CN113644340A

CN113644340A - Lithium battery with multilayer film heat dissipation structure and heat equalizing method of battery pack of lithium battery

Info

Publication number: CN113644340A
Application number: CN202110926162.8A
Authority: CN
Inventors: 邓业林; 陈梦婷; 沙盈盈; 陈兴际
Original assignee: Suzhou University
Current assignee: Suzhou University
Priority date: 2021-08-12
Filing date: 2021-08-12
Publication date: 2021-11-12
Anticipated expiration: 2041-08-12
Also published as: CN113644340B

Abstract

The invention relates to a lithium battery with a multilayer film heat dissipation structure and a heat soaking method of a battery pack of the lithium battery, wherein the lithium battery is respectively provided with a battery core, HDPE, a phase change material and a heating shell from inside to outside, the HDPE is added between the battery core and the phase change material to form a tightly connected heat conduction layer, so that the heat resistance is reduced to strengthen the heat dissipation of the battery, the safety of the lithium battery is enhanced, the lithium batteries are connected in series to form the battery pack, and the surface temperature of each single lithium battery in the battery pack is balanced by adjusting the thickness proportion of a combination body of the HDPE and the phase change material at different parts in the battery pack, so that the heat soaking of all lithium battery cores in the battery pack is realized. The soaking method can effectively solve the problems of shortened service life and insufficient electricity of the battery pack caused by uneven temperature rise of the battery pack so as to prolong the service life of the battery, and in addition, the method is low in implementation cost, and the lithium battery with the multilayer film heat dissipation structure can be subjected to mechanized mass production, so that the industrialization is favorably realized.

Description

Lithium battery with multilayer film heat dissipation structure and heat equalizing method of battery pack of lithium battery

Technical Field

The invention relates to the technical field of batteries, in particular to a lithium battery with a multilayer film heat dissipation structure and a heat equalizing method of a battery pack of the lithium battery.

Background

In recent years, the development of electric automobile technology and new energy power station energy storage technology is rapid, and the requirements of the technologies on the used batteries are higher and higher. Compared with other batteries, the lithium battery has better application prospect due to the advantages of high conversion efficiency, large energy density, environmental friendliness and the like. However, the characteristics of the lithium battery, such as the service life and the safety, are greatly affected by the temperature. The lithium battery can generate a large amount of heat in the using process, and the heat is accumulated for a long time to cause the internal temperature of the lithium battery to rise, so that the attenuation of the battery capacity is accelerated, and the service life of the battery is shortened. If the temperature continues to rise to a certain degree, even safety accidents such as explosion and the like occur.

The existing phase change material, referred to as PCM for short, is a substance that changes the state of a substance and can provide latent heat under the condition of constant temperature. The process of changing physical properties is called a phase change process, and in this case, the phase change material absorbs or releases a large amount of latent heat. Passive thermal management, which absorbs battery heat by using latent heat of PCM in a phase change process and prevents the battery temperature from rising too fast, has become an important research direction and research hotspot of a battery thermal management system, but at present, the temperature of a lithium battery in a use process is reduced by a single layer of phase change material, and the heat transfer effect is weakened because the single layer of phase change material is not in close contact with the battery, and the accumulated heat causes the temperature of a battery core to increase.

In addition, the lithium battery pack formed by assembling the lithium batteries has the advantages that the temperature rise of the batteries at the middle part is faster than that of the batteries at two sides when the lithium batteries are charged, the temperature difference is increased along with the increase of charging current, the temperature difference can reach more than 10 ℃ in a large-current charging battery, the service life of the whole battery pack can be greatly shortened due to the problem of local overheating, and the soaking treatment of the battery pack is a problem worthy of attention for avoiding the wooden barrel effect. At present, in the design of a soaking system of a battery pack, a certain distance is usually kept between batteries for ventilation or adding a soaking plate, the methods do not carry out cooling design according to the temperature rise characteristics of the batteries in the battery pack, only the whole system is cooled singly and to the same extent, the design can cause resource waste and cost increase, and the part with higher temperature rise can not achieve the expected cooling effect.

Disclosure of Invention

The invention aims to provide a lithium battery with a multilayer film heat dissipation structure and a heat equalizing method of a battery pack of the lithium battery, wherein high-density polyethylene (HDPE) is added between a phase-change material and a battery core to reduce thermal resistance, so that the heat absorption capacity of the phase-change material is enhanced; utilize the battery package that the lithium cell that has above-mentioned heat radiation structure constitutes, according to the uneven problem of battery intensification of each position in the battery package, to wrapping up the phase change material and the HDPE of different thickness on the electric core of different position batteries, guarantee the difference in temperature minimum between the battery when satisfying the heat dissipation requirement, and then the life-span of extension battery package.

In order to solve the technical problems, the invention provides the following technical scheme:

the invention provides a lithium battery with a multilayer film heat dissipation structure, which consists of a battery core, HDPE, a phase change material and a heat conduction shell from inside to outside; the HDPE is tightly attached to the battery core; the phase change material is tightly attached to the HDPE; and the phase change material is wrapped by a heat conduction shell.

Further, the phase-change material is expanded graphite or an expanded graphite/paraffin composite material.

Further, the specific operation of the tight fit of the HDPE and the electric core and the phase-change material is as follows: HDPE is heated, HDPE which becomes soft after being heated is wrapped on the battery core, and the phase change material is rapidly wrapped on HDPE after being tensioned and laid after being cooled.

Further, the heating temperature is 35-100 ℃; the temperature of tensioning and laying is 35-50 ℃ after cooling.

Further, the thickness ratio of the HDPE to the phase change material is 1: 2.5-5.

Further, the HDPE has a thermal conductivity of 0.42-0.5W/(m.K).

Because the problem of large thermal resistance caused by loose contact of a phase change material and a battery exists in the battery utilizing phase change to enhance heat dissipation, the problem of fitting performance is solved by using a heat-conducting glue and a heat-conducting silicone grease at present, but the problem of uneven temperature rise of the battery caused by uneven smearing and bubble generation of the heat-conducting glue in the smearing process is solved, and the problem similar to the heat-conducting glue exists when the cost of the heat-conducting silicone grease is high.

The thermal conductivity coefficient of HDPE is far higher than the thermal conductivity coefficient of air (0.01-0.04W/(m.K)), the cost is far lower than that of heat-conducting glue and heat-conducting silicone grease, and the HDPE can be firmly attached to the phase-change material and the battery cell after being heated and softened without generating bubbles on the contact surface, so that the thermal resistance can be effectively reduced by wrapping the HDPE between the battery cell and the phase-change material, the phase-change material can be further ensured to achieve the cooling effect through phase-change heat absorption, the heat dissipation of the battery is enhanced, the overall temperature rise is reduced, and the safety of the power lithium battery is enhanced.

In a second aspect, the invention provides a battery pack obtained by connecting the lithium batteries of the first aspect in series.

A third aspect of the present invention provides a heat equalizing method for a battery pack according to the second aspect, where the heat equalizing method specifically includes: according to different temperature rises of monocells at different positions in the battery pack, HDPE and phase-change materials with different thicknesses are wrapped on the battery core of each battery, and the temperature difference between the batteries is minimum.

The invention provides the application of the soaking method of the battery pack in the third aspect in the 20V 2Ah battery pack.

Further, the lithium battery pack in the 20V 2Ah battery pack is formed by connecting 5 lithium batteries of 18650 models in series.

Further, in the 20V 2Ah battery pack, five batteries are arranged in a row, the middle three batteries are middle part batteries, and the two batteries at two ends are two side part batteries.

Further, the thickness ratio of the phase change material to the HDPE in the two-side-part cell is controlled to be 4-5: 1.

Further, the thickness ratio of the phase change material to the HDPE in the middle cell is controlled to be 3-4: 1.

Further, the total thickness of the heat-conducting adhesive film and the phase-change material in the battery is 5.5-6.5mm, such as 6 mm.

Compared with the prior art, the invention has the beneficial effects that:

1. the HDPE film is added between the phase-change material and the battery core to reduce the thermal resistance between the phase-change material and the battery core, improve the heat transfer and heat dissipation effects, reduce the overall temperature rise, further improve the safety and prolong the service life of the battery; in addition, the HDPE film is low in price, the coating process can be processed in batches mechanically, the realization cost is low, and the HDPE film is suitable for industrial production.

2. According to the invention, lithium batteries with a multi-layer film heat dissipation structure are connected in series to form a battery pack, and the temperature difference between each battery cell in the battery pack is reduced by adjusting the thickness ratio of phase change materials and HDPE in the batteries at different positions so as to realize uniform heating of the battery pack; the method is different from the non-differential cooling in the prior art, and a specific structure is designed aiming at the problem of unbalanced temperature rise of the batteries at different parts in the battery pack, so that the heat dissipation requirement is met, the minimum temperature difference among the batteries is ensured, the problems of shortened service life and insufficient power of the battery pack caused by uneven temperature rise of the battery pack can be effectively solved, the service life of the battery pack is prolonged, and meanwhile, the waste of unnecessary resources is avoided.

Drawings

Fig. 1 is a schematic diagram of a single cell: 1 is an electric core, 2 is an HDPE layer, 3 is a graphite layer, and 4 is a shell;

fig. 2 is a temperature rise curve of a bare cell, a graphite-coated cell, and a HDPE/graphite-coated cell at 10C discharge rate;

FIG. 3 is a schematic diagram of a lithium battery pack in a 20V 2Ah battery pack;

fig. 4 is a flow chart of a research experiment of the soaking method.

Detailed Description

The present invention is further described below in conjunction with the following figures and specific examples so that those skilled in the art may better understand the present invention and practice it, but the examples are not intended to limit the present invention.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

The experimental methods used in the following examples are conventional methods unless otherwise specified, and materials, reagents and the like used therein are commercially available without otherwise specified.

Example 1: performance comparison of single cell, single cell wrapped with phase change material only, and single cell wrapped with phase change material and HDPE

Sample 1: a single cell;

sample 2: 6mm of expanded graphite is wrapped outside the single electric core;

sample 3: 1.2mm of HDPE and 4.8mm of expanded graphite wrap the single electric core;

the single cells in samples 1-3 are the same, the single cell is sample 1, the single cell + graphite is sample 2, the single cell + HDPE/graphite (1:4) is sample 3, and the structure of sample 3 is shown in fig. 1: 1 is an electric core, 2 is an HDPE layer, 3 is a graphite layer, and 4 is a shell; the temperature rise conditions of the samples 1-3 under the discharge rate of 10C are studied, as shown in FIG. 2, wherein the temperature rise of the sample 1 is fastest in the whole process, the temperature increase of the sample 2 is smallest before 150s, the temperatures of the sample 2 and the sample 3 are consistent when the temperature of the sample 2 is about 150s, the temperature rising trend of the sample 3 is gradually reduced after 150s along with the time extension, the temperature rise rate of the sample 2 is almost unchanged, and the temperature difference between the sample 2 and the sample 3 is increased along with the time extension. From the above results, it can be seen that sample 3, which is wrapped with HDPE and expanded graphite at the same time outside the cell, has a better cooling effect for a lithium battery requiring a relatively long working time (greater than 150 seconds).

Example 2: performance comparison of a single cell, phase change material wrapped in different thickness ratios and a single cell of HDPE

Sample 1: a single cell;

sample 2: 1.5mm of HDPE and 4.5mm of expanded graphite wrap the single electric core;

sample 4: 1mm of HDPE and 5mm of expanded graphite wrap the single cell;

the single cores in the samples 1-4 are the same, the temperature rise of the samples 1-4 under the discharge rate of 5C is studied, the temperature change of each sample is shown in the following table 1 between 710s and 720s, and the results in the table show that the temperature of each sample rises along with the prolonging of the discharge time, wherein the temperature of the sample 1 reaches 38.7 ℃ at 710s, the temperature of the sample 2 wrapping HDPE and the thickness ratio of the phase-change material is 1:3, the temperature at 710s is only about 30.87 ℃ and is about 8 ℃ different from that of the sample 1;

samples

3 and 4 had slightly higher temperatures than sample 2 throughout the process, but much lower temperatures than the surface of sample 1 in the single cell.

TABLE 1 temperature Change between 710s and 720s for each sample

Time(s)	Sample 1 (. degree. C.)	Sample 2 (. degree. C.)	Sample 3 (. degree. C.)	Sample 4 (. degree. C.)
					710	38.74	30.87	31.34	32.31
711	38.75	30.87	31.35	32.32
					712	38.76	30.88	31.36	32.33
713	38.77	30.89	31.36	32.33
					714	38.79	30.90	31.37	32.34
715	38.80	30.91	31.38	32.35
					716	38.81	30.92	31.39	32.36
717	38.82	30.92	31.40	32.37
					718	38.83	30.93	31.41	32.38
719	38.84	30.94	31.41	32.38
					720	38.85	30.95	31.42	32.39

Example 3: A20V 2Ah battery pack (HDPE: graphite at two sides 1:4 and HDPE: graphite at the middle 1:3)

Connect five lithium batteries of 18650 models in series and constitute the lithium cell group in the 20V 2Ah battery package, wherein single lithium battery nominal voltage is 3.7V, and the single lithium battery of the full charge state of reality can reach 4V, places five lithium batteries side by side, as shown in FIG. 3: the cells at

positions

1 and 5 in the figure are two-side cells, the cells at positions 2-4 in the figure are middle cells, and the preparation of the two-side cells and the middle cells is as follows:

two side position batteries: and (3) wrapping 1.2mm of HDPE and 4.8mm of expanded graphite outside the single electric core, and wrapping a heat-conducting shell to obtain the batteries placed at the two side parts.

Battery in the middle: and (3) wrapping 1.5mm of HDPE and 4.5mm of expanded graphite outside the single electric core, and wrapping a heat-conducting shell to obtain the batteries placed at the two side parts.

The temperature rise of the battery pack at the 5C discharge rate of 710-720 s is studied, the temperature change of the batteries at different positions in the battery pack is shown in the following table 2, the temperature difference between the battery 3 and the

batteries

1 and 5 in the battery pack is about 4 ℃, the average temperature of the battery pack is about 35 ℃, and the temperature difference between the batteries at different positions and the average temperature is less than 3 ℃.

Table 2 example 3 temperature change between 710s and 720s for batteries at different locations in a battery pack

Example 4: A20V 2Ah battery pack (HDPE: graphite at two sides 1:5, HDPE: graphite at the middle 1:4)

Five 18650 models of lithium batteries are connected in series to form a lithium battery pack in a 20V 2Ah battery pack, wherein the nominal voltage of a single lithium battery is 3.7V, the single lithium battery in a full charge state can reach 4V, the arrangement mode of the five lithium batteries is the same as that of embodiment 3, and the batteries at two sides and the battery at the middle part are prepared as follows:

two side position batteries: and (3) wrapping 1mm of HDPE and 5mm of expanded graphite outside the single electric core, and then wrapping the heat-conducting shell to obtain the batteries placed at the two side parts.

Battery in the middle: and (3) wrapping 1.2mm of HDPE and 4.8mm of expanded graphite outside the single electric core, and wrapping a heat-conducting shell to obtain the batteries placed at the two side parts.

The temperature of the battery pack at 5C discharge rate was measured to be 710-720 s, and the temperature change of the batteries at different positions in the battery pack is shown in table 3 below, where the temperature difference between the battery 3 and the battery 1 in the battery pack is the largest, but only about 1 ℃, and at 720s, the average temperature of the battery pack is about 37.67 ℃, and the temperature difference between the batteries at different positions in the battery pack and the average temperature is less than 1 ℃.

Table 3 example 4 temperature change between 710s and 720s for batteries in different locations in a battery pack

Comparative example: 20V 2Ah battery pack (bare cell for both sides and middle)

Five 18650 models of lithium batteries are connected in series to form a lithium battery pack in a 20V 2Ah battery pack, wherein the nominal voltage of a single lithium battery is 3.7V, the single lithium battery in an actual fully charged state can reach 4V, the arrangement mode of the five lithium batteries is the same as that of embodiment 3, and the batteries on two sides and in the middle are bare cells.

The temperature rise of the battery pack at the 5C discharge rate within 710-720 s is studied, the temperature change of the batteries at different positions in the battery pack is shown in the following table 4, the temperature of the battery in the middle of the battery pack is highest and is gradually decreased from inside to outside, the temperature of the battery at the position 3 is up to 68.77 ℃ at 710s, and the temperature difference of the battery at the same position in the battery pack of the

embodiments

3 and 4 exceeds 20 ℃; the temperature of the batteries at the two sides in the battery pack is relatively low, the temperature difference between the batteries at the two sides and the middle battery is more than 9 ℃, and the temperature difference is far higher than that between the batteries in the battery packs of the

embodiments

3 and 4.

Table 4 temperature change between 710s and 720s for cells at different locations in a comparative example package

To sum up, can improve heat transfer, radiating effect through increasing the HDPE membrane between phase change material and electric core, reduce whole temperature rise, establish ties into the battery package with this kind of lithium cell that possesses multilayer film heat radiation structure, adjusts the thickness ratio of phase change material and HDPE in the battery of different positions, can reduce the temperature difference between each electric core in the battery package, realizes the soaking effect of battery package.

The above-mentioned embodiments are merely preferred embodiments for fully illustrating the present invention, and the scope of the present invention is not limited thereto. The equivalent substitution or change made by the technical personnel in the technical field on the basis of the invention is all within the protection scope of the invention. The protection scope of the invention is subject to the claims.

Claims

1. A lithium battery with a multi-layer film heat dissipation structure is characterized in that the lithium battery consists of a battery cell, HDPE, a phase change material and a heat conduction shell from inside to outside; the HDPE is tightly attached to the battery core; the phase change material is tightly attached to the HDPE; and the phase change material is wrapped by a heat conduction shell.

2. The lithium battery with the multilayer film heat dissipation structure as recited in claim 1, wherein the phase change material is expanded graphite or an expanded graphite/paraffin composite material.

3. The lithium battery with the multilayer film heat dissipation structure of claim 1, wherein the HDPE, the battery core and the phase change material are tightly attached by the following specific operations: HDPE is heated, HDPE which becomes soft after being heated is wrapped on the battery core, and the phase change material is rapidly wrapped on HDPE after being tensioned and laid after being cooled.

4. The lithium battery with the multilayer film heat dissipation structure as recited in claim 3, wherein the heating temperature is 35-100 ℃; the temperature of tensioning and laying is 35-50 ℃ after cooling.

5. The lithium battery with the multilayer film heat dissipation structure as recited in claim 1, wherein the thickness ratio of the HDPE to the phase change material is 1: 2.5-5.

6. A battery pack obtained by connecting the lithium batteries according to any one of claims 1 to 5 in series.

7. The heat equalizing method for a battery pack according to claim 6, wherein the heat equalizing method is specifically: according to different temperature rises of monocells at different positions in the battery pack, HDPE and phase-change materials with different thicknesses are wrapped on the battery core of each battery, and the temperature difference between the batteries is minimum.

8. The application of the soaking method of the battery pack in the 20V 2Ah battery pack according to claim 7, wherein the lithium battery pack in the 20V 2Ah battery pack is formed by connecting 5 lithium batteries of 18650 models in series.

9. The use according to claim 8, characterized in that in a 20V 2Ah battery pack, five batteries are arranged in a row, the middle three batteries are middle part batteries, and the two batteries at two ends are two side part batteries; the thickness ratio of the phase-change material to the HDPE in the two side cells is controlled to be 4-5:1, and the thickness ratio of the phase-change material to the HDPE in the middle cell is controlled to be 3-4: 1.

10. Use according to claim 8, wherein the HDPE and the phase change material in the cell have a total thickness of 5.5-6.5 mm.