High-entropy lithium negative electrode material for thermal battery and preparation method of high-entropy lithium negative electrode material

Abstract

The invention relates to a high-entropy lithium negative electrode material for a thermal battery and a preparation method of the high-entropy lithium negative electrode material in the technical field of thermal batteries. The high-entropy lithium negative electrode material for the thermal battery mainly comprises Li7B6, Li, Li13Si4 and MWCNTS. Wherein Li7B6 is generated by reaction of elemental Li and elemental B in the sintering process, Li13Si4 is generated by reaction of elemental Li and elemental Si in the sintering process, and Li which is not completely reacted is retained in a free state. Through the synergistic effect of the high-entropy material and the MWCNTS, the performance breakthrough of the high-entropy lithium negative electrode material is finally realized, so that the high-entropy lithium negative electrode material has the comprehensive advantages of improving the high specific characteristics (such as specific capacity and specific power) of a thermal battery, prolonging the working time of the battery and shortening the activation time of the battery, and the defects of the existing lithium-boron alloy are comprehensively made up.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of thermal batteries, in particular to a high-entropy lithium negative electrode material for thermal batteries and a preparation method thereof. BACKGROUND

[0002] As a kind of thermal activation reserve battery, the core working principle of thermal battery is to heat the originally non-conductive solid salt electrolyte to a molten state by its own heating system, so that it is converted into an ionic conductor, thereby entering the working state. Based on this principle, thermal batteries have three key features: activation at any angle, fast activation speed, long storage time, and strong ability to withstand environmental mechanical conditions. These features make them irreplaceable in many fields, and they have been widely used in various products that require emergency or special environment power supply (such as military equipment, emergency equipment, etc.). Currently, they are gradually expanding to civilian scenarios, and some research reports have shown that they can be used as emergency power supply for airplanes, fire alarm power supply, and underground high-temperature exploration power supply, further demonstrating their technical potential.

[0003] With the development of thermal battery technology, lithium boron alloy has become a new type of thermal battery negative electrode material in recent years, which has unique structure and performance advantages: (1) special dual-phase structure: the structure of lithium boron alloy is "heat-resistant porous skeleton lithium boride + adsorbed free Li". This structure allows it to retain chemical properties close to pure Li, and through the adsorption of lithium boride, it can prevent free Li from overflowing at high temperatures of 600℃, fully meeting the actual use temperature requirements of thermal batteries at around 500℃; (2) key performance advantages: compared with traditional negative electrode materials, lithium boron alloy has high specific capacity and good comprehensive performance, which can meet the basic performance requirements of thermal battery negative electrode materials.

[0004] Although lithium boron alloy solves some problems of traditional negative electrode materials, it still has obvious technical shortcomings in actual application, namely poor conductivity in the later stage of discharge. This problem directly affects the use effect of thermal batteries: as the discharge process progresses, the decrease in material conductivity will lead to an increase in battery internal resistance, thereby affecting battery output stability and shortening effective working time, which cannot meet the higher demand of thermal batteries for long-term stable power supply, and becomes a key bottleneck restricting the performance improvement of thermal batteries. SUMMARY

[0005] The present application aims to provide a high-entropy lithium negative electrode material for thermal batteries and a preparation method thereof to solve the technical problem of poor conductivity of lithium boron alloy negative electrode materials with superior performance in the later stage of discharge in the prior art.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: a high-entropy lithium negative electrode material for thermal batteries, mainly composed of Li7B6, Li, Li 13 Si4, MWCNTS.

[0007] A preparation method of a high-entropy lithium negative electrode material for thermal batteries, comprising the following steps: (1) preparing raw materials: the raw materials include Li, B, Si, and MWCNTS, and the raw materials B, Si, and MWCNTS are placed in an inert drying box at a temperature of 120 DEG C to 300 DEG C for drying; (2) according to the weight ratio, 55% to 70% of Li, 25% to 40% of B, 1% to 5% of Si, and 1% to 3% of MWCNTS are ball milled for 0.5 h to 2 h; (3) the ball-milled material is placed in a high-temperature furnace, heated to 180 DEG C to 220 DEG C at a heating rate of 5 DEG C / min to 10 DEG C / min, and then kept for 1 h to 2 h, and then heated to 500 DEG C to 700 DEG C at a heating rate of 5 DEG C / min to 10 DEG C / min, and then kept for 1 h to 6 h, and stirring is kept during the sintering process; During the sintering process, the elemental Li reacts with the elemental B to generate a lithium boride compound Li7B6, the elemental Li reacts with the elemental Si to generate a lithium silicon compound Li 13 Si4, and the unreacted Li remains in a free state.

[0008] Further, the whole process is completed in an environment with a water oxygen content of less than 1 ppm.

[0009] Further, the B adopts superfine boron powder with a D(50) of less than 5 um.

[0010] Further, the MWCNTS has an inner diameter of 5 to 10 nm, a diameter of 10 to 20 nm, and a purity of greater than 95%. The beneficial technical effects of the present application are as follows: 1. The high-entropy negative electrode material is introduced: the characteristics of the high-entropy material can increase the driving force of the electrochemical reaction, improve the electrochemical activity of the material from the reaction nature, and alleviate the performance degradation problem caused by the insufficient reaction dynamics of the traditional material.

[0011] 2. The MWCNTS (multi-walled carbon nanotube) is added: the MWCNTS has excellent conductivity and structural stability, and after being added, a stable conductive channel can be constructed inside the material, the conductive network of the material is directly improved, and the problem of poor conductivity in the later stage of discharge can be solved, and the internal resistance of the battery in the later stage is reduced.

[0012] 3. The combined effect: through the combination of the high-entropy material (Li7B6, Li, Li 13The synergistic effect of Si4) + MWCNTS" ultimately realizes the performance breakthrough of high-entropy lithium negative electrode material, and makes it have the comprehensive advantages of improving the specific characteristics (such as specific capacity and specific power) of thermal batteries, prolonging the working time of batteries, and shortening the activation time of batteries, and fully compensating for the defects of existing lithium boron alloys. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 Discharge comparison of high-entropy lithium negative electrode material and conventional negative electrode material battery in Example 1; Figure 2 Left: high-entropy negative electrode; right: conventional lithium boron negative electrode; Figure 3 Activation time comparison of high-entropy lithium negative electrode material and conventional negative electrode material battery in Example 1. DETAILED DESCRIPTION

[0014] The following is further described in detail through specific embodiments: In the following scheme, MWCNTS is selected to have an inner diameter of 5-10 nm, a diameter of 10-20 nm, and a purity of greater than 95%. B is ultra-fine boron powder, and D(50) is less than 5 um.

[0015] Example 1: Preparation of high-entropy lithium negative electrode material, including the following steps: 1) First, put B, Si, and MWCNTS raw materials into an inert drying box (argon atmosphere) at a temperature of 200°C for drying; 2) According to the weight ratio, respectively weigh Li 640g, B 310g, Si 30g, and MWCNTS 20g; put Li, B, Si, and MWCNTS into a ball mill jar and ball mill at a speed of 200r / min for 1h to ensure uniform mixing of the raw materials; 3) Put the ball-milled material into a high-temperature furnace, heat to 200°C at a rate of 5°C / min, and keep at 200°C for 2h; then heat to 650°C at a rate of 5°C / min, and keep at 650°C for 2h, with stirring during the sintering process.

[0016] The synthesis process of all material tests is completed in a glove box with water and oxygen content <1ppm.

[0017] Example 2: Preparation of high-entropy lithium negative electrode material, including the following steps: 1) First, put B, Si, and MWCNTS raw materials into an inert drying box (helium atmosphere) at a temperature of 250°C for drying; 2) According to the weight ratio, respectively weigh Li 700g, B 250g, Si 30g, and MWCNTS 20g; put Li, B, Si, and MWCNTS into a ball mill jar and ball mill at a speed of 250r / min for 0.8h to improve the mixing efficiency; 3) Put the ball milled material into a high temperature furnace, heat to 220℃ at a rate of 8℃ / min, keep sintering at 220℃ for 1.5h; then heat to 700℃ at a rate of 8℃ / min, keep sintering at 700℃ for 3h, keep stirring during sintering process.

[0018] The synthesis process of all material tests is completed in a glove box with water and oxygen content <1ppm.

[0019] Example 3: Preparation of high-entropy lithium negative electrode material, including the following steps: 1) First, put B, Si, MWCNTS raw materials into an inert drying box (argon atmosphere) at a temperature of 120℃ for drying; 2) According to the weight ratio, respectively weigh Li 550g, B 400g, Si 30g, and MWCNTS 20g; Put Li, B, Si, and MWCNTS into a ball mill tank, and ball mill at a speed of 180r / min for 2h to ensure uniformity; 3) Put the ball milled material into a high temperature furnace, heat to 180℃ at a rate of 5℃ / min, keep sintering for 2h; then heat to 500℃ at a rate of 5℃ / min, keep sintering for 6h, keep stirring during sintering process.

[0020] The synthesis process of all material tests is completed in a glove box with water and oxygen content <1ppm.

[0021] The negative electrode is prepared from lithium boron alloy of LB20250727 (304C) type purchased from "Hunan Ruilin New Energy Technology Co., Ltd.".

[0022] Test example: The high-entropy lithium negative electrode material prepared in Example 1 and the conventional lithium boron negative electrode material prepared in the comparative example are respectively assembled into 32 single cell series unit thermal cells for electrical performance test, and the test results are shown in Figure 1 As can be seen from the figure, the high-entropy lithium negative electrode material used for preparing series unit thermal cells has many advantages such as improving the specific characteristics of thermal cells, prolonging the working time of the cells, and shortening the activation time of the cells.

[0023] The above is only an embodiment of the present application, and the specific technical solutions and / or common knowledge of the scheme are not described in detail. It should be noted that for those skilled in the art, without departing from the technical solutions of the present application, a number of modifications and improvements can be made, which should also be considered as the protection scope of the present application, which will not affect the effect and practicality of the present application. The protection scope of the present application should be subject to the content of its claims, and the specific implementation mode and the like in the specification can be used to explain the content of the claims.

Claims

1. A high-entropy lithium anode material for thermal batteries, characterized in that: Mainly composed of Li7B6, Li, and Li 13 Composed of Si4 and MWCNTS.

2. The method for preparing a high-entropy lithium anode material for a thermal battery as described in claim 1, characterized in that: Includes the following steps: (1) Prepare raw materials: The raw materials include Li, B, Si, MWCNTS. Place the raw materials B, Si, and MWCNTS in an inert drying oven at 120℃~300℃ for later use. (2) Based on the weight percentage, 55%–70% Li, 25%–40% B, 1%–5% Si, and 1%–3% MWCNTS are ball-milled for 0.5h–2h. (3) Put the ball-milled material into a high-temperature furnace and heat it to 180℃~220℃ at a heating rate of 5℃ / min~10℃ / min and hold it for 1h~2h; then heat it to 500℃~700℃ at a heating rate of 5℃ / min~10℃ / min and hold it for 1h~6h. Keep stirring during the sintering process. During sintering, elemental Li reacts with elemental B to form the lithium-boron compound Li7B6; elemental Li reacts with elemental Si to form the lithium-silicon compound Li. 13 Si4, and unreacted Li remains in a free state.

3. The method for preparing a high-entropy lithium anode material for a thermal battery according to claim 2, characterized in that: The entire process is completed in an environment where the oxygen content in the water is less than 1 ppm.

4. The method for preparing a high-entropy lithium anode material for a thermal battery according to claim 3, characterized in that: The B is made of ultrafine boron powder, and D(50) is less than 5 μm.

5. The method for preparing a high-entropy lithium anode material for a thermal battery according to claim 4, characterized in that: The MWCNTS has an inner diameter of 5-10 nm, a diameter of 10-20 nm, and a purity greater than 95%.

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