For decades, portable electrical power supplies have taken the form of batteries that release electrical energy from an electrochemical reaction. Various battery chemistries, such as traditional “dry cell” carbon flashlight batteries, and lead acid “wet” cells common in automobiles have provided adequate portable electrical power for most uses. Modern electronics, however, place significantly greater demands on the longevity and mass of batteries. Battery power has traditionally come at a premium of the mass required for the charge material for generating sufficient current. Conventional flashlight batteries deliver only low current. Automobile batteries for delivering an intense but brief high amperage flow to a starter motor are very dense and large. Modern electronic devices, such as cell phones, computing devices, and automobiles, demand substantial current delivery while being lightweight and small enough to avoid hindering the portability of the host device.
Rechargeable nickel-cadmium (NiCad) and nickel metal hydride (NiMH) had gained popularity for rechargeable batteries for portable devices. Recently, however, advances in lithium-ion batteries (LIBs) have been significant such that that they have become the most popular power source for portable electronics equipment, and are also growing in popularity for military, electric vehicle, and aerospace applications. Continuing development of personnel electronics, hybrid and electric vehicles, and industrial power storage and support ensures that Li-ion batteries will continue to be increasingly in demand.
A battery housing for lithium ion cells includes a plurality of cell modules, having a plurality of cells between a top conductive plate and a bottom conductive plate and attached to the conductive plate by tabs attached to similarly polarized ends of each of the cells in the module to define a parallel connection between all of the cells in the module. A battery housing stacks the modules to define a series connection between the stacked charge plates, and electrically couples adjacent stacks with a common charge plate to define a series connection between each of the stacks. Charge logic for preventing excessive charging or discharging of the cells, and permits charge and discharge rates up to 6 C. Tabs on each conductive plate provide a redundant connection to each circular face of the cells for resisting shock and vibration. The housing further includes an ultrasonically welded top, and insulating plates screwed between each module for containing the modules in resilient engagement sufficient to pass scrutiny under standards such as UN 38.3 Lithium metal and lithium ion batteries.
An example configuration disclosed herein includes a 2*2 arrangement of modules, each module including 14 cylindrical cells in which each cell has circular faces of opposed polarity. Conductive plates welded to the circular faces of the cells allow each conductive plate to electrically couple circular faces of like polarity, as each cell in the module is disposed in a parallel orientation between 2 opposed conductive plates for electrically coupling the cells in the module in parallel. Pinch welds between each stack of two modules electrically couple conductive plates of opposed polarity for defining a series connection between the modules, and a bottom, common conductive plate between two adjacent modules electrically couples each stack in series. The series connection between each module of 14 parallel cells yields a so-called 4s14p arrangement yielding 14.8 volts when the cells are 26650 cells with a nominal voltage of 3.7 v, and a discharged voltage of 2.5 v, and is intended for 12 v applications.
Configurations herein are based, in part, on the observation that lithium ion batteries enjoy substantial advantages over earlier battery chemistries such as Nickel cadmium (NiCad) and Nickel medal hydride (NiMH) cells. Lithium ion chemistry allows faster charge and discharge rates, as well as being lighter than their prior art counterparts.
Unfortunately, conventional approaches to lithium ion battery construction may not incorporate sufficient structural and electrical redundancy for rugged environments such as vehicles or high reliability industrial applications such as grid support and periodic generation (e.g. solar panels, windmills). Due to the high discharge rates available with Lithium ion (Li) chemistry, runaway currents and short circuits can damage electronics and even cause a fire.
Accordingly, configurations herein substantially overcome the shortcoming of conventional battery construction and assembly by providing safeguards against overcurrent discharge, overheating, and mechanical degradation. Redundant battery tabs and welded conductors avoid shock and vibration effects that can interrupt connections. Multiple welded connections between cells and cell modules provide electrical redundancy. Multiple fusible couplings at the cell, module, and pack level, as well as redundant thermal sensing, quickly stems overcurrent situations before heat generation rises to detrimental levels.
Configurations herein are directed toward compliance with the UN (United Nations) standard on the transport of dangerous goods pertaining to tests and criteria for lithium metal and lithium ion batteries, promulgated as UN 38.3 Lithium metal and lithium ion batteries. Industry standards such as UN 38.3 and CAN bus demand resiliency and protection against runaway charge to avoid hazardous conditions when lithium batteries are employed in mobile applications such as hybrid and electric vehicles and trailer mounted grid support.
The foregoing and other objects, features and advantages of the invention will be apparent from the following description of particular 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 the principles of the invention.
Depicted below are configurations of a battery enclosure and battery cell (cell) arrangement for a lithium ion battery. Due to the potentially high discharge rates available with lithium ion cells, the enclosure exhibits structural and electrical robustness and redundancy to guard against accidental discharge, or so-called “runaway” currents. Since power based cells are relied upon for high discharge rates, in contrast to counterparts in portable, personal devices which emphasize longevity, it is important to ensure that the architecture and design of the enclosure and the cells therein anticipates the working environment of such batteries, particularly since usage often involves vehicular transport and other context where physical shock and vibration tend to occur. Further, several industry standards, most notably UN 38.3 and CAN bus are relied upon as exemplary criteria.
Configurations herein depict a battery enclosure having a plurality of multi-cell modules connected in series, in which each module has a number of cells in parallel. In a particular example configuration shown, the battery enclosure (battery) has 4 modules, each with 14 cells, and may be referred to as a 4s14p enclosure. The modules are connected in series to an adjacent module or to a bussbar leading to one of the terminals of the battery. All 14 cells in the module are oriented similarly to connect in parallel to conductive plates at each end of the cells. One of the conductive plates is positive (+), and the opposed plate is negative (−), based on which end of the similarly positioned cells the conductive plate is attached.
The example arrangement anticipates 26650 lithium ion cells, aptly named for cylindrical shaped cells having a diameter of 26 mm and a length of 650 mm. Each cell has opposed voltages at each circular end, thus has a (+) side and a (−) side, as cell orientation will be referred to below. A nominal voltage of 3.7 v yields a battery pack of 14.8 volts when four modules connect in series.
The 4s14p mechanical assembly is broken up into two modules. The “top” module holds 28 26650 cells. The bottom module holds another 28 26650 cells also, for a total of 56 cells per 4s14p unit. The configuration is 4 cell groups (modules) in series with 14 cells in each group in parallel. Each module has two Fire Retardant ABS plastic end caps that hold the cells in place. The two end caps per module may be assembled with thread forming plastite screws.
As lithium ion batteries have the capacity for high current discharge, resilience in design to avoid accidental sudden discharge that could result in high temperatures or fires is paramount. Further, for high current and industrial applications, where substantial voltages and currents are employed, there is also an increased risk of impact and shock related incidents as banks of batteries undergo vehicular transport for hybrid automobiles and trailer-based deployment.
The controller layer allows charging and discharging up to co-called “6 c” rates, allowing approximately a 6*current draw over the amp hour rating on the cells. Charging also enjoys similar enhanced rates.
A pair of terminals 140-1, 140-2 (140 generally) are configured for external connection to the serially interconnected modules 120. In particular configurations, control interfaces 132-1, 132-2 allow daisy chaining across a plurality of batteries 110 for monitoring and controlling charging and discharging. An enclosure 150 and ultrasonically welded top 152 encapsulate the modules and control circuitry, and have portals for the terminals 140 and control interfaces. In the example configuration, the brass terminals 140 are round at the top, with a threaded hole for battery lug connections. The terminals also have a hex shape that matches up with the fire retardant ABS cover. The hex shape in the cover along with the epoxy provides the strength to secure the terminal in place and protect the PCB from being stressed for up to 160 in-lbs of torque on terminal.
Each conductive surface of the conductive plates 124 includes an insulating plate 156-1 . . . 156-2 between the adjacent, or stacked, modules 120, such that the insulating plate has at least one post having a concave shape, the concave shape for engaging a convex protrusion on the conductive plate. To maintain alignment of the insulating plate with the corresponding conductive plate, the concave and convex shapes engage frictionally compressively. In an example configuration, the concave shape may be a cross (+) and the convex shape being a similar cutout on the conductive plate such that the convex “points” of the cross cutout engage the protruding (+) in a barb-like manner.
Each module 120-1 . . . 120-4 has a top and bottom conductive plate 124-1-T/B . . . 124-4-T/B for top and bottom, respectively. Each conductive plate defines a parallel connection for each of the cells 122 in the module 120, and therefore each module 120 has a positive (+) and negative (−) conductive plate with an adjacent module 120. The conductive plates are electrically coupled to a conductive plate of an adjacent module, in which the coupled conductive plates having an opposed polarity. The modules 124 therefore form a series connection to the adjacent module by coupling to a conductive plate of an opposed polarity, and to a bussbar 162-1 . . . 162-2 at respective ends of the series (modules 120-1 to the negative bussbar 162-2 and module 120-4 to the positive bussbar, in the example shown.
The modules 120 couple either vertically or horizontally to adjacent modules 120, thus forming a series of adjacent “stacked” modules. The example configuration shows two stacks of two modules, to form a series of 4 modules, but alternate arrangements may be invoked. In the vertical coupling, as between modules 120-1 to 120-2 and modules 120-3 to 120-4, the electrical coupling includes pinch welding 170 to an adjacent module to join the conductive plates 124. In the stack, the top and bottom modules are screwed together with thread forming plastite screws. The two modules are then “pinch” welded at 4 locations per side to make the module to module electrical connection. An insulator 156 is assembled between the two modules to isolate the connections and improve the voltage sense. Each weld strap has a faston connection that provides a voltage sense point connection with a wire that travels back to the PCB.
In the horizontal coupling, as between modules 120-2 and 120-4, a continuous conductive plate spans multiple adjacent modules, shown as 124-2-B and 124-4-B. Alternatively, separate conductive plates 124 could be joined by welding, rather than providing a continuous plate spanning two modules. The resulting arrangement includes a plurality of modules 120 stacked in a longitudinal direction of the cylindrical cells 122 (i.e. stacked in the direction of the longer, cylindrical side of the cells) and electrically coupled to an adjacent stack of modules 120 sharing a common conductive plate, such that the common conductive plate forms a series connection between module 124-2-B and an opposed polarity of module 124-2-B of the plurality of modules.
In the example arrangement, following assembly of the modules by welding or other suitable coupling, the system is now a “pack” and is placed in the plastic housing 150 thread forming plastite screws securing the bottom end cap to the bottom of the case. The top cover is placed on top of the case so that the brass terminals are centered on the cover holes. The cover has a groove designed around the perimeter which mates with a rib at the top of the case. The rib on the case has an interference with a “shear” design for ultrasonic welding. The entire assembly is then placed into a fixture and the top cover is ultrasonically welded to the case. The gap around the terminals is then sealed with epoxy to join the hex shaped terminals to a corresponding receptacle on the cover for torque resistance. The epoxy fills the gap around the terminal, provides strength, and helps to seal out water and dust in order to meet IP54 rating.
A plurality of FETs (Field-Effect Transistors) 184 are responsive to the control interfaces 132 for switching charge and discharge current, and hence, the charge/discharge rate. A sufficient number of FETs allows a 6 c discharge rate of up to 210 amps for 35 Ah (Amp hour) cells.
A leg 178 in the cutout is a narrower portion that is deformed toward the cell end 174. The legs 178 are deformed to dispose the tabs out of plane with the conductive plate for biasing against an end 174 of the cells 122. The tabs 172 are affixed by spot welds 180. Two spot welds 180 on each tab 172 avoid rotation of the tab 172 on the cell end 174 resulting from a single weld. Additional welds may be employed depending on an area of the tab 172. The tabs 172 and legs 178 are adapted to maintain electrical connectivity and withstand shock and vibration according to a predetermined standard, such as UN 38.3.
The cutouts 176 facilitate welding of the tabs by directing a welding current to the other of the pair of tabs rather than shorting the weld circuit. Each conductive plate 124 has a plurality of tabs are welded to each end of the cells, in which a welding circuit including at least two of the tabs and a distance of the leg is sufficiently long to avoid shorting the welding circuit between the pair of tabs. In other words, a surface distance between the tabs 172-1 and 172-2 is sufficient that a welding current applying opposed polarity to each tab 172-1, 172-2 will not travel across the leg to the opposed polarity and effectively short the current flow providing the weld arc. Therefore, each cell end 174 couples to a pair of tabs 172-1, 172-2 spot welded to each of the opposed ends of each of the cells 120, such that each tab 172 of the pair of tabs receives opposed electrodes of the same welding circuit, in which the cutout 176 and legs 178 defining each pair is sufficiently large to disrupt an electrical path between the opposed electrodes. Rather, a welding current path travels across the ends 174 of the cell 122 to the tab 172 corresponding to the opposed electrode of the weld circuit. In other words, the electrical “distance” between the weld electrodes is shortest across the ends 174 of the cell 122, rather than around the cutout 176 via the legs, directing the weld current to arc at the tab 172 as it contacts the cell 122 end 174. The tabs 172 may have dimples to define the weld 180 points,
Each of the legs connected to at least one of the ends of each cell has a width and thickness based on a maximum allowable current flow, in which the legs configured such that current flow exceeding the maximum disrupts a connection through the leg by melting the leg material. Therefore, the leg may act as a fuse for limiting a runaway or excessife discharge by melting and interrupting the circuit. In an example arrangement, the fusable legs connect to one side (polarity), although could be applied to all legs. The plurality of tabs also provides redundancy for shock and vibration resistance. In the example arrangement, the negative weld tabs are designed as a fuse in case of a runaway cell condition.
While the methods and apparatus defined herein have been particularly shown and described with references to 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.