Rare earth oxyhalide solid electrolyte and preparation method and application thereof

Abstract

The invention relates to a rare earth oxyhalide solid electrolyte and a preparation method and application thereof, the structure of the rare earth oxyhalide solid electrolyte is an amorphous structure, and the chemical general formula is Li < 3-y > MOX < 4-y >, wherein M comprises any one or a combination of at least two of Sc, Y or lanthanide elements; x comprises any one or a combination of at least two of F, Cl, Br and I; 0 < = y < = 1. The amorphous rare earth oxyhalide solid electrolyte provided by the invention has relatively high room-temperature ionic conductivity, low electronic conductivity, excellent electrochemical stability and good moisture resistance, and has a relatively great application prospect in lithium batteries.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a solid electrolyte, and a preparation method and application thereof. Background Art

[0002] Traditional liquid lithium-ion batteries are about to reach their energy density limit and there are great safety risks. Therefore, there is an urgent need to develop a new next-generation battery system that has both high energy density and high safety. Solid electrolytes exhibit high intrinsic safety due to their non-flammable / difficult to burn characteristics. In addition, solid electrolytes are expected to be directly compatible with lithium metal negative electrodes, which will greatly increase the energy density of the assembled battery. Therefore, solid-state lithium metal batteries are considered to be the most promising next-generation energy storage technology.

[0003] Solid electrolyte is one of the core components of solid-state batteries, and its physical and chemical properties are crucial to the comprehensive performance of the battery. At present, solid electrolytes mainly include inorganic solid electrolytes, organic polymer solid electrolytes and organic-inorganic composite solid electrolytes. Among them, inorganic solid electrolytes include sulfide solid electrolytes, oxide solid electrolytes and halide solid electrolytes. They usually have high room temperature ionic conductivity, so they have attracted much attention from researchers. Halide solid electrolytes have become a research hotspot in the field of solid-state batteries due to their outstanding advantages such as high room temperature ionic conductivity, compatibility with high voltage positive electrodes, and good deformability.

[0004] Up to now, the methods used to prepare halide solid electrolytes are mainly high-energy ball milling and wet chemical methods. When prepared by high-energy ball milling, anhydrous halide metal salts are usually required as raw materials, which will significantly increase the preparation cost and restrict the large-scale application of halide solid electrolytes. Although the wet chemical method can use hydrated halide metal salts, the easy hydrolysis of metal ions causes the final product to usually contain impurities. In addition, the wet chemical preparation process is relatively complicated, and the synthesis process is easily affected by many factors such as temperature, atmosphere, and atmospheric pressure. Strict control of these factors will significantly increase production costs. In addition, halide solid electrolytes still have bottleneck problems such as poor humidity stability and poor electrochemical stability, which still cannot meet the needs of actual applications.

[0005] Therefore, there is an urgent need to develop a new type of halide solid electrolyte material with simple preparation methods, low cost, easy large-scale production and excellent chemical and electrochemical stability. Summary of the invention

[0006] In order to solve the above technical problems, the purpose of the present invention is to provide a rare earth oxyhalide solid electrolyte and its preparation method and application. The amorphous rare earth oxyhalide solid electrolyte provided by the present invention has high room temperature ionic conductivity, low electronic conductivity, excellent electrochemical stability and good moisture resistance, and has great application prospects in lithium batteries.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a rare earth oxyhalide solid electrolyte, wherein the rare earth oxyhalide solid electrolyte has an amorphous structure and a chemical formula of Li 3-y MOX 4-y ;

[0009] Wherein: M includes any one of Sc, Y or lanthanide elements or a combination of at least two; X includes any one of F, Cl, Br, I or a combination of at least two; 0≤y≤1, for example, it can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0010] The amorphous rare earth oxyhalide solid electrolyte provided by the present invention has high room temperature ionic conductivity, low electronic conductivity, excellent electrochemical stability and good moisture resistance, wherein the introduction of the O element can reduce the electronic conductivity of the material and improve the anti-oxidation ability of the material.

[0011] Preferably, 0.5≤y≤1.

[0012] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0013] In a second aspect, the present invention provides a method for preparing the rare earth oxyhalide solid electrolyte as described in the first aspect, the preparation method comprising the following steps:

[0014] The hydrated rare earth halide is subjected to heat treatment to obtain a MOX precursor; the obtained MOX precursor is mixed with LiX, and the rare earth halide oxide solid electrolyte is obtained after ball milling.

[0015] The present invention uses hydrated rare earth halide as a raw material, which is decomposed after heat treatment to generate a MOX precursor, which can provide a rare earth metal source and an oxygen source simultaneously during the reaction process, greatly reducing the preparation cost; then, ball milling is used to obtain a rare earth oxyhalide solid electrolyte without sintering. The preparation method is simple and low-cost, matches existing production process equipment, and is suitable for large-scale production applications.

[0016] Preferably, the temperature of the heat treatment is 300-800°C, for example, it can be 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 70°C, 750°C or 800°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0017] Preferably, the heat treatment time is 60-600 min, for example, it can be 60 min, 100 min, 150 min, 200 min, 250 min, 300 min, 350 min, 400 min, 450 min, 500 min, 550 min or 600 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0018] The purpose of heat treatment of hydrated rare earth halide in the present invention is to obtain MOX precursor. The heat treatment temperature affects the composition of the obtained precursor. If the heat treatment temperature is too low, the transformation of hydrated rare earth halide to rare earth element oxyhalide cannot be achieved.

[0019] Preferably, the molar ratio of the MOX precursor to LiX is 1:(2-3), for example, 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, 1:2.6, 1:2.7, 1:2.8, 1:2.9 or 1:3, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0020] In the present invention, the molar ratio of MOX precursor to LiX directly affects the chemical composition of the rare earth oxyhalide solid electrolyte obtained. When the content of MOX precursor is too much, that is, the content of rare earth elements is too much, an amorphous MOX impurity phase will be present in the product, which will hinder the Li + When the molar ratio of LiX is too high, that is, the halogen content is too high, or the molar ratio of metallic lithium is too high, the product will contain LiX crystal phase, which is not conducive to the transport of Li + transmission.

[0021] Preferably, the ball-to-material mass ratio of the ball mill is (5-30):1, for example, it can be 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 21:1, 22:1, 23:1, 24:1, 25:1, 26:1, 27:1, 28:1, 29:1 or 30:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0022] Preferably, the rotation speed of the ball mill is 100-400 rpm, for example, it can be 100 rpm, 150 rpm, 200 rpm, 250 rpm, 300 rpm, 350 rpm or 400 rpm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0023] Preferably, the ball milling time is 12-60 h, for example, it can be 12 h, 14 h, 16 h, 18 h, 20 h, 24 h, 28 h, 30 h, 32 h, 34 h, 36 h, 38 h, 40 h, 42 h, 45 h, 48 h, 50 h, 52 h, 54 h, 56 h, 58 h or 60 h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] The rotation speed and time of the ball milling in the present invention jointly affect the phase structure and chemical composition of the rare earth oxyhalide solid electrolyte finally obtained. If the ball milling time is too long, the ionic conductivity of the obtained solid electrolyte will be reduced; if the ball milling time is too short, the raw material reaction will not be sufficient and impurities will exist in the product.

[0025] As a preferred technical solution of the preparation method of the present invention, the preparation method comprises the following steps:

[0026] The hydrated rare earth halide is heat treated at 300-800°C for 60-600min to obtain a MOX precursor; the obtained MOX precursor and LiX are mixed in a molar ratio of 1:(2-3), and the rare earth halide solid electrolyte is obtained after mechanical ball milling for 12-60h at a ball-to-material ratio of (5-30):1 and a rotation speed of 100-400rpm.

[0027] In a third aspect, the present invention provides a secondary battery, comprising the rare earth oxyhalide solid electrolyte described in the first aspect or the rare earth oxyhalide solid electrolyte prepared by the preparation method described in the second aspect.

[0028] Preferably, the rare earth oxyhalide solid electrolyte provided by the present invention can be used in any component of a battery, and more preferably, it is applied to a positive electrode, an electrolyte, a negative electrode, an interface layer, a modification layer, a protective layer, etc.

[0029] The secondary battery assembled with the rare earth oxyhalide solid electrolyte of the present invention has higher energy density and better cycle life.

[0030] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0031] Compared with the prior art, the present invention has at least the following beneficial effects:

[0032] (1) The amorphous rare earth oxyhalide solid electrolyte provided by the present invention has high room temperature ionic conductivity, low electronic conductivity, excellent electrochemical stability and good moisture resistance.

[0033] (2) The present invention uses hydrated rare earth halides as metal sources and oxygen sources, which greatly reduces the preparation cost. The preparation method is simple and low-cost, matches the existing production process equipment, and is suitable for large-scale production applications.

[0034] (3) The secondary battery assembled with the rare earth oxyhalide solid electrolyte of the present invention has higher energy density and better cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is the XRD pattern of YCl3·6H2O after heat treatment in Example 1 of the present invention;

[0036] Figure 2 is the XRD pattern of Li3YOCl4 prepared in Example 1 of the present invention;

[0037] Figure 3 This is the AC impedance test spectrum of the Li3YOCl4 electrolyte sheet prepared in Example 1 of the present invention at room temperature;

[0038] Figure 4 The Li prepared in Example 2 of the present invention 2.5 YOCl 3.5 XRD pattern of

[0039] Figure 5 Li prepared in Example 2 of the present invention 2.5 YOCl 3.5 AC impedance test spectrum of electrolyte at room temperature;

[0040] Figure 6 This is the AC impedance test spectrum of the Li2YOCl3 electrolyte prepared in Example 3 of the present invention at room temperature. DETAILED DESCRIPTION

[0041] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and through specific implementation methods. However, the following examples are only simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0042] In the following examples, unless otherwise specified, all reagents and consumables were purchased from conventional reagent manufacturers in the field; unless otherwise specified, the experimental methods and technical means used were conventional methods and means in the field.

[0043] Example 1

[0044] This embodiment provides a rare earth oxyhalide solid electrolyte, wherein the rare earth oxyhalide solid electrolyte has an amorphous structure and a chemical formula of Li3YOCl4;

[0045] The method for preparing the rare earth oxyhalide solid electrolyte provided in this embodiment comprises the following steps:

[0046] 5.0 g of YCl3·6H2O was weighed and heat treated at 600°C in an air atmosphere for 300 min to obtain a YOCl precursor.

[0047] Weigh 2.0 g of YOCl precursor and 1.81 g of LiCl, place them in a ball mill for ball milling with a ball-to-material mass ratio of 15:1 and a rotation speed of 400 rpm for 30 hours to obtain the rare earth oxyhalide solid electrolyte Li3YOCl4.

[0048] The XRD pattern of YCl3·6H2O after heat treatment is as follows Figure 1 As shown in the figure, it can be seen that after heat treatment, YCl3·6H2O is basically converted into YOCl;

[0049] The XRD pattern of the prepared rare earth oxyhalide solid electrolyte Li3YOCl4 is as follows: Figure 2 As shown in the figure, the synthesized solid electrolyte is an amorphous phase, and the observed crystalline phase is incompletely reacted LiCl; the AC impedance test results of the Li3YOCl4 electrolyte sheet at room temperature are shown in Figure 3 As shown in the figure, its ionic conductivity at room temperature is 5.04×10 -6 S / cm.

[0050] Example 2

[0051] This embodiment provides a rare earth oxyhalide solid electrolyte, the rare earth oxyhalide solid electrolyte structure is an amorphous structure, and the chemical formula is Li 2.5 YOCl 3.5 ;

[0052] The method for preparing the rare earth oxyhalide solid electrolyte provided in this embodiment comprises the following steps:

[0053] 5.0 g of YCl3·6H2O was weighed and heat-treated at 400°C in an air atmosphere for 500 min to obtain a YOCl precursor.

[0054] Weigh 2.0 g of YOCl precursor and 1.51 g of LiCl, place them in a ball mill for ball milling, with a ball-to-material mass ratio of 10:1 and a rotation speed of 400 rpm for 20 h to obtain a rare earth oxyhalide solid electrolyte Li 2.5 YOCl 3.5 .

[0055] The prepared rare earth oxyhalide solid electrolyte Li 2.5 YOCl 3.5 XRD Figure 4 As shown in the figure, it can be seen that the synthesized solid electrolyte is an amorphous phase; Li 2.5 YOCl 3.5 The results of the AC impedance test of the electrolyte sheet at room temperature are as follows: Figure 5 As shown in the figure, its ionic conductivity at room temperature is 4.1×10 -5 S / cm.

[0056] Example 3

[0057] This embodiment provides a rare earth oxyhalide solid electrolyte, wherein the rare earth oxyhalide solid electrolyte has an amorphous structure and a chemical formula of Li2YOCl3;

[0058] The method for preparing the rare earth oxyhalide solid electrolyte provided in this embodiment comprises the following steps:

[0059] 5.0 g of YCl3·6H2O was weighed and heat-treated at 800°C in an air atmosphere for 150 min to obtain a YOCl precursor.

[0060] Weigh 2.0 g of YOCl precursor and 1.21 g of LiCl, place them in a ball mill for ball milling with a ball-to-material mass ratio of 20:1 and a rotation speed of 200 rpm for 48 hours to obtain the rare earth oxyhalide solid electrolyte Li2YOCl3.

[0061] The AC impedance test results of Li2YOCl3 electrolyte sheet at room temperature are as follows Figure 6 As shown in the figure, its ionic conductivity at room temperature is 2.37×10 -6 S / cm.

[0062] Example 4

[0063] This embodiment provides a rare earth oxyhalide solid electrolyte, wherein the rare earth oxyhalide solid electrolyte has an amorphous structure and a chemical formula of Li3ScOBr4;

[0064] The method for preparing the rare earth oxyhalide solid electrolyte provided in this embodiment comprises the following steps:

[0065] 5.0 g of ScBr3·6H2O was weighed and heat treated at 600°C in an air atmosphere for 300 min to obtain a ScOBr precursor.

[0066] Weigh 2.0 g of ScOBr precursor and 2.28 g of LiBr, place them in a ball mill for ball milling, with a ball-to-material mass ratio of 15:1 and a rotation speed of 400 rpm for 30 hours to obtain the rare earth oxyhalide solid electrolyte Li3ScOBr4.

[0067] Example 5

[0068] This embodiment provides a rare earth oxyhalide solid electrolyte, which is different from Embodiment 2 only in that the heat treatment temperature is 250° C. when preparing the rare earth oxyhalide solid electrolyte.

[0069] Example 6

[0070] This embodiment provides a rare earth oxyhalide solid electrolyte, which is different from Embodiment 2 only in that the heat treatment temperature is 900° C. when preparing the rare earth oxyhalide solid electrolyte.

[0071] Example 7

[0072] This embodiment provides a rare earth oxyhalide solid electrolyte, which is different from Embodiment 2 only in that the rotation speed of the ball mill is 600 rpm when preparing the rare earth oxyhalide solid electrolyte.

[0073] Example 8

[0074] This embodiment provides a rare earth oxyhalide solid electrolyte, which is different from Embodiment 2 only in that the ball milling time is 80 hours when preparing the rare earth oxyhalide solid electrolyte.

[0075] Comparative Example 1

[0076] This comparative example provides a rare earth oxyhalide solid electrolyte, which is different from Example 1 only in that rare earth oxide is used as a raw material for rare earth element and oxygen when preparing the rare earth oxyhalide solid electrolyte.

[0077] Test method: (1) Test method for ionic conductivity: 150 mg of the prepared yttrium oxychloride solid electrolyte was placed in a customized mold and assembled into a titanium-titanium symmetrical cell. A pressure of 300 MPa was applied by a tablet press to perform an AC impedance test. Based on the impedance obtained, the corresponding ionic conductivity value was calculated.

[0078] (2) Test method for electronic conductivity: 150 mg of the prepared yttrium oxychloride solid electrolyte was placed in a customized mold and assembled into a titanium-titanium symmetrical battery. A pressure of 300 MPa was applied by a tablet press to perform a DC polarization test with a polarization voltage of 500 mV. The corresponding electronic conductivity value was calculated based on the stabilized current size.

[0079] (3) Electrochemical stability test method: 150 mg of the prepared yttrium oxychloride solid electrolyte was placed in a customized mold and pressed into tablets using a tablet press. Surface-modified lithium metal was used as the counter electrode and reference electrode to assemble a titanium-lithium half-cell, and a linear scan test was performed to determine the electrochemical stability window at a scan rate of 0.5 mV / s.

[0080] (4) Air stability test method: 150 mg of the prepared yttrium oxychloride solid electrolyte was placed in an air atmosphere with a humidity of 70% for 5 minutes and then an AC impedance test was performed; based on the impedance obtained, the corresponding ionic conductivity value was calculated.

[0081] Table 1

[0082]

[0083]

[0084] The test results show that:

[0085] (1) It can be seen from Examples 1-4 that the amorphous rare earth halide oxide solid electrolyte prepared by using hydrated rare earth halide as a raw material has high room temperature ionic conductivity, low electronic conductivity, excellent electrochemical stability and good moisture resistance. As the oxygen content increases, the electronic conductivity of the obtained solid electrolyte decreases, but its antioxidant capacity increases. The lower the decrease in the ionic conductivity of the electrolyte after exposure to air, it can be seen that the introduction of oxygen can improve the moisture resistance of the electrolyte.

[0086] (2) By comparing Example 2 with Examples 5-6, it can be seen that the present invention further controls the temperature of the heat treatment of the hydrated rare earth halide so that rare earth element oxyhalide MOX can be generated after the heat treatment, thereby achieving the subsequent preparation of a rare earth oxyhalide solid electrolyte with a suitable chemical composition by ball milling.

[0087] (3) By comparing Example 2 with Examples 7-8, it can be seen that the rare earth halide oxide solid electrolyte with a reasonable phase structure and chemical composition is finally obtained by further controlling the rotation speed and time of the ball mill. If the rotation speed of the ball mill is too fast or the ball milling time is too long, the lithium ion conductivity of the product will decrease slightly; if the rotation speed of the ball mill is too slow or the ball milling time is too short, the reaction cannot be fully carried out, resulting in the presence of impurities in the product, which will also cause the lithium ion conductivity of the material to be low.

[0088] (4) It can be seen from Example 1 and Comparative Example 1 that the present invention can greatly reduce the production cost of materials by using low-cost hydrated rare earth halides as reaction raw materials and providing rare earth element sources and oxygen sources at the same time. However, when rare earth oxides are directly used as raw materials for preparation, it is impossible to successfully prepare oxyhalide solid electrolytes.

[0089] In summary, the yttrium oxychloride solid electrolyte provided by the present invention has high room temperature ionic conductivity, low electronic conductivity, good electrochemical stability and humidity stability, and the preparation method is simple and the raw material price is low. Therefore, it has good application prospects in lithium batteries.

[0090] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A rare earth oxyhalide solid electrolyte, characterized in that: The rare earth oxyhalide solid electrolyte has an amorphous structure and a general chemical formula of Li 3-y MOX 4-y ; Wherein: M includes any one of Sc, Y or lanthanide elements or a combination of at least two thereof; X includes any one of F, Cl, Br, I or a combination of at least two thereof; 0≤y≤1.

2. The rare earth oxyhalide solid electrolyte according to claim 1, characterized in that: 0.5≤y≤1。 3. A method for preparing the rare earth oxyhalide solid electrolyte as claimed in claim 1 or 2, characterized in that: The preparation method comprises the following steps: The hydrated rare earth halide is subjected to heat treatment to obtain a MOX precursor; the obtained MOX precursor is mixed with LiX, and the rare earth halide oxide solid electrolyte is obtained after ball milling.

4. The preparation method according to claim 3, characterized in that: The temperature of the heat treatment is 300-800°C.

5. The preparation method according to claim 3 or 4, characterized in that: The heat treatment time is 60-600 min.

6. The preparation method according to any one of claims 3 to 5, characterized in that: The molar ratio of the MOX precursor to LiX is 1:(2-3).

7. The preparation method according to any one of claims 3 to 6, characterized in that: The ball-to-material mass ratio of the ball mill is (5-30):

1.

8. The preparation method according to any one of claims 3 to 7, characterized in that: The rotation speed of the ball mill is 100-400 rpm; Preferably, the ball milling time is 12-60 hours.

9. The preparation method according to any one of claims 3 to 8, characterized in that: The preparation method comprises the following steps: The hydrated rare earth halide is subjected to heat treatment at 300-800° C. for 60-600 min to obtain a MOX precursor; the obtained MOX precursor and LiX are mixed in a molar ratio of 1:(2-3), and the rare earth halide solid electrolyte is obtained after mechanical ball milling for 12-60 h at a ball-to-material ratio of (5-30):1 and a rotation speed of 100-400 rpm.

10. A secondary battery, characterized in that: The secondary battery comprises the rare earth oxyhalide solid electrolyte according to claim 1 or 2, or the rare earth oxyhalide solid electrolyte prepared by the preparation method according to any one of claims 3 to 9.

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