Claims:We Claim:
1. A holder assembly (101) for energy storage cells (105) of an energy storage pack (100) of an electronic device, said holder assembly (101) being configured to actively cool said energy storage cells (105) comprises:
a cell holder (103) holding said energy storage cells (105) and disposed within an outer casing (102) made of conductive material;
a phase change material (104) lining configured on at least two sides/surfaces of said cell holder (103);
at least two graphite sheets (106) lining the length of at least two sides/surfaces of said phase change material (104) and held to be in thermal contact with said phase change material (104); and
a plurality of Peltier devices (107) lining along length of said graphite sheets (106) and held to be in thermal contact with said graphite sheets (106) on one side and with said outer casing (102) on the other side.
2. The holder assembly (101) as claimed in claim 1, wherein said Peltier devices (107) are lined along length of said graphite sheets (106), with each of said devices (107) being disposed at regular intervals from one another.
3. The holder assembly (101) as claimed in claim 1, wherein said Peltier devices (107) held to be in thermal contact with said graphite sheets (106) and said outer casing (102), have a cool surface each in contact with at least a portion of said graphite sheets (106) and a hot surface each in contact with at least a portion of said outer casing (102).
4. The holder assembly (101) as claimed in claim 1, wherein said phase change material is coated with an electrically insulating material.
5. The holder structure (101) as claimed in claim 1, wherein said holder assembly (101) is manufactured using a method (200) comprising steps of:
providing said cell holder (103) for accommodating said energy storage cells (105);
lining said cell holder (103) with said phase change material (104) coated with electrically insulating material so that each energy storage cell of said cells (105) remains in thermal contact with said phase change material (104);
disposing at least two graphite sheets (106) along length of at least two sides/surfaces of said phase change material (104) to remain in thermal contact with said phase change material (104);
disposing a plurality of Peltier devices (107) at regular intervals along length of each of said graphite sheets (106) so that a cool surface (side) of each Peltier device (106) remains in thermal contact with said graphite sheet (106) and a hot surface (side) of each Peltier device (107) remains in thermal contact with an inner surface (102c) of said outer casing (102); and
inserting said cell holder (103) holding said cells (105) and provided with said phase change material (104), said graphite sheets (106) and said Peltier devices (107) into said outer casing (102) and covering said outer casing (102) with a pair of left and right cover members (102L, 102R).
6. A method for manufacturing a holder assembly (101) for energy storage cells (105) of an energy storage pack (100) of an electronic device, said holder assembly (101) being configured to actively cool said energy storage cells (105), said method comprising steps of:
lining said cell holder (103) with said phase change material (104) coated with electrically insulating material so that each energy storage cell of said cells (105) remains in thermal contact with said phase change material (104);
disposing at least two graphite sheets (106) along length of at least two sides/surfaces of said phase change material (104) to remain in thermal contact with said phase change material (104);
disposing a plurality of Peltier devices (107) at regular intervals along length of each of said graphite sheets (106) so that a cool surface (side) of each Peltier device (106) remains in thermal contact with said graphite sheet (106) and a hot surface (side) of each Peltier device (107) remains in thermal contact with an inner surface (102c) of said outer casing (102); and
inserting said cell holder (103) holding said cells (105) and provided with said phase change material (104), said graphite sheets (106) and said Peltier devices (107) into said outer casing (102) and covering said outer casing (102) with a pair of left and right cover members (102L, 102R).
7. An energy storage pack (100) of an electronic device comprises:
a plurality of energy storage cells (105);
a cell holder (103) holding said energy storage cells (105) and disposed within an outer casing (102) made of conductive material;
a phase change material (104) lining configured on at least two sides/surfaces of said cell holder (103);
at least two graphite sheets (106) lining the length of at least two sides/surfaces of said phase change material (104) and held to be in thermal contact with said phase change material (104); and
a plurality of Peltier devices (107) lining along length of said graphite sheets (106) and held to be in thermal contact with said graphite sheets (106) on one side and with said outer casing (102) on the other side.
8. The energy storage pack (100) as claimed in claim 7, wherein said Peltier devices (107) are lined along length of said graphite sheets (106), with each of said devices (107) being disposed at regular intervals from one another.
9. The energy storage pack (100) as claimed in claim 7, wherein said Peltier devices (107) held to be in thermal contact with said graphite sheets (106) and said outer casing (102), have a cool surface each in contact with at least a portion of said graphite sheets (106) and a hot surface each in contact with at least a portion of said outer casing (102).
10. The energy storage pack (100) as claimed in claim 7, wherein said phase change material is coated with an electrically insulating material.
, Description:TECHNICAL FIELD
[0001] The present subject matter relates to an energy storage device such as a battery. More particularly, the present subject matter relates to a holder assembly of said energy storage device and a method for manufacturing the same.
BACKGROUND
[0002] Battery powered electric vehicles are being looked upon as the alternative to IC engine powered vehicles in the years to come and are likely to play a key role in future mobility scenarios. For example, lithium ion battery packs have become increasingly popular for use in automotive applications and in various commercial electronic devices owing to their rechargeability, light weight and high energy density. However, in order to ensure that the battery packs (hereinafter referred to as ‘energy storage packs’) retain their charge for an extended duration of time, it is essential that said energy storage packs are stored and operated at an optimal operating temperature. Maintaining the energy storage packs at an optimal temperature also allows them to be charged at faster charging rates.
[0003] A known energy storage pack comprises of one or more energy storage cells electrically connected with one another either in series or in parallel, or as combination of series connection and parallel connection. Typically, as current is drawn off (discharging) the energy storage cells of said energy storage pack, heat is generated within said energy storage pack. Likewise, even during charging, the energy storage cells get heated up, resulting in the heating up of the entire energy storage pack. The heat generated during discharging as well as charging of the battery pack, causes a severe effect on the life expectancy and performance of the battery pack. Typically, the energy storage cells tend to get into a thermal runaway when there is either a violation of safe temperature limit, or a manufacturing process induced cell short circuit, or when they are subjected to overcharging, resulting in a chain reaction capable of destroying the entire battery pack and causing a potential safety risk to the user of the vehicle.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] The detailed description described with reference to the accompanying figures. The same numbers have been used throughout the drawings to reference like features and components.
[0005] Fig.1 is a perspective view of at least one energy storage pack of an energy storage device, as per an embodiment of the present subject matter.
[0006] Fig.2 is an exploded view of said at least one energy storage pack, as per an embodiment of the present subject matter.
[0007] Fig.3 is an exploded view of a holder assembly of said at least one energy storage pack, as per one embodiment of the present subject matter.
[0008] Fig.4 illustrates a comparative graphical representation to show the effect on temperature of said at least one energy storage pack, with and without the use of graphite sheets as per an embodiment of the present subject matter.
[0009] Fig.5 illustrates the method of manufacturing said at least one holder assembly as per one embodiment of the present invention.
DETAILED DESCRIPTION
[00010] Typically, a known energy storage device comprises of at least one energy storage pack that includes at least one holder assembly configured to hold a plurality of energy storage cells therein. Further, said at least one holder assembly typically comprises an outer casing made of a metal of high conductivity. However, if the energy storage cells of said energy storage device are held to be in direct contact with said outer casing for thermal conductivity and for dissipation of heat, there exists a threat of short circuit between said energy storage cells and any other electrical part contained within said casing due to the heat generated during charging and discharging process of said one or more of the energy storage cells, thereby damaging the energy storage device because of thermal impact to adjacent energy storage cells. This results in the inception of a chain reaction which can lead to fire accident and be a potential safety hazard.
[00011] A known holder assembly comprises of at least one cell holder held in contact with a phase change material (PCM) for supporting said energy storage cells of the energy storage pack. As the latent heat of fusion of the phase change material (PCM) is high, it absorbs significant amount of heat while ensuring that its temperature does not rise significantly. Typically, during charging and discharging of the energy storage device, the phase change material absorbs heat generated from said energy storage cells and changes its state from solid to liquid. However, due to its low thermal conductivity and poor heat dissipating properties, the phase change material takes a long time to regain its original solid state. This nature of the phase change material prevents the energy storage device from being subjected to back to back as well as recurring (frequent) charging and discharging cycles.
[00012] In order to improve the thermal conductivity of the phase change material (PCM), one or more thermal conductivity enhancer additives, for example: carbon fibres, aluminium foam etc., are added to the phase change material (PCM). However, addition of the above-mentioned additives to the phase change material renders the phase change electrically conductive, thereby resulting in risk of electric short-circuiting within the energy storage device, thereby rendering said holder assembly unsuitable for storing said energy storage cells therein.
[00013] In another existing energy storage device, said at least one holder assembly is provided with Peltier devices disposed at regular intervals and held to be in contact with said Phase change material on one side and in contact with said outer casing on the other side in order to improve thermal conductivity of the Phase change material, so that heat dissipation from the phase change material to said outer casing is improved and so that the risk of short circuit occurring between said cells of said energy storage pack is also mitigated. However, owing to the small size of the Peltier devices, temperature of the Phase change material at the site of Peltier devices tends to be different from the temperature at other sites (non-Peltier), thereby resulting in non-uniform distribution of heat from the Phase change material. This non-uniform heat distribution from the phase change material results in formation of thermal cracks in the phase change material, thereby affecting overall cooling performance of the energy storage pack.
[00014] With the above challenges in view, the present subject matter provides an improved holder assembly for said energy storage cells, said assembly having high thermal conductivity, high heat absorbing and heat dissipating capability, thereby improving rate of cooling of said energy storage cells, while also minimizing risk of electric short circuit between cells. Particularly, said improved holder assembly is configured to have improved thermal and electrical properties that mitigates the risk of thermal runway of cells and protects the energy storage device from damage and safety risk.
[00015] According to one embodiment of the present subject matter, each energy storage pack of the energy storage device comprises at least one holder assembly for disposing said energy storage cells. As per one embodiment, said holder assembly comprises of an outer casing made of highly conductive material and which encloses a cell holder lined with a Phase change material, said cell holder accommodating said energy storage cells. Further, at least two sides/surfaces of said phase change material are lined with graphite sheets. Further, a plurality of Peltier devices are configured in a manner such that they are lined along the length of said graphite sheets and disposed at regular intervals along the length of the graphite sheets, and in a manner so that a cool surface (side) of each of said Peltier devices is held in thermal contact with said graphite sheets, and a hot surface (side) of each of said Peltier devices is held to be in thermal contact with at least a portion of an inner surface of said outer casing.
[00016] Configuring graphite sheets lined along length of at least two sides/surfaces of said phase change material ensures that heat from the phase change material is uniformly distributed to said Peltier devices. Uniform transfer of heat from the phase change material to the graphite sheets ensures that no thermal cracks are formed on the surface of the phase change material. Graphite being an excellent conductor of heat, configuring graphite sheets ensures that heat is effectively transferred from the phase change material to the Peltier devices, thereby ensuring that state change of the phase change material to and from liquid state to solid state is transitioned quickly. Further, provision of the Peltier devices ensures that heat absorbed by said cool surface from the graphite sheet is effectively transferred to the hot surface, so that one side gets cooler and the other side gets hotter; and with said hot surface being in thermal contact with said outer casing which is a highly conductive material, it is ensured that this absorbed heat is effectively dissipated to the outside environment/atmosphere. Thus, said Peltier devices in conjunction with said graphite sheets ensure active cooling of the energy storage pack and thereby ensure active cooling of the energy storage device.
[00017] Various other features and advantages of the invention are described in detail below with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements.
[00018] Fig.1 is a perspective view of said at least one energy storage pack 100 composed of a holder assembly 101 accommodating a plurality of energy storage cells 105 (shown in Fig.2) as per one embodiment of the present subject matter. In one embodiment, and as may be seen in Fig.1, said holder assembly 101 comprises an outer casing 102 made of a highly conductive material such as aluminum to accommodate said energy storage cells 105 therein. Said outer casing 101 includes a pair of left and right cover members 102L, 102R to ensure that said energy storage cells 105 remain enclosed within said outer casing 102.
[00019] Fig.2 is an exploded view of said at holder assembly 101, as per one embodiment of the present subject matter. In one embodiment, said outer casing 102 provided with the pair of left and right cover members 102L, 102R is designed to enclose a cell holder 103 that holds said energy storage cells 105. In the present embodiment, said cell holder 103 is made of resin and comprises a plurality of slots (not shown) to hold said plurality of energy storage cells 105 therein. One of said left and right cover members 102L, 102R also aid in supporting an energy control device (not shown) used for controlling operation of said energy storage device within said outer casing 102.
[00020] Fig.3 is an exploded view of the holder assembly 101 including said cell holder 103, as per one embodiment of the present subject matter. As per one embodiment of the present invention, said cell holder 103 designed to hold said energy storage cells 105 is lined with a phase change material 104. Further, said energy storage cells 105 are inserted into said cell holder 103 lined with said phase change material 104 so that said phase change material 104 remains in thermal contact with each cell of said energy storage cells 105. Said holder assembly 101 also comprises a thermally conductive material such as graphite sheets 106 lining at least a portion of said phase change material 104. In the present embodiment, said graphite sheets 106 are disposed to line at least two sides/surfaces of said phase change material 104 so that said graphite sheets 106 remain in thermal contact with said phase change material 104. Further, said holder assembly 101 comprises a plurality of Peltier devices 107 disposed at regular intervals along length of said graphite sheets 106 so that said Peltier devices 107 remain in thermal contact with said graphite sheets 106. Particularly, said Peltier devices 107 are disposed in a manner such that a cold surface (side) each, of each Peltier device 107 remains in thermal contact with surface of each of said graphite sheets 106, while a hot surface (side) each of each of said Peltier device 106 is held to be in thermal contact with an inner surface of said outer casing 102 for efficient and effective heat dissipation. As per another embodiment, the Peltier devices may be configured in a random pattern. Thus, in the present embodiment, said energy storage cells 105 are held to be in thermal contact with the outer casing 102 through said graphite sheets 106 and said Peltier devices 107.
[00021] Graphite being an excellent conductor of heat serves to take away the heat absorbed by the phase change material 104. Moreover, since the graphite sheets 106 are lined along the entire length of at least two sides/surfaces of the phase change material 104, it is ensured that heat is uniformly taken away from the phase change material 104 and transferred to said Peltier devices 107 lined at regular intervals on the graphite sheets 106. Said Peltier devices 107 perform active cooling and quickly take away heat from the graphite sheets 106 and transfer the same to said outer casing 102. Particularly, while each cold surface (side) of each of said Peltier devices 107 absorbs heat from respective portions of each of said graphite sheets 106 and transfers the heat to corresponding hot surface of respective Peltier devices 107; each of said hot surfaces (sides) transfers absorbed heat actively to said inner surface 102c of said outer casing 102. The outer casing 102 finally dissipates heat to the outside. Such design configuration enables quick heat dissipation & thereby frequent/recurring charging & discharging cycle of operation without any risk or problem outlined earlier.
[00022] Fig. 4 is a comparative graphical representation shown to illustrate the effect on temperature of said energy storage pack 100 with and without the use of said holder assembly 101 comprising graphite sheets. As may be seen in Fig.4, whereas the dotted line represented by “A” corresponds to the temperature of said energy pack comprising graphite sheets, the lines represented by “B” corresponds to the rise and fall in temperature of said energy pack not provided with graphite sheets. As may be seen in Fig.4, temperature of said energy pack remains constant throughout in a condition where graphite sheet 106 is used, and in a condition where graphite sheets 106 are not used, non-uniformity in temperature of the energy storage pack is observed (refer “B”). The use of graphite sheets 106 in the holder assembly 101 therefore ensures that temperature is uniformly transferred from the phase change material 104 to said Peltier device 107 and proves to be superior over the use of only phase change material 104 for conduction of heat to said Peltier devices 107. Thus, since the graphite sheets 106 enables uniform heat transfer across the lateral directions of the energy storage pack, from the phase change material 104, it is ensured that no thermal cracks are formed on the surface of the phase change material 104, unlike the case wherein only Peltier devices are disposed directly on the phase change material, thereby causing localized cooling of the phase change material and resulting in the formation of thermal cracks on the surface of said phase change material.
[00023] Fig. 5 illustrates a method of manufacturing said at holder assembly 101 as per an embodiment of the present subject matter. In one embodiment, the method 200 of manufacturing said holder assembly 101 comprises of steps 201-205 as illustrated in Fig.5. A first step of said method 200 involves providing a cell holder 103 for accommodating energy storage cells 105 of said energy storage pack 100 as illustrated by 201. Further, a second step as illustrated by 202 involves lining said cell holder 103 of said holder assembly 101 with said phase change material 104 coated with electrically insulating material so that each energy storage cell remains in thermal contact with said phase change material 104. Coating said phase change material 104 with an electrically insulating material ensures that no short-circuiting occurs within said holder assembly 101 when said graphite sheets 106, which are also electrically conductive come in contact with said phase change material 104. Step three of said method 200 and as illustrated by 203, involves disposing at least two graphite sheets 106 along length of at least two sides/surfaces of said phase change material 104 to remain in thermal contact with said phase change material 104. Further, a fourth step 204 involves disposing a plurality of Peltier devices 107 at regular intervals along length of each of said graphite sheets 106 so that a cool surface (side) of each Peltier device 106 remains in thermal contact with said graphite sheet 106 and a hot surface (side) of each Peltier device 107 remains in thermal contact with an inner surface 102c of said outer casing 102 of said holder assembly 101. The fifth step as illustrated by 205 involves inserting said cell holder 103 holding said cells 105 and configure it with said phase change material 104, said graphite sheets 106 and said Peltier devices 107 as described in foregoing steps into said outer casing and covering said outer casing 102 with pair of left and right cover members 102L, 102R.
[00024] As can be made out from the teachings of the present subject matter, designing and manufacturing a holder assembly comprising energy storage cells lined with phase change material, which in turn is held to be in thermal contact with graphite sheets which are held in thermal contact with Peltier devices, said Peltier devices being in thermal contact with an outer casing made of highly conductive material, ensures that said energy storage cells are always maintained at an optimal temperature during the charging and discharging cycles due to uniform heat transfer. Thus, the longevity and operational efficiency of said energy storage pack of any electronic device is ensured. Further, provision of said holder assembly manufactured through the foregoing steps of the method of manufacturing ensures that said holder assembly has high thermal conductivity, high heat absorbing and dissipating capability; thereby ensuring improved cooling efficiency of said energy storage pack, which aids in mitigating the risk of electric short circuit between cells, which may result in a fire hazard. Thus, the holder assembly with improved thermal and electrical properties enables continuous as well as frequent charging and recharging of said electronic device, without any safety risk to the user.
[00025] Improvements and modifications may be incorporated herein without deviating from the scope of the invention.