Method for operating a battery assembly, device and vehicle

Abstract

A method for operating a battery arrangement (30) by means of a control unit (23), which battery arrangement (30) comprises battery cells (31), comprises the following steps: A) When a first state is activated, the battery arrangement (30) is charged during a charging process, wherein the control unit (23) is configured to limit the cell voltage of the battery cells (31) to a predetermined first limit value (UM1) during the charging process; B) When a second state is activated, the battery arrangement (30) is charged during a charging process, wherein the control unit (23) is configured to limit the cell voltage of the battery cells (31) to a predetermined second limit value (UM2) during the charging process, which second limit value (UM2) is higher than the first limit value (UM1), and wherein at least one predetermined first time point (t2) after completion of the charging process by the control unit (23) is a voltage measurement of the cell voltage and in the event of an exceedance of a predetermined third limit value (UM3) a first discharge of the battery cells (31) is carried out.

Description

[0001] The invention relates to a method for operating a battery arrangement, a device and a vehicle.

[0002] DE 10 2007 042 578 A1 discloses a method for standardizing the state of several cells connected in series of a battery by charging the battery with a charging current, in which a bypass current path is activated for each cell whose cell voltage has reached an upper threshold and is subsequently deactivated again as soon as the cell voltage in question has reached a lower threshold.

[0003] DE 10 2015 209 131 A1 shows a battery which allows for short-term overcharging of the battery cells in the event of regenerative braking.

[0004] DE 10 2006 004 737 A1 shows a charging method in which, depending on the state of charge of the individual energy storage cells, the charges of these are balanced.

[0005] DE 10 2007 010 988 B3 discloses a method for determining the initial charge of an accumulator when the accumulator is overcharged beyond a nominal full charge state.

[0006] It is therefore an object of the invention to provide a new method for operating a battery arrangement, a new device and a new vehicle.

[0007] This problem is solved by the independent claims.

[0008] A method for operating a battery arrangement by means of a control unit, which battery arrangement comprises battery cells, comprises the following steps: A) When a first state is activated, the battery arrangement is charged during a charging process, the control unit being configured to limit the cell voltage of the battery cells to a predetermined first limit value during the charging process; B) When a second state is activated, the battery arrangement is charged during a charging process, wherein the control unit is configured to limit the cell voltage of the battery cells to a predetermined second limit value during the charging process, which second limit value is higher than the first limit value, and wherein at least one predetermined first time point after completion of the charging process by the control unit a voltage measurement of the cell voltage is carried out and in the event of an exceedance of a predetermined third limit value a first discharge of the battery cells is carried out in order to lower the cell voltage.

[0009] The second state allows for a temporary increase in cell voltage. This enables the battery cells to be operated temporarily at a voltage range that would eventually damage them, but which is largely unproblematic in terms of affecting their lifespan for short periods. This is particularly useful in vehicle races, where an overvoltage can be provided at the start.

[0010] According to a preferred embodiment, the third limit value corresponds to a cell voltage that is lower than the cell voltage corresponding to the second limit value.

[0011] According to a preferred embodiment, the first discharge is carried out by activating a consumer. If a consumer is available, the discharge can be performed via it.

[0012] According to a preferred embodiment, the consumer is a secondary consumer. Secondary consumers can often be activated without difficulty.

[0013] According to a preferred embodiment, at least one first consumer is selected as the consumer from a consumer group consisting of: - Stoker, - Cooler, - Fans, and - Pump.

[0014] These consumers have proven beneficial for lowering cell voltage.

[0015] According to a preferred embodiment, the first discharge is carried out by transferring energy from battery cells with a higher cell voltage to battery cells with a lower cell voltage in order to approximate the state of charge of the battery cells. This improves the overall state of charge of the battery assembly while simultaneously reducing the maximum cell voltage.

[0016] According to a preferred embodiment, the second limit value lies in the range between 103% and 130% of the first limit value, preferably in the range of 104% to 120%, and particularly preferably in the range of 105% to 115%. Tests have shown that battery cells with such a limit value can be advantageously operated in the overvoltage range.

[0017] According to a preferred embodiment, the state of charge of the battery arrangement reaches 100% in the first state. This enables a long range or energy storage capacity of the battery arrangement even in the first state.

[0018] According to a preferred embodiment, the first limit value corresponds to a cell voltage that is equal to or lower than the nominal voltage of the battery cells. This has virtually no effect on the service life of the battery assembly.

[0019] According to a preferred embodiment, the second limit value is above the nominal voltage of the battery cells. The method enables the battery cells to be used in this range.

[0020] According to a preferred embodiment, the first limit value corresponds to a charging voltage that is less than or equal to the maximum permissible charging voltage specified by the battery cell manufacturer. This has a comparatively small impact on the service life.

[0021] According to a preferred embodiment, the first discharge is terminated as soon as the cell voltage falls below a predetermined fourth limit, which fourth limit is lower than the third limit. Forced discharge is no longer necessary when the battery cells are within the predetermined cell voltage range.

[0022] According to a preferred embodiment, the first time point is determined such that it is based on a second time point at which the charging process is completed after a predetermined initial time period. This advantageously allows the initial time period to be specified depending on the type of battery cell and the degree of overcharging.

[0023] According to a preferred embodiment, the first time point is determined such that, starting from a third time point at which the cell voltage of the battery cell reaches the second limit value, it lies after a predetermined second time period has elapsed. This determination of the first time point reduces the damage to the battery cell in the event of an overvoltage in a more physically precise manner.

[0024] A device comprises a battery assembly and a control unit, which battery assembly contains battery cells, and which device is configured to carry out such a procedure. This device enables high performance, for example, at the start of a vehicle race.

[0025] A vehicle has such a device. Such a vehicle has high performance.

[0026] Further details and advantageous embodiments of the invention will become apparent from the exemplary embodiments described below and illustrated in the drawings, which are in no way to be understood as limiting the invention, as well as from the dependent claims. It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the present invention. It shows: Fig. 1 in a schematic representation a vehicle with a device, Fig. 2. A diagram showing the state of charge and cell voltage, Fig. 3. A schematic diagram shows a cell voltage over time. Fig. 4 a diagram showing the cathode voltage of a lithium-ion battery cell as a function of the lithiation, and Fig. 5 a diagram showing the anode voltage of a lithium-ion battery cell as a function of the lithiation.

[0027] In the following, identical or similarly functioning parts are designated with the same reference symbols and are usually described only once. The description builds upon itself across figures to avoid unnecessary repetition.

[0028] Fig. Figure 1 shows a schematic representation of a vehicle 10 with a device 20.

[0029] The device 20 has a battery arrangement 30 and a control unit 23.

[0030] The battery arrangement 30 has battery cells 31 and a voltage measuring device 32, and it is controllable by the control unit 23.

[0031] The voltage measuring device 32 enables the cell voltage of the battery cells 31 to be measured. The voltage measuring device 32 can, for example, have a measuring capability for parallel measurement of all battery cells 31, or it can be designed like a multiplexer to measure the cell voltage of the individual battery cells 31 one after the other.

[0032] The control unit 23 also enables the control of consumers 40, 42, 44, which can be supplied by the battery arrangement 30.

[0033] In the exemplary embodiment, the consumer 40 is a main consumer, for example a drive motor for the vehicle 10.

[0034] In the exemplary embodiment, consumers 42, 44 are secondary consumers, for example a heater, a cooler, a fan and / or a pump.

[0035] The vehicle 10 has a connection 34, via which electrical energy can be supplied to the battery arrangement 30 for charging from an external charging station, or vice versa.

[0036] Fig. Figure 2 shows an example diagram with a characteristic curve 51 of a lithium-ion battery. The abscissa shows the state of charge (SOC), and the ordinate shows the cell voltage UZ of one of the battery cells 31.

[0037] Battery cell manufacturers define the permissible operating range for the cell voltage. In this example, the cell voltage is 3.10 V at a state of charge of 0%, and 4.20 V at a state of charge of 100%. Battery cell manufacturers specify the cell voltage of 4.20 V for a state of charge of 100% as the nominal voltage of the battery cells.

[0038] The term "electrode loading" refers to the degree to which the electrodes of a battery cell 31 are filled, or charged, with lithium ions. The loading is expressed as a percentage. For example, in graphite anodes, approximately one lithium ion can be incorporated for every six carbon atoms. In cathode materials, the uptake of lithium ions depends on the crystal structure of the material and varies considerably.

[0039] The charging of the electrodes, i.e., the cathode and the anode, must always be limited, as excessive charging can lead to aging effects, degradation, and material damage. Therefore, charging should never exceed the 100% specified by the battery cell manufacturer, as this would compromise the battery cell's safety. Manufacturers specify a lower limit for the cell voltage during discharge and an upper limit for the cell voltage during charging. For a long service life, the cell voltage of battery cells 31 should generally remain within the manufacturer's specified operating voltage range between the lower and upper limits; in this example, between 3.50 V and 4.20 V. A limit for the charging current is also typically specified.

[0040] As a result, the maximum capacity of a lithium-ion battery cell is not utilized in order to prevent destruction or damage of battery cell 31 and to enable a long service life.

[0041] Tests have shown that damage to battery cells 31 when exceeding the operating voltage range depends on the duration of the overvoltage. In the exemplary embodiment, a state of charge of 100% to 120% is also shown, at which the cell voltage lies between 4.20 V and 4.50 V. In this range, and especially above it, damage to battery cell 31 can occur over time due to a decomposition reaction at the electrodes. The electrolyte can decompose, and lithium plating can occur at the anode. During lithium plating, metallic lithium is deposited on at least one of the electrodes, and the concentration of lithium ions required for the electrochemical process decreases.

[0042] Damage to the battery cells 31 initially occurs very slowly in the depicted overvoltage range. Therefore, for high-performance applications of the battery cells 31, such as those encountered in motorsports, it is possible to briefly select a state of charge above 100% and operate the battery cells 31 outside the specification of the usual cell voltage window. This also allows for a higher overall voltage of the battery assembly 30 and leads to lower currents and thus lower losses.

[0043] If the cell voltage window is exceeded, limiting the duration of the exceedance, for example to 2 minutes, 5 minutes, or 10 minutes, is highly advantageous for increasing battery lifespan. The exact maximum possible duration must be determined through testing. The expected lifespan of the battery cells is also important in this regard. For example, a longer battery lifespan is expected in a production sports car than in a prototype for an electric racing series.

[0044] The cell voltage and also the charging voltage depend on the material combination of the battery cells 31.

[0045] NMC-type lithium-ion batteries are typically charged with a voltage of approximately 4.2 V per battery cell. These batteries have lithium nickel manganese cobalt oxides at the positive terminal.

[0046] Lithium-ion batteries of type LFP are typically charged with a voltage of approximately 3.65 V per battery cell. These batteries contain lithium iron phosphate (LFP) at the positive terminal.

[0047] Fig. Figure 3 shows the cell voltage of one of the battery cells 31 in a method for operating the battery arrangement 30.

[0048] The process allows for a first state and a second state.

[0049] In the first state, the battery cells are used within the cell voltage window specified by the manufacturer for continuous use.

[0050] In the second state, the cell voltage window for continuous use is left at its upper end, and the battery cells 31 are briefly operated with an overvoltage. This enables, for example, additional power at the start of a car race, as well as a higher energy content and thus a greater range.

[0051] Switching between the first and second states, or selecting either the first or second state, can preferably be done via an input interface of the control unit 23. For example, the driver can select the desired state in the cockpit.

[0052] In the first state (normal operation), the cell voltage rises during charging according to line 61 until the manufacturer's specified nominal voltage with the limit value UM1 is reached at time t0. The charging process then ends, and the cell voltage remains approximately constant according to line 62. As a result, the cell voltage is limited to the limit value UM1.

[0053] The first limit value UM1 preferably corresponds to a cell voltage that is equal to or lower than the nominal voltage of the battery cells 31 for a long service life.

[0054] The first limit value UM1 preferably corresponds to a charging voltage that is less than or equal to the maximum permissible charging voltage specified by the manufacturer of the battery cells 31.

[0055] The state of charge (SOC) of the battery arrangement 30 preferably reaches 100% in the first state upon a full charge.

[0056] In the second state (maximum power for a short time), after reaching the limit value UM1, battery cell 31 is further charged along line 63 until a limit value UM2 is reached, which is above the limit value UM1. At time t1, the limit value UM2 is reached, and the charging of battery cell 31 is terminated. After the charging process is complete, the cell voltage remains constant or only drops slightly, as shown by line 64.

[0057] The limit value UM2 is preferably above the nominal voltage of the battery cells 31.

[0058] The limit value UM2 is preferably in the range between 103% and 130% of the limit value UM1, more preferably in the range of 104% to 120%, and particularly preferably in the range of 105% to 115%. In these ranges, on the one hand, excessively rapid deterioration of the battery cells 31 is avoided, and on the other hand, a significant increase in the maximum possible power and the usable energy content is still achieved.

[0059] Charging up to the UM2 limit is preferably carried out in such a way that the battery cells reach the cell voltage corresponding to the UM2 limit shortly before power is required, for example, just before a race starts. If, for example, a race then begins, the cell voltage drops according to line 65 and after a short time enters the cell voltage range for continuous use.

[0060] However, if no electrical power is required after time t1, for example because a race start is postponed due to rain, the cell voltage should be reduced to prevent deterioration or damage to the battery cells 31. For this purpose, a cell voltage measurement is taken at time t2 and it is checked whether the cell voltage is less than or equal to a predefined limit UM3.

[0061] If this is the case, as with line 65 in the event of a race start, battery cell 31 is within an acceptable cell voltage window, and no additional action is required to maintain cell health.

[0062] However, if the cell voltage at time t2 is greater than the limit value UM3, for example at line 66, the battery cells 31 are discharged at time t2 to bring them within the specified cell voltage window. This prevents damage to the battery cells 31 caused by a prolonged overvoltage outside the cell voltage window.

[0063] To reduce the cell voltage, discharge preferably takes place until a limit value UM4 is reached. The limit value UM4 preferably lies within the specified cell voltage range for continuous operation and can correspond to the limit value UM1.

[0064] The discharge is preferably terminated as soon as the cell voltage falls below a predetermined limit value UM4. The limit value UM4 is preferably less than or equal to the third limit value UM3.

[0065] The time t2 can be determined in different ways.

[0066] One possibility is to determine the time t2 in such a way that it lies after a predetermined time period T1, starting from the time t1 when the charging process ends.

[0067] Another possibility is to determine the time t2 in such a way that, starting from the time t1 at which the cell voltage of battery cell 31 reaches the limit value UM2, it lies after the expiry of a predetermined second time period T1.

[0068] Another possibility is to determine the time t2 in such a way that, starting from the time t0, at which the cell voltage of battery cell 31 exceeds the limit value UM1 and is in the overvoltage range, it lies after a predetermined period of time.

[0069] In the present embodiment, at time t1 both the charging process ends and the cell voltage corresponding to the limit value UM2 is reached. However, these times may differ in other embodiments. It is also possible to select different time durations T1 for the two possibilities and to perform the voltage check at several times t2.

[0070] The discharge of battery cells 31 at time t2 can take place in different ways.

[0071] In the case of a control unit 23 from Fig. Upon activation of one or more of the consumers 40, 42, 44, energy is transferred from the battery arrangement 30 to the consumer(s), and the cell voltage of the battery cells 31 decreases accordingly.

[0072] Preferably, one of the auxiliary consumers is activated by the control unit 23. This is advantageous because, for example, automatic activation of the vehicle's drive motor 10 is only possible to a limited extent without a driver present. In contrast, the presence of a driver is not required when discharging via the auxiliary consumers.

[0073] Preferably, as consumer 40, 42, 44, at least one first consumer is selected from a consumer group consisting of: - Stoker, - Cooler, - Fan - electric air conditioning compressor, and - Pump.

[0074] These consumers can use energy from battery arrangement 30 without major restrictions.

[0075] Another way to discharge the battery cells 31 is to transfer energy from battery cells 31 with a higher cell voltage to battery cells 31 with a lower cell voltage (active balancing) or to equalize them (passive balancing) in order to approximate the state of charge of the battery cells 31. This is also referred to as balancing. The state of charge of the battery cells 31 in a battery arrangement 30 is always slightly different. This can be due to differences in manufacturing or to different loads on the battery cells 31 during operation.

[0076] The different unloading options can naturally be combined.

[0077] The device 20 of Fig. 1 is preferably equipped to carry out such a procedure.

[0078] The vehicle 10 preferably has such a device 20.

[0079] Fig. Figure 4 shows a diagram with a curve 71, which describes the cathode voltage of a lithium-ion battery cell as a function of the lithiation.

[0080] In the area to the right of line 76, at a lithiation level of 0.4, decomposition reactions begin, but these occur relatively slowly. For short durations in a lithiation range between 0.4 and 0.3, the impact on battery life is comparatively minor. For example, the manufacturers of battery cells 31 specify the voltage at line 76 of approximately 4.0 V as the nominal voltage of battery cells 31. The range above the nominal voltage is referred to as the overvoltage range. Similarly, a cathode voltage below approximately 3.6 V at line 75, at a lithiation level of approximately 0.94, is detrimental to the battery cell 31's lifespan.

[0081] It should also be noted that, for example, a cathode voltage greater than 4.3 V can cause the electrolyte in the battery cell to decompose or become unstable.

[0082] Plating also becomes problematic at higher cathode voltages.

[0083] Fig. Figure 5 shows a diagram with a curve 72, which describes the anode voltage of a lithium-ion battery cell as a function of the lithiation.

[0084] Here, too, an example of a left limit 77 with a lithiation of approx. 0.01 and a right limit 78 with a lithiation of approx. 0.80 is shown, as they are usually specified by the manufacturers for the battery cells 31.

[0085] For graphite and / or silicon anodes, there is typically a capacity reserve of 5-15% to the right of the limit of 78. This can be utilized in the second state. However, lithium plating occurs further to the right. This limitation does not apply to lithium metal anodes.

[0086] Based on such diagrams and on investigations of the effects occurring, a suitable exceedance range of the usual voltage window can be determined, and improved use of the battery cells for high-performance applications can be achieved with comparatively little deterioration of the battery cells.

[0087] The primary goal is to prevent the anode from being overcharged during the planned overcharging process, thus preventing lithium plating. The electrolyte must also remain sufficiently stable.

[0088] Naturally, various variations and modifications are possible within the scope of the present invention. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2007 042 578 A1

[0002] DE 10 2015 209 131 A1

[0003] DE 10 2006 004 737 A1

[0004] DE 10 2007 010 988 B3

[0005]

Claims

[1] Method for operating a battery arrangement (30) by means of a control device (23), which battery arrangement (30) has battery cells (31), which method comprises the following steps: A) Upon activation of a first state, the battery arrangement (30) is charged during a charging process, wherein the control unit (23) is configured to limit the cell voltage of the battery cells (31) to a predetermined first limit value (UM1) during the charging process; B) When a second state is activated, the battery arrangement (30) is charged during a charging process, wherein the control unit (23) is set up to limit the cell voltage of the battery cells (31) to a predetermined second limit value (UM2) during the charging process, which second limit value (UM2) is higher than the first limit value (UM1), and wherein at least a predetermined first time (t2) after completion of the charging process by the control unit (23) a voltage measurement of the cell voltage is carried out and if a predetermined third limit value (UM3) is exceeded, a first discharge of the battery cells (31) is carried out. [2] Method according to claim 1, wherein the first discharge is carried out by activating a consumer (40, 42, 44). [3] Method according to claim 2, wherein the consumer (40, 42, 44) is a secondary consumer (42, 44). [4] Method according to claim 2 or 3, in which at least one first consumer is selected as the consumer (40, 42, 44) from a consumer group consisting of: - Stoker, - cooler, - electric air conditioning compressor, - fan, and - Pump. [5] Method according to one of the preceding claims, in which the first discharge is carried out by transferring energy from battery cells (31) with higher cell voltage to battery cells (31) with lower cell voltage in order to bring the state of charge of the battery cells (31) closer to one another. [6] Method according to one of the preceding claims, in which the second limit value (UM2) is in the range between 103% and 130% of the first limit value, preferably in the range 104% to 120% and particularly preferably in the range 105% to 115%. [7] Method according to one of the preceding claims, wherein the state of charge (SOC) of the battery arrangement (30) reaches 100% in the first state. [8] Method according to one of the preceding claims, wherein the first limit value (UM1) corresponds to a cell voltage which corresponds to the nominal voltage of the battery cells (31) or is lower than the nominal voltage of the battery cells (31). [9] Method according to one of the preceding claims, in which the second limit value (UM2) is above the nominal voltage of the battery cells (31). [10] Method according to one of the preceding claims, in which the first limit value (UM1) corresponds to a charging voltage which is less than or equal to the maximum permissible charging voltage specified by the manufacturer of the battery cells (31). [11] Method according to one of the preceding claims, in which the first discharge is terminated as soon as the cell voltage falls below a predetermined fourth limit value (UM4), which fourth limit value (UM4) is smaller than the third limit value (UM3). [12] Method according to one of the preceding claims, in which the first time (t2) is determined such that it is located after a predetermined first time period (T1) starting from a second time (t1) of the termination of the charging process. [13] Method according to one of the preceding claims, in which the first time (t2) is determined such that, starting from a third time (t1) at which the cell voltage of the battery cell (31) reaches the second limit value (UM2), it is after the expiry of a predetermined second time period (T1). [14] Device (20) which has a battery arrangement (30) and a control unit (23), which battery arrangement (30) has battery cells (31), and which device (20) is designed to carry out a method according to one of the preceding claims. [15] Vehicle (10) comprising a device (20) according to claim 14.

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