DE102011089982B4 - total energy storage - Google Patents

Abstract

Total electrochemical store for storing electrical energy, which comprises a number of cell modules (4a-4c), which consist of a number of two-pole lithium-ion cells (1a-1k), characterized in that- an insulating material (8) of each cell module (4a-4c ) encloses- each cell module (4a-4c) is clamped in a clamping frame (6) enclosing this cell module (4a-4c).

Description

The invention relates to an overall electrochemical store for electrical energy, which comprises a number of cell modules which consist of a number of two-pole lithium-ion cells.

The alkali metal lithium serves as the starting material for all electrochemical energy storage devices using lithium technology. Lithium-ion batteries in particular, which are made up of lithium-ion cells, are considered to be a promising energy storage technology for electromobility.

For the transport of entire lithium-ion batteries or their components, for example from a supplier's production facility to a vehicle OEM's final assembly plant, there are numerous transport regulations that ensure safe transport.

From Scripture U.S. 7,763,380 B2 For example, a packaging container for lithium-ion cells is produced that meets transport specifications and enables individual cells to be transported safely.

The document DE 103 08 382 B3 addresses the stressing of a high temperature fuel cell stack, discussing a method of placing insulation between the means for stressing the stack and the high temperature fuel cell stack.

The writing WO 95/16583 A1 FIG. 1 shows how a fastening strap for a battery pack of an electrified vehicle is used to fasten subcomponents of the battery pack in or on a battery housing.

The document US 4,936,409A discusses a fixation mechanism for clamping a battery in a motor vehicle to prevent movement of the battery in the event of sudden deceleration or acceleration. The retention mechanism includes a non-metallic tray that connects to the vehicle and a strap with a two-piece quick-release fastener for securing the battery in place.

It is an object of the invention to describe an improved overall store which can be transported particularly safely.

From the state of the art it is inconclusive as to how a short circuit can be prevented from forming between the cell modules of an overall storage unit during transport.

It is an object of the invention to describe the improved overall memory that can be transported in accordance with international regulations and standards.

This object is achieved by an overall memory according to claim 1. Advantageous embodiments and developments of the invention result from the dependent claims.

According to the invention, an insulating material encloses each cell module, each cell module is clamped in a clamping frame enclosing the cells of the cell module.

This offers the advantage that a cell module is designed as a mechanically fixed structural unit made up of a number of cells. The clamping frame encloses the cells in such a way that the clamping frame exerts pressure on the cells adjacent to the clamping frame and these cells on other cells that are not in contact with the clamping frame, so that all cells are held in the network of the cell module at least against their own weight. The clamping frame is part of the cell module. In addition, the network of cells forming the cell module is surrounded by a high-voltage insulating protective jacket, i.e. the contact between the cells and the clamping frame takes place via the protective jacket.

The insulating material is preferably high-voltage safe.

According to a further embodiment of the invention, the overall store comprises a base plate common to several cell modules, the clamping frame of these cell modules being mechanically connected to the base plate.

Fastening the clamping frames of the cell modules to the common base plate ensures that the cell modules cannot be displaced relative to one another in space up to the mechanical load capacity limit of the base plate, the anchorage between the clamping frame and base plate, and the clamping frame itself. If necessary, the overall energy store comprises a plurality of base plates for a plurality of cell modules in each case, with the plurality of base plates being rigidly connected relative to one another up to the mechanical load capacity limit of the base plates. In this way, a total energy store can be designed to have “multi-levels”. In any case, all cell modules are fixed on a base plate.

It is also advantageous if there is a minimum clearance between the cell modules connected to the base plate, which is designed in such a way that the cell modules connected to the base plate have a minimum distance in Shape of the air gap exists and the minimum distance prevents a short circuit due to air ionization between two cell modules up to an impulse withstand voltage of at least once the open-circuit voltage of a cell module.

This ensures that all cell modules are structurally arranged relative to all other cell modules such that there is a minimum distance between the cell modules. This air gap prevents a short circuit caused by air ionization between two cell modules up to an impulse withstand voltage that is at least one times the open-circuit voltage of a cell module. Ideally, the structural arrangement of the cell modules is designed in such a way that the air gap prevents a short circuit caused by air ionization up to an impulse withstand voltage that is up to 50 times the open-circuit voltage of a cell module.

According to a further variant of the present invention, each cell contains a safety membrane and a fuse which trips at a certain current intensity flowing across the membrane, with gas pressure in the cell deforming the safety membrane and the deformed safety membrane short-circuiting the two poles of the cell.

Since one pole of the cell is connected to one of the two electrodes of the cell, there is a short circuit between the two electrodes inside the cell housing due to a low-impedance electrical connection between the two poles. This allows the cell to discharge in a controlled manner, which allows the gas pressure in the cell to be released through overheating.

When the fuse is blown, the short circuit between the two poles inside the cell is preferably broken and when the fuse is blown, a short circuit is created between the two poles outside the cell.

This means that when the fuse is blown, the two poles of the cell are conductively connected to each other via the safety membrane. However, with at least one pole there is no conductive connection between the pole and the associated electrode inside the cell housing. In this case, the two electrodes of the lithium-ion cell do not form a complete electrochemical system, since there is only an electrochemical interaction via the electrolyte.

• Der Transport von Lithium-Ionen-Batterien ist zahlreichen Vorschriften und Regularien unterworfen. Zum Beispiel wird in internationalen Tests im Wesentlichen gefordert, dass Batterien auf Lithium-Ionen-Basis nur transportiert werden können, wenn bestimmte Tests nachweislich von baugleichen Bauteilen erfolgreich bestanden wurden.

The invention is based on the considerations set out below:

• The transport of lithium-ion batteries is subject to numerous rules and regulations. For example, international tests essentially require that batteries based on lithium-ion can only be transported if certain tests have been proven to have been successfully passed by identical components.

The term battery is often referred to a functional electrochemical energy storage unit that consists of several lithium-ion cells. In this context, a cell module is to be understood as a battery.

In the present document, an overall memory is to be understood as meaning a plurality of cell modules that are functionally electrically connected to one another. The concept of the overall store can include other components of an energy storage system, such as a housing, control electronics and a cooling device.

The correspondence of the nomenclature in the present document and in international transport regulations is that a battery unit can also be subsumed under an overall memory and a battery can also be subsumed under a cell module.

The transport of an entire storage unit or a battery assembly makes numerous technical demands on the assembly groups of the entire storage unit.

A technical challenge is to enable the battery assembly to be transported safely, and this can only be guaranteed if the entire storage system consists of individual batteries that can be transported safely.

Another technical task is that for safe transport of the entire storage unit, i.e. for the combination of individual batteries, short circuits or excessive discharge of each battery of the entire storage unit are prevented during transport and overheating or overcharging of the entire storage unit is prevented.

The prior art does not describe any conclusive teaching on the design of a total lithium-ion storage device for safe transport, in particular with regard to preventing short circuits and/or overcharging between the individual batteries during transport.

Consequently, this leads to the fact that cost-intensive and logistically complex empirical investigations and tests have to be carried out on various samples of expensive overall storage devices on complex test benches in order to provide evidence of short-circuit prevention between the individual batteries.

It is therefore proposed to integrate insulation between the batteries or cell modules between certain current paths for possible short circuits. This isolating effect is ensured by a combination of air gaps and isolating materials. The current paths of possible short circuits are in turn determined by the design of the batteries and the constructive integration of the batteries within the overall memory.

By fixing the cell modules relative to each other in combination with the insulating effect between the cell modules, a low-impedance connection between two cell modules is effectively prevented.

By implementing these measures, the number of overall memory tests to be performed to verify prevention of short-circuiting or excessive discharge of each battery of the battery assembly and prevention of overheating or overcharging of the entire battery assembly during transportation can be greatly reduced.

This means reduced test piece costs, reduced test implementation costs, reduced logistics costs and more efficiency in energy storage development.

• 1 Schematische Übersicht eines Gesamtspeichers
• 2 Zelle mit Sicherheitsmembran

A preferred exemplary embodiment of the invention is described below with reference to the attached drawing. This results in further details, preferred embodiments and developments of the invention. In detail shows schematically

• 1 Schematic overview of a total memory
• 2 Cell with safety membrane

1 shows a schematic overview of an overall electrochemical store for a vehicle with an electrified drive train. In order to be able to transport the entire storage system safely and reliably (e.g. by truck from one production plant to another production plant or in the intended vehicle), safety tests are carried out on test benches in advance. Such tests for an overall memory, which can also be referred to as a battery assembly, sometimes result from international transport regulations.

A total storage is made up of several cell modules, in 1 three cell modules are shown as an example (4a-4c). Each cell module consists of a certain number of two-pole electrochemical lithium-ion cells as the smallest electrochemical unit. In 1 the individual cell modules show a different number of cells (1a-1k) per cell module. A series connection of the cells within a cell module is preferred. The cells of a module are alternately electrically connected to one another by cell connectors (2a-2i), ie a positive pole is connected to the negative pole of the connected cell. Cells can also be connected in parallel.

The individual cell modules are electrically connected to one another by module connectors (3). The cell modules are preferably connected in series. If the cell modules are connected in parallel, it is important to ensure that the cell modules have a uniform nominal voltage, i.e. the number of cells connected in series per cell module should be the same for all cell modules (if the cells are of the same type).

The permissible, safe transport of the entire storage system requires that an individual cell module fulfills existing transport specifications. This is assumed here. It should be noted that a cell module is also referred to as a battery in this context. This means that in the present document the terms overall memory and battery assembly, as well as the terms cell module and battery, are understood synonymously.

Furthermore, for reliable and safe transport of the entire storage unit, it must be ensured that short circuits or excessive discharge of each battery in the battery assembly, i.e. of each cell module of the overall storage unit, are prevented during transport and overheating or overcharging of the entire battery assembly is prevented.

the end 1 a combination of technical measures emerges which, in combination, effectively and reproducibly guarantee this requirement for the reliable and safe transportability of the entire storage system.

The cells within each cell module are surrounded by a high-voltage-resistant insulating material (8) and held in place by a clamping frame (6). The high-voltage-resistant insulating material has an insulating effect against voltages that are a multiple of the no-load voltage of a cell module, for example with a no-load voltage of a cell module of 40-50 V up to the range of 1-3 kV. The clamping frame can be made of aluminum. The clamping frame encloses the cells, which are geometrically designed as round cells or as prismatic cells, so that they form a dense package of cells. The high-voltage-resistant insulating material isolates the dense packing of the cells from the clamping frame. The dense packing of the pack also means that the cells do not fall out of the pack under their own weight and fall into all of them against a given acceleration six spatial directions the cells are not shifted against each other. A force in the range of 50 g to 150 g is to be assumed as the specified accelerating force for safe transport even in the event of a crash. For example, with an assumed dead weight of a cell module of 12 kg and a specified acceleration of 50 g, this means that the clamping frame must have a clamping force of at least 6 kN.

The cells and their housing are specified for this mutually braced installation. This is caused in particular by the selected wall thickness of the cell housing, which is often made of aluminum.

A single cell module is anchored to the associated clamping frame on a base plate (5) of the overall store by one or more screw, plug or welded connections (7). In 1 the clamping frame has a rectangular basic shape and is anchored to the base plate at the four corners. The base plate and the screw connection are designed in such a way that a predetermined accelerating force fixes the cell modules immovably on the base plate. A force in the range of 50 g to 150 g is to be assumed as the specified accelerating force for safe transport even in the event of a crash.

The clamping frames of the cell modules (4), the anchoring and the base plate ensure that a direct short circuit (indicated by dashed lines in 1 ) between individual cell modules is prevented by the action of a predetermined accelerating force. A force in the range of 50 g to 150 g is to be assumed as the specified accelerating force for safe transport even in the event of a crash.

In addition, the arrangement of the cells and cell modules 1 effective short-circuit protection against air ionization, ie against a low-impedance connection between electrical potentials between two cell modules. In such a case, a closed circuit is created by air ionization. This is based on the technical implementation in 1 preventable by an air gap between the poles of the cell modules that are connected to the module connectors, which exceeds a predetermined distance. An order of magnitude for an impulse withstand voltage between two cell modules, i.e. a temporary overvoltage between two cell modules of a lithium-ion battery for automotive applications with an open-circuit voltage of the cell modules of e.g. 40-50 V, is at least 50 times the open-circuit voltage of a cell module, i.e at eg 40-50 V open-circuit voltage about 2.5 kV. The specified distance is influenced by other parameters such as sea level or possible contamination inside the high-voltage battery. Depending on the other parameters, the magnitude of the specified distance is at least 3 mm for a cell module open-circuit voltage of 40-50 V to ensure an impulse withstand voltage of 2.5 kV.

The short-circuit protection for the transport of the entire accumulator can only fail if an external force acts in such a way that the base plate is deformed or destroyed or two cell modules break from the anchorage and their respective clamping frame and the insulation material are destroyed. Alternatively, a conductive part that does not belong to the overall memory could be introduced into the overall memory. Both scenarios are accompanied by effects that cannot be secured according to the current test regulations. Rather, this could be considered intentional abuse or force majeure.

The prevention of a short circuit also ensures that there is no uncontrolled discharge of the cells.

The reliable transport of an entire storage unit also presupposes that the risk of overheating and/or overcharging of the cells can be ruled out.

For this purpose, each cell according to 2 a safety membrane (9) with a safety fuse (10).

The safety membrane is primarily used to protect each individual cell from overcharging and overheating. Excessive charging and overheating can lead to increased gas formation in a lithium-ion cell.

The concentric volume expansion associated with the gas development presses against a conductive membrane and deforms it with regard to a specified degree of freedom. The safety membrane in the deformed state (9a) creates a cell-internal short circuit between the positive and the negative electrode and a cell-external short circuit between the negative pole (11) and the positive pole of the cell. As a result, on the one hand, the current from the external source is short-circuited without inducing further electrochemical reactions and, on the other hand, an internal discharge of the cell is brought about. With regard to the internal discharge current, the membrane is protected by a safety fuse (10). When the fuse blows, an electrode (in 2 the negative electrode (13), the housing (15) being at the potential of the positive electrode (14) from the associated one Pole separated so that there is a permanent electrical break between the electrodes inside the cell. When the fuse melts, the cell's external circuit remains intact, so that the external circuit is short-circuited across the membrane. This effectively prevents each individual cell from being overcharged. The "normal state" of the safety membrane is in 2 with (9), in which there is no short circuit between the two poles.

The special combination of the measures described 1 with 2 ensures the high, reproducible probability of proving certain criteria for safe transport of a battery assembly, such as preventing short circuits between cell modules and overheating of cell modules.

Claims (6)

Total electrochemical store for storing electrical energy, which comprises a number of cell modules (4a-4c) which consist of a number of two-pole lithium-ion cells (1a-1k), characterized in that - an insulating material (8) of each cell module (4a-4c ) encloses - each cell module (4a-4c) is clamped in a clamping frame (6) enclosing this cell module (4a-4c). total storage after claim 1 , characterized in that - the insulating material (8) is high-voltage safe. total storage after claim 1 or 2 , characterized in that - the overall store comprises a base plate (5) common to several cell modules (4a-4c), - the clamping frame (6) of each of the several cell modules (4a-4c) is mechanically connected to the base plate (5). total storage after claim 3 , characterized in that - there is a minimum distance between the cell modules (4a-4c) connected to the base plate (5) in the form of an air gap, - the minimum distance is a short circuit due to air ionization between two cell modules (4a-4c) up to one Prevents surge withstand voltage that is at least once the open-circuit voltage of a cell module (4a-4c). Overall store according to one of the preceding claims, characterized in that - each cell (1a-1k) comprises a safety membrane (9), - each cell (1a-1k) comprises a fuse which trips at a specific current intensity flowing across the membrane, - a gas pressure in the cell (1a-1k) deforms the safety membrane (9,9a), - the deformed safety membrane (9a) short-circuits the two poles (11,12) of the cell (1a-1k). total storage after claim 5 , characterized in that - when the fuse is triggered, the short-circuit of the two poles (11,12) inside the cell (1a-1k) is interrupted - when the fuse is triggered, the short-circuit of the two poles (11,12) with an external connection of the poles (11,12) is established.

Images