Boron-fluorine co-doped halide solid electrolyte, preparation method thereof and all-solid-state battery

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a boron-fluorine co-doped halide solid electrolyte, a preparation method thereof and an all-solid-state battery, the boron-fluorine co-doped halide solid electrolyte is a boron-fluorine co-doped LiaMXb solid electrolyte, X is one of Cl, Br and I, M is Y, Sc, In or Zr, a is equal to 2-3.5, b is equal to 6, and a is equal to 1-3. According to the invention, a stable substance formed in situ by the boron-fluorine co-doped halide solid electrolyte after circulation inhibits the problems of electrolyte structure damage, ionic conductivity reduction, harmful reaction byproduct generation and the like caused by chemical reaction or electrochemical side reaction pathway of the electrolyte in the circulation process at low temperature; the problem of battery capacity attenuation caused by composite positive electrode side polarization increase in the cycle process of the battery is effectively improved, and the service life of the all-solid-state battery is prolonged.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a boron-fluorine co-doped halide solid electrolyte and its preparation method, and an all-solid-state battery. Background Technology

[0002] All-solid-state lithium batteries (ASSLB) have attracted increasing research interest due to their enormous potential for achieving high energy density and extremely high safety. In recent years, significant efforts have been devoted to developing various inorganic solid-state electrolytes (SEs), including oxide, sulfide, and halide solid-state electrolytes. With advancements in solid-state electrolytes, ASSLB can now exhibit excellent electrochemical performance over a temperature range of 20°C to 70°C. However, the electrochemical performance of ASSLB deteriorates significantly when exposed to low temperatures, limiting their application in cold conditions. Therefore, developing all-solid-state lithium-ion batteries with excellent low-temperature performance is crucial for their widespread application, and this remains a significant challenge.

[0003] At low temperatures, the key factor limiting the electrochemical performance of batteries has always been the slow lithium kinetics. In particular, for all-solid-state batteries (ASSLBs), the kinetic challenges can be summarized as follows: (1) the ionic conductivity of inorganic SE decreases sharply, (2) the limited solid-solid contact and aggravated contact loss in SE / cathode composites, and (3) interfacial impedance from unstable or unfavorable interfaces.

[0004] To address this issue, an electrochemically inert layer (such as LiNbO3) is typically coated onto the cathode to construct an artificial interface. However, the composition of the electrochemically inert layer can also adversely affect the lithium-ion kinetics across the interface, thus impacting the battery's performance at low temperatures.

[0005] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the present invention provides a boron-fluorine co-doped halide solid electrolyte and its preparation method, as well as an all-solid-state battery, thereby solving the problem of the sharp decrease in ionic conductivity of existing halide solid electrolytes in low-temperature environments.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0008] In a first aspect, the present invention provides a boron-fluorine co-doped halide solid electrolyte, wherein the boron-fluorine co-doped halide solid electrolyte is a boron-fluorine co-doped Li₂. a MX bSolid electrolyte, wherein X is one of Cl, Br, I, M is Y, Sc, In or Zr, a = 2-3.5, b = 6.

[0009] Preferably, the main crystal plane of the XRD diffraction peak of the boron-fluorine co-doped halide solid electrolyte is (131).

[0010] Preferably, in the boron-fluorine co-doped halide solid electrolyte, the boron doping amount is 0.0356 and the fluorine doping amount is 0.1426.

[0011] A second aspect of the present invention provides a method for preparing a boron-fluorine co-doped halide solid electrolyte, the method comprising the following steps:

[0012] LiBF4 and Li3InCl6 are mixed and then compressed to obtain the tablet material;

[0013] The tableting material is heat-treated to obtain a heat-treated material;

[0014] The heat-treated material is cooled to obtain the boron-fluorine co-doped halide solid electrolyte.

[0015] Preferably, the mixing is ball milling or manual mixing;

[0016] The ball milling mixing speed is 400-700 rpm, and the time is 20-25 h;

[0017] The artificial mixing is carried out using a mortar and pestle, and the grinding time is 15-30 minutes.

[0018] Preferably, the pressure of the tableting process is 300-400 MPa.

[0019] Preferably, the heat treatment temperature is 200-300℃ and the time is 3-7h.

[0020] Preferably, the cooling process is air cooling or furnace cooling.

[0021] Preferably, the cooling process specifically involves cooling the room to 25 degrees Celsius at a cooling rate of 2–50°C / min.

[0022] A third aspect of the present invention provides an all-solid-state battery, the all-solid-state battery comprising a positive electrode, a negative electrode, and the aforementioned boron-fluorine co-doped halide solid electrolyte disposed between the positive electrode and the negative electrode.

[0023] Beneficial effects:

[0024] This invention discloses a boron-fluorine co-doped halide solid electrolyte, its preparation method, and an all-solid-state battery. In the boron-fluorine co-doped halide solid electrolyte, boron and fluorine selectively occupy specific lattice sites, forming a novel halide solid electrolyte structure. The stable material formed in situ by the boron-fluorine co-doped halide solid electrolyte after cycling not only promotes interfacial charge transfer but also acts as a protective barrier, preventing the boron-fluorine co-doped halide solid electrolyte from penetrating into the active material, thereby reducing interfacial side reactions. Simultaneously, it suppresses problems such as electrolyte structure damage, decreased ionic conductivity, and the generation of harmful reaction byproducts caused by chemical reactions or electrochemical side reactions during cycling at low temperatures. This effectively improves the battery capacity decay problem caused by increased polarization on the composite cathode side during cycling, extending the lifespan of the all-solid-state battery. Attached Figure Description

[0025] Figure 1 The SEM and XRD patterns of the halide solid electrolyte prepared in Example 1 of this invention are shown.

[0026] Figure 2 The image shows the EDS test results of the halide solid electrolyte prepared in Example 1 of this invention.

[0027] Figure 3 The results show the stability test results of the battery prepared using the halide solid electrolyte prepared in Example 2 of this invention.

[0028] Figure 4 The results show the stability test results of the battery prepared using the halide solid electrolyte prepared in Example 1 of this invention. Detailed Implementation

[0029] This invention provides a boron-fluorine co-doped halide solid electrolyte and its preparation method, as well as an all-solid-state battery. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0030] This invention provides a boron-fluorine co-doped halide solid electrolyte, wherein the boron-fluorine co-doped halide solid electrolyte is a boron-fluorine co-doped Li₂. a MX b Solid electrolyte, wherein X is one of Cl, Br, I, M is Y, Sc, In or Zr, a = 2-3.5, b = 6.

[0031] This invention employs fluorine (F) doping to impart excellent oxidation resistance to halide solid electrolytes due to F's extremely strong electronegativity. During battery cycling, F doping generates LiF in situ. This compound, due to its low lithium-ion diffusion barrier and excellent chemical stability, can significantly improve the stability of the halide solid electrolyte-electrode interface. However, studies have found that single-doping of F has limited effect on improving lithium-ion migration kinetics at low temperatures.

[0032] To this end, embodiments of the present invention further introduce element B for synergistic doping. The incorporation of element B enables the formation of a fast ion conductor, Li3BO3, during battery cycling. This substance provides an efficient transport channel for lithium ions at low temperatures. In low-temperature environments, the presence of Li3BO3 effectively alleviates the problem of ion transport rate decay caused by temperature decreases by lowering the lithium-ion migration barrier, thereby maintaining efficient ion transport at the electrode-electrolyte interface and ultimately improving the overall performance of the full battery over a wide temperature range (especially in low-temperature environments).

[0033] In some embodiments, the main crystal plane of the XRD diffraction peak of the boron-fluorine co-doped halide solid electrolyte is (131).

[0034] In some embodiments, the boron-fluorine co-doped halide solid electrolyte has a boron doping amount of 0.0356 and a fluorine doping amount of 0.1426.

[0035] Adding too little LiBF4 will result in insufficient generation of interfacial substances such as LiF during cycling, leading to poor interfacial stability and thus poor battery cycle performance. Adding too much LBF4 will generate a thick coating layer during ball milling. Since LBF4 is not a fast ion conductor, excessive addition will result in poor electrochemical performance.

[0036] This invention provides a method for preparing a boron-fluorine co-doped halide solid electrolyte, the method comprising the following steps:

[0037] LiBF4 (LBF4) and Li3InCl6 are mixed and then compressed to obtain the tablet material;

[0038] The tableting material is heat-treated to obtain a heat-treated material;

[0039] The heat-treated material is cooled to obtain the boron-fluorine co-doped halide solid electrolyte.

[0040] The preparation method provided in this invention uses a dry mixing method, which, compared to the wet chemical synthesis followed by vacuum heat treatment in the prior art, effectively improves the utilization rate of raw materials and is safer and more environmentally friendly.

[0041] The preparation method of this invention has simple operation steps, readily available raw materials, low cost, and is easy to industrialize. At the same time, it has high production efficiency, is suitable for large-scale industrial production, has broad commercial application prospects, and has significant theoretical and practical implications.

[0042] In some embodiments, the mixing is ball milling or manual mixing;

[0043] The ball milling mixing speed is 400-700 rpm, and the time is 20-25 h;

[0044] The artificial mixing is carried out using a mortar and pestle, and the grinding time is 15-30 minutes.

[0045] In some embodiments, the pressure of the tableting process is 300-400 MPa.

[0046] In some embodiments, the heat treatment is performed at a temperature of 200-300°C for 3-7 hours.

[0047] In some embodiments, the cooling process is air cooling or furnace cooling.

[0048] In some embodiments, the cooling process specifically involves cooling the temperature to room temperature at a rate of 2–50 °C / min.

[0049] The embodiments of the present invention employ a rapid cooling method to regulate crystal phase growth.

[0050] This invention provides an all-solid-state battery, which includes a positive electrode, a negative electrode, and the aforementioned boron-fluorine co-doped halide solid electrolyte disposed between the positive and negative electrodes.

[0051] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are merely some embodiments of the present invention, not all embodiments, and are intended only to illustrate the present invention and not to limit it. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] Example 1

[0053] The preparation of a boron-fluorine co-doped halide solid electrolyte includes the following steps:

[0054] Weigh out a total of 101g of LBF4 and Li3InCl6 (LIC) and place them in a ball mill jar (1g of LBF4 and 100g of LIC). Set the planetary high-speed ball mill to 600 rpm and mill for 20 hours. Place the milled mixture in a tableting mold and press it into tablets at 400 MPa. Place the tablets with a diameter of 10mm and a thickness of 2-5mm into a quartz tube and vacuum it to -0.2 MPa. Then seal the tube and place it in a muffle furnace. Heat treat it at 260℃ for 6 hours at a heating rate of 2℃ / min. Then cool it at a cooling rate of 30℃ / min and grind it in a mortar for 30 minutes to obtain a boron-fluorine co-doped halide solid electrolyte.

[0055] Example 2

[0056] The preparation of fluorine-doped halide solid electrolyte materials includes the following steps:

[0057] Weigh out a total of 101g of LiF and Li3InCl6 (1g of LiF and 100g of LIC) into a ball mill jar. Set the planetary high-speed ball mill to 600 rpm and mill for 20 hours. Place the milled mixture into a tableting mold and press it into tablets at 400 MPa. Place the tablets with a diameter of 10 mm and a thickness of 2-5 mm into a quartz tube and vacuum it to -0.2 MPa. Then seal the tube and place it in a muffle furnace. Heat treat it at 260℃ for 6 hours at a heating rate of 2℃ / min. Then cool it at a cooling rate of 30℃ / min. Finally, grind it in a mortar for 30 minutes to obtain a single-doped F halide solid electrolyte material.

[0058] The LIC that is single-doped with F and mixed with LiF is named FD-LIC; the LIC that is co-doped with B and F and mixed with LBF4 is named BFD-LIC.

[0059] Performance testing

[0060] like Figure 1 As shown in the XRD pattern, the boron-fluorine co-doped halide solid electrolyte prepared in Example 1 exhibits main characteristic peaks of (001), (133), and (131). The inorganic halide solid electrolyte Li3InCl6 prepared in this example was subjected to the following tests:

[0061] (1) Dual-element doping test: Rigaku-target-rotation XRD was used, with a test range of 10-90° and a speed of 10° / min. The test results are as follows: Figure 1 ,Depend on Figure 1 It can be seen that peak shifts occur in (131) and (133), indicating that elemental doping has occurred. Furthermore, in conjunction with… Figure 2The EDS results indicate that elements B and F are uniformly incorporated into Li3InCl6.

[0062] (2) Secondary battery stability test: Half-cells were assembled for testing. The solid electrolyte material used in the test was LIC, and the negative electrode was LiIn alloy. From... Figure 3 As can be seen from ,4, the half-cell cycle stability and capacity of BFD-LIC are better than those of FD-LIC half-cell.

[0063] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A boron-fluorine co-doped halide solid electrolyte, characterized in that, The boron-fluorine co-doped halide solid electrolyte is a boron-fluorine co-doped Li₂. a MX b Solid electrolyte, wherein X is one of Cl, Br, I, M is Y, Sc, In or Zr, a = 2-3.5, b = 6.

2. The boron-fluorine co-doped halide solid electrolyte according to claim 1, characterized in that, The main crystal plane of the XRD diffraction peak of the boron-fluorine co-doped halide solid electrolyte is (131).

3. The boron-fluorine co-doped halide solid electrolyte according to claim 1, characterized in that, In the boron-fluorine co-doped halide solid electrolyte, the boron doping amount is 0.0356 and the fluorine doping amount is 0.1426.

4. A method for preparing a boron-fluorine co-doped halide solid electrolyte according to any one of claims 1-3, characterized in that, The preparation method includes the following steps: LiBF4 and Li3InCl6 are mixed and then compressed to obtain the tablet material; The tableting material is heat-treated to obtain a heat-treated material; The heat-treated material is cooled to obtain the boron-fluorine co-doped halide solid electrolyte.

5. The method for preparing the boron-fluorine co-doped halide solid electrolyte according to claim 4, characterized in that, The mixing is either ball milling or manual mixing; The ball milling mixing speed is 400-700 rpm, and the time is 20-25 h; The artificial mixing is carried out using a mortar and pestle, and the grinding time is 15-30 minutes.

6. The method for preparing the boron-fluorine co-doped halide solid electrolyte according to claim 4, characterized in that, The pressure for tablet compression is 300-400 MPa.

7. The method for preparing the boron-fluorine co-doped halide solid electrolyte according to claim 4, characterized in that, The heat treatment is performed at a temperature of 200-300℃ for 3-7 hours.

8. The method for preparing the boron-fluorine co-doped halide solid electrolyte according to claim 4, characterized in that, The cooling process is either air cooling or furnace cooling.

9. The method for preparing the boron-fluorine co-doped halide solid electrolyte according to claim 8, characterized in that, The cooling process specifically involves cooling the temperature to room temperature at a rate of 2–50 °C / min.

10. An all-solid-state battery, characterized in that, The all-solid-state battery includes a positive electrode, a negative electrode, and a boron-fluorine co-doped halide solid electrolyte disposed between the positive electrode and the negative electrode as described in any one of claims 1-3.

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