A low-melting high-conductivity electrolyte for thermal batteries and a method of making the same

Abstract

The application relates to the technical field of electrolytes, in particular to a low-melting-point high-conductivity electrolyte for a thermal battery and a preparation method thereof. The technical scheme of the low-melting-point high-conductivity electrolyte is prepared from 40-60% of low-melting-point eutectic salt, 3-35% of organic anion lithium salt and 35-57% of an adsorption carrier according to the mass percentage, and the low-melting-point eutectic salt is LiBr-KBr-CsBr. The organic anion lithium salt is added in the inorganic low-melting-point eutectic salt system for the first time, the organic anion and lithium ion interact weakly by virtue of the highly delocalized charge characteristics of the organic anion, the melting point is low, the lithium ion conductivity is high in a low-temperature range, the addition amount is not limited by the eutectic proportion, the self melting point can realize the conduction of lithium ions in a lower working temperature range, and the ionic conductivity of the low-melting-point electrolyte of the thermal battery is improved.

Description

Technical Field

[0001] This invention relates to the field of electrolyte technology, and in particular to a low-melting-point, high-conductivity electrolyte for thermal batteries and its preparation method. Background Technology

[0002] A thermal battery is a high-temperature primary battery that uses molten salt as the electrolyte. During operation, the internal heating system of the thermal battery heats the solid electrolyte, causing the salt to melt and acquire ionic conductivity.

[0003] Commonly used molten salt systems for thermal batteries include LiCl-KCl, LiF-LiCl-LiBr, and LiF-LiBr-KBr. LiCl-KCl has a melting point of 354℃ and can operate for a relatively long time under normal current density conditions. However, at higher current densities, side reactions occur at the positive electrode, forming complex phases (such as LiK6Fe24S26Cl), increasing the battery's internal resistance. LiF-LiCl-LiBr possesses advantages in high ionic activity and high ion mobility, but its melting point is 436℃. LiF-LiBr-KBr has a melting point of only 324℃, but its ionic conductivity limits its application to only moderate current densities. Due to the unique operating mechanism of thermal batteries, low melting point and high conductivity of the electrolyte remain the goals of performance development. Low-melting-point eutectic salt systems are relatively mature, but their poor carrying capacity restricts their widespread application in the field of thermal batteries.

[0004] In existing technologies, the main research and development approach for low-melting-point, high-conductivity electrolyte systems in the thermal battery field involves adding inorganic lithium halide salts to a low-melting-point eutectic salt system. This increases the lithium-ion concentration and thus improves the electrolyte's ionic conductivity. However, this is often limited by the eutectic ratio. The added inorganic lithium halide salt needs to form a low-melting-point eutectic with the original molten salt system to melt and conduct lithium ions during thermal battery operation. Inorganic lithium salts such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide are used as additives to improve the ionic conductivity of low-melting-point eutectic salt systems. However, these inorganic lithium halide salts must melt during thermal battery use to possess lithium-ion transport capabilities. Inorganic lithium salts such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide have high melting points, and their addition ratio must strictly adhere to the eutectic ratio to form a eutectic with the original low-melting-point eutectic system in order to improve ionic conductivity. The limited addition ratio also restricts their ability to improve ionic conductivity. Therefore, we propose a low-melting-point, high-conductivity electrolyte for thermal batteries and its preparation method. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the prior art by proposing a low-melting-point, high-conductivity electrolyte for thermal batteries and its preparation method.

[0006] The present invention provides a low-melting-point, high-conductivity electrolyte for thermal batteries, wherein the low-melting-point, high-conductivity electrolyte is formulated by mass percentage of 40%-60% low-melting-point eutectic salt, 3%-25% organic anionic lithium salt, and 35%-57% adsorbent carrier.

[0007] Optionally, the low-melting-point eutectic salt is LiBr-KBr-CsBr.

[0008] Optionally, the organic anionic lithium salt is at least one of LiFSI, LiTFSI, Li(CF3SO2)2N, and LiC(CF3SO2)3.

[0009] Optionally, the adsorbent support is an oxide, and the oxide is at least one of MgO, SiO2, ZrO2, and Al2O3.

[0010] On the other hand, the present invention provides a method for preparing a low-melting-point, high-conductivity electrolyte for thermal batteries, comprising the following steps:

[0011] Step 1: Dehydrate LiBr, KBr, CsBr, organic anionic lithium salt, and adsorbent support by vacuum drying at a temperature of 60℃-180℃.

[0012] Step 2: Weigh and mix the dried LiBr, KBr, and CsBr according to the eutectic ratio;

[0013] Step 3: Treat the salt processed in Step 2 at 300℃-450℃ for 2 hours, then air-cool it to room temperature;

[0014] Step 4: Crush the salt processed in Step 3 and pass it through a 50-mesh sieve to obtain a low-melting-point eutectic salt;

[0015] Step 5: Weigh and mix the low-melting-point eutectic salt, organic anionic lithium salt, and adsorption support material according to the specified proportions.

[0016] Step 6: Place the material processed in Step 5 at 100℃-200℃ for 2 hours, then cool it to room temperature;

[0017] Step 7: Crush the material processed in Step 6 and pass it through a 50-mesh sieve to obtain a new type of low-melting-point, high-conductivity electrolyte powder.

[0018] Compared with the prior art, the present invention has the following beneficial technical effects:

[0019] In the technical solution of this invention, an organic anionic lithium salt is added to an inorganic low-melting-point eutectic salt system for the first time. Taking advantage of the highly delocalized charge characteristics of organic anions, the interaction between organic anions and lithium ions is weak, the melting point is low, and the lithium-ion conductivity is high in the low-temperature range. As an additive, it can further reduce the melting point of the electrolyte when added to the low-melting-point electrolyte system. Moreover, the amount added is not limited by the eutectic ratio. Its own melting point can enable the conduction of lithium ions in a lower operating temperature range, thereby improving the ionic conductivity of the low-melting-point electrolyte of the thermal battery. Attached Figure Description

[0020] Figure 1 This is the DSC test curve of the electrolyte in Embodiment 1 of the present invention.

[0021] Figure 2 This is the DSC test curve of the electrolyte in Comparative Example 1 of this invention.

[0022] Figure 3 These are comparison curves of the discharge internal resistance of the electrolyte in Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0023] The specific embodiments of the present invention will be described in further detail below. However, the present invention is not limited to these embodiments. Any improvement or substitution on the basic scheme of this embodiment shall still fall within the scope of protection claimed by the claims of the present invention.

[0024] The following are examples and comparative examples:

[0025] Example 1

[0026] A low-melting-point, high-conductivity electrolyte for thermal batteries, comprising, by mass percentage, 40% LiBr-KBr-CsBr eutectic salt, 20% LiTFSI, and 40% MgO. The specific preparation method of the electrolyte in this embodiment mainly includes drying, preparing the eutectic salt, and preparing the electrolyte.

[0027] The preparation process is as follows:

[0028] Step 1: Dehydrate LiBr, KBr, CsBr, LiTFSI, and MgO by vacuum drying at 120℃.

[0029] Step 2: Weigh and mix the dried LiBr, KBr, and CsBr according to the eutectic molar ratio of 56.1:18.1:25.3.

[0030] Step 3: Treat the salt from Step 2 at 300℃ for 2 hours, then air-cool it to room temperature;

[0031] Step 4: Crush the salt processed in Step 3 and pass it through a 50-mesh sieve to obtain a low-melting-point eutectic salt;

[0032] Step 5: Weigh and mix the LiBr-KBr-CsBr eutectic salt, LiTFSI, and MgO in a mass ratio of 40:20:40.

[0033] Step 6: Place the material processed in Step 5 at 200℃ for 2 hours, then cool it to room temperature;

[0034] Step 7: Crush the material processed in Step 6 and pass it through a 50-mesh sieve to obtain a new type of low-melting-point, high-conductivity electrolyte powder.

[0035] The prepared low-melting-point, high-conductivity electrolyte powder was subjected to DSC and discharge tests, and the electrolyte melting point was found to be 222.5℃.

[0036] Comparative Example 1

[0037] Currently, the LiF-LiBr-KBr material used in thermal battery products has a melting point of 324℃. Under testing conditions of 280℃, it did not melt and exhibited extremely low ionic conductivity. Therefore, the LiBr-KBr-CsBr eutectic salt from the low-melting-point eutectic salt system of thermal batteries was used as the electrolyte material for comparison. The specific preparation steps are as follows:

[0038] Step 1: Dehydrate LiBr, KBr, CsBr, and MgO by vacuum drying at 120℃.

[0039] Step 2: Weigh and mix the dried LiBr, KBr, and CsBr according to the eutectic molar ratio of 56.1:18.1:25.3.

[0040] Step 3: Treat the salt from Step 2 at 300℃ for 2 hours, then air-cool it to room temperature;

[0041] Step 4: Crush the salt processed in Step 3 and pass it through a 50-mesh sieve to obtain a low-melting-point eutectic salt;

[0042] Step 5: Weigh and mix the LiBr-KBr-CsBr eutectic salt and MgO in a mass ratio of 60:40.

[0043] Step 6: Place the material processed in Step 5 at 200℃ for 2 hours, then cool it to room temperature;

[0044] Step 7: Crush the material processed in Step 6 and pass it through a 50-mesh sieve to obtain a new type of low-melting-point, high-conductivity electrolyte powder.

[0045] The prepared low-melting-point, high-conductivity electrolyte powder was subjected to DSC and discharge tests, and the results showed that the electrolyte melting point was 236℃.

[0046] Example 2

[0047] A low-melting-point, high-conductivity electrolyte for thermal batteries, wherein the formulation of the low-melting-point, high-conductivity electrolyte comprises, by mass percentage, 60% LiBr-KBr-CsBr eutectic salt, 3% LiFSI, and 37% SiO2.

[0048] The preparation process is as follows:

[0049] Step 1: Dehydrate LiBr, KBr, CsBr, LiFSI, and SiO2 separately under vacuum at a temperature of 120℃.

[0050] Step 2: Weigh and mix the dried LiBr, KBr, and CsBr according to the eutectic molar ratio of 56.1:18.1:25.3.

[0051] Step 3: Treat the salt from Step 2 at 300℃ for 2 hours, then air-cool it to room temperature;

[0052] Step 4: Crush the salt processed in Step 3 and pass it through a 50-mesh sieve to obtain a low-melting-point eutectic salt;

[0053] Step 5: Weigh and mix the LiBr-KBr-CsBr eutectic salt, LiFSI, and SiO2 according to the specified ratio;

[0054] Step 6: Place the material processed in Step 5 at 200℃ for 2 hours, then cool it to room temperature;

[0055] Step 7: Crush the material processed in Step 6 and pass it through a 50-mesh sieve to obtain a new type of low-melting-point, high-conductivity electrolyte powder.

[0056] Example 3

[0057] A low-melting-point, high-conductivity electrolyte for thermal batteries, wherein the formulation of the low-melting-point, high-conductivity electrolyte comprises, by mass percentage, 40% LiBr-KBr-CsBr eutectic salt, 25% Li(CF3SO2)2N, and 35% ZrO2.

[0058] The preparation process is as follows:

[0059] Step 1: Dehydrate LiBr, KBr, CsBr, Li(CF3SO2)2N, and ZrO2 by vacuum drying at 120℃.

[0060] Step 2: Weigh and mix the dried LiBr, KBr, and CsBr according to the eutectic molar ratio of 56.1:18.1:25.3.

[0061] Step 3: Treat the salt from Step 2 at 380℃ for 2 hours, then air-cool it to room temperature;

[0062] Step 4: Crush the salt processed in Step 3 and pass it through a 50-mesh sieve to obtain a low-melting-point eutectic salt;

[0063] Step 5: Weigh and mix the LiBr-KBr-CsBr eutectic salt, Li(CF3SO2)2N, and ZrO2 according to the specified proportions.

[0064] Step 6: Place the material processed in Step 5 at 150℃ for 2 hours, then cool it to room temperature;

[0065] Step 7: Crush the material processed in Step 6 and pass it through a 50-mesh sieve to obtain a new type of low-melting-point, high-conductivity electrolyte powder.

[0066] Example 4

[0067] A low-melting-point, high-conductivity electrolyte for thermal batteries, wherein the formulation of the low-melting-point, high-conductivity electrolyte comprises, by mass percentage, 40% LiBr-KBr-CsBr eutectic salt, 3% LiC(CF3SO2)3, and 57% Al2O3.

[0068] The preparation process is as follows:

[0069] Step 1: Dehydrate LiBr, KBr, CsBr, LiC(CF3SO2)3, and Al2O3 by vacuum drying at 120℃.

[0070] Step 2: Weigh and mix the dried LiBr, KBr, and CsBr according to the eutectic molar ratio of 56.1:18.1:25.3.

[0071] Step 3: Treat the salt from Step 2 at 300℃ for 2 hours, then air-cool it to room temperature;

[0072] Step 4: Crush the salt processed in Step 3 and pass it through a 50-mesh sieve to obtain a low-melting-point eutectic salt;

[0073] Step 5: Weigh and mix the LiBr-KBr-CsBr eutectic salt, LiC(CF3SO2)3, and Al2O3 according to the specified proportions.

[0074] Step 6: Place the material processed in Step 5 at 200℃ for 2 hours, then cool it to room temperature;

[0075] Step 7: Crush the material processed in Step 6 and pass it through a 50-mesh sieve to obtain a new type of low-melting-point, high-conductivity electrolyte powder.

[0076] Example 5

[0077] A low-melting-point, high-conductivity electrolyte for thermal batteries, comprising, by mass percentage, 40% LiBr-KBr-CsBr eutectic salt, 20% LiTFSI, and 40% MgO.

[0078] The preparation process is as follows:

[0079] Step 1: Dehydrate LiBr, KBr, CsBr, LiTFSI, and MgO separately under vacuum at a temperature of 60℃.

[0080] Step 2: Weigh and mix the dried LiBr, KBr, and CsBr according to the eutectic molar ratio of 56.1:18.1:25.3.

[0081] Step 3: Treat the salt from Step 2 at 300℃ for 2 hours, then air-cool it to room temperature;

[0082] Step 4: Crush the salt processed in Step 3 and pass it through a 50-mesh sieve to obtain a low-melting-point eutectic salt;

[0083] Step 5: Weigh and mix the LiBr-KBr-CsBr eutectic salt, LiTFSI, and MgO according to the specified proportions.

[0084] Step 6: Place the material processed in Step 5 at 100℃ for 2 hours, then cool it to room temperature;

[0085] Step 7: Crush the material processed in Step 6 and pass it through a 50-mesh sieve to obtain a new type of low-melting-point, high-conductivity electrolyte powder.

[0086] Example 6

[0087] A low-melting-point, high-conductivity electrolyte for thermal batteries, comprising, by mass percentage, 40% LiBr-KBr-CsBr eutectic salt, 20% LiTFSI, and 40% MgO.

[0088] The preparation process is as follows:

[0089] Step 1: Dehydrate LiBr, KBr, CsBr, LiTFSI, and MgO separately under vacuum at a temperature of 120℃.

[0090] Step 2: Weigh and mix the dried LiBr, KBr, and CsBr according to the eutectic molar ratio of 56.1:18.1:25.3.

[0091] Step 3: Treat the salt from Step 2 at 375℃ for 2 hours, then air-cool it to room temperature;

[0092] Step 4: Crush the salt processed in Step 3 and pass it through a 50-mesh sieve to obtain a low-melting-point eutectic salt;

[0093] Step 5: Weigh and mix the LiBr-KBr-CsBr eutectic salt, LiTFSI, and MgO according to the specified proportions.

[0094] Step 6: Place the material processed in Step 5 at 150℃ for 2 hours, then cool it to room temperature;

[0095] Step 7: Crush the material processed in Step 6 and pass it through a 50-mesh sieve to obtain a new type of low-melting-point, high-conductivity electrolyte powder.

[0096] Example 7

[0097] A low-melting-point, high-conductivity electrolyte for thermal batteries, comprising, by mass percentage, 40% LiBr-KBr-CsBr eutectic salt, 20% LiTFSI, and 40% MgO.

[0098] The preparation process is as follows:

[0099] Step 1: Dehydrate LiBr, KBr, CsBr, LiTFSI, and MgO separately under vacuum at a temperature of 180℃.

[0100] Step 2: Weigh and mix the dried LiBr, KBr, and CsBr according to the eutectic molar ratio of 56.1:18.1:25.3.

[0101] Step 3: Treat the salt from Step 2 at 450℃ for 2 hours, then air-cool it to room temperature;

[0102] Step 4: Crush the salt processed in Step 3 and pass it through a 50-mesh sieve to obtain a low-melting-point eutectic salt;

[0103] Step 5: Weigh and mix the LiBr-KBr-CsBr eutectic salt, LiTFSI, and MgO according to the specified proportions.

[0104] Step 6: Place the material processed in Step 5 at 200℃ for 2 hours, then cool it to room temperature;

[0105] Step 7: Crush the material processed in Step 6 and pass it through a 50-mesh sieve to obtain a new type of low-melting-point, high-conductivity electrolyte powder.

[0106] The embodiments of the present invention have been described in detail above, but the content described is only an embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A low-melting-point, high-conductivity electrolyte for thermal batteries, characterized in that: The low-melting-point, high-conductivity electrolyte is formulated by mass percentage as follows: 40%-60% inorganic low-melting-point eutectic salt, 3%-25% organic anionic lithium salt, and 35%-57% adsorption carrier; the organic anionic lithium salt is at least one of LiFSI, Li(CF3SO2)2N, and LiC(CF3SO2)3.

2. The low-melting-point, high-conductivity electrolyte for thermal batteries according to claim 1, characterized in that, The low-melting-point eutectic salt is LiBr-KBr-CsBr.

3. The low-melting-point, high-conductivity electrolyte for thermal batteries according to claim 1, characterized in that, The adsorbent carrier is an oxide, and the oxide is at least one of MgO, SiO2, ZrO2, and Al2O3.

4. A method for preparing a low-melting-point, high-conductivity electrolyte for a thermal battery according to any one of claims 1-3, characterized in that, Includes the following steps: Step 1: Dehydrate LiBr, KBr, CsBr, organic anionic lithium salt, and adsorbent support by vacuum drying at a temperature of 60℃-180℃. Step 2: Weigh and mix the dried LiBr, KBr, and CsBr according to the eutectic ratio; Step 3: Treat the salt processed in Step 2 at 300℃-450℃ for 2 hours, then air-cool it to room temperature; Step 4: Crush the salt processed in Step 3 and pass it through a 50-mesh sieve to obtain a low-melting-point eutectic salt; Step 5: Weigh and mix the low-melting-point eutectic salt, organic anionic lithium salt, and adsorption support material according to the specified proportions. Step 6: Place the material processed in Step 5 at 100℃-200℃ for 2 hours, then cool it to room temperature; Step 7: Crush the material processed in Step 6 and pass it through a 50-mesh sieve to obtain a new type of low-melting-point, high-conductivity electrolyte powder.

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