Electrolyte material for thermal battery and preparation method thereof

Abstract

The invention discloses a novel electrolyte material for a thermal battery and a preparation method of the novel electrolyte material, the electrolyte material takes ZrO2 as a flow inhibitor, ZrO2 is mixed with all-lithium eutectic salts LiCl, LiBr and LiF, and a series of preparation processes are performed to obtain the required material. The preparation method comprises the following steps: (1) powder heat treatment and impurity removal; (2) electrolyte mixing; (3) electrolyte melting: keeping the temperature at 500 DEG C for 4 hours, reducing the temperature to 450 DEG C, and keeping the temperature for 3 hours; (4) crushing and ball-milling; (5) sieving and screening; and (6) drying and storing. The preparation method of the electrolyte material is similar to a preparation method using MgO as a flow inhibitor at present, a new process and a new method are not introduced, and the electrolyte material has reliability and can be suitable for mass production of the electrolyte material. The ZrO2 used as the thermal battery electrolyte flow inhibitor has the advantages of (1) low content requirement, (2) difficulty in seepage at high temperature and (3) certain ionic conductivity at high temperature.

Description

Technical Field

[0001] The invention relates to the fields of thermal batteries and material chemistry, and in particular to an electrolyte material for a thermal battery and a preparation method thereof. Background Art

[0002] At present, thermal batteries are heat-activated storage batteries that use the battery's own heating system to heat and melt non-conductive solid salt electrolytes into ionic conductors and enter the working state. According to the classification of negative electrode materials, thermal batteries are generally divided into two types: Ca system and Li system. Whether it is a Ca system or a Li system, the electrolyte is formed by high-temperature melting of eutectic salt and flow inhibitor. Among them, the purpose of high-temperature melting is to make the flowing molten salt infiltrate the flow inhibitor to ensure the retention of the flow inhibitor on the molten salt. Depending on the negative electrode material, the type of flow inhibitor used is also different. When using Ca as the negative electrode, SiO2 is a more ideal flow inhibitor. Its specific surface area is as high as 390m 2 / g, with extremely high adsorption capacity. When Li is used as the negative electrode, SiO2 is abandoned in Li-based thermal batteries because it can react quickly with molten lithium at high temperatures. Subsequently, Y2O3, BN, and AlN were also envisioned as flow inhibitors for molten salt electrolytes, but none of them have been widely used. At present, the electrolyte flow inhibitor widely used in Li-based thermal batteries is MgO, which has a specific surface area of ​​60-80m 2 / g, because its activity is lower than that of SiO2, the amount of MgO used should be 2-3 times that of SiO2.

[0003] The content of flow inhibitor in the electrolyte is an important physical parameter. Taking the Li-based thermal battery as an example, if the MgO ratio is too low, there may be no physical isolation between the positive and negative electrodes or the electrolyte may seep out of the battery stack, which may cause a short circuit and affect the safety of the battery. However, if the MgO ratio is too high, the internal resistance of the battery will increase, affecting the safety of the battery. In practical applications, the safety of thermal batteries is often ensured as a principle, and there are technical problems such as sacrificing the internal resistance of thermal batteries, which limits the high-power transient output capability of thermal batteries.

[0004] In order to solve the above problems, the use of new flow inhibitor materials or electrolyte materials has achieved the goal of improving the internal resistance of thermal batteries, which is an effective method. Among them (CN105703002A) uses Al2O3 instead of MgO as a flow inhibitor in a thermal battery electrolyte material and its preparation method. The introduction of Al2O3 can indeed reduce the amount of flow inhibitor added to a certain extent, but it cannot change the situation that the flow inhibitor itself will affect the internal resistance of the battery. Summary of the invention

[0005] The object of the present invention is to provide an electrolyte material for a thermal battery and a preparation method thereof, so as to solve the problem of sacrificial thermal battery internal resistance existing in the flow inhibitor MgO of the Li-based thermal battery.

[0006] In order to solve the above technical problems, the technical solution of the present invention is: to provide an electrolyte material for a thermal battery, wherein ZrO2 is used as a flow inhibitor, mixed with all-lithium eutectic salts LiCl, LiBr, and LiF, and then subjected to high-temperature melting, crushing and ball milling, sieving, and drying to obtain the electrolyte material;

[0007] Calculated by mass percentage, the content of ZrO2 flow inhibitor in the electrolyte material is 20% to 40%, and the content of all-lithium eutectic salt LiCl, LiBr, LiF is 60% to 80%.

[0008] Another technical solution of the present invention provides a method for preparing an electrolyte material for a thermal battery, comprising the following steps:

[0009] Step S1: Powder heat treatment:

[0010] In an environment where the dew point is less than -40°C, the ZrO2 powder is treated at 550°C ± 20°C for 4 to 5 hours to remove dust and impurities in the powder; LiCi, LiBr, and LiF are placed in a vacuum drying oven and dried for 4 hours, with a relative vacuum degree of ≤-0.0095MPa;

[0011] Step S2, electrolyte mixing:

[0012] The treated ZrO2 powder is mixed with a fixed ratio of LiCi, LiBr, and LiF full lithium electrolyte, wherein the mass percentage of ZrO2 is 20% to 40%, the mass percentage of full lithium eutectic salt is 60% to 80%, and the total amount after mixing is 100%;

[0013] Step S3, electrolyte melting:

[0014] The mixed electrolyte was kept at 500°C in a high temperature furnace for 4 hours, then the temperature was reduced to 450°C and kept for 3 hours before being taken out of the furnace and cooled;

[0015] Step S4, crushing and ball milling:

[0016] The electrolyte bulk was manually crushed into small pieces and then ball-milled. The small batch was ball-milled for 3 hours and the large batch was ball-milled for 5 hours.

[0017] Step S5, sieving:

[0018] The ball-milled electrolyte powder is passed through a 100-mesh sieve. The electrolyte powder that cannot pass through the sieve is mixed with the next batch of electrolyte and then continued to be ball-milled;

[0019] Step S6, dry storage:

[0020] The material is dried in a vacuum drying oven at 150°C and a vacuum degree of ≤-0.095MPa for 8 hours. After drying, the material is canned and sealed with wax to obtain the electrolyte material for thermal batteries.

[0021] The thermal battery electrolyte material and the preparation method thereof provided by the present invention have the following beneficial effects:

[0022] The advantages of using ZrO2 as a flow inhibitor to replace the currently used MgO are: ① ZrO2 has a lower mass fraction in the electrolyte than MgO; ② Like MgO, ZrO2 can also make the electrolyte less likely to seep out under high temperature conditions; ③ ZrO2 has a higher ionic conductivity at high temperatures, which can further improve the ion mobility of the electrolyte and reduce the internal resistance of the thermal battery.

[0023] The preparation method of the new electrolyte material for thermal batteries is similar to the preparation method when MgO is used as a flow inhibitor. The electrolyte preparation method has a mature process system that can ensure the reliability and large-scale production capacity of the prepared powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The invention will be further described below in conjunction with the accompanying drawings:

[0025] Figure 1 The discharge curve of the novel electrolyte prepared in Example 1 of the present invention when used in a thermal battery;

[0026] Figure 2 This is the voltage fluctuation curve after applying a pulse current during the discharge process. DETAILED DESCRIPTION

[0027] The following is a further detailed description of the thermal battery electrolyte material and the preparation method thereof proposed by the present invention in conjunction with the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the following description and claims. It should be noted that the accompanying drawings are in a very simplified form and use non-precise ratios, which are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0028] The electrolyte material for the thermal battery of the present invention adopts the following design scheme:

[0029] The thermal battery electrolyte material is characterized in that the mass percentage of the ZrO2 flow inhibitor in the thermal battery electrolyte material is 20%-40%, and the mass percentage of the full lithium eutectic salt is 60%-80%.

[0030] A second object of the present invention is to provide a method for preparing the aforementioned thermal battery electrolyte which can be mass-produced and has a simple process flow.

[0031] The preparation method of the electrolyte material for thermal battery of the present invention is as follows:

[0032] (1) Heat treatment of powder: In an environment with a dew point less than -40°C, treat ZrO2 powder at 550°C ± 20°C for 4-5 hours to remove dust and impurities in the powder. Dry LiCi, LiBr, and LiF in a vacuum drying oven for 4 hours with a relative vacuum degree of ≤ -0.0095MPa;

[0033] (2) Electrolyte mixing: The treated ZrO2 powder is mixed with a fixed ratio of LiCi, LiBr, and LiF full lithium electrolyte, wherein the mass percentage of ZrO2 is 20%-40%, the mass percentage of full lithium eutectic salt is 60%-80%, and the total amount after mixing is 100%;

[0034] (3) Electrolyte melting: The mixed electrolyte is kept at 500°C in a high-temperature furnace for 4 hours, then the temperature is reduced to 450°C and kept for 3 hours before being taken out of the furnace and cooled;

[0035] (4) Crushing and ball milling: The electrolyte blocks are manually crushed into small pieces and then ball milled. Small batches are ball milled for 3 hours, and large batches are ball milled for 5 hours.

[0036] (5) Sieving: The milled electrolyte powder is passed through a 100-mesh sieve. The powder that cannot pass through the sieve is mixed with the next batch of electrolyte and then ball-milled.

[0037] (6) Drying and storage: Dry in a vacuum drying oven at 150°C, vacuum degree ≤-0.095MPa for 8 hours. After drying, pack into cans and seal with wax.

[0038] Example 1

[0039] (1) Heat treatment of powder: In an environment with a dew point less than -40°C, treat ZrO2 powder at 550°C ± 20°C for 4-5 hours to remove dust and impurities in the powder. Dry LiCi, LiBr, and LiF in a vacuum drying oven for 4 hours with a relative vacuum degree of ≤ -0.0095MPa;

[0040] (2) Electrolyte mixing: The treated ZrO2 powder is mixed with a fixed ratio of LiCi, LiBr, and LiF all-lithium electrolyte, wherein the mass of ZrO2 is 200g and the mass of all-lithium eutectic salt is 800g;

[0041] (3) Electrolyte melting: The mixed electrolyte is kept at 500°C in a high-temperature furnace for 4 hours, then the temperature is reduced to 450°C and kept for 3 hours before being taken out of the furnace and cooled;

[0042] (4) Crushing and ball milling: The electrolyte blocks are manually crushed into small pieces and then ball milled. Small batches are ball milled for 3 hours, and large batches are ball milled for 5 hours.

[0043] (5) Sieving: The milled electrolyte powder is passed through a 100-mesh sieve. The powder that cannot pass through the sieve is mixed with the next batch of electrolyte and then ball-milled.

[0044] (6) Drying and storage: Dry in a vacuum drying oven at 150°C, vacuum degree ≤-0.095MPa for 8 hours. After drying, pack into cans and seal with wax.

[0045] The electrical performance of the thermal battery with the new electrolyte prepared in this example as electrolyte is as follows Figure 1 As shown, the battery is composed of 44 cells connected in series. During the test, a 20A experimental current and an 80A pulse current were used. Figure 2 This is an enlarged diagram of the discharge curve at the pulse current. The corresponding voltages are 73.39V and 60.12V respectively. The calculated internal resistance of the battery is 0.22Ω, and the internal resistance of each monomer is 5mΩ.

[0046] Example 2

[0047] A method for preparing a new electrode material for a thermal battery, same as Example 1.

[0048] Among them, ZrO2 powder is treated at 550℃ for 4-5 hours, LiCi, LiBr and LiF are dried for 4 hours; 300g ZrO2 and 700g full lithium eutectic salt are mixed; the mixture is kept at 500℃ for 4 hours and then kept at 450℃ for 3 hours; the mixture is crushed and ball-milled; the mixture is sieved, bottled and wax-sealed.

[0049] Example 3

[0050] A method for preparing a new type of electrode material for a thermal battery, same as in Example 1.

[0051] Among them, ZrO2 powder is treated at 550℃ for 4-5 hours, LiCi, LiBr and LiF are dried for 4 hours; 400g ZrO2 and 600g all-lithium eutectic salt are mixed; the mixture is kept at 500℃ for 4 hours and then kept at 450℃ for 3 hours; the mixture is crushed and ball-milled; the mixture is sieved, bottled and wax-sealed.

[0052] The contents not described in detail in this specification belong to the prior art known to those skilled in the art. It is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention.

Claims

1. An electrolyte material for a thermal battery, characterized in that ZrO2 is used as a flow inhibitor, mixed with all-lithium eutectic salts LiCl, LiBr, and LiF, and then subjected to high-temperature melting, crushing and ball milling, sieving, and drying to obtain the product; Calculated by mass percentage, the content of ZrO2 flow inhibitor in the electrolyte material is 20% to 40%, and the content of all-lithium eutectic salt LiCl, LiBr, LiF is 60% to 80%.

2. The method for preparing the electrolyte material for a thermal battery according to claim 1, characterized in that: The steps include: Step S1: Powder heat treatment: In an environment where the dew point is less than -40°C, the ZrO2 powder is treated at 550°C ± 20°C for 4 to 5 hours to remove dust and impurities in the powder; LiCi, LiBr, and LiF are placed in a vacuum drying oven and dried for 4 hours, with a relative vacuum degree of ≤-0.0095MPa; Step S2, electrolyte mixing: The treated ZrO2 powder is mixed with a fixed ratio of LiCi, LiBr, and LiF full lithium electrolyte, wherein the mass percentage of ZrO2 is 20% to 40%, the mass percentage of full lithium eutectic salt is 60% to 80%, and the total amount after mixing is 100%; Step S3, electrolyte melting: The mixed electrolyte was kept at 500°C in a high temperature furnace for 4 hours, then the temperature was reduced to 450°C and kept for 3 hours before being taken out of the furnace and cooled; Step S4, crushing and ball milling: The electrolyte bulk was manually crushed into small pieces and then ball-milled. The small batch was ball-milled for 3 hours and the large batch was ball-milled for 5 hours. Step S5, sieving: The ball-milled electrolyte powder is passed through a 100-mesh sieve. The electrolyte powder that cannot pass through the sieve is mixed with the next batch of electrolyte and then continued to be ball-milled; Step S6, dry storage: The material is dried in a vacuum drying oven at 150°C and a vacuum degree of ≤-0.095 MPa for 8 hours. After drying, the material is canned and sealed with wax to obtain the electrolyte material for thermal batteries.

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