The present invention relates to a heat-insulating sheet that is used as a heat insulation measure and also relates to a method for manufacturing the heat-insulating sheet.
In recent years, there have been demands for energy saving, and insulating a unit from heat provides an improvement in energy efficiency, thus serving as an energy saving method. For such heat insulation, a heat-insulating sheet that provides excellent heat insulation is required. A heat-insulating device including a fiber sheet that supports silica xerogel has a lower thermal conductivity than air, and thus being used to this end. A conventional heat-insulating sheet having such a configuration is disclosed, for example, in PTL 1.
While demand for energy saving recently increases, insulation from heat for a unit is an energy saving method that improves energy efficiency. Heat insulation between plural battery cells installed in a secondary battery is demanded for preventing one hot battery cell from affecting adjacent battery cells. A heat-insulating sheet that provides excellent heat insulation may be provided between the battery cells in a heat insulation measure. A conventional heat-insulating sheet having such an application is disclosed, for example, in PTL 2.
PTL 1: Japanese Patent Laid-Open Publication No. 2011-136859
PTL 2: International Publication No. WO 2018/003545
Fiber sheets each including internal pores therein are prepared. A fibrous body including the fiber sheets is formed by stacking the fiber sheets and joining the fiber sheets to each other at joining regions. Silica xerogel is put into the internal pores of each of the fiber sheets of the fibrous body by impregnation. The put silica xerogel is hydrophobized while a space is formed between the fiber sheets in a non-joining region between the joining regions of the fibrous body.
This method provides a heat-insulating device resistant to a force in surface directions force and having a predetermined thickness.
Another heat-insulating device includes a first heat insulator and a second heat insulator. The second heat insulator faces a lower surface of the first heat insulator and has ends joined to ends of the first heat insulator at joining regions respectively. The first heat insulator includes a first fiber sheet and a first silica xerogel impregnating the first fiber sheet. The second heat insulator includes a second fiber sheet and a second silica xerogel impregnating the second fiber sheet. The first heat insulator has a compression rate larger than or equal to 15% in response to a pressure of 5 MPa applied to the first heat insulator. The second heat insulator has a compression rate smaller than or equal to 10% in response to a pressure of 5 MPa applied to the second heat insulator. Ends of the first fiber sheet are joined to ends of the second fiber sheet at the joining regions, respectively.
This heat-insulating device prevents a battery cell from affecting another battery cell while the cell is heated and expands.
Heat-insulating sheet 501 includes heat insulator 51 and heat insulator 151 which has ends 151a and 151b joined to ends 51a and 51b of heat insulator 51 at joining regions 12a and 12b, respectively. Heat insulators 51 and 151 are stacked in stacking direction D1. Ends 51a and 51b are opposite to each other in direction D2 perpendicular to stacking direction D1. Ends 151a and 151b are opposite to each other in direction D2. Therefore, joining regions 12a and 12b are opposite to each other in direction D2.
Heat insulators 51 and 151 have sheet shapes. Heat insulator 51 includes fiber sheet 11 and silica xerogel 21 with which fiber sheet 11 is impregnated. Fiber sheet 11 is made of fibers 11p intertwined with one another to provide internal pore 11q among fibers 11p. Silica xerogel 21 is put into internal pore 11q of fiber sheet 11 by the impregnation. Heat insulator 151 includes fiber sheet 111 and silica xerogel 21 with which fiber sheet 111 is impregnated as well. Fiber sheet 111 is made of fibers 11p intertwined with one another to provide internal pore 11q among fibers 11p. Silica xerogel 21 is put into internal pore 11q of fiber sheet 111 by impregnation.
A method for manufacturing heat-insulating sheet 501 will be described below.
Firstly, fiber sheets 11 and 111 each including internal pores 11q are prepared. Fibers 11p composing each fiber sheet 11 and 111 are made of polyethylene terephthalate (hereinafter referred to as PET), and have an average fiber diameter of about 10 μm. A volumetric proportion of internal pores 11q in each fiber sheet 11 and 111 is about 90%. Each of fiber sheet 11 and 111 has a thickness of about 1.5 mm and has a rectangular shape of about 80 mm by 150 mm when viewed in stacking direction D1 (see
Next, as illustrated in
In the case that fibers 11p are made of material, such as glass fiber, that does not melt easily, fiber sheets 11 and 111 are hot-pressed while a sheet made of thermoplastic resin, such as PET, is sandwiched between fiber sheets 11 and 111. The sheet has a thickness of about 1 mm and a width of about 3 mm. The hot-pressing causes the sheet to melt. The molten thermoplastic resin is soaked into fiber sheets 11 and 111 to join fiber sheets 11 and 111 to each other. This method allows fibrous body 101 to have a smaller thickness at joining regions 12a and 12b than at non-joining region 22 as well. Three or more fiber sheets 11 may be stacked on one another in stacking direction D1 and joining fiber sheets 11 to one another at joining regions 12a and 12b to similarly provide fibrous body 101.
Next, the impregnation to put silica xerogel 21 into internal pores 11q of fiber sheets 11 and 111 is prepared. A silica sol is prepared by adding concentrated hydrochloric acid that serves as a catalyst to a high-molar silicate aqueous solution that is material of silica xerogel 21. Fibrous body 101 is soaked in this silica sol to allow the silica sol solution to fill internal pores 11q of fiber sheets 11 and 111. Fiber sheets 11 and 111 each having a large proportion of internal pores 11q enables silica xerogel 21 to reach and fill depths of fiber sheets 11 and 111 regardless of the thickness of fiber sheets 11 and 111. Fiber sheets 11 and 111 may be impregnated with silica xerogel 21 by a method, such as dribbling or printing of the silica sol. While being impregnated with the silica sol, fiber sheets 11 and 111 are left for about 15 minutes in order to allow the silica sol to gel. When the gelling of the silica sol is confirmed, fibrous body 101 impregnated with the gelled silica sol is pressed to have a uniform thickness. The uniform thickness may be provided by, e.g. a roll press. Fibrous body 101 having the uniform thickness is put and stored in a thermohygrostat for about three hours in a constant temperature of about 85° C. and a constant humidity of about 85% to grow secondary silica particles for strengthening a gel skeleton structure. This impregnation puts silica xerogel 21 into internal pores 11q of fiber sheets 11 and 111.
Next, silica xerogel 21 put by the impregnation is hydrophobized. Fiber sheets 11 and 111 of fibrous body 101 impregnated with silica xerogel 21 are soaked in 12 N hydrochloric acid for about 1 hour for reaction between the gel and the hydrochloric acid. After that, as a second step of the hydrophobization, fibrous body 101 is soaked in a silylating solution that is mixture of silylating agent and alcohol, and is stored for about 2 hours in a constant temperature bath set at a temperature of about 55° C. This is when the mixture of the silylating agent and the alcohol permeates fibrous body 101. When trimethylsiloxane bonds start forming with progress of reaction, silica treatment progresses. Specifically, the aqueous hydrochloric acid is discharged out of fiber sheet 11 each containing the gel. Following completion of the silylation, the gel is dried for about 2 hours in the constant temperature bath set at a temperature of about 150° C., thereby providing heat-insulating sheet 501 illustrated in
Upon absorbing moisture, silica xerogel breaks easily. Hydrophobization is necessary to prevent the moisture absorption. On the other hand, a heat-insulating sheet has heat insulation that is proportional to its thickness. Therefore, the heat-insulating sheet accordingly has a large thickness to have significant heat insulation. However, if the fiber sheet is too thick, it is difficult to sufficient hydrophobize the silica xerogel at a middle portion of the fiber sheet, so that the thick sheet may degrade reliability. Accordingly, a required number of heat insulators that have been prepared to each have a predetermined thickness and covered with a protective film are stacked to provide an equivalently thick heat-insulating sheet. However, the heat insulators are not joined to each other, so that this heat-insulating sheet is vulnerable to a force in surface directions.
As described above, heat-insulating sheet 501 according to Embodiment 1 has significant resistance to a force in surface directions perpendicular to stacking direction D1.
Heat-insulating sheet 701 includes heat insulators 211, 212, and 311 that are stacked on one another in stacking direction D1. Heat insulator 212 has lower surface 212d and upper surface 212c that faces lower surface 211d of heat insulator 211. Heat insulator 212 has ends 212a and 212b joined to ends 211a and 211b of heat insulator 211 at joining regions 215a and 215b, respectively. Third heat insulator 311 has upper surface 311c that faces lower surface 212d of heat insulator 212. Heat insulator 311 has ends 311a and 311b joined to ends 212a and 212b of heat insulator 212 at joining regions 215a and 215b, respectively. Ends 211a, 212a, and 311a of heat insulators 211, 212, and 311 are aligned with ends 211b, 212b, and 311b of heat insulators 211, 212, and 311 in direction D2 perpendicular to stacking direction D1, respectively. Heat-insulating sheet 701 has a rectangular shape of about 80 mm by 150 mm. Joining regions 215a and 215b are positioned along two long sides of the rectangular shape, respectively. In accordance with Embodiment 2, each of joining regions 215a and 215b has a width of about 3 mm in direction D2. Heat insulator 211 includes fiber sheet 213 and silica xerogel 221 with which fiber sheet 213 is impregnated. Fiber sheet 213 is made of fibers 211p that are intertwined with one another to have internal pores 211q among fibers 211p. Silica xerogel 221 is put into internal pores 211q of fiber sheet 213 by impregnation. In accordance with Embodiment 2, fiber sheet 213 has a thickness of about 1 mm, and fibers 211p are made of, for example, glass fiber. Heat insulator 212 includes fiber sheet 214 and silica xerogel 221 with which fiber sheet 214 is impregnated. Specifically, fiber sheet 214 is made of fibers 211p that are intertwined with one another to have internal pores 211q among fibers 211p. Silica xerogel 221 is put into internal pores 211q of fiber sheet 214 by the impregnation. In accordance with Embodiment 2, fiber sheet 214 has a thickness of about 1 mm, and fibers 211p are made of glass fiber. Heat insulator 311 includes fiber sheet 313 and silica xerogel 221 with which fiber sheet 313 is impregnated. Specifically, fiber sheet 313 is made of fibers 211p that are intertwined with one another to have internal pores 211q among fibers 211p. Silica xerogel 221 is put into internal pores 211q of fiber sheet 313 by impregnation. In accordance with Embodiment 2, fiber sheet 313 has a thickness of about 1 mm, and fibers 211p are made of, for example, glass fiber.
Each of heat insulators 211 and 311 has a compression rate of about 18% in response to a pressure of 5 MPa applied to heat insulator 211 and 311. Heat insulator 212 has a compression rate of about 8% in response to a pressure of 5 MPa applied to heat insulator 212. The compression rate of each of heat insulator 211 and 311 is thus larger than the compression rate of heat insulator 212 in response to the same pressure applied to heat insulators 211, 212, and 311. Compression rate P1 is expressed as P1=(T0−T1)/T0 with an initial thickness T0 of the heat insulator before the pressure is applied, and a thickness T1 of the heat insulator having the pressure applied thereto. In accordance with Embodiment 2, a value of compression rate P1 is expressed as a percentage.
Heat insulators 211, 212, and 311 are joined to each other preferably while fiber sheets 213, 214, and 313 per se are joined to each other. Heat insulators 211, 212, and 311 having surfaces where silica xerogel 221 is exposed hardly provide high joining strengths. Therefore, fiber sheets 213, 214, and 313 are preferably joined to each other. This configuration eliminates or minimizes a displacement of each heat insulator 211, 212, 311 in surface directions perpendicular to stacking direction D1.
In the case that heat-insulating sheet 701 has a rectangular shape, heat insulators 211, 212, and 311 are preferably joined to one another along at least the two long sides of the rectangular shape. This configuration prevents displacement in surface directions more effectively.
In the case that fiber sheets 213, 214, and 313 are made of thermoplastic resin, such as polyethylene terephthalate (hereinafter referred to as PET), fiber sheets 213, 214, and 313 are joined to one another by heat welding to join heat insulators 211, 212, and 311 to one another. In the case that fiber sheets 213, 214, and 313 are made of material, such as glass fiber, that does not melt easily, in order to join heat insulators 211, 212, and 311 to one another, liquid adhesive is used to join fiber sheets 213, 214, and 313 to one another. Alternatively, sheets made of thermoplastic resin are sandwiched and are heated so that the melted thermoplastic resin fills portions of internal pores 211q of each of fiber sheets 213, 214, and 313 to join fiber sheets 213, 214, and 313 to one another.
A method for manufacturing heat-insulating sheet 701 according to Embodiment 2 will be described below.
Fiber sheets 213, 214, and 313 each including internal pores 211q therein are prepared. Each of fiber sheets 213, 214, and 313 has a thickness of about 1 mm, has a rectangular shape of about 80 mm by 150 mm, and is made of fibers 211p with average fiber diameter of about ϕ2 μm that are intertwined with one another. In accordance with Embodiment 2, fibers 211p are made of glass fiber. A grammage per a thickness of 1 mm of each of fiber sheets 213 and 313 is about 127 g/m2 while and a grammage per a thickness of 1 mm of fiber sheet 214 is about 180 g/m2. The grammage per a thickness of 1 mm of each fiber sheet 213 and 313 is thus smaller than the grammage per a thickness of 1 mm of fiber sheet 214.
Next, fiber sheet 213 is placed on upper surface 214c of fiber sheet 214, fiber sheet 313 is placed on lower surface 214d of fiber sheet 214, and fiber sheets 213, 214, and 313 are joined to one another over a width of about 3 mm along each of the long sides extending in longitudinal direction D3 to define joining regions 215a and 215b, thereby providing fibrous body 601 illustrated in
Fiber sheets 213, 214, and 313 are not fixed to one another at non-joining region 222 between joining regions 215a and 215b, and thus can be displaced with respect to one another. A method for joining fiber sheets 213, 214, and 313 to one another includes sandwiching a sheet made of thermoplastic resin, such as PET, and having a thickness of about 1 mm and a width of about 3 mm between ends 213a and 214a of fiber sheets 213 and 214, sandwiching a sheet made of similar plastic resin between ends 213b and 214b of fiber sheets 213 and 214, sandwiching a sheet made of similar plastic resin between ends 214a and 313a of fiber sheets 214 and 313, sandwiching a sheet made of similar plastic resin between ends 214b and 313b of fiber sheets 214 and 313 and performing hot pressing. The melted thermoplastic resin is soaked into fiber sheets 213, 214, and 313 to join fiber sheets 213, 214, 313 to one another.
Next, a preparation is made for the impregnation that puts silica xerogel 221 into internal pores 211q of fiber sheets 213, 214, and 313. A silica sol is prepared by adding a carbonate ester that serves as a catalyst to 20% of water glass that is a material of silica xerogel 221. Fibrous body 601 including fiber sheets 213, 214, and 313 that have been joined to one another is soaked in this silica sol to allow the silica sol solution to fill internal pores 211q of fiber sheets 213, 214, and 313. Fiber sheets 213, 214, and 313 each having a large proportion of internal pores 211q allow the silica sol to reach and fill depths of fiber sheets 213, 214, and 313 regardless of the thicknesses of fiber sheets 213, 214, and 313. While being impregnated with the silica sol, fibrous body 601 is left for about 1 minute in order for the silica sol to gel. When the gelling is confirmed, fibrous body 601 is pressed to have an adjusted uniform thickness. Fibrous body 601 may have a thickness adjusted with, e.g. a roll press. Having been impregnated with the gelled silica sol and having the adjusted thickness, fibrous body 601 is sandwiched between films and is left in an atmosphere for about 1 hour to grow secondary silica particles for strengthening a gel skeleton structure. This impregnation puts silica xerogel 221 into internal pores 211q of fiber sheets 213, 214, and 313.
Next, fiber sheets 213, 214, and 313 of fibrous body 601 impregnated with silica xerogel 221 are rinsed with water for about 30 minutes. After that, silica xerogel 221 is hydrophobized. Fiber sheets 213, 214, and 313 impregnated with silica xerogel 221 are soaked in 6 N hydrochloric acid for about 30 minutes for reaction between gel 221 and the hydrochloric acid. After that, as a second step of the hydrophobization, fibrous body 601 is soaked and stored in silylating solution that is mixture of silylating agent and alcohol for about 2 hours in a constant temperature bath set at a temperature of about 55° C. At this moment, the mixture of the silylating agent and the alcohol permeates fibrous body 601. When trimethylsiloxane bonds start forming with progress of reaction, the aqueous hydrochloric acid is discharged out of fiber sheets 213, 214, and 313 of fibrous body 601 each containing gel 221. Following completion of the silylation, fibrous body 601 is dried for about 2 hours in a he constant temperature bath set at a temperature of about 150° C., thereby providing heat-insulating sheet 701 illustrated in
While fiber sheets 213, 214, are 313 are soaked in the solution, such as the hydrochloric acid or the silylating solution, for the hydrophobization with internal pores 211q of fiber sheets 213, 214, and 313 filled with the silica xerogel, the hydrophobizing solution does not easily and sufficiently permeate fibrous body 601, particularly fiber sheet 214 to reach depths of fiber sheet 214 if fibrous body 601 is too thick having, for example, an overall thickness of more than 2 mm. In contrast, in accordance with Embodiment 2, the soaking for the silylation involved in the hydrophobization with space 216 formed between fiber sheets 213 and 214 and with space 218 formed between fiber sheets 214 and 313 in non-joining region 222 between joining regions 215a and 215b. In accordance with Embodiment 2, as shown in
Spacer 217a out of spacers 217a and 217b inserted in space 216 is closer to joining region 215a than spacer 217b is while spacer 217b is closer to joining region 215b than spacer 217a is. Spacer 217a has a larger diameter than spacer 217b. Spacer 219a out of spacers 219a and 219b inserted in space 218 is closer to joining region 215a than spacer 219b is while spacer 219b is closer to joining region 215b than spacer 219a is. Spacer 219a has a smaller diameter than spacer 219b. In other words, portion 216a of space 216 connected to joining region 215a has a larger width in stacking direction D1 than portion 216b of space 216 connected to joining region 215b. Portion 218a of space 218 connected to joining region 215a has a smaller width in stacking direction D1 than portion 218b of space 218 connected to joining region 215b. Portion 216a of space 216 connected to joining region 215a has a larger width in stacking direction D1 than portion 218a of space 218 connected to joining region 215a. Portion 216b of space 216 connected to joining region 215b has a smaller width in stacking direction D1 than portion 218b of space 218 connected to joining region 215b. As described above, the relationship between the diameter sizes of the two spacers inserted in the one of the spaces is reversed in the space adjacent to the one of the spaces to increase the size of each space without preventing fibrous body 601 from having a large overall thickness.
Silica xerogel 221 is, in a broad sense, a xerogel formed from a gel by drying and may be obtained by means of ordinary drying or a method such as supercritical drying or freeze drying.
In accordance with Embodiment 2, the grammage per thickness of 1 mm of each of fiber sheets 213 and 313 is about 127 g/m2 while the grammage per thickness of 1 mm of fiber sheet 214 is about 180 g/m2. In other words, each of fiber sheets 213 and 313 has the smaller grammage per thickness of 1 mm than fiber sheet 214. As the grammage per thickness of 1 mm becomes smaller, a weight per unit region decreases, and the volumetric proportion of internal pores 211q in the entire fiber sheet increases. Therefore, silica xerogel 221 that is included in a fiber sheet with a smaller grammage has more spaces, providing a larger compression rate in response to a predetermined pressure applied. Accordingly, fiber sheets of different grammages that are stacked and are impregnated simultaneously with silica xerogel 221 provides a heat-insulating device having different compression rates in a thickness direction. In accordance with Embodiment 2, the compression rate of each of heat insulators 211 and 311 is about 18% in response to a pressure of 5 MPa applied to heat insulator 211 and 311, and the compression rate of heat insulator 212 is about 8% in response to a pressure of 5 MPa applied to heat insulator 212. In other words, the compression rate of each of heat insulators 211 and 311 is larger than the compression rate of heat insulator 212 in response to the same given pressure applied to heat insulators 211, 311, and 212. The compression rate of each of heat insulators 211 and 311 larger than or equal to 15% in response to the pressure of 5 MPa applied to each of heat insulator 211 and 311 and the compression rate of heat insulator 212 smaller than or equal to 10% in response to the pressure of 5 MPa applied to heat insulator 212. This configuration allows heat insulators 211 and 311 of heat-insulating sheet 701 disposed between battery cells 801a and 801b of device 801 illustrated in
At an end of life of a secondary battery, a battery cell has an expanded central portion due to gas produced inside the battery cell. If a heat-insulating sheet having fiber sheets that support a uniformly dense silica xerogel is too firm, the heat-insulating sheet may not fully absorb the expansion of the battery cell while the heat-insulating sheet is compressed and exhibits deteriorated heat insulation if the heat-insulating sheet is too soft. Therefore, one battery cell that has become hot may possibly affect an adjacent battery cell.
When, for example, single battery cell 801a becomes hot in device 801 according to Embodiment 2, as described above, heat insulator 212 not being compressed provides the heat insulation to prevent adjacent battery cell 801b from being affected.
In accordance with Embodiment 2, terms, such as “upper surface” and “lower surface”, indicating directions indicate relative directions determined only by relative position of components, such as the fiber sheets of the heat insulating sheet, and do not indicate absolute directions, such as a vertical direction.
Number | Date | Country | Kind |
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2018-214768 | Nov 2018 | JP | national |
2019-028980 | Feb 2019 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2019/039323 | 10/4/2019 | WO | 00 |