CN113699685A - Two-stage phase transition energy storage membrane, superposed membrane and preparation method thereof - Google Patents

Abstract

The invention provides a two-stage phase transition energy storage membrane, an overlying membrane and a preparation method thereof, wherein the two-stage phase transition energy storage membrane is a reticular membrane formed by coaxial fibers, the coaxial fibers consist of a shell layer and a core layer, the core layer is polyethylene oxide, the shell layer is levorotatory polylactic acid, and the two-stage phase transition energy storage membrane is prepared by adopting a coaxial electrostatic spinning method; the phase transition energy storage superposed membrane comprises a polyethylene oxide fiber membrane, wherein the two-stage phase transition energy storage membranes are arranged on two sides of the polyethylene oxide fiber membrane. The degradable two-stage phase change energy storage film is prepared by using the melting point of polyoxyethylene and the glass transition of the levorotatory polylactic acid material, so that the energy storage efficiency of the phase change material is improved.

Description

Two-stage phase transition energy storage membrane, superposed membrane and preparation method thereof

Technical Field

The invention relates to the technical field of phase transition energy storage membranes, in particular to a two-stage phase transition energy storage membrane, a superposed membrane and a preparation method thereof.

Background

At present, energy crisis and environmental pollution are two most serious problems faced in the industrialization process, the development of clean energy and the improvement of the energy utilization rate are effective ways for solving the problems, and the development and preparation of a simple and efficient energy storage method for improving the energy utilization rate is a good choice. The solid-liquid phase change energy storage material is an important thermal energy storage material, and has the advantages of large heat storage density, small volume of a heat storage container, high thermal efficiency, constant heat absorption and release temperature and the like, so that the solid-liquid phase change energy storage material can be used for controlling the temperature of a system or the environment. The repeated cycles of the phase change material remelting and cooling process, however, experience repeated changes in phase state and inevitably leak into the surrounding environment, which leaks shorten their lifetime. At present, in order to prevent the phase change material from leaking, capsules, porous materials, polymer materials, or the like are often used as supports to wrap the phase change material in small spaces one by one, so as to ensure that a certain shape is maintained during phase change. The coaxial electrostatic spinning is a novel technology for preparing the composite nano-fiber, has simple process flow and easily adjustable process parameters, and the prepared polymer fiber is concerned about due to light weight, small diameter, continuity, larger specific surface area, unique network structure and rich gaps, and has potential application in the field of micro-packaging.

At present, a core-shell structure is prepared by a coaxial electrostatic spinning method in many documents to coat a phase change material to prevent the leakage of the phase change material, but the problems of low coating rate, unstable energy storage content and the like exist in part of the core-shell structure, and the problems of low energy storage rate, poor thermal buffering performance and the like exist in part of the core-shell structure because a fiber membrane is generally in single-stage phase transition.

In the literature (Aziz Babapoor et al, Coaxial electro-spun PEG/PA6 composite fibers: Fabrication and chromatography, Applied Thermal Engineering 118(2017) 398) the problems of single-stage phase transition, insufficient Thermal buffer performance and the like caused by the adoption of PEG as a core layer material and PA6 as a shell layer material and adoption of electrostatic spinning for preparing Coaxial fibers.

In the literature (Sun Shaoxing, etc., low-temperature phase change fibers prepared by coaxial electrostatic spinning and performance research thereof, novel chemical materials, 2016 (8) th month, 44 th volume, 8 th period), polyvinyl butyral is selected as a fiber shell material, a phase change material n-pentadecane is selected as a core material, the low-temperature phase change fibers are successfully prepared by the coaxial electrostatic spinning method, and the problems of low encapsulation efficiency or low phase change material ratio and the like are caused by adopting unipolar phase change.

Disclosure of Invention

The invention provides a two-stage phase-change energy storage membrane, a superposed membrane and a preparation method thereof, wherein the two-stage phase-change degradable energy storage membrane is prepared by utilizing a polyethylene oxide (PEO) melting process and the glass transition of a levorotatory polylactic acid (PLLA) material, and the energy storage efficiency of the phase-change material is improved.

The technical scheme of the invention is realized as follows: the two-stage phase transition energy storage membrane is a reticular membrane formed by coaxial fibers, the coaxial fibers consist of a core layer and a shell layer, the core layer is polyethylene oxide (PEO), and the shell layer is levorotatory polylactic acid (PLLA).

Furthermore, in the two-stage phase transition energy storage membrane, the content of polyoxyethylene is a, and a is more than 0 and less than or equal to 49 weight percent.

Furthermore, in the two-stage phase transition energy storage membrane, the content of polyoxyethylene is a, and a is more than or equal to 39 weight percent and less than or equal to 49 weight percent.

The phase transition energy storage superposed membrane comprises a polyethylene oxide fiber membrane, wherein the two-stage phase transition energy storage membranes are arranged on two sides of the polyethylene oxide fiber membrane.

A preparation method of a two-stage phase transition energy storage membrane comprises the following steps: the polyethylene oxide solution is used as an internal phase solution, the levorotatory polylactic acid solution is used as an external phase solution, a coaxial fiber membrane is prepared through coaxial electrostatic spinning, and the coaxial fiber membrane is a two-stage phase transformation energy storage membrane.

Furthermore, the external voltage of the coaxial electrostatic spinning is 18-20KV, the receiving distance is 20cm, the pushing speed of the external phase solution is 1ml/h, and the pushing speed of the internal phase solution is 0.55-0.8 ml/h.

Further, the method for preparing polyethylene oxide is as follows: dissolving polyoxyethylene into a mixed solution of dichloromethane and N, N-dimethylformamide, and stirring to form a homogeneous solution; the mass concentration of the polyoxyethylene solution is 8-12%, and the volume ratio of dichloromethane to N, N-dimethylformamide is 9-6: 1-4.

Further, the preparation method of the levorotatory polylactic acid solution comprises the following steps: dissolving levorotatory polylactic acid in a mixed solution of dichloromethane and N, N-dimethylformamide, and stirring to form a homogeneous solution; the mass concentration of the levorotatory polylactic acid solution is 6-10%, and the volume ratio of dichloromethane to N, N-dimethylformamide is 9-6: 1-4.

A preparation method of a phase-transition energy storage superposed film comprises the following steps: (1) firstly, preparing a two-stage phase transition energy storage film;

(2) superposing a polyethylene oxide fiber membrane on the upper side of the two-stage phase transition energy storage membrane in the step (1) through electrostatic spinning;

(3) and (3) repeating the step (1), and superposing a two-stage phase transformation energy storage membrane on the upper side of the polyethylene oxide fiber membrane.

The invention has the beneficial effects that:

the coaxial fiber prepared by coaxial electrostatic spinning takes PLLA as a shell and PEO as a core, and the PLLA has good encapsulation effect on the phase-change material; the phase-change energy storage membrane prepared by the invention is a two-stage phase-change energy storage membrane, has good thermal property and good thermal buffering property, and reduces the pollution to the environment by utilizing degradable materials PLLA and PEO; two-stage phase change is adopted, the glass transition temperature of PLLA and the low-temperature melting point of PEO further increase the energy storage content of the fiber membrane; the phase-change energy storage superposed membrane is composed of a two-stage phase-change energy storage membrane, a PEO fiber membrane and a two-stage phase-change energy storage membrane, the phase-change material PEO is packaged through the net structure of the coaxial fiber membranes on the two sides and the PLLA shell, leakage of the phase-change material PEO is reduced, and the phase-change material PEO has good thermal buffering performance and energy storage effect.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a schematic view of coaxial electrospinning according to the present invention;

FIG. 2 is a TEM image of different fibers;

FIG. 3 is a schematic diagram of a phase-change energy storage superposed film;

FIG. 4 is a DSC temperature rise profile for fiber membranes of different PEO content;

FIG. 5 is a DSC cooling curve for fiber membranes of different PEO content;

FIG. 6 is a DSC curve of a two-stage phase-change energy storage membrane and a phase-change energy storage superposed membrane;

FIG. 7 is a temperature increase curve for a thermal convection experiment for fiber membranes of different PEO contents;

FIG. 8 is a graph of the temperature drop for thermal convection experiments for fiber membranes of different PEO contents;

FIG. 9 is a temperature reduction curve for multiple iterations of fiber membranes of different PEO contents;

fig. 10 is a graph of the temperature drop curve of a thermal convection experiment for different fiber membranes.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.

A two-stage phase transformation energy storage membrane is a reticular membrane formed by coaxial fibers, the coaxial fibers are composed of a core layer and a shell layer, the shell layer is coaxially wrapped on the outer side of the core layer, the core layer is polyethylene oxide (PEO), and the shell layer is levorotatory polylactic acid (PLLA); in the two-stage phase transition energy storage membrane, the content of polyoxyethylene is a, and a is more than 0 and less than or equal to 49 wt%.

A preparation method of a two-stage phase transition energy storage membrane comprises the following steps: the polyethylene oxide solution is used as an internal phase solution, the levorotatory polylactic acid solution is used as an external phase solution, a coaxial fiber membrane is prepared through coaxial electrostatic spinning, and the coaxial fiber membrane is a two-stage phase transformation energy storage membrane. The external voltage of the coaxial electrostatic spinning is 18-20KV, the receiving distance is 20cm, the pushing speed of the external phase solution is 1ml/h, and the pushing speed of the internal phase solution is 0.55-0.8 ml/h. The polyethylene oxide is prepared as follows: dissolving polyoxyethylene into a mixed solution of dichloromethane and N, N-dimethylformamide, and stirring to form a homogeneous solution; the preparation method of the levorotatory polylactic acid solution comprises the following steps: dissolving levorotatory polylactic acid in a mixed solution of dichloromethane and N, N-dimethylformamide, and stirring to form a homogeneous solution; the mass concentration of the levorotatory polylactic acid solution is 6-10%, and the mass concentration of the polyoxyethylene solution is 8-12%; in the mixed solution, the volume ratio of dichloromethane to N, N-dimethylformamide is 9-6: 1-4.

Example 1

A preparation method of a two-stage phase transition energy storage membrane comprises the following steps:

dissolving polyethylene oxide (PEO) with the molecular weight of 10 ten thousand into a mixed solution of dichloromethane and N, N-dimethylformamide, and stirring to form a homogeneous solution to obtain a polyethylene oxide solution; in the polyoxyethylene solution, the content of polyoxyethylene is 12 wt%; ratio of dichloromethane and N, N-dimethylformamide in the mixed solution 7: 3;

dissolving levorotatory polylactic acid (PLLA) into a mixed solution of dichloromethane and N, N-dimethylformamide, and stirring to form a homogeneous solution to obtain a levorotatory polylactic acid solution; in the levorotatory polylactic acid solution, the content of the levorotatory polylactic acid is 10 wt%; in the mixed solution, the ratio of dichloromethane to N, N-dimethylformamide was 6: 4, configuring;

as shown in fig. 1, prepared PLLA and PEO solutions were injected into 10ml syringes, respectively, the PLLA solution was used as an external phase spinning solution, the PEO solution was used as an internal phase solution, an injection pump was connected to pump the solutions into a coaxial spinning needle, an external voltage of 18KV was applied, the distance between the positive coaxial nozzle and the negative electrode tinfoil was 20cm, the temperature was 25 ℃, the humidity was 45%, and the ratio of the external phase solution push speed to the internal phase solution push speed was 1: 0.8, the push speed of the external phase solution is adjusted to be 1ml/h, the push speed of the internal phase solution is adjusted to be 0.8ml/h, and the coaxial fiber membrane is the two-stage phase transformation energy storage membrane, in the embodiment, in the two-stage phase transformation energy storage membrane, the mass of PEO accounts for 49% of the total mass, namely, 49% of PEO/PLLA membrane.

Example 2

A phase transition energy storage superposed membrane comprises a polyethylene oxide fiber membrane, wherein the two-stage phase transition energy storage membrane of the first embodiment is superposed on both sides of the polyethylene oxide fiber membrane, and the preparation method comprises the following steps: (1) preparing a two-stage phase transition energy storage film by the preparation method of example 1;

(2) superposing a polyoxyethylene fiber membrane on the upper side of the two-stage phase transition energy storage membrane in the step (1) through electrostatic spinning, wherein the polyoxyethylene fiber membrane is a reticular membrane formed by superposing polyoxyethylene fibers, the parameters of the electrostatic spinning are the same as those in the step (1), but an external phase solution is not pushed, and the pushing speed of an internal phase solution is 4 ml/h;

(3) and (3) repeating the step (1), and superposing a two-stage phase transition energy storage membrane on the upper side of the polyethylene oxide fiber membrane in the step (2).

Example 3

This embodiment is substantially the same as embodiment 1 except that: the external voltage is 18KV, the distance between the anode coaxial nozzle and the cathode tinfoil is 20cm, the temperature is 25 ℃, the humidity is 45%, and the ratio of the pushing speed of the external phase solution to the pushing speed of the internal phase solution is 1: 0.55, and the same proportion is increased or decreased, the push rate of the external phase solution is adjusted to be 1ml/h, and the push rate of the internal phase solution is adjusted to be 0.55ml/h, in the embodiment, in the two-stage phase transition energy storage membrane, the mass of PEO accounts for 39% of the total mass, namely, 39% of the PEO/PLLA membrane.

Example 4

This embodiment is substantially the same as embodiment 1 except that: in the polyoxyethylene solution, the content of polyoxyethylene is 8 wt%; ratio of dichloromethane and N, N-dimethylformamide in the mixed solution 9: 1; in the solution of the poly-L-lactic acid, the content of the poly-L-lactic acid is 6 wt%; ratio of dichloromethane and N, N-dimethylformamide in the mixed solution 9: 1 is configured.

The external voltage is 20KV, the distance between the anode coaxial nozzle and the cathode tinfoil is 20cm, the temperature is 25 ℃, the humidity is 45%, the pushing speed of the external phase solution is adjusted to be 1ml/h, and the pushing speed of the internal phase solution is adjusted to be 0.7 ml/h.

Example 4

This embodiment is substantially the same as embodiment 1 except that: in the polyoxyethylene solution, the content of polyoxyethylene is 10 wt%; in the mixed solution, the ratio of dichloromethane to N, N-dimethylformamide was 6: 4; in the solution of the poly-L-lactic acid, the content of the poly-L-lactic acid is 8 wt%; ratio of dichloromethane and N, N-dimethylformamide in the mixed solution 7: and 3, configuring.

Comparative example 1

The PLLA fiber membrane is prepared by electrostatic spinning, the voltage is 20KV, the pushing speed is 5ml/h, the distance is 20cm, the temperature is 25 ℃, and the humidity is 45%.

Comparative example 2

The PEO fiber membrane is prepared by electrostatic spinning, the voltage is 18KV, the pushing speed is 4ml/h, the distance is 20cm, the temperature is 25 ℃, and the humidity is 45%.

Collecting a sample by using a copper mesh, observing the core-shell structure of the coaxial fiber by using a Transmission Electron Microscope (TEM), wherein as shown in figure 2, a picture is a pure PLLA fiber which is in a solid column shape, the surface of the PLLA fiber is smooth and flat, and the diameter of the PLLA fiber is about 518 nm; and b, a graph is a PEO/PLLA coaxial fiber, a obvious fiber core-shell structure is shown in the graph, the diameter of a shell layer is about 1950nm, the diameter of a core layer is about 1050nm, the overall diameter of the composite fiber is increased compared with that of a pure PLLA fiber, the thickness of the shell layer is thin, and a PEO phase change material is well encapsulated in the PLLA fiber without obvious leakage. The c picture shows that the PLLA of the shell layer is subjected to similar melting change under the long-time impact of electron beams, thereby revealing PEO fibers in the shell layer, and further proving that PEO and PLLA coexist on the same fiber and the PEO fibers are coated by the PLLA fibers. The invention successfully obtains the fiber with an obvious core-shell structure by a coaxial electrostatic spinning technology, reduces the leakage of the phase-change material in the phase-change process by the good coating of the degradable high-molecular PLLA on the PEO, and is expected to form a good phase-change energy storage film.

In order to analyze the structure evolution in the electrostatic spinning process, Differential Scanning Calorimetry (DSC) is used for researching the thermal behavior of a fiber film, coaxial fibers are placed in an aluminum crucible, the temperature is increased and decreased at a constant speed in a nitrogen atmosphere, the temperature increase curve is recorded from 0 ℃ to 200 ℃ at a speed of 10 ℃/min, the thermal history of a sample is eliminated after the temperature is kept for 5 minutes, the temperature decrease curve is recorded from 5 ℃/min to 0 ℃, and the phase transition point and the transition enthalpy in the phase transition process of the phase-thinned film are measured. Fig. 4 is a DSC temperature increase curve of two-stage phase transition energy storage films with different PEO contents, and fig. 5 is a DSC temperature decrease curve of two-stage phase transition energy storage films with different PEO contents. Table 1 shows the phase transition point and the enthalpy of transition obtained by the peak area in the curve.

TABLE 1 thermal Property data for phase Change fibers

Sample (I)	Phase transition Point/. degree.C	Enthalpy of transformation/(J. g)-1)	Crystallization temperature/. degree.C	Enthalpy of crystallization (J.g)-1)
					PEO fiber membrane	60.98	144.1	48.17	136.1
Superposed film	63.38	83.91	48.64	60.26
					49% PEO/PLLA membranes	60.51	75.41	47.64	46.0
39% PEO/PLLA membranes	60.19	67.05	47.07	35.16
					PLLA fibrous membrane	63.29	5.23	--	--

As can be seen from fig. 4, the pure PLLA fiber film undergoes glass transition at about 63 ℃ and absorbs part of the heat, and the pure PEO fiber film melts at 60.98 ℃ and absorbs a large amount of heat. The 49% PEO/PLLA membrane (49 wt% PEO content in the two-stage phase change energy storage membrane) reached a peak phase change at 60.51 ℃, and the 39% PEO/PLLA membrane (39 wt% PEO content in the two-stage phase change energy storage membrane) reached a peak phase change at 60.19 ℃. As can be seen from table 1, the 49% PEO/PLLA containing membranes had higher phase transition points and enthalpies of transition than the 39% PEO/PLLA containing membranes, and the phase transition point of the 49% PEO/PLLA membranes was closer to that of pure PEO than the 39% PEO/PLLA membranes; it can be concluded that the two-stage phase transition energy storage membrane prepared by the invention can load PEO and absorb heat, and as the content of PEO increases, the fiber membrane can load more PEO and absorb more heat.

The phase-change energy storage superposed membrane is a superposed membrane of a two-stage phase-change energy storage membrane + a PEO fiber membrane + a two-stage phase-change energy storage membrane, FIG. 6 is a DSC curve of the phase-change energy storage superposed membrane, and as shown in FIG. 6, if the two-stage phase-change energy storage membrane is a 49% PEO/PLLA membrane, the phase-change energy storage superposed membrane absorbs 75.41J/g of energy at about 60.51 ℃ and releases 46J/g of energy at about 47.64 ℃. The phase transformation energy storage superposed membrane has a higher phase transformation point reaching about 63 ℃ along with the increase of the content of PEO, and can absorb 83.91J/g of energy, and the crystallization point is about 48.64 ℃ and releases 60.26J/g of energy. Compared with the single two-stage phase-change energy storage membrane, the phase-change energy storage superposed membrane has a higher enthalpy change value, is beneficial to improving the energy storage content of the composite phase-change energy storage membrane, and brings a better energy storage effect. The composite phase change energy storage film prepared by the invention has good heat absorption and release effects, which are consistent with TEM observation results, the fiber is of a core-shell structure and is coated with the phase change material, and the two-stage phase change film acts simultaneously, so that the composite phase change energy storage film has good thermal properties.

The heat storage performance was investigated using a thermal convection experiment. Injecting 10ml of deionized water into a 10ml glass bottle, taking a fiber membrane with equal mass, respectively wrapping the glass bottle with a PLLA fiber membrane and two-stage phase transition energy storage membranes with different contents of PEO, and measuring the temperature rise process of a curve of the water in the glass bottle changing with time under the heating environment of an oven by using a thermocouple; and measuring the temperature reduction process of the water temperature in the bottle along with the change of time under the room temperature environment. Fig. 7 is a temperature rise curve of different fiber membranes, and fig. 8 is a temperature drop curve of different fiber membranes. As can be seen from FIG. 7, the fastest change in water temperature (water curve) was in bottles without fiber film wrapping, and only 975s were needed to reach 65 ℃. 1489s is required for the water temperature in the bottle wrapped by the PLLA fiber membrane to change to 65 ℃, and the PLLA delays the change of the water temperature by isolating air. In contrast, the water temperature in the 39% PEO/PLLA film-wrapped bottle changed to 65 ℃ in 1888s, and the water temperature in the 49% PEO/PLLA film-wrapped bottle changed to 65 ℃ in 2041 s. Therefore, the two-stage phase transition energy storage film prepared by the invention has better thermal buffering effect in the temperature rising process, and can delay the adverse effect caused by the rapid change of the external temperature. As can be seen from FIG. 8, the bottle without the film wrap had the fastest water temperature drop, only cooling to 40 ℃ in 1010s, the bottle with the PLLA film wrap had a slightly slower water temperature drop rate, cooling to 40 ℃ in 1373s, while 39% of the PEO/PLLA film was 1445s and 49% of the PEO/PLLA film was 1499 s. Therefore, the two-stage phase transition energy storage membrane prepared by the invention has a remarkable speed slowing phenomenon probably at about 55 ℃, which is that PEO releases heat when undergoing phase transition and delays the speed of temperature change. Therefore, the two-stage phase-change energy storage film prepared by the invention has good thermal buffering effect and good energy storage effect, and is favorable for enabling the phase-change energy storage film to have good heat storage performance.

In order to test the stability and repeatability of different fiber membranes, the wrapped fiber membranes were subjected to a cycle test, fig. 9 is a thermal convection experiment performed by repeating more than ten times, and water wrapped by the two-stage phase-change energy storage membrane still starts to have an obvious slow rate of decrease at about 55 ℃.

The prepared phase-transition energy storage superposed film is also subjected to a thermal convection experiment, as shown in fig. 10: the water temperature in the bottle without the film package is still the fastest, only 391s is used from 65 ℃ to 50 ℃, 717s are used for cooling by the PLLA fiber film, and 807s and 809s are respectively used for wrapping the 49% PEO/PLLA film and the phase-change energy storage superposed film. The slow cooling rate of PLLA is to reduce the heat loss by using the fiber film to wrap, while the continuous heat release of the phase-change material is used by using the 49% PEO/PLLA film and the phase-change energy storage film to reduce the heat loss. From the curves, we can see that 49% PEO/PLLA films are gradually exothermic, again with a gap from about 56 ℃ to the PLLA cooling rate. However, the phase-change energy storage superposed film is different from the two-stage phase-change energy storage film in enthalpy change value in DSC test, and in the thermal convection curve, the phase-change energy storage superposed film gradually releases heat from about 57 ℃ and releases more heat than the two-stage phase-change energy storage film, so that the phase-change energy storage superposed film also has coaxial thermal buffering performance, and the heat loss rate can be slowed down by the heat release of the phase-change material. Meanwhile, the phase change material can be packaged through the reticular structure of the fiber, and the packaging effect is similar to that of the coaxial phase change material in a certain temperature range.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (9)

1. A two-stage phase transition energy storage membrane, characterized in that: the two-stage phase transition energy storage membrane is a reticular membrane formed by coaxial fibers, the coaxial fibers consist of a core layer and a shell layer, the core layer is polyethylene oxide, and the shell layer is levorotatory polylactic acid.

2. A two-stage phase change energy storage membrane according to claim 1, wherein: in the two-stage phase transition energy storage membrane, the content of polyoxyethylene is a, and a is more than 0 and less than or equal to 49 wt%.

3. A two-stage phase change energy storage membrane according to claim 2, wherein: in the two-stage phase transition energy storage membrane, the content of polyoxyethylene is a, and a is more than or equal to 39 weight percent and less than or equal to 49 weight percent.

4. A phase transition energy storage superposed film is characterized in that: comprising a polyethylene oxide fiber membrane provided on both sides with the two-stage phase change energy storage membrane of claims 1-3.

5. A preparation method of a two-stage phase transition energy storage membrane is characterized by comprising the following steps: the polyethylene oxide solution is used as an internal phase solution, the levorotatory polylactic acid solution is used as an external phase solution, a coaxial fiber membrane is prepared through coaxial electrostatic spinning, and the coaxial fiber membrane is a two-stage phase transformation energy storage membrane.

6. The method for preparing a two-stage phase transition energy storage membrane according to claim 5, wherein the applied voltage of the coaxial electrospinning is 18-20KV, the receiving distance is 20cm, the pushing speed of the external phase solution is 1ml/h, and the pushing speed of the internal phase solution is 0.55-0.8 ml/h.

7. The method for preparing a two-stage phase transition energy storage membrane according to claim 5 or 6, wherein the polyethylene oxide is prepared by the following steps: dissolving polyoxyethylene into a mixed solution of dichloromethane and N, N-dimethylformamide, and stirring to form a homogeneous solution; the mass concentration of the polyoxyethylene solution is 8-12%, and the volume ratio of dichloromethane to N, N-dimethylformamide is 9-6: 1-4.

8. The method for preparing a two-stage phase transition energy storage membrane according to claim 5 or 6, wherein the method for preparing the L-polylactic acid solution comprises the following steps: dissolving levorotatory polylactic acid in a mixed solution of dichloromethane and N, N-dimethylformamide, and stirring to form a homogeneous solution; the mass concentration of the levorotatory polylactic acid solution is 6-10%, and the volume ratio of dichloromethane to N, N-dimethylformamide is 9-6: 1-4.

9. A preparation method of a phase-transition energy storage superposed film comprises the following steps: (1) preparing a two-stage phase transition energy storage film by the preparation method of any one of claims 5 to 8;

(2) superposing a polyethylene oxide fiber membrane on the upper side of the two-stage phase transition energy storage membrane in the step (1) through electrostatic spinning;

(3) and (3) repeating the step (1), and superposing a two-stage phase transformation energy storage membrane on the upper side of the polyethylene oxide fiber membrane.

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