LiBH4-based composite solid electrolyte and preparation method thereof

Abstract

The invention belongs to the technical field of design and preparation of solid electrolyte materials, and particularly relates to a LiBH4-based composite solid electrolyte material and a preparation method thereof.The LiBH4-based composite solid electrolyte material is obtained by performing high-energy ball milling on a mixture of LiBH4 and one or two metal halides MX2 in a certain molar ratio in an argon atmosphere; m is Mg, Zn, Ni or Bi; x is F, Cl, Br or I. According to the LiBH4 composite solid electrolyte prepared by the preparation method disclosed by the invention, the ionic conductivity at room temperature is improved to 10 <-4 > S cm <-1 > or above, and the ion diffusion activation energy is only 0.16 eV; the process is simple, the preparation time is short, the repeatability is high, no pollution is caused to the environment, and the industrial production requirement is met, so that the all-solid-state lithium ion battery electrolyte is expected to realize commercialized application.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of solid electrolyte material design and preparation, and particularly relates to a LiBH4-based composite solid electrolyte and a preparation method thereof. BACKGROUND

[0002] With the rapid development of portable electronic devices, electric vehicles and large-scale energy storage systems, there is an increasing demand for high energy density and safe and reliable batteries. Commercial lithium-ion batteries generally use liquid organic electrolytes, which have inherent defects such as low thermal safety threshold, narrow electrochemical window, easy gas production and easy dendrite formation. The energy density and safety performance of traditional lithium-ion batteries have gradually approached the theoretical limit. To completely solve the safety and energy density bottlenecks brought by the liquid system, all-solid-state batteries (ASSB) are considered as an important development direction of the next generation of energy storage technology, and the core is to use solid electrolyte (SSE) to replace liquid electrolyte.

[0003] LiBH4 has the characteristics of light weight and high ionic conductivity, and it is thermodynamically stable to metal lithium and has good processing performance, which has attracted researchers to widely study LiBH4 as a solid electrolyte material. When LiBH4 is heated to above 110 ℃, it undergoes phase transition to form a hexagonal phase, and the ionic conductivity can jump to 10 -3 S cm -1 However, this temperature has exceeded the working interval of conventional batteries and will change into an orthorhombic phase with low ionic conductivity when it drops to room temperature. Therefore, how to reduce the phase transition temperature of LiBH4-based electrolyte and improve the room temperature ionic conductivity without sacrificing the lightweight and lithium storage capacity has become a technical bottleneck that needs to be broken through in the field.

[0004] Patent CN201811445051.X improves the room temperature ionic conductivity of LiBH4 to 10 -6 S cm -1 by ball milling lithium borohydride for 20-30 hours in advance and then mixing it with molybdenum disulfide. Patent CN202010081727.2 improves the room temperature ionic conductivity of LiBH4 to 10 -5 S cm -1 by doping graphite-like carbon nitride to stabilize the hexagonal phase of LiBH4 at room temperature. However, the graphite-like carbon nitride needs to be prepared in a complicated process in advance. The common problem of the above-mentioned solutions is that the room temperature ionic conductivity is still difficult to meet the design requirements, and the preparation process is complicated. SUMMARY

[0005] The application discloses a LiBH4-based metal halide composite solid electrolyte and a preparation method thereof, which overcomes the problems of low room temperature ionic conductivity and complicated process in the prior art.

[0006] To achieve the above object, the application adopts the following technical solutions: a preparation method of LiBH4-based composite solid electrolyte material, a mixture of a certain molar ratio of LiBH4 and one or two metal halides MX2 is high-energy ball milled in an argon atmosphere to obtain the LiBH4-based composite solid electrolyte material; the M=Mg, Zn, Ni, Bi; X=F, Cl, Br, I.

[0007] Further, the molar ratio of LiBH4 to metal halide MX2 is from 4:1 to 7:1.

[0008] Further, the molar ratio of the two metal halides MX2 is from 2:1 to 1:2.

[0009] Further, the ball milling adopts a planetary ball mill, the revolution speed is 200-500 rpm, and the ball milling time is 5-25 h.

[0010] Further, the LiBH4-based composite solid electrolyte material prepared by the preparation method.

[0011] Compared with the prior art, the application has the following advantages: (1) The application optimizes the ratio of LiBH4 to metal halide by selecting co-doping of anions and cations, and provides the best parameters in the ball milling process. The LiBH4 composite solid electrolyte prepared by the application has a room temperature ionic conductivity of 10 -4 Scm -1 The above, the ion diffusion activation energy is only 0.16 eV.

[0012] (2) The method of the application adopts a one-step mechanical ball milling method, so the process is simple, the preparation time is short, and the ionic conductivity of the LiBH4-based composite solid electrolyte can reach 10 -4 S cm -1 Since the preparation process is single and no waste is generated during the process, it has strong repeatability and meets the needs of industrial production, so as a solid-state lithium ion battery electrolyte, it is expected to realize commercial application. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is the XRD diffraction pattern of LiBH4BM, LNIClm511; Figure 2 is the EIS graph of LiBH4BM, LNIClm511 at 30°C; Figure 3 is the DCP graph of LiBH4BM, LNIClm511 at 30°C; Figure 4 is the ion conduction activation energy Arrhenius graph of LiBH4BM, LNIClm511; Figure 5 EIS plot of LBIm5 at 30°C; Figure 6 DCP plot of LBIm5 at 30°C; Figure 7 Arrhenius plot of ion conduction activation energy of LBIm5; Figure 8 EIS plot of LMClm7 at 30°C; Figure 9 DCP plot of LMClm7 at 30°C; Figure 10 Arrhenius plot of ion conduction activation energy of LMClm7; Figure 11 EIS plot of LMINBrm511 at 30°C; Figure 12 DCP plot of LMINBrm511 at 30°C; Figure 13 Arrhenius plot of ion conduction activation energy of LMINBrm511. DETAILED DESCRIPTION

[0014] The present application will be described in detail below with reference to the accompanying drawings and specific examples.

[0015] Example 1: A preparation method of LiBH4-NiI2-NiCl2 composite solid-state electrolyte, comprising the following steps: (1) In an argon-filled glove box, LiBH4 and NiI2-NiCl2 with a total mass of 1 g were weighed in a molar ratio of 5:1, and the molar ratio of NiI2 to NiCl2 was 1:1, to obtain a mixture; (2) The mixture was mechanically ball milled by a planetary ball mill, the revolution speed was 300 rpm, the ball milling time was 15 h, and the ball milling obtained LNIClm511 composite (LiBH4-NiI2-NiCl2 composite solid-state electrolyte).

[0016] Comparative Example 1: Different from Example 1 is that only LiBH4 with a total mass of 1 g was weighed, and no NiI2-NiCl2 was added, to obtain a comparative sample LiBH4BM.

[0017] As Figure 1 The XRD spectra of the prepared LNIClm511 composite and LiBH4BM were as shown in the figure, from which it can be seen that the LNIClm511 composite showed the characteristic peaks of high-temperature hexagonal phase lithium borohydride (LiBH4-P63mc), while no high-temperature hexagonal phase peak was observed in the LiBH4BM prepared in the comparative example, which was still mainly in the low-temperature orthorhombic phase.

[0018] The electrochemical performance of the composite solid electrolyte prepared in Example 1 was characterized using a solid-state battery test mold, assembled in an argon-filled glove box with water and oxygen contents both less than 0.1 ppm. The prepared sample powder was pressed into electrolyte discs with a diameter of 10 mm and a thickness of approximately 1 mm under a pressure of 6 MPa. These discs were then assembled into a solid-state battery using a sandwich structure of "stainless steel | solid electrolyte | stainless steel".

[0019] The EIS and DCP curves of the LNIClm511 composite solid electrolyte at room temperature (30℃) are shown in the figure below. Figure 2 and Figure 3 As shown. From Figure 2 It can be seen that the impedance spectrum curve of the LNIClm511 composite material at room temperature consists of a semicircular arc in the high-frequency region and a straight line in the low-frequency region. However, due to the influence of high ionic impedance, the straight line of the impedance spectrum curve of LiBH4BM at room temperature is less obvious, and the semicircular diameter is larger, 100 times that of LNIClm511 under the same conditions. Based on the semicircular diameter in the high-frequency region, the ionic conductivity of the LNIClm511 composite and LiBH4BM at room temperature is 2.78 × 10⁻⁶, respectively. -4 S cm -1 and 4.14×10 -6 S cm -1 It is evident that the ionic conductivity of the LNIClm511 composite at room temperature is significantly improved compared to LiBH4BM. From... Figure 3 It can be seen that the electronic conductivity of the LNIClm511 composite solid electrolyte is only 2.71 × 10⁻⁶. -8 S cm -1 It still maintains good electronic insulation capabilities, and combined with its extremely high ionic conductivity at room temperature, it indicates that the LNIClm511 composite is a LiBH4-based solid electrolyte material that can be used at room temperature.

[0020] Furthermore, AC impedance spectroscopy was performed on LNIClm511 and LiBH4BM at different temperatures. Impedance spectra were collected every 25°C at temperatures of 30, 55, 80, 105, and 130°C. Ionic conductivity and ion diffusion activation energy were calculated, and Arrhenius plots were plotted as shown below. Figure 4 As shown, compared with LiBH4BM, the ionic conductivity of the LNIClm511 composite solid electrolyte was significantly improved at any test temperature, and the ion diffusion activation energy was significantly reduced to 0.16 eV, greatly reducing the Li ion diffusion resistance and significantly improving the ionic conductivity. LNIClm511 achieved an ionic conductivity as high as 1.08 × 10⁻⁶ at 55 °C. -3 S cm -1When the temperature reaches 130℃, the ionic conductivity of LNIClm511 reaches 1.05×10⁻⁶. -2 S cm -1 .

[0021] Example 2: A method for preparing a LiBH4-BiI2 composite solid electrolyte, comprising the following steps: In an argon-filled glove box, a mixture of LiBH4 and BiI2 with a total mass of 1g was weighed at a molar ratio of 5:1 and ball-milled under the same conditions as in Example 1 to obtain the LBIm5 complex.

[0022] The EIS and DCP curves of the LBIm5 complex at room temperature (30℃) are shown below. Figure 5 and Figure 6 As shown. From Figure 5 It can be seen that, based on the semi-circular diameter in the high-frequency region, the LBIm5 composite solid electrolyte exhibits an ionic conductance as high as 1.09 × 10⁻⁶ at 30℃. -4 S cm -1 .Depend on Figure 6 Calculations show that the electronic conductivity of the LBIm5 composite solid electrolyte is only 1.92 × 10⁻⁶. -8 S cm -1 The LBIm5 composite with high ionic conductivity and low electronic conductivity is a LiBH4-based solid electrolyte material that can be used at room temperature.

[0023] Furthermore, AC impedance spectroscopy was performed on LBIm5 at different temperatures. Impedance spectra were collected every 25°C at temperatures of 30, 55, 80, 105, and 130°C. Ionic conductivity and ion diffusion activation energy were calculated, and Arrhenius plots were generated. Figure 7 As shown, the ion diffusion activation energy of the LBIm5 composite solid electrolyte is significantly reduced to 0.16 eV, the Li ion diffusion resistance is greatly reduced, and the ion conductivity is significantly improved.

[0024] Example 3: A method for preparing a LiBH4-MgCl2 composite solid electrolyte, comprising the following steps: In an argon-filled glove box, a mixture of LiBH4 and MgCl2 with a total mass of 1g was weighed at a molar ratio of 7:1 and ball-milled under the same conditions as in Example 1 to obtain the LMClm7 complex.

[0025] The EIS and DCP curves of the LMClm7 complex at room temperature (30℃) are shown below. Figure 8 and Figure 9 As shown. From Figure 8 It can be seen that the ionic conductivity of the LMClm7 complex at room temperature is 1.12 × 10⁻⁶, which can be obtained from the semicircle diameter in the high-frequency region. -4 S cm-1 .from Figure 9 It can be seen that the electronic conductivity of the LMClm7 complex is only 3.58 × 10⁻⁶. -8 S cm -1 It maintains good electronic insulation capabilities, and combined with its excellent ion conductivity at room temperature, the LMClm7 composite is a LiBH4-based solid electrolyte material that can be used at room temperature.

[0026] Furthermore, AC impedance spectroscopy was performed on LMClm7 at different temperatures. Impedance spectra were collected every 25°C at temperatures of 30, 55, 80, 105, and 130°C. Ionic conductivity and ion diffusion activation energy were calculated, and Arrhenius plots were generated. Figure 10 As shown, the ionic conductivity of the LMClm7 complex can reach 2.67 × 10⁻⁶ at 55 °C. -4 S cm -1 Meanwhile, the ion diffusion activation energy of the LMClm7 complex is also reduced to 0.16 eV, and the diffusion resistance of Li ions is relatively small.

[0027] Example 4: A method for preparing a LiBH4-MgI2-NiBr2 composite solid electrolyte, comprising the following steps: In an argon-filled glove box, a mixture of LiBH4 and MgI2-NiBr2 (MgI2 to NiBr2 molar ratio of 1:1) with a total mass of 1 g was weighed at a molar ratio of 5:1. The ball milling conditions were the same as in Example 1 to obtain the LMINBrm511 composite.

[0028] The EIS and DCP curves of the LMINBrm511 complex at room temperature (30℃) are shown below. Figure 11 and Figure 12 As shown. From Figure 11 It can be seen that the LMINBrm511 composite solid electrolyte exhibits a low impedance value at 30℃. Based on the semi-circular diameter in the high-frequency region, the ionic conductivity of the LMINBrm511 composite at room temperature is as high as 2.18 × 10⁻⁶. -4 S cm -1 .from Figure 12 It can be seen that the electronic conductivity of the LMINBrm511 composite solid electrolyte is only 8.08 × 10⁻⁶. -8 S cm -1 The extremely high ionic conductivity at room temperature indicates that the LMINBrm511 composite is a LiBH4-based solid electrolyte material that can be used at room temperature.

[0029] Furthermore, the AC impedance of LMINBrm5 was tested at different temperatures. Impedance spectra were collected every 25°C at temperatures of 30, 55, 80, 105, and 130°C. The ionic conductivity and ion diffusion activation energy were calculated, and an Arrhenius plot was plotted as shown below. Figure 13 As shown, the LMINBrm511 composite solid electrolyte exhibits an ionic conductivity as high as 1.39 × 10⁻⁶ at 80 °C. -3 Scm -1 Furthermore, the LMINBrm511 composite solid electrolyte has an ultra-low ion diffusion activation energy of 0.14 eV.

[0030] The above embodiment 1 is the best embodiment.

[0031] The above description is only a preferred embodiment of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a LiBH4-based composite solid electrolyte material, characterized in that: A mixture of LiBH4 and one or two metal halides MX2 in a certain molar ratio is subjected to high-energy ball milling under an argon atmosphere to obtain a LiBH4-based composite solid electrolyte material; wherein M = Mg, Zn, Ni, Bi; X = F, Cl, Br, I.

2. The method for preparing a LiBH4-based composite solid electrolyte material according to claim 1, characterized in that: The molar ratio of LiBH4 to metal halide MX2 ranges from 4:1 to 7:

1.

3. The method for preparing a LiBH4-based composite solid electrolyte material according to claim 2, characterized in that: The molar ratio of the two metal halides MX2 ranges from 2:1 to 1:

2.

4. The method for preparing a LiBH4-based composite solid electrolyte material according to claim 3, characterized in that: The ball milling process employs a planetary ball mill with a revolution speed of 200–500 rpm and a milling time of 5–25 h.

5. The LiBH4-based composite solid electrolyte material prepared by the preparation method according to claim 1.

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