween includes a step of forming a resistance portion along a winding direction in a central portion in a width direction of the separator, and a resistance difference in a thickness direction between an end portion and a central portion in a width direction of the positive electrode mixture layer of the positive electrode plate of the electrode assembly is defined as ΔR P [Ω], and the difference in resistance in the thickness direction between the end and center in the width direction of the negative electrode mixture layer of the negative electrode plate is ΔR N[Ω], and the difference in resistance between the end and center in the thickness direction of the separator in the width direction is ΔR S [Ω], (ΔR N +ΔR S -ΔR P ) is set to a value equal to or less than a threshold value for suppressing Li deposition in the negative electrode plate. S The characteristic of this method is that it is set to [Ω].

[0013] In this case, the above (ΔR N +ΔR S -ΔR P ) is set to a value equal to or greater than a threshold value for suppressing deterioration of the positive electrode active material in the positive electrode plate. S [Ω] may be set. N +ΔR S -ΔR P The resistance difference ΔR of the separator is set to 13 [Ω] or less. S [Ω] may be set.

[0014] In addition, (ΔR N +ΔR S -ΔR P ) to be 0 [Ω] or more. S [Ω] may be set. The resistor portion may be made of a material containing insulating particles, and the insulating particles forming the resistor portion may be boehmite or alumina.

[0015] The resistor portion may be formed by applying a paste of the insulator and binder to the separator using a solvent, thereby forming a coating of the resistor portion on the surface of the separator. Effect of the Invention

[0016] According to the lithium ion secondary battery and the manufacturing method thereof of the present invention, deterioration of the electrode body of the lithium ion secondary battery can be suppressed. [Brief description of the drawings]

[0017] [Figure 1] 1 is a perspective view showing the outline of the external configuration of a lithium-ion secondary battery according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a schematic diagram showing the configuration of a wound electrode body. [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] 1A is a graph showing the difference in resistance RP [Ω] depending on the position of the positive electrode composite layer, (b) is a graph showing the difference in resistance RS [Ω] depending on the position of the separator, and (c) is a graph showing the difference in resistance RN [Ω] depending on the position of the negative electrode composite layer in the lithium ion secondary battery of the present embodiment. [Diagram 5] 1 is a graph showing the change in resistance value [Ω] of a positive electrode mixture layer versus SOC [%] of the positive electrode. [Figure 6] 1 is a graph showing a difference in resistance depending on a position in a positive electrode mixture layer. [Figure 7] 1 is a graph showing the relationship between the position in the positive electrode plate of the example and the resistance RP [Ω] of the positive electrode mixture layer. [Figure 8] 1 is a graph showing the relationship between the position and the resistance RN [Ω] of the negative electrode mixture layer in the negative electrode plate of the example. [Figure 9] 1 is a graph showing the relationship between the thickness [μm] of a resistor portion and the resistance [Ω] of the resistor portion in an embodiment. [Figure 10] 1A and 1B are schematic diagrams showing the movement of lithium ions during charging and discharging of a conventional lithium ion secondary battery, respectively. [Figure 11] FIG. 1 is a schematic diagram showing the movement of lithium ions during discharging of a conventional lithium ion secondary battery. [Figure 12] 1A is a graph showing the difference in resistance RP [Ω] depending on the position of the positive electrode composite layer, (b) is a graph showing the difference in resistance RS [Ω] depending on the position of the separator, and (c) is a graph showing the difference in resistance RN [Ω] depending on the position of the negative electrode composite layer in a conventional lithium-ion secondary battery. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The lithium ion secondary battery and the manufacturing method thereof of the present invention will be described below with reference to FIGS. 1 to 12, taking an embodiment of a lithium ion secondary battery 10 as an example. (Principle of this embodiment) <Unevenness in SOC [%] of positive electrode mixture layer 32 resulting from the structure of electrode body 12> FIG. 5 shows the resistance R of the positive electrode mixture layer 32 versus the SOC [%] of the lithium ion secondary battery. P 1 is a graph showing the change in resistance R [Ω] of the positive electrode mixture layer 32 of the lithium ion secondary battery 10. P [Ω] depends on SOC [%]. That is, the lower the SOC [%], the more lithium-ion Li + The higher the density of the P Lithium ion Li + Conversely, the higher the SOC [%], the lower the capacity of the battery to absorb lithium ions (Li + The lower the density of the P becomes smaller and lithium ion Li + In addition, the resistance R P , R N , R S [Ω] was measured in the thickness direction by cutting out each part to create a test piece.

[0019] FIG. 10(a) shows the lithium ions Li during charging of a conventional lithium ion secondary battery 10. + FIG. 10(b) is a schematic diagram showing the movement of lithium ions Li during discharging of the conventional lithium ion secondary battery 10. + FIG.

[0020] As described in the background art, negative electrode mixture layer 22 is formed to be larger in width direction W than positive electrode mixture layer 32. Therefore, negative electrode mixture layer 22 has central portion 22a and end portion 22b facing positive electrode mixture layer 32, and non-facing portion 22c not facing positive electrode mixture layer 32.

[0021] As shown in FIG. 10(a), during charging, lithium ions Li are transported from the positive electrode mixture layer 32 to the central portion 22a and the end portion 22b of the negative electrode mixture layer 22 facing the positive electrode mixture layer 32. + Then, lithium ions Li move in the negative electrode mixture layer 22. + When the negative electrode mixture layer 22 receives the lithium ions Li + As a result, lithium ions Li diffuse to end portion 22b and move to non-facing portion 22c. + In other words, the SOC [%] is lower in end portion 22b of negative electrode mixture layer 22 than in central portion 22a. In other words, the density of lithium ions Li + The density of is increasing.

[0022] On the other hand, as shown in FIG. 10(b), during discharging, the lithium ions Li + The distance from the positive electrode mixture layer 32 increases. + Since it takes a certain amount of time for the lithium ions Li to move within the negative electrode mixture layer 22, the lithium ions Li + The lithium ions Li cannot immediately migrate to the positive electrode mixture layer 32 through the separator 4. In addition, the end 22b of the negative electrode mixture layer 22 contains lithium ions Li + Since the density of the positive electrode mixture layer 32 is low, the lithium ions Li move to the end 32b of the positive electrode mixture layer 32 facing the positive electrode mixture layer 32. + The amount of lithium ion Li + In other words, during discharge, the end 32b of the positive electrode mixture layer 32 is filled with lithium ions Li + and the SOC [%] is high.

[0023] On the other hand, in the central portion 32a of the positive electrode mixture layer 32, lithium ions Li + The higher the density, the lower the SOC [%], resulting in a lower resistance R P [Ω] is high. 6 is a graph showing the difference in resistance depending on the position in the positive electrode mixture layer 32. The horizontal axis of the graph indicates the distance [mm] from the end of the positive electrode plate 3 on the positive electrode current collector 33 side. The left-right center of the graph indicates the center part of the positive electrode mixture layer 32 in the width direction W, and the left and right ends of the graph indicate the center part of the positive electrode mixture layer 32 in the width direction W. As can be seen from this graph, for the reasons mentioned above, the center part of the positive electrode mixture layer 32 actually has a resistance R P [Ω] is high at about 31 [Ω], and the resistance R P It can be seen that [Ω] is generally low at 27 [Ω].

[0024] <Unevenness in SOC [%] due to the presence of Na in negative electrode mixture layer 22> In the lithium ion secondary battery 10, a coating of SEI (Solid Electrolyte Interface) is formed on the surface of the negative electrode mixture layer 22 during initial charging. The coating of SEI exists between the negative electrode mixture layer 22 and the non-aqueous electrolyte solution 13, and lithium ions Li + The SEI film facilitates the absorption and release of lithium ions (Li) into and from the negative electrode, and also suppresses the decomposition of the non-aqueous electrolyte 13. For this reason, the SEI film is essential for maintaining good battery characteristics. However, the SEI film is formed by decomposition products of the non-aqueous electrolyte 13 and additives, and in the process of formation, the decomposition products turn into lithium ions (Li). + Therefore, the SEI film becomes thicker 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.

[0025] 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 to form a stable coating derived from BOB ions on the surface of the negative electrode active material particles. This makes it possible to suppress the growth of the SEI coating.

[0026] 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 negative electrode active material, a binder, a thickener, an additive, a solvent, and the like, and some negative electrode mixture layers 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 the negative electrode mixture layer 22. + 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.

[0027] When the non-aqueous electrolyte 13 is poured into the battery case 11, it permeates 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, the NaBOB coating is likely to be formed more in the central portion 22a in the width direction W of the negative electrode mixture layer 22. The central portion 22a of the negative electrode mixture layer 22, where the amount of coating is excessively large, has a resistance R N The resistance [Ω] becomes high, and resistance unevenness is formed in negative electrode mixture layer 22.

[0028] That is, for the above reasons, the central portion 22a of the negative electrode mixture layer 22 in this embodiment has a resistance R N [Ω] is getting larger. <Conventional separator> FIG. 11 shows the lithium ion Li during discharging of a conventional lithium ion secondary battery 10. + 6 is a schematic diagram showing the state of movement of the positive electrode mixture layer 32. As shown in FIG. PIt is known that the resistance R [Ω] is high. In addition, the separator 4 of the conventional technology has a uniform resistance R S In addition, in the negative electrode mixture layer 22, the resistance R N [Ω] is getting larger.

[0029] 12 is a graph for a conventional lithium ion secondary battery 10. FIG. 12(a) shows the resistance R P FIG. 12(b) is a graph showing the difference in resistance R [Ω] depending on the position of the separator 4. S 12(c) is a graph showing the difference in resistance R [Ω] depending on the position of the negative electrode mixture layer 22. N 1 is a graph showing the difference in [Ω].

[0030] In the conventional electrode assembly 12, the central portion 4a and the end portion 4b of the separator 4 contain lithium ions Li + Therefore, the lithium ions Li that move to the central portion 32a of the positive electrode mixture layer 32 having a high resistance [Ω] are + The central portion 32a of the positive electrode mixture layer 32 cannot accept the charged particles, and deterioration occurs due to reasons such as a change in the crystal structure of the positive electrode active material.

[0031] <Separator 4 of this embodiment> FIG. 3 shows the lithium ion Li when the lithium ion secondary battery 10 of this embodiment is discharged. + 3 is a schematic diagram showing a state of movement of the separator 4. As shown in Fig. 3, a resistance portion 41 is provided in a central portion 4a of a separator 4 of a lithium ion secondary battery 10 of this embodiment.

[0032] The resistor portion 41 in this embodiment is formed by forming highly insulating particles such as boehmite or alumina into a paste using a binder and a solvent, applying the paste in a strip shape to the central portion 4a in the width direction W of the separator 4 along the winding direction, and then drying and fixing the paste. Therefore, the central portion 4a of the separator 4 on which the resistor portion 41 is provided has a resistance R S [Ω] is getting larger.

[0033] <Configuration of Resistor Part 41> FIG. 4(a) shows the resistance R depending on the position of the positive electrode mixture layer 32 in the lithium ion secondary battery 10 of the present embodiment. P FIG. 4(b) is a graph showing the difference in resistance R [Ω] depending on the position of the separator 4. S 4(c) is a graph showing the difference in resistance R [Ω] depending on the position of the negative electrode mixture layer 22. N 1 is a graph showing the difference in [Ω].

[0034] The difference in resistance in the thickness direction between the end portion 32b and the central portion 32a in the width direction W of the positive electrode mixture layer 32 of the positive electrode plate 3 of the electrode body 12 shown in FIG. 4(a) is defined as ΔR P The difference in resistance in the thickness direction between end portion 22b and center portion 22a in width direction W of negative electrode mixture layer 22 of negative electrode plate 2 shown in FIG. N The difference in resistance between the end portion 4b and the central portion 4a in the width direction W of the separator 4 shown in FIG. 4(b) is ΔR S Let be [Ω].

[0035] In this embodiment, in order to suppress deterioration in the positive electrode mixture layer 32 during discharge, (ΔR N +ΔR S -ΔR P In this embodiment, the value of (ΔR N +ΔR S -ΔR P ) is set to 0 [Ω] or more by changing the resistance difference ΔR S [Ω] is set.

[0036] In addition, in this embodiment, (ΔR N +ΔR S -ΔR P ) is set to a value equal to or less than a threshold value for suppressing Li deposition on the negative electrode plate 2 during charging. S In this embodiment, (ΔR N +ΔR S -ΔR P The resistance difference ΔR of the resistor part 41 is set so that the value of S [Ω] is set.

[0037] <Function of Resistance Part 41> In the electrode body 12 of this embodiment, the resistance R P Even in the central portion 32a where the resistance [Ω] is high, the central portion 4a of the separator 4 has a higher resistance R S The central portion 4a is configured so that the lithium ion Li + This makes it difficult for the current to pass through resistor R P Lithium ions Li that migrate to the central portion 32a of the positive electrode mixture layer 32 having a high [Ω] + Therefore, the lithium ions Li are also present in the central portion 32a of the positive electrode mixture layer 32. + This makes it possible to suppress deterioration due to reasons such as changes in the crystal structure of the positive electrode active material.

[0038] On the other hand, during charging, the resistance R N The high-Ω central section 22a contains lithium ion Li + By preventing excessive movement of Li, deposition of metallic Li in negative electrode mixture layer 22 is suppressed.

[0039] (Configuration of this embodiment) The lithium ion secondary battery 10 of this embodiment, which is provided with the separator 4 having the resistance portion 41 as described above, will be described in detail below.

[0040] <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.

[0041] 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).

[0042] <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 large number of negative electrode plates 2 and positive electrode plates 3 with separators 4 arranged between them. The stacked negative electrode plates 2, positive electrode plates 3 and separators 4 are wound to form a flat shape. The negative electrode plates 2 have 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.

[0043] 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.

[0044] <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.

[0045] 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 collector 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.

[0046] A laminate is formed by stacking the negative electrode plate 2 and the positive electrode plate 3 with a separator 4 interposed therebetween. As shown in Fig. 1, this laminate is wound in the longitudinal direction around the winding axis to form a wound-type electrode body 12 that is shaped into a flat shape as shown in Fig. 2.

[0047] <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.

[0048] 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.

[0049] <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.

[0050] <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.

[0051] <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.

[0052] <Negative electrode composite layer 22> In this embodiment, the negative electrode active material is a powdered carbon material made of graphite or the like having a layered structure, and lithium ions Li + It is a material that can absorb and release energy.

[0053] <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.

[0054] <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.

[0055] 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.

[0056] <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 positive electrode active material particles.

[0057] <Composition of positive electrode active material> The positive electrode active material particles 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 having a lithium transition metal oxide containing all of Ni, Co, and Mn.

[0058] 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.

[0059] <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.

[0060] In this embodiment, a resistance portion 41 is provided. (Example) Next, the resistor portion 41 of this embodiment will be described in detail using an example.

[0061] <Configuration of Resistor Part 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 of the lithium ion secondary battery 10 according to the present embodiment. A thin layer-like resistance portion 41 is provided in the central portion 4a of the separator 4 of the lithium ion secondary battery 10 of the present embodiment. The resistance portion 41 contains insulating particles. Examples of the insulating particles include ceramics obtained by sintering metal oxides, which have high insulating 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.

[0062] 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.

[0063] <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.

[0064] 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.

[0065] In this embodiment, in order to avoid clogging of the separator 4, the average particle diameter (d 50 The average diameter (d 50 ) is the average value measured by laser diffraction.

[0066] <Binding material 34c> For example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyacrylic acid, polyacrylate, or the like can be used as the binder 34c.

[0067] <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, PP with high mechanical strength is used for the surface layer, 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.

[0068] The separator 4 in this embodiment has a width of 100 mm and a thickness of 15 to 19 μm. <Method of forming resistor portion 41> The resistor part 41 is manufactured by adding a solvent to the insulating particles and the binder and kneading them in a kneader to produce a resistor part 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.

[0069] While conveying the long uncut separator 4 in the length direction, such resistor paste is applied using a die nozzle (not shown). The die nozzle stores the resistor paste in an internal die, pressurizes it and discharges it from the nozzle. The nozzle discharges the paste from a predetermined position in the width direction W of the separator 4 (a position of 34 to 66 mm in this embodiment) to a predetermined width (32 mm in this embodiment) onto the central portion 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 ]), coating thickness (0.17 to 4.48 [μm] in this embodiment), etc. are adjusted.

[0070] Although the nozzles can discharge the same amount of ink in the width direction W, it is 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 resistor paste is applied, the solvent is volatilized by hot air or infrared rays, and the resistor paste is fixed onto the separator 4.

[0071] Thereafter, the long separator 4 on which the resistance portion 41 is formed is cut to fit the product. <Resistance R of resistor 41 S [Ω] Settings> The resistance of the resistor portion 41 is the resistance R of the separator 4. S The difference in resistance in the thickness direction between the end portion 32b and the central portion 32a in the width direction W of the positive electrode mixture layer 32 of the positive electrode plate 3 of the electrode body 12 is ΔR P The difference in resistance in the thickness direction between the end portion 32b and the central portion 32a in the width direction W of the negative electrode mixture layer 22 of the negative electrode plate 2 is represented as ΔR N The difference in resistance between the end portion 4b and the central portion 4a in the width direction W of the separator 4 in the thickness direction is ΔR S Let be [Ω].

[0072] At this time, in order to suppress the precipitation of metallic Li in the negative electrode mixture layer 22 (ΔR N +ΔR S -ΔR P ) is the resistance difference ΔR S In this embodiment, (ΔR N +ΔR S -ΔR P ) is set to 0[Ω] or higher.

[0073] In addition, the resistance difference ΔR of the resistor portion 41 is set to be equal to or less than the threshold value for suppressing Li deposition in the negative electrode mixture layer 22. S In this embodiment, (ΔR N +ΔR S -ΔR P The resistance difference ΔR of the resistor part 41 is set so that the value of S Set [Ω].

[0074] FIG. 7 shows the relationship between the position on the positive electrode plate 3 and the resistance R of the positive electrode mixture layer 32 in this embodiment. P 7 is a graph showing the relationship between the resistance R and the distance [mm] from the end of the positive plate 3 in the width direction (here, the positive current collector 33 side). Here, the portion 0 to 5 [mm] is the positive current collector 33 made of Al foil, and the resistance R can be considered to be 0 [Ω]. P As shown in FIG. 7, [Ω] is the resistance R P There is a peak of [Ω]. This resistance R P The peak of [Ω] is roughly R P On the other hand, at a position approximately 32 mm away from the width direction end of the positive electrode plate 3, the resistance R P There is a bottom of [Ω], and this resistance R P = 24[Ω] as the base. And the peak resistance R P = 31[Ω] and base resistance R P = 24[Ω] is the resistance difference ΔR P = 7[Ω].

[0075] FIG. 8 shows the relationship between the position on the negative electrode plate 2 of the embodiment and the resistance R N 8 is a graph showing the relationship between the resistance [Ω] and the distance [mm] from the end of the width direction of the negative electrode plate 2 (here, the side of the negative electrode current collector 23) on the horizontal axis. Here, the portion 0 to 5 [mm] is the negative electrode current collector 23 made of Cu foil, and the resistance can be considered to be 0 [Ω]. Resistance R N As shown in FIG. 8, [Ω] is the resistance R N There is a peak of [Ω]. This resistance R N The peak of [Ω] is roughly R N On the other hand, at a position approximately 90 mm away from the width direction end of the negative electrode plate 2, the resistance R P = 21[Ω], but the resistance is lower here for another reason, so the resistance R N= 22[Ω] as the base. And the peak resistance R N = 28[Ω] and base resistance R N = 22 [Ω] is the resistance difference ΔR N = 6[Ω].

[0076] Specifically, the inventors have experimentally determined that (ΔR N +ΔR S -ΔR P It has been found that, by setting the value of 0 [Ω] or more, deterioration in positive electrode mixture layer 32 during discharge can be suppressed.

[0077] In addition, the resistance difference ΔR of the separator 4 is set to be equal to or less than the threshold value for suppressing Li deposition on the negative electrode plate 2 during charging. S Specifically, the inventors set the following through experiments: (ΔR N +ΔR S -ΔR P It has been found that, when the resistance (resistance) of the negative electrode plate 2 is 13 [Ω] or less, Li deposition on the negative electrode plate 2 can be suppressed.

[0078] In this embodiment, ΔR S ≦ΔR P -ΔR N +13 ≦7-6+13 ≦14[Ω], ΔR S If the resistance is less than or equal to 14 [Ω], Li deposition on the negative electrode plate 2 during charging can be suppressed.

[0079] In addition, (ΔR N +ΔR S -ΔR P ) ≧ 0, ΔR S ≧ΔR P -ΔR N ≧7-6 ≧1[Ω], ΔR S If ≧1 [Ω], deterioration of the positive electrode plate 3 during discharge can be suppressed.

[0080] From the above, in this embodiment, 1≦ΔR S When the resistance is less than or equal to 14 [Ω], Li deposition on the negative electrode plate 2 can be suppressed. <Separator 4 resistance R S Adjustment > As described above, in this embodiment, 1≦ΔR S It was found that when the resistance is ≦14 [Ω], Li deposition can be suppressed in the negative electrode plate 2. Fig. 9 is a graph showing the relationship between the thickness [µm] of the resistor portion 41 in the example and the resistance [Ω] in the thickness direction of the resistor portion 41.

[0081] As shown in FIG. 9, when the thickness of the resistor portion 41 is 0.17 μm, ΔR S = 1 [Ω]. In addition, when the thickness of the resistor portion 41 is 4.48 [μm], ΔR S = 14[Ω].

[0082] <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.

[0083] (Function of the Lithium-Ion Secondary Battery 10 of the Present Embodiment) Separator 4 of the present embodiment has resistance portion 41. In positive electrode mixture layer 32 that has a high SOC [%] during discharge, resistance R P [Ω] is high, and lithium ion Li + If discharge is continued in this state, the crystal structure of the positive electrode active material may be destroyed, or the nonaqueous electrolyte 13 may be reduced and decomposed. For this reason, the separator 4 of the present embodiment has a low (ΔR N +ΔR S -ΔR P ) is set to 0 [Ω] or more at the resistance portion 41, and the resistance R S [Ω] is increased within an appropriate range.

[0084] As a result, the positive electrode mixture layer 32 is filled with receptive lithium ions Li + By receiving the positive electrode active material, it is possible to suppress the collapse of the crystal structure of the positive electrode active material and the reductive decomposition of the nonaqueous electrolyte solution 13. During charging, lithium ions Li are transferred from the positive electrode mixture layer 32 to the negative electrode mixture layer 22. + moves, but at this time (ΔR N +ΔR S -ΔR P If the value of (ΔR N +ΔR S -ΔR P The resistance R at the center portion 4a in the width direction W is set to 13 [Ω] or less. S [Ω] is increased within an appropriate range.

[0085] (Effects of this embodiment) (1) The lithium ion secondary battery 10 and the manufacturing method thereof according to the present embodiment have the advantage that deterioration of the electrode body 12 of the lithium ion secondary battery 10 can be suppressed.

[0086] (2)(ΔR N +ΔR S -ΔRP ) is set to a value equal to or less than the threshold value for suppressing Li deposition on the negative electrode plate 2. S Therefore, there is an effect of suppressing Li deposition on the negative electrode plate 2.

[0087] (3) (ΔR N +ΔR S -ΔR P ) is set to 0 [Ω] or more by adjusting the resistance difference ΔR S As a result, there is an effect that the collapse of the crystal structure of the positive electrode active material in the positive electrode plate 3 can be suppressed.

[0088] (4) (ΔR N +ΔR S -ΔR P The resistance difference ΔR of separator 4 is set so that the value of S Therefore, accurate adjustments can be easily made to match the characteristics of positive electrode mixture layer 32 and negative electrode mixture layer 22.

[0089] (5) The resistor portion 41 is made of a material containing insulating particles, so that the resistance of the resistor portion 41 can be appropriately and stably adjusted. (6) The insulating particles forming the resistor portion 41 are made of boehmite or alumina. This provides excellent insulation, heat resistance, mechanical strength, and corrosion resistance, and allows for stable quality at low cost.

[0090] (7) The resistor portion 41 is formed by applying a paste of an insulator and a binder to the separator 4 using a solvent, thereby forming a coating of the resistor portion 41 on the surface of the separator 4. Therefore, the resistance value can be easily adjusted by adjusting the application process, and the resistor portion 41 can have an appropriate resistance [Ω].

[0091] (Another example) 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.

[0092] Although the lithium ion secondary battery 10 has a flat electrode body 12 as an example, the electrode body 12 may be cylindrical. Although the resistance portion 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 portion 41 may be formed separately in advance and attached.

[0093] 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.

[0094] Although the resistance portion 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.

[0095] 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.

[0096] 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]

[0097] 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 3…Positive electrode plate 31...Positive electrode current collector 32...Positive electrode mixture layer 33…Positive electrode current collector 4…Separator 41...Resistance section

Claims

1. In a lithium ion secondary battery having an electrode body in which a positive electrode plate and a negative electrode plate are stacked and wound with a separator interposed therebetween, a resistor portion is formed along the winding direction in a central portion in a width direction of the separator, The difference in resistance in the thickness direction between the end portion and the center portion in the width direction of the positive electrode mixture layer of the positive electrode plate of the electrode body is defined as ΔR Ｐ [Ω], and the difference in resistance in the thickness direction between the end portion and the center portion in the width direction of the negative electrode mixture layer of the negative electrode plate is ΔR Ｎ [Ω], and the difference in resistance in the thickness direction between the end portion and the center portion in the width direction of the separator is ΔR Ｓ When set to [Ω], (ΔR Ｎ +ΔR Ｓ -ΔR Ｐ ) is set to a value equal to or less than a threshold value for suppressing Li deposition on the negative electrode plate. Ｓ A lithium-ion secondary battery characterized in that [Ω] is set.

2. The above (ΔR Ｎ +ΔR Ｓ -ΔR Ｐ ) is set to a value equal to or greater than a threshold value for suppressing deterioration of the positive electrode active material in the positive electrode plate. Ｓ 2. The lithium ion secondary battery according to claim 1, wherein the resistance [Ω] is set.

3. The above (ΔR Ｎ +ΔR Ｓ -ΔR Ｐ The resistance difference ΔR of the separator is set to 13 [Ω] or less. Ｓ 2. The lithium ion secondary battery according to claim 1, wherein the resistance [Ω] is set.

4. The above (ΔR Ｎ +ΔR Ｓ -ΔR Ｐ ) is set to 0 [Ω] or more. Ｓ 3. The lithium ion secondary battery according to claim 2, wherein the resistance [Ω] is set.

5. 5. The lithium ion secondary battery according to claim 1, wherein the resistor portion is formed from a material containing insulating particles.

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

7. A method for manufacturing 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, comprising the steps of: forming a resistor portion along a winding direction in a central portion in a width direction of the separator, The difference in resistance in the thickness direction between the end portion and the center portion in the width direction of the positive electrode mixture layer of the positive electrode plate of the electrode body is defined as ΔR Ｐ [Ω], and the difference in resistance in the thickness direction between the end portion and the center portion in the width direction of the negative electrode mixture layer of the negative electrode plate is ΔR Ｎ [Ω], and the difference in resistance in the thickness direction between the end portion and the center portion in the width direction of the separator is ΔR Ｓ When set to [Ω], (ΔR Ｎ +ΔR Ｓ -ΔR Ｐ ) is set to a value equal to or less than a threshold value for suppressing Li deposition on the negative electrode plate. Ｓ A method for manufacturing a lithium ion secondary battery, characterized in that [Ω] is set.

8. The above (ΔR Ｎ +ΔR Ｓ -ΔR Ｐ ) is set to a value equal to or greater than a threshold value for suppressing deterioration of the positive electrode active material in the positive electrode plate. Ｓ 8. The method for producing a lithium ion secondary battery according to claim 7, wherein the resistance [Ω] is set.

9. The above (ΔR Ｎ +ΔR Ｓ -ΔR Ｐ The resistance difference ΔR of the separator is set to 13 [Ω] or less. Ｓ 8. The method for producing a lithium ion secondary battery according to claim 7, wherein the resistance [Ω] is set.

10. The above (ΔR Ｎ +ΔR Ｓ -ΔR Ｐ ) is set to 0 [Ω] or more. Ｓ 9. The method for producing a lithium ion secondary battery according to claim 8, wherein the resistance [Ω] is set.

11. 8. The method for producing a lithium ion secondary battery according to claim 7, wherein the resistor portion is made of a material containing insulating particles.

12. 12. The method for producing a lithium ion secondary battery according to claim 11, wherein the insulating particles forming the resistor portion are made of boehmite or alumina.

13. 12. The method for producing a lithium ion secondary battery according to claim 11, wherein the resistor portion is formed by forming a coating of the resistor portion on a surface of the separator by applying a paste of the insulator and binder with a solvent to the separator.

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