A multi-element composite lithium borohydride-based solid-state electrolyte, a preparation method therefor, and applications thereof

Abstract

This invention relates to the field of lithium-ion battery technology, and discloses a multi-component composite lithium borohydride-based solid electrolyte, its preparation method, and its applications. The multi-component composite lithium borohydride-based solid electrolyte includes a core layer and a shell layer covering the core layer; the core layer comprises lithium borohydride modified with nickel iodide doping; the shell layer comprises zirconium dioxide. In the multi-component composite lithium borohydride-based solid electrolyte of this invention, by doping LiBH4 with NiI2 and providing a shell layer containing ZrO2, the bidirectional promoting effect between NiI2 and ZrO2 can be utilized to impart higher ionic conductivity to the solid electrolyte.

Description

Technical Field

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

[0002] With the rapid development of electric vehicles and large-scale energy storage technologies, the demand for high-energy-density and high-safety rechargeable batteries is becoming increasingly urgent across various sectors. Traditional lithium-ion batteries use organic liquid electrolytes, which pose safety hazards such as easy leakage, flammability, and explosion, severely restricting their further development. All-solid-state lithium batteries use non-flammable inorganic solid electrolytes to replace liquid electrolytes, fundamentally solving the safety problem. At the same time, they are expected to be matched with high-voltage, high-capacity cathode materials, thereby achieving a significant increase in energy density, and are widely recognized as the ideal choice for next-generation energy storage devices.

[0003] Among numerous solid-state electrolyte systems, hydride solid-state electrolytes, represented by lithium borohydride (LiBH4), have attracted widespread attention due to their excellent electrochemical stability with lithium metal anodes, high lithium-ion transference numbers, and rapid ion conduction performance. However, LiBH4 exhibits extremely low ionic conductivity at room temperature, only 10⁻⁶. -8 The S / cm value is insufficient to meet the requirements of practical battery applications. Studies have shown that the main reason for its low ionic conductivity is the excessively high lithium-ion migration barrier, and the crystal structure is not conducive to the rapid conduction of lithium ions at room temperature.

[0004] To improve the ionic conductivity of LiBH4, researchers have explored various modification methods. Currently, the mainstream methods include elemental doping and structural composites. Regarding elemental doping, anion doping (such as using I₂) is a common approach. - Partially replaces [BH4] - This has been proven to be an effective strategy, the principle of which is that introducing large-size anions can expand lattice channels and promote the growth of Li. + Transport. However, existing single-ion doping methods have significant shortcomings, limiting their contribution to improving the ionic conductivity of LiBH4. For example, patent CN119674203A uses LiI to dope LiBH4, but the ionic conductivity at 40℃ can only reach 1.66 × 10⁻⁶. -5 ~4.12×10 -5 S / cm. Summary of the Invention

[0005] To address the technical problem that existing ion doping modification methods have limited effectiveness in improving the ionic conductivity of LiBH4, this invention provides a multi-component composite lithium borohydride-based solid electrolyte. By using NiI2-doped LiBH4 in the core layer and setting a shell layer containing ZrO2, the ionic conductivity of the lithium borohydride-based solid electrolyte can be improved to a greater extent.

[0006] The specific technical solution of this invention is as follows: In a first aspect, the present invention discloses a multi-component composite lithium borohydride-based solid electrolyte, comprising a core layer and a shell layer covering the core layer; the core layer comprises lithium borohydride modified by nickel iodide (NiI2) doping; the shell layer comprises zirconium dioxide (ZrO2).

[0007] In this invention, NiI2 is used to dope and modify LiBH4. 2+ The introduction of I can generate cation vacancies in LiBH4. - The introduction of NiI2 can expand the lithium-ion transport channels, thereby improving lithium-ion transport efficiency. Simultaneously, the nickel iodide doped in the core layer of lithium borohydride and the zirconium dioxide in the shell can achieve a bidirectional promoting effect, further improving the ionic conductivity of the solid electrolyte: the modification of the LiBH4 crystal structure by NiI2 enables ZrO2 to better connect with boron and form a benign interface; the ZrO2 coating further extends the lithium-ion transport channels broadened by NiI2. The realization of this bidirectional promoting effect depends on the specific dopant NiI2 and the specific coating agent ZrO2. Changing the choice of dopant and coating agent will weaken or prevent the bidirectional promoting effect from occurring. For example, if NiI2 is changed to ZrO2, the bidirectional promoting effect will be weakened or not generated at all. 2+ Replace with other metal cations (such as Mg) 2+ (etc.), which will cause it to affect [BH4] - The Coulomb gravitational pull weakens, making it unable to effectively control Li. + From [BH4] - This releases the Coulomb effect between the two, resulting in a decrease in ionic conductivity; if I... - Replace with Br - or Cl - , due to Br - Cl - Its relatively low polarity results in a weaker ability to expand the lattice, leading to [BH4] in the lattice... - With fewer contact sites with oxides, ZrO2 cannot effectively promote the formation of connections and a benign interface between ZrO2 and B elements. If ZrO2 is replaced with other metal oxides, the BO bonds formed are weaker or difficult to form. As a result, the bonding between the metal oxide and LiBH4 decreases, leading to severe phase separation and a large grain boundary impedance, which interferes with ion transport. The coating of metal oxides is unable to further extend the lithium-ion transport channels broadened by NiI2.

[0008] Preferably, the zirconium dioxide content in the multi-component composite lithium borohydride-based solid electrolyte is 20-30 wt%.

[0009] Preferably, in the lithium borohydride and nickel iodide, the proportion of nickel iodide is 2~10 mol.

[0010] As a further preferred embodiment, the proportion of nickel iodide in the lithium borohydride and nickel iodide is 6-8 mol.

[0011] Secondly, this invention discloses a method for preparing the aforementioned multi-component composite lithium borohydride-based solid electrolyte, comprising the following steps: S1: Mix lithium borohydride and nickel iodide and ball mill to obtain nickel iodide-doped lithium borohydride; S2: The product of S1 was mixed with zirconium dioxide and ball-milled to obtain a multi-component composite lithium borohydride-based solid electrolyte.

[0012] The above preparation process adopts a stepwise ball milling method, which physically and temporally separates the two key modification steps of bulk ion doping and surface interface engineering. This effectively avoids the competition and interference between the doping reaction and the formation of the coating layer in a single ball milling process, ensuring the formation of NiI2 doping and ZrO2 coating structure, thereby enabling a bidirectional promoting effect between the two.

[0013] The mechanism of forming NiI2 doping and ZrO2 coating through ball milling in this invention is as follows: In step S1, due to the weak Ni-I bond energy, NiI2 is prone to bond breakage during ball milling. 2+ and I - In step S2, ZrO2 has high hardness and strong Zr-O bond energy, so the Zr-O bond is not easily broken during ball milling, causing ions to enter the interior of the LiBH4 lattice. Instead, it mainly forms a coating layer in the form of ZrO2.

[0014] Preferably, in steps S1 and S2, the mixing and ball milling process is carried out under inert gas protection, and the ball-to-material ratio is 50~200:1.

[0015] Preferably, in step S1, the mixing ball milling speed is 400~1000 rpm and the time is 10~20 h.

[0016] Preferably, in step S2, the mixing ball mill rotates at a speed of 250-350 rpm for 3-5 hours.

[0017] The differentiated ball milling speed and time design in steps S1 and S2 above will be more conducive to forming NiI2 doped and ZrO2 coated structures.

[0018] Preferably, before step S1, lithium borohydride is heat-treated; the heat treatment process is carried out under vacuum at a temperature of 100~180℃ for 8~12 h.

[0019] Thirdly, this invention discloses the application of the multi-component composite lithium borohydride-based solid electrolyte in lithium-ion batteries.

[0020] Preferably, the lithium-ion battery includes a positive electrode, a solid electrolyte membrane, and a negative electrode stacked in sequence, wherein the solid electrolyte membrane contains the multi-component composite lithium borohydride-based solid electrolyte.

[0021] Compared with the prior art, the present invention has the following advantages: (1) In the multi-component composite lithium borohydride-based solid electrolyte of the present invention, by doping NiI2 in LiBH4 and setting a shell containing ZrO2 on the outside, the bidirectional promoting effect between NiI2 and ZrO2 can be utilized to give the solid electrolyte higher ionic conductivity.

[0022] (2) In the process of preparing multi-component composite lithium borohydride-based solid-state electrolyzers, the present invention adopts a stepwise ball milling method. First, LiBH4 and NiI2 are mixed and ball milled, and then the product is mixed and ball milled with ZrO2. This method can ensure the formation of NiI2 doping and ZrO2 coating structure, thereby realizing the bidirectional promoting effect between the two. Attached Figure Description

[0023] Figure 1 The Arrhenius curves are for the solid electrolytes of Example 1 and Comparative Examples 1-3.

[0024] Figure 2 The image shows the electrochemical impedance spectroscopy (EIS) curve of the solid electrolyte in Example 1 at 30°C.

[0025] Figure 3 The Arrhenius curves are for the solid electrolytes of Examples 1 and Comparative Examples 4-7.

[0026] Figure 4 The Arrhenius curves are for the solid electrolytes in Examples 1-5.

[0027] Figure 5 The step current charge-discharge curve of the lithium-ion battery made using the solid electrolyte of Example 1 at 60°C is shown.

[0028] Figure 6 The cyclic voltammetry curves of the lithium-ion battery made using the solid electrolyte of Example 1 at 60°C are shown. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0030] First, the present invention relates to a multi-component composite lithium borohydride-based solid electrolyte, comprising a core layer and a shell layer covering the core layer; the core layer comprises lithium borohydride modified by nickel iodide doping; the shell layer comprises zirconium dioxide.

[0031] In some specific embodiments, the proportion of zirconium dioxide in the multi-component composite lithium borohydride-based solid electrolyte is 20-30 wt%.

[0032] In some specific embodiments, the proportion of nickel iodide in lithium borohydride and nickel iodide is 2~10 mol.

[0033] Second, the present invention relates to a method for preparing the aforementioned multi-component composite lithium borohydride-based solid electrolyte, the steps of which include: S1: Mix lithium borohydride and nickel iodide and ball mill to obtain nickel iodide-doped lithium borohydride; S2: The product of S1 was mixed with zirconium dioxide and ball-milled to obtain a multi-component composite lithium borohydride-based solid electrolyte.

[0034] In some specific embodiments, in steps S1 and S2, the mixing and ball milling process is carried out under inert gas protection, with a ball-to-material ratio of 50 to 200:1. The inert gas can be selected from one or more of nitrogen, helium, and argon.

[0035] In some specific embodiments, in step S1, the mixing ball mill rotates at a speed of 400~1000 rpm for a time of 10~20 h.

[0036] In some specific embodiments, in step S2, the mixing ball mill rotates at a speed of 250~350 rpm for a time of 3~5 h.

[0037] In some specific embodiments, lithium borohydride is heat-treated before step S1; the heat treatment process is carried out under vacuum at a temperature of 100~180℃ for 8~12 h.

[0038] Third, the present invention relates to the application of the multi-component composite lithium borohydride-based solid electrolyte in lithium-ion batteries.

[0039] In some specific embodiments, the lithium-ion battery includes a positive electrode, a solid electrolyte membrane, and a negative electrode stacked in sequence, wherein the solid electrolyte membrane contains the multi-component composite lithium borohydride-based solid electrolyte.

[0040] The present invention will now be described with reference to 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.

[0041] Example 1: Solid electrolyte 0.92LiBH4-0.08NiI2-25wt%ZrO2 This embodiment prepares a multi-component composite lithium borohydride-based solid electrolyte through the following steps: 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. After being kept at 140℃ for 10 hours, the tube was allowed to cool naturally to room temperature to obtain pretreated LiBH4 powder.

[0042] Step Two: First Ball Milling According to the molar ratio of 92:8, the pretreated LiBH4 powder and NiI2 powder obtained in step one were placed in a quartz mortar and manually ground and mixed evenly. Then, the mixture was sealed in a ball mill jar, and grinding balls were added. The ball-to-powder ratio was 100:1. The mixture was then subjected to planetary ball milling at 400 rpm for 10 h in an argon atmosphere to obtain NiI2-doped modified LiBH4 (denoted as "0.92LiBH4-0.08NiI2").

[0043] Step 3: Secondary ball milling The 0.92LiBH4-0.08NiI2 and ZrO2 powders obtained in step two were taken at a mass ratio of 3:1 and manually ground and mixed evenly in a quartz mortar. Then, the mixture was sealed in a ball mill jar, and grinding balls were added. The ball-to-powder ratio was 100:1. The mixture was then subjected to planetary ball milling at 300 rpm for 5 h in an argon atmosphere, thereby coating the 0.92LiBH4-0.08NiI2 with a ZrO2 shell, thus obtaining the multi-component composite lithium borohydride-based solid electrolyte of this embodiment (denoted as "0.92LiBH4-0.08NiI2-25wt%ZrO2").

[0044] Comparative Example 1: Solid electrolyte 0.92LiBH4-0.08NiI2-25wt%NiI2 The only difference between this comparative example and Example 1 is that the ZrO2 powder in step three is replaced with an equal mass of NiI2 powder; all other raw materials and steps are the same as in Example 1. Specifically, this comparative example prepares a multi-component composite lithium borohydride-based solid electrolyte through the following steps: 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. After being kept at 140℃ for 10 hours, the tube was allowed to cool naturally to room temperature to obtain pretreated LiBH4 powder.

[0045] Step Two: First Ball Milling According to the molar ratio of 92:8, the pretreated LiBH4 powder and NiI2 powder obtained in step one were placed in a quartz mortar and manually ground and mixed evenly. Then, the mixture was sealed in a ball mill jar, and grinding balls were added. The ball-to-powder ratio was 100:1. The mixture was then subjected to planetary ball milling at 400 rpm for 10 h in an argon atmosphere to obtain NiI2-doped modified LiBH4 (denoted as "0.92LiBH4-0.08NiI2").

[0046] Step 3: Secondary ball milling According to the mass ratio of 3:1, the 0.92LiBH4-0.08NiI2 and NiI2 powder obtained in step two were placed in a quartz mortar and manually ground and mixed evenly. Then, the mixture was sealed in a ball mill jar, and grinding balls were added. The ball-to-material ratio was 100:1. The mixture was then subjected to planetary ball milling at 300 rpm for 5 h in an argon atmosphere to obtain the multi-component composite lithium borohydride-based solid electrolyte of this comparative example (denoted as "0.92LiBH4-0.08NiI2-25wt%NiI2").

[0047] Comparative Example 2: Solid electrolyte 0.92LiBH4-0.08ZrO2-25wt%ZrO2 The only difference between this comparative example and Example 1 is that the NiI2 powder in step two is replaced with an equimolar amount of ZrO2 powder; all other raw materials and steps are the same as in Example 1. Specifically, this comparative example prepares a multi-component composite lithium borohydride-based solid electrolyte through the following steps: 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. After being kept at 140℃ for 10 hours, the tube was allowed to cool naturally to room temperature to obtain pretreated LiBH4 powder.

[0048] Step Two: First Ball Milling According to the molar ratio of 92:8, the pretreated LiBH4 powder and ZrO2 powder obtained in step one were placed in a quartz mortar and manually ground and mixed evenly. Then, the mixture was sealed in a ball mill jar, and grinding balls were added. The ball-to-powder ratio was 100:1. The mixture was then subjected to planetary ball milling at 400 rpm for 10 h in an argon atmosphere to obtain the complex of LiBH4 and ZrO2 (denoted as "0.92LiBH4-0.08ZrO2").

[0049] Step 3: Secondary ball milling The 0.92LiBH4-0.08ZrO2 and ZrO2 powder obtained in step two were taken at a mass ratio of 3:1, placed in a quartz mortar and manually ground and mixed evenly. Then, the mixture was sealed in a ball mill jar, and grinding balls were added. The ball-to-material ratio was 100:1. The mixture was then subjected to planetary ball milling at 300 rpm for 5 h in an argon atmosphere to obtain the multi-component composite lithium borohydride-based solid electrolyte of this comparative example (denoted as "0.92LiBH4-0.08ZrO2-25wt%ZrO2").

[0050] Comparative Example 3: Solid electrolyte 0.92LiBH4-0.08NiI2 / 25wt%ZrO2 The only difference between this comparative example and Example 1 is that steps two and three are combined into one step; all other raw materials and steps are the same as in Example 1. Specifically, this comparative example prepares a multi-component composite lithium borohydride-based solid electrolyte through the following steps: 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. After being kept at 140℃ for 10 hours, the tube was allowed to cool naturally to room temperature to obtain pretreated LiBH4 powder.

[0051] Step 2: Ball milling The pretreated LiBH4 powder, NiI2 powder, and ZrO2 powder obtained in step one (the amounts of pretreated LiBH4 powder, NiI2 powder, and ZrO2 powder are the same as in Example 1) were placed in a quartz mortar and manually ground and mixed evenly. Then, the mixture was sealed in a ball mill jar, and grinding balls were added. The ball-to-powder ratio was 100:1. The mixture was then subjected to planetary ball milling at 400 rpm for 10 h in an argon atmosphere to obtain the multi-component composite lithium borohydride-based solid electrolyte of this comparative example (denoted as "0.92LiBH4-0.08NiI2 / 25wt%ZrO2").

[0052] Test Example 1: The bidirectional promoting effect between NiI2 and ZrO2 The solid electrolytes prepared in Examples 1 and 1-3 were analyzed by electrochemical impedance spectroscopy (EIS) to detect their ionic conductivity at different temperatures, and Arrhenius curves were plotted. The results are shown in […]. Figure 1 ( Figure 1 In the diagram, "T" on the horizontal axis represents temperature in Kelvin (K); "σ" on the vertical axis represents ionic conductivity. The EIS curve of the solid electrolyte in Example 1, measured at room temperature (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. The measured impedance is 216.2 Ω (30℃), and the ionic conductivity is 3.87 × 10⁻⁶.-4 S / cm (30℃).

[0053] contrast Figure 1 The Arrhenius curves of various solid electrolytes show that: (1) Compared with Comparative Example 1 and Comparative Example 2, the solid electrolyte of Example 1 has a higher ionic conductivity. This is because the nickel iodide doped in the core layer of lithium borohydride and the zirconium dioxide in the shell layer can also achieve a bidirectional promoting effect through the following mechanism, which further improves the ionic conductivity of the solid electrolyte: the modification of the LiBH4 crystal structure by NiI2 can enable ZrO2 to better connect with the B element and form a good interface. After ZrO2 coating, the lithium ion transport channel broadened by NiI2 can be further extended.

[0054] (2) In Comparative Example 3, a one-step ball milling method was used to mix and mill LiBH4, NiI2 and ZrO2 together. The ionic conductivity of the solid electrolyte obtained was lower than that in Example 1. This is because the stepwise ball milling method used in Example 1 (first mixing and milling LiBH4 and NiI2, and then mixing and milling the product with ZrO2) can physically and temporally separate the two key modification steps of bulk ion doping and surface interface engineering. This avoids the competition and interference between the doping reaction and the formation of the coating layer in the one-step ball milling method (Comparative Example 3), which helps to ensure the formation of NiI2 doping and ZrO2 coating structure, thereby enabling a bidirectional promoting effect between the two.

[0055] Comparative Example 4: Solid electrolyte 0.92LiBH4-0.08NiCl2-25wt%ZrO2 The only difference between this comparative example and Example 1 is that the NiI2 powder in step two is replaced with an equimolar amount of NiCl2 powder; all other raw materials and steps are the same as in Example 1. Specifically, this comparative example prepares a multi-component composite lithium borohydride-based solid electrolyte through the following steps: 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. After being kept at 140℃ for 10 hours, the tube was allowed to cool naturally to room temperature to obtain pretreated LiBH4 powder.

[0056] Step Two: First Ball Milling According to the molar ratio of 92:8, the pretreated LiBH4 powder and NiCl2 powder obtained in step one were placed in a quartz mortar and manually ground and mixed evenly. Then, the mixture was sealed in a ball mill jar, and grinding balls were added. The ball-to-powder ratio was 100:1. The mixture was then subjected to planetary ball milling at 400 rpm for 10 h in an argon atmosphere to obtain NiCl2-doped modified LiBH4 (denoted as "0.92LiBH4-0.08NiCl2").

[0057] Step 3: Secondary ball milling The 0.92LiBH4-0.08NiCl2 and ZrO2 powder obtained in step two were taken at a mass ratio of 3:1 and manually ground and mixed evenly in a quartz mortar. Then, the mixture was sealed in a ball mill jar, and grinding balls were added. The ball-to-powder ratio was 100:1. The mixture was then subjected to planetary ball milling at 300 rpm for 5 h in an argon atmosphere to coat the 0.92LiBH4-0.08NiCl2 with a ZrO2 shell, thus obtaining the multi-component composite lithium borohydride-based solid electrolyte of this comparative example (denoted as "0.92LiBH4-0.08NiCl2-25wt%ZrO2").

[0058] Comparative Example 5: Solid electrolyte 0.92LiBH4-0.08NiBr2-25wt%ZrO2 The only difference between this comparative example and Example 1 is that the NiI2 powder in step two is replaced with an equimolar amount of NiBr2 powder; all other raw materials and steps are the same as in Example 1. Specifically, this comparative example prepares a multi-component composite lithium borohydride-based solid electrolyte through the following steps: 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. After being kept at 140℃ for 10 hours, the tube was allowed to cool naturally to room temperature to obtain pretreated LiBH4 powder.

[0059] Step Two: First Ball Milling According to the molar ratio of 92:8, the pretreated LiBH4 powder and NiBr2 powder obtained in step one were placed in a quartz mortar and manually ground and mixed evenly. Then, the mixture was sealed in a ball mill jar, and grinding balls were added. The ball-to-powder ratio was 100:1. The mixture was then subjected to planetary ball milling at 400 rpm for 10 h in an argon atmosphere to obtain NiBr2-doped modified LiBH4 (denoted as "0.92LiBH4-0.08NiBr2").

[0060] Step 3: Secondary ball milling The 0.92LiBH4-0.08NiBr2 and ZrO2 powders obtained in step two were taken at a mass ratio of 3:1 and manually ground and mixed evenly in a quartz mortar. Then, the mixture was sealed in a ball mill jar, and grinding balls were added. The ball-to-powder ratio was 100:1. The mixture was then subjected to planetary ball milling at 300 rpm for 5 h in an argon atmosphere to coat the 0.92LiBH4-0.08NiBr2 with a ZrO2 shell, thus obtaining the multi-component composite lithium borohydride-based solid electrolyte of this comparative example (denoted as "0.92LiBH4-0.08NiBr2-25wt%ZrO2").

[0061] Comparative Example 6: Solid electrolyte 0.92LiBH4-0.08MgI2-25wt%ZrO2 The only difference between this comparative example and Example 1 is that the NiI2 powder in step two is replaced with an equimolar amount of MgI2 powder; all other raw materials and steps are the same as in Example 1. Specifically, this comparative example prepares a multi-component composite lithium borohydride-based solid electrolyte through the following steps: 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. After being kept at 140℃ for 10 hours, the tube was allowed to cool naturally to room temperature to obtain pretreated LiBH4 powder.

[0062] Step Two: First Ball Milling According to the molar ratio of 92:8, the pretreated LiBH4 powder and MgI2 powder obtained in step one were placed in a quartz mortar and manually ground and mixed evenly. Then, the mixture was sealed in a ball mill jar, and grinding balls were added. The ball-to-powder ratio was 100:1. The mixture was then subjected to planetary ball milling at 400 rpm for 10 h in an argon atmosphere to obtain MgI2-doped modified LiBH4 (denoted as "0.92LiBH4-0.08MgI2").

[0063] Step 3: Secondary ball milling The 0.92LiBH4-0.08MgI2 and ZrO2 powders obtained in step two were taken at a mass ratio of 3:1 and manually ground and mixed evenly in a quartz mortar. Then, the mixture was sealed in a ball mill jar, and grinding balls were added. The ball-to-powder ratio was 100:1. The mixture was then subjected to planetary ball milling at 300 rpm for 5 h in an argon atmosphere to coat the 0.92LiBH4-0.08MgI2 with a ZrO2 shell, thus obtaining the multi-component composite lithium borohydride-based solid electrolyte of this comparative example (denoted as "0.92LiBH4-0.08MgI2-25wt%ZrO2").

[0064] Comparative Example 7: Solid electrolyte 0.92LiBH4-0.08NiI2-25wt%MgO The only difference between this comparative example and Example 1 is that the ZrO2 powder in step three is replaced with an equal mass of MgO powder; all other raw materials and steps are the same as in Example 1. Specifically, this comparative example prepares a multi-component composite lithium borohydride-based solid electrolyte through the following steps: 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. After being kept at 140℃ for 10 hours, the tube was allowed to cool naturally to room temperature to obtain pretreated LiBH4 powder.

[0065] Step Two: First Ball Milling According to the molar ratio of 92:8, the pretreated LiBH4 powder and NiI2 powder obtained in step one were placed in a quartz mortar and manually ground and mixed evenly. Then, the mixture was sealed in a ball mill jar, and grinding balls were added. The ball-to-powder ratio was 100:1. The mixture was then subjected to planetary ball milling at 400 rpm for 10 h in an argon atmosphere to obtain NiI2-doped modified LiBH4 (denoted as "0.92LiBH4-0.08NiI2").

[0066] Step 3: Secondary ball milling The 0.92LiBH4-0.08NiI2 and MgO powder obtained in step two were mixed by hand in a quartz mortar at a mass ratio of 3:1. The mixture was then sealed in a ball mill jar, and grinding balls were added at a ball-to-powder ratio of 100:1. The mixture was then subjected to planetary ball milling at 300 rpm for 5 h in an argon atmosphere to coat the 0.92LiBH4-0.08NiI2 with a MgO shell, thus obtaining the multi-component composite lithium borohydride-based solid electrolyte of this comparative example (denoted as "0.92LiBH4-0.08NiI2-25wt%MgO").

[0067] Test Example 2: The effect of dopant and coating agent selection and step-by-step ball milling on ionic conductivity The solid electrolytes prepared in Examples 1 and Comparative Examples 4-7 were analyzed by electrochemical impedance spectroscopy (EIS) to detect their ionic conductivity at different temperatures, and Arrhenius curves were plotted. The results are shown in […]. Figure 3 ( Figure 3 In the diagram, "T" on the horizontal axis represents temperature in Kelvin (K); "σ" on the vertical axis represents ionic conductivity.

[0068] contrast Figure 3 The Arrhenius curves of various solid electrolytes show that: (1) When LiBH4 is modified by doping with metal halides only (without coating with ZrO2), the room temperature (30°C) ionic conductivity of 0.92LiBH4-0.08NiCl2 (the product obtained in step two of Comparative Example 4) and 0.92LiBH4-0.08NiBr2 (the product obtained in step two of Comparative Example 5) are 2.13×10⁻⁶. -4 S / cm and 2.08×10 -4 The ionic conductivity (S / cm) is higher than that of 0.92LiBH4-0.08NiI2 (the product obtained in step two of Example 1), which is 1.97 × 10⁻⁶. -4S / cm. However, when coated with ZrO2, the room temperature (30°C) ionic conductivity of 0.92LiBH4-0.08NiCl2-25wt%ZrO2 (the final product obtained in Comparative Example 4) and 0.92LiBH4-0.08NiBr2-25wt%ZrO2 (the final product obtained in Comparative Example 5) were 2.97 × 10⁻⁶ S / cm. -4 S / cm and 3.15×10 -4 The ionic conductivity of the product (S / cm) is 3.87 × 10⁻¹⁰, which is lower than that of 0.92LiBH₄-0.08NiI₂-25wt%ZrO₂ (the final product obtained in Example 1). -4 S / cm. This is because the modification of the LiBH4 crystal structure by NiI2 enables ZrO2 to better form connections and benign interfaces with the B element, while Br - Cl - Since NiCl2 and NiBr2 have relatively low polarity, their doping effect on promoting the connection and benign interface between ZrO2 and B is poor.

[0069] (2) When ZrO2 is used for coating, the room temperature (30°C) ionic conductivity of 0.92LiBH4-0.08MgI2-25wt%ZrO2 (the final product obtained in Comparative Example 6) is lower than that of 0.92LiBH4-0.08NiI2-25wt%ZrO2 (the final product obtained in Example 1). This is because Ni... 2+ Replace with Mg 2+ This will then lead to its effect on [BH4]. - The Coulomb gravitational pull weakens, making it unable to effectively control Li. + From [BH4] - This releases the Coulomb effect between the two, resulting in a decrease in ionic conductivity.

[0070] (3) Compared with the solid electrolyte 0.92LiBH4-0.08NiI2-25wt%MgO in Comparative Example 7, the solid electrolyte 0.92LiBH4-0.08NiI2-25wt%ZrO2 in Example 1 has a higher ionic conductivity. This is because the ZrO2 coating can further extend the lithium-ion transport channel broadened by NiI2. However, when ZrO2 is replaced with MgO, the constructed BO bond is weaker, so the binding between the metal oxide and LiBH4 decreases, resulting in severe phase separation and generating a large grain boundary impedance, which interferes with ion transport. The coating of metal oxide is difficult to further extend the lithium-ion transport channel broadened by NiI2.

[0071] Example 2: Solid electrolyte 0.98LiBH4-0.02NiI2-25wt%ZrO2 The only difference between this embodiment and Example 1 is that the molar ratio between the pretreated LiBH4 powder and NiI2 powder in step two is changed; all other raw materials and steps are the same as in Example 1. Specifically, this embodiment prepares a multi-component composite lithium borohydride-based solid electrolyte through the following steps: 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. After being kept at 140℃ for 10 hours, the tube was allowed to cool naturally to room temperature to obtain pretreated LiBH4 powder.

[0072] Step Two: First Ball Milling According to the molar ratio of 98:2, the pretreated LiBH4 powder and NiI2 powder obtained in step one were placed in a quartz mortar and manually ground and mixed evenly. Then, the mixture was sealed in a ball mill jar, and grinding balls were added. The ball-to-powder ratio was 100:1. The mixture was then subjected to planetary ball milling at 400 rpm for 10 h in an argon atmosphere to obtain NiI2-doped modified LiBH4 (denoted as "0.98LiBH4-0.02NiI2").

[0073] Step 3: Secondary ball milling The 0.98LiBH4-0.02NiI2 and ZrO2 powders obtained in step two were taken at a mass ratio of 3:1 and manually ground and mixed evenly in a quartz mortar. Then, the mixture was sealed in a ball mill jar, and grinding balls were added. The ball-to-powder ratio was 100:1. The mixture was then subjected to planetary ball milling at 300 rpm for 5 hours in an argon atmosphere. This process resulted in a ZrO2 shell coating on the 0.98LiBH4-0.02NiI2, yielding the multi-component composite lithium borohydride-based solid electrolyte of this embodiment (denoted as "0.98LiBH4-0.02NiI2-25wt%ZrO2").

[0074] Example 3: Solid electrolyte 0.96LiBH4-0.04NiI2-25wt%ZrO2 The only difference between this embodiment and Example 1 is that the molar ratio between the pretreated LiBH4 powder and NiI2 powder in step two is changed; all other raw materials and steps are the same as in Example 1. Specifically, this embodiment prepares a multi-component composite lithium borohydride-based solid electrolyte through the following steps: 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. After being kept at 140℃ for 10 hours, the tube was allowed to cool naturally to room temperature to obtain pretreated LiBH4 powder.

[0075] Step Two: First Ball Milling According to the molar ratio of 96:4, the pretreated LiBH4 powder and NiI2 powder obtained in step one were placed in a quartz mortar and manually ground and mixed evenly. Then, the mixture was sealed in a ball mill jar, and grinding balls were added. The ball-to-powder ratio was 100:1. The mixture was then subjected to planetary ball milling at 400 rpm for 10 h in an argon atmosphere to obtain NiI2-doped modified LiBH4 (denoted as "0.96LiBH4-0.04NiI2").

[0076] Step 3: Secondary ball milling The 0.96LiBH4-0.04NiI2 and ZrO2 powders obtained in step two were taken at a mass ratio of 3:1 and manually ground and mixed evenly in a quartz mortar. Then, the mixture was sealed in a ball mill jar, and grinding balls were added. The ball-to-powder ratio was 100:1. The mixture was then subjected to planetary ball milling at 300 rpm for 5 hours in an argon atmosphere. This process resulted in a ZrO2 shell coating on the 0.96LiBH4-0.04NiI2, yielding the multi-component composite lithium borohydride-based solid electrolyte of this embodiment (denoted as "0.96LiBH4-0.04NiI2-25wt%ZrO2").

[0077] Example 4: Solid electrolyte 0.94LiBH4-0.06NiI2-25wt%ZrO2 The only difference between this embodiment and Example 1 is that the molar ratio between the pretreated LiBH4 powder and NiI2 powder in step two is changed; all other raw materials and steps are the same as in Example 1. Specifically, this embodiment prepares a multi-component composite lithium borohydride-based solid electrolyte through the following steps: 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. After being kept at 140℃ for 10 hours, the tube was allowed to cool naturally to room temperature to obtain pretreated LiBH4 powder.

[0078] Step Two: First Ball Milling According to the molar ratio of 94:6, the pretreated LiBH4 powder and NiI2 powder obtained in step one were placed in a quartz mortar and manually ground and mixed evenly. Then, the mixture was sealed in a ball mill jar, and grinding balls were added. The ball-to-powder ratio was 100:1. The mixture was then subjected to planetary ball milling at 400 rpm for 10 h in an argon atmosphere to obtain NiI2-doped modified LiBH4 (denoted as "0.94LiBH4-0.06NiI2").

[0079] Step 3: Secondary ball milling The 0.94LiBH4-0.06NiI2 and ZrO2 powders obtained in step two were taken at a mass ratio of 3:1 and manually ground and mixed evenly in a quartz mortar. Then, the mixture was sealed in a ball mill jar, and grinding balls were added. The ball-to-powder ratio was 100:1. The mixture was then subjected to planetary ball milling at 300 rpm for 5 h in an argon atmosphere. This process resulted in a ZrO2 shell coating on the 0.94LiBH4-0.06NiI2, yielding the multi-component composite lithium borohydride-based solid electrolyte of this embodiment (denoted as "0.94LiBH4-0.06NiI2-25wt%ZrO2").

[0080] Example 5: Solid electrolyte 0.9LiBH4-0.1NiI2-25wt%ZrO2 The only difference between this embodiment and Example 1 is that the molar ratio between the pretreated LiBH4 powder and NiI2 powder in step two is changed; all other raw materials and steps are the same as in Example 1. Specifically, this embodiment prepares a multi-component composite lithium borohydride-based solid electrolyte through the following steps: 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. After being kept at 140℃ for 10 hours, the tube was allowed to cool naturally to room temperature to obtain pretreated LiBH4 powder.

[0081] Step Two: First Ball Milling According to a molar ratio of 90:10, the pretreated LiBH4 powder and NiI2 powder obtained in step one were placed in a quartz mortar and manually ground and mixed evenly. Then, the mixture was sealed in a ball mill jar, and grinding balls were added. The ball-to-powder ratio was 100:1. The mixture was then subjected to planetary ball milling at 400 rpm for 10 h in an argon atmosphere to obtain NiI2-doped modified LiBH4 (denoted as "0.9LiBH4-0.1NiI2").

[0082] Step 3: Secondary ball milling According to a mass ratio of 3:1, the 0.9LiBH4-0.1NiI2 and ZrO2 powder obtained in step two were placed in a quartz mortar and manually ground and mixed evenly. Then, the mixture was sealed in a ball mill jar, and grinding balls were added. The ball-to-powder ratio was 100:1. The mixture was then subjected to planetary ball milling at 300 rpm for 5 h in an argon atmosphere, thereby coating the 0.9LiBH4-0.1NiI2 with a ZrO2 shell, thus obtaining the multi-component composite lithium borohydride-based solid electrolyte of this embodiment (denoted as "0.9LiBH4-0.1NiI2-25wt%ZrO2").

[0083] Test Example 3: Ionic conductivity under different NiI2 doping concentrations The solid electrolytes prepared in Examples 1-5 were analyzed by electrochemical impedance spectroscopy (EIS) to detect their ionic conductivity at different temperatures, and Arrhenius curves were plotted. The results are shown in […]. Figure 4 ( Figure 4 In the diagram, "T" on the horizontal axis represents temperature in Kelvin (K); "σ" on the vertical axis represents ionic conductivity.

[0084] contrast Figure 4 The Arrhenius curves of the solid electrolytes show that, in the solid electrolyte system of this invention, as the doping amount of LiBH4 increases, the room temperature (30°C) ionic conductivity of the solid electrolyte first increases and then decreases; when the doping amount of NiI2 in the core layer is 8 mol%, the solid electrolyte has the highest ionic conductivity at room temperature (30°C).

[0085] Test Example 4: Stability Test Using the solid electrolyte prepared in Example 1, a lithium-to-lithium symmetric battery (composed of lithium sheets, solid electrolyte sheets, and lithium sheets stacked sequentially) was assembled. The specific steps are as follows: First, 100 mg of electrolyte was weighed and placed into a mold, and then compacted into a sheet shape using a pressure of 10 MPa. The mold bottom was then removed, and a lithium sheet with a diameter of 10 mm was placed inside. The mold bottom was then reinstalled. Next, the pressure bar was removed, and a lithium sheet with a diameter of 10 mm was placed inside. The locking nut and pressure bar were then reinserted. Finally, circular insulating pads were placed on top and bottom of the mold, and the mold was clamped using stainless steel clamps. A torque wrench was used to control the clamping pressure, with a torque of 0.5 N·m.

[0086] 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 5 The results showed that, at 60°C, when using the solid electrolyte of Example 1, the limiting current density (CCD) of the lithium-to-lithium symmetric battery was 2.0 mA / cm². -2 This indicates that it has stability against lithium.

[0087] Cyclic voltammetry curves of lithium-to-lithium symmetric cells at 60°C were tested, and the results are shown in [reference needed]. Figure 6 The results showed that at 60°C, when using the solid electrolyte of Example 1, the chemical window of the lithium-to-lithium symmetric battery could reach 5 V, and the peak current decreased during subsequent cycling, indicating that the stability of the electrolyte was improved during cycling and further decomposition was suppressed.

Claims

1. A multi-component composite lithium borohydride-based solid electrolyte, characterized in that, It includes a core layer and a shell layer covering the core layer; the core layer includes lithium borohydride modified by nickel iodide doping; the shell layer includes zirconium dioxide.

2. The multi-component composite lithium borohydride-based solid electrolyte according to claim 1, characterized in that, In the multi-component composite lithium borohydride-based solid electrolyte, the proportion of zirconium dioxide is 20~30 wt%.

3. The multi-component composite lithium borohydride-based solid electrolyte according to claim 1, characterized in that, In the lithium borohydride and nickel iodide, the proportion of nickel iodide is 2~10 mol.

4. A method for preparing a multi-component composite lithium borohydride-based solid electrolyte according to any one of claims 1 to 3, characterized in that the step include: S1: Mix lithium borohydride and nickel iodide and ball mill to obtain nickel iodide-doped lithium borohydride; S2: The product of S1 was mixed with zirconium dioxide and ball-milled to obtain a multi-component composite lithium borohydride-based solid electrolyte.

5. The preparation method according to claim 4, characterized in that, In steps S1 and S2, the ball milling process is carried out under inert gas protection, and the ball-to-material ratio is 50~200:

1.

6. The preparation method according to claim 4 or 5, characterized in that, In step S1, the rotation speed of the mixing ball mill is 400~1000 rpm, and the time is 10~20 h.

7. The preparation method according to claim 4 or 5, characterized in that, In step S2, the mixing ball mill rotates at a speed of 250-350 rpm for 3-5 hours.

8. The preparation method according to claim 4, characterized in that, Before step S1, lithium borohydride is first subjected to heat treatment; the heat treatment process is carried out under vacuum at a temperature of 100~180℃ for 8~12 h.

9. The application of the multi-component composite lithium borohydride-based solid electrolyte according to any one of claims 1 to 3 in lithium-ion batteries.

10. The application according to claim 9, characterized in that, The lithium-ion battery includes a positive electrode, a solid electrolyte membrane, and a negative electrode stacked in sequence, wherein the solid electrolyte membrane contains the multi-component composite lithium borohydride-based solid electrolyte.

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