Non-aqueous electrolyte secondary battery

Abstract

A non-aqueous electrolyte secondary battery according to an embodiment of the present disclosure comprises: an electrode group including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; and a nonaqueous electrolyte. The positive electrode comprises a positive electrode current collector and a positive electrode mixture layer disposed on at least one surface of the positive electrode current collector. The negative electrode comprises a negative electrode current collector and a lithium layer disposed on at least one surface of the negative electrode current collector, and includes a negative electrode current collector exposure section where the lithium layer is not disposed. The lithium layer includes at least one of a lithium metal and a lithium alloy. The negative electrode encompasses a first negative electrode edge region including one width-direction end of the negative electrode and a second negative electrode edge region including the other width-direction end of the negative electrode. The first negative electrode edge region and the second negative electrode edge region include at least one of a facing section facing the positive electrode mixture layer and a non-facing section not facing the positive electrode mixture layer. Additionally, in at least one of the first negative electrode edge region and the second negative electrode edge region, the negative electrode current collector exposure section is disposed in at least one of the facing section and the non-facing section.

Description

Nonaqueous electrolyte secondary battery

[0001] This invention relates to a non-aqueous electrolyte secondary battery.

[0002] A non-aqueous electrolyte secondary battery comprises an electrode group and a non-aqueous electrolyte. The electrode group includes, for example, a strip-shaped positive electrode, a strip-shaped negative electrode, and a strip-shaped separator placed between the positive and negative electrodes. Examples of non-aqueous electrolyte secondary batteries include lithium-ion batteries and lithium secondary batteries. In a lithium secondary battery, lithium metal is deposited on the negative electrode during charging, and the lithium metal is dissolved in the non-aqueous electrolyte during discharge. The lithium metal dissolved in the non-aqueous electrolyte is then released as lithium ions in the non-aqueous electrolyte. A lithium secondary battery is also called a lithium metal secondary battery, and a lithium metal secondary battery is synonymous with a metallic lithium secondary battery, which will be described later.

[0003] During the charging and discharging of lithium secondary batteries, significant volume changes occur in the electrode group due to the deposition and dissolution of lithium metal as described above. Large volume changes in the electrode group can lead to damage to the separator and internal short circuits, potentially reducing the cycle life. Therefore, various studies are being conducted to suppress large volume changes in the electrode group.

[0004] Patent Document 1 discloses a metallic lithium secondary battery in which a negative electrode, which uses lithium or a lithium alloy as the negative electrode active material, and a positive electrode, which is made of a rechargeable material, are arranged opposite each other via a separator, and the metallic lithium secondary battery is characterized in that there is a buffer space between the negative electrode or the positive electrode and the separator for accommodating lithium deposited on the surface of the negative electrode. Furthermore, Patent Document 1 discloses that in a metallic lithium secondary battery with the above configuration, lithium deposited on the surface of the negative electrode can be accommodated in the buffer space formed between the negative electrode or the positive electrode and the separator, thereby preventing damage to the separator and preventing abnormal deposition of lithium. Moreover, Patent Document 1 discloses that in a metallic lithium secondary battery, by preventing damage to the separator and abnormal deposition of lithium, internal short circuits are suppressed, and as a result, the battery life can be extended.

[0005] Japanese Patent Application Publication No. 10-12279

[0006] As described above, various publicly available documents, including Patent Document 1, have examined configurations to address the reduction in cycle life of lithium secondary batteries caused by internal short circuits resulting from at least one of separator damage and abnormal lithium deposition. However, it is difficult to say that sufficient consideration has been given to configurations to address the reduction in cycle life of lithium secondary batteries caused by factors other than those mentioned above. Therefore, there is room for further investigation into suppressing the reduction in cycle life.

[0007] Therefore, the objective of this disclosure is to provide a non-aqueous electrolyte secondary battery that can suppress the reduction in cycle life.

[0008] One aspect of the present invention relates to a non-aqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery comprises an electrode group including a strip-shaped positive electrode, a strip-shaped negative electrode, and a strip-shaped separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The positive electrode comprises a strip-shaped positive electrode current collector and a positive electrode mixture layer disposed on at least one surface of the positive electrode current collector. The negative electrode comprises a strip-shaped negative electrode current collector and a strip-shaped lithium layer disposed on at least one surface of the negative electrode current collector, and has an exposed portion of the negative electrode current collector where the lithium layer is not disposed. The lithium layer includes at least one of lithium metal and lithium alloy. The negative electrode includes a first negative electrode edge region including one end in the width direction of the negative electrode, and a second negative electrode edge region including the other end in the width direction of the negative electrode. The first negative electrode edge region and the second negative electrode edge region include at least one of a facing portion facing the positive electrode mixture layer and a non-facing portion not facing the positive electrode mixture layer. In at least one of the first negative pole edge region and the second negative pole edge region, the exposed portion of the negative electrode current collector is located in at least one of the opposing portion and the non-opposing portion.

[0009] According to this disclosure, it is possible to provide a non-aqueous electrolyte secondary battery that can suppress the reduction in cycle life.

[0010] This is a cross-sectional view in the width direction of an electrode group according to the first embodiment. This is a cross-sectional view in the width direction of an electrode group according to the second embodiment. This is a cross-sectional view in the width direction of an electrode group according to the third embodiment. This is a cross-sectional view in the width direction of an electrode group according to the fourth embodiment. This is a cross-sectional view in the width direction of an electrode group according to the fifth embodiment. This is a cross-sectional view in the width direction of an electrode group according to the sixth embodiment. This is a schematic cross-sectional view showing a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure.

[0011] The embodiments of this disclosure will be described below with examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be given as examples, but other numerical values, materials, etc. may be applied as long as the effects of this disclosure are obtained. Notwithstanding, known components may be applied to components of parts that are characteristic of this disclosure. In this specification, when "the range of numerical values ​​A to numerical values ​​B" is used, that range includes numerical values ​​A and B.

[0012] In the following explanation, when examples are given for the lower and upper limits of numerical values ​​related to specific physical properties or conditions, any combination of either of the given lower limits and any of the given upper limits is permitted, as long as the lower limit does not exceed the upper limit. When multiple materials are given as examples, unless otherwise specified, one type may be selected and used alone, or two or more types may be used in combination.

[0013] This disclosure includes any combination of two or more claims that can be arbitrarily selected from the claims set forth in the attached claims. In other words, any combination of two or more claims that can be arbitrarily selected from the claims set forth in the attached claims is possible, as long as it does not result in a technical inconsistency.

[0014] [Non-aqueous electrolyte secondary battery] A non-aqueous electrolyte secondary battery according to the embodiment of the present disclosure comprises an electrode group including a strip-shaped positive electrode, a strip-shaped negative electrode, and a strip-shaped separator disposed between the positive electrode and the negative electrode.

[0015] In the non-aqueous electrolyte secondary battery according to the embodiments of this disclosure, the positive electrode comprises a strip-shaped positive electrode current collector and a positive electrode mixture layer disposed on at least one surface of the positive electrode current collector. In the non-aqueous electrolyte secondary battery according to the embodiments of this disclosure, the negative electrode comprises a strip-shaped negative electrode current collector and a strip-shaped lithium layer disposed on at least one surface of the negative electrode current collector, and has an exposed portion of the negative electrode current collector where the lithium layer is not disposed. In the non-aqueous electrolyte secondary battery according to the embodiments of this disclosure, the lithium layer comprises at least one of lithium metal and lithium alloy.

[0016] In the non-aqueous electrolyte secondary battery according to the embodiment of the present disclosure, the negative electrode includes a first negative electrode edge region including one end in the width direction of the negative electrode, and a second negative electrode edge region including the other end in the width direction of the negative electrode. In the non-aqueous electrolyte secondary battery according to the embodiment of the present disclosure, the first negative electrode edge region and the second negative electrode edge region include at least one of a facing portion facing the positive electrode mixture layer and a non-facing portion not facing the positive electrode mixture layer. In the non-aqueous electrolyte secondary battery according to the embodiment of the present disclosure, in at least one of the first negative electrode edge region and the second negative electrode edge region, the exposed portion of the negative electrode current collector is arranged in at least one of the facing portion and the non-facing portion.

[0017] In the non-aqueous electrolyte secondary battery according to the embodiment of this disclosure, it is important that (i) the negative electrode has an exposed portion of the negative electrode current collector on which the lithium layer is not disposed; (ii) the negative electrode includes a first negative electrode edge region including one end in the width direction of the negative electrode and a second negative electrode edge region including the other end in the width direction of the negative electrode; (iii) the first negative electrode edge region and the second negative electrode edge region include at least one of a facing portion that faces the positive electrode mixture layer and a non-facing portion that does not face the positive electrode mixture layer; and (iv) in at least one of the first negative electrode edge region and the second negative electrode edge region, the exposed portion of the negative electrode current collector is disposed on at least one of the facing portion and the non-facing portion. The reasons for this will be explained below.

[0018] A non-aqueous electrolyte secondary battery comprises an electrode group including a strip-shaped positive electrode, a strip-shaped negative electrode, and a strip-shaped separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. In a non-aqueous electrolyte secondary battery, the negative electrode may comprise a strip-shaped negative electrode current collector and a lithium layer disposed on at least one surface of the negative electrode current collector. In such a non-aqueous electrolyte secondary battery, lithium metal precipitates on the surface of the negative electrode through charging, and the lithium metal precipitated on the surface of the negative electrode dissolves as lithium ions into the non-aqueous electrolyte through discharging.

[0019] In the non-aqueous electrolyte secondary battery as described above, the negative electrode expands due to the lithium metal precipitated on the surface of the negative electrode during charging. When the negative electrode expands, the separator becomes pressed toward the positive electrode, which may cause stress due to pressing in the separator. When the stress generated in the separator becomes excessively large, damage occurs to the separator. When such damage occurs to the separator, an internal short circuit occurs inside the non-aqueous electrolyte secondary battery. As described above, when an internal short circuit occurs inside the non-aqueous electrolyte secondary battery, the cycle life of the non-aqueous electrolyte secondary battery decreases. Note that the above stress tends to concentrate on both end sides in the width direction of the strip-shaped separator, so damage to the separator is particularly likely to occur remarkably on both end sides in the width direction of the separator.

[0020] Here, the non-aqueous electrolyte secondary battery according to an embodiment of the present disclosure is configured to satisfy the above (i) to (iv). In short, a space for alleviating expansion of the negative electrode accompanying precipitation of lithium metal is formed between the separator and at least one of the first negative electrode edge region and the second negative electrode edge region where the exposed portion of the negative electrode current collector is disposed. Therefore, it is possible to suppress an excessive increase in stress generated in the separator due to pressing from the negative electrode, and thus it is possible to suppress the occurrence of damage to the separator. In particular, the occurrence of damage to the separator can be suppressed at both end sides in the width direction of the separator where stress concentration is likely to occur. Accordingly, the occurrence of an internal short circuit inside the non-aqueous electrolyte secondary battery can be suppressed, and thus a decrease in the cycle life of the non-aqueous electrolyte secondary battery can be suppressed.

[0021] As described above, the non-aqueous electrolyte secondary battery according to the embodiment of this disclosure includes a strip-shaped negative electrode, the negative electrode comprising a strip-shaped negative electrode current collector and a strip-shaped lithium layer disposed on at least one surface of the negative electrode current collector. In such a non-aqueous electrolyte secondary battery, lithium metal is deposited on the surface of the negative electrode by charging, and the lithium metal deposited on the surface of the negative electrode dissolves as lithium ions in the non-aqueous electrolyte by discharging. Therefore, the negative electrode may be an electrode in which lithium metal is deposited during charging and the lithium metal dissolves in the non-aqueous electrolyte during discharge. Such a non-aqueous electrolyte secondary battery is also called a lithium secondary battery (or lithium metal secondary battery). Hereinafter, the configuration of the non-aqueous electrolyte secondary battery according to the embodiment of this disclosure will be specifically described using a lithium secondary battery as an example.

[0022] In lithium secondary batteries, for example, more than 70% of the rated capacity is generated by the deposition and dissolution of lithium metal. The movement of electrons at the negative electrode during charging and discharging is mainly caused by the deposition and dissolution of lithium metal at the negative electrode. Specifically, 70-100% of the electron movement (or current, from another perspective) at the negative electrode during charging and discharging is caused by the deposition and dissolution of lithium metal. The electron movement at the negative electrode during charging and discharging may be 80-100% or 90-100% caused by the deposition and dissolution of lithium metal. Therefore, the negative electrode of a lithium secondary battery differs from that of a lithium-ion secondary battery, where the electron movement during charging and discharging is mainly caused by the intercalation and release of lithium ions in the negative electrode active material (e.g., graphite).

[0023] (Negative Electrode) A lithium secondary battery includes a strip-shaped negative electrode. The negative electrode includes a strip-shaped negative electrode current collector and a strip-shaped lithium layer disposed on at least one surface of the negative electrode current collector. In a lithium secondary battery, lithium metal is precipitated on the surface of the negative electrode by charging. More specifically, lithium ions contained in the non-aqueous electrolyte receive electrons on the surface of the negative electrode during charging, become lithium metal, and precipitate on the surface of the negative electrode. The lithium metal precipitated on the surface of the negative electrode dissolves as lithium ions into the non-aqueous electrolyte during discharging. The surface of the negative electrode means both the surface of the negative electrode current collector and the surface of the lithium layer. That is, lithium metal precipitates on both the surface of the negative electrode current collector and the surface of the lithium layer during charging.

[0024] The lithium layer contains at least one of lithium metal and a lithium alloy. The lithium layer may be a lithium metal layer, a lithium alloy layer, or a layer containing both lithium metal and a lithium alloy. The lithium alloy layer is composed of lithium and one or more elements other than lithium. Examples of the other elements (for example, other metal elements) include magnesium, aluminum, indium, copper, zinc, potassium, calcium, sodium, silver, and gold. The content of the other elements may be 5% by mass or less (for example, 3% by mass or less). When the negative electrode includes the lithium layer, even if lithium ions are deactivated during charge and discharge of the non-aqueous electrolyte secondary battery, the deactivated lithium ions can be compensated.

[0025] The method for forming the lithium layer is not particularly limited, and various known methods may be applied. For example, the lithium layer may be formed by pressing a lithium foil onto the negative electrode current collector (first embodiment). The lithium layer may be formed by vapor deposition (second embodiment). The lithium layer may be formed using a resin sheet on which the lithium layer is formed (third embodiment). As an example of obtaining a lithium layer in the third embodiment, first, the resin sheet on which the lithium layer is formed and the negative electrode current collector are laminated and pressed so that the lithium layer and the negative electrode current collector are in contact. Next, the resin sheet is peeled off to obtain a negative electrode current collector on which the lithium layer is formed. Methods using a resin sheet on which the lithium layer is formed and vapor deposition are suitable for forming a thin lithium layer.

[0026] The configuration of the negative electrode will be described in detail below with reference to Figures 1A to 1E. Figures 1A to 1E show an example of an electrode group 14 including a positive electrode 11, a negative electrode 12, and a separator 13 placed between the positive electrode 11 and the negative electrode 12. The electrode groups shown in Figures 1A to 1E are electrode groups according to the first to fifth embodiments, respectively. In the electrode group 14 shown in Figures 1A to 1E, the positive electrode 11 comprises a positive electrode current collector 11A and a positive electrode mixture layer 11B disposed on the surface of the positive electrode current collector 11A, and the negative electrode 12 comprises a negative electrode current collector 12A and a lithium layer 12B disposed on the surface of the negative electrode current collector 12A. Figures 1A to 1E all show a cross-section in the width direction W of the electrode group 14. First, an example of the configuration of the negative electrode 12 will be described with reference to Figures 1A to 1C.

[0027] As shown in Figures 1A to 1C, the negative electrode 12 has an exposed portion 12C of the negative electrode current collector where the lithium layer 12B is not arranged. The negative electrode 12 also includes a first negative electrode edge region NE1 including one end E1 in the width direction W of the negative electrode 12, and a second negative electrode edge region NE2 including the other end E2 in the width direction W of the negative electrode 12. In the example shown in Figure 1A, the first negative electrode edge region NE1 and the second negative electrode edge region NE2 include a facing portion O that faces the positive electrode mixture layer 11B, and a non-facing portion NO that does not face the positive electrode mixture layer 11B. In contrast, in the example shown in Figure 1B, the first negative pole edge region NE1 and the second negative pole edge region NE2 include only the non-opposing portion NO that does not face the positive electrode mixture layer 11B, and in the example shown in Figure 1C, the first negative pole edge region NE1 and the second negative pole edge region NE2 include only the opposing portion O that faces the positive electrode mixture layer 11B. Therefore, it is preferable that the first negative pole edge region NE1 and the second negative pole edge region NE2 include at least one of the opposing portion O that faces the positive electrode mixture layer 11B and the non-opposing portion NO that does not face the positive electrode mixture layer 11B. However, in lithium secondary batteries, from the viewpoint of suitably exhibiting capacity, it is preferable that the first negative pole edge region NE1 and the second negative pole edge region NE2 include both the opposing portion O and the non-opposing portion NO. That is, among Figures 1A to 1C, the configuration shown in Figure 1A is preferred.

[0028] The first negative pole edge region NE1 refers to the region inside the negative electrode 12 up to 1.5 mm from one end E1 in the width direction W (in other words, one end E1 in the width direction W of the negative electrode current collector 12A) when the total length WL in the width direction W of the negative electrode current collector 12A is 50 mm or more, and to the region inside the negative electrode 12 up to WL × 0.03 from one end E1 in the width direction W of the negative electrode current collector 12A when the total length WL in the width direction W of the negative electrode current collector 12A is less than 50 mm. For example, when WL is 50 mm and when WL is 100 mm, the first negative pole edge region NE1 is the region inside the negative electrode 12 up to 1.5 mm from one end E1 in the width direction W of the negative electrode 12. Also, when WL is 40 mm, the first negative pole edge region NE1 is the region inside the negative electrode 12 up to 1.2 mm (40 × 0.03) from one end E1 in the width direction W of the negative electrode 12. The second negative pole edge region NE2 has the same meaning as the first negative pole edge region NE1, except that one end E1 in the width direction W of the negative pole 12 is read as the other end E2 in the width direction W of the negative pole 12.

[0029] In the examples shown in Figures 1A to 1C, the exposed portion 12C of the negative electrode current collector is located in both the first negative electrode edge region NE1 and the second negative electrode edge region NE2. On the other hand, the exposed portion 12C of the negative electrode current collector may be located in either the first negative electrode edge region NE1 or the second negative electrode edge region NE2. That is, the exposed portion 12C of the negative electrode current collector is located in at least one of the first negative electrode edge region NE1 and the second negative electrode edge region NE2. Also, in the examples shown in Figures 1A and 1B, the exposed portion 12C of the negative electrode current collector is not facing the positive electrode mixture layer 11B. That is, in the examples shown in Figures 1A and 1B, the lithium layer 12B is formed to be wider than the positive electrode mixture layer 11B, and the exposed portion 12C of the negative electrode current collector is located outside both ends of the positive electrode mixture layer 11B in the width direction W. On the other hand, in the example shown in Figure 1C, the exposed portion 12C of the negative electrode current collector faces the positive electrode mixture layer 11B. That is, in the example shown in Figure 1C, the lithium layer 12B is formed to be narrower than the positive electrode mixture layer 11B, and the exposed portion 12C of the negative electrode current collector is positioned inward from both ends of the positive electrode mixture layer 11B in the width direction W.

[0030] In the examples shown in Figures 1A and 1B, the exposed portion 12C of the negative electrode current collector is located in the non-opposing portion NO in the first negative pole edge region NE1 and the second negative pole edge region NE2, while in the example shown in Figure 1C, the exposed portion 12C of the negative electrode current collector is located in the opposing portion O in the first negative pole edge region NE1 and the second negative pole edge region NE2.

[0031] Next, other configuration examples of the negative electrode 12 will be described with reference to Figures 1D and 1E.

[0032] In the example shown in Figure 1D, the exposed portion 12C of the negative electrode current collector has a first portion C1 facing the positive electrode mixture layer 11B and a second portion C2 that does not face the positive electrode mixture layer 11B. That is, in the example shown in Figure 1D, the lithium layer 12B is formed to be narrower than the positive electrode mixture layer 11B, and the exposed portion 12C of the negative electrode current collector is positioned not only outside both ends of the positive electrode mixture layer 11B in the width direction W, but also inside.

[0033] The example shown in Figure 1E is similar to the example shown in Figure 1D in that the exposed portion 12C of the negative electrode current collector has a first portion C1 and a second portion C2, but differs from the example shown in Figure 1D in that the lithium layer 12B is intermittently arranged on the surface of the negative electrode current collector 12A. The lithium layer 12B is formed to be narrower than the positive electrode mixture layer 11B and is similar to the example shown in Figure 1D in that it includes a main layer portion 12BM facing the positive electrode mixture layer 11B, but differs from the example shown in Figure 1D in that it includes a layer end portion 12BE that includes one end E1 and the other end E2 in the width direction E of the negative electrode current collector 12A, respectively. Therefore, the exposed surface of the exposed portion 12C of the negative electrode current collector is smaller in the example shown in Figure 1E by the amount of the layer end portion 12BE compared to the example shown in Figure 1D. In the example shown in Figure 1E, the lithium layer 12B can be formed, for example, by placing a first lithium foil or the like at a location corresponding to the main layer portion 12BM of the negative electrode current collector 12A, and then placing a second lithium foil or the like at a location corresponding to the end portion 12BE of the negative electrode current collector 12A.

[0034] In the examples shown in Figures 1D and 1E, the exposed portion 12C of the negative electrode current collector is located on both the opposing portion O and the non-opposing portion NO in the first negative pole edge region NE1 and the second negative pole edge region NE2. Therefore, considering the examples shown in Figures 1A to E, it can be seen that in the first negative pole edge region NE1 and the second negative pole edge region NE2, the exposed portion 12C of the negative electrode current collector is located on at least one of the opposing portion O and the non-opposing portion NO.

[0035] In addition, although the above describes a configuration in which the exposed portion 12C of the negative electrode current collector is arranged in both the first negative electrode edge region NE1 and the second negative electrode edge region NE2, the exposed portion 12C of the negative electrode current collector only needs to be arranged in at least one of the first negative electrode edge region NE1 and the second negative electrode edge region NE2. Furthermore, from the viewpoint of forming a space to mitigate the expansion of the negative electrode at the widthwise end where separator damage is particularly likely to occur, it is preferable that in at least one of the first negative electrode edge region NE1 and the second negative electrode edge region NE2, the exposed portion 12C of the negative electrode current collector occupies 5.0% or more of the non-facing portion NO that does not face the positive electrode mixture layer 11B, more preferably occupies 15.0% of the non-facing portion NO, and even more preferably occupies the entire area of ​​the non-facing portion NO.

[0036] When the area of ​​the positive electrode side surface in the exposed portion of the negative electrode current collector is S0, the area of ​​the positive electrode side surface in the first negative electrode edge region is S1, and the area of ​​the positive electrode side surface in the second negative electrode edge region is S2, at least one of the ratio of S0 to S1 (S0 / S1 × 100) and the ratio of S0 to S2 (S0 / S2 × 100) is preferably 6.6% or more, and more preferably 19.2% or more. By having the ratio of S0 to S1 and the ratio of S0 to S2 within the above range, a more sufficient area can be secured in the first negative electrode edge region and the second negative electrode edge region where the exposed portion of the negative electrode current collector is located. Therefore, a more sufficient space can be secured between the first negative electrode edge region and the strip-shaped separator, and between the second negative electrode edge region and the separator, to mitigate the expansion of the negative electrode due to the deposition of lithium metal. On the other hand, in lithium secondary batteries, from the viewpoint of securing a lithium layer that can fully realize capacity, at least one of the ratio of S0 to S1 and the ratio of S0 to S2 is preferably 70% or less, and more preferably 50% or less. Taking the above into consideration, at least one of the ratio of S0 to S1 and the ratio of S0 to S2 is preferably 6.6% or more and 70% or less, and more preferably 19.2% or more and 50% or less.

[0037] Areas S0, S1, and S2 can be calculated using a digital microscope. Specifically, after capturing images of the first and second negative extreme edge regions using a digital microscope, areas S0, S1, and S2 can be calculated using the digital microscope's automatic area measurement function based on the captured images. For example, a digital microscope such as the VHX-7000 manufactured by KEYENCE can be used.

[0038] When lithium foil is used to construct the lithium layer 12B, the proportion of the exposed portion of the negative electrode current collector can be adjusted, for example, by limiting the area on the negative electrode current collector 12A where the lithium layer 12B is placed. Alternatively, when the lithium layer 12B is constructed as a plating layer, the proportion of the exposed portion of the negative electrode current collector can be adjusted, for example, by the size of the mask covering the area on the negative electrode current collector 12A where the lithium layer 12B is not placed. In this case, the plating layer is formed in the area not covered by the mask.

[0039] The lithium layer comprises a pair of first lithium layer regions positioned at both edges in the width direction, and a second lithium layer region positioned between the pair of first lithium layer regions. Preferably, at least one of the pair of first lithium layer regions includes a thin-walled portion that is thinner than the second lithium layer region. By including such a thin-walled portion, the lithium layer can form a space to mitigate the expansion of the negative electrode due to the deposition of lithium metal, thereby further improving the durability of the non-aqueous electrolyte secondary battery. The first lithium layer region refers to the region inside the lithium layer from one end to 10% of the total width of the lithium layer, and the second lithium layer region refers to the region inside the lithium layer from the other end to 10% of the total width of the lithium layer. The shape of the thin-walled portion is not particularly limited. The thin-walled portion may be linearly sloped from the boundary between the second lithium layer region and the first lithium layer region to one end of the lithium layer, or it may be curved from the boundary between the second lithium layer region and the first lithium layer region to one end of the lithium layer. The curve may be convex upwards or convex downwards. Furthermore, the first lithium layer region may be formed to have a step difference with respect to the second lithium layer region. In other words, the first lithium layer region may be formed to have a stepped shape with respect to the second lithium layer region.

[0040] The negative electrode may include a lithium ion storage layer supported on the negative electrode current collector. In this case, it is preferable that a lithium layer is arranged on one surface of the negative electrode current collector and the lithium ion storage layer is supported on the other surface of the negative electrode current collector. The lithium ion storage layer is a layer that exhibits capacity through the absorption and release of lithium ions by the negative electrode active material such as graphite. In this case, the open-circuit potential of the negative electrode when fully charged may be 70 mV or less relative to the lithium metal (lithium dissolution and release potential). In this case, lithium metal is present on the surface of the lithium ion storage layer when fully charged. Therefore, even when the negative electrode is configured in this way, capacity is exhibited through the deposition and dissolution of lithium metal.

[0041] Here, "fully charged" refers to the state when the battery is charged to a charge level of, for example, 0.98 × C or higher, where C is the rated capacity of the battery. The open-circuit potential of the negative electrode at full charge can be measured by disassembling the fully charged battery under an argon atmosphere, removing the negative electrode, and assembling a cell with lithium metal as the counter electrode. The non-aqueous electrolyte contained in the cell may have the same composition as the non-aqueous electrolyte contained in the disassembled battery.

[0042] The lithium-ion storage layer is formed by creating layers of a negative electrode composite material containing a negative electrode active material. In addition to the negative electrode active material, the negative electrode composite material may also contain binders, thickeners, and conductive agents.

[0043] Examples of negative electrode active materials include carbonaceous materials, Si-containing materials, and Sn-containing materials. The negative electrode may contain one type of negative electrode active material alone, or it may contain a combination of two or more types of negative electrode active materials. Examples of carbonaceous materials include graphite, easily graphitizable carbon (soft carbon), and poorly graphitizable carbon (hard carbon).

[0044] The conductive agent is, for example, a carbon material. Examples of carbon materials include carbon black, carbon nanotubes, and graphite. Examples of carbon black include acetylene black and Ketjenblack.

[0045] Examples of binders include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubbery polymers. Examples of fluororesins include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF).

[0046] On the other hand, from the viewpoint of ensuring sufficient battery discharge capacity and improving volumetric energy density, it is preferable that the negative electrode does not contain the lithium-ion storage layer mentioned above.

[0047] The negative electrode current collector can be any conductive sheet. Examples of conductive sheets include foil and film.

[0048] The material forming the negative electrode current collector can be any conductive material other than lithium metal and lithium alloys. The conductive material may be a metallic material such as metals and alloys. It is preferable that the conductive material is one that does not react with lithium. Examples of such conductive materials include copper (Cu), nickel (Ni), iron (Fe), and alloys containing these metallic elements, or graphite in which the basal surface is preferentially exposed. Examples of alloys include copper alloys and stainless steel (SUS). Among these conductive materials, it is preferable to use at least one of copper and copper alloys because they have high conductivity. Alternatively, a laminated sheet may be used as the negative electrode current collector, in which a metal such as copper or nickel, or an alloy such as a copper alloy, nickel alloy, or stainless steel is laminated on the surface of a resin film. The material forming the resin film is not particularly limited and examples include polyester, polyethylene, polypropylene, polyamide, and polyimide. Examples of polyester include polyethylene terephthalate (PET) and polybutylene terephthalate (PBT).

[0049] The thickness of the negative electrode current collector is not particularly limited, but is, for example, 5 μm or more and 300 μm or less.

[0050] (Positive electrode) The positive electrode comprises, for example, a positive electrode current collector and a positive electrode mixture layer disposed on at least one surface of the positive electrode current collector. The positive electrode mixture layer includes, for example, a positive electrode active material, a conductive agent, and a binder. The positive electrode mixture layer may be disposed on only one side of the positive electrode current collector or on both sides of the positive electrode current collector. The positive electrode can be obtained, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder to at least one surface of the positive electrode current collector to form a coating, and then drying this coating. The dried coating may be rolled.

[0051] The positive electrode active material is a material capable of intercalating and releasing lithium ions. Examples of positive electrode active materials include lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, and transition metal sulfides. Due to their low manufacturing cost and high average discharge voltage, lithium-containing transition metal oxides are preferred as the positive electrode active material.

[0052] During charging, lithium contained in the lithium-containing transition metal oxide is released from the positive electrode as lithium ions and deposited as lithium metal on the surface of the negative electrode. The surface of the negative electrode also includes the surface of the negative electrode current collector. During discharge, lithium metal dissolves from the negative electrode, releasing lithium ions, which are then absorbed into the lithium-containing transition metal oxide contained in the positive electrode. Therefore, the lithium ions involved in charging and discharging generally originate from the solute in the non-aqueous electrolyte and the positive electrode active material.

[0053] Examples of transition metal elements included in lithium-containing transition metal oxides include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, and W. Lithium-containing transition metal oxides may contain one transition metal element alone or a combination of two or more transition metal elements. The transition metal element may be at least one selected from the group consisting of Ni, Co, and Mn. Lithium-containing transition metal oxides may optionally contain one or more main group elements. Examples of main group elements include Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, and Bi. Lithium-containing transition metal oxides preferably contain Al as a main group element.

[0054] Among lithium-containing transition metal oxides, it is preferable to use a composite oxide that contains at least one transition metal element selected from the group consisting of Ni, Co, and Mn, has a layered structure, and has a rock salt-type crystalline structure. Such a composite oxide may also contain Al, a typical element, as an optional component. Such a composite oxide is advantageous in that it contributes to increasing the capacity of lithium secondary batteries. In a lithium secondary battery using such a composite oxide as the positive electrode active material, the molar ratio (MLi / mM) of the total amount of lithium in the positive and negative electrodes (MLi) to the amount of metal M other than lithium in the positive electrode (mM) is set to, for example, 1.1 or less.

[0055] The binder and conductive agent can be those exemplified for the negative electrode.

[0056] The positive electrode current collector can be any conductive sheet. Examples of conductive sheets include foil and film.

[0057] Examples of materials for forming the positive electrode current collector (conductive sheet) include metallic materials such as metals and alloys. Examples of metals include Al and Ti, and examples of alloys include Al alloys, Ti alloys, and Fe alloys. Fe alloys may be stainless steel (SUS). Alternatively, a laminated sheet may be used as the positive electrode current collector, in which a metal such as aluminum or titanium, or an alloy such as an aluminum alloy or stainless steel, is laminated on the surface of a resin film. The material for forming the resin film is not particularly limited and examples include polyester, polyethylene, polypropylene, polyamide, and polyimide. Examples of polyesters include polyethylene terephthalate (PET) and polybutylene terephthalate (PBT).

[0058] The thickness of the positive electrode current collector is not particularly limited, but is, for example, 5 μm or more and 30 μm or less.

[0059] (Separator) As described above, in this embodiment, the separator has a strip shape. The separator comprises at least a strip-shaped base material. Preferably, a spacer is placed between the separator and at least one of the positive electrode and the negative electrode. Preferably, the spacer is placed between the separator and the positive electrode. The spacer may be placed as a component of the separator between the separator and at least one of the positive electrode and the negative electrode, or as a component of at least one of the positive electrode and the negative electrode between the separator and at least one of the positive electrode and the negative electrode. When the spacer is a component of the separator, the separator comprises a base material and a spacer placed on one surface of the base material. Below, the case in which the spacer is a component of the separator will be mainly described as an example.

[0060] When a separator comprises a substrate and a spacer disposed on one surface of the substrate, such a separator is arranged in the electrode group as shown in Figure 1F. Specifically, as shown in Figure 1F, the separator 13 comprises a substrate 13A and a spacer 13B disposed on one surface of the substrate 13A, and in the electrode group 14, the spacer 13B is positioned on the surface opposite to the positive electrode 11 (more specifically, the strip-shaped positive electrode mixture layer 11B). By providing the spacer 13B in the separator 13, a space can be formed between the positive electrode mixture layer 11B and the substrate 13A. Furthermore, even if the negative electrode expands due to lithium metal deposited on the surface of the negative electrode during charging, this space can reduce the volume change of the electrode group 14. This improves the cycle characteristics of the lithium secondary battery.

[0061] As the substrate, a porous sheet having ion permeability and insulating properties is used. Examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. The material constituting the porous sheet is not particularly limited, and examples include polymer materials. Examples of polymer materials include olefin resins, polyamide resins, and cellulose. Examples of olefin resins include polyethylene, polypropylene, and copolymers of ethylene and propylene. The substrate may contain additives as needed. Examples of additives include inorganic fillers.

[0062] The thickness of the substrate is not particularly limited, and is, for example, 5 μm or more and 20 μm or less. Preferably, the thickness of the substrate is 10 μm or more and 20 μm or less.

[0063] The substrate may include a porous sheet and a composite material layer (heat-resistant layer). The composite material layer may be located on one surface of the porous sheet or on both surfaces. The composite material layer is a layer that allows lithium ions to pass through. The composite material layer contains inorganic particles. The composite material layer may optionally contain a resin material. The thickness of the composite material layer may be 5% to 50% of the total thickness of the substrate.

[0064] The composite material layer may be placed on the surface facing the positive electrode or on the surface facing the negative electrode in the porous sheet. When the composite material layer is placed on the surface facing the positive electrode, degradation of the porous sheet due to oxidation can be suppressed. When the composite material layer is placed on the surface facing the negative electrode, degradation of the porous sheet due to reduction can be suppressed. As described above, if the separator is equipped with a spacer, the spacer may be placed on the composite material layer. In this case, the effect of suppressing thermal shrinkage of the substrate is enhanced.

[0065] Considering the possibility of abnormal heat generation inside the battery due to a short circuit, it is preferable to use inorganic compound particles that have thermal stability and insulating properties as inorganic particles. Examples of inorganic particles include inorganic oxides, inorganic hydroxides, inorganic nitrides, inorganic carbides, and inorganic sulfides. Examples of inorganic oxides include aluminum oxide, boehmite, magnesium oxide, titanium oxide, zirconium oxide, silicon oxide, yttrium oxide, and zinc oxide. Examples of inorganic nitrides include silicon nitride, aluminum nitride, boron nitride, and titanium nitride. Examples of inorganic carbides include silicon carbide and carbon-boron. Examples of inorganic sulfides include barium sulfate. Examples of inorganic hydroxides include aluminum hydroxide. The average particle size of the inorganic particles may be 0.2 to 2.0 μm.

[0066] The average particle size of inorganic particles can be determined as the median diameter (D50) in a volume-based particle size distribution. The median diameter in a volume-based particle size distribution of inorganic particles can be measured, for example, using a laser diffraction / scattering particle size distribution analyzer (e.g., Microtrac manufactured by Nikkiso Co., Ltd.). Alternatively, the average particle size of inorganic particles may be determined using images taken with a transmission electron microscope (TEM). For example, a cross-section of a substrate can be observed with a transmission electron microscope (TEM) to take a TEM image, the area (area of ​​the portion enclosed by the contour) of any 100 inorganic particles in the image can be calculated, the diameter of an equivalent circle (true circle) having the same area as each of the calculated areas can be determined, and these can be arithmetically averaged to obtain the average particle diameter of the inorganic particles.

[0067] Examples of resin materials included in the composite material layer (heat-resistant layer) include fluororesins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene; fluororubbers such as vinylidene fluoride-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer; styrene-butadiene copolymer or its hydride, acrylonitrile-butadiene copolymer or its hydride, methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, ethylene propylene rubber, polyvinyl alcohol, and polyvinyl acetate. Examples include rubbers; cellulose derivatives such as ethylcellulose, methylcellulose, hydroxyethylcellulose, and carboxymethylcellulose; acrylic resins such as acrylic acid-methacrylic acid copolymers; polyphenylene ethers; polysulfones; polyethersulfones; polyphenylene sulfides; polyetherimides; polyimides; polyamides such as fully aromatic polyamides (aramids); polyimides; polyacrylonitriles; polyvinyl alcohols; polyethers; polyacrylic acid; polymethacrylic acid; polyesters; polyolefins; silicone resins; urethane resins; melamine resins; urea resins; epoxy resins, etc.

[0068] It is preferable to use a polymer material as the resin material included in the composite material layer (heat-resistant layer). It is preferable that such a polymer material has higher heat resistance than the polymer material constituting the porous sheet. It is preferable that such a polymer material includes at least one selected from the group consisting of aromatic polyamide, aromatic polyimide, and aromatic polyamide-imide. All of these have high heat resistance. From the viewpoint of heat resistance, it is preferable to use aramid as the polymer material. In other words, it is preferable to use meta-aramid (meta-total aromatic polyamide) or para-aramid (para-total aromatic polyamide) as the polymer material.

[0069] The inorganic particle content in the composite material layer may be in the range of 50% to 99% by mass, or in the range of 85% to 99% by mass.

[0070] A composite material layer can be obtained, for example, by applying a coating solution containing inorganic particles, a resin material, and a liquid component (dispersion medium) to a porous sheet to form a coating film, and then drying this coating film. Examples of liquid components include N-methyl-2-pyrrolidone.

[0071] The spacer is placed, for example, on one surface of the substrate. It is preferable that the substrate and the spacer are integrated, as this facilitates the fabrication of the electrode group. The spacer may be placed on the surface of the substrate facing the positive electrode, on the surface facing the negative electrode, or on both the surface facing the positive electrode and the surface facing the negative electrode. Alternatively, the spacer may be placed on the surface facing the separator at the positive electrode, or on the surface facing the separator at the negative electrode.

[0072] When a spacer is placed on the substrate surface facing the positive electrode, compared to when the spacer is placed on the substrate surface facing the negative electrode, Li precipitates between the spacers in a way that stretches the substrate towards the positive electrode. This creates compressive stress on the precipitated Li, making it easier for the Li to precipitate densely. When Li precipitates densely in this way, the discharge efficiency and cycle characteristics of the lithium secondary battery are improved. Therefore, from the viewpoint of improving the discharge efficiency and cycle characteristics of the lithium secondary battery, it is preferable to place the spacer on the substrate surface facing the positive electrode.

[0073] When a spacer is placed on the surface of the substrate facing the negative electrode, a space is pre-formed between the substrate and the negative electrode, which reduces the tensile load on the substrate that occurs as Li precipitates. This makes it easier to maintain the insulating properties of the substrate and also easier to maintain its short-circuit resistance.

[0074] In lithium-ion batteries, the main role of the spacer is to create a space for the deposition of lithium metal. By housing the lithium metal within the space provided by the spacer, the expansion of the negative electrode during charging can be suppressed.

[0075] The spacer may contain a resin material (for example, an insulating resin), or it may contain a resin material and particles. The proportion of resin material in the spacer may be 10% by volume or more, 30% by volume or more, or 50% by volume or more. Alternatively, the proportion of resin material in the spacer may be 100% by volume or less, or 80% by volume or less.

[0076] The resin material used in the spacer can be the same as the resin material used in the composite material layer.

[0077] It is preferable to use a resin material that does not allow lithium ions to permeate the resin material contained in the spacer. Suitable resin materials include, for example, polyimide, polyvinylidene fluoride, and acrylonitrile-acrylic acid ester copolymers, with polyimide being particularly preferred. A non-porous spacer formed using these resin materials to have a certain height or higher is a layer that does not allow lithium ions to permeate. Because the spacer is formed in a non-porous manner as described above, it is possible to suppress an increase in the gas generation reaction rate when an internal short circuit occurs in a lithium secondary battery.

[0078] The particles may be inorganic or organic. Inorganic particles are preferred, and among inorganic particles, inorganic oxides, inorganic hydroxides, inorganic nitrides, inorganic carbides, and inorganic sulfides are preferred. Examples of inorganic oxides include aluminum oxide (alumina and boehmite), magnesium oxide, titanium oxide (titania), zirconium oxide, and silicon oxide (silica). Examples of inorganic hydroxides include aluminum hydroxide. Examples of inorganic nitrides include silicon nitride, aluminum nitride, boron nitride, and titanium nitride. Examples of inorganic carbides include silicon carbide and boron carbide. Examples of inorganic sulfides include barium sulfate. Furthermore, examples of inorganic particles include aluminosilicates, layered silicates, barium titanate, and strontium titanate. Among the above inorganic particles, alumina, silica, and titania are preferred.

[0079] The average particle size is not particularly limited and may be 0.1 μm or more, or 0.5 μm or more. The average particle size may be 10 μm or less, 5 μm or less, or 2 μm or less. The average particle size can be measured by the following method. First, the cross-section of the spacer in the thickness direction of the separator is photographed with an electron microscope to obtain an image of the cross-section. Next, image processing such as binarization is performed on this image to identify the particle portion. Next, for any number of particles (for example, 100 or more), the diameter of a circle having the same area as the cross-sectional area (equivalent circle diameter) is calculated for each particle, and the average particle size can be measured by taking the arithmetic mean of each of the calculated equivalent circle diameters.

[0080] When the spacer contains resin material and particles, it is preferable that the particle content in the spacer be 50% by volume or less. This makes it possible to obtain a spacer with sufficient strength.

[0081] The spacer includes protrusions. The spacer may include at least one of linear protrusions and dot-shaped protrusions. In one view, the linear protrusions are ridge-shaped protrusions. The linear protrusions may be intermittently arranged or continuously arranged. The linear protrusions may be straight or curved.

[0082] The width of the linear protrusion may be 100 μm or more, or 200 μm or more. The width of the linear protrusion may be 2000 μm or less, or 1000 μm or less.

[0083] The spacer preferably has a predetermined repeating pattern. In other words, it is preferable that the protrusions are arranged in a predetermined repeating pattern. Linear protrusions may be arranged in a stripe pattern or in a mesh pattern. The mesh pattern may be an aggregate of polygons. The mesh pattern may include, for example, shapes in which polygons are combined so as to share sides. Polygons include triangles, quadrilaterals, and hexagons. A mesh pattern may be formed by combining polygons having different shapes. The mesh pattern may be honeycomb-shaped. In addition, dot-shaped protrusions may be arranged in a predetermined repeating pattern.

[0084] The thickness of the spacer (height of the protrusion) TC may be greater than the thickness of the base material T. The ratio of height TC to thickness T, TC / T, may be greater than 1, 1.5 or more, or 2 or more. TC / T may be 5 or less, 4 or less, or 3 or less. From the viewpoint of suppressing the expansion of the electrode group, TC / T may be, for example, greater than 1 and 3 or less. Also, TC / T may be between 1.5 and 3.

[0085] The spacer thickness (height of the protrusion) TC can be measured, for example, by photographing the spacer with a laser microscope to obtain a height profile, and then using this height profile. Specifically, TC can be determined by selecting six arbitrary points in the height profile, measuring the thickness (height of the protrusion) of the spacer at these six points, and then taking the arithmetic mean of the obtained measurements. For example, a hybrid laser microscope manufactured by Lasertec can be used as the laser microscope.

[0086] The thickness T of the substrate can be measured using a contact-type thickness measuring device. Specifically, after selecting any six locations on the substrate, the thickness of each location is measured using the contact-type thickness measuring device, and the thickness can be calculated by taking the arithmetic mean of the obtained measurements. As a contact-type thickness measuring device, for example, the thickness measuring device (PEACOCK) manufactured by Ozaki Seisakusho Co., Ltd. can be used.

[0087] Spacers can be formed, for example, by applying a coating solution containing the spacer components and liquid components to a predetermined location on a substrate to obtain a coating film, and then drying this coating film. For example, N-methyl-2-pyrrolidone can be used as the liquid component. Coating may be carried out using a dispenser or by various known printing methods such as gravure printing, inkjet printing, and screen printing. The coating film may be heat-dried or air-dried. The thickness of the spacer can be adjusted by adjusting the amount of coating solution applied or by adjusting the viscosity of the coating solution. Spacers can also be formed on the surface of the positive electrode (the surface facing the separator) and on the surface of the negative electrode (the surface facing the separator) in the same manner as described above.

[0088] (Non-aqueous electrolytes) Non-aqueous electrolytes are ionic conductive (e.g., lithium ion conductive). Non-aqueous electrolytes may be liquid electrolytes (electrolytes), gel electrolytes, or solid electrolytes. A liquid electrolyte is, for example, an electrolyte containing a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. The concentration of the lithium salt in the electrolyte is, for example, 0.5 mol / L or more and 2 mol / L or less. The electrolyte may contain various known additives.

[0089] The gel electrolyte contains a lithium salt and a matrix polymer, or contains a non-aqueous solvent in addition to a lithium salt and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels is used. Examples of the polymer material include fluororesins, acrylic resins, polyether resins, and polyethylene oxide.

[0090] As the solid electrolyte, for example, various known materials used in all-solid lithium ion secondary batteries and the like can be mentioned. Examples of such solid electrolytes include oxide-based solid electrolytes, sulfide-based solid electrolytes, and halide-based solid electrolytes.

[0091] A liquid non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent. When the lithium salt dissolves in the non-aqueous solvent, lithium ions and anions are generated.

[0092] The anions include BF ４ － , ClO ４ － , PF ６ － , CF ３ SO ３ － , CF ３ CO ２ － , anions of imides, and anions of oxalate complexes. Examples of the anions of imides include N(SO ２ CF ３ ) ２ － , N(C ｍ F2 ｍ＋１ SO ２ ) ｘ (C ｎ F ２ｎ＋１ SO ２ ) ｙ －Examples include the following. Note that m and n are each independently 0 or an integer greater than or equal to 1, and x and y are each independently 0, 1 or 2, satisfying x + y = 2. The anion of the oxalate complex may contain at least one of boron and phosphorus. Examples of anions of the oxalate complex include the bisoxalate borate anion and the difluorooxalate borate anion (BF ２ (C ２ O ４ ) ― ), PF ４ (C ２ O ４ ) － , and PF ２ (C ２ O ４ ) ２ － These are some examples. The liquid non-aqueous electrolyte may contain one of these anions alone, or it may contain two or more in combination.

[0093] From the viewpoint of suppressing the dendritic deposition of lithium metal, the liquid non-aqueous electrolyte preferably contains at least an oxalate complex anion. Furthermore, the oxalate complex anion preferably contains fluorine. The interaction between the fluorine-containing oxalate complex anion and lithium makes it easier to uniformly precipitate lithium metal in fine particulate form. Therefore, localized deposition of lithium metal can be suppressed. The fluorine-containing oxalate complex anion may be combined with other anions. The other anions are PF ６ － And at least one of the anions of the imide group.

[0094] Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and halogen-substituted derivatives thereof. The liquid non-aqueous electrolyte may contain one non-aqueous solvent alone or a combination of two or more. Examples of halogen-substituted derivatives include fluorides.

[0095] Examples of esters include carbonate esters and carboxylic acid esters. Examples of carbonate esters include cyclic carbonate esters and linear carbonate esters. Examples of cyclic carbonate esters include ethylene carbonate (EC), propylene carbonate (PC), and fluoroethylene carbonate (FEC). FEC has the function of forming a film on the surface of the negative electrode, as will be described later. Examples of linear carbonate esters include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate. Examples of carboxylic acid esters include cyclic carboxylic acid esters and linear carboxylic acid esters. Examples of cyclic carboxylic acid esters include γ-butyrolactone and γ-valerolactone. Examples of linear carboxylic acid esters include ethyl acetate, methyl propionate, and methyl fluoropropionate.

[0096] Examples of ethers include cyclic ethers and linear ethers. Examples of cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran. Examples of linear ethers include 1,2-dimethoxyethane, diethyl ether, ethyl vinyl ether, methylphenyl ether, benzyl diethyl ether, diphenyl ether, dibenzyl ether, 1,2-diethoxyethane, and diethylene glycol dimethyl ether.

[0097] The concentration of lithium salt in the liquid non-aqueous electrolyte is, for example, 0.5 mol / L or more and 3.5 mol / L or less. In the liquid non-aqueous electrolyte, the concentration of the anion may be 0.5 mol / L or more and 3.5 mol / L or less. In addition, in the liquid non-aqueous electrolyte, the concentration of the oxalate complex anion may be 0.5 mol / L or more and 3.5 mol / L or less.

[0098] The liquid non-aqueous electrolyte may contain additives. The additives may form a film on the surface of the negative electrode. The formation of a film derived from the additive on the surface of the negative electrode makes it easier to suppress dendrite formation. Examples of such additives include vinylene carbonate, FEC, and vinyl ethyl carbonate (VEC).

[0099] Below, an example of a non-aqueous electrolyte secondary battery of this disclosure will be described in detail with reference to the drawings. The components of the example non-aqueous electrolyte secondary battery described below can be the components described above. Furthermore, the components of the example described below can be modified based on the above. In addition, in the non-aqueous electrolyte secondary battery described below, components that are not essential to the non-aqueous electrolyte secondary battery of this disclosure may be omitted. Note that the scale of the components in the following figures has been changed to facilitate understanding.

[0100] Figure 1 is a schematic longitudinal cross-sectional view showing a lithium secondary battery as an example of a non-aqueous electrolyte secondary battery according to Embodiment 1. The cylindrical lithium secondary battery 10 shown in Figure 1 includes a cylindrical battery case, a wound electrode group 14 housed inside the battery case, and a non-aqueous electrolyte (not shown). The battery case includes a case body 15, which is a bottomed cylindrical metal container, and a sealing body 16 that seals the opening of the case body 15. A gasket 27 is placed between the case body 15 and the sealing body 16. The gasket 27 ensures the airtightness of the battery case. Inside the case body 15, insulating plates 17 and 18 are placed at both ends of the electrode group 14 in the winding axis direction, respectively.

[0101] The case body 15 has, for example, a stepped portion 21 formed by partially pressing the side wall of the case body 15 from the outside. The stepped portion 21 may be formed in an annular shape along the circumferential direction of the case body 15 on the side wall of the case body 15. In this case, the sealing body 16 is supported on the opening side surface of the stepped portion 21.

[0102] The sealing body 16 includes a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26. In the sealing body 16, these members are stacked in this order. The sealing body 16 is fitted into the opening of the case body 15 such that the cap 26 is located on the outside of the case body 15 and the filter 22 is located on the inside of the case body 15. Each of the above-mentioned members constituting the sealing body 16 has, for example, a disc shape or a ring shape. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, with the insulating member 24 interposed at their respective peripheries. The filter 22 and the lower valve body 23 are connected to each other at their respective centers. The upper valve body 25 and the cap 26 are connected to each other at their respective centers. Therefore, each member except the insulating member 24 is electrically connected to each other.

[0103] The lower valve body 23 has a ventilation hole (not shown) formed therein. Therefore, if the internal pressure of the battery case rises due to abnormal heat generation or the like, the upper valve body 25 bulges towards the cap 26 and separates from the lower valve body 23. This interrupts the electrical connection between the lower valve body 23 and the upper valve body 25. If the internal pressure rises further, the upper valve body 25 ruptures, and gas is released from an opening (not shown) formed in the cap 26.

[0104] The electrode group 14 includes a positive electrode 11, a negative electrode 12, and a separator 13. The separator 13 has a base material. A spacer may be placed on one surface of the base material of the separator 13. The positive electrode 11, the negative electrode 12, and the separator 13 are all strip-shaped. The base material of the separator 13 also has a strip shape. The electrode group 14 is formed by winding the strip-shaped positive electrode 11, the strip-shaped negative electrode 12, and the strip-shaped separator 13 in the longitudinal direction so that the strip-shaped separator 13 is placed between the strip-shaped positive electrode 11 and the strip-shaped negative electrode. If the strip-shaped separator 13 comprises a strip-shaped base material and a spacer placed on one surface of the strip-shaped base material, it is preferable that the spacer is placed on the surface of the strip-shaped base material facing the strip-shaped positive electrode 11.

[0105] (Note) The following technologies are disclosed as described above. (Technical 1) An electrode group comprising a strip-shaped positive electrode, a strip-shaped negative electrode, and a strip-shaped separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein the positive electrode comprises a strip-shaped positive electrode current collector and a positive electrode mixture layer disposed on at least one surface of the positive electrode current collector, the negative electrode comprises a strip-shaped negative electrode current collector and a strip-shaped lithium layer disposed on at least one surface of the negative electrode current collector, and has an exposed portion of the negative electrode current collector where the lithium layer is not disposed, the lithium layer comprises at least one of lithium metal and lithium alloy, the negative electrode comprises a first negative electrode edge region including one end in the width direction of the negative electrode, and a second negative electrode edge region including the other end in the width direction of the negative electrode, the first negative electrode edge region and the second negative electrode edge region each include at least one of a facing portion facing the positive electrode mixture layer and a non-facing portion not facing the positive electrode mixture layer. (Technical 2) A non-aqueous electrolyte secondary battery, wherein in at least one of the first negative pole edge region and the second negative pole edge region, the exposed portion of the negative electrode current collector is located in at least one of the opposing portion and the non-opposing portion. (Technical 1) The non-aqueous electrolyte secondary battery according to Technical 1, wherein in at least one of the first negative pole edge region and the second negative pole edge region, the exposed portion of the negative electrode current collector is located in the entire area of ​​the non-opposing portion. (Technical 3) The non-aqueous electrolyte secondary battery according to Technical 1 or 2, wherein the lithium layer has a pair of first lithium layer regions located on both end edges in the width direction and a second lithium layer region located between the pair of first lithium layer regions, and at least one of the pair of first lithium layer regions includes a thin-walled portion that is thinner than the second lithium layer region. (Technology 4) A non-aqueous electrolyte secondary battery according to any one of Technologies 1 to 3, wherein when the area of ​​the positive electrode side surface in the exposed portion of the negative electrode current collector is S0, the area of ​​the positive electrode side surface in the first negative electrode edge region is S1, and the area of ​​the positive electrode side surface in the second negative electrode edge region is S2, at least one of the ratio of S0 to S1 (S0 / S1 × 100) and the ratio of S0 to S2 (S0 / S2 × 100) is 6.6% or more.(Technology 5) The non-aqueous electrolyte secondary battery according to Technology 4, wherein at least one of the ratio of S0 to S1 (S0 / S1 × 100) and the ratio of S0 to S2 (S0 / S2 × 100) is 19.2% or more. (Technology 6) The non-aqueous electrolyte secondary battery according to any one of Technology 1 to 5, wherein a spacer is disposed between the separator and at least one of the positive electrode and the negative electrode. (Technology 7) The non-aqueous electrolyte secondary battery according to any one of Technology 1 to 6, wherein the negative electrode is an electrode in which lithium metal is deposited during charging and the lithium metal dissolves in the non-aqueous electrolyte during discharge.

[0106] The present disclosure will be described below in detail based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0107] (Example 1) (1) Preparation of the positive electrode A positive electrode slurry was prepared by mixing a positive electrode active material, acetylene black (AB, conductive agent), polyvinylidene fluoride (PVdF, binder), and an appropriate amount of N-methyl-2-pyrrolidone (NMP). A rock salt type lithium-containing transition metal oxide (NCA) having a layered structure and containing Li, Ni, Co, and Al was used as the positive electrode active material. In the NCA, the molar ratio of Li to the total of Ni, Co, and Al was 1.0. In the positive electrode slurry, the mass ratio of NCA, AB, and PVdF was NCA:AB:PVdF = 95:2.5:2.5. The positive electrode slurry was applied to both sides of a strip-shaped Al foil (positive electrode current collector) to obtain a coating film, and then this coating film was dried. Then, the dried coating film was rolled to form positive electrode mixture layers on both sides of the positive electrode current collector. The positive electrode current collector, with positive electrode mixture layers formed on both sides, was cut to a predetermined size to obtain the positive electrode according to Example 1.

[0108] (2) Manufacturing of the negative electrode As the negative electrode according to Example 1, a strip of copper foil (negative electrode current collector) with a strip of lithium layer formed on one side was prepared. The lithium layer was formed by pressing and bonding the lithium foil to the copper foil. The strip of lithium layer was laminated on the strip of copper foil so that the length direction and width direction coincided. The negative electrode according to Example 1 was configured as shown in Figure 1A. Specifically, the negative electrode 12 had exposed portions 12C of the negative electrode current collector in both the first negative electrode edge region NE1 including one end E1 in the width direction W of the negative electrode 12 and the second negative electrode edge region NE2 including the other end E2 in the width direction W of the negative electrode. In addition, the exposed portions 12C of the negative electrode current collector and the positive electrode mixture layer 11B were not facing each other. Furthermore, the exposed portions 12C of the negative electrode current collector extended to one end E1 and the other end E2 in the width direction W, respectively.

[0109] (3) Preparation of the substrate A 10 μm thick microporous thin film (substrate) made of polyethylene was prepared. A coating solution containing paraphenylene terephthalamide (aromatic polyamide) and alumina (inorganic particles) as resin materials was applied to one surface of the microporous thin film to form a coating film. As the solvent for the coating solution, N-methyl-2-pyrrolidone in which 5.8% by mass of calcium chloride was dissolved was used. The coating solution was also made to contain 2% by mass of aromatic polyamide and 4% by mass of alumina. The substrate with the coating film was left for 1 hour in an atmosphere of 25°C and 70% relative humidity to precipitate aromatic polyamide on the surface of the substrate. Next, the surface of the substrate was washed with water to remove NMP and calcium chloride from the coating film. Next, the coating film was dried at 60°C for 5 minutes to form a composite material layer (heat-resistant layer) on one surface of the substrate. This obtained a substrate having a composite material layer.

[0110] A coating solution containing polyvinylidene fluoride and alumina particles (inorganic filler) was applied to the surface of the composite material layer on the substrate to form a coating film, which was then dried. This formed a honeycomb-shaped spacer on the composite material layer of the substrate. In this way, a separator was obtained in which the composite material layer and spacer were formed in this order on the surface of the substrate.

[0111] In the spacer, the width of the linear protrusion was set to 0.25 mm (250 μm), and the thickness (height) TC of the spacer was set to 30 μm.

[0112] (4) Preparation of non-aqueous electrolytes 1,2-dimethoxyethane (DME) and 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether (CHF ２ (CF ２ OCH ２ ) CF ３ A mixed solvent containing ) and in a volume ratio of 1:2 was prepared. In addition to dissolving lithium bissulfonyliimide (LiFSI) at a concentration of 1 mol / L in this mixed solvent, LiBF was added. ２ (C ２ O ４ A liquid non-aqueous electrolyte was prepared by dissolving ) at a concentration of 0.1 mol / L.

[0113] (5) Fabrication of a non-aqueous electrolyte secondary battery An electrode group was fabricated by spirally winding a strip-shaped positive electrode and a strip-shaped negative electrode in an inert gas atmosphere with a strip-shaped separator in between. The separator was positioned so that the side on which the spacer was formed faced the positive electrode. Furthermore, when the area of ​​the surface on the positive electrode 11 side in the exposed portion 12C of the negative electrode current collector was defined as S0, the area of ​​the surface on the positive electrode 11 side in the first negative electrode edge region NE1 was defined as S1, and the area on the positive electrode 11 side in the second negative electrode edge region NE2 was defined as S2, the ratio of S0 to S1 (S0 / S1 × 100) and the ratio of S0 to S2 (S0 / S2 × 100) were both 4.2%.

[0114] After housing the electrode group in a bottomed cylindrical case body, a non-aqueous electrolyte was injected into the case body. Next, a sealing body was placed at the opening of the case body via a gasket, sealing the electrode group and non-aqueous electrolyte in the battery case. In this way, a non-aqueous electrolyte secondary battery (lithium secondary battery) with the structure shown in Figure 2 was completed.

[0115] (Example 2) A non-aqueous electrolyte secondary battery according to Example 2 was completed in the same manner as in Example 1, except that the ratio of S0 to S1 (S0 / S1 × 100) and the ratio of S0 to S2 (S0 / S2 × 100) in the negative electrode were both set to 6.6%.

[0116] (Example 3) A non-aqueous electrolyte secondary battery according to Example 3 was completed in the same manner as in Example 1, except that the ratio of S0 to S1 (S0 / S1 × 100) and the ratio of S0 to S2 (S0 / S2 × 100) in the negative electrode were both set to 19.2%.

[0117] (Example 4) A non-aqueous electrolyte secondary battery according to Example 4 was completed in the same manner as in Example 1, except that the ratio of S0 to S1 (S0 / S1 × 100) and the ratio of S0 to S2 (S0 / S2 × 100) in the negative electrode were both set to 40%.

[0118] (Example 5) The negative electrode according to Example 5 was configured as shown in Figure 1D. Specifically, the negative electrode 12 had exposed portions 12C of the negative electrode current collector in both a first negative electrode edge region NE1 including one end E1 in the width direction W of the negative electrode 12, and a second negative electrode edge region NE2 including the other end E2 in the width direction W of the negative electrode. Furthermore, the exposed portions 12C of the negative electrode current collector were located in both the non-facing and facing portions with respect to the positive electrode mixture layer 11B. In addition, the exposed portions 12C of the negative electrode current collector extended to both one end E1 and the other end E2 in the width direction W. The ratio of S0 to S1 (S0 / S1 × 100) and the ratio of S0 to S2 (S0 / S2 × 100) were both set to 19.2%. Except for these, the non-aqueous electrolyte secondary battery according to Example 5 was completed in the same manner as in Example 1.

[0119] (Example 6) The negative electrode according to Example 6 was configured as shown in Figure 1E. Specifically, the lithium layer 12B was configured to have layer ends 12BE that include one end E1 and the other end E2 in the width direction W of the negative electrode current collector 12A, respectively, except that the negative electrode was configured in the same manner as in Example 5. In addition, the ratio of S0 to S1 (S0 / S1 × 100) and the ratio of S0 to S2 (S0 / S2 × 100) were both set to 19.2%. The non-aqueous electrolyte secondary battery according to Example 6 was completed in the same manner as in Example 1.

[0120] (Comparative Example 1) A non-aqueous electrolyte secondary battery according to Comparative Example 1 was completed in the same manner as in Example 1, except that the negative electrode was constructed by arranging a strip-shaped lithium layer on one side of a strip-shaped negative electrode current collector 12A so as not to have an exposed portion 12C of the negative electrode current collector. That is, in the negative electrode of Comparative Example 1, the dimensions in the length direction and width direction of the strip-shaped lithium layer 12B were the same as the dimensions in the length direction and width direction of the strip-shaped negative electrode current collector 12A.

[0121] [Evaluation] <Number of cycles when abnormal charging occurs> Charge-discharge tests were conducted using the non-aqueous electrolyte secondary batteries related to each example (Examples 1 to 6 and Comparative Example 1). Specifically, 10 mA / cm ２ After performing constant current charging up to a voltage of 4.1V with the specified current, 1mA / cm² was applied at a voltage of 4.1V. ２ Constant voltage charging is performed until the current reaches 10 mA / cm². ２ Charge-discharge tests were conducted on each example of non-aqueous electrolyte secondary battery, with one cycle defined as constant current discharge until the voltage reached 3.0V. For each example of non-aqueous electrolyte secondary battery, if the charge capacity in one cycle was 1% or more greater than the charge capacity in the cycle immediately preceding it, it was evaluated that abnormal charging had occurred in that cycle due to an internal short circuit. The number of cycles up to the first cycle was evaluated as the number of cycles when abnormal charging occurred. The results are shown in Table 1 below. Note that "No abnormality" in Table 1 means that even after conducting charge-discharge tests until the discharge capacity of the first cycle was 90%, the phenomenon of the charge capacity in one cycle being 1% or more greater than the charge capacity in the cycle immediately preceding it did not occur. In addition, Table 1 also shows, for each example, the ratio of S0 to S1 and the ratio of S0 to S2, whether or not the exposed portion of the negative electrode current collector faced the positive electrode mixture layer, and whether or not the negative electrode current collector was exposed at both ends in the width direction.

[0122]

[0123] Table 1 shows that in the non-aqueous electrolyte secondary batteries of each example (Examples 1 to 6), the evaluation of the number of cycles when abnormal charging occurred was either "no abnormality" or 200 cycles or more, whereas in the non-aqueous electrolyte secondary battery of Comparative Example 1, the evaluation of the number of cycles when abnormal charging occurred was less than 100 cycles. Furthermore, comparing the non-aqueous electrolyte secondary batteries of Examples 1 to 4, it can be seen that the higher the ratio of S0 to S1 and the ratio of S0 to S2 in the non-aqueous electrolyte secondary battery, the better the evaluation of the number of cycles when abnormal charging occurred. From this, it can be seen that in a non-aqueous electrolyte secondary battery, when there is "no" opposition between the exposed portion of the negative electrode current collector and the positive electrode mixture layer, and there is "exposed" portion of the negative electrode current collector at both ends in the width direction, the larger the proportion of the exposed portion of the negative electrode current collector, the more the decrease in cycle life can be suppressed. Furthermore, comparing the non-aqueous electrolyte secondary batteries of Examples 5 and 6, it can be seen that when there is an exposed portion of the negative electrode current collector at both ends in the width direction, the evaluation of the number of cycles in which abnormal charging occurs is good. From this, it can be seen that in non-aqueous electrolyte secondary batteries, having an exposed portion of the negative electrode current collector at both ends in the width direction can suppress the decrease in cycle life.

[0124] Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

[0125] The non-aqueous electrolyte secondary battery described herein can be used in applications where it is required to suppress a decrease in cycle life.

[0126] 10: Non-aqueous electrolyte secondary battery, 11: Positive electrode, 12: Negative electrode, 13: Separator, 14: Electrode group

Claims

An electrode group including a strip-shaped positive electrode, a strip-shaped negative electrode, and a strip-shaped separator disposed between the positive electrode and the negative electrode, A non-aqueous electrolyte is provided, The positive electrode comprises a strip-shaped positive electrode current collector and a positive electrode mixture layer disposed on at least one surface of the positive electrode current collector. The negative electrode comprises a strip-shaped negative electrode current collector and a strip-shaped lithium layer disposed on at least one surface of the negative electrode current collector, and has an exposed portion of the negative electrode current collector where the lithium layer is not disposed. The lithium layer comprises at least one of lithium metal and lithium alloy. The negative electrode includes a first negative electrode edge region including one end in the width direction of the negative electrode, and a second negative electrode edge region including the other end in the width direction of the negative electrode. The first negative edge region and the second negative edge region include at least one of a facing portion that faces the positive electrode mixture layer and a non-facing portion that does not face the positive electrode mixture layer. In at least one of the first negative pole edge region and the second negative pole edge region, the exposed portion of the negative electrode current collector is located in at least one of the opposing portion and the non-opposing portion. Nonaqueous electrolyte secondary battery. 　 The exposed portion of the negative electrode current collector is located in at least one of the first negative electrode edge region and the second negative electrode edge region, and is arranged over the entire area of ​​the non-facing portion. The non-aqueous electrolyte secondary battery according to claim 1. 　 The lithium layer comprises a pair of first lithium layer regions arranged on both end edges in the width direction, and a second lithium layer region arranged between the pair of first lithium layer regions. At least one of the pair of first lithium layer regions includes a thin-walled portion that is thinner than the second lithium layer region. The non-aqueous electrolyte secondary battery according to claim 1. 　 When the area of ​​the positive electrode side surface in the exposed portion of the negative electrode current collector is S0, the area of ​​the positive electrode side surface in the first negative electrode edge region is S1, and the area of ​​the positive electrode side surface in the second negative electrode edge region is S2, At least one of the ratio of S0 to S1 (S0 / S1 × 100) and the ratio of S0 to S2 (S0 / S2 × 100) is 6.6% or more. A non-aqueous electrolyte secondary battery according to any one of claims 1 to 3. 　 At least one of the ratio of S0 to S1 (S0 / S1 × 100) and the ratio of S0 to S2 (S0 / S2 × 100) is 19.2% or more. The non-aqueous electrolyte secondary battery according to claim 4. 　 The spacer is positioned between the separator and at least one of the positive electrode and the negative electrode. A non-aqueous electrolyte secondary battery according to any one of claims 1 to 3. 　 The negative electrode is an electrode in which lithium metal is deposited during charging and the lithium metal dissolves in the non-aqueous electrolyte during discharge. A non-aqueous electrolyte secondary battery according to any one of claims 1 to 3.

Images