WO2004093221A2

WO2004093221A2 - Electrochemical cells

Info

Publication number: WO2004093221A2
Application number: PCT/EP2004/003981
Authority: WO
Inventors: Allan Knudsen; Erik Christensen; Jesper Villekjaer; Peder Madsen
Original assignee: Danionics International A/S
Priority date: 2003-04-17
Filing date: 2004-04-08
Publication date: 2004-10-28
Also published as: WO2004093221A3

Abstract

A cell unit has a cell and an electronic circuit board assembly. The circuit board assembly has a rigid part 13 and a flexible part 14, the rigid part 13 being arranged at a sealed and narrowed end of the cell and being connected to the cell terminals. The flexible part extends 14 from the rigid part so as to partly overlie the cell, and the flexible part is bendable to a position in which it extends away from the cell for connection to a host device. In another arrangement, the rigid part is at the opposite end of the cell, and the flexible part extends to the other end of the cell and provides the connections to the cell terminals.

Description

ELECTROCHEMICAL CELLS

The present invention relates to electrochemical cells, in particular an arrangement of a cell or cells provided with additional electrical circuitry on an associated circuit board.

In recent years there have been large advances in the design and production of batteries. In particular, lithium-ion batteries provide many advantages over conventional nickel cadmium batteries. Lithium-ion batteries can be formed by flattened "jelly-rolls" of interleaved electrodes and electrolyte, the thus formed electrical cell being packaged in a flexible pack formed, for example, from thin laminated foil material. Other types of cell may also be manufactured using this construction technique. In recent years, it has become popular to seal such flattened jelly rolls within flexible housings. This sealing technique prevents leakage, and has become a popular production method, for example for polymer lithium ion batteries, using a gelled or solid polymer electrolyte.

The widths and lengths of the flattened jelly rolls can be freely selected, as can the thickness of the cells. This flexibility of design, and the flexibility of the finished cell, makes polymer lithium-ion cells particularly suitable for use in portable telephones and computers, as well as in other electronic devices where space is at an absolute premium. It will be well understood that a compromise must often be reached between the energy to be delivered by a battery and the space available for the battery.

Examples of lithium-ion cells construction and the use of flexible packages for such cells are described in more detail in, for example, WO-A-97/03475 (Danionics), EP-A-0845821 (Sanyo), US 5609974 (Battery Engineering), US 4997732 (MHB), US 5478668 (Bell), WO-A- 95/13629 (Valence), US 5591540 (Motorola), US 5716421 (Motorola) and US 5445856 (Gill).

There is a general demand for cell units to include both an electrochemical cell or cells and an electronic circuit board having control circuitry, for example for safety reasons. The circuitry may provide charge monitoring/control, temperature monitoring/control or other functions, as well as providing interconnections.

Usually, such additional circuitry is arranged at the end of a cell or a stack or row of individual cells, adj acent the temiinals . Wliile attempts are made to optimise the energy density of the cells, the energy density of the cell unit, including the control circuitry, is compromised by the space occupied by the control circuitry. There is an ever present demand for further space saving so that the maximum energy density can be achieved, particularly for cell units to be used in mobile phones etc.

Electrochemical cells are often produced as relatively thin square or rectangular cells-, as described in the above-mentioned US patent 5445856. The production method of the cells - often by winding strips of electrodes and separator- gives rise to the square or rectangular shape. The cells are then generally sealed within packages of foil or foil laminate material, for example using a conventional blister-pack sealing process. Alternatively, the cells are sealed in the foil using a so-called "flow-packing" process, wherein cells are placed between unrolling sheets of laminate material. Such a process is described, for example, in WO-A-97/38905 and WO-A-02/47184. ha US 5637418, an electrochemical cell stack is described in combination with a flexible circuit board. In the patent, the circuit board is folded around the electrochemical cell stack.

WO-A-01/99210 discloses a cell unit comprising at least one electrochemical cell and an associated electronic circuit board carrying control circuitry for the cell, the casing having at least one sealed end through which connection terminals project, and the sealed end having a thickness which is less than the thickness of the remainder of the cell. The circuit board is connected to the sealed end of the cell, and has a thickness such that the combined thickness of the sealed end of the cell and the circuit board is less than or equal to the thickness of the remainder of the cell. The space available for the cell unit in a portable product is typically a prismatic space. The cell unit of WO-A-01/99210 takes advantage of the locally thinner part of the cell at a sealed end of the cell to provide the circuit board. In this way, the thickness of the cell unit is not increased. With appropriate selection of the other dimensions of the board, the cell unit may occupy the same prismatic space as the cell, so that the energy density of the cell is not compromised by providing the control circuitry.

Other solutions for connecting printed circuit boards (PCBs) to electrochemical cells are known from Japanese Patents Abstract Nos. 2001-250520, 2001-250519 and 2002-124235.

According to a first aspect of the invention, there is provided a cell unit comprising at least one electrochemical cell and an associated electronic circuit board assembly, the cell having at least one sealed end through which connection terminals project, the sealed end having a thickness which is substantially less than the cell thickness, wherein the circuit board assembly comprises a rigid part and a flexible part, the rigid part being arranged at the sealed end of the cell at least partly within the space provided by the reduced thickness, the flexible part extending from the rigid part so as to partly overlie the cell, the flexible part being bendable to a position in which it extends away from the cell for connection to a host device.

The invention provides an improved cell unit which includes a printed circuit board and which has high space-efficiency and thus energy-density. Also, the cell unit should be secure and relatively easy to connect to a host device. By "secure" is meant that there is minimal risk of short circuits, of mechanical damage to the electrical components and the cell, and of accidental disconnection of the cell under normal conditions of use.

The flexible part may be of a "Z" formation and is preferably arranged centrally of the rigid part, so that it will be between the terminals of the cell.

According to a second aspect of the invention, there is provided a cell unit comprising at least one electrochemical cell and an associated electronic circuit board assembly, the cell having sealed ends of a thickness substantially less than the thickness of the cell, connection terminals protruding through one of the sealed ends, wherein the circuit board assembly comprises a rigid part and a flexible part, the rigid part being arranged at the sealed end of the cell without the temiinals at least partly within the space provided by the reduced thickness, the flexible part extending from the rigid part so as to at least partly overlie the cell and provide connections to the cell temiinals.

In this arrangement, the rigid part of the board assembly is at one end of the cell, whereas connections to the cell are at the opposite end. This keeps the cell connections remote from the main circuit board components.

Preferably, the circuit board has a width corresponding substantially to the width of the cell, hi this way, the full available area of the thinner part at the sealed end of the cell is utilised.

According to a third aspect of the invention, there is provided a cell unit comprising at least one electrochemical cell and an associated electronic circuit board assembly, the cell having sealed ends of a thickness substantially less than the thickness of the cell, connection terminals protruding through one of the sealed ends, wherein the circuit board assembly comprises a rigid part and a flexible part, the rigid part being positioned at a side of one of the at least one electrochemical cells, the flexible part extending from the ligid part so as to at least partly overlie the cell and provide connections to the cell terminals at the sealed end with the terminals.

This arrangement provides external connection to the rigid part of the circuit board assembly near a side edge of one cell, whilst the connections of the circuit board assembly to the cell temiinals are by connection between the flexible part and the end edge of the cell. Thus, a safe distance can be maintained between the cell teπriinals (i.e. tabs) and the external connections. The rigid part of the cell can be positioned wherever most convenient, namely on either side of the cell or cell assembly, and at any position along the side.

The cell unit may comprise a plurality of cells, and the flexible part of the circuit board assembly connects to the connection terminals of all of the cells and at least partly overlies all of the cells. There may, of course, be rigid parts on both opposite sides of the cell assembly.

The invention also provides a method of manufacturing a cell unit comprising: manufacturing at least one electrochemical cell comprising a laminate structure encased in a foil casing, the casing having at least one sealed end through which connection terminals project; manufacturing an associated electronic circuit board carrying control circuitry for the cell, the circuit board having a rigid part and a flexible part, wherein the thickness of the rigid part is such that the combined thickness of the sealed end of the cell and the rigid part thickness is less than or equal to the thickness of the remainder of the cell; mechanically and electrically connecting the rigid part to the sealed end of the cell; and bending the flexible part from a position overlying the cell to a position extending away from the cell.

By connecting the circuit board to the cell in its unbent state, access is provided to the rigid part for connection to the cell terminals from both sides. This simplifies the connection process.

Preferred embodiments of the present invention are described in more detail below, by example only, and with reference to the accompanying drawings wherein:

Fig. 1 illustrates a known cell having a typical shape;

Fig. 2 shows a circuit board assembly for use in a cell unit of the invention;

Fig.3 shows a front view of a cell unit according to the invention with the circuit board of Fig. 1 connected thereto;

Fig. 4 is a cross-section through the sealed end of the cell of Fig. 3 showing the flexible parts of circuit board bent into their operative positions in use with the host device (not shown);

Figs. 5a and 5b are rear and front views of a printed circuit board assembly for use in a cell unit according to the second aspect of the invention;

Fig.6 is a view showing the circuit board assembly of Fig. 5 fitted to a cell;

Fig. 7 shows a cell unit according to the third aspect of the invention; and

Fig. 8 shows the flexible part of the circuit board assembly of the cell unit of Figure 7.

Fig. 1 shows a flat electrochemical cell 2, which may be a lithium-ion battery, a different type of battery cell, or a capacitor, comprising a laminate structure encased in a foil casing. The cell is formed by the flow-packing process described above. The casing is sealed at one or both ends, and the seal defines a region 4 where the thickness is less than the thickness t of the remainder of the cell 6. Preferably, the seal is nearer the front or back of the cell, rather than being centrally positioned in cross-section, so that a greater volume is available to the front or rear of the seal. Connection terminals 8 project through the, or one of the, sealed ends of the cell, which terminals comprise thin metal foils. The example shows one terminal of each polarity, although two could be provided. The remainder of the cell has a substantially constant thickness t. The dimensions are a design parameter of the cell, but by way of example, one conventional cell size is 70mm x 32mm x 3.8mm. The internal design of the cell is not relevant to the present application, but it maybe as described in US patent number 5445856, i.e. flat wound cells around a cell-precurser housed in a thin foil laminate package.

^• As shown in Fig. 2, the circuit board assembly 12 comprises a relatively rigid part 13 and a relatively flexible part 14. The rigid part 13 has an inherent stiffness such that it cannot easily bend under normal usage, whereas the flexible part is substantially thinner and can easily be bent or folded. The rigid part 13 forms a circuit board (PCB) which is generally rectangular and is sized so as to fit along the sealed end of the cell where the temiinals protrude, i.e. within the region 4 described above. The flexible part 14 is a flexible printed circuit board and extends laterally of the rigid part 13. In tins embodiment the flexible part has a generally "Z" shape or a "dog-leg" shape, but it could have any other shape e.g. a simple square or rectangular shape. The "Z" shape illustrated provide a high degree of flexibility to the part 14. The flexible part is preferably resilient or springy, so that it will tend to maintain the same position relative to the rigid part. The flexible part can be attached to the rigid part by an Infra Red welding process. The flexible part 14 carries means 17 for connecting the cell to the host device, as discussed in more detail below.

The rigid circuit board 13 of the circuit board assembly 12 carries control circuitry 15 for the cell, for example for supervising and controlling the cell condition, for controlling the charging or discharging conditions and/or for carrying out other functions for example safety related functions. The rigid part also carries tabs 16 for connection to the temiinals of the cell. The tabs extend away from the opposite edge of the rigid part to the edge from which the flexible part extends. The rigid circuit board preferably has SMD components, i.e. surface mounted components. The PCB is thus formed using advantageous SMD technology, which is suitable for use with rigid PCBs. This type of PCB also keeps the overall thickness of the PCB as low as possible.

Fig. 3 shows the circuit board assembly of Fig.2 attached to a cell such as shown in Fig. 1. The rigid part of the circuit board is located in the region 4 of the cell, taped into place by a label or tape 18 which also protects the circuitry and components. With the rigid part attached to the cell, the flexible part 14 will lie over the front of the cell. Because this part is thin, it will not add substantially to the thickness of the cell. More significant, however, is the fact that the flexible part is in a position which is within the overall envelope defined by the shape of the cell so that it does not interfere with the handling of the cell during the final operational steps, e.g. charging. The flexible part is preferably arranged centrally of the rigid part, so that it is between the teπninals of the cell and thus does not interfere in any way with the welding of the terminals to the rigid part. The sectional view of Fig.4 shows the connection of the tabs 16 of the rigid circuit board 13 to the temiinals 8 of the cell. The tabs 16 are bent back behind the board so as to sandwich the terminals 8 between the tabs 16 and the board 13. The tabs 16 can be connected to me terminals 8 by means of an automatic welding process, in a known fashion. It will be appreciated that during this process the flexible part 14 is in a position away from the welding area. Fig.4 also shows the flexible part bent over into its position for attachment to the host device, i.e. bent back through approximately 180 degrees. The connectors 17 on the side of the flexible part are connected to the host device, for example by plugging in or clamping, and this connection keeps the flexible part in place while the cover of the host device is closed.

The rigid circuit board is fabricated in any known manner. The flexible part can be a flexible circuit board, e.g. a so-called "flex print circuit board", where the circuit is printed onto a flexible insulating substrate, and then preferably coated by a further insulating substrate. Alternatively, the flexible part maybe provided with components on one side of a single flexible substrate. The printed substrate could be formed by etching a copper-clad flexible board having a copper conductor and a base film of polyamide.

As shown in Fig.2, the circuit components 15 are on the remote part of the rigid board from the bent over tabs 16, so that they are protected from the heat generated by the welding process. The board can be attached to a charged cell, or else the cell may be discharged during connection to the circuit board, so as to eliminate the risk of short-circuiting the cell during welding. The cell can subsequently be partly charged (for supply to the customer) using the tabs, which are then covered with insulating tape. The safety circuit for the cell is thus attached to the cell at an early stage in the production of the cell unit. Once the tabs have been insulated, safety in the handling of the cell unit is improved.

The cell unit is supplied for connection to external circuitry with the flexible circuit board still in the unbent state. Connection terminals 17 for connection to the host device are provided on the upper side of the flexible board when in the unbent position of Fig. 3, so that these are easily attached to the corresponding components on the hosting device.

Cells are typically supplied in a partly charged state. This is because the charging parameters for the first charge are critical, so this operation is performed by the manufacturer. Hoλvever, this has implications on the safety of handling and transport of the cells, hi particular, the circuit board is preferably provided with short circuit protection. The connection temiinals are insulated so that the exposed terminals of the cell unit are coupled to the cell only through the short circuit protection device, for example a fuse.

The second aspect of the invention is exemplified by the circuit board assembly shown in Figs. 5a and 5b, this assembly being for connection to a cell such as shown in Fig.l. The assembly comprises a rigid part 23 similar to the rigid PCB 13 of Fig. 2. A flexible part 24 extends sideways from the rigid part. The flexible part is an elongate rectangular shape and extends at an angle of substantially 90 degrees to the rigid part. At its end remote from the rigid circuit board, the flexible part has a wider section 25 which includes tabs 26 for connection to the teπninals 8 of the cell.

The circuit board assembly of Figs. 5a and 5b is dimensioned such that the rigid circuit board 23 can be positioned in the space alongside one sealed end of the cell while the tabs 26 are positioned for connection to the terminals of the cell. It will be understood that the rigid circuit board 23 is thus arranged at the sealed end of the cell opposite to the end from which the terminals protrude. Figure 5a shows one side of the arrangement, which in use is the side facing the cell, and hence pressing against the cell. Figure 5b shows the opposite side, which will face outwardly when connected to the cell.

The fitting of the circuit board assembly to the cell is illustrated in Fig. 6. As shown, the tabs are bent over after connection to the terminals of the cell.

This arrangement has the advantage that circuit board is remote from the terminals. It is easier to avoid short circuits of the terminal/tab connections and of the circuitry of the PCB. Also the PCB is kept remote from the operation to connect the tabs to the terminals and there is a greater freedom to design the PCB as the location of the terminals is no longer a design issue which needs to be factored in.

Obviously with the terminal connection being at the opposite end of the cell to the rigid circuit board, longer connections are required. Preferably these connections are foimed by a flat PCB or flat wires mounted on a foil, so that the thickness of the flexible part is not significant. In a preferred embodiment, the flexible part is sized and positioned relative to the rigid part such that in use it locates on the surface of the cell, adjacent the fin seal of a conventionally flow-packed cell. This means that the overall prismatic volume of the cell is not increased by the flexible part (or by the rigid part at the end seal).

The third aspect of the invention is exemplified by the circuit board assembly shown in Figs. 7 and 8.

In the example shown in Figure 7, two cells 30 together define a cell assembly. The circuit board assembly again has a rigid part 32 and a flexible part 34. The rigid part 32 is positioned at a side of one of the cells 30 and carries a connector plug 36 as well as electronic components (not shown). The flexible part 34 extends from the rigid part 32 and is connected to it with two tabs 38. The flexible part at least partly overlies both cells and provides connections 40 to the cell terminals.

The flexible PCB part should be as thin as possible, in order not to increase the thickness of the cell significantly. The rigid part containing the electronic components/plug is attached to the top of the flexible part, outside the cell region in this example.

The two cells are, in the example shown, connected to the same edge of the flexible part 34.

An advantage of this construction is that there is a more safe distance between external connections and battery tabs. In general,^' there is a higher freedom in the design of the pack, as the rigid PCB part can be placed where most convenient and not necessarily at the.tab end of the cell as in the examples above. The flexible part 34 of the circuit board assembly further makes it possible to level out differences in levels between the cell casings and the PCB casing. The current connection tabs of the flexible part 34 can be made relatively wide and thin so that the impedance of the cell can be kept low and the thickness is not increased significantly.

Figure 8 shows the shape of the flexible part of the circuit board assembly, using the same references as in Figure 7 for the various tabs.

The invention is applicable to cell units formed by any manufacturing process, for example the flow-packing process or a blister-packing process. The invention applies equally to electrochemical capacitor cells as to battery cells. The design of such electrochemical capacitor cells is similar to that of lithium-ion cells. An example of such a capacitor - sometimes known as a "super capacitor" - is described in more detail in US Patent 5646815 (Medtronic) or in EP-A- 0625787 (Matsushita). Generally speaking, electrochemical capacitors, either based on the double layer principle or on the pseudo-capacitance principle, differ from batteries in providing high discharge rates over a short length of time, whereas batteries are better suited to providing a power output over a longer period of time. Electrochemical capacitors also tend to be able to be recharged many more times than batteries. In some situations, the capacitors can replace batteries and in other situations they can be used together with batteries, for example as load levelling devices. The capacitors can also be used as memory back-up elements in electronic devices, and in mobile transr tting equipment, for example in connection with mobile telephones where there is a demand for high current rate pulses. In this context, therefore, a combination of capacitors and high density battery cells is often required. In connection with capacitors, the circuitry is required for load levelling functions rather than for safety.

The advantages of the invention will be apparent from the above description. However, the invention is not limited to the details of the above examples of the invention.

Claims

1. A cell unit comprising at least one electrochemical cell and an associated electronic circuit board assembly, the cell having at least one sealed end through which connection terminals project, the sealed end having a thickness which is substantially less than the cell thickness, wherein the circuit board assembly comprises a rigid part and a flexible part, the rigid part being arranged at the sealed end of the cell at least partly within the space provided by the reduced thickness, the flexible part extending from the rigid part so as to partly overlie the cell, the flexible part being bendable to a position in which it extends away from the cell for connection to a host device.

2. A cell unit as claimed in claim 1 , wherein the flexible part has a bend region at a region of connection to the rigid part, and a component-carrying region wider than the bend region.

3. A cell unit as claimed in claim 1 or 2, wherein the flexible part is arranged centrally of the rigid part between the terminals of the cell.

4. A cell unit as claimed in any preceding claim, wherein the rigid part has tabs connected to the terminals of the cell.

5. A cell unit comprising at least one electrochemical cell and an associated electronic circuit board assembly, the cell having sealed ends of atliickness substantially less than the thickness of the cell, connection terminals protruding through one of the sealed ends, wherein the circuit board assembly comprises a rigid part and a flexible part, the rigid part being arranged at the sealed end of the cell without the tenninals at least partly within the space provided by the reduced thickness, the flexible part extending from the rigid part so as to at least partly overlie the cell and provide connections to the cell tenninals at the sealed end with the tenninals.

6. A cell unit as claimed in any preceding claim, wherein the circuit board has a width conesponding substantially to the width of the cell.

7. A cell unit comprising at least one electrochemical cell and an associated electronic circuit board assembly, the cell having sealed ends of a thickness substantially less than the thickness of the cell, connection terminals protruding through one of the sealed ends, wherein the circuit board assembly comprises a rigid part and a flexible part, the rigid part being positioned at a side of one of the at least one electrochemical cells, the flexible part extending from the rigid part so as to at least partly overlie the cell and provide connections to the cell terminals at the sealed end with the terminals.

8. A cell unit as claimed in claim 7, comprising a plurality of cells, and wherein the flexible part of the circuit board assembly connects to the connection terminals of all of the cells and at least partly overlying all of the cells.

9. A cell unit as claimed in claim 7 or 8 , wherein the circuit board has a width corresponding substantially to the length of the cell.

10. A cell unit as claimed in any preceding claim, wherein the rigid part comprises a rigid printed circuit board.

11. A cell unit as claimed in any preceding claim, wherein the flexible part comprises a flexible printed circuit board.

12. A cell unit as claimed in any preceding claim, wherein the flexible part is attached to the rigid part by an infra red welding process.

13. A cell unit as claimed in any preceding claim, wherein the rigid part canϊes control circuitry for the cell arranged as SMD components.

14. A method of manufacturing a cell unit comprising: manufacturing at least one electrochemical cell comprising a laminate structure encased in a foil casing, the casing having at least one sealed end through which connection tenninals project; manufacturing an associated electronic circuit board canying control circuitry for the cell, the circuit board having a rigid part and a flexible part, wherein the thickness of the rigid part is such that the combined thickness of the sealed end of the cell and the rigid part thickness is less than or equal to the thickness of the remainder of the cell; mechanically and electrically connecting the rigid part to the sealed end of the cell; and bending the flexible part from a position overlying the cell to a position extending away from the cell.