Oxidized boron cage compound solid electrolyte and preparation method thereof

Abstract

The invention belongs to the technical field of battery energy storage, and particularly relates to an oxidized boron cage compound solid electrolyte and a preparation method thereof. According to the invention, the high-performance oxidized M2B12H12 (M = Li, Na) solid electrolyte is obtained through oxidation treatment of M2B12H12 (M = Li, Na), and the solid electrolyte has good thermal stability and mechanical properties; the room-temperature conductivity of the oxidized Na2B12H12 solid electrolyte is as high as 10 <-3 > S / cm or above, the electrochemical window reaches 5.0 V, and the ion transference number is 0.95; the room temperature conductivity of the oxidized Li2B12H12 solid electrolyte can reach 10 <-4 > S / cm, the electrochemical window reaches 6.8 V, and the ion transference number is 0.92. The oxidized boron cage solid electrolyte is compounded with various materials, so that the ionic conductivity and the cycling stability of the material can be further improved. The high-efficiency solid electrolyte can be used for a solid-state lithium ion battery and a solid-state sodium ion battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery energy storage, and in particular relates to a solid electrolyte material for a battery and a preparation method thereof. Background Art

[0002] With the development of the battery energy storage industry, traditional liquid batteries have poor safety performance, are not suitable for high-capacity metal negative electrodes, and have obvious interface side reactions, which cannot meet practical needs. The development of new and efficient solid-state batteries is expected to solve these problems and is a key research direction in this field. The new boron cage solid electrolyte is considered to have broad application prospects in the field of solid electrolytes due to its high thermal stability, low density, non-toxicity, and good compatibility with negative electrode metals.

[0003] Boron cage solid electrolytes mainly include closed boron cage compound solid electrolytes, nested borane compound solid electrolytes, carborane solid electrolytes, etc. Compared with other types of boron cage solid electrolytes, closed boron cage compound solid electrolytes have attracted people's attention due to their good thermal stability, chemical stability and good economy. At present, many studies have reported on the research work of closed boron cage compounds as solid electrolytes. Motoaki et al. found that Na 2 B 10 H 10 At high temperatures, a phase transition occurs, causing its ionic conductivity to increase from 10 -9 S / cm to 10 at 383K -2 S / cm. In 2014, Orimo et al. first proposed Na 2 B 12 H 12 It can be used as a fast ion conductor. In the range of 270℃~300℃, Na 2 B 12 H 12 The ionic conductivity is close to or exceeds 0.1S cm -1 In 2017, Yoshida et al. prepared a series of Na 2 B 12 H 12 / Na 2 B 10 H 10 Fast ion conductors, it was found that the composite fast ion conductor mixed in a ratio of 3:1 has the highest ionic conductivity of 10 at room temperature -3.5 S cm -1. So far, a lot of research has been carried out on the development of room temperature high ionic conductivity boron cage compound solid electrolytes, and great progress has been made. However, most materials currently still have some performance deficiencies or are difficult to prepare on a large scale, which hinders the application of the materials. Therefore, the preparation of a practical boron cage compound solid electrolyte with high ionic conductivity and high electrochemical stability has important application value. Summary of the invention

[0004] The object of the present invention is to provide an oxidized boron cage compound solid electrolyte with high ionic conductivity, excellent electrochemical stability and good thermal stability and a preparation method thereof.

[0005] The oxidized boron cage compound solid electrolyte provided by the present invention can be obtained by M 2 B 12 H 12 (M=Li,Na) is obtained by heat treatment in air or oxygen atmosphere; the oxidized type M obtained by thermal oxidation 2 B 12 H 12 The large grain size of the (M=Li,Na) solid electrolyte makes its ionic conductivity low. The M 2 B 12 H 12 (M=Li,Na) or its complex to obtain an oxidized M with suitable grain size 2 B 12 H 12 (M=Li,Na) solid electrolyte or its composite electrolyte.

[0006] The oxidized boron cage compound solid electrolyte provided by the present invention can also be obtained by M 2 B 12 H 12 (M=Li, Na) and its composites are prepared by high-energy ball milling in air or oxygen atmosphere.

[0007] The oxidized boron cage compound solid electrolyte provided by the present invention, the oxidized M obtained by thermal oxidation method 2 B 12 H 12 (M=Li,Na) solid electrolyte, suitable for large-scale preparation. Oxidized M obtained by high-energy ball milling 2 B 12 H 12 (M=Li,Na) The solid electrolyte method is simpler.

[0008] The method for preparing the oxidized boron cage compound solid electrolyte provided by the present invention comprises the following specific steps:

[0009] M 2 B12 H 12 (M=Li,Na) is heat-treated and oxidized in air or oxygen atmosphere at a temperature of 250-500°C for 0.5-6 hours to obtain an oxidized M 2 B 12 H 12 (M = Li, Na) solid electrolyte; further ball milling the above product or its composite in an inert atmosphere at a ball milling speed of 200-600 rpm for 0.5-8 hours to obtain an oxidized M with a suitable grain size 2 B 12 H 12 A solid electrolyte or a composite solid electrolyte thereof.

[0010] or:

[0011] M 2 B 12 H 12 (M=Li, Na), or a complex thereof, is ball-milled in air or oxygen atmosphere at a ball-milling speed of 200-1000 rpm for 0.5-12 hours to obtain an oxidized Na containing a boron oxide compound. 2 B 12 H 12 or Li 2 B 12 H 12 , or a composite solid electrolyte thereof.

[0012] Here, the composite material used in the composite solid electrolyte is selected from materials such as halides, oxides, sulfides, borohydrides, etc.

[0013] Pure Oxidized M 2 B 12 H 12 The (M=Li,Na) solid electrolyte, or its composite electrolyte, can be directly applied to the solid electrolyte of the battery, or used as a salt in a liquid electrolyte or a polymer electrolyte.

[0014] The oxidized M prepared by the present invention 2 B 12 H 12 (M=Li,Na) solid electrolyte, by 2 B 12 H 12 (M=Li,Na) in situ generates complex boron oxides, inducing M 2 B 12 H 12 (M=Li,Na) lattice distortion, causing M 2 B 12 H 12(M=Li,Na) transforms from low temperature phase to M 2 B 12 H 12 The high-temperature disordered phase of (M=Li,Na) leads to rapid ion conduction; at the same time, the complex boron oxide exhibits higher thermal and electrochemical stability; these aspects make the oxidized M 2 B 12 H 12 (M=Li,Na) and its composite electrolyte have high ionic conductivity, excellent electrochemical stability and good thermal stability. 2 B 12 H 12 (M=Li,Na) solid electrolyte is stable at 400℃. 2 B 12 H 12 The room temperature ionic conductivity of the solid electrolyte is as high as 10 -3 S / cm or more, electrochemical window higher than 5.0V, ion migration number 0.95. Oxidized Li 2 B 12 H 12 The room temperature conductivity of solid electrolytes can reach 10 -4 S / cm, the electrochemical window reaches 6.8V, and the ion mobility is 0.92.

[0015] This type of electrolyte has excellent comprehensive performance, is easy to prepare in batches, and has application prospects in solid-state batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 for Na 2 B 12 H 12 and oxidized Na 2 B 12 H 12 XRD pattern of .

[0017] Figure 2 for Na 2 B 12 H 12 and oxidized Na 2 B 12 H 12 FTIR graph of.

[0018] Figure 3 Oxidized Na 2 B 12 H 12 Plot of electrical conductivity at different temperatures.

[0019] Figure 4 for Na 2 B 12 H12 and oxidized Na 2 B 12 H 12 Electrochemical window diagram.

[0020] Figure 5 Oxidized Na 2 B 12 H 12 Ion mobility graph.

[0021] Figure 6 Na|oxidized Na 2 B 12 H 12 | Diagram of a Na symmetric cell.

[0022] Figure 7 for Na 3 V 2 (PO 4 ) 3 |oxidized Na 2 B 12 H 12 |Na full battery diagram.

[0023] Figure 8 For Li 2 B 12 H 12 and oxidized Li 2 B 12 H 12 XRD pattern of .

[0024] Fig. 9 For Li 2 B 12 H 12 and oxidized Li 2 B 12 H 12 FTIR graph of.

[0025] Fig.10 Li is oxidized 2 B 12 H 12 Plot of electrical conductivity at different temperatures.

[0026] Fig.11 For Li 2 B 12 H 12 and oxidized Li 2 B 12 H 12 Electrochemical window diagram.

[0027] Fig.12 Li is oxidized 2 B12 H 12 Ion mobility graph.

[0028] Fig.13 Li|oxidized Li 2 B 12 H 12 |Diagram of a Li symmetric battery.

[0029] Fig.14 LiFePO 4 / oxidized Li 2 B 12 H 12 / Li full battery results.

[0030] Fig.15 Li is oxidized 2 B 12 H 12 XRD patterns of composites with different ratios of LiI.

[0031] Fig.16 Li is oxidized 2 B 12 H 12 Ionic conductivity diagram of composites with different ratios of LiI.

[0032] Fig.17 400-0.6Li 2 B 12 H 12 -Electrochemical stability window diagram of 0.4LiI.

[0033] Fig.18 400-0.6Li 2 B 12 H 12 -0.4LiI ion transference number results.

[0034] Fig.19 400-0.6Li 2 B 12 H 12 -0.4LiI temperature-dependent ionic conductivity results.

[0035] Fig. 20 400-0.6Li 2 B 12 H 12 -0.4LiI critical current density results.

[0036] Fig.21 400-0.6Li 2 B 12 H 12Symmetrical battery result diagram of -0.4LiI. DETAILED DESCRIPTION

[0037] The present invention is further described below by means of specific examples.

[0038] Example 1, Oxidized Na 2 B 12 H 12 Preparation of solid electrolytes.

[0039] Will Na 2 B 12 H 12 Put it into a ball mill, introduce oxygen and mill it at 900 rpm to obtain the oxidized Na2O3 containing boron oxide compounds. 2 B 12 H 12 Solid electrolyte. Its XRD pattern is as follows Figure 1 As shown, oxidized Na 2 B 12 H 12 The main characteristic peaks of the solid electrolyte shift to a lower angle, and the oxidized substances show new peaks. Figure 2 As shown, Na 2 B 12 H 12 There are BO and BOH bonds in the material, and complex boron oxides are generated inside. The impedance diagram of this material at different temperatures is shown in the figure below. Figure 3 As shown, by the formula σ=L / (R×S)(1)(where: σ(S cm -1 )、L(cm)、R(Ω)、S(cm 2 ) represent the ionic conductivity of the solid electrolyte SE, the film thickness, and the area of ​​the solid electrolyte SE respectively. It is calculated that the ionic conductivity at room temperature can reach 1.0×10 -3 S / cm. Oxidized Na is tested by LSV 2 B 12 H 12 The electrochemical stability of Figure 4 As shown, oxidized Na 2 B 12 H 12 With a wide electrochemical window (5V vs.Na / Na + Oxidized Na 2 B 12 H 12 The sodium ion migration number τNa + =0.95, the result is as follows Figure 5 As shown. Figure 6 As shown, Na|oxidized Na 2 B 12H 12 |Na symmetric battery can maintain overpotential below 20mV in 100 hours of cycling. 3 V 2 (PO 4 ) 3 As the positive electrode material, assemble Na 3 V 2 (PO 4 ) 3 |oxidized Na 2 B 12 H 12 |Na full battery, the result is as follows Figure 7 As shown, Na 3 V 2 (PO 4 ) 3 |oxidized Na 2 B 12 H 12 |The Na full cell can maintain 75.3% capacity after 100 cycles.

[0040] Example 2, Oxidized Li 2 B 12 H 12 Preparation of solid electrolyte

[0041] Li 2 B 12 H 12 The product was placed in a tube furnace, purged with oxygen for 10 minutes at room temperature to fill the tube furnace with oxygen, and heated to 350°C at a heating rate of 5°C / min and kept at a constant temperature for 2 hours; the oxidized product was ball milled at a speed of 400 rpm in an argon atmosphere to obtain an oxidized Li containing boron oxide compounds. 2 B 12 H 12 Solid electrolyte, its XRD spectrum is shown in Figure 8 FTIR images are shown in Fig. 9 As shown, it can be observed that Li 2 B 12 H 12 BH and BOH bonds are generated in the oxidized Li 2 B 12 H 12 The conductivity results are as follows Fig.10 As shown, its ionic conductivity at room temperature is 1.0×10 -4 S / cm. Assembled Li|oxidizedLi 2 B 12 H 12 |SUS half-cell and Li|oxidized Li 2 B12 H 12 |Li symmetric battery, testing oxidized Li 2 B 12 H 12 The electrochemical window and ion mobility of Fig.11 , 12 The results show that Li 2 B 12 H 12 With a wide electrochemical window (6.8V vs.|Li / |Li + ) and a higher ion migration number (τLi + =0.92). Fig.13 As shown, Li|oxidized Li 2 B 12 H 12 |Li symmetric battery can maintain overpotential below 80mV after 100 hours of cycling. 4 As the positive electrode material, LiFePO 4 / oxidized Li 2 B 12 H 12 / Li full battery, the results are shown in 14, LiFePO 4 / oxidized Li 2 B 12 H 12 The / Li full battery can maintain 80.3% of its capacity after 100 cycles.

[0042] Example 3, Oxidized Li 2 B 12 H 12 Preparation of composite solid electrolyte

[0043] Li 2 Oxidized by heating in air at 400°C was prepared according to the method of Example 2. 2 B 12 H 12 , to obtain oxidized Li 2 B 12 H 12 , referred to as 400-Li 2 B 12 H 12 . The oxidized Li 2 B 12 H 12 LiI with different proportions was added to a ball mill and milled under argon atmosphere for 5 hours at a speed of 450 rpm. The new solid electrolyte structure was 400-(1-x)Li 2 B 12 H12 -xLiI,0.2≤x≤0.5.

[0044] Fig.15 400-Li 2 B 12 H 12 XRD patterns of solid electrolytes prepared by ball milling with LiI at different molar ratios. The results show that 400-Li 2 B 12 H 12 And the crystal form of LiI gradually disappears, and an amorphous solid electrolyte is obtained. Fig.16 400-Li 2 B 12 H 12 Solid electrolyte 400-(1-x)Li obtained by ball milling with different proportions of LiI 2 B 12 H 12 -xLiI ionic conductivity. 400-0.6Li obtained when x = 0.4 2 B 12 H 12 -0.4LiI solid electrolyte has the highest ionic conductivity, which is 7.5×10 -4 S / cm. Fig.17 400-0.6Li 2 B 12 H 12 -0.4LiI solid electrolyte electrochemical stability window, up to 6.0V. Fig.18 400-0.6Li 2 B 12 H 12 The lithium ion transference number of -0.4LiI solid electrolyte is 0.94. Fig.19 400-0.6Li 2 B 12 H 12 -0.4LiI temperature-dependent ionic conductivity, similar to Li 2 B 12 H 12 With 400-Li 2 B 12 H 12 Compared with 400-0.6Li 2 B 12 H 12 -0.4LiI migration activation energy decreases. Fig. 20 and Fig.21 Based on 400-0.6Li 2 B 12 H 12-0.4LiI assembled lithium symmetric battery limiting current density and long-term cycle stability test results, 400-0.6Li 2 B 12 H 12 The critical current density of -0.4LiI is 5.0 mA cm -1 , at 0.1 mA cm -1 Under the same conditions, it can stably cycle for 1000h, and the overpotential does not exceed 20mV.

Claims

1. A method for preparing an oxidized boron cage compound solid electrolyte, characterized in that: The specific steps are as follows: First, M2B 12 H 12 Heat treatment oxidation is carried out in air or oxygen atmosphere, the heat treatment oxidation temperature is 250-500°C, the time is 0.5-6 hours, and the oxidized M2B containing boron oxide compounds is obtained. 12 H 12 solid electrolyte; further ball milling the above product or its composite under an inert atmosphere at a ball milling speed of 200-600 rpm for 0.5-8 hours to obtain an oxidized M2B having a suitable grain size; 12 H 12 A solid electrolyte or a composite solid electrolyte thereof; or, M2B 12 H 12 , or its composite, is directly ball-milled in air or oxygen atmosphere at a ball-milling speed of 200-1000 rpm for 0.5-12 hours to obtain an oxidized M2B containing a boron oxide compound. 12 H 12 A solid electrolyte, or a composite solid electrolyte thereof; Here, M is Li or Na; the composite used in the composite solid electrolyte is selected from halides, oxides, sulfides, and borohydrides.

2. An oxidized boron cage compound solid electrolyte prepared by the preparation method according to claim 1.

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