Patent Application
20240339620
The present disclosure relates to a positive electrode for an all-solid-state battery and an all-solid-state battery comprising the same, and more specifically, to a positive electrode for an all-solid-state battery with a simplified process and improved electrochemical characteristics and cycle characteristics, and an all-solid-state battery comprising the same.
With the development of portable mobile electronic devices such as smart phones, MP3 players, and tablet PCs, the demand for secondary batteries capable of storing electrical energy is increasing explosively. In particular, with the advent of electric medium- and large-sized energy storage systems, and portable devices requiring high energy density, the demand for lithium secondary batteries is increasing. With such an increase in demand for lithium secondary batteries, various research and development for improving the characteristics of positive electrodes used in lithium secondary batteries are being conducted.
On the other hand, the conventional lithium secondary battery uses a liquid non-aqueous organic electrolyte, and thus has a risk of ignition and explosion. In fact, since explosion accidents of products to which it is applied are continuously occurring, it is urgent to solve these problems.
An all-solid-state battery is a battery in which these organic electrolytes are replaced with solid electrolytes, and thus all the battery components such as electrodes and electrolytes are made of solid, wherein due to the high safety of the accommodated solid electrolyte itself, it is possible to fundamentally solve the risk of ignition and explosion. However, there is a problem that since most solid electrolytes have lower ion conductivity than liquid electrolytes, the capacity of the battery is low when applied in practice, and the cycle characteristics at room temperature are lower than those of liquid electrolytes.
That is, the safety of the battery can be secured by using the solid electrolyte, but the cycle characteristics are deteriorated and thus become problematic. Therefore, in order to solve these problems, various studies are being conducted.
The background description provided herein is for the purpose of generally presenting context of the disclosure. Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art, or suggestions of the prior art, by inclusion in this section.
One technical problem to be solved by the present application is to provide a positive electrode for an all-solid-state battery with improved productivity by manufacturing a positive electrode without using a solvent and thus simplifying the process, and an all-solid-state battery comprising the same.
Another technical problem to be solved by the present application is to provide a positive electrode for an all-solid-state battery with improved electrochemical characteristics and cycle characteristics, by using a novel binder to have excellent binding properties between the positive electrode active materials, and an all-solid-state battery comprising the same.
The technical problem to be solved by the present application is not limited to those described above.
In order to solve the above technical problems, the present disclosure provides a positive electrode for an all-solid-state battery and an all-solid-state battery comprising the same.
In one embodiment, the present disclosure provides a positive electrode for an all-solid-state battery comprising: a positive electrode active material; a perfluorinated ionomer comprising lithium substituted sulfonate; a solid electrolyte; and a conductive carbon.
In one embodiment, the perfluorinated ionomer may be represented by the following Formula 1.
wherein A is each independently a substituted or unsubstituted C1 to C30 alkylene group, a substituted or unsubstituted C1 to C30 haloalkylene group or a substituted or unsubstituted C1 to C30 hydroxyalkylene group, and n and m are each an integer from 1 to 100.
In one embodiment, in Formula 1, A is —(CF2—CF2)p—, and p may be an integer of 1 to 15.
In one embodiment, the positive electrode according to the present disclosure is a dry mixing product of the positive electrode active material, the perfluorinated ionomer containing lithium substituted sulfonate, a solid electrolyte, and conductive carbon.
In one embodiment, the positive electrode active material may comprise at least one of LiCoO2, Li(NixCoyMnz)O2 [x+y+z=1], Li(NixCoyAlz)O2 [x+y+z=1], and LiFePO4.
In one embodiment, the solid electrolyte may comprise a halide-based solid electrolyte or a sulfide-based solid electrolyte.
In one embodiment, the sulfide-based solid electrolyte may comprise at least one of Li6PS5Cl, Li10GeP2S12, Li3PS4, and Li7P3S11, and the halide-based solid electrolyte may comprise at least one of Li3YCl6, Li3InCl6, and Li2ZrCl6, respectively.
In one embodiment, the conductive carbon may comprise at least one of vapor grown carbon fiber (VGCF), carbon nanotube (CNT), Super P, Super C, carbon black, Ketjen black, acetylene black, coke, glassy carbon, and activated carbon.
In one embodiment, in the positive electrode, the positive electrode may comprise 60% by weight to 95% by weight of the positive electrode active material, 5% by weight to 40% by weight of the solid electrolyte, 0.1% by weight to 10% by weight of the conductive carbon, and 0.1% by weight to 10% by weight of the perfluorinated ionomer.
In one embodiment, the perfluorinated ionomer is a copolymer containing polytetrafluoroethylene, and the perfluorinated ionomer may be comprised in an amount of 0.1% by weight to 5% by weight in the positive electrode.
According to another aspect of the present disclosure, there is provided an all-solid-state battery comprising: the above-described positive electrode for an all-solid-state battery; a negative electrode; and a solid electrolyte layer interposed between the positive electrode and the negative electrode.
In one embodiment, the solid electrolyte layer may comprise a material same as the solid electrolyte contained in the positive electrode for the all-solid-state battery.
In one embodiment, the solid electrolyte and the solid electrolyte layer may comprise at least one of Li6PS5Cl, Li10GeP2S12, Li3PS4, and Li7P3S11.
In one embodiment, the negative electrode may comprise at least one of lithium metal and indium-lithium alloy.
According to the present disclosure as described above, it is possible to obtain a positive electrode for an all-solid-state battery with high bonding strength between the positive electrode active materials without using a solvent by using a novel perfluorinated ionomer in manufacturing the positive electrode in the present disclosure, and an all-solid-state battery comprising the same.
In addition, the positive electrode for the all-solid-state battery according to the present disclosure and the all-solid-state battery comprising the same are provided to have ion conductivity similar to that of the liquid electrolyte in spite of using a solid electrolyte, and thus the capacity and cycle characteristics of the battery can be improved.
Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. However, the technical spirit of the present disclosure is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided so that this disclosure will be thorough and complete, and that the spirit of the present disclosure may be sufficiently conveyed to those skilled in the art.
In this specification, when a component is referred to as being on another component, that means it may be formed directly on other components or a third component may be interposed therebetween. In addition, in the drawings, the thicknesses of the films and regions are exaggerated for effective explanation of technical content.
In addition, in various embodiments of the present specification, terms such as first, second, third, etc. are used to describe various components, but these components should not be limited by these terms. These terms are only used to distinguish one component from another. Accordingly, what is referred to as a first component in one embodiment may be referred to as a second component in another embodiment. Each embodiment described and illustrated herein also comprises a complementary embodiment thereof. Also, in this specification, the term ‘and/or’ is used in the sense of including at least one of the elements listed before and after it.
In the specification, the singular forms “a,” “an,” and “the” comprise plural referents unless the context clearly dictates otherwise. It is to be understood that the terms such as “comprise” or “have” as used in the present specification, are intended to designate the presence of stated features, numbers, steps, components, or combinations thereof, but not to preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.
In addition, when it is determined that a detailed description of a related well-known function or configuration in describing the present disclosure may unnecessarily obscure the gist of the present disclosure, the detailed description thereof will be omitted.
In addition, in the present application, “mol %” is interpreted as indicating the content of any metal included in the positive electrode active material or the precursor of the positive electrode active material, when the sum of the metals other than sodium and oxygen in the positive electrode active material or the precursor of the positive electrode active material is assumed to be 100%.
One embodiment of the present disclosure may comprise a positive electrode for an all-solid-state battery comprising a positive electrode active material; a perfluorinated ionomer comprising lithium substituted sulfonate; a solid electrolyte; and a conductive carbon.
The positive electrode for the all-solid-state battery can be manufactured by physically mixing the positive electrode active material, the perfluorinated ionomer, the solid electrolyte and the conductive carbon without using a solvent, and the positive electrode active material, the solid electrolyte and the conductive carbon may be bound to each other in a uniformly mixed state by the perfluorinated ionomer.
In general, the positive electrode for the all-solid-state battery is manufactured as a positive electrode by using a solvent to uniformly mix solid powders such as the positive electrode active material, the binder, the solid electrolyte, and the conductive carbon, and dispersing them in the solvent to form a slurry. On the other hand, as such, in the casting method using a solvent, when a positive electrode is prepared, there is a problem that the solvent reacts with the solid electrolyte, such as the sulfide-based solid electrolyte, to destroy the crystallinity of the solid electrolyte, thereby reducing the ion conductivity. In addition, when a solvent is used, there is a limitation in the selection of the type of binder that only the polymer binder that can be dissolved in the solvent should be used.
On the other hand, the perfluorinated ionomer according to the present embodiment is a kind of novel polymer binder, and since the perfluorinated ionomer has flexible properties in the process of dry mixing without using a solvent, it can be easily mixed with the positive electrode active material, the solid electrolyte, and the conductive carbon to bind them to each other. In addition, since the perfluorinated ionomer contains lithium substituted sulfonate, conductivity to lithium ions may be further improved, thereby exhibiting high capacity.
The positive electrode for the all-solid-state battery repeatedly contracts and expands by charging/discharging lithium ions, but the perfluorinated ionomer according to present embodiment has flexible characteristics, and thus, even when contraction and expansion are repeated, since the contact between the positive electrode active materials bound to each other by the perfluorinated ionomer is easily maintained, lifetime characteristics can be improved.
Specifically, the perfluorinated ionomer may be represented by Formula 1 below.
wherein A is each independently a substituted or unsubstituted C1 to C30 alkylene group, a substituted or unsubstituted C1 to C30 haloalkylene group or a substituted or unsubstituted C1 to C30 hydroxyalkylene group, and n and m are each an integer from 1 to 100. For example, the perfluorinated ionomer of Formula 1 may be a random copolymer.
More specifically, in Formula 1, A is —(CF2—CF2)p—, and p may include an integer of 1 to 15.
For example, the perfluorinated ionomer is a polytetrafluoroethylene-based copolymer represented by the following Formula 2, and may contain lithium ions, and specifically, may be poly (tetrafluoroethylene-co-perfluoro (3-oxa-4-pentenesulfonicacid)) lithium salt.
wherein n is an integer from 1 to 100, m may be an integer from 1 to 20, and specifically, n may be an integer 5 times the number of m. More specifically, it may be a random copolymer in which n is 5 and m is 1.
The positive electrode active material may be manufactured by firing a composite metal hydroxide including at least one of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al) with a lithium compound. For example, the positive electrode active material may have a layered structure, and include a high content of nickel of 50% or more, and may exhibit a high capacity.
The positive electrode active material may comprise at least one of LicoO2, Li(NixCoyMhz)O2 [x+y+z=1], Li(NixCoyAlz)O2 [x+y+z=1], and LiFePO4.
The positive electrode for the all-solid-state battery according to this embodiment may contain a solid electrolyte, wherein the solid electrolyte may comprise a halide-based solid electrolyte or a sulfide-based solid electrolyte. For example, the sulfide-based solid electrolyte may comprise at least one of Li6PS5Cl, Li10GeP2S12, Li3PS4, and Li7P3S11. In addition, the halide-based solid electrolyte may comprise at least one of Li3YCl6, Li3InCl6, and Li2ZrCl6.
The solid electrolyte can be mixed with the positive electrode active material to further improve the mobility of ions. Specifically, the solid electrolyte may be a sulfide-based solid electrolyte.
The conductive carbon may comprise at least one of vapor grown carbon fiber (VGCF), carbon nanotube (CNT), Super P, Super C, carbon black, Ketjen black, acetylene black, coke, glassy carbon, and activated carbon.
In one embodiment of the present disclosure, the positive electrode may comprise 60% by weight to 95% by weight of the positive electrode active material, 5% by weight to 40% by weight of the solid electrolyte, 0.1% by weight to 10% by weight of the conductive carbon, and 0.1% by weight to 10% by weight of the perfluorinated ionomer.
Specifically, the perfluorinated ionomer is a copolymer containing polytetrafluoroethylene, and the perfluorinated ionomer may be contained in an amount of 0.1% by weight to 5% by weight. More specifically, the perfluorinated ionomer may be contained in an amount of 0.1% by weight or more, 0.2% by weight or more, 0.3% by weight or more, 0.4% by weight or more, 0.5% by weight or more, 0.6% by weight or more, 0.7% by weight or more, 0.8% by weight or more, 0.9% by weight or more, or 1.0% by weight or more, and 5.0% by weight or less, 4.9% by weight or less, 4.8% by weight or less, 4.7% by weight or less, 4.6% by weight or less, 4.5% by weight or less, 4.4% by weight or less, 4.3% by weight or less, 4.2% by weight or less, 4.1% by weight or less, 4.0% by weight or less, 3.9% by weight or less, 3.8% by weight or less, 3.7% by weight or less, 3.6% by weight or less, 3.5% by weight or less, 3.4% by weight or less, 3.3% by weight or less, 3.2% by weight or less, 3.1% by weight or less, or 3.0% by weight or less. If the content of the perfluorinated ionomer is less than 0.1% by weight, the amount contained is too small, and thus there is a problem that the positive electrode active material cannot be sufficiently bound. If the content of the perfluorinated ionomer exceeds 5% by weight, the electron and ion conduction properties in the positive electrode may be deteriorated, or the content of the positive electrode active material may be unnecessarily reduced, thereby reducing the capacity.
According to another aspect of the present disclosure, an embodiment of the present disclosure comprises an all-solid-state battery comprising the positive electrode for the all-solid-state battery described above; a negative electrode; and a solid electrolyte layer interposed between the positive electrode and the negative electrode.
The solid electrolyte layer may be made of the same material as the solid electrolyte contained in the positive electrode for the all-solid-state battery. Since the solid electrolyte contained in the positive electrode for the all-solid-state battery and the solid electrolyte layer are made of the same material, the mobility of lithium ions may be improved, the overall structure of the all-solid-state battery may be stabilized, and the production efficiency may be improved.
The solid electrolyte and the solid electrolyte layer may be a sulfide-based solid electrolyte comprising at least one of Li6PS5Cl, Li10GeP2S12, Li3PS4, and Li7P3S11.
Since the positive electrode for the all-solid-state battery according to this embodiment is manufactured in a solvent-free manner by the perfluorinated ionomer without using a solvent, it is possible to prevent the solvent remaining in the positive electrode for the all-solid-state battery from reacting with the sulfide-based solid electrolyte to decrease the crystallinity of the solid electrolyte. The negative electrode may be formed of at least one of lithium metal and indium-lithium alloy.
Hereinafter, Examples of the present disclosure and Comparative Examples will be described. However, the following Examples are only preferred examples of the present disclosure, and the scope of the present disclosure is not limited by the following examples.
1. Manufacture of Positive Electrode of all-Solid-State Battery
A positive electrode active material, LiNi0.7Co0.15Mn0.15O2 (hereinafter referred to as NCM) having a nickel content of 70%, a cobalt content of 15%, and a manganese content of 15% were mixed with Li6PS5Cl, which is a sulfide-based solid electrolyte, at room temperature. Next, a conductive material (VGCF, Sigma Aldrich company) and a polytetrafluoroethylene-based copolymer ionomer binder (see (a) of
A composite positive electrode was manufactured in the same manner as in Example 1, but the loading level of the composite positive electrode was manufactured to be lower than Example 1 as shown in Table 1 below when manufacturing an all-solid-state battery.
A composite positive electrode was manufactured in the same manner as in Example 1, but the loading level of the composite positive electrode was manufactured to be higher than Example 1 as shown in Table 1 below when manufacturing an all-solid-state battery.
A composite positive electrode was manufactured in the same manner as in Example 1, except that the content of the polytetrafluoroethylene-based copolymer ionomer binder was lowered as shown in Table 1 and the content of the solid electrolyte was increased. An all-solid-state battery was manufactured at the same loading level as Example 1 using the manufactured composite positive electrode.
A composite positive electrode was manufactured in the same manner as in Example 1, except that the content of the polytetrafluoroethylene-based copolymer ionomer binder was increased as shown in Table 1 and the content of the solid electrolyte was lowered. An all-solid-state battery was manufactured at the same loading level as Example 1 using the manufactured composite positive electrode.
A composite positive electrode was manufactured in the same manner as in Example 1, except that the content of the polytetrafluoroethylene-based copolymer ionomer binder was increased as shown in Table 1 and the content of the solid electrolyte was lowered. An all-solid-state battery was manufactured at the same loading level as Example 1 using the manufactured composite positive electrode.
A positive electrode active material, LiNi0.7Co0.15Mn0.15O2 (hereinafter NCM) with a nickel content of 70%, a cobalt content of 15%, and a manganese content of 15%, and Li6PS5Cl, which is a sulfide-based solid electrolyte, were added to xylene solvent (Sigma Aldrich company) and then mixed at room temperature. Next, a conductive material (Super-P) and a nitrile-butadiene rubber binder (poly (acrylonitrile-co-butadiene), Sigma Aldrich company, see (b) of
A composite positive electrode was manufactured in the same manner as in Example 1, except that a polytetrafluoroethylene binder (Sigma Aldrich company, see (c) of
After preparing a mixture of the solid electrolytes and the binders according to Comparative Examples 1 and 2 and Example 1, 100 mg of the mixture was pressurized at 300 MPa to prepare pellets. SUS electrodes were placed on both sides of the prepared pellet and the ion conductivity was measured by an impedance analyzer (ZIVE MP1, Wona Tech company) at room temperature. Table 2 is a table comparing the types and compositions of the solid electrolytes and the binders according to the composite positive electrodes of Comparative Examples 1 and 2 and Example 1 of the present disclosure with their respective ion conductivity. In Comparative Example 1, Comparative Example 2 and Example 1, only the type of binder is different, and the content of the binder and the solid electrolyte constituting the composite positive electrode is the same in a weight ratio of solid electrolyte: binder=25:2. If the binder is not comprised, the ion conductivity of the Li6PS5Cl solid electrolyte itself is 1.67 mS cm−1. If the polymer binder is comprised as in Comparative Examples 1 and 2 and Example 1, it can be seen that the ion conductivity is lower than 1.67 mS cm−1.
When the nitrile-butadiene rubber binder applied to Comparative Example 1 was comprised, it was found to be 0.71 mS cm−1, when the polytetrafluoroethylene binder applied to Comparative Example 2 was comprised, it was found to be 1.31 mS cm−1, and when the polytetrafluoroethylene-based copolymer ionomer binder applied to Example 1 was comprised, it was found to be 1.45 mS cm−1. That is, if the polytetrafluoroethylene-based copolymer ionomer binder containing lithium ions is used as in Example 1, it can be confirmed that the ion conductivity is higher than that of the conventional binder.
A charging/discharging cycle was performed at 30° C. at 0.5 C (1.153 mA) with 4.3 V charging and 3.0 V (vs Li/Lit) discharging, and the voltage and the capacity were measured at each cycle.
In the case of Comparative Example 1 to which the nitrile-butadiene rubber binder was applied, the initial capacity was shown to be lower than those of Comparative Examples 2 and Example 1, and a phenomenon was shown in which the capacity was decreased and the overvoltage was increased as the cycles were progressed. In the case of Comparative Example 2 to which the polytetrafluoroethylene binder was applied, the damage to the solid electrolyte was reduced by applying a solvent-free process, as compared to Comparative Example 1, and thus the initial capacity was increased, but a decrease in capacity and an increase in overvoltage were observed in the course of the cycles. In the case of Example 1 to which a polytetrafluoroethylene-based copolymer ionomer binder is applied, it showed a high initial capacity compared to Comparative Example 1 and Comparative Example 2, and it can be seen that even in the course of the cycles, there was little increase in overvoltage and little decrease in capacity, and they were maintained. In the case of Example 1 and Comparative Example 1, it can be confirmed that by manufacturing the composite positive electrode by a solvent-free process, no damage to the solid electrolyte or the crystal of the electrolyte membrane by the solvent occurs, thereby indicating a high initial capacity. In the case of Example 1 which is the case of applying a polytetrafluoroethylene-based copolymer ionomer binder to the composite positive electrode, it can be seen that the cycle characteristics are excellent compared to Comparative Example 1 and Comparative Example 2. Example 1 is considered to be because the movement of lithium ions is efficiently performed, as the bonding force between the positive electrode active materials is excellently maintained even with the reversible contraction and expansion of the positive electrode that occurs during charging and discharging.
Comparing Comparative Example 1 and Comparative Example 2, it can be seen that Comparative Example 2 exhibits superior discharging capacity and cycle characteristics compared to Comparative Example 1. In the case of Comparative Example 2, a composite positive electrode was manufactured by a solvent-free process, but in the case of Comparative Example 1, a composite positive electrode was manufactured by a wet process using a solvent, thereby confirming that the discharging capacity and cycle characteristics were affected. Specifically, since the solvent contained in the composite positive electrode can react with the solid electrolyte during the manufacturing process, a xylene solvent with sufficiently small polarity was used in Comparative Example 1, and a material with low polarity was also applied for the polymer binder. Accordingly, Comparative Example 1 to which the positive electrode of high loading was applied showed low discharge capacity and cycle characteristics.
Comparing Comparative Example 2 and Example 1, it can be seen that in both cases a composite positive electrode was prepared without using a solvent, and Example 1 exhibits superior cycle characteristics compared to Comparative Example 2. This is considered to be because the polytetrafluoroethylene-based copolymer ionomer binder of Example 1 effectively binds the positive electrode active material, the conductive material, and the solid electrolyte, which is maintained even during the course of the cycles, and the mobility of lithium ions is improved by the ions lithium contained in the polytetrafluoroethylene-based copolymer ionomer binder.
That is, it can be confirmed that if the composite positive electrode is manufactured using a binder capable of a solvent-free dry process, the discharging capacity and cycle characteristics are improved, and in particular, if the polytetrafluoroethylene-based copolymer ionomer binder is used as in Example 1, excellent cycle characteristics are maintained.
In the case of Comparative Example 1, it can be seen that the capacity is reduced as the charging/discharging current density is increased, and it can be seen that the capacity expression is hardly achieved at a high rate of 1.0 C or higher. In the case of Comparative Example 2, it can be seen that even at 1.0 C, it shows an excellent capacity compared to Comparative Example 1, but it can be seen that the discharge capacity is greatly reduced at a high rate of 2.0 C. It can be seen that Example 1 exhibits superior c-rate characteristics compared to Comparative Example 1 and Comparative Example 2, and even at a high rate of 2.0 C, there was almost no decrease in capacity and excellent characteristics were exhibited. That is, in the case of Example 1, it can be seen that it can be applied even to high-rate/fast charging/discharging in an all-solid-state battery, and the output characteristics are improved.
It will be understood by those of ordinary skill in the art to which the present disclosure pertains that the present disclosure may be embodied in other specific forms without changing the technical spirit or essential features thereof. Therefore, it should be understood that the examples described above are illustrative in all respects and not restrictive. The scope of the present disclosure is indicated by the following claims rather than the above detailed description, and it should be construed that all modifications or variations, which are derived from the meaning and scope of the claims and the concept of equivalents thereof, are included within the scope of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2021-0107946 | Aug 2021 | KR | national |
This application is a National Phase entry pursuant to 35 U.S.C. § 371 of International Application No. PCT/KR2022/012237, filed on Aug. 17, 2022, and claims the benefit of and priority to Korean Patent Application No. 10-2021-0107946, filed on Aug. 17, 2021, the disclosures of which are incorporated by reference in their entirety for all purposes as if fully set forth herein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2022/012237 | 8/17/2022 | WO |
