Battery pack and power tool

Abstract

The application provides a battery pack and an electric tool, the battery pack comprising: a shell; an electric core assembly arranged in the shell, the electric core assembly comprising a plurality of electric core units; a heat-absorbing body made of a composite phase change material, the heat-absorbing body being in thermal contact with at least one of the electric core units to absorb heat generated by the electric core assembly during charging and discharging of the battery pack; and the composite phase change material comprising at least a main phase change material and phase change microcapsules. The above technical scheme can provide a battery pack with compact structure, effective temperature rise inhibition and stable performance at high temperature.

Description

TECHNICAL FIELD

[0001] The present application relates to a battery pack for powering electric tools, in particular a battery pack comprising a phase change material. BACKGROUND

[0002] Electric hand tools using rechargeable batteries are widely used in factories, farms, lawns and households, and since these electric tools use multiple battery cell units, multiple battery cell units are usually packaged into a battery pack. Due to the existence of the internal resistance of the rechargeable battery, heat will be generated during charging and discharging, and these rechargeable batteries are tightly packaged in the shell of the battery pack, making it difficult to dissipate heat. When the heat accumulates to a certain extent, it will affect the efficiency and service life of the battery pack, and even cause serious safety problems such as explosion. Especially when discharging at a large current, if the heat is not dissipated in time and effectively, it will rise to an extremely high temperature in a short time, thereby affecting the performance of the battery pack. At present, the conventional heat dissipation method for the battery pack is to use gas convection or heat dissipation fins, but it is necessary to set up additional convection air ducts, fans and heat dissipation fins in the battery pack, which will increase the volume of the battery pack and the structure is relatively complex.

[0003] At present, phase change materials are used to manage the heat of the battery pack. Phase change materials use the property of absorbing a large amount of heat when the substance undergoes a phase change to store heat, and have the advantages of high heat storage density, small volume and high thermal efficiency. However, the phase change materials currently used for heat management of the battery pack on the market all have the property of dissolving in water, and are prone to liquid leakage and material loss during the phase change process and in a humid environment, which will affect the user's use and the reliability of the battery pack. SUMMARY

[0004] To solve the problems of the prior art, the present application provides a battery pack and an electric tool, which has a compact structure, effectively suppresses temperature rise and has stable performance at high temperature.

[0005] To achieve the above-mentioned objectives, the present application adopts the following technical solutions:

[0006] A battery pack is provided for powering electric tools, the battery pack comprising: a shell; an electric cell assembly arranged in the shell, the electric cell assembly comprising a plurality of battery cell units; a heat absorber made of a composite phase change material, the heat absorber being in thermal contact with at least one of the battery cell units to absorb heat generated by the electric cell assembly during charging and discharging of the battery pack; the composite phase change material comprising at least a main phase change material and phase change microcapsules.

[0007] Further, in the composite phase change material, the mass ratio of the main phase change material to the phase change microcapsules is greater than or equal to 2.5 and less than or equal to 5.5.

[0008] Further, the phase change microcapsules account for 15% to 25% of the mass of the composite phase change material.

[0009] Further, the phase change microcapsules are uniformly distributed in the bulk phase change material.

[0010] Further, the phase change microcapsules have an average particle size greater than or equal to 5 microns and less than or equal to 20 microns.

[0011] Further, the bulk phase change material includes polyethylene glycol, silica sol and water; and the composite phase change material further includes glass fiber and graphite.

[0012] Further, the glass fiber accounts for 1% to 5% of the mass of the composite phase change material.

[0013] Further, the phase change microcapsules include n-alkane phase change material arranged in a capsule shell, and the capsule shell is made of polyimide resin.

[0014] Further, the composite phase change material is filled at least in the gap between the plurality of battery cell units. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a structural schematic diagram of a specific embodiment of the present application;

[0016] Figure 2 is an exploded view of the structure of the battery pack as a first embodiment;

[0017] Figure 3 is Figure 2 a structural diagram of the heat sink of the battery pack in

[0018] Figure 4 is a partial structural diagram of the battery pack as a second embodiment;

[0019] Figure 5 is Figure 4 a position diagram of the heat sink in

[0020] Figure 6 is a schematic diagram of the heat sink and the battery cell unit of the battery pack as a third embodiment;

[0021] Figure 7 is a distribution diagram of the bulk phase change material and the phase change microcapsules in the composite phase change material. DETAILED DESCRIPTION

[0022] The present application will be specifically described below in combination with the drawings and specific embodiments.

[0023] The battery pack in the present application can be applied to electric drills, electric wrenches, electric screwdrivers, electric hammer drills, electric circular saws, sanders, and other hand-held power tool machines, as well as electric lawn mowers, grass trimmers, electric scissors, brush cutters, electric saws, and other garden tools. For the convenience of description, the hand-held power tool machines and garden tools will be collectively referred to as electric tools in the following. The battery pack can be detachably connected to the above-mentioned electric tools or fixedly arranged in the above-mentioned electric tools. Obviously, the battery pack of the present application is not limited to the above-mentioned electric tools, nor is it limited to the specified nominal voltage. In fact, the teachings of the present application can be applied to any type of cordless electric tool powered by a battery, any shape of battery pack, and any rated nominal voltage.

[0024] The battery pack in the present application is a rechargeable lithium chemical battery, such as a lithium-ion battery, especially a cylindrical lithium-ion battery and a soft-pack battery commonly used in electric tool applications. In some embodiments, the battery pack can include at least one rechargeable cell unit, or a plurality of rechargeable cell units, depending on the different rated nominal values of the battery pack. These battery packs with different nominal values can be achieved by connecting a plurality of rechargeable cell units in series. Of course, the rechargeable cell unit can also be configured as other lithium-based lithium chemical batteries, or rechargeable batteries with other chemical bases such as nickel-cadmium and nickel-hydrogen.

[0025] The battery pack in the present application can be, but is not limited to, square, cylindrical, tower-shaped, or other shapes. In general, the battery pack includes a housing, at least one cell unit, electronic devices for performing internal and external control and protection measures, battery pack terminals connected to an external charger or an electric tool, a cell unit connection mechanism, and a phase change material arranged adjacent to the cell unit. Obviously, the above-mentioned housing of the battery pack, at least one cell unit, electronic devices for performing internal and external control and protection measures, battery pack terminals connected to an external charger or an electric tool, and the cell unit connection mechanism are configured as a general configuration, so they will not be described again in this specification and the drawings. The internal heat dissipation structure of the battery pack in the present application and the configuration of the phase change material for dissipating heat from the cell unit will be described in detail below with reference to the drawings. This configuration can solve the heat dissipation problem of the battery pack during charging and discharging, especially during discharging for providing power to the electric tool, and the problem of easy leakage of the phase change material in a humid environment, as well as the distribution of the cell unit in the battery pack and the compactness of the battery pack

[0026] Referring to Figures 1 to 3The battery pack 100 shown as an embodiment includes a housing 10 formed by assembling an upper housing 11 and a lower housing 12, a cell assembly 20 disposed in the housing 10, and a plurality of cell units 21 arranged compactly with each other to form the cell assembly 20. The battery pack 100 further includes a first support 13 and a second support 14 distributed at both ends of the cell units 21 and the cell assembly 20 formed by the cell units 21, and arranged in a plane perpendicular to the longitudinal direction of the cell units 21 to support the cell units 21 and the cell assembly 20 formed by the cell units 21, and fixed by mechanical means such as screws, buckles, etc. to form a compact structure of the cell assembly 20. The battery pack 100 further includes a heat sink 30 in thermal contact with at least one of the cell units 21 to absorb heat generated by the cell assembly 20 during charging and discharging of the battery pack 100. It should be noted that the heat sink 30 is in thermal contact with at least one of the cell units 21, which can be understood as the heat sink 30 being in contact with the surface of the cell unit 21 to achieve heat conduction. Of course, it can also be understood that the heat sink 30 is not in direct contact with the surface of the cell unit 21 to achieve indirect heat conduction.

[0027] The plurality of cell units 21 are arranged compactly with each other to form a cell assembly 20. Gaps 22 are formed between adjacent cell units 21 and between the cell units 21 and the first support 13 and the second support 14, and the heat sink 30 is partially filled in the gaps 22. The first support 13 and the second support 14 can be made of a heat-conducting material such as aluminum, silicon carbide, etc. The first support 13 and the second support 14 are fixed by mechanical means such as screws to encapsulate the cell assembly 20 and the heat sink 30. The first support 13 and the second support 14 are in full contact with the heat sink 30, which can well conduct the heat generated by the cell assembly 20 to achieve good heat dissipation effect.

[0028] Referring to Figure 4 The battery pack shown as another embodiment includes cell units 21a arranged compactly to form a cell assembly 20a. Unlike the above embodiment, the cell units 21a in the cell assembly 20a are arranged differently. The heat sink 30a is configured as a ring structure that fits the outer contour of each cell unit 21a and is fitted on the maximum heat dissipation area of the cell unit 21a. In some embodiments, the maximum heat dissipation area is defined as the area extending from the middle position A of the outer surface of the cell unit 21a to the positive electrode end portion. As shown in the figure, the heat sink 30a is in contact with the maximum heat dissipation area of the cell unit 21a, which can well conduct the heat generated by the cell unit 21a to achieve good heat dissipation effect. Figure 5As shown, the length of the battery cell unit 21a is about 65mm, and the diameter is about 18mm. The region of the battery cell unit 21a where the temperature rises fastest during charging and discharging is the region in the middle of the outer surface of the battery cell unit 21a and 5mm toward the positive electrode end. The region defined by extending 5mm from the middle position A (about 32.5mm) of the longitudinal direction of the battery cell unit 21a to the positive electrode end to the position B (about 37.5mm) is the region where the temperature of the battery cell unit 21a rises most easily and fastest to the limit protection temperature, and thus, in some embodiments, this region is preferably the largest heat dissipation region of the battery cell unit 21a, and the heat sink 30a is sleeved on this region. In order to achieve a more ideal heat dissipation effect, in some embodiments, the heat sink 30a can also be sleeved on the region defined by extending a greater distance from the middle position A (about 32.5mm) of the longitudinal direction of the battery cell unit 21a to the positive electrode end to the position C (about 43.3mm) which is two-thirds of the longitudinal length of the battery cell unit 21a, or the region defined by extending a greater distance from the middle position A (about 32.5mm) of the longitudinal direction of the battery cell unit 21a to the positive electrode end to the position D (about 48.75mm) which is three-thirds of the longitudinal length of the battery cell unit 21a, and these positions are preferably the largest heat dissipation region of the battery cell unit 21a. In this embodiment, the heat sink 30a is configured as a circular ring, and the specific size can be adjusted according to the size and arrangement of the battery cell unit 21a, and is sleeved on the battery cell unit 21a by tooling or other means.

[0029] Referring to Figure 6 As another embodiment of the battery pack shown, the battery pack includes a plurality of battery cell units 21b constituting a battery cell assembly 20b. Unlike the above-mentioned embodiments, the battery cell unit 21b is flat, and a plurality of battery cell units 21b are stacked and arranged. Preferably, the heat sink 30b is arranged between the connected battery cell units 21b. Of course, the positional relationship between the heat sink 30b and the battery cell unit 21b should be arranged according to the actual internal structure of the battery pack, and thus it can be understood that the positional relationship between the heat sink 30b and the battery cell unit 21b or the battery cell assembly 20b cannot be regarded as a limitation of the present application.

[0030] The heat-absorbing body in the above embodiments is made of a phase change material. It has small corrosion, is non-toxic, and has stable phase change form. In particular, a phase change material with polyethylene glycol as a carrier and silica gel solution as a nano support structure has a phase change enthalpy of 150 to 350 J / g. The phase change material can absorb heat through a phase change reaction. When the phase change material absorbs heat, a phase change reaction occurs. The phase change material with polyethylene glycol as a carrier has the property of dissolving in water, which is easy to cause material leakage and material loss in a humid environment, which will affect the use of users and the reliability of the battery pack. To prevent the phase change material from leaking after phase change or in a humid environment, an encapsulation layer is usually installed on the covered area of the phase change material. The encapsulation layer can be a sealing covered area or a sealing entire unit cell outer cylindrical profile. The encapsulation layer is an insulating material, such as a heat-sealed tube, and is preferably an encapsulation layer that is the same as the encapsulation material of the battery cell body.

[0031] A composite phase change material is preferably used in the present application. Specifically, the composite phase change material includes at least a main phase change material and phase change microcapsules. In some embodiments, the main phase change material includes polyethylene glycol, silica sol, and water. The polyethylene glycol is used as a carrier, and the silica sol and water are added as nano support structures to form the main phase change material. Specifically, in the present embodiment, the polyethylene glycol accounts for 70.4% of the mass of the main phase change material, the silica sol accounts for 21.6% of the mass of the main phase change material, and the remaining is water, accounting for 8% of the mass of the main phase change material.

[0032] The capsule shell of the phase change microcapsule is made of polyimide resin, and the capsule shell contains n-alkane phase change material. The capsule shell of the phase change microcapsule is ultra-thin, has good tightness, good mechanical strength and thermal stability, controllable particle size, high phase change latent heat value, and is resistant to low temperature, high temperature, and has good thermal stability. It will not break at extremely low temperatures (-269℃).

[0033] The composite phase change material in the embodiment is prepared by mixing the bulk phase change material and the phase change microcapsule in a certain ratio. In the composite phase change material, the mass ratio of the bulk phase change material to the phase change microcapsule is greater than or equal to 2.5 and less than or equal to 5.5. Specifically, the phase change microcapsule accounts for 15% to 25% of the mass of the composite phase change material. Further, the phase change microcapsule accounts for 15% to 20% of the mass of the composite phase change material, or the phase change microcapsule accounts for 20% to 25% of the mass of the composite phase change material. Further, the phase change microcapsule accounts for 20% of the mass of the composite phase change material. The bulk phase change material accounts for 66% to 78% of the mass of the composite phase change material. Further, the bulk phase change material accounts for 66.7% to 77.3% of the mass of the composite phase change material. Further, the bulk phase change material accounts for 66.7% to 71% of the mass of the composite phase change material, or 71% to 77.3%. Further, the bulk phase change material accounts for 71% of the mass of the composite phase change material. In addition, the composite phase change material also includes glass fibers. Specifically, the mass of the glass fibers in the composite phase change material is 1% to 5%. Further, the mass of the glass fibers in the composite phase change material is 2.7%. The composite phase change material also includes graphite. Specifically, the mass of the graphite in the composite phase change material is 5% to 6%. Further, the mass of the graphite in the composite phase change material is 5.6%. It should be noted that the above-mentioned ratio of the composite phase change material is obtained after multiple tests, and for the battery pack, both the cost and the performance are good.

[0034] In the embodiment, the composite phase change material is formed by adding the phase change microcapsule to the bulk phase change material in a certain ratio. Referring to FIG. 3, which is an effect diagram of adding the phase change microcapsule 31b to the bulk phase change material 31a. Specifically, the phase change microcapsule 31b is uniformly arranged in the bulk phase change material 31a. When the composite phase change material absorbs the heat generated by the battery pack and undergoes a phase change reaction, the phase change microcapsule 31b and the glass fiber combination is equivalent to increasing the mesh structure (indicated by the dashed line in FIG. 3) in the bulk phase change material 31a, thereby increasing the constraint of the polyethylene glycol molecules in the bulk phase change material 31a, avoiding the leakage of polyethylene glycol during the phase change reaction. Specifically, the average particle size of the phase change microcapsule 31b used in the embodiment ranges from 5 microns to 20 microns. Further, the phase change microcapsule with an average particle size of 10 microns is used. Figure 7 Figure 7

[0035] ​​Since the phase change microcapsule itself is also a phase change material, it can absorb the heat generated by the battery pack through phase change reaction. By mixing the bulk phase change material with the phase change microcapsule at a reasonable ratio, the moisture resistance of the bulk phase change material can be increased, and the material leakage and material loss will not occur in a humid environment. On the other hand, compared with the same mass of bulk phase change material, the phase change enthalpy of the composite phase change material is higher. Specifically, compared with the same mass of bulk phase change material, the composition that can undergo phase change reaction in the composite phase change material accounts for 80-90%, so the composite phase change material has higher phase change enthalpy, which is about 17% higher.

[0036] The composite phase change material contains phase change microcapsules, so that the composite phase change material has a reticular structure inside after phase change during heat absorption, thereby increasing the constraint of polyethylene glycol molecules in the bulk phase change material, avoiding the leakage of polyethylene glycol after phase change reaction, and thus eliminating the need for traditional sealing layer and sealing structure. Therefore, the battery pack has higher heat dissipation efficiency, more compact structure and simpler assembly.

[0037] Table 1 below is a test result table of battery pack 1 and battery pack 2. In table 1, battery pack 1 represents a battery pack using only bulk phase change material, and battery pack 2 represents a battery pack using composite phase change material. As can be seen from table 1, under the same output current, to make the cell unit reach the same surface temperature, battery pack 2 needs longer time than battery pack 1. For example, under the condition of 25 degrees Celsius, control the battery pack 1 and the battery pack 2 to discharge at 30A, and record the time of battery pack 1 and battery pack 2 reaching 65 degrees Celsius as 378 seconds and 434 seconds respectively. Compared with battery pack 1, the discharge efficiency of battery pack 2 is improved by 14.8%.

[0038] Table 1 Test result table of battery pack 1 and battery pack 2

[0039]

[0040] As can be seen from table 1, when the battery pack 1 and the battery pack 2 discharge at about 50A, the discharge efficiency of the battery pack 2 can be improved by 21% compared with the battery pack 1, which has obvious effect. As can be seen from the test data in table 1, the heat dissipation effect of the battery pack using composite phase change material is more obvious.

[0041] Note that the above merely describes preferred embodiments of the present application and the principles of the technology applied. Those skilled in the art will understand that the present application is not limited to the specific embodiments described herein, and that various obvious changes, modifications and substitutions can be made without departing from the scope of the present application. Therefore, although the present application has been described in detail through the above embodiments, the present application is not limited to the above embodiments, and can include more other equivalent embodiments without departing from the concept of the present application, and the scope of the present application is determined by the scope of the claims.

Claims

1. A battery pack configured to power a power tool, the battery pack comprising: case; A battery cell assembly is disposed within the housing, and the battery cell assembly includes multiple battery cell units; This also includes: A heat absorber made of composite phase change material is in thermal contact with at least one of the battery cell units to absorb the heat generated by the battery cell assembly during the charging and discharging of the battery pack. The composite phase change material includes at least a host phase change material and phase change microcapsules; the phase change microcapsules are uniformly distributed in the host phase change material, and the average particle size of the phase change microcapsules is greater than or equal to 5 micrometers and less than or equal to 20 micrometers; the host phase change material includes polyethylene glycol, silica sol and water; the composite phase change material also includes glass fiber and graphite. When the composite phase change material absorbs the heat generated by the battery pack, a phase change reaction occurs. The phase change microcapsules disposed inside the composite phase change material and the glass fiber form a network structure after the phase change, thereby preventing the polyethylene glycol from leaking after the phase change reaction.

2. The battery pack according to claim 1, characterized in that, In the composite phase change material, the ratio of the mass of the main phase change material to the mass of the phase change microcapsule is greater than or equal to 2.5 and less than or equal to 5.

5.

3. The battery pack according to claim 2, characterized in that, The phase change microcapsules account for 15% to 25% of the mass of the composite phase change material.

4. The battery pack according to claim 1, characterized in that, The glass fiber accounts for 1% to 5% of the mass of the composite phase change material.

5. The battery pack according to claim 1, characterized in that, The phase change microcapsule includes a n-alkane-based phase change material disposed within the capsule shell, and the capsule shell is made of polyimide resin.

6. The battery pack according to claim 1, characterized in that, The composite phase change material fills at least the gaps between the plurality of battery cells.

7. A power tool comprising a battery pack according to any one of claims 1-6.

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