All-solid-state lithium-ion battery and evaluation method for all-solid-state lithium-ion battery

Abstract

To provide an all-solid-state lithium-ion battery and an evaluation method for an all-solid-state lithium-ion battery stably having good battery characteristics.SOLUTION: An all-solid-state lithium-ion battery includes a solid electrolyte layer composed of a sulfide-based solid electrolyte, a positive electrode layer, and a negative electrode layer, and the positive electrode layer is composed of a positive electrode mixture layer having a coating density of 10 to 25 mg / cm2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an all-solid-state lithium-ion battery and a method for evaluating an all-solid-state lithium-ion battery. [Background technology]

[0002] With the recent rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones, the development of batteries to be used as their power sources has become increasingly important. Among these batteries, lithium-ion batteries have attracted attention due to their high energy density. Furthermore, high energy density and improved battery characteristics are also required for lithium secondary batteries for large-scale applications such as vehicle-mounted power sources and load leveling.

[0003] However, in the case of lithium-ion batteries, the electrolyte is mostly organic, and even if a flame-retardant compound is used, it cannot be said that the risk of fire is completely eliminated. All-solid-state lithium-ion batteries, which use a solid electrolyte, have been attracting attention in recent years as an alternative to liquid-based lithium-ion batteries. Among these, all-solid-state lithium-ion batteries using sulfides such as Li2S-P2S5 or lithium halides added to them as solid electrolytes are becoming mainstream (Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Journal of The Electrochemical Society,164(2017)A2474. Summary of the Invention [Problem to be solved by the invention]

[0005] All-solid-state lithium-ion batteries with sulfide-based solid electrolytes include a sulfide-based solid electrolyte layer, a positive electrode layer, and a negative electrode layer. Various compositions of these components have been developed and researched to improve battery characteristics. However, factors other than the composition of each component in all-solid-state lithium-ion batteries may also improve battery characteristics, and from this perspective, there is still room for development.

[0006] Furthermore, when an all-solid-state lithium-ion battery using a predetermined sulfide-based solid electrolyte is produced and its battery characteristics are evaluated, it is desirable to design a configuration that brings out the best battery characteristics of the all-solid-state lithium-ion battery, but there is still room for development in this regard as well.

[0007] In view of the above problems, an object of the present invention is to provide an all-solid-state lithium-ion battery that stably exhibits favorable battery characteristics and a method for evaluating the all-solid-state lithium-ion battery. [Means for solving the problem]

[0008] In one aspect, the present invention, which was completed based on the above findings, includes a solid electrolyte layer made of a sulfide-based solid electrolyte, a positive electrode layer, and a negative electrode layer, and the positive electrode layer has a density of 10 to 25 mg / cm 2 This is an all-solid-state lithium-ion battery composed of a positive electrode composite layer with a coating density of .

[0009] In one embodiment of the all-solid-state lithium-ion battery of the present invention, the positive electrode mixture layer includes a positive electrode active material, a solid electrolyte formed of a sulfide-based solid electrolyte, and a conductive additive.

[0010] In another aspect, the present invention provides an all-solid-state lithium-ion battery including a solid electrolyte layer made of a sulfide-based solid electrolyte, a positive electrode layer, and a negative electrode layer, wherein the positive electrode layer has a concentration of 10 to 25 mg / cm. 2 and evaluating the battery characteristics of the all-solid-state lithium ion battery by determining whether the all-solid-state lithium ion battery is constituted by a positive electrode mixture layer having a coating density of 1000 or more. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an all-solid-state lithium-ion battery that stably exhibits favorable battery characteristics and a method for evaluating the all-solid-state lithium-ion battery. [Brief explanation of the drawings]

[0012]

Figure 1

[0013] Next, embodiments for carrying out the present invention will be described in detail with reference to the drawings. It should be understood that the present invention is not limited to the following embodiments, and that appropriate design changes and improvements may be made based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention.

[0014] <All-solid-state lithium-ion battery> A schematic diagram of an all-solid-state lithium-ion battery according to an embodiment of the present invention is shown in Figure 1. The all-solid-state lithium-ion battery includes a solid electrolyte layer made of a sulfide-based solid electrolyte, a positive electrode layer, and a negative electrode layer.

[0015] (Solid electrolyte layer) The solid electrolyte layer of the all-solid-state lithium-ion battery according to the embodiment of the present invention is composed of a sulfide-based solid electrolyte. The sulfide-based solid electrolyte is not particularly limited and any known sulfide-based solid electrolyte can be used. However, from the viewpoint of further improving battery characteristics, a sulfide-based solid electrolyte having an argyrodite structure is preferred. The argyrodite structure of the sulfide-based solid electrolyte can be confirmed, for example, by X-ray diffraction measurement using CuKα radiation. The argyrodite structure has strong diffraction peaks at 2θ=24.6±1.0° and 28.7±1.0°. The diffraction peaks of the argyrodite structure may also appear at 2θ=15.0±1.0°, 17.3±1.0°, 30.0±1.0°, 42.8±1.5°, or 45.5±1.5°, for example. The sulfide-based solid electrolyte according to the present embodiment may have these peaks. The sulfide-based solid electrolyte having an argyrodite structure may contain an amorphous component in part, or may contain a structure or raw material other than the argyrodite structure. The sulfide-based solid electrolyte may also be Li3PS4 glass ( Li 2 S-P 2 S 5 series glass), Li7P3S 11 Glass ceramics, LGPS, etc. may also be used.

[0016] The average particle size of the sulfide-based solid electrolyte according to the embodiment of the present invention is not particularly limited, but may be 0.01 to 100 μm, 0.1 to 100 μm, or 0.1 to 50 μm.

[0017] (positive electrode layer) The positive electrode layer of the all-solid-state lithium ion battery is a layer of a positive electrode mixture obtained by mixing a positive electrode active material for an all-solid-state lithium ion battery with the sulfide-based solid electrolyte used in the solid electrolyte layer, or a sulfide-based solid electrolyte having a composition different from the sulfide-based solid electrolyte used in the solid electrolyte layer.

[0018] The positive electrode mixture may further contain a conductive additive. Examples of the conductive additive include carbon materials, metal materials, and mixtures thereof. The conductive additive may include at least one element selected from the group consisting of carbon, nickel, copper, aluminum, indium, silver, cobalt, magnesium, lithium, chromium, gold, ruthenium, platinum, beryllium, iridium, molybdenum, niobium, osmium, rhodium, tungsten, and zinc. The conductive additive is preferably a highly conductive carbon element, or a metal element, mixture, or compound containing carbon, nickel, copper, silver, cobalt, magnesium, lithium, ruthenium, gold, platinum, niobium, osmium, or rhodium. Examples of the carbon material include carbon black, such as ketjen black, acetylene black, denka black, thermal black, and channel black; graphite; carbon fiber; and activated carbon.

[0019] The positive electrode layer of the all-solid-state lithium ion battery according to the embodiment of the present invention has a density of 10 to 25 mg / cm 2 The coating density of the positive electrode mixture layer is 10 mg / cm. 2 When the coating density of the positive electrode mixture layer is 25 mg / cm or more, an increase in the resistance after charging of the all-solid-state lithium ion battery can be suppressed, the variation in resistance is reduced, and stable measurement of the battery characteristics of the all-solid-state lithium ion battery is possible. 2 When the density is 10 to 25 mg / cm or less, the rate-limiting effect of the movement of lithium ions in the solid electrolyte can be suppressed, resulting in good discharge capacity and rate characteristics. 2 By using a positive electrode mixture layer having a coating density of 12 to 18 mg / cm, the all-solid-state lithium ion battery can stably obtain good discharge capacity, resistance, rate characteristics, and capacity retention rate. 2 It is more preferable that the positive electrode mixture layer has a coating density of 1000 MPa or less.

[0020] The coating density of the positive electrode mixture layer is obtained by dividing the mass of the positive electrode mixture layer by its coating area.

[0021] The average thickness of the positive electrode layer of the all-solid-state lithium ion battery is not particularly limited and can be appropriately designed depending on the purpose. The average thickness of the positive electrode layer of the all-solid-state lithium ion battery may be, for example, 1 μm to 100 μm, or 1 μm to 10 μm.

[0022] Next, a method for forming a positive electrode layer of an all-solid-state lithium-ion battery will be described. Since the positive electrode layer is composed of a positive electrode composite layer, first, a positive electrode composite is prepared. To prepare the positive electrode composite, a positive electrode active material for lithium-ion batteries having a desired composition, a sulfide-based solid electrolyte, a conductive additive, and a binder are mixed in a predetermined mass ratio. A solvent is added to obtain a positive electrode composite slurry so that the solid content of the slurry is 50 to 80 mass%. The sulfide-based solid electrolyte may be the same as that used in the solid electrolyte layer, or a sulfide-based solid electrolyte having a different composition from that used in the solid electrolyte layer. Known solvents such as anisole, heptane, and tetralin may be used. Next, the positive electrode mixture slurry is applied to the surface of a positive electrode current collector (described later) by using an applicator having a gap of 300 to 600 μm between itself and the surface of the positive electrode current collector and moving the applicator at a speed of 5 to 50 mm / s. Next, the positive electrode current collector with the positive electrode mixture slurry coated on its surface is dried to remove the solvent, thereby forming a positive electrode mixture layer on the surface of the positive electrode current collector.

[0023] (negative electrode layer) The negative electrode layer of the all-solid-state lithium-ion battery may be a layer of a known negative electrode active material for all-solid-state lithium-ion batteries, or may be a layer of a negative electrode mixture obtained by mixing a known negative electrode active material for all-solid-state lithium-ion batteries with the sulfide-based solid electrolyte according to the embodiment of the present invention or another sulfide-based solid electrolyte.

[0024] The negative electrode layer, like the positive electrode layer, may contain a conductive additive. The conductive additive may be the same material as described for the positive electrode layer. Examples of the negative electrode active material include carbon materials, specifically, artificial graphite, graphite carbon fiber, resin-baked carbon, pyrolytic vapor-grown carbon, coke, mesocarbon microbeads (MCMB), furfuryl alcohol resin-baked carbon, polyacene, pitch-based carbon fiber, vapor-grown carbon fiber, natural graphite, and non-graphitizable carbon, or mixtures thereof. Examples of the negative electrode material include metals such as lithium metal, indium metal, aluminum metal, and silicon metal, as well as alloys of these metals combined with other elements or compounds.

[0025] The average thickness of the negative electrode layer of the all-solid-state lithium ion battery is not particularly limited and can be appropriately selected depending on the purpose. The average thickness of the negative electrode layer of the all-solid-state lithium ion battery may be, for example, 1 μm to 100 μm, or 1 μm to 10 μm.

[0026] The method for forming the negative electrode layer of the all-solid-state lithium ion battery is not particularly limited and can be appropriately selected depending on the purpose. Examples of the method for forming the negative electrode layer of the all-solid-state lithium ion battery include sputtering using a target material for the negative electrode active material, compression molding of the negative electrode active material, and vapor deposition of the negative electrode active material.

[0027] The average thickness of the solid electrolyte layer of the all-solid-state lithium-ion battery formed using the sulfide-based solid electrolyte according to the embodiment of the present invention is not particularly limited and can be appropriately designed depending on the purpose. The average thickness of the solid electrolyte layer of the all-solid-state lithium-ion battery may be, for example, 1 μm to 500 μm, or 50 μm to 100 μm.

[0028] The method for forming the solid electrolyte layer of the all-solid-state lithium ion battery is not particularly limited and can be appropriately selected depending on the purpose. Examples of the method for forming the solid electrolyte layer of the all-solid-state lithium ion battery include sputtering using a target material for the solid electrolyte and compression molding of the solid electrolyte.

[0029] Other components constituting the all-solid-state lithium-ion battery are not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include a positive electrode current collector, a negative electrode current collector, a battery case, etc. The form of the all-solid-state lithium-ion battery is not particularly limited, and may have a configuration in which a positive electrode current collector / positive electrode layer / solid electrolyte / negative electrode layer / negative electrode current collector are laminated in this order, and may further have a configuration in which these are surrounded by a battery case.

[0030] The size and structure of the positive electrode current collector are not particularly limited and can be appropriately selected depending on the purpose. Examples of materials for the positive electrode current collector include die steel, stainless steel, aluminum, aluminum alloys, titanium alloys, copper, gold, and nickel. The positive electrode current collector may be in the form of, for example, a foil, a plate, or a mesh. The average thickness of the positive electrode current collector may be, for example, 10 μm to 500 μm, or 50 μm to 100 μm.

[0031] The size and structure of the negative electrode current collector are not particularly limited and can be appropriately selected depending on the purpose. Examples of materials for the negative electrode current collector include die steel, gold, indium, nickel, copper, and stainless steel. The negative electrode current collector may be in the form of, for example, a foil, a plate, or a mesh. The average thickness of the negative electrode current collector may be, for example, 10 μm to 500 μm, or 50 μm to 100 μm.

[0032] The battery case is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include known laminate films that can be used in conventional all-solid-state batteries, such as resin laminate films and films in which metal is vapor-deposited on resin laminate films. The shape of the battery is not particularly limited and can be appropriately selected depending on the purpose. Examples include cylindrical, square, button, coin, and flat types.

[0033] <Evaluation method for all-solid-state lithium-ion batteries> The method for evaluating an all-solid-state lithium ion battery according to an embodiment of the present invention is to fabricate an all-solid-state lithium ion battery, and then measure the thickness of the positive electrode layer at 10 to 25 mg / cm. 2 The battery characteristics of the all-solid-state lithium-ion battery are evaluated based on the results of the determination. 2 When the positive electrode mixture layer has a coating density of 10 to 25 mg / cm, the battery characteristics are evaluated as good. 2 If the positive electrode composite layer does not have a coating density of 0.05, the battery characteristics can be evaluated as being poor. With such a configuration, evaluation of the battery characteristics of the all-solid-state lithium-ion battery is simplified, and battery evaluation can be carried out efficiently. Note that the battery characteristics of the all-solid-state lithium-ion battery include discharge capacity, resistance, rate characteristics, and capacity retention, and each can be evaluated as follows for confirmation.

[0034] (Evaluation of discharge capacity) The discharge capacity of an all-solid-state lithium-ion battery can be evaluated as the initial discharge capacity at 30°C by measuring the impedance after the initial charge to determine the resistance, and then discharging.

[0035] (Resistance rating) The resistance of an all-solid-state lithium-ion battery can be evaluated as the resistance after the first charge by measuring AC impedance from 0.1 Hz to 1 MHz and analyzing the obtained Cole-Cole plot.

[0036] (Evaluation of rate characteristics) The rate characteristics (%) of an all-solid-state lithium-ion battery can be evaluated by measuring the initial capacity (30°C, upper limit charge voltage: 4.55V, lower limit discharge voltage: 3.7V) obtained at a discharge rate of 0.05C, and then measuring the high-rate capacity (30°C, upper limit charge voltage: 4.55V, lower limit discharge voltage: 3.7V) obtained at a discharge rate of 0.2C, and then calculating the ratio of (high-rate capacity) / (initial capacity) as a percentage.

[0037] (Evaluation of capacity retention rate) The capacity retention rate of an all-solid-state lithium-ion battery can be evaluated as the 10-cycle capacity retention rate by dividing the discharge capacity after 10 cycles by the initial discharge capacity obtained at a discharge current of 0.2 C at 30°C. [Example]

[0038] The following examples are provided to provide a better understanding of the present invention and its advantages, but the present invention is not limited to these examples.

[0039] Example 1 Cathode active material (Li(Ni) 0.82 Co 0.15 Mn 0.03 )O2), sulfide-based solid electrolyte (75Li2S-25P2S5), acetylene black, and binder were mixed in the following order in a mass ratio of 60:35:5:1.5. Anisole was added as a solvent so that the solid content of the slurry was 65 mass%. The mixture was mixed for 400 seconds with a Mazerustar to form a positive electrode composite slurry, which was then applied to the surface of a 0.03 mm thick aluminum foil positive electrode current collector. The positive electrode composite slurry was applied to the positive electrode current collector surface using an applicator with a gap of 300 μm, moving the applicator at a speed of 15 mm / s. Next, the positive electrode current collector with the positive electrode composite slurry coated on its surface was left at room temperature for one week to dry and remove the solvent, thereby forming a positive electrode composite layer on the surface of the positive electrode current collector. Here, the mass of the positive electrode composite layer (9.3 mg) was calculated based on the coating area (0.785 cm2). 2 ), the coating density of the positive electrode mixture layer is 11.8 mg / cm 2As described above, the positive electrode mixture slurry was dried by being left at room temperature, but it may also be dried using a dryer to dry more quickly. Next, the above-mentioned positive electrode composite layer was placed on a sulfide-based solid electrolyte having the same composition as the sulfide-based solid electrolyte used in producing the positive electrode composite layer, and pressed at 333 MPa to produce a laminate of solid electrolyte layer / positive electrode composite layer / positive electrode current collector. Next, metal In was pressed onto the negative electrode side of the solid electrolyte layer at 37 MPa to form a negative electrode layer. The laminate thus produced was placed in a battery test cell made of SUS304 and subjected to a confining pressure to form an all-solid-state secondary battery. The all-solid-state secondary battery produced by applying the confining pressure was then placed in a sealed container to block the air.

[0040] Example 2 The positive electrode mixture slurry was applied to the surface of the positive electrode current collector using an applicator with a gap of 400 μm, resulting in a positive electrode mixture layer with a mass of 13.7 mg and a coating density of 17.5 mg / cm. 2 An all-solid-state lithium ion battery was produced in the same manner as in Example 1, except that:

[0041] Example 3 The positive electrode mixture slurry was applied to the surface of the positive electrode current collector using an applicator with a gap of 500 μm, resulting in a positive electrode mixture layer with a mass of 17.8 mg and a coating density of 22.6 mg / cm. 2 An all-solid-state lithium ion battery was produced in the same manner as in Example 1, except that:

[0042] Example 4 The positive electrode mixture slurry was applied to the surface of the positive electrode current collector using an applicator with a gap of 600 μm, resulting in a positive electrode mixture layer with a mass of 17.2 mg and a coating density of 22.0 mg / cm. 2 An all-solid-state lithium ion battery was produced in the same manner as in Example 1, except that:

[0043] (Comparative Example 1) The positive electrode mixture slurry was applied to the surface of the positive electrode current collector using an applicator with a gap of 100 μm, resulting in a positive electrode mixture layer mass of 2.7 mg and a coating density of 3.4 mg / cm. 2 An all-solid-state lithium ion battery was produced in the same manner as in Example 1, except that:

[0044] (Comparative Example 2) The positive electrode mixture slurry was applied to the surface of the positive electrode current collector using an applicator with a gap of 200 μm, resulting in a positive electrode mixture layer with a mass of 6.3 mg and a coating density of 8.0 mg / cm. 2 An all-solid-state lithium ion battery was produced in the same manner as in Example 1, except that:

[0045] (Comparative Example 3) The positive electrode mixture slurry was applied to the surface of the positive electrode current collector using an applicator with a gap of 700 μm, resulting in a positive electrode mixture layer with a mass of 29.4 mg and a coating density of 37.5 mg / cm. 2 An all-solid-state lithium ion battery was produced in the same manner as in Example 1, except that:

[0046] Comparative Example 4 The positive electrode mixture slurry was applied to the surface of the positive electrode current collector using an applicator with a gap of 800 μm, resulting in a positive electrode mixture layer with a mass of 25.3 mg and a coating density of 32.2 mg / cm. 2 An all-solid-state lithium ion battery was produced in the same manner as in Example 1, except that:

[0047] (Comparative Example 5) The positive electrode mixture slurry was applied to the surface of the positive electrode current collector using an applicator with a gap of 1000 μm, resulting in a positive electrode mixture layer with a mass of 38.3 mg and a coating density of 48.7 mg / cm. 2 An all-solid-state lithium ion battery was produced in the same manner as in Example 1, except that:

[0048] (Evaluation of discharge capacity) The sample (all-solid-state lithium ion battery) prepared as described above was subjected to an initial charge, and the impedance was measured to determine the resistance. The battery was then discharged to obtain the initial discharge capacity at 30°C.

[0049] (Resistance rating) The samples (all-solid-state lithium-ion batteries) prepared as described above were subjected to AC impedance measurements from 0.1 Hz to 1 MHz, and the resulting Cole-Cole plots were analyzed to determine the resistance after initial charge. Based on the magnitude of the resistance after initial charge, it was evaluated whether an increase in the resistance after charge of the all-solid-state lithium-ion battery could be suppressed.

[0050] (Evaluation of rate characteristics) For the sample (all-solid-state lithium-ion battery) prepared as described above, the initial capacity (30°C, upper limit charge voltage: 4.55V, lower limit discharge voltage: 3.7V) obtained at a discharge rate of 0.05C was measured, and then the high-rate capacity (30°C, upper limit charge voltage: 4.55V, lower limit discharge voltage: 3.7V) obtained at a discharge rate of 0.2C was measured, and the ratio of (high-rate capacity) / (initial capacity) was expressed as a percentage to provide the rate characteristics (%).

[0051] (Evaluation of capacity retention rate) For the sample (all-solid-state lithium-ion battery) prepared as described above, the 10-cycle capacity retention rate was measured by dividing the discharge capacity after 10 cycles by the initial discharge capacity obtained at a discharge current of 0.2 C at 30°C. The test results are shown in Table 1. The values ​​for "amount of positive electrode composite layer" and "coating density" in Table 1 are all rounded to one decimal place.

[0052] [Table 1]

[0053] (Evaluation results) In Examples 1 to 4, the positive electrode layer had a thickness of 10 to 25 mg / cm 2 Since the positive electrode composite layer had a coating density of 1000 MPa, it exhibited good characteristics in the initial discharge capacity, resistance after the initial charge, rate characteristics, and 10-cycle capacity retention rate. In Examples 1 to 4, the positive electrode active material of the positive electrode mixture layer was Li(Ni0.82 Co 0.15 Mn 0.03 The cathode active material had a composition of 75Li2S-25P2S5, and the sulfide-based solid electrolyte for the cathode composite layer had a composition of 75Li2S-25P2S5. However, regardless of the composition of the cathode active material and sulfide-based solid electrolyte for the cathode composite layer, the coating density of the cathode composite layer was set to 10 to 25 mg / cm. 2 By controlling the coating density of the positive electrode mixture layer to 10 mg / cm, it is possible to improve the battery characteristics such as the initial discharge capacity, the resistance after the first charge, the rate characteristics, and the 10-cycle capacity retention rate. 2 When the coating density of the positive electrode mixture layer is 25 mg / cm or more, an increase in the post-charge resistance of the all-solid-state lithium-ion battery can be suppressed regardless of the composition, and the variation in resistance is reduced, enabling stable measurement of the battery characteristics of the all-solid-state lithium-ion battery. 2 This is because, when the content is equal to or less than this, it is possible to prevent the movement of lithium ions in the solid electrolyte from becoming rate-determining, regardless of the composition, and the discharge capacity and rate characteristics become good. In Comparative Examples 1 and 2, the coating density of the positive electrode mixture layer was 10 mg / cm 2 Because it was less than this, the resistance was poor after the first charge. In Comparative Examples 3 to 5, the coating density of the positive electrode mixture layer was 25 mg / cm 2 Since the discharge capacity exceeded 100%, at least one of the initial discharge capacity, rate characteristics, and 10-cycle capacity retention rate was poor.

Claims

1. The battery includes a solid electrolyte layer made of a sulfide-based solid electrolyte, a positive electrode layer, and a negative electrode layer, The positive electrode layer has a density of 10 to 17.5 mg / cm 2 The positive electrode mixture layer has a coating density of The positive electrode composite layer includes a positive electrode active material having an elemental composition of LiNiCoMnO, a solid electrolyte made of Li2S-P2S5-based glass, and a conductive additive.

2. The battery includes a solid electrolyte layer made of a sulfide-based solid electrolyte, a positive electrode layer, and a negative electrode layer, In the all-solid-state lithium ion battery, the positive electrode layer is formed of a positive electrode composite layer containing a positive electrode active material having an elemental composition of LiNiCoMnO, a solid electrolyte made of Li2S-P2S5-based glass, and a conductive additive, The positive electrode layer has a density of 10 to 17.5 mg / cm 2 and evaluating battery characteristics of the all-solid-state lithium ion battery by determining whether the all-solid-state lithium ion battery is constituted by a positive electrode mixture layer having a coating density of 1000 or more.

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