Preparation method of a cluster cage-shaped metal borohydride solid electrolyte

Abstract

The present invention belongs to the technical field of material synthesis, and specifically relates to a preparation method of a cluster-caged metal borohydride solid electrolyte. In the present invention, metal borohydride and inorganic oxidant powder are used as raw materials, and a precursor is obtained by grinding and mixing; in an inert gas atmosphere, through high-temperature heat treatment, the metal borohydride with relatively strong reducibility and the non-metal oxidant react to generate a cluster-caged metal borohydride with slightly weaker reducibility, denoted as M-B-H-X; X is an inorganic substance such as S, P or Se, and M is a metal element such as Li, Na, K, Ca, Zn, Mg, Cs or Rb. The present invention has universality, and the production process has low energy consumption and low cost, overcoming the disadvantages of the traditional preparation of cluster-caged metal borohydride electrolytes that require high temperature and high pressure as well as expensive raw materials. The prepared electrolyte has high ionic conductivity and a wide electrochemical window near room temperature, and can be used in many aspects such as the preparation of all-solid-state alkali metal batteries and stable solid electrolyte-electrode interface layers.

Description

Technical Field

[0001] The present invention belongs to the technical field of material synthesis, and particularly relates to a preparation method of a cluster-cage metal borohydride solid electrolyte. Background Art

[0002] Cluster-cage metal borohydrides have extensive applications in the field of solid-state batteries. Orimo et al. studied the influence of the synthesis method of lithium borohydride on its components, and pointed out that with the change of the ratio of lithium borohydride to decaborane, complex cluster-cage metal borohydrides with different components will be generated. The study on the ionic conductivity of these products shows that as the ratio of lithium borohydride to decaborane increases from 1:1 to 4:1, the room-temperature ionic conductivity of the product will also increase from 1.4 x 10 -6 S cm -1 to 2.1 x 10 -5 S cm -1 (Naoki Toyama, Sangryun Kim, Hiroyuki Oguchi et al. Lithium ion conductivity of complex hydrides incorporating multiple closo-type complex anions[J]. Journal of Energy Chemistry, 2019, 38: 84-87). Previous researchers assembled solid-state lithium-ion batteries using cluster-cage metal borohydrides. When using TiS2 as the positive electrode, an initial discharge specific capacity of 217 mAh g -1 can be obtained, and after 10 cycles, a specific capacity of 193 mAh g -1 still remains (Atsushi Unemoto, Koji Yoshida, Tamio Ikeshoji et al. Bulk-Type All-Solid-State Lithium Batteries Using Complex Hydrides Containing Cluster-Anions[J]. Materials Transactions, 2016, 57(9): 1639-1644). Recently, some researchers modified cluster-cage metal borohydrides by the method of C atom doping to obtain a super lithium-ion conductor (0.7Li(CB9H 10 )-0.3Li(CB 11 H 12 )), and this material has an ionic conductivity exceeding 10 -3 S cm -1Ionic conductivity, the lithium-sulfur battery assembled with this electrolyte was cycled at a temperature of 25 °C and a current magnitude of 1 C, and a high specific capacity of 1469 mAh g could still be obtained after 20 cycles (Sangryun Kim, Hiroyuki Oguchi, Naoki Toyama et al. A complex hydride lithium superionic conductor for high-energy-density all-solid-state lithium metal batteries[J]. Nature Communications, 2019, 10(1)). -1

[0003] Based on the above research results, cluster-cage metal borohydride electrolytes are an important class of materials in the energy field and have attracted extensive attention. Currently, the methods for preparing cluster-cage metal borohydride electrolytes focus on using lithium borohydride for dehydrogenation reactions, which require harsh conditions of high temperature and high pressure, or the introduction of some expensive raw materials. For example: by calcining at 260 °C, the mixture of LiBH4 and LiBF4 was reacted to convert it into Li2B modified with LiF (X. Shi, Y. Pang, B. Wang et al. In situ forming LiF nanodecorated electrolyte / electrode interfaces for stable all-solid-state batteries[J]. Materials Today Nano, 2020, 10:100079); reacting LiBH4 with decaborane at 135 12 H 12 °C for 3 h, followed by reacting at 180 o °C for 2 h to obtain Li2B o H 12 12 ​​(Mengfei Zhu, Yuepeng Pang, Fuqiang Lu et al. In Situ Formed Li–B–H Complex with High Li-Ion Conductivity as a Potential Solid Electrolyte for Li Batteries[J]. ACS Applied Materials & Interfaces, 2019, 11(15): 14136-14141). These preparation methods all require high temperatures or raw materials that are highly toxic and costly, which is not conducive to the popularization and use of cluster-caged metal borohydrides as solid electrolytes. Summary of the Invention

[0004] The object of the present invention is to provide a preparation method for cluster-caged alkali metal / alkaline earth metal borohydride electrolytes that is simple in process, low in cost, and universal.

[0005] The preparation method of the cluster-caged metal borohydride solid electrolyte (M-B-H-X) provided by the present invention uses metal borohydride (MBH) and inorganic oxidant powder (X) as raw materials. The precursor is obtained by grinding and mixing, denoted as X@MBH. In an inert gas (such as argon) atmosphere, the temperature is raised to 130-500 °C and kept warm for 1-360 minutes to allow the oxidant powder and metal borohydride to react fully, generating a cluster-caged metal borohydride electrolyte material, denoted as M-B-H-X. Here, X is an inorganic substance such as S, P, or Se, and M is a metal element such as Li, Na, K, Ca, Zn, Mg, Cs, or Rb.

[0006] The preparation method of the cluster-caged metal borohydride solid electrolyte (M-B-H-X) described in the present invention has the following specific operating steps:

[0007] (1) Synthesis of the precursor X@MBH:

[0008] Weigh inorganic oxidant powder (X) and metal borohydride (MBH) in a mass ratio of 10 wt.% - 80 wt.%. Mix the metal borohydride and inorganic oxidant evenly to obtain the corresponding precursor X@MBH powder.

[0009] (2) Preparation of the M-B-H-X electrolyte:

[0010] In an argon atmosphere, place the obtained powder precursor in a glass bottle. After sealing the glass bottle with silica gel, place it in a muffle furnace or tube furnace and raise the temperature to 130-500 °C at a heating rate of 5-10 °C per minute, and keep warm for 1-360 minutes.

[0011] The reaction process is as follows: MBH4 + X → M[BH] ct + H2O + L2X.

[0012] The method of the present invention utilizes the strong reducibility of metal borohydride (MBH4), and performs heat treatment at a certain temperature to generate a cluster cage-like metal borohydride with relatively weak reducibility.

[0013] In the present invention, the metal borohydride includes but is not limited to substances such as lithium borohydride, sodium borohydride, potassium borohydride, calcium borohydride, zinc borohydride, magnesium borohydride, aluminum borohydride or zinc borohydride.

[0014] In the present invention, the inorganic oxidant includes but is not limited to materials such as sulfur powder, selenium powder, and phosphorus powder.

[0015] In the present invention, to mix the metal borohydride and the inorganic oxidant evenly, methods including but not limited to ball milling, manual grinding, and liquid phase dispersion can be used. For example, grind in a glove box under an inert gas (such as argon) atmosphere for 5 - 30 minutes until evenly mixed; or seal in a ball milling jar under an inert gas (such as argon) atmosphere and ball mill at a rotation speed of 400 - 500 revolutions per minute for 5 - 8 hours; collect the mixed product.

[0016] In the present invention, the heating device includes but is not limited to devices such as a muffle furnace and a tube furnace that can provide a high-temperature environment.

[0017] In the present invention, the heat preservation time is preferably 10 - 100 minutes.

[0018] In the present invention, the borohydride raw material refers to a compound containing - the [BH4]

[0019] In the present invention, the cluster cage-like metal borohydride refers to a compound containing 12 B 12 H 2- 10 B 10 H 2- ct and other cluster cage-like borohydride groups (closo-type, [BH]

[0020] The positive effects of the method of the present invention are:

[0021] (1) This method is simple to operate, only requiring a relatively low reaction temperature and simple mechanical mixing;

[0022] (2) The oxidant used in this method is a common industrial raw material, with rich reserves and low price, suitable for industrial production;

[0023] ​​(3) This method can be used to prepare a variety of cluster cage metal borohydride electrolytes such as Li, Na, K, Ca, Mg, Zn, Cs, and Rb, and the method is universal.

[0024] This invention is universally applicable, featuring low energy consumption, low cost, and simple process. It overcomes the shortcomings of traditional cluster-cage metal borohydride electrolytes, which require high temperatures, high pressures, and expensive raw materials. The resulting electrolyte exhibits high ionic conductivity and a wide electrochemical window near room temperature, and can be applied to the preparation of all-solid-state alkali metal batteries and the stabilization of solid-state electrolyte-electrode interfaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the Raman spectrum of the TF-S@LBH material synthesized in Example 1.

[0026] Figure 2 This is a graph showing the ionic conductivity-temperature relationship of the TF-S@LBH material synthesized in Example 1.

[0027] Figure 3 This is the thermogravimetric analysis curve of the TF-Se@LBH material synthesized in Example 2.

[0028] Figure 4 This is the thermogravimetric analysis curve of sodium borohydride and sulfur synthesized in Example 3.

[0029] Figure 5 1 is a graph showing the ionic conductivity-temperature relationship of sodium borohydride and sulfur synthesized in Example 3. DETAILED DESCRIPTION

[0030] The preparation method of the present invention is described in detail below with reference to the examples and drawings.

[0031] Example 1: Preparation of Li-BHS electrolyte and its ionic conductivity

[0032] 180 mg of lithium borohydride (LiBH4) and 120 mg of sulfur powder (S) were placed in a ball mill under an argon atmosphere and sealed with black tape. Ball milling was performed at a speed of 400 rpm for 6 hours. The ball-milled mixture was taken out from the glove box and recorded as S@LBH. S@LBH was placed in a small glass bottle in the glove box and the glass bottle was sealed with silica gel. S@LBH was heat-treated at 155°C for 6 hours in a muffle furnace. The heat-treated product was taken out from the glove box and recorded as Li-BHS. Figure 1 As shown in the Raman spectrum, Li2B exists in Li-BHS. 12 H 12 The ionic conductivity of Li-BHS was tested, as shown in Figure 2As shown, at 60 °C, Li-B-H-S has an ionic conductivity of 10 -4 S cm -1 orders of magnitude. This is two orders of magnitude higher than that of pure lithium borohydride. The above experimental results indicate that a new type of cluster-caged metal borohydride electrolyte, Li-B-H-S, has been successfully synthesized.

[0033] Example 2: Preparation of Li-B-H-Se Material

[0034] 180 mg of lithium borohydride (LiBH4) and 120 mg of selenium powder (Se) were loaded into a ball milling jar under an argon atmosphere, and the ball milling jar was sealed with black tape. Ball milling was carried out at a rotation speed of 400 revolutions per minute for 6 hours. The ball-milled mixture was taken out in a glove box and denoted as Se@LBH. Se@LBH was loaded into a small glass bottle in the glove box and the glass bottle was sealed with silica gel. The Se@LBH was heat-treated in a muffle furnace at 160 °C for 6 hours. The heat-treated product was taken out in a glove box and denoted as Li-B-H-Se. Figure 3 are the thermogravimetric analysis curves of lithium borohydride and selenium. It can be seen from the DSC curve that selenium also reacts with lithium borohydride and, similar to sulfur, forms complex cluster-caged borohydrides. The experimental results indicate that this heat treatment method is universal.

[0035] Example 3: Preparation of Na-B-H-S Material

[0036] 160 mg of sodium borohydride (NaBH4) and 40 mg of sulfur powder (S) were loaded into a ball milling jar under an argon atmosphere, and the ball milling jar was sealed with black tape. Ball milling was carried out at a rotation speed of 400 revolutions per minute for 6 hours. The ball-milled mixture was taken out in a glove box and denoted as S@NBH. S@NBH was loaded into a small glass bottle in the glove box and the glass bottle was sealed with silica gel. The S@NBH was heat-treated in a muffle furnace at 250 °C for 6 hours. The heat-treated product was taken out in a glove box and denoted as Na-B-H-S. Figure 4 are the thermogravimetric analysis curves of sodium borohydride and sulfur. It can be seen from the DSC curve that sulfur also reacts with sodium borohydride to form complex cluster-caged borohydrides. The experimental results indicate that this heat treatment method is universal. The ionic conductivity of Na-B-H-S was tested, as Figure 5 shown.

Claims

1. A preparation method of a cluster cage-like metal borohydride solid electrolyte, characterized in that, The specific operation steps are as follows: (1) Synthesis of precursor X@MBH: Using metal borohydride MBH and inorganic oxidant powder X as raw materials, with the mass ratio of inorganic oxidant powder X being 10 wt.% - 80 wt.%, the metal borohydride and inorganic oxidant are ground and mixed evenly to obtain the corresponding precursor X@MBH powder; (2) Preparation of M-B-H-X electrolyte: Under an argon atmosphere, the obtained powder precursor is placed in a glass bottle. After the glass bottle is sealed with silica gel, it is placed in a muffle furnace or tube furnace and heated to 130 - 500 °C at a heating rate of 5 - 10 °C per minute and held for 1 - 360 minutes to allow the oxidant powder and metal borohydride to react fully, generating a cluster-cage-shaped metal borohydride electrolyte material, denoted as M-B-H-X; here X is sulfur powder, selenium powder or phosphorus powder, and M is a metal element such as Li, Na, K, Ca, Zn, Mg, Cs or Rb; The borohydride raw material described contains [BH4] - group; The described cluster-cage-like metal borohydride electrolyte material contains [B 12 H 12 2- , [B 10 H 10 2- cluster-cage-like borohydride group compounds.​​ 2. The preparation method of the cluster-caged metal borohydride solid electrolyte according to claim 1, wherein, The mixing of the metal borohydride and the inorganic oxidant evenly is carried out by ball milling, manual grinding or liquid-phase dispersion method.

3. The preparation method of the cluster-cage metal borohydride solid electrolyte according to claim 2, characterized in that, The mixing of the metal borohydride and the inorganic oxidant evenly is carried out by grinding in a glove box under an inert gas atmosphere for 5 - 30 minutes until evenly mixed; or sealed in a ball milling jar under an inert gas atmosphere and ball milled at a rotation speed of 400 - 500 revolutions per minute for 5 - 8 hours; collect the mixed product.

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