Methods for increasing the performance of a battery, battery management system and motor vehicle

Abstract

Method for increasing the performance of a battery, in particular a lithium-ion battery, by increasing the temperature of the battery, characterized by that the temperature increase is achieved by alternating charging (10) and discharging (20) of the battery, wherein the respective charging (10) or discharging (20) takes place over a maximum time period (tch), and after reaching a certain temperature limit, the charge (Q) of the battery is changed in a charge change process (50), wherein in the charge change process (50) the charge (Q) of the battery is decreased or increased over a charge change time (tap), and the maximum time period (tch) of a respective charging (10) or discharging (20) is in the following ratio to the charge change time (tap): tch ≤ 1 / 3 tap; wherein a charging pause (40) with a pause time (tp) is performed between at least two phases of alternating charging (10) and discharging (20); and wherein the pause time (tp) is in a ratio of tp ≥ tch to the maximum duration (tch) of a respective charging (10) or discharging (20).

Description

[0001] The present invention relates to a method for increasing the performance of a battery, in particular a lithium-ion battery, and to a battery management system with which the method for increasing the performance according to the invention can be implemented. Furthermore, the present invention relates to a motor vehicle having a battery management system according to the invention.

[0002] Battery cells and batteries composed of battery cells are widely known. A battery cell, as well as a battery composed of battery cells, is an accumulator that can be electrically charged and discharged. The battery cell is a single galvanic cell that delivers a characteristic voltage depending on the combination of the cell's electrode materials. To construct a battery from several battery cells, these are electrically connected in series or parallel.

[0003] Lithium-ion batteries are particularly well known, as rechargeable energy storage devices, particularly in mobile devices or equipment. Lithium-ion batteries are intended, in particular, for the electrification or partial electrification of electrically powered vehicles.

[0004] The batteries of such vehicles can be charged via a generator, which may also have an electric motor function, or via a connection to an external network.

[0005] Especially with lithium-ion batteries, the charging and discharging performance of the battery is temperature-dependent. At low temperatures, the battery allows a significantly lower charging or discharging current than when the battery is within its optimal operating temperature range. This means, among other things, that charging the battery takes significantly longer at low temperatures, such as in winter, than at higher temperatures, significantly delaying the starting ability and operational readiness of the electric vehicle. Furthermore, excessive charging or discharging current, particularly at low temperatures, can cause irreversible damage to the battery cells, meaning that safe operation can no longer be guaranteed in the long term.Such damage can even lead to a so-called thermal runaway of the battery cells or an entire battery, with the possible consequences of a battery fire and / or the release of dangerous chemical substances. State of the art

[0006] To control the temperature of batteries, it is known to increase the temperature of the battery cells or the battery to a desired temperature level using an external heat source.

[0007] Furthermore, it is known that during charging, a battery's temperature level increases, so that after charging, the battery can be operated within its optimal operating temperature limits. However, it should be noted that when charging at relatively low temperatures, the charging current must be relatively low to avoid exceeding the battery's operating limits.

[0008] Conventional methods for increasing the performance of a battery, battery management systems and motor vehicles are disclosed in EP 2 518 817 A2 and US 2002 / 0 070 710 A1. Disclosure of the invention

[0009] The invention is defined by the appended claims. The following description is subject to this limitation. Any disclosure outside the scope of the claims is intended for illustrative and comparative purposes only.

[0010] According to the invention, a method for increasing the performance of a battery, in particular a lithium-ion battery, is provided, in which the temperature of the battery is increased, wherein the temperature increase is realized by alternating charging and discharging of the battery and the respective charging or discharging takes place over a maximum time period tch, and after reaching a certain temperature limit value, the charge of the battery is changed in a charge change process, wherein in the charge change process the charge of the battery is reduced or increased over a charge change time tap, and the maximum time period tch of a respective charging or discharging to the charge change time tap is in the ratio of tch ≤ 1 / 3 tap.A charging pause with a pause time (tp) is carried out between at least two phases of alternating charging and discharging; and the pause time (tp) is in a ratio of tp ≥ tch to the maximum time duration (tch) of a respective charging (10) or discharging (20).

[0011] The battery can have one or more battery cells. Preferably, several charging and discharging processes are carried out alternately, with a discharging process being carried out after each charging process. The ratio of tch ≤ 1 / 3 thp expresses that the phase of the charge change process, in which the battery charge is reduced over a change time tap, for example by feeding an electrical consumer or increased, for example by charging, is considerably longer than the time of the respective phases of the charging or discharging processes, which serve to increase the temperature of the battery. The charge change process does not have to take place immediately after the alternating charging and discharging. The maximum time duration tch for each charging or discharging process can be, for example, between 1 and 3 seconds, whereby the charge change time tap can be at least 1 minute.In a typical charge change process during battery charging to increase the charge, the charge change time is at least 5 minutes. When normally supplying at least one electric motor to drive an electrically powered vehicle, the charge change time is also at least 1 minute in over 95% of applications. Advantages of the invention

[0012] The charging strategy described according to the invention allows the charging current to be significantly increased, especially at low initial temperatures, and the battery to be charged gently, thus extending its service life. Furthermore, exceeding an operating limit and the resulting failure can be avoided if the method according to the invention prevents the battery from overcooling during charging or discharging during its intended use.

[0013] The advantage of the invention lies in the fact that, due to the optimal temperature control of the battery, higher charging currents can be achieved, which enables shorter charging times. This significantly increases the convenience of using the battery or a motor vehicle connected to it, as long waiting times before reusing the vehicle are eliminated. Furthermore, the safety of the battery's operation is increased, as it can be operated away from safety-relevant operating limits.

[0014] Furthermore, the method according to the invention increases the battery's service life if it can be operated continuously within the optimal temperature range. In addition, no external electrical heat source is required to implement thermal management of the battery.

[0015] To implement the method according to the invention, only temperature sensors are required that measure the temperature in the battery or battery pack and that of the environment. If a predefined low-temperature threshold is undershot in the battery and an intended change in the battery's charge is detected, the method according to the invention is implemented to heat the battery. The threshold value is defined such that a high charging or discharging current is possible. The threshold value can, for example, be a temperature of 10 °C. This allows the battery of an electrically powered vehicle to be kept warm even after it has been switched off, so that the battery can be operated within the optimal temperature range when the vehicle is later restarted or the battery is recharged.

[0016] Preferably, the method according to the invention is carried out in such a way that the charge of the battery, after performing the alternating charging and discharging, has a value within the charge value range between the amplitudes of the first charging process and the first discharging process. This means that the charge does not change or changes only insignificantly, namely only within the charge value range between the amplitudes of the first charging process and the first discharging process.

[0017] The method according to the invention has the effect that the battery heats up during charging and discharging. The heat produced in the battery cells during charging and discharging is primarily composed of a Joule effect and reaction heat, but depending on the current strength, both components have a greater or lesser influence.

[0018] The heating of the battery according to the invention by means of alternating charging and discharging can be carried out by means of a so-called “large current strategy” and a so-called “small current strategy”.

[0019] In the high-current strategy, the battery is alternately charged and discharged at a rate of at least 10C for a battery intended for a typical hybrid motor vehicle; and at least 2C for a battery that can be charged via an external grid connection and is also intended for a typical hybrid motor vehicle; or for a battery intended for a purely electric motor vehicle.

[0020] This means, for example, that a battery with a charge storage capacity of 5 Ah (battery intended for a typical hybrid vehicle) is charged with a current of at least 50 A; and a battery with a charge storage capacity of 60 Ah (so-called plug-in battery, i.e. battery that can be charged via an external mains connection and is also intended for a typical hybrid vehicle; or battery intended for a purely electrically powered vehicle) is charged with a current of at least 120 A.

[0021] The specified values ​​are based on a state of charge (SOC) of approximately 50% and must therefore be adjusted accordingly if the state of charge is significantly higher or lower.

[0022] This means that the charge-discharge current profile is generated with a relatively high current. Heat generation occurs primarily due to the Joule effect via the battery's internal ohmic resistance. Constant charge-discharge cycles are preferred, although at the end of these cycles the battery is not fully charged but is merely heated by the current flow or maintained at a suitable temperature level. The current intensity for each charge and discharge depends on the target temperature but is limited by the maximum permissible charging current for safety reasons. The maximum permissible charging current can be defined with regard to service life and / or temperature dependence.

[0023] The advantage of this process configuration is that the battery can be kept warm or heated without the need for additional external heating. The process is ideally suited for preconditioning the battery for time-controlled charging. Several operating strategies, such as rapid charging, can be implemented immediately following the heating according to the invention.

[0024] This method embodiment can be implemented such that a charging pause with a pause time tp is performed between at least two phases of alternating charging and discharging. Preferably, charging pauses with a pause time tp are performed between all phases of alternating charging and discharging. This means that, as in the previously mentioned method variant, essentially continuous charging-discharging cycles with a constant (relatively high) current are realized, wherein the magnitude of the charging current is equal to the magnitude of the discharging current and the charging time window (charging duration) is equal to the discharging time window (discharging duration). Thus, no charging of the battery is recorded after the alternating charging and discharging. However, pauses are performed between the charging and discharging phases.Since Joule heat production is quadratic to the current flow, increasing the current flow can greatly reduce the time required to produce the same amount of heat. This means that a pause can be integrated between the charging and discharging phases. This can be achieved using simple control such as pulse width modulation (PWM). This process design is particularly suitable for applications with rapid capacitive charging and discharging. This means that, in principle, supercapacitors can also be used as a charging source. The pause time tp to the maximum duration tch of a respective charging or discharging cycle should preferably be in the ratio tp ≥ tch. However, during a charging pause, the charge value of the battery is not changed as in the charge change process; instead, the charge value remains the same throughout the pause time.

[0025] To implement the low-current strategy, the alternating charging and discharging of the battery can be carried out in such a way that the alternating charging and discharging of the battery occurs at a maximum of a 10C rate for a battery intended for a typical hybrid motor vehicle; and at a maximum of a 2C rate for a battery that can be charged via an external grid connection and is also intended for a typical hybrid motor vehicle; or for a battery intended for a purely electrically powered motor vehicle.

[0026] This means, for example, that a battery with a charge storage capacity of 5 Ah is charged with a maximum current of 50 A, and a battery with a charge storage capacity of 60 Ah is charged with a maximum current of 120 A.

[0027] These specified values ​​also assume a state of charge (SOC) of approximately 50% and must therefore be adjusted accordingly if the state of charge is significantly higher or lower.

[0028] This means that the reaction heat generated during the charge-discharge process with a low current flow is utilized. In this process configuration, both of the aforementioned heat production options are utilized, with reaction heat playing a relatively large role in heating the battery. Thus, battery heating can also be achieved with a relatively low current. The reaction heat is not constant across the entire charge range from 0 to 100%; rather, there is a charge range where the reaction heat exhibits a maximum or minimum. In particular, the charge range with the maximum reaction heat is utilized according to the invention.

[0029] The method according to the invention is advantageous when the battery temperature increase through charging and discharging occurs at a time or over a period of time when the price of electricity from the grid for charging the battery is above a certain price limit. This means that, during periods of high electricity tariffs, the relatively expensive electricity is drawn from the grid during charging and fed back into the grid at the same conditions during discharging. This allows the battery to continue to be heated cost-effectively even during periods of relatively expensive electrical energy.

[0030] In a further embodiment of the method, the battery is charged in parallel with the alternating charging and discharging, so that the battery charge after the alternating charging and discharging has a value above the charge value range limited by the amplitudes of the first charging process and its subsequent discharging process. This keeps or warms the battery during and / or by means of the charging process.

[0031] This process variant is preferably implemented when the price of purchasing electricity from the grid for charging the battery is below a certain price limit. This means that, preferably during periods of low electricity tariffs, the battery temperature is increased by charging, parallel to alternating charging and discharging.

[0032] For example, the battery can be charged to a predefined SOC (state of charge) value that is less than 10% of the possible charge.

[0033] The battery temperature is still lower than a predefined minimum value. The charging and discharging cycles according to the invention can then be implemented, so that the battery temperature reaches the desired minimum temperature value relatively quickly. The battery can then be further charged, for example, with the maximum charging current.

[0034] In a smart grid, where the battery of an electric vehicle is also used as an energy buffer, for example, the method according to the invention has the advantage that alternating charging and discharging can be carried out at a relatively cost-neutral rate, since the electricity drawn from the grid during charging is fed back into the grid during discharging at the same or a similar rate. However, the battery can also be charged at a time when electricity tariffs are favorable. By preheating the battery, subsequent charging can also be carried out more quickly, thus reducing dependence on tariff fluctuations.

[0035] If the described processes were controlled over a longer period, it would also be possible to slowly discharge the battery while keeping it warm, for example, during periods of relatively high electricity rates. During periods of low electricity rates, keeping it warm could be done while charging it in parallel, so that at a predetermined time when an electric vehicle is ready to drive, the battery is fully charged again and in the optimal temperature range.

[0036] A further aspect of the present invention is a battery management system which is designed such that it can control an alternating charging and discharging of the battery such that the temperature of the battery increases, wherein the respective charging or discharging is carried out over a maximum time period tch, and the battery management system is further designed such that after a certain temperature limit value has been reached, the charge of the battery can be changed in a charge change process, wherein in the charge change process the charge of the battery is reduced or increased over a change time tap, and the maximum time period tch of a respective charging or discharging to the charge change time tap is in a ratio of tch ≤ 1 / 3 tap.This means that the battery management system according to the invention controls such charging and discharging processes, as well as the subsequent charging or supplying of a consumer with electrical energy from the battery, wherein one of the alternating charging or discharging processes lasts a maximum of one-third of the time with which the charge state is subsequently changed, such as when charging the battery or when operating a motor vehicle equipped with the battery and the battery management system. This means that the battery management system according to the invention is designed to carry out the method according to the invention for increasing the performance of a battery. The battery management system can also comprise the battery.

[0037] According to the invention, a motor vehicle is also provided, which can in particular be an electrically driven motor vehicle, and which has a battery management system according to the invention.

[0038] The method according to the invention for increasing the performance of a battery or the battery management system according to the invention enables a multitude of charging and operating scenarios to be implemented, such as rapid charging, immediate driveability, rapid auxiliary heating of a motor vehicle, and / or flexible use of the battery as a buffer in a smart grid. This essentially requires a battery, in particular a lithium-ion battery, and an electrically powered vehicle, which can also be a hybrid vehicle. Furthermore, a charger for implementing the charging processes and a power source, which can be, for example, a charging station for feeding in alternating current from a grid or a charging station for feeding in direct current from energy storage devices, are required.The charger should be able to provide power from a grid to the battery and, conversely, feed power provided by the battery into the grid. Drawings

[0039] The invention will be explained in more detail below with reference to the exemplary embodiments illustrated in the accompanying drawings. They show: Fig. 1 a continuous charging and discharging process according to the invention with subsequent charge change process, Fig. 2 an inventive charging and discharging with pauses between the respective phases, Fig. 3 the charging and discharging according to the invention with initial charging, and Fig. 4 the charging and discharging according to the invention with simultaneous charging. Embodiments of the invention

[0040] In the Fig. 1, Fig. 2 and Fig. Figure 4 shows the charging current with a current I plotted against time t. This results in the respective current profile 1.

[0041] In Fig. 3 shows the charge Q over time t. This results in the Fig. 3 shown load profile 2.

[0042] In its simplest form, the method according to the invention is carried out according to Fig. 1 is carried out, starting from a battery which is charged in a first charging process 11 and discharged again in a subsequent first discharging process 21, with the charging processes 10 and discharging processes 20 alternating. This results in the alternating charging 10 and discharging 20 according to the invention. The charging 10 takes place over a charging period 12 and the discharging 20 takes place over a discharging period 22. The charging 10 or discharging 20 takes place over a maximum time period tch. The charge value range 30 is defined by the amplitudes of the charging 10 or discharging 20. After the last process of the alternating charging 10 or discharging 20, a charge change process 50 is carried out, which, however, does not have to follow immediately on from the last process of charging 10 or discharging 20.

[0043] In Fig. 1, the charge change process 50 is associated with a current release and thus with a charge reduction.

[0044] However, the present invention is not limited to the fact that the charge is reduced in the charge change process, but the charge can also be increased by charging the battery if necessary. However, it is essential that the time tap over which the charge is changed is significantly greater than the maximum time duration tch of charging 10 or discharging 20. This shows that the battery can be heated by a relatively rapid alternation of relatively short charging 10 or discharging processes 20 until it is at a corresponding temperature level that allows an efficient charge change process, such as charging or feeding an electrical consumer. This means that in the Fig. In the embodiment shown in Figure 1, the magnitude of the charging current is equal to the magnitude of the discharging current. Preferably, the charging time 12 is also equal to the discharging time 22. A net charge of the battery at the end of the alternating charging and discharging has a value within the charge value range 30. This means that the battery charge has not changed beyond the amplitude values ​​of the alternating charging and discharging processes 10, 20.

[0045] In Fig. Figure 2 shows a process variant in which phases of alternating charging and discharging are each interrupted by a charging pause 40 with a pause time tp. To clarify the difference compared to the first, in Fig. 1, the process variant is also shown in Fig. 2 is indicated by dashed lines. The advantage of the Fig. The advantage of the process variant shown in Figure 2 lies in the fact that battery heating can be efficiently achieved through continuous charge-discharge cycles 10, 20 with constant, but possibly higher, currents and integrated pauses. Since Joule heat production is proportional to the square of the current flow, increasing the current flow can significantly reduce the time required to produce the same amount of heat. Consequently, pauses can also be integrated into the alternating charging and discharging process.

[0046] As already mentioned, charging sources that realize fast capacitive charging, such as so-called supercapacitors, can also be used to implement this process. The pause time tp should be in the ratio tp ≥ tch to the maximum duration tch of a respective charging 10 or discharging 20 cycle.

[0047] In Fig. 3 shows a further method alternative in which the first charging process 11 causes a charge increase amount that is no longer reached by the further amounts of charging 10 or discharging 20. After reaching the predetermined charge value, the method according to the invention, as Fig. 1, but preferably with a lower current intensity. The Joule component of the heat production QJ is constant, namely both during charging 10 and during discharging 20 due to the constant current. The reaction enthalpy Qrev, indicated by the dashed line, is exothermic (positive value) during charging 10 and endothermic (negative value) during discharging 20, whereby the heat production during charging 10 is greater than the heat sink during discharging 20. This results in a total heat production Qtotal, which is made up of the sum of the Joule component QJ and the reaction enthalpy Qrev. The total heat production Qtotal is greater than the Joule component QJ in the overall balance.

[0048] In Fig.Figure 4 illustrates a further embodiment of the method, wherein it can be seen that each charging 10 results in a charging 60, so that the battery charge value achievable at the end of the alternating charging 10 or discharging 20 is above the charge value range 30 defined by the amplitudes of the first charging process 11 and the first discharging process 21. This allows the battery tempering process to be combined with a charging of the battery, so that the battery already has a desired charge value at the end of the alternating charging or discharging.

Claims

[1] Method for increasing the performance of a battery, in particular a lithium-ion battery, in which the temperature of the battery is increased, characterized by , that the temperature increase is achieved by alternating charging (10) and discharging (20) of the battery, wherein the respective charging (10) or discharging (20) takes place over a maximum time period (tch), and after reaching a certain temperature limit, the charge (Q) of the battery is changed in a charge change process (50), wherein in the charge change process (50) the charge (Q) of the battery is reduced or increased over a charge change time (tap), and the maximum time period (tch) of a respective charging (10) or discharging (20) to the charge change time (tap) is in the following ratio: tch ≤ 1 / 3 tap; wherein a charging pause (40) with a pause time (tp) is carried out between at least two phases of alternating charging (10) and discharging (20); and wherein the pause time (tp) is in a ratio of tp ≥ tch to the maximum time duration (tch) of a respective charging (10) or discharging (20). [2] Method for increasing the performance of a battery according to claim 1, wherein the charge (Q) of the battery after carrying out the alternating charging (10) and discharging (20) has a value within the charge value range (30) between the amplitudes of the first charging process (11) and the first discharging process (21). [3] A method for increasing the performance of a battery according to claim 2, wherein the alternating charging (10) and discharging (20) of the battery is carried out at least at a 10C rate for a battery intended for a typical hybrid motor vehicle; and at least at a 2C rate for a battery which is chargeable via an external mains connection and is also intended for a typical hybrid motor vehicle; or for a battery which is intended for a purely electrically driven motor vehicle. [4] A method for increasing the performance of a battery according to claim 2, wherein the alternating charging (10) and discharging (20) of the battery takes place at a maximum of a 10C rate for a battery intended for a typical hybrid motor vehicle; and at a maximum of a 2C rate for a battery which is chargeable via an external mains connection and is also intended for a typical hybrid motor vehicle; or for a battery which is intended for a purely electrically driven motor vehicle. [5] Method for increasing the performance of a battery according to one of the preceding claims, in which the temperature increase of the battery is realized by charging (10) and discharging (20) when the price of the electricity from a network for charging the battery is above a certain price limit. [6] Method for increasing the performance of a battery according to one of claims 1 or 3 to 5, in which a charging (60) of the battery is carried out in parallel with the alternating charging (10) and discharging (20), so that the charge (Q) of the battery after carrying out the alternating charging (10) and discharging (20) has a value above the charge value range (30) limited by the amplitudes of the first charging process (11) and the first discharging process (21). [7] Method for increasing the performance of a battery according to claim 6, in which the temperature increase of the battery is realized by charging (60) when the price of the electricity from a network for charging (10) the battery is below a certain price limit. [8] Battery management system which is designed in such a way that it can control an alternating charging (10) and discharging (20) of a battery in such a way that the temperature of the battery increases, wherein the respective charging (10) or discharging (20) is carried out over a maximum period of time (tch), and the battery management system is designed such that, after reaching a certain temperature limit value, the charge (Q) of the battery can be changed in a charge change process (50), wherein in the charge change process (50) the charge (10) of the battery is reduced or increased over a charge change time (tap), and the maximum time duration (tch) of a respective charge (10) or discharge (20) to the charge change time (tap) is in the following ratio: tch ≤ 1 / 3 tap; wherein a charging pause (40) with a pause time (tp) is carried out between at least two phases of alternating charging (10) and discharging (20); and wherein the pause time (tp) is in a ratio of tp ≥ tch to the maximum time duration (tch) of a respective charging (10) or discharging (20). [9] Motor vehicle, in particular an electrically driven motor vehicle, comprising a battery management system according to claim 8.

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