Electrode body for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery

Abstract

To provide an electrode body of a nonaqueous electrolyte secondary battery and a nonaqueous electrolyte secondary battery, capable of achieving both a reduction in battery resistance and a suppression in shortened battery life.SOLUTION: A negative electrode 20 of an electrode body 15 includes a current collector 21 and an active material layer 22. The active material layer 22 includes active material particles 24 formed of a carbon material. The active material particles 24 have a volume distribution with respect to particle size, the volume distribution including a first peak f1 corresponding to a first particle size D1 and a second peak f2 corresponding to a second particle size D2 smaller than the first particle size D1. The first particle size D1 is 7.0 μm or more and 9.0 μm or less. The second particle size D2 is 0.8 μm or more and 1.0 μm or less. A separator 40 has a surface roughness Ra of 1.54 μm or more. A peak ratio Rr of a volume of the active material particles 24 at the second peak f2 to a volume of the active material particles 24 at the first peak f1 is 0.42 or more and 0.71 or less.SELECTED DRAWING: Figure 2

Description

Technical Field

[0006] , , ,

[0005] , , ,

[0001] The present invention relates to an electrode body of a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery.

Background Art

[0002] Conventionally, the negative electrode of a non-aqueous electrolyte secondary battery has a current collector and an active material layer provided on at least one surface of the current collector. The active material layer contains active material particles. Such active material particles include those formed of a carbon material such as graphite.

[0003] Further, Patent Document 1 describes active material particles containing Si. The active material particles described in Patent Document 1 include large particle size particles and small particle size particles having a particle size of 1 / 2 or less with respect to the particle size of the large particle size particles. The particle size of the large particle size particles is 1.4 μm to 10 μm. The particle size of the small particle size particles is smaller than 1.38 μm. The small particle size particles enter the gaps between the large particle size particles, and thus the gaps between the large particle size particles are filled by the small particle size particles.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in a secondary battery provided with a negative electrode having an active material layer containing active material particles formed of a carbon material, it is required to achieve both reduction of battery resistance and suppression of shortening of battery life.

Means for Solving the Problems

[0006] Each aspect of an electrode body of a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery for solving the above problems is described. [Aspect 1] An electrode body for a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a separator provided between the positive electrode and the negative electrode, wherein the negative electrode comprises a current collector and an active material layer provided on at least one surface of the current collector, the active material layer contains active material particles formed of a carbon material, the volume distribution of the particle size of the active material particles is configured to have a first peak with a peak at a first particle size and a second peak with a peak at a second particle size smaller than the first particle size, the first particle size being 7.0 μm or more and 9.0 μm or less, the second particle size being 0.8 μm or more and 1.0 μm or less, the surface roughness of the separator being 1.54 μm or more, and the peak ratio, which is the ratio of the volume of the active material particles at the second peak to the volume of the active material particles at the first peak, being 0.42 or more and 0.71 or less.

[0007] The inventors of this application have found the following relationship between the surface roughness of the separator, the peak ratio, the DC resistance of the battery at 25°C, and the battery capacity retention rate after 10 days, when the first particle size is 7.0 μm or more and 9.0 μm or less, and the second particle size is 0.8 μm or more and 1.0 μm or less. Here, a secondary battery with a separator surface roughness of 1.07 μm and a peak ratio of 0.12 is used as a comparative example. When the separator surface roughness is 1.54 μm or more and the peak ratio is 0.42 or more and 0.71 or less, the DC resistance ratio of the secondary battery with the above configuration to that of the comparative example is 98.69% or less. Furthermore, the battery capacity retention rate ratio of the secondary battery with the above configuration to that of the comparative example after 10 days is 97% or more.

[0008] Therefore, with the above configuration, it is possible to achieve both a reduction in battery resistance and a suppression of shortening battery life. [Aspect 2] The electrode body for a non-aqueous electrolyte secondary battery according to [Aspect 1], wherein the surface roughness of the separator is 2.29 μm or more, and the peak ratio is 0.42 or more and 0.61 or less.

[0009] According to this configuration, if the surface roughness of the separator is 2.29 μm or more, and the peak ratio is 0.42 or more and 0.61 or less, the DC resistance ratio of the secondary battery with the above configuration compared to the comparative example will be 97.7% or less. Furthermore, the battery capacity retention rate ratio of the secondary battery with the above configuration after 10 days compared to the comparative example will be 97% or more.

[0010] Therefore, the above configuration allows for a further reduction in battery resistance. [Aspect 3] A non-aqueous electrolyte secondary battery comprising an electrode body as described in [Aspect 1] or [Aspect 2], a non-aqueous electrolyte, and a battery case for housing the electrode body and the non-aqueous electrolyte.

[0011] According to this configuration, the same effects and advantages as those described in [Aspect 1] above can be achieved. [Effects of the Invention]

[0012] According to the present invention, it is possible to achieve both a reduction in battery resistance and a suppression of shortening of battery life. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a perspective view of a non-aqueous electrolyte secondary battery according to one embodiment. [Figure 2] Figure 2(a) is a cross-sectional view of the electrode body shown in Figure 1, and Figure 2(b) is an enlarged cross-sectional view of a part of the same electrode body. [Figure 3] Figure 3 is a graph showing the volume distribution of particle sizes of the active material particles that make up the active material layer of the negative electrode. [Figure 4] Figure 4 is a table showing the surface roughness of the separator, the peak ratio, the DC resistance ratio of the battery, and the battery capacity retention ratio for the comparative example, each example, and each reference example. [Figure 5] Figure 5 is a graph showing the relationship between the surface roughness of the separator and the DC resistance ratio of the battery for each peak ratio. [Modes for carrying out the invention]

[0014] Hereinafter, an electrode body of a non-aqueous electrolyte secondary battery and an embodiment of the non-aqueous electrolyte secondary battery will be described with reference to FIGS. 1 to 5. In this embodiment, the non-aqueous electrolyte secondary battery is embodied as a lithium ion battery (hereinafter referred to as the battery).

[0015] <Battery case 10> As shown in FIG. 1, the battery includes a battery case 10. The battery case 10 has a case body 11 and a lid body 12.

[0016] Inside the case body 11, an electrode body 15 and a non-aqueous electrolyte 18 are accommodated. On the outer surface of the lid body 12, a negative electrode external terminal 13 and a positive electrode external terminal 14 used for charging and discharging of electric power are provided. On the inner surface of the lid body 12, a current collecting portion 16 and a current collecting portion 17 are provided.

[0017] <Non-aqueous electrolyte 18> The non-aqueous electrolyte 18 is a composition in which a supporting salt is contained in a non-aqueous solvent. The non-aqueous solvent is, for example, ethylene carbonate (EC). The non-aqueous solvent may be one or more materials selected from the group consisting of propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and the like.

[0018] In addition, as the supporting salt, LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC4F9SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, LiI, etc. can be used. As the supporting salt, one or more lithium compounds (lithium salts) selected from these can be used. Thus, the non-aqueous electrolyte 18 contains a lithium compound.

[0019] <Electrode body 15> As shown in FIG. 2(a), the electrode body 15 includes a negative electrode 20, a positive electrode 30, and a plate-like separator 40 provided between the positive electrode 30 and the negative electrode 20.

[0020] The electrode body 15 is formed, for example, by winding a laminate in which a negative electrode 20, a positive electrode 30, and a separator 40 are stacked. <Negative electrode 20> As shown in Figures 2(a) and 2(b), the negative electrode 20 has a current collector 21 and an active material layer 22. The active material layer 22 is provided on one side of the current collector 21.

[0021] The current collector 21 is formed of, for example, copper foil. The current collector 21 has the function of collecting electricity from the active material layer 22. The current collector 21 has a connection portion 23. The negative electrode 20 is connected to the negative electrode external terminal 13 via the current collector portion 16 (see Figure 1).

[0022] The active material layer 22 contains active material particles 24 formed from a carbon material. The active material particles 24 are, for example, graphite. The negative electrode 20 is formed, for example, by kneading active material particles 24, a solvent, and a binder (none of which are shown) into a paste, applying it to the current collector 21, and then drying it.

[0023] As shown in Figure 3, the volume distribution of the particle size of the active material particles 24 is configured to have a first peak f1 with a peak at the first particle size D1, and a second peak f2 with a peak at the second particle size D2, which is smaller than the first particle size D1.

[0024] The first particle size D1 is preferably 7.0 μm or more and 9.0 μm or less. In this embodiment, the first particle size D1 is 8.0 μm. The second particle size D2 is preferably 0.8 μm or more and 1.0 μm or less. In this embodiment, the second particle size D2 is 0.8 μm.

[0025] The particle size values ​​mentioned above were measured using an image-based particle size distribution analysis method with MORPHOLOGIG3 (manufactured by Malvern Panalytical). The first peak, f1, is larger than the second peak, f2.

[0026] If the ratio of the volume of active material particles 24 at the second peak f2 to the volume of active material particles 24 at the first peak f1 is defined as the peak ratio Rt (= f2 / f1), then it is preferable that the peak ratio Rt is 0.42 or greater and 0.71 or less. It is more preferable that the peak ratio Rt is 0.42 or greater and 0.61 or less.

[0027] <Positive electrode 30> As shown in Figure 2(a), the positive electrode 30 has a current collector 31 and an active material layer 32. The active material layer 32 is provided on one side of the current collector 31.

[0028] The current collector 31 is formed from, for example, aluminum foil or aluminum alloy foil. The current collector 31 has the function of collecting electricity from the active material layer 32. The current collector 31 has a connection portion 33. The positive electrode 30 is connected to the positive electrode external terminal 14 via the current collector portion 17 (see Figure 1).

[0029] The active material layer 32 contains active material particles and a conductive material (neither of which are shown in the figure). The active material particles are materials capable of intercalating and releasing lithium, such as lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), and lithium nickel oxide (LiNiO2). Alternatively, a material mixture of LiCoO2, LiMn2O4, and LiNiO2 in any proportion may be used.

[0030] Examples of conductive materials that can be used include acetylene black (AB), carbon black such as Ketjenblack, and graphite. The positive electrode 30 is formed by, for example, kneading active material particles, a conductive material, a solvent, and a binder (none of which are shown) to form a paste, applying it to the current collector 31, and then drying it.

[0031] <Separator 40> As shown in Figure 2(a), the separator 40 is a porous nonwoven fabric or a porous membrane made of synthetic resin. Examples of synthetic resins include polypropylene, polyethylene, polyolefin, and polyvinyl chloride.

[0032] The surface roughness Ra of the separator 40 is 1.54 μm or more, more preferably 2.29 μm or more. The upper limit of the surface roughness Ra of the separator 40 is not particularly limited, but it is 5.2 μm or less, more preferably 3.27 μm or less. This is because if it exceeds this value, the shutdown time, which is the time from when the battery overheats abnormally until it shuts down, will be shorter than the specified time that is used as a safety standard.

[0033] The surface roughness Ra of separator 40 was measured using a shape-measuring laser microscope VK-X100 (manufactured by Keyence Corporation). Next, referring to Figure 4, the DC resistance values ​​at 25°C and the battery capacity retention rate after 10 days for the batteries of the following 1st to 4th embodiments will be explained based on a comparison with the comparative examples.

[0034] Hereafter, the DC resistance ratio Rr in the example battery is the value obtained by dividing the DC resistance value of the example battery at 25°C by the DC resistance value of the comparative example battery at 25°C. Also, the battery capacity retention ratio Rc in the example battery is the value obtained by dividing the battery capacity retention rate of the example battery by the battery capacity retention rate of the comparative example battery.

[0035] The battery capacity retention rate refers to the rate at which the battery capacity is maintained after 10 days of high-temperature storage at 75°C with a State of Charge (SOC) of 80%. <Comparative Example> The surface roughness Ra of separator 40 is 1.07 μm. The peak ratio Rt is 0.12%.

[0036] <Example 1> The surface roughness Ra of separator 40 is 3.27 μm. The peak ratio Rt is 0.42%. The DC resistance ratio Rr is 96.4%. The battery capacity retention ratio Rc is 97%.

[0037] <Example 2> The surface roughness Ra of separator 40 is 3.27 μm. The peak ratio Rt is 0.61%. The DC resistance ratio Rr is 95.78%. The battery capacity retention ratio Rc is 97%.

[0038] <Example 3> The surface roughness Ra of separator 40 is 2.29 μm. The peak ratio Rt is 0.61%. The DC resistance ratio Rr is 97.7%. The battery capacity retention ratio Rc is 98%.

[0039] <Example 4> The surface roughness Ra of separator 40 is 1.54 μm. The peak ratio Rt is 0.71%. The DC resistance ratio Rr is 98.69%. The battery capacity retention ratio Rc is 98%.

[0040] <Reference example 1> The surface roughness Ra of separator 40 is 1.07 μm. The peak ratio Rt is 0.61%. The DC resistance ratio Rr is 99.98%. The battery capacity retention ratio Rc is 97%.

[0041] <Reference example 2> The surface roughness Ra of separator 40 is 1.54 μm. The peak ratio Rt is 0.87%. The DC resistance ratio Rr is 97.54%. The battery capacity retention ratio Rc is 92%.

[0042] <Reference example 3> The surface roughness Ra of separator 40 is 1.54 μm. The peak ratio Rt is 0.12%. The DC resistance ratio Rr is 99.36%. The battery capacity retention ratio Rc is 101%.

[0043] From the above, when the surface roughness Ra of separator 40 is 1.54 μm or more, and the peak ratio Rt is 0.42 or more and 0.71 or less, the DC resistance ratio Rr of each embodiment will be 98.69% or less. In addition, the battery capacity retention ratio Rc of each embodiment will be 97% or more.

[0044] In Reference Example 1, the low surface roughness Ra of the separator 40 resulted in increased air permeability of the separator 40. In other words, it became more difficult for lithium ions to move within the separator 40, which likely led to an increase in the DC resistance of the battery.

[0045] In Reference Example 2, the large peak ratio Rt increases the surface area of ​​the active material particles 24, leading to an increase in side reactions. As a result, the battery capacity retention rate decreases, meaning the battery life is shortened.

[0046] Next, with reference to Figure 5, the relationship between the surface roughness Ra of the separator 40 and the DC resistance ratio Rr of the battery will be explained. Figure 5 is a graph plotting the relationship between the surface roughness Ra of the separator 40 and the DC resistance ratio Rr of the battery in the comparative example, Examples 1 to 4, and Reference Example 1 shown in Figure 4.

[0047] As shown in Figure 5, when the surface roughness Ra of separator 40 is 1.54 μm or more and the peak ratio Rt is in the range of 0.42 to 0.71, the DC resistance ratio Rr is smaller than that of the comparative example where the surface roughness Ra is 1.07 μm and the peak ratio Rt is 0.12.

[0048] Furthermore, as can be seen from the three points where the peak ratio Rt is 0.61 (plot point ■ in Figure 5), the DC resistance ratio Rr decreases as the surface roughness Ra of the separator 40 increases. This is thought to be because the greater the surface roughness Ra of the separator 40, the lower the air permeability of the separator 40, or in other words, lithium ions move more easily within the separator 40, thereby reducing the DC resistance of the battery. In other words, although Figure 4 only has data up to a surface roughness Ra of 3.27 μm for the separator 40, it can be said that even when the surface roughness Ra of the separator 40 exceeds 3.27 μm, the DC resistance ratio Rr is still sufficiently smaller than in the comparative example.

[0049] Next, the effects of this embodiment will be described. (1) The first particle size D1 is 7.0 μm or more and 9.0 μm or less. The second particle size D2 is 0.8 μm or more and 1.0 μm or less. The surface roughness Ra of the separator 40 is 1.54 μm or more. The peak ratio Rt, which is the ratio of the volume of the active material particles 24 at the second peak f2 to the volume of the active material particles 24 at the first peak f1, is 0.42 or more and 0.71 or less.

[0050] With this configuration, the above-mentioned effects can be achieved, making it possible to achieve both a reduction in battery resistance and a suppression of shortening battery life. (2) The surface roughness Ra of the separator 40 is 2.29 μm or greater. The peak ratio Rt is 0.42 or greater and 0.61 or less.

[0051] With this configuration, if the surface roughness Ra of the separator 40 is 2.29 μm or more, and the peak ratio Rt is 0.42 or more and 0.61 or less, the DC resistance ratio Rr of the secondary battery with the above configuration compared to the comparative example will be 97.7% or less. Furthermore, the battery capacity retention ratio Rc of the secondary battery with the above configuration after 10 days compared to the comparative example will be 97% or more.

[0052] Therefore, the above configuration allows for a further reduction in battery resistance. (3) By providing the electrode body 15 in a non-aqueous electrolyte secondary battery, the above effects can be achieved, thereby achieving both a reduction in battery resistance and a suppression of shortening of battery life.

[0053] <Variation> This embodiment can be implemented with the following modifications. This embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0054] The active material layer 22 may be provided on both sides of the current collector 21. • Non-aqueous electrolyte secondary batteries are not limited to lithium-ion batteries. For example, the present invention can also be embodied as a nickel-metal hydride battery. [Explanation of Symbols]

[0055] 10…Battery case 11…Case body 12... Lid 13…Negative external terminal 14…Positive external terminal 15...Electrode body 16... Current collector 17... Current collection section 18...Nonaqueous electrolyte 20...Negative electrode 21... Current collector 22...Active material layer 23...Connection part 24...Active material particles 30...Positive electrode 31... Current collector 32...Active material layer 33…Connection part 40... Separator

Claims

1. In an electrode body of a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a porous separator made of synthetic resin provided between the positive electrode and the negative electrode, The negative electrode comprises a current collector and an active material layer provided on at least one surface of the current collector. The active material layer contains active material particles formed from a carbon material, and the volume distribution of the particle size of the active material particles is configured to have a first peak with a peak at a first particle size and a second peak with a peak at a second particle size smaller than the first particle size. The first particle size is 7.0 μm or more and 9.0 μm or less. The second particle size is 0.8 μm or more and 1.0 μm or less. The surface roughness of the separator is 1.54 μm or more. The peak ratio, which is the ratio of the volume of the active material particles at the second peak to the volume of the active material particles at the first peak, is 0.42 or more and 0.71 or less. Electrode body for a non-aqueous electrolyte secondary battery.

2. The surface roughness of the separator is 2.29 μm or more. The aforementioned peak ratio is 0.42 or higher and 0.61 or lower. An electrode body for a non-aqueous electrolyte secondary battery according to claim 1.

3. The device comprises an electrode body according to claim 1 or claim 2, a non-aqueous electrolyte, and a battery case for housing the electrode body and the non-aqueous electrolyte. Non-aqueous electrolyte secondary battery.

Images