Not penetrated the electrode body

Abstract

To provide a power storage device in which a negative electrode SEI film derived from a supporting electrolyte is formed almost evenly in a negative electrode active material layer in a wound electrode body to inhibit increase in resistance.SOLUTION: A power storage device 1 includes: an electrolytic solution 6 which includes ethylene carbonate 6VE, a solvent 6VL having a lower melting point than that of ethylene carbonate, and a supporting electrolyte 6S containing P; a wound electrode body 2 which includes a strip-shaped positive electrode plate 3, a strip-shaped negative electrode plate 4 including a strip-shaped negative electrode active material layer 4A in which an SEI film 4AC is formed, and a strip-shaped separator 5, and in which the electrolytic solution is impregnated inside; and a case 7 in which the electrode body and the electrolytic solution are housed. The negative electrode active material layer of the electrode body has a width AW of 180 mm or larger. A P amount MP contained in the SEI film 4AC formed in the negative electrode active material layer is defined such that the center P amount MPT in a center portion 4AT in a width direction WH is 90% to 105% of an end portion P amount MPE on an end portion 4AE in the width direction WH of the negative electrode active material layer.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention provides Unpenetrated electrode body Regarding. [Background technology]

[0002] Conventionally, in an electricity storage device such as a battery that includes an electrode body and an electrolyte in a case, it has been necessary to consider uneven penetration (uneven impregnation) of the electrolyte into the electrode body. For example, Patent Document 1 discloses a method for producing a lithium ion battery in which an electrolyte is impregnated into at least one of the separator and the electrode active material layer (B) before a lamination step in which an electrode active material layer (A), a separator, and an electrode active material layer (B) are laminated to obtain a lamination unit, thereby preventing or suppressing uneven penetration of the electrolyte. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-212464 Summary of the Invention [Problem to be solved by the invention]

[0004] However, as described in Patent Document 1, when a wound-type electrode body is used instead of a stacked unit, i.e., a stacked-type electrode body, it becomes necessary to handle a strip-shaped separator impregnated with an electrolyte solution or a strip-shaped electrode plate impregnated with an electrolyte solution, which makes handling difficult.

[0005] On the other hand, as a solvent for the electrolyte of an electricity storage device, ethylene carbonate (hereinafter also referred to as EC), which forms an SEI film, may be used in addition to dimethyl carbonate (hereinafter also referred to as DMC), ethyl methyl carbonate (hereinafter also referred to as EMC), etc., in order to facilitate the formation of an SEI film on the negative electrode active material layer during initial charging. For example, an EC / DMC / EMC mixed solvent may be used for the electrolyte.

[0006] However, when an electrolyte containing EC is allowed to penetrate into the electrode body from the edge of the electrode body where the electrolyte has not yet penetrated, it has been found that the penetration rate of EC is relatively slow compared to supporting electrolytes such as DMC, EMC, and LiPF6 dissolved in these. EC has a melting point of approximately 34-37°C, which is relatively higher than DMC (melting point 2-4°C) and EMC (melting point -53°C), and its viscosity is also high, so it is thought that it penetrates more slowly into the electrode body along the negative electrode active material layer and separator than DMC.

[0007] For example, in an electricity storage device using a wound-type electrode assembly, in which the belt-shaped electrode plates are wide and therefore the electrolyte permeates a long distance, even if the electrolyte permeates from both axial ends and reaches the center in the axial direction, thereby permeating the entire electrode assembly, there may be cases where the EC has not yet sufficiently reached the center in the axial direction. In other words, during initial charging, there may be cases where the amount of EC per unit area (hereinafter also referred to as area density) present in various places in the electrode assembly is uneven, that is, where EC permeation is uneven.

[0008] When an electric storage device such as a secondary battery is initially charged in this state and an attempt is made to form a negative electrode SEI coating on the negative electrode active material layer, a negative electrode SEI coating derived from EC and a supporting electrolyte (e.g., LiPF6) is formed. However, as described above, the negative electrode SEI coating derived from EC is less likely to form near the axial center of the electrode body, where the EC content is low. In this case, a relatively large negative electrode SEI coating derived from the supporting electrolyte is formed to compensate for this. However, the negative electrode SEI coating derived from the supporting electrolyte has a higher resistance than the negative electrode SEI coating derived from EC. Therefore, it has been found that the negative electrode SEI coating derived from the supporting electrolyte is locally increased near the axial center of the electrode body, where the EC area density is low, compared to regions of high EC area density, such as near both axial ends, resulting in a negative electrode active material layer with a relatively high resistance. This results in a high resistance for the entire electric storage device.

[0009] The present invention has been made in view of the above-mentioned circumstances, and aims to provide a method for producing a negative electrode SEI film derived from a supporting salt in a negative electrode active material layer in a wound-type electrode body in a substantially uniform manner, thereby suppressing an increase in resistance. Unpermeated electrode body that can be This provides: [Means for solving the problem]

[0010] above One aspect of the present invention for solving the above problem is a strip-shaped positive electrode plate, a strip-shaped Negative a negative electrode plate having an electrode active material layer and a strip-shaped separator; In a wound-type non-permeated electrode body in which an electrolyte solution containing ethylene carbonate, a solvent having a melting point lower than that of ethylene carbonate, and a supporting salt containing P is not permeated inside, The width of the negative electrode active material layer is 180 mm or more. ri, front The negative electrode active material layer of the negative electrode plate contains ethylene carbonate in the central portion in the width direction, but does not contain ethylene carbonate in the end portions in the width direction. Non-permeated electrode body is.

[0011] This energy storage device includes an electrolyte solution containing a supporting salt containing EC and P, and an electrode body in which the width dimension of the negative electrode active material layer is 180 mm or more. As a result, as described above, uneven penetration of EC is likely to occur, and in the central portion where EC has difficulty reaching, an SEI coating derived from EC is unlikely to be formed, and instead, an SEI coating derived from the supporting salt containing P tends to be formed in excess. However, in this electricity storage device, the amount of P in the SEI coating of the negative electrode active material layer is within a range of 90 to 105% of the amount of P at the end portions. That is, the amount of P in the center portion is roughly equal to or slightly less than the amount of P at the end portions. In other words, in this electricity storage device, even in the center portion of the negative electrode active material layer, an excessive amount of negative electrode SEI coating derived from the P-containing supporting salt is not formed, and the local increase in IV resistance occurring in the axial direction within the electrode body (the width direction of the negative electrode plate) is suppressed, resulting in an electricity storage device that suppresses an increase in resistance throughout the electrode body.

[0012] Examples of the power storage device include secondary batteries such as lithium ion secondary batteries and sodium ion secondary batteries, and capacitors such as lithium ion capacitors. Examples of the wound electrode body include cylindrical wound electrode bodies and flat wound electrode bodies.

[0013] The electrolyte may be a non-aqueous electrolyte obtained by dissolving a supporting salt in an organic solvent. Examples of organic solvents used for the electrolyte include ethylene carbonate (EC), as well as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), which can be mixed with EC to form a mixed solvent and have a lower melting point than EC.

[0014] The electrolyte may contain, as a supporting salt, a lithium salt containing P, such as LiPF6, or a sodium salt, such as NaPF6.

[0015] In addition to the EC contained in the electrolyte, the electrode body may also contain a substance capable of forming a negative electrode SEI coating on the negative electrode active material particles during the initial charging step, such as EC, vinylene carbonate, or LiBOB, which is used separately from the electrolyte.

[0016] (2) The electricity storage device according to (1) above may be such that the amount of P in a middle portion of the negative electrode active material layer that is located midway between the end portion and the central portion in the width direction is 96 to 104% of the amount of P in the end portion.

[0017] In this electricity storage device, the amount of P in the middle portion is also 96 to 104% of the amount of P at the end portions. That is, in this electricity storage device, an SEI coating derived from the supporting electrolyte containing P is uniformly formed over the entire device, suppressing a local increase in IV resistance that occurs in the axial direction within the electrode body and suppressing an increase in resistance of the entire electrode body.

[0018] (3) In the electricity storage device described in (1) or (2) above, the amount of P may be the amount of P obtained by ICP-MS analysis using the negative electrode plate that has been removed from the electricity storage device and washed to remove the adhering electrolyte.

[0019] In this electricity storage device, the P amount in each part of the negative electrode active material layer is obtained by ICP-MS analysis, so that the accurate P amount and relative P amount can be obtained. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a partially cutaway perspective view of a battery according to an embodiment. [Figure 2] 3 is an explanatory view showing a state in which a negative electrode SEI coating is formed on a negative electrode active material particle of a negative electrode active material layer according to the embodiment. FIG. [Figure 3] FIG. 2 is a perspective view of a flat wound electrode body and an unpermeated electrode body according to the embodiment. [Figure 4] FIG. 2 is an explanatory diagram showing a flat wound unpermeated electrode body developed to show a positive electrode plate, a negative electrode, and a separator according to an embodiment. [Figure 5] 1 is a flowchart of a method for manufacturing a battery according to an embodiment. [Figure 6] FIG. 3 is an explanatory diagram illustrating the manufacturing process of an unpermeated negative electrode plate according to the embodiment. [Figure 7] FIG. 10 is an explanatory diagram showing a stripe pattern in which the non-containing negative electrode paste and the additional negative electrode paste are applied to a wide negative electrode foil by a die coater according to the embodiment. [Figure 8] FIG. 10 is an explanatory view showing a flat wound unpermeated electrode body in a developed state to show a positive electrode plate, a negative electrode, and a separator according to Comparative Example 1. [Figure 9] FIG. 10 is an explanatory view showing a flat wound unpermeated electrode body in a comparative example 2, showing a positive electrode plate, a negative electrode, and a separator. [Figure 10] 1 is an explanatory diagram showing an examination site in an electrode body of a battery according to an embodiment and comparative examples 1 and 2. FIG. [Figure 11] 1 is a graph showing the relationship between the investigated portion in the electrode body of the batteries according to the embodiment and comparative examples 1 and 2 and the relative content of ethylene carbonate. [Figure 12] 1 is a graph showing the relationship between the relative P amount and the investigated portion in the electrode body of the batteries according to the embodiment and comparative examples 1 and 2. [Figure 13] 1 is a graph showing the relationship between the relative IV resistance value and the investigated portion in the electrode body of the batteries according to the embodiment and comparative examples 1 and 2. DETAILED DESCRIPTION OF THE INVENTION

[0021] (Embodiment) Hereinafter, a battery 1 (an example of an electricity storage device) which is a lithium ion secondary battery according to an embodiment of the present invention and its manufacture will be described with reference to Figures 1 to 7. The battery 1 is a rectangular, sealed lithium ion secondary battery, and is installed in vehicles such as hybrid cars, plug-in hybrid cars, and electric cars, as well as in various devices.

[0022] The battery 1 of this embodiment includes a case 7, an electrode assembly 2, and an electrolyte 6 housed inside the case 7. The case 7 is made of metal (aluminum in this embodiment) and has a rectangular box shape. The case 7 is made of a metal and includes a bottomed, square-tubular case body 7H and a lid 7L located at the upper part BH1 in the height direction BH. A positive electrode terminal 8P and a negative electrode terminal 8N are fixed to the lid 7L via an insulating member 9. The lid 7L is perforated with a liquid filling hole 7LH for pouring the electrolyte 6, which is sealed with a liquid filling plug 7LP after pouring. The electrode assembly 2 is covered in a bag-shaped insulating film (not shown) inside the case 7. A portion of the electrolyte 6 housed in the case 7 is impregnated into the electrode assembly 2, and the remainder is collected at the bottom of the case 7.

[0023] The unpermeated electrode body 12 (see FIGS. 3 and 4), which is not impregnated with the electrolyte solution 6, is a so-called flat-wound electrode body, and is formed by winding a strip-shaped unpermeated positive electrode plate 13 and a strip-shaped unpermeated negative electrode plate 14 (an example of an additional electrode plate) with a pair of strip-shaped unpermeated separators 15 between them and pressing them in the thickness direction CH to flatten them. Therefore, the electrode body 2 (see FIGS. 1, 3, and 4), which is housed in the case 7 and in which the unpermeated electrode body 12 is impregnated with the electrolyte solution 6, is also formed by winding a strip-shaped positive electrode plate 3 and a strip-shaped negative electrode plate 4, each impregnated with the electrolyte solution 6, with a pair of strip-shaped separators 5 between them, and is thinned and flattened in the thickness direction CH, which is perpendicular to the plane of the paper in FIG. 1. This electrode body 2 is housed in the case 7 in a horizontal position with the winding axis AX coinciding with the width direction AH (the left-right direction in FIG. 1).

[0024] As described below, the electrode body 2 in the battery 1 is initially charged after the electrolyte solution 6 has been impregnated into the unpermeated electrode body 12 housed in the case 7. Therefore, as shown in Fig. 2, a negative electrode SEI coating 4AC derived from ethylene carbonate 6VE, a solvent contained in the electrolyte solution 6, and a supporting salt 6S containing P are formed around the negative electrode active material particles 4AP constituting the negative electrode active material layer 4A formed on the negative electrode foil 4F of the electrode body 2. The formation of this negative electrode SEI coating 4AC enables stable charging and discharging of the battery 1 with low resistance, compared to a case in which the negative electrode SEI coating 4AC is not formed or is insufficiently formed.

[0025] Of the flat wound electrode body 2 and the unpermeated electrode body 12, positive electrode current collecting portions 2P, 12P formed by wound current collecting portions 3S, 13S of the positive electrode plate 3 or the unpermeated positive electrode plate 13 are provided on one side XH1 in the axial direction XH along the winding axis AX (in this embodiment, this corresponds to one side AH1 in the width direction AH of the battery 1; upper side in FIG. 3). Conversely, negative electrode current collecting portions 2N, 12N formed by wound current collecting portions 4S, 14S of the negative electrode plate 4 or the unpermeated negative electrode plate 14 are provided on the other side XH2 in the axial direction XH (in this embodiment, this corresponds to the other side AH2 in the width direction AH of the battery 1; lower side in FIG. 3). The portion between the positive electrode current collecting portion 2P, 12P and the negative electrode current collecting portion 2N, 12N is a main body portion 2H, 12H in which a positive electrode plate 3 and a negative electrode plate 4 are wound with a separator 5 interposed therebetween, or an unpermeated positive electrode plate 13 and an unpermeated negative electrode plate 14 are wound with an unpermeated separator 15 interposed therebetween.

[0026] The positive electrode terminal 8P is made of an aluminum plate bent into a predetermined shape. An inner connection portion 8PI forming one end of the positive electrode terminal 8P is connected to a positive electrode current collector 2P arranged on one side AH1 in the width direction AH of the electrode assembly 2. Meanwhile, the other end of the positive electrode terminal 8P is drawn out of the case 7 (specifically, onto the lid 7L) to form an external terminal portion 8PO. The negative electrode terminal 8N is made of a copper plate bent into a predetermined shape. An inner connection portion 8NI forming one end of this negative electrode terminal 8N is connected to a negative electrode current collector 2N arranged on the other side AH2 in the width direction AH of the electrode assembly 2. Meanwhile, the other end of the negative electrode terminal 8N is drawn out of the case 7 (specifically, onto the lid 7L) to form an external terminal portion 8NO.

[0027] The electrolyte 6 is a non-aqueous electrolyte containing an organic solvent 6V and a supporting salt 6S. In this embodiment, the organic solvent 6V is a mixture of ethylene carbonate (EC) 6VE and another solvent 6VL, dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC), in a weight ratio of 3:4:3. LiPF6 is used as the supporting salt 6S containing P. The concentration of LiPF6 in the electrolyte 6 is 1.1 mol / L.

[0028] As shown in FIG. 4, the strip-shaped unpermeated positive electrode plate 13 of the unpermeated electrode body 12 includes a positive electrode foil 13F made of aluminum foil and a positive electrode active material layer 13A laminated on both surfaces of the positive electrode foil 13F. The positive electrode active material layer 13A is composed of positive electrode active material particles, conductive particles, and a binder (not shown). In this embodiment, the positive electrode active material particles are lithium transition metal composite oxide particles, specifically, for example, lithium nickel cobalt manganese composite oxide particles. The conductive particles are, for example, acetylene black (AB). The binder is, for example, polyvinylidene fluoride (PVDF). At the end of one side WH1 (upper side in FIG. 4) in the width direction WH of the strip-shaped unpermeated positive electrode plate 13, the positive electrode active material layer 13A is not present on the positive electrode foil 13F, and the positive electrode foil 13F is exposed, forming a current collecting portion 13S. On the other hand, the remaining portion of the unpermeated positive electrode plate 13 is a positive electrode portion 13P in which positive electrode active material layers 13A are laminated on both surfaces of a positive electrode foil 13F. As can be seen from Figures 3 and 4, the width direction WH (the vertical direction in Figure 4) of the unpermeated positive electrode plate 13 etc. coincides with the axial direction XH, and one side WH1 coincides with one side XH1.

[0029] On the other hand, of the unpermeated electrode body 12, the strip-shaped unpermeated negative electrode plate 14 includes a negative electrode foil 14F made of copper foil and a negative electrode active material layer 14A laminated on both surfaces of the negative electrode foil 14F, and does not contain P. The negative electrode active material layer 14A is composed of a negative electrode active material particle 14AP and a binder (not shown). In this embodiment, graphite particles are used as the negative electrode active material particle 14AP. The binder is, for example, carboxymethyl cellulose (CMC). Note that, at the end of the other side WH2 (lower in FIG. 4 ) in the width direction WH of the strip-shaped unpermeated negative electrode plate 14, the negative electrode active material layer 14A is not present on the negative electrode foil 14F, and the negative electrode foil 14F is exposed, forming a current collecting portion 14S. On the other hand, the remaining portion of the unpermeated negative electrode plate 14 is a negative electrode portion 14N in which the negative electrode active material layer 14A is laminated on both surfaces of the negative electrode foil 14F. In this embodiment, the width dimension AW of the negative electrode active material layers 4A and 14A in the width direction WH is AW=180 mm.

[0030] Furthermore, a pair of strip-shaped unpermeated separators 15 of the unpermeated electrode body 12 are made of porous resin. As shown in FIG. 4, the unpermeated separator 15 is stacked so as to be interposed between the unpermeated negative electrode plate 14 and the unpermeated positive electrode plate 13 when wound. The unpermeated negative electrode plate 14 and the negative electrode portion 14N are slightly wider in the width direction WH than the unpermeated positive electrode plate 13 and the positive electrode portion 13P. Furthermore, the negative electrode portion 14N is arranged so as to cover the entire positive electrode portion 13P in the width direction WH, i.e., so that the negative electrode active material layer 14A faces the positive electrode active material layer 13A at any portion of the positive electrode active material layer 13A. Furthermore, the unpermeated separator 15 is slightly wider in the width direction WH than the negative electrode portion 14N and the positive electrode portion 13P. Moreover, the unpermeated separator 15 is arranged so as to cover the entire negative electrode portion 14N and the positive electrode portion 13P in the width direction WH, that is, so that the unpermeated separator 15 covering the positive electrode active material layer 13A and the negative electrode active material layer 14A is present at every portion of the positive electrode active material layer 13A and the negative electrode active material layer 14A.

[0031] When the unpermeated electrode body 12 is connected to the positive electrode terminal 8P and the negative electrode terminal 8N and housed in the case 7, and the electrolyte 6 is poured into the case 7, the electrolyte 6 permeates from the outside XHO in the axial direction XH of the unpermeated electrode body 12, i.e., from one side XH1 and the other side XH2, toward the inside of the unpermeated electrode body 12. Specifically, the electrolyte 6 permeates along the unpermeated positive electrode plate 13, the unpermeated negative electrode plate 14, and the unpermeated separator 15 from one side WH1 and the other side WH2 in the width direction WH that coincides with the axial direction XH (upper and lower in FIG. 4 ), respectively, toward the center line ML of the width direction WH of the negative electrode active material layer 14A, i.e., toward the inside WHI of the width direction WH.

[0032] However, as described above, when the electrolyte solution 6 permeates into the unpermeated electrode body 12, the ethylene carbonate 6VE, among the components of the organic solvent 6V, has a slower permeation rate than the other solvents 6VL (in this embodiment, DMC and EMC, which have a lower melting point than EC). For this reason, when considering the distance EL from the end edges 14AE1, 14AE2 in the width direction WH of the negative electrode active material layer 14A of the unpermeated negative electrode plate 14 as the starting point toward the inner side WHI in the width direction WH, it is thought that the concentration of ethylene carbonate 6VE in the electrolyte solution at the leading portion of the electrolyte solution 6 permeating toward the inner side WHI decreases as the distance EL increases. Therefore, when the electrolyte solution 6 has penetrated up to the center line ML of the negative electrode active material layer 14A in the width direction WH, as shown by the dashed line in Figure 4, and the penetration of the electrolyte solution 6 has been completed throughout the unpermeated electrode body 12, resulting in an electrode body 2 impregnated with the electrolyte solution 6 (for example, when the waiting time TT from the start of injection to the completion of permeation of the electrolyte solution 6 has elapsed), it is thought that the concentration of ethylene carbonate 6VE in the permeated electrolyte solution 6 located near the center line ML is relatively lower than that of the electrolyte solution 6 located outside (upper or lower in Figure 4) in the width direction WH rather than near the center line ML.

[0033] Here, the electrolyte solution 6 that permeates (advances) along the negative electrode active material layer 14A to the inner side WHI in the width direction WH has been described. However, the same applies to the electrolyte solution 6 that permeates (advances) along the positive electrode active material layer 13A of the unpermeated positive electrode plate 13 or the unpermeated separator 15 to the inner side WHI in the width direction WH, and differences in permeation speed cause unevenness in the concentration of ethylene carbonate 6VE in the electrolyte solution 6. That is, when the electrolyte solution 6 is poured into the case 7 and permeates into the unpermeated electrode body 12, the amount of ethylene carbonate 6VE that reaches the vicinity of the center 2M in the axial direction XH of the electrode body 2 (see FIG. 3 ) impregnated with the electrolyte solution 6 tends to be small.

[0034] In particular, when the width dimension AW of the negative electrode active material layers 4A, 14A of the electrode body 2 (unpermeated electrode body 12) is 180 mm or more (in this embodiment, the width dimension AW = 180 mm), the electrolyte solution 6 that has permeated from both end edges 14AE1, 14AE2 in the width direction WH of the negative electrode active material layer 14A must permeate (travel) a distance EL of 90 mm or more along the negative electrode active material layer 14A before reaching the center line ML. Therefore, due to the difference in permeation rate with other solvents 6VL, the concentration of ethylene carbonate 6VE in the electrolyte solution 6 located near the center line ML becomes low, and the area density of ethylene carbonate 6VE present near the center line ML also becomes low.

[0035] Note that when the electrolyte solution 6 that permeates from both end edges 14AE1 and 14AE2 of the negative electrode active material layer 14A toward the inner WHI reaches the vicinity of the center line ML and meets with each other, the electrolyte solution 6 does not subsequently migrate toward the inner WHI in the width direction WH by permeation. Therefore, the uneven concentration of ethylene carbonate 6VE between the electrolyte solution 6 located near the center line ML and the electrolyte solution 6 located further outward in the width direction WH (upper or lower in FIG. 4 ) is thought to be gradually resolved by diffusion due to the concentration gradient of ethylene carbonate 6VE. However, it is estimated that it takes longer (e.g., several days) for the uneven concentration to be resolved than the movement of the electrolyte solution 6 due to permeation. Therefore, it is difficult to wait a long time from the point at which the electrolyte solution 6 has completely permeated the entire electrode body 2 until the uneven concentration is resolved before proceeding to initial charging.

[0036] Therefore, if initial charging of the battery 1 is started immediately after the waiting time TT has elapsed, which is the time required for the electrolyte 6 to completely permeate the case 7 after the electrolyte 6 has been poured into the case 7, the initial charging will be performed in a state where the concentration of ethylene carbonate 6VE in the electrode body 2 is uneven.

[0037] However, as described above, the ethylene carbonate 6VE contained in the electrolyte solution 6 is a raw material for forming the anode SEI coating 4AC around the anode active material particles 4AP that constitute the anode active material layer 4A. Therefore, as described above, if the area density of the ethylene carbonate 6VE present near the center line ML of the anode active material layer 4A is low, the anode SEI coating 4AC derived from ethylene carbonate cannot be properly formed around the anode active material particles 4AP near the center line ML of the anode active material layer 4A, which is likely to cause problems such as an increase in the resistance of the battery 1.

[0038] 4, in the battery 1 of this embodiment, the negative electrode active material layer 14A of the unpermeated negative electrode plate 14 constituting the unpermeated electrode body 12 is formed such that the distance EL from both end edges 14AE1, 14AE2 is equal to or greater than the additional portion distance ELF (in this embodiment, the additional portion distance ELF = 80 mm), and the central portion 14AM in the width direction WH is formed as a strip-shaped additional negative electrode active material layer 14AF pre-impregnated with a coating-forming substance CS. Meanwhile, one side portion 14AS1 on one side WH1 in the width direction WH and the other side portion 14AS2 on the other side WH2 in the width direction WH are formed as strip-shaped non-containing negative electrode active material layers 14AN1, 14AN2, respectively, which do not contain the coating-forming substance CS, as in the prior art. In this embodiment, ethylene carbonate CS1 was used as the coating-forming substance CS. As a result, the unpermeated electrode body 12 becomes an unpermeated electrode body 12 in which the coating-forming substance CS (ethylene carbonate CS1) that forms the negative electrode SEI coating 4AC on the negative electrode active material layer 4A is previously disposed in the central portion 12M in the axial direction XH.

[0039] To form the negative electrode active material layer 14A of the unpermeated negative electrode plate 14, as described below, the same negative electrode paste PAN as before, which does not contain the film-forming substance CS, is used to form the negative electrode active material layers 14AN1 and 14AN2, while the additional negative electrode paste PAF, which contains the film-forming substance CS, is used to form the additional negative electrode active material layer 14AF in the central portion 14AM in the width direction WH. In this embodiment, the negative electrode paste PAN is a mixture of 99 wt. % graphite particles and 1 wt. % binder (CMC) mixed with water as a solvent. The additional negative electrode paste PAF is the above-mentioned negative electrode paste PAN to which 5 wt. % ethylene carbonate CS1 is added as the film-forming substance CS.

[0040] Because the additional negative electrode active material layer 14AF is provided in the central portion 14AM of the negative electrode active material layer 14A in this manner, when the electrolyte solution 6 permeating from both end edges 14AE1, 14AE2 in the width direction WH of the negative electrode active material layer 14A toward the inner side WHI reaches the additional negative electrode active material layer 14AF, the film-forming substance CS in the additional negative electrode active material layer 14AF dissolves into the electrolyte solution 6, and the electrolyte solution 6 further permeates toward the center line ML. Therefore, even in the electrode body 2 in which the permeation of the electrolyte solution 6 has been completed, the concentration of ethylene carbonate 6VE derived from the electrolyte solution 6 is reduced in the electrolyte solution 6 located near the center line ML of the negative electrode active material layer 14A, i.e., in the central portion 14AM. However, the electrolyte solution 6 in the central portion 14AM still contains the film-forming substance CS (ethylene carbonate CS1) in the additional negative electrode active material layer 14AF.

[0041] Therefore, even when the initial charging step is performed in a state where ethylene carbonate 6VE derived from the electrolyte solution 6 has not sufficiently reached the central portion 14AM, the pre-deposited coating material CS can appropriately form the anode SEI coating 4AC on the anode active material particles 4AP (see FIG. 2 ). Thus, it is possible to manufacture a battery 1 in which the non-uniformity of the formation of the anode SEI coating in the anode active material layer 4A is suppressed, the non-uniformity of the resistance of the anode active material layer 4A in the electrode body 2 is suppressed, and an increase in resistance is suppressed.

[0042] In particular, in this embodiment, ethylene carbonate CS1 is used as the film-forming substance CS. That is, ethylene carbonate CS1 is disposed in advance as the film-forming substance CS in the central portion 14AM of the negative electrode active material layer 14A where there is a shortage of ethylene carbonate 6VE derived from the electrolyte solution 6. This prevents a shortage of ethylene carbonate in various locations of the negative electrode active material layer 4A, and allows an ethylene carbonate-derived negative electrode SEI film to be appropriately formed over the entire negative electrode active material layer 4A.

[0043] Next, the manufacture of this battery 1 will be described with reference to Figures 5 to 7. First, in the electrode body formation step S1, a wound-type unpermeated electrode body 12 is formed that is not permeated with the electrolyte solution 6. More specifically, in the unpermeated negative electrode plate formation step S11, an unpermeated negative electrode plate 14 having a strip-shaped negative electrode active material layer 14A is formed.

[0044] More specifically, a central portion 14AM of the strip-shaped negative electrode active material layer 14A in the width direction WH is a strip-shaped additional negative electrode active material layer 14AF containing the coating-forming substance CS, while one side portion 14AS1 and the other side portion 14AS2 of the WHO outside the additional negative electrode active material layer 14AF in the width direction WH are strip-shaped non-containing negative electrode active material layers 14AN1 and 14AN2 that do not contain the coating-forming substance CS, thereby forming an unpermeated negative electrode plate 14 having a negative electrode active material layer 14A (see FIG. 4). As described above, in this embodiment, ethylene carbonate CS1 is used as the coating-forming substance CS.

[0045] In this unpermeated negative electrode plate formation step S11, non-containing negative electrode active material layers 14AN1 and 14AN2 are formed using non-containing negative electrode paste PAN, which contains negative electrode active material particles 14AP and a binder but does not contain film-forming substance CS, while additional negative electrode paste PAF, which contains negative electrode active material particles 4AP and film-forming substance CS, is used to form additional negative electrode active material layer 14AF.

[0046] Specifically, in the coating step S111, as shown in Fig. 6, a wide negative electrode foil 24F having twice the width of the negative electrode foil 4F of the negative electrode plate 4 is wound around a backup roll BR1, and a wide negative electrode paste layer 24AT is coated using a die coater DC. More specifically, within the die coater DC, a storage tank DCT1 stores the uncontained negative electrode paste PAN, and a storage tank DCT2 stores the additional negative electrode paste PAF. Using a die DCD equipped with multiple partitions (not shown), the uncontained negative electrode paste PAN supplied from the storage tank DCT1 and the additional negative electrode paste PAF supplied from the storage tank DCT2 are ejected in stripes from slits DCS of the die DCD, and coated onto the wide negative electrode foil 24F wound around the backup roll BR1 (see Fig. 7). Specifically, wide negative electrode paste layers 24AT, each twice as wide as the negative electrode foil 14F, are applied to both sides of a wide negative electrode foil 24F, leaving a space for the current collector 14S of the unpermeated negative electrode plate 14. The wide negative electrode paste layers 24AT are formed symmetrically about the cutting center line CL shown by the dashed-dotted line in FIG. 7 , and are applied in a five-stripe pattern with two additional negative electrode paste layers 24ATF interposed between three non-containing negative electrode paste layers 24ATN. After drying and cutting as described below, the non-containing negative electrode paste layers 24ATN become the non-containing negative electrode active material layers 14AN1 and 14AN2 of the negative electrode active material layer 14A. After drying and cutting, the additional negative electrode paste layers 24ATF become the additional negative electrode active material layers 14AF.

[0047] Thereafter, in a drying step S112, the wide negative electrode paste layer 24AT applied to the wide negative electrode foil 24F is dried in a drying oven DR to form a wide negative electrode active material layer 24A. The application step S111 and the drying step S112 are repeated for the front and back surfaces of the wide negative electrode foil 24F to form a wide unpermeated negative electrode plate 24 in which the wide negative electrode active material layer 24A is provided on both sides of the wide negative electrode foil 24F. Note that Fig. 6 shows the application and drying of the wide negative electrode paste layer 24AT to a wide single-sided negative electrode plate 24S in which the wide negative electrode active material layer 24A is provided on one side of the wide negative electrode foil 24F.

[0048] Furthermore, in a cutting step S113, the wide unpermeated negative electrode plate 24, in which the wide negative electrode active material layers 24A are provided on both sides of the wide negative electrode foil 24F, is cut along a cutting center line CL (see FIG. 7) to form two strip-shaped unpermeated negative electrode plates 14. Thereafter, the unpermeated negative electrode plates 14 are sorted by a sorting roll FR and then wound up around winding rolls SR1 and SR2, respectively. In this way, the unpermeated negative electrode plate forming step S11 obtains the unpermeated negative electrode plate 14 (see FIG. 4).

[0049] Next, in a winding step S12, the unpermeated negative electrode plate 14 is wound together with a separately formed unpermeated positive electrode plate 13 and an unpermeated separator 15 to form a cylindrical wound electrode body (not shown). Further, in a flattening step S13, this cylindrical electrode body is pressed to form a plate-like, flat wound unpermeated electrode body 12 (see FIG. 3). Thus, the unpermeated electrode body 12 is obtained in the electrode body forming step S1.

[0050] Thereafter, in a housing step S2, the unpermeated electrode body 12 is housed in the case 7. Specifically, first, in a terminal connection step S21, the positive electrode current collector 12P of the unpermeated electrode body 12 is welded to the inner connection portion 8PI of the positive electrode terminal 8P fixed to the lid body 7L via the insulating member 9, and similarly, the positive electrode current collector 12P is welded to the inner connection portion 8NI of the negative electrode terminal 8N, thereby fixing the unpermeated electrode body 12 to the lid body 7L via the positive electrode terminal 8P and the negative electrode terminal 8N (see FIG. 1 ).

[0051] In the subsequent insertion step S22, a bag-shaped resin cover (not shown) made of resin film is placed over the unpermeated electrode body 12, and the unpermeated electrode body 12 is inserted into the case body 7H, and the case body 7H is sealed with the lid body 7L. Furthermore, in the sealing step S23, the entire periphery of the lid body 7L is laser welded to the case body 7H in an airtight manner, sealing it. Thus, the unpermeated electrode body 12 is accommodated in the case 7 by the accommodation step S2.

[0052] Thereafter, in the liquid injection step S3, a predetermined amount of electrolyte 6 is injected into the case 7 through the liquid injection hole 7LH of the lid 7L. As a result, as described above, the unpermeated electrode body 12 in the case 7 is impregnated with the electrolyte 6. Note that in the liquid injection step S3, the electrolyte 6 is injected in a predetermined injection pattern. Furthermore, prior to the liquid injection, the unpermeated battery 1 can be placed in a chamber and the pressure can be reduced or increased while the unpermeated electrode body 12 is impregnated with the electrolyte 6.

[0053] In the waiting step S4, a predetermined waiting time TT is waited for to elapse from the start of the injection. The waiting time TT is the time from the start of the injection until the electrolyte solution 6 has permeated the entire unpermeated electrode body 12 (until the electrode body 2 is impregnated with the electrolyte solution 6), and this waiting time TT is obtained in advance by, for example, disassembling battery samples with different elapsed times from the start of the injection and observing the state of permeation of the electrolyte solution 6.

[0054] After the waiting time TT has elapsed, the process proceeds to the initial charging step S5, in which a power source (not shown) is connected to the positive electrode terminal 8P and the negative electrode terminal 8N, and a voltage is applied to the electrode assembly 2 of the battery 1 via the positive electrode terminal 8P and the negative electrode terminal 8N to perform initial charging. That is, a voltage is applied between the positive electrode plate 3 and the negative electrode plate 4 of the electrode assembly 2 in a predetermined initial charging pattern, and a negative electrode SEI coating 4AC is formed on the negative electrode active material layer 4A of the negative electrode plate 4 (see FIG. 2). In this embodiment, initial charging is performed in an initial charging pattern of 0.5 C-CCCV charging (SOC 90%). Thereafter, the liquid filling hole 7LH is sealed with the liquid filling plug 7LP.

[0055] As described above, in the battery 1 of this embodiment, the additional negative electrode active material layer 14AF is provided in the central portion 14AM of the negative electrode active material layer 14A of the unpermeated negative electrode plate 14 of the unpermeated electrode assembly 12. Therefore, in the electrode assembly 2 in which the electrolyte solution 6 has permeated the entire unpermeated electrode assembly 12 after the waiting time TT has elapsed, a decrease in the area density of the ethylene carbonate present near the center line ML of the negative electrode active material layer 4A of the negative electrode plate 4 can be prevented. Therefore, in the initial charging step S5, a negative electrode SEI coating 4AC can be appropriately formed on the negative electrode active material particles 4AP at any location in the negative electrode active material layer 4A.

[0056] Next, in a high-temperature aging step S6, the battery 1 is subjected to high-temperature aging by being left in an environment at 60° C. for 20 hours, and then in an inspection step S7, the battery 1 is inspected, and the battery 1 is completed.

[0057] (Comparative forms 1 and 2) To compare with the battery 1 according to the embodiment, batteries 1C1 and 1C2 according to comparative embodiments 1 and 2 were also manufactured and investigated as described below. First, the manufacture of the batteries 1C1 and 1C2 according to comparative embodiments 1 and 2 will be described with reference to FIGS.

[0058] The battery 1C1 of Comparative Example 1 is a conventional battery. In the battery 1 of the embodiment, an unpermeated negative electrode plate 14 having an additional negative electrode active material layer 14AF provided in the central portion 14AM of the negative electrode active material layer 14A was used to form the unpermeated electrode assembly 12, which was then impregnated with the electrolyte solution 6. In contrast, as shown in FIG. 8 , the battery 1C1 of Comparative Example 1 was formed by forming an unpermeated negative electrode plate 14C1 without providing an additional negative electrode active material layer 14AF on the negative electrode active material layer 14A, and instead forming the entire negative electrode active material layer 14A as a non-containing negative electrode active material layer 14AN that does not contain the coating-forming substance CS. The unpermeated negative electrode plate 14C1 was then used to form the unpermeated electrode assembly 12C1. Other than this, the battery 1 of Comparative Example 1 was similarly treated, and the initial charging step S5, high-temperature aging step S6, and other steps were also performed in the same manner to obtain the battery 1C1 of Comparative Example 1.

[0059] On the other hand, the battery 1C2 according to Comparative Example 2 is a battery having the opposite structure to the unpermeated negative electrode plate 14C1 of the battery 1C1 according to Comparative Example 1. Specifically, as shown in FIG. 9 , the unpermeated negative electrode plate 14C2 was formed by eliminating the non-containing negative electrode active material layer 14AN that does not contain the coating-forming substance CS from the negative electrode active material layer 14A, and replacing the entire negative electrode active material layer 14A with an additional negative electrode active material layer 14AF that contains the coating-forming substance CS (ethylene carbonate CS1). This unpermeated negative electrode plate 14C2 was used to form the unpermeated electrode body 12C2. Other than this, the battery 1 according to Comparative Example 2 was obtained by similarly performing the initial charging step S5 and the high-temperature aging step S6.

[0060] (Ethylene carbonate content survey) The manufactured batteries 1, 1C1, and 1C2 were disassembled in a glove box with an inert atmosphere, and each electrode assembly 2, 2C1, and 2C2 was removed. The electrode assembly 2, 2C1, and 2C2 were then unwound, and the negative electrode plate 4 was removed and allowed to dry. A 20 x 20 mm sample was cut from each negative electrode plate 4 at the middle of the winding (approximately the center in the longitudinal direction LH), corresponding to the positions indicated by I, II, III, IV, and V in Figure 10, to obtain a total of 15 negative electrode samples for extraction. Each negative electrode sample for extraction was immersed in an extraction solvent to extract ethylene carbonate. NMR measurements were performed on a reference solution with a known ethylene carbonate concentration and each extract, and the ethylene carbonate content in each extract was calculated from the ratio of the ethylene carbonate detection intensity in the reference solution to that in the extract. Furthermore, in each of the electrode assemblies 2, 2C1, and 2C2, the relative EC content (%) at each of the investigation positions I to V was obtained, with the ethylene carbonate content obtained at investigation position I being set at 100%.

[0061] As shown in FIG. 10 , the inspection positions I, II, III, IV, and V are flat plate-shaped portions of the negative electrode active material layer 4A of the negative electrode plate 4 in each electrode body 2, 2C1, and 2C2. The inspection positions I, II, III, IV, and V are aligned in the axial direction XH, and have distances EL1, EL2, EL3, EL4, and EL5, respectively, measured from the edge 4AE2 (see FIG. 4 ) of the current collector 4S, which is the negative electrode current collector 2N, to the inner side XHI in the axial direction XH (inner side WHI in the width direction WH). Specifically, in this embodiment, EL1 = 10 mm, EL2 = 30 mm, EL3 = 50 mm, EL4 = 70 mm, and EL5 = 90 mm. The inspection position V is located on the center line ML of the negative electrode active material layer 4A. That is, the distance EL5 is half the width dimension AW of the negative electrode active material layer 4A in the width direction WH (AW = 180 mm in this embodiment).

[0062] The results are shown in the graph in Figure 11. In the electrode body 2C1 of the battery 1C1 of Comparative Form 1, indicated by the thick dashed line, the content of ethylene carbonate 6VE gradually decreases from inspection position I to inspection position IV, i.e., from the edge 4AE2 toward the inner side XHI in the axial direction XH. However, at inspection position V, i.e., at the central portion 2M in the axial direction XH of the electrode body 2C1 (see Figure 3), the content of ethylene carbonate 6VE is significantly reduced (in this Comparative Form 1, the content is reduced by approximately 30% compared to inspection position I).

[0063] This is thought to be due to the following reasons. As mentioned above, the permeation rate of ethylene carbonate 6VE contained in the electrolyte solution 6 is slower than that of other solvents 6VL (specifically, DMC and EMC). Therefore, it is thought that the concentration of ethylene carbonate 6VE in the electrolyte solution 6 located at the leading edge of the permeation of the electrolyte solution 6 permeating into the electrode body 2C1 decreases as the distance EL from the edge 4AE2 to the inspection position V increases. In particular, when the distance EL exceeds 80 mm, the decrease in the concentration of ethylene carbonate 6VE increases. Moreover, near the inspection position V located on the center line ML of the negative electrode active material layer 4A, i.e., the central portion 2M of the electrode body 2C1, the electrolyte solutions 6 that permeate from both end edges 4AE1, 4AE2 (see FIG. 8 ) of the negative electrode active material layer 4A to the inner side WHI in the width direction WH (the inner side XHI in the axial direction XH) meet and stop permeating. Therefore, the content (area density) of ethylene carbonate 6VE reaching the central portion 2M tends to remain low.

[0064] On the other hand, in the electrode body 2C2 of the battery 1C2 of Comparative Form 2, indicated by the thick dashed dotted line, the ethylene carbonate content is maintained at a high value of nearly 100% from inspection position I to inspection position IV. In particular, the ethylene carbonate content at inspection positions II and III is slightly higher than at inspection position I near the edge 4AE2 of the outer WHO in the width direction WH. However, the ethylene carbonate content is slightly reduced at inspection position IV. However, at inspection position V, i.e., at the central portion 2M in the axial direction XH of the electrode body 2C1 (see FIG. 9 ), it is found that the ethylene carbonate content is significantly reduced (approximately 35% reduced compared to inspection position I in Comparative Form 2).

[0065] The reason for this is believed to be as follows: The electrode body 2C2 of the battery 1C2 of Comparative Form 2 uses an unpermeated negative electrode plate 14C2 in which the entire negative electrode active material layer 14A is made of an additional negative electrode active material layer 14AF containing a coating-forming substance CS (specifically, ethylene carbonate CS1). Therefore, in the range from the inspection positions I to III, where the distance EL from the edge 4AE2 is relatively small, the decrease in concentration due to the slow permeation rate of ethylene carbonate 6VE contained in the electrolyte solution 6 (see the graph of Comparative Form 1) is compensated for by the dissolution of ethylene carbonate CS1 derived from the additional negative electrode active material layer 14AF in the electrolyte solution 6; rather, the concentration of ethylene carbonate is thought to increase as the electrolyte solution 6 permeates.

[0066] However, as described above, ethylene carbonate dissolved in electrolyte solution 6 has a slower permeation rate and higher viscosity than other solvents 6VL (specifically, DMC and EMC). Therefore, when the concentration of ethylene carbonate dissolved in electrolyte solution 6 increases near inspection positions II and III, the increased viscosity causes a rapid decrease in the permeation rate of ethylene carbonate, resulting in a significant decrease in the concentration of ethylene carbonate in electrolyte solution 6 reaching inspection position V. For this reason, even if the ethylene carbonate CS1 derived from additional negative electrode active material layer 14AF near inspection position V compensated, it is presumed that this could not fully compensate for the significant decrease in the ethylene carbonate content at inspection position V, i.e., at central portion 2M.

[0067] In contrast, in the battery 1 (electrode assembly 2) of this embodiment, indicated by the thick solid line, at inspection positions I to IV, the ethylene carbonate content gradually decreases generally from inspection position I toward inspection position IV, i.e., from the edge 4AE2 toward the inner side XHI in the axial direction XH, similarly to the battery 1C1 of Comparative Form 1. However, unlike the battery 1C1 of Comparative Form 1, the ethylene carbonate content at inspection position V in the battery 1 of this embodiment is approximately the same as that at inspection position IV. That is, in the electrode assembly 2 of the battery 1 of this embodiment, the decrease in the ethylene carbonate content at the central portion 2M in the axial direction XH (see FIG. 3 ) is suppressed. Specifically, in this embodiment, the decrease in the content at inspection position V compared to inspection position I is kept to approximately 10% or less.

[0068] The reason for this is believed to be as follows: The electrode body 2 of the battery 1 of this embodiment uses an unpermeated negative electrode plate 14 in which an additional negative electrode active material layer 14AF containing a film-forming substance CS (specifically, ethylene carbonate CS1) is formed only in a central portion 14AM of the negative electrode active material layer 14A, the central portion being at a distance EL of 80 mm or more from the inspection position V (see FIG. 4). Therefore, in the range from inspection positions I to IV, as in Comparative Form 1, it is believed that the concentration decreased due to the slow permeation rate of ethylene carbonate 6VE derived from the electrolyte solution 6.

[0069] However, as described above, when the permeated electrolyte solution 6 reaches the additional negative electrode active material layer 14AF in the central portion 14AM of the negative electrode active material layer 14A, the ethylene carbonate CS1 derived from the additional negative electrode active material layer 14AF dissolves in and replenishes the electrolyte solution 6. This is thought to have allowed the ethylene carbonate content at inspection position V to be maintained at the same level as at inspection position IV.

[0070] (P content survey) To investigate the origin of the negative electrode SEI coating 4AC formed on the negative electrode active material layer 4A of the batteries 1, 1C1, and 1C2, we also investigated the amount of phosphorus (MP) contained in the negative electrode SEI coating 4AC. Specifically, for the negative electrode plates 4 extracted from each of the electrode bodies 2, 2C1, and 2C2 investigated for the ethylene carbonate content described above, we cut out 20 × 20 mm pieces from the middle of the winding of the plates, corresponding to the measurement positions I, III, and V in Figure 10 (the end portion 4AE, middle portion 4AM, and center portion 4AT of the negative electrode active material layer 4A). Nine negative electrode samples for phosphorus content measurement were obtained. Each sample was washed with EMC to remove the electrolyte 6 and then dried. Each sample was then placed in an extraction solution and subjected to acid treatment, etc., and the negative electrode active material layer 4A of each sample was analyzed by ICP-MS to calculate the amount of phosphorus contained in the negative electrode active material layer 4A, i.e., the negative electrode SEI coating 4AC. Furthermore, for each electrode body 2, 2C1, 2C2, the end P amount MPE obtained at investigation position I (end 4AE) was set to 100%, and the relative middle P amount MPM (%) and middle P amount MPT (%) at each investigation position III, V (middle portion 4AM, central portion 4AT) were obtained.

[0071] The results are shown in the graph in Figure 12. In the electrode body 2C1 of the battery 1C1 of Comparative Form 1, indicated by the thick dashed line, it can be seen that the P amount gradually increases generally from inspection position I toward inspection position V, that is, from the edge 4AE2 toward the inner side XHI in the axial direction XH. Specifically, compared to the end P amount MPE corresponding to inspection position I (end 4AE), the middle portion P amount MPM corresponding to inspection position III (middle portion 4AM) increases by about 2%. Also, it can be seen that compared to the end P amount MPE, the center portion P amount MPT corresponding to inspection position V (the center portion 2M in the axial direction XH of the electrode body 2C1 (see Figure 3)) increases by about 8%.

[0072] Considering these results in conjunction with the results of FIG. 11, in the battery 1C1 of Comparative Form 1, the electrolyte solution 6 reached the central portion 2M of the electrode body 2C1 during the initial charging step S5, but the area density of ethylene carbonate 6VE in the central portion 2M was thought to have been significantly reduced. Therefore, near the inspection position III (middle portion 4AM), similar to the inspection position I (end portion 4AE), it is thought that the EC-derived negative electrode SEI coating 4AC was sufficiently produced, and that the P-containing negative electrode SEI coating was derived from the supporting salt 6S (LiPF6 in this embodiment) contained in the electrolyte solution 6, and therefore, a similar amount of P-containing negative electrode SEI coating was also produced. However, at the central portion 2M of the electrode body 2C1, the EC-derived negative electrode SEI coating 4AC was not sufficiently produced. However, instead, the P-containing negative electrode SEI coating derived from the supporting salt 6S was excessively produced, which is thought to have resulted in an increase in the central portion P amount MPT compared to the end portion P amount MPE.

[0073] On the other hand, in the electrode body 2C2 of the battery 1C2 of Comparative Form 2, indicated by the thick dashed dotted line, it can be seen that, contrary to the battery 1C1 of Comparative Form 1, the amount of P decreases from the inspection position I toward the inspection position V, that is, from the edge 4AE2 toward the inner side XHI in the axial direction XH. Specifically, it can be seen that, compared to the end P amount MPE corresponding to inspection position I, the middle portion P amount MPM corresponding to inspection position III (middle portion 4AM) decreases by approximately 4%, and the central portion P amount MPT corresponding to inspection position V (central portion 2M of the electrode body 2C2) decreases by approximately 16%.

[0074] 11, in battery 1C2 of Comparative Form 2, the areal density of ethylene carbonate dissolved in electrolyte 6 was slightly higher near inspection position III during initial charging step S5, and near inspection position III (middle portion 4AM), the formation of the negative electrode SEI coating 4AC derived from EC was as sufficient as or even greater than that at inspection position I (end portion 4AE). Instead, it appears that the formation of the negative electrode SEI coating derived from supporting electrolyte 6S and containing P was somewhat suppressed.

[0075] However, as mentioned above, the high viscosity of ethylene carbonate reduces not only the permeation rate of ethylene carbonate but also the permeation rate of the electrolyte solution 6. Therefore, it is presumed that the amount of electrolyte solution 6 reaching the inspection position V (center portion 4AT) also decreased. In other words, it is presumed that the electrolyte solution 6 did not sufficiently reach the center portion 2M of the electrode body 2C2 in the first place. Therefore, at the center portion 2M (inspection position V) of the electrode body 2C2, the negative electrode SEI coating 4AC derived from EC was not sufficiently formed. Furthermore, the negative electrode SEI coating derived from the supporting electrolyte 6S and containing P was not sufficiently formed. Therefore, it is presumed that the central portion P content MPT was significantly reduced compared to the edge P content MPE.

[0076] In contrast, in the electrode body 2 of the battery 1 of this embodiment, indicated by the thick solid line, the middle portion P amount MPM corresponding to the inspection position III is almost the same (about 1% increase) as the end portion P amount MPE corresponding to the inspection position I. On the other hand, the central portion P amount MPT corresponding to the inspection position V is about 6% smaller than the end portion P amount MPE.

[0077] Considering this result in conjunction with the results shown in FIG. 11, the battery 1 of this embodiment uses an unpermeated negative electrode plate 14 in which the additional negative electrode active material layer 14AF is formed only in the central portion 14AM of the negative electrode active material layer 14A (see FIG. 4). Therefore, when the initial charging step S5 was performed, the electrolyte solution 6 reached the central portion 2M of the electrode assembly 2. Near the inspection position III (middle portion 4AM), as at the inspection position I (end portion 4AE), a sufficient amount of the negative electrode SEI coating 4AC derived from EC was produced. This is likely due to the P-containing supporting electrolyte 6S (LiPF6 in this embodiment) contained in the electrolyte solution 6, and therefore, a similar amount of the P-containing negative electrode SEI coating was also produced. Furthermore, the replenishment of ethylene carbonate CS1 from the additional negative electrode active material layer 14AF suppressed the decrease in the EC concentration at the central portion 2M (inspection position V). Therefore, in the center portion 2M of the electrode body 2C2, the negative electrode SEI coating 4AC derived from EC was sufficiently formed, which suppressed the formation of the negative electrode SEI coating derived from the supporting electrolyte 6S and containing P. It is estimated that this is why the P content in the center portion MPT decreased by about 6% compared to the P content in the edge portion MPE.

[0078] (IV resistance value survey) To investigate the effects of different ethylene carbonate concentrations and P content on battery characteristics, the following investigations were also conducted. The manufactured batteries 1, 1C1, and 1C2 were charged to 50% SOC and disassembled in a glove box under an inert atmosphere, and the electrode bodies 2, 2C1, and 2C2 were removed. Each electrode body 2, 2C1, and 2C2 was then unwound, and the positive electrode plate, the opposing negative electrode plate, and the separator sandwiched between them were cut out from the center of the winding, corresponding to the investigation positions I, III, and V in Figure 10, to obtain nine small-cell samples consisting of small positive electrode plates, small negative electrode plates, and small separators. These were then washed and dried in an EMC, stacked with a small separator sandwiched between the small positive and negative electrode plates, surrounded by a laminate film, and filled with new electrolyte 6 and sealed to form new small cells (not shown).

[0079] For each of the small cells (nine types in total) corresponding to the test positions I, III, and V of each electrode body 2, 2C1, and 2C2, constant-current discharge was performed at a current A equivalent to a discharge current rate of 0.2C, 0.5C, 1C, or 2C at 25°C, and the voltage drop ΔV was measured after 10 seconds. The obtained data was plotted on a graph with current A on the X-axis and voltage drop ΔV on the Y-axis, and the slope of the approximated line was used as the IV resistance value of each small cell (IV resistance = voltage drop ΔV / current A). Furthermore, for each configuration, the relative IV resistance values ​​of the small cells at test positions I, III, and V were calculated, with the IV resistance value obtained for the small cell at test position I set to 100%.

[0080] The results are shown in the graph in Figure 13. Of the small cells of the electrode body 2C1 of battery 1C1 of comparative form 1, indicated by the thick dashed line, the small cells at inspection positions I and III had almost the same relative IV resistance value. However, it can be seen that the small cell at inspection position V had a significantly higher relative IV resistance value than the small cells at inspection positions I and III (in comparative form 1, the relative IV resistance value was approximately 18% higher than that at inspection position I).

[0081] This is thought to be due to the following reasons. As described above, the ethylene carbonate content did not change significantly at the inspection positions I to III in the electrode body 2C1 of the battery 1C1 of Comparative Form 1 (see FIG. 11). Specifically, the decrease at inspection positions II and III was at most about -7% compared to inspection position I. The amount of P in the middle portion MPM at inspection position III also showed almost no increase compared to the amount of P at the end portion MPE at inspection position I (see FIG. 12). When the battery 1C1 of Comparative Form 1 was initially charged in the initial charge step S5, an ethylene carbonate-derived negative electrode SEI coating was appropriately formed as the negative electrode SEI coating 4AC on the negative electrode active material particles 4AP in the negative electrode active material layer 4A of the negative electrode plate 4 near inspection positions I and III. Therefore, an equivalent amount of an ethylene carbonate-derived negative electrode SEI coating 4AC was also formed near inspection positions I and III. Thus, it is considered that the relative IV resistance values ​​of the small cells using the small positive electrode plates, small negative electrode plates, and small separators at the investigation positions I and III were comparable to each other.

[0082] However, as mentioned above, the ethylene carbonate content at the inspection position V of the electrode body 2C1 was significantly reduced (-28% decrease) (see FIG. 11). Therefore, in the negative electrode active material layer 4A of the negative electrode plate 4 after the initial charge, the negative electrode SEI coating 4AC derived from ethylene carbonate was not sufficiently formed on the negative electrode active material particles 4AP near the inspection position V, i.e., near the center line ML (see FIG. 10). Instead, a large amount of negative electrode SEI coating derived from the supporting electrolyte 6S containing relatively high resistance P was formed. Therefore, it is believed that the relative IV resistance value of the small cell using the small positive electrode plate, small negative electrode plate, and small separator at the inspection position V was 18% higher than that of the small cell at the inspection position I. This is consistent with the fact that the amount of P at the center (MPT) at the inspection position V was approximately 8% higher than the amount of P at the end (MPE) at the inspection position I (see FIG. 12). This shows that in the electrode body 2C1 of the battery 1C1 of Comparative Example 1, the IV resistance value is locally high in the central portion 2M, and the IV resistance value of the electrode body 2C1 as a whole is also high.

[0083] In addition, in the electrode body 2C2 of the battery 1C2 of Comparative Form 2, shown by the thick dashed line, the small cells at the inspection positions I and III had almost the same relative IV resistance values. However, it can be seen that the small cell at the inspection position V had a significantly higher relative IV resistance value than the small cells at the inspection positions I and III (in Comparative Form 2, it was approximately 24% higher than the inspection position I).

[0084] This is thought to be due to the following reasons. As described above, the ethylene carbonate content in the electrolyte 6 hardly changed at the inspection positions I to III in the electrode body 2C2 of the battery 1C2 of Comparative Form 2 (see FIG. 11). Therefore, when the battery 1C2 of Comparative Form 2 was initially charged in the initial charge step S5, an ethylene carbonate-derived negative electrode SEI coating 4AC was properly formed on the negative electrode active material particles 4AP in the negative electrode active material layer 4A of the negative electrode plate 4 near the inspection positions I and III. Accordingly, the formation of an ethylene carbonate-derived negative electrode SEI coating 6S near the inspection position III was suppressed. Therefore, the intermediate P amount MPM at the inspection position III was thought to be approximately 4% lower than the end P amount MPE at the inspection position I (see FIG. 12). This is thought to have resulted in the relative IV resistance values ​​being approximately the same in the small cells using the small positive electrode plates, small negative electrode plates, and small separators at the inspection positions I and III.

[0085] However, as mentioned above, the ethylene carbonate content at the inspection position V of the electrode assembly 2C2 was significantly reduced (-36% reduction) (see Figure 11). Additionally, the central P content (MPT) at inspection position V was reduced by approximately 16% compared with the edge P content (MPE) at inspection position I (see Figure 12). Because the electrolyte 6 did not sufficiently reach the central portion 2M of the electrode assembly 2C2, the negative electrode SEI coating 4AC derived from ethylene carbonate was not sufficiently formed on the negative electrode active material particles 4AP near the central portion 4AT (inspection position V) of the negative electrode active material layer 4A of the negative electrode plate 4 after the initial charge. Furthermore, the negative electrode SEI coating derived from the supporting electrolyte 6S was not sufficiently formed, i.e., the negative electrode SEI coating 4AC was not sufficiently formed. This is thought to be why the relative IV resistance of the small cell using the small positive electrode plate, small negative electrode plate, and small separator at inspection position V was 24% higher than that of the small cell at inspection position I. This shows that the electrode body 2C2 of the battery 1C2 of Comparative Example 2 also has a locally high IV resistance value at the center portion 2M, and the IV resistance value of the electrode body 2C2 as a whole is also high.

[0086] In contrast to these, in the battery 1 (electrode body 2) of this embodiment indicated by the thick solid line, no significant change occurs in the relative IV resistance value at any of the inspection positions I, III, and V.

[0087] This is thought to be due to the following reasons. As described above, in the electrode body 2 of the battery 1 of this embodiment, the ethylene carbonate content in the electrolyte 6 is not significantly reduced not only at the inspection positions II to IV but also at the inspection position V, compared to the inspection position I. Specifically, the content at the inspection position V is only reduced by -9% compared to the inspection position I (see FIG. 11). The amount of P in the middle portion MPM at the inspection position III also shows almost no increase compared to the amount of P in the end portion MPE at the inspection position I. Meanwhile, the amount of P in the center portion MPT at the inspection position V is reduced by approximately 6% (see FIG. 12). From these findings, when the battery 1 of this embodiment is initially charged, the negative electrode SEI coating 4AC derived from ethylene carbonate can be appropriately formed on the negative electrode active material particles 4AP in the negative electrode active material layer 4A of the negative electrode plate 4, not only near the inspection positions I and III but also near the inspection position V. Accordingly, the formation of the negative electrode SEI coating derived from the supporting electrolyte 6S is suppressed near the inspection position V. Therefore, it is considered that the relative IV resistance values ​​of the small cells using the small positive electrode plate, small negative electrode plate, and small separator at the inspection positions I, III, and V were similar to each other. From this, it can be seen that in the electrode assembly 2 of the battery 1 of this embodiment, non-uniform formation of the negative electrode SEI coating in the negative electrode active material layer 4A in the wound-type electrode assembly 2 can be suppressed, the IV resistance value does not become locally high in the central portion 2M, and an increase in the IV resistance value of the electrode assembly 2 as a whole can be suppressed. In other words, it can be seen that the battery 1 of this embodiment has a lower IV resistance than the batteries 1C1 and 1C2 of Comparative Examples 1 and 2.

[0088] As described above, the battery 1 of this embodiment includes an electrolyte solution 6 containing ethylene carbonate 6VE and a supporting salt 6S containing P, and includes an electrode body 2 in which the width dimension AW of the negative electrode active material layer 4A is 180 mm or more. Therefore, as shown in Comparative Example 1, uneven penetration of EC is likely to occur, and in the central portion 2M where EC cannot easily reach, an SEI coating derived from EC is unlikely to be formed, and instead, an SEI coating derived from the supporting salt containing P tends to be formed in excess. However, in the battery 1 of this embodiment, the central P amount MPT of the P amount MP contained in the negative electrode SEI coating 4AC of the negative electrode active material layer 4A is within a range of 90 to 105% (specifically, 94%) of the end P amount MPE. That is, the central P amount MPT is approximately equal to or slightly less than the end P amount MPE. In other words, in this battery 1, even in the central portion 4AT of the negative electrode active material layer 4A, an excessive amount of the negative electrode SEI coating derived from the P-containing supporting electrolyte 6S is not formed. This suppresses a local increase in IV resistance occurring in the axial direction XH within the electrode body 2 (the width direction WH of the negative electrode plate 4), resulting in a battery 1 in which an increase in the resistance of the entire electrode body 2 is suppressed.

[0089] In particular, in the battery 1 of this embodiment, the amount of P in the middle portion MPM is also 96 to 104% (specifically, 101%) of the amount of P in the end portion MPE. That is, in this battery 1, the negative electrode SEI coating 4AC derived from the supporting electrolyte 6S containing P is uniformly formed throughout the entire battery 1, suppressing a local increase in IV resistance occurring in the axial direction XH within the electrode body 2 and suppressing an increase in the resistance of the entire electrode body 2.

[0090] Although the present invention has been described above in accordance with the embodiments, it goes without saying that the present invention is not limited to the embodiments and can be modified and applied as appropriate within the scope of the invention. For example, in the embodiment, a battery 1 was formed using an unpermeated negative electrode plate 14 in which an additional negative electrode active material layer 14AF, to which ethylene carbonate CS1 was added as the film-forming substance CS, was provided in the central portion 14AM of the negative electrode active material layer 14A. However, instead of ethylene carbonate CS1, vinylene carbonate, LiBOB, or the like may be added as the film-forming substance CS to form a negative electrode SEI film and suppress excessive formation of the negative electrode SEI film derived from the supporting electrolyte 6S. [Explanation of symbols]

[0091] 1,1C1,1C2 battery (energy storage device) 2,2C1,2C2 Electrode body 2M central part 3 positive electrode plate 4 negative plates 4A negative electrode active material layer 4AE End 4AT central part 4AM Middle AW (negative electrode active material layer) width dimension 4AE1, 4AE2 (widthwise) edges 4AP negative electrode active material particles 4AC negative electrode SEI coating MP amount MPE end P amount MPT center P amount MPM Middle P amount 6 Electrolyte 6V Organic Solvent 6VE Ethylene Carbonate 6VL Other solvents 6S supporting salt (supporting salt containing P) 7 Cases 14A Anode active material layer 14AE1, 14AE2 (widthwise) edges ML Centerline 14AM Central part 14AS1 One side part (edge ​​side part) 14AS2 Other side part (edge ​​side part) EL Distance 14AF additional negative electrode active material layer 14AN1,14AN2,14AN-free negative electrode active material layer 14AP negative electrode active material particles XH Axial direction XHI Inside XHO outside WH width direction WHI inside

Claims

[Claim 1] a strip-shaped positive electrode plate, a strip-shaped negative electrode plate having a negative electrode active material layer, and a strip-shaped separator; A wound-type non-permeated electrode body in which an electrolyte solution containing ethylene carbonate, a solvent having a melting point lower than that of ethylene carbonate, and a supporting salt containing P is not permeated inside, the width dimension of the negative electrode active material layer is 180 mm or more, The negative electrode active material layer of the negative electrode plate contains ethylene carbonate in the central portion in the width direction, but does not contain ethylene carbonate in the end portions in the width direction. Unpenetrated electrode body.

Images