Solid electrolyte, method for preparing same, and lithium secondary battery comprising same

Abstract

The present invention relates to a solid electrolyte, a method for preparing same, and a lithium secondary battery comprising same. More specifically, the present invention relates to a sulfide-based solid electrolyte comprising at least one of Li2SO4 or P2O5, a method for preparing same, and a lithium secondary battery comprising same.

Description

Solid electrolyte, method for producing same, and lithium secondary battery comprising same

[0001] The present invention relates to a solid electrolyte, a method for producing the same, and a lithium secondary battery comprising the same. Specifically, the present invention relates to a sulfide-based solid electrolyte comprising at least one of Li2SO4 and P2O5, a method for producing the same, and a lithium secondary battery comprising the same.

[0002] With the recent surge in demand for small power-driven devices such as IT mobile devices, electric bicycles, and compact electric vehicles, interest in high-capacity batteries is growing. Furthermore, improving the safety and energy density of these high-capacity batteries is emerging as key issues. Consequently, interest in all-solid-state batteries is growing to improve the safety of existing secondary batteries and increase their energy density, leading to active research into them. All-solid-state batteries replace the liquid electrolytes used in conventional lithium secondary batteries with solid electrolytes. Because they do not use flammable solvents, they eliminate the risk of ignition or explosion due to reactions such as the decomposition of conventional electrolytes, thereby improving battery safety. Furthermore, the ability to use lithium metal or lithium alloys as anode materials improves the energy density relative to the mass and volume of the battery. Inorganic solid electrolytes are typically used in these all-solid-state batteries, and solid electrolytes with compositions such as Li6PS5Cl with an argyrodite structure are being studied extensively. However, sulfide-based solid electrolytes have the problem of being difficult to handle in the general atmosphere due to side reactions with moisture, and improving this has become an important task.

[0003] The technical problem to be solved by the present invention is to provide a solid electrolyte with improved moisture stability and initial capacity.

[0004] Another technical problem to be solved by the present invention is to provide a method for manufacturing a solid electrolyte having the aforementioned advantages.

[0005] Another technical problem to be solved by the present invention is to provide a lithium secondary battery including a solid electrolyte having the aforementioned advantages.

[0006] A solid electrolyte according to one embodiment of the present invention includes at least one of Li2SO4 and P2O5, and can be expressed by the following chemical formula 1.

[0007] [Chemical Formula 1] Li 7-5a-x+ax P 1-a+2b S 6-5a-x+ax O 4a+5b Cl x-ax (However, 1 ≤ x ≤ 2, 0 < a ≤ 0.2, 0 ≤ b ≤ 0.1.)

[0008] A method for manufacturing a solid electrolyte according to another embodiment includes the steps of preparing a lithium raw material, a sulfur raw material, a halogen raw material, and P2O5 as raw materials; mixing the raw materials; forming a pellet by pressurizing the mixture; and heat-treating the pellet; and may include forming a solid electrolyte represented by the following chemical formula 1.

[0009] [Chemical Formula 1] Li 7-5a-x+ax P 1-a+2b S 6-5a-x+ax O 4a+5b Cl x-ax (However, 1 ≤ x ≤ 2, 0 < a ≤ 0.2, 0 ≤ b ≤ 0.1.)

[0010] According to another embodiment of the present invention, a lithium secondary battery comprises: a cathode including a cathode active material;

[0011] A cathode including a cathode active material; and a solid electrolyte positioned between the cathode and the anode; wherein the solid electrolyte is Li2SO -4 And it includes at least one of P2O5, and can be expressed by the following chemical formula 1.

[0012] [Chemical Formula 1] Li 7-5a-x+ax P 1-a+2b S 6-5a-x+ax O 4a+5b Cl x-ax (However, 1 ≤ x ≤ 2, 0 < a ≤ 0.2, 0 ≤ b ≤ 0.1.)

[0013] A solid electrolyte according to one embodiment of the present invention can provide a solid electrolyte having improved moisture stability and initial capacity compared to existing sulfide-based solid electrolytes by including at least one of Li2SO4 and P2O5.

[0014] According to another embodiment of the present invention, a method for producing a solid electrolyte can provide a method for producing a solid electrolyte having the above-described advantages.

[0015] According to another embodiment of the present invention, a lithium secondary battery can provide a lithium secondary battery including a solid electrolyte having the above-described advantages.

[0016] Figure 1 shows the results of XRD analysis of a solid electrolyte according to an embodiment of the present invention.

[0017] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0018] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising," as used herein, specifies particular features, regions, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0019] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0020] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0021] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0022] Hereinafter, a solid electrolyte according to one embodiment of the present invention will be described.

[0023] A solid electrolyte according to one embodiment includes at least one of Li2SO4 and P2O5, and can be represented by the following chemical formula 1.

[0024] [Chemical Formula 1] Li 7-5a-x+ax P 1-a+2b S 6-5a-x+ax O 4a+5b Clx-ax (However, 1 ≤ x ≤ 2, 0 < a ≤ 0.2, 0 ≤ b ≤ 0.1.)

[0025] The above a may refer to the content of Li2SO4 included in the solid electrolyte, and the above b may refer to the content of P2O5 included in the solid electrolyte.

[0026] According to one embodiment, the solid electrolyte has an X-ray diffraction (XRD) value of 1.02 A / I B <1.11 can be satisfied.

[0027] (However, I A represents the XRD peak intensity at 2θ=15.5±1.0°, and I B ) represents the XRD peak intensity at 2θ=18.0±1.0°.

[0028] The ratio of the above peak intensities I A / I B When the above-mentioned range is included, the water stability and initial capacity of the solid electrolyte can be improved. On the other hand, the ratio of the peak intensity I A / I B If the range described above is exceeded, there may be problems with moisture stability, discharge capacity, and ionic conductivity deterioration.

[0029] In a solid electrolyte according to one embodiment, the content of Li2SO4 may be in the range of 3 to 5 mol% based on 100 mol% of the total amount of the solid electrolyte.

[0030] ​When the content of the Li2SO4 is within the above-mentioned range, the moisture stability and initial capacity of the sulfide-based solid electrolyte can be improved. On the other hand, when the content of the Li2SO4 exceeds the upper limit of the above-mentioned range, the specific gravity of the impurity Li2SO4 increases, which may rather reduce the ionic conductivity and discharge capacity of the solid electrolyte. In addition, when the specific gravity of the Li2SO4 is high, the Li2SO4 may be separated from the solid electrolyte structure, which may lower the stability of the solid electrolyte. In addition, when the content of the Li2SO4 is less than the lower limit of the above-mentioned range, the moisture stability of the solid electrolyte may be low.

[0031] In a solid electrolyte according to one embodiment, the content of P2O5 may be in the range of 3 to 5 mol% based on 100 mol% of the total amount of the solid electrolyte.

[0032] When the content of P2O5 is within the aforementioned range, the moisture stability and initial capacity of the sulfide-based solid electrolyte can be improved. On the other hand, when the content of P2O5 exceeds the upper limit of the aforementioned range, the ionic conductivity and discharge capacity of the solid electrolyte may be reduced. The moisture stability may also be reduced.

[0033] Hereinafter, a method for manufacturing a solid electrolyte according to another embodiment of the present invention will be described.

[0034] A method for manufacturing a solid electrolyte according to another embodiment includes the steps of preparing a lithium raw material, a sulfur raw material, a halogen raw material, and P2O5 as raw materials; mixing the raw materials; forming a pellet by pressurizing the mixture; and heat-treating the pellet; and may include forming a solid electrolyte represented by the following chemical formula 1.

[0035] [Chemical Formula 1] Li 7-5a-x+ax P 1-a+2b S 6-5a-x+ax O 4a+5b Clx-ax (However, 1 ≤ x ≤ 2, 0 < a ≤ 0.2, 0 ≤ b ≤ 0.1.)

[0036] In a method for manufacturing a solid electrolyte according to another embodiment, the lithium raw material may include Li2S containing Li2SO4 as an impurity.

[0037] In the raw material preparation step of the method for manufacturing a solid electrolyte according to another embodiment, it may include additionally mixing Li2SO4.

[0038] In a method for manufacturing a solid electrolyte according to another embodiment, the additionally mixed Li2SO4 may be added in a range of 3 to 5 mol% based on 100 mol% of the total amount of raw materials.

[0039] When the amount of Li2SO4 added is within the above-mentioned range, the moisture stability and initial capacity of the sulfide-based solid electrolyte can be improved. On the other hand, when the amount of Li2SO4 added exceeds the upper limit of the above-mentioned range, the specific gravity of Li2SO4 as an impurity increases, which may rather reduce the ionic conductivity and discharge capacity of the solid electrolyte. In addition, when the specific gravity of Li2SO4 is high, Li2SO4 may be separated from the solid electrolyte structure, which may lower the stability of the solid electrolyte. In addition, when the amount of Li2SO4 added is less than the lower limit of the above-mentioned range, the moisture stability of the solid electrolyte may be low.

[0040] In the raw material preparation step of the method for manufacturing a solid electrolyte according to another embodiment, the P2O5 may be added in a range of 3 to 5 mol% based on 100 mol% of the total amount of the raw material.

[0041] When the amount of P2O5 added is within the aforementioned range, the moisture stability and initial capacity of the sulfide-based solid electrolyte can be improved. On the other hand, when the amount of P2O5 added exceeds the upper limit of the aforementioned range, the ionic conductivity and discharge capacity of the solid electrolyte may be reduced. The moisture stability may also be reduced.

[0042] In a method for manufacturing a solid electrolyte according to another embodiment, when X-ray diffraction analysis (XRD) was performed on the solid electrolyte, 1.02 A / I B <1.11 may be included. (However, I A represents the XRD peak intensity at 2θ=15.5±1.0°, and I B ) represents the XRD peak intensity at 2θ=18.0±1.0°.

[0043] The ratio of the above peak intensities I A / I B When the above-mentioned range is included, the water stability and initial capacity of the solid electrolyte can be improved. On the other hand, the ratio of the peak intensity I A / I B If the range described above is exceeded, there may be problems with moisture stability, discharge capacity, and ionic conductivity deterioration.

[0044] Hereinafter, a lithium secondary battery according to another embodiment of the present invention will be described.

[0045] According to another embodiment, a lithium secondary battery comprises: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and a solid electrolyte positioned between the positive electrode and the negative electrode; wherein the solid electrolyte is Li2SO -4 And it may include at least one of P2O5 and may include one represented by the following chemical formula 1.

[0046] [Chemical Formula 1] Li 7-5a-x+ax P 1-a+2b S 6-5a-x+ax O​4a+5b Cl x-ax (However, 1 ≤ x ≤ 2, 0 < a ≤ 0.2, 0 ≤ b ≤ 0.1.)

[0047] In another embodiment, in a lithium secondary battery, when X-ray diffraction analysis (XRD) was performed on the solid electrolyte, 1.02 A / I B <1.11 may be included. (However, I A represents the XRD peak intensity at 2θ=15.5±1.0°, and I B ) represents the XRD peak intensity at 2θ=18.0±1.0°.

[0048] The ratio of the above peak intensities I A / I B When the above-mentioned range is included, the water stability and initial capacity of the solid electrolyte can be improved. On the other hand, the ratio of the peak intensity I A / I B If the range described above is exceeded, there may be problems with moisture stability, discharge capacity, and ionic conductivity deterioration.

[0049]

[0050] Hereinafter, examples, comparative examples, and experimental examples of the present invention will be described. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to these examples. Furthermore, various modifications and variations are possible within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and such modifications may also fall within the scope of the present invention.

[0051] <Comparative Example 1> Li -6 Preparation of PS5Cl (without Li2SO4 and P2O5)

[0052] Li above -6 PS5Cl was synthesized via dry milling.

[0053] ​After mixing the raw materials in the stoichiometric ratio, they were mixed at a speed of 300 rpm for about 8 hours using a planetary mill. Afterwards, a pressure of 300 MPa was applied to form pellets, and the pellets were heat-treated at a temperature of 550°C in an Ar atmosphere to obtain Li -6 PS5Cl was manufactured.

[0054] <Example 1> Li 6.06 PS 5.03 O 0.12 Preparation of Cl (Li2SO4:3mol%; P2O5:0mol%)

[0055] As a raw material, mix in the stoichiometric ratio ([chemical formula 1] Li 7-5a-x+ax P 1-a+2b S 6-5a-x+ax O 4a+5b Cl x-ax After applying x = 1, a = 0.03, b = 0), the mixture was mixed at a speed of 300 rpm for about 8 hours using a planetary mill. Afterwards, a pressure of 300 MPa was applied to form pellets, and the pellets were heat-treated at a temperature of 550°C in an Ar atmosphere to obtain Li 6.06 PS 5.03 O 0.12 Cl was manufactured.

[0056] <Example 2> Li 5.88 PS 4.88 O 0.2 Cl 0.97 Preparation of (Li2SO4:3mol%; P2O5:1.5mol%)

[0057] As a raw material, mix in the stoichiometric ratio ([chemical formula 1] Li 7-5a-x+ax P 1-a+2b S 6-5a-x+ax O 4a+5b Cl x-ax After applying x = 1, a = 0.03, b = 0.015), the mixture was mixed at a speed of 300 rpm for about 8 hours using a planetary mill. Afterwards, a pressure of 300 MPa was applied to form pellets, and the pellets were heat-treated at a temperature of 550°C in an Ar atmosphere to obtain Li5.88 PS 4.88 O 0.2 Cl 0.97 was manufactured.

[0058] <Example 3> Li 5.71 PS 4.74 O 0.26 Cl 0.94 Preparation of (Li2SO4:3mol%; P2O5:3mol%)

[0059] As a raw material, mix in the stoichiometric ratio ([chemical formula 1] Li 7-5a-x+ax P 1-a+2b S 6-5a-x+ax O 4a+5b Cl x-ax After applying x = 1, a = 0.03, b = 0.03), the mixture was mixed at a speed of 300 rpm for about 8 hours using a planetary mill. Afterwards, a pressure of 300 MPa was applied to form pellets, and the pellets were heat-treated at a temperature of 550°C in an Ar atmosphere to obtain Li 5.71 PS 4.74 O 0.26 Cl 0.94 was manufactured.

[0060] <Comparative Example 2> Li 5.39 PS 4.48 O 0.39 Cl 0.89 Preparation of (Li2SO4:3mol%; P2O5:6mol%)

[0061] As a raw material, mix in the stoichiometric ratio ([chemical formula 1] Li 7-5a-x+ax P 1-a+2b S 6-5a-x+ax O 4a+5b Cl x-ax After applying x = 1, a = 0.03, b = 0.06), the mixture was mixed at a speed of 300 rpm for about 8 hours using a planetary mill. Afterwards, a pressure of 300 MPa was applied to form pellets, and the pellets were heat-treated at a temperature of 550°C in an Ar atmosphere to obtain Li 5.39 PS 4.48 O 0.39 Cl 0.89 was manufactured.

[0062]

[0063] <Experimental Example 1> Evaluation of ionic conductivity at 30℃ and 0.1C

[0064] Electrochemical evaluations were conducted on the solid electrolytes of Comparative Examples 1 and 2 and Examples 1 to 3 using a pressure cell. The electrolyte was added and densified to 300 MPa. Thereafter, the cell was clamped using a SUS electrode at a pressure of 70 MPa, and the impedance was measured by applying 10 mV at 25 degrees.

[0065] <Experimental Example 2> Moisture Stability Evaluation

[0066] After applying 0.5 g of solid electrolyte to the watch face, it was exposed to a dry room with a dew point of -45°C for 8 hours, and the ionic conductivity before and after exposure was compared and evaluated.

[0067] <Experimental Example 3> Electrochemical Characteristics Evaluation

[0068] After fabricating solid electrolyte pellets, the positive electrode was bonded to the top and the counter electrode, In, to the bottom, and the density was increased to 500 MPa. After assembling the all-solid-state battery cell, a formation cycle was performed at 0.1 C in a 30-degree chamber, and the life characteristics were evaluated at 0.5 C.

[0069] <Experimental Example 4> X-ray diffraction analysis (XRD)

[0070] Figure 1 shows the results of XRD analysis of a solid electrolyte according to an embodiment of the present invention.

[0071] According to the above drawing 1 and the following table 1, I confirmed in examples 1 to 3 A / I B (I A is the XRD peak intensity at 2θ=15.5°, and I B refers to the XRD peak intensity at 2θ=18.0°) is I of Comparative Example 1 A / I B Higher than, I of Comparative Example 2 A / I B It showed a lower value than .

[0072] That is, the XRD peak intensity ratio I A / I B When the value is within the range of 1.02 to 1.11, it can be confirmed that the discharge capacity is improved and the moisture stability is also generally improved.

[0073] ClassificationLi2SO4content(mol%)P2O5content(mol%)Sulphide-based solid electrolyte(LSPCl) compositionIonic conductivity(mS / cm)Discharge capacity(mAh / g)Moisture stability(%)XRD peak intensity ratioI A / I B Comparative Example 100Li6PS5Cl2.70203.0771.02Example 130Li 6.06 PS 5.03 O 0.12 Cl2.78204.6801.03Example 231.5Li 5.88 PS 4.88 O 0.2 Cl 0.97 2.65206.5821.06 Example 333Li 5.71 PS 4.74 O 0.26 Cl 0.94 2.66204.8761.09Comparative Example 236Li 5.39 PS 4.48 O 0.39 Cl 0.89 2.26201.1711.11

Claims

1. Li 2 SO 4 and P 2 O 5 Contains at least one of the following: Expressed by the following chemical formula 1, Solid electrolyte. [Chemical Formula 1] Li 7-5a-x+ax P 1-a+2b S 6-5a-x+ax O 4a+5b Cl x-ax (But, 1 ≤ x ≤ 2, 0 < a ≤ 0.2, 0 ≤ b ≤ 0.1.) 2. In paragraph 1, When X-ray diffraction analysis (XRD) was performed on the above solid electrolyte, 1.02 A / I B <1.11 satisfies,​ Solid electrolyte. (But, I A represents the XRD peak intensity at 2θ=15.5±1.0°, and I B ) represents the XRD peak intensity at 2θ=18.0±1.0°.

3. In paragraph 1, Li above 2 SO 4 The content is in the range of 3 to 5 mol% based on 100 mol% of the total amount of the solid electrolyte. Solid electrolyte.

4. In paragraph 1, Above P 2 O 5 The content is in the range of 3 to 5 mol% based on 100 mol% of the total amount of the solid electrolyte. Solid electrolyte.

5. Lithium raw materials, sulfur raw materials, halogen raw materials and P 2 O 5 A step for preparing raw materials; A step of mixing the above raw materials; A step of forming the mixture by pressurizing to form pellets; and A step of heat treating the above pellets; Forming a solid electrolyte represented by the following chemical formula 1, Method for manufacturing a solid electrolyte. [Chemical Formula 1] Li 7-5a-x+ax P 1-a+2b S 6-5a-x+ax O 4a+5b Cl x-ax (But, 1 ≤ x ≤ 2, 0 < a ≤ 0.2, 0 ≤ b ≤ 0.1.) 6. In paragraph 5, The above lithium raw material is Li 2 SO 4 Li containing as an impurity 2 S person, Method for manufacturing a solid electrolyte.

7. In paragraph 5, In the above raw material preparation step, Li 2 SO 4 Including further mixing of Method for manufacturing a solid electrolyte.

8. In paragraph 7, Li further mixed with the above 2 SO 4 It is added in the range of 3 to 5 mol% based on 100 mol% of the total amount of raw materials. Method for manufacturing a solid electrolyte.

9. In paragraph 5, In the raw material preparation stage, the above P 2 O 5 It is added in the range of 3 to 5 mol% based on 100 mol% of the total amount of raw materials. Method for manufacturing a solid electrolyte.

10. In paragraph 5, When X-ray diffraction analysis (XRD) was performed on the above solid electrolyte, 1.02 A / I B <1.11 is satisfied,​ Method for manufacturing a solid electrolyte. (But, I A represents the XRD peak intensity at 2θ=15.5±1.0°, and I B ) represents the XRD peak intensity at 2θ=18.0±1.0°.

11. A cathode comprising a cathode active material; A negative electrode comprising a negative active material; and A solid electrolyte positioned between the positive and negative electrodes; The above solid electrolyte is Li 2 SO -4 and P 2 O 5 Containing at least one of the following and represented by the following chemical formula 1: Lithium secondary battery. [Chemical Formula 1] Li 7-5a-x+ax P 1-a+2b S 6-5a-x+ax O 4a+5b Cl x-ax (But, 1 ≤ x ≤ 2, 0 < a ≤ 0.2, 0 ≤ b ≤ 0.1.) 12. In paragraph 11, When X-ray diffraction analysis (XRD) was performed on the above solid electrolyte, 1.02 A / I B <1.11 is satisfied,​ Lithium secondary battery. (But, I A represents the XRD peak intensity at 2θ=15.5±1.0°, and I B represents the XRD peak intensity at 2θ=18.0±1.0°.

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