Cell holder with intermediate tray

A cell holder made up of a top tray, an intermediate tray and a frame. Cells are placed with minimal force in the frame to stand proud of it. The intermediate tray is placed over the projecting tops of the cells and serves to locate the cells. A busbar in the intermediate tray is connected to one set of terminals. A top tray is placed over the intermediate tray and snap-locked through the intermediate tray to the frame. The snap-lock distance is short. A busbar in the top tray is connected to the other set of terminals. The top tray shields the first busbar. Vents may be included to allow for the escape of hot cell gases in the event of failure.

TECHNICAL FIELD

This invention relates to a system for holding electrical cells. More specifically, it relates to a cell holder that is an assembly of trays and a frame to host one or more cells.

BACKGROUND

The demand for electrically based vehicles and devices has increased these last years due to their relatively low environmental impact compared to prior technologies. The development of safer and more efficient electrical cells and associated technologies is important for the economic expansion of these fields.

Safely assembling and mechanically retaining battery cells in a battery pack can be difficult. Failures to correctly assemble the battery packs or loose cells in the packs may cause an electrical danger or fire, either during manufacturing, in use or in service.

This background is not intended, nor should be construed, to constitute prior art against the present invention.

SUMMARY OF INVENTION

The present invention is a system for securing cells into a cell holder. The system may provide a small assembly stroke distance. The cells do not need to be pressed into place, which reduces chances of damaging a cell during the assembly of a cell holder. The cell holder provides sufficient mechanical restraint of the cells without the use of traditional screws or connectors, which may otherwise become loose, creating the risk of electrical shock or fire.

The assembly of the cell holder involves slipping the cells into a frame with little to no force and then positioning an intermediate tray onto the frame to help locate the cells. The cell holder is then secured with a top tray, which is a short stroke snap fit tray with integral locating features that locate it relative to the frame. The two parts of the tray assembly are snapped together to the frame in a pressing operation, securing the cells in place with no screws or fasteners.

Disclosed herein is a cell holder for one or more cells comprising: a frame that hosts one or more cells such that a portion of each cell projects beyond a top of the frame; an intermediate tray on top of the frame and having one or more recesses each of which accommodate one of the projecting portions of the one or more cells; and a top tray on top of the intermediate tray and fastened to the frame through the intermediate tray, thereby holding the intermediate tray in place.

Also disclosed is a method for assembling a cell holder for one or more cells comprising: placing one or more cells in a frame that hosts the one or more cells such that a portion of each cell projects beyond a top of the frame; placing an intermediate tray over the frame, the intermediate tray having one or more recesses each of which accommodate one of the projecting portions of the one or more cells; connecting a busbar in the intermediate tray to a terminal on each of the one or more cells; placing a top tray over the intermediate tray; fastening the top tray to the frame through the intermediate tray, thereby holding the intermediate tray in place; and connecting another busbar in the top tray to a second terminal on each of the one or more cells.

In some embodiments, the intermediate tray, the top tray, or both the intermediate and top trays define vents between top surfaces of the one or more cells and an exterior of the cell holder.

DESCRIPTION

Cell or electrical cell—this refers to a device capable of generating electricity from a chemical reaction. Cells may be rechargeable.

Clearance distance—this refers to the shortest distance through air between two conductors, such as the positive and negative terminals of a cell. It may be a line of sight between the two conductors or it may include multiple straight segments if there is an insulting obstruction on the direct path between the conductors.

Creepage distance—this refers to the shortest distance across the surface of an insulator between two conductors, such as the positive and negative terminals of a cell.

Busbar—this refers to a metallic strip, which is used as an electrical conductor for multiple components.

Snap lock—this refers to a device or a feature on a device that is capable of fastening two or more components together. One component is fastened to another component by one portion of the snap lock being set in position relative to the other portion of the snap lock, either by sliding, rotating or any other suitable movement. Snap locks may be permanent or temporary, or irreversible or reversible.

Referring toFIG.1, there is shown a sectional drawing of the cell holder2as seen from the side. The cell holder2is an assembly of a cell holding frame or cell frame6, an intermediate tray10and a top tray14. A cell18to be hosted by the cell holder2is inserted into a cavity20present in the cell frame6. A top portion of the cell18projects upwards out of the frame6. The intermediate tray10is placed on top of the cell frame6and has a recess24that accommodates the projecting portion of the cell when the cell18is already in place. The intermediate tray10and the cell frame6enclose the battery cells18.

The top tray14is placed on top of the intermediate tray10. The top tray14has studs22that are inserted into holes26of the intermediate tray10and then through to holes30in the cell frame6. A positive busbar34is located in the intermediate tray10. A negative busbar38is located in the top tray14. The positive busbar34extends from the intermediate tray10into the hole42of the intermediate tray to contact the positive terminal at the top of the cell18.

The hole26in the intermediate tray10is aligned with the hole30in the frame6in order for the stud22to slide properly through them. The stud22has at its extremity a snap lock46that goes through the intermediate tray10to be fastened into the cell frame6. The snap lock46has a head that engages with a step50or other retaining surface formed between wider and narrower portions of the hole30in the cell frame6. By locking the top tray14to the cell frame6, the snap lock46fastens the top tray14, the intermediate tray10and the cell frame6together. In some embodiments, the configuration of the snap lock46of the stud is different. Any type of snap lock may be used so long as it fastens the top tray14to the cell frame6as the top tray and the cell frame are pressed together.

The deforming action of the snap lock46into the plastic mating feature, e.g. step50, in the cell frame6results in the cell18being retained in the cell holder as well as both the top tray14and the intermediate tray10. The snap lock46slips easily into the cavities26and30in order to be engaged with the step50in the hole30. The pressure needed to be applied to the top tray14in order to fasten the assembly is generally low. For example, the cell holder is fastened together using hand pressure, which may be something more than that needed for a slip fit and something less than that needed for a press fit. The extent of the movement required to locate the top tray14ready for fastening is about equal to the height of the snap lock stud26. The extent of the movement required to fasten the cell holder together is about equal to the height of the snap lock46. In other embodiments, the extent of the movement may be reduced by making the height of the intermediate tray smaller, and by raising the locking feature, e.g. step50, in the cell frame.

The trays10and14are made of a flexible material that provides electrical insulation between the busbars34and38. In other embodiments, the material may be rigid. When fully assembled, the cell holder2may be considered to be touch-safe as the positive busbar is largely covered by the top tray14and the connection to the positive busbar may be covered with a cap and/or located away from the exposed, negative busbar. Assembly workers, not being exposed to the cell terminals, can handle the assembled cell holder more safely. In some embodiments, a sealing material, adhesive or coating is placed between the trays10and14and between the intermediate tray10and the cell frame6. In some embodiments, a paper-like flame barrier material such as Nomex® is incorporated into the cell holder2at positions where hot gas from the cells may come in contact with the plastic.

When the top tray14is locked into the cell frame6, it is irreversible. This is achieved by using irreversible snap locks. In some embodiments, the assembly is reversible, using reversible snap locks, however in this case the strength of the assembly may be less than that of an irreversible fit.

In some embodiments, the height of the assembly is checked after the top tray14is locked to the cell frame6, via the intermediate tray10, in order to make sure that all the snap locks are engaged properly.

The cavity20in the cell frame6that hosts the cell battery18has three bottom protrusions54on its vertical wall. The bottom protrusions54are spaced around the circumference of the cavity20. In the same manner, the recess24in the lower portion of the intermediate tray10has three top protrusions58. The top protrusions58and the bottom protrusions54form guides to hold the cell18and secure it centrally in position in the volume formed by the cavity20and recess24. Each set of protrusions54,58aligns the cell in the center of the cavity20or recess24in the respective plane of the protrusions.

The top protrusions58are molded on the wall of the recess24of the intermediate tray10. The bottom protrusions54are molded on the wall of the cavity20of the cell frame6. In some embodiments, the geometry of the protrusions54,58in the cell frame6and intermediate tray10is different to that shown in order for the intermediate tray and the cell frame to be more easily molded. In some embodiments, the protrusions54and58are separate elements from the intermediate tray10and the cell frame6rather than being integral with the trays. The top protrusions58and the bottom protrusions54prevent the cell18from moving sideways or tilting in the cavity20and recess24. As a result, the top protrusions58and the bottom protrusions54facilitate efficient contact between the busbars34and38and the cells18during assembly. The top protrusions58and the bottom protrusions54enforce an air gap around the cell18. In some embodiments, the top protrusions58and the bottom protrusions54have a rounded profile to avoid damaging the wall of the cell18.

At the bottom of the cavity20of the cell frame6, there is a ledge62. The ledge62supports the cell18from below. The ledge62and bottom surface of the cell18form a well66to accommodate an epoxy resin material that is used to adhere the cells to a cold plate. Heat from the cells is conducted away through the epoxy and the cold plate as current is drawn from the cells, or as the cells are being charged. The bottom of the cell18is in contact with the epoxy resin material. In some embodiments, another material for thermal conductibility is used instead of the epoxy.

Optionally, a locating feature52may be incorporated to locate the intermediate tray10in the correct location on the cell frame6. The locating feature may be, for example, a boss projecting upward from the upper surface of the cell frame10and a corresponding recess in the bottom surface of the intermediate tray10. One or more locating features may be incorporated into the cell holder. Other forms of locating features may be used, such as a pin and hole combination, or a ridge and slot.

In some embodiments, the cell frame6, the intermediate tray10and the top tray14are made of a plastic material, such as a polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) blend polymer or a fiber reinforced polycarbonate. Different plastics may be used for each of the cell frame6, the intermediate tray10and the top tray14. Different plastics may be used, for example, to tune a snap fit or to resist slumping when exposed to venting gases.

In some embodiments, for manufacturing purposes, the geometry of the cell frame6and the trays10and14may be different. For example, the walls of cell frame6may be slightly inclined to facilitate the molding process. Other lead-ins and molding drafts may also be incorporated.

In some embodiments, there are no protrusions54,58. Instead, the recess24in the lower portion of the intermediate tray10acts as a guide to align the cell18in the cavity20of the cell frame6. To do this, the recess24in the lower portion of the intermediate tray10is smaller in diameter than the cavity20that hosts the cell18in the cell frame6. This way, the cell18positioned in the cavity20of the cell frame6is centered in the cavity20by the recess24of the lower portion of the intermediate tray10.

Referring toFIG.2there is shown the cell holder2as seen from above, with the top tray14and the negative busbar38. The cell holder2hosts five cells18with the negative terminal of each one of them connected to ends70of the negative busbar38.

Referring toFIG.3there is shown a top portion of the cell holder2without the cell18. The negative busbar38is inserted through a hole80in the top tray14and a correspondingly aligned hole82in the intermediate tray10. The holes80,82are large enough to allow the negative busbar38to be spot welded to the negative terminal, or crimp, of the cell18. In some embodiments, the negative busbar38is bonded ultrasonically to the cell terminals. The negative busbar38has an approximately horizontal tab84that is flush with or enters slightly into the recess24of the intermediate tray10, depending on the particular dimensions of the cells18and the cell holder2. The negative busbar38has a middle vertical section88and a top horizontal section92. The top horizontal section92fits into a slot in the top surface of the top tray14.

Referring toFIG.4there is shown a bottom portion of the cell holder2. The bottom protrusions54hold the cell18centrally in the cavity20of the cell frame6. The ledge62supports the cell18. The ledge62forms a well filled with epoxy resin material100. The epoxy resin material100glues the bottom of the cell18to a cold plate102positioned underneath the cell frame6. In some embodiments, there may be a mechanical connection, using screws for example, of the cell holder2to the cold plate102to ensure that there is an even pressure and flatness of the cold plate. The cold plate may be referred to as a cooled plate, with cooling provided by circulating coolant fluid or by air cooling during operation. The use of screws here allows for the completion of the assembly of the cell holder before the glue cures. Such completion may involve, for example, the welding of the negative busbar to the cells.

Referring toFIG.5there is shown the battery cell holder2as seen from the side. The top tray10is positioned over the intermediate tray14. The intermediate tray14is positioned over the cell frame6.

Referring toFIG.6there is shown the cell frame6as seen from above. The cell frame6has cavities20with bottom protrusions54and ledge62. The cell frame6has cavities30that host the studs22from the top tray14. In some embodiments, the ratio of snap locks to cells is between 1:1 and 10:1.

Referring toFIG.7there is shown an example of a cell holder120for numerous cells. In some embodiments, a cell holder may be a module in a battery pack that has four or any other number of connected modules. The modules are mechanically connected to each other, including the connections between the busbars of the different modules. There is no welding between adjacent modules. A module is thus the smallest changeable unit of the battery pack if a defective cell needs to be replaced.

Referring toFIG.8, there is shown the steps to assemble the cell holder. In step140, the cells are placed in the cell frame. Then in step144, the intermediate tray is set over the cell frame with the cells already in place. After that, the positive busbar is connected to the terminals in step148, for example by welding. The top tray is set over the intermediate tray in step152. Next, the top tray is fastened to the cell frame in step156, holding the intermediate tray in place. Optionally, the cold plate is then glued to the bottoms of the cells in the cell holder, in step158. After this, the negative busbar is welded to the negative terminals in step160.

Referring toFIG.9, an embodiment is shown in which there are vent paths incorporated into the cell holder. The upper portion of the cell170is shown with the intermediate tray172above and around it, locating it centrally in the recess of the intermediate tray with the protrusions174. The top tray176is located above the intermediate tray172, and has studs178that project down from the underside of the planar portion of the top tray. Not shown are snap locks at the bottom of the studs178that hold the cell holder together. Positive busbar180and negative busbar182connect to the terminals of the cell170.

In contrast to other embodiments, this embodiment has vents184,186formed in the upper region of the intermediate tray172. The vents184,186may be, for example, channels that are present in the upper surface of the intermediate tray172. Other forms of the vents may be used in other embodiments. The vents184,186allow hot gases from the cells170to escape in the event that one or more of the cells begin to fail. By allowing the hot gases to escape, the other cells around the failing one do not get heated by the hot gases.

Other implementations of the vent routing are possible in other embodiments. For example, channels may be present in the lower surface of the top, planar portion of the top tray. The main requirement is to provide a path that directs the hot gases away from the failing cell and to the exterior of the cell holder, so as not to cause a potential thermal runaway effect.

In other embodiments, the snap lock engages with slots on the inner surface of the hole30rather than on a step. An alternate connection method to join together the trays and the frame is a heat stake. Heat staking has the advantage of the stake shrinking when cooled to tension the joint.

In other embodiments there are more than three protrusions54,58in each cell cavity. In other embodiments, there are two or even one protrusion shaped like ribs that extend sufficiently around the circumference of the cell cavity to centralize it. Busbars may be connected to the polarities opposite to those described above.

In general, unless otherwise indicated, singular elements may be in the plural and vice versa with no loss of generality.

Depending on the embodiment, one or more of the advantages described herein may be provided.

Throughout the description, specific details have been set forth in order to provide a more thorough understanding of the invention. However, the invention may be practiced without these particulars. In other instances, well known elements have not been shown or described in detail and repetitions of steps and features have been omitted to avoid unnecessarily obscuring the invention. Accordingly, the specification and drawings are to be regarded in an illustrative, rather than a restrictive, sense.

It will be clear to one having skill in the art that further variations to the specific details disclosed herein can be made, resulting in other embodiments that are within the scope of the invention disclosed. All parameters, proportions, materials, and configurations described herein are examples only and may be changed depending on the specific embodiment. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.