Liquid additive having high lithium ion conductivity and low reactivity with solid electrolyte, and all-solid-state battery

Abstract

The present application relates to a liquid additive having high lithium ion conductivity and low reactivity with solid electrolytes and an all-solid-state battery operating at low pressure at room temperature comprising the same. Specifically, by adding a liquid additive having low reactivity and high lithium ion conductivity with a solid electrolyte to an anode layer, a cathode layer, or a solid electrolyte layer, ionic conductivity and current density robustness of an all-solid-state battery under room temperature and low voltage conditions can be improved.

Description

Technical Field

[0001] The present application relates to a liquid additive for an all-solid-state battery capable of operating under conditions of room temperature and low pressure, and an all-solid-state battery including the liquid additive. More particularly, by adding a liquid additive having low reactivity with a solid electrolyte and high lithium-ion conductivity to a composite anode layer, a composite cathode layer, or a solid electrolyte layer, the ion conductivity and current density robustness of the all-solid-state battery can be improved under conditions of room temperature and low pressure. Background Art

[0002] An all-solid-state battery, which has drawn attention as a next-generation secondary battery, is configured such that all components are made of solids, and thus has advantages of low risk of fire and explosion and high mechanical strength compared to a lithium-ion battery that uses a combustible organic solvent as an electrolyte. Such an all-solid-state battery generally includes a cathode layer attached to a cathode current collector, an anode layer attached to an anode current collector, and a solid electrolyte layer disposed between the cathode layer and the anode layer.

[0003] The anode layer is used in the form of a composite anode layer obtained by mixing an anode active material (e.g., graphite, silicon, etc.) with a solid electrolyte for lithium ion (Li + ) conduction. Since the specific gravity of the solid electrolyte is higher than that of the liquid electrolyte, a conventional all-solid-state battery is disadvantageous because its energy density is lower than that of a lithium-ion battery, and the ion conductivity may be reduced due to voids between the solid electrolyte and the anode active material.

[0004] In addition, the cathode layer can be used in the form of a composite cathode layer obtained by mixing a cathode active material (e.g., a lithium composite oxide) with a solid electrolyte. Therefore, the density is also lower than that of a lithium-ion battery, and due to the presence of voids between the solid electrolyte and the cathode active material, the internal resistance increases and the ion conductivity decreases, which is undesirable.

[0005] For commercialization, an all-solid-state battery must be able to operate under conditions of room temperature and low clamping pressure. However, when the clamping pressure of the all-solid-state battery is reduced, it is difficult to compensate for voids generated by volume changes of the solid electrolyte layer or the electrode including the solid electrolyte. Internal voids generated in a layer including a solid electrolyte (e.g., a solid electrolyte layer, a composite anode layer, a composite cathode layer) may block the lithium-ion conduction path, resulting in poor battery performance (including current density robustness).

[0006] Meanwhile, an energy storage type anode-free all-solid-state battery has been proposed, which eliminates the anode layer of the all-solid-state battery or uses only a small amount of anode active material, and directly deposits lithium ions (Li + ) in the form of lithium metal or a lithium alloy on the anode current collector.

[0007] An anode-free all-solid-state battery does not use an anode active material capable of storing lithium ions. During charging, lithium ions (Li + ) released from the cathode layer are converted into lithium metal by being reduced using electrons on the surface of the anode current collector through passing through the solid electrolyte layer. During discharging, the reverse electrochemical reaction occurs. In short, even without an anode active material, the anode-free all-solid-state battery can be charged and discharged.

[0008] In such an anode-free all-solid-state battery, due to the irregular surface of the solid electrolyte layer and the hardness of the anode current collector, voids are generated between the solid electrolyte layer and the anode current collector, making it difficult for lithium metal to precipitate uniformly. These problems may become more serious when the anode-free all-solid-state battery operates at room temperature and low clamping pressure to commercialize the all-solid-state battery. SUMMARY OF THE INVENTION

[0009] As described above, in order for an all-solid-state battery (especially an anode-free all-solid-state battery) to operate at room temperature and low clamping pressure, the voids between the active material and the solid electrolyte or the voids between the solid electrolytes need to be filled with a compound having a high lithium ion conductivity.

[0010] This application is made in consideration of these problems and aims to provide a liquid additive that can maintain ionic conductivity by filling the solid electrolyte-containing layer in the multiple layers constituting the all-solid-state battery with a material having a high lithium ion conductivity even when voids are generated in the layer containing the solid electrolyte under the conditions of room temperature and low clamping pressure.

[0011] The object of this application is not limited to the above object. The object of this application will be clearly understood through the following description, and the object of this application can be achieved through the methods and combinations described in the claims.

[0012] An embodiment of this application provides a liquid additive for a solid electrolyte, the liquid additive comprising a lithium salt and a solvent capable of dissolving the lithium salt and compatible with the solid electrolyte, wherein the solvent includes an orthoester compound.

[0013] In one aspect, the solvent orthoester compound can have the formula (RC(OR’)3), where R is H or an optionally substituted C1-C12 alkyl group, preferably H or an optionally substituted C1-C6 alkyl group, still more preferably H; and each R’ is the same or different optionally substituted C1-C12 alkyl group, preferably an optionally substituted C1-C6 alkyl group (such as methyl, ethyl, propyl, butyl, pentyl or hexyl (including branched groups such as isopropyl, sec-butyl, etc.)). In certain embodiments, the groups R and R’ of the formula (RC(OR’)3) can be unsubstituted.

[0014] For example, the solvent may include any one selected from trimethyl orthoformate (TMOF), triethyl orthoformate (TEOF), tripropyl orthoformate (TPOF), tributyl orthoformate (TBOF), diethyl phenyl orthoformate (DPOF), and combinations thereof.

[0015] Preferably, the solvent includes trimethyl orthoformate (TMOF).

[0016] In an embodiment, the dipole moment of the solvent may be less than 2.00 Debye (e.g., trimethyl orthoformate: 1.70 Debye; triethyl orthoformate: 1.67 Debye; tripropyl orthoformate: 1.64 Debye; tributyl orthoformate: 1.66 Debye).

[0017] In an embodiment, the lithium salt may include any one selected from LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 , LiAlCl4, LiAlO4, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2 (lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF2CF3)2 (lithium bis(pentafluoroethylsulfonyl)imide, LiBETI), LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfonyl)imide, LiTFSI), and combinations thereof.

[0018] In an embodiment, the concentration of the lithium salt may be from 0.1 M to 10 M.

[0019] Another embodiment of the present application provides a solid electrolyte layer comprising a solid electrolyte and the above liquid additive.

[0020] Here, the solid electrolyte may include a sulfide-based solid electrolyte.

[0021] In addition, the solid electrolyte layer may contain 0.1 wt% to 20 wt% of the liquid additive.

[0022] Another embodiment of the present application provides a composite cathode layer comprising a cathode active material, a solid electrolyte, and the above liquid additive.

[0023] Here, the solid electrolyte may include a sulfide-based solid electrolyte or a sulfide-containing solid electrolyte.

[0024] Another embodiment of the present application provides a composite anode layer comprising an anode active material, a solid electrolyte, and the above liquid additive.

[0025] Here, the solid electrolyte may include a sulfide-based solid electrolyte or a sulfide-containing solid electrolyte.

[0026] Another embodiment of the present application provides a all-solid-state battery, the all-solid-state battery including an anode, a cathode, and a solid electrolyte layer, the anode including an anode current collector and an anode layer, the cathode including a cathode current collector and a cathode layer, and the solid electrolyte layer disposed between the anode and the cathode.

[0027] In an embodiment, the all-solid-state battery may further include a restricting portion disposed outside the anode, the solid electrolyte layer, and the cathode and configured to squeeze the anode, the solid electrolyte layer, and the cathode along the stacking direction, wherein the clamping pressure applied by the restricting portion to the anode, the solid electrolyte layer, and the cathode is 0.1 MPa to 10 MPa.

[0028] In an embodiment, the all-solid-state battery may be configured to operate under room temperature conditions.

[0029] In another aspect, a vehicle including the all-solid-state battery disclosed herein is provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The above and other features of the present application will now be described in detail with reference to certain exemplary embodiments shown in the accompanying drawings, which are given hereinafter by way of illustration only and thus do not limit the present application, wherein:

[0031] Figure 1 Displays an all-solid-state battery containing a liquid additive according to the present application;

[0032] Figure 2 Displays the results of a symmetric battery test of a battery containing Examples 1-1 and 2;

[0033] Figure 3 Displays the evaluation results of the electrochemical properties of a half-button battery containing Examples 1-1, 2, and Comparative Example 1;

[0034] Figure 4 Displays the results of impedance measurement of the solid electrolyte containing Example 1-1;

[0035] Figure 5 Displays the results of impedance measurement of the solid electrolyte containing Example 2;

[0036] Figure 6 Displays the results of impedance measurement of the solid electrolyte containing Example 3;

[0037] Figure 7Shows the results of impedance measurements of the solid electrolyte containing Example 4;

[0038] Figure 8 Shows the results of impedance measurements of the solid electrolyte containing Example 5;

[0039] Figure 9 Shows the results of impedance measurements of a sulfide-based solid electrolyte or a sulfide-containing solid electrolyte and a sulfide-containing solid electrolyte mixed with the solid electrolyte of Example 1 in a predetermined weight ratio;

[0040] Figure 10 Shows the results of impedance measurements of a sulfide-containing solid electrolyte and a sulfide-containing solid electrolyte mixed with the solid electrolyte of Comparative Example 1 in a predetermined weight ratio;

[0041] Figure 11 Shows the results of symmetric cell tests of the cells containing Examples 1-2; and

[0042] Figure 12 Shows the results of symmetric cell tests of the cells that do not contain liquid additives. DETAILED DESCRIPTION

[0043] The above and other objects, features, and advantages of the present application will be more clearly understood by referring to the following preferred embodiments presented in conjunction with the accompanying drawings. However, the present application is not limited to the embodiments disclosed herein and may be modified into different forms. These embodiments are provided to fully explain the present application and convey the spirit of the present application to those skilled in the art.

[0044] Throughout the drawings, the same reference numerals will represent the same or equivalent elements. For the clarity of the present application, the dimensions of the structures are depicted as larger than their actual sizes. It should be understood that although terms such as "first," "second," etc. may be used herein to describe various elements, these elements are not limited by these terms. These terms are only used to distinguish one element from another. For example, the "first" element discussed below may be referred to as the "second" element without departing from the scope of the present application. Similarly, the "second" element may also be referred to as the "first" element. As used herein, unless the context clearly dictates otherwise, the singular form is also intended to include the plural form.

[0045] It will also be understood that the terms "comprising", "including", "having", etc. used in this specification denote the presence of the stated features, values, steps, operations, elements, components, or combinations thereof, but do not preclude the presence or addition of one or more other features, values, steps, operations, elements, components, or combinations thereof. Further, it will be understood that when an element (e.g., a layer, film, region, or sheet) is referred to as being "on" another element, it can be directly on the other element or there can be intervening elements between them. Similarly, when an element (e.g., a layer, film, region, or sheet) is referred to as being "under" another element, it can be directly under the other element or there can be intervening elements between them.

[0046] As used herein, the term "sheet type" or derivatives thereof refers to the three-dimensional shape of a sheet, film, or thin layer having a planar surface and a thickness that is significantly reduced compared to the width or length of the planar surface (e.g., on the millimeter scale, micrometer scale, or nanometer scale).

[0047] As used herein, the term "cylindrical" or derivatives thereof refers to the three-dimensional shape of an object having a hollow, empty internal space, and a cylinder can be defined using the cross-sectional shape and length of the object having an inner diameter and an outer diameter, where the inner diameter is the diameter of the hollow space of the object and the outer diameter is the diameter of the outer barrier of the cross-section of the object.

[0048] It should be understood that the term "vehicle" or "vehicular" or other similar terms used herein generally include motor vehicles, such as passenger cars including sport utility vehicles (SUVs), buses, trucks, various commercial vehicles, vessels including various boats and ships, aircraft, etc., and include hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles, and other alternative fuel vehicles (e.g., fuels derived from non-petroleum energy sources). As mentioned herein, a hybrid vehicle is a vehicle having two or more power sources, such as a vehicle having both gasoline power and electric power.

[0049] As used herein, the term "optionally substituted" with respect to the groups R and R' of the formula (RC(OR')3) means that a particular group (e.g., alkyl b) can be substituted at one or more available positions with a suitable group (e.g., halogen (F, Br, Cl, or I), amino, aminoalkyl, alkyl sulfide, ketoalkyl, hydroxyalkyl (e.g., -CH2-CH(OH)C1-C4 alkyl), phenyl, or other carbocyclic aryl, etc.).

[0050] Unless otherwise indicated, all numbers, numerical values, and / or expressions representing the amounts of components, reaction conditions, polymer compositions, and mixtures used herein should be considered approximate values, which include the various uncertainties inherent in obtaining these values that affect the measurements, and should therefore be understood to be modified in all cases by the term "about". Unless specifically stated or obvious from the context, as used herein, the term "about" is understood to be within the normal tolerances in the art, e.g., within two standard deviations of the mean value. "About" can be understood to be within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the specified value. All numerical values provided herein are modified by the term "about" unless obvious from the context. In addition, when a numerical range is disclosed in this specification, unless otherwise indicated, the range is continuous and includes all values from the minimum value to the maximum value of the range. In addition, when the range pertains to integer values, unless otherwise indicated, it includes all integers from the minimum value to the maximum value.

[0051] In this specification, when describing the range of a variable, it should be understood that the variable includes all numerical values (including the endpoints) described within the range. For example, the range of "5 to 10" should be understood to include any sub-ranges (e.g., 6 to 10, 7 to 10, 6 to 9, 7 to 9, etc.) as well as the individual values of 5, 6, 7, 8, 9, and 10, and should also be understood to include any values between the valid integers within the range, e.g., 5.5, 6.5, 7.5, 5.5 to 8.5, 6.5 to 9, etc. In addition, for example, the range of "10% to 30%" should be understood to include sub-ranges (e.g., 10% to 15%, 12% to 18%, 20% to 30%, etc.) as well as all integers including the values from 10%, 11%, 12%, 13%, etc. up to 30%, and should also be understood to include any values between the valid integers within the range, e.g., 10.5%, 15.5%, 25.5%, etc.

[0052] Liquid additive

[0053] Generally, since all components are solids, all-solid-state batteries require a high clamping pressure of several hundred MPa to operate effectively. To apply all-solid-state batteries to electric vehicles and other applications, all-solid-state batteries must be able to operate under conditions of room temperature and low clamping pressure. However, under these conditions, there are limitations in operating at a certain level or higher level of current density. In addition, at low clamping pressures, it may be difficult to compensate for the voids generated within the electrodes due to the volume change of the electrodes caused by charging and discharging.

[0054] Void spaces generated inside the electrode or inside the solid electrolyte layer may block the lithium ion conduction path, resulting in poor battery performance (including current density robustness). The present application aims to solve the above problems.

[0055] The liquid additive for a solid electrolyte according to the present application may include a lithium salt and a solvent capable of dissolving the lithium salt and compatible with the solid electrolyte.

[0056] The lithium salt can be used without particular limitation as long as it is commonly used in lithium ion batteries using liquid electrolytes. For example, the lithium salt may include any one selected from LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 , LiAlCl4, LiAlO4, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2 (lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF2CF3)2 (lithium bis(pentafluoroethylsulfonyl)imide, LiBETI), LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfonyl)imide, LiTFSI), and combinations thereof.

[0057] In an embodiment, the concentration of the lithium salt added to the solvent can be from 0.1 M to 10 M. When the concentration of the lithium salt falls within the above numerical range, appropriate lithium ion conductivity can be provided. If the concentration of the lithium salt is less than 0.1 M, it may be necessary to add an excessive amount of the liquid additive to provide sufficient lithium ion conductivity to each layer of the all-solid-state battery. On the other hand, if the concentration of the lithium salt exceeds 10 M, it may be difficult to uniformly add it to the layer containing the solid electrolyte due to the high viscosity of the liquid additive.

[0058] The liquid additive may include a lithium salt and thus may have high lithium ion conductivity. The liquid additive (which is in the liquid phase) can be loaded into the void spaces in the anode layer 20, cathode layer 40, or solid electrolyte layer 30 containing the solid electrolyte that cause a reduction in lithium ion conduction. In this way, by eliminating the cause of the reduction in lithium ion conductivity (such as void spaces), materials with high lithium ion conductivity can replace them and act as a liquid electrolyte within each layer.

[0059] In an embodiment, the solvent may include, for example, orthoesters, such as materials having the formula (RC(OR’)3) (wherein R and R’ are as defined above) and being suitably capable of dissolving or solvating lithium salts. An orthoester is an organic material in which three alkoxy groups (OR’) are attached to one carbon atom, and the types of R or R’ can be applied without particular limitation as long as it can dissolve lithium salts. Preferred R and R’ groups for (RC(OR’)3) are such that R is H or an optionally substituted C1-C12 alkyl group, preferably H or an optionally substituted C1-C6 alkyl group, still more preferably H; and each R’ is the same or different optionally substituted C1-C12 alkyl group, preferably an optionally substituted C1-C6 alkyl group (such as methyl, ethyl, propyl, butyl, pentyl or hexyl (including branched groups such as isopropyl, sec-butyl, etc.)). In certain embodiments, the groups R and R’ of the formula (RC(OR’)3) may be unsubstituted.

[0060] Preferably, as described above, the solvent includes a formic orthoester compound. In a preferred aspect, the formic orthoester compound is configured such that hydrogen (H) is applied to the R group of the orthoester compound. For example, the solvent may preferably include any one selected from trimethyl orthoformate (TMOF), triethyl orthoformate (TEOF), tripropyl orthoformate (TPOF), tributyl orthoformate (TBOF), diethyl phenyl orthoformate (DPOF), and combinations thereof.

[0061] More preferably, the solvent includes trimethyl orthoformate (TMOF). Here, triisopropyl orthoformate (TIPOF) is a formic orthoester compound, but it cannot dissolve lithium salts, making it difficult to be used as a solvent according to the present application.

[0062] In addition, a solvent compatible with the solid electrolyte can be used. Here, “compatible” may mean having a low reactivity with the solid electrolyte. In particular, the solvent can be compatible with sulfide-based solid electrolytes.

[0063] Due to high lithium ion conductivity and electrochemical stability, sulfide-based solid electrolytes are being studied worldwide. Depending on the presence or absence of a crystal structure, sulfide-based solid electrolytes are classified into crystalline electrolytes and non-crystalline electrolytes. Representatively, crystalline electrolytes can have a thio-LISICON, LGPS, and argyrodite-type crystal structure, and non-crystalline electrolytes have a glass structure or a glass-ceramic structure depending on the heat treatment temperature.

[0064] Sulfide-based solid electrolytes can react with solvents having high polarity, destroying their crystallinity and resulting in a decrease in lithium ion conductivity. To prevent this, the solvent for the liquid additive can be a non-polar or low-polarity solvent having a low reactivity with sulfide-based solid electrolytes.

[0065] For example, the dipole moment of the solvent can be less than 2.00 Debye. The dipole moment is determined by measuring the polarity of a molecule or chemical bond, and the closer its value is to 0, the more likely the solvent is a low-polarity solvent or has low polarity. The liquid additive according to the present application contains a solvent with a dipole moment less than 2.00 Debye, and thus has low reactivity with a solid electrolyte, preferably with a sulfide-based solid electrolyte, more preferably with a crystalline sulfide-based solid electrolyte.

[0066] If the dipole moment of the solvent is 2.00 Debye or greater, the interfacial resistance may increase and the lithium-ion conductivity may decrease due to an increase in side reactions with the sulfide-based solid electrolyte.

[0067] In specific examples of the solvent, the dipole moment of trimethyl orthoformate (TMOF) is 1.70 Debye, the dipole moment of triethyl orthoformate (TEOF) is 1.67 Debye, the dipole moment of tripropyl orthoformate (TPOF) is 1.64 Debye, the dipole moment of tributyl orthoformate is 1.66 Debye, and the dipole moment of diethylphenyl orthoformate (DPOF) is 2.00 Debye or less.

[0068] Figure 1 A all-solid-state battery is shown, in which the liquid additive according to the present application is included in at least one layer selected from the anode layer 20, the solid electrolyte layer 30, and the cathode layer 40. Refer to Figure 1 , the all-solid-state battery includes an anode current collector 10, an anode layer 20, a solid electrolyte layer 30, a cathode layer 40, and a cathode current collector 50. The anode layer 20 is disposed on the anode current collector 10. The solid electrolyte layer 30 is disposed on the anode layer 20 and configured to include a solid electrolyte. The cathode layer 40 is disposed on the solid electrolyte layer 30 and configured to include a cathode active material. The cathode current collector 50 is disposed on the cathode layer 40.

[0069] The following is a schematic description of its configuration.

[0070] The anode current collector 10 can be a plate-shaped substrate having conductivity. Specifically, the anode current collector 10 can be in the form of a sheet, a film, or a foil.

[0071] The anode current collector 10 can include a material that does not react with lithium. Specifically, the anode current collector 10 can include at least one selected from nickel (Ni), copper (Cu), stainless steel, and combinations thereof.

[0072] The thickness of the anode current collector 10 is not particularly limited and can be, for example, 1 μm to 500 μm.

[0073] The anode layer 20 may contain an anode active material and may also contain a binder and a solid electrolyte as needed. The anode active material may be a compound capable of reversibly storing and releasing lithium. For example, the anode active material may include any one selected from graphite-based active materials, silicon-based active materials, lithium titanate, or a combination thereof.

[0074] In addition, the anode layer 20 may be an anode-free anode layer 20 that does not contain a separate anode active material or contains only a very small amount of the anode active material.

[0075] The anode layer 20 containing a solid electrolyte to improve the lithium ion conductivity may be referred to as a "composite anode layer".

[0076] According to an embodiment, a composite anode layer containing an anode active material, a solid electrolyte, and a liquid additive may be provided. Since the composite anode layer contains a liquid additive, the lithium ion conductivity can be improved by filling the voids therein, and the operation of the all-solid-state battery under conditions of room temperature and low clamping pressure can be improved. Preferably, the solid electrolyte includes a sulfide-based solid electrolyte.

[0077] The solid electrolyte layer 30 may be disposed between the anode layer 20 and the cathode layer 40 and may contain a solid electrolyte having lithium ion conductivity.

[0078] The solid electrolyte may include at least one selected from oxide-based solid electrolytes, sulfide-based solid electrolytes, polymer electrolytes, and combinations thereof. Preferably, a sulfide-based solid electrolyte having high lithium ion conductivity is used.

[0079] The sulfide-based solid electrolyte is not particularly limited, but examples thereof may include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (where m and n are positive numbers, and Z is any one selected from Ge, Zn, and Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (where x and y are positive numbers, and M is any one selected from P, Si, Ge, B, Al, Ga, and In), Li 10 GeP2S12 etc.

[0080] Sulfide-based solid electrolytes can have a thiogermanate-type crystal structure. The thiogermanate-type crystal structure is a solid electrolyte that exhibits lithium ion conductivity and has the same crystal structure as the thiogermanite ore with the composition Ag8GeS6. It is known that Li7PS6 and Li6PS5X (X = Cl, Br, I) can be used as Li-thiogermanate electrolytes with lithium ion (Li + ) conductivity in all-solid-state batteries.

[0081] Examples of oxide-based solid electrolytes can include perovskite-type LLTO (Li 3x La 2 / 3-x TiO3), phosphate-based NASICON-type LATP (Li 1+x Al x Ti 2-x (PO4)3), etc.

[0082] Examples of polymer electrolytes can include gel polymer electrolytes, solid polymer electrolytes, etc.

[0083] The solid electrolyte layer 30 can also contain a binder. Examples of the binder can include butadiene rubber, nitrile rubber, hydrogenated nitrile rubber, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), etc.

[0084] The solid electrolyte layer 30 can contain a liquid additive according to the present application to improve lithium ion conductivity by filling the voids between the solid electrolyte particles. This enables the all-solid-state battery to operate effectively under room temperature and low clamping pressure conditions.

[0085] Therefore, the solid electrolyte layer 30 can contain 0.1 wt% to 20 wt% of the liquid additive. If the amount of the liquid additive present in the solid electrolyte layer 30 is less than 0.1 wt%, it is too little to improve the lithium ion conductivity and battery operability under common conditions. On the other hand, if the amount of the liquid additive exceeds 20 wt%, the lithium ion conductivity or battery operability can be improved, but the liquid content in the solid electrolyte layer 30 may become too large, resulting in a slurry-like form. Therefore, it may be difficult to process it into a pellet form.

[0086] In addition, the cathode active material layer 40 is configured to reversibly store and release lithium ions and can contain a cathode active material, a conductive material, and a binder. In addition, a part of the solid electrolyte can be mixed.

[0087] The cathode active material can be an oxide active material or a sulfide active material.

[0088] Examples of the oxide active material may include a rock salt layer-type active material (e.g., LiCoO2, LiMnO2, LiNiO2, LiVO2, Li 1+x Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc.), a spinel-type active material (e.g., LiMn2O4, Li(Ni 0.5 Mn 1.5 )O4, etc.), an inverse spinel-type active material (e.g., LiNiVO4, LiCoVO4, etc.), an olivine-type active material (e.g., LiFePO4, LiMnPO4, LiCoPO4, LiNiPO4, etc.), a silicon-containing active material (e.g., Li2FeSiO4, Li2MnSiO4, etc.), a rock salt layer-type active material in which a part of the transition metal is replaced with a different metal (e.g., LiNi 0.8 Co (0.2-x) Al x O2 (0 < x < 0.2)), a spinel-type active material in which a part of the transition metal is replaced with a different metal (e.g., Li 1+x Mn 2-x-y M y O4 (where M is at least one selected from Al, Mg, Co, Fe, Ni, and Zn, 0 < x + y < 2)), a lithium titanium oxide (e.g., Li4Ti5O 12 ), etc.).

[0089] Examples of the sulfide active material may include Chevrel copper, iron sulfide, cobalt sulfide, nickel sulfide, etc.

[0090] Examples of the conductive material may include carbon black, conductive graphite, ethylene black, carbon fiber, graphene, etc.

[0091] Examples of the binder may include butadiene rubber, nitrile rubber, hydrogenated nitrile rubber, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), etc.

[0092] The cathode layer 40 further containing a solid electrolyte to improve the lithium ion conductivity may be referred to as a "composite cathode layer".

[0093] According to another embodiment of the present application, a composite cathode layer including a cathode active material, a solid electrolyte, and a liquid additive may be provided. Since the composite cathode layer contains a liquid additive, the lithium ion conductivity can be improved by filling the voids in the layer, thereby improving the operability of the all-solid-state battery under conditions of room temperature and low clamping pressure. Preferably, the solid electrolyte includes a sulfide-based solid electrolyte.

[0094] The solid electrolytes included in the composite anode layer, the composite cathode layer, and the solid electrolyte layer 30 may be the same as or different from each other. Here, the fact that the same solid electrolyte is used means that the same type of solid electrolyte may be included, and does not necessarily mean that the same solid electrolyte must be included.

[0095] Meanwhile, in an all-solid-state battery, all components are solid, which is different from using a liquid electrolyte. This may result in a non-uniform interfacial bonding state between the solid electrolyte layer 30 and the cathode layer 40 or between the solid electrolyte layer 30 and the anode layer 20. Therefore, the interfacial resistance may be high. To solve this problem, a typical all-solid-state battery can squeeze the anode, the solid electrolyte layer 30, and the cathode with a strong clamping pressure of several tens to several hundreds of MPa.

[0096] In an embodiment, the all-solid-state battery may further include a restricting portion disposed outside the anode, the solid electrolyte layer 30, and the cathode and configured to squeeze the anode, the solid electrolyte layer 30, and the cathode along the stacking direction. The clamping pressure applied by the restricting portion to the anode, the solid electrolyte layer 30, and the cathode may be from 0.1 MPa to 10 MPa.

[0097] If the clamping pressure is less than 0.1 MPa, voids in the anode layer 20, the solid electrolyte layer 30, and the cathode layer 40 may expand excessively during the charging process of the all-solid-state battery. This may increase the interfacial resistance and cause an internal short circuit of the battery. On the other hand, if the clamping pressure exceeds 10 MPa, it may be difficult to commercialize the all-solid-state battery according to the present application.

[0098] The restricting portion can be applied without particular limitation as long as it is generally used to provide a clamping pressure to the all-solid-state battery. For example, the restricting portion may have a plate-like shape.

[0099] In an embodiment, the anode includes an anode current collector 10 and an anode layer 20, and the anode layer 20 may be a composite anode layer configured to include an anode active material, a solid electrolyte, and a liquid additive. In addition, the anode layer 20 may be provided in a form for constructing an anode-free all-solid-state battery that does not include an anode active material. The cathode includes a cathode current collector 50 and a cathode layer 40, and the cathode layer 40 may be a composite cathode layer 40 configured to include a cathode active material, a solid electrolyte, and a liquid additive. In addition, the solid electrolyte layer 30 may be configured to include a solid electrolyte and a liquid additive.

[0100] In the all-solid-state battery according to the present application, at least one selected from the anode, the solid electrolyte layer 30, and the cathode may include a liquid additive such that the all-solid-state battery can operate at a clamping pressure lower than the several hundreds of MPa clamping pressure used for a conventional all-solid-state battery.

[0101] In an embodiment, a all-solid-state battery containing a liquid additive can be configured to operate under room temperature conditions. Thus, room temperature conditions do not necessarily mean about 25 °C, but can represent the temperature at which a product incorporating the all-solid-state battery is typically used or distributed. For example, when the all-solid-state battery is applied to an electric vehicle, the room temperature conditions can be from -10 °C to 50 °C.

[0102] The present application can be better understood through the following examples and comparative examples. However, these examples should not be construed as limiting the technical spirit of the present application.

[0103] Example 1-1 (1M LiFSI TMOF)

[0104] Approximately 60 μl of LiFSI as a lithium salt was added to trimethyl orthoformate (TMOF) as a solvent at a concentration of 1 M. Then, the mixture was stirred for a sufficient time to obtain a liquid additive in which the lithium salt was dissolved in the solvent.

[0105] Example 1-2 (2M LiFSI TMOF)

[0106] A liquid additive was prepared by the same method as in Example 1-1, except that LiFSI as a lithium salt was added at a concentration of 2 M.

[0107] Example 2 (1M LiFSI TEOF)

[0108] A liquid additive was prepared by the same method as in Example 1-1, except that triethyl orthoformate (TEOF) was used as a solvent.

[0109] Example 3 (1M LiFSI TPOF)

[0110] A liquid additive was prepared by the same method as in Example 1-1, except that tripropyl orthoformate (TPOF) was used as a solvent.

[0111] Example 4 (1M LiFSIDPOF)

[0112] A liquid additive was prepared by the same method as in Example 1-1, except that diethyl phenyl orthoformate (DPOF) was used as a solvent.

[0113] Example 5 (1M LiFSI TBOF)

[0114] A liquid additive was prepared by the same method as in Example 1-1, except that tributyl orthoformate (TBOF) was used as a solvent.

[0115] Comparative Example 1 (1M LiFSIDME)

[0116] A liquid additive was prepared by the same method as in Example 1, except that dimethyl ether (DME), which is commonly used in lithium-ion batteries, was used as a solvent.

[0117] Test Example 1 - Confirmation of the operability of the liquid additive

[0118] Symmetric cells and half-button cells were tested to confirm whether the liquid additives according to the present application can function as a liquid electrolyte for lithium-ion conduction.

[0119] In the symmetric cell, lithium metal was used for both electrodes, and the liquid additive according to Example 1-1 or Example 2 was used as the electrolyte. In the half-button cell, aluminum foil was used as the cathode current collector, NCM811-based active material was used as the cathode active material, lithium metal was used as the counter electrode, and the liquid additive according to Example 1-1, Example 2, or Comparative Example 1 was used as the electrolyte.

[0120] Reference Figure 2 (which shows the results of the symmetric cell test), both the TMOF solvent and the TEOF solvent exhibited a lower overvoltage, and Example 1-1 using the TMOF solvent exhibited a lower overvoltage than when using the TEOF solvent.

[0121] Reference Figure 3 , regarding the half-button cell test, both the TMOF solvent and the TEOF solvent exhibited a discharge capacity similar to that of DME (which is a conventional solvent for liquid electrolytes). In addition, Example 1-1 using the TMOF solvent showed a higher discharge capacity than Example 2 using the TEOF solvent.

[0122] Test Example 2 - Lithium ion conductivity of the solid electrolyte layer added with the liquid additive and the solid electrolyte layer added with the conventional liquid electrolyte Figure 4 to Figure 8

[0123] (1) A solid electrolyte layer containing a sulfide-based solid electrolyte and the liquid additive according to the present application was fabricated to confirm changes in the ionic conductivity or side reactivity between the sulfide-based solid electrolyte and the liquid additive. The fabrication method is described below.

[0124] 100 mg of Li6PS5Cl as a sulfide-based solid electrolyte and approximately 10 μl (about 6.67 wt% in terms of weight) of the liquid additive according to Example 1-1 were placed in a Thinky mixer (THINKY, ARE-500).

[0125] After thoroughly mixing the sulfide-based solid electrolyte and the liquid additive, the obtained mixture was immediately placed in a pellet die and pressed to form a cylindrical solid electrolyte layer. In addition, after mixing the sulfide-based solid electrolyte and the liquid additive, the mixture was left (overnight) for about 12 hours to allow the solid electrolyte to react with the liquid additive, and then the solid electrolyte layer was fabricated by the same method. The same process was carried out for the liquid additives according to Examples 2 to 5, and two solid electrolyte layers were fabricated for each example.

[0126] (2) The impedance of a total of 10 solid electrolyte layer samples thus fabricated was measured by the two-probe method using an impedance analyzer (Solartron 1400A / 1455A). The frequency range was from 0.1 Hz to 1 MHz, and the amplitude voltage was 10 mV. The results are shown in Figure 4 to Figure 8 .

[0127] Reference Figure 4 to Figure 8 , in the same example, there was almost no difference in the resistance between the solid electrolyte layer fabricated immediately after mixing the solid electrolyte and the liquid additive and the solid electrolyte layer fabricated by placing it for 12 hours after mixing. This is considered to be due to the low reactivity of the liquid additive according to the present application with the sulfide-based solid electrolyte.

[0128] Furthermore, the resistance change of Example 1-1 using the TMOF solvent was the lowest among the examples. This is considered because the molecular weight of TMOF is lower than that of other solvents (TEOF, TPOF, DPOF, and TBOF), so its viscosity is lower, making it easier to fill the voids inside the solid electrolyte layer.

[0129] (3) A solid electrolyte layer was fabricated by mixing a sulfide-based solid electrolyte and the liquid additive according to Example 1-1 at the weight ratios shown in Table 1 below. Then, the impedance was measured using an impedance analyzer under the Figure 9 same conditions, and the results are shown in Figure 9 . In addition, as a control, the impedance of a solid electrolyte layer fabricated using Li6PS5Cl without adding a liquid additive was measured, and the results are shown in Figure 4 to Figure 8 .

[0130] Meanwhile, a solid electrolyte layer was fabricated by mixing a sulfide-based solid electrolyte and a liquid additive or a liquid electrolyte using the DME solvent according to Comparative Example 1 at the weight ratios shown in Table 1 below. Then, the impedance was measured using an impedance analyzer under the Figure 10 same conditions, and the results are shown in Figure 10 . In addition, as a control, the impedance of a solid electrolyte layer fabricated using Li6PS5Cl without adding a liquid additive was measured, and the results are shown in Figure 9 .

[0131] [Table 1]

[0132]

[0133]

[0134] (4) Reference Figure 10The solid electrolyte layer containing the liquid additive according to Example 1-1 had improved ion conductivity (lowered impedance) at all weight ratios compared to the solid electrolyte alone. This is believed to be because the effect of improving lithium ion conductivity due to the addition of the liquid additive was greater than the effect of reducing lithium ion conductivity due to the side reaction between the liquid additive and the sulfide-based solid electrolyte.

[0135] refer to Figure 9 , different from Figure 9 When the solid electrolyte and the liquid additive according to Comparative Example 1 were mixed at a ratio of 7:1 or 9:1, the ion conductivity decreased (impedance increased) compared to LPSCl as a control. This is believed to be because the effect of reducing lithium ion conductivity due to the side reaction between DME used as a solvent and the sulfide-based solid electrolyte was greater than the effect of increasing lithium ion conductivity due to the addition of the liquid additive according to Comparative Example 1.

[0136] In addition, when the liquid additive was added in a larger amount (at weight ratios of 4:1, 3:1, and 2:1), the effect of improving lithium ion conductivity due to the liquid additive was greater than the effect of reducing lithium ion conductivity due to the side reaction with the sulfide-based solid electrolyte.

[0137] Test Example 3 - Confirmation of the critical current density through the lithium symmetric battery

[0138] (1) Li6PS5Cl as a sulfide-based solid electrolyte and the liquid additive (2MLiFSI TMOF) according to Example 1-2 were added to a Thinky mixer (THINKY, ARE-500) and mixed. After the sulfide-based solid electrolyte and the liquid additive were thoroughly mixed, the resulting mixture was immediately placed in a pellet mold and pressed to form a cylindrical solid electrolyte layer. Therefore, the amount of the liquid additive according to Example 1-2 in the solid electrolyte layer was approximately 20% by weight.

[0139] A symmetrical cell (#1) was then fabricated using the solid electrolyte layer. Lithium metal was used for both electrodes, and a symmetrical cell (#2) with the same composition was also fabricated to ensure reproducibility of the test results. Furthermore, as a control, a solid electrolyte layer containing Li6PS5Cl as a sulfide-based solid electrolyte without the liquid additive according to the present application and a symmetrical cell using the solid electrolyte layer were fabricated.

[0140] In order to confirm the improvement effect of the current density robustness of the battery containing the liquid additive according to the present application and the improvement effect of the operability under the conditions of room temperature and low clamping pressure, symmetrical batteries #1 and #2 and a control symmetrical battery were tested at increasing current density under the conditions of 25°C and 2 MPa clamping pressure. The results are shown in Figure 11 andFigure 12 In addition, in order to apply a clamping pressure to the symmetric cell, restricting portions are arranged at the top and bottom of the symmetric cell.

[0141] Reference Figure 11 , the critical current density of the symmetric cell containing the liquid additive (Examples 1-2) according to the present application was determined to be approximately 1.2 mA / cm 2 . In contrast, the critical current density of the symmetric cell without the liquid additive was determined to be approximately 0.9 mA / cm 2 .

[0142] Based on these results, under the conditions of room temperature (25 °C) and low clamping pressure (2 MPa), the symmetric cell containing the liquid additive according to the present application has a higher critical current density than the symmetric cell without the liquid additive. This is considered to be because the symmetric cell of the present application can conduct lithium ions not only through the solid electrolyte but also through the liquid additive. This dual path maintains the lithium ion conductivity despite the generation of voids during charging and discharging.

[0143] According to the present application, the liquid additive contains a lithium salt and an orthoester solvent (preferably an orthoformate solvent) capable of solvating the lithium salt, thereby imparting high ionic conductivity to the solid electrolyte layer, composite anode layer, or composite cathode layer containing the solid electrolyte.

[0144] In addition, since a solvent with a low dipole moment is used, side reactions with the solid electrolyte (especially sulfide-based solid electrolytes) can be reduced. This prevents a decrease in lithium ion conductivity due to the destruction of the crystallinity of the solid electrolyte.

[0145] Therefore, the all-solid-state battery can operate stably under the conditions of room temperature and low clamping pressure.

[0146] The effects of the present application are not limited to the above effects. It should be understood that the effects of the present application include all effects that can be inferred from the description of the present application in the specification.

[0147] Although the embodiments of the present application have been described above, those skilled in the art will understand that various modifications and changes are possible by changing, deleting, or adding components without departing from the scope and spirit of the present application as described in the appended claims, which will also be considered to be included within the scope of the present application.

Claims

1. A liquid additive for a solid electrolyte, the liquid additive comprising: a lithium salt; and a solvent comprising an orthoester compound.

2. The liquid additive for a solid electrolyte according to claim 1, wherein, The orthoester compound has a structure of RC(OR’)3, where R is H or an optionally substituted C1-C12 alkyl group, and each R’ is the same or different optionally substituted C1-C12 alkyl group.

3. The liquid additive for a solid electrolyte according to claim 1, wherein, The solvent can solvate the lithium salt and is compatible with the solid electrolyte.

4. The liquid additive for a solid electrolyte according to claim 1, wherein, The solvent includes one selected from trimethyl orthoformate, triethyl orthoformate, tripropyl orthoformate, tributyl orthoformate, diethylphenyl orthoformate, and combinations thereof.

5. The liquid additive for a solid electrolyte according to claim 1, wherein, The solvent includes trimethyl orthoformate.

6. The liquid additive for a solid electrolyte according to claim 1, wherein, The dipole moment of the solvent is less than 2.00 Debye.

7. The liquid additive for a solid electrolyte according to claim 1, wherein, The lithium salt includes one selected from LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 , LiAlCl4, LiAlO4, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2, LiN(SO2CF2CF3)2, LiN(SO2CF3)2, and combinations thereof.

8. The liquid additive for a solid electrolyte according to claim 1, wherein, The concentration of the lithium salt is from 0.1 M to 10 M.

9. A solid electrolyte layer, the solid electrolyte layer comprising: a solid electrolyte; and the liquid additive according to claim 1.

10. The solid electrolyte layer according to claim 9, wherein, The solid electrolyte includes a sulfide-based solid electrolyte.

11. The solid electrolyte layer according to claim 9, wherein, The solid electrolyte layer contains 0.1 wt% to 20 wt% of the liquid additive.

12. A composite cathode layer, the composite cathode layer comprising: a cathode active material; a solid electrolyte; and the liquid additive according to claim 1.

13. The composite cathode layer according to claim 12, wherein, The solid electrolyte includes a sulfide-based solid electrolyte.

14. The composite cathode layer according to claim 13, wherein, The solid electrolyte layer contains 0.1 wt% to 20 wt% of the liquid additive.

15. A composite anode layer, the composite anode layer comprising: an anode active material; a solid electrolyte; and the liquid additive according to claim 1.

16. The composite anode layer according to claim 15, wherein, The solid electrolyte includes a sulfide-based solid electrolyte.

17. A all-solid-state battery, the all-solid-state battery comprising: an anode, the anode including an anode current collector and an anode layer; a cathode, the cathode including a cathode current collector and a cathode layer; and the solid electrolyte layer according to claim 9, the solid electrolyte layer being disposed between the anode and the cathode.

18. The all-solid-state battery according to claim 17, the all-solid-state battery further comprising a restricting portion disposed outside the anode, the solid electrolyte layer, and the cathode, and configured to squeeze the anode, the solid electrolyte layer, and the cathode along the stacking direction, Among them, the clamping pressure applied by the restricting portion to the anode, the solid electrolyte layer, and the cathode is from 0.1 MPa to 10 MPa.

19. The all-solid-state battery according to claim 17, wherein, The all-solid-state battery is configured to operate under room temperature conditions.

20. A vehicle, the vehicle including the all-solid-state battery according to claim 17.

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