Method for manufacturing a storage device

Abstract

To provide a method for producing a power storage device in which a negative electrode SEI film is inhibited from being formed unevenly 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 containing ethylene carbonate 6VE and a solvent 6VL having a lower melting point than that of the ethylene carbonate, a wound-type electrode body 2, and a case 7, the electrode body including a negative electrode active material layer 4A having a width dimension AW of 180 mm or larger. A method for producing the power storage device includes an injecting step S3 of injecting the electrolytic solution 6 into the case 7 where a to-be-permeated electrode body 12 is housed, a waiting step S4 of waiting for lapse of a predetermined waiting time TT, and an initial charging step S5. A to-be-permeated electrode body forming step S1 is a step of forming the to-be-permeated electrode body 12 placed in advance with a film-forming material CS for forming the negative electrode SEI film 4AC on the negative electrode active material layer 4A in a center portion 12M of the to-be-permeated electrode body 12 in an axial direction XH.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a power storage device.

Background Art

[0002] Conventionally, in a power storage device such as a battery having an electrode body and an electrolytic solution in a case, it has been necessary to consider uneven penetration (impregnation unevenness) of the electrolytic solution into the electrode body. Therefore, for example, in Patent Document 1, before a lamination step of obtaining a lamination unit in which an electrode active material layer (A), a separator, and an electrode active material layer (B) are laminated, at least one of the separator and the electrode active material layer (B) contains an electrolytic solution, thereby preventing or suppressing uneven penetration of the electrolytic solution. A method for manufacturing a lithium-ion battery is disclosed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems 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 laminated unit, that is, a laminated electrode body, it is necessary to handle a belt-shaped separator impregnated with an electrolytic solution or a belt-shaped electrode plate impregnated with an electrolytic solution, and handling is difficult.

[0005] On the other hand, as a solvent forming the electrolytic solution of the power storage device, together with dimethyl carbonate (hereinafter also referred to as DMC), ethyl methyl carbonate (hereinafter also referred to as EMC), etc., ethylene carbonate (hereinafter also referred to as EC) for forming an SEI film may be used together to facilitate the formation of the SEI film on the negative electrode active material layer during the first charge. For example, it is a case where an EC / DMC / EMC mixed solvent is used for the electrolytic solution.

[0006] However, when an electrolytic solution containing EC is allowed to penetrate into the electrode body from the end of the electrode body where the electrolytic solution has not penetrated, it has been found that EC has a relatively slow penetration rate compared to supporting salts such as DMC, EMC, and LiPF6 dissolved therein. EC has a melting point of about 34 - 37°C, which is relatively high compared to DMC (melting point 2 - 4°C), EMC (melting point -53°C), etc., and also has a high viscosity. Therefore, when penetrating into the electrode body along the negative electrode active material layer, separator, etc., it is considered that EC is more difficult to penetrate compared to DMC, etc.

[0007] Then, for example, among power storage devices using a wound electrode body, in a power storage device having an electrode body with a long penetration distance of the electrolytic solution because the strip-shaped electrode plate is wide, even if the electrolytic solution is allowed to penetrate from both axial ends and the electrolytic solution reaches the center in the axial direction and penetrates the entire electrode body, there may be a case where EC has not sufficiently reached the vicinity of the center in the axial direction. That is, during the first charge, there may be non-uniformity in the amount per unit area (hereinafter also referred to as the area density) of EC present in various parts of the electrode body.

[0008] In this state, when a first charge is performed on a power storage device such as a secondary battery and an attempt is made to form a negative electrode SEI film on the negative electrode active material layer, it becomes difficult to form a negative electrode SEI film derived from EC in the vicinity of the center in the axial direction where the EC content in the electrode body is low. For this reason, it has been found that in the electrode body, in the vicinity of the center in the axial direction where the area density of EC is low, compared to parts such as near both axial ends where the area density of EC is high, the characteristics of the negative electrode active material layer are different. Specifically, it becomes a negative electrode active material layer with a relatively high resistance. As a result, the resistance of the entire power storage device also increases.

[0009] The present invention has been made in view of such a situation, and provides a method for manufacturing a power storage device that suppresses non-uniform generation of a negative electrode SEI film in the negative electrode active material layer in a wound electrode body and suppresses an increase in resistance.

Means for Solving the Problems

[0010] (1) One aspect of the present invention for solving the above problems is an electrolytic solution containing ethylene carbonate and a solvent having a melting point lower than that of ethylene carbonate, a strip-shaped positive electrode plate, a strip-shaped negative electrode plate having a strip-shaped negative electrode active material layer, and a strip-shaped separator, and a wound electrode body in which the electrolytic solution penetrates therein, and a case containing the electrode body and the electrolytic solution. The electrode body is a method for manufacturing a power storage device in which the width dimension of the negative electrode active material layer is 180 mm or more. The method includes an unpenetrated electrode body forming step of forming an unpenetrated wound electrode body in which the electrolytic solution does not penetrate, a housing step of housing the unpenetrated electrode body in the case, a liquid injection step of injecting the electrolytic solution into the case housing the unpenetrated electrode body, a standby step of waiting for the elapse of a predetermined standby time after the liquid injection step during which the electrolytic solution penetrates the entire unpenetrated electrode body, and a first charging step of performing a first charge to form a negative electrode SEI film on the negative electrode active material layer after the standby step. The unpenetrated electrode body forming step forms the unpenetrated electrode body in which Ethylene carbonate is previously disposed at the central portion in the axial direction of the unpenetrated electrode body for forming the negative electrode SEI film on the negative electrode active material layer Among them, in the strip-shaped negative electrode active material layer, the central portion in the width direction is made into a strip-shaped additional negative electrode active material layer containing ethylene carbonate, while the edge side portions on both sides in the width direction are respectively made into strip-shaped non-containing negative electrode active material layers not containing ethylene carbonate, and an additional negative electrode plate forming step for forming an additional negative electrode plate is provided This is a method for manufacturing a power storage device.

[0011] The power storage device according to this manufacturing method uses an electrolytic solution containing EC. Moreover, in the wound electrode body, the dimension in the width direction of the strip-shaped negative electrode active material layer is 180 mm or more. Therefore, as described above, even if the standby time has elapsed and the electrolytic solution has penetrated the entire unpenetrated electrode body, the first charging step is performed while EC has not sufficiently reached the central portion in the axial direction of the wound electrode body, and there is a risk that the generation of the negative electrode SEI film in the negative electrode active material layer becomes non-uniform in the electrode body.

[0012] However, in this manufacturing method, in the unpenetrated electrode body forming step, at the central portion in the axial direction of the unpenetrated electrode body, a negative electrode SEI film is formed on the negative electrode active material layer Ethylene carbonate is previously disposed to form the unpenetrated electrode body. Therefore, even when the first charging step is performed in a state where EC derived from the electrolytic solution has not sufficiently reached the central portion in the standby step, Ethylene carbonateThus, it is possible to manufacture an electricity storage device in which the negative electrode SEI coating is appropriately formed by suppressing unevenness in the formation of the negative electrode SEI coating in the negative electrode active material layer in the electrode body and thus suppressing an increase in resistance.

[0013] 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.

[0014] As the electrolyte, a non-aqueous electrolyte obtained by dissolving a supporting salt in an organic solvent can be used. Examples of organic solvents used in 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.

[0015] In addition, the electrolyte may contain, as a supporting salt, lithium salts such as LiBF4, LiAsF6, LiPF6, LiCF3SO3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), etc. In addition, sodium salts such as NaPF6, Na + (CF3SO2)2N - (NaTFSI), etc.

[0017] In the non-permeated electrode body forming step, Ethylene carbonate As a method for forming an unpermeated electrode body in which the negative electrode active material layer is previously arranged, for example, Ethylene carbonate In addition, a method of forming a non-permeated electrode body using an additional negative electrode plate containing Ethylene carbonate Alternatively, an unpermeated electrode body may be formed by using an additional separator containing the above-mentioned.

[0019] In the method for manufacturing this power storage device, the unpenetrated electrode body forming step includes an additional negative electrode plate forming step of forming an additional negative electrode plate having a strip-shaped additional negative electrode active material layer and strip-shaped non-including negative electrode active material layers on both sides in the width direction thereof. By using the additional negative electrode plate thus formed, a wound-type unpenetrated electrode body can be formed in the same manner as a strip-shaped negative electrode plate without an additional negative electrode active material layer, and moreover, a film-forming material can be disposed in advance on the unpenetrated electrode body.

[0020] (2) The above-mentioned (1) In the method for manufacturing the power storage device according to the above, in the additional negative electrode plate forming step, a non-including negative electrode paste containing negative electrode active material particles but not containing Ethylene carbonate is used to form the non-including negative electrode active material layer, and an additional negative electrode paste containing the negative electrode active material particles and Ethylene carbonate is used to form the additional negative electrode active material layer. This is a preferable method for manufacturing the power storage device.

[0021] In the method for manufacturing this power storage device, in the additional negative electrode plate forming step, a non-including negative electrode paste is used to form the non-including negative electrode active material layer, and an additional negative electrode paste is used to form the additional negative electrode active material layer. Therefore, the additional negative electrode plate can be formed at low cost.

[0022] As a method of forming a non-including negative electrode active material layer using a non-including negative electrode paste and forming an additional negative electrode active material layer using an additional negative electrode paste, there is a method of applying and drying a strip of negative electrode paste / additional negative electrode paste / negative electrode paste on a strip-shaped negative electrode current collector foil by using a die coater provided with partitions between a portion for discharging the additional negative electrode paste and one-side and the other-side portions for discharging the negative electrode paste. Not containing Also, there is a method of providing a time difference in coating, for example, a method of coating the additional negative electrode paste in a strip shape on a strip-shaped negative electrode current collector foil, then coating the negative electrode paste in a strip shape on both sides in the width direction of the layer of the additional negative electrode paste, and then drying.

[0023] ​Further, in the method for manufacturing the above-described power storage device, in the additional negative electrode plate forming step, after forming a non-containing negative electrode active material layer that contains negative electrode active material particles but does not contain the film-forming material, a paste containing the film-forming material is applied to the central portion in the width direction of the non-containing negative electrode active material layer and dried to form an additional negative electrode plate having an additional negative electrode active material layer, which is also preferable.

[0024] (3) The above-mentioned (1) Or (2) In the method for manufacturing the power storage device described in the above, in the additional negative electrode plate forming step, it is preferable to use, as the additional negative electrode active material layer, the central portion of the strip-shaped negative electrode active material layer where the distances from both end edges in the width direction are each 80 mm or more apart.

[0025] Due to the difference in the ease of penetration between EC and other solvents, at a site where the penetration distance along the negative electrode active material layer is 80 mm or more, the tendency for EC to reach relatively becomes stronger, and as described above, it becomes more difficult to form a negative electrode SEI film derived from EC in the electrolytic solution. On the other hand, in the above-described manufacturing method, in the wound-type unpenetrated electrode body, since the central portion in the width direction where the distances from both end edges in the width direction of the strip-shaped tortuous active material layer are 80 mm or more apart is used as the additional negative electrode active material layer, it is possible to surely assist the formation of the negative electrode SEI film.

[0027] In this method for manufacturing the power storage device, since ethylene carbonate as a film-forming material is arranged in advance at a site where ethylene carbonate derived from the electrolytic solution is insufficient, it is possible to form a negative electrode SEI film derived from ethylene carbonate on the entire negative electrode active material layer.

Brief Description of the Drawings

[0028]

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MODE FOR CARRYING OUT THE INVENTION

[0029] (Embodiment) Hereinafter, a battery 1 (an example of a power storage device), which is a lithium ion secondary battery according to an embodiment of the present invention, and its manufacturing will be described with reference to FIGS. 1 to 7. This battery 1 is a rectangular sealed lithium ion secondary battery and is mounted on vehicles such as hybrid cars, plug-in hybrid cars, electric vehicles, and various devices.

[0030] The battery 1 of this embodiment includes a case 7, an electrode body 2 and an electrolytic solution 6 housed inside the case 7. The case 7 made of metal (aluminum in this embodiment) and having a rectangular parallelepiped box shape is composed of a bottomed square cylindrical case body 7H and a lid body 7L located above BH1 in the height direction BH. A positive electrode terminal 8P and a negative electrode terminal 8N are fixedly provided on this lid body 7L via an insulating member 9. A liquid injection hole 7LH for injecting the electrolytic solution 6 is formed in this lid body 7L and is sealed with a liquid injection plug 7LP after the injection. The electrode body 2 is covered with a bag-shaped insulating film (not shown) inside the case 7. Further, a part of the electrolytic solution 6 housed in the case 7 is impregnated into the electrode body 2, and the remainder accumulates at the bottom of the case 7.

[0031] The non-impregnated electrode body 12 (see FIGS. 3 and 4) in which the electrolytic solution 6 is not impregnated is a so-called flat wound type electrode body, and a strip-shaped non-impregnated positive electrode plate 13 and a strip-shaped non-impregnated negative electrode plate 14 (an example of an additional negative electrode plate) are wound via a pair of strip-shaped non-impregnated separators 15 and pressed in the thickness direction CH to be flattened. Therefore, the electrode body 2 (see FIGS. 1, 3, and 4) housed in the case 7 and impregnated with the electrolytic solution 6 in the non-impregnated electrode body 12 also has a strip-shaped positive electrode plate 3 and a strip-shaped negative electrode plate 4 impregnated with the electrolytic solution 6 wound via a pair of strip-shaped separators 5 and thinned and flattened in the thickness direction CH orthogonal to the paper surface in FIG. 1. This electrode body 2 is housed in the case 7 in a lying-down posture in which the winding axis AX coincides with the width direction AH (the left-right direction in FIG. 1).

[0032] Note that the electrode body 2 in the battery 1 has been subjected to initial charging after allowing the electrolytic solution 6 to penetrate into the non-impregnated electrode body 12 housed in the case 7 as will be described later. Therefore, as shown in FIG. 2, a negative electrode SEI film 4AC derived from ethylene carbonate 6VE and lithium salt 6S of the solvent contained in the electrolytic solution 6 is 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 film 4AC enables the battery 1 to perform stable charge and discharge with low resistance as compared with the case where the negative electrode SEI film 4AC is not formed.

[0033] Of the flat wound electrode body 2 and the unpenetrated electrode body 12, on one side XH1 in the axial direction XH along the winding axis AX (which coincides with one side AH1 in the width direction AH of the battery 1 in this embodiment; above in FIG. 3), there are provided positive electrode current collecting portions 2P and 12P around which the current collecting portions 3S and 13S of the positive electrode plate 3 or the unpenetrated positive electrode plate 13 are wound. Conversely, on the other side XH2 in the axial direction XH (which coincides with the other side AH2 in the width direction AH of the battery 1 in this embodiment; below in FIG. 3), there are provided negative electrode current collecting portions 2N and 12N around which the current collecting portions 4S and 14S of the negative electrode plate 4 or the unpenetrated negative electrode plate 14 are wound. The portion between the positive electrode current collecting portions 2P and 12P and the negative electrode current collecting portions 2N and 12N is a main body portion 2H and 12H in which the positive electrode plate 3 and the negative electrode plate 4 are wound with the separator 5 interposed therebetween, or the unpenetrated positive electrode plate 13 and the unpenetrated negative electrode plate 14 are wound with the unpenetrated separator 15 interposed therebetween.

[0034] The positive electrode terminal 8P is made of an aluminum plate bent into a predetermined shape. The inner connection portion 8PI forming one end of the positive electrode terminal 8P is connected to the positive electrode current collecting portion 2P disposed on one side AH1 in the width direction AH of the electrode body 2. On the other hand, the other end of the positive electrode terminal 8P is drawn out outside the case 7 (specifically, on the lid body 7L) to form an external terminal portion 8PO. Further, the negative electrode terminal 8N is made of a copper plate bent into a predetermined shape. The inner connection portion 8NI forming one end of this negative electrode terminal 8N is connected to the negative electrode current collecting portion 2N disposed on the other side AH2 in the width direction AH of the electrode body 2. On the other hand, the other end of the negative electrode terminal 8N is drawn out outside the case 7 (specifically, on the lid body 7L) to form an external terminal portion 8NO.

[0035] The electrolytic solution 6 is a non-aqueous electrolytic solution having an organic solvent 6V and a lithium salt 6S (an example of a supporting salt). In this embodiment, as the organic solvent 6V, an organic solvent in which ethylene carbonate (EC) 6VE and other solvents 6VL, dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC), are mixed at a weight ratio of 3:4:3 is used. Further, as the lithium salt 6S, LiPF6 is used. The concentration of LiPF6 in the electrolytic solution 6 is 1.1 mol / L.

[0036] As shown in FIG. 4, among the unpenetrated electrode bodies 12, the strip-shaped unpenetrated positive electrode plate 13 includes a positive electrode foil 13F made of aluminum foil and positive electrode active material layers 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 (not shown), conductive particles, and a binder. In this embodiment, as the positive electrode active material particles, lithium transition metal composite oxide particles, specifically, for example, lithium nickel cobalt manganese composite oxide particles are used. As the conductive particles, for example, acetylene black (AB) is used. Further, as the binder, for example, polyvinylidene fluoride (PVDF) is used. Among the strip-shaped unpenetrated positive electrode plates 13, at the end on one side WH1 (upper side in FIG. 4) in the width direction WH, there is no positive electrode active material layer 13A on the positive electrode foil 13F, and it becomes a current collecting portion 13S where the positive electrode foil 13F is exposed. On the other hand, the remaining part of the unpenetrated positive electrode plate 13 is a positive electrode portion 13P in which positive electrode active material layers 13A are laminated on both surfaces of the positive electrode foil 13F. As can be understood from FIGS. 3 and 4, the width direction WH (vertical direction in FIG. 4) of the unpenetrated positive electrode plate 13 and the like coincides with the axial direction XH, and one side WH1 coincides with one side XH1.

[0037] On the other hand, among the unpenetrated electrode bodies 12, the strip-shaped unpenetrated negative electrode plate 14 includes a negative electrode foil 14F made of copper foil and negative electrode active material layers 14A laminated on both surfaces of the negative electrode foil 14F. The negative electrode active material layer 14A is composed of negative electrode active material particles 14AP and a binder (not shown). In this embodiment, graphite particles are used as the negative electrode active material particles 14AP. Further, as the binder, for example, carboxymethyl cellulose (CMC) is used. Among the strip-shaped unpenetrated negative electrode plates 14, at the end on the other side WH2 (lower side in FIG. 4) in the width direction WH, there is no negative electrode active material layer 14A on the negative electrode foil 14F, and it becomes a current collecting portion 14S where the negative electrode foil 14F is exposed. On the other hand, the remaining part of the unpenetrated negative electrode plate 14 is a negative electrode portion 14N in which negative electrode active material layers 14A are 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, 14A in the width direction WH is AW = 180 mm.

[0038] Also, among the unimpregnated electrode body 12, the pair of strip-shaped unimpregnated separators 15 are made of a porous resin. As shown in FIG. 4, when wound, the unimpregnated separators 15 are overlapped so as to be interposed between the unimpregnated negative electrode plate 14 and the unimpregnated positive electrode plate 13. The unimpregnated negative electrode plate 14 and the negative electrode portion 14N are slightly wider than the unimpregnated positive electrode plate 13 and the positive electrode portion 13P in the width direction WH. Moreover, the negative electrode portion 14N is arranged so as to cover the entire width direction WH of the positive electrode portion 13P, that is, the negative electrode active material layer 14A facing the positive electrode active material layer 13A exists at any part of the positive electrode active material layer 13A. Also, the unimpregnated separator 15 is slightly wider than the negative electrode portion 14N and the positive electrode portion 13P in the width direction WH. Moreover, the unimpregnated separator 15 is arranged so as to cover the entire width direction WH of the negative electrode portion 14N and the positive electrode portion 13P, that is, the unimpregnated separator 15 covering the positive electrode active material layer 13A and the negative electrode active material layer 14A exists at any part of the positive electrode active material layer 13A and the negative electrode active material layer 14A.

[0039] When the unimpregnated electrode body 12 is connected to the positive electrode terminal 8P and the negative electrode terminal 8N, housed in the case 7, and the electrolytic solution 6 is poured into the case 7, the electrolytic solution 6 penetrates into the unimpregnated electrode body 12 from the outside XHO in the axial direction XH of the unimpregnated electrode body 12, that is, from one side XH1 and the other side XH2. Specifically, the electrolytic solution 6 penetrates along the unimpregnated positive electrode plate 13, the unimpregnated negative electrode plate 14, and the unimpregnated separator 15 from one side WH1 and the other side WH2 (upper and lower in the figure in FIG. 4) in the width direction WH that coincides with the axial direction XH, respectively, toward the center line ML in the width direction WH of the negative electrode active material layer 14A, that is, toward the inside WHI in the width direction WH.

[0040] However, as described above, when the electrolytic solution 6 penetrates into the unpenetrated electrode body 12, among the components of the organic solvent 6V, ethylene carbonate 6VE has a slower penetration rate compared to other solvents 6VL (in this embodiment, DMC and EMC having a lower melting point than EC). For this reason, considering the distance EL that progresses toward the inside WHI in the width direction WH starting from both end edges 14AE1 and 14AE2 in the width direction WH of the negative electrode active material layer 14A of the unpenetrated negative electrode plate 14, it is considered that the concentration of ethylene carbonate 6VE in the leading portion of the electrolytic solution 6 that penetrates toward the inside WHI decreases as the distance EL increases. For this reason, when the electrolytic solution 6 penetrates up to the center line ML in the width direction WH of the negative electrode active material layer 14A indicated by the dashed-dotted line in FIG. 4, and the penetration of the electrolytic solution 6 is completed throughout the unpenetrated electrode body 12, and the electrode body 2 is impregnated with the electrolytic solution 6 (for example, at the time when the waiting time TT from the start of liquid injection until the penetration of the electrolytic solution 6 is completed has elapsed), it is considered that the concentration of ethylene carbonate 6VE in the electrolytic solution 6 located near the center line ML is relatively lower than that in the electrolytic solution 6 located outside the width direction WH (above or below in FIG. 4) compared to the vicinity of the center line ML.

[0041] Here, the electrolytic solution 6 that penetrates (progresses) toward the inside WHI in the width direction WH along the negative electrode active material layer 14A has been described. However, similarly, for the electrolytic solution 6 that penetrates (progresses) toward the inside WHI in the width direction WH along the positive electrode active material layer 13A of the unpenetrated positive electrode plate 13 and the unpenetrated separator 15, non-uniformity occurs in the concentration of ethylene carbonate 6VE in the electrolytic solution 6 due to the difference in penetration rate. That is, when the electrolytic solution 6 is injected into the case 7 and the electrolytic solution 6 is allowed to penetrate into the unpenetrated electrode body 12, the amount of ethylene carbonate 6VE reaching near the central portion 2M in the axial direction XH of the electrode body 2 impregnated with the electrolytic solution 6 (see FIG. 3) tends to be small.

[0042] Particularly, as in this embodiment, when the electrode body 2 (unpenetrated electrode body 12) has a width dimension AW of the negative electrode active material layers 4A and 14A of 180 mm or more (in this embodiment, the width dimension AW = 180 mm), the electrolytic solution 6 that has penetrated from both end edges 14AE1 and 14AE2 in the width direction WH of the negative electrode active material layer 14A needs to penetrate (move) a distance EL of 90 mm or more along the negative electrode active material layer 14A before reaching the center line ML. For this reason, due to the difference in the penetration rate with other solvents 6VL, the concentration of ethylene carbonate 6VE in the electrolytic solution 6 located near the center line ML becomes low, and the areal density of ethylene carbonate 6VE present near the center line ML also becomes low.

[0043] In addition, when the electrolytic solutions 6 that have penetrated from both end edges 14AE1 and 14AE2 of the negative electrode active material layer 14A toward the inside WHI both reach near the center line ML and meet each other, thereafter, the electrolytic solution 6 does not move to the inside WHI in the width direction WH by penetration. For this reason, among the penetrated electrolytic solution 6, the non-uniformity in the concentration of ethylene carbonate 6VE that occurs between the electrolytic solution 6 located near the center line ML and the electrolytic solution 6 located outside (above or below in FIG. 4) the width direction WH of this is considered to be gradually eliminated by diffusion movement due to the concentration gradient of ethylene carbonate 6VE. However, it is presumed that it takes more time (for example, several days, etc.) until the non-uniformity in concentration is eliminated compared to the movement of the electrolytic solution 6 by penetration. For this reason, it is difficult to wait for a long time until the non-uniformity in concentration is eliminated from the time when the penetration of the electrolytic solution 6 into the entire electrode body 2 is completed to proceed to the first charge.

[0044] For this reason, after injecting the electrolytic solution 6 into the case 7, when the first charge of the battery 1 is started without delay after the elapse of the waiting time TT until the penetration of the electrolytic solution 6 is completed, the first charge will be performed in a state where the non-uniformity in the concentration of ethylene carbonate 6VE in the electrode body 2 has occurred.

[0045] However, as described above, ethylene carbonate 6VE contained in the electrolytic solution 6 serves as a raw material for forming the negative electrode SEI film 4AC around the negative electrode active material particles 4AP that make up the negative electrode active material layer 4A. Therefore, as described above, when the amount per unit area of ethylene carbonate 6VE present near the center line ML of the negative electrode active material layer 4A is small, it is not possible to appropriately form a negative electrode SEI film derived from ethylene carbonate as the negative electrode SEI film 4AC around the negative electrode active material particles 4AP near the center line ML of the negative electrode active material layer 4A, and problems such as an increase in the resistance of the battery 1 are likely to occur.

[0046] Therefore, in the battery 1 of the present embodiment, as shown in FIG. 4, in the negative electrode active material layer 14A of the unpenetrated negative electrode plate 14 that forms the unpenetrated electrode body 12, a central portion 14AM in the width direction WH, where the distance EL from both end edges 14AE1 and 14AE2 is equal to or greater than the additional portion distance ELF (in the present embodiment, the additional portion distance ELF = 80 mm), is made into a strip-shaped additional negative electrode active material layer 14AF preliminarily containing the film-forming substance CS. On the other hand, one-side portion 14AS1 on one side WH1 of the width direction WH and the other-side portion 14AS2 on the other side WH2 of the width direction WH are each made into strip-shaped non-containing negative electrode active material layers 14AN1 and 14AN2 that do not contain the film-forming substance CS, as before. In the present embodiment, ethylene carbonate CS1 is used as the film-forming substance CS. As a result, the unpenetrated electrode body 12 becomes an unpenetrated electrode body 12 in which the film-forming substance CS (ethylene carbonate CS1) for forming the negative electrode SEI film 4AC on the negative electrode active material layer 4A is preliminarily arranged at the central portion 12M in the axial direction XH.

[0047] To form the negative electrode active material layer 14A of the unimpregnated negative electrode plate 14, as will be described later, the non-including negative electrode active material layers 14AN1 and 14AN2 are formed using the same non-including negative electrode paste PAN as before that does not contain the film-forming substance CS, while the additional negative electrode active material layer 14AF is formed in the central portion 14AM in the width direction WH using the additional negative electrode paste PAF containing the film-forming substance CS. In the present embodiment, as the non-including negative electrode paste PAN, a mixture of 99% by weight of graphite particles and 1% by weight of a binder (CMC) in water as a solvent is used. Further, as the additional negative electrode paste PAF, 5% by weight of ethylene carbonate CS1 as the film-forming substance CS is added to the above-described non-including negative electrode paste PAN and used.

[0048] Since 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 way, when the electrolytic solution 6 that penetrates inward WHI from both end edges 14AE1 and 14AE2 in the width direction WH of the negative electrode active material layer 14A reaches the additional negative electrode active material layer 14AF, the film-forming substance CS in the additional negative electrode active material layer 14AF dissolves in the electrolytic solution 6 while the electrolytic solution 6 further penetrates toward the center line ML. Therefore, even in the electrode body 2 where the penetration of the electrolytic solution 6 is completed, in the electrolytic solution 6 located near the center line ML of the negative electrode active material layer 14A, that is, in the central portion 14AM, the concentration of ethylene carbonate 6VE derived from the electrolytic solution 6 is decreased. However, the film-forming substance CS (ethylene carbonate CS1) in the additional negative electrode active material layer 14AF is added to the electrolytic solution 6 in the central portion 14AM.

[0049] For this reason, as described above, even when the initial charging process is performed in a state where ethylene carbonate 6VE derived from the electrolytic solution 6 does not sufficiently reach the central portion 14AM, the negative electrode SEI film 4AC can be appropriately formed on the negative electrode active material particles 4AP by the previously arranged film-forming substance CS (see FIG. 2). Thus, it is possible to manufacture the battery 1 that suppresses the non-uniformity of the formation of the negative electrode SEI film in the negative electrode active material layer 4A, suppresses the non-uniformity of the resistance of the negative electrode active material layer 4A in the electrode body 2, and suppresses the increase in resistance.

[0050] Particularly 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 ethylene carbonate 6VE from the electrolytic solution 6 is insufficient. For this reason, ethylene carbonate deficiency does not occur at various locations in the negative electrode active material layer 4A, and a negative electrode SEI film derived from ethylene carbonate can be appropriately formed over the entire negative electrode active material layer 4A.

[0051] Next, the manufacturing of this battery 1 will be described with reference to FIGS. 5 to 7. First, in the electrode body forming step S1 (an example of an unimpregnated electrode body forming step), an unimpregnated wound-type unimpregnated electrode body 12 in which the electrolytic solution 6 is not impregnated is formed. Specifically, in the unimpregnated negative electrode plate forming step S11 (an example of an additional negative electrode plate forming step), an unimpregnated negative electrode plate 14 having a strip-shaped negative electrode active material layer 14A is formed.

[0052] More specifically, in the strip-shaped negative electrode active material layer 14A, the central portion 14AM in the width direction WH is a strip-shaped additional negative electrode active material layer 14AF containing the film-forming substance CS, while on one side portion 14AS1 and the other side portion 14AS2 of the outer side WHO in the width direction WH than the additional negative electrode active material layer 14AF, strip-shaped negative electrode active material layers 14AN1 and 14AN2 not containing the film-forming substance CS are provided respectively, and an unimpregnated negative electrode plate 14 having a negative electrode active material layer 14A is formed (see FIG. 4). As described above, in this embodiment, ethylene carbonate CS1 is used as the film-forming substance CS.

[0053] In this unimpregnated negative electrode plate forming step S11, negative electrode active material layers 14AN1 and 14AN2 not containing the film-forming substance CS are formed using a non-containing negative electrode paste PAN that contains negative electrode active material particles 14AP and a binder but does not contain the film-forming substance CS. On the other hand, an additional negative electrode active material layer 14AF is formed using an additional negative electrode paste PAF that contains negative electrode active material particles 4AP and the film-forming substance CS.

[0054] Specifically, in the coating step S111, as shown in FIG. 6, a wide negative electrode foil 24F having a width twice that of the negative electrode foil 4F of the negative electrode plate 4 wound around the backup roll BR1 is coated with a wide negative electrode paste layer 24AT using a die coater DC. More specifically, among the die coaters DC, the non-included negative electrode paste PAN is stored in the storage tank DCT1, and the additional negative electrode paste PAF is stored in the storage tank DCT2. Using a die DCD provided with a plurality of partitions (not shown), the non-included negative electrode paste PAN supplied from the storage tank DCT1 and the additional negative electrode paste PAF supplied from the storage tank DCT2 are discharged in a stripe shape from the slit DCS of the die DCD and applied to the wide negative electrode foil 24F wound around the backup roll BR1 (see FIG. 7). Specifically, sites serving as current collecting portions 14S of the non-permeated negative electrode plate 14 are left uncoated on both sides of the wide negative electrode foil 24F having a width twice that of the negative electrode foil 14F, and a wide negative electrode paste layer 24AT having a width twice that of the negative electrode active material layer 14A is applied. This wide negative electrode paste layer 24AT is formed symmetrically about the cutting center line CL indicated by the dashed-dotted line in FIG. 7, and is applied in a pattern of five stripes with two additional negative electrode paste layers 24ATF intervening between three non-included negative electrode paste layers 24ATN. Note that the non-included negative electrode paste layer 24ATN becomes the non-included negative electrode active material layers 14AN1 and 14AN2 of the negative electrode active material layer 14A after drying and cutting as described below. Also, the additional negative electrode paste layer 24ATF becomes the additional negative electrode active material layer 14AF after drying and cutting.

[0055] Thereafter, in the drying step S112, the wide negative electrode paste layer 24AT applied to the wide negative electrode foil 24F is dried in a drying furnace DR to form a wide negative electrode active material layer 24A. Note that the coating 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 non-permeated negative electrode plate 24 provided with wide negative electrode active material layers 24A on both sides of the wide negative electrode foil 24F. In FIG. 6, the state of applying and drying the wide negative electrode paste layer 24AT to the wide single-sided negative electrode plate 24S provided with the wide negative electrode active material layer 24A on one surface of the wide negative electrode foil 24F is shown.

[0056] Further, in the cutting step S113, a wide non-impregnated negative electrode plate 24 having wide negative electrode active material layers 24A provided on both sides of a wide negative electrode foil 24F is cut along a cutting center line CL (see FIG. 7) to form two strip-shaped non-impregnated negative electrode plates 14. Thereafter, after the non-impregnated negative electrode plates 14 are distributed by a distribution roll FR, they are wound around winding rolls SR1 and SR2, respectively. Thus, the non-impregnated negative electrode plates 14 (see FIG. 4) are obtained by the non-impregnated negative electrode plate forming step S11.

[0057] Next, in the winding step S12, the non-impregnated negative electrode plate 14 is wound together with a separately formed non-impregnated positive electrode plate 13 and a non-impregnated separator 15 to form a cylindrical wound electrode body (not shown). Further, in the flattening step S13, this cylindrical electrode body is pressed to form a plate-shaped and flat wound non-impregnated electrode body 12 (see FIG. 3). Thus, the non-impregnated electrode body 12 is obtained by the electrode body forming step S1.

[0058] Thereafter, in the housing step S2, the non-impregnated electrode body 12 is housed in the case 7. Specifically, first, in the terminal connection step S21, the positive electrode current collecting portion 12P of the non-impregnated 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 collecting portion 12P is welded to the inner connection portion 8NI of the negative electrode terminal 8N, respectively, to fix the non-impregnated electrode body 12 to the lid body 7L via the positive electrode terminal 8P and the negative electrode terminal 8N (see FIG. 1).

[0059] In the subsequent insertion step S22, a bag-shaped resin cover (not shown) made of a resin film is placed over the non-impregnated electrode body 12, and then the non-impregnated electrode body 12 is inserted into the case main body 7H, and the case main body 7H is sealed with the lid body 7L. Further, in the sealing step S23, the periphery of the lid body 7L is hermetically welded to the case main body 7H by laser welding over the entire circumference for sealing. Thus, the non-impregnated electrode body 12 is housed in the case 7 by the housing step S2.

[0060] After that, in the electrolyte injection step S3, a predetermined amount of electrolyte 6 is injected into the case 7 through the electrolyte injection hole 7LH of the lid body 7L. As a result, as described above, the electrolyte 6 is impregnated into the unpenetrated electrode body 12 in the case 7. In the electrolyte injection step S3, the electrolyte 6 is injected in a predetermined injection pattern. Further, prior to the electrolyte injection, the un-injected battery 1 can be placed in a chamber and decompressed or pressurized while impregnating the electrolyte 6 into the unpenetrated electrode body 12.

[0061] In the standby step S4, it waits until a predetermined standby time TT elapses from the start of the electrolyte injection. The standby time TT is the time until the electrolyte 6 penetrates into the entire unpenetrated electrode body 12 (until it becomes the electrode body 2 impregnated with the electrolyte 6). This standby time TT is obtained in advance by disassembling battery samples with different elapsed times from the start of the electrolyte injection and observing the penetration state of the electrolyte 6.

[0062] After the standby time TT has elapsed, it proceeds to the first charging step S5, connects a power source (not shown) to the positive electrode terminal 8P and the negative electrode terminal 8N, and applies a voltage to the electrode body 2 of the battery 1 through the positive electrode terminal 8P and the negative electrode terminal 8N to perform the first charging. That is, a voltage is applied between the positive electrode plate 3 and the negative electrode plate 4 of the electrode body 2 in a predetermined first charging pattern to form a negative electrode SEI film 4AC on the negative electrode active material layer 4A of the negative electrode plate 4 (see FIG. 2). In this embodiment, the first charging was performed in a first charging pattern of 0.5C-CCCV charging (SOC 90%). After that, the electrolyte injection hole 7LH is sealed with the electrolyte injection plug 7P.

[0063] As described above, in the battery 1 of this embodiment, an additional negative electrode active material layer 14AF is provided at the central portion 14AM of the negative electrode active material layer 14A of the unpenetrated negative electrode plate 14 in the unpenetrated electrode body 12. Therefore, in the electrode body 2 in which the standby time TT has elapsed and the electrolyte 6 has penetrated into the entire unpenetrated electrode body 12, it is possible to prevent a decrease in the area density of ethylene carbonate existing near the center line ML in the negative electrode active material layer 4A of the negative electrode plate 4. For this reason, in the first charging step S5, the negative electrode SEI film 4AC can be appropriately formed on the negative electrode active material particles 4AP at any location in the negative electrode active material layer 4A.

[0064] Next, in the high-temperature aging process S6, the battery 1 is subjected to high-temperature aging by being left in an environment of 60°C for 20 hours, and the battery 1 is inspected in the inspection process S7 to complete the battery 1.

[0065] (Comparative Forms 1, 2) To compare with the battery 1 according to the embodiment, the batteries 1C1 and 1C2 according to Comparative Forms 1 and 2 were also manufactured, and the investigations described below were conducted. First, the manufacturing of the batteries 1C1 and 1C2 according to Comparative Forms 1 and 2 will be described with reference to FIGS. 8 and 9.

[0066] The battery 1C1 according to Comparative Form 1 is the same as a conventional battery. In the battery 1 of the embodiment, an unpenetrated negative electrode plate 14 provided with an additional negative electrode active material layer 14AF in the central portion 14AM of the negative electrode active material layer 14A was used to form an unpenetrated electrode body 12, which was impregnated with the electrolytic solution 6. On the other hand, in the battery 1C1 of Comparative Form 1, as shown in FIG. 8, no additional negative electrode active material layer 14AF was provided in the negative electrode active material layer 14A, and the entire negative electrode active material layer 14A was formed into an unpenetrated negative electrode plate 14C1 having a non-negative electrode active material layer 14AN that does not contain the film-forming substance CS. Then, an unpenetrated electrode body 12C1 was formed using this unpenetrated negative electrode plate 14C1. Otherwise, it was the same as the battery 1 of Embodiment 1, and the first charging process S5, the high-temperature aging process S6, etc. were also carried out in the same manner to obtain the battery 1C1 of Comparative Form 1.

[0067] On the other hand, the battery 1C2 according to Comparative Form 2 is a battery opposite to the unpenetrated negative electrode plate 14C1 of the battery 1C1 of Comparative Form 1. That is, as shown in FIG. 9, no non-negative electrode active material layer 14AN that does not contain the film-forming substance CS was provided in the negative electrode active material layer 14A, and the entire negative electrode active material layer 14A was formed into an additional negative electrode active material layer 14AF containing the film-forming substance CS (ethylene carbonate CS1) to form an unpenetrated negative electrode plate 14C2, and an unpenetrated electrode body 12C2 was formed using this unpenetrated negative electrode plate 14C2. Otherwise, it was the same as the battery 1 of Embodiment 1, and the first charging process S5, the high-temperature aging process S6, etc. were also carried out in the same manner to obtain the battery 1C2 of Comparative Form 2.

[0068] (Ethylene Carbonate Content Investigation) The manufactured batteries 1, 1C1, and 1C2 are disassembled in a glove box with an inert atmosphere, and each electrode body 2, 2C1, and 2C2 is taken out. Further, each electrode body 2, 2C1, and 2C2 is unwound to take out the negative electrode plate 4, which is then left standing to dry. Among each negative electrode plate 4, at the intermediate part of winding (approximately the center in the longitudinal direction LH) and at the sites corresponding to the investigation positions I, II, III, IV, and V in FIG. 10, samples are cut out to a size of 20×20 mm to obtain a total of 15 types of extraction negative electrode samples. Each extraction negative electrode sample is immersed in an extraction solvent to extract ethylene carbonate, and NMR measurements are performed on the reference solution with a known ethylene carbonate concentration and each extract. The content of ethylene carbonate contained in each extract is calculated from the ratio of the detection intensities of ethylene carbonate in the reference solution and the extract. Further, with the content of ethylene carbonate obtained at the investigation position I in each electrode body 2, 2C1, and 2C2 taken as 100%, the relative EC content (%) at each of the investigation positions I to V is obtained.

[0069] Note that, as shown in FIG. 10, the investigation positions I, II, III, IV, and V are the sites that were flat-plate-shaped in each electrode body 2, 2C1, and 2C2 in the negative electrode active material layer 4A of the negative electrode plate 4. They are arranged in the axial direction XH, and the distance EL measured from the edge 4AE2 (see FIG. 4) on the current collector part 4S side that becomes the negative electrode current collector part 2N inward in the axial direction XH (inward WHI in the width direction WH) is the site of each of the distances EL1, EL2, EL3, EL4, and EL5 (in this embodiment, specifically, EL1 = 10 mm, EL2 = 30 mm, EL3 = 50 mm, EL4 = 70 mm, EL5 = 90 mm). Note that the investigation position V is the position on the center line ML of the negative electrode active material layer 4A. That is, the distance EL5 is half the size of the width dimension AW (in this embodiment, AW = 180 mm) of the negative electrode active material layer 4A in the width direction WH.

[0070] This result is shown in the graph of Fig. 11. In the electrode body 2C1 of the battery 1C1 of Comparative Form 1 indicated by the thick broken line, generally, as going from the investigation position I to the investigation position IV, that is, as proceeding from the edge 4AE2 toward the inside XHI in the axial direction XH, the content of ethylene carbonate 6VE gradually decreases. However, at the investigation position V, that is, at the central portion 2M (see Fig. 3) in the axial direction XH of the electrode body 2C1, it can be seen that the content of ethylene carbonate 6VE has significantly decreased (in this Comparative Form 1, it has decreased by approximately 30% compared to the investigation position I).

[0071] This is considered to be due to the following reasons. As described above, the penetration rate of ethylene carbonate 6VE contained in the electrolytic solution 6 is slower than that of other solvents 6VL (specifically DMC and EMC). Therefore, it is considered that the concentration of ethylene carbonate 6VE in the electrolytic solution 6 located at the tip portion of the penetration among the electrolytic solution 6 penetrating into the electrode body 2C1 decreases as the distance EL from the edge 4AE2 to the investigation position V increases. In particular, when the distance EL exceeds 80 mm, the decrease in the concentration of ethylene carbonate 6VE becomes significant. Moreover, near the investigation position V located on the center line ML of the negative electrode active material layer 4A, that is, at the central portion 2M of the electrode body 2C1, since the electrolytic solution 6 penetrating from both edges 4AE1 and 4AE2 (see Fig. 8) of the negative electrode active material layer 4A toward the inside WHI in the width direction WH (inside XHI in the axial direction XH) meets and the penetration stops, the content (areal density) of ethylene carbonate 6VE reaching the central portion 2M tends to remain low.

[0072] On the other hand, in the electrode body 2C2 of the battery 1C2 in Comparative Form 2 shown by the thick dotted line, from the investigation position I to the investigation position IV, the content of ethylene carbonate is maintained at a high value near 100%. In particular, at the investigation positions II and III, the content of ethylene carbonate is slightly higher than that at the investigation position I near the edge 4AE2 of the outer side WHO in the width direction WH. However, at the investigation position IV, the content of ethylene carbonate is slightly decreased. However, at the investigation position V, that is, at the central portion 2M (see FIG. 9) in the axial direction XH of the electrode body 2C1, it can be seen that the content of ethylene carbonate is greatly decreased (in Comparative Form 2, it is decreased by approximately 35% compared to the investigation position I).

[0073] This is considered to be due to the following reasons. In the electrode body 2C2 of the battery 1C2 in Comparative Form 2, an unpenetrated negative electrode plate 14C2 is used in which the entire negative electrode active material layer 14A is an additional negative electrode active material layer 14AF containing a film-forming substance CS (specifically, ethylene carbonate CS1). For this reason, in the range from the investigation position I to III where the distance EL from the edge 4AE2 is relatively small, the decrease in concentration (see the graph of Comparative Form 1) due to the slow penetration rate of ethylene carbonate 6VE contained in the electrolytic solution 6 is compensated by the dissolution of ethylene carbonate CS1 derived from the additional negative electrode active material layer 14AF into the electrolytic solution 6. Rather, it is considered that the concentration of ethylene carbonate has increased with the penetration of the electrolytic solution 6.

[0074] However, as described above, ethylene carbonate dissolved in the electrolytic solution 6 has a slow penetration rate compared to other solvents 6VL (specifically, DMC and EMC), and in addition, has a high viscosity. For this reason, when the concentration of ethylene carbonate dissolved in the electrolytic solution 6 increases near the investigation positions II and III, due to the influence of the increase in its viscosity, the penetration rate of ethylene carbonate rapidly decreases, and the concentration of ethylene carbonate in the electrolytic solution 6 reaching the investigation position V greatly decreases. For this reason, even if the ethylene carbonate CS1 derived from the additional negative electrode active material layer 14AF near the investigation position V compensates, it is presumed that the significant decrease in the content of ethylene carbonate at the investigation position V, that is, the central portion 2M, cannot be fully compensated.

[0075] In contrast, in the battery 1 (electrode body 2) of the present embodiment shown by the thick solid line, at the investigation positions I to IV, similar to the battery 1C1 of Comparative Form 1 generally, generally from the investigation position I toward the investigation position IV, that is, as it proceeds from the edge 4AE2 to the inside XHI in the axial direction XH, the content of ethylene carbonate gradually decreases. However, different from the battery 1C1 of Comparative Form 1, in the battery 1 of the present embodiment, the content of ethylene carbonate at the investigation position V is almost the same as that at the investigation position IV. That is, in the electrode body 2 of the battery 1 of the present embodiment, the decrease in the content of ethylene carbonate in the central portion 2M (see FIG. 3) in the axial direction XH is suppressed. Specifically, in the present embodiment, the decrease in the content at the investigation position V compared to the investigation position I remains generally at 10% or less.

[0076] This is considered to be due to the following reasons. In the electrode body 2 of the battery 1 of the present embodiment, in the negative electrode active material layer 14A, an unpenetrated negative electrode plate 14 having an additional negative electrode active material layer 14AF containing a film-forming substance CS (specifically, ethylene carbonate CS1) is used only in the central portion 14AM having a distance EL including the investigation position V of 80 mm or more (see FIG. 4). For this reason, in the range from the investigation positions I to IV, it is considered that a decrease in concentration occurred due to the slow penetration rate of ethylene carbonate 6VE derived from the electrolytic solution 6, similar to Comparative Form 1.

[0077] However, as described above, when the penetrated electrolytic solution 6 reaches the additional negative electrode active material layer 14AF in the central portion 14AM of the negative electrode active material layer 14A, ethylene carbonate CS1 derived from the additional negative electrode active material layer 14AF dissolves and is replenished into the electrolytic solution 6. Thereby, it is considered that the content of ethylene carbonate at the investigation position V can be maintained at the same level as that at the investigation position IV.

[0078] (IV Resistance Value Investigation) To investigate the influence of the difference in the concentration of ethylene carbonate on battery characteristics, the following investigations were also conducted. The manufactured batteries 1, 1C1, and 1C2 were set to a SOC 50% charged state and disassembled in a glove box under an inert atmosphere, respectively, and each electrode body 2, 2C1, and 2C2 was taken out. Further, each electrode body 2, 2C1, and 2C2 was unwound, and among the positive electrode plate, the negative electrode plate facing it, and the separator sandwiched between them, at the middle part of the winding and at the positions corresponding to the investigation positions I, III, and V in FIG. 10, parts were cut out to a size of 20×20 mm each to obtain a total of nine types of samples for small cells consisting of a small positive electrode plate, a small negative electrode plate, and a small separator. These were washed and dried with EMC, laminated with a small separator sandwiched between the small positive electrode plate and the small negative electrode plate, surrounded by a laminate film, and a new electrolyte 6 was injected and sealed to form a new small cell (not shown).

[0079] For each of the small cells (a total of nine types) corresponding to the investigation positions I, III, and V of each electrode body 2, 2C1, and 2C2, constant current discharge was performed at 25°C in an environment with the current A set to magnitudes corresponding to discharge current rates of 0.2C, 0.5C, 1C, and 2C, and the voltage drop ΔV at the time when 10 seconds had elapsed was obtained for each. The obtained data was plotted on a graph with the current A on the X-axis and the voltage drop ΔV on the Y-axis, and the slope of the approximate straight line was taken as the value of the IV resistance of each small cell (IV resistance = voltage drop ΔV / current A). Further, for each form, relative IV resistance values of the small cells at the investigation positions I, III, and V were obtained with the IV resistance value obtained from the small cell at the investigation position I taken as 100%.

[0080] This result is shown in the graph of FIG. 12. Among the small cells of the electrode body 2C1 of the battery 1C1 in the comparative form 1 indicated by the thick broken line, the small cells at the investigation positions I and III had almost the same relative IV resistance values. However, it can be seen that the small cell at the investigation position V had a significantly increased relative IV resistance value compared to the small cells at the investigation positions I and III (in the comparative form 1, it was approximately 18% higher compared to the investigation position I).

[0081] This is considered to be due to the following reasons. As described above, among the electrode bodies 2C1 of the battery 1C1 in Comparative Form 1, at the investigation positions I to III, the content of ethylene carbonate has not changed much (see Fig. 11). Specifically, with respect to the investigation position I, at the investigation positions II and III, the decrease is only about -7% at most. Therefore, when the first charge is performed in the first charge step S5 on the battery 1C1 of Comparative Form 1, among the negative electrode active material layers 4A of the negative electrode plate 4, at the vicinity of the investigation positions I and III, a negative electrode SEI film 4AC derived from ethylene carbonate is appropriately formed on the negative electrode active material particles 4AP. As a result, in the small cells using the small positive electrode plate, the small negative electrode plate, and the small separator at the investigation positions I and III, it is considered that the relative IV resistance values are approximately the same as each other.

[0082] However, as described above, at the investigation position V of the electrode body 2C1, the content of ethylene carbonate has decreased significantly (-28% decrease). Therefore, among the negative electrode active material layers 4A of the negative electrode plate 4 after the first charge, in the vicinity of the investigation position V, that is, in the vicinity of the center line ML (see Fig. 10), a negative electrode SEI film 4AC derived from ethylene carbonate cannot be sufficiently formed on the negative electrode active material particles 4AP. For this reason, in the small cell using the small positive electrode plate, the small negative electrode plate, and the small separator at the investigation position V, it is considered that the relative IV resistance value is 18% higher than that of the small cell at the investigation position I. From this, it can be seen that in the electrode body 2C1 of the battery 1C1 in Comparative Form 1, the IV resistance value is locally high at the central portion 2M, and the IV resistance value is also high for the entire electrode body 2C1.

[0083] Also, in the electrode body 2C2 of the battery 1C2 in Comparative Form 2 indicated by the thick one-dot chain line, the small cells at the investigation positions I and III also had almost the same relative IV resistance values. However, it can be seen that the small cell at the investigation position V has a significantly increased relative IV resistance value compared to the small cells at the investigation positions I and III (in Comparative Form 2, it is approximately 24% higher compared to the investigation position I).

[0084] This is considered to be due to the following reasons. As described above, among the electrode bodies 2C2 of the battery 1C2 in Comparative Form 2, at the investigation positions I to III, the content of ethylene carbonate contained in the electrolytic solution 6 has hardly changed (see Fig. 11). Therefore, when the first charge is performed in the first charge step S5 on the battery 1C2 of Comparative Form 2, in the negative electrode active material layer 4A of the negative electrode plate 4, near the investigation positions I and III, a negative electrode SEI film 4AC derived from ethylene carbonate is appropriately formed on the negative electrode active material particles 4AP. As a result, in the small cells using the small positive electrode plate, the small negative electrode plate, and the small separator at the investigation positions I and III, it is considered that the relative IV resistance values have become approximately the same as each other.

[0085] However, as described above, at the investigation position V in the electrode body 2C2, the content of ethylene carbonate has decreased significantly (-36% decrease). Therefore, in the negative electrode active material layer 4A of the negative electrode plate 4 after the first charge, near the investigation position V, that is, near the center line ML (see Fig. 10), a negative electrode SEI film 4AC derived from ethylene carbonate cannot be sufficiently formed on the negative electrode active material particles 4AP. As a result, in the small cell using the small positive electrode plate, the small negative electrode plate, and the small separator at the investigation position V, it is considered that the relative IV resistance value is 24% higher than that of the small cell at the investigation position I. From this, it can be understood that even in the electrode body 2C2 of the battery 1C2 in Comparative Form 2, the IV resistance value is locally high at the central portion 2M, and the IV resistance value is also high for the entire electrode body 2C2.

[0086] In contrast, in the battery 1 (electrode body 2) of the present embodiment shown by the thick solid line, there is no significant change in the relative IV resistance value at any of the investigation positions I, III, and V.

[0087] This is considered to be due to the following reasons. As described above, in the electrode body 2 of the battery 1 of the present embodiment, not only at the investigation positions II to IV but also at the investigation position V, the content of ethylene carbonate contained in the electrolytic solution 6 does not decrease so much compared to the investigation position I (see FIG. 11). Specifically, the content at the investigation position V relative to the investigation position I remains a decrease of -9%. Therefore, when the initial charge is performed in the initial charge step S5 on the battery 1 of the present embodiment, in the negative electrode active material layer 4A of the negative electrode plate 4, not only in the vicinity of the investigation positions I and III but also in the vicinity of the investigation position V, a negative electrode SEI film 4AC derived from ethylene carbonate can be appropriately formed on the negative electrode active material particles 4AP. For this reason, it is considered that the small cells using the small positive electrode plate, small negative electrode plate, and small separator at the investigation positions I, III, and V have relative IV resistance values that are approximately the same as each other. From this, it can be seen that in the electrode body 2 of the battery 1 of the present embodiment, non-uniformity in the formation of the negative electrode SEI film in the negative electrode active material layer 4A in the wound electrode body 2 can be suppressed, and the IV resistance value does not locally increase at the central portion 2M, and it is also possible to suppress an increase in the IV resistance value of the entire electrode body 2. That is, it can be seen that the battery 1 of the present embodiment has a lower IV resistance than the batteries 1C1 and 1C2 of the comparative forms 1 and 2.

[0088] As described above, the present invention has been described in accordance with the embodiments. However, it goes without saying that the present invention is not limited to the embodiments and can be appropriately modified and applied without departing from the gist thereof. For example, in the embodiment, in addition to the non-containing negative electrode paste PAN similar to the conventional one, an additional negative electrode paste PAF containing the film-forming substance CS was prepared and applied all at once to the wide negative electrode foil 24F with the die coater DC to form an additional negative electrode paste layer 24ATF and a non-containing negative electrode paste layer 24ATN, which were then dried and cut to form an unpenetrated negative electrode plate 14 having an additional negative electrode active material layer 14AF and non-containing negative electrode active material layers 14AN1 and 14AN2. However, first, an additional negative electrode paste PAF may be applied to the wide negative electrode foil 24F to form an additional negative electrode paste layer 24ATF. Then, a non-containing negative electrode paste PAN may be applied to the wide negative electrode foil 24F to form a non-containing negative electrode paste layer 24ATN. This is dried and cut to form an unpenetrated negative electrode plate 14 having an additional negative electrode active material layer 14AF and non-containing negative electrode active material layers 14AN1 and 14AN2.

[0089] Conversely, a non-containing negative electrode paste PAN may be applied to the wide negative electrode foil 24F to form a non-containing negative electrode paste layer 24ATN. Then, an additional negative electrode paste PAF may be applied to form an additional negative electrode paste layer 24ATF. This is dried and cut to form the unpenetrated negative electrode plate 14.

[0090] Alternatively, only the same non-containing negative electrode paste PAN as before may be applied to the wide negative electrode foil 24F and dried to form a non-containing negative electrode active material layer. Then, a solution (such as a solution of water, alcohol, or organic solvent) containing a separately prepared film-forming substance CS may be applied to a strip-shaped portion that becomes the central portion 14AM of the negative electrode active material layer 14A, dried, and cut to form the unpenetrated negative electrode plate 14. Alternatively, after applying only the non-containing negative electrode paste PAN, a solution containing the film-forming substance CS may be applied before drying or during semi-drying, and dried and cut together with the non-containing negative electrode paste PAN to form the unpenetrated negative electrode plate 14.

[0091] Also, for example, in the embodiment, a strip-shaped additional negative electrode active material layer 14AF containing the film-forming substance CS was formed in the central portion 14AM in the width direction WH of the negative electrode active material layer 14A of the unpenetrated negative electrode plate 14 forming the unpenetrated electrode body 12. On the other hand, in the unpenetrated separator 15 forming the unpenetrated electrode body 12, a strip-shaped additional layer containing the film-forming substance CS may be formed in the central portion in the width direction WH, that is, in the portion facing the central portion 14AM in the width direction WH of the negative electrode active material layer 14A. This strip-shaped additional layer may be formed by applying the above-mentioned solution containing the film-forming substance CS to the unpenetrated separator 15. Further, a strip-shaped additional positive electrode active material layer containing a film-forming material CS may be formed in the central portion in the width direction WH of the positive electrode active material layer 13A of the unpenetrated positive electrode plate 13 forming the unpenetrated electrode body 12. Furthermore, among the unpenetrated negative electrode plate 14, the unpenetrated separator 15, and the unpenetrated positive electrode plate 13, which all contain the film-forming material CS, two or all of them may be combined to form the unpenetrated electrode body 12.

Explanation of Signs

[0092] 1,1C1,1C2 Battery (Power Storage Device) 2,2C1,2C2 Electrode Body 2M Central Portion 3 Positive Electrode Plate 4 Negative Electrode Plate 4A Negative Electrode Active Material Layer AW Width Dimension (of Negative Electrode Active Material Layer) 4AE1,4AE2 Edges (in Width Direction) 4AP Negative Electrode Active Material Particles 4AC Negative Electrode SEI Film 5 Separator 6 Electrolyte 6V Organic Solvent 6VE Ethylene Carbonate 6VL Other Solvents 7 Case 12,12C1,12C2 Unpenetrated Electrode Body 12M Central Portion 13 Unpenetrated Positive Electrode Plate 14 Unpenetrated Negative Electrode Plate (Additional Negative Electrode Plate) 14C1,14C2 Unpenetrated Negative Electrode Plate 14N Negative Electrode Portion 14A Negative Electrode Active Material Layer 14AE1,14AE2 Edges (in Width Direction) ML Center Line 14AM Central Portion 14AS1 One Side Portion (Edge Side Portion) 14AS2 The Other Side Portion (Edge Side Portion) CS Film-Forming Material CS1 Ethylene Carbonate EL Distance 14AF Additional negative electrode active material layer 14AN1, 14AN2, 14AN Negative electrode active material layer-free 14AP Negative electrode active material particles PAF Additional negative electrode paste PAN Negative electrode paste-free AX Winding axis XH Axis direction XH1 One side XH2 The other side XHI Inner side XHO Outer side WH Width direction WH1 One side WH2 The other side WHI Inner side WHO Outer side S1 Electrode body forming process (unpenetrated electrode body forming process) S11 Unpenetrated negative electrode plate forming process (additional negative electrode plate forming process) S2 Accommodation process S3 Liquid injection process S4 Standby process TT Standby time S5 Initial charging process

Claims

1. An electrolytic solution containing ethylene carbonate and a solvent having a melting point lower than that of ethylene carbonate, A wound electrode body having a strip-shaped positive electrode plate, a strip-shaped negative electrode plate having a strip-shaped negative electrode active material layer, and a strip-shaped separator, and the electrolytic solution penetrating therein, A case containing the electrode body and the electrolytic solution, In the electrode body, the width dimension of the negative electrode active material layer is 180 mm or more A method for manufacturing a power storage device, An unpenetrated electrode body forming step of forming an unpenetrated wound electrode body in which the electrolytic solution does not penetrate, A housing step of housing the unpenetrated electrode body in the case, A liquid injection step of injecting the electrolytic solution into the case containing the unpenetrated electrode body, A standby step of waiting for the elapse of a predetermined standby time during which the electrolytic solution penetrates throughout the unpenetrated electrode body after the liquid injection step, An initial charging step of performing an initial charge to form a negative electrode SEI film on the negative electrode active material layer after the standby step, The unpenetrated electrode body forming step includes A step of forming the unpenetrated electrode body in which ethylene carbonate for forming the negative electrode SEI film on the negative electrode active material layer is previously arranged at the central portion in the axial direction of the unpenetrated electrode body, Among the strip-shaped negative electrode active material layers, while making the central portion in the width direction into a strip-shaped additional negative electrode active material layer containing ethylene carbonate, the edge side portions on both sides in the width direction are respectively strip-shaped non-containing negative electrode active material layers not containing ethylene carbonate, and an additional negative electrode plate forming step of forming an additional negative electrode plate is included A method for manufacturing a power storage device.

2. A method for manufacturing a power storage device according to claim 1, The additional negative electrode plate forming step includes Using a non-containing negative electrode paste containing negative electrode active material particles but not containing ethylene carbonate to form the non-containing negative electrode active material layer, Forming the additional negative electrode active material layer using the additional negative electrode paste containing the negative electrode active material particles and ethylene carbonate Method for manufacturing a power storage device.

3. A method for manufacturing a power storage device according to claim 1 or claim 2, wherein The additional negative electrode plate forming step is Of the strip-shaped negative electrode active material layer, the central portion that is 80 mm or more away from both end edges in the width direction is used as the additional negative electrode active material layer Method for manufacturing a power storage device.

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