GB2379553A

GB2379553A - Electrochemical cell and onboard circuit board.

Info

Publication number: GB2379553A
Application number: GB0120831A
Authority: GB
Inventors: Frederik Flemming
Original assignee: Danionics AS
Current assignee: Danionics AS
Priority date: 2001-08-28
Filing date: 2001-08-28
Publication date: 2003-03-12
Also published as: GB0120831D0

Abstract

A cell unit 10 has a cell 2 and associated electronic circuit board 12 carrying for example charge/discharge control circuitry or temperature monitoring circuitry. The cell may be a lithium ion cell and comprises a casing 8 with projecting terminals 8. The circuit board as at least two openings 20, with connection tabs 22 of the control circuitry extending into each opening. The connection terminals 8 and tabs 22 overly and are connected to one another. The openings allow access to both sides of each tab such that a welding operation may be used to make the connection. The tabs are stated to still be within the outer envelope of the cell such that no folding of the tabs is required to ensure that the circuit board remains close to the cell.

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 control, temperature control or other functions, as well as providing interconnects.

Usually, such additional circuitry is arranged at the end of a stack or row of individual cells, adjacent the terminals. While 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.

The control circuitry PCB is therefore attached as close to the cell or cells as possible, and in such a way to keep the total prismatic space of the cell package to a minimum. In addition, the PCB should be attached to the cell in a manner which makes handling of the package safe and easy, and provides easy connection to the cell package terminals.

Typically, the control circuitry PCB includes a first set of terminals for attachment to cell connection tabs, and a second set of terminals providing external connection to the cell package.

The first set of terminals may simply be pads on the PCB, and connection between the cell tabs and the first set of terminals is then made by soldering. However, soldering too close to the lithium ion cell should be avoided and the restricted space close to the cell makes implementing an automatic soldering process difficult.

It has therefore been proposed to provide connection tabs on the PCB during fabrication of the PCB, for example nickel tabs. These can be connected to the cell tabs using a lower temperature process, for example ultrasonic welding or spot welding. In order to keep the cell and PCB as close together as possible, the tabs of one or both of the cell and the PCB may require folding before being connected together. This adds an additional processing step, which may also be difficult to automate.

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 carrying control circuitry for the cell, the cell comprising a casing having at least one sealed end through which connection terminals project, the electronic circuit board having at least two openings, a connection tab of the control circuitry extending into each opening, wherein the electronic circuit board is located at the sealed end of the casing with the connection terminals and the connection tabs overlying each other and electrically connected to each other.

By providing the control circuitry connection tabs in openings within the board, access to both sides of each tab is obtained, so that a welding operation may be employed for connection of the tabs to the cell terminals. The tabs are still within the outer envelope of the circuit board, so that no folding of tabs is required to ensure that the circuit board remains close to the cell.

Preferably, the openings are provided at an edge of the board, and thereby define recesses in the edge. With these recesses in an edge of the board facing away from the cell, the distance of the welding location from the cell is maximised.

Preferably, the sealed end has a thickness which is less than the thickness of the remainder of the cell, and the circuit board 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. This enables the cell unit prismatic volume to be kept to a minimum.

The circuit board area may comprise first and second regions on opposite sides of a centreline, with the openings provided in one region and with connection terminals for external connection to the cell unit provided in the other region. This keeps the external connection terminals a safe distance from the cell terminals, reducing the risk of external conductors coming into contact with the cell terminals (thereby bypassing the protection circuitry).

The control circuitry preferably comprises voltage equalising components and/or temperature sensing components and/or charge control circuitry.

According to a second aspect of the invention, there is provided an electronic circuit board carrying control circuitry for an electrochemical cell and for connection to the cell, the electronic circuit board having at least two openings, a connection tab of the control circuitry extending into each opening, the connection tabs being provided for connection to terminals of the cell.

This aspect provides the circuit board used in the cell unit of the invention.

The invention also provides a method of manufacturing a cell unit comprising: manufacturing at least one electrochemical cell comprising a 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 at least two openings, a connection tab of the control circuitry extending into each opening; aligning the connection terminals with the connection tabs; mechanically and electrically connecting the connection terminals and the connection tabs. This method enables manufacture of the cell unit of the first aspect of the invention. The need to fold tabs is avoided, and because the connection tabs are located within openings, acess is

provided to both sides of the tabs. This enables the mechanical and electrical connection to be achieved using welding, for example spot welding or ultrasonic welding.

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 carrying control circuitry for the cell, the cell comprising a casing having at least one sealed end through which connection terminals project, the control circuitry having at least two connection tabs for connection to the cell terminals and at least two connection terminals for external connection to the cell unit, wherein the electronic circuit board is located at the sealed end of the casing with the connection terminals electrically connected to the connection tabs, wherein the circuit board area comprises first and second regions at opposite ends of the board, and wherein the connection tabs are provided in one region and the connection terminals are provided in the other region.

As discussed above, this arrangement keeps the external cell unit terminals a safe distance from the cell terminals, reducing the risk of external conductors coming into contact with the cell terminals.

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 cell unit of the invention ; and Fig. 3 shows more clearly the circuit board used in the cell unit of Figure 2.

Fig. I 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 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. Connection terminals 8 project through the, or one of the, sealed ends of the cell. The terminals comprise thin metal foils. The example shows one terminal of each polarity, although more than one terminal for each polarity may 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 may be 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 Figure 2, a cell unit 10 is defined by a cell 2 and a circuit board 12. The circuit board 12 carries control circuitry 16 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. Connection pins 17 are provided for mounting of components on the circuit board, these components forming part of the control circuitry 16. The circuit board also includes external connections 18 to enable the cell unit 10 to be connected to external equipment to be powered by the cell unit, such as a mobile telephone.

The circuit board 12 is connected to the sealed terminal end of the cell, and preferably has a thickness such that the combined thickness of the sealed end 4 of the cell and the circuit board 12 is less than or equal to the thickness t of the remainder of the cell. Thus, the locally thinner part of the cell at the sealed end of the cell is at least partially occupied by the circuit board. The overall thickness is then not increased by the circuit board. The thickness of the cell is typically the smallest dimension, and therefore increasing the thickness of the required prismatic volume provides the greatest reduction in energy density.

In the specific example shown in Figure 2, the length of the circuit board is approximately equal to the length I of the sealed end of the cell. This length I corresponds to the width of the rectangular cell.

In accordance with the invention, and as shown more clearly in Figure 3, the circuit board has two openings 20. A connection tab 22 of the control circuitry 16 extends into each opening. These connection tabs 22 are for connection of the circuitry 16 to the cell terminals 8. The openings 20 are provided along an edge 24 of the board, and thus define open recesses. It is, however, equally possible for the openings to be away from the edges of the circuit board.

In the example shown, the openings 20 are in an edge of the circuit board 12 to be furthest from the cell, so that connection between the cell terminals 8 and the tabs 22 is as far as possible from the cell, but without requiring folding of the tabs 22 or terminals 8.

In accordance with one preferred aspect of the invention, the circuit board area comprises first and second regions at opposite ends of the board. The openings 20 (and therefore the tabs 22)

are provided in one region on one side of a centreline 26, and the external connection terminals 18 are provided in the other region, on the other side of the centreline 26. This physically separates the external connections to the cell unit from the cell terminals 8, and thereby reduces the risk of accidental short circuit to the cell terminals during mounting of the cell unit to the client equipment.

In order to provide this arrangement, the conventional cell configuration shown in Figure 1 is modified to locate both (or all) terminals 8 to one side of the sealed end of the cell, as shown in Figure 2.

The circuit board is fabricated in a known manner. For example, the circuit board 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 board may be 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.

During assembly of the cell unit, the electronic circuit board is attached to the sealed end of the cell, for example using double sided tape. Preferably, the back side of the circuit board (opposite the side carrying the mounted components) is connected to the cell. This tape connects the lower part of the board to the sealed end of the cell, and only covers the lower part ofthe circuit board. In this way, both sides of the tabs 22 and the external connections 18 (which are nearer the top of the board) are still exposed within the openings, so that welding of the circuit board tabs to the terminals is easily carried out. No folding or bending of the tabs or terminals is required. The circuit components 16 are on the other half of the board, so that they are protected from the heat generated by the welding process. Furthermore, the welding takes place at the top edge of the board, away from the cell.

The tabs and terminals can be relatively short, so that connection between them provides a stable mounting of the circuit board to the cell.

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 tab-terminal connections, 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 external connection terminals 18 are also preferably accessible from both sides, so that the cell unit can easily be attached to the customer equipment using welding or soldering, and with the safety circuitry operating to protect the cell during this 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 transmitting 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 carrying control circuitry for the cell, the cell comprising a casing having at least one sealed end through which connection terminals project, the electronic circuit board having at least two openings, a connection tab of the control circuitry extending into each opening, wherein the electronic circuit board is located at the sealed end of the casing with the connection terminals and the connection tabs overlying each other and electrically connected to each other.

2. A cell unit as claimed in claim 1, wherein the openings are provided at an edge of the board.

3. A cell unit as claimed in claim 2, wherein the openings are provided at an edge of the board facing away from the cell.

4. A cell unit as claimed in any preceding claim, wherein the cell comprises a laminate structure encased in a foil casing.

5. A cell unit as claimed in any preceding claim, wherein the sealed end has a thickness which is less than the thickness of the remainder of the cell, and the circuit board 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.

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

7. A cell unit as claimed in any preceding claim, wherein the circuit board area comprises first and second regions at opposite ends of the board, and wherein the openings are provided in one region and connection terminals for external connection to the cell unit are provided in the other region.

8. A cell unit according to any preceding claim, wherein the at least one cell is square or rectangular and the circuit board is rectangular.

9. A cell unit according to any preceding claim, wherein the control circuitry comprises voltage equalising components and/or temperature sensing components and/or charge control circuitry.

10. A cell unit according to any preceding claim, comprising a plurality of cells and a single associated circuit board connected to one of the cells.

Il. A cell unit according to any preceding claim, in which the electrochemical cell comprises a lithium-ion cell.

12. An electronic circuit board carrying control circuitry for an electrochemical cell and for connection to the cell, the electronic circuit board having at least two openings, a connection tab of the control circuitry extending into each opening, the connection tabs being provided for connection to terminals of the cell.

13. A circuit board as claimed in claim 12, wherein the openings are provided at an edge of the board.

14. A circuit board as claimed in claim 12 or 13, wherein the circuit board area comprises first and second regions at opposite ends of the board, and wherein the openings are provided in one region and connection terminals for external connection to circuit board are provided in the other region.

15. A circuit board as claimed in any one of claims 12 to 14, wherein the control circuitry comprises voltage equalising components and/or temperature sensing components and/or charge control circuitry.

16. A method of manufacturing a cell unit comprising: manufacturing at least one electrochemical cell comprising a 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 at least two openings, a connection tab of the control circuitry extending into each opening; aligning the connection terminals with the connection tabs; mechanically and electrically connecting the connection terminals and the connection tabs.

117 A 11

17. A method as claimed in claim 16, wherein the mechanical and electrical connection is achieved using welding. achieved using welding.

18. A cell unit comprising at least one electrochemical cell and an associated electronic circuit board carrying control circuitry for the cell, the cell comprising a casing having at least one sealed end through which connection terminals project, the control circuitry having at least two connection tabs for connection to the cell terminals and at least two connection terminals for external connection to the cell unit, wherein the electronic circuit board is located at the sealed end of the casing with the connection terminals electrically connected to the connection tabs, wherein the circuit board area comprises first and second regions at opposite ends of the board, and wherein the connection tabs are provided in one region and the connection terminals are provided in the other region.

19. A cell unit as claimed in claim 18, wherein one region is to one side of a centreline of the electronic circuit board and the other region is to the other side of the centreline.

20. A cell unit as claimed in claim 19, wherein the electronic circuit board is rectangular.

21. A cell unit as claimed in any one of claims 18 to 20, wherein the cell comprises a laminate structure encased in a foil casing.

22. A cell unit as claimed in any one of claims 18 to 21, wherein the circuit board has a width corresponding substantially to a width of the sealed end of the cell.