Lithium battery

Abstract

To realize high-performance lithium batteries. [Solution] The lithium battery includes an electrode 200 having a current collector 210 and an active material layer 220 in which the current collector 210 is embedded. The electrode 200 has a gap 240 at its end face 230 that divides the active material layer 220 into two parts 221 and 222 on one side and the other side in its thickness direction D3. By providing such a gap 240 at the end face 230 of the electrode 200, the absorption of the electrolyte used in the lithium battery from the electrode 200 is enhanced. This improves the performance of the lithium battery.

Description

Technical Field

[0007] ,

[0001] The present invention relates to a lithium battery.

Background Art

[0002] There is known a battery in which an electrode plate for a battery, in which a current collector's width-direction end face or both the width-direction end face and the length-direction end face are covered with an active material layer or an insulating layer so that the current collector is not exposed, is housed together with an electrolytic solution in an exterior body (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a lithium battery including an electrode in which a current collector is embedded in an active material layer, sufficient battery performance may not be obtained depending on the configuration of the electrode. On one side, the present invention aims to realize a high-performance lithium battery.

Means for Solving the Problems

Effects of the Invention

[0006] On one side, it becomes possible to realize a high-performance lithium battery. [[ID=5B]]

Brief Description of the Drawings

[0007] [Figure 1]This is a diagram illustrating an example of a lithium battery. [Figure 2] This is a diagram (part 1) illustrating an example of an electrode formation method. [Figure 3] This is a diagram (part 2) illustrating an example of an electrode formation method. [Figure 4] This is a diagram (part 3) illustrating an example of an electrode formation method. [Figure 5] This diagram illustrates an example of electrode configuration. [Modes for carrying out the invention]

[0008] Figure 1 illustrates an example of a lithium battery. Figure 1 schematically shows a cross-sectional view of the main components of an example of a lithium battery. Here, we will use a cylindrical lithium battery (also called a "primary lithium battery") 1 as an example. The lithium battery 1 shown in Figure 1 comprises an outer casing 10, battery elements 20, electrolyte 30, insulating plate 40, insulating plate 50, sealing body 60, gasket 70, positive terminal 80, and washer 90.

[0009] The outer container 10 is a bottomed cylindrical conductive container with one end open. The outer container 10 is made of materials such as steel, nickel-plated steel, or stainless steel. The battery element 20 is an example of a power generation element housed within the outer casing 10. Figure 1 illustrates, as an example, a battery element 20 having a configuration including a sheet-shaped positive electrode 21, a sheet-shaped negative electrode 22, and a sheet-shaped separator 23. The battery element 20 has a so-called spiral electrode structure in which the positive electrode 21 and the negative electrode 22 are wound in a spiral shape via the separator 23.

[0010] The positive electrode 21 of the battery element 20 uses a positive electrode material containing a positive electrode active material. Manganese dioxide (MnO2) or the like is used as the positive electrode active material. The positive electrode 21 may be formed by laminating the positive electrode material on a core made of stainless steel or the like, which functions as a current collector. A conductive positive electrode tab 21a is connected to the positive electrode 21.

[0011] The negative electrode 22 of the battery element 20 uses a negative electrode material containing a negative electrode active material. Lithium is used as the negative electrode active material. Examples of negative electrode materials containing a negative electrode active material include metallic lithium (Li), or lithium alloys such as lithium aluminum (LiAl) alloy, lithium magnesium (LiMg) alloy, lithium tin (LiSn) alloy, lithium zinc (LiZn) alloy, lithium antimony (LiSb) alloy, and lithium silicon (LiSi) alloy. The negative electrode 22 may be formed by laminating the negative electrode material on a core body such as copper that functions as a current collector. A conductive negative electrode tab 22a is connected to the negative electrode 22.

[0012] The positive electrode 21 and the negative electrode 22 are wound around each other via a separator 23. The separator 23 can be made of a porous membrane, woven fabric, or nonwoven fabric made of polyolefin or cellulose. Preferably, the separator 23 has shutdown performance at relatively low temperatures.

[0013] The electrolyte 30 of the lithium battery 1 is a non-aqueous organic electrolyte obtained by dissolving a lithium electrolyte salt in an organic solvent. Examples of lithium electrolyte salts include lithium trifluoromethanesulfonate (LiCF3SO3), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), and lithium perchlorate (LiClO4). Examples of organic solvents include propylene carbonate (PC), ethylene carbonate (EC), and 1,2-dimethoxyethane (DME).

[0014] Inside the outer casing 10, for example, insulating plates 40 and 50 are provided at the bottom and above the battery element 20 that is housed therein, respectively. The sealing body 60 has, for example, an annular bottom plate portion with an opening in the center and side wall portions rising from the outer edge thereof. The gasket 70 is made of an insulating material such as resin. The positive electrode terminal 80 and washer 90 are made of a conductive material such as metal. The positive electrode terminal 80 and washer 90 are fixed to the opening provided in the bottom plate portion of the sealing body 60 via the gasket 70.

[0015] The positive electrode tab 21a connected to the positive electrode 21 of the battery element 20 is connected to the positive electrode terminal 80 fixed together with the washer 90 to the sealing body 60 via the gasket 70. The negative electrode tab 22a connected to the negative electrode 22 of the battery element 20 is connected to the inner wall of the outer can 10. A part of the outer can 10 (for example, a part such as its bottom surface) functions as a negative electrode terminal.

[0016] The sealing body 60 is fitted to the opening end portion of the outer can 10 and fixed to the outer can 10 by welding or the like. Incidentally, the sealing body 60 may be fixed to the outer can 10 by caulking or the like at the opening end portion of the outer can 10. The outer can 10 containing the battery element 20 together with the electrolytic solution 30 is sealed and closed by the sealing body 60 to which the positive electrode terminal 80 and the washer 90 are fixed via the gasket 70.

[0017] The lithium battery 1 having the above-described configuration is manufactured, for example, using the following method. A bottomed cylindrical outer can 10, a sheet-like positive electrode 21, a sheet-like negative electrode 22, and a sheet-like separator 23 are respectively prepared. The prepared positive electrode 21, negative electrode 22, and separator 23 are wound in a spiral shape to produce a battery element 20 having a spiral electrode structure.

[0018] The produced battery element 20 is inserted and accommodated into the outer can 10 from the opening end portion side. Incidentally, before the accommodation of the battery element 20, an insulating plate 40 is provided at the bottom inside the outer can 10. Also, after the accommodation of the battery element 20, an insulating plate 50 is provided above the battery element 20 inside the outer can 10.

[0019] Also, a sealing body 60 to which the positive electrode terminal 80 and the washer 90 are fixed via the gasket 70 is prepared. The positive electrode tab 21a connected to the positive electrode 21 of the battery element 20 is connected to the positive electrode terminal 80. The negative electrode tab 22a connected to the negative electrode 22 of the battery element 20 is connected to the inner wall of the outer can 10.

[0020] A predetermined electrolyte 30 is injected into the outer can 10 that houses the battery element 20 connected in this way. The sealing body 60 is fixed to the open end of the outer can 10 using a method such as welding. As a result, a structure of a sealed container in which the outer can 10 is sealed by the sealing body 60 provided with the gasket 70, the positive electrode terminal 80, and the washer 90 is realized.

[0021] For example, such a method is used to manufacture the lithium battery 1. During discharge of the lithium battery 1, lithium is ion-conducted from the negative electrode 22 through the separator 23 to the positive electrode 21 and taken in. In the lithium battery 1, such ion conduction of lithium realizes the discharge operation.

[0022] Here, the electrodes applicable to the battery element 20 as described above will be explained. As described above, the battery element 20 has a positive electrode 21 and a negative electrode 22. The positive electrode 21 can be, for example, a laminate of a positive electrode material containing a positive electrode active material on a core body that functions as a current collector. Similarly, for example, the negative electrode 22 can also be a laminate of a negative electrode material containing a negative electrode active material on a core body that functions as a current collector.

[0023] Hereinafter, for the sake of convenience, one or both of the positive electrode and the negative electrode will also be referred to as "electrode". Also, one of the positive electrode and the negative electrode will also be referred to as the "first electrode", and the other will also be referred to as the "second electrode". Also, one or both of the positive electrode active material and the negative electrode active material will also be referred to as "active material".

[0024] Figures 2 to 4 are diagrams for explaining an example of a method for forming an electrode. First, referring to Figure 2, the formation of the electrode formation sheet 200a will be described. Figure 2(A) schematically shows a perspective view of the main part of an example of the electrode formation sheet 200a. Figure 2(B) schematically shows a cross-sectional view taken along the line II-II of Figure 2(A).

[0025] In electrode formation, for example, first an electrode-forming sheet 200a, as shown in Figures 2(A) and 2(B), is prepared. The electrode-forming sheet 200a includes a current collector 210 and an active material layer 220 in which the current collector 210 is embedded.

[0026] For example, the current collector 210 may be made of expanded metal having an opening 211 that penetrates from the front to the back. In addition, perforated metal or the like may be used for the current collector 210. For example, stainless steel such as SUS316 and SUS444, aluminum, copper, etc., can be used for the current collector 210. The current collector 210 is made of a material that has corrosion resistance to electrode potential. For example, the current collector 210 can be made of a material with a thickness in the range of 0.05 mm to 0.15 mm.

[0027] A material containing the active material (such as a mixture) is prepared, and this material is formed on the front and back surfaces of the current collector 210. As shown in Figure 2(B), this material is formed not only on the front and back surfaces of the current collector 210, but also inside the opening 211. This material containing the active material, formed on the current collector 210, becomes the active material layer 220 in the electrode forming sheet 200a. For example, the active material layer 220 is formed to have a thickness in the range of 0.15 mm to 0.75 mm. The electrode forming sheet 200a is formed to have a thickness in the range of 0.2 mm to 0.8 mm.

[0028] This results in the formation of an electrode-forming sheet 200a as shown in Figures 2(A) and 2(B), which includes a current collector 210 and an active material layer 220 in which the current collector 210 is embedded.

[0029] Next, the cutting of the electrode-forming sheet 200a will be explained with reference to Figure 3. Figure 3(A) schematically shows a perspective view of the main part of an example of the process of cutting the electrode-forming sheet 200a. Figures 3(B) and 3(C) schematically show examples of cutting the electrode-forming sheet 200a with cutting blades 310 and 320, respectively.

[0030] The electrode-forming sheet 200a is cut to a predetermined size according to the battery configuration. For cutting the electrode-forming sheet 200a, for example, a slitter like the one shown in Figure 3(A) is used. The slitter shown in Figure 3(A) has disc-shaped cutting blades 310 and 320 set vertically, and by rotating them and passing the electrode-forming sheet 200a between them, the electrode-forming sheet 200a is continuously cut in the longitudinal direction D1. By passing the electrode-forming sheet 200a through such a slitter, the electrode-forming sheet 200a is cut at predetermined cutting points 201 by the cutting blades 310 and 320, and a strip-shaped electrode 200 having a predetermined width in the short direction D2 is formed from the electrode-forming sheet 200a.

[0031] For the slitter's cutting blades 310 and 320, blades with a cutting edge shape such as that shown in Figure 3(B) or Figure 3(C) can be used. Figure 3(B) shows an example where the cutting blades 310 and 320 have a flat cutting edge, that is, a flat cutting edge that is parallel to the surface of the electrode-forming sheet 200a that is to be cut. When cutting blades 310 and 320 with such cutting edge shapes are used, the electrode-forming sheet 200a is cut between the corners 311a and 321a of their flat surfaces, and the electrode 200 is cut out from the electrode-forming sheet 200a.

[0032] Figure 3(C) shows an example where the cutting blades 310 and 320 have inclined cutting edges, that is, cutting edges that are inclined with respect to the surface of the electrode-forming sheet 200a to be cut. When cutting blades 310 and 320 with such cutting edge shapes are used, the electrode-forming sheet 200a is cut between their tips 311b and 321b, and the electrode 200 is cut out from the electrode-forming sheet 200a. When using cutting blades 310 and 320 with inclined cutting edges, cutting blades 310 and 320 with various inclination angles θ can be used.

[0033] Furthermore, the cutting of the electrode-forming sheet 200a, that is, the cutting of the electrode 200 from the electrode-forming sheet 200a, may be carried out not only by the method using a slitter as described above, but also by methods such as punching with a Thomson blade.

[0034] Next, with reference to Figure 4, the electrode 200 cut from the electrode-forming sheet 200a will be described. Figure 4(A) schematically shows a perspective view of the main part of an example of the cut electrode 200. Figure 4(B) schematically shows a cross-sectional view of IV-IV of Figure 4(A).

[0035] From the electrode-forming sheet 200a, for example, strip-shaped electrodes 200 as shown in Figures 4(A) and 4(B) are cut out. The cut-out electrodes 200 are used as the positive electrode 21 or negative electrode 22 of the battery element 20 in the lithium battery 1.

[0036] The electrode 200 is wound together with the separator 23 in the longitudinal direction D1. That is, one end face 231 of the electrode 200 in the longitudinal direction D1 becomes the winding center side when applied to the battery element 20, and the other end face 231 in the longitudinal direction D1 becomes the winding outer circumference side when applied to the battery element 20. Furthermore, the opposing end faces 231 of the electrode 200 in the longitudinal direction D1 can also be said to be end faces extending in the short direction D2.

[0037] When the electrode 200 is wound in this manner to create the battery element 20 and inserted into the outer casing 10, one end face 230 of the electrode 200 in the short direction D2 faces the bottom side of the outer casing 10, and the other end face 230 in the short direction D2 faces the open end side of the outer casing 10 (the side that is sealed by the sealing body 60). In other words, the end face 230 of the electrode 200 in the short direction D2 becomes the end face facing the axial direction O1 of the outer casing 10. Note that the opposing end faces 230 of the electrode 200 in the short direction D2 can also be said to be end faces extending in the longitudinal direction D1.

[0038] One end face 230 and the other end face 230 of the electrode 200 in the short direction D2 are formed by cutting the electrode forming sheet 200a in the longitudinal direction D1 with the cutting blades 310 and 320 as described above (Figure 3(A), etc.). At this time, a void 240 is formed on the end face 230 of the electrode 200, dividing the active material layer 220 into two parts 221 and 222 on one side and the other side in the thickness direction D3, as schematically shown in Figures 4(A) and 4(B).

[0039] Here, the end face 230 of the electrode 200 formed by cutting the electrode-forming sheet 200a exposes the cut surface of the current collector 210 (the part not at the opening 211) by the cutting blades 310 and 320. Multiple gaps 240 are arranged intermittently in the longitudinal direction D1 on the end face 230. On the end face 230 of the electrode 200, the cut surface of the current collector 210 and multiple gaps 240 arranged intermittently through the cut surface of the current collector 210 are arranged alternately. One or more gaps 240 do not necessarily have a constant width in the thickness direction D3, and there may be parts within a single gap 240 with different widths in the thickness direction D3, or the widths in the thickness direction D3 of different gaps 240 may differ from each other.

[0040] The void 240 is formed when the electrode 200 is cut out by cutting the electrode-forming sheet 200a. When the electrode-forming sheet 200a is cut using the cutting blades 310 and 320, contact resistance is generated between the cutting blades 310 and 320 and the current collector 210 in the electrode-forming sheet 200a. Due to the friction caused by this contact resistance, a void 240 is formed in the active material layer 220 on the current collector 210, dividing it into two parts 221 and 222 in the thickness direction D3. When an expanded metal-like material is used as the current collector 210, the contact resistance with the cutting blades 310 and 320 is greater than when a metal foil-like material is used, and the void 240 tends to be more easily formed.

[0041] The shape of the gap 240 can be changed depending on the type of current collector 210 used in the electrode-forming sheet 200a to be cut, for example, the difference in contact resistance with the cutting blade 310 and the cutting blade 320. In addition, the shape of the gap 240 can be changed depending on the type of cutting blade 310 and the cutting blade 320 used to cut the electrode-forming sheet 200a, for example, the blade tip shape as shown in Figure 3(B) or Figure 3(C).

[0042] Here, when cutting is performed using cutting blades 310 and 320 with a flat blade tip shape as shown in Figure 3(B), a relatively large gap 240 tends to be formed. Also, when cutting is performed using cutting blades 310 and 320 with a blade tip shape as shown in Figure 3(C), the shape of the gap 240 can be changed by the difference in the inclination angle θ of the cutting blades 310 and 320, and the larger the inclination angle θ, the easier it tends to form a larger gap 240. When using cutting blades 310 and 320 with a flat blade tip shape as shown in Figure 3(B), or when using cutting blades 310 and 320 with a blade tip shape as shown in Figure 3(C) and a relatively large inclination angle θ, it is thought that the force applied to the current collector 210 increases when cutting the electrode forming sheet 200a, the gap between the current collector 210 and the active material layer 220 tends to widen, and a relatively large gap 240 tends to be formed.

[0043] Figures 4(A) and 4(B) illustrate the gap 240 provided on the end face 230 of the electrode 200 in the short direction D2. In addition, a similar gap may be provided on the end face 231 of the electrode 200 in the long direction D1, dividing the active material layer 220 into two parts, one side and the other side, in its thickness direction D3.

[0044] An electrode 200 as described above, that is, an electrode 200 having a gap 240 at least on its end face 230, is used as the positive electrode 21 or negative electrode 22 of the battery element 20 in the lithium battery 1 as described above. The electrode 200 used as the positive electrode 21 or negative electrode 22 is wound together with the separator 23 in the longitudinal direction D1 and housed together with the electrolyte 30 in the outer container 10.

[0045] At this time, the electrolyte 30 is absorbed into the active material layer 220 of the electrode 200 (positive electrode 21 or negative electrode 22). The electrode 200 has a gap 240 at its end face 230, which increases the absorption capacity of the electrolyte 30 compared to when the gap 240 is not provided. That is, in the electrode 200, the electrolyte 30 is absorbed from the outer surface of the active material layer 220 into its interior, and also enters the gap 240 provided at least at the end face 230, and is absorbed into the interior of the active material layer 220 from the gap 240.

[0046] Thus, in the electrode 200, where the electrolyte 30 is absorbed not only from the outer surface of the active material layer 220 but also from the voids 240, the electrolyte 30 is quickly absorbed into the interior of the active material layer 220. This prevents the electrolyte 30 from overflowing from the outer container 10 or from taking a long time to complete when injecting it into the outer container 10 containing the electrode 200.

[0047] Furthermore, in the electrode 200, where the electrolyte 30 is absorbed not only from the outer surface of the active material layer 220 but also from the void 240, the absorption rate of the electrolyte 30 absorbed into the interior of the active material layer 220 is increased. Moreover, in the electrode 200, the uneven distribution of the electrolyte 30 absorbed into the interior of the active material layer 220 is suppressed. As a result, insufficient battery capacity and uneven discharge in the electrode 200 are suppressed, and the performance degradation of the lithium battery 1 using the electrode 200 is suppressed.

[0048] As explained above, when an electrode 200 has a gap 240 at least on its end face 230, it is possible to improve the liquid absorption of the electrolyte 30 contained in the outer casing 10 along with the electrode (positive electrode 21 or negative electrode 22) of the battery element 20. Furthermore, if a gap is also provided on the end face 231 of the electrode 200 in addition to the end face 230, it is possible to further improve the liquid absorption of the electrolyte 30. By improving the liquid absorption of the electrolyte 30 to the electrode 200, it becomes possible to realize a high-performance lithium battery 1.

[0049] Examples and comparative examples are described below. As sample lithium battery 1, a cylindrical lithium battery was fabricated in which a battery element 20 with a spiral electrode structure was housed together with an electrolyte 30 inside a cylindrical outer casing 10.

[0050] (Electrode fabrication) The positive electrode 21 was fabricated as follows. A composite material was prepared by mixing electrolytic manganese dioxide as the positive electrode active material, carbon as the conductive material, and a fluorine-based binder in a mass ratio of positive electrode active material:conductive material:binder = 90:5:5.

[0051] The prepared mixture was formed by rolling it onto the front and back surfaces of a current collector 210 made of expanded metal, according to the examples in Figures 2(A) and 2(B) above, and an electrode-forming sheet 200a was formed having a structure in which the current collector 210 is embedded in an active material layer 220 formed from the mixture.

[0052] The formed electrode-forming sheet 200a was cut to predetermined dimensions using a slitter according to the examples in Figures 3(A) and 3(B) or 3(C). Specifically, the electrode-forming sheet 200a was passed between the rotating upper and lower cutting blades 310 and 320, and continuously cut in the longitudinal direction D1 at cutting points 201 that had a predetermined width in the short direction D2. As a result, an electrode 200 (positive electrode 21) having a predetermined width was formed from the electrode-forming sheet 200a according to the examples in Figures 4(A) and 4(B). The thickness of the electrode 200 in the thickness direction D3 is in the range of 0.2 mm to 0.8 mm, the thickness of the active material layer 220 in the thickness direction D3 is in the range of 0.15 mm to 0.75 mm, and the thickness of the current collector 210 in the thickness direction D3 is in the range of 0.05 mm to 0.15 mm.

[0053] Here, at the end face 230 of the electrode 200 cut out from the electrode forming sheet 200a at the cutting point 201, a gap 240 is formed that divides the active material layer 220 into two parts 221 and 222 in the thickness direction D3 due to the contact resistance between the cutting blades 310 and 320 and the current collector 210. As mentioned above, the shape of this gap 240 can be changed depending on the type of current collector 210 and the types of cutting blades 310 and 320.

[0054] Here, as Comparative Example 1, Example 1, and Example 2, electrodes 200A, 200B, and 200C were formed, having the configurations shown in Figures 5(A) to 5(C), respectively.

[0055] Figure 5 illustrates an example of electrode configuration. Figure 5(A) schematically shows a cross-sectional view of the main part of electrode 200A of Comparative Example 1. Figure 5(B) schematically shows a cross-sectional view of the main part of electrode 200B of Example 1. Figure 5(C) schematically shows a cross-sectional view of the main part of electrode 200C of Example 2.

[0056] The electrode 200A of Comparative Example 1 shown in Figure 5(A) includes a current collector 210 and an active material layer 220 in which it is embedded, and has a configuration in which no void 240 is provided at the end face 230 formed by cutting the electrode forming sheet 200a as described above.

[0057] The electrode 200B of Example 1 shown in Figure 5(B) and the electrode 200C of Example 2 shown in Figure 5(C) include a current collector 210 and an active material layer 220 in which it is embedded, and have a configuration in which a gap 240 is provided in the end face 230 formed by cutting the electrode forming sheet 200a as described above.

[0058] Electrodes 200B and 200C differ in the shape of the void 240 and the shape of the region where the void 240 exists. Electrode 200C has a shape in which the void 240 is wider inward than at the end face 230, and the thickness T2 of the region where the void 240 exists is thicker than the thickness T3 of the region where the void 240 does not exist.

[0059] Both electrodes 200B and 200C have a structure in which a gap 240 is formed on the end face 230 after cutting, but this is an example in which a difference in the thickness of the end region where the gap 240 exists can be observed due to the formation of the gap 240.

[0060] (End face void ratio of electrodes) For electrodes 200B and 200C, the width of the void 240 at the end face 230 was defined as W1, and the total thickness of the active material layer 220 including the void 240 at the end face 230 was defined as T1. The ratio of the width W1 to the total thickness T1 at the end face 230, i.e., the porosity (also called "end face porosity"), was calculated using the following equation (1).

[0061] End surface porosity [%]=W1 / T1×100...(1) (Electrode absorption rate) Furthermore, the absorption rate of the electrolyte 30 was measured for electrodes 200A, 200B, and 200C. To measure the absorption rate of the electrolyte 30, first, electrodes 200A, 200B, and 200C were each wound onto a 6mm diameter core, and the outermost part was secured with tape to create a wound body. The mass M1 of the prepared wound body (also called the "wound body before absorption") was measured. Next, 2g of electrolyte 30 was placed in the outer container 10, and then the prepared wound body was placed inside the outer container 10 and the wound body was brought into contact with the electrolyte 30 for 1 minute. Then, after 1 minute had elapsed, the winding was removed from the outer can 10, and the mass M2 of the removed winding (also called the "winding after liquid absorption") was measured. Using the masses of the winding before and after contact with the electrolyte 30, i.e., the masses M1 and M2 of the winding before and after liquid absorption, the liquid absorption rate of the electrolyte 30 was calculated from the following equation (2).

[0062] Liquid absorption rate [%]=(M2-M1) / M1×100...(2) Furthermore, the electrolyte 30 used was a base electrolyte containing PC, EC, and DME in a weight ratio of PC:EC:DME=10:10:80, to which a predetermined amount of additives were added, and 0.5 M (mol / L) of LiCF3SO3 was added as the lithium electrolyte salt.

[0063] (Manufacturing of lithium batteries) Furthermore, electrodes 200A, 200B, and 200C were used as positive electrodes 21 to fabricate a lithium battery 1.

[0064] A LiAl alloy was used for the negative electrode 22 of the lithium battery 1. A microporous film made of polyolefin was used for the separator 23. The positive electrode 21 (electrode 200A, electrode 200B, or electrode 200C) and the negative electrode 22 were wound together with the separator in between, facing each other, to fabricate the battery element 20. The fabricated battery element 20 was housed in a cylindrical outer casing 10 together with the electrolyte 30. The electrolyte 30 had the above composition, i.e., a base electrolyte containing PC, EC, and DME (weight ratio 10:10:80) with additives and a predetermined amount of LiCF3SO3 added. The negative electrode 22 of the battery element 20 was electrically connected to the outer casing 10. A sealing body 60, to which the positive electrode terminal 80 electrically connected to the positive electrode 21 is fixed via a gasket 70, was welded to the open end of the outer casing 10 by laser welding. As a result, a cylindrical spiral-type lithium primary battery with an outer diameter of 17 mm and a height of 450 mm was fabricated as lithium battery 1.

[0065] (Battery evaluation) Ten lithium batteries 1 were fabricated using electrodes 200A, 200B, and 200C as the positive electrode 21, and the number of lithium batteries 1 with a faulty voltage (defective number) out of the total 10 was determined.

[0066] Furthermore, the pulse voltage of the fabricated lithium battery 1 was measured. The pulse voltage was determined by measuring the closed-circuit voltage when a current was passed through lithium battery 1, with a discharge depth of 70%, for 1.2 seconds with a 5Ω load attached at a temperature of -30°C.

[0067] (result) Table 1 shows the presence or absence of voids 240 at the end faces 230 of electrode 200A of Comparative Example 1, electrode 200B of Example 1, and electrode 200C of Example 2, as well as the results of the end face void ratio, liquid absorption rate, number of voltage defects, and pulse voltage change obtained as described above.

[0068] [Table 1]

[0069] Table 1 shows that in Comparative Example 1, electrode 200A, where no void 240 is formed on the end face 230, the absorption rate of the electrolyte 30 was 3%, while in Example 1, electrode 200B, and in Example 2, electrode 200C, where a void 240 is formed on the end face 230, the absorption rates were 6% and 7%, respectively. It was confirmed that the absorption rate of the electrolyte 30 is increased by forming a void 240 on the end face 230, as in electrode 200B of Example 1 and electrode 200C of Example 2.

[0070] In Example 1, electrode 200B had an end face void ratio of 11%, and in lithium battery 1 using this as the positive electrode 21, there were 0 voltage failures out of 10 units. In contrast, electrode 200C in Example 2 had an end face void ratio of 28%, and in lithium battery 1 using this as the positive electrode 21, there were 2 voltage failures out of 10 units.

[0071] In the case of electrode 200C of Example 2, the void 240 becomes larger and the end face porosity increases, which has the effect of increasing the absorption rate of the electrolyte 30. However, because the void 240 becomes larger and the thickness of the region where the void 240 exists increases, the possibility of the active material layer 220 peeling off from the current collector 210 may be higher compared to electrode 200B of Example 1. In the lithium battery 1 using electrode 200C of Example 2 as the positive electrode 21, it is thought that the number of voltage failures increased compared to the lithium battery 1 using electrode 200B of Example 1 as the positive electrode 21 because the active material layer 220 that peeled off from the current collector 210 penetrated the separator 23.

[0072] Furthermore, while the pulse voltage change of lithium battery 1 using electrode 200A of Comparative Example 1 as the positive electrode 21 was ±0V, the pulse voltage change of lithium battery 1 using electrode 200B of Example 1 and electrode 200C of Example 2 as the positive electrode 21 was improved to +0.1V in both cases.

[0073] From the above results, the following can be said. In order to increase the electrolyte absorption rate, it is preferable to form a gap 240 on the end face 230, as in electrode 200B of Example 1 and electrode 200C of Example 2, and to make the end face porosity greater than 0%. Furthermore, in order to suppress the occurrence of voltage defects caused by the large gap 240 on the end face 230, it is preferable to make the end face porosity less than 28%, as in electrode 200B of Example 1. The end face porosity is preferably greater than 0% and less than 28%, even more preferably less than 20%, and even more preferably less than 11%. As with electrode 200B in Example 1, forming a void 240 on the end face 230 and making the end face void ratio greater than 0% and less than 28% improves the electrolyte 30's absorption, suppresses the increase in the electrode 200B's thickness due to the formation of the void 240, reduces peeling of the active material layer 220 and the resulting voltage defects, and further improves the pulse voltage.

[0074] Furthermore, the above explanation shows an example in which a void 240 is formed on the end face 230 of the electrode 200 obtained from the electrode-forming sheet 200a when the electrode-forming sheet 200a is cut by cutting with a slitter or punching with a die-cutting tool. In addition, it is also possible to obtain an electrode 200 without a void 240 on the end face 230 when cutting the electrode-forming sheet 200a, and then form the void 240 by scraping the active material layer 220 on the end face 230 of the electrode 200 after cutting. Alternatively, when forming the electrode-forming sheet 200a, it is also possible to adjust the pressure when rolling the mixture of the active material layer 220 onto the current collector 210 to adjust the density of the active material layer 220 and leave a void 240 within the active material layer 220.

[0075] Furthermore, although the above explanation uses a cylindrical lithium battery as an example, the battery form is not limited to this cylindrical shape. Electrodes with air gaps at the end faces, as described above, can be applied to the electrodes (positive or negative electrodes) of battery elements in various forms of lithium batteries, such as rectangular and thin types. By using electrodes with air gaps at the end faces, as described above, high-performance lithium batteries in various forms can be realized. [Explanation of symbols]

[0076] 1 Lithium battery 10 outer cans 20 Battery Elements 21 Positive electrode 21a Positive Tab 22 Negative electrode 22a Negative Electrode Tab 23 Separator 30 Electrolyte 40, 50 insulating boards 60 Sealing body 70 Gasket 80 Positive terminal 90 Washers 200, 200A, 200B, 200C electrode 200a Electrode Forming Sheet 201 Cutting point 210 Current collector 211 Opening 220 Active material layer 221, 222 parts 230, 231 end face 240 void 310, 320 cutting blade 311a, 321a corner 311b, 321b tip D1 Longitudinal direction D2 Width direction D3 Thickness direction M1, M2 mass O1 Axial direction T1 Total Thickness T2, T3 thickness W1 width

Claims

1. Current collector and, The active material layer in which the current collector is embedded, Includes a first electrode having A lithium battery having a gap at the end face of the first electrode that divides the active material layer into two parts, one on one side and the other on the other side, in the thickness direction.

2. The first electrode is strip-shaped, The lithium battery according to claim 1, wherein the end face is an end face extending in the longitudinal direction of the first electrode.

3. The lithium battery according to claim 1, wherein the region where the void exists in the first electrode is thicker than the region where the void does not exist.

4. The lithium battery according to claim 1, wherein the ratio of the voids to the total thickness of the active material layer, including the voids, at the end face is greater than 0% and less than 28%.

5. A battery element in which the first electrode and the second electrode are wound with a separator in between, An outer casing in which the aforementioned battery element is housed, A lithium battery according to claim 1, comprising:

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