Abstract:
The invention relates to a cell coil ( 30, 40, 50, 60, 100, 200 ) for a lithium-ion battery, comprising at least two sub-cells ( 10, 32, 42, 44, 52, 54, 68, 70, 80, 82 ), which are wound in a space-saving manner and are thermally coupled to each other. According to the invention, the at least two sub-cells ( 10, 32, 42, 44, 52, 54, 68, 70, 80, 82 ) are electrically connected in parallel in normal operation, and, in the event of a fault, in particular in the event of an internal short circuit in at least one defective sub-cell ( 10, 32, 42, 44, 52, 54, 68, 70, 80, 82 ), at least one defective sub-cell ( 10, 32, 42, 44, 52, 54, 68, 70, 80, 82 ) can be electrically separated from the at least one intact sub-cell ( 10, 32, 42, 44, 52, 54, 68, 70, 80, 82 ). Because of the at least one defective sub-cell ( 10, 32, 42, 44, 52, 54, 68, 70, 80, 82 ) that can be immediately electrically separated from the intact sub-cells ( 10, 32, 42, 44, 52, 54, 68, 70, 80, 82 ) by means of an electronic monitoring device ( 36 ) in the “event of a fault”, a high level of robustness of the cell coil ( 30, 40, 50, 60, 100, 200 ) in respect of internal short circuits is achieved. Among other things, the intact sub-cells ( 10, 32, 42, 44, 52, 54, 68, 70, 80, 82 ) act, because of the thermal coupling between the sub-cells ( 10, 32, 42, 44, 52, 54, 68, 70, 80, 82 ), as a damage-reducing heat sink for the waste heat that is released during the fast discharge of the affected defective sub-cell ( 10, 32, 42, 44, 52, 54, 68, 70, 80, 82 ) generally occurring in the event of a short circuit.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a cell coil for a lithium-ion accumulator having at least two sub-cells which are wound in a space-saving fashion and thermally coupled to one another. 
         [0002]    It is apparent that in future new battery systems or accumulator systems which will have to fulfill very stringent requirements in terms of reliability, safety, efficiency and service life will be used in stationary applications, for example in wind turbines, in motor vehicles which are configured as hybrid vehicles or electric vehicles as well as in electrical appliances. 
         [0003]    Owing to their high energy density, in particular lithium-ion accumulators are used as energy stores for electrically driven motor vehicles. 
         [0004]    DE 10 2011 017 613 A1 discloses a cell coil for a lithium-ion accumulator. The cell coil comprises two current conductors which are wound to form the cell coil with the intermediate positioning of two separators. 
         [0005]    DE 10 2011 110 876 A1 discloses an energy storage device. The energy storage device comprises, inter alia, an energy storage cell, for example in the form of an electrode coil, and a container for holding the energy storage cell. So that the function of the energy storage cell can be reliably ensured, a thermally conductive layer, by which heat can be carried away from the energy storage cell in the direction of the container wall, is provided between the electrode coil and the container wall. In one preferred configuration there is provision that the thermally conductive layer has a partial layer composed of an electrically insulating material. The partial layer ensures, on the one hand, that released heat can flow away satisfactorily from the cell, and on the other hand the partial layer prevents an outer side of the cell from coming into electrical contact with the container wall. Furthermore, the partial layer ensures that in the case of punctiform penetration by a foreign body from the outside short-circuits between the individual electrodes are avoided. 
         [0006]    It is disadvantageous, inter alia, that in the case of a fault, in particular in the case of an internal short-circuit of a cell or the like, the energy storage cell does not have any individual cells which can be switched off selectively in order to limit damage. 
         [0007]    The probability of the occurrence of internal short-circuits in lithium-ion accumulators can be reduced e.g. by enhanced quality measures during production. However, in this context, all faults cannot be detected and eliminated continuously at an acceptable level of expenditure. Moreover, it is possible to make lithium-ion accumulators mechanically more robust, with the result that external effects, in particular mechanical and thermal effects cannot so easily cause an internal short-circuit. The relatively large material thicknesses which are generally necessary for this purpose and the additional mechanical protective components also have the effect of increasing costs and additionally reduce the volume portion and weight portion of the overall weight which is made up by the active material, and in association with this the electrical energy density of the accumulator. Furthermore, the tendency of lithium-ion accumulators to short circuit can be positively influenced by the selection of other active materials for the electrocoating and/or the use of less active material on the electrodes. However, in this case a reduction in the available capacity of the lithium-ion accumulator also occurs. 
       SUMMARY OF THE INVENTION 
       [0008]    An object of the invention is therefore to specify a lithium-ion accumulator in which the thermal loading is reduced in the case of an internal short circuit and in the case of a rapid discharge which is necessary to limit damage. 
         [0009]    According to the invention, the at least two sub-cells are connected electrically in parallel in the normal operating mode, and in the case of a fault, in particular in the case of an internal short-circuit in at least one defective sub-cell, at least one defective sub-cell can be electrically disconnected from the at least one intact sub-cell. 
         [0010]    Owing to the inventive configuration of the cell coil, if rapid discharge of a sub-cell becomes necessary—e.g. owing to a detected fault—and if uncontrolled discharging occurs e.g. owing to an internal cell short-circuit in a sub-cell or the like—the at least one remaining intact sub-cell can be quickly electrically disconnected. The intact sub-cell functions as a heat sink for the ohmic dissipated heat which is released during the rapid discharge, and contributes to the damage limitation. Moreover, the entire capability of the lithium-ion accumulator to conduct away current is available to the defective sub-cell, with the result that relatively high discharge current rates are possible, depending on its electrical design. In addition, if appropriate a defective sub-cell can be selectively disconnected from the other, still intact sub-cells. The electrical disconnection of faulty sub-cells from the remaining, still functionally capable sub-cells is carried out using a suitable open-loop and/or closed-loop control device which is preferably an electronic monitoring device or the like which is designed to perform rapid and selective electrical disconnection of defective sub-cells of the lithium ion accumulator. The disconnection itself can be carried out e.g. electromechanically by means of a relay or electrically in order to bring about the galvanic isolation without disconnecting the potential using power semiconductors. The cell coil for use in a lithium-ion accumulator can basically have more than two wound sub-cells. 
         [0011]    In this context, the release of heat in the event of a fault is limited to a non-critical quantity of heat and, in particular, a chain reaction, in the case of which further internal short circuits and other exothermic reactions could be triggered by the released heat, is prevented. 
         [0012]    In a further advantageous refinement of the concept on which the invention is based, each sub-cell has a cathode which is coated at least partially with a first active material and an anode which is coated at least partially with a second active material, and a separation layer runs between the first and the second active materials. The cell coil therefore has a plurality of anodes and a plurality of cathodes. As a result, each sub-cell constitutes per se an independent electromechanical element of the lithium-ion accumulator which is constructed from them. 
         [0013]    In a further advantageous refinement of the proposed solution according to the invention, the cathode and/or the anode of at least one sub-cell are provided with an insulating layer which electrically insulates the sub-cells from one another. As a result, internal short-circuits between the web-shaped sub-cells in the wound state are reliably prevented. 
         [0014]    In one embodiment the at least two sub-cells are wound in an essentially serpentine shape in order to form a prismatic shape of the cell coil. This provides largely cavity-free and therefore space-saving integration of the cell coil into a cuboid housing shape of a lithium-ion accumulator. 
         [0015]    In the case of a further embodiment, the at least two sub-cells are wound in an essentially helical shape in order to form a cylindrical shape of the cell coil. This results in an alternative shape of the cell coil in order to implement lithium-ion accumulators with other housing shapes. 
         [0016]    In a further advantageous refinement, the cell coil has an inner winding and an outer winding which surrounds the latter, wherein the inner winding and the outer winding are each formed with a wound sub-cell. As a result, production means which are already present for winding lithium-ion accumulators can be used to manufacture the cell coils according to the invention without substantial modifications. 
         [0017]    In the case of a further embodiment, at least one further outer winding which contains a further sub-cell is wound onto the outer winding. As a result, an increase in the capacity is possible in this embodiment of the cell coil. 
         [0018]    In the case of a technically favorable development, in each case an electrically insulating separation layer is provided between the inner winding and the outer winding and/or between the at least two outer windings. This provides reliable electrical insulation between the inner winding and the outer winding in addition to the insulating layers of the sub-cells. 
         [0019]    The separation layer can have an increased level of robustness against mechanical and thermal damage. Likewise, the separation layer can have lower thermal conductivity than the separation layer. As a result, the probability of a defect propagating to an adjacent sub-cell is minimized. If the separation layer is provided only between the sub-cells, increased costs and an increased space requirement are minimized by the additional robustness. 
         [0020]    In the continuation of the inventive concept, each sub-cell has in the unwound state an essentially web-shaped form with a width B. As a result, the cell coil can be implemented easily in terms of fabrication technology by winding the sub-cells which are preferably present as web-shaped semi-finished products and which each comprise an anode, cathode and separation layer. 
         [0021]    In order to fabricate a cell coil with an inner winding and an outer winding, the inner winding is firstly wound from the semi-finished product. Then, the semi-finished product is cut and the separation layer is applied to the inner winding. Subsequently, the semi-finished product is wound further to form the outer winding. As a result, necessary changes to existing fabrication systems and known fabrication processes to fabricate conventional cell coils are minimized. 
         [0022]    The cathode and the anode of each sub-cell advantageously have, for the formation of electrical contact, preferably at least one cathode lug and one anode lug lying opposite one another, wherein the at least one cathode lug and the at least one anode lug each project beyond, in each case, one of the two longitudinal edges of the sub-cell by a width b, transversely with respect to a longitudinal axis of the sub-cell. As a result, the cathode lugs and anode lugs can be formed in terms of fabrication technology as trapezoidal protrusions on both sides of the cathode or of the anode. 
         [0023]    Continuing the inventive concept further, at least two cathode lugs and at least two anode lugs are formed axially offset with respect to one another by a distance L on each longitudinal edge of the sub-cell. As a result, in order to ensure a sufficiently high current-carrying capability of the electrical contact-forming means, a multiplicity of cathode lugs or anode lugs which are located one on top of the other are available. The cathode lugs and the anode lugs of various sub-cells are electrically disconnected from one another here. 
         [0024]    In accordance with one favorable refinement there is provision that the distance L is varied in each case such that in the wound state of each sub-cell the cathode lugs and the anode lugs, which belong to the same sub-cell, lie essentially congruently one on top of the other in order to form in each case a cathode contact and an anode contact. As a result, inter alia, the increasing radius of the cell coil can be compensated when winding the sub-cells. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    The invention will be described in more detail below with reference to the drawing, in which: 
           [0026]      FIG. 1  shows a schematic cross section through a sub-cell having an insulating layer, 
           [0027]      FIG. 2  shows a basic illustration of an embodiment of a cell coil having two sub-cells and a monitoring device, 
           [0028]      FIG. 3  shows an embodiment of a cell coil having a prismatic shape, 
           [0029]      FIG. 4  shows an embodiment of a cell coil having a cylindrical shape, 
           [0030]      FIG. 5  shows an embodiment of a cell coil having an inner winding and an outer winding surrounding the latter coaxially, 
           [0031]      FIG. 6  shows a schematic plan view of two unrolled web-shaped sub-cells which lie one on top of the other and have cathode lugs and anode lugs for the electrical connection, 
           [0032]      FIG. 7  shows a basic plan view of a cell coil having two sub-cells, and 
           [0033]      FIG. 8  shows a basic plan view of an embodiment of a cell coil having four sub-cells. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]      FIG. 1  shows a schematic cross section through a sub-cell  10  for use in a cell coil  30 ,  40 ,  50 ,  60 ,  100 ,  200  according to the invention for a lithium-ion accumulator (not illustrated in the drawings). 
         [0035]    The sub-cell  10  comprises a cathode  12  which is provided with a first electrochemical active material  14 , and a cathode  16  which is at least partially coated with a second electrochemical active material  18 . The two active materials  14 ,  18  which run parallel one on top of the other in the unrolled or non-rolled state of the sub-cell  10  are disconnected from one another by a separation layer  20  made of micro-porous polyethylene and/or polypropylene. The cathode  12  and the anode  16  each form a first and a second current conductor  22 ,  24  for feeding current to the sub-cell  10 . For example, the cathode  12  is provided here with an insulating layer  26  in order to avoid intercellular short-circuits during the winding of the sub-cell  10 . The insulating layer  26  can, however, also be provided in the region of the anode  16  and in the region of the cathode  12  and the anode  16 . The insulating layer  26  can be embodied here as a fixed component of the sub-cell  10  or can be positioned on the layered structure composed of the cathode  12  with the first active material  14 , the separation layer  20  and the anode  16  with the second active material  18 . The active materials  14 ,  18  can have a material composition of the same or of different substances, while the cathode  12  is formed with aluminum, and the anode  16  with copper. The unrolled, web-shaped sub-cell  10  here is preferably held in reserve as an “endless” semi-finished product in the form of a roll and can easily be processed to form cell coils  30 ,  40 ,  50 ,  60 ,  100 ,  200  with a wide variety of different shapes by winding or rolling. 
         [0036]    Basically, any desired number of sub-cells  10  whose layered structure respectively corresponds to the structure of the sub-cell  10  described above can be stacked one on top of the other to form a structure which comprises a plurality of sub-cells  10 . 
         [0037]      FIG. 2  shows a basic illustration of a cell coil  30  with two sub-cells  10 ,  32  as well as with a monitoring device  36 . 
         [0038]    A cell coil  30  is formed with the sub-cell  10  in  FIG. 1  and with a further sub-cell  32  which is of the same design, wherein an inner thermal coupling  34  is present between the sub-cells  10 ,  32  which lie one on top of the other. The two sub-cells  10 ,  32  are connected electrically in parallel in a “normal operating mode” of the cell coil  30 . In “the case of a fault” such as e.g. a short circuit in one of the two sub-cells  10 ,  32 , these can be electrically disconnected by means of a preferably electronic monitoring device  36 . The electrical disconnection can be carried out e.g. with a switch  38  which is embodied as a normally closed switch and which can be actuated by means of the monitoring device  36 . The switch  38  can be implemented with an electromechanical relay or with suitable power semiconductors, wherein in the latter case no galvanic or potential-free disconnection of the sub-cells  10 ,  32  is possible. 
         [0039]      FIG. 3  shows an embodiment of a cell coil  40  with a prismatic shape. 
         [0040]    In order to construct a prismatic shape, a cell coil  40  is formed with a first and a second sub-cell  42 ,  44  which lie one on top of the other and are wound one into the other in an approximately serpentine shape. The structural design of the sub-cells  42 ,  44  corresponds in each case to that of the sub-cell  10  described in  FIG. 1 . The prismatic cell coil  40  is preferably provided with a cuboid housing for use for a lithium-ion accumulator. In contrast with the two sub-cells  42 ,  44  which are merely shown here by way of example, the cell coil  40  can also have three or more sub-cells  10 ,  42 ,  44 . According to the invention, the two sub-cells  42 ,  44  of the cell coil  40  can be electrically disconnected from one another by means of the monitoring device  36  in  FIG. 2 . 
         [0041]    In the “normal operating mode” of the cell coil  40 , the two sub-cells  42 ,  44  are connected in parallel in order to ensure, in particular, uniform charging. In the “event of a fault” of the cell coil  40 , which fault is present e.g. in the event of an internal short circuit in the sub-cell  42 , the defective sub-cell  42  is immediately electrically disconnected from the still intact sub-cell  44  by means of the monitoring device  36 . This electrical disconnection or switching off is carried out by means of the preferably electronic monitoring device  36  (illustrated schematically in  FIG. 2 ) by means of a relay or using suitable power semiconductors. As a result of the electrical disconnection which takes place approximately in real time, the intact sub-cell  44  additionally functions as a heat sink for ohmic dissipated heat which is released during the rapid discharging of the defective sub-cell  42  which is generally initiated in order to limit damage in the case of a short circuit, wherein at the same time the full current-carrying capacity of the cell coil  40  can be utilized for the rapid discharging process, with the result that shortening of the rapid discharging time can be achieved. 
         [0042]      FIG. 4  illustrates a further embodiment of a cell coil  50  with a cylindrical shape. 
         [0043]    In order to construct a cylindrical shape, a cell coil  50  is formed with two sub-cells  52 ,  54  which lie one on top of the other and are wound approximately in a helical shape and whose structural design corresponds in turn in each case to the sub-cell  10  already explained in  FIG. 1 . The cell coil  50  is predominantly suitable for lithium-ion accumulators whose housing has a non-polygonal shape which deviates from the cuboid shape. In contrast to the first and second sub-cells  52 ,  54  which are merely exemplary here, the cell coil  50  can also have three or more sub-cells  10 ,  52 ,  54 . 
         [0044]      FIG. 5  illustrates a further embodiment of a cell coil  60  with an inner winding  62  and an outer winding  64  which surrounds the latter coaxially. 
         [0045]    A cell coil  60  is formed with an inner winding  62  and an outer winding  64  which surrounds the latter coaxially, wherein an electrically insulating separation layer  66  is provided between the inner winding  62  and the outer winding  64 . The inner winding  62  is formed with a wound first sub-cell  68  and the outer winding  64  is formed with a rolled second sub-cell  70 . The rolled sub-cells  68 ,  70  each lie one on top of the other or against one another in the inner winding  62  and in the outer winding  64 . 
         [0046]    The separation layer  66  functions, in particular not only as an insulating layer  72  of the outer second sub-cell  70  but also as an additional electrical insulating means between the inner winding  62  and the outer winding  64 . Where necessary, at least one further outer winding  64  can be wound onto the illustrated outer winding  64  with the intermediate positioning of a further separation layer  66 . 
         [0047]      FIG. 6  illustrates a schematic plan view of two unrolled web-shaped sub-cells  80 ,  82  which lie one on top of the other and have cathode lugs K 11 , K 12 , K 21 , K 22  and anode lugs A 11 , A 12 , A 21 , A 22  for electrical connection. 
         [0048]    The two unrolled web-shaped or strip-shaped sub-cells  80 ,  82  which lie one on top of the other have in each case a width B over their common longitudinal axis  84  here. The layered structure of the two sub-cells  80 ,  82  corresponds in turn to the structural configuration of the sub-cell  10  which is already explained in  FIG. 1 . 
         [0049]    On a first longitudinal edge  86  of the first sub-cell  80 , for example two e.g. trapezoidal cathode lugs K 11  and K 12  are formed here as integral components of the metallic cathode  12  (not illustrated here in detail for sake of better clarity of the drawing) or of the first current conductor  22  of the first sub-cell  80  in each case transversely with respect to the longitudinal axis  84 . Correspondingly, on a second longitudinal edge  88  of the first sub-cell  80  in each case two anode lugs A 11  and A 12  are constructed lying opposite the cathode lugs K 11  and K 12  or in a mirror-inverted fashion with respect to the longitudinal axis  84 . 
         [0050]    The cathode lugs K 11  and K 12  as well as the anode lugs A 11  and A 12  each project beyond the longitudinal edges  86 ,  88  of the first sub-cell  80  by a width b, transversely with respect to the longitudinal axis  84 . Between the cathode lugs K 11  and K 12  as well as between the anode lugs A 11  and A 12  there is, related in each case to their center in the axial direction, an axial distance of L 1 . The first sub-cell  80  has a multiplicity of cathode lugs K 11  and K 12  and anode lugs A 11 , A 12  (not shown here) which are constructed in accordance with the cathode lugs K 11 , K 12  and the anode lugs A 11 , A 12  and the distances L 1  between which vary in each case in such a way that the cathode lugs K 11 , K 12  and the anode lugs A 11 , A 12  lie, in the wound state of the first sub-cell  80 , ideally in each case in a congruent fashion one on top of the other on the circumferential side in order to provide sufficiently mechanically stable and current-carrying-capable cathode contacts  102  and anode contacts (cf.  FIGS. 7 and 8 ) for the formation of electrical contact or for the connection of the cell coil  100 ,  200 . 
         [0051]    Correspondingly, a multiplicity of correspondingly configured cathode lugs K 21 , K 22  and anode lugs A 21 , A 22  are formed on both longitudinal edges  90 ,  92  of the second sub-cell  82 , of which cathode lugs and anode lugs in each case only two cathode lugs K 21 , K 22  and anode lugs A 21 , A 22  are indicated with dashed lines in a way which is representative of all the others. Between the cathode lugs K 21 , K 22  and the anode lugs A 21 , A 22  there is a distance of L 2 . The distances L 2  between the individual cathode lugs K 21 , K 22  and anode lugs A 11 , A 12  vary along the longitudinal extent of the second sub-cell  82 , in particular as a function of the coil geometry, e.g. helical or serpentine, used, such that the cathode lugs K 21 , K 22  and anode lugs A 21 , A 22  in the wound state of the second sub-cell  82  ideally lie one on top of the other or lie one against the other again in a congruent fashion. 
         [0052]      FIG. 7  shows a highly simplified plan view of a prismatic cell coil  100  with two sub-cells  10 ,  32 ,  42 ,  44 ,  52 ,  54 ,  68 ,  70 ,  80 ,  82  which can be electrically disconnected from one another by means of the monitoring device  36 . 
         [0053]    An exemplary, in turn prismatic, cell coil  100  has on both sides a multiplicity of cathode lugs K 11 , K 12 , K 21 , K 22  and anode lugs A 11 , A 12 , A 21 , A 22  which are not denoted individually and which together form the two upper-side cathode contacts  102 ,  104  which can be seen here, while two anode contacts lying at the bottom cannot be seen in the illustration in  FIG. 6 . The first and the second sub-cells  10 ,  32 ,  42 ,  44 ,  52 ,  54 ,  68 ,  70 ,  80 ,  82  of the cell coil  100  are electrically connected independently of one another and actuated via the total of four cathode contacts  102 ,  104  and anode contacts, wherein the sub-cells  10 ,  32 ,  42 ,  44 ,  52 ,  54 ,  68 ,  70 ,  80 ,  82  are continuously automatically monitored in the “normal operating mode” of the cell coil  100  by means of the automatic monitoring device  36 , and in “the event of a fault” can be electrically disconnected from one another immediately by means of said monitoring device  36 . 
         [0054]      FIG. 8  shows a basic plan view of an embodiment of a cell coil  200  with four sub-cells  10 ,  32 ,  42 ,  44 ,  52 ,  54 ,  68 ,  70 ,  80 ,  82 . 
         [0055]    The cell coil  200  is constructed here by way of example with four sub-cells  10 ,  32 ,  42 ,  44 ,  52 ,  54 ,  68 ,  70 ,  80 ,  82 , the cathode lugs K 11 , K 12 , K 21 , K 22  and anode lugs A 11 , A 12 , A 21 , A 22  of which are combined to form four upper-side cathode contacts  202 ,  204 ,  206  and  208  which can be seen here, while four lower-side anode contacts are in turn concealed or not visible here.