GB2450794A

GB2450794A - Battery with temperature-dependant element

Info

Publication number: GB2450794A
Application number: GB0811847A
Authority: GB
Inventors: Thomas Heinrich
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2007-07-06
Filing date: 2008-06-27
Publication date: 2009-01-07
Anticipated expiration: 2028-06-27
Also published as: GB2450794B; GB0811847D0

Abstract

A battery comprises a cell (1) accommodated in a cell container (2), and a temperature-dependent element, particularly a PTC element (20), which at least partly surrounds the cell container (2), for temperature monitoring of the cell (1). The element (20) can comprise a first metallic layer (10), an outlying intermediate layer with the desired temperature characteristic, and a further outlying second metallic layer (12). Such a battery is particularly suitable for battery packs requiring battery temperature monitoring, the battery being capable of inclusion in such a pack without requiring increase in the battery installation space within the pack.

Description

1 2450794

BATTERY WITH TEMPERATURE-DEPENDENT ELEMENT

The present invention relates to a battery especially with an integrated temperature sensing capability and to a battery pack comprising such a battery.

Batteries and battery packs are discharged in use and can be designed to be rechargeable, in which connection a charging apparatus is provided for the latter task. In that case it Is Important, apart from charging process, to monitor the battery temperature during the discharging process so as to prevent a too-high temperature rise or an excessive temperature during that process. For this purpose use is made of posistors, i.e. positive temperature coefficient (PTC) elements, which increase their resistance with increasing temperature. At lower temperatures the resistance is low and there is good current conduction. The PTC element is connected in series with other batteries of the battery pack. The accommodation of the PTC element at the battery itself or in the battery pack is frequently difficult due to the tight space conditions which prevail. Moreover, a costly wiring is necessary in order to connect the PTC element with the battery or cell.

There is therefore scope for improvement in the arrangement for battery temperature monitoring in, for example, the circumstances described.

According to the present invention there is provided a battery comprising a cell accommodated in a cell container, wherein a temperature-dependent element, particularly a positive temperature coefficient element, is provided for temperature monitoring of the cell and at least partly surrounds the cell container.

A battery embodying the present invention or a battery pack incorporating such a battery has the advantage that the temperature-dependent element, particularly a PTC element, can be directly mounted in simple and space-saving manner, without costly wiring, insulation or mechanical fixing, at the battery or the cell thereof and is connectible with the other batteries. It is advantageous in that case that essentially no additional installation space is required for the temperature-dependent element at the battery or within a housing of the battery pack. In addition, an effective thermal coupling of the temperature-dependent element with the battery or cell is made possible and the volume occupied by the temperature-dependent element can be comparatively small. This enables management of temperature monitoring of the batteries in a battery pack by simple exchange of a conventional battery by a battery embodying the invention without the need for any constructional change to a housing of the battery pack.

It is advantageous, for good thermally conductive connection of the temperature-dependent element with the cell container, if the element surrounds the cell container of the battery in desired manner. i.e. to a predetermined extent, preferably by approximately half. Equally, it is possible for the temperature-dependent element to completely surround the cell container in the manner of a sleeve.

Advantageously, charging temperature munitoring and discharging temperature monitoring of the battery can be managed in simple manner through the temperature-dependent element being electrically connected with the cell container, for which purpose a series connection of temperature-dependent element and cell is provided.

It is advantageous, for compact construction of the electrical connection of the temperature-dependent element and the cell container or cell without costly wiring, to solder and/or weld and/or glue a first metallic layer of the temperature-dependent element to the cell container, wherein an intermediate layer with temperature-dependent characteristics, particularly characteristics of a positive temperature coefficient resistor, is connected with the first metallic layer and is covered by a second metallic layer of the temperature-dependent element.

A compact mode of construction results when for insulation purposes an insulation layer is provided at least partly between the first metallic layer and the second metallic layer of the temperature-dependent element.

Moreover, it is advantageous to provide an insulation layer between the second metallic layer and the cell container for insulation purposes. This enables production in very simple manner of an electrical connection with the other batteries of a battery pack by way of a cell connector bearing against the second layer.

It is of advantage, for simple production of the insulation layer, to construct it from a film.

In the case of a battery pack including a battery according to the invention and at least one further, conventional battery, a simple, secure and reliable connection of the batteries can . be achieved by use of a cell connector which has an angled form. This may allow maintenance of installation spaces, without change, for the batteries in the battery pack. It is thus possible in advantageous manner to provide temperature monitoring for the battery pack merely through replacement of a single conventional battery by a battery according to the invention.

Preferred embodiments of the present invention will now be more particularly described by way of example only with reference to the accompanying drawings, in which: Fig. I is a schematic sectional side view of a first battery embodying the invention; Fig. 2 is a cross-section (not true to scale) of a battery embodying the invention, with a first cross-sectional form; Fig. 3 is a cross-section (not true to scale) of a battery embodying the invention, with a second cross-sectional form; Fig. 4 is a schematic sectional side view of a second battery embodying the invention, with the first or second cross-sectional form; Fig. 5 is a plan view of a battery embodying the invention and connected with a conventional battery, in a battery pack embodying the invention; and Fig. 6 is a perspective view of a battery pack embodying the invention.

Referring now to the drawings, there is shown a battery, which is also termed accumulator or secondary cell, functioning as a store for electrical energy, usually on the basis of an electrochemical system. Known batteries with such a system are, for example, nickel-cadmium batteries, nickel-metalhydride batteries, lithium-ion batteries and lithium-polymer batteries, which contain an electrical cell rechargeable after discharge. In order to achieve a specific voltage these cells can be packed into a battery pack and connected together.

Individual cells in that case are of the same type. The desired or rated voltage of the battery pack results from the sum of the cells connected in series.

The battery contains an electric cell I, which is schematically shown in Fig. I and which in known manner is surrounded by a cell container 2. The cell I has an elongate cylindrical form with a circumferential surface 3 and two end faces. A first flat end face 4 in that case usually forms a negative pole of the cell I. A second end face 5 disposed opposite the first face 4 has a flat surface which surrounds a positive pole 6 of the cell I. For connection of individual cells or serial connection of the same, a cell connector 24 as shown in Fig. 6 is provided between the negative pole of each cell 16 and the adjoining positive pole of the respectively succeeding cell 16.

Battery packs, consisting of at least one to ten cells depending on the respectIvely desired voltage, are commonplace. In the example according to Fig. 6, four cells 1, 16 are connected together to form a battery pack 17, as is usual in the case of, for example, power tools (cell size, for example, Baby, Mono, AA, AAA, 4/5 sub-C cell, sub-C cell, 18650-cell, 26650-cell and the like).

For temperature monitoring it is usual to equip at least one of the cells I with a temperature-sensitive element 20. Switching-off during discharging and/or charging can then be carried out by means of this element 20. A hard' switching-off of the current takes place when the temperature-sensitive element 20 is a positive temperature coefficient (PlC) resistor. The PTC resistor or element is a so-called posistor. Elements of that kind consist of a material which conducts electrical current and which conducts the current better at lower temperatures than at high temperatures. Its electrical resistance increases with increasing temperature. This special kind of resistor thus has a positive temperature coefficient. PTC resistors of that kind have a steep rise in resistance and in general are therefore not suitable for regulation of current and voltage. The PTC resistor is therefore provided for switching off during charging and discharging of the batteries or cells.

In addition, a negative temperature coefficient (NTC) resistor can be incorporated in each battery or battery pack, the resistance value of the resistor being read off by charging apparatus. An NTC resistor is a thermistor with negative temperature coefficient. Its electrical resistance reduces with increasing temperature.

The battery pack 17 comprises, in accordance with conventional understanding, a number of batteries which are arranged together in a common housing 21, possibly additionally with further switching elements. The electrical connection with the battery pack 17 is effected by way of a plug strip or several contact elements 22 at the housing 21 of the battery pack 17. In order to protect batteries of that kind from, in particular, excessive discharging and over-charging it is known to arrange a temperature-dependent element in the battery pack 17 in the immediate vicinity of or in direct contact with a battery 1, wherein the characteristic curve of the temperature-dependent element is then monitored or measured during the discharging or charging process in order to recognise potential impermissible heating up of the batteries 1, 16 and to take preventative steps.

In order to provide this temperature monitoring, particularly in the discharging process of the cell 1, the cell is equipped with a temperature-dependent element 20 which does not cause significant change in the cell size. Accordingly, the temperature-dependent element has the form of a PTC element 20 which, as Figs. 1 to 4 show, directly surrounds or encloses the cell container 2 at least partly, in particular to a desired extent. A series connection is realised between the cell I and PTC element 20. When the cell I heats up the resistance of the element 20 increases so that, for example, the current extracted from the cell can be reduced in controlled manner by appropriate means so as to avoid an excessive temperature of the cell 1.

A PTC element normally consists of two metallic plates, between which a layer of plastics material with the special characteristics of the PTC lies. The usual form is a flat constructional shape. In the battery embodying the present invention there is now departure from this constructional shape and a cylindrical or semi-cylindrical form of the PTC element is provided, which, as Fig. 1 schematically indicates, at least partly surrounds the cell container 2. Fig. 2 shows a first version with a PTC element completely circumferentially surrounding the cell I or the cell container 2 (360 degrees). The PTC element 20 thus forms a casing for the cell container 2. Fig. 3 shows a second version with a PTC element 20 only partly surrounding the cell container 2, wherein approximately degrees of enclosure (half round) is provided. A somewhat smaller degree of enclosure of less than 180 degrees, for example 100 degrees, would also be conceivable.

The extent of enclosure should not, however, be too small, since otherwise a good thermal coupling of PTC element 20 and cell container 2 for the temperature monitoring would be jeopardised. Moreover, it is to be noted that with Increasing current flow In the cell I the required area of the PTC element 20 should be greater.

The construction of the PTC element 20 is such that a first metallic layer 10 is electrically connected with the cell container 2 or the circumferential surface 3 thereof by means of soldenng, welding, gluing, etc. It is obviously also possible to use a combination of these methods, such as gluing and soldering. For preference, the first layer 10 is welded to the cell container 2 or the circumferential surface 3 thereof.

An intermediate layer 11 of plastics material, which has the PlC-typical posistor characteristics and for this purpose consists of, for example, a polymer material, is connected radially outwardly with the first layer 10. The intermediate layer 11 is surrounded by a second layer 12 which, like the first layer 10, comprises metal. The second metallic layer 12 thus forms the new negative pole of the cell 1. The first layer 10, the intermediate layer 11 and the second layer 12 form the temperature-dependent electrical element 20 or the Plc 20. A series connection of cell I and PTC 20 is achieved by this construction. In longitudinal direction of the cell I the first layer 10 extends into the vicinity of the positive pole 6. The intermediate layer 11, which is somewhat shorter and further removed from the positive pole 6, then follows and is in turn substantially covered, without offset, by the second layer 12. The PTC element 20 is thus thermally coupled with the cell I in very effective manner, wherein the volume which the PTC element 20 occupies is only minimal, particularly by comparison with a flat construction of the PTC element, which would then need additional installation space in the battery pack 12. The layers 10, 11 and 12 shown in Figs. I to 4 are in reality very much narrower than depicted.

Fig. 4 shows an embodiment of the battery with a form of PlC element 20 for connection with other cells 16 without a PTC element. In correspondence with Fig. I the PTC element comprises three layers 10, 11 and 12, but in departure from Fig. 1 the second layer 12 not only covers the circumferential surface 3 of the container 2 of the cell 1, but also partially covers the first end face 4, which forms the former negative pole, of the cell. This extension of the second layer 12 is denoted in Fig. 4 by 23. An insulation layer 14 is provided for insulation of the former negative pole from the extension or new negative pole 23 formed by the PlC element 20. The insulation layer 14 can, for example, consist of a film and can cover not only part of the first end face 4, but also part of the circumferential surface 3 as seen in longitudinal direction of the cell 1.

As is illustrated in Fig. 6, conventional flat cell connectors 24 in the battery pack connect the negative pole of a cell 16 with the positive pole 6' of the next cell 16. For secure electrical connection of the cell 1, which is quasi covered by the PTC element 20, with a cell 16 without a PTC element use is made of an adapted cell connector 15 which, as shown in particular by Fig. 5, has a bent-over form. A first limb 26 in that case bears against the cell 1 at the second layer 12 in longitudinal direction and a second limb 27 bears against the next cell 16 at the positive pole or projection 6'. The insulation layer 14 covered by the second layer 12 is indicated in Fig. 6.

The adapted cell connector 15 can be produced, for example, simply by bending over a conventional flat cell connector 24. It is possible by means of the bent-over cell connector to install the battery 1, or snap it into place, in the battery pack 17 without constructional change of the pack housing, which battery is of somewhat longer construction by virtue of the insulation layer 14 superimposed on the first end face 4 and the second layer extension 23. In order to provide compensation for the somewhat greater battery length, the flat cell connector 24 usually provided between two or more receptacles 25 in the housing 21 as seen in longitudinal direction of the cell I is then simply replaced by the bent-over cell connector 15.

Claims

1. A battery comprises a cell accommodated in a cell container, and a temperature-dependent element for monitoring the temperature of the cell, the element being arranged to at least partly surround the cell container.

2. A battery according to claim 1, wherein the temperature-dependent element comprises a positive temperature coefficient element.

3. A battery according to claim I or claim 2, wherein the temperature-dependent element surrounds the cell container to a predetermined extent.

4. A battery according to claim 3, wherein the temperature-dependent element surrounds the cell container by substantially half.

5. A battery according to claim 3, wherein the temperature-dependent element surrounds the cell container entirely.

6. A battery according to any one of the preceding claims, wherein the temperature-dependent element is electrically connected with the cell container to form a series connection of the element and cell.

7. A battery according to any one of the preceding daims, wherein the temperature-dependent element comprises a first metallic layer electrically connected with the cell container, an intermediate layer having a temperature-dependent characteristic and outlying the first metallic layer and a second metallic layer outlying the intermediate layer.

8. A battery according to claim 7, wherein the first metallic layer is connected with the cell container by at least one of soldering, welding and gluing.

9. A battery according to claim 7 or claim 8, wherein the temperature-dependent element comprises an electrical insulation layer extending between the first metallic layer and the second metallic layer.

10. A battery according to claim 9, wherein the insulation layer comprises a film.

11. A battery according to any one of claims 7 to 10, wherein the temperature-dependent element comprises an electrical insulation layer extending between the second metallic layer and the cell container.

12. A battery according to claim 11, wherein the insulation layer extending between the second metallic layer and the cell container comprises a film.

13. A battery pack comprising at least one battery according to any one of the claims I to 12.

14. A battery pack according to claim 13, wherein the connector has a bent-over form defining a first limb connected with a pole of the temperature-dependent element and a second limb connected with a pole of the battery without a temperature-dependent element.

14. A battery pack according to daim 13, further comprising at least one battery without a temperature-dependent element, and a cell connector connecting that battery with the at least one battery according to any one of daims I to 12.

15. A battery pack according to claim 14, wherein the connector has a bent-over form defining a first limb connected with a pole of the temperature-dependent element and a second limb connected with a pole of the battery without a temperature-dependent element.

RD

Amendments to the claims have been filed as follows

1. A battery comprising a cell accommodated in a cell container, and a temperature-dependent element for monitoring the temperature of the cell, the element being arranged to at least partly surround the cell container and being electrically connected with the cell container to form a series connection of the element and cell.

3. A battery according to claim 1 or claim 2, wherein the temperature-dependent element surrounds the cell container to a predetermined extent.

4 A battery according to claim 3, wherein the temperature-dependent element surrounds the cell container by substantially half.

6. A battery according to any one of the preceding claims, wherein the temperature-dependent element comprises a first metallic layer electrically connected with the cell container, an intermediate layer having a temperature-dependent characteristic and outlying the first metallic layer and a second metallic layer outlying the intermediate layer.

7. A battery according to claim 6, wherein the first metallic layer is connected with the cell container by at least one of soldering, welding and gluing.

8. A battery according to claim 6 or claim 7, wherein the temperature-dependent element comprises an electrical insulation layer extending partly between the first metallic layer and the second metallic layer.

9. A battery according to claim 8. wherein the insulation layer comprises a film.

10. A battery according to any one of claims 6 to 9, wherein the temperature-dependent element comprises an electrical insulation layer extending partly between the second metallic layer and the cell container.

11. A battery according to claim 10, wherein the insulation layer extending between the second metallic layer and the cell container comprises a film.

12. A battery pack comprising at least one battery according to any one of the claims 1 to 11.

13. A battery pack according to claim 12, further comprising at least one battery without a temperature-dependent element, and a cell connector connecting that battery with the at least one battery according to any one of claims 1 to 11.