Method for charging electrical energy storage system

Abstract

The present disclosure relates to a method (100) for charging an electrical energy storage system (10) comprising a first electrical energy storage unit (12) and a second electrical energy storage unit (14). The disclosure also relates to an electrical energy storage system (10), a vehicle (1) comprising the electrical energy storage system (10) and a computer program product associated with the method (100).

Description

Technical Field

[0001] The present disclosure relates to a method for charging an electrical energy storage system, an electrical energy storage system, a vehicle, and a computer program product. Background Art

[0002] Rapid charging of an electrical energy storage system has a significant impact on the degradation of its battery cells. Specifically, the highest rate of capacity fade and battery cell degradation occurs during rapid charging of battery cells at high state of charge (SOC) levels of the battery cells.

[0003] However, fast charging is a highly desirable method for different electrical energy storage systems, such as those used in vehicles, particularly battery electric vehicles. Fast charging enables battery electric vehicles to travel long distances in a single trip, albeit with limited range. Summary of the invention

[0004] A charging method that is fast but less degrading to the battery to extend its life is needed.

[0005] This problem is at least partly solved or alleviated by the subject matter of the independent claims of the present disclosure, wherein further examples are incorporated in the dependent claims.

[0006] According to a first aspect, there is provided a method for charging an electrical energy storage system, the electrical energy storage system comprising a first electrical energy storage unit and a second electrical energy storage unit, the method comprising:

[0007] charging the first energy storage unit and the second energy storage unit with electrical energy; and

[0008] Electrical energy is transferred from the second electrical energy storage unit to the first electrical energy storage unit, thereby discharging the second electrical energy storage unit.

[0009] According to the method, the first energy storage unit is charged twice. Specifically, the first energy storage unit is further charged by transferring electrical energy from the second energy storage unit to the first energy storage unit. The two charging processes of the first energy storage unit can be distinguished by the use of the term "charging" and the term "further charging" in this article. As will be further explained below, charging can specifically refer to the rapid charging of the first energy storage unit or in particular the entire energy storage system by rapidly charging the first energy storage unit and the second energy storage unit. However, the further charging of the first energy storage unit specifically refers to transferring electrical energy from the second energy storage unit to the first energy storage unit. The further charging can be performed specifically based on the electrical energy stored in the second energy storage unit during the charging process.

[0010] The method for charging an electrical energy storage system may be divided into two steps or phases. In a first step or phase, charging of the two electrical energy storage units may be performed. In a second step or phase, transfer of electrical energy stored in the second electrical energy storage unit during the first step or phase to the first electrical energy storage unit may be performed. In this two-step or two-phase method, different types of electrical energy storage units with different charging and degradation characteristics may be utilized, as will be explained in more detail below.

[0011] The two energy storage units may be of different types, as will be described in more detail below. Specifically, the first energy storage unit may be configured and / or designed so that it is best to be charged only to a specific state of charge in order to limit its degradation as much as possible. On the other hand, the second energy storage unit may be configured and / or designed so that its charging has little effect on its degradation.

[0012] In an example, the first energy storage unit may include at least one battery cell, and the second energy storage unit may include at least one capacitor. Such different types of energy storage units are advantageous relative to the charging and transfer steps as described herein. Specifically, battery cells can hold charges and discharge for good use (e.g., in a vehicle), but may be susceptible to degradation when charged quickly. On the other hand, capacitors may be relatively poor at holding charges and discharging for use, but may be less susceptible to degradation when charged quickly and can be charged very quickly. Combining these two types in different energy storage units allows for advantageous energy storage systems and methods as described herein.

[0013] In an example, at least one capacitor may be, for example, a lithium ion capacitor. The at least one battery cell may be, for example, a lithium ion battery cell. A specific advantage of lithium ion capacitors is that they are stable when charged quickly, and the battery cells have negligible degradation compared to battery cells. In addition, the specific power of lithium ion capacitors may be about ten times higher than that of lithium ion batteries, so lithium ion capacitors may be charged significantly faster.

[0014] Lithium ion capacitors have been found to be particularly advantageous capacitors in electrical energy storage systems. In particular, lithium ion capacitors have several advantages over other capacitor types (such as, but not limited to, supercapacitors). Supercapacitors have low specific energy, so in order to utilize these in an electrical energy storage system as described herein, the electrical energy storage system will become very heavy. Therefore, supercapacitors in the electrical energy storage system as described herein, as well as many other forms of capacitors, may not be practical in several applications (such as, but not limited to, in vehicles). However, the lithium ion capacitors proposed herein have high specific energy and therefore can have a relatively small weight in an electrical energy storage system, which is very advantageous for several applications (such as, but not limited to, vehicles).

[0015] The at least one lithium ion capacitor may include an anode, a cathode, an electrolyte, and a separator. The anode of the lithium ion capacitor may be a negative electrode and based on a lithium ion battery element. The cathode of the lithium ion capacitor may be a positive electrode and be carbon-based. The lithium ion capacitor may be operated based on an electrochemical reaction, and the lithium ion capacitor may be charged using reversible intercalation of lithium ions.

[0016] Therefore, the lithium ion capacitor proposed herein exhibits high specific power with high specific energy capacity, which is much higher than other capacitors (e.g., supercapacitors). The lithium ion capacitor proposed herein does not have an inflection point at which rapid capacity decay behavior (e.g., the case in lithium ion batteries) is observed. After 3 years of cycle testing, the capacity decay of the lithium ion capacitor proposed herein can be less than 1%.

[0017] In an electric energy storage system, the proposed second electric energy storage unit having the lithium ion capacitor can play a protective role during rapid charging of the overall electric energy storage system by preventing lithium plating from forming in the battery cell of the first electric energy storage unit. For this purpose, the second electric energy storage unit does not need to be too large.

[0018] It may be sufficient that the second energy storage unit is configured to have less than 40%, in particular less than 30% or less than 20%, further in particular in the range of 5% to 40%, in the range of 7% to 30% or in the range of 10% to 20% of the total or overall energy capacity or battery capacity of the energy storage system. The remaining capacity of the energy storage system may be provided by the first energy storage unit.

[0019] By fast charging the two energy storage units, the two energy storage units can be charged to a specific SOC. The first energy storage unit can be charged to a specific or predetermined SOC, for which the first energy storage unit is not negatively affected by the fast charging process in terms of its maximum life, or is less negatively affected than if it were charged to exceed the specific or predetermined SOC. However, the cost is that the first energy storage unit may not be charged to the desired higher SOC but only to a lower SOC associated with limited degradation. For this purpose, the method also includes transferring electrical energy from the second energy storage unit to the first energy storage unit, which is also referred to as further charging in this article. This transfer of electrical energy may be slower than charging the two energy storage units. Therefore, the first energy storage unit can still reach the desired SOC but will not be adversely affected by the fast charging process at a high SOC.

[0020] The electrical energy storage system may be of a vehicle, such as a battery electric vehicle. However, the application of the method is not limited to electrical energy storage systems in vehicles.

[0021] In an example, charging the first energy storage unit with electrical energy can be performed at least partially or completely in parallel with charging the second energy storage unit. This means that both energy storage units can be charged (in particular quickly charged) at the same time. The same electrical energy source (in particular a charging station) can be used to charge both energy storage units.

[0022] In an example, the transfer of electrical energy from the second energy storage unit to the first energy storage unit may be performed after the first energy storage unit has been charged to a predetermined state of charge. The predetermined state of charge has the advantage that charging (in particular rapid charging) may be interrupted or stopped before charging the first energy storage unit at an SOC higher than a predetermined SOC, at which the first energy storage unit may be significantly degraded. Thus, when the predetermined state of charge of the first energy storage unit is reached, charging of at least the first energy storage unit may be stopped. Alternatively, when the predetermined state of charge of the first energy storage unit is reached, charging of at least the first energy storage unit (in particular in the form of rapid charging) may be stopped, but charging may continue at a slower rate than the previous charging (in particular performed with rapid charging). Thus, the energy storage system may be charged to a state of charge higher than the predetermined state of charge, but the first energy storage unit is not significantly degraded because rapid charging is not performed at an SOC higher than the predetermined SOC.

[0023] In an example, the predetermined state of charge of the first energy storage unit may be at least 40%, at least 50% or at least 60%. In particular, the predetermined state of charge of the first energy storage unit may be at least one of 40%, 45%, 50%, 55%, 60%, 65% and / or 70%. The proposed SOC has been found to be advantageous with respect to the required SOC of many use cases of the energy storage system (e.g., in a vehicle) and in terms of degradation. For example, the predetermined state of charge may be selectable or fixed. By selecting a predetermined SOC, the user can control the charging method in a way that he can influence the SOC after charging according to his needs.

[0024] In the example, the first energy storage unit can be discharged while the electrical energy from the second energy storage unit can be transferred to the first energy storage unit. Therefore, when the electrical energy is transferred from the second energy storage unit to the first energy storage unit, the energy storage system may have been used. This has the following advantages: although the method for charging the energy storage system can still be performed, the user of the energy storage system (e.g., the driver of a vehicle with the energy storage system) may have used the energy storage system (e.g., by driving the vehicle using the electrical energy in the first energy storage unit). For example, in the case of a vehicle, when the vehicle is quickly charged at a charging station (e.g., at a highway rest stop), both energy storage units can be charged, but the first energy storage unit can only be charged to a predetermined SOC. The driver can then interrupt the charging via the charging station and continue driving. However, the first energy storage unit can then still be further charged via the electrical energy transferred from the second energy storage unit, thereby effectively providing the driver with a greater driving range to drive the vehicle.

[0025] In the example, the speed at which electric energy is transferred from the second electric energy storage unit to the first electric energy storage unit may be slower than (particularly previously) when electric energy is supplied to the first electric energy storage unit and the second electric energy storage unit during charging. Therefore, although the electric energy storage unit can be charged quickly, the transfer of electric energy from the second electric energy storage unit to the first electric energy storage unit may not be a fast charging process, but a slower charging process. Specifically, electric energy can be gradually transferred from the second electric energy storage unit to the first electric energy storage unit. This is because the electric energy storage system may have used the SOC of the first electric energy storage unit obtained by fast charging, and may not be in a hurry to charge the first electric energy storage unit with electric energy from the second electric energy storage unit. For example, if the first electric energy storage unit of the electric energy storage system of the above example of the vehicle has been charged to 60% SOC, the vehicle can usually be driven for a long duration so that the first electric energy storage unit may not need the charge from the second electric energy storage unit for a long time, and the first electric energy storage unit can be gradually charged with electric energy from the second electric energy storage unit.

[0026] In an example, after transferring the electrical energy from the second energy storage unit to the first energy storage unit, the state of charge of the first energy storage unit may be at least 60% or at least 80%. The SOC after the energy transfer may depend on whether the first energy storage unit was discharged in the meantime, i.e., for example, for the purpose of driving the vehicle.

[0027] In an example, the second energy storage unit can be charged to a predetermined state of charge of at least 80% or at least 90%. In particular, the second energy storage unit can be charged to a predetermined state of charge of substantially 100%. In particular, as will be further explained below, the second energy storage unit can be very fast chargeable. Thus, the second energy storage unit can be charged to a very high SOC or be fully charged.

[0028] In an example, electrical energy can be transferred from the second electrical energy storage unit to the first electrical energy storage unit until the second electrical energy storage unit is substantially fully discharged. Thus, the second electrical energy storage unit can be used only to charge the first electrical energy storage unit and not for any further functions. Thus, the second electrical energy storage unit can be provided with limited functionality and thus in a very cost-effective manner.

[0029] In an example, charging may be performed as fast charging of a first energy storage unit and a second energy storage unit. The first energy storage unit may be charged at a fast charging rate in the range of 1C to 5C (particularly, in the range of 1C to 3C). The second energy storage unit may be charged at a fast charging rate of at least 3C (particularly, at least 5C or at least 10C). For example, the fast charging rate of the second energy storage unit may be in the range of 3C to 20C (particularly, 5C to 15C). Different C rates for fast charging of different energy storage units may be associated with different types of energy storage units, wherein the first energy storage unit may be more susceptible to degradation during fast charging, while the second energy storage unit may be less susceptible to degradation during fast charging.

[0030] According to a second aspect, an electric energy storage system is provided, comprising a first electric energy storage unit and a second electric energy storage unit. The electric energy storage system may be configured to be charged using the method of the present disclosure.

[0031] The electric energy storage system may further include a charging control unit for controlling the charging process of the electric energy storage system as described herein. The electric energy storage system may be configured to be charged using the method of the present disclosure through corresponding configuration of the charging control unit.

[0032] The two energy storage units can be electrically connected in parallel or can be electrically connected in parallel to a charging control unit and / or an external charging station so that the two can be charged in parallel. In addition, the two energy storage units can be electrically connected in series with each other so that the second energy storage unit can charge the first energy storage unit.

[0033] In an example, the first energy storage unit may include at least one battery cell, and the second energy storage unit may include at least one capacitor. Such different types of energy storage units are advantageous relative to the charging and transfer steps as described herein. Specifically, battery cells can hold a charge and discharge for good use (e.g., in a vehicle), but may be susceptible to degradation when quickly charged. On the other hand, capacitors may be relatively poor at holding a charge and discharging for use, but may be less susceptible to degradation when quickly charged and can be charged very quickly. Combining these two types in different energy storage units allows for advantageous energy storage systems and methods as described herein.

[0034] In one example, at least one capacitor may be, for example and as described above, a lithium ion capacitor. The at least one battery cell may be, for example, a lithium ion battery cell. A particular advantage of lithium ion capacitors is that they are stable when charged quickly and that the battery cells have negligible degradation compared to battery cells. Furthermore, the specific power of lithium ion capacitors may be about ten times higher than that of lithium ion batteries, so lithium ion capacitors may be charged significantly faster.

[0035] According to a third aspect, there is provided a vehicle comprising the electrical energy storage system of the present disclosure.

[0036] According to a fourth aspect, a computer program product is provided, comprising instructions for causing the electric energy storage system or the vehicle of the present disclosure to execute the method of the present disclosure.

[0037] A computer program product may be the computer program itself or a product on which instructions are stored, such as a computer-readable storage medium.

[0038] It should be noted that the above examples can be combined with each other, regardless of the aspects involved. Thus, the method can be combined with structural features, and likewise, the electrical energy storage system and the vehicle can be combined with the features described above with respect to the method, for example.

[0039] These and other aspects of the disclosure will be apparent from and elucidated with reference to the examples described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Examples of the present disclosure will be described below with reference to the following drawings.

[0041] Figure 1 shows a schematic diagram of a vehicle and an electrical energy storage system according to the present disclosure;

[0042] Figure 2 A schematic diagram of a method according to the present disclosure is shown;

[0043] Figure 3 Shown in Figure 2 A schematic diagram of a state of charge of an electrical energy storage system after a first step of the method; and

[0044] Figure 4 Shown in Figure 2 Schematic representation of the charge state of the electrical energy storage system after the second step of the method. DETAILED DESCRIPTION

[0045] The drawings are merely schematic representations and serve only to illustrate examples of the present disclosure. Identical or equivalent elements are in principle provided with the same reference numerals.

[0046] Currently, in vehicle applications, an electrical energy storage system in a vehicle is usually charged via a charging station until fully charged.

[0047] Figure 1 A schematic diagram of a vehicle 1 is shown. The vehicle 1 may be a battery electric vehicle or any other vehicle utilizing an electrical energy storage system 10, for example.

[0048] The vehicle 1 of this example includes an energy storage system 10 having a first energy storage unit 12, a second energy storage unit 14, and a charging control unit 16. The first energy storage unit 12 may include, for example, a lithium-ion battery cell, and the second energy storage unit 14 may include, for example, a lithium-ion capacitor.

[0049] The vehicle 1 further comprises a load 20 connected to the energy storage system 10, which discharges the energy storage system 10 (specifically, the first energy storage unit 12). For example, the load 20 may be an electric motor. Additional or other loads of the vehicle 10 may also be connected to the energy storage system 10.

[0050] The vehicle 1 or the energy storage system 10 of this example is electrically connected to a charging station 30, which is configured to charge the energy storage system 10. The charging station 30 may be configured to charge the energy storage system 10 quickly.

[0051] The first energy storage unit 12 and the second energy storage unit 14 are configured (particularly by means of the charging control unit 16) to be charged in parallel or simultaneously by a charging station 30 electrically connected to the energy storage system 10. In addition, the first energy storage unit 12 and the second energy storage unit 14 are electrically connected to each other and are configured (particularly by means of the charging control unit 16) such that the second energy storage unit 14 can transfer the electric energy stored therein to the first energy storage unit 12, thereby discharging.

[0052] Figure 2 A schematic diagram of a method 100 is shown. The method 100 is configured for charging the electrical energy storage system 10 and may be performed by the charging control unit 16, for example.

[0053] In a first step 102 of the method 100, the first energy storage unit 12 and the second energy storage unit 14 are supplied with electrical energy from the charging station 30 and are thus charged. Charging both energy storage units 12, 14 may be performed in parallel and as a fast charging process.

[0054] In a second step 104 of the method 100, after both energy storage units 12, 14 are charged, the energy stored in the second energy storage unit 14 during the first step 102 is transferred to the first energy storage unit 12, thereby further charging the first energy storage unit 12 and discharging the second energy storage unit 14. This energy transfer or further charging of the first energy storage unit 12 may be performed more slowly than the fast charging process of the first step 102.

[0055] Figure 3 The state of charge (SOC) of each of the electrical energy storage units 12 , 14 and the electrical energy storage system 10 as a whole (combining both electrical energy storage units 12 , 14 ) after the first step 102 has been performed is shown.

[0056] like Figure 3 As shown, the energy storage units 12, 14 and the energy storage system 10 are each charged to a predetermined state of charge, which are selected herein only as examples, in a first step 102. In this example, during the fast charging process of the first step 102, the first energy storage unit 12 is charged to 60% SOC and the second energy storage unit 14 is charged to 100% SOC.

[0057] The maximum energy storage capacity of the second energy storage unit 14 is less than the maximum energy storage capacity of the first energy storage unit 12. In this example, the maximum energy storage capacity of the second energy storage unit 14 is 0.2 of the maximum energy storage capacity of the first energy storage unit 12. Therefore, the SOC of the entire energy storage system 10 is Figure 3 The average rate is 80%.

[0058] Figure 4 The state of charge of each of the electrical energy storage units 12 , 14 and the electrical energy storage system 10 as a whole (combining both electrical energy storage units 12 , 14 ) after the second step 104 has been performed is shown.

[0059] Thus, the second energy storage unit 14 has been completely discharged so that its SOC is at 0%, while the first energy storage unit 12 has been further charged by transferring the energy stored in the second energy storage unit 14 to the first energy storage unit 12. In this example, the first energy storage unit 12 is thus charged from 60% to 80% SOC in the second step 104. The SOC of the entire energy storage system 10 is maintained at 80%, as shown in FIG. Figure 3 The situation in.

[0060] Figure 4 It is assumed that the first energy storage unit 12 is not discharged during driving and / or other use of the vehicle 1. However, after the fast charging process of step 102 has been performed, the charging cable of the charging station 30 can be unplugged from the vehicle 1 and the vehicle 1 can be driven, so that the first energy storage unit 12 is discharged. However, while discharging, the first energy storage unit 12 can be further charged according to the second step 104, so that its discharge can be at least partially compensated.

[0061] Furthermore, if the user does not disconnect the vehicle 1 from the charging station 30 to further charge the energy storage system 10, the first step 102 may be interrupted when a predetermined SOC of the first energy storage unit 12 is reached (e.g., 60% SOC in this exemplary case). In an alternative, the first step 102 may be continued, i.e., the first energy storage unit 12 may be charged beyond 60% SOC. However, the charging may no longer be performed as a fast charge (i.e., with a slower charging speed than before). As a result, the degradation of the first energy storage unit 12 may be kept low.

[0062] By studying the drawings, the disclosure and the appended claims, those skilled in the art can understand and implement other variations of the disclosed examples when practicing the disclosure claimed for protection. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may implement the functions of several items or steps recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not mean that a combination of these measures cannot be used to advantage. The computer program may be stored / distributed on a suitable medium, such as an optical storage medium or solid-state medium provided with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems. Any reference numerals in the claims should not be interpreted as limiting the scope of the claims.

[0063] Reference numerals list

[0064] 1 Vehicle

[0065] 10Electric Energy Storage System

[0066] 12First electrical energy storage unit

[0067] 14 Second energy storage unit

[0068] 16 Charging control unit

[0069] 20 load

[0070] 30 Charging Stations

[0071] 100 Methods

[0072] 102 First Step

[0073] 104 Step 2

Claims

1. A method (100) for charging an energy storage system (10), the energy storage system (10) comprising a first energy storage unit (12) and a second energy storage unit (14), the method (100) comprising: charging the first energy storage unit (12) and the second energy storage unit (14) with electrical energy; as well as Electrical energy is transferred from the second electrical energy storage unit (14) to the first electrical energy storage unit (12), thereby discharging the second electrical energy storage unit (14).

2. The method (100) according to claim 1, wherein: Charging the first energy storage unit (12) with electrical energy is at least partially performed in parallel with charging the second energy storage unit (14).

3. The method (100) according to claim 1 or 2, wherein: After the first energy storage unit (12) has been charged to a predetermined state of charge, transferring electrical energy from the second energy storage unit (14) to the first energy storage unit is performed.

4. The method (100) according to claim 3, wherein: The predetermined state of charge of the first electrical energy storage unit (12) is at least 40%, at least 50% or at least 60%.

5. The method (100) according to claim 1 or 2, wherein: While transferring electrical energy from the second electrical energy storage unit (14) to the first electrical energy storage unit (12), the first electrical energy storage unit (12) is discharged.

6. The method (100) according to claim 1 or 2, wherein: Electrical energy is transferred from the second electrical energy storage unit (14) to the first electrical energy storage unit (12) more slowly than electrical energy is supplied to the first electrical energy storage unit (12) and the second electrical energy storage unit (14) during charging.

7. The method (100) according to claim 1 or 2, wherein: After transferring electrical energy from the second electrical energy storage unit (14) to the first electrical energy storage unit (12), the state of charge of the first electrical energy storage unit (12) is at least 60% or at least 80%.

8. The method (100) according to claim 1 or 2, wherein: The second electrical energy storage unit (14) is charged to a predetermined state of charge of at least 80% or at least 90%.

9. The method (100) according to claim 1 or 2, wherein: Electrical energy is transferred from the second electrical energy storage unit (14) to the first electrical energy storage unit (12) until the second electrical energy storage unit (14) is substantially fully discharged.

10. The method (100) according to claim 1 or 2, wherein: Charging is performed as fast charging of the first energy storage unit (12) and the second energy storage unit (14), wherein the first energy storage unit (12) is charged at a fast charging rate in the range of 1C to 5C, and the second energy storage unit (14) is charged at a fast charging rate of at least 3C.

11. An electrical energy storage system (10), comprising a first electrical energy storage unit (12) and a second electrical energy storage unit (14), wherein: The electrical energy storage system (10) is configured to be charged using a method (100) according to any one of the preceding claims.

12. The electrical energy storage system (10) according to claim 12, wherein: The first electrical energy storage unit (12) includes at least one battery cell, and the second electrical energy storage unit (14) includes at least one capacitor.

13. The electrical energy storage system (10) according to claim 13, wherein: The at least one capacitor is a lithium ion capacitor.

14. A vehicle (1) comprising an electrical energy storage system (10) according to any one of claims 11 to 13.

15. A computer program product comprising instructions for causing an electrical energy storage system (10) according to claims 10 to 13 or a vehicle (1) according to claim 14 to perform a method according to any one of claims 1 to 10.

Images