Solid-state electrolyte for lithium ion battery and preparation method and application thereof

Abstract

The application relates to the technical field of lithium ion batteries, and discloses a solid electrolyte for a lithium ion battery and a preparation method and application thereof. The solid electrolyte is lithium borohydride doped and modified by MX2; in the MX2, M is one or more of Fe, Co and Ni, and X is Cl and / or Br; the MX2 at least comprises CoBr2. By doping and modifying lithium borohydride with a specific dopant, the ionic conductivity of the lithium borohydride-based solid electrolyte can be improved to a greater extent.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a solid electrolyte for lithium-ion batteries, its preparation method, and its application. Background Technology

[0002] Compared to the organic liquid electrolytes used in current commercial lithium-ion batteries, solid electrolytes can reduce the risk of electrolyte leakage, combustion, and even explosion, avoiding battery safety hazards from the material source. At the same time, their solid-state characteristics make the battery system structure simpler, which is expected to achieve higher energy density. In addition, solid electrolytes usually have a wider electrochemical stability window, which makes it possible to match high-voltage cathode materials, thereby further improving the energy density of the whole battery.

[0003] Among numerous candidate solid-state electrolyte materials, lithium borohydride (LiBH4)-based hydride electrolytes stand out. They effectively suppress lithium dendrite growth and do not undergo violent side reactions with lithium metal, an advantage not possessed by many high-conductivity sulfide electrolytes. However, their intrinsically low room-temperature ionic conductivity (approximately 10⁻⁶) is a significant drawback. -8 The S / cm ratio severely restricts rapid ion transport. This fundamental problem stems from its orthorhombic crystal structure at room temperature, which limits [BH4]... - The rotation of functional groups and the migration of lithium ions result in an excessively high lithium ion migration barrier.

[0004] To address this, researchers have attempted to improve the ionic conductivity of lithium borohydride-based solid electrolytes using ion doping strategies. However, existing ion doping strategies have significant limitations, leading to a bottleneck in improving ionic conductivity. For example, patent CN119674203A discloses a lithium borohydride-lithium iodide composite solid electrolyte material, its preparation method, and its application. This material combines LiBH4 with LiI, and through I... - Replacement part [BH4] - This allows lithium borohydride to maintain its hexagonal phase structure at room temperature, thereby improving its room temperature ionic conductivity. However, the effect is limited; the ionic conductivity at 40°C can only reach 1.66 × 10⁻⁶. -5 ~4.12×10 -5 S / cm. Summary of the Invention

[0005] To address the aforementioned technical problem—that existing ion doping strategies have limited effectiveness in improving the room-temperature ionic conductivity of lithium borohydride-based solid electrolytes—this invention provides a solid electrolyte for lithium-ion batteries, its preparation method, and its applications. This invention, by employing specific dopants to modify lithium borohydride, can significantly improve the ionic conductivity of lithium borohydride-based solid electrolytes.

[0006] The specific technical solution of this invention is as follows: In a first aspect, the present invention provides a solid electrolyte for lithium-ion batteries, wherein the solid electrolyte is lithium borohydride modified by MX2 doping; wherein in MX2, M is one or more of Fe, Co and Ni, and X is Cl and / or Br; and MX2 includes at least CoBr2.

[0007] In the MX2 used for doping modification of lithium borohydride in this invention, by employing specific cations and anions, the effect of MX2 on improving the ionic conductivity of lithium borohydride can be enhanced. Specifically: Fe 2+ Co 2+ Ni 2+ The ionic radius is less than or equal to that of Li + The proximity helps to reduce the uniformity of the crystal structure when it is incorporated into the lithium borohydride lattice, avoiding excessive distortion, thereby increasing vacancies while maintaining the stable state of the original ion transport channels; Cl - and Br - Its reducing power is weaker than that of I, which is beneficial for improving the oxidation stability of lithium borohydride-based solid electrolytes and their compatibility with high-voltage cathodes.

[0008] Based on this, the dopant MX2 used in this invention includes at least CoBr2, which can further improve the ionic conductivity of the lithium borohydride-based solid electrolyte. Specifically: Co 2+ The ionic radius is 74.5 pm, similar to Li. + Its radius is similar to 76 pm, thus it can better integrate into the lattice of lithium borohydride, maintaining the stability of the crystal structure and ion transport channels to a greater extent; at the same time, Br - The radius is greater than Cl - , for Li + The attraction and binding power are weaker, which is also beneficial to Li. + Migration. Therefore, compared to other metal halides, the present invention uses CoBr2 as a dopant, which can improve the ionic conductivity of lithium borohydride-based solid electrolyte to a greater extent.

[0009] Preferably, MX2 is NiCl2, NiBr2, CoBr2 and FeBr2; the molar ratio of NiCl2, NiBr2, CoBr2 and FeBr2 is 0.5~1:0.5~1:1:0.5~1.

[0010] While CoBr2 can significantly improve the ionic conductivity of lithium borohydride compared to other metal halides (including NiCl2, NiBr2, and FeBr2) when using a single dopant, this invention has found that, compared to using CoBr2 alone, partially replacing it with NiCl2, NiBr2, and FeBr2 (i.e., using these three specific dopants together with CoBr2) and controlling the ratio of the four dopants within a specific range can further improve the ionic conductivity of lithium borohydride. The mechanism is as follows: co-doping with NiCl2, NiBr2, CoBr2, and FeBr2 can increase the configuration entropy of the material, inducing a higher concentration of vacancies, which is beneficial for Li. + The migration of Li provides abundant, pre-existing low-energy pathways, enabling Li + Migration can be accomplished by "jumping into" a nearby vacancy, which significantly reduces the activation energy of migration and thus improves the ionic conductivity of the material. Furthermore, among the four dopants, NiCl2, NiBr2, CoBr2 and FeBr2 have better lattice stability than different combinations of the same element, and can form a solid solution with LiBH4 more effectively, which is beneficial to improving the room temperature ionic conductivity, thermal stability and chemical stability of the material.

[0011] Preferably, the molar ratio between lithium borohydride and MX2 is 8~9:1.

[0012] Secondly, the present invention provides a method for preparing the solid electrolyte, the steps of which include: heat-treating lithium borohydride powder in a vacuum environment, mixing it with MX2 powder, and ball milling it in an inert atmosphere to obtain a solid electrolyte.

[0013] Preferably, the heat treatment temperature is 100~180℃ and the time is 8~12 h.

[0014] Preferably, the mixing method is grinding and mixing in a mortar.

[0015] Preferably, the ball milling method is planetary ball milling, with a ball-to-material ratio of 50~200:1, a rotation speed of 300~1000 rpm, and a milling time of 6~20 h.

[0016] Preferably, the inert atmosphere is one or more of nitrogen, helium, and argon.

[0017] Thirdly, the present invention provides the application of the solid electrolyte in lithium-ion batteries.

[0018] Preferably, the lithium-ion battery includes a positive electrode, a solid electrolyte sheet, and a negative electrode sheet stacked sequentially, wherein the solid electrolyte sheet contains the solid electrolyte.

[0019] Compared with the prior art, the present invention has the following advantages: (1) In the present invention, the dopant MX2 used for doping modification of lithium borohydride is improved by using specific metal elements (one or more of Fe, Co and Ni) and non-metal elements (Cl and / or Br), and by making MX2 contain at least CoBr2, thereby improving the effect of the dopant on improving the conductivity of lithium borohydride ions.

[0020] (2) By using four specific dopants, NiCl2, NiBr2, CoBr2 and FeBr2, in a certain ratio, the present invention can further improve the ionic conductivity of lithium borohydride-based solid electrolyte. Attached Figure Description

[0021] Figure 1 Arrhenius curves for the solid electrolytes of Example 1 and Comparative Examples 1-6.

[0022] Figure 2 The image shows the electrochemical impedance spectroscopy (EIS) curve of the solid electrolyte in Example 2.

[0023] Figure 3 The step current charge-discharge curves of the lithium-ion battery made using the solid electrolyte of Example 2 are shown. Detailed Implementation

[0024] The present invention will be further described below with reference to embodiments.

[0025] First, the present invention relates to a solid electrolyte for lithium-ion batteries, wherein the solid electrolyte is lithium borohydride modified by MX2 doping; wherein in MX2, M is one or more of Fe, Co and Ni, and X is Cl and / or Br; and MX2 includes at least CoBr2.

[0026] In some specific embodiments, MX2 is NiCl2, NiBr2, CoBr2 and FeBr2; the molar ratio between NiCl2, NiBr2, CoBr2 and FeBr2 is 0.5~1:0.5~1:1:0.5~1.

[0027] In some specific embodiments, the molar ratio between lithium borohydride and MX2 is 8~9:1.

[0028] Second, the present invention relates to a method for preparing the solid electrolyte, the steps of which include: heat-treating lithium borohydride powder in a vacuum environment, mixing it with MX2 powder, and ball milling it in an inert atmosphere to obtain a solid electrolyte.

[0029] In some specific embodiments, the heat treatment temperature is 100~180℃ and the time is 8~12 h.

[0030] In some specific embodiments, the mixing method is to grind and mix in a mortar.

[0031] In some specific embodiments, the ball milling method is planetary ball milling, the ball-to-material ratio is 50~200:1, the rotation speed is 300~1000 rpm, and the ball milling time is 6~20 h.

[0032] In some specific embodiments, the inert atmosphere is one or more of nitrogen, helium, and argon.

[0033] Third, the present invention relates to the application of the solid electrolyte in lithium-ion batteries.

[0034] In some specific embodiments, the lithium-ion battery includes a positive electrode sheet, a solid electrolyte sheet, and a negative electrode sheet stacked sequentially, wherein the solid electrolyte sheet contains the solid electrolyte.

[0035] The present invention will now be described through specific embodiments and comparative examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0036] Example 1: Solid electrolyte for lithium-ion batteries 0.9LiBH4-0.1CoBr2 and its preparation The solid electrolyte for the lithium-ion battery in this embodiment is LiBH4 modified with CoBr2 doping, denoted as "0.9LiBH4-0.1CoBr2", and its preparation steps are as follows: Step 1: Pretreatment of LiBH4 powder LiBH4 powder was sealed in a glass tube, and the environment inside the tube was evacuated to a vacuum using an oil pump. The tube was kept at 140℃ for 10 hours and then allowed to cool naturally to room temperature to obtain pretreated LiBH4 powder.

[0037] Step 2: Doping and Modification of LiBH4 Powder Take the pretreated LiBH4 powder from step one and place it in a quartz mortar with CoBr2 powder at a molar ratio of 9:1. Grind and mix it manually until uniform. Then seal it in a ball mill jar, add grinding balls, and the ball-to-powder ratio is 100:1. Perform planetary ball milling at 400 rpm for 10 h in an argon atmosphere to obtain the solid electrolyte 0.9LiBH4-0.1CoBr2 of this embodiment.

[0038] Comparative Example 1: Solid electrolyte for lithium-ion batteries: 0.9LiBH4-0.1CoCl2 and its preparation The solid electrolyte for the lithium-ion battery in this comparative example is LiBH4 modified with CoCl2 doping, denoted as "0.9LiBH4-0.1CoCl2", and its preparation steps are as follows: Step 1: Pretreatment of LiBH4 powder LiBH4 powder was sealed in a glass tube, and the environment inside the tube was evacuated to a vacuum using an oil pump. The tube was kept at 140℃ for 10 hours and then allowed to cool naturally to room temperature to obtain pretreated LiBH4 powder.

[0039] Step 2: Doping and Modification of LiBH4 Powder Take the pretreated LiBH4 powder from step one and place it in a quartz mortar with CoCl2 powder at a molar ratio of 9:1. Grind and mix it manually until uniform. Then seal it in a ball mill jar, add grinding balls, and the ball-to-powder ratio is 100:1. Perform planetary ball milling at 400 rpm for 10 h in an argon atmosphere to obtain the solid electrolyte 0.9LiBH4-0.1CoCl2 of this comparative example.

[0040] Comparative Example 2: Solid electrolyte for lithium-ion batteries 0.9LiBH4-0.1NiBr2 and its preparation The solid electrolyte for the lithium-ion battery in this comparative example is NiBr2-doped LiBH4, denoted as "0.9LiBH4-0.1NiBr2", and its preparation steps are as follows: Step 1: Pretreatment of LiBH4 powder LiBH4 powder was sealed in a glass tube, and the environment inside the tube was evacuated to a vacuum using an oil pump. The tube was kept at 140℃ for 10 hours and then allowed to cool naturally to room temperature to obtain pretreated LiBH4 powder.

[0041] Step 2: Doping and Modification of LiBH4 Powder Take the pretreated LiBH4 powder from step one and place it in a quartz mortar with NiBr2 powder at a molar ratio of 9:1. Grind and mix it manually until uniform. Then seal it in a ball mill jar, add grinding balls, and the ball-to-powder ratio is 100:1. Perform planetary ball milling at 400 rpm for 10 h in an argon atmosphere to obtain the solid electrolyte 0.9LiBH4-0.1NiBr2 of this comparative example.

[0042] Comparative Example 3: Solid electrolyte for lithium-ion batteries: 0.9LiBH4-0.1NiCl2 and its preparation The solid electrolyte for the lithium-ion battery in this comparative example is NiCl2-doped LiBH4, denoted as "0.9LiBH4-0.1NiCl2", and its preparation steps are as follows: Step 1: Pretreatment of LiBH4 powder LiBH4 powder was sealed in a glass tube, and the environment inside the tube was evacuated to a vacuum using an oil pump. The tube was kept at 140℃ for 10 hours and then allowed to cool naturally to room temperature to obtain pretreated LiBH4 powder.

[0043] Step 2: Doping and Modification of LiBH4 Powder Take the pretreated LiBH4 powder from step one and place it in a quartz mortar with NiCl2 powder at a molar ratio of 9:1. Grind and mix it manually until uniform. Then seal it in a ball mill jar, add grinding balls, and the ball-to-powder ratio is 100:1. Perform planetary ball milling at 400 rpm for 10 h in an argon atmosphere to obtain the solid electrolyte 0.9LiBH4-0.1NiCl2 of this comparative example.

[0044] Comparative Example 4: Solid electrolyte for lithium-ion batteries: 0.9LiBH4-0.1FeBr2 and its preparation The solid electrolyte for the lithium-ion battery in this comparative example is FeBr2-doped LiBH4, denoted as "0.9LiBH4-0.1FeBr2", and its preparation steps are as follows: Step 1: Pretreatment of LiBH4 powder LiBH4 powder was sealed in a glass tube, and the environment inside the tube was evacuated to a vacuum using an oil pump. The tube was kept at 140℃ for 10 hours and then allowed to cool naturally to room temperature to obtain pretreated LiBH4 powder.

[0045] Step 2: Doping and Modification of LiBH4 Powder Take the pretreated LiBH4 powder from step one and place it in a quartz mortar with FeBr2 powder at a molar ratio of 9:1. Grind and mix it manually until uniform. Then seal it in a ball mill jar, add grinding balls, and the ball-to-powder ratio is 100:1. Perform planetary ball milling at 400 rpm for 10 h in an argon atmosphere to obtain the solid electrolyte 0.9LiBH4-0.1FeBr2 of this comparative example.

[0046] Comparative Example 5: Solid electrolyte for lithium-ion batteries: 0.9LiBH4-0.1FeCl2 and its preparation The solid electrolyte for the lithium-ion battery in this comparative example is FeCl2-doped LiBH4, denoted as "0.9LiBH4-0.1FeCl2", and its preparation steps are as follows: Step 1: Pretreatment of LiBH4 powder LiBH4 powder was sealed in a glass tube, and the environment inside the tube was evacuated to a vacuum using an oil pump. The tube was kept at 140℃ for 10 hours and then allowed to cool naturally to room temperature to obtain pretreated LiBH4 powder.

[0047] Step 2: Doping and Modification of LiBH4 Powder Take the pretreated LiBH4 powder from step one and place it in a quartz mortar with FeCl2 powder at a molar ratio of 9:1. Grind and mix it manually until uniform. Then seal it in a ball mill jar, add grinding balls, and the ball-to-powder ratio is 100:1. Perform planetary ball milling at 400 rpm for 10 h in an argon atmosphere to obtain the solid electrolyte 0.9LiBH4-0.1FeCl2 of this comparative example.

[0048] Comparative Example 6: Solid Electrolyte for Lithium-ion Batteries 0.9LiBH4-0.1FCN and its Preparation The solid electrolyte for lithium-ion batteries in this comparative example is LiBH4 modified with FeBr2, CoBr2, and NiBr2 doping, denoted as "0.9LiBH4-0.1FCN". Its preparation steps are as follows: Step 1: Pretreatment of LiBH4 powder LiBH4 powder was sealed in a glass tube, and the environment inside the tube was evacuated to a vacuum using an oil pump. The tube was kept at 140℃ for 10 hours and then allowed to cool naturally to room temperature to obtain pretreated LiBH4 powder.

[0049] Step 2: Doping and Modification of LiBH4 Powder Take the pretreated LiBH4 powder from step one and mix it with FCN powder (composed of equimolar amounts of FeBr2 powder, CoBr2 powder and NiBr2 powder) in a quartz mortar at a molar ratio of 9:1. Grind and mix them manually until uniform, then seal them in a ball mill jar, add grinding balls, and the ball-to-powder ratio is 100:1. Perform planetary ball milling at 400 rpm for 10 h in an argon atmosphere to obtain the solid electrolyte 0.9LiBH4-0.1FCN of this comparative example.

[0050] Test Example 1: The effect of a single dopant on improving the ionic conductivity of LiBH4 The solid electrolytes prepared in Example 1 and Comparative Examples 1-6 were used to test their ionic conductivity at different temperatures. The results are shown in […]. Figure 1 ( Figure 1 In this context, "T" represents temperature in Kelvin (K); "σ" represents ionic conductivity. The solid electrolyte of Example 1 has an ionic conductivity of 5.07 × 10⁻⁶ at room temperature (30°C). -4 S / cm.

[0051] from Figure 1It can be seen that, at the same doping concentration (10 mol%), compared with other metal halides (CoCl2, NiBr2, NiCl2, FeBr2, FeCl2) and FCN, using CoBr2 as a dopant to modify LiBH4 can significantly improve the ionic conductivity of LiBH4 (e.g., ...). Figure 1 (As shown). The reason for this analysis is: Co 2+ The ionic radius is 74.5 pm, similar to Li. + Its radius is similar to 76 pm, so it can be better integrated into the lattice of lithium borohydride, maintaining the stability of the crystal structure and ion transport channels to a greater extent, which is beneficial to Li + The transmission; at the same time, Br - The radius is greater than Cl - , for Li + The attraction and binding power are weaker, which is also beneficial to Li. + The migration.

[0052] Example 2: Solid electrolyte for lithium-ion batteries: 0.9LiBH4-0.025NiCl2-0.025NiBr2-0.025CoBr2-0.025FeBr2 and its preparation. The solid electrolyte for lithium-ion batteries in this embodiment is LiBH4 modified by doping with NiCl2, NiBr2, CoBr2 and FeBr2, denoted as "0.9LiBH4-0.025NiCl2-0.025NiBr2-0.025CoBr2-0.025FeBr2", and its preparation steps are as follows: Step 1: Pretreatment of LiBH4 powder LiBH4 powder was sealed in a glass tube, and the environment inside the tube was evacuated to a vacuum using an oil pump. The tube was kept at 140℃ for 10 hours and then allowed to cool naturally to room temperature to obtain pretreated LiBH4 powder.

[0053] Step 2: Doping and Modification of LiBH4 Powder Take the pretreated LiBH4 powder from step one, and place it in a quartz mortar with NiCl2 powder, NiBr2 powder, CoBr2 powder and FeBr2 powder in a molar ratio of 9:0.25:0.25:0.25:0.25. Grind and mix them evenly by hand, then seal them in a ball mill jar, add grinding balls, and the ball-to-powder ratio is 100:1. Perform planetary ball milling at 400 rpm for 10 h in an argon atmosphere to obtain the solid electrolyte 0.9LiBH4-0.025NiCl2-0.025NiBr2-0.025CoBr2-0.025FeBr2 of this embodiment.

[0054] Example 3: Solid electrolyte for lithium-ion batteries: 0.9LiBH4-0.02NiCl2-0.02NiBr2-0.04CoBr2-0.02FeBr2 and its preparation The solid electrolyte for lithium-ion batteries in this embodiment is LiBH4 modified by doping with NiCl2, NiBr2, CoBr2 and FeBr2, denoted as "0.9LiBH4-0.02NiCl2-0.02NiBr2-0.04CoBr2-0.02FeBr2", and its preparation steps are as follows: Step 1: Pretreatment of LiBH4 powder LiBH4 powder was sealed in a glass tube, and the environment inside the tube was evacuated to a vacuum using an oil pump. The tube was kept at 140℃ for 10 hours and then allowed to cool naturally to room temperature to obtain pretreated LiBH4 powder.

[0055] Step 2: Doping and Modification of LiBH4 Powder Take the pretreated LiBH4 powder from step one and place it in a quartz mortar with NiCl2 powder, NiBr2 powder, CoBr2 powder and FeBr2 powder in a molar ratio of 9:0.2:0.2:0.4:0.2. Grind and mix them evenly by hand, then seal them in a ball mill jar, add grinding balls, and the ball-to-powder ratio is 100:1. Perform planetary ball milling at 400 rpm for 10 h in an argon atmosphere to obtain the solid electrolyte 0.9LiBH4-0.02NiCl2-0.02NiBr2-0.04CoBr2-0.02FeBr2 of this embodiment.

[0056] Example 4: Solid electrolyte for lithium-ion batteries: 0.9LiBH4-0.03NiCl2-0.03NiBr2-0.01CoBr2-0.03FeBr2 and its preparation The solid electrolyte for lithium-ion batteries in this embodiment is LiBH4 modified by doping with NiCl2, NiBr2, CoBr2 and FeBr2, denoted as "0.9LiBH4-0.03NiCl2-0.03NiBr2-0.01CoBr2-0.03FeBr2", and its preparation steps are as follows: Step 1: Pretreatment of LiBH4 powder LiBH4 powder was sealed in a glass tube, and the environment inside the tube was evacuated to a vacuum using an oil pump. The tube was kept at 140℃ for 10 hours and then allowed to cool naturally to room temperature to obtain pretreated LiBH4 powder.

[0057] Step 2: Doping and Modification of LiBH4 Powder Take the pretreated LiBH4 powder from step one, and place it in a quartz mortar with NiCl2 powder, NiBr2 powder, CoBr2 powder and FeBr2 powder in a molar ratio of 9:0.3:0.3:0.1:0.3. Grind and mix them evenly by hand, then seal them in a ball mill jar, add grinding balls, and the ball-to-powder ratio is 100:1. Perform planetary ball milling at 400 rpm for 10 h in an argon atmosphere to obtain the solid electrolyte 0.9LiBH4-0.03NiCl2-0.03NiBr2-0.01CoBr2-0.03FeBr2 of this embodiment.

[0058] Example 5: Solid electrolyte for lithium-ion batteries: 0.9LiBH4-0.01NiCl2-0.01NiBr2-0.07CoBr2-0.01FeBr2 and its preparation The solid electrolyte for lithium-ion batteries in this embodiment is LiBH4 modified by doping with NiCl2, NiBr2, CoBr2 and FeBr2, denoted as "0.9LiBH4-0.01NiCl2-0.01NiBr2-0.07CoBr2-0.01FeBr2", and its preparation steps are as follows: Step 1: Pretreatment of LiBH4 powder LiBH4 powder was sealed in a glass tube, and the environment inside the tube was evacuated to a vacuum using an oil pump. The tube was kept at 140℃ for 10 hours and then allowed to cool naturally to room temperature to obtain pretreated LiBH4 powder.

[0059] Step 2: Doping and Modification of LiBH4 Powder Take the pretreated LiBH4 powder from step one, and place it in a quartz mortar with NiCl2 powder, NiBr2 powder, CoBr2 powder and FeBr2 powder in a molar ratio of 9:0.1:0.1:0.7:0.1. Grind and mix them evenly by hand, then seal them in a ball mill jar, add grinding balls, and the ball-to-powder ratio is 100:1. Ball mill in an argon atmosphere at a speed of 400 rpm for 10 h to obtain the solid electrolyte 0.9LiBH4-0.01NiCl2-0.01NiBr2-0.07CoBr2-0.01FeBr2 of this embodiment.

[0060] Example 6: Solid electrolyte for lithium-ion batteries: 0.9LiBH4-0.025CoCl2-0.025NiBr2-0.025CoBr2-0.025FeBr2 and its preparation The solid electrolyte for lithium-ion batteries in this embodiment is LiBH4 modified by doping with CoCl2, NiBr2, CoBr2 and FeBr2, denoted as "0.9LiBH4-0.025CoCl2-0.025NiBr2-0.025CoBr2-0.025FeBr2", and its preparation steps are as follows: Step 1: Pretreatment of LiBH4 powder LiBH4 powder was sealed in a glass tube, and the environment inside the tube was evacuated to a vacuum using an oil pump. The tube was kept at 140℃ for 10 hours and then allowed to cool naturally to room temperature to obtain pretreated LiBH4 powder.

[0061] Step 2: Doping and Modification of LiBH4 Powder Take the pretreated LiBH4 powder from step one, and place it in a quartz mortar with CoCl2 powder, NiBr2 powder, CoBr2 powder and FeBr2 powder in a molar ratio of 9:0.25:0.25:0.25:0.25. Grind and mix them evenly by hand, then seal them in a ball mill jar, add grinding balls, and the ball-to-powder ratio is 100:1. Perform planetary ball milling at 400 rpm for 10 h in an argon atmosphere to obtain the solid electrolyte 0.9LiBH4-0.025CoCl2-0.025NiBr2-0.025CoBr2-0.025FeBr2 of this embodiment.

[0062] Test Example 2: The effect of composite dopants on improving the ionic conductivity of LiBH4 The solid electrolytes prepared in Examples 1-6 were used to test their ionic conductivity at room temperature (30°C), and the results are shown in Table 1. In particular, the EIS curve of the solid electrolyte in Example 2 measured at 30°C is shown below. Figure 2 As shown ( Figure 2 In the figure, the horizontal axis Z' and the vertical axis -Z'' represent the real and imaginary parts of the impedance, respectively.

[0063] Table 1. Room temperature ionic conductivity of solid electrolytes in Examples 1-6

[0064] As can be seen from Table 1: (1) With the same total doping amount (10 mol%), compared with using CoBr2 alone as a dopant (Example 1), using NiCl2, NiBr2, CoBr2 and FeBr2 together in a certain proportion (Examples 2 and 3) can improve the ionic conductivity of LiBH4 to a greater extent. The reason is that co-doping with NiCl2, NiBr2, CoBr2 and FeBr2 can increase the configuration entropy of the material, inducing a higher concentration of vacancies, which is beneficial for Li +The migration of Li provides abundant, pre-existing low-energy pathways, enabling Li + Migration can be accomplished by "jumping" into a nearby vacancy, which significantly reduces the activation energy of migration and thus improves the ionic conductivity of the material.

[0065] (2) Although the four dopants NiCl2, NiBr2, CoBr2 and FeBr2 were also used in Examples 4 and 5, the ionic conductivity of the obtained solid electrolyte was significantly lower than that of Examples 2 and 3, and even lower than that of Example 1 which used only CoBr2 as a dopant. This indicates that the ratio of the four dopants affects their effect on improving the ionic conductivity of LiBH4. The reason for this is that when using a single dopant, CoBr2 can improve the ionic conductivity of lithium borohydride to a greater extent than other metal halides (including NiCl2, NiBr2 and FeBr2) (see the detection results in Test Example 1). Therefore, when the ratio of NiCl2, NiBr2, CoBr2 and FeBr2 is not properly controlled, the synergistic effect between these dopants is weak. On the contrary, the improvement effect on the ionic conductivity of LiBH4 may be weakened because some CoBr2 is replaced by NiCl2, NiBr2 and FeBr2.

[0066] (3) In Example 6, four dopants, CoCl2, NiBr2, CoBr2 and FeBr2, were used. The ionic conductivity of the solid electrolyte obtained was lower than that in Example 2. The reason for this is that, in the selection of the four dopants, NiCl2, NiBr2, CoBr2 and FeBr2 have better lattice stability than different combinations of the same element. They can form a solid solution with LiBH4 better, which is beneficial to improving the room temperature ionic conductivity, thermal stability and chemical stability of the material.

[0067] Test Example 3: Lithium Stability Test The solid electrolyte prepared in Example 2 was used to assemble a lithium-to-lithium symmetric battery (composed of lithium sheets, solid electrolyte sheets, and lithium sheets stacked sequentially). The specific steps are as follows: First, 100 mg of solid electrolyte was weighed and placed into a mold. It was then pressed into a sheet shape with a pressure of 10 MPa. The bottom of the mold was then removed, and a lithium sheet with a diameter of 10 mm was placed in it. The bottom of the mold was then put back in. Next, the pressure bar was removed, and a lithium sheet with a diameter of 10 mm was placed in it. The lock nut and pressure bar were then put back in. Finally, circular insulating pads were placed on the top and bottom of the mold, and the mold was pressed tightly with a stainless steel clamp. The pressure during pressing was controlled by a torque wrench, and the torque was 0.5 N·m.

[0068] The step current charge-discharge curves of lithium-to-lithium symmetric batteries at 60°C were tested, and the results are shown in [reference needed]. Figure 3At 60°C, when using the solid electrolyte of Example 2, the limiting current density (CCD) of the lithium-to-lithium symmetric battery is 9.8 mA / cm². 2 This far exceeds the limit current density of untreated pure LiBH4 (when using pure LiBH4 as a solid electrolyte, the limiting current density of lithium-to-lithium symmetric cells is 3.5 mA / cm²). 2 This indicates that doping LiBH4 with NiCl2, NiBr2, CoBr2 and FeBr2 can effectively improve its stability against lithium.

Claims

1. A solid electrolyte for lithium-ion batteries, characterized in that, The solid electrolyte is LiBH4 modified with MX2 doping; the MX2 is NiCl2, NiBr2, CoBr2 and FeBr2 in a molar ratio of 0.5~1:0.5~1:1:0.5~1; the molar ratio between LiBH4 and MX2 is 8~9:

1.

2. A method for preparing a solid electrolyte according to claim 1, characterized in that, step... include: After heat treatment of LiBH4 powder in a vacuum environment, it is mixed with MX2 powder and ball-milled in an inert atmosphere to obtain a solid electrolyte.

3. The preparation method according to claim 2, characterized in that, The heat treatment temperature is 100~180℃.

4. The preparation method according to claim 2, characterized in that, The heat treatment time is 8~12 h.

5. The preparation method according to claim 2, characterized in that, The mixing method involves grinding and mixing in a mortar.

6. The preparation method according to claim 2, characterized in that, The ball milling method is planetary ball milling, with a ball-to-material ratio of 50~200:1, a rotation speed of 300~1000 rpm, and a milling time of 6~20 h.

7. The preparation method according to claim 2, characterized in that, The inert atmosphere is one or more of nitrogen, helium, and argon.

8. The application of the solid electrolyte according to claim 1 in lithium-ion batteries.

9. The application according to claim 8, characterized in that, The lithium-ion battery includes a positive electrode, a solid electrolyte sheet, and a negative electrode sheet stacked in sequence, wherein the solid electrolyte sheet contains the solid electrolyte.

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