CN113764821A

CN113764821A - Boron nitride fiber diaphragm, diaphragm preparation method and lithium thermal battery

Info

Publication number: CN113764821A
Application number: CN202111048768.2A
Authority: CN
Inventors: 李茹; 齐学礼; 张铭霞; 王重海; 吕锋; 郑俊; 王玉娇; 徐浩南; 尹承国; 王克宏
Original assignee: Shandong Industrial Ceramics Research and Design Institute Co Ltd
Current assignee: Shandong Industrial Ceramics Research and Design Institute Co Ltd
Priority date: 2021-09-08
Filing date: 2021-09-08
Publication date: 2021-12-07

Abstract

The invention discloses a preparation method of a boron nitride fiber diaphragm, which comprises the following steps of adding 0.01-0.2 part by mass of boron nitride fibers into 80-120 parts by mass of water, adding 10-30 parts by mass of a thickening agent solution and 0.005-0.1 part by mass of a dispersing agent, and uniformly mixing to obtain mixed slurry; preparing the mixed slurry into boron nitride fiber paper by adopting a papermaking process; and compounding the boron nitride fiber paper with the precursor solution, and carrying out heat treatment to obtain the boron nitride fiber diaphragm. The invention also discloses a boron nitride fiber diaphragm and a lithium thermal battery. The boron nitride fiber diaphragm prepared by the invention has the advantages of good flexibility, light weight, high mechanical strength, good liquid absorption and retention capacity, high safety, good conductive effect, corrosion resistance and high temperature resistance, and can be applied to a high-temperature molten lithium environment.

Description

Boron nitride fiber diaphragm, diaphragm preparation method and lithium thermal battery

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a boron nitride fiber diaphragm, a preparation method of the diaphragm and a lithium thermal battery.

Background

With the rapid development of national defense technology and various weapon systems, the power supply used by these systems also faces new challenges, and the thermal battery with high specific power, high specific energy and long service life is the main development direction in the future. The separator material, as a major component of the battery, is one of the major factors affecting the long life and performance of the high temperature battery.

At present, the lithium-based high-temperature battery diaphragm is mainly realized by an electrolyte sheet formed by mixing and pressing powdered MgO and electrolyte in a certain proportion, but the battery diaphragm has the following defects of 1, complex preparation process, low mechanical strength, easy breakage, threat to the safety and reliability of the diaphragm, 2, larger thickness (about 0.5mm) of a magnesium oxide spacer and surface density of about 0.10g/cm²The bulk density is about 2.70g/cm³The mass of the reserved electrolyte is 1 time of that of the magnesium oxide, and the use requirements of high-efficiency, small volume, high specific power, high specific energy, reliability and high-heat batteries cannot be met.

The compatibility of lithium (lithium alloy) with different types of ceramic materials at high temperature was obtained in the 70 th century by a large number of experimental research data in the american atton laboratory, which concluded that: the BN fiber membrane is the only material which can be used as the LiAl/FeSx molten salt storage battery membrane. The applicant selects boron nitride fiber to prepare the fiber diaphragm, and the corrosion resistance of the boron nitride fiber can overcome the defect that the fiber diaphragm cannot be applied to a molten lithium environment, but the prepared assembled thermal battery also has the following problems 1 that the diaphragm prepared by adopting the traditional weaving mode has overlarge pore structure and is easy to short circuit 2, the diaphragm prepared by adopting the traditional paper making process has the defects that the organic binder is easy to carbonize at high temperature, the framework structure is easy to damage in the molten environment 3, and the prepared lithium thermal battery has certain conductivity.

Therefore, there is a need for a boron nitride fiber membrane that overcomes the above-mentioned disadvantages of the prior art.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention discloses a boron nitride fiber diaphragm with strong liquid absorption and retention capacity, high safety and high ionic conductivity and a preparation method thereof, and the following technical scheme is adopted:

a preparation method of a boron nitride fiber diaphragm comprises the following steps,

adding 0.01-0.2 part by mass of boron nitride fibers into 80-120 parts by mass of water, adding 10-30 parts by mass of a thickener solution and 0.005-0.1 part by mass of a dispersant, and uniformly mixing to obtain a mixed slurry;

preparing the mixed slurry into boron nitride fiber paper by adopting a papermaking process;

compounding the boron nitride fiber paper with a precursor solution;

and carrying out heat treatment on the boron nitride fiber paper adsorbed with the precursor solution to obtain the boron nitride fiber diaphragm.

Further, in the above-mentioned case,

the precursor solution is a magnesium oxide precursor solution or an aluminum oxide precursor solution.

Further, the preparation method of the precursor solution comprises the following steps: stirring 30-80 parts by mass of water, 30-80 parts by mass of a small molecular organic solvent and 30-80 parts by mass of an aluminum salt or a magnesium salt to form a uniform and transparent solution.

Further, the compounding method comprises the following steps:

and (3) dipping the boron nitride fiber paper into the precursor solution for 0.5-25 h, taking out and drying.

Further, the impregnation method comprises the following specific steps: dipping for 0.5-1 h under the vacuum condition of-0.07 to-0.1 MPa, and then dipping at normal pressure.

Further, the temperature of the heat treatment is 500-650 ℃.

Further, before uniformly mixing, 5-20 parts by mass of alumina fiber and/or silicon nitride fiber are added.

Further, the papermaking process comprises the following specific steps:

wet papermaking is carried out on the mixed slurry to obtain a wet fiber paper blank;

and adding a binder and a curing agent into the wet fiber paper blank, and curing to obtain the boron nitride fiber paper.

A boron nitride fiber diaphragm is prepared by any one of the preparation methods.

The invention also discloses a lithium thermal battery which comprises the boron nitride fiber diaphragm, and the boron nitride fiber diaphragm is prepared by any one of the preparation methods.

By adopting the technical scheme, the invention has the beneficial effects that:

according to the invention, the boron nitride fiber is made into fiber paper to prepare the fiber diaphragm, so that the prepared fiber diaphragm has the advantages of good flexibility, light weight and corrosion resistance; by compounding the fiber paper with the precursor solution, the mechanical strength, the liquid absorption and retention capacity and the high-temperature resistance of the fiber diaphragm are improved, the ionic conductivity after the battery is assembled is further improved, the internal resistance of the battery is reduced, the fiber diaphragm can be applied to a high-temperature molten lithium environment, and the application range of the fiber diaphragm is expanded.

Drawings

FIG. 1 is a discharge curve of a single battery cell according to an embodiment of the present invention

FIG. 2 is a discharge curve of a single cell according to another embodiment of the present invention

FIG. 3 is a no-load curve of a single battery according to another embodiment of the present invention

FIG. 4 is a normal discharge curve of a single battery according to another embodiment of the present invention

FIG. 5 is an SEM image of boron nitride fiber paper prepared by the invention

FIG. 6 is an SEM image of a boron nitride fiber membrane compounded with an alumina precursor solution according to the present invention

FIG. 7 is an SEM image of the boron nitride fiber membrane adsorbing electrolyte of the invention

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The invention discloses a preparation method of a boron nitride fiber diaphragm, which comprises the following steps,

the method comprises the following steps: adding 0.01-0.2 part by mass of boron nitride fibers into 80-120 parts by mass of water, adding 10-30 parts by mass of a thickener solution and 0.005-0.1 part by mass of a dispersant, and uniformly mixing to obtain a mixed slurry;

step two: preparing the mixed slurry into boron nitride fiber paper by adopting a papermaking process;

step three: compounding the boron nitride fiber paper with the precursor solution, wherein the compounding mode can be dipping, spraying and the like, and the method is not limited in the above;

step four: and carrying out heat treatment on the boron nitride fiber paper adsorbed with the precursor solution to obtain the boron nitride fiber diaphragm.

In the prior art, the fiber material for preparing the battery diaphragm is low in corrosion resistance, so that the fiber diaphragm prepared in the prior art is usually applied to a normal-temperature lithium ion battery, the boron nitride fiber has a melting point of about 3000 ℃, can stably exist in binary and ternary electrolyte molten salts within the temperature range of 350-550 ℃, does not react with an electrolyte material and an electrode material, is good in corrosion resistance and chemical stability, and can be applied to a lithium thermal battery.

According to the invention, boron nitride fiber is prepared into boron nitride fiber paper by adopting a paper making process, and then the boron nitride fiber diaphragm is prepared by adopting a way of compounding the boron nitride fiber paper and a precursor solution, so that the prepared boron nitride fiber diaphragm has the advantages of good flexibility and light weight of the fiber paper, and also has the advantages of high specific mechanical strength, high porosity and good liquid absorption and retention capacity, the mass of the boron nitride fiber diaphragm for absorbing electrolyte is more than 10 times of the weight of the diaphragm, the mass of the retained electrolyte is more than 8 times of the diaphragm, the liquid absorption and retention performance is improved by more than 5 times compared with that of the traditional magnesium oxide spacer, the ionic conductivity is improved, the internal resistance of the battery is reduced, the output capacity reaches more than 90%, and the boron nitride fiber diaphragm can be used as a better battery diaphragm material to be applied to a thermal battery power supply system.

In one embodiment of the present invention, the preparation process of the mixed slurry of the first step is as follows:

adding 0.01-0.2 part by mass of boron nitride fibers into 80-120 parts by mass of water, adding 10-30 parts by mass of thickener solution and 0.005-0.1 part by mass of dispersant, uniformly mixing to obtain mixed slurry,

during preparation, the fiber amount is calculated according to the gram weight of the required fiber and the area of the filter screen, and in order to achieve a better dispersion effect, the boron nitride fiber can be cut into chopped fibers with the diameter of less than 25mm and then dispersed in water to obtain initial slurry;

the mass fraction of the thickening agent solution can be 0.5% -2%, the thickening agent solution can be added into the initial slurry one by one, the viscosity of the initial slurry is adjusted to be 5-50 mPa & s, preferably 10-20 mPa & s, and then a dispersing agent is added according to the dispersing effect;

wherein, the thickening agent can be selected from synthetic or natural hydrophilic high molecular compounds such as acrylic thickener, polyacrylamide, methylcellulose, carboxymethyl cellulose, carboxyethyl fiber, carboxypropyl fiber, sodium carboxymethyl cellulose, sodium carboxyethyl fiber, sodium carboxypropyl fiber, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, chitosan, starch, polyanion cellulose derivatives, polyvinylpyrrolidone, polyvinyl alcohol, pectin, alginate and the like.

Any known surfactant can be used as the dispersant, and a quaternary ammonium salt cationic surfactant with 11-19 carbon atoms is preferred.

Furthermore, 5-20 parts by mass of ceramic fibers such as alumina fibers and silicon nitride fibers can be added into the mixed slurry so as to improve the rigidity and strength of the prepared boron nitride fiber paper.

In one embodiment of the invention, the second papermaking process comprises the following specific steps:

wet papermaking is carried out on the mixed slurry to obtain a uniform wet fiber paper blank, and residual white water on the surface of the fiber can be sucked away from the bottom of a filter screen by adopting a vacuum filtration device or other water absorption devices;

in order to improve the compactness and the mechanical strength of the fiber paper at normal temperature, the wet blank of the fiber paper can be added with a binder and a curing agent and then cured to obtain the boron nitride fiber paper, fig. 5 is an SEM image of the boron nitride fiber paper prepared by the invention, and as can be seen from fig. 5, the fibers are uniformly lapped together and have uniform structure.

The solid content of the binder is 2-20%, the adding mode can be spraying, dipping and the like, the binder can be selected from all binders with adhesive functions such as acrylates, epoxy resins, polyimide, urea-formaldehyde resin, phenolic resin and the like, and the curing agent can be randomly matched according to the selection of the binder, and the method is not limited.

The curing temperature in this invention is selected according to the curing temperature of the resin, and is not limited, and the fiber paper can be cured by means of weighting or pressing in an oven, so as to improve the compactness and strength of the fiber paper.

In a preferred embodiment of the present invention, in the third step, the precursor solution may be an aluminum oxide precursor solution or a magnesium oxide precursor solution, and after the aluminum oxide precursor or the magnesium oxide precursor solution is subjected to heat treatment, the aluminum oxide precursor or the magnesium oxide precursor solution exists on the boron nitride fiber membrane in the form of aluminum oxide or magnesium oxide;

the precursor solution can be prepared by the following method: stirring 30-80 parts by mass of water, 30-80 parts by mass of a small molecular organic solvent and 30-80 parts by mass of an aluminum salt or a magnesium salt to form a uniform transparent solution, wherein the small molecular organic solvent can be methanol, ethanol, isopropanol and the like, the aluminum salt can be aluminum chloride hexahydrate, aluminum nitrate, aluminum isopropoxide and the like, and the magnesium salt can be magnesium acetate/magnesium nitrate and the like.

According to the invention, boron nitride fiber paper is compounded with the alumina precursor solution or the magnesia precursor solution, and the finally prepared fiber diaphragm has strong liquid absorption and retention capacities due to the strong adsorption property of alumina or magnesia; meanwhile, the fiber paper compounded with magnesium oxide or aluminum oxide can maintain high mechanical strength in a high-temperature environment, mainly because the binder of a common fiber paper diaphragm can be carbonized and cracked at a high application temperature, so that fibers collapse or crack, the fiber paper is scattered, and the fiber paper diaphragm can not be used any more, and the generated magnesium oxide or aluminum oxide can also play a role in bonding in the high-temperature environment of the fiber paper compounded with a magnesium oxide precursor or an aluminum oxide precursor, so that the fiber paper can still maintain high mechanical strength, fig. 6 is an SEM image of the BN fiber diaphragm compounded with an aluminum oxide precursor solution, and it can be seen from fig. 6 that aluminum oxide is uniformly compounded between fibers and on the surface of the fibers, and aluminum oxide particles can be uniformly adhered on the surface of the fibers. The modified boron nitride fiber diaphragm has uniform structure, can still keep good skeleton structure in high-temperature environment, and improves the electrolyte adsorption capacity of the diaphragm. Fig. 7 is an SEM image of the boron nitride fiber membrane adsorbed electrolyte, and it can be seen from fig. 7 that the boron nitride fiber membrane adsorbed electrolyte can reach a near-saturated state and has a good liquid absorption effect (the white surface is caused by moisture absorption of the electrolyte during the test).

In a preferred embodiment of the invention, the precursor solution is an alumina precursor solution, although the diaphragm compounded with magnesium oxide and alumina has little difference in liquid absorption and retention effects, the diaphragm compounded with alumina has better electrolyte fixing capability and larger diaphragm loaded electrolyte mass, so that the resistance of the diaphragm is smaller, the conductive effect is better, and the finally prepared lithium-based thermal battery has better conductivity.

TABLE 1 comparison of liquid absorption and retention capacities of boron nitride fiber membranes

Table 1 shows the liquid absorption and retention capability test results of the boron nitride fiber membrane prepared by the preparation method of the present invention, wherein 1-6 are boron nitride fiber membranes compounded with magnesium oxide, 7-12 are boron nitride fiber membranes compounded with aluminum oxide, and other preparation conditions of the boron nitride fiber membranes of 1-12 are the same, and it can be seen from table 1 that the liquid absorption and retention effects of the boron nitride fiber membranes compounded with magnesium oxide and aluminum oxide are not much different.

Fig. 1 shows two groups of single batteries prepared under the same conditions, and the difference between fig. 1 and fig. 2 is that the boron nitride fiber diaphragm of the battery in fig. 1 is compounded with aluminum oxide, the boron nitride fiber diaphragm of the battery in fig. 2 is compounded with magnesium oxide, and the other preparation conditions are the same.

From the comparison of the discharge performance of the two single batteries in fig. 1 and fig. 2, it is apparent that the resistance of the single battery in fig. 1 is smaller, and the discharge time of the single battery in fig. 1 is longer under the condition of the same cut-off voltage.

That is, by comparing fig. 1 and fig. 2, it can be found that the boron nitride fiber membrane compounded with alumina has a smaller resistance and is superior to the boron nitride fiber membrane compounded with magnesium oxide solution in performance.

In an embodiment of the invention, in the fourth step, the precursor solution and the boron nitride fiber paper can be compounded by adopting a dipping method, that is, the boron nitride fiber paper is dipped into the precursor solution for 0.5-25 h, then taken out and dried, and can be dried in an oven at 50-80 ℃.

In a better method, in order to improve the dipping efficiency, the vacuum dipping method can be adopted for dipping in advance, namely, the dipping is carried out for 0.5 to 1 hour under the vacuum condition of-0.07 to-0.1 MPa, and then the normal pressure dipping is carried out.

In a preferred embodiment of the present invention, the heat treatment temperature is 500-650 ℃, the heat treatment equipment can be a muffle furnace, and the heat treatment time can be 30 min-1 h.

The heat treatment temperature after the boron nitride fiber paper and the precursor solution are compounded has great influence on the performance of the boron nitride fiber diaphragm, when the heat treatment temperature is too low, the boron nitride fiber diaphragm is easy to generate carbon residue, when the boron nitride fiber diaphragm with carbon residue is assembled on a battery, short circuit is easily caused, and the safety is poor; when the temperature of the heat treatment is too high, the mechanical properties of the boron nitride fiber membrane are attenuated.

Fig. 3 is an idle curve of a battery cell according to the present invention, and fig. 4 is a normal discharge curve of a battery cell according to the present invention.

The method for manufacturing the single battery in fig. 3 is the same as that in fig. 4 except that the heat treatment temperature is different.

The heat treatment temperature of the single cell in fig. 3 is 450 ℃, and as can be seen from fig. 3, the single cell assembled by the boron nitride fiber diaphragm prepared at the temperature has a short circuit phenomenon in no load, which is mainly due to the low heat treatment temperature and carbon residue generated after organic matter is cracked.

The heat treatment temperature of the single cell in fig. 4 is 500 ℃, and as can be seen from fig. 4, the single cell assembled by the boron nitride fiber diaphragm prepared at the temperature can normally discharge at a constant current. It was found that the residual carbon in the boron nitride fiber membrane was substantially zero at this temperature.

The experiment proves that when the heat treatment temperature of the boron nitride fiber diaphragm is lower than 500 ℃, the prepared boron nitride fiber diaphragm has poor discharge effect and poor safety, when the heat treatment temperature is 500-650 ℃, the prepared boron nitride fiber diaphragm can achieve excellent discharge effect, the safety is high, the carbon deposition phenomenon of the boron nitride fiber diaphragm can be improved through the selection of the heat treatment temperature, and the safety performance of the battery is improved.

The invention also discloses a boron nitride fiber diaphragm which is prepared by any preparation method; the invention also discloses a lithium thermal battery which comprises the boron nitride fiber diaphragm prepared by any preparation method.

In conclusion, the boron nitride fiber diaphragm prepared by the invention has the advantages of high mechanical strength, good corrosion resistance, excellent liquid absorption and retention performance, small resistance, good conductive effect and high safety, can be used in a lithium thermal battery, and overcomes the defect that the common fiber paper diaphragm cannot be suitable for a molten lithium environment. The boron nitride fiber paper and the diaphragm prepared by the invention can also be popularized and applied to the fields of heat filtering materials, insulating heat conduction materials, fiber reinforced ceramic matrix composite materials, fiber paper reinforcing materials and the like.

The above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art may still modify the technical solutions described in the foregoing embodiments, or may equally substitute some or all of the technical features; such modifications and substitutions do not depart from the spirit and scope of the present invention, and they should be construed as being included in the following claims and description.

Claims

1. A preparation method of a boron nitride fiber diaphragm is characterized by comprising the following steps: comprises the following steps of (a) carrying out,

compounding the boron nitride fiber paper with a precursor solution;

2. The method of claim 1, wherein:

3. The method of claim 2, wherein: the preparation method of the precursor solution comprises the following steps: stirring 30-80 parts by mass of water, 30-80 parts by mass of a small molecular organic solvent and 30-80 parts by mass of an aluminum salt or a magnesium salt to form a uniform and transparent solution.

4. The method of claim 1, wherein: the compounding method comprises the following steps:

5. The method of claim 4, wherein: the specific method for impregnation comprises the following steps: dipping for 0.5-1 h under the vacuum condition of-0.07 to-0.1 MPa, and then dipping at normal pressure.

6. The method of claim 1, wherein: the temperature of the heat treatment is 500-650 ℃.

7. The method of claim 1, wherein: and before the uniformly mixing step, 5-20 parts by mass of alumina fibers and/or silicon nitride fibers are added.

8. The method of claim 1, wherein: the papermaking process comprises the following specific steps:

9. A boron nitride fiber membrane characterized by: the preparation method of any one of claims 1 to 8.

10. A lithium-based thermal battery characterized in that: the preparation method comprises the step of preparing the boron nitride fiber membrane by the preparation method of any one of claims 1 to 8.