Patent Application
20140335398
Multi-cell battery blocks (cells in parallel and/or in series) and battery packs (blocks in parallel and/or in series) are susceptible to propagation of individual cell failures. For lithium-ion batteries, if one cell goes into thermal runaway (i.e. due to internal fault or exposure to out-of-specification or abuse conditions) the cell typically heats to levels sufficient to then propagate the failure to adjacent cells via thermal transfer of heat energy through direct and indirect contact between cells. This cell-to-cell propagation of failures can eventually cascade to all cells in the battery block or pack. This cell-to-cell propagation is more likely to occur with prismatic cells as they tend to be constructed of materials that allow for the expansion and contraction of the cell surfaces during normal charge and discharge cycles, and the cell's planar surfaces tend to expand during a cell runaway event. To effectively achieve a design that does not allow propagation of cell thermal runaway failures typically requires a large amount of spacing between cells, thus creating a larger battery pack, or a large amount of mass of a non-thermally or thermally conducting material surrounding each cell, thus creating a heavier battery pack. Since high volumetric and gravimetric energy density are critical requirements for battery packs, adding volume or weight has a negative impact on performance and can result in an unacceptable battery solution for a given application. Some of these materials can also impede air flow which will inhibit the convective cooling of the cells needed for proper thermal management.
Therefore, there is a need for an improved method of preventing cell-to-cell propagation of failures.
The invention is generally directed to a battery block having a thermal barrier inserted between cells to reduce heat conduction between a failing cell and the adjacent cells, thereby preventing propagation of the initial failure. In one embodiment, a battery block includes a first prismatic battery cell defining a first substantially planar surface, a second prismatic battery cell defining a second substantially planar surface, the second substantially planar surface being in opposing relation to the first substantially planar surface, and a thermal barrier suspended between the first and second substantially planar surfaces, wherein the thermal barrier is spaced from both the first and second substantially planar surfaces. The thermal barrier defines a first end and a second end opposite the first end. The thermal barrier can have a thickness in a range of between about 0.3 mm and about 1.6 mm. The battery block can further include a supporting spacer at each of the opposing ends of the thermal barrier that separates the first and second substantially planar surfaces and suspends the thermal barrier therebetween. The supporting spacer can be a flexible supporting spacer. In some embodiments, the supporting spacers can adhere to at least one of the first and second substantially planar surfaces. The battery block can further include a housing that supports the batteries of the battery block. The thermal barrier can cover a surface area in a range of between about 60% and about 100% of the surface area of the opposing first and second substantially planar surfaces. The thermal barrier can include, for example, a ceramic fiber material or a polymeric material, such as a meta-aramid polymeric material. The thermal barrier including ceramic fiber material can have a thickness such as about 0.8 mm or about 1.6 mm. The thermal barrier including meta-aramid polymeric material can have a thickness such as about 0.3 mm, about 0.5 mm, or about 0.8 mm.
This invention has many advantages, such as preventing cell thermal runaway propagation after one or more cells in a battery block experiences a thermal event without significantly impacting the energy density of the battery block.
The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention.
A description of example embodiments of the invention follows.
Battery blocks are generally desired to have as high an energy density as possible, and so cells will be positioned very close to each other. Typically, cells will be positioned either in contact with each other, or in sufficient proximity to each other such that, during a thermal runaway, failure of one cell will expand to neighboring cells, thereby causing cell failure to propagate to neighboring cells to enable the propagation of the failure to adjacent cells. In some pack designs, the problem of propagation can be exacerbated by the presence of thermally conductive pack packaging material between adjacent cells.
The invention is generally directed to a battery block having a thermal barrier suspended between cells to reduce heat conduction between the failing cell and the adjacent cells, thereby minimizing or eliminating the chance that failure of a cell will propagate thermally to adjacent cells in a battery block. The method described herein also minimizes or eliminates cell thermal runaway propagation without significantly impacting the battery block energy density or assembly cost.
As used herein, a battery block is a parallel and/or series array of prismatic cells. In one embodiment shown in
Battery block 100 can further include supporting spacers 180 at each of opposing ends 160 and 170 of thermal barrier 150 that separates first 120 and second 140 substantially planar surfaces and suspend thermal barrier 150 therebetween. The thickness of supporting spacers 180 typically are in a range of between about 0.1 mm and about 0.3 mm, such as about 0.15 mm, about 0.2 mm, or about 0.25 mm.
The spacing “D” between surfaces 120 and 140 is sufficient to minimize or eliminate the likelihood of thermal propagation of cell failure from one of cell 110, 130 to the other cell 110, 130, and will depend upon the batteries, the material of the thermal barrier, and the distance between the batteries and the thermal barrier. The spacing D between surfaces 120 and 140 can be, for example, in a range of between about 2 mm and about 3 mm, such as about 2.1 mm, about 2.2 mm, about 2.3 mm, about 2.4 mm, about 2.5 mm, about 2.6 mm, about 2.7 mm, about 2.8 mm, or about 2.9 mm. Supporting spacers 180 generally are sufficiently flexible to substantially follow the contours of substantially planar surfaces 120, 140. In some embodiments, supporting spacers 180 adhere to at least one of the first 120 and second 140 substantially planar surfaces. An example of a suitable spacer 180 is adhesive tape, such as foam tape, for example very high bond (VHB) foam tape made by 3M (Minneapolis, Minn.). Typically, the adhesive tape has sufficient thermal stability to hold the thermal barrier in position during a thermal event, and also an ability to bond well to cell insulating materials such as cell insulating wrapper which is composed of a PET plastic material.
Battery block 100 can further include housing 190 that supports the batteries 110 and 130 of battery block 100. In various embodiments, thermal barrier 150 can cover at least about 60%, such as about 70%, about 80%, about 90%, or about 100% of the surface area of the opposing first 120 and second 140 substantially planar surfaces.
In another embodiment, a method to prevent cell-to-cell thermal runaway propagation in a battery block includes suspending a thermal barrier between a first substantially planar surface of a first prismatic battery cell and a second substantially planar surface of a second prismatic battery cell, wherein the thermal barrier is spaced from both the first and second substantially planar surfaces. The method can further include suspending a supporting spacer at each of a first end and a second end opposite the first end of the thermal barrier that separates the first and second substantially planar surfaces. The battery block, thermal barrier and supporting spacer are as described above. The thermal barrier should be applied to center it on the first or second substantially planar surface of the prismatic cell. In an exemplary embodiment, the method includes securing a tape insulator coupon alignment jig to a work table with double stick foam tape or screws, cutting VHB tape into four pieces about 125 mm in length, and loading seven insulator coupons into the insulator coupon alignment jig. The method then includes applying the VHB tape along the top edge of the insulator coupons, keeping the tape centered left-to-right, and repeating the tape application along the bottom edge of the insulator coupons. The method then further includes flipping the coupons over and realigning the insulator coupons in the insulator coupon alignment jig, followed by repeating the tape application on the rear side of the insulator coupons at the top and bottom edges, keeping the tape centered left to right. Then the method includes removing the clear protective film from top and bottom VHB tapes only on the front side of the insulator coupons, and cutting the top and bottom tapes between each insulator coupon. Installing the insulator coupons on cells includes placing a coupon face up (side with the clear protective film removed facing up) in a cell coupon alignment jig, and placing a cell over the insulator coupon, such that the insulator coupon is centered on the substantially planar surface of the cell.
A test method was developed to provide data which was used to rate the effectiveness of various insulating materials. The first step was to create a test scenario that would reliably initiate thermal runaway in a prismatic lithium ion cell. The initiation of thermal runaway was accomplished by forcing a conductive, hardened, machined steel nail through a fully charged prismatic lithium ion cell. The prismatic cell tested was a 5300 mAh cell in an 18×37×65 oblong prismatic case (trade name Swing® 5300). As shown in
As shown in
The test setup as shown in
The relevant teachings of all patents, published applications and references cited herein are incorporated by reference in their entirety.
While this invention has been particularly shown and described with references to example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.
This application claims the benefit of U.S. Provisional Application No. 61/820,468, filed on May 7, 2013. The entire teachings of this application are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61820468 | May 2013 | US |
