Negative electrode and battery

Abstract

The present invention relates to a negative electrode and a battery provided with the same. The negative electrode includes a current collector layer, a first active material layer bonded to the current collector layer, and a second active material layer bonded to the first active material layer. In the negative electrode, the first active material layer contains first graphite and a silicon elementary substance or a silicon compound. Furthermore, in the negative electrode, the second active material layer contains second graphite having an average particle diameter smaller than that of the first graphite. Furthermore, in the negative electrode, the surfaces of the first active material layer along the longitudinal direction are all covered by the second active material layer except for the surface joined to the collector layer. And a negative electrode, average thickness between an end face of the second active material layer above the short-side direction and an end face of the first active material layer above the short-side direction and / or average thickness between an end face of the second active material layer below the short-side direction and an end face of the first active material layer below the short-side direction is greater than the first active material The average thickness of the layers in the lamination direction is thick. Thus, the durability of the battery can be improved.

Description

Technical Field

[0001] The present disclosure relates to a negative electrode and a battery. Background Art

[0002] Batteries having a negative electrode including a plurality of active material layers are conventionally known (see, for example, Patent Documents 1 to 7). Prior art literature Patent Literature

[0003] Patent Document 1: International Publication No. 2011 / 114433 Patent Document 2: Japanese Patent Application Publication No. 2009-009858 Patent Document 3: Japanese Patent Application Publication No. 2013-008707 Patent Document 4: Japanese Patent Application Publication No. 2013-246900 Patent Document 5: Japanese Patent Application Publication No. 2014-007148 Patent Document 6: Japanese Patent Application Publication No. 2018-116820 Patent Document 7: Japanese Patent Application Publication No. 2021-077591 Summary of the invention Problem that the invention aims to solve

[0004] There is a demand for improvement in the durability of batteries developed to increase battery capacity and in which SiO is introduced into the active material layer of the negative electrode. Technical means of solving problems

[0005] The negative electrode disclosed herein comprises a current collecting layer, a first active material layer bonded to the current collecting layer, and a second active material layer bonded to the first active material layer. The first active material layer comprises a first graphite and a silicon element or a silicon compound. The second active material layer comprises a second graphite having an average particle size smaller than that of the first graphite. The surfaces of the first active material layer along the long side direction are covered by the second active material layer except for the surface bonded to the current collecting layer. The average thickness between the end face above the short side direction of the second active material layer and the end face above the short side direction of the first active material layer and / or the average thickness between the end face below the short side direction of the second active material layer and the end face below the short side direction of the first active material layer is thicker than the average thickness of the first active material layer in the stacking direction.

[0006] The battery disclosed in the present invention comprises the negative electrode, the positive electrode and an electrolyte. Effects of the Invention

[0007] According to the battery including the negative electrode of the present disclosure, the durability of the battery is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is a perspective view showing a battery 1 according to the embodiment. Figure 2 1 is a perspective view showing a charging and discharging body 100 included in the battery 1 . Figure 3 In order to express the positive electrode 110, the negative electrode 120 and the separator 130 in a manner that the positions of the side ends are different Figure 2 1 is a three-dimensional view of a portion of the charge-discharge body 100 including the positive electrode tab 111b and the negative electrode tab 121b. Figure 4 To express Figure 3 Side view of the charge and discharge body 100 Figure 1 . Figure 5 To express Figure 3 Side view of the charge and discharge body 100 Figure 2 . Figure 6 To express Figure 3 Side view of the charge and discharge body 100 Figure 3 . Figure 7 This is a schematic enlarged view of a portion of a die head and a backing roll used in the production of a negative electrode. Figure 8 This is a schematic cross-sectional view of a positive electrode and a negative electrode of a separatorless battery including a positive electrode and a negative electrode according to another example of the embodiment. Fig. 9 This is a schematic enlarged cross-sectional view of the interface between the positive electrode second active material layer and the positive electrode electron insulating layer of the positive electrode active material layer of another example of the embodiment and its vicinity. DETAILED DESCRIPTION

[0009] The various embodiments of the present disclosure are described with reference to the accompanying drawings. In order to make the various embodiments easier to understand, the sizes or ratios of the components are sometimes exaggerated in the various drawings. In the various drawings, the same symbols are marked for the same components. In the various drawings, arrows are used to indicate the lateral width direction X (X-axis direction), depth direction Y (Y-axis direction), and height direction Z (Z-axis direction) of the battery 1 and the components of the battery 1. However, in the various drawings, the lateral width direction X, the depth direction Y, and the height direction Z show a relative directional relationship. That is, for example, when the battery 1 is rotated 180 degrees and the upper and lower surfaces are reversed for configuration, or when the battery 1 is rotated 90 degrees and the upper surface is configured as a side surface, the lateral width direction X, the depth direction Y, and the height direction Z of the battery 1 change.

[0010] (Configuration of Battery 1 Having Negative Electrode 120 According to Embodiment) refer to Figures 1 to 6, the configuration of the battery 1 including the negative electrode 120 according to the embodiment will be described.

[0011] like Figure 1 As shown, the battery 1 includes a charge / discharge body 100 for charging and discharging electric power, a container 200 for accommodating the charge / discharge body 100 , and an external terminal 300 connected to the charge / discharge body 100 and mounted on the container 200 .

[0012] like Figures 2 to 4 As shown, the charge-discharge body 100 includes a positive electrode 110, a negative electrode 120, and a separator 130. The charge-discharge body 100 is contained in a container 200, and the separator 130 is impregnated with an electrolyte. Figure 2 and Figure 3 As shown, the charge-discharge body 100 is formed by winding a long positive electrode 110 and a long negative electrode 120 with a long separator 130 interposed therebetween. In the wound state, the charge-discharge body 100 is formed into a rectangular parallelepiped with rounded ends.

[0013] like Figure 3 and Figure 4 As shown, the positive electrode 110 includes a positive electrode current collecting layer 111 and a positive electrode active material layer 112 connected to the positive electrode current collecting layer 111 .

[0014] The positive electrode current collecting layer 111 is formed in a long strip shape extending along the horizontal width direction X. Figure 3 and Figure 4 As shown in FIG. 1 , the positive electrode current collecting layer 111 includes a current collecting portion 111 a and a positive electrode tab 111 b. The current collecting portion 111 a is long in the horizontal width direction X and is formed in a foil shape. Figure 4 As shown, the positive electrode active material layer 112 is bonded to the collector portion 111a. The positive electrode active material layer 112 may be formed on both sides of the collector portion 111a. For example, the positive electrode active material layer 112 faces the entire region along the short side direction (height direction Z) of the collector portion 111a. Figure 3 and Figure 4 As shown, the positive electrode tab 111b protrudes from the side edge 111c along the long side direction of the current collecting portion 111a toward the short side direction of the current collecting portion 111a (upward in the height direction Z). The positive electrode tab 111b is formed integrally with the current collecting portion 111a. For example, one positive electrode tab 111b is formed on the current collecting portion 111a. The current collecting portion 111a is formed of, for example, aluminum or an aluminum alloy, for example, aluminum foil having a plate-like (sheet-like) shape.

[0015] The positive electrode active material layer 112 includes a positive electrode active material composed of a lithium-containing composite oxide, a binder, and a conductive additive.

[0016] As the lithium-containing composite oxide, for example, metal elements such as nickel, cobalt, and manganese and lithium are used.

[0017] As the lithium-containing composite oxide, for example, a ternary lithium-containing composite oxide represented by the following formula may be used: Li 1+X M A O2(1) (Where X satisfies -0.15≤X≤0.15, M A represents an element group including at least one selected from the group consisting of Mn and Al, Ni, and Co) The ternary lithium-containing composite oxide represented by the general formula (1) has high thermal stability and stability in a high potential state, and by using this oxide, the safety and various battery characteristics of the battery 1 can be improved.

[0018] As the binder, for example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyethylene, polystyrene, polybutadiene, polyacrylonitrile, polyvinyl fluoride, polypropylene fluoride, polychloroprene fluoride, butyl rubber, nitrile rubber, styrene-butadiene rubber (SBR), polysulfide rubber, nitrocellulose, cyanoethyl cellulose, various latexes, acrylic resins or mixtures thereof can be used.

[0019] As the conductive agent, a carbon material can be used. The carbon material can be crystalline carbon, amorphous carbon or a mixture thereof. Examples of crystalline carbon include artificial graphite, natural graphite (e.g., flake graphite) or a mixture thereof. Examples of amorphous carbon include carbon black (e.g., acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black or a mixture thereof).

[0020] For example, the positive electrode 110 can be formed as follows. The positive electrode active material and an arbitrarily selected binder and conductive agent are dispersed in a solvent (for example, N-methyl-2-pyrrolidone (NMP), water) to prepare a paste or slurry positive electrode mixture composition. The positive electrode mixture composition is applied to the surface (one side or both sides) of the positive electrode collector layer 111 and dried, and a calendering treatment is performed as needed to form a positive electrode mixture layer. The positive electrode 110 is thus obtained. However, the positive electrode is not limited to being manufactured by the above manufacturing method, and can also be manufactured by other methods.

[0021] like Figure 3 and Figure 4As shown, the negative electrode 120 includes a negative electrode current collecting layer 121, a negative electrode first active material layer 122 (first active material layer) bonded to the negative electrode current collecting layer 121, and a negative electrode second active material layer 123 (second active material layer) bonded to the negative electrode first active material layer 122. That is, the negative electrode 120 includes a plurality of active material layers.

[0022] The negative electrode current collecting layer 121 is formed in a strip shape extending along the horizontal width direction X. Figure 3 and Figure 4 As shown in FIG. 1 , the negative electrode current collecting layer 121 includes a current collecting portion 121 a and a negative electrode tab 121 b. The current collecting portion 121 a is long in the horizontal width direction X and is formed in a foil shape. Figure 4 As shown, the width of the collector portion 121a along the short side direction (height direction Z) is longer than the width of the collector portion 111a of the positive electrode 110 along the short side direction. Both ends of the collector portion 111a of the positive electrode 110 along the short side direction (the upper end to the lower end in the height direction Z) are located within the range of the collector portion 121a of the negative electrode 120 along the short side direction (the upper end to the lower end in the height direction Z) via the separator 130. The negative electrode first active material layer 122 is bonded to the collector portion 121a. The negative electrode first active material layer 122 can be formed on both surfaces of the collector portion 121a. Figure 3 and Figure 4 As shown, the negative electrode tab 121b protrudes from the side edge 121c along the long side direction of the collector portion 121a toward the short side direction of the collector portion 121a (above the height direction Z). When stacked with the positive electrode 110 via the separator 130, the negative electrode tab 121b protrudes in the same direction as the positive electrode tab 111b of the positive electrode 110 (above the height direction Z). When stacked with the positive electrode 110 via the separator 130, the negative electrode tab 121b is separated from the positive electrode tab 111b of the positive electrode 110 in the horizontal width direction X. The negative electrode tab 121b is formed integrally with the collector portion 121a. For example, one negative electrode tab 121b is formed on the collector portion 121a. The collector portion 121a is formed of, for example, copper or a copper alloy. The tensile strength of the negative electrode collector layer 121 is, for example, 30 kg / mm 2 above.

[0023] like Figure 4 As shown, the negative electrode first active material layer 122 is bonded to the negative electrode collector layer 121. The negative electrode first active material layer 122 corresponds to a high-capacity layer in the negative electrode 120. A high-capacity layer means a layer that can store relatively more lithium ions. That is, the negative electrode first active material layer 122 corresponds to a lithium ion receiving layer that can store more lithium ions than the negative electrode collector layer 121 in the negative electrode 120. The negative electrode first active material layer 122 includes a first graphite 122a and a first silicon single substance or silicon compound 122b.

[0024] The first graphite 122a is a negative electrode active material composed of a carbon-based material. The average particle size of the first graphite 122a is larger than the average particle size of the second graphite 123a. The average particle size of the first graphite 122a can be, for example, 10 μm or more and 35 μm or less at D50. In a certain embodiment, the average particle size of the first graphite 122a can be, for example, 15 μm or more and 30 μm or less at D50. Here, D50 is the diameter of the particles when the cumulative value is 50% in the particle size distribution measurement measured by the laser diffraction scattering particle size distribution measurement method. In a certain embodiment, the amount of the first graphite 122a can be, for example, 60% by weight and 98.5% by weight relative to the total weight of the negative electrode first active material layer 122. Weight % is wt%, that is, weight percentage concentration. In a certain embodiment, the amount of the first graphite 122a can be, for example, 90% by weight and 98.5% by weight relative to the total weight of the negative electrode first active material layer 122. In one embodiment, the amount of the first graphite 122 a may be, for example, 95 wt % or more and 98.5 wt % or less with respect to the total weight of the negative electrode first active material layer 122 .

[0025] The first silicon single substance or silicon compound 122b is a negative electrode active material. Examples of silicon compounds include silicon oxides such as SiO. The amount of the first silicon single substance or silicon compound 122b is 1% by weight or more and 90% by weight or less relative to the total weight of the negative electrode first active material layer 122. In one embodiment, the amount of the first silicon single substance or silicon compound 122b, for example, relative to the total weight of the negative electrode first active material layer 122 may be 1% by weight or more and 50% by weight or less. In one embodiment, the amount of the first silicon single substance or silicon compound 122b, for example, relative to the total weight of the negative electrode first active material layer 122 may be 1% by weight or more and 35% by weight or less.

[0026] The weight ratio of the first graphite 122a to the first silicon simple substance or silicon compound 122b (first graphite 122a: first silicon simple substance or silicon compound 122b) is, for example, generally 5:95 to 15:85. In one embodiment, the weight ratio of the first graphite 122a to the first silicon simple substance or silicon compound 122b may be 8:92 to 12:88. In one embodiment, the weight ratio of the first graphite 122a to the first silicon simple substance or silicon compound 122b may be 9:91 to 11:89.

[0027] The negative electrode first active material layer 122 further includes, for example, at least one first binder 122c (binder) selected from the group consisting of rubber, acrylic, polyamide-imide, and polyimide. The amount of the first binder 122c, for example, can be 0.5% by weight or more and 10% by weight or less relative to the total weight of the negative electrode first active material layer 122. In one embodiment, the amount of the first binder 122c, for example, can be 1% by weight or more and 5% by weight or less relative to the total weight of the negative electrode first active material layer 122.

[0028] The negative electrode first active material layer 122 further includes, for example, a conductive aid, etc. As the conductive aid, etc., for example, carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, etc. is included. The amount of the conductive aid, etc., for example, relative to the total weight of the negative electrode first active material layer 122, can be 0 weight % or more and 5 weight % or less. In a certain embodiment, the amount of the conductive aid, etc., for example, relative to the total weight of the negative electrode first active material layer 122, can be 0 weight % or more and 3 weight % or less.

[0029] The thickness (second thickness T2) of one side of the stacking direction (depth direction Y) of the negative electrode first active material layer 122 may be, for example, 5 μm or more and 500 μm or less in average thickness. In one embodiment, the thickness (second thickness T2) of one side of the stacking direction (depth direction Y) of the negative electrode first active material layer 122 may be, for example, 10 μm or more and 300 μm or less in average thickness.

[0030] The surface of the negative electrode first active material layer 122 along the longitudinal direction (lateral width direction X) is covered with the negative electrode second active material layer 123 except for the surface bonded to the negative electrode current collecting layer 121 .

[0031] like Figure 4 As shown, the negative electrode second active material layer 123 is bonded to the negative electrode first active material layer 122. The negative electrode second active material layer 123 is equivalent to a high input-output layer in the negative electrode 120. The high input-output layer means a layer that can input and output lithium ions at a relatively high speed. In other words, the negative electrode second active material layer 123 is equivalent to a lithium ion receiving layer in the negative electrode 120 that can input and output lithium ions at a higher speed than the negative electrode collector layer 121. The negative electrode second active material layer 123 includes a second graphite 123a having an average particle size smaller than that of the first graphite 122a under D50.

[0032] The second graphite 123a is a negative electrode active material composed of a carbon-based material. Except for the average particle size described below, the second graphite 123a may be the same material as the first graphite 122a. The average particle size of the second graphite 123a at D50 is smaller than the average particle size of the first graphite 122a. In one embodiment, the average particle size of the second graphite 123a may be, for example, greater than 2 μm and less than 15 μm at D50. In one embodiment, the average particle size of the second graphite 123a may be, for example, greater than 5 μm and less than 12 μm at D50.

[0033] The negative electrode second active material layer 123, for example, further includes a second silicon single substance or silicon compound 123b. The second silicon single substance or silicon compound 123b is a negative electrode active material. As the silicon compound, for example, silicon oxides such as SiO can be cited. The second silicon single substance or silicon compound 123b may be the same material as the first silicon single substance or silicon compound 122b. The amount of the second silicon single substance or silicon compound 123b, for example, relative to the total weight of the negative electrode second active material layer 123 may be greater than 0 weight % and less than 1 weight %. In a certain embodiment, the amount of the second silicon single substance or silicon compound 123b, for example, relative to the total weight of the negative electrode second active material layer 123 may be greater than 0 weight % and less than 0.5 weight %. In a certain embodiment, the negative electrode second active material layer 123 may not contain the second silicon single substance or silicon compound 123b.

[0034] The negative electrode second active material layer 123 further includes, for example, at least one second binder 123c (binder) selected from the group consisting of rubber, acrylic, polyamide-imide, and polyimide. The second binder 123c may be the same material as the first binder 122c. The amount of the second binder 123c may be, for example, 0.2% by weight or more and 5% by weight or less relative to the total weight of the negative electrode second active material layer 123. In one embodiment, the amount of the second binder 123c may be, for example, 0.5% by weight or more and 2% by weight or less relative to the total weight of the negative electrode second active material layer 123.

[0035] The negative electrode second active material layer 123, for example, further includes at least one additional carbon selected from the group consisting of easily graphitized carbon, difficult graphitized carbon, amorphous carbon, and low-crystalline carbon. Easy graphitized carbon is equivalent to soft carbon. Difficult graphitized carbon is equivalent to hard carbon. Amorphous carbon is, for example, carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, etc. The amount of additional carbon, for example, relative to the total weight of the negative electrode second active material layer 123 can be greater than 0 weight% and less than 50 weight%. In a certain embodiment, the amount of additional carbon, for example, relative to the total weight of the negative electrode second active material layer 123 can be greater than 5 weight% and less than 50 weight%. In a certain embodiment, the amount of additional carbon, for example, relative to the total weight of the negative electrode second active material layer 123 can be greater than 10 weight% and less than 40 weight%.

[0036] In addition, the additional carbon plays a role as a conductive aid, for example. The amount of the conductive aid, for example, can be 0% by weight or more and 5% by weight or less relative to the total weight of the negative electrode second active material layer 123. In one embodiment, the amount of the conductive aid, for example, can be 0% by weight or more and 3% by weight or less relative to the total weight of the negative electrode second active material layer 123.

[0037] The negative electrode second active material layer 123 covers the surface of the negative electrode first active material layer along the longitudinal direction (lateral width direction X) except the surface bonded to the negative electrode current collecting layer 121. In other words, Figure 4 As shown, the negative electrode second active material layer 123 is respectively bonded to the surface (surface) 122p of the negative electrode first active material layer 122 intersecting the stacking direction (depth direction Y) and the surfaces (side surfaces) 122q and 122r of the negative electrode first active material layer 122 along the stacking direction. In the following, the relationship between the end surface above the short side direction of the negative electrode second active material layer 123 and the end surface 122q above the short side direction of the negative electrode first active material layer 122 in the present disclosure is described, but this relationship can also be applied to the relationship between the end surface below the short side direction of the negative electrode second active material layer 123 and the end surface 122r below the short side direction of the negative electrode first active material layer 122. Therefore, in the present disclosure, as long as either one of the relationship between the upper end face in the short-side direction of the negative electrode second active material layer 123 and the upper end face 122q in the short-side direction of the negative electrode first active material layer 122 described below or the relationship between the lower end face in the short-side direction of the negative electrode second active material layer 123 and the lower end face 122r in the short-side direction of the negative electrode first active material layer 122 using this relationship is established, or both of the relationships are established. By establishing such a relationship, the effects of the present disclosure described below can be obtained.

[0038] The average thickness between the end surface of the negative electrode second active material layer 123 in the short side direction (height direction Z) and the end surface 122q in the short side direction of the negative electrode first active material layer 122 is thicker than the average thickness of the negative electrode first active material layer 122 in the stacking direction. Figure 4 As shown in FIG. 1 , when the average thickness in the short-side direction of the side surface 123t of the negative electrode second active material layer 123 bonded to the end surface 122q above the short-side direction of the negative electrode first active material layer 122 is referred to as the first thickness T1, and the average thickness in the stacking direction of the negative electrode first active material layer 122 is referred to as the second thickness T2, the first thickness T1 is thicker than the second thickness T2 (T1>T2). Here, as Figure 4 As shown in FIG. 1 , the first thickness T1 corresponds to the thickness of the side surface portion 123 t of the negative electrode second active material layer 123 in the height direction Z. Figure 4 As shown in FIG. 1 , the second thickness T2 corresponds to the thickness of the negative electrode first active material layer 122 in the depth direction Y. In addition, when the first thickness T1 varies along the side surface 122q of the upper part in the short side direction of the negative electrode first active material layer 122, that is, in the depth direction Y, for example, the average value is used. When the second thickness T2 varies along the surface 122p of the negative electrode first active material layer 122, that is, in the height direction Z, for example, the average value is used.

[0039] Furthermore, the side surface 123t of the negative electrode second active material layer 123, which is bonded to the end surface 122q above the short side direction of the negative electrode first active material layer 122, is bonded to the negative electrode collector layer 121 at the end 123u of the negative electrode second active material layer 123. That is, the end 123u of the side surface 123t of the negative electrode second active material layer 123 is bonded to the negative electrode collector layer 121. Therefore, the negative electrode second active material layer 123 covers and bonds to the negative electrode first active material layer 122, and is also bonded to the surface of the negative electrode collector layer 121.

[0040] In addition, the average thickness between the end face of the negative electrode second active material layer 123 in the short-side direction and the end face 122q of the negative electrode first active material layer 122 in the short-side direction is thicker than the average thickness between the surface portion 123s of the negative electrode second active material layer 123 stacked on the negative electrode first active material layer 122, that is, the end face of the negative electrode second active material layer 123 in the stacking direction (the end face bonded to the separator 130) and the surface 122p of the negative electrode first active material layer 122. That is, Figure 4 As shown in FIG. 1 , when the average thickness of the surface portion 123s bonded to the surface 122p of the negative electrode first active material layer 122 is referred to as the third thickness T3, the first thickness T1 is thicker than the third thickness T3 (T1>T3). Figure 4As shown, the third thickness T3 corresponds to the thickness of the surface portion 123s in the depth direction Y. When the third thickness T3 varies along the surface 122p of the negative electrode first active material layer 122, that is, along the height direction Z, for example, the average value is used.

[0041] The first thickness T1 of the negative electrode second active material layer 123 may be, for example, 10 μm or more and 1200 μm or less in average thickness. In one embodiment, the first thickness T1 of the negative electrode second active material layer 123 may be, for example, 200 μm or more and 1000 μm or less in average thickness.

[0042] The thickness (third thickness T3) of one side of the stacking direction (depth direction Y) of the negative electrode second active material layer 123 may be, for example, 5 μm or more and 500 μm or less in average thickness. In one embodiment, the thickness (third thickness T3) of one side of the stacking direction (depth direction Y) of the negative electrode second active material layer 123 may be, for example, 10 μm or more and 300 μm or less in average thickness.

[0043] In one embodiment, if Figure 5 As shown in FIG. 6 , the upper end surface of the short side direction of the negative electrode second active material layer 123 and / or the upper end surface 122q of the short side direction of the negative electrode first active material layer 122 are changed to have an inclined portion. Figure 5 As shown in FIG. 6 , the slope of the negative electrode first active material layer 122 refers to the slope where the thickness of the negative electrode first active material layer 122 in the stacking direction becomes thinner as it goes upward in the short side direction (that is, the distance between the surface of the negative electrode current collector layer 121 and the surface of the negative electrode first active material layer 122 becomes shorter). Figure 5 As shown in FIG. 6 , the inclined portion of the negative electrode second active material layer 123 means that the inclined portion of the negative electrode second active material layer 123 is arranged in a manner facing the inclined portion of the negative electrode first active material layer 122 and the surface of the negative electrode collector layer 121 on the outside (upper in the short side direction) of the negative electrode first active material layer 122 (that is, the portion of the negative electrode collector layer 121 not stacked with the negative electrode first active material layer 122). In this case, as Figure 5 As shown in or 6, the thickness between the uppermost portion X2-1 or X2-2 of the end face above the short side direction of the negative electrode second active material layer 123 and the uppermost portion X1 of the end face above the short side direction of the negative electrode first active material layer 122 is called the 1st 'thickness T'1, and the thickness between the starting portion X0 of the inclined portion of the negative electrode first active material layer 122 and the uppermost portion X1 of the end face above the short side direction is called the 4th thickness T4.

[0044] For example, Figure 5As shown, the negative electrode second active material layer 123 covers the negative electrode first active material layer 122 while thinning the thickness between the negative electrode first active material layer 122 in a manner facing the inclined portion of the negative electrode first active material layer 122, and as a result, the 1st thickness T'1 is less than the 3rd thickness T3 (T'1<T3). In a certain embodiment, the 1st thickness T'1 is less than the 2nd thickness T2 (T'1<T2). In a certain embodiment, the 1st thickness T'1 is greater than the 2nd thickness T2 (T'1>T2). In a certain embodiment, the 1st thickness T'1 is greater than the 4th thickness T4 (T'1>T4).

[0045] For example, Figure 6 As shown, the negative electrode second active material layer 123 gradually increases the thickness between the negative electrode first active material layer 122 and the negative electrode first active material layer 122 in a manner facing the inclined surface of the negative electrode first active material layer 122 (that is, as shown in FIG. Figure 6 In one embodiment, the first active material layer 122 of the negative electrode is covered while the first thickness T'1 of the negative electrode is covered (such as the thickness T1-1 of the first part is less than the thickness T1-2 of the second part), and as a result, the first thickness T'1 is greater than the third thickness T3 (T'1>T3). In one embodiment, the first thickness T'1 is greater than the second thickness T2 (T'1>T2). In one embodiment, the first thickness T'1 is greater than the fourth thickness T4 (T'1>T4). In one embodiment, the first thickness T'1 is greater than the second thickness T2 (T'1>T2) and is greater than the fourth thickness T4 (T'1>T4).

[0046] like Figure 3 and Figure 4 As shown in FIG. 1 , the separator 130 has an insulating function of insulating the positive electrode 110 and the negative electrode 120 to prevent a short circuit between the positive electrode 110 and the negative electrode 120 and a function of retaining a non-aqueous electrolyte. The separator 130 allows lithium ions to pass through the electrolyte. The separator 130 is formed in a long strip shape. Figure 4As shown, the width of the separator 130 along the short side direction (height direction Z) is longer than the width of the collector portion 111a of the positive electrode 110 and the collector portion 121a of the negative electrode 120 along the short side direction. Both ends of the collector portion 111a of the positive electrode 110 along the short side direction (the upper end to the lower end in the height direction Z) are located within the range of the separator 130 along the short side direction (the upper end to the lower end in the height direction Z), and both ends of the collector portion 121a of the negative electrode 120 along the short side direction (the upper end to the lower end in the height direction Z) are located within the range of the separator 130 along the short side direction (the upper end to the lower end in the height direction Z). The separator 130 is made of a porous material. As the separator 130 , a porous sheet made of a resin such as polyethylene (PE: PolyEthylene), polypropylene (PP: PolyPropylene), polyester, cellulose, polyamide, or a laminated sheet thereof (for example, a sheet consisting of three layers of PP / PE / PP) is used.

[0047] A layer containing an inorganic material (such as alumina particles) and a binder may be provided on one or both sides of the separator 130. Thus, even when the battery 1 is used in an abnormal state (for example, when the temperature of the lithium-ion secondary battery rises to 160° C. or above due to overcharging or crushing), the separator 130 can be prevented from melting and the insulation function can be maintained. Therefore, the safety of the battery 1 is improved.

[0048] The electrolyte is equivalent to the so-called electrolytic solution. The electrolyte is impregnated in the separator 130 and is in contact with the positive electrode 110 and the negative electrode 120. The electrolyte includes an organic solvent, a supporting salt, and an additive. As an organic solvent, for example, carbonates are used. As a supporting salt, for example, a lithium salt is used. As an additive, for example, vinylene carbonate or fluoroethylene carbonate is used.

[0049] like Figure 1 As shown, the container 200 contains the charge-discharge body 100. The container 200 includes a case 201 and a lid 202. The lid 202 is joined to the opening of the case 201 and seals the charge-discharge body 100 together with the case 201. The charge-discharge body 100 sealed by the case 201 and the lid 202 is filled with an electrolyte.

[0050] like Figure 1As shown, the external terminal 300 includes a positive terminal 301 and a negative terminal 302. The positive terminal 301 and the negative terminal 302 relay the input and output of power between the charge-discharge body 100 and the external device. In addition, when a plurality of batteries 1 are used to form an assembled battery, the positive terminal 301 of an adjacent battery and the negative terminal 302 of another adjacent battery are joined via a busbar. The positive terminal 301 is indirectly or directly joined to the positive electrode tab 111b via the positive electrode collector plate. The negative terminal 302 is indirectly or directly joined to the negative electrode tab 121b via the negative electrode collector plate. The positive terminal 301 and the negative terminal 302 are mounted on the cover 202.

[0051] (Negative Electrode 120 and Method for Manufacturing Battery 1 Including Negative Electrode 120 According to Embodiment) The negative electrode 120 of the embodiment and the battery 1 having the negative electrode 120 are manufactured by coating the negative electrode first active material layer 122 described above with the negative electrode mixture composition (that is, a composition containing the materials contained in the negative electrode first active material layer 122 and a solvent such as N-methyl-2-pyrrolidone (NMP) and / or water) on the negative electrode collector layer 121 by known techniques, and coating the negative electrode second active material layer 123 described above with the negative electrode mixture composition (that is, a composition containing the materials contained in the negative electrode second active material layer 123 and a solvent such as N-methyl-2-pyrrolidone (NMP) and / or water) on the negative electrode first active material layer 122 by known techniques as in the embodiment described above. Otherwise, the negative electrode 120 can be manufactured using techniques known in the technical field.

[0052] For example, the negative electrode 120 can be formed as follows. First, prepare the material contained in the negative electrode first active material layer 122. The material can be in a granular form. The material is dispersed in a solvent (for example, N-methyl-2-pyrrolidone (NMP) and / or water) to prepare a paste or slurry-like negative electrode mixture composition for the negative electrode first active material layer 122. The prepared negative electrode mixture composition is applied to the surface (one side or both sides) of the negative electrode collector layer 121 and dried, and a calendering treatment is performed as needed to form the negative electrode first active material layer 122. Furthermore, prepare the material contained in the negative electrode second active material layer 123. The material can be in a granular form. The material is dispersed in a solvent (for example, N-methyl-2-pyrrolidone (NMP) and / or water) to prepare a paste or slurry-like negative electrode mixture composition for the negative electrode second active material layer 123. The prepared negative electrode mixture composition is applied to the surface (one side or both sides) of the negative electrode first active material layer 122 as in the above-described embodiment and dried, and calendering is performed as needed to form the negative electrode second active material layer 123. Thus, the negative electrode 120 is obtained. However, the negative electrode 120 is not limited to being manufactured by the above-described manufacturing method, and may also be manufactured by other methods.

[0053] Furthermore, as a method for manufacturing the negative electrode 120 of the embodiment, a method for manufacturing a negative electrode first active material layer and a negative electrode second active material layer in which the negative electrode active material layer is formed by simultaneous coating may be used. Figure 7 , the manufacturing method is described.

[0054] In this manufacturing method, the materials contained in the first negative electrode active material layer (e.g., negative electrode active material, conductive aid, binder, etc.) are prepared. These materials are mixed and the resulting mixture is dispersed in a solvent (e.g., N-methyl-2-pyrrolidone (NMP) and / or water) to obtain a first negative electrode slurry. In addition, the materials contained in the second negative electrode active material layer (e.g., negative electrode active material, conductive aid, binder, etc.) are prepared. These materials are mixed and the resulting mixture is dispersed in a solvent (e.g., N-methyl-2-pyrrolidone (NMP) and / or water) to obtain a second negative electrode slurry.

[0055] Then, for example, use Figure 7The die head 50 shown in the figure applies the negative electrode first slurry and the negative electrode second slurry to the negative electrode collector 34a at the same time. The die head 50 has an outlet block 57, a three-dimensional gasket 58 and an inlet block 59. A manifold 52 for the negative electrode second slurry and a manifold 51 for the negative electrode first slurry are provided inside the die head 50. The negative electrode second slurry and the negative electrode first slurry are discharged from each manifold 52, 51 simultaneously to the negative electrode collector 34a conveyed along the back roller 56. Thus, the negative electrode second slurry layer 33d and the negative electrode first slurry layer 33b are formed. Next, the solvent contained in the negative electrode first slurry layer 33b and the negative electrode second slurry layer 33d is volatilized by means of a drying furnace or the like, so that the negative electrode first slurry layer 33b and the negative electrode second slurry layer 33d are dried. Thus, a negative electrode first active material layer (not shown) and a negative electrode second active material layer (not shown) are formed on one side of the negative electrode collector 34a. Next, the negative electrode collector 34a, the negative electrode first active material layer and the negative electrode second active material layer are pressed. Specifically, a stack including the negative electrode collector 34a, the negative electrode first active material layer and the negative electrode second active material layer is clamped with a roller heated to 60 to 120°C to apply pressure. Thereafter, the stack is cut to a specified width. Thus, a negative electrode is obtained.

[0056] In a battery having a negative electrode manufactured by the above manufacturing method using double-layer simultaneous coating, the interface between the negative electrode first slurry layer 33b and the negative electrode second slurry layer 33d has a concave-convex shape, so the adhesion between the negative electrode first slurry layer 33b and the negative electrode second slurry layer 33d is improved, and even if volume changes accompanying charging and discharging occur, the two layers will not peel off, thereby achieving the effect of improving the reliability of the battery.

[0057] (Effects of the Battery 1 Having the Negative Electrode 120 of the Embodiment) refer to Figure 4 , the effects of the battery 1 including the negative electrode 120 according to the embodiment will be described.

[0058] The first active material layer (negative electrode first active material layer 122) of the negative electrode 120 includes a first graphite 122a and a first silicon simple substance or silicon compound 122b. The second active material layer (negative electrode second active material layer 123) of the negative electrode 120 includes a second graphite 123a having an average particle size smaller than that of the first graphite. The surface of the negative electrode first active material layer 122 along the long side direction is covered by the negative electrode second active material layer 123 except for the surface bonded to the negative electrode current collector layer 121. The average thickness (first thickness T1) between the end surface above the short side direction of the negative electrode second active material layer 123 and the end surface 122q above the short side direction of the negative electrode first active material layer 122 is thicker than the average thickness (second thickness T2) of the negative electrode first active material layer 122 in the stacking direction (i.e., T1>T2). The battery 1 includes the negative electrode 120, the positive electrode 110, and an electrolyte.

[0059] According to such a configuration, the durability of the battery 1 is improved. Therefore, by improving the durability of the battery 1, it is possible to suppress the degradation of the negative electrode 120 accompanying repeated charge and discharge of the battery 1, thereby suppressing the reduction of the charge and discharge cycle characteristics of the battery 1. Therefore, the battery 1 can be charged rapidly while suppressing the reduction of the life.

[0060] Specifically, in the negative electrode 120, the negative electrode first active material layer 122 includes a first graphite 122a, and the first graphite 122a has an average particle size relatively large compared to the average particle size of the second graphite 123a included in the negative electrode second active material layer 123 (that is, a relatively small specific surface area). As the battery 1 is charged and discharged, the first graphite 122a and the second graphite 123a in the negative electrode 120 may react with the electrolyte to form a film on the surface of these graphites. The film will capture lithium ions and reduce the lithium ion storage capacity of the graphite. Therefore, to improve the lithium ion storage capacity of the negative electrode first active material layer 122, it is sufficient to avoid the formation of the film. To avoid the formation of the film, it is sufficient to reduce the surface area of ​​the graphite that reacts with the electrolyte, that is, to reduce the specific surface area of ​​the graphite (that is, to increase the average particle size). Therefore, in the negative electrode 120, the average particle size of the first graphite 122a contained in the negative electrode first active material layer 122 is made larger than the average particle size of the second graphite 123a contained in the negative electrode second active material layer 123, thereby reducing the amount of film that may be formed due to the reaction between the graphite and the electrolyte and ensuring good lithium ion storage properties. As a result, the negative electrode first active material layer 122 can function as a high-capacity layer of the negative electrode 120.

[0061] In addition, the end surface 122q of the negative electrode first active material layer 122 in the short-side direction is covered by the negative electrode second active material layer 123. Furthermore, the first thickness T1>the second thickness T2. Therefore, even if the first silicon single substance or silicon compound 122b contained in the negative electrode first active material layer 122 expands or contracts with the charge and discharge of the battery 1, the end surface 122q of the negative electrode first active material layer 122 in the short-side direction is not exposed, and further, the portion of the first thickness T1 of the negative electrode second active material layer 123 can fully maintain the end surface 122q of the negative electrode first active material layer 122 in the short-side direction. Therefore, the negative electrode first active material layer 122 can be suppressed from peeling off from the negative electrode collector layer 121 and the negative electrode second active material layer 123 starting from the end surface 122q of the negative electrode first active material layer 122 in the short-side direction.

[0062] Furthermore, the first thickness T1 may be, for example, greater than the average thickness (third thickness T3 ) of the surface portion 123 s of the negative electrode second active material layer 123 stacked on the negative electrode first active material layer 122 (ie, T1 > T3 ).

[0063] According to such a structure, even if the first silicon element or silicon compound 122b contained in the negative electrode first active material layer 122 expands or contracts with the charge and discharge of the battery 1, since the end face 122q above the short side direction of the negative electrode first active material layer 122 is not exposed, and further, the first thickness T1 portion of the negative electrode second active material layer 123 can fully maintain the end face 122q above the short side direction of the negative electrode first active material layer 122, it is possible to suppress the negative electrode first active material layer 122 from the negative electrode collector layer 121 and the negative electrode second active material layer 123 with the end face 122q above the short side direction of the negative electrode first active material layer 122 as the starting point.

[0064] In addition, the side surface 123 t of the negative electrode second active material layer 123 bonded to the upper end surface 122 q of the negative electrode first active material layer 122 in the short-side direction is bonded to the negative electrode collector layer 121 at, for example, an end 123 u of the negative electrode second active material layer 123 .

[0065] According to such a configuration, since the negative electrode second active material layer 123 is bonded to the negative electrode current collecting layer 121 while covering the negative electrode first active material layer 122 , it is possible to suppress the negative electrode first active material layer 122 from being separated from the negative electrode current collecting layer 121 .

[0066] Furthermore, the negative electrode first active material layer 122 includes a first silicon simple substance or silicon compound 122b. When the negative electrode first active material layer 122 includes the first silicon simple substance or silicon compound 122b having excellent lithium ion storage properties, the capacity of the battery 1 can be increased.

[0067] The negative electrode first active material layer 122 may include, for example, at least one first binder 122 c selected from the group consisting of rubber, acrylic, polyamide-imide, and polyimide.

[0068] According to such a configuration, even if the first silicon simple substance or silicon compound 122b included in the negative electrode first active material layer 122 expands or contracts relatively greatly with the charge and discharge of the battery 1, the first binder 122c can relatively reduce the decrease in the tensile strength of the negative electrode current collector layer 121 and / or the negative electrode first active material layer 122 and / or the negative electrode second active material layer 123 caused by repeated input of stress. That is, the decrease in the tensile strength of the negative electrode current collector layer 121 and / or the negative electrode first active material layer 122 and / or the negative electrode second active material layer 123 over time caused by the expansion or contraction of the first silicon simple substance or silicon compound 122b accompanying the repeated charge and discharge of the battery 1 is relatively reduced due to the first binder 122c compared with the case where the binder is not included. In more detail, even if the first silicon single substance or silicon compound 122b contained in the first negative electrode active material layer 122 expands relatively greatly during the charge of the battery 1, the first binder 122c can fully retain the first silicon single substance or silicon compound 122b. The first binder 122c can fully retain the first silicon single substance or silicon compound 122b, for example, the first binder 122c can fully maintain the state in which the first silicon single substance or silicon compound 122b is fixed to the negative electrode current collector layer 121 and / or the negative electrode second active material layer 123. On the other hand, even if the first silicon single substance or silicon compound 122b contained in the first negative electrode active material layer 122 shrinks relatively greatly during the discharge of the battery 1, the first binder 122c can fully retain the first silicon single substance or silicon compound 122b. That is, even if the first silicon simple substance or silicon compound 122b contained in the negative electrode first active material layer 122 expands or contracts relatively greatly with the charge and discharge of the battery 1, the peeling of the negative electrode first active material layer 122 and the negative electrode collector layer 121 and / or the negative electrode second active material layer 123 can be suppressed. In other words, the degradation of the battery characteristics of the charge and discharge body 100 can be suppressed. As a result, the degradation of the quality of the negative electrode 120 accompanying the repeated charge and discharge of the battery 1 can be suppressed, the degradation of the charge and discharge cycle characteristics of the battery 1 can be suppressed, and the life of the battery 1 can be extended.

[0069] The tensile strength of the negative electrode current collector layer 121 can be, for example, 30 kg / mm 2 above.

[0070] According to such a configuration, even if the first silicon simple substance or silicon compound 122b contained in the first negative electrode active material layer 122 expands or contracts relatively greatly with the charge and discharge of the battery 1, the expansion or contraction can be suppressed by the negative electrode collector layer 121 bonded to the first negative electrode active material layer 122. Therefore, the peeling of the negative electrode collector layer 121 and the first negative electrode active material layer 122 can be suppressed. In addition, since the relatively large expansion or contraction of the first silicon simple substance or silicon compound 122b contained in the first negative electrode active material layer 122 is suppressed, the peeling of the second negative electrode active material layer 123 bonded to the first negative electrode active material layer 122 and the first negative electrode active material layer 122 can be suppressed. That is, the degradation of the battery characteristics of the charge and discharge body 100 can be suppressed. As a result, the degradation of the quality of the negative electrode 120 caused by the repeated charge and discharge of the battery 1 can be suppressed, the degradation of the charge and discharge cycle characteristics of the battery 1 can be suppressed, and the life of the battery 1 can be extended.

[0071] In addition, in the negative electrode 120, the negative electrode second active material layer 123 includes a second graphite 123a, and the second graphite 123a has an average particle size (that is, a relatively small volume) that is relatively small compared to the average particle size of the first graphite 122a included in the negative electrode first active material layer 122. The smaller the volume of graphite, the shorter the distance that lithium ions move inside, so lithium ions can be input and output at a high speed. Therefore, in the negative electrode 120, the average particle size of the second graphite 123a included in the negative electrode second active material layer 123 is made smaller than the average particle size of the first graphite 122a included in the negative electrode first active material layer 122, thereby enabling the input and output of lithium ions at a high speed. As a result, the negative electrode second active material layer 123 can function as a high input and output layer of the negative electrode 120.

[0072] Furthermore, the negative electrode second active material layer 123 may contain the second silicon single substance or silicon compound 123b, for example, in a range of 0 wt% or more and less than 1 wt%. In other words, the proportion of the second silicon single substance or silicon compound 123b in the negative electrode second active material layer 123 may be smaller than the proportion of the first silicon single substance or silicon compound 122b in the negative electrode first active material layer 122. The first silicon single substance or silicon compound 122b and the second silicon single substance or silicon compound 123b in the negative electrode 120 expand as the battery 1 is charged and shrink as the battery 1 is discharged. Therefore, by making the negative electrode second active material layer 123 contain a second silicon single substance or silicon compound 123b that is less than the first silicon single substance or silicon compound 122b contained in the negative electrode first active material layer 122, it is possible to suppress the expansion or contraction of the second silicon single substance or silicon compound 123b in the negative electrode second active material layer 123 that may occur along with the charge and discharge of the battery 1, and to suppress the peeling of the negative electrode second active material layer 123 from the negative electrode first active material layer 122. As a result, the durability of the battery 1 and the rapid charging characteristics of the battery 1 that conflict with the high energy density of the battery 1 can be improved.

[0073] The negative electrode second active material layer 123 may include at least one second binder 123 c selected from the group consisting of, for example, rubber-based, acrylic-based, polyamide-imide, and polyimide.

[0074] According to such a configuration, even if the second silicon simple substance or silicon compound 123b included in the negative electrode second active material layer 123 expands or contracts relatively greatly with the charge and discharge of the battery 1, the second binder 123c can relatively reduce the decrease in the tensile strength of the negative electrode current collector layer 121 and / or the negative electrode first active material layer 122 and / or the negative electrode second active material layer 123 caused by repeated input of stress. That is, the decrease in the tensile strength of the negative electrode current collector layer 121 and / or the negative electrode first active material layer 122 and / or the negative electrode second active material layer 123 over time caused by the expansion or contraction of the second silicon simple substance or silicon compound 123b accompanying the repeated charge and discharge of the battery 1 is relatively reduced due to the second binder 123c compared with the case where the binder is not included. More specifically, even if the second silicon single substance or silicon compound 123b contained in the negative electrode second active material layer 123 expands relatively greatly during the charge of the battery 1, the second binder 123c can fully retain the second silicon single substance or silicon compound 123b. The second binder 123c can fully retain the second silicon single substance or silicon compound 123b, for example, the second binder 123c can fully maintain the state in which the second silicon single substance or silicon compound 123b is fixed to the negative electrode current collector layer 121 and / or the negative electrode first active material layer 122. On the other hand, even if the second silicon single substance or silicon compound 123b contained in the negative electrode second active material layer 123 shrinks relatively greatly during the discharge of the battery 1, the second binder 123c can fully retain the second silicon single substance or silicon compound 123b. That is, even if the second silicon simple substance or silicon compound 123b contained in the negative electrode second active material layer 123 expands or contracts relatively greatly with the charge and discharge of the battery 1, the peeling of the negative electrode second active material layer 123 and the negative electrode current collector layer 121 and / or the negative electrode first active material layer 122 can be suppressed. In other words, the degradation of the battery characteristics of the charge and discharge body 100 can be suppressed. As a result, the degradation of the quality of the negative electrode 120 accompanying the repeated charge and discharge of the battery 1 can be suppressed, the degradation of the charge and discharge cycle characteristics of the battery 1 can be suppressed, and the life of the battery 1 can be extended.

[0075] The negative electrode second active material layer 123 may include, for example, at least one selected from the group consisting of easily graphitizable carbon, hardly graphitizable carbon, amorphous carbon, and low-crystalline carbon.

[0076] According to such a configuration, lithium ions can be input and output at a relatively high speed by at least one selected from the group consisting of easily graphitizable carbon, hardly graphitizable carbon, amorphous carbon, and low-crystalline carbon. That is, the negative electrode second active material layer 123 can function as a high input and output layer of the negative electrode 120. As a result, the battery 1 can be charged rapidly while suppressing a reduction in the life of the battery 1.

[0077] Next, refer to Figure 5 or Figure 6, the effects of the battery 1 including the negative electrode 120 according to the embodiment will be described.

[0078] The upper end surface of the negative electrode second active material layer 123 in the short-side direction and / or the upper end surface 122 q of the negative electrode first active material layer 122 in the short-side direction may be changed to have a slope, for example.

[0079] In the case where each end face above the short side direction has a sloped portion, the thickness (T'1) between the uppermost portion X2-1 or X2-2 of the end face above the short side direction of the negative electrode second active material layer 123 and the uppermost portion X1 of the end face 122q above the short side direction of the negative electrode first active material layer 122 may be thicker than the thickness (T4) between the starting portion X0 of the sloped portion of the negative electrode first active material layer 122 and the uppermost portion X1 of the end face above the short side direction (T'1>T4).

[0080] According to such a configuration, the thick negative electrode second active material layer 123 is formed to cover the end face 122q above the short side direction of the negative electrode first active material layer 122, so the distance from the end face above the short side direction of the negative electrode second active material layer 123 to the first silicon single substance or silicon compound 122b contained in the negative electrode first active material layer 122 can be further lengthened. This helps, for example, to inhibit the formation of a film by the first silicon single substance or silicon compound 122b. In addition, the effect of lengthening the distance is not limited to this, and other effects may also be provided. Furthermore, by having an inclined portion on the end face 122q above the short side direction of the negative electrode first active material layer 122, the area facing the positive electrode, which is prone to react with lithium ions, becomes larger, and the area not facing the positive electrode, which is not prone to react with lithium ions, becomes narrower, thereby efficiently ensuring the area that can be used for electrode reaction.

[0081] When the end faces above each short side direction have an inclined portion, the negative electrode second active material layer 123 can gradually increase the thickness between the negative electrode first active material layer 122 and the negative electrode first active material layer 122 in a manner opposite to the inclined portion of the negative electrode first active material layer 122, that is, the thickness T1-1 of the first portion is less than the thickness T1-2 of the second portion, while covering the negative electrode first active material layer 122. As a result, the 1st thickness T'1 is greater than the 3rd thickness T3 (T'1>T3).

[0082] The average particle size of the second graphite 123a contained in the second active material layer 123 of the negative electrode is smaller than the average particle size of the first graphite 122a contained in the first active material layer 122 of the negative electrode (that is, the specific surface area of ​​the second graphite 123a is larger than the specific surface area of ​​the first graphite 122a), so the contact area between the second binder 123c and the second graphite 123a is larger than the contact area between the first binder 122c and the first graphite 122a. In other words, the consumption of the surface of the second graphite 123a particles of the second binder 123c is greater than the consumption of the surface of the first graphite 122a particles of the first binder 122c. Therefore, if such a structure is also taken into consideration, since the thickness T1-2 of the second portion is greater than the thickness T1-1 of the first portion, the negative electrode second active material layer 123, which is difficult to be carried on the negative electrode collector layer 121 compared to the negative electrode first active material layer 122, can be fully maintained on the negative electrode collector layer 121. Furthermore, since the thickness T1-1 of the first portion is smaller than the thickness T1-2 of the second portion, the area where the electrode reaction occurs outside the surface portion of the negative electrode first active material layer 122 and the negative electrode second active material layer 123 can be reduced, thereby efficiently ensuring the area that can be used for the electrode reaction. Example

[0083] (Experimental Results of Battery 1 Having Negative Electrode 120 of Embodiment) The experimental results of the battery 1 having the negative electrode 120 of the embodiment are described with reference to Tables 1 to 3. In addition, Tables 1 and 2 show the configurations of the batteries of Examples 1 to 10 and Comparative Examples 1 to 7, and Table 3 shows the test results of each battery (capacity after 1 cycle and after 100 cycles and direct current resistance (DCR) after 1 cycle). The methods for measuring battery capacity, charge and discharge cycles, and DCR are as follows.

[0084] 〈Battery capacity〉 Regarding the battery capacity, constant voltage-constant current charging (CC-CV charging) was performed for a total of 2.5 hours at a charging current of 1 C until the battery voltage reached 4.2 V. Then, after a rest period of 30 minutes, constant current discharge (CC discharge) was performed at a discharge current of 0.2 C until the battery voltage reached 2.9 V to obtain the initial capacity.

[0085] 〈Charge and discharge cycle〉 Regarding the charge and discharge cycle test, the charge and discharge were repeated 99 times after the battery capacity was measured. Constant voltage-constant current charging (CC-CV charging) was performed for a total of 2.5 hours at a charging current of 1C until the battery voltage reached 4.2V. Then, it was paused for 30 minutes, and then constant current discharge (CC discharge) was performed at a discharge current of 1C until the battery voltage reached 2.9V. Then, it was paused for 30 minutes. After the charge and discharge cycle, the battery capacity was measured again and compared with the initial battery capacity.

[0086] 〈DCR〉 Regarding the relationship between SOC and open circuit voltage (OCV), the voltage after discharging the battery capacity by 5% from 4.2 V and resting for 2 hours was taken as OCV, and its relationship with SOC was obtained.

[0087] Regarding the DCR in the low SOC region, i.e., SOC25%, CC-CV charging is performed at a charging current of 1C from SOC0% to SOC25% according to the SOC-OCV relationship. The lithium-ion secondary battery is then kept in a constant temperature chamber at -10°C for 5 hours. Thereafter, the lithium-ion secondary battery is discharged at a constant current of 0.5C for 10 seconds, and the voltage drop value caused by the discharge is measured. Furthermore, the same constant current discharge is performed at discharge currents of 1C, 1.5C, and 2C. The discharge current is plotted as the horizontal axis and the voltage drop value as the vertical axis, and the slope of the graph is obtained as the DCR. The DCR (relative value) of the lithium-ion secondary batteries of each embodiment and comparative example is calculated after standardization with the DCR of the lithium-ion secondary battery of Example 1 as 100. The smaller the value of the DCR at SOC25%, the lower the internal resistance of the lithium-ion secondary battery in the low SOC region.

[0088] [Table 1] Table 1 SBR: styrene-butadiene rubber AR:Acrylic resin PI: polyimide D50:

[0089] [Table 2] Table 2 Thickness ratio: thickness of first active material layer (first thickness T1) / thickness of second active material layer (second thickness T2)

[0090] [Table 3] Table 3 Capacity [Ah]: Relative value when the capacity after one cycle of Example 1 is set as 100% (*reference value) DCR [Ω]: Relative value when the DCR of Example 1 is set as 100% (*reference value) Test temperature = -10°C, discharge time = 10 seconds, DOC = 25%

[0091] The following facts are known from Tables 1 to 3. Here, Example 1 is used as a reference to compare Example 1 with Examples 2 to 10 or Comparative Examples 1 to 7. In addition, the capacity is preferably large, and the direct current resistance value (DCR) is a characteristic related to rapid charging and is preferably small.

[0092] Example 1 is compared with Examples 2 to 10. In Example 2, since there is no bonding between the side portion of the second active material layer and the collector layer, the capacity after 100 cycles is reduced. In Example 3, it is found that the average particle size D50 of the first graphite 122a in the first active material layer 122 of the negative electrode is larger than the average particle size D50 of the second graphite 123a in the second active material layer 123 of the negative electrode, which is 8 μm, but is reduced to 12 μm. In this case, the capacity after 100 cycles is slightly reduced, but the direct current resistance (DCR) is reduced. In Example 4, it is found that when the average particle size D50 of the first graphite 122a in the first active material layer 122 of the negative electrode is increased to 30 μm, the DCR is slightly increased, but the capacity after 100 cycles is increased. In Example 5, it was found that when the average particle size D50 of the second graphite 123a in the negative electrode second active material layer 123 was reduced to 3 μm, the capacity after 100 cycles was slightly reduced, but the DCR was reduced. In Example 6, it was found that the average particle size D50 of the second graphite 123a in the negative electrode second active material layer 123 was smaller than the average particle size D50 of the first graphite 122a in the negative electrode first active material layer 122, which was 20 μm, but increased to 12 μm. In this case, the DCR was slightly increased, but the capacity after 100 cycles increased. In Example 7, it was found that when the first binder 122c in the negative electrode first active material layer 122 was changed to an acrylic resin (AR), the capacity after 100 cycles increased and the DCR decreased. In Example 8, it was found that when the first binder 122c in the negative electrode first active material layer 122 was changed to polyimide (PI), the capacity after one cycle decreased and the DCR increased, but the capacity after 100 cycles increased. In Example 9, it was found that when the second binder 123c in the negative electrode second active material layer 123 was changed to acrylic resin (AR), the DCR decreased. In Example 10, it was found that when the second binder 123c in the negative electrode second active material layer 123 was changed to polyimide (PI), the DCR increased slightly, but the performance was able to maintain substantially the same as that of Example 1.

[0093] Next, Example 1 is compared with Comparative Examples 1 to 7. In Comparative Example 1, it is known that in the absence of the negative electrode first active material layer 122, the capacity after 100 cycles increases and the DCR decreases, but the capacity after 1 cycle decreases significantly. In Comparative Example 2, it is known that in the absence of the negative electrode second active material layer 123, the capacity after 1 cycle increases slightly, but the capacity after 100 cycles decreases significantly, and the DCR also increases significantly. In Comparative Example 3, it is known that in the case where the first silicon single substance or silicon compound 122b is not added to the negative electrode first active material layer 122, the capacity after 100 cycles increases, but the capacity after 1 cycle decreases significantly. In Comparative Example 4, it is known that in the case where the first graphite 122a is not added to the negative electrode first active material layer 122, the capacity after 1 cycle increases to about 2.6 times, the DCR decreases slightly, but the capacity after 100 cycles decreases significantly. In Comparative Example 5, it was found that when the average particle size D50 of the first graphite 122a in the first negative active material layer 122 was reduced to 8 μm and the average particle size D50 of the second graphite 123a in the second negative active material layer 123 was increased to 20 μm, thereby making the average particle size D50 of the first graphite 122a smaller than the average particle size D50 of the second graphite 123a, the consumption of lithium ions increased, and as a result, the capacity after 100 cycles was greatly reduced and the DCR was also greatly increased. In Comparative Example 6, it was found that when the second negative active material layer 123 and the negative current collector layer 121 were not bonded, that is, when the end face 122q of the first negative active material layer 122 in the short side direction was exposed above the end face of the second negative active material layer 123 in the short side direction, the capacity after 100 cycles was greatly reduced. In Comparative Example 7, it was found that when the first thickness T1 was thinner than the second thickness T2, the capacity after 100 cycles was significantly reduced.

[0094] Therefore, based on the comparison between Example 1 and one or more of Examples 2 to 10 and Comparative Examples 1 to 7, the negative electrode 120 and the battery 1 of the embodiment described above have the following configuration or preferably have the following configuration.

[0095] According to the comparison between Example 1 and Comparative Examples 1 and 2, the negative electrode 120 includes a negative electrode first active material layer 122 and a negative electrode second active material layer 123. According to the comparison between Example 1 and Comparative Examples 3 and 4, the negative electrode first active material layer 122 includes a first graphite 122a and a first silicon simple substance or silicon compound 122b. According to the comparison between Example 1 and Examples 3 to 6 and Comparative Example 5, the first active material layer 122 of the negative electrode includes the first graphite 122a having an average particle size larger than that of the second active material layer 123 of the negative electrode. Specifically, it is preferred that the first active material layer 122 of the negative electrode includes the first graphite 122a, wherein the first graphite 122a has an average particle size larger than that of the second graphite 123a included in the second active material layer 123 of the negative electrode, and is greater than 10 μm and less than 35 μm at D50; the second active material layer 123 of the negative electrode includes the second graphite 123a, wherein the second graphite 123a has an average particle size smaller than that of the first graphite 122a included in the first active material layer 122 of the negative electrode, and is greater than 2 μm and less than 15 μm at D50. According to the comparison between Example 1 and Examples 7 to 10, the negative electrode first active material layer 122 further includes a first binder 122c, and the negative electrode second active material layer 123 further includes a second binder 123c. Specifically, the negative electrode first active material layer 122 preferably further includes at least one first binder 122c selected from the group consisting of rubber, acrylic, polyamide-imide, and polyimide, and the negative electrode second active material layer 123 preferably further includes at least one second binder 123c selected from the group consisting of rubber, acrylic, polyamide-imide, and polyimide. According to the comparison between Example 1 and Comparative Example 6, the surface of the negative electrode first active material layer 122 along the long side direction is covered by the negative electrode second active material layer 123 except for the surface bonded to the negative electrode current collector layer 121. According to the comparison between Example 1 and Comparative Example 7, the average thickness T1 between the end surface of the negative electrode second active material layer 123 above the short side direction and the end surface 122q of the negative electrode first active material layer 122 above the short side direction is thicker than the average thickness T2 of the negative electrode first active material layer 122 in the stacking direction.

[0096] (Other embodiments) The negative electrode and the lithium ion secondary battery disclosed herein are not limited to the configuration of the lithium ion secondary battery 1 described in the embodiment, and can be configured as appropriate according to the contents described in the claims.

[0097] The embodiments are to explain the disclosure in detail or briefly in an easy-to-understand manner, and do not necessarily have all the structures described, or may also have structures not shown. In addition, a part of the structure of the embodiment may also be deleted, or replaced with the structure of other embodiments, or combined with the structure of other embodiments.

[0098] The lithium ion secondary battery 1 is not limited to a battery installed in an electric vehicle to supply power to a driving motor of the electric vehicle. For example, the lithium ion secondary battery 1 can be used as a battery installed in a portable electronic device such as a smartphone (registered trademark) or a battery installed in a stationary power generation device.

[0099] The negative electrode 120 is not limited to a configuration in which two or more active material layers are provided on the negative electrode current collecting layer 121 . For example, the negative electrode 120 may be a configuration in which three or more active material layers are provided on the negative electrode current collecting layer 121 .

[0100] The negative electrode 120 is not limited to a configuration in which two active material layers are provided only on one side of the negative electrode current collecting layer 121. For example, the negative electrode 120 may be configured to have two active material layers provided on both sides of the negative electrode current collecting layer 121. In addition, the negative electrode 120 may be configured to have two active material layers provided on one side of the negative electrode current collecting layer 121 and one active material layer provided on the other side of the negative electrode current collecting layer 121.

[0101] The negative electrode 120 is not limited to the configuration in which the negative electrode tab 121b protruding from the negative electrode collector 121a is provided. For example, the negative electrode 120 may be configured such that the end of the wound negative electrode collector 121a is electrically connected to the negative electrode terminal 302 via the negative electrode collector plate. In addition, the negative electrode 120 may be configured such that the end of the wound negative electrode collector 121a is electrically connected to the negative electrode terminal 302.

[0102] The charge-discharge body 100 is not limited to a winding type in which a long strip of positive electrode 110 and a long strip of negative electrode 120 are wound with a long strip of separator 130 interposed therebetween. For example, the charge-discharge body 100 can also be configured as a stacked type in which a plurality of positive electrodes, separators, and negative electrodes each formed in a rectangular shape are stacked. In addition, the charge-discharge body 100 can also be configured as a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes formed in a short strip relative to a separator formed in a long strip are alternately arranged while being opposite to each other with a separator interposed therebetween. The charge-discharge body 100 of such a configuration is stacked by folding the separator so that the positive electrode and the negative electrode are opposite to each other with a separator interposed therebetween.

[0103] The separator 130 for insulating the positive electrode 110 from the negative electrode 120 may also be composed of an insulating member stacked on the electrode. The insulating member is formed by bonding to the positive electrode 110 or the negative electrode 120. The insulating member preferably has heat resistance. For example, ceramic is used for the insulating member. Such a structure is equivalent to a so-called separator-free structure. It is also possible to use a structure in which an insulating member is used in addition to the separator 130, that is, a structure in which both the separator 130 and the insulating member are used.

[0104] The lithium ion secondary battery 1 is not limited to the configuration in which the charging and discharging body 100 is sealed by the case 201 and the lid 202. For example, the lithium ion secondary battery 1 may be configured in which the charging and discharging body 100 is sealed by a laminate film.

[0105] The lithium ion secondary battery 1 is not limited to the one using a liquid electrolyte, and for example, the lithium ion secondary battery 1 may be configured as an all-solid secondary battery.

[0106] Furthermore, as a battery of an embodiment, the battery may be a battery having a solid electrolyte as an electrolyte and a charge-discharge body, wherein the charge-discharge body has a positive electrode, a negative electrode, and a solid electrolyte layer containing a solid electrolyte, and the solid electrolyte layer is interposed between the positive electrode and the negative electrode. For example, the battery is characterized in that each of the positive electrode electronic insulating layer and the negative electrode electronic insulating layer contains a solid electrolyte. The battery is characterized in that both the positive electrode electronic insulating particles and the negative electrode electronic insulating particles are solid electrolyte particles.

[0107] A battery having such a solid electrolyte does not need to contain an electrolyte solution and can therefore have high safety.

[0108] In addition, examples of solid electrolytes include sulfide-based solid electrolytes such as Li 10 GeP2S 12 , Li6PS5Cl, Li2S-P2S5 glass, Li2S-SiS2 glass, Li2S-P2S5-GeS2 glass, Li2S-B2S3 glass, oxide solid electrolytes such as Li7La3Zr2O 12 , LiLaTiO3, LiTi(PO4)3, LiGe(PO4)3, and complex hydride-based solid electrolytes such as LiBH4-LiI, LiBH4-LiNH2, and mixtures of these two or more.

[0109] A battery including the negative electrode of another embodiment may further include a positive electrode electron insulating layer provided on the positive electrode and a negative electrode electron insulating layer provided on the negative electrode in place of the separator.

[0110] (Configuration of a separator-less battery having a negative electrode according to another embodiment) Below, reference Figure 8 and Fig. 9 , the structure of such a separator-less battery is described.

[0111] like Figure 8As shown, in a separatorless battery 1 (lithium ion secondary battery) having a positive electrode 34 and a negative electrode 32 of another embodiment, the positive electrode 34 comprises a positive electrode collector 34a, a positive electrode first active material layer 34b1 bonded to both surfaces of the positive electrode collector 34a, a positive electrode second active material layer 34b2 bonded to each positive electrode first active material layer 34b1, and a positive electrode electronic insulating layer 34d bonded to each positive electrode second active material layer 34b2. The negative electrode 32 comprises a negative electrode collector 32a, a negative electrode active material layer 32b bonded to both surfaces of the negative electrode collector 32a, and a negative electrode electronic insulating layer 32d bonded to each negative electrode active material layer 32b.

[0112] A portion (hereinafter referred to as "positive electrode collector exposure portion") 34c that is not covered by the positive electrode active material layer 34b including the positive electrode first active material layer 34b1 and the positive electrode second active material layer 34b2 or the positive electrode electronic insulating layer 34d is provided at one end of the positive electrode collector 34a. The positive electrode collector exposure portion 34c is provided at the end surface of the winding group (not shown) and its vicinity. The positive electrode collector exposure portion 34c is opposite to and electrically connected to the positive electrode side connection end portion (not shown) of the positive electrode collector plate (not shown). Similarly, a portion (hereinafter referred to as "negative electrode collector exposure portion") 32c that is not covered by the negative electrode active material layer 32b or the negative electrode electronic insulating layer 32d is provided at one end of the negative electrode collector 32a. The negative electrode collector exposure portion 32c is provided at the end surface of the winding group and its vicinity. The negative electrode current collector exposed portion 32 c faces and is electrically connected to a negative electrode side connecting end portion (not shown) of a negative electrode current collector plate (not shown).

[0113] The positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d have the function of preventing the short circuit between the positive electrode active material layer 34b and the negative electrode active material layer 32b and the function of conducting ions between the positive electrode active material layer 34b and the negative electrode active material layer 32b. The positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d can also be a porous layer composed of an electrically insulating (i.e., electronically insulating and ionically insulating) material. The porous layer can retain an electrolyte in its micropores, so that ions can be conducted between the positive electrode active material layer 34b and the negative electrode active material layer 32b with the help of the electrolyte.

[0114] The porous positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d can also have the function of buffering the expansion and contraction of the electrode mixture layer 34b and 32b accompanying the charging and discharging of the lithium-ion secondary battery. The expansion and contraction of the negative electrode active material layer 32b accompanying the charging and discharging of the battery 1 is usually larger than the expansion and contraction of the positive electrode active material layer 34b. Therefore, the negative electrode electronic insulating layer 32d may have an average micropore diameter larger than the average micropore diameter of the positive electrode electronic insulating layer 34d, so as to buffer the expansion and contraction of the larger negative electrode active material layer 32b. In addition, in the present application, the average micropore diameter of the positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d means the average value of the volume-based micropore diameter measured by mercury intrusion.

[0115] The total content of Na and Fe in the positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d can be 300 ppm or less based on the weight of the positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d. The amount of each element contained in the positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d can be measured by ICP (Inductive Coupled Plasma) method.

[0116] The positive electrode electronic insulating layer 34d may include positive electrode electronic insulating particles, and the negative electrode electronic insulating layer 32d may include negative electrode electronic insulating particles. Hereinafter, the positive electrode electronic insulating particles and the negative electrode electronic insulating particles are collectively referred to as electronic insulating particles as appropriate. The electronic insulating particles may be electrically insulating particles. As examples of electrically insulating particles, ceramic particles may be cited. The ceramic particles may contain at least one selected from the group consisting of aluminum oxide (Al2O3), boehmite (Al2O3 hydrate), magnesium oxide (MgO), zirconium oxide (ZrO2), titanium oxide (TiO2), iron oxide, silicon dioxide (SiO2) and barium titanate (BaTiO2), preferably containing at least one selected from the group consisting of aluminum oxide, boehmite, magnesium oxide, zirconium oxide and titanium oxide. The electronic insulating particles may have an average particle size in the range of 0.7μm to 1.1μm. The average particle size of the electronic insulating particles can be obtained by calculating the arithmetic mean of the projected area circle equivalent diameters of 100 or more randomly selected electronic insulating particles based on the microscope observation images of the positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d. The electronic insulating particles can contain at least one of 100ppm to 200ppm of Na, 50ppm to 100ppm of Fe, or 50ppm to 100ppm of Ca based on the weight of the electronic insulating particles.

[0117] The positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d may further include a binder. The binder may be a binder dispersed or dissolved in an aqueous solvent or a non-aqueous solvent (e.g., N-methyl-2-pyrrolidone (NMP)), and may contain at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), and carboxymethyl cellulose (CMC).

[0118] The positive electrode electron insulating layer 34d and the negative electrode electron insulating layer 32d may further contain a dispersant. The dispersant may contain at least one selected from the group consisting of a carboxylic acid compound and a phosphoric acid compound.

[0119] The interface 34e between the positive electrode electronic insulating layer 34d and the positive electrode active material layer 34b has a concavo-convex shape, and the height of the concavo-convex is greater than 2 μm, preferably within the range of 2 μm to 4 μm. The interface 32e between the negative electrode electronic insulating layer 32d and the negative electrode active material layer 32b has a concavo-convex shape, and the height of the concavo-convex is greater than 2 μm, preferably within the range of 2 μm to 4 μm. By making the concavo-convex heights of the interface 34e between the positive electrode electronic insulating layer 34d and the positive electrode active material layer 34b and the interface 32e between the negative electrode electronic insulating layer 32d and the negative electrode active material layer 32b greater than 2 μm, the adhesion between the positive electrode electronic insulating layer 34d and the positive electrode active material layer 34b and the adhesion between the negative electrode electronic insulating layer 32d and the negative electrode active material layer 32b can be improved. This can prevent or reduce the separation of the positive electrode electronic insulating layer 34 d and the negative electrode electronic insulating layer 32 d from the positive electrode active material layer 34 b and the negative electrode active material layer 32 b , respectively, thereby improving the reliability of the lithium ion secondary battery.

[0120] The height of the unevenness of the interface 34e between the positive electrode second active material layer 34b2 (positive electrode active material layer 34b) and the positive electrode electronic insulating layer 34d can be controlled, for example, by the particle size of the positive electrode active material particles and the positive electrode electronic insulating particles. Fig. 9As shown, when the average particle size of the positive electrode second active material particles 34b2p (positive electrode second active material) contained in the positive electrode second active material layer 34b2 is larger than the average particle size of the positive electrode electronic insulating particles 34dp, the positive electrode electronic insulating particles 34dp enter the gaps between the positive electrode first active materials 34b1p, so that the interface 34e between the positive electrode active material layer 34b and the positive electrode electronic insulating layer 34d has a concavoconvex shape. For example, by using a spherical positive electrode first active material 34b1p having an average particle size in the range of 4.5μm to 5.5μm and a positive electrode electronic insulating particle 34dp having an average particle size in the range of 0.7μm to 1.1μm, the concavoconvex height of the interface 34e between the positive electrode active material layer 34b and the positive electrode electronic insulating layer 34d can be set to 2μm or more, preferably in the range of 2 to 4μm.

[0121] The concavo-convex height of the interface 32e between the negative electrode active material layer 32b and the negative electrode electronic insulating layer 32d can also be controlled by the particle size of the negative electrode active material particles and the negative electrode electronic insulating particles. For example, by using flaky negative electrode active material particles with an average particle size in the range of 9 μm to 11 μm and negative electrode electronic insulating particles with an average particle size in the range of 0.7 μm to 1.1 μm, the concavo-convex height of the interface 32e between the negative electrode active material layer 32b and the negative electrode electronic insulating layer 32d can be set to 2 μm or more, preferably in the range of 2 μm to 4 μm.

[0122] In the present application, the concavo-convex height of the interface 34e between the positive electrode electronic insulating layer 34d and the positive electrode active material layer 34b, and the interface 32e between the negative electrode active material layer 32b and the negative electrode electronic insulating layer 32d are measured as follows. A scanning electron microscope (SEM) is used to obtain cross-sectional SEM images of any three locations of the positive electrode 34 or the negative electrode 32, and the distance from any 10 or more points on the interface 34e, 32e to a specified reference plane is measured in each cross-sectional SEM image (for example, the distance from any 10 or more points on the interface 34e, 32e to the surface 34f of the positive electrode electronic insulating layer 34d, the surface 32f of the negative electrode electronic insulating layer 32d, that is, the thickness of the positive electrode electronic insulating layer 34d at any 10 locations and the thickness of the negative electrode electronic insulating layer 32d). The standard deviation of the obtained distance value is taken as the concavo-convex height of the interface 34e, 32e. In addition, the surface 34f of the positive electrode electronic insulating layer 34d and the surface 32f of the negative electrode electronic insulating layer 32d are opposite to each other and can be sufficiently flat compared to the interfaces 34e and 32e. For example, the surface 34f of the positive electrode electronic insulating layer 34d and the surface 32f of the negative electrode electronic insulating layer 32d can have a concave-convex height that is less than one tenth of the concave-convex height of the interfaces 34e and 32e, respectively.

[0123] “The interface 34e between the positive electrode electronic insulating layer 34d and the positive electrode active material layer 34b has a concavo-convex shape” can also be expressed as “a positive electrode mixed layer containing a positive electrode active material and an electronic insulating material is provided between the positive electrode electronic insulating layer 34d and the positive electrode active material layer 34b”. Similarly, “the interface 32e between the negative electrode electronic insulating layer 32d and the negative electrode active material layer 32b has a concavo-convex shape” can be expressed as “a negative electrode mixed layer containing a negative electrode active material and an electronic insulating material is provided between the negative electrode electronic insulating layer 32d and the negative electrode active material layer 32b”. The thickness of the positive electrode mixed layer is greater than 2 μm, preferably in the range of 2 μm to 4 μm. The thickness of the negative electrode mixed layer is greater than 2 μm, preferably in the range of 2 μm to 4 μm. The thickness of the positive electrode mixed layer and the negative electrode mixed layer can be measured in the same manner as the concavo-convex height of the interfaces 34e, 32e between the positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d and the electrode mixture layers 34b, 32b.

[0124] The positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d may contact each other. Preferably, the positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d may contact each other without being fixed to each other. By not fixing the positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d to each other, the stress generated by the expansion and contraction of the negative electrode active material layer 32b and the positive electrode active material layer 34b accompanying the charging and discharging of the lithium ion secondary battery can be alleviated, and the dendrites that may cause a short circuit between the positive electrode active material layer 34b and the negative electrode active material layer 32b can be prevented or reduced from penetrating the positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d and growing.

[0125] The peel strength of the positive electrode electronic insulating layer 34d relative to the positive electrode active material layer 34b and the peel strength of the negative electrode electronic insulating layer 32d relative to the negative electrode active material layer 32b may be greater than the peel strength of the positive electrode electronic insulating layer 34d relative to the negative electrode electronic insulating layer 32d. The peel strength can be measured, for example, by a 180° tape peel test in accordance with JIS C 0806-3 1999.

[0126] The concavo-convex height of the interface 34e between the positive electrode active material layer 34b and the positive electrode electronic insulating layer 34d can be controlled by the particle size of the positive electrode active material particles and the positive electrode electronic insulating particles, and can also be controlled by the type and viscosity of the solvent of the positive electrode mixture slurry and the positive electrode electronic insulating material slurry. Similarly, the concavo-convex height of the interface 32e between the negative electrode active material layer 32b and the negative electrode electronic insulating layer 32d can also be controlled by the type and viscosity of the solvent of the negative electrode mixture slurry and the negative electrode electronic insulating material slurry.

[0127] The average micropore diameter of the positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d can be controlled by the particle diameter of the electronic insulating particles and the pressing pressure during the pressing process. Specifically, the higher the pressing pressure, the smaller the average micropore diameter, and the smaller the particle diameter of the electronic insulating particles, the smaller the average micropore diameter.

[0128] In the separator-less battery 1 including the positive electrode 34 and the negative electrode 32 of the above other example, the strength of the electron insulating layer is higher than that of the separator, so that the safety of the battery is improved.

[0129] (Variation Example) Furthermore, in a modification of the membrane-free battery 1 having the positive electrode 34 and the negative electrode 32 of another example above, the positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d are each a layer containing a solid electrolyte (i.e., a material having electronic insulation and ion conductivity). The battery (lithium ion secondary battery) of this modification does not need to contain an electrolyte, so it can have high safety. In this modification, the electronic insulating particles contained in the positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d can be solid electrolyte particles. The solid electrolyte can be well formed by compression molding, so, in this case, the positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d do not necessarily contain a binder and a dispersant.

[0130] Furthermore, at least one of the first positive electrode active material layer 34b1 and the second positive electrode active material layer 34b2 included in the positive electrode active material layer 34b may contain a solid electrolyte in addition to the active material and an arbitrarily selected binder, conductive aid, and dispersant. Thus, the ion conductivity of at least one of the first positive electrode active material layer 34b1 and the second positive electrode active material layer 34b2 can be improved.

[0131] The negative electrode active material layer 32 b may contain a solid electrolyte in addition to the electrode active material and an optionally selected binder, conductive aid, and dispersant, thereby improving the ion conductivity of the negative electrode active material layer 32 b.

[0132] The battery 1 of the above-described modified example does not need to contain an electrolyte solution and the strength of the electronic insulating layer is higher than that of the separator, so it can have high safety.

[0133] The battery 1 includes a positive electrode and a negative electrode, wherein the positive electrode includes a positive electrode collector, a positive electrode mixture layer disposed on the positive electrode collector, and a positive electrode electronic insulating layer disposed on the positive electrode mixture layer, and the negative electrode includes a negative electrode collector, a negative electrode mixture layer disposed on the negative electrode collector, and a negative electrode electronic insulating layer disposed on the negative electrode mixture layer, wherein the positive electrode electronic insulating layer and the negative electrode electronic insulating layer are in contact with each other. Furthermore, the positive electrode electronic insulating layer and the negative electrode electronic insulating layer are in contact without being fixed to each other.

[0134] (Method for Manufacturing Separatorless Battery Having Negative Electrode According to Another Example of Embodiment) Such a separator-less battery can be manufactured using a technique known in the technical field of the present disclosure, except for the method for manufacturing the negative electrode of another example of the embodiment.

[0135] The negative electrode of another embodiment can be produced by, for example, simultaneously applying the negative electrode first active material layer and the negative electrode second active material layer of the negative electrode active material layer and the negative electrode electron insulating layer as follows.

[0136] First, prepare the materials contained in the first active material layer of the negative electrode (for example, a negative electrode active material, a conductive aid, a binder, etc.). Mix these materials and disperse the resulting mixture in a solvent (for example, N-methyl-2-pyrrolidone (NMP) and / or water) to obtain the first negative electrode slurry. In addition, prepare the materials contained in the second active material layer of the negative electrode (for example, a negative electrode active material, a conductive aid, a binder, etc.). Mix these materials and disperse the resulting mixture in a solvent (for example, N-methyl-2-pyrrolidone (NMP) and / or water) to obtain the second negative electrode slurry. Further, prepare the materials contained in the negative electrode electronic insulating layer (for example, negative electrode electronic insulating particles, a binder, a dispersant, etc.). Mix these materials and disperse the resulting mixture in a solvent (for example, N-methyl-2-pyrrolidone (NMP) and / or water) to obtain a negative electrode electronic insulating material slurry.

[0137] Next, the first negative electrode slurry, the second negative electrode slurry, and the negative electrode electronic insulating material slurry are simultaneously applied to the negative electrode collector. Thus, the second negative electrode slurry layer, the first negative electrode slurry layer, and the negative electrode electronic insulating material slurry layer are formed. Next, the solvent contained in the second negative electrode slurry layer, the first negative electrode slurry layer, and the negative electrode electronic insulating material slurry layer is volatilized by means of a drying furnace, etc., so that the second negative electrode slurry layer, the first negative electrode slurry layer, and the negative electrode electronic insulating material slurry layer are dried. Thus, the first negative electrode active material layer, the second negative electrode active material layer, and the negative electrode electronic insulating layer are formed on one side of the negative electrode collector. Next, the negative electrode collector, the first negative electrode active material layer, the second negative electrode active material layer, and the negative electrode electronic insulating layer are pressed. Specifically, a laminate including a negative electrode current collector, a negative electrode first active material layer, a negative electrode second active material layer, and a negative electrode electronic insulating layer is sandwiched by rollers heated to 60 to 120° C. and pressure is applied. The laminate is then cut to a predetermined width to obtain a negative electrode.

[0138] The battery 1 having a negative electrode manufactured by the above manufacturing method using three-layer simultaneous coating does not need to contain an electrolyte, and has unevenness at the interface of each layer, so that it can be firmly bonded, so high safety and reliability can be obtained. In particular, when the interface 1 between the negative electrode insulating layer and the negative electrode second active material layer and the interface 2 between the negative electrode second active material layer and the first active material layer form large unevenness compared to the surface of the negative electrode electronic insulating layer facing the roller, stable ion conductivity can be obtained, so it is relatively ideal. From this point of view, it is preferred that the difference between the unevenness of the interface 1 and the unevenness of the interface 2 is smaller than the difference between the unevenness of the surface and the unevenness of the interface 2. Explanation of symbols

[0139] 1…Battery 100…Charge and discharge body 110…Positive 111…Positive electrode collector layer 111a…current collection part 111b…positive electrode tab 111c…Side edge 112…Positive electrode active material layer 120…Negative 121…Negative electrode current collecting layer (current collecting layer) 121a…current collection part 121b…Negative electrode tab 121c…Side edge 122 ... negative electrode first active material layer (first active material layer) 122a…1st Graphite 122b…1st silicon element or silicon compound 122c…1st adhesive (adhesive) 122p…Surface 122q…side 122r…side 123 ... negative electrode second active material layer (second active material layer) 123a…2nd Graphite 123b…Second silicon element or silicon compound 123c…Second adhesive (adhesive) 123s…Surface 123t…side part 123u…end 130…Diaphragm 200…Container 201…Housing 202… Cover 300…external terminal 301…Positive terminal 302…Negative terminal T1…1st thickness T'1...1st thickness T2…2nd thickness T3…Third thickness X…width direction of battery 1 Y…depth direction of battery 1 Z…height direction of the battery 1 .

Claims

1. A negative electrode, characterized in that: comprising a current collecting layer, a first active material layer bonded to the current collecting layer, and a second active material layer bonded to the first active material layer, The first active material layer includes first graphite and silicon simple substance or silicon compound, The second active material layer includes a second graphite having an average particle size smaller than that of the first graphite. The surface of the first active material layer along the longitudinal direction is covered by the second active material layer except for the surface bonded to the current collecting layer. The average thickness between the end face above the short side direction of the second active material layer and the end face above the short side direction of the first active material layer and / or the average thickness between the end face below the short side direction of the second active material layer and the end face below the short side direction of the first active material layer is thicker than the average thickness of the first active material layer in the stacking direction.

2. The negative electrode according to claim 1, characterized in that The average thickness between the end face above the short side direction of the second active material layer and the end face above the short side direction of the first active material layer and / or the average thickness between the end face below the short side direction of the second active material layer and the end face below the short side direction of the first active material layer is thicker than the average thickness in the stacking direction of the surface portion of the second active material layer stacked on the first active material layer.

3. The negative electrode according to claim 1, characterized in that The second active material layer has side surfaces that are bonded to the current collecting layer at the upper and / or lower sides in the short-side direction.

4. The negative electrode according to claim 1, characterized in that The end surface of the first active material layer in the short-side direction and / or the end surface of the second active material layer in the short-side direction has an inclined surface. The inclined portion of the first active material layer refers to an inclined portion where the thickness of the first active material layer in the stacking direction becomes thinner as it goes upward or downward in the short-side direction. The inclined portion of the second active material layer refers to an inclined portion where the second active material layer is arranged so as to face the inclined portion of the first active material layer and the surface of the collector layer above or below the first active material layer in the short side direction. The thickness between the uppermost portion of the end surface of the second active material layer in the short-side direction and the uppermost portion of the end surface of the first active material layer in the short-side direction is thicker than the thickness between the starting portion of the inclined portion of the first active material layer and the uppermost portion of the end surface of the first active material layer in the short-side direction, or The thickness between the lowest portion of the end surface of the second active material layer in the short-side direction and the lowest portion of the end surface of the first active material layer in the short-side direction is thicker than the thickness between the starting portion of the inclined portion of the first active material layer and the lowest portion of the end surface of the first active material layer in the short-side direction.

5. The negative electrode according to claim 1, characterized in that The end surface of the first active material layer in the short-side direction and / or the end surface of the second active material layer in the short-side direction has an inclined surface. The inclined portion of the first active material layer refers to an inclined portion where the thickness of the first active material layer in the stacking direction becomes thinner as it goes upward or downward in the short-side direction. The inclined portion of the second active material layer refers to an inclined portion where the second active material layer is arranged so as to face the inclined portion of the first active material layer and the surface of the collector layer above or below the first active material layer in the short side direction. The thickness between the uppermost portion of the end face above the short side direction of the second active material layer and the uppermost portion of the end face above the short side direction of the first active material layer and / or the thickness between the lowermost portion of the end face below the short side direction of the second active material layer and the lowermost portion of the end face below the short side direction of the first active material layer is thicker than the average thickness in the stacking direction of the surface portion of the second active material layer stacked on the first active material layer.

6. The negative electrode according to claim 1, characterized in that The average particle size of the first graphite is 10 μm or more and 35 μm or less. The second graphite has an average particle size of 2 μm or more and 15 μm or less.

7. The negative electrode according to claim 1, characterized in that The first active material layer further includes at least one binder selected from the group consisting of rubber-based, acrylic-based, polyamide-imide, and polyimide.

8. The negative electrode according to claim 1, characterized in that The second active material layer further includes at least one binder selected from the group consisting of rubber, acrylic, polyamide-imide, and polyimide.

9. The negative electrode according to claim 1, characterized in that The second active material layer further includes a second silicon simple substance or a silicon compound in an amount of 0 wt % or more and less than 1 wt % based on the total weight of the second active material layer.

10. A battery, characterized in that: It has a negative electrode, a positive electrode and an electrolyte. The negative electrode includes a current collecting layer, a first active material layer bonded to the current collecting layer, and a second active material layer bonded to the first active material layer. The first active material layer includes first graphite and silicon simple substance or silicon compound, The second active material layer includes a second graphite having an average particle size smaller than that of the first graphite. The surface of the first active material layer along the longitudinal direction is covered by the second active material layer except for the surface bonded to the current collecting layer. The average thickness between the end face above the short side direction of the second active material layer and the end face above the short side direction of the first active material layer and / or the average thickness between the end face below the short side direction of the second active material layer and the end face below the short side direction of the first active material layer is thicker than the average thickness of the first active material layer in the stacking direction.

Images