JP2018018645A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery arranged so that the degradation of a battery performance can be suppressed even if deposition of a coating is concentrated on a surface of a negative electrode.SOLUTION: A secondary battery 10 is a lithium ion secondary battery comprising an electrode plate group 20 and a nonaqueous electrolyte solution which are encased in a battery case. The electrode plate group 20 is arranged by winding a positive electrode plate 21 and a negative electrode plate 22 with a separator 23 put therebetween. The negative electrode plate 22 includes an additive having a sodium salt. The nonaqueous electrolyte solution includes an additive agent having a lithium salt. In the electrode plate group 20, a center portion 24, including a position corresponding to a center between opposing sides in a winding axis direction and having a predetermined width W in the winding axis direction, is provided to extend in a wound direction. In the center portion 24, a negative electrode capacity of the negative electrode plate 22 to a positive electrode capacity of the positive electrode plate 21 is larger than those in portions adjacent to the center portion 24 on the opposing sides thereof.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a lithium ion secondary battery in which a film forming agent is added to a nonaqueous electrolytic solution.

  Lithium ion secondary batteries have high energy density and high capacity, and are therefore used as driving power sources for electric vehicles (EV) and hybrid vehicles (HEV). If the lithium ion secondary battery is an electrode body obtained by winding or laminating a positive electrode plate and a negative electrode plate provided with active material layers on both sides of an electrode core through a separator, the opposing area of the positive electrode plate and the negative electrode plate is large. Therefore, it becomes easy to take out a large current.

  On the other hand, lithium ion secondary batteries, when used in a high temperature environment, are affected by the environment in which they are used. For example, the capacity retention rate of the battery decreases, and the internal resistance of the electrode increases. There is a problem of doing.

  Therefore, lithium bisoxalate borate (LiBOB) as a film-forming agent is added to the non-aqueous electrolyte, and a film derived from LiBOB is formed on the negative electrode in a uniform state. The technique to maintain is described in patent document 1, for example.

  The lithium ion secondary battery described in Patent Document 1 includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode is provided with a coating derived from LiBOB, and the peak intensity resulting from the tricoordinate structure of the coating measured by the X-ray absorption fine structure analysis (XAFS) method is “α”, and the coating 4 measured by the XAFS method is used. When the intensity of the peak due to the coordinate structure is “β”, the film satisfies the condition of “α / (α + β) ≧ 0.4”.

JP 2013-97973 A

According to the lithium ion secondary battery described in Patent Document 1, the effect of the coating derived from LiBOB formed on the negative electrode can be surely exhibited.
By the way, it is known that the concentration distribution of LiBOB on the electrode plate after injection is uneven. Then, due to this uneven concentration distribution, a coating derived from LiBOB is partially concentrated on the negative electrode surface, which may deteriorate the battery performance.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a lithium ion secondary battery capable of suppressing deterioration of battery performance even when the concentration of a coating film occurs on the negative electrode surface. There is.

  A lithium ion secondary battery that solves the above problem is a lithium ion secondary battery that contains an electrode plate group and a non-aqueous electrolyte in a battery case, and the electrode plate group includes a positive electrode plate and a negative electrode plate. Is wound around a separator, the negative electrode plate includes an additive having a sodium salt, the non-aqueous electrolyte includes an additive having a lithium salt, and the electrode plate group has a winding axis direction. A center portion having a predetermined width in the winding axis direction including a center position between both side surfaces of the negative electrode plate is extended in the winding direction, and the negative electrode plate corresponding to the positive electrode capacity of the positive electrode plate The negative electrode capacity is larger in the central portion than in a portion adjacent to both side surfaces of the central portion.

  The non-aqueous electrolyte contains an additive containing a lithium salt for the purpose of forming a protective film. By the way, the inventors have found that the lithium (Li) precipitation resistance indicated by the charging current at which Li is deposited decreases in the portion where the protective film is thicker than usual. That is, when the nonaqueous electrolytic solution penetrates into the electrode plate group, the additive containing a lithium salt having a low affinity with the negative electrode active material has a slow penetration into the negative electrode mixture. Moreover, although an additive reacts with the binder which has sodium salt, the product derived from sodium salt is produced | generated, This also has low affinity with a negative electrode active material, and the penetration | permeation to a negative electrode compound material is slow. Therefore, in the nonaqueous electrolytic solution that permeates the separator from the end of the electrode plate group, the concentration of the additive and the product derived from the additive is high at the top when permeating along the separator. Due to such a concentration distribution, the protective coating produced based on the additive or the like becomes thicker at the central portion of the electrode plate group than at the other portions. The lithium deposition resistance is reduced by a film thicker than the other portions. As a result, the charging current of the secondary battery is limited to the Li deposition resistance that is reduced, and the battery performance is reduced.

  In this regard, according to the above configuration, the negative electrode capacity of the negative electrode plate relative to the positive electrode capacity of the opposite positive electrode plate in the central portion of the electrode plate group where the coating derived from lithium salt concentrates is larger than that in the portion adjacent to the central portion. large. By increasing the negative electrode capacity of the negative electrode plate relative to the positive electrode capacity of the positive electrode plate, the charging current per unit volume in the negative electrode plate becomes relatively small. In other words, the charging current in the portion adjacent to the central portion can be made larger than the charging current in the central portion by the amount that the charging current of the negative electrode plate in the central portion can be reduced. As a result, while the charging current is limited to the Li deposition resistance of the central portion, the portion adjacent to the central portion can be charged with more current than the central portion. That is, the charging current between the central portion and the other portions can be appropriately balanced. Thereby, even if the concentration of the coating occurs on the negative electrode surface, it is possible to suppress the deterioration of the battery performance.

  Moreover, local deterioration of the central portion can be suppressed by reducing the charging current to the central portion where the coating derived from the lithium salt on the negative electrode plate is concentrated. Furthermore, although the charging current in the central portion is reduced, the width of the central portion is sufficiently narrow with respect to the length of the electrode plate group in the winding axis direction, so that the charging capacity can be maintained without increasing the number of wrinkles. .

As a preferred configuration, in the positive electrode plate, the amount of the positive electrode mixture in the central portion is smaller than the amount of the positive electrode mixture in the portion adjacent to both side surfaces of the central portion.
According to such a configuration, the positive electrode capacity of the positive electrode plate becomes smaller than the portions adjacent to both side surfaces of the central portion by reducing the amount of the positive electrode mixture in the central portion of the electrode plate group. In other words, the negative electrode capacity of the negative electrode plate corresponding to the positive electrode capacity of the positive electrode plate is larger in the central part of the electrode plate group than in the part adjacent to both side surfaces of the central part. Thereby, the charging current per unit volume of the negative electrode mixture of the negative electrode plate in the central portion is reduced. The amount of the composite material can be changed by adjusting the thickness to be applied when creating the positive electrode plate. In general, the positive electrode mixture after application is deformed in a form in which irregularities are smoothed in a subsequent compression process or winding process.

As a preferred configuration, in the positive electrode composite material, the amount of the composite material in the central portion is smaller by 3% or more and 70% or less than the amount of the composite material in the portions adjacent to both side surfaces of the central portion.
According to such a configuration, the amount of the composite material of the positive electrode mixture in the central portion of the electrode plate group is reduced by 3% or more and 70% or less compared to the amount of the composite material in the adjacent portion, The balance of the charging current between the part and the adjacent part can be made appropriate.

As a preferable configuration, in the negative electrode plate, the amount of the negative electrode mixture in the central portion is larger than the amount of the negative electrode mixture in the portion adjacent to both side surfaces of the central portion.
According to such a structure, the negative electrode capacity | capacitance of a negative electrode plate increases more than the part adjacent to the both sides | surfaces side of a center part by increasing the compound material amount of the negative electrode compound material of the center part of an electrode group. In other words, the negative electrode capacity of the negative electrode plate corresponding to the positive electrode capacity of the positive electrode plate is larger in the central part of the electrode plate group than in the part adjacent to both side surfaces of the central part. Thereby, the charging current per unit volume of the negative electrode mixture of the negative electrode plate is reduced. The amount of the composite material can be changed by adjusting the thickness to be applied when creating the negative electrode plate. In general, the negative electrode mixture after application is deformed in a form in which irregularities are smoothed in a subsequent compression process or winding process.

As a preferable configuration, the negative electrode composite material has a composite material amount in the central portion that is 5% or more and 122% or less larger than a composite material amount in a portion adjacent to both side surfaces of the central portion.
According to such a configuration, the amount of the negative electrode mixture in the central portion of the electrode plate group is increased by 5% or more and 122% or less as compared with the amount of the mixture in the adjacent portion. The balance of the charging load between the part and the adjacent part can be made appropriate.

As a preferred configuration, the predetermined width of the central portion is 0.5 cm or more and 4 cm or less.
According to such a configuration, the additive having the lithium salt in the electrolytic solution penetrating from both ends of the electrode plate group stays in the center and has a high concentration around the additive. In other words, by setting the width of the central portion of the electrode plate group in the range of 0.5 cm or more and 4 cm or less, it is possible to deal with a thick film generated in the central portion.

As a preferable configuration, lithium bisoxalate borate is included as the lithium salt.
According to such a configuration, LiBOB as an additive can form a relatively stable coating on the negative electrode plate that can extend the battery life.

  Further, since LiBOB has low affinity with the negative electrode active material, when it penetrates into the electrode plate group together with the non-aqueous electrolyte, it is seen from the head that penetrates toward the central portion, that is, from both ends of the electrode plate group. Therefore, the concentration is high in the central part and a film is easily formed. In this respect, according to the above configuration, the negative electrode capacity at the central portion of the negative electrode plate with respect to the positive electrode capacity of the positive electrode plate is increased, the formation of a coating film at the central portion is suppressed, and the deterioration of the battery performance is suppressed. .

As a preferred configuration, carboxymethyl cellulose is included as the sodium salt.
According to such a configuration, with respect to the negative electrode plate including CMC as a binder in the negative electrode mixture, the effect of appropriately balancing the charging current between the central part of the electrode plate group and the part adjacent to the central part is obtained. It can be played reliably.

  According to this lithium ion secondary battery, even if the coating is concentrated on the negative electrode surface, deterioration of battery performance can be suppressed.

The front view which shows the internal structure about 1st Embodiment which actualized the lithium ion secondary battery. The schematic diagram which shows typically the cross-section of the electrode group in the same embodiment. The schematic diagram which shows typically schematic structure of the apparatus which manufactures the electrode group in the same embodiment. The front view which shows the front structure of the die | dye which apply | coats positive mix with the apparatus which manufactures the electrode group in the same embodiment. The schematic diagram which shows typically the aspect which the non-aqueous electrolyte in which an additive is contained in the electrode group in the same embodiment osmose | permeates. The schematic diagram which shows typically the aspect in which the nonaqueous electrolyte solution containing the additive which osmose | permeated the electrode group in the same embodiment formed the protective film. The schematic diagram which shows the aspect of charge typically about the conventional electrode group. The schematic diagram which shows typically the aspect of the charge in the said 1st Embodiment. The front view which shows the front structure of the die | dye which apply | coats a negative mix with the apparatus which manufactures the electrode group about 2nd Embodiment which actualized the lithium ion secondary battery. The schematic diagram which shows typically the cross-section of the electrode group in the same embodiment, and the aspect of charge.

(First embodiment)
1st Embodiment which actualized the secondary battery 10 as a lithium ion secondary battery is described according to FIGS. The secondary battery 10 of this embodiment comprises an assembled battery by connecting two or more with a bus bar. The assembled battery is mounted on an electric vehicle or a hybrid vehicle, and supplies power to an electric motor or the like. The secondary battery 10 is a sealed battery whose outer shape is a rectangular parallelepiped shape. The lithium ion secondary battery is a so-called non-aqueous electrolyte secondary battery.

  As shown in FIG. 1, the secondary battery 10 includes a rectangular parallelepiped battery case 11 having an opening on the upper side, a lid body 12 that seals the battery case 11, and an electrode plate that is accommodated in the battery case 11. A group 20 and a non-aqueous electrolyte 25 (see FIG. 5) injected into the battery case 11 are provided. The battery case 11 and the lid 12 are made of a metal such as an aluminum alloy. The secondary battery 10 has a sealed battery case by attaching a lid 12 to the battery case 11. In addition, the secondary battery 10 includes two external terminals 13 used for charging and discharging power on the lid 12.

  The electrode plate group 20 is formed by flatly winding a positive electrode plate 21, a negative electrode plate 22, and a separator 23 arranged therebetween. The electrode plate group 20 includes a positive electrode portion 21A in which a positive electrode plate 21 protrudes from one end side in a direction (winding axis direction) orthogonal to a winding direction (winding direction) and a negative electrode on the other end side in the same orthogonal direction. The plate 22 has a protruding negative electrode portion 22A. The winding axis direction is also the direction in which the rewinding portion 26 extends.

  A part of each of the positive electrode part 21A and the negative electrode part 22A is compressed, and electrode terminals 14 connected to the external terminals 13 are welded to the compressed parts of the positive electrode part 21A and the negative electrode part 22A, respectively. Yes.

The configuration of the electrode plate group 20 will be described with reference to FIG. In the positive electrode plate 21, the positive electrode mixture 212 is applied to the surface of the positive electrode base material 211.
The positive electrode mixture 212 has a positive electrode active material. The positive electrode active material is a material capable of inserting and extracting lithium. For example, lithium cobaltate (LiCoO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium nickelate (LiNiO ₂ ), and the like can be used. _{It may} also be a material obtained by mixing LiCoO 2, LiMn ₂ O _4, the LiNiO ₂ at an arbitrary ratio.

  Further, the positive electrode mixture 212 may include a conductive material. As the conductive material, for example, carbon black such as acetylene black (AB) and ketjen black, and graphite (graphite) can be used.

  The positive electrode plate 21 is obtained by, for example, kneading a positive electrode active material, a conductive material, a solvent, and a binder (binder), applying the kneaded positive electrode mixture 212 to the positive electrode base material 211 and drying it. Produced. Here, as the solvent, for example, an NMP (N-methyl-2-pyrrolidone) solution can be used. As the binder, for example, polyvinylidene fluoride (PVdF), styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), or the like can be used. As the positive electrode base material 211, a thin film made of aluminum or an alloy containing aluminum as a main component can be used.

In the negative electrode plate 22, a negative electrode mixture 222 is applied to the surface of the negative electrode base material 221. In the present embodiment, the surface of the negative electrode base material 221 constitutes the surface of the negative electrode.
The negative electrode active material is a material capable of inserting and extracting lithium, and for example, a powdery carbon material made of graphite or the like can be used. The negative electrode plate 22 is produced by kneading a negative electrode active material, a solvent, and a binder, and applying the kneaded negative electrode mixture 222 to the negative electrode base material 221 and drying it, like the positive electrode plate 21. The In this embodiment, the binder includes carboxymethyl cellulose (CMC) having a sodium salt. Here, as the negative electrode substrate 221, for example, a thin film made of copper, nickel, or an alloy thereof can be used.

The nonaqueous electrolytic solution 25 will be described with reference to FIG. The nonaqueous electrolytic solution 25 is a composition in which a supporting salt is contained in a nonaqueous solvent. Here, as the non-aqueous solvent, one or two selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and the like. More than one type of material can be used. The supporting salts include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiI 1 type, or 2 or more types of lithium compounds (lithium salt) selected from these etc. can be used.

  In the secondary battery 10 according to the present embodiment, lithium bisoxalate borate (LiBOB) as a lithium salt as an additive is added to the non-aqueous electrolyte 25. For example, LiBOB is added to the nonaqueous electrolytic solution 25 so that the concentration of LiBOB in the nonaqueous electrolytic solution 25 is 0.001 to 0.1 [mol / L].

  The separator 23 will be described with reference to FIG. FIG. 2 is a view when the electrode plate group 20 is cut in the winding axis direction. The separator 23 is a nonwoven fabric made of polypropylene or the like for holding the nonaqueous electrolyte solution 25 between the positive electrode plate 21 and the negative electrode plate 22. Further, as the separator 23, a porous polymer film such as a porous polyethylene film, a porous polyolefin film, and a porous polyvinyl chloride film, or a lithium ion or ion conductive polymer electrolyte film is used alone or in combination. You can also

  Referring to FIG. 1, secondary battery 10 has a central position between both side surfaces (positive electrode portion 21 </ b> A and negative electrode portion 22 </ b> A) in the winding axis direction of electrode plate group 20, and the central position is A central portion 24 is included which has a predetermined width W in the winding axis direction. The central portion 24 extends in the winding direction in the electrode plate group 20. Here, the predetermined width W is not less than 0.5 cm and not more than 4 cm.

  As shown in FIG. 2, in the secondary battery 10 of the present embodiment, the negative electrode capacity of the negative electrode plate 22 corresponding to the positive electrode capacity of the positive electrode plate 21 is in the central portion 24 in the central portion 24 of the electrode plate group 20. It is larger than the adjacent portion 24A. Here, the portion 24 </ b> A adjacent to the central portion 24 is a portion on the side surface side than the central portion 24 when viewed from the winding axis direction.

  More specifically, the positive electrode plate 21 has a dent 212a of the positive electrode mixture 212 in the central portion 24 immediately after the mixture is applied. The recess 212a has a predetermined width W in the winding axis direction and extends in the winding direction. The thickness of the positive electrode mixture 212 applied to the positive electrode substrate 211 at the adjacent portion 24A is the thickness DP1, and the thickness of the positive electrode mixture 212 applied to the positive electrode substrate 211 at the center portion 24 is the thickness DP2. (B). The thickness DP1 is thicker than the thickness DP2. For example, the thickness DP2 is 3% or more and 70% or less thinner than the thickness DP1, and preferably 20% or more and 60% or less. That is, the thickness of the composite material amount of the positive electrode composite material 212 applied to the central portion 24 and the composite material amount of the positive electrode composite material 212 applied to the adjacent portion 24A are adjusted. That is, in the central portion 24, the amount of the positive electrode mixture 212 is 3% or more and 70% or less as compared with the adjacent portion 24A. The amount of the composite material is proportional to the positive electrode capacity. As described above, the amount of the positive electrode mixture 212 can be adjusted by the applied thickness. In general, the positive electrode plate 21 is deformed in the form of unevenness caused by the difference in thickness of the positive electrode mixture 212 or the like in the subsequent compression process or winding process. Explain in a way that the unevenness is maintained constant.

With reference to FIG.3 and FIG.4, the manufacturing method of the positive electrode plate 21 apply | coated to the positive electrode base material 211 so that the positive electrode compound material 212 may have the dent 212a in the center part 24 is demonstrated.
As shown in FIG. 3, the manufacturing apparatus 30 that manufactures the positive electrode plate 21 manufactures the positive electrode plate 21 by applying a slurry of the positive electrode mixture 212 to the positive electrode base material 211 by a die coating method.

  The manufacturing apparatus 30 discharges the slurry of the positive electrode mixture 212 onto the surface of the positive electrode base material 211 and the base material transport units 31 and 32 wound with the positive electrode base material 211 before the slurry of the positive electrode mixture 212 is applied. And die 33 to be used.

  The die 33 has a discharge port 33 a and is provided on one side of the conveyance path of the positive electrode substrate 211 so as to face the substrate conveyance unit 31. The die 33 has a discharge port 33a communicating with a manifold 33c that receives the slurry via a slot 33b. The die 33 is connected to a tank 38 in which slurry is stored through a pipe line 36 communicating with the manifold 33c. When the pump 37 provided in the middle of the pipeline 36 is driven, the slurry is supplied from the tank 38 to the die 33 through the filter 35 provided in the middle.

  Referring to FIG. 4, the die 33 has a discharge port 33 a that is horizontally long when viewed from the positive electrode base material 211 side. The discharge port 33a has an opening extending in the width direction (winding axis direction) of the positive electrode base material 211, and the opening width is made different in the length direction (winding direction) that is the feed direction of the positive electrode base material 211. ing. Slurry discharged at an opening width from the discharge port 33 a is applied to the surface of the positive electrode base material 211. Therefore, the positive electrode mixture 212 is applied to the surface of the positive electrode base material 211 at a thickness that is determined in proportion to the opening width of the discharge port 33a. The discharge port 33a includes a convex portion 33d that narrows the opening width at a portion corresponding to the central portion 24 so that the thickness of the central portion 24 is reduced and the amount of the mixed material is reduced when the electrode plate group 20 is configured. Yes. That is, since the convex portion 33d has a smaller opening width than the portion corresponding to the adjacent portion 24A, the amount of slurry discharged from the convex portion 33d is reduced. Therefore, the positive electrode mixture 212 is applied to the surface of the positive electrode base material 211 so as to form a dent 212a in a portion corresponding to the central portion 24 when the electrode plate group 20 is configured. In this way, the positive electrode plate 21 having the recess 212a in the positive electrode base material 211 applied to the surface is manufactured.

  The electrode plate group 20 is inserted into the battery case 11 through the opening. The battery case 11 in which the electrode plate group 20 is inserted encloses the electrode plate group 20 by welding the lid 12 that contacts the opening. Then, after the inside of the battery case is dried, the nonaqueous electrolyte solution 25 is injected into the battery case, the inlet of the nonaqueous electrolyte solution 25 opened in the lid 12 is sealed, and the battery case is sealed. The Thereby, the secondary battery 10 is manufactured.

In the present embodiment, the secondary battery 10 is subjected to a conditioning process for forming a protective coating 27 (see FIG. 6) derived from LiBOB on the surface of the negative electrode plate 22.
The conditioning process can be performed by repeating charging and discharging of the secondary battery 10 a predetermined number of times. For example, the conditioning process is an operation of charging at constant current and constant voltage up to 4.1 V at a charging rate of 0.1 C under a temperature condition of 20 ° C., and constant current and constant voltage discharging up to 3.0 V at a discharging rate of 0.1 C. This operation can be performed by repeating each operation three times. The conditioning process is not limited to this condition, and the charge rate, discharge rate, and set voltage for charge / discharge can be set arbitrarily. In the secondary battery 10 of this embodiment, the protective film 27 which is a film derived from LiBOB can be formed on the surface of the negative electrode plate 22 by performing a conditioning process after manufacturing. The protective coating 27 is formed by depositing LiBOB added to the non-aqueous electrolyte 25 on the surface of the negative electrode plate 22 when conditioning treatment is performed.

Next, with reference to FIG. 5 and FIG. 6, it will be described that a film is formed on the surface of the negative electrode plate 22 by LiBOB added to the nonaqueous electrolytic solution 25.
First, the outline will be described. The nonaqueous electrolytic solution 25 contains LiBOB containing a lithium salt for the purpose of forming the protective coating 27. By the way, the inventors found that the lithium deposition resistance indicated by the charging current at which Li is deposited decreases in the portion where the protective coating 27 is thicker than usual. That is, when the nonaqueous electrolytic solution 25 penetrates into the electrode plate group 20, LiBOB having a low affinity with the negative electrode active material has a slow penetration into the negative electrode mixture 222. In addition, LiBOB reacts with CMC having a sodium salt to produce NaBOB, which is a product derived from the sodium salt, which also has low affinity with the negative electrode active material and slow penetration into the negative electrode mixture 222. Therefore, in the nonaqueous electrolytic solution 25 that permeates the separator 23 from the end portion of the electrode plate group 20, the concentration of LiBOB and NaBOB increases at the leading portion 25 c when permeating along the separator 23. With such a concentration distribution, the protective film 27 generated based on LiBOB or the like becomes thicker at the central portion 24 of the electrode plate group 20 than at the other portions. And a lithium deposition tolerance falls by the film thicker than another part. As a result, the charging current of the secondary battery 10 is limited to the reduced Li deposition resistance of the central portion 24, and the battery performance of the secondary battery 10 as a whole is reduced.

  As shown in FIG. 5, when the non-aqueous electrolyte 25 is injected into the battery case 11 in which the electrode plate group 20 is sealed, both side surfaces (positive electrode portion 21A and negative electrode portion 22A) of the electrode plate group 20 in the winding axis direction. Penetrates into the electrode plate group 20. When the nonaqueous electrolyte 25 penetrates into the electrode plate group 20, it reacts with the CMC of the negative electrode mixture 222, and a part thereof becomes sodium bisoxalate borate (NaBOB), and this NaBOB follows the flow of the nonaqueous electrolyte 25. Move to the central portion 24 of the plate group 20. Here, since LiBOB and NaBOB have low affinity with the negative electrode active material, they move along the separator 23 to the central portion 24 of the electrode plate group 20 without penetrating the negative electrode mixture 222 much. On the other hand, the substance that easily penetrates into the negative electrode mixture 222 contained in the non-aqueous electrolyte 25 penetrates into the negative electrode mixture 222 while moving toward the central portion 24 of the electrode plate group 20. For this reason, the concentration of LiBOB or NaBOB having a low affinity with the negative electrode active material is naturally higher in the head portion 25c near the head 25b of the flow of the nonaqueous electrolyte solution 25 than in the position 25a at the beginning of the flow. .

  As shown in FIG. 6, in the central portion 24 of the electrode plate group 20, the two heads 25 b of the nonaqueous electrolyte solution 25 that have infiltrated from both side surfaces of the electrode plate group 20 collide with each other and the infiltration is finished. When the permeation is completed, the leading portion 25c near the two leading portions 25b and having a high concentration of LiBOB or NaBOB remains in the central portion 24 of the electrode plate group 20. In the conditioning process, the protective coating 27 is formed with a film thickness corresponding to the concentration of LiBOB or NaBOB. Therefore, when the conditioning process is performed in this state, the central portion 24 of the electrode plate group 20 has LiBOB or NaBOB. A protective film 27 having a thick film thickness corresponding to the concentration is formed. For example, the formed protective coating 27 has a first coating 27a in the adjacent portion 24A and a second coating 27b in the central portion 24. The second film 27b is thicker than the first film 27a.

  By the way, the inventors have shown that the electrode group 20 having the protective coating 27 formed in this manner has a lower lithium deposition resistance of the second coating 27b during charging than that of the first coating 27a. I found. Here, the resistance to lithium deposition can be indicated by a charging current when lithium is to be deposited. The resistance increases as the charging current increases, and the resistance decreases as the charging current value decreases.

  Referring to FIG. 7 in detail, at the time of charging, lithium ions C1 pass through the first coating 27a from the positive electrode plate 21 to the corresponding negative electrode mixture portion M1 of the negative electrode plate 22 in the adjacent portion 24A. In the central portion 24, it passes through the second coating 27 b and moves from the positive electrode plate 21 to the corresponding negative electrode mixture portion M 2 of the negative electrode plate 22. At this time, the first coating 27a and the second coating 27b obstruct the movement of the lithium ions C1, but if the charging current does not exceed the lithium deposition resistance, the lithium ions C1 can sufficiently pass through. Lithium does not precipitate on the surface of the second coating 27b. On the other hand, when the charging current exceeds the lithium deposition resistance, the amount of lithium ions C1 reaching from the positive electrode plate 21 is larger than the amount passing through, and lithium is deposited on the surfaces of the first coating 27a and the second coating 27b. . In addition, the second coating 27b is thicker than the first coating 27a and more difficult for lithium ions C1 to pass therethrough, so that the lithium deposition resistance is lower than that of the first coating 27a.

  The secondary battery 10 is preferably charged with a charging current that does not cause lithium deposition. For this reason, when the 2nd film 27b with low lithium precipitation tolerance is formed in the protective film 27, the charging current as the secondary battery 10 will be controlled so that the lithium precipitation tolerance of the 2nd film 27b may be made into an upper limit. That is, the charging current is regulated based on the lithium deposition resistance of the central portion 24 having the second coating 27b, even though the adjacent portion 24A having the first coating 27a has a margin for lithium deposition resistance. Thus, the lithium deposition resistance of the secondary battery 10 as a whole is lowered, and the battery performance is lowered.

  Next, with reference to FIG. 8, the charging operation of the electrode plate group 20 of the secondary battery 10 of the present embodiment will be described. As described above, the shape of the positive electrode plate 21 may be deformed through a compression process or a winding process after manufacturing. However, for convenience of explanation, the positive electrode plate 21 is formed between the central portion 24 and the adjacent portion 24A. The difference in material amount will be described based on the difference between the first thickness DP1 of the adjacent portion 24A of the positive electrode mixture 212 and the second thickness DP2 of the central portion 24.

  As shown in FIG. 8, in the present embodiment, in the positive electrode plate 21, the thickness of the central portion 24 is the second thickness DP2, and the thickness of the adjacent portion 24A is the first thickness DP1. The relationship between these thicknesses is “first thickness DP1> second thickness DP2”. That is, the amount of mixture in the concave portion 212a of the positive electrode mixture 212 of the central portion 24 is smaller than the amount of mixture of the positive electrode mixture 212 of the adjacent portion 24A. When the electrode plate group 20 is charged, the lithium ions C2 and C3 move from the positive electrode plate 21 to the corresponding negative electrode mixture portions M1 and M2 of the negative electrode plate 22. At this time, the positive electrode plate 21 has an amount of lithium ions C3 released from the portion of the recess 212a of "second thickness DP2" rather than an amount of lithium ions C2 released from the portion of "first thickness DP1". Is relatively less. That is, the amount of lithium ions C3 released from the portion of “second thickness DP2” is relatively small, so that the second coating 27b of the negative electrode plate 22 has a margin for lithium deposition resistance, and this margin is the secondary. The charging current of the battery 10 can be increased. If the charging current increases, the amount of lithium ions C3 released from the “first thickness DP1” portion also increases. However, since the portion of the first coating 27a of the negative electrode plate 22 is highly resistant to lithium deposition, the charging current is reduced. Even if the lithium deposition resistance of the portion of the second coating 27b of the negative electrode plate 22 is matched, the charge capacity can be increased. That is, battery performance can be maintained high.

As described above, according to the secondary battery 10 of the present embodiment, the following effects can be obtained.
(1) In the central portion 24 of the electrode plate group 20, the negative electrode capacity of the negative electrode plate 22 relative to the positive electrode capacity of the opposing positive electrode plate 21 is made larger than that of the adjacent portion 24A. By increasing the negative electrode capacity of the negative electrode plate 22 relative to the positive electrode capacity of the positive electrode plate 21, the charging current per unit volume in the negative electrode plate 22 becomes relatively small. In other words, the charging current of the portion 24A adjacent to the central portion 24 can be made larger than the charging current of the central portion 24 by the amount that the charging current of the negative electrode plate 22 of the central portion 24 can be reduced. As a result, the charging current is limited to the Li deposition resistance of the central portion 24, but the portion 24A adjacent to the central portion 24 can be charged with more current than the central portion. That is, the charging current between the central portion 24 and the other portions can be appropriately balanced. Thereby, even if the concentration of the coating (second coating 27b) occurs on the surface of the negative electrode, the deterioration of the battery performance can be suppressed.

  Moreover, the local deterioration of the center part 24 can be suppressed by reducing the charging current with respect to the center part 24 with the 2nd film | membrane 27b in the negative electrode plate 22. FIG. Furthermore, although the charging current of the central portion 24 is reduced, the predetermined width W of the central portion is sufficiently narrow with respect to the length of the electrode plate group 20 in the winding axis direction, so that the charging capacity can be increased without increasing the number of wrinkles. It can also be maintained.

  (2) By reducing the amount of the positive electrode mixture 212 in the central portion 24 of the electrode plate group 20, the positive electrode capacity of the positive electrode plate 21 is smaller than that of the portions 24 </ b> A adjacent to both side surfaces of the central portion 24. In other words, the negative electrode capacity of the negative electrode plate 22 corresponding to the positive electrode capacity of the positive electrode plate 21 is larger in the central part 24 of the electrode plate group 20 than in the parts 24A adjacent to both side surfaces of the central part 24. Thereby, the charging current per unit volume of the negative electrode mixture 222 of the negative electrode plate 22 of the central portion 24 is reduced. Note that the amount of the composite material can be changed by adjusting the thickness to be applied when the positive electrode plate 21 is formed.

  (3) The central portion is reduced by 3% or more and 70% or less of the composite material amount of the positive electrode mixture 212 of the central portion 24 of the electrode plate group 20 compared to the composite material amount of the adjacent portion 24A. The charging current balance between the adjacent portion 24A and the adjacent portion 24A can be made appropriate.

  (4) In the nonaqueous electrolytic solution 25 that permeates from both ends of the electrode plate group 20, LiBOB that is an electrolytic solution additive and NaBOB that is derived from a sodium salt stay in the center, and the concentration increases around the center. That is, it is possible to cope with the thick protective film 27 generated in the central portion 24 by setting the width of the central portion 24 of the electrode plate group 20 in the range of 0.5 cm or more and 4 cm or less.

(5) LiBOB can form the protective film 27 on the negative electrode plate 22 with relatively high stability that can extend the battery life.
Further, since LiBOB has low affinity with the negative electrode active material, when it penetrates into the electrode plate group together with the non-aqueous electrolyte, the leading 25b that penetrates toward the central portion 24, that is, the electrode plate group 20 The density increases at the central portion 24 when viewed from both ends. In this regard, according to the present embodiment, the negative electrode capacity at the central portion 24 of the negative electrode plate 22 with respect to the positive electrode capacity of the positive electrode plate 21 is increased, the formation of a coating film at the central portion 24 is suppressed, and deterioration in battery performance is suppressed. Be able to.

  (6) With respect to the negative electrode plate 22 including CMC as a binder in the negative electrode mixture 222, the effect of appropriately balancing the charging current between the central portion 24 of the electrode plate group 20 and the portion 24A adjacent to the central portion is obtained. It can be played reliably.

(Second Embodiment)
A second embodiment in which the secondary battery 10 as a lithium ion secondary battery is embodied will be described with reference to FIGS. 9 and 10. In the present embodiment, the amount of the composite material of the negative electrode composite material 222 in the central portion 24 of the negative electrode plate 22 is increased, which is the amount of the composite material of the positive electrode composite material 212 in the central portion 24 of the positive electrode plate 21 in the first embodiment. It is different from the point that I decreased. That is, in the present embodiment, the negative electrode capacity of the negative electrode plate 22 corresponding to the positive electrode capacity of the positive electrode plate 21 is larger in the central portion 24 than in the adjacent portion 24A. The thickness is increased.

  As shown in FIG. 9, the die 33A for applying the negative electrode mixture 222 to the surface of the negative electrode base material 221 of the negative electrode plate 22 includes a discharge port 33a. The discharge port 33 a includes a recess 33 e that discharges a large amount of the mixture in a range corresponding to the central portion 24 when the electrode plate group 20 is configured. According to the die 33A, the negative electrode plate 22 in which the thickness of the negative electrode mixture 222 in the central portion 24 is increased can be manufactured.

  Referring to FIG. 10, negative electrode plate 22 has a convex portion 222 a that protrudes from adjacent portion 24 </ b> A at central portion 24 of negative electrode composite material 222. The thickness of the adjacent portion 24A is the thickness DM2, the thickness of the convex portion 222a is the thickness DM1, and the relationship of the thickness is “thickness DM2 <thickness DM1”. In the negative electrode composite material 222, the thickness of the central portion 24 is 5% or more and 122% or less, preferably 25% or more and 122% or less, compared to the adjacent portion 24A. That is, in the central portion 24, the amount of the composite material of the negative electrode composite material 222 is larger by 5% or more and 122% or less than the adjacent portion 24A. Further, the amount of the composite material is proportional to the negative electrode capacity.

  A first coating 27 a of the protective coating 27 is formed on the adjacent portion 24 A, and a second coating 27 c of the protective coating 27 is formed on the central portion 24. The second film 27c is thicker than the first film 27a.

  When the electrode plate group 20 wound around the negative electrode plate 22 is charged, the lithium ions C4 and C5 move from the positive electrode plate 21 to the negative electrode plate 22. At this time, the positive electrode plate 21 releases the same amount of lithium ions C4 and C5 from any portion. On the other hand, the lithium deposition resistance of the protective coating 27 is lower in the second coating 27 c than in the first coating 27 a, so the same amount of lithium ions C 5 as the lithium ions C 4 supplied to the adjacent portion 24 A is supplied to the central portion 24. In this case, first, the lithium deposition resistance of the second coating 27 c is reached at the central portion 24. On the other hand, since the negative electrode mixture 222 of the negative electrode plate 22 is “the thickness DM1 of the central portion 24> the thickness DM2 of the adjacent portion 24A”, the negative electrode composite portion M3 of the thickness DM1 of the central portion 24 is More lithium ions can be absorbed than the negative electrode mixture portion M1 having the thickness DM2 of the adjacent portion 24A. In other words, since the negative electrode mixture portion M3 having a thickness DM1 has a stronger ability to absorb lithium ions than the negative electrode mixture portion M1 having a thickness DP2, even if the second coating 27c of the protective coating 27 is thick. The amount of lithium ion permeation increases and the resistance to lithium deposition increases. Then, the charging current of the electrode plate group 20 can be increased by an amount corresponding to the increased lithium deposition resistance. As the charging current increases, the amount of lithium ions C4 supplied to the adjacent portion 24A of the thickness DM2 also increases. However, since the first coating 27a of the adjacent portion 24A has high lithium deposition resistance, the lithium of the second coating 27c The charging capacity can be increased as the deposition resistance increases. That is, battery performance can be maintained high.

  As described above, according to the secondary battery 10 of the present embodiment, in addition to the effects (1) and (4) to (6) described in the first embodiment, the effects as described below. Can be obtained.

  (7) By increasing the amount of the negative electrode mixture 222 in the central portion 24 of the electrode plate group 20, the negative electrode capacity of the negative electrode plate 22 is greater than that of the portions 24 </ b> A adjacent to both side surfaces of the central portion 24. In other words, the negative electrode capacity of the negative electrode plate 22 corresponding to the positive electrode capacity of the positive electrode plate 21 is larger in the central part 24 of the electrode plate group 20 than in the parts 24A adjacent to both side surfaces of the central part 24. Thereby, the charging current per unit volume of the negative electrode composite material 222 of the negative electrode plate 22 decreases. The amount of the composite material can be changed by adjusting the thickness to be applied when creating the negative electrode plate.

  (8) The central portion is increased by 5% or more and 122% or less of the composite material amount of the negative electrode composite material 222 of the central portion 24 of the electrode plate group 20 as compared with the composite material amount of the adjacent portion 24A. The balance of the charging load between the part 24A adjacent to the part 24 can be made appropriate.

(Other embodiments)
In addition, each said embodiment can also be implemented with the following aspects.
In each of the above embodiments, the case where the protective film 27 is formed on the surface of the negative electrode plate 22 is exemplified. However, the present invention is not limited to this, and when a protective film is formed on the surface of the positive electrode plate, the negative electrode capacity of the negative electrode plate corresponding to the positive electrode capacity of the positive electrode plate is smaller in the central part than in the parts adjacent to both side surfaces of the central part. It may be made to become.

  In each of the above embodiments, the case where the predetermined width W is not less than 0.5 cm and not more than 4 cm is exemplified. However, the present invention is not limited thereto, and the predetermined width may be less than 0.5 cm or wider than 4 cm as long as the thickness of the protective coating is increased.

  In the second embodiment, the case where the composite material amount of the negative electrode composite material 222 in the central portion 24 is larger by 5% or more and 122% or less than the composite material amount of the adjacent portion 24A is illustrated. However, the present invention is not limited to this, and if the negative electrode capacity in the central portion increases, the amount of the negative electrode composite in the central portion may be an increase of less than 5% compared to the amount of the adjacent portion of the composite material, The increase may be greater than 122%.

  In the first embodiment, the case where the composite material amount of the positive electrode composite material 212 of the central portion 24 is smaller by 3% or more and 70% or less than the composite material amount of the adjacent portion 24A is illustrated. However, the present invention is not limited to this, and if the positive electrode capacity in the central portion is reduced, the amount of the positive electrode mixture in the central portion may be a decrease of less than 3% compared to the amount of the mixture in the adjacent portion, The amount of decrease may be greater than 70%.

  -You may combine the said 1st Embodiment and 2nd Embodiment. That is, a dent may be provided in the positive electrode mixture, and a convex portion may be provided in the negative electrode mixture. Thereby, the charging current between the central portion and the adjacent portion can be adjusted between the positive electrode mixture and the negative electrode mixture.

  In each of the above embodiments, when applying the slurry, the case where the amount of the composite material in the central portion 24 is changed depending on the thickness to be applied is illustrated. However, the present invention is not limited to this, and if the amount of the composite material in the central portion can be changed, the composite material in the central portion or an adjacent portion can be removed after application, or a composite material having a different density can be applied to the central portion during application. You may do it.

  In each of the above embodiments, the case where the secondary battery 10 is mounted on an electric vehicle or a hybrid vehicle is illustrated, but the present invention is not limited thereto, and the secondary battery may be mounted on a vehicle such as a gasoline vehicle or a diesel vehicle. Good. Further, the secondary battery may be used as a power source for a moving body such as a railway, a ship, an aircraft, a robot, or an electrical product such as an information processing apparatus.

  DESCRIPTION OF SYMBOLS 10 ... Secondary battery, 11 ... Battery case, 12 ... Cover, 13 ... External terminal, 14 ... Electrode terminal, 20 ... Electrode plate group, 21 ... Positive electrode plate, 21A ... Positive electrode part, 22 ... Negative electrode plate, 22A ... Negative electrode Part, 23 ... separator, 24 ... central part, 24A ... part, 25 ... non-aqueous electrolyte, 25a ... position, 25b ... head, 25c ... head part, 26 ... rewinding part, 27 ... protective coating, 27a ... first coating 27b, 27c ... second coating, 30 ... manufacturing apparatus, 31,32 ... base material conveying portion, 33,33A ... die, 33a ... discharge port, 33b ... slot, 33c ... manifold, 33d ... convex, 33e ... concave , 35 ... filter, 36 ... pipe, 37 ... pump, 38 ... tank, 211 ... positive electrode base material, 212 ... positive electrode base material, 221 ... negative electrode base material, 222 ... negative electrode base material, 222a ... convex part.

Claims (8)

A lithium ion secondary battery containing a plate group and a non-aqueous electrolyte in a battery case,
In the electrode plate group, a positive electrode plate and a negative electrode plate are wound with a separator interposed therebetween,
The negative electrode plate includes an additive having a sodium salt,
The non-aqueous electrolyte includes an additive having a lithium salt,
The electrode plate group includes a center portion having a predetermined width in the winding axis direction including a center position between both side surfaces in the winding axis direction, and extends in the winding direction. The lithium ion secondary battery, wherein a negative electrode capacity of the negative electrode plate corresponding to a positive electrode capacity is larger in the central portion than in a portion adjacent to both side surfaces of the central portion. 2. The lithium ion secondary according to claim 1, wherein the positive electrode plate has a smaller amount of a mixture of positive electrodes in the central portion than an amount of a mixture of positive electrodes in portions adjacent to both side surfaces of the central portion. battery. 3. The lithium according to claim 2, wherein the positive electrode composite material has a composite material amount of the central portion that is 3% or more and 70% or less smaller than a composite material amount of a portion adjacent to both side surfaces of the central portion. Ion secondary battery. 4. The negative electrode plate has a larger amount of the negative electrode mixture in the central portion than an amount of the negative electrode mixture in portions adjacent to both side surfaces of the central portion. The lithium ion secondary battery described in 1. 5. The lithium composite material according to claim 4, wherein the negative electrode composite material has a composite material amount in the central portion that is 5% or more and 122% or less larger than a composite material amount in a portion adjacent to both side surfaces of the central portion. Ion secondary battery. The lithium ion secondary battery according to any one of claims 1 to 5, wherein the predetermined width of the central portion is 0.5 cm or more and 4 cm or less. The lithium ion secondary battery according to claim 1, wherein the lithium salt includes lithium bisoxalate borate. The lithium ion secondary battery according to claim 1, wherein the sodium salt includes carboxymethyl cellulose.