Non-aqueous electrolyte secondary battery

Abstract

To provide a non-aqueous electrolyte secondary battery which can maintain a high energy density after discharge-charge cycles.SOLUTION: The battery includes: a positive electrode; a negative electrode; and a separator, the negative electrode including a negative electrode current collector, a negative electrode active material part on a surface of the negative electrode current collector, and an insulating part containing ceramic on the surface, and the insulating part being 5 vol% to 40 vol% with respect to the entire volume of the negative electrode after charging.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery. [Background technology]

[0002] A nonaqueous electrolyte secondary battery, such as a lithium ion secondary battery, has a separator disposed between a positive electrode and a negative electrode and is provided with an electrolyte containing a nonaqueous electrolyte. Regarding such lithium ion secondary batteries, Patent Document 1 discloses a negative electrode current collector having a surface with multiple protrusions that protrude toward the separator. In the nonaqueous electrolyte secondary battery disclosed in Patent Document 1, the use of a negative electrode current collector having the multiple protrusions results in a uniform distribution of the nonaqueous electrolyte, and lithium metal is uniformly deposited in the portions of the negative electrode current collector where the multiple protrusions are not formed.

[0003] As a result, the nonaqueous electrolyte secondary battery disclosed in Patent Document 1 is said to be able to improve the cycle life while maintaining charging efficiency. The protrusions on the negative electrode current collector are made of a conductive material other than lithium metal or a lithium alloy, or an insulating material such as polyolefin or polyimide. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-195572 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the nonaqueous electrolyte secondary battery disclosed in Patent Document 1 has a problem of a decrease in energy density after charge-discharge cycles. In view of the above-described circumstances, an object of one embodiment of the present disclosure is to provide a nonaqueous electrolyte secondary battery that can maintain a high energy density after charge-discharge cycles. [Means for solving the problem]

[0006] The present disclosure, which achieves the above-mentioned objectives, includes the following. <1> A non-aqueous electrolyte secondary battery comprising: a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; the negative electrode includes a negative electrode current collector, a negative electrode active material portion disposed on a surface of the negative electrode current collector, and an insulating portion containing ceramic disposed on the surface, the insulating portion occupying 5% by volume to 40% by volume of the total volume of the negative electrode after charging. <2> The ceramic contained in the insulating part is alumina or Li7La3Zr2O 12 That is, <1> The non-aqueous electrolyte secondary battery according to claim 1. <3> the insulating portion includes the ceramic and a binder, and the ceramic accounts for 95 mass% or more of the total of the ceramic and the binder; <1> or <2> The non-aqueous electrolyte secondary battery according to claim 1. <4> the insulating portion is a plurality of protrusions arranged on the surface of the negative electrode current collector, <1> ~ <3> 10. The non-aqueous electrolyte secondary battery according to claim 9, wherein the non-aqueous electrolyte secondary battery is a <5> The protrusion is columnar. <4> The non-aqueous electrolyte secondary battery according to claim 1. [Effects of the Invention]

[0007] According to the nonaqueous electrolyte secondary battery of one embodiment of the present disclosure, it is possible to maintain a high energy density after charge-discharge cycles. Because the high energy density is maintained even after repeated charge-discharge cycles, it is also possible to extend the life of the secondary battery. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic cross-sectional view of a portion including a negative electrode and a separator, which is one embodiment of a nonaqueous electrolyte secondary battery according to the present disclosure. [Figure 2] FIG. 2 is a schematic cross-sectional view of a portion including a negative electrode and a separator, which is another embodiment of a nonaqueous electrolyte secondary battery according to the present disclosure. [Figure 3] FIG. 2 is a perspective view schematically illustrating a procedure for forming an insulating portion on a negative electrode current collector in the nonaqueous electrolyte secondary battery of the present disclosure. [Figure 4] FIG. 10 is a characteristic diagram showing the relationship between the volume ratio of the insulating portion to the entire negative electrode and the energy density ratio after a cycle test for Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described. The description is for illustrating the embodiments and is not intended to limit the scope of the present disclosure.

[0010] In this specification, a numerical range indicated using "to" indicates a range that includes the numerical values before and after "to" as the minimum and maximum values, respectively. In the present specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range. In addition, in the present specification, the upper or lower limit of a numerical range may be replaced with a value shown in the examples.

[0011] In this specification, when an embodiment is described with reference to drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. Furthermore, the sizes of components in each drawing are conceptual, and the relative size relationships between components are not limited to these.

[0012] In this specification, each component may contain a plurality of corresponding substances. When referring to the amount of each component in the composition in this embodiment, if a plurality of substances corresponding to each component are present in the composition, the amount refers to the total amount of the plurality of substances present in the composition unless otherwise specified.

[0013] The nonaqueous electrolyte secondary battery of the present disclosure includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and the negative electrode includes a negative electrode current collector, a negative electrode active material portion disposed on the surface of the negative electrode current collector, and an insulating portion containing ceramic disposed on the surface, and the insulating portion occupies 5% to 40% by volume of the total volume of the negative electrode after charging.

[0014] The nonaqueous electrolyte secondary battery of the present disclosure can prevent a decrease in energy density after charge / discharge cycles, and therefore can achieve a long lifespan, i.e., can maintain a high energy density even after repeated charge / discharge.

[0015] In the nonaqueous electrolyte secondary battery of the present disclosure, the insulating portion disposed on the surface of the negative electrode current collector contains ceramic, and the insulating portion accounts for 5% to 40% by volume of the total volume of the negative electrode after charging. Therefore, the dielectric properties of the ceramic promote ion migration at the lithium metal deposition interface. Therefore, in the nonaqueous electrolyte secondary battery of the present disclosure, a uniform lithium metal deposition reaction is possible, and the deposited lithium metal is prevented from becoming porous. In the nonaqueous electrolyte secondary battery of the present disclosure, the lithium metal deposited on the negative electrode current collector functions as the negative electrode active material. It is presumed that this mechanism allows the nonaqueous electrolyte secondary battery of the present disclosure to maintain a high energy density even after repeated charge and discharge. If the insulating portion disposed on the surface of the negative electrode current collector did not contain ceramic, the deposited lithium metal would become porous, resulting in a decrease in energy density with repeated charge and discharge. Furthermore, if the insulating portion falls outside the range of 5% to 40% by volume relative to the total volume of the negative electrode after charging, the deposited lithium metal will become porous, resulting in a decrease in energy density with repeated charging and discharging.

[0016] Furthermore, in the nonaqueous electrolyte secondary battery of the present disclosure, the insulating portion disposed on the surface of the negative electrode current collector contains ceramic, and the insulating portion accounts for 5% to 40% by volume of the total volume of the negative electrode after charge. This makes it less likely that the insulating portion will expand due to penetration of the nonaqueous electrolyte or deform due to stress associated with lithium metal deposition, thereby preventing a decrease in energy density due to an increase in the volume of the insulating portion. If the insulating portion disposed on the surface of the negative electrode current collector does not contain ceramic, the swelling or deformation of the insulating portion due to repeated charge and discharge would result in a decrease in energy density. If the insulating portion accounts for a volume outside the range of 5% to 40% by volume of the total volume of the negative electrode after charge, the swelling or deformation of the insulating portion due to repeated charge and discharge would result in a decrease in energy density.

[0017] In the nonaqueous electrolyte secondary battery of the present disclosure, as described above, the volume ratio (vol %) of the insulating portion to the total volume of the negative electrode after charging is set to a range of 5 to 40 volume %, but is particularly preferably 9 to 36 volume %, more preferably 17 to 26 volume %, even more preferably 20 to 25 volume %, and most preferably 23 volume %.

[0018] [Negative electrode current collector] The negative electrode current collector is not particularly limited, and any negative electrode current collector conventionally used in producing negative electrodes can be used. The material of the negative electrode current collector is not particularly limited, and examples thereof include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel, with Cu being preferred. The thickness of the negative electrode current collector is not particularly limited, and can be, for example, in the range of 0.1 μm to 1 mm. The negative electrode current collector can also be in the form of a strip, such as a foil, a perforated foil, or a mesh.

[0019] [Insulation part] In the non-aqueous electrolyte secondary battery of the present disclosure, the ceramic contained in the insulating portion is preferably an insulating material (preferably having a volume resistivity of 10 or more). 6A wide range of non-metallic inorganic materials that exhibit a resistivity (Ω·m) and are manufactured through firing can be used. Ceramics include alumina (Al2O3), sapphire (Al2O3), zirconium oxide (ZrO2), barium titanate (BaTiO3), aluminum nitride (AlN), silicon nitride (Si3N4), boron nitride (BN), cordierite (2MgO·2Al2O3·5SiO2), steatite (MgO·SiO2), forsterite (2MgO·SiO2), yttria (Y2O3), silicon dioxide (SiO2), magnesium oxide (MgO), and bismuth(III) oxide (Bi2O3). These ceramics can be used alone or in combination as insulating materials. Of these ceramics, alumina is particularly preferred.

[0020] Furthermore, it is preferable to use a ceramic with a high relative dielectric constant as the ceramic contained in the insulating portion. The ceramic with a high relative dielectric constant is not particularly limited, but any solid electrolyte can be used. Crystalline nitrides, oxides, sulfides, and oxoacid salts, as well as amorphous glass-structured materials, can be used as such solid electrolytes. Specifically, sulfide solid electrolytes that can be used as the solid electrolyte include at least one selected from the group consisting of LiI-LiBr-Li3PS4, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2O-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-P2S5, Li3PS4, LiCl-LiBr-Li3PS4, LiCl-LiBr-Li2S-P2S5, and LiCl-LiBr-Li2S-SiS2. Furthermore, oxide-based solid electrolytes include, for example, Li 0.34 La 0.56 TiO3, Li 3 / 8 Sr 7 / 16 Ta 3 / 4 M 1 / 4 O3 (M=Zr or Hf), Li7La3Zr2O 12 , Li 1.3 Al 0.7 Ti 1.3 (PO4)3, Li1.5 Al 0.5 Ge 1.5 (PO4)3, Li 3.5 Ge 0.5 V 0.5 O, Li 2.88 PO 3.73 N 0.14 , and Li 2.9 Si 0.45 PO 1.6 N 1.3 In addition to these, complex hydride-based lithium ion conductors and halide-based lithium ion conductors may also be used as solid electrolytes. One or a combination of these may be used as the ceramic contained in the insulating portion of the nonaqueous electrolyte secondary battery according to the present disclosure. Among these, the ceramic may be Li7La3Zr2O 12 It is preferable to use (LLZO).

[0021] The insulating portion is disposed on the surface of the negative electrode current collector. When the surface of the negative electrode current collector is observed from above, the insulating portion may be either a band-like or an island-like shape, and may also be a band-like shape including a curve when the surface of the negative electrode current collector is observed from above, or may be a circular or polygonal island-like shape when the surface is observed from above.

[0022] The insulating portion of the nonaqueous electrolyte secondary battery of the present disclosure can be formed into a desired shape on the surface of the negative electrode current collector by mixing the above-described ceramic with a binder to form a slurry, and using the slurry. The amount of ceramic contained in the insulating portion is not particularly limited, but can be, for example, 70 mass% or more, preferably 75 mass% or more, more preferably 80 mass% or more, even more preferably 85 mass% or more, even more preferably 90 mass% or more, and most preferably 95 mass% or more, based on the total amount of the ceramic and the binder. The amount of ceramic contained in the insulating portion can also be 99.5 mass%. By setting the amount of ceramic contained in the insulating portion within this range, it is possible to reliably prevent the lithium metal from becoming porous and to reliably prevent the volume of the insulating portion from increasing, thereby more reliably maintaining a high energy density even after repeated charge and discharge.

[0023] The binder is not particularly limited, and examples that can be used include butadiene rubber (BR), butylene rubber (IIR), acrylate butadiene rubber (ABR), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVdF), and polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP).

[0024] [Negative electrode active material part] In the nonaqueous electrolyte secondary battery of the present disclosure, a negative electrode active material portion is disposed on the surface of the negative electrode current collector. The negative electrode active material portion is composed of lithium metal deposited on the surface of the negative electrode current collector. The lithium metal is deposited on the surface of the negative electrode current collector by assembling a nonaqueous electrolyte secondary battery (described later) using the negative electrode current collector having the insulating portion described above and then charging the battery.

[0025] Hereinafter, embodiments of the nonaqueous electrolyte secondary battery of the present disclosure will be described with reference to the drawings.

[0026] 1 and 2 show cross-sectional views of a portion including a negative electrode and a separator in a nonaqueous electrolyte secondary battery of the present disclosure. That is, the nonaqueous electrolyte secondary battery 1 shown in Fig. 1 and 2 includes a negative electrode including a negative electrode current collector 2, an insulating portion 3 disposed on one main surface of the negative electrode current collector 2, and a negative electrode active material portion 5 disposed on the same main surface of the negative electrode current collector 2. In the nonaqueous electrolyte secondary battery 1 shown in Fig. 1 and 2, the negative electrode and a positive electrode (not shown) face each other with a separator 4 interposed therebetween.

[0027] In particular, in the nonaqueous electrolyte secondary battery 1 shown in Figures 1 and 2, the insulating portions 3 are formed as a plurality of protrusions on the surface of the negative electrode current collector 2. The insulating portions 3 formed as a plurality of protrusions are arranged at predetermined equal intervals. That is, in the nonaqueous electrolyte secondary battery 1 shown in Figures 1 and 2, the insulating portions 3 are formed in a columnar shape on one main surface of the negative electrode current collector 2.

[0028] In particular, in the nonaqueous electrolyte secondary battery 1 shown in FIG. 1 , the upper surface of the insulating portion 3 abuts against the separator 4. In this case, the negative electrode active material portion 5 is made of lithium metal deposited between the insulating portions 3 formed as these multiple protrusions. In the nonaqueous electrolyte secondary battery 1 shown in FIG. 2 , the upper surface of the insulating portion 3 is separated from the separator 4. In this case, the negative electrode active material portion 5 is made of lithium metal deposited so as to fill the spaces between the insulating portions 3 formed as these multiple protrusions and the spaces between the insulating portion 3 and the separator 4.

[0029] In the nonaqueous electrolyte secondary battery 1 shown in FIGS. 1 and 2 , the method schematically shown in FIG. 3 can be used to form the insulating portion 3 on the surface of the negative electrode current collector 2. FIG. 3 illustrates the procedure for forming the insulating portion 3 from left to right. First, a perforated foil 10 is prepared to be placed on one main surface of the negative electrode current collector 2. The perforated foil 10 has a thickness corresponding to the height of the insulating portion 3 and has a plurality of through-holes 11 formed therein that correspond to the shape of the insulating portion 3. The perforated foil 10 is then placed on one main surface of the negative electrode current collector 2. In this state, a slurry 12 containing the ceramic mixed with a binder is applied to the top surface of the perforated foil 10, and the through-holes 11 are filled with the slurry 12. The perforated foil 10 is then peeled off from the negative electrode current collector 2 and dried, thereby forming the insulating portions 3 corresponding to the through-holes 11 on one main surface of the negative electrode current collector 2.

[0030] [Nonaqueous electrolyte secondary battery] The nonaqueous electrolyte secondary battery of the present disclosure includes a negative electrode including the insulating portion described above. The nonaqueous electrolyte secondary battery may include the negative electrode described above, a positive electrode, a separator disposed between the negative electrode and the positive electrode, and a nonaqueous electrolyte. In the secondary battery of the present disclosure, the positive electrode, separator, and nonaqueous electrolyte are not particularly limited, and conventionally known ones can be used.

[0031] The positive electrode can be obtained by forming a positive electrode mixture portion on the surface of a positive electrode current collector. Examples of non-aqueous electrolytes that can be used include so-called organic electrolytes obtained by dissolving a lithium salt such as an electrolyte Li(FSO2)2N, LiClO4, LiPF6, LiAsF6, LiBF4, or LiSO3CF3 in a non-aqueous solvent such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, cyclopentanone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, 3-methyl-1,3-oxazolidin-2-one, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, or ethyl acetate, either alone or as a mixture of two or more components.

[0032] The structure of the secondary battery of the present disclosure is not particularly limited, and typically, a positive electrode, a separator, and a negative electrode are wound into a flat spiral shape to form a wound electrode plate assembly, or these are stacked as flat plates to form a stacked electrode plate assembly, and the electrode plate assembly is sealed in an exterior case. The secondary battery of the present disclosure is not particularly limited, and is used as a paper-type battery, a button-type battery, a coin-type battery, a stacked battery, a cylindrical battery, a prismatic battery, etc. [Example]

[0033] The present disclosure will be described in more detail below using examples, but the technical scope of the present disclosure is not limited to the following examples.

[0034] [Example 1] <Preparation of negative electrode> In this example, an insulating portion was formed on one main surface of a negative electrode current collector foil according to the procedure shown in Figure 3. Specifically, a copper foil with a thickness of 30 μm was patterned with circular through-holes with a diameter of 500 μm, and then etched to produce a perforated foil with through-holes. Alumina and a binder (polyvinylidene fluoride (PVdF)) were mixed in a solvent (N-methyl-2-pyrrolidone (NMP)) at a volume ratio of 99.5:0.5. This prepared a slurry for producing the insulating portion.

[0035] Then, a perforated foil was placed on one side of a 10 μm thick electrolytic copper foil. In this state, a slurry was applied to the perforated foil, filling the through-holes formed in the perforated foil with the slurry. The perforated foil was then removed from the electrolytic copper foil, and the insulating portion formed on the electrolytic copper foil was dried. In this way, a negative electrode current collector with an insulating portion was prepared as a negative electrode.

[0036] <Test cell fabrication> In this example, LiNi 0.5 Co 0.2 Mn 0.3 A positive electrode slurry was prepared by mixing O2, acetylene black as a conductive additive, and PVdF as a binder. The positive electrode slurry was applied to aluminum foil (thickness: 15 μm) and pressed to prepare a positive electrode. The positive and negative electrodes prepared as described above were then placed opposite each other with a separator (polyethylene) interposed between them and housed in a laminate film together with an electrolyte (4 M LiFSI / DME solution) to prepare a test cell. In the test cell prepared in this example, the insulating portion accounted for 9 vol% of the total volume of the negative electrode after cell activation (described below), i.e., after charging.

[0037] <Cycle test> For the test cell fabricated as described above, 0.4 mA / cm 2 The cell was activated at a current density of 1 mA / cm and a voltage range of 3.0 to 4.3 V. Lithium metal was deposited on the negative electrode current collector by the cell activation. 2A cycle test was performed for 20 cycles at a current density of 1000 kJ / s and a voltage range of 3.0 to 4.3 V. The capacity was divided by the apparent volume of the negative electrode after charging to obtain the post-cycle electrode energy density. The post-cycle electrode energy density ratio was obtained by dividing the measured post-cycle electrode energy density by the post-cycle electrode energy density in the test cell prepared in Comparative Example 1, which will be described later.

[0038] [Examples 2 to 5] Test cells were prepared in the same manner as in Example 1, except that the volume ratio of the insulating portion to the entire negative electrode was adjusted by adjusting the size and / or number of the through-holes in the perforated foil in Example 1, and the energy density after the cycle test was measured. For Examples 2 to 5, the electrode energy density ratio after the cycle test was calculated in the same manner as in Example 1.

[0039] [Example 6] In Example 1, Li7La3Zr2O was used instead of alumina. 12 A test cell was prepared in the same manner as in Example 1, except that (LLZO) was used and the volume ratio of the insulating portion to the entire negative electrode was set to 20 volume %, and the energy density after the cycle test was measured. For Example 6, the electrode energy density ratio after the cycle test was calculated in the same manner as in Example 1.

[0040] [Comparative Example 1] In Comparative Example 1, a test cell was prepared in the same manner as in Example 1, except that a 10 μm thick electrolytic copper foil was used instead of the negative electrode current collector having an insulating portion, and the energy density after the cycle test was measured. By definition, the post-cycle electrode energy density ratio calculated for the test cell of Comparative Example 1 was 1.000.

[0041] Comparative Example 2 A test cell was prepared in the same manner as in Example 1, except that the volume ratio of the insulating portion to the entire negative electrode was set to 45% by volume by adjusting the size and / or number of the through-holes in the perforated foil in Example 1. The post-cycle electrode energy density ratio was also calculated for Comparative Example 2 in the same manner as in Example 1.

[0042] Comparative Example 3 A test cell was prepared in the same manner as in Example 1, except that polyimide (PI) was used instead of alumina and the volume ratio of the insulating portion to the entire negative electrode was set to 20% by volume, and the energy density after the cycle test was measured. For Comparative Example 3, the electrode energy density ratio after the cycle test was calculated in the same manner as in Example 1.

[0043] [result] The results for Examples 1 to 6 and Comparative Examples 1 to 3 are shown in Table 1 and Fig. 4. In Fig. 4, black circles represent Comparative Example 1, Examples 1 to 5, and Comparative Example 2, hatched circles represent Example 6, and open circles represent Comparative Example 3. The vertical axis of Fig. 4 represents the post-cycle energy density ratio, and the horizontal axis represents the volume % of the insulating portion relative to the entire negative electrode.

[0044] [Table 1] As shown in Table 1 and Figure 4, it was revealed that in a negative electrode having an insulating part containing ceramic, when the insulating part is 9 to 36 volume % relative to the total volume of the negative electrode after charging, a high energy density can be maintained after the cycle test. In particular, when the ceramic is Li7La3Zr2O 12 It was found that when (LLZO) was used, a higher energy density could be maintained after the cycle test. [Explanation of symbols]

[0045] 1... nonaqueous electrolyte secondary battery, 2... negative electrode current collector, 3... insulating part, 4... separator, 5... negative electrode active material part, 10... perforated foil, 11... through-hole, 12... slurry

Claims

1. a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; the negative electrode includes a negative electrode current collector, a negative electrode active material portion disposed on a surface of the negative electrode current collector, and a ceramic-containing insulating portion disposed on the surface, The nonaqueous electrolyte secondary battery comprises an insulating portion that occupies 5% to 40% by volume of the total volume of the negative electrode after charging.

2. The ceramic contained in the insulating part is alumina or Li ７ La ３ Zr ２ O １２ 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein

3. 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the insulating portion includes the ceramic and a binder, and the ceramic accounts for 95 mass % or more of the total of the ceramic and the binder.

4. 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the insulating portion is a plurality of protrusions arranged on the surface of the negative electrode current collector.

5. 5. The nonaqueous electrolyte secondary battery according to claim 4, wherein the protrusions are columnar.

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