Secondary battery and method for manufacturing same

Abstract

In this secondary battery, a positive electrode 11 having a positive electrode active material and a negative electrode 12 having a negative electrode active material are laminated across a separator 13. The secondary battery is characterized in that the positive electrode active material is a mixture of a first active material 1 having an average particle diameter (D50, median diameter) of 10-20 μm, a second active material 2 having an average particle diameter (D50, median diameter) of 3-5 μm, and a third active material 3 having an average particle diameter (D50, median diameter) larger than that of the second active material and a tap density lower than that of the second active material. As a result, it is possible to provide a secondary battery having excellent output characteristics as well as higher energy density of the battery due to the higher density of the positive electrode.

Description

Secondary battery and its manufacturing method

[0001] The present disclosure relates to batteries.

[0002] In the automotive industry, fuel efficiency and environmental regulations are becoming stricter in each country and region. To comply with these regulations, electric vehicles that are powered by batteries and do not emit carbon dioxide are beginning to become popular. In addition, plug-in hybrid electric vehicles (PHEVs) and hybrid electric vehicles (HEVs), which are powered by both an internal combustion engine and a battery and emit low amounts of carbon dioxide, are becoming popular in some areas. In both systems, the development of high-performance batteries is key to improving efficiency.

[0003] Patent Document 1 describes the relationship between the average particle size and particle disintegration rate of active material particles, which enables an improvement in the volume density of the active material in a positive electrode. Patent Document 2 describes the relationships between particle structure, average particle size, tap density, average aspect ratio of voids, weight ratio, etc., of a positive electrode active material that enables an increase in capacity and output of a lithium ion secondary battery.

[0004] JP 2017-107727 A JP 2021-120937 A

[0005] Electric vehicles require secondary batteries that have sufficient energy density and excellent output characteristics. The present disclosure has been made in view of such issues, and aims to provide a high-output secondary battery that ensures high energy density of the cell by increasing the density of the positive electrode.

[0006] The present disclosure solves the above problems by the following main means: a secondary battery, in which the positive electrode active material is a mixture of a first active material having an average particle diameter (D50, median diameter) of 10 μm or more and 20 μm or less, a second active material having an average particle diameter (D50, median diameter) of 3 μm or more and 5 μm or less, and a third active material having an average particle diameter (D50, median diameter) larger than that of the second active material and a tap density lower than that of the second active material.

[0007] Another aspect of the present disclosure is a secondary battery having the above configuration, wherein the positive electrode active materials are mixed in the positive electrode active material layer so that the weight ratio is first active material > second active material > third active material.

[0008] Yet another aspect of the present disclosure is a secondary battery characterized in that a charging / discharging body in which the positive electrode and the negative electrode are stacked has an exposed first side surface, a first tab connected to the positive electrode and a second tab connected to the negative electrode are present on the first side surface, the charging / discharging body is housed in a battery container having multiple surfaces including a first surface, a first terminal and a second terminal are arranged on the first surface, and the first surface and the first stacking surface are opposed to each other.

[0009] According to the present disclosure, it is possible to provide a secondary battery that has a high energy density due to a high density positive electrode and is excellent in output characteristics.

[0010] 1 is a schematic diagram defining a first active material 1, a second active material 2, and a third active material 3. FIG. 2 is a graph showing the relationship between tap density and electrode density for a specific positive electrode active material. FIG. 3 is a table showing the configurations of examples and comparative examples of the present disclosure and battery performance. FIG. 4 is a perspective view showing the appearance of a battery 5. FIG. 5 is a perspective view showing a cross section of components around a negative electrode terminal 42 of the battery 5. FIG. 6 is a perspective view showing a cross section of components around a positive electrode terminal 41 of the battery 5. FIG. 7 is an exploded perspective view of the battery 5. FIG. 8 is a perspective view showing a charging / discharging body 10 of the battery 5. FIG. 9 is a perspective view showing details of the lid of the battery 5. FIG. 10 is a cross section showing a method for manufacturing a positive electrode. FIG. 11 is a cross section showing a separatorless battery. FIG. 12 is a detailed cross section showing a separatorless battery.

[0011] The configuration of the battery 5 will be described with reference to Figures 1 to 9. A feature of the present disclosure is the configuration of the positive electrode, which will be described in detail in the following description of the battery configuration. The battery 5 has, as its main components, a charging / discharging body 10 that charges and discharges electricity, a current collector 20 connected to the charging / discharging body 10, a current interrupting body 30 connected to the current collector 20, and an external terminal 40 connected to the current collector 20 and the current interrupting body 30. The components of the battery 5 are housed in or attached to an exterior body 50.

[0012] FIG. 8 is a perspective view of a charge / discharge unit 10. The charge / discharge unit 10 charges and discharges electricity. The charge / discharge unit 10 includes a positive electrode 11, a negative electrode 12, a separator 13, and an electrolyte. In FIG. 8, the positive electrode 11 includes an elongated positive electrode current collecting layer 11M and a positive electrode active material layer 11N bonded to the positive electrode current collecting layer 11M. The positive electrode current collecting layer 11M includes a current collecting portion 11a and a positive electrode tab 11b. The positive electrode active material layer 11N is bonded to the current collecting portion 11a. The positive electrode tab 11b protrudes in the short direction of the current collecting portion 11a from a side edge 11c along the longitudinal direction of the current collecting portion 11a. The positive electrode tab 11b is formed integrally with the current collecting portion 11a. Multiple positive electrode tabs 11b are formed on one current collecting portion 11a. The current collecting portion 11a is formed of, for example, aluminum or an aluminum alloy.

[0013] The positive electrode active material layer 11N is formed of a compound represented by the following formula (1): Li １＋Ｘ M Ａ O ２ (1) (wherein X satisfies −0.15≦X≦0.15, and M Ａ represents an element group containing at least one selected from the group consisting of Mn and Al, Ni, and Co).

[0014] When −0.15≦X≦0.15 is satisfied, the positive electrode active material has a high true density and high reversibility, that is, a high battery capacity and excellent cycle characteristics.

[0015] M Ａ However, by including at least one selected from the group consisting of Mn and Al in addition to Ni and Co, the positive electrode active material has high thermal stability and high stability in a high potential state, thereby providing a lithium ion secondary battery with high safety.

[0016] M Ａ may further include at least one selected from the group consisting of Zr, Ti, Cr, Fe, Cu, Zn, Ge, Sn, Mg, Ag, Ta, Nb, B, P, Ca, Sr, and Ba. ＡWhen M contains Zr, the internal resistance of the lithium ion secondary battery at low temperatures is reduced. The content of Zr may be 0.1 to 2.0 mol %, particularly 0.2 to 1.0 mol %, based on the total amount of Ni, Co, Mn, and Al. Ａ The proportion of elements other than Ni, Co, Mn, and Al in all elements constituting the lithium ion secondary battery is, for example, 10 mol % or less, particularly 3 mol % or less, thereby allowing the lithium ion secondary battery to have a sufficient discharge capacity.

[0017] The amount of each element in the positive electrode active material can be measured by an ICP (Inductive Coupled Plasma) method. When the amount of an element in the positive electrode material is examined by disassembling the battery, the battery before disassembly is discharged to, for example, 2.7 V, and then disassembled, and the positive electrode active material is removed. The removed positive electrode active material is brought into a molten state by, for example, an oxidative decomposition method or an alkaline solution decomposition method, and then measured by the ICP method.

[0018] The positive electrode active material contains three or more materials with different average particle sizes. When the first active material 1 has the largest average particle size, the second active material 2 has the smallest average particle size, and the third active material 3 has the second largest average particle size, the voids between the particles of the first active material can be efficiently filled with particles of the second active material and the third active material. Therefore, when the positive electrode active material for a lithium-ion secondary battery contains the third active material, it becomes possible to further increase the density of the positive electrode.

[0019] The average particle diameter (D50, median diameter) of the first active material is 10 μm to 20 μm, and the average particle diameter (D50, median diameter) of the second active material is 3 μm to 5 μm. The average particle diameter (D50, median diameter) of the third active material is smaller than that of the first active material and larger than that of the second active material.

[0020] Fig. 1 is a schematic cross-sectional view of a positive electrode in which a first active material 1, a second active material 2, and a third active material 3 are mixed. In Fig. 1, the second active material 2 and the third active material 3 are present between the first active material 1, which has the largest particle size, which allows for an increase in the electrode density of the positive electrode. In other words, the energy density of the battery can be improved.

[0021] 1, the first active material 1, the second active material 2, and the third active material 3 are secondary particles formed by aggregation of primary particles. In FIG. 1, the density of the primary particles of the third active material 3 is smaller than the tap density of the secondary particles of the first active material 1 and the second active material 2.

[0022] Such a configuration can also be produced by changing the materials constituting the first active material 1 and the second active material 2 and the third active material 3. For example, the first active material and the second active material can contain 60 mol% or more of Ni, and the third active material can contain less than 60 mol% of Ni. By changing the materials, the degree of freedom in material combinations to achieve desired characteristics increases. Alternatively, even if the materials constituting the first active material 1 and the second active material 2 and the third active material 3 are the same material, this can be achieved by changing the production method. Since the same materials can be used, this has excellent economical efficiency. Furthermore, since the basic characteristics are similar, handling is easy.

[0023] When the first active material 1, the second active material 2, and the third active material 3 are produced by a crystallization method, there is a nucleation step and a particle growth step, and this configuration can be achieved by changing the nucleation step of the third active material 3 from the nucleation steps of the first active material 1 and the second active material 2. Even when the active material is formed by crushing raw materials using a ball mill or the like, mixing them, and firing them under certain conditions, the structures of the first active material 1, the second active material 2, and the third active material 3 can be changed by changing the conditions of mixing, firing, etc.

[0024] The tap density of the third active material 3 is smaller than the tap density of the second active material 2. Generally, the larger the particle diameter, the stronger the van der Waals force, and the higher the tap density tends to be. However, in the present disclosure, by making the tap density of the third active material 3, which has the second largest average particle diameter, smaller than the tap density of the second active material 2, it is possible to achieve a configuration in which the electrolyte can penetrate evenly throughout the positive electrode even when the positive electrode is highly filled, thereby enabling improved output characteristics.

[0025] In the positive electrode active material layer 11N, the positive electrode active materials are mixed in a weight ratio of first active material > second active material > third active material. The first active material 1, second active material 2, and third active material 3 are mixed, and a conductive material and a binder are added to form a paste. After drying, the mixture is pressed, for example, with a roller press at a linear pressure of 100 N / mm to a thickness of about 95 mm. Even in this state, the third active material 3 does not collapse, and 80% or more of it maintains its shape as a secondary particle.

[0026] That is, even after the positive electrode active material layer 11N is pressed, the first active material 1, the second active material 2, and the third active material 3 can be distinguished. For example, this can be achieved by taking a cross-sectional photograph of the positive electrode active material layer 11N using an SEM. When disassembling a battery to examine the positive electrode active material layer 11N, the battery is discharged to, for example, 2.7 V and then disassembled. Then, multiple SEM photographs of the cross section of the positive electrode active material layer 11N are taken to confirm the presence of the first active material 1, the second active material 2, and the third active material 3. Thereafter, the binder and conductive material are removed, and the tap densities of the first active material 1, the second active material 2, and the third active material 3 are measured. The same applies to the weight ratios of the first active material 1, the second active material 2, and the third active material 3. It is assumed that this battery has a terminal voltage of 4.2 V in a fully charged state and a terminal voltage of 2.7 V in a fully discharged state.

[0027] The average particle size of the positive electrode active material can be measured, for example, using a laser diffraction / scattering particle size distribution analyzer. In this case, the particle group is obtained by extracting the positive electrode active material from the positive electrode active material layer 11N and measuring its particle size distribution. Furthermore, when measuring the particle size of the positive electrode active material by disassembling the battery, the battery is discharged, for example, to 2.7 V, and then disassembled. The positive electrode active material is extracted from the positive electrode mixture and its particle size distribution is measured.

[0028] The tap density of the positive electrode active material can be obtained by mechanically tapping a measuring cylinder or container containing a powder sample. After measuring the initial mass of the powder, the measuring cylinder or container is mechanically tapped, and when almost no volume change is observed, the volume is read, and the tap density is calculated from the initial mass and the final volume.

[0029] 2 is a graph showing the relationship between the tap density of a specific particle and the electrode density of the positive electrode mixture after pressing. As shown in FIG. 2, for the same particle group, the tap density and the electrode density are in a proportional relationship. In FIG. 2, R ２ is a parameter called the coefficient of determination. Since the positive electrode active material layer 11N according to the present disclosure contains three types of positive electrode active materials, the electrode density is a weighted average of the active materials. The electrode density can be estimated by determining the proportion of active materials with a predetermined tap density. In other words, the energy density of the battery can be designed. Furthermore, by controlling the proportion of the third active material 3, which has a low tap density, it is possible to design a high-rate battery.

[0030] There are methods for combining cathode materials with different particle size distributions to increase the tap density of cathode active materials. However, conventional techniques have not been able to achieve sufficient energy density. Another technique involves using a highly collapsible material for a single cathode active material, collapsing it when pressing the cathode active material layer, and filling the voids between the particles with the collapsed particles. However, this method carries the risk of collapsing the electron conduction network, degrading input / output characteristics, and reducing battery life.

[0031] To improve the input / output of the battery, one approach is to increase the specific surface area of ​​the conductive additive for the positive electrode or to make it fibrous. However, this approach reduces the handleability of the slurry used to form the positive electrode mixture and increases the unit price of the positive electrode mixture.

[0032] In contrast to this, the configuration of the present disclosure described above has a relatively simple configuration in which the positive electrode active material is a mixture of, for example, a first active material 1 having an average particle diameter (D50, median diameter) of 10 μm or more and 20 μm or less, a second active material 2 having an average particle diameter (D50, median diameter) of 3 μm or more and less than 5 μm, and a third active material 3 having an average particle diameter (D50, median diameter) larger than that of the second active material 2 and a tap density lower than that of the second active material 2. This makes it possible to realize a battery having a high positive electrode density, i.e., a high energy density and high input / output characteristics.

[0033] For example, the first active material 1 and the second active material 2 have a large difference in particle size, and the second active material has a higher tap density than the third active material, allowing for effective high-density packing. This allows for the battery characteristics obtained by high-density packing to be utilized. The third active material has a lower tap density than the second active material. Furthermore, the average particle size is larger than that of the second active material. This allows for the active material to have particles with a lower packing density but still have capacity, making it easier to obtain output characteristics different from the above structure. For example, higher input / output characteristics can be utilized. Furthermore, in order to obtain more preferable output characteristics, it is preferable for the third active material to have a lower tap density than the first active material. Alternatively, it is preferable for the third active material to have a larger average particle size than the first active material.

[0034] In this example, the packing degree (or porosity) of the first active material, second active material, and third active material was compared using tap density. While tap density is preferred for evaluating the actual state, when tap density is difficult to measure, the density or packing rate (porosity) may be compared using a known method for measuring density or packing rate (porosity). In this case, the "third active material 3 having a larger average particle size (D50, median size) than the second active material 2 and a lower tap density than the second active material 2" can be referred to as "a third active material 3 having a larger average particle size (D50, median size) than the second active material 2 and a lower density than the second active material 2" when compared by other densities, or as "a third active material 3 having a larger average particle size (D50, median size) than the second active material 2 and a higher porosity than the second active material 2" when compared by porosity.

[0035] When comparing the porosities of the positive electrode active materials, which are porous secondary particles contained in the positive electrode active materials, the porosity can be calculated, for example, by observing the cross-sectional structure of the positive electrode active materials with an SEM and performing image processing or the like. A known calculation method can be used for the calculation. For example, the calculation method involves first observing the cross-sectional structures of multiple (e.g., 100 or more) positive electrode active materials with an SEM, and then comparing the porosity using the average of the porosities of the target positive electrode active materials.

[0036] Next, the overall configuration of the battery will be described.

[0037] FIG. 4 is a perspective view showing the appearance of the secondary battery.

[0038] The secondary battery is a flat rectangular parallelepiped and is composed of a first main surface with a large area, a second main surface opposite the first main surface, rectangular side surfaces, a rectangular bottom surface, and a rectangular lid 52. The long sides of the rectangular lid 52 are longer than the long sides of the rectangular side surfaces.

[0039] In other words, the first or second principal surface having the larger area is rectangular, with its long side coinciding with the long side of the rectangular lid and its short side coinciding with the long side of the rectangular side. The ratio of the long side to the short side of the principal surface is preferably 1.5 or more, and, considering the ease of fabricating the charge / discharge unit 10 described below, is preferably 4.0 or less. More preferably, it is 2.0 or more and 2.5 or less.

[0040] 4, the negative electrode terminal 42 and the positive electrode terminal 41 are arranged at a distance from each other on the lid 52. A split valve for preventing high pressure inside the battery is arranged near the center of the lid 52. A sealing plug 53 for sealing the injection hole for injecting the electrolyte is also arranged.

[0041] FIG. 8 is a perspective view of the charge / discharge body 10. In FIG. 8, the negative electrode 12 includes a long negative electrode current collecting layer 12M and a negative electrode active material layer 12N bonded to the negative electrode current collecting layer 12M. The negative electrode current collecting layer 12M includes a current collecting portion 12a and a negative electrode tab 12b. The negative electrode active material layer 12N is bonded to the current collecting portion 12a. The negative electrode tab 12b protrudes in the short direction of the current collecting portion 12a from a side edge 12c along the longitudinal direction of the current collecting portion 12a. When stacked with the positive electrode 11 via the separator 13, the negative electrode tab 12b protrudes in the same direction as the positive electrode tab 11b of the positive electrode 11. When stacked with the positive electrode 11 via the separator 13, the negative electrode tab 12b is separated from the positive electrode tab 11b of the positive electrode 11. The negative electrode tab 12b is formed integrally with the current collecting portion 12a. A plurality of negative electrode tabs 12b are formed on one current collector 12a. The current collector 12a is formed of, for example, copper or a copper alloy. The negative electrode active material layer 12N contains a negative electrode active material made of a carbon-based material, a binder, a conductive additive, and the like. The carbon-based material is, for example, graphite.

[0042] The separator 13 provides insulation between the positive electrode 11 and the negative electrode 12 while allowing lithium ions to pass through. The separator 13 is formed in a long shape. The separator 13 is made of a porous material. Polyethylene (PE) or polypropylene (PP) is used for the separator 13. The electrolyte contains an organic solvent, a supporting salt, and an additive. For example, a carbonate ester is used as the organic solvent. For example, a lithium salt is used as the supporting salt.

[0043] Fig. 5 is a cross-sectional perspective view of the vicinity of the negative electrode terminal 42, and Fig. 6 is a cross-sectional perspective view of the vicinity of the positive electrode terminal 41. The current collector 20 shown in Fig. 5 and Fig. 6 is connected to the charge / discharge body 10. The current collector 20 includes a positive electrode current collector plate 21 and a negative electrode current collector plate 22.

[0044] In Fig. 5, the negative electrode current collector 22 electrically connects the negative electrode tab 12b of the charge / discharge body 10 to the negative electrode terminal 42. The negative electrode current collector 22 includes a rectangular parallelepiped base 22a and an insertion hole 22b penetrating the base 22a. The insertion portion 42b of the negative electrode terminal 42 is inserted into the insertion hole 22b of the negative electrode current collector 22. The negative electrode current collector 22 is formed of, for example, copper or a copper alloy. In Fig. 5, reference numeral 70 denotes a seal and 72 denotes a gasket.

[0045] 6 is a cross-sectional perspective view of the positive electrode terminal and its vicinity. In FIG. 6, the configuration including the current interrupter 30 electrically connects the current collector 20 and the positive electrode terminal 41. The current interrupter 30 includes a diaphragm 31, a conductive member 32, and a pair of support bases 33.

[0046] Fig. 7 is an exploded perspective view of the battery 5. In Fig. 7, the external terminals 40 are connected to the current collector 20 or the current interrupter 30. The external terminals 40 include a positive electrode terminal 41 and a negative electrode terminal 42. In Fig. 7, the components of the battery 5 are housed or attached in an exterior body 50. The exterior body 50 includes a container 51, a lid 52, and a sealing plug 53.

[0047] The container 51 contains the charging / discharging unit 10 and other components. The container 51 is a rectangular metal can. The container 51 includes an opening 51a extending along the longitudinal direction and a container portion 51b connected to the opening 51a. The container 51 is made of, for example, aluminum or an aluminum alloy.

[0048] 7 and 9 , a lid 52 seals an opening 51 a of a container 51. The container 51 is formed from a long metal plate. The lid 52 has a positive electrode insertion hole 52 a formed as a circular through-hole at one end in the longitudinal direction. The lid 52 has a liquid injection insertion hole 52 c formed as a circular through-hole. An insertion portion 53 b of a sealing plug 53 is inserted into the liquid injection insertion hole 52 c. A split valve 52 d is formed in the center of the lid 52 in the longitudinal direction. The lid 52 is welded to the container 51. The lid 52 is formed from, for example, aluminum or an aluminum alloy.

[0049] The sealing plug 53 seals the injection insertion hole 52c of the lid 52. The sealing plug 53 is formed in a cylindrical shape. The sealing plug 53 includes a head portion 53a having a relatively large outer diameter and an insertion portion 53b that is continuous with the head portion 53a and has a relatively small outer diameter. The head portion 53a of the sealing plug 53 is welded to the lid 52. The sealing plug 53 is formed of, for example, aluminum or an aluminum alloy.

[0050] 7, an insulator 60 insulates the components of the battery 5 from the exterior body 50. The insulator 60 includes an insulating cover 61, a first positive electrode side insulating plate, a first negative electrode side insulating plate, a second positive electrode side insulating plate, and a second negative electrode side insulating plate.

[0051] The insulating cover 61 covers the charging / discharging unit 10. The insulating cover 61 exposes one side 10a of the charging / discharging unit 10 to the outside and covers the rest of the charging / discharging unit 10 except for the one side 10a. The insulating cover 61 is formed, for example, in a pentahedral shape and folded into a box shape. The insulating cover 61 is formed, for example, from polypropylene.

[0052] As shown in FIG. 7 , the side 10a of the charge / discharge body 10 is exposed. The positive electrode tab 11b and the positive electrode terminal 41 are disposed in close proximity. The negative electrode tab 12b and the negative electrode terminal 42 are disposed in close proximity. With this configuration, by using the positive electrode active material according to the present disclosure, the positive electrode mixture is densified, and heat transfer between the charge / discharge body and its exterior is facilitated even when the heat transfer between the charge / discharge body and its exterior increases during charging and discharging. Therefore, the battery output can be stabilized.

[0053] The present disclosure will be specifically described below using examples, but the present disclosure is not limited to these examples. Unless otherwise specified, the configurations shown below are common to Examples 1 to 7 and Comparative Examples 1 to 3. １．０ Ni ０．６ Co ０．２ Mn ０．２ O ２ Powder, acetylene black as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder were prepared.

[0054] The positive electrode active material, the conductive agent, and the binder were mixed in a weight ratio of 98:1:1. N-methyl-2-pyrrolidone (NMP) was added to the obtained mixture to adjust the viscosity, thereby obtaining a positive electrode slurry.

[0055] A 12 μm thick aluminum foil was prepared as a positive electrode current collector. An uncoated area was left on both sides of the positive electrode current collector to serve as a weld (exposed portion of the positive electrode current collector). The positive electrode slurry was simultaneously applied to both the front and back surfaces of the positive electrode current collector using a slot die coating method to form a positive electrode slurry layer. The positive electrode slurry layer was then dried and pressed to form a positive electrode active material layer 11N, thereby producing a positive electrode.

[0056] Pitch-coated natural graphite particles (negative electrode active material A) and artificial graphite particles (negative electrode active material B) were prepared as negative electrode active materials, styrene butadiene rubber (SBR) was prepared as a binder, and carboxymethyl cellulose (CMC) was prepared as a dispersant.

[0057] Negative electrode active material A, negative electrode active material B, binder, and dispersant were mixed so that the weight ratio of the total of negative electrode active material A and negative electrode active material B:binder:dispersant was 100:1:1. Ion-exchanged water was added to the obtained mixture to adjust the viscosity, thereby obtaining a negative electrode slurry.

[0058] The negative electrode slurry was simultaneously applied to both sides of a 10 μm-thick copper foil, leaving uncoated areas to serve as welds (exposed areas of the negative electrode current collector), by a slot die coating method, to form two layers (front and back) of the negative electrode slurry. The negative electrode slurry layer was then dried and pressed to form a negative electrode active material layer 12N, thereby producing a negative electrode.

[0059] Next, a separator 13 was sandwiched between the prepared positive electrode 11 and negative electrode 12 to prepare a charge / discharge body 10 having the configuration shown in Fig. 8. The positive electrode connection end and negative electrode connection end of the positive electrode current collector 21 and negative electrode current collector 22 connected to the lid 52 were welded to the uncoated portions (exposed portion of the positive electrode current collector and exposed portion of the negative electrode current collector) of the charge / discharge body 10, the charge / discharge body 10 was covered with an insulating protective film, and the charge / discharge body 10 was enclosed in a container 51, and the lid 52 and the container 51 were welded together.

[0060] Next, LiPF was added to a non-aqueous electrolyte solution prepared by mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:2. ６ The above was dissolved at a concentration of 1.0 mol / L to prepare an electrolyte solution. The prepared electrolyte solution was poured into the pouring port, and then the opening was sealed with a pouring plug to prepare a lithium ion secondary battery.

[0061] The differences in the structures of Examples 1 to 7 and Comparative Examples 1 to 3 are shown in the table of FIG. 3 . Specifically, in Examples 1 to 7, various combinations of three active materials, namely, a first active material 1, a second active material 2, and a third active material 3, were blended as the positive electrode mixture. In contrast, the Comparative Examples used only two active materials. Specifically, Comparative Example 1 used the first active material 1 and the second active material 2, Comparative Example 2 used the first active material 1 and the third active material 3, and Comparative Example 3 used the second active material 2 and the third active material 3. In FIG. 3 , the battery energy density, i.e., the positive electrode density, and the rate characteristics, i.e., (2C / 0.2C), were evaluated as the battery performance for these Examples and Comparative Examples.

[0062] The positive electrode density in Fig. 3 was measured as follows: After pressing the positive electrode, a positive electrode having a predetermined area was punched out, and the weight and thickness were measured to calculate the positive electrode density.

[0063] The rate characteristics in Figure 3 were measured as follows. That is, the fabricated lithium-ion secondary battery was initialized by charging and discharging, and then the battery capacities at 0.2C and 2C were measured. Thereafter, constant voltage-constant current charging (CC-CV charging) was performed at a charging current of 1C for a total of 2.5 hours until the battery voltage reached 4.2V. After a 30-minute rest, the battery was discharged at a constant current of 0.1C (CC discharge) until the battery voltage reached 2.7V, and the initial capacity was obtained. Thereafter, the battery was charged under the same charging conditions, and then the discharge current was changed from 0.1C to 0.2C and 2C, and the battery capacities at 0.2C and 2C were measured. The rate characteristics (2C / 0.2C) shown in Table 1 are the ratios of the battery capacity at 2C to the battery capacity at 0.2C.

[0064] In terms of battery performance, it is better if both the positive electrode density and the rate characteristics (2C / 0.2C) are high, but even if the performance of either the positive electrode density or the rate characteristics is excellent, if the other performance is poor, the battery performance will be unbalanced and the performance as a battery will be insufficient. ３ As described above, the target rate characteristic is to have a (2C / 0.2C) characteristic of 85% or more.

[0065] In Examples 1 to 7, the weight ratios of the active materials were 70% first active material 1, 25% second active material 2, and 5% third active material 3 in Examples 1 to 6, and 70% first active material 1, 20% second active material 2, and 10% third active material 3 in Example 7. As shown in Fig. 3, in Examples 1 to 7, the average particle size, tap density, and combinations of the first active material 1, second active material 2, and third active material 3 were changed to evaluate the battery performance.

[0066] In FIG. 3, the average particle size of the first active material 1 in Examples 1 to 7 is 10 to 20 μm, and the tap density is 2.6 to 2.8 g / cm ３ The second active material 2 has an average particle size of 3.2 to 4.8 μm and a tap density of 2.0 to 2.3 g / cm ３ The third active material 3 has an average particle size of 10 to 20 μm and a tap density of 1.8 to 1.9 g / cm ３ That is, the particle size of the first active material 1 is in the range of 10 μm to 20 μm, the particle size of the second active material 2 is in the range of 3 to 5 μm, and the relationship of particle size of the third active material > particle size of the second active material is satisfied. Also, in each example, the relationship of weight of the first active material > weight of the second active material > weight of the third active material is satisfied.

[0067] As shown in Figure 3, Examples 1 to 7 satisfy the target performance of the present disclosure in terms of both positive electrode density and rate characteristics. That is, all Examples have a positive electrode density of 3.5 g / cm ３ Furthermore, the rate characteristics (2C / 0.2C) are 85% or more. Therefore, a battery with high energy density and excellent input / output characteristics has been realized.

[0068] In contrast, Comparative Example 1 is a case in which two types of positive electrode active materials, a first active material 1 and a second active material 2, are used. In Comparative Example 1, the positive electrode density is 3.8 / cm ３ Although the rate characteristic (2C / 0.2C) was 75%, which was insufficient. Comparative Example 2 was a case in which two types of positive electrode active materials, a first active material 1 and a third active material 3, were used. In Comparative Example 2, the rate characteristic (2C / 0.2C) was 87%, which was within the acceptable range, but the positive electrode density was 3.3 / cm ３ Comparative Example 3 is a case where two types of positive electrode active materials, a second active material 2 and a third active material 3, were used. In Comparative Example 3, the rate characteristic (2C / 0.2C) was 96%, which was a very high value, but the positive electrode density was 2.7 / cm ３ As described above, in the comparative example using only two types of active materials, it is not possible to realize a battery in which both the positive electrode density and the rate characteristics are within the allowable range.

[0069] As described above, according to the present disclosure, including Examples 1 to 7, it is possible to realize an excellent battery that has high performance in both positive electrode density and rate characteristics (2C / 0.2C) and a well-balanced set of characteristics. In other words, it is possible to realize a battery that has excellent energy density and input / output characteristics.

[0070] The battery of the present disclosure is not limited to the configurations described in the embodiments, and can be configured appropriately based on the contents described in the claims. Furthermore, the battery of the present disclosure is not limited to lithium-ion batteries. The battery of the present disclosure can be applied to, for example, nickel-metal hydride batteries and lead-acid batteries. The battery of the present disclosure is not limited to secondary batteries. The battery of the present disclosure can be applied to primary batteries. The charge / discharge body of the battery of the present disclosure is not limited to a wound-type charge / discharge body in which a positive electrode, a separator, and a negative electrode, each formed in a long shape, are bundled and wound.

[0071] The charge / discharge body of the battery of the present disclosure may be a laminated type in which multiple rectangular positive electrodes, separators, and negative electrodes are alternately stacked. The charge / discharge body of the battery of the present disclosure may be a laminated type in which multiple relatively short positive electrodes and multiple negative electrodes are alternately arranged facing each other with the separator interposed between them, with a single long separator. In a charge / discharge body of this configuration, the separator is folded and stacked, so that the positive electrode and the negative electrode face each other with the separator interposed between them. The battery of the present disclosure is not limited to a configuration in which the charge / discharge body is sealed with a container and a lid. The battery of the present disclosure may also be applied to a configuration in which the charge / discharge body is sealed with a laminate film.

[0072] Another method for manufacturing a positive electrode will be described below. A method for manufacturing a positive electrode according to an embodiment may be a method for simultaneously forming the first and second positive electrode active material layers of the positive electrode active material layer. This method will be described below with reference to FIG. 10 .

[0073] In this manufacturing method, materials to be contained in the first positive electrode active material layer (e.g., a positive electrode active material, a conductive additive, a 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 positive electrode slurry. Furthermore, materials to be contained in the second positive electrode active material layer (e.g., a positive electrode active material, a conductive additive, a 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 positive electrode slurry.

[0074] Next, for example, using a die head 150 as shown in FIG. 10 , the positive electrode first slurry and the positive electrode second slurry are simultaneously applied onto the positive electrode current collector 134a. The die head 150 has an outlet block 157, a three-dimensional shim 158, and an inlet block 159. A positive electrode second slurry manifold 152 and a positive electrode first slurry manifold 151 are provided inside the die head 150. The positive electrode second slurry and the positive electrode first slurry are simultaneously ejected from the respective manifolds 152, 151 toward the positive electrode current collector 134a being transported along back rollers 156. As a result, a positive electrode second slurry layer 133d and a positive electrode first slurry layer 133b are formed. Next, the solvent contained in the positive electrode first slurry layer 133b and the positive electrode second slurry layer 133d is volatilized using a drying oven or the like, and the positive electrode first slurry layer 133b and the positive electrode second slurry layer 133d are dried. As a result, a positive electrode first active material layer (not shown) and a positive electrode second active material layer (not shown) are formed on one surface of the positive electrode current collector 134a. Next, the positive electrode current collector 134a, the positive electrode first active material layer, and the positive electrode second active material layer are pressed. Specifically, a laminate including the positive electrode current collector 134a, the positive electrode first active material layer, and the positive electrode second active material layer is sandwiched between rollers heated to 60 to 120°C and pressure is applied. Thereafter, the laminate is slit to a predetermined width. This results in a positive electrode.

[0075] In a battery having a positive electrode manufactured by the manufacturing method in which the above-described two-layer simultaneous coating is applied, the interface between the positive electrode first slurry layer 133b and the positive electrode second slurry layer 133d has an uneven shape, which improves the adhesion between the positive electrode first slurry layer 133b and the positive electrode second slurry layer 133d, and prevents the two layers from peeling off even when a volume change occurs during charge and discharge, thereby improving the reliability of the battery.

[0076] The present disclosure can also be applied to solid-state batteries. That is, the battery according to the embodiment may be a battery including a solid electrolyte as an electrolyte, which includes a positive electrode, a negative electrode, and a solid electrolyte layer including the solid electrolyte, and which includes a charge / discharge body in which the solid electrolyte layer is interposed between the positive electrode and the negative electrode.

[0077] For example, the positive electrode electronic insulating layer and the negative electrode electronic insulating layer each contain a solid electrolyte. The positive electrode electronic insulating particles and the negative electrode electronic insulating particles are both solid electrolyte particles. A battery including such a solid electrolyte does not require an electrolytic solution, thereby improving safety.

[0078] Examples of the solid electrolyte include sulfide-based solid electrolytes, such as Li １０ GeP ２ S １２ , Li ６ P.S. ５ Cl and Li ２ S-P ２ S ５ Li-based glass ２ S-SiS ２ Li-based glass ２ S-P ２ S ５ -GeS ２ Li-based glass ２ S-B ２ S ３ oxide-based solid electrolytes, for example, Li ７ La ３ Zr ２ O １２ , LiLaTiO ３ , LiTi(PO ４ ) ３ , LiGe(PO ４ ) ３ , and complex hydride-based solid electrolytes, such as LiBH ４ - LiI, LiBH ４ -LiNH ２ and mixtures of two or more thereof.

[0079] Furthermore, the present disclosure can also be used in separator-less batteries, the structure of which will be described below with reference to Figures 11 and 12.

[0080] 11 , in a separatorless battery (lithium ion secondary battery) including a positive electrode 134 according to another example of the embodiment, the positive electrode 134 includes a positive electrode current collector 134a, a positive electrode first active material layer 134b1 bonded to both surfaces of the positive electrode current collector 134a, a positive electrode second active material layer 134b2 bonded to each of the first positive electrode active material layers 134b1, and a positive electrode electronic insulating layer 134d bonded to each of the second positive electrode active material layers 134b2. The negative electrode 132 includes a negative electrode current collector 132a, a negative electrode active material layer 132b bonded to both surfaces of the negative electrode current collector 132a, and a negative electrode electronic insulating layer 132d bonded to each of the negative electrode active material layers 132b.

[0081] One end of the positive electrode current collector 134a is provided with a positive electrode current collector exposed portion 134c, which is a portion not covered by either the positive electrode active material layer 134b, including the positive electrode first active material layer 134b1 and the positive electrode second active material layer 134b2, or the positive electrode electronic insulating layer 134d. The positive electrode current collector exposed portion 134c is provided on an end face of a wound pack (not shown) or in its vicinity. The positive electrode current collector exposed portion 134c faces and is electrically connected to a positive electrode connection end (not shown) of a positive electrode current collector plate (not shown). Similarly, one end of the negative electrode current collector 132a is provided with a negative electrode current collector exposed portion 132c, which is a portion not covered by either the negative electrode active material layer 132b or the negative electrode electronic insulating layer 132d. The negative electrode current collector exposed portion 132c is provided on an end face of the wound pack or in its vicinity. The negative electrode current collector exposed portion 132c faces and is electrically connected to the negative electrode side connection end portion (not shown) of the negative electrode current collector plate (not shown).

[0082] The positive electrode electronic insulating layer 134d and the negative electrode electronic insulating layer 132d have the functions of preventing short-circuiting between the positive electrode active material layer 134b and the negative electrode active material layer 132b and conducting ions between the positive electrode active material layer 134b and the negative electrode active material layer 132b. The positive electrode electronic insulating layer 134d and the negative electrode electronic insulating layer 132d may be porous layers made of an electrically insulating (i.e., electronically insulating and ionically insulating) material. The porous layer can retain an electrolyte solution in its pores, and ions can be conducted between the positive electrode active material layer 134b and the negative electrode active material layer 132b via this electrolyte solution.

[0083] The porous positive electrode electronic insulating layer 134d and negative electrode electronic insulating layer 132d may also function to buffer the expansion and contraction of the positive electrode active material layer 134b and negative electrode active material layer 132b that accompany charging and discharging of the lithium-ion secondary battery. The expansion and contraction of the negative electrode active material layer 132b that accompanies charging and discharging of the battery is generally greater than that of the positive electrode active material layer 134b. Therefore, the negative electrode electronic insulating layer 132d may have an average pore diameter larger than that of the positive electrode electronic insulating layer 134d so as to buffer the expansion and contraction of the larger negative electrode active material layer 132b. In this disclosure, the average pore diameters of the positive electrode electronic insulating layer 134d and the negative electrode electronic insulating layer 132d refer to the average values ​​of the volumetric pore diameters measured by mercury intrusion porosimetry.

[0084] The total content of Na and Fe in the positive electrode electronic insulating layer 134d and the negative electrode electronic insulating layer 132d may be 300 ppm or less based on the weight of the positive electrode electronic insulating layer 134d and the negative electrode electronic insulating layer 132d. The amount of each element contained in the positive electrode electronic insulating layer 134d and the negative electrode electronic insulating layer 132d can be measured by ICP (Inductive Coupled Plasma) spectroscopy.

[0085] The positive electrode electronic insulating layer 134d may contain positive electrode electronic insulating particles, and the negative electrode electronic insulating layer 132d may contain negative electrode electronic insulating particles. Hereinafter, the positive electrode electronic insulating particles and the negative electrode electronic insulating particles will be collectively referred to as electronic insulating particles as appropriate. The electronic insulating particles may be electrically insulating particles. Examples of electrically insulating particles include ceramic particles. The ceramic particles may be made of alumina (Al ２ O ３ ), boehmite (Al ２ O ３ hydrate), magnesia (MgO), zirconia (ZrO ２ ), titania (TiO ２ ), iron oxide, silica (SiO ２ ), and barium titanate (BaTiO ２), and preferably contains at least one selected from the group consisting of alumina, boehmite, magnesia, zirconia, and titania. The electronically insulating particles may have an average particle diameter in the range of 0.7 to 1.1 μm. The average particle diameter of the electronically insulating particles can be determined by calculating the arithmetic mean of the projected area circle equivalent diameters of 100 or more randomly selected electronically insulating particles based on microscope observation images of the positive electrode electronic insulating layer 134d and the negative electrode electronic insulating layer 132d. The electronically insulating particles may contain at least one of 100 to 200 ppm of Na, 50 to 100 ppm of Fe, or 50 to 100 ppm of Ca, based on the weight of the electronically insulating particles.

[0086] The positive electrode electronic insulating layer 134d and the negative electrode electronic insulating layer 132d may further contain a binder. The binder may be dispersed or dissolved in an aqueous solvent or a non-aqueous solvent (e.g., N-methyl-2-pyrrolidone (NMP)), and may contain, for example, at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), and carboxymethyl cellulose (CMC).

[0087] The positive electrode electronic insulating layer 134d and the negative electrode electronic insulating layer 132d 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.

[0088] The interface 134e between the positive electrode electronic insulating layer 134d and the positive electrode active material layer 134b has an uneven shape, and the height of the unevenness is 2 μm or more, preferably in the range of 2 to 4 μm. The interface 132e between the negative electrode electronic insulating layer 132d and the negative electrode active material layer 132b has an uneven shape, and the height of the unevenness is 2 μm or more, preferably in the range of 2 to 4 μm. By making the unevenness height of the interface 134e between the positive electrode electronic insulating layer 134d and the positive electrode active material layer 134b and the interface 132e between the negative electrode electronic insulating layer 132d and the negative electrode active material layer 132b 2 μm or more, the adhesion between the positive electrode electronic insulating layer 134d and the positive electrode active material layer 134b and the adhesion between the negative electrode electronic insulating layer 132d and the negative electrode active material layer 132b can be improved. This makes it possible to prevent or reduce peeling of the positive electrode electronic insulating layer 134d and the negative electrode electronic insulating layer 132d from the positive electrode active material layer 134b and the negative electrode active material layer 132b, respectively, thereby improving the reliability of the lithium ion secondary battery.

[0089] The height of the unevenness at the interface 134e between the positive electrode second active material layer 134b2 (positive electrode active material layer 134b) and the positive electrode electronic insulating layer 134d can be controlled, for example, by the particle diameters of the positive electrode active material particles and the positive electrode electronic insulating particles. As shown in Figure 12, when the average particle diameter of the positive electrode second active material particles 134b2p (positive electrode second active material) contained in the positive electrode second active material layer 134b2 is larger than the average particle diameter of the positive electrode electronic insulating particles 134dp, the positive electrode electronic insulating particles 134dp enter the gaps between the positive electrode first active material layers 134b1p, and the interface 134e between the positive electrode active material layer 134b and the positive electrode electronic insulating layer 134d has an uneven shape. For example, by using spherical positive electrode first active material 134b1p having an average particle diameter in the range of 4.5 to 5.5 μm and positive electrode electronic insulating particles 134dp having an average particle diameter in the range of 0.7 to 1.1 μm, the height of the irregularities at interface 134e between positive electrode active material layer 134b and positive electrode electronic insulating layer 134d can be set to 2 μm or more, preferably in the range of 2 to 4 μm.

[0090] The height of the irregularities at the interface 132e between the negative electrode active material layer 132b and the negative electrode electronic insulating layer 132d can also be controlled by the particle sizes of the negative electrode active material particles and the negative electrode electronic insulating particles. For example, by using scale-like negative electrode active material particles having an average particle size in the range of 9 to 11 μm and negative electrode electronic insulating particles having an average particle size in the range of 0.7 to 1.1 μm, the height of the irregularities at the interface 132e between the negative electrode active material layer 132b and the negative electrode electronic insulating layer 132d can be set to 2 μm or more, preferably in the range of 2 to 4 μm.

[0091] In the present disclosure, the unevenness height of the interface 134e between the positive electrode electronic insulating layer 134d and the positive electrode active material layer 134b and the interface 132e between the negative electrode active material layer 132b and the negative electrode electronic insulating layer 132d is measured as follows: Cross-sectional SEM images of three arbitrary locations on the positive electrode 134 or the negative electrode 132 are obtained using a scanning electron microscope (SEM), and in each cross-sectional SEM image, the distances from 10 or more arbitrary points on the interface 134e, 132e to a predetermined reference plane are measured (e.g., the distances from 10 or more arbitrary points on the interface 134e, 132e to the surface 134f of the positive electrode electronic insulating layer 134d and the surface 132f of the negative electrode electronic insulating layer 132d, i.e., the thickness of the positive electrode electronic insulating layer 134d and the thickness of the negative electrode electronic insulating layer 132d at 10 or more arbitrary points). The standard deviation of the obtained distance values ​​is defined as the unevenness height of the interface 134e, 132e. The surface 134f of the positive electrode electronic insulating layer 134d and the surface 132f of the negative electrode electronic insulating layer 132d are surfaces facing each other and may be sufficiently flat compared to the interfaces 134e and 132e. For example, the height of the irregularities on the surfaces 134f and 132f of the positive electrode electronic insulating layer 134d and the negative electrode electronic insulating layer 132d may be one-tenth or less of the height of the irregularities on the interfaces 134e and 132e, respectively.

[0092] The phrase "the interface 134e between the positive electrode electronic insulating layer 134d and the positive electrode active material layer 134b has an uneven shape" can also be rephrased as "a positive electrode mixed layer containing a positive electrode active material and an electronic insulating material is present between the positive electrode electronic insulating layer 134d and the positive electrode active material layer 134b." Similarly, the phrase "the interface 132e between the negative electrode electronic insulating layer 132d and the negative electrode active material layer 132b has an uneven shape" can also be rephrased as "a negative electrode mixed layer containing a negative electrode active material and an electronic insulating material is present between the negative electrode electronic insulating layer 132d and the negative electrode active material layer 132b." The thickness of the positive electrode mixed layer is 2 μm or more, preferably in the range of 2 to 4 μm. The thickness of the negative electrode mixed layer is 2 μm or more, preferably in the range of 2 to 4 μm. The thicknesses of the positive electrode mixed layer and the negative electrode mixed layer can be measured in the same manner as the height of the irregularities at the interface 134e between the positive electrode electronic insulating layer 134d and the positive electrode active material layer 134b and the interface 132e between the negative electrode electronic insulating layer 132d and the negative electrode active material layer 132b.

[0093] The positive electrode electronic insulating layer 134d and the negative electrode electronic insulating layer 132d may be in contact with each other. Preferably, the positive electrode electronic insulating layer 134d and the negative electrode electronic insulating layer 132d may be in contact without being fixed to each other. By not fixing the positive electrode electronic insulating layer 134d and the negative electrode electronic insulating layer 132d to each other, stress caused by expansion and contraction of the negative electrode active material layer 132b and the positive electrode active material layer 134b due to charging and discharging of the lithium ion secondary battery can be alleviated, and dendrites that may cause a short circuit between the positive electrode active material layer 134b and the negative electrode active material layer 132b can be prevented or reduced from growing through the positive electrode electronic insulating layer 134d and the negative electrode electronic insulating layer 132d.

[0094] The peel strength of the positive electrode electronic insulating layer 134 d from the positive electrode active material layer 134 b and the peel strength of the negative electrode electronic insulating layer 132 d from the negative electrode active material layer 132 b may be greater than the peel strength of the positive electrode electronic insulating layer 134 d from the negative electrode electronic insulating layer 132 d. The peel strengths can be measured, for example, by a 180° tape peel test in accordance with JIS C 0806-3 1999.

[0095] The height of the unevenness at the interface 134e between the positive electrode active material layer 134b and the positive electrode electronic insulating layer 134d can be controlled by the particle sizes of the positive electrode active material particles and the positive electrode electronic insulating particles, as well as by the type and viscosity of the solvent for the positive electrode mixture slurry and the positive electrode electronic insulating material slurry. Similarly, the height of the unevenness at the interface 132e between the negative electrode active material layer 132b and the negative electrode electronic insulating layer 132d can be controlled by the type and viscosity of the solvent for the negative electrode mixture slurry and the negative electrode electronic insulating material slurry.

[0096] The average pore diameters of the positive electrode electronic insulating layer 134d and the negative electrode electronic insulating layer 132d can be controlled by the particle diameter of the electronic insulating particles, the pressing pressure during pressing, etc. Specifically, the higher the pressing pressure, the smaller the average pore diameter, and the smaller the particle diameter of the electronic insulating particles, the smaller the average pore diameter.

[0097] In the separator-less battery provided with the positive electrode 134 of the other example described above, the strength of the electronic insulating layer is greater than that of the separator, and therefore the safety of the battery is improved.

[0098] Furthermore, in a modified example of the separatorless battery including the positive electrode 134 of the other example described above, the positive electrode electronic insulating layer 134d and the negative electrode electronic insulating layer 132d are each a layer containing a solid electrolyte (i.e., an electronically insulating and ionically conductive material). This modified battery (lithium ion secondary battery) does not require an electrolytic solution, thereby improving safety. In this modified example, the electronically insulating particles contained in the positive electrode electronic insulating layer 134d and the negative electrode electronic insulating layer 132d may be solid electrolyte particles. Because solid electrolytes can be easily molded by press molding, in this case, it is not essential that the positive electrode electronic insulating layer 134d and the negative electrode electronic insulating layer 132d contain a binder and a dispersant.

[0099] Furthermore, at least one of the first positive electrode active material layer 134b1 and the second positive electrode active material layer 134b2 included in the positive electrode active material layer 134b may further contain a solid electrolyte in addition to the active material and optional binders, conductive additives, and dispersants, thereby improving the ionic conductivity of at least one of the first positive electrode active material layer 134b1 and the second positive electrode active material layer 134b2.

[0100] The negative electrode active material layer 132b may further contain a solid electrolyte in addition to the electrode active material and optional binders, conductive additives, and dispersants, thereby improving the ionic conductivity of the negative electrode active material layer 132b.

[0101] The battery of the above modification does not require an electrolyte solution and has a stronger electronic insulating layer than the separator, thereby improving safety. The battery includes a positive electrode including a positive current collector, a positive electrode mixture layer provided on the positive current collector, and a positive electrode electronic insulating layer provided on the positive electrode mixture layer, and a negative electrode including a negative current collector, a negative electrode mixture layer provided on the negative current collector, and a negative electrode electronic insulating layer provided on the negative electrode mixture layer, where 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 with each other without being fixed to each other.

[0102] In another example of a positive electrode according to the embodiment, the first and second positive electrode active material layers and the positive electrode electronic insulating layer of the positive electrode active material layer can be manufactured by simultaneous coating, for example, as follows. First, materials to be included in the first positive electrode active material layer (e.g., a positive electrode active material, a conductive additive, a 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 positive electrode slurry. Furthermore, materials to be included in the second positive electrode active material layer (e.g., a positive electrode active material, a conductive additive, a 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 positive electrode slurry. Furthermore, materials to be included in the positive electrode electronic insulating layer 134d (e.g., positive electrode electronic insulating particles, a binder, a dispersant, etc.) are prepared. The materials are mixed and the resulting mixture is dispersed in a solvent (eg, N-methyl-2-pyrrolidone (NMP) and / or water) to obtain a positive electrode electronic insulation slurry.

[0103] Next, the positive electrode first slurry, the positive electrode second slurry, and the positive electrode electronic insulating material slurry are simultaneously applied onto the positive electrode current collector. This forms a positive electrode second slurry layer, a positive electrode first slurry layer, and a positive electrode electronic insulating material slurry layer. Next, the solvents contained in the positive electrode second slurry layer, the positive electrode first slurry layer, and the positive electrode electronic insulating material slurry layer are volatilized using a drying oven or the like, thereby drying the positive electrode second slurry layer, the positive electrode first slurry layer, and the positive electrode electronic insulating material slurry layer. This forms a positive electrode first active material layer, a positive electrode second active material layer, and a positive electrode electronic insulating layer on one side of the positive electrode current collector. Next, the positive electrode current collector, the positive electrode first active material layer, the positive electrode second active material layer, and the positive electrode electronic insulating layer are press-formed. Specifically, a laminate including a positive electrode current collector, a first positive electrode active material layer, a second positive electrode active material layer, and a positive electrode electronic insulating layer is sandwiched between rollers heated to 60 to 120°C and pressure is applied. Then, the laminate is slit to a predetermined width, thereby obtaining a positive electrode.

[0104] Batteries equipped with a positive electrode manufactured using the above-described method of simultaneous coating of three layers do not require the use of an electrolyte solution, and since the interfaces between the layers are uneven and firmly adhere to each other, they are highly safe and reliable.

[0105] 1...first active material, 2...second active material, 3...third active material, 5...battery, 10...charge / discharge body, 10a...side portion, 11...positive electrode, 11a...current collecting portion, 11b...positive electrode tab, 11c...side edge, 11M...positive electrode current collecting layer, 11N...positive electrode active material layer, 12...negative electrode, 12a...current collecting portion, 12b...negative electrode tab, 12c...side edge, 12M...negative electrode current collecting layer, 12N...negative electrode active material layer, 13...separator, 20...current collector, 21...positive electrode current collecting plate, 22...negative electrode current collecting plate, 30...current interrupter, 40...external terminal, 50...exterior body, 60...insulator, 70...sealing body.

Claims

1. A secondary battery in which a positive electrode having a positive electrode active material and a negative electrode having a negative electrode active material are laminated, wherein the positive electrode active material has a first active material with an average particle diameter (D50, median diameter) of 10 μm or more and 20 μm or less, a second active material with an average particle diameter (D50, median diameter) of 3 μm or more and 5 μm or less, and a third active material with an average particle diameter (D50, median diameter) larger than that of the second active material and a tap density lower than that of the second active material, and the secondary battery is characterized by having a mixture of these.

2. The secondary battery according to claim 1, wherein the positive electrode active material layer is formed by mixing the positive electrode active materials such that the weight ratio is the first active material > the second active material > the third active material.

3. The secondary battery according to claim 1, wherein the second active material and the third active material are formed of different material compositions.

4. The charge / discharge body in which the positive electrode and the negative electrode are laminated has an exposed first side portion, and a first tab connected to the positive electrode and a second tab connected to the negative electrode are present on the first side portion. The charge / discharge body is housed in a battery container having a plurality of surfaces including a first surface, and a first terminal and a second terminal are arranged on the first surface, and the secondary battery according to claim 1 is characterized in that the first surface and the first side portion face each other.

5. The secondary battery according to claim 4, wherein the charge / discharge body has a main surface having a long side and a short side, and the first side portion is present on the long side.

6. A method for manufacturing a secondary battery in which a positive electrode having a positive electrode active material and a negative electrode having a negative electrode active material are laminated with a separator therebetween, wherein the positive electrode active material is formed by mixing a first active material with an average particle diameter (D50, median diameter) of 10 μm or more and 20 μm or less, a second active material with an average particle diameter (D50, median diameter) of 3 μm or more and less than 5 μm, and a third active material with an average particle diameter (D50, median diameter) larger than that of the second active material and a tap density lower than that of the second active material, and the method for manufacturing a secondary battery is characterized by this.

7. The method for manufacturing a secondary battery according to claim 6, wherein a positive electrode active material layer is formed by mixing the positive electrode active materials such that the weight ratio is the first active material > the second active material > the third active material.

8. The method for manufacturing a secondary battery according to claim 7, wherein the second active material and the third active material are formed of different material compositions.

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