Patent Publication Number: US-2016226113-A1

Title: Battery pack

Description:
RELATED APPLICTION INFORMATION 
     This application claims the benefit under 35 U.S.C. §119(a) of Chinese Patent Application No. CN 201510047351.2, filed on Jan. 29, 2015, the disclosure of which is incorporated herein by reference in its entirety. 
     FIELD OF THE DISCLOSURE 
     The present disclosure relates generally to power storage devices and, more particularly, to a battery pack. 
     BACKGROUND OF THE DISCLOSURE 
     Battery packs can generate heat during the charging and discharging process. To, among other things, prolong the life of the battery packs, it is needed to avoid the temperature of the battery packs rising dramatically and make the battery packs work in a safe temperature range (for example less than 80 degrees C.). Further, in order to save the charging time of the battery packs after discharging, it is expected that the temperature of the battery packs can quickly drop to less than 60 degrees C. That is, the slower the temperature of the battery packs rises the better during the discharging process, and the quicker the temperature of the battery packs drops the better during the charging process. However, with the development of the Li-ion battery technology, the capacity and the discharging current of the battery packs are increased constantly so the temperature management of these battery packs becomes a very important problem in the field. 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     SUMMARY 
     In one aspect of the disclosure, a battery pack includes a first housing arranged on the outmost side of the battery pack, a second housing arranged within the first housing, battery cells, which are at least partially contained in the second housing, and a filling body which is at least filled in a space between two adjacent battery cells. The filling body is arranged in the second housing. The filling body has a first specific heat capacity when a temperature of the filling body is below a first temperature and has a second specific heat capacity when the temperature of the filling body is above the first temperature. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the invention hereinafter claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view showing a partial structure of an exemplary battery pack. 
         FIG. 2  is a schematic view showing an exemplary filling body and battery cells of the battery pack of  FIG. 1 . 
         FIG. 3  is a schematic view of the filling bodies in  FIG. 2 . 
         FIG. 4  is a schematic view showing another exemplary filling body and battery cells of a battery pack. 
         FIG. 5  is a schematic view of the filling body in  FIG. 4 . 
     
    
    
     The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the invention hereinafter claimed. Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention hereinafter claimed, its application, or uses. 
     As shown in  FIGS. 1-2 , a battery pack  1  includes a first housing  10 , a second housing  20 , battery cells  30  and a filling body  40 . The first housing  10  is arranged on the outmost side of the battery pack  1 . The second housing  20  is arranged within the first housing  10 . The battery cells  30  are at least partially contained in the second housing  20 . The filling body  40  is at least filled in a space between adjacent battery cells  30 . The filling body  40  is arranged in the second housing  20 . The filling body  40  has a first specific heat capacity when a temperature of the filling body  40  is below a first temperature and has a second specific heat capacity when the temperature of the filling body  40  is above the first temperature. 
     The first housing  10  is used to assemble the battery pack  1  as a whole, which forms the outmost side of the battery pack  1 . The first housing  10  can be made of plastic or rubber material. Preferably, the first housing  10  is made of two kinds of material. Specifically, the first housing  10  includes several basic bodies which are made of plastic material. The basic bodies are connected with each other through rubber material and/or the basic bodies are covered by rubber material. Thus, the battery pack  1  has high structural strength and a cushioning effect. 
     The second housing  20  is arranged within the first housing  10 , which is used to fix battery cells  30  and the filling body  40 . The second housing  20  is preferably made of plastic material. The second housing  20  is formed with a containing chamber for receiving the battery cells  30  and the filling body  40 . 
     The battery pack  1  can include different numbers of battery cells  30 , but at least two battery cells  30 , according to its nominal voltage. The battery cells  30  are connected in series or in parallel. The battery cells  30  are partially contained in the second housing  20 . Further, all the battery cells  30  are contained in the containing chamber of the second housing  20 . 
     The filling body  40  is used to absorb the heat generated by the battery cells  30  during the charging and discharging process of the battery pack  1 , thus slowing down the temperature rise of the battery cells  30  so the temperature of the battery pack  1  is inhibited from rising and can be cooled quickly. 
     The filling body  40  is arranged in the containing chamber of the second housing  20 , which is filled in the space between adjacent battery cells  30 . All the spaces between adjacent battery cells  30  are filled by the filling body  40 . Thus, the quantity of the filling body  40  is increased and the effect of heat absorption is enhanced. The filling body  40  has the first specific heat capacity when the temperature of the filling body  40  is below the first temperature and has the second specific heat capacity when the temperature is above the first temperature. That is, the specific heat capacity of the filling body  40  varies with the temperature and the specific heat capacity of the filling body  40  varies with the charging time and discharging time so the effect of heat absorption of the filling body  40  varies with the temperature. Preferably, the second specific heat capacity is greater than the first specific heat capacity. Thus, the effect of heat absorption of the filling body  40  is better with the temperature rise of the battery pack  1 . It is noted that the first and second specific heat capacity is applicable in the condition of phase change. The second specific heat capacity is very different from the first specific heat capacity and is applicable in the condition that the second specific heat capacity is slightly different from the first specific heat capacity when the temperature of the filling body  40  rises in the same condition. 
     As shown in  FIG. 2 , each battery cell  30  of the battery pack  1  has a central axis Y. The battery cells  30  are so arranged that the central axes Y of all the battery cells  30  are parallel to each other. The arranged battery cells  30  are configured as a battery cell group. The battery cell group may include edged cells that arranged at the edge thereof and middle cells that are surrounded by the edged cells. In the embodiment shown in  FIG. 2 , all the battery cells  30  of the battery cell group are edged cells. It is appreciated that the battery cell group can include middle cells when the number of the battery cells is increased. 
     The second housing  20  contains several filling bodies  40 . According to the different positions and structure of the filling bodies, the several filling bodies  40  include a first filling body  41  and a second filling body  42 . The first filling body  41  includes external surface  411  arranged at the edge of the battery cell group and internal surface  412  which is partially and directly contacted with the edged cells. The internal surface  412  is formed with first bulges  413  projecting toward the spaces inbetween adjacent battery cells  30 . The first bulges  413  fill the partial spaces inbetween adjacent battery cells  30  so that the adjacent battery cells  30  are indirectly contacted with each other through the filling bodies  40 . Thus, the adjacent battery cells  30  have the same cooling effect and the temperature equalization of the battery cell group is achieved and the individual battery cell  30  is avoided damage due to the over temperature rise. 
     The second filling body  42  is arranged within the battery cell group, which includes second bulges  421  projecting toward adjacent edged cells, adjacent middle cells, or adjacent edged cells and middle cells. That is, the second filling body  42  is at least partially surrounded by several edged cells or middle cells. So the adjacent middle cells and the adjacent middle cells and edge cells are indirectly contacted with each other through the filling bodies  40  and the temperature equalization of the battery cell group is well achieved. Further, the first bulges  413  of the first filling body  41  and the second bulges  421  of the second filling body  42  are contacted with each other so the first filling body  41  is engaged with the second filling body  42 . The battery cells  30  in the second housing  20  are surrounded by more than two filling bodies  40  so that the surface of each battery cell  30  is fully contacted with the filling bodies  40 . 
     The filling bodies  40  absorb heat when the temperature thereof rises to the first temperature and the temperature of the filling bodies  40  can rise to the first temperature during the discharging process of the battery cells  30 . Preferably, the filling bodies  40  are made of phase change material and the first temperature is the phase transformation point of the phase change material. The phase transformation point of the phase change material is set between the highest temperature and the lowest temperature generated during the charging and discharging process of the battery pack  1 . Thereby, during the charging and discharging process of the battery pack  1 , the temperature of the filling bodies  40  can rise to the first temperature, and the phase change material can reach the phase transformation point and change phase so as to absorb lots of the heat. 
     The filling bodies  40  made of phase change material has a first specific heat capacity when the temperature thereof is below the first temperature and has a second specific heat capacity after changing phase, namely when the temperature thereof is above the first temperature. The second specific heat capacity is greater than the first specific heat capacity. As a result, the filling bodies  40  can absorb more heat after changing phase so as to inhabit the temperature of the battery cells  30  from rising. The phase change material, for example without limit, consists of 90%-99.9% of polyethylene glycol and 0.1%-10% of cellulose diacetate. 
     Preferably, the filling bodies  40  have a viscosity greater than 15 cP at the first temperature. When the phase change material changes phase, the viscosity after the phase change is less than that before the phase change. Here, the viscosity of the filling bodies  40  is defined greater than 15 cP after the phase change. Thus the phase change material cannot flow and shape of the phase change material cannot change to influence the cooling effect. 
     The second housing  20  of the battery pack  1  is used to not only mount the battery cells  30 , but also fix the filling bodies  40 . The second housing  20  is directly contacted with the filling bodies  40  and maintain the shape of the filling bodies  40 . 
     In order to enhance the cooling effect, the second housing  20  may be provided with an air flue as shown in  FIG. 4 . The air flue  43 ′ includes several recesses  431 ′ sunk from an outside surface of the second housing  20  departing from the battery cells toward the inside of the second housing  20 . With the recesses  431 ′ on the outside surface of the second housing  20 , the air flue  43 ′ is formed on the second housing  20 . Thus, the air can flow within the battery pack  1  so as to enhance the cooling effect. Otherwise, the heat radiating area of the second housing  20  is increased due to the recesses  431 ′, and the cooling effect is further enhanced. 
     Preferably, in order to make the air flow from the inside to outside of the battery pack  1 , the first housing  10  is provided with an air inlet and an air outlet so the air can cycle between the air inlet, the air flue and the air outlet. The temperature rise is slowed down during the charging and discharging process of the batter pack  1 . 
     Preferably, the filling bodies  40  further include basic material which is used to support the phase change material. The basic material has a porous structure. The phase change material is filled in the porous structure. A part of the battery cells  30  that is contained in the second housing  20  is surrounded by the filling bodies  40 . The basic material is elastic material. 
     Preferably, the first temperature is between 50-60 degrees C. Namely, the phase transformation point of the phase change material is between 50-60 degrees C. With the filling bodies  40  being filled between the battery cells  30 , the temperature of the battery cells  30  can at least drop about 15 degrees C. in a condition that the battery pack  1  is discharged with the discharging current of  40 A and ended the discharging process in 330 seconds. Thus, the cooling effect is enhanced greatly due to the filling bodies  40  between the battery cells  30 . 
     Referring to  FIGS. 4-5 , illustrated is a battery pack  1  having the same first housing  10 , the second housing, and the battery cells  30  as described above. The difference between this illustrated battery pack and the previously described battery pack is that a filling body  40 ′is integrally formed. Specifically, the filling body  40 ′is made of high polymer material. The high polymer material has a first specific heat capacity which is greater than 1.5 J/g. degrees C. Thus, even the high polymer material does not change phase, it can provide good cooling effect. The high polymer material may be polypropylene or silicone rubber material. The filling body  40 ′ is formed with several chambers  41 ′ extending along the central axis Y. The battery cells  30  are arranged in the chambers  41 ′ respectively. The chambers  41 ′ have inside surfaces which are directly contacted with the battery cells  30 . In other embodiments, the battery pack  1  may not include the second housing  20 . The air flue can be formed on the outside surface of the filling body  40 . 
     The above illustrates and describes basic principles, main features and advantages of the present invention. Those skilled in the art should appreciate that the above embodiments do not limit the present invention in any form. Technical solutions obtained by equivalent substitution or equivalent variations all fall within the scope of the invention hereinafter claimed.