WO2012153230A1

WO2012153230A1 - Cell stack and battery module with integrated heater and heater panels therefor

Info

Publication number: WO2012153230A1
Application number: PCT/IB2012/052181
Authority: WO
Inventors: Wilhelm Franz Fuls; Julian GERBER
Original assignee: Optimal Energy (Pty) Ltd
Priority date: 2011-05-06
Filing date: 2012-05-02
Publication date: 2012-11-15
Also published as: ZA201308242B

Abstract

A battery component is provided in which at least two cells of a pouch or prismatic type have an electrical resistance heater panel sandwiched between them with the heater panel extending over a substantial area of the cell units. The heater panel may have an electrically insulating support panel with one surface carrying an electrically conductive heating element in the nature of a generally rigid or semi-rigid printed circuit board in which the heater element is a sinuous printed circuit board conductor. The heating element may terminate in contacts at or adjacent an edge region of the support layer. The support layer may have an area thereof forming an outwardly projecting connection tab having a plurality of contacts associated therewith. The support layer may carry one or more temperature sensors with associated signal carrying electrical conductors terminating in contacts at an edge region of the panel. A cell stack and a heater panel in the form of a printed circuit board formed to provide an electrically conductive heating element are also provided.

Description

CELL STACK AND BATTERY MODULE WITH INTEGRATED HEATER AND HEATER PANELS THEREFOR

FIELD OF THE INVENTION

This invention relates to a cell stack, and a battery module composed of a plurality of cell stacks with an integrated heater for heating the cell stacks and battery module to an optimal temperature or temperature range for operation.

The invention also relates to a heater panel for use in such a cell stack or battery module.

More particularly, but not exclusively, the invention relates to a lithium ion cell stack and battery module for an electric vehicle having an integrated battery heater and wherein the battery module has a plurality of series-connected cell stacks each of which includes a plurality of parallel-connected cells.

The invention also relates to a cell stack and a battery module in which cell balancing during charging can be effectively achieved.

BACKGROUND TO THE INVENTION

Rechargeable lithium ion cells are available on the market in different types such as pouch cells, prismatic cells and cylindrical cells. Of particular, but not exclusive interest, are pouch cell assemblies that are made up of plural pouch cells assembled in parallel connected stacks thereof with multiple stacks being connected in series to form a battery module. One battery module, for example, may consist of six cell stacks connected in series with each cell stack consisting of say five individual lithium ion cells connected in parallel. Any other required numbers of individual cells in each cell stack and of cell stacks in a battery module may be employed according to requirements and characteristics of the assembled module.

At around freezing point, it is generally detrimental to charge a traction battery of the lithium ion type with carbon-based anodes, and below 5^QC, restrictions on the maximum allowable power supplied by the battery can limit the performance of the relevant vehicle.

In order to overcome this difficulty it is necessary, in cold conditions, to evenly and safely heat the battery cells, in a relatively short time, up to a minimum effective operating temperature. A suitable heater should be as close to the cells as possible such as in the cell packaging. Such a heater should also take up minimal space; should be of light weight; and should ensure that as much heat as possible goes into the battery module rather than into the structures around it. This is because the power for the heating comes from the batteries themselves and, when heating while driving, any wasted power results in an unnecessary reduction in driving range.

When re-charging such a battery in cold conditions, the charging current will firstly be diverted to the heater until such time as an acceptable temperature is reached, whereupon normal charging is commenced.

When charging a lithium ion battery, it is also necessary to equalize or balance the cells in a series string so that each cell is charged to the same voltage. Imbalances in the string of charged battery cells may limit the maximum capacity of the battery to the capacity of the lowest and weakest cell.

Charge balancing may be what is referred to as active balancing in which charge is removed from one cell and delivered to another in methods known as charge shuttle (flying capacitor); charge distribution (using capacitors) and inductive shuttle charge distribution (using inductors). On the other hand it may be what is referred to as passive balancing in which dissipative techniques find the cells with the highest charge in a battery module and remove excess energy through a bypass resistor until the voltage or charge matches the voltage of the weaker cells in the module. In passive balancing, energy is drawn from the most charged cell and is wasted as heat.

Published international patent application WO2006015082 to EnerDel Inc describes a method and apparatus for warming up cold temperature lithium chemistry batteries using a temperature sensor configured to generate a temperature signal indicative of a temperature of the cells of a multi-cell battery. The cells are coupled to a respective balancing circuit having a dissipative resistor that is selectively shunted across the cell for dissipating charge from the most highly charged cells to achieve cell-to-cell balancing. When the temperature is below a temperature threshold, a battery controller engages the balancing resistors to dissipate energy and generate heat to warm up the cells. The cold-temperature shunting is discontinued when a warm-up threshold is reached. United States patent application US20080226969 to EnerDel Inc describes a battery pack assembly preferably made up of a plurality of lithium ion cells in which a heating device is formed of a flexible material including a meandering heating strip that flexes and envelops, or at least partly covers, a battery pack of cylindrical cells. A thermal sensor is surrounded by the heating strip to sense the temperature of the battery pack. Electric current is applied to the heating strip to heat the battery pack when its temperature falls too low. The heating device also includes a plurality of tabs extending beyond the peripheral sides of the heating device for direct connection to the cells. Thus, electric current for the heating strip is provided directly from the cells of the battery pack. Published international patent application WO200801 1095 to A123 SYSTEMS INC describes a system for balancing energy delivery devices within one or more battery packs and for providing isolated monitoring of the battery packs. The system includes a balancing circuit for each adjacent pair of energy delivery devices. The balancing circuit adjusts charge stored in each energy delivery device of the pair so that the charge stored in the energy delivery devices of the pair is substantially equal, and the charge stored in each energy delivery device remains above a threshold. The system also includes a voltage monitoring module for sequentially selecting each of the energy delivery devices and providing a voltage associated with the selected device at an output port. The voltage monitoring module uses a low on-resistance differential multiplexer to select each of the energy delivery devices. There is thus a need for a battery stack or a battery module of the type having a plurality of cells, generally arranged in cell stacks, with an integrated heater operable by electrical energy.

There is also a need for a battery module of the type having a plurality of cells, generally arranged in parallel cell stacks, in which an energy balancing arrangement is provided.

There is still further a need for a heater panel for inclusion in a battery stack or battery module according to the invention.

SUMMARY OF THE INVENTION

In accordance with a first aspect of this invention there is provided a battery component comprising at least two cells of a pouch or prismatic type characterized in that an electrical resistance heater panel is sandwiched between two adjacent cell units with the heater panel extending over a substantial area of the cell units. Further features of the first aspect of the invention provide for the heater panel to comprise at least one electrically insulating support layer having one surface carrying an electrically conductive heating element having an appropriate resistance; for the heater panel to be of the nature of a printed circuit board in which the heating element is formed utilizing a printed circuit board production process to form a sinuous heating element; for the heating element to terminate in contacts at or adjacent an edge region of the support layer; for the support layer to have an area thereof forming an outwardly projecting connection tab having a plurality of contacts associated therewith; for the support layer to be generally rigid or semi-rigid of the nature of a conventional printed circuit board support layer; for the support layer to carry a pair of signal carrying electrical conductors terminating at one or more suitable locations for one or more temperature sensors with the signal carrying electrical conductors terminating in contacts at an edge region of the panel, preferably an outwardly projecting connection tab; and for at least one temperature sensor to be located at an operatively lower edge region of the heater panel.

Still further features of the invention provide for the support layer of the heater panel to carry an under-voltage isolator element and that operatively prevents the heater from operating if the cell voltage is below an acceptable lower limit; for the support layer to carry a static protection element that operatively prevents over-voltage transients and electro-static discharge from damaging the cell heater circuitry; and for a fuse to be included on the support layer for the purpose of isolating the heater element in the event of excessive current flowing through the heater element.

In one variation of the invention conductors communicating with the heating element terminate in contacts at an edge of the support layer, typically on an outwardly projecting tab and control of electrical current to the heating element is achieved by a switch carried by a battery control circuit board. In another variation of the invention the conductors communicating with the heating element terminate in contacts inwards of the edge of the support layer and the contacts are arranged to be permanently connected to the contacts of other heater panels associated with the same battery module with a control switch for the heating element being mounted on the support layer with control conductors communicating with contacts at the edge of the support layer that in turn become connected to a battery control circuit board in the assembled condition. In accordance with a second aspect of the invention there is provided a cell stack comprising a plurality of generally planar pouch or prismatic cells, characterized in that an electrical resistance heater panel is interposed between selected adjacent cells of the cell stack. Further features of this aspect of the invention provide for electrical contacts to be provided at or immediately inwards of an edge region of the heater panels for connecting an electrical supply to the heater panels as and when appropriate; for the electrical connection to the heater panels to be controlled by a control circuit; and for a plurality of cell stacks to be arranged together as a battery module with the cells of each cell stack being connected in parallel with each other and the cell stacks being connected in series.

Still further features of the invention provide for each cell stack to have heat dissipating, thermally conductive separator panels between adjacent cells of a cell stack for dissipating heat; and for the control circuit to include a voltage monitoring facility for cells in the cell stack or module with a control function being included to enable any one or more cells or cell stacks having a voltage higher than that of other cells in the stack or cell stacks to switch on the heater panels to dissipate excess electrical energy and enable the control circuit to even out the voltages of the cells in the cell stack or cell stacks in the module with excess energy being dissipated by way of the heat dissipating separator panels. In accordance with a third aspect of the invention there is provided a heater panel in the form of a printed circuit board formed to provide an electrically conductive heating element that serves as a resistance heating element for the purpose of heating a battery cell stack, in use.

A further feature of this aspect of the invention provides for the printed circuit board to also have signal carrying electrical conductors between contacts located in an edge region of the printed circuit board and a location for a thermal sensor for sensing temperature within a cell stack.

The above and other features of the invention will become more apparent from the following more detailed description thereof wherein reference is made to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:-

Figure 1 is an isometric illustration of a battery module made

multiple cell stacks;

Figure 2 is an exploded perspective view of one cell stack taken from one end of the top thereof;

Figure 3 is a schematic end view of one cell stack;

Figure 4 is an elevation of the electrically conductive side of a simpler embodiment of printed circuit board heater panel; Figure 5 is a schematic circuit diagram of part of the control circuit of a battery module; and, Figure 6 is a view similar to Figure 4 of a more sophisticated embodiment of printed circuit board heater panel according to the invention. DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

In one embodiment of the invention of which the various components are illustrated in the drawings, a battery module (1 ) comprises six cell stacks (2) connected in series with each other and wherein each cell stack is composed of five individual pouch cells (3) (each of which has multiple parallel connected anodes and cathodes within the pouch).

In this particular embodiment of the invention each cell stack has two heater panels with the one heater panel being sandwiched between an outer pouch cell (3a) of the stack and the next adjacent inner cell pouch. Each heater panel extends over a substantial area of the cell pouches and consists of a printed circuit board (4) having a sinuous electrical conductor formed that is to serve as the electrically conductive heating element (5) on the surface of an electrically insulating support panel in the normal manner of production of printed circuit boards.

The sinuous conductor is designed as a heating element so as to have an appropriate resistance for generating the required heat from electricity that may emanate from the individual cells of a cell stack or from a charging electrical supply. The production process of the heater panels enables the design of the heating element to be fine-tuned to achieve the required value of the heater resistance. If the width of the heating element (track) is selected appropriately a standard copper thickness of 35μιτι (micrometre) can be used to achieve the necessary resistance. By using a standard printed circuit board stock, costly carbon tracks or variable plating-up processes can be avoided. It is also possible to use conventional FR4 printed circuit board in a thin layer rather than more expensive "flexi" printed circuit board films. Such a printed circuit board is only 0.3mm thick, which is thin enough to be fitted in-between the cells without requiring unique, pocketed cell support structures. The thickness can be reduced even further by removing the copper on the opposing side (which is not serving any purpose in this application). Functional estimates indicate a heater that would produce about 20W of heating when connected to a 4V cell. The result was a heater with a 0.8 Ω resistance track. A serpentine track was chosen to minimize any inductive effects.

In the embodiment of the heater panel illustrated in Figure 4, the electrically conductive heating element terminates in contacts (6) on an outwardly projecting connection tab (7) positioned centrally up the height of an edge of the electrically insulating support layer so that the tab projects outwardly from the cell stack between the usual laterally offset cell terminals (8) for connecting the individual cells to each other. The construction of the cell stacks may include the use of cell trays of basically known type that serve to locate the cells relative to each other.

In addition to the heating element, the printed circuit board of the heater element of the embodiment of the invention illustrated in Figure 4, also has a pair of signal carrying electrical conductors (10) terminating at a suitable location for a temperature sensor (1 1 ) with the signal carrying electrical conductors terminating in contacts (12) on the outwardly projecting connection tab. A single temperature sensor is, in this instance, located approximately centrally along the lower edge region of the heater panel. It should be noted that this arrangement of temperature sensor avoids any risk of damaging the cell by a conventionally mounted sensor. The electrical connection to the heater panels is controlled by a control circuit, indicated by numeral (15) in Figure 5, that includes a voltage monitoring facility for each cell stack with a switching arrangement being included to enable any one or more cell stacks having a voltage higher than that of other cell stacks to be connected to the heater panels to dissipate electrical energy and even out the voltages of the cells in the module.

In order to dissipate such heat as well as dissipating heat generated during use of the battery, each cell stack has heat dissipating, thermally conductive separator panels (16) between adjacent cells of a cell stack such that each side surface of each cell contacts an adjacent heat conductive separator panel (other than an end panel). These separator panels have upwardly directed extensions (17) projecting out of the cell stack for dissipating heat into the surrounding air that may be subjected to a forced draft from time to time as may be required.

Thus, during charging, when it is necessary to equalize or balance the cells in a series string, so that each is at the same voltage for optimal pack performance, the excess electrical energy is passed through the relevant heater panels and dissipated in the form of heat by way of the thermally conductive separator panels. This arrangement can dissipate significantly more power and balance the cells several times faster than prior art methods of which applicant is aware as the power is dissipated away from any control circuits. The cell temperatures will generally rise slightly, but this can be managed in the usual way.

The embodiment of the invention illustrated in Figure 4 incorporates cell temperature monitoring by way of the temperature sensors that are carried by the printed circuit boards of the heater panels and are therefore simple to incorporate into the control circuit thereby resulting in several cost savings. With this arrangement, during heating, the temperature sensor will reflect the temperature of the heater panel more than the cell temperature. This is, however, desirable since the maximum allowable temperature of the printed circuit board heater can be monitored in this way. Once heating has been completed, the generally thin printed circuit board heater panel will rapidly adopt the same temperature as the surrounding cells.

It should be noted that the thin protruding printed circuit board connection tab may, as may be required, be provided with a stiffening back-end. Physical tests may be used to determine whether or not any stiffening is required.

As an alternative to using contacts located at the edge of the tab for supplying electrical energy to the heating element, the more sophisticated embodiment of the invention that is illustrated in Figure 6 may be employed. In this instance the sinuous heater element (21 ) is electrically connected to a pair of spaced contacts (22) that assume the form of generally rectangular electrically conductive pads having a suitable surface finish and optionally texture to ensure good electrical contact. One of such contacts (22) is located inwards of the edge of the support layer on each side of an outwardly projecting tab (23) so that the more heavy duty electrical currents that need to be transferred to the heating element may be transferred directly from one pair of contacts to the other, optionally by way of other conductors, in a stack of cells. In this instance it is necessary that a control switch (24) be included on the support layer of the heater panel in the electrical circuit to the sinuous heater element and the control switch (24) is controlled by way of control conductors (25) that terminate in control contacts (26) on the tab for connection to the battery control circuit. This has two advantages in that electrical current is more effectively transferred to the heating element using such enlarged contacts and it removes the physical switch from the battery control circuit board. With this arrangement the contacts communicating with the heating element terminate in contacts permanently connected to the contacts of other heater panels associated with the same battery module.

In order to ensure proper alignment of the power contacts (22), the support layer of this embodiment of the invention has a pair of holes (27) through the heater panel towards the corners of the panel associated with the site from which the tab projects. These holes, in use, receive formations (28) shown in dotted lines that are associated with the cell trays that serve to locate the cells come in use.

In this more sophisticated embodiment of heater panel according to the invention, there are two temperature sensors (31 , 32), the one (31 ) being located in the central region of the lower edge of the heater panel with the other (32) being located near the edge of the heater panel from which the tab projects. This arrangement enables an enhanced average temperature to be detected and also enables excessive temperature near the tab to be sensed.

In this more sophisticated embodiment of heater panel, the support layer of also carries an under-voltage isolator element (33) that operatively prevents the heater from operating if the cell voltage is below an acceptable lower limit that is selected according to the design of the heater panel and the properties of the cells.

The support layer in this embodiment of the invention also carries a static protection element (34) that operatively prevents over-voltage transients and electro-static discharge from damaging the cell heater circuitry.

Still further, this embodiment of the invention includes a fuse (35) on the support layer for the purpose of isolating the heater element in the event of excessive current flowing through the heater element as would occur in the event of a circuit failure. The invention therefore also provides for the use of the cell heater panels for dissipating excess electrical energy and in place of the conventional bypass resistors for balancing the cells when charging a battery module. When used as a heater, the heater panel spans the full extent of the cells and thus ensures a uniform heat transfer to the cells. It also helps to locate the heater inside the cell tray with very little play.

The invention therefore provides a simple yet highly effective cell stack and battery module arrangement with integrated heater panels that may also serve to dissipate excess electrical energy in order to achieve cell balancing during charging.

Numerous variations may be made to the embodiment of the invention described above without departing from the scope hereof.

Claims

CLAIMS:

1 . A battery component comprising at least two cells of a pouch or prismatic type characterized in that an electrical resistance heater panel is sandwiched between two adjacent cell units with the heater panel extending over a substantial area of the cell units.

2. A battery component as claimed in claim 1 in which the heater panel comprises at least one electrically insulating support panel having one surface carrying an electrically conductive heating element having an appropriate resistance.

3. A battery component as claimed in either one of claims 1 or 2 in which the heater panel is of the nature of a generally rigid or semi-rigid printed circuit board in which the heater element is a sinuous printed circuit board conductor.

4. A battery component as claimed in any one of the preceding claims in which the heating element terminates in contacts at or adjacent an edge region of the support layer.

5. A battery component as claimed in any one of the preceding claims in which the support layer has an area thereof forming an outwardly projecting connection tab having a plurality of contacts associated therewith.

6. A battery component as claimed in any one of the preceding claims in which the support layer carries a pair of signal carrying electrical conductors terminating at one or more suitable locations for one or more temperature sensors with the signal carrying electrical conductors terminating in contacts at an edge region of the panel.

A battery component as claimed in any one of the preceding claims in which at least one temperature sensor is located at an operatively lower edge region of the heater panel.

A battery component as claimed in any one of the preceding claims in which the support layer of the heater panel carries one or more of an under-voltage isolator element that operatively prevents the heater from operating if the cell voltage is below an acceptable lower limit; a static protection element that operatively prevents over-voltage transients and electro-static discharge from damaging the cell heater circuitry; and a fuse on the support layer for the purpose of isolating the heater element in the event of excessive current flowing through the heater element.

A battery component as claimed in any one of the preceding claims in which contacts communicating with the heating element terminate in contacts at an edge of the support layer and control of electrical current to the heating element is achieved by a switch carried by a battery control circuit board.

A battery component as claimed in any one of claims 1 to 8 in which the contacts communicating with the heating element terminate in contacts inwards of the edge of the support layer and the contacts are arranged to be permanently connected to the contacts of other heater panels associated with the same battery stack with a control switch for the heating element being mounted on the support layer with control conductors communicating with contacts at the edge of the support layer that in turn are operatively connected to a battery control circuit board in the assembled condition.

1 1 . A cell stack comprising a plurality of generally planar pouch or prismatic cells, characterized in that an electrical resistance heater panel is interposed between selected adjacent cells of the cell stack.

A cell stack as claimed in claim 1 1 in which electrical contacts are provided at or immediately inwards of an edge region of the heater panels for connecting an electrical supply to the heater panels as and when appropriate.

13. A cell stack as claimed in claim 12 in which the cell stack has heat dissipating, thermally conductive separator panels between adjacent cells of the cell stack for dissipating heat and a control circuit includes a voltage monitoring facility for cells in the cell stack or module with a control function being included to enable any one or more cells or cell stacks having a voltage higher than that of other cells in the stack or cell stacks to switch on the heater panels to dissipate excess electrical energy and enable the control circuit to even out the voltages of the cells in the cell stack or cell stacks in the module with excess energy being dissipated by way of the heat dissipating separator panels..

14. A heater panel in the form of a printed circuit board formed to provide an electrically conductive heating element that serves as a resistance heating element for the purpose of heating a battery component or cell stack, in use.

15. A heater panel as claimed in claim 14 and in which the heater panel is configured especially for use in a battery component as claimed in any one of claims 1 to 10 or in a cell stack as claimed in any one of claims 1 1 to 13.