Lithium metal secondary batteries and gel electrolytes

Abstract

To provide a lithium metal secondary battery capable of improving durability even using a gelling material using π-π stacking interaction.SOLUTION: A lithium metal secondary battery 10 includes a gel electrolyte layer 14 between a positive electrode 11 and a negative electrode 12. The positive electrode 11 has a positive electrode current collector 11a and a positive electrode mixture layer 11b including a lithium composite oxide. The negative electrode 12 has a negative electrode current collector 12a. The gel electrolyte layer 14 includes a gelling agent using π-π stacking interactions having perfluoroalkyl and phenylene groups and an electrolyte.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a lithium metal secondary battery and a gel electrolyte. [Background technology]

[0002] In light of climate-related disasters, there is a growing need to reduce CO2 emissions, leading to increased interest in electric vehicles. As an example of a secondary battery to be installed in electric vehicles, high-energy-density lithium-metal batteries are being considered.

[0003] As an example of a lithium metal secondary battery, a lithium metal secondary battery is known that comprises a positive electrode having a positive electrode current collector and a positive electrode composite material layer containing a lithium composite oxide, a negative electrode having a negative electrode current collector, and a solid electrolyte layer, wherein a gel electrolyte layer containing a polymer compound having a gelling effect and an electrolyte is provided between the negative electrode current collector and the solid electrolyte layer (see Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-206757 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, it is known that the cell resistance increases because the gel electrolyte layer contains polymer compounds that have a gelling effect.

[0006] Therefore, it is conceivable to use a gelling agent that utilizes π-π stacking interactions instead of polymer compounds that have gelling properties. However, the amount of gelling agent added changes the solvation structure of the electrolyte, which reduces the durability of the lithium metal secondary battery.

[0007] An object of the present invention is to provide a lithium metal secondary battery that can improve durability without changing the solvation structure of an electrolytic solution even when using a gelling material utilizing π-π stacking interaction.

Means for Solving the Problems

[0008] One aspect of the present invention is a lithium metal secondary battery including a gel electrolyte layer between a positive electrode and a negative electrode, the positive electrode having a positive electrode current collector and a positive electrode composite material layer containing a lithium composite oxide, the negative electrode having a negative electrode current collector, and the gel electrolyte layer including a gelling material utilizing π-π stacking interaction having a perfluoroalkyl group and a phenylene group, and an electrolytic solution.

[0009] The above lithium metal secondary battery may further include a solid electrolyte layer between the positive electrode and the negative electrode, and the gel electrolyte layer may be provided between the negative electrode and the solid electrolyte layer.

[0010] The negative electrode may further have a lithium metal layer.

[0011] The electrolytic solution includes dimethyl carbonate and lithium bis(fluorosulfonyl)imide, and the molar ratio of dimethyl carbonate to lithium bis(fluorosulfonyl)imide may be 1.1 or more and 3.0 or less.

[0012] Another aspect of the present invention is a gel electrolyte including a gelling material utilizing π-π stacking interaction having a perfluoroalkyl group and a phenylene group, and an electrolytic solution.

Effects of the Invention

[0013] According to the present invention, it is possible to provide a lithium metal secondary battery that can improve durability without changing the solvation structure of an electrolytic solution even when using a gelling material utilizing π-π stacking interaction.

Brief Description of the Drawings

[0014] [Figure 1] It is a cross-sectional view showing an example of a lithium metal secondary battery of the present embodiment.

Mode for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be described.

[0016] [Lithium Metal Secondary Battery] The lithium metal secondary battery of the present embodiment includes a gel electrolyte layer between a positive electrode and a negative electrode. Here, the positive electrode has a positive electrode current collector and a positive electrode composite material layer containing a lithium composite oxide. The negative electrode has a negative electrode current collector and a lithium metal layer.

[0017] That is, when the lithium metal secondary battery of the present embodiment is charged, lithium metal is deposited on the negative electrode, and when it is discharged, lithium ions elute from the negative electrode. Therefore, the lithium metal secondary battery of the present embodiment does not necessarily have a lithium metal layer on the negative electrode in the initial state. In this case, before using the lithium metal secondary battery, by charging the lithium metal secondary battery, lithium metal is deposited on the negative electrode current collector, and a lithium metal layer is formed.

[0018] The gel electrolyte layer (the gel electrolyte constituting it) includes a gelling material utilizing a π-π stacking interaction having a perfluoroalkyl group and a phenylene group, and an electrolytic solution. Thereby, when the lithium metal secondary battery is charged, the reduction decomposition of the gelling material utilizing the π-π stacking interaction is suppressed, and the durability of the lithium metal secondary battery is improved. The lithium metal secondary battery of the present embodiment can improve the durability by using a gelling material utilizing a π-π stacking interaction within a range where the solvation structure is not changed.

[0019] Specific examples of the compound represented by the general formula (1) include, for example, compounds represented by the following chemical formulas.

[0020]

Chemical formula

[0021] The content of the gelling agent utilizing π-π stacking interactions in the gel electrolyte is preferably 0.5% by mass or more and 2% by mass or less. If the content of the gelling agent utilizing π-π stacking interactions in the gel electrolyte is 0.5% by mass or more, dendrite growth is suppressed when charging the lithium metal secondary battery, improving the durability of the lithium metal secondary battery. If it is 2% by mass or less, the solvation structure of the electrolyte is not changed, improving the durability of the lithium metal secondary battery of this embodiment.

[0022] The electrolyte is not particularly limited, as long as it has lithium ion conductivity and can be gelled using a gelling material that utilizes π-π stacking interactions having perfluoroalkyl groups and phenylene groups.

[0023] The electrolyte preferably contains dimethyl carbonate and lithium bis(fluorosulfonyl)imide. In this case, the molar ratio of dimethyl carbonate to lithium bis(fluorosulfonyl)imide is preferably 1.1 to 3.0, and more preferably 1.1 to 2.5. When the molar ratio of dimethyl carbonate to lithium bis(fluorosulfonyl)imide is 1.1 or higher, the solubility of lithium bis(fluorosulfonyl)imide in dimethyl carbonate is improved, and when it is 3.0 or lower, dendrite growth is suppressed when charging the lithium metal secondary battery, improving the durability of the lithium metal secondary battery.

[0024] The thickness of the gel electrolyte layer is not particularly limited, but for example, it is between 0.1 μm and 20 μm.

[0025] The positive electrode current collector is not particularly limited, but examples include aluminum foil.

[0026] The thickness of the positive electrode current collector is not particularly limited, but for example, it is 12 μm or more and 22 μm or less.

[0027] The positive electrode composite material layer contains a lithium composite oxide, but may further contain other components.

[0028] The lithium composite oxide is not particularly limited, but for example, LiCoO2, Li(Ni 5 / 10 Co 2 / 10 Mn 3 / 10 )O 2、 Li(Ni 6 / 10 Co 2 / 10 Mn 2 / 10 )O 2、 Li(Ni 8 / 10 Co 1 / 10 Mn 1 / 10 )O 2、 Li(Ni 0.8 Co 0.15 Al 0.05 )O 2、 Li(Ni 1 / 6 Co 4 / 6 Mn 1 / 6 )O 2、 Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 )O 2、 LiCoO4, LiMn2O4, LiNiO2, LiFePO4, etc. may be mentioned, and two or more kinds may be used in combination.

[0029] The content of the lithium composite oxide in the positive electrode composite material layer is not particularly limited, but for example, it is 60% by mass or more and 98.5% by mass or less.

[0030] Examples of other components include positive electrode active materials other than the lithium composite oxide, conductive aids, binders, and the like.

[0031] The thickness of the positive electrode composite material layer is not particularly limited, but for example, it is 50 μm or more and 100 μm or less.

[0032] The negative electrode current collector is not particularly limited, but for example, copper foil and the like may be mentioned.

[0033] The thickness of the negative electrode current collector is not particularly limited, but for example, it is between 1 μm and 20 μm.

[0034] The thickness of the lithium metal layer is not particularly limited, but for example, it is 80 μm or less.

[0035] Furthermore, the lithium metal secondary battery of this embodiment can be manufactured using known methods.

[0036] Figure 1 shows an example of a lithium metal secondary battery according to this embodiment.

[0037] The lithium metal secondary battery 10 comprises a solid electrolyte layer 13 between a positive electrode 11 and a negative electrode 12, and a gel electrolyte layer 14 between the negative electrode 12 and the solid electrolyte layer 13. Here, the positive electrode 11 has a positive electrode current collector 11a and a positive electrode composite material layer 11b containing a lithium composite oxide, and the negative electrode 12 has a negative electrode current collector 12a and a lithium metal layer 12b. The gel electrolyte layer 14 contains a gelling material that utilizes π-π stacking interactions having perfluoroalkyl groups and phenylene groups, and an electrolyte.

[0038] The solid electrolyte constituting the solid electrolyte layer 13 is not particularly limited as long as it has lithium ion conductivity, but examples include oxide-based electrolytes and sulfide-based electrolytes.

[0039] The thickness of the solid electrolyte layer 13 is not particularly limited, but for example, it is between 5 nm and 20 μm.

[0040] Furthermore, the negative electrode 12 does not necessarily have to have a lithium metal layer 12b in its initial state.

[0041] Alternatively, the solid electrolyte layer 13 may be omitted. In this case, the gel electrolyte layer 14 functions as a separator.

[0042] Although embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and the above embodiments may be modified as appropriate within the scope of the spirit of the present invention. [Examples]

[0043] The following describes embodiments of the present invention, but the present invention is not limited to these embodiments.

[0044] [Example 1] A coating solution for the positive electrode composite layer was obtained by mixing lithium nickel cobalt manganese composite oxide as a lithium composite oxide, acetylene black as a conductive additive, and polyvinylidene fluoride as a binder.

[0045] As a positive electrode current collector, with a surface area of ​​12 cm² 2 A coating solution for the positive electrode composite layer was applied to a 15 μm thick aluminum foil and dried, and then 20 mg / cm³ was added. 2 After forming the positive electrode composite layer, it was rolled to obtain the positive electrode.

[0046] The negative electrode current collector and the solid electrolyte layer each have a surface area of ​​12 cm². 2 , Cu foil with a thickness of 12 μm and a surface area of ​​12 cm² 2 A porous polyolefin film with a thickness of 20 μm was used.

[0047] Dimethyl carbonate and lithium bis(fluorosulfonyl)imide were mixed so that the molar ratio of dimethyl carbonate to lithium bis(fluorosulfonyl)imide was 2 to obtain an electrolyte.

[0048] An electrolyte and a compound represented by the following chemical formula, which acts as a gelling agent utilizing π-π stacking interactions, were mixed so that the content of the gelling agent utilizing π-π stacking interactions was 1% by mass (see Table 1). The mixture was then stirred at 80°C for 12 hours to dissolve and obtain a gel electrolyte layer.

[0049] [ka] A lithium metal secondary battery was obtained by laminating a positive electrode, a solid electrolyte layer, a gel electrolyte layer, and a negative electrode current collector in this order, and then sealing them with a laminate film.

[0050] [Durability of lithium metal rechargeable batteries] The discharge capacity per unit area of ​​the positive electrode is 3.78 mAh / cm². 2 The following conditions were specified, and a cycle test of lithium metal secondary batteries was conducted to evaluate their durability. The lithium metal secondary batteries were assembled into a jig, restrained with a restraining pressure of 0.05 MPa, and then aged for 3 cycles at 0.1C. Initial characteristics were obtained at 25°C, and then a cycle test was conducted at 45°C under the conditions of charging at 0.3 CCV and discharging at 0.3C.

[0051] Furthermore, 1C was defined as the current value required to complete discharge in one hour relative to the discharge capacity of the positive electrode.

[0052] Table 1 shows the evaluation results for the durability of lithium metal secondary batteries. Here, the capacity retention rate refers to the ratio of the capacity after 20 cycles to the capacity after the first cycle.

[0053] [Table 1] Table 1 shows that the lithium metal secondary battery of Example 1 has a high capacity retention rate and high durability. [Explanation of Symbols]

[0054] 10 Lithium metal rechargeable batteries 11 Positive electrode 11a Positive electrode current collector 11b Positive electrode composite layer 12 Negative electrode 12a Negative electrode current collector 12b Lithium metal layer 13 Solid electrolyte layer 14. Gel electrolyte layer

Claims

1. A solid electrolyte layer is provided between the positive electrode and the negative electrode, and a gel electrolyte layer is provided between the negative electrode and the solid electrolyte layer. The positive electrode comprises a positive electrode current collector and a positive electrode composite material layer containing a lithium composite oxide. The aforementioned negative electrode has a negative electrode current collector, The gel electrolyte layer comprises a gelling material having a perfluoroalkyl group and a phenylene group and utilizing π-π stacking interactions, and an electrolyte, wherein the content of the gelling material is 0.5% by mass or more and 2% by mass or less. The gelling material is a general formula 【Chemistry 1】 (Here, a, b, and n are independently positive integers.) A compound represented by, or the general formula 【Chemistry 2】 (Here, a, b, and n are independently positive integers.) It is a compound represented by the following: The electrolyte comprises dimethyl carbonate and lithium bis(fluorosulfonyl)imide, and the molar ratio of dimethyl carbonate to lithium bis(fluorosulfonyl)imide is 1.1 or more and 2.5 or less, in a lithium metal secondary battery.

2. The lithium metal secondary battery according to claim 1, wherein the negative electrode further comprises a lithium metal layer.

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