[0040] (First embodiment)
[0041] use figure 1 with figure 2 The first embodiment of the present invention will be described. figure 1 Is a perspective view showing the secondary battery (lithium ion secondary battery) according to the present embodiment, figure 2 Middle (1) shows the edge figure 1 A-A′ line cross-sectional view, figure 2 Middle (2) shows the edge figure 1 A cross-sectional view of the line B-B'.
[0042] The secondary battery 1 of the present invention is mounted in, for example, an electric vehicle. The secondary battery 1 includes a case 11 having a substantially rectangular parallelepiped shape and a cover 12 arranged at an opening of the case 11 to seal the case 11. Such as figure 2 As shown, the case 11 accommodates the electrode body 13. In addition, the electrolyte 14 is injected into the casing 11, and the electrode body 13 is immersed in the electrolyte 14. The electrode body 13 is formed by stacking a positive electrode plate and a negative electrode plate with a separator sandwiched therebetween, and then winding them. The horizontal direction in the figure is the stacking direction.
[0043] As the electrolytic solution 14, it may be a commonly used solvent such as cyclic carbonate (ethylene carbonate) or propylene carbonate and chain carbonate (dimethyl carbonate) or methyl carbonate. Lithium hexafluorophosphate (LiPF6) is added to the mixed solution of ethyl methyl carbonate and diethyl carbonate to dissolve it to form an organic electrolyte with a concentration of about 1mol/1l.
[0044] The cover 12 is provided with a positive terminal 15 and a negative terminal 16. The positive terminal 15 is connected to the positive current collector 17. In addition, the negative terminal 16 is connected to the negative current collector 18. The positive electrode collector 17 and the negative electrode collector 18 are respectively connected to the positive electrode plate and the negative electrode plate of the electrode body 13. That is, the positive electrode plate and the positive electrode current collector 17 and the positive electrode terminal 15 are electrically connected to each other. In addition, the negative electrode plate and the negative electrode current collector 18 and the negative electrode terminal 16 are electrically connected to each other.
[0045] The electrode body 13 is formed by winding a positive electrode plate and a negative electrode plate provided with a separator sandwiched therebetween. Such as image 3 As shown in (1), the electrode body 13 is composed of a positive electrode plate 22 and a negative electrode plate 23 with a separator 21 sandwiched therebetween. The positive electrode plate 22 is composed of a positive electrode current collector foil 24 and a positive electrode active material layer 25 provided on both sides of the positive electrode current collector foil 24 and each containing a positive electrode active material. The negative electrode plate 23 is composed of a negative electrode current collector foil 26 and a negative electrode active material layer 27 provided on both sides of the negative electrode current collector foil 26 and each containing a negative electrode active material. Each current collector foil is made of metals commonly used as wiring, such as copper or silver, and is made of aluminum in this embodiment.
[0046] The negative electrode active material contained in the negative electrode active material layer 27 may be an active material generally used for a negative electrode, for example, an amorphous carbon material such as graphite, soft carbon, or hard carbon. In addition, graphite may be artificial graphite or natural graphite. And, Li can be used 4 Ti 5 O 12 And other oxide-based anode materials, or alloy-based anode materials, the alloy-based anode materials include Al, Si, Ge, Sn, etc., based on the reversible electrochemical reaction with lithium ions, can make Li near 0 volts (V) Or Li ions become lithium alloys. In addition, the negative electrode active material applicable to the present invention is not limited to this, as long as it can cause the negative electrode to cause a battery reaction. For example, metal lithium, metal oxide, metal sulfide, metal nitride, etc. can be used in addition to this. The metal oxide may also be a substance having an irreversible capacity such as tin oxide or silicon oxide.
[0047] In addition, the negative electrode active material layer 27 may further contain a conductivity enhancer such as acetylene black and an electrolyte (for example, a lithium salt (supporting electrolyte), an ion conductive polymer, etc.). And when an ion conductive polymer is included, a polymerization initiator for polymerizing the polymer may also be included.
[0048] use image 3 (2) The positive electrode active material layer 25 will be described in detail. The positive electrode active material layer 25 is respectively composed of a first positive electrode layer (first active material layer) 31 formed on the positive electrode current collector foil 24 and a second positive electrode layer (second active material layer) 32 formed on the first positive electrode layer 31. constitute. The first positive electrode layer 31 is configured to have a higher capacity than the second positive electrode layer 32. The second positive electrode layer 32 is configured to have a higher output than the first positive electrode layer 31.
[0049] For the first positive electrode layer 31 and the second positive electrode layer 32, as long as the first positive electrode layer 31 has a higher capacity than the second positive electrode layer 32 and the second positive electrode layer 32 has a higher output than the first positive electrode layer 31, then Any configuration may be adopted, as long as the output characteristics and capacity characteristics of the active material, the average particle diameter of the active material, the thickness of each layer, and the like, are appropriately set in consideration.
[0050] The positive electrode active material will now be described. In this embodiment, the second positive electrode layer 32 contains lithium nickelate, and the first positive electrode layer 31 contains lithium manganate. By constituting each layer with such an active material, it is possible to easily make the first positive electrode layer 31 have a higher capacity than the second positive electrode layer 32 and make the second positive electrode layer 32 have a higher output than the first positive electrode layer 31.
[0051] The positive electrode active material constituting each layer is not limited to this. For example, in consideration of output characteristics and capacity characteristics, it is possible to select from the positive electrode active materials described below so that the second positive electrode layer 32 has a higher output than the first positive electrode layer 31 and the first positive electrode layer 31 is compared with the second positive electrode. Layer 32 has a high capacity.
[0052] The positive electrode active material may be spinel type metal oxides and metal compounds, phosphate type metal oxides, and the like. The layered structure type metal oxide can be lithium nickel composite oxide, lithium cobalt composite oxide and ternary composite oxide (LiCo 1/3 Ni 1/3 Mn 1/3 O 2 )Wait. As the lithium nickel composite oxide, lithium nickelate (LiNiO 2 ). As the lithium cobalt composite oxide, lithium cobalt oxide (LiCoO 2 ). The spinel type metal oxide can be lithium manganate (LiMn 2 O 4 ) And other lithium manganese composite oxides. The phosphate type metal oxide can be lithium iron phosphate (LiFePO 4 ), lithium manganese phosphate (LiMnPO 4 )Wait.
[0053] Regarding the above-mentioned positive electrode active material, whether the capacity characteristic is high or not can be judged based on, for example, the theoretical capacity of the active material. For example, LiCoO 2 The theoretical capacity is 274mA h/g, LiNiO 2 The theoretical capacity is 274mA h/g, LiMn 2 O 4 The theoretical capacity is 148mA h/g, LiFePO 4 The theoretical capacity is 170mA h/g. LiCoO 2 And LiNiO 2 Compared to LiMn 2 O 4 And LiFePO 4 The theoretical capacity is high, so it can be judged to have relatively high capacity characteristics.
[0054] In addition, the active material can also be selected in consideration of output characteristics and capacity characteristics, and by adjusting the particle size of the active material described below or the blending of conductive additives, the second positive electrode layer 32 can be configured to have a higher value than the first positive electrode layer 31. The output is high and the first positive electrode layer 31 has a higher capacity than the second positive electrode layer 32.
[0055] The average particle diameter of the active material contained in the second positive electrode layer 32 is preferably 0.1 to 100 μm, and more preferably 30 μm or less. The reason is that the total surface area of the active material increases within this range and accordingly the reactivity can be enhanced to increase the output. The second positive electrode layer 32 further includes a conductive aid. The conductive aid may be acetylene black or Ketjen Black. Acetylene black is contained in this embodiment. The second positive electrode layer 32 preferably contains 3-30% by mass of the conductive assistant, and more preferably the content of the conductive assistant is 20% by mass or more. By containing 3-30% by mass of the conductive auxiliary agent, the output characteristics of the second positive electrode layer 32 can be enhanced. The thickness of the second positive electrode layer 32 is 1-100 μm.
[0056] The average particle diameter of the positive electrode active material contained in the first positive electrode layer 31 is preferably 0.1 to 200 μm, and more preferably larger than 30 μm. Within this range, capacity characteristics can be enhanced. The first positive electrode layer 31 may further include a conductive aid. In this embodiment, acetylene black is contained as a conductive auxiliary agent. It preferably contains 0-25% by mass of the conductive assistant, and more preferably the content of the conductive assistant is less than 20% by mass. By containing 0-25% by mass of the conductive auxiliary agent, the capacity characteristics of the first positive electrode layer 31 can be improved without reducing the capacity. The thickness of the first positive electrode layer 31 is 5 to 300 μm, preferably thicker than 100 μm.
[0057] Considering the output characteristics and capacity characteristics of these active materials, the average particle size of the active materials, the blending of the conductive assistant or the layer thickness, the second positive electrode layer 32 has a higher output than the first positive electrode layer 31, and the first positive electrode layer 31 Compared with the second positive electrode layer 32, it has a higher capacity. That is, in order for the second positive electrode layer 32 to have a higher output than the first positive electrode layer 31 and the first positive electrode layer 31 to have a higher capacity than the second positive electrode layer 32, the average particle size of the active material of the second positive electrode layer 32 If it becomes smaller, the average particle diameter of the active material of the first positive electrode layer 31 may be increased. And in order to make the second positive electrode layer 32 have a higher output than the first positive electrode layer 31, and the first positive electrode layer 31 has a higher capacity than the second positive electrode layer 32, the thickness can be thickened when the capacity performance is improved. When improving output performance, the thickness can be reduced.
[0058] As described above, in this embodiment, considering the output characteristics and capacity characteristics of these active materials, as well as the average particle size and layer thickness of the active materials, the first positive electrode layer 31 and the second positive electrode layer 32 are formed so that the second positive electrode layer 32 has a higher output than the first positive electrode layer 31, and the first positive electrode layer 31 has a higher capacity than the second positive electrode layer 32.
[0059] In addition, even if the same active material is used in the second positive electrode layer 32 and the first positive electrode layer 31, the average particle size of the active material in the first positive electrode layer 31 can be reduced or a conductive auxiliary agent can be added. While the output characteristics of the second positive electrode layer 32 are improved relative to the first positive electrode layer 31, the capacity characteristics of the first positive electrode layer 31 can be relatively improved.
[0060] In this embodiment, since the positive electrode active material layer is configured as a two-layer positive electrode layer having such different characteristics, the secondary battery can achieve high output and high capacity. That is, if the positive electrode layer is composed of only the first positive electrode layer 31 or the second positive electrode layer 32, only one of the output characteristics and the capacity characteristics can be satisfied. Therefore, in this embodiment, the first positive electrode layer 31 and the second positive electrode layer 31 The two positive electrode layers 32 constitute a positive electrode layer.
[0061] However, in order for the electrons from the second positive electrode layer 32 to reach the positive electrode current collector foil 24 during output, the electrons must pass through the first positive electrode layer 31. This may cause the hidden danger that the expected output performance cannot be exhibited. Prevent this. Therefore, in this embodiment, a through hole 33 is formed in the first positive electrode layer 31, the positive electrode collector foil 24 is exposed from the through hole 33, and the inside of the through hole 33 is buried with the same material as the second positive electrode layer 32 to form The second positive electrode portion 34 electrically connects the second positive electrode layer 32 and the positive electrode current collector foil 24 via the second positive electrode portion 34.
[0062] Hereinafter, this point will be specifically explained.
[0063] In this embodiment, a plurality of through holes 33 are formed in each first positive electrode layer 31. The shape of the through hole 33 is not limited, and in this embodiment is a cylindrical shape with the same diameter in the axial direction. The positive electrode current collector foil 24 is exposed from each through hole 33. The through hole 33 is buried in the same material as the second positive electrode layer 32, and accordingly, the second positive electrode portion 34 is formed in the through hole 33. Therefore, the second positive electrode layer 32 and the second positive electrode portion 34 are connected, and since the second positive electrode portion 34 and the second positive electrode layer 32 are the same, the second positive electrode layer 32 and the positive electrode current collector foil 24 are directly connected.
[0064] In this embodiment, the second positive electrode portion 34 as described above is provided, so the output characteristics of the second positive electrode layer 32 can be further improved. That is, since the second positive electrode portion 34 is provided, the second positive electrode layer 32 with high output characteristics and the positive electrode current collector foil 24 can be electrically connected. Accordingly, when high output is required, since electrons in the second positive electrode layer 32 can reach the positive electrode current collector foil 24 through the second positive electrode portion 34, a higher responsive output can be obtained from the second positive electrode layer 32.
[0065] As described above, in this embodiment, in order to improve output characteristics while maintaining capacity characteristics, a high-capacity first positive electrode layer 31 and a high-output second positive electrode layer 32 are provided, and the second positive electrode layer 32 and the positive electrode The collector foil 24 is electrically connected. If the electrons existing in the second positive electrode layer 32 cannot reach the positive electrode current collector foil 24 unless they pass through the first positive electrode layer 31, the high output characteristics of the second positive electrode layer 32 cannot be exerted. However, in this embodiment The electrons in the second positive electrode layer 32 do not reach the positive electrode current collector foil 24 through the first positive electrode layer 31 but reach the positive electrode current collector foil 24 through the second positive electrode portion 34. Therefore, the movement of electrons is easier than when passing through the first positive electrode layer 31. As a result, the secondary battery of the present embodiment can exert the output characteristics of the second positive electrode layer 32 and satisfy the requirement for high output.
[0066] In addition, each of the negative electrode active material layer 27 and the positive electrode active material layer 25 may further include a binder such as polyvinylidene fluoride.
[0067] use Figure 4 The method of manufacturing the positive electrode plate of the secondary battery of this embodiment will be described. First, like Figure 4 As shown in (1), for the positive electrode current collector foil 24, the slurry used to form the first positive electrode layer 31 is adjusted, and the slurry is applied and dried to form the first positive electrode layer 31. After that, a through hole 33 is formed in the first positive electrode layer 31. The through hole 33 may be formed by physically removing a part of the first positive electrode layer 31 by drilling, for example, or may be formed by etching or the like. That is, it is formed by removing the first positive electrode layer 31 by the above-mentioned known removal method. Alternatively, before applying the slurry, a jig or mold can be set on the positive electrode current collector foil 24 and the slurry can be applied in this state, so that the first through hole 33 can be directly obtained without removing unnecessary parts. A positive electrode layer 31. After that, like Figure 4 As shown in (2), the slurry used to form the second positive electrode layer 32 is adjusted, and the slurry is applied and dried to form the second positive electrode layer 32. When the second positive electrode layer 32 is formed, since the slurry for forming the second positive electrode layer 32 enters the through hole 33, the second positive electrode portion 34 is formed in the through hole 33. As described above, according to the method of manufacturing a secondary battery of the present embodiment, the second positive electrode layer 32 and the second positive electrode portion 34 can be manufactured at the same time. Therefore, the positive electrode active material layer 25 constructed according to this embodiment can be easily formed. In addition, heating can be performed during drying, and a press process can also be performed after drying.
